871 research outputs found
Gamma-ray observations of Cygnus X-1 above 100 MeV in the hard and soft states
We present the results of multi-year gamma-ray observations by the AGILE
satellite of the black hole binary system Cygnus X-1. In a previous
investigation we focused on gamma-ray observations of Cygnus X-1 in the hard
state during the period mid-2007/2009. Here we present the results of the
gamma-ray monitoring of Cygnus X-1 during the period 2010/mid-2012 carried out
for which includes a remarkably prolonged `soft state' phase (June 2010 -- May
2011). Previous 1--10 MeV observations of Cyg X-1 in this state hinted at a
possible existence of a non-thermal particle component with substantial
modifications of the Comptonized emission from the inner accretion disk. Our
AGILE data, averaged over the mid-2010/mid-2011 soft state of Cygnus X-1,
provide a significant upper limit for gamma-ray emission above 100 MeV of
F_soft < 20 x 10^{-8} ph/cm^2/s, excluding the existence of prominent
non-thermal emission above 100 MeV during the soft state of Cygnus X-1. We
discuss theoretical implications of our findings in the context of high-energy
emission models of black hole accretion. We also discuss possible gamma-ray
flares detected by AGILE. In addition to a previously reported episode observed
by AGILE in October 2009 during the hard state, we report a weak but important
candidate for enhanced emission which occurred at the end of June 2010
(2010-06-30 10:00 - 2010-07-02 10:00 UT) exactly in coincidence with a
hard-to-soft state transition and before an anomalous radio flare. An appendix
summarizes all previous high-energy observations and possible detections of
Cygnus X-1 above 1 MeV.Comment: 16 pages, 12 figures, 1 table, accepted for publication in Ap
Dynamic causal modelling on infant fNIRS data: A validation study on a simultaneously recorded fNIRS-fMRI dataset
Tracking the connectivity of the developing brain from infancy through childhood is an area of increasing research interest, and fNIRS provides an ideal method for studying the infant brain as it is compact, safe and robust to motion. However, data analysis methods for fNIRS are still underdeveloped compared to those available for fMRI. Dynamic causal modelling (DCM) is an advanced connectivity technique developed for fMRI data, that aims to estimate the coupling between brain regions and how this might be modulated by changes in experimental conditions. DCM has recently been applied to adult fNIRS, but not to infants. The present paper provides a proof-of-principle for the application of this method to infant fNIRS data and a demonstration of the robustness of this method using a simultaneously recorded fMRI-fNIRS single case study, thereby allowing the use of this technique in future infant studies. fMRI and fNIRS were simultaneously recorded from a 6-month-old sleeping infant, who was presented with auditory stimuli in a block design. Both fMRI and fNIRS data were preprocessed using SPM, and analysed using a general linear model approach. The main challenges that adapting DCM for fNIRS infant data posed included: (i) the import of the structural image of the participant for spatial pre-processing, (ii) the spatial registration of the optodes on the structural image of the infant, (iii) calculation of an accurate 3-layer segmentation of the structural image, (iv) creation of a high-density mesh as well as (v) the estimation of the NIRS optical sensitivity functions. To assess our results, we compared the values obtained for variational Free Energy (F), Bayesian Model Selection (BMS) and Bayesian Model Average (BMA) with the same set of possible models applied to both the fMRI and fNIRS datasets. We found high correspondence in F, BMS, and BMA between fMRI and fNIRS data, therefore showing for the first time high reliability of DCM applied to infant fNIRS data. This work opens new avenues for future research on effective connectivity in infancy by contributing a data analysis pipeline and guidance for applying DCM to infant fNIRS data. [Abstract copyright: Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.
Genome-annotated bacterial collection of the barley rhizosphere microbiota
A culture collection of 41 bacteria isolated from the rhizosphere of cultivated barley (Hordeum vulgare subsp. vulgare) is available at the Division of Plant Sciences, University of Dundee (UK). The data include information on genes putatively implicated in nitrogen fixation, HCN channels, phosphate solubilization, and linked whole-genome sequences
On the Angular Resolution of the AGILE gamma-ray imaging detector
We present a study of the Angular Resolution of the AGILE gamma-ray imaging
detector (GRID) that is operational in space since April 2007. The AGILE
instrument is made of an array of 12 planes each equipped with a Tungsten
converter and Silicon micros trip detectors and is sensitive in the energy
range 50 MeV - 10 GeV. Among the space instruments devoted to gamma-ray
astrophysics, AGILE uniquely exploits an analog readout system with dedicated
electronics coupled with Silicon detectors. We show the results of Monte Carlo
simulations carried out to reproduce the gamma-ray detection by the GRID, and
we compare them to in-flight data. We use the Crab (pulsar + Nebula) system for
discussion of real data performance, since its E^{-2} energy spectrum is
representative of the majority of gamma-ray sources. For Crab-like spectrum
sources, the GRID angular resolution (FWHM of ~4deg at 100 MeV; ~0.8deg at 1
GeV; ~0.9deg integrating the full energy band from 100 MeV to tens of GeV) is
stable across a large field of view, being characterized by a flat response up
to 30deg off-axis. A comparison of the angular resolution obtained by the two
operational gamma-ray instruments, AGILE-GRID and Fermi-LAT, is interesting in
view of future gamma-ray missions, that are currently under study. The two
instruments exploit different detector configurations affecting the angular
resolution: the former being optimized in the readout and track reconstruction
especially in the low-energy band, the latter in terms of converter thickness
and power consumption. We show that, despite these differences, the angular
resolution of both instruments is very similar between 100 MeV and a few GeV.Comment: 19 pages, 8 figures, accepted for publication in Ap
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