20,646 research outputs found
Astrophysics with High Energy Gamma Rays
Recent results, the present status and the perspectives of high energy
gamma-ray astronomy are described. Since the satellite observations by the
Compton Gamma Ray Observatory and its precursor missions have been reviewed
extensively, emphasis is on the results from the ground-based gamma-ray
telescopes. They concern the physics of Pulsar Nebulae, Supernova Remnants in
their assumed role as the Galactic sources of Cosmic Rays, Jets from Active
Galactic Nuclei, and the Extragalactic Background radiation field due to stars
and dust in galaxies. Since the gamma-ray emission is nonthermal, this kind of
astronomy deals with the pervasive high-energy nonequilibrium states in the
Universe. The present build-up of larger and more sensitive instruments, both
on the ground and in space, gives fascinating prospects also for observational
cosmology and astroparticle physics. Through realistically possible further
observational developments at high mountain altitudes a rapid extension of the
field is to be expected.Comment: 23 pages, 11 figures. To appear in "Astronomy, Cosmology and
Fundamental Physics", ed. P. A. Shaver, L. Di Lella, and A. Gimenez, Proc.
ESA-CERN-ESO Symposium, Garching, March 2002. Springer-Verlag, Berlin,
Heidelberg, series "ESO Astrophysics Symposia
Propagation of detonations in hydrazine vapor
In the range of greater hydrazine vapor pressure, detonation speed depends exclusively on the extent of the ammonia decomposition in the second reaction stage. As vapor pressure decreases, the ammonia disintegration speed becomes increasingly slower and the reaction reached in the reaction zone increasingly decreases until finally, in the vapor pressure range between 53 and 16 Torr, the contribution of the second stage to detonation propagation disappears, and only the first stage remains active. Since the disintegration speed of the hydrazine in this pressure range has decreased markedly as well, no level, but rather only spinning, detonations occur. Temporary separations of the impact front and the reaction zone in the process lead to fluctuations of the detonation speed
Absolute neutrino masses: physics beyond SM, double beta decay and cosmic rays
Absolute neutrino masses provide a key to physics beyond the standard model.
We discuss the impact of absolute neutrinos masses on physics beyond the
standard model, the experimental possibilities to determine absolute neutrinos
masses, and the intriguing connection with the Z-burst model for extreme-energy
cosmic rays.Comment: 11 pages, 4 figures. Talk given by H. Paes at the NOON2001 workshop,
ICRR, University of Tokyo, Kashiwa, Japan; 2 references update
On The {\it Fermi} -Lat Surplus of the Diffuse Galactic Gamma-Ray Emission
Recent observations of the diffuse Galactic \gr emission (DGE) by the {\it
Fermi} Large Area Telescope ({\it Fermi}-LAT) have shown significant
deviations, above a few GeV until about 100 GeV, from DGE models that use the
GALPROP code for the propagation of cosmic ray (CR) particles outside their
sources in the Galaxy and their interaction with the target distributions of
the interstellar gas and radiation fields. The surplus of radiation observed is
most pronounced in the inner Galaxy, where the concentration of CR sources is
strongest. The present study investigates this "{\it Fermi}-LAT Galactic Plane
Surplus" by estimating the \gr emission from the sources themselves, which is
disregarded in the above DGE models. It is shown that indeed the expected hard
spectrum of CRs, still confined in their sources (SCRs), can explain this
surplus. The method is based on earlier studies regarding the so-called EGRET
GeV excess which by now is generally interpreted as an instrumental effect. The
contribution from SCRs is predicted to increasingly exceed the DGE models also
above 100 GeV, up to \gr energies of about ten TeV, where the corresponding
surplus exceeds the hadronic part of the DGE by about one order of magnitude.
Above such energies the emission surplus should decrease again with energy due
to the finite life-time of the assumed supernova remnant sources. Observations
of the DGE in the inner Galaxy at 15 TeV with the Milagro \gr detector and, at
TeV energies, with the ARGO-YBJ detector are interpreted to provide
confirmation of a significant SCR contribution to the DGE.Comment: 6 pages, 1 figure. Accepted for publication in The Astrophysical
Journal, 2013; added referenc
Tools for NLO automation: extension of the golem95C integral library
We present an extension of the program golem95C for the numerical evaluation
of scalar integrals and tensor form factors entering the calculation of
one-loop amplitudes, which supports tensor ranks exceeding the number of
propagators. This extension allows various applications in Beyond the Standard
Model physics and effective theories, for example higher ranks due to
propagators of spin two particles, or due to effective vertices. Complex masses
are also supported. The program is not restricted to the Feynman diagrammatic
approach, as it also contains routines to interface to unitarity-inspired
numerical reconstruction of the integrand at the tensorial level. Therefore it
can serve as a general integral library in automated programs to calculate
one-loop amplitudes.Comment: 17 pages, 1 figure, the program can be downloaded from
http://golem.hepforge.org/95/. arXiv admin note: substantial text overlap
with arXiv:1101.559
Cream-Skimming, Parking and Other Intended and Unintended Effects of Performance-Based Contracting in Social Welfare Services
In a growing number of countries, the delivery of social welfare services is contracted out to private providers, and increasingly, using performance-based contracts. Critics of performance-based incentive contracts stress their potential unintended effects, including cream-skimming and other gaming activities intended to raise measured performance outcomes. We analyze the incentive effects of performance-based contracts, as well as their impacts on provider job placement rates, using unique data on Dutch cohorts of unemployed and disabled workers that were assigned to private social welfare providers in 2002-2005. We take advantage of variation in contract design over this period, where procured contracts gradually moved from partial performance-contingent pay to contracts with 100%-performance contingent reward schemes, and analyze the impact of these changes using panel data that allow us to control for cohort types and to develop explicit measures of selection into the programs. We find evidence of cream-skimming and other gaming activities on the part of providers but little impact of these activities on job placement rates. Overall, moving to a system with contract payments fully contingent on performance appears to increase job placements for more readily employable workers, although it does not affect the duration of their jobs.social welfare, performance contracting
- âŠ