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排序方式: 共有4524条查询结果,搜索用时 15 毫秒
831.
Neson Varghese K. Vinod Ashok Rao Y.K. Kuo U. Syamaprasad 《Journal of Alloys and Compounds》2009,470(1-2):63-66
A systematic study on the superconducting properties of polycrystalline MgB2 synthesized by in situ Powder-In-Sealed-Tube technique is carried out at different temperatures (750–900 °C). Both XRD and SEM results show well-crystallized MgB2 grains in all the samples and grain size is found to be increasing with the sintering temperature. Sharp superconducting transitions are observed for all samples, irrespective of sintering temperatures, which implies the high degree phase purity and homogeneity of MgB2 formed, while JC(H) plot gives sample dependent critical current density. The samples heat treated at relatively low temperatures show enhanced flux pinning and hence improved JC(H) performance. The reduced grain size and hence increased density of grain boundary pinning centers of MgB2 bulks synthesized at low temperature are mainly responsible for the enhanced flux pinning and JC. 相似文献
832.
Hsin-Pao Chen Hsin-Hung Kuo Der-Min Tsay 《Journal of Materials Processing Technology》2009,209(17):5810-5817
Focused on the reverse movements of moving axes along five-axis tool paths, this study presents a procedure of removing a gouge phenomenon on impeller surfaces in five-axis machining. That is, when an impeller of a centrifugal compressor is being cut in finish milling, reverse movements and/or other linearization problems of moving axes along a five-axis interference-free tool path may make a cutter leave tool marks on the impeller surfaces. For generating interference-free cutter location (CL) data needed in rough, semi-finish and finish five-axis cutting processes, first, a simple yet useful approach is proposed. To identify the potential gouge area and to solve the problem for a tool path having reverse motion directions with its moving axes in finish milling, the CL data are further smoothed to remove the reverse movements about its rotating and tilting axes. The effectiveness of this procedure has been experimentally confirmed by successful five-axis finish milling of an impeller without leaving tool marks on its surfaces. In addition, with the spline tool paths, the machining time can be saved up to 23.57%. 相似文献
833.
Chih-Chung Chang Yu-Fu Kuo Jung-Chang Wang Sih-Li Chen 《Applied Thermal Engineering》2010,30(11-12):1360-1368
This article experimentally and numerically investigates the thermal performance of a large-scale motor with a capacity of 2350 kW. The large-scale motor consists of a centrifugal fan, two axial fans, a shaft, a stator, a rotor and a heat exchanger with 637 cooling tubes. The test rigs are set up to measure the performance of the fans and the temperature distributions of the motor. The models of the fan and motor have been implemented in a Fluent software package to predict the flow and temperature fields inside the motor. The calculated results show good agreement with the measured data. In order to improve the motor thermal performance, several methods have been adopted, which are aiming to enhance the fan performance by changing the geometry, to redesign a new heat exchanger with guide vanes, and to optimize the distance between the axial fans. The modified design can decrease the temperature rise by 6 °C in both the stator and rotor. 相似文献
834.
The effects of the additive elements X (V, W, Mo, Hf, Ta and Zr) on the ideal cleavage fracture of the C15 Cr2Nb were investigated using the first-principles method. The brittle cleavage energy Gc and critical stress σc were calculated. The results show that V on Cr sites and X (W and Zr) on Nb sites can increase the cleavage strength of Cr2Nb, while X (W and Mo) on Cr sites and X (Mo, Ta and Hf) on Nb sites can reduce the cleavage strength of Cr2Nb. Our results are consistent with available experimental ones. We also find that the effect of the element W on the cleavage strength of Cr2Nb strongly depends on its site preference in Cr2Nb. The charge densities induced by the additive elements X were also calculated in order to reveal the origin of the effects of X on the ideal cleavage fracture of Cr2Nb. 相似文献
835.
Chu-Chi Ting Chang-Hung Li Chih-You Kuo Chia-Chen Hsu Hsiang-Chen Wang Ming-Hsun Yang 《Thin solid films》2010,518(15):4156-7701
Highly c-axis-oriented ZnO nanorod thin films were obtained on silica glass substrates by a simple solution-growth technique. The most compact and vertically-aligned ZnO nanorod thin film with the thickness of ∼ 800 nm and average hexagonal grain size of ∼ 200 nm exhibits the average visible transmittance 85%, refractive index 1.74, packing density 0.84, and energy band gap 3.31 eV, and it was fabricated under the optimum parameters: 0.05 M, 75 °C, 6 h, multiple-stepwise, and ZnO seed layer with an average grain size of ∼ 20 nm. The photoluminescence spectrum indicates that the densest ZnO nanorod thin film possesses lots of oxygen vacancies and interstitials. As we demonstrate here, the solution-growth technique was used to produce high-quality and dense ZnO nanorod thin films, and is an easily controlled, low-temperature, low-cost, and large-scale process for the fabrication of optical-grade thin films. 相似文献
836.
Sputter-deposited FePt films exhibit an in-plane magnetic anisotropy when MgO is used as the capped layer. The perpendicular magnetic anisotropy of FePt films can be enhanced by introducing a Ag capped layer instead of a MgO capped layer. Although the in-plane coercivity (Hc//) of FePt films decreases slightly after introducing a Ag capped layer instead of a MgO capped layer, the perpendicular coercivity (Hc⊥) is increased significantly from 3169 Oe to 6726 Oe. Auger electron spectroscopy analysis confirms that Ag atoms diffuse from the capped layer into the FePt magnetic layer and are mainly distributed at the grain boundary of FePt. This phenomenon results in enhancement of the grain boundary energy and inhibition of grain growth, thus increasing the perpendicular coercivity and reducing the grain size of the FePt film. 相似文献
837.
838.
Naris Thengchaisri Travis W. Hein Yi Ren Lih Kuo 《International journal of molecular sciences》2021,22(18)
Protein kinase C (PKC) activation can evoke vasoconstriction and contribute to coronary disease. However, it is unclear whether PKC activation, without activating the contractile machinery, can lead to coronary arteriolar dysfunction. The vasoconstriction induced by the PKC activator phorbol 12,13-dibutyrate (PDBu) was examined in isolated porcine coronary arterioles. The PDBu-evoked vasoconstriction was sensitive to a broad-spectrum PKC inhibitor but not affected by inhibiting PKCβ2 or Rho kinase. After exposure of the vessels to a sub-vasomotor concentration of PDBu (1 nmol/L, 60 min), the endothelium-dependent nitric oxide (NO)-mediated dilations in response to serotonin and adenosine were compromised but the dilation induced by the NO donor sodium nitroprusside was unaltered. PDBu elevated superoxide production, which was blocked by the superoxide scavenger Tempol. The impaired NO-mediated vasodilations were reversed by Tempol or inhibition of PKCβ2, xanthine oxidase, c-Jun N-terminal kinase (JNK) and Rho kinase but were not affected by a hydrogen peroxide scavenger or inhibitors of NAD(P)H oxidase and p38 kinase. The PKCβ2 protein was detected in the arteriolar wall and co-localized with endothelial NO synthase. In conclusion, activation of PKCβ2 appears to compromise NO-mediated vasodilation via Rho kinase-mediated JNK signaling and superoxide production from xanthine oxidase, independent of the activation of the smooth muscle contractile machinery. 相似文献
839.
Wen-Yi Kuo 《Selected Areas in Communications, IEEE Journal on》2000,18(7):1159-1168
This paper presents a methodology for analyzing the forward link performance of a pilot-aided coherent DS-CDMA system under correlated Rician fading. In the forward link of a CDMA system, orthogonal modulation is usually used to minimize the self-interference. To maintain the orthogonality and reduce the receiver complexity, a common pilot channel (shared by all users) is employed to provide the reference for coherent demodulation. A tradeoff shows that a higher pilot ratio yields good channel estimates but takes away some capacity from traffic users, while a lower pilot ratio results in poorer channel estimates and leads to higher traffic power per user. This paper derives the analytical error performance, which includes (1) imperfect channel estimation by the pilot channel, (2) a very general channel model where correlations between paths as well as Rician fading are considered, and (3) interference patterns due to multiple paths and the surrounding base stations' transmissions. This paper also considers self-interference due to the loss of orthogonality caused by pulse shaping 相似文献
840.
盐蚀环境对沥青混合料耐久性劣化作用具有普遍性和直接性.为探究盐分-水-温度-荷载共同作用下沥青混合料宏观力学性能损伤演化规律,采用自行研制的沥青混合料动水-盐蚀冲刷试验仪,合理设置试验参数,以25℃劈裂强度指标评价盐蚀-动水条件下沥青混合料力学性能损伤程度,利用灰熵分析与t检验研究冲刷温度、冲刷次数、盐浓度对沥青混合料... 相似文献