Buoyancy convection in a cavity with mutually orthogonal heated plates

Buoyancy driven convection in a square cavity induced by two mutually orthogonal arbitrarily placed heated thin plates is studied numerically under isothermal and isoflux boundary conditions. The flow is assumed to be two-dimensional. The coupled governing equations were solved by the finite difference method using the Alternating Direction Implicit technique and Successive Over Relaxation method. The steady state results are depicted in terms of streamline and isotherm plots. It is found that the resulting convection pattern is stronger for the isothermal boundary condition. A better overall heat transfer can be achieved by placing one of the plates far away from the center of the cavity for isothermal boundary condition and near the center of the cavity for isoflux boundary condition.     

Interaction Between Two Mutually Orthogonal Heat-Generating Baffles in a Square Cavity

Laminar free convection induced by two mutually orthogonal discrete heat-generating baffles in a two-dimensional square cavity is analyzed numerically. The computations were carried out for different locations and combinations of heat source strengths of the baffles for a fixed Grashof number of 10⁶and Prandtl number of 0.71. The coupled governing equations were solved bya finite-difference method using alternating direction implicit technique and successive overrelaxation methods. The obtained results clearly show that the hydrodynamic and thermal fields in the cavity depend on both the location and strength of the heat-generating baffles. Though the flow inhibition is caused by both the baffles, the baffle with higher source strength plays a decisive role in inducing the flow. The locations of baffles with unequal source strengths produce significant changes in the net heat transfer rate. This is further magnified for higher contrast in source strengths. This study provides qualitative suggestions that may improve the thermal design of sealed enclosures, which are encountered frequently in the electronics industry.     

An experimental evaluation of I/O optimizations on different applications

Many large scale applications have significant I/O requirements as well as computational and memory requirements. Unfortunately, the limited number of I/O nodes provided in a typical configuration of the modern message-passing distributed-memory architectures such as Intel Paragon and IBM SP-2 limits the I/O performance of these applications severely. We examine some software optimization techniques and evaluate their effects in five different I/O-intensive codes from both small and large application domains. Our goals in this study are twofold. First, we want to understand the behavior of large-scale data-intensive applications and the impact of I/O subsystems on their performance and vice versa. Second, and more importantly, we strive to determine the solutions for improving the applications' performance by a mix of software techniques. Our results reveal that different applications can benefit from different optimizations. For example, we found that some applications benefit from file layout optimizations whereas others take advantage of collective I/O. A combination of architectural and software solutions is normally needed to obtain good I/O performance. For example, we show that with a limited number of I/O resources, it is possible to obtain good performance by using appropriate software optimizations. We also show that beyond a certain level, imbalance in the architecture results in performance degradation even when using optimized software, thereby indicating the necessity of an increase in I/O resources.     

High temperature superconductivity in orthorhombic LaBa2Cu3O7−δ

High temperature superconducting LaBa₂Cu₃O_7−δ has been prepared by ceramic and nitrate methods to understand the influence of preparation conditions on superconductivity. The characterization was carried out by X-ray diffraction and magnetic susceptibility measurements.T _c onset was observed at 88 K. Meissner effect has been observed above the liquid nitrogen temperature.     

Chitosan modified with a polydentate crosslinker for metal‐ion adsorption

Extensive study of solution properties of sodium hyaluronate including about 140 samples and covering broad molar mass range was carried out by classical viscometry using an Ubbelohde capillary viscometer and by combination of size‐exclusion chromatography with a multi‐angle light scattering detector and an on‐line viscometer. The study also involved critical overview of literature data of Mark‐Houwink relation for sodium hyaluronate. Continuous decrease of the Mark‐Houwink exponent with increasing molar mass to the values markedly lower than those typical of linear random coils in thermodynamically good solvents was observed. This fact was attributed to branched molecular structure of hyaluronic acid as a result of unknown side reactions during the manufacturing process. The molar mass dependence of the second virial coefficient was determined and proved aqueous salt solutions to be thermodynamically good solvents for sodium hyaluronate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Quench solvent evaluation: An e.s.r. study

An in-situ radical-quenching experiment was performed in an e.s.r. microwave cavity by using a solution flow system. Diphenylmethyl radicals produced from pyrolysis of 1,1,2,2-tetraphenylethane were quenched by several H-donor solvents. Among the solvents used, indan was the fastest in quenching, followed by hydrophenanthrene, tetralin, mesitylene and cumene in decreasing order of quenching rate.     

Folded Architecture for Digital Gammatone Filter Used in Speech Processor of Cochlear Implant

Emerging trends in the area of digital very large scale integration (VLSI) signal processing can lead to a reduction in the cost of the cochlear implant. Digital signal processing algorithms are repetitively used in speech processors for filtering and encoding operations. The critical paths in these algorithms limit the performance of the speech processors. These algorithms must be transformed to accommodate processors designed to be high speed and have less area and low power. This can be realized by basing the design of the auditory filter banks for the processors on digital VLSI signal processing concepts. By applying a folding algorithm to the second‐order digital gammatone filter (GTF), the number of multipliers is reduced from five to one and the number of adders is reduced from three to one, without changing the characteristics of the filter. Folded second‐order filter sections are cascaded with three similar structures to realize the eighth‐order digital GTF whose response is a close match to the human cochlea response. The silicon area is reduced from twenty to four multipliers and from twelve to four adders by using the folding architecture.     

Goubau line based end‐fire antenna

This article proposes a simple and low profile planar Goubau line based end‐fire antenna. End‐fire radiation is achieved by modifying the Goubau line into inverted periodic arrangement of V‐shaped unit cells. Designed prototype is simulated and verified experimentally. Both the simulated and measured results are in good agreement. Proposed antenna radiates toward end‐fire direction between 7.8 and 8.3 GHz. The maximum gain of the antenna is obtained around 7.2 dBi. The average efficiency is observed 70% over the entire operating bandwidth. Proposed end‐fire antenna has a single metallic layer with simple configuration which is easy to fabricate and also easy to integrate with other electronics circuits. The proposed antenna can be used for satellite and RADAR applications.     

Effect of baffle–cavity ratios on buoyancy convection in a cavity with mutually orthogonal heated baffles

Buoyancy driven convection in a square cavity induced by two mutually orthogonal and arbitrarily located baffles is studied numerically. The baffles are of different sizes and the flow is two-dimensional. The coupled governing equations were solved by finite difference method using Alternating Direction Implicit technique and Successive Over-Relaxation method. The steady state results are presented in the form of streamline and isotherm plots. It is found that buoyancy force plays a key role and overall heat transfer in the cavity is enhanced for higher values of both baffle–cavity ratios. Flow inhibition emerges as a deciding factor and diminishes heat transfer when the horizontal baffle is located above the center of the cavity.