Polar molecule dominated electrorheological effect

The yield stress of our newly developed electrorheological (ER) fluids consisting of dielectric nano-particles suspended in silicone oil reaches hundreds of kPa, which is orders of magnitude higher than that of conventional ones. We found that the polar molecules adsorbed on the particles play a decisive role in such new ER fluids. To explain this polar molecule dominated ER (PM-ER) effect a model is proposed based on the interaction of polar molecule-charge between the particles, where the local electric field is significantly enhanced and results in the polar molecules aligning in the direction of the electric field. The model can well explain the giant ER effect and a near-linear dependence of the yield stress on the electric field. The main effective factors for achieving high-performance PM-ER fluids are discussed. The PM-ER fluids with the yield stress higher than one MPa can be expected.     

Preparation of carbon nanotubes-incorporated polymeric microspheres for electrorheological fluids

Electrically conducting polymeric microspheres having an average diameter of 92 μm were prepared from composites of multiwalled carbon nanotubes (MWCNTs) and suspension-polymerized poly(vinyl chloride) (PVC) particles. Cetyl trimethylammonium bromide and sodium dodecylbenzene sulfonate were selected as the surfactants to stably disperse the MWCNTs in water. Strong adhesion of MWCNTs on the surfaces of the PVC microspheres was observed from the images obtained by field emission scanning electron microscopy. The amount of MWCNTs adsorbed on the microspheres was approximately 2 wt.%, determined by thermogravimetric analysis. The electrical conductivity of these composite-microspheres was remarkably increased upto 1.5 × 10⁻⁴ S/cm compared with that of the pure PVC microspheres (less than 10⁻¹⁴ S/cm), because of the electrically conducting MWCNTs on their surfaces. These microspheres also showed an electrorheological (ER) effect under an electric field (1.8 kV/mm) owing to the interfacial polarization of the MWCNTs-adsorbed microspheres, when they were dispersed in silicone oil (20 wt.%). The MWCNT-adsorbed PVC microspheres formed linear structures by electric force; i.e. the individual microspheres were connected to neighboring microspheres.     

巨电流变效应及其机理

文章介绍了一种全新的电流变材料，即一种具有巨电流变(giant electro-rheological，简称GER)效应的纳米颗粒电流变液．之所以称之为“巨”，是因为此类材料的电流变效应远远突破了通常理论所预测到的“上限”，其剪切强度超过100kPa．同时文章作者还发现，此类电流变效应与外加电场呈线性变化关系，而非通常的二次方关系．用所提出的“表面极化饱和”模型圆满地解释了GER效应的实验结果．     

Conductivity effect in electrorheological fluids

Based on conduction model and cubic particle model, the relationship between current density and shear yield stress of electrorheological (ER) fluids was calculated and compared with some reported experimental results. The conductivity of the insulating oils is found to have been changed by the mixed particles. Several ways to decrease insulating liquid conductivity and increase the conductivity ratio of ER fluids have been proposed to prepare ER fluids with high shear yield stresses but low current densities.     

Nonlinear optical properties of 75TeO2－20Nb2O5－5ZnO glasses doped with CeO2

Nonlinear optical properties of 75TeO_2－20Nb_2O_5－5ZnO glasses doped with CeO_2 have been investigated with a self-diffracted time-resolved degenerate four-wave mixing (DFWM) technique at different excitation intensities and lattice temperatures. The DFWM signal exhibits three peaks at higher excitation intensities, where a main peak appears at zero delay time and two rather weak side peaks are located symmetrically at the negative and positive time delay. Due to destructive interferences between the fifth- and third-order polarizations, the line-shape of the main peak around the zero time delay evolves from single peak into a double-peak structure with increasing excitation intensity. Two side peaks emerge at the positive and negative time delay and gradually intensify with increasing excitation intensity or lattice temperature, and their positions are independent of the pulse duration, temperature and excitation intensity, which are attributed to the many-body Coulomb interaction.     

可控阻尼介质中摆的运动行为

利用电流变液体的电流变效应，实现可控阻尼介质，并测量了可控阻尼介质中摆的运动行为。     

Measurement-induced disturbance between two atoms in Tavis-Cummings model with dipole dipole interaction

Quantum correlation, measured by measurement-induced disturbance （MID）, between two two-level atoms is investi- gated in detail in Tavis-Cummings model with dipole--dipole interaction （DDI）. We find that MID can be determined only by the dipole-dipole interaction between the two atoms when the cavity and atoms are at resonance. Moreover, DDI will have different effects on MID for two different kinds of initial states.     

Longitudinal field-induced polarized light transmittance of magnetic fluids

The complete optical transmittance for a polarized light passing through the magnetic fluids is investigated theoretically and experimentally, when the externally magnetic field is applied along the propagation direction of the incident light. Hybrid effects due to the geometric shadowing and Faraday rotation are considered simultaneously. The Langevin-like functions are employed to describe the magnetic-field-dependent volume concentration of the particle-aggregation (φ′) and the approximate number of magnetic nanoparticles in the particle-aggregation (βN₀). Based on the experiments on the geometric shadowing effect of our magnetic fluid sample, the analytical expression for the total transmitted power with externally magnetic field after an analyzer is derived. Theoretical simulations disclose the influence of certain critical parameters of the magnetic fluids on the field-dependent optical transmittance. For the entire polarized light transmittance, qualitative agreement between the calculations and the experiments is achieved. Applications of magnetic fluids to several polarized devices operating in longitudinal field arrangement are proposed and discussed. The results presented in this work may be useful for designing the corresponding magnetic-fluid-based optical devices.     

钠原子主线系精细结构的多体微扰计算

在相对论的框架下采用多体微扰理论(MBPT)方法计算了纳原子 np(n=3—9)态的能级精细结构分裂值. 为避免多体微扰计算中需要计算大量连续态的困扰, 通过引入外势的方法可以构建离散、有限和近似完备的数值基函数. 经求解相对论Hartree-Fock (RHF)方程及外势作用下的RHF方程可获得零级近似波函数和能级值. 为了使微扰展开能够收敛, 计算中用到了轨道角量子数l≤ 6的在一定能量分布范围内的中间态, 其中以在外势作用下的收缩态为主. 依此方法计算了纳原子主线系系列能级二阶微扰修正值, 同时还考虑了Breit效应的一级微扰修正对精细结构的影响. 通过与其他理论计算结果比较可看出, 本文计算结果在较大程度上更接近于实验值.     

A thin-film model for corotational Jeffreys fluids under strong slip

We derive a thin-film model for viscoelastic liquids under strong slip which obey the stress tensor dynamics of corotational Jeffreys fluids.     

Y型Langmuir-Blodgett膜中分子聚集行为的偶极作用模型

利用经典静电场理论，描述了Y型Langmuir-Blodgett (LB) 膜中棒状分子聚集行为的偶极作用模型，给出了Y型LB膜结构与光谱性质的关系.讨论了Y型膜中分子间距、层间距、分子取向、膜层数等结构参数对分子聚集行为的影响，并在此基础上比较了Y型膜和Z型膜分子聚集行为的异同.理论结果与实验规律符合较好.     

Proposal for all-optical controllable switch using dipole induced transparency (DIT)

We propose a novel all-optical controllable switch using photonic crystal cavity. For doing this work, the dipole induced transparency phenomenon realized through interaction of light with multilevel nanocrystals is used. Multilevel nanocrystals are doped to photonic crystal rods. Using the proposed structure and applying the control field, the absorbing medium converts to transparent one and switching operation is obtained. Analytical relation for evaluation of the proposed device considering quantum optical effects is presented and studied by investigation of effects of parameters on switching characteristics. We show that high quality all-optical switching operation can be obtained.     

Classical charged fluids at equilibrium near an interface: Exact analytical density profiles and surface tension

The structure of equilibrium density profiles in an electrolyte in the vicinity of an interface with an insulating or conductive medium is of crucial importance in chemical physics and colloidal science. The Coulomb interaction is responsible for screening effects, and in dilute solutions the latter effects give rise to universal leading corrections to nonideality, which distinguish electrolyte from nonelectrolyte solutions. An example is provided by the excess surface tension for an air-water interface, which is determined by the excess particle density, and which was first calculated by Onsager and Samaras. Because of the discrepancy between the dielectric constants on both sides of the interface, every charge in the electrolyte interacts with an electrostatic image, and the Boltzmann factor associated with the corresponding self-energy has an essential singularity over the length scalel from the wall. Besides Coulomb interactions, short-range repulsions must be taken into account in order to prevent the collapse between charges with opposite signs or between each charge and its image when the solvent dielectric constant is lower than that of the continuous medium on the other side of the interface. For a dilute and weaklycoupled electrolyte,l is negligible with respect to the bulk Debye screening length ξ_D. In the framework of the grand-canonical ensemble, systematic partial resummations in Mayer diagrammatics allow one to exhibit that, in this regime, the exact density profiles at leading order are the same as if they were calculated in a partially-linearized mean-field theory, where the screened pair interaction obeys an inhomogeneous Debye equation. In the latter equation the effective screening length depends on the distancex from the interface: it varies very fast over the lengthl and tends to its bulk value over a few ξDs. The equation can be solved iteratively at any distancex, and the exact density profiles are calculated analytically up to first order in the coupling parameter l/ξ_D. They show the interplay between three effects: (1) the geometric repulsion from the interface associated with the deformation of screening clouds, (2) the polarization effects described by the images on the other side of the interface, (3) the interaction between each charge and the potential drop created by the electric layer which appears as soon as the fluid has not a charge-symmetric composition. Moreover, the expressions allow us to go beyond Onsager-Samaras theory: the surface tension is calculated for charge-asymmetric electrolytes and for any value of the ratio between the dielectric constants on both sides of the interface. Similar diagrammatic techniques also allow one to investigate the charge renormalization in the dipolar effective pair interaction along the interface with an insulating medium.     

On a conjecture of Alley and Alder for fluids and Lorentz models

We discuss a conjecture of Alley and Alder predicting a relation between the four-point and the two-point velocity autocorrelation functions for fluids and Lorentz models at sufficiently long times. If the conjecture is correct a modified Burnett coefficient can be defined, which has a finite value, contrary to the ordinary Burnett coefficient, which is divergent. The conjecture is tested for four classes of models with different methods: for three-dimensional fluids mode-coupling theory yields a negative result. The conjecture is confirmed for thed-dimensional deterministic Lorentz gas (d 2) and for a class ofd-dimensional stochastic Lorentz models (d 1) by low-density kinetic theory, as well as by rigorous results, available for one dimension. For yet another class of one-dimensional stochastic Lorentz models, which are exactly solvable in one dimension, the result is negative again. All four classes of models show long-time tails in the velocity autocorrelation function and have a finite diffusion coefficient.     

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阐述了FAIR收集环二极超导磁体电流引线的基本原理,给出了电流引线的主要参数及初步设计方案,提出了使用复合材料和通过结构优化以减小电流引线的漏热,并根据电流引线的传热特性进行了漏热的分析和计算,实验结果验证了概念设计的可行性。     

Density functional approximations for classical fluids with long-range interactions

Density functional approximations for systems interacting via long-range forces are revisited. The theory is illustrated with examples of one-component plasmas in two and three dimensions.Dedicated to Philippe Choquard, Coulomb fluid expert.     

Behavioral model for magnetorheological fluid under a magnetic field using Lekner summation method

Magnetorheological (MR) fluid is used for various applications due to its controllable viscosity. To predict the behavior of MR fluid under certain three-dimensional (3D) magnetic and shear strain fields, it is essential to model the fluid in an appropriate manner. The behavioral models used in the previous research, however, have serious limitations because most of them oversimplify the inter-particle interactions and employ assumptions valid only under specific geometric configurations and field conditions. In this study, a new model that can predict the behavior of MR fluid under arbitrary 3D magnetic and shear strain fields is proposed. The present work considers an MR fluid configured as a 3D infinite lattice structure. Using the proposed model, the shear stress components themselves, not the dipolar interaction energy, are calculated directly to avoid the mathematical singularity otherwise encountered. The resulting stress functions of the proposed model are transformed into rapidly convergent functions using the Lekner summation method. Finally, the characteristics of the stiffened MR fluid under a magnetic field are investigated using the transformed functions. Numerical computations on the original and transformed functions are performed and compared under selected conditions to ensure the validity and prove the high convergence efficiency of the proposed model.     

FAIR收集环二极超导磁体电流引线的概念设计

阐述了FAIR收集环二极超导磁体电流引线的基本原理,给出了电流引线的主要参数及初步设计方案,提出了使用复合材料和通过结构优化以减小电流引线的漏热,并根据电流引线的传热特性进行了漏热的分析和计算,实验结果验证了概念设计的可行性。     

Aggregation of particles settling in shear-thinning fluids

We have experimentally studied the coaxial settling of three identical non-Brownian spheres in a shear-thinning fluid at small Reynolds numbers. While settling, the particles create corridors of reduced viscosity in their wake and, if they are initially close enough to one another, they can form stable clusters. By analogy with previous results obtained on two-particle interaction in the first part of this work, we show that the particle velocities can be satisfactorily described using a first-order expression and assuming that the reduced viscosity remains constant. We report systematic experiments performed at different initial separation distances between particles and the use of our simple model allows the prediction of the settling behaviour and in particular the conditions for clusters formation. We thus show that particle aggregation can occur even for large initial distances between particles and within times that are small compared to the time scales in Newtonian fluids. Received 10 July 2002 RID="a" ID="a"e-mail: talini@fast.u-psud.fr     

Band effects on conduction electron density of states for the anderson model

Summary The effects of the shape of free conduction density of states on the physical quantities for the periodic Anderson model have been investigated.