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排序方式: 共有113条查询结果,搜索用时 15 毫秒
81.
Dimitrios Gunopulos George Kollios Vassilis J. Tsotras Carlotta Domeniconi 《The VLDB Journal The International Journal on Very Large Data Bases》2005,14(2):137-154
Estimating the selectivity of multidimensional range queries over real valued attributes has significant applications in data exploration and database query optimization. In this paper, we consider the following problem: given a table of d attributes whose domain is the real numbers and a query that specifies a range in each dimension, find a good approximation of the number of records in the table that satisfy the query. The simplest approach to tackle this problem is to assume that the attributes are independent. More accurate estimators try to capture the joint data distribution of the attributes. In databases, such estimators include the construction of multidimensional histograms, random sampling, or the wavelet transform. In statistics, kernel estimation techniques are being used. Many traditional approaches assume that attribute values come from discrete, finite domains, where different values have high frequencies. However, for many novel applications (as in temporal, spatial, and multimedia databases) attribute values come from the infinite domain of real numbers. Consequently, each value appears very infrequently, a characteristic that affects the behavior and effectiveness of the estimator. Moreover, real-life data exhibit attribute correlations that also affect the estimator. We present a new histogram technique that is designed to approximate the density of multidimensional datasets with real attributes. Our technique defines buckets of variable size and allows the buckets to overlap. The size of the cells is based on the local density of the data. The use of overlapping buckets allows a more compact approximation of the data distribution. We also show how to generalize kernel density estimators and how to apply them to the multidimensional query approximation problem. Finally, we compare the accuracy of the proposed techniques with existing techniques using real and synthetic datasets. The experimental results show that the proposed techniques behave more accurately in high dimensionalities than previous approaches.Received: 30 January 2001, Accepted: 9 June 2003, Published online: 4 March 2004Edited by: Y. IoannidisDimitrios Gunopulos: Supported by NSF ITR-0220148, NSF IIS-9907477 CAREER Award, NSF IIS-9984729, and NRDRP.George Kollios: Supported by NSF IIS-0133825 CAREER Award.Vassilis J. Tsotras: Supported by NSF IIS-9907477 and the US Dept. of Defense. 相似文献
82.
Rida T. Farouki Carlotta Giannelli Maria Lucia Sampoli Alessandra Sestini 《Computer Aided Geometric Design》2014
An orthonormal frame (f1,f2,f3) is rotation-minimizing with respect to fi if its angular velocity ω satisfies ω⋅fi≡0 — or, equivalently, the derivatives of fj and fk are both parallel to fi. The Frenet frame (t,p,b) along a space curve is rotation-minimizing with respect to the principal normal p, and in recent years adapted frames that are rotation-minimizing with respect to the tangent t have attracted much interest. This study is concerned with rotation-minimizing osculating frames (f,g,b) incorporating the binormal b, and osculating-plane vectors f, g that have no rotation about b. These frame vectors may be defined through a rotation of t, p by an angle equal to minus the integral of curvature with respect to arc length. In aeronautical terms, the rotation-minimizing osculating frame (RMOF) specifies yaw-free rigid-body motion along a curved path. For polynomial space curves possessing rational Frenet frames, the existence of rational RMOFs is investigated, and it is found that they must be of degree 7 at least. The RMOF is also employed to construct a novel type of ruled surface, with the property that its tangent planes coincide with the osculating planes of a given space curve, and its rulings exhibit the least possible rate of rotation consistent with this constraint. 相似文献
83.
84.
Adverse pregnancy outcomes in a population exposed to the emissions of a municipal waste incinerator
Vinceti M Malagoli C Teggi S Fabbi S Goldoni C De Girolamo G Ferrari P Astolfi G Rivieri F Bergomi M 《The Science of the total environment》2008,407(1):116-121
Some contaminants emitted by municipal waste incinerators are believed to adversely affect reproductive health in the exposed populations; yet only limited and conflicting epidemiologic evidence on this issue has been provided so far. In this study we analyzed rates of spontaneous abortion and prevalence at birth of congenital anomalies in women residing or working near the municipal solid waste incinerator of Modena, northern Italy, during the 2003--2006 period and who experienced higher levels of exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans, compared to the remaining municipal population. In women residing in two areas close to the incinerator plant with increasing exposure to dioxins, we did not detect an excess risk of miscarriage (relative risk [RR] 1.00, 95% confidence interval [CI] 0.65-1.48) and of birth defects (RR 0.64, 95% CI 0.20-1.55), nor did any indication of dose-response relation emerge. Among female workers employed in the factories located in the exposed areas, we did not observe a higher risk of spontaneous abortion (RR 1.04, 95% CI 0.38-2.30); however, an increase in prevalence of birth defects was noted (RR 2.26), although this risk estimate was statistically very unstable (95% CI 0.57-6.14). Overall, the study results provide little evidence of an excess risk of adverse pregnancy outcomes in women exposed to emissions from a modern municipal solid waste incinerator. 相似文献
85.
Alessandra Colombini Paola De Luca Davide Cangelosi Carlotta Perucca Orfei Enrico Ragni Marco Vigan Michela Malacarne Mauro Castagnetta Marco Brayda-Bruno Domenico Coviello Laura de Girolamo 《International journal of molecular sciences》2021,22(17)
Vitamin D showed a protective effect on intervertebral disc degeneration (IDD) although conflicting evidence is reported. An explanation could be due to the presence of the FokI functional variant in the vitamin D receptor (VDR), observed as associated with spine pathologies. The present study was aimed at investigating—through high-throughput gene and protein analysis—the response of human disc cells to vitamin D, depending on the VDR FokI variants. The presence of FokI VDR polymorphism was determined in disc cells from patients with discopathy. 1,25(OH)2D3 was administered to the cells with or without interleukin 1 beta (IL-1β). Microarray, protein arrays, and multiplex protein analysis were performed. In both FokI genotypes (FF and Ff), vitamin D upregulated metabolic genes of collagen. In FF cells, the hormone promoted the matrix proteins synthesis and a downregulation of enzymes involved in matrix catabolism, whereas Ff cells behaved oppositely. In FF cells, inflammation seems to hamper the synthetic activity mediated by vitamin D. Angiogenic markers were upregulated in FF cells, along with hypertrophic markers, some of them upregulated also in Ff cells after vitamin D treatment. Higher inflammatory protein modulation after vitamin D treatment was observed in inflammatory condition. These findings would help to clarify the clinical potential of vitamin D supplementation in patients affected by IDD. 相似文献
86.
Mihaela Aneta Dumitrescu Marialaura Lucariello Elisabetta Arca Maela Manzoli Carlotta Francia Elisa Paola Ambrosio 《Journal of Applied Electrochemistry》2009,39(11):2115-2121
Pt–Co alloys prepared by high energy ball milling synthesis were tested as electrocatalysts for hydrogen fueled Polymer Electrolyte Membrane Fuel Cells (PEMFC). In the present contribution we report on the first results regarding the electrochemical behaviour of two samples of Pt–Co alloys. One sample contains 20 wt.% alloy Pt:Co in the molar ratio 0.25:0.75 and C 80 wt.% and the second one Pt:Co in the molar ratio 0.75:0.25 and C 80 wt.%. The electrochemically active surface (EAS) was determined by cyclic voltammetry data while the electrocatalyst performance in a real cell was obtained by assembling Membrane Electrode Assemblies (MEAs) with the considered sample at the cathode. The results obtained, though indicating a lower performance than all-Pt catalysts, are quite interesting as they point out the importance of the C/Pt, Nafion/Pt and Pt/Co ratios that exert a deep influence onto the cell performance. 相似文献
87.
Roberta Giaccari Francesco Marchesani Carlotta Compari Emilia Fisicaro Andrea Mozzarelli Barbara Campanini Stefano Bettati Stefano Bruno Serena Faggiano 《International journal of molecular sciences》2022,23(9)
Human serine racemase (hSR) is a pyridoxal-5′-phosphate (PLP)-dependent dimer that catalyzes the formation of D-serine from L-serine, as well as the dehydration of both L- and D-serine to pyruvate and ammonia. As D-serine is a co-agonist of N-methyl-D-aspartate receptors (NMDARs), hSR is a key enzyme in glutamatergic neurotransmission. hSR activity is finely regulated by Mg2+, ATP, post-translational modifications, and the interaction with protein partners. In particular, the C-terminus of murine SR binds the third PDZ domain (PDZ3) of postsynaptic density protein 95 (PSD-95), a member of the membrane-associated guanylate kinase (MAGUK) family involved in the trafficking and localization of glutamate receptors. The structural details of the interaction and the stability of the complex have not been elucidated yet. We evaluated the binding of recombinant human PSD-95 PDZ3 to hSR by glutaraldehyde cross-linking, pull-down assays, isothermal titration calorimetry, nuclear magnetic resonance, and enzymatic assays. Overall, a weak interaction was observed, confirming the binding for the human orthologs but supporting the hypothesis that a third protein partner (i.e., stargazin) is required for the regulation of hSR activity by PSD-95 and to stabilize their interaction. 相似文献
88.
Invited review: Dairy proteins and bioactive peptides: Modeling digestion and the intestinal barrier
Carlotta Giromini Federica Cheli Raffaella Rebucci Antonella Baldi 《Journal of dairy science》2019,102(2):929-942
Dairy products are one of the most important sources of biologically active proteins and peptides. The health-promoting functions of these peptides are related to their primary structure, which depends on the parent protein composition. A crucial issue in this field is the demonstration of a cause-effect relationship from the ingested protein form to the bioactive form in vivo. Intervention studies represent the gold standard in nutritional research; however, attention has increasingly been focused on the development of sophisticated in vitro models of digestion to elucidate the mechanism of action of dairy nutrients in a mechanistic way and significantly reduce the number of in vivo trials. On the other hand, the epithelial intestinal barrier is the first gate that actively interacts with digestion metabolites, making the intestinal cells the first target tissue of dairy nutrients and respective metabolites. An evolution of the in vitro digestion approach in the study of dairy proteins and derived bioactive compounds is the setup of combined in vitro digestion and cell culture models taking into consideration the endpoint to measure the target organism (e.g., animal, human) and the key concepts of bioaccessibility, bioavailability, and bioactivity. This review discusses the relevance and challenges of modeling digestion and the intestinal barrier, focusing on the implications for the modeling of dairy protein digestion for bioactivity evaluation. 相似文献
89.
Carlotta Francia Vijaykumar S. IjeriStefania Specchia Paolo Spinelli 《Journal of power sources》2011,196(4):1833-1839
It is well known that the membrane electrode assembly (MEA) of proton exchange membrane fuel cells (PEMFCs) can undergo deterioration, during long term operation, of both the electrode materials and the membrane. Hydrogen crossover, i.e., the undesired diffusion of the gas from the anode to the cathode through the membrane, has been ascribed as one of the main causes of deterioration of perfluorinated ionomer membranes, normally employed in PEMFCs. One of the effects of the hydrogen permeation across the membrane is the decrease of the cell's open circuit voltage (OCV), due to the reaction between the fuel and the oxidant at the cathode surface. Such reaction can lead to the production of peroxide radicals, causing the degradation of both the PEM and the catalyst layer. Hydrogen crossover increases when temperature, pressure and humidity of the cell rise. The hydrogen permeation rate through a very thin PEM is typically lower than 1 mA cm−2 for a new MEA, but it can exceed 10-20 mA cm−2 after long term operation. Various methods have been proposed to measure the rate of hydrogen crossover, mainly based on electrochemical tests on a single FC with a flow of nitrogen at the cathode, so that the steady state current corresponds to the oxidation of crossed hydrogen. Hydrogen crossover has been also determined indirectly by assuming that the changes in the OCV values are due to the passage of fuel from the anode to the cathode.In this paper, a simplified mathematical model for the direct determination of hydrogen crossover permeation rate is presented. Such a model is based on analytical expressions of the polarization terms and it is employed to determine the hydrogen crossover rate. The main results show that the hydrogen crossover current densities increased from 0.12 to 0.32 mA cm−2, by decreasing the thickness of the membranes and increasing the operating cell temperature. Moreover, the hydrogen crossover determined for a fresh MEA was compared with that of a degraded one, exposed to repetitive freezing/thawing cycles. It was found that the hydrogen crossover for the degraded MEA was more than twice the value obtained with the fresh one at the same temperature. 相似文献
90.