An (m, M) machine repair problem with spares and state dependent rates: A diffusion process approach

The diffusion approximation model for (m, M) general machine repair problems with spare part support has been developed. The inter-failure time and repair times are assumed to be generally identically and independently distributed (i.i.d.). The failure rate of operating units in a short system when fewer than M units are operating and all spares are being used, is faster than a normal system. The spare units may also fail with rates different from operating units. The repairmen switch to the faster rate to reduce a backlog of down units in the case of a busy repair facility. By using reflecting boundaries, the approximate formulae for some performance measures, namely, expected number of inoperative/operative units and probability that the system is short/down have been obtained.     

Regulation of transport pathways in tumor vessels: role of tumor type and microenvironment

Novel anti-neoplastic agents such as gene targeting vectors and encapsulated carriers are quite large (approximately 100-300 nm in diameter). An understanding of the functional size and physiological regulation of transvascular pathways is necessary to optimize delivery of these agents. Here we analyze the functional limits of transvascular transport and its modulation by the microenvironment. One human and five murine tumors including mammary and colorectal carcinomas, hepatoma, glioma, and sarcoma were implanted in the dorsal skin-fold chamber or cranial window, and the pore cutoff size, a functional measure of transvascular gap size, was determined. The microenvironment was modulated: (i) spatially, by growing tumors in subcutaneous or cranial locations and (ii) temporally, by inducing vascular regression in hormone-dependent tumors. Tumors grown subcutaneously exhibited a characteristic pore cutoff size ranging from 200 nm to 1.2 microm. This pore cutoff size was reduced in tumors grown in the cranium or in regressing tumors after hormone withdrawal. Vessels induced in basic fibroblast growth factor-containing gels had a pore cutoff size of 200 nm. Albumin permeability was independent of pore cutoff size. These results have three major implications for the delivery of therapeutic agents: (i) delivery may be less efficient in cranial tumors than in subcutaneous tumors, (ii) delivery may be reduced during tumor regression induced by hormonal ablation, and (iii) permeability to a molecule is independent of pore cutoff size as long as the diameter of the molecule is much less than the pore diameter.     

Reasoning about edges in scale space

Explores the role of reasoning in early vision processing. In particular, the problem of detecting edges is addressed. The authors do not try to develop another edge detector, but rather, they study an edge detector rigorously to understand its behavior well enough to formulate a reasoning process that allow appliance of the detector judiciously to recover useful information. They present a multiscale reasoning algorithm for edge recovery: reasoning about edges in scale space (RESS). The knowledge in RESS is acquired from the theory of edge behavior in scale space and represented by a number of procedures. RESS recovers desired edge curves through a number of reasoning processes on zero crossing images at various scales. The knowledge of edge behavior in scale space enables RESS to select proper scale parameters, recover missing edges, eliminate noise or false edges, and correct the locations of edges. A brief evaluation of RESS is performed by comparing it with two well-known multistage edge detection algorithms     

Texture segmentation using Voronoi polygons

Textures are defined in terms of primitives called tokens. A texture segmentation algorithm based on the Voronoi tessellation is discussed. The algorithm first builds the Voronoi tessellation of the tokens that make up the textured image. It then computes a feature vector for each Voronoi polygon. These feature vectors are used in a probabilistic relaxation labeling on the tokens, to identify the interior and the border regions of the textures. Some experimental results are shown     

Internal optical loss measurements in InGaAs-InAlGaAs quantum-well lasers operating around 1550 nm

A multisection device technique is employed to carry out internal optical loss measurements in two types of InGaAs-InAlGaAs quantum-well structures. One structure consists of conventional identical-width quantum wells and the other, a broader spectral-width material, consists of multiple-width quantum wells in the active region. The temperature dependence of the internal optical losses is also investigated for both structures.     

Experimental validation of mechanical stress models by micro-Raman spectroscopy

It is shown that micro-Raman spectroscopy offers a unique tool for the validation of stress models for microelectronics devices. Starting from an analytical or numerical model that describes the variation of local stress in a device, the corresponding Raman shift is calculated and compared with the data. In this way feed-back is given to the model. This technique is demonstrated for stripes (Si₃N₄, COSi₂, W) on a Si substrate, but can be applied to any device where Raman data can be obtained.     

Effectiveness of visual interactive modeling in the context of multiple-criteria Group decisions

Significant research about the impact of information presentation on decision processes, group-decision support systems, and multicriteria decision making has occurred over the past 10 to 15 years. Advances in hardware and software technologies have significantly reduced costs and enhanced information presentation capability, specifically in the areas of virtual reality and visual interactive modeling (VIM). These visualization technologies can aid in the assimilation of complex qualitative and quantitative information by the decision maker and allow the abstraction of vast information space. Thus, in group-decision situations, visualization has the potential to enhance the decision makers' ability to make appropriate tradeoffs and improve communication between group members resulting in quicker and better consensus decisions. This paper focuses on the study of the effectiveness of advanced information-presentation technologies, such as VIM in complex decision situations involving multiple criteria and groups of decision makers. The effectiveness of VIM is evaluated through a controlled experimental study. The study finds that VIM leads to greater efficiency in decision making and improved group-member attitude and satisfaction with the decision-making process and group-decision solution. However, somewhat contrary to our a priori expectations, the quality of the decision that is made by the groups using visual-interaction modeling is not better than those without this support.     

Development of a novel mounting method for the fabrication of Pb-salt laser grown on [110] oriented BaF/sub 2/ substrate

The development of a novel mounting method for the fabrication of a cleaved cavity Pb-salt laser grown on [110] BaF/sub 2/ substrate is reported. The method involves bonding of the [110] oriented Pb-salt epitaxial layer on [100]-oriented GaAs wafers and removal of the BaF/sub 2/ substrate. After epitaxial layers were grown by molecular beam epitaxy on the BaF/sub 2/ substrate, the sample was bonded with the epilayer side down on GaAs wafers followed by an alignment process. The substrate was then completely etched away. The alignment and bonding technique allows the cleaving of Pb-salt layers in the natural cleavage plane {100}, leading to the formation of a cleaved cavity for the fabrication of a Fabry-Pe/spl acute/rot Pb-salt diode laser.