829 research outputs found
Arsenite-Induced Alterations of DNA Photodamage Repair and Apoptosis After Solar-Simulation UVR in Mouse Keratinocytes in Vitro
Our laboratory has shown that arsenite markedly increased the cancer rate caused by solar-simulation ultraviolet radiation (UVR) in the hairless mouse skin model. In the present study, we investigated how arsenite affected DNA photodamage repair and apoptosis after solar-simulation UVR in the mouse keratinocyte cell line 291.03C. The keratinocytes were treated with different concentrations of sodium arsenite (0.0, 2.5, 5.0 ÎŒM) for 24 hr and then were immediately irradiated with a single dose of 0.30 kJ/m(2) UVR. At 24 hr after UVR, DNA photoproducts [cyclobutane pyrimidine dimers (CPDs) and 6â4 photoproducts (6-4PPs)] and apoptosis were measured using the enzyme-linked immunosorbent assay and the two-color TUNEL (terminal deoxynucleotide transferase dUTP nick end labeling) assay, respectively. The results showed that arsenite reduced the repair rate of 6-4PPs by about a factor of 2 at 5.0 ÎŒM and had no effect at 2.5 ÎŒM. UVR-induced apoptosis at 24 hr was decreased by 22.64% at 2.5 ÎŒM arsenite and by 61.90% at 5.0 ÎŒM arsenite. Arsenite decreased the UVR-induced caspase-3/7 activity in parallel with the inhibition of apoptosis. Colony survival assays of the 291.03C cells demonstrate a median lethal concentration (LC(50)) of arsenite of 0.9 ÎŒM and a median lethal dose (LD(50)) of UVR of 0.05 kJ/m(2). If the present results are applicable in vivo, inhibition of UVR-induced apoptosis may contribute to arseniteâs enhancement of UVR-induced skin carcinogenesis
Beam normal spin asymmetry in elastic lepton-nucleon scattering
We discuss the two-photon exchange contribution to observables which involve
lepton helicity flip in elastic lepton-nucleon scattering. This contribution is
accessed through the spin asymmetry for a lepton beam polarized normal to the
scattering plane. We estimate this beam normal spin asymmetry at large momentum
transfer using a parton model and we express the corresponding amplitude in
terms of generalized parton distributions.Comment: 17 pages, 5 figure
Determination of gluon polarization from deep inelastic scattering and collider data
We investigate impact of -production data at Relativistic Heavy Ion
Collider (RHIC) and future E07-011 experiment for the structure function
of the deuteron at the Thomas Jefferson National Accelerator Facility (JLab) on
studies of nucleonic spin structure, especially on the polarized gluon
distribution function. By global analyses of polarized lepton-nucleon
scattering and the -production data, polarized parton distribution
functions are determined and their uncertainties are estimated by the Hessian
method. Two types of the gluon distribution function are investigated. One is a
positive distribution and the other is a node-type distribution which changes
sign at . Although the RHIC data seem to favor the node
type for , it is difficult to determine a precise functional form
from the current data. However, it is interesting to find that the gluon
distribution is positive at large () due to constraints
from the scaling violation in and RHIC data. The JLab-E07-011
measurements for should be also able to reduce the gluon uncertainty,
and the reduction is comparable to the one by RUN-5 -production data at
RHIC. The reduction is caused by the error correlation between polarized
antiquark and gluon distributions and by a next-to-leading-order (NLO) gluonic
effect in the structure function . We find that the JLab-E07-011 data
are accurate enough to probe the NLO gluonic term in . Both RHIC and JLab
data contribute to better determination of the polarized gluon distribution in
addition to improvement on polarized quark and antiquark distributions.Comment: 11 pages, 9 eps figures, To be published in Nuclear Physics B. AAC08
FORTRAN package is available at the web site http://spin.riken.bnl.gov/aac
Virtual Compton Scattering at Low Energy and the Generalized Polarizabilities of the Nucleon o
Virtual Compton Scattering on the nucleon: is a new
and rapidly developing field at low and high energies. This lecture is about
the low energy part, i.e. for energies in the center-of-mass
mainly up to the resonance region. I review the concept of
Generalized Polarizabilities of the Nucleon, and the experiments dedicated to
their measurement.Comment: 16 pages, 8 figures. lecture given at the Erice School "Lepton
Scattering and the Structure of Hadrons and Nuclei," Erice, 16 - 24 Sept.
2004; to appear in "Progress in Particle and Nuclear Physics
Repair of UV-induced thymine dimers is compromised in cells expressing the E6 protein from human papillomaviruses types 5 and 18
Ultraviolet (UV) irradiation is a major mutagenic environmental agent, causing the appearance of DNA adducts that, if unrepaired, may give rise to mutations. Ultraviolet radiation has been indicated as a major risk factor in the development of nonmelanoma skin cancers; however, recent reports have suggested that infections with human papillomaviruses, a widespread family of epitheliotropic DNA viruses, may also contribute to the tumorigeneic process. Here, we investigated whether expression of the E6 protein from different HPV types interfere with the repair of thymine dimers caused by UV-B radiation. Results show that unrepaired DNA damage can be observed in UV-B-irradiated cells expressing the E6 protein of HPV types found in cervical and epithelial cancers. Moreover, such cells have the ability to overcome the G(1) cell cycle checkpoint induced as a result of unrepaired DNA. (C) 2004 Cancer Research UK
Effect of gluon-exchange pair-currents on the ratio G(E(P))/G(M(P))
The effect of one-gluon-exchange (OGE) pair-currents on the ratio for the proton is investigated within a nonrelativistic
constituent quark model (CQM) starting from nucleon wave
functions, but with relativistic corrections. We found that the OGE
pair-currents are important to reproduce well the ratio .
With the assumption that the OGE pair-currents are the driving mechanism for
the violation of the scaling law we give a prediction for the ratio of the neutron.Comment: 5 pages, 4 figure
Relativistically invariant analysis of polarization effects in exclusive deuteron electrodisintegration process
A general formalism for the calculation of the differential cross section and
polarization observables, for the process of deuteron electrodisintegration, is
developed in the framework of relativistic impulse approximation. A detailed
analysis of the general structure of the differential cross section and
polarization observables for the reaction is derived, using
the formalism of the structure functions. The obtained expressions have a
general nature and they hold in the one--photon--exchange mechanism, assuming
P--invariance of the hadron electromagnetic interaction. The model of
relativistic impulse approximation is introduced and the final state
interaction is taken into account by means of the unitarization of the helicity
amplitudes. A detailed description of the unitarization procedure is also
presented.
Using different parametrizations of the deuteron wave functions, the
following polarization observables are calculated in the kinematical region of
quasi--elastic deuteron electrodisintegration: the asymmetry for the scattering
of longitudinally polarized electrons on a polarized deuteron target, the
proton and neutron polarizations (for longitudinally polarized electron beam or
vector--polarized deuteron target). The sensitivity to the neutron electric
form factor is also thorougly investigated.
The predictions of the model are compared with the results of recent
polarization measurements and a good agreement with the existing experimental
data has been obtained.Comment: 90 pages, 17 figure
Dispersion relations in real and virtual Compton scattering
A unified presentation is given on the use of dispersion relations in the
real and virtual Compton scattering processes off the nucleon. The way in which
dispersion relations for Compton scattering amplitudes establish connections
between low energy nucleon structure quantities, such as polarizabilities or
anomalous magnetic moments, and the nucleon excitation spectrum is reviewed. We
discuss various sum rules for forward real and virtual Compton scattering, such
as the Gerasimov-Drell-Hearn sum rule and its generalizations, the
Burkhardt-Cottingham sum rule, as well as sum rules for forward nucleon
polarizabilities, and review their experimental status. Subsequently, we
address the general case of real Compton scattering (RCS). Various types of
dispersion relations for RCS are presented as tools for extracting nucleon
polarizabilities from the RCS data. The information on nucleon polarizabilities
gained in this way is reviewed and the nucleon structure information encoded in
these quantities is discussed. The dispersion relation formalism is then
extended to virtual Compton scattering (VCS). The information on generalized
nucleon polarizabilities extracted from recent VCS experiments is described,
along with its interpretation in nucleon structure models. As a summary, the
physics content of the existing data is discussed and some perspectives for
future theoretical and experimental activities in this field are presented.Comment: 120 pages, 42 figures, to appear in Phys. Re
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