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121.
Interaction flow field of the sonic air jet through diamond shaped orifices at different incidence angles (10 degrees, 27.5 degrees, 45 degrees and 90 degrees) and total pressures (0.10 MPa and 0. 46 MPa) with a Mach 5.0 freestream was studied experimentally. A 90 degrees circular injector was examined for comparison. Crosssection Mach number contours were acquired by a Pitot-cone five-hole pressure probe. The results indicate that the low Mach semicircular region close to the wall is the wake region. The boundary layer thinning is in the areas adjacent to the wake. For the detached case, the interaction shock extends further into the freestream, and the shock shape has more curvature, also the low-Mach upwash region is larger. The vortices of the plume and the height of the jet interaction shock increase with increasing incidence angle and jet pressure. 90 degrees diamond and circular injector have stronger plume vorticity, and for the circular injector low-Mach region is smaller than that for the diamond injector. Tapered ramp increases the plume vorticity, and the double ramp reduces the level of vorticity. The three-dimensional interaction shock shape was modeled from the surface shock shape, the center plane shock shape, and crosssectional shock shape. The shock total pressure was estimated with the normal component of the Mach number using normal shock theory. The shock induced total pressure losses decrease with decreasing jet incidence angle and injection pressure, where the largest losses are incurred by the 90 degrees, circular injector. 相似文献
122.
This paper studies the possibility of using the scattering of cosmic muons to identify threatening high-Z materials. Various scenarios of threat material detection are simulated with the Geant4 toolkit. PoCA (Point of Closest Approach) algorithm reconstructing muon track gives 3D radiography images of the target material. Z-discrimination capability, effects of the placement of high-Z materials, shielding materials inside the cargo, and spatial resolution of position sensitive detector for muon radiography are carefully studied. Our results show that a detector position resolution of 50 μm is good enough for shielded materials detection. 相似文献
123.
Resistive switching characteristic and uniformity of low-power HfO_x-based resistive random access memory with the BN insertion layer 下载免费PDF全文
In this letter,the Ta/HfO_x/BN/TiN resistive switching devices are fabricated and they exhibit low power consumption and high uniformity each.The reset current is reduced for the HfO_x/BN bilayer device compared with that for the Ta/HfO_x/TiN structure.Furthermore,the reset current decreases with increasing BN thickness.The HfO_x layer is a dominating switching layer,while the low-permittivity and high-resistivity BN layer acts as a barrier of electrons injection into TiN electrode.The current conduction mechanism of low resistance state in the HfO_x/BN bilayer device is space-chargelimited current(SCLC),while it is Ohmic conduction in the HfO_x device. 相似文献
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Simulation of Femtosecond Pulse Propagation through Hollow Fibre Filled with Noble Gases of Gradient Temperature 下载免费PDF全文
We propose a novel technique for generating intense few to mono-cycle femtosecond pulses. The simulation demonstrate that for the temperature difference of 300K, the spectrum of the output pulses is increased by 67% and the transform limited pulse width is reduced almost by half, compared with those obtained with hollow fibres in uniform temperature. 相似文献
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与电子自旋相关的效应在散射过程中起着十分重要的作用,但却常常被较强的库仑相互作用所淹没,使得以自然电子为探针的散射实验很难对其进行直接观测.以极化电子作为探针,研制极化电子碰撞谱仪,将为开展自旋相关效应的实验研究奠定基础.本文简述了极化电子与原子分子碰撞研究的意义,并介绍了清华大学物理系极化物理实验室自行开发的GaAs极化电子源及基于该极化电子源的碰撞谱仪的研制情况. 相似文献
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129.
采用动力学方法研究了MnO2颗粒物对TiO2光催化降解苯胺活性的影响,对比考察了光催化降解过程中苯胺溶液的UV吸收光谱的变化,并用HPLC方法鉴别了中间产物.结果表明,少量MnO2颗粒物就能使TiO2光催化降解苯胺的活性受到明显的抑制,不同结构的二氧化锰致毒效应由大到小的顺序为:δ-MnO2α-MnO2β-MnO2;降解不同时间后溶液的UV吸收光谱的变化也反映了MnO2颗粒物具有同样的致毒效应;MnO2颗粒物不改变TiO2光催化降解苯胺的途径,但对生成中间产物的基元步骤的抑制程度不同。 相似文献
130.
本文第一部分回顾了DEMS方法原理和发展,这里继续介绍DEMS方法的一些应用结果,如CH3OH,HCOOH,CO,CO2,NO^-2,NO^-3以及一些不饱和碳氢化合物的电化学氧化或还原研究。 相似文献