1,152 research outputs found
Comment on "Hole-Burning Experiments within Glassy Models with Infinite Range Interactions"
Comment on: L.F. Cugliandolo and J.L. Iguain; Phys. Rev. Lett. {\bf 85} 3448
(2000)Comment: 1 page, RevTe
A new two-sphere singularity in general relativity
The Florides solution, proposed as an alternative to the interior
Schwarzschild solution, represents a static and spherically symmetric geometry
with vanishing radial stresses. It is regular at the center, and is matched to
an exterior Schwarzschild solution. The specific case of a constant energy
density has been interpreted as the field inside an Einstein cluster. In this
work, we are interested in analyzing the geometry throughout the permitted
range of the radial coordinate without matching it to the Schwarzschild
exterior spacetime at some constant radius hypersurface. We find an interesting
picture, namely, the solution represents a three-sphere, whose equatorial
two-sphere is singular, in the sense that the curvature invariants and the
tangential pressure diverge. As far as we know, such singularities have not
been discussed before. In the presence of a large negative cosmological
constant (anti-de Sitter) the singularity is removed.Comment: 17 pages, 3 figure
A note on dilaton gravity with non-smooth potentials
Recent interest in brane world models motivates the investigation of generic
first order dilaton gravity actions, with potentials having some
non-smoothness. We consider two different types of \delta-like contributions in
the action and analyse their effects on the solutions. Furthermore a second
source of non-smoothness arises due to the remaining ambiguities in the
solutions in the separated smooth patches, after fixing all other constants by
matching and asymptotic conditions. If moreover staticity is assumed, we
explicitly construct exact solutions.
With the methods described, for example models with point like sources or
brane world models (where the second source of non-smoothness becomes crucial),
can now be treated as non-smooth dilaton gravity theories.Comment: 10 pages, 1 table; two new references, some typos corrected,
Dedicated to Wolfgang Kummer at the occasion of his Emeritierun
Origin of non-exponential relaxation in a crystalline ionic conductor: a multi-dimensional 109Ag NMR study
The origin of the non-exponential relaxation of silver ions in the
crystalline ion conductor Ag7P3S11 is analyzed by comparing appropriate
two-time and three-time 109Ag NMR correlation functions. The non-exponentiality
is due to a rate distribution, i.e., dynamic heterogeneities, rather than to an
intrinsic non-exponentiality. Thus, the data give no evidence for the relevance
of correlated back-and-forth jumps on the timescale of the silver relaxation.Comment: 4 pages, 3 figure
Ion and polymer dynamics in polymer electrolytes PPO-LiClO4: II. 2H and 7Li NMR stimulated-echo experiment
We use 2H NMR stimulated-echo spectroscopy to measure two-time correlation
functions characterizing the polymer segmental motion in polymer electrolytes
PPO-LiClO4 near the glass transition temperature Tg. To investigate effects of
the salt on the polymer dynamics, we compare results for different ether oxygen
to lithium ratios, namely, 6:1, 15:1, 30:1 and infinity. For all compositions,
we find nonexponential correlation functions, which can be described by a
Kohlrausch function. The mean correlation times show quantitatively that an
increase of the salt concentration results in a strong slowing down of the
segmental motion. Consistently, for the high 6:1 salt concentration, a high
apparent activation energy E_a=4.1eV characterizes the temperature dependence
of the mean correlation times at Tg < T< 1.1T_g, while smaller values E_a=2.5eV
are observed for moderate salt contents. The correlation functions are most
nonexponential for 15:1 PPO-LiClO4, whereas the stretching is reduced for
higher and lower salt concentrations. A similar dependence of the correlation
functions on the evolution time in the presence and in the absence of ions
indicates that addition of salt hardly affects the reorientational mechanism.
For all compositions, mean jump angles of about 15 degree characterize the
segmental reorientation. In addition, comparison of results from 2H and 7Li NMR
stimulated-echo experiments suggests a coupling of ion and polymer dynamics in
15:1 PPO-LiClO4.Comment: 14 pages, 12 figure
Symptoms of gastroesophageal reflux disease in severely mentally retarded people: a systematic review
<p>Abstract</p> <p>Background</p> <p>Gastroesophageal reflux disease (GERD) occurs when stomach acid frequently backs up (or refluxes) into the gullet (or esophagus), and it has serious consequences for the quality of life. Usually this is felt as heartburn. Because severely mentally retarded people usually do not utter complaints of heartburn, it requires a high index of suspicion to discover possible GERD. Therefore it is relevant for care professionals such as nurses to have knowledge of those with a higher risk of GERD and of the possible manifestations of GERD.</p> <p>Methods</p> <p>Using a predefined search method, electronic databases were searched for studies relating the presence of symptoms to the presence of GERD. Relevant data were extracted and the methodological quality of the studies assessed. The results of the included studies were synthesized and conclusions about the level of evidence were drawn.</p> <p>Results</p> <p>Nineteen studies were found relating symptoms to the presence of GERD. Only four were of good methodological quality. The studies were very diverse concerning the studied population, the study method, and the kind of symptoms examined. This makes it difficult to synthesize the results of the studies. There is evidence that patients with cerebral palsy, patients using anticonvulsive drugs, and those with an IQ lower than 35 more frequently have GERD. There is also evidence that vomiting, rumination and hematemesis are associated with a higher risk of the presence of GERD, whereas there is no clear scientific evidence that particular behavior symptoms are indicative for GERD.</p> <p>Conclusion</p> <p>The possible manifestations of GERD are many and varied. A guideline will be made for care professionals to aid systematic observation of possible manifestations of GERD.</p
Imaging Orbital-selective Quasiparticles in the Hund's Metal State of FeSe
Strong electronic correlations, emerging from the parent Mott insulator
phase, are key to copper-based high temperature superconductivity (HTS). By
contrast, the parent phase of iron-based HTS is never a correlated insulator.
But this distinction may be deceptive because Fe has five active d-orbitals
while Cu has only one. In theory, such orbital multiplicity can generate a
Hund's Metal state, in which alignment of the Fe spins suppresses inter-orbital
fluctuations producing orbitally selective strong correlations. The spectral
weights of quasiparticles associated with different Fe orbitals m should
then be radically different. Here we use quasiparticle scattering interference
resolved by orbital content to explore these predictions in FeSe. Signatures of
strong, orbitally selective differences of quasiparticle appear on all
detectable bands over a wide energy range. Further, the quasiparticle
interference amplitudes reveal that , consistent with
earlier orbital-selective Cooper pairing studies. Thus, orbital-selective
strong correlations dominate the parent state of iron-based HTS in FeSe.Comment: for movie M1, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M1.mp4, for movie M2, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M2.mp4, for movie M3, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M3.mp4, for movie M4, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M4.mp4, for movie M5, see
http://www.physik.uni-leipzig.de/~kreisel/osqp/M5.mp
Dynamic heterogeneities in the out-of-equilibrium dynamics of simple spherical spin models
The response of spherical two-spin interaction models, the spherical
ferromagnet (s-FM) and the spherical Sherrington-Kirkpatrick (s-SK) model, is
calculated for the protocol of the so-called nonresonant hole burning
experiment (NHB) for temperatures below the respective critical temperatures.
It is shown that it is possible to select dynamic features in the
out-of-equilibrium dynamics of both models, one of the hallmarks of dynamic
heterogeneities. The behavior of the s-SK model and the s-FM in three
dimensions is very similar, showing dynamic heterogeneities in the long time
behavior, i.e. in the aging regime. The appearence of dynamic heterogeneities
in the s-SK model explicitly demonstrates that these are not necessarily
related to {\it spatial} heterogeneities. For the s-FM it is shown that the
nature of the dynamic heterogeneities changes as a function of dimensionality.
With incresing dimension the frequency selectivity of the NHB diminishes and
the dynamics in the mean-field limit of the s-FM model becomes homogeneous.Comment: 16 pages, 8 figure
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