SiH4＋CH4激光等离子体动力学时空特性

采用时间，空间分辨的等离子体光辐射诊断技术，研究了脉冲ＴＥＡＣＯ２激光诱发ＳｉＨ４＋ＣＨ４击穿产生的等离子体膨胀过程，得到不同空间位置，不同实验条件下等离子体发光的时间特性，证明了ＳｉＨ４＋ＣＨ４气体击穿产生爆燃波而后诱发激波是等离子体中基本宏观动力学过程，并在实验上分析了激波对等离体内化学反应的影响，为激光等离子体合成ＳｉＣ粉末微观反应动力学过程的研究提供了参考数据。     

钢卷尺刻度在线测量系

本文介绍了一种钢卷尺刻度在线测量系统 ,它采用了高速摄像及计算机数据处理技术 ,文章阐述了系统的非接触动态测量原理 ,描述了光电信号的处理方法 .     

Viscoelasticity and birefringence of polyisoprene

The complex Young's modulus, E^*(ω), and the complex strain-optical coefficient, O^*(ω), which is the ratio of the birefringence to the strain, were measured for polyisoprene (PIP) over a frequency range of 1 ～ 130 Hz and a temperature range of 22 ～ ?100°C. The imaginary part of O^*, O″, was positive at low frequencies and negative at high frequencies. The real part, O′, was always positive and showed a maximum. The complicated behavior of O^* could be understood by the assumption that E^* = E_R^* + E_G^* and O^* = C_RE_R^* + C_GE_G^*, where E_R^* and E_G^* were complex quantities and C_R and C_G were constants. The C_R value, equal to the ordinary stress-optical coefficient measured in the rubbery plateau zone, was 2.0 × 10^?9 Pa^?1. The C_G value, defined as the ratio O″/E″ in the glassy zone, was ?1.1 × 10^?11 Pa^?1. The E_G^*, which was the major component of E^* in the glassy zone, showed almost the same frequency dependence as that of polystyrene and polycarbonate. The E_R^*, which was dominant in the rubbery zone, was described well by the bead-spring theory. The temperature dependence of the E_G^* was stronger than that of the E_R^*. This difference caused the breakdown of the thermorheological simplicity for E^* and O^* around the glass-to-rubber transition zone. © 1995 John Wiley & Sons, Inc.     

PHASE INVERSION AND ITS MECHANICAL MODEL STUDIES FOR THE TWO-PHASE POLYMER BLEND SYSTEMS (Ⅱ)——DYNAMIC VISCOELASTIC RESPONSE

The dynamic viscoelastic response of the two-phase polymer blend systems shows the characteristics of the thermorheologically complex materials. In this paper theoretical equations for describing the dynamic viscoelastic response of such polymer blend systems have been established by means of the mechanical modeling technique. The dynamic viscoelastic response of the blend systems at any blend composition can be predicted theoretically by using the equations established, provided that the dynamic viscoelastic response of the two pure components and the mechanical model parameters are known in advance. Thus, we provide an effective method for studying the dynamic mechanical properties and the molecular relaxation characteristics of the two-phase polymer blend systems.     

Age related changes in the thermal transition of Turkey leg flexor tendon collagen

A differential scanning calorimetric, thermogravimetric and electron microscopic investigation has been carried out on the uncalcified areas of turkey leg flexor tendon as a function of age. Rehydrated samples exhibit an increase of thermal stability with age. The H_D values drop from about 11 cal·g^–1 in the first weeks of life down to 7 cal·g^–1 after the 11th week.At about 11 weeks, the collagen fibril diameter distribution passes from unimodal to multimodal. The DSC curves as well as the TG-DTG curves recorded from dried samples do not show any appreciable difference with ageing. The variations in thermal behaviour of rehydrated samples and fibril diameter distribution could be related to modifications in water binding with ageing.The Authors are grateful to Dr. G. Fabris for discussion and help in the selection of the samples. They also wish to thank Mr. G. Pizzuto for excellent technical assistance. The financial support by Consiglio Nazionale delle Ricerche is gratefully acknowledged.     

Surface forces in foam films from ABA block copolymer: a dynamic method study

The thinning of foam films from aqueous solutions of an ABA triblock copolymer of polyethylene oxide and polypropylene oxide (average molecular weight 14,000 g/mol) is studied experimentally. The dependence of the surface forces on film thickness is obtained by the dynamic method of Scheludko and Exerowa.The total surface force measured in foam films (radius 60–70 m) from 10^–5 M (0.014 wt%) polymer solution with 0.1 M NaCl is positive at thicknesses from about 800 down to 460 . The electrostatic repulsion is negligible while the contribution of van der Waals attraction is small (within 15%). Therefore a positive surface force component predominates. Most probably it arises from steric interactions between the hydrophilic polyethylene oxide tails of the polymer. The dynamic method appears to be a suitable technique for exploring the stabilization of foam films from ABA copolymers.     

On Aging of Acid-Catalyzed Silica Sols—A Dynamic Light Scattering Study

Dynamic light scattering experiments in acid-catalyzed silica sols are discussed. It is shown that in spite of limited parameter accuracy and limited absolute knowledge of the particle sizes, the scattering data from various experiments are comparable with one another and give information about structural differences. Measurements at various angles indicate changes between non-spherical and nearly spherical particles and allow the estimation of gelling times before gelation.     

Isoperichoric focusing field-flow fractionation and thin layer isoperichoric focusing based on coupling of gradient generated by primary field with secondary field action: general principles and performances

The primary field forces can generate spatially oriented gradient of the effective property of a continuum or pseudo-continuum fluid (carrier liquid). When this gradient is coupled with the action of a secondary field of identical or different nature the isoperichoric focused zones of the dispersed species can appear. Consequently, they can be separated according to differences responding to the property gradient of the carrier liquid. This concept can be applied under static (non-flow) conditions in thin layer focusing as well as under dynamic conditions with the elution due to the carrier liquid flow in focusing field-flow fractionation. The gradient established by the action of the primary field and the concentration distribution of the isoperichoric focused zone formed by the coupled effect of the gradient and of the primary or secondary field are described theoretically. The rigorous relationship describing the shape of the focused zone is compared with the approximate solutions. The performances of the proposed principle were evaluated by model calculations. Potential experimental configurations considering the implementation of the static and dynamic conditions are discussed. The generalized isoperichoric focusing theory can be applied to describe the particular processes operating in analytical and preparative focusing separations of the particles of various, but especially of biological origin.     

Simple algorithm for isothermal-isobaric molecular dynamics

We review principles of non-Hamiltonian statistical mechanics and present a new set of equations and integration algorithm for isothermal-isobaric dynamics. The chief advantage of the present scheme is that it is somewhat simpler than previous methods. We perform numerical simulations to test the accuracy of the algorithm and compare its stability to that of a "gold standard," a symplectic integrator for Hamiltonian dynamics of the same system. The stability of the isothermal-isobaric algorithm is comparable to the stability of the symplectic integrator.