5 May 2006 Vol 312, Issue 5774, Pages 653-762 土卫六上的沙丘科学家报告说，土卫六（泰坦）上有许多沙丘，它们与地球上非洲的撒哈拉、纳米比沙漠以及澳洲和阿拉伯沙漠中的沙丘有许多类似之处。这项新研究用的是来自卡西尼无线电探测和测距仪(RADAR)拍摄的土卫六的图像。土卫六的沙丘高达150米、长度达几公里。它们占据了土卫六表面很大的面积-在卫星赤道附近几千公里都有沙丘。沙丘由什么材料构成现在还不清楚，比较大可能是有机的固体或水冰。文章作者说，土卫六上沙丘的存在表明其上有产生沙子大小颗粒的地质过程，以及没有的可作为沙陷的持久赤道表面液体的存在。这些沙丘大约东西向排列，它们表现出的其他流动特性提示，沙丘是由表面的东风和由土星引力驱动的南北方向的潮汐涨落共同作用形成的。相关研究评述的作者Nicholas Lancaster 指出，土卫六上的沙丘的几何形状-它们的宽度、长度、以及丘顶到丘顶的间距与纳米比沙漠和阿拉伯Rub al Khali沙漠的线性沙丘很类似。
报告：The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes, R. D. Lorenz, et al.
研究评述：Linear Dunes on Titan, Nicholas Lancaster
寒武纪之前的动物化石尽管地球上最早动物中的大多数可能在埃迪卡拉(Ediacaran)纪后消失了，但是研究人员发现了一个看起来存活到寒武纪动物的新化石，这也许能为动物进化这个转变时期提供一点线索。这些被称为"vendobionts"的动物是埃迪卡拉纪的几种神秘动物之一。人们不清楚它们与后来动物的进化关系；其实许多埃迪卡拉纪动物似乎都没有后来的亲戚。舒德干和同事现在描述了来自中国寒武纪早期的新vendobiont化石，并提出这些vendobionts是从埃迪卡拉纪存活下来的。这个叶状化石被定为Stromatoveris 属，它保存得极为完整，能看到内部的软组织。这个动物看起来是靠一个茎依附在海洋底生活的。
报告：Lower Cambrian Vendobionts from China and Early Diploblast Evolution, D.-G. Shu, et al.
循环宇宙与宇宙学常数宇宙的一个循环模型也许能帮助解释为什么现在宇宙空间的能量密度很低，与物质的能量密度可比。(在循环模型中，宇宙经历了几次大爆炸和大紧缩。)这就是所谓的"暗能量"，在数学上表现为一个宇宙学常数。最近的观察表明宇宙在膨胀，意味着宇宙真空中小的、正的几乎是常数的能量加速这一膨胀。Paul Steinhardt 和Neil Turok在他们的心计算中提出，这个宇宙学常数自最近的一次大爆炸以来不断地减小，但是这一减小在常数趋于零时几乎停止。这意味着宇宙将"与达到这个宇宙学常数的时间相比相对永久地"处于一个极小的宇宙学常数的水平，作者说。但是这个过程所需的时间之长，将使宇宙中所有的其他物质耗散掉，除非宇宙是循环的，不断地通过一系列的大爆发产生新物质。Steinhardt 和Turok描述的这个新情景也许能解释为什么我们看到的宇宙是这个样的-具有小的宇宙学常数和相对稀疏的物质。在此以前，一个解释宇宙为什么是这样的主要理论是所谓的"人择原理"，也就是说宇宙的物理测量之所以是这样的，是因为如果不是这样的，人类就不会存从而能观察之。在一篇相关的研究评述中，Alexander Vilenkin指出人择原理也许仍是为什么宇宙学常数的可能最小值与宇宙现今密度可比的最好的解释。
科学特快研究文章：Why the Cosmological Constant Is Small and Positive, Paul J. Steinhardt and Neil Turok
科学特快研究评述：The Vacuum Energy Crisis, Alexander Vilenkin
用移动电话网络监测降雨研究人员说，移动电话公司收集的有关大气层的信息也许比现有的气象学方法提供了更好的降雨测量。降雨、降雪、以及大气条件的其他变化引起无线通讯网络中传送的无线电信号强度的变化。Hagit Messer和同事说，这些变化为大范围、实时地监测降水提供了一个方法，而不需要过多的人工干预和额外的费用。为了演示这个想法，研究人员用一场暴雨期间每15分钟从一个以色列蜂窝电话网络收集的数据计算了表面降雨量。他们的结果与计雨量器和气象雷达测量的结果相当。
简报：Environmental Monitoring by Wireless Communication Networks, Hagit Messer, Artem Zinevich, and Pinhas Alpert
免疫B细胞的伸展与抗体生产免疫系统的B细胞搭乘在其它细胞的表面巡逻搜索异种蛋白，新研究说，这些B细胞伸展出去包住其它细胞，将侵犯蛋白收集成一个中心块。Sebastian Fleire和同事说，这个伸展和收集的应答也许帮助细调B细胞的激活。这些研究人员用实时实验观察了B细胞在其它细胞的表面伸展它们的细胞膜，然后在收缩时收集刺激B细胞受体的任何异种蛋白。研究人员发现，这个伸展行为由B细胞受体与异种蛋白作用的强度、以及异种蛋白的密度控制。Margaret Harnett在一篇相关的研究评述中指出，这个敏感的过程帮助B细胞估计需要多强的抗体应答。
报告：B Cell Ligand Discrimination Through a Spreading and Contraction Response, S. J. Fleire, J. P. Goldman, Y. R. Carrasco, M. Weber, D. Bray, and F. D. Batista
研究评述：B Cells Spread and Gather, Margaret M. Harnett
动物照料指导方针本期政策论坛的作者指出，有关动物照料的国际指导方针对在全球基于动物的科学研究中促进适当的行为与保护用于实验动物的福利很重要。作者没有提出建立一组世界范围的规则，而是描述了一个旨在“和谐”动物照料和使用指导方针的动议，其中每个国家保持自己的依照文化、传统、宗教、法律和条例的针对科学用动物的监督机制。各国机制的和谐将会改善目前由于对动物照料和使用的不同标准给比较动物实验研究结果以及重复这些结果时的复杂性，这些复杂性给国际科学合作带来麻烦。作者介绍了国际实验动物科学理事会的一个工作组关于建立动物研究和动物安乐死仁慈终点的原则。仁慈终点第一原则陈述，强有力的证据表明动物在与给人带来疼痛和痛苦相当的条件下也感受疼痛和痛苦。动物安乐死第一原则陈述，每当需要结束动物的生命时，应该用最敬重生命的方法来做。
政策论坛：Harmonization of Animal Care and Use Guidance, Gilles Demers, et al.
ContentsThis Week in Science
Editor summaries of this week's papers.
Science 5 May 2006: 653.
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Editorial:
The High Cost of Coming to America
Al Teich and Wendy D. White
Science 5 May 2006: 657.
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Editors' Choice
Highlights of the recent literature.
Science 5 May 2006: 659.
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NetWatch
Best of the Web in science.
Science 5 May 2006: 665.
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News of the Week
VETERANS ADMINISTRATION: Texas Earmark Allots Millions to Disputed Theory of Gulf War Illness
Jennifer Couzin
Science 5 May 2006: 668.
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BIOMEDICINE: Genes and Chronic Fatigue: How Strong Is the Evidence?
Jocelyn Kaiser
Science 5 May 2006: 669-671.
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U.S. RESEARCH FUNDING: Industry Shrinks Academic Support
Yudhijit Bhattacharjee
Science 5 May 2006: 671.
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QUANTUM OPTICS: A New Way to Beat the Limits on Shrinking Transistors?
Adrian Cho
Science 5 May 2006: 672.
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IMMUNOLOGY: Differences in Immune Cell "Brakes" May Explain Chimp-Human Split on AIDS
Jon Cohen
Science 5 May 2006: 672-673.
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NEUROBIOLOGY: Despite Mutated Gene, Mouse Circadian Clock Keeps on Ticking
Greg Miller
Science 5 May 2006: 673.
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ENERGY RESEARCH: Industry Conservation Programs Face White House Cuts
Eli Kintisch
Science 5 May 2006: 675.
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ScienceScope
Science 5 May 2006: 671.
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Random Samples
Science 5 May 2006: 667.
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Newsmakers
Science 5 May 2006: 687.
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News Focus
CLIMATOLOGY: A Tempestuous Birth for Hurricane Climatology
Richard A. Kerr
Science 5 May 2006: 676-678.
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NUCLEAR PHYSICS: Indian Angst Over Atomic Pact
Pallava Bagla
Science 5 May 2006: 679.
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NEUROSCIENCE: The Map in the Brain: Grid Cells May Help Us Navigate
Karen Heyman
Science 5 May 2006: 680-681.
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PHYSICS: Tipping the Scales--Just Barely
Robert F. Service
Science 5 May 2006: 683.
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ASTRONOMY: Rising From the Ashes
Dennis Normile
Science 5 May 2006: 684-685.
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Letters
This Week's Letters
Science 5 May 2006: 689.
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Debating Sexual Selection and Mating Strategies
Sasha R. X. Dall, John M. McNamara, Nina Wedell, David J. Hosken;, C. (Kate) M. Lessells, Andrew T. D. Bennett, Tim R. Birkhead, Nick Colegrave, Paul H. Harvey, Ben Hatchwell, John Hunt, Allen J. Moore, Geoff A. Parker, Scott Pitnick, Tommaso Pizzari, Jacek Radwan, Mike Ritchie, Ben C. Sheldon, David M. Shuker, Leigh W. Simmons, Paula Stockley, Tom Tregenza, Marlene Zuk;, Mark W. Blows, Rob Brooks, Katherine L. Buchanan, Tim H. Clutton-Brock, Michael D. Jennions, Hanna Kokko, Janne S. Kotiaho, Constantino Macias-García, Linda Partridge, Rhonda R. Snook;, David M. Buss;, Troy Day, David Houle, Locke Rowe;, Michael T. Ghiselin;, Peter L. Hurd;, Geoffrey Miller;, Jeffrey Stewart;, Joan Roughgarden, Erol Akçay, and Meeko Oishi
Science 5 May 2006: 689-697.
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Corrections and Clarifications
Science 5 May 2006: 697.
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Books et al.
BIOMEDICINE: Lipids, Genes, and Health
James M. Ntambi
Science 5 May 2006: 698.
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RESEARCH CONDUCT: Under Suspicion
Derek T. Scholes
Science 5 May 2006: 698-699.
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Browsings
Science 5 May 2006: 699.
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Books Received
Science 5 May 2006: 699.
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Policy Forum
ANIMAL RESEARCH: Enhanced: Harmonization of Animal Care and Use Guidance
Gilles Demers, Gilly Griffin, Guy De Vroey, Joseph R. Haywood, Joanne Zurlo, and Marie Bédard
Science 5 May 2006: 700-701.
Summary »| Full Text »| PDF »| Supporting Online Material »|
Perspectives
PLANETARY SCIENCE: Linear Dunes on Titan
Nicholas Lancaster
Science 5 May 2006: 702-703.
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CHEMISTRY: Shuttling Polyolefins to a New Materials Dimension
Vernon C. Gibson
Science 5 May 2006: 703-704.
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SOCIAL SCIENCE: The Pleasures and Pains of Information
George Loewenstein
Science 5 May 2006: 704-706.
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PLANETARY SCIENCE: The Primordial Porridge
Bernard Marty
Science 5 May 2006: 706-707.
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GEOCHEMISTRY: Follow the Nitrogen
Douglas G. Capone, Radu Popa, Beverly Flood, and Kenneth H. Nealson
Science 5 May 2006: 708-709.
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IMMUNOLOGY: B Cells Spread and Gather
Margaret M. Harnett
Science 5 May 2006: 709-710.
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RETROSPECTIVE: Nicholas J. Shackleton (1937-2006)
William F. Ruddiman
Science 5 May 2006: 711.
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Brevia
Environmental Monitoring by Wireless Communication Networks
Hagit Messer, Artem Zinevich, and Pinhas Alpert
Science 5 May 2006: 713.
A real-time map of rainfall intensity can be recovered by measuring the attenuation in signals from cell phones in a network.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Research Article
Catalytic Production of Olefin Block Copolymers via Chain Shuttling Polymerization
Daniel J. Arriola, Edmund M. Carnahan, Phillip D. Hustad, Roger L. Kuhlman, and Timothy T. Wenzel
Science 5 May 2006: 714-719.
A molecule that shuttles growing polymers back and forth between two catalysts to produce a segmented chain allows high efficiency and fine control of the polymers?elastic properties.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Reports
Producing Ultrastrong Magnetic Fields in Neutron Star Mergers
D. J. Price and S. Rosswog
Science 5 May 2006: 719-722.
Published online 30 March 2006 [DOI: 10.1126/science.1125201] (in Science Express Reports)
Simulations of the merging of a neutron star binary pair show that magnetic fields can be amplified strongly and quickly, before the stars collapse to form a black hole.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Cyclopropenylidenes: From Interstellar Space to an Isolated Derivative in the Laboratory
Vincent Lavallo, Yves Canac, Bruno Donnadieu, Wolfgang W. Schoeller, and Guy Bertrand
Science 5 May 2006: 722-724.
Published online 13 April 2006 [DOI: 10.1126/science.1126675] (in Science Express Reports)
The triangular C3H2 molecule, which appears to be stable only in the near-vacuum of interstellar space, has been isolated by appending amino groups to the ring.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes
R. D. Lorenz, S. Wall, J. Radebaugh, G. Boubin, E. Reffet, M. Janssen, E. Stofan, R. Lopes, R. Kirk, C. Elachi, J. Lunine, K. Mitchell, F. Paganelli, L. Soderblom, C. Wood, L. Wye, H. Zebker, Y. Anderson, S. Ostro, M. Allison, R. Boehmer, P. Callahan, P. Encrenaz, G. G. Ori, G. Francescetti, Y. Gim, G. Hamilton, S. Hensley, W. Johnson, K. Kelleher, D. Muhleman, G. Picardi, F. Posa, L. Roth, R. Seu, S. Shaffer, B. Stiles, S. Vetrella, E. Flamini, and R. West
Science 5 May 2006: 724-727.
Radar images of Saturn抯 moon Titan show that large regions of its surface are covered in dunes up to 150 meters high, produced by regular winds acting on sand-sized grains.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Interstellar Chemistry Recorded in Organic Matter from Primitive Meteorites
Henner Busemann, Andrea F. Young, Conel M. O'D. Alexander, Peter Hoppe, Sujoy Mukhopadhyay, and Larry R. Nittler
Science 5 May 2006: 727-730.
Hydrogen and nitrogen isotopes in organic matter of primitive meteorites suggest that much of this material is unaltered and formed in the cold presolar nebula, not later.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Lower Cambrian Vendobionts from China and Early Diploblast Evolution
D.-G. Shu, S. Conway Morris, J. Han, Y. Li, X.-L. Zhang, H. Hua, Z.-F. Zhang, J.-N. Liu, J.-F. Guo, Y. Yao, and K. Yasui
Science 5 May 2006: 731-734.
A Cambrian fossil with closely spaced branches closely resembles one of several enigmatic animals from the late Precambrian, providing a possible evolutionary link.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Defective Lipolysis and Altered Energy Metabolism in Mice Lacking Adipose Triglyceride Lipase
Guenter Haemmerle, Achim Lass, Robert Zimmermann, Gregor Gorkiewicz, Carola Meyer, Jan Rozman, Gerhard Heldmaier, Robert Maier, Christian Theussl, Sandra Eder, Dagmar Kratky, Erwin F. Wagner, Martin Klingenspor, Gerald Hoefler, and Rudolf Zechner
Science 5 May 2006: 734-737.
Mice deficient in the enzyme that degrades the lipids in fat show abnormal metabolism and massive lipid accumulation in the heart, resulting in premature death.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
B Cell Ligand Discrimination Through a Spreading and Contraction Response
S. J. Fleire, J. P. Goldman, Y. R. Carrasco, M. Weber, D. Bray, and F. D. Batista
Science 5 May 2006: 738-741.
For maximal activation, antibody-producing immune cells extend their membranes over the surface of other cells, thus gathering stimulating molecules into a cluster.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Structure of the Multidrug Transporter EmrD from Escherichia coli
Yong Yin, Xiao He, Paul Szewczyk, That Nguyen, and Geoffrey Chang
Science 5 May 2006: 741-744.
A transporter in the E. coli inner membrane confers resistance to hydrophobic drugs by binding them with specialized loops within the membrane and then exporting them.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Signal Recognition Particle Receptor Exposes the Ribosomal Translocon Binding Site
Mario Halic, Marco Gartmann, Oliver Schlenker, Thorsten Mielke, Martin R. Pool, Irmgard Sinning, and Roland Beckmann
Science 5 May 2006: 745-747.
New proteins emerging from ribosomes can form a docking complex that exposes a binding site for the translocon, which guides the new proteins across the membrane.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Recognition of Histone H3 Lysine-4 Methylation by the Double Tudor Domain of JMJD2A
Ying Huang, Jia Fang, Mark T. Bedford, Yi Zhang, and Rui-Ming Xu
Science 5 May 2006: 748-751.
Published online 6 April 2006 [DOI: 10.1126/science.1125162] (in Science Express Reports)
Tandem domains form an interdigitated structure that is required to recognize and demethylate methylated histone tails, a reaction important for gene regulation.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
The Embryonic Vertebrate Heart Tube Is a Dynamic Suction Pump
Arian S. Forouhar, Michael Liebling, Anna Hickerson, Abbas Nasiraei-Moghaddam, Huai-Jen Tsai, Jay R. Hove, Scott E. Fraser, Mary E. Dickinson, and Morteza Gharib
Science 5 May 2006: 751-753.
Imaging shows that the embryonic, unchambered vertebrate heart develops as a fluid dynamic pump, not a peristaltic pump as had been assumed.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Neurobiological Substrates of Dread
Gregory S. Berns, Jonathan Chappelow, Milos Cekic, Caroline F. Zink, Giuseppe Pagnoni, and Megan E. Martin-Skurski
Science 5 May 2006: 754-758.
The pain centers are preferentially activated in the brains of people who prefer to suffer unpleasantness promptly, avoiding anticipatory dread.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
Conjunctive Representation of Position, Direction, and Velocity in Entorhinal Cortex
Francesca Sargolini, Marianne Fyhn, Torkel Hafting, Bruce L. McNaughton, Menno P. Witter, May-Britt Moser, and Edvard I. Moser
Science 5 May 2006: 758-762.
In rats, one region of the cortex contains cells that code the animal抯 position, head direction, and speed, and may integrate this information to provide a sense of its spatial location.
Abstract »| Full Text »| PDF »| Supporting Online Material »|
