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101.
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103.
The gyrator is a lossless two-port network which transforms one-port networks into its dual with respect to its gyration conductance. For example, capacitance at the gyrator output is viewed as inductance at the input and a voltage source is transformed to a current source. 相似文献
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105.
Significance of urban and agricultural land use for biocide and pesticide dynamics in surface waters 总被引:1,自引:0,他引:1
Biocides and pesticides are designed to control the occurrence of unwanted organisms. From their point of application, these substances can be mobilized and transported to surface waters posing a threat to the aquatic environment. Historically, agricultural pesticides have received substantially more attention than biocidal compounds from urban use, despite being used in similar quantities.This study aims at improving our understanding of the influence of mixed urban and agricultural land use on the overall concentration dynamics of biocides and pesticides during rain events throughout the year. A comprehensive field study was conducted in a catchment within the Swiss plateau (25 km2). Four surface water sampling sites represented varying combinations of urban and agricultural sources. Additionally, the urban drainage system was studied by sampling the only wastewater treatment plant (WWTP) in the catchment, a combined sewer overflow (CSO), and a storm sewer (SS). High temporal resolution sampling was carried out during rain events from March to November 2007.The results, based on more than 600 samples analyzed for 23 substances, revealed distinct and complex concentration patterns for different compounds and sources. Five types of concentration patterns can be distinguished: a) compounds that showed elevated background concentrations throughout the year (e.g. diazinon >50 ng L−1), indicating a constant household source; b) compounds that showed elevated concentrations driven by rain events throughout the year (e.g. diuron 100-300 ng L−1), indicating a constant urban outdoor source such as facades; c) compounds with seasonal peak concentrations driven by rain events from urban and agricultural areas (e.g. mecoprop 1600 ng L−1 and atrazine 2500 ng L−1 respectively); d) compounds that showed unpredictably sharp peaks (e.g. atrazine 10,000 ng L−1, diazinon 2500 ng L−1), which were most probably due to improper handling or even disposal of products; and finally, e) compounds that were used in high amounts but were not detected in surface waters (e.g. isothiazolinones).It can be safely concluded that in catchments of mixed land use, the contributions of biocide and pesticide inputs into surface waters from urban areas are at least as important as those from agricultural areas. 相似文献
106.
Miles AM Singer PC Ashley DL Lynberg MC Mendola P Langlois PH Nuckols JR 《Environmental science & technology》2002,36(8):1692-1698
Trihalomethane (THM) concentrations in blood and tap water were measured for 50 women living in two locations with different bromide concentrations and disinfectant types. Blood samples were taken from each woman early in the morning prior to any major water-use activity and again immediately after showering. Each residence was sampled for THMs in tap water prior to the woman's shower. Cobb County, GA, tap water exhibited high THM concentrations composed primarily of chloroform. Corpus Christi, TX, tap water exhibited lower THM concentrations with significant proportions of brominated THMs. THMs in tap water and blood were compared using mole fraction speciation, extent of bromine incorporation, and correlation analysis. Results indicated that THMs in the blood rose significantly as a result of showering, that showering shifted the THM distribution in the blood toward that found in the corresponding tap water, and that THMs measured in the blood of women living in the two locations reflected species and concentration differences in their respective tap waters. In general, blood concentrations were not significantly correlated with tap water concentrations. This finding suggests that other factors, in addition to tap water concentrations, may be important in determining THM concentrations in the blood. 相似文献
107.
Velikson B; Cohen P; Rholam M; Rose JP; Wang BC; Smith JC 《Protein engineering, design & selection : PEDS》1998,11(10):909-916
The hormonal precursor pro-ocytocin-neurophysin is activated by selective
cleavage at Arg2-Ala13, producing mature ocytocin and neurophysin. To
understand the cleavage mechanism better, and in particular the recognition
of the cleavage site, it is necessary to characterize the three-dimensional
structure of the precursor molecule. Here we combine a variety of
experimental data with molecular modeling and dynamics calculations to
derive possible precursor conformations. In the models obtained, the
N-terminus of the precursor, corresponding to the ocytocin segment, is
hydrogen bonded in a pocket of the neurophysin moiety in a similar manner
to a crystallographically obtained non-covalent complex between the two
molecules. The calculations suggest that although the ocytocin segment is
relatively flexible, it adopts a stable, broad loop structure in the
vicinity of the cleavage region, which may constitute the structural
element recognized by the cleaving enzyme. The calculations also suggest a
possible widening of the distance between the two neurophysin domains in
the precursor relative to that in the non-covalent neurophysin- ocytocin
complex.
相似文献
108.
109.
The endurance of ion-beam-assist-deposited (IBAD) MoS2 is correlated with coating structure and orientation. Structure and orientation are determined by X-ray diffraction, while endurance is measured with a ball-on-disk tribometer operating in dry air. The IBAD MoS2 coatings contain both crystalline and non-crystalline components. Only two orientations of the crystalline component are observed: the (001) planes parallel (basal orientation) and perpendicular (edge orientation) to the surface. Endurance of the coating is not related to coating thickness or substrate chemistry, but is related to the relative amount of the two MoS2 crystal orientations. Coating endurance decreases with increasing edge (100) intensity. Furthermore, MoS2 coatings with poor crystallinity exhibit good endurance. These results are discussed in terms of a possible oxidative wear mechanism and stress-induced basal re-orientation of the non-crystalline IBAD MoS2. 相似文献
110.
We sketch the universal critical properties of a quantum superconductor to insulator transition in two spatial dimensions, using the scaling theory of quantum critical phenomena. Comparison with experimental data reveals that the resulting universal relations among transition temperature, zero temperature penetration depth, and residual resistivity, as well as for the asymptotic linear temperature dependence of the penetration depth, appear to apply in a rather extended doping regime, ranging from the underdoped limit up to the nearly optimum dopant concentration. This behavior uncovers the dominant role of quantum fluctuations in this doping regime. 相似文献