The pressure dependences of elastic and lattice dynamic properties of AlAs from ab initio calculations

Ab initio calculations,based on norm-conserving nonlocal pseudopotentials and density functional theory(DFT),are performed to investigate the structural,elastic,dielectric,and vibrational properties of aluminum arsenide(AlAs) with a zinc-blende(B3) structure and a nickel arsenide(B81) structure under hydrostatic pressure.Firstly,the path for the phase transition from B3 to B81 is confirmed by analyzing the energies of different structures,which is in good agreement with previous theoretical results.Secondly,we find that the elastic constants,bulk modulus,static dielectric constants,and the optical phonon frequencies vary in a nearly linear manner under hydrostatic pressure.What is more,the softening mode of the transversal acoustic mode at the X point supports the phase transition in AlAs.     

Bound states of the Dirac equation with position-dependent mass for the Eckart potential

Studying with the asymptotic iteration method, we present approximate solutions of the Dirac equation for the Eckart potential in the case of position-dependent mass. The centrifugal term is approximated by an exponential form, and the relativistic energy spectrum and the normalized eigenfunctions are obtained explicitly.     

Calculation of the photoelectron spectra under a scaling transform

By solving the time-dependent Schro¨dinger equation, the dependence of photoelectron energy spectra on the binding energy of targets, wavelength and the intensity of laser pulse is exhibited and a scaling law of kinetic energy spectra of both the direct and the rescattered photoelectrons is concluded. The scaling law provides a convenient tool to determine the equivalent photoionization process of various atoms or molecules in various laser fields. The verification of the scaling law by independent methods provides incontestable support to the validity of the scaling law.     

A low specific on-resistance SOI MOSFET with dual gates and a recessed drain

A low specific on-resistance(Ron,sp) integrable silicon-on-insulator(SOI) metal-oxide semiconductor field-effect transistor(MOSFET) is proposed and investigated by simulation.The MOSFET features a recessed drain as well as dual gates,which consist of a planar gate and a trench gate extended to the buried oxide layer(BOX)(DGRD MOSFET).First,the dual gates form dual conduction channels,and the extended trench gate also acts as a field plate to improve the electric field distribution.Second,the combination of the trench gate and the recessed drain widens the vertical conduction area and shortens the current path.Third,the P-type top layer not only enhances the drift doping concentration but also modulates the surface electric field distributions.All of these sharply reduce Ron,sp and maintain a high breakdown voltage(BV).The BV of 233 V and Ron,sp of 4.151 mΩ·cm2(VGS = 15 V) are obtained for the DGRD MOSFET with 15-μm half-cell pitch.Compared with the trench gate SOI MOSFET and the conventional MOSFET,Ron,sp of the DGRD MOSFET decreases by 36% and 33% with the same BV,respectively.The trench gate extended to the BOX synchronously acts as a dielectric isolation trench,simplifying the fabrication processes.     

The distribution of Ga and Sb impurities in Ge-Si crystals grown by the Bridgman method using a feeding rod

Gallium- and antimony-doped Ge_{1 ? x} Si _x crystals (0 ≤ x ≤ 0.25) have been grown by the improved Bridgman method using a silicon seed and a macrohomogeneous feeding Ge-Si rod of the corresponding composition. The impurity concentration profiles along the grown crystals were determined from Hall measurements. The mathematical problem of impurity distribution along two-component mixed crystals grown from a melt with uniform and graded composition is solved in the Pfann approximation and within the virtual-crystal model for the solid solution. It is shown that the experimental impurity distributions in Ge_{1 ? x} Si _x crystals are described well by the data calculated on the assumption of linear change in the impurity segregation coefficient with the crystal composition.     

Tb1-xLnxA3(A=对氨基苯甲酸,x=0-0.9)固体配合物的光谱分析和荧光增强

合成了一系列组成为 Tb1-x Lnx A3 (L n=Gd、Y、La,A=对氨基苯甲酸 ,x=0— 0 .9)的固体配合物。利用红外光谱和荧光光谱研究了配合物的结构和荧光性质 ,结果表明 ,掺杂配合物的结构与未掺杂的对氨基苯甲酸铽相似。荧光光谱的结果显示 ,Gd3 对 Tb3 的发光有明显的增敏作用 ,探讨了荧光增敏机理。     

Designing shielded radio-frequency phased-array coils for magnetic resonance imaging

In this paper, an approach to the design of shielded radio-frequency (RF) phased-array coils for magnetic resonance imaging (MRI) is proposed. The target field method is used to find current densities distributed on primary and shield coils. The stream function technique is used to discretize current densities and to obtain the winding patterns of the coils. The corresponding highly ill-conditioned integral equation is solved by the Tikhonov regularization with a penalty function related to the minimum curvature. To balance the simplicity and smoothness with the homogeneity of the magnetic field of the coil’s winding pattern, the selection of a penalty factor is discussed in detail.     

Effects of non-Gaussian noise on a calcium oscillation system

We investigate the effects of the non-Gaussian colored noise on a calcium oscillation system using stochastic simulation methods. It is found that the reciprocal coefficient of variance R has a maximum (R max ) with increasing noise intensity Q. The non-Gaussian noise parameter q has an important effect on the system. For some values of q (e.g., q = 0.9, q = 1.0), R has a maximum with increasing correlation time τ. Non-Gaussian noise induced spikes are more regular than Gaussian noise induced spikes when q is small and Q has large values. The R has a maximum with increasing q. Therefore, non-Gaussian noise could play more effective roles in the calcium oscillation system.     

Electrical characteristics of AlInN/GaN HEMTs under cryogenic operation

Electrical properties of an AlInN/GaN high-electron mobility transistor (HEMT) on a sapphire substrate are investi-gated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AlInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density.     

Asymptotic solving method for sea-air coupled oscillator ENSO model

The ENSO is an interannual phenomenon involved in the tropical Pacific ocean-atmosphere interaction.In this article,we create an asymptotic solving method for the nonlinear system of the ENSO model.The asymptotic solution is obtained.And then we can furnish weather forecasts theoretically and other behaviors and rules for the atmosphere-ocean oscillator of the ENSO.