9,901 research outputs found
Study of quantum current enhancement, eigenenergy spectra and magnetic moments in a multiply connected system at equilibrium
A multiply connected system in both its open and closed form variations but
in equilibrium is studied using quantum waveguide theory. The system exhibits
remarkable features, in its open form variation we see current enhancement,
hitherto seen only in non-equilibrium systems in absence of magnetic flux. In
its closed form analog parity effects are broken. Further we analyse the global
and local current densities of our system and also show that the orbital
magnetic response of the system calculated from the current densities (and
inherently linked to the topological configuration) is qualitatively not same
as that calculated from the eigenenergy spectra.Comment: 10 pages, 15 figures, 3 table
Tetrahydrobiopterin analogues with NO-dependent pulmonary vasodilator properties
Reduced NO levels due to the deficiency of tetrahydrobiopterin (BH4) contribute to impaired vasodilation in pulmonary hypertension Due to the chemically unstable nature of BH4 it was hypothesised that oxidatively stable analogues of BR, would be able to support NO synthesis to improve Endothelial dysfunction in pulmonary hypertension Two analogues of BH4 namely 6-hydroxymethyl pterin (HMP) and 6-acetyl 7 7-dimethyl 7 8-dihydropterin (ADDP) were evaluated for vasodilator activity on precontracted rat pulmonary artery rings ADDP was administered to pulmonary hypertensive rats followed by measurement of pulmonary vascular resistance in perfused lungs and eNOS expression by immunohistochemistry ADDP and HMP caused significant relaxation in vitro in rat pulmonary arteries depleted of BH4 with a maximum relaxation at 0 3 mu M (both P<005) Vasodilator activity of ADDP and HMP was completely abolished following preincubation with the NO synthase inhibitor L-NAME ADDP and HMP did not alter relaxation induced by carbachol or spermine NONOate BH4 Itself did not produce relaxation In rats receiving ADDP 141 mg/kg/day pulmonary vasodilation induced by calcium ionophore A23187 was augmented and eNOS immunoreactivity was increased In conclusion ADDP and HMP are two analogues of BH4 which can act as oxidatively stable alternatives to BH4 in causing NO-mediated vasorelaxation Chronic treatment with ADDP resulted in Improvement of NO-mediated pulmonary artery dilation and enhanced expression of eNOS in the pulmonary vascular endothelium Chemically stable analogue, of BH4 may be able to limit endothelial dysfunction in the pulmonary vasculatur
Self-organization of charge under pressure in the organic conductor (TMTSF)2ReO4
(TMTSF)2ReO4 presents a phase coexistence between two anion orderings defined
by their wave vectors q_2=(1/2,1/2,1/2) and q_3=(0,1/2,1/2) in a wide range of
pressure (8-11kbar) and temperature. From the determination of the anisotropy
of the conductivity and the superconducting transitions in this regime we were
able to extract the texture which results from a self-organization of the
orientations of the ReO4 anions in the sample. At the lowest pressures, the
metallic parts, related to the q_3 order, form droplets elongated along the
a-axis embedded in the semiconducting matrix associated with the q_2 order.
Above 10kbar, filaments along the a-axis extend from one end of the sample to
the other nearly up to the end of the coexistence regime. A mapping of the
system into an anisotropic Ising lattice is satisfactory to analyze the data.
satisfactory to analyze the data.Comment: 7 pages, 3 figures, EPL forma
The Global Structure and Evolution of a Self-Gravitating Multi-phase Interstellar Medium in a Galactic Disk
Using high resolution, two-dimensional hydrodynamical simulations, we
investigate the evolution of a self-gravitating multi-phase interstellar medium
in the central kiloparsec region of a galactic disk. We find that a
gravitationally and thermally unstable disk evolves, in a self-stabilizing
manner, into a globally quasi-stable disk that consists of cold (T < 100 K),
dense clumps and filaments surrounded by hot (T > 10^4 K), diffuse medium. The
quasi-stationary, filamentary structure of the cold gas is remarkable. The hot
gas, characterized by low-density holes and voids, is produced by shock
heating. The shocks derive their energy from differential rotation and
gravitational perturbations due to the formation of cold dense clumps. In the
quasi-stable phase where cold and dense clouds are formed, the effective
stability parameter, Q, has a value in the range 2-5. The dynamic range of our
multi-phase calculations is 10^6 - 10^7 in both density and temperature. Phase
diagrams for this turbulent medium are analyzed and discussed.Comment: 10 pages, 3 figures, ApJ Letters in press (vol. 516
Upper critical field divergence induced by mesoscopic phase separation in the organic superconductor (TMTSF)2ReO4
Due to the competition of two anion orders, (TMTSF)2ReO4, presents a phase
coexistence between semiconducting and metallic (superconducting) regions
(filaments or droplets) in a wide range of pressure. In this regime, the
superconducting upper critical field for H parallel to both c* and b' axes
present a linear part at low fields followed by a divergence above a cross-over
field. This cross-over corresponds to the 3D-2D decoupling transition expected
in filamentary or granular superconductors. The sharpness of the transition
also demonstrates that all filaments are of similar sizes and self organize in
a very ordered way. The distance between the filaments and their cross-section
are estimated.Comment: 4 pages, 4 figure
Mesoscopic correlations in Tb2Ti2O7 spin liquid
We have studied the spin correlations with = (, ,
) propagation vector which appear below 0.4\, K in \tbti\ spin liquid
by combining powder neutron diffraction and specific heat on
TbTiO samples with =0, 0.01, -0.01. The =
(, , ) order clearly appears on all neutron patterns
by subtracting a pattern at 1.2(1)\,K. Refining the subtracted patterns at
0.07\,K yields two possible spin structures, with spin-ice-like and
monopole-like correlations respectively. Mesoscopic correlations involve Tb
moments of 1 to 2 \mub\ ordered on a length scale of about 20 \AA. In addition,
long range order involving a small spin component of 0.1 to 0.2 \mub\ is
detected for the = 0 and 0.01 samples showing a peak in the specific heat.
Comparison with previous single crystals data suggests that the (,
, ) order settles in through nanometric spin textures with
dominant spin ice character and correlated orientations, analogous to
nanomagnetic twins
Optimization of large homogeneous air Cherenkov arrays and application to the design of a 1TeV-100TeV gamma-ray observatory
At the time large air Cherenkov arrays are being discussed for future
gamma-ray observatories, we review the relationship between the targeted
capabilities and the main design parameters taking into account construction
costs. As an example application, we describe a telescope array optimized for
observations between 1 TeV and a few 100 TeV and use detailed simulations to
estimate its performances in comparison to science objectives.Comment: 23 pages, 16 figures, accepted for publication in Astroparticle
Physic
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