Flow Bifurcations in a Thin Gap Between Two Rotating Spheres

This paper presents the use of a parameter continuation method and a test function to solve the steady, axisymmetric incompressible Navier–Stokes equations for spherical Couette flow in a thin gap between two concentric, differentially rotating spheres. The study focuses principally on the prediction of multiple steady flow patterns and the construction of bifurcation diagrams. Linear stability analysis is conducted to determine whether or not the computed steady flow solutions are stable. In the case of a rotating inner sphere and a stationary outer sphere, a new unstable solution branch with two asymmetric vortex pairs is identified near the point of a symmetry-breaking pitchfork bifurcation which occurs at a Reynolds number equal to 789. This solution transforms smoothly into an unstable asymmetric 1-vortex solution as the Reynolds number increases. Another new pair of unstable 2-vortex flow modes whose solution branches are unconnected to previously known branches is calculated by the present two-parameter continuation method. In the case of two rotating spheres, the range of existence in the (Re ₁ , Re ₂ ) plane of the one and two vortex states, the vortex sizes as a function of both Reynolds numbers are identified. Bifurcation theory is used to discuss the origin of the calculated flow modes. Parameter continuation indicates that the stable states are accompanied by certain unstable states. Received 26 November 2001 and accepted 10 May 2002 Published online 30 October 2002 Communicated by M.Y. Hussaini     

Mach Wave Radiation by Mixing Layers. Part II: Analysis of the Source Field

In Part II a large-scale sound source in a time-developing planar free mixing layer is studied using an acoustic analogy approach. It is shown that only the non-compact character of the source resembles well the character of the corresponding source in a spatially developing flow. A model based on a continuous assembly of wave packets is derived and applied to direct numerical simulation results of two supersonic time-developing mixing layers undergoing transition to turbulence. The analysis predicts two distinctive dominant Mach wave sources in agreement with the direct analysis of Part~I. The first dominates during the stage of the Λ-vortex structure and the second just prior to the final breakdown to a fine-scale structure. The convective velocity of the second Mach wave source is higher than the first and thus its Mach angle of radiation is higher. The second source has a reduced strength at the higher free-stream Mach number. Directivity and frequency spectra compare well with the results of Part I, demonstrating that the assumptions inherent in the analogy are quite reasonable. Received 5 August 1997 and accepted 6 April 1998     

双层旋转壳流固耦合振动有限元分析

本文采用旋转壳体元和流体元分析了双层旋转壳体流固耦合振动特性,基于Novozhilov壳体理论、水弹性理论以及Hamilton变分原理推导出耦合系统运动方程,计算结果与实测值比较表明本分析方法有较好的精度。     

复合材料光弹性分析的近似方法

本文提出了一种用于光弹性复合材料的简化应变——光学定律。按照这一简化定律。模型材料的主应变差和主应变方向只要利用光弹性实验测出的等差线与等倾线即可求得。些是一种正交异性光弹性分析的近似方法,这一方法所得结果与实验数据比较,最大误差在10％左右。由于采用简化应变——光学定律使得正交异性光弹性分析工作大为简便,因此它是一种适合于工程应用的近似方法。     

Delayed Fluorescent Emission from Pyrene Doped Phenanthrene Nanoparticles Based on Triplet-triplet Energy Transfer

Doped nanoparticles were prepared from pyrene and phenanthrene using a facile reprecipitation method. The doped nanoparticles presented unique delayed fluorescent emissions of pyrene under the unprotected condition. The ratio of the intensity of delayed fluorescence (I_DF) to that of phosphorescence (I_P) is about 4:1, which almost keeps unchanged with the decrease of pyrene content at room temperature. The intensity of the delayed fluorescence emissions is dependent on the relative content of pyrene, as well as the aggregation degree of nanoparticles. The delayed emissions are contributed to efficient triplet‐triplet energy transfer from phenanthrene (donor) to pyrene (acceptor). Steady fluorescence measurement have proved that the singlet‐singlet energy transfer process was also existent dominated by the radiation energy transfer mechanism.     

The crystal structures of chiral (<Emphasis Type="Italic">R</Emphasis>/<Emphasis Type="Italic">S</Emphasis>) (C<Subscript>8</Subscript>H<Subscript>11</Subscript>N)<Subscript>2</Subscript>·CuCl<Subscript>2</Subscript>

Two opposite configuration (R/S) of chiral complexes (C₈H₁₁N)₂·CuCl₂ were obtained from the reaction of chiral d(+)/l(−)-α-ethylphenyl amine with copper chloride (II) in dry ethanol. The crystal structures of 1a and 1b were characterized by IR, elemental analysis and X-ray crystallography.     

Immunosuppressive Resveratrol Aneuploids from Hopea chinensis

Two novel resveratrol aneuploids, hopeachinols A ( 1 ) and B ( 2 ), as well as a potent immunosuppressive polyphenol diptoindonesin G ( 3 ) were characterized from the ethanol extract of Hopea chinensis stem barks. The structure of the polyphenols was accommodated by comprehensive spectroscopic analysis with the absolute stereochemistry determined by the CD approach coupled with theoretical ECD spectra computer‐generated through the Gaussian 03 program. The distinct structure and biological profile of 3 recommended it as a starting molecule for the relevant drug discovery.     

Palladium-catalyzed reduction of alkynes employing HSiEt3: stereoselective synthesis of trans- and cis-alkenes

The palladium-catalyzed semi-hydrogenation of alkynes to trans- or cis-alkenes employing HSiEt₃ as the reductant is developed. The CuSO₄ played a significant role for the trans/cis stereoselectivity. The labeling study revealed that the two olefinic hydrogen atoms came from HSiEt₃ and H₂O, respectively.     

Nonaqueous catalytic water oxidation

The complex [Ru(Mebimpy)(bpy)(OH(2))](2+) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine] and its 4,4'-(PO(3)H(2)CH(2))(2)bpy derivative on oxide electrodes are water oxidation catalysts in propylene carbonate and 2,2,2-trifluoroethanol (TFE) to which water has been added as a limiting reagent. The rate of water oxidation is greatly enhanced relative to that with water as the solvent and occurs by a pathway that is first-order in H(2)O; an additional pathway that is first-order in acetate appears when TFE is used as the solvent.     

Enantioselective henry reactions catalyzed by chiral N-metal complexes containing R(+)/S(−)-α-ethylphenyl amines

A series of novel N-metal complexes containing chiral α-ethylphenyl amines was synthesized and they catalyzed asymmetric Henry reactions affording products with high enantioselectivity.