Large-Eddy Simulation of the Lid-Driven Cubic Cavity Flow by the Spectral Element Method

This paper presents the large-eddy simulation of the lid-driven cubic cavity flow by the spectral element method (SEM) using the dynamic model. Two spectral filtering techniques suitable for these simulations have been implemented. Numerical results for Reynolds number Re=12,000 are showing very good agreement with other experimental and DNS results found in the literature.     

Optimal terrain-following for towed-aerial-cable sensors

Towed-aerial cable systems are often used for towing decoys from aircraft and for collecting electromagnetic data from low altitudes. Airborne cable systems are typically controlled by maneuvering the aircraft, which can limit the safe altitude of the towed-sensor package. In this paper, a real-time optimal control strategy for controlling a towed-cable system is proposed that uses cable winch control to control the altitude of the towed-body. The controller is based on a receding horizon control approach, where the aircraft senses the terrain profile ahead of the towed-body with a relatively short time horizon. This information is sent to the controller, which updates the cable winch reel acceleration to safely avoid colliding with the terrain, while keeping the towed-sensor close to the desired altitude for obtaining good measurements. The controller is developed for a simplified system model and implemented in a multibody cable system model that incorporates cable flexibility and elasticity.     

Virtual machines for enterprise desktop security

A virtual machine monitor (VMM) allows a single computer to run two or more operating systems at the same time. VMMs are relatively simple and are typically built to high assurance standards, which means that the quality of isolation provided by a virtual machine monitor is usually greater than that which can be achieved with a general-purpose operating system. This paper discusses how the flexibility afforded by multiple OS environments and the robust isolation provided by a virtual machine monitor can be used to improve client PC security. A prototype system is also described.This paper is neither a product announcement nor an official Microsoft position paper, but rather it is a discussion of interesting configuration options that can be constructed using existing Microsoft and third-party products: in this case two or more operating systems running in conjunction with a virtual machine monitor.     

Skeletonization based on error reduction

The accuracy of a non-pixel-based skeletonization method is largely dependent on the contour information chosen as input. When using a Constrained Delaunay Triangulation to construct an object's skeleton, a number of contour pixels must be chosen as a basis for triangulation. This paper presents a new method of selecting these contour pixels. A new method for measuring skeletonization error is proposed, which quantifies the deviation of a skeleton segment from the true medial axis of a stroke in an image. The goal of the proposed algorithm is to reduce this error to an acceptable level, whilst retaining the superior efficiencies of previous non-pixel-based techniques. Experimental results show that the proposed method is adept at following the medial axis of an image, and is capable of producing a skeleton that is confirmed by a human's perception of the image. It is also computationally efficient and robust against noise.     

Robust control of uncertain distributed delay systems with application to the stabilization of combustion in rocket motor chambers

The problems of robust stability and robust stabilization of uncertain linear systems with distributed delay occurring in the state variables are studied in this paper. The essential requirement for the uncertainties is that they are norm-bounded with known bounds. Conditions for the robust stability of distributed time delay systems are given and a design method for the robust stabilizing control law of the uncertain systems is presented. The proposed method is applied to the stabilization of combustion in the chamber of a liquid monopropellant rocket motor. It is found that the combustion can be robustly stabilized when the two parameters pressure exponent γ and maximal time lag r vary in specified intervals, respectively.     

Rapid simulator development for multicast protocol analysis

When evaluating new protocols and algorithms it is often desirable to be able to rapidly build a specialized simulator from scratch. The advantage of this approach is that software designers can avoid the often‐steep learning curve associated with using existing simulators, and that specialized simulators can have significant computational advantages over general‐purpose programs. The drawback is that simulators can be complex to develop and debug. This paper describes our experiences developing SESAME, a Java‐based simulator designed to analyze multicast protocol performance. By using an appropriate set of design patterns we were able to rapidly develop a reusable and easy‐to‐implement framework for multicast algorithm and protocol analysis. We developed several useful approaches for rapid simulation development, including a multicast visualization tool and techniques for simulating concurrent processing within a computer network that substantially simplified code development and maintenance. Owing to performance concerns, we also ran an extensive series of performance tests of different priority queue implementations. Our design approach and the lessons that we learned in developing SESAME can be applied to rapid simulation development in general. Further, our performance results suggest that by using commercial off‐the‐shelf Java development environments it is possible to obtain sufficient performance for many time‐sensitive applications such as discrete event simulation. Copyright © 2001 John Wiley & Sons, Ltd.     

Analysis and design of ribbon cables for high‐speed digital applications

Ribbon cables have been widely used as subsystem interconnections in a large number of digital systems, because they can convey numerous bits of a digital signal simultaneously. In this article, finite difference and finite difference time domain (FDTD) methods are used to analyze and optimize the electrostatic analysis design of ribbon cables, and measurements are used to verify the numerical results. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12: 148–158, 2002.     

Die kritischen Erfolgsfaktoren für EDI-Dienstleistungsanbieter

The potential of Electronic Data Interchange (EDI) has not yet been fully realized despite the existence of appropriate standards and technologies. Service providers in this area play an important role as providers of the infrastructure, providers of conversion programs, or consultants. This paper examines the critical success factors of EDI service providers as perceived by them and their customers. It finds that the views of these groups are partly divergent, especially with respect to the need for knowledge of business processes. The findings can help providers to improve their services for their own benefit and the benefit of their users.     

Interruption modelling in medium voltage electrical networks

Failures frequently occur in developing countries' electrical energy distribution networks. This paper proposes an approach to network reliability through modelling the interruptions on medium voltage lines. This modelling is based on a representative feeder sampling of a source station in an urban area. In order to determine the probability law governing these interruptions, statistical techniques were used: density estimation using the kernel method and approximation by the least squares. The results we obtained show that, from the quality of the equipment and their maintenance, interruptions for a given network follow a truncated and shifted gamma distribution or a truncated normal law. For the managers of such systems, these results would allow, amongst other things, reduction in the probability of failure, thus improving operational safety on electricity distribution with medium voltage lines.     

The New Business Currency

Thomas H. Davenport and John C. Beck, The Attention Economy: Understanding the New Currency of Business, Boston, MA: Harvard Business School Press (2001), 253 pp.

Brad Hansen, The Dictionary of Computing and Digital Media: Terms and Acronyms, Wilsonville, OR: Franklin, Beedle, and Associates (1999), 543 pp.

Piotr Jankowski and Timothy Nyerges, Geographic Information Systems for Group Decision Making: Towards a Participatory Geographic Information Science, New York: Taylor and Francis (2001), 273 pp.

Jeffrey A. Rohlfs, Bandwagon Effects in High Technology Industries, Cambridge, MA: MIT Press (2001), 256 pp.