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561.
为了解决煤矿掘进面风筒出风口参数不能动态变化,而传统风幕全断面控尘效果不理想引起的粉尘浓度高等问题,通过分析风幕和出风口参数对粉尘分布规律的影响,以此得到合理的出风口风流与风幕综合调控方案,降低粉尘浓度。以陕西神木柠条塔煤矿N1212巷道为研究对象,利用Fluent软件建立出风口风流与风幕综合调控的粉尘场有限元模型,设计出风口风流及风幕综合调控响应曲面实验,得到最佳综合调控方案为:风幕射流出口宽度为0.16 m,风幕射流出口速度为6 m/s,出风口口径为0.9 m,出风口右偏角度为3°。搭建相似模拟实验平台来验证最佳综合调控方案,研究结果表明:调控后回风侧行人呼吸处和司机位置处粉尘平均浓度分别降低89%和81%,有效改善掘进面作业环境。 相似文献
562.
明确三峡库区紫色土旱坡地氮流失的年际变化特征,为库区的施肥管理措施和面源污染治理提供参考.依托中国科学院成都山地灾害与环境研究所三峡库区试验站,于2018~2020年连续3 a设置不施肥(CK)、常规施肥(F)、优化施肥(OF)、化肥减量配施生物炭(BF)和化肥减量配施秸秆覆盖(SF)5种处理,研究紫色土旱坡地在油菜-玉米轮作模式下氮流失的年际变化特征.结果表明:(1)三峡库区紫色土旱坡地地表径流主要发生在5月和8月,壤中流主要发生在6~10月. 2018~2020年降雨量逐年增加,各处理地表径流产流量逐年减少,壤中流产流量大致呈逐年增加的趋势,年尺度下,壤中流产流量和产流次数均高于地表径流.(2)2018~2020年每年各形态氮的最高流失浓度出现时间大概一致,地表径流全氮、铵态氮和硝态氮最高流失浓度分别出现在5、 8~10和7月,壤中流各形态氮最高流失浓度分别出现在10、 10和5~7月.(3)地表径流各形态氮流失通量呈逐年降低趋势,壤中流各形态氮流失通量大致逐年增加.(4)生物炭和秸秆还田第一年降低氮流失通量的效果较好,但后续两年还田反而加剧了氮素流失通量.因此,三峡库区紫色土旱坡... 相似文献
563.
三十年来的中国泥石流研究 总被引:41,自引:1,他引:41
本文通过对我国泥石流研究成果的总结,结合作者们工作的心得体会,就我国30年来的泥石流研究工作进行回顾与展望;并针对国情和灾情,提出了相应的意见和建议。 相似文献
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In the present work we investigate whether the distribution of energy flows in ecosystems responds to criteria of trophic organization. We analyzed weighted and unweighted food webs estimating, for each node, trophic position (TP), Shannon's index of inflow diversity (H) and individual contribution to the whole average mutual information (AMI). Finally, we performed the same analysis on simulated webs that were constructed using the following criteria: (a) preserving topology and varying link strength; (b) modifying position of links and their intensities. 相似文献
568.
Modeling compensated root water and nutrient uptake 总被引:1,自引:0,他引:1
Plant root water and nutrient uptake is one of the most important processes in subsurface unsaturated flow and transport modeling, as root uptake controls actual plant evapotranspiration, water recharge and nutrient leaching to the groundwater, and exerts a major influence on predictions of global climate models. In general, unsaturated models describe root uptake relatively simple. For example, root water uptake is mostly uncompensated and nutrient uptake is simulated assuming that all uptake is passive, through the water uptake pathway only. We present a new compensated root water and nutrient uptake model, implemented in HYDRUS. The so-called root adaptability factor represents a threshold value above which reduced root water or nutrient uptake in water- or nutrient-stressed parts of the root zone is fully compensated for by increased uptake in other soil regions that are less stressed. Using a critical value of the water stress index, water uptake compensation is proportional to the water stress response function. Total root nutrient uptake is determined from the total of active and passive nutrient uptake. The partitioning between passive and active uptake is controlled by the a priori defined concentration value cmax. Passive nutrient uptake is simulated by multiplying root water uptake with the dissolved nutrient concentration, for soil solution concentration values below cmax. Passive nutrient uptake is thus zero when cmax is equal to zero. As the active nutrient uptake is obtained from the difference between plant nutrient demand and passive nutrient uptake (using Michaelis–Menten kinetics), the presented model thus implies that reduced passive nutrient uptake is compensated for by active nutrient uptake. In addition, the proposed root uptake model includes compensation for active nutrient uptake, in a similar way as used for root water uptake. The proposed root water and nutrient uptake model is demonstrated by several hypothetical examples, for plants supplied by water due to capillary rise from groundwater and surface drip irrigation. 相似文献
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EcoTroph (ET) is a model articulated around the idea that the functioning of aquatic ecosystems may be viewed as a biomass flow moving from lower to higher trophic levels, due to predation and ontogenetic processes. Thus, we show that the ecosystem biomass present at a given trophic level may be estimated from two simple equations, one describing biomass flow, the other their kinetics (which quantifies the velocity of biomass transfers towards top predators). The flow kinetic of prey partly depends on the abundance of their predators, and a top-down equation expressing this is included in the model. Based on these relationships, we simulated the impact on a virtual ecosystem of various exploitation patterns. Specifically, we show that the EcoTroph approach is able to mimic the effects of increased fishing effort on ecosystem biomass expected from theory. Particularly, the model exhibits complex patterns observed in field data, notably cascading effects and ‘fishing down the food web’. EcoTroph also provides diagnostic tools for examining the relationships between catch and fishing effort at the ecosystem scale and the effects of strong top-down controls and fast-flow kinetics on ecosystems resilience. Finally, a dynamic version of the model is derived from the steady-state version, thus allowing simulations of time series of ecosystem biomass and catches. Using this dynamic model, we explore the propagation of environmental variability in the food web, and illustrated how exploitation can induce a decrease of ecosystem stability. The potential for applying EcoTroph to specific ecosystems, based on field data, and similarities between EcoTroph and Ecopath with Ecosim (EwE) are finally discussed. 相似文献