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Search Results: 1 - 10 of 415464 matches for " E. J. Brash "
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Human Telomeres Are Hypersensitive to UV-Induced DNA Damage and Refractory to Repair
Patrick J. Rochette,Douglas E. Brash
PLOS Genetics , 2010, DOI: 10.1371/journal.pgen.1000926
Abstract: Telomeric repeats preserve genome integrity by stabilizing chromosomes, a function that appears to be important for both cancer and aging. In view of this critical role in genomic integrity, the telomere's own integrity should be of paramount importance to the cell. Ultraviolet light (UV), the preeminent risk factor in skin cancer development, induces mainly cyclobutane pyrimidine dimers (CPD) which are both mutagenic and lethal. The human telomeric repeat unit (5′TTAGGG/CCCTAA3′) is nearly optimal for acquiring UV-induced CPD, which form at dipyrimidine sites. We developed a ChIP–based technique, immunoprecipitation of DNA damage (IPoD), to simultaneously study DNA damage and repair in the telomere and in the coding regions of p53, 28S rDNA, and mitochondrial DNA. We find that human telomeres in vivo are 7-fold hypersensitive to UV-induced DNA damage. In double-stranded oligonucleotides, this hypersensitivity is a property of both telomeric and non-telomeric repeats; in a series of telomeric repeat oligonucleotides, a phase change conferring UV-sensitivity occurs above 4 repeats. Furthermore, CPD removal in the telomere is almost absent, matching the rate in mitochondria known to lack nucleotide excision repair. Cells containing persistent high levels of telomeric CPDs nevertheless proliferate, and chronic UV irradiation of cells does not accelerate telomere shortening. Telomeres are therefore unique in at least three respects: their biophysical UV sensitivity, their prevention of excision repair, and their tolerance of unrepaired lesions. Utilizing a lesion-tolerance strategy rather than repair would prevent double-strand breaks at closely-opposed excision repair sites on opposite strands of a damage-hypersensitive repeat.
New empirical fits to the proton electromagnetic form factors
E. J. Brash,A. Kozlov,Sh. Li,G. M. Huber
Physics , 2001, DOI: 10.1103/PhysRevC.65.051001
Abstract: Recent measurements of the ratio of the elastic electromagnetic form factors of the proton, G_Ep/G_Mp, using the polarization transfer technique at Jefferson Lab show that this ratio decreases dramatically with increasing Q^2, in contradiction to previous measurements using the Rosenbluth separation technique. Using this new high quality data as a constraint, we have reanalyzed most of the world e-p elastic cross section data. In this paper, we present a new empirical fit to the reanalyzed data for the proton elastic magnetic form factor in the region 0 < Q^2 < 30 GeV^2. As well, we present an empirical fit to the proton electromagnetic form factor ratio, G_Ep/G_Mp, which is valid in the region 0.1 < Q^2 < 6 GeV^2.
The Structure of the Nucleon: Elastic Electromagnetic Form Factors
V. Punjabi,C. F. Perdrisat,M. K. Jones,E. J. Brash,C. E. Carlson
Physics , 2015,
Abstract: Precise proton and neutron form factor measurements at Jefferson Lab, using spin observables, have recently made a significant contribution to the unraveling of the internal structure of the nucleon. Accurate experimental measurements of the nucleon form factors are a test-bed for understanding how the nucleon's static properties and dynamical behavior emerge from QCD, the theory of the strong interactions between quarks. There has been enormous theoretical progress, since the publication of the Jefferson Lab proton form factor ratio data, aiming at reevaluating the picture of the nucleon. We will review the experimental and theoretical developments in this field and discuss the outlook for the future.
Measurement of GEp/GMp in ep -> ep to Q2 = 5.6 GeV2
O. Gayou,E. J. Brash,M. K. Jones,C. F. Perdrisat,V. Punjabi,L. Pentchev,A. Kozlov
Physics , 2001, DOI: 10.1103/PhysRevLett.88.092301
Abstract: The ratio of the electric and magnetic form factors of the proton, GEp/GMp, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic $\vec ep \to e\vec p$ reaction. The new data presented in this article span the range 3.5 < Q2 < 5.6 GeV2 and are well described by a linear Q2 fit. Also, the ratio QF2p/F1p reaches a constant value above Q2=2 GeV2.
Common Contaminants in Next-Generation Sequencing That Hinder Discovery of Low-Abundance Microbes
Martin Laurence, Christos Hatzis, Douglas E. Brash
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0097876
Abstract: Unbiased high-throughput sequencing of whole metagenome shotgun DNA libraries is a promising new approach to identifying microbes in clinical specimens, which, unlike other techniques, is not limited to known sequences. Unlike most sequencing applications, it is highly sensitive to laboratory contaminants as these will appear to originate from the clinical specimens. To assess the extent and diversity of sequence contaminants, we aligned 57 “1000 Genomes Project” sequencing runs from six centers against the four largest NCBI BLAST databases, detecting reads of diverse contaminant species in all runs and identifying the most common of these contaminant genera (Bradyrhizobium) in assembled genomes from the NCBI Genome database. Many of these microorganisms have been reported as contaminants of ultrapure water systems. Studies aiming to identify novel microbes in clinical specimens will greatly benefit from not only preventive measures such as extensive UV irradiation of water and cross-validation using independent techniques, but also a concerted effort to sequence the complete genomes of common contaminants so that they may be subtracted computationally.
A Preliminary Investigation of Age and Growth of Otolithes ruber from KwaZulu-Natal, South Africa
J M Brash, S T Fennessy
Western Indian Ocean Journal of Marine Science , 2005,
Abstract: This study investigated age and growth of Otolithes ruber, found in KwaZulu-Natal, South Africa. The specimens were collected from prawn trawlers that operate off the shallow water Tugela Bank and from a recreational boat fishery in Durban. Estimates of age and growth parameters were based on the examination of sectioned sagittal otoliths. There was difficulty in estimating growth parameters for separate sexes because the small fish were not sexed and the numbers of males was low. Periodicity of growth zone formation was assumed to be annual although periodicity of growth zone deposition could not be established by marginal zone analysis. The von Bertalanffy growth curve was used to describe the combined male and female growth of O. ruber: Lt = 419mm TL (1-e-0.31 (t+0.96)) The maximum age estimated was eight years. The repeatability of the age estimates was relatively high (Average Percentage Error: 12.5%). The information gathered from this study will be used in a subsequent stock assessment.
Helicity Signatures in Subthreshold rho Production on Nuclei
G. J. Lolos,G. M. Huber,A. Shinozaki,Z. Papandreou,E. J. Brash,K. Hossain,M. Iurescu,D. Nordin,G. Garino,K. Maruyama,K. Maeda,T. Suda,A. Toyofuku,A. Sasaki,H. Yamashita
Physics , 2001,
Abstract: We report a helicity analysis of subthreshold rho production on 2H and 12C nuclei at low photoproduction energies and large |t|. The results are indicative of a large longitudinal rho polarization (l=1, m=0) and are consistent with a strong helicity-flip mechanism of rho production. The analysis is model-independent and supports the large mass shift reported from the earlier 3He experiments.
In-Medium rho^0 Spectral Function Study via the 2H, 3He, 12C(gamma,pi+pi-) Reaction
G. M. Huber,G. J. Lolos,Z. Papandreou,A. Shinozaki,E. J. Brash,M. Iurescu,G. Garino,K. Maruyama,K. Maeda,T. Suda,A. Toyofuku,B. K. Jennings,A. Sasaki,H. Yamashita
Physics , 2003, DOI: 10.1103/PhysRevC.68.065202
Abstract: We report a helicity analysis of sub-threshold rho^0 production on 2H, 3He and 12C at low photo-production energies. The results are indicative of a large longitudinal rho^0 polarization (l=1, m=0) and are consistent with a strong helicity-flip production mechanism. This signature is used to extract in-medium rho^0_L invariant mass distributions for all three nuclei in a manner which is less model-dependent than previous measurements. The results are compared to kinematic and phenomenological models of the rho^0 spectral function. The 2H and 3He data distributions support the role of N*(1520) excitation in shaping the in-medium rho^0_L invariant mass distribution, while the 12C distributions are consistent with quasi-free rho^0_L production. The data support an in-medium modification of the rho^0_L invariant mass distribution.
Proton Polarimeter Calibration between 82 and 217 MeV
J. Glister,G. Ron,B. Lee,A. Beck,E. Brash,A. Camsonne,S. Choi,J. Dumas,R. Feuerbach,R. Gilman,D. W. Higinbotham,X. Jiang,M. K. Jones,S. May-Tal Beck,E. McCullough,M. Paolone,E. Piasetzky,J. Roche,Y. Rousseau,A. J. Sarty,B. Sawatzky,S. Strauch
Physics , 2009, DOI: 10.1016/j.nima.2009.04.051
Abstract: The proton analyzing power in carbon has been measured for energies of 82 to 217 MeV and proton scattering angles of 5 to 41 degrees. The measurements were carried out using polarized protons from the elastic scattering H(pol. e, pol. p) reaction and the Focal Plane Polarimeter (FPP) in Hall A of Jefferson Lab. A new parameterization of the FPP p-C analyzing power was fit to the data, which is in good agreement with previous parameterizations and provides an extension to lower energies and larger angles. The main conclusions are that all polarimeters to date give consistent measurements of the carbon analyzing power, independently of the details of their construction and that measuring on a larger angular range significantly improves the polarimeter figure of merit at low energies.
Cross Sections and Transverse Single-Spin Asymmetries in Forward Jet Production from Proton Collisions at $\sqrt{s}=500$ GeV
L. C. Bland,E. J. Brash,H. J. Crawford,A. A. Derevschikov,K. A. Drees,J. Engelage,C. Folz,M. K. Jones,E. G. Judd,X. Li,N. K. Liyanage,Y. Makdisi,N. G. Minaev,R. N. Munroe,L. Nogach,A. Ogawa,C. F. Perdrisat,C. Perkins,M. Planinic,V. Punjabi,G. Schnell,G. Simatovic,T. G. Throwe,C. Van Hulse,A. N. Vasiliev
Physics , 2013, DOI: 10.1016/j.physletb.2015.10.001
Abstract: Measurements of the production of forward jets from transversely polarized proton collisions at $\sqrt{s}=500$ GeV conducted at the Relativistic Heavy Ion Collider (RHIC) are reported. Our measured jet cross section is consistent with hard scattering expectations. Our measured analyzing power for forward jet production is small and positive, and provides constraints on the Sivers functions that are related to partonic orbital angular momentum through theoretical models.
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