1,824 research outputs found
Proximity effect on hydrodynamic interaction between a sphere and a plane measured by Force Feedback Microscopy at different frequencies
In this article, we measure the viscous damping and the associated
stiffness of a liquid flow in sphere-plane geometry in a large frequency
range. In this regime, the lubrication approximation is expected to dominate.
We first measure the static force applied to the tip. This is made possible
thanks to a force feedback method. Adding a sub-nanometer oscillation of the
tip, we obtain the dynamic part of the interaction with solely the knowledge of
the lever properties in the experimental context using a linear transformation
of the amplitude and phase change. Using a Force Feedback Microscope (FFM)we
are then able to measure simultaneously the static force, the stiffness and the
dissipative part of the interaction in a broad frequency range using a single
AFM probe. Similar measurements have been performed by the Surface Force
Apparatus with a probe radius hundred times bigger. In this context the FFM can
be called nano-SFA
Continuous atom laser with Bose-Einstein condensates involving three-body interactions
We demonstrate, through numerical simulations, the emission of a coherent
continuous matter wave of constant amplitude from a Bose-Einstein Condensate in
a shallow optical dipole trap. The process is achieved by spatial control of
the variations of the scattering length along the trapping axis, including
elastic three body interactions due to dipole interactions. In our approach,
the outcoupling mechanism are atomic interactions and thus, the trap remains
unaltered. We calculate analytically the parameters for the experimental
implementation of this CW atom laser.Comment: 11 pages, 4 figure
Cross-Over between universality classes in a magnetically disordered metallic wire
In this article we present numerical results of conduction in a disordered
quasi-1D wire in the possible presence of magnetic impurities. Our analysis
leads us to the study of universal properties in different conduction regimes
such as the localized and metallic ones. In particular, we analyse the
cross-over between universality classes occurring when the strength of magnetic
disorder is increased. For this purpose, we use a numerical Landauer approach,
and derive the scattering matrix of the wire from electron's Green's function.Comment: Final version, accepted for publication in New Journ. of Physics, 27
pages, 28 figures. Replaces the earlier shorter preprint arXiv:0910.427
Extreme Value Statistics and Traveling Fronts: Various Applications
An intriguing connection between extreme value statistics and traveling
fronts has been found recently in a number of diverse problems. In this brief
review we outline a few such problems and consider their various applications.Comment: A brief review (6 pages, 2 figures) to appear in Physica A as part of
the proceedings of Statphys-Kolkata IV (2002
Analysis of an atom laser based on the spatial control of the scattering length
In this paper we analyze atom lasers based on the spatial modulation of the
scattering length of a Bose-Einstein Condensate. We demonstrate, through
numerical simulations and approximate analytical methods, the controllable
emission of matter-wave bursts and study the dependence of the process on the
spatial dependence of the scattering length along the axis of emission. We also
study the role of an additional modulation of the scattering length in time.Comment: Submitted to Phys. Rev.
Freezing transitions and the density of states of 2D random Dirac Hamiltonians
Using an exact mapping to disordered Coulomb gases, we introduce a novel
method to study two dimensional Dirac fermions with quenched disorder in two
dimensions which allows to treat non perturbative freezing phenomena. For
purely random gauge disorder it is known that the exact zero energy eigenstate
exhibits a freezing-like transition at a threshold value of disorder
. Here we compute the dynamical exponent which
characterizes the critical behaviour of the density of states around zero
energy, and find that it also exhibits a phase transition. Specifically, we
find that (and ) with for and
for . For a finite system size we find large
sample to sample fluctuations with a typical .
Adding a scalar random potential of small variance , as in the
corresponding quantum Hall system, yields a finite noncritical whose scaling exponent exhibits two transitions, one
at and the other at . These transitions are shown
to be related to the one of a directed polymer on a Cayley tree with random
signs (or complex) Boltzmann weights. Some observations are made for the strong
disorder regime relevant to describe transport in the quantum Hall system
Quantification and identification of allele specific proteins for polyploidnon-model crops: Proof of principle for 3 banana genotypes/phenotypes
Reconstruction of the Water-Oxidizing Complex in Manganese-Depleted Photosystem II Preparations Using Mononuclear Manganese Complexes
Increasing of entanglement entropy from pure to random quantum critical chains
It is known that the entropy of a block of spins of size embedded in an
infinite pure critical spin chain diverges as the logarithm of with a
prefactor fixed by the central charge of the corresponding conformal field
theory. For a class of strongly random spin chains, it has been shown that the
correspondent block entropy still remains universal and diverges
logarithmically with an "effective" central charge. By computing the
entanglement entropy for a family of models which includes the -states
random Potts chain and the clock model, we give some definitive answer to
some recent conjectures about the behaviour of the effective central charge. In
particular, we show that the ratio between the entanglement entropy in the pure
and in the disordered system is model dependent and we provide a series of
critical models where the entanglement entropy grows from the pure to the
random case.Comment: 4 pages, 2 eps figures, added reference
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