Route optimization in mobile ATM networks

This paper presents an algorithm for optimizing the route of a connection that becomes suboptimal due to operations such as handoffs and location-based reroutes, and applies this algorithm to the handoff management problem in mobile ATM (Asynchronous Transfer Mode) networks based on the PNNI (Private Network-to-Network Interface) standard. The route optimization algorithm uses hierarchical route information of the connection and summarized topology and loading information of the network to determine a “crossover node” such that adjusting the connection from that crossover node results in an optimally routed connection. Handoff management schemes that perform local rerouting of connections have been proposed in order to support fast handoffs. These methods result in suboptimally routed connections. In this paper, we demonstrate how this route optimization algorithm can be used to optimize the route of a connection after such a handoff is executed, as the second phase of a two-phase handoff scheme. This route optimization procedure can also be executed as part of the handoff procedure resulting in a one-phase handoff scheme. Applying this route optimization algorithm, we propose two one-phase schemes, the one-phase optimal scheme and the one-phase minimal scheme. A comparative performance analysis of one- and two-phase handoff schemes is presented. Measures of comparison are handoff latency and the amount of network resources used by a connection. Handoff latency in the one-phase optimal scheme is greater than that in the two-phase schemes, and handoff latency in the one-phase minimal scheme is smaller than that in the two-phase schemes. The one-phase methods show a significant increase in efficiency of the connection compared to the two-phase methods. This revised version was published online in June 2006 with corrections to the Cover Date.     

Current sheet applicators for clinical microwave hyperthermia

Small lightweight applicators, intended to be operated in array configurations are described. Their radiative fields are induced by RF currents in a conducting sheet embedded a few millimeters below the dielectric covered aperture surface. In arrays, these elements can be used where conformity to body curvatures is necessary. The clinical prototypes are tuned to 434 MHZ and have a bandwidth of almost 20 MHZ, which accommodates the tuning and coupling changes due to different body movement, and tissue heterogeneities. They are relatively insensitive to air bubbles in bolus and scar tissue. Their inherent linear polarization allows easy visualization of the superposition of electric field vectors of each element of an array and provides deeper penetration on curved surfaces due to electric field vector addition in the medium. In the case of a large breast tumor, depth of heating of over 4 cm was achieved along the central axis of a 2×2 coherent array. Experimental evaluation of these elements, leading to clinical implementation, is described along with a clinical example     

A heuristic method for optimum redundancy allocation in non-coherent systems

This paper presents a heuristic method for optimum redundancy allocation in non-coherent systems. The method uses two forms of redundancy, namely parallel and series forms. System reliability of non-coherent systems cannot be generally improved by using only parallel redundancy. So use of series or parallel redundancy, whichever gives better system reliability, is recommended. The proposed method retains all the advantages of the most recommended [2,4,5] heuristic reliability optimization techniques. The method is general and can be used with linear or non-linear, separable or non-separable constraints.     

Linearized dynamic models for trajectory control of robot manipulators

To make an appropriate choice of linear model for the development of real-time control of robot manipulators, four direct linearization schemes have been studied here on the basis of computation and accuracy. Accuracy is assured in the state linearization method, whereas the rate linearization method leads to a satisfactory trade-off between computational effort and accuracy. In the case of high-velocity motions, a combination of state and rate linearization is proposed.     

Induced liquid phase mixing due to bubble motion at low gas velocity

Liquid phase mixing induced by gas bubbles at low gas velocities was studied experimentally. An experimental technique based on the principle of spectrophotometry was developed and applied in the experimental work. Experimental evidence suggests that the mixing phenomenon can be described as a diffusive process characterized by an effective diffusivity which is found to be a linear function of superficial gas velocity.     

Electronic conduction in bulk Se1−x Te x glasses at high pressures and at low temperatures

The electrical resistivity of bulk Se_1−x Te _x glasses is reported as a function of pressure (up to 8 GPa) and temperature (down to 77K). The activation energy for electronic conduction has been calculated at different pressures. The samples with 0⩽x⩽0·06 show a single activation energy throughout the temperature range of investigations. On the other hand samples with 0·08⩽x⩽0·3 show two activation energies in the different regions of temperature. The observed behaviour has been explained on the basis of band picture of amorphous semiconductors.     

Estimation of the magnitude and spatial distribution of combustible materials in urban areas. A case study of the San Jose area,California

This paper describes a methodology for estimating the magnitude and spatial distribution of urban fuel loadings using San Jose, California, as a case study. The study was undertaken to provide basic inputs into the modeling of large urban fires ignited by nuclear explosions, which has important implications for studies of the global climatic effects of nuclear war, or the so-called ‘nuclear winter’ phenomenon. The methodology is based on the measurement of the numbers and sizes of different building occupancy types from aerial photographs for approximately 6000 1000-ft (304.8-m) grid cells covering the study area. These measurements were combined with literature-derived average fuel loadings for each building type to yield the total fuel loading per cell. The total fuel loading thus calculated is approximately 4558.56 × 10⁶ kg, yielding an average of 8.4 kg m⁻² (1.7 lb ft⁻²) for the built-up area of the city and 9.4 kg m⁻² (1.9 lb ft⁻²) if unoccupied cells (i.e. cells containing no fuel) within the built-up area are excluded. These figures are lower than previously published average values, due to the low-density character of San Jose and the exclusion of certain components of total fuel loading by the methodology.     

Network transparency: the plaNET approach

Fast packet-switching has been chosen as the basis for future high speed, “universal” networks. The successful deployment of such networks will clearly depend on a wide range of factors such as cost and technology, but the authors believe that foremost among all is how well they will support existing and future applications. Emphasizing an application oriented perspective is one of the main motivation of the paper. The authors denote by “transparency” the ability of a network to transport application information while altering or manipulating it as little as possible, and believe it will be key to the acceptance of high-speed networks. While the concept is clearly not new, they articulate the need for it and illustrate its feasibility and the advantages it affords through the example of the plaNET network. In particular, they argue that a “transparent” data transfer mechanism can be provided that is both compatible with current standard proposals such as ATM and frame relay, and offers applications the choice of the data transfer mode that best meet their needs. A number of examples are used to illustrate these claims     

Realization of very long wavelength infrared photovoltaic detector arrays on mercury cadmium telluride epitaxial layers grown on Si substrates

This paper proposes a development of n-on-p structures for realizing very long wavelength infrared (VLWIR) detector arrays on mercury cadmium telluride (HgCdTe) epitaxial layers grown on Si substrates. It is shown from a comparative study of zero-bias resistance-area product (R₀A) of diodes in n-on-p and p-on-n configurations that the n-on-p structure has promising potential to control contribution of dislocations, without actually reducing dislocation density below the current level (mid-10⁶ cm⁻²) of HgCdTe/Si material technology. The resulting gain will be in terms of both higher numerical magnitudes of R₀A and its reduced scatter.     

Direct Pyrolysis of Raw Rice Husks for Maximization of Silicon Carbide Whisker Formation

A new alternate route for the production of SiC from rice husks has been described. The proposed single-stage process has the advantage of reduced time of production and a much higher yield of SiC whiskers than the conventional two-stage process. Direct pyrolysis of raw rice husks was carried out in a graphite furnace under vacuum and the reaction products were analyzed through macroscopic examination, XRD, SEM, and chemical analysis. Effects of time and temperature on the relative yields of the various reaction products have been determined over a wide range. The pyrolysis of raw rice husks has been found to be accompanied by four different competitive processes, viz., formation of SiC whiskers, formation of SiC polycrystals, crystallization of amorphous silica, and graphitization of amorphous carbon. Crystallization of silica and formation of SiC( w ) are dominant processes at 1150° to 1310°C. At higher temperatures formation of SiC polycrystals and graphitization of carbon are more favored. A multistep pyrolysis to 1310°C was found to yield a still higher amount of SiC( w ) than direct pyrolysis.