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排序方式: 共有1038条查询结果,搜索用时 46 毫秒
921.
922.
贾司光 《中国安全科学学报》1995,5(6):1-5
较系统地阐述了人体力学的内涵、生理基础,各种力学作业(搬运、负重)的力学特征.改善力学负荷,提高工效的成就。还具体阐述了人体力学对于提高人类从事体力作业的工效的作用与意义,对其推广应用将会起到积极作用。 相似文献
923.
传统的大气污染评价方法是以Pi/Pio为基础,用于特殊环境的大气污染控制存在一定的缺陷,本文提出影响负荷分析法,是建立在大气污染物输送扩散的基础上的,并用以研究峨眉山风景保护区大气污染控制的对策,其结论更为科学合理。 相似文献
924.
Jay W. Hawkins 《Journal of the American Water Resources Association》1994,30(5):861-869
ABSTRACT: Under an approved remining program, a coal mine operator can remine abandoned sites without legally assuming treatment responsibilities of the previously degraded water, as long as these discharging waters are not further degraded. Determination of discharge degradation caused by remining of abandoned coal mines requires knowledge of mine water quality and discharge flow rate characteristics both before and after remining. Normality tests performed on the water quality and flow data from 57 mine discharges indicate generally nonnormal distributions and extreme right-skewness. Exploratory data analysis (notched box-and-whisker plots) of the differences among medians indicates that the water quality of underground mines was more highly degraded in terms of acidity, iron, and sulfate concentrations than that from surface mines. Spearman's rank correlation tests, normality testing, and exploratory data analysis indicate that discharge flow rate is the primary controlling factor on the variability of pollution load rate. Reduction of recharge from the surface and adjacent unmined strata should decrease the mine discharge flow rate and in turn the pollution load. 相似文献
925.
Sullivan TJ Cosby BJ Webb JR Dennis RL Bulger AJ Deviney FA 《Environmental monitoring and assessment》2008,137(1-3):85-99
A modeling study was conducted to evaluate the acid-base chemistry of streams within Shenandoah National Park, Virginia and
to project future responses to sulfur (S) and nitrogen (N) atmospheric emissions controls. Many of the major stream systems
in the park have acid neutralizing capacity (ANC) less than 20 μeq/L, levels at which chronic and/or episodic adverse impacts
on native brook trout are possible. Model hindcasts suggested that none of these streams had ANC less than 50 μeq/L in 1900.
Model projections, based on atmospheric emissions controls representative of laws already enacted as of 2003, suggested that
the ANC of those streams simulated to have experienced the largest historical decreases in ANC will increase in the future.
The levels of S deposition that were simulated to cause streamwater ANC to increase or decrease to three specified critical
levels (0, 20, and 50 μeq/L) ranged from less than zero (ANC level not attainable) to several hundred kg/ha/year, depending
on the selected site and its inherent acid-sensitivity, selected ANC endpoint criterion, and evaluation year for which the
critical load was calculated. Several of the modeled streams situated on siliciclastic geology exhibited critical loads <0 kg/ha/year
to achieve ANC >50 μeq/L in the year 2040, probably due at least in part to base cation losses from watershed soil. The median
modeled siliciclastic stream had a calculated critical load to achieve ANC >50 μeq/L in 2100 that was about 3 kg/ha/year,
or 77% lower than deposition in 1990, representing the time of model calibration. 相似文献
926.
Robert Coats Melissa Larsen Alan Heyvaert James Thomas Matthew Luck John Reuter 《Journal of the American Water Resources Association》2008,44(3):754-770
Abstract: In efforts to control the degradation of water quality in Lake Tahoe, public agencies have monitored surface water discharge and concentrations of nitrogen, phosphorus, and suspended sediment in two separate sampling programs. The first program focuses on 20 watersheds varying in size from 162 to 14,000 ha, with continuous stream gaging and periodic sampling; the second focuses on small urbanized catchments, with automated sampling during runoff events. Using data from both programs, we addressed the questions (1) what are the fluxes and concentrations of nitrogen and phosphorus entering the lake from surface runoff; (2) how do the fluxes and concentrations vary in space and time; and (3) how are they related to land use and watershed characteristics? To answer these questions, we calculated discharge‐weighted average concentrations and annual fluxes and used multiple regression to relate those variable to a suite of GIS‐derived explanatory variables. The final selected regression models explain 47‐62% of the variance in constituent concentrations in the stormwater monitoring catchments, and 45‐72% of the variance in mean annual yields in the larger watersheds. The results emphasize the importance of impervious surface and residential density as factors in water quality degradation, and well‐developed soil as a factor in water quality maintenance. 相似文献
927.
928.
负载对实际道路重型柴油车排放的影响研究 总被引:1,自引:0,他引:1
利用车载测试系统对重型柴油货车空载、50%负载和100%负载不同负载情况下在实际道路的排放进行测试,基于测试数据分析负载对重型柴油货车排放CO、HC、NOx和微小颗粒物(PM)等4种污染物的影响.不同速度区间和行驶模式下负载对排放的影响分析表明,在有负载时,大多数工况下4种污染物排放呈现增加趋势,但各速度区间和行驶模式下的增幅不尽相同,部分工况出现下降.空载时测试柴油车基于新欧洲行驶循环测试(NEDC)工况的标准化CO、HC、NOx和PM排放因子分别为3.38、0.39、6.27、0.39 g/km.对于柴油车重点污染物NOx和PM而言,与空载相比,50%负载时分别增加43%和59%,100%负载时分别增加62%和44%. 相似文献
929.
930.
基于工程实例和数值模拟,分析了高速公路加宽工程中,原有路基荷载作用引起的软基性质改善对路基沉降变形的影响机理。研究表明:新、老路基的沉降变形均受软基性质改善的影响;软基性质改善改变了新路基荷载在老路地基中引起的附加应力分布,这种附加应力的改变也对老路基的沉降产生影响,而传统的计算方法不能考虑附加应力的变化对沉降的影响;对比考虑与不考虑老路基荷载作用的影响,新路基的沉降量会不同,这种沉降差异随路基高度、新路基宽度以及软基厚度的增加而逐渐增大,但老路基的沉降差异只受软基深度的影响。 相似文献