720 research outputs found
Phase transition in Schwarzschild-de Sitter spacetime
Using a static massive spherically symmetric scalar field coupled to gravity
in the Schwarzschild-de Sitter (SdS) background, first we consider some
asymptotic solutions near horizon and their local equations of state(E.O.S) on
them. We show that near cosmological and event horizons our scalar field
behaves as a dust. At the next step near two pure de-Sitter or Schwarzschild
horizons we obtain a coupling dependent pressure to energy density ratio. In
the case of a minimally couplling this ratio is -1 which springs to the mind
thermodynamical behavior of dark energy. If having a negative pressure behavior
near these horizons we concluded that the coupling constant must be
>. Therefore we derive a new constraint on the value of our coupling .
These two different behaviors of unique matter in the distinct regions of
spacetime at present era can be interpreted as a phase transition from dark
matter to dark energy in the cosmic scales and construct a unified scenario.Comment: 7 pages,no figures,RevTex, Typos corrected and references adde
Predicted Infrared and Raman Spectra for Neutral Ti_8C_12 Isomers
Using a density-functional based algorithm, the full IR and Raman spectra are
calculated for the neutral Ti_8C_12 cluster assuming geometries of Th, Td, D2d
and C3v symmetry. The Th pentagonal dodecahedron is found to be dynamically
unstable. The calculated properties of the relaxed structure having C3v
symmetry are found to be in excellent agreement with experimental gas phase
infrared results, ionization potential and electron affinity measurements.
Consequently, the results presented may be used as a reference for further
experimental characterization using vibrational spectroscopy.Comment: 6 pages, 5 figures. Physical Review A, 2002 (in press
Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials
We investigate the cosmological evolution of the tachyon and phantom-tachyon
scalar field by considering the potential parameter () as a function of another potential parameter
(), which correspondingly extends the
analysis of the evolution of our universe from two-dimensional autonomous
dynamical system to the three-dimension. It allows us to investigate the more
general situation where the potential is not restricted to inverse square
potential and .One result is that, apart from the inverse square potential,
there are a large number of potentials which can give the scaling and dominant
solution when the function equals for one or some
values of as well as the parameter satisfies
condition Eq.(18) or Eq.(19). We also find that for a class of different
potentials the dynamics evolution of the universe are actually the same and
therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal
C(2010), online first,
http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=
Higher Dimensional Cosmology with Some Dark Energy Models in Emergent, Logamediate and Intermediate Scenarios of the Universe
We have considered N-dimensional Einstein field equations in which
four-dimensional space-time is described by a FRW metric and that of extra
dimensions by an Euclidean metric. We have chosen the exponential forms of
scale factors a and d numbers of b in such a way that there is no singularity
for evolution of the higher dimensional Universe. We have supposed that the
Universe is filled with K-essence, Tachyonic, Normal Scalar Field and
DBI-essence. Here we have found the nature of potential of different scalar
field and graphically analyzed the potentials and the fields for three scenario
namely Emergent Scenario, Logamediate Scenario and Intermediate Scenario. Also
graphically we have depicted the geometrical parameters named statefinder
parameters and slow-roll parameters in the higher dimensional cosmology with
the above mentioned scenarios.Comment: 21 pages, 36 figure
Stability, Electronic Structure and Vibrational Modes of Ti_8C_12 Dimer
We present our density functional results of the geometry, electronic
structure and dissociation energy of Ti_8C_12 dimer. We show that as opposed to
the currently held view that Ti_8C_12 are highly stable monodispersed clusters,
the neutral Ti_8C_12 clusters form covalent bonds and form stable dimers. We
determine that the Ti atoms bond weakly (0.9 eV/bond) to organic ligands such
as ammonia. Alternatively the Met-Car dimer has a cohesive energy of 4.84 eV or
approximately 1.2 eV per bond. While Met-Car dimers are stable, formation of
these dimers may be quenched in an environment that contains a significant
population of organic ligands. The ionization and dissociation energies of the
dimer are of same order which prevents the observation of the dimer in the ion
mass spectroscopy. The analysis of the vibrational frequencies show the
lowest-energy structure to be dynamically stable. We also present infrared
absorption and Raman scattering spectra of the Ti_8C_12 dimer.Comment: 5 pages, 3 figures (Better quality figures available on request).
Physical Review B (Rapid Communication) (2002, in press
Loss of viability during freeze-thaw of intact and adherent human embryonic stem cells with conventional slow-cooling protocols is predominantly due to apoptosis rather than cellular necrosis
10.1007/s11373-005-9051-9Journal of Biomedical Science133433-44
Magnetism in Dense Quark Matter
We review the mechanisms via which an external magnetic field can affect the
ground state of cold and dense quark matter. In the absence of a magnetic
field, at asymptotically high densities, cold quark matter is in the
Color-Flavor-Locked (CFL) phase of color superconductivity characterized by
three scales: the superconducting gap, the gluon Meissner mass, and the
baryonic chemical potential. When an applied magnetic field becomes comparable
with each of these scales, new phases and/or condensates may emerge. They
include the magnetic CFL (MCFL) phase that becomes relevant for fields of the
order of the gap scale; the paramagnetic CFL, important when the field is of
the order of the Meissner mass, and a spin-one condensate associated to the
magnetic moment of the Cooper pairs, significant at fields of the order of the
chemical potential. We discuss the equation of state (EoS) of MCFL matter for a
large range of field values and consider possible applications of the magnetic
effects on dense quark matter to the astrophysics of compact stars.Comment: To appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
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