International Journal of Modern Physics B

The energy-weighted sum rule for an electric dipole transition operator of a Schiff type differs from the Thomas–Reiche–Kuhn (TRK) sum rule by several corrective terms which depend on the number of system components, . For illustration the formalism was applied to the case of Na clusters. One concludes that the random phase approximation (RPA) results for Na clusters obey the modified TRK sum rule.

With the help of the Euler–MacLaurin formula, the statistic characteristics of quantum gases confined in a rectangular box are investigated by using a unified way. Three components of the pressure tensor and the internal energy of the system are analytically derived. The important relation between the pressure tensor and the internal energy is strictly proved. It is pointed out that these results are different from those obtained in literature and textbooks under the thermodynamic limit condition. Moreover, the pressure of the system is rationally introduced with the help of the property of the diagonal tensor, so that some thermodynamic functions of the system may be conveniently obtained. The statistic characteristics of quantum and classical gases confined in some different containers are discussed, the influence of the size effect of the containers on the properties of gases is analyzed and some new significant results are obtained.

Work is reported on the characterizations of pulsed laser deposited aluminum–nitride thin films. The films were deposited on silicon substrate with a KrF 248 nm pulse laser operating in a Riber LDM-22 system. Optical reflection spectroscopy (400–900 nm) was carried out, which revealed that, under certain deposition conditions, the films could show strong periodic spectra with reflection gaps of about 50–100 nm in width. The microscopic structures, such as crystalline status and element composition, were also investigated with Auger electron spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and profilometry etc. Relations between the optical responses and the microscopic structures were established. The foundations underlying the relations were studied and discussed.

In this paper, a generalized variable-coefficient nonlinear Schrödinger equation with higher-order and gain/loss effects which can be used to describe the femtosecond pulse propagation is analytically investigated via symbolic computation. Under sets of coefficient constraints, such an equation is transformed into a completely integrable constant-coefficient higher-order nonlinear Schrödinger equation. Furthermore, through the transformation, the dark one- and two-soliton solutions for the generalized variable-coefficient higher-order nonlinear Schrödinger equation are derived by means of the bilinear method.

In this study, we calculate the Raman frequencies as a function of temperature for the fixed pressures of 706, 1080 and 6355 bars using the volume data for phase II of ammonium iodide. The Raman frequencies calculated here are for the translational optic ν₅TO_M(125 cm^-1) lattice mode that is located at the zone boundary (M point) of the Brillouin zone of phase II for NH₄I. For this calculation the volume data obtained at zero pressure, is used through the mode Grüneisen parameter for the disordered phase II (β phase) which has the CsCl structure of NH₄I.

Our predicted frequencies of the ν₅TO_M(125 cm^-1) mode can be compared when the Raman data for this lattice mode is available at various temperatures for fixed pressures of 706, 1080 and 6355 bars in the disordered phase II of ammonium iodide.

Secure communications via chaotic synchronization is demonstrated in this literature. At first we have designed a feedback controller for chaotic synchronization utilizing the Lyapunov stability theory for cascade-connected systems.The method has been applied successfully to make two identical systems globally asymptotically synchronized. The result of numerical simulations are given to validate the effectiveness of this method. Then we have discussed a new method of cryptography for this coupled system which is very simple to implement and effective.

We have fabricated the Sn/p-Si Schottky barrier diodes with the interfacial layer metal–insulator–semiconductor (D-MIS) and the surface passivation metal–semiconductor MS (D-MS) by the anodization or chemical treatment method. The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the devices were measured at room temperature. We obtained that the excess capacitance (C₀) value of the MIS Sn/p-Si diode with the anodic oxide layer of 16.88 pF and 0.12 pF for the MS Sn/p-Si ideal diode with the surface passivation by the anodization or chemical treatment method from reverse bias C–V characteristics. Thus, we have succeeded to diminish the excess capacitance value to the limit of 0.12 pF for the MS Sn/p-Si diode by using the anodization or chemical treatment method.

We have developed a simplified molecular-dynamical model for simulating ablation of solid surfaces by laser pulses, and specifically investigated expansion of Cu cloud in vacuum vaporized on the surface, showing that the angular distributions of the plume depend on the shape of the laser spot on the surface. In particular, experimentally observed flipover effects have been obtained, and an adiabatic constant determined from our simulations via an adiabatic expansion model agrees well with previous measurements.

High-pressure angle-dispersive X-ray diffraction experiments were performed on UGa₃ up to 30 GPa within a diamond-anvil cell. UGa₃ remains in its cubic AuCu₃ type structure up to the maximum pressure studied and does not show any structural phase transition. To understand the structural stability of UGa₃, band structure calculations were performed as a function of reduced volume using the full-potential linear augmented plane wave (FP-LAPW) method. The results show that the Fermi level coincides with a deep valley in the density of states (DOS) curve in the antiferromagnetic state, whereas it lies near a valley (towards the bonding side) in the nonmagnetic state. At high pressures, the DOS near E_F does not show much variation in both the cases. The experimental and theoretical equation of state, bulk modulus, and its pressure derivative values are also reported. The pressure dependence of magnetic moment shows a linear decrease at the rate of dμ/dP = -0.027 μ_B/GPa.

In this paper, we investigate effects of the Dresselhaus spin-orbit coupling, inter-well coupling, and external bias on the dynamics of resonance tunneling through a semiconductor double-well structure. Based on the transfer matrix technique and the single band effective-mass approximation method, the numerical results demonstrate that the transmission peaks of the spin-up and spin-down electrons split due to the Dresselhaus spin-orbit coupling in the double-well structure. As the in-plane wave vector and external electric field increase, the split becomes farther apart. There is a prominent difference between the lifetime of the quasibound energy level for different spin-polarized electrons. The spin-dependent tunneling time is obtained using the time-dependent Schrödinger equation.

The electronic band structure, structural phase transition, metallization and superconducting transition of cubic zinc blende-type indium phosphide (InP) and indium nitride (InN), under pressure, are studied using TB-LMTO method. These indium compounds become metals and superconductors under high pressure but before that they undergo structural phase transition from ZnS to NaCl structure. The ground-state properties and band gap values are compared with the experimental and previous theoretical results. From our analysis, it is found that the metallization pressure increases with increase of lattice constant. The superconducting transition temperatures (T_c) of InP and InN are obtained as a function of pressure for both the ZnS and NaCl structures and these compounds are identified as pressure-induced superconductors. When pressure is increased T_c increases in both the normal (ZnS) and high pressure (NaCl) structures. The dependence of T_c on electron–phonon mass enhancement factor λ shows that InP and InN are electron–phonon mediated superconductors. The non-occurrence of metallization, phase transition and onset of superconductivity simultaneously in InP and InN are confirmed.

A lattice BGK model for simulating solitary waves of the combined KdV–MKDV equation, u_t+αuu_x-βu²u_x+δu_xxx = 0, is established. The tunable parameters in Chapman–Enskog expansion of the local equilibrium distribution function are determined by the coefficient of the combined KdV–MKDV equation. Simulating results fit close in with the theoretical results.

By means of the Ford–Kac–Mazur formalism, the heat current and local kinetic energy of a dielectric chain with Fermi–Pasta–Ulam–β nonlinear interactions are derived out in the stationary equilibrium and analyzed numerically. We find that the anharmonicity reduces the heat current for repulsive interactions and enhances the heat current for attractions. The magnitudes of heat current are relevant strong at low frequencies, while the local kinetic energy is bigger in the high-frequency regime. The local kinetic energy displays a periodic oscillation due to the interference of the thermal waves. In particular, the transmission matrix exhibits oscillations due to scattering of phonons for the imperfect contacts. In general, the thermal transport is qualitatively altered by the differences of temperature between reservoirs, nonlinear interactions and the size of chain as well as the contacts.

The effects of quantum and thermal fluctuations on collective pinning and critical current density J_c are investigated for bulk type-II superconductors by utilizing quantum statistics. It is shown that for a constant magnetic field, J_c is nearly independent of temperature in the quantum limit; however, in the classical limit, J_c decreases weakly with increasing temperature when T < T_dp (depinning temperature); when T_dp < T < T_f (boundary fluctuation temperature), J_c is power-law-decaying, and when T > T_f, J_c decays exponentially. For constant temperature, J_c first decreases, then increases after reaching a maximum, and finally decreases again. These results are in agreement with the experiments.