电磁超声检测钢板厚度实验的参数优化

为提高电磁超声检测信号的信噪比,研究激励信号频率、脉宽及换能器提离距离对厚度测量结果的影响,搭建了电磁超声实验系统。该系统利用RITEC-SNAP 5000产生高能正弦波激励电磁超声换能器EMAT ( Electromagnetic Acoustic Trans-ducer),通过调节激励信号的频率、脉宽,改变提离距离来观测超声回波幅度的变化。实验结果表明：当激励频率和EMAT固有频率相同时其换能效率最高,采用6个周期的脉冲串时前后波包之间分界明显,为获得较大的回波幅度应尽可能减小提离距离。     

一种高效强K—栅栏覆盖构建算法

K－栅栏覆盖是无线传感器网络覆盖控制的研究热点之一。本文构建了强栅栏覆盖模型,提出了分区强K－栅栏覆盖构建算法PMNSB,用最少的节点形成强栅栏。首先把监控区域分成多个子区域,通过匈牙利算法选用移动距离之和最少的网格集合为基准1－栅栏覆盖,缺少移动节点的子区域,选择附近区域的剩余移动节点修补形成1－栅栏覆盖。水平相邻的两个子区域之间构建竖直栅栏,这些1－栅栏合起来构成强K－栅栏覆盖。仿真结果证明了该方法的有效性,本文的研究对提升无线传感器网络的性能具有重要的理论与实际意义。     

基于三角模算子的RPL协议路由优化算法

针对当前低功耗有损网络拓扑构建及路径选择的参考度量单一,能量均衡性差的问题,提出了一种基于三角模算子的RPL协议路由优化算法。本文阐述了低功耗有损网络路由协议的网络拓扑构建机理和路由过程,基于三角模融合算法,重新定义了网络节点的能量指标和逻辑距离隶属度并进行了融合,更为合理地进行父节点选定,实现数据采集传输业务可靠性和有效性的进一步提升,最后通过实验仿真验证了改进后的路由协议性能。     

基于欧氏空间相似度的云模型协同过滤算法

传统的基于余弦相似度度量的云模型协同过滤推荐算法未考虑特征向量的长度和维度,忽略了三个重要数字特征云期望、熵和超熵的关系,如各数字特征具有不同的性质和权重,导致特征丢失、区分度过小的问题。针对这些问题,提出了一种采用标准化的多维欧几里德相似度计算方法,通过将三个数字特征映射为三维空间的点,计算经指数函数标准化的欧几里德相似度,生成更合理的用户k近邻集,最终产生推荐。实验结果表明,该相似度计算方法能够为云特征向量提供更显著的区分度,并在一定程度上提高了推荐质量。     

无线传感器网络分簇路由节能研究

在大规模传感和环境监测中,节约能源延长传感器节点生命已成为无线传感器网络最重要的研究课题之一。提供合理的能源消耗和改善无线网络生命周期的传感器网络系统,必须设计一种新的有效的节能方案和节能路由体系。方案采用一种聚类算法减少无线传感器网络的能量消耗,创建一种cluster-tree分簇路由结构的传感器网络。该方案主要目标是做一个理想的分簇分配,减少传感器节点之间的数据传输距离,降低传感器节点能源消耗,延长寿命。实验结果表明,该方案有效地降低了能源消耗从而延长无线传感器网络生命。     

移动终端交通动态图形化信息受信位置研究

交通动态信息图形化发布是通过对道路网抽象简化形成简易道路图形,并在此基础上发布实时路况的交通信息发布方式。在移动终端上发布图形化动态信息时,应充分考虑移动终端的可移动性以及实时在线特性,在关键的位置发布合理的图形信息,才可提高交通动态信息的识别度和提升信息诱导效果。通过分析驾驶人信息接收过程和线路的调整行为特性,研究图形化数据受信距离的设置方法,建立受信距离计算模型,给出了模型关键参数的计算方法和参考数据,从而为后期规模性图形化发布位置的布设奠定基础。     

A study of optimal viewing distance in a parallax barrier 3D display

The optimal viewing distance was proposed as a parameter for designing a parallax barrier 3D display. It can be designed based on simple geometric method and by considering the pitches of image display pixels and parallax barrier, or even including the aperture ratios of the image display pixels and parallax barrier. It can be analyzed by using ray tracing method. By considering the optical refraction index of the cover glass, the angular behavior of the system becomes more realistic; however, the geometric method is difficult to be used. We propose a revised method for estimating the view distance and angular behavior. In this paper, we have demonstrated a designated eye position (DEP) for each view and shown that multiple DEPs make a circular curve around the center of the display. We prove the new concept by comparing the optical ray tracing calculations and optical measurement.     

A Review of “What They Don’t Teach You in Library School”

SUMMARY

Distance learning students may not think of the “campus” library as the first place to fulfill their information needs and may not even be aware of the services available to them. One way to reach these students is to adopt and adapt marketing techniques from the business world. This article examines the findings of a survey conducted at Emporia State University concerning the awareness of distance learning services. It will also examine marketing techniques and illustrate how they can be applied to increase awareness of reference support services for distance learners.     

The Buck Stops Where?

SUMMARY

University students-whether adult, distance learner, or traditional age-need access to university services and quick accurate answers to their questions beyond traditional “business” hours. Students' busy schedules and changing life patterns dictate that university services meet their needs. At DePaul University in Chicago, student focus groups repeatedly pointed to the need for one central place to get an answer or solve a problem. DePaul Central was created as an information and referral service to satisfy that student need, at the same capitalizing on the value of the librarian skill set.     

Using Courseware Discussion Boards to Engage Graduate Students in Online Library Workshops

ABSTRACT

Librarians at Oregon State University (OSU) Libraries used the discussion board features of Blackboard courseware to create an interactive experience for graduate students at a distance who could not attend the on-campus “Literature Review Workshops.” These recently developed workshops have been extremely popular with graduate students across the disciplines and have generated a growing demand from distance education graduate students and faculty to offer similar information online. Reluctant to simply deliver content via an online tutorial, librarians sought to duplicate the workshop atmosphere by making the sessions available for a short time-period online, asking participants to respond to discussion questions at specific points in the workshop, and offering audio-mediated online demonstrations of tools and resources. Student feedback and follow-up requests for more workshops support the perception that this approach offered a rewarding learning experience that addressed their specific adult learning needs.