Four turbulence models including three k-epsilon related turbulence models (standard k-epsilon model, RNG k-epsilon model and realizable k-epsilon model) and v(2)-f turbulence model are performed for axisymmetric conf...
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ISBN:
(纸本)9781424448135
Four turbulence models including three k-epsilon related turbulence models (standard k-epsilon model, RNG k-epsilon model and realizable k-epsilon model) and v(2)-f turbulence model are performed for axisymmetric confined jets and the results are compared with the experimental data. As a source to evaluate the numerical results, the physical model consists of a sudden pipe expansion section, with an expansion ratio of 3.75. The results show that each model has its superiority and some limitations and it's not applicable to introduce a definite model as the best model for simulations of such a kind of flow. But the author believes that, overall, the accuracy of the RNG k-epsilon model appears to be superior to other models even though in comparison to other k-epsilon models it needs more computational efforts per iteration due to the strong nonlinear terms in its transformed equations.
As a reversible reaction, the hydrolysis conversion of ethyl lactate is controlled by thermodynamic equilibrium. In order to improve the yield and conversion rate of hydrolysis of ethyl lactate, ethanol in the product...
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As a reversible reaction, the hydrolysis conversion of ethyl lactate is controlled by thermodynamic equilibrium. In order to improve the yield and conversion rate of hydrolysis of ethyl lactate, ethanol in the products should be removed in time. Hydrolysis of ethyl lactate coupled by vapor permeation (VP) for removing ethanol in the products was proposed. Here, the vapor permeation was carried out with a new polydimethylsiloxane (PDMS)/ceramic composite membrane prepared by our team. The PDMS/ceramic composite membrane was first characterized by scanning electron microscopy (SEM) images, pervaporation, and vapor permeation of ethanol/water mixtures. The characterization results showed that the PDMS/ceramic composite membrane was dense and uniform and had good separation performances. The permeate flux of pervaporation of 5 wt % ethanol arrived at 2541 g.m(-2).h(-1), and the separation factor was 7.5 at 353 K. As for vapor permeation of 10 wt % ethanol, the permeate flux was above 400 g.m(-2).h(-1) and separation factor was around 11. Then, the VP aided hydrolysis of ethyl lactate was investigated with the prepared PDMS/ceramic composite membrane. By coupling with VP, the final conversion of the ethyl lactate increased from 77.1% to 98.2% with the initial molar ratio of water to ethyl lactate 10:1 at 358 K. The larger initial molar ratio of water to ethyl lactate was helpful to improve the conversion of VP aided hydrolysis of ethyl lactate. The VP aided hydrolysis of ethyl lactate with the prepared PDMS/ceramic composite membrane was significantly enhanced.
This paper puts forward a novel cognitive cross-layer design algorithms for multihop wireless networks optimization across physical,mediam access control （MAC）,network and transport *** is well known,the conventiona...
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This paper puts forward a novel cognitive cross-layer design algorithms for multihop wireless networks optimization across physical,mediam access control （MAC）,network and transport *** is well known,the conventional layered-protocol architecture can not provide optimal performance for wireless networks,and cross-layer design is becoming increasingly important for improving the performance of wireless *** this study,we formulate a specific network utility maximization （NUM） problem that we believe is appropriate for multihop wireless *** using the dual algorithm,the NUM problem has been optimal decomposed and solved with a novel distributed cross-layer design algorithm from physical to transport *** solution enjoys the benefits of cross-layer optimization while maintaining the simplicity and modularity of the traditional layered *** proposed cross-layer design can guarantee the end-to-end goals of data flows while fully utilizing network *** simulations have evaluated an enhanced performance of the proposed algorithm at both average source rate and network ***,the proposed algorithm has low implementation complexity for practical reality.
Natural composite materials such as bones and seashells have been refined and perfected over millions of years of evolutionary selection. Thus they possess many advantages both on micro-structures and macroscopical pe...
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Natural composite materials such as bones and seashells have been refined and perfected over millions of years of evolutionary selection. Thus they possess many advantages both on micro-structures and macroscopical performances. Inspired by the natural composites, for the first time, laminated hydroxyapatite (HAp)/chitosan (CS) nanocomposites were prepared by means of solution intercalation in this paper. Intercalated and exfoliated structures were obtained by varying CS contents. Fourier transform infrared (FTIR) result reveals that there is interaction between HAp and CS. Tensile strength test indicates that the HAp lamellae can improve the poor strength of CS evidently, especially in moist environments. The results reported here can be expanded to other HAp-polymer systems, thus may offer a new approach for fabricating biomimetic nanocomposites. (C) 2010 Elsevier B.V. All rights reserved.
A bio-inspired suction cup actuated by shape memory alloy(SMA)for miniature wall climbing robots is developed based on studying characteristics of biological suction *** fast control strategies are introduced to impro...
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A bio-inspired suction cup actuated by shape memory alloy(SMA)for miniature wall climbing robots is developed based on studying characteristics of biological suction *** fast control strategies are introduced to improve negative pressure *** model of the suction cup is built,and simulation and experiments results indicate the effectiveness of the fast control *** largest negative pressure of the suction cup can reach 14 000 Pa,and its generating and cancelling just need 5 *** results indicate the suction cup can be used as an adhesion mechanism for miniature wall climbing robots.
In this letter, the resistive random access memory (RRAM) with metal-insulator-metal structure is investigated for the first time under radiation conditions. The fabricated Cu-doped HfO2-based RRAM devices are found t...
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In this letter, the resistive random access memory (RRAM) with metal-insulator-metal structure is investigated for the first time under radiation conditions. The fabricated Cu-doped HfO2-based RRAM devices are found to have immunity from Co-60 gamma ray of various dose ranges. The basic RRAM parameters such as high-resistance state, low-resistance state, SET/RESET voltages, operation speed, and endurance have nearly no degradation after Co-60 gamma ray treatment with a total dose as high as 3.6 x 10(5) rad (Si). Furthermore, a retention characteristic of 10(5) s is also achieved during radiation. The highly stable characteristics of Cu-doped HfO2-based RRAM devices under radiation provide RRAM a great potential for aerospace and nuclear applications.
PANI/ZnPcCl_（16）（polyaniline doped with sulfosalicylic acid/hexadecachloro zinc phthalocyanine） powders were vacuum co-deposited onto Si substrates,where Pt interdigitated electrodes were made by *** PANI/ZnPcCl_...
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PANI/ZnPcCl_（16）（polyaniline doped with sulfosalicylic acid/hexadecachloro zinc phthalocyanine） powders were vacuum co-deposited onto Si substrates,where Pt interdigitated electrodes were made by *** PANI/ZnPcCl_（16） films were characterized and analyzed by SEM,and the influencing factors on its intrinsic performance were analyzed and sensitivities of the sensors were investigated by exposure to chlorine（Cl_2） *** results showed that powders prepared with a stoichiometric ratio of（ZnPcCl_（16））_（0.6）（PANI）_（0.4） had a preferential sensitivity to Cl_2 gas, superior to those prepared otherwise;the optimal vacuum co-deposition conditions for the films are a substrate temperature of 160℃,an evaporation temperature of 425℃and a film thickness of 75 nm;elevating the operation temperature （above 100℃） or increasing the gas concentration（over 100 ppm） would improve the response characteristics,but there should be upper levels for ***,the gas sensing mechanism of PANI/ZnPcCl_（16） films was also discussed.
The calibration experiment data at Dunhuang radiometric calibration site in October, 2008 were used to achieve the on-orbit radiometric calibration for HJ-1A hyper spectral imager (HSI). Two other field experiments da...
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The calibration experiment data at Dunhuang radiometric calibration site in October, 2008 were used to achieve the on-orbit radiometric calibration for HJ-1A hyper spectral imager (HSI). Two other field experiments data were used to validate the Dunhuang calibration results. One field experiment took place in Inner-Mongolia, china in September, 2008, and the other field experiment took place in Lake Frome, Australia in February, 2009. Finally, the ‘confidence interval of calibration error’ concept was put forward for quantitatively computing the calibration coefficient error confidence interval. The results showed that the Dunhuang calibration results in 2008 had high reliability. The confidence intervals of calibration error for all HSI channels were between 2% to 12%, which could satisfy the requirement of the HSI quantitative applications.
IIn order to improve the performance of wireless distributed peer-to-peer(P2P)files sharing systems,a general system architecture and a novel peer selecting model based on fuzzy cognitive maps(FCM)are proposed in this...
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IIn order to improve the performance of wireless distributed peer-to-peer(P2P)files sharing systems,a general system architecture and a novel peer selecting model based on fuzzy cognitive maps(FCM)are proposed in this *** new model provides an effective approach on choosing an optimal peer from several resource discovering results for the best file *** with the traditional min-hops scheme that uses hops as the only selecting criterion,the proposed model uses FCM to investigate the complex relationships among various relative factors in wireless environments and gives an overall evaluation score on the *** also has strong scalability for being independent of specified P2P resource discovering ***,a complete implementation is explained in concrete *** simulation results show that the proposed model is effective and feasible compared with min-hops scheme,with the success transfer rate increased by at least 20% and transfer time improved as high as 34%.
A highly reliable interchip optical interconnection network on a printed circuit board (PCB) was designed and realized, and experiments confirmed that the data rate in each channel could reach above 3.125 Gbps and the...
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A highly reliable interchip optical interconnection network on a printed circuit board (PCB) was designed and realized, and experiments confirmed that the data rate in each channel could reach above 3.125 Gbps and the bit error rate (BER) could be up to 1.27 x 10(-18), which would be a good solution to the problem of communication bottlenecks between high-speed VLSI chips. (c) 2010 Elsevier Ltd. All rights reserved.
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