1,735 research outputs found
Source population synthesis and the Galactic diffuse gamma-ray emission
Population synthesis is used to study the contribution from undetected
sources to the Galactic ridge emission measured by EGRET. Synthesized source
counts are compared with the 3rd EGRET catalogue at low and high latitudes. For
pulsar-like populations, 5-10% of the emission >100 MeV comes from sources
below the EGRET threshold. A steeper luminosity function can increase this to
20% without violating EGRET source statistics. Less luminous populations can
produce much higher values without being detected. Since the unresolved source
spectrum is different from the interstellar spectrum, it could provide an
explanation of the observed MeV and GeV excesses above the predictions, and we
give an explicit example of how this could work.Comment: Astrophysics and Space Science, in press. (Proceedings of Conference
'The multi-messenger approach to high-energy gamma-ray sources', Barcelona,
2006). Minor changes for accepted version, updated reference
Astrophysical S-factor of the Be(B reaction from Coulomb dissociation of B
The Coulomb dissociation method to obtain the astrophysical S-factor,
, for the Be(B reaction at solar energies is
investigated by analysing the recently measured data on the breakup reaction
PbB,BePb at 46.5 MeV/A beam energy. Breakup cross
sections corresponding to E1, and transitions are calculated with a
theory of Coulomb excitation that includes the effects of the Coulomb recoil as
well as relativistic retardation. The interplay of nuclear and Coulomb
contributions to the breakup process is studied by performing a full quantum
mechanical calculation within the framework of the distorted-wave Born
Approximation. In the kinematical regime of the present experiment, both
nuclear as well as Coulomb-nuclear interference processes affect the pure
Coulomb breakup cross sections very marginally. The cross sections are
strongly dependent on the model used to describe the structure of B. The
value of is deduced with and without and contributions
added to the cross sections and the results are discussed.Comment: 10 pages, with 4 figures included with psfig; Physics Letters B, in
pres
Endothelial function and insulin sensitivity during acute non-esterified fatty acid elevation: effects of fat composition and gender
Background and Aims: We have reported that adverse effects on flow-mediated dilation of an acute elevation of non-esterified fatty acids rich in saturated fat (SFA) are reversed following addition of long-chain (LC) n-3 polyunsaturated fatty acids (PUFA), and hypothesised that these effects may be mediated through alterations in insulin signalling pathways. In a subgroup, we explored the effects of raised NEFA enriched with SFA, with or without LC n-3 PUFA, on whole body insulin sensitivity (SI) and responsiveness of the endothelium to insulin infusion.
Methods and Results: Thirty adults (mean age 27.8 y, BMI 23.2 kg/m2) consumed oral fat loads on separate occasions with continuous heparin infusion to elevate NEFA between 60-390 min. For the final 150 min, a hyperinsulinaemic-euglycaemic clamp was performed, whilst FMD and circulating markers of endothelial function were measured at baseline, pre-clamp (240 min) and post-clamp (390 min). NEFA elevation during the SFA-rich drinks was associated with impaired FMD (P=0.027) whilst SFA+LC n-3 PUFA improved FMD at 240 min (P=0.003). In males, insulin infusion attenuated the increase in FMD with SFA+LC n-3 PUFA (P=0.049), with SI 10% greater with SFA+LC n-3 PUFA than SFA (P=0.041).
Conclusion: This study provides evidence that NEFA composition during acute elevation influences both FMD and SI, with some indication of a difference by gender. However our findings are not consistent with the hypothesis that the effects of fatty acids on endothelial function and SI operate through a common pathway.
Trial registered at clinicaltrials.gov, NCT01351324
Binding of Nucleobases with Single-Walled Carbon Nanotubes
We have calculated the binding energy of various nucleobases (guanine (G),
adenine (A), thymine (T) and cytosine (C)) with (5,5) single-walled carbon
nanotubes (SWNTs) using ab-initio Hartre-Fock method (HF) together with force
field calculations. The gas phase binding energies follow the sequence G A
T C. We show that main contribution to binding energy comes from
van-der Wall (vdW) interaction between nanotube and nucleobases. We compare
these results with the interaction of nucleobases with graphene. We show that
the binding energy of bases with SWNTs is much lower than the graphene but the
sequence remains same. When we include the effect of solvation energy
(Poisson-Boltzman (PB) solver at HF level), the binding energy follow the
sequence G T A C , which explains the experiment\cite{zheng}
that oligonucleotides made of thymine bases are more effective in dispersing
the SWNT in aqueous solution as compared to poly (A) and poly (C). We also
demonstrate experimentally that there is differential binding affinity of
nucleobases with the single-walled carbon nanotubes (SWNTs) by directly
measuring the binding strength using isothermal titration (micro) calorimetry.
The binding sequence of the nucleobases varies as thymine (T) adenine (A)
cytosine (C), in agreement with our calculation.Comment: 7 pages, 6 figure
Effective Electromagnetic Lagrangian at Finite Temperature and Density in the Electroweak Model
Using the exact propagators in a constant magnetic field, the effective
electromagnetic Lagrangian at finite temperature and density is calculated to
all orders in the field strength B within the framework of the complete
electroweak model, in the weak coupling limit. The partition function and free
energy are obtained explicitly and the finite temperature effective coupling is
derived in closed form. Some implications of this result, potentially
interesting to astrophysics and cosmology, are discussed.Comment: 14 pages, Revtex
Structural studies of thermal- and light- induced transitions in iron(II) spin-crossover complexes
Investigation of the Neutron Form Factors by Inclusive Quasi-Elastic Scattering of Polarized Electrons off Polarized He: A Theoretical Overview
The theory of quasi-elastic inclusive scattering of polarized leptons off
polarized He is critically reviewed and the origin of different expressions
for the polarized nuclear response function appearing in the literature is
explained. The sensitivity of the longitudinal asymmetry upon the neutron form
factors is thoroughly investigated and the role played by the polarization
angle for minimizing the proton contribution is illustrated.Comment: Phys. Rev C in press; 9 figs. (available upon request
Instabilities in the Flux Line Lattice of Anisotropic Superconductors
The stability of the flux line lattice has been investigated within
anisotropic London theory. This is the first full-scale investigation of
instabilities in the `chain' state. It has been found that the lattice is
stable at large fields, but that instabilities occur as the field is reduced.
The field at which these instabilities first arise, ,
depends on the anisotropy and the angle at which the
lattice is tilted away from the -axis. These instabilities initially occur
at wavevector , and the component of along the
average direction of the flux lines, , is always finite. As the
instability occurs at finite the dependence of the cutoff on is
important, and we have used a cutoff suggested by Sudb\ospace and Brandt. The
instabilities only occur for values of the anisotropy appropriate to
a material like BSCCO, and not for anisotropies more appropriate to YBCO. The
lower critical field is calculated as a function of the angle
at which the applied field is tilted away from the crystal axis. The
presence of kinks in is seen to be related to instabilities in
the equilibrium flux line structure.Comment: Extensively revised paper, with modified analysis of elastic
instabilities. Calculation of the lower critical field is included, and the
presence of kinks in is seen to be related to the elastic
instabilities. 29 pages including 16 figures, LaTeX with epsf styl
A gamma- and X-ray detector for cryogenic, high magnetic field applications
As part of an experiment to measure the spectrum of photons emitted in
beta-decay of the free neutron, we developed and operated a detector consisting
of 12 bismuth germanate (BGO) crystals coupled to avalanche photodiodes (APDs).
The detector was operated near liquid nitrogen temperature in the bore of a
superconducting magnet and registered photons with energies from 5 keV to 1000
keV. To enlarge the detection range, we also directly detected soft X-rays with
energies between 0.2 keV and 20 keV with three large area APDs. The
construction and operation of the detector is presented, as well as information
on operation of APDs at cryogenic temperatures
Second harmonics and compensation effect in ceramic superconductors
A three-dimensional lattice of the Josephson junctions with a finite
self-conductance is employed to model the ceramic superconductors. The
nonlinear ac susceptibility and the compensation effect are studied by Monte
Carlo simulations in this model. The compensation effect is shown to be due to
the existence of the chiral glass phase. We demonstrate, in agreement with
experiments, that this effect may be present in the ceramic superconductors
which show the paramagnetic Meissner effect.Comment: 6 pages, latex, 4 figures, Phys. Rev. B (accepted
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