A dynamic data model for mobile GIS

A fast response time is a major objective for Mobile Geographic Information System (GIS) applications. This study provides a solution for improving the performance of response time by a dynamic data model. A conceptual dynamic data model is proposed, which covers (a) “position” information of selected geographic objects relevant to the GIS user's interest within his current location, (b) the selected attribute information in which the mobile GIS user is interested. In this approach, first, the attribute information is selected through a validating process making use of the temporal and attribute filters. Second, a specially designed dynamic database is employed to enable the implementation of the conceptual dynamic data model. This dynamic database is continually updated in accordance with the spatial, temporal and attribute constraints specified for the conceptual model. This design of a dynamic data model increases the availability of spatial data to mobile GIS users by providing up to date accurate information relevant to the area of interest, in a limited communication bandwidth. Third, an experimental study has been conducted and the results demonstrate that by using a dynamic database the response time can be reduced to one-third of that of a conventional database. The response time performance can be further improved as the size of the database is increased.     

On collaborative tracking of a target group using binary proximity sensors

In order to track multiple targets in a wireless sensor network, existing work has mostly focused on tracking the trajectories of each individual target that can be identified. However, such algorithms are often ineffective to handle a large number of targets—identifying each of them is too hard due to the fact that the targets usually move together and their locations may also be close to each other. This paper investigates the problem of tracking a group of targets when their motions are correlated. Specifically, we propose a family of algorithms for collaborative tracking with the help of binary proximity sensors. More specifically, our contributions include a fault-tolerant target group detection algorithm, two target group localization algorithms, and dynamic reporter node selection and redeployment control algorithms. Furthermore, we explore the fundamental limit on the accuracy of localizing a target group.     

Approximation algorithm for constructing data aggregation trees for wireless sensor networks

This paper considers the problem of constructing data aggregation trees in wireless sensor networks (WSNs) for a group of sensor nodes to send collected information to a single sink node. The data aggregation tree contains the sink node, all the source nodes, and some other non-source nodes. Our goal of constructing such a data aggregation tree is to minimize the number of non-source nodes to be included in the tree so as to save energies. We prove that the data aggregation tree problem is NP-hard and then propose an approximation algorithm with a performance ratio of four and a greedy algorithm. We also give a distributed version of the approximation algorithm. Extensive simulations are performed to study the performance of the proposed algorithms. The results show that the proposed algorithms can find a tree of a good approximation to the optimal tree and has a high degree of scalability.     

A Direct Execution Approach to Simulating Mobile Agent Algorithms

Mobile agent technology has been applied to develop the solutions for various kinds of parallel and distributed computing problems. However, performance evaluation of mobile agent algorithms remains a difficult task, mainly due to the characteristics of mobile agents such as distributed and asynchronous execution, autonomy and mobility. This paper proposes a general approach based on direct execution simulation for evaluating the performance of mobile agent algorithms by collecting and analyzing the information about the agents during their execution. We describe the proposed generic simulation model, named MADES, the architecture of a software environment based on MADES, and a prototype implementation. A mobile agent-based distributed load balancing algorithm has been used for experiments with the prototype.     

Dynamic partner identification in mobile agent-based distributed job workflow execution

This paper is concerned with the design, implementation, and evaluation of algorithms for communication partner identification in mobile agent-based distributed job workflow execution. We first describe a framework for distributed job workflow execution over the Grid: the Mobile Code Collaboration Framework (MCCF). Based on the study of agent communications during a job workflow execution on MCCF, we identify the unnecessary agent communications that degrade the system performance. Then, we design a novel subjob grouping algorithm for preprocessing the job workflow's static specification in MCCF. The obtained information is used in both static and dynamic algorithms to identify partners for agent communication. The mobile agent dynamic location and communication based on this approach is expected to reduce the agent communication overhead by removing unnecessary communication partners during the dynamic job workflow execution. The proof of the dynamic algorithm's correctness and effectiveness are elaborated. Finally, the algorithms are evaluated through a comparison study using simulated job workflows executed on a prototype implementation of the MCCF on a LAN environment and an emulated WAN setup. The results show the scalability and efficiency of the algorithms as well as the advantages of the dynamic algorithm over the static one.     

A heuristic multicast algorithm to support QoS group communications in heterogeneous network

This paper examines the problem of quality-of-service group communications in a heterogeneous network, which consists of multiple mobile ad hoc networks attached to the backbone Internet. A heuristic multicast algorithm named delay and delay variation multicast algorithm (DDVMA) is proposed. DDVMA is designed for solving the delay- and delay-variation-bounded multicast tree problem, which has been proved to be NP-complete. It can find a multicast tree satisfying the multicast end-to-end delay constraint and minimizing the multicast delay variation. Two concepts, which can help the DDVMA achieve better performance in terms of multicast delay variation than the delay and delay variation constraint algorithm that is known to be the most efficient so far, are proposed, namely, 1) the proprietary second shortest path and 2) the partially proprietary second shortest path. An analysis is given to show the correctness of DDVMA, and simulations are conducted to demonstrate the performance improvement of DDVMA in terms of multicast delay variation. It is also shown that the strategy employed by DDVMA is also applicable to handling the mobility of mobile hosts in a heterogeneous network.     

A robust monitor construct with runtime fault detection

The monitor concept provides a structured and flexible high‐level programming construct to control concurrent accesses to shared resources. It has been widely used in a concurrent programming environment for implicitly ensuring mutual exclusion and explicitly achieving process synchronization. This paper proposes an extension to the monitor construct for detecting runtime errors in monitor operations. Monitors are studied and classified according to their functional characteristics. A taxonomy of concurrency control faults over a monitor is then defined. The concepts of a monitor event sequence and a monitor state sequence provide a uniform approach to history information recording and fault detection. Rules for detecting various types of faults are defined. Based on these rules, fault‐detection algorithms are developed. A prototypical implementation of the proposed monitor construct with runtime fault detection mechanisms has been developed in Java. We shall briefly report our experience with and the evaluation of the robust monitor prototype. Copyright © 2005 John Wiley & Sons, Ltd.     

火电厂SCR烟气脱硝反应器前设置灰斗及增加烟道截面的探讨

阐述了飞灰对火电厂脱硝催化剂的磨损和堵塞机理.通过分析国内燃煤电厂飞灰的特性,说明飞灰对催化剂的磨损作用是较强的.探讨了通过在选择性催化还原烟气脱硝反应器前设置灰斗和增加烟道截面的方式,来提高大颗粒飞灰的去除效率,有效减少飞灰对催化剂的磨损和阻塞,延长催化剂寿命的可行性.