Control of lattice spacing in a triangular lattice of feeble magnetic particles formed by induced magnetic dipole interactions

We studied methods of controlling the spacing between particles in the triangular lattice formed by feeble magnetic particles through induced magnetic dipole interaction. Formation of a triangular lattice is described by the balance between the magnetic force and the interaction of induced magnetic dipoles. The intensity of the magnetic force is proportional to the volume of particles V and the difference in the magnetic susceptibilities between the particles and the surrounding medium Δχ. On the other hand, the intensity of the induced magnetic dipole interaction depends on the square of V and Δχ. Therefore, altering the magnetic susceptibility difference by changing the susceptibility of the surrounding medium, volume of the particles, and intensity and spatial distribution of the applied magnetic field effectively controls the distance between the particles. In this study, these three methods were evaluated through experiment and molecular dynamics simulations. The distance between the particles, i.e. the lattice constant of the triangular lattice, was varied from 1.7 to 4.0 in units of the particle diameter. Formation of self-organized triangular lattice through the induced magnetic dipole interaction is based on magnetism, a physical property that all materials have. Therefore, this phenomenon is applicable to any materials of any size. Consequently, structure formation through induced magnetic dipole interaction is a potential way of fabricating materials with ordered structures.     

Numerical simulation of chainlike cluster movement of feeble magnetic particles by induced magnetic dipole moment under high magnetic fields

In this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid.     

Numerical simulation of chainlike cluster movement of feeble magnetic particles by induced magnetic dipole moment under high magnetic fields

Abstract

In this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid.     

磁性智能混合体MAGIC中磁性颗粒分布的研究

磁性智能混合体MAGIC(magnetic intelligent compounds)是一种含有磁性颗粒、磨粒以及粘结剂的可固化的磁性抛光材料,其抛光性能很大程度受其中颗粒分布的影响.MAGIC颗粒分布的研究是MAGIC抛光体制备及其抛光性能研究的基础,通过试验方法深入研究外加磁场、颗粒浓度、颗粒大小对磁性智能混合体中颗粒分布的影响.研究发现,当外加磁场强度大、磁性颗粒粒径小、磁性颗粒浓度高时,磁性颗粒容易形成交叉链和团簇链分布;而外加磁场强度小、磁性颗粒粒径大、磁性颗粒浓度低时,磁性颗粒容易形成短链分布.     

尖劈状磁场中磁流体磁性微粒的受力分析

通过有限元方法对尖劈形磁场中磁流体磁性微粒所受的磁场力进行了数值分析,分别给出了磁场气隙处磁通量和磁场强度随不同气隙宽度和夹角的变化规律.在此基础上,利用虚位移法和麦克斯韦应力张量法计算磁流体磁性微粒在气隙上方所受的磁场力.结果表明,随着气隙宽度的减小,磁通量、磁场强度和磁场力明显增加;随着气隙夹角的增加,磁通量、磁场...     

Control of nonmagnetic particles using a magnetic field

Abstract

A force and/or torque are induced in a material under the imposition of a magnetic field. Their magnitudes are different from those acting on the surrounding materials because of the difference in their physical properties. Therefore, a magnetic field is a powerful tool for controlling a second phase in a mother phase such as particles suspended in a liquid. In this paper, we focus on two processes. The first one is a novel method of magnetic filtration in which schwertmannite particles in wastewater are controlled using a magnetic field. The second one is a refining process for a metallic alloy structure during solidification in which solid particles suspended in the liquid phase are controlled using the force excited by the simultaneous imposition of a magnetic field and alternating current.     

PMMA-CI复合磁性粒子的磁流变液性能研究

采用自由基聚合法，通过改变MMA与CI的质量配比制备不同结构的PMMA-CI复合磁性粒子。并对PMMA-CI复合磁性粒子的表面形貌、粒度、密度以及热失重进行表征。考察了复合磁性粒子的结构变化对其磁流变液沉降稳定性和流变学性能的影响。结果表明：复合磁性粒子与CI粒子相比，其磁流变液的沉降稳定性有所提高，但是流变学性能下降；提高MMA与CI的质量配比会使复合磁性粒子粒径和高分子包覆量逐渐增大、密度减小，粒子的这种结构变化可以改善磁流变液的沉降稳定性，而流变学性能会逐渐降低。     

Selective activation of mechanosensitive ion channels using magnetic particles.

This study reports the preliminary development of a novel magnetic particle-based technique that permits the application of highly localized mechanical forces directly to specific regions of an ion-channel structure. We demonstrate that this approach can be used to directly and selectively activate a mechanosensitive ion channel of interest, namely TREK-1. It is shown that manipulation of particles targeted against the extended extracellular loop region of TREK-1 leads to changes in whole-cell currents consistent with changes in TREK-1 activity. Responses were absent when particles were coated with RGD (Arg-Gly-Asp) peptide or when magnetic fields were applied in the absence of magnetic particles. It is concluded that changes in whole-cell current are the result of direct force application to the extracellular loop region of TREK-1 and thus these results implicate this region of the channel structure in mechano-gating. It is hypothesized that the extended loop region of TREK-1 may act as a tension spring that acts to regulate sensitivity to mechanical forces, in a nature similar to that described for MscL. The development of a technique that permits the direct manipulation of mechanosensitive ion channels in real time without the need for pharmacological drugs has huge potential benefits not only for basic biological research of ion-channel gating mechanisms, but also potentially as a tool for the treatment of human diseases caused by ion-channel dysfunction.     

An improved immersed moving boundary for hydrodynamic force calculation in lattice Boltzmann method

Particles suspension is considerably prevalent in petroleum industry and chemical engineering. The efficient and accurate simulation of such a process is always a challenge for both the traditional computational fluid dynamics and lattice Boltzmann method. Immersed moving boundary (IMB) method is promising to resolve this issue by introducing a particle-fluid interaction term in the standard lattice Boltzmann equation, which allows for the smooth hydrodynamic force calculation even for a large grid size relative to the solid particle. Although the IMB method was proved good for stationary particles, the deviation of hydrodynamic force on moving particles exists. In this work, we reveal the physical origin of this problem first and figure out that the internal fluid effect on the hydrodynamic force calculation is not counted in the previous IMB. An improved immersed moving boundary method is therefore proposed by considering the internal fluid correction, which is easy to implement with the little extra computation cost. A 2D single elliptical particle and a 3D sphere sedimentation in Newtonian fluid is simulated directly for the validation of the corrected model by excellent agreements with the standard data.     

Ferrofluid squeeze film between curved annular plates including rotation of magnetic particles

The effects of ferrofluid on the curved squeeze film between two annular plates, when the upper plate approaches the lower one normally, are studied including the rotation of the magnetic particles and their magnetic moments. The aim is to study the effects of rotation of the magnetic particles on the characteristics of the squeeze film. The main equation is derived in the Appendix A. Expressions for the pressure, load capacity and response time are obtained. Load capacity and response time are found to increase when the volume concentration of the solid phase, Langevins parameter or the curvature of the upper plate are increased.     

Variety of valence bond states formed of frustrated spins on triangular lattices based on a two-level system Pd(dmit)2

Abstract

Recent studies on the physical properties of the triangular system based on the Pd(dmit)₂ salts (dmit=1,3-dithiole-2-thione-4,5-dithiolate) are reviewed. Quantum chemical architectures of the Pd(dmit)₂ molecule and its dimer are introduced with emphasis on the strong dimerization of a two-level system, which provides unique physical properties of the salts. The magnetic properties are outlined in view of the magneto-structural correlation specific to the frustrated spin systems. Some newly discovered ground states and their origins are discussed, for which the valence bond formation plays a key role. Among them, the two-level structure is crucial for the novel charge-separated state found in two salts. The valence bond ordering, similar to the spin-Peierls transition, has been found in a two-dimensional frustrated spin system. The physical aspects and possible relation to the pressure-induced superconductivity are discussed.     

Preparation of carboxylic magnetic polymeric composite particles by miniemulsion polymerization in the absence of hydrophobe

Carboxylic magnetic polymeric composite particles (C-MPCPs) were prepared by miniemulsion polymerization in the absence of hydrophobe using styrene (St) as monomer, methacrylic acid (MAA) as comonomer, sodium dodecyl sulfate (SDS) as emulsifier, and azodiisobutyronitrile (AIBN) as initiator in the presence of hydrophobic magnetite particles. For comparison, non-carboxylic magnetic polymeric composite particles (N-MPCPs) were also prepared under the same conditions as C-MPCPs but without MAA as comonomer. Microscopic morphology of resulting C-MPCPs and N-MPCPs was observed by Transmission Electron Microscopy (TEM). Magnetic properties of C-MPCPs in dry condition were investigated by vibrating sample magnetometer (VSM). The results showed that the encapsulation of magnetite to prepare C-MPCPs by miniemulsion in the absence of hydrophobe was successful but not totally successful in the preparation of N-MPCPs, and the resultant C-MPCPs exhibited a broad practical size distribution, superparamagnetism and a certain level of magnetic response. The mechanism of miniemulsion polymerization to encapsulate magnetite particles successfully in the absence of hydrophobes was hypothesized that the hydrophobic magnetite particles could act as a hydrophobe and MAA could enhance the hydrophobicity of magnetite particles by ensuring oleic acid adsorption on magnetite particles' surface in acid form instead of salt form.     

磁致双折射和二向色性对磁性液体薄片的光透射率弛豫特性的影响

基于Xu等人的经典振荡磁偶极子模型和Matsumoto等人给出的双折射驰豫理论,研究了磁致双折射和二向色性对磁性液体薄片的光透射率弛豫特性的影响。理论推导了磁性液体的双折射和二向色性函数的偏振光透射率具体表达式,并进行了数值模拟计算。该问题的研究对磁性液体光学各向异性的深入认识以及相关磁性液体光学器件的应用具有一定的指导意义。     

Study of airflow induced by regular particles in freefall through tubes

Airflow induced by falling particles can be a significant factor in causing dust emission during the conveyance of bulk materials. Heretofore, there have been few experimental studies on the effect of the particle size and the diameter of the tubes through which they are falling on the induced airflow. This study involved the experimental analysis of the correlation between those two factors and the induced airflow. The results were as follows: within the range of the total drag coefficient (0.62–0.94) of the experimental setup, the induced airflow velocity increased with an increment of the mass flow rate of the particles and drop height, and the power exponents of a fitted curve were approximately 0.35 and 1.29, respectively. Within the particle diameter range of 3.247–9.223 mm, the power coefficients and power exponents of a fitted curve for induced airflow velocity increased from 0.224 and 0.269 to 0.458 and 0.384, respectively, with the increase in particle size. As the tube diameter decreased from 200 mm to 120 mm, both the induced airflow velocity and the quantity of specific induced airflow increased, while the quantities decreased when the tube diameter decreased from 120 mm to 75 mm. The semi-empirical equation of the induced airflow velocity was established to predict the quantity of induced airflow under various operation conditions.     

磁性粒子浓悬浮液体系中非磁性粒子的磁流变液性能增强效应

报导在磁性粗粒子浓悬浮液体系中,加入非磁性粒子对磁流变液性能的增强效应,以及增加体系的沉降稳定性,并简要讨论了这些添加物对磁流变液“相变”的影响。     

铝熔体中磁性杂质颗粒的电磁分离

分析了磁性杂质颗粒在电磁场中的受力情况,采用磁平衡法测量了铝熔体中两种典型富铁相杂质颗粒的磁化率,指出铝熔体中的富铁相杂质是顺磁性物质,在电磁场中受到电磁力和磁场力的驱动作用,确定其在分离器上的聚集方式．静态电磁分离试验结果表明,当磁场强度大于145mT时,电磁力起主要作用;当磁场强度小于120mT时,磁场力起主要作用．     

Organization of gold nanorods on a substrate using a strong magnetic field

The effects of magnetic processing on the organization of gold nanorods (AuNRs)/poly(styrenesulfonate) (PSS) composites using a strong magnetic field were examined by absorption spectra corresponding to surface plasmon on a glass plate and TEM images. The results in the absorption spectra and the TEM images showed that the side-to-side aggregation of AuNRs/PSS composites formed in the presence of a magnetic field directed horizontally to the surface of the sample. In the absence of the magnetic field, side-to-side AuNRs/PSS aggregates were not observed. The effects of magnetic processing are attributed to the induced magnetic dipoles of the AuNRs.     

Time evolution of few-cycle pulse in a dense V-type three-level medium

Propagation of a few-cycle laser pulse in a dense V-type three-level atomic medium is investigated by the numerical solution of the full Maxwell–Bloch equations without the rotating wave and slowly varying envelope approximations, and the numerical solution is obtained by using the predictor–corrector method and the finite-difference time-domain method. It is shown that, due to the strength of the electric field induced by the macroscopic polarization in a dense medium being stronger than that in a dilute medium and the influence of the near dipole–dipole (NDD) interaction, the time evolution of a few-cycle pulse in the dense medium is remarkably different from that in the corresponding dilute medium. In the dilute medium, oscillation arises at the trailing edge of the pulse; while in the dense medium, it appears at both the leading and trailing edges of the pulse; moreover, the oscillation at the leading edge is more obvious with the pulse area decreasing. The carrier-envelope phase has an obvious difference in the two cases with and without NDD interaction. The ratio, γ, of the transition dipole moments has strong influence on the time evolution and split of the pulse. In the dense medium, when?γ?= 1, NDD interaction delays propagation and split of the pulse; while when?γ?> 1, NDD interaction accelerates propagation and split of the pulse, moreover, the phenomenon is more obvious with the input pulse area decreasing. In the dilute medium, the larger area pulse doesn't split when?γ?= 1 while it splits when?γ?> 1.     

锰锌铁氧体磁流体中Zn2+的作用及其影响机理的研究

采用化学共沉淀法制备了Mn1-xZnxFe2O4磁流体,全面分析并探讨了Zn2+的作用及其影响机理.研究表明Zn2+的含量对于Mn1-xZnxFe2O4磁流体的磁性能具有至关重要的影响,当Zn2+的含量为0.22时,所制得磁流体的磁性能最好.X射线衍射分析结果表明磁性粒子由单一物相构成,其晶格常数为a=0.846nm,介于MnFe2O4与ZnFe2O4之间.Mn0.78Zn0.22Fe2O4磁流体在外加磁场作用下显示出超顺磁性,其比饱和磁化强度随着质量百分比浓度的增加而增大,最高可达32.17A*m2/kg.     

取向磁场对钴颗粒填充硅橡胶磁流变弹性体动态黏弹性的影响

为了研究取向磁场强度对磁流变弹性体（MRE）动态黏弹性的影响规律及影响机制,采用溶剂热法制备球状钴颗粒,SEM和XRD表征结果显示,其粒径为1~2 μm,呈密排六方结构。以硅橡胶为基体,以钴颗粒为填充相,分别在0 mT、480 mT、1 154 mT取向磁场强度下制备MRE,并在不同工况下测试其动态黏弹性。实验结果表明,Co颗粒填充的MRE微观结构的有序性随取向磁场强度增大而增加,其储能模量G'、损耗模量G ″和磁流变效应也随之提高;当取向磁场强度增大到一定程度,由于有序结构趋于稳定,动态黏弹性随取向磁场的变化较小。