International Journal of Modern Physics B

We review both synthesis and magnetorheological (MR) characteristics of magnetic particles concerning electro-thermoconductive MR suspensions. Various MR systems from nanoparticles to microparticles of iron, iron oxides and metallic solids with and without additives or modifications with polymers are summarized. Methods for electro-thermoconductive MR suspensions and mechanisms that lend them these properties, experimental results and discussions on them are presented.

We give an elementary construction of the Fibonacci model, a unitary braid group representation that is universal for quantum computation. This paper is dedicated to Professor C. N. Yang, on his 85th birthday.

A brief introduction and overview is given of the complexity that is possible and the challenges its study poses in many-body systems in which spatial dimension is irrelevant and naively one might have expected trivial behaviour.

A closed analytic form for relativistic bound-unbound and unbound-unbound transition matrix elements of hydrogenic atoms by using the plane-wave expansion for the electromagnetic-field vector potential is derived. By applying the obtained formulae, these transition matrix elements can be evaluated analytically and numerically.

This work reports the internal potential distributions in double-barrier structure due to electron-electron interaction in mesoscopic ac transport. We focus on the properties of the internal potential in some special external voltages. It is found that the internal potential is stable in general situations, but it becomes auto-fluctuating and even random fluctuating in some special cases. In these special cases, the system becomes unstable.

Industrial robot arms experience position inaccuracies due to the output cogging torques of the DC servomotors. Therefore, in an attempt to resolve these position problems, an electro-rheological (ER) robotic system is considered as an actuator to drive the robot arm rapidly in both directions. This ER robotic system consists of two ER clutches, an ER brake, a gear train, an encoder and a robot arm. The ER clutches produce clockwise and anti-clockwise rotations. The ER brake decelerates and halts the robot arm. The main aim of this paper is to validate a controller model of the ER robotic arm. Next, a trend study is used to determine the optimum working conditions of the ER actuated-robotic arm. The robotic displacements of both the ER rotary devices and the commercial DC servomotors are compared in terms of position accuracy and speed of response. Finally, the repeatability of the robotic end positions is examined in order to determine the importance of the ER brake.

General complex variable method for solving plane elasticity problems of quasicrystals with point group 10 has been proposed. The stress and displacement components of phonon and phason fields are expressed by four arbitrary analytic functions. Explicit real-form displacement expressions for the dislocation problem of the quasicrystal is obtained through the use of this method.The interaction between two parallel dislocations is also discussed in detail. All the present results can be reduced to the exact solutions for the quasicrystals with point group 10 mm in the special case.

Anharmonic effective potential, Extended X-ray Absorption Fine Structure (EXAFS) and its parameters of hcp crystals have been theoretically and experimentally studied. Analytical expressions for the anharmonic effective potential, effective local force constant, three first cumulants, a novel anharmonic factor, thermal expansion coefficient and anhamonic contributions to EXAFS amplitude and phase have been derived. This anharmonic theory is applied to analyze the EXAFS of Zn and Cd at 77 K and 300 K, measured at HASYLAB (DESY, Germany). Numerical results are found to be in good agreement with experiment, where unnegligible anharmonic effects have been shown in the considered theoretical and experimental quantities.

Gallium nitride (GaN) is a highly promising wide band gap semiconductor with applications in high power electronic and optoelectronic devices. Thin films of GaN are most commonly grown in the hexagonal wurtzite structure on sapphire substrates. Growth of GaN onto silicon substrates offers a very attractive opportunity to incorporate GaN devices onto silicon-based integrated circuits. Although direct epitaxial growth of GaN films on Si substrates is a difficult task (mainly due to the 17% lattice mismatch present), substantial progress in the crystal quality can be achieved using a buffer layer. A full characterization of the quality of the material needs to be assessed by a combination of different techniques.

In this work, a thin AlN cap layer of 50 nm was incorporated in GaN Schottky diode to enhance the effective Schottky barrier height and reduces the dark current. A barrier height of 0.52 eV for normal GaN Schottky diode was increased to the effective barrier height of 0.63 eV. The resulting Schottky diodes show a dark current of as low as 6.3×10^-5 A at 5 V bias, which is about two orders of magnitude lower than that of normal GaN (5.2×10^-3 A at 5 V bias) Schottky diode.

This article deals with the connection between a.m. the diagonal matrix elements with the P. A. M. Dirac radial functions g(r) and f(r) and the diagonal matrix elements <r^k>_nl with the E. R. Schrödinger radial functions R_nl(r) of H-like atoms (as Z=1, n≤8 and -7≤k≤4) and new properties of the P. E. Appell function F₂(x,y) to the vicinity of the singular point (1, 1). In Tables 1–4, exact numerical values of these integrals are first given here, i.e., actually for all the D. I. Mendeleev table. (The author has all values of these integrals and graphs of Dirac's radial functions for the arbitrary nlj-states of H-like atoms and Z ≤ 137).

The propagation of a monochromatic high-frequency longitudinal acoustic wave along the normal to the layer (z-axis) in a bulk quasi-two-dimensional conductor (Q2D), in the absence of an external magnetic field under assumption of arbitrary scattering of the charge carriers from the boundary surface, is studied theoretically. The effect of the Q2D electron energy spectrum features on the attenuation of an ordinary acoustic wave (OAW) and of an anomalous acoustic wave (AAW) is discussed. It is shown that for certain values of the characteristic parameters, the OAW in Q2D is strongly attenuated, and the asymptotic form of the acoustic field in the conductor is determined by the AAW. In the case of a Q2D conductor, the anomalous acoustic field is transmitted by electrons belonging to the belt points of the Fermi surface.

We present the metal–insulator transition study of a quantum site percolation model on simple cubic lattice. Transfer matrix method is used to calculate transport properties — Landauer conductance — for the binary distribution of energies. We calculate the mobility edge in disorder (ratio of insulating sites) — energy plane in detail and we find the extremal critical disorder somewhat closer to the classical percolation threshold than formerly reported. We calculate the critical exponent ν along the mobility edge and find it constant and equal to the one of 3D Anderson model, confirming common universality class. Possible exception is the center of the conduction band, where either the single-parameter scaling is not valid anymore, or finite size effects are immense. One of the reasons for such statement is the difference between results from arithmetic and geometric averaging of conductance at special energies. Only the geometric mean yields zero critical disorder in band center, which was theoretically predicted.

Considering the problems of potentially generating a disconnected network in the WS small-world network model [Watts and Strogatz, Nature393, 440 (1998)] and of adding edges in the NW small-world network model [Newman and Watts, Phys. Lett. A263, 341 (1999)], we propose a novel small-world network model. First, generate a regular ring lattice of N vertices. Second, randomly rewire each edge of the lattice with probability p. During the random rewiring procedure, keep the edges between the two nearest neighbor vertices, namely, always keep a connected ring. This model need not add edges and can maintain connectivity of the network at all times in the random rewiring procedure. Simulation results show that the novel model has the typical small-world properties which are small characteristic path length and high clustering coefficient. For large N, the model is approximately equal to the WS model. For large N and small p, the model is approximately equal to the WS model or the NW model.