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51.
Bruce Solomon 《Geometriae Dedicata》2007,128(1):33-37
We produce skew loops—loops having no pair of parallel tangent lines—homotopic to any loop in a flat torus or other quotient of R
n
. The interesting case here is n = 3. More subtly for any n, we characterize the homotopy classes that will contain a skew loop having a specified loop as tangent indicatrix.
A fellowship from the Lady Davis foundation helped support this work. 相似文献
52.
该文证明了复射影空间中两种类型的法丛平坦全实伪脐子流形必是极小的,并在紧致的情形确定了它们的具体形状.此外,还说明了复射影空间中的全实全脐子流形一定不是法丛平坦的. 相似文献
53.
This study developed a two-dimensional generalized vortex method to analyze the shedding of vortices and the hydrodynamic forces resulting from a solitary wave passing over a submerged circular cylinder placed near a flat seabed. Numerical results for validation are compared with other numerical and experimental results, and satisfactory agreement is found. A series of simulations were performed to study the effects of gap-to-diameter ratio and incident wave height on vorticity pattern as well as the forces exerted on the cylinder. The range of the heights of incident waves is from 0.3h to 0.7h, where h is the still water depth. The range of the gap-to-diameter ratios is from 0.1 to 0.8. The results indicate that the flow pattern and the pressure distribution change significantly because of the close proximity of the seabed where the vorticity flux on the seabed-side surface of the cylinder is suppressed. Placing the cylinder nearer the seabed increases the drag and the positive lift on the cylinder. When the gap-to-diameter ratio increases, the pattern of vortices changes because of the interaction between the main recirculation zone and the shear layers separated from the gap. The maxima of drag, lift and total force increase linearly with the height of the incident wave. 相似文献
54.
目前微槽平板热管成为热管研究和开发的重点。文中简要介绍了平板热管的设计要点及制造工艺,并通过实验,对设计制作的平板热管进行了性能测试。得出如下结论:该平板热管具有良好的启动特性和工作特性;在设计中要注意工质与管壳材料的相容性;制作时要严格控制清洗、检漏、充装等关键工序以保证制作质量。 相似文献
55.
56.
We find all the flat surfaces in the unit 3-sphere $\mathbb{S}^{3}We find all the flat surfaces in the unit 3-sphere
that pass through a given regular curve of
with a prescribed tangent plane distribution along this curve. The formula that solves this problem may be seen as a geometric
analogue of the classical D’Alembert formula that solves the Cauchy problem for the homogeneous wave equation. We also provide
several applications of this geometric D’Alembert formula, including a classification of the flat M?bius strips of
.
相似文献
57.
Indranil Biswas 《Journal of Geometry and Physics》2002,41(4):286-295
We consider equivariant holomorphic immersions of a universal cover
of a compact Riemann surface X into a Grassmannian
satisfying a nondegeneracy condition. The equivariance condition says that there is a homomorphism ρ of the Galois group to
that takes the natural action of the Galois group on
to the action of the Galois group on
defined using ρ. We prove that the space of such embeddings are in bijective correspondence with the space of all holomorphic differential operators of order two on a rank n vector bundle over X with the property that the symbol of the operator is an isomorphism. 相似文献
58.
59.
Experimental study of rotation effect on film cooling over the flat wall with a single hole 总被引:3,自引:0,他引:3
Zhi Tao Xiaojun Yang Shuiting Ding Guoqiang Xu Hongwei Wu Hongwu Deng Xiang Luo 《Experimental Thermal and Fluid Science》2008,32(5):1081-1089
A new rotating test rig was set up to investigate the rotation effect on the film cooling over the flat wall. A simple flat blade with an inclined 30° film hole, which is parallel to the hot mainstream, was installed. And different rotation orientations were selected to simulate the blade pressure or suction side of a turbine blade. A steady liquid crystal technique was applied to obtain detailed distribution of the temperature over the blade surface. And the average adiabatic film cooling effectiveness of the area adjacent to the film hole was selected to evaluate the cooling effect. Five different rotational speeds, i.e., 0, 300, 500, 800, 1000 r/min, were considered. Experimental results indicate that the film trajectory could bend under the rotating condition. With the increase of the rotational speed, on the pressure side, the film trajectory inclines centripetally firstly and then centrifugally; whereas, on the suction side the film trajectory bends centrifugally. On the other hand, as the rotational speed increases, the cooling effect is improved firstly and then worsened when Ω > 500–600 r/min on the pressure side. On the suction side, however, the cooling effect is not sensitive to the rotational speed. 相似文献
60.
表面过剩S2-对CdS光催化的影响与带位匹配 总被引:2,自引:0,他引:2
用ESR方法研究了硫化镉超微粒子表面被不同浓度的过剩硫离子S2-改性后对其光诱导电子转移及底物的氧化还原反应进程的影响.结果表明,在较高浓度下光还原反应易于进行.若所用底物的氧化还原电位E0为负值,在无过剩S2-存在及低浓度S2-环境中不发生光还原反应,但却可在高浓度S2-环境发生反应; 若底物的E0为正值,则在无硫离子及较低硫离子浓度下能够发生的光氧化反应,在高浓度时则被完全抑止.这是由于表面过剩S2-的作用,改变了底物的氧化还原电位与半导体超细微粒带隙间的匹配关系.根据Langmuir 等温吸附模型,进一步导出了修饰物的浓度c与平带电位负移值间的关系表达式ΔEfb=Δ Kc/(1+Kc).可以合理解释修饰物 S2-的浓度越高,Efb负移越大,越有利于光还原反应的实验事实.因此根据需要,适当地选择修饰物并控制浓度,使带隙位置与底物氧化还原电位间能有合适的匹配,有助于调节光化学反应的选择性与方向. 相似文献