云安全研究进展综述

 随着云计算在学术界和工业界的兴起,云计算也不可避免的带来了一些安全问题.本文对云计算的安全需求进行了总结,指出云计算不仅在机密性、数据完整性、访问控制和身份认证等传统安全性上存在需求,而且在可信性、配置安全性、虚拟机安全性等方面具有新的安全需求.我们对云计算的两个典型产品Amazon Web Services和Windows Azure的安全状况进行了总结,并阐述了针对云计算的拒绝服务攻击和旁通道攻击.基于云计算的安全需求和面临的攻击,对现有安全机制进行了优缺点分析,系统的总结了现有的安全机制.     

媒体信息技术在中小学体育教学中的运用

随着我国教育体制改革的不断进步,各大中小学在各个学科的教学过程中也取得了重要的成就。中小学阶段作为整个人生教育的初级阶段,对学生的今后成长和发展具有重要的影响。伴随着媒体信息技术的发展为我国中小学的教学提供了多种多样的教学工具。体育课程的开设对中小学生的体质塑造和发展发挥了重要的作用。因此,笔者在文中针对我国中小学阶段体育教学中存在的问题进行了简单地阐述,并对媒体信息技术在教学中的优势以及应用进行了详细地探讨,希望为我国中小学体育教学提供一定的指导意义和借鉴意义。     

氩离子激光泵浦的掺钛宝石激光器研究

本文报导用氩离子激光连续泵浦的掺钛宝石(Ti~(3+),Al_2O_3)可调谐固体激光器的实验结果。泵浦光为全谱线,基模,激光器采用消象散的折叠谐振腔结构,获得基模激光输出功率0.67W,效率大于10.8％,可调谐范围为735nm～900nm。     

新型陶瓷刀具材料JX－2－I界面结构的实验研究

利用ＴＥＭ和电子衍射图谱分析，研究了新型陶瓷刀具材料ＪＸ－２－Ｉ的界面微观结构。ＴＥＭ分析表明，ＪＸ－２－Ｉ刀具材料的界面结合状态较好，Ａｌ＿２Ｏ＿３／ＳｉＣｗ界面上形成了具有较高强度的“钢筋混凝土”结构，在Ａｌ＿２Ｏ＿３／ＳｉＣｗ和Ａｌ＿２Ｏ＿３／ＳｉＣｐ界面上没有剧烈的化学反应发生；通过ＴＥＭ和电子衍射图分析，发现在Ａｌ＿２Ｏ＿３的晶粒边界上有尖晶石（ＭｇＡｌ＿２Ｏ＿４）生成，这有利于控制Ａｌ＿２Ｏ＿３晶粒的长大，提高复合材料的强度。     

一种新型LED发光矩阵测试系统

由于ＬＥＤ信息显示屏快速发展的需要，一种新颖的ＬＥＤ发光矩阵测试系统已研制成功。它采用微机技术和具有ＣＩＥ标准观察者曲线光谱响应的多通道光电检测系统。能测试各种ＬＥＤ发光矩阵每个发光元的发光强度，正向压降和反向电流。测试数据显示在计算机显示屏和存在计算机内存中。     

工业级卡托辛成分分析及其双核二茂铁制备工艺

2,2-双(乙基二茂铁)丙烷(卡托辛)因其优异的催化活性和制药工艺性,成为当前复合固体推进剂中主要的燃速催化剂之一.由于卡托辛合成工艺复杂,工业级产品成分也很复杂,使得其相关产品的性能难以得到保证.利用气相色谱-质谱联用技术和高效液相色谱技术,对工业级卡托辛的成分进行了分析;依据各成分结构特性及其极性、溶解度差异,通过...     

Experimental investigation of propagation mechanisms and fracture morphology for coalbed methane reservoirs

Fracture propagation mechanisms in coalbed methane (CBM) reservoirs are very complex due to the development of the internal cleat system. In this paper, the characteristics of initiation and propagation of hydraulic fractures in coal specimens at different angles between the face cleat and the maximum horizontal principal stress were investigated with hydraulic fracturing tests. The results indicate that the interactions between the hydraulic fractures and the cleat system have a major effect on fracture networks. “Step-like” fractures were formed in most experiments due to the existence of discontinuous butt cleats. The hydraulic fractures were more likely to divert or propagate along the butt cleat with an increase in the angles and a decrease in the horizontal principal stress difference. An increase in the injection rate and a decrease in the fracturing fluid viscosity were more conducive to fracture networks. In addition, the influence on fracture propagation of the residual coal fines in the wellbore was also studied. The existence of coal fines was an obstacle in fracturing, and no effective connection can be formed between fractures. The experimental investigation revealed the fracture propagation mechanisms and can provide guidance for hydraulic fracturing design of CBM reservoirs.     

Sequential packing algorithm for channel assignment under cochanneland adjacent-channel interference constraint

Generally, the channel-assignment problem (CAP) for mobile cellular systems is solved by graph-coloring algorithms. These algorithms, though sometimes can yield an optimal solution, do not supply any information on whether an optimal solution has been found or bow far away it is from the optimum. In view of these undesirable features, two relevant results are presented. First, a lower bound for the minimum number of channels required to satisfy a given call-traffic demand is derived. This lower bound is tighter than the existing ones under certain conditions and can be used as a supplement for other approximate algorithms. Second, we propose an efficient heuristic algorithm to solve this problem. Although the CAP is nondeterministic polynomial (NP) complete in general, our algorithm provides an optimal solution for a special class of network topologies. For the general case, promising results are obtained, and numerical examples show that our algorithm has a better performance than many existing algorithms     

Ion implantation doping of OMCVD grown GaN

Doping by ion implantation using Si, O, Mg, and Ca has been studied in single crystal semi-insulating and n-type GaN grown on a-sapphire substrates. The n-and p-type dopants used in this study are Si and O; Mg and Ca, respectively. Room temperature activation of Si and O donors has been achieved after 1150°C annealing for 120 s. The activation of Mg and Ca acceptors is too low to measure at both room temperature and 300°C. Using higher doses to achieve a measurable p-type conduction increases the amount of damage created by the implantation. Rutherford back scattering measurements on this material indicate that the damage is still present even after the maximum possible heat treatment. Secondary ion mass spectrometry measurements have indicated a redistribution in the measured profiles of Mg due to annealing.     

Al2O3／TiB2和Al2O3／TiB2／SiCW陶瓷材料氧化层的显微结构分析

用Ｘ射线衍射，扫描电子显微镜和透射电镜／能谱仪分析了Ａｌ２Ｏ３／ＴｉＢ２和Ａｌ２Ｏ３／ＴｉＢ２／ＳｉＣＷ陶瓷材料在１３００℃氧化３０小时后氧化层的相组成及显著结构。