微全分析系统中的介电泳技术发展

近年来,在微全分析系统成为环境监测、生物、医学、药学等学者孜孜以求的目标的背景下,由电泳技术发展起来的介电泳技术作为微全分析系统的组成部分,成为微粒分离、捕捉和操纵的热门技术之一,吸引着学者们的关注.通过介绍介电泳技术的研究内容、发展现状和应用,旨在剖析介电泳芯片的发展趋势.     

集成阻抗识别的介电泳芯片设计及其关键工艺

以微粒的阻抗识别为目的,设计出一种三维网格阵列微电极传感器.传感器将介电泳分离与阻抗识别集成在同一芯片上.首先通过介电泳将微粒中的一种分离至测试区域,再通过阻抗信号描述微粒特性.针对芯片关键区域,提出了调节SU8曝光时间以提高阻抗测试有效信号的工艺解决方案.实验表明,SU8最佳曝光时间为70 s.对芯片性能的相关实验表明,芯片可对不同直径的乳胶微粒进行介电泳分离与阻抗识别.     

基于介电电泳的粒子分离微流控芯片的研究

文中制备了一种用于粒子分离的介电电泳微流控芯片,利用粒子介电性质不同实现粒子批量、高效分离。采用MEMS工艺,由光刻有电极的ITO玻璃基底和PDMS微通道制备而成。在此基础上,测定了当缓冲溶液的电导率为1μS/cm、交流信号电压为10 V时聚苯乙烯小球和酵母菌的正负介电泳响应,确定了两种微粒的分离条件:酵母菌细胞在1~50 k Hz时表现负介电泳响应,50 k Hz~5 MHz时表现正介电泳响应,50 k Hz为交叉频率;聚苯乙烯小球在1 k Hz~5 MHz始终表现负介电泳响应。选取10 V、5 MHz交流电压信号作为分离条件,对直径均为5μm的聚苯乙烯小球和酵母菌进行了分离,分离效率达到92.4%。     

基于光诱导介电泳的单粒子操纵技术

在综合分析当前生物粒子微操纵技术的基础上,设计一种基于光诱导介电泳技术的微操纵芯片,并完成芯片关键部件——光电导薄膜的加工。在准静态电场条件下,对光斑操纵模式进行建模仿真,光斑光强服从高斯分布,光斑尺寸直接影响电场平方梯度的分布,随着光斑尺寸缩小电场平方的x向梯度峰值增大,而随着高度升高电场平方的x向梯度峰值急剧减小。最后通过光诱导介电泳测试平台对单粒子操纵性能进行试验验证。试验结果表明,在去离子水中,当电压峰—峰值为20 V,频率1 MHz时,粒子受负介电泳作用而远离光斑,并且在光斑模式下直径50μm的粒子移动的最大速度可达45μm/s;而在环型虚拟电极模式下能有效控制单粒子运动方向。     

磷酸盐缓冲液对人外周血单个核细胞趋化因子分泌的影响

磷酸盐缓冲液（PBS）通常在实验室中被作为稀释液、冲洗细胞悬浮液以及用于清洗培养瓶和培养皿,也常作为细胞培养基的添加物。这项研究评估了含有不同浓度的钙离子和镁离子的PBS溶液基质对人外周血液单个核细胞（PB-MCs）趋化因子释放的影响。当PBMCs暴露于含量增加的＋/＋PBS中时,发现白介素-8也会相应增加。因为细胞外钙离子浓度对细胞迁移有一定影响,趋化因子的分泌表明细胞培养过程中增加钙离子浓度是另一种很重要的调节机理。     

实时可重构的共面型光诱导介电泳微操纵平台

归纳与总结了各类单细胞微操作技术的最新研究进展,提出一种新的实时可重构的共面型光诱导操控平台,完成了光诱导介电泳芯片的设计、加工与操控平台的搭建.在通过采用机器视觉及模式识别技术实现微粒自动识别与实时追踪的基础上,通过视觉反馈控制在光电导层上生成动态可重构的光模式虚拟电极阵列,形成特定的空间势能形貌,并基于介电泳效应实现微粒的可编程操作.最后,基于多物理场耦合模型及数值模拟技术,定量分析了新式光诱导介电泳芯片的捕获及释放模式,并基于临界最大流速Q这一品质因数,对比分析了共面型与经典式光诱导介电泳捕获模型的尺寸选择性与槽道高度相关性.研究结果表明,共面型光诱导介电泳模型相对于经典光电子镊而言,在单细胞排布方面更具有优势--更高的捕获强度、稳定性、选择性以及分选效率.     

电导率测定中的离子束缚

对废碱液电导率测定中产生的离子浓度很高而电导率不高的反常现象进行深入的试验和研究,认为是由于浓电解质溶液的离子束缚的结果,并对离子束缚的定义、产生原因、机理、用途等进行了探讨。     

介电电泳细胞分析芯片结构设计及富集效率优化

为了研制高富集效率的介电电泳细胞分析芯片,首先从介电电泳力出发,推导了悬浮细胞所受的介电电泳力公式。通过对比常规微电极的电场强度分布,选择叉指式阵列微电极构建介电电泳芯片;通过模拟不同结构参数下微通道中的电场分布对芯片结构参数进行优化设计。针对Hep G2肝癌细胞,分别分析了细胞受介电电泳力、流体力以及重力作用下的运动情况,获得了Hep G2肝癌细胞富集的初步优化条件。为了对模拟结果进行验证,采用微加工技术制作了介电电泳细胞分析芯片。以Hep G2肝癌细胞为待测样品,当芯片所施加正弦交流电压为5 V,频率为4 MHz时,获得了88.89%的富集效率。     

湍流通道中椭球形微粒的受力分析

微粒运动和沉降对柴油机排气微粒的测量、废气再循环系统的正常工作以及微粒的净化捕集等具有重要的影响。微粒形态决定了其在湍流通道中的受力,而微粒受力对湍流通道中微粒的运动及其沉降具有重要的作用。建立椭球形微粒的运动学方程和动力学方程以及湍流场中椭球形微粒的受力及力矩模型;利用所建模型对湍流通道中椭球形微粒的受力及力矩进行研究,着重对微粒形态的变化对微粒受力的影响进行分析。研究结果表明,对于亚微米级和微米级微粒来说,微粒形态对微粒受力具有重要的影响;微粒形态的变化一方面会造成微粒受力及力矩的变化,另一方面也有可能对曳力、布朗力、升力以及热泳力等不同作用力在微粒受力中所处的地位产生一定的影响。研究结果对于加深柴油机微粒在湍流通道中运动及沉降规律的理解具有重要的意义。     

N-甲基-N-苄基吗啉盐酸盐离子液体的合成及性能

采用价格比较低廉的N-甲基吗啉为原料,合成了N-甲基-N-苄基吗啉盐酸盐离子液体.研究结果表明:该离子液体易溶于极性溶剂而难溶于非极性溶剂中;在水中和无水乙醇中的电导率随浓度的增大而增大并且在水中的电导率大于无水乙醇中的电导率;红外光谱分析表明合成的产物与目标产物结构相符;DSC分析表明该离子液体的熔融温度为116℃,低于150℃.属于离子液体范畴.通过对该离子液体的物理、化学性质进行测定,为该离子液体的应用提供依据.     

介电泳辅助的药物洗脱支架载药机理

针对微探针型药物洗脱支架局部载药的特殊要求,提出基于介电泳自组织的载药新方法。首先根据介电泳装配原理,建立介电泳辅助的药物洗脱支架载药模型,并结合量纲一介电泳力及粒子运动控制方程,对解空间内介电泳力分布及粒子运动轨迹进行有限元模拟,讨论粒子相对电极位置及布朗运动对其装配效率的影响,在理论上证明基于介电泳装配的载药方案完全可行。最后在数值模拟的基础上,通过支架表面尖端载药测试平台,对理论预测进行了试验验证。试验结果表明：在去离子水中,当电压峰—峰值为10 V,频率处于0.1～1.0 MHz范围内时,直径4.4 mm的乳胶颗粒在正介电泳力作用下向尖端聚集,且当频率约为500 kHz时,其粒子运动速度达到最大。     

Dynamic simulation of particles in optoelectronic tweezers based on the monte carlo method

Optoelectronic tweezers to manipulate cells and particles into a desirable arrangement have contributed to the concentration, separation, and transportation for biological investigations and applications. In this article, a novel numeric model is presented based on the Monte Carlo method for understanding the behavior of polystyrene beads. The polarization effects between an electric field and the dielectric particles are determined, obeying both random events and the energy reduction rule. The manipulated forces such as dipole-dipole electrostatic attraction forces and light-induced dielectrophoretic forces are analyzed in uniform and nonuniform electric fields. In addition to steady analysis, the dynamic behavior of the particles experiencing negative dielectrophoresis has been described so that this model may be used to solve for the particle transport in the time domain. The particle distribution in the optoelectronic tweezer chip is in good agreement with experimental results. The numerical model is expected to provide simulation software to predict the behavior of particles in future experiments.     

Inverse and Double Electromagnetic-Acoustic Conversion in Ferromagnetic Plates for an Arbitrary Ratio between Wavelengths of Acoustic Vibrations and Electromagnetic Oscillations

Secondary magnetic fields generated due to the inverse and double electromagnetic-acoustic conversion (EMAC) of any mode of the Lamb waves have been calculated. The behavior of these fields in transforming zeroth modes has been analyzed as a function of the thickness, electrical conductivity, and magnetic susceptibility of plates. It has been established that the dependences of the secondary field amplitudes on the plate thickness and conductivity are interrelated. It has been shown that the possibility of increase in the effectiveness of conversion due to electromagnetic-acoustic resonance in low-conducting materials revealed in the direct EMAC is conserved in the inverse and double EMAC.     

A study on the effective hydraulic conductivity of an anisotropie porous medium

Effective hydraulic conductivity of a statistically anisotropic heterogeneous medium is obtained for steady two-dimensional flows employing stochastic analysis. Flow equations are solved up to second order and the effective conductivity is obtained in a semi-analytic form depending only on the spatial correlation function and the anisotropy ratio of the hydraulic conductivity field, hence becoming a true intrinsic property independent of the flow field. Results are obtained using a statistically anisotropic Gaussian correlation function where the anisotropy is defined as the ratio of integral scales normal and parallel to the mean flow direction. Second order results indicate that the effective conductivity of an anisotropic medium is greater than that of an isotropic one when the anisotropy ratio is less than one and vice versa. It is also found that the effective conductivity has upper and lower bounds of the arithmetic and the harmonic mean conductivities.     

Measurement of the effective thermal conductivities of molding sands at high temperatures

It is well known that the effective thermal conductivity of bonded molding sands depends on the volume fraction, thermal conductivity and arrangement of the components e.g., sand particles, bonding medium and air. The arrangement of components is known to be affected by particle size distribution, average size and shape. In this study, an experimental system using the line-heat-source method was designed and effective thermal conductivities of molding sands at temperatures up to 750°C were measured. The effects of binder content, initial moisture content, dry density and temperature were also investigated for four selected sand types: silica, olovine, zircon and chromite sands. The effect of dry density on the effective thermal conductivity of bintonite-bonded molding sands turned out to be more significant than the effect of either binder content or initial moisture content. The minimum effective thermal conductivity for bentonite bonded silica sand occurred at about 500°C. The effective thermal conductivity of silica sands bonded with western bentonite was found to be higher than that of silica sands bonded with southern bentonite up to 750°C.     

Analysis of the Calibration Constant of a Heat Conduction Calorimeter

Abstract

The variation of the calibration constant of a heat conduction calorimeter is discussed. Our model was proved by the experimental results. The results illustrated that in order to keep the calibration constant as invariable as possible, the following measures can be taken. Electrical calibration and experimental determinations are done in the same medium; the diameter of the lead and stirrer should be small; the stirrer should be made with a material of low thermal conductivity; the heating coil is submerged completely in the medium; the volume of the medium is kept invariate during electrical calibration and experimental determination. In addition, there is a linear relationship between the calibration constant and the reciprocal of the thermal conductivity. Based on the analysis, thermal conductivity can be determined by using a heat conduction calorimeter.     

Modification of electrical conductivity by friction stir processing of aluminum alloys

A wide range of solid-state manufacturing technologies for joining and modification of material original properties are assuming increasing importance in industrial applications. Among these, friction stir-based technologies are the most significant, namely, friction stir processing (FSP) and friction stir surfacing. The electrical conductivity is a significant property undergoing modification, but this property has not been characterized and fully exploited from the technological point of view. The present work aims to study the electrical conductivity behavior in FSP of aluminum alloys in order to identify the major factors governing this property. FSP was applied on AA1100, AA6061-T6, and AA5083-H111 alloys with different parameters. Electrical conductivity profiles were measured at different depths and compared with hardness profiles and microstructures. It was found that solid-state friction stir processing of aluminum alloys lead to electrical conductivity changes of about 4%IACS (International Annealed Copper Standard). These changes are more intense in heat-treatable alloys than in work-hardenable ones. Higher rotating versus travel speed ratios (??/V) induce higher variations in the electrical conductivity. In FSP, the factors governing the electrical conductivity variations are mostly the grain size and the presence of precipitates. It was shown that, for some FSP applications, electrical conductivity may be a process characterization method more precise and meaningful than hardness to assess local material condition.     

Magnetic induction tomography guided electrical capacitance tomography imaging with grounded conductors

Electrical capacitance tomography (ECT) is an imaging technique commonly used for imaging dielectric permittivity of insulating objects. In applications such industrial process tomography and non-destructive testing (NDT), the objects under test may exhibit variations in both dielectric permittivity and electrical conductivity. In particular, a sample that includes high conductivity, such as metal, can cause a large change in electrical field in ECT. The metal sample in imaging area will cause a large change in the sensitivity map of ECT compared to free space, which will make the ECT image reconstruction inaccurate. This effect is more severe in grounded conductor than floating conductors, so this paper focuses on grounded conductor. In order to update the sensitivity map, one needs to gain information about the conductivity distribution in ECT problem. Magnetic induction tomography (MIT) is sensitive to electrical conductivity and not sensitive to permittivity variations; therefore, it can be used to visualize the conductivity distribution of the target under test. In this paper, a dual-modality MIT and ECT system is proposed to image a medium including conductors and dielectrics. Both simulated and experimental results are presented, which demonstrate the feasibility of the proposed method.     

Evidence for the importance of particle distribution in effective medium theory: a model study

This study investigates the fundamental effects of particle distribution in a heterogeneous composite, which has never been revealed before. This work is based on the Laplace equation in cylindrical coordinates and shows that the effective thermal conductivity has a different value even at the same volume fraction depending on the particle distribution configuration. Consequently, applying the effective medium approximation without using detailed information about the particle spatial distribution can result in considerable error. This is especially true for the case of augmented conduction by insertion particles.     

钛合金钻削加工及其新发展

从钛合金自身的切削加工性能出发,系统介绍了钛合金的切削加工基本原则。阐述了传统钛合金在钻削加工中常出现的几点问题:钻头材料、钻头几何参数分析和冷却介质的选择。根据钛合金的导热率低、弹性模量低、硬度较低和化学活性强等特点合理地调整钻头材料的选择,对原有钻头几何参数进行优化,正确选取冷却介质。并介绍了当前钛合金切削加工技术的新发展。