二茂铁基化合物的ESR研究进展

二茂铁基化合物因具有独特的氧化还原、电、光、磁和催化性能,而被广泛研究与应用.电子自旋共振(ESR)技术是观察物质顺磁性最直接的手段,在研究二茂铁基化合物的电子结构、电子转移和分子间相互作用等方面具有独特的优势.ESR技术还具有灵敏度高、样品处理简单、直接检测不破坏样品等优点.该文综述了二茂铁基化合物的ESR研究进展.     

多光谱遥感在重大自然灾害评估中的应用与展望

重大自然灾害发乍后,及时、准确的灾情评估对决策部门制定科学和有效的救灾减灾方案具有关键性的作用.多光游遥感具有数据获取范围广、速度快等特点.应用在灾害评估中具有非常大的优势和潜力.在我国近年来的多次重大自然灾害评估中,多光谱遥感技术都发挥了重要的作用.该文首先以地震灾害、洪涝火害和十旱灾害为例,简要总结了多光谱遥感在重...     

理想气体中的内势能

本文证明在无壁空间或无束缚力约束空间中,压力是气体以物态存在的束缚力.证明了热力学压力不仅是动量交换的统计平均值的量度,而且也是分子或原子空间位置分布(密度)的表征.理想气体在有限空间中的统计构形空间,具有逸散势-pV.这种系统构形空间内的各能级粒子具有相应的动量空间分布,其统计构形空间具有无序势TS.热力学平衡态具有处处相等p、T和总势能TS-pV.理想气体的二种势能具有对称性,总势能等于零;但其相应的无序势和逸散势都不等于零.     

Ge组分分布对基区杂质非均匀分布的SiGe HBT温度特性的影响

众所周知, 双极型晶体管的设计主要是基区的设计. 一般而言, 基区的杂质分布是非均匀的. 本文首先研究了非均匀的杂质高斯分布对器件温度分布、增益和截止频率的温度特性的影响, 发现增益和截止频率具有正温度系数, 体内温度较高. 随后研究了基区Ge组分分布对这些器件参数的影响. 均匀Ge组分分布和梯形Ge组分分布的SiGe 异质结双极型晶体管增益和截止频率具有负温度系数, 具有较好的体内温度分布. 进一步的研究表明, 具有梯形Ge组分分布的SiGe 异质结双极型晶体管, 由于Ge组分缓变引入了少子加速电场, 不但使它的增益和截止频率具有较高的值, 而且保持了较弱的温度敏感性, 在增益、特征频率大小及其温度敏感性、体内温度分布达到了很好的折中.     

物理课堂教学评价内容构想

课堂教学评价是促进学生成长、教师专业发展和提高课堂教学质量的重要手段.其功能是具有导向作用,能够促进课堂教学改革;具有激励作用,可以加强教师之间的相互交流;是促进教师专业发展的重要途径;具有决策和鉴定作用等.所以,课堂教学评价是现代教学中至关重要的一个环节.     

基于变换热力学的任意形状热集中器研究与设计

如何灵活地控制和操纵热流是目前研究的热点.本文根据变换热力学方法,导出了具有任意横截面形状热集中器的材料参数表达式,并在此基础上设计了具有圆形、椭圆形、正五边形等规则横截面形状的热集中器和具有共形、非共形任意横截面形状的热集中器.全波仿真结果表明,这些热集中器使等温线和热通量向其压缩区弯曲,靠近热源的一侧热扩散加快而相反的一侧热扩散减慢,在很小的区域内表现出对热量的集中作用,这一特点在热能工程中有潜在应用.此外,研究了圆柱形热集中器的层化实现方法.结果显示,热集中器可通过将同性材料沿角向分层交替填充来实现.这项工作对热集中器的设计及制备具有指导意义.     

一种新型GRIN透镜光纤加速度计的研究

研究了一种新颖的光纤加速度计,阐述了三光纤GRIN透镜加速度敏感元件的工作原理及其结构设计.该传感器包括三根光纤、一个GRIN透镜和一个质量块.根据光功率耦合原理,对透镜倾斜时的误差进行了定量分析.该加速度计具有结构新颖、体积小和灵敏度高等优点,是一种具有多用途的加速度传感器.     

具有强迫过流旋转圆盘系统流动实验研究

应用PIV技术,实验研究了具有大的径向过流的动静圆盘系统间隙内流动.实验在流量系数Cw=26705和间隙比G=0.0845下,实验获得了在不同雷诺数和过流方向时的涡量、湍流强度、雷诺应力和速度分布.实验表明过流方向是流场结构变化的主要因素.同时,实验发现了一个重要的物理现象,即具有强迫过流的动静圆盘系统的流场分布,是由无过流时的动静圆盘系统流场和具有强迫过流双静止圆盘系统流场的叠加而形成.     

仿生辐射制冷的研究进展

辐射制冷是一种通过光谱调控来实现降温的新型制冷技术,相比于传统的主动制冷技术,如吸收式制冷、压缩制冷等,具有独特的优势,在环境保护和能源利用方面具有重要意义.本文首先从辐射制冷的基本原理出发,介绍了自然界中生物所具有的辐射降温特性.不同生物通过其材料、微观结构、行为等实现辐射制冷调控,为人类探究新型辐射制冷材料和器件带来了启发.本文也归纳了生物的辐射制冷机制,总结了生物结构的优化方法,并介绍了当前仿生辐射制冷的研究进展,对仿生辐射制冷的研究方向、应用前景和材料制备方法进行了展望.高功率、智能化的辐射制冷材料和器件是未来仿生辐射制冷的重要发展方向,先进微纳加工技术的融入将使仿生辐射制冷在未来具有更广阔的市场和应用.     

基于结构的O-GlcNAc转移酶抑制剂的虚拟筛选

利用O-GlcNAc 转移酶同UDP-GlcNAc复合物的晶体结构,针对其催化位点,对ZINC库中的7134792个分子和FOG库中的4287550个分子进行三轮(HTVS、SP、XP)虚拟筛选,结果发现具有更好类药性的FOG库中包含更多对接得分更低的小分子,且具有更多新颖的化学片段.ZINC库中具有较低对接得分的分子可分为2类,分别占据UDP-GlcNAc的UDP和GlcNAc的结合位置,在此基础上设计得到的分子具有更好的对接得分.证明FOG分子库具有产生更多对接得分更低的分子,所预测和设计的小分子化合物可以成为潜在的抑制剂药物分子.     

溶剂化的热力学集团展开理论

把二元溶液的过剩内能（ｅｘｃｅｓｓ ｅｎｅｒｇｙ）分成溶剂－溶剂、溶剂－溶质及溶质－溶质相互作用部分。利用集团展开方法给出了二元溶液在正则系综的配分函数的表达式,利用该表达式得到了溶质的偏摩尔内能（ｐａｒｔｉａｌ ｍｏｌａｒ ｅｎｅｒｇｙ）和偏摩尔熵（ｐａｒｔｉａｌ ｍｏｌａｒ ｅｎｔｒｏｐｙ）的表达式。在无限稀溶液情形,过剩偏摩尔内能的溶剂－溶剂部分又称重组织内能（ｒｅｏｒｇａｎｉｚａｔｉｏｎ ｅｎｅｒｇｙ）,它反映了溶质存在时对其周围溶剂分子之间的相互作用能的影响。研究表明,在溶质的粒子数密度相对较大时,溶质分子之间的相互作用将影响过过剩偏摩尔内能的溶剂－溶剂部分,对于稀溶液,过氧偏摩尔内能的溶剂－溶剂部分与溶质的摩尔分数成线性关系。对低蜜度二元溶液,溶质的过剩偏摩尔内能和过剩偏摩尔熵也与溶质的摩尔分数成线     

内窥镜校正中棋盘格标志点自动提取方法

为了解决具有大畸变内窥镜标定的标志点提取困难和人工参与较多等问题,提出了一种简单快速准确的棋盘格标志点提取方法。该方法是采用粗提取和优化来完成棋盘格标志点的提取的:首先利用高斯滤波去除图像噪声,并计算两次图像的梯度特征,利用梯度极值约束得到粗提取的角点;然后利用棋盘格标志点的对称特点消除噪声点的影响,并得到优化的角点位置。实验结果表明,该方法简单易行,计算量小,不需要人工干预即可获得全部标志点,反投影误差小于0.2pixel。     

Figure of merit for spectrometers for EDXRF

How should one select the best detector for a particular measurement in energy dispersive X‐ray fluorescence (EDXRF)? How should one select the optimum system configuration, i.e. the best shaping time and beam current? Manufacturers provide a variety of specifications, such as energy resolution and maximum count rate, but these are indirectly related to the end use of an EDXRF instrument, the measurement and detection limit of the measured elemental concentrations. We suggest in this paper using the time required to achieve a given statistical uncertainty as a figure of merit. We derive scaling rules for this figure of merit based on conventional specifications, including energy resolution, peaking time, maximum count rate, detector area, and intrinsic efficiency. These scaling rules also include the peak to background ratio of a photopeak and the number of overlapping peaks. We then show how this figure of merit can be used to select the optimum detector and spectrometer configuration for specific applications and compare the results to data obtained with typical systems. Copyright © 2012 John Wiley & Sons, Ltd.     

Memory for pitch versus memory for loudness

The decays of pitch traces and loudness traces in short-term auditory memory were compared in forced-choice discrimination experiments. The two stimuli presented on each trial were separated by a variable delay (D); they consisted of pure tones, series of resolved harmonics, or series of unresolved harmonics mixed with lowpass noise. A roving procedure was employed in order to minimize the influence of context coding. During an initial phase of each experiment, frequency and intensity discrimination thresholds [P(C) = 0.80] were measured with an adaptive staircase method while D was fixed at 0.5 s. The corresponding physical differences (in cents or dB) were then constantly presented at four values of D: 0.5, 2, 5, and 10 s. In the case of intensity discrimination, performance (d') markedly decreased when D increased from 0.5 to 2 s, but was not further reduced when D was longer. In the case of frequency discrimination, the decline of performance as a function of D was significantly less abrupt. This divergence suggests that pitch and loudness are processed in separate modules of auditory memory.     

Requirements for Optical Systems for Virtual Displays

Currently, there are many types of virtual displays and new types arise every year. However, their vast majority appear technically inapplicable because they are inconsistent with a number of key factors related to the eye physiology. In this paper, we present the general requirements for optical systems of virtual displays, taking into account human eye physiology.     

Convolution identities for quasiprobabilities for Bose functions

We present identities relating the equations of motion of various quasiprobabilities for quantum oscillators. These identities turn out useful for checking the consistency of approximations made in constructing the equations of motion with the basic Bose commutator. Moreover, our identities allow to identify the quasiprobability distributions which have the easiest-to-solve equations of motion.     

Microscopic basis for Fick's law for self-diffusion

We investigate self-diffusion in a classical fluid composed of two species which are distinguished through the color of their particles, either black or white, but are identical as regards their mechanical properties. Disregarding color the fluid is in thermal equilibrium. We show that if a single test particle in the one-component fluid moves asymptotically as Brownian motion, then the color density and current in certain classes of nonequilibrium states are related, on the appropriate macroscopic scale, through Fick's law, and the former is governed by the diffusion equation. If in addition several test particles move asymptotically as independent Brownian motions, then the colored fluid is, on a macroscopic scale, in local equilibrium with parameters governed by the solution of the diffusion equation.Part of this work was done while both authors were at IHES, Bures-sur-Yvette, France.Supported in part by NSF Grant No. PHY 78-15920-02.Supported by a Heisenberg fellowship of the Deutsche Forschungsgemeinschaft.     

一种寻找团簇异构体的准动力学方法

建立了一套普遍适用的寻找团簇异构体的准动力学方法,该方法能够迅速给出在一般气相生长条件下形成概率较大的异构体.用该方法得到了C21的异构体谱,并采用分子动力学方法模拟了21个自由的碳原子在氦气氛中形成稳定团簇的过程,表明动力学过程中形成概率较大的异构体都已包含在该方法所得到的异构体谱中.所得到的C21最稳定结构的势能远低于采用遗传算法所得到的结果(Chem. Phys. Lett. 364 213,2002). 关键词： 团簇 异构体 最低势能 全局优化     

Boundary conditions for regularized 13-moment-equations for micro-channel-flows

Boundary conditions are the major obstacle in simulations based on advanced continuum models of rarefied and micro-flows of gases. In this paper, we present a theory how to combine the regularized 13-moment-equations derived from Boltzmann’s equation with boundary conditions obtained from Maxwell’s kinetic accommodation model. While for the linear case these kinetic boundary conditions suffice, we need additional conditions in the non-linear case. These are provided by the bulk solutions obtained after properly transforming the equations while keeping their asymptotic accuracy with respect to Boltzmann’s equation.After finding a suitable set of boundary conditions and equations, a numerical method for generic shear flow problems is formulated. Several test simulations demonstrate the stable and oscillation-free performance of the new approach.