442 research outputs found
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
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
Nucleation of quark matter in protoneutron star matter
The phase transition from hadronic to quark matter may take place already
during the early post-bounce stage of core collapse supernovae when matter is
still hot and lepton rich. If the phase transition is of first order and
exhibits a barrier, the formation of the new phase occurs via the nucleation of
droplets. We investigate the thermal nucleation of a quark phase in supernova
matter and calculate its rate for a wide range of physical parameters. We show
that the formation of the first droplet of a quark phase might be very fast and
therefore the phase transition to quark matter could play an important role in
the mechanism and dynamics of supernova explosions.Comment: v3: fits version published in Physical Review
Scour features at wood bundles
Structures like blunt-nosed chevrons, log deflectors and double-winged log frames help in modifying the flow regime in the channel by concentrating the flow and increasing navigability. Moreover, they create scour pools in the downstream stilling basin, which can be used either as fish refuge or as an in-stream storage site for previously dredged material. In this respect, the use of wood debris in the channel in the form of wood bundles has gained attention for the ability of these structures to integrate into the surrounding fluvial habitat and to divert the flow partially towards the central part of the channel when placed in curves. Considering the absence of studies dealing with wood bundles as a restoration structure, the aim of this paper is to analyse the scour mechanism and equilibrium scour morphology of wood bundles in straight and curved channels. In doing so, a wide range of hydraulic conditions, structure positions and configurations were tested. Thereafter, dimensional analysis was carried out to derive useful empirical relationships to predict the maximum scour depth and length as well as the maximum dune height based on a novel, equivalent Froude number, which accounts for the effects of channel curvature and structure position. Moreover, the various resulting scour morphology types were classified, and conditions of their existence were determined depending on the abovementioned Froude number and other key hydraulic parameters
Reflectance and photoluminescence characterization of CdS and CdSe heteroepitaxial films deposited by laser ablation technique
Optical properties of CdSe and CdS films, deposited on sapphire substrate by means of pulsed laser ablation technique, have been investigated in order to study the effect of such a transparent substrate on the photoluminescence efficiency of the deposited epilayers. CdSe and CdS films present intrinsic (excitonic) emission at low temperature, differently from the same films deposited on quartz. The temperature dependence of the excitonic energy has been analyzed taking into account the contribution of both the thermal dilatation and electron-phonon interaction
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
Bulk Viscosity in Hybrid Stars
We compute the bulk viscosity of a mixed quark-hadron phase. In the first
scenario to be discussed, the mixed phase occurs at large densities and we
assume that it is composed of a mixing of hyperonic matter and quarks in the
Color Flavor Locked phase. In a second scenario, the mixed phase occurs at
lower densities and it is composed of a mixing of nucleons and unpaired quark
matter. We have also investigated the effect of a non-vanishing surface tension
at the interface between hadronic and quark matter. In both scenarios, the bulk
viscosity is large when the surface tension is absent, while the value of the
viscosity reduces in the second scenario when a finite value for the surface
tension is taken into account. In all cases, the r-mode instabilities of the
corresponding hybrid star are suppressed.Comment: 8 pages, 7 figures, extended version in print on Phys.Rev.
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