647 research outputs found
The systematic study of the influence of neutron excess on the fusion cross sections using different proximity-type potentials
Using different types of proximity potentials, we have examined the trend of
variations of barrier characteristics (barrier height and its position) as well
as fusion cross sections for 50 isotopic systems including various collisions
of C, O, Mg, Si, S, Ca, Ar, Ti and Ni nuclei with condition
for compound systems. The results of our studies reveal that the relationships
between increase of barrier positions and decrease of barrier heights are both
linear with increase of ratio. Moreover, fusion cross sections also
enhance linearly with increase of this ratio.Comment: 28 pages, 7 figures, 5 Table
Two different banana NPR1-like coding sequences confer similar protection against pathogens in Arabidopsis
Differences between the coding sequences of two banana homologues of the Non-expressor of Pathogenesis-Related 1 (NPR1) genes (MNPR1A and MNPR1B) were investigated as a possible cause for the differential activity of the two genes. Each of the MNPR1 coding sequences were expressed under the control of the cauliflower mosaic virus 35S promoter/terminator sequences in the transgenic Arabidopsis npr1-2 mutant. These MNPR1-expressing plants were then exposed to either the biotrophic oomycete Hyaloperonospora arabidopsidis, the necrotrophic fungus Botrytis cinerea, or the hemi-biotrophic bacterial pathogen Pseudomonas syringae. Expression of either MNPR1A or MNPR1B increased Pathogenesis-related 1 (PR-1) transcription in a similar manner in mutant plants and reduced pathogen growth, restoring resistance of the Arabidopsis npr1-2 mutant plants to pathogens. Sequence differences between MNPR1A and MNPR1B coding sequences did not affect MNPR1activity, suggesting a possible role for the involvement of other regulatory sequences in differential MNPR1 gene expression.Rockefeller Foundation and the University of Pretoria.http://link.springer.com/journal/12042hb2016Forestry and Agricultural Biotechnology Institute (FABI)Plant Scienc
Antagonistic effects of transforming growth factor-beta on vitamin D3 enhancement of osteocalcin and osteopontin transcription: reduced interactions of vitamin D receptor/retinoid X receptor complexes with vitamin E response elements
Osteocalcin and osteopontin are noncollagenous proteins secreted by
osteoblasts and regulated by a complex interplay of systemic and locally
produced factors, including growth factors and steroid hormones. We
investigated the mechanism by which transforming growth factor-beta (TGF
beta) inhibits 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)-enhanced expression
of the osteocalcin (OC) and osteopontin (OP) genes. ROS 17/2.8 cells, in
which both genes are expressed, were transfected with reporter constructs
driven by native (i.e. wild-type) rat OC and mouse OP promoters. TGF beta
abrogated the 1,25-(OH)2D3 enhanced transcription of both the OC and OP
genes. The inhibitory TGF beta response for each requires vitamin D
response element (VDRE) sequences, although there are additional
contributions from proximal basal regulatory elements. These
transcriptional effects were further investigated for contribution of the
trans-activating factors, which interact with OC and OP VDREs, involving
the vitamin D receptor (VDR) and retinoid X receptor (RXR). Gel mobility
shift assays show that TGF beta significantly reduces induction of the
heterodimers VDR/RXR complexes in 1,25-(OH)2D3-treated ROS 17/2.8 cells.
However, Western blot and ligand binding analysis reveal that TGF beta
does not affect nuclear availability of the VDR. We also show that
activator protein-1 activity is up-regulated by TGF beta; thus, activator
protein-1 binding sites in the OC promoter may potentially contribute to
inhibitory effects of TGF beta on basal transcription. Our studies
demonstrate that the inhibitory action of TGF beta on the 1,25-(OH)2D3
enhancement of OC and OP transcription in osteoblastic cells results from
modulations of protein-DNA interactions at the OC and OP VDRE, which
cannot be accounted for by changes in VDR protein levels. As OC and OP
participate in bone turnover, our results provide insight into the
contributions of TGF beta and 1,25-(OH)2D3 to VDR-mediated gene regulatory
mechanism operative in bone formation and/or resorption events
Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed Processes
A chromosphere is a universal attribute of stars of spectral type later than
~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae
binaries) show extended and highly turbulent chromospheres, which develop into
slow massive winds. The associated continuous mass loss has a significant
impact on stellar evolution, and thence on the chemical evolution of galaxies.
Yet despite the fundamental importance of those winds in astrophysics, the
question of their origin(s) remains unsolved. What sources heat a chromosphere?
What is the role of the chromosphere in the formation of stellar winds? This
chapter provides a review of the observational requirements and theoretical
approaches for modeling chromospheric heating and the acceleration of winds in
single cool, evolved stars and in eclipsing binary stars, including physical
models that have recently been proposed. It describes the successes that have
been achieved so far by invoking acoustic and MHD waves to provide a physical
description of plasma heating and wind acceleration, and discusses the
challenges that still remain.Comment: 46 pages, 9 figures, 1 table; modified and unedited manuscript;
accepted version to appear in: Giants of Eclipse, eds. E. Griffin and T. Ake
(Berlin: Springer
Highly deformed Ca configurations in Si + C
The possible occurrence of highly deformed configurations in the Ca
di-nuclear system formed in the Si + C reaction is investigated
by analyzing the spectra of emitted light charged particles. Both inclusive and
exclusive measurements of the heavy fragments (A 10) and their
associated light charged particles (protons and particles) have been
made at the IReS Strasbourg {\sc VIVITRON} Tandem facility at bombarding
energies of Si) = 112 MeV and 180 MeV by using the {\sc ICARE}
charged particle multidetector array. The energy spectra, velocity
distributions, and both in-plane and out-of-plane angular correlations of light
charged particles are compared to statistical-model calculations using a
consistent set of parameters with spin-dependent level densities. The analysis
suggests the onset of large nuclear deformation in Ca at high spin.Comment: 33 pages, 11 figure
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
Measurement of the Strong Coupling alpha s from Four-Jet Observables in e+e- Annihilation
Data from e+e- annihilation into hadrons at centre-of-mass energies between
91 GeV and 209 GeV collected with the OPAL detector at LEP, are used to study
the four-jet rate as a function of the Durham algorithm resolution parameter
ycut. The four-jet rate is compared to next-to-leading order calculations that
include the resummation of large logarithms. The strong coupling measured from
the four-jet rate is alphas(Mz0)=
0.1182+-0.0003(stat.)+-0.0015(exp.)+-0.0011(had.)+-0.0012(scale)+-0.0013(mass)
in agreement with the world average. Next-to-leading order fits to the
D-parameter and thrust minor event-shape observables are also performed for the
first time. We find consistent results, but with significantly larger
theoretical uncertainties.Comment: 25 pages, 15 figures, Submitted to Euro. Phys. J.
Search for R-Parity Violating Decays of Scalar Fermions at LEP
A search for pair-produced scalar fermions under the assumption that R-parity
is not conserved has been performed using data collected with the OPAL detector
at LEP. The data samples analysed correspond to an integrated luminosity of
about 610 pb-1 collected at centre-of-mass energies of sqrt(s) 189-209 GeV. An
important consequence of R-parity violation is that the lightest supersymmetric
particle is expected to be unstable. Searches of R-parity violating decays of
charged sleptons, sneutrinos and squarks have been performed under the
assumptions that the lightest supersymmetric particle decays promptly and that
only one of the R-parity violating couplings is dominant for each of the decay
modes considered. Such processes would yield final states consisting of
leptons, jets, or both with or without missing energy. No significant
single-like excess of events has been observed with respect to the Standard
Model expectations. Limits on the production cross- section of scalar fermions
in R-parity violating scenarios are obtained. Constraints on the supersymmetric
particle masses are also presented in an R-parity violating framework analogous
to the Constrained Minimal Supersymmetric Standard Model.Comment: 51 pages, 24 figures, Submitted to Eur. Phys. J.
Measurement of Rb in e+e- Collisions at 182 - 209 GeV
Measurements of Rb, the ratio of the bbbar cross-section to the qqbar cross-
section in e+e- collisions, are presented. The data were collected by the OPAL
experiment at LEP at centre-of-mass energies between 182 GeV and 209 GeV.
Lepton, lifetime and event shape information is used to tag events containing b
quarks with high efficiency. The data are compatible with the Standard Model
expectation. The mean ratio of the eight measurements reported here to the
Standard Model prediction is 1.055+-0.031+-0.037, where the first error is
statistical and the second systematic.Comment: 21 pages, 5 figures, Submitted to Phys. Letts
Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2
The hadronic structure function of the photon F_2^gamma is measured as a
function of Bjorken x and of the factorisation scale Q^2 using data taken by
the OPAL detector at LEP. Previous OPAL measurements of the x dependence of
F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of
F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted
by QCD, the data show positive scaling violations in F_2^gamma. Several
parameterisations of F_2^gamma are in agreement with the measurements whereas
the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001,
Ascona, Switzerlan
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