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991.
We have discovered a class of fractal functions that are differentiable. Fractal interpolation functions have been used for
over a decade to generate rough functions passing through a set of given points. The integral of a fractal interpolation function
remains a fractal interpolation function, and this new fractal interpolation function is differentiable. Tensor products of
pairs of these fractal functions form fractal surfaces with a well-defined tangent plane. We use this surface normal to shade
fractal surfaces, and demonstrate its use with renderings of fractal mirrors. 相似文献
992.
不确定离散时滞系统的保性能控制 总被引:31,自引:3,他引:28
针对一类具有范数有界不确定性和状态滞后的离散时间线性系统,结合一个二次型
性能指标,采用线性矩阵不等式方法,提出了无记忆状态反馈保性能控制律的存在条件,并利
用一个线性矩阵不等式的解给出了保性能控制律的一个参数化表示. 相似文献
993.
Optimizing multiple dimensional queries simultaneously in multidimensional databases 总被引:1,自引:0,他引:1
Weifa Liang Maria E. Orlowska Jeffrey X. Yu 《The VLDB Journal The International Journal on Very Large Data Bases》2000,8(3-4):319-338
Some significant progress related to multidimensional data analysis has been achieved in the past few years, including the
design of fast algorithms for computing datacubes, selecting some precomputed group-bys to materialize, and designing efficient
storage structures for multidimensional data. However, little work has been carried out on multidimensional query optimization
issues. Particularly the response time (or evaluation cost) for answering several related dimensional queries simultaneously
is crucial to the OLAP applications. Recently, Zhao et al. first exploited this problem by presenting three heuristic algorithms.
In this paper we first consider in detail two cases of the problem in which all the queries are either hash-based star joins
or index-based star joins only. In the case of the hash-based star join, we devise a polynomial approximation algorithm which
delivers a plan whose evaluation cost is $ O(n^{\epsilon }$) times the optimal, where n is the number of queries and is a fixed constant with . We also present an exponential algorithm which delivers a plan with the optimal evaluation cost. In the case of the index-based
star join, we present a heuristic algorithm which delivers a plan whose evaluation cost is n times the optimal, and an exponential algorithm which delivers a plan with the optimal evaluation cost. We then consider
a general case in which both hash-based star-join and index-based star-join queries are included. For this case, we give a
possible improvement on the work of Zhao et al., based on an analysis of their solutions. We also develop another heuristic
and an exact algorithm for the problem. We finally conduct a performance study by implementing our algorithms. The experimental
results demonstrate that the solutions delivered for the restricted cases are always within two times of the optimal, which
confirms our theoretical upper bounds. Actually these experiments produce much better results than our theoretical estimates.
To the best of our knowledge, this is the only development of polynomial algorithms for the first two cases which are able
to deliver plans with deterministic performance guarantees in terms of the qualities of the plans generated. The previous
approaches including that of [ZDNS98] may generate a feasible plan for the problem in these two cases, but they do not provide
any performance guarantee, i.e., the plans generated by their algorithms can be arbitrarily far from the optimal one.
Received: July 21, 1998 / Accepted: August 26, 1999 相似文献
994.
This paper describes a novel knowledge-based methodology and toolset for helping business process designers and participants
better manage exceptions (unexpected deviations from an ideal sequence of events caused by design errors, resource failures,
requirement changes, etc.) that can occur during the enactment of a process. This approach is based on an on-line repository
exploiting a generic and reusable body of knowledge, which describes what kinds of exceptions can occur in collaborative work
processes, how these exceptions can be detected, and how they can be resolved. This work builds upon previous efforts from
the MIT Process Handbook project and from research on conflict management in collaborative design.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
995.
An important challenge concerning the design of future microprocessors is that current design methodologies are becoming impractical due to long simulation runs and due to the fact that chip layout considerations are not incorporated in early design stages. In this paper, we show that statistical modeling can be used to speed up the architectural simulations and is thus viable for early design stage explorations of new microarchitectures. In addition, we argue that processor layouts should be considered in early design stages in order to tackle the growing importance of interconnects in future technologies. In order to show the applicability of our methodology which combines statistical modeling and processor layout considerations in an early design stage, we have applied our method on a novel architectural paradigm, namely a fixed-length block structured architecture. A fixed-length block structured architecture is an answer to the scalability problem of current architectures. Two important factors prevent contemporary out-of-order architectures from being scalable to higher levels of parallelism in future deep-submicron technologies: the increased complexity and the growing domination of interconnect delays. In this paper, we show by using statistical modeling and processor layout considerations, that a fixed-length block structured architecture is a viable architectural paradigm for future microprocessors in future technologies thanks to the introduction of decentralization and a reduced register file pressure. 相似文献
996.
N. Y. Kuznetsov 《Cybernetics and Systems Analysis》2000,36(2):188-195
The probability of monotone system failure on a fixed time interval is studied. The failure and repair distribution functions
are assumed to be of a general form. A new accelerated simulation method is proposed, which makes it possible to investigate
systems consisting of components with essentially different reliability characteristics.
Translated from Kibernetika i Sistemnyi Analiz, No. 2, pp. 45–54, March–April, 2000. 相似文献
997.
Modeling and analysis of wormhole formation in reactive dissolution of carbonate rocks 总被引:2,自引:0,他引:2
Nitika Kalia 《Chemical engineering science》2007,62(4):919-928
A two-scale continuum model is used to simulate reactive dissolution of carbonate rocks in radial flow. The three main types of patterns observed in linear and radial flow experiments, namely, compact, wormhole and uniform patterns are numerically simulated. The fractal nature of wormholes observed in laboratory experiments is established and confirmed through simulations and the fractal dimension is quantitatively matched. The dependence of wormhole fractal dimension, optimum injection rate and minimum pore volumes required to breakthrough the medium on heterogeneity magnitude and aspect ratio is investigated. A new criterion to predict the optimum injection rate for wormhole formation in radial flow is derived and validated. It is observed that the wormhole penetration depth increases with injection time as tb, where the exponent b is found to be approximately 0.66, as observed in the experiments. A critical level of heterogeneity magnitude seems to exist below which the minimum pore volumes required to breakthrough are much higher. 相似文献
998.
999.
杨华 《西安工业大学学报》2013,(11):942-946
契斯恰科夫与安格尔都是19世纪美术史上出现过的学院派素描大师,他们的素描作品影响着古今中外众多艺术学子.他们都强调素描的重要性,也师出同源,而他们后来的画风却融入了自己对素描艺术的理解,形成了彼此不同的差异表现.文中通过结合两人的艺术言论,对照两人素描作品中对绘画角度选择、表现手法、造型方式以及对形体塑造的理解和表达来探析一脉相承下的学院派素描大师的艺术差异性表现的原因和特色,旨在理清素描表现体系的差异. 相似文献
1000.
为了研究杀虫剂氟虫腈对斑马鱼的毒性机理,以秀丽隐杆线虫谷氨酸受体[在蛋白质数据库(ProteinDataBank,PDB)登记号为3RHW]作为模板,通过蛋白质同源模建的方法构建了斑马鱼A型γ-氨基丁酸受体跨膜段,利用分子动力学和拉氏图验证了模型的合理性.将构建的模型与氟虫腈及其衍生物进行分子对接.氟虫腈及其衍生物与跨膜蛋白对接结果在分子水平上解释了氟虫腈对斑马鱼的毒性机理:10个不同构象的氟虫睛与跨膜蛋白对接各个打分和结合自由能都比较稳定,氟虫腈垂直地定位于跨膜段的胞质端,跨膜蛋白上28位天冬酰胺和38位精氨酸与氟虫腈分子产生氢键;苯环上的取代基CF3,CI,CI和吡唑环上取代基SOCF2或SO2CF3是产生毒性作用的重要基团;基于氟虫腈结构虚拟筛选的化合物与跨膜蛋白的对接结果也进一步验证了,上述结论. 相似文献