Optimal virtual topologies for one-to-many communication in WDM paths and rings

In this paper we examine the problem of constructing optimal virtual topologies for one-to-many communication in optical networks employing wavelength-division multiplexing. A virtual topology is a collection of optical lightpaths embedded in a physical topology. A packet sent from the source node travels over one or more lightpaths en route to its destination. Within a lightpath, transmission is entirely optical. At the terminus of a lightpath the data is converted into the electronic domain where it may be retransmitted on another lightpath toward its destination. Since the conversion of the packet from the optical to the electronic domain introduces delays and uses limited physical resources, one important objective is to find virtual topologies which minimize either the maximum or average number of lightpaths used from the source to all destination nodes. Although this problem is NP-complete in general, we show that minimizing the maximum or average number of lightpaths in path and ring topologies can be solved optimally by efficient algorithms.     

Vision-based obstacle detection for rotorcraft flight

The ability of rotorcraft to fly at low altitude is hindered by the high pilot workload required to avoid obstacles. The development of automation tools that can detect obstacles in the rotorcraft flight path, warn the crew, and interact with the guidance system to avoid detected obstacles would significantly reduce pilot workload and increase safety. This article describes an obstacle detection approach based on feature tracking and recursive range estimation that takes into account the characteristics of rotorcraft flight. The merits and weaknesses of the approach are discussed using image sequences from the laboratory and from flight. © 1992 John Wiley & Sons, Inc.     

Scattering of plane SH-waves by a cylindrical canyon of arbitrary shape in anisotropic media

The scattering and diffraction of plane SH-waves, by an arbitrary-shaped cylindrical canyon in anisotropic media is formulated here. Analytical solutions are obtained via the complex function theory, using the orthogonal property of the Hermite functions to solve the resulting set of infinite algebraic equations. Expressions for scattered displacements and scattered stresses are given. Three cross-sectional profile types are used in the numerical simulation of the two-dimensional canyon topography: (a) a semi-circular profile, (b) a semi-elliptical profile and (c) a triangular profile. The results obtained in (a) and (b) are consistent with known solutions computed by Trifunac and his co-workers [1,3] using a different method. As the exact solution for (c) is not known to exist, the result given here is believed to be new and would therefore serve as a useful check for numerical analysts working in this area.     

Some aspects of deformation behavior

The deformation behavior of several single- and two-phase coarse microstructures has been examined using microhardness measurements. It has been found that the strength response of a coarse phase in isolation is distinctly different from its response when it exists in a two-phase system. The second phase alters the mechanical state of the first one andvice versa even in the plastically undeformed condition. This phenomenon is explained in terms of the existence of an appreciable amount of residual stresses in two-phase coarse microstructures. These stresses primarily arise due to the difference in thermal expansion coefficients of the phases. The in- fluence of elastic stress field on microhardness response is shown with a new type of experiment to support the proposed explanation. The present results question the existing expressions for deformation modeling of multiphase materials because of the uncertainties in the estimation of the average strength of the phases in a two-phase system.     

A comparison of lightness contrast effects in CRT and surface colours

The simultaneous contrast effect is investigated in this article. A total of 174 and 154 test/induction combinations were studied for CRT and surface colours respectively. Each combination was assessed by nine observers using a matching technique. The test and induction colours used for CRT colours were similar to surface colours using fabric samples. The results indicated a strong lightness contrast effect for both CRT and surface media; that is, the lightness of a test colour surrounded by a lighter induction colour was reduced for both CRT and surface colours. However, the effect in CRT medium was more pronounced than in the surface medium. © 2004 Wiley Periodicals, Inc. Col Res Appl, 30, 13–20, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20074     

Assessment of service exposed boiler tubes

Boiler tubes in power plants have finite life because of prolonged exposure to high temperature, stress and aggressive environment. Service-exposed platen superheater and reheater tubes (148,900 h) made of 2.25Cr-1 Mo steels in a 120 MW boiler of a thermal power plant were evaluated for remnant life. The investigation included hot tensile tests, hardness measurement, dimensional measurement, microscopy and creep tests. Experimentally determined yield and ultimate tensile strength, and estimated 10,000–100,000 h rupture strength in the temperature range 520–580 °C, exhibited a decreasing trend with increasing temperature. Microstructural study did not reveal any significant degradation in terms of creep cavities, cracks, graphitization, etc. Analysis of tensile and stress rupture data revealed that although there was degradation of the tubes due to prolonged service exposure in terms of the ultimate tensile strength values, stress rupture plots showed that the service exposed superheater and reheater tubes could remain in service for a length of more than 10 years at the operating hoop stress of 40 MPa/540 °C, provided no localised damage in the form of cracks or dents develop.