			Home About us Contact

First Problem (first + problem)

Distribution by Scientific Domains

Engineering	80%

Selected Abstracts

Locating a Surveillance Infrastructure in and Near Ports or on Other Planar Surfaces to Monitor Flows

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 2 2010
Pitu B. Mirchandani
This article addresses the problem of locating surveillance radars to cover a given target surface that may have barriers through which radar signals cannot penetrate. The area of coverage of a radar is assumed to be a disc, or a partial disc when there are barriers, with a known radius. The article shows that the corresponding location problems relate to two well studied problems: the set-covering model and the maximal covering problem. In the first problem, the minimum number of radars is to be located to completely cover the target area; in the second problem a given number M of radars are to be located to cover the target area as much as possible. Based on a discrete representation of the target area, a Lagrangian heuristic and a two-stage procedure with a conquer-and-divide scaling are developed to solve the above two models. The computational experiences reported demonstrate that the developed method solves well the radar location problems formulated here. [source]

A smooth switching adaptive controller for linearizable systems with improved transient performance

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2006
Jeng Tze Huang
Abstract The certainty equivalent control has achieved asymptotic tracking stability of linearizable systems in the presence of parametric uncertainty. However, two major drawbacks remain to be tackled, namely, the risk of running into singularity for the calculated control input and the poor transient behaviour arising frequently in a general adaptive system. For the first problem, a high gain control is activated in place of the certainty equivalent control until the risk is bypassed. Among others, it requires less control effort by taking advantages of the bounds for the input vector field. Moreover, the switching mechanism is smooth and hence avoids possible chattering behaviour. Next, to solve the second problem, a new type of update algorithm guaranteeing the exponential stability of the overall closed-loop system, on a weaker persistent excitation (PE) condition, is proposed. In particular, it requires no filtering of the regressor and hence is easier to implement. Simulation results demonstrating the validity of the proposed design are given in the final. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Joint power, subcarrier and subframe allocation in Multihop relay networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 7 2009
Tolga Girici
Abstract In this paper we study the problem of subframe, subchannel and power allocation in OFDMA-based multihop relay networks. The system consists of a base station (BS), a number of relay stations (RS) and mobile stations (MS). We consider frame by frame scheduling, where the frame is divided into two subframes such as BS-RS and RS-MS subframes. We study two different problems, satisfying link rate requirements with minimum-weighted total power and maximizing proportional fairness. For the first problem, we find the optimal solution and also propose a less complex subframe and bandwidth allocation scheme with good performance. For the second problem, we propose an algorithm that outperforms an existing scheme with less feedback. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Effective Efficiency as a Tool for Sustainable Water Resources Management,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2008
Naim Haie
Abstract:, The sufficiency and usefulness of Effective Efficiency (EE) as a water resources index is shown through conceptual formulation of a generalized EE and practical applications. Two EE models are proposed: one is based on water quantity and the other on quantity and quality, with the possibility of considering water reuse (recycling) in both. These models were developed for two scales: the first is called Project EE and the second Basin EE. The latter gives the influence of the project on the water resources systems of the basin while the former does not make such connection to the whole basin. Such considerations give proper signals as to the adequacy of any intervention to increase efficiency. A crucial distinction is made between depletion and diversion water savings. Classical Efficiency (CE) models are analyzed and compared with the various EE models. CE results in values that are less than EE because of not considering water reuse and water quality in its calculation. Some authors, pointing to these problems , particularly the first problem , have advocated the use of hydrological "fractions" instead of efficiency concepts. This paper defends the use of a proper efficiency model such as EE and suggests putting an end to the use of the CE indicators. To test the models, they are applied to five cases of irrigation and city water use in the United States and Egypt. The analysis of the results demonstrates all the points mentioned above and the potential of the EE models to adequately describe the water resources efficiency and sustainability at a location. [source]

Maximizing residual flow under an arc destruction

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2001
Y. P. Aneja
Abstract In this paper, we consider two problems related to single-commodity flows on a directed network. In the first problem, for a given s , t flow, if an arc is destroyed, all the flow that is passing through that arc is destroyed. What is left flowing from s to t is the residual flow. The objective is to determine a flow pattern such that the residual flow is maximized. We provide a strongly polynomial algorithm for this problem, called the maximum residual flow problem, and consider various extensions of this basic model. In the second problem, known as the "most vital arc" problem, the objective is to remove an arc so that the maximal flow on the residual network is as small as possible. Results are also derived which help implement an efficient scheme for solving this problem. © 2001 John Wiley & Sons, Inc. [source]