学术篇 « Vintage

This Week in Science

05/18/2007 at 4:30 PM (学术篇)

Polariton Condensation

When bosons are packed together such that the density exceeds a critical threshold, and when temperatures are sufficiently low, they can undergo a phase transition and condense into a single quantum state. This Bose-Einstein condensation has been demonstrated in a number of systems, including cold atoms, superfluids, and superconductors. There is a desire, because of the small effective mass (and the potential to drive the phenomenon to higher temperatures) to create condensed states in semiconductor systems. Balili et al. (p. 1007; see the Perspective by Littlewood) show that an ensemble of polaritons, which are quasiparticles formed by photons coupled to excitons, can be generated and trapped in a microcavity in a way analogous to cold-atom traps. The authors then demonstrate the signatures of Bose-Einstein condensation in their system.

From Leaf to Flower

As spring begins, many plants turn to flower under the control of florigen. The molecular nature of florigen has long been unknown, but the signal was known to originate in leaves, and thus had to travel through the plant to the growing buds. Now Corbesier et al. (p. 1030, published online 19 April) and Tamaki et al. (p. 1033, published online 19 April) show that it is a protein rather than its coding RNA that is the likely florigen signal that moves within the plant (see the 20 April news story by Pennisi). The florigen RNA and protein are encoded by the FLOWERING LOCUS T gene in Arabidopsis and the Hd3a gene in rice.

Smart Drugs, Smarter Tumors

A promising class of "smart" cancer drugs work by inhibiting specific tyrosine kinases linked to uncontrolled growth. Gefitinib and erlotinib, drugs that target the kinase activity of the epidermal growth factor receptor (EGFR), can be very effective when initially administered to lung cancer patients whose tumors contain activating mutations in the EGFR gene. Almost inevitably, however, these tumors develop resistance to the drugs and begin to regrow. Engelman et al. (p. 1039, published online 26 April) find that drug resistance in a subset of these tumors is caused by amplification of the MET oncogene, an event that in turn activates, via a different route, the same cellular signaling pathway originally activated by the mutant EGFR.

Equal-Opportunity Polymer Crystallization

Melted polymer chains are stretched during flow, and those that are greater than a critical length undergo a transition from a coiled state to an almost fully extended one. When these flow-extended materials cool and crystallize, they form a "shish-kebab" morphology where primary crystallization occurs in the shish, followed by secondary crystallization in which the kebabs form off the shish backbone. It has long been thought that these extended chains segregated and clumped together to form the shish. However, using fractions of either short, medium, or long chains that were deuterated, Kimata et al. (p. 1014) show that the proportion of long chains in the shish is similar to that in the original melt. They suggest that the extended long chains act as catalysts for crystallization, but once the process begins, they drag in chains of all lengths during the initial stages of crystallization.

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《Nature》~ Research Highlights

02/09/2007 at 12:32 AM (学术篇)

Optoelectronics: Speedy Silicon

Silicon is the material of choice for computer chips, but has traditionally lagged behind in optics, unable to compete with other materials for speed. That could soon change.

Ansheng Liu and his colleagues at Intel have developed an optical device (pictured) that can write up to 30 gigabits of data per second to a laser beam — three times faster than any previous silicon device. The optical modulator’s speed stems in part from a design that transmits the electrical signal carrying the data and the light through a single channel, or ‘waveguide’.

Materials Science: Stiffer Than Diamond

For hardness and stiffness, it’s long been thought that nothing beats diamond. But Roderic Lakes of the University of Wisconsin -Madison and his colleagues have made a material that is almost ten times stiffer, by embedding small particles of barium titanate in a matrix of tin.

This extreme stiffness is remarkable, given that neither of the materials involved are especially stiff on their own. The composite isn ‘t, however, expected to be particularly hard or strong.

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新项目～启航！

11/05/2006 at 4:08 PM (学术篇)

几番波折，新的项目终于在上周定了下来——跟着Prof. Jeffery Derby 做溶液晶体生长的计算和建模。

这个项目，听起来和我原来的实验反差很大：以前做生物实验，现在是数学建模，好像完全不搭边的东西。

事实上，我原来的项目“蛋白质晶体学”，其实本质就是“溶液晶体生长”，也就是我现在的研究项目。只是原来的项目以实验为主，力求精于一点，内容限于从实验上研究蛋白质的结晶环境及原理。现在的项目，从理论计算入手，其实实质也是想弄清物质“溶液结晶”的过程和原理。

实验和计算，说不上我会更喜欢那个，不过感情上觉得自己更适合做计算。因为做实验很多时候需要精于过程。这个过程中会让人掌握很多的技术，但是有时候每一步的操作都会对结果有很大影响。而我毛手毛脚的，难免浪费很多光阴。而做计算，可能会更强调对理论的掌握及自己的分析和对数学方法的运用，应该会学到更多的理论知识。而相对来说，觉得自己也会更擅长一些。而且，凡事追源溯本，能从根本上证明一个现象的原委，嗯，我是非常感兴趣的。^_^

其实跟Jeff谈这个项目的过程还算是蛮顺利的。第一次找他，他的态度就挺positive。第二次谈过，他就说，不official的说，他很愿意要我了。第三次去找他，在他的建议下，我在自己比较感兴趣的两个项目中选定了这个“溶液晶体生长”的项目，而且他还说99%这件事就定了，只要等到这个funding的confirmation就行了。然而，这个Confirmation却让我足足等了一个多星期。终于在上周，确认通知来了，我心里这块不重不轻的石头才总算落地……^_^

话说回来，在这次换导师的过程当中，斯光的导师Prof. Hu的态度着实让我受宠若惊。这位台湾老板，人很牛，在新生选导师时也是超受欢迎。但是，他在我们中国学生中的口碑并不是很好，总说他是个超级严厉的老板。而这一次，他却好几次过来关心我选导师的情况。还让斯光转告我一些选导师的技巧。当他听说Jeff 99%确定要我的时候，还亲自去找 Jeff 确认他是否确定了要接收我这个学生……这些都让我感到他的细心，以及间接表现出来的他对斯光的关心。谢谢Prof. Hu.^_^

最后大体说一下我的新项目吧。这个项目是和 Prof. Michael Ward 合作研究物质“溶液结晶”的过程及原理。现在，溶液结晶技术主要应用在有机分子的块体晶体生长及无机非线性光学材料的大尺寸单晶的生长上。虽然这个技术被人们使用已久，但其基本原理还是poorly understood。我们的工作，是从溶液的传质极限、热场等方面入手，先宏观的研究溶液晶体生长的一些极限和性质及其原理；再深入到结晶物质本身的性质，来具体研究各种不同的结晶过程和原理。

从这个蓝图上，我能看到这个项目的意义以及自己跃跃欲试的冲劲。但是具体的每一步，还是需要自己扎扎实实的来走。

由于这个项目是多学科交叉，发现自己还有很多的知识空洞要补，超多的东西要学、要掌握。希望自己能克服“讨懒”这一大恶习，认真学习、脚踏实地、充分发挥自己的“聪明才智”，早日做出些成绩来。^_^

听听可爱的音乐；），！

back ground music ,lovely,It's not?

バックグラントのオルゴールかわいい＾０＾

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06诺贝尔奖 & 结构生物学

10/05/2006 at 3:02 AM (学术篇)

今天，06年的诺贝尔化学奖揭晓，结构生物学家，斯坦福大学的 Roger Kornberg 教授因其在研究RNA聚合酶的晶体结构上的巨大贡献而夺此桂冠。

      不由得感慨了一下——怎么大家都是做蛋白质晶体学，我还在探路，别人都已经跑完赛程拿了冠军，连颁奖典礼都快举行了……不过，科学没有终点，讲贡献和成就却没有输赢可言。而且，自己的实验项目即将被迫更换，在这个领域，也只能算有缘相识无缘相知了……^_^

      其实，结构生物学在科学界的热潮已经持续了一段时间。这一点，从近一年来在Nature和Science两本杂志上，几乎每期两篇相关文章的上座率就可以看出。而且，Nature还专门以结构生物学为重心出了一本子杂志：《 Nature Structural & Molecular Biology 》。

      Roger获奖，除了他站在科学热点的风头浪尖，还和他所研究项目的特殊难度与重要性紧要相关。
      RNA聚合酶，是至今为此人们能获得晶体结构的蛋白质中最大的一个。而且，不同于那些可以通过克隆轻松得到的蛋白质，RNA聚合酶作为功能性蛋白质，很难获得和提纯。然而，要让一个蛋白质结晶，除去蛋白质本身性质，纯度和浓度是非常关键的条件。可见Roger在研究上，确实如Jennifer所说，投入了“a huge amount of work”。
      而且，Roger的成果对生物细胞的研究，也是非常重要的。现在，人们习惯性认为DNA是生物细胞功能的密码。而事实上，DNA只是一个蓝图，RNA聚合酶才是让蓝图发挥作用的关键。所以，RNA聚合酶分子结构的获得，使人们从原子角度出发研究细胞内部运作机理真正成为了可能。

总之一句话，Roger的研究是相当了得相当牛的。（否则也不会捧走诺贝尔奖了^_^）

最后报一则八卦：Roger Kornberg的父亲，Arthur Kornberg（同为斯坦福大学教授）曾因研究DNA和RNA的合成而获得了1959年的诺贝尔医学奖。于是，Kornberg父子，成为继居里夫人与其女儿伊伦居里双双获得诺贝尔奖之后的又一“子承父业”——实在是Amazing的消息吧!^_^

References
Cramer P., Bushnell D. A.& Kornberg R. D. et al. Science, 292. 1863 – 1876 (2001).
Gnatt A. L., Gnatt A. L., Cramer P., Fu J., Bushnell D. A. & Kornberg R. D. Science, 292. 1876 – 1882 (2001).
Bushnell D. A., Westover K. D. , Davis R. E.& Kornberg R. D. Science, 303. 983 – 988 (2004).

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Research Highlight on Nature

07/05/2006 at 8:42 PM (学术篇)

Biophysics: Off the tracks

Nano Lett. doi:10.1021/nl060921t (2006)

Kinesin proteins are responsible for transporting materials around in cells, guided along protein rods known as microtubules. Scientists filmed them going about their work in living mammalian cells by attaching semiconductor nanoparticles to the motor proteins. The nanoparticles glowed like light bulbs under a fluorescence microscope, allowing the researchers to track each protein’s trajectory (pictured above).

The kinesin molecules typically switched between spells of linear motion, when they were attached to microtubules, and random, diffusive motion when they left the tracks.

Animal behaviour: Mice show empathy

A mouse watching a cage-mate writhe in pain will writhe more itself, an observation that Jeffrey Mogil and his team at McGill University in Montreal conclude is evidence of rodent empathy.

The researchers tested mice in twos, giving one or both mildly painful shots of acetic acid. If the two were strangers, they behaved as if they were on their own. But if they had lived together for a few weeks, and both got a shot, they both showed more abdominal constrictions, termed writhing, than when given a shot alone. The effect vanished if the roomies could not see one another.

Empathy has previously been considered an attribute of primates alone. Of course, the empathetic response does not indicate that the mice consciously felt sorry for one another — only that they respond to each other’s pain.

Nanotechnology: Bridging the gap

Mechanical switches in electrical circuits work by introducing a gap, a behaviour that Marc Bockrath of the California Institute of Technology in Pasadena and his colleagues have replicated at the nanoscale.

The researchers bridged two electrodes with a multiwalled carbon nanotube. Applying a high voltage broke the tube, which put the system into an ‘off’ state. But the broken ends, the researchers found, could be reunited by charging them. This set up an electrostatic repulsion between the concentric walls of the nanotube, causing the inner tubes to telescope out. The gap was then bridged and the ciruit switched on. For double-walled tubes this switching proved reversible, so it could potentially be used to store information bits in a rewritable memory chip.

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