2,423 research outputs found
Rotation-induced 3D vorticity in 4He superfluid films adsorbed on a porous glass
Detailed study of torsional oscillator experiments under steady rotation up
to 6.28 rad/sec is reported for a 4He superfluid monolayer film formed in 1
micrometer-pore diameter porous glass. We found a new dissipation peak with the
height being in proportion to the rotation speed, which is located to the lower
temperature than the vortex pair unbinding peak observed in the static state.
We propose that 3D coreless vortices ("pore vortices") appear under rotation to
explain this new peak. That is, the new peak originates from dissipation close
to the pore vortex lines, where large superfluid velocity shifts the vortex
pair unbinding dissipation to lower temperature. This explanation is confirmed
by observation of nonlinear effects at high oscillation amplitudes.Comment: 4pages, 5figure
Kinetic energy of solid neon by Monte Carlo with improved Trotter- and finite-size extrapolation
The kinetic energy of solid neon is calculated by a path-integral Monte Carlo
approach with a refined Trotter- and finite-size extrapolation. These accurate
data present significant quantum effects up to temperature T=20 K. They confirm
previous simulations and are consistent with recent experiments.Comment: Text and figures revised for minor corrections (4 pages, 3 figures
included by psfig
Search for supersolidity in 4He in low-frequency sound experiments
We present results of the search for supersolid 4He using low-frequency,
low-level mechanical excitation of a solid sample grown and cooled at fixed
volume. We have observed low frequency non-linear resonances that constitute
anomalous features. These features, which appear below about 0.8 K, are absent
in 3He. The frequency, the amplitude at which the nonlinearity sets in, and the
upper temperature limit of existence of these resonances depend markedly on the
sample history.Comment: Submitted to the Quantum Fluids and Solids Conf. Aug. 2006 Kyot
Characterizing correlations of flow oscillations at bottlenecks
"Oscillations" occur in quite different kinds of many-particle-systems when
two groups of particles with different directions of motion meet or intersect
at a certain spot. We present a model of pedestrian motion that is able to
reproduce oscillations with different characteristics. The Wald-Wolfowitz test
and Gillis' correlated random walk are shown to hold observables that can be
used to characterize different kinds of oscillations
High-Efficiency Resonant RF Spin Rotator with Broad Phase Space Acceptance for Pulsed Polarized Cold Neutron Beams
We have developed a radio-frequency resonant spin rotator to reverse the
neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high
efficiency over a broad cold neutron energy range. The effect of the spin
reversal by the rotator on the neutron beam phase space is compared
qualitatively to RF neutron spin flippers based on adiabatic fast passage. The
spin rotator does not change the kinetic energy of the neutrons and leaves the
neutron beam phase space unchanged to high precision. We discuss the design of
the spin rotator and describe two types of transmission-based neutron spin-flip
efficiency measurements where the neutron beam was both polarized and analyzed
by optically-polarized 3He neutron spin filters. The efficiency of the spin
rotator was measured to be 98.0+/-0.8% on resonance for neutron energies from
3.3 to 18.4 meV over the full phase space of the beam. As an example of the
application of this device to an experiment we describe the integration of the
RF spin rotator into an apparatus to search for the small parity-violating
asymmetry A_gamma in polarized cold neutron capture on para-hydrogen by the
NPDGamma collaboration at LANSCE
New measurement of the scattering cross section of slow neutrons on liquid parahydrogen from neutron transmission
Liquid hydrogen is a dense Bose fluid whose equilibrium properties are both
calculable from first principles using various theoretical approaches and of
interest for the understanding of a wide range of questions in many body
physics. Unfortunately, the pair correlation function inferred from
neutron scattering measurements of the differential cross section from different measurements reported in the literature are
inconsistent. We have measured the energy dependence of the total cross section
and the scattering cross section for slow neutrons with energies between
0.43~meV and 16.1~meV on liquid hydrogen at 15.6~K (which is dominated by the
parahydrogen component) using neutron transmission measurements on the hydrogen
target of the NPDGamma collaboration at the Spallation Neutron Source at Oak
Ridge National Laboratory. The relationship between the neutron transmission
measurement we perform and the total cross section is unambiguous, and the
energy range accesses length scales where the pair correlation function is
rapidly varying. At 1~meV our measurement is a factor of 3 below the data from
previous work. We present evidence that these previous measurements of the
hydrogen cross section, which assumed that the equilibrium value for the ratio
of orthohydrogen and parahydrogen has been reached in the target liquid, were
in fact contaminated with an extra non-equilibrium component of orthohydrogen.
Liquid parahydrogen is also a widely-used neutron moderator medium, and an
accurate knowledge of its slow neutron cross section is essential for the
design and optimization of intense slow neutron sources. We describe our
measurements and compare them with previous work.Comment: Edited for submission to Physical Review
Proceedings of the second "international Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST'14)
The implicit objective of the biennial "international - Traveling Workshop on
Interactions between Sparse models and Technology" (iTWIST) is to foster
collaboration between international scientific teams by disseminating ideas
through both specific oral/poster presentations and free discussions. For its
second edition, the iTWIST workshop took place in the medieval and picturesque
town of Namur in Belgium, from Wednesday August 27th till Friday August 29th,
2014. The workshop was conveniently located in "The Arsenal" building within
walking distance of both hotels and town center. iTWIST'14 has gathered about
70 international participants and has featured 9 invited talks, 10 oral
presentations, and 14 posters on the following themes, all related to the
theory, application and generalization of the "sparsity paradigm":
Sparsity-driven data sensing and processing; Union of low dimensional
subspaces; Beyond linear and convex inverse problem; Matrix/manifold/graph
sensing/processing; Blind inverse problems and dictionary learning; Sparsity
and computational neuroscience; Information theory, geometry and randomness;
Complexity/accuracy tradeoffs in numerical methods; Sparsity? What's next?;
Sparse machine learning and inference.Comment: 69 pages, 24 extended abstracts, iTWIST'14 website:
http://sites.google.com/site/itwist1
Precision Measurement of PArity Violation in Polarized Cold Neutron Capture on the Proton: the NPDGamma Experiment
The NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE) is
dedicated to measure with high precision the parity violating asymmetry in the
emission after capture of spin polarized cold neutrons in
para-hydrogen. The measurement will determine unambiguously the weak
pion-nucleon-nucleon () coupling constant {\it f}Comment: Proceedings of the PANIC'05 Conference, Santa Fe, NM, USA, October
24-28, 2005, 3 pages, 2 figure
Hypoglycaemic unawareness: A systematic review of qualitative studies of significant others' (SO) supportive interventions for patients with diabetes mellitus
BackgroundHypoglycemia unawareness (HU) has been attributed to both a downward shift in central nervous system (CNS)-triggered sympatho-adrenal responses to low glycaemic thresholds and a subsequent loss of adrenergic symptoms, which, in addition, to cerebral cortex adaptations permit normal function under hypoglycaemic conditions. Both of these mechanisms are brought about by recurring hypoglycemic events (hypoglycemia-associate autonomic failure, HAAF). This can contribute to repetitive cycles of increasingly severe hypoglycaemia, the consequences of which have considerable impact on relatives and significant others (SO) when providing care to patients with diabetes.MethodsA Systematic Review (SR) of 639 qualitative studies was carried out in accordance with the Preferred Reporting Items for Systematic Review (PRISMA) principles. The search strategy was developed using MeSH terms for a range of electronic databases: CINAHL, Pubmed, EMBASE, Medline, AMED and ASSIA were systematically searched in order to identify a variety of literature relevant to the review topic. Four duplicate studies were removed and a further 630 studies were excluded due to being irrelevant. Five qualitative studies were retained and analysed.ResultsThe three resultant findings from the literature appraised were i) Experiences and views of Significant Others' (SO) with adult relatives that have HU ii) Support needs of SO and iii) Health professionals interventions to address SO support needs and improve overall HU care. A clear finding was that SO experience difficulties managing HU and this can impact on the relationships that SO and HU patients have. Support needs of SO highlighted were both educational and psychological in nature, with there being a requirement for additional raised awareness within the wider community.ConclusionIt is essential that healthcare professionals offer support, such as teaching and support groups. In addition, providing interventions into improving family knowledge of diabetes and support with regard to psychosocial, behavioural and practical support for the person with diabetes. Moreover, improving resources for families to improve diabetes care. However, as the literature was of a qualitative nature, future recommendations would be quantitative research into these suggested nursing implementations to quantitatively assess their usefulness in practice
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