2,821 research outputs found
Dynamics and interactions of active rotors
We consider a simple model of an internally driven self-rotating object; a
rotor, confined to two dimensions by a thin film of low Reynolds number fluid.
We undertake a detailed study of the hydrodynamic interactions between a pair
of rotors and find that their effect on the resulting dynamics is a combination
of fast and slow motions. We analyse the slow dynamics using an averaging
procedure to take account of the fast degrees of freedom. Analytical results
are compared with numerical simulations. Hydrodynamic interactions mean that
while isolated rotors do not translate, bringing together a pair of rotors
leads to motion of their centres. Two rotors spinning in the same sense rotate
with an approximately constant angular velocity around each other, while two
rotors of opposite sense, both translate with the same constant velocity, which
depends on the separation of the pair. As a result a pair of counter-rotating
rotors are a promising model for controlled self-propulsion.Comment: 6 pages, 6 figure
Finite-temperature effects in helical quantum turbulence
We perform a study of the evolution of helical quantum turbulence at different temperatures by solving numerically the Gross-Pitaevskii and the stochastic Ginzburg-Landau equations, using up to 40963 grid points with a pseudospectral method. We show that for temperatures close to the critical one, the fluid described by these equations can act as a classical viscous flow, with the decay of the incompressible kinetic energy and the helicity becoming exponential. The transition from this behavior to the one observed at zero temperature is smooth as a function of temperature. Moreover, the presence of strong thermal effects can inhibit the development of a proper turbulent cascade. We provide Ansätze for the effective viscosity and friction as a function of the temperature.Fil: Clark Di Leoni, Patricio. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de FÃsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FÃsica de Buenos Aires; Argentina. University of Rome Tor Vergata; ItaliaFil: Mininni, Pablo Daniel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de FÃsica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de FÃsica de Buenos Aires; ArgentinaFil: Brachet, Marc E.. Universite Pierre et Marie Curie; Franci
Spatio-temporal detection of Kelvin waves in quantum turbulence simulations
We present evidence of Kelvin excitations in space-time resolved spectra of
numerical simulations of quantum turbulence. Kelvin waves are transverse and
circularly polarized waves that propagate along quantized vortices, for which
the restitutive force is the tension of the vortex line, and which play an
important role in theories of superfluid turbulence. We use the
Gross-Pitaevskii equation to model quantum flows, letting an initial array of
well-organized vortices develop into a turbulent bundle of intertwined vortex
filaments. By achieving high spatial and temporal resolution we are able to
calculate space-time resolved mass density and kinetic energy spectra. Evidence
of Kelvin and sound waves is clear in both spectra. Identification of the waves
allows us to extract the spatial spectrum of Kelvin waves, clarifying their
role in the transfer of energ
Spontaneous imbibition in a slit pore: a lattice-gas dynamic mean field study
We present a theoretical study of spontaneous imbibition in a slit pore using
a lattice-gas model and a dynamic mean-field theory. Emphasis is put on the
influence of the precursor films on the speed of the imbibition front due to
liquid mass conservation. This work is dedicated to Bob Evans for his 65th
birthday in recognition of his seminal contributions to the theory of fluids in
confining geometries.Comment: 17 pages, 13 figure
Insulator-Metal transition in the Doped 3d1 Transition Metal Oxide LaTiO3
The doping induced insulator-metal transition in is
studied using the ab-initio LDA+DMFT method. Combining the LDA bandstructure
for the actual, distorted structure found recently with multi-orbital DMFT to
treat electronic correlations, we find: ferro-orbital order in the Mott
insulating state without orbital degeneracy, a continuous filling
induced transition to the paramagnetic metal (PM) with , and
excellent quantitative agreement with published photoemission data for the case
of 6% doping. Our results imply that this system can be described as a
Mott-Hubbard system without orbital (liquid) degeneracy.Comment: 4 pages, 3 figures, submitted to PR
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