8,332 research outputs found
Factors Associated with Blockages to Outdoor Recreation Participation: A State Survey
Data from a random sample of Ohio residents were used in an attempt to isolate factors that were hypothesized to be related to outdoor recreation blockages. The study revealed that socio-demographic variables failed to explain the variance in factor scores created to measure blockages to outdoor recreation. Findings from descriptive statistics and the factor analyses are discussed in a planning context
Vortex spectrum in superfluid turbulence: interpretation of a recent experiment
We discuss a recent experiment in which the spectrum of the vortex line
density fluctuations has been measured in superfluid turbulence. The observed
frequency dependence of the spectrum, , disagrees with classical
vorticity spectra if, following the literature, the vortex line density is
interpreted as a measure of the vorticity or enstrophy. We argue that the
disagrement is solved if the vortex line density field is decomposed into a
polarised field (which carries most of the energy) and an isotropic field
(which is responsible for the spectrum).Comment: Submitted for publication
http://crtbt.grenoble.cnrs.fr/helio/GROUP/infa.html
http://www.mas.ncl.ac.uk/~ncfb
Polarization of superfluid turbulence
We show that normal fluid eddies in turbulent helium II polarize the tangle
of quantized vortex lines present in the flow, thus inducing superfluid
vorticity patterns similar to the driving normal fluid eddies. We also show
that the polarization is effective over the entire inertial range. The results
help explain the surprising analogies between classical and superfluid
turbulence which have been observed recently.Comment: 3 figure
Linking Classical and Quantum Key Agreement: Is There "Bound Information"?
After carrying out a protocol for quantum key agreement over a noisy quantum
channel, the parties Alice and Bob must process the raw key in order to end up
with identical keys about which the adversary has virtually no information. In
principle, both classical and quantum protocols can be used for this
processing. It is a natural question which type of protocols is more powerful.
We prove for general states but under the assumption of incoherent
eavesdropping that Alice and Bob share some so-called intrinsic information in
their classical random variables, resulting from optimal measurements, if and
only if the parties' quantum systems are entangled. In addition, we provide
evidence that the potentials of classical and of quantum protocols are equal in
every situation. Consequently, many techniques and results from quantum
information theory directly apply to problems in classical information theory,
and vice versa. For instance, it was previously believed that two parties can
carry out unconditionally secure key agreement as long as they share some
intrinsic information in the adversary's view. The analysis of this purely
classical problem from the quantum information-theoretic viewpoint shows that
this is true in the binary case, but false in general. More explicitly, bound
entanglement, i.e., entanglement that cannot be purified by any quantum
protocol, has a classical counterpart. This "bound intrinsic information"
cannot be distilled to a secret key by any classical protocol. As another
application we propose a measure for entanglement based on classical
information-theoretic quantities.Comment: Accepted for Crypto 2000. 17 page
Quantum turbulence at finite temperature: the two-fluids cascade
To model isotropic homogeneous quantum turbulence in superfluid helium, we
have performed Direct Numerical Simulations (DNS) of two fluids (the normal
fluid and the superfluid) coupled by mutual friction. We have found evidence of
strong locking of superfluid and normal fluid along the turbulent cascade, from
the large scale structures where only one fluid is forced down to the vorticity
structures at small scales. We have determined the residual slip velocity
between the two fluids, and, for each fluid, the relative balance of inertial,
viscous and friction forces along the scales. Our calculations show that the
classical relation between energy injection and dissipation scale is not valid
in quantum turbulence, but we have been able to derive a temperature--dependent
superfluid analogous relation. Finally, we discuss our DNS results in terms of
the current understanding of quantum turbulence, including the value of the
effective kinematic viscosity
Evaporation of a packet of quantized vorticity
A recent experiment has confirmed the existence of quantized turbulence in
superfluid He3-B and suggested that turbulence is inhomogenous and spreads away
from the region around the vibrating wire where it is created. To interpret the
experiment we study numerically the diffusion of a packet of quantized vortex
lines which is initially confined inside a small region of space. We find that
reconnections fragment the packet into a gas of small vortex loops which fly
away. We determine the time scale of the process and find that it is in order
of magnitude agreement with the experiment.Comment: figure 1a,b,c and d, figure2, figure
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