The finite element method was used in this study to investigate cutoff walls and downstream filters to control seepage, the exit hydraulic gradient, and uplift forces for dams. Experimental data was used for validating the numerical modelling. The effective parameters are the length of filter and its distance downstream from the dam, the depth of the cutoff walls, the upstream dam head, and the thickness of alluvial foundation. The results show that by increasing filter length, the exit hydraulic gradient, uplift force, and seepage are reduced. The optimum relative length of the filter is L/H?=?0.028 which results in a decrease of about 65% in the exit hydraulic gradient, a 35% decrease in seepage and 10% reduction in the uplift force at the upstream foundation and a 60% decrease in the uplift force at the downstream foundation. Increase of cutoff wall depth reduces the exit hydraulic gradient, uplift force, and seepage. Using two cutoff walls both upstream and downstream of the dam decreases seepage, hydraulic gradient, and uplift force 132%, 450% and 11% respectively. However, using an upstream cutoff and downstream filter decreases seepage, hydraulic gradient, and uplift force by 180%, 490%, and 119% respectively. Thus, based on this study, recommendations for suitable combinations of upstream cutoff and downstream filter are provided.
We have built a database that provides term vector information for large numbers of pages (hundreds of millions). The basic operation of the database is to take URLs and return term vectors. Compared to computing vectors by downloading pages via HTTP, the Term Vector Database is several orders of magnitude faster, enabling a large class of applications that would be impractical without such a database. This paper describes the Term Vector Database in detail. It also reports on two applications built on top of the database. The first application is an optimization of connectivity-based topic distillation. The second application is a Web page classifier used to annotate results returned by a Web search engine. 相似文献
Active contour models can be successfully used in multimedia database retrieval systems if they have good accuracy and high speed. The majority of existing active contour models do not lock on to interest objects very accurately and quickly especially in complex images. The behavior of the active contour is generally controlled by its internal and external energies. Internal energy is composed of two parts; the first part acts to shorten the active contour as it iterates towards the interest object, while the second part is the curvature of the active contour and forces smoothness of active contour during its movement towards interest object. In this paper, first a reformulated internal energy is proposed to improve the computation of curvature at point vi by making use of the three points vi – 1, vi and vi + 1. Second, an accurate and high speed active contour model, SAC is proposed based on reformulating internal energy by removing the curvature part and using Gaussian filtering with low scale of smoothing. The SAC model has only one parameter that affects the internal energy of active contour and as a result of using the Curvature Scale Space (CSS)1 technique for smoothing, the SAC model is more independent of model parameter setting and the initial snake. 相似文献
Vaccination, being able to prevent millions of cases of infectious diseases around the world every year, is the most effective medical intervention ever introduced. However, immunosenescence makes vaccines less effective in providing protection to older people. Although most studies explain that this is mainly due to the immunosenescence of T and B cells, the immunosenescence of innate immunity can also be a significant contributing factor. Alterations in function, number, subset, and distribution of blood neutrophils, monocytes, and natural killer and dendritic cells are detected in aging, thus potentially reducing the efficacy of vaccines in older individuals. In this paper, we focus on the immunosenescence of the innate blood immune cells. We discuss possible strategies to counteract the immunosenescence of innate immunity in order to improve the response to vaccination. In particular, we focus on advances in understanding the role and the development of new adjuvants, such as TLR agonists, considered a promising strategy to increase vaccination efficiency in older individuals. 相似文献
The study of the Web as a graph is not only fascinating in its own right, but also yields valuable insight into Web algorithms for crawling, searching and community discovery, and the sociological phenomena which characterize its evolution. We report on experiments on local and global properties of the Web graph using two AltaVista crawls each with over 200 million pages and 1.5 billion links. Our study indicates that the macroscopic structure of the Web is considerably more intricate than suggested by earlier experiments on a smaller scale. 相似文献
The aim of this study is to couple molten carbonate fuel cell (MCFC) stack with integrated gasification combined cycle fed by refinery residues, to remove CO2 from gas turbine exhaust gases that have CO2 emission rate of 14,200 ton/year. By applying multi-objective optimisation (MOO) using genetic algorithm, the optimal values of operating load and the corresponding values of objective functions are obtained. The MOO of the MCFC system regarding two scenarios is performed. The first scenario is minimisation of cost of electricity (COE) and CO2 emission rate. Objective functions of the second scenario are the same as in the first scenario while CO2 tax is taken into account. Results show that the second scenario has 29.5% lower average optimal COE and 2.5% lower average emission rate in comparison with the first scenario. A sensitivity analysis is also performed to study the effect of fuel price and CO2 tax variations on optimal solutions. 相似文献
Recently, the hole transport layer-free planar perovskite solar cells(HTL-free PSCs) have attracted intense attention. However, the poor absorption of light in the wavelengths longer than 800 nm is an important challenge in all configurations of PSCs. In this study, the HTL-free PSC with a gold rectangular grating at back contact is proposed. In order to improve the performance of the solar cell, effects of grating dimensions and periodicity on the absorption of the active layer are numerically ... 相似文献
In this research, polishing flat surfaces has been done by using a completely new and innovative method. In this method, rotary magnetic tool that carry magnetic abrasive powders, is placed in a very strong thermal induction field, and magnetic rotary tool frequently change its direction from clockwise (CW) to counterclockwise (CCW) and CCW to CW. The frequency of changing rotation direction is an important parameter of this innovation method. The intended pieces for polishing operations have been placed on a synchronic two-axis Cartesian CNC table, and the gap between rotary magnetic tool and the sheet surface can be controlled by a power transmission screw operating in the direction of the vertical axis. Several experiments have proved high performance of the new proposed method in the process of polishing. 相似文献