56,268 research outputs found
Gumsense - a high power low power sensor node
The development of increasingly complex algorithms for sensor networks has made it difficult for researchers to implement their design on typical sensor network hardware with limited computing resources. The demands on hardware can also mean that small microcontrollers are not the ideal platform for testing computationally and/or memory intensive algorithms. Researchers would also like access to high level programming languages and a wider range of open source libraries. To address this problem we have designed and implemented an architecture, Gumsense which combines a low power micro-controller (8MHz MSP430) with a powerful processor (100-600MHz ARM) on a Gumstix board running Linux. This Open Embedded OS supports a wide variety of programming languages, package management and development tools. A similar hybrid approach was also used in the LEAP platform. The microcontroller wakes up frequently to manage tasks such as activating sensors and gathering data. The intended use-case is to power-up the ARM board and storage only during the brief periods it is needed, for example performing computation or communication
CCD photometry in the region of NGC 6994: the remains of an old open cluster
We present the results of BV(RI)_KC CCD photometry down to V=21 mag in the
region of NGC 6994. To our knowledge, no photometry has previously been
reported for this object and we find evidences that it is a poor and sparse old
open cluster, with a minimum angular diameter of 9 arcmin, i.e. larger than the
3 arcmin originally assigned to it. We obtain a color excess E(B-V) = 0.07 +/-
0.02 mag by means of the BVI_(C) technique. Based on the theoretical isochrones
from VandenBergh (1985) that are in better agreement with our data, we estimate
for this cluster a distance from the Sun of 620 pc (Vo-Mv = 9 +/- 0.25 mag) and
an age lying within the range of 2 - 3 Gyr, adopting solar metallicity. Thus,
the corresponding cluster's Galactocentric distance is 8.1 kpc and is placed at
about 350 pc below the Galactic plane. According to this results, NGC 6994
belongs to the old open cluster population located in the outer disk and at
large distances from the Galactic plane, and must have suffered significant
individual dynamical evolution, resulting in mass segregation and evaporation
of low mass stars.Comment: 10 pages including 11 figures and 1 table. Accepted for publication
in Astronomy & Astrophysic
DGSAT: Dwarf Galaxy Survey with Amateur Telescopes II. A catalogue of isolated nearby edge-on disk galaxies and the discovery of new low surface brightness systems
The connection between the bulge mass or bulge luminosity in disk galaxies
and the number, spatial and phase space distribution of associated dwarf
galaxies is a discriminator between cosmological simulations related to galaxy
formation in cold dark matter and generalized gravity models. Here, a nearby
sample of isolated Milky Way class edge-on galaxies is introduced, to
facilitate observational campaigns to detect the associated families of dwarf
galaxies at low surface brightness. Three galaxy pairs with at least one of the
targets being edge-on are also introduced. About 60% of the catalogued isolated
galaxies contain bulges of different size, while the remaining objects appear
to be bulge-less. Deep images of NGC 3669 (small bulge, with NGC 3625 at the
edge of the image) and NGC 7814 (prominent bulge), obtained with a 0.4-m
aperture, are also presented, resulting in the discovery of two new dwarf
galaxy candidates, NGC3669-DGSAT-3 and NGC7814-DGSAT-7. Eleven additional low
surface brightness galaxies are identified, previously notified with low
quality measurement flags in the Sloan Digital Sky Survey (SDSS). Integrated
magnitudes, surface brightnesses, effective radii, Sersic indices, axis ratios,
and projected distances to their putative major hosts are displayed. At least
one of the galaxies, NGC3625-DGSAT-4, belongs with a surface brightness of
approximately 26 mag per arcsec^2 and effective radius >1.5 kpc to the class of
ultra-diffuse galaxies (UDGs). NGC3669-DGSAT-3, the galaxy with lowest surface
brightness in our sample, may also be an UDG.Comment: 12 pages including 6 figures, 4 tables, a brief appendix, accepted
for publication in Astronomy & Astrophysics (A&A). Paper slightly modified
after A&A language editing, updating very few references and correcting a
small typo at the start of the Appendi
A linear filter to reconstruct the ISW effect from CMB and LSS observations
The extraction of a signal from some observational data sets that contain
different contaminant emissions, often at a greater level than the signal
itself, is a common problem in Astrophysics and Cosmology. The signal can be
recovered, for instance, using a simple Wiener filter. However, in certain
cases, additional information may also be available, such as a second
observation which correlates to a certain level with the sought signal. In
order to improve the quality of the reconstruction, it would be useful to
include as well this additional information. Under these circumstances, we have
constructed a linear filter, the linear covariance-based filter, that extracts
the signal from the data but takes also into account the correlation with the
second observation. To illustrate the performance of the method, we present a
simple application to reconstruct the so-called Integrated Sachs-Wolfe effect
from simulated observations of the Cosmic Microwave Background and of
catalogues of galaxies.Comment: 8 pages, 6 figures, accepted for publication in the IEEE Journal of
Selected Topics in Signal Processin
Minkowski-type and Alexandrov-type theorems for polyhedral herissons
Classical H.Minkowski theorems on existence and uniqueness of convex
polyhedra with prescribed directions and areas of faces as well as the
well-known generalization of H.Minkowski uniqueness theorem due to
A.D.Alexandrov are extended to a class of nonconvex polyhedra which are called
polyhedral herissons and may be described as polyhedra with injective spherical
image.Comment: 19 pages, 8 figures, LaTeX 2.0
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