Femtosecond X-ray protein nanocrystallography

X-ray crystallography provides the vast majority of macromolecular structures, but the success of the method relies on growing crystals of sufficient size. In conventional measurements, the necessary increase in X-ray dose to record data from crystals that are too small leads to extensive damage before a diffraction signal can be recorded. It is particularly challenging to obtain large, well-diffracting crystals of membrane proteins, for which fewer than 300 unique structures have been determined despite their importance in all living cells. Here we present a method for structure determination where single-crystal X-ray diffraction 'snapshots' are collected from a fully hydrated stream of nanocrystals using femtosecond pulses from a hard-X-ray free-electron laser, the Linac Coherent Light Source. We prove this concept with nanocrystals of photosystem I, one of the largest membrane protein complexes. More than 3,000,000 diffraction patterns were collected in this study, and a three-dimensional data set was assembled from individual photosystem I nanocrystals (～200?nm to 2?μm in size). We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes. This offers a new approach to structure determination of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources or are particularly sensitive to radiation damage.     

Onset of submarine debris flow deposition far from original giant landslide

Submarine landslides can generate sediment-laden flows whose scale is impressive. Individual flow deposits have been mapped that extend for 1,500 km offshore from northwest Africa. These are the longest run-out sediment density flow deposits yet documented on Earth. This contribution analyses one of these deposits, which contains ten times the mass of sediment transported annually by all of the world's rivers. Understanding how this type of submarine flow evolves is a significant problem, because they are extremely difficult to monitor directly. Previous work has shown how progressive disintegration of landslide blocks can generate debris flow, the deposit of which extends downslope from the original landslide. We provide evidence that submarine flows can produce giant debris flow deposits that start several hundred kilometres from the original landslide, encased within deposits of a more dilute flow type called turbidity current. Very little sediment was deposited across the intervening large expanse of sea floor, where the flow was locally very erosive. Sediment deposition was finally triggered by a remarkably small but abrupt decrease in sea-floor gradient from 0.05 degrees to 0.01 degrees. This debris flow was probably generated by flow transformation from the decelerating turbidity current. The alternative is that non-channelized debris flow left almost no trace of its passage across one hundred kilometres of flat (0.2 degrees to 0.05 degrees) sea floor. Our work shows that initially well-mixed and highly erosive submarine flows can produce extensive debris flow deposits beyond subtle slope breaks located far out in the deep ocean.     

Dating the origin of the Orchidaceae from a fossil orchid with its pollinator

Since the time of Darwin, evolutionary biologists have been fascinated by the spectacular adaptations to insect pollination exhibited by orchids. However, despite being the most diverse plant family on Earth, the Orchidaceae lack a definitive fossil record and thus many aspects of their evolutionary history remain obscure. Here we report an exquisitely preserved orchid pollinarium (of Meliorchis caribea gen. et sp. nov.) attached to the mesoscutellum of an extinct stingless bee, Proplebeia dominicana, recovered from Miocene amber in the Dominican Republic, that is 15-20 million years (Myr) old. This discovery constitutes both the first unambiguous fossil of Orchidaceae and an unprecedented direct fossil observation of a plant-pollinator interaction. By applying cladistic methods to a morphological character matrix, we resolve the phylogenetic position of M. caribea within the extant subtribe Goodyerinae (subfamily Orchidoideae). We use the ages of other fossil monocots and M. caribea to calibrate a molecular phylogenetic tree of the Orchidaceae. Our results indicate that the most recent common ancestor of extant orchids lived in the Late Cretaceous (76-84 Myr ago), and also suggest that the dramatic radiation of orchids began shortly after the mass extinctions at the K/T boundary. These results further support the hypothesis of an ancient origin for Orchidaceae.     

一种多视图的本体匹配结果可视化框架

目的针对目前本体匹配结果可视化方法表现形式单一、信息冗杂等问题,设计了一种本体匹配结果可视化的框架,用以解决这些问题,从而达到清晰而简明的可视化效果。方法将拥有不同优缺点的可视化技术有机地结合在一起,优势互补,组成多视图,并通过动态刷和链接技术在每个视图之间建立联动机制。结果与结论提出了一种多视图的本体匹配结果可视化框架。     

Android应用中即时视频图像放大显示方法

Android视频通讯应用中通常使用View类显示视频解码图像。为解决使用常用图像拉伸方式将解码到的视频图像实时放大输出时遇到的内存严重消耗和输出延迟的问题, 分析了问题的原因, 并研究了基于Android自带API（Application Programming Interface）或使用JNI（Java Native Interface）算法的即时图像放大显示方法, 对得到的图像放大效果和放大所需的时间进行实验分析, 并根据实验结果进行源代码分析研究, 发现改进的方法, 最终提出一个解决问题的最合适的方案。     

Experimental observation of electron-hole recollisions

An intense laser field can remove an electron from an atom or molecule and pull the electron into a large-amplitude oscillation in which it repeatedly collides with the charged core it left behind. Such recollisions result in the emission of very energetic photons by means of high-order-harmonic generation, which has been observed in atomic and molecular gases as well as in a bulk crystal. An exciton is an atom-like excitation of a solid in which an electron that is excited from the valence band is bound by the Coulomb interaction to the hole it left behind. It has been predicted that recollisions between electrons and holes in excitons will result in a new phenomenon: high-order-sideband generation. In this process, excitons are created by a weak near-infrared laser of frequency f(NIR). An intense laser field at a much lower frequency, f(THz), then removes the electron from the exciton and causes it to recollide with the resulting hole. New emission is predicted to occur as sidebands of frequency f(NIR)?+?2nf(THz), where n is an integer that can be much greater than one. Here we report the observation of high-order-sideband generation in semiconductor quantum wells. Sidebands are observed up to eighteenth order (+18f(THz), or n = 9). The intensity of the high-order sidebands decays only weakly with increasing sideband order, confirming the non-perturbative nature of the effect. Sidebands are strongest for linearly polarized terahertz radiation and vanish when the terahertz radiation is circularly polarized. Beyond their fundamental scientific significance, our results suggest a new mechanism for the ultrafast modulation of light, which has potential applications in terabit-rate optical communications.     

基于GIS和GM的土地利用空间格局和动态预测情景分析——以宜都市为例

应用GIS技术和景观生态学方法对湖北省宜都市2001年土地利用空间格局情景进行了研究,并结合1999年、2000年、2002年、2003年的土地利用变更调查数据,运用拓广的灰色动态预测模型预测2010年、2015年土地利用结构的变化趋势．研究结果表明：1）地处平原区几个乡镇的景观指数如景观偏离度、多样性、均匀度、破碎度大,优势度小,山地区则相反;2）拓广的GM模型提高了预测精度,预测结果表明研究区耕地将迅速减少,取而代之的是园地、林地和交通用地。其它类型用地变化不大．研究结果对制定科学合理的土地利用规划和动态管理具有重要意义．     

索牵引弹体装填机器人的尺寸优化设计

针对海军大型武器的对接装填自动化需求,为提高装填安全性和效率,该文提出一种三索并联机器人,实现弹体自动化转运和装填,并完成了该三索并联机器人的尺寸优化设计方法研究.考虑索塔高度对于建造难度、重量及成本等影响,将参数优化设计分为全局搜索优化及局部搜索优化.全局搜索通过对所有设计参数进行采样搜索得到索塔高度为关键设计参数,...     

Whole-genome sequence of Schistosoma haematobium

Schistosomiasis is a neglected tropical disease caused by blood flukes (genus Schistosoma; schistosomes) and affecting 200 million people worldwide. No vaccines are available, and treatment relies on one drug, praziquantel. Schistosoma haematobium has come into the spotlight as a major cause of urogenital disease, as an agent linked to bladder cancer and as a predisposing factor for HIV/AIDS. The parasite is transmitted to humans from freshwater snails. Worms dwell in blood vessels and release eggs that become embedded in the bladder wall to elicit chronic immune-mediated disease and induce squamous cell carcinoma. Here we sequenced the 385-Mb genome of S. haematobium using Illumina-based technology at 74-fold coverage and compared it to sequences from related parasites. We included genome annotation based on function, gene ontology, networking and pathway mapping. This genome now provides an unprecedented resource for many fundamental research areas and shows great promise for the design of new disease interventions.