2,850 research outputs found
Analytic structure of the Landau gauge gluon propagator
The analytic structure of the non-perturbative gluon propagator contains
information on the absence of gluons from the physical spectrum of the theory.
We study this structure from numerical solutions in the complex momentum plane
of the gluon and ghost Dyson-Schwinger equations in Landau gauge Yang-Mills
theory. The resulting ghost and gluon propagators are analytic apart from a
distinct cut structure on the real, timelike momentum axis. The propagator
violates the Osterwalder-Schrader positivity condition, confirming the absence
of gluons from the asymptotic spectrum of the theory.Comment: 5 pages, 7 figure
Multi-frequency investigation of the parsec- and kilo-parsec-scale radio structures in high-redshift quasar PKS 1402+044
We investigate the frequency-dependent radio properties of the jet of the
luminous high-redshift (z = 3.2) radio quasar PKS 1402+044 (J1405+0415) by
means of radio interferometric observations. The observational data were
obtained with the VLBI Space Observatory Programme (VSOP) at 1.6 and 5 GHz,
supplemented by other multi-frequency observations with the Very Long Baseline
Array (VLBA; 2.3, 8.4, and 15 GHz) and the Very Large Array (VLA; 1.4, 5, 15,
and 43 GHz). The observations span a period of 7 years. We find that the
luminous high-redshift quasar PKS 1402+044 has a pronounced "core-jet"
morphology from the parsec to the kilo-parsec scales. The jet shows a steeper
spectral index and lower brightness temperature with increasing distance from
the jet core. The variation of brightness temperature agrees well with the
shock-in-jet model. Assuming that the jet is collimated by the ambient magnetic
field, we estimate the mass of the central object as ~10^9 M_sun. The upper
limit of the jet proper motion of PKS 1402+044 is 0.03 mas/yr (~3c) in the
east-west direction.Comment: 9 pages, 6 figures
The Parkes quarter-Jansky flat-spectrum sample 3. Space density and evolution of QSOs
We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of
space density, including the redshift distribution, the radio luminosity
function, and the evidence for a redshift cutoff. With regard to the luminosity
function, we note the strong evolution in space density from the present day to
epochs corresponding to redshifts ~ 1. We draw attention to a selection effect
due to spread in spectral shape that may have misled other investigators to
consider the apparent similarities in shape of luminosity functions in
different redshift shells as evidence for luminosity evolution. To examine the
evolution at redshifts beyond 3, we develop a model-independent method based on
the V_max test using each object to predict expectation densities beyond z=3.
With this we show that a diminution in space density at z > 3 is present at a
significance level >4 sigma. We identify a severe bias in such determinations
from using flux-density measurements at epochs significantly later than that of
the finding survey. The form of the diminution is estimated, and is shown to be
very similar to that found for QSOs selected in X-ray and optical wavebands.
The diminution is also compared with the current estimates of star-formation
evolution, with less conclusive results. In summary we suggest that the
reionization epoch is little influenced by powerful flat-spectrum QSOs, and
that dust obscuration does not play a major role in our view of the QSO
population selected at radio, optical or X-ray wavelengths.Comment: 18 pages, 11 figures, accepted 18 Dec 2004, Astron. & Astrophys. The
accepted version is expanded to include an analysis of the form of the
decline in radio-QSO space density at high redshifts. This is compared with
the forms of epoch dependence derived for optically-selected QSOs, for
X-ray-selected QSOs, and for star formation rat
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Congressional Careers, Committee Assignments, and Seniority Randomization in the US House of Representatives
This paper estimates the effects of initial committee seniority on the career histories of Democratic members of the House of Representatives from 1949 to 2006. When more than one freshman representative is assigned to a committee, positions in the seniority queue are established by lottery. Randomization ensures that queue positions are uncorrelated in expectation with other legislator characteristics within these groups. This natural experiment allows us to estimate the causal effect of seniority on a variety of career outcomes. Lower-ranked committee members areless likely to serve as subcommittee chairs on their initial committee; are more likely to transfer to other committees; and have fewer sponsored bills passed in the jurisdiction of their initial committee. On the other hand, there is little evidence that the seniority randomization has a net effect on reelection outcomes or noncommittee bills passed.GovernmentOther Research Uni
ICPL_ESIQuant – a Powerful Freeware Tool for Handling Proteomics LCESI- MS2 Experiments
Among the MS-based quantitative methods using stable isotope labelling, the Isotope-Coded Protein Label (ICPL) technique has emerged as a powerful tool to identify and relatively quantify thousands of proteins within complex protein mixtures. The ICPL_ESIQuant 3.0 software package is one of the key components of the ICPL-ESI workflow, covering data processing steps like LC-MS feature detection, ICPL doublet/triplet/quadruplet quantification as well as a merging step of LC-MS features and Mascot search results. As unique features, the software performs isotope pattern overlap corrections and utilizes additional chemical knowledge, e.g. the physico-chemical properties of the ICPL labels, to discard false positive isotope pattern, which significantly improves the quality of the final peptide and protein results. ICPL_ESIQuant is the first freeware tool on the market, which supports both the shotgun proteomics strategy using Data Dependent Acquisition (DDA) and the directed proteomics strategy using mass inclusion lists for precursor ion selection. ICPL_ESIQuant 3.0 (32 and 64 bit versions) can be downloaded from https://sourceforge.net/projects/icplquant/ files
Alternativas para la recuperación, conservación y uso del Bosque de Araucaria en Brasil: el caso de la Reserva Forestal Embrapa/EPAGRI (Caçador).
When native species become invasive: the case of bamboos in fragmented forests of Southern Brazil.
ESA 2013. Abstract. COS 29-2
The running coupling from the four-gluon vertex in Landau gauge Yang-Mills theory
We consider the running coupling from the four-gluon vertex in Landau gauge,
SU() Yang-Mills theory as given by a combination of dressing functions of
the vertex and the gluon propagator. We determine these functions numerically
from a coupled set of Dyson-Schwinger equations. We reproduce asymptotic
freedom in the ultraviolet momentum region and find a coupling of order one at
mid-momenta. In the infrared we find a nontrivial (i.e. nonzero) fixed point
which is three orders of magnitude smaller than the corresponding fixed point
in the coupling of the ghost-gluon vertex. This result explains why the
Dyson-Schwinger and the functional renormalization group equations for the two
point functions can agree in the infrared, although their structure is quite
different. Our findings also support Zwanziger's notion of an infrared
effective theory driven by the Faddeev-Popov determinant.Comment: 25 pages, 4 figures; v2: minor clarifications added and typos
corrected, version accepted by PR
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