Millisecond-order rapid micromixing with non-equilibrium electrokinetic phenomena

We report an active micromixer utilizing vortex generation due to non-equilibrium electrokinetics near micro/nanochannel interfaces. Its design is relatively simple, consisting of a U-shaped microchannel and a set of nanochannels. We fabricated the micromixer just using a two-step reactive ion etching process. We observed strong vortex generation in fluorescent microscopy experiments. The mixing performance was evident in a combined pressure-driven and electroosmotic flows, compared with the case with a pure pressure-driven flow. We characterized the micromixer for several conditions: different applied voltages, ion concentrations, flow rates, and nanochannel widths. The experimental results show that the mixing performance is better with a higher applied voltage, a lower ion concentration, and a wider nanochannel width. We quantified the mixing characteristics in terms of mixing time. The lowest mixing time was 2 milliseconds with the voltage of 230 V and potassium chloride solutions of 0.1 mM. We expect that the micromixer is beneficial in several applications requiring rapid mixing.     

Numerical modeling of multiphase flows in microfluidics and micro process engineering: a review of methods and applications

This article presents a comprehensive review of numerical methods and models for interface resolving simulations of multiphase flows in microfluidics and micro process engineering. The focus of the paper is on continuum methods where it covers the three common approaches in the sharp interface limit, namely the volume-of-fluid method with interface reconstruction, the level set method and the front tracking method, as well as methods with finite interface thickness such as color-function based methods and the phase-field method. Variants of the mesoscopic lattice Boltzmann method for two-fluid flows are also discussed, as well as various hybrid approaches. The mathematical foundation of each method is given and its specific advantages and limitations are highlighted. For continuum methods, the coupling of the interface evolution equation with the single-field Navier–Stokes equations and related issues are discussed. Methods and models for surface tension forces, contact lines, heat and mass transfer and phase change are presented. In the second part of this article applications of the methods in microfluidics and micro process engineering are reviewed, including flow hydrodynamics (separated and segmented flow, bubble and drop formation, breakup and coalescence), heat and mass transfer (with and without chemical reactions), mixing and dispersion, Marangoni flows and surfactants, and boiling.     

Simple and low-cost fabrication of PDMS microfluidic round channels by surface-wetting parameters optimization

Convenient for both biologists and MEMS designers, Polydimethylsiloxane (PDMS) polymer is intensively investigated for its biocompatibility, transparency, high resistance under plasma treatment, flexibility and resistance to high temperature. However, for microfluidic applications, the fabrication of PDMS circular channels is difficult to achieve except by wire moulding. In this article, we present a simple, fast and low-cost fabrication method which can be applied out of clean-room environment. It is based on the deposition of alginic acid sodium salt aqueous solution, enabling the formation of a liquid cylinder on the most hydrophilic part of a hydrophilic/hydrophobic patterned surface. We experimentally studied the interaction between liquid rivulets and surfaces presenting a contrast of wettability and/or a stepwise texture. Subsequent moulding of the half-cylinder of liquid produces round PDMS microfluidic channels. The optimal parameters for hydrophilic/hydrophobic patterns have then been applied to produce the roundest possible channels. The realisation of both straight channels 300–500 μm wide, 1 cm long and 75° tangent chord angle at best, and Y-shaped channels with the same dimensions and 55° TCA is demonstrated.     

2D system approach based output feedback repetitive control for uncertain discrete-time systems

This paper presents a two-dimensional (2D)-based approach to the problem of output feedback repetitive control for uncertain discrete-time systems. It is shown first how the proposed repetitive control scheme can be equivalently formulated in the form of a distinct class of 2D system. Then sufficient conditions for the existence of output feedback control law are derived in terms of linear matrix inequality (LMI), and the control law matrices are characterized by the feasible solutions to this LMI. Moreover, an optimization problem is introduced to efficiently solve the optimal output feedback control law by minimizing the upper bound of a given cost function. Compared with the commonly used 1D-based method, the proposed approach increases the degree of freedom of controller design by not only including in the scheme an output feedback gain but also a feed forward one which can be simultaneously solved using the 2D-based procedures presented in the paper. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed method.     

Parameter identification and design of a robust attitude controller using <Emphasis Type="Italic">H</Emphasis><Subscript>∞</Subscript> methodology for the raptor E620 small-scale helicopter

Rigorous control synthesis for an unmanned aerial vehicle necessitates the availability of a good, reasonable model for such a vehicle. The work reported in this paper focuses on the modeling of a rotary unmanned aerial vehicle (RUAV) and the development of a robust controller that can handle parameter uncertainties and disturbances. The parameters of the plant model are obtained through the use of the prediction error method with real flight data. The response of the identified linear model shows a good match with the measured flight data. The H _∞ control scheme is applied to obtain a robustly stable controller using the identified model. The proposed controller is analyzed using frequency-domain analysis and time-domain simulations. The performance of the proposed H _∞ controller is better than that of the conventional proportional derivative controller in that the proposed controller has a shorter settling time and less overshoot. Furthermore, the degradation of the proposed controller performance is negligible and stability is maintained when the input gains to the plant are doubled, which demonstrates the good performance and robustness of the controller.     

An investigation into vehicle rollover prevention by coordinated control of active anti-roll bar and electronic stability program

This paper presents a method for designing a controller that uses an active anti-roll bar (AARB) and an electronic stability program (ESP) for rollover prevention. ESP with longitudinal speed control (LSC) can carry out active braking to reduce vehicle speed and lateral acceleration to prevent a rollover. To enhance the rollover prevention capability of the ESP, an AARB is adopted. The controller for the AARB was designed based on linear quadratic (LQ) static output feedback (SOF) control methodology, which attenuates the effect of lateral acceleration on the roll angle and roll rate by control of the suspension stroke and the tire deflection of the vehicle. Although this AARB significantly increases ride comfort and rollover prevention, it has a drawback — the vehicle loses its maneuverability. Therefore, the ESP with LSC is used to overcome this drawback. Simulations showed that the proposed method was effective in preventing a rollover.     

单晶硅化物及其应用

本文评述了单晶CoSi_2和NiSi_2的结构特点、各种制备方法、器件应用和发展前景。采用分子束外延(MBE)和“内延”法(Mesotaxy)制备的单晶硅化物质量,电学性能和热稳定性较好。由于首次得到理想的突变的金属——半导体接触,使对金属——半导体接触的理论分析成为可能。硅/单晶硅化物/硅结构在实际应用中非常重要,如单晶硅化物作集电极埋层,能降低集电极串联电阻,克服重掺杂埋层的横扩和自掺杂问题,提高了电路工作速度,减小了器件面积。埋层硅化物也可作为微波传输线的地线,是实现高频集成电路互连的好方法。而采用该结构制备的高速器件——金属基区晶体管(MBT)和穿透基区晶体管(PBT),具有很好的应用前景。     

Deciding bisimilarity is<Emphasis Type="Italic">P</Emphasis>-complete

In finite labelled transition systems the problems of deciding strong bisimilarity, observation equivalence and observation congruence areP-complete under many—oneNC-reducibility. As a consequence, algorithms for automated analysis of finite state systems based on bisimulation seem to be inherently sequential in the following sense: the design of anNC algorithm to solve any of these problems will require an algorithmic breakthrough, which is exceedingly hard to achieve.     

基于协同管理的软件检测平台应用研究

构建和应用基于协同管理的软件检测平台是软件检测机构技术发展的必然趋势,也是软件检测机构对软件测试项目实施有效管理的重要技术手段。本文首先阐述了应用协同管理平台的目的和意义,接着,本文对协同理论及其在软件检测中的应用做了详细的论述,在此基础上,对基于协同管理的软件检测平台的作用、基本框架和其主要功能做了阐述。最后,给出了本文的结束语。     

Petri网在计费系统中的应用研究

本文从Petri网理论研究入手,介绍了基于Petri网的工作流,详细描述了petri网在计费系统中的应用,包括Petri中间件的总体设计和主要功能,最后针对计费系统的现状提出了如何应用Petri。