Performance Characteristics of Alpha-Particle Corona-Streamer Counter

Alpha-particle wire-plate corona counters in air can be operated either in the spark or in the corona-streamer modes. The streamer mode is preferred over the spark mode since it has the advantages of low dead time and the absence of electrode corrosion by sparking. An analysis of the alpha-particle corona-streamer counter is described. The alpha-particle triggered corona pulse characteristics (e.g., pulse shape, amplitude, repetition rate, etc.) are calculated. Not only the pulse characteristics but also the inception voltages of the corona-mode regime are determined. For each wire diameter, a transition gap length between corona and spark modes exists, which is termed ``critical gap length.' The counting rate characteristics have been obtained for wire diameters 0.05-0.1 mm. All the theoretical findings are confirmed by experiment.     

Dynamic Simulation of Radially Oriented Permanent Magnet-Type Electronically Operated Synchronous Machines with Parameters Obtained from Finite Element Field Solutions

A dynamic model for simulation of the transient interaction between radially oriented permanent magnet-type synchronous machines and their corresponding transistorized current source power conditioners is presented. Some key machine parameters used in this dynamic model were obtained from finite element field solutions. This dynamic model was used to obtain the transient interaction between a 15-hp samarium cobalt radially oriented permanent magnet electronically operated synchronous machine and its corresponding power conditioner. This machine was constructed for electric vehicle propulsion. Excellent correlation between various digitally simulated and actual test current and voltage waveforms, in various branches of the machine-conditioner network, has been achieved. These results are given. This modeling approach is applied to machines during the design stage, where the finite element modeling is the only way to obtain the necessary machine parameters for dynamic simulation. It is shown how such a combination of the computer-aided design tools can help in prevention of design mis-judgements that can prove costly to remedy once the hardware is in place. This is done through an actual design example of an additional machine being manufactured for electric propulsion applications.     

Optimizing Concentration of Drag Reducing Polymer in Case of One- and Two-Phase Flow in 90° Copper Elbow

Journal of Failure Analysis and Prevention - The rate of diffusion-controlled corrosion of 90° Copper Elbow by acidified dichromate has been investigated in relation to the following...     

Evaluating drought response of Southern Cape Indigenous Forests,South Africa,using MODIS data

Indigenous forests in South Africa cover less than 0.5% of the total land area but are a valued resource under threat from fragmentation, fires, exploitation, and climate change. The largest indigenous forest complex is located along the southern coast of the Western Cape Province. This complex is made up of sub-forests distinguished by different structural and edaphoclimatic attributes. It has been hypothesized that these sub-forests exhibit different resistance to stressors, such as drought. A time series of MODIS 250 m enhanced vegetation index (EVI) data were used to characterize the foliage condition of the three distinctive sub-forests before, during, and after a severe drought in 2009. The goal was to determine how these sub-forests responded to this disturbance. EVI anomalies for the drought and post-drought periods were calculated using annual median EVI values, since removal of outliers based on quality control flags that accompany the MODIS products or noise-filtering techniques proved to be ineffective. Results of the study indicated that pre-drought foliage density EVI was not controlled by differences in water availability, but may have been due to other edaphoclimatic or structural attributes. Maximum foliage loss occurred one year after the driest year, indicating the cumulative effects of drought stress on forest production and retention of foliage. The hypothesized stress resistance capacity of the three sub-forests was found to correspond to their rate of post-drought recovery. There is a need to tie these satellite observations of forest drought response to ground observations of forest condition, growth, and specific site attributes.     

Variability on the Propagation of a Plane Wave Using Stochastic Collocation Methods in a Bio Electromagnetic Application

In this letter, the uncertainties on the angles of propagation of a plane wave in a bio electromagnetic application are studied using two non intrusive stochastic collocation methods. The proposed techniques are used in this application, which employs a finite-difference time-domain scheme, but they can be used when applying other kinds of methods without modifying programs. The results obtained using the two approaches are compared. The stochastic collocation methods are used to determine the influence of the uncertainty on the angle of propagation of a plane wave on the obtained specific absorption rate. Global sensitivity is analyzed.     

Effect of mutation schemes on convergence to optimum design of steel frames

In this paper an attempt is made to modify a distributed genetic algorithm (DGA) to minimize the weight of steel frames. The main aspects of modifications include the twin analogy and a number of mutation schemes. Although the mutation is a secondary operator in the GA, it plays an influential role in diversifying the population and exploring more feasible design space. In this research, four different mutation schemes are examined and their effects on convergence to optimum solutions are evaluated. Using three benchmark examples, it is demonstrated that mutation operator can efficiently influence on the speed of convergence and consequently saving computation time. As coding a program is required, the DO-DGA software has been developed to handle the algorithm. DO-DGA applies modified DGA, including different mutation schemes, to obtain the global optimum solution.     

Convective flow and heat transfer in a tall porous cavity side-cooled with temperature profile

Natural convection in an air-filled (Prandtl number = 0.7) porous cavity with profiled side cooling and constant bottom heating is investigated over the Rayleigh number range of 1×10⁴ to 1×10⁸ at two Darcy numbers: 1×10^-4 and 1×10^-6. The aspect ratio based on cavity height was varied from 0.5 to 0.1 to investigate penetration length according to linear or sinusoidal temperature profile. The general non-Darcy model adopted in this work was validated against experimental and theoretical results in the literature and Nusselt number was predicted within less than 3% in the worst case. The effect of left wall imposed temperature profile was investigated in detail. Different convective regimes were observed depending on the imposed profile. An active region was found to take place with the linear temperature profile and with extent proportional to Rayleigh number as predicted by scale analysis.     

Effect of frozen storage of hake,sardine and mixed minces on natural actomyosin extracted in salt solutions

Natural actomyosin extracted in salt solutions from mixtures of hake and sardine minces (3:1; 1:1 and 1:3 w/w) stored frozen for up to 1 year differed in the amount extracted and in the characteristics of the extracts. In the mixed minces the amount of natural actomyosin extracted decreased during frozen storage at a higher rate than that theoretically corresponding to the amount of hake in the mixes. With increasing storage time and proportion of sardine a lower percentage of myosin heavy chain and actin was observed by electrophoresis. An increased size of aggregates was also observed by electrophoresis and transmission electron microscopy. The stability of emulsions was enhanced when aggregates appeared in the extracts. The decrease in the amount of natural actomyosin extracted does not explain the changes observed in the texture of the minces during frozen storage. This may indicate that the size of the aggregates unextractable in salt solutions, independently of the type of bonds that bind the proteins in the aggregates, plays an important role in the textural changes observed. Copyright © 2003 Society of Chemical Industry