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排序方式: 共有190条查询结果,搜索用时 171 毫秒
31.
Zahid S Udenigwe CC Ata A Eze MO Segstro EP Holloway P 《Natural product research》2006,20(14):1283-1289
Chemical studies on the crude methanolic extract of Coprinus micaceus, collected from the Canadian Prairie region, have resulted in the isolation of two new natural products, micaceol (1), a sterol and (Z,Z)-4-oxo-2,5-hetpadienedioic acid (2). Compound 2 was isolated for the first time as a natural product. Structures of these new compounds were established with the aid of extensive NMR spectroscopic studies. Compound 1 has shown anti-bacterial activity against Corynebacterium xerosis and Staphylococcus aureus, whereas compound 2 exhibited glutathione S-transferase inhibition. 相似文献
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34.
Zhao X Outlaw RA Wang JJ Zhu MY Smith GD Holloway BC 《The Journal of chemical physics》2006,124(19):194704
Carbon nanosheets are a unique nanostructure that, at their thinnest configuration, approach a single freestanding graphene sheet. Temperature desorption spectroscopy (TDS) has shown that the hydrogen adsorption and incorporation during growth of the nanosheets by radio frequency plasma-enhanced chemical vapor deposition are significant. A numerical peak fitting to the desorption spectra (300-1273 K) via the Polanyi-Wigner equation showed that desorption followed a second order process, presumably by the Langmuir-Hinshelwood mechanism. Six peaks provide the best fit to the TDS spectra. Surface desorption activation energies were determined to be 0.59, 0.63, and 0.65 eV for the external graphite surface layers and 0.85, 1.15, and 1.73 eV for desorption and diffusion from the bulk. In contrast to TDS data from previously studied a-C:H films [Schenk et al. J. Appl. Phys. 77, 2462 (1995)], a greater amount of hydrogen bound as sp(2) hybridized carbon was observed. A previous x-ray diffraction study of these films has shown a significant graphitic character with a crystallite dimension of L(a)=10.7 nm. This result is consistent with experimental results by Raman spectroscopy that show as-grown carbon nanosheets to be crystalline as commercial graphite with a crystallite size of L(a)=11 nm. Following TDS, Raman data indicate that the average crystallite increased in size to L(a)=15 nm. 相似文献
35.
We study the deformation, spreading, and fingering of small droplets of a yield-stress fluid subjected to a centrifugal force
on a rotating substrate. At low rotation rates and for small enough droplets, the droplets deform elastically but retain their
essentially circular contact line. For large enough droplet volumes and rotation speeds, however, one or more fingers eventually
form and grow at the edge of the drop. This fingering is qualitatively different from the contact line instability observed
in other fluids, and appears to be a localized phenomenon that occurs when the stress at some point on the perimeter of the
drop exceeds the yield stress. 相似文献
36.
The aim of this brief report is to study the behaviour of sheath structure in a multi-component plasma with dust-neutral collisions.
The plasma consists of electrons, ions, micron size negatively charged dust particles and neutrals. The sheath-edge potential
and sheath width are calculated for collisionally dominated sheath. Comparison of collisionless and collisionally dominated
sheath are made. 相似文献
37.
The enthalpy of hydrolysis of solid tungsten thiotetrafluoride, WF(in4)S, in aqueous sodium hydroxide solution is -528.2 kJ mo1-1. Hence its standard enthalpy of formation has been calculated to be -1150.5 kJ mo1-1. 相似文献
38.
On the lamb solution and Rayleigh-wave-induced cracking 总被引:1,自引:0,他引:1
This paper examines the extension of surface microcracks induced by a surface or Rayleigh wave (R-wave). This problem is examined
both theoretically and experimentally. The theoretical approach involves a full-field reappraisal of the Lamb solution for
a surface wave propagating in a homogeneous, isotropic, elastic, two-dimensional material for the cases of plane strain and
plane stress. Using the Griffith-Irwin energy-release-rate fracture criterion for cracks under combined Mode I and Mode II
loading, a prediction is made of the path and final length of the surface microcrack extension produced by the R-wave. Predictions
of the crack-extension direction are also obtained using the maximum normal-stress fracture criterion. The experimental approach
uses dynamic photoelasticity to observe the isochromatic patterns associated with an R-wave propagating along the narrow edge
of a transparent birefringent plate, examining in detail the process of crack extension. When the theoretically and experimentally
obtained results are compared, reasonable agreement is obtained. 相似文献
39.
Synthesis of water-dispersible fluorescent, radio-opaque, and paramagnetic CdS:Mn/ZnS quantum dots: a multifunctional probe for bioimaging 总被引:3,自引:0,他引:3
Santra S Yang H Holloway PH Stanley JT Mericle RA 《Journal of the American Chemical Society》2005,127(6):1656-1657
Ultra-small (3.1 nm) multifunctional CdS:Mn/ZnS core-shell semiconductor quantum dots (Qdots), which possess fluorescent, radio-opacity, and paramagnetic properties, have been shown here. To demonstrate in vivo bioimaging capability, a rat was administered endovascularly with Qdots conjugated with a TAT peptide. The labeling efficacy of these Qdots was demonstrated on the basis of the histological analysis of the microtome sliced brain tissue, clearly showing that TAT-conjugated Qdots stained brain blood vessels. 相似文献
40.
K. Kretzschmar J.K. Sass P. Hofmann A. Ortega A.M. Bradshaw S. Holloway 《Chemical physics letters》1981,78(2):410-412
Infrared reflection absorption spectroscopy has been employed to study adsorption of water on Ru(001) at liquid nitrogen temperatures. For even the lowest H2O coverages a broad absorption band at ≈3400 cm?1 is observed on the clean surface, indicating formation of hydrogen-bonded clusters Small amounts of preadsorbed oxygen delay the clustering process. 相似文献