The effect of chemical composition of a crystallization medium on the cBN stoichiometry

Abstract

The effect of chemical composition of the crystallization medium in synthesis on and some properties of cubic boron nitride (cBN) has been studied. Cubic BN crystals with the lowest free boron content and a boron-nitrogen ratio close to the stoichiometric one are grown in a multicomponent crystallization medium in a Li₃N-BN system. These crystals are characterized by a higher strength and thermal stability.     

表面等离子共振现象的新应用——微弱磁场的测量

提出了一种新的表面等离子体共振传感器, 它包含三层结构: 棱镜、金属薄膜及二能级介质. 通过理论分析发现, 与通常表面等离子体共振系统不同, 这一物理系统中同时存在两种共振效应 (表面等离子体共振和能级间量子跃迁的共振效应), 它们共同作用的结果导致一系列新的物理现象, 其中一个令人感兴趣的现象是入射光的反射率对外场导致的微小能级移动十分敏感 (这一现象是通常的表面等离子体共振系统所不具有的). 由于能级移动依赖于外场, 所以最终入射光的反射率对外场具有灵敏的响应. 本文以外磁场导致能级移动的情况进行了理论计算, 结果表明, 这种表面等离子体共振系统的入射光的反射率对外加磁场极其敏感. 这一特性可以用来测量物质表面附近的微弱磁场, 有可能发展成为一种新型检测技术.     

Radiation hardness of gas discharge tubes and avalanche diodes used for transient voltage suppression

The widespread use of gas discharge tubes (GDTs) and avalanche diodes for transient voltage suppression (TVS) in many cases results in their exposure to ionizing radiation. The aim of this paper is to investigate the influence of irradiation on these TVS devices’ characteristics, by exposing them to a combined neutron/gamma radiation field. Experimental results show that irradiation of TVS diodes causes a lasting degradation of their protective characteristics. On the other hand, GDTs exhibit a temporary change of performance. The observed effects are presented with the accompanying theoretical interpretations, based on the interaction of radiation with materials constituting the investigated devices.     

Homogenization of the layered medium equation

A new partial differential equation to be called the layered medium equation is introduced, and it is proved that certain relevant initial or periodic boundary conditions give well-posed problems. Then, the homogenized limit of the layered medium equation is studied. It is shown to be preserved in limit in the limit in the physical problem in which the coefficients that arise from the dielectric layer are both proportional to thickness. Otherwise, a non-local problem is obtained as the limiting form     

A porous medium equation with nonlocal boundary condition and a localized source

This article studies the blow-up properties of solutions to a porous medium equation with nonlocal boundary condition and a general localized source. Conditions for the existence of global or blow-up solutions are obtained. Moreover, it is proved that the unique solution has global blow-up property whenever blow-up occurs. Blow-up rate estimates are also obtained for some special cases.     

Controlled diffusions in a random medium

Using homogenization theory we treat the problem of controlled diffusions in a random medium with rapidly varying composition. This involves homogenization of a nonlinear Bellman dynamic programming equation wtih rapidly varying random coefficients. The appropriate "averaged form" of this equation is derived to define the limiting contrl problem; and a precise convergence result is given     

Critical Homogenization of SDEs Driven by a Levy Process in Random Medium

We are concerned with homogenization of stochastic differential equations (SDE) with stationary coefficients driven by Poisson random measures and Brownian motions in the critical case, that is, when the limiting equation admits both a Brownian part as well as a pure jump part. We state an annealed convergence theorem. This problem is deeply connected with homogenization of integral partial differential equations.     

Enhancing the performance of thin film CdS/PbS photovoltaic solar cells

This work investigates dependence of the short-circuit current density, open-circuit voltage, fill factor and efficiency of a thin film CdS/PbS solar cell on thickness of transparent conductive oxide (TCO) layer, thickness of window layer (CdS), concentration of uncompensated acceptors (width of space-charge region), carrier lifetime in PbS and the reflectivity from metallic back contact. The effect of optical losses, front and rear recombination losses as well as the recombination losses on space-charge region are also considered in this study. As a result, by thinning the front contact layer indium tin oxide from 400 to 100 nm and window layer (CdS) from 200 to 100 nm it is possible to reduce the optical losses from 32 to 20%. The effect of electron lifetime on the internal and external quantum efficiency can be neglected at high width of the space-charge region. The maximum current density of 18.4 mA/cm² is achieved at wide space-charge region (concentration of uncompensated acceptors = 10¹⁵ cm^?3) and the longest lifetime (τ_n = 10^?6 s) where the optical and recombination losses are about 55%. The maximum efficiency of 5.17%, maximum open-circuit voltage of 417 mV and approximately fixed fill factor of 74% are yielded at optimum conditions such as: electron lifetime = 10^?6 s; concentration of uncompensated acceptors = 10¹⁶ cm^?3; thickness of TCO = 100 nm; thickness of CdS = 100 nm; velocity of surface and rear recombination = 10⁷ cm/s and thickness of absorber layer = 3 μm. When the reflectance from the back contact is 100%, the cell parameters improve and the cell efficiency records a value of 6.1% under the above conditions.     

Application of an electrostatically actuated cantilevered carbon nanotube with an attached mass as a bio-mass sensor

In the present paper, another latent capability of SWCNT as a mass sensor is investigated. The relationship between the resonant frequency, dynamic pull-in voltage at the resonance frequency shift, and the attached mass is established by using the nonlocal Euler–Bernoulli beam theory. Using this relationship, a general closed-form nonlinear sensor-equation has been derived for the detection of the mass attached to the SWCNT. The aim of this study and present model is to show the sensitivity of the Cantilevered SWCNT to the values and positions of attached mass. Moreover, the results indicate that by increasing the value of attached mass and considering a single non-local scaling parameter (e₀), the values of dynamic pull-in voltage at the resonance frequency shift are decreased. Because of the small scaling parameter (e₀), the mass sensitivity of carbon nanotube increases, when the position of the attached mass is in the tip of a Cantilevered SWCNT length. The authority and the accuracy of these formulas are examined with other pull-in sensor equations in literatures. The results demonstrate that the new sensor equation can be applied for CNT-based mass sensors with rational accuracy.