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Search Results: 1 - 10 of 654306 matches for " J. A. Detwiler "
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A Generic Surface Sampler for Monte Carlo Simulations
J. A. Detwiler,R. Henning,R. A. Johnson,M. G. Marino
Physics , 2008, DOI: 10.1109/TNS.2008.2001063
Abstract: We present an implementation of a Monte Carlo algorithm that generates points randomly and uniformly on a set of arbitrary surfaces. The algorithm is completely general and only requires the geometry modeling software to provide the intersection points of an arbitrary line with the surface being sampled. We demonstrate the algorithm using the Geant4 Monte Carlo simulation toolkit. The efficiency of the sampling algorithm is discussed, along with various options in the implementation and example applications.
Uncertainties in the Anti-neutrino Production at Nuclear Reactors
Z. Djurcic,J. A. Detwiler,A. Piepke,V. R. Foster Jr.,L. Miller,G. Gratta
Physics , 2008, DOI: 10.1088/0954-3899/36/4/045002
Abstract: Anti-neutrino emission rates from nuclear reactors are determined from thermal power measurements and fission rate calculations. The uncertainties in these quantities for commercial power plants and their impact on the calculated interaction rates in electron anti-neutrino detectors is examined. We discuss reactor-to-reactor correlations between the leading uncertainties and their relevance to reactor anti-neutrino experiments.
Validation of spallation neutron production and propagation within Geant4
M. G. Marino,J. A. Detwiler,R. Henning,R. A. Johnson,A. G. Schubert,J. F. Wilkerson
Physics , 2007, DOI: 10.1016/j.nima.2007.08.170
Abstract: Using simulations to understand backgrounds from muon-induced neutrons is important in designing next-generation low-background underground experiments. Validation of relevant physics within the Geant4 simulation package has been completed by comparing to data from two recent experiments. Verification focused on the production and propagation of neutrons at energies important to underground experiments. Discrepancies were observed between experimental data and the simulation. Techniques were explored to correct for these discrepancies.
Lesula: A New Species of Cercopithecus Monkey Endemic to the Democratic Republic of Congo and Implications for Conservation of Congo’s Central Basin
John A. Hart, Kate M. Detwiler, Christopher C. Gilbert, Andrew S. Burrell, James L. Fuller, Maurice Emetshu, Terese B. Hart, Ashley Vosper, Eric J. Sargis, Anthony J. Tosi
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044271
Abstract: In June 2007, a previously undescribed monkey known locally as “lesula” was found in the forests of the middle Lomami Basin in central Democratic Republic of Congo (DRC). We describe this new species as Cercopithecus lomamiensis sp. nov., and provide data on its distribution, morphology, genetics, ecology and behavior. C. lomamiensis is restricted to the lowland rain forests of central DRC between the middle Lomami and the upper Tshuapa Rivers. Morphological and molecular data confirm that C. lomamiensis is distinct from its nearest congener, C. hamlyni, from which it is separated geographically by both the Congo (Lualaba) and the Lomami Rivers. C. lomamiensis, like C. hamlyni, is semi-terrestrial with a diet containing terrestrial herbaceous vegetation. The discovery of C. lomamiensis highlights the biogeographic significance and importance for conservation of central Congo’s interfluvial TL2 region, defined from the upper Tshuapa River through the Lomami Basin to the Congo (Lualaba) River. The TL2 region has been found to contain a high diversity of anthropoid primates including three forms, in addition to C. lomamiensis, that are endemic to the area. We recommend the common name, lesula, for this new species, as it is the vernacular name used over most of its known range.
Cellular Origin of Spontaneous Ganglion Cell Spike Activity in Animal Models of Retinitis Pigmentosa
David J. Margolis,Peter B. Detwiler
Journal of Ophthalmology , 2011, DOI: 10.1155/2011/507037
Abstract: Here we review evidence that loss of photoreceptors due to degenerative retinal disease causes an increase in the rate of spontaneous ganglion spike discharge. Information about persistent spike activity is important since it is expected to add noise to the communication between the eye and the brain and thus impact the design and effective use of retinal prosthetics for restoring visual function in patients blinded by disease. Patch-clamp recordings from identified types of ON and OFF retinal ganglion cells in the adult (36–210 d old) rd1 mouse show that the ongoing oscillatory spike activity in both cell types is driven by strong rhythmic synaptic input from presynaptic neurons that is blocked by CNQX. The recurrent synaptic activity may arise in a negative feedback loop between a bipolar cell and an amacrine cell that exhibits resonant behavior and oscillations in membrane potential when the normal balance between excitation and inhibition is disrupted by the absence of photoreceptor input.
Cellular Origin of Spontaneous Ganglion Cell Spike Activity in Animal Models of Retinitis Pigmentosa
David J. Margolis,Peter B. Detwiler
Journal of Ophthalmology , 2011, DOI: 10.1155/2011/507037
Abstract: Here we review evidence that loss of photoreceptors due to degenerative retinal disease causes an increase in the rate of spontaneous ganglion spike discharge. Information about persistent spike activity is important since it is expected to add noise to the communication between the eye and the brain and thus impact the design and effective use of retinal prosthetics for restoring visual function in patients blinded by disease. Patch-clamp recordings from identified types of ON and OFF retinal ganglion cells in the adult (36–210 d old) rd1 mouse show that the ongoing oscillatory spike activity in both cell types is driven by strong rhythmic synaptic input from presynaptic neurons that is blocked by CNQX. The recurrent synaptic activity may arise in a negative feedback loop between a bipolar cell and an amacrine cell that exhibits resonant behavior and oscillations in membrane potential when the normal balance between excitation and inhibition is disrupted by the absence of photoreceptor input. 1. Introduction Retinitis pigmentosa (RP) refers to a number of related diseases that result in the death of rod and cone photoreceptors causing blindness in about one in 3,500 people, nearly 2 million people worldwide. Not surprisingly, PubMed lists more than 7,000 papers on RP that provide an abundant source of information about the genetic, biochemical, physiological, and therapeutic characteristics of the disease. The goal of much recent work on RP has been to develop methods to restore vision by resuscitating the retina using gene therapy to repair the mutation that gives rise to the dystrophy [1] or by driving it artificially using neural prosthetics that are based on either electrical stimulation via implanted retinal electrodes [2] or optical stimulation via light activation of ectopically expressed photosensitive proteins [3–9]. The success of any of these approaches ultimately depends on the functional integrity of retinal ganglion cells (RGCs), the output cells of the retina whose axons carry spike-encoded information to the visual centers in the central nervous system. To make optimal use of ganglion cells for communicating with the brain, it is necessary to know how they are affected by the degenerative loss of photoreceptors and the accompanying changes in the cellular architecture of the retina [10–15]. 2. RP Increases Spontaneous Spike Activity in Ganglion Cells Out of the several thousand publications on RP, less than a dozen have addressed questions about the effects of retinal degeneration on RGC firing properties. The responses of individual
Determining the Drift Time of Charge Carriers in P-Type Point-Contact HPGe Detectors
R. D. Martin,M. Amman,Y. D. Chan,J. A. Detwiler,J. C. Loach,Q. Looker,P. N. Luke,A. W. P. Poon,J. Qian,K. Vetter,H. Yaver
Physics , 2011, DOI: 10.1016/j.nima.2012.02.047
Abstract: An algorithm to measure the drift time of charge carriers in p-type point contact (PPC) high-purity germanium (HPGe) detectors from the signals processed with a charge-sensitive preamplifier is introduced. It is demonstrated that the drift times can be used to estimate the distance of charge depositions from the point contact and to characterize losses due to charge trapping. A correction for charge trapping effects over a wide range of energies is implemented using the measured drift times and is shown to improve the energy resolution by up to 30%.
The MGDO software library for data analysis in Ge neutrinoless double-beta decay experiments
M. Agostini,J. A. Detwiler,P. Finnerty,K. Kr?ninger,D. Lenz,J. Liu,M. G. Marino,R. Martin,K. D. Nguyen,L. Pandola,A. G. Schubert,O. Volynets,P. Zavarise
Physics , 2011, DOI: 10.1088/1742-6596/375/1/042027
Abstract: The GERDA and Majorana experiments will search for neutrinoless double-beta decay of germanium-76 using isotopically enriched high-purity germanium detectors. Although the experiments differ in conceptual design, they share many aspects in common, and in particular will employ similar data analysis techniques. The collaborations are jointly developing a C++ software library, MGDO, which contains a set of data objects and interfaces to encapsulate, store and manage physical quantities of interest, such as waveforms and high-purity germanium detector geometries. These data objects define a common format for persistent data, whether it is generated by Monte Carlo simulations or an experimental apparatus, to reduce code duplication and to ease the exchange of information between detector systems. MGDO also includes general-purpose analysis tools that can be used for the processing of measured or simulated digital signals. The MGDO design is based on the Object-Oriented programming paradigm and is very flexible, allowing for easy extension and customization of the components. The tools provided by the MGDO libraries are used by both GERDA and Majorana.
Nuclear Propelled Vessels and Neutrino Oscillation Experiments
J. Detwiler,G. Gratta,N. Tolich,Y. Uchida
Physics , 2002, DOI: 10.1103/PhysRevLett.89.191802
Abstract: We study the effect of naval nuclear reactors on the study of neutrino oscillations. We find that the presence of naval reactors at unknown locations and times may limit the accuracy of future very long baseline reactor-based neutrino oscillation experiments. At the same time we argue that a nuclear powered surface ship such as a large Russian ice-breaker may provide an ideal source for precision experiments. While the relatively low reactor power would in this case require a larger detector, the source could be conveniently located at essentially any distance from a detector built at an underground location near a shore in a region of the world far away from other nuclear installations. The variable baseline would allow for a precise measurement of backgrounds and greatly reduced systematics from reactor flux and detector efficiency. In addition, once the oscillation measurement is completed, the detector could perform geological neutrino and astrophysical measurements with minimal reactor background.
Recent Results from KamLAND
Jason Detwiler
Physics , 2003,
Abstract: The Kamioka Liquid-scintillator Anti-Neutrino Detector (KamLAND) has detected for the first time the disappearance of electron antineutrinos from a terrestrial source at the 99.95% C.L. Interpreted in terms of neutrino oscillations, the best fit to the KamLAND data gives a mixing angle 1.0 and a mass-squared difference 6.9 x 10^-5 eV^2, in excellent agreement with the Large Mixing Angle solution to the solar neutrino problem. Assuming CPT invariance, this result excludes other solutions to the solar neutrino problem at > 99.95% C.L.
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