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901.
本文提出了防灾工程中计算机仿真的作用、思路及主要技术关键,并通过若干例子,包括混凝土构件破坏,岩石块体崩塌,地震作用下房屋碎片分布,房屋在爆炸作用下倒塌等说明仿真技术的应用。 相似文献
902.
Methane fluxes from artificial wetlands: A global appraisal 总被引:1,自引:0,他引:1
Methane emissions make an important contribution to the enhanced greenhouse effect, emissions from rice growing being one
of its major anthropogenic sources. The estimation of global fluxes of methane from rice and from coarse fiber production
depends on extrapolating observed data across countries and agroclimatic zones: the estimates are therefore imprecise. We
present a revised estimate of global emissions of 96 Tg CH4/yr, given 1991 rice areas, and 1991 production data for those tropical coarse fibers that also produce methane under anaerobic
conditions. This is higher than many previous studies, which systematically underestimated the fluxes from tropical countries.
As the world's population increases, the demand for rice will rise. This demand can only be satisfied through greater rice
production, either by bringing new areas into rice growing or by using the present area more intensively. Strategies based
on improved water management and fertilizer use will allow increased rice production and yields and reduce the methane flux
per unit or rice production. 相似文献
903.
The sulphur dioxide and nitrogen oxides emissions from all sources in Alberta, Canada, during 1982 amounted to 488,297 and 353,511 tonnes, respectively. During this year deposition of wet sulphate from all stations in the province, 8 kg ha–1 yr–1, compares well with the five-year average (1978–1982) value of 10 kg ha–1 yr–1. These measurements are about one-half of the wet sulphate deposition criteria of 20 kg ha–1 yr–1 established for protecting the moderately sensitive aquatic ecosystem in eastern Canada. Due to dry, cold, continental climate conditions of Alberta, dry sulphate or sulphur deposition is equally or more important than wet deposition. No effects of the long-range transport of atmospheric pollutants (LRTAP) on the ecosystems in Alberta have been observed to date. Atmospheric deposition target loadings of SO4
–2, NO3
–, and H+ for Alberta and western Canadian environmental conditions should be developed to protect the highly sensitive ecosystems. Some future research and monitoring priorities for Alberta and western Canada are outlined. 相似文献
904.
ABSTRACT The flooding conditions in the basin of the Red River of the North are reviewed in terms of the accuracy of the flood forecasts and the response of both the floodplain occupants and government agencies to these forecasts. The flood prediction methods in Canada and the United States are compared. The accuracy of these prediction measures for the major floods in recent history is reviewed. The differences between the way in which the American and Canadian authorities approach the flood emergencies are outlined. The accuracy of the forecasts are plotted against a number of parameters which reflect the efficiency of the flood fighting measures initiated by those flood forecasts. The significant features of these plots are discussed. 相似文献
905.
Monitoring the results of Canada/U.S.A acid rain control programs: some lake responses 总被引:1,自引:0,他引:1
Jeffries DS Brydges TG Dillon PJ Keller W 《Environmental monitoring and assessment》2003,88(1-3):3-19
Aquatic acidification by deposition of airborne pollutants emerged as an environmental issue in southeastern Canada during the 1970s. Drawing information from the extensive research and monitoring programs, a sequence of issue assessments demonstrated the necessity of reducing the anthropogenic emissions of acidifying pollutants, particularly sulphur dioxide (SO2). The 1991 Canada-U.S. Air Quality Agreement (AQA) was negotiated to reduce North American SO2 emissions by 40% relative to 1980 levels by 2010, and at present, both countries have reduced emissions beyond their AQA commitment. In response to reduced SO2 emissions, atmospheric deposition of sulphate (SO4
2–) and SO4
2– concentrations in many lakes have declined, particularly in south-central Ontario and southern Québec. Sulphate deposition still exceeds aquatic critical loads throughout southeastern Canada however. Increasing pH or alkalinity (commonly deemed recovery) has been observed in only some lakes. Several biogeochemical factors have intervened to modify the lake chemistry response to reduced SO4
2– input, notably release of stored SO4
2– from wetlands following periods of drought and reduction in the export of base cations from terrestrial soils. Three examples from Ontario are presented to illustrate these responses. Significant increases in pH and alkalinity have been observed in many lakes in the Sudbury area of Ontario due to the large reductions in local SO2 emissions; early-stage biological recovery is evident in these lakes. An integrated assessment model predicts that AQA emission reductions will not be sufficient to promote widespread chemical or biological recovery of Canadian lakes. Monitoring and modeling are mutually supporting assessment activities and both must continue. 相似文献
906.
Diamando Vlachogiannis Spyros Andronopoulos Artemis Passamichali Nikos Gounaris John G. Bartzis 《Environmental monitoring and assessment》2000,65(1-2):41-48
This study concentrated on the effects of Biogenic Volatile Organic Compounds (BVOC) emissions on ozone (O3) in an area of the Eastern Spain on June 12, 1997, a day characterised by sea breeze. Simulation of meteorology was performed with the three-dimensional model ADREA-I. Comparisons of the model results with observations have revealed overall a good agreement in temperature and wind velocity. Two runs were performed with UAM-IV for the photochemical calculations. The first simulated the effects of the anthropogenic emissions only (run A) and the second the combined effects of anthropogenic and biogenic emissions, (run B). Comparisons of the model O3 concentrations with measurements showed a general agreement with the experimental data. Discrepancies between the calculated results and the observations during the early morning hours could be attributed to inaccuracies in nitrogen oxides (NOx) from the anthropogenic emissions inventory. Comparisons between runs A and B yielded differences up to 30% in the morning, over inland areas. It was deduced that the inclusion of BVOC in total emissions could result in an increase or decrease of tropospheric O3, depending on the available amounts of anthropogenic emissions. 相似文献
907.
908.
909.
N2O emissions from agricultural soils in the North China Plain:the effect of chemical nitrogen fertilizer and organic manure 总被引:1,自引:0,他引:1
IntroductionNitrousoxide (N2 O)isaveryimportantgreenhousegasintheatmosphere.InterestintheincreaseofatmosphericN2 OhasbeenrecentlystimulatedbytheunderstandingthatN2 Ogasplaysanimportantroleinthechemistryandozonelayerdestructionofthestratosphere.Theradiativ… 相似文献
910.