ON CALIBRATION AND STRUCTURE FROM MOTION FOR GENERIC CAMERA MODELS

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Boundary Quantum Mechanics

a rXiv:q uant-ph/03865v112A ug23Boundary Quantum Mechanics ∗Pavel Krtouˇs †Institute of Theoretical Physics,Faculty of Mathematics and Physics,Charles University,V Holeˇs oviˇc k´a ch 2,18000Prague 8,Czech Republic October 25,2001A reformulation of a physical theory in which measurements at the initial and ﬁnal moments of time are treated independently is discussed,both on the classical and quantum levels.Methods of the standard quantum mechanics are used to quantize boundary phase space to obtain boundary quantum mechanics —a theory that does not depend on the distinction between the initial and ﬁnal moments of time,a theory that can be formulated without reference to the causal structure.As a supplementary material,the geometrical description of quantization of a general (e.g.curved)conﬁguration space is presented.IntroductionMotivationIn this work we formulate boundary quantum mechanics—a modiﬁcation of the standard quantum mechanics where states at the initial andﬁnal moments of time are treated independently.Our primary motivation for building the boundary quantum mechanics was an observation that in aﬁeld theory one usually has to deﬁne similar structures(such as e.g.,Fock bases,vacuum states,coherent states,ﬁeld and momentum observables) both for the initial andﬁnal moments of time and these structures only diﬀer in the time at which they are deﬁned.An eﬀort to simplify handling of diﬀerent structures at the initial andﬁnal time led to a uniﬁed picture in which both time boundaries play a completely equivalent role.The main idea is to treat both the initial andﬁnal states of a physical system in an independent way,as if they would be states of diﬀerent systems.The Hilbert space of boundary quantum mechanics is thus given as a tensor product of the initial andﬁnal Hilbert spaces.The dynamics of the boundary quantum mechanics is given by specifying a special physical state|phys)that contains all information about dynamical correlations.Surprisingly,the resulting theory does not need to distinguish between the initial andﬁnal states—it can be formulated in a way in which we do not need to split the boundary of a(space)time domain on which we study the system to the initial andﬁnal parts.The consequence of this fact is that we can use the formalism of boundary quantum mechanics in situations when we do not have a reasonable causal structure which would allow us to identify the“initial”and“ﬁnal”moments of time,particularly,we can use the formalism in the Euclidian form of a theory.The material presented here is based on some parts of Ref.[1].The work[1]was concerned mainly with a study of the relation between quantizations of a scalarﬁeld theory and relativistic particle theory.Boundary quantum mechanics was used for an alternative description of the scalarﬁeld theory.The general framework leading to boundary quantum mechanics was scattered in several places in Ref.[1].Here, the material is presented in a modiﬁed and more compact form with an emphasis on the construction of the general formulation of the boundary mechanics.After boundary quantum mechanics was constructed and used in Ref.[1]the author has found out that similar ideas have been pursued in the context of quantum gravity[2,3],however,in these works the idea of treating the diﬀerent moments of time independently has been extended much farther—here“all moments of time”are treated independently,hence,the constructed Hilbert space of the theory is given by some kind of a continuous tensor product of Hilbert spaces for each time. Plan of workThe explanation of the formalism is divided to three chapters.In Chapter1a clas-sical analogue of boundary quantum mechanics is constructed,namely the bound-ary phase space is deﬁned and its connection to standard phase spaces is studied. This chapter formulates the theory on a very general level.It allows to deﬁne theboundary phase space without a reference to the causal structure.However,these details are not necessary for the following chapters—if one is not interested in the causal(in)dependence of the boundary phase space,it is suﬃcient to understand the boundary phase space on the level explained in the overview and summary of Chapter1.The way of treating the general dynamical theory has been mainly inspired by Ref.[4].The material presented in Chapter2is actually independent of the main sub-ject—of boundary quantum mechanics.In this chapter we present a geometrical formulation of quantization for a system with a phase space with cotangent bundle structure T⋆V over some conﬁguration space V.This is a generalization of the standard quantum mechanical methods of quantization of the position and mo-mentum variables to the situation when the space of“positions”V does not have a linear structure—when it is a general manifold.Only a construction of“position”and“momentum”observables and their position representation is presented here, dynamical questions are not discussed.Finally,boundary quantum mechanics is formulated in Chapter3.First,the theory is built on the basis of the usual quantum mechanics.Afterwards,it is shown that boundary quantum mechanics can be constructed immediately from the boundary phase space without reference to quantum mechanics at a given time.At the end the issue of dynamics is discussed.The main text is supplemented by three appendices in which some of the ge-ometrical notions are reviewed.Appendix C deﬁnes the notion of densities of a general(complex)weight on a manifold.Appendices A,B contain a geometri-cal formultaion of symplectic geometry.Most of this material is well known(see, e.g.,[5,6])and it is included mainly toﬁx the notation and remind the reader of properties of diﬀerent introduced objects.However,let us note that Appendix B also deﬁnes covariant partial derivatives on tangent and cotangent bundles—a notion which,to the author’s knowledge,is not deﬁned elsewhere.NotationWe use abstract indices to denote the tensor structure of diﬀerent tensor objects (see e.g.[7]).They indicate which space the object is from and allow us to write down a contraction in the tensor algebra by the usual repetition of the indices.We distinguish tensors with abstract indices from their coordinate representation.We use bold letters for the abstract indices and normal letters for coordinate indices (but you can hardlyﬁnd them here).Hence,choosing a base e a a and dual baseǫa a,a=1,2,...,we can write A a...b...=A a...b...e a aǫb b...,and A a...b...=A a...b...ǫa a e b b....HereA a...b...is a tensor object and A a...b...is a“bunch”of numbers depending on the base.Because it can be tiresome to write indices all the time(but it is sometimes inescapable),we drop them if it is clear what structure the object has.(In fact,we view the abstract indices as some kind of a“dress”of the tensor object which serves to specify tensor operations.)We also use an alternative notation for contraction using an inﬁx operator dot(we use diﬀerent dots for diﬀerent spaces),i.e.,for example,a·ω=ω·a=a nωn or(a·g)n=a m g mn.1Boundary,canonical,and covariant phase spacesOverviewThe main goal of this chapter is to deﬁne a boundary phase space—a kinematical area of the classical counterpart of boundary quantum mechanics.We will start our construction on a very general level and we will see that the boundary phase space can be introduced for a very broad class of theories.However,after this general introduction we turn to a more speciﬁc theory to grasp the meaning of the boundary phase space and to understand its relation to standard phase spaces used in physics.We represent it as a cotangent bundle over the boundary value space and,at the end,we introduce special types of observables that will be quantized in the next chapter.Before turning to a discussion of a general situation let us note that the basic idea lying behind the boundary phase space is very simple.The boundary phase space is a space of canonical data(“values”and“momenta”)at both the initial andﬁnal time with a symplectic structure induced from canonical phase spaces at the initial andﬁnal moment of time.The main nontrivial output of the general discussion below is a construction of the boundary phase space without reference to the causal structure,without necessity of splitting the boundary data to the initial andﬁnal parts.The space of histories and the actionA physical theory can be speciﬁed by a space of elementary histories H and a dynamical structure on it.Elementary histories represent a wide class of potentially imaginable evolutions of the system,not necessarily realized in the nature.Examples of the spaces of histories are the space of all possible trajectories in the spacetime(theory of a relativistic particle),the space of all possibleﬁeld conﬁguration on the spacetime(ﬁeld theory),the space of all possible connections on a spacetime(gaugeﬁeld theory)or the space of all maps from one manifold to another(target)manifold(strings,membranes,...).The space of histories of a general nonrelativistic system is a space of trajectories in a conﬁguration space V o —in space of“positions”.We restrict ourselves to theories that are local on some inner manifold N and we pay attention to this dependence.Generally,histories of such local theories can be represented as sections of someﬁbre bundle over the inner manifold.We use x,y,...as tensor indices for objects from tangent tensor spaces T H and the dot •for contraction in these spaces.Let us note that“vectors”from T H are againsections of some bundles over the inner manifold,i.e.,they are essentially functions (or distributions),and their tensor indices x,...denote also the inner manifold dependence.The contraction•thus includes integration over the inner manifold.Almost all known theories can be reformulated in this way.For example,el-ementary histories of a general nonrelativistic system can be viewed as mapping from a one dimensional inner manifold N(“time-line”manifold)to the so-called target manifold V o,i.e.,as sections of the trivialﬁbre bundle N×V o over N.The realization of aﬁeld theory is even more straightforward—the inner manifold isspacetime and histories are sections of some bundle over it.We will restrict our-selves mainly to these two cases.Typical examples are a particle in a curved space and the scalarﬁeld theory(see[1]for a discussion of the latter case).We assume that we are able to restrict the theory to any domainΩin the inner manifold N.It means that we are able to speak about space of histories H[Ω]on the domainΩ.We will see that the domain of dependence plays an important role in the dynamics.On the general level,we admit any suﬃciently bounded domainΩwith a smooth boundary∂Ω.We need to deal with a bounded domain to assure that the action functional is well deﬁned on a suﬃciently wide set of histories.Generally,if the domain is compact,the action is deﬁned for all smooth histories.However,we can also allow domains that are not compact“in some insigniﬁcant directions”.A typical example is a sandwich domain in a globally hyperbolic spacetime between two non-intersecting non-compact Cauchy surfaces.Such a domain is unbounded in the spatial direction and this fact has to be compensated by a restriction of the set of histories to those that fall-oﬀsuﬃciently fast at spatial inﬁnity.We cannot do the same thing in the temporal direction because we would exclude physically interesting histories—speciﬁcally,the solutions of the classical equations of motion. In case of a nonrelativistic system the domainΩis simply a compact interval in the one dimensional inner manifold N.The localization of histories on the domainΩalso gives us a localization of elements of the tangent spaces T H,i.e.,we can speak about a space T H[Ω].We call these tangent vectors linearized histories.As we said,the tangent space at h can be represented as a vector bundle over the inner manifold(or over the domain Ω).The dynamics of the system is given by a domain-dependent action S[Ω]S[Ω]:H→R.(1.1) Let us note that we cannot generalize the action to a functional S[N]on the whole inner manifold—it would be inﬁnite for most physically interesting histories.The action is local,i.e.,for anyΩS[Ω](h1)=S[Ω](h2)if h1=h2onΩ,(1.2) and additive under smooth joining of domains,i.e.,S[Ω](h)=S[(Ω1](h)+S[Ω2](h),(1.3) whereΩ=Ω1∪Ω2is a domain andΩ1∩Ω2is a submanifold without boundary which is a subset of both∂Ω1and∂Ω2.The equation of motionIn general,we work with smooth histories and smooth domains with a boundary, unless stated otherwise.We assume suﬃcient smoothness of the action but we skip the discussion of this issue.However,we explicitly assume that the action is essentially of theﬁrst-order.In short,this means that the action leads to second-order equations of motion.On ageneral level,this can be formulated by a condition that the variation of the action (keeping the domainΩﬁxed)can be written in the following wayd S[Ω](h)=χ[Ω]δS(h)−P[∂Ω](h).(1.4) This relation represents an“integration by parts”usually employed in the variation of the action.A description of individual terms follows.We use the gradient operator d x on the space of histories H to denote the variation.It is deﬁned by the usual relationdδh•d S[Ω](h)=a The symbol“δ”does not represent any operation here;it should be understood as a part of the symbolδS.is a derivative of the form δS using an ultralocal connection D .It is easy to check that for a classical history h,thanks to (1.6),the second variation of the action δ2S (h)does not depend on the choice of the connection D .We deﬁneδ2S xy = δ2S yx andδ2S [Ω]=(χ[Ω]δ)• δ2S , δ2S [Ω]=δ2S •(χ[Ω]δ),(1.9)satisfying again δ2S xy [Ω]= δ2S yx [Ω].We assume that the equation of motion has a well-deﬁned boundary problem on the domain Ω,i.e.,we assume the existence of a unique solution from S for a given restriction of a history to the boundary.Moreover,we assume that the lin-earized equation of motion has a well-formulated Dirichlet and Neumann boundary problem,i.e.,there is a unique solution to the linearized equation of motion for a given linearized value on the boundary or linearized momentum on the boundary.This requires some generality of the action —for example we exclude a massless scalar ﬁeld.More serious is the restriction that we must also exclude theories with local symmetries —see [4]for some details on this case.When working with the manifold S ,we use A ,B ,...for tangent tensor indices.Boundary phase space Next we deﬁne the boundary symplectic structure d P [∂Ω]to be the external deriva-tive of the generalized momentum 1-form P [∂Ω],which turns out to be the Wron-skian of the second variation of the action (see (1.8)),d P [∂Ω]= δ2S [Ω]− δ2S [Ω].(1.10)We say that two histories are canonically equivalent on the boundary if they have the same restriction on the boundary and the same momentum P .We call the quotient of the space H with respect to this equivalence the boundary phase space B [∂Ω].A point from the boundary phase space thus represents values and momenta on the entire boundary ∂Ω,i.e.,at both the initial and ﬁnal time.We use A ,B ,...as tensor indices for tensors from the tangent spaces T B [∂Ω].It is straightforward to check that vectors tangent to the orbits of equivalence are degenerate directions of the boundary symplectic form d P [∂Ω]and therefore we can deﬁne its action on the space B [∂Ω].We will require that the form d P [∂Ω]is non-degenerate on the boundary phase space.Because the external derivative of this form is zero,it is indeed a symplectic form in the sense of Appendix A,and it gives a symplectic space structure to the space B [∂Ω],thus justifying the name boundary phase space.The space S is a submanifold of H and,therefore,it deﬁnes a submanifold of the space B [∂Ω],which we denote by the same letter S .Lagrangian densityUntil now,we have been developing the formalism on a very general level.In the following we restrict to theories with the action given byS[Ω](h)= ΩL(h,Dh),(1.11)where L is the Lagrangian density—density on the inner manifold N—ultralocally dependent on the value of the history and“velocities”,i.e.,inner space derivatives of the history.bIn general,we need some additional structure on theﬁbre bundle H to deﬁne the“velocity”(an inner space derivative of the history)—we need,for example, a connection on the bundle.There can exist a natural connection(e.g.if we can identifyﬁbres of the bundle)or a choice of the connection can be equivalent to a speciﬁcation of an externalﬁeld(a gaugeﬁeld of Yang-Mills theories).In the following we will have in mind mainly a general nonrelativistic system,where we do not need any additional structure—the velocity can be simply understood as a derivative of the trajectory h:N→V o with respect to the“proper time”(a preferred coordinate on N).In this simple case the variation of the action and an integration by parts gives us the decomposition(1.4)withδS and P[∂Ω]as follows:δS(h)=∇L∂˙h(h,˙h) .,(1.12)P[∂Ω](h)=∂Lb The formalism developed until now is more general—it covers for example the case of the Einstein-Hilbert action for gravity for which the Lagrangian density contains second spacetime derivatives of the metric.But this dependence is degenerate and it is possible to satisfy the above conditions if a proper boundary term is chosen.the space of histories H is the space of functions on spacetime,and the indices x,... used for vectors from T H actually represent points in spacetime.Similarly,the space V[∂Ω]is the space of functions on the boundary∂Ωof a spacetime domainΩand indices x,...represent points on the boundary.In case of the target manifold being not so simple,all these indices also carry information about a direction in the target manifold.Another simple case is the nonrelativistic system where the inner manifold is one dimensional.In this case the linearized historyδh x represents a time dependent target-manifold-vector-valued function,i.e.,the index x represents a time variable and a direction in the target manifold.The boundary∂Ωconsists only of two points from N and the boundary value x of a trajectory h is a pair of end points x=[x f,x i]. The space of boundary values V[∂Ω]is thus isomorﬁc to V o×V o and the tangent space T V[∂Ω]to a direct sum T V o⊕T V o.Therefore,the tensor indices x,... correspond to pairs of directions in the target manifold and the contraction·reduces to a contraction overﬁnite dimensional vector spaces.We denote the projection from H to V[∂Ω]by x[∂Ω].We already said that the condition that the generalized momentum does not contain inner space derivatives normal to the boundary in its variational argument ensures that P x[∂Ω]can be realized as a distribution(in the x argument)on the boundary values od the lin-earized histories—we do not need any other information about a linearized history δh x except its value on the boundary to computeδh x P x[∂Ω].Translation between linearized histories and its boundary values is,of course,the diﬀerential D x[∂Ω]of the projection x[∂Ω].Hence,we can represent the generalized momentum in the following form:P x[∂Ω]=p x[∂Ω]D x x x[∂Ω].(1.14)Here p[∂Ω](h)is from the cotangent bundle T⋆x(h)V[∂Ω].The diﬀerential D xxx[∂Ω]understood as a distribution(in the x argument)is actually a delta function with a support on the boundary(multiplied by a(ﬁnite dimensional)unit tensor on the target manifold).x[∂Ω](h)and p[∂Ω](h)represent the values and the momenta of the history h at both the initial andﬁnal time.The meaning of x[∂Ω](h)is clear from its deﬁnition; the meaning of p[∂Ω](h)can be seen—at least in case of a one dimensional inner manifold—by comparing Eq.(1.14)and Eq.(1.13).The same interpretation holds in the general case,too(see[1]for the details of the scalarﬁeld case).In the following,we drop the boundary dependence of x and p.Next we deﬁne the classical history¯h(x)with a given boundary value xδS(¯h(x))=0,x(¯h(x))=x(1.15) and the classical action¯S[Ω](x)=S[Ω](¯h(x)).(1.16) We use¯h also for the induced map from the space V[∂Ω]to the boundary phase space B[∂Ω],and x and p for the induced maps from the boundary phase space B[∂Ω]to the spaces V[∂Ω]and T⋆V[∂Ω].This suggests that we can represent the boundary phase space B[∂Ω]as a cotangent bundle T⋆V[∂Ω].Indeed,thecanonical symplectic structure of the cotangent bundle(B.7)does coincide with d P[∂Ω]:∇A p x∧D x B x=d A(p x D x B x)=d A P B.(1.17) The space S as a submanifold of B[∂Ω]can be characterized using the conditionp=−d¯S(x),(1.18) which follows fromd x¯S=D x x¯h d x S(¯h)=D x x¯h δS x[Ω](¯h)−P x[∂Ω](¯h) ==−D x x¯h D y x x(¯h)p y(¯h)=−p x(¯h).(1.19) Linearization of Eq.(1.18)givesD A x¯h=∇A x∂p y(1.20)(see Appendix B for deﬁnitions of objects used here,especially Eq.(B.6)).Causal structureUntil now we have not needed any timeﬂow in the underlying inner manifold N. It could be spacetime,an inner sheet of a string,or a one dimensional time-line—in all these cases we do have some kind of timeﬂow.However,the formalism also works in a more general situation.We can use it,for example,for the Euclidian form of the theory,where we do not have any time direction.Now,we will use the timeﬂow for theﬁrst time and we will add an additional causal structure that will allow us to deﬁne concepts such as canonical and covariant phase spaces.All what we will use is an assumtion that the boundary of the domain can be split into two disjoint parts without a boundary∂Ω=∂Ωf∪∂Ωi=−Σf∪Σi,∂Ωf=−Σf,∂Ωi=Σi,(1.21)each of them carrying a full set of data(see the condition below).Here the minus sign suggests an opposite choice of the normal direction orientation for one part of the boundary.Clearly,we have in mind two Cauchy hypersurfaces that deﬁne a sandwich domain in a globally hyperbolic spacetime,or two end points of the interval in the one dimensional inner manifold N in the case of a non-relativistic system.The decomposition in(1.21)allows us to writeV[∂Ω]=V[Σf]×V[Σi],B[∂Ω]=−B[Σf]⊕B[Σi],T V[∂Ω]=T V[Σf]⊕T V[Σi],(1.22)and we will use shorthands V,V f,V i and B,B f,B i.In case ofﬁeld theory,the space V f(or V i,respectively)represents the space ofﬁeld conﬁgurations on theﬁnal(or the initial)Cauchy hypersurface.In case of particle theory,spaces V f,V i represent positions of the particle at theﬁnal orinitial time,i.e.,V f=V i=V o.Similarly B f(or B i)represent canonical data (values and momenta)at theﬁnal(or initial)time.We require that both parts contain a full set of boundary data—there should exist a unique classical history for a given element from B f or B i.Thanks to the locality,we can decompose the symplectic structure d P[∂Ω]asd P[∂Ω]=−d P[Σf]+d P[Σi].(1.23)d P[Σf]and d P[Σi]play the role of the symplectic structure on B f and B i.We will call these spaces canonical phase spaces.The minus sign in the relations(1.22) reﬂects the relation of these spaces as symplectic spaces.The canonical phase spaces can be again represented as cotangent bundles T V f and T V i through the maps x f,p f and x i,p i.Let us note that p f takes into account the opposite orientation of the normal direction toΣf and∂Ωf,so thatp=−p f⊕p i.(1.24) Covariant phase spaceFinally,we can also give a phase space structure to the space of classical histories S. First we note that,thanks to(1.10),solutionsξ1,ξ2∈T S of linearized equations of motion(1.7)satisfyξ1•d P[∂Ω]•ξ2=0.(1.25) Therefore,it follows from(1.23)that d P[Σf]and d P[Σi]have the same restrictionωon the space S.ξA1 ωABξB2=ξ1•d P[Σf]•ξ2=ξ1•d P[Σi]•ξ2.(1.26) In the same way,we check that the same expression for ωholds for any future-oriented Cauchy hypersurfaceΣ.It means that we have equipped the space of classical histories S with the symplectic structure ω.We will call this space the covariant phase space.From Eq.(1.17)follows that the V f,V i and T⋆V f,T⋆V i-valued observables x f,x i and p f,p i are canonically conjugate on this space(cf. Appendix A):ωAB =∇Ap f x∧D xBx f=∇Ap i x∧D xBx i.(1.27)We can invert the symplectic form ωto get ω-1:ω-1AM ωBM = ω-1M A ωM B=δAB.(1.28)If we view S as a subspace of the boundary phase space B we can understandω-1as a tensor from T2B tangent to S in both indices.Because the diﬀerential D¯h of the map¯h:V→B(it is a restriction of the map(1.15)to B)plays the role of a projector of vectors from T V to vectors from T B tangent to S,we can writeω-1=D¯h·g c·D¯h(1.29) with an antisymmetric tensor g c∈ing(1.20),(1.28),and(1.27)we getg c·(d f d i¯S−d i d f¯S)=δV.(1.30)This means thatg c =g if −g ﬁ,g yx if =g xy ﬁ,g if ·d f d i ¯S =δV i ,g ﬁ·d i d f ¯S =δV f ,(1.31)and,using Eq.(1.20)again,we getω-1= ∇x ∂p u (∇u d x ¯S ) g xy c ∇y ∂p v == ∂∂x f −∇u ∂p f u + ∂∂x i −∇u ∂p i u ++ ∇x ∂x ++ ∂∂p i y−∂∂p f y ++∇x ∂p f u−∂∂x i ++ ∇x ∂p i u −∂∂x f.(1.32)Here,∇is any covariant derivative on the value space V ,∇f and ∇i are its restric-tions to V f and V i ,and d f ,d i are gradients on V f and V i .Or,if we view S as a subspace of the space of histories H we can understand ω-1as a tangent tensor from T 2H that satisﬁes the linear equation of motion in both indices.We call this representation the causal Green function G cG xy c =D x x ¯h g xy c D y y ¯h ,(1.33)where we now understand ¯has a map from V to H .In the space T H ,Eq.(1.28)takes the formG c •d P [Σ]=−D C [Σ],(1.34)where D C [Σ]is a Cauchy projector of a history on the linearized classical history with the same value and momentum on the surface Σ.It is,of course,an identity on T S .Similarly to Eq.(1.33)we can introduce G if and G ﬁ,which turn out to be the advanced and retarded Green functions.g c ,g if ,and g ﬁare thus the corresponding Green functions evaluated on the boundary ∂Ω.Poisson bracketsThe Poisson brackets of two observables on a phase space are deﬁned by (A.5).We can compare Poisson brackets in the sense of diﬀerent phase spaces.Clearly,any observable on H generates an observable on S and we can deﬁne{A,B }S =d x A G xy c d y Bon S .(1.35)For observables depending only on the boundary values and momenta —i.e.,for observables on B —we can deﬁne the Poisson brackets in the sense of the boundary phase space{A,B }B =d A A d P -1AB d B B =∂A ∂x −∇x A∂p x .(1.36)With the help of (1.32)we ﬁnd that the covariant Poisson brackets for such ob-servables are given by{A,B }S =d A A ω-1AB d B B ==∂A ∂x f −∇u A ∂p f u + ∂A ∂x i −∇u A ∂p i u ++∇x A ∂x ++ ∂A ∂p i y−∂A∂p f y ++ ∇x A ∂p f u −∂A ∂x i ++ ∇x A ∂p i u−∂A ∂x f .(1.37)Moreover,for observables localized only on Σf or Σi we have{A f ,B f }B f =−{A f ,B f }B ={A f ,B f }S ,{A i ,B i }B i ={A i ,B i }B ={A i ,B i }S .(1.38)Observables at most linear in momentaDuring the quantization we will be interested in a special kind of observables on the boundary phase space B (or,in general,on any phase space with the cotangent bundle structure).We will investigate observables dependent only on the value and observables linear in the momentum.We deﬁne the following observables for a function f and a vector ﬁeld a on VF f =f (x ),(1.39)G a =a x (x )p x .(1.40)The Poisson brackets of these observables are{F f 1,F f 2}B =0,{F f ,G a }B =−F a ·d f ,{G a 1,G a 2}B =G [a 1,a 2].(1.41)Here [a 1,a 2]is the Lie bracket of the vector ﬁelds a 1,a 2.In the sense of the covariant phase space we have{F f 1,F f 2}S =F d f 1·g c ·d f 2on S (1.42)。

Fluid-Structure Interaction and Dynamics

Fluid-Structure Interaction and Dynamics Fluid-structure interaction (FSI) is a complex and fascinating field that involves the interaction between deformable structures and surrounding fluids. This interaction can lead to a wide range of dynamic behaviors and phenomena, making it a crucial area of study in various engineering disciplines. From flutter in aircraft wings to the movement of blood in the human body, FSI plays a significant role in understanding and predicting the behavior of systems where fluids and structures interact. One of the key challenges in FSI is accurately modeling and simulating the interaction between the fluid and structure. This requires a deep understanding of the physics involved, as well as advanced computational tools and techniques. Computational fluid dynamics (CFD) and finite element analysis (FEA) are commonly used to model and simulate FSI problems, allowing engineers to predict how a structure will deform under the influence of fluid forces, and how the fluid flow will be affected by the presence of the structure. In addition to modeling and simulation, experimental testing is also crucial in validating FSI models and understanding the real-world behavior offluid-structure systems. Wind tunnel tests, water tank tests, and other experimental techniques can provide valuable insights into the dynamics of FSI systems, helping engineers to refine their models and improve the performance and safety of structures exposed to fluid forces. From a practical standpoint, FSI has numerous applications in various industries, including aerospace, automotive, civil engineering, and biomechanics. In aerospace, FSI is critical for designing aircraft wings that can withstand aerodynamic forces and vibrations, while in automotive engineering, FSI is used to optimize the performance of vehicle bodies and components under different flow conditions. In civil engineering, FSI is essential for designing bridges, dams, and other structures that are exposed to wind, water, and other fluid forces, while in biomechanics, FSI is used to study the flow of blood in arteries and veins, and its impact on the cardiovascular system. Despite its importance and widespread applications, FSI remains a challenging and evolving field, with many open research questions andopportunities for innovation. Researchers and engineers continue to explore new techniques for modeling and simulating FSI systems, as well as developing advancedmaterials and structures that can better withstand fluid forces. By advancing our understanding of FSI, we can improve the performance, efficiency, and safety of a wide range of engineering systems, leading to better designs and solutions that benefit society as a whole. In conclusion, fluid-structure interaction is a fascinating and important field that plays a crucial role in understanding and predicting the behavior of systems where fluids and structures interact. By combining advanced modeling and simulation techniques with experimental testing and practical applications, engineers can gain valuable insights into the dynamics of FSI systems and develop innovative solutions to complex engineering challenges. As we continue to push the boundaries of FSI research, we can unlock new opportunities for improving the performance and safety of structures exposed to fluid forces, leading to a more sustainable and resilient built environment.。

全国大学英语CET四级考试试卷及答案指导(2025年)

2025年全国大学英语CET四级考试模拟试卷及答案指导一、写作（15分）CET-4 Writing SectionDirections: For this part, you are allowed 30 minutes to write a short essay entitled “The Importance of Teamwork”. You should write at least 120 words but no more than 180 words.Sample Essay: The Importance of TeamworkIn today’s fast-paced and highly competitive world, the concept of teamwork has become more crucial than ever. It is often said that one can go fast alone, but to go far, one must go together. This saying underlines the importance of teamwork in achieving common goals effectively and efficiently.Teamwork allows for the pooling of diverse skills and talents, which leads to more innovative solutions and better decision-making. When individuals with different backgrounds and expertise collaborate, they bring unique perspectives to the table, fostering an environment where creativity thrives. Furthermore, working as a team builds a support system, enabling members to rely on each other during challenging times, thus reducing stress and increasing job satisfaction.Another significant benefit of teamwork is the ability to accomplish tasksthat would be impossible for an individual to handle. By dividing work among team members based on their strengths, teams can tackle complex projects, ensuring all aspects are thoroughly covered. This not only improves the quality of work but also accelerizes the completion time.In conclusion, the value of teamwork cannot be overstated. It is through collaboration and mutual support that we can achieve great things, overcome obstacles, and reach our full potential. Embracing the spirit of teamwork is essential for both personal and professional success in our interconnected world.Analysis:•Introduction: The essay begins with a clear statement about the increasing significance of teamwork in the modern era, setting up the main argument.•Body Paragraphs:•The first body paragraph discusses how teamwork enhances innovation and decision-making by combining varied skills and viewpoints.•The second body paragraph highlights the supportive nature of teamwork, emphasizing its role in managing stress and boosting morale.• A third point is made about the efficiency and effectiveness gained from dividing labor according to individual strengths, allowing for thesuccessful execution of complex tasks.•Conclusion: The concluding paragraph reinforces the thesis, summarizing the key benefits of teamwork and linking them to broader concepts ofachievement and personal growth.This sample response adheres to the word limit (156 words), maintains a coherent structure, and provides specific examples to support the main points, making it a strong example for the CET-4 writing section.二、听力理解-短篇新闻（选择题，共7分）第一题News Item 1:A new study has found that the popularity of online shopping has led to a significant increase in the use of plastic packaging. The researchers analyzed data from various e-commerce platforms and discovered that the amount of plastic packaging used in online orders has doubled over the past five years. This has raised concerns about the environmental impact of e-commerce and the need for more sustainable packaging solutions.Questions:1、What is the main issue addressed in the news?A) The decline of traditional shopping methods.B) The environmental impact of online shopping.C) The growth of e-commerce platforms.D) The advantages of plastic packaging.2、According to the news, what has happened to the use of plastic packaging in online orders over the past five years?A) It has decreased by 50%.B) It has remained stable.C) It has increased by 25%.D) It has doubled.3、What is the primary concern raised by the study regarding online shopping?A) The increase in the number of e-commerce platforms.B) The high cost of online shopping.C) The environmental impact of plastic packaging.D) The difficulty in returning products.Answers:1、B) The environmental impact of online shopping.2、D) It has doubled.3、C) The environmental impact of plastic packaging.第二题Section B: Short NewsIn this section, you will hear one short news report. At the end of the news report, you will hear three questions. After each question, there is a pause. During the pause, you must read the four choices marked A), B), C) and D), and decide which is the best answer. Then mark the corresponding letter on the Answer Sheet with a single line through the center.News Report:The World Health Organization announced today that it has added the ChineseSinovac COVID-19 vaccine to its list of vaccines approved for emergency use. This move will facilitate the distribution of the vaccine in lower-income countries participating in the COVAX initiative aimed at ensuring equitable access to vaccines globally. The WHO praised the Sinovac vaccine for its easy storage requirements, making it ideal for areas with less sophisticated medical infrastructure.Questions:1、According to the news report, what did the WHO announce?A)The end of the pandemicB)Approval of a new vaccineC)Launch of a global health campaignD)Increased funding for vaccine researchAnswer: B) Approval of a new vaccine2、What was highlighted about the Sinovac vaccine by the WHO?A)It is the most effective vaccine availableB)It requires simple storage conditionsC)It is cheaper than other vaccinesD)It has no side effectsAnswer: B) It requires simple storage conditions3、What is the purpose of the COVAX initiative mentioned in the report?A)To speed up vaccine developmentB)To provide financial support to vaccine manufacturersC)To ensure equal access to vaccines worldwideD)To promote travel between countriesAnswer: C) To ensure equal access to vaccines worldwide三、听力理解-长对话（选择题，共8分）第一题Part Three: Long ConversationsIn this section, you will hear 1 long conversation. The conversation will be played twice. After you hear a part of the conversation, there will be a pause. Both the questions and the conversation will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C), and D). Then mark the corresponding letter on Answer Sheet 2 with a single line through the center.Now, listen to the conversation.Conversational Excerpt:M: Hey, Jane, how was your day at the office today?W: Oh, it was quite a challenge. I had to deal with a lot of issues. But I think I handled them pretty well.M: That’s good to hear. What were the main issues you faced?W: Well, first, we had a problem with the new software we’re tryin g to implement. It seems to be causing some technical difficulties.M: Oh no, that sounds frustrating. Did you manage to fix it?W: Not yet. I’m still trying to figure out what’s wrong. But I’m workingon it.M: That’s important. The company can’t afford a ny downtime with this software.W: Exactly. And then, I had to deal with a customer complaint. The customer was really upset because of a delayed shipment.M: That’s never a good situation. How did you handle it?W: I tried to be understanding and offered a discount on their next order. It seemed to calm them down a bit.M: That was a good move. Did it resolve the issue?W: Yes, it did. They’re satisfied now, and I think we’ve avoided a bigger problem.M: It sounds like you had a busy day. But you did a good job handling everything.W: Thanks, I’m glad you think so.Questions:1、What was the main issue the woman faced with the new software?A) It was causing problems with the computer systems.B) It was taking longer to install than expected.C) It was causing technical difficulties.D) It was not compatible with their existing systems.2、How did the woman deal with the customer complaint?A) She escalated the issue to her supervisor.B) She offered a discount on the customer’s next order.C) She apologized directly to the customer.D) She sent the customer a refund check.3、What was the woman’s impression of her day at work?A) It was uneventful and unchallenging.B) It was quite stressful but rewarding.C) It was a day filled with unnecessary meetings.D) It was a day where she didn’t accomplish much.4、What did the man say about the woman’s day at work?A) He thought it was unproductive.B) He felt she had handled everything well.C) He thought she should have asked for help.D) He believed she should take a break.Answers:1、C2、B3、B4、B第二题对话内容:Man:Hey, Sarah. I heard you’re planning to go on a trip next month. Where are you heading?Sarah:Oh, hi, Mike! Yes, I’m really excited about it. I’m going to Japan. It’s my first time there.Man:That sounds amazing! How long will you be staying? And what places are you planning to visit?Sarah:I’ll be there for two weeks. My plan is to start in Tokyo and then travel to Kyoto, Osaka, and Hiroshima. I’ve always been fascinated by the mix of traditional and modern culture in Japan.Man: Two weeks should give you plenty of time to see a lot. Are you going alone or with someone?Sarah:Actually, I’m going with a group of friends from college. We all decided to take this trip together after graduation. It’ll be great to experience it with them.Man:That’s wonderful! Do you have everything planned out, like accommodations and transportation?Sarah:Mostly, yes. We’ve booked our flights and hotels, and we’re using the Japan Rail Pass for getting around. B ut we’re leaving some room for spontaneity too. Sometimes the best experiences come unexpectedly!Man:Absolutely, that’s the spirit of traveling. Well, I hope you have an incredible time. Don’t forget to try some local food and maybe bring back some souvenirs!Sarah:Thanks, Mike! I definitely won’t miss out on trying sushi and ramen, and I already have a list of gifts to buy for family and friends. I can’t waitto share my adventures with everyone when I get back.1、How long is Sarah planning to stay in Japan?•A) One week•B) Two weeks•C) Three weeks•D) One month答案: B) Two weeks2、Which of the following ci ties is NOT mentioned as part of Sarah’s itinerary?•A) Tokyo•B) Kyoto•C) Sapporo•D) Hiroshima答案: C) Sapporo3、Who is Sarah going to Japan with?•A) By herself•B) With her family•C) With a group of friends•D) With coworkers答案: C) With a group of friends4、What has Sarah and her friends prepared for their trip besides booking flights and hotels?•A) They have hired a personal guide.•B) They have reserved spots for cultural workshops.•C) They have purchased a Japan Rail Pass.•D) They have enrolled in a language course.答案: C) They have purchased a Japan Rail Pass.四、听力理解-听力篇章（选择题，共20分）第一题Section CDirections: In this section, you will hear a passage three times. When the passage is read for the first time, listen carefully for its general idea. When the passage is read for the second time, fill in the blanks with the exact words you have just heard. Finally, when the passage is read for the third time, check what you have written.Passage:In recent years, the concept of “soft skills” has become increasingly popular in the workplace. These are skills that are not traditionally taught in schools but are essential for success in the professional world. Soft skills include communication, teamwork, problem-solving, and time management.1、Many employers believe that soft skills are just as important as technical skills because they help employees adapt to changing work environments.2、One of the most important soft skills is communication. Effectivecommunication can prevent misunderstandings and improve relationships with colleagues.3、Teamwork is also crucial in today’s workplace. Being able to work well with others can lead to better productivity and innovation.4、Problem-solving skills are essential for overcoming obstacles and achieving goals. Employees who can think creatively and solve problems efficiently are highly valued.5、Time management is another key soft skill. Being able to prioritize tasks and manage time effectively can help employees meet deadlines and reduce stress.Questions:1、What is the main idea of the passage?A) The importance of technical skills in the workplace.B) The definition and examples of soft skills.C) The increasing popularity of soft skills in the workplace.D) The impact of soft skills on employee performance.2、Why do many employers believe soft skills are important?A) They are easier to teach than technical skills.B) They are not necessary for most jobs.C) They help employees adapt to changing work environments.D) They are more difficult to acquire than technical skills.3、Which of the following is NOT mentioned as a soft skill in the passage?A) Communication.B) Leadership.C) Problem-solving.D) Time management.Answers:1、C) The increasing popularity of soft skills in the workplace.2、C) They help employees adapt to changing work environments.3、B) Leadership.Second Part: Listening Comprehension - Passage QuestionsListen to the following passage carefully and then choose the best answer for each question.Passage:Every year, millions of people flock to beaches around the world for their vacations. While enjoying the sun and sand, few give much thought to the tiny organisms that make up the very sand they’re lying on. Sand is actually made from rock particles that have been broken down over time by natural processes. However, on some unique beaches, like those found in Hawaii, the sand has a significant component of coral and shell fragments, giving it a distinctive white color. Beaches not only provide relaxation but also play a crucial role in supporting marine life and protecting coastal areas from erosion.Questions:1、What do millions of people go to the beaches for annually?2、What makes the sand on Hawaiian beaches distinctive?3、Besides providing relaxation, what other important role do beaches serve?Answers:1、Vacations.2、The presence of coral and shell fragments.3、Supporting marine life and protecting coastal areas from erosion.第三题PassageThe rise of e-commerce has revolutionized the way we shop. With just a few clicks, customers can purchase products from all over the world and have them delivered to their doorstep. However, this convenience has also brought about some challenges, particularly in terms of logistics and environmental impact.One of the biggest concerns is the environmental impact of packaging. Traditional packaging materials, such as plastic bags and boxes, are not biodegradable and often end up in landfills, contributing to pollution.E-commerce companies have started to address this issue by offering packaging-free options and promoting the use of sustainable materials.Another challenge is the issue of returns. With the ease of online shopping, customers often order more items than they need, leading to a high rate of returns. This not only increases the carbon footprint of shipping but also creates additional waste. Some companies have introduced policies to encourage customers to return fewer items, such as offering incentives for reuse or donation.Despite these challenges, the e-commerce industry is not standing still. There are innovative solutions being developed to make the process more sustainable. For example, some companies are experimenting with drone delivery to reduce the number of vehicles on the road. Others are investing in energy-efficient data centers to power their operations.1、What is one of the main concerns related to e-commerce packaging?A)The high cost of shipping materials.B)The environmental impact of non-biodegradable materials.C)The difficulty in recycling packaging materials.2、How does the high rate of returns affect e-commerce?A)It increases the demand for new packaging materials.B)It leads to a decrease in the cost of shipping.C)It creates additional waste and increases the carbon footprint.3、What is an innovative solution being developed to make e-commerce more sustainable?A)The use of reusable packaging.B)The implementation of strict return policies.C)The introduction of drone delivery.Answers:1、B2、C3、A五、阅读理解-词汇理解（填空题，共5分）First QuestionPassage:In today’s fast-paced world, conservation has become a major concern for environmentalists and policymakers alike. Preserving natural resources is not just about protecting the environment; it also plays a critical role in ensuring sustainable development and improving the quality of life for future generations. Innovative methods are being explored to achieve this goal, including the use of renewable energy sources and promoting eco-friendly practices in industries.Questions:1、The word “conservation” in the passage most likely means:A) The act of using something economically or sparingly.B) The protection of natural resources from being wasted.C) The process of changing something fundamentally.D) The act of restoring something to its original state.Answer: B) The protection of natural resources from being wasted.2、The word “innovative” in the passage is closest in meaning to:A) Outdated.B) Traditional.C) Creative.D) Unchanged.Answer: C) Creative.3、Based on the context, t he term “eco-friendly” would be best described as:A) Practices that are harmful to the environment.B) Practices that are beneficial to the environment.C) Practices that have no impact on the environment.D) Practices that focus solely on economic growth.Answer: B) Practices that are beneficial to the environment.4、The phrase “sustainable development” in the text refers to:A) Development that uses up all available resources quickly.B) Development that meets present needs without compromising the ability of future generations to meet their own needs.C) Development that focuses only on immediate economic gains.D) Development that disregards environmental concerns.Answer: B) Development that meets present needs without compromising the ability of future generations to meet their own needs.5、When the passage mentions “quality of life,” it implies:A) A decrease in living standards over time.B) An improvement in the overall conditions under which people live and work.C) The absence of any efforts to improve living conditions.D) The focus on increasing industrial activities regardless of their impact.Answer: B) An improvement in the overall conditions under which people live and work.This format closely follows the structure you might find in an actual CET Band 4 exam, with a passage followed by vocabulary questions that test understanding of context and word meanings.第二题Reading PassagesIn today’s fast-paced world, staying informed about current events is more important than ever. One of the best ways to keep up with the news is to read newspapers. However, not all newspapers are created equal. Here is an overview of some of the most popular newspapers in the world.1.The New York Times (USA): Established in 1851, The New York Times is one of the most prestigious and influential newspapers in the world. It covers a wide range of topics, including national and international news, politics, business, science, technology, and culture.2.The Guardian (UK): The Guardian is a British newspaper that has been in circulation since 1821. It is known for its liberal bias and its commitment to investigative journalism. The Guardian covers a variety of issues, including politics, the environment, and social justice.3.Le Monde (France): Le Monde is a French newspaper that was founded in 1944. It is one of the most widely read newspapers in France and is known for its in-depth reporting and analysis of global events.4.The Times (UK): The Times is another British newspaper that has been in circulation since 1785. It is a conservative newspaper that focuses on politics, business, and finance.5.El País (Spain): El País is a Spanish newspaper that was founde d in 1976. It is one of the most popular newspapers in Spain and is known for its comprehensive coverage of national and international news.Vocabulary UnderstandingChoose the best word or phrase to complete each sentence. Write your answers in the spaces provided.1、The____________of The New York Times is that it is one of the most prestigious and influential newspapers in the world.a.reputationb.historyc.popularityd.bias2、The Guardian is known for its____________bias and its commitment to investigative journalism.a.liberalb.conservativec.moderated.biased3、Le Monde is one of the most widely read newspapers in France and is known forits____________reporting and analysis.a.shallowb.superficialc.in-depthd.brief4、The Times is a conservative newspaper that focuses on____________issues.a.socialb.economicc.politicald.cultural5、El País is one of the most popular newspapers in Spain and is known for its comprehensive____________of national and international news.a.reportingb.analysisc.coveraged.editorialAnswers:1、a. reputation2、a. liberal3、c. in-depth4、c. political5、c. coverage六、阅读理解-长篇阅读（选择题，共10分）第一题Reading Passage OneIn recent years, with the rapid development of the internet and mobile technology, online learning has become increasingly popular among students. Online courses, such as those offered by MOOCs (Massive Open Online Courses), provide students with convenient access to high-quality educational resources from around the world. However, despite the benefits of online learning, there are also some challenges and considerations that need to be addressed.1.The following passage is about:A. The advantages and disadvantages of online learningB. The impact of online learning on traditional educationC. The history of MOOCs and their role in educationD. The challenges faced by students in online learning2.According to the passage, what is one of the main benefits of online learning?A. It allows students to study at their own paceB. It provides access to a wider range of educational resourcesC. It increases the interaction between students and teachersD. It reduces the cost of education3.The passage mentions that online learning has become increasingly popular due to:A. The advancements in internet technologyB. The decline of traditional education systemsC. The desire for flexible learning schedulesD. All of the above4.What is one of the challenges mentioned in the passage that online learners may face?A. Limited access to technological devicesB. Difficulty in maintaining self-disciplineC. Lack of face-to-face interaction with teachersD. All of the above5.The passage suggests that in order to succeed in online learning, students should:A. Attend online classes regularlyB. Engage in active discussions with peersC. Set clear goals and deadlines for their studiesD. All of the above答案：1.A2.B3.D4.D5.D第二题Reading Passage OneThe rise of the Internet has revolutionized the way we communicate and accessinformation. One of the most significant impacts has been the transformation of education, with online learning becoming increasingly popular. This passage explores the benefits and challenges of online learning.The Benefits of Online Learning1.Flexibility: Online learning offers students the flexibility to study at their own pace and on their own schedule. This is particularly beneficial for working professionals and those with other commitments.2.Access to a Wide Range of Resources: Online courses often provide access to a wealth of resources, including textbooks, videos, and interactive materials that can enhance the learning experience.3.Diverse Learning Opportunities: Online learning platforms offer a wide variety of courses, ranging from traditional academic subjects to specialized and niche areas of study.4.Cost-Effective: Online courses can be more affordable than traditional classroom-based programs, especially for those who live far from educational institutions.The Challenges of Online Learning1.Self-Discipline: Online learning requires a high level of self-discipline and motivation, as students must manage their time and stay focused without the structure of a traditional classroom.2.Limited Interaction: Online courses often lack the face-to-face interaction that is common in traditional classrooms, which can impact the learning experience and social development of students.3.Technical Issues: Online learning relies heavily on technology, which can lead to technical issues that disrupt the learning process.4.Quality Assurance: With the proliferation of online courses, ensuring the quality and integrity of these courses can be a challenge.Questions:1、What is one of the main advantages of online learning mentioned in the passage?A. It is more expensive than traditional education.B. It requires students to be self-disciplined.C. It provides flexibility in studying.D. It lacks face-to-face interaction.2、According to the passage, what can online learning platforms offer that traditional classrooms might not?A. Limited access to textbooks.B. Fewer specialized courses.C. More interactive learning materials.D. No video resources.3、Which of the following is a challenge that online learning may present?A. Students can easily attend classes at a local university.B. There are no technical issues with online learning.C. It is difficult to ensure the quality of online courses.D. Online learning is always more affordable than traditional education.4、The passage suggests that online learning can be beneficial for:A. Students who prefer face-to-face interaction.B. Individuals with other commitments.C. Those who want to avoid textbooks.D. People who have no access to technology.5、What is one potential drawback of online learning that the passage discusses?A. The ability to study at any time.B. The use of a wide range of resources.C. The possibility of technical disruptions.D. The convenience of studying from home.Answers:1、C2、C3、C4、B5、C七、阅读理解-仔细阅读（选择题，共20分）第一题Reading PassagesIn the following passage, there are some blanks. For each blank there arefour choices marked A, B, C, and D. You should choose the one that best fits into the passage.The digital revolution is changing the way we live, work, and communicate. One of the most significant changes is the rise of artificial intelligence (AI). AI refers to the development of computer systems that can perform tasks that typically require human intelligence, such as visual perception, speech recognition, and decision-making.The potential of AI is enormous. It has the potential to transform industries, improve efficiency, and make our lives more convenient. However, with great power comes great responsibility. The ethical implications of AI are complex and multifaceted.1、The passage is mainly aboutA. the benefits of the digital revolutionB. the rise of artificial intelligenceC. the challenges of the digital revolutionD. the ethical implications of AI2、What is the main concern regarding AI mentioned in the passage?A. Its potential to disrupt traditional industriesB. Its potential to replace human jobsC. Its potential to be used for unethical purposesD. Its potential to cause social inequalities3、The author suggests that AI has the potential to。

管理学英语试题及答案

管理学英语试题及答案一、选择题（每题2分，共20分）1. The term "management" refers to the process of:A. Making decisionsB. Organizing resourcesC. Directing and controlling activitiesD. All of the above答案：D2. Which of the following is NOT a function of management?A. PlanningB. StaffingC. MotivatingD. Selling答案：D3. The process of setting goals and deciding on actions to achieve these goals is known as:A. OrganizingB. LeadingC. PlanningD. Controlling答案：C4. Which of the following is an example of a managementprinciple?A. Division of laborB. CentralizationC. DelegationD. All of the above答案：D5. In the context of management, "controlling" refers to:A. The process of ensuring that things are done as plannedB. The process of making plansC. The process of organizing resourcesD. The process of motivating employees答案：A6. The concept of "span of control" is related to:A. The number of employees a manager can effectively superviseB. The range of activities a manager is responsible forC. The level of authority a manager hasD. The type of control systems a manager uses答案：A7. The management function that involves influencing people to work towards organizational goals is:A. OrganizingB. LeadingC. PlanningD. Controlling答案：B8. Which of the following is a characteristic of effective communication?A. ClarityB. AmbiguityC. DisorganizationD. Lack of feedback答案：A9. The "scientific management" theory was developed by:A. Henri FayolB. Max WeberC. Frederick TaylorD. Abraham Maslow答案：C10. In the context of management, "empowerment" means:A. Giving employees the authority to make decisionsB. Centralizing all decision-making powerC. Reducing the role of employees in decision-makingD. Ignoring employee input in decision-making答案：A二、填空题（每题1分，共10分）1. The four basic functions of management are planning, organizing, leading, and ________.答案：controlling2. The management principle that suggests that there is an optimal span of control for each manager is known as ________.答案：span of control3. The management approach that focuses on the social needsof employees is known as the ________ approach.答案：human relations4. The process of identifying, selecting, orienting, training, and compensating employees is known as ________.答案：staffing5. A management style that involves a high level of task orientation and a low level of relationship orientation is known as ________ leadership.答案：autocratic6. The concept of "management by objectives" was developed by ________.答案：Peter Drucker7. The "Maslow's hierarchy of needs" theory suggests that people are motivated by a series of needs, starting with physiological needs and ending with ________ needs.答案：self-actualization8. In a ________ structure, there is a clear chain of command and a narrow span of control.答案：hierarchical9. The process of comparing actual performance with planned performance is known as ________.答案：budgeting10. The management function that involves setting goals and determining the sequence of actions needed to achieve them is known as ________.答案：strategic planning三、简答题（每题5分，共30分）1. What are the three key characteristics of an effective organizational structure?答案：An effective organizational structure should havethe following characteristics: clarity of roles and responsibilities, a clear chain of command, and a balance between centralization and decentralization.2. Explain the difference between leadership and management.答案：Leadership is the process of influencing, motivating, and directing individuals towards the achievement of organizational goals. Management, on the other hand, is a broader concept that includes planning, organizing, leading, and controlling organizational resources to achieve goals.3. What are the main principles of scientific management according to Frederick Taylor?答案：The main principles of scientific management includethe scientific selection and training of workers, the scientific selection of tasks and tools, the scientific determination of work methods, and the scientific scheduling of work and rest periods.4. Describe the four stages of the control process.。

Equivalence and Equivalent Effect(等值和等效)

a. Linguistic Meaning of Newmark
He agrees with Saussure（塞绪尔）that the signifier(the spoken and written signal) and the signified (the concept signified) together form the linguistic sign, but that sign is arbitrary or unmotivated. For example, the English word cheese is the acoustic（声音的）signifier which denotes the concept “food made of pressed curds”(the signified), although there is no inherent reason for that to be so.
Among these techniques, hierarchical structuring differentiates series of words according to their level. For instance, the superordinate animal and its hyponyms goat, dog, cow, etc. Componential analysis identifies and discriminates specific features of a range of related words. One example is the plotting of relationship terms (grandmother, mother, cousin, etc.) according to the values of sex (male, female), generation (the same, one, two or more apart) and lineality (direct ancestor/ descendant or not). Such results are useful for a translator working with languages that have very different kinship terms.

CCP3SURF ACESCIENCENEWSLETTERCollaborative Computational Project3on Surface ScienceNumber26-January2000ISSN1367-370XDaresbury LaboratoryContents1Editorial1 2Scientiﬁc Articles2 3SRRTNet-a new global network124High performance computing164.1Cluster-Computing Developments in the UK (16)4.2New HPC Support Mechanisms (22)5Reports on visits256Meetings,Workshops,Conferences296.1Reports on Bursaries (29)6.2Reports from Meetings (32)6.3Upcoming meetings (34)7Abstracts of forthcoming papers37 8Surface Science Related Jobs40 9Members of the working group43 Contributions to the newsletter from all CCP3members are welcome and should be sent to ccp3@eful Links:CCP3Home Page /Activity/CCP3CCP3Program Library /Activity/CCP3+896 SRRTNet /Activity/SRRTNetDLV /Activity/DLVCRYSTAL /Activity/CRYSTALCASTEP /Activity/UKCPMany useful items of software are available from the UK Distributed Computing Support web site,DISCO /Activity/DISCOEditors:Dr.Klaus Doll and Dr.Adrian Wander,Daresbury Laboratory,Daresbury, Warrington,WA44AD,UK1EditorialThe renewal of CCP3,which is due in the summer,is on all our minds,and this edition of the newsletter reminds us of our aims and achievements.Theﬂagship project supported by the post-doc is at the heart of the CCP–new programs can be developed which would not get oﬀthe ground otherwise.Over the last three years CCP3has been very lucky to have had Klaus Doll working on the development of analytic gradient methods for the CRYSTAL electronic structure package.This will lead to much more eﬃcient structure optimization,of particular beneﬁt to surface scientists where surface relaxation and reconstructions are so important.Klaus’achievements so far are described in theﬁrst article,and it is most satisfactory that tests on the CO molecule and bulk MgO have proved successful.The next step is to build in symmetry,to achieve greater computational eﬃciency,and then the new code can be released.As theﬂagship in the renewal proposal,the working group has chosen the development of methods to study the electronic structure and physical properties of large clusters.These clusters themselves possess surface-like properties, but at the same time it is proposed to study their interaction with surfaces.Such systems are a topic of active research for several of the members of the working group,both theoretical and experimental,and it is expected that their expertise will contribute greatly to the success of the project.Having Adrian Wander as a permanent member of staﬀat Daresbury supporting CCP3will lead to very welcome support for the synchrotron radiation community in the development of new surface program packages.In this newsletter he describes developments in SRRTNet,originally an American collaboration for providing sup-port for surface scientists using synchrotron radiation,which is likely to develop into an international collaboration based on the CCP model.Adrian is also in discussion with the Daresbury-based X-ray community with a view to developing new codes for the analysis of near-edge spectra in a wider range of systems than can be tackled at the moment,using the improved self-consistent electron potentials available for complex materials.This work would be based at Daresbury,and will form part of the CCP3collaboration.This issue contains short articles on our visitor programme,and by Ally Chan (Nottingham)and Yu Chen(Birmingham)who received student bursaries for participating in ECOSS-18.Please continue to apply for CCP3support!It is interesting to read in the pieces by Ally and Yu what most impressed them at ECOSS–I was struck by Ally’s comment that surface science has broadened to include nanoparticles and nanowires.Just what we thought in our choice ofﬂagship project next time round.John Inglesﬁeld12Scientiﬁc ArticlesAnalytical Hartree-Fock gradients for periodic systemsK.Doll,V.R.Saunders,and N.M.HarrisonCLRC,Daresbury Laboratory,Daresbury,Warrington,WA44AD,UKWe report on the progress of the implementation of analytic gradients in the program package CRYSTAL.The algorithm is brieﬂy summarised and tests illustrate that highly accurate analytic gradients of the Hartree-Fock energy can be obtained for molecules and periodic systems.IntroductionComputational materials science has been a fast growingﬁeld in the last years. This is mainly because methods which were developed earlier(density functional theory,molecular dynamics,Hartree-Fock and correlated quantum chemical meth-ods,Monte Carlo schemes,the GW method,etc)can now be applied to demanding realistic systems due to the increase in computational resources(faster CPUs,par-allelisation,cheaper memory and diskspace).CCP3is a collaboration in the area of surfaces and interfaces where progress de-pends on an interaction between experimental and theoretical approaches.There-fore,codes which provide a better theoretical understanding are important.One of the key issues in surface science is the determination of surface structure and adsorption energetics.From the computational point of view,a fast structural optimisation must be possible.Availability of numerical or analytical gradients facil-itatesﬁnding a minimum energy structure,and availability of analytical gradients can make optimisation algorithms more eﬃcient.As a rule of thumb,analyticalgradients are about N3times more eﬃcient than numerical gradients(with N beingthe number of variables).Also,for future developments such asﬁnding transition states,gradients are essential.Analytical gradients in quantum chemistry were pioneered by Pulay who did the ﬁrst implementation for multicentre basis sets[1].In many molecular codes based on quantum chemistry methods,analytical gradients are now implemented and gradient development has become an important task in quantum chemistry[2,3,4,5].Simi-larly,in solid-state codes such as CASTEP,WIEN,or LMTO,analytic gradients are available.Analytic Hartree-Fock gradients have already been implemented in a code for systems periodic in one dimension[6].CRYSTAL[7,8]was born in Turin and is now jointly developed in Turin and Daresbury.CRYSTAL was initially designed to deal with the exact exchange in and to solve the Hartree-Fock equations for real systems.With the modern versions of the code,density-functional2calculations or calculations using Hybrid functionals such as B3LYP with the ad-mixture of exact exchange are also possible.The target of this project,which began in October1997,was the implementation of analytical gradients in CRYSTAL and in autumn1999,theﬁrst test calculations on periodic systems were performed.In this article,we try to outline the theory and implementation of analytical gra-dients.We try to keep the mathematics at a minimum;a more formal publication is intended in the near future[9].A very comprehensive summary of the theory underpinning CRYSTAL will appear in the future[10].Total energyFirst,we want to brieﬂy summarise how the total energy is obtained.The total energy consists of•kinetic energy of the electrons•nuclear-electron attraction•electron-electron repulsion•nuclear-nuclear repulsionCRYSTAL,similar to molecular codes such as GAMESS-UK,MOLPRO(Stuttgart and Birmingham),GAUSSIAN,TURBOMOLE,etc,solves the single particle Schr¨o dinger equation and a wavefunction is calculated.The wavefunction is based on crystalline orbitalsΨi( r, k)which are linear combinations of Bloch functionsΨi( r, k)= µaµ,i( k)ψµ( r, k)(1) with the Bloch functions constructed fromψµ( r, k)= gφµ( r− Aµ− g)exp(i k g)(2) g are direct lattice vectors, Aµdenotes the coordinate of the nuclei.φµare the basis functions which are Gaussian type orbitals.For example,an s-type function centred at R a=(X a,Y a,Z a)is expressed asφ(α, r− R a,n=0,l=0,m=0)=φµ( r− R a)= Nexp(−α( r− R a)2).In molecular calculations,no mathematical problem arises from any of the interac-tions.In periodic systems,however,there are several divergent terms which have to3be dealt with:for example,in a one dimensional periodic system with lattice con-stant a and n being an index numerating the cells,the electron-electon interaction per unit cell would have contributions like:∞n=1e2na(3)This sum is divergent(similarly in two and three dimensions).Therefore,an indi-vidual treatment of this term is not possible.Instead,all the charges(nuclei and electrons)are partitioned and a scheme based on the Ewald method is used to sum the interactions[11].The Hartree-Fock equations are solved in terms of Bloch functions because the Hamiltonian becomes block-diagonal(i.e.at each k-point the equations are solved independently).The wavefunction coeﬃcients aµ,i are optimised due to this procedure and the total energy can be evaluated.For the computation of gradients,the dependence of the total energy on the nuclear coordinates must be analysed.There are three dependencies of the total energy on the nuclear coordinates:•nuclear-nuclear repulsion and nuclear-electron attraction:obviously,the coor-dinates of the nuclei enter•wavefunction coeﬃcients(or density matrix):we will obtain a diﬀerent solution with diﬀerent density matrix when moving the nuclei•basis functions:the basis functions are centred at the position of the nu-clei and therefore moving the nuclei will change integrals over the basis func-tions.These additional terms are called Pulay forces.They are missing when the Hellmann-Feynman theorem is applied and therefore Hellmann-Feynman forces often diﬀer substantially from energy derivative forces in the case of a local basis set(see[1]and references therein).Density matrix derivatives are diﬃcult to evaluate.However,for the solution of the Hartree-Fock equations,this problem can be circumvented and instead a new term is introduced,the so-called energy-weighted density matrix which is easily evaluated [12].However,this is only strictly correct for the exact Hartree-Fock solution. In practice,convergence is achieved up to a certain numerical threshold(e.g.a convergence of10−6E h of the total energy corresponding to27.2114×10−6eV).For very accurate gradient calculations,it may be necessary to make this threshold even lower.The remaining main problem is to generate all the derivatives of the integrals. In a second step,these derivatives have to be mixed with the density matrix.4Evaluation of integralsIn this section we summarise the types of integral which occur.The simplest type is the overlap integral between two basis functions at two centres:Sµν R k R l= φµ( r− R k)φν( r− R l)d3r(4) Obviously we can shift R k to the origin,and suppressing 0in the notation,we obtain:Sµν R i= φµ( r)φν( r− R i)d3r(5) with R i= R l− R k.A kinetic energy integral has the form:Tµν R i= φµ( r)(−12∆ r)φν( r− R i)d3r(6) the nuclear attraction integral has the form:Nµν R i= φµ( r)Z c| r− A c|φν( r− R i)d3r(7) and the electron-electron interaction has the form:Bµν R iτσ R j = φµ( r)φν( r− R i)φτ( r′)φσ( r′− R j)| r− r′|d3rd3r′(8)These integrals are in principle suﬃcient to deal with molecules.In the case of periodic systems,new types of integrals appear(e.g.multipolar integrals,integrals over the Ewald potential and its derivatives)[11,13,14].The fast evaluation of integrals is one of the main issues in the development of quan-tum chemistry codes.CRYSTAL uses a McMurchie-Davidson algorithm[15].Its idea is to map a product of two Gaussian type orbitals at two centres in an expan-sion of Hermite polynomials at an intermediate centre.This algorithm has proven to eﬃciently evaluate integrals,although in recent years progress in this specialised ﬁeld of quantum chemistry has been made(see for example the introduction in[16] or two recent reviews[17,18]).The expansion[15,14]looks like:5φ(α, r− A,n,l,m)φ(β, r− B,n′,l′,m′)= t,u,v E(n,l,m,n′,l′,m′,t,u,v)Λ(γ, r− P,t,u,v)(9)withγ=α+βand P=α A+β Bα+β.Λis a so-called Hermite Gaussian type function Λ(γ, r− P,t,u,v)= ∂∂P x t ∂∂P y u ∂∂P z v exp(−γ( r− P)2)(10)The start value E(0,0,0,0,0,0,0,0,0)=exp(−αβ( B− A)2)can be veriﬁed by inserting it in equation9.It can be derived from the Gaussian product rule[19,20]:exp(−α( r− A)2)exp(−β( r− B)2)=exp −αβα+β( B− A)2 exp −(α+β) r−α A+β Bα+β 2(11) General values E(n,l,m,n′,l′,m′,t,u,v)are obtained from recursion relations[15, 14].The E-coeﬃcients depend on the distance( B− A),but not on P or r.All the integrals can be expressed in terms of E-coeﬃcients[15,14,11,13].Evaluation of gradients of the integralsOne of the issues of the gradient project is to generalise the algorithms used to generate the energy integrals to obtain the gradients of the integrals.This madea new implementation of recursion relations necessary which are used to obtainthe coeﬃcients G in the expansion of the gradients of the integrals in Hermite polynomials.∂Φ(α, r− A,n,l,m)Φ(β, r− B,n′,l′,m′)∂A x= t,u,v G A x(n,l,m,n′,l′,m′,t,u,v)Λ(γ, r− P,t,u,v)(12)Once the coeﬃcients are known,the integration can be performed.The integrationfor the case of gradients of integrals is similar to the case of integrals for the total energy.The only diﬀerence is that,instead of the coeﬃcientsE(n,l,m,n′,l′,m′,t,u,v)which enter the energy expression,the gradient coeﬃcientsG A x(n,l,m,n′,l′,m′,t,u,v),G A y,G A z,G B x,G B y,and G B z6are used.The coeﬃcients G B x can eﬃciently be obtained together with the coeﬃ-cients G A x[21].For example,the evaluation of the overlap integral is done as follows:Sµν R i = φµ( r)φν( r− R i)d3r=t,u,v E(n,l,m,n′,l′,m′,t,u,v)Λ(γ, r− P,t,u,v)d3r=E(n,l,m,n′,l′,m′,0,0,0)Λ(γ, r− P,0,0,0)d3r=ME(n,l,m,n′,l′,m′,0,0,0)From theﬁrst line to the second,we have used the McMurchie-Davidson scheme, from the second to the third we exploited a property of the Hermite Gaussian type functions:all the integrals of the type Λ(γ, r− P,t,u,v)d3r with t=0or u=0or v=0vanish because of the orthogonality of these functions.The integration(fromthe third to the fourth line)is trivial.M is a normalisation constant. Calculating the gradient is easy once we know the new expansion:∂Sµν R i ∂A x =∂∂A xφµ( r)φν( r− R i)d3r=∂ t,u,v E(n,l,m,n′,l′,m′,t,u,v)Λ(γ, r− P,t,u,v)∂A x d3r=t,u,v G A x(n,l,m,n′,l′,m′,t,u,v)Λ(γ, r− P,t,u,v)d3r=G A x(n,l,m,n′,l′,m′,0,0,0)Λ(γ, r− P,0,0,0)d3r=MG A x(n,l,m,n′,l′,m′,0,0,0)This way,all the derivatives can be calculated!There are some integrals which involve three centres(for example nuclear attraction)where we exploit translational invariance:∂∂C x =−∂∂A x−∂∂B x(13)because the value of the integral is invariant to a simultaneous uniform translation of the three centres.Four centre integrals can be reduced to a product of two integrals over two centres which makes the calculation of gradients straightforward.As a whole,the calculation of gradients of the integrals is closely related to calcu-lating the integrals itself.This means that most of the subroutines can be used for7the gradient code.One of the main diﬀerences is that array dimensions need to be changed-dealing with gradients is similar to increasing the quantum number(a derivative of an s-function is a p-function,and so on).However,the task of adjusting the subroutines should not be underestimated.After obtaining the derivatives of the integrals,we mix them with the density ma-trix just like in the energy calculation.We have to take into account the new term which arose because we did not calculate a density matrix derivative—the energy weighted density matrix.Again,coding this additional term can be done by modi-fying existing subroutines.After this,weﬁnally obtain the forces on the individual atoms.Results from test calculationsIn this section,we summarise results from test calculations.We have considered the CO molecule which was arranged as a single molecule,as a molecule which is peri-odically reproduced with a periodicity of4˚A in one spatial direction(”polymer”), periodically reproduced with a periodicity of4˚A in two spatial directions(”slab”), and periodically reproduced with a periodicity of4˚A in three spatial directions (”solid”).Because of the large distance of4˚A,the molecules can be considered as nearly independent and the forces are quite similar.Still,the calculation of energy and gradient is completely diﬀerent and therefore this is an important test of Ewald technique and multipolar expansion.The results are given in table1.The results agree in the best case to at least6digits which is the numerical noise and in the worst case up to4digits.The diﬀerence between analytic and numerical gradi-ents in periodic systems mainly originates from an approximation made within the evaluation of the integrals[22]and from the number of k-points which aﬀects the accuracy of the energy-weighted density matrix.In table2,we display results from a MgO solid with one oxygen atom slightly distorted from the symmetrical position.Again,the forces agree well up to5digits with numerical derivatives.Future developments and ConclusionThe present version of the code is able to calculate Hartree-Fock forces for periodic systems up to a precision of4and more digits.There is no extra diskspace needed and the additional memory usage is moderate.This code will certainly be useful for structural optimisation and for future program development towards molecular dynamics or the calculation of response functions.The present version,however,is not yet ready for a release.Instead,the following steps are necessary:Firstly,the usage of symmetry must be implemented.This is of highest importance to make the code fast enough so that it can be used for practical optimisations.We expect8Table1:Force on a CO molecule with a carbon atom located at(0˚A,0˚A,0˚A)and an oxygen atom located at(0.8˚A,0.5˚A,0.4˚A).In the periodic case,the molecule is generated with a periodicity of4˚A.This means,that in one dimension,for example,there would be other molecules with a carbon atom at(n×4˚A,0˚A,0˚A)and an oxygen atom at((n×4+0.8)˚A,0.5˚A,0.4˚A),with n running overall positive and negative integers.Forces are given in E h,with E h=27.2114eVand a0=0.529177˚A.Higher ITOLs means a lower level of approximation in the evaluation of the integrals[22].ITOLs) k-points) numerical force0.3769140.37660(0.37664)0.376310.37566(0.37566) analytical force0.3769130.37663(0.37665)0.376330.37588(0.37578))on the atoms of an MgO solid.The MgO solid was chosen Table2:Forces(in E ha0to have an artiﬁcially high lattice constant of6.21˚A to make the calculation faster. Coordinates are given in fractional units,e.g.the second Mg is at0˚A,0.5×6.21˚A,0.5×6.21˚A.A normal fcc lattice would be obtained if the sixth atom(Oxygenat0.53,0,0)was at(0.5,0,0).Moving this atom from its normal position has ledto the nonvanishing forces.Mg(0.00.00.0)-0.03018-0.03019Mg(0.00.50.5)-0.00314-0.00314Mg(0.50.00.5)0.008950.00895Mg(0.50.50.0)0.008950.00895O(0.50.50.5)-0.00379-0.00379O(0.530.00.0)0.004290.00430O(0.00.50.0)0.007460.00746O(0.00.00.5)0.007460.00746that a version of the present code with symmetry will already be fast enough to compete with numerical derivatives.Further developments will be the coding of the bipolar expansion(a method to evaluate the electron-electron repulsion integrals faster),and sp-shells(s and p shells are often chosen to have the same exponentsto make the evaluation of integrals faster).Also,the newly written subroutines arenot yet optimal and they will certainly go through a technical optimisation(moreeﬃcient coding).In later stages,the code should be made applicable to metals (there is an extra term coming from the shape of the Fermi surface[23]which is notyet coded)and to magnetic systems(unrestricted Hartree-Fock gradients).Finally, pseudopotential gradients and density functional gradients should be included. References[1]P.Pulay,Mol.Phys.17,197(1969).[2]P.Pulay,Adv.Chem.Phys.69,241(1987).[3]P.Pulay,in Applications of Electronic Structure Theory,edited by H.F.Schae-fer III,153(Plenum,New York,1977).[4]H.B.Schlegel,Adv.Chem.Phys.67,249(1987).[5]T.Helgaker and P.Jørgensen,Adv.in Quantum Chem.19,183(1988)[6]H.Teramae,T.Yamabe,C.Satoko,A.Imamura,Chem.Phys.Lett.101,149(1983).[7]C.Pisani,R.Dovesi,and C.Roetti,Hartree-Fock Ab Initio Treatment of Crys-talline Systems,edited by G.Berthier et al,Lecture Notes in Chemistry Vol.48(Springer,Berlin,1988).[8]V.R.Saunders,R.Dovesi,C.Roetti,M.Caus`a,N.M.Harrison,R.Orlando,C.M.Zicovich-Wilson crystal98User’s Manual,Theoretical Chemistry Group, University of Torino(1998).[9]K.Doll,V.R.Saunders,N.M.Harrison(in preparation)[10]V.R.Saunders,N.M.Harrison,R.Dovesi,C.Roetti,Electronic StructureTheory:From Molecules to Crystals(in preparation)[11]V.R.Saunders,C.Freyria-Fava,R.Dovesi,L.Salasco,and C.Roetti,Mol.Phys.77,629(1992).[12]S.Bratoˇz,in Calcul des fonctions d’onde mol´e culaire,Colloq.Int.C.N.R.S.82,287(1958).[13]R.Dovesi,C.Pisani,C.Roetti,and V.R.Saunders,Phys.Rev.B28,5781(1983).[14]V.R.Saunders,in Methods in Computational Molecular Physics,edited by G.H.F.Diercksen and S.Wilson,1(Reidel,Dordrecht,Netherlands,1984).[15]L.E.McMurchie and E.R.Davidson,put.Phys.26,218(1978).[16]R.Lindh,Theor.Chim.Acta85,423(1993).[17]T.Helgaker and P.R.Taylor,in Modern Electronic Structure Theory.Part II,World Scientiﬁc,Singapore,725(1995)[18]P.M.W.Gill,in Advances in Quantum Chemistry,edited by P.-O.L¨o wdin,141(Academic Press,New York,1994)[19]S.F.Boys,Proc.Roy.Soc.A200,542(1950).[20]R.McWeeny,Nature166,21(1950).[21]T.Helgaker and P.R.Taylor,Theor.Chim.Acta83,177(1992).[22]The integrals Bµν R iτσ R j =Bτσ R jµν R iwhich should have the same value,are notnecessarily evaluated within the same level of approximation—this is nearly inevitable for periodic systems,as enforcing this symmetry would require a much higher computational eﬀort and much more data storage.The derivation of the equations for the analytic gradients,however,relies on these integrals be-ing equivalent.Therefore,the introduced asymmetry will lead to inaccuracies in the gradients.This can be controlled with the ITOL-parameters(tolerances as described in the CRYSTAL manual[8])which control the level of approx-imation.Higher ITOLs lead to a higher accuracy in the forces.However,the defaults appear to give forces with an accuracy up to4digits which should be good enough for most purposes.[23]M.Kertesz,Chem.Phys.Lett.106,443(1984).3SRRTNet-a new global networkFrascati’99-Birth of a NetworkScientiﬁc MeetingFrom the23rd to the25th September1999,a workshop on Theory and Computation for Synchrotron Radiation was held at the laboratory in Frascati just outside Rome, Italy.This was the third in an ongoing series of meetings on various aspects of synchrotron radiation,and follows meetings on Theory and Computation for Syn-chrotron Applications held at the Advanced Light Source in Berkeley in October 1997and Needs for a Photon Spectroscopy Theory Center held at the Argonne National Laboratory in August1998.This was an excellent meeting,featuring a variety of high quality scientiﬁc pre-sentations from both experimental and theoretical participants.Theﬁrst day was devoted to presentations concentrating on resonant x-ray processes and orbital or-dering eﬀects,particularly in V2O5.The second day then moved on to discussions of photoemission,photoelectron diﬀraction and holography,and studies of high T c superconductors.This day was concluded with an excellent conference dinner which ﬁnished rather late!Theﬁnal day then concluded with discussions of EXAFS,and x-ray spectroscopies.The overheads used in all the presentations can be viewed on line at http://wwwsis.lnf.infn.it/talkshow/srrtnet99.htmSRRTNet DiscussionsThe Friday programme also included a two hour session devoted to the idea of forming a global network concentrating on theory for synchrotron radiation re-search based research.The session began with a talk from Michel Van Hove of the Lawrence Berkeley National Laboratory who outlined the purposes and function of the proposed network.This was then followed by presentations by John Rehr of the University of Washington who highlighted moves to extend the synchrotron radia-tion research theory network(SRRTNet)in North America,by Maurizio Benfatto of the INFN Frascati,who presented the European perspective,by Kenji Makoshi of Himeji Institute of technology who discussed the Japanese eﬀorts and by Adrian Wander of the Daresbury Laboratory who presented CCP3as a possible model of how the network could be run.The concept of establishing a global network was received with enthusiasm from all present.OutcomeGiven the support of the meeting for the concept of global network of this sort,it was decided to extend SRRTNet into the global arena.The aims of the network are:•To provide a central repository for information of relevance to synchrotron radiation research•To develop theoretical methods pertaining to the experiments performed on synchrotron facilities•To provide state of the art and user friendly software for the analysis and interpretation of experiments•To provide training in the use of relevant software through workshops and site visits•To host visiting scientists•To hold periodic workshops for the dissemination of new results and method-ologiesThe directors of the network are Michel Van Hove and John Rehr.As aﬁrst step in the development of the network,Daresbury has agreed to host the web pages, and theoretical groups have been contacted and ask to provide input to this central web hub of what will grow into a globe encompassing network.If you are interested in contributing to the network and missed our e-mail announcement,the invitation letter follows;Dear Colleague,You may know of the recently established Synchrotron Radiation Research Theory Network(SRRTNet).We are contacting you to invite you,and all theorists inter-ested in this topic,to actively participate in the next phase of the network. SRRTNet aims to provide theory for experiments that use synchrotron radiation,by means of a global,web-based network linking theoretical and experimental research groups.The driving philosophy is to promote interactions between theory and exper-iment for mutual beneﬁt,by means of web-based information,workshops,exchange of theoretical methods and computer codes,as well as establishing visiting scientist programs.At the last SRRTNet workshop,conducted at Frascati near Rome in September1999, it was decided to strengthen the global character of this network by establishing a cen-tral,web-based source of information.Daresbury Laboratory is hosting this web site with Dr.Adrian Wander acting as editor.It is anticipated that all synchrotron facilities will provide direct links for their users to this web site,and consequently we expect this site to grow into an essential resource for synchrotron radiation re-searchers.An importantﬁrst function of the web site will be to provide information about theorists’research interests and links to relevant web pages.The network will be all the more valuable as this coverage becomes complete:it will thus allow theorists and experimentalists alike toﬁnd the best sources of information about the various methods for solving speciﬁc scientiﬁc problems.The purpose of this message is to ask you to provide such information and links about your group.You may visit the new web site/Activity/SRRTNetand see not only an overview of the network in general,but also the beginnings of such information about speciﬁc theoretical groups.The idea is to put a list of your research topics on the SRRTNet web site,while providing links to your own web site for more detailed and up-to-date information. If you prefer,the SRRTNet site can itself host a more complete web page covering your activities.The information we wish to present(or link to)includes as many as possible of the following items:•your topics of scientiﬁc activity related to synchrotron radiation(directly or by methodology);•your computer codes,with their capabilities and availability;•your publications,such as abstracts,papers,databases and web-presentations;•how to contact you or your group.。

211091475_β-葡寡糖的制备及其结构鉴定和生物活性研究进展

马冠骅，姜斯琪，张劲松，等. β-葡寡糖的制备及其结构鉴定和生物活性研究进展[J]. 食品工业科技，2023，44（8）：429−436. doi:10.13386/j.issn1002-0306.2022050169MA Guanhua, JIANG Siqi, ZHANG Jingsong, et al. Research Progress on Preparation, Structure Identification and Bioactivity of β-Glucooligosaccharides[J]. Science and Technology of Food Industry, 2023, 44(8): 429−436. (in Chinese with English abstract). doi:10.13386/j.issn1002-0306.2022050169· 专题综述 ·β-葡寡糖的制备及其结构鉴定和生物活性研究进展马冠骅1,2，姜斯琪1,2，张劲松1，秦　秀1，冯　杰1，刘艳芳1,2,*（1.上海市农业科学院食用菌研究所，农业农村部南方食用菌资源利用重点实验室，国家食用菌工程技术研究中心，上海 201403；2.上海理工大学健康科学与工程学院，上海 200093）摘　要：低聚糖是一种新型功能性糖原，在食品领域应用广泛。

β-葡寡糖是一类由2~20个葡萄糖通过β-糖苷键连接而成的低聚糖，主要由葡聚糖经不同方法降解制备得到，因其分子量低、水溶性好、结构独特、吸收效率高等特点，在调节肠道菌群、增强免疫、抗肿瘤等方面表现出较好的生物活性，在食品、保健品和药品等领域具有广阔的应用前景。

为促进β-葡寡糖的研究与开发，本文就近年有关β-葡寡糖的降解制备、分离纯化、结构表征方法及其生物活性方面的研究进行系统综述，以期为β-葡寡糖的深度研究与利用提供一定的参考。

_心理学报_2009年第41卷总目录_

《心理学报》2009年第41卷总目录1认知和实验心理学复合字母刺激心理旋转加工中的整体优先效应......................................................邱香傅小兰隋丹妮等 (1) 被试自身人手初始状态对心理旋转加工的影响: 眼动研究...................................陶维东黄希庭张慧等 (10) 定向遗忘中提取抑制的机制: 成功提取引起抑制...........................................................慕德芳宋耀武陈英和(26) 人机交互过程中认知负荷的综合测评方法.....................................................................................李金波许百华(35) 两种学习模式下类别学习的结果: 原型和样例..............................................................................刘志雅莫雷(44)负数的空间表征机制.................................................................................................高在峰水仁德陈晶等(95)类别不确定下的特征推理是基于类别还是基于特征联结...........................................................莫雷陈琳 (103)汉字词和图片命名与分类的比较....................................................................................................方燕红张积家 (114)听写困难儿童在笔画加工中的整体干扰效应..........................................................杨双宁宁刘翔平等 (127)封面故事、选项框架和损益概率对风险偏好的影响......................................................孙彦许洁虹陈向阳 (189)决策中损益值大小效应的发生条件及机制再探......................................................李小平葛明贵崔立中等 (196)藏-汉-英三语者语言联系模式探讨..................................................................................................崔占玲张积家 (208)中文句子阅读中语义信息对眼动预视效应的影响..................................................王穗苹佟秀红杨锦绵等 (220)时序知觉重复启动效应的作用机制.................................................................................张锋黄希庭郭秀艳 (233)图形识别中学习和再认取样的时间进程及其策略.........................................................................曹晓华曹立人 (242)用“你”表述物体的功能会抑制成因对分类的影响......................................................王哲孙宇浩傅小兰 (283)工作记忆负载对位置干扰子激活加工和抑制加工的影响.............................................................胡耿丹金志成 (292)视觉表象操作加工的眼动实验研究................................................................................................张霞刘鸣 (305)P300和CNV在GKT的延时反应范式中测谎效果的分离....................................................................................................................................................................崔茜张庆林邱江刘强杜秀敏阮小林 (316)中文阅读的副中央凹-中央凹效应: 词n的语义透明度对词n-1加工的影响...............白学军胡笑羽闫国利 (377) 准备间隔对口吃者言语反应速度的影响..........................................宁宁杨双彭聃龄丁国盛董方白 (387) 谜语问题解决中线索的作用.............................................................................................朱新秤李瑞菊周治金 (397) 两位数的整体与局部加工.................................................................................................陈兰翟细春周新林 (406) 空间场景表征中的参照系选取.........................................................谢超香刘强黎安娟陶维东孙弘进 (414) 中国二语学习者英语句子加工的心理机制初探：以主动句为例...................................常欣张国礼王沛 (471) 情绪对危机决策质量的影响............................................................................................................杨继平郑建君 (481) 世界知识在句子理解中的整合时程.................................金花钟伟芳徐贵平蔡梦娴杨玉芳莫雷 (565) 汉语语音范畴性知觉及其发展.........................................................................席洁姜薇张林军舒华 (572) 言语产生和理解中汉语个体量词的通达.........................................................................................张积家刘红艳 (580) 情绪干扰听觉反应冲突的ERP研究................................................................................余凤琼袁加锦罗跃嘉 (594) 汉语惯用语的产生机制....................................................................................................................张积家石艳彩 (659) 阅读中的元理解监测与元理解调控................................................................................................................陈启山 (676) 记叙文中倒叙事件的时间表征........................................................................................................何先友刘地秀 (684) 内隐与外显记忆的编码与提取非对称性关系.................................................................................孟迎芳郭春彦 (694) 海洛因延迟强化物超快速折扣倾向的心理机制..............................张锋水仁德周艳艳梁君英沈模卫 (763) 拼音输入法经验对汉字字形和语音加工的影响..............................................朱朝霞刘丽丁国盛彭聃龄 (785) 语篇理解中动允性信息的提取.........................................................................................鲁忠义陈笕桥邵一杰 (793) 工作记忆中汉语反词长效应机制....................................................................................................徐展李毕琴 (802) 时距的短时保持: 缩短还是变长......................................................................................贾丽娜张志杰王丽丽 (812) 负性情绪刺激是否总是优先得到加工: ERP研究..........................................................................黄宇霞罗跃嘉 (822) 视觉表象产生的大脑半球专门化效应............................................................................................游旭群宋晓蕾 (911) 多目标追踪任务中不同运动方式非目标的抑制机制......................................................张学民刘冰鲁学明 (922) 情绪记忆增强效应的时间依赖性.....................................................................................王海宝张达人余永强 (932) 眼睛注视线索提示效应: 内源性注意还是外源性注意?................................................................赵亚军张智君 (1133)非预想刺激的运动速率对无意视盲的影响.....................................................................................冯成志冯霞 (1143)2发展与教育心理学幼儿生气和伤心情绪情景理解........................................................................................................何洁徐琴美 (62) 4岁儿童对他人记忆的评判与错误信念理解的关系......................................................................陆慧菁苏彦捷 (135) 多主体评定青少年外化问题行为的一致性问题..............................................................陈光辉张文新王姝琼 (144) 主题关系在4~5岁儿童不同属性归纳推理发展中的作用......................................马晓清冯廷勇李红等 (249) 抑制控制能力衰退对知觉组织老年化的影响.................................................................谢宁王程吴艳红 (424) 童年中期身体侵害、关系侵害与儿童的情绪适应...........张文新陈亮纪林芹张玲玲陈光辉王姝琼 (433) 青年学生自信问卷的编制................................................................................................................毕重增黄希庭 (444) 小学学习不良儿童言语交际策略理解水平及其发展特点.............................................................闫嵘俞国良 (602) 家庭收入与儿童早期的社会能力：中介效应与调节效应..............................张晓陈会昌张银娜孙炳海 (613) 老年期语义理解能力与空间定向能力的交叉滞后分析..................................彭华茂王大华申继亮林崇德 (624) 纵向再探学前儿童心理理论发展模式...........................方富熹 Henry M. Wellman 刘玉娟刘国雄亢蓉 (706) 成人言语输入对儿童早期单词获得影响的个案追踪......................陈杰 Setoh Peipei 孟祥芝 Tardif Twila (715) 学前儿童朴素情绪理论的发展........................................................................................................刘国雄方富熹 (939) 儿童行为与心理水平的特质推理的发展.........................................................................................王美芳陈会昌 (947) 愿望采择发展水平对幼儿情感决策的影响......................................................陈璟孙昕怡李红李秀丽 (958) 1992年以来中学生心理健康的变迁：一项横断历史研究............................................................辛自强张梅 (969) 流动儿童歧视知觉与心理健康水平的关系及其心理机制..............................蔺秀云方晓义刘杨兰菁 (967) 我国当代青少年情感素质现状调查....卢家楣刘伟贺雯袁军竺培梁卢盛华王俊山田学英 (1152) 家庭功能对青少年疏离感的影响: 有调节的中介效应...................................................徐夫真张文新张玲玲 (1165)3管理和社会心理学迫选规则体验法: 检验规范性和描述性风险决策理论的新尝试...................................饶俪琳梁竹苑李纾 (726) 禀赋效应对产品更换决策的影响....................................................................................................黄劲松孙建伟 (737) 得失程数的变化: 损失规避现象的新视点......................................................................刘欢梁竹苑李纾 (1123) 主管认知信任和情感信任对员工行为及绩效的影响.....................................................................韦慧民龙立荣 (86) 参照群体类型与自我—品牌联系.....................................................................................杜伟强于春玲赵平 (156) 服务消费中多次情绪感染对消费者负面情绪的动态影响机制......................................................杜建刚范秀成 (346) 卷入影响广告理性诉求信息加工效果的眼动研究.........................................................................周象贤金志成 (357) 职业认知、社会支持对农民择业倾向的影响.................................................................................赵立郑全全 (367) 挑战性-阻断性压力(源)与员工心理和行为的关系：自我效能感的调节作用..............................张韫黎陆昌勤 (501) 辱虐管理与员工表现：传统性与信任的作用..................................................................吴隆增刘军刘刚 (510) 复杂任务中共享心智模型间的缓冲作用..........................................................徐寒易马剑虹杨凯方慧珍 (519) 团队学习、交互记忆系统与团队绩效：基于IMOI范式的纵向追踪研究...................................莫申江谢小云 (639) 预期性思考、自我调节导向与非计划购买......................................................朱华伟涂荣庭林倩蓉涂碧桂 (649) 期望、体验和回忆: 当消费者不能从体验中学习..........................................................................徐菁蒋多 (745) 企业员工工作伦理的结构.................................................................................王明辉郭玲玲赵国祥凌文辁 (853) 工作-家庭支持的结构与测量及其调节作用...................................................................................李永鑫赵娜 (863) 心理资本: 本土量表的开发及中西比较..........................................................................柯江林孙健敏李永瑞 (875) 匹配对创造性的影响: 集体主义的调节作用..................................................................................杜旌王丹妮 (980) 关系规范对消费者抱怨意愿及潜在动机的影响模型......................................黄敏学才凤艳周元元朱华伟 (989) 上司不当督导对下属建言行为的影响及其作用机制......................................................李锐凌文辁柳士顺 (1189) 组织创新气氛的测量及其在员工创新能力与创新绩效关系中的调节效应...................郑建君金盛华马国义 (1203) 两种社会交换对组织公民行为的影响: 组织认同和自尊需要的不同作用...................................................................................................................................................沈伊默袁登华张华杨东张进辅张庆林 (1215) 高低自我监控者在不同互动情境中的被洞悉错觉.........................................................................胡金生杨丽珠 (79) 责任对后悔强度的影响：来自ERP的证据....................................................................张慧君周立明罗跃嘉 (454) 冲突与支持影响情侣依恋的文化差异...............................................................................................................................................................陆爱桃张积家 Michael Harris Bond 张学新 Michael Friedman Chan Ching (534)选择、自我表达与选择扩散效应...........................................................曹文陈红高笑 Todd Jackson (753)当代中国人价值观的结构与特点.....................................................................................金盛华郑建君辛志勇 (1000)暴力游戏中射杀动作和血腥成分对玩家和观看者攻击倾向的影响..............................................................................................................................................................................张学民李茂宋艳李永娜魏柳青 (1228)4生理心理、医学心理与人格慢性应激诱导的抑郁小鼠神经肽Y的表达及抗抑郁药的作用..............................沈悦娣许百华刘娜等 (53)伏隔核和中脑腹侧被盖区内食欲素在吗啡奖赏中的作用.............................................................................................................................................................................白云静韩锦李勇辉黄砚北杨晓燕隋南 (329)东莨菪碱对大鼠空间参考记忆和工作记忆的不同影响..................于萍渠春环石密李新旺郭春彦 (337)奖惩线索条件下内外倾个体的自主唤醒和行为反应......................................白学军朱昭红沈德立刘楠 (492)围生期双酚A暴露对不同性别子代小鼠行为的影响.....................张婧徐晓虹王亚民罗清清叶银萍 (832)暴力电子游戏的短期脱敏效应：两种接触方式比较......................................................郭晓丽江光荣朱旭 (259)网络成瘾者不同情绪状态下的认知加工特征.................................................................................................郑希付 (630)自谦: 中国人一种重要的行事风格初探.........................................................................................胡金生黄希庭 (842)抑郁个体对情绪面孔的返回抑制能力不足.....................................................................................戴琴冯正直 (1175)5认知老化与神经科学专辑老化和其他研究领域中认知心理学与认知神经科学的整合rs-Göran Nilsson (1037)前临床期痴呆的认知特征：当前研究进展和未来研究展望rs Bäckman (1040)年龄和性别对气味和词汇的语义识别的不同影响...............Maria Larsson, Margareta Hedner, and Jonas Olofsson (1049)工作记忆的保持与操控：腹侧和背侧额叶皮层的特异性功能磁共振成像活动..........................................................................................................................................Sara Pudas, Jonas Persson, L-G Nilsson, and Lars Nyberg (1054)保留的跨通道启动与老化：对于近期观点的总结...........................................Soledad Ballesteros and Julia Mayas (1063)季节性情感障碍存在记忆损伤吗？........................................................................................................Erik Nilsson (1075)认知功能的性别差异.............................................................................................Agneta Herlitz and Johanna Lovén (1081)老年人记忆补偿的长期稳定性和变异性: 来自维多利亚纵向研究的证据............................................................... ......................................................................................................................Roger A. 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WB 术语及缩略语表

WB 术语及缩略语表-A-Alias: 假眼点，芯片或者引线框上的区域,可能被PRS误认为是有效的眼点/识别区域。

Alignment: 对正，物料对正是在焊接区域的材料的定位。

可以用模式识别系统或者由操作人员来完成，取决于焊接程序的参数和设置。

Alignment Tolerance: 对正公差，一个参照系统的两个操作人员之间的设计的距离的最大容许偏差。

只对2-点参照系统有效。

建议的公差应该是最小的焊盘尺寸的10%个。

对于外侧引脚，应该参照引脚公差，也可能更大以允许潜在的热胀。

Alternate Eye point: 备用眼点/识别区域，作备用参照的一个眼点/识别区域。

例如：如果有两个销售商生产使用某种特殊的芯片，而两种芯片不相同，程序就会起用一个备用的的参照系统/眼点。

也请参阅“Backup Eye point备份眼点”。

Axis Position Indicators: 轴位置指示器，屏幕右上方的X，Y和Z的值。

X和Y的十字准线值与之间输入的X-Y坐标原点有关。

Z指的是焊接头高度，关于之前输入的坐标原点位置。

-B-Backup Eye point: 备份眼点/识别区域，另一个在相同参照系统但不同位置的眼点/识别区域。

其目的是给视觉系统第二次机会去寻找对正的眼点/识别区域。

BITS: Bond Integrity Test System. 焊接完整性测试系统。

用来监测芯片的不粘焊接(NSOP)，引线框的不粘焊接，或者在焊接期间的短尾(SHTL)。

Bimodal: 双模态，只有两个主要的亮度级别。

Bond Force: 焊接压力，获得良好焊接所需的压力(可以提供电气连接)。

这是接触压力，以grams为单位，在焊接期间应用在焊线上。

Bond Height: 焊接高度，焊接工具接触到工作表面的高度。

Bond Off: 切线，一旦焊线穿过焊针(有一英寸的部分伸出焊针以外)形成一个金球的过程。

在修理一条断线或者替换一个焊线轴时使用。

Novel method for structured light system calibration

Novel method for structured light system calibrationSong Zhang,MEMBER SPIEHarvard UniversityMathematics DepartmentCambridge,Massachusetts02138E-mail:szhang@Peisen S.Huang,MEMBER SPIEState University of New York at Stony Brook Department of Mechanical Engineering Stony Brook,New York11794E-mail:peisen.huang@ Abstract.System calibration,which usually involves complicated and time-consuming procedures,is crucial for any3-D shape measurement system.In this work,a novel systematic method is proposed for accurate and quick calibration of a3-D shape measurement system we developed based on a structured light technique.The key concept is to enable the projector to“capture”images like a camera,thus making the calibration of a projector the same as that of a camera.With this new concept,the calibration of structured light systems becomes essentially the same as the calibration of traditional stereovision systems,which is well estab-lished.The calibration method is fast,robust,and accurate.It signiﬁ-cantly simpliﬁes the calibration and recalibration procedures of struc-tured light systems.This work describes the principle of the proposed method and presents some experimental results that demonstrate its performance.©2006Society of Photo-Optical Instrumentation Engineers.͓DOI:10.1117/1.2336196͔Subject terms:3-D shape measurement;calibration;structured light system;pro-jector image;phase shifting.Paper050866received Oct.31,2005;accepted for publication Jan.9,2006; published online Aug.21,2006.1IntroductionAccurate measurement of the3-D shape of objects is a rapidly expandingﬁeld,with applications in entertainment, design,and manufacturing.Among the existing3-D shape measurement techniques,structured-light-based techniques are increasingly used due to their fast speed and noncontact nature.A structured light system differs from a classic ste-reo vision system in that it avoids the fundamentally difﬁ-cult problem of stereo matching by replacing one camera with a light pattern projector.The key to accurate recon-struction of the3-D shape is the proper calibration of each element used in the structured light system.1Methods based on neural networks,2,3bundle adjustment,4–9or absolute phase10have been developed,in which the calibration pro-cess varies depending on the available system parameters information and the system setup.It usually involves com-plicated and time-consuming procedures.In this research,a novel approach is proposed for accu-rate and quick calibration of the structured light system we developed.In particular,a new method is developed that enables a projector to“capture”images like a camera,thus making the calibration of a projector the same as that of a camera,which is well established.Project calibration is highly important because today,projectors are increasingly used in various measurement systems,yet so far no system-atic way of calibrating them has been developed.With this new method,the projector and the camera can be calibrated independently,which avoids the problems related to the coupling of the errors of the camera and the projector.By treating the projector as a camera,we essentially uniﬁed the calibration procedures of a structured light system and a classic stereo vision system.For the system developed in this research,a linear model with a small look-up Table ͑LUT͒for error compensation is found to be sufﬁcient.The rest of the work is organized as follows.Section2 introduces the principle of the proposed calibration method. Section3shows some experimental results.Section4 evaluates the calibration results.Section5discusses the advantages and disadvantages of this calibration method. Finally,Sec.6concludes the work.2Principle2.1Camera ModelCamera calibration has been extensively studied over the years.A camera is often described by a pinhole model,with intrinsic parameters including focal length,principle point, pixel skew factor,and pixel size;and extrinsic parameters including rotation and translation from a world coordinate system to a camera coordinate system.Figure1shows a typical diagram of a pinhole camera model,where p is an arbitrary point with coordinates͑x w,y w,z w͒and͑x c,y c,z c͒in the world coordinate system͕o w;x w,y w,z w͖and camera coordinate system͕o c;x c,y c,z c͖,respectively.The coordi-nate of its projection in the image plane͕o;u,v͖is͑u,v͒. The relationship between a point on the object and its pro-jection on the image sensor can be described as follows based on a projective model:sI=A͓R,t͔X w,͑1͒where I=͕u,v,1͖T is the homogeneous coordinate of the image point in the image coordinate system,X w =͕x w,y w,z w,1͖T is the homogeneous coordinate of the point in the world coordinate system,and s is a scale factor.0091-3286/2006/$22.00©2006SPIEOptical Engineering45͑8͒,083601͑August2006͓͒R ,t ͔,called an extrinsic parameters matrix,represents ro-tation and translation between the world coordinate systemand camera coordinate system.A is the camera intrinsic parameters matrix and can be expressed asA =΄␣␥u 00␤v 0001΅,where ͑u 0,v 0͒is the coordinate of principle point,␣and ␤are focal lengths along the u and v axes of the image plane,and ␥is the parameter that describes the skewness of two image axes.Equation ͑1͒represents the linear model of the camera.More elaborate nonlinear models are discussed in Refs.11–14.In this research,a linear model is found to be sufﬁcient to describe our system.2.2Camera CalibrationTo obtain intrinsic parameters of the camera,a ﬂat check-erboard is usually used.In this research,instead of a stan-dard black-and-white ͑B/W ͒checkerboard,we use a red/blue checkerboard with a checker size of 15ϫ15mm,as shown in Fig.2.The reason of using such a colored check-erboard is explained in detail in Sec.2.3.The calibration procedures follow Zhang’s method.15The ﬂat checker-boards positioned with different poses are imaged by the camera.A total of ten images,as shown in Fig.3,are used to obtain intrinsic parameters of the camera using the Mat-lab toolbox provided by Bouguet.16The intrinsic param-eters matrix based on the linear model is obtained asA c =΄25.80310 2.7962025.7786 2.4586001΅mm,for our camera ͑Dalsa CA-D6-0512͒with a 25-mm lens ͑Fujinon HF25HA-1B ͒.The size of each charge-coupled device ͑CCD ͒pixel is 10ϫ10-␮m square and the total number of pixels is 532ϫ500.We found that the principle point deviated from the CCD center,which might have been caused by misalignment during the camera assem-bling process.2.3Projector CalibrationA projector can be regarded as the inverse of a camera,because it projects images instead of capturing them.In this research,we propose a method that enables a projector to “capture”images like a camera,thus making the calibration of a projector essentially the same as that of a camera,which is well established.2.3.1Digital micromirror device image generation If a projector can capture images like a camera,its calibra-tion will be as simple as the calibration of a camera.How-ever,a projector obviously cannot capture images directly.In this research,we propose a new concept of using a cam-era to capture images “for”the projector and then trans-forming the images into projector images,so that they are as if captured directly by the projection chip ͑digital micro-mirror device or DMD ͒in the projector.The key to realiz-ing this concept is to establish the correspondence between camera pixels and projector pixels.In this research,we use a phase-shifting method to ac-complish this task.The phase-shifting method is also the method used in our structured light system for 3-D shape measurement.In this method,three sinusoidal phase-shifted fringe patterns are generated in a computer and projected to the object sequentially by a projector.These patterns are then captured by a camera.Based on a phase-shifting algo-rithm,the phase at each pixel can be calculated,which is between 0and 2␲.If there is only one sinusoidal fringe in the fringe patterns,then the phase value at each camera pixel can be used to ﬁnd a line of corresponding pixels on the DMD.If vertical fringe patterns are used,this line is a vertical line.If horizontal fringe patterns are used,then this line is a horizontal line.If both vertical and horizontal fringe patterns are used,then the pixel at the intersection of these two lines is the corresponding pixel of the camera pixel on the DMD.Since the use of a single fringe limits phase measurement accuracy,fringe patterns with multiple fringes are usually used.When multiple fringes are used,the phase-shifting algorithm provides only a relativephaseFig.1Pinhole cameramodel.Fig.2Checkerboard for calibration:͑a ͒red/blue checkerboard,͑b ͒B/W image with white light illumination,and ͑c ͒B/W image with red light illumination ͑Color online only ͒.Fig.3Checkerboard images for camera calibration.value.To determine the correspondence,the absolute phase value is required.In this research,we use an additional centerline image to determine absolute phase at each pixel. The following paragraph explains the details of this method.Figure4illustrates how the correspondence between the CCD pixels and the DMD pixels is established.The red point shown in the upper left three fringe images is an arbitrary pixel whose absolute phase value needs to be de-termined.Here,absolute phase value means the phase value of the corresponding pixel on the DMD.The upper left three images are the horizontal fringe images captured by a camera.Their intensities areI1͑x,y͒=IЈ͑x,y͒+IЉ͑x,y͒cos͓␾͑x,y͒−2␲/3͔,͑2͒I2͑x,y͒=IЈ͑x,y͒+IЉ͑x,y͒cos͓␾͑x,y͔͒,͑3͒I3͑x,y͒=IЈ͑x,y͒+IЉ͑x,y͒cos͓␾͑x,y͒+2␲/3͔,͑4͒where IЈ͑x,y͒is the average intensity,IЉ͑x,y͒is the inten-sity modulation,and␾͑x,y͒is the phase to be determined. Solving these three equations simultaneously,we obtain ␾͑x,y͒=arctan͓ͱ3͑I1−I3͒/͑2I2−I1−I3͔͒.͑5͒This equation provides the so-called modulo2␲phase at each pixel,whose values range from0to2␲.If there is only one fringe in the projected pattern,this phase is the absolute phase.However,if there are multiple fringes in the projected pattern,2␲discontinuity is generated,the re-moval of which requires the use of a so-called phase un-wrapping algorithm.17The phase value so obtained is relative and does not represent the true phase value of the corresponding pixel on the DMD,or the absolute phase.To obtain the absolute phase value at each pixel,additional information is needed. In this research,we use an additional centerline image͑see the fourth image on the upper row of Fig.4͒to convert the relative phase map to its corresponding absolute phase map.The bright line in this centerline image corresponds to the centerline on the DMD,where the absolute phase value is assumed to be zero.By identifying the pixels along this centerline,we can calculate the average phase of these pix-els in the relative phase map as follows:␾¯0=͚n=0N␾n͑i,j͒N,͑6͒where N is the number of pixels on the centerline.Obvi-ously at these pixels,the absolute phase value should be zero.Therefore,we can convert the relative phase map into its corresponding absolute phase map by simply shifting the relative phase map by␾0.That is,␾a͑i,j͒=␾͑i,j͒−␾¯0.͑7͒After the absolute phase map is obtained,a unique point-to-line mapping between the CCD pixels and DMD pixels can be established.Once the absolute phase value at the pixel marked in red in the upper left three images is determined,a correspond-ing horizontal line in the DMD image,shown in red in the last image of the upper row in Fig.4,can be identiﬁed.This is a one-too-many mapping.If similar steps are applied to the fringe images with vertical fringes,as shown on the lower row of images in Fig.3,another one-too-many map-ping can be established.The same point on the CCD im-ages is mapped to a vertical line in the DMD image,which is shown in red in the last image of the lower row of images in Fig.4.The intersection point of the horizontal line and the vertical line is the corresponding point on the DMD of the arbitrary point on the CCD.Therefore,by usingthis Fig.5CCD image and its corresponding DMD image:͑a͒CCD im-age and͑b͒DMDimage.Fig.6World coordinatesystem.Fig.7World coordinate system construction:͑a͒CCD image and͑b͒DMDimage.Fig.4Correspondence between the CCD image and the DMD im-age.Images in theﬁrst row from left to right are horizontal CCDfringe images I1͑−120deg͒,I2͑0deg͒,and I3͑120deg͒,CCD center-line image,and DMD fringe image.The second row shows the cor-responding images for vertical fringe images.method,we can establish a one-to-one mapping between a CCD image and a DMD image.In other words,a CCD image can be transformed to the DMD pixel by pixel to form an image,which is called the DMD image and is regarded as the image “captured”by the projector.For camera calibration,a standard B/W checkerboard is usually used.However,in this research,a B/W checker-board cannot be used,since the fringe images captured by the camera do not have enough contrast in the areas of the black squares.To avoid this problem,a red/blue checker-board,illustrated in Fig.2͑a ͒is utilized.Because the re-sponses of the B/W camera to red and blue colors are simi-lar,the B/W camera can only see a uniform board ͑in the ideal case ͒if the checkerboard is illuminated by white light,as illustrated in Fig.2͑b ͒.When the checkerboard is illumi-nated by red or blue light,the B/W camera will see a regu-lar checkerboard.Figure 2͑c ͒shows the image of the checkerboard with red light illumination.This checker-board image can be mapped onto the DMD chip to form its corresponding DMD image for projector calibration.In summary,the projector captures the checkerboard im-ages through the following steps.1.Capture three B/W phase-shifted horizontal fringe images and a horizontal centerline image projected by the projector with B/W light illumination.2.Capture three B/W phase-shifted vertical fringe images and vertical centerline images projected by the projector with B/W light illumination.3.Capture the image of the checkerboard with red light illumination.4.Determine the one-to-one pixel-wise mapping be-tween the CCD and DMD.5.Map the image of the checkerboard with red light illumination to the DMD to create the correspond-ing DMD image.Figure 5shows an example of converting a CCD check-erboard image to its corresponding DMD image.Figure 5͑a ͒shows the checkerboard image captured by the camera with red light illumination,while Fig.5͑b ͒shows the cor-responding DMD image.One can verify the accuracy of the DMD image by projecting it onto the real checkerboard and checking its alignment.If the alignment is good,it means that the DMD image created is accurate.2.3.2Projector calibrationAfter a set of DMD images is generated,the calibration of intrinsic parameters of a projector can follow that of a cam-era.The followingmatrix,Fig.8Structured light systemconﬁguration.Fig.93-D measurement result of a planar surface:͑a ͒3-D plot of the measured plane and ͑b ͒measurement error ͑rms:0.12mm ͒.A p =΄31.13840 6.7586031.1918−0.1806001΅,is the intrinsic parameter matrix obtained for our projector͑Plus U2-1200͒.The DMD has a resolution of 1024ϫ768pixels.Its micromirror size is 13.6ϫ13.6␮m square.We notice that the principle point deviates from the nominal center signiﬁcantly in one direction,even outside the DMD chip.This is due to the fact that the projector is designed to project images along an off-axis direction.2.4System CalibrationAfter intrinsic parameters of the camera and the projector are calibrated,the next task is to calibrate the extrinsic parameters of the system.For this purpose,a unique world coordinate system for the camera and projector has to be established.In this research,a world coordinate system is established based on one calibration image set with its xy axes on the plane,and z axis perpendicular to the plane and pointing toward the system.Figure 6shows a checker square on the checkerboard and its corresponding CCD and DMD images.The four corners 1,2,3,4of this square are imaged onto the CCD and DMD,respectively.We chose corner 1as the origin of the world coordinate system,the direction from 1to 2as the x positive direction,and the direction from 1to 4as the y positive direction.The z axis is deﬁned based on the right-hand rule in Euclidean space.In this way,we can deﬁne the same world coordinate system based on CCD and DMD images.Figure 7illustrates the origin and the directions of the x ,y ,and z axes on these images.Table 1Measurement data of the testing plane at different positions and orientations.Plane Normalx range ͑mm ͒y range ͑mm ͒z range ͑mm ͒rms error ͑mm ͒1͑−0.1189,0.0334,0.9923͓͒−32.55,236.50͔͓−58.60,238.81͔͓−43.47,−1.47͔0.102͑−0.3660,0.0399,0.9297͓͒−36.05,234.77͔͓−64.24,243.10͔͓−102.24,14.61͔0.103͑−0.5399,0.0351,0.8410͓͒−40.46,234.93͔͓−72.86,248.25͔͓−172.84,11.61͔0.134͑0.1835,0.0243,0.9827͓͒−60.11,233.74͔͓−60.11,233.74͔͓−22.37,33.31͔0.105͑0.1981,0.0259,0.9798͓͒−17.52,217.04͔͓−38.04,221.09͔͓156.22,209.44͔0.116͑−0.1621,0.0378,0.9860͓͒−22.33,216.39͔͓−37.42,226.71͔͓122.37,171.38͔0.117͑−0.5429,0.0423,0.8387͓͒−27.41,212.85͔͓−47.36,232.86͔͓38.06,202.34͔0.108͑−0.0508,0.0244,0.9984͓͒−50.66,272.30͔͓−96.88,260.18͔͓−336.22,−310.53͔0.229͑−0.0555,0.0149,0.9983͓͒−56.38,282.45͔͓−108.03,266.72͔͓−425.85,−400.54͔0.2210͑−0.3442,0.0202,0.9387͓͒−57.74,273.35͔͓−106.63,268.37͔͓−448.48,−322.44͔0.2211͑0.4855,−0.0000,0.8742͓͒−43.70,281.07͔͓−106.88,260.01͔͓−394.84,−214.85͔0.2012͑0.5217,−0.0037,0.8531͓͒−31.12,256.75͔͓−81.14,245.23͔͓−185.51,−10.41͔0.16Fig.103-D measurement result of sculpture Zeus.Fig.11Positions and orientations of the planar board for calibration evaluation.The purpose of system calibration is to ﬁnd the relation-ships between the camera coordinate system and the world coordinate system,and also the projector coordinate system and the same world coordinate system.These relationships can be expressed as X c =M c X w ,X p=M pX w,where M c=͓R c,t c͔is the transformation matrix between the camera coordinate system and the world coordinate system,M p =͓R p ,t p ͔is the transformation matrix between the pro-jector coordinate system and the world coordinate system,and X c =͕x c ,y c ,z c ͖T ,X p =͕x p ,y p ,z p ͖T ,and X w =͕x w ,y w ,z w ,1͖T are the coordinate matrices for point p ͑see Fig.8͒in the camera,projector,and the world coordinate systems,respectively.X c and X p can be further transformed to their CCD and DMD image coordinates ͑u c ,v c ͒and ͑u p ,v p ͒by applying the intrinsic matrices A c and A p ,be-cause the intrinsic parameters are already calibrated.That is,s c ͕u c ,v c ,1͖T =A c X c ,s p ͕u p ,v p ,1͖T =A p X p .The extrinsic parameters can be obtained by the same procedures as those for the intrinsic parameters estimation.The only difference is that only one calibration image is needed to obtain the extrinsic parameters.The same Matlab toolbox provided by Bouguet 16was utilized to obtain the extrinsic parameters.Example extrinsic parameter matrices for the system setup areM c =΄0.01630.9997−0.0161−103.43540.9993−0.01580.0325−108.19510.0322−0.0166−0.99931493.0794΅,M p =΄0.01970.9996−0.0192−82.08730.9916−0.01710.1281131.56160.1277−0.0216−0.99151514.1642΅.2.5Phase-to-Coordinate ConversionReal measured object coordinates can be obtained based on the calibrated intrinsic and extrinsic parameters of the cam-era and the projector.Three phase-shifted fringe images and a centerline image are used to reconstruct the geometry of the surface.In the following,we discuss how to solve for the coordinates based on these four images.For each arbitrary point ͑u c ,v c ͒on the CCD image plane,its absolute phase can be calculated based on four images.This phase value can then be used to identify a line in the DMD image,which has the same absolute phase value.Without loss of generality,the line is assumed to be a vertical line with u p =␨͓␾a ͑u c ,v c ͔͒.Assuming world co-ordinates of the point to be ͑x w ,y w ,z w ͒,we have the follow-ing equation that transforms the world coordinates to the camera image coordinates:s ͕u c ,v c ,1͖T =P c ͕x w ,y w ,z w ,1͖T ,͑8͒where P c =A c M c is the calibrated matrix for the camera.Similarly,we have the coordinate transformation equation for the projector,s ͕u p ,v p ,1͖T =P p ͕x w ,y w ,z w ,1͖T ,͑9͒where P p =A p M p is the calibrated matrix for the projector.From Eqs.͑8͒and ͑9͒,we can obtain three linear equations,f 1͑x w ,y w ,z w ,u c ͒=0,͑10͒f 2͑x w ,y w ,z w ,v c ͒=0,͑11͒f 3͑x w ,y w ,z w ,u p ͒=0,͑12͒where u c ,v c ,and u p are known.Therefore,the world coor-dinates ͑x w ,y w ,z w ͒of the point p can be uniquely solved for the image point ͑u c ,v c ͒.Fig.12Measurement result of a cylindrical surface:͑a ͒cross sec-tion of the measured shape and ͑b ͒shape error.3ExperimentsTo verify the calibration procedures introduced in this re-search,we measured a planar board with a white surface using our system.18The measurement result is shown in Fig.9͑a ͒.To determine the measurement error,we ﬁt the measured coordinates with an ideal ﬂat plane and calculate the distances between the measured points and the ideal plane.From the result,which is shown in Fig.9͑b ͒,we found that the measurement error is less than rms 0.12mm.In addition,we measured a sculpture Zeus,and the result is shown in Fig.10.The ﬁrst image is the object with texture mapping,the second image is the 3-D model of the sculp-ture in shaded mode,and the last one is the zoom-in view of the 3-D model.The reconstructed 3-D model is very smooth with details.4Calibration EvaluationFor more rigorous evaluation of this calibration method,we measured the same planar white board at 12different posi-tions and orientations.The results are shown in Fig.11.The whole measurement volume is approximately 342͑H ͒ϫ376͑V ͒ϫ658͑D ͒mm.The normals,x ,y ,z ranges,and the corresponding errors of the plane for each pose are listed in Table 1.We found that the error of the calibration method,which varies from rms 0.10to 0.22mm,did not depend on the orientation of the measured plane.We also found that the error was larger when the measured plane is far away from the system.We believe that this is primarily due to the fact that the images for our calibration were taken with the checkerboard located relatively close to the system.Therefore,for large volume measurement,calibra-tion needs to be performed in the same volume to assure better accuracy.To further verify that our calibration method is not sig-niﬁcantly affected by the surface normal direction,we mea-sured a cylindrical surface with a diameter of 200mm.Fig-ure 12shows the measurement results.The error between the measured shape and the ideal one is less than rms 0.10mm.These results demonstrate that the calibration is robust and accurate over a large volume.5DiscussionsThe calibration method proposed in this research for struc-tured light systems has the following advantages over other methods•Simple .The proposed calibration method separates the projector and camera calibration,which makes the calibration simple.•Simultaneous .For each checkerboard calibration pose,the camera image and the projector image can be ob-tained simultaneously.Therefore,the camera and the projector can be calibrated simultaneously.•Fast .The calibration of the projector and the camera follows the same procedures of camera calibration.A checkerboard can be utilized to calibrate the camera and the projector simultaneously.This is much faster than other calibration methods,in which complex op-timization procedures often have to be involved to ob-tain the relationship between the camera and projector parameters.•Accurate .Since the projector and camera calibrations are independent,there is no coupling issue involved,and thus more accurate parameters of the camera and projector can be obtained.For the system we developed,we did not use the non-linear model for the camera or the projector.Our experi-ments showed that the nonlinear model generated worse results.This is probably because the nonlinear distortion of the lenses used in our system is small,and the use of the nonlinear model might have caused numerical instability.19,20To verify that the nonlinear distortions oftheFig.13Error caused by nonlinear image distortions:͑a ͒error for the camera and ͑b ͒error for the projector.camera and the projector are indeed negligible,we compute the errors of the corner points of the checkerboard at the image planes of the camera and projector,assuming a linear model.Here the error is deﬁned as the difference between the coordinates of a checker corner point as computed from the real captured image and from the back projected image based on a linear model.Figure13shows the results.The errors for both the camera and projector are within±1 pixel.Therefore,the linear model is sufﬁcient to describe the camera and the projector of our system.6ConclusionsWe introduce a novel calibration method for structured light systems that use projectors.The key concept is to treat the projector as a camera,and calibrate the camera and the projector independently using the traditional calibration method for cameras.To allow the projector to be treated as a camera,we develop a new method that enables the pro-jector to“capture”images like a camera.With this new concept,the calibration of structured light systems becomes essentially the same as that of traditional stereovision sys-tems,which is well established.This calibration method is implemented and tested in our structured light system.The maximum calibration error is found to be rms0.22mm over a volume of342͑H͒ϫ376͑V͒ϫ658͑D͒mm.The cali-bration method is fast,robust,and accurate.It signiﬁcantly simpliﬁes the calibration and recalibration procedures of structured light systems.In addition to applications in cali-bration,the concept of enabling a projector to“capture”images may also have potential other applications in com-puter graphics,medical imaging,plastic surgery,etc. AcknowledgmentsThis work was supported by the National Science Founda-tion under grant number CMS-9900337and National Insti-tute of Health under grant number RR13995. 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D.C.Ghiglia and M.D.Pritt,Two-Dimensional Phase Unwrapping:Theory,Algorithms,and Software,John Wiley and Sons,New York ͑1998͒.18.S.Zhang and P.Huang,“High-resolution,real-time3-d shape acqui-sition,”IEEE Computer Vision Patt.Recog.Workshop(CVPRW’04) 3͑3͒,28–37͑2004͒.19.R.Y.Tsai,“A versatile camera calibration technique for high-accuracy3d machine vision metrology using off-the-shelf tv camera and lenses,”IEEE J.Rob.Autom.3͑4͒,323–344͑1987͒.20.G.Wei and S.Ma,“Implicit and explicit camera calibration:Theoryand experiments,”IEEE Trans.Pattern Anal.Mach.Intell.16͑5͒, 469–480͑1994͒.Song Zhang is a post-doctoral fellow atHarvard University.He obtained his BS de-gree from the University of Science andTechnology of China in2000,and his MSand PhD degrees the mechanical engineer-ing department of the State University ofNew York at Stony Brook,in2003and2005,respectively.His research interests includeoptical metrology,3-D machine and com-puter vision,human computer interaction,image processing,computer graphics,etc.Peisen S.Huang obtained his BS degree inprecision instrumentation engineering fromShanghai Jiao Tong University,China,in1984,his ME and DrEng degrees in preci-sion engineering and mechatronics from To-hoku University,Japan,in1988and1995,respectively,and his PhD degree in me-chanical engineering from The University ofMichigan,Ann Arbor,in1993.He has beena faculty member in the Department of Me-chanical Engineering,Stony Brook Univer-sity,since1993.His research interests include optical metrology, image processing,3-D computer vision,etc.。

Fermi-liquid behaviour of the low-density 2D hole gas in GaAsAlGaAs heterostructure at larg

a r X i v :c o n d -m a t /0101195v 1 [c o n d -m a t .m e s -h a l l ] 12 J a n 2001Fermi-liquid behaviour of the low-density 2D hole gas in GaAs/AlGaAsheterostructure at large values of r s .Y.Y.Proskuryakov 1,A.K.Savchenko 1,S.S.Safonov 1,M.Pepper 2,M.Y.Simmons 2,D.A.Ritchie 21School of Physics,University of Exeter,Stocker Road,Exeter,EX44QL,U.K.2Cavendish laboratory,University of Cambridge,Madingley Road,Cambridge CB3OHE,U.K.We examine the validity of the Fermi-liquid description of the dilute 2D hole gas in the crossover from ’metallic’-to-’insulating’behaviour of ρ(T ).It has been established that,at r s as large as 29,negative magnetoresistance does exist and is well described by weak localisation.The dephasing time extracted from the magnetoresistance is dominated by the T 2-term due to Landau scattering in the clean limit.The eﬀect of hole-hole interactions,however,is suppressed when compared with the theory for small r s .There has recently been much attention drawn to the unusual crossover in the temperature dependence of re-sistivity with varying carrier concentration from ’metal-lic’(dρ/dT >0)to ’insulating’(dρ/dT <0)behaviour,which has been seen in some low-density 2D systems [1].With decreasing carrier density p the ratio of the Coulomb to Fermi energy r s =U/E F ∝m ∗/p 1/2in-creases,so it was suggested that in these systems the Fermi-liquid description is not valid and new approaches are needed [2].In [3]the insulating state at low hole densities,p ≃7.7×109cm −2and interaction parameter r s ≃35(with m ∗=0.37m 0),was attributed to Wigner crystallisation [4].At the same time,it was shown that even at r s ∼10−14the 2D hole gas can manifest it-self as a normal Fermi liquid,as far as weak localisation (WL)and weak hole-hole interaction (HHI)eﬀects are concerned [5,6].As conventional theories of weak localisation and elec-tron interactions [7,8]are derived for r s ≪1,their ap-plicability to r s ∼10−14in [5,6]is already a surprising fact.One can argue though that in the structures stud-ied the carrier density was not low enough and mobility not high enough for the deviations from the Fermi liq-uid description to be seen (p ≃4.6×1010cm −2and peak mobility µp =2.5×105cm 2V −1s −1in [5]).In this work,we examine the existence of WL and HHI in a 2D hole gas with lower density down to p =1.17×1010cm −2.In our high mobility structures,with peak mobil-ity µp =6.5×105cm 2V −1s −1,the experimental con-ditions approach those in [3]where the Wigner crys-tal formation has been claimed.We show that even at r s =29the strong Coulomb interaction does not aﬀect the WL description of the negative magnetoresistance [9,10],although it suppresses the contributions to thephase-breaking time and Hall coeﬃcient of the weak hole interactions expected in a disordered system with small r s .The experiments have been performed on a high mobil-ity heterostructure formed on a (311)A GaAs substrate,where the 2D hole gas at the GaAs/AlGaAs interface is separated from the Si-modulation doped layer by a 500˚A AlGaAs undoped spacer.A standard four-terminal low-frequency lock-in technique has been used for resistivity measurements at temperatures down to 45mK,with cur-rents of 1-10nA to avoid electron heating.The hole den-sity p is varied by the front gate voltage to provide the range of r s from 10to 29(with eﬀective mass m ∗taken as 0.38m 0[11]).Fig.1a shows a typical temperature dependence of the longitudinal resistivity in our samples.The lower part of the plot,corresponding to higher densities,has a ’metallic’behaviour with dρ/dT >0.As the hole den-sity is decreased,ρ(T )becomes nonmonotonic,and fur-ther decreasing p leads to an ’insulating’dependence with dρ/dT <0.In the ’metal’to ’insulator’crossover,where r s varies from 23to 29,we have observed negative per-pendicular magnetoresistance,Fig.1b,which increases with lowering the hole density.It is natural to ascribe this eﬀect to WL which occurs due to quantum interference of elastically scattered carriers on closed phase-coherent paths.However,great care should be taken in analysing WL in high-mobility structures.Firstly,the application of the conventional theory of WL is based on the diﬀusion approximations and is re-stricted by the range of magnetic ﬁelds B <B tr ,where B tr =¯h /4Deτis the ’transport’magnetic ﬁeld,D is diﬀusion coeﬃcient and τis momentum relaxation time [8].Physically,this means that the magnetic length L B has to be larger than the mean free path l .Within this approach,no negative magnetoresistance is expected at B >B tr ,when L B <l .In our high mobility samples the value of B tr is very small,ranging from 0.003to 0.08T for the densities studied.At the same time,the NMR is observed up to ∼0.2T,where Shubnikov-de Haas os-cillations start.This means that even at B >B tr there is a phase-breaking eﬀect of magnetic ﬁeld,which acts on the trajectories which are still smaller than L B (and smaller than l ).The theory of WL in such a regime has been considered in several papers [9,10],although no ex-perimental tests of the theories have yet been performed.Secondly,all theories of WL discuss the positive mag-1netoconductivity△σxx(B)=δσxx(T,B)−δσxx(T,0), which is due to the decrease of the negative correction δσxx(T,B)to the longitudinal classical(Drude)ually,the phase-breaking eﬀect of magnetic ﬁeld is seen at smallﬁelds where its eﬀect on the Drude conductivity is negligible.In a high mobility system, however,the phase-breaking eﬀect will coexist with the magneticﬁeld dependence of the Drude conductivity it-self:σD xx(B)=σ0πh(1+γ)2 N n=0 b·ψ3n(b)γ ,(2)whereγ=τ/τϕ,τϕis the dephasing time,b=1B tr,ψn(b)= ∞0dξ·e−ξ−bξ2/4L n(bξ2/2),and L n are the La-guerre polynomials.In Fig.3a we show representative data at diﬀerent densities in the middle of the temper-ature range studied,plotted against dimensionless mag-neticﬁeld B/B tr(B tr is found as(4π¯hµσ0/e2)−1).Solid lines in Fig.3are obtained from Eq.(2),whereγis used as an adjustable parameter.At lowest p and T the error in determiningγis10%,but as the density or/and tem-perature increases it steeply drops to5%.The obtained γ-values range from0.04to0.43and satisfy the condition τ<τϕ.The apparent agreement with WL theory suggests that,surprisingly,even at r s∼23−29the Fermi-liquid description of the system remains valid.The further ev-idence of this has been obtained from the analysis of the temperature dependenceτ−1ϕ(T)of the dephasing rate.Estimations show that the contribution toτ−1ϕ(T)of electron-phonon scattering[12]is negligible in the studied temperature range.According to the Fermi-liquid the-ory[15,13,7],the dephasing rate due to electron-electron scattering is dominated either by a linear or quadratic term,dependent on the parameterτk B T/¯h:τ−1ϕ(T)=α(k B T)2k B T ,when k B Tτ/¯h≫1(3)τ−1ϕ(T)=k B T¯h ,when k B Tτ/¯h≪1(4) whereα=π/8[15].The quadratic term in Eq.(3)is due to Landau-Baber scattering associated with collisions in a clean Fermi-liquid with large momentum transfer,and the linear term in Eq.(4)corresponds to particle-particle interactions with small energy transfer in disordered con-ductors.In the experiment,the parameter k B Tτ/¯h varies from0.06to0.8for the lowest studied density and from 0.1to0.9for the highest density,so that we need to examine the applicability of both expressions to the de-pendenceτ−1ϕ(T)extracted from the analysis of the mag-netoresistance data,Fig.4a.It is interesting to note that in the whole range of p,in-cluding the lowest densities with’insulating’dependence ρ(T),we have seen Shubnikov-de Haas oscillations.In the studied sample a shift of the Shubnikov-de Haas min-ima was seen with increasing temperature from45mK to 600mK,indicating a weak(∼10%)increase of the hole density.Thus,it was convenient to analyse the dephas-ing rate as the productτ−1ϕ·p,with density p directly measured at each temperature by the Shubnikov-de Haas eﬀect.In this case Eqs.(3-4)are re-written asτ−1ϕ·p=m∗k B T (5)τ−1ϕ·p=m∗2τln 2E FτWe suggest two possible reasons for the suppression of the linear term.According to the conventional theories [7,13],the T-term originates from electron-electron scat-tering in systems with a diﬀusive character of transport, when the interaction potential between electrons is weak (r s<<1).The interactions in our system are strong. In addition,in our high mobility system,the coherent paths of size Lϕcontain only a small number of scatter-ers(∼10),thus the diﬀusion approximation may not be valid.The non-diﬀusive transport does not aﬀect,how-ever,the T2term which is an intrinsic property of clean systems.Let us brieﬂy discuss the saturation ofτ−1ϕ.The prob-lem of saturation of the dephasing rate at low T has been known for many years[14,16],with several expla-nations of this eﬀect suggested.A characteristic feature of the saturation in our case is that it becomes more pro-nounced with increasing density.Then a possible origin of the saturation can be a nonequilibrium external noise which does not disturb the temperature dependence ofτ−1ϕin the Fermi liquid and manifests itself simply as anadditive to the dephasing rate[14].According to[14]the saturation due to noise is1/τsatϕ≃D1/5(ΩeE ac)2/5,whereΩis the radiation frequency and E ac is amplitudeof the ac electricﬁeld.In Fig.4b the value1/τsatϕisplotted as a function of D and shows agreement with the D1/5dependence.In a conventional Fermi liquid,WL is usually accom-panied by electron-electron interaction eﬀects,which are seen as quantum corrections to the conductivity and Hall coeﬃcient.At small r s,the two corrections are related asδR H(T)/R H=−2δσ(T)/σ[7].In[5]it was argued that in p-GaAs heterostructures the weak hole-hole in-teraction eﬀect persists up to r s∼10−14.Now we have measured the temperature dependence of the Hall coef-ﬁcient at much larger r s.In Fig.4c we plot the Hall coeﬃcient as(R H e)−1for diﬀerent temperatures in the range from45to400mK at the density p=1.45×1010 cm-2(solid squares).The decrease of R H with increasing T appears to be of the same order of magnitude as that estimated from theory[7].However,the observed shift of Shubnikov-de Haas minima has indicated an increase of the hole density with temperature in this experiment (circles in Fig.4c),such that it agrees well,within2%, with the change in R H.The inset in Fig.4c shows good agreement between the densities measured by Hall and Shubnikov-de Haas eﬀects at diﬀerent V g for T=45mK. One can then conclude that the interaction eﬀects in the Hall coeﬃcient appear to be much weaker than expected from the perturbation theory derived at small r s.We believe that this suppression of the temperature depen-dence in the Hall coeﬃcient has the same origin as the absence of the linear term in the dephasing rate,namely strong interactions at large r s and,possibly,breakdown of the diﬀusion approximation.To summarise,we have investigated the applicability of the Fermi-liquid description to a high mobility,low den-sity2D hole gas with large r s,approaching the conditions of expected Wigner crystallisation.We have found that the negative magnetoresistance in the crossover region from’metal’to’insulator’persists up to r s∼29,and is caused by weak localisation.The dephasing rateτ−1ϕ(T) is dominated by a T2-contribution due to Landau-Baber scattering,which is a characteristic property of a Fermi-liquid in the clean limit.At the same time,the linear in T-term in the scattering rate,due to scattering with small energy transfer,is suppressed.Its decrease is ac-companied by absence of the temperature dependence in the Hall coeﬃcient.This demonstrates directly that con-ventional understanding of interaction eﬀects,developed at r s≪1,has to be modiﬁed for a high-mobility Fermi liquid with strong interactions.We are grateful to B.L.Altshuler and D.L.Maslov for stimulating discussions,Harry Clark for help with fabri-cating the samples,EPSRC and ORS fund forﬁnancial support.Rev.Lett.78,3366(1997).Figure captions:Fig.1(a)Temperature dependence of the resistivity atdiﬀerent hole densities.The dashed box encloses the do-main of the negative magnetoresistance(NMR)study.(b)NMR at T=45mK,for diﬀerent hole densities.Fig.2(a,b)Experimental(total)conductivityσxx(B)shown by solid lines in theﬁgures and circles in the in-sets(the insets present zoomed-in regions).Dashed linesin the insets represent the classical magnetoconductivityEq.(1).as a function of di-Fig.3Magnetoconductivity∆σW Lxxmensionless magneticﬁeld(B tr=¯h/4Deτ).(a)p=1.17;1.21;1.3;1.45;1.7×1010cm−2at T=200mK;(b)p=1.21×1010cm-2at T=45,120,200,300,400,500mK.Solid lines areﬁt to Eq.(2).Fig.4(a)Temperature dependence of the dephasing rateat diﬀerent gate voltages.The low-temperature densi-ties from bottom to top are:p=1.17;1.21;1.3;1.45;1.7×1010cm−2.Solid lines areﬁts to Eq.(5)with thevalues ofαshown in the inset.The straight line is plottedusing equation Eq.(3).(b)The saturation value of the dephasing rate at T=0against diﬀusion coeﬃcient.(c)The Hall coeﬃcient at diﬀerent temperatures,pre-sented as(eR H)−1(solid squares)for p=1.45×1010cm-2at T=45mK.The density determined from theShubnikov-de Haas eﬀect is shown by open circles.In-set:hole density measured by the Hall and Shubnikov-deHaas eﬀects at diﬀerent V g,T=45mK.40.00.30.60.90.8124681020(a)T (K)1.411.9p=1010cm -2×1.171.251.551.72.22.6ρx x (k Ω)-0.4-0.20.00.20.4234567891020(b)1.851.551.71.451.3T=45 mKp=1010cm -2× 1.211.17ρx x (k Ω)B (T)-0.20.00.20.40.60.8 1.00.000.030.060.090.120.15(b)T=45 mK p=1.45×1010cm-2B (T)σx x (m S )0.000.030.06DrudeexperimentB (T)0.020.030.040.050.060.07-0.20.00.20.40.60.8 1.0(a)T=45 mK p=1.17×1010cm-2B (T)σx x (m S )0.000.050.100.15DrudeexperimentB (T)12345670123(a)∆σW L(µS )1.7×1010T=200 mKp h =1.17×1010cm-2B/B tr1230246810(b)500 mKT=45 mK p h =1.21×1010 cm-2B/B tr∆σW L(µS )1.21.41.60.040.060.08(b)D 1/5(cm 2/s)1/51/τφs a t(1011s -1)0.10.20.30.40.00.40.81.21.6(c)(e R H )-1, p (1010c m -2)T (K)0.00.10.20.30.40.50100200300400500600T (mK)(a)τφ−1(1011s -1) · p (1010 c m -2)0.00.30.61.2 1.4 1.6π/8p (1010cm -2)α2672702731.01.52.0V g (mV)。

创智激发创新思维的英语作文

Innovation is the driving force behind progress in any field,and it is essential for the development of society.The ability to think innovatively is a skill that can be cultivated and nurtured through various means.Here are some ways to stimulate innovative thinking in English composition:1.Embrace Curiosity:Encourage a sense of wonder and curiosity about the world.Ask questions that go beyond the surface,such as What if?or Why not?This can lead to new perspectives and ideas.2.Diverse Reading:Read a wide range of materials in English,from scientific journals to fiction,poetry,and essays.Exposure to different styles and ideas can spark creativity.3.Cultural Exchange:Engage with Englishspeaking cultures from around the world. Understanding different viewpoints can lead to innovative solutions that are not limited by ones own cultural biases.4.Critical Thinking:Practice critical thinking by analyzing and evaluating information. This helps in identifying potential areas for innovation.5.Brainstorming Sessions:Participate in or organize brainstorming sessions where ideas are freely shared without immediate judgment.This collaborative environment can foster creative thinking.e of Metaphors and Analogies:Employing metaphors and analogies in English writing can help visualize complex ideas in simpler terms,making it easier to explore new concepts.7.Learning from Failure:Embrace the process of trial and error.Each failure is an opportunity to learn and improve,which is crucial for innovation.8.CrossDisciplinary Approach:Combine knowledge from different fields.For example, applying principles from physics to solve problems in economics can lead to novel approaches.9.Reflective Writing:Regularly write reflections on what you have learned and how you can apply it in new ways.This practice can help in identifying patterns and making connections between seemingly unrelated ideas.10.Technological Tools:Utilize technology to aid in the creative process.Software for mind mapping,for instance,can help visualize complex ideas and relationships.11.Innovation Challenges:Participate in or create challenges that require innovative solutions.This can be a competition or a personal goal to solve a problem in a new way.12.Mindfulness and Meditation:Incorporate mindfulness practices into your routine. These can help clear the mind and allow for more creative thinking.nguage Play:Experiment with the English language itself.Play with words,create neologisms,or invent new phrases to express your ideas.14.Feedback and Revision:Seek feedback on your writing and be open to revising your work.This iterative process can lead to more refined and innovative compositions.15.Time for Incubation:Allow ideas to incubate.Sometimes stepping away from a problem and returning to it later with a fresh perspective can lead to innovative solutions. By incorporating these strategies into your approach to English composition,you can foster an environment that is conducive to innovative thinking and creative expression.。

液态纯Mg黏度与自扩散系数的分子动力学模拟研究

文章编号：1671-7872(2023)03-0261-08吴永全，钢铁冶金专业工学博士，上海大学材料科学与工程学院教授、博士生导师。

主要从事高温冶金熔体(包括熔渣和金属熔体)和固体材料微观结构及其与宏观物性之间关系的基础理论研究，尤其是计算机模拟和光谱理论和实验方面的研究。

主持国家自然科学基金项目6项、教育部及上海市科委基金项目6项、宝钢集团横向课题8项，主要参与973等国家重点项目5项。

出版中文学术专著2部：《冶金/陶瓷/地质熔体离子簇理论研究》(科学出版社，2007年)和《熔融金属物理初步》(冶金工业出版社，2012年)。

出版英文学术专著1部：“A study of Ion ClusterTheory of Molten Silicates and Some Inorganic Substances”(Trans Tech PublicationsInc, Switzerland, UK, USA, 2009)。

在Physical Chemistry Chemical Physics, ScriptaMaterialia, Applied Surface Science, The Journal of Chemical Physics，Journal of Raman Spectroscopy, Journal of Alloys and Compounds, Chemical Physics Letters，Modelling and Simulation in Materials Science and Engineering, Journal of Molecular Modeling, Computational Materials Science, Journal of Crystal Growth, Chinese Physical Letters, Steel Research International,《物理化学学报》《物理学报》《金属学报》等期刊及国内外学术会议论文集上发表论文80余篇，其中SCI收录50余篇，SCI总引频次数700多次、他引500多次。

(完整版)英语语言学概论--整理

Chapter 1 Language语言1. Design feature (识别特征) refers to the defining properties of human language that distinguish it from any animal system of communication.2. Productivity(能产性) refers to the ability that people have in making and comprehending indefinitely large quantities of sentences in theirnative language.3. arbitrariness (任意性) Arbitrariness refers to the phenomenon that there is no motivated relationship between a linguistic form and itsmeaning.4. symbol (符号) Symbol refers to something such as an object, word, or sound that represents something else by association or convention.5. discreteness (离散性) Discreteness refers to the phenomenon that the sounds in a language are meaningfully distinct.6. displacement (不受时空限制的特性) Displacement refers to the fact that human language can be used to talk about things that are not in theimmediate situations of its users.7. duality of structure (结构二重性) The organization of language into two levels, one of sounds, the other of meaning, is known as duality ofstructure.8. culture transmission (文化传播) Culture transmission refers to the fact that language is passed on from one generation to the next throughteaching and learning, rather than by inheritance.9. interchangeability (互换性) Interchangeability means that any human being can be both a producer and a receiver of messages.1. ★What is language?Language is a system of arbitrary vocal symbols used for human communication. This definition has captured the main features of language.First, language is a system.Second, language is arbitrary in the sense.The third feature of language is symbolic nature.2. ★What are the design features of language?Language has seven design features as following:1) Productivity.2) Discreteness.3) Displacement4) Arbitrariness.5) Cultural transmission6) Duality of structure.7) Interchangeability.3. Why do we say language is a system?Because elements of language are combined according to rules, and every language contains a set of rules. By system, the recurring patterns or arrangements or the particular ways or designs in which a language operates. And the sounds, the words and the sentences are used in fixed patterns that speaker of a language can understand each other.4. ★ (Function of language.) According to Halliday, what are the initial functions of children’s language? And what are the threefunctional components of adult language?I. Halliday uses the following terms to refer to the initial functions of children’s language:1) Instrumental function. 工具功能2) Regulatory function. 调节功能3) Representational function. 表现功能4) Interactional function. 互动功能5) Personal function. 自指性功能6) Heuristic function. 启发功能[osbQtq`kf`h]7) Imaginative function. 想象功能II. Adult language has three functional components as following:1) Interpersonal components. 人际2) Ideational components.概念3) Textual components.语篇1. general linguistics and descriptive linguistics (普通语言学与描写语言学) The former deals with language in general whereas the latter isconcerned with one particular language.2. synchronic linguistics and diachronic linguistics (共时语言学与历时语言学) Diachronic linguistics traces the historical development of thelanguage and records the changes that have taken place in it between successive points in time. And synchronic linguistics presents an account of language as it is at some particular point in time.3. theoretical linguistics and applied linguistics (理论语言学与应用语言学) The former copes with languages with a view to establishing atheory of their structures and functions whereas the latter is concerned with the application of the concepts and findings of linguistics to all sorts of practical tasks.4. microlinguistics and macrolinguistics(微观语言学与宏观语言学) The former studies only the structure of language system whereas thelatter deals with everything that is related to languages.5. langue and parole (语言与言语) The former refers to the abstract linguistics system shared by all the members of a speech communitywhereas the latter refers to the concrete act of speaking in actual situation by an individual speaker.6. competence and performance (语言能力与语言运用) The former is one’s knowledge of all the linguistic regulation systems whereas the latteris the use of language in concrete situation.7. speech and writing (口头语与书面语) Speech is the spoken form of language whereas writing is written codes, gives language new scope.8. linguistics behavior potential and actual linguistic behavior (语言行为潜势与实际语言行为) People actually says on a certain occasion to acertain person is actual linguistics behavior. And each of possible linguistic items that he could have said is linguistic behavior potential.9. syntagmatic relation and paradigmatic relation(横组合关系与纵聚合关系) The former describes the horizontal dimension of a languagewhile the latter describes the vertical dimension of a language.10. verbal communication and non-verbal communication(言语交际与非言语交际) Usual use of language as a means of transmittinginformation is called verbal communication. The ways we convey meaning without using language is called non-verbal communication.1. ★How does John Lyons classify linguistics?According to John Lyons, the field of linguistics as a whole can be divided into several subfields as following:1) General linguistics and descriptive linguistics.2) Synchronic linguistics and diachronic linguistics.3) Theoretical linguistics and applied linguistics.4) Microlinguistics and macrolinguistics.2. Explain the three principles by which the linguist is guided: consistency, adequacy and simplicity.1) Consistency means that there should be no contradictions between different parts of the theory and the description.2) Adequacy means that the theory must be broad enough in scope to offer significant generalizations.3) Simplicity requires us to be as brief and economic as possible.3. ★What are the sub-branches of linguistics within the language system?Within the language system there are six sub-branches as following:1) Phonetics. 语音学is a study of speech sounds of all human languages.2) Phonology. 音位学studies about the sounds and sound patterns of a speaker’s native language.3) Morphology. 形态学studies about how a word is formed.4) Syntax. 句法学studies about whether a sentence is grammatical or not.5) Semantics. 语义学studies about the meaning of language, including meaning of words and meaning of sentences.6) Pragmatics. 语用学★The scope of language: Linguistics is referred to as a scientific study of language.★The scientific process of linguistic study: It involves four stages: collecting data, forming a hypothesis, testing the hypothesis and drawing conclusions.1. articulatory phonetics(发音语音学) The study of how speech organs produce the sounds is called articulatory phonetics.2. acoustic phonetics (声学语音学) The study of the physical properties and of the transmission of speech sounds is called acoustic phonetics.3. auditory phonetics (听觉语音学) The study of the way hearers perceive speech sounds is called auditory phonetics.4. consonant (辅音) Consonant is a speech sound where the air form the language is either completely blocked, or partially blocked, or where theopening between the speech organs is so narrow that the air escapes with audible friction.5. vowel (元音) is defined as a speech sound in which the air from the lungs is not blocked in any way and is pronounced with vocal-cord vibration.6. bilabials (双唇音) Bilabials means that consonants for which the flow of air is stopped or restricted by the two lips. [p][b] [m] [w]7. affricates (塞擦音) The sound produced by stopping the airstream and then immediately releasing it slowly is called affricates. [t X] [d Y] [tr] [dr]8. glottis (声门) Glottis is the space between the vocal cords.9. rounded vowel (圆唇元音) Rounded vowel is defined as the vowel sound pronounced by the lips forming a circular opening. [u:] [u] [OB] [O]10. diphthongs (双元音) Diphthongs are produced by moving from one vowel position to another through intervening positions.[ei][ai][O i] [Q u][au]11. triphthongs(三合元音) Triphthongs are those which are produced by moving from one vowel position to another and then rapidly andcontinuously to a third one. [ei Q][ai Q][O i Q] [Q u Q][au Q]12. lax vowels (松元音) According to distinction of long and short vowels, vowels are classified tense vowels and lax vowels. All the long vowelsare tense vowels but of the short vowels,[e] is a tense vowel as well, and the rest short vowels are lax vowels.1. ★How are consonants classified in terms of different criteria?The consonants in English can be described in terms of four dimensions.1) The position of the soft palate.2) The presence or the absence of vocal-cord vibration.3) The place of articulation.4) The manner of articulation.2. ★How are vowels classified in terms of different criteria?Vowel sounds are differentiated by a number of factors.1) The state of the velum2) The position of the tongue.3) The openness of the mouth.4) The shape of the lips.5) The length of the vowels.6) The tension of the muscles at pharynx.3. ★What are the three sub-branches of phonetics? How do they differ from each other?Phonetics has three sub-branches as following:1) Articulatory phonetics is the study of how speech organs produce the sounds is called articulatory phonetics.2) Acoustic phonetics is the study of the physical properties and of the transmission of speech sounds is called acoustic phonetics.3) Auditory phonetics is the study of the way hearers perceive speech sounds is called auditory phonetics.4. ★What are the commonly used phonetic features for consonants and vowels respectively?I. The frequently used phonetic features for consonants include the following:1) Voiced.2) Nasal.3) Consonantal.4) Vocalic.5) Continuant.6) Anterior.7) Coronal.8) Aspirated.II. The most common phonetic features for vowels include the following:1) High.2) Low.3) Front.4) Back.5) Rounded.6) Tense.1. phonemes (音位) Phonemes are minimal distinctive units in the sound system of a language.2. allophones (音位变体) Allophones are the phonetic variants and realizations of a particular phoneme.3. phones (单音) The smallest identifiable phonetic unit found in a stream of speech is called a phone.4. minimal pair (最小对立体) Minimal pair means words which differ from each other only by one sound.5. contrastive distribution (对比分布) If two or more sounds can occur in the same environment and the substitution of one sound for anotherbrings about a change of meaning, they are said to be in contrastive distribution.6. complementary distribution(互补分布) If two or more sounds never appear in the same environment ,then they are said to be incomplementary distribution.7. free variation (自由变异) When two sounds can appear in the same environment and the substitution of one for the other does not cause anychange in meaning, then they are said to be in free variation.8. distinctive features (区别性特征) A distinctive feature is a feature which distinguishes one phoneme from another.9. suprasegmental features (超切分特征) The distinctive (phonological) features which apply to groups larger than the single segment are knownas suprasegmental features.10. tone languages (声调语言) Tone languages are those which use pitch to contrast meaning at word level.11. intonation languages (语调语言) Intonation languages are those which use pitch to distinguish meaning at phrase level or sentence level.12. juncture (连音) Juncture refers to the phonetic boundary features which may demarcate grammatical units.1. ★What are the differences between English phonetics and English phonology?1) Phonetics is the study of the production, perception, and physical properties of speech sounds, while phonology attempts to account forhow they are combined, organized, and convey meaning in particular languages.2) Phonetics is the study of the actual sounds while phonology is concerned with a more abstract description of speech sounds and tries todescribe the regularities of sound patterns.2. Give examples to illustrate the relationship between phonemes, phones and allophones.When we hear [pit],[tip],[spit],etc, the similar phones we have heard are /p/. And /p/ and /b/ are separate phonemes in English, while [ph] and [p] are allophones.3. How can we decide a minimal pair or a minimal set?A minimal pair should meet three conditions:1) The two forms are different in meaning.2) The two forms are different in one sound segment.3) The different sounds occur in the same position of the two strings.4. ★Use examples to explain the three types of distribution.1) Contrastive distribution. Sounds [m] in met and [n] in net are in contrastive distribution because substituting [m] for [n] will result in achange of meaning.2) Complementary distribution. The aspirated plosive [ph] and the unaspirated plosive [p] are in complementary distribution because theformer occurs either initially in a word or initially in a stressed syllable while the latter never occurs in such environments.3) Free variation. In English, the word “direct” may be pronounce in two ways: /di’rekt/ and /dia’rekt/, and the two different sounds /i/ and /ai/can be said to be in free variation.5. What’s the difference between segmental features and suprasegmental features? What are the suprasegmental features in English?I. 1) Distinctive features, which are used to distinguish one phoneme from another and thus have effect on one sound segment, are referred toas segmental features.2) The distinctive (phonological) features which apply to groups larger than the single segment are known as suprasegmental features.3) Suprasegmental features may have effect on more than one sound segment. They may apply to a string of several sounds.II.The main suprasegmental features include stress, tone, intonation and juncture.6. What’s the difference between tone languages and intonation language?Tone languages are those which use pitch to contrast meaning at word level while intonation languages are those which use pitch to distinguish meaning at phrase level or sentence level7. ★What’s the difference between phonetic transcriptions and phonemic transcriptions?The former was meant to symbolize all possible speech sounds, including even the most minute shades of pronunciation, while the latter was intended to indicate only those sounds capable of distinguishing one word from another in a given language.1. morphemes (语素) Morphemes are the minimal meaningful units in the grammatical system of a language.allomorphs (语素变体) Allomorphs are the realizations of a particular morpheme.morphs (形素) Morphs are the realizations of morphemes in general and are the actual forms used to realize morphemes.2. roots (词根) Roots is defined as the most important part of a word that carries the principal meaning.affixes (词缀) Affixes are morphemes that lexically depend on roots and do not convey the fundamental meaning of words.free morphemes (自由语素) Free morphemes are those which can exist as individual words.bound morphemes (粘着语素) Bound morphemes are those which cannot occur on their own as separate words.3. inflectional affixes (屈折词缀) refer to affixes that serve to indicate grammatical relations, but do not change its part of speech.derivational affixes (派生词缀) refer to affixes that are added to words in order to change its grammatical category or its meaning.4. empty morph (空语子) Empty morph means a morph which has form but no meaning.zero morph (零语子) Zero morph refers to a morph which has meaning but no form.5. IC Analysis (直接成分分析) IC analysis is the analysis to analyze a linguistic expression (both a word and a sentence) into a hierarchicallydefined series of constituents.6. immediate constituents(直接成分) A immediate constituent is any one of the largest grammatical units that constitute a construction.Immediate constituents are often further reducible.ultimate constituents (最后成分) Ultimate constituents are those grammatically irreducible units that constitute constructions.7. morphological rules (形态学规则) The principles that determine how morphemes are combined into new words are said to be morphologicalrules.8. word-formation process (构词法) Word-formation process mean the rule-governed processes of forming new words on the basis of alreadyexisting linguistic resources.1. ★What is IC Analysis?IC analysis is the analysis to analyze a linguistic expression (both a word and a sentence) into a hierarchically defined series of constituents.2. How are morphemes classified?1) Semantically speaking, morphemes are grouped into two categories: root morphemes and affixational morphemes.2) Structurally speaking, they are divided into two types: free morphemes and bound morphemes.3. ★Explain the interrelations between semantic and structural classifications of morphemes.a) All free morphemes are roots but not all roots are free morphemes.b) All affixes are bound morphemes, but not all bound morphemes are affixes.4. What’s the difference between an empty morph and a zero mor ph?a) Empty morph means a morph that has form but no meaning.b) Zero morph refers to a morph that has meaning but no form.5. Explain the differences between inflectional and derivational affixes in term of both function and position.a) Functionally:i.Inflectional affixes sever to mark grammatical relations and never create new words while derivational affixes can create new words.ii.Inflectional affixes do not cause a change in grammatical class while derivational affixes very often but not always cause a change in grammatical class.b) In term of position:i.Inflectional affixes are suffixes while derivational affixes can be suffixes or prefixes.ii.Inflectional affixes are always after derivational affixes if both are present. And derivational affixes are always before inflectional suffixes if both are present.6. What are morphological rules? Give at least four rules with examples.The principles that determine how morphemes are combined into new words are said to be morphological rules.For example:a) un- + adj. ->adj.b) Adj./n. + -ify ->v.c) V. + -able -> adj.d) Adj. + -ly -> adv.1. syntagmatic relations (横组关系) refer to the relationships between constituents in a construction.paradigmatic relations (纵聚合关系) refer to the relations between the linguistic elements within a sentence and those outside the sentence.hierarchical relations (等级关系) refer to relationships between any classification of linguistic units which recognizes a series of successively subordinate levels.2. IC Analysis (直接成分分析) is a kind of grammatical analysis, which make major divisions at any level within a syntactic construction.labeled IC Analysis(标记法直接成分分析) is a kind of grammatical analysis, which make major divisions at any level within a syntactic construction and label each constituent.phrase markers (短语标记法) is a kind of grammatical analysis, which make major divisions at any level within a syntactic construction, and label each constituent while remove all the linguistic forms.labeled bracketing (方括号标记法) is a kind of grammatical analysis, which is applied in representing the hierarchical structure of sentences by using brackets.3. constituency (成分关系)dependency (依存关系)4. surface structures (表层结构)refers to the mental representation of a linguistic expression, derived from deep structure by transformationalrules.deep structures (深层结构) deep structure of a linguistic expression is a theoretical construct that seeks to unify several related structures. 5. phrase structure rules (短语结构规则)are a way to describe a given language's syntax. They are used to break a natural language sentencedown into its constituent parts.6. transformational rules (转换规则)7. structural ambiguity (结构歧义)1. What are the differences between surface structure and deep structure?They are different from each other in four aspects:1) Surface structures correspond directly to the linear arrangements of sentences while deep structures correspond to the meaningful groupingof sentences.2) Surface structures are more concrete while deep structures are more abstract.3) Surface structures give the forms of sentences whereas deep structures give the meanings of sentences.4) Surface structures are pronounceable but deep structures are not.2. Illustrate the differences between PS rules and T-rules.1) PS rules frequently applied in generating deep structures.2) T-rules are used to transform deep structure into surface structures.3. What’s the order of generating sentences? Do we st art with surface structures or with deep structures? How differently are theygenerated?To generate a sentence, we always start with its deep structure, and then transform it into its corresponding surface structure.Deep structures are generated by phrase structure rules (PS rules) while surface structures are derived from their deep structures by transformational rules (T-rules).4. What’s the difference between a compulsory constituent and an optional one?Optional constituents may be present or absent while compulsory constituents must be present.5. What are the three syntactic relations? Illustrate them with examples.1) Syntagmatic relations2) Paradigmatic relations.3) Hierarchical relations.1. Lexical semantics (词汇语义学) is defined as the study of word meaning in language.2. Sense (意义) refers to the inherent meaning of the linguistic form.3. Reference (所指) means what a linguistic form refers to in the real world.4. Concept (概念) is the result of human cognition, reflecting the objective world in the human mind.5. Denotation (外延) is defined as the constant ,abstract, and basic meaning of a linguistic expression independent of context and situation.6. Connotation (内涵) refers to the emotional associations which are suggested by, or are part of the meaning of, a linguistic unit.7. Componential analysis (成分分析法) is the way to decompose the meaning of a word into its components.8. Semantic field (语义场) The vocabulary of a language is not simply a listing of independent items, but is organized into areas, within whichwords interrelate and define each other in various ways. The areas are semantic fields.9. Hyponymy (上下义关系) refers to the sense relation between a more general, more inclusive word and a more specific word.10. Synonymy (同义关系) refers to the sameness or close similarity of meaning.11. Antonymy (反义关系) refers to the oppositeness of meaning.12. Lexical ambiguity (词汇歧义)13. Polysemy (多义性) refers to the fact that the same one word may have more than one meaning.14. Homonymy (同音(同形)异义关系) refers to the phenomenon that words having different meanings have the same form.15. Sentence semantics (句子语义学) refers to the study of sentence meaning in language.1. What’s the criterion of John Lyons in classifying semantics into its sub-branches? And how does he classify semantics?In terms of whether it falls within the scope of linguistics, John Lyons distinguishes between linguistic semantics and non-linguistic semantics.According John Lyons, semantics is one of the sub-branches of linguistics; it is generally defined as the study of meaning.2. What are the essential factors for determining sentence meaning?1) Object, 2) concept, 3) symbol, 4) user, 5) context.3. What is the difference between the theory of componential analysis and the theory of semantic theory in defining meaning of words?4. What are the sense relations between sentences?1) S1 is synonymous with S2.2) S1 entails S2.3) S1 contradicts S2.4) S1 presupposes S2.5) S1 is a tautology, and therefore invariably true.6) S1 is a contradiction, and therefore invariably false.7) S1 is semantically anomalous.1. Speech act theory (言语行为理论)2. Cooperative principle and its maxims (合作原则及其准则)3. Politeness principle and its maxims (礼貌原则及其准则)4. Conversational implicature (会话含义)5. Indirect speech act (间接言语行为)6. Pragmatic presupposition (语用学预设)7. Relevance theory (关联理论)8. Illocutionary act (言外行为)9. (Horn’s) Q-Principle and R-Principle10. Perfrmative verbs (施为句动词)1. Make comments on the different definitions of pragmatics.2. What are the main types of deixis?3. Explain the statement: context is so indispen sable in fully understanding interpreting the speaker’s meaning.4. How are Austin’s and Searle’s speech act theories related to each other?5. What’s the relationship between CP and PP?6. What do you know about presupposition triggers in English? Explain them briefly with examples.7. What is ostensive-referential communication?8. Explain the obvious presupposition of speaker who say each of the following:1) When did you stop beating your wife?2) Where did Tom buy the watch?3) Your car is broken.9. What do you think of the fol lowing statement? “Tom participated in spreading rumors” entails “Tom engaged in spreading rumors”.Chapter 9 话语分析1. text(语篇) = discourse 语篇是指实际使用的语言单位，是一次交际过程中的一系列连续的话段或句子所构成的语言整体。

From gaze to focus of attention

From Gaze to Focus of AttentionRainer Stiefelhagen,Michael Finke,Jie Yang,Alex Waibelstiefel@a.de,ﬁnkem@,yang+@,ahw@Interactive Systems LaboratoriesUniversity of Karlsruhe—Germany,Carnegie Mellon University—USAAbstractIdentifying human gaze or eye-movement ultimately serves the purpose of identifying an individual’s focus of at-tention.The knowledge of a person’s object of interest helps us effectively communicate with other humans by allow-ing us to identify our conversants’interests,state of mind, and/or intentions.In this paper we propose to track focus of attention of several participants in a meeting.Attention does not necessarily coincide with gaze,as it is a perceptual variable,as opposed to a physical one(eye or head posi-tioning).Automatic tracking focus of attention is therefore achieved by modeling both,the persons head movements as well as the relative locations of probable targets of interest in a room.Over video sequences taken in a meeting situa-tion,the focus of attention could be identiﬁed up to98%of the time.1.IntroductionDuring face-to-face communication such as discussions or meetings,humans not only use verbal means,but also a variety of visual cues for communication.For example, people use gestures;look at each other;and monitor each other’s facial expressions during a conversation.In this re-search we are interested in tracking at whom or what a per-son is looking during a meeting.Theﬁrst step towards this goal is toﬁnd out at which direction a person is looking,i.e.his/her gaze.Whereas a person’s gaze is determined by his head pose as well as his eye gaze,we only consider head pose as the indicator of the gaze in this paper.Related work on estimating human head pose can be categorized in two approaches:model based and example based approaches:In model-based approaches usually a number of facial features,such as eyes,nostrils, lip-corners,have to be located.Knowing the relative po-sitions of these facial features,the head pose can be com-puted[2,8,3].Detecting the facial features,however,is a challenging problem and tracking is likely to fail.Example based approaches either use some kind of function approxi-mation technique such as neural networks[1,7,6],or a face database[4]to encode example images.Head pose of new images is then estimated using the function approximator, such as the neural networks,or by matching novel images to the examples in the database.With example based ap-proaches usually no facial landmark detection is needed, instead the whole facial image is used for classiﬁcation. In the Interactive Systems Lab,we have worked on both approaches.We employed purely neural network[7]and model-based approaches to estimate a user’s head pose[8]. We also demonstrated that a hybrid approach could enhance robustness of a model based system[9].In this paper,we extend the neural network approach to estimating the head pose in a more unrestricted situation.A major contribution of this paper is to use hidden markov model(HMM)to detect a user’s focus of attention from an observed sequence of gaze estimates.We are not only interested in which direction a user is looking at dur-ing the meeting,but also want to know at whom or what he is looking.This requires a way of incorporating knowledge about the world into the system to interpret the observed data.HMMs can provide an integrated framework for prob-abilistically interpreting observed signals over time.We have incorporated knowledge about the meeting situation, i.e.the approximate location of participants in the meeting into the HMMs by initializing the states of person depen-dent HMMs appropriately.We are applying these HMMs to tracking at whom the participants in a meeting are looking. The feasibility of the proposed approach have been evalu-ated by experimental results.Figure1shows an overview of our system:For each user,neural nets are used to produce a sequence of gaze observations given the preprocessed facial images.This sequence of gaze observations is used by the HMM to compute the sequence of foci of attention of the user.The remainder of the paper is organized as follows:Sec-tion2describes the neural network based head pose esti-mation approach.In section3we introduce the idea of in-terpreting an observed sequence of gaze directions toﬁnd a user’s focus of attention in each frame;deﬁne the under-lying probability model and give experimental results.We summarize the paper in section4.ANNs HMM2.Estimating Head Pose with Neural NetsThe main advantage of using neural networks to estimate head pose as compared to using a model based approach is its robustness:With model based approaches to head pose estimation[2,8,3],head pose is computed byﬁnding corre-spondences between facial landmarks points(such as eyes, nostrils,lip corners)in the image and their respective lo-cations in a head model.Therefore these approaches rely on tracking a minimum number of facial landmark points in the image correctly,which is a difﬁcult task and is likely to fail.On the other hand,the neural network-based approach doesn’t require tracking detailed facial features because the whole facial region is used for estimating the user’s head pose.In our approach we are using neural networks to esti-mate pan and tilt of a person’s head,given automatically ex-tracted and preprocessed facial images as input to the neural net.Our approach is similar to the approach as described by Schiele et.al.[7].However,the system described in[7]es-timated only head rotation in pan direction.In this research we use neural network to estimate head rotation in both pan and tilt directions.In addition,we have studied two differ-ent image preprocessing approaches.Rae et.al.[6]describe a user dependent neural network based system to estimate pan and tilt of a person.In their approach,color segmenta-tion,ellipseﬁtting and Gabor-ﬁltering on a segmented face are used for preprocessing.They report an average accuracy of9degrees for pan and7degrees for tilt for one user with a user dependent system.In the remainder of this section we describe our neural net based approach to estimate user’s head pose(pan and tilt).First we desribe how we collected data to train and test the neural networks.Then the two different image pre-processing approaches that we investigated and the neural network architecture are described.Finally we present ex-perimental results that we obtained using different types and combinations of input images for the neural nets.2.1.Data Collection SetupDuring data collection,the person that we collected data from had to sit on a chair on a speciﬁc location in the room, with his eyes at a height of approximately130cm.In a dis-tance of one meter and at a height of one meter a video camera to record the images was placed on a tripod.We placed marks on three walls and theﬂoor on which the user had to look one after another.The marks where placed in such a way that the user had to look in speciﬁc well known directions.The marks ranged from-90degrees to+90de-grees for pan,with one mark each ten degrees,and from +15degrees to-60degrees for tilt,with one mark each15 degrees.This means that during data collection the user had to look at19x6speciﬁc points,from top to bottom and left to right.Once the user was looking at a mark,he could press a mouse-button,and5images were being recorded to hard-disk,together with the labels indicating the current head pose.This resulted in a set of570images per user. In order to collect slightly different facial images for each pose,the user was asked to speak with the person assisting the data collection.Figure2shows two example images recorded during data collection.In this way,we collected data of14male and2female subjects.Approximately half of the persons were wearingglasses.2.2.Preprocessing of ImagesWe investigated two different preprocessing approaches: Using normalized grayscale images of the user’s face as the input to the neural nets and applying edge detection to the images before feeding them into the nets.To locate and ex-tract the faces from the collected images,we have used a statistical skin color model[10].The largest skin colored region in the input image was selected as the face.In theﬁrst preprocessing approach,histogram normal-ization was applied to the grayscale face images as a means towards normalizing against different lighting conditions. No additional feature extraction was performed and the nor-malized grayscale images were downsampled to aﬁxed size of20x30images and then used as input to the nets.In the second approach,we applied a horizontal and a vertical edge operator plus tresholding to the facial grayscale images.Then the resulting edge images were downsampled to20x30pixels and were both used as input to the neural nets.Figure3and4show the corresponding preprocessed facial images of the person depicted in Figure 2.From left to right,the normalized grayscale image,thehorizontal and vertical edge images aredepicted.PersonAPersonB2.3.ANN ArchitectureWe trained separate nets to estimate pan and tilt of a per-son’s head.Training was done using a multilayer perceptronarchitecture with one hidden layer and standard backpropa-gation with momentum term.The output layer of the net estimating pan consisted of19units representing19different angles(-90,-80,...,+80,+90degrees).The output layer of the tilt estimating netconsisted of6units representing the tilt angles+15,0,-15,..-60degrees.For both nets we used gaussian output rep-resentation.With a gaussian output representation not onlythe single correct output unit is activated during training,butalso its neighbours receive some training activation decreas-ing with the distance from the correct label.The input retinaof the neural nets varied between20x30units and3x20x30units depending on the different number and types of inputimages that we used for training(see2.4).2.4.Training and ResultsWe trained separate user independent neural nets to es-timate pan and tilt.The neural nets were trained on datafrom twelve subjects from our database and evaluated onthe remaining four other subjects.The data for each userconsisted of570images,which results in a training set sizeof6840images and a test set size of2280images.As input to the neural nets,we have evaluated three dif-ferent approaches:ing histogram normalized grayscale images as in-put to the netsing horizontal and vertical edge images as inputing both,normalized grayscale plus horizontal andvertical edge images as input.Table1summarizes the results that we obtained usingthe different types of input images.When using normal-ized grayscale images as input we obtained a mean error of12.0degrees for pan and13.5degrees for tilt on our fouruser test set.With horizontal and vertical edge images asinput,a slightly worse accuracy for estimating the pan wasing both,normalized grayscale image as wellas the edge images as input to the neural net signiﬁcantlyincreased the accuracy and led to accuracy of9.0degreesand12.9degrees mean error for pan and tilt respectively.These results show,that it is indeed feasible to train aperson independent neural net based system for head poseestimation.In fact,the obtained results are only slightlyworse than results obtained with a user dependent neural netbased system as described by Rae et.al.[6].As comparedto their results,we did not observe serious degradation ondata from new users.To the contrary,our results indicatethat the neural nets can generalize well to new users.Net Input Pan TiltGrayscale12.013.5Edges14.013.5Edges+Grayscale9.012.9However with the system that we have developed so far, we have observed a problem which still limits the use of the system signiﬁcantly:when we tested the system on previously recorded data from a meeting that took place in another room,the accuracy of the estimation seriously degraded.We believe that this is mainly due to the very different lighting conditions between the room where data collection for training the nets took place(computer lab,no windows),and the room where the meeting took place(day-light+artiﬁcial illumination).Figure5shows two example images recorded during the meeting.Possible solutions to this problem might be to investi-gate other preprocessing methods to reduce the inﬂuence of changing illumination and/or collecting more training data under different lighting conditions.3.Modelling Focus of Attention Using HiddenMarkov ModelsThe idea of this research is to map the observed vari-able over time namely the gaze direction to discrete states of what the person is looking at,i.e.his focus of attention. Hidden Markov Models(HMM)can provide an integrated framework for probabilistically interpreting observed sig-nals over time.In this section we describe how we have designed the HMMs to estimate a user’s focus of attention.We have incorporated knowledge about the observed scene,i.e.the approximate location of likely foci of at-tention such as other people in the room,in the Hidden Markov Models.In our model,looking at a certain target is modelled as being in a certain state of the HMM and the observed gaze estimates are considered as being probabilis-tic functions of the different states.Given this model and an observation sequence of gaze directions,as provided by the neural nets,it is then possible toﬁnd the most likely sequence of HMM states that produced the observations. Interpreting being in a certain state as looking at a certain target,it is now possible to estimate a person’s focus of at-tention in each frame.Furthermore,we can iteratively rees-timate the parameters of the HMM so as to maximize the likelihood of the observed gaze directions,leading to more accurate estimates of foci of attention.We have tested our models on image sequences recordedfrom a meeting.In the meeting,four people were sittingaround a table,talking to and looking at each other and sometimes looking onto the table.During this meetingwe had taped each of the speakers using a camera stand-ing on top of the table and having one person in itsﬁeld of view.Figure5shows two example images taken dur-ing data collection of the meeting.For two of the speakers we then estimated their gaze trajectory with the neural netsdescribed in the previous section.For each user we haveapplied an HMM to detect his focus of attention given the observed gaze directions over time.We then applied theuser-dependent HMMs to detect the foci of attention giventhe observed gaze directions over time.In the remainder of this section we describe the design of the HMM,how we have adapted HMM parameters andgive evaluation results on the two videosequences.3.1.HMM DesignKnowing that there were four people sitting around a ta-ble,we modelled the targets for each person P as the fol-lowing four states:P is looking to the person sitting to his right,P is looking to the person to his left,P is looking tothe person in front of him,P is looking down on the table.In our model the observable symbols of each state arethe pose estimation results as given by the neural nets,thatis the angles for pan and tilt and.We have param-eterized the state dependent observation probabilities for each state,where, as two-dimensional gaussian distributions with diagonal co-variance matrices:Assuming that we know the approximate positions of the participants of the meeting relative to each other,we initial-ized the observation probability distributions of the different states with the means of the gaussians set to the expected viewing angle,when looking at the corresponding target. Table2shows the initial values that we have chosen for the respective means.All variances were set to the same value initially.The transition matrix was initialized toStateleft-450center00right+450table0-45have high transition probabilities for remaining in the same state()and uniformly distributed state transition probabilities for all other transitions.The initial state distri-bution was chosen to be uniform.3.2.Probabilistic ModelLet be the sequence of gaze direc-tion observations as predicted by the neural nets.The probability of the observation sequence given the HMM is given by the sum over all possible state sequences q:Toﬁnd the single best state sequence of foci of attention, for a given observation sequence,we need to ﬁndThis can be efﬁciently computed by the Viterbi algorithm [5].Thus,given the HMM and the observation sequence of gaze directions,we can efﬁcientlyﬁnd the sequence of foci of attention using the Viterbi algorithm.So far we have considered the HMM to be initialized by knowledge about the setup of the meeting.It is further-more possible to adapt the model parametersof the HMM so as to maximize.This can be done in the EM(Expectation-Maximizaton)framework by itera-tively computing the most likely state sequence and adapt-ing the model parameters as follows:means:,wherevariances:transition probabilities:number of transition from state toOn our two evaluation sequences,parameter reestimation converged after three andﬁve iterations respectively.3.3.ResultsTo evaluate the performance of the proposed model,we compared the state-sequence given by the Viterbi-decoding to hand-made labels of where the person was looking to. Both of the evaluated sequences contained500frames and lasted about one and a half minute each.We evaluated the performance of the HMM without model parameter adap-tion and with automatic parameter adaption.Furthermore we evaluated the results obtained by directly mapping the output of the neural nets to the different viewing targets. This mapping was obtained by assigning the network out-put directly to a speciﬁc target as described in table3.Table 4reports the obtained results.It can be seen that compared to directly using the output of the neural nets,a signiﬁcant error reduction can already be obtained by using an HMM without parameter adaption on top of the ANN -ing parameter reestimation however,the error can be fur-thermore reduced by a factor of two to three on our evalua-tion sequences.While performing parameter reestimation on the two se-quences,a signiﬁcant improvement of the accuracy of the adapted HMMs over the HMMs that were initialized us-ing knowledge could be observed.The means of the gaus-sians,which represent the viewing angles of the different targets,shifted from their initial estimates to values that bet-ter matched the observations over time.assigned state[-90,-30]any“left”[-20,+20][-15,+15]“center”[+30,+90]any“right”[-20,+20][-30,-60]“table”Seq.no HMM HMM,no reest.HMM,reest.A9.4% 5.4% 1.8%B11.6%8.8% 3.8%4.ConclusionIn this paper we have addressed the problem of track-ing a person’s focus of attention during a meeting situation. We have proposed the use of a HMM framework to detect focus of attention from a trajectory of gaze observations and have evaluated the proposed approach on two video se-quences that were taken during a meeting.The obtained results show the feasability of our pared to hand-made labels,accuracy of96%and98%was obtained with the HMM-based estimation of focus of attention.To estimate a person’s gaze we have trained neural net-works to estimate head pose from facial ing a combination of normalized grayscale images,horizontal and vertical edge images of faces as input to the neural nets, we have obtained accuracy of9.0degrees and12.9degrees for pan and tilt respectively on a test set of four users which have not been in the training set of the neural nets.However we observed that under changed lighting con-ditions the neural network based pose estimaton seriously degraded.Possible solutions to this problem could be us-ing other preproceesing methods to reduce the inﬂuence of changing illumination and/or collecting more data under different lighting conditions to train the neural nets.References[1] D.Beymer,A.Shashua,and T.Poggio.Example-based im-age analysis and synthesis.In Proceedings of Siggraph’94, 1994.[2] A.H.Gee and R.Cipolla.Non-intrusive gaze tracking forhuman-computer interaction.In Proc.Mechatronics and Machine Vision in Practise,pages112–117,1994.[3]T.Jebara and A.Pentland.Parametrized structure from mo-tion for3d adaptive feedback tracking of faces.In Proceed-ings of Computer Vision and Pattern Recognition,1997. [4] A.Pentland,B.Moghaddam,and T.Starner.View-basedand modular eigenspaces for face recognition.In Proceed-ings of IEEE Conference on Computer Vision and Pattern Recognition,1994.[5]L.R.Rabiner.Readings in Speech Recognition,chapter ATutorial on Hidden Markov Models and Selected Applica-tions in Speech Recognition,pages267–295.Morgan Kauf-mann,1989.[6]R.Rae and H.J.Ritter.Recognition of human head orienta-tion based on artiﬁcial neural networks.IEEE Transactions on neural networks,9(2):257–265,March1998.[7] B.Schiele and A.Waibel.Gaze tracking based on face-color.In International Workshop on Automatic Face-and Gesture-Recognition,pages344–348,1995.[8]R.Stiefelhagen,J.Yang,and A.Waibel.A model-basedgaze tracking system.In Proceedings of IEEE International Joint Symposia on Intelligence and Systems,pages304–310,1996.[9]R.Stiefelhagen,J.Yang,and A.Waibel.Towards track-ing interaction between people.In Proceedings of the AAAI Spring Symposium on Intelligent Environments,pages123–127.AAAI Press,March1998.[10]J.Yang and A.Waibel.A real-time face tracker.In Proceed-ings of WACV,pages142–147,1996.。

Calibration from Images with known Objects

British Machine Vision Conference, 1995, pp 167{176
3-D Reconstruction and Camera Calibration from Images with known Objects
Gudrun Socher
Universitat Bielefeld, Technische Fakultat, AG Angewandte Informatik, Postfach 100131, 33501 Bielefeld, Germany
2 Model-based 3-D Reconstruction and Camera Parameter Estimation
Model-based 3-D reconstruction is a quantitative method to estimate simultaneously the best viewpoint of all cameras and the object pose parameters by tting the projection of a three-dimensional model to given two-dimensional features. The model- tting is accomplished by minimising a cost function measuring all di erences between projected model features and detected image features as a function of the objects' pose and the camera parameters. Common features in the scenes we are dealing with are points and circles. The projection of circles results in ellipses.

学生的一些想法英语作文

As an English teacher with a French influence,I understand the importance of encouraging students to express their thoughts and ideas in English.Here are some tips and prompts that can help students to write an essay on their thoughts and ideas:1.Brainstorming Session:Encourage students to start with a brainstorming session.They can jot down any thoughts or ideas that come to their mind.This will help them to identify the main theme of their essay.2.Choose a Topic:Once they have a list of ideas,they should choose a topic that interests them the most.It could be anything from their favorite hobby,a social issue,or a personal experience.3.Create an Outline:Before they start writing,its essential to create an outline.This will help them to organize their thoughts and ensure that their essay has a clear structure.4.Introduction:The introduction should be engaging and should provide a brief overview of the topic.It should also include a thesis statement that clearly states the main idea of the essay.5.Body Paragraphs:Each body paragraph should focus on one main idea related to the topic.Students should provide examples,facts,or personal experiences to support their ideas.They should also ensure that each paragraph is wellconnected to the thesis statement.6.Transitions:Smooth transitions between paragraphs are crucial for a coherent essay. Students should use transition words and phrases to connect their ideas and make their essay flow well.7.Conclusion:The conclusion should summarize the main points of the essay and restate the thesis statement.It should also provide a final thought or a call to action that leaves a lasting impression on the reader.8.Revise and Edit:After completing the first draft,students should revise and edit their essay.They should check for grammar,punctuation,and spelling errors.They should also ensure that their essay is wellorganized and that their ideas are clearly expressed.9.Peer Review:Encourage students to share their essays with their peers for feedback. This can help them to gain new perspectives and improve their writing skills.10.Final Draft:After incorporating feedback and making necessary revisions,studentsshould submit their final draft.They should be proud of their work and feel confident in their ability to express their thoughts and ideas in English.Remember,the key to a successful essay is clear communication and a wellstructured argument.Encourage your students to be creative,think critically,and express themselves confidently in English.。

问老师哪些问题英语作文

问老师哪些问题英语作文Title: Inquiring with the Teacher: Essential Questions for English Compositions。

As students, it's crucial to engage with our teachers to deepen our understanding and refine our skills. Here are some questions you can ask your English teacher to enhance your composition writing:1. Understanding the Assignment:What is the main objective or purpose of this assignment?Could you clarify any specific guidelines or requirements for the composition?Are there any recommended resources or references we should consider?2. Structuring the Composition:What are the key elements of a well-structured English composition?Can you provide guidance on organizing ideas effectively?How should we balance creativity with adherence to structural norms?3. Developing Content:How can we generate compelling ideas or themes for our compositions?What strategies can we employ to develop coherent and engaging arguments or narratives?Are there any common pitfalls to avoid in content development?4. Language and Style:How can we enhance the clarity and precision of our language?What techniques can we use to vary sentencestructure and avoid monotony?Are there any specific stylistic devices or literary techniques we should incorporate?5. Revision and Editing:What steps should we take during the revisionprocess to refine our compositions?How can we identify and correct grammar, punctuation, and spelling errors effectively?Do you have any tips for self-editing and peer review?6. Feedback and Improvement:What criteria do you use to evaluate English compositions?How can we interpret and apply feedback to improve our writing skills?Are there any additional resources or exercises you recommend for further improvement?7. Cultivating a Writing Habit:What strategies can we adopt to overcome writer's block and maintain motivation?How important is regular practice in honing our writing skills?Are there any specific writing prompts or exercises you suggest for ongoing practice?8. Beyond the Classroom:How can we continue to develop our English writing skills outside of class?Are there any extracurricular activities or competitions you recommend for aspiring writers?What career opportunities or pathways are available for students with strong writing abilities?By asking these questions and actively engaging with your teacher, you can gain valuable insights and support to excel in English composition writing. Remember, effective communication and collaboration with your teacher are essential steps towards academic success and personal growth.。

发明物英语作文

Invention is the cornerstone of human progress and has shaped the world we live in today.When writing an essay on an invention,its important to consider several key aspects:the purpose of the invention,its impact on society,and the process of its creation. Heres a detailed outline for an English essay on an invention:Title:The Marvel of Invention:Transforming LivesIntroduction:Hook the reader with a thoughtprovoking statement or question about the role of inventions in human history.Briefly introduce the chosen invention and its significance.Paragraph1:The Inventions GenesisDescribe the historical context in which the invention was created.Discuss the inventors background and motivations.Explain the initial challenges faced during the invention process.Paragraph2:The Functionality of the InventionDetail the inventions primary function and how it works.Use technical descriptions to explain the mechanics or principles behind the invention.Paragraph3:The Impact on SocietyDiscuss the immediate and longterm effects of the invention on society.Include examples of how the invention has improved or changed daily life,industry,or culture.Paragraph4:The Inventions EvolutionTrace the development of the invention over time,noting any significant improvements or adaptations.Discuss how the invention has been integrated into modern technology or practices.Paragraph5:Controversies and Ethical ConsiderationsAddress any controversies or ethical dilemmas associated with the invention. Consider the environmental,social,or health implications of the invention. Paragraph6:Personal ReflectionShare personal thoughts or experiences related to the invention.Reflect on how the invention has influenced ones perspective on technology and innovation.Conclusion:Summarize the main points discussed in the essay.Reiterate the inventions importance and its potential for future development.End with a call to action or a thoughtprovoking statement about the role of invention in shaping the future.Word Bank:Innovation:The introduction of new ideas,methods,or products.Prototype:An early model of a product used for testing and development. Paradigm shift:A fundamental change in approach or underlying assumptions. Technological advancement:Progress in the development and application of technology. Ethical dilemma:A situation that requires a choice between two or more conflicting values or principles.Sample Sentences:The invention of the steam engine by James Watt in the18th century was not just a mechanical breakthrough it was the catalyst for an industrial revolution.The advent of the internet has revolutionized communication,making the world a global village where information is shared instantaneously.While the benefits of genetic engineering are immense,it also raises ethical questions about the manipulation of life at its most fundamental level.Remember to use a variety of sentence structures and vocabulary to maintain the readers interest.Additionally,ensure that your essay is wellorganized,with a clear flow of ideas that logically progresses from one paragraph to the next.。

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of pixels; each pixel captures light that travels along a ray in 3D. The camera is fully described by [13]: the coordinates of these rays (given in some local coordinate frame). the mapping between rays and pixels; this is basically a simple indexing. This general imaging model allows to describe virtually any camera that captures light rays travelling along straight lines 1 . Examples are (cf. ﬁgure 1): a camera with any type of optical distortion, such as radial or tangential. a camera looking at a reﬂective surface, e.g. as often used in surveillance, a camera looking at a spherical or otherwise curved mirror [?]. Such systems, as opposed to central catadioptric systems [1] composed of cameras and parabolic mirrors, do not in general have a single effective viewpoint. multi-camera stereo systems: put together the pixels of all image planes; they “catch” light rays that deﬁnitely do not travel along lines that all pass through a single point. Nevertheless, in the above general camera model, a stereo system (with rigidly linked cameras) is considered as a single camera. other acquisition systems, see e.g. [3, 28, 31], insect eyes, etc. In this article, we ﬁrst review some recent work on calibration and structure from motion for this general camera model. Concretely, we outline basics for
Keywords:
ON CALIBRATION AND STRUCTURE FROM MOTION FOR GENERIC CAMERA MODELS
Peter Sturm1 , Srikumar Ramalingam2 , and Suresh Lodha2
1 INRIA Rhône-Alpes, 2 University of California
i Peter Sturm1 , Srikumar Ramalingam2 , and Suresh Lodha2
1 INRIA Rhône-Alpes, 655 Avenue de l’Europe, 38330 Montbonnot, France Peter.Sturm@inrialpes.fr 2 Dept. of Computer Science, University of California, Santa Cruz, USA
Keywords:
1.
Introduction
Many different types of cameras including pinhole, stereo, catadioptric, omnidirectional and non-central cameras have been used in computer vision. Most existing camera models are parametric (i.e. deﬁned by a few intrinsic parameters) and address imaging systems with a single effective viewpoint (all rays pass through one point). In addition, existing calibration or structure from motion procedures are often taylor-made for speciﬁc camera models. The aim of this work is to relax these constraints: we want to propose and develop calibration and structure from motion methods that should work for any type of camera model, and especially also for cameras without a single effective viewpoint. To do so, we ﬁrst renounce on parametric models, and adopt the following very general model: a camera acquires images consisting
2
Figure 1. Examples of imaging systems. (a) Catadioptric system. Note that camera rays do not pass through their associated pixels. (b) Central camera (e.g. perspective, with or without radial distortion). (c) Camera looking at reﬂective sphere. This is a non-central device (camera rays are not intersecting in a single point). (d) Omnivergent imaging system [28, 31]. (e) Stereo system (non-central) consisting of two a}@
Abstract We consider calibration and structure from motion tasks for a previously introduced, highly general imaging model, where cameras are modeled as possibly unconstrained sets of projection rays. This allows to describe most existing camera types (at least for those operating in the visible domain), including pinhole cameras, sensors with radial or more general distortions, catadioptric cameras (central or non-central), etc. Generic algorithms for calibration and structure from motion tasks (pose and motion estimation and 3D point triangulation) are outlined. The foundation for a multi-view geometry of non-central cameras is given, leading to the formulation of multi-view matching tensors, analogous to the fundamental matrices, trifocal and quadrifocal tensors of perspective cameras. Besides this, we also introduce a natural hierarchy of camera models: the most general model has unconstrained projection rays whereas the most constrained model dealt with here is the central model, where all rays pass through a single point. Calibration, motion estimation, 3D reconstruction, camera models, non-central cameras.
Abstract
We consider calibration and structure from motion tasks for a previously introduced, highly general imaging model, where cameras are modeled as possibly unconstrained sets of projection rays. This allows to describe most existing camera types (at least for those operating in the visible domain), including pinhole cameras, sensors with radial or more general distortions, catadioptric cameras (central or non-central), etc. Generic algorithms for calibration and structure from motion tasks (pose and motion estimation and 3D point triangulation) are outlined. The foundation for a multi-view geometry of non-central cameras is given, leading to the formulation of multi-view matching tensors, analogous to the fundamental matrices, trifocal and quadrifocal tensors of perspective cameras. Besides this, we also introduce a natural hierarchy of camera models: the most general model has unconstrained projection rays whereas the most constrained model dealt with here is the central model, where all rays pass through a single point. Calibration, motion estimation, 3D reconstruction, camera models, non-central cameras.