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71.
72.
Hazem Elmeleegy Jayant Madhavan Alon Halevy 《The VLDB Journal The International Journal on Very Large Data Bases》2011,20(2):209-226
A large number of web pages contain data structured in the form of ??lists??. Many such lists can be further split into multi-column tables, which can then be used in more semantically meaningful tasks. However, harvesting relational tables from such lists can be a challenging task. The lists are manually generated and hence need not have well-defined templates??they have inconsistent delimiters (if any) and often have missing information. We propose a novel technique for extracting tables from lists. The technique is domain independent and operates in a fully unsupervised manner. We first use multiple sources of information to split individual lines into multiple fields and then, compare the splits across multiple lines to identify and fix incorrect splits and bad alignments. In particular, we exploit a corpus of HTML tables, also extracted from the web, to identify likely fields and good alignments. For each extracted table, we compute an extraction score that reflects our confidence in the table??s quality. We conducted an extensive experimental study using both real web lists and lists derived from tables on the web. The experiments demonstrate the ability of our technique to extract tables with high accuracy. In addition, we applied our technique on a large sample of about 100,000 lists crawled from the web. The analysis of the extracted tables has led us to believe that there are likely to be tens of millions of useful and query-able relational tables extractable from lists on the web. 相似文献
73.
Ryan Bouldin Sethumadhavan Ravichandran Akshay Kokil Rahul Garhwal Subhalakshmi Nagarajan Jayant Kumar Ferdinando F. Bruno Lynne A. Samuelson Ramaswamy Nagarajan 《Synthetic Metals》2011,161(15-16):1611-1617
Enzymatic polymerization is an environmentally friendly alternative route for the synthesis of advanced π-functional materials. Until recently, synthetic methods for production of polypyrrole (PPy) were confined to the use of chemical oxidants or electrochemical methods. Here, we report the low temperature, oxidative polymerization of pyrrole using soybean peroxidase as the catalyst in aqueous non-toxic media. In addition to the benefits of the mild synthetic conditions, enzyme catalysis also affords PPy with fewer structural defects. Poly(sodium 4-styrenesulfonate) (PSS) was used as a charge-balancing dopant and dispersant for PPy to monitor changes in the absorption spectra of the polymer over time. However, the polymerization methodology is amenable to other dopants, including small molecule dopants like 10-camphor sulfonic acid. Spectroscopic characterization indicated that the PPy was conductive, and was produced in higher yields and at faster rates at lower temperatures. Careful temperature control combined with the appropriate choice of dopant ensured production of more electrically conductive PPy with conductivities that exceeded 3 S/cm. UV–Vis spectroscopy was used to provide evidence of favorable interactions between pyrrole and the dopant that may have facilitated the reaction. These interactions, combined with a low synthesis temperature and controlled enzyme-catalyzed radical generation, synergistically favored the formation of PPy with fewer defects and a more linear structure. 相似文献
74.
Secure buffering in firm real-time database systems 总被引:2,自引:0,他引:2
Binto George Jayant R. Haritsa 《The VLDB Journal The International Journal on Very Large Data Bases》2000,8(3-4):178-198
Many real-time database applications arise in electronic financial services, safety-critical installations and military systems
where enforcing security is crucial to the success of the enterprise. We investigate here the performance implications, in terms of killed transactions,
of guaranteeing multi-level secrecy in a real-time database system supporting applications with firm deadlines. In particular, we focus on the buffer management aspects of this issue.
Our main contributions are the following. First, we identify the importance and difficulties of providing secure buffer management
in the real-time database environment. Second, we present SABRE, a novel buffer management algorithm that provides covert-channel-free security. SABRE employs a fully dynamic one-copy allocation policy for efficient usage of buffer resources. It also incorporates
several optimizations for reducing the overall number of killed transactions and for decreasing the unfairness in the distribution
of killed transactions across security levels. Third, using a detailed simulation model, the real-time performance of SABRE
is evaluated against unsecure conventional and real-time buffer management policies for a variety of security-classified transaction
workloads and system configurations. Our experiments show that SABRE provides security with only a modest drop in real-time
performance. Finally, we evaluate SABRE's performance when augmented with the GUARD adaptive admission control policy. Our
experiments show that this combination provides close to ideal fairness for real-time applications that can tolerate covert-channel
bandwidths of up to one bit per second (a limit specified in military standards).
Received March 1, 1999 / Accepted October 1, 1999 相似文献
75.
Three-dimensional (3-D) ray-tracing and analysis is used to characterize the path angles in a rectangular building in which all interior walls are parallel or perpendicular to the exterior walls. Path angles are recorded for 500 random transmitter and receiver locations, maintaining constant range throughout a particular building model. The main contribution of this paper is the observation that when all of the path angles from all 500 trials are measured relative to one building wall and collectively analyzed in a signal strength distribution, clustering is clearly apparent. While this angle clustering in the ensemble of channels is not the same as clustering in a single channel trial, it may partially account for the clusters observed in single trials. As a practical matter, these results may impact the use and placement of directional antennas for wireless LANs in buildings of this type. 相似文献
76.
77.
Advances in MOS devices on silicon carbide (SiC) have been greatly hampered by the low inversion layer mobilities. In this paper, the electrical characteristics of lateral n-channel MOSFETs fabricated on 4H-SiC are reported for the first time. Inversion layer electron mobilities of 165 cm2/V·s in 4H-SiC MOSFETs were measured at room temperature. These MOSFETs were fabricated using a low temperature deposited oxide, with subsequent oxidation anneal, as the gate dielectric 相似文献
78.
Biomethanation of herbaceous biomass feedstock has the potential to provide clean energy source for cooking and other activities in areas where such biomass availability predominates. A biomethanation concept that involves fermentation of biomass residues in three steps, occurring in three zones of the fermentor is described. This approach while attempting take advantage of multistage reactors simplifies the reactor operation and obviates the need for a high degree of process control or complex reactor design. Typical herbaceous biomass decompose with a rapid VFA flux initially (with a tendency to float) followed by a slower decomposition showing balanced process of VFA generation and its utilization by methanogens that colonize biomass slowly. The tendency to float at the initial stages is suppressed by allowing previous days feed to hold it below digester liquid which permits VFA to disperse into the digester liquid without causing process inhibition. This approach has been used to build and operate simple biomass digesters to provide cooking gas in rural areas with weed and agro-residues. With appropriate modifications, the same concept has been used for digesting municipal solid wastes in small towns where large fermentors are not viable. With further modifications this concept has been used for solid–liquid feed fermentors. Methanogen colonized leaf biomass has been used as biofilm support to treat coffee processing wastewater as well as crop litter alternately in a year. During summer it functions as a biomass based biogas plants operating in the three-zone mode while in winter, feeding biomass is suspended and high strength coffee processing wastewater is let into the fermentor achieving over 90% BOD reduction. The early field experience of these fermentors is presented. 相似文献
79.
Assumptions regarding the magnitude and direction of energy-related technological change have long been recognized as critical determinants of the outputs and policy conclusions derived from integrated assessment models. Particularly in the case of developing countries, however, empirical analysis of technological change has lagged behind simulation modeling. This paper presents estimates of sectoral productivity trends and energy-augmenting technological change for several energy-intensive industries in India and South Korea, and, for comparison, the United States. The key findings are substantial heterogeneity among both industries and countries, and a number of cases of declining energy efficiency. The results are subject to certain technical qualifications both in regards to the methodology and to the direct comparison to integrated assessment parameterizations. Nevertheless, they highlight the importance of closer attention to the empirical basis for common modeling assumptions. 相似文献
80.
The present paper deals with interval estimation of variance components in two way nested unbalanced random model. Employing
a suitable transformation a statistic has been developed and its distribution is well approximated by chi-square. The confidence
intervals for variance components and the simultaneous confidence interval for their ratios have been derived. 相似文献