X射线质量厚度测量研究

拟合了能量在200 keV以下的中低能光子质量减弱系数的实验数据,发现基于光电效应,瑞利散射和康普顿散射的半经验公式能够精确地模拟光子质量减弱系数的实验数据.计算了X射线管发出的连续能谱X射线经过吸收片过滤后的能谱分布,发现能谱呈峰形.将它用作物质的透射模拟实验,发现在一定厚度范围内,它与某单能光子的强度减弱规律相同而等效.利用拟合求得的减弱系数半经验公式,求出并讨论了这一等效能量的数值和规律.讨论了X射线束的光电流和光子计数两种探测方式,计算发现经过低能过滤后的X射线,两者都能够反映强度减弱规律.进行了吸收实验,证明低能过滤X射线束的能量探测的确可以用来进行物质的质量厚度测量.     

Envelope structure of Semliki Forest virus reconstructed from cryo-electron micrographs

The basic principles of the architecture of many viral protein shells have been successfully established from electron microscopy and X-ray data, but enveloped viruses have been more difficult to study because they resist crystallization and are easily deformed when prepared for electron microscopy. To avoid the limitations of conventional techniques when applied to enveloped viruses, we have used a cryo-electron microscopy method in which unfixed and unstained viruses are observed in an unsupported thin layer of vitrified suspension. Because of electron beam damage, the many different views required for high-resolution three-dimensional reconstruction cannot be obtained from a tilt series of the same particle. The images of many differently oriented viruses are combined using a novel reconstruction method, 'reconstruction by optimized series expansion' (ROSE). The structure of the envelope of Semliki Forest virus has been reconstructed to 3.5-nm resolution. The T = 4 geometry of the surface lattice, the shape of the trimeric spikes and their arrangement on the lipid bilayer are visualized.     

质谱双探针法对食品中N- 亚硝胺化合物的全检测

食品中亚硝胺化合物的种类达300种,当前的亚硝胺检测国标只检测代表性的4种亚硝胺化合物.选择亚硝胺类化合物在EI源质谱中电离出的亚硝酰胺基(N2O)和亚硝酰(NO)2个独特碎片离子作双探针信号,以市售腊肉为检测对象,探索出一种亚硝胺类化合物全检测的方法,大幅度减少了现有国家标准对食品中亚硝胺类化合物的漏检.该检测方法原理简单、实验操作方便、测试成本低.     

Determination of the optical thickness and effective particle radius of clouds from transmitted solar radiation measurements

A method is presented for determining the optical thickness (τ_c) and effective particle radius (r_e) of stratiform cloud layers from transmitted solar radiation measurements. A detailed study shows that the cloud optical thickness and effective particle radius of water clouds can be determined from transmission function measurements at 0.75 and 2.13 μm, provided that the scaled optical thickness τ′_0.75>1 and r_e>5 μm. The wavelengths adopted by our study are similar to the channels of the moderate resolution imaging spectrometer (MODIS). The proposed method is invalid for optically thin clouds since transmission at 2.13 μm is less sensitive to r_e. The retrieval errors of τ′_0.75 and r_e monotonically decrease with increasing τ_c. For clouds having τ′0.75≥2， the retrieval errors of τ′_0.75 and r_e are below 10% and 20%, respectively. Transmissions at 0.75 and 1.65 μm can also be used to retrieve τ_c and r_e.     

Determination of the optical thickness and effective particle radius of clouds from transmitted solar radiation measurements

A method is presented for determining the optical thickness (τc) and effective particle radius (re) of stratiform cloud layers from transmitted solar radiation measurements. A detailed study shows that the cloud optical thickness and effective particle radius of water clouds can be determined from transmission function measurements at 0.75 and 2.13 μm, provided that the scaled optical thickness τ′0.75>1 and re>5 μm. The wavelengths adopted by our study are similar to the channels of the moderate resolution imaging spectrometer (MODIS). The proposed method is invalid for optically thin clouds since transmission at 2.13 μm is less sensitive to re. The retrieval errors of τ′0.75 and re monotonically decrease with increasing τc. For clouds having τ′0.75≥2, the retrieval errors of τ′0.75 and re are below 10% and 20%, respectively. Transmissions at 0.75 and 1.65 μm can also be used to retrieve τc and re.     

Polymer-supported membranes as models of the cell surface

Lipid-bilayer membranes supported on solid substrates are widely used as cell-surface models that connect biological and artificial materials. They can be placed either directly on solids or on ultrathin polymer supports that mimic the generic role of the extracellular matrix. The tools of modern genetic engineering and bioorganic chemistry make it possible to couple many types of biomolecule to supported membranes. This results in sophisticated interfaces that can be used to control, organize and study the properties and function of membranes and membrane-associated proteins. Particularly exciting opportunities arise when these systems are coupled with advanced semiconductor technology.     

主减速器装配过程中垫片厚度选择

汽车主减速器装配质量的影响因素很多,其中一个重要的因素是如何选取垫片厚度的问题。文章采用有限元法对某商务车后桥主减速器装配过程进行力学分析,获得了主减速器装配过程中的变形和应力状态;针对主减速器工作中应满足最小驱动力矩的指标,通过数值计算得到垫片实际的厚度,为主减速器的一次性装配成功提供了依据。     

细胞膜通道的发现

细胞膜水通道的发现,以及离子通道结构和机理的研究构成了2003年诺贝尔化学奖的主要内容.文章探索了这些发现的研究过程以及它们对医学研究的重要性.     

Determination of hydration film thickness using atomic force microscopy

Surface forces between particles control phenomenasuch as dispersion, agglomeration, coatings, adhesion,wetting, friction, and polishing, which play a crucial rolein materials processing. The importance of surface forcesis more appreciated especially in colloidal processing,while materials in a colloidal state are frequently preferredin industrial processing operations (e.g., printing inks,toners, paints, skin creams, blood substitutes, gels used asdrug-delivery systems, etc.) because their lar…     

单能电子半吸收厚度测量中射线吸收强度计算方法研究

在单能电子半吸收厚度测量实验中,现用的取谱方法存在信号区间选择困难、本底扣除不准、主观性太强等问题,导致测量结果误差较大、实验可重复性较差.文中利用蒙特卡罗模拟结合实验验证的方法研究了准单能电子在铝中的输运过程,研究了TPA法、Covell法、Wasson法和半峰净计数法对半吸收厚度计算的影响,结果发现Covell法信号区间选取简单、本底扣除方便、误差最小,适合用于单能电子半吸收厚度计算.     

SDS-PAGE电泳法测定蒜头果蛋白的相对分子质量

蒜头果蛋白(malanin)是从广西、云南特有植物蒜头果中分离、纯化出的一种新的、具有抗肿瘤活性的植物蛋白质.采用变性十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)测定malanin的相对分子质量.结果表明,malanin是一种双链蛋白质,由A、B 2条肽链通过二硫键连接而成,其相对分子质量约为65.94×103.方法具有简单、快速、直观的特点.     

聚氨酯微孔膜的防水透湿性及电镜分析

以聚氨酯微孔膜的电膜照片，分析在不同组成和不同的成型条件下制取的膜的结构和性能，得到了采用配比为１０／０５／０５的ＮＮ二甲基甲酰胺／四氢呋喃／乙二醇的混合溶剂和高温分级快干条件下形成的ＰＵ膜．该膜具有细密微孔结构和优良的防水透湿性     

Determination of the solvation film thickness of dispersed particles with the method of Einstein viscosity equation

The dispersion of a solid particle in a liquid may lead to the formation of solvation film onthe particle surface, which can strongly increase the repulsive force between particles and thus strongly affect the stability of dispersions. The solvation film thickness, which varies with the variation of the property of suspension particles and solutions, is one of the most important parameters of the solvation film, and is also one of the most difficult parameters that can be measured accurately. In this paper, a method, based on the Einstein viscosity equation of dispersions, for determining the solvation film thickness of particles is developed. This method was tested on two kinds of silica spherical powders (namely M1 and M2) dispersed in ethyl alcohol, in water, and in a water-ethyl alcohol mixture (1:1 by volume) through measuring the relative viscosity of dispersions of the particles as a function of the volume fraction of the dry particles in the dispersion, and of the specific surface area and the density of the particles. The calculated solvation film thicknesses on M1 are 7.48, 18.65 and 23.74 nm in alcohol, water and the water-ethyl alcohol mixture, 12.41, 12.71 and 13.13 nm on M2 in alcohol, water and the water-ethyl alcohol mixture, respectively.     

手性选择性阴离子交换膜的制备及性能

为得到较高通量的手性选择性阴离子交换膜,将β环糊精作为手性选择剂添加在膜相中,制得具有手性选择性的阴离子交换膜。将其用于拆分DL-对羟基苯甘氨酸外消旋混合物的电渗析过程。在碱性条件下L-对羟基苯甘氨酸优先通过手性阴膜,分离因子达1.25,通量达到60.4 g.m-2.h-1,验证了预期的拆分效果。使用普通阴膜,并在电渗析实验中对比了在料液中添加β环糊精以及不添加β环糊精的分离性能,β环糊精添加在料液中有明显的拆分效果,不添加β环糊精的普通电渗析几乎没有拆分效果。结果进一步验证了手性选择性来源于手性膜的β环糊精。     

Determination of electron orbital magnetic moments in carbon nanotubes

The remarkable transport properties of carbon nanotubes (CNTs) are determined by their unusual electronic structure. The electronic states of a carbon nanotube form one-dimensional electron and hole sub-bands, which, in general, are separated by an energy gap. States near the energy gap are predicted to have an orbital magnetic moment, mu(orb), that is much larger than the Bohr magneton (the magnetic moment of an electron due to its spin). This large moment is due to the motion of electrons around the circumference of the nanotube, and is thought to play a role in the magnetic susceptibility of CNTs and the magnetoresistance observed in large multiwalled CNTs. But the coupling between magnetic field and the electronic states of individual nanotubes remains to be quantified experimentally. Here we report electrical measurements of relatively small diameter (2-5 nm) individual CNTs in the presence of an axial magnetic field. We observe field-induced energy shifts of electronic states and the associated changes in sub-band structure, which enable us to confirm quantitatively the predicted values for mu(orb).