International Journal of Modern Physics B

Discrete Uehling–Uhlenbeck models together with the introduction of the disorder or an orientation-free parameter are adopted to study the possible localization of plane waves propagating in dilute hard-sphere Bose–Einstein gases under very-low temperature environment based on the acoustical analog. The curves of the localization length versus the disorder and Pauli-blocking measure we obtained here resemble qualitatively those proposed before.

Combination effects of structure disorder of protein molecules containing the fluctuations of spring constant, dipole-dipole interaction constant and exciton-phonon coupling constant and diagonal disorder, resulting from nonuniform distribution of masses of amino acid residues and impurities, on the soliton transported the bio-energy in the proteins have been numerically simulated by fourth-order Runge–Kutta method in the improved model. The results obtained show that these structure disorders can change the states of solitons but as the solitons are quite robust against these disorder effects, they can only be dispersed or disrupted in the cases of quite large structure disorders. From these results and the properties of molecular structure of biological proteins we can conclude that the new soliton in the improved model is quite stable in normal conditions. Thus the soliton is possibly a carrier of bio-energy transport in the protein molecules.

La_0.67Ca_0.33MnO₃ samples prepared by polymeric precursor route method are investigated using the thermogravimetric, differential thermal analysis, X-ray powder diffraction, scanning electron microscope, infrared spectroscopy and magnetic measurements. The unit cell parameters and grain size for all the samples are refined using X-ray diffraction and scanning electron microscope. It is observed that the IR bands at about 400 cm^-1 is are most likely due to Mn–O–Mn bending mode and the band at 600 cm^-1 is the result of the in plane Mn–O stretching mode. Magnetization measurements indicated that the Curie temperature increases from 241.3 K for the sample sintered at 600°C to 268.86 K for the sample sintered at 1000°C as a function of sintering temperature. The magnetic entropy change reaches the maximum value of about 4.8J/kg·K for the sample sintered at 1150°C at an applied field of 1 T.

The capacitance and loss tangent of thermally evaporated zinc phthalocyanine, ZnPc, semiconducting thin films were measured in the temperature range of 180–430 K and frequency between 0.1 and 20 kHz. Aluminum and gold electrical contact electrodes were employed to sandwich ZnPc films. For both electrode types, the capacitance and loss tangent showed strong dependence on both temperature and frequency. Such dependence is related to the relevant temperature and frequency range under consideration. The capacitance has strong temperature dependence for T>240 K and frequency below 3 kHz, while it becomes a constant at higher frequencies and all temperatures. The loss tangent dependence on temperature is more evident at low frequencies and a minimum or an indication of a minimum was observed in tan δ versus f curves. Loss tangent variation with temperature was not monotonic for all frequencies. An anomaly (maximum) in tan δ was observed approximately between 300 and 360 K. This maximum was attributed to the presence of oxygen molecules in the sample and their subsequent exhaustion as the temperature is increased. The behavior of capacitance and loss tangent (for both Al and Au-electrodes) may be explained qualitatively and successfully in terms of an equivalent circuit model.

The notion of representative statistical ensembles, correctly representing statistical systems, is strictly formulated. This notion allows for a proper description of statistical systems, avoiding inconsistencies in theory. As an illustration, a Bose-condensed system is considered. It is shown that a self-consistent treatment of the latter, using a representative ensemble, always yields a conserving and gapless theory.

In this paper, a three-dimensional (3D) thermal lattice Boltzmann model is proposed to simulate 3D incompressible thermal flow problem. Our model is based on the double-distribution function approach. We found that a new and simple lattice type of eight-velocity model for the internal energy density distribution function can be developed, where the viscous and compressive heating effects are negligible. Numerical results of 3D natural convection flow in a cubic cavity are presented.

From the path-integral method, the diagrammatics and Feynman rules for the Lagrangian theory based on the spl(2,1) graded algebra are constructed. The first-order Lagrangian we have obtained is written in terms of the graded Hubbard operators. By using functional techniques, the correlation generating functional is given in terms of the proper effective Lagrangian of the model. Once the Feynman rules, propagators and vertices were found, a physical discussion about the free propagators is given. Finally, the expressions of the boson self-energy and the renormalized boson propagator are used to study the hole effects on the magnetic properties of the high-T_c cuprates.

The viscous dissipation term in energy equation is investigated with the lattice Boltzmann method, and the double distribution functions (DDF) are applied, respectively, to simulate the velocity and the temperature fields. Compared with other existing models, the complicated evolution equation is simplified and the energy equilibrium density function is completely independent of the density distribution function in present model [unlike the authors He et al. [J. Comput. Phys.146, 282 (1998)]], when dealing with viscous dissipation term problem. In this paper, the viscous dissipation term is directly treated as a source term and the complex space discretion in the evolution equation can also be avoided by special method in part 2. Efficiency and accuracy of present model is validated through numerical experiments on Couette and natural convection flows.

The scaling behavior of the effective activation energy of high-quality epitaxial c-oriented Bi₂Sr₂Ca(Cu_1-xCo_x)₂O_d thin films with 0≤x ≤0.025 has been studied as a function of temperature and magnetic field. For all samples, the effective activation energy scales as U(T, μ_oH)=Uo(1-T/T_c)^mHⁿ with exponent m=1.25±0.03, n=-1/2 and the field scaling 1/μ_oH and -Uμ_oH for thick films and ultra thin films, respectively. The results are discussed taking into account of the influence of the Co substitution with a model in which U(T, H) arises from plastic deformations of the viscous flux liquid above the vortex-glass transition temperature.

Thermal expansion of MgB₂ at normal state is measured experimentally in the temperature range 300–400 K. Lattice and electronic contribution to the thermal expansion is determined from the Gruneisen relation using electronic and lattice specific heat. This is compared with the low temperature measurements for predicting superconducting transition.