239 research outputs found
Anisotropy of the space orientation of radio sources. I: The catalog
A catalog of the extended extragalactic radio sources consisting of 10461
objects is compiled based on the list of radio sources of the FIRST survey. A
total of 1801 objects are identified with galaxies and quasars of the SDSS
survey and the Veron-Veron catalog. The distribution of the position angles of
the axes of radio sources from the catalog is determined, and the probability
that this distribution is equiprobable is shown to be less then 10^(-7). This
result implies that at Z equal to or smaller then 0.5, spatial orientation of
the axes of radio sources is anisotropic at a statistically significant level.Comment: 8 pages, 7 figure
On the Hadronic Beam Model for Gamma-ray Production in Blazars
We consider, herein, a model for gamma-ray production in blazars in which a
relativistic, highly-collimated electron-proton beam interacts with a dense,
compact cloud as the jet propagates through the broad and perhaps narrow line
regions (BLR and NLR) of active galactic nuclei (AGN). During the propagation
of the beam through the cloud, the process of excitation of plasma waves
becomes an important energy loss mechanism, especially for mildly relativistic
proton beams. We compute the expected spectra of gamma-rays from the decay of
neutral pions produced in hadronic collisions of the beam with the cloud,
taking into account collisionless losses of the electron-proton beam. This
model may explain the X-ray and TeV gamma-ray (both low and high emission
states) of Mrk 421 as a result of synchrotron emission of secondary pairs from
the decay of charged pions and gamma-ray emission from the decay of neutral
pions for the plausible cloud parameters. However clouds can not be too hot and
too dense. Otherwise the TeV gamma-rays can be attenuated by the bremsstrahlung
radiation in the cloud and the secondary pairs are not able to efficiently
produce synchrotron flares because of the dominant role of inverse Compton
scattering.
The non-variable -ray emission observed from Mrk 421 in the EGRET
energy range cannot be described by the -rays from decay of neutral
pions provided that the spectrum of protons in the beam is well described by a
simple power law. These -rays might only be produced by secondary pairs
scattering the soft non-variable X-rays which might originate in the inner part
of the accretion disk.Comment: 14 pages,3 figures, latex, submitted to Ap
Evidence of Segregated Spawning in a Single Marine Fish Stock: Sympatric Divergence of Ecotypes in Icelandic Cod?
There is increasing recognition of intraspecific diversity and population structure within marine fish species, yet there is little direct evidence of the isolating mechanisms that maintain it or documentation of its ecological extent. We analyzed depth and temperature histories collected by electronic data storage tags retrieved from 104 Atlantic cod at liberty ≥1 year to evaluate a possible isolating mechanisms maintaining population structure within the Icelandic cod stock. This stock consists of two distinct behavioral types, resident coastal cod and migratory frontal cod, each occurring within two geographically distinct populations. Despite being captured together on the same spawning grounds, we show the behavioral types seem reproductively isolated by fine-scale differences in spawning habitat selection, primarily depth. Additionally, the different groups occupied distinct seasonal thermal and bathymetric niches that generally demonstrated low levels of overlap throughout the year. Our results indicate that isolating mechanisms, such as differential habitat selection during spawning, might contribute to maintaining diversity and fine-scale population structure in broadcast-spawning marine fishes
First Measurements with the ATLAS Level-1 Calorimeter Trigger PreProcessor System
The ATLAS level-1 calorimeter trigger is a hardware-based system with the goal of identifying high-pT objects within an overall latency of 2.5 μs. It is composed of a PreProcessor system which digitises 7200 analogue channels, determines the bunchcrossing of the interaction and provides a fine timing and energy calibration; and two subsequent digital processors. The PreProcessor plays a central role during integration of the system as it provides digitisation and readout of calorimeter signals and serves as a digital signal source for the subsequent processors. In this presentation the system architecture, the board production testing, and cable installation are described. Results on commissioning efforts and signal integrity tests are presented
Long term follow up after surgery in congenitally corrected transposition of the great arteries with a right ventricle in the systemic circulation
Aim of the study: To investigate the long-term outcome of surgical treatment for congenitally corrected transposition of the great arteries (CCTGA), in patients with biventricular repair with the right ventricle as systemic ventricle.Methods: A total of 32 patients with CCTGA were operated between January 1972 and October 2008. These operations comprised 18 patients with a repair with a normal left ventricular outflow tract, 11 patients with a Rastelli repair of the left ventricle to the pulmonary artery and 3 patients with a cardiac transplantation.Results: Excluding the cardiac transplantation patients, mean age at operation was 16 years (sd 15 years, range 1 week - 49 years). Median follow-up was 12 years (sd 10 years, range 7 days - 32 years). Survival obtained from Kaplan-Meier analysis at 20 years after surgery was 63% (CI 53-73%). For the non-Rastelli group these data at 20 years were
Digital signal integrity and stability in the ATLAS Level-1 Calorimeter Trigger
The ATLAS Level-1 calorimeter trigger is a hardware-based system with the goal of identifying high-pT objects and to measure total and missing ET in the ATLAS calorimeters within an overall latency of 2.5 microseconds. This trigger system is composed of the Preprocessor which digitises about 7200 analogue input channels and two digital processors to identify high-pT signatures and to calculate the energy sums. The digital part consists of multi-stage, pipelined custom-built modules. The high demands on connectivity between the initial analogue stage and digital part and between the custom-built modules are presented. Furthermore the techniques to establish timing regimes and verify connectivity and stable operation of these digital links will be described
Commissioning of the Jet/Energy-sum and Cluster Processors for the ATLAS Level-1 Calorimeter Trigger System
The ATLAS first-level calorimeter trigger is a hardwarebased system designed to identify high-pT jets, electron/photon and tau candidates, and to measure total and missing ET. The trigger consists of a Preprocessor system which digitises 7200 analogue inputs, and two digital multicrate processor systems which find jets, measure energy sums, and identify localised energy deposits (electron/photon and tau candidates). In order to provide a trigger quickly enough, the hardware is parallel and pipelined. Experience so far of the Jet/Energy-sum and Cluster Processor system production, commissioning, and integration into ATLAS will be described
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