International Journal of Modern Physics B

Besides the growing interest in old concepts such as temperature and entropy at the nanoscale, theories of relaxation and transport have recently regained a lot of attention. With the electronic circuits and computer chips getting smaller and smaller, a fresh look on the equilibrium and nonequilibrium thermodynamics at small length scales far below the thermodynamic limit, i.e. on the theoretical understanding of original macroscopic processes, e.g. transport of energy, heat, charge, mass, magnetization, etc., should be appropriate. Only from the foundations of a theory its limits of applicability may be inferred. This review tries to give an overview on the background and recent developments in the field of nonequilibrium quantum thermodynamics, focusing on the transport of heat in small quantum systems.

High pressure-high temperature electrical resistivity study on composition-controlled Nd_0.9Ca_0.1Ba₂Cu₃O_7-δ high T_c superconductor (HTSC) is carried out by a four-probe technique using Bridgman anvils. A simple heating coil arrangement is used for heating the samples. Electrical resistivity behavior under pressure (up to a maximum of 8 GPa) at various temperatures (up to a maximum of 523 K) were studied and reported in this paper. Simulation of energy dispersive X-ray diffraction confirms substitution of calcium at the Nd site of Nd-123. Variation of the electrical resistivity under pressure is compared with that of the structural changes and the bulk modulus was determined.

Synthesis of Er³⁺, Eu³⁺ ions activated strontium hexa-aluminate phosphor using the combustion method is described. An efficient phosphor can be prepared by this method at reaction temperatures as low as 500°C in a few minutes. Powder X-ray diffraction and the optical properties were studied by photoluminescence spectra.

On the basis of the finite element approach, we systematically investigated the strain field distribution of conical-shaped InAs/GaAs self-organized quantum dot using the two-dimensional axis-symmetric model. The normal strain, the hydrostatic strain and the biaxial strain components along the center axis path of the quantum dots are analyzed. The dependence of these strain components on volume, height-over-base ratio and cap layer (covered by cap layer or uncovered quantum dot) is investigated for the quantum grown on the (001) substrate. The dependence of the carriers' confining potentials on the three circumstances discussed above is also calculated in the framework of eight-band k·p theory. The numerical results are in good agreement with the experimental data of published literature.

By using the magnetic entangled state 〈λ| representation and the squeezing transform we derive Feynman propagator for a charged particle in a quantum dot in the presence of a uniform magnetic field. It is the neat expression of the squeezing operator in 〈λ| representation that provides the concise way and the brevity. The partition function of this sytem is thus obtained.

In this paper we investigate the average frequency of a certain positive slope which is produced when the velocity and magnetic fields V_y and B_x are crossed by the level in the magnetohydrodynamic equation. This level crossing analysis is in the inviscid limit where υ→0 and of course before the appearance of the shocks. The main goal of this paper is to show that this quantity, , is a good measure for the fluctuations of the velocity and magnetic fields in the magnetohydrodynamic turbulence.

The dependence of reverse-biased leakage current on both voltage and temperature for InP-In_xGa_1-xAs_yP_1-yDH (double heterostructures) has been analyzed. We find that at the whole of the temperature range and at a wide range of reverse bias voltages, the reverse current varies exponentially with applied voltage, indicating that the band-to-band tunneling current mechanism prevails. An agreement is obtained between theory and experimental results. The tunneling current becomes substantial at peak junction electric fields as low as 10⁵V/m due to the small direct energy gaps and small effective masses of the structures tested. The process of breakdown in the investigated structures was of the avalanche type. The impact ionization coefficients in In_xGa_1-xAs_yP_1-y have been experimentally determined for composition x=0.68.

In a biased two-dimensional electron gas, the presence of spin-orbit coupling of both the Rashba and Dresselhaus type leads to a Hall conductivity of charge carriers in the absence of an external magnetic field. We study the dynamical charge-Hall effect, the field-induced spin accumulation, and the magnetoelectric effect for a system with short-range elastic impurity scattering by analytically solving the kinetic equations for the spin-density matrix in the linear response regime. By tuning the strength of the Rashba and Dresselhaus spin-orbit coupling as well as the frequency and direction of the applied electric field, eigenmodes of the spin-coupled system are identified.

In this paper we discuss a noisy mean field model for the genetic toggle switch. We show that this model approximates very well the characteristics of the system, observed using the exact Gillespie stochastic simulation algorithm. Also, we show that the system can be made exponentially stable depending on reaction parameters.

Vertically aligned arrays of multi-walled carbon nanotubes (VACNTs) were grown by spray pyrolysis of turpentine oil and ferrocene mixture at temperatures higher than 700°C. Using this simple method, we report the successful growth of vertically aligned nanotubes of ~300μm length and diameter in the range of ?20–80nm on Si(100) substrate. The ferrocene acts as an in situFe catalyst precursor, forming the nano-sized metallic iron particles for formation of VACNTs on the Si substrate. The morphological characteristics of VACNTs are confirmed by SEM, TEM and Raman spectroscopy and growth mechanism is discussed in short.