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91.
Chun-Yen Lai Tzu-Chiao Chien Ting-Yi Lin Teng Ke Shih-Han Hsu Yun-Ju Lee Chien-ying Su Jeng-Tzong Sheu Ping-Hung Yeh 《Nanoscale research letters》2014,9(1):281
In this work, we have demonstrated that amorphous ZnO nanobranches (a-ZnO NBs) could spontaneously react from the crystalline ZnO NWs (c-ZnO NWs) at specific humid environment. The spontaneous reaction mechanism and result can be analyzed by humidity controlling and optical microscope (OM)/scanning electron microscope (SEM)/Kelvin probe force microscopy (KPFM)/transmission electron microscopy (TEM) system. We can make the c-ZnO NWs spontaneous reaction happen at different humid environments and suppress the a-ZnO NBs spontaneous reaction by oxygen/hydrogen plasma surface passivation. The hydrogen plasma surface treatment also can improve the UV sensing sensitivity more than twofold. This work provides the mechanism and methods of the a-ZnO NBs spontaneous growth and offers the passivation treatment for strengthening and enhancing ZnO-based nanodevice application in humid environment and UV light detection, respectively. 相似文献
92.
Wei-Je Huang Ching-Tsung Yu Wen-Jenn Sheu Yen-Cho Chen 《International Journal of Hydrogen Energy》2021,46(31):16522-16533
The effect of non-uniform temperature on the sorption-enhanced steam methane reforming (SE-SMR) in a tubular fixed-bed reactor with a constant wall temperature of 600 °C is investigated numerically by an experimentally verified unsteady two-dimensional model. The reactor uses Ni/Al2O3 as the reforming catalyst and CaO as the sorbent. The reaction of SMR is enhanced by removing the CO2 through the reaction of CaO + CO2 → CaCO3 based on the Le Chatelier's principle. A non-uniform temperature distribution instead of a uniform temperature in the reactor appears due to the rapid endothermic reaction of SMR followed by an exothermic reaction of CO2 sorption. For a small weight hourly space velocity (WHSV) of 0.67 h?1 before the CO2 breakthrough, both a low and a high temperature regions exist simultaneously in the catalyst/sorbent bed, and their sizes are enlarged and the temperature distribution is more non-uniform for a larger tube diameter (D). Both the CH4 conversion and the H2 molar fraction are slightly increased with the increase of D. Based on the parameters adopted in this work, the CH4 conversion, the H2 and CO molar fractions at D = 60 mm are 84.6%, 94.4%, and 0.63%, respectively. After CO2 breakthrough, the reaction of SMR dominates, and the reactor performance is remarkably reduced due to low reactor temperature.For a higher value of WHSV (4.03 h?1) before CO2 breakthrough, both the reaction times for SMR and CO2 sorption become much shorter. The size of low temperature region becomes larger, and the high temperature region inside the catalyst/sorbent bed doesn't exist for D ≥ 30 mm. The maximum temperature difference inside the catalyst/sorbent bed is greater than 67 °C. Both the CH4 conversion and H2 molar fraction are slightly decreased with the increase of D. However, this phenomenon is qualitatively opposite to that for small WHSV of 0.67 h?1. The CH4 conversion and H2 molar fraction at D = 60 mm are 52.6% and 78.7%, respectively, which are much lower than those for WHSV = 0.67 h?1. 相似文献
93.
Maxim A. Solovchuk Tony W.H. Sheu Win-Li Lin Ihyuan Kuo Marc Thiriet 《International Journal of Heat and Mass Transfer》2012,55(4):1261-1270
This study investigates the influence of blood vessels on temperature distribution during high-intensity focused ultrasound (HIFU) ablation of liver tumors. A three-dimensional acoustics-thermal-fluid coupling model is simulated to compute the temperature field in the hepatic cancerous region. The model is based on the linear Westervelt and bioheat equations as well as the non-linear Navier–Stokes equations for the liver parenchyma and blood vessels. The effect of acoustic streaming is also taken into account in the present HIFU simulation study. We found from this three-dimensional coupling study that in large blood vessel both the convective cooling and acoustic streaming can significantly change the temperature field and thermal lesion near blood vessels. 相似文献
94.
Yan-Hom Li Ching-Yao Chen Shih-Tsung Sheu Jay-Min Pai 《Microfluidics and nanofluidics》2012,13(4):579-588
The dynamics of microchains containing superparamagnetic particles in an oscillating field are studied experimentally. The chains are first formed by a static directional field, and then manipulated by an additional dynamical perpendicular field. The present methodology represents a simple reversible chaining process, whose particles can be re-dispersed after removal of the field. The motion of superparamagnetic chains is dominated by magnetic torque and induced hydrodynamic drag. The effects of key parameters, such as field strengths and the lengths of particle chains, are thoroughly analyzed. Distinct behaviors, from rigid body oscillations and bending distortions to rupture failures, are observed by increasing the amplitudes of oscillating fields or chains’ lengths. Because of lower induced drag, a shorter chain follows the field trajectory closely and oscillates more synchronically with the external field. On the other hand, the influences of field strengths are not consistent. Even the overall oscillating phase trajectory in a stronger external field deviates less significantly from the corresponding field trajectory, a stronger dynamical component of the external field results in larger phase angle lags at certain points. The experimental results confirm the criterion of ruptures can be effectively determined by the value of (N*Mn 1/2), where Mn is the Mason number defined as the ratio of induced drag to dipolar attraction, and N represents the number of particles contained in a chain. 相似文献
95.
A sputtering technique was adopted to synthesize Sn-Cu thin film electrodes. Island Sn particles were obtained on the copper foil. Cu6Sn5 was spontaneously generated at the interface between Sn and Cu foil. To further improve the cycling stability, Cu source was introduced to increase the formation of Cu6Sn5 and to serve as a buffer during cycling. Moreover, the phase and elemental ratio of Sn and Cu varied in the synthesized electrode by alternately adjusting sputtering time for Sn and Cu. The cell synthesized by sputtering Sn for 5 min and Cu for 9 s alternately exhibited the best cycling stability. The 1st charge capacity of cell was 635 mA hg−1, and the 1st efficiency was even higher than 97%. The capacity remained higher than 500 mA hg−1 after 15 cycles. The phase transformation of cell was investigated through voltage profile, CV curve and in situ XRD analysis. The in situ XRD analysis confirmed that Cu6Sn5 could react with lithium directly without the presence of Li2CuSn during cycling. The reaction mechanism of Cu6Sn5 with lithium during cycling was demonstrated to be an alloying process, and the structure of Cu6Sn5 was thus a low-temperature monoclinic phase. 相似文献
96.
Tsang‐Ling Sheu Chia‐Nan Lin Jenq‐Neng Hwang 《Wireless Communications and Mobile Computing》2015,15(12):1589-1605
This paper presents a channel reservation and preemption (CRP) model using overlapping regions in a cellular network with multiple sectors. To fully exploit and reuse the frequencies, directional antennas are installed on base stations (BSs) to divide the coverage into a number of equal‐sized sectors. When traffic is unevenly distributed across the sectors in a BS, channel utilization in every sector may become very different; low‐traffic sectors may be underutilized while high‐traffic sectors may be overutilized. A CRP scheme is thus proposed to more efficiently utilize free channels among sectors. CRP aims at reducing the dropping probabilities of handoff calls. Specifically, when free channels in a sector are not available, a handoff call, instead of being dropped, is allowed to preempt an ongoing call residing in the overlapping region of two adjacent sectors or two neighbor cells. Under CRP, the preempted ongoing call will not be disconnected, because it can switch over its service to the BS of a neighbor cell or to another directional antenna of an adjacent sector. For the purpose of evaluation, we build an analytical model for the proposed CRP using six‐tuple Markov chains. Analytical results show that the proposed CRP can significantly reduce the dropping probabilities of inter‐sector handoff calls, particularly when traffic between two sectors is not evenly distributed. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
97.
Low-resistivity Mg-doped Al0.15Ga0.85N/GaN strained-layer superlattices were grown. In these superlattices, the maximum hole concentration is 3×1018/cm3 at room temperature. Hall-effect measurements indicate high conductivity of this structure in which the high activation efficiency is attributed to the strain-induced piezoelectric fields. This work also fabricated InGaN/GaN blue LEDs that consist of a Mg-doped Al0.15Ga0.85N/GaN SLs. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 3 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V 相似文献
98.
Abstract Numerical calculations are reported for the transient cooling of a solidified intrusion embedded in a water-saturated porous layer. Heat transfer rates are increased greatly when the intrusion undergoes thermal cracking as it cools. The effects of a uniform heat flux into the porous layer from below are considered. Solutions are obtained for porous layers that are initially above or below the critical-layer Rayleigh number for thermal convection. For conditions considered in this study, the effects on the cooling intrusion of initial convection and layer aspect ratio are small. Results are correlated by scaling velocities with the intrusion Rayleigh number. 相似文献
99.
本文对卷筒组的参数优化设计进行了详细讨论,通过实例分析,提出了设计卷筒组时参数选择的一般原则。在PC机上研制出了相应的优化设计软件,该程序使用灵活、方便,并可纳入整个启闭机的CAD系统。 相似文献
100.
Seidel aberration coefficients can be expressed by Zernike coefficients. The least-squares matrix-inversion method of determining Zernike coefficients from a sampled wave front with measurement noise has been found to be numerically unstable. We present a method of estimating the Seidel aberration coefficients by using a two-dimensional discrete wavelet transform. This method is applied to analyze the wave front of an optical system, and we obtain not only more-accurate Seidel aberration coefficients, but we also speed the computation. Three simulated wave fronts are fitted, and simulation results are shown for spherical aberration, coma, astigmatism, and defocus. 相似文献