排序方式: 共有29条查询结果,搜索用时 328 毫秒
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Peter J. Perkins Frederick G. Lindzey Jay A. Roberson Gregory McDaniel Randy Berger 《西北部美国博物学家》2011,49(2)
Winter habitat use and food habits of Blue Grouse ( Dendragapus obscurus ) were studied in an isolated Utah desert mountain range that contained little typical Douglas-fir ( Pseudotsuga menziesii ) winter habitat. Habitat use was concentrated in the Douglas-fir and pinyon ( Pinus edulis )-juniper ( Juniperus spp. ) habitat. Douglas-fir and pinyon pine were the most consumed foods. Other foods that represented >15% of the composition of an individual fecal sample were limber pine ( Pinus flexilis ), mahogany ( Cercocarpus ledifoliu ), juniper, and an Anteunaria-Cirsium type. The breadth in winter diet indicates that Blue Grouse may successfully occupy other habitats when typical winter habitat is scarce. 相似文献
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The structure of the combining site of the DNP binding IgA mouse myeloma protein MOPC 315 has been determined by a combination of high resolution nuclear magnetic resonance, electron spin resonance, model building and chemical modifications. This approach yields that general dimensions of the site, its polarity and asymmetry features, the assignment of the DNP-contact residues and their three-dimensional coordinates. 相似文献
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Enhancement of the high-magnetic-field critical current density of superconducting MgB2 by proton irradiation 总被引:2,自引:0,他引:2
Bugoslavsky Y Cohen LF Perkins GK Polichetti M Tate TJ Gwilliam R Caplin AD 《Nature》2001,411(6837):561-563
Magnesium diboride, MgB2, has a relatively high superconducting transition temperature, placing it between the families of low- and high-temperature (copper oxide based) superconductors. Supercurrent flow in MgB2 is unhindered by grain boundaries, making it potentially attractive for technological applications in the temperature range 20-30 K. But in the bulk material, the critical current density (Jc) drops rapidly with increasing magnetic field strength. The magnitude and field dependence of the critical current are related to the presence of structural defects that can 'pin' the quantized magnetic vortices that permeate the material, and a lack of natural defects in MgB2 may be responsible for the rapid decline of Jc with increasing field strength. Here we show that modest levels of atomic disorder induced by proton irradiation enhance the pinning of vortices, thereby significantly increasing Jc at high field strengths. We anticipate that either chemical doping or mechanical processing should generate similar levels of disorder, and so achieve performance that is technologically attractive in an economically viable way. 相似文献
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W. Lohmann A. J. Moss Jr. W. H. Perkins C. F. Fowler 《Cellular and molecular life sciences : CMLS》1963,19(11):568-569
Zusammenfassung Die Veränderung der Strahlenempfindlichkeit von Katalase durch Diglycyl-glycin wurde spektralphotometrisch untersucht. Die Bestrahlungsdosen variierten zwischen 0–2,7 × 106
r. Der Schutzeffekt lässt sich durch einen Radikal-abfangenden Mechanismus erklären. Strahlenbiologische Folgerungen werden diskutiert. 相似文献
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James R. PERKINS 《系统科学与系统工程学报(英文版)》2011,20(4):400-415
This paper discusses a class of interval alignment (IA) scheduling policies, which are particularly effective for the systems that do not have Markovian structure. The numerical results show that IA policies effectively smooth part flows, improve performance and decrease average Work-in-Process (WIP) by adding intermediate delays to the system. The boundary of IA policy is proven and the applications of IA policy in the system with multiple stream arrivals have been discussed. With the combination of release policy, it is practical to implement IA to multiple stream arrival system. 相似文献