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31.
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A synecological study of aquatic macrophyte plant communities was conducted across northern Idaho and western Montana during the summers of 1997, 1998, and 1999. A total of 111 natural and man-made water bodies were sampled based on a stratification of environmental variables thought to influence plant species distribution (i.e., elevation, landform, geology, and water body size). Plant species foliar cover data were used to develop a hierarchical, floristic-based community type classification with TWINSPAN and DECORANA software. Six planmergent (conspicuous portion of vegetative plant body on the water surface) and 24 submergent (vegetative plant body found primarily underwater) community types were identified. Multivariate analysis indicated that all community types displayed significant differences in plant species composition, and the Sorensons floristic similarity between communities averaged 10% for planmergent and 8% for submergent types. Canonical correspondence analysis was used to inspect relationships between abiotic factors and plant species abundance. Results of this analysis indicated some relationships between species distributions and abiotic factors; however, chance introduction of plant species to water bodies is a process considered to be equally important to the presence of the community types described. 相似文献
33.
M. G. Freire N. J. Schweigmann W. S. Svagelj M. V Loetti O. Jensen 《Journal of Natural History》2016,50(21-22):1369-1380
Ochlerotatus albifasciatus is associated with aquatic environments that are frequently flooded. Awareness of blood hematophagic activity of female mosquitoes is particularly important in species which are vectors of human disease and domestic animals. The study of host-seeking activity allows us to infer the risk of transmission of these parasites. The objective of this work was to study in an agro-ecosystem and urban area of central Argentine Patagonia the relationship between the circadian rhythm of activity of host-seeking of Oc. albifasciatus, and environmental variables. During January 2003, 99 human bait catches were carried out, of which 77.8% registered at least one individual of Oc. albifasciatus. Generalised linear models were used to evaluate the relationship between Oc. albifasciatus biting activity rate and capture time, environmental humidity, air temperature, sunshine degree, wind speed, habitat type and proximity of larval habitat. The model that best explained the variation in biting activity rate included the capture time, environmental humidity, air temperature, sunshine degree and wind speed as predictor variables. Host-seeking activity was higher in the evening than in the morning or afternoon, and it was positively related to mean air temperature and environmental relative humidity (RH), but negatively to sunshine degree and wind speed. The combination of these characteristics (wind speed less than 20 km/h, environmental temperature greater than 26°C, sunshine less than 40% and (RH) greater than 50%) would provide favourable conditions to allow seeking activity and to feed on the host. The dispersion of this mosquito could be among environmental patches that present these characteristics. 相似文献
34.
James A. Jensen 《西北部美国博物学家》2011,48(2)
The new sauropod, Cathetosaurus lewisi , is named and assigned to the Camarasauridae; it was collected from the Upper Jurassic Morrison Formation in western Colorado in 1967. Novel structural features of the skeleton in this genus, particularly in the axial skeleton, enabled it to assume and function to an unknown degree in a bipedal posture. Comparisons are made between C. lewisi and previously described sauropods. The following problems of sauropod locomotion are discussed; (1) sauropods lack two elements, sesamoids and patella, present in titanotheres; (2) sauropod limb and foot musculature, lacking leverage, is very inferior to that of titanotheres; (3) no previously described sauropod displays adequate structural specializations for voluntary bipedalism comparable to that of the new genus Cathetosaurus; (4) great weight and cartilaginous limb and foot joint structure restricted sauropods to a slow tempo of locomotion, suggesting a moderate to low rate of catabolic metabolism. Mammal and sauropod foot bones and their function are compared, and comparisons are made between the weight and structure of modern mobile machines and the locomotion and movement of large sauropods. Occurrence and taphonomy of C. lewisi are discussed. 相似文献
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Najmabadi H Hu H Garshasbi M Zemojtel T Abedini SS Chen W Hosseini M Behjati F Haas S Jamali P Zecha A Mohseni M Püttmann L Vahid LN Jensen C Moheb LA Bienek M Larti F Mueller I Weissmann R Darvish H Wrogemann K Hadavi V Lipkowitz B Esmaeeli-Nieh S Wieczorek D Kariminejad R Firouzabadi SG Cohen M Fattahi Z Rost I Mojahedi F Hertzberg C Dehghan A Rajab A Banavandi MJ Hoffer J Falah M Musante L Kalscheuer V Ullmann R Kuss AW Tzschach A Kahrizi K Ropers HH 《Nature》2011,478(7367):57-63
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The neonatal Fc receptor (FcRn) transports maternal IgG across epithelial barriers, thereby providing the fetus or newborn with humoral immunity before its immune system is fully functional. In newborn rats, FcRn transfers IgG from milk to blood by apical-to-basolateral transcytosis across intestinal epithelial cells. The pH difference between the apical (pH 6.0-6.5) and basolateral (pH 7.4) sides of intestinal epithelial cells facilitates the efficient unidirectional transport of IgG, because FcRn binds IgG at pH 6.0-6.5 but not at pH 7 or more. As milk passes through the neonatal intestine, maternal IgG is removed by FcRn-expressing cells in the proximal small intestine (duodenum and jejunum); remaining proteins are absorbed and degraded by FcRn-negative cells in the distal small intestine (ileum). Here we use electron tomography to make jejunal transcytosis visible directly in space and time, developing new labelling and detection methods to map individual nanogold-labelled Fc within transport vesicles and simultaneously to characterize these vesicles by immunolabelling. Combining electron tomography with a non-perturbing endocytic label allowed us to conclusively identify receptor-bound ligands, resolve interconnecting vesicles, determine whether a vesicle was microtubule-associated, and accurately trace FcRn-mediated transport of IgG. Our results present a complex picture in which Fc moves through networks of entangled tubular and irregular vesicles, only some of which are microtubule-associated, as it migrates to the basolateral surface. New features of transcytosis are elucidated, including transport involving multivesicular body inner vesicles/tubules and exocytosis through clathrin-coated pits. Markers for early, late and recycling endosomes each labelled vesicles in different and overlapping morphological classes, revealing spatial complexity in endo-lysosomal trafficking. 相似文献
39.
Type VI secretion systems are bacterial virulence-associated nanomachines composed of proteins that are evolutionarily related to components of bacteriophage tails. Here we show that protein secretion by the type VI secretion system of Vibrio cholerae requires the action of a dynamic intracellular tubular structure that is structurally and functionally homologous to contractile phage tail sheath. Time-lapse fluorescence light microscopy reveals that sheaths of the type VI secretion system cycle between assembly, quick contraction, disassembly and re-assembly. Whole-cell electron cryotomography further shows that the sheaths appear as long tubular structures in either extended or contracted conformations that are connected to the inner membrane by a distinct basal structure. These data support a model in which the contraction of the type VI secretion system sheath provides the energy needed to translocate proteins out of effector cells and into adjacent target cells. 相似文献
40.
The current technology of proton exchange membrane fuel cells (PEMFC) is based on perfluorosulfonic acid (PFSA) membranes (e. g. Nation ) as electrolyte. It operates on pure hydrogen and oxygen/air at typically 80℃ with high power density and long-term durability. For the membranes to be conductive, a minimum threshold of absorbed water molecules is about 6 to 7 mole per sulfonic site. The highest conductivity is only obtained under fully hydrated conductions, i.e. 21 - 22 mole water per sulfonic acid site. In other words, the proton conductivity is achieved by the locally liquid-like hydrophilic domain of the nanostructure. This strong dependence of conductivity on the water content in membranes limits the operational temperature of PEMFC below 100 ℃. 相似文献