球对称无限空间中稀薄气体的一种弛豫

本文把平面对称空间中Boltzmann方程的奇异扰动解法推广到球对称空间,并通过具体模型讨论了初始阶段弛豫过程的一些特点。 关键词：     

分子手性和生物学时间箭头

本文首先研究手性分子旋光强度的对称性质,以此参数描写分子的手性。结果表明,在时间反演和空间反射操作下,此参数改变符号。这意味着不仅在三维空间中,而且在四维时-空流形中分子也是手性的。因而在此意义下,时间反演和空间反射出现偶合。然后,还试图在一种对映体形式占优势的分子系统中,去找出在何种条件下手性特征可以嵌入到系统的Hamiltonian中去。文中借助非平衡统计力学,研究了分子手性的热力学或宏观表现,发现为了计及分子系统的手性,经典的Onsager倒易关系必须给予修正。最后,根据这些结果讨论了生物学系统的时间箭头问题。     

塔里木盆地奥陶系碳酸盐岩热液蚀变类型及蚀变流体的分带特征

已探明塔里木盆地下古生界碳酸盐岩地层储量巨大。对塔里木盆地西北部柯坪-巴楚-阿图什一带的4块区域开展了系统的野外和重点观测工作,包括蓬莱坝剖面、柯坪水泥厂剖面、托普郎剖面等。本研究通过考察塔里木盆地奥陶系碳酸盐岩热液溶蚀及相关现象。从野外产状、伴生关系以及矿物岩石学特征角度解剖奥陶系地层中热液矿物组合的地质特征。研究表明,该区域存在富镁流体、富氟流体和富硫流体3种流体,分别来源于封存卤水、火成活动和TSR热液。不同性质流体蚀变具有相似的分带性。     

普遍的磁偏转三级象差系数以及它们与PI枪光栅图形的关系

本文将磁偏转三级象差的工作推广,使适用于电子束入射处就有磁场的情况,导出一个能在任意平面上求三级偏转象差的公式,并经过数学处理,使公式简洁、换算方便。最后运用这套象差系数就水平一列式电子枪(PI枪)经偏转后所产生的光栅图形进行了分析和探讨。     

渔网电磁超介质左手通带的超常透射及其电场增强效应的数值研究

本文利用电磁场数值模拟方法研究了分布矩形孔阵列的"金属-电介质-金属"三明治渔网电磁超介质在其左手通带发生的超常透射现象和不同模式激发下的电场增强效应。结果证实左手通带紧邻的超常光学传输峰源于波导共振模式,利用超常传输效应可以有效降低电磁超介质的损耗,提高左手性能;波导共振模和左手通带对应的反对称磁模能够分别在孔洞和金属夹层区域激发超过11倍的增强电场,因此渔网电磁超介质结构在表面增强光谱和传感等方面也具有潜在应用价值。     

Characterization of different-Al-content AlGaN/GaN heterostructures on sapphire

Al x Ga 1-x N/GaN high-electron-mobility transistor (HEMT) structures with Al composition ranging from x = 0.13 to 0.36 are grown on sapphire substrates by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The effects of Al content on crystal quality, surface morphology, optical and electrical characteristics of the AlGaN/GaN heterostructures have been analyzed. Although high Al-content (36%) heterostructure exhibits a distinguished photoluminescence peak related to recombination between the two-dimensional electron gas and photoexcited holes (2DEG-h), its crystal quality and rough surface morphology are poor. 2DEG mobility increases with the Al content up to 26% and then it apparently decreases for high Al-content (36%) AlGaN/GaN heterostructure. The increase of sheet carrier density with the increase of Al content has been observed. A high mobility at room temperature of 2105 cm 2 /V s with a sheet carrier density of n s = 1.10 × 10 13 cm -2 , for a 26% Al-content AlGaN/GaN heterostructure has been obtained, which is approaching state-of-the-art for HEMT grown on SiC. Sheet resistance as low as 274 Ω/□ has also been achieved.     

Electrostatics of ligand binding: parametrization of the generalized Born model and comparison with the Poisson-Boltzmann approach

An accurate and fast evaluation of the electrostatics in ligand-protein interactions is crucial for computer-aided drug design. The pairwise generalized Born (GB) model, a fast analytical method originally developed for studying the solvation of organic molecules, has been widely applied to macromolecular systems, including ligand-protein complexes. However, this model involves several empirical scaling parameters, which have been optimized for the solvation of organic molecules, peptides, and nucleic acids but not for energetics of ligand binding. Studies have shown that a good solvation energy does not guarantee a correct model of solvent-mediated interactions. Thus, in this study, we have used the Poisson-Boltzmann (PB) approach as a reference to optimize the GB model for studies of ligand-protein interactions. Specifically, we have employed the pairwise descreening approximation proposed by Hawkins et al.(1) for GB calculations and DelPhi for PB calculations. The AMBER all-atom force field parameters have been used in this work. Seventeen protein-ligand complexes have been used as a training database, and a set of atomic descreening parameters has been selected with which the pairwise GB model and the PB model yield comparable results on atomic Born radii, the electrostatic component of free energies of ligand binding, and desolvation energies of the ligands and proteins. The energetics of the 15 test complexes calculated with the GB model using this set of parameters also agrees well with the energetics calculated with the PB method. This is the first time that the GB model has been parametrized and thoroughly compared with the PB model for the electrostatics of ligand binding.     

被动式DMFC水滴积聚及对放电性能影响

本文结合恒电流放电时阴极水滴积聚过程,对影响被动式直接甲醇燃料电池恒流放电性能的甲醇浓度、电流密度及环境湿度等因素进行了实验研究及讨论。结果表明:甲醇浓度高于4 M时,阴极水淹所造成的氧气传输限制为电池放电时间的控制因素;低电流密度放电时,恒电流放电时间主要受阴极侧水淹的影响;高电流密度时,主要受甲醇消耗的影响;湿度越大越易引起阴极水淹。     

Band Structures of Metal-Oxide Capped Graphene： A First Principles Study

We perform a first-principles calculation based on density functional theory to investigate the interface between single layer graphene and metal oxides. Our study reveals that the monolayer graphene becomes semiconducting by single crystal SiO2 and Al2O3 contact, with energy gaps to - 0.9 and - 1.8 eV, respectively. We find the gap originates from the breakage of π bond integrity, whose extent is related to the interface atom configuration. We believe that our results highlight a promising direction for the feasibility to apply large scale graphene layers as building blocks in future electronics devices.     

Two-Photon Fluorescence Property and Ultrafast Dynamics of Two Dipolar Compounds with Dipicolinate as Electron Acceptor

Linear and nonlinear photophysical properties of two novel dipolar compounds named as trans- dimethyl-4-[4＇-（N,N-dimethylamino）-styry1]-pyridin-2,6-dicarboxylate （Xiao-1） and trans-dimethyl-4-[4＇-（N,N-diphenylamino）-styry1]-pyridin-2,6-dicarboxylate （Xiao-2） are investigated by steady-state absorption and fluorescence spectroscopy, Z-scan and two-photon excited fluorescence measurements. Strong two-photon fluorescence emission and the pronounced positive solvatochromism are observed from two compounds. The two-photon absorption cross section of Xiao-2 is about 1.5 times larger than that of Xiao-1. One-color and two-color femtosecond pump-probe experiments are employed to investigate the excited state dynamics of two compounds. The relaxation lifetime of the intra-molecular charge transfer state is determined to be in the hundreds of picosecond domain for both the compounds in THF, and several tens of picosecond in DMSO solutions.