15,573 research outputs found
Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles
To gain a better understanding of the inner disc region that comprises active
galactic nuclei it is necessary to understand the pattern in which the disc is
illuminated (the emissivity profile) by X-rays emitted from the continuum
source above the black hole (corona). The differences in the emissivity
profiles produced by various corona geometries are explored via general
relativistic ray tracing simulations. Through the analysis of various
parameters of the geometries simulated it is found that emissivity profiles
produced by point source and extended geometries such as cylindrical slabs and
spheroidal coronae placed on the accretion disc are distinguishable. Profiles
produced by point source and conical geometries are not significantly
different, requiring an analysis of reflection fraction to differentiate the
two geometries. Beamed point and beamed conical sources are also simulated in
an effort to model jet-like coronae, though the differences here are most
evident in the reflection fraction. For a point source we determine an
approximation for the measured reflection fraction with the source height and
velocity. Simulating spectra from the emissivity profiles produced by the
various geometries produce distinguishable differences. Overall spectral
differences between the geometries do not exceed 15 per cent in the most
extreme cases. It is found that emissivity profiles can be useful in
distinguishing point source and extended geometries given high quality spectral
data of extreme, bright sources over long exposure times. In combination with
reflection fraction, timing, and spectral analysis we may use emissivity
profiles to discern the geometry of the X-ray source.Comment: 15 pages, 12 figures. Accepted for publication in MNRA
Wearable Platform for Automatic Recognition of Parkinson Disease by Muscular Implication Monitoring
The need for diagnostic tools for the characterization of progressive movement disorders - as the Parkinson Disease (PD) - aiming to early detect and monitor the pathology is getting more and more impelling. The parallel request of wearable and wireless solutions, for the real-time monitoring in a non-controlled environment, has led to the implementation of a Quantitative Gait Analysis platform for the extraction of muscular implications features in ordinary motor action, such as gait. The here proposed platform is used for the quantification of PD symptoms. Addressing the wearable trend, the proposed architecture is able to define the real-time modulation of the muscular indexes by using 8 EMG wireless nodes positioned on lower limbs. The implemented system “translates” the acquisition in a 1-bit signal, exploiting a dynamic thresholding algorithm. The resulting 1-bit signals are used both to define muscular indexes both to drastically reduce the amount of data to be analyzed, preserving at the same time the muscular information. The overall architecture has been fully implemented on Altera Cyclone V FPGA. The system has been tested on 4 subjects: 2 affected by PD and 2 healthy subjects (control group). The experimental results highlight the validity of the proposed solution in Disease recognition and the outcomes match the clinical literature results
A Method for the Measurement of Digitizers’ Absolute Phase Error
A lot of engineering applications, from telecommunications to power systems, require
accurate measurement of phase angles. Some of them, like synchrophasor measurement and
calibration of instrument transformers with digital output, in order to reach high phase
measurement accuracy, require the knowledge of phase error of digitizers. Therefore, in this
paper a method for the measurement of digitizers’ absolute phase errors is proposed. It adopts a
sinewave and two square waves, that are the digitizer sample clock and a phase reference signal.
Combining the measurements of the relative phase differences between the adopted signals it is
possible to accurately evaluate the absolute phase error of a digitize
The MEV project: design and testing of a new high-resolution telescope for Muography of Etna Volcano
The MEV project aims at developing a muon telescope expressly designed for
the muography of Etna Volcano. In particular, one of the active craters in the
summit area of the volcano would be a suitable target for this experiment. A
muon tracking telescope with high imaging resolution was built and tested
during 2017. The telescope is a tracker based on extruded scintillating bars
with WLS fibres and featuring an innovative read-out architecture. It is
composed of three XY planes with a sensitive area of \SI{1}{m^2}; the angular
resolution does not exceeds \SI{0.4}{\milli\steradian} and the total angular
aperture is about \SI{45}{\degree}. A special effort concerned the design
of mechanics and electronics in order to meet the requirements of a detector
capable to work in a hostile environment such as the top of a tall volcano, at
a far distance from any facility. The test phase started in January 2017 and
ended successfully at the end of July 2017. An extinct volcanic crater (the
Monti Rossi, in the village of Nicolosi, about 15km from Catania) is the target
of the measurement. The detector acquired data for about 120 days and the
preliminary results are reported in this work
Double dynamical regime of confined water
The Van Hove self correlation function of water confined in a silica pore is
calculated from Molecular Dynamics trajectories upon supercooling. At long time
in the relaxation region we found that the behaviour of the real space
time dependent correlators can be decomposed in a very slow, almost frozen,
dynamics due to the bound water close to the substrate and a faster dynamics of
the free water which resides far from the confining surface. For free water we
confirm the evidences of an approach to a crossover mode coupling transition,
previously found in Q space. In the short time region we found that the two
dynamical regimes are overimposed and cannot be distinguished. This shows that
the interplay between the slower and the faster dynamics emerges in going from
early times to the relaxation region, where a layer analysis of the
dynamical properties can be performed.Comment: 6 pages with 9 figures. RevTeX. Accepted for pulbication in J. Phys.
Cond. Mat
Revealing structure and evolution within the corona of the Seyfert galaxy I Zw 1
X-ray spectral timing analysis is presented of XMM-Newton observations of the
narrow line Seyfert 1 galaxy I Zwicky 1 (I Zw 1) taken in 2015 January. After
exploring the effect of background flaring on timing analyses, X-ray time lags
between the reflection-dominated 0.3-1.0keV energy and continuum-dominated
1.0-4.0keV band are measured, indicative of reverberation off the inner
accretion disc. The reverberation lag time is seen to vary as a step function
in frequency; across lower frequency components of the variability, 3e-4 to
1.2e-3Hz a lag of 160s is measured, but the lag shortens to (59 +/- 4)s above
1.2e-3Hz. The lag-energy spectrum reveals differing profiles between these
ranges with a change in the dip showing the earliest arriving photons. The low
frequency signal indicates reverberation of X-rays emitted from a corona
extended at low height over the disc while at high frequencies, variability is
generated in a collimated core of the corona through which luminosity
fluctuations propagate upwards. Principal component analysis of the variability
supports this interpretation, showing uncorrelated variation in the spectral
slope of two power law continuum components. The distinct evolution of the two
components of the corona is seen as a flare passes inwards from the extended to
the collimated portion. An increase in variability in the extended corona was
found preceding the initial increase in X-ray flux. Variability from the
extended corona was seen to die away as the flare passed into the collimated
core leading to a second sharper increase in the X-ray count rate.Comment: 18 pages, 11 figures. Accepted for publication in MNRA
Exploiting Textons Distributions on Spatial Hierarchy for Scene Classification
This paper proposes a method to recognize scene categories using bags of visual words obtained by hierarchically partitioning into subregion the input images. Specifically, for each subregion the Textons distribution and the extension of the corresponding subregion are taken into account. The bags of visual words computed on the subregions are weighted and used to represent the whole scene. The classification of scenes is carried out by discriminative methods (i.e., SVM, KNN). A similarity measure based on Bhattacharyya coefficient is proposed to establish similarities between images, represented as hierarchy of bags of visual words. Experimental tests, using fifteen different scene categories, show that the proposed approach achieves good performances with respect to the state-of-the-art methods
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