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71.
Approximate range aggregate queries are one of the most frequent and useful kinds of queries for Decision Support Systems
(DSS), as they are widely used in many data analysis tasks. Traditionally, sampling-based techniques have been proposed to
tackle this problem. However, their effectiveness degrade when the underlying data distribution is skewed. Another approach
based on the outlier management can limit the effect of data skews but fails to address other requirements of approximate
range aggregate queries, such as error guarantees and query processing efficiency. In this paper, we present a technique that
provides approximate answers to range aggregate queries on OLAP data cubes efficiently, with theoretical guarantees on the
errors. Our basic idea is to build different data structures to manage outliers and the rest of the data. Carefully chosen
outliers are organized in a quad-tree based indexing data structure to provide efficient access for query processing. A query-workload adaptive, tree-like synopsis data structure, called T
unable
P
artition-Tree (TP-Tree), is proposed to organize samples extracted from non-outlier data. Our experiments clearly demonstrate the merits of our
technique, by comparing with previous well-known techniques. 相似文献
72.
Sandra A. Mayén-Hernández Gerardo Torres-Delgado Rebeca Castanedo-Pérez Mario Gutiérrez Villarreal Alfredo Cruz-Orea Julio G. Mendoza Alvarez Orlando Zelaya-Angel 《Journal of Materials Science: Materials in Electronics》2007,18(11):1127-1130
ZnO + Zn2TiO4 thin films were obtained by the sol–gel method using precursor solutions with different Ti/Zn ratios in the 0.18–2.13 range.
The films were deposited on glass substrates and annealed in an open atmosphere at 550 °C. The oxide was characterized by
X-ray diffraction and photoacoustic (PA) spectroscopy. The films were constituted of polycrystalline ZnO for the lowest Ti/Zn
ratio (0.18), polycrystalline Zn2TiO4 for the 0.70 and 1.0 ratios, and mixes of both oxides for the intermediate ratios (0.32 and 0.50). For the highest ratios
studied (1.44 and 2.13), the films were amorphous. The energy band gap (Eg) values were determined from optical absorption spectra, measured by means of the PA technique spectra. Eg varied in the 3.15 eV (ZnO) to 3.70 eV (Zn2TiO4) range. 相似文献
73.
Alfredo H Saaband Steve Logan 《电子设计技术》2007,14(10):108-108,110
随着新一代的LED实现了较高的功率和效率,这些元件的应用逐渐扩展到了新的领域,如手电筒或车辆应用等.大功率LED与白炽灯泡及荧光灯管等共同应用于环境照明中. 相似文献
74.
Electrocatalytic Detection: Magnetic Bead/Gold Nanoparticle Double‐Labeled Primers for Electrochemical Detection of Isothermal Amplified Leishmania DNA (Small 2/2016) 下载免费PDF全文
75.
Carmelo Cassisi Alfredo Ferro Rosalba Giugno Giuseppe Pigola Alfredo Pulvirenti 《Information Systems》2013
Clustering is a widely used unsupervised data mining technique. It allows to identify structures in collections of objects by grouping them into classes, named clusters, in such a way that similarity of objects within any cluster is maximized and similarity of objects belonging to different clusters is minimized. In density-based clustering, a cluster is defined as a connected dense component and grows in the direction driven by the density. The basic structure of density-based clustering presents some common drawbacks: (i) parameters have to be set; (ii) the behavior of the algorithm is sensitive to the density of the starting object; and (iii) adjacent clusters of different densities could not be properly identified. In this paper, we address all the above problems. Our method, based on the concept of space stratification, efficiently identifies the different densities in the dataset and, accordingly, ranks the objects of the original space. Next, it exploits such a knowledge by projecting the original data into a space with one more dimension. It performs a density based clustering taking into account the reverse-nearest-neighbor of the objects. Our method also reduces the number of input parameters by giving a guideline to set them in a suitable way. Experimental results indicate that our algorithm is able to deal with clusters of different densities and outperforms the most popular algorithms DBSCAN and OPTICS in all the standard benchmark datasets. 相似文献
76.
Stéphane Bressan Alfredo Cuzzocrea Panagiotis Karras Xuesong Lu Sadegh Heyrani Nobari 《Journal of Parallel and Distributed Computing》2013
The widespread usage of random graphs has been highlighted in the context of database applications for several years. This because such data structures turn out to be very useful in a large family of database applications ranging from simulation to sampling, from analysis of complex networks to study of randomized algorithms, and so forth. Amongst others, Erd?s–Rényi Γv,p is the most popular model to obtain and manipulate random graphs. Unfortunately, it has been demonstrated that classical algorithms for generating Erd?s–Rényi based random graphs do not scale well in large instances and, in addition to this, fail to make use of the parallel processing capabilities of modern hardware. Inspired by this main motivation, in this paper we propose and experimentally assess a novel parallel algorithm for generating random graphs under the Erd?s–Rényi model that is designed and implemented in a Graphics Processing Unit (GPU), called PPreZER. We demonstrate the nice amenities due to our solution via a succession of several intermediary algorithms, both sequential and parallel, which show the limitations of classical approaches and the benefits due to the PPreZER algorithm. Finally, our comprehensive experimental assessment and analysis brings to light a relevant average speedup gain of PPreZER over baseline algorithms. 相似文献
77.
78.
79.
Paulo H. G. Zarbin Marcy G. Fonseca Daiane Szczerbowski Alfredo R. M. Oliveira 《Journal of chemical ecology》2013,39(3):358-363
We determined the site of pheromone production tissues and a partial route for the biosynthesis of the sex pheromone in Hedypathes betulinus (Coleoptera: Cerambycidae: Lamiinae), Brazil’s main green maté pest. Pheromone was found predominantly in the prothorax of males, suggesting that this is the region of production of pheromones in this insect. Scanning electron microscopy revealed small pores that may be associated with pheromone release in males; these pores also were observed in females. A deuterium-labeled putative precursor (geranyl acetone-D5) of the sex pheromone of H. betulinus was synthesized. When applied to the prothorax of males, label from the precursor was incorporated into the pheromone components, confirming that pheromone production occurs in the prothorax and that the pheromone components are biosynthesized from geranyl acetone. 相似文献
80.
Michele Casini Simonetta Ciuffi Adolfo Fiordelisi Alfredo Mazzotti Eusebio Stucchi 《Geothermics》2010
In the last 15 years geothermal exploration in Tuscany, Italy, has addressed deep reservoirs (depth ≥ 3000 m), hosted within complex geological systems, such as metamorphic formations and/or intrusive bodies. Reservoir productivity is linked to fractured and permeable zones that are rather confined and not uniformly distributed. In this context, the seismic methods represent one of the most reliable geophysical techniques for locating potential drilling targets. A 3D seismic survey has been acquired at the Travale test site, and its results have been used to develop a geological and structural model of the site, and to identify and characterize fractured zones inside the deep geothermal reservoir. A correlation between a high-amplitude reflector (H marker) and fractured contact-metamorphic rocks has been highlighted. More than 70% of the total geothermal fluid production at the Travale area comes from this seismic marker. 相似文献