基于校园私有云的实训教学环境的应用研究

针对高职院校现有的计算机实训室中,计算机实训机房管理中的资源分配复杂、利用不高、运维成本高等问题,采取基于校园私有云的方式来构建实训教学环境,使得实训教学环境高可用、自动交付.最后通过效果分析,验证所构建的环境平台是可行和有效的.     

Distributed Contention-Aware Call Admission Control for IEEE 802.11 Multi-Radio Multi-Rate Multi-Channel Wireless Mesh Networks

In this paper, we focus on call admission control (CAC) in IEEE 802.11 multi-radio multi-rate multi-channel (MR²-MC) wireless mesh networks (WMNs). CAC is the key component of QoS routing protocols. The goal of CAC is to protect existing flows from QoS violations and fully utilize available radio resource on channels. We propose a CAC mechanism, called Contention-Aware Multi-channel Call Admission Control (CMC), for MR²-MC WMNs based on IEEE 802.11 DCF. CMC is fully distributed, relies on local information to estimate the residual bandwidth of a path, and can be integrated into existing routing protocols for MR²-MC WMNs to provide QoS. We evaluate the performance of CMC via ns-2 simulations. The results show that CMC can precisely predict the end-to-end residual bandwidths of paths, successfully protects existing flows from QoS violations, and fully utilizes the bandwidths on channels.     

Secure Communications System Through Concurrent AJ and LPD Evaluation

In this paper, a systematic approach and their corresponding metrics for concurrent anti-jamming (AJ) and low probability of detection (LPD) performance evaluations of a secure communications system are investigated. In general, it is necessary to deal simultaneously with adversary threats of both active jamming and passive detection for a secure communications system concern. For independent or concurrent AJ and LPD performance evaluations, a single varying paired and multiple paired fixed collocated jammers/interceptors scenario is explored with real sinc type (sin(x)/x) antenna patterns being considered for the communicators. The error probability with both AJ and LPD being considered simultaneously can be derived as system- and geometry-dependent factors and categorized as system metrics related to jammers, interceptors, and communicators themselves only. Whenever multiple collocated jammers/interceptors are considered, we can observe interesting “smoothed” effects for bit energy to jamming density ratio (E _b /J _o ), when one of these varying jammers/interceptors is approaching or receding. In addition, by means of these system metrics, it is intuitive and straightforward to enhance system performance for the victim or to deteriorate system performance for the adversary, respectively. Moreover, the proposed approach and metrics have also paved one practical way for the developments of the latest emphasized cognitive radio (CR) communications systems, if all the collocated jammers/interceptors on the proposed scenario are replaced with “cooperative” communicators.

Structural and optical properties of (Al,K)-co-doped ZnO thin films deposited by a sol–gel technique

Thin films of Al-doped ZnO (AZO) and (Al, K)-co-doped ZnO (AKZO) were synthesized by sol–gel spin coating and their structural and optical properties were investigated. All the films had a preferential orientation in which the c-axis was perpendicular to the substrate. The optical bandgap increased after Al doping, but decreased after K doping at a given Al doping concentration. UV emission and a broad visible emission band were observed in photoluminescence (PL) spectra. The intensity of both emission bands decreased after Al and K co-doping. PL excitation (PLE) spectra of the blue emission band indicate that the initial state is possibly the same for all the samples and a similar case occurs for the orange–red emission band. The green emission can be attributed to electronic transitions involving oxygen vacancies. A possible process for the orange–red emission of the thin films is radiative recombination of an electron trapped in a zinc interstitial defect with a hole deeply trapped in interstitial oxygen.     

基于代理方式的私网穿越技术的研究及改进

本文从常见的私网穿越问题解决方案入手,重点分析了基于代理方式的私网穿越问题,提出了在SIP(Session Initiation Protocol)控制下的基于RTP(Real-time Transport Protocol)报文预发送机制的代理方式私网穿越改进方案.     

梯度折射率纤维端面耦合成像元件的设计

根据抛物型梯度折射率纤维透镜的近轴成像公式,分析了具有一定缩放倍率的梯度折射率纤维端面耦合成像的特性,探讨了这种纤维端面耦合成像元件的设计。     

On clutter dof for phased array airborne early warning radars

In recent years, considerable attention has been paid to adaptive clutter suppression for airborne early warning (AEW) radars. A necessary condition for efficient clutter suppression is that the number of adaptive degrees of freedom (DOF) is no less than that of clutter DOF. This paper analyzes the DOF of clutter for phased array AEW radars. The new results obtained here are helpful to design and adaptive system for clutter suppression.     

64位声表面波可编程抽头延迟线

本文叙述了一种64位声表面波可编程抽头延迟线的结构及性能参数,采用专门设计的有源三极管作开关阵列单元,获得一个时钟速率大于1MHz,可编程速率为15kbit/s的器件。该器件性能基本满足系统实验要求,但在稳定性及波形一致性方面有待进一步提高。     

Performance of SBR-Modified Asphalt Yufeng Cong

A dose of SBR modifier added to asphalt can improve asphalt's performance in stability, permanence, viscosity, and resistance to aging. Better application performances of asphalt pavement are affected directly by proper SBR modifying. This paper shows some investigations that confirm the relationship between the addition of SBR with the structure and the properties of SBR-modified asphalt. This paper also discusses the modified asphalt high temperature property, low temperature ductility, and mechanism of SBR-modified asphalt. The addition of SBR modifier showed an increase in viscosity, softening point, and elastic recovery of modified asphalt with rising temperature. When the temperature rises, the improvement of SBR-modified asphalt in softening point, elastic recovery, and visco-toughness result from SBR cross-linking. Although the lengths of low temperature ductility of SBR-modified asphalt are increased, the viscosities of modified asphalt increase; however, the softening point between the upper layer and lower layer were about 1.8°C after the isolated experiment.     

Corporate R&D strategy portfolio in Japanese and Australiantechnology-based firms: an empirical study

This paper presents an empirical study on the strategic structure of corporate R&D in Japanese and Australian technology-based companies. The perceived importance and distribution of basic research, precompetitive strategic research and applied research within a corporate R&D portfolio are examined through a comparative analysis of survey data. The results suggest that Japanese firms tend to place great emphasis on basic and precompetitive strategic research, although applied research still retains its importance. They recognize that basic research is critical to achieve long-term competitive advantages in the marketplace. Australian firms also realize the importance of basic research and the use of portfolio approach in R&D management. However, research work in Australian firms tends to focus on applied research with only a limited involvement in medium- and long-term research. Finally, it is concluded that Japanese firms utilize a portfolio approach to corporate R&D management more systematically than do their Australian counterparts