2,613 research outputs found
A Statistical Description of AGN Jet Evolution from the VLBA Imaging and Polarimetry Survey (VIPS)
A detailed analysis of the evolution of the properties of core-jet systems
within the VLBA Imaging and Polarimetry Survey (VIPS) is presented. We find a
power-law relationship between jet intensity and width that suggests for the
typical jet, little if any energy is lost as it moves away from its core. Using
VLA images at 1.5 GHz, we have found evidence that parsec-scale jets tend to be
aligned with the the direction of emission on kiloparsec scales. We also found
that this alignment improves as the jets move farther from their cores on
projected scales as small as ~50-100 pc. This suggests that realignment of jets
on these projected scales is relatively common. We typically find a modest
amount of bending (a change in jet position angle of ~5 deg.) on these scales,
suggesting that this realignment may typically occur relatively gradually.Comment: Accepted to ApJ, 20 pages, 8 figure
Characteristics of Gamma-Ray Loud Blazars in the VLBA Imaging and Polarimetry Survey
The radio properties of blazars detected by the Large Area Telescope (LAT) on
board the Fermi Gamma-ray Space Telescope have been observed as part of the
VLBA Imaging and Polarimetry Survey (VIPS). This large, flux-limited sample of
active galactic nuclei (AGN) provides insights into the mechanism that produces
strong gamma-ray emission. At lower flux levels, radio flux density does not
directly correlate with gamma-ray flux. We find that the LAT-detected BL Lacs
tend to be similar to the non-LAT BL Lacs, but that the LAT-detected FSRQs are
often significantly different from the non-LAT FSRQs. The differences between
the gamma-ray loud and quiet FSRQs can be explained by Doppler boosting; these
objects appear to require larger Doppler factors than those of the BL Lacs. It
is possible that the gamma-ray loud FSRQs are fundamentally different from the
gamma-ray quiet FSRQs. Strong polarization at the base of the jet appears to be
a signature for gamma-ray loud AGN.Comment: 32 pages, 9 figures, accepted by Ap
Outbreak of acute hepatitis C following the use of anti-hepatitis C virus--screened intravenous immunoglobulin therapy
BACKGROUND and AIMS: Hepatitis C virus (HCV) infection has been associated with intravenous (IV) immunoglobulin (Ig), and plasma donations used to prepare IV Ig are now screened to prevent transmission. Thirty-six patients from the United Kingdom received infusions from a batch of anti-HCV antibody-screened intravenous Ig (Gammagard; Baxter Healthcare Ltd., Thetford, Norfolk, England) that was associated with reports of acute hepatitis C outbreak in Europe. The aim of this study was to document the epidemiology of this outbreak. METHODS: Forty-six patients from the United Kingdom treated with Gammagard (34 exposed and 12 unexposed to the batch) returned epidemiological questionnaires. RESULTS: Eighty-two percent of the exposed patients (28 of 34) became positive for HCV RNA. Eighteen percent of the patients (6 of 34) who had infusions with this batch tested negative for HCV RNA, but 2 of the patients had abnormal liver function and subsequently seroconverted to anti-HCV antibody positive. Twenty-seven percent of the patients (9 of 34) developed jaundice, and 79% (27 of 34) had abnormal liver transferase levels. Virus isolates (n=21), including an isolate from the implicated batch, were genotype 1a and virtually identical by sequence analysis of the NS5 region, consistent with transmission from a single source. CONCLUSIONS: Hepatitis C infection can be transmitted by anti-HCV-screened IV Ig. Careful documentation of IV Ig batch numbers and regular biochemical monitoring is recommended for all IV Ig recipients
The State of Open Source Software (OSS) In South Africa
This paper explores the state of Open Source Software (OSS) in South Africa. The use of OSS in the business and government environment, as well as the supply and demand of OSS professionals in the South African environment are investigated. This research can also provide businesses with an objective tool with which to help them evaluate OSS in their businesses.
The results depict a growing trend in the use of OSS in South Africa. Only a small percentage of SA organisations have significant usage levels of OSS, with the majority of OSS users planning on maintaining their current levels of usage. It was observed that 67% of non-OSS users are considering OSS use in the future, with the majority of these respondents having made preliminary investigations into the viability of OSS use.
Further results show an association between the size of an organisation and the usage of OSS, with smaller and medium sized enterprises using OSS more than larger organisations. It was also observed that the majority of training institutes perceive that there will be a growth in demand for OSS training within the next 5 years, which correlates with findings that the number of training workshops and institutes are increasing to accommodate the increase in demand
J16021+3326: New Multi-Frequency Observations of a Complex Source
We present multifrequency Very Long Baseline Array (VLBA) observations of
J16021+3326. These observations, along with variability data obtained from the
Owens Valley Radio Observatory (OVRO) candidate gamma-ray blazar monitoring
program, clearly indicate this source is a blazar. The peculiar characteristic
of this blazar, which daunted previous classification attempts, is that we
appear to be observing down a precessing jet, the mean orientation of which is
aligned with us almost exactly.Comment: 16 pages, 7 Figures, 2 Tables, accepted to Ap
Neighbours matter and the weak succumb: Ash dieback infection is more severe in ash trees with fewer conspecific neighbours and lower prior growth rate
The epidemiology and severity of ash dieback (ADB), the disease caused by the ascomycete fungus Hymenoscyphus fraxineus, has been linked to a variety of site conditions; however, there has been a lack of analysis at an individual tree scale.Symptoms of ADB were scored on ca. 400 trees of Fraxinus excelsior (ash) in permanent sample plots during two successive years in a UK natural woodland reserve. Using comprehensive plot records maintained since 1945, and detailed spatial records updated since 1977, we assembled an array of potential explanatory variables, including site environment factors, ash tree density, previous and present tree condition and near neighbourhood summary statistics (NNSS), such as species mingling and size dominance. Their impact on the severity of ADB of focal ash trees was tested with generalised linear mixed effects models (GLMM).The severity of ADB was much greater in the lower slope parts of the site with moister soils and least in a managed area subject to tree thinning in the previous 35 years. Severity of ADB had a negative association with focal ash tree prior relative growth rate over a period of a decade immediately before the disease was detected at the site. Greater ADB severity was also significantly associated with smaller diameter at breast height of ash trees. Additionally, ADB was significantly positively associated with a greater proportion of heterospecific trees amongst the six nearest neighbours of the focal tree.Synthesis. The relationship of the severity of ADB disease with site environment, tree condition and neighbourhood is complex but nevertheless important in the progression of the disease. The findings suggest some silvicultural interventions, such as thinning to increase the vigour of retained ash trees, might reduce the impact of ADB
Rotating strings
Analytical expressions are provided for the configurations of an
inextensible, flexible, twistable inertial string rotating rigidly about a
fixed axis. Solutions with trivial radial dependence are helices of arbitrary
radius and pitch. Non-helical solutions are governed by a cubic equation whose
roots delimit permissible values of the squared radial coordinate. Only curves
coplanar with the axis of rotation make contact with it.Comment: added to discussion and made small revisions to tex
Nonlocal appearance of a macroscopic angular momentum
We discuss a type of measurement in which a macroscopically large angular
momentum (spin) is "created" nonlocally by the measurement of just a few atoms
from a double Fock state. This procedure apparently leads to a blatant
nonconservation of a macroscopic variable - the local angular momentum. We
argue that while this gedankenexperiment provides a striking illustration of
several counter-intuitive features of quantum mechanics, it does not imply a
non-local violation of the conservation of angular momentum.Comment: 10 pages, 1 figur
Super-roughening versus intrinsic anomalous scaling of surfaces
In this paper we study kinetically rough surfaces which display anomalous
scaling in their local properties such as roughness, or height-height
correlation function. By studying the power spectrum of the surface and its
relation to the height-height correlation, we distinguish two independent
causes for anomalous scaling. One is super-roughening (global roughness
exponent larger than or equal to one), even if the spectrum behaves non
anomalously. Another cause is what we term an intrinsically anomalous spectrum,
in whose scaling an independent exponent exists, which induces different
scaling properties for small and large length scales (that is, the surface is
not self-affine). In this case, the surface does not need to be super-rough in
order to display anomalous scaling. In both cases, we show how to extract the
independent exponents and scaling relations from the correlation functions, and
we illustrate our analysis with two exactly solvable examples. One is the
simplest linear equation for molecular beam epitaxy , well known to display
anomalous scaling due to super-roughening. The second example is a random
diffusion equation, which features anomalous scaling independent of the value
of the global roughness exponent below or above one.Comment: 9 pages, 6 figures, Revtex (uses epsfig), Phys. Rev. E, submitte
CGRaBS: An All-Sky Survey of Gamma-Ray Blazar Candidates
We describe a uniform all-sky survey of bright blazars, selected primarily by
their flat radio spectra, that is designed to provide a large catalog of likely
gamma-ray AGN. The defined sample has 1625 targets with radio and X-ray
properties similar to those of the EGRET blazars, spread uniformly across the
|b| > 10 deg sky. We also report progress toward optical characterization of
the sample; of objects with known R < 23, 85% have been classified and 81% have
measured redshifts. One goal of this program is to focus attention on the most
interesting (e.g., high redshift, high luminosity, ...) sources for intensive
multiwavelength study during the observations by the Large Area Telescope (LAT)
on GLAST.Comment: 18 pages, 6 figures, 1 machine-readable table available at
http://astro.stanford.edu/CGRaBS/ ; accepted for publication in ApJ
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