基于OPNET的无线传感器网络MAC协议研究

在无线传感器网络中,MAC协议是网络高效通信的重要保证。本文利用OPNET仿真平台,对低速无线个域网(LR-WPAN)中IEEE802.15.4的MAC协议的超帧结构和时隙保障(GTS)机制进行研究。仿真实验中构建了小型星型网络,能更清楚地反映网络中的平均能量消耗情况,并通过设置不同的仿真场景,说明了GTS机制能有效节省电源能量,为大型无线传感器网络的设计提供了重要依据。     

一种基于超时机制的分簇无线传感器网络MAC协议

首先分析了基于簇的TDMA机制,针对其存在的问题,提出了一个基于超时机制的分簇的MAC协议(TC-MAC)。该协议为每个时隙分配了一个超时时间#来减少传感器节点的空闲侦听,避免能量的浪费。仿真结果显示,TC-MAC协议能有效地延长无线传感器网络的生存周期,提高网络能量的有效性。     

WSN中一种能量均衡的分簇路由协议的设计

无线传感器网络中,LEACH协议是典型的分簇路由协议.文章针对LEACH协议的缺点,结合PEGASIS协议的优点,从簇首选择、簇的形成、簇间路由等方面对LEACH协议进行了改进,设计了一种能量均衡的分簇路由协议EBLP,并进行了仿真分析.仿真结果表明,EBLP协议节约了能量,平衡了能量消耗,延长了无线传感器网络的生存时间.     

基于能耗均衡的LEACH-DC协议的设计

为了解决LEACH协议无法控制簇首位置和簇首选择方式而导致能量消耗太大的缺点,提出了以非均匀分簇和双簇头路由作为改进方法的一种基于能耗均衡的LEACH-DC协议.对改进的LEACH-DC协议使用NS2进行了仿真实验,仿真实验结果表明,改进后的路由协议在网络总能耗以及数据传送量等方面均得到明显改进,从而均衡了无线传感器的网络能耗,延长了网络生命周期.     

一种新的基于簇头优化的WSN路由协议

在无线传感器网络的分簇路由协议中,低功耗自适应分簇(Low Energy Adaptive Clustering Hierarchy)算法是其中比较流行的协议之一.文章根据Leach协议提出了一种新型的簇头选举算法LEACH-NOC(New Optimal Cluster),其簇头选举采用两个步骤,首先通过LEACH分簇的思想,将网络分成若干个簇,然后在簇内重新选择簇首时使其尽量靠近簇的质心且能量大于该簇内剩余节点的平均值.MATLAB仿真结果显示,改进的协议能够具有更好的能量有效性,延长了第一个节点簇头死亡(FND)的时间.     

一种基于簇的无线传感器网MAC协议

MAC协议对无线传感网络的运行和性能具有重要的影响。为此,分析了基于簇的无线传感器网络的MAC协议,针对它们存在的缺陷,提出了一种新的基于簇的MAC协议(C-MAC)。该协议能够根据簇成员节点数目和通信负载动态地改变TDMA帧的长度,减少节点的空闲侦听时间,提高信道的利用率,从而延长网络的生命周期。模拟结果显示,该协议在数据包延迟、能量消耗和数据包接收率等性能上有很大提高。     

基于能量约束的LEACH分簇协议的改进与仿真

对现有的LEACH协议进行改进,在局部簇中得出簇内节点的平均能量基础上,使簇头满足一定的能量约束,建立了能量参考模型,给出了正确性与复杂性分析,并在NS2平台下对改进后的协议进行了仿真实验和分析.仿真结果表明,改进的LEACH路由协议有效地延长了无线传感器网络的生存周期,从而提高了网络性能,并对下一步改进工作作了简要介绍.     

适用于周期休眠MAC协议的分簇时间同步算法

无线传感器网络中节点能量有限,常采用周期休眠的方式工作,而周期性休眠机制的实现依赖于节点间的时间同步方法.基于竞争的周期性休眠MAC协议的典型代表是S-MAC,在S-MAC协议的时间同步算法基础上,通过引入簇控制和边界节点控制方法提出一种分簇时间同步算法,该算法适用于周期性休眠的MAC协议.仿真和物理实验表明,分簇时间同步相比S-MAC时间同步方法能够有效控制网络中的簇数和边界节点数,减少时间同步开销和端到端传输时延,从而节省能耗,延长网络生存周期.     

基于无线传感器网络LEACH协议的改进算法

基于无线传感器节点的位置信息及剩余能量,提出了一种基于LEACH协议的改进算法-PE-LEACH协议。PE—LEACH协议基于节点的位置信息进行分簇,基于节点的剩余能量及位置信息进行簇头的选择,当簇头距离汇聚节点较远时采取中转方式传送数据。较好的平衡了网络能量负载,延长了网络的生命周期。仿真结果表明：PE—LEACH协议与LEACH协议相比,提高了网络能量的利用率,延长了节点的生命周期。     

无线传感器网络中LEACH路由算法的研究与改进

如何有效地降低节点的能耗,延长网络的生命周期,一直是无线传感器网络路由协议的研究重点.该文分析了传统的LEACH协议并总结了当前一些典型基于LEACH思想的路由改进算法,针对产生簇头个数的随机性,通过考虑节点的剩余能量、离基站的距离及曾经当选过簇头的次数等因素,提出了一种基于时间的改进算法.最后通过NS2对改进后的算法进行仿真,仿真实验结果表明,改进后的算法能较好地均衡网络中节点的能耗,有效地延长了整个网络的生命周期.     

Activity-based mass spectrometric characterization of proteases and inhibitors in human saliva

Proteases present in oral fluid effectively modulate the structure and function of some salivary proteins and have been implicated in tissue destruction in oral disease. To identify the proteases operating in the oral environment, proteins in pooled whole saliva supernatant were separated by anion-exchange chromatography and individual fractions were analyzed for proteolytic activity by zymography using salivary histatins as the enzyme substrates. Protein bands displaying proteolytic activity were particularly prominent in the 50–75 kDa region. Individual bands were excised, in-gel trypsinized and subjected to LC/ESI-MS/MS. The data obtained were searched against human, oral microbial and protease databases. A total of 13 proteases were identified all of which were of mammalian origin. Proteases detected in multiple fractions with cleavage specificities toward arginine and lysine residues, were lactotransferrin, kallikrein-1, and human airway trypsin-like protease. Unexpectedly, ten protease inhibitors were co-identified suggesting they were associated with the proteases in the same fractions. The inhibitors found most frequently were alpha-2-macroglobulin-like protein 1, alpha-1-antitrypsin, and leukocyte elastase inhibitor. Regulation of oral fluid proteolysis is highly important given that an inbalance in such activities has been correlated to a variety of pathological conditions including oral cancer.     

一种说话者识别的新方法

利用短时傅立叶变换方法对语音信号进行了分析,得到了由各个语音信号相同频率点能量序列构成的时间序列簇。运用时间序列预处理和数理统计的方法,建立了时间序列簇中每一列向量序列与由时间序列簇的每一行向量序列的均值构成的序列之间的线性回归方程。分离了时间序列簇的趋势量和波动量,提取了说话者语音信号的特征参数,并通过这些参数对被识别语音信号进行说话者识别。实验表明在8个说话者194个语音集合中,以文中描述的距离参数为识别指标、取3个特征频率点时,开集平均识别率最高为97.94%。     

基于事件的新闻报道分析技术研究进展*

首先给出基于事件的新闻报道分析技术相关概念的定义,并提出一个基于事件的新闻报道分析技术框架;然后从四个方面介绍了基于事件的新闻报道分析中的关键技术,包括事件探测、事件追踪、事件相关文档摘要和事件RSU检索.对一些关键技术进行了分类和评价,剖析其优势及不足,通过对各种方法的分析和比较,提出了一些改进的方法和建议.最后展望了未来基于事件的新闻报道分析技术的发展方向.     

A Review.of: “Man and Motor Cars: An Ergonomic Study.” By S. Black. (Seeker and Warburg, 1966.) [Pp. 373.] 63s

This study was concerned with examining driver patterns for three different sized vehicles (small cars, family cars, trucks and buses) through an intersection controlled by a traffic signal. Observations were made morning, noon and afternoon, when there was precipitation and no precipitation. Records were also kept as to whether the drivers wore alone or with passengers and whether the drivers were males or fomales. Results were found showing that family car drivers were the most cautious and that small ear, truck and bus drivers were approximately similar to each other, being less cautious. Drivers with passengers were more cautious and did not violate the law by passing a red light as frequently as did drivers without passengers. Approximately similar driving patterns were found for males and fomales. Different driving patterns were obtained for the three-sized vehicles during morning, noon and afternoon, when there was precipitation and no precipitation.     

离散混沌系统类随机性的符号熵分析法

采用符号熵分析法,分析和讨论了经典的Logistic映射和Henon映射的类随机性强弱.先将离散混沌系统产生的实数序列转化为二进制序列,然后进行编码,计算其符号熵,绘制其符号熵图,并深入讨论了系统参数和初始值对符号熵的影响.数值仿真分析表明,符号熵法能定量区别不同离散混沌系统类随机性的强弱.同时作为随机源,Logistic映射比Henon映射好.     

2011年3月份十大重要安全漏洞分析

2011年02月21日至3月20日,国家计算机网络入侵防范中心发布漏洞总条目为342条,漏洞总数比2月[1]减少了24.84。其中威胁级别为＂紧急＂的有68条,＂高＂的有110条,＂中＂的有146条,＂低＂的有18条。威胁级别为紧急和高的漏洞占到总量的52.05,从漏洞利用方式来看,远程攻击的有305条,本地攻击的有31条,局域网攻击的有6条。可见,能够从远程进行攻击的漏洞占绝大多数,这使得攻击者利用相应漏洞发动攻击更为容易。在此期间微软共发布3个安全公告,其中1个为严重等级,2个为重要等级,共修复微软媒体组件、Windows远程桌面客户端中的4个＂远程代码执行＂漏洞。在3月举行的全球黑客大赛Pwn2Own中,发现了InternetExplorer8浏览器中的两个零日漏洞以及苹果Safari浏览器中的一个代码执行漏洞。此外,Adobe也发布通告公布了FlashPlayer中存在的一个零日远程内存破坏漏洞。部分零日漏洞已经被利用进行攻击。建议广大用户及时安装补丁,增强系统安全性,做好安全防范工作,保证信息系统安全。     

Comparison of posture and muscle control pattern between male and female computer users with musculoskeletal symptoms

The primary purpose of this study was to compare the posture and muscle control patterns between male and female computer users with musculoskeletal symptoms. Forty computer users were recruited. Each subject performed a preferred speed typing, a fast speed typing, and a repetitive mouse task. The independent variables were gender, typing speed, and time. There were significant differences between genders for head and neck flexion angles when they were performing the preferred speed typing task. Significant differences between genders were also found for upper extremity angles when they were performing the repetitive mouse task. Male computer users had a smaller root mean square of the right extensor digitorium than females. In general, postural differences were significant between genders, even when the subjects' table and chair were adjusted to meet their anthropometry. Our results suggest that modifications of the computer working environment may be different between genders.     

Changes in oculomotor functions before and after loading of a 3-D visually-guided task by using a head-mounted display

Changes in visual and oculomotor functions were tested in eight young volunteer subjects after performing a 3-D visually-guided task for 25min. The visual stimuli were given by using a head-mounted display. No significant change was detected in the AC/A ratio and the stereo-acuity. Changes were found in refraction and ocular convergence. Slight but significant hyperopic changes were detected in refraction after the task. The mean amplitude of convergence eye movement elicited by test Stimuli after the task was significantly changed in the pooled data. They were significantly reduced when the subjects were tested by the disparity step of 0.7°, but significantly increased when tested by the step of 6°. The mean amplitudes were not significantly changed after the task when the subjects were tested by the intermediate disparity steps of 1.5 and 3°. In data obtained for each subject, the amplitude of ocular convergence evoked by test stimuli after the task was reduced significantly in most subjects. In the majority of subjects, however, the results were not consistently significant when they were tested by step stimuli with different disparities. In only a few subjects, the changes were consistently significant except when the largest disparity was tested. On the other hand, the mean peak velocities of ocular convergence after the task were not significantly changed in the pooled data. In individual subjects, the changes of velocities of ocular convergence evoked by test stimuli after the task were more variable: they increased in some subjects but decreased in other subjects. Consequently, in only one subject, both amplitudes and peak velocities of ocular convergence tested by the-disparity steps of 0.7, 1.5 and 3° were consistently reduced after the task. The changes in refraction or ocular convergence found in this study were relatively small, and were not in the pathological range. The significance of these data are discussed. The results of the present study provide the basis for the more detailed analyses of the human factor in the head-mounted display.     

2011年2月份十大重要安全漏洞分析

2011年01月21日至2月20日,国家计算机网络入侵防范中心发布漏洞总条目为455条,漏洞总数比2011年1月增加了41.30%[1]。其中威胁级别为＂紧急＂的有157条,＂高＂的有68条,＂中＂的有199条,＂低＂的有31条。威胁级别为紧急和高的漏洞占到总量的49.45%,从漏洞利用方式来看,远程攻击的有389条,本地攻击的有64条,局域网攻击的有2条。可见,能够从远程进行攻击的漏洞占绝大多数,这使得攻击者利用相应漏洞发动攻击更为容易。本月微软发布12个安全公告,其中3个为严重等级,9个为重要等级,共修复Windows操作系统、IE浏览器等软件中的22个安全漏洞,受影响的操作系统为包括Windows7在内的多个Windows版本。其中,微软发布安全公告修复了InternetExplorer中的一个零日漏洞和Windows图像渲染引擎中的一个零日漏洞,以及潜伏期长达19年的Windows内核漏洞。这些零日漏洞已经被利用进行攻击。建议广大用户及时安装补丁,增强系统安全性,做好安全防范工作,保证信息系统安全。     

面向对手建模的意图识别方法综述

首先介绍了对手建模的几种不同的类型,引出行为建模中的意图识别问题;随后针对意图识别的过程、分类、主要研究方法、研究展望以及实际应用进行了归纳分析,总结并讨论了相关领域取得的最新研究成果;最后指出意图识别目前存在的不足以及未来的发展方向。