Short-time self-diffusion, collective diffusion and effective viscosity of dilute hard sphere magnetic suspensions

2016 ◽  
Vol 791 ◽  
pp. 237-259
Author(s):  
Krzysztof A. Mizerski ◽  
Eligiusz Wajnryb
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Effective Viscosity ◽  
Hard Spheres ◽  
Magnetic Interactions ◽  
Point Dipole ◽  
Basic Principles ◽  
Self Diffusion ◽  
Viscosity Coefficients ◽  
Short Time

The virial corrections to short-time self- and collective diffusion coefficients as well as the effective viscosity are calculated for suspensions of hard spheres with the same radii and constant (blocked within the particle) magnetization modelled by a point dipole. Analytic, integral formulae derived from basic principles of statistical mechanics are provided for both cases – in the absence and in the presence of an external magnetic field. In the former case the diffusion and viscosity coefficients are evaluated numerically as a function of the strength of magnetic interactions between the particles and it is reported that the translational collective diffusion coefficient is significantly greater than all the other coefficients. In the presence of an external magnetic field the coefficients become anisotropic and are evaluated in the asymptotic regime of weak interparticle magnetic interactions.

Thermodynamics of Bidisperse Ferrofluids in Zero External Magnetic Field: Theory and Simulations

2015 ◽  
Vol 233-234 ◽  
pp. 331-334
Author(s):  
Anna Yu. Solovyova ◽  
Ekaterina A. Elfimova
Keyword(s):  
Magnetic Field ◽  
Field Theory ◽  
Free Energy ◽  
External Magnetic Field ◽  
Volume Concentration ◽  
Helmholtz Free Energy ◽  
Hard Spheres ◽  
Particle Volume ◽  
Simulation Data ◽  
Theoretical Predictions

The thermodynamic properties of a ferrofluid modeled by a bidisperse system of dipolar hard spheres in the absence of external magnetic field are investigated using theory and simulations. The theory is based on the virial expansion of the Helmholtz free energy in terms of particle volume concentration. Comparison between the theoretical predictions and simulation data shows a great agreement of the results.

Microwave Synthesis of Nano SiC Doping Mg(B1-2x(SiC)x)2 Superconductor and Superconductivity

2012 ◽  
Vol 512-515 ◽  
pp. 11-16
Author(s):  
Yuan Dong Peng ◽  
Qing Lin Xia ◽  
Qian Ming Huang ◽  
Li Ya Li ◽  
Hong Zhong Wang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Direct Synthesis ◽  
Xrd Analysis ◽  
Magnetization Measurement ◽  
Superconducting Transition ◽  
Short Time

Superconductor samples Mg(B1-2x(SiC)x)2 (x=0, 5%, 10%) are synthesized from nano SiC, Mg and amorphous boron powders by microwave direct synthesis in a short time. Powder X-ray diffraction (XRD) analysis indicates that the phases of the synthesis sample are MgB2 (major phase) and a small amount of MgO and Mg2Si. The main peaks of MgB2, (100), (101), (002) and (110) are shift to the higher diffraction angle position and the width of half height of the diffraction plane is broaden for the SiC doping Mg(B1-2x(SiC)x)2, which show that the B positions of MgB2 are partly substituted and the grains of MgB2 are fine. Scanning electron microscope (SEM) observation shows that the MgB2 grain size is very small and the sample is tightness (compact). The onset superconducting transition temperature of the Mg(B1-2x(SiC)x)2 (x=0, 5%, 10%) samples measured by magnetization measurement are about 37.6 K, 37.0 K, 36.8 K respectively. The critical current density Jc are calculated according to the Bean model from the magnetization hysteresis loop of the slab Mg(B1-2x(SiC)x)2 (x=0, 5%, 10%) samples. The critical current density Jc of nano SiC doping Mg(B1-2x(SiC)x)2 samples are greatly enhanced. In higher external magnetic field, the Jc of 10% SiC doped sample is the highest; in lower external magnetic field, the Jc of 5% SiC doped sample is the highest; while in the whole external magnetic field, the Jc of undoped sample is the lowest.

scholarly journals Review on functionalized magnetic nanoparticles for the pretreatment of organophosphorus pesticides

2021 ◽  
Vol 10 (1) ◽  
pp. 485-498
Author(s):  
Junpeng Tan ◽  
Ting Wang ◽  
Yong Li ◽  
Shenghui Xu ◽  
Simin Chen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Nanoparticles ◽  
External Magnetic Field ◽  
Organophosphorus Pesticides ◽  
Complex Matrix ◽  
Preparation Methods ◽  
Simple Preparation ◽  
Functionalized Magnetic Nanoparticles ◽  
Short Time

Abstract Organophosphorus pesticides are currently extensively applied on the control of agricultural and forestry pests. The number of poisonings and deaths caused by organophosphorus pesticides are increasing year by year. Because of the complex matrix, numerous interfering substances, and low poison content, pretreatment methods are crucial for the detection and analysis of such cases. As an adsorbent used for pretreatment, magnetic nanoparticles have the advantages of simple preparation, convenient modification, superparamagnetism, and hydrophilicity. Microextraction can be performed with small amount of magnetic nanoparticles in a short time, and the target substances can be separated with an external magnetic field. In this paper, the latest research achievements are reviewed. Based on the introduced characteristics and preparation methods of magnetic nanoparticles, this paper outlines the applications of different functionalized magnetic nanoparticles for the pretreatment of organophosphorus pesticides and predict the potential research prospects.

scholarly journals Modeling of Magnetorheological Fluids by the Discrete Element Method

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Mickaël Kargulewicz ◽  
Ivan Iordanoff ◽  
Victor Marrero ◽  
John Tichy
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Discrete Element Method ◽  
Discrete Element ◽  
Magnetic Interactions ◽  
Time Interval ◽  
Mr Fluid ◽  
Carrier Fluid ◽  
Mr Fluids ◽  
Element Method

Magnetorheological (MR) fluids are fluids whose properties vary in response to an applied magnetic field. Such fluids are typically composed of microscopic iron particles (~1-20μm diameter, 20-40% by volume) suspended in a carrier fluid such as mineral oil or water. MR fluids are increasingly proposed for use in various mechanical system applications, many of which fall in the domain of tribology, such as smart dampers and clutches, prosthetic articulations, and controllable polishing fluids. The goal of this study is to present an overview of the topic to the tribology audience, and to develop an MR fluid model from the microscopic point of view using the discrete element method (DEM), with a long range objective to better optimize and understand MR fluid behavior in such tribological applications. As in most DEM studies, inter-particle forces are determined by a force-displacement law and trajectories are calculated using Newton’s second law. In this study, particle magnetization and magnetic interactions between particles have been added to the discrete element code. The global behavior of the MR fluid can be analyzed by examining the time evolution of the ensemble of particles. Microscopically, the known behavior is observed: particles align themselves with the external magnetic field. Macroscopically, averaging over a number of particles and a significant time interval, effective viscosity increases significantly when an external magnetic field is applied. These preliminary results would appear to establish that the DEM is a promising method to study MR fluids at the microscopic and macroscopic scales as an aid to tribological design.

Short-time self-diffusion of nearly hard spheres at an oil–water interface

2009 ◽  
Vol 618 ◽  
pp. 243-261 ◽  
Author(s):  
Y. PENG ◽  
W. CHEN ◽  
TH. M. FISCHER ◽  
D. A. WEITZ ◽  
P. TONG
Keyword(s):  
Diffusion Coefficient ◽  
Surface Coverage ◽  
Hard Spheres ◽  
Hydrodynamic Interactions ◽  
Water Interface ◽  
Self Diffusion ◽  
Oil Water ◽  
Short Time ◽  
Self Diffusion Coefficient ◽  
Good Agreement

Optical microscopy and multi-particle tracking are used to study hydrodynamic interactions of monodisperse polymethylmethacrylate (PMMA) spheres at a decalin–water interface. The short-time self-diffusion coefficient measured at low surface coverage has the formDSS(n) = αD0(1 − βn), wherenis the area fraction occupied by the particles, andD0is the Stokes–Einstein diffusion coefficient in the bulk suspension of PMMA spheres in decalin. The measured values of α are found to be in good agreement with the numerical calculation for the drag coefficient of interfacial particles. The measured values of β differ from that obtained for bulk suspensions, indicating that hydrodynamic interactions between the particles have interesting new features at the interface.

VELOCITY AUTOCORRELATIONS OF CHARGED PARTICLES IN A MAGNETOIONIC MEDIUM WITH APPLICATIONS TO TURBULENT DIFFUSION

1960 ◽  
Vol 38 (9) ◽  
pp. 1213-1223 ◽  
Author(s):  
R. C. Bourret
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Cross Correlation ◽  
Charged Particles ◽  
The Self ◽  
External Forcing ◽  
Random Series ◽  
Neutral Species ◽  
Self Diffusion ◽  
Constant External Magnetic Field

A system of charged particles in a slightly ionized medium is considered subject to (1) collisions with members of the neutral species, (2) a constant external magnetic field, and (3) a fluctuating force field, either external or representing the collision forces. On the assumption that their motions are satisfactorily described by the Langevin equation, the cross-correlation functions in time between velocity components of these charged particles are calculated. These functions may be used, as described elsewhere by the author, to describe the self-diffusion of the charged particles. The cases treated are: purely random external forcing, forcing by exponentially correlated (Markovian) forces, and forcing by a random series of pulses corresponding to collision forces.

scholarly journals A Cascading Mean-Field Approach to the Calculation of Magnetization Fields in Magnetoactive Elastomers

Polymers ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1372
Author(s):  
Dirk Romeis ◽  
Marina Saphiannikova
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Mean Field ◽  
Magnetic Interactions ◽  
Interacting Particles ◽  
Precise Calculation ◽  
Magnetization Field ◽  
Individual Particles ◽  
Composite Samples ◽  
Magnetoactive Elastomer

We consider magnetoactive elastomer samples based on the elastic matrix and magnetizable particle inclusions. The application of an external magnetic field to such composite samples causes the magnetization of particles, which start to interact with each other. This interaction is determined by the magnetization field, generated not only by the external magnetic field but also by the magnetic fields arising in the surroundings of interacting particles. Due to the scale invariance of magnetic interactions (O(r−3) in d=3 dimensions), a comprehensive description of the local as well as of the global effects requires a knowledge about the magnetization fields within individual particles and in mesoscopic portions of the composite material. Accordingly, any precise calculation becomes technically infeasible for a specimen comprising billions of particles arranged within macroscopic sample boundaries. Here, we show a way out of this problem by presenting a greatly simplified, but accurate approximation approach for the computation of magnetization fields in the composite samples. Based on the dipole model to magnetic interactions, we introduce the cascading mean-field description of the magnetization field by separating it into three contributions on the micro-, meso-, and macroscale. It is revealed that the contributions are nested into each other, as in the Matryoshka’s toy. Such a description accompanied by an appropriate linearization scheme allows for an efficient and transparent analysis of magnetoactive elastomers under rather general conditions.

Multiferroic properties of S = 1∕2 chain cuprates LiCuVO4: Comparison with LiCu2O2

2015 ◽  
Vol 29 (17) ◽  
pp. 1550086 ◽  
Author(s):  
A. T. Apostolov ◽  
I. N. Apostolova ◽  
S. G. Bahoosh ◽  
S. Trimper ◽  
M. T. Georgieva ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Dielectric Constant ◽  
External Magnetic Field ◽  
Field Dependence ◽  
Magnetic Field Dependence ◽  
Magnetic Phase ◽  
Magnetic Interactions ◽  
Multiferroic Properties ◽  
Transition Formula

We propose a microscopic model in order to study the multiferroic (MF) properties of [Formula: see text] (LCVO) taking into account the competing nearest and next-nearest magnetic interactions, frustration and a linear magnetoelectric (ME) coupling. We obtain for [Formula: see text]. The temperature and magnetic field dependence of the polarization [Formula: see text] and [Formula: see text] is observed. It is shown that the dielectric constant [Formula: see text] has a kink near the magnetic phase transition [Formula: see text] K which disappears with increasing of the external magnetic field. Some differences in the MF behavior between [Formula: see text] (LCO) and LCVO are discussed.

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