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61.
Thermosolutal convection flow and its effect on the heat and the mass transfer in a square enclosure is studied experimentally. Both thermal and solute diffusion are induced from the sides, and natural convection is initiated by the combined thermal and solutal buoyancies, which either augment or oppose to each other. The solute diffusion is initiated in an electrochemical system that uses copper sulfate-sulfuric acid solution as an electrolyte. Depending on the magnitude of buoyancy ratio, three different kinds of flow regimes and structures can occur, which lead to different distributions of concentration in the enclosure. The formation and growth of layered flow structure is attributed to the solutal boundary-layer flow that can intrude and accumulate along the horizontal wall. The nearly stagnant layer that occurs can reduce the heat transfer rate. The Nusselt numbers at different flow regimes are measured and correlated in terms of relevant nondimensional parameters. This suggests the correlation of Sherwood number in different ranges of buoyancy ratio. The visualization of flow structures and measurements of both heat and mass transfer allow better understanding of the complicated system. 相似文献
62.
63.
It is shown that if is a compact operator on a Hilbert space with its numerical range contained in the closed unit disc and with intersecting the unit circle at infinitely many points, then is equal to . This is an infinite-dimensional analogue of a result of Anderson for finite matrices.
64.
Let A be a contraction on a Hilbert space H. The defect index dA of A is, by definition, the dimension of the closure of the range of I-A∗A. We prove that (1) dAn?ndA for all n?0, (2) if, in addition, An converges to 0 in the strong operator topology and dA=1, then dAn=n for all finite n,0?n?dimH, and (3) dA=dA∗ implies dAn=dAn∗ for all n?0. The norm-one index kA of A is defined as sup{n?0:‖An‖=1}. When dimH=m<∞, a lower bound for kA was obtained before: kA?(m/dA)-1. We show that the equality holds if and only if either A is unitary or the eigenvalues of A are all in the open unit disc, dA divides m and dAn=ndA for all n, 1?n?m/dA. We also consider the defect index of f(A) for a finite Blaschke product f and show that df(A)=dAn, where n is the number of zeros of f. 相似文献
65.
We have investigated the ripening of breath figures with variable initial order. A dramatic impact of the degree of order on the coalescence behavior is observed. As opposed to the two-droplet coalescence events common to the usual disordered droplet arrays, four-droplet coalescence cascades predominate in a perfectly hexagonal breath figure. Upon introduction of disorder, a gradual transition to a regime dominated by three-droplet cascades is observed. The statistics of coalescence cascades allows for detailed conclusions on the microscopic droplet dynamics. 相似文献
66.
67.
Several novel ligands that are based on the camphor skeleton or contain the O‐sulfonyl group were synthesized and used in the asymmetric addition of phenylacetylene to aldehydes. This enantioselective reaction afforded chiral propargylic alcohols in high yields and with good to excellent levels of enantiopurity (up to 99% enantiomeric excess). Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
68.
Xun Yang Dr. Dinesh Nath Michael R. Gau Prof. Omar W. Steward Prof. Fraser F. Fleming 《Angewandte Chemie (International ed. in English)》2017,56(25):7257-7260
The first general sulfone–metal exchange is described. Treating substituted 2-pyridylsulfonylacetonitriles with either BuLi or Bu3MgLi generates metalated nitriles that efficiently intercept a variety of electrophiles to afford quaternary nitriles. The 2-pyridylsulfone is critical for the sulfone–metal exchange because chelation anchors the organometallic proximal to the electrophilic, tetrasubstituted sulfone to override complex-induced deprotonation. Alkylating commercial 2-pyridinesulfonylacetonitrile with mild bases, either K2CO3 or DBU, and subsequent sulfone–metal exchange and alkylation rapidly assembles quaternary nitriles by three alkylations, only one of which requires an organometallic reagent. 相似文献
69.
70.
C.S. YangD.Z. Jeng Yaw-Jou YangHong-Rong Chen C. Gau 《Experimental Thermal and Fluid Science》2011,35(1):73-81
Experiments have been performed to study the heat transfer process of swirling flow issued into a heated convergent pipe with a convergent angle of 5° with respect to the pipe axis. A flat vane swirler situated at the entrance of the pipe is used to generate the swirling flow. During the experiments, the Reynolds number ranges from 7970 to 47,820, and the swirl number from 0 to 1.2. It is found that the convergence of the pipe can accelerate the flow which has an effect to suppress the turbulence generated in the flow and reduce the heat transfer. However, in the region of weak swirl (S = 0-0.65), the Nusselt numbers increase with increasing swirl numbers until S = 0.65, where turbulence intensity is expected to be large enough and not suppressible. In the region of strong swirl (S > 0.65), where recirculation flow is expected to be generated in the core of the swirling flow, the heat transfer characteristic can be altered significantly. At very high swirl (S ? 1.0), the accelerated flow in the circumferential direction is expected to be dominant, which leads to suppress the turbulence and reduce the heat transfer. The Nusselt number is found proportional to the swirl number. Correlations of the Nusselt numbers in terms of the swirl number, the Reynolds number and the dimensionless distance are attempted and are very successful in both the weak and the strong swirl regions. 相似文献