373 research outputs found
Beyond the binary collision approximation for the large- response of liquid He
We discuss corrections to the linear response of a many-body system beyond
the binary collision approximation. We first derive for smooth pair
interactions an exact expression of the response , considerably
simplifying existing forms and present also the generalization for interactions
with a strong, short-range repulsion. We then apply the latter to the case of
liquid He. We display the numerical influence of the correction
around the quasi-elastic peak and in the low-intensity wings of the response,
far from that peak. Finally we resolve an apparent contradiction in previous
discussions around the fourth order cumulant expansion coefficient. Our results
prove that the large- response of liquid He can be accurately understood
on the basis of a dynamical theory.Comment: 19 p. Figs. available on reques
Magnetic Oscillations in Dense Cold Quark Matter with Four-Fermion Interactions
The phase structures of Nambu-Jona-Lasinio models with one or two flavours
have been investigated at non-zero values of and , where is an
external magnetic field and is the chemical potential. In the phase
portraits of both models there arise infinitely many massless chirally
symmetric phases, as well as massive ones with spontaneously broken chiral
invariance, reflecting the existence of infinitely many Landau levels. Phase
transitions of first and second orders and a lot of tricritical points have
been shown to exist in phase diagrams. In the massless case, such a phase
structure leads unavoidably to the standard van Alphen-de Haas magnetic
oscillations of some thermodynamical quantities, including magnetization,
pressure and particle density. In the massive case we have found an oscillating
behaviour not only for thermodynamical quantities, but also for a dynamical
quantity as the quark mass. Besides, in this case we have non-standard, i.e.
non-periodic, magnetic oscillations, since the frequency of oscillations is an
-dependent quantity.Comment: latex, 29 pages, 8 figure
Effect of nearest neighbor repulsion on the low frequency phase diagram of a quarter-filled Hubbard-Holstein chain
We have studied the influence of nearest-neighbor (NN) repulsion on the low
frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN
repulsion term induces the apparition of two new long range ordered phases (one
CDW for positive and one CDW for
negative ) that did not exist in the V=0 phase diagram. These results
are put into perspective with the newly observed charge ordered phases in
organic conductors and an interpretation of their origin in terms of
electron-molecular vibration coupling is suggested.Comment: 10 pages, 10 figure
Self-trapping transition for nonlinear impurities embedded in a Cayley tree
The self-trapping transition due to a single and a dimer nonlinear impurity
embedded in a Cayley tree is studied. In particular, the effect of a perfectly
nonlinear Cayley tree is considered. A sharp self-trapping transition is
observed in each case. It is also observed that the transition is much sharper
compared to the case of one-dimensional lattices. For each system, the critical
values of for the self-trapping transitions are found to obey a
power-law behavior as a function of the connectivity of the Cayley tree.Comment: 6 pages, 7 fig
Model estimates of metazoans' contributions to the biological carbon pump
Funding: This work was supported by the Centre for Ocean Life, a VKR Centre of Excellence funded by the Villum Foundation, and by the Gordon and Betty Moore Foundation (grant no. 5479). AndrĂŠ W. Visser was funded in part through the Horizon 2020 project ECOTIP (grant no. 869383). Andrew S. Brierley and Roland Proud were funded in part through the EU BG3 project âSUMMERâ and BG8 project âMission Atlanticâ. Collated echo-sounder data obtained from the British Oceanographic Data Centre (BODC) included observations made during the Atlantic Meridional Transect. The Atlantic Meridional Transect (AMT) is funded by the UK Natural Environment Research Council through its National Capability Long-term Single Centre Science Programme, Climate Linked Atlantic Sector Science (grant number NE/R015953/1).The daily vertical migrations of fish and other metazoans actively transport organic carbon from the ocean surface to depth, contributing to the biological carbon pump. We use an oxygen-constrained, game-theoretic food-web model to simulate diel vertical migrations and estimate near-global (global ocean minus coastal areas and high latitudes) carbon fluxes and sequestration by fish and zooplankton due to respiration, fecal pellets, and deadfalls. Our model provides estimates of the carbon export and sequestration potential for a range of pelagic functional groups, despite uncertain biomass estimates of some functional groups. While the export production of metazoans and fish is modest (âź20 % of global total), we estimate that their contribution to carbon sequestered by the biological pump (âź800 PgC) is conservatively more than 50 % of the estimated global total (âź1300 PgC) and that they have a significantly longer sequestration timescale (âź250 years) than previously reported for other components of the biological pump. Fish and multicellular zooplankton contribute about equally to this sequestered carbon pool. This essential ecosystem service could be at risk from both unregulated fishing on the high seas and ocean deoxygenation due to climate change.Publisher PDFPeer reviewe
Lattice QCD Constraints on the Nuclear Equation of State
Based on the quasi-particle description of the QCD medium at finite
temperature and density we formulate the phenomenological model for the
equation of state that exhibits crossover or the first order deconfinement
phase transition. The models are constructed in such a way to be
thermodynamically consistent and to satisfy the properties of the ground state
nuclear matter comply with constraints from intermediate heavy--ion collision
data. Our equations of states show quite reasonable agreement with the recent
lattice findings on temperature and baryon chemical potential dependence of
relevant thermodynamical quantities in the parameter range covering both the
hadronic and quark--gluon sectors. The model predictions on the isentropic
trajectories in the phase diagram are shown to be consistent with the recent
lattice results. Our nuclear equations of states are to be considered as an
input to the dynamical models describing the production and the time evolution
of a thermalized medium created in heavy ion collisions in a broad energy range
from SIS up to LHC.Comment: 13 pages, 11 figure
Effect of acute hypobaric hypoxia on the endothelial glycocalyx and digital reactive hyperemia in humans
Introduction: Hypoxia is associated with increased capillary permeability. This study tested whether acute hypobaric hypoxia involves degradation of the endothelial glycocalyx. Methods: We exposed 12 subjects to acute hypobaric hypoxia (equivalent to 4,500 m for 2-4 hours) and measured venous blood concentrations of biomarkers reflecting endothelial and glycocalyx degradation (catecholamines, syndecan-1, soluble CD40 ligand, protein C, soluble thrombomodulin, tissue-type plasminogen activators, histone-complexed DNA fragments and nitrite/nitrate). Endothelial function was assessed by the hyperemic response to brachial artery occlusion by peripheral arterial tonometry. Results: Compared with normoxic baseline levels, hypoxia increased concentrations of syndecan-1 from 22 (95% confidence interval: 17-27) to 25 (19-30) ng/ml (p < 0.02) and protein C from 76 (70-83) % to 81 (74-88) % (p < 0.02). Nitrite/nitrate decreased from 23 (18-27) ÎźM at baseline to 19 (14-24) ÎźM and 18 (14-21) ÎźM in hypoxia and recovery, respectively (p < 0.05). Other biomarkers remained unchanged. The post-occlusion/pre-occlusion ratio (reactive hyperemia index, RHI) decreased from 1.80 (1.52â2.07) in normoxia to 1.62 (1.28â1.96) after 2 to 4 hours of hypobaric hypoxia and thereafter increased to 2.43 (1.99-2.86) during normoxic recovery (p < 0.01). Conclusions: The increase in syndecan-1 and protein C suggests that acute hypobaric hypoxia produces minor degree of glycocalyx degradation and overall cellular damage. After hypoxia RHI rebounded to higher than baseline levels suggesting improved endothelial functionality
On the Afterglow of the X-ray Flash of 2003 July 23: Photometric evdence for an Off-Axis Gamma-Ray burst with an Associated Supernova
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