11,427 research outputs found
Blind multiuser deconvolution in fading and dispersive channels
An adaptive near-far resistant technique for the blind joint multiuser identification and detection in asynchronous CDMA systems is analyzed in fading and dispersive GSM channels.Peer ReviewedPostprint (published version
Searching for efficient Markov chain Monte Carlo proposal kernels
Markov chain Monte Carlo (MCMC) or the Metropolis-Hastings algorithm is a simulation algorithm that has made modern Bayesian statistical inference possible. Nevertheless, the efficiency of different Metropolis-Hastings proposal kernels has rarely been studied except for the Gaussian proposal. Here we propose a unique class of Bactrian kernels, which avoid proposing values that are very close to the current value, and compare their efficiency with a number of proposals for simulating different target distributions, with efficiency measured by the asymptotic variance of a parameter estimate. The uniform kernel is found to be more efficient than the Gaussian kernel, whereas the Bactrian kernel is even better. When optimal scales are used for both, the Bactrian kernel is at least 50% more efficient than the Gaussian. Implementation in a Bayesian program for molecular clock dating confirms the general applicability of our results to generic MCMC algorithms. Our results refute a previous claim that all proposals had nearly identical performance and will prompt further research into efficient MCMC proposals
The ALMA Early Science View of FUor/EXor objects. III. The Slow and Wide Outflow of V883 Ori
We present Atacama Large Millimeter/ sub-millimeter Array (ALMA) observations
of V883 Ori, an FU Ori object. We describe the molecular outflow and envelope
of the system based on the CO and CO emissions, which together
trace a bipolar molecular outflow. The CO emission traces the rotational
motion of the circumstellar disk. From the CO blue-shifted emission, we
estimate a wide opening angle of 150 for the outflow
cavities. Also, we find that the outflow is very slow (characteristic velocity
of only 0.65 km~s), which is unique for an FU Ori object. We calculate
the kinematic properties of the outflow in the standard manner using the
CO and CO emissions. In addition, we present a P Cygni profile
observed in the high-resolution optical spectrum, evidence of a wind driven by
the accretion and being the cause for the particular morphology of the
outflows. We discuss the implications of our findings and the rise of these
slow outflows during and/or after the formation of a rotationally supported
disk.Comment: 12 pages, 7 figures, 2 tables. Accepte
Probing the Circumnuclear Stellar Populations of Starburst Galaxies in the Near-infrared
We employ the NASA Infrared Telescope Facility's near-infrared spectrograph
SpeX at 0.8-2.4m to investigate the spatial distribution of the stellar
populations (SPs) in four well known Starburst galaxies: NGC34, NGC1614,
NGC3310 and NGC7714. We use the STARLIGHT code updated with the synthetic
simple stellar populations models computed by Maraston (2005, M05). Our main
results are that the NIR light in the nuclear surroundings of the galaxies is
dominated by young/intermediate age SPs (yr), summing from
40\% up to 100\% of the light contribution. In the nuclear aperture of
two sources (NGC1614 and NGC3310) we detected a predominant old SP component
(yr), while for NGC34 and NGC7714 the younger component
prevails. Furthermore, we found evidence of a circumnuclear star formation
ring-like structure and a secondary nucleus in NGC1614, in agreement with
previous studies. We also suggest that the merger/interaction experienced by
three of the galaxies studied, NGC1614, NGC3310 and NGC7714 can explain the
lower metallicity values derived for the young SP component of these sources.
In this scenario the fresh unprocessed metal poorer gas from the
destroyed/interacting companion galaxy is driven to the centre of the galaxies
and mixed with the central region gas, before star formation takes place. In
order to deepen our analysis, we performed the same procedure of SP synthesis
using Maraston (2011, M11) EPS models. Our results show that the newer and
higher resolution M11 models tend to enhance the old/intermediate age SP
contribution over the younger ages
Three-body decays: structure, decay mechanism and fragment properties
We discuss the three-body decay mechanisms of many-body resonances. R-matrix
sequential description is compared with full Faddeev computation. The role of
the angular momentum and boson symmetries is also studied. As an illustration
we show the computed -particle energy distribution after the decay of
12C(1^+) resonance at 12.7 MeV.Comment: 4 pages, 3 figures. Proceedings of the workshop "Critical Stability
of Few-Body Quantum Systems" 200
Sentinel 2 as a visualization tool of the historical urban growth of cities
La observación multiespectral de las ciudades desde el espacio es una herramienta sumamente valiosa para
conocer la situación actual de las mismas. Sin embargo, estas mismas imágenes pueden aportar información también
sobre la historia pasada de las mismas. En este trabajo se propone el procesado de imágenes Sentinel 2 para visualizar el
crecimiento urbano de las ciudades a lo largo del tiempo. En concreto, se ha usado la combinación de bandas 12,11,4 y
12,8,3 para obtener imágenes en falso color que resaltan intensamente los diferentes materiales de techado utilizados en
el tiempo. Esta combinación de bandas infrarrojas y roja resultan muy útiles para diferenciar materiales como la teja, el
cemento o los materiales sintéticos impermeabilizantes, permitiendo diferenciar a simple vista los distintos barrios que
forman la ciudad en función de su época de construcción, dando una visión global de las fases de crecimiento de la ciudad.
Este tipo de imágenes resultan muy intuitivas para los estudiantes, convirtiéndose en una valiosa herramienta didáctica y
de divulgaciónMultispectral observation of cities from space is a key tool for understanding their current state. Moreover, this
kind of imagery may provide insight into the past history of cities. This work proposes the process of Sentinel 2 images for
visualizing urban growth of cities in time. In particular, RGB composite of bands 12,11,4 and 12,8,3 provide false color
images that highlight the different roofing materials used through history. This particular combination of infrared and
red bands are very useful for differentiating materials such as red tile, cement or sinthetic impermeabilization materials,
allowing to visually different phases of city growth. These images are very intuitive for students and non professionals,
becoming a valuable tool for history teaching and divulgatio
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