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101.
A hybrid photovoltaic-thermal (PV/T) solar air heater system which generates both electricity and heat energy simultaneously was studied. This hybrid system consists of monocrystalline silicon cells pasted to an absorber plate with fins attached at the other side of the absorber surface. Air as heat removing fluid is made to flow through an upper channel and then under the absorber plate or lower channel of the collector. Only a small part of the absorbed solar radiation is converted to electricity, while the rest increases the temperature of the cells. Improvements to the total efficiency of the system can be achieved by the use of a double-pass collector system and fins. This paper presents the experimental and theoretical studies on a finned double-pass PV/T solar air heater suitable for low temperature applications. A steady-state closed-form solution to determine the outlet and mean photovoltaic temperature has been obtained. An experimental setup has been developed. Comparisons are made between the experimental and theoretical results and close agreement, is obtained.  相似文献   
102.
In this paper, the Rama distribution (RD) is considered, and a new model called extended Rama distribution (ERD) is suggested. The new model involves the sum of two independent Rama distributed random variables. The probability density function (pdf) and cumulative distribution function (cdf) are obtained and analyzed. It is found that the new model is skewed to the right. Several mathematical and statistical properties are derived and proved. The properties studied include moments, coefficient of variation, coefficient of skewness, coefficient of kurtosis and moment generating function. Some simulations are undertaken to illustrate the behavior of these properties. In addition, the reliability analysis of the distribution is investigated through the hazard rate function, reversed hazard rate function and odds function. The parameter of the distribution is estimated based on the maximum likelihood method. The distributions of order statistics for ERD are also presented. The performance of the suggested model is compared with several other lifetime distributions based on some goodness of fit tests on a real dataset. It turns out that the suggested model is more flexible than its competitors considered in this study, for modeling real lifetime data.  相似文献   
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An analog baseband chain for a synthetic aperture radar receiver implemented in a 130 nm CMOS technology is presented in this paper. Occupying 0.23 mm2 of silicon area, the baseband chain consists of a three-stage variable gain amplifier (VGA), a 5th-order gm-C low-pass filter (LPF) and an output buffer. The gain of the chain can be controlled by tuning the control voltages of the VGA and has a range from 25 to 34 dB. 8 dB of the gain is embedded into the LPF. The bandwidth of the LPF is programmable from 100 to 190 MHz by means of capacitor matrices. The chain, which uses a 1.2 V supply voltage, achieves an input-referred noise density of 4 nV/ $ \sqrt {\text{Hz}} $ and an in-band IIP3 of ?46 dBV rms.  相似文献   
105.
In this paper, water absorption behavior of pultruded kenaf fiber reinforced unsaturated polyester composites was investigated. Residual compressive properties of the composites after immersion were also reported. Composites were prepared using pultrusion method with minimum kenaf fiber content of 70% w/w. Water absorption tests were performed at room temperature under three different solutions, i.e. distilled water, sea water and acidic solution. The diffusion coefficient of water absorption and maximum moisture content were calculated by measuring the water uptake of specimen at regular time interval. Diffusion coefficient and the highest moisture content values were recorded for composite immersed in distilled water followed by acidic solution and sea water. The water absorption of kenaf fiber reinforced unsaturated polyester composites was found to follow a Fickian’s behavior where it reach equilibrium. The compressive properties were found to decrease with the increase in the percentage of water uptake. The decay in compression properties is attributed to the plasticization of the fiber–matrix interface and swelling of the kenaf fiber.  相似文献   
106.
The development of high-performance engineering products made from natural resources is increasing worldwide, due to renewable and environmental issues. Among the many different types of natural resources, kenaf plants have been extensively exploited over the past few years. Therefore, this paper presents an overview of the developments made in the area of kenaf fiber reinforced composites, in terms of their market, manufacturing methods, and overall properties. Several critical issues and suggestions for future work are discussed, which underscore the roles of material scientists and manufacturing engineers, for the bright future of this new “green” material through value addition to enhance its use.  相似文献   
107.
The specific enthalpy of fracture due to ductile crack propagation in commercial polycarbonate sheet is calculated as * =A 1c/R 1c, whereA 1c is the critical energy release rate associated with the onset of unstable crack propagation andR 1c is the corresponding amount of damage (yielded material) formed per unit crack extension.A 1c andR 1c are determined from fatigue crack propagation experiments conducted at different maximum loads, load ratios and frequencies. The value of * obtained from all experiments is found to be 9.8±1.4 cal g–1 (1cal = 4.184 J) which indicates that * is a material constant. This finding substantiates predictions of the crack layer theory.  相似文献   
108.
The ever-increasing amount of waste from electrical and electronic equipment (WEEE) has become a common problem due to the significant environmental and health impacts associated with inappropriate End-of-Life (EoL) management. The current ad hoc applications of WEEE recycling are often based on limited knowledge and cannot cope with the complex range of materials and products in such waste. A knowledge-based approach has been utilised to investigate the realisation of a recycling process planner which aims to determine the most suitable EoL options for WEEE. A number of case studies have been used to show that a 20-30% improvement on economical and environmental performance could be achieved through adoption of such a systematic approach to recycling process planning.  相似文献   
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110.
BACKGROUND: Adipate esters are used as low‐temperature and low‐viscosity plasticizers for polyvinyl chloride and its copolymers. In this work, optimization of lipase‐catalyzed production of dilauryl adipate was carried out using response surface methodology (RSM) based on a four‐factor‐five‐level central composite rotatable design (CCRD). Immobilized lipase from Candida antarctica (Novozym 435) was used as catalyst in this reaction. Various reaction parameters affecting the synthesis of adipate ester, including alcohol/acid molar ratio, amount of enzyme, temperature and reaction time, were investigated. RESULTS: Statistical analysis showed that the amount of enzyme was less significant than the other three factors. The optimal conditions for the enzymatic reaction were obtained at 5.7:1 substrate molar ratio using 0.18 g of enzyme at 53.1 °C for 282.2 min. Under these conditions the esterification percentage was 96.0%. CONCLUSIONS: The results demonstrated that response surface methodology can be applied effectively to optimize the lipase‐catalyzed synthesis of adipate ester. The optimum conditions can obtained be used to scale up the process. Copyright © 2008 Society of Chemical Industry  相似文献   
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