2,181 research outputs found
An exact self-similar solution for an expanding ball of radiation
We give an exact solution of the Einstein equations which in 4D can be
interpreted as a spherically symmetric dissipative distribution of matter, with
heat flux, whose effective density and pressure are nonstatic, nonuniform, and
satisfy the equation of state of radiation. The matter satisfies the usual
energy and thermodynamic conditions. The energy density and temperature are
related by the Stefan-Boltzmann law. The solution admits a homothetic Killing
vector in , which induces the existence of self-similar symmetry in 4D,
where the line element as well as the dimensionless matter quantities are
invariant under a simple "scaling" group.Comment: New version expanded and improved. To appear in Int. J. Mod. Phys.
The Non-Relativistic Evolution of GRBs 980703 and 970508: Beaming-Independent Calorimetry
We use the Sedov-Taylor self-similar solution to model the radio emission
from the gamma-ray bursts (GRBs) 980703 and 970508, when the blastwave has
decelerated to non-relativistic velocities. This approach allows us to infer
the energy independent of jet collimation. We find that for GRB 980703 the
kinetic energy at the time of the transition to non-relativistic evolution,
t_NR ~ 40 d, is E_ST ~ (1-6)e51 erg. For GRB 970508 we find E_ST ~ 3e51 erg at
t_NR ~ 100 d, nearly an order of magnitude higher than the energy derived in
Frail, Waxman and Kulkarni (2000). This is due primarily to revised
cosmological parameters and partly to the maximum likelihood fit we use here.
Taking into account radiative losses prior to t_NR, the inferred energies agree
well with those derived from the early, relativistic evolution of the
afterglow. Thus, the analysis presented here provides a robust,
geometry-independent confirmation that the energy scale of cosmological GRBs is
about 5e51 erg, and additionally shows that the central engine in these two
bursts did not produce a significant amount of energy in mildly relativistic
ejecta at late time. Furthermore, a comparison to the prompt energy release
reveals a wide dispersion in the gamma-ray efficiency, strengthening our
growing understanding that E_gamma is a not a reliable proxy for the total
energy.Comment: Submitted to ApJ; 13 pages, 6 figures, 1 table; high-resolution
figures can be found at: http://www.astro.caltech.edu/~ejb/NR
An all-optical event horizon in an optical analogue of a Laval nozzle
Exploiting the fact that light propagation in defocusing nonlinear media can
mimic the transonic flow of an equivalent fluid, we demonstrate experimentally
the formation of an all-optical event horizon in a waveguide structure akin to
a hydrodynamic Laval nozzle. The analogue event horizon, which forms at the
nozzle throat is suggested as a novel platform for analogous gravity
experiments
Pedagogical education quality rating system development in academic physical education discipline
© Copyright 2018 American Scientific Publishers. The study considers the academic education quality rating system development initiatives among the top-priority social and educational matters. In this context, an objective of the study was to offer the most efficient avenues for the university activities to develop the pedagogical education quality rating system applicable to the academic Physical Education discipline. The empirical data mining study performed for an academic year gave the grounds to rate progress of the ongoing academic project to rate the physical education quality. The stakeholders involved in the study appreciated practical benefits of the initiative. The study findings approximated with 5% error level gave the grounds to state that the difference of the data arrays prior to and after the initiative are not accidental. Therefore, the ongoing initiatives were found to be of positive effect on the academic education quality rates in the academic Physical Education discipline as verified by the cause-and-effect correlations analysed. The study made it possible to offer the most promising ways to improve the system, as follow: formalise the key education quality criteria by the relevant operable definitions; improve the education quality assurance culture to guarantee the stakeholders' interests being satisfied; and apply the education quality rating results to improve the education quality management and planning system
Spin resonance induced by a mechanical rotation of a polariton condensate
We study theoretically the polarization dynamics in a ring-shape bosonic
condensate of exciton-polaritons confined in a rotating trap. The interplay
between the rotating potential and TE-TM splitting of polariton modes offers a
tool of control over the spin state and the angular momentum of the condensate.
Specific selection rules describing the coupling of pseudospin and angular
momentum are formulated. The resonant coupling between states having linear and
circular polarizations leads to the polarization beats. The effect may be seen
as a polariton analogy to the electronic magnetic resonance in the presence of
constant and rotating magnetic fields. Remarkably, spin beats are induced by a
purely mechanical rotation of the condensate
Persistent polarization oscillations in ring-shape polariton condensates
We predict the limit cycle solution for a ring-shape bosonic condensate of
exciton-polaritons confined in an optically induced rotating trap. The limit
cycle manifests itself with polarization oscillations on a characteristic
timescale of tens of picoseconds. The effect arises due to the interplay
between orbital motion and the polarization degree of freedom. It is specific
to spinor bosonic condensates and would be absent in a scalar case, where a
bi-stability of stationary solutions would be observed instead. This work
offers a tool of initialisation and control of qubits based on superpositions
of polariton condensates characterised by different topologic charges
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