辐射沙脊群条子泥动力地貌演变遥感分析

针对辐射沙脊群汇聚带条子泥冲淤多变的特性,采用遥感与地面测量相结合的方法,重点选用10期低潮位遥感影像和2006-2009年4期地形测量数据,研究了条子泥二分水动力均衡、沙洲稳定性、主要潮水沟演变和近期地形冲淤.研究结果表明:条子泥相对稳定区主要分布于弶港近岸边滩和二分水滩脊;二分水总体稳定、先北后南摆动;近40年来,...     

短小芽孢杆菌木聚糖酶的同源建模及分子动力学模拟

克隆并测序来源于短小芽孢杆菌的木聚糖酶基因,测定其编码产物的理化件质并鉴定其表达产物为常温酶蛋白.利用同源建模构建出具有较高精度的三级结构模型,并进行优化和评估.利用分子动力学模拟木聚糖酶基因对热不稳定的分子机制,了解影响该酶热稳定性的因素,寻找对热不稳定性的区域.通过与嗜热木聚糖酶比较发现,两者在3个区域的分子动力学...     

A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes

The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ～34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5?km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1?km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.     

FADD prevents RIP3-mediated epithelial cell necrosis and chronic intestinal inflammation

Intestinal immune homeostasis depends on a tightly regulated cross talk between commensal bacteria, mucosal immune cells and intestinal epithelial cells (IECs). Epithelial barrier disruption is considered to be a potential cause of inflammatory bowel disease; however, the mechanisms regulating intestinal epithelial integrity are poorly understood. Here we show that mice with IEC-specific knockout of FADD (FADD(IEC-KO)), an adaptor protein required for death-receptor-induced apoptosis, spontaneously developed epithelial cell necrosis, loss of Paneth cells, enteritis and severe erosive colitis. Genetic deficiency in RIP3, a critical regulator of programmed necrosis, prevented the development of spontaneous pathology in both the small intestine and colon of FADD(IEC-KO) mice, demonstrating that intestinal inflammation is triggered by RIP3-dependent death of FADD-deficient IECs. Epithelial-specific inhibition of CYLD, a deubiquitinase that regulates cellular necrosis, prevented colitis development in FADD(IEC-KO) but not in NEMO(IEC-KO) mice, showing that different mechanisms mediated death of colonic epithelial cells in these two models. In FADD(IEC-KO) mice, TNF deficiency ameliorated colon inflammation, whereas MYD88 deficiency and also elimination of the microbiota prevented colon inflammation, indicating that bacteria-mediated Toll-like-receptor signalling drives colitis by inducing the expression of TNF and other cytokines. However, neither CYLD, TNF or MYD88 deficiency nor elimination of the microbiota could prevent Paneth cell loss and enteritis in FADD(IEC-KO) mice, showing that different mechanisms drive RIP3-dependent necrosis of FADD-deficient IECs in the small and large bowel. Therefore, by inhibiting RIP3-mediated IEC necrosis, FADD preserves epithelial barrier integrity and antibacterial defence, maintains homeostasis and prevents chronic intestinal inflammation. Collectively, these results show that mechanisms preventing RIP3-mediated epithelial cell death are critical for the maintenance of intestinal homeostasis and indicate that programmed necrosis of IECs might be implicated in the pathogenesis of inflammatory bowel disease, in which Paneth cell and barrier defects are thought to contribute to intestinal inflammation.     

Molecular mechanism of anaerobic ammonium oxidation

Two distinct microbial processes, denitrification and anaerobic ammonium oxidation (anammox), are responsible for the release of fixed nitrogen as dinitrogen gas (N(2)) to the atmosphere. Denitrification has been studied for over 100 years and its intermediates and enzymes are well known. Even though anammox is a key biogeochemical process of equal importance, its molecular mechanism is unknown, but it was proposed to proceed through hydrazine (N(2)H(4)). Here we show that N(2)H(4) is produced from the anammox substrates ammonium and nitrite and that nitric oxide (NO) is the direct precursor of N(2)H(4). We resolved the genes and proteins central to anammox metabolism and purified the key enzymes that catalyse N(2)H(4) synthesis and its oxidation to N(2). These results present a new biochemical reaction forging an N-N bond and fill a lacuna in our understanding of the biochemical synthesis of the N(2) in the atmosphere. Furthermore, they reinforce the role of nitric oxide in the evolution of the nitrogen cycle.     

Crystal算子的Hypercyclicity

称复可分Banach空间上的算子T是Crystal算子,如果T在其任意非零不变子空间上的限制相似于T.对于某个x∈X,称T是超循环的(Hypercyclic),若{x,Tx,T2x,…,Tnx,…}=X;若V{Tnx∶n≥0}=X,则称T是循环的;称T是严格循环的,如果存在x∈ X使得fv(T)x=X,其中fv(T)是...     

基于表观特征的单目视觉算法实现的注视方向估计

视线跟踪作为一种重要的人机接口模式,能够提供丰富的人机交互信息.提出了基于单目视觉的视线跟踪方法( Monocular Vision Approach,MVA).从眼部图像提取的表观特征,再经过支持向量回归( Support Vector Regression,SVR)计算实现可头部动作的注视方向估计.本方法仅用一个摄像机采集一副人脸图像作为输入数据,输出的计算结果是人的头部姿态和注视方向,以摄像机坐标系为参照系.采用的表观特征是基于方向二值模式( Directional Binary Pattern,DBP)算法,解析瞳孔在眼窝中运动引起的图像纹理变化.视线跟踪方法首先将双眼分割出来,并编码成高维的方向二值模式特征,最终通过支持向量回归作为匹配函数计算注视视角.共有11个人共23 676回归样本,按照姿态分成5个聚类集合.实验结果显示,基于本方法进行注视方向估计可以获得3°的测试误差.     

泽泻的组织培养研究

以泽泻的块茎茎尖为外植体,对泽泻进行离体培养研究.结果表明,泽泻茎尖诱导分化最适宜的启动培养基为MS＋6-BA 2.0 mg/L＋NAA 1.0 mg/L,芽体诱导分化率为84.77%;继代增殖最适宜的培养基为MS＋6-BA 2.0 mg/L＋NAA 0.2 mg/L,增殖系数为5.1;以1/2 MS＋IBA 0.2 mg/L＋NAA 0.4 mg/L培养基组合生根效果较好,生根率为91%.     

Grains and grain boundaries in single-layer graphene atomic patchwork quilts

The properties of polycrystalline materials are often dominated by the size of their grains and by the atomic structure of their grain boundaries. These effects should be especially pronounced in two-dimensional materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, which is a hexagonal, two-dimensional crystal of carbon atoms. Single-atom-thick graphene sheets can now be produced by chemical vapour deposition on scales of up to metres, making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic, magnetic, chemical and mechanical properties that strongly depend on their atomic arrangement. Yet because of the five-order-of-magnitude size difference between grains and the atoms at grain boundaries, few experiments have fully explored the graphene grain structure. Here we use a combination of old and new transmission electron microscopy techniques to bridge these length scales. Using atomic-resolution imaging, we determine the location and identity of every atom at a grain boundary and find that different grains stitch together predominantly through pentagon-heptagon pairs. Rather than individually imaging the several billion atoms in each grain, we use diffraction-filtered imaging to rapidly map the location, orientation and shape of several hundred grains and boundaries, where only a handful have been previously reported. The resulting images reveal an unexpectedly small and intricate patchwork of grains connected by tilt boundaries. By correlating grain imaging with scanning probe and transport measurements, we show that these grain boundaries severely weaken the mechanical strength of graphene membranes but do not as drastically alter their electrical properties. These techniques open a new window for studies on the structure, properties and control of grains and grain boundaries in graphene and other two-dimensional materials.     

Decoherence in crystals of quantum molecular magnets

Quantum decoherence is a central concept in physics. Applications such as quantum information processing depend on understanding it; there are even fundamental theories proposed that go beyond quantum mechanics, in which the breakdown of quantum theory would appear as an 'intrinsic' decoherence, mimicking the more familiar environmental decoherence processes. Such applications cannot be optimized, and such theories cannot be tested, until we have a firm handle on ordinary environmental decoherence processes. Here we show that the theory for insulating electronic spin systems can make accurate and testable predictions for environmental decoherence in molecular-based quantum magnets. Experiments on molecular magnets have successfully demonstrated quantum-coherent phenomena but the decoherence processes that ultimately limit such behaviour were not well constrained. For molecular magnets, theory predicts three principal contributions to environmental decoherence: from phonons, from nuclear spins and from intermolecular dipolar interactions. We use high magnetic fields on single crystals of Fe(8) molecular magnets (in which the Fe ions are surrounded by organic ligands) to suppress dipolar and nuclear-spin decoherence. In these high-field experiments, we find that the decoherence time varies strongly as a function of temperature and magnetic field. The theoretical predictions are fully verified experimentally, and there are no other visible decoherence sources. In these high fields, we obtain a maximum decoherence quality-factor of 1.49?×?10(6); our investigation suggests that the environmental decoherence time can be extended up to about 500 microseconds, with a decoherence quality factor of ～6?×?10(7), by optimizing the temperature, magnetic field and nuclear isotopic concentrations.