5,298 research outputs found
One-dimensional polynomial maps, periodic points and multipliers
We discuss tangent maps related to the multipliers of periodic points of a
typical one-dimensional polynomial map.Comment: We correct inaccuracies (wrong signs) in the computation of gradients
of multiplier functions (Sect. 2). The statements and proofs of main results
remain unchange
Spectra and Light Curves of GRB Afterglows
We performed accurate numerical calculations of angle-, time-, and
frequency-dependent radiative transfer for the relativistic motion of matter in
gamma-ray burst (GRB) models. Our technique for solving the transfer equation,
which is based on the method of characteristics, can be applied to the motion
of matter with a Lorentz factor up to 1000. The effect of synchrotron
self-absorption is taken into account. We computed the spectra and light curves
from electrons with a power-law energy distribution in an expanding
relativistic shock and compare them with available analytic estimates. The
behavior of the optical afterglows from GRB 990510 and GRB 000301c is discussed
qualitatively.Comment: 8 pages, 7 figure
Radio Emission and Particle Acceleration in SN 1993J
The radio light curves of SN 1993J are found to be well fit by a synchrotron
spectrum, suppressed by external free-free absorption and synchrotron
self-absorption. A standard r^-2 circumstellar medium is assumed, and found to
be adequate. The magnetic field and number density of relativistic electrons
behind the shock are determined. The strength of the magnetic field argues
strongly for turbulent amplification behind the shock. The ratio of the
magnetic and thermal energy density behind the shock is ~0.14. Synchrotron and
Coulomb cooling dominate the losses of the electrons. The injected electron
spectrum has a power law index -2.1, consistent with diffusive shock
acceleration, and the number density scales with the thermal electron energy
density. The total energy density of the relativistic electrons is, if
extrapolated to gamma ~ 1, ~ 5x10^-4 of the thermal energy density. The
free-free absorption required is consistent with previous calculations of the
circumstellar temperature of SN 1993J, T_e ~ (2-10)x10^5 K. The relative
importance of free-free absorption, Razin suppression, and the synchrotron
self-absorption effect for other supernovae are briefly discussed. Guidelines
for the modeling and interpretation of VLBI observations are given.Comment: accepted for Ap.
The Case Against Cosmology
It is argued that some of the recent claims for cosmology are grossly
overblown. Cosmology rests on a very small database: it suffers from many
fundamental difficulties as a science (if it is a science at all) whilst
observations of distant phenomena are difficult to make and harder to
interpret. It is suggested that cosmological inferences should be tentatively
made and sceptically received.Comment: 9 pages, no figure
`In pursuit of the Nazi mind?' the deployment of psychoanalysis in the allied struggle against Germany
This paper discusses how psychoanalytic ideas were brought to bear in the Allied struggle against the Third Reich and explores some of the claims that were made about this endeavour. It shows how a variety of studies of Fascist psychopathology, centred on the concept of superego, were mobilized in military intelligence, post-war planning and policy recommendations for âdenazificationâ. Freud's ideas were sometimes championed by particular army doctors and government planners; at other times they were combined with, or displaced by, competing, psychiatric and psychological forms of treatment and diverse studies of the Fascist âpersonalityâ. This is illustrated through a discussion of the treatment and interpretation of the deputy leader of the Nazi Party, Rudolf Hess, after his arrival in Britain in 1941
Forming Galaxies with MOND
Beginning with a simple model for the growth of structure, I consider the
dissipationless evolution of a MOND-dominated region in an expanding Universe
by means of a spherically symmetric N-body code. I demonstrate that the final
virialized objects resemble elliptical galaxies with well-defined relationships
between the mass, radius, and velocity dispersion. These calculations suggest
that, in the context of MOND, massive elliptical galaxies may be formed early
(z > 10) as a result of monolithic dissipationless collapse. Then I reconsider
the classic argument that a galaxy of stars results from cooling and
fragmentation of a gas cloud on a time scale shorter than that of dynamical
collapse. Qualitatively, the results are similar to that of the traditional
picture; moreover, the existence, in MOND, of a density-temperature relation
for virialized, near isothermal objects as well as a mass-temperature relation
implies that there is a definite limit to the mass of a gas cloud where this
condition can be met-- an upper limit corresponding to that of presently
observed massive galaxies.Comment: 9 pages, 9 figures, revised in response to comments of referee. Table
added, extended discussion, accepted MNRA
Observing H2 Emission in Forming Galaxies
We study the H2 cooling emission of forming galaxies, and discuss their
observability using the future infrared facility SAFIR. Forming galaxies with
mass >10^11 Msun emit most of their gravitational energy liberated by
contraction in molecular hydrogen line radiation, although a large part of
thermal energy at virialization is radiated away by the H Ly alpha emission.
For more massive objects, the degree of heating due to dissipation of kinetic
energy is so great that the temperature does not drop below 10^4 K and the
gravitational energy is emitted mainly by the Ly alpha emission. Therefore, the
total H2 luminosity attains the peak value of about 10^42 ergs/s for forming
galaxies whose total mass 10^11 Msun. If these sources are situated at redshift
z=8, they can be detected by rotational lines of 0-0S(3) at 9.7 micron and
0-0S(1) at 17 micron by SAFIR. An efficient way to find such H2 emitters is to
look at the Ly alpha emitters, since the brightest H2 emitters are also
luminous in the Ly alpha emission.Comment: 20 pages, 7 figures, ApJ accepte
Theory of photospheric emission from relativistic outflows
In this paper we reexamine the optical depth of ultrarelativistic spherically
symmetric outflows and reevaluate the photospheric radius for each model during
both the acceleration and coasting phases. It is shown that for both the wind
and the shell models there are two asymptotic solutions for the optical depth
during the coasting phase of the outflow. In particular we show that quite
counterintuitively a geometrically thin shell may appear as a thick wind for
photons propagating inside it. For this reason we introduce notions of photon
thick and photon thin outflows, which appear more general and better physically
motivated with respect to winds and shells. Photosphere of relativistic outflow
is a dynamic surface. We study its geometry and find that the photosphere of
photon thin outflow has always a convex shape, while in the photon thick one it
is initially convex (there is always a photon thin layer in any outflow) and
then it becomes concave asymptotically approaching the photosphere of an
infinitely long wind. We find that both instantaneous and time integrated
observed spectra are very close to the thermal one for photon thick outflows,
in line with existing studies. It is our main finding that the photospheric
emission from the photon thin outflow produces non thermal time integrated
spectra, which may be described by the Band function well known in the GRB
literature. We find that energetic GRBs should produce photon thin outflows
with photospheric emission lasting less than one second for the total energy
erg and baryonic loading parameter . It means
that only time integrated spectra may be observed from such GRBs.Comment: Revision of the previous version, new effect is discussed.
Conclusions remain unchange
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