1,815 research outputs found
The HIFI spectral survey of AFGL 2591 (CHESS). II. Summary of the survey
This paper presents the richness of submillimeter spectral features in the
high-mass star forming region AFGL 2591. As part of the CHESS (Chemical
Herschel Survey of Star Forming Regions) Key Programme, AFGL 2591 was observed
by the Herschel/HIFI instrument. The spectral survey covered a frequency range
from 480 up to 1240 GHz as well as single lines from 1267 to 1901 GHz (i.e. CO,
HCl, NH3, OH and [CII]). Rotational and population diagram methods were used to
calculate column densities, excitation temperatures and the emission extents of
the observed molecules associated with AFGL 2591. The analysis was supplemented
with several lines from ground-based JCMT spectra. From the HIFI spectral
survey analysis a total of 32 species were identified (including
isotopologues). In spite of the fact that lines are mostly quite week, 268
emission and 16 absorption lines were found (excluding blends). Molecular
column densities range from 6e11 to 1e19 cm-2 and excitation temperatures range
from 19 to 175 K. One can distinguish cold (e.g. HCN, H2S, NH3 with
temperatures below 70 K) and warm species (e.g. CH3OH, SO2) in the protostellar
envelope.Comment: Accepted to A&
The classification of irreducible admissible mod p representations of a p-adic GL_n
Let F be a finite extension of Q_p. Using the mod p Satake transform, we
define what it means for an irreducible admissible smooth representation of an
F-split p-adic reductive group over \bar F_p to be supersingular. We then give
the classification of irreducible admissible smooth GL_n(F)-representations
over \bar F_p in terms of supersingular representations. As a consequence we
deduce that supersingular is the same as supercuspidal. These results
generalise the work of Barthel-Livne for n = 2. For general split reductive
groups we obtain similar results under stronger hypotheses.Comment: 55 pages, to appear in Inventiones Mathematica
Probing the BLR in AGNs using time variability of associated absorption line
It is know that most of the clouds producing associated absorption in the
spectra of AGNs and quasars do not completely cover the background source
(continuum + broad emission line region, BLR). We note that the covering factor
derived for the absorption is the fraction of photons occulted by the absorbing
clouds, and is not necessarily the same as the fractional area covered. We show
that the variability in absorption lines can be produced by the changes in the
covering factor caused by the variation in the continuum and the finite light
travel time across the BLR. We discuss how such a variability can be
distinguished from the variability caused by other effects and how one can use
the variability in the covering factor to probe the BLR.Comment: 12 pages, latex(aaspp4.sty), 2 figures, (To appear in ApJ
Staphylococcus aureus proteins Sbi and Efb recruit human plasmin to degrade complement C3 and C3b
Upon host infection, the human pathogenic microbe Staphylococcus aureus (S. aureus) immediately faces innate immune reactions such as the activated complement system. Here, a novel innate immune evasion strategy of S. aureus is described. The staphylococcal proteins surface immunoglobulin-binding protein (Sbi) and extracellular fibrinogen-binding protein (Efb) bind C3/C3b simultaneously with plasminogen. Bound plasminogen is converted by bacterial activator staphylokinase or by host-specific urokinase-type plasminogen activator to plasmin, which in turn leads to degradation of complement C3 and C3b. Efb and to a lesser extend Sbi enhance plasmin cleavage of C3/C3b, an effect which is explained by a conformational change in C3/C3b induced by Sbi and Efb. Furthermore, bound plasmin also degrades C3a, which exerts anaphylatoxic and antimicrobial activities. Thus, S. aureus Sbi and Efb comprise platforms to recruit plasmin(ogen) together with C3 and its activation product C3b for efficient degradation of these complement components in the local microbial environment and to protect S. aureus from host innate immune reactions
Multi-source self-calibration: Unveiling the microJy population of compact radio sources
Context. Very Long Baseline Interferometry (VLBI) data are extremely
sensitive to the phase stability of the VLBI array. This is especially
important when we reach {\mu}Jy r.m.s. sensitivities. Calibration using
standard phase referencing techniques is often used to improve the phase
stability of VLBI data but the results are often not optimal. This is evident
in blank fields that do not have in-beam calibrators. Aims. We present a
calibration algorithm termed Multi-Source Self-Calibration (MSSC) which can be
used after standard phase referencing on wide-field VLBI observations. This is
tested on a 1.6 GHz wide-field VLBI data set of the Hubble Deep Field-North and
the Hubble Flanking Fields. Methods. MSSC uses multiple target sources detected
in the field via standard phase referencing techniques and modifies the
visibili- ties so that each data set approximates to a point source. These are
combined to increase the signal to noise and permit self-calibration. In
principle, this should allow residual phase changes caused by the troposphere
and ionosphere to be corrected. By means of faceting, the technique can also be
used for direction dependent calibration. Results. Phase corrections, derived
using MSSC, were applied to a wide-field VLBI data set of the HDF-N comprising
of 699 phase centres. MSSC was found to perform considerably better than
standard phase referencing and single source self-calibration. All detected
sources exhibited dramatic improvements in dynamic range. Using MSSC, one
source reached the detection threshold taking the total detected sources to
twenty. 60% of these sources can now be imaged with uniform weighting compared
to just 45% with standard phase referencing. The Parseltongue code which
implements MSSC has been released and made publicly available to the
astronomical community (https://github.com/jradcliffe5/multi_self_cal).Comment: 7 pages, 4 figures, accepted to A&
Ratchet effect in dc SQUIDs
We analyzed voltage rectification for dc SQUIDs biased with ac current with
zero mean value. We demonstrate that the reflection symmetry in the
2-dimensional SQUID potential is broken by an applied flux and with appropriate
asymmetries in the dc SQUID. Depending on the type of asymmetry, we obtain a
rocking or a simultaneously rocking and flashing ratchet, the latter showing
multiple sign reversals in the mean voltage with increasing amplitude of the ac
current. Our experimental results are in agreement with numerical solutions of
the Langevin equations for the asymmetric dc SQUID.Comment: 10 pages including 5 Postscript figure
Moving in the Dark-Evidence for an Influence of Artificial Light at Night on the Movement Behaviour of European Hedgehogs (Erinaceus europaeus).
Berger A, Lozano B, Barthel LMF, Schubert N. Moving in the Dark-Evidence for an Influence of Artificial Light at Night on the Movement Behaviour of European Hedgehogs (Erinaceus europaeus). Animals. 2020;10(8): 1306.With urban areas growing worldwide comes an increase in artificial light at night (ALAN), causing a significant impact on wildlife behaviour and its ecological relationships. The effects of ALAN on nocturnal and protected European hedgehogs (Erinaceus europaeus) are unknown but their identification is important for sustainable species conservation and management. In a pilot study, we investigated the influence of ALAN on the natural movement behaviour of 22 hedgehogs (nine females, 13 males) in urban environments. Over the course of four years, we equipped hedgehogs at three different study locations in Berlin with biologgers to record their behaviour for several weeks. We used Global Positioning System (GPS) tags to monitor their spatial behaviour, very high-frequency (VHF) loggers to locate their nests during daytime, and accelerometers to distinguish between active and passive behaviours. We compared the mean light intensity of the locations recorded when the hedgehogs were active with the mean light intensity of simulated locations randomly distributed in the individual's home range. We were able to show that the ALAN intensity of the hedgehogs' habitations was significantly lower compared to the simulated values, regardless of the animal's sex. This ALAN-related avoidance in the movement behaviour can be used for applied hedgehog conservation
Infrared-detected AGNs in the local Universe
Spitzer/IRAC color selection is a promising technique to identify hot
accreting nuclei, that is to say AGN, in galaxies. We demonstrate this using a
small sample of SAURON galaxies, and explore this further. The goal of this
study is to find a simple and efficient way to reveal optically obscured
nuclear accretion in (nearby) galaxies. We apply an infrared selection method
to the Spitzer Survey of Stellar Structures in Galaxies (S4G) sample of more
than 2500 galaxies, together with its extension sample of more than 400
galaxies. We use the Spitzer colors to find galaxies in the SG survey
containing a hot core, suggesting the presence of a strong AGN, and study the
detection fraction as a function of morphological type. We test this infrared
color selection method by examining the radio properties of the galaxies, using
the VLA NVSS and FIRST surveys. Using the radio data, we demonstrate that
galaxies displaying hot mid-infrared nuclei stand out as being (candidate)
active galaxies. When using, instead of Spitzer, colors from the lower spatial
resolution WISE mission, we reproduce these results. Hence multi-band infrared
imaging represents a useful tool to uncover optically obscured nuclear activity
in galaxies.Comment: 11 pages, accepted in Astronomy and Astrophysic
Entanglement entropy in collective models
We discuss the behavior of the entanglement entropy of the ground state in
various collective systems. Results for general quadratic two-mode boson models
are given, yielding the relation between quantum phase transitions of the
system (signaled by a divergence of the entanglement entropy) and the
excitation energies. Such systems naturally arise when expanding collective
spin Hamiltonians at leading order via the Holstein-Primakoff mapping. In a
second step, we analyze several such models (the Dicke model, the two-level BCS
model, the Lieb-Mattis model and the Lipkin-Meshkov-Glick model) and
investigate the properties of the entanglement entropy in the whole parameter
range. We show that when the system contains gapless excitations the
entanglement entropy of the ground state diverges with increasing system size.
We derive and classify the scaling behaviors that can be met.Comment: 11 pages, 7 figure
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