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Bose-Einstein Condensates in a One-Dimensional Optical Lattice: from Superfluidity to Number-Squeezed States 下载免费PDF全文
We study the phase coherence property of Bose-Einstein condensates confined in a one-dimensional optical lattice formed by a standing-wave laser field. The lattice depth is determined using a method of Kapitza-Dirac scattering between a condensate and a short pulse lattice potential. Condensates are then adiabatically loaded into the optical lattice. The phase coherence property of the confined condensates is reflected by the interference patterns of the expanded atomic cloud released from the optical lattice. For weak lattice, nearly all of the atoms stay in a superfluid state. However, as the lattice depth is increased, the phase coherence of the whole condensate sample is gradually lost, which confirms that the sub-condensates in each lattice well have evolved into number-squeezed states. 相似文献
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Using the high precision data of the proper motions and parallaxes from Hipparcos catalogue, we obtained the orbital parameters of 1302 stars in the Galaxy based on the mass distribution model provided by Allen and Santillón. Fe abundances of 1295 stars among our samples were analyzed. With the correlation analyses between [Fe/H] and orbital parameters, we obtained that the Fe gradient is - 0.057 ± 0.007 dex/kpc along the direction of the maximum galactocentric distance (hereafter DGmax) in the range of 8.5 kpc < DGmax < 17 kpc. We also got the result that the vertical gradient is steeper than the radial gradient. Furthermore, we divided the samples into two subgroups: giants and dwarfs; F, G and K stars; and then analyzed them respectively. Our results show that the gradient becomes flatter and flatter from giants to dwarfs, from F type to G and K type stars. We also divided the samples into disk and halo stars using maximum vertical distance Zmax = 1 kpc as the criterion and got the result that the abundances of the disk stars are much higher than that of the halo stars. Our work suggests the existence of the galactic gradient and supports those chemlcal evolution medels which show that the halo was formed before the disk at the early stage of the Galaxy. 相似文献
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在积累知识的过程中,除如何猎取知识外,还有一个如何储存知识的问题.深刻的理解加上合理的储存,就能运用自如地掌握知识,而靠死记硬背储存知识,遇到灵活性强、比较隐蔽的问题就束手无策了.合理的知识结构应当具有以下特征:一、系统性.处于游离状态的知识,完全失去了其应有价值,成了大脑的负担;而系统化的知识,各个知识点前后呼应,表现出1+1>2的价值,减少了记忆量和记忆难度.因此,学习中不仅要善于获得知识,更要善于整理自己的知识系统. 相似文献
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为了快捷、精准测量脆性易解理氧化镓晶体的断裂韧度,为氧化镓精密加工提供理论依据。采用G200纳米压痕仪对氧化镓晶体进行纳米压痕试验,通过扫描电子显微镜分析压痕形貌,分别采用纳米压痕法、能量法两种方法计算断裂韧度。纳米压痕法测得(010)面氧化镓晶体的断裂韧度为0.769 MPa·m1/2;能量法测得其断裂韧度为0.782 MPa·m1/2。与传统的断裂韧度检测方法相比,基于纳米压痕仪的压痕法和能量法能够微损伤快速检测脆性材料的断裂韧度。能量法是更精准、更便捷的纳米级断裂韧度检测方法。 相似文献
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The relationship between abundances and orbital parameters for 235 F- and G-type intermediate- and low- mass stars in the Galaxy is analyzed. We foundthat there are abundance gradients in the thin disk in both radial and verticaldirections (-0.116 dex kpc-1 and -0.309 dex kpc-1 respectively). The gradients appear to be flatter as the Galaxy evolves. No gradient is found in the thick disk based on 18 thick disk stars. These results indicate that the ELS model is mainly suitable for the evolution of the thin disk, while the SZ model is more suitable for the evolution of the thick disk. Additionally, these results indicate that in-fall and out-flow processes play important roles in the chemical evolution of the Galaxy. 相似文献