Investigations of ZnO thin films deposited by a reactive pulsed laser ablation

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...     

Riffle beetles (Coleoptera: Elmidae) of Death Valley National Monument, California

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.).     

FDTD计算功率变换器近场到近/远场的转换

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．     

Positional cloning of zebrafish ferroportin1 identifies a conserved vertebrate iron exporter

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.     

Scaling laws of marine predator search behaviour

Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology. Lévy walks are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators-sharks, bony fishes, sea turtles and penguins-exhibit Lévy-walk-like behaviour close to a theoretical optimum. Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms, from microbes to humans, as a 'rule' that evolved in response to patchy resource distributions.     

Calileuctra , a new genus, and two new species of stoneflies from California (Plecoptera: Leuctridae)

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 .