73,068 research outputs found
Free energy determination of phase coexistence in model C60: A comprehensive Monte Carlo study
The free energy of the solid and fluid phases of the Girifalco C60 model are
determined through extensive Monte Carlo simulations. In this model the
molecules interact through a spherical pair potential, characterized by a
narrow and attractive well, adjacent to a harshly repulsive core. We have used
the Widom test particle method and a mapping from an Einstein crystal, in order
to estimate the absolute free energy in the fluid and solid phases,
respectively; we have then determined the free energy along several isotherms,
and the whole phase diagram, by means of standard thermodynamic integrations.
We highlight how the interplay between the liquid-vapor and the liquid-solid
coexistence conditions determines the existence of a narrow liquid pocket in
the phase diagram, whose stability is assessed and confirmed in agreement with
previous studies. In particular, the critical temperature follows closely an
extended corresponding-states rule recently outlined by Noro and Frenkel [J.
Chem. Phys. 113:2941 (2000)].
We discuss the emerging "energetic" properties of the system, which drive the
phase behavior in systems interacting through short-range forces [A. A. Louis,
Phil. Trans. R. Soc. A 359:939 (2001)], in order to explain the discrepancy
between the predictions of several structural indicators and the results of
full free energy calculations, to locate the fluid phase boundaries.
More generally, we aim to provide extended reference data for calculations of
the free energy of the C60 fullerite in the low temperature regime, as for the
determination of the phase diagram of higher order fullerenes and other
fullerene-related materials, whose description is based on the same model
adopted in this work.Comment: RevTeX, 11 pages, 9 figure
Kaons and pions in strange quark matter
The behavior of kaons and pions in strange quark matter in weak equilibrium,
is investigated within the SU(3) Nambu-Jona-Lasinio [NJL] model. This work
focuses a region of high densities where the behavior of mesons has not been
explored in the framework of this model. It is found that above the density
where strange valence quarks appear in the medium, , a
change of behavior of different observables is observed indicating a tendency
to the restoration of flavor symmetry. In particular, the splitting between
charge multiplets, decrease and
the low energy modes with quantum numbers of , which
are excitations of the Fermi sea, are less relevant than for lower densities.Comment: 10 pages, 3 figures included; revised version, some changes in the
discussio
Interplay between chiral and axial symmetries in a SU(2) Nambu--Jona-Lasinio Model with the Polyakov loop
We consider a two flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model where the
Lagrangian includes an interaction term that explicitly breaks the U
anomaly. At finite temperature, the restoration of chiral and axial symmetries,
signaled by the behavior of several observables, is investigated. We compare
the effects of two regularizations at finite temperature, one of them, that
allows high momentum quarks states, leading to the full recovery of chiral
symmetry. From the analysis of the behavior of the topological susceptibility
and of the mesonic masses of the axial partners, it is found in the SU(2) model
that, unlike the SU(3) results, the recovery of the axial symmetry is not a
consequence of the full recovery of the chiral symmetry. Thus, one needs to use
an additional idea, by means of a temperature dependence of the anomaly
coefficient, that simulates instanton suppression effects.Comment: 21 pages, 5 figures; PRD versio
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Presumed Neuroglycopenia Caused by Severe Hypoglycemia in Horses.
BackgroundNeuroglycopenia refers to a shortage of glucose in the brain resulting in neuronal dysfunction and death if left untreated. Presumed neuroglycopenia has not been described in horses.ObjectiveTo report neurological signs in horses with presumed neuroglycopenia as the result of severe hypoglycemia.AnimalsNinety horses (hours to 28 years of age) diagnosed with hypoglycemia (blood glucose concentration < 75 mg/dL [< 4.2 mmol/L]).MethodsRetrospective study. Electronic medical records were searched. Signalment, history, complaint, clinical signs, laboratory findings including CSF analysis, electroencephalogram, clinical or definitive diagnosis, and outcome were recorded. Kruskal-Wallis analysis of variance and logistic regression were used to investigate association between blood glucose concentration and data extracted. Statistical significance was set at P < 0.05.ResultsThirty-eight and 52 horses had mild (50-74 mg/dL [2.8-4.1 mmol/L]), and severe hypoglycemia (< 50 mg/dL [< 2.8 mmol/L]), respectively. Most common causes of hypoglycemia included liver and gastrointestinal (40%) disease, sepsis (33%), neoplasia (7%), and insulin-induced (4%). Most common neurologic deficits included obtundation (100%), seizures (42%), and disorientation (22%). CSF-glucose was severely low (mean 2.5 mg/dL [0.1 mmol/L], median 0 mg/dL). Paroxysmal discharges in support of seizures were identified in the occipital (visual) and parietal (closest to temporal-auditory) cortical regions upon EEG examination (8/8 horses).Conclusions and clinical importanceNeuroglycopenia is presumed to occur in horses as the result of severe hypoglycemia. Subclinical seizures, and intermittent blindness and deafness of cortical origin can occur. Severe altered state of consciousness and seizures can be observed at a blood glucose cut-off value of < 42 mg/dL (< 2.3 mmol/L)
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