Combinatorial auction-based allocation of virtual machine instances in clouds

Most of the current cloud computing providers allocate virtual machine instances to their users through fixed-price allocation mechanisms. We argue that combinatorial auction-based allocation mechanisms are especially efficient over the fixed-price mechanisms since the virtual machine instances are assigned to users having the highest valuation. We formulate the problem of virtual machine allocation in clouds as a combinatorial auction problem and propose two mechanisms to solve it. The proposed mechanisms are extensions of two existing combinatorial auction mechanisms. We perform extensive simulation experiments to compare the two proposed combinatorial auction-based mechanisms with the currently used fixed-price allocation mechanism. Our experiments reveal that the combinatorial auction-based mechanisms can significantly improve the allocation efficiency while generating higher revenue for the cloud providers.     

Java中的Abstract Class与Interface技术研究

Abstract class和Interface是Java语言中对于抽象类定义进行支持的两种机制,正是由于这两种机制的存在,才赋予了Java强大的面向对象能力。Abstract class和Interface之间在对于抽象类定义的支持方面具有很大的相似性,因此很多开发者在进行抽象类定义时对于Abstract class和Interface的选择显得比较随意。但是,两者之间的区别还是很大的。文中从两者的定义、程序编辑、设计意图3个方面加以了比较。由此,对于它们的选择,反映出对于问题领域本质的理解和对于设计意图的理解是否正确、合理。     

摇杆式移动机器人的齿轮式差动机构研究

为了使差动机构在摇杆式移动机器人上得到更好的应用,分析了摇杆式移动机器人差动机构的作用和特征;它可以将两摇杆的转角线性平均为机器人的车体转角．在此基础上,提出了6种齿轮式差动机构,包括ZUWGW型、NW型、DW型、WW型、NGWW型等5种2K-H行星齿轮机构和1种由两个NGW型2K-H行星齿轮机构组成的差动机构．分析了各机构的工作原理和特点,推导出了各差动机构的实现条件,并为其中的ZUWGW型锥齿轮式差动机构和NGWW型行星齿轮相互啮合式差动机构提供了详细的结构设计实例．     

一种可信的网上银行认证协议的分析与设计

随着电子支付的普及,安全问题成为了影响其发展的关键问题之一。可信计算平台、PKI认证系统都是保证安全的有效机制。在分析这两种安全机制的基础上,提出了一种结合可信平台和PKI认证系统的网上银行认证协议,通过可信平台模块TPM保证了参与方的计算平台可信性,使用PKI系统和智能卡对银行、持卡人、读卡器进行了身份认证,完成了认证过程,达到安全可信的认证目的。     

Research into two source-based control algorithms for Internet traffic flows

TCP and UDP are the major applications over the Internet, the characteristics of them lead to different network transmission behaviors. Two source-based mechanisms are proposed in this paper to regulate TCP and UDP flows. One is the congestion control mechanism, which uses TCP flows’ congestion signal to regulate the flows at the source node. The other is the time slot mechanism, which is a time-sharing application to control their flow transmission. Based on the priorities of flows, different bandwidth proportions are allocated and differential services are provided for flows. Several scenarios are simulated to observe the transmission operations of these two mechanisms. Simulation results show some insights into two mechanisms. Moreover, the several simulation parameters that may impact the performance of these two mechanisms are summarized.     

PKI信任机制及在信任模型中的应用

描述了四种PKI信任机制,对它们的功能和特点进行了讨论;对这些机制如何和CA配置形成层次式和桥式信任模型进行了分析,并对这两种信任模型的特性进行了比较.     

Java抽象类和接口解析

在Java语言中,abstract class和interface是支持抽象类定义的两种机制。正是由于这两种机制的存在,才赋予了Java强大的面向对象能力。本文对抽象类和接口的区别与联系进行了深入解析。     

Multidisciplinary design optimization of mechanisms

The optimization of mechanisms is usually done in the field of mechanism itself. As a result the structural safety of the mechanism is neglected. To ensure the safety and improve the dynamic characteristics of mechanisms, a multidisciplinary design optimization procedure is proposed in this paper to synthesize optimum mechanisms. Two disciplines are involved in the multidisciplinary design optimization. They are the mechanism and the structure. The multi-level decomposition approach is chosen to generate optimum mechanisms. The optimized mechanisms not only satisfy mechanism and structural constraints but also have optimum objective function values in the two disciplines. In order to solve general mechanism design problems two widely used commercial softwares MSC/NASTRAN and MSC/ADAMS are integrated in the procedure to do the structural and the mechanism analysis, respectively. When the structural optimization is performed, a compromised approach is introduced to treat multiple configurations of mechanisms during operation. Two mechanism design problems are given to test the proposed method.     

IPv4/IPv6互通技术

IPv4向IPv6过渡的基本技术包括双协议栈、隧道技术和NAT-PT技术。基于这三种技术派生出多种互通和转换机制。这些机制分为两类,一类是实现IPv4海洋中的IPv6节点之间的通信;一类是IPv6小岛与Ipv4海洋之间的通信。该文对这些实现机制进行了具体分析和比较。     

信息网络对抗机制的攻防分析

攻击和防御是对抗的两个基本方面。本文首先对信息网络的对抗机制进行了归纳分类,然后讨论了各种信息网络防御机制,重点分析了不同防御机制中所存在的脆弱性,并提出了相应的攻击机制。最后,对当前信息网络对抗机制间的攻防关系进行了总结。