7,537 research outputs found
Vortex density spectrum of quantum turbulence
The fluctuations of the vortex density in a turbulent quantum fluid are
deduced from local second-sound attenuation measurements. These measurements
are performed with a micromachined open-cavity resonator inserted across a flow
of turbulent He-II near 1.6 K. The power spectrum of the measured vortex line
density is compatible with a (-5/3) power law. The physical interpretation,
still open, is discussed.Comment: Submitted to Europhys. Let
Prevention of pressure build-up in electrochemical cells Patent
Preventing pressure buildup in electrochemical cells by reacting palladium oxide with evolved hydroge
Stationary and non-stationary fluid flow of a Bose-Einstein condensate through a penetrable barrier
We experimentally study the fluid flow induced by a broad, penetrable barrier
moving through an elongated dilute gaseous Bose-Einstein condensate. The
barrier is created by a laser beam swept through the condensate, and the
resulting dipole potential can be either attractive or repulsive. We examine
both cases and find regimes of stable and unstable fluid flow: At slow speeds
of the barrier, the fluid flow is stationary due to the superfluidity of the
condensate. At intermediate speeds, we observe a non-stationary regime in which
the condensate gets filled with dark solitons. At faster speeds, soliton
formation completely ceases and a remarkable absence of excitation in the
condensate is seen again.Comment: 4 pages, 4 figure
An abstract formulation of the concept of entropy
Entropy is presented as a concave function relating two sets of quantities called densities and field. It allows a simple classification of the standard relations of classical thermodynamics and yields a simple derivation of the conditions for concavity of the entropy function. It also allows a formal derivation of the equations of fluid motion. Dissipation, mixtures, and phase changes may also be included in the theory in a natural manner
Some exact solutions in moving finite elements
It is shown that when the moving finite elements are used on a number of parabolic problems there are steady-state, stationary, similarity, or travelling-wave solutions that can be found numerically
Spontaneous squeezing of a vortex in an optical lattice
We study the equilibrium states of a vortex in a Bose-Einstein condensate in
a one-dimensional optical lattice. We find that quantum effects can be
important and that it is even possible for the vortex to be strongly squeezed,
which reflects itself in a different quantum mechanical uncertainty of the
vortex position in two orthogonal directions. The latter is observable by
measuring the atomic density after an expansion of the Bose-Einstein condensate
in the lattice.Comment: 8 pages, 3 figures, more details added, some new citation
Pseudo-contact angle due to superfluid vortices in He
We have investigated spreading of superfluid He on top of polished
MgF and evaporated SiO substrates. Our results show strongly varying
contact angles of 0 - 15 mrad on the evaporated layers. According to our
theoretical calculations, these contact angles can be explained by a spatially
varying distribution of vortex lines, the unpinning velocity of which is
inversely proportional to the liquid depth.Comment: 10 pages, 4 figure
Coherence vortices in one spatial dimension
Coherence vortices are screw-type topological defects in the phase of
Glauber's two-point degree of quantum coherence, associated with pairs of
spatial points at which an ensemble-averaged stochastic quantum field is
uncorrelated. Coherence vortices may be present in systems whose dimensionality
is too low to support spatial vortices. We exhibit lattices of such
quantum-coherence phase defects for a one-dimensional model quantum system. We
discuss the physical meaning of coherence vortices and propose how they may be
realized experimentally.Comment: 5 pages, 3 figure
Semi-inclusive charged-current neutrino-nucleus reactions
The general, universal formalism for semi-inclusive charged-current
(anti)neutrino-nucleus reactions is given for studies of any hadronic system,
namely, either nuclei or the nucleon itself. The detailed developments are
presented with the former in mind and are further specialized to cases where
the final-state charged lepton and an ejected nucleon are presumed to be
detected. General kinematics for such processes are summarized and then
explicit expressions are developed for the leptonic and hadronic tensors
involved and for the corresponding responses according to the usual charge,
longitudinal and transverse projections, keeping finite the masses of all
particles involved. In the case of the hadronic responses, general symmetry
principles are invoked to determine which contributions can occur. Finally, the
general leptonic-hadronic tensor contraction is given as well as the cross
section for the process
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