基于TL494的单闭环温度控制系统的设计

针对传统温度控制系统设计复杂的缺点,提出了一种新的温度控制设计思路。以TL494为控制单元,采用AD590为温度传感器,组成温度闭环控制系统.该系统具有结构新颖、电路简单和控制方便等优点。实际运行结果表明,该系统控制精度高、运行稳定,控制效果良好。     

基于LabVIEW嵌入式的便携式检测仪采集系统软件的设计

介绍一种基于LabVIEW嵌入式的便携式检测仪采集系统设计方法.该便携式检测仪设计结合功能强大的ARM微处理器与图形化的虚拟仪器技术,体现其优越性和机动性.同时,该检测仪采集系统用于实际采集各种光电信号,根据不同的应用需求,能够进行正确的标度转换,结果表明该方法得到较好的效果.     

Molecular simulation of phase coexistence: Finite-size effects and determination of critical parameters for two- and three-dimensional Lennard-Jones fluids

Abstact The subject of this paper is the investigation of finite-size effects and the determination of critical parameters for a class of truncated Lennard-Jones potentials. Despite significant recent progress in our ability to model phase equilibria in multicomponent mixtures from direct molecular simulations, the accurate determination of critical parameters remains a difficult problem. Gibbs ensemble Monte Carlo simulations with systems of controlled linear system size are used to obtain the phase behavior in the near-critical region for two- and three dimensional Lennard-Jones fluids with reduced cutoff radii of 3, 3.5, and 5. For the two-dimensional systems, crossover of the effective exponent for the width of the coexistence curve from mean field ( = 1/2 in the immediate vicinity of the critical point to Ising-like (= 1/8) farther away is observed. Critical parameters determined by fitting the data that follow Ising-like behavior are in good agreement with literature values obtained with finite-size scaling methods. For the three-dimensional systems, no crossover to mean field-type behavior was apparent. Extrapolated results for the critical parameters are consistent with literature estimates for similar fluids. For both two- and three-dimensional fluids, system size effects on the coexistence curves away from the critical point are small, normally within simulation statistical uncertainties.Invited paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder. Colorado, U.S.A.     

Orbital pairing effects in fullerenes

We propose a theory of superconductivity for a crystal having multiple band structure. The theory is valid for the parameter(k _F)/1 when the splitting between bands(k _F ) is small in comparison with the phonon frequency. The theory may be applicable to the doped fullerenes where it is widely supposed that pairing occurs through high-energy intramolecular phonons. As in semiconductors, the bunch of bands is treated by ascribing the highest spin to electrons. We derive the analytic expression for the critical temperature, which strongly depends on the value of the total spin of the Cooper pair, which may be equal toY=0,1,.... In all cases the order parameter is a vector with components proportional to spherical harmonics and at the same time the superconducting gap has no zeros. The data may be fitted to doped fullerenes, if the superconductivity arises fromd-pairing.     

Critical dynamics of a sheared micellar solution

We have investigated the dynamic behavior of a nonionic micellar solution of tetra-ethylene glycoln-decylether (C₁₀ E₄) in water near its critical point in the presence of shear. The non-Newtonian behavior of the viscosity can be represented by * = [ 1 +a(S₄)=]², where* is the viscosity in the absence of shear,S is the shear rate. ₄ is the lifetime of the critical Iluctuations,a is a system-dependent constant, and = 0.02 In addition, we have found that, before attaining a steady state, the sheared mixture undergoing phase separation shows significant shear-dependent rheological effects due to the presence of concentration domains.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24. 1994, Boulder, Colorado, U.S.A.     

Analysis of Critical Factors in Manufacturing by Adopting a Cloud Computing Service

The advantages of a cloud computing service are cost advantages, availability, scalability, flexibility, reduced time to market, and dynamic access to computing resources. Enterprises can improve the successful adoption rate of cloud computing services if they understand the critical factors. To find critical factors, this study first reviewed the literature and established a three-layer hierarchical factor table for adopting a cloud computing service based on the Technology-Organization-Environment framework. Then, a hybrid method that combines two multi-criteria decision-making tools—called the Fuzzy Analytic Network Process method and the concept of VlseKriterijumska Optimizacija I Kompromisno Resenje acceptable advantage—was used to objectively identify critical factors for the adoption of a cloud computing service, replacing the subjective decision of the authors. The results of this study determined five critical factors, namely data access security, information transmission security, senior management support, fallback cloud management, and employee acceptance. Finally, the paper presents the findings and implications of the study.     

基于低频触发的高精度RFID定位系统的设计与实现

为了解决传统RFID定位技术中存在的定位精度差和电子标签功耗高这2个问题,提出了一种基于低频触发的2.4GHz高精度区域定位系统的设计方案。该方案将低频125kHz触发信号与2.4GHz射频信号相结合,采用低频唤醒的方法极大降低了电子标签的功耗,利用可调节触发距离的触发机制将RFID系统的定位精度进一步提高.基于该方案设计了2.4GHz有源电子标签、125kHz触发器和2.4GHz阅读器三个子系统。阅读器与触发器的分离式设计,节约了铺设成本。系统硬件电路设计中加入了可调电位器和数字电压调节器,分别对识别距离和触发距离进行调节,使设备的配置更为方便,增强了系统的实用性。测试数据显示,阅读器与标签的最大通信距离长达120m,有源电子标签的待机时间约为2a(年),RFID定位系统能够实现1~5.2m的可调定位精度。测试结果验证了该方案的有效性。     

A mechanistic approach to evaluate the potential of the debonding distress in asphalt pavements

The debonding distress in asphalt pavement structures is a critical problem that affects the performance of asphalt concrete pavements. It occurs at the layer interface due to the poor bond quality between adjacent asphalt concrete layers and/or when stresses at the layer interface exceed the strengths of the material at the interface. The debonding of the adjacent layers, especially the top surface layer of an asphalt pavement, is a contributing factor to the premature cracking of pavements. Hence, the debonding distress can lead to a reduction in the life of the pavement. This paper presents an analytical and experimental framework to evaluate the potential for debonding at the layer interface of asphalt concrete pavements. Computational analysis was performed to determine the critical stress and strain states in layered asphalt pavements under moving vehicle loads using the Layered ViscoElastic pavement analysis for Critical Distresses (LVECD) computer program developed at North Carolina State University. This computational analysis enables a greater understanding of the critical stress that is involved in debonding and the ways that such stress is affected by pavement design parameters and environmental conditions. In addition, a prediction model was developed that can determine the shear bond strength at the interface of asphalt concrete layers with different tack coat materials at various temperatures, loading rates and normal confining stresses. The systematic and mechanistic framework developed in this study employs the maximum shear ratio concept as a shear failure criterion and provides a tool to evaluate the effects of various loading, environmental and pavement factors on the debonding potential of asphalt pavements. The overall advantages of the mechanistic framework and approach using the LVECD analysis tool will help lead to better understanding of the debonding mechanism, proper selection of the tack coats, and economic benefit in highway pavement maintenance and rehabilitation costs.     

Anticipating Cutoff Diameters in Deterministic Lateral Displacement (DLD) Microfluidic Devices for an Optimized Particle Separation

Deterministic lateral displacement (DLD) devices enable to separate nanometer to micrometer‐sized particles around a cutoff diameter, during their transport through a microfluidic channel with slanted rows of pillars. In order to design appropriate DLD geometries for specific separation sizes, robust models are required to anticipate the value of the cutoff diameter. So far, the proposed models result in a single cutoff diameter for a given DLD geometry. This paper shows that the cutoff diameter actually varies along the DLD channel, especially in narrow pillar arrays. Experimental and numerical results reveal that the variation of the cutoff diameter is induced by boundary effects at the channel side walls, called the wall effect. The wall effect generates unexpected particle trajectories that may compromise the separation efficiency. In order to anticipate the wall effect when designing DLD devices, a predictive model is proposed in this work and has been validated experimentally. In addition to the usual geometrical parameters, a new parameter, the number of pillars in the channel cross dimension, is considered in this model to investigate its influence on the particle trajectories.