3,086 research outputs found
Conditions for Phase Equilibrium in Supernovae, Proto-Neutron and Neutron Stars
We investigate the qualitative properties of phase transitions in a general
way, if not the single particle numbers of the system but only some particular
charges like e.g. baryon number are conserved. In addition to globally
conserved charges we analyze the implications of locally conserved charge
fractions, like e.g. local electric charge neutrality or locally fixed proton
or lepton fractions. The conditions for phase equilibrium are derived and it is
shown, that the properties of the phase transition do not depend on the locally
conserved fractions. Finally, the general formalism is applied to the
liquid-gas phase transition and the hadron-quark phase transition for typical
astrophysical environments like in supernovae, proto-neutron or a neutron
stars. We demonstrate that the Maxwell construction known from
cold-deleptonized neutron star matter with two locally charge neutral phases
requires modifications and further assumptions concerning the applicability for
hot lepton-rich matter. All possible combinations of local and global
conservation laws are analyzed, and the physical meaningful cases are
identified. Several new kinds of mixed phases are presented, as e.g. a locally
charge neutral mixed phase in proto-neutron stars which will disappear during
the cooling and deleptonization of the proto-neutron star.Comment: 18 page
A new possible quark-hadron mixed phase in protoneutron stars
The phase transition from hadronic matter to quark matter at high density
might be a strong first order phase transition in presence of a large surface
tension between the two phases. While this implies a constant-pressure mixed
phase for cold and catalyzed matter this is not the case for the hot and lepton
rich matter formed in a protoneutron star. We show that it is possible to
obtain a mixed phase with non-constant pressure by considering the global
conservation of lepton number during the stage of neutrino trapping. In turn,
it allows for the appearance of a new kind of mixed phase as long as neutrinos
are trapped and its gradual disappearance during deleptonization. This new
mixed phase, being composed by two electric neutral phases, does not develop a
Coulomb lattice and it is formed only by spherical structures, drops and
bubbles, which can have macroscopic sizes. The disappearance of the mixed phase
at the end of deleptonization might lead to a delayed collapse of the star into
a more compact configuration containing a core of pure quark phase. In this
scenario, a significant emission of neutrinos and, possibly, gravitational
waves are expected.Comment: 4 pages, 4 figure
On thermal nucleation of quark matter in compact stars
The possibility of a hadron-quark phase transition in extreme astrophysical
phenomena such as the collapse of a supernova is not discarded by the modern
knowledge of the high-energy nuclear and quark-matter equations of state. Both
the density and the temperature attainable in such extreme processes are
possibly high enough to trigger a chiral phase transition. However, the time
scales involved are an important issue. Even if the physical conditions for the
phase transition are favorable (for a system in equilibrium), there may not be
enough time for the dynamical process of phase conversion to be completed. We
analyze the relevant time scales for the phase conversion via thermal
nucleation of bubbles of quark matter and compare them to the typical
astrophysical time scale, in order to verify the feasibility of the scenario of
hadron-quark phase conversion during, for example, the core-collapse of a
supernova.Comment: 6 pages, 4 figures, talk given at the International Conference
SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200
Light clusters in nuclear matter: Excluded volume versus quantum many-body approaches
The formation of clusters in nuclear matter is investigated, which occurs
e.g. in low energy heavy ion collisions or core-collapse supernovae. In
astrophysical applications, the excluded volume concept is commonly used for
the description of light clusters. Here we compare a phenomenological excluded
volume approach to two quantum many-body models, the quantum statistical model
and the generalized relativistic mean field model. All three models contain
bound states of nuclei with mass number A <= 4. It is explored to which extent
the complex medium effects can be mimicked by the simpler excluded volume
model, regarding the chemical composition and thermodynamic variables.
Furthermore, the role of heavy nuclei and excited states is investigated by use
of the excluded volume model. At temperatures of a few MeV the excluded volume
model gives a poor description of the medium effects on the light clusters, but
there the composition is actually dominated by heavy nuclei. At larger
temperatures there is a rather good agreement, whereas some smaller differences
and model dependencies remain.Comment: 12 pages, 6 figures, published version, minor change
Phase transition from nuclear matter to color superconducting quark matter: the effect of the isospin
We compute the mixed phase of nuclear matter and 2SC matter for different
temperatures and proton fractions. After showing that the symmetry energy of
the 2SC phase is, to a good approximation, three times larger than the one of
the normal quark phase, we discuss and compare all the properties of the mixed
phase with a 2SC component or a normal quark matter component. In particular,
the local isospin densities of the nuclear and the quark component and the
stiffness of the mixed phase are significantly different whether the 2SC phase
or the normal quark phase are considered. If a strong diquark pairing is
adopted for the 2SC phase, there is a possibility to eventually enter in the
nuclear matter 2SC matter mixed phase in low energy heavy ions collisions
experiments. Possible observables able to discern between the formation of the
2SC phase or the normal quark phase are finally discussed.Comment: 9 pages, 8 figure
The Effect of Ketoconazole on Amphotericin B in a Model of Disseminated Aspergillosis
The potential of ketoconazole prophylaxis to antagonize the activity of amphotericin B against aspergilli was investigated in vitro and in neutropenic mice. Exposure of Aspergillus fumigatus (six strains) and of Aspergillus flavus or Aspergillus niger to ketoconazole resulted in a uniform increase of the minimal fungicidal activity of amphotericin B, from 0.15-0.63 mg/liter to >2.5 mg/liter in a microwell assay. To test the relevance of this antagonism in vivo, we challenged neutropenic mice iv with a lethal dose of conidia from two strains of A. fumigatus and then treated the mice first with ketoconazole and then with amphotericin B or amphotericin B plus ketoconazole. Pretreatment with ketoconazole for 48 hr completely abolished the protective effect of a subsequent therapy with amphotericin B, whether ketoconazole therapy was stopped (P < .001) or not (P <.001). Ketoconazole given alone had no significant effect on survival. Our data show that ketoconazole not only antagonized the fungicidal activity of amphotericin B in vitro but also abolished in vivo the protective effect of the only drug shown to be useful in the therapy of aspergillosis. The clinical importance of this antagonism, which is not limited to Aspergilli in vitro, requires careful consideration before ketoconazole prophylaxis can be recommended for patients at high risk of developing invasive opportunistic fungal infection
Stability of CFL cores in Hybrid Stars
We study the equation state of strongly interacting quark matter within a
NJL-like model in which the chiral condensates and the color superconducting
gaps are computed self-consistently as a function of the baryon density. A
vector interaction term is added to the Lagrangian in order to render the quark
matter equation of state stiffer. For the low density hadronic phase we use a
relativistic mean field model. The phase transition to quark matter is computed
by a Maxwell construction. We show that stable CFL cores in hybrid stars are
possible if the superconducting gap is sufficiently large. Moreover we find
stable stellar configurations in which two phase transitions occur, a first
transition from hadronic matter to 2SC quark matter and a second transition
from 2SC quark matter to CFL quark matter.Comment: 10 pages, 6 figure
Strangeness in Astrophysics and Cosmology
Some recent developments concerning the role of strange quark matter for
astrophysical systems and the QCD phase transition in the early universe are
addressed. Causality constraints of the soft nuclear equation of state as
extracted from subthreshold kaon production in heavy-ion collisions are used to
derive an upper mass limit for compact stars. The interplay between the
viscosity of strange quark matter and the gravitational wave emission from
rotation-powered pulsars are outlined. The flux of strange quark matter nuggets
in cosmic rays is put in perspective with a detailed numerical investigation of
the merger of two strange stars. Finally, we discuss a novel scenario for the
QCD phase transition in the early universe, which allows for a small
inflationary period due to a pronounced first order phase transition at large
baryochemical potential.Comment: 8 pages, invited talk given at the International Conference on
Strangeness in Quark Matter (SQM2009), Buzios, Brasil, September 28 - October
2, 200
Strange Exotic States and Compact Stars
We discuss the possible appearance of strange exotic multi-quark states in
the interior of neutron stars and signals for the existence of strange quark
matter in the core of compact stars. We show how the in-medium properties of
possible pentaquark states are constrained by pulsar mass measurements. The
possibility of generating the observed large pulsar kick velocities by
asymmetric emission of neutrinos from strange quark matter in magnetic fields
is outlined.Comment: 10 pages, invited talk given at the International Conference on
Strangeness in Quark Matter 2006 (SQM2006), UCLA, USA, March 26-31, 2006,
Journal of Physics G in press, refs. adde
Economic Effects of Added Growing Season Rainfall on North Dakota Agriculture
Farm Management, Resource /Energy Economics and Policy,
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