9,721 research outputs found
Spatially resolved physical and chemical properties of the planetary nebula NGC 3242
Optical integral-field spectroscopy was used to investigate the planetary
nebula NGC 3242. We analysed the main morphological components of this source,
including its knots, but not the halo. In addition to revealing the properties
ofthe physical and chemical nature of this nebula, we also provided reliable
spatially resolved constraints that can be used for future photoionisation
modelling of the nebula. The latter is ultimately necessary to obtain a fully
self-consistent 3D picture of the physical and chemical properties of the
object. The observations were obtained with the VIMOS instrument attached to
VLT-UT3. Maps and values for specific morphological zones for the detected
emission-lines were obtained and analysed with routines developed by the
authors to derive physical and chemical conditions of the ionised gas in a 2D
fashion. We obtained spatially resolved maps and mean values of the electron
densities, temperatures, and chemical abundances, for specific morphological
structures in NGC 3242. These results show the pixel-to-pixel variations of the
the small- and large-scale structures of the source. These diagnostic maps
provide information free from the biases introduced by traditional single
long-slit observations. In general, our results are consistent with a uniform
abundance distribution for the object, whether we look at abundance maps or
integrated fluxes from specified morphological structures. The results indicate
that special care should be taken with the calibration of the data and that
only data with extremely good signal-to-noise ratio and spectral coverage
should be used to ensure the detection of possible spatial variations.Comment: 11 pages, 8 figures accepted for publication in Astronomy &
Astrophysic
Estado Confusional Agudo após Corticoterapia Inalada
Background: The connection between corticotherapy and neuropsychiatric symptoms is
widely known, being one of the first questions
we need to assess when presenting with first
episode psychiatric symptoms or confusional
state.
Aims: To date, data on cases related to inhaled
corticotherapy and neuropsychiatric effects is
scarce. In this paper we describe a rare case in
a young woman.
Methods: The clinical case presented led us
to try to understand the data published on the
subject in order to discuss it in greater length.
Results and Conclusions: We present and
discuss a 27-year-old patient’s case, with no
previous psychiatric disease, who was admitted to our Psychiatric ward after the onset of
severe acute behavioural disturbance characterized by aggressiveness, visual and auditory
hallucinatory activity, misidentification and
altered conscience status. It was later found
that seven days earlier she had been prescribed
inhaled corticotherapy for a minor respiratory
infection. A few days after corticotherapy withdrawal, the clinical symptoms improved significantly.info:eu-repo/semantics/publishedVersio
The Quantum Algebraic Structure of the Twisted XXZ Chain
We consider the Quantum Inverse Scattering Method with a new R-matrix
depending on two parameters and . We find that the underlying algebraic
structure is the two-parameter deformed algebra enlarged by
introducing an element belonging to the centre. The corresponding Hamiltonian
describes the spin-1/2 XXZ model with twisted periodic boundary conditions.Comment: LateX file, 9 pages, Minor changes (including authors` names in the
hep-th heading
3-D Photoionization Structure and Distances of Planetary Nebulae III. NGC 6781
Continuing our series of papers on the three-dimensional (3-D) structures of
and accurate distances to Planetary Nebulae (PNe), we present our study of the
planetary nebula NGC6781. For this object we construct a 3-D photoionization
model and, using the constraints provided by observational data from the
literature we determine the detailed 3-D structure of the nebula, the physical
parameters of the ionizing source and the first precise distance. The procedure
consists in simultaneously fitting all the observed emission line morphologies,
integrated intensities and the 2-D density map from the [SII] line ratios to
the parameters generated by the model, and in an iterative way obtain the best
fit for the central star parameters and the distance to NGC6781, obtaining
values of 950+-143pc and 385 Lsun for the distance and luminosity of the
central star respectively. Using theoretical evolutionary tracks of
intermediate and low mass stars, we derive the mass of the central star of
NGC6781 and its progenitor to be 0.60+-0.03 Msun and 1.5+-0.5 Msun
respectively.Comment: 16 pp, 6 figues, 2 tables, submitted to the Ap
Estimation of Risk-Neutral Density Surfaces
Option price data is often used to infer risk-neutral densities for future prices of an underlying asset. Given the prices of a set of options on the same underlying asset with different strikes and maturities, we propose a nonparametric approach for estimating risk-neutral densities associated with several maturities. Our method uses bicubic splines in order to achieve the desired smoothness for the estimation and an optimization model to choose the spline functions that best fit the price data. Semidefinite programming is employed to guarantee the nonnegativity of the densities. We illustrate the process using synthetic option price data generated using log-normal and absolute diffusion processes as well as actual price data for options on the S&P500 index. We also used the risk-neutral densities that we computed to price exotic options and observed that this approach generates prices that closely approximate the market prices of these options.
Some boundary effects in quantum field theory
We have constructed a quantum field theory in a finite box, with periodic
boundary conditions, using the hypothesis that particles living in a finite box
are created and/or annihilated by the creation and/or annihilation operators,
respectively, of a quantum harmonic oscillator on a circle. An expression for
the effective coupling constant is obtained showing explicitly its dependence
on the dimension of the box.Comment: 12 pages, Late
Dynamical instability in kicked Bose-Einstein condensates: Bogoliubov resonances
Bose-Einstein condensates subject to short pulses (`kicks') from standing
waves of light represent a nonlinear analogue of the well-known chaos paradigm,
the quantum kicked rotor. Previous studies of the onset of dynamical
instability (ie exponential proliferation of non-condensate particles)
suggested that the transition to instability might be associated with a
transition to chaos. Here we conclude instead that instability is due to
resonant driving of Bogoliubov modes. We investigate the excitation of
Bogoliubov modes for both the quantum kicked rotor (QKR) and a variant, the
double kicked rotor (QKR-2). We present an analytical model, valid in the limit
of weak impulses which correctly gives the scaling properties of the resonances
and yields good agreement with mean-field numerics.Comment: 8 page
BitTorrent based transmission of real-time scalable video over P2P networks
The number of software applications available on the Internet for distributing video streams in real time over P2P networks has grown quickly in the last two years. Typical this kind of distribution is made by television channel broadcasters which try to make their content globally available, using viewer's resources to support a large scale distribution of video without incurring in incremental costs. However, the lack of adaptation in video quality, combined with the lack of a standard protocol for this kind of multimedia distribution has driven content providers to basically ignore it as a solution for video delivery over the Internet. While the scalable extension of the H.264 encoding (H.264/SVC) can be used to support terminal and network heterogeneity, it is not clear how it can be integrated in a P2P overlay to form a large scale and real time distribution. In this paper, we start by defining a solution that combines the most popular P2P file-sharing protocol, the Bit Torrent, with the H.264/SVC encoding for a real-time video content delivery. Using this solution we then evaluate the effect of several parameters in the quality received by peers
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