飞行器尾涡对的不稳定性建模

为了确定飞行器尾流的保持距离和诱导失稳运动性质,首先在一阶近似Biot-Savart定律的基础上,推导了任意多个涡对的诱导运动模型,进而利用线性组合方法得到涡系诱导运动的对称以及反对称模态,并结合模态矩阵特征值的性质描述对称分布涡系的稳定性.因为尾涡结构的不稳定性依赖于相应的模态矩阵特征值的取值,所以在利用对称分布的二涡对的模态验证所推导的模态矩阵理论的正确性的基础上,进一步给出了三涡对的模态矩阵对应的失稳模态.理论推导和特征值的计算显示随着涡丝数量的不断增加,三涡系的不稳定性增强,并且涡系对扰动的放大作用增强.     

生物聚合物交联网络的力学响应

生物聚合物交联网络(crosslinked biopolymer networks)是由肌动蛋白微丝等生物纤维相互交联形成的复杂网络结构,它广泛存在于细胞骨架和生物凝胶等系统中,对维持细胞完整性、使细胞具有主动变形和抵抗被动变形能力起着不可或缺的作用,其力学响应及工作机理对细胞工程、组织工程的发展非常重要.生物聚合物交联网络中交联蛋白的结合能量通常较低,其解离和重连过程容易受到网络结构变形和环境热涨落等因素的影响.实验中发现生物聚合物交联网络在小变形时刚度较低,但随着变形的增加,网络整体刚度会呈现数量级的增加,如果变形继续增加并超过一定阈值,网络刚度将急剧下降,这种应变硬化到软化的现象引起了研究者的广泛关注.已有理论模型和数值模拟发现,生物聚合物交联网络的硬化主要来源于纤维变形模式从弯曲到拉伸的转化,而软化则是由于网络中交联蛋白解离导致结构弱化和应力松弛.从生物聚合物交联网络的微观组成和结构出发,综述了生物聚合物纤维的力学模型、交联蛋白的力学属性和交联方式、交联网络的主要构型以及测量网络力学响应的实验方法,重点讨论了理论建模、有限元模拟、分子动力学等方法在研究生物聚合物交联网络非线性力学行为的进展,旨在为具有不同专业背景的研究者了解并开展生物聚合物交联网络力学响应的相关研究提供参考,也有助于机理化、定量化地理解细胞骨架中蕴含的结构-功能关系.     

The propagation dynamics of ultraviolet light filament with Rayleigh scattering in air

In this paper we present for the first time the effects of Rayleigh scattering on the long distance propagation of ultraviolet （UV） light filament in air based on the stationary analysis. The simulation results show that the effects of Rayleigh scattering on the propagation of UV laser filaments may not be ignored. These influences are slightly dependent on the laser wavelength. We also compare the UV filament propagations at different input powers in the presence and the absence of the Rayleigh scattering and discuss the mechanisms of power loss and beam defocusing. In the absence of Rayleigh scattering, the filament propagation is determined by the oscillating behaviour of the beam size. In the presence of the scattering, the propagation lengths of filament are close to each other at different initial powers and determined by the Rayleigh scattering.     

Intermediate Filaments in Higher Plant Cells and Their Reconstitution in vitro

Delicate networks of 10-nm filaments were found to exist widely in suspension cells of cultured carrot and root tip cells of pea by selective extraction combined with whole mount and diethylene glycol distearate plastic embedment-free section for electron microscopy. These filament components are polypeptides of 52, 58, 62—64 and 50kD using Western blot analysis. A relatively uniform 10-nm filaments, as well as bundle of such filaments could be reconstituted in vitro. The reconstituted filaments were indistinguishable from native plant intermediate filaments in morphology and protein components. Thus the intermediate filaments are actually present in cytoplasm of higher plants. We also found no obvious specificity in tissues and species by comparison of the proteins among various types of plant cells.     

一种新型的多功能细丝直径测量仪

本文介绍了一种新型的细丝直径测量仪,文章详细地介绍了该仪器的测量系统,该仪器不仅能进行静态测量,还可进行在线动态测量,并能测量细丝的不圆度。测量范围为20～200微米,测量速度200次/秒,测量精度±0.5微米。本文还对它的功能和性能与国内外同类产品进行了比较,该仪器总体上是先进的。     

Didactic experiment of a one-dimensional process of solidification from nuclei at random to a linear polycrystal. Part I: Nuclei,nuclei distances,and grain lengths

We show theexperimental verification of a didactic model which is named one-dimensional (1D) process of solidification (crystallization) from nuclei at random to linear polycrystal.This one-dimensional model assumes: 1) Nuclei are distributed at random. 2) From these the grains start to grow instantaneously, circularly, and with the same and constant growth rate. 3) Growth stops where two grains touch. This model was theoretically treated by Schulze [1,2] and about 20 statements were derived; here, these statements were experimentally verified. To that end, the 1D model is experimentally approximated by a spun filament of 15-m diameter. The filament consists of polypropylene and, therefore, the grains are spherulites; it is embedded in a glue, which acts as a capillary tube. A later heat-treatment of the embedded filament (including melting, nucleation, grain (spherulite) growth) finally shows the nuclei, the nuclei distances, and the grain (spherulite) lengths. These values are measured: there are 1601 nuclei and the mean nuclei distance (and the mean grain length) is 361 m. The growth rate of the grain (spherulite) is 4.15 m/min. A comparison between theory and experiment shows agreement.     

电子辐射对聚乙烯高弹性性能的影响

<正> 由于超高模量聚乙烯(Ultra-High Modulus Polyethylene,简称UHMPE)纤维可望作绳索和复合材料等工程材料而在工程上获得广泛应用,面临的一个重要任务就是设法尽可能地改善其力学性能,已有几篇研究论文报道了不同拉伸比,不同分子量和γ辐射对UHMPE结构和性能的影响,这些方法都在不同程度上改善了纤维的性能。本实验则研究了各种不同剂量的电子辐射对UHMPE高弹性性能及结构的影响。至于电     

有关白炽灯的几个重要参数的测量

在已有的实验结果的基础上，通过建立物理模型，应用近似处理等方法简洁地测出了白炽灯正常发光时的灯丝温度值、可见光所占总能的比例、光通量等重要参数．     

逸出功测定实验研究

文章讨论了在逸出电位测定过程中两种灯丝电流和加速电压的调节方法。认为如果先固定加速电压当灯丝电流增大后,会导致加速电压的减小,使测量逸出电位的不确定度增大。所以在这种调节方法中,应该增大加速电压值,这样测量精度更高。