11,745 research outputs found
Density dependent strong coupling constant of QCD derived from compact star data
The present work is an endeavour to connect the properties of tiny nearly
massless objects with those of some of the most massive ones, the compact
stars.
Since 1996 there is major influx of X-ray and ray data from binary
stars, one or both of which are compact objects that are difficult to explain
as neutron stars since they contain a mass M in too small a radius R . The
suggestion has been put forward that these are strange quark stars (SS)
explainable in a simple model with chiral symmetry restoration (CSR) for the
quarks and the M, R and other properties like QPOs (quasi periodic
oscillations) in their X-ray power spectrum.
It would be nice if this astrophysical data could shed some light on
fundamental properties of quarks obeying QCD. One can relate the strong
coupling constant of QCD, to the quark mass through the
Dyson-Schwinger gap equation using the real time formalism of Dolan and Jackiw.
This enables us to obtain the density dependence of from the simple
CSR referred to above. This way fundamental physics, difficult to extract from
other models like for example lattice QCD, can be constrained from present-day
compact star data and may be put back to modelling the dense quark phase of
early universe.Comment: 7 pages, 4 figure
Ongoing rehabilitation of coastal communities in Aceh province : a new project
This article presents an overview of the project on Rehabilitation of Fisheries and Aquaculture in Tsunami-affected Coastal Communities in Aceh Province. Building on the research results from the recently completed projects detailed in the previous articles, this project shall synthesize information on coastal fishing communities and resources in order to develop site-specific management options to support rehabilitation of fisheries and aquaculture.Disasters, Coastal zone, ISEW, Indonesia, Aceh,
Phase transition between non-extremal and extremal Reissner-Nordstr\"om black holes
We discuss the phase transition between non-extremal and extremal
Reissner-Nordstr\"om black holes. This transition is considered as the
limit of the transition between the non-extremal and near-extremal
black holes.
We show that an evaporating process from non-extremal black hole to extremal
one is possible to occur, but its reverse process is not possible to occur
because of the presence of the maximum temperature.
Furthermore, it is shown that the Hawking-Page phase transition between small
and large black holes unlikely occurs in the AdS Reissner-Nordstr\"om black
holes.Comment: 12 pages, 6 figures, version to appear in MPL
Control of beam propagation in optically written waveguides beyond the paraxial approximation
Beam propagation beyond the paraxial approximation is studied in an optically
written waveguide structure. The waveguide structure that leads to
diffractionless light propagation, is imprinted on a medium consisting of a
five-level atomic vapor driven by an incoherent pump and two coherent spatially
dependent control and plane-wave fields. We first study propagation in a single
optically written waveguide, and find that the paraxial approximation does not
provide an accurate description of the probe propagation. We then employ
coherent control fields such that two parallel and one tilted Gaussian beams
produce a branched waveguide structure. The tilted beam allows selective
steering of the probe beam into different branches of the waveguide structure.
The transmission of the probe beam for a particular branch can be improved by
changing the width of the titled Gaussian control beam as well as the intensity
of the spatially dependent incoherent pump field.Comment: 10 pages, 9 figure
Causality in Propagation of a Pulse in a Nonlinear Dispersive Medium
We investigate the causal propagation of the pulse through dispersive media
by very precise numerical solution of the coupled Maxwell-Bloch equations
without any approximations about the strength of the input field. We study full
nonlinear behavior of the pulse propagation through solid state media like ruby
and alexandrite. We have demonstrated that the information carried by the
discontinuity, {\it i.e}, front of the pulse, moves inside the media with
velocity even though the peak of the pulse can travel either with
sub-luminal or with super-luminal velocity. We extend the argument of
Levi-Civita to prove that the discontinuity would travel with velocity even
in a nonlinear medium.Comment: 4 pages, 4 figures, 2 table
Spatially Resolved Gas Kinematics within a Ly Nebula: Evidence for Large-scale Rotation
We use spatially extended measurements of Ly as well as less
optically thick emission lines from an 80 kpc Ly nebula at
to assess the role of resonant scattering and to disentangle
kinematic signatures from Ly radiative transfer effects. We find that
the Ly, CIV, HeII, and CIII] emission lines all tell a similar story in
this system, and that the kinematics are broadly consistent with large-scale
rotation. First, the observed surface brightness profiles are similar in extent
in all four lines, strongly favoring a picture in which the Ly photons
are produced in situ instead of being resonantly scattered from a central
source. Second, we see low kinematic offsets between Ly and the less
optically thick HeII line (100-200 km s), providing further
support for the argument that the Ly and other emission lines are all
being produced within the spatially extended gas. Finally, the full velocity
field of the system shows coherent velocity shear in all emission lines:
500 km s over the central 50 kpc of the nebula. The
kinematic profiles are broadly consistent with large-scale rotation in a gas
disk that is at least partially stable against collapse. These observations
suggest that the Ly nebula represents accreting material that is
illuminated by an offset, hidden AGN or distributed star formation, and that is
undergoing rotation in a clumpy and turbulent gas disk. With an implied mass of
M(<R=20 kpc) , this system may represent the
early formation of a large Milky Way mass galaxy or galaxy group.Comment: Accepted to ApJ; 25 pages in emulateapj format; 15 figures, 4 table
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