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Owing to the influence of the viscosity of the flow field, the strength of the shedding vortex decreases gradually in the process of backward propagation. Large-scale vortexes constantly break up, forming smaller vortexes. In engineering, when numerical simulation of vortex evolution process is carried out, a large grid is needed to be arranged in the area of outflow field far from the boundary layer in order to ensure the calculation efficiency. As a result, small scale vortexes at the far end of the flow field cannot be captured by the sparse grid in this region, resulting in the dissipation or even disappearance of vortexes. In this paper, the effect of grid scale is quantified and compared with the viscous effect through theoretical derivation. The theoretical relationship between the mesh viscosity and the original viscosity of the flow field is established, and the viscosity term in the turbulence model is modified. This method proves to be able to effectively improve the intensity of small-scale shedding vortexes at the far end of the flow field under the condition of sparse grid. The error between the simulation results and the results obtained by using fine mesh is greatly reduced, the calculation time is shortened, and the high-precision and efficient simulation of the flow field is realized. 相似文献
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The lifetimes of excited states in the yrast band of 176Os have been measured up to I=20h level using the Doppler shift attenuation method. The high-spin states of 176Os were populated via fusion evaporation reaction 152Sm(28Si, 4n)176Os at a beam energy of 140 MeV. The results support an X(5) structure for 176Os at low spin. This structure disappears at high spin and shows a symmetry rotor character. The shape change of 176Os is similar to that of 178Os. 相似文献
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Lifetimes of high spin states in 129Cs axe measured using the Doppler shift attenuation method. The high spin states of 129 Cs axe populated following the fusion evaporation reaction 124 Sn(UB, 6n)129 Cs at a beam energy of 65 MeV. The reduced transition probabilities B(E2) and the transition quadrupole moments Qt in the negativeand positive-paxity bands are deduced. The experimental results indicate that the Qt values of the negative parity band are smaller than those of the positive parity bands, probably due to different γ-deformation driving effects of different proton orbitals. The Qt values exhibit a considerable increase near the band crossing region in these bands. This behavior demonstrates that nuclear shape changing results from the neutron or proton alignments. The signature splitting of the πh11/2 and πg7/2 bands shows the opposite changing trend after backbending due to the h11~2 neutron and h11/2 proton alignments, respectively. 相似文献
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用荧光光谱法研究超支化聚合物组装体的质子捕获能力,共三种组装体结构,HBPO-star-PDMAEMA胶束、BP囊泡(HBPO-star-PEO)和BPD囊泡(HBPO-star-PEO和HBPO-star-PDMAEMA共组装)。结果发现由于质子海绵型结构PDMAEMA的存在,HBPO-star-PDMAEMA胶束和BPD囊泡在叔胺质子化过程中,具有较强的质子捕获能力,而Pyranine包埋于BP囊泡内与其在水中的光谱随环境pH值变化无明显差异。因而,通过调节HBPO-star-PEO和HBPO-star-PDMAEMA的比例,我们可以制备得到一系列质子捕获能力的超支化聚合物囊泡。 相似文献
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报道了在Si基上用简便的真空反应法制备出GaN外延层.光致发光光谱测试结果表明不同的生长温度和退火工艺会对GaN外延层的发光特性产生影响,在1050℃下生长的GaN外延层的发光强度高于其他温度下生长的发光强度,退火可以使GaN外延层的发光强度增强.二次离子质谱(SIMS)测试结果表明外延层中Ga和N分布均匀,在表面处Ga发生了偏聚,同时外延层中还存在Si,O等杂质,这使得外延层中背景电子浓度高达1.7×1018/cm3. SIMS测试结果还表明,在外延生长前采用
关键词: 相似文献
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Si_(82)笼状分子的第一性原理研究 总被引:1,自引:1,他引:0
本文构建了Si82笼状分子的具有C2v对称性的初始原子结构模型.采用基于密度泛函的第一性原理方法对其结构进行优化计算.研究发现:经过结构驰豫,Si82分子对称性从C2v下降为Cs,部分硅原子从顶点位置向内凹陷,导致键长和键角均发生变化.对Si82笼状分子的稳定性、轨道分布和电荷分布等性质进行了分析和讨论. 相似文献
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利用原位扫描隧道显微镜和低能电子衍射分析了Si的纳米颗粒在Si3N4/Si(111)和Si3N4/Si(100)表面生长过程的结构演变.在生长早期T为350—1075K范围内,Si在两种衬底表面上都形成高密度的三维纳米团簇,这些团簇的大小均在几个纳米范围内,并且在高温退火时保持相当稳定的形状而不相互融合.当生长继续时,Si的晶体小面开始显现.在晶态的Si3N4(0001)/S
关键词:
氮化硅
扫描隧道显微镜
纳米颗粒 相似文献