Volume 433 Number 7028 pp785-906封面故事：什么是科学的饮食
谁决定我们应吃什么？这种建议是否真能帮助解决我们今天所面临的健康问题（主要是肥胖症）？我们目前的食谱是演化的产物、抑或是人为的设定？世界上谁拥有“最好的”食谱？这些都是在我们本期关于科学饮食的News Feature专辑（从794页开始）中所讨论的问题。这些问题的答案可能并不是简单的，但它们却是有启发意义的。
修复龋齿的一种新型合成材料
龋齿通常是通过用机械手段除去受影响部分、再用树脂或金属合金来填充空洞的方法治疗的。这种方法对早期轻度龋齿的治疗不太理想，因为要使填充物粘住，需要将太多的健康牙质去掉。一种新开发的合成牙釉质涂料有可能避免这一问题。这种白色晶体涂料用改性的羟磷灰石制成，在化学上和结构上都与天然牙釉质相似，能快速、无缝地通过纳米晶体生长修复早期龋齿。这种新型牙釉质涂料可用来重建牙釉质，而不需要钻孔；它不但能修复龋齿，而且还能通过强化天然牙釉质来防止龋齿发生。
北半球冰川化的真正原因
在距今270万年前的晚新生代冰期，在北半球开始出现冰川化，这是文献记录中最剧烈的气候变化事件之一，但其原因尚不清楚。过去曾被认为是造成这次事件的一个因素的北大西洋环流的变化现在却被认为是在这次冰川化之前很久就发生了。新的古海洋学数据结合一个气候模型的结果表明，在亚北极北太平洋所发生的变化可能造成了这次气候变化。北太平洋较强烈的季节变化（北美大陆上游大气中水蒸气的主要来源），似乎通过诱导晚夏和秋季天气变暖、从而增加可供降雪的水量供应的方式诱发了北半球的冰川化。
非结合态gp120的结构
与寄主细胞CD4受体相结合的HIV（人免疫缺陷病毒）的包膜蛋白gp120的结构自1998年以来就已经为人们所知，但其在与受体结合之前的结构却仍然不清楚。现在，来自“猴免疫缺陷病毒”（SIV）的、未与受体结合的gp120终于被成功结晶，其结构也以4埃的分辨率被确定。该蛋白的形状在结合态和非结合态很不相同：这种大尺度的结构变化可能是gp120用来躲避寄主免疫系统的花招之一。
金星与地球的大气层为什么不同
上个世纪60年代和70年代发射到金星上的Mariner和Venera探测器显示出金星和地球的大气层有很多不同。最难解释的不同之一是，金星上主要是惰性气体，尤其是氩-36的浓度是地球上的50倍。一种新的理论将这一差别的原因追溯到距今约45亿年前，当时地球和金星被认为由于几个火星大小的行星之间的碰撞已经诞生。数值模拟显示，当一次巨大碰撞发生时，一个海洋的存在会大大增加大气损失的速度。在地球上，在行星形成期间积累的几乎所有原始大气在这些碰撞过程中会全部失去。而金星由于离太阳更近，不大可能有很大的海洋，所以其原始大气会保留下来。
新型“拉曼”半导体激光器
“拉曼效应”指的是一种材料通过吸收入射光子的部分能量来改变入射光束波长的效应，该效应在化学和材料学中作为一种强大的诊断工具具有广泛应用。现有的用在光谱和显微观测方面的“拉曼激光器”只有很小的增益（或称信号放大），需要用强光学激光从外部泵哺。本期Nature介绍的一种新型电动半导体激光器利用“拉曼效应”来改变内部产生的一束激光的波长。这种低功率紧凑型“拉曼激光器”可在大部分红外波段使用，所以有希望用来增加半导体激光器的可调性、适用波长范围和用途。
南半球首次发现“恐爪龙类”化石
“恐爪龙类”（Deinonychosaurs）是与鸟类关系最密切的“兽脚类”恐龙，人们主要是从来自北美和亚洲的化石知道它们的。来自巴塔哥尼亚的一个新发现的化石是在南半球（晚白垩纪冈瓦那超级大陆的一部分）发现的这类恐龙的第一个化石。它与北半球化石的相似性说明，南半球和北半球陆块之间的差别比所认为的要小。
海底沉积物中的细菌
海床下的沉积物听起来并不像是很好的栖息地，但根据细胞数量所做的估计表明，海床下的沉积物占地球上全部真核细胞的一半以上。该数字并未区分活细胞与死细胞，但依据核糖体DNA检测所做的一项新的研究对活细胞与死细胞做了区分。该研究的数据表明，这些细胞中有很多是活的，即便是在距今已有1600万年、在海床之下400米深的沉积物中。所有可检测到的活细胞都是细菌，它们似乎“人丁兴旺”，因为其周转率可与地表沉积物中细菌的周转率相比。
“痢疾阿米巴”的基因组序列
本期Nature报告了病原体“痢疾阿米巴”（Entamoeba histolytica）的基因组序列。该病原体引起阿米巴病（也叫变形虫病），是仅次于疟疾的第二种最致命的原生动物疾病。其基因组包含与“毛滴虫”（Trichomonas）和“贾第鞭毛虫”（Giardia）等其他厌氧病原体共享的适应性变化。有证据表明，该基因组曾被来自细菌的很多基因转移所改变，这有可能成为针对这些细菌的药物的作用目标。大量传感和信号蛋白的发现向认为“痢疾阿米巴”是一种简单生物的观点提出了挑战：事实上该生物是非常适合其生存环境的。
大脑学习新指令的过程
能够遵从如“红灯停”这样的强制性指令的本领，是日常行为的组成部分，灵长类的大脑可以很快学会。“额叶前体”和“纹状体”都与这一过程有关，但它们各自所起的作用我们基本上不知道。在一项实验中，当猴子学习新的关联指令时，研究人员对其大脑中这两个区域的活动做了记录。该实验结果表明，与学习有关的变化在“纹状体”中发生的速度要快得多，但在“额叶前体”中发生的变化与猴子在完成新任务时表现水平的提高关系更密切。实际过程有可能是这样的：“纹状体”首先学习，然后对“额叶前体”进行“训练”。
决定成年干细胞命运的因素
成年干细胞已在大量器官中发现。它们不是“全能的”，而是被保持在一种无差异的状态，一旦从这种状态释放出来，会导致有限数量的细胞命运。维持这种平衡的分子程序的性质现在已在成年黑色素细胞中被研究，结果表明，Pax3转录因子是胚胎神经脊发育和成年黑色素干细胞功能的一个调节回路的组成部分。它通过诱导另一转录因子Mitf来使一个细胞成为黑色素细胞；与此同时，它通过与Mitf竞争结合点来阻止干细胞的分化。一个细胞若以这种方式被决定命运，能够通过选择走分化之路来对外部刺激做出快速反应。了解这种调节机制，将使利用成年干细胞进行组织再生的希望更大一些。
本期目录：
Editorials
Making sense of the world p785
The Earth and our effects on it require monitoring and analysis worthy of their complexity and importance. Now is the time to bring global observation into the twenty-first century.
doi: 10.1038/433785a
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Sooner than you think p785
Nature's back-page fiction is good for you.
doi: 10.1038/433785b
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Top of pageNews
Tests in Tokyo reveal flaws in Vietnam's bird flu surveillance p787
Cases of avian influenza have been overlooked, new evidence shows.
David Cyranoski
doi: 10.1038/433787a
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Flu gene discovery prompts calls for tighter monitoring p788
Lab-made virus from 1940 may have found its way into Korean pigs.
Erika Check
doi: 10.1038/433788a
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New York draws fire over case of drug-resistant HIV p788
Rare, aggressive form of AIDS used to publicize dangers of unprotected sex.
Erika Check
doi: 10.1038/433788b
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Global observation project gets green light p789
Sixty nations sign up to Earth-watching satellite system.
Declan Butler
doi: 10.1038/433789a
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Russian security arrests institute head for spying p789
Scientist accused of selling state secrets to South Korea.
Bryon MacWilliams
doi: 10.1038/433789b
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Speech transcript stokes opposition to Harvard head p790
University president Larry Summers under fire for remarks on women in science.
Emily Singer
doi: 10.1038/433790a
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Vioxx may go back on sale after scraping past FDA panel p790
US advisers vote not to ban painkillers that boost risk of heart attack.
Meredith Wadman
doi: 10.1038/433790b
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Nitrogen study fertilizes fears of pollution p791
UK field project highlights problems of excess nitrogen.
Jim Giles
doi: 10.1038/433791a
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news in brief p792
doi: 10.1038/433792a
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Top of pageNews Features
Dietary advice: Flash in the pan? p794
Obesity is the main target in the US government's latest dietary guidelines. But can this advice really make a difference? Nature's reporters sift through the heady mix of politics and science to get a taste of things to come.
doi: 10.1038/433794a
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Around the world in three square meals p797
doi: 10.1038/433797a
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Food FAQs p798
Eating a healthy diet is hard work. There are hundreds of guides out there — often providing conflicting instructions. Deciding what advice to take means wrestling with a number of tough questions.
doi: 10.1038/433798a
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Top of pageCorrespondence
Vital resource should be open to all physicists p800
Putting control in the hands of a few can enforce orthodoxy and stifle innovative ideas.
Brian D. Josephson
doi: 10.1038/433800a
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Climate blog could score with newer hockey stick p800
Shaopeng Huang
doi: 10.1038/433800b
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Best way to protect rock art is to leave it alone p800
Luc Allemand and Paul G. Bahn
doi: 10.1038/433800c
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Online submission makes authors do all the work p800
John P. Moore
doi: 10.1038/433800d
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Top of pageBooks and Arts
Scandals and safeguards p801
Is scientific fraud on the increase?
Daniel S. Greenberg reviews The Great Betrayal: Fraud in Science by Horace Freeland Judson
doi: 10.1038/433801a
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A scientific feast p802
Hervé This reviews On Food and Cooking: The Science and Lore of the Kitchen, 2nd edition by Harold McGee
doi: 10.1038/433802a
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Looking ahead to future brain studies p803
David Papineau reviews The New Brain Sciences: Perils and Prospects
doi: 10.1038/433803a
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Exhibition: Leonardo's legacy p803
doi: 10.1038/433803b
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Top of pagePhysics detective
Schr?dinger's mousetrap p805
Part 6: A cryptic response.
Ilana Goldhaber-Gordon and David Goldhaber-Gordon
doi: 10.1038/433805a
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Top of pageEssay
Concept
Elephant breakdown p807
Social trauma: early disruption of attachment can affect the physiology, behaviour and culture of animals and humans over generations.
G. A. Bradshaw, Allan N. Schore, Janine L. Brown, Joyce H. Poole and Cynthia J. Moss
doi: 10.1038/433807a
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Top of pageNews and Views
Climate change: Snow maker for the ice ages p809
In the Northern Hemisphere, large-scale glaciation was initiated comparatively recently. Paradoxically, it seems that the trigger was a seasonal warming of the sea surface in an upwind oceanic region.
Katharina Billups
doi: 10.1038/433809a
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Hearing: Aid from hair force p810
Mammals hear with exquisite sensitivity and precision over a huge range of frequencies; tiny amplifiers in the inner ear make this possible. New results challenge current thinking on how these amplifiers work.
Corné Kros
doi: 10.1038/433810a
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Photonics: Expect more delays p811
Slow light research has been a fast-moving topic in recent years, with potential applications from quantum computing to telecommunications. Techniques are now emerging that can slow down light in optical fibres.
Joe T. Mok and Benjamin J. Eggleton
doi: 10.1038/433811a
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Immunology: Guide for a cell-fate decision p813
How does an immature cell know how to develop into a specialized one? A fortunate observation has revealed one of the cues that guide precursor immune cells to their ultimate fate.
Ellen A. Robey
doi: 10.1038/433813a
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100 and 50 years ago p814
doi: 10.1038/433814a
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Planetary science: Being there p814
The protoplanets that collided to make the Earth may themselves have had atmospheres and oceans. Venus has vastly more argon and neon than Earth: fossil evidence, perhaps, of protoplanetary atmospheres?
Kevin Zahnle
doi: 10.1038/433814b
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Human immunodeficiency virus: Refolding the envelope p815
HIV has evolved to avoid neutralization by human antibodies. New atomic-level details reveal that such evasion involves substantial refolding of its exterior glycoprotein.
Peter D. Kwong
doi: 10.1038/433815a
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Obituary: Eduard Kellenberger (1920?2004) p817
Bruno J. Strasser and Jacques Dubochet
doi: 10.1038/433817a
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research highlights p818
doi: 10.1038/433818a
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Top of pageBrief Communications
Materials chemistry: A synthetic enamel for rapid tooth repair p819
Seamless fixing of an early caries lesion can be achieved without prior excavation.
Kazue Yamagishi, Kazuo Onuma, Takashi Suzuki, Fumio Okada, Junji Tagami, Masayuki Otsuki and Pisol Senawangse
doi: 10.1038/433819a
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Ecology: A niche for cyanobacteria containing chlorophyll d p820
Michael Kühl, Min Chen, Peter J. Ralph, Ulrich Schreiber and Anthony W. D. Larkum
doi: 10.1038/433820a
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Top of pageArticles
North Pacific seasonality and the glaciation of North America 2.7 million years ago p821
Gerald H. Haug, Andrey Ganopolski, Daniel M. Sigman, Antoni Rosell-Mele, George E. A. Swann, Ralf Tiedemann, Samuel L. Jaccard, J?rg Bollmann, Mark A. Maslin, Melanie J. Leng and Geoffrey Eglinton
doi: 10.1038/nature03332
Abstract | Full Text | PDF (377K) | Supplementary information
See also: Editor's summary | News and Views by Billups
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The zinc finger transcription factor Th-POK regulates CD4 versus CD8 T-cell lineage commitment p826
Xiao He, Xi He, Vibhuti P. Dave, Yi Zhang, Xiang Hua, Emmanuelle Nicolas, Weihong Xu, Bruce A. Roe and Dietmar J. Kappes
doi: 10.1038/nature03338
Abstract | Full Text | PDF (498K) | Supplementary information
See also: News and Views by Robey
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Structure of an unliganded simian immunodeficiency virus gp120 core p834
Bing Chen, Erik M. Vogan, Haiyun Gong, John J. Skehel, Don C. Wiley and Stephen C. Harrison
doi: 10.1038/nature03327
Abstract | Full Text | PDF (589K) | Supplementary information
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Top of pageLetters to Nature
Enhanced atmospheric loss on protoplanets at the giant impact phase in the presence of oceans p842
Hidenori Genda and Yutaka Abe
doi: 10.1038/nature03360
First paragraph | Full Text | PDF (177K) | Supplementary information
See also: Editor's summary | News and Views by Zahnle
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Raman injection laser p845
Mariano Troccoli, Alexey Belyanin, Federico Capasso, Ertugrul Cubukcu, Deborah L. Sivco and Alfred Y. Cho
doi: 10.1038/nature03330
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Quantum chemical calculations show that the uranium molecule U2 has a quintuple bond p848
Laura Gagliardi and Bj?rn O. Roos
doi: 10.1038/nature03249
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Lithospheric structure of the Rio Grande rift p851
David Wilson, Richard Aster, Michael West, James Ni, Steve Grand, Wei Gao, W. Scott Baldridge, Steve Semken and Paresh Patel
doi: 10.1038/nature03297
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Counter-rotating microplates at the Galapagos triple junction p855
Emily M. Klein, Deborah K. Smith, Clare M. Williams and Hans Schouten
doi: 10.1038/nature03262
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New evidence on deinonychosaurian dinosaurs from the Late Cretaceous of Patagonia p858
Fernando E. Novas and Diego Pol
doi: 10.1038/nature03285
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Prokaryotic cells of the deep sub-seafloor biosphere identified as living bacteria p861
Axel Schippers, Lev N. Neretin, Jens Kallmeyer, Timothy G. Ferdelman, Barry A. Cragg, R. John Parkes and Bo B. J?rgensen
doi: 10.1038/nature03302
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The genome of the protist parasite Entamoeba histolytica p865
Brendan Loftus, Iain Anderson, Rob Davies, U. Cecilia M. Alsmark, John Samuelson, Paolo Amedeo, Paola Roncaglia, Matt Berriman, Robert P. Hirt, Barbara J. Mann, Tomo Nozaki, Bernard Suh, Mihai Pop, Michael Duchene, John Ackers, Egbert Tannich, Matthias Leippe, Margit Hofer, Iris Bruchhaus, Ute Willhoeft, Alok Bhattacharya, Tracey Chillingworth, Carol Churcher, Zahra Hance, Barbara Harris, David Harris, Kay Jagels, Sharon Moule, Karen Mungall, Doug Ormond, Rob Squares, Sally Whitehead, Michael A. Quail, Ester Rabbinowitsch, Halina Norbertczak, Claire Price, Zheng Wang, Nancy Guillén, Carol Gilchrist, Suzanne E. Stroup, Sudha Bhattacharya, Anuradha Lohia, Peter G. Foster, Thomas Sicheritz-Ponten, Christian Weber, Upinder Singh, Chandrama Mukherjee, Najib M. El-Sayed, William A. Petri, Jr, C. Graham Clark, T. Martin Embley, Bart Barrell, Claire M. Fraser and Neil Hall
doi: 10.1038/nature03291
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Excitatory cortical neurons form fine-scale functional networks p868
Yumiko Yoshimura, Jami L. M. Dantzker and Edward M. Callaway
doi: 10.1038/nature03252
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Different time courses of learning-related activity in the prefrontal cortex and striatum p873
Anitha Pasupathy and Earl K. Miller
doi: 10.1038/nature03287
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CFTR channel opening by ATP-driven tight dimerization of its nucleotide-binding domains p876
Paola Vergani, Steve W. Lockless, Angus C. Nairn and David C. Gadsby
doi: 10.1038/nature03313
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Force generation by mammalian hair bundles supports a role in cochlear amplification p880
H. J. Kennedy, A. C. Crawford and R. Fettiplace
doi: 10.1038/nature03367
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Pax3 functions at a nodal point in melanocyte stem cell differentiation p884
Deborah Lang, Min Min Lu, Li Huang, Kurt A. Engleka, Maozhen Zhang, Emily Y. Chu, Shari Lipner, Arthur Skoultchi, Sarah E. Millar and Jonathan A. Epstein
doi: 10.1038/nature03292
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Toll-like receptor 3 promotes cross-priming to virus-infected cells p887
Oliver Schulz, Sandra S. Diebold, Margaret Chen, Tanja I. N?slund, Martijn A. Nolte, Lena Alexopoulou, Yasu-Taka Azuma, Richard A. Flavell, Peter Liljestr?m and Caetano Reis e Sousa
doi: 10.1038/nature03326
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State transitions and light adaptation require chloroplast thylakoid protein kinase STN7 p892
Stéphane Bellafiore, Frédy Barneche, Gilles Peltier and Jean-David Rochaix
doi: 10.1038/nature03286
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Functional cartography of complex metabolic networks p895
Roger Guimerà and Luís A. Nunes Amaral
doi: 10.1038/nature03288
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Top of pageNaturejobs
Prospects
Job movements p901
Paul Smaglik
doi: 10.1038/nj7028-901a
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Careers and Recruitment
India in demand p902
What's a company to do when it needs faster, cheaper new drugs and chemists are hard to find? Look for a source of bright graduates with low living costs, where legal changes have pushed firms to seek work, and you're there, says Emma Marris.
Emma Marris
doi: 10.1038/nj7028-902a
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Career View
Graduate Journal: A story to tell p904
Anne Margaret Lee
doi: 10.1038/nj7028-904a
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Scientists & Societies p904
Ralf Jauch
doi: 10.1038/nj7028-904b
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Movers p904
doi: 10.1038/nj7028-904c
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Top of pageFutures
The party's over p906
It was only a game....
Penelope Kim Crowther
doi: 10.1038/433906a
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