29,437 research outputs found
Recession and Umemployment in the OECD
Konjunkturelle Arbeitslosigkeit; ErwerbstÀtigkeit; Arbeitsmarktpolitik; LebensqualitÀt; OECD-Staaten
Discovery of Two High-Magnetic-Field Radio Pulsars
We report the discovery of two young isolated radio pulsars with very high
inferred magnetic fields. PSR J1119-6127 has period P = 0.407 s, and the
largest period derivative known among radio pulsars, Pdot = 4.0e-12. Under
standard assumptions these parameters imply a characteristic spin-down age of
only tau = 1.6 kyr and a surface dipole magnetic field strength of B = 4.1e13
G. We have measured a stationary period-second-derivative for this pulsar,
resulting in a braking index of n = 2.91+-0.05. We have also observed a glitch
in the rotation of the pulsar, with fractional period change Delta_P/P =
-4.4e-9. Archival radio imaging data suggest the presence of a previously
uncataloged supernova remnant centered on the pulsar. The second pulsar, PSR
J1814-1744, has P = 3.975 s and Pdot = 7.4e-13. These parameters imply tau = 85
kyr, and B = 5.5e13 G, the largest of any known radio pulsar.
Both PSR J1119-6127 and PSR J1814-1744 show apparently normal radio emission
in a regime of magnetic field strength where some models predict that no
emission should occur. Also, PSR J1814-1744 has spin parameters similar to the
anomalous X-ray pulsar (AXP) 1E 2259+586, but shows no discernible X-ray
emission. If AXPs are isolated, high magnetic field neutron stars
(``magnetars''), these results suggest that their unusual attributes are
unlikely to be merely a consequence of their very high inferred magnetic
fields.Comment: 7 pages, 3 embedded EPS figures, to be published in Ap
Dark Matter Annihilation Signatures from Electroweak Bremsstrahlung
We examine observational signatures of dark matter annihilation in the Milky
Way arising from electroweak bremsstrahlung contributions to the annihilation
cross section. It has been known for some time that photon bremsstrahlung may
significantly boost DM annihilation yields. Recently, we have shown that
electroweak bremsstrahlung of W and Z gauge bosons can be the dominant
annihilation channel in some popular models with helicity-suppressed 2 --> 2
annihilation. W/Z-bremsstrahlung is particularly interesting because the gauge
bosons produced via annihilation subsequently decay to produce large correlated
fluxes of electrons, positrons, neutrinos, hadrons (including antiprotons) and
gamma rays, which are all of importance in indirect dark matter searches. Here
we calculate the spectra of stable annihilation products produced via
gamma/W/Z-bremsstrahlung. After modifying the fluxes to account for the
propagation through the Galaxy, we set upper bounds on the annihilation cross
section via a comparison with observational data. We show that stringent cosmic
ray antiproton limits preclude a sizable dark matter contribution to observed
cosmic ray positron fluxes in the class of models for which the bremsstrahlung
processes dominate.Comment: 11 pages, 6 figures. Updated to match PRD versio
Regional unemployment in Scotland
One of the primary aims of the Eraser of Allander Institute is to try to form a detailed and consistent view of the structure of the Scottish economy. Disaggregation is an essential prerequisite to an appreciation of the diverse character of the Scottish economy. This article explores Scotland's first 'tier' of disaggregation under the new regional authority structure. Estimates of the numbers of employees in employment in the new regions for the period 1964 to 1973 have been made by the Department of Employment. These employment statistics provide one viewpoint from which can be formed a picture of the differing industrial structures in the regions, and the changes which have taken place in patterns of industrial activity over this period. The outstanding feature is the decline in employment in the Strathclyde region. Approximately 92,000 jobs have been lost there during this 10 year period. Nearly half of this decline has occurred in manufacturing industry. In contrast the Grampian and Highland regions have increased employment between 1964 and 1973. Their gains are concentrated in the manufacturing and service sectors. Although the employment figures for these regions support the view that the centre of economic activity in Scotland is moving north and east the figures for the other regions exhibit no clear spatial pattern. Fife gained approximately 4000 jobs between 1964 and 1973, while Tayside lost over 10,000. The Central region marginally increased its workforce, but around 17,000 jobs disappeared from the Lothians. The Borders lost over 1000 jobs but little net change was experienced in Dumfries and Galloway
A new test of conservation laws and Lorentz invariance in relativistic gravity
General relativity predicts that energy and momentum conservation laws hold
and that preferred frames do not exist. The parametrised post-Newtonian
formalism (PPN) phenomenologically quantifies possible deviations from general
relativity. The PPN parameter alpha_3 (which identically vanishes in general
relativity) plays a dual role in that it is associated both with a violation of
the momentum conservation law, and with the existence of a preferred frame. By
considering the effects of alpha_3 neq 0 in certain binary pulsar systems, it
is shown that alpha_3 < 2.2 x 10^-20 (90% CL). This limit improves on previous
results by several orders of magnitude, and shows that pulsar tests of alpha_3
rank (together with Hughes-Drever-type tests of local Lorentz invariance) among
the most precise null experiments of physics.Comment: Submitted to Classical Quantum Gravity, LaTeX, requires ioplppt.sty,
no figure
Timing the Parkes Multibeam Pulsars
Measurement of accurate positions, pulse periods and period derivatives is an
essential follow-up to any pulsar survey. The procedures being used to obtain
timing parameters for the pulsars discovered in the Parkes multibeam pulsar
survey are described. Completed solutions have been obtained so far for about
80 pulsars. They show that the survey is preferentially finding pulsars with
higher than average surface dipole magnetic fields. Eight pulsars have been
shown to be members of binary systems and some of the more interesting results
relating to these are presented.Comment: 6 pages, 2 embedded EPS figures, to be published in proceedings of
"Pulsar Astronomy - 2000 and Beyond", ASP Conf. Se
A Numerical Method for General Relativistic Magnetohydrodynamics
This paper describes the development and testing of a general relativistic
magnetohydrodynamic (GRMHD) code to study ideal MHD in the fixed background of
a Kerr black hole. The code is a direct extension of the hydrodynamic code of
Hawley, Smarr, and Wilson, and uses Evans and Hawley constrained transport (CT)
to evolve the magnetic fields. Two categories of test cases were undertaken. A
one dimensional version of the code (Minkowski metric) was used to verify code
performance in the special relativistic limit. The tests include Alfv\'en wave
propagation, fast and slow magnetosonic shocks, rarefaction waves, and both
relativistic and non-relativistic shock tubes. A series of one- and
two-dimensional tests were also carried out in the Kerr metric: magnetized
Bondi inflow, a magnetized inflow test due to Gammie, and two-dimensional
magnetized constant- tori that are subject to the magnetorotational
instability.Comment: 37 pages, 14 figures, submitted to ApJ. Animations can be viewed at
http://www.astro.virginia.edu/~jd5v/grmhd/grmhd.htm
Toward a Deterministic Model of Planetary Formation IV: Effects of Type-I Migration
In a further development of a deterministic planet-formation model (Ida & Lin
2004), we consider the effect of type-I migration of protoplanetary embryos due
to their tidal interaction with their nascent disks. During the early embedded
phase of protostellar disks, although embryos rapidly emerge in regions
interior to the ice line, uninhibited type-I migration leads to their efficient
self-clearing. But, embryos continue to form from residual planetesimals at
increasingly large radii, repeatedly migrate inward, and provide a main channel
of heavy element accretion onto their host stars. During the advanced stages of
disk evolution (a few Myr), the gas surface density declines to values
comparable to or smaller than that of the minimum mass nebula model and type-I
migration is no longer an effective disruption mechanism for mars-mass embryos.
Over wide ranges of initial disk surface densities and type-I migration
efficiency, the surviving population of embryos interior to the ice line has a
total mass several times that of the Earth. With this reservoir, there is an
adequate inventory of residual embryos to subsequently assemble into rocky
planets similar to those around the Sun. But, the onset of efficient gas
accretion requires the emergence and retention of cores, more massive than a
few M_earth, prior to the severe depletion of the disk gas. The formation
probability of gas giant planets and hence the predicted mass and semimajor
axis distributions of extrasolar gas giants are sensitively determined by the
strength of type-I migration. We suggest that the observed fraction of
solar-type stars with gas giant planets can be reproduced only if the actual
type-I migration time scale is an order of magnitude longer than that deduced
from linear theories.Comment: 32 pages, 8 figures, 1 table, accepted for publication in Ap
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