1,372 research outputs found
Stability of vortex lines in liquid 3He-4He mixtures at zero temperature
At low temperatures and 3He concentrations below 6.6 %, there is experimental
evidence about the existence in liquid helium mixtures, of stable vortices with
3He-rich cores. When the system is either supersaturated or submitted to a
tensile strength, vortices lose stability becoming metastable and eventually
completely unstable, so that their cores freely expand. Within a density
functional approach, we have determined the pressure-3He concentration curve
along which this instability appears at zero temperature.Comment: Typeset using Revtex, 9 pages and 5 Postscript figure
Imaging features and differential diagnoses of non-neoplastic diffuse mediastinal diseases.
Acute or chronic non-neoplastic diffuse mediastinal diseases have multiple causes, degrees of severity, and a wide range of management. Some situations require emergency care while others do not need specific treatment. Although the diagnosis may be suspected on chest X-ray, it is mainly based on CT. A delayed recognition is not uncommonly observed. Some findings may prompt the radiologist to look for specific associated injuries or lesions.This pictorial review will successively describe the various non-neoplastic causes of diffuse mediastinal diseases with their typical findings and major differentials.First, pneumomediastinum that can be provoked by extra- or intra-thoracic triggers requires the knowledge of patient's history or recent occurrences. Absence of any usual etiological factor should raise suspicion of cocaine inhalation in young individuals.Next, acute mediastinitis may be related to post-operative complications, esophageal perforation, or contiguous spread of odontogenic or retropharyngeal infections. The former diagnosis is not an easy task in the early stage, owing to the similarities of imaging findings with those of normal post-operative appearance during the first 2-3 weeks.Finally, fibrosing mediastinitis that is linked to an excessive fibrotic reaction in the mediastinum with variable compromise of mediastinal structures, in particular vascular and airway ones. Differential diagnosis includes tumoral and inflammatory infiltrations of the mediastinum
Venous lactate improves the prediction of in-hospital adverse outcomes in normotensive pulmonary embolism
Background: Arterial lactate is an established risk marker in patients with pulmonary embolism (PE). However, its clinical applicability is limited by the need of an arterial puncture. In contrast, venous lactate can easily be measured from blood samples obtained via routine peripheral venepuncture. Methods: We investigated the prognostic value of venous lactate with regard to in-hospital adverse outcomes and mortality in 419 consecutive PE patients enrolled in a single-center registry between 09/2008 and 09/2017. Results: An optimised venous lactate cut-off value of 3.3 mmol/l predicted both, in-hospital adverse outcome (OR 11.0 [95% CI 4.6?26.3]) and all-cause mortality (OR 3.8 [95%CI 1.3?11.3]). The established cut-off value for arterial lactate (2.0 mmol/l) and the upper limit of normal for venous lactate (2.3 mmol/l) had lower prognostic value for adverse outcomes (OR 3.6 [95% CI 1.5?8.7] and 5.7 [95% CI 2.4?13.6], respectively) and did not predict mortality. If added to the 2019 European Society of Cardiology (ESC) algorithm, venous lactate Conclusion: Venous lactate above the upper limit of normal was associated with increased risk for adverse outcomes and an optimised cut-off value of 3.3 mmol/l predicted adverse outcome and mortality. Adding venous lactate to the 2019 ESC algorithm may improve risk stratification. Importantly, the established cut-off value for arterial lactate has limited specificity in venous samples and should not be used.Peer reviewe
Phase Transitions Driven by Vortices in 2D Superfluids and Superconductors: From Kosterlitz-Thouless to 1st Order
The Landau-Ginzburg-Wilson hamiltonian is studied for different values of the
parameter which multiplies the quartic term (it turns out that this
is equivalent to consider different values of the coherence length in
units of the lattice spacing ). It is observed that amplitude fluctuations
can change dramatically the nature of the phase transition: for small values of
(), instead of the smooth Kosterlitz-Thouless transition
there is a {\em first order} transition with a discontinuous jump in the vortex
density and a larger non-universal drop in the helicity modulus. In
particular, for sufficiently small (), the density of
bound pairs of vortex-antivortex below is so low that, drops to zero
almost for all temperature .Comment: 8 pages, 5 .eps figure
Nucleating Black Holes via Non-Orientable Instantons
We extend the analysis of black hole pair creation to include non- orientable
instantons. We classify these instantons in terms of their fundamental
symmetries and orientations. Many of these instantons admit the pin structure
which corresponds to the fermions actually observed in nature, and so the
natural objection that these manifolds do not admit spin structure may not be
relevant. Furthermore, we analyse the thermodynamical properties of
non-orientable black holes and find that in the non-extreme case, there are
interesting modifications of the usual formulae for temperature and entropy.Comment: 27 pages LaTeX, minor typos are correcte
Vortex lines in the three-dimensional XY model with random phase shifts
The stability of the ordered phase of the three-dimensional XY-model with
random phase shifts is studied by considering the roughening of a single
stretched vortex line due to the disorder. It is shown that the vortex line may
be described by a directed polymer Hamiltonian with an effective random
potential that is long range correlated. A Flory argument estimates the
roughness exponent to and the energy fluctuation exponent to
, thus fulfilling the scaling relation . The
Schwartz-Edwards method as well as a numerical integration of the corresponding
Burger's equation confirm this result. Since the ordered phase of the
original XY-model is stable.Comment: 8 pages RevTeX, 3 eps-figures include
High-momentum dynamic structure function of liquid 3He-4He mixtures: a microscopic approach
The high-momentum dynamic structure function of liquid 3He-4He mixtures has
been studied introducing final state effects. Corrections to the impulse
approximation have been included using a generalized Gersch-Rodriguez theory
that properly takes into account the Fermi statistics of 3He atoms. The
microscopic inputs, as the momentum distributions and the two-body density
matrices, correspond to a variational (fermi)-hypernetted chain calculation.
The agreement with experimental data obtained at \AA is not
completely satisfactory, the comparison being difficult due to inconsistencies
present in the scattering measurements. The significant differences between the
experimental determinations of the 4He condensate fraction and the 3He kinetic
energy, and the theoretical results, still remain unsolved.Comment: 18 pages, 11 figures, to appear in Phys. Rev.
Surface and capillary transitions in an associating binary mixture model
We investigate the phase diagram of a two-component associating fluid mixture
in the presence of selectively adsorbing substrates. The mixture is
characterized by a bulk phase diagram which displays peculiar features such as
closed loops of immiscibility. The presence of the substrates may interfere the
physical mechanism involved in the appearance of these phase diagrams, leading
to an enhanced tendency to phase separate below the lower critical solution
point. Three different cases are considered: a planar solid surface in contact
with a bulk fluid, while the other two represent two models of porous systems,
namely a slit and an array on infinitely long parallel cylinders. We confirm
that surface transitions, as well as capillary transitions for a large
area/volume ratio, are stabilized in the one-phase region. Applicability of our
results to experiments reported in the literature is discussed.Comment: 12 two-column pages, 12 figures, accepted for publication in Physical
Review E; corrected versio
Eco-evolutionary dynamics on deformable fitness landscapes
Conventional approaches to modelling ecological dynamics often do not include evolutionary changes in the genetic makeup of component species and, conversely, conventional approaches to modelling evolutionary changes in the genetic makeup of a population often do not include ecological dynamics. But recently there has been considerable interest in understanding the interaction of evolutionary and ecological dynamics as coupled processes. However, in the context of complex multi-species ecosytems, especially where ecological and evolutionary timescales are similar, it is difficult to identify general organising principles that help us understand the structure and behaviour of complex ecosystems. Here we introduce a simple abstraction of coevolutionary interactions in a multi-species ecosystem. We model non-trophic ecological interactions based on a continuous but low-dimensional trait/niche space, where the location of each species in trait space affects the overlap of its resource utilisation with that of other species. The local depletion of available resources creates, in effect, a deformable fitness landscape that governs how the evolution of one species affects the selective pressures on other species. This enables us to study the coevolution of ecological interactions in an intuitive and easily visualisable manner. We observe that this model can exhibit either of the two behavioural modes discussed in the literature; namely, evolutionary stasis or Red Queen dynamics, i.e., continued evolutionary change. We find that which of these modes is observed depends on the lag or latency between the movement of a species in trait space and its effect on available resources. Specifically, if ecological change is nearly instantaneous compared to evolutionary change, stasis results; but conversely, if evolutionary timescales are closer to ecological timescales, such that resource depletion is not instantaneous on evolutionary timescales, then Red Queen dynamics result. We also observe that in the stasis mode, the overall utilisation of resources by the ecosystem is relatively efficient, with diverse species utilising different niches, whereas in the Red Queen mode the organisation of the ecosystem is such that species tend to clump together competing for overlapping resources. These models thereby suggest some basic conditions that influence the organisation of inter-species interactions and the balance of individual and collective adaptation in ecosystems, and likewise they also suggest factors that might be useful in engineering artificial coevolution
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