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Search Results: 1 - 10 of 659712 matches for " A. St. J. Murphy "
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A consistent formalism for the Thomas-Ehrman Level Displacement
J. J. He,A. St. J. Murphy
Physics , 2007,
Abstract: Usage of the Thomas-Ehrman Level Displacement formalism has been examined. Mistakes and inconsistencies are found in several papers, being repeated in subsequent works. Here, we present a complete formalism with a consistent set of definitions. Full algorithms are made available, both as a {\tt FORTRAN} source file and as a user-friendly Visual Basic executable tool, available for download on the World Wide Web.
A consistent scalar-tensor cosmology for inflation, dark energy and the Hubble parameter
C. H. -T. Wang,J. A. Reid,A. St J. Murphy,R. Bingham,J. T. Mendonca,T. B. Davies
Physics , 2013,
Abstract: A generic homogenous and isotropic cosmology is investigated based on the scalar-tensor theory of gravitation involving general metric coupling and scalar potential functions. We show that for a broad class of such functions, the scalar gravitational field can be dynamically trapped using a recently suggested mechanism. The corresponding scalar potential can drive inflation, accelerating expansion in the early and late universe respectively, with features consistent with standard requirements. Remarkably, the inflationary phase admits a natural exit with a well-defined value of the Hubble parameter dictated by the duration of inflation in a parameter independent manner, regardless of the detailed forms of the metric coupling and scalar potential. For an inflation duration consistent with the GUT description of the early universe, the resulting Hubble parameter is found to be consistent with its observed value.
Dynamical trapping and relaxation of scalar gravitational fields
C. H. -T. Wang,A. O. Hodson,A. St J. Murphy,T. B. Davies,J. T. Mendonca,R. Bingham
Physics , 2013, DOI: 10.1016/j.physletb.2013.09.002
Abstract: We present a framework for nonlinearly coupled scalar-tensor theory of gravity to address both inflation and core-collapse supernova problems. The unified approach is based on a novel dynamical trapping and relaxation of scalar gravity in highly energetic regimes. The new model provides a viable alternative mechanism of inflation free from various issues known to affect previous proposals. Furthermore, it could be related to observable violent astronomical events, specifically by releasing a significant amount of additional gravitational energy during core-collapse supernovae. A recent experiment at CERN relevant for testing this new model is briefly outlined.
Multiple factors interact to produce responses resembling spectrum of human disease in Campylobacter jejuni infected C57BL/6 IL-10-/- mice
Julia A Bell, Jessica L St Charles, Alice J Murphy, Vijay AK Rathinam, Anne E Plovanich-Jones, Erin L Stanley, John E Wolf, Jenna R Gettings, Thomas S Whittam, Linda S Mansfield
BMC Microbiology , 2009, DOI: 10.1186/1471-2180-9-57
Abstract: In the comparative study, C57BL/6 interleukin-10-/- mice were infected with seven genetically distinct C. jejuni strains. Four strains colonized the mice and caused disease; one colonized with no disease; two did not colonize. A DNA:DNA microarray comparison of the strain that colonized mice without disease to C. jejuni 11168 that caused disease revealed that putative virulence determinants, including loci encoding surface structures known to be involved in C. jejuni pathogenesis, differed from or were absent in the strain that did not cause disease. In the experimental study, the five colonizing strains were passaged four times in mice. For three strains, serial passage produced increased incidence and degree of pathology and decreased time to develop pathology; disease shifted from watery to bloody diarrhea. Mice kept on an ~6% fat diet or switched from an ~12% fat diet to an ~6% fat diet just before infection with a non-adapted strain also exhibited increased incidence and severity of disease and decreased time to develop disease, although the effects of diet were only statistically significant in one experiment.C. jejuni strain genetic background and adaptation of the strain to the host by serial passage contribute to differences in disease manifestations of C. jejuni infection in C57BL/6 IL-10-/- mice; differences in environmental factors such as diet may also affect disease manifestation. These results in mice reflect the spectrum of clinical presentations of C. jejuni gastroenteritis in humans and contribute to usefulness of the model in studying human disease.Campylobacter jejuni is a major cause of food-borne gastroenteritis worldwide. In addition to causing disease in humans, this microorganism can colonize a variety of domestic animals, common and exotic pets, and domestic and wild birds; some of these alternate hosts experience disease [1,2]. Successful experimental colonization of several mouse strains with C. jejuni has been reported, but disease does
The DRIFT Dark Matter Experiments
E. Daw,A. Dorofeev,J. R. Fox,J. -L. Gauvreau,C. Ghag,L. J. Harmon,J. L. Harton,M. Gold,E. R. Lee,D. Loomba,E. H. Miller,A. St. J. Murphy,S. M. Paling,J. M. Landers,N. Phan,M. Pipe,K. Pushkin,M. Robinson,S. W. Sadler,D. P. Snowden-Ifft,N. J. C. Spooner,D. Walker,D. Warner
Physics , 2011,
Abstract: The current status of the DRIFT (Directional Recoil Identification From Tracks) experiment at Boulby Mine is presented, including the latest limits on the WIMP spin-dependent cross-section from 1.5 kg days of running with a mixture of CS2 and CF4. Planned upgrades to DRIFT IId are detailed, along with ongoing work towards DRIFT III, which aims to be the world's first 10 m3-scale directional Dark Matter detector.
Measurement of the Range Component Directional Signature in a DRIFT-II Detector using 252Cf Neutrons
S. Burgos,E. Daw,J. Forbes,C. Ghag,M. Gold,C. Hagemann,V. A. Kudryavtsev,T. B. Lawson,D. Loomba,P. Majewski,D. Muna,A. St. J. Murphy,G. G. Nicklin,S. M. Paling,A. Petkov,S. J. S. Plank,M. Robinson,N. Sanghi,D. P. Snowden-Ifft,N. J. C. Spooner,J. Turk,E. Tziaferi
Physics , 2008, DOI: 10.1016/j.nima.2008.11.147
Abstract: The DRIFT collaboration utilizes low pressure gaseous detectors to search for WIMP dark matter with directional signatures. A 252Cf neutron source was placed on each of the principal axes of a DRIFT detector in order to test its ability to measure directional signatures from the three components of very low energy (~keV/amu) recoil ranges. A high trigger threshold and the event selection procedure ensured that only sulfur recoils were analyzed. Sulfur recoils produced in the CS2 target gas by the 252Cf source closely match those expected from massive WIMP induced sulfur recoils. For each orientation of the source a directional signal from the range components was observed, indicating that the detector is directional along all 3 axes. An analysis of these results yields an optimal orientation for DRIFT detectors when searching for a directional signature from WIMPs. Additional energy dependent information is provided to aid in understanding this effect.
Low Energy Electron and Nuclear Recoil Thresholds in the DRIFT-II Negative Ion TPC for Dark Matter Searches
S. Burgos,E. Daw,J. Forbes,C. Ghag,M. Gold,C. Hagemann,V. A. Kudryavtsev,T. B. Lawson,D. Loomba,P. Majewski,D. Muna,A. St. J. Murphy,S. M. Paling,A. Petkov,S. J. S. Plank,M. Robinson,N. Sanghi,D. P. Snowden-Ifft,N. J. C. Spooner,J. Turk,E. Tziaferi
Physics , 2009, DOI: 10.1088/1748-0221/4/04/P04014
Abstract: Understanding the ability to measure and discriminate particle events at the lowest possible energy is an essential requirement in developing new experiments to search for weakly interacting massive particle (WIMP) dark matter. In this paper we detail an assessment of the potential sensitivity below 10 keV in the 1 m^3 DRIFT-II directionally sensitive, low pressure, negative ion time projection chamber (NITPC), based on event-by-event track reconstruction and calorimetry in the multiwire proportional chamber (MWPC) readout. By application of a digital smoothing polynomial it is shown that the detector is sensitive to sulfur and carbon recoils down to 2.9 and 1.9 keV respectively, and 1.2 keV for electron induced events. The energy sensitivity is demonstrated through the 5.9 keV gamma spectrum of 55Fe, where the energy resolution is sufficient to identify the escape peak. The effect a lower energy sensitivity on the WIMP exclusion limit is demonstrated. In addition to recoil direction reconstruction for WIMP searches this sensitivity suggests new prospects for applications also in KK axion searches.
Is γ-ray emission from novae affected by interference effects in the 18F(p,α)15O reaction?
A. M. Laird,A. Parikh,A. St. J. Murphy,K. Wimmer,A. A. Chen,C. M. Deibel,T. Faestermann,S. P. Fox,B. R. Fulton,R. Hertenberger,D. Irvine,J. José,R. Longland,D. Mountford,B. Sambrook,D. Seiler,H. -F. Wirth
Physics , 2012, DOI: 10.1103/PhysRevLett.110.032502
Abstract: The 18F(p,\alpha)15O reaction rate is crucial for constraining model predictions of the \gamma-ray observable radioisotope 18F produced in novae. The determination of this rate is challenging due to particular features of the level scheme of the compound nucleus, 19Ne, which result in interference effects potentially playing a significant role. The dominant uncertainty in this rate arises from interference between J\pi=3/2+ states near the proton threshold (Sp = 6.411 MeV) and a broad J\pi=3/2+ state at 665 keV above threshold. This unknown interference term results in up to a factor of 40 uncertainty in the astrophysical S-factor at nova temperatures. Here we report a new measurement of states in this energy region using the 19F(3He,t)19Ne reaction. In stark contrast with previous assumptions we find at least 3 resonances between the proton threshold and Ecm=50 keV, all with different angular distributions. None of these are consistent with J\pi= 3/2+ angular distributions. We find that the main uncertainty now arises from the unknown proton-width of the 48 keV resonance, not from possible interference effects. Hydrodynamic nova model calculations performed indicate that this unknown width affects 18F production by at least a factor of two in the model considered.
Resonances in 19Ne with relevance to the astrophysically important 18F(p,α)15O reaction
D. J. Mountford,A. St J. Murphy,N. L. Achouri,C. Angulo,J. R. Brown,T. Davinson,F. de Oliveira Santos,N. de Séréville,P. Descouvemont,O. Kamalou,A. M. Laird,S. T. Pittman,P. Ujic,P. J. Woods
Physics , 2011, DOI: 10.1103/PhysRevC.85.022801
Abstract: The most intense gamma-ray line observable from novae is likely to be from positron annihilation associated with the decay of 18F. The uncertainty in the destruction rate of this nucleus through the 18F(p,{\alpha})15O reaction presents a limit to interpretation of any future observed gamma-ray flux. Direct measurements of the cross section of both this reaction and the 18F(p,p)18F reaction have been performed between center of mass energies of 0.5 and 1.9 MeV. Simultaneous fits to both data sets with the R-Matrix formalism reveal several resonances, with the inferred parameters of populated states in 19Ne in general agreement with previous measurements. Of particular interest, extra strength has been observed above ECM \sim1.3 MeV in the 18F(p,p)18F reaction and between 1.3-1.7 MeV in the 18F(p,{\alpha})15O reaction. This is well described by a broad 1/2+ state, consistent with both a recent theoretical prediction and an inelastic scattering measurement. The astrophysical implications of a broad sub-threshold partner to this state are discussed.
Measurements of neutrons produced by high-energy muons at the Boulby Underground Laboratory
H. M. Araujo,J. Blockley,C. Bungau,M. J. Carson,H. Chagani,E. Daw,B. Edwards,C. Ghag,E. V. Korolkova,V. A. Kudryavtsev,P. K. Lightfoot,A. Lindote,I. Liubarsky,R. Luscher,P. Majewski,K. Mavrokoridis,J. E. McMillan,A. St. J. Murphy,S. M. Paling,J. Pinto da Cunha,R. M. Preece,M. Robinson,N. J. T. Smith,P. F. Smith,N. J. C. Spooner,T. J. Sumner,R. J. Walker,H. Wang,J. White
Statistics , 2008, DOI: 10.1016/j.astropartphys.2008.05.004
Abstract: We present the first measurements of the muon-induced neutron flux at the Boulby Underground Laboratory. The experiment was carried out with an 0.73 tonne liquid scintillator that also served as an anticoincidence system for the ZEPLIN-II direct dark matter search. The experimental method exploited the delayed coincidences between high-energy muon signals and gamma-rays from radiative neutron capture on hydrogen or other elements. The muon-induced neutron rate, defined as the average number of detected neutrons per detected muon, was measured as $0.079 \pm 0.003$ (stat.) neutrons/muon using neutron-capture signals above 0.55 MeV in a time window of 40-190 $\mu$s after the muon trigger. Accurate Monte Carlo simulations of the neutron production, transport and detection in a precisely modeled laboratory and experimental setup using the GEANT4 toolkit gave a result 1.8 times higher than the measured value. The difference greatly exceeds all statistical and systematic uncertainties. As the vast majority of neutrons detected in the current setup were produced in lead we evaluated from our measurements the neutron yield in lead as $(1.31 \pm 0.06) \times 10^{-3}$ neutrons/muon/(g/cm$^2$) for a mean muon energy of about 260 GeV.
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