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Search Results: 1 - 10 of 144999 matches for " B. Quinn "
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An LED pulser for measuring photomultiplier linearity
M. Friend,G. B. Franklin,B. Quinn
Physics , 2011, DOI: 10.1016/j.nima.2012.02.015
Abstract: A light-emitting diode (LED) pulser for testing the low-rate response of a photomultiplier tube (PMT) to scintillator-like pulses has been designed, developed, and implemented. This pulser is intended to simulate 80 ns full width at half maximum photon pulses over the dynamic range of the PMT, in order to precisely determine PMT linearity. This particular design has the advantage that, unlike many LED test rigs, it does not require the use of multiple calibrated LEDs, making it insensitive to LED gain drifts. Instead, a finite-difference measurement is made using two LEDs which need not be calibrated with respect to one another. These measurements give a better than 1% mapping of the response function, allowing for the testing and development of particularly linear PMT bases.
The impact of adolescent pertussis immunization, 2004-2009: lessons from Australia
Quinn,Helen E; McIntyre,Peter B;
Bulletin of the World Health Organization , 2011, DOI: 10.1590/S0042-96862011000900013
Abstract: objective: to compare the impact of three strategies for delivering a booster dose of adult-formulated tetanus-diphtheria-pertussis (tdap) vaccine to adolescents in australia. these comprise: (i) administering tdap to: a one-year age cohort; (ii) administering tdap to the entire high school and to subsequent entrant cohorts; and (iii) administering tdap to the entire high school but without continuing to immunize entrant cohorts. methods: a series of ecologic analyses of pertussis notifications during epidemic periods in relevant age cohorts were conducted. the primary outcome measure was the incidence rate ratio (irr), calculated by dividing pertussis incidence after the introduction of tdap delivery programmes by pertussis incidence during the most recent pre-programme epidemic. findings: during the epidemic period of 2008-2009, the national-level irr among age cohorts targeted for tdap was 0.6 (95% confidence interval, ci: 0.6-0.7), but among other age cohorts it was 1.1 (95% ci: 1.1-1.2). only the jurisdiction that implemented strategy 2 (western australia) experienced sustained decreases in pertussis notifications in both adolescents and infants under 6 months of age (irr: 0.4; 95% ci: 0.3-0.6) until 2009. conclusion: if confirmed by longer experience in australia and elsewhere, a broad school-based catch-up programme followed by immunization of school entrants may be the optimum strategy for the implementation of adolescent tdap programmes.
Z Boson Asymmetry Measurements at the Tevatron
B. Quinn,for the CDF,D0 Collaborations
Physics , 2014,
Abstract: We present measurements of the forward-backward asymmetry (A_fb) in dilepton pair decays of Z bosons produced in ppbar collisions using the full Tevatron dataset. The CDF experiment extracts a value for the effective weak mixing angle parameter sin^{2}\theta^{l}_{eff} of 0.2315 +/- 0.0010 from the A_fb distribution of dimuon events in 9.2 fb^{-1} of integrated luminosity. From dielectron events in 9.7 fb^{-1} of data, the D0 experiment finds sin^{2}\theta^{l}_{eff} = 0.23106 +/- 0.00053, the world's most precise measurement of sin^{2}\theta^{l}_{eff} from hadron colliders and with light quark couplings.
Spatial and temporal predictions of soil moisture patterns and evaporative losses using TOPMODEL and the GASFLUX model for an Alaskan catchment
P. F. Quinn,B. Ostendorf,K. Beven,J. Tenhunen
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 1998,
Abstract: By using topographic indices as derived from a Digital Terrain Models (DTM), it is possible to represent the heterogeneity within a landscape. This heterogeneity can reflect both long term evolutionary patterns seen in a landscape and the short term forcing of flow dynamics during storm events. By spatial analysis, the linkage between the geomorphological- hydrological-plant physiological phenomena can be examined. In this study, a direct link will be established between the topographically-driven hydrological phenomena and the eco-physiological response. The topographic distribution function of TOPMODEL is used to control the spatial and temporal flux of the channel flow and water table. The plant physiological model GAS-FLUX is used to give a spatially and temporally dissaggregated species-sensitive estimate of evapotranspiration flux. Evapotranspiration is sensitive to the vegetation phonology, to tundra community physiology and to the temperature regime. A simple linking of TOPMODEL and the GAS-FLUX model is applied to a summer snow-free period to the Imnavait catchment, Alaska (2.2 km2). A species-sensitive evapotranspiration model proved to give the highest quality results when validated against flow observations. Predicted dynamics of variable source area and the component hydrological processes are illustrated.
The Electron Drift Instrument on Cluster: overview of first results
G. Paschmann,J. M. Quinn,R. B. Torbert,H. Vaith
Annales Geophysicae (ANGEO) , 2003,
Abstract: EDI measures the drift velocity of artificially injected electron beams. From this drift velocity, the perpendicular electric field and the local magnetic field gradients can be deduced when employing different electron energies. The technique requires the injection of two electron beams at right angles to the magnetic field and the search for those directions within the plane that return the beams to their associated detectors after one or more gyrations. The drift velocity is then derived from the directions of the two beams and/or from the difference in their times-of-flight, measured via amplitude-modulation and coding of the emitted electron beams and correlation with the signal from the returning electrons. After careful adjustment of the control parameters, the beam recognition algorithms, and the onboard magnetometer calibrations during the commissioning phase, EDI is providing excellent data over a wide range of conditions. In this paper, we present first results in a variety of regions ranging from the polar cap, across the magnetopause, and well into the magnetosheath. Key words. Electron drift velocity (electric fields; plasma convection; instruments and techniques)
Cluster EDI convection measurements across the high-latitude plasma sheet boundary at midnight
J. M. Quinn,G. Paschmann,R. B. Torbert,H. Vaith
Annales Geophysicae (ANGEO) , 2003,
Abstract: We examine two crossings of three Cluster satellites from the polar cap into the high-latitude plasma sheet at midnight local time, using data from the Electron Drift Instrument (EDI). EDI measures the full electron drift velocity in the plane perpendicular to the magnetic field for any field and drift directions. The context of the measured convection velocities is established by their relation to the intense enhancements in 1 keV electrons, also measured by EDI, as the satellites move from the polar cap into the plasma sheet boundary. In both cases presented here, the cross B convection in the polar cap is anti-sunward (toward the nightside plasma sheet) with a small duskward component. As the satellites enter the plasma sheet boundary region, the dawn-dusk convective flow component reverses its sign, and the flow in the meridianal plane (toward the center of the plasma sheet) drops substantially. The relatively stable convection in the polar cap becomes highly variable as the PSBL is encountered. The timing and sequence of the boundary crossings by the Cluster satellites are consistent with a relatively static structure on a time scale of the few minutes in satellite separations. In one of the two events, the plasma sheet boundary has a spatially separate structure that is crossed by the satellites before entering the plasma sheet. Key words. Magnetospheric physics (electric fields; magnetopause, cusp and boundary layers; instruments and techniques)
The Orbital Evolution Induced by Baryonic Condensation in Triaxial Halos
M. Valluri,V. P. Debattista,T. Quinn,B. Moore
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.16192.x
Abstract: Using spectral methods, we analyse the orbital structure of prolate/triaxial dark matter (DM) halos in N-body simulations to understand the processes that drive the evolution of shapes of DM halos and elliptical galaxies in which central masses are grown. A longstanding issue is whether the change in the shapes of DM halos is the result of chaotic scattering of box orbits, or whether they change shape adiabatically in response to the evolving galactic potential. We use orbital frequencies to classify orbits, to quantify orbital shapes, and to identify resonant orbits and chaotic orbits. The frequency-based method overcomes the limitations of Lyapunov exponents which are sensitive to numerical discreteness effects. Regardless of the distribution of the baryonic component, the shape of a DM halo changes primarily due to changes in the shapes of individual orbits within a given family. Orbits with small pericentric radii are more likely to change both their orbital type and shape than orbits with large pericentric radii. Whether the evolution is regular (and reversible) or chaotic (and irreversible), depends primarily on the radial distribution of the baryonic component. The growth of an extended baryonic component of any shape results in a regular rather than chaotic change in orbital populations. In contrast the growth of a massive and compact central component results in chaotic scattering of a significant fraction of both box and long-axis tube orbits. The growth of a disk causes a significant fraction of halo particles to become trapped by major global orbital resonances. Despite the fact that shape of a DM halo is always quite oblate following the growth of a central baryonic component, a significant fraction of its orbit population has characteristics of its triaxial or prolate progenitor (ABRIDGED).
A damage model for fracking
J. Quinn Norris,Donald L. Turcotte,John B. Rundle
Physics , 2015, DOI: 10.1177/1056789515572927
Abstract: Injections of large volumes of water into tight shale reservoirs allows the extraction of oil and gas not previously accessible. This large volume "super" fracking induces damage that allows the oil and/or gas to flow to an extraction well. The purpose of this paper is to provide a model for understanding super fracking. We assume that water is injected from a small spherical cavity into a homogeneous elastic medium. The high pressure of the injected water generates hoop stresses that reactivate natural fractures in the tight shales. These fractures migrate outward as water is added creating a spherical shell of damaged rock. The porosity associated with these fractures is equal to the water volume injected. We obtain an analytic expression for this volume. We apply our model to a typical tight shale reservoir and show that the predicted water volumes are in good agreement with the volumes used in super fracking.
Loopless non-trapping invasion percolation model for fracking
J. Quinn Norris,Donald L. Turcotte,John B. Rundle
Physics , 2014, DOI: 10.1103/PhysRevE.89.022119
Abstract: Recent developments in hydraulic fracturing (fracking) have enabled the recovery of large quantities of natural gas and oil from old, low permeability shales. These developments include a change from low-volume, high-viscosity fluid injection to high-volume, low-viscosity injection. The injected fluid introduces distributed damage that provides fracture permeability for the extraction of the gas and oil. In order to model this process, we utilize a loopless non-trapping invasion percolation previously introduced to model optimal polymers in a strongly disordered medium, and for determining minimum energy spanning trees on a lattice. We performed numerical simulations on a 2D square lattice and find significant differences from other percolation models. Additionally, we find that the growing fracture network satisfies both Horton-Strahler and Tokunaga network statistics. As with other invasion percolation models, our model displays burst dynamics, in which the cluster extends rapidly into a connected region. We introduce an alternative definition of bursts to be a consecutive series of opened bonds whose strengths are all below a specified value. Using this definition of bursts, we find good agreement with a power-law frequency-area distribution. These results are generally consistent with the observed distribution of microseismicity observed during a high-volume frack.
Anisotropy in Fracking: A Percolation Model for Observed Microseismicity
J. Quinn Norris,Donald L. Turcotte,John B. Rundle
Physics , 2014, DOI: 10.1007/s00024-014-0921-9
Abstract: Hydraulic fracturing (fracking) using high pressures and a low viscosity fluid allow the extraction of large quantiles of oil and gas from very low permeability shale formations. The initial production of oil and gas at depth leads to high pressures and an extensive distribution of natural fractures which reduce the pressures. With time these fractures heal, sealing the remaining oil and gas in place. High volume fracking opens the healed fractures allowing the oil and gas to flow the horizontal productions wells. We model the injection process using invasion percolation. We utilize a 2D square lattice of bonds to model the sealed natural fractures. The bonds are assigned random strengths and the fluid, injected at a point, opens the weakest bond adjacent to the growing cluster of opened bonds. Our model exhibits burst dynamics in which the clusters extends rapidly into regions with weak bonds. We associate these bursts with the microseismic activity generated by fracking injections. A principal object of this paper is to study the role of anisotropic stress distributions. Bonds in the $y$-direction are assigned higher random strengths than bonds in the $x$-direction. We illustrate the spatial distribution of clusters and the spatial distribution of bursts (small earthquakes) for several degrees of anisotropy. The results are compared with observed distributions of microseismicity in a fracking injection. Both our bursts and the observed microseismicity satisfy Gutenberg-Richter frequency-size statistics.
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