Doping dependence of the vortex glass and sublimation transitions in the high-T<Subscript>c</Subscript> superconductor La<Subscript>2-x</Subscript>Sr<Subscript>x</Subscript>CuO<Subscript>4</Subscript> as determined from macroscopic measurements

Magnetization and ac-susceptibility measurements are used to characterize the mixed phase of the high-temperature cuprate superconductor La_2-xSr_xCuO₄ over a large range of doping (0.075 0.20). The first order vortex lattice phase transition line H_FOT(T), the upper critical field H_c2(T) and the second peak H_sp(T) have been investigated up to high magnetic fields (8 Tesla applied perpendicular to the CuO₂ planes). Our results reveal a strong doping dependence of the magnetic phase diagram, which can mainly be explained by the increasing anisotropy with underdoping. Within our interpretation, the first order vortex lattice phase transition is due to the sublimation (rather than melting) of the vortex lattice into a gas of pancake vortices, whereas the second peak is related to the transition to a more disordered vortex glass state.     

Multiple-frequency current oscillations in GaAs-AlGaAs quantum wells containing a thin semi-insulating layer

We have investigated non-equilibrium electron transport properties of a quantum well with an inserted thin semi-insulating potential barrier layer in nonlinear bias using a time-dependent simulation technique. We find that the charge redistribution with time in the whole structure has an important effect on the final current-voltage (I-V) curves. The results show that there are two evident current hysteresis phenomena in the negative differential conductance regions and the inserted semi-insulating potential barrier layer induces the formation of multiple emitter quantum wells, which leads to high-frequency terahertz current oscillations with multiple-frequency relations around the valley of current.     

Dynamical thermostatting and statistical ensembles

Dynamical thermostatting constitutes a procedure for computing thermodynamical mean values of classical dynamical systems that is of interest both from the practical and from the conceptual points of view. Here we extend and unify previous partial results, showing that the dynamical thermostatting approach can be implemented in order to simulate a wide family of statistical ensembles of general dynamical systems with a vanishing divergence and admitting an integral of motion. As a particular illustration, the thermostatting procedure is applied to power law-like maximum entropy ensembles.     

Study of traffic flow at an unsignalized T-shaped intersection by cellular automata model

In this paper, the traffic flow at an unsignalized T-shaped intersection in which there are three input directions of vehicles and two right-turnings and one left-turning has been investigated by using the cellular automata traffic model. The interactions between vehicles on different lanes and effects of traffic flow states of different roads on capacity of T-shaped intersection system are analyzed. The phase transition characteristics of traffic states on different lanes are studied. The research indicates that the model can be applied to the real traffic analysis and traffic forecast.     

Exact calculation of the phase properties of one dimensional finite lattice gas systems

The small-size partially filled one-dimensional (1D) lattice gas system with 1/r^δ repulsive interactions is numerically studied. Our results indicate that phase change with vacancy ordering involved exists in the partially filled 1D lattice gas systems, and the phase properties of the studied system strongly depend on the occupancy n_av and the interaction strength δ. Most interestingly, it is found that the phase change still exists in the 1D finite-size lattice gas systems even with nearest neighbor interactions, i.e. δ is infinite. These results provide valuable information about the phase properties of 1D confined systems, such as molecules inside the carbon nanotubes, with long-range interactions between particles.     

Optical transmission properties of light propagation through Fibonacci-class ring-resonators

An interesting topology with easy integration capability (from mask designing aspect) for optical filters using Fibonacci-class (FC(J,n)) ring-resonators is introduced. For some special cases, analytical transfer function (Transmission Coefficient H_m⁽ⁿ⁾) is obtained and corresponding simulated result is illustrated. In this work, optical multi-band filter design and analysis using Fibonacci-class ring resonators is considered. With suitable selection of system parameters and FC(J,n), we report multi-band characteristic for this structure. Also, dominant factors effects on multi-band operation are shown. We show that the coupling coefficients, effectively affects (e.g. generation or annihilation of additional band) the multi-band properties obtained in proposed structure. Also, the bandwidth and position of additional band can be controlled using Fibonacci-class basic elements (A, B) parameters such as rings diameters. Also, proposed system is easier than general multistage rings coupled to main waveguide from implementation point of view.     

Electrical properties of hybrid phthalocyanines thin films using gold and lead electrodes

The electrical properties of mixed copper phthalocyanine (CuPc) and nickel phthalocyanine (NiPc) thin films devices with gold and lead electrodes have been investigated. The two phthalocyanines were co-evaporated and deposited on to a pre-cleaned glass substrate by thermal evaporation technique at room temperature. By the co-sublimation technique an integrated phthalocyanine sample was prepared. At low voltages the film showed an ohmic conduction whereas at higher voltage levels the conduction mechanisms were dominated by space charged limited conduction (SCLC). The value of mobility of holes were calculated as μ= 3.1×10^-8 m² V^-1 s^-1 which is lower for the mixed phthalocyanines whereas the trap concentrations N_t(e) = 8.06 ×10²⁵ m^-3 have increased in the SCLC region. Further the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident.     

Magnetic reordering in the vicinity of a ferromagnetic/antiferromagnetic interface

The magnetic arrangement in the vicinity of the interface between a ferromagnet and an antiferromagnet is investigated, in particular its dependence on the exchange couplings and the temperature. Applying a Heisenberg model, both sc(001) and fcc(001) lattices are considered and solved by a mean field approximation. Depending on the parameter values a variety of different magnetic configurations emerge. Usually the subsystem with the larger ordering temperature induces a magnetic order into the other one (magnetic proximity effect). With increasing temperature a reorientation of the magnetic sublattices is obtained. For coupled sc(001) systems both FM and AFM films are disturbed from their collinear magnetic order, hence exhibit a similar behavior. This symmetry is absent for fcc(001) films which, under certain circumstances, may exhibit two different critical temperatures. Analytical results are derived for simple bilayer systems.     

HSSH-model of Hole transfer in DNA

A method based on a selfconsistent solution of a quantum-mechanical system with temperature fluctuations described by Langevin equations is developed to calculate the charge carrier mobility in DNA. To model the charge transfer in DNA, a combined Holstein – SSH Hamiltonian is considered. As an example the hole mobility is calculated at room temperature for synthetic poly (G)/poly (C) duplex with regard to main structural fluctuations.     

Mean field theory and geodesics in general relativity

It is proven that all geodesics in a mean gravitational field can be interpreted locally as the averages of geodesics in the unaveraged field. The respective time-like, space-like or null character of averaged and unaveraged geodesics is discussed carefully. Finally, some important astrophysical and cosmological applications and consequences are investigated.