Comparison of Displacement and Mixing Diffusers

In order to cumpare the peformance of different supply diffuers of ventilation air, the airflow passern, temperature stratifiation and contaminant dispersion in a furnitured office ventilated by three kinds of air diffuer were numerically investigated. The air diffuers studied in this paper are a quarter-cylinder displacement diffuer on the floor and mixing diffuers (linear and vortex diffuers) on the ceiling. The heat sources in the of-fice are considered to be 50% convective and 50% radiative. The k-? two-equatwn model of turbulence is employed to predict the turbulent diffusion. The results show that the displacement diffuser provides a rather uniform flow field with low velocify in most areas, and the vertical temperature difference from floor to ceiling is as high as 6 K. With the linear diffuser, the air velociry is high, and the temperature is uniform both horizontally and vertically. The air velocity generated by the vortex diffuser is moderate. The distributions of the temperature and the contaminant are rather uniform.     

Analysis of a resonant-cavity enhanced GaAs/AlGaAs MSMphotodetector

The authors have developed a 2-D device simulator for heterostructure metal-semiconductor-metal (MSM) photodetectors. They have incorporated a model of multilayer optics into the simulator and used it to analyze the temporal response of a resonant-cavity enhanced heterostructure with a confining buffer layer and a distributed Bragg reflector (DBR). The authors show that through fine tuning the layer thicknesses, optical resonance enhancement of the light absorption can be obtained     

一种实验炼钢渣的穆斯堡尔谱研究

一种实验炼钢渣不同炉次样品的室温透射穆斯堡尔谱由两组裂距较大的四极分裂双峰和一组裂距较小的双峰组成，它们分别相应于具有不同微观环境的Ｆｅ＾２＋和Ｆｅ＾３＋。参照文献中已知ＦｅｘＯ的穆斯堡尔谱数据，可确定该渣中的主要含铁相为ＦｅｘＯ。Ｘ射线衍射相分析给出相同的结果。按亚谱的面积比计算出Ｆｅ＾２＋和Ｆｅ＾３＋的相对含量分别为８５％和１５％左右。进一步选取与样品晶体结构相联系的原子簇模型。用ＭＳ－Ｘａ方     

Improving power factor in the presence of harmonics usinglow-voltage tuned filters

The development of a simplified approach for sizing and placement of tuned filters for power factor correction of nonlinear loads is outlined. This approach has been successfully applied to industrial power distribution systems ranging in size from 550 to 10000 kVA. Six case studies that illustrate different aspects of the approach are presented. In all instances, power factor was improved to meet the goal, and in many cases, harmonic distortion was significantly reduced     

Neurocomputing strategies in structural design — on analysing weights of feedforward neural networks

The sequel of two papers explores the applicability of selected neurocomputing strategies in the optimization of structural systems. The present paper describes the use of interconnection weights of a multilayer, feedforward neural network to extract information pertinent to a design space modelled by such a network. It is shown that aweights analysis provides a technique to assess the effect of all input quantities on a given output. Such dependencies are expressed in the form of atransition matrix, and their evaluation is reduced to the inspection of elements of a matrix row. Explicit formulae are derived for networks with one and two hidden layers and can easily be generalized to networks with an arbitrary number of hidden layers. In addition to its use as a tool to partition design spaces, the weights analysis may be employed to assist in determining the size of hidden layers and an adequate number of training patterns (input-output pairs). Several numerical examples from the field of structural analysis are provided, and the paper underscores the utility of the present technique in decomposition driven optimal design; such optimization is treated in full in the companion paper.     

Removal of endocrine disrupting chemicals (EDCs) using low pressure reverse osmosis membrane (LPROM).

Endocrine disrupting chemicals (EDCs) are the focus of current environmental issues, as they can cause adverse health effects to animals and human, subsequent to endocrine function. The objective of this study was to remove a specific compound of EDCs (i.e. pentachlorophenol, C(6)OCL(5)Na, molecular weight of 288 g/mol) using low pressure reverse osmosis membrane (LPROM). A cross flow module of LPROM was used to observe the effects of operating parameters, i.e. pH, operating pressure and temperature. The design of the experiment was based on MINITAB(TM) software, and the analysis of results was conducted by factorial analysis. It was found that the rejection of pentachlorophenol was higher than 80% at a recovery rate of 60 to 70%. The rejection was subjected to increase with the increase of pH. The flux was observed to be increased with the increase of operating pressure and temperature. This study also investigated the interaction effects between operating parameters involved.     

Acidogenic fermentation of blended food‐waste in combination with primary sludge for the production of volatile fatty acids

The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm^?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm^?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO₂ and CH₄), the organic matter was converted into CO₂ through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFA_produced g^?1 VS_fed day^?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry     

Effects of solid retention time on the performance of submerged anoxic/oxic membrane bioreactor.

In this study, four similar bench-scale submerged Anoxic/Oxic Membrane Bioreactors (MBR) were used simultaneously to investigate the effects of solids retention time (SRT) on organic and nitrogen removal in MBR for treating domestic wastewater. COD removal efficiencies in all reactors were consistently above 94% under steady state conditions. Complete conversion of NH(4+)-N to NO(3-)-N was readily achieved over a feed NH(4+)-N concentration range of 30 to 50 mg/L. It was also observed that SRT did not significantly affect the nitrification in the MBR systems investigated. The average denitrification efficiencies for the 3, 5, 10 and 20 days SRT operations were 43.9, 32.6, 47.5 and 66.5%, respectively. In general, the average effluent nitrogen concentrations, which were mainly nitrate, were about 22.2, 27.6, 21.7 and 13.9 mg/L for the 3, 5, 10 and 20 days SRT systems, respectively. The rate of membrane fouling at 3 days SRT operation was more rapid than that observed at 5 days SRT. No fouling was noted in the 10 days and 20 days SRT systems during the entire period of study.