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21.
A two-dimensional cross-section finite difference model is presented to simulate density dependent leachate migration in leaky aquifers. Unlike existing models, a new approach is adopted to couple the groundwater-flow equation and the hydrodynamic dispersion equation with the elimination of the intermediate step of calculating velocities. The concept of the reference density is employed, permitting increased accuracy (over pressure-based models) in the representation of the transport process. The model is then used to study the effect of several hydraulic and transport parameters on the flow pattern and plume migration which are found to be very sensitive to most of these parameters. Equiconcentration and equipotential lines are overlapped to provide a better understanding of the coupling effect. 相似文献
22.
企业每一项经营决策都应该进行成本效益分析,市场竞争中可以根据本企业的成本曲线和需求曲线,预测出竞争策略实施后对内部成本和外部需求可能产生的影响,从而计算出某项决策的经济效果。 相似文献
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提出采用具有附加线性约束的网络规划法,可把混联梯级水电站分解为几个子网络,简化了每个子网络的求解计算,从而加速大电网复杂的经济调度的计算速度。 相似文献
26.
襄樊北站驼峰自动化控制系统于2001年11月28日正式投入运用,根据该系统在运用中出现的问题及产生原因,通过采用自动化驼峰作业预想控制法,将人的作业经验与自动化精确控制相结合,取得了扬长避短充分发挥自动控制作用、提高编组站驼峰作业能力的效果。 相似文献
27.
Simulation of water and nitrogen dynamics in soils during wastewater applications by using a finite-element model 总被引:4,自引:0,他引:4
Vassilis Z. Antonopoulos 《Water Resources Management》1993,7(3):237-251
A mathematical model was developed to simulate water movement, mass transport, and nitrogen transformations in soils during wastewater applications. The model is one-dimensional and based on the Galerkin finite-element method. The submodel of mass transport of nitrogen incorporates the convection-dispersion processes of ammonium and nitrate nitrogen, nitrification, denitrification, ammonium exchange and uptake of ammonium and nitrate ions. The accuracy and validity of the proposed model was examined by comparison with an explicit-implicit finite-difference model results. The model was used for simulation of water and nitrogen dynamics during wastewater application in homogeneous and multi-layered soils under different N concentration, rate, duration and scheduling of application. 相似文献
28.
Aerodynamic loads on a multi-bladed helicopter rotor in hovering flight were calculated by solving the three-dimensional incompressible Navier-Stokes equations. The rotor wake effects were accounted by the correction of local geometric angle of attack according to a free-wake modeling in addition to an empirical modification for the tip flow effect. The validity and efficiency of the present method were verified by the comparisons between numerical results and experimental data. 相似文献
29.
Guojie Zhao" Tianjin Zhiyong Shi Guojie Zhao 《美中经济评论(英文版)》2006,5(2):9-12
The selective principle of mutually exclusive project is the maximum of net present value, It is difficult to make decision when NPVA is equal to NPVLB. Some assistant analyses are put forward in "Enterprise Investment Decision Management". The scientific marginal analysis shows that the assistant analyses including the duration analysis are wrong. This problem can be solved by the classical marginal analysis. 相似文献
30.
Abstract: We explore to what extent firms deliberately manage their financial reports by exploiting the flexibility of generally accepted accounting principles. Using a sample of Oslo Stock Exchange-listed firms with 20–50% equity holdings in other firms, we find that firms with high financial leverage tend to maximize reported earnings from these investments through their choice between the cost method and the equity method, possibly in an attempt to reduce debt renegotiation costs or to avoid regulatory attention. In contrast, managers do not systematically bias reported earnings to extract private benefits or to signal revised expectations about future cash flows. Firms use different earnings management tools in a consistent way, as the earnings effect of the cost/equity choice is not offset by discretionary accruals. 相似文献