4,952 research outputs found
The Nuclear Outflow in NGC 2110
We present a HST/STIS spectroscopic and optical/radio imaging study of the
Seyfert NGC 2110 aiming to measure the dynamics and understand the nature of
the nuclear outflow in the galaxy. Previous HST studies have revealed the
presence of a linear structure in the Narrow-Line Region (NLR) aligned with the
radio jet. We show that this structure is strongly accelerated, probably by the
jet, but is unlikely to be entrained in the jet flow. The ionisation properties
of this structure are consistent with photoionisation of dusty, dense gas by
the active nucleus. We present a plausible geometrical model for the NLR,
bringing together various components of the nuclear environment of the galaxy.
We highlight the importance of the circum-nuclear disc in determining the
appearance of the emission line gas and the morphology of the jet. From the
dynamics of the emission line gas, we place constraints on the accelerating
mechanism of the outflow and discuss the relative importance of radio source
synchrotron pressure, radio jet ram pressure and nuclear radiation pressure in
accelerating the gas. While all three mechanisms can account for the energetics
of the emission line gas, gravitational arguments support radio jet ram
pressure as the most likely source of the outflow.Comment: 15 pages, 7 figures; accepted to MNRA
Adiabatic quantum dynamics of the Lipkin-Meshkov-Glick model
The adiabatic quantum evolution of the Lipkin-Meshkov-Glick (LMG) model
across its quantum critical point is studied. The dynamics is realized by
linearly switching the transverse field from an initial large value towards
zero and considering different transition rates. We concentrate our attention
on the residual energy after the quench in order to estimate the level of
diabaticity of the evolution. We discuss a Landau-Zener approximation of the
finite size LMG model, that is successful in reproducing the behavior of the
residual energy as function of the transition rate in the most part of the
regimes considered. We also support our description through the analysis of the
entanglement entropy of the evolved state. The system proposed is a paradigm of
infinite-range interaction or high-dimensional models.Comment: 8 pages, 7 figures. (v2) minor revisions, published versio
Ionization Mechanisms in Jet-Dominated Seyferts: A Detailed Case Study
For the past 10 years there has been an active debate over whether fast
shocks play an important role in ionizing emission line regions in Seyfert
galaxies. To investigate this claim, we have studied the Seyfert 2 galaxy Mkn
78, using HST UV/optical images and spectroscopy. Since Mkn 78 provides the
archetypal jet-driven bipolar velocity field, if shocks are important anywhere
they should be important in this object. Having mapped the emission line fluxes
and velocity field, we first compare the ionization conditions to standard
photoionization and shock models. We find coherent variations of ionization
consistent with photoionization model sequences which combine optically thick
and thin gas, but are inconsistent with either autoionizing shock models or
photoionization models of just optically thick gas. Furthermore, we find
absolutely no link between the ionization of the gas and its kinematic state,
while we do find a simple decline of ionization degree with radius. We feel
this object provides the strongest case to date against the importance of shock
related ionization in Seyferts.Comment: 4 pages, 1 figure, to appear in the proceedings of IAU Symposium 222
"The Interplay among Black Holes, Stars and ISM in Galactic Nuclei", T.
Storchi Bergmann, L.C. Ho & H.R. Schmitt, ed
Fuzzy Inference System for VOLT/VAR control in distribution substations in isolated power systems
This paper presents a fuzzy inference system for voltage/reactive power
control in distribution substations. The purpose is go forward to automation
distribution and its implementation in isolated power systems where control
capabilities are limited and it is common using the same applications as in
continental power systems. This means that lot of functionalities do not apply
and computational burden generates high response times. A fuzzy controller,
with logic guidelines embedded based upon heuristic rules resulting from
operators at dispatch control center past experience, has been designed.
Working as an on-line tool, it has been tested under real conditions and it has
managed the operation during a whole day in a distribution substation. Within
the limits of control capabilities of the system, the controller maintained
successfully an acceptable voltage profile, power factor values over 0,98 and
it has ostensibly improved the performance given by an optimal power flow based
automation system
Speeding up critical system dynamics through optimized evolution
The number of defects which are generated on crossing a quantum phase
transition can be minimized by choosing properly designed time-dependent
pulses. In this work we determine what are the ultimate limits of this
optimization. We discuss under which conditions the production of defects
across the phase transition is vanishing small. Furthermore we show that the
minimum time required to enter this regime is , where
is the minimum spectral gap, unveiling an intimate connection between
an optimized unitary dynamics and the intrinsic measure of the Hilbert space
for pure states. Surprisingly, the dynamics is non-adiabatic, this result can
be understood by assuming a simple two-level dynamics for the many-body system.
Finally we classify the possible dynamical regimes in terms of the action
.Comment: 6 pages, 6 figure
Information-capacity description of spin-chain correlations
Information capacities achievable in the multi-parallel-use scenarios are
employed to characterize the quantum correlations in unmodulated spin chains.
By studying the qubit amplitude damping channel, we calculate the quantum
capacity , the entanglement assisted capacity , and the classical
capacity of a spin chain with ferromagnetic Heisenberg interactions.Comment: 12 pages, 3 figures; typos corrected (to appear in PRA
Light harvesting with Ge quantum dots embedded in SiO2 and Si3N4
Cataloged from PDF version of article.Germanium quantum dots (QDs) embedded in SiO2 or in Si3N4 have been studied for light harvesting purposes. SiGeO or SiGeN thin films, produced by plasma enhanced chemical vapor deposition, have been annealed up to 850 degrees C to induce Ge QD precipitation in Si based matrices. By varying the Ge content, the QD diameter can be tuned in the 3-9 nm range in the SiO2 matrix, or in the 1-2 nm range in the Si3N4 matrix, as measured by transmission electron microscopy. Thus, Si3N4 matrix hosts Ge QDs at higher density and more closely spaced than SiO2 matrix. Raman spectroscopy revealed a higher threshold for amorphous-to-crystalline transition for Ge QDs embedded in Si3N4 matrix in comparison with those in the SiO2 host. Light absorption by Ge QDs is shown to be more effective in Si3N4 matrix, due to the optical bandgap (0.9-1.6 eV) being lower than in SiO2 matrix (1.2-2.2 eV). Significant photoresponse with a large measured internal quantum efficiency has been observed for Ge QDs in Si3N4 matrix when they are used as a sensitive layer in a photodetector device. These data will be presented and discussed, opening new routes for application of Ge QDs in light harvesting devices. (C) 2014 AIP Publishing LLC
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