5,993 research outputs found
Extended instantons generated on the lattice
We have been able to observe directly extended instantons on the lattice,
with a new method that does not require dislocations to measure them, and where
we do not perform cooling. We showed, based on the simple Abelian Higgs model
in dim., that one can extract the instanton and anti-instanton density
and their size, by measuring the topological charge, , on sub-volumes
larger than the instanton sizes, but smaller than the periodic lattice of size
. We are working on the generalization for non-abelian models.Comment: Talk presented at the LATTICE96(topology) ,uuencoded 3 pp in Latex, 1
ps fig., uses espcrc2.sty and epsf to include fi
A Common Origin for Quasar Extended Emission-Line Regions and Their Broad-Line Regions
We present a correlation between the presence of luminous extended
emission-line regions (EELRs) and the metallicity of the broad-line regions
(BLRs) of low-redshift quasars. The result is based on ground-based [O III]
5007 narrow-band imaging and Hubble Space Telescope UV spectra of 12 quasars at
0.20 < z < 0.45. Quasars showing luminous EELRs have low-metallicity BLRs (Z <
0.6 Z_Solar), while the remaining quasars show typical metal-rich gas (Z >
Z_Solar). Previous studies have shown that EELRs themselves also have low
metallicities (Z < 0.5 Z_Solar). The correlation between the occurrence of
EELRs and the metallicity of the BLRs, strengthened by the sub-Solar
metallicity in both regions, indicates a common external origin for the gas,
almost certainly from the merger of a gas-rich galaxy. Our results provide the
first direct observational evidence that the gas from a merger can indeed be
driven down to the immediate vicinity (< 1 pc) of the central black hole.Comment: Accepted for publication in ApJ Letters. 4 pages, 1 figure, 1 tabl
The bar PANDA focussing-lightguide disc DIRC
bar PANDA will be a fixed target experiment internal to the HESR antiproton storage ring at the future FAIR complex. The ANDA detector requires excellent particle-identification capabilities in order to achieve its scientific potential. Cherenkov counters employing the DIRC principle were chosen as PID detectors for the Target Spectrometer. The proposed Focussing-Lightguide Disc DIRC will cover the forward part of the Target Spectrometer acceptance in the angular range between 5° and 22°. Its design includes a novel approach to mitigate dispersion effects in the solid radiator of a DIRC counter using optical elements. The dispersion correction will enable the Focussing-Lightguide Disc DIRC to provide pion-kaon identification for momenta well above 3.5 GeV/c
Reconstruction methods — P‾ANDA focussing-light guide disc DIRC
The Focussing-Lightguide Disc DIRC will provide crucial Particle Identification (PID) information for the P‾ANDA experiment at FAIR, GSI. This detector presents a challenging environment for reconstruction due to the complexity of the expected hit patterns and the operating conditions of the P‾ANDA experiment. A discussion of possible methods to reconstruct PID from this detector is given here. Reconstruction software is currently under development
Strain accommodation through facet matching in LaSrCuO/NdCeCuO ramp-edge junctions
Scanning nano-focused X-ray diffraction (nXRD) and high-angle annular
dark-field scanning transmission electron microscopy (HAADF-STEM) are used to
investigate the crystal structure of ramp-edge junctions between
superconducting electron-doped NdCeCuO
and superconducting hole-doped LaSrCuO
thin films, the latter being the top layer. On the ramp, a new growth mode of
LaSrCuO with a 3.3 degree tilt of the
c-axis is found. We explain the tilt by developing a strain accommodation model
that relies on facet matching, dictated by the ramp angle, indicating that a
coherent domain boundary is formed at the interface. The possible implications
of this growth mode for the creation of artificial domains in morphotropic
materials are discussed.Comment: 5 pages, 4 figures & 3 pages supplemental information with 2 figures.
Copyright (2015) American Institute of Physics. This article may be
downloaded for personal use only. Any other use requires prior permission of
the author and the American Institute of Physics. The following article
appeared in APL Mat. 3, 086101 (2015) and may be found at
http://dx.doi.org/10.1063/1.492779
Lack of evidence for western flower thrips biotypes base don intra and inter-strain variation in gut bacteria
Western flower thrips is a polyphagous insect, which during the last 30 years has become a world wide pest. It was found earlier that these thrips are associated with a type of Erwinia species gut bacteria. In this study we examine the variation of bacteria within and between thrips individuals and try to find evidence for biotypes in western flower thrips regarding the type of gut bacteria. The existence of biotypes in this thrips species has been suggested by different authors. For example, thrips populations have been found that differ in resistance against pesticides and in their ability to transmit plant viruses. With biotypes we mean groups of individuals (strains, populations, lines) of a species which differ in one or more traits with other groups of that species. The gut bacteria of thrips are acquired by young thrips larvae via the host plant and have a beneficial effect on thrips development and oviposition. We studied thrips strains from different countries and host plants, and the isofemale lines that were created from them, on bean plant leaves. All thrips lines that we studied contained Erwinia species gut bacteria. Morphological and biochemical characteristics of gut bacteria from the thrips isofemale lines were similar to the Erwinia type strain from the reference, a thrips strain cultured on chrysanthemum in Amsterdam (TAC 93.XII.8). Per isofemale line we studied five thrips individuals and per thrips we studied four bacterial colonies, with RAPD markers. The genetic variation between bacteria isolated from thrips was as large among isofemale lines as within isofemale lines. No evidence for thrips biotypes was found. Bacteria within one thrips individual show a stronger degree of similarity than bacteria from different thrips individuals within a single rearing. This is probably due to a bottleneck caused by the limited number of successful infections of bacteria into the gut of the thrip
The evolution of the stellar populations in low surface brightness galaxies
We investigate the star formation history and chemical evolution of low
surface brightness (LSB) disk galaxies by modelling their observed
spectro-photometric and chemical properties using a galactic chemical and
photometric evolution model incorporating a detailed metallicity depen dent set
of stellar input data. For a large fraction of the LSB galaxies in our sample,
observed properties are best explained by models incorporating an exponentially
decreasing global star formation rate (SFR) ending at a present-day gas
fraction (M_{gas}/(M_{gas}+M_{stars}) = 0.5 for a galaxy age of 14 Gyr. For
some galaxies small amplitude star formation bursts are required to explain the
contribution of the young (5-50 Myr old) stellar population to the galaxy
integrated luminosity. This suggests that star formation has proceeded in a
stochastic manner.
The presence of an old stellar population in many late-type LSB galaxies
suggests that LSB galaxies roughly follow the same evolutionary history as HSB
galaxies, except at a much lower rate. In particular, our results imply that
LSB galaxies do not form late, nor have a delayed onset of star formation, but
simply evolve slowly.Comment: To be published in A&
Damped Lyman alpha Absorbing Galaxies At Low Redshifts z<1 From Hierarchical Galaxy Formation Models
We investigate Damped Ly-alpha absorbing galaxies (DLA galaxies) at low
redshifts z<1 in the hierarchical structure formation scenario to clarify the
nature of DLA galaxies because observational data of such galaxies mainly at
low redshifts are currently available. We find that our model well reproduces
distributions of fundamental properties of DLA galaxies such as luminosities,
column densities, impact parameters obtained by optical and near-infrared
imagings. Our results suggest that DLA systems primarily consist of low
luminosity galaxies with small impact parameters (typical radius about 3 kpc,
surface brightness from 22 to 27 mag arcsec^{-2}) similar to low surface
brightness (LSB) galaxies. In addition, we investigate selection biases arising
from the faintness and from the masking effect which prevents us from
identifying a DLA galaxy hidden or contaminated by a point spread function of a
background quasar. We find that the latter affects the distributions of DLA
properties more seriously rather than the former, and that the observational
data are well reproduced only when taking into account the masking effect. The
missing rate of DLA galaxies by the masking effect attains 60-90 % in the
sample at redshift 0<z<1 when an angular size limit is as small as 1 arcsec.
Furthermore we find a tight correlation between HI mass and cross section of
DLA galaxies, and also find that HI-rich galaxies with M(HI) \sim 10^{9} M_sun
dominate DLA systems. These features are entirely consistent with those from
the Arecibo Dual-Beam Survey which is a blind 21 cm survey. Finally we discuss
star formation rates, and find that they are typically about 10^{-2} M_sun
yr^{-1} as low as those in LSB galaxies.Comment: 21 pages, 13 figures, Accepted for publication in Astrophsical
Journa
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