Accumulation and filtering of nanoparticles in microchannels using electrohydrodynamically induced vortical flows

We present an approach for the accumulation and filtering of nano- and microparticles in microfluidic devices that is based on the generation of electric traveling waves in the radio-frequency range. Upon application of the electric field via a microelectrode array, complex particle trajectories and particle accumulation are observed in well-defined regions in a microchannel. Through the quantitative mapping of the 3-D flow pattern using two-focus fluorescence cross-correlation spectroscopy, two vortices could be identified as one of the sources of the force field that induces the formation of particle clouds. Dielectrophoretic forces that directly act on the particles are the second source of the force field. A thorough 2-D finite element analysis identifies the electric traveling wave mechanism as the cause for the unexpected flow behavior observed. Based on these findings, strategies are discussed, first, for avoiding the vortices to optimize electrohydrodynamic micropumps and, secondly, for utilizing the vortices in the development of microdevices for efficient particle accumulation, separation, and filtering. Such devices may find numerous biomedical applications when highly diluted nano- and microsuspensions have to be processed.     

Elimination of Anti-spiral Waves by Local Inhomogeneity in Oscillatory Systems

Anti-spiral waves are controlled in an oscillatory system by using a local inhomogeneity. The inhomogeneity acts as a wave source, and gives rise to the propagating plane waves. It is found that there is a critical pacemaking domain size below which no wave will be created at all. Two types of ordered waves (target waves and traveling waves) are created depending on the geometry of the local inhomogeneity. The competition between the anti-spiral waves and the ordered waves is discussed. Two different competition mechanisms were observed, which are related to the ordered waves obtained from different local inhomogeneities. It is found that traveling waves with either lower frequency or higher frequency can both eliminate the anti-spiral waves, while only the target waves with lower absolute value of frequency can eliminate the anti-spiral waves.This method also applies to outwardly rotating spiral waves. The control mechanism is intuitively explained and the control method is easily operative.     

Fading memory of deformation history in carbon black-filled thermoplastic elastomers

Observations are reported on a carbon black–reinforced thermoplastic elastomer in multistep uniaxial tensile cyclic tests with a mixed deformation program (oscillations between maximum elongation ratios k_max and various minimum stresses σ_min with k_max monotonically increasing with number of cycles n). Fading memory of deformation history is demonstrated: when specimens are subjected to two loading programs that differ along the first n −1 cycles of deformation and coincide afterwards, their stress–strain diagrams become identical starting from the nth cycle. A constitutive model is developed in cyclic viscoplasticity with finite deformations, and its adjustable parameters are found by fitting the observations. Ability of the stress–strain relations to describe the fading memory phenomenon and to predict the mechanical response of polymer composites in multi-step cyclic tests with large strains is confirmed by numerical simulation.     

Theoretical modeling of photo-induced wave propagation in liquid-crystalline Langmuir monolayers

A phenomenological model of wave propagation in photo-excited liquid-crystalline Langmuir monolayers is constructed. The spontaneous splay deformation of the liquid-crystalline order and the anisotropy of photo-excitation of molecules are taken into account in this model. Numerical simulations of the model well reproduce qualitative features of the wave propagation phenomenon observed in recent experiments. A linear stability analysis of the model equations reveals that an interplay between the spontaneous splay deformation and the anisotropy of the photo-excitation can lead to the wave propagation.     

具有平方衰减项的平方自催化开放系统中的化学波研究

建立了开放系统中伴随平方衰减反应的双分子自催化反应理论模型,给出了系统的动力学分析,在给定初边值下解的估计及存在化学波的必要条件、化学波波速的最小值及平方衰减项对化学波的影响.随着衰减系数的增加,平方衰减项逐步成为系统反应中化学波波形的决定因素.     

Numerical studies of vertically propagating acoustic and magnetoacoustic waves in an isothermal atmosphere (III)

In this paper we investigate, numerically, the generation and propagation of acoustic and magnetoacoustic waves and their roles in the heating process of the chromosphere. The combined effects of viscosity, thermal conduction and a uniform horizontal magnetic field on an upward and a downward propagating wave in an isothermal atmosphere are considered. It is shown that when the heating mechanisms are dominated by the effects of thermal conduction.

The chromosphere atmosphere can be divided into three distinct regions, low, middle and high. The middle region acts like a semitransparent transition layer and it is produced by thermal conduction and connects middle and high chromosphere. In the transition region part of the energy transmitted upward, part is dissipated and the other part is reflected downward. Moreover, viscosity creates an absorbing and reflecting layer and the magnetic field forms a totally reflecting barrier because of its dissipationless nature. When the combined effects of the viscosity and magnetic field dominated the oscillatory process, thermal conduction can be eliminated because the solution decays exponentially with altitude before the effects of thermal conduction take place.

The formulation of the model leads to a system of differential equations of the velocity and temperature and it will be used for the numerical solutions, and for the analytical solutions we have a fourth order differential equation. The differential equations in both cases are linear but with exponential coefficients. Approximate and exact solutions of the mathematical model are studied, in low, middle, and high chromospheres, both numerically and analytically. The analysis of both studies is in complete agreement with previously observed and reported results and conclusions about the heating process of the chromosphere. The results of the numerical solutions are discussed in connection with the heating mechanisms of the three regions of the chromosphere. Finally, the case where the values of thermal conduction, viscosity and magnetic field are arbitrary is considered.     

光盘存储材料及其新进展

本文简要叙述光盘写入、读出和擦除的机理并对近年来有机记录介质的研究重点及其相应的技术动向做了分析.当前的研究与开发的重点是具有高记录密度,数据传输速率快、稳定性好、载噪比大和误码率低的可擦型光盘存储材料.     

形状记忆高分子材料

作为一种新型的功能材料,形状记忆高分子不仅具有形变量大、赋形容易、形状恢复温度便于调整、加工方便的优点,而且种类丰富、质轻价廉.按形状记忆的方式,它可分为热致感应型、光致感应型和化学物质感应型等,能满足不同的应用需求.     

Ternary Flexible Electro‐resistive Memory Device based on Small Molecules

Flexible memory devices have continued to attract more attention due to the increasing requirement for miniaturization, flexibility, and portability for further electronic applications. However, all reported flexible memory devices have binary memory characteristics, which cannot meet the demand of ever‐growing information explosion. Organic resistive switching random access memory (RRAM) has plenty of advantages such as simple structure, facile processing, low power consumption, high packaging density, as well as the ability to store multiple states per bit (multilevel). In this study, we report a small molecule‐based flexible ternary memory device for the first time. The flexible device maintains its ternary memory behavior under different bending conditions and within 500 bending cycles. The length of the alkyl chains in the molecular backbone play a significant role in molecular stacking, thus guaranteeing satisfactory memory and mechanical properties.     

个人叙事与集体记忆：口述史的多维建构

口述史是个体对自我生命历程的叙述,也是我们认识和理解群体或共同体集体记忆的有效途径。口述史的叙述过程既是叙事主体能动性的体现,同时也充满了诸多的被动性因素,认识和重视口述史研究过程中的能动性和被动性,将有助于研究者更好地理解记忆的检索性、被触发性和被建构性。而记忆的被触发性提示我们,现实的口述史不仅是历史与社会宏观建构的结果,也是访问者与亲历者微观互动的建构结果。研究中,必须重视承载共同体成员个体记忆的口述史研究过程,才能真正洞察共同体成员的集体记忆。     

Triple shape memory effect in multiple crystalline polyurethanes

Remembering more than one permanent shape is an attractive research topic for shape memory materials (SMMs). In this paper, multiple crystalline shape memory polyurethanes (SMPUs) are prepared with PCL10000 and PTMG2900 by a three‐step polymerization method. DSC and WAXD results show that the obtained polyurethane contains, simultaneously and independently, two kinds of crystals. In addition, it is confirmed through DMA analysis that reversible soft phase and hard domains are formed in the PCL‐PTMG based SMPU system; and two‐step modulus decreases at low temperature range can be obtained in the SMPU with suitable mass proportion of PCL to PTMG, e.g., 1:7. Thus, shape memory effect (SME) can be achieved in this system. Moreover, it is found that the PTMG soft segment dominates the shape memory effect when the PCL mass is lower than that of PTMG; while the PCL soft segment dominates the SME when PCL mass is higher than that of PTMG; and a two‐step programing shape recovery can be achieved when the mass proportion of PCL/PTMG reaches a balance value, e.g., 3:5. Copyright © 2009 John Wiley & Sons, Ltd.     

An Electrochemical Robotic System for Routine Cathodic Adsorptive Stripping Analysis of Ni2+ Ion Release from Corroding NiTi Shape Memory Alloys

Cathodic adsorptive stripping voltammetry (AdSV) as highly sensitive and selective method for quantifying trace amounts of dissolved Ni²⁺‐ions has been integrated into an electrochemical robotic device using the wells of microtiter plates as low‐volume electrochemical cells. A three‐electrode assembly integrating a Bismuth film‐modified glassy carbon electrode as working electrode and a glass capillary for delivering Ni²⁺ standard solution in conjunction with an adapted software allowed multiple AdSV measuring cycles to be performed one after the other in the individual compartments of a 24‐well microtiter plate. Of advantage for the automation was the possibility of an in‐well electrochemical removal of used and a replating of fresh Bi films in between distinct measuring cycles. With optimized parameters for the accumulation of the complex between Ni²⁺‐ions and dimethylglyoxime onto the surface of the Bi film electrode and the subsequent stripping procedure, automated adsorptive stripping voltammetry in the established system offered a linear dynamic range of up to 170 nM, a sensitivity of 12 nA/nM Ni²⁺ and a limit of of detection of 2.1 nM (N=16) for the detection of trace levels of Ni²⁺‐ions. Automated AdSV certainly is of convenience for studying larger number of samples due to the high‐throughput capability of the robotic apparatus. As example, the automatic quantification of Ni²⁺‐ion release from electropolished surfaces of NiTi shape memory alloys during corrosion in NaCl solutions is described.     

Shape memory fiber spun with segmented polyurethane ionomer

The effect of cationic groups within hard segments on shape memory polyurethane (SMPU) fibers was studied and the cyclic tensile testing was conducted to assess the shape memory effect. Mechanical properties, hard segment crystallization, and dynamic mechanical properties of SMPU ionomer fibers composed of 1,4‐butanediol (BDO), N‐methyldiethanolamine (NMDA), 4,4′‐methylenebis(phenyl isocyanate) (MDI), and poly(butylene adipate)diol (PBA) were investigated using a universal tensile tester, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results demonstrate that only 2 wt% NMDA can significantly change the glass transition temperature of the soft segment phase. DSC shows that the ionic group within hard segments can facilitate the crystallization of hard segments in unsteamed SMPU ionomer fibers. But for steamed fiber specimens, this effect is insignificant. Moreover, the ionic groups in hard segments with different hard segment contents (HSC) have different effects. In unsteamed fibers with 64 wt% HSC, 2 wt% NMDA increases the glass transition of soft segments from 63.5 to 70.6°C. However, in fibers with 55 wt% HSC, the glass transition temperature is lowered from 46.7 to 33.5°C. The post‐treatment, high‐pressure steaming is an effective way to remove the internal stress and subsequently improve the dimensional stability of SMPU ionomer fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

The S-matrix version of the Hulthén-Kohn variational principle for quantum scattering: Finite element calculations for state-to-state reaction probabilities

Summary The finite element (FE) method can be applied to solve the reactive scattering problem of the A + BC AB + C type. We are using the S-matrix version of the Hulthén-Kohn variational principle for the two-dimensional collinear problem. The asymptotic wavefunction is described by analytical functions and the interaction part by FE functions.Two approaches are used and compared to each other: 1) FE functions are employed as the basis functions for the interior part of the potential; 2) the FE method is used in order to calculate eigenfunctions for the interior region of the potential and then these eigenfunctions are used as a new basis. In the second case two ways of choosing grid points are applied. First a grid is built that covers both reaction channels, secondly we considered the two reactions channels separately and two basis sets are used in the scattering calculations. This last version would be more helpful from the point of application to three-dimensional non-collinear problems. Results obtained by raising the number of elements, or by increasing the polynomial order, are compared. General formulas for the formfunctions in case of arbitrary order of the polynomials will be presented.Dedicated to the 60th birthday of Prof. Jan Linderberg (Aarhus)