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Biological cells can be treated as an inhomogeneous particle. In addition to biomaterials, inhomogeneous particles are also important in more traditional colloidal science. By using two energy methods that are based on Legendre polynomials and Green's function, respectively, we investigate the interaction between biological cells or colloidal particles in the presence of an external electric field, in an attempt to investigate the effect of inhomogeneity on crossover frequencies across which the interaction force changes from attraction to repulsion or vice versa. The predictions by the two methods agree with each other very well. It is shown that there exist two kinds of crossover frequencies ¿p, one from attraction to repulsion and the other from repulsion to attraction as external frequencies increase. The first ¿p strongly depends on the degree of inhomogeneity, while the second ¿p does not. This work has relevance to manipulation of biological cells or colloidal particles. [ABSTRACT FROM AUTHOR]

The local electric field has been derived analytically inside multilayer metallic films with weak nonlinearity, and hence the effective linear dielectric constant and third-order nonlinear susceptibility of the layered structures are calculated. As the number of layers increases, the comparison with the previous results of graded metallic films shows a gradual transition from sharp peaks to a broad continuous band. These results give further evidence of the emerging absorption band reported recently [J. P. Huang and K. W. Yu, Appl. Phys. Lett. 85, 94 (2004)]. Thus, multilayer metallic films can serve as optical materials with a giant enhancement of optical nonlinearity and a large figure of merit. [ABSTRACT FROM AUTHOR]

We apply a Langevin model to investigate the nonlinear ac responses of electro-magnetorheological (ERMR) fluids under the application of two crossed dc magnetic (z axis) and electric (x axis) fields and a probing ac sinusoidal magnetic field. We focus on the influence of the magnetic fields which can yield nonlinear behaviors inside the system due to the particles with a permanent magnetic dipole moment. Based on a perturbation approach, we extract the harmonics of the magnetic field and orientational magnetization analytically. To this end, we find that the harmonics are sensitive to the degree of anisotropy of the structure as well as the field frequency. Thus, it is possible to real-time-monitor the structure transformation of ERMR fluids by detecting the nonlinear ac responses. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the multipole polarizability of a graded spherical particle in a nonuniform electric field, in which the conductivity can vary radially inside the particle. The main objective of this work is to access the effects of multipole interactions at small interparticle separations, which can be important in non-dilute suspensions of functionally graded materials. The nonuniform electric field arises either from that applied on the particle or from the local field of all other particles. We developed a differential effective multipole moment approximation (DEMMA) to compute the multipole moment of a graded spherical particle in a nonuniform external field. Moreover, we compare the DEMMA results with the exact results of the power-law graded profile and the agreement is excellent. The extension to anisotropic DEMMA will be studied in an Appendix. [ABSTRACT FROM AUTHOR]

We exploit theoretically nonlinear optical materials by graded multilayered colloidal crystals, whose basic layer is made of metallodielectric nanoparticles immersed periodically in a host fluid. In the crystals, either the volume fraction of nanoparticles or the dielectric constant of host fluid can vary gradually within layers. The electric field distribution can be shown to exhibit a peak in a certain layer, and that the position of the peak can change by tuning the incident angular frequency. Such a gradation-controlled electric field distribution serves as a physical mechanism for understanding the enhanced nonlinear optical responses with a broad plasmon band. [ABSTRACT FROM AUTHOR]

Based on nonlinear composite materials, we exploit theoretically a class of electrically tunable one-dimensional double-layer photonic crystals (PCs), namely, composite-dielectric and composite-composite PCs. For such PCs, extensive and precise tunability of photonic band gaps can be readily achieved by choosing appropriate pump ac or dc electric fields. [ABSTRACT FROM AUTHOR]

In this paper, we will propose a dielectrophoresis-based microchannel system. Based on numerical calculations and theoretical analysis, we investigate the dynamic behaviors of a microparticle in this system, in the presence of nonuniform electric fields generated by point microelectrodes. Good agreement is shown between them. It is found that the microelectrodes enable the system equilibrium to shift between monostable and bistable states. Further, we reveal that the microparticle can oscillate along the microchannel with a fixed period for the ideal case without a drag force, and that it can be located in either monostable or bistable states for the cases with drag forces. In view of these findings, we carefully address the possibility to design several microfluidic devices, namely, a microparticulate clock for timing, a binary random number generator for conducting stochastic calculations, and a flip-flop device for system memory. [ABSTRACT FROM AUTHOR]

By using a perturbation approach, we investigate dynamic effects on nonlinear alternating current (ac) responses in electrorheological (ER) fluids under an ac or a direct current electric field. We show that the dynamic effect due to a shear flow plays a significant role in the responses. Our results can be well interpreted in the dielectric dispersion spectral representation, and they offer a convenient method to determine the relaxation time and rotation velocity of ER particles by measuring the nonlinear ac responses. [ABSTRACT FROM AUTHOR]

Particle rotation leads to a steady-state which is different from the equilibrium state in the absence of rotational motion. The change of the polarization of the particle due to the rotational motion is called the dynamic electrorheological effect (DER). There are three cases to be considered: rotating particles in a dc field, particle rotation due to a rotating field and spontaneous rotation of particle in dc field (Quincke rotation). In the DER of rotating particles, the particle rotational motion generally reduces the interparticle force between the particles. The effect becomes pronounced when the frequency is on the order of the relaxation rate of the surface charges. In the electrorotation of particles, the mutual interaction between approaching particles will change the electrorotation spectrum significantly. The electrorotation spectrum depends strongly on the medium conductivity as well as the conductivity contrast between the particle and the medium. In the collective behaviors of Quincke rotors, the mutual interactions between the individual rotors lead to the assembly of chain-like structures which make an angle with the applied field. This has an implication of a new class of material. [ABSTRACT FROM AUTHOR]

When a suspension consisting of electric particles having nonlinear characteristics is subjected to a sinusoidal alternating current (ac) electric field, the electric response will generally consist of ac fields at frequencies of higher-order harmonics. We experimentally report on harmonic generation by erythrocytes subjected to an ac electric field. We find that both even and odd harmonics are sensitive to cell shapes, conductivities, field frequencies, and field magnitude. Theoretical analysis based on a phenomenological model yield predictions that are in excellent agreement with the experiments. Thus, it becomes possible to detect nonlinear characteristics, shapes, and conductivities of erythrocytes by measuring such ac responses. [ABSTRACT FROM AUTHOR]

We develop two energy methods to investigate interparticle forces in a chain of three microparticles in an electric field, two of which are fixed and symmetrically located in the two opposite sides of the third free microparticle. We reveal that, if the free microparticle is laterally dragged and released, it can oscillate perpendicular to the line joining the centers of the two fixed microparticles, being in simple harmonic oscillation with a fixed period for small oscillation amplitudes. This work demonstrates that microparticles can be used to record time, which makes it possible to design a new class of microparticulate clocks. [ABSTRACT FROM AUTHOR]