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Highly transparent ZnO thin films were deposited at different substrate temperatures by pulsed laser deposition in an oxygen atmosphere.The thin films were characterized by various techniques including X-ray diffraction,scanning electron microscopy,optical absorption,and photoluminescence.We demonstrated that oriented wurtzite ZnO thin films could be deposited at room temperature using a high purity zinc target.Variable temperature photoluminescence revealed new characteristics in the band edge emission.The... 相似文献
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Teratogenic activity of nitrous oxide 总被引:8,自引:0,他引:8
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William D. Shepard 《西北部美国博物学家》2011,52(4)
Three species of Elmidae occur in Death Valley National Monument: Stenelmis calida is in three springs in the Ash Meadows area; Microcylloepus formicvideus is only in Travertine Springs; and Microcylloepus similis is in several springs throughout Death Valley and Ash Meadows. Only permanent springs support elmids. Considerable morphological variation occurs in the disjunct populations of M. similis . The evolution of elmids in Death Valley National Monument is equivalent to that of the local pupfish ( Cyprinodon spp.). 相似文献
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Positional cloning of zebrafish ferroportin1 identifies a conserved vertebrate iron exporter 总被引:81,自引:0,他引:81
Donovan A Brownlie A Zhou Y Shepard J Pratt SJ Moynihan J Paw BH Drejer A Barut B Zapata A Law TC Brugnara C Lux SE Pinkus GS Pinkus JL Kingsley PD Palis J Fleming MD Andrews NC Zon LI 《Nature》2000,403(6771):776-781
Defects in iron absorption and utilization lead to iron deficiency and overload disorders. Adult mammals absorb iron through the duodenum, whereas embryos obtain iron through placental transport. Iron uptake from the intestinal lumen through the apical surface of polarized duodenal enterocytes is mediated by the divalent metal transporter, DMTi. A second transporter has been postulated to export iron across the basolateral surface to the circulation. Here we have used positional cloning to identify the gene responsible for the hypochromic anaemia of the zebrafish mutant weissherbst. The gene, ferroportin1, encodes a multiple-transmembrane domain protein, expressed in the yolk sac, that is a candidate for the elusive iron exporter. Zebrafish ferroportin1 is required for the transport of iron from maternally derived yolk stores to the circulation and functions as an iron exporter when expressed in Xenopus oocytes. Human Ferroportin1 is found at the basal surface of placental syncytiotrophoblasts, suggesting that it also transports iron from mother to embryo. Mammalian Ferroportin1 is expressed at the basolateral surface of duodenal enterocytes and could export cellular iron into the circulation. We propose that Ferroportin1 function may be perturbed in mammalian disorders of iron deficiency or overload. 相似文献
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从理论上分析了利用时间有限差分法由近场到近场或远场转换的频域和时域两种方法,并选择时域的方法计算在FDTD计算范围内一给定点的电场值,与直接利用FDTD法得到的结果相比较,两者非常一致;最后利用该方法计算了功率变换器FDTD计算范围外一给定点的电磁场时间响应. 相似文献
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We examined algal flora in the aquatic system of Devils Hole, Nevada. The water is seasonally warm, near neutral in pH, and rich in dissolved carbonate, indicative of deeply circulating groundwater flowing through carbonate rock. Most algae were benthic, with only a few planktonic representatives. Eighty-four terminal identifications in 44 genera were recorded, with diatoms and blue-green algae the most speciose groups. Diatoms were major contributors to the grazing food web. Large, mat-forming filamentous algae have an important influence on the physicochemical and general structure of the benthic substrates in Devils Hole. 相似文献
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Calileuctra is proposed as new genus in the family Leuctridae, with Calileuctra ephemera designated as the type species. All stages of Calileuctra ephemera are descpribed. Calileuctra dobryi is described in the male and female stages. Both species inhabit Mediterranean climatic region of California. A phylogenetic analysis of the genera in the family Leuctridae is given, which places Calileuctra near the genus of Perlomyia . 相似文献