1,304 research outputs found
Formation of the seed black holes: a role of quark nuggets?
Strange quark nuggets (SQNs) could be the relics of the cosmological QCD
phase transition, and they could very likely be the candidate of cold quark
matter if survived the cooling of the later Universe, although the formation
and evolution of these SQNs depend on the physical state of the hot QGP
(quark-gluon plasma) phase and the state of cold quark matter. We reconsider
the possibility of SQNs as cold dark matter, and find that the formation of
black holes in primordial halos could be significantly different from the
standard scenario. In a primordial halo, the collision between gas and SQNs
could be frequent enough, and thus the viscosity acting on each SQN would
decrease its angular momentum and make it to sink into the center of the halo,
as well as heat the gas. The SQNs with baryon numbers less than could
assemble in the center of the halo before the formation of primordial stars. A
black hole could form by merger of these SQNs, and then its mass could quickly
become about or higher, by accreting the surrounding SQNs or
gas. The black holes formed in this way could be the seeds for the supermassive
black holes at redshift as high as .Comment: 15 page
BOUT++: a framework for parallel plasma fluid simulations
A new modular code called BOUT++ is presented, which simulates 3D fluid
equations in curvilinear coordinates. Although aimed at simulating Edge
Localised Modes (ELMs) in tokamak X-point geometry, the code is able to
simulate a wide range of fluid models (magnetised and unmagnetised) involving
an arbitrary number of scalar and vector fields, in a wide range of geometries.
Time evolution is fully implicit, and 3rd-order WENO schemes are implemented.
Benchmarks are presented for linear and non-linear problems (the Orszag-Tang
vortex) showing good agreement. Performance of the code is tested by scaling
with problem size and processor number, showing efficient scaling to thousands
of processors.
Linear initial-value simulations of ELMs using reduced ideal MHD are
presented, and the results compared to the ELITE linear MHD eigenvalue code.
The resulting mode-structures and growth-rate are found to be in good agreement
(BOUT++ = 0.245, ELITE = 0.239). To our knowledge, this is the first time
dissipationless, initial-value simulations of ELMs have been successfully
demonstrated.Comment: Submitted to Computer Physics Communications. Revised to reduce page
count. 18 pages, 16 figure
Influence of Organic Acids on Diltiazem HCl Release Kinetics from Hydroxypropyl Methyl Cellulose Matrix Tablets
The matrix tablets of diltiazem hydrochloride were prepared by direct compression using hydroxypropyl methyl cellulose (HPMC) and various amounts (2.5%, 5.0%, 10% and 20%) of citric acid, malic acid and succinic acid. The characterization of physical mixture of drug and organic acids was performed by Infra-red spectroscopy. An organic acid was incorporated to set up a system bringing about gradual release of this drug. The influence of organic acids on the release rate were described by the Peppas equation: M t /Mâ = Kt n and Higuchiâs equation: Q t = K1t1/2. The addition of organic acids and the pH value of medium could notably influence the dissolution behavior and mechanism of drug-release from matrices. Increasing amounts of organic acid produced an increase in drug release rate, which showed a good linear relationship between contents of organic acid and drug accumulate release (%) in phosphate buffer, pH 7.4. The drug release increased significantly (P < 0.05) with use of succinic acid in tablet formulation. Increasing amounts of succinic acid above 10% produced decreasing values of n and increasing values of k, in a linear relationship, which indicated there was a burst release of drug from the matrix. Optimized formulations are found to be stable upon 3-month study
Spectral functions of isoscalar scalar and isovector electromagnetic form factors of the nucleon at two-loop order
We calculate the imaginary parts of the isoscalar scalar and isovector
electromagnetic form factors of the nucleon up to two-loop order in chiral
perturbation theory. Particular attention is paid on the correct behavior of Im
and Im at the two-pion threshold
in connection with the non-relativistic 1/M-expansion. We recover the
well-known strong enhancement near threshold originating from the nearby
anomalous singularity at . In the
case of the scalar spectral function Im one finds a significant
improvement in comparison to the lowest order one-loop result. Higher order
-rescattering effects are however still necessary to close a remaining
20%-gap to the empirical scalar spectral function. The isovector electric and
magnetic spectral functions Im get additionally enhanced near
threshold by the two-pion-loop contributions. After supplementing their
two-loop results by a phenomenological -meson exchange term one can
reproduce the empirical isovector electric and magnetic spectral functions
fairly well.Comment: 10 pages, 6 figures, submitted to Physical Review
Radiating black hole solutions in arbitrary dimensions
We prove a theorem that characterizes a large family of non-static solutions
to Einstein equations in -dimensional space-time, representing, in general,
spherically symmetric Type II fluid. It is shown that the best known
Vaidya-based (radiating) black hole solutions to Einstein equations, in both
four dimensions (4D) and higher dimensions (HD), are particular cases from this
family. The spherically symmetric static black hole solutions for Type I fluid
can also be retrieved. A brief discussion on the energy conditions,
singularities and horizons is provided.Comment: RevTeX 9 pages, no figure
Phase transitions of hadronic to quark matter at finite T and \mu_B
The phase transition of hadronic to quark matter and the boundaries of the
mixed hadron-quark coexistence phase are studied within the two Equation of
State (EoS) model. The relativistic effective mean field approach with constant
and density dependent meson-nucleon couplings is used to describe hadronic
matter, and the MIT Bag model is adopted to describe quark matter. The
boundaries of the mixed phase for different Bag constants are obtained solving
the Gibbs equations.
We notice that the dependence on the Bag parameter of the critical
temperatures (at zero chemical potential) can be well reproduced by a fermion
ultrarelativistic quark gas model, without contribution from the hadron part.
At variance the critical chemical potentials (at zero temperature) are very
sensitive to the EoS of the hadron sector. Hence the study of the hadronic EoS
is much more relevant for the determination of the transition to the
quark-gluon-plasma at finite baryon density and low-T. Moreover in the low
temperature and finite chemical potential region no solutions of the Gibbs
conditions are existing for small Bag constant values, B < (135 MeV)^4. Isospin
effects in asymmetric matter appear relevant in the high chemical potential
regions at lower temperatures, of interest for the inner core properties of
neutron stars and for heavy ion collisions at intermediate energies.Comment: 24 pages and 16 figures (revtex4
Rotating metrics admitting non-perfect fluids in General Relativity
In this paper, by applying Newman-Janis algorithm in spherical symmetric
metrics, a class of embedded rotating solutions of field equations is
presented. These solutions admit non-perfect fluidsComment: LaTex, 39 page
Collective modes of asymmetric nuclear matter in Quantum HadroDynamics
We discuss a fully relativistic Landau Fermi liquid theory based on the
Quantum Hadro-Dynamics () effective field picture of Nuclear Matter
({\it NM}).
From the linearized kinetic equations we get the dispersion relations of the
propagating collective modes. We focus our attention on the dynamical effects
of the interplay between scalar and vector channel contributions. A beautiful
``mirror'' structure in the form of the dynamical response in the
isoscalar/isovector degree of freedom is revealed, with a complete parallelism
in the role respectively played by the compressibility and the symmetry energy.
All that strongly supports the introduction of an explicit coupling to the
scalar-isovector channel of the nucleon-nucleon interaction. In particular we
study the influence of this coupling (to a -meson-like effective field)
on the collective response of asymmetric nuclear matter (). Interesting
contributions are found on the propagation of isovector-like modes at normal
density and on an expected smooth transition to isoscalar-like oscillations at
high baryon density. Important ``chemical'' effects on the neutron-proton
structure of the mode are shown. For dilute we have the isospin
distillation mechanism of the unstable isoscalar-like oscillations, while at
high baryon density we predict an almost pure neutron wave structure of the
propagating sounds.Comment: 18 pages (LATEX), 8 Postscript figures, uses "epsfig
Proton Differential Elliptic Flow and the Isospin-Dependence of the Nuclear Equation of State
Within an isospin-dependent transport model for nuclear reactions involving
neutron-rich nuclei, we study the first-order direct transverse flow of protons
and their second-order differential elliptic flow as a function of transverse
momentum. It is found that the differential elliptic flow of mid-rapidity
protons, especially at high transverse momenta, is much more sensitive to the
isospin dependence of the nuclear equation of state than the direct flow.
Origins of these different sensitivities and their implications to the
experimental determination of the isospin dependence of the nuclear equation of
state by using neutron-rich heavy-ion collisions at intermediate energies are
discussed.Comment: 15 pages, 6 figures. Phys. Rev. C (2001) in pres
Nucleon Charge and Magnetization Densities from Sachs Form Factors
Relativistic prescriptions relating Sachs form factors to nucleon charge and
magnetization densities are used to fit recent data for both the proton and the
neutron. The analysis uses expansions in complete radial bases to minimize
model dependence and to estimate the uncertainties in radial densities due to
limitation of the range of momentum transfer. We find that the charge
distribution for the proton is significantly broad than its magnetization
density and that the magnetization density is slightly broader for the neutron
than the proton. The neutron charge form factor is consistent with the Galster
parametrization over the available range of Q^2, but relativistic inversion
produces a softer radial density. Discrete ambiguities in the inversion method
are analyzed in detail. The method of Mitra and Kumari ensures compatibility
with pQCD and is most useful for extrapolating form factors to large Q^2.Comment: To appear in Phys. Rev. C. Two new figures and accompanying text have
been added and several discussions have been clarified with no significant
changes to the conclusions. Now contains 47 pages including 21 figures and 2
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