1,175 research outputs found
Background modeling by shifted tilings of stacked denoising autoencoders
The effective processing of visual data without interruption is currently of supreme importance. For that purpose, the analysis system must adapt to events that may affect the data quality and maintain its performance level over time. A methodology for background modeling and foreground detection, whose main characteristic is its robustness against stationary noise, is presented in the paper. The system is based on a stacked denoising autoencoder which extracts a set of significant features for each patch of several shifted tilings of the video frame. A probabilistic model for each patch is learned. The distinct patches which include a particular pixel are considered for that pixel classification. The experiments show that classical methods existing in the literature experience drastic performance drops when noise is present in the video sequences, whereas the proposed one seems to be slightly affected. This fact corroborates the idea of robustness of our proposal, in addition to its usefulness for the processing and analysis of continuous data during uninterrupted periods of time.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Functional approach to quantum friction: effective action and dissipative force
We study the Casimir friction due to the relative, uniform, lateral motion of
two parallel semitransparent mirrors coupled to a vacuum real scalar field,
. We follow a functional approach, whereby nonlocal terms in the action
for , concentrated on the mirrors' locii, appear after functional
integration of the microscopic degrees of freedom. This action for ,
which incorporates the relevant properties of the mirrors, is then used as the
starting point for two complementary evaluations: Firstly, we calculate the {
in-out} effective action for the system, which develops an imaginary part,
hence a non-vanishing probability for the decay (because of friction) of the
initial vacuum state. Secondly, we evaluate another observable: the vacuum
expectation value of the frictional force, using the { in-in} or Closed Time
Path formalism. Explicit results are presented for zero-width mirrors and
half-spaces, in a model where the microscopic degrees of freedom at the mirrors
are a set of identical quantum harmonic oscillators, linearly coupled to $\phi
Growth and formation of inverse GaP and InP opals
Opals consist of an ordered array of SiO2 spheres. This leads to a modulation of the refractive index and hence photonic stop bands behaviour over the visible/IR range of the electro-magnetic spectrum. The exact position of the stop bands depends on the size of the silica spheres. However, the refractive index contrast between the SiO2 spheres and air spaces is not great enough to open up a full photonic band gap (PBG), only the pseudogap. To increase the contrast the air spaces are filled with a material of high refractive index such as InP or GaP. To further increase the contrast the SiO2 is removed leaving a III-V framework as the inverse opal structure.
By use of MOCVD we have been able to infill opals with InP and GaP to such a level that has supported the inversion of the composite forming a structure of air holes within a III-V lattice. XRD and Raman confirmed the quality of the III-V infill, while the extent of the infill was studied by SEM and reflectance measurements
870 micron continuum observations of the bubble-shaped nebula Gum 31
We are presenting here a study of the cold dust in the infrared ring nebula
Gum 31. We aim at deriving the physical properties of the molecular gas and
dust associated with the nebula, and investigating its correlation with the
star formation in the region, that was probably triggered by the expansion of
the ionization front. We use 870 micron data obtained with LABOCA to map the
dust emission. The obtained LABOCA image was compared to archival IR,radio
continuum, and optical images. The 870 micron emission follows the 8 micron
(Spitzer), 250 micron, and 500 micron (Herschel) emission distributions showing
the classical morphology of a spherical shell. We use the 870 micron and 250
micron images to identify 60 dust clumps in the collected layers of molecular
gas using the Gaussclumps algorithm. The clumps have effective deconvolved
radii between 0.16 pc and 1.35 pc, masses between 70 Mo and 2800 Mo, and volume
densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the
clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21
K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass
distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to
M^(-alpha), with alpha=0.93+/-0.28. The slope differs from those obtained for
the stellar IMF in the solar neighborhood, suggesting that the clumps are not
direct progenitors of single stars/protostars. The mass-radius relationship for
the 41 clumps detected in the 870 microns emission shows that only 37% of them
lie in or above the high-mass star formation threshold, most of them having
candidate YSOs projected inside. A comparison of the dynamical age of the HII
region with the fragmentation time, allowed us to conclude that the collect and
collapse mechanism may be important for the star formation at the edge of Gum
31, although other processes may also be acting.Comment: 15 pages, 10 figures. Accepted for publication in A&
The molecular environment of the pillar-like features in the HII region G46.5-0.2
At the interface of HII regions and molecular gas peculiar structures appear,
some of them with pillar-like shapes. Understanding their origin is important
for characterizing triggered star formation and the impact of massive stars on
the interstellar medium. In order to study the molecular environment and the
influence of the radiation on two pillar-like features related to the HII
region G46.5-0.2, we performed molecular line observations with the Atacama
Submillimeter Telescope Experiment, and spectroscopic optical observations with
the Isaac Newton Telescope. From the optical observations we identified the
star that is exciting the HII region as a spectral type O4-6. The molecular
data allowed us to study the structure of the pillars and a HCO+ cloud lying
between them. In this HCO+ cloud, which have not any well defined 12CO
counterpart, we found direct evidence of star formation: two molecular outflows
and two associated near-IR nebulosities. The outflows axis orientation is
perpendicular to the direction of the radiation flow from the HII region.
Several Class I sources are also embedded in this HCO+ cloud, showing that it
is usual that the YSOs form large associations occupying a cavity bounded by
pillars. On the other hand, it was confirmed that the RDI process is not
occurring in one of the pillar tips.Comment: Accepted in MNRAS (2017 June 13
Determining water use of sorghum from two-source energy balance and radiometric temperatures
Estimates of surface actual evapotranspiration (ET) can assist in predicting crop water requirements. An alternative to the traditional crop-coefficient methods are the energy balance models. The objective of this research was to show how surface temperature observations can be used, together with a two-source energy balance model, to determine crop water use throughout the different phenological stages of a crop grown. Radiometric temperatures were collected in a sorghum (<i>Sorghum bicolor</i>) field as part of an experimental campaign carried out in Barrax, Spain, during the 2010 summer growing season. Performance of the Simplified Two-Source Energy Balance (STSEB) model was evaluated by comparison of estimated ET with values measured on a weighing lysimeter. Errors of ±0.14 mm h<sup>−1</sup> and ±1.0 mm d<sup>−1</sup> were obtained at hourly and daily scales, respectively. Total accumulated crop water use during the campaign was underestimated by 5%. It is then shown that thermal radiometry can provide precise crop water necessities and is a promising tool for irrigation management
Molecular gas and star formation towards the IR dust bubble S24 and its environs
We present a multi-wavelength analysis of the infrared dust bubble S24, and
its environs, with the aim of investigating the characteristics of the
molecular gas and the interstellar dust linked to them, and analyzing the
evolutionary status of the young stellar objects (YSOs) identified there. Using
APEX data, we mapped the molecular emission in the CO(2-1), CO(2-1),
CO(2-1), and CO(3-2) lines in a region of about 5'x 5' in size
around the bubble. The cold dust distribution was analyzed using ATLASGAL and
Herschel images. Complementary IR and radio data were also used.The molecular
gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities
between -48.0 km sec and -40.0 km sec. The gas distribution
reveals a shell-like molecular structure of 0.8 pc in radius bordering
the bubble. A cold dust counterpart of the shell is detected in the LABOCA and
Herschel images.The presence of extended emission at 24 m and radio
continuum emission inside the bubble indicates that the bubble is a compact HII
region. Part of the molecular gas bordering S24 coincides with the extended
infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the
interface between S24 and G341.217-0.237. As regards G341.220-0.213, the
presence of an arc-like molecular structure at the northern and eastern
sections of this IR source indicates that G341.220-0.213 is interacting with
the molecular gas. Several YSO candidates are found to be linked to the IR
extended sources, thus confirming their nature as active star-forming regions.
The total gas mass in the region and the H ambient density amount to 10300
M and 5900 cm, indicating that G341.220-0.213, G341.217-0.237,
and the S24 HII region are evolving in a high density medium. A triggering star
formation scenario is also investigated.Comment: 17 pages, 16 figures. Submitted to A&A. Revised according to the
referee repor
Background modeling for video sequences by stacked denoising autoencoders
Nowadays, the analysis and extraction of relevant information in visual data flows is of paramount importance. These images sequences can last for hours, which implies that the model must adapt to all kinds of circumstances so that the performance of the system does not decay over time. In this paper we propose a methodology for background modeling and foreground detection, whose main characteristic is its robustness against stationary noise. Thus, stacked denoising autoencoders are applied to generate a set of robust characteristics for each region or patch of the image, which will be the input of a probabilistic model to determine if that region is background or foreground. The evaluation of a set of heterogeneous sequences results in that, although our proposal is similar to the classical methods existing in the literature, the inclusion of noise in these sequences causes drastic performance drops in the competing methods, while in our case the performance stays or falls slightly.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Casimir Force for Absorbing Media in an Open Quantum System Framework: Scalar Model
In this article we compute the Casimir force between two finite-width mirrors
at finite temperature, working in a simplified model in 1+1 dimensions. The
mirrors, considered as dissipative media, are modeled by a continuous set of
harmonic oscillators which in turn are coupled to an external environment at
thermal equilibrium. The calculation of the Casimir force is performed in the
framework of the theory of quantum open systems. It is shown that the Casimir
interaction has two different contributions: the usual radiation pressure from
vacuum, which is obtained for ideal mirrors without dissipation or losses, and
a Langevin force associated with the noise induced by the interaction between
dielectric atoms in the slabs and the thermal bath. Both contributions to the
Casimir force are needed in order to reproduce the analogous of Lifshitz
formula in 1+1 dimensions. We also discuss the relation between the
electromagnetic properties of the mirrors and the spectral density of the
environmentComment: Minor changes, version to appear in Phys. Rev.
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