International Journal of Modern Physics B

Following recent rapid development of researches in utilizing Magnetorheological (MR) fluid, a smart material that can be magnetically controlled to change its apparent viscosity instantaneously, a lot of applications have been established to exploit the benefits and advantages of using the MR fluid. One of the most important applications for MR fluid in devices is the MR valve, where it uses the popular flow or valve mode among the available working modes for MR fluid. As such, MR valve is widely applied in a lot of hydraulic actuation and vibration reduction devices, among them are dampers, actuators and shock absorbers. This paper presents a review on MR valve, discusses on several design configurations and the mathematical modeling for the MR valve. Therefore, this review paper classifies the MR valve based on the coil configuration and geometrical arrangement of the valve, and focusing on four different mathematical models for MR valve: Bingham plastic, Herschel–Bulkley, bi-viscous and Herschel–Bulkley with pre-yield viscosity (HBPV) models for calculating yield stress and pressure drop in the MR valve. Design challenges and opportunities for application of MR fluid and MR valve are also highlighted in this review. Hopefully, this review paper can provide basic knowledge on design and modeling of MR valve, complementing other reviews on MR fluid, its applications and technologies.

The temperature and voltage dependence profile of the surface states (N_ss), series resistance (R_s) and electrical conductivity (σ_ac) have been investigated in temperature and voltage ranges of 140–400 K and (-5 V)-(6 V), respectively. The value of barrier height (BH) decreases with increasing temperature as Φ_B(T) = (1.02 - 4×10^-4⋅T) eV. These values of negative temperature coefficient (-4×10^-4eV⋅K^-1) is in good agreement with the α of band gap of SiC (-3.1×10^-4 eV⋅K^-1). Capacitance-voltage (C–V) plots for all temperatures show an anomalous peak in the accumulation region because of the effect of series resistance (R_s) and N_ss. The effect of R_s and N_ss on the C and conductance (G) are found noticeable high especially at low temperatures. The decrease in C values also corresponds to an increase in G/ω values in the accumulation region. In addition, Ln(σ_ac) versus q/kT plots have two straight lines with different slopes which are corresponding to below and above room temperatures for various forward biases which are an evident two valid possible conduction mechanisms. The values of activation energy (E_a) were obtained from the slope of these plots and they changed from 6.3 meV to 4.7 meV below room temperatures and 42.5 meV to 34.4 meV for above room temperatures, respectively.

The time-dependent barrier passage of an activated rate process is studied where the heat bath in the system-reservoir coupling environment is modulated by an external fluctuation. For a thorough inspection on the barrier recrossing dynamics, the Kramers rate and effective transmission coefficient are calculated of the reactive flux method. In the particular case of a δ-correlated noise activated Ornstein–Uhlenbeck process, it is found that, the external modulation can in some cases result in an maximum effective transmission coefficient. This reveals a maximum net flux and can be obtained from the minimum barrier recrossing resulted from appropriate external modulation.

A fast scheme based on the multi-level substructure technique is proposed for the band structure and transmission characteristics calculation of phononic crystals uniformly. The main idea is that finite element models of phononic crystals are divided into several domains by a special multi-level decomposition. For the band structure calculation, the upscaling calculation is employed to condense the internal stiffness matrix of the unit cell into the Bloch boundary. Due to the internal stiffness matrix does not change along with reduced wave vectors in an iteration process, the scheme can reduce the computational scale and improve the efficiency greatly, meanwhile it does not introduce approximation into the traditional finite element model. For the transmission characteristics calculation, the unit cell of the phononic crystal is periodic which is taken as a substructure with the same coefficient matrix. Moreover, the downscaling calculation of internal displacements can be selected flexibly. Some closely watched examples of the three-dimensional locally resonant, defect state of Lamb wave and Bragg waveguide are analyzed. Numerical results indicate that the proposed scheme is efficient and accurate, which may widely be applicable and suitable for complex phononic crystal problems, and provides a reliable numerical tool to optimize and design crystal devices.

The electronic structure and optical properties of wurtzite gallium arsenide (GaAs) nanowires (NWs) are investigated within the first-principles plane-wave pseudo-potential method based on the density functional theory (DFT). The calculated results show that GaAs NWs are direct band gap semiconductor and demonstrate the achievement of p-type behavior. These NWs of the electronic behavior transitions from semiconductor to metal after hydrogen-passivated. The complex dielectric function, absorption coefficient and optical reflectivity are calculated and the peak position distributions of imaginary parts of the complex dielectric function have been explained. We may conclude GaAs NWs belongs to what crystal system through the dielectric tensors. Optical reflectivity is obtained and the peak position distributions of imaginary parts of the complex dielectric function have been explained, and their absorption spectra are sensitive to the large radius of GaAs NWs.

The gelling process of particle suspension in a capillary which is crucial for in-situ preparing small size foam products has been simulated with an off-lattice diffusion limited cluster aggregation (DLCA) model by the three-dimensional Monte Carlo simulations. The effects of the model parameters, such as the interaction between capillary wall and particles, particle volume fraction, capillary size etc. on the density distribution of the system have been fully explored. And the aggregation kinetics process over a broad range of volume fractions and interactions have also been discussed. The results show that the geometric constraint of capillary can be analogous to a weak repulsive interaction between capillary wall and particles. And we found that as the capillary size or particle volume fraction increase, particle concentration distribution will be more uniform with other parameters constant. Porous network with relatively uniform density distribution can be also obtained through controlling the interaction between capillary wall and particles. In addition, by analyzing the aggregation kinetics process, we found that the attraction of capillary wall dramatically reduces the probability of gelation in the small-scale capillary. The obtained results will be of great importance in controlling the density distribution of porous materials prepared by in-situ methods.

Activation process for unimolecular reaction has been considered by means of radiation theory. The formulae of information entropy of activation have been derived for the Boltzmann–Arrhenius model and the activation process model (APM). The physical meaning of this entropy has been determined. It is a measure of conversion of thermal radiation energy to mechanical energy that moves atoms in a molecule during elementary activation act. It is also a measure of uncertainty of this energy conversion. The uncertainty is due to unevenness of distribution function representing the activation process. It has been shown that Arrhenius dependence is caused by the entropy change. Efficiency comparison of the two models under consideration for low-temperature fluctuations of a myoglobin molecule structure shows that the APM should be favored over the Boltzmann–Arrhenius one.

In this paper, we study the band gaps (BGs) of two-dimensional (2D) phononic crystals (PCs) composed of self-similarity shape inclusions embedded in the homogenous matrix. The dispersion relations, transmission spectra, and displacement fields of eigenmodes of the proposed structures are calculated by use of finite element method. Due to the simultaneous mechanisms of the Bragg scattering, the structure can exhibit low-frequency BGs, which can be effectively shifted by changing the geometries and degree of the self-similarity structure. The BGs are significantly dependent upon the geometrical parameters and degree of the self-similarity structure. It is concluded that, the PCs with self-similarity structure, can modulate the location and width of BGs. But it must be pointed out, the shape of self-similarity inclusion exercises a great influence on the BGs. The study in this paper is relevant to the design of tuning BGs and isolators in the low-frequency range.

Effect of proximity-induced unconventional p-wave superconductivity in a three-dimensional topological insulator-based S/F/S structure on the Andreev bound states (ABSs) and Josephson supercurrent is studied. We investigate, in detail, the suppression of Andreev reflection and helical ABSs in the presence of three types of triplet superconducting gap. The magnetization of ferromagnetic section is perpendicular to the surface of junction. The influence of such features on the supercurrent flow on the surface of the topological insulator is studied. We carry out our goal by introducing a relevant form of Dirac spinors for gapless renormalized by chemical potential μ excitation states. Therefore, it enables us to consider the virtual Andreev process, simultaneously, and we propose to investigate it in a tunneling conductance junction. It is shown that the results obtained in this case are completely different from those in conventional superconductivity, as s- or d-waves, for example, the magnetization is found to decrease the gap for p_x and p_x+ip_y case, whereas increase it for p_y order. Strongly suppressed Andreev reflection is demonstrated.