Optimum power from a solar thermal power plant using solar concentrators

In this paper, the optimum temperature of operation of a solar concentrator and thus the maximum power obtained from a solar thermal power plant has been calculated. Results are plotted graphically and discussed.     

An experimentally validated thermo-mechanical model for the prediction of thermal contact conductance

A predictive model for estimating thermal contact conductance between two nominally flat metallic rough surfaces has been developed and experimentally validated. The predictive model consists of two complementary parts, the first of which is a surface deformation analysis to calculate the actual area of contact for each contact spot, while the second accounts for the effects of constriction resistance and gas gap conductance between the contacting surfaces. A surface characterization technique is developed which generates an equivalent 3-D surface profile from multiple 2-D profiles and determines the unique wavelengths of importance for the surface deformation and constriction resistance models. For given surface profiles and material properties of two contacting surfaces, and a specified contact pressure, the surface characterization technique filters out non-essential wavelengths on the surface, after which the surface deformation analysis calculates the deformation and contact area of each contacting asperity by considering three different modes of deformation, namely, elastic, elastic–plastic, and plastic. The constriction resistance model is then used to calculate the constriction resistance for each contacting asperity based on the area of contact and radius of curvature of the asperity. The constriction resistance values for all the contacting asperities are then used to calculate the total thermal contact conductance. An experimental facility has also been constructed to measure thermal contact conductance of interfaces to verify the results of the predictive model. Good agreement has been found between the model predictions and experimental measurements, validating the modeling approach.     

Normalized Kemeny and Snell distance: a novel metric for quantitative evaluation of rank-order similarity of images

There are needs for evaluating rank order-based similarity between images. Region importance maps from image understanding algorithms or human observer studies are ordered rankings of the pixel locations. We address three problems with Kemeny and Snell's distance (d/sub KS/), an existing measure from ordinal ranking theory, when applied to images: its high-computational cost, its bias in favor of images with sparse histograms, and its image-size dependent range of values. We present a novel computationally efficient algorithm for computing d/sub KS/ between two images and we derive a normalized form d/sub KS/ with no bias whose range is independent of image size. For evaluating similarity between images that can be considered as ordered rankings of pixels, d/sub KS/ is subjectively superior to cross correlation.     

Nystatin prophylaxis: its inability to prevent fungal peritonitis in patients on continuous ambulatory peritoneal dialysis

OBJECTIVE: To evaluate the potential effectiveness of nystatin as prophylaxis for fungal peritonitis (FP) in patients on continuous ambulatory peritoneal dialysis (CAPD). DESIGN: This historically controlled study was designed to investigate the effectiveness of nystatin in the prevention of FP. For this purpose we compared the incidence of FP among 240 (new and prevalent) CAPD patients between January 1996 and November 1996 (period A) with its incidence in 240 new and prevalent CAPD patients in our program between January 1997 and November 1997 (period B) when nystatin prophylaxis was used. There were 2400 patient-months in each period. Nystatin (500,000 IU four times per day), was given orally at the beginning of other antibiotic therapy (usually for peritonitis) and continued for 5 days after the end of the antibiotic therapy. RESULTS: During period A, 133 peritonitis episodes were recorded, and during period B, 99 episodes were recorded. Six episodes of FP were identified in over 2400 patient-months of period A, and 12 in over 2400 patient-months of period B. This difference was not statistically significant. Three episodes of antibiotic-related FP were seen in period A, and four in period B. The remaining episodes arose de novo, that is, unrelated to the use of antibiotics. We observed no side effects for nystatin. CONCLUSION: In CAPD patients the use of nystatin, a nonabsorbable antifungal agent, as prophylaxis in every instance of peritonitis or other indications for antibiotics, did not lower the incidence of fungal peritonitis.     

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.     

Yield strength of overaged alloys containing coherent ordered precipitates

The existing models for yielding of overaged alloys do not account for the observed strain rate sensitivity of the yield stress and predict a sharper decrease in stress as a function of particle size than the experimental observations. A dynamic model has been presented here to account for the yield strength of overaged alloys containing coherent ordered precipitates which takes into consideration the intrinsic characteristics of the precipitates. Concentric glide loops are supposed to form around precipitate particles. Their sizes as a function of applied stress have been computed. The stress on the innermost loop rises with increasing applied stress and when it exceeds the opposing force due to antiphase boundary, the loops shrink. The rate of shrinkage of loops has been calculated for different values of applied stresses. The yielding occurs when the external stress is high enough to account for the applied strain rate. The model has been applied to calculate the yield strength of an austenitic stainless steel containingγ’ precipitates. The antiphase boundary energy of the precipitates was measured by dislocation pair spacing method. The mode of variation of calculated yield stress values with particle size is predicted more accurately than by earlier models. The model qualitatively accounts for the observed sensitivity of yield stress to strain rate and antiphase boundary energy of the precipitates. Formerly Manager Research & Development, Alloy Steels Plant, Durgapur     

A hard diffusion boride coating for ferrous materials

A pack cementation method is described for forming a hard dense boride coating on ferrous materials. The coating produced on different steels was characterized by metallography, X-ray diffraction and electron microprobe analysis. The coating on all the steels studied consisted predominantly of iron borides, though small amounts of chromium could also be incorporated in the coating by varying the pack chemistry. The adherence of the coating was observed to depend on its thickness and the particular base material; greater thicknesses and greater amounts of alloying elements in the base material resulted in a generally greater tendency for the coating to spall. The coating exhibited good resistance to corrosion in slightly acidic water as long as it remained free of any microcracks; it also showed a much better resistance against erosion by flowing pressurized water than either tungsten carbide or Stellite did.