The Study of Chiral Adsorption Systems Using Synchrotron-Based Structural and Spectroscopic Techniques: Stereospecific Adsorption of Serine on Au-Modified Chiral Cu{531} Surfaces

We apply modern synchrotron-based structural techniques to the study of serine adsorbed on the pure and Au-modified intrinsically chiral Cu{531} surface. XPS and NEXAFS data in combination with DFT show that on the pure surface both enantiomers adsorb in ??₄ geometries (with de-protonated ??-OH groups) at low coverage and in ??₃ geometries at saturation coverage. Significantly larger enantiomeric differences are seen for the ??₄ geometries, which involve substrate bonds of three side groups of the chiral center, i.e. a three-point interaction. The ??₃ adsorption geometry, where only the carboxylate and amino groups form substrate bonds, leads to smaller but still significant enantiomeric differences, both in geometry and the decomposition behavior. When Cu{531} is modified by the deposition of 1 and 2 ML Au the orientations of serine at saturation coverage are significantly different from those on the clean surface. In all cases, however, a ??₃ bond coordination is found at saturation involving different numbers of Au atoms, which leads to relatively small enantiomeric differences.     

Behavioral models of odor similarity.

Carbon chain length in several classes of straight-chain aliphatic odorants has been proposed as a model axis of similarity for olfactory research, on the basis of successes of studies in insect and vertebrate species. To assess the influence of task on measured perceptual similarities among odorants and to demonstrate that the systematic similarities observed within homologous odorant series are not task specific, the authors compare 3 different behavioral paradigms for rats (olfactory habituation, generalization, and discrimination). Although overall patterns of odorant similarity are consistent across all 3 of these paradigms, both quantitative measurements of perceptual similarity and comparability with 2-deoxyglucose imaging data from the olfactory bulb are dependent on the specific behavioral tasks used. Thus, behavioral indices of perceptual similarity are affected by task parameters such as learning and reward associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

突破现有CMOS工艺限制的晶体管技术

很多人都有过这样尴尬的经历,当有急事需要打电话时,却发现手机没电了,而身边又没有固定电话,如果Cornell大学的研究人员成功了,今后,你将不会再碰到这种尴尬事。Cornell大学的一个研究小组将放射材料与MEMS（微型机电系统）悬臂和电路结合在一起,将核能转变为电能,这种能量源的半衰期大约为100年,基于这种技术的新电池可谓是能“永久”供电的电池。近日,     

Phospholipase A2 action on planar lipid bilayers generates a small, transitory current that is voltage independent

Addition of either bee venom or Trimeresurus flavoviridis phospholipase A2 (PLA2) to the solution bathing the front side of a voltage-clamped, planar lipid bilayer consistently produced a transitory current lasting approximately 100 s. This current is consistent with anions moving through the membrane to the rear side. The peak current is independent of holding potential. PLA2 activity on phospholipid membranes not only produced a current but also led to membrane rupture within 300 s. The current depends on Ca2+ and lipid type. Addition of PLA2 in the absence of Ca2+ or to membranes made of nonsubstrate lipids (e.g., glycerol monooleate or lysophosphatidylcholine) produced no current and did not break the bilayer. Peak current height, signal decay time, and time to membrane rupture all depended on PLA2 dose, whereas total charge produced was constant. This current does not flow through ion channels because there are no channels present and the current is not voltage dependent. The evidence is consistent with the hypothesis that the current is generated by the movement of ionized fatty acid produced by PLA2 action. These results demonstrate a simple method to measure enzyme activity in the presence of different substrates and varied environmental conditions.     

Raman and CD spectroscopy of recombinant 68-kDa DNA human topoisomerase I and its complex with suicide DNA-substrate

N-terminally truncated recombinant 68-kDa human topoisomerase (topo) I exhibits the same DNA-driving activities as the wild-type protein. In the present study, Raman and circular dichroism techniques were employed for detailed structural characterization of the 68-kDa human topo I and its transformations induced by the suicide sequence-specific oligonucleotide (solig) binding and cleavage. Spectroscopic data combined with statistical prediction techniques were employed to construct a model of the secondary structure distribution along the primary protein structure in solution. The 68-kDa topo I was found to consist of ca. 59% alpha-helix, 24% beta-strand and/or sheets, and 17% other structures. A secondary structure transition of the 68-kDa topo I was found to accompany solig binding and cleavage. Nearly 15% of the alpha-helix of 68-kDa topo I is transferred within the other structures when in the complex with its DNA substrate. Raman spectroscopy analysis also shows redistribution of the structural rotamers of the 68-kDa topo I disulfide bonds and significant changes in the H-bonding of the Tyr residues and in the microenvironment/conformation of the Trp side chains. No structural modifications of the DNA substrate were detected by spectroscopic techniques. The data presented provide the first direct experimental evidence of the human topo I conformational transition after the cleavage step in the reaction of binding and cleavage of DNA substrate by the enzyme. This evidence supports the model of the enzyme function requiring the protein conformational transition. The most probable location of the enzyme transformations was the core and the C-terminal conservative 68-kDa topo I structural domains. By contrast, the linker domain was found to have an extremely low potential for solig-induced structural transformations. The pattern of redistribution of protein secondary structures induced by solig binding and covalent suicide complex formation supports the model of an intramolecular bipartite mode of topo I/DNA interaction in the substrate binding and cleavage reaction.     

APEC大会令电源行业的专业人士齐聚一堂

第20届应用电源电子产品大会暨展览会于2005年3月6日至10日在美国德克萨斯州奥斯汀(Austin)的希尔顿饭店(Hnton Hotel)举行，本次大会不仅为业界的专业人士目睹新产品和讨论最新技术提供了契机，同时还安排了数百场有关电源电子产品行业最新发展的演示技术报告。大会的精彩内容还有由《Electronic Products》杂志组织的电源行业联盟小组的技术讨论会，以及众多的新产品展示。     

Polynomial time algorithms for the UET permutation flowshop problem with time delays

This paper addresses the problem of scheduling a set of n unit execution time (UET) jobs on an m-permutation flowshop with arbitrary time delays, so as to minimize the makespan criterion. A polynomial time algorithm is exhibited for the three-machine and four-machine cases, respectively.     

SID大会展现了业界未来的技术和产品走向

近期在美国西雅图举行的信息显示学会大会(Society for Information Display Confenrence)，是迄今为止展出新型显示技术及尚处于开发阶段的显示技术最多的一届盛会。     

Analysis of Film-Boiling Heat Transfer on a High Temperature Sphere Immersed into Liquid Sodium

Film-boiling heat transfer is a key phenomenon governing severe accident sequence in a sodium-cooled fast reactor. Experimental the fuel-coolant interaction process which may occur during a and theoretical work on film-boiling heat transfer in sodium has hardly been carried out in the past. An experiment has been conducted in the early seventies to investigate sodium pool boiling. In this experiment, a hot tantalum sphere was immersed into subcooled liquid sodium. Film boiling was obtained for various sets of parameters： sodium subcooling from 4.1 K to 29. 1 K, initial sphere temperature ranging from 1,802.6 K to 2,633.7 K, sphere diameters of 1.27, 1.91 and 2.54 cm and sodium depths of 7.6 cm and 11.4 cm. In the present work, a simplified analysis based on the boundary layer theory is developed to describe pool film-boiling heat transfer on a hot sphere in liquid sodium. Two extreme cases are considered depending on sodium subcooling. In the case of high subcooling, most of the heat lost by the sphere is used to heat the sodium while for low subcooling, it is used to vaporize the liquid at the liquid-vapor interface. It will be shown that the scaling analysis predicts the heat fluxes within the order of magnitude when compared to the available experimental data. Besides, it allows an estimation of the contribution of these fluxes to the liquid heating and vaporization processes.