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Harold J. Egoscue 《西北部美国博物学家》2011,48(4)
Collections from several scattered western localities have (1) extended the ranges in Nevada of two sagebrush vole fleas, Oropsylla bacchi johnsoni and Megabothris clantoni prince , (2) provided a second record for Utah of the rarely collected flea, Delotelis telegoni , and (3) included additional examples of unusual and seldom reported host-flea relationships for the area. 相似文献
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Most inner main-belt asteroids are primitive rock and metal bodies in orbit about the Sun between Mars and Jupiter. Disruption, through high-velocity collisions or rotational spin-up, is believed to be the primary mechanism for the production and destruction of small asteroids and a contributor to dust in the Sun's zodiacal cloud, while analogous collisions around other stars feed dust to their debris disks. Unfortunately, direct evidence about the mechanism or rate of disruption is lacking, owing to the rarity of the events. Here we report observations of P/2010?A2, a previously unknown inner-belt asteroid with a peculiar, comet-like morphology. The data reveal a nucleus of diameter approximately 120?metres with an associated tail of millimetre-sized dust particles. We conclude that it is most probably the remnant of a recent asteroidal disruption in February/March 2009, evolving slowly under the action of solar radiation pressure, in agreement with independent work. 相似文献
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Gilman AG Simon MI Bourne HR Harris BA Long R Ross EM Stull JT Taussig R Bourne HR Arkin AP Cobb MH Cyster JG Devreotes PN Ferrell JE Fruman D Gold M Weiss A Stull JT Berridge MJ Cantley LC Catterall WA Coughlin SR Olson EN Smith TF Brugge JS Botstein D Dixon JE Hunter T Lefkowitz RJ Pawson AJ Sternberg PW Varmus H Subramaniam S Sinkovits RS Li J Mock D Ning Y Saunders B Sternweis PC Hilgemann D Scheuermann RH DeCamp D Hsueh R Lin KM Ni Y Seaman WE Simpson PC O'Connell TD Roach T Simon MI 《Nature》2002,420(6916):703-706
The Alliance for Cellular Signaling is a large-scale collaboration designed to answer global questions about signalling networks. Pathways will be studied intensively in two cells--B lymphocytes (the cells of the immune system) and cardiac myocytes--to facilitate quantitative modelling. One goal is to catalyse complementary research in individual laboratories; to facilitate this, all alliance data are freely available for use by the entire research community. 相似文献
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At the heart of modern oxide chemistry lies the recognition that beneficial (as well as deleterious) materials properties can be obtained by deliberate deviations of oxygen atom occupancy from the ideal stoichiometry. Conversely, the capability to control and confine oxygen vacancies will be important to realize the full potential of perovskite ferroelectric materials, varistors and field-effect devices. In transition metal oxides, oxygen vacancies are generally electron donors, and in strontium titanate (SrTiO3) thin films, oxygen vacancies (unlike impurity dopants) are particularly important because they tend to retain high carrier mobilities, even at high carrier densities. Here we report the successful fabrication, using a pulsed laser deposition technique, of SrTiO3 superlattice films with oxygen doping profiles that exhibit subnanometre abruptness. We profile the vacancy concentrations on an atomic scale using annular-dark-field electron microscopy and core-level spectroscopy, and demonstrate absolute detection sensitivities of one to four oxygen vacancies. Our findings open a pathway to the microscopic study of individual vacancies and their clustering, not only in oxides, but in crystalline materials more generally. 相似文献
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It is widely accepted that the development of carcinoma--the most common form of human cancer--is due to the accumulation of somatic mutations in epithelial cells. The behaviour of carcinomas is also influenced by the tumour microenvironment, which includes extracellular matrix, blood vasculature, inflammatory cells and fibroblasts. Recent studies reveal that fibroblasts have a more profound influence on the development and progression of carcinomas than was previously appreciated. These new findings have important therapeutic implications. 相似文献
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Atlas R Campbell P Cozzarelli NR Curfman G Enquist L Fink G Flanagin A Fletcher J George E Hammes G Heyman D Inglesby T Kaplan S Kennedy D Krug J Levinson R Marcus E Metzger H Morse SS O'Brien A Onderdonk A Poste G Renault B Rich R Rosengard A Salzberg S Scanlan M Shenk T Tabor H Varmus H Wimmer E Yamamoto K;Journal Editors Authors Group 《Nature》2003,421(6925):771
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Extra-embryonic function of Rb is essential for embryonic development and viability 总被引:31,自引:0,他引:31
Wu L de Bruin A Saavedra HI Starovic M Trimboli A Yang Y Opavska J Wilson P Thompson JC Ostrowski MC Rosol TJ Woollett LA Weinstein M Cross JC Robinson ML Leone G 《Nature》2003,421(6926):942-947
The retinoblastoma (Rb) gene was the first tumour suppressor identified. Inactivation of Rb in mice results in unscheduled cell proliferation, apoptosis and widespread developmental defects, leading to embryonic death by day 14.5 (refs 2-4). However, the actual cause of the embryonic lethality has not been fully investigated. Here we show that loss of Rb leads to excessive proliferation of trophoblast cells and a severe disruption of the normal labyrinth architecture in the placenta. This is accompanied by a decrease in vascularization and a reduction in placental transport function. We used two complementary techniques-tetraploid aggregation and conditional knockout strategies-to demonstrate that Rb-deficient embryos supplied with a wild-type placenta can be carried to term, but die soon after birth. Most of the neurological and erythroid abnormalities thought to be responsible for the embryonic lethality of Rb-null animals were virtually absent in rescued Rb-null pups. These findings identify and define a key function of Rb in extra-embryonic cell lineages that is required for embryonic development and viability, and provide a mechanism for the cell autonomous versus non-cell autonomous roles of Rb in development. 相似文献
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Ohne Zusammenfassung
Vorgelegt von
M. Kline
The work of H. Edwards was supported by part by the U. S. National Science Foundation Grant SOC-7905162 and by the Vaughn Foundation. 相似文献