A micro/nanocasting method for replicating soft micro/nanosurface structures using a dynamic electrical field

We propose a new electric field-induced micro/nanocasting method to replicate soft patterns using micro/nanocasting techniques without pressure. The process uses an alternating current (AC) electrical field and rotation of one electrode, generating a dynamic electrical field that induces electrokinetic flow motion in a dielectric solution (polydimethylsilane, PDMS). We used a lotus leaf as a replication template and characterised the PDMS flow motion to observe the effects of various process parameters (e.g., electrical field strength, rotation speed of an electrode, and electrode shape). The unstable flow motion was significantly dependent on the processing parameters, especially the rotation speed of the electrode. Using the optimised processing conditions, the replication efficiency was about 88%. We believe that this method has potential for fabricating soft micro/nanosized structures.     

Living fluids

One of the major emerging fields of research of the beginning of this century concerns living fluids. By “living fluids”, we mean two major categories of complex fluids: (i) fluids which are essential to life, like blood, and (ii) active fluids made of particles that are able to propel themselves in the suspending fluid by converting a form of their energy into mechanical motion. Studies on active fluids have known a considerable interest since the last decade. Blood might be viewed as an old topic, but the progresses in experimental techniques, analytical concepts and numerics, have contributed nowadays to a dramatic renewal of the interest in this field, with a great potential towards understanding physical and mechanical factors in cardiovascular diseases. These fields have considerably strengthened interdisciplinary research. The series of reviews of this dossier focus on the tremendous recent progress achieved in research on living fluids both from the experimental and theoretical points of views. These reviews present also the major open issues, making of this dossier a unique guide for future research in these fields. This project grew up thanks to the international summer school that we organized on the topic “living fluids” at the IES (Institut dʼétudes scientifiques) of Cargèse (Corsica) in 2012.     

远场来流对过冷熔体中球状晶体生长的影响

利用渐近分析方法研究了远场来流引起的对流对过冷熔体中球状晶体的生长形态的影响.结果表明,由远场来流导致的对流使得正在生长的球状晶体的界面在向着来流的前部朝来流方向相反的方向生长, 并且提高了朝来流的相反方向的生长速度, 在背风方向衰减；正在衰减的球状晶体的界面在向着来流的前部加速衰减, 在背风方向减缓衰减. 关键词： 球状晶体 远场来流 对流 界画形态     

非定常瞬态流动过程中的Lagrangian拟序结构与物质输运作用

从Lagrangian角度数值分析了圆柱瞬时起动过程中的非定常瞬态流动现象,如分离泡产生、破裂和涡脱落等及其产生的非定常效应,揭示了所列现象诱导的物质输运和迁移效应,首先采用双时间步长的特征线算子分裂算法数值模拟了圆柱起动过程中的瞬时流场,然后采用数值方法从流场中提取出Lagrangian拟序结构(LCSs),并根据非线性动力学理论研究了流动分离和旋涡演化过程中的物质输运作用,结果表明,圆柱瞬时起动后所产生的非定常阻力与相应瞬态现象中的物质输运有密切的关系:对称分离泡产生及其在流向方向的生长,能够使分离泡内压力升高且分布均匀,从而减小阻力;对称分离泡的失稳增强了分离泡与主流之间的物质输运作用,最终导致涡的脱落,并有利于推迟流动分离和减小分离区域,非定常流动中LCSs所描述的物质输运和迁移作用对流动控制的机理研究具有一定指导意义。     

多孔介质BISQ模型中的慢纵波

着重研究了多孔介质BISQ模型中慢纵波的基本特性.给出了BISQ模型下慢纵波速度 和衰减的低频近似公式.与Biot理论对比，BISQ模型中慢纵波的衰减随频率降低急剧增大， 且随喷射流长度的减小而增加；相速度随喷射流长度的减小而增加，其低频极限值不是零； 孔隙流体位移与固相骨架位移之比的幅值随喷射流长度的增加而减小，其相位特点与Biot模 型预测的不同；在流体与孔隙介质的边界上可产生更大的渗流.为对比，同时也给出快纵波 的行为.依据BISQ模型可推断：非黏滞流体饱和孔隙介质中不存在喷射流机理；BISQ模型中 关键词： 多孔介质 喷射流 慢纵波 动力协调     

A Split-Flow Enzyme Thermistor

Abstract

The split-flow system is comprised of two identical micro-columns, one of which contains an immobilized enzyme preparation, the other an inert support material.

The heat produced in each column on introduction of a sample is measured with thermistors placed in these columns. The use of a reference column virtually eliminates the influence on the measurements of artifactual signals as unspecific heat, i.e., heat not produced by the enzymic reaction. The performance of the split-flow enzyme thermistor at a variety of pH's, ionic strengths or viscosities associated with the sample has been investigated and compared with previously described alternative enzyme thermistor arrangements. In this comparative study glucose at a concentration of 5 · 10^?4 M was used throughout. On passage through the imnobilized glucose oxidase preparation this solution gave rise to a heat change At of about 0.01°C. The insensitivity of the system described herein towards such variations makes it particularly suitable for the analysis of metabolities present in crude solutions such as urine and skim-milk.     

Surface tension and viscosity measurements of liquids with the survismeter: a single instrumental unit

Surface tension (γ) and viscosity (η) data of aqueous solutions of the deoxyadenosine (DOA) and the deoxyribose (DOR) sugars have been measured with the survismeter, a new instrument, along with tetrahydrofuran (THF), dimethylformamide (DMF), acetonitrile and dimethylsulphoxide (DMSO) solvents. The same properties have also been measured with a stalagmometer and a viscosimeter, respectively, which afford the same information, albeit at the expense of a larger amount of chemicals and solvents. We obtain comparatively better accuracy in both kinds of measurements than with conventional methods. Therefore, the survismeter lends itself as a simple and reliable instrument.     

Three‐dimensional computation for flow‐induced vibrations in in‐line and cross‐flow directions of a circular cylinder

We present numerical results for in‐line and cross‐flow vibrations of a circular cylinder, which is immersed in a uniform flow and is elastically supported by damper‐spring systems to compute vibrations of a rigid cylinder. In the case of a circular cylinder with a low Scruton number, it is well‐known that two types of self‐excited vibrations appear in the in‐line direction in the range of low reduced velocities. On the other hand, a cross‐flow vibration of the circular cylinder can be excited in the range of high reduced velocities. Therefore, we compute the flow‐induced vibrations of the circular cylinder in the wide range of the reduced velocities at low and high Scruton numbers and discuss about excitation mechanisms in the in‐line and cross‐flow directions. Copyright © 2011 John Wiley & Sons, Ltd.     

On the Motion of Substance in a Channel of a Network: Extended Model and New Classes of Probability Distributions

We discuss the motion of substance in a channel containing nodes of a network. Each node of the channel can exchange substance with: (i) neighboring nodes of the channel, (ii) network nodes which do not belong to the channel, and (iii) environment of the network. The new point in this study is that we assume possibility for exchange of substance among flows of substance between nodes of the channel and: (i) nodes that belong to the network but do not belong to the channel and (ii) environment of the network. This leads to an extension of the model of motion of substance and the extended model contains previous models as particular cases. We use a discrete-time model of motion of substance and consider a stationary regime of motion of substance in a channel containing a finite number of nodes. As results of the study, we obtain a class of probability distributions connected to the amount of substance in nodes of the channel. We prove that the obtained class of distributions contains all truncated discrete probability distributions of discrete random variable ω which can take values 0,1,⋯,N. Theory for the case of a channel containing infinite number of nodes is presented in Appendix A. The continuous version of the discussed discrete probability distributions is described in Appendix B. The discussed extended model and obtained results can be used for the study of phenomena that can be modeled by flows in networks: motion of resources, traffic flows, motion of migrants, etc.