本科毕业设计的管理及问题分析

针对本科毕业设计中存在的毕业设计选题不当,指导教师职责不规范,论文质量不高等现象,文章分析其存在原因,介绍了本科毕业设计的管理中需要注意的各个环节以及可能出现的问题,并提出问题的解决方法。     

一种支持通用θ-Join的并行查询处理机制

并行查询处理,特别是并行连接查询处理技术是并行数据库中的关键技术.然而,目前的并行查询处理方法尚存在着一些局限性,如绝大多数的并行Join算法依赖于Hash方法对数据进行分治,因此只能支持等值Join等查询类型.为了解决这一问题,提出了一种基于伪半连接的通用θ-Join查询处理算法,并给出了基于查询语法树及并行执行计划的并行数据库通用查询处理方法.在此基础上,实现了一个并行分布式数据库原型系统PD-DBMS,实验结果表明,此方法提供了良好的并行查询处理性能.     

企业VOIP数据安全解决途径的探讨与实践

多媒体应用与企业传统网络结合使得VOIP技术迅猛发展,VOIP成为现在以及未来会成为话音的主流技术。针对企业VOIP应用的攻击日渐繁多。顾名思义,VOIP与运行在IP网络上的其他基于IP的应用,如网页浏览(web)和电子邮件(email)一样有着共同的安全威胁和弱点,包括所有的来自IP网络层的威胁。网管人员和邮件系统管理员迫切需要解决这些威胁还包括标准网络安全技术和优秀的网络设计试图解决的问题。本文主要就如何通过采取一个仔细规划的、多层次的VoIP网络防护措施让VOIP数据高枕无忧以及除了这些网络层的若干威胁外,VOIP应用还需要面对一系列的协议和应用特有的威胁和一系列内容相关的威胁做一些讨论。     

An adaptive signal-to-noise ratio estimator in mobile communication channels

Representing the reception condition directly, signal-to-noise ratio (SNR) is an important parameter in mobile propagation channels, and therefore is widely used in system performance evaluations and adaptive applications. Hence, this paper puts forward a frequency domain SNR estimator in mobile communications, where we exploit the signal model with the band-limited fading channel and the additive white Gaussian noise. With the above model, the noise power spectrum density can be estimated from the periodogram of channel-plus-noise signals, subsequently leading to our SNR estimation. Moreover, in order to degrade the intrinsic spectrum leakage of fast Fourier transform in periodogram calculation, the leakage expression is derived analytically and then an adaptive process is proposed to make a tradeoff between leakage reduction and noise smoothing. We verify our algorithm by simulations and observe high accuracy in a wide range of velocities and SNRs. Additionally, unlike the conventional work, the proposed estimator is not strictly based on the assumption of specific Doppler spectral shapes except for the requirement of the band-limited channel, hence it is robust to general mobile channels.     

A novel digital filter structure with minimum roundoff noise

In this paper, a novel structure is derived for efficient implementation of digital filters as well as minimizing the finite word length (FWL) errors. Such a structure is actually an improved version of that reported previously. The performance of this new structure and the famous normalized lattice structure are analyzed by deriving the corresponding expression for the roundoff noise gain. Design examples are presented to illustrate the behavior of the proposed structure and to compare it with some existing ones. It is shown that the proposed structure outperforms the others in terms of minimizing roundoff noise as well as implementation efficiency.     

电离层垂测仪系统信号源设计与实现

为了克服传统电离层垂测仪射频信号软件延时的缺点,提高大气电离层垂测仪系统信号源产生信号的精度,更充分地研究电离层物理特性,利用DDS技术和嵌入μC/OS-Ⅱ操作系统的miniARM微处理器,给出了一个新型的电离层垂测仪系统信号源的架构方案;该系统利用了32位ARM嵌入式微处理器LPC2220的定时器匹配硬件功能,控制DDS芯片Q2368完成无延时的相位调制;实验结果表明,该信号源所产生的高频信号具有精度高,频率转换时间短等特点,其他信号也完全满足电离层垂测仪对信号源的技术要求.     

Robust design of feedback integrated with iterative learning control for batch processes with uncertainties and interval time-varying delays

A robust feedback integrated with iterative learning control (FILC) scheme for batch processes with uncertain perturbations and interval time-varying delay is developed. The batch process is modeled as a two-dimensional (2D) Rosser system with a delay varying in a range. The design of FILC scheme is transformed into a robust control problem of uncertain 2D system. New delay-range-dependent stability criteria and stabilization conditions are derived in terms of linear matrix inequalities (LMIs), which depend on not only the difference between the upper and lower delay bounds but also the upper delay bound of the interval time-varying delay. Parameterized characterizations for stabilizing the controller are given in terms of the feasibility solutions to the LMIs. Applications to injection velocity control show that the proposed FILC achieve the design objectives well.     

电阻抗扫描成像计算机辅助诊断方法研究

为了提高电阻抗扫描成像EISI(Electrical Impedance Scanning Imaging)在乳腺疾病检查方面的准确性,将独立分量方法(ICA)应用于EISI数据的特征提取,并结合支持向量机(SVM)进行乳腺疾病计算机辅助诊断(CAD)。实验结果表明:ICA方法所提取的特征对于乳腺疾病分类是有效的。对于良性肿瘤和恶性肿瘤的鉴别,提出的CAD方法灵敏度为74.2%,特异度为82.8%,准确度为80%。结合所提出的CAD方法和传统的EISI检查方法,可以提高EISI在乳腺疾病检查方面的可靠性,降低假阳性率,避免对良性肿瘤患者进行活检。