30,530 research outputs found
Long-Range Order and Dynamic Structure Factor of a Nematic under a Thermal Gradient
We use a fluctuating hydrodynamic approach to calculate the orientation
fluctuations correlation functions of a thermotropic nematic liquid crystal in
a nonequilibrium state induced by a stationay heat flux. Since in this
nonequilibrium stationary state the hydrodynamic fluctuations evolve on three
widely separated times scales, we use a time-scale perturbation procedure in
order to partially diagonalize the hydrodynamic matrix. The wave number and
frequency dependence of these orientation correlation functions is evaluated
and their explicit functional form on position is also calculated analytically
in and out of equilibrium. We show that for both states these correlactions are
long-ranged. This result shows that indeed, even in equilibrium there is
long-range orientational order in the nematic, consistently with the well known
properties of these systems.We also calculate the dynamic structure of the
fluid in both states for a geometry consistent with light scattering
experiments experiments. We find that as with isotropic simple fluids, the
external temperature gradient introduces an asymmetry in the spectrum shifting
its maximum by an amount proportional to the magnitude of the gradient. This
effect may be of the order of 7 per cent. Also, the width at half height may
decrease by a factor of about 10 per cent. Since to our knowledge there are no
experimental results available in the literature to compare with, the
predictions of our model calculation remains to be assessed.Comment: 11 pages, 3 figures, presented at the 3rd NEXT-SigmaPhi International
Conference (13-18 August 2005, Kolymbari CRETE
Solution to the Landau-Zener problem via Susskind-Glogower operators
We show that, by means of a right-unitary transformation, the fully quantized
Landau-Zener Hamiltonian in the weak-coupling regime may be solved by using
known solutions from the standard Landau-Zener problem. In the strong-coupling
regime, where the rotating wave approximation is not valid, we show that the
quantized Landau-Zener Hamiltonian may be diagonalized in the atomic basis by
means of a unitary transformation; hence allowing numerical solutions for the
few photons regime via truncation.Comment: 6 pages, 5 figure
Pion's valence-quark GPD and its extension beyond DGLAP region
We briefly report on a recent computation, with the help of a fruitful
algebraic model, sketching the pion valence dressed-quark generalized parton
distribution and, very preliminary, discuss on a possible avenue to get
reliable results in both Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and
Efremov-Radyushkin-Brodsky-Lepage (ERBL) kinematial regions.Comment: 6 pages, 4 figures, contribution to 21st International conference on
Few-Body Problem
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