Low-cost clock synchronization

Summary We show how synchronized clocks can be realized in a distributed system as a byproduct of a common communication paradigm where processors periodically perform broadcasts. Our approach decouples theprecision concern of clock synchronization—limiting how much correct clocks can differ from each other—from theaccuracy concern—limiting the rate at which any correct clock may drift from real time. Given a system that guarantees only precision, we develop a protocol whereby high accuracy can be achieved on demand. In this manner, the lazy protocol we obtain incurs the cost of high accuracy only when needed while keeping the basic synchronization procedure extremely simple and cheap. Rogério Drummond is Associate Professor of Computer Science at the Universidade de Campinas (Unicamp), Brazil. He received his Ph.D. in computer science from Cornell University in 1986. He has previously worked on distributed fault-tolerant computing, such as the present paper. Currently, he heads the A_HAND project which aims to provide an object-oriented distributed programming environment for the development of very large software systems. Özalp Babaolu is Professor of Computer Science at the University of Bologna, Italy. His research interests include distributed algorithms, fault tolerance and parallel computing. He received a BS in electrical engineering from George Washington University, Washington, D.C. in 1976. From the University of California, Berkeley, he received a MS in 1977 and a Ph.D. in 1981, both in computer science. While at Berkeley, he designed and implemented the virtual memory extensions to BSD Unix. From 1981 to 1987 he was on the faculty at the Department of Computer Science, Cornell University.Partial support for this work was provided by the National Science Foundation under Grant DCR-86-01864, AT&T under a Foundation Grant, the Commission of the European Communities under the ESPRIT Programme Basic Research Action Number 3092 (Predictably Dependable Computing Systems) and the Italian Ministry of University and Research. Drummond was partially supported through a Fellowship from the CAPES Agency of the Government of Brazil     

Measurement of Solid-Liquid Interfacial Energy for Solid Zn in Equilibrium with the ZnMg Eutectic Liquid

The equilibrated grain boundary groove shapes for solid Zn in equilibrium with the ZnMg eutectic liquid were observed on rapidly quenched samples. The Gibbs–Thomson coefficient for the solid Zn has been determined to be (10.64± 0.43) × 10⁻⁸ K m from the observed grain boundary groove shapes with the present numerical model, and the solid-liquid interfacial energy for the solid Zn in equilibrium with the ZnMg eutectic liquid has been obtained to be (89.16 ± 8.02) × 10⁻³Jm⁻² from the Gibbs–Thomson equation. The grain boundary energy for the solid Zn has also been calculated to be (172.97 ± 20.76) × 10⁻³J m⁻² from the observed grain boundary groove shapes. This article is based on a presentation made in the symposium entitled ”Solidification Modeling and Microstructure Formation: In Honor of Professor John Hunt” which occurred March 13-15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.     

Scenario-based query processing for video-surveillance archives

Automated video surveillance has emerged as a trendy application domain in recent years, and accessing the semantic content of surveillance video has become a challenging research area. The results of a considerable amount of research dealing with automated access to video surveillance have appeared in the literature; however, significant semantic gaps in event models and content-based access to surveillance video remain. In this paper, we propose a scenario-based query-processing system for video surveillance archives. In our system, a scenario is specified as a sequence of event predicates that can be enriched with object-based low-level features and directional predicates. We introduce an inverted tracking scheme, which effectively tracks the moving objects and enables view-based addressing of the scene. Our query-processing system also supports inverse querying and view-based querying, for after-the-fact activity analysis. We propose a specific surveillance query language to express the supported query types in a scenario-based manner. We also present a visual query-specification interface devised to facilitate the query-specification process. We have conducted performance experiments to show that our query-processing technique has a high expressive power and satisfactory retrieval accuracy in video surveillance.     

Student teachers’ satisfaction for blended learning via Edmodo learning management system

In a digitally driven world, behaviours of future teachers for blended learning (both face-to-face and on-line classes) need to be examined. This study serves three purposes. The first is to examine student teachers’ preferences for Community-of-Inquiry model-driven blended learning via Edmodo. Second, predicting student satisfaction on b-learning from a combination of four variables (gender, having internet access, using the internet for information access, and previous experience in on-line learning) was questioned. And third, b-learning orientations of participants were investigated. One of the mixed methods, the concurrent triangulation design was employed in which both qualitative and quantitative methods were applied. The study group included 135 freshmen and junior students (29 males and 106 females) from a western Turkish educational faculty. The findings for the first question indicated that 70.4% of student teachers prefer b-learning. For the second, 15% of the variance in satisfaction on b-learning was explained by the proposed model with a medium effect. And for the third, the qualitative findings were discussed under Perceived Usefulness (PU) and Perceived Uselessness and Unease-of-Use (PU-UU) themes. Although less than a quarter of participants found b-learning useless, most held positive notions for b-learning practices via Edmodo.     

A New Bootstrapped Hybrid Artificial Neural Network Approach for Time Series Forecasting

Computational Economics - In this study, a new bootstrapped hybrid artificial neural network is proposed for forecasting. This new neural network provides input significance, linearity and...     

高g_n值MEMS加速度传感器封装的研究

对一种新型双悬臂梁高gn 值MEMS加速度传感器进行有限元模拟。采用双悬臂梁传感芯片的一种实际封装结构 ,进行频域分析和时域分析 ,讨论封合传感器芯片和封装基体的封合材料对其输出信号的影响。频域分析表明 ,封合材料的杨氏模量对封装后加速度传感器整体的振动模态有一定影响 ,封合胶的杨氏模量很小时 ,会致使加速度传感器的信号失真 ,模拟表明可选用杨氏模量足够高的环氧树脂类作高gn 值传感器的封合材料。时域分析静态模拟表明 ,封合材料的杨氏模量 ,对最大等效应力和沿加载垂直方向的正应力最大最小值基本无影响。时域分析动态模拟表明 ,随着封合材料杨氏模量的提高 ,动态模拟输出的悬臂梁末端节点位移的波形和其经数字滤波后输出的信号变好 ,封合材料的杨氏模量不影响输出信号的频率和均值 ,在加速度脉冲幅值输入信号变化时 ,悬臂梁末端位移平均值输出信号与输入有良好的线性关系。     

一种多级无缓存高阶路由器的设计与实现

随着高性能网络规模的增加,高阶路由器结构设计成为高性能计算研究的重点和热点。使用高阶路由器,网络能实现更低的报文传输延迟、网络功耗和网络构建成本,同时高阶路由器的应用还可以提高网络可靠性。高性能路由器的阶数不断提高,仅靠扩展单级crossbar交换结构的阶数使路由器内部的连线资源急速增长,交叉开关的实现代价将不可接受,这就需要为高阶路由器设计新型的交换结构。近十年来,出现了以YARC为代表的经典结构化设计以及"network within a network"等新型设计方法,未来的研究重点是解决高阶路由器结构设计中遇到的缓存、仲裁和扩展性等各种问题。鉴于此,实现了一种多级无缓存高阶路由器,这种高阶路由器内部是一个多级Clos网络,每一级有相应的仲裁模块对请求进行调度,数据包缓存在输入/输出端口实现,除去这些缓冲区单元,该网络是无缓存的。最后通过BookSim模拟器进行了大量的性能测试,所设计的路由器能够正常工作,性能良好。     

Use of social network sites among depressed adolescents

Social network sites (SNSs) are relatively new phenomena, and the relationship between SNSs and psychopathology remains unclear. The purpose of this study was to evaluate the type of SNSs depressed adolescents use and the incidence of depressive disclosure on SNSs among them. The study was designed to be cross-sectional. The sample consisted of 53 adolescents diagnosed with depressive disorder, as confirmed by K-SADS-PL, and 55 non-depressed adolescents. The Children’s Depression Inventory, Social Anxiety Scale and Social Network Use Questionnaire were administered. The primary finding was that the amount of time spent on the Internet and on SNSs was significantly higher among depressed adolescents than non-depressed adolescents. Additionally, depressed adolescents reported significantly higher disclosure of anhedonia, worthlessness, guilt, loss of concentration, irritability and thoughts of suicide on SNSs. The intensity of the depression sharing was significantly higher in the depressed group. Depressed young people use social networks to express their symptoms. Adolescents’ disclosure on social networks may be able to guide relatives, friends and mental health professionals.     

On the generality of the part-set cuing effect: Evidence from nonmemory tasks.

A puzzling finding in memory research is that part–set cuing, or the presentation of some of the to-be-recalled items as cues, impairs recall of the remaining items. In this article a series of four experiments involving nonmemory tasks extends this finding to other cognitive domains. Specifically, it is shown that providing possible responses impairs the production of other responses when words are constructed from the letters of a lengthy word (Experiment 1), when differences between almost identical pairs of pictures are discovered (Experiment 2), when blurred pictures brought gradually into focus are identified (Experiment 3), and when nonsense figures are likened to meaningful objects or scenes (Experiment 4). These findings suggest that the part–set cuing effect in memory may be only one instantiation of a much broader phenomenon. And such a perspective might elicit a more satisfactory explanation of this puzzling effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Salmonella typhi infections. A 10-year retrospective study

Enteric fever is still a common health problem in many countries, especially in children. Thus a ten-year retrospective study was carried out to evaluate the clinical and laboratory properties of enteric fever and the incidence of antimicrobial resistance in children. Throughout the past 10 years, Salmonella was isolated in 105 patients by blood culturing, 27 of which were Salmonella typhi. Most of the patients were above the age of two. Besides the typical symptoms and signs of enteric fever, 29.2% of the patients had some neurologic findings. Besides, 68.5% had elevated liver enzymes while only 44.4% had hepatomegaly with or without splenomegaly. Anemia was present in 44%, leukopenia in 16% and leukocytosis in 11.1% of the cases. The emergence of antimicrobial resistance during the last five years against ampicillin, chloramphenicol and trimetoprim-sulfamethoxazole has created a challenge in treating these infections.