1,183 research outputs found
Dynamical description of the buildup process in resonant tunneling: Evidence of exponential and non-exponential contributions
The buildup process of the probability density inside the quantum well of a
double-barrier resonant structure is studied by considering the analytic
solution of the time dependent Schr\"{o}dinger equation with the initial
condition of a cutoff plane wave. For one level systems at resonance condition
we show that the buildup of the probability density obeys a simple charging up
law, where is the
stationary wave function and the transient time constant is exactly
two lifetimes. We illustrate that the above formula holds both for symmetrical
and asymmetrical potential profiles with typical parameters, and even for
incidence at different resonance energies. Theoretical evidence of a crossover
to non-exponential buildup is also discussed.Comment: 4 pages, 2 figure
Harmonic index and harmonic polynomial on graph operations
Some years ago, the harmonic polynomial was introduced to study the harmonic topological index. Here, using this polynomial, we obtain several properties of the harmonic index of many classical symmetric operations of graphs: Cartesian product, corona product, join, Cartesian sum and lexicographic product. Some upper and lower bounds for the harmonic indices of these operations of graphs, in terms of related indices, are derived from known bounds on the integral of a product on nonnegative convex functions. Besides, we provide an algorithm that computes the harmonic polynomial with complexity O(n 2 ).This work was supported in part by two grants from Ministerio de Economía y Competititvidad, Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) (MTM2016-78227-C2-1-P and MTM2017-90584-REDT), Spain
A self-consistent stellar and 3D nebular model for Planetary Nebula IC418
We present a coherent stellar and nebular model reproducing the observations
of the Planetary Nebula IC418. We want to test whether a stellar model obtained
by fitting the stellar observations is able to satisfactory ionize the nebula
and reproduce the nebular observations, which is by no mean evident. This
allows us to determine all the physical parameters of both the star and the
nebula, including the abundances and the distance. We used all the
observational material available (FUSE, IUE, STIS and optical spectra) to
constrain the stellar atmosphere model performed using the CMFGEN code. The
photoionization model is done with Cloudy_3D, and is based on CTIO, Lick, SPM,
IUE and ISO spectra as well as HST images. More than 140 nebular emission lines
are compared to the observed intensities. We reproduce all the observations for
the star and the nebula. The 3D morphology of the gas distribution is
determined. The effective temperature of the star is 36.7kK. Its luminosity is
7700 solar luminosity. We describe an original method to determine the distance
of the nebula using evolutionary tracks. No clumping factor is need to
reproduce the age-luminosity relation. The distance of 1.25 kpc is found in
very good agreement with recent determination using parallax method. The
chemical composition of both the star and the nebula are determined. Both are
Carbon-rich. The nebula presents evidence of depletion of elements Mg, Si, S,
Cl (0.5 dex lower than solar) and Fe (2.9 dex lower than solar). This is the
first self-consistent stellar and nebular model for a Planetary Nebula that
reproduces all the available observations ranging from IR to UV, showing that
the combined approach for the modeling process leads to more restrictive
constraints and, in principle, more trustworthy results.Comment: Accepted for publication in Astronomy and Astrophysics. V2: after
corrections language edito
Anti-correlated Soft Lags in the Intermediate State of Black Hole Source GX 339-4
We report the few hundred second anti-correlated soft lags between soft and
hard energy bands in the source GX 339-4 using RXTE observations. In one
observation, anti-correlated soft lags were observed using the ISGRI/INTEGRAL
hard energy band and the PCA/RXTE soft energy band light curves. The lags were
observed when the source was in hard and soft intermediate states, i.e., in a
steep power-law state.We found that the temporal and spectral properties were
changed during the lag timescale. The anti-correlated soft lags are associated
with spectral variability during which the geometry of the accretion disk is
changed. The observed temporal and spectral variations are explained using the
framework of truncated disk geometry. We found that during the lag timescale,
the centroid frequency of quasi-periodic oscillation is decreased, the soft
flux is decreased along with an increase in the hard flux, and the power-law
index steepens together with a decrease in the disk normalization parameter. We
argue that these changes could be explained if we assume that the hot corona
condenses and forms a disk in the inner region of the accretion disk. The
overall spectral and temporal changes support the truncated geometry of the
accretion disk in the steep power-law state or in the intermediate state.Comment: published in ApJ, 9 pages, 8 figure
The use of deep learning to improve player engagement in a video game through a dynamic difficulty adjustment based on skills classification
The balance between game difficulty and player skill in the evolving landscape of the video game industry is a significant factor in player engagement. This study introduces a deep learning (DL) approach to enhance gameplay by dynamically adjusting game difficulty based on a player’s skill level. Our methodology aims to prevent player disengagement, which can occur if the game difficulty significantly exceeds or falls short of the player’s skill level. Our evaluation indicates that such dynamic adjustment leads to improved gameplay and increased player involvement, with 90% of the players reporting high game enjoyment and immersion levels
Complex regional pain syndrome (CRPS), a review
Complex regional pain syndrome is a chronic and painful condition that affects the quality of life of patients. It is usually triggered by a traumatic event of the soft tissues involving the nervous tissue. Although the factors that cause the syndrome are varied and not well
known, different etiopathologic concepts have been proposed to explain the presence of this syndrome, such as autonomic dysfunction and changes in CNS plasticity, among others. The patient characteristically presents pain, sensory abnormalities, vasomotor disturbances in the skin, edema, changes in sweating, and motor alterations. The pain is associated with changes in the autonomic nervous system and has a distal predominance. Since there is no definitive diagnostic test, diagnosis is mainly based on a complete medical history and physical examination. Treatment is multidisciplinary and based on pain relief. Although in most cases evolution is
favorable, rapid diagnosis and treatment are recommended to avoid dystrophic stage as much as possibl
Photovoltaic LiNbO3particles: Applications to Biomedicine/Biophotonics
Recently, a novel method to trap and pattern ensembles of nanoparticles has been proposed and
tested. It relies on the photovoltaic (PV) properties of certain ferroelectric crystals such as LiNbO3 [1,2].
These crystals, when suitably doped, develop very high electric fields in response to illumination with
light of suitable wavelength. The PV effect lies in the asymmetrical excitation of electrons giving rise to
PV currents and associated space-charge fields (photorefractive effect). The field generated in the bulk
of the sample propagates to the surrounding medium as evanescent fields. When dielectric or metal
nanoparticles are deposited on the surface of the sample the evanescent fields give rise to either
electrophoretic or dielectrophoretic forces, depending on the charge state of the particles, that induce
the trapping and patterning effects [3,4].
The purpose of this work has been to explore the effects of such PV fields in the biology and
biomedical areas. A first work was able to show the necrotic effects induced by such fields on He-La
tumour cells grown on the surface of an illuminated iron-doped LiNbO3 crystal [5]. In principle, it is
conceived that LiNbO3 nanoparticles may be advantageously used for such biomedical purposes
considering the possibility of such nanoparticles being incorporated into the cells. Previous experiments
using microparticles have been performed [5] with similar results to those achieved with the substrate.
Therefore, the purpose of this work has been to fabricate and characterize the LiNbO3 nanoparticles and
assess their necrotic effects when they are incorporated on a culture of tumour cells.
Two different preparation methods have been used: 1) mechanical grinding from crystals, and 2)
bottom-up sol-gel chemical synthesis from metal-ethoxide precursors. This later method leads to a more
uniform size distribution of smaller particles (down to around 50 nm). Fig. 1(a) and 1(b) shows SEM
images of the nanoparticles obtained with both method.
An ad hoc software taking into account the physical properties of the crystal, particullarly donor
and aceptor concentrations has been developped in order to estimate the electric field generated in
noparticles. In a first stage simulations of the electric current of nanoparticles, in a conductive media,
due to the PV effect have been carried out by MonteCarlo simulations using the Kutharev 1-centre
transport model equations [6] . Special attention has been paid to the dependence on particle size and
[Fe2+]/[Fe3+]. First results on cubic particles shows large dispersion for small sizes due to the random
number of donors and its effective concentration (Fig 2).
The necrotic (toxicity) effect of nanoparticles incorporated into a tumour cell culture subjected to
30 min. illumination with a blue LED is shown in Fig.3. For each type of nanoparticle the percent of cell
survival in dark and illumination conditions has been plot as a function of the particle dilution factor. Fig.
1a corresponds to mechanical grinding particles whereas 1b and 1c refer to chemically synthesized
particles with two oxidation states. The light effect is larger with mechanical grinding nanoparticles, but
dark toxicity is also higher. For chemically synthesized nanoparticles dark toxicity is low but only in
oxidized samples, where the PV effect is known to be larger, the light effect is appreciable.
These preliminary results demonstrate that Fe:LiNbO· nanoparticles have a biological damaging
effect on cells, although there are many points that should be clarified and much space for PV
nanoparticles optimization. In particular, it appears necessary to determine the fraction of nanoparticles
that become incorporated into the cells and the possible existence of threshold size effects.
This work has been supported by MINECO under grant MAT2011-28379-C03
The O3N2 and N2 abundance indicators revisited: improved calibrations based on CALIFA and Te-based literature data
The use of IFS is since recently allowing to measure the emission line fluxes
of an increasingly large number of star-forming galaxies both locally and at
high redshift. The main goal of this study is to review the most widely used
empirical oxygen calibrations, O3N2 and N2, by using new direct abundance
measurements. We pay special attention to the expected uncertainty of these
calibrations as a function of the index value or abundance derived and the
presence of possible systematic offsets. This is possible thanks to the
analysis of the most ambitious compilation of Te-based HII regions to date.
This new dataset compiles the Te-based abundances of 603 HII regions extracted
from the literature but also includes new measurements from the CALIFA survey.
Besides providing new and improved empirical calibrations for the gas
abundance, we also present here a comparison between our revisited calibrations
with a total of 3423 additional CALIFA HII complexes with abundances derived
using the ONS calibration by Pilyugin et al. (2010). The combined analysis of
Te-based and ONS abundances allows us to derive their most accurate calibration
to date for both the O3N2 and N2 single-ratio indicators, in terms of all
statistical significance, quality and coverage of the space of parameters. In
particular, we infer that these indicators show shallower abundance
dependencies and statistically-significant offsets compared to those of Pettini
and Pagel (2004), Nagao et al. (2006) and P\'erez-Montero and Contini (2009).
The O3N2 and N2 indicators can be empirically applied to derive oxygen
abundances calibrations from either direct abundance determinations with random
errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a
large amount of data) reaching an average precision of 0.08 and 0.09 dex
(random) and 0.02 and 0.08 dex (systematic; compared to the direct
estimations),respectively.Comment: 12 pages, 5 figures, accepted for publication in A&
The effects of spatial resolution on Integral Field Spectrograph surveys at different redshifts. The CALIFA perspective
Over the past decade, 3D optical spectroscopy has become the preferred tool
for understanding the properties of galaxies and is now increasingly used to
carry out galaxy surveys. Low redshift surveys include SAURON, DiskMass,
ATLAS3D, PINGS and VENGA. At redshifts above 0.7, surveys such as MASSIV, SINS,
GLACE, and IMAGES have targeted the most luminous galaxies to study mainly
their kinematic properties. The on-going CALIFA survey () is the
first of a series of upcoming Integral Field Spectroscopy (IFS) surveys with
large samples representative of the entire population of galaxies. Others
include SAMI and MaNGA at lower redshift and the upcoming KMOS surveys at
higher redshift. Given the importance of spatial scales in IFS surveys, the
study of the effects of spatial resolution on the recovered parameters becomes
important. We explore the capability of the CALIFA survey and a hypothetical
higher redshift survey to reproduce the properties of a sample of objects
observed with better spatial resolution at lower redshift. Using a sample of
PINGS galaxies, we simulate observations at different redshifts. We then study
the behaviour of different parameters as the spatial resolution degrades with
increasing redshift.Comment: 20 pages, 16 figures. Accepted for publication in A&
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