Ultraslow electron spin dynamics in GaAs quantum wells probed by optically pumped NMR     

NN Kuzma  P Khandelwal  SE Barrett  LN Pfeiffer  KW West 《Science (New York, N.Y.)》1998,281(5377):686-690

Optically pumped nuclear magnetic resonance (OPNMR) measurements were performed in two different electron-doped multiple quantum well samples near the fractional quantum Hall effect ground state nu = 13. Below 0.5 kelvin, the spectra provide evidence that spin-reversed charged excitations of the nu = 13 ground state are localized over the NMR time scale of about 40 microseconds. Furthermore, by varying NMR pulse parameters, the electron spin temperature (as measured by the Knight shift) could be driven above the lattice temperature, which shows that the value of the electron spin-lattice relaxation time tau1s is between 100 microseconds and 500 milliseconds at nu = 13.  相似文献   

CFT inaccurate for epididymitis     

J.D. Hicks  D.R. Marshall  G.R. Burr  B.M. Vidler 《New Zealand veterinary journal》2013,61(5)

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3种藏药复方抗ORFV作用研究     

姚海潮  鲁志平  梁剑平  色珠  曾江勇  拉巴次旦  夏晨阳 《中兽医医药杂志》2011,30(3):32-35

将岩青、轮叶棘豆等3种藏药材按一定比例配成复方,采用乙醇提取法进行提取,将浓缩药液用细胞维持液配制成1g／L的药液,并根据对兔肾细睁（PRK）安全浓度的测定结果,稀释成不同梯度浓度,分别与脓疱皮炎病毒（ORFV）加入到已培养24h的单层PRK中,通过M1TI’法测定OD值,分析其对ORFV病毒增殖的影响。经回归分析,复方药液在7．81—62·5mg／mL浓度范围内,药物浓度与活细胞存在线性关系,对病毒增势有显著的抑制作用（P〈0·05）。表明藏药材复方药液具有抗脓疱皮炎病毒感染的作用。  相似文献   

Twentieth-Century Sea Surface Temperature Trends   总被引：4，自引：0，他引：4  

MA Cane  AC Clement  A Kaplan  Y Kushnir  D Pozdnyakov  R Seager  SE Zebiak  R Murtugudde 《Science (New York, N.Y.)》1997,275(5302):957-960

An analysis of historical sea surface temperatures provides evidence for global warming since 1900, in line with land-based analyses of global temperature trends, and also shows that over the same period, the eastern equatorial Pacific cooled and the zonal sea surface temperature gradient strengthened. Recent theoretical studies have predicted such a pattern as a response of the coupled ocean-atmosphere system to an exogenous heating of the tropical atmosphere. This pattern, however, is not reproduced by the complex ocean-atmosphere circulation models currently used to simulate the climatic response to increased greenhouse gases. Its presence is likely to lessen the mean 20th-century global temperature change in model simulations.  相似文献   

HARRY BURR FERRIS     

Burr HS 《Science (New York, N.Y.)》1940,92(2396):499-500

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Relationships among cold hardiness, root growth potential and bud dormancy in three conifers     

Burr KE  Tinus RW  Wallner SJ  King RM 《Tree physiology》1989,5(3):291-306

Greenhouse-cultured, container-grown ponderosa pine (Pinus ponderosa var. scopulorum Engelm.), interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and Engelmann spruce (Picea engelmannii (Parry) Engelm.) were cold acclimated and deacclimated in growth chambers over 19 weeks. Stem cold hardiness, total new root length at 14 days and days to bud break were measured weekly. Relationships among cold hardiness, root growth potential (RGP) and bud dormancy suggest that cold hardiness, which can be measured quickly, could provide a useful basis for estimating the two other parameters. During cold acclimation, there was a lag period in which stem cold hardiness remained at -15 degrees C and RGP was at a minimum, in all three species. Douglas-fir and Engelmann spruce buds remained fully dormant during this lag period. Ponderosa pine buds had no chilling requirement for the loss of dormancy, and reached quiescence during the lag period. Immediately following the lag period, as stem cold hardiness progressed to -22 degrees C, RGP increased to a high plateau in all three species, and Douglas-fir and Engelmann spruce buds approached quiescence. Cold deacclimation and bud development began immediately on exposure to warm, long days, but RGP remained high until stem cold hardiness returned to approximately -15 degrees C. At bud break, cold hardiness and RGP were at the minimum.  相似文献   

Growth and Location of Economic Activity: The Spatial Dynamics of Industries in Canada 1971–2001     

MARIO POLSE  RICHARD SHEARMUR 《Growth and change》2006,37(3):362-395

ABSTRACT A growing literature has accumulated that points to the stability of industrial location patterns. Can this be reconciled with spatial dynamics? This article starts with the premise that demonstrable regularities exist in the manner in which individual industries locate (and relocate) over space. For Canada, spatial distributions of employment are examined for seventy‐one industries over a thirty‐year period (1971–2001). Industry data is organized by “synthetic regions” based on urban size and distance criteria. “Typical” location patterns are identified for industry groupings. Industrial spatial concentrations are then compared over time using correlation analysis, showing a high degree of stability. Stable industrial location patterns are not, the article finds, incompatible with differential regional growth. Five spatial processes are identified, driving change. The chief driving force is the propensity of dynamic industries to start up in large metro areas, setting off a process of diffusion (for services) and crowding out (for manufacturing), offset by the centralizing impact of greater consumer mobility and falling transport costs. These changes do not, however, significantly alter the relative spatial distribution of most industries over time.  相似文献   

Analysis of type III effector genes in typical and atypical Aeromonas salmonicida     

Burr SE  Frey J 《Journal of fish diseases》2007,30(11):711-714

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SOME ASPECTS OF THE PANAMA CANAL     

Burr WH 《Science (New York, N.Y.)》1906,24(603):71-78

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Heterothallism in Plasmopara viticola   总被引：5，自引：0，他引：5  

F. P. Wong  †‡  H. N. Burr  W. F. Wilcox 《Plant pathology》2001,50(4):427-432

Sexuality in the oomycete Plasmopara viticola , the causal agent of grapevine downy mildew, was studied using isolates from five populations from North America and Europe. Leaf discs of Vitis vinifera cv. 'Chardonnay' were inoculated with either individual single-sporangiophore isolates, or in all possible pairwise combinations of 25 isolates from New York State, USA. The occurrence of oospores in leaf discs indicated that the pathogen was heterothallic with two mating types, P1 and P2 in a ratio of 11 : 14 for this population. Heterothallism was confirmed when three representative isolates of each mating type from New York were coinoculated with each of 40 isolates from populations of P. viticola from Michigan, Missouri (USA), Germany and Italy. For each isolate tested, oospores formed with either test isolates of P1 or test isolates of P2 mating types, indicating that the isolates were exclusively P1 or P2 only. For these same isolates, no oospores formed as a result of self-crosses. The ratio of P1 : P2 mating types for all isolates in the study was 27 : 38, statistically equivalent to a 1 : 1 ratio according to χ² analysis ( P  = 0·68).  相似文献