Monte Carlo Modeling of Phonon-assisted Carrier Transport in Cubic and Hexagonal Gallium Nitride

Monte Carlo method is employed for the calculations of electron and hole transport characteristics of cubic and hexagonal GaN at T = 300 K in the fields of E ≤ 1000 kV/cm⁻¹. It is shown that electron drift velocity and mobility is heavily reduced in hexagonal crystals due to additional phonon modes (~ 26 meV) and by fast electron scattering between the lowest Γ₁ valley and the minimally (~ 400 meV) up-shifted Γ₃ valley. Intervalley scattering is mediated most efficiently by the low-energy (~ 2 meV) acoustic phonons. The randomizing scattering is even more pronounced in p-type crystals where the sub-bands of light and heavy holes merge at the Γ-point of Brillouin zone. Cubic phase crystals are concluded to be advantageous for ultrafast electronic and photonics device performance because electron drift mobility is higher by an order of magnitude, and the hole mobility is several times higher than those in hexagonal phase.     

Continuous Miscibility from Dilute Solution to Fused Salt: Volumetric Properties of Binary Solutions of Nitrobenzene, 1-Butanol, and Anisole with Tetra-n-Butylammonium Picrate from 298.15 to 371.1 K

The densities and speeds of sound of binary solutions of nitrobenzene, 1-butanol, and anisole with tetra-n-butylammonium picrate have been measured over the full composition range from 298.15 to 371.1 K, in order to study the volumetric behavior of continuously miscible systems, made from an organic fused salt and a molecular organic liquid, at just above the melting point of the salt. The calculated apparent molar volumes and compressibilities are analyzed by using the equations of Petrenko and Pitzer. The thermal expansion coefficients of the above systems are also reported.     

Analysis of an early measurement of the speed of sound propagation in the atmosphere

Spanish and French scientists made a determination of the speed of sound close to Quito (Ecuador) in 1738. There was a particular interest in this measurement at that time because it was thought that the proximity of the Equator and the great altitude would have a major influence on this magnitude. The difference in time between the perceptions of the flash of a gunshot and of the corresponding sound was measured at two different sites. At one of them, Jorge Juan and Louis Godin obtained a value of 341 m/s for the speed of sound, and at the other, Antonio de Ulloa and Pierre Bouguer deduced a value of 348 m/s. Juan and Ulloa published these experiments in their book “Observaciones Astronomicas y Phisicas” (1748). They also presented possible applications of these studies of sound propagation to geometry, navigation, and warfare.     

Errata to “Cyclic strength of imperfectly saturated sands and analysis of liquefaction”: [Proc. Jpn. Acad., Ser. B 80, No. 8, 372–391 (2004)]

The simplified method of analysis to assess liquefaction potential of a given sand deposit is briefly introduced in the first part of this paper. Then, recent advances in the laboratory testing for evaluating liquefaction resistance are described with a particular emphasis on the sand partly saturated with water. As a means to identify the degree of saturation which is applicable for both field deposits and laboratory samples, the use of the longitudinal wave (P-wave) is proposed based on a suite of data obtained from the triaxial tests in the laboratory. It is recommended that the non-destructive P-wave measurements be carried out first to determine the degree of saturation, and then the cyclic triaxial tests involving large destructive strains should be performed to determine the cyclic strength on the same sample of the sand. In order to demonstrate usefulness of the proposed approach, two sets of undisturbed samples were secured from two sites; one is located in Sakai-minato city which has suffered severe liquefaction at the time of the 2000 Tottoriken-Seibu earthquake and the other site is located in Koshigaya city, Saitama, where likelihood of liquefaction to occur in a future earthquake is of major concern. Penetration tests and in-situ velocity logging were also conducted at these two sites. By adjusting the P-wave velocity of the undisturbed samples in the laboratory so as to have the same velocity in the field, the in-situ state of saturation was reproduced in the laboratory samples. Then, the cyclic loading tests were conducted to determine the cyclic strength of intact samples. The results of the laboratory tests as above were incorporated into the simple method of liquefaction analysis described in the first section of this paper. The analysis seems to yield results which are in reasonably good agreement with what was observed at the time of the earthquake.     

Solving the driven flow by linearized elimination with differential quadrature

In the Navier‐Stokes equations the velocity and the pressure are coupled together by the incompressibility condition div u = 0( u = (u,v)^T) which makes the equations difficult to solve numerically. In this article, a new method named linearized elimination of unknowns with differential quadrature method is applied to the Navier‐Stokes equations. The method is of second‐order accuracy in time and of spectral accuracy in space. The numerical results show that our method is of high accuracy, of good convergence with little computational efforts. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005     

Mathematical modeling of the sound induced in a subsonic flow around cascades in relative motion

A method of mathematical modeling of the tonal sound induced by the unsteady aerodynamic interaction of two plane airfoil cascades in a subsonic flow and in uniform relative motion in the direction of their fronts is developed. The method is based on the numerical integration of the unsteady flow equations using a simplified model for the periodic system of edge wakes shed from the airfoils of the first (leading) cascade in the viscous flow and acting on the second (trailing) cascade. An analysis of the distinctive features of the flow under consideration demonstrates the efficiency of the model proposed.     

Linux操作系统下声卡编程的实验

介绍了针对物理与电子专业的Linux课程中对声卡进行编程实验的内容和方法。     

The effect of restricted velocity in the two-lane on-ramp system

Usually there are multi-lane on the main road of the on-ramp system. The drivers may decelerate for more safety when they are near the on-ramp. In addition, the car velocity may be restricted according to the traffic regulation. In this paper, we study phenomenon using the cellular automata traffic flow model. We find that: (i) the phase diagram of the two-lane on-ramp system appears a new region, in which the traffic of the on-ramp reaches maximum flow. (ii) The introduction of restricted velocity region will decrease capacity of the on-ramp, but reduce the drastic velocity fluctuation near the on-ramp.     

碘化钠弹性常数和声速的量子力学从头算

采用从头算平面波赝势(PWP)方法结合电子交换关联能的广义梯度近似(GGA)理论,对不同压力下碘化钠的晶体结构进行几何优化计算,得到体系的最稳定优化构型和相应的能量,利用胡克定律计算得到了相应压力下的弹性性质,取得了碘化钠单晶在零温条件下、压力0~30 GPa范围内弹性常数与压力的关系.根据弹性波在晶体中的传播行为求解了碘化钠单晶[100][、110]、[111]三个主要方向的声速.     

利用双光栅的多普勒频移测速度

衍射光的多普勒频移是与光栅运动速度有关的量.激光束依次通过动光栅、静光栅衍射,然后使1对光频不同、彼此平行又能部分重叠的衍射光束通过硅光电池进行光电转换,得到的信号电流的频率等于多普勒频移.信号电流经I/V转换、f/V转换和A/D转换后,由单片机测出电压,由此就可以确定动光栅的运动速度.最后对利用双光栅的多普勒频移测气垫导轨上滑块的速度进行分析和讨论.