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11.
Influence of AlN buffer layer thickness on structural properties of GaN epilayer grown on Si (111) substrate with AlGaN interlayer
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We present the growth of GaN epilayer on Si (111)
substrate with a single AlGaN interlayer sandwiched between the GaN
epilayer and AlN buffer layer by using the metalorganic chemical
vapour deposition. The influence of the AlN buffer layer thickness
on structural properties of the GaN epilayer has been investigated
by scanning electron microscopy, atomic force microscopy, optical
microscopy and high-resolution x-ray diffraction. It is found that
an AlN buffer layer with the appropriate thickness plays an important
role in increasing compressive strain and improving crystal quality
during the growth of AlGaN interlayer, which can introduce a more
compressive strain into the subsequent grown GaN layer, and
reduce the crack density and threading dislocation density in GaN
film. 相似文献
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评分函数是Vague集多准则决策过程中影响决策结果的一个重要因素.针对模糊环境下多准则决策问题,首先,指出现有文献所构造的评分函数的缺陷.其次,在整合前人工作的基础上,为同时兼顾真、假隶属度的绝对差距和未知度对决策结果的贡献,提出了一种新的评分函数,有效地解决了决策结果与直觉判断不符的问题,并在多方案的评分函数值相等时,给出了合理的决策规则,为决策者做出科学决策提供了一种方便有效的方法.最后,通过实例阐明新评分函数的有效性和优越性. 相似文献
15.
血管介入手术训练系统是利用虚拟现实技术帮助医生学员快速、高效、低成本地掌握血管介入手术技能的训练系统。由于国外商业产品存在较高技术壁垒且我国对本课题的研究起步较晚,导致系统存在血管形变仿真缺失、力反馈计算方法简单等诸多不足。针对这些问题研发了一套血管介入手术虚拟训练系统,实现了系统的血管与导丝柔性形变、血管碰撞检测、力反馈计算与导丝运动控制等功能。分别基于张量有限元和杆单元有限元构建了血管和导丝的物理模拟模型;研究了血管与导丝模型的碰撞检测方法;通过导丝前端碰撞模型与血管壁碰撞模型间的接触面积构造非线性力学方程,提出了非线性力反馈计算方法。实验结果表明,系统中血管张量有限元物理模型具有良好的柔性形变效果,为系统提供了较好的视觉反馈信息;非线性力反馈计算方法更好的模拟了导丝与血管间作用力的特性;系统实现了手术训练功能,并具有良好的实时性。 相似文献
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In this paper we propose a new method for measuring the thickness of the GaN epilayer, by using the ratio of the integrated intensity of the GaN epilayer X-ray diffraction peaks to that of the sapphire substrate ones. This ratio shows a linear dependence on the GaN epilayer thickness up to 2 μm. The new method is more accurate and convenient than those of using the relationship between the integrated intensity of GaN epilayer diffraction peaks and the GaN thickness. Besides, it can eliminate the absorption effect of the GaN epilayer. 相似文献
18.
针对现有海底地声参数估计方法的不足,提出了利用相控参量阵浅地层剖面仪接收的多角度海底反向散射信号进行地声参数估计的方法,首先利用正下方和斜入射方向上沉积层上、下表面的差频反向散射信号进行沉积层厚度和声速估计,然后利用正下方沉积层上、下表面两个不同频率的差频信号的反向散射信号估计沉积层衰减系数,最后利用正下方沉积层上表面原频反向散射信号估计沉积层阻抗,计算沉积层密度从而解决和声速的耦合性,通过水池试验验证了该方法的有效性。 相似文献
19.
Ergodic stationary distribution of a stochastic rumor propagation model with general incidence function
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Yuhuai Zhang 《中国物理 B》2022,31(6):60202-060202
In daily lives, when emergencies occur, rumors will spread widely on the internet. However, it is quite difficult for the netizens to distinguish the truth of the information. The main reasons are the uncertainty of netizens' behavior and attitude, which make the transmission rates of these information among social network groups be not fixed. In this paper, we propose a stochastic rumor propagation model with general incidence function. The model can be described by a stochastic differential equation. Applying the Khasminskii method via a suitable construction of Lyapunov function, we first prove the existence of a unique solution for the stochastic model with probability one. Then we show the existence of a unique ergodic stationary distribution of the rumor model, which exhibits the ergodicity. We also provide some numerical simulations to support our theoretical results. The numerical results give us some possible methods to control rumor propagation. Firstly, increasing noise intensity can effectively reduce rumor propagation when $\widehat{\mathcal{R}}$0>1. That is, after rumors spread widely on social network platforms, government intervention and authoritative media coverage will interfere with netizens' opinions, thus reducing the degree of rumor propagation. Secondly, speed up the rumor refutation, intensify efforts to refute rumors, and improve the scientific quality of netizen (i.e., increase the value of β and decrease the value of α and γ), which can effectively curb the rumor propagation. 相似文献
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