6,616 research outputs found
Modeling Neutrino Quasielastic Cross Sections on Nucleons and Nuclei
We calculate the total and differential quasielastic cross sections for
neutrino and antineutrino scattering on nucleons using up to date fits to the
nucleon elastic electromagnetic form factors , , ,
, and and pseudoscalar form factors. We compare predictions of the
cross sections for nucelons and nuclei to experimental data.Comment: 5 pages, 4 figures, Presented by Arie Bodek at CIPANP2003, New York
City, NY 2003 - to be published in proceeding
Significance of the dissociation of Dna2 by flap endonuclease 1 to Okazaki fragment processing in Saccharomyces cerevisiae
Okazaki fragments are initiated by short RNA/DNA primers, which are displaced into flap intermediates for processing. Flap endonuclease 1 (FEN1) and Dna2 are responsible for flap cleavage. Replication protein A (RPA)-bound flaps inhibit cleavage by FEN1 but stimulate Dna2, requiring that Dna2 cleaves prior to FEN1. Upon cleavage, Dna2 leaves a short flap, which is then cut by FEN1 forming a nick for ligation. Both enzymes require a flap with a free 5'-end for tracking to the cleavage sites. Previously, we demonstrated that FEN1 disengages the tracking mechanism of Dna2 to remove it from the flap. To determine why the disengagement mechanism evolved, we measured FEN1 dissociation of Dna2 on short RNA and DNA flaps, which occur during flap processing. Dna2 tracked onto these flaps but could not cleave, presenting a block to FEN1 entry. However, FEN1 disengaged these nonproductively bound Dna2 molecules, proceeding on to conduct proper cleavage. These results clarify the importance of disengagement. Additional results showed that flap substrate recognition and tracking by FEN1, as occur during fragment processing, are required for effective displacement of the flap-bound Dna2. Dna2 was recently shown to dissociate flap-bound RPA, independent of cleavage. Using a nuclease-defective Dna2 mutant, we reconstituted the sequential dissociation reactions in the proposed RPA/Dna2/FEN1 pathway showing that, even without cutting, Dna2 enables FEN1 to cleave RPA-coated flaps. In summary, RPA, Dna2, and FEN1 have evolved highly coordinated binding properties enabling one protein to succeed the next for proper and efficient Okazaki flap processing
Oblique-incidence secondary emission from charged dielectrics
Secondary electron emission coefficients were measured on FEP-Teflon for normal and oblique incidence in the presence of a normal electric field. Such measurements require knowledge of the electrostatic environment surrounding the specimen, and they require calculation of particle trajectories such that particle impact parameters can be known. A simulation using a conformal mapping, a Green's integral, and a trajectory generator provides the necessary mathematical support for the measurements, which were made with normal fields of 1.5 and 2.7 kV/mm. When incidence is normal and energy exceeds the critical energy, the coefficient is given by (V sub 0/V) to the .58 power, and for oblique incidence this expression may be divided by the cosine of the angle. The parameter V sub 0 is a function of normal field
Resolving the Axial Mass Anomaly in neutrino Scattering
We present a parametrization of the observed enhancement in the transverse
electron quasielastic (QE) response function for nucleons bound in carbon as a
function of the square of the four momentum transfer (Q2) in terms of a
correction to the magnetic form factors of bound nucleons. The parametrization
should also be applicable to the transverse cross section in neutrino
scattering. If the transverse enhancement originates from meson exchange
currents (MEC), then it is theoretically expected that any enhancement in the
longitudinal or axial contributions is small. We present the predictions of the
"Transverse Enhancement" model (which is based on electron scattering data
only) for the neutrino and anti-neutrino differential and total QE cross
sections for nucleons bound in carbon. The 2Q2 dependence of the transverse
enhancement is observed to resolve much of the long standing discrepancy
("Axial Mass Anomaly}) in the QE total cross sections and differential
distributions between low energy and high energy neutrino experiments on
nuclear targets.Comment: 3 pages, 3 Figures, Presented by Arie Bodek at the 19th Particles and
Nuclei International Conference, PANIC 2011, MIT, Cambridge, MA July 201
Vector and Axial Nucleon Form Factors:A Duality Constrained Parameterization
We present new parameterizations of vector and axial nucleon form factors. We
maintain an excellent descriptions of the form factors at low momentum
transfers, where the spatial structure of the nucleon is important, and use the
Nachtman scaling variable xi to relate elastic and inelastic form factors and
impose quark-hadron duality constraints at high momentum transfers where the
quark structure dominates. We use the new vector form factors to re-extract
updated values of the axial form factor from neutrino experiments on deuterium.
We obtain an updated world average value from neutrino-d and pion
electroproduction experiments of M_A = 1.014 +- 0.014 GeV/c2. Our
parameterizations are useful in modeling neutrino interactions at low energies
(e.g. for neutrino oscillations experiments). The predictions for high momentum
transfers can be tested in the next generation electron and neutrino scattering
experiments.Comment: 5 pages, 3 figures, to be published in EPJ
Dna2 is a structure-specific nuclease, with affinity for 5'-flap intermediates
Dna2 is a nuclease/helicase with proposed roles in DNA replication, double-strand break repair and telomere maintenance. For each role Dna2 is proposed to process DNA substrates with a 5'-flap. To date, however, Dna2 has not revealed a preference for binding or cleavage of flaps over single-stranded DNA. Using DNA binding competition assays we found that Dna2 has substrate structure specificity. The nuclease displayed a strong preference for binding substrates with a 5'-flap or some variations of flap structure. Further analysis revealed that Dna2 recognized and bound both the single-stranded flap and portions of the duplex region immediately downstream of the flap. A model is proposed in which Dna2 first binds to a flap base, and then the flap threads through the protein with periodic cleavage, to a terminal flap length of ~5 nt. This resembles the mechanism of flap endonuclease 1, consistent with cooperation of these two proteins in flap processing
Sound And Storytellingāan Auditory Angle on Internalized Racism In Invisible Man And the Lone Ranger And Tonto Fistfight In Heaven
Studies of American literature and, more specifically, literature by authors of color quite often focus on aspects of āotheringā, that is, the practice of separating minority culture and literature from the larger or more dominant culture. Even before the onset of the Civil Rights Era, issues of racism have informed much of the literature of the United States, and just as long as racism has played a role in American literature, scholars, critics, and readers have discussed it. The bulk of criticism discussing African American and Native American literature examines the issues of racism as perpetrated by white society. What is not as commonly examined is the role that internalized racism plays. Ralph Ellison and Sherman Alexie are two of the most extensively studied authors of African American and Native American descent respectively, but analysis of their work tends to overlook the racism that a person can experience against his own race, choosing instead to focus on the hegemonic master narrative. Both authors used a blend of narratological self-deprecation to illustrate a desire both from and for their respective races within a larger, āAmericanā identity; however, whereas Ellisonās novel is a bildungsroman that uses a single narratorās self-hatred, Alexie employs multiple narrators and points of view to stitch bricolage that ultimately serves as a cohesive narrative. Eschewing the typical line of argument about visual imagery, this paper intends to explore how each author uses elements of sound, auditory metaphors, and, especially storytelling and folklore to depict internalized racism, how it works its way under the skin, and how it can be used to expose the effects of overt racism
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