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101.
Hanging gardens of the Narrows, Zion National Park, Utah, are plant communities growing at permanent seeps on the canyon walls. The gardens are isolated from each other and from other plant communities by vertical expanses of sandstone. Gardens consist mostly of herbaceous species less than 1 m tall. Though not individually species-rich, the hanging gardens are diverse as a group, and very dissimilar. This study considers two explanations of the heterogeneous distribution of species in hanging gardens. The assemblages of dispersal types in gardens of different spatial attributes and disturbance frequencies are examined. The G H statistic, a log likelihood ratio test, analyzes the incidence of dispersal types among classes of three spatial and two disturbance variables. The disturbance variables of expected flood frequency and soil depth segregate dispersal types; and the spatial variables of area, distance to possible seed sources, and relative isolation do not. Ferns and mosses, dispersing through spores, dominate a heterogeneous fugitive guild in the flood-prone gardens. Infrequently flooded gardens support more large-seeded species. 相似文献
102.
P. Laxman Mani Kanta V. C. Srivastava K. Venkateswarlu Sharma Paswan B. Mahato Goutam Das K. Sivaprasad K. Gopala Krishna 《矿物冶金与材料学报》2017,24(11):1293-1305
The objectives of this study were to produce ultrafine-grained (UFG) AA2024 aluminum alloy by cryorolling followed by aging and to evaluate its corrosion behavior. Solutionized samples were cryorolled to ~85% reduction in thickness. Subsequent aging resulted in a UFG structure with finer precipitates of Al2CuMg in the cryorolled alloy. The (1) solutionized and (2) solutionized and cryorolled samples were uniformly aged at 160℃/24 h and were designated as CGPA and CRPA, respectively; these samples were subsequently subjected to corrosion studies. Potentiodynamic polarization studies in 3.5wt% NaCl solution indicated an increase in corrosion potential and a decrease in corrosion current density for CRPA compared to CGPA. In the case of CRPA, electrochemical impedance spectroscopic studies indicated the presence of two complex passive oxide layers with a higher charge transfer resistance and lower mass loss during intergranular corrosion tests. The improved corrosion resistance of CRPA was mainly attributed to its UFG structure, uniform distribution of fine precipitates, and absence of coarse grain-boundary precipitation and associated precipitate-free zones as compared with the CGPA alloy. 相似文献
103.
Human ES-cell-derived cardiomyocytes electrically couple and suppress arrhythmias in injured hearts 总被引:1,自引:0,他引:1
Y Shiba S Fernandes WZ Zhu D Filice V Muskheli J Kim NJ Palpant J Gantz KW Moyes H Reinecke B Van Biber T Dardas JL Mignone A Izawa R Hanna M Viswanathan JD Gold MI Kotlikoff N Sarvazyan MW Kay CE Murry MA Laflamme 《Nature》2012,489(7415):322-325
Transplantation studies in mice and rats have shown that human embryonic-stem-cell-derived cardiomyocytes (hESC-CMs) can improve the function of infarcted hearts, but two critical issues related to their electrophysiological behaviour in vivo remain unresolved. First, the risk of arrhythmias following hESC-CM transplantation in injured hearts has not been determined. Second, the electromechanical integration of hESC-CMs in injured hearts has not been demonstrated, so it is unclear whether these cells improve contractile function directly through addition of new force-generating units. Here we use a guinea-pig model to show that hESC-CM grafts in injured hearts protect against arrhythmias and can contract synchronously with host muscle. Injured hearts with hESC-CM grafts show improved mechanical function and a significantly reduced incidence of both spontaneous and induced ventricular tachycardia. To assess the activity of hESC-CM grafts in vivo, we transplanted hESC-CMs expressing the genetically encoded calcium sensor, GCaMP3 (refs 4, 5). By correlating the GCaMP3 fluorescent signal with the host ECG, we found that grafts in uninjured hearts have consistent 1:1 host–graft coupling. Grafts in injured hearts are more heterogeneous and typically include both coupled and uncoupled regions. Thus, human myocardial grafts meet physiological criteria for true heart regeneration, providing support for the continued development of hESC-based cardiac therapies for both mechanical and electrical repair. 相似文献
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保罗凯依 《曲靖师范学院学报》2007,26(5):80-84
人们对颜色词汇的语言学研究一直关注把语言的“基本”颜色词语分离出来:说话者可以说出任何一个颜色词语的一种语言学层面的最小一组的简单语言表达。 相似文献
106.
Microstructure studies of air-plasma-spray-deposited CoNiCrAlY coatings before and after thermal cyclic loading for high-temperature application 下载免费PDF全文
In the present study, bond-coats for thermal barrier coatings were deposited via air plasma spraying (APS) techniques onto Inconel 800 and Hastelloy C-276 alloy substrates. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to investigate the phases and microstructure of the as-sprayed, APS-deposited CoNiCrAlY bond-coatings. The aim of this work was to study the suitability of the bond-coat materials for high temperature applications. Confirmation of nanoscale grains of the γ/γ′-phase was obtained by TEM, high-resolution TEM, and AFM. We concluded that these changes result from the plastic deformation of the bond-coat during the deposition, resulting in CoNiCrAlY bond-coatings with excellent thermal cyclic resistance suitable for use in high-temperature applications. Cyclic oxidative stability was observed to also depend on the underlying metallic alloy substrate. 相似文献
107.
A trio of thiolate-protected atomically precise gold nanoclusters, [Au_(23)(S-c-C_6H_(11))_(16)]~–, Au24(SCH_2pH~tBu)_(20)and [Au_(25)(SCH_2CH_2pH)_~(18)]~–, are utilized as catalysts for 4-nitrophenol(4-NP) reduction to 4-aminophenol(4-AP).Despite nearly identical sizes(~1 nm), the three nanoclusters possess distinctly different atomic packing structures and surface ligand binding modes, which contribute to different catalytic performance. The [Au_(23)(Sc-C_6H_(11))_(16)]~–nanocluster shows the highest activity with a kinetic rate constant of 0.0370 s~(-1), which is higher than those of Au24(SCH_2pH~tBu)_(20)(0.0090 s~(-1)) and [Au_(25)(SCH_2CH_2pH)_~(18)]~–(0.0242 s~(-1)). Such a trio of gold nanoclusters indicate that the atomic packing mode and electronic structure play a crucial role in determining their catalytic performance. 相似文献
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G. R. Pettit B. Green A. K. Das Gupta G. L. Dunn 《Cellular and molecular life sciences : CMLS》1964,20(5):248-249
Zusammenfassung Ein einfacher Weg zur Synthese eines von zwei möglichen isomeren Cardenoliden wurde entwickelt und die Reaktionsfolge an Hand der Überführung von Pregnenolon in Isocardenolide V gezeigt.
Steroids and Related Natural Products XXI. For the previous contribution refer to:G. R. Pettit andP. Hofer, Helv. chim. Acta46, 2142 (1963).
A preliminary account of this study was presented (December 1963) at the VI. Pan-American Congress of Pharmacy and Biochemistry, Mexico City (Mexico).
This investigation was supported by PHS Research Grants CY-4074 (C3) to CA-04074-06 from the National Cancer Institute, Public Health Service. 相似文献
Steroids and Related Natural Products XXI. For the previous contribution refer to:G. R. Pettit andP. Hofer, Helv. chim. Acta46, 2142 (1963).
A preliminary account of this study was presented (December 1963) at the VI. Pan-American Congress of Pharmacy and Biochemistry, Mexico City (Mexico).
This investigation was supported by PHS Research Grants CY-4074 (C3) to CA-04074-06 from the National Cancer Institute, Public Health Service. 相似文献