Measuring the Trilinear Couplings of MSSM Neutral Higgs Bosons at High-Energy e^+e^- Collid
Supersymmetric Grand Unification Model with the Orbifold Symmetry Breaking in the Six Dimen
a r X i v :h e p -p h /0108152v 1 19 A u g 2001UT-962Supersymmetric Grand Unification Model with the Orbifold Symmetry Breaking in the Six Dimensional Supergravity T.Watari a and T.Yanagida a,b a Department of Physics,University of Tokyo,Tokyo 113-0033,Japan b Research Center for the Early Universe,University of Tokyo,Tokyo 113-0033,Japan Abstract We construct supersymmetric (SUSY)grand unification (GUT)models in the six dimensional space-time where the GUT symmetry is broken down to the standard-model gauge group by a simple orbifolding T 2/Z 4or T 2/Z 6and a pair of massless Higgs doublets in the SUSY standard model are naturally obtained.Since the background geometry here is simple compared with models using the Scherk-Schwarz mechanism,one might hope for an approximate gauge coupling unification in the present models.Here,the presence of the massless Higgs multiplets in the bulk is quite natural,since the anomaly cancellation inthe six dimensional space-time requires N=2hyper multiplets in the bulk,some of which are origins of the Higgs doublets.However,the origin of the quarks and leptons is still not clear at all.Search for a solution to the doublet-triplet splitting problem in the supersymmetric (SUSY)grand unification theory(GUT)has led us to consider various extensions of the minimal SU(5)SUSY-GUT[1,2,3].Recently,Kawamura[4]has pointed out an interesting solution to this problem utilizing an S1/Z2orbifold in afive dimensional space-time,which is deeply related to the early suggestion by Witten[5]1.Although this original model is non SUSY-GUT,it is easily extended to the SUSY-GUT if one assumes an S1/(Z2 σ1 ×Z′2 σ2 )orbifold[7,8].Here,this orbifold is also regarded as R1/(Z σ1σ2 ×′Z2 σ1 ),where the Z σ1σ2 gives the symmetry-breaking boundary condition a la Scherk-Schwarz[9].A number of interesting features in this approach have been discussed[10].However,it is claimed[11]recently that the Scherk-Schwarz breaking is equivalent to the Wilson line breaking[12]localized at afixed point.Thus, the nontrivial background of gaugefield exists at thefixed point,and its effect to the tree level gauge coupling is incalculable and it may be beyond the naive dimensional analysis[8]2.Therefore,it is not necessarily obvious to maintain the gauge coupling unification even at the tree level.The purpose of this letter is to show that a SUSY-GUT model with the orbifold GUT breaking mechanism is constructed in the six dimensional space-time without the Scherk-Schwarz breaking3.In this letter,we use the term“orbifold GUT breaking model”as a class of models that do not use the Scherk-Schwarz(or boundary breaking) mechanism.Since the background geometry here is simple compared with models using the Scherk-Schwarz mechanism,one might hope for an approximate gauge coupling unification in the present models.We consider a simple orbifold T2/Z4.Wefind that only a pair of the Higgs doublets H f and¯H f survive together with the gauge multiplets of SU(3)C×SU(2)L×U(1)Y in the extra two dimensional bulk.The matter multiplets 5∗and10are assumed to reside on afixed point that preserves SU(5)symmetry.Wealsofind that a similar model can be constructed on another simple orbifold T2/Z6.Wefirst note that thefive dimensional space-time is too small to have the desired orbifold GUT breaking model(without the Scherk-Schwarz mechanism).The orbifold projection associated with the S1/Z2compactification is not enough to eliminate all the unwanted particles contained in the N=2SUSY SU(5)multiplets.Such an elimination is possible only by using the Scherk-Schwarz mechanism in the S1/(Z2×Z′2)≃R1/(Z×′Z2)compactification.Therefore,we consider the orbifold GUT breaking model in the six dimensional space-time.Furthermore,there is another reason to assume the higher dimensional space-time;the R-symmetry that is a crucial and unique symmetry to forbid a constant term in the superpotential[15]may arise from a rotation symmetry in the extra space.In this sense the present analysis provides thefirst basic and natural GUT model in a higher dimensional space-time4.We restrict ourselves to the six dimensional supergravity in this letter,since if we go further the consistency condition becomes more restrictive.We do not consider that the effectivefield theory should be necessarily formulated in the ten dimensional supergravity,even if the underlying fundamental theory is given by the string theory.The possible rotational symmetry that the two dimensional torus T2in the extra dimensional space possesses is Z2,Z3,Z4or Z6.These are the symmetries that rotate the4th-5th plane byπ,2π/3,π/2andπ/3,respectively.We require that the orbifold projection condition explicitly distinguishes the color SU(3)and theflavor SU(2)of the SU(5)indices and breaks the SU(5)GUT down to the standard-model gauge group.The N=2SU(5)vector multiplet propagates in the six dimensional bulk.The lengths L of the extra dimensions are assumed to be of order of1/(GUT scale)and the fun-damental scale of the theory M∗is of order1017GeV.This lower cut-offscale is a crucial point in keeping the approximate gauge coupling unification at the effective GUT scale∼1016GeV[8,16].The volume of the extra two dimensional space5is about (M∗L)2∼102.Now that the SU(5)vector multiplet propagates in the six dimensional bulk,the six dimensional box anomaly must be canceled.Six dimensional box anomalies consist ofpure gauge anomalies tr(F4)and(tr(F2))2,a gauge-gravity mixed anomaly tr(F2)tr(R2) and pure gravitational anomalies[18].Among these,pure gravitational anomalies can be canceled by introduction of SU(5)singletfields and reducible anomalies(tr(F2))2 and tr(F2)tr(R2)can be canceled by the Green-Schwarz mechanism[19].Thus we only care about the pure gauge tr(F4)anomaly of the SU(5)gauge theory.In(1,0)-SUSY (N=2SUSY in four dimensional sense)gauge theories in six dimensions,N=2hyper multiplets have chirality opposite to that of the N=2vector multiplet.Therefore,the pure gauge box anomaly from the gauge fermions of the N=2SU(5)vector multiplet can be canceled by introducing N=2hyper multiplets.The anomaly of the SU(n)N=2 vector multiplet is−2n times that of the N=2hyper multiplet in SU(n)-fundamental representation(up to reducible anomaly)[18],and hence we introduce ten(5+5∗)hyper multiplets in the six dimensional bulk6.We expect that the four dimensional N=1vector multiplets of the SU(3)C×SU(2)L×U(1)Y in the minimal SUSY standard model(MSSM)comes from the above N=2SU(5) vector multiplet.Since we introduced N=2hyper multiplets in5+5∗representation,it is possible that the H f and¯H f N=1chiral multiplets in the MSSM also originate from the bulkfields.Spectrum of massless particles that live in the bulk are determined by the orbifold projection condition that distinguishes the color SU(3)and theflavor SU(2),and hence the remaining particles may be chosen as only doublets by adopting an appropriate orbifold projection as shown below.The phenomenological reason for which we identify the Higgs as bulkfields(not asfixed pointfields),will be explained later.On the contrary,we postulate by hand that the quarks and leptons N=1chiral multiplets,(5∗+10),reside on orbifoldfixed points.This is the weakest point in the present approach.In the model construction of the orbifold GUT breaking,the existence of thefixed point that preserves the SU(5)symmetry is an important ingredient[8].A natural explanation of the anomaly cancellation in terms of the SU(5)GUT which is nothing but a miracle in the standard model,the charge quantization of the U(1)Y,and the bottom-tau Yukawa unification are the major reasons that we believe SUSY-GUT alongwith the gauge coupling unification suggested from the experiments.The above three features are still maintained if the orbifold geometry has afixed point that preserves the four dimensional SU(5)GUT symmetry even though the orbifold GUT breaking model has no complete higher dimensional SU(5)symmetry.We consider the model in which the three families of quarks and leptons5∗+10reside on such afixed point.In order to have afixed point which preserves the SU(5)symmetry,the orbifold group must have nontrivial and proper subgroup.First,the isotropy group associated to such afixed point7is not trivial by definition.Secondly,if the isotropy group were identical to the whole orbifold group,then the orbifold projection associated to the isotropy group of such afixed point would distinguish the color SU(3)and theflavor SU(2)subgroups of the SU(5),and hence the SU(5)symmetry would not be preserved. Therefore,the isotropy group of such afixed point is nontrivial and proper subgroup of the whole orbifold group.This means that the orbifold group candidate are Z4and Z6since Z2and Z3do not have such a subgroup.Therefore,we consider the T2/Z4 σ and T2/Z6 σ model where theσis the generator of the each orbifold group Z4and Z6.Let usfirst consider the model on T2/Z4 σ orbifold.The generatorσof the Z4 transformation rotates the4th-5th plane byπ/2:(z≡(x4+ix5))→σ·z=e i(θ=2π7Isotropy(sub)group of a point is a subgroup of a transformation group,say the orbifold group, which consists of elements thatfix the point.8In this letter,we call thefixed point whose isotropy group is Z2 σ2 as Z2 σ2 fixed point for brevity.Similar terminology is also used later in the T2/Z6orbifold model.F(x,z)j=e iθn j γσF(x,e iθz)j,¯F(x,z)j=e iθ(−1−n j) γ−1σ¯F(x,e iθz)j,(3) whereθ=(2π)/4.Rotational charges n j for the hyper multiplet can be n/2(n= 0,1,2,3,...). γσis the(5×5)gauge twisting matrix associated to the generatorσthat must satisfy( γσ)4=1.We take the gauge twisting matrix γσasγσ=diag(e iθm,e iθm,e iθm,e i(θm+π),e i(θm+π)),(4) where m is an arbitrary integer andθ=(2π)/4.Under this choice,the Z2 σ2 fixed point preserves the SU(5)symmetry because the gauge twisting matrix γσ2≡( γσ)2∝1 does not make any discrimination between the color SU(3)and theflavor SU(2).We put the three families of quarks and leptons on thisfixed point.Now we can see that the massless particles(Kaluza-Klein zero modes)from the N=2 SU(5)vector multiplet are just the N=1vector multiplets of the MSSM.Only one pair of the N=1chiral multiplets H f from the F1and the¯H f from the¯F2survive the orbifold projection conditions Eq.(3)if we take n1=(2−m),n2=(1−m)and n j(j=3, (10)to be half integers.These are exactly the pair of Higgs doublets in the MSSM.No other unwanted particle remains massless.We can also see that the triangle anomalies which might appear atfixed points because of the orbifolding completely vanish[20].We obtain the desired massless Higgs multiplets H f and¯H f in the bulk.As a matter of fact,this is a necessary property as long as the third family of the quarks and leptons reside on the SU(5)preservingfixed point.The reason is the following.Suppose that the two Higgs doublets reside on one of the two Z4 σ fixed points and the third family reside on the Z2 σ2 fixed point.Let us consider how the Yukawa couplings in the superpotential are generated.Since the quark and lepton multiplets are separated from the two Higgs doublets by the distance M∗L∼10,an exchange of particles of mass of order of the fundamental scale M∗is not enough to induce the Yukawa couplings because of the damping of the wave function e−M∗L<∼10−4.Only the Kaluza-Klein particles of the5+5∗hyper multiplets can do the job.However,we can see that all those Kaluza-Klein particles have zero wave function at the Z4fixed points in models where no massless Higgs multiplet remains in the bulk.Therefore,necessary Yukawa couplings are not generated by the exchanges of the Kaluza-Klein particles.It is easy to see that a similar argument to the above also holds in the model ofT2/Z6 σ orbifold.The generatorσrotates the4th-5th plane byπ/3:z→e iθz θ=2πported by“Priority Area:Supersymmetry and Unified Theory of Elementary Particles (#707)”(T.Y.).References[1]A.Masiero,D.V.Nanopoulos,K.Tamvakis and T.Yanagida,Phys.Lett.B115(1982)380;I.Antoniadis,J.Ellis,J.S.Hagelin and D.V.Nanopoulos,Phys.Lett.B194(1987)231.[2]S.Dimopoulos and F.Wilczek,NSF-ITP-82-07;M.Srednicki,Nucl.Phys.B202(1982)327.[3]T.Yanagida,Phys.Lett.B344(1995)211[hep-ph/9409329];J.Hisano and T.Yanagida,Mod.Phys.Lett.A10(1995)3097[hep-ph/9510277];T.Hotta,K.I.Izawa and T.Yanagida,Phys.Rev.D53(1996)3913[hep-ph/9509201],Phys.Rev.D54(1996)6970[hep-ph/9602439];K.I.Izawa and T.Yanagida,Prog.Theor.Phys.97(1997)913[hep-ph/9703350].[4]Y.Kawamura,Prog.Theor.Phys.103(2000)613[hep-ph/9902423].[5]P.Candelas,G.T.Horowitz,A.Strominger and E.Witten,Nucl.Phys.B258(1985)46;E.Witten,Nucl.Phys.B258(1985)75.[6]Y.Imamura,T.Watari and T.Yanagida,hep-ph/0103251;T.Watari and T.Yanagida,hep-ph/0108057;C.Csaki,G.D.Kribs and J.Terning,hep-ph/0107266.[7]Y.Kawamura,Prog.Theor.Phys.105(2001)999[hep-ph/0012125].[8]L.Hall and Y.Nomura,Phys.Rev.D64(2001)055003[hep-ph/0103125].[9]J.Scherk and J.H.Schwarz,Nucl.Phys.B153(1979)61;J.Scherk and J.H.Schwarz,Phys.Lett.B82(1979)60.[10]G.Altarelli and F.Feruglio,Phys.Lett.B511(2001)257[hep-ph/0102301];T.Kawamoto and Y.Kawamura,hep-ph/0106163;A.Hebecker and J.March-Russell,hep-ph/0106166;N.Haba,T.Kondo,Y.Shimizu,T.Suzuki and ai,hep-ph/0108003.[11]A.Hebecker and J.March-Russell,hep-ph/0107039.See also,L.J.Hall,H.Murayama and Y.Nomura,hep-th/0107245.[12]Y.Hosotani,Phys.Lett.B126(1983)309,Annals Phys.190(1989)233.[13]J.Polchinski,String Theory,(Cambridge University Press,UK,1998).[14]T.Asaka,W.Buchmuller and L.Covi,hep-ph/0108021;L.Hall,Y.Nomura,T.Okui and D.Smith,hep-ph/0108071.[15]K.I.Izawa and T.Yanagida,Prog.Theor.Phys.97(1997)913[hep-ph/9703350].[16]R.Contino,L.Pilo,R.Rattazzi and E.Trincherini,hep-ph/0108102.[17]D.E.Kaplan,G.D.Kribs and M.Schmaltz,Phys.Rev.D62(2000)035010[hep-ph/9911293];Z.Chacko,M.A.Luty,A.E.Nelson and E.Ponton,JHEP0001(2000)003[hep-ph/9911323].See also for the early work,K.Inoue,M.Kawasaki,M.Yamaguchi and T.Yanagida, Phys.Rev.D45(1992)328.[18]See,for example,N.Borghini,Y.Gouverneur and M.H.Tytgat,hep-ph/0108094,and references therein.[19]M.B.Green and J.H.Schwarz,Phys.Lett.B149(1984)117.[20]N.Arkani-Hamed,A.G.Cohen and H.Georgi,hep-th/0103135.Figure1:T2/Z4orbifold geometry is described.There are two Z4 σ fixed points(•’s in thefigure)and onefixed point(◦in thefigure)whose isotropy group is Z2 σ2 .The arrow denotes the identification between mirror images under Z4/Z2.This Z2 σ2 fixed point is the SU(5)preservingfixed point.Figure2:Geometry of T2/Z6is described.This orbifold has threefixed points whose isotropy groups are all different:namely the•(Z3 σ2 fixed),the◦(Z2 σ3 fixed)and the•-◦(Z6 σ fixed)in thisfigure.Each of thefixed point•and◦can be an SU(5) preservingfixed point.Arrows denote the identification between mirror images under Z6/Z3(•’s)and Z6/Z2(◦’s),respectively.。
Double-Pole Approximation in Time-Dependent Density Functional Theory
(1)
where the matrix W is given by ˜ qq′ (Ω) = ω 2 δqq′ + 4 √ωq ωq′ Mqq′ (Ω) W q and Mqq′ (Ω) = d3 r
′ ′ d3 r′ Φ∗ q (r) K (rr Ω) Φq′ (r ).
(2)
(3)
Here ωi is the Kohn-Sham transition frequency and for single particle transitions q (q ≡ k → j ) the shorthand Φq (r) := ϕk (r)ϕ∗ j (r) has been introduced. The kernel K (r, r ′ , ω ) consists of the bare Coulomb interaction and the approximate XC kernel fXC (r, r′ , ω ): K (r, r′ , ω ) = 1 + fXC(r, r′ , ω ). |r − r′ | (4)
itself. Unfortunately, this is rarely the case in practice. In the present work, we generalize the SPA to a doublepole approximation (DPA), in which we explicitly solve the TDDFT response equations for exactly two transitions. This produces a variety of results beyond that of SPA. Most importantly, one can study TDDFT XC corrections to KS levels when there is strong coupling between levels. But one can also see when SPA fails, and recover G¨ orling-Levy perturbation theory [14] results for the coupling-constant expansion of excited states [11]. DPA has recently been successfully applied to core-hole interaction in the X-ray absorption spectroscopy of 3d transition metals [15].
DNV_DRAFT_OS_J102_DESIGN_AND_MANUFACTURE_OF_WIND_TURBINE_BLADE
FOREWORD
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高分子材料与工程专业英语答案
高分子材料与工程专业英语答案【篇一：高分子材料专业英语第二版部分答案2】t all polymers are built up from bonding together a single kindof repeating unit. at the other extreme ,protein molecules are polyamides in which n amino acide repeat units are bonded together. although we might still call n the degree of polymerization in this case, it is less usefull,since an aminoacid unit might be any one of some 20-odd molecules that are found in proteins. in this case the molecular weightitself,rather than the degree of the polymerization ,is generally used to describe the molecule. when the actual content of individual amino acids is known,it is their sequence that is of special interest to biochemists and molecular biologists.并不是所有的聚合物都是由一个重复单元链接在一起而形成的。
在另一个极端的情形中，蛋白质分子是由n个氨基酸重复单元链接在一起形成的聚酰胺。
尽管在这个例子中，我们也许仍然把n称为聚合度，但是没有意义，因为一个氨基酸单元也许是在蛋白质中找到的20多个分子中的任意一个。
Rexnord Omega Elastomer Couplings Installation Ins
Installation Instructions• Rexnord® Omega® ElastomerCouplings(Page 1 of 6) Type E and ES•Sizes 2-140 This is the Original Document in English LanguageT he designation ATEX (A tmosphere E xplosibles) has established itself for the new guidelines. ATEX 100a controls allregulations for the condition of explosion-proof equipment.Model No. _____________________Category ______________________Reference _____________________Mfg Year _______________________Max Temperature _______________1. General Information1.1. Omega Couplings are designed to provide a mechanical connection between the rotating shafts of mechanical equipment, using atorsionally soft flexible element to accommodate inherent misalignment while transmitting the power and torque between the shafts.1.2. These instructions are intended to help you to install and maintain your Omega coupling. Please read these instructions prior toinstalling the coupling, and prior to maintenance of the coupling and connected equipment. Keep these instructions near the coupling installation and available for review by maintenance personnel.1.3. Rexnord Industries, LLC owns the copyright of this material. These Installation and Maintenance instructions may not bereproduced in whole or in part for competitive purposes.1.4. Symbol descriptions:Danger of injury to persons.Damages on the machine possible.Pointing to important items.2. Safety and Advice HintsDANGER!2.1. Safety should be a primary concern in all aspects of coupling installation, operation, and maintenance.2.2. All rotating power transmission products are potentially dangerous and can cause serious injury. They must be guarded incompliance with OSHA, ANSI, ATEX and any other local standard for the applications they are used. It is the responsibility ofthe user to provide proper guarding.2.3. Failure to secure capscrews properly could cause coupling component(s) to dislodge during operation and result in personalinjury. See table 3 for proper tightening torques.2.4. Do not use on turbine drives if the coupling cannot be protected from steam leakage or overspeed situations beyond thecouplings published speed rating.2.5. Before installing this coupling on systems involving sleeve bearings, herringbone gearsets or other axially sensitive devices,consult Rexnord.2.6. Elastomeric couplings can hold a static electric charge that may discharge and ignite in an explosive environment Both shafts ofthe connected equipment must have a path to ground.Installation Instructions • Rexnord ® Omega ® Elastomer Couplings (Page 2 of 6) Type E and ES • Sizes 2-1403. Rexnord Omega Coupling Design and Part NumbersType EType ES4.Drive AlignmentDANGER!Stop the motor and lock it out to prevent start-up during installation of coupling.A TTENTION! Improper alignment of the equipment or hubs may result in hub contact and sparking.⑥⑤①④⑥⑦③②Table 1 - Omega part numbersSizeElastomer ElementHubsElementcapscrews METRIC ⑥High speedrings⑦SleeveextensionE①ES ②Rough bore③BSW UNFQD hub⑤Taper Bush hub ④Taper Bush hub ④27300005M 7300075M 7300215M ---7301410-37300010M 7300080M 7300240M 7300795M 7300730M-73014207369574M 47300015M 7300085M 7300270M 7300800M 7300740M 7300860M 73014207369575M 57300020M 7300090M 7300305M 7300805M 7300745M 7300865M 73014207369576M 107300025M 7300095M 7300340M 7300810M 7300750M 7300870M 73014507369577M207300030M 7300100M 7300650M 7300815M 7300755M 7300875M 7393101 7301100M 7369578M 307300035M 7300105M 7300660M 7300820M 7300760M 7300880M 7393101 7301105M 7369579M 407300040M 7300110M 7300670M 7300825M 7300765M 7300885M 7393105 7301110M 7369580M 507300045M 7300115M 7300680M 7300830M 7300770M 7300890M 7393105 7301115M 7369581M 607300050M 7300120M 7300690M 7300835M 7300775M 7300895M 7393109 7301120M 7369582M 707300055M 7300125M 7300700M 7300840M 7300780M 7300900M 7393109 7301125M 7369583M 807300060M 7300130M 7300710M 7300845M 7300785M 7300905M 7393109 7301130M 7369584M1007300065M -7300720M 7300850M 7300850M -7301530-7369834M 1207300070M -7300725M 7300855M 7300855M -7301540-7369835M1407300071M-7300727M7300858M7300857M-7301545--5. Rexnord Omega Coupling InstallationSTEp 15.1. Clean dirt and burrs from shafts and hub bores.5.2. Be sure the keys fit shafts properly .5.3. Position both hubs on the shaft without tighteningthe setscrews.5.4. Use a half element to set proper hub spacing. 5.5. When the hubs are properly spaced, tighten the setscrews.5.6.When using tapered bushings, follow bushing manufacturers instructions.STEp 25.7. Mount first half element to the hubs using cap screws provided.5.8. Rotate the shaft 180 degrees and secure second half element.5.9.If shaft cannot be rotated, mount half elements at 90 degrees.STEp 35.10. Tighten all cap screws to the torques specified in Table 3. 5.11. Align equipment.5.12. Install proper guarding prior to equipment start up.A TTENTION! When installing the element, first seat all the cap screws with a light torque, then tighten all cap screws to proper torque using a torque wrench.Type E Type ESType EType ESType EType ESTable 2 - Drive Alignment23451020304050607080100120140(b-a)mm 3456767911881091214Δ Kr mm222222222333555Installation Instructions • Rexnord ® Omega ® Elastomer Couplings (Page 4 of 6) Type E and ES • Sizes 2-1406. Rexnord Omega Hub Mounting Options6.1.Hubs can be installed:• flush with the shaft end (D)• extended beyond the end of the shaft (E) • recessed behind the shaft end (F)A TTENTION! Shaft engagement length should be >0,8 times shaft diameter , bushed hubs must engage 100%.7. Cap Screw Torque7.1.Do not lubricate cap screws threads.7.2.Cap screws must have a thread-locking adhesive applied.7.3. Tighten cap screws by using torque wrench.A TTENTION! Do not lubricate cap screw threads 8. Rexnord Omega “Type E” Mounting OptionsArrangementAArrangementBCE Table 3 - Cap Screw Torque Couplingsize Quantity Torque - DRYMetricIn. Lbs Nm Part number Steel Part number Stainless steel Thread size Wrench size28+82042373014107301417M61038+87301420730142748+87301420730142758+8730142073014271012+87301450730145720124685373931017393102M101630127393101739310240167393105739310650167393105739310660168169273931097393110M12187016739310973931108016739310973931101002032403707301530-M203012024730154073015471403270808007301545-M24Table 4 - Type E Mounting Options23451020304050607080100120140A 368888131281181817445776B 4127273434394142515364837091102C4646465959656975919710914995124127Installation Instructions • Rexnord® Omega® ElastomerCouplings(Page 5 of 6) Type E and ES•Sizes 2-140 9.Rexnord Omega “Type ES” Mounting Optionsoutward One hub mounted inwardinwardTable 5 - Spacer coupling (ES) Hub mounting options for industry shaft gaps* Hub mounted inboardInstallation Instructions • Rexnord ® Omega ® Elastomer Couplings (Page 6 of 6) Type E and ES • Sizes 2-14010. Preventative MaintenanceDANGER!Do not make contact with the coupling when it is rotating and/or in operation10.1. Periodic visual inspection is necessary to evaluate the condition of the flex element. Inspection can be done during the operationusing a strobe light.10.2. When inspecting the element look for:• Fatigue cracks at element splits • Discoloration• Surface cracking in body of element.A TTENTION! Replace Element if necessary.11. Element ReplacementDANGER!Stop the motor and lock it out to prevent start-up during installation of coupling.11.1.Always replace both half elements.11.2. Install both half elements from the same box.11.3. Follow installation instructions (see Section 5, Rexnord Omega Coupling Installation).11.4.Tighten element cap screws to proper torque (see Table 3).。
英语专业八级考前拉力赛答案与详解（2）
KEY PART Ⅰ LISTENING COMPREHENSION. SECTION A 1 答案B 「解题思路」了解讲话者的⾝份。
「详细解答」⽂中讲的是slang的使⽤，以及与native speakers的交流，涉及的都是language.应该选B. 2 答案D 「解题思路」了解“hip”在这个talk中的含义。
「详细解答」the talk中指出：hip在六、七⼗年代指的是社会潮流的追随者，但在本⽂来⾃更加久远的⽤法。
3 答案C 「解题思路」了解俚语以及时髦语存在的问题。
「详细解答」“trendy”为“in accord with the latest fashion；fashionable”时髦，潮流的。
the talk中有： the problem with slang and trendy expressions in general is that they change fast， so that only those who are using them all the time can keep up. 4 答案D 「解题思路」掌握在Newcastle“hinny”的意思。
「详细解答」讲话者指出：If you are in Newcastle， you might hear people refer to each other as“hinny”—a common term of endearment. 表亲近的称呼。
“endearment”为“an expression of affection.”亲近，亲热，友好。
5 答案B 「解题思路」掌握讲话者对听众的要求。
「详细解答」The talker在最后指出：既然英语不是本族语，⼈们会觉得奇怪，如果你使⽤。
但你仍旧需要花时间与⼈交流，来学习本地⼈，从⽽理解不同的表达。
SECTION B 6 答案D 「解题思路」了解在上个世纪道路建设的材料。
2021高考英语黄金预测卷二含解析
2021届高考英语黄金预测卷（二）本试卷满分120分，考试时间100分钟。
第一部分阅读理解（共两节，满分50分）第一节（共15小题；每小题2.5分，满分37.5分）阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。
ATravel in EuropeInstead of Santorini, TinosSantorini has been struggling with overtourism for years, a victim of its own success, and the Greek government, sought to lure tourists back following an 8-year financial crisis. Now this idyllic destination has reached saturation point (饱和点).A more authentic Greece--the one that Santorini offered before the crowds--can be found in the Cycladic haven of Tinos. With its own enchanting sunsets and rugged charm, this under-the-radar gem is an alluring alternative.Instead of Amsterdam, Delft and The HagueIn 2017, Amsterdam was visited by 19 million people, two million more than those who live in the entire country. The city has a particular problem with tourists on a tight budget--many arriving via low-cost airlines from Britain, France, Germany and beyond, and staying at Airbnbs, in hostels or in their cars. The crowds there get so dense that on weekend summer nights rescue workers often can't get to people who fall sick or faint.Another two destinations can be easily combined: Delft, about 10 miles away, and The Hague, the seat of Dutch government. Both are ideal for visitors looking for great museums, canals, wild North Sea beaches--and no crowds.Instead of Barcelona, ValenciaFor a less frenetic close of cosmopolitan Mediterranean charm, head 350 kilometers down the coast to Valencia, Spain's third-largest city, with 800 ,000 residents and barely 2 million visitors per year. Founded as a retirement communityfor Roman soldiers, it has many of the same attributes as Barcelona--both were ancient walled cities--with a sprawling, maze-like (迷宫般的) center filled with Gothic,Romanesque, Renaissance and Baroque architecture. All styles were combined in Valencia Cathedral, built between the 13th and 18th centuries; architectural purists (纯粹主义者) should not miss the 15th-century Silk Exchange, a UNESCO World Heritage Site and a stunning reminder of the city's mercantile importance.1.What can we learn about Santorini?A.It is still a popular place for tourists.B.It is an attractive choice.C.It will win tourists back.D.It suffered overtourism.2.In Amsterdam, the crowds are so dense that ______ .A.the streets are bustling with noise and excitementB.some people can't be treated in timeC.more visitors will be disturbedD.many people fall sick or faint3.What's the author's purpose of writing this passage?A.Recommend some better places to visit.B.Introduce some new places to visit.C.Criticize some crowded places.D.Blame the improper tourism.BThe 2020 Nobel Prize in Literature was awarded to the former U. S. Poet Laureate (桂冠诗人) L ouise Glück. The prize committee cited "her unique poetic voice that with plain beauty makes individual existence universal". Glück has been the first American wom an to win the award since Toni Morrison in 1993. Glück joined a list of literary giants and previous Nobelists that included, in this century, Canadian short-story master Alice Munro, Chinese magical-realist Mo Yan, etc.Glück's works include 12 collec tions of poetry and a few volumes of essays on literary writing. "All are characterized by a striving for clarity (清晰). Childhood and family life, the close relationship with parents and siblings, is a theme that has remained central to her," Anders Olsson, the chairman of the NobelCommittee for Literature, said. "She seeks the universal, and in this she takes inspiration from myths and classical motifs," Olsson added, citing her 2006 collection Averno, which the committee described as "masterly" for its "visionary interpretation of the myth of Persephone's fall into hell in the captivity (囚禁) of Hades, the god of death".Being a professor at Yale and a resident of Cambridge, Glück also served as U. S. Poet Laureate from 2003 to 2004 and is no stranger to awards. She won the Pulitzer Prize in 1993 for her collection of poems titled The Wild Iris, in which "she describes the incredible return of life after winter in the poem Snowdrops." She also won the 2014 National Book Award for the poem Faithful and Virtuous Night. In 2016, former President Obama awarded the National Humanities Medal to Glück in a White House ceremony.The publicity-shy Glück did not immediately issue any comment about the latest honor for her body of work, which has spanned more than half a century. In a 2012 interview, she acknowledged that prizes can make "existence in the world easier" but did not amount to the immortality (不朽) of a true artist.4. What can we know about Glück from Paragraph 1?A. She is as popular as the Chinese novelist Mo Yan.B. She won the Nobel Prize for her special literary style.C. She is the first American to win a Nobel Prize in Literature.D. She is the only Poet Laureate in modem American history.5. What do Glück's poems mainly focus on?A. Daily life.B. Nature.C. Careers.D. Classical myths.6. What is the purpose of Paragraph 3?A. To show Glück's contributions to literature.B. To prove Glück's great passion for writing.C. To present Glück's outstanding achievements.D. To stress Glück's influence on other poets.7. What does Glück think about the latest honor she has received?A. She is content with it.B. She takes it very seriously.C. She deserves a higher honor.D. She doesn't attach great importance to it.CSchool pupils in England will be grouped into "bubbles" when the new academic year starts in September, with mass activities such as assemblies discouraged under new regulations announced by Education Secretary Gavin Williamson.Schools were shut down in March, 2020. Currently around 1.6 million of the country's 9 million school-age children are back in the classroom, but the government says a proper return in September is "critical to our national recovery" and attendance will be compulsory.Social distancing will not be applied in schools, and masks will not be worn, but instead so-called bubbles, based on avoiding contact between individual classes or year groups, will be deployed. This will mean separate start and finish times, and also different times for lunch and playtime.Pupils will be discouraged from using public transport, which could bring many other challenges. Mobile testing units will be sent to schools which have an outbreak, and schools will have testing kits to give parents if required, but if there are two confirmed cases in 14 days, potentially the whole school could be shut down.Geoff Barton, the general secretary of the Association of School and College Leaders, says, "It will be immediately apparent to anyone reading this guidance that it is enormously challenging to carry out this proposal. The logistics of keeping apart many different 'bubbles' of children in a full school, including whole-year groups comprising hundreds of pupils, is incredible."Meanwhile, before the much-anticipated next stage of easing lockdown in England takes place this weekend, the number of COVID-19 cases has risen in 36 local authorities across England. Easing measures have already had to be delayed in the East Midlands city of Leicester, but now other spikes (激增) in infection rate are being reported all across England. The areas with the largest increases are Knowsley and Bolton, both in the North West of the country, and the London borough of Hammersmith and Fulham. In Knowsley, close to the city of Liverpool, the rate ofinfection rose from 6 people out of every 100,000 to 20.8.What does Gavin group the students into "bubbles" for?A.Setting different time for school activities.B.Asking all students to wear masks in class.C.Keeping social distance among all students.D.Calling on students to take a bus for school.9.A school will possibly be closed again in England when _______.A.two cases of infection are confirmed in 14 daysB.there is a lack of testing units for pupilsC.the attendance of students isn't enoughD.the rate of infection rises from 6 people out of every 100,000 to 2010.What's the attitude of Barton toward Gavin's measure?A.Tolerant.B.Doubtful.C.Hopeful.D.Ambiguous.11.What can we infer from the last paragraph?A.England has already ended the lockdown.B.More reports are about the spread of COVID-19.C.The number of COVID-19 infections is increasing in England.D.COVID-19 is more serious in England than in other countries.DRising Seas Will Erase (消除) More Cities by 2050, New Research ShowsRising seas could affect three times more people by 2050 than previously thought, according to new research, threatening to all but erase some of the world's great coastal cities.The authors of a paper published on Tuesday developed a more accurate way of calculating land elevation (海拔) based on satellite readings, and found that the previous numbers were far too optimistic. The new research shows that some 150 million people are now living on the land that will be below the high-tide line by mid-century. In Thailand, more than 10 percent of citizens now live on the land that is likely to be covered with water by 2050, compared with just 1 percent according to the earlier technique. The political and commercial capital, Bangkok, isparticularly dangerous.In other places, the migration caused by rising seas could cause or worsen regional conflicts. Basra, the second largest city in Iraq, could be mostly underwater by 2050. If that happens, the effects could be felt well beyond Iraq's borders, according to John Castellaw, a retired Marine Corps general."Further loss of land owing to rising waters there threatens to drive further social and political instability in the region, which could lead to armed conflicts again and increase the likelihood of terrorism," said Castellaw, who is now on the advisory board of the Center for Climate and Security, a research and advocacy group in Washington. "So this is far more than an environmental problem," he said. "It'sa humanitarian, security and possibly military problem too."12. How many people will be threatened by 2050 according to the research?A. About 15 million.B. About 50 million.C. About 150 million.D. About 450 million.13. What can we learn from the text?A. The migration caused rising seas.B. Basra could be entirely underwater by 2050.C. Rising seas could erase all the world's great coastal cities.D. Further loss of land owing to rising waters could cause armed conflicts.14. What is the purpose of the text?A. To advise people to move house.B. To tell new research.C. To warn the danger of conflicts.D. To appeal for environmental protection.15. Where is this text most likely from?A. A science magazine.B. A geography textbook.C. Science fiction.D. A medical journal.第二节（共5小题；每小题2.5分，满分12.5分）阅读下面短文，从短文后的选项中选出可以填入空白处的最佳选项。
Entropy of the Randall-Sundrum brane world with the generalized uncertainty principle
Entropy of the Randall-Sundrum brane world with the generalized uncertainty principle
Wontae Kim1,a , Yong-Wan Kim2,b , and Young-Jai Park1,c
(5) 16πGN
d4 x
dy −g(5) R(5) + 12k 2 −g(−) λ(−) , (1)
−
d4 x
−g(+) λ(+) +
where λ(+) and λ(−) are tensions of the branes at y = 0 and y = πrc , respectively, while 12k 2 is a cosmological constant. We assume that orbifold S 1 /Z2 possesses a periodicity in the extra coordinate y , and identify −y with y . Two singular points on the orbifold are located at y = 0 and y = πrc . Two 3-branes are placed at these points. Note that the metric on each brane is (+) (5) µ (−) (5) µ defined as gµν ≡ gµν (x , y = 0) and gµν ≡ gµν (x , y = πrc ). Since we are interested in black holes, let us assume the bulk metric as
Oscillating magnetoresistance in diluted magnetic semiconductor barrier structures
Kai Chang∗ and J. B. Xia
NLSM, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
distances (≥ 100µm) and for long time (up to nanoseconds) [16]. In this work, we report an interesting oscillating tunneling magnetoresistance (TMR) and spin polarization (SP) through NMS/DMS structures. The DMS structure is similar to the saal study of Ref. [10]. We find theoretically that the TMR for the double barrier structure oscillates with increasing magnetic field and exhibits a peculiar beat pattern. The underlying physics of the phenomena arises from the interplay of the spin-up and the spin-down channels which are split by the s-d exchange interaction. Note that bandstructure effects and spin-orbit interaction are not very efficient spin-flip processes for electrons. [17] Recently, Egues et al [12] presented results on spin filtering and magnetoresistance through ballistic tunneling junctions. These results are complementary to ours, i.e. the beat pattern in the double NMS barriers with DMS contacts is similar to what we found, but we additionally studied double DMS barriers with NMS contacts which we found to exchibit also beat patterns. Furthermore, in our calculation we used a different approach which is more easily applicable to more complicated cases, such as e.g. the case with an electric bias. In this work we prove that the beat pattern which arises from the superposition of the spin-up and the spin-down channel is a rather general phenomena and can be observed in either NMS double barrier structures with DMS contacts or DMS barriers with NMS contacts. Instead of ZnSe/Zn1−x Mnx Se structures used in the calculation of Ref. [12], we propose Cd1−y Mgy Te / Cd1−x Mnx Te structures to realize single and double NMS(Cd1−y Mgy Te) barrier structures with DMS contacts(Cd1−x Mnx Te). Consider a spin unpolarized electron injected into a NSM/DMS/NSM single or double barrier structure in the presence of a perpendicular magnetic field. Due to the s-d exchange interaction, an external magnetic field gives rise to a giant Zeeman splitting of the conduction band states which results in a striking difference of the potential profiles seen by the spin-up and the spin-down electron (see the insets of the figures) [11]. In this simple system, the electric current has contributions from spinup and spin-down channels. Since the sample dimensions are much smaller than the spin coherence length, which may reach up to 100µm in semiconductors [14,16], spin-
新SAT评分详解及样题
* Combined score of two raters, each scoring on a 1– 4 scale 1-4
SAT 1. Composite Score 2 2. SAT raw score 3 3. SAT Test Score Evidence-Based Reading and Writing raw score 4. SAT Studies OG 1—15 5. SAT Subscore 7 Cross-section Score 3 Section Score 400—1600
3.
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25+15min 49
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2-12 25min
2-8 50min
History Questions 1-5 are based on the following passage.
This passage is adapted from a speech delivered by Congresswoman Barbara Jordan of Texas on July 25, 1974, as a member of the Judiciary Committee of the United States House of Representatives. In the passage, Jordan discusses how and when a United States president may be impeached, or charged with serious offenses, while in office. Jordan’s speech was delivered in the context of impeachment hearings against then president Richard M. Nixon.
Data Reduction Methods for Reverse Engineering
Int J Adv Manuf Technol(2001)17:735–743©2001Springer-Verlag LondonLimitedData Reduction Methods for Reverse EngineeringK.H.Lee,H.Woo and T.SukKwangju Institute of Science and Technology(K-JIST),1Oryong-dong,Puk-gu,Kwangju,500–712,KoreaReverse engineering is an emerging technology that promises to play a role in reducing product development time.Reverse engineering in this paper refers to the process of creating engineering design data from existing parts.It creates or clones an existing part by acquiring its surface data using a scanning or measurement device.Recently,laser scanning technology has improved significantly and has become a viable option in capturing geometries of complicated design models. 3D laser scanners have become more accurate and the speed of data acquisition has increased dramatically.However,they generate up to thousands of points per second,and handling the huge amount of point data is a major problem.It becomes quite important,therefore,to reduce the amount of acquired point data and convert it into formats required by the manufac-turing processes while maintaining the accuracy.This paper presents methods that can reduce efficiently the amount of point data.Keywords:Point cloud data;Point data reduction;Reverse engineering;3D laser scanner;Uniform and non-uniform grid methods1.IntroductionProducts are manufactured from2D or3D CAD models,but these CAD models are not always available in the production environment,and thus it is often necessary to generate a model from an existing physical part.Reverse engineering technology makes it possible to recreate an existing part by reconstructing its surface geometry in a3D digitalfile using a scanning or measurement device.This technology enables us to create a CAD model of a part that has no design data or has gone through many design changes.For certain industries such as in the automotive industry,the part geometry is obtained from a mock-up model using this technology.Correspondence and offprint requests to:Dr K.H.Lee,Department of Mechatronics,Kwangju Institute of Science and Technology, 1Oryong-dong,Puk-gu,Kwanglu,500–712,Korea.E-mail: leeȰkyebek.kjist.ac.krIn capturing surface information,either contact or non-contact measuring devices can be used.Coordinate measuring machines have usually been used in the past for capturing surface information.These machines typically use touch probes and the data acquisition process is very slow when they are used for measuring parts having complex freeform surfaces.In contrast,non-contact devices such as3D-laser scanners are extremely fast in data acquisition,but they are rarely used in production lines because of their poor accuracy compared to that of contact devices[1].Among these devices,those using laser-scanning technology have been improved significantly in recent years,and are now being used in the production mode [2].However,there are problems in using these scanning devices since they produce extremely dense point data at a great rate.Not all these point data are necessary for generating a surface model,moreover,bottlenecks are created owing to inefficiencies in storing and manipulating them.Therefore,it takes a long time to generate a surface model from these scanned data.To avoid these problems,it is important to reduce the amount of scanned data while maintaining the required accuracy.This paper presents data reduction methods that can reduce the amount of point data acquired during laser scanning.The proposed methods are applied to different types of surfaces and the results are discussed.1.1Previous ResearchContact devices were usually used to acquire surface geometry in the past,and research issues were mainly on point-sampling strategies for different types of surface.The amount of point data did not need to be reduced for contact devices.However, in recent years,some workers have shown interest in managing the large amount of point data acquired by laser scanners. Some research related to point data reduction for reverse engineering is described below.Martin et al.[3]proposed a data reduction method using a uniform grid in their EU Copernicus project.Their method uses a“medianfiltering”approach,which has been widely used in image processing.The procedure starts by building a grid structure,and the input data points are assigned to the corresponding grid.From all of the points assigned to a given736K.H.Lee et al.grid,a median point is selected to represent data points belong-ing to that cell.This approach overcomes the limitation of averaging or simple sampling methods.Their method,however, has a drawback due to the use of uniform size grids that can be insensitive in capturing a part shape.Fujimoto and Kariya[4]also indicated that the amount of data should be reduced since a large amount of point data causes problems in downstream manufacturing operations.They suggested an improved sequential data reduction method for 2D digitised point data.Their method guarantees that an error range of the reduced data remains within the given angle and distance tolerances.Chen et al.[5]suggested a method to reduce the point data by reducing the number of triangles required in a polyhedral model.They generated the STLfile of a part directly from the point data acquired by a coordinate measuring machine, and reduced the amount of data by decreasing the number of triangles in the STLfile.Triangles in planar or near planar regions are combined by comparing the normal vectors of neighbouring triangles.As a result,larger triangles are formed forflat areas and smaller ones for highly curved areas.They demonstrated their algorithm by reducing the number of tri-angles in an STLfile of a human face digitised by a CMM machine.Hamann[6]also presented a method of data reduction for triangulationfiles based on an iterative triangle removal prin-ciple.As a measure of the reduction offile size,each triangu-lation is weighted according to the principal curvature estimates at its vertices and interior angles.Ve´ron and Le´on[7]introduced an approach to reduce the number of nodes of a polyhedral model using error zones assigned to each point of the initial polyhedron so that the simplified polyhedron intersects with each error zone. Hamann and Chen[8]proposed a method to reduce the point data in making various planar curves,compressing2D images,and visualising volumes.In their method,points are selected with respect to local absolute curvature estimates for piecewise linear curve approximation.The degree of reduction is controlled either by the number of points to be selected or by the error tolerance level.Major research efforts in the existing data reduction methods lie in manipulating polyhedral models.Various schemes are also used to reduce the amount of point data from the initial point clouds;however,none of the existing methods has con-sidered the characteristics of the scanning device.2.Reverse Engineering by LaserScanningThe reverse engineering process consists of the following steps, as shown in Fig.1:point data acquisition,noisefiltering,data reduction/arrangement/registration,segmentation,curve/surface fitting,and3D surface model generation.The data acquisition step creates raw point data to work with and it is considered as a crucial step in reverse engineering since in many cases,the quality of raw point data determines the quality of the resulting surfaces.Once raw point data are acquired,noisy data points,so called outliers or spikes,gener-Fig.1.General procedure for reverse engineering.ated during a scanning process,must be eliminated.The quality of point data can be further improved by performing pre-process operations such as spike removal,smoothing and merg-ing.For spike removal,several methods can be used:1.The angles between two consecutive points are considered,and a point that makes an angle with the previous point larger than the given value is eliminated.2.The points can be moved to a median value.3.The points can be moved either upward or downward closeto the given level along the specified axis within the allow-able distance[9].The data reduction methods are applied after the removal of spikes and they should be performed with consideration of the characteristics of the scanning devices.2.13D Laser ScanningA3D laser-scanning device acquires the surface information of a part,by sending laser beams which are radiated from the surface and received by CCD cameras.In general,the probe of a laser scanner consists of a beam projector radiating the laser beam and a CCD camera sensing the reflected beam from the surface.The laser beam can typically be categorised as a point type,or a stripe type.A stripe-type scanner radiates a line of laser beams,called a stripe,onto the surface so that several points can be acquired at once,whereas a point type laser scanner obtains only one point at a ser scanning devices can also be classified based on the configuration of the machine,as shown in Fig.2.There are other configurations,but these three are the most popular ones.Each one has advantages and disadvantages;the choice of a machine depends on the characteristics of the part to be scanned,as well as its application.Thefirst type shown in Fig.2(a)uses three linear axes that are perpendicular to each other.This one follows the same structure as for the traditional fabrication machines and shows better accuracy compared to the others owing to its structural stability.A coordinate measuring machine can be retrofitted to form this type by mounting a scanning probe.Extra degrees of freedom can be obtained by adding a rotary table with tilt and other motions.In the second type of device,the scanning is perfor-Data Reduction Methods for Reverse Engineering737Fig.2.Types of laser scanning device.med by rotating the platform on which the object is mounted,as depicted in Fig.2(b ).In this configuration,at times,the object is stationary and the laser probe rotates around it.Scanners of this type are operated by obtaining contours of an object from the bottom to the top by lowering the platform in a stepwise manner.This operation is similar to obtaining magnetic resonance images in medical applications.It can be advantageous for acquiring the entire surface data of a part,compared to the first type.However,it may collect less accurate point data since the z -increment generally is much larger than the stripe intervals used in the machines of the first type.The third type uses an articulated robot arm with a laser probe attached,as the end of arm tooling.This type usually requires a skilled operator to move the laser head around the part while maintaining certain spacing between the heads and the part.This type has a greater flexibility in scanning since it allows us to scan any shape of part by moving the robot arm,as long as the probe motion is within the robot work envelope.The surface data of a scaled model of a car,for example,can be collected efficiently using this type of scanner,but,this type also has poor accuracy compared to the first type.As the laser probe scans an object,the rays sensed by the CCD camera are stored as intensity data in pixels;this infor-mation is then converted to 3D coordinates for scanned points through image processing and triangulation methods.Figure 3(a )shows the principle of the triangulation method.The laser scanner considered in this research belongs to the first type.It uses a probe that radiates a series of laser stripes while moving along the scan path illustrated by Fig.3(b ).Among the coordinates of 3D points,x -and y -values are obtained according to the position of the probe that is directly controlled by the transport mechanism.The x -and y -values are mostly reliable,but z -values generally show poor accuracy since they are determined by processing the sensed rays at the CCD camera.The error range in the z -axis depends on the quality of the scanning devices,but most current state-of-the-art devices can accommodate ranges from 0.01mm to over 0.10mm with a good calibrated accuracy.In managingtheFig.3.(a )Triangulation methods.(b )Scanning operation.point cloud data generated from laser scanners,therefore,the z-axis errors should be controlled in order to create accurate surfaces.2.2Point Data Reduction Using Uniform GridsThe amount of point data can be reduced by dividing it into grids and by sampling a representative point from each grid.Martin et al.[3]used a uniform grid method as described below.An array of grids perpendicular to the scanning direction (z -direction)is used for extracting points from the point cloud data.Since z -values,as discussed in the previous section,are more prone to errors due to the characteristics of laser scanners,median filtering is used with the grids.First,a grid plane is created consisting of same-sized grids perpendicular to the scanning direction.The data reduction ratio is determined by the size of a grid which is user defined.The smaller the grid size,the more points are sampled from the entire point cloud.After creating a uniform grid plane,all the points are projected on the grid plane and each grid is assigned with the corresponding points.Then,one point from each grid is selected based on the median-filtering rule [10].The points within each grid are sorted with respect to the distances from the grid plane,and a point,which is located in the middle,is chosen,as shown in Fig.4.When the number of points within a grid is n ,the (n +1)/2th point is selected if n is odd and the n /2th point or the (n +2)/2th point is selected if n is even.Using median filtering with uniform grids,those points that are regarded as noise are likely to be discarded.This method shows better performance if the scanned surface is perpendicular to the scanning direction.Furthermore,this method is good for maintaining the original point data,asFig.4.Uniform grid method.738K.H.Lee etal.Fig.5.Scanned data using a laserscanner.Fig.6.Angular deviationmethod.Fig.7.One-directional non-uniform grid generation.it selects points rather than changes the positions of points.The uniform grid method is especially useful in cases where data reduction must be done very quickly for parts having relatively simple surfaces.3.Improved Data Reduction Methods Using Non-Uniform GridsWhen applying the uniform grid method,some points for which the part shape drastically changes,such as edges,can be lost because no consideration of part shape is provided.In reverse engineering,it is critical to recreate part shape accu-rately,and the uniform grid method has limitations in this regard.In this work,non-uniform grid methods are proposed in which the size of grids can be varied based on the part shape.Two levels of non-uniform grid methods are proposed:one-directional and bi-directional.They can be applied con-sidering the characteristics of the measured data.When measuring a part with a stripe-type laser scanner,the scan path and the interval between laser stripes are usually specified by the user.The moving direction of the laser probe follows the scan path,and the interval between laser stripes controls the density of the scanned points.When a part having simple surfaces is measured,it does not have to be scanned densely in all directions.The point data shown in Fig.5(a )have more points along one direction (v -direction)than in the other direction (u -direction).In this case,the one-directional non-uniform grid method is appropriate for capturing the shape of the surface,and is,therefore,recommended.On the other hand,when a part to be measured has complex and freeform surfaces,the point data should be dense along both the u -and v -directions,as shown in Fig.5(b ).In this case,the bi-direc-tional non-uniform grid method is more appropriate than the one-directional method.For applying both one-directional and bi-directional methods,the scan data are obtained from one view and therefore can be projected on a 2D plane.If the user requires a complete 3D model of an object,the object must be scanned several times by changing the set-up.Upon completion of scanning of all surfaces,the point clouds from different views should be registered together to construct a complete 3D model.However,the single-view scan data is sufficient in many cases,for meeting various purposes required by industrial parts.3.1One-Directional Non-Uniform Grid MethodIn the one-directional non-uniform grid method,points are sampled from the point cloud acquired from the surfaces of a part using an angular deviation method.As shown in Fig.6,the angular deviation method selects the points based on the angle which is calculated by the vectors created from three consecutive points,for example,(x 1,y 1),(x 2,y 2)and (x 3,y 3).The angles represent the curvature information;the curvature is small when the angle is small and vice ing these angles,the points with high curvature can be extracted.The size of grids along the u -direction is fixed by the interval of the laser stripes,which is determined by the user.In the v -direction,the grid size is determined depending on the geo-metric information about the part shape.The points extracted by angular deviation represent high curvature areas,and they must be preserved during data reduction in order to express the part shape accurately.Thus,after extracting points by using the angular deviation method,the grid along the v -direction isData Reduction Methods for Reverse Engineering739Fig.8.Normal value calculation.divided based on the extracted points,as shown in Fig.7(a ).When dividing the grids,if a grid is larger than the maximum size,which is predetermined by the user,it is further divided so as not to exceed the maximum grid size as shown in Fig.7(b ).Then,median filtering is applied to the points in each grid.This will result in a representative point for each grid,as in the case of the uniform grid method.The final retained points in this method include the points selected by using median filtering for each grid and the points extracted by angular ing these points,this method reduces the point data more effectively while maintaining the accuracy of the part shape,when compared to the uniform grid method.3.2Bi-Directional Non-Uniform Grid MethodIn the bi-directional non-uniform grid method,the normal vectors of individual points are calculated and data reduction is performed based on this information.First,the point data are polygonised using triangles.In determining the normal vector of a point,the normal vectors of neighbouring triangles are used.As shown in Fig.8,for the point,p ,six neighbouring triangles exist and the normal value of the point,N ,can be calculated using Eq.(1).N =n 1+n 2+n 3+n 4+n 5+n 6͉n 1+n 2+n 3+n 4+n 5+n 6͉(1)Upon calculating the normal vectors of all points,a grid plane is generated.The grid size is defined by the user,andFig.9.Bi-directional non-uniform grid method.(a )Initial cell.(b )Firstsplit.(c )Second split.(d )QuadTreestructure.Fig.10.(a )Original data with uniform grids,and (b )reduced data.Table parison of flatness.Plane CMM Original Uniform Uniform point data grid sampling Flatness 0.00500.09530.06530.0826Number of 501461112211219pointsTable parison between uniform grid method and uniform sampling for a shpere (unit:mm).Reduction ratio Number of Positive Negative Radius points deviationdeviationdifferenceOriginal16857Uniform grid method 0.116690.04685−0.055890.02670.011660.03901−0.059070.02320.001170.02323−0.027160.0111Uniform sampling 0.117000.05606−0.074120.027360.011790.0377−0.079180.034920.001190.03438−0.035360.04822it depends on the intended data reduction ratio for the given part shape.If it is necessary to reduce the point data greatly,the size of a grid will be increased;whereas,if less reduction of point data is necessary,the grid size will be decreased.By projecting the points on the grid plane,the points corresponding740K.H.Lee et al.Table 3.Summary of deviation for sample model 1(unit:mm).Reduction ratio Number of Positive deviationNegative points deviationOriginal 27861One-directional non-uniform grid method 1/562760.00289−0.004251/1029670.0057−0.005121/2015560.00859−0.0061/505550.0288−0.01591/1002670.0411−0.0405Uniform sampling 1/565630.00489−0.004961/1028750.00722−0.007851/2015640.0157−0.012651/505580.10318−0.088571/1002660.1825−0.17825Uniform grid 1/564210.00324−0.003821/1028900.00675−0.007281/2016000.01178−0.009881/505520.0923−0.061811/1002720.16214−0.16783Chordal deviation sampling 1/565000.00311−0.004221/1029270.00628−0.007351/2015860.0105−0.008151/505620.0509−0.04121/1002680.0615−0.0866to each grid are grouped and the normal values of these points are averaged.As a criterion for subdivision of grids,the standard deviation of the point normal values is used.The level of standard deviation is predetermined considering both the part shape and the desired point data reduction ratio.If the standard deviation in a grid is,for instance,large,it indicates that the part geometry corresponding to the grid is complicated,and therefore,further subdivision of the grid is required in order to sample more points.The process of subdivision is shown in Fig.9.This is called quadtree sub-division and it has been widely used for image processing and computer graphics from the early 1970s [11,12].If the standard deviation of a grid is larger than the given value,the grid is subdivided into four cells.This process repeats until the stan-dard deviation of a grid is smaller than the given value,or the grid size reaches the minimum limit specified by theuser.Fig.11.Point data deviations in the Z -direction.(a )Original data.(b )Reduced data by uniform sampling.(c )Reduced data by uniform grids.The minimum size of a grid varies depending on the complexity of the part shape.Upon completion of grid making,a represen-tative point is selected from the points belonging to each grid,using median filtering.This bi-directional method extracts more points compared to the one-directional method,and thereby represents the part shape more accurately.4.Experimental ResultsThe proposed non-uniform grid based point data reduction methods are tested using different types of part surfaces,and the results are discussed.In implementing the data reduction methods,a commercial laser scanner,Surveyor Model 1200from Laser Design Inc.,was used to acquire the point data.The algorithms were developed using the open architecture of a reverse engineering software package,Surfacer version 7.1from Imageware Inc.,and were run on a Silicon Graphics Indigo2engineering workstation.Before applying the reduction algorithms,outliers or spikes were removed from the initial point cloud.4.1Uniform Grids to Simple SurfacesBefore we discuss the experimental results of the proposed data reduction methods,the uniform grid method is performed to show the effectiveness of median filtering for a point cloud obtained by a laser scanner.Figure 10shows the result of applying the uniform grid method with median filtering to the point cloud of a planar surface.A comparison is made between the uniformly sampled data [13]and the reduced data using the uniform grid method.Figure 11shows the difference by displaying points using polylines,projected on the Y ,Z -plane.The point cloud reduced by the uniform grid method expresses the measured plane with less fluctuation compared to that by the uniform sampling method.The flatness and the number of points in the original point cloud,in the point cloud by uniform grids,and in the point cloud by uniform sampling are summarised in Table 1.The result shows that the error range of the point cloud in the z -axis is minimised using median filtering.Median filtering is also used in the non-uniform sampling method proposed in this work and this result shows that median filtering can generate reliable point data for a point cloud created by a laser scanning device.The uniform grid method with median filtering also gives a good perform-ance for a surface having constant curvature such as a sphereData Reduction Methods for Reverse Engineering741Table 4.Summary of deviation for sample model 2(unit:mm).Reduction ratio Number of Positive Negative points deviationdeviationOriginal36000Bi-directional non-uniform grid method 1/546810.00100−0.000981/1035530.00125−0.002061/2015340.01552−0.019271/507020.01682−0.026141/1003490.09671−0.09322Uniform sampling 1/546800.00187−0.001551/1037200.00248−0.003141/2015640.0157−0.012651/507200.78819−0.684221/100360 2.14127−1.92231Uniform grid 1/546900.00200−0.001501/1034680.00280−0.002581/2015840.02402−0.020391/507200.08142−0.088451/1003630.11683−0.13511Chordal deviation sampling 1/546920.00370−0.052911/1035760.00861−0.004171/2015340.08364−0.002431/507200.31240−0.260351/1003602.14100−1.92221Fig.12.Sample model 1for the one-directional non-uniform grid method.(a )Initial data.(b )Reduceddata.Fig.13.Errors at different reduction ratio (for sample model 1).(a )Positive deviation.(b )Negative deviation.or a cylinder.The uniform grid method is applied to a master ball whose diameter is 12.7mm,and Table 2shows the result.4.2Non-Uniform Grids to Freeform SurfacesIn the case of a freeform shaped object,the uniform grid method may not be the best choice.However,it is still worthwhile in cases where the data reduction must be perfor-med very quickly without considering accuracy.The non-uniform grid methods are more effective in dealing with free-form shaped objects owing to the flexibility of the grid size:for example,smaller grids are used for highly curved and detailed areas and larger grids are used for planar and near planar areas.Two clay models having freeform surfaces are made to demonstrate the performance of both the one-directional and bi-directional non-uniform grid methods.The measured point data for the first model is shown in Fig.12(a );Fig.12(b )shows the reduced point data after using the one-directional non-uniform grid method.Table 3summarises the results of the one-directional non-uniform grid method and other methods such as uniform sampling,chordal deviation sampling,and the uniform grid method.Figure 13shows the results for different levels of data reduction.The size of deviation increases as the reduction ratio increases from 1/5to 1/100;however,the deviation values of the one-directional non-uniform grid method are smaller than those of other methods at each level.742K.H.Lee etal.Fig.14.Sample model 2for the bi-directional non-uniform grid method (a )Measured point data.(b )Reduced data with non-uniform grid.The second clay model shown in Fig.14(a )was used to observe the performance of the bi-directional non-uniform grid method.Figure 14(b )shows the point cloud reduced with the bi-directional non-uniform grids generated using point normal vectors.For comparison purposes,other data reduction methods are also applied to the same model,and the results are summar-ised in Table 4.As the reduction ratio increases,the reduced point data set shows more deviation from the original model;however,for all levels of reduction,the bi-directional non-uniform grid method shows less deviation than the other methods.Furthermore,even for an increase in the reduction,e.g.up to 1/100,the amount of deviation from the proposed method is kept constant whereas that of the conventional methods increases quickly as shown in Figs 15(a )and 15(b ).Determining the optimal data reduction ratio considering both the accuracy and the number of points depends upon the part shape.Although only one freeform model was tested for each method,this study demonstrated the effectiveness of the non-uniform grid method in reducing the point cloud data for freeform shaped parts.5.ConclusionIn this paper,a procedure for handling point cloud data acquired by laser scanners has been studied.As thetechnologyFig.15.Errors at different reduction ratios (for sample model 2).(a )Positive deviation.(b )Negative deviation.of scanning devices improves,it is likely that the speed of data acquisition will increase,and this will automatically increase the amount of point data that must be handled.From the point of view of part shape and z -axis error occurring in laser scanning,the data reduction methods using non-uniform grids are proposed and implemented.These non-uniform grid methods are implemented either by using one-directional or bi-directional non-uniform grids.The proposed methods are applied to sample models having freeform shapes,and the results are analysed in comparison with the other conventional methods.The proposed methods demonstrated that data reduction can be performed effectively while maintaining the quality of the point data.When a complete 3D model of a part needs to be processed,these 2D grid methods may not be suitable,since they are projection-based techniques.However,these methods are still useful if the registration of point clouds is performed after reducing the data size for each point cloud.The non-projection based data reduction method that deals with 3D scanned data will be the subject of our further research.References1.B.L.Curless,“New methods for surface reconstruction from range images”,PhD thesis,Stanford University,June 1997.2.S.Gaspardo,“Applications of reverse engineering”,Rapid Proto-typing and Manufacturing ’99Conference,Rosemont,Illinois,USA,vol.3,pp.515–518,1999.3.R.R.Martin,I.A.Stroud and A.D.Marshall,“Data reduction for reverse engineering”,RECCAD,Deliverable Document 1。
Using environmentally friendly geotextiles for soil reinforcement
Technical ReportUsing environmentally friendly geotextiles for soil reinforcement:A parametric studyAbrahams Mwasha *University of West Indies,Researching Construction Materials and Problematic Soils,St.Augustine Campus,Port of Spain,Trinidad and Tobagoa r t i c l e i n f o Article history:Received 29May 2008Accepted 4July 2008Available online 19July 2008a b s t r a c tBuilt environment protection is important because construction represents a major contribution to cli-mate change,resource depletion and pollution at a global level.Global strategy for more sustainable con-struction is a significant step towards a more successful,socially and environmental friendly atmosphere making a strong contribution to the better quality of life signaled by sustainable development strategy.The brightest sustainable strategy in ground engineering is the consideration of substituting the use of biodegradable materials as substitute to the non-biodegradable (man-made materials)in a situation where there is requirement for short-term ground improvement.The most important properties of bio-degradable geotextiles such as vegetable fibres for soil reinforcement are their high initial tensile strength.Widespread use of biodegradable fabrics in ground engineering has not happened due to the limited service life of these fabrics and availability of chemical fibres,which are superior to vegetable fibres.The overall aim of this paper demonstrates the potential for the use of sustainable biodegradable vegetable fibres over man-made polymeric materials in ground improvement.Ó2008Elsevier Ltd.All rights reserved.1.IntroductionLow-cost roads whether bound or unbound,reinforced or unreinforced are exposed to both short-term and long-term re-peated,high and focused loads which can cause premature fail-ure.The major applications of reinforcement during road construction are to strengthen the pavement,provide an in-creased working life,reduce deflections,reduce rutting and fati-gue cracking and reduce the amount of base materials.A wide range of ground conditions,require a wide range of reinforcement products as well as the duration of which reinforcement is re-quired during the life cycle of either bound or unbound roads.The question on whether reinforcement is required for short-term or long-term should be addressed during the design period since one style of geotextiles will not be optimal for all ground types.The potential to reduce construction materials in these roads saves on the export and import of materials from site,by using sustainable materials such as limited life geotextiles manufac-tured using vegetable fibre especially in developing countries where vegetable fibres are abundant.Environment protection is important because construction rep-resents a major contribution to climate change,resource depletion and pollution at a global level.This strategy for more sustainable construction is a significant step towards a more successful,so-cially and environmental friendly atmosphere making a strongcontribution to the better quality of life signaled by our sustainable development strategy.Consumption of plastics by the building and construction sec-tor in Western Europe is predicted to rise by more than 60%,to almost 8million tones in 2010.Construction is already the second largest market for plastics after packaging,accounting for 20%(4.89million tonnes)of total plastics consumption in 1995.High consumption of plastics in construction industry has critical envi-ronmental effects since 47chemical plants ranked highest in car-cinogenic emissions by the Environmental Protection Agency (EPA),35are involved in plastic production.Plastics such as poly-vinyl chloride (PVC),used for indoor and outdoor construction works are potential sources of highly toxic dioxins [1].Other polymeric materials used in construction such as polystyrene products are often made with chlorofluorocarbons (CFCs)and hydrochlorofluorocarbons (HCFCs),both of which are ozone-destroying chemicals.There are many other disadvantages associated with the use of polymeric materials in construction industry such as:The polymeric materials are manufactured using petroleum products which are expensive especially for the developing countries.Polymeric materials are usually non-renewable resource. Polymeric materials can create environmental pollutants.As litter it defiles private and public land and poses a serious threat to domestic and wildlife often causing death through suf-focation or entanglement.0261-3069/$-see front matter Ó2008Elsevier Ltd.All rights reserved.doi:10.1016/j.matdes.2008.07.018*Tel.:+1(868)6622002.E-mail address:amwasha@Materials and Design 30(2009)1798–1803Contents lists available at ScienceDirectMaterials and Designj o u r n a l h o m e p a g e :w w w.e l s e vier.c om/loc ate/matdesUNCTAD[2]identified two approaches to reduce harmful envi-ronmental impacts namely:Reduce the consumption in the developed countries,while con-comitantly avoiding replication in developing countries of the consumption patterns of the developed ones.Reduce the environmental impact of consumption by identifying environmentally preferable products with less harmful environ-mental impacts during their life cycles,improve the awareness of consumers and industries about the existence of such alterna-tives,improve the competitiveness of these products,and shift demand towards them.2.Applications of vegetablefibres for ground engineeringThe biobased geotextiles research project has been conducted by several Institutions in United Kingdom by[3–5]in USA by USDA (United States Department of Agriculture)Forest services,Forest Products laboratory(FPL).Today most biodegradable geotextiles are used in erosion control where they serve to stabilize the soil surface while natural vegetation is established.There are other numerous ground engineering situations where the critical period for stability is immediately,or very shortly,after construction,e.g.any form of‘foundation loading’of free-draining or slow-draining soils.In such situations it is common practice to incorporate geosynthetic basal reinforcement to provide an addi-tional stabilizing force.If the foundation soil is slow-draining then loading of the ground will create pore pressure excess within the foundation.Subsequently,with time,pore water in the foundation will migrate from beneath the loaded area and the shear strength of the foundation will increase.Hence the stability of the system will improve in time and so the stabilizing force,which needs to be provided by the geosynthectic,will diminish.After a certain time(typically between a few months and a few years)the whole system will be stable with little or no assistance from the geosyn-thetic–in many cases the geosynthetic becomes totally redundant. It is the authors’contention that,in such a situation,the use of a non-conventional geosynthetic,which has a limited,but predict-able working life,is sound engineering practice this is the concept of limited life geotextiles[6].For the foregoing situation the variation of required tensile strength of the reinforcing geosynthetic with time has been desig-nated as the design time-strength envelope for the geosynthetic, i.e.it defines the minimum tensile strength that the geosynthetic must have at any time in its design life.Vegetablefibres are an ideal‘raw material’for the manufacture of limited life geotextiles (LLGs).Such materials certainly degrade with time,but there is a huge range of naturalfibres available and these exhibit very differ-ent strength and durability characteristics such as:Somefibres have very high initial tensile strength–for instancea Sisalfibre is almost as strong as the equivalent polyesterfibrewhich itself would be about three times the strength of the cor-responding coirfibre.Somefibres exhibit very slow,progressive loss of tensile strength with time–a coirfibre subjected to cycles of wetting and drying would only lose around8%of its strength after6 months,20%after12months and30%after2years,whereas with Flax the corresponding strength losses would be45%,60% and90%,respectively[7].3.Basal reinforcement of an embankment built on soft clayIn order to investigate the potential for the use of vegetablefi-bres geotextiles(VFGs)in ground engineering a parametric study was undertaken of the time-dependent basal reinforcement requirements of an embankment built on a normally consolidated, saturated,soft,clay layer.Typical3m high embankment was ana-lyzed.On the basis of published data,typical values were assigned to geotechnical parameters relating to foundation soil and the embankment.3.1.Parametric studyFor an embankment constructed on the soft ground,the shear strength of the foundation soil is increasing with time.To show how this increase in shear strength will affect the stability of slopes,the parametric study was conducted.The parameters for embankment,foundation soil are shown in Table1.In order to specify the number of analyses to be undertaken,the factors which affect the behaviour of embankments were priori-tized.The highest priority factors were embankment slope,and effective friction angle of the foundation soil(15°;20°;23°;26°) as illustrated in Table1.For this preliminary investigation the embankment was assumed to be composed of free-drainingfill and a range of typical embankment face slopes(from1vertical: 2horizontal to1v:5h)was analyzed.It was assumed that the embankmentfill was placed instantaneously,i.e.there was no con-solidation during construction.Post-construction consolidation of the foundation soil was accounted for by using one-dimensional consolidation theory.A rotational stability analysis was used to back-calculate the reinforcement force required to achieve a par-ticular factor of safety at any given time after completion of con-struction using computer program GEO5[8].The behaviour of an embankment was investigated by observ-ing the change in Factor of Safety(FOS)with time.As the Time Fac-tor(Tv)increases,the consolidation increases and the stability of all slopes increase regardless of the slope angle as shown in Fig.1.In fact this increase means that even though all slopes are initially unstable at Tv is zero i.e.all have a FOS less than unity, they subsequently acquire FOS in excess of unity,i.e.they become stable when consolidated.Further investigation on the stability of slope was conducted by varying the degree of consolidation(Time factor varying from0.01 to2.00).The consolidation effect was registered by varying the fac-tor of safety.From Fig.2it is shown that if minimum factor of safety is taken as unity then with time the consolidation will increase the resist-ing moment by enhancing the shearing resistance of soil.Another way to increase the resisting moment is to include soil reinforce-ment where horizontal force multiplied by the distance from the centre of rotation of the failure surface.If the lever arm is more or less constant with time then as the value of the required added resisting moment decreases then so does the horizontal force pro-vided by the soil reinforcement.On considering the time factorTable1Typical value of the relevant parameters for the parametric studyEmbankment Typical slopes(V:H)Slope range chosen for analysisV:H1v:1h to1v:5h1v:2h to1v:5hTypical shear strengthparametersSelected shear strengthparametersc0=0(kN/m2),/0=35–41°c0(kN/m2)=0,/0=35°and41°Range of bulk unit weight Selected bulk unit weight18–20(kN/m3)18(kN/m3)Soft soil Typical shear strengthparametersSelected shear strengthparametersc0=0,/0=14–26°c0=0,/0=14–26°Range of bulk unit weight Selected bulk unit weight15–20(kN/m3)15–22(kN/m3)A.Mwasha/Materials and Design30(2009)1798–18031799then the amount of required reinforcement to stabilize the slope must vary with the slope angle.If the duration of reinforcement that could be required to reinforce slope1:5will take5.4months to attain stability(FOS=1)for slope V:H=1:4,11months will be required to attain the same stability.Depending on the slope angle limited life geotextiles could be a solution on maintaining stability of these slopes.In this work it is considered that the stability of slope is satisfactory if FOS is not less than1.2.In Fig.3it is clearly shown that in order to maintain FOS=1.25for slope1:3,7years are required while just3and1.5years for slopes1:4and1:5, respectively.In order to maintain FOS=1.4,7years are required for slope1:4and3.0years for slope1:5.The conclusion to be drawn from this analysis is that reinforcement is needed for lim-ited time.4.Time-strengthening envelopThe slope stability is performed to ensure that the resisting mo-ment is sufficiently greater than disturbing moment tending to cause a slope to fail.The calculations usually consist of computing factor of safety which is the smallest value of the ratio of the resist-ing forces F p to the driving forces F A.FOS¼F pF Að1ÞThis factor of safety(FOS)could be defined with respect to mo-ment and load as shown in expression1.The global factor of safety (F GLOBAL)expression2is obtained by directly adding reinforcement strength as passive force in the expression1traditional method.F GLOBAL¼PF PþT R YRP að2ÞR–radius of critical slip surface;T R–required geotextiles tensile strength for the given factor of safety;Y–lever arm of reinforce-ment;W–weight of soil mass;a–inclination of the slice base to the horizontal.Therefore global factor of safety F GLOBAL is composed of FOS from soil alone(FOS ALONE)as well as FOS TR.FOS TRis the result of adding resisting force from reinforcement T R with the active force compo-nent in expression3,Y is lever arm of reinforcement and R is the1800 A.Mwasha/Materials and Design30(2009)1798–1803radius of critical slip circle.T R is the resulting force in the horizon-tal direction provided by the reinforcementF GLOBAL¼F SOILþYRT RP Wsin að3ÞBy dividing both sides of Eq.(4)by F GLOBAL it is possible to obtain re-quired mobilized reinforcement strength(T RM)in expression5 which can be re-written as expression6.1¼F SOIL ALONEF GLOBALþYRT RF GLOBAL1P Wsin að4Þ1¼F SOIL ALONEF GLOBALþYRT RM1P Wsin a¼Kð5ÞIf YR1P Wsin a¼KTherefore expression5can be rewritten as1¼F SOIL ALONEF GLOBALþT RM Kð6ÞK depends on critical circle centre parameters and driving moment.From expression6,it is possible to estimate the amount of re-quired mobilized reinforcement on varying the time factor asillustrated in Fig.3where is revealed that immediately after end-ing of construction(T v=0.00)in order to maintain FOS=1,theamount of required reinforcement is at maximum and is reducedwith time.This phenomenon does not apply when the FOS is more thanunity.For FOS=1.20;1.50and2.00at T v=0.00the amount of re-quired reinforcement is lower but rises sharply to when T v=0.1and then lowers again.Generally it was found that for slopeV:H=1:3,there was need for reinforcement at T v=0.3;T v=0.62to maintain FOS=1and1.2,respectively.The amount of reinforce-A.Mwasha/Materials and Design30(2009)1798–18031801ment required to maintain stability for FOS 2.00and 1.5at the end of consolidation (T v =2)was reduced by 73%and 86%,respectively.The effect of degree of consolidation on the stability of slopes is shown in Fig.4.In this case if the degree of consolidation is 25%there is no required reinforcement to maintain stability for slope 1:5.If at the end of construction of slope 1:2amount of reinforce-ment required was 75kN/m,there was no need of reinforcement after 85%consolidation of the foundation Table 4.5.Identification of suitable vegetable fibres as reinforcing materialsThe most appropriate method of selecting suitable vegetable fi-bres for use as geotextile is through eliminating the most unsuit-able fibres after doing a literature review of characteristic properties.The chemical composition of plant fibres which could be used in ground strengthening are given in Table 2.The main aspects of the production/extraction of vegetable fi-bres which has influence as the base materials for making textiles are:The quantity of fibre obtained from a plant must be adequate to make fibre extraction a viable proposition.There must be a practical and economical procedure for extract-ing the fibres,without causing damage to them if they are to be of any value as a geotextile material.The pertinent properties of the fibre must be equivalent or supe-rior to the existing chemical fibres.The annual yield of the fibre must be repeatable and sufficiently large to sustain the demand for the raw fibres.The lack of demand (availability)for the fibre properties on the market.On comparing vegetable fibre properties with synthetic and other natural fibre the general properties of chemical fibres tend to fall into distinct categories.As shown in Table 3the strength of cotton fibre is higher by 67%but extensibility is lower by 70%when compared to polyethylene.Synthetic fibres have relatively low moisture uptake.Ghavami et al.[9]found that VFGs have superior soil reinforce-ment properties when compared to mid-range synthetic geotex-tiles,when considering average tensile strength between 100and 200kN/m at approximately 10%failure strain and frictional resis-tance (a approximately 1).Pritchard noted that the high degree of frictional resistance of the VFGs was probably developed from both the coarseness of the natural yarns and the novel structure forms.6.Durability of vegetable fibre as construction material Durability and mechanical properties of vegetable fibre i.e.sisal and coir for the reinforcement of ground has been reported by [10].The authors studied the behaviour of composite soil reinforced with natural fibres.They measured the mechanical properties of long and short sisal fibres and compared them with that of coconut fibres.The durability of the fibres were assessed by immersing in drinking water for 30days intervals for 210days.All the samples were dried before testing.The results confirmed the superiority of sisal tensile strength when compared with coconut fibres.Mean values of tensile strength of 580Mpa and 150Mpa for sisal and coconut fibres,respectively,was recorded.The authors investi-gated the behaviour of soil fibre-composite and they found the fail-ure mode of the specimen made of natural clay soil was very quick and almost without warning.This indicated that the unreinforced soil is relatively more brittle than the reinforced soil.There are abundant supply of VFGs in the market for preventing soil erosion.These geotextiles could be used for soil strengthening according to specifications shown in Table 5.These woven geotextiles are made to matrix by running the yarns in warp and weft direction forming open mesh matrix.The open area vary according to the number of warp and weft yarn running in a specified area.These woven geo-textiles can be made out of either coconut coir yarn or high tensile bristle machine spun coir twine [11].The characteristics of these two grades of geotextiles are as follows:Table 2Chemical composition of plant fibres [9]FibreCellulose Hemicellulose Pectin Lignin Extractives Fats and waxes Per cent dry weight Cotton 91.8 6.3–– 1.10.7Flax (bast)71.218.5 2.0 2.2 4.3 1.6Hemp (bast)78.3 5.4 2.5 2.9––Jute (bast)71.513.30.213.1 1.20.6Coir (brown)35.615.4 5.132.7 3.0–Coir (white)36.715.2 4.732.5 3.1–Coir pith 19.911.97.053.30.3–Sisal 73.113.30.911.0 1.30.3Abaca70.221.70.65.61.60.2Table 4Specification of available coir fibe geotextiles [11]SpecificationASTM TEST 400g/m 2700g/m 2900g/m 2Weight/m 2ASTM 460780980d-3776Tensile strength-dry–wetASTM 28/26kg s 58/47kg s 78/47kg s d-4632ASTM 18/19kg s 48/28kg s 62/38kg s d-4632Elongation at failure-dry–wetASTM 38/29%41/34%33/34%d-4632ASTM 33/30%43/37%40/40%d -4632Table 3Comparing values of physical properties for some important fibres Physical properties Polyethylene (PE)Polypropylene (PP)Polyester (PET)Cotton Strength2–45–95–103–7Extensibility (%)20–4015–3010–208–10Moistureabsorption (%)0007.00Density (g/cm3)0.950.911.381.541802A.Mwasha /Materials and Design 30(2009)1798–1803Coir yarn geotextiles–high wet tensile strength and functional longevity of2–4years combined with heavier weight is suitable for use in less steep slopes.Coir twine geotextiles–due to its high tensile strength and func-tional longevity of5–7years,these mats can be used in very steep slopes.The standard weighs of the coir yarn and coir twine woven geotextiles are400,700and900g/m squired.As shown in Table5VFGs such as Sisal could be used for short-term reinforcement for an embankment erected on the soft soil.7.Conclusion and recommendationsCareful analysis and selection of the materials used and the way they are combined can yield significant improvements in cost effectiveness and energy efficiency in construction industry.Vege-tablefibre geotextiles provide an invaluable solution to the prob-lem of constructing embankments over soft compressible ground.A review of the strengths and weakness of the vegetablefibre geo-textiles in relation to the competition is essential for its competi-tive positioning.It is essentially important to recognize the opportunities that can be taken advantage of the entire shortcom-ing the product has to face and tackle effectively.Since the user of geotextiles in civil engineering vary greatly,it is important to develop products as per end user requirement with design and specifications criteria and cost factor should be custom-ized with specified norms.Standardization of the vegetablefibre geotextiles(VFGs)for soil reinforcement with defined specifica-tions are always possible in view of the variation in characteristics of the products required by users depending upon the applications and site parameters.This paper is based on parametric study with no consideration of particular type of climatic zone including soil salinity and con-taminated effects.Future study on these areas in general is rec-ommended to undertakefield trial in the countries producing potentialfibres for geotextiles such as Trinidad and Tobago so that the biodegradation of VFGs can be controlled with strength gain of the foundation soil in this particular climatic and soil condition.References[1]</pilot_projs/PVC_FAQ.pdf>;cited2008.[2]World Trade Organization;1994</en/docs/edmmisc232add33_en.pdf>;cited2007<http://www.civilengineeringnetbase.com/books/5371/wp9097fm.pdf>;cited2007.[3]Sarsby R,Mwasha A,Searle D,Karri RS.Sisalfibre geotextiles for soilstrengthening.In:8ICG8th international geosynthetics conference lpress Science Publisher.ISBN:9059660447;2006.[4]Mwasha A.Limited life geotextiles for reinforcing an embankment on softground.PhD thesis,University of Wolverhampton;2005.[5]Mwasha A,Sarsby e of vegetablefibre geotextiles(VFGs)for groundimprovement.Proceedings Cobra,University Wolverhampton;2003.[6]Sarsby RW.Limited life geotextiles2007.[7]Prichard M.Vegetablefibre geotextiles.PhD thesis,Bolton Institute;1999.[8]GEO5Geotechnical Software SuiteÓ1999–2007environmental expert S.L.<http://www.environmental-expert>;cited2008.[9]Ghavami K,Tolêdo RD,Filho,Filho Barbosa NP.Behaviour of composite soilreinforced with naturalfibres.Cem Concr Compos1999;21:39–48.[10]Kirby RH.Vegetablefibres.World crops books.London UK:Leonard Hill Ltd.;1963.[11]</default.html>;cited2008.Table5Required and available time-strength envelopsTensile force required(kN/m)for1v:2h Duration after erection of an embankment(years)012345F GLOBAL=190543222128 Plain weave,sisal(warp/weft-2layers)135********Knitted,flux grid/weft sisal inlay-2layers11558322212A.Mwasha/Materials and Design30(2009)1798–18031803。
2002年全国硕士研究生考试英语阅读理解_2002年全国硕士研究生考试英语试卷及答案
2002年全国硕士研究生考试英语阅读理解_2002年全国硕士研究生考试英语试卷及答案考生注意事项?1．考生必须严格遵守各项考场规则，得到监考人员指令后方可开始答题。
?2．答题前，考生应将答题卡上的“考生姓名”、“报考单位”、“考试语种”、“考生编号”等信息填写清楚，并与准考证上的一致。
?3．全国硕士研究生入学考试英语分为试题（一）、试题（二）。
?4．本试题为试题（一），共4页（1～4页）。
考生必须在规定的时间内作答。
?5．试题（一）为听力部分。
该部分共有A、B、C三节，所有答案都应填写或填涂在答题卡1上。
A、B两节必须用蓝（黑）圆珠笔答题，注意字迹清楚。
C节必须用2B铅笔按照答题卡上的要求填涂，如要改动，必须用橡皮擦干净。
?6．听力考试进行时，考生应先将答案写或标记在试题上，然后在听力部分结束前专门留出的5分钟内，将答案整洁地誊写或转涂到答题卡1上。
仅写或标记在试题上不给分。
Section I Listening prehension?Directions:This Section is designed to test your ability to understand spoken English. You will hear a selection of recorded materials and you must answer the questions that acPAny them. There are three parts in this section, Part A, Part B and Part C.?Remember, while you are doing the test, you should first put down your answers in your test booklet. At the end of the listening prehension section, you will have 5 minutes to transfer all your answers from your test booklet to ANSWER SHEET 1.Now look at Part A in your test booklet.?Part A?Directions:For Questions 1-5, you will hear an introduction about the life of Margaret Welch. While you listen, fill out the table with the information you#39;ve heard. Some of the information has been given to you in the table. Write only 1 word or number in each numbered box. Youwill hear the recording twice. You now have 25 seconds to read the table below. (5 points)?Welch#39;s Personal InformationPlace of Birth PhiladelphiaYear of Birth 1901Transfer to Barnard University (Year) 1920Major at University 1Final Degree PhDYear of Marriage 1928Growing Up In New Guinea Published (Year) 2Field Study in the South Pacific (Age) 3Main Interest 4Professorship at Columbia Started (Year) 5Death (Age) 77Part BDirections:For questions 6-10, you will hear a talk by a well-known U.S. journalist. While you listen, plete the sentences or answer the questions. Use not more than 3 words for each answer. You will hear the recording twice. You now have 25 seconds to read the sentences and questions below. (5 points)?_____________________________________________________ _______________________Besides reporters, who else were ced out for days outside the speaker#39;s home? 6One reporter got to the speaker#39;s apartment pretending to pay 7The speaker believed the reporter wanted a picture of her looking 8Where is a correction to a false story usually placed? 9According to the speaker, the press will lost readers unless the editors and the news directors 10Part CDirections:You will hear three pieces of recorded material. Before listening to each one, you will have time to read the questions related to it. While listening, answer each question by choosing A, B, C or D. After listening, youwill have time to check your answers. You will hear each piece once only. (10 points)??Questions 11 - 13 are based on a report aboutchildren#39;s healthy development. You now have 15seconds to read Questions 11 - 13.??11. What unusual question may doctors ask when giving kids a checkup next time?［A］ How much exercise they get every day.?［B］ What they are most worried about.?［C］ How long their parents acPAny them daily.?［D］ What entertainment they are interested in.?12. The academy suggests that children under agetwo .?［A］ get enough entertainment.?［B］ have more activities.?［C］ receive early education.?［D］ have regular checkups.??13. According to the report, children#39;s bedrooms should .?［A］ be no place for play.?［B］ be near a mon area.?［C］ have no TV sets.?［D］ have a puter for study.??Questions 14 - 16 are based on the following talk about how to save money. You now have 15 seconds to read Questions 14 - 16.??14. According to the speaker, what should one pay special attention to if he wants to save up??［A］ Family debts. ? ［B］ Bank savings.?［C］ Monthly bills. ? ［D］ Spending habits.15. How much can a person save by retirement if he gives up his pack-a-day habit??［A］ $190,000.? ［B］ $330,000.? ［C］ $500,000. ? ［D］ $1,000,000.??16. What should one do before paying monthly bills, if he wants to accumulate wealth??［A］ Invest into a mutual fund.?［B］ Use the discount tickets.?［C］ Quit his eating-out habit.?［D］ Use only paper bills and save coins.??Questions 17-20 are based on an interview with Herbert A. Glieberman, a domestic-relations lawyer. You now have 20 seconds to read Questions 17 - 20.??17. Which word best describes the lawyer#39;s prediction of the change in divorce rate??［A］ Fall.? ［B］ Rise. ? ［C］ V-shape.18. What do people nowadays desire to do concerning their marriage??［A］ To embrace changes of thought.?［B］ To adapt to the disintegrated family life.?［C］ To return to the practice in the #39;60s and#39;70s.?［D］ To create stability in their lives.??19. Why did some people choose not to divorce 20 years ago??［A］ They feared the plicated procedures.?［B］ They wanted to go against the trend.?［C］ They were afraid of losing face.?［D］ they were willing to stay together.??20. Years ago a divorced man in a PAny would have .?［A］ been shifted around the country.?［B］ had difficulty being promoted.?［C］ enjoyed a happier life.?［D］ tasted little bitterness of disgrace.??Section II Use of EnglishDirections:Read the following text. Choose the best word(s) for each numbered blank and mark A, B, C or D on ANSWER SHEET 1. (10 points)??parisons were drawn between the development of television in the 20th century and the diffusion of printing in the 15th and 16th centuries. Yet much had happened ( 21 ) . As was discussed before, it was not ( 22 ) the 19th century that the newspaper became the dominant pre-electronic ( 23 ) , following in the wake of the phlet and the book and in the ( 24 ) of the periodical. It was during the same time that the munications revolution ( 25 ) up, beginning with transport, the railway, and leading ( 26 ) through the telegraph, the telephone, radio, and motion pictures( 27 ) the 20th-century world of the motor car and theair plane. Not everyone sees that process in ( 28 ) . It is important to do so.?It is generally recognized, ( 29 ) , that the introduction of the puter in the early 20th century,( 30 ) by the invention of the integrated circuit during the 1960s, radically changed the process, ( 31 ) its impact on the media was not immediately ( 32 ) . As time went by, puters became smaller and more powerful, and they became “personal" too, as well as ( 33 ) , wi th display being sharper and storage ( 34 ) increasing. Theywere thought of, like people, ( 35 ) generations, withthe distance between generations much ( 36 ).?It was within the puter age that the term“information society" began to be widely used todescribe the ( 37 ) within which we now live. The munications revolution has ( 38 ) both work and leisure and how we think and feel both about place and time, but there have been ( 39 ) view about its economic, political, social and cultural implications. "Benefits"have been weighed ( 40 ) “harmful" outes. And generalizations have proved difficult.??21. ［A］ between ［B］ before ［C］ since ［D］later22. ［A］ after ［B］ by ［C］ during ［D］ until23. ［A］ means ［B］ method ［C］ medium ［D］measure24. ［A］ process ［B］ pany ［C］ light ［D］ form25. ［A］ gathered ［B］ speeded ［C］ worked ［D］picked26. ［A］ on ［B］ out ［C］ over ［D］ off27. ［A］ of ［B］ for ［C］ beyond ［D］ into28. ［A］ concept ［B］ dimension ［C］ effect ［D］perspective29. ［A］ indeed ［B］ hence ［C］ however ［D］therefore30. ［A］ brought ［B］ followed ［C］ stimulated ［D］ characterized31. ［A］ unless ［B］ since ［C］ lest ［D］although32. ［A］ apparent ［B］ desirable ［C］ negative ［D］ plausible33. ［A］ institution ［B］ universal ［C］fundamental ［D］ instrumental34. ［A］ ability ［B］ capability ［C］ capacity ［D］ faculty35. ［A］ by means of ［B］ in terms of ［C］ with regard to［D］ in line with36. ［A］ deeper ［B］ fewer ［C］ nearer ［D］smaller37. ［A］ context ［B］ range ［C］ scope ［D］territory38. ［A］ regarded ［B］ impressed ［C］ influenced ［D］ effected39. ［A］ petitive ［B］ controversial ［C］distracting ［D］ irrational40. ［A］ above ［B］ upon ［C］ against ［D］ withSection III Reading prehensionPart ADirections:Read the following four texts. Answer the questions below each text by choosing A, B, C or D. Mark your answers on ANSWER SHEET 1. (40 points)?Text 1?If you intend using humor in your talk to make people smile, you must know how to identify shared experiences and problems. Your humor must be relevant to the audience and should help to show them that you are one of them or that you understand their situation and are in syMPAthy with their point of view. Depending on whom you are addressing, the problems will be different. If you are talking to a group of managers, you may refer to the disorganized methods of their secretaries; alternatively if you are addressing secretaries, you may want to ment on their disorganized bosses.?Here is an exle, which I heard at a nurses#39; convention, of a story which works well because the audience all shared the same view of doctors. A manarrives in heaven and is being shown around by St. Peter. He sees wonderful acmodations, beautiful gardens, sunny weather, and so on. Everyone is very peaceful,polite and friendly until, waiting in a line for lunch, the newarrival is suddenly pushed aside by a man in a white coat, who rushes to the head of the line, grabs his food and stomps over to a table by himself. “Who is that?" thenew arrival asked St. Peter. “On, that#39;s God," camethe reply, “but sometimes he thinks h e#39;s a doctor."?If you are part of the group which you are addressing, you will be in a position to know the experiences and problems which are mon to all of you and it#39;ll be appropriate for you to make a passing remark about the inedible canteen food or the chairman#39;s notorious bad taste in ties. With other audiences you mustn#39;tattempt to cut in with humor as they will resent an outsider making disparaging remarks about their canteenor their chairman. You will be on safer ground if youstick to scapegoats like the Post Office or the telephone system.?If you feel awkward being humorous, you must practice so that it bees more natural. Include a few casual and apparently off-the-cuff remarks which you can deliver ina relaxed and unforced manner. Often it#39;s the delivery which causes the audience to smile, so speak slowly and remember that a raised eyebrow or an unbelieving look may help to show that you are making a light-hearted remark.Look for the humor. It often es from the unexpected.A t wist on a familiar e “If at first you don#39;t succeed, give up" or a play on words or on a situation. Search for exaggeration and understatements. Look at your talk and pick out a few words or sentences which you can turn about and inject with humor. (447 words)??41. To make your humor work, you should . ?［A］ take advantage of different kinds of audience.?［B］ make fun of the disorganized people.?［C］ address different problems to different people.?［D］ show syMPAthy for your listeners.??42. The joke about doctors implies that, in the eyesof nurses, they are .?［A］ impolite to new arrivals.?［B］ very conscious of their godlike role.?［C］ entitled to some privileges.?［D］ very busy even during lunch hours.?43. It can be inferred from the text that public services .?［A］ have benefited many people.?［B］ are the focus of public attention.?［C］ are an inappropriate subject for humor.?［D］ have often been the laughing stock.??44. To achieve the desired result, humorous stories should be delivered .?［A］ in well-worded language.?［B］ as awkwardly as possible.?［C］ in exaggerated statements.?［D］ as casually as possible.??45. The best title for the text may be .?［A］ Use Humor Effectively.?［B］ Various Kinds of Humor.?［C］ Add Humor to Speech.?［D］ Different Humor Strategies.?Text 2?Since the dawn of human ingenuity, people have devised ever more cunning tools to cope with work that is dangerous, boring, burdensome, or just plain nasty. That pulsion has resulted in robotics—the science of conferring various human capabilities on machines. And if scientists have yet to create the mechanical version of science fiction, they have begun to e close.?As a result, the modern world is increasingly populated by intelligent gizmos whose presence we barely notice but whose universal existence has removed much human labor. Our factories hum to the rhythm of robot assembly arms. Our banking is done at automated teller terminals that thank us with mechanical politeness for the transaction. Our subway trains are controlled by tireless robo-drivers. And thanks to the continual miniaturization of electronics and micro-mechanics, there are already robot systems that can perform some kinds of brain and bonesurgery with submillimeter accuracy—far greater precision than highly skilled physicians can achieve with their hands alone.?But if robots are to reach the next stage of laborsaving utility, they will have to operate with lesshuman supervision and be able to make at least a few decisions for themselves—goals that pose a real challenge. “While we know how to tell a robot to handle a specific error," says Dave Lavery, manager of arobotics program at NASA, “we can#39;t yet give a robot enough #39;mon sense#39; to reliably interact with a dynamic world."?Indeed the quest for true artificial intelligence has produced very mixed results. Despite a spell of initial optimism in the 1960s and 1970s when it appeared that transistor circuits and microprocessors might be able to copy the action of the human brain by the year 2021, researchers lately have begun to extend that forecast by decades if not centuries.?What they found, in attempting to model thought, is that the human brain#39;sroughly one hundred billion nerve cells are much more talented—and human perception far more plicated—than previously imagined. They have built robots that can recognize the error of a machine panel by a fraction of a millimeter in a controlled factory environment. But the human mind can glimpse a rapidly changing scene and immediately disregard the 98percent that is irrelevant, instantaneously focusing onthe monkey at the side of a winding forest road or the single suspicious face in a big crowd. The most advanced puter systems on Earth can#39;t approach that kind of ability, and neuroscientists still don#39;t know quitehow we do it. ??46. Human ingenuity was initially demonstrated in .?［A］ the use of machines to produce science fiction.?［B］ the wide use of machines in manufacturing industry.?［C］ the invention of tools for difficult and dangerous work.?［D］ the elite#39;s cunning tackling of dangerousand boring work.?47. The word “gizmos" (line 1, paragraph 2) most probably means .［A］ programs.? ［B］ experts.? ［C］ devices. ? ［D］ creatures.??48. According to the text, what is beyond man#39;s ability now is to design a robot that can .?［A］ fulfill delicate tasks like performing brain surgery.?［B］ interact with human beings verbally.?［C］ have a little mon sense.?［D］ respond independently to a changing world.??49. Besides reducing human labor, robots can also .?［A］ make a few decisions for themselves.?［B］ deal with some errors with human intervention.?［C］ improve factory environments.?［D］ cultivate human creativity.??50. The author uses the exle of a monkey to arguethat robots are .［A］ expected to copy human brain in internal structure.?［B］ able to perceive abnormalities immediately.?［C］ far less able than human brain in focusing on relevant information.?［D］ best used in a controlled environment.?Text 3?Could the bad old days of economic decline be about to return? Since OPEC agreed to supply-cuts in March, the price of crude oil has jumped to almost $26 a barrel, up from less than $10 last December. This near-tripling of oil prices calls up scary memories of the 1973 oil shock,when prices quadrupled, and 1979-80, when they also almost tripled. Both previous shocks resulted in double-digitinflation and global economic decline. So where are the headlines warning of gloom and doom this time??The oil price was given another push up this week when Iraq suspended oil exports. Strengthening economic growth, at the same time as winter grips the northern hemisphere, could push the price higher still in the short term.?Yet there are good reasons to expect the economic consequences now to be less severe than in the 1970s. In most countries the cost of crude oil now accounts for a smaller share of the price of petrol than it did in the 1970s. In Europe, taxes account for up to four-fifths of the retail price, so even quite big changes in the price of crude have a more muted effect on pump prices than in the past.?Rich economies are also less dependent on oil than they were, and so less sensitive to swings in the oil price. Energy conservation, a shift to other fuels and a decline in the importance of heavy, energy-intensive industries have reduced oil consumption. Software,consultancy and mobile telephones use far less oil than steel or car production. For each dollar of GDP (in constant prices) rich economies now use nearly 50% less oil than in 1973. The OECD estimates in its latest Economic Outlook that, it oil prices averaged $22 abarrel for a full year, PAred with $13 in 1998, this would increase the oil import bill in rich economies by only 0.25-0.5% of GDP. That is less than one-quarter of the ine loss in 1974 or 1980. On the other hand, oil-importing emerging economies—to which heavy industry has shifted—have bee more energy-intensive, and so could be more seriously squeezed.?One more reason not to lose sleep over the rise inoil prices is that, unlike the rises in the 1970s, it has not occurred against the background of general modity-price inflation and global excess demand. A sizable portion of the world is only just emerging from economic decline. The Economist#39;s modity price index is broadly unchanging from a year ago. In 1973 modity prices jumped by 70%, and in 1979 by almost 30%. ??51. The main reason for the latest rise of oil price is .?［A］ global inflation.? ［B］ reduction in supply.?［C］ fast growth in economy.? ［D］ Iraq#39;s suspension of exports.?52. It can be inferred from the text that the retail price of petrol will go up dramatically if .?［A］ price of crude rises.? ［B］ modity prices rise.［C］ consumption rises. ? ［D］ oil taxes rise.?53. The estimates in Economic Outlook show that inrich countries .［A］ heavy industry bees more energy-intensive.?［B］ ine loss mainly results from fluctuating crudeoil prices.?［C］ manufacturing industry has been seriously squeezed.?［D］ oil price changes have no significant iMPAct on GDP.??54. We can draw a conclusion from the text that .?［A］ oil-price shocks are less shocking now.?［B］ inflation seems irrelevant to oil-price shocks.?［C］ energy conservation can keep down the oil prices.?［D］ the price rise of crude leads to the shrinking of heavy industry.??55. From the text we can see that the writer seems .?［A］ optimistic. ? ［B］ sensitive.? ［C］ gloomy. ? ［D］ scared.?Text 4?The Supreme Court#39;s decisions on physician-assisted suicide carry important implications for how medicine seeks to relieve dying patients of pain and suffering.?Although it ruled that there is no constitutional right to physician-assisted suicide, the Court in effect supported the medical principle of “double effect," a centuries-old moral principle holding that an action having two effects—a good one that is intended and a harmful one that is foreseen—is permissible if the actor intends only the good effect.?Doctors have used that principle in recent years to justify using high doses of morphine to controlterminally ill patients#39; pain, even though increasing dosages will eventually kill the patient.?Nancy Dubler, director of Montefiore Medical Center, contends that the principle will shield doctors who “until now have very, very strongly insisted that they could not give patients sufficient mediation to control their pain if that might hasten death."?George Annas, chair of the health law department at Boston University, maintains that, as long as a doctor prescribes a drug for a legitimate medical purpose, the doctor has done nothing illegal even if the patient uses the drug to hasten death. “It#39;s like surgery," he says. “We don#39;t call those deaths homicides because the doctors didn#39;t intend to kill their patients, although they risked their death. If you#39;re a physician, you can risk your patient#39;s suicide as long as you don#39;t intend their suicide."?On another level, many in the medical munity acknowledge that the assisted-suicide debate has been fueled in part by the despair of patients for whom modern medicine has prolonged the physical agony of dying.?Just three weeks before the Court#39;s ruling on physician-assisted suicide, the National Academy of Science (NAS) released a two-volume report, ApproachingDeath: Improving Care at the End of Life. It identifies the undertreatment of pain and the aggressive use of “ineffectual and forced medical procedures that may prolong and even dishonor the period of dying" as the twin problems of end-of-life care.?The profession is taking steps to require young doctors to train in hospices, to test knowledge of aggressive pain management therapies, to develop a Medicare billing code for hospital-based care, and to develop new standards for assessing and treating pain at the end of life.?Annas says lawyers can play a key role in insisting that these well-meaning medical initiatives translateinto better care. “Large numbers of physicians seem unconcerned with the pain their patients are needlessly and predictably suffering," to the extent that itconsti tutes “systematic patient abuse." He says medical licensing boards “must make it clear…that painful deaths are presumptively ones that are inpetently managed and should result in license suspension."56. From the first three paragraphs, we learn that .?［A］ doctors used to increase drug dosages tocontrol their patients#39; pain.［B］ it is still illegal for doctors to help the dying end their lives.?［C］ the Supreme Court strongly opposes physician-assisted suicide.?［D］ patients have no constitutional right to mit suicide.??57. Which of the following statements its true according to the text??［A］ Doctors will be held guilty if they risk their patients#39; death.?［B］ Modern medicine has assisted terminally ill patients in painless recovery.?［C］ The Court ruled that high-dosage pain-relieving medication can be prescribed.?［D］ A doctor#39;s medication is no longer justified by his intentions.58. According to the NAS#39;s report, one of the problems in end-of-life care is .?［A］ prolonged medical procedures.?［B］ inadequate treatment of pain.?［C］ systematic drug abuse.?［D］ insufficient hospital care.??59. Which of the following best defines the word “aggressive" (line 3, paragraph 7)??［A］ Bold. ? ［B］ Harmful. ? ［C］ Careless. ?［D］Desperate.??60. George Annas would probably agree that doctors should be punished if they .?［A］ manage their patients inpetently.?［B］ give patients more medicine than needed.?［C］ reduce drug dosages for their patients.?［D］ prolong the needless suffering of the patients.??Part BDirections:Read the following text carefully and then translate the underlined segments into Chinese. Your translation should be written clearly on ANSWER SHEET 2. (10 points)??Almost all our major problems involve human behavior, and they cannot be solved by physical and biological technology alone. What is needed is a technology of behavior, but we have been slow to develop the sciencefrom which such a technology might be drawn. 61) One difficulty is that almost all of what is called behavioral science continues to trace behavior to states of mind, feelings, traits of character, human nature, and so on. Physics and biology once followed similar practices and advanced only when they discarded them. 62) The behavioral sciences have been slow to change partly because the explanatory items often seem to be directly observed and partly because other kinds of explanations have been hard to find. The environment is obviously important, but its role has remained obscure. It does not push or pull, it selects, and this function is difficult to discover and analyze. 63) The role of naturalselection in evolution was formulated only a little more than a hundred years ago, and the selective role of the environment in shaping and maintaining the behavior of the individual is only beginning to be recognized and studied. As the interaction between organis m and environment has e to be understood, however, effects once assigned to states of mind, feelings, and traits are beginning to be traced to accessible conditions, and a technology of behavior may therefore bee available. Itwill not solve our problems, however, until it replaces traditional prescientific views, and these are strongly entrenched. Freedom and dignity illustrate the difficulty.64) They are the possessions of the autonomous (self-governing) man of traditional theory, and they are essential to practices in which a person is held responsible for his conduct and given credit for his achievements. A scientific analysis shifts both the responsibility and the achievement to the environment. It also raises questions concerning “values." Who will usea technology and to what ends?65) Until these issues are resolved, a technology of behavior will continue to be rejected, and with itpossibly the only way to solve our problems.Section IV Writing?66. Directions:Study the following picture carefully and write an essay entitled “Cultures —National and International".?In the essay you should?1) describe the picture and interpret its meaning, and?2) give your ment on the phenomenon.?You should write about 200 words neatly on ANSWER SHEET 2. (20 points)?/。
Contact of single asperities with varying adhesion
a r X i v :c o n d -m a t /0606588v 1 [c o n d -m a t .m t r l -s c i ] 22 J u n 2006Contact of Single Asperities with Varying Adhesion:ComparingContinuum Mechanics to Atomistic SimulationsBinquan Luan and Mark O.Robbins Department of Physics and Astronomy,The Johns Hopkins University,3400N.Charles Street,Baltimore,Maryland 21218(Dated:March 22,2006)Abstract Atomistic simulations are used to test the equations of continuum contact mechanics in nanome-ter scale contacts.Nominally spherical tips,made by bending crystals or cutting crystalline or amorphous solids,are pressed into a flat,elastic substrate.The normal displacement,contact radius,stress distribution,friction and lateral stiffness are examined as a function of load and adhesion.The atomic scale roughness present on any tip made of discrete atoms is shown to have profound effects on the results.Contact areas,local stresses,and the work of adhesion change by factors of two to four,and the friction and lateral stiffness vary by orders of magnitude.The microscopic factors responsible for these changes are discussed.The results are also used to test methods for analyzing experimental data with continuum theory to determine information,such as contact area,that can not be measured directly in nanometer scale contacts.Even when the data appear to be fit by continuum theory,extracted quantities can differ substantially from their true values.PACS numbers:81.40.Pq 68.35.Np 62.20.Dc 68.37.PsI.INTRODUCTIONThere has been rapidly growing interest in the behavior of materials at nanometer scales [1].One motivation is to construct ever smaller machines [2],and a second is to improve material properties by controlling their structure at nanometer scales [3].For example,decreasingcrystallite size may increase yield strength by suppressing dislocation plasticity,and material properties may be altered near free interfaces or grain boundaries.To make progress,this research area requires experimental tools for characterizing nanoscale prop-erties.Theoretical models are also needed both to interpret experiments and to allow new ideas to be evaluated.One common approach for measuring local properties is to press tips with characteristic radii of 10to 1000nm into surfaces using an atomic force microscope (AFM)or nanoindenter[4,5,6,7,8,9,10,11,12,13,14,15].Mechanical properties are then extracted from the measured forces and displacements using classic results from continuum mechanics [16].A potential problem with this approach is that continuum theories make two key assumptions that must fail as the size of contacting regions approaches atomic dimensions.One is to replace the atomic structure in the bulk of the solid bodies by a continuous medium with internal stresses determined by a continuously varying strain field.The second is to model interfaces by continuous,differentiable surface heights with interactions depending only on the surface separation.Most authors go further and approximate the contacting bodies by smooth spheres.In a recent paper [17],we analyzed the limits of continuum mechanics in describing nanometer scale contacts between mental probes.As in studies of other bulk could be described by continuum atomic diameters.However,the atomic structure of surfaces had profound consequences for much larger contacts.In particular,atomic-scale changes in the configuration of atoms on nominally cylindrical or spherical surfaces produced factor of two changes in the width of the contacting region and the stress needed to produce plastic yield,and order of magnitude changes in friction and stiffness.In this paper we briefly revisit non-adhesive contacts with an emphasis on the role of surface roughness.We then extend our atomistic studies to the more common case of通常 AFM 的针尖直径在10nm~1000nm 之间。
Fukushima_Accident_2011(世界核能协会)
Organisational acronyms:Tepco = Tokyo Electric Power CompanyNISA = Nuclear & Industrial Safety Agency (Japan, regulator),NSC = Nuclear Safety Commission (Japan, policy body)METI = Ministry of Trade, Economy & Industry (Japan),IAEA = International Atomic Energy Agency (UN body),JAIF = Japan Atomic Industrial Forum (industry body)ISRN = Institute for Radiological Protection & Nuclear Safety (France)Fukushima Daiichi 1-3 & 4Reactors 1-3 were shut down in response to the earthquake, as designed, since the groundacceleration was about 500 Gal. The reactors then reverted to an auxiliary Residual Heat Removal (RHR) cooling system, since the steam is no longer being conveyed to the turbines and condenser circuit. The RHR system is driven by electric pumps. Mains power was lost due to the quake, so the emergency diesel generators located in the basements of the turbine buildings started up to drive this system and ran for 56 minutes, but then stopped when submerged by the tsunami. This put those reactors in a dire situation and led the authorities to order, and subsequently extend, an evacuation while engineers worked to restore power. About nine hours later mobile power supply units had reached the plant and were being connected. The capacity of these would be less than the main plant diesel system. Meanwhile units 1-3 had only battery power, insufficient to drive the main RHR cooling system. The batteries were apparently depleted in about 8 hours anyway.Site and earthquakes: backgroundThe Daiichi (first) and Daini (second) Fukushima plants are sited about 11 km apart on the coast.Japanese nuclear power plants are designed to withstand specified earthquake intensities evident in ground motion. If theyregister ground acceleration of a set level, systems will be activated to automatically bring the plant to an immediate safeshutdown. In this case the set scram level was 135 Gal (150 Gal at Daini). The maximum response acceleration againstdesign basis ground motion for both Fukushima plants had been upgraded since 2006, and is now quoted at horizontal 438-489 Gal for Daiichi and 415-434 Gal for Daini. At this level they must retain their safety functions. In 2008 Tepco upgraded itsestimates of likely Design Basis Earthquake Ground Motion Ss for Fukushima to 600 Gal, and other Japanese operators haveadopted the same figure. The interim recorded data for both plants shows that 550 Gal (0.56 g) was the maximum for Daiichi,in the foundation of unit 2 (other figures 281-548 Gal), and 254 Gal was maximum for Daini. Units 2, 3 and 5 exceeded theirmaximum response acceleration design basis in E-W direction by about 20%. Recording was over 130-150 seconds. Allnuclear plants in Japan are built on rock (ground acceleration was around 2000 Gal a few kilometres north, on sediments).The design basis tsunami height is 5.7 m for Daiichi and 5.2 m for Daini, though the plants were built higher than this abovesea level. Tsunami heights were reported as 14 metres for both plants. Reactors: backgroundThe Fukushima Daiichi reactors are GE boiling water reactors (BWR) of an early (1960s) design supplied by GE and Toshiba,with what is known as a Mark I containment. Reactors 1-3 came into commercial operation 1971-75. Reactor power is 460 MWefor unit 1, 784 MWe for units 2-5, and 1100 MWe for unit 6. The fuel assemblies are about 4 m long, and there are 400 in unit 1,548 in units 2-5, and 764 in unit 6. Each assembly has 60 fuel rods containing the uranium oxide fuel within zirconium alloycladding. Unit 3 has a partial core of mixed-oxide (MOX) fuel (32 MOX assemblies, 516 LEU). They all operate normally at 286°C at core outlet under a pressure of 6930 kPa and with about 400 kPa pressure in dry containment.The BWR Mark I has a Primary Containment system comprising a free-standing bulb-shaped drywell of 30 mm steel backed by areinforced concrete shell, and connected to a torus-shaped wetwell beneath it containing the suppression pool. The drywell, alsoknown as the Primary Containment Vessel (PCV), contains the reactor pressure vessel (RPV). For simplicity, we will use the term'dry containment' here. The water in the suppression pool acts as an energy-absorbing medium in the event of an accident. Thewetwell is connected to the dry containment by a system of vents, which discharge under the suppression pool water in the eventof high pressure in the dry containment. The function of the primary containment system is to contain the energy released duringany loss-of-coolant accident (LOCA) of any size reactor coolant pipe, and to protect the reactor from external assaults. TheJapanese version of the Mark I is slightly larger than the original GE version.During normal operation, the dry containment atmosphere and the wetwell atmosphere are filled with inert nitrogen, and thewetwell water is at ambient temperature.If a loss of coolant accident (LOCA) occurs, steam flows from the dry containment (drywell) through a set of vent lines and pipesinto the suppression pool, where the steam is condensed. Steam can also be released from the reactor vessel through the safetyrelief valves and associated piping directly into the suppression pool. Steam will be condensed in the wetwell, but hydrogen andnoble gases are not condensable and will pressurise the system, as will steam if the wetwell water is boiling. In this caseemergency systems will activate to cool the wetwell, see below. Excess pressure from the wetwell can be vented through the 120m emission stack via a hardened pipe or it may leak into the secondary containment or reactor service floor of the building. If there has been fuel damage, vented gases will include noble gases (krypton & xenon), iodine and caesium, the latter beingscrubbed in some scenarios. Less volatile elements in any fission product release will plate out in the containment. (The laterMark II containments are similar to Mark I, but both are much smaller than the Mark III and those which became standard inPWRs.)The secondary containment houses the emergency core cooling systems and the spent/ used fuel pool. It is not designed to /info/fukushima_accident_inf129.html 2 / 11Fukushima_Accident_2011of high pressure in the dry containment. The function of the primary containment system is to contain the energy released duringany loss-of-coolant accident (LOCA) of any size reactor coolant pipe, and to protect the reactor from external assaults. TheJapanese version of the Mark I is slightly larger than the original GE version.During normal operation, the dry containment atmosphere and the wetwell atmosphere are filled with inert nitrogen, and the wetwell water is at ambient temperature.If a loss of coolant accident (LOCA) occurs, steam flows from the dry containment (drywell) through a set of vent lines and pipesinto the suppression pool, where the steam is condensed. Steam can also be released from the reactor vessel through the safetyrelief valves and associated piping directly into the suppression pool. Steam will be condensed in the wetwell, but hydrogen andnoble gases are not condensable and will pressurise the system, as will steam if the wetwell water is boiling. In this caseemergency systems will activate to cool the wetwell, see below. Excess pressure from the wetwell can be vented through the 120m emission stack via a hardened pipe or it may leak into the secondary containment or reactor service floor of the building. Ifthere has been fuel damage, vented gases will include noble gases (krypton & xenon), iodine and caesium, the latter beingscrubbed in some scenarios. Less volatile elements in any fission product release will plate out in the containment. (The laterMark II containments are similar to Mark I, but both are much smaller than the Mark III and those which became standard inPWRs.)The secondary containment houses the emergency core cooling systems and the spent/ used fuel pool. It is not designed tocontain high pressure.The primary cooling circuit of the BWR takes steam from above the core, in the reactor pressure vessel, to the turbine in anadjacent building. After driving the turbines it is condensed and the water is returned to the pressure vessel. There are also twopowerful jet-pump recirculation systems forcing water down around the reactor core and shroud. When the reactor is shut down,the steam in the main circuit is diverted via a bypass line directly to the condensers, and the heat is dumped there, to the sea. Inboth situations a steam-driven turbine drives the pumps, at least until the pressure drops to about 350 kPa (50 psi). In shutdownmode, the Residual Heat Removal (RHR) system then operates in a secondary circuit (RHR is connected into the two jet-pumprecirculation circuits), driven by electric pumps, and circulates water from the pressure vessel to RHR heat exchangers whichdump the heat to the sea. There is also a Reactor Core Isolation Cooling (RCIC) which can provide make-up water to thereactor,though without any heat removal circuit. It is driven by a small steam turbine using steam from decay heat, injectingwater from a condensate storage tank or the suppression pool. (The NISA account does not mention the RCIC, possibly treatingit as part of the ECCS, though it has been confirmed that the RCIC systems played a helpful role in all three units until thesuppression pool water boiled, to 11am on 12th in unit 3 and to 2pm on 14th in unit 2.)Then there is an Emergency Core Cooling System (ECCS) as further back-up for loss of coolant. It has high-pressure and low-pressure elements. The high pressure coolant injection (HPCI) system has pumps powered by steam turbines which are deignedto work over a wide pressure range. The HPCI draws water from the large torus suppression chamber beneath the reactor as wellas a water storage tank. For use below about 700 kPa, there is also a Low-Pressure Coolant Injection (LPCI) mode through theRHR system but utilising suppression pool water, and a core spray system, all electrically-driven. All ECCS sub-systems requiresome power to operate valves etc, and the battery back-up to generators may provide this.Beyond these original systems, Tepco in 1990s installed provision for water injection via the fire extinguisher system through theRHR system (injecting via the jet-pump nozzles) as part of it Severe Accident Management (SAM) countermeasures./info/fukushima_accident_inf129.html 3 / 11Fukushima_Accident_2011When the power failed about one hour after shutdown, the reactor cores would still be producing about 1.5% of their nominal thermal power, from fission product decay - about 22 MW in unit 1 and 33 MW in units 2 & 3, according to calculations from well-established models. Without heat removal by circulation to an outside heat exchanger, this produced a lot of steam in the reactor pressure vessels housing the cores. The steam would be condensed in the suppression chamber under the reactor, within the containment, but their internal temperature and pressure rose quite rapidly. At4.36 pm water injection using the Emergency Core Cooling System (ECCS), failed in units 1 & 2, less than an hour after power loss. At 7.03 pm a Nuclear Emergency was declared, and at 8.50pm the Fukushima Prefecture issued an evacuation order for people within 2 km of the plant. At 9.23 pm the Prime Minister extended this to 3 km, and at5.44 am on 12th he extended it to 10 km. He visited the plant soon after. At6.25 pm on Saturday 12th he extended the evacuation zone to 20 km.Then there is an Emergency Core Cooling System (ECCS) as further back-up for loss of coolant. It has high-pressure and low-pressure elements. The high pressure coolant injection (HPCI) system has pumps powered by steam turbines which are deignedto work over a wide pressure range. The HPCI draws water from the large torus suppression chamber beneath the reactor as wellas a water storage tank. For use below about 700 kPa, there is also a Low-Pressure Coolant Injection (LPCI) mode through the RHR system but utilising suppression pool water, and a core spray system, all electrically-driven. All ECCS sub-systems requiresome power to operate valves etc, and the battery back-up to generators may provide this.Beyond these original systems, Tepco in 1990s installed provision for water injection via the fire extinguisher system through theRHR system (injecting via the jet-pump nozzles) as part of it Severe Accident Management (SAM) countermeasures.A frequently-voiced concern during the first week of the accident was regarding fuel meltdown. This would start to occur if thefuel itself reached 2500°C (or more, up to 2800°C, depending on make -up). At this point, the fuel rods slump within theassemblies. Conceivably, the “corium ” (a mixture of molten cladding, fuel, and structural steel) begins to move to the bottom ofthe reactor vessel. If the hot fuel or cladding is exposed to cooling water en route, it may solidify and fracture, falling to thebottom of the reactor vessel. Given that the melting point of the steel reactor vessel is about 1500°C, there is an obviouspossibility on the corium penetrating the steel if it remains hot enough. (In fact, in the 1979 US Three Mile Island accident, itdidn't, though about half the core melted and it went 15 mm into the 225 mm thick pressure vessel steel. The pressure vesselglowed red-hot for an hour.) But the whole fuel melt scenario is much more probable with a sudden major loss of coolant whenthe reactor is at full power than in the Fukushima situation. Before this, cladding cracks at about 1200°C, its oxidation begins atabout 1300°C and the Zr cladding melts at about 1850°C. /info/fukushima_accident_inf129.html 4 / 11Fukushima_Accident_2011When the power failed about one hour after shutdown, the reactor cores would still be producing about 1.5% of their nominal thermal power, from fission product decay - about 22 MW in unit 1 and 33 MW in units 2 & 3, according to calculations from well-established models. Without heat removal by circulation to an outside heat exchanger, this produced a lot of steam in the reactor pressure vessels housing the cores. The steam would be condensed in the suppression chamber under the reactor, within the containment, but their internal temperature and pressure rose quite rapidly. At4.36 pm water injection using the Emergency Core Cooling System (ECCS), failed in units 1 & 2, less than an hour after power loss.At 7.03 pm a Nuclear Emergency was declared, and at 8.50pm the Fukushima Prefecture issued an evacuation order for people within 2 km of the plant. At 9.23 pm the Prime Minister extended this to 3 km, and at 5.44 am on 12th he extended it to 10 km. He visited the plant soon after. At 6.25 pm on Saturday 12th he extended the evacuation zone to 20 km.Over the first twelve hours pressure inside the containment structures increased steadily and led to this being vented to the atmosphere repeatedly, starting with unit 1 early on Saturday 12th, where pressure had reached more than three times the design level (840 kPa above the normal 400 kPa). This would damage pump seals and possibly the top O-ring, so that inside, water levels dropped, exposing fuel, and this was addressed by pumping seawater into the reactor pressure vessels (RPV) using external pumps brought to site, starting with unit 1 at 8.20 pm on 12th. This was apparently via the Low Pressure Coolant Injection System, connected into the RHR system. On 25th, water from a nearby dam started to be used instead of seawater. Boron was added to the injected water, to guard against any criticality.Meanwhile, vented gases and vapour included hydrogen, produced by the exothermic interaction of the fuel's very hot zirconium cladding with steam and water. At 3.36 pm on 12th, there was a hydrogen explosion in the building above unit 1 reactor containment, blowing off much of the roof and cladding on the top part of the building, after vented hydrogen mixed with air and ignited. On Sunday 13th, seawater injection to unit 1's Primary Containment started. Pressure inside unit 1 has remained high since then (300-400 kPa), and water injection has been via the feedwater line. On 6 April Tepco started injecting nitrogen into the containment vessel on account of suspected hydrogen levels there.I n unit 2, as mentioned above, water injection using the Emergency Core Cooling System (ECCS) failed at 4.36 pm on 11th. However, the steam-driven Reactor Core Isolation Cooling (RCIC) system functioned until the morning of 14th. Pressure was vented on 13th and again on 15th, and meanwhile the blowout panel near the top of the building was opened. The reactor water level was found to be low on Monday 14th, so seawater injection to the containment was started on 15th, via the fire-fighting line. Then at 6.14 am on Tuesday 15th, unit 2 apparently ruptured its pressure suppression chamber under the actual reactor, releasing some radioactivity and dropping thepressure inside. At 10.30 am Tepco was told to inject water into the pressure vessel and to vent the containment, and these activities continued. Containment damage is suspected. On 1 April Tepco discovered a crack in the wall of a 2m deep cable pit which was leaking highly-contaminated water, apparently from the reactor itself. The company eventually plugged it early in 6 April.In unit 3, the RCIC system failed at 11 am on Saturday 12th and venting the containment was done late in the day. On Sunday 13th, at 5.10 am, water injection using the Emergency Core Cooling System (ECCS) failed in this unit also, and at 9.20 am venting the containment was repeated. At 11.55 am fresh water injection to the RPV commenced, soon being replaced by seawater through to 25th. On Monday 14th at 5.20 am venting was repeated, then at 11.01 am a hydrogen explosion in the building above unit 3 reactor containment blew off much of the roof and walls on the top part of the building. Early on Wednesday 16th there was a major release of smoke and/or steam from the top of the building. Because of the possibility that the Primary Containment of Unit 3 wasdamaged, the operators evacuated from the central control room of Unit 3 & 4 (a shared facility) at 10:45 am, but they returned to the control room and restarted the operation for water injection 45 minutes later. Pressure then built up to 320 kPa in the containment but no further venting wasrequired. Since at least 16th, pressure vessel damage has been suspected, and some leakage is apparently confirmed by radioactivity levels in the building. Also since 20th the reactor pressure and drywell pressure decreased and then remained stable, leading TEPCO to believe that “the reactor pressure vessel is not seriously damaged.” By the end of March internal pressure was little more than atmospheric.The heat from the fuel in the reactor cores was estimated by France's ISRN as 2.5 MW thermal in /info/fukushima_accident_inf129.html 5 / 11Fukushima_Accident_2011in the building above unit 3 reactor containment blew off much of the roof and walls on the top part of the building. Early on Wednesday 16th there was a major release of smoke and/or steam from the top of the building. Because of the possibility that the Primary Containment of Unit 3 was damaged, the operators evacuated from the central control room of Unit 3 & 4 (a shared facility) at 10:45 am, but they returned to the control room and restarted the operation for water injection 45 minutes later. Pressure then built up to 320 kPa in the containment but no further venting wasrequired. Since at least 16th, pressure vessel damage has been suspected, and some leakage is apparently confirmed by radioactivity levels in the building. Also since 20th the reactor pressure and drywell pressure decreased and then remained stable, leading TEPCO to believe that “the reactor pressure vessel is not seriously damaged.” By the end of March internal pressure was little more than atmospheric.The heat from the fuel in the reactor cores was estimated by France's ISRN as 2.5 MW thermal in unit 1 and 4.2 MW in units 2 & 3 after almost three weeks. This is enough to boil away 95 tonnes and 160 tonnes of water per day respectively if all external circulation to heat sinks ceases, indicating the need for constant top up while the heat is not being dumped in the normal heat exchanger circuits. From 30th, 7-8 m 3/hour was being injected into each reactor. These heatproduction levels will diminish only slowly from this point. The cores remained partly uncovered, and Tepco said on 15th that 70% of the fuel rods in unit 1 and one third in unit 2 were damaged. At one stage unit 2 core was dry for some hours, and a German source said that unit 1 core was without water for 27 hours, causing major fuel damage.Since Sunday 20th JAIF has said that the containment vessel of unit 2 is thought to be damaged, and that of unit 3 could possibly be also, but unit 1 and 4 were intact. (Unit 4 has no fuel in it.).MIT Nuclear Science & Engineering info hubThe AC electricity supply from external source was connected to all units by 22nd, enabling more accurate monitoring of the plants and progress towards restoring the RHR cooling system of units 1-3. Power was restored to instrumentation in all units except unit 3 by 25th. Tepco said that once the control rooms are operational, water levels can be checked as well as temperatures in the fuel storage pools, and normal cooling of those pools can be resumed. However, at least some pumps have been damaged by seawater and Tepco says that radiation levels inside the plant are so high that normal access is still impossible. It is giving priority to removing contaminated water so as to allow better access.Summary on 4 April : All three units have fuel damage and low water levels, units 2 & 3 have lost /info/fukushima_accident_inf129.html 6 / 11Fukushima_Accident_2011MIT Nuclear Science & Engineering info hubThe AC electricity supply from external source was connected to all units by 22nd, enabling more accurate monitoring of the plants and progress towards restoring the RHR cooling system of units 1-3. Power was restored to instrumentation in all units except unit 3 by 25th. Tepco said that once the control rooms are operational, water levels can be checked as well as temperatures in the fuel storage pools, and normal cooling of those pools can be resumed. However, at least some pumps have been damaged by seawater and Tepco says that radiation levels inside the plant are so high that normal access is still impossible. It is giving priority to removing contaminated water so as to allow better access.Summary on 4 April : All three units have fuel damage and low water levels, units 2 & 3 have lost pressure and are suspected to have pressure vessel or containment damage (only unit 1 is still above atmospheric pressure). Cooling still needs to be provided from external sources, using fresh water and pump trucks, while work continues to establish a stable heat removal path to external heat sinks. Tepco has said that it is inevitable that the three reactors, with unit 4, will be written off and decommissioned. On 4 April both NISA and NSC said it could take months to repair the cooling systems due to the amount of contaminated water in the turbine buildings.Fuel ponds: developing problemsA separate set of problems arose as the fuel ponds, holding fresh and used fuel, in the upper part of the reactor structures were found to be depleted in water. It has not been explained why or how the low water levels came about, though elevated temperatures due to loss of cooling circulation would have been a major cause, especially in heavily-loaded unit 4. On 13 March Tepco said it was consulting with NISA and METI regarding cooling of the pondsI n unit 4, at about 6 am on Tuesday 15th, there was an explosion in the top part of the building, near the fuel pond, which destroyed the top of the building and damaged unit 3's superstructure further. Then there was a fire and soon after the radiation level near the building reached 400 mSv/hr, apparently from this source. The fire was extinguished in three hours. Evidently the used fuel there became exposed and got hot enough to form hydrogen. At 10 pm on 15th Tepco was told to implement injection of water to unit 4 pond. The gates which give access in refueling may havebeen disturbed by the earthquake, allowing some water to drain out. Apart from this, it appears that the water level dropped due to evaporation, if not boiling, caused by the high heat load from 1535 fuel assemblies once circulation ceased. The focus from Tuesday 15th was on replenishing the water in the ponds of units 3 and 4, through the gaps in the roof and cladding, using seawater. On 19th, unit 3 pond was reported to be stable, and on 24th it was able to be replenished using built-in plumbing for FPC system. On 25th the sameFuel ponds: backgroundUsed fuel needs to be cooled and shielded. This is initially by water, in ponds. After about three years under water, used fuelcan be transferred to dry storage, with air ventilation simply by convection. Used fuel generates heat, so the water is circulatedby electric pumps through external heat exchangers, so that the heat is dumped and a low temperature maintained.There are fuel ponds near the top of all six reactor buildings at the plant, adjacent to the top of each reactor so that the fuelcan be unloaded under water, when the top is off the reactor pressure vessel and it is flooded. The ponds hold some fresh fueland some used fuel, pending its transfer to the central used/spent fuel storage on site. (There is some dry storage to extendthe site's capacity.) From here it is periodically shipped for reprocessing, that being now to Rokkasho for recycling.At the time of the accident, unit 4's pond also held a full core load of 548 fuel assemblies while the reactor was undergoingmaintenance, these having been removed at the end of November.The temperature of these ponds is normally low, around 30°C when circulation is maintained with the Fuel Pool Circulationand Clean-up (FCP) system, but they are designed to be safe at about 85°C in the absence of pumped circulation (andpresumably with low fuel load). They are about 12 metres deep, so the fuel is normally covered by 7 metres of water.Unit 3 & 4 ponds are about 12 x 10 metres, with 1220 and 1590 assemblies capacity respectively (unit 1 is about 12 x 7 m,900 assemblies). Unit 4 pond has a total 1331 used assemblies, giving it a heat load of about 3 MW thermal, according toFrance's IRSN, which in that case could lead to 115 cubic metres of water boiling off per day, or about one tenth of itsvolume. Unit 3's pool contains 514 fuel assemblies, unit 1 has 292 and unit 2 has 587. There is no MOX fuel in any of theponds.The central fuel storage on site has a pond about 12 x 29 metres, 11 m deep, with capacity of 3828 m3 and 6840 fuelassemblies. Its building is about 55 x 73 m. (There are 6375 assemblies in the undamaged central pool storage on site, withvery low decay heat, and 408 in dry cask storage - utilized since 1995 for used fuel no longer needing much cooling.) /info/fukushima_accident_inf129.html 7 / 11Fukushima_Accident_2011。
Large N orbifold field theories on the twisted torus
arXiv:hep-th/0512303v2 13 Feb 2006
ቤተ መጻሕፍቲ ባይዱ
Large N orbifold field theories on the twisted torus
C. Hoyos
Instituto de F´ ısica Te´ orica UAM/CSIC, Facultad de Ciencias, Cantoblanco. 28049 Madrid, Spain c.hoyos@uam.es Abstract We study the planar equivalence of orbifold field theories on a small three-torus with twisted boundary conditions, generalizing the analysis of hep-th/0507267. The nonsupersymmetric orbifold models exhibit different large N dynamics from their supersymmetric ”parent” counterparts. In particular, a moduli space of Abelian zero modes is lifted by an O(N 2 ) potential in the ”daughter” theories. We also find disagreement between the number of discrete vacua of both theories, due to fermionic zero modes in the parent theory, as well as the values of semiclassical tunneling contributions to fermionic correlation functions, induced by fractional instantons.
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arXiv:hep-ph/9806351v2 4 Dec 1998
b c d
Department of Physics, North Eastern Hill University, Shillong 793 022, India∗
Abstract We present a detailed analysis of multiple production of the lightest CP -even Higgs boson (h) of the Minimal Supersymmetric Standard Model (MSSM) at highenergy e+ e− colliders. We consider the production of the heavier CP -even Higgs boson (H ) via Higgs-strahlung e+ e− → ZH , in association with the CP -odd Higgs boson (A) in e+ e− → AH , or via the fusion mechanism e+ e− → νe ν ¯e H , with H subsequently decaying through H → hh, thereby resulting in a pair of lighter Higgs bosons (h) in the final state. These processes can enable one to measure the trilinear Higgs couplings λHhh and λhhh , which can be used to theoretically reconstruct the Higgs potential. We delineate the regions of the MSSM parameter space in which these trilinear Higgs couplings could be measured at a future e+ e− collider. In our calculations, we include in detail the radiative corrections to the Higgs sector of the MSSM, especially the mixing in the squark sector.
a
Department of Physics, University of Bergen, N-5007 Bergen, Norway∗ Deutsches Elektronen-Synchrotron DESY, D-22603 Hamburg, Germany Theoretical Physics Division, CERN, CH 1211 Geneva 23, Switzerland
1
When unambiguous, we shall denote the CP -even Higgs particles as h and H .
2
Haber and Zerwas [4] (referred to as ‘DHZ’ in the following), of the measurement of these couplings at the LHC and at a high-energy e+ e− linear collider, respectively, are encouraging. In this paper we consider in detail the question of possible measurements of the trilinear Higgs couplings of the MSSM at a high-energy e+ e− linear collider. We assume that such a facility will operate at an energy of 500 GeV with an integrated luminosity per year of Lint = 500 fb−1 [5]. (This is a factor of 10 more than the earlier estimate.) In a later phase one may envisage an upgrade to an energy of 1.5 TeV. Since the ‘interesting’ cross sections fall off like 1/E 2 , the luminosity should increase by a corresponding factor. An earlier estimated luminosity of 500 fb−1 at 1.5 TeV may turn out to be too conservative. The trilinear Higgs couplings that are of interest are λHhh , λhhh , and λhAA , involving both the CP -even (h, H ) and CP -odd (A) Higgs bosons.2 The couplings λHhh and λhhh are rather small with respect to the corresponding trilinear coupling λSM hhh in the SM (for a given mass of the lightest Higgs boson mh ), unless mh is close to the upper value (decoupling limit). The coupling λhAA remains small for all parameters. Throughout, we include one-loop radiative corrections [6] to the Higgs sector in the effective potential approximation. In particular, we take into account the parameters A and µ, the soft supersymmetry breaking trilinear parameter and the bilinear Higgs(ino) parameter in the superpotential, respectively, and as a consequence the left–right mixing in the squark sector, in our calculations. We thus include all the relevant parameters of the MSSM in our study, which is more detailed than the preliminary one of DHZ. For a given value of mh , the values of these couplings significantly depend on the soft supersymmetry-breaking trilinear parameter A, as well as on µ, and thus on the resulting mixing in the squark sector. Since the trilinear couplings tend to be small, and depend on several parameters, their effects are somewhat difficult to estimate. The plan of the paper is as follows. In Section 2 we review the Higgs sector of the
PACS: 14.80.Cp, 12.60.Jv, 13.90.+i * Permanent addresses CERN-TH/98-189 June 1998
1
Introduction
The Higgs potential of the Standard Model (SM), which is crucial in implementing the mechanism of spontaneous symmetry breaking, contains the unknown quartic coupling of the Higgs field. As a consequence, the mass of the only Higgs boson in the SM, which is determined by this quartic coupling, is not known [1]. If a Higgs boson is discovered and its mass measured, the Higgs potential of the Standard Model can be uniquely determined. On the other hand, supersymmetry is at present the only known framework in which the Higgs sector of the Standard Model (SM), so crucial for its internal consistency, is natural [2]. The minimal version of the Supersymmetric Standard Model (MSSM) contains two Higgs doublets (H1 , H2 ) with opposite hypercharges: Y (H1 ) = −1, Y (H2 ) = +1, so as to generate masses for up- and down-type quarks (and leptons), and to cancel gauge anomalies. After spontaneous symmetry breaking induced by the neutral components of H1 and H2 obtaining vacuum expectation values, H1 = v1 , H2 = v2 , tan β = v2 /v1 , the MSSM contains two neutral CP -even1 (h, H ), one neutral CP -odd (A), and two charged (H ± ) Higgs bosons [1]. Although gauge invariance and supersymmetry fix the quartic couplings of the Higgs bosons in the MSSM in terms of SU (2)L and U (1)Y gauge couplings, g and g ′ , respectively, there still remain two independent parameters that describe the Higgs sector of the MSSM. These are usually chosen to be tan β and mA , the mass of the CP -odd Higgs boson. All the Higgs masses and the Higgs couplings in the MSSM can be described (at tree level) in terms of these two parameters. In particular, all the trilinear self-couplings of the physical Higgs particles can be predicted theoretically (at the tree level) in terms of mA and tan β . Once a light Higgs boson is discovered, the measurement of these trilinear couplings can be used to reconstruct the Higgs potential of the MSSM. This will go a long way toward establishing the Higgs mechanism as the basic mechanism of spontaneous symmetry breaking in gauge theories. Although the measurement of all the Higgs couplings in the MSSM is a difficult task, preliminary theoretical investigations by Plehn, Spira and Zerwas [3], and by Djouadi,