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Search Results: 1 - 10 of 534606 matches for " T. A. Forest "
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Measurement of Inclusive Spin Structure Functions of the Deuteron
J. Yun,S. E. Kuhn,G. E. Dodge,T. A. Forest,M. Taiuti,for the CLAS collaboration
Physics , 2002, DOI: 10.1103/PhysRevC.67.055204
Abstract: We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer ($Q^2$ = 0.27 -- 1.3 (GeV/c)$^2$) and final hadronic state mass in the nucleon resonance region ($W$ = 1.08 -- 2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target ($^{15}$ND$_3$) and detected the scattered electrons with the CEBAF Large Acceptance Spectrometer (CLAS). From our data, we extract the longitudinal double spin asymmetry $A_{||}$ and the spin structure function $g_1^d$. Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function $g_1^d$ and study its approach to both the deep inelastic limit at large $Q^2$ and to the Gerasimov-Drell-Hearn sum rule at the real photon limit ($Q^2 \to 0$). We find that the first moment varies rapidly in the $Q^2$ range of our experiment and crosses zero at $Q^2$ between 0.5 and 0.8 (GeV/c)$^2$, indicating the importance of the $\Delta$ resonance at these momentum transfers.
On High Explosive Launching of Projectiles for Shock Physics Experiments
Damian C. Swift,Charles A. Forest,David A. Clark,William T. Buttler,Mark Marr-Lyon,Paul Rightley
Physics , 2007, DOI: 10.1063/1.2746769
Abstract: The hydrodynamic operation of the `Forest Flyer' type of explosive launching system for shock physics projectiles was investigated in detail using one- and two-dimensional continuum dynamics simulations. The simulations were insensitive to uncertainties in the material properties, and reproduced measurements of the projectile. The most commonly-used variant, with an Al alloy case, was predicted to produce a slightly curved projectile, subjected to some shock heating, and likely exhibiting some porosity from tensile damage. The flatness can be improved by using a case of lower shock impedance, such as polymethyl methacrylate. High-impedance cases, including Al alloys but with denser materials improving the launching efficiency, can be used if designed according to the physics of oblique shock reflection. The tensile stress induced in the projectile depends on the relative thickness of the explosive, expansion gap, and projectile. The thinner the projectile with respect to the explosive, the smaller the tensile stress. If the explosive is initiated with a plane wave lens, the tensile stress is lower than for initiation with multiple detonators over a plane. The previous plane wave lens designs did however induce a tensile stress close to the spall strength of the projectile. The tensile stress can be reduced by changes in the component thicknesses. Experiments to verify the operation of explosively-launched projectiles should attempt to measure porosity induced in the projectile: arrival time measurements may be insensitive to porous regions caused by damaged or recollected material.
Quark-Hadron Duality in Spin Structure Functions g1p and g1d
P. E. Bosted,K. V. Dharmawardane,G. E. Dodge,T. A. Forest,S. E. Kuhn,Y. Prok et al.
Physics , 2006, DOI: 10.1103/PhysRevC.75.035203
Abstract: New measurements of the spin structure functions of the proton and deuteron g1p(x,Q2) and g1d(x,Q2) in the nucleon resonance region are compared with extrapolations of target-mass-corrected next-to-leading-order (NLO) QCD fits to higher energy data. Averaged over the entire resonance region (W<2 GeV), the data and QCD fits are in good agreement in both magnitude and Q2 dependence for Q2>1.7 GeV2. This global duality appears to result from cancellations among the prominent local resonance regions: in particular strong sigma{3/2} contributions in the Delta(1232) region appear to be compensated by strong sigma{1/2} contributions in the resonance region centered on 1.5 GeV. These results are encouraging for the extension of NLO QCD fits to lower W and Q2 than have been used previously.
Experimental study of isovector spin sum rules
A. Deur,P. Bosted,V. Burkert,D. Crabb,V. Dharmawardane,G. E. Dodge,T. A. Forest,K. A. Griffioen,S. E. Kuhn,R. Minehart,Y. Prok
Physics , 2008, DOI: 10.1103/PhysRevD.78.032001
Abstract: We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for $0.05
A High Power Hydrogen Target for Parity Violation Experiments
E. J. Beise,D. H. Beck,E. Candell,R. Carr,F. Duncan,T. Forest,W. Korsch,J. W. Mark,R. D. McKeown,B. A. Mueller,S. Wells
Physics , 1996, DOI: 10.1016/0168-9002(96)00489-5
Abstract: Parity-violating electron scattering measurements on hydrogen and deuterium, such as those underway at the Bates and CEBAF laboratories, require luminosities exceeding $10^{38}$cm$^{-2}$s$^{-1}$, resulting in large beam power deposition into cryogenic liquid. Such targets must be able to absorb 500 watts or more with minimal change in target density. A 40~cm long liquid hydrogen target, designed to absorb 500~watts of beam power without boiling, has been developed for the SAMPLE experiment at Bates. In recent tests with 40~$\mu$A of incident beam, no evidence was seen for density fluctuations in the target, at a sensitivity level of better than 1\%. A summary of the target design and operational experience will be presented.
Extinction Risk and Diversification Are Linked in a Plant Biodiversity Hotspot
T. Jonathan Davies,Gideon F. Smith,Dirk U. Bellstedt,James S. Boatwright,Benny Bytebier,Richard M. Cowling,Félix Forest,Luke J. Harmon,A. Muthama Muasya,Brian D. Schrire,Yolande Steenkamp,Michelle van der Bank,Vincent Savolainen
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1000620
Abstract: It is widely recognized that we are entering an extinction event on a scale approaching the mass extinctions seen in the fossil record. Present-day rates of extinction are estimated to be several orders of magnitude greater than background rates and are projected to increase further if current trends continue. In vertebrates, species traits, such as body size, fecundity, and geographic range, are important predictors of vulnerability. Although plants are the basis for life on Earth, our knowledge of plant extinctions and vulnerabilities is lagging. Here, we disentangle the underlying drivers of extinction risk in plants, focusing on the Cape of South Africa, a global biodiversity hotspot. By comparing Red List data for the British and South African floras, we demonstrate that the taxonomic distribution of extinction risk differs significantly between regions, inconsistent with a simple, trait-based model of extinction. Using a comprehensive phylogenetic tree for the Cape, we reveal a phylogenetic signal in the distribution of plant extinction risks but show that the most threatened species cluster within short branches at the tips of the phylogeny—opposite to trends in mammals. From analyzing the distribution of threatened species across 11 exemplar clades, we suggest that mode of speciation best explains the unusual phylogenetic structure of extinction risks in plants of the Cape. Our results demonstrate that explanations for elevated extinction risk in plants of the Cape flora differ dramatically from those recognized for vertebrates. In the Cape, extinction risk is higher for young and fast-evolving plant lineages and cannot be explained by correlations with simple biological traits. Critically, we find that the most vulnerable plant species are nonetheless marching towards extinction at a more rapid pace but, surprisingly, independently from anthropogenic effects. Our results have important implications for conservation priorities and cast doubts on the utility of current Red List criteria for plants in regions such as the Cape, where speciation has been rapid, if our aim is to maximize the preservation of the tree-of-life.
Extinction Risk and Diversification Are Linked in a Plant Biodiversity Hotspot
T. Jonathan Davies ,Gideon F. Smith,Dirk U. Bellstedt,James S. Boatwright,Benny Bytebier,Richard M. Cowling,Félix Forest,Luke J. Harmon,A. Muthama Muasya,Brian D. Schrire,Yolande Steenkamp,Michelle van der Bank,Vincent Savolainen
PLOS Biology , 2011, DOI: 10.1371/journal.pbio.1000620
Abstract: It is widely recognized that we are entering an extinction event on a scale approaching the mass extinctions seen in the fossil record. Present-day rates of extinction are estimated to be several orders of magnitude greater than background rates and are projected to increase further if current trends continue. In vertebrates, species traits, such as body size, fecundity, and geographic range, are important predictors of vulnerability. Although plants are the basis for life on Earth, our knowledge of plant extinctions and vulnerabilities is lagging. Here, we disentangle the underlying drivers of extinction risk in plants, focusing on the Cape of South Africa, a global biodiversity hotspot. By comparing Red List data for the British and South African floras, we demonstrate that the taxonomic distribution of extinction risk differs significantly between regions, inconsistent with a simple, trait-based model of extinction. Using a comprehensive phylogenetic tree for the Cape, we reveal a phylogenetic signal in the distribution of plant extinction risks but show that the most threatened species cluster within short branches at the tips of the phylogeny—opposite to trends in mammals. From analyzing the distribution of threatened species across 11 exemplar clades, we suggest that mode of speciation best explains the unusual phylogenetic structure of extinction risks in plants of the Cape. Our results demonstrate that explanations for elevated extinction risk in plants of the Cape flora differ dramatically from those recognized for vertebrates. In the Cape, extinction risk is higher for young and fast-evolving plant lineages and cannot be explained by correlations with simple biological traits. Critically, we find that the most vulnerable plant species are nonetheless marching towards extinction at a more rapid pace but, surprisingly, independently from anthropogenic effects. Our results have important implications for conservation priorities and cast doubts on the utility of current Red List criteria for plants in regions such as the Cape, where speciation has been rapid, if our aim is to maximize the preservation of the tree-of-life.
Mechanistic Model of Rothia mucilaginosa Adaptation toward Persistence in the CF Lung, Based on a Genome Reconstructed from Metagenomic Data
Yan Wei Lim, Robert Schmieder, Matthew Haynes, Mike Furlan, T. David Matthews, Katrine Whiteson, Stephen J. Poole, Christopher S. Hayes, David A. Low, Heather Maughan, Robert Edwards, Douglas Conrad, Forest Rohwer
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0064285
Abstract: The impaired mucociliary clearance in individuals with Cystic Fibrosis (CF) enables opportunistic pathogens to colonize CF lungs. Here we show that Rothia mucilaginosa is a common CF opportunist that was present in 83% of our patient cohort, almost as prevalent as Pseudomonas aeruginosa (89%). Sequencing of lung microbial metagenomes identified unique R. mucilaginosa strains in each patient, presumably due to evolution within the lung. The de novo assembly of a near-complete R. mucilaginosa (CF1E) genome illuminated a number of potential physiological adaptations to the CF lung, including antibiotic resistance, utilization of extracellular lactate, and modification of the type I restriction-modification system. Metabolic characteristics predicted from the metagenomes suggested R. mucilaginosa have adapted to live within the microaerophilic surface of the mucus layer in CF lungs. The results also highlight the remarkable evolutionary and ecological similarities of many CF pathogens; further examination of these similarities has the potential to guide patient care and treatment.
Nuclear spins, magnetic moments and quadrupole moments of Cu isotopes from N = 28 to N = 46: probes for core polarization effects
P. Vingerhoets,K. T. Flanagan,M. Avgoulea,J. Billowes,M. L. Bissell,K. Blaum,B. A. Brown,B. Cheal,M. De Rydt,D. H. Forest,Ch. Geppert,M. Honma,M. Kowalska,J. Kramer,A. Krieger,E. Mane,R. Neugart,G. Neyens,W. Nortershauser,T. Otsuka,M. Schug,H. H. Stroke,G. Tungate,D. T. Yordanov
Physics , 2010, DOI: 10.1103/PhysRevC.82.064311
Abstract: Measurements of the ground-state nuclear spins, magnetic and quadrupole moments of the copper isotopes from 61Cu up to 75Cu are reported. The experiments were performed at the ISOLDE facility, using the technique of collinear laser spectroscopy. The trend in the magnetic moments between the N=28 and N=50 shell closures is reasonably reproduced by large-scale shell-model calculations starting from a 56Ni core. The quadrupole moments reveal a strong polarization of the underlying Ni core when the neutron shell is opened, which is however strongly reduced at N=40 due to the parity change between the $pf$ and $g$ orbits. No enhanced core polarization is seen beyond N=40. Deviations between measured and calculated moments are attributed to the softness of the 56Ni core and weakening of the Z=28 and N=28 shell gaps.
Sequencing at sea: challenges and experiences in Ion Torrent PGM sequencing during the 2013 Southern Line Islands Research Expedition
Yan Wei Lim,Daniel A. Cuevas,Genivaldo Gueiros Z. Silva,Kristen Aguinaldo,Elizabeth A. Dinsdale,Andreas F. Haas,Mark Hatay,Savannah E. Sanchez,Linda Wegley-Kelly,Bas E. Dutilh,Timothy T. Harkins,Clarence C. Lee,Warren Tom,Stuart A. Sandin,Jennifer E. Smith,Brian Zgliczynski,Mark J.A. Vermeij,Forest Rohwer,Robert A. Edwards
PeerJ , 2015, DOI: 10.7717/peerj.520
Abstract: Genomics and metagenomics have revolutionized our understanding of marine microbial ecology and the importance of microbes in global geochemical cycles. However, the process of DNA sequencing has always been an abstract extension of the research expedition, completed once the samples were returned to the laboratory. During the 2013 Southern Line Islands Research Expedition, we started the first effort to bring next generation sequencing to some of the most remote locations on our planet. We successfully sequenced twenty six marine microbial genomes, and two marine microbial metagenomes using the Ion Torrent PGM platform on the Merchant Yacht Hanse Explorer. Onboard sequence assembly, annotation, and analysis enabled us to investigate the role of the microbes in the coral reef ecology of these islands and atolls. This analysis identified phosphonate as an important phosphorous source for microbes growing in the Line Islands and reinforced the importance of L-serine in marine microbial ecosystems. Sequencing in the field allowed us to propose hypotheses and conduct experiments and further sampling based on the sequences generated. By eliminating the delay between sampling and sequencing, we enhanced the productivity of the research expedition. By overcoming the hurdles associated with sequencing on a boat in the middle of the Pacific Ocean we proved the flexibility of the sequencing, annotation, and analysis pipelines.
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