Modern Physics Letters B

We point out that a special case of an ideal gas exhibits concentration of the volume of its phase space, which is a sphere, around its equator in the thermodynamic limit. The rate of approach to the thermodynamic limit is determined. Our argument relies on the spherical isoperimetric inequality of Lévy and Gromov.

The deconvolution method has received much attention recently, and is becoming one of the major tools for well test and production data analysis in oil and gas industry. Here, we present a new deconvolution approach, which we believe is relevant and can be an important addition to the existing efforts made in this field. We show that the solution of the deconvolution problem can be successfully represented as a linear combination of non-orthogonal exponential functions. Also, we present three deconvolution algorithms. The first two algorithms are based on regularization concepts borrowed from the well-known Tikhonov and Krylov methods, while the third algorithm is based on the stochastic Monte Carlo method.

Group velocity and dispersion property of slow light in one-dimensional photonic crystal with different defect layer thicknesses are studied. It is found that the increase of defect layer thickness will induce the decrease of group velocity, which is an advantage to the design of optical buffer. However, the dispersion slope is increased, inducing a limited factor to keep the shape of ultra-short pulses. Then the effect of slight violation of defect layer thicknesses, refractive index and incident angle on the slow light is studied. The result shows that these influences are smaller at the first gap which is useful for the practical uses.

Uniform and aligned ZnO nanotube arrays have been synthesized by annealing Zn nanowire arrays in anodic aluminum oxide (AAO) membrane. In our method, Zn nanowire arrays were fabricated by electrochemical deposition technique based on ordered nanoporous AAO, and then a heat-treatment method was used to convert Zn nanowire arrays to ZnO nanotube arrays. The ZnO arrays were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and absorption spectra. The results show that the polycrystalline ZnO nanotubes have a diameter of about 45 nm. This method can also be used to fabricate other metal oxide nanotube arrays.

Polyhedron structures changes in Lennard–Jones (LJ) liquid argon containing 108 atoms are investigated by means of molecular dynamics (MD) simulations during the glass transition. The local bond orientational parameter and the bond angle distribution are calculated. In particular, a new parameter is introduced to simultaneously quantify the changes of all the major polyhedral structures: tetrahedron, hexahedron, octahedron, dodecahedron, and icosahedron. The results show that icosahedral order, hexahedral order and octahedral order increase with decreasing temperature, while tetrahedral order and dodecahedral order decrease. This indicates that the glass transition is a solidification process with complex microstructure changes.

The deposition of lanthanum boride (LaB₆) thin films by the DC magnetron sputtering were studied. XRD, AFM and Stylus Profiler were used to characterize the properties of the deposited films. The XRD was used to study the crystallinity. The results of the XRD showed that the dominant crystal face is the (100) face. The crystallinity decreased with the increased bias-voltage value, but the influence of bias-voltage on the films is different on different crystal faces. The intensity (100) face was influenced by the bias-voltage more obviously than other faces except the influence of thickness. The diffraction peak maximal intensity of the (100) face changed from 1256 (on 0 V) to 580 (on -150 V), but the intensity of (110) face changed from 614 (on 0 V) to 486 (on -150 V). The rel. int (100%) of the (110) face changed from 38.70 to 74.52. The deposition rate decreased with the increased bias-voltage value, but the decrease was not obvious. The maximum and minimum of the deposition ratio were 17.53 nm and 13.75 nm respectively. Surface morphology of the films was studied by the AFM. The crystallite of the films was less than 50 nm. The maximal roughness of the films decreased first and increased afterward, and the maximum was obtained on the -50 V bias-voltage.

Calculations of the optical conductivity σ(ω) for hole-doped cubic La_0.7Ca_0.3MnO₃ manganites have been made within the two-component scheme. One is the coherent Drude free carrier excitations. The other is the incoherent motion of carriers from one site to another leading to a polaron formation. This originated from interband transitions between the Hund rule split bands (Mn–Mn) and is due to charge-transfer transitions between the O 2p and the Mn e_g bands. The model successfully accounts for the anomalies reported in the optical measurements for the ferromagnetic metallic state. The frequency-dependent relaxation rates are expressed in terms of memory functions and the coherent Drude carriers from the effective interaction potential leads to a sharp peak at zero frequency and a long tail at higher frequencies, i.e. in the infrared region. The hopping of carriers from Mn site to Mn and Mn site to O (incoherent motion of doped carriers) yields two peak values around 0.4 and 4.0 eV in the optical conductivity centered in the mid-infrared region. Both the Drude and hopping carriers in the manganites contribute to the optical process of conduction in the Mn–O planes and shows similar results on optical conductivity in the mid-infrared as well as infrared frequency regions as those revealed from experiments.

The steady-state and transient electron transport in ZnO field effect transistor have been studied using an ensemble Monte Carlo simulation which takes into account the hot-electron transport phenomena. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible, and the predicted I–V and transfer charateristics for the intrinsic devices show fair agreement with the available experimental data. Simulations of the effect of modulating the gate bias have also been carried out to test the device response and derived the frequency bandwidth. The value of 80 ± 5 GHz has been derived for the intrinsic current gain cut-off frequency of the ZnO MESFETs.

Very little information is available about the structural properties of III-nitride binary compounds in the rock-salt phase. We report/review a comprehensive theoretical study of structural properties of these compounds in rock-salt, zinc-blende and wurtzite phases. Calculations have been made using full-potential linearized augmented plane wave plus local orbitals (FP-L(APW+lo)) method as embodied in WIEN2k code framed within density functional theory (DFT). In this approach of calculations, local density approximation (LDA) [J. P. Perdew and Y. Wang, Phys. Rev. B45 (1992) 13244] and generalized gradient approximation (GGA) [J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett.72 (1996) 3865] have been used for exchange-correlation energy and corresponding potential. Calculated results for lattice constants, bulk modulus, its pressure derivative and cohesive energy of these compounds are consistent with the experimental results. Following these calculations, besides many new results for the rock-salt and other phases, a comprehensive review of the structural properties emerges. We also list some peculiar features of these compounds.