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421.
The influence of use-related,environmental, and managerial factors on soil loss from recreational trails 总被引:2,自引:0,他引:2
Recreational uses of unsurfaced trails inevitably result in their degradation, with the type and extent of resource impact influenced by factors such as soil texture, topography, climate, trail design and maintenance, and type and amount of use. Of particular concern, the loss of soil through erosion is generally considered a significant and irreversible form of trail impact. This research investigated the influence of several use-related, environmental, and managerial factors on soil loss on recreational trails and roads at Big South Fork National River and Recreation Area, a unit of the U.S. National Park Service. Regression modeling revealed that trail position, trail slope alignment angle, grade, water drainage, and type of use are significant determinants of soil loss. The introduction of individual and groups of variables into a series of regression models provides improved understanding and insights regarding the relative influence of these variables, informing the selection of more effective trail management actions. Study results suggest that trail erosion can be minimized by avoiding “fall-line” alignments, steep grades, and valley-bottom alignments near streams, installing and maintaining adequate densities of tread drainage features, applying gravel to harden treads, and reducing horse and all-terrain vehicle use or restricting them to more resistant routes. 相似文献
422.
设计良好的导电回路对真空断路器灭弧性能的提高有着重要的意义。本文首先从结构上分析了三种不同导电回路的优缺点,接着,分析了三种不同导电回路的电动斥力和吹弧磁场,为通过选择不同导电回路,触头直径和开距提高真空断路器灭弧性能提供方法和思路。 相似文献
423.
苏里格气田试气队伍节能减排工作现状及改进建议 总被引:1,自引:1,他引:0
苏里格气田试气队伍因涉及数家企业单位,节能减排工作有其特殊性和复杂性。通过调查试气过程中的排污状况,分析了其节能减排工作中出现的几个问题,如计量粗放、管理薄弱、措施简单等,提出了健全管理制度,完善计量系统,鼓励技术研究,加强自主创新,创建统一平台,依靠丙方监管等措施,以促进其节能减排工作健康有序地发展。 相似文献
424.
425.
公众灾害风险可接受性与避灾意愿的初探——以川渝地区旱灾风险为例 总被引:2,自引:0,他引:2
在综述前人研究的基础上,以川渝地区旱灾为例,通过实地调查与访谈,从公众可接受的旱灾损失与频率、假定旱灾风险情景下的避险意愿等角度,对公众旱灾风险可接受性进行了初步探讨。结果表明,公众合理可接受的旱灾损失与频率分别在26.5%~52.8%与32.0%~64.3%区间范围内;并以一般旱灾、严重旱灾风险情景为限制线,确定了公众合理可接受风险区域;随着灾害损失风险增加,公众规避风险投资意愿呈现出中间高两头低的趋势,当灾害损失达到约50%~70%时,公众避险投资意愿达到最高,意愿避险投资占可能损失的比重约为62%。鉴于川渝地区的旱灾形势,今后旱灾风险管理的关键,一是加强对旱灾的监测与预警预报;二是完善旱灾风险的常规化管理,发展高效灌溉农业,充分利用客水资源,完善提高现有农田水网建设;三是积极探索公众-企业-政府多方共同参与的高效风险管理模式。 相似文献
426.
汶川地震在江苏的强震动记录及地震影响场 总被引:1,自引:0,他引:1
2008年5月12日四川汶川发生M8.0大地震,江苏数字强震动台网固定观测台站、宿迁和溧阳断层观测存放台阵共获取该次地震有效强震动事件45个,计134条加速度记录。本文介绍了这些强震动记录分析处理的基本情况及其时域与频域的一些特点;编写SICalculate谱烈度计算程序和D2InterP二维插值程序,输入所获取的汶川地震26组实测强震动记录数据,得到该次地震在江苏地区的峰值加速度与谱烈度的等值线图,并就区域内地震影响场特征进行了初步研究。 相似文献
427.
Radioxenon isotopes play a major role in confirming whether or not an underground explosion was nuclear in nature. It is then of key importance to understand the sources of environmental radioxenon to be able to distinguish them from those of a nuclear explosion. 相似文献
428.
The results of monitoring the dates of the onset of flowering and leaf budding in eight herbaceous and woody plant species and the first appearance of three insect species in the Il’men Reserve (1972–2005) were processed by means of regression and correlation analyses. No significant changes in test parameters were revealed in the majority of these species. Only two early spring plants, coltsfoot (Tussilago farfara L.) and goat willow (Salix caprea L.), showed a weak tendency toward earlier flowering in the 1980s and 1990s. This is explained primarily by the absence of any significant trends in spring and summer air temperatures in the study region over the observation period. On the other hand, interannual fluctuations in the dates of plant flowering and insect appearance were well manifested not only in early spring but also in late-spring species. These fluctuations proved to depend largely on spring temperatures: in years with early and warm springs, flowering and leaf budding in plants and the appearance of first individuals in insects were recorded on significantly earlier dates. 相似文献
429.
Qing Xie Jingwen Chen Jianping Shao Changer Chen Hongxia Zhao Ce Hao 《Chemosphere》2009,76(11):1486-1490
Photolysis of deca-bromodiphenyl ether (BDE-209) was investigated in tetrahydrofuran, dichloromethane, isopropanol, acetone, ethanol, methanol, acetonitrile and dimethylsulfoxide. Noticeable differences of the photolytic rates and quantum yields were found in the diverse solvents. Different to the previous deductions, hydrogen donating efficiency and electron donating efficiency of solvents were not the decisive factors for the photolytic rate in this study, which was proved by the fast photolysis of BDE-209 in CCl4, a solvent without hydrogen and difficult to donate electrons. Besides hydrogen addition process, intermolecular polymerization might occur during the photolysis. Density functional theory (DFT) calculation was performed to understand the molecular properties of BDE-209 in different solvents. The lowest singlet vertical excitation energy (Eex) and the average formal charge on Br () of BDE-209, reflecting the difficulty for the excitation of BDE-209 and for the departing of Br atom, respectively, were changed by the reaction fields formed by the different solvents. Eex and linearly correlated with the photolytic activity (log k). This study is helpful to better understand the photolytic behavior of BDE-209 in different media. 相似文献
430.
Influence of temporally variable groundwater flow conditions on point measurements and contaminant mass flux estimations 总被引:2,自引:0,他引:2
Arno Rein Sebastian Bauer Peter Dietrich Christof Beyer 《Journal of contaminant hydrology》2009,108(3-4):118-133
Monitoring of contaminant concentrations, e.g., for the estimation of mass discharge or contaminant degradation rates, often is based on point measurements at observation wells. In addition to the problem, that point measurements may not be spatially representative, a further complication may arise due to the temporal dynamics of groundwater flow, which may cause a concentration measurement to be not temporally representative. This paper presents results from a numerical modeling study focusing on temporal variations of the groundwater flow direction. “Measurements” are obtained from point information representing observation wells installed along control planes using different well frequencies and configurations. Results of the scenario simulations show that temporally variable flow conditions can lead to significant temporal fluctuations of the concentration and thus are a substantial source of uncertainty for point measurements. Temporal variation of point concentration measurements may be as high as the average concentration determined, especially near the plume fringe, even when assuming a homogeneous distribution of the hydraulic conductivity. If a heterogeneous hydraulic conductivity field is present, the concentration variability due to a fluctuating groundwater flow direction varies significantly within the control plane and between the different realizations. Determination of contaminant mass fluxes is also influenced by the temporal variability of the concentration measurement, especially for large spacings of the observation wells. Passive dosimeter sampling is found to be appropriate for evaluating the stationarity of contaminant plumes as well as for estimating average concentrations over time when the plume has fully developed. Representative sampling has to be performed over several periods of groundwater flow fluctuation. For the determination of mass fluxes at heterogeneous sites, however, local fluxes, which may vary considerably along a control plane, have to be accounted for. Here, dosimeter sampling in combination with time integrated local water flux measurements can improve mass flux estimates under dynamic flow conditions. 相似文献