788 research outputs found
Kinematic differences between NLS1 and BLAGN sources
It is well-known that the higher policyclic aromatic hydrocarbon (PAH)
abundance, lower black hole mass, higher accretion rate and lower luminosities
are among the major characteristics of Narrow-Line Seyfert galaxies (NLS1),
when they are compared to Broad line Seyfert galaxies (BLS1). NLS1s may be
normal Seyfert galaxies at an early stage of evolution, their black holes may
still be growing and/or they could be special for some other reason. In this
work we discuss the findings that NLS1s have most of line and continuum
luminosities correlated with FWHM(H), which may be the trace of their
rapid black hole mass grow. BLS1 do not show such trends. Also, PAHs may be
destroyed as the black hole grows and the starbursts are removed, for NLS1
objects.Comment: Revisiting narrow-line Seyfert 1 galaxies and their place in the
Universe - NLS1 Padov
EMG Map for Designing the Electrode Shape for Functional Electrical Therapy of Upper Extremities
Achieving the functional grasp by electrical stimulation using surface electrodes is a demanding task. The innervations of muscles come via ulnar, radial and median nerves. The anatomy of nerve branches connecting various muscles in the forearm differs significantly between individuals. We hypothesize that the anatomical differences between the paretic and nonparetic arms are minimal. Based on this assumption we developed a method where the differences of muscle activities (EMG) between the healthy and paretic arms recorded by the 24-contact electrode within an array define the target zones to be stimulated on the affected forearm. We used special electrode where magnetic contacts allow simple change of the stimulation pads. The examiner positions the magnetic contact on the pads where the EMG differences are maximal. The stimulator delivers asynchronous stimulation to the selected pads. We proved that the method is working in stroke patients by measuring joint angles and the grasping force. Ā© 2019, Springer Nature Switzerland AG.Biosystems and Biorobotics, Vol. 21This is the peer-reviewed version of the following article: PopoviÄ-Maneski, L., TopaloviÄ, I., 2019. EMG Map for Designing the Electrode Shape for Functional Electrical Therapy of Upper Extremities, in: Masia, L., Micera, S., Akay, M., Pons, J.L. (Eds.), Converging Clinical and Engineering Research on Neurorehabilitation III, Biosystems & Biorobotics. Springer International Publishing, pp. 1003ā1007, http://dx.doi.org/10.1007/978-3-030-01845-0_20
Line shifts in accretion disks - the case of Fe K
Here we present a short overview and main results of our investigations of
several effects which can induce shifts in the broad Fe K line emitted
from relativistic accretion disks around single and binary supermassive black
holes. We used numerical simulations based on ray-tracing method in the Kerr
metric to study the role of classical Doppler shift, special relativistic
transverse Doppler shift and Doppler beaming, general relativistic
gravitational redshift, and perturbations of the disk emissivity in the
formation of the observed Fe K line profiles. Besides, we also
investigated whether the observed line profiles from the binary systems of
supermassive black holes could be affected by the Doppler shifts due to
dynamics of such systems. The presented results demonstrate that all these
effects could have a significant influence on the observed profiles of the
broad Fe K line emitted from relativistic accretion disks around single
and binary supermassive black holes.Comment: 9 pages, 5 figures, 1 table. Accepted for publication in Astrophysics
and Space Scienc
Aging Effects Across the Metal-Insulator Transition in Two Dimensions
Aging effects in the relaxations of conductivity of a two-dimensional
electron system in Si have been studied as a function of carrier density. They
reveal an abrupt change in the nature of the glassy phase at the
metal-insulator transition (MIT): (a) while full aging is observed in the
insulating regime, there are significant departures from full aging on the
metallic side of the MIT, before the glassy phase disappears completely at a
higher density ; (b) the amplitude of the relaxations peaks just below the
MIT, and it is strongly suppressed in the insulating phase. Other aspects of
aging, including large non-Gaussian noise and similarities to spin glasses,
also have been discussed.Comment: 4+ pages, 5 figures; minor changes, accepted for publication in PR
Mesoscopic Behavior Near a Two-Dimensional Metal-Insulator Transition
We study conductance fluctuations in a two-dimensional electron gas as a
function of chemical potential (or gate voltage) from the strongly insulating
to the metallic regime. Power spectra of the fluctuations decay with two
distinct exponents (1/v_l and 1/v_h). For conductivity , we find a third exponent (1/v_i) in the shortest samples, and
non-monotonic dependence of v_i and v_l on \sigma. We study the dependence of
v_i, v_l, v_h, and the variances of corresponding fluctuations on \sigma,
sample size, and temperature. The anomalies near
indicate that the dielectric response and screening length are critically
behaved, i.e. that Coulomb correlations dominate the physics.Comment: Revised according to referee remark
Plasma Processing of Large Curved Surfaces for SRF Cavity Modification
Plasma based surface modification of niobium is a promising alternative to
wet etching of superconducting radio frequency (SRF) cavities. The development
of the technology based on Cl2/Ar plasma etching has to address several crucial
parameters which influence the etching rate and surface roughness, and
eventually, determine cavity performance. This includes dependence of the
process on the frequency of the RF generator, gas pressure, power level, the
driven (inner) electrode configuration, and the chlorine concentration in the
gas mixture during plasma processing. To demonstrate surface layer removal in
the asymmetric non-planar geometry, we are using a simple cylindrical cavity
with 8 ports symmetrically distributed over the cylinder. The ports are used
for diagnosing the plasma parameters and as holders for the samples to be
etched. The etching rate is highly correlated with the shape of the inner
electrode, radio-frequency (RF) circuit elements, chlorine concentration in the
Cl2/Ar gas mixtures, residence time of reactive species and temperature of the
cavity. Using cylindrical electrodes with variable radius, large-surface
ring-shaped samples and d.c. bias implementation in the external circuit we
have demonstrated substantial average etching rates and outlined the
possibility to optimize plasma properties with respect to maximum surface
processing effect
Photo-centric variability of quasars caused by variations in their inner structure: Consequences on Gaia measurements
We study the photocenter position variability due to variations in the quasar
inner structure. We consider variability in the accretion disk emissivity and
torus structure variability due to different illumination by the central
source. We discuss possible detection of these effects by Gaia. Observations of
the photocenter variability in two AGNs, SDSS J121855+020002 and SDSS
J162011+1724327 have been reported and discussed. With investigation of the
variations in the quasar inner structure we explore how much this effect can
affect the position determination and whether it can be (or not) detected with
Gaia mission. We used (a) a model of a relativistic disk, including the
perturbation that can increase brightness of a part of the disk, and
consequently offset the photocenter position, and (b) a model of a dusty torus
which absorbs and re-emits the incoming radiation from accretion disk. We
estimated the value of the photocenter offset due to these two effects. We
found that perturbations in the inner structure can significantly offset the
photocenter. It depends on the characteristics of perturbation and accretion
disk and structure of the torus. In the case of two considered QSOs the
observed photocenter offsets cannot be explained by variations in the accretion
disk and other effects should be considered. We discussed possibility of
exploding stars very close to the AGN source, and also possibility that there
are two variable sources in the center of these two AGNs that may indicate a
binary super-massive black hole system on a kpc (pc) scale. The Gaia mission
seems to be very perspective, not only for astrometry, but also for exploring
the inner structure of AGNs. We conclude that variations in the quasar inner
structure can affect the observed photocenter (up to several mas). There is a
chance to observe such effect in the case of bright and low-redshifted QSOs.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysics. Language improved, typos correcte
The influence of gravitational lensing on the spectra of lensed QSOs
We consider the influence of (milli/micro)lensing on the spectra of lensed
QSOs. We propose a method for the observational detection of microlensing in
the spectra of lensed QSOs and apply it to the spectra of the three lensed QSOs
(PG 1115+080, QSO 1413+117 and QSO 0957+561) observed with Hubble Space
Telescope (HST). We find that the flux ratio between images A1 and A2 of PG
1115+080 is wavelength-dependent and shows differential magnification between
the emission lines and the continuum. We interpret this magnification as
arising from millilensing. We also find that the temporal variations in the
continuum of image C of QSO 1413+117 may be caused by microlensing, while the
temporal variation observed in QSO 0957+561 was probably an intrinsic one.Comment: 11 pages, accepted for publication in MNRA
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