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Collective dynamics of 'small-world' networks
Nature © Macmillan Publishers Ltd 19988typically slower than ϳ1km s −1)might differ significantly from what is assumed by current modelling efforts 27.The expected equation-of-state differences among small bodies (ice versus rock,for instance)presents another dimension of study;having recently adapted our code for massively parallel architectures (K.M.Olson and E.A,manuscript in preparation),we are now ready to perform a more comprehensive analysis.The exploratory simulations presented here suggest that when a young,non-porous asteroid (if such exist)suffers extensive impact damage,the resulting fracture pattern largely defines the asteroid’s response to future impacts.The stochastic nature of collisions implies that small asteroid interiors may be as diverse as their shapes and spin states.Detailed numerical simulations of impacts,using accurate shape models and rheologies,could shed light on how asteroid collisional response depends on internal configuration and shape,and hence on how planetesimals evolve.Detailed simulations are also required before one can predict the quantitative effects of nuclear explosions on Earth-crossing comets and asteroids,either for hazard mitigation 28through disruption and deflection,or for resource exploitation 29.Such predictions would require detailed reconnaissance concerning the composition andinternal structure of the targeted object.ⅪReceived 4February;accepted 18March 1998.1.Asphaug,E.&Melosh,H.J.The Stickney impact of Phobos:A dynamical model.Icarus 101,144–164(1993).2.Asphaug,E.et al .Mechanical and geological effects of impact cratering on Ida.Icarus 120,158–184(1996).3.Nolan,M.C.,Asphaug,E.,Melosh,H.J.&Greenberg,R.Impact craters on asteroids:Does strength orgravity control their size?Icarus 124,359–371(1996).4.Love,S.J.&Ahrens,T.J.Catastrophic impacts on gravity dominated asteroids.Icarus 124,141–155(1996).5.Melosh,H.J.&Ryan,E.V.Asteroids:Shattered but not dispersed.Icarus 129,562–564(1997).6.Housen,K.R.,Schmidt,R.M.&Holsapple,K.A.Crater ejecta scaling laws:Fundamental forms basedon dimensional analysis.J.Geophys.Res.88,2485–2499(1983).7.Holsapple,K.A.&Schmidt,R.M.Point source solutions and coupling parameters in crateringmechanics.J.Geophys.Res.92,6350–6376(1987).8.Housen,K.R.&Holsapple,K.A.On the fragmentation of asteroids and planetary satellites.Icarus 84,226–253(1990).9.Benz,W.&Asphaug,E.Simulations of brittle solids using smooth particle put.mun.87,253–265(1995).10.Asphaug,E.et al .Mechanical and geological effects of impact cratering on Ida.Icarus 120,158–184(1996).11.Hudson,R.S.&Ostro,S.J.Shape of asteroid 4769Castalia (1989PB)from inversion of radar images.Science 263,940–943(1994).12.Ostro,S.J.et al .Asteroid radar astrometry.Astron.J.102,1490–1502(1991).13.Ahrens,T.J.&O’Keefe,J.D.in Impact and Explosion Cratering (eds Roddy,D.J.,Pepin,R.O.&Merrill,R.B.)639–656(Pergamon,New York,1977).14.Tillotson,J.H.Metallic equations of state for hypervelocity impact.(General Atomic Report GA-3216,San Diego,1962).15.Nakamura,A.&Fujiwara,A.Velocity distribution of fragments formed in a simulated collisionaldisruption.Icarus 92,132–146(1991).16.Benz,W.&Asphaug,E.Simulations of brittle solids using smooth particle put.mun.87,253–265(1995).17.Bottke,W.F.,Nolan,M.C.,Greenberg,R.&Kolvoord,R.A.Velocity distributions among collidingasteroids.Icarus 107,255–268(1994).18.Belton,M.J.S.et al .Galileo encounter with 951Gaspra—First pictures of an asteroid.Science 257,1647–1652(1992).19.Belton,M.J.S.et al .Galileo’s encounter with 243Ida:An overview of the imaging experiment.Icarus120,1–19(1996).20.Asphaug,E.&Melosh,H.J.The Stickney impact of Phobos:A dynamical model.Icarus 101,144–164(1993).21.Asphaug,E.et al .Mechanical and geological effects of impact cratering on Ida.Icarus 120,158–184(1996).22.Housen,K.R.,Schmidt,R.M.&Holsapple,K.A.Crater ejecta scaling laws:Fundamental forms basedon dimensional analysis.J.Geophys.Res.88,2485–2499(1983).23.Veverka,J.et al .NEAR’s flyby of 253Mathilde:Images of a C asteroid.Science 278,2109–2112(1997).24.Asphaug,E.et al .Impact evolution of icy regoliths.Lunar Planet.Sci.Conf.(Abstr.)XXVIII,63–64(1997).25.Love,S.G.,Ho¨rz,F.&Brownlee,D.E.Target porosity effects in impact cratering and collisional disruption.Icarus 105,216–224(1993).26.Fujiwara,A.,Cerroni,P .,Davis,D.R.,Ryan,E.V.&DiMartino,M.in Asteroids II (eds Binzel,R.P .,Gehrels,T.&Matthews,A.S.)240–265(Univ.Arizona Press,Tucson,1989).27.Davis,D.R.&Farinella,P.Collisional evolution of Edgeworth-Kuiper Belt objects.Icarus 125,50–60(1997).28.Ahrens,T.J.&Harris,A.W.Deflection and fragmentation of near-Earth asteroids.Nature 360,429–433(1992).29.Resources of Near-Earth Space (eds Lewis,J.S.,Matthews,M.S.&Guerrieri,M.L.)(Univ.ArizonaPress,Tucson,1993).Acknowledgements.This work was supported by NASA’s Planetary Geology and Geophysics Program.Correspondence and requests for materials should be addressed to E.A.(e-mail:asphaug@).letters to nature440NATURE |VOL 393|4JUNE 1998Collective dynamics of ‘small-world’networksDuncan J.Watts *&Steven H.StrogatzDepartment of Theoretical and Applied Mechanics,Kimball Hall,Cornell University,Ithaca,New York 14853,USA.........................................................................................................................Networks of coupled dynamical systems have been used to model biological oscillators 1–4,Josephson junction arrays 5,6,excitable media 7,neural networks 8–10,spatial games 11,genetic control networks 12and many other self-organizing systems.Ordinarily,the connection topology is assumed to be either completely regular or completely random.But many biological,technological and social networks lie somewhere between these two extremes.Here we explore simple models of networks that can be tuned through this middle ground:regular networks ‘rewired’to intro-duce increasing amounts of disorder.We find that these systems can be highly clustered,like regular lattices,yet have small characteristic path lengths,like random graphs.We call them ‘small-world’networks,by analogy with the small-world phenomenon 13,14(popularly known as six degrees of separation 15).The neural network of the worm Caenorhabditis elegans ,the power grid of the western United States,and the collaboration graph of film actors are shown to be small-world networks.Models of dynamical systems with small-world coupling display enhanced signal-propagation speed,computational power,and synchronizability.In particular,infectious diseases spread more easily in small-world networks than in regular lattices.To interpolate between regular and random networks,we con-sider the following random rewiring procedure (Fig.1).Starting from a ring lattice with n vertices and k edges per vertex,we rewire each edge at random with probability p .This construction allows us to ‘tune’the graph between regularity (p ¼0)and disorder (p ¼1),and thereby to probe the intermediate region 0Ͻp Ͻ1,about which little is known.We quantify the structural properties of these graphs by their characteristic path length L (p )and clustering coefficient C (p ),as defined in Fig.2legend.Here L (p )measures the typical separation between two vertices in the graph (a global property),whereas C (p )measures the cliquishness of a typical neighbourhood (a local property).The networks of interest to us have many vertices with sparse connections,but not so sparse that the graph is in danger of becoming disconnected.Specifically,we require n q k q ln ðn Þq 1,where k q ln ðn Þguarantees that a random graph will be connected 16.In this regime,we find that L ϳn =2k q 1and C ϳ3=4as p →0,while L ϷL random ϳln ðn Þ=ln ðk Þand C ϷC random ϳk =n p 1as p →1.Thus the regular lattice at p ¼0is a highly clustered,large world where L grows linearly with n ,whereas the random network at p ¼1is a poorly clustered,small world where L grows only logarithmically with n .These limiting cases might lead one to suspect that large C is always associated with large L ,and small C with small L .On the contrary,Fig.2reveals that there is a broad interval of p over which L (p )is almost as small as L random yet C ðp Þq C random .These small-world networks result from the immediate drop in L (p )caused by the introduction of a few long-range edges.Such ‘short cuts’connect vertices that would otherwise be much farther apart than L random .For small p ,each short cut has a highly nonlinear effect on L ,contracting the distance not just between the pair of vertices that it connects,but between their immediate neighbourhoods,neighbourhoods of neighbourhoods and so on.By contrast,an edge*Present address:Paul zarsfeld Center for the Social Sciences,Columbia University,812SIPA Building,420W118St,New York,New York 10027,USA.Nature © Macmillan Publishers Ltd 19988letters to natureNATURE |VOL 393|4JUNE 1998441removed from a clustered neighbourhood to make a short cut has,at most,a linear effect on C ;hence C (p )remains practically unchanged for small p even though L (p )drops rapidly.The important implica-tion here is that at the local level (as reflected by C (p )),the transition to a small world is almost undetectable.To check the robustness of these results,we have tested many different types of initial regular graphs,as well as different algorithms for random rewiring,and all give qualitatively similar results.The only requirement is that the rewired edges must typically connect vertices that would otherwise be much farther apart than L random .The idealized construction above reveals the key role of short cuts.It suggests that the small-world phenomenon might be common in sparse networks with many vertices,as even a tiny fraction of short cuts would suffice.To test this idea,we have computed L and C for the collaboration graph of actors in feature films (generated from data available at ),the electrical power grid of the western United States,and the neural network of the nematode worm C.elegans 17.All three graphs are of scientific interest.The graph of film actors is a surrogate for a social network 18,with the advantage of being much more easily specified.It is also akin to the graph of mathematical collaborations centred,traditionally,on P.Erdo¨s (partial data available at /ϳgrossman/erdoshp.html).The graph of the power grid is relevant to the efficiency and robustness of power networks 19.And C.elegans is the sole example of a completely mapped neural network.Table 1shows that all three graphs are small-world networks.These examples were not hand-picked;they were chosen because of their inherent interest and because complete wiring diagrams were available.Thus the small-world phenomenon is not merely a curiosity of social networks 13,14nor an artefact of an idealizedmodel—it is probably generic for many large,sparse networks found in nature.We now investigate the functional significance of small-world connectivity for dynamical systems.Our test case is a deliberately simplified model for the spread of an infectious disease.The population structure is modelled by the family of graphs described in Fig.1.At time t ¼0,a single infective individual is introduced into an otherwise healthy population.Infective individuals are removed permanently (by immunity or death)after a period of sickness that lasts one unit of dimensionless time.During this time,each infective individual can infect each of its healthy neighbours with probability r .On subsequent time steps,the disease spreads along the edges of the graph until it either infects the entire population,or it dies out,having infected some fraction of the population in theprocess.p = 0p = 1Regular Small-worldRandomFigure 1Random rewiring procedure for interpolating between a regular ring lattice and a random network,without altering the number of vertices or edges in the graph.We start with a ring of n vertices,each connected to its k nearest neighbours by undirected edges.(For clarity,n ¼20and k ¼4in the schematic examples shown here,but much larger n and k are used in the rest of this Letter.)We choose a vertex and the edge that connects it to its nearest neighbour in a clockwise sense.With probability p ,we reconnect this edge to a vertex chosen uniformly at random over the entire ring,with duplicate edges forbidden;other-wise we leave the edge in place.We repeat this process by moving clockwise around the ring,considering each vertex in turn until one lap is completed.Next,we consider the edges that connect vertices to their second-nearest neighbours clockwise.As before,we randomly rewire each of these edges with probability p ,and continue this process,circulating around the ring and proceeding outward to more distant neighbours after each lap,until each edge in the original lattice has been considered once.(As there are nk /2edges in the entire graph,the rewiring process stops after k /2laps.)Three realizations of this process are shown,for different values of p .For p ¼0,the original ring is unchanged;as p increases,the graph becomes increasingly disordered until for p ¼1,all edges are rewired randomly.One of our main results is that for intermediate values of p ,the graph is a small-world network:highly clustered like a regular graph,yet with small characteristic path length,like a random graph.(See Fig.2.)T able 1Empirical examples of small-world networksL actual L random C actual C random.............................................................................................................................................................................Film actors 3.65 2.990.790.00027Power grid 18.712.40.0800.005C.elegans 2.65 2.250.280.05.............................................................................................................................................................................Characteristic path length L and clustering coefficient C for three real networks,compared to random graphs with the same number of vertices (n )and average number of edges per vertex (k ).(Actors:n ¼225;226,k ¼61.Power grid:n ¼4;941,k ¼2:67.C.elegans :n ¼282,k ¼14.)The graphs are defined as follows.Two actors are joined by an edge if they have acted in a film together.We restrict attention to the giant connected component 16of this graph,which includes ϳ90%of all actors listed in the Internet Movie Database (available at ),as of April 1997.For the power grid,vertices represent generators,transformers and substations,and edges represent high-voltage transmission lines between them.For C.elegans ,an edge joins two neurons if they are connected by either a synapse or a gap junction.We treat all edges as undirected and unweighted,and all vertices as identical,recognizing that these are crude approximations.All three networks show the small-world phenomenon:L ՌL random but C q C random.00.20.40.60.810.00010.0010.010.11pFigure 2Characteristic path length L (p )and clustering coefficient C (p )for the family of randomly rewired graphs described in Fig.1.Here L is defined as the number of edges in the shortest path between two vertices,averaged over all pairs of vertices.The clustering coefficient C (p )is defined as follows.Suppose that a vertex v has k v neighbours;then at most k v ðk v Ϫ1Þ=2edges can exist between them (this occurs when every neighbour of v is connected to every other neighbour of v ).Let C v denote the fraction of these allowable edges that actually exist.Define C as the average of C v over all v .For friendship networks,these statistics have intuitive meanings:L is the average number of friendships in the shortest chain connecting two people;C v reflects the extent to which friends of v are also friends of each other;and thus C measures the cliquishness of a typical friendship circle.The data shown in the figure are averages over 20random realizations of the rewiring process described in Fig.1,and have been normalized by the values L (0),C (0)for a regular lattice.All the graphs have n ¼1;000vertices and an average degree of k ¼10edges per vertex.We note that a logarithmic horizontal scale has been used to resolve the rapid drop in L (p ),corresponding to the onset of the small-world phenomenon.During this drop,C (p )remains almost constant at its value for the regular lattice,indicating that the transition to a small world is almost undetectable at the local level.Nature © Macmillan Publishers Ltd 19988letters to nature442NATURE |VOL 393|4JUNE 1998Two results emerge.First,the critical infectiousness r half ,at which the disease infects half the population,decreases rapidly for small p (Fig.3a).Second,for a disease that is sufficiently infectious to infect the entire population regardless of its structure,the time T (p )required for global infection resembles the L (p )curve (Fig.3b).Thus,infectious diseases are predicted to spread much more easily and quickly in a small world;the alarming and less obvious point is how few short cuts are needed to make the world small.Our model differs in some significant ways from other network models of disease spreading 20–24.All the models indicate that net-work structure influences the speed and extent of disease transmis-sion,but our model illuminates the dynamics as an explicit function of structure (Fig.3),rather than for a few particular topologies,such as random graphs,stars and chains 20–23.In the work closest to ours,Kretschmar and Morris 24have shown that increases in the number of concurrent partnerships can significantly accelerate the propaga-tion of a sexually-transmitted disease that spreads along the edges of a graph.All their graphs are disconnected because they fix the average number of partners per person at k ¼1.An increase in the number of concurrent partnerships causes faster spreading by increasing the number of vertices in the graph’s largest connected component.In contrast,all our graphs are connected;hence the predicted changes in the spreading dynamics are due to more subtle structural features than changes in connectedness.Moreover,changes in the number of concurrent partners are obvious to an individual,whereas transitions leading to a smaller world are not.We have also examined the effect of small-world connectivity on three other dynamical systems.In each case,the elements were coupled according to the family of graphs described in Fig.1.(1)For cellular automata charged with the computational task of density classification 25,we find that a simple ‘majority-rule’running on a small-world graph can outperform all known human and genetic algorithm-generated rules running on a ring lattice.(2)For the iterated,multi-player ‘Prisoner’s dilemma’11played on a graph,we find that as the fraction of short cuts increases,cooperation is less likely to emerge in a population of players using a generalized ‘tit-for-tat’26strategy.The likelihood of cooperative strategies evolving out of an initial cooperative/non-cooperative mix also decreases with increasing p .(3)Small-world networks of coupled phase oscillators synchronize almost as readily as in the mean-field model 2,despite having orders of magnitude fewer edges.This result may be relevant to the observed synchronization of widely separated neurons in the visual cortex 27if,as seems plausible,the brain has a small-world architecture.We hope that our work will stimulate further studies of small-world networks.Their distinctive combination of high clustering with short characteristic path length cannot be captured by traditional approximations such as those based on regular lattices or random graphs.Although small-world architecture has not received much attention,we suggest that it will probably turn out to be widespread in biological,social and man-made systems,oftenwith important dynamical consequences.ⅪReceived 27November 1997;accepted 6April 1998.1.Winfree,A.T.The Geometry of Biological Time (Springer,New Y ork,1980).2.Kuramoto,Y.Chemical Oscillations,Waves,and Turbulence (Springer,Berlin,1984).3.Strogatz,S.H.&Stewart,I.Coupled oscillators and biological synchronization.Sci.Am.269(6),102–109(1993).4.Bressloff,P .C.,Coombes,S.&De Souza,B.Dynamics of a ring of pulse-coupled oscillators:a group theoretic approach.Phys.Rev.Lett.79,2791–2794(1997).5.Braiman,Y.,Lindner,J.F.&Ditto,W.L.Taming spatiotemporal chaos with disorder.Nature 378,465–467(1995).6.Wiesenfeld,K.New results on frequency-locking dynamics of disordered Josephson arrays.Physica B 222,315–319(1996).7.Gerhardt,M.,Schuster,H.&Tyson,J.J.A cellular automaton model of excitable media including curvature and dispersion.Science 247,1563–1566(1990).8.Collins,J.J.,Chow,C.C.&Imhoff,T.T.Stochastic resonance without tuning.Nature 376,236–238(1995).9.Hopfield,J.J.&Herz,A.V.M.Rapid local synchronization of action potentials:Toward computation with coupled integrate-and-fire neurons.Proc.Natl A 92,6655–6662(1995).10.Abbott,L.F.&van Vreeswijk,C.Asynchronous states in neural networks of pulse-coupled oscillators.Phys.Rev.E 48(2),1483–1490(1993).11.Nowak,M.A.&May,R.M.Evolutionary games and spatial chaos.Nature 359,826–829(1992).12.Kauffman,S.A.Metabolic stability and epigenesis in randomly constructed genetic nets.J.Theor.Biol.22,437–467(1969).gram,S.The small world problem.Psychol.Today 2,60–67(1967).14.Kochen,M.(ed.)The Small World (Ablex,Norwood,NJ,1989).15.Guare,J.Six Degrees of Separation:A Play (Vintage Books,New Y ork,1990).16.Bollaba´s,B.Random Graphs (Academic,London,1985).17.Achacoso,T.B.&Yamamoto,W.S.AY’s Neuroanatomy of C.elegans for Computation (CRC Press,BocaRaton,FL,1992).18.Wasserman,S.&Faust,K.Social Network Analysis:Methods and Applications (Cambridge Univ.Press,1994).19.Phadke,A.G.&Thorp,puter Relaying for Power Systems (Wiley,New Y ork,1988).20.Sattenspiel,L.&Simon,C.P .The spread and persistence of infectious diseases in structured populations.Math.Biosci.90,341–366(1988).21.Longini,I.M.Jr A mathematical model for predicting the geographic spread of new infectious agents.Math.Biosci.90,367–383(1988).22.Hess,G.Disease in metapopulation models:implications for conservation.Ecology 77,1617–1632(1996).23.Blythe,S.P .,Castillo-Chavez,C.&Palmer,J.S.T oward a unified theory of sexual mixing and pair formation.Math.Biosci.107,379–405(1991).24.Kretschmar,M.&Morris,M.Measures of concurrency in networks and the spread of infectious disease.Math.Biosci.133,165–195(1996).25.Das,R.,Mitchell,M.&Crutchfield,J.P .in Parallel Problem Solving from Nature (eds Davido,Y.,Schwefel,H.-P.&Ma¨nner,R.)344–353(Lecture Notes in Computer Science 866,Springer,Berlin,1994).26.Axelrod,R.The Evolution of Cooperation (Basic Books,New Y ork,1984).27.Gray,C.M.,Ko¨nig,P .,Engel,A.K.&Singer,W.Oscillatory responses in cat visual cortex exhibit inter-columnar synchronization which reflects global stimulus properties.Nature 338,334–337(1989).Acknowledgements.We thank B.Tjaden for providing the film actor data,and J.Thorp and K.Bae for the Western States Power Grid data.This work was supported by the US National Science Foundation (Division of Mathematical Sciences).Correspondence and requests for materials should be addressed to D.J.W.(e-mail:djw24@).0.150.20.250.30.350.00010.0010.010.11rhalfpaFigure 3Simulation results for a simple model of disease spreading.The community structure is given by one realization of the family of randomly rewired graphs used in Fig.1.a ,Critical infectiousness r half ,at which the disease infects half the population,decreases with p .b ,The time T (p )required for a maximally infectious disease (r ¼1)to spread throughout the entire population has essen-tially the same functional form as the characteristic path length L (p ).Even if only a few per cent of the edges in the original lattice are randomly rewired,the time to global infection is nearly as short as for a random graph.0.20.40.60.810.00010.0010.010.11pb。
水肥调控对西北地区马铃薯产量和水肥利用效率影响的Meta分析
2024年3月 灌溉排水学报第43卷 第3期 Mar. 2024 Journal of Irrigation and Drainage No.3 Vol.4319文章编号：1672 - 3317（2024）03 - 0019 - 08水肥调控对西北地区马铃薯产量和水肥利用效率影响的Meta 分析苏丹丹1,2，张恒嘉1,2*，邓浩亮3，周晨莉1,2，陈谢田1,2（1.甘肃农业大学，兰州 730070；2.聊城大学，山东 聊城 252059；3.河西学院，甘肃 张掖 734000）摘 要：【目的】评估水肥调控对马铃薯产量、水分利用效率（WUE ）和肥料偏生产率（PFP ）的影响。
【方法】采用数据整合（Meta ）分析，以马铃薯产量和水肥利用效率为决策因子，筛选获得目标文献29篇，建立水-肥-产量（440组）、水-肥-WUE （318组）、水-肥-PFP （428组）共计1 186组观测值的数据库。
分析水肥调控对西北地区马铃薯产量和水肥利用效率的影响，优选西北地区马铃薯最优水肥调控区间。
【结果】对宁夏马铃薯生产而言，适量增加灌水量和施肥量至最佳水肥调控区间可增产14.12 t/hm 2，增加2.96 kg/m 3的WUE 和32.83 kg/kg 的PFP ；对甘肃马铃薯生产而言，降低施肥量至最佳施肥区间可增加27.58 kg/kg 的PFP ；对内蒙古马铃薯生产而言，降低灌水量并增加施肥量至最佳水肥调控区间，可增产17.92 t/hm 2，同时增加3.33 kg/m 3的WUE 和30.91 kg/kg 的PFP 。
【结论】西北四省（自治区）马铃薯最优水肥调控区间分别为：宁夏（灌水量900~2 100 m 3/hm 2，施肥量345~531.6 kg/hm 2）、甘肃（灌水量2 895~3 550 m 3/hm 2，施肥量420~630 kg/hm 2）、陕西（灌水量1 650~2 940 m 3/hm 2，施肥量415~630 kg/hm 2）、内蒙古（灌水量1 350~2 070 m 3/hm 2，施肥量435~675 kg/hm 2）。
文心兰侧花瓣转录组分析与调控唇瓣化变异相关转录因子的挖掘
文心兰侧花瓣转录组分析与调控唇瓣化变异相关转录因子的挖掘作者：曾思娴余让才范燕萍来源：《热带作物学报》2024年第05期关键词：文心兰；唇瓣化；转录组测序；差异表达基因中图分类号：S432.1 文献标志码：A兰科植物因其独特的花型倍受人们喜爱，MADS-box 转录因子是花的起始和发育过程中的关键调控成分，在参与花器官的发育、开花时间的调节等过程中均起着重要作用[1]。
ABCDE 模型由MADS-box 基因家族中的五类同源基因组成，这些基因通过相互作用共同决定花器官身份[2]。
因此，大多数关于兰花花器官发育的研究都集中在这些ABCDE 基因上，而关于调控兰花唇瓣发育的其他转录因子及下游相关调控网络仍不清晰，因此，探究其他相关调控机制对兰花植物分子育种具有重要意义。
文心兰是兰科文心兰属植物，因其独特的花型和艳丽的颜色是世界上具有较高观赏价值的切花品种[3]。
在长期的文心兰生长进化过程中，极易产生花型多样性，这种花型多样性主要体现在唇瓣的变化上，使其具有更高的观赏价值和生物学价值[4]。
因此揭示文心兰唇瓣多样性形成机制显得极其重要。
“花被密码模型”是目前被广泛接受的兰花花器官发育模型，该模型中，不同MADS-box 基因分别组成唇瓣复合物和萼片/花瓣复合物，这2 种蛋白复合物相互竞争决定兰花花器官身份形成[5]，而文心兰花瓣形态结构多样化的其他调控网络研究仍鲜有报道。
本研究以柠檬绿文心兰（Oncidium. flexuosum‘Honey Angel’）和其侧花瓣唇瓣化变异种（突变体）为材料，对2 种侧花瓣进行RNA 转录组测序，通过MADS-box 及其他转录因子的差异表达挖掘调控文心兰唇瓣化变异关键转录因子，为建立文心兰唇瓣化变异调控关系网络，培育花型独特兰花新品种奠定基础。
1 材料与方法1.1 材料供試材料为种植在华南农业大学花卉研究中心种质资源圃中生长健壮的柠檬绿文心兰侧花瓣发生唇瓣化变异种（突变体），对照为柠檬绿文心兰（图1）。
基于蒙卡算法的乳腺癌术中放疗模型的剂量学优化
基于蒙卡算法的乳腺癌术中放疗模型的剂量学优化杨波;孔旭东;魏贤顶;孟东;陈建江【摘要】目的：探讨蒙特卡罗算法在乳腺癌术中放疗（IORT）模型剂量学优化中的应用价值。
方法采用MCTP的MCBEAM程序建立乳腺癌术中放疗模型，利用MCSIM程序对患者术前CT模拟术中影像模型进行剂量计算，分析其剂量学特点，并对靶区剂量进行优化。
结果通过蒙卡计算，优化的乳腺癌术中放疗模型方案为：靶区表面添加2~3 mm等效材料，靶区后缘添加5 mm等效材料再加2 mm铅板，这可以使90%以上等剂量线包绕整个靶区，同时可以消除＞110%的热点区域，肺最大剂量＜1 Gy。
结论蒙特卡罗算法在乳腺癌IORT模型剂量学优化中的应用能显著提高IORT靶区剂量的计算精度，优化剂量分布，值得临床推广。
%ObjectiveToexplorethevalueofMonteCarloalgorithminthedoseoptimiz ationofIORTmodel forbreastcancer. MethodsTheIORTmodelforbreastcancerwasestablishedwithMCTPMCBEAM program. Then the dose calculation of the intraoperative image simulated by CT was conducted with MCBEAM program to analyze the dosimetric characteristics and optimize the target dose. ResuIts Based on Monte Carlo calculation, the optimization scheme of IORT model for breast cancer was designed as the follow:adding2~3mmequivalentmaterialonthetargetsurfaceandadding5mmequivalentmaterialand 2mm leadplateonthetrailingedgeofthetarget.Thustheentiretargetregioncanbesurr oundedbymorethan 90%isodoselineandmorethan110%hotregioncanbeeliminatedwhilethemaxiumdoseofthelungislessthan 1Gy. ConcIusion The application of Monte Carlo algorithm in the dose optimization of IORT model for breast cancer can significantly improve the calculation precision of the target dose and optimize the dose distribution, which indicates that Monte Carlo algorithm is worth to be promoted in clinic.【期刊名称】《中国医疗设备》【年(卷),期】2014(000)012【总页数】4页(P105-108)【关键词】蒙特卡罗算法;乳腺癌;术中放疗;剂量优化【作者】杨波;孔旭东;魏贤顶;孟东;陈建江【作者单位】江南大学附属医院无锡市第四人民医院肿瘤放疗科，江苏无锡214062;江南大学附属医院无锡市第四人民医院肿瘤放疗科，江苏无锡214062;江南大学附属医院无锡市第四人民医院肿瘤放疗科，江苏无锡214062;江南大学附属医院无锡市第四人民医院肿瘤放疗科，江苏无锡214062;江南大学附属医院无锡市第四人民医院肿瘤放疗科，江苏无锡214062【正文语种】中文【中图分类】R730.55;TH774早期乳腺癌患者行保乳术加前哨淋巴结活检及腋窝淋巴结清扫的同时进行术中放疗（Intraoperative Radiotherapy，IORT），能显著减少局部复发和远处转移，其局控率可以与乳腺癌保乳术后全乳放疗相媲美，形成了早期乳腺癌患者保乳手术加术中放疗的治疗模式[1-2]。
常用公差
1.几何特性名词与符号(a)几何特性符号符号名词类别形体区分直度,真直度(Straightness)平面度,真平度(Flatness)真圆度(Roundness)圆柱度(Cylindrically)曲线轮廓度(Profile of a line)曲线轮廓度平行度(Parallelism)垂直度(Perpendicularity)倾斜度(Angularity)正位度,位置度(Position)同心度(Concentricity)对称度（Symmetry）(1982年起由取代)圆周偏转度,圆形偏转度(Circular runout)总偏转度,全面偏转度(Total runout)(b) 其它符号符 号 名 词直径符号(Diameter symbol)不考虑形体呎寸加添条件,和特性的尺寸无关 (Regardless of feature size modifier) 最多留料情况之加添条件,最大材料条件 (Maximum material condition modifier) 最小留情况加添条件,最小材料条件 (Least material condition modifier) 基本尺寸,精密尺寸(Basic dimension)基准形体符号,基准识别符号(Datum feature symbol)最多留料情况(MMC),Maximum- Material Condition最多留料情况是指一个形体包容最大的材料量,即零件重量最重的时候。
例如最小孔的尺寸或最大轴的尺寸。
如下面图示，直径为0.490~0.510的销子,当直径 为0.510时的重量比直径为0.490时重。
一个零件包含一个直径为0.490~0.510的孔,则零件当直径 为0.490时比0.510时,包含更多中更重.A1 .100 -A-最少留料情况,Least Material Condition最少留料情况是指一个形体它包容最小的材料量,即零件重量最轻的时候,例如最大孔的尺寸或最小轴的尺寸,它与最多留料情况(MMC)正好相反。
Ford_福特GDT形位公差培训材料_全集
GD&T for Body Engineering
7
Application
• It provides the opportunity for proper Datum selection and has the potential to significantly reduce product changes, especially those changes following final product release.
GD&T for Body Engineering
3
What is GD&T
• Geometric Dimensioning and Tolerancing is a technical data base through which our Product Design and Manufacturing Organisations can talk to one another via Product Data, whether on paper or the computer graphics screen
When should the Meeting take place. • Initial design concept stage, knowing the components
parameters such as size and function
Current methods use; • Past evidence, past experience, can sometimes hinder rather
• This can only be successfully achieved by the relevant PD representative attending the Master Control Plan (MCP) Meetings.
上新世云南铁杉木化石的化学成分
viously ( Zhao et al . 2005 a, b , 2006 ; Giannasi and Niklas, 1977; Niklas and Giannasi, 1977 , 1978; ) . Abundant plant and animal fossils occured in complicated strata in west Yunnan Province, China ( Ge et al . 1999) , part of which were buried in coal-bearing basins . Tsuga dumosa is an economically important conifer indigenous to the Yunnan Province of China (Southwest College of Forestry , Yunnan Forestry Administration , 1988) . Sesquilignans and lignans from this genus have been reported, previously (Zhao et al . 2004 , 2005c ) . A piece of Pliocene-fossil wood of T. dumosa , which was preserved morphologically , was discovered in an
关于形位公差二
半径和控制半径半径半径是从圆心到圆弧或圆的表面的一条直线。
半径的符号是R。
符号R 使用时，就产生了由两条圆弧（最小半径和最大半径）定义的公差带。
零件表面必需位于公差带内。
控制半径控制半径是不准许平直和相反的半径。
控制半径的符号为CR。
当CR 使用时，就产生了由两条圆弧（最小半径和最大半径）定义的公差带。
零件表面位于新月型的公差带内，并且不是平直和相反圆弧。
6Radius and Controlled RadiusRadiusA radius is a straight line extending from the center to the surface of an arc or a circle. The symbol for a radius is “R”. When the “R” symbol is used, it create a zone defined by two arcs(the minimum and maximum radii). Thepart surface must lie within this zone.Controlled RadiusA controlled radius is a radius with no flats of reversals allowed. The symbol for controlled radius is “CR”. When the “CR” symbol is used, it creates a tolerance zone defined by two arcs (the minimum and maximum radii). The part surface must be within the crescent-shaped tolerance zoneand be an arc without flats or reversals.6统计公差符号统计公差符号表示被应用的尺寸公差是由统计方法建立的.。
复合公差基础培训
工要求。
基准目标 Datum Target
点基准目标
线基准目标
面基准目标
通常给出车身坐标xyz
基准目标的位置必须用理论正确尺寸表示。面目标还应标注其表 面的大小尺寸。
基准的顺序
基准体系中基准的顺序前后表示不同的设计要求
强调4孔轴线 与A轴线平行
强调4孔轴线 与B平面垂直
基准后有、
无附加符号 又表示了不 同的设计要 求。详见公 差原则。
公差符号 Symbols
Type of
Tolerance 公差类型
For Individual Features 单一要素
Form 形状
For Individual Features or
Related Features
Profile 轮廓
单一要素或关联要素
For Related Features 关联要素
内表面(孔) D LM = 最大极限尺寸D max； 外表面(轴) d LM = 最小极限尺寸d min。
练习
孔: Ø15+/-0.5, MMC= Ø14.5 轴: Ø15+/-0.5, MMC= Ø15.5
LMC＝ Ø15.5 LMC＝ Ø14.5
实效状态 Virtual Condition
实效状态 － 实际要素处于最大实体状态，同时形位误差等于给出 的形位公差值时的一种状态。 尺寸公差和形位公差的组合效应，是一个常值。 多对应检具的尺寸。 实效尺寸－实效状态下的作用尺寸
公差框格Feature Control Frame
基准要素的字母及修正符号(可选) 公差值及修正符号 公差特征符号 无基准要求的形状公差，公差框格仅有前两项；有基准要求 的位置公差，公差框格包含三项，为三格至五格。 通常的公差框格为
本科植生专题作业参考文献(叶德)
Control of male germ-celldevelopment in flowering plantsMohan B.Singh and Prem L.Bhalla*SummaryPlant reproduction is vital for species survival,and is also central to the production of food for human consumption.Seeds result from the successful fertilization of male and female gametes,but our understanding of the develop-ment,differentiation of gamete lineages and fertilization processes in higher plants is limited.Germ cells in animals diverge from somatic cells early in embryo development,whereas plants have distinct vegetative and reproductive phases in which gametes are formed from somatic cells after the plant has made the transition to flowering and the formation of the reproductive organs.Recently,novel insights into the molecular mechanisms underlying male germ-line initiation and male gamete development in plants have been obtained.Transcrip-tional repression of male germ-line genes in non-male germ-line cells have been identified as a key mechanism for spatial and temporal control of male germ-line development.This review focuses on molecular events controlling male germ-line development especially,on the nature and regulation of gene expression programs operating in male gametes of flowering plants.BioEssays 29:1124–1132,2007.ß2007Wiley Periodicals,Inc.IntroductionMost of the grains and seeds that form the world staple food supply are the result of successful functioning of male and female gametes during fertilization.Despite the importance of plant reproduction,our understanding of the development,differentiation and fertilization processes of gamete lineages in higher plants is limited.Most studies in recent decades have investigated the reproductive development of the anther and ovule (1–5)within the context of androecium and gynoecium,and can be regarded as early sexual organ differentiation stages of the flower ,which,except for a few cells,is largely a sporophytic and thus somatic lineage.In contrast,this paper focuses on reviewing progress towards understanding the molecular basis of male germ-line initiation and male gamete development in flowering plants.The germ-line cells in most animals diverge from somatic cells during early embryo development and remain as a distinct stem cell population throughout the life of the animal (Fig.1A).In contrast,plants exhibit distinct vegetative and reproductive phases,and the male germ line in plants originates in flowers from the cells of a previous somatic lineage (Fig.1B,Fig.2).Cell-cycle decisions in plant anther tissues from mitosis to meiosis initiate a complicated cascade of development processes that leads to the formation of four haploid microspores from a single diploid microspore mother cell (Fig.2).The male germ line is initiated from the haploid microspore via asymmetric division,following which the smaller generative cell,which defines the male germ-cell lineage becomes wholly encased within the much larger vegetative cell to form a unique ‘‘cell-within-a-cell structure’’.The generative cell subsequently divides to produce two sperm cells (Fig.3).In some plants,such as Arabidopsis and rice,the division of generative cell to produce two sperm cells takes place during pollen maturation in the anther ,whereas in other plants,such as tobacco and lily ,this division occurs after pollination,inside the pollen tube (Fig.3).During pollen germination,the wall of the vegetative cell extends to produce a pollen tube via tip elongation and,by this mechanism,the two sperm cells are ultimately delivered to the embryo sac.Asymmetric division of the microspore is essential for establishing the male germ line,since experimental manipu-lations of division lead to the failure of generative cell formation.(6)Moreover,Arabidopsis pollen mutants (such as gem1and gem2and scp)that show defects in asymmetric division of the microspores show failure of male gamete transmission (7–10)indicating that the male germ-line initiation pathway that leads to the formation of generative and sperm cells is decisively dependent on asymmetric division of the haploid e of colchicine as a microtubulePlant Molecular Biology and Biotechnology Laboratory ,Australian Research Council Centre of Excellence for Integrative Legume Research,Faculty of Land and Food Resources,The University of Melbourne,Australia.*Correspondence to:Prem L.Bhalla,Plant Molecular Biology and Biotechnology Laboratory ,Australian Research Council Centre of Excellence for Integrative Legume Research,Faculty of Land and Food Resources,The University of Melbourne,Parkville,Victoria 3010,Australia.E-mail:premlb@.au DOI 10.1002/bies.20660Published online in Wiley InterScience (www.interscience.wiley .com).1124BioEssays 29.11BioEssays 29:1124–1132,ß2007Wiley Periodicals,Inc.Abbreviations:EST ,expressed sequence tags;GC,generative cell;GFP ,green florescent protein;GRSF ,germ-line-restrictive silencing factor;GUS,b -glucuronidase;LGC1,lily generative-cell-specific 1;SC,sperm cells;VC,vegetative cell.disruptive drug (6)and identification of GEM1/MOR1as a microtubule-associated protein also indicated that the cell cytoskeleton appears to play a key role in establishing the division plane for asymmetric cell division.(7,10,11)Despite these advances in our knowledge,the key intrinsic molecular determinants that control asymmetric polarity division and the founding of male germ line have not been identified.It appears that the key intrinsic steps that specify asymmetric division ofthe microspore and subsequent determination of the cell fate are determined by the haploid genome in a cell-autonomous manner ,since microspores removed from their anther niche and cultured in artificial media are capable of sperm cell formation in vitro.(12)In contrast to the significant understanding of the molecular genetic basis of male gamete development and fertilization in animals,most of the mechanisms underlying themolecularFigure 1.Outline of the landmark stages in the formation of germ lines in animals and plants.A:An early embryo formed from a zygote that results from the fusion of male and female gametes generates not only all the parts of animal body (somatic cells)but also demarcates germ cells for the next generation.Note pre-meiosis establishment of germ lines and the continuous production of functional male gametes is dependent on germ-line stem cells during the adult life of an animal.B:Seeds resulting from double fertilization in higher plants have well-developed embryos.Seed germination results in a fully developed plant at the vegetative stage.The transition to the flowering stage initiates the formation of the reproductive organs,followed by gametes.Origin of gametes from gametophyte is a post-meiotic event.Gamete development within a reproductive organ is not a continuousprocess.Figure 2.Male germ-line development in plants.A:Lily flower showing the male reproductive anther organ (yellow).B:Diagrammatic representation of early anther showing microsporocytes (2n)within the developing anther .C:Microsporocyte undergoing meiosis resulting in the formation of a tetrad of haploid microspores (n)(D ).E:A microspore.F:Early bicellular pollen.Asymmetric division within a microspore results in the formation of a larger vegetative cell (VC)and a smaller generative cell (GC).G:Mature bicellular pollen.BioEssays 29.111125basis of flowering-plant germ-cell specification,differentiation and gamete interactions remain unknown.However ,with the availability of new molecular biology and genetic tools,there has been exciting progress in recent years towards the understanding of flowering plant gamete development.There-fore,this review will focus on molecular and genetic control of male germ-line development in plants and in particular on the nature and regulation of gene expression programs operating in the male gametes.Transcriptome-based approaches toinvestigating male germ-line developmentUntil recently little information was available regarding the gene expression programs underpinning flowering plant male germ-line initiation and male gamete development.This lack of knowledge was mainly attributable to the inaccessibility of generative and sperm cells due to their encasement within the male gametophyte.Moreover ,this important area remained neglected because of a long-held view in the literature that the condensed state of the chromatin and the very small amount of cytoplasm relative to the nucleus probably reflected the transcriptionally quiescent nature of generative and sperm cells.The development of novel protocols to isolate generative and sperm cells (13,14)eventually led to dawn of molecular era in plant gamete research.These gamete isolation protocols provided opportunities to address several outstanding ques-tions such as whether these cells are transcriptionally active and have protein synthesis machinery that is independent ofthe outer vegetative cell.(15–17)The presence of translatable mRNA in generative and sperm cells was initially confirmed by metabolic labelling experiments.(18–20)This observation led to the construction of cDNA libraries from isolated generative and sperm cells and the identification of male gamete-specific genes in flowering plants.(21,22)Currently ,transcriptome data are available for Arabidopsis pollen (23–25)as well as EST data from maize sperm cell (22)and lily generative cell.(26)Transcriptional profiling of Arabidopsis pollen using an Affymetrix 8K chip showed that the tran-scriptome of pollen is clearly distinct from that of vegetative tissues.(23)Out of 7,792annotated genes,992were shown to be pollen expressed and 40%of these pollen-expressed genes were found to be pollen specific.Subsequent use of ATH1genome arrays identified 13,977male gametophyte-expressed transcripts of which 9.7%(1355)were male gametophytic specific (24)while use of same ATH1chip by different investigators identified 6,587genes to be expressed in pollen.(25)While RNA prepared using total Arabidopsis pollen contains contributions from both vegetative and sperm cells,it is worth noting that due to very small size of the latter ,the Arabidopsis pollen transcriptome is likely to highly biased towards reporting genes expressed in much larger vegetative cells.Hence,transcriptome data for isolated sperm cells would be desirable to gain insight into molecular events governing sperm cell development and function.Fluorescence-activated cell sorting (FACS)has been used to isolate maize (Zea mays )sperm cells.(22)Isolated maize sperm cells were usedtoFigure 3.Formation of sperm cells.Bicellular pollen showing a smaller generative cell (GC)and a larger vegetative cell.Mature pollen in plants such as lily is released from the anther at this stage for pollination.In plants such as Arabidopsis and rice,the pollen undergoes further division whereby the generative cell divides mitotically to produce two sperm cells (SC).Tricellular pollen is released from the anther for pollination,whereas bicellular pollen undergoes a second mitotic division during pollen tube elongation while growing through female reproductive tissues.1126BioEssays 29.11prepare cDNA library and5,093ESTs sequences have been obtained.Several transcripts encoding proteins similar to hypothetical Arabidopsis proteins were identified in the sperm cells of mature pollen.Analysis of886expressed sequence tags(ESTs)from lily generative cells revealed the presence of 637non-redundant genes,(26)nearly61%of which repre-sented novel genes and hence targets for investigating male germ-line-specific functions.The identification of several transcripts present specifically in the generative and sperm cells indicated that despite their condensed chromatin organization,these male germ cells have their own genetic program.(27–29)Sequencing of re-presentative sets of cDNAs revealed classes of genes that are developmentally regulated in the male germ-line cells,includ-ing(a)genes that are shared with somatic cells but are upregulated in the male germ line,(b)germ-cell-specific gene variants and(c)genes that are exclusively expressed in male germ line cells.(26,30)Genes that are shared with somatic cells but are upregulated in plant male germ-line cells include those involved in the DNA repair pathway.(31)A plant homologue of the human nucleotide excision repair gene ERCC1was found to be upregulated several-fold in lily generative cells compared to pollen vegetative cells and plant somatic cells.In plants, the germ line is not set aside early in embryo development, with germ cells instead originating from cells of a previous somatic lineage.Thus,plant germ-line cells can carry several mutations that accumulate during somatic growth.It has been proposed that a stringent haploid selection process during gametophyte development filters out most of the deleterious mutations.However,the fully developed male pollen game-tophyte is exposed to solar UV radiation and other environ-mental mutagens after being released from the anther. Upregulation of DNA repair genes in the male germ line most likely protects germ-line DNA from heritable mutations resulting from DNA damage.Other genes that are upregulated in generative cells include a cluster of genes related to the cell-cycle-progression pathway.(26,30)Genes encoding ubiquitin-pathway-related proteins such as polyubiquitin,proteasome subunit,ubiquitin-conjugating enzyme,Skp1and Ring box protein were found to be highly upregulated in the generative cells.(30)Ubiquitin-pathway-related genes have been found to be active in Plumbago species and maize sperm cells.(22,28)The ubiquitin system has also been shown to play an essential role in male gameto-genesis in mice and humans.(32,33)The high level of expression of ubiquitin-pathway-related genes in generative cells suggests that the ubiquitin proteolysis system plays a critical role in the male gametogenesis of higher plants.In addition to the normal complement of histones present in plant somatic cells and pollen vegetative cell,the male germ-line cell possesses cell-specific variants of histones H3and H2B.(26,27,29,30,34–37)Comparison of lily generative cell ESTs with maize sperm cell ESTs indicated an overlap(168out of637lily ESTs)in male gamete gene expression in generative and sperm cells in these plant species while comparison with Arabidopsis male gametophyte-specific transcripts(24)indicated that129lily generative cell ESTs showed significant similarity to Arabi-dopsis male gametophyte-specific genes.In addition,micro-array studies showed unique gene expression profile of lily generative cells;(30)83%(356transcripts out of430genes) of the transcripts were enriched in generative cells.A high percentage of cell-specific transcripts in generative cell,a distinctive feature,is unique to these male gametic cells. Further,a significant overlap in the expressed genes among lily generative-cell ESTs,maize sperm-cell ESTs and Arabidopsis pollen-specific transcriptome is apparent throughout all functional role categories.(26)This comparative approach has been successful in maize to identify germ-line-specific promoters GEX1,GEX2in Arabidopsis.(38)Further, these genome-wide and expressed genes data sets could be useful in identifying conserved male-gamete-specific genes and formulating hypothesis about their potential cellular functions.Genes that are vital for male gamete development and for controlling gamete interactions are likely to include those that encode proteins that are exclusively expressed in germ-line cells.Several transcripts in lily generative cells that encode proteins that are similar to proteins classified as hypothetical in the Arabidopsis databases appear to be specific to the male germ line in mature pollen.The first such identified gene from a generative cell cDNA library was LGC1(lily generative cell-specific1;accession no.AF110779),which encodes a small protein of128amino acids with a calculated molecular mass of 13.8kDa.(21)The presence of a hydrophobic domain exhibiting the characteristics of a GPI anchor suggests that this protein is located on the surface of the cell membrane of the male germ cell,and this has been confirmed by immunolocalization experiments,with expression analysis showing that LGC1is expressed specifically in the generative and sperm cells of lily.(21,26,30)We recently found that LGC1was represented by11out of886sequenced lily generative cell ESTs.(26) The initial identification of male germ-line-specific genes in lily and subsequent investigation of their functions via disrupting the expression of their homologues in the model plant Arabidopsis has turned out be a highly successful strategy for determining the male gamete proteins that are critical to development and fertilization of higher plants.Mori et al.(39)used isolated lily generative cells to identify a higher plant homologue of GlsA,which is a chaperone-like protein essential for gonidia formation in Volvox.(40)Using degenerate PCR primers,the authors reported amplification of cDNA from lily generative cell RNA that was highly similar to Volvox counterparts.Immunolocalization analysis revealed the co-localization of this putative chaperone protein withBioEssays29.111127a-tubulin,suggesting that this plays an important role in the morphogenesis of the generative cell by stabilizing cytoske-letal structures.Further differential display experiments performed in the same laboratory to compare the gene expression patterns of unicellular microspores,bicellular pollen and isolated gener-ative cells led to the identification of a novel generative-cell-specific protein(GCS1)from lily generative cells.(41)GCS1 possesses a carboxy(C)-terminal transmembrane domain and is localized to the surface of generative and sperm cells, suggesting its role in gamete interactions.A GCS1homologue is also present in Arabidopsis.The failure of gamete fusion leading to male sterility in Arabidopsis plants possessing a mutation in the GCS1locus suggests that this gene-encoded function is essential for fertilization.It was further proposed that GCS1is anchored on the surface of sperm cells via its C-terminal transmembrane domain.The presence of LGC1on the surface of lily male germ cells and the conservation of LGC1homologues in Arabidopsis and rice suggest that this protein is a key player in the gamete interactions of flowering plants.Other lily genes reported to be represented in the lily generative cell EST library,particularly those showing homology in Arabidopsis,represent a unique starting point for investigating the repertoire of proteins involved in male gamete differentiation.Although these tran-scriptomic approaches are providing valuable insight into the portions of flowering-plant genomes that are expressed in male germ-line cells,they do not provide information on which of the mRNAs are actually translated and when this occurs. Whether there is a temporal disconnection between mRNA transcription and translation to proteins in male germ cells is unclear.Whether certain mRNAs are sequestered in ribonu-cleoprotein particles and stored prior to being translated also remains to be addressed.It should be noted that pollen generative cells that have already undergone dehydration as part of the maturation process contain abundant and diverse mRNAs,even when protein synthesis is not active.Since transcriptional profiling of generative and sperm cells has been based on cells isolated from mature desiccated pollen,it is suggested that these RNAs will be translated following re-hydration of the pollen on the stigma surface following pollina-tion.An integrative transcriptomic approach is likely to identify the most-relevant male-germ-cell-expressed proteins. Genetic approaches for unravellingthe male-germ-cell genes critical tomale-germ-cell differentiationSeveral genetic segregation screening studies of the genes expressed in haploid male gametophyte have been performed using Arabidopsis as a model system.The genetic lesions in most of the mutants identified via such screenings are in genes expressed in the larger cell of the pollen,whose knockout induces aberrations in pollen development that lead to male sterility.(8,42–47).Since pollen has a haploid genome,any mutation in the genes that are essential for general cellular functions is likely to lead to the termination of development.For example,mutations in pollen-expressed genes that are involved in sucrose transport,membrane trafficking or cation transport showed a sterility phenotype.(48)Genetic compen-sation due to gene redundancy is also another shortcoming of the genetic approach,since gene redundancy is a normal phenomenon in plants and is considered to be responsible for the absence of phenotypes in the majority of single loss-of-function mutants.(49)These limitations question the ability to identify genes that are expressed only in the male germ cells of pollen.The screening for such mutants has to be limited to a subset in which pollen development and tube growth are normal,but where there is still no transmission of the male genome to the next generation.Arabidopsis mutants duo1and duo2are two such identified mutants,in which the pollen morphology appears normal but where blocked generative cell division results in the formation of bicellular pollen at an-thesis.(50)It is worth mentioning here that these mutants were not identified by segregation screen,but in a direct morpho-logical screen for germ-line defects.In duo2mutant specifi-cally generative cell mitosis at pro-metaphase was blocked.(52) DUO,which was subsequently identified by map-based cloning,encodes a novel R2R3-MYB transcription factor that is expressed specifically in the male germ line.(51)The DUO1 protein was reportedly localized to the nucleus of generative and sperm cells,with a proposed function of promoting generative cell by activating specific targets such as cyclin genes.The mitotic division of generative cell also fails in Arabidopsis mutant cdc2a,(52,53)in which only one sperm cell (rather than two)is produced.The viable mutant pollen can only fertilize one cell in the embryo sac.Intriguingly,the single gamete fertilizes only the egg cell.The serine/threonine protein kinase cdc2is a key regulator of the cell cycle,acting through cyclin-dependent phosphorylation.Another Arabidopsis mutant has been described in which the generative cell divides normally and sperm cells that are delivered to the embryo sac fail to fuse with either the egg cell or the central cell.(42,45,54)It was also confirmed that the absence of fertilization in HAP2mutants was not due to a defect in sperm development or to migration of sperm within the pollen tube.HAP2was found to be allelic to GCS1.(41) HAP2encodes a705-amino-acid membrane protein with a histidine-rich C terminus.This protein is not similar to genes of known function and has no obvious functional motifs.Database searches have revealed that HAP2homo-logues are present in other flowering plants.HAP2is specifically expressed in sperm cells,as confirmed by reporter gene analysis in transgenic Arabidopsis plants.Thus,these data suggest that unique molecules are involved in gamete function.1128BioEssays29.11Chromatin remodelling and malegerm-cell-specific histone variantsAs soon as asymmetric cell division of a microspore leads to the formation of two unequal cells,it becomes apparent that the chromatin of the generative nucleus is much more condensed than that of the vegetative nucleus.(55)This condensed nature of the chromatin is also retained in sperm nuclei.This characteristic of higher plants is also present in animals,(56)with the condensation of male chromatin in animal sperm cells being mediated by the exchange of somatic histones with transition proteins,followed by protamines or sperm-specific histones that are,in turn,replaced by somatic histones provided by the egg cell following fertilization. Proteins similar to protamines have been reported in the motile sperm cells of lower plants,(57)but these proteins are not conserved in higher plants.A biochemical approach to comparing chromatin proteins from vegetative and generative cell nuclei in lily and testing the comparative mobility of these proteins on two-dimensional electrophoresis gels revealed that at least five nuclear basic proteins were either specific to or enriched in generative cell nuclei.(34)Two of these proteins were identified as variants of histones H3and H2B,and were designated gH3and gH2B,respectively.Immunocytochem-ical staining of these histone variants showed that they were not only present in generative cells but also in the two sperm cells formed by the division of the generative nucleus.(35) The first study to investigate the expressed genes repre-sented in cDNA libraries constructed from isolated gene-rative cells revealed an abundance of transcripts encoding histone variants.(58)At least five cell-specific histone H3 variants are expressed in lily male germ cells.(31)In histone variants gcH3and leH3,the lysine at position9is substituted by methionine.Despite sharing conserved structural features with centromeric histone H3,the germ-line-specific variant form gH3is distributed throughout the chromatin.In addition, the methylation pattern of lily histones associated with male germ-line cell appears to differ from that observed in somatic cells.In Arabidopsis,one histone H3gene,At1g19890,is expressed specifically in germ cells.(27)In contrast to lily germ-line histone variants,the amino acid sequence of this Arabidopsis variant is highly conserved in somatic histones.It is notable that histone genes are highly conserved in plants, and the only histones that show significant sequence variations are in those variants expressed in male germ-line cells.There exists the tantalizing possibility of a causal relationship between the expression of histone variants and the differential condensation and/or differential gene expres-sion programming in male germ cells of higher plants.Further experiments involving either ectopic expression of germ-line variants in somatic cells or individual knockout mutants exhibiting disrupted function of germ-line-specific genes are required to address these outstanding questions.Transcriptional regulation of malegerm-line-specific gene expressionMolecular studies are beginning to elucidate the regulators of germ-line-specific gene expression,which is essential to understanding the gene circuits underpinning male germ-cell differentiation.Transcriptome analyses have revealed that a significant number of flowering-plant genes are transcribed exclusively in the male germ line.(27,30,54,58,59)What is the nature of transcriptional regulation programs that control the cell specificity of male germ-cell-specific genes?The identi-fication of LGC1as the first-identified male germ-line cell-specific transcript expressed under the control of generative/ sperm cell promoter provided a unique model system in which to investigate the underlying transcriptional regulatory mechanisms.Use of the LGC1-GFP reporter gene construct in transient transformation experiments of lily pollen revealed the gen-erative cell-specific expression of LGC1,(60)while stable transformation of a heterologous plant,tobacco with LGC1-GUS,showed the generative cell-specific expression of a reporter gene in the generative cells of transgenic tobacco, indicating that the transcriptional factors required to control the specificity of expression of LGC1promoter are conserved in male germ-line cells.The strict generative cell specificity of LGC1promoter was confirmed by obtaining transgenic plants carrying the LGC1promoter fused with the DT/A cytotoxin gene.(60)Such plants showed specific ablation of pollen grains containing DT/A expression in the generative cells.Deletion analysis of the LGC1promoter showed the presence of a43bp nucleotide regulatory silencer element whose excision from the promoter led to a constitutive pattern of expression of truncated promoter in all the plant tissues tested.Gel retardation assays showed that nuclear extracts of lily petal cells contain a protein that specifically interacts with the LGC1 silencer sequence.(60)The gene encoding this repressor protein was recently cloned by southwestern blotting of a lily petal cDNA expression library.(61)GRSF(Germline Restrictive Silencer Factor)is a novel24-kDa DNA-binding repressor protein encoded by a gene expressed ubiquitously in plant tissues with the exception of generative cells.Immunolocali-zation showed that GRSF is present in the nuclei of uninucleate microspores and pollen vegetative cells but is absent in the generative cell nucleus.Chromatin immunopre-cipitation assays showed that GRSF interacts with a specific domain in promoter region of LGC1and with the male germ-line-specific histone gcH3.Promoter mutagenesis experi-ments led to the identification of a conserved8-bp motif in the LGC1and gH3promoters.This sequence motif is likely to be core-binding site for GRSF.These data show that the male germ-cell-specific gene expression of LGC1and other coordinately expressed genes might be controlled by GRSF by repressing their expression in other plant cells.The promoter region of the Arabidopsis male germ-line-specificBioEssays29.111129。
基于机器学习的香豆素衍生物的建模研究
基于机器学习的香豆素衍生物的建模研究作者：张培俭夏润泽高湛刘壮来源：《青岛大学学报（工程技术版）》2023年第04期摘要：為了筛选潜在药物治疗乳腺癌，本文采用机器学习方法对香豆素衍生物建立定量构效关系模型。
基于启发式方法筛选出3种香豆素衍生物的分子描述符，通过支持向量机、广义回归神经网络和K近邻方法建立3种机器学习预测模型，拟合57种香豆素衍生物对MCF-7乳腺癌细胞的抑制作用并作出预测。
预测结果表明，3种模型的预测结果与实测值吻合度较高，其中支持向量机的效果和鲁棒性最佳，通过网格搜索确定后的参数为C=1.43，γ= 499.768，其测试集的均方根误差为0.15。
该研究为设计新的乳腺癌药物分子提供研究方向以及活性预测。
关键词：乳腺癌；香豆素衍生物；定量构效关系；机器学习中图分类号：TP181文献标识码：A收稿日期：2023-04-10；修回日期：2023-09-18基金项目：山东省自然科学基金资助项目（ZR2019PF012）；青岛大学国家级大学生创新训练项目（S202011065021）作者简介：张培俭（1974-），男，博士，副教授，主要研究方向为药物大数据分析。
Email：*****************乳腺癌是女性最常见的恶性肿瘤之一，也是女性癌症死亡的主要原因，其发病率随着年龄的增长急剧上升[1-2]，全球癌症统计发现，2018年乳腺癌新发病例约208.9万例[3]，其中包含死亡病例627 000例，约占全球女性癌症死亡总数的15%[4]。
自上世纪60年代，科学家研制出选择性雌激素调制器（SERM），首次被批准用于辅助治疗乳腺癌的SERM是他莫昔芬，该药物已为许多患者提供治疗。
虽然SERM改善了ERα阳性乳腺癌患者的症状，但其价格昂贵，且伴有诸多副作用，严重限制了其治疗效果[5]，目前活性高但副作用低的SERM尚未发现。
近几年，香豆素发展成一种多功能的分子支架，广泛分布在自然界，具有多种药理及治疗作用，如抗细菌，抗真菌，抗疟疾和抗癌等[6]。
第六章 妊娠与胚胎发育
自然环境 于母系的妊娠期，即雌性骡驹的平均妊娠期341天，雄性则338天，比
马驹长约11—12天(Hamori，1960)
影响妊娠的因素
遗传因素
品种
在各品种之间存在着怀孕日期的微小差异，可能是由 于遗传、季节或地区的影响。如不同品种奶牛的怀孕
妊娠维持
生出现的一系列变化是受生殖激素所调节，孕激素是维持妊娠的重 要激素。猪和兔等动物只须孕激素即可维持妊娠，不有一些动物则需要孕激 素和雌激素协同作用来维持妊娠，但有个别的动物妊娠的维持与孕激素并无 密切的联系，如大象的妊娠并不需要孕激素的作用。
排卵后形成的黄体母体妊娠而长期存在分泌孕酮，或者在妊娠后期由其分泌 机能逐渐由胎盘所替代后而消失。孕酮在维持子宫继续发育的同时，降低了 子宫肌的活动抑制了催产素对子宫的收缩刺激，这保证了子宫内环境适于胚 胎及胎儿的发育。
牛马羊猪是具有上皮绒毛膜式结缔组织绒毛膜胎盘的家畜这种类形的胎盘胎儿与母体间的血液联系并不是很紧密所以组织营养不但对早期胚胎而且在整个妊娠期间都是重要的营养来源孕酮在决定附植前的变化中和附植后妊娠的维持起主导作用
妊娠与胚胎发育
第一节 妊娠
妊娠的定义
妊娠(Pregnancy)又称“怀孕”，它是哺乳动物所特有的一种生理 现象，自卵子受精开始一直到胎儿发育成熟后，胎儿与其附属物 共同排出前，母体复杂的生理过程。
家畜妊娠认别和建立及其基本机理
妊娠的认别和妊娠的建立是密切相关的，先有孕体产 生信号，然后母体作出相应的反应，继而开始相互联 系和相互作用，并将此联系固定下来。胚胎产生的激 素信号作用于子宫和卵巢上的黄体，有使黄体抗溶、 并能维持和促进黄体功能的作用，这抵消了PGF2α的 溶黄体作用，维持了在妊娠期间黄体的形态和内分泌 机能。
脑胶质瘤表观扩散系数与肿瘤分级及IDH1突变的关系
Apr. 2021Vol. 42 No. 22021年 4月第42卷第2期首都医科大学学报Jousial of Capital Medical University[doi : 10. 3969/j. issu. 1006-7795. 2021. 02. 021] ・ 临床研究 ・脑胶质瘤表观扩散系数与肿瘤分级及IDH1突变的关系闫新亭宋双双卢洁*基金项目：北京市医院管理局"登峰"计划专项经费资助(DFL20180802) & This study was supported by Beijing Municipal Administration of Hospitals ' Ascent Plan ( DFL20180802).* Corresponding authos , E-mail : imavinglu@ hotmail. com网络出版时间：2021 -04 -12 14： 29 网络出版地址：https ：//kns. ski. nelkcms/detaii/11.3662. R. 20210412. 1140.042. html(首都医科大学宣武医院放射科与核医学科磁共振成像脑信息学北京市重点实验室，北京100053)【摘要】 目的 探讨MR 扩散加权成像(dWfusion weighted imaaing , DWI )的表观扩散系数(apparent dWfusion coefficient , ADC )在 脑胶质瘤分级及分型中的意义，进一步探讨ADC 与异柠檬酸脱氢酶9 ( isocitrate dehydsgenascY , IDH1)突变分型的相关性。
方法 收集首都医科大学宣武医院经病理证实的82例脑胶质瘤患者的影像资料，测量肿瘤实质区、对侧正常白质ADC 值，并计算最小 ADC 值(minimum ADC , ADC mW )、平均 ADC 值(mean ADC , ADC mecn )、相对最小 ADC 值(relative minimum ADC,rADC mW )、 相对平均ADC 值(relliw mean ADC ,r ADC mi )值，探讨所有ADC 值在各级别胶质瘤及亚型间的差异以及其与DH1突变的关系。
Ford_福特GDT形位公差培训材料_全集
Result of meeting • May be documented in CAD, or paper form
GD&T for Body Engineering
16
Step 2
Establish Datum Reference Frame
• It is the engineering product definition standard that geometrically describes design intent and provides the documentation base for the design of the quality and production system.
Who attends the Meeting • PD and Manufacturing, i.e. Body Engineering, DCD, Stamping,
Body and Assembly.
GD&T for Body Engineering
15
Master Control Plan
Master Control Plan
What is the purpose of the MCP meeting in relation to PD • To establish a common understanding for the verification process
of the major panels, e.g. Bodyside, Hood, Deck Lid, Door, Roof, Underbody, etc. • To obtain agreement at an early stage of the design for the datum reference frame, die approach, etc.