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排序方式: 共有67条查询结果,搜索用时 31 毫秒
1.
The TSIMMIS Approach to Mediation: Data Models and Languages 总被引:18,自引:2,他引:16
Hector Garcia-Molina Yannis Papakonstantinou Dallan Quass Anand Rajaraman Yehoshua Sagiv Jeffrey Ullman Vasilis Vassalos Jennifer Widom 《Journal of Intelligent Information Systems》1997,8(2):117-132
TSIMMIS—The Stanford-IBM Manager of Multiple InformationSources—is a system for integrating information. It offers a datamodel and a common query language that are designed to support thecombining of information from many different sources. It also offerstools for generating automatically the components that are needed tobuild systems for integrating information. In this paper we shalldiscuss the principal architectural features and their rationale. 相似文献
2.
Towards More Complete Models of TCP Latency and Throughput 总被引:2,自引:0,他引:2
Recently, several researchers have developed equations for modeling TCP behaviors, such as the expected throughput or latency, based on Markov chains derived from TCP with additional simplifying assumptions. In this paper, we suggest new directions for Markov chain analyses of TCP. Our first contribution is to closely examine not just the expectation but the entire cumulative distribution function of transfer times under various models. Particularly for short or medium transfers, the distribution is likely to be more useful than the expectation in terms of measuring end-user satisfaction. We find that the shapes of TCP cumulative distribution functions are remarkably robust to small changes in the model. Our results suggest that simplifying Markov analyses can be extended to yield approximations for the entire distribution as well as for the expectation.Our second contribution is to consider correction procedures to enhance these models. A correction procedure is a rule of thumb that allows equations from one model to be used in other situations. As an example, several analyses use a Drop-Tail loss model. We determine correction procedures for the deviation between this model and other natural loss models based on simulations. The existence of a simple correction procedure in this instance suggests that the high-level behavior of TCP is robust against changes in the loss model. 相似文献
3.
Several commercial applications, such as online comparison shopping and process automation, require integrating information that is scattered across multiple websites or XML documents. Much research has been devoted to this problem, resulting in several research prototypes and commercial implementations. Such systems rely on wrappers that provide relational or other structured interfaces to websites. Traditionally, wrappers have been constructed by hand on a per-website basis, constraining the scalability of the system. We introduce a website structure inference mechanism called compact skeletons that is a step in the direction of automated wrapper generation. Compact skeletons provide a transformation from websites or other hierarchical data, such as XML documents, to relational tables. We study several classes of compact skeletons and provide polynomial-time algorithms and heuristics for automated construction of compact skeletons from websites. Experimental results show that our heuristics work well in practice. We also argue that compact skeletons are a natural extension of commercially deployed techniques for wrapper construction. 相似文献
4.
P. Sivakumar A. Rajaraman G. M. Samuel Knight D. S. Ramachandramurthy 《Canadian Metallurgical Quarterly》2004,18(2):162-171
A new approach is presented for the optimization of steel lattice towers by combining genetic algorithms and an object-oriented approach. The purpose of this approach is to eliminate the difficulties in the handling of large size problems such as lattice towers. Improved search and rapid convergence are obtained by considering the lattice tower as a set of small objects and combining these objects into a system. This is possible with serial cantilever structures such as lattice towers. A tower consists of panel objects, which can be classified as separate objects, as they possess an independent property as well as inherent properties. This can considerably reduce the design space of the problem and enhance the result. An optimization approach for the steel lattice tower problem using objects and genetic algorithms is presented here. The paper also describes the algorithm with practical design considerations used for this approach. To demonstrate the approach, a typical tower configuration with practical constraints has been considered for discrete optimization with the new approach and compared with the results of a normal approach in which the full tower is considered. 相似文献
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In this paper we give a generalized predictor-corrector algorithm for solving ordinary differential equations with specified initial values. The method uses multiple correction steps which can be carried out in parallel with a prediction step. The proposed method gives a larger stability interval compared to the existing parallel predictor-corrector methods. A method has been suggested to implement the algorithm in multiple processor systems with efficient utilization of all the processors. 相似文献
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Nanobelts are a new class of semiconducting metal oxide nanowires. The ribbon-like nanobelts are chemically pure and structurally uniform single crystals, with clean, sharp, smooth surfaces, and rectangular cross-sections. Positive and negative dielectrophoresis (DEP) was demonstrated for the first time on semiconducting oxide nanobelts. This effect was then used for the fabrication of a nanodevice, which consisted of SnO2 nanobelts attached to castellated gold electrodes defined on a glass substrate, and covered by a microchannel. The SnO2 nanobelts (width ∼ 100-300 nm, thickness ∼ 30-40 nm) were suspended in ethanol and introduced into the microchannel. An alternating (AC) voltage of ∼9.8 V peak to peak, with variable frequency, was applied between the electrodes (minimum electrode gap ∼ 20 μm), which corresponds to an average electric field strength of less than 2.5 × 105 V/m. In the 10 Hz-1 kHz range, repulsion between the nanobelts and the electrodes occurred, while in the 1-10 MHz range, attraction was observed. Once the nanobelts touched the electrodes, those that were sufficiently long bridged the electrode gaps. The device was characterized and can potentially be used as a nanosensor. 相似文献
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R Govindaraj R Rajaraman K P Gopinathan B Viswanathan 《Bulletin of Materials Science》1998,21(5):427-431
Time differential perturbed angular correlation (TDPAC) and positron life-time measurements on cold-worked and hydrogen chargedNbHf indicate a strong binding of hydrogen decorated vacancy clusters with Hf impurities. Both TDPAC and positron lifetime results
are mutually consistent on this aspect. Transformation of H-vacancy clusters into H-bubbles is indicated by the positron lifetime
behaviour at annealing temperatures beyond 900 K. Impurity effects like oxygen pickup and coating of voids cannot be ruled
out at elevated temperatures. 相似文献