Scour in Long Contractions

Experimental results on local scour in long contractions for uniform and nonuniform sediments (gravels and sands) under clear-water scour are presented. An emphasis was given to conduct the experiments on scour in long contractions for gravels. The findings of the experiments are used to describe the effects of various parameters (obtained from dimensional analysis) on equilibrium scour depth under clear-water scour. The equilibrium scour depth increases with decrease in opening ratio and with increase in sediment size for gravels. But the curves of scour depth versus sediment size have considerable sag at the transition of sand and gravel. The scour depth decreases with increase in densimetric Froude number, for larger opening ratios, and increases with increase in approaching flow depth at lower depths. However, it becomes independent of approaching flow depth at higher flow depths. The effect of sediment gradation on scour depth is pronounced for nonuniform sediments, which reduce scour depth significantly due to the formation of armor layer in the scour hole. Using the continuity and energy equations, a simple analytical model for the computation of clear-water scour depth in long contractions is developed with and without sidewall correction for contracted zone. The models agree satisfactorily with the present and other experimental data. Also, a new empirical equation of maximum equilibrium scour depth, which is based on the experimental data at the limiting stability of sediments in approaching channel under clear-water scour, is proposed. The potential predictors of the maximum equilibrium scour depth in long contractions are compared with the experimental data. The comparisons indicate that the equations given by Komura and Lim are the best predictors among those examined.     

Libra: a computational economy‐based job scheduling system for clusters

Clusters of computers have emerged as mainstream parallel and distributed platforms for high‐performance, high‐throughput and high‐availability computing. To enable effective resource management on clusters, numerous cluster management systems and schedulers have been designed. However, their focus has essentially been on maximizing CPU performance, but not on improving the value of utility delivered to the user and quality of services. This paper presents a new computational economy driven scheduling system called Libra, which has been designed to support allocation of resources based on the users' quality of service requirements. It is intended to work as an add‐on to the existing queuing and resource management system. The first version has been implemented as a plugin scheduler to the Portable Batch System. The scheduler offers market‐based economy driven service for managing batch jobs on clusters by scheduling CPU time according to user‐perceived value (utility), determined by their budget and deadline rather than system performance considerations. The Libra scheduler has been simulated using the GridSim toolkit to carry out a detailed performance analysis. Results show that the deadline and budget based proportional resource allocation strategy improves the utility of the system and user satisfaction as compared with system‐centric scheduling strategies. Copyright © 2004 John Wiley & Sons, Ltd.     

A taxonomy of computer‐based simulations and its mapping to parallel and distributed systems simulation tools

In recent years, extensive research has been conducted in the area of simulation to model large complex systems and understand their behavior, especially in parallel and distributed systems. At the same time, a variety of design principles and approaches for computer‐based simulation have evolved. As a result, an increasing number of simulation tools have been designed and developed. Therefore, the aim of this paper is to develop a comprehensive taxonomy for design of computer‐based simulations, and apply this taxonomy to categorize and analyze various simulation tools for parallel and distributed systems. Copyright © 2004 John Wiley & Sons, Ltd.     

Leakage current and charge in RTV coated insulators under pollution conditions

Room temperature vulcanizing (RTV) silicone rubber coating has excellent leakage current suppression characteristics. It is used extensively on porcelain and glass insulators in pollution prone areas as an anti-pollution measure. A pollution aging chamber has been fabricated and an on line 4-channel personal computer (PC) based data acquisition system has been developed to conduct tests on RTV coated porcelain samples. A study of the dependence of the leakage current and the charge on the flow rate, conductivity and pressure of the solution forming the fog is reported. It was observed that a higher charge and a higher average leakage current were obtained at a higher flow rate and a higher conductivity. The results with coated HV insulators are consistent with those published in the literature with RTV coated fiber glass reinforced plastic (FRP) rods.     

Performance enhancement in coal fired thermal power plants. Part II: steam turbines

This paper presents the results of the performance enhancement study on 22 coal fired thermal power stations of capacities 30–500 MW. The oldest units (30 MW) have served for 33yr and the newer units (500 MW) have been in operation since 7yr. The turbine efficiencies are in the range 31·00–41·90% as compared to the design range of 34·80–43·97%. The isentropic efficiencies are in the range 74·13–86·40% as compared to design values of 83·20–89·10%. Considerable scope for efficiency improvement through low cost solutions: operational optimization, capital overhaul, simple modifications, etc., exists for all classes of units. The efficiencies can be restored to their design values. The developments in turbines over the last quarter of this century which have led to improved isentropic and thermal efficiencies must be adopted for existing units through retrofits, upgrades and revamps. The turbine efficiencies can be improved to 38·0% for 30 MW units and to 47% for 500 MW units. The maximum potential is for improvement in 210 and 500 MW units followed by 110 and 120 MW units. The potential for 30 and 62·5 MW units is rather limited because of their low capacity share, lack of interest in manufacturers to sell spares (because of the low volume of requirement) and large pay back periods for modernisation schemes. Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesis of Metastable, Wurzite-Based Zinc Oxide-Cobalt(II) Oxide Solid Solutions by Spray Pyrolysis

Aqueous solutions of acetates and nitrates of zinc and cobalt have been spray decomposed to study the production of extended solid solutions in the ZnO–CoO system. Examination of the products of a variety of synthesis conditions indicates that up to 70% CoO may be retained in the solid solution in the wurzite phase, even though a comparison of the equilibrium solubility in the phase diagram might be expected to favor the formation of a rock-salt-based solid solution.     

Impact of polyphenols from banana pseudostem on sunflower oil stability

The present investigation is focused on the potential use of banana pseudostem, which otherwise is disposed off as a waste, as a source of polyphenols or antioxidants. The polyphenols extracted from the outer leaf sheaths of 3 Indian banana (Musa spp.) cultivars namely, ‘Nendhran’, ‘Robusta’, and ‘Kathali’ were tested for antioxidant activities. The extracts showed effective DPPH, hydroxyl, and superoxide radical scavenging ability. Among the banana cultivars, ‘Nendhran’ followed by ‘Robusta’ contained the highest total phenolic (110.45 and 94.03 mg GAE/g extract, respectively) and total flavonoid (49.62 and 38.61 mg QE/g extract, respectively) contents and antiradical activity. Further, the study was aimed to evaluate the protective effects of the polyphenolic extracts in stabilizing sunflower oil, tested in terms of peroxide value, free fatty acid contents, and p-anisidine values in comparison with the synthetic antioxidants, butylated hydroxyanisole and butylated hydroxytoluene. In addition, the antioxidant activity and total phenolic contents of the extract-treated oil samples were also monitored to obtain a complete perspective of the influence exerted by the polyphenols in oil stability. The results demonstrated that polyphenols from pseudostem of banana cultivars are potent source of natural antioxidants and might serve as a substitute for synthetic antioxidants in oil industry.     

Neuroscience instrumentation and distributed analysis of brain activity data: a case for eScience on global Grids

The distribution of knowledge (by scientists) and data sources (advanced scientific instruments), and the need for large‐scale computational resources for analyzing massive scientific data are two major problems commonly observed in scientific disciplines. Two popular scientific disciplines of this nature are brain science and high‐energy physics. The analysis of brain‐activity data gathered from the MEG (magnetoencephalography) instrument is an important research topic in medical science since it helps doctors in identifying symptoms of diseases. The data needs to be analyzed exhaustively to efficiently diagnose and analyze brain functions and requires access to large‐scale computational resources. The potential platform for solving such resource intensive applications is the Grid. This paper presents the design and development of MEG data analysis system by leveraging Grid technologies, primarily Nimrod‐G, Gridbus, and Globus. It describes the composition of the neuroscience (brain‐activity analysis) application as parameter‐sweep application and its on‐demand deployment on global Grids for distributed execution. The results of economic‐based scheduling of analysis jobs for three different optimizations scenarios on the world‐wide Grid testbed resources are presented along with their graphical visualization. Copyright © 2005 John Wiley & Sons, Ltd.     

Rework techniques process evaluation for chip scale packages

The packaging formats, chip scale package (CSP) and ball grid array (BGA) have allowed significant reductions in component size compared to conventional surface mount devices (SMD) such as quad flat packs (QFP). However, the position of the solder joints formed (underneath the chip) after reflow means that visual inspection is impossible. For the defective chip, the only realistic method of rework is to remove and replace it. Component removal can be easily achieved, however replacement may be more complex. Difficulties in the procedure may arise from loss of terminations during the removal process, and high component population densities on printed circuit boards (PCB) may also inhibit access to the component pad site. The typical rework process consists of a number of steps including; component removal, PCB pad clean-up, flux or solder paste application, component placement and reflow. In this paper, we evaluate the pad clean up stage of the CSP rework process, including the design and analysis of a variety of solder paste or flux deposition techniques. Two PCB pad-cleaning methods have been compared and conclusions drawn from the resultant pad finish. Four deposition techniques have been assessed; these include mini-stencil, dip transfer, on- and off-contact stamping. Mini-stencil is the traditional method used in the electronics manufacturing industry for the deposition of solder paste onto reworked component sites. The remaining deposition techniques have been developed in order to overcome access restrictions that might exist on densely populated PCB's