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排序方式: 共有273条查询结果,搜索用时 46 毫秒
1.
We consider the plane-strain buckling of a cylindrical shellof arbitrary thickness which is made of a Varga material andis subjected to an external hydrostatic pressure on its outersurface. The WKB method is used to solve the eigenvalue problemthat results from the linear bifurcation analysis. We show thatthe circular cross-section buckles into a non-circular shapeat a value of µ1 which depends on A1/A2 and a mode number,where A1 and A2 are the undeformed inner and outer radii, andµ1 is the ratio of the deformed inner radius to A1. Inthe large mode number limit, we find that the dependence ofµ1 on A1/A2 has a boundary layer structure: it is constantover almost the entire region of 0 < A1/A2 < 1 and decreasessharply from this constant value to unity as A1/A2 tends tounity. Our asymptotic results for A1 1 = O(1) and A1 1 = O(1/n) are shown to agree with the numerical resultsobtained by using the compound matrix method. 相似文献
2.
M. Akbari A. Behzadmehr F. Shahraki 《International Journal of Heat and Fluid Flow》2008,29(2):545-556
Fully developed laminar mixed convection of a nanofluid consists of water and Al2O3 in horizontal and inclined tubes has been studied numerically. Three-dimensional elliptic governing equations have been solved to investigate the flow behaviors over a wide range of the Grashof and Reynolds numbers. Comparisons with previously published experimental and numerical works on mixed convection in a horizontal and inclined tube are performed and good agreements between the results are observed. Effects of nanoparticles concentration and tube inclinations on the hydrodynamics and thermal parameters are presented and discussed. It is shown that the nanoparticles concentration does not have significant effects on the hydrodynamics parameters. Heat transfer coefficient increases by 15% at 4 Vol.% Al2O3. Skin friction coefficient continually increases with the tube inclination, but the heat transfer coefficient reaches a maximum at the inclination angle of 45°. 相似文献
3.
Models, describing relativistic particles, where Lagrangian densities depend linearly on both the curvature and the torsion of the trajectories, are revisited in D=3 space forms. The moduli spaces of trajectories are completely and explicitly determined using the Lancret program. The moduli subspaces of closed solitons in the three sphere are also determined. 相似文献
4.
三维内肋管内插入螺旋扭带的强化传热实验 总被引:4,自引:0,他引:4
本文分别以水和乙二醇为工质,在Re数范围为:600~40000,Pr数范围为:5.5~110之间,对四根分别插入三种不同扭率螺旋扭带的三维内助管内的换热和流阻特性进行了实验研究。结果表明:三维内肋管内加装扭带的强化传热技术适用于低Re数下高Pr数工质的管内对流换热强化。根据实验值得到了流阻和换热关联式。 相似文献
5.
6.
Summary The concept of a diffusion-averaged molecular weight, Md is presented, and Md is defined for polydisperse samples. It is shown via oligostyrene mixtures that Md can be determined in 20 minutes with common chromatographic equipment. If Md is measured and Mn or Mw is known, the polydispersity can be obtained. 相似文献
7.
Summary The generator contains diffusion tubes of known length and internal diameter. Once produced, the mixture of the carrier gas and acetone, the reference material, is sent through a chromatographic flame ionisation detector. Its signal reaches a constant level after a time corresponding to the stabilization time of the generator. The technique described is simple and gives repeatable results. 相似文献
8.
Shyh-Horng Chiou 《中国化学会会志》1989,36(5):435-442
A rapid peptide-bond hydrolysis by means of microwave irradiation is introduced for the facile preparation of protein hydrolysates used for amino acid analysis. The optimal hydrolysis condition has been determined using several enzymes with known amino acid compositions. The effects of hydrolysis time on the recovery of various labile and hydrophobic amino acids are also exemplified in the microwave heating of standard amino acids. The method has been applied to the complete amino acid analysis with a single nonvolatile solvent of methanesulfonic acid with good recovery of tryptophan and half-cystine. It provides a radical expedition of protein and peptide hydrolysis via commercial microwave ovens and specially-designed Teflon-Pyrex tubes, circumventing the tedious procedures using vacuum-sealed pyrex lubes heating at 110°C for more than 24 h. This novel type of microwave chemistry associated with rapid peptide-bond cleavage is of great potential in the automation of the complete process of amino acid analysis starting from the preparation of protein hydrolysates. 相似文献
9.
Summary The successful application of the formerly presented concept of diffusion-averaged molecular weight, Md, to vacuum residues of crude oils, or their fractions, is described. The samples for establishing the calibration curve, logDvs. logM, were crude oil fractions with polydispersities smaller than 1.1. In a surprisingly good approximation the calibration curve is independent of the origin of these fractions if 500<M<10000. The validity of our calibration curve was demonstrated with more than 10 crude oil residues and with some of their hydrogenation residues [2]. 相似文献
10.
A. Haunold E. Rosenberg M. Grasserbauer 《International journal of environmental analytical chemistry》2013,93(1-4):157-172
Abstract Reliable and comprehensive sampling methods are required to obtain accurate data for VOC concentrations in air samples. The major drawback of the adsorption tube sampling method, widely employed in environmental studies, is the fact that C2 compounds are usually not trapped quantitatively. The focus of this work was thus to improve sampling based on adsorption tubes packed with Molsieve and Carbosieve. To improve the sampling efficiency for the C2 compounds, a cooling device, based on Peltier cooling was constructed, which could be operated at a temperature down to ?30°C. Experiments under laboratory and field conditions were carried out to study the influence of the sampling temperatuie on the recovery of ethane and ethene as the most volatile VOCs. The results clearly demonstrate the need for a cooled sampling device for the analysis of C2 compounds in air. Under the investigated conditions, the recoveries with ambient temperature sampling were only in the range of 38–46% for ethane and 33–59% for ethene respectively, in comparison to the cooled sampling device. These findings are only valid for the described conditions and can change significantly with temperature and concentration. A generalisation of the recovery is thus very difficult to give. The use of the sampling device for a field study is reported, where samples were collected simultaneously at three different altitudes in a diurnal profile on the slope of the Schulterberg mountain in Tyrol (Austria). 相似文献