Locating and identifying compact ferrous objects

A solution to the problem of magnetostatic location and identification of compact ferrous objects of arbitrary shape is presented. It is shown that, in practice, the inversion of the magnetostatic dipole field or field gradient is a necessary first step toward determining object location and identity. Several iterative and noniterative methods of determinating the dipole moment and location from field or gradient measurements are described and compared. It is shown that, given the dipole-moment estimates, it is possible to determine the identity of the dipole source in practical situations by pattern recognition. A unique prototype total field magnetometer which is capable of explicitly and accurately locating and identifying axially symmetric compact ferrous objects is described. It has performed well in preliminary tests using spheres and spheroids     

Distributed database systems in high-speed wide-area networks

The issues involved in developing a distributed database system (DDBS) in a high-speed environment are discussed. The inadequacy of existing database protocols in utilizing the gigabit network is described. A concurrency control protocol that performs better than traditional DDBSs in high-speed networks is developed. Both analytical and simulation results are presented. The focus is on the concurrency control aspect of DDBS since this protocol is at the heart of the overall functioning of the distributed system     

Managing distributed objects in peer-to-peer systems

Peer-to-peer systems that dynamically organize, interact and share resources are increasingly being deployed in large-scale environments. The location, intermittent connectivity, and organization of the peers have significant impact on meeting the quality of service requirements of distributed applications. This article presents the design, implementation, and empirical evaluation of a middleware architecture for managing distributed objects in peer-to-peer systems. The architecture consists of a self-organizing infrastructure that uses only local knowledge to dynamically form overlays of multiple peers and respond to changing processing and networking conditions; and a management layer that monitors the behavior of the applications transparently, schedules object invocations over multiple machines, and obtains accurate resource projections. The system works in a two-level feedback loop structure that uses measurements of elapsed time and resource loads to refine the initial estimates and revise the peer connections. Our empirical evaluation shows that the system manipulates the peer connections dynamically in response to changes in resource utilization to meet application end-to-end soft real-time requirements.     

Growth trends in wide-area TCP connections

A recently completed single-site study has yielded information about how Internet traffic will evolve, as new users discover the Internet and existing users find new ways to incorporate the Internet into their work patterns. The author reviews existing statistics and studies of network growth, which show that network traffic generally grows exponentially with time, at least until the network carrying capacity is reached. He then describes how he captured and reduced the data used in this study. The following points are also addressed: the overall growth in the site's wide-area traffic; the appearance of periodic traffic; the growth in network use by individual computers or users; and the changing geographic profile of the traffic. The implications and limitations of the results are also summarizes     

Designing mobile computing systems using distributed objects

This article examines the application of distributed objects to the construction of highly available distributed systems for mobile, ubiquitous computing. High availability for the end user entails the provision of ubiquitous access and flexible resource-sharing. The defining characteristics of mobile computing, such as the frequent movement of users and hosts, the scarcity of network and local computing resources available to the mobile host, and the possibility of disconnections, present difficult challenges in providing high availability for clients in a distributed object system. Meeting these challenges requires dynamic object management techniques in the distributed server architecture on the fixed wired network, as well as object replica management techniques to achieve connection transparency and disconnected operation in the mobile client architecture. Various issues and solutions in constructing a dynamic distributed object-oriented architecture capable of supporting mobile computing are presented     

Graph marginalization for rapid assignment in wide-area surveillance

Decentralizing optimization problems across a network can reduce the time required to achieve a solution. We consider a wide-area surveillance sensor network observing an environment by varying the state of each sensor so as to assign it to one or more moving objects. The aim is to maximize an arbitrary utility function related to object tracking or object identification, using graph marginalization in the form of belief propagation. The algorithm performs well in an example application with six heterogeneous sensors. In larger network simulations, the time savings owing to decentralization quickly exceed 90%, with no reduction in optimality.     

Jitter-based delay-boundary prediction of wide-area networks

The delay-boundary prediction algorithms currently implemented by transport protocols are lowpass filters based on autoregressive and moving average (ARMA) models. However, previous studies have revealed a fractal-like structure of delay sequences, which may not be well suited to ARMA models. We propose a novel delay-boundary prediction algorithm based on a deviation-lag function (DLF) to characterize the end-to-end delay variations. Compared to conventional algorithms derived from ARMA models, the new algorithm can adapt to delay variations more rapidly and share the delay's robust high-order statistical information (jitter deviation) among competing connections along a common network path. Preliminary experiments show that it outperforms Jacobson's (1988) algorithm, which is based on an ARMA model, by significantly reducing the prediction error rate. To show the practical feasibility of the DLF algorithm, we also propose a skeleton implementation model     

采用MEMS技术的磁力计阵列可以在宽范围内进行探测

以MEMS技术为基础的检测器件，大小只有苍蝇那么大，却可以隐藏在100英尺的地面下检测军事装备。     

Quantum communication for wireless wide-area networks

In this paper, a quantum routing mechanism is proposed to teleport a quantum state from one quantum device to another wirelessly even though these two devices do not share EPR pairs mutually. This results in the proposed quantum routing mechanism that can be used to construct the quantum wireless networks. In terms of time complexity, the proposed mechanism transports a quantum bit in time almost the same as the quantum teleportation does regardless of the number of hops between the source and destination. From this point of view, the quantum routing mechanism is close to optimal in data transmission time. In addition, in order to realize the wireless communication in the quantum domain, a hierarchical network architecture and its corresponding communication protocol are developed. Based on these network components, a scalable quantum wireless communication can be achieved.     

Routing and flow control in high-speed wide-area networks

The routing and flow control techniques developed for wide-area, local-area, and metropolitan-area networks are surveyed. A classification that shows the characteristics that are desirable for high-speed wide-area networks is developed. On the basis of the classification, techniques that should and should not be considered for future high-speed networks are identified. In particular, an attempt is made to determine the effect of increasing transmission rates on the routing and flow control algorithms that are used in packet-switched networks     

A mobile bazaar for wide-area wireless services

We introduce MoB, an infrastructure for collaborative wide-area wireless data services. MoB proposes to change the current model of data services in the following fundamental ways: (1) it decouples infrastructure providers from services providers and enables fine-grained competition, (2) it allows service interactions on arbitrary timescales, and, (3) it promotes flexible composition of these fine-grained service interactions based on user and application needs. At the heart of MoB is an open market architecture in which mobile users can opportunistically trade various services with each other in a flexible manner. In this paper we first describe the overall architecture of MoB including various enablers like user reputation management, incentive management, and accounting services. We next present our experience from both simulations as well as our prototype implementation of MoB in enhancing application performance in multiple different scenarios—file transfers, web browsing, media streaming, and location-enhanced services. This work is supported in part by NSF grants CNS-0520152, CNS-0639434, CNS-0627589 and CNS-0627102. Rajiv Chakravorty received the B.E. degree from Nagpur University, Nagpur, India, in 1997 and the M.Tech. degree form the Indian Institute of Technology, Delhi in 1999. He is working towards the Ph.D. degree at the Computer Laboratory, University of Cambridge, U.K. In 2005 he was a visiting research scholar in the Department of Computer Sciences, University of Wisconsin, Madison. He has worked with Philips Research, ASA Laboratories, Eindhoven, The Netherlands. He also pursued research at ComNets, RWTH-Aachen, Germany. His current interests include mobile and wireless systems, and networking. He is a recipient of DAAD Scholarship Award from Germany, and the Sun Microsystems Scholarship and the Hughes Hall Commonwealth scholarhip from Cambridge Univeristy. Sulabh Agarwal received the B.Tech. degree in Computer Science and Engineering from Indian Institute of Technology, Delhi in 2000, and the M.S. degree in Computer Science from University of Maryland, College Park in 2002. His research interest is in the area of computer networking. Suman Banerjee received the B.Tech. degree in Computer Science and Engineering from Indian Institute of Technology, Kanpur in 1996, and the M.S. and the Ph.D. degrees in Computer Science from University of Maryland, College Park in 1999 and 2003 respectively. He is an Assistant Professor of Computer Sciences at University of Wisconsin-Madison and heads the Wisconsin Wireless and NetworkinG Systems (WiNGS) laboratory. His broad research interests are in the areas of networking and distributed systems with a special focus in the area of wireless and mobile networking systems. Ian Pratt received the Ph.D. in Computer Science from University of Cambridge, Cambridge, U.K. He was elected a Fellow of King’s College, Cambridge, U.K., in 1996. He is a Senior Faculty member at the Computer Loboratory, University of Cambridge, Cambridge, U.K. He is a a leader of the Systems Research Group, where he has been architect of a number of influential projects, including the Desk Area Network workstation, the Cambridge Open Mobile System, the Xen Virtual Machine Monitor, and the XenoServer infrastructure for global computing. His research interests cover a broad range if systems topics, including computer architecture, operating system design, mobile systems, and networking.     

The PIM architecture for wide-area multicast routing

The purpose of multicast routing is to reduce the communication costs for applications that send the same data to multiple recipients. Existing multicast routing mechanisms were intended for use within regions where a group is widely represented or bandwidth is universally plentiful. When group members, and senders to those group members, are distributed sparsely across a wide area, these schemes are not efficient; data packets or membership report information are occasionally sent over many links that do not lead to receivers or senders, respectively. We have developed a multicast routing architecture that efficiently establishes distribution trees across wide area internets, where many groups will be sparsely represented. Efficiency is measured in terms of the router state, control message processing, and data packet processing, required across the entire network in order to deliver data packets to the members of the group. Our protocol independent multicast (PIM) architecture: (a) maintains the traditional IP multicast service model of receiver-initiated membership, (b) supports both shared and source-specific (shortest-path) distribution trees, (c) is not dependent on a specific unicast routing protocol, and (d) uses soft-state mechanisms to adapt to underlying network conditions and group dynamics. The robustness, flexibility, and scaling properties of this architecture make it well-suited to large heterogeneous internetworks     

Analysis of quality-of-service in a wide-area interactive distance learning system

Interactive distance learning (IDL) is an evolving paradigm of instruction and learning that attempts to overcome both distance and time constraints found in traditional classroom learning. The electronic classrooms at two sites of the University of Oslo and two further sites in Norway overcome separations in space by exchanging digital audio, video, and whiteboard information via the Norwegian academic ATM-based network Supernett II. The electronic classrooms are used since 1993 for teaching graduate level courses. This paper presents measurements and analysis results of transport, application, and user level Quality-of-Service (QoS) of the electronic classrooms. We describe our general experiences with this system for synchronous IDL. The lessons learned represent the motivation for the ongoing extension to support asynchronous IDL by a multimedia database system (MMDBS) to manage all data used and generated in the electronic classrooms.     

Processing of multiple-receiver spaceborne arrays for wide-area SAR

The instantaneous area illuminated by a single-aperture synthetic aperture radar (SAR) is fundamentally limited by the minimum SAR antenna area constraint. This limitation is due to the fact that the number of illuminated resolution cells cannot exceed the number of collected data samples. However, if spatial sampling is added through the use of multiple-receiver arrays, then the maximum unambiguous illumination area is increased because multiple beams can be formed to reject range-Doppler ambiguities. Furthermore, the maximum unambiguous illumination area increases with the number of receivers in the array. One spaceborne implementation of multiple-aperture SAR that has been proposed is a constellation of formation-flying satellites. In this implementation, several satellites fly in a cluster and work together as a single coherent system. There are many advantages to the constellation implementation including cost benefits, graceful performance degradation, and the possibility of performing in multiple modes. The disadvantage is that the spatial samples provided by such a constellation will be sparse and irregularly spaced; consequently, traditional matched filtering produces unsatisfactory results. We investigate SAR performance and processing of sparse, multiple-aperture arrays. Three filters are evaluated: the matched filter, maximum-likelihood filter, and minimum mean-square error filter     

Simulation of measuring data obtained from RFID-tags in systems of spatial localization of objects

Paper presents the simulation of processes of spatial localization of objects using systems of radio-frequency identification (RFID systems). The simulation technique for simulation modeling the measuring data of proximity type, received signal strength (RSS) type, and read rate (RR) type obtained from passive RFID-tags has been developed. The technique allows us to carry out the preliminary comparison of localization accuracy ensured in case of using different algorithms of localization and types of measuring data for arbitrary regions of localization. The testing of this technique indicated that the relative error of simulation results as compared to experimental results amounted on average to 8% and did not exceed 28%.     

基于专家系统的广域后备保护

对电力系统中的多点信息进行采集,通过计算动作系数确定故障影响范围,如专家系统不能做出决策再通过二级策略确定,逐步缩小故障范围以及最终得出故障隔离方案,使故障对系统的影响降低.通过算例对比分析,验证了基于专家系统的广域后备保护优于传统后备保护,提高了传统后备保护的选择性.