Search results for "relation"

Nonequilibrium effective temperature of superfluid vortex tangle

2006

An effective nonequilibrium temperature in counterflow superfluid turbulence is proposed, as a parameter characterizing a canonical probability distribution function of vortex orientation, and relating the diffusion coefficient of vortex lines to the vortex friction through an Einstein relation.

New expressions for string loop amplitudes leading to an ultrasimple conception of string dynamics

1991

New expressions are derived for string loop amplitudes as overlap integrals of string wave functionals. They are shown to take the form of exchange terms coming from the Bose-Einstein symmetrization between string segments. One is thus led to the ultrasimple conception that string theory is basically free, and that ``string interactions'' are merely due to the fact that strings are composite objects with Bose-Einstein segments as constituents.

Laser-induced collective excitations in a two-component Fermi gas

2002

We consider the linear density response of a two-component (superfluid) Fermi gas of atoms when the perturbation is caused by laser light. We show that various types of laser excitation schemes can be transformed into linear density perturbations, however, a Bragg spectroscopy scheme is needed for transferring energy and momentum into a collective mode. This makes other types of laser probing schemes insensitive for collective excitations and therefore well suited for the detection of the superfluid order parameter. We show that for the special case when laser light is coupled between the two components of the Fermi gas, density response is always absent in a homogeneous system.

2021

Previously, rotons were observed in correlated quantum systems at low temperatures, including superfluid helium and Bose-Einstein condensates. Here, following a recent theoretical proposal, we repo...

Bose-Einstein correlations in W-pair decays

2000

Bose-Einstein correlations are studied in semileptonic (WW --> q (q) over bar lv) and fully hadronic (WW --> q (q) over bar q (q) over bar) W-pair decays with the ALEPH detector at LEP at centre-of-mass energies of 172, 183 and 189 GeV. They are compared with those made at the Z peak after correction for the different flavour compositions. A Monte Carlo model of Bose-Einstein correlations based on the JETSET hadronization scheme was tuned to the Z data and reproduces the correlations in the WW --> q (q) over bar lv events. The same Monte Carlo reproduces the correlations in the WW --> q (q) over bar q (q) over bar channel assuming independent fragmentation of the two W's. A variant of this …

Approaching the limits of multiple scattering decorrelation: 3D light-scattering apparatus utilising semiconductor lasers

2007

Light scattering as a function of scattering angle can be regarded as a standard method to investigate the dynamics of dilute colloidal suspensions. Concentrated suspensions, which are of interest if interactions between the particles are to be investigated, usually show strong multiple scattering. Decorrelation of multiple scattered light, which isolates single scattering events at the expense of a reduced signal-to-noise ratio, has been proven to work using the two-colour crosscorrelation scheme.

The interplay between wetting and phase behaviour in binary polymer films and wedges: Monte Carlo simulations and mean field calculations

2005

By confining a binary mixture, one can profoundly alter its miscibility behaviour. The qualitative features of miscibility in confined geometry are rather universal and are shared by polymer mixtures as well as small molecules, but the unmixing transition in the bulk and the wetting transition are typically well separated in polymer blends. We study the interplay between wetting and miscibility of a symmetric polymer mixture via large scale Monte Carlo simulations in the framework of the bond fluctuation model and via numerical self-consistent field calculations. The film surfaces interact with the monomers via short-ranged potentials, and the wetting transition of the semi-infinite system …

Raman Scattering in CuCl under Pressure

1999

Raman spectra of CuCl were measured under hydrostatic pressures up to 14 GPa at low temperatures (T = 5 K). The anomaly in the Raman lineshape of zincblende CuCl at frequencies near the transverse-optic (TO) mode, which consists of a broad structure with several maxima, disappears at a pressure near 3 GPa. This effect is well reproduced by a model calculation of the anharmonic coupling of the TO mode to acoustic two-phonon states (Fermi resonance). Alternative interpretations of the TO Raman anomaly in terms of local vibrational modes of Cu atoms in off-center positions are not supported by the present results. Raman spectra indicate the existence of the phase CuCl-IIa in a narrow pressure …

Testing Mode-Coupling Theory for a Supercooled Binary Lennard-Jones Mixture I: The van Hove Correlation Function

1995

We report the results of a large scale computer simulation of a binary supercooled Lennard-Jones liquid. We find that at low temperatures the curves for the mean squared displacement of a tagged particle for different temperatures fall onto a master curve when they are plotted versus rescaled time $tD(T)$, where $D(T)$ is the diffusion constant. The time range for which these curves follow the master curve is identified with the $\alpha$-relaxation regime of mode-coupling theory (MCT). This master curve is fitted well by a functional form suggested by MCT. In accordance with idealized MCT, $D(T)$ shows a power-law behavior at low temperatures. The critical temperature of this power-law is t…

Calculations of the atomic and electronic structure for SrTiO3 perovskite thin films

2001

The results of calculations of SrTiO3 (100) surface relaxation and rumpling with two different terminations (SrO and TiO2) are presented and discussed. We have used the ab initio Hartree–Fock (HF) method with electron correlation corrections and the density functional theory (DFT) with different exchange–correlation functionals, including hybrid exchange techniques. All methods agree well on surface energies and on atomic displacements, as well as on the considerable increase of covalency effects near the surface. More detailed experiments on surface rumpling and relaxation are necessary for further testing of theoretical predictions.