87,784 research outputs found
Properties of Phase transitions of a Higher Order
The following is a thermodynamic analysis of a III order (and some aspects of
a IV order) phase transition. Such a transition can occur in a superconductor
if the normal state is a diamagnet. The equation for a phase boundary in an H-T
(H is the magnetic field, T, the temperature) plane is derived. by considering
two possible forms of the gradient energy, it is possible to construct a field
theory which describes a III or a IV order transition and permits a study of
thermal fluctuations and inhomogeneous order parameters.Comment: 13 pages, revtex, no figure
D mesons and charmonium states in asymmetric nuclear matter at finite temperatures
We investigate the in-medium masses of and mesons in the
isospin-asymmetric nuclear matter at finite temperatures arising due to the
interactions with the nucleons, the scalar isoscalar meson , and the
scalar iso-vector meson within a SU(4) model. The in-medium masses of
and the excited charmonium states ( and ) are
also calculated in the hot isospin asymmetric nuclear matter in the present
investigation. These mass modifications arise due to the interaction of the
charmonium states with the gluon condensates of QCD, simulated by a scalar
dilaton field introduced to incorporate the broken scale invariance of QCD
within the effective chiral model. The change in the mass of in the
nuclear matter with the density is seen to be rather small, as has been shown
in the literature by using various approaches, whereas, the masses of the
excited states of charmonium ( and ) are seen to have
considerable drop at high densities. The present study of the in-medium masses
of () mesons as well as of the charmonium states will be of
relevance for the observables from the compressed baryonic matter, like the
production and collective flow of the () mesons, resulting from the
asymmetric heavy ion collision experiments planned at the future facility of
the FAIR, GSI. The mass modifications of and mesons as well as of
the charmonium states in hot nuclear medium can modify the decay of the
charmonium states () to pairs in the hot
dense hadronic matter. The small attractive potentials observed for the
mesons may lead to formation of the mesic nuclei.Comment: 61 pages, 19 figues, to be published in Phys. Rev.
Differential rotation enhanced dissipation of tides in the PSR J0045-7319 Binary
Recent observations of PSR J0045-7319, a radio pulsar in a close eccentric
orbit with a massive B-star companion, indicate that the system's orbital
period is decreasing on a timescale of years, which is
much shorter than the timescale of 10^9 years given by the standard
theory of tidal dissipation in radiative stars. Observations also provide
strong evidence that the B-star is rotating rapidly, perhaps at nearly its
break up speed. We show that the dissipation of the dynamical tide in a star
rotating in the same direction as the orbital motion of its companion (prograde
rotation) with a speed greater than the orbital angular speed of the star at
periastron results in an increase in the orbital period of the binary system
with time. Thus, since the observed time derivative of the orbital period is
large and negative, the B-star in the PSR J0045-7319 binary must have
retrograde rotation if tidal effects are to account for the orbital decay. We
also show that the time scale for the synchronization of the B-star's spin with
the orbital angular speed of the star at periastron is comparable to the
orbital evolution time. From the work of Goldreich and Nicholson (1989) we
therefore expect that the B-star should be rotating differentially, with the
outer layers rotating more slowly than the interior. We show that the
dissipation of the dynamical tide in such a differentially rotating B-star is
enhanced by almost three orders of magnitude leading to an orbital evolution
time for the PSR J0045-7319 Binary that is consistent with the observations.Comment: 8 pages, tex. Submitted to Ap
Giant Tunneling Magnetoresistance, Glassiness, and the Energy Landscape at Nanoscale Cluster Coexistence
We present microscopic results on the giant tunneling magnetoresistance that
arises from the nanoscale coexistence of ferromagnetic metallic (FMM) and
antiferromagnetic insulating (AFI) clusters in a disordered two dimensional
electron system with competing double exchange and superexchange interactions.
Our Monte Carlo study allows us to map out the different field regimes in
magnetotransport and correlate it with the evolution of spatial structures. At
coexistence, the isotropic O(3) model shows signs of slow relaxation, and has a
high density of low energy metastable states, but no genuine glassiness.
However, in the presence of weak magnetic anisotropy, and below a field
dependent irreversibility temperature , the response on field cooling
(FC) differs distinctly from that on zero field cooling (ZFC). We map out the
phase diagram of this `phase coexistence glass', highlight how its response
differs from that of a standard spin glass, and compare our results with data
on the manganites.Comment: Final published versio
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