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991.
周斌 《西华大学学报(自然科学版)》2012,(6):39-42
将P系统引入到图像阈值分割中,提出了一种基于P系统的图像阈值分割方法。采用一个两层膜的组织型P系统作为其计算框架,每个膜作为独立的并行计算单元,速度一位置模型作为进化规则,同时采用同向/反向转运规则交换和共享膜之间的对象。实验结果表明,这个基于P系统框架的阈值分割方法具有可用性和有效性,能为图像寻找最优的分割阈值。 相似文献
992.
考察了一类非线性常微分方程的m点边值问题,通过考察非线性项在有界集上的性质,运用Krasnosel’skii锥拉伸与锥压缩型不动点定理及格林函数的性质,获得了其正解的存在性与多解性,推广和改进了以前文献的相关结果. 相似文献
993.
侧向引水及进水泵站进水流态CFD
模拟分析与优化 总被引:1,自引:0,他引:1
应用realizable k - e紊流模型与SIMPLEC算法,对某侧向引水及进水泵站进水侧水流流场进行数值模拟和流动分析,分析表明,该泵站的进水侧水流具有弯道水流特点,数值模拟结果与理论分析结论相吻合。根据该类泵站进水侧水流流场特点,提出采用导流栅作为水力优化途径,并以泵站进水断面处动量分布和进水池断面平均流速均匀度为评判依据,对不同的导流栅整流方案的水力优化效果进行数值模拟研究。成果表明,设置导流栅对泵站引水段的动量分布具有明显的调整作用,泵站进水断面的流速分布与引水段动量分配均匀度有关。适宜尺寸的导流栅可以有效减弱引水段的进水环流作用,使水流在转向后纵向流速较快地恢复正常分布,从而进一步提高泵站进水池流量分配的均匀度。 相似文献
994.
1引言新疆下坂地水利枢纽工程地下洞室衬砌混凝土浇筑一般采用泵送入仓,其坍落度多在14~16 cm,局部范围由于仓位狭窄,无法入仓振捣,坍落度可达18 cm左右,同时对混凝土的和易性、流动性要求较高,一些过水建筑物还要求水胶比不大于0.5, 相似文献
995.
996.
Aggregate keyword search on large relational databases 总被引:2,自引:1,他引:1
Keyword search has been recently extended to relational databases to retrieve information from text-rich attributes. However,
all the existing methods focus on finding individual tuples matching a set of query keywords from one table or the join of
multiple tables. In this paper, we motivate a novel problem of aggregate keyword search: finding minimal group-bys covering
a set of query keywords well, which is useful in many applications. We develop two interesting approaches to tackle the problem.
We further extend our methods to allow partial matches and matches using a keyword ontology. An extensive empirical evaluation
using both real data sets and synthetic data sets is reported to verify the effectiveness of aggregate keyword search and
the efficiency of our methods. 相似文献
997.
The primary purpose of this paper is to propose a computer aided optimal design system to support a generalized oval–round pass design, which is widely used as both intermediate and final passes in the process of rod rolling. This system, which is based on a hybrid model and the genetic algorithm, is developed to improve the efficiency, to reduce the manufacturing errors, as well as to extend the useful life of rolls through uniform wear design. Generalized parametric equations are established for geometrical modeling, graphic plotting of oval–round passes, as well as calculation of the cross section area, contact area and the lengths of contact arcs along the cross section of round groove in the MATLAB programming environment. Moreover, these equations can also realize the parametric transformation between roll profile and mathematical models for the oval–round pass design and optimization. The genetic algorithm is employed for the optimal design of oval–round passes in this paper. The objective functions are formulated for minimization of power consumption in the rolling process, variances between ideal dimensions and design dimensions, as well as variances between the lengths of contact arcs. To reduce the complexity and computational burden of the system, some reliable empirical formulas for the calculations of contact area and contact arc length are applied. Finally, the proposed approach is applied to an oval–round pass design. Through simulation and comparison of results against experimental data acquired from literature, it is found that this system is reliable, effective and easier to use. 相似文献
998.
Jiuming Huang Bin Zhou Quanyuan Wu Xiaowei Wang Yan Jia 《Journal of Intelligent Information Systems》2012,38(2):449-464
Short text message streams are produced by Instant Messaging and Short Message Service which are wildly used nowadays. Each
stream contains more than one thread usually. Detecting threads in the streams is helpful to various applications, such as
business intelligence, investigation of crime and public opinion analysis. Existing works which are mainly based on text similarity
encounter many challenges including the sparse eigenvector and anomaly of short text message. This paper introduces a novel
concept of contextual correlation instead of the traditional text similarity into single-pass clustering algorithm to cover
the challenges of thread detection. We firstly analyze the contextually correlative nature of conversations in short text
message streams, and then propose an unsupervised method to compute the correlative degree. As a reference, a single-pass
algorithm employing the contextual correlation is developed to detect threads in massive short text stream. Experiments on
large real-life online chat logs show that our approach improves the performance by 11% when compared with the best similarity-based
algorithm in terms of F1 measure. 相似文献
999.
Bin Jiang Jian Pei Xuemin Lin Yidong Yuan 《Journal of Intelligent Information Systems》2012,38(1):1-39
Uncertain data are inherent in some important applications. Although a considerable amount of research has been dedicated
to modeling uncertain data and answering some types of queries on uncertain data, how to conduct advanced analysis on uncertain
data remains an open problem at large. In this paper, we tackle the problem of skyline analysis on uncertain data. We propose a novel probabilistic skyline model where an uncertain object may take a probability to be in the skyline, and a p-skyline contains all objects whose skyline probabilities are at least p (0 < p ≤ 1). Computing probabilistic skylines on large uncertain data sets is challenging. We develop a bounding-pruning-refining
framework and three algorithms systematically. The bottom-up algorithm computes the skyline probabilities of some selected
instances of uncertain objects, and uses those instances to prune other instances and uncertain objects effectively. The top-down
algorithm recursively partitions the instances of uncertain objects into subsets, and prunes subsets and objects aggressively.
Combining the advantages of the bottom-up algorithm and the top-down algorithm, we develop a hybrid algorithm to further improve
the performance. Our experimental results on both the real NBA player data set and the benchmark synthetic data sets show
that probabilistic skylines are interesting and useful, and our algorithms are efficient on large data sets. 相似文献
1000.
Qinchuan Xin Curtis E. Woodcock Jicheng Liu Bin Tan Rae A. Melloh Robert E. Davis 《Remote sensing of environment》2012
Binary snow maps and fractional snow cover data are provided routinely from MODIS (Moderate Resolution Imaging Spectroradiometer). This paper investigates how the wide observation angles of MODIS influence the current snow mapping algorithm in forested areas. Theoretical modeling results indicate that large view zenith angles (VZA) can lead to underestimation of fractional snow cover (FSC) by reducing the amount of the ground surface that is viewable through forest canopies, and by increasing uncertainties during the gridding of MODIS data. At the end of the MODIS scan line, the total modeled error can be as much as 50% for FSC. Empirical analysis of MODIS/Terra snow products in four forest sites shows high fluctuation in FSC estimates on consecutive days. In addition, the normalized difference snow index (NDSI) values, which are the primary input to the MODIS snow mapping algorithms, decrease as VZA increases at the site level. At the pixel level, NDSI values have higher variances, and are correlated with the normalized difference vegetation index (NDVI) in snow covered forests. These findings are consistent with our modeled results, and imply that consideration of view angle effects could improve MODIS snow monitoring in forested areas. 相似文献