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排序方式: 共有358条查询结果,搜索用时 15 毫秒
271.
272.
Carlos E. Canosa-Mas Hilary R. Hutton-Squire Martin D. King David J. Stewart Katherine C. Thompson Richard P. Wayne 《Journal of Atmospheric Chemistry》1999,34(1):163-170
The rate coefficients for the reaction between atomic chlorine and a number of naturally occurring species have been measured at ambient temperature and atmospheric pressure using the relative rate technique. The values obtained were (4.0 ± 0.8) × 10-10, (2.1 ± 0.5) × 10-10, (3.2 ± 0.5) × 10-10, and (4.9 ± 0.5) × 10-10 cm3 molecule-1 s-1, for reactions with isoprene, methyl vinyl ketone, methacrolein and 3-carene, respectively. The value obtained for isoprene compares favourably with previously reported values. No values have been reported to date for the rate constants of the other reactions. 相似文献
273.
Characterization of the shallow groundwater system in an alpine watershed: Handcart Gulch,Colorado, USA 总被引:2,自引:2,他引:0
Katherine Gurley Kahn Shemin Ge Jonathan Saul Caine Andrew Manning 《Hydrogeology Journal》2008,16(1):103-121
Water-table elevation measurements and aquifer parameter estimates are rare in alpine settings because few wells exist in these environments. Alpine groundwater systems may be a primary source of recharge to regional groundwater flow systems. Handcart Gulch is an alpine watershed in Colorado, USA comprised of highly fractured Proterozoic metamorphic and igneous rocks with wells completed to various depths. Primary study objectives include determining hydrologic properties of shallow bedrock and surficial materials, developing a watershed water budget, and testing the consistency of measured hydrologic properties and water budget by constructing a simple model incorporating groundwater and surface water for water year 2005. Water enters the study area as precipitation and exits as discharge in the trunk stream or potential recharge for the deeper aquifer. Surficial infiltration rates ranged from 0.1–6.2×10?5 m/s. Discharge was estimated at 1.28×10?3 km3. Numerical modeling analysis of single-well aquifer tests predicted lower specific storage in crystalline bedrock than in ferricrete and colluvial material (6.7×10?5–2.0×10?3 l/m). Hydraulic conductivity in crystalline bedrock was significantly lower than in colluvial and alluvial material (4.3×10?9–2.0×10?4 m/s). Water budget results suggest that during normal precipitation and temperatures water is available to recharge the deeper groundwater flow system. 相似文献
274.
The ease and affordability of the herbicide glyphosate and the development of glyphosate tolerant crops has encouraged a simplified weed management system in the U.S. However, the overuse of this technological package in recent years has led to an explosion in the number of herbicide resistant weeds and a decrease in the effectiveness of glyphosate. In addition to this bio-chemical problem, many growers appear to be stuck within a farming ideology that focuses on a reduction in time/labor, an increase in profitability and a vision of ever-increasing efficiencies of scale. This may prevent them from conceptualizing and implementing solutions that fall outside of a simple herbicide application plan. The objective of this paper is to begin describing the current ideology of industrial corn and soybean farmers in the United States, as well as how this ideology contributes to farmers’ resistance to complex weed management strategies. 相似文献
275.
Spatial and social transformations in a secondary city: the role of mobility in Sekondi-Takoradi,Ghana 总被引:1,自引:1,他引:0
Paul W. K. Yankson Katherine V. Gough James Esson Ebenezer F. Amankwaa 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2017,117(2):82-92
AbstractExisting research on urban Ghana mainly focuses on processes occurring within the country’s major cities, thereby reproducing a trend within the social sciences to overlook the role of intermediate and secondary cities. This paper aims to address this shortcoming by exploring spatial and social transformations in Sekondi–Takoradi, one of Ghana’s secondary cities and the metropolitan area serving the region’s emerging rubber industries as well as the country’s oil and gas economy. Using qualitative interviews conducted with residents in five of the city’s neighbourhoods, and a modified version of Kaufmann’s typology of mobility, we examine migration into Sekondi–Takoradi, residential mobility within the city and the daily mobility of the city’s residents. The paper highlights how these diverse forms of mobility interact with processes taking place both within and outside Sekondi–Takoradi, most notably influencing and being influenced by livelihood strategies. It is argued that the city and its hinterlands can best be envisaged as a mobile networked whole, rather than consisting of disconnected and compartmentalized locales. The paper thus contributes to broader debates on how mobility shapes urbanization by providing new empirical data on events unfolding in Africa’s secondary cities, and extends existing research by providing a counter-narrative to literature that examines the city and its surrounding rural areas separately. 相似文献
276.
Gunnar?LudererEmail author Christoph?Bertram Katherine?Calvin Enrica?De?Cian Elmar?Kriegler 《Climatic change》2016,135(1):127-141
While the international community has agreed on the long-term target of limiting global warming to no more than 2 °C above pre-industrial levels, only a few concrete climate policies and measures to reduce greenhouse gas (GHG) emissions have been implemented. We use a set of three global integrated assessment models to analyze the implications of current climate policies on long-term mitigation targets. We define a weak-policy baseline scenario, which extrapolates the current policy environment by assuming that the global climate regime remains fragmented and that emission reduction efforts remain unambitious in most of the world’s regions. These scenarios clearly fall short of limiting warming to 2 °C. We investigate the cost and achievability of the stabilization of atmospheric GHG concentrations at 450 ppm CO2e by 2100, if countries follow the weak policy pathway until 2020 or 2030 before pursuing the long-term mitigation target with global cooperative action. We find that after a deferral of ambitious action the 450 ppm CO2e is only achievable with a radical up-scaling of efforts after target adoption. This has severe effects on transformation pathways and exacerbates the challenges of climate stabilization, in particular for a delay of cooperative action until 2030. Specifically, reaching the target with weak near-term action implies (a) faster and more aggressive transformations of energy systems in the medium term, (b) more stranded investments in fossil-based capacities, (c) higher long-term mitigation costs and carbon prices and (d) stronger transitional economic impacts, rendering the political feasibility of such pathways questionable. 相似文献
277.
Katherine M. Blundell & Anthony J. Beasley 《Monthly notices of the Royal Astronomical Society》1998,299(1):165-170
Two rival hypotheses have been proposed for the origin of the compact radio flux observed in radio-quiet quasars (RQQs). It has been suggested that the radio emission in these objects, typically some two or three orders of magnitude less powerful than in radio-loud quasars (RLQs), either represents emission from a circumnuclear starburst or is produced by radio jets with bulk kinetic powers ∼ 103 times lower than those of RLQs with similar luminosity ratios in other wavebands. We describe the results of high-resolution (∼pc-scale) radio-imaging observations of a sample of 12 RQQs using the Very Long Baseline Array (VLBA). We find strong evidence for jet-producing central engines in eight members of our sample. 相似文献
278.
279.
Paulin Gabriel Legorreta Mickelson Katherine A. Contreras Trevor A. Gallin William Jacobacci Kara E. Bursik Marcus 《Landslides》2022,19(4):901-912
Landslides - Geomorphological analysis of landslide processes in mountainous terrains with difficult access has benefited from virtual representation of topography through the use of... 相似文献
280.
The Interaction of Natural Organic Matter with Iron in a Wetland (Tennessee Park, Colorado) Receiving Acid Mine Drainage 总被引:3,自引:0,他引:3
Pore water from a wetland receiving acid mine drainage was studied for its iron and natural organic matter (NOM) geochemistry
on three different sampling dates during summer 1994. Samples were obtained using a new sampling technique that is based on
screened pipes of varying length (several centimeters), into which dialysis vessels can be placed and that can be screwed
together to allow for vertical pore-water sampling. The iron concentration increased with time (through the summer) and had
distinct peaks in the subsurface. Iron was mainly in the ferrous form; however, close to the surface, significant amounts
of ferric iron (up to 40% of 2 mmol L-1 total iron concentration) were observed. In all samples studied, iron was strongly
associated with NOM. Results from laboratory experiments indicate that the NOM stabilizes the ferric iron as small iron oxide
colloids (able to pass a 0.45μm dialysis membrane). We hypothesize that, in the pore water of the wetland, the high NOM concentrations
(>100 mg C L-1) allow formation of such colloids at the redoxcline close to the surface and at the contact zone to the adjacent
oxic aquifer. Therefore, particle transport along flow paths and resultant export of ferric iron from the wetland into ground
water might be possible.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献