International Journal of Modern Physics B

In the present paper, we compute the magnetic susceptibility of graphene by using Gaussian correction. The collective excitations away from Fermi points of graphene are gapless, chiral fermions, with linear dispersion. The system is modeled as N massless Dirac fermions in two spatial dimensions interacting with 1/r Coulomb interactions. We find that the magnetic susceptibility is suppressed by the interaction between these collective excitations. And it has ln T correction due to the long-ranged Coulomb interaction, which is different from Landau Fermi liquid theory.

We study the survival probability of a particle diffusing in a two-dimensional domain, bounded by a smooth absorbing boundary. The short-time expansion of this quantity depends on the geometric characteristics of the boundary, whilst its long-time asymptotics is governed by the lowest eigenvalue of the Dirichlet Laplacian defined on the domain. We present a simple algorithm for calculation of the short-time expansion for an arbitrary "star-shaped" domain. The coefficients are expressed in terms of powers of boundary curvature, integrated around the circumference of the domain. Based on this expansion, we look for a Padé interpolation between the short-time and the long-time behavior of the survival probability, i.e., between geometric characteristics of the boundary and the lowest eigenvalue of the Dirichlet Laplacian.

A generalization of quantum mechanics is proposed, where the Lagrangian is the general form. The new quantum wave equation can describe the particle which is in general potential , and the Schrödinger equation is only suited for the particle in common potential V(r, t). We think these new quantum wave equations can be used in some fields.

In this paper, due to the effect of positively-charged screening holes, Coulomb potential energy 1/r is modified to be 1/r^p, which is assumed to deviate slightly from the former. Using many-body perturbation theory, we obtain a simple analytic representation of the ground-state energy and correlation energy for a uniform electron gas. Our results agree with those obtained by the numerical and semi-analytic methods at low-density limit. Higher ground-state energies at high-density limit are calculated from our model. High order r expansion terms are found at high-density region. A curve of transition density versus p is drawn via the Misawa spin-scaling relation, which is in consistent with Perdew's study at low-density limit.

Nanocrystalline iron–nickel alloys are electrodeposited by direct and pulse current densities with the grain sizes between 8–16 nm. XRD patterns showed a variety of structure in alloys from fcc, bcc and mixed (fcc+bcc) by variation of Fe content of alloy. The fcc structure was observed for lower Fe content, dual phase structure for Fe content between 60–70% and bcc structure for higher Fe content. By applying pulse current, an increase in Fe content of alloys was observed. Magnetic property measurements showed a high saturation magnetization for the alloys increased with increase in Fe content and a low coercivity decreased with decrease in grain size for alloys with iron content below 60%.

The band structures of GaSb in the Γ-valley as well as L/X-valley are excellently reproduced with sp³d⁵s* nearest-neighbor tight-binding model. The electron spin splitting energy and the spin–orbit interaction coefficients in the Γ, L and X multi-valleys are calculated. In the Γ-valley, the results obtained are in good agreement with experimental report. We then further extend our calculations to the GaSbL- and X-valleys. We also present the results of the top three valence bands in the Γ-valley. Due to the small band offset and large difference of the density of states between Γ- and L-valleys, it is shown that even at zero electric field, there is still an explicit electron population in the L-valley. These results are important to the realization of spintronic device and the investigation of spin dynamics far away from equilibrium.

This paper proposes a new symmetric key encryption algorithm based on one-dimensional chaotic map. This algorithm uses the random-like property and ergodicity of chaotic systems. In the process of encryption or decryption, this algorithm generates a chaotic pseudo-random sequence, changes the initial iterative times and the increment to encrypt the plaintext, and realizes fast encryption and decryption of all kinds of files. When analyzing the algorithm's performance and security, the result shows that, compared with the method of Baptista, the proposed method is safer, faster and more powerful.

In this paper, we investigate the influence of past citations k_i on papers' attachment rate Π(k, t) and propose a method to consider these influences by assigning different weights to k_i. The correlation r between Π(k, t) and k_i decrease rapidly with time, which suggests the different influences of past citations on the preferential attachment in citation networks. According to the different influences of k_i on Π(k, t), we put different weights to k_i and find a good linear dependence between Π(k, t) and the weighted past citations in three actual citation networks.

The temperature dependence of the damping constant is calculated for various Raman modes in (NH₄)₂SO₄ by the expressions derived from the soft mode–hard mode coupling model and the energy fluctuation model. The expressions for the damping constant are fitted to the measured Raman bandwidths and then the activation energies are extracted, which are equal to ~0.2 eV for the Raman modes studied. The damping constant of a soft mode is also calculated and the activation energy (~0.1 eV) is deduced in this crystal. Values of the activation energies obtained here, can be compared with the value of k_BT_C = 0.02 eV for (NH₄)₂SO₄. This indicates that this ferroelectric material undergoes an order–disorder transition. It is concluded that the observed behaviour of (NH₄)₂SO₄ can be described reasonably by the soft mode–hard mode coupling model considered here.

Quantum kinetic model together with the introduction of a field-tuned orientation parameter are adopted to study the acoustic attenuations of heavy fermion systems in high magnetic fields. The calculated attenuation-peak results near the critical (magnetic) field (B_c) obtained here resemble qualitatively those measured before in heavy fermion systems.

Numerical studies were conducted on the ballistic performance of alumina ceramic (AD95) tiles based on depth of penetration method, when subjected to normal impact of tungsten long rod projectiles at velocities ranging from 1100 to 2000 ms^-1. The residual depth on after-effect target was derived in each case, and the ballistic efficiency factor was determined using the corresponding penetration depth on medium carbon steel. Anti-penetration experiment study of the AD95 ceramic tiles to tungsten long rod projectiles has been carried out to verify the accuracy of numerical simulation model. The result shows that numerical simulation results agree well with the corresponding experiment results and AD95 ceramic has excellent ballistic performance than medium carbon steel. The ballistic efficiency factor increases with velocity increasing when impact velocity lower than 1300 ms^-1, and when it was higher than 1300 ms^-1 the ballistic efficiency factor has almost no difference.

The properties of polarons in a wurtzite GaN/Al_x Ga_1-xN quantum well (QW) are investigated by adopting an effective-mass approximation and a modified Lee–Low–Pines variational method. The ground-state energy, the transition energy and the phonon contributions due to various optical-phonon modes to the ground-state energy as functions of the well width are given. The effects of the confined (CF) optical phonon mode, interface (IF)-optical phonon modes, half-space (HS) phonon modes, the anisotropy of the electron effective band mass and the phonon frequency are respectively considered (or included) in the calculation. The results have been compared with those of the zinc-blende structure. The numerical result indicates that both the ground-state energies of polaron and the transition energy decrease with increasing well width. For QWs with larger well width (> 10 nm), the total contribution to polaronic energy mainly comes from the confined mode, and for QWs with narrower well width (< 2 nm), the total contribution to polaronic energy mainly comes from the IF-optical phonon and HS phonon modes. And the phonon contribution in GaN/Al_xGa_1-xN QW is much larger than that in GaAs/Al_xGa_1-xAs QW. The two IF-optical phonon modes with lower frequency, the transverse optical-like CF and HS modes are extremely small so that they can be neglected in the further discussion.