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排序方式: 共有71条查询结果,搜索用时 15 毫秒
1.
2.
Hot-wire and oil-film interferometry measurements are taken for 3D rough wall boundary layers at very high Reynolds numbers
(61,000 < Re θ < 120,000) with low blockage ratios, 10 < δ/H < 135, and high roughness, 100 < H
+ < 4,900. The results cover flows over both rough walls and over obstacles and are compared with and provide extension to
recent lower Reynolds number results. The validity of the Townsend ‘wall similarity hypothesis’ in relation to consistently
increasing 3D roughness is interrogated. In agreement with recent work, Schultz and Flack (J Fluid Mech 580:381–405, 2007) and Castro (J Fluid Mech 585:469–485, 2007) found that, for relatively low roughness, Townsend’s hypothesis holds for the mean velocity field. With increasing roughness,
the equilibrium layer diminishes and gradually vanishes. The viscous component of the wall shear stress decreases, while the
turbulent component increases as the roughness effects extend across the boundary layer. 相似文献
3.
Optical computing 总被引:1,自引:0,他引:1
4.
Schoolyard Shade and Sun Exposure: Assessment of Personal Monitoring During Children's Physical Activity 下载免费PDF全文
Jennifer K. Vanos Grant R. McKercher Kylie Naughton Marc Lochbaum 《Photochemistry and photobiology》2017,93(4):1123-1132
Childhood exposure to ultraviolet radiation (UVR) is a major risk factor for the development of melanoma later in life. However, it is challenging to accurately determine personal outdoor exposure to UVR, specifically erythemally weighted UVR (UVEry), due to technological constraints, variable time–activity patterns, and the influence of outdoor environmental design. To address this challenge, this study utilized mobile and stationary techniques to examine the UVEry exposures of 14 children in a schoolyard in Lubbock, TX, in spring 2016. The aims of the study were to examine the influence of artificial shade on personal UVEry exposures and to assess full sun exposure ratios (ERs) within the same playground microenvironment. On average, personal wrist dosimeters worn during play in the sun measured 18% of the total onsite UVEry measured by a stationary UV pyranometer. Shade was found to significantly reduce the personal UVEry exposures by 55%, UVB280–315 nm exposures by 91%, and the overall solar radiation by 84%. Substantial benefits can be garnered through focused design of children's recreational space to utilize shade—both natural and artificial—to reduce UVR exposures during play, and to extend safe outdoor stays. Finally, although the wrist is a practical location for a dosimeter, it often underestimates full exposures, particularly during physical activity. 相似文献
5.
Spencer Knapp Andrew B. J. Naughton Paivi J. Kukkola Wen-Chung Shieh 《Journal of carbohydrate chemistry》2013,32(6):981-993
ABSTRACT For five carbohydrate substrates [methyl 4,6-O-(phenylmethylene)-1-thio-α-D-glucopyranoside 1a, 1-cyano-1-deoxy-4,6-O-(phenylmethylene)-α-D-galactopyranose 2a, methyl α-D-xylopyranoside 3a, methyl β-D-arabinopyranoside 4a, and methyl 5-O-(tert-butyldiphenylsilyl)-α-D-ribofuranoside 5a], selective mono-triflation was achieved where the reacting hydroxyl is cis and vicinal to a heteroatom. 相似文献
6.
7.
KL Britton HF Rogers Y Asano T Dairi Y Kato TJ Stillman DW Rice 《Acta crystallographica. Section D, Biological crystallography》1998,53(4):124-126
The novel NAD+-linked opine dehydrogenase from a soil isolate Arthrobacter sp. strain 1C belongs to an enzyme superfamily whose members exhibit quite diverse substrate specificites. Crystals of this opine dehydrogenase, obtained in the presence or absence of co-factor and substrates, have been shown to diffract to beyond 1.8 ? resolution. X-ray precession photographs have established that the crystals belong to space group P21212, with cell parameters a = 104.9, b = 80.0, c = 45.5 ? and a single subunit in the asymmetric unit. The elucidation of the three-dimensional structure of this enzyme will provide a structural framework for this novel class of dehydrogenases to enable a comparison to be made with other enzyme families and also as the basis for mutagenesis experiments directed towards the production of natural and synthetic opine-type compounds containing two chiral centres. 相似文献
8.
Swern oxidation of 2,3,4,5-tetra-O-benzyl-D -glucose ( 1 ) followed by ammonolysis gave the crystalline amide 3 which was oxidized (DMSO/pyridine · SO3) to yield the oxo-amide 4 and the hydroxy-lactams 5 and 6 . Cyclization of 4 to the very slowly equilibrating 5 and 6 was completed by treatment with AcOH in CHCl3. The configuration of the hydroxy-lactams was assigned on the basis of NOEs. Reduction (Et3SiH/BF3 · Et2O) of the hydroxy-lactams either individually or as a mixture led to 2,3,4,6-tetra-O-benzyl-D-gluconolactam ( 7 ). The procedure, based upon modifications of a patent, does not require chromatography; the overall yield of 7 from 1 is 43%. Hydrogenolysis of 7 gave D-nojirilactam ( 8 ); benzylation led to the known pentabenzyl-D-nojirilactam ( 9 ) and to the unsaturated lactam 10 . 相似文献
9.
In hole-doped cuprates, Nernst experiments imply that the superconducting state is destroyed by spontaneous creation of vortices which destroy phase coherence. Using torque magnetometry on Bi2Sr2CaCu2O(8+delta), we uncover a field-enhanced diamagnetic signal M above the transition temperature Tc that increases with applied field to 32 Tesla and scales just like the Nernst signal. The magnetization results above Tc distinguish M from conventional amplitude fluctuations and strongly support the vortex scenario for the loss of phase coherence at Tc. 相似文献
10.
Kempa K Zhou Y Engelbrecht JR Bakshi P Ha HI Moser J Naughton MJ Ulrich J Strasser G Gornik E Unterrainer K 《Physical review letters》2002,88(22):226803
We show theoretically that in quantum wells subjected to a strong magnetic field the intersubband current peaks at magnetic field values, which reveal the underlying specific intersubband scattering mechanism. We have designed and grown a superlattice structure in which such current oscillations are clearly visible, and in which the transition from the purely single-electron to the mixed single- and two-electron scattering regimes can be observed by tuning the applied voltage bias. The measurements were conducted in ultrahigh magnetic fields (up to 45 T) to obtain the full spectrum of the current oscillations. 相似文献