144 research outputs found
QuickSel: Quick Selectivity Learning with Mixture Models
Estimating the selectivity of a query is a key step in almost any cost-based
query optimizer. Most of today's databases rely on histograms or samples that
are periodically refreshed by re-scanning the data as the underlying data
changes. Since frequent scans are costly, these statistics are often stale and
lead to poor selectivity estimates. As an alternative to scans, query-driven
histograms have been proposed, which refine the histograms based on the actual
selectivities of the observed queries. Unfortunately, these approaches are
either too costly to use in practice---i.e., require an exponential number of
buckets---or quickly lose their advantage as they observe more queries.
In this paper, we propose a selectivity learning framework, called QuickSel,
which falls into the query-driven paradigm but does not use histograms.
Instead, it builds an internal model of the underlying data, which can be
refined significantly faster (e.g., only 1.9 milliseconds for 300 queries).
This fast refinement allows QuickSel to continuously learn from each query and
yield increasingly more accurate selectivity estimates over time. Unlike
query-driven histograms, QuickSel relies on a mixture model and a new
optimization algorithm for training its model. Our extensive experiments on two
real-world datasets confirm that, given the same target accuracy, QuickSel is
34.0x-179.4x faster than state-of-the-art query-driven histograms, including
ISOMER and STHoles. Further, given the same space budget, QuickSel is
26.8%-91.8% more accurate than periodically-updated histograms and samples,
respectively
Onset of menisci
When a vertical solid is brought in contact with the surface of a wetting liquid, a meniscus starts rising up the solid, until it reaches its steady state. We study this dynamical phenomenon experimentally with liquids of low and high viscosity, and taking as solids either large rods or small fibres. In the inviscid limit, we show that the rising time scales as Ïr 3 0 /Ï, where Ï and Ï are the density and surface tension of the wetting liquid and r 0 the radius of the fibre. This characteristic time holds for small fibres, with radii smaller than the capillary length a. For large rods or planar solids, r 0 is replaced by a in the expression for the rising time. In the viscous limit, the rising time scales as ηr 0 /Ï where η is the dynamical viscosity. Again, r 0 is replaced by the capillary length a for large rods. Introduction In ancient Greek, 'mĂȘnĂȘ' designated the moon. It became the root of the word 'meniscus' which stands for a crescent of the moon and is associated with the wetting of a liquid on a solid. An example of liquid meniscus is presented in figure 1(b): a vertical planar wall initially held above a horizontal interface (figure 1a) is lowered to contact with a wetting liquid (contact angle Ξ e smaller than Ï/2), which forces the liquid to develop a meniscus of typical size l. The liquid being characterized by its density Ï and surface tension Ï, the shape of the interface results from the equilibrium between the Laplace depression, of order Ï/l, and the gravitational depression of order Ïgl, where g is the acceleration due to gravity. The balance between these two terms leads to l ⌠a, where a ⥠Ï/Ïg is the capillary length of the interface. In the case of a water/air interface on Earth, Ï â 0.073 kg s â2 , Ï â 10 3 kg m â3 , g â 9.81 m s â2 so that a â 2.7 mm. This shape remains unchanged as long as the radius of the wall r 0 is larger than a (r 0 = â for a planar wall). In the limit r 0 a, the pressure balance is dominated by the Laplace pressure associated with the two radii of curvature of the interface, and gravity can be neglected in the region close to the fibre. In this limit, l becomes of the order of r 0 , as it can be observed in Historically, the physical origin and the shape of the static meniscus have been among the first phenomena studied in capillarity, in particular by Hauksbee (1709), as cited by Maxwell (1875) in his introduction to the Capillary Action written for the Encyclopaedia Britannica: "the first accurate observations of the capillary action o
Chemical composition and evaluation of antibacterial and antioxidant activities of the essential oil of Croton urucurana Baillon (Euphorbiaceae) stem bark
Prevalence and trends of markers of hepatitis B virus, hepatitis C virus and human Immunodeficiency virus in Argentine blood donors
BACKGROUND: Transfusion-transmitted infections are a major problem associated with blood transfusion. The aim of this study was to determine prevalence and trends of HBV, HCV and HIV in blood donors in Argentina. METHODS: A retrospective study was carried out in blood donors of 27 transfusion centers covering the whole country over a period of eight years (2004-2011). Serologic screening assays for HBsAg, anti-HBc, anti-HCV, and anti-HIV were performed in all centers and nucleic acid amplification testing (NAT) was performed in 2 out of the 27 centers. RESULTS: The 2,595,852 samples tested nationwide from 2004 to 2011 showed that the prevalence of HBsAg decreased from 0.336% to 0.198% (p < 0.0001), that of anti-HBc from 2.391% to 2.007% (p < 0.0001), that of anti-HCV from 0.721% to 0.460%, (p < 0.0001) and that of anti-HIV from 0.208% to 0.200 (p = 0.075). The prevalence of HBV, HCV and HIV was unevenly distributed among the different regions of the country. Two out of 74,838 screening- negative samples were positive in NAT assays (1 HIV-RNA and 1 HCV-RNA); moreover, HBV-DNA, HCV-RNA and HIV-RNA were detected in 60.29, 24.54 and 66.67% of screening-positive samples of the corresponding assays. As regards donors age, positive HBV-DNA and HCV-RNA donors were significantly older than healthy donors (46.6, 50.5 and 39.5 y respectively, p < 0.001). CONCLUSIONS: Argentina has a low prevalence of HBsAg, anti-HCV and anti-HIV in blood donors, with a decreasing trend for HBsAg, anti-HBc and anti-HCV but not for anti-HIV over the last 8 years. The uneven distribution of transfusion-transmitted infections prevalence among the different regions of the country highlights the need to implement regional awareness campaigns and prevention. The discrepancy between samples testing positive for screening assays and negative for NAT assays highlights the problem of blood donors who test repeatedly reactive in screening assays but are not confirmed as positive upon further testing. The uneven distribution of age between healthy donors and NAT-positive donors could be related to changes in risks of these pathogens in the general population and might be attributed to a longer exposure to transmission risk factors in elderly people.Fil: Flichman, Diego Martin. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de MicrobiologĂa, InmunologĂa y BiotecnologĂa. CĂĄtedra de VirologĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Blejer, Jorgelina L.. FundaciĂłn Hemocentro; ArgentinaFil: Livellara, Beatriz I.. Hospital Italiano; ArgentinaFil: RĂ©, Viviana Elizabeth. Universidad Nacional de Cordoba. Facultad de Medicina. Instituto de VirologĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Bartoli, Sonia. Centro regional de Hemoterapia Jujuy; ArgentinaFil: Bustos, Juan A.. Banco de sangre San Jorge; ArgentinaFil: Ansola, Claudia P.. Provincia de Mendoza. Servicio de Hemoterapia; ArgentinaFil: Hidalgo, Susana. Hospital Dr. Enrique Vera Barros; ArgentinaFil: Cerda, MartĂn E.. Hospital Dr. Lucio Molas; ArgentinaFil: Levin, Alicia E.. Provincia de Mendoza. Servicio de Hemoterapia; ArgentinaFil: Huenul, Adriana. Hospital ArtĂ©mides Zatti; ArgentinaFil: Riboldi, Victoria. Hospital Regional RĂo Gallegos; ArgentinaFil: Treviño, Elena M. C.. Universidad Nacional de CĂłrdoba; ArgentinaFil: Salamone, Horacio J.. FundaciĂłn Favaloro; ArgentinaFil: Nuñez, Felix A.. Hospital Italiano; ArgentinaFil: FernĂĄndez, Robert J.. FundaciĂłn Hemocentro; ArgentinaFil: Reybaud, Juan F.. FundaciĂłn Favaloro; ArgentinaFil: Campos, Rodolfo Hector. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de MicrobiologĂa, InmunologĂa y BiotecnologĂa. CĂĄtedra de VirologĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentin
Previous exposure to musical auditory stimulation immediately influences the cardiac autonomic responses to the postural change maneuver in women
Background\ud
Chronic exposure to musical auditory stimulation has been reported to improve cardiac autonomic regulation. However, it is not clear if music acutely influences it in response to autonomic tests. We evaluated the acute effects of music on heart rate variability (HRV) responses to the postural change maneuver (PCM) in women.\ud
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Method\ud
We evaluated 12 healthy women between 18 and 28 years old and HRV was analyzed in the time (SDNN, RMSSD, NN50 and pNN50) and frequency (LF, HF and LF/HF ratio) domains. In the control protocol, the women remained at seated rest for 10 minutes and quickly stood up within three seconds and remained standing still for 15 minutes. In the music protocol, the women remained at seated rest for 10 minutes, were exposed to music for 10 minutes and quickly stood up within three seconds and remained standing still for 15 minutes. HRV was recorded at the following time: rest, music (music protocol) 0â5, 5â10 and 10â15 min during standing.\ud
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Results\ud
In the control protocol the SDNN, RMSSD and pNN50 indexes were reduced at 10â15 minutes after the volunteers stood up, while the LF (nu) index was increased at the same moment compared to seated rest. In the protocol with music, the indexes were not different from control but the RMSSD, pNN50 and LF (nu) were different from the music period.\ud
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Conclusion\ud
Musical auditory stimulation attenuates the cardiac autonomic responses to the PCM.This study received financial support from Fundação para o Desenvolvimento da UNESP (FUNDUNESP â Process number 9139213)
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