12,766 research outputs found
Exploiting graphic processing units parallelism to improve intelligent data acquisition system performance in JET's correlation reflectometer
The performance of intelligent data acquisition systems relies heavily on their processing capabilities and local bus bandwidth, especially in applications with high sample rates or high number of channels. This is the case of the self adaptive sampling rate data acquisition system installed as a pilot experiment in KG8B correlation reflectometer at JET. The system, which is based on the ITMS platform, continuously adapts the sample rate during the acquisition depending on the signal bandwidth. In order to do so it must transfer acquired data to a memory buffer in the host processor and run heavy computational algorithms for each data block. The processing capabilities of the host CPU and the bandwidth of the PXI bus limit the maximum sample rate that can be achieved, therefore limiting the maximum bandwidth of the phenomena that can be studied. Graphic processing units (GPU) are becoming an alternative for speeding up compute intensive kernels of scientific, imaging and simulation applications. However, integrating this technology into data acquisition systems is not a straight forward step, not to mention exploiting their parallelism efficiently. This paper discusses the use of GPUs with new high speed data bus interfaces to improve the performance of the self adaptive sampling rate data acquisition system installed on JET. Integration issues are discussed and performance evaluations are presente
Comparing different methods to retrieve cloud top height from Meteosat satellite data
Cloud parameters such as the Cloud Top Height (CTH), Cloud Top Temperature (CTT), emissivity, particle size and optical depth have always been matter of interest for the atmospheric community. Particularly the CTH provides information leading to better understand the cloud radiative effects. Although there are many meteorological satellites providing the CTH, there are other sensors, not devoted to this purpose, that give some information from which this crucial parameter can be estimated. In this contribution we will describe three different methodologies to retrieve the CTH. The first technique is based on stereo-vision algorithms and requires two different views of the same scene and does not need of extra atmospheric information. In the second one, brightness temperatures in two IR spectral bands are converted to real cloud temperature by means of the proposed algorithms. From the CTT, the CTH is estimated using temperature vertical profiles (measured or modeled). The third technique retrieves the CTH from the output parameters of post event simulations performed by a Numerical Weather Prediction (NWP) model that in this work will be the mesoscale model WRF (Weather Research Forecast). This article presents a preliminary work, in which the heights retrieved by the three methodologies applied to the geostationary satellite Meteosat 10 are compared with the heights given by MODIS sensor installed on the polar satellite AQUA. This promising results show that valuable information about CTH can be retrieved from Meteosat which provide high frequency and large scale data useful for weather and climate research
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
Localization of Dirac electrons by Moire patterns in graphene bilayers
We study the electronic structure of two Dirac electron gazes coupled by a
periodic Hamiltonian such as it appears in rotated graphene bilayers. Ab initio
and tight-binding approaches are combined and show that the spatially periodic
coupling between the two Dirac electron gazes can renormalize strongly their
velocity. We investigate in particular small angles of rotation and show that
the velocity tends to zero in this limit. The localization is confirmed by an
analysis of the eigenstates which are localized essentially in the AA zones of
the Moire patterns.Comment: 4 pages, 5 figure
The Large Aperture GRB Observatory
The Large Aperture GRB Observatory (LAGO) is aiming at the detection of the
high energy (around 100 GeV) component of Gamma Ray Bursts, using the single
particle technique in arrays of Water Cherenkov Detectors (WCD) in high
mountain sites (Chacaltaya, Bolivia, 5300 m a.s.l., Pico Espejo, Venezuela,
4750 m a.s.l., Sierra Negra, Mexico, 4650 m a.s.l). WCD at high altitude offer
a unique possibility of detecting low gamma fluxes in the 10 GeV - 1 TeV range.
The status of the Observatory and data collected from 2007 to date will be
presented.Comment: 4 pages, proceeding of 31st ICRC 200
Water Cherenkov Detectors response to a Gamma Ray Burst in the Large Aperture GRB Observatory
In order to characterise the behaviour of Water Cherenkov Detectors (WCD)
under a sudden increase of 1 GeV - 1 TeV background photons from a Gamma Ray
Burst (GRB), simulations were conducted and compared to data acquired by the
WCD of the Large Aperture GRB Observatory (LAGO). The LAGO operates arrays of
WCD at high altitude to detect GRBs using the single particle technique. The
LAGO sensitivity to GRBs is derived from the reported simulations of the gamma
initiated particle showers in the atmosphere and the WCD response to
secondaries.Comment: 5 pages, proceeding of the 31st ICRC 200
The 2HWC HAWC Observatory Gamma Ray Catalog
We present the first catalog of TeV gamma-ray sources realized with the
recently completed High Altitude Water Cherenkov Observatory (HAWC). It is the
most sensitive wide field-of-view TeV telescope currently in operation, with a
1-year survey sensitivity of ~5-10% of the flux of the Crab Nebula. With an
instantaneous field of view >1.5 sr and >90% duty cycle, it continuously
surveys and monitors the sky for gamma ray energies between hundreds GeV and
tens of TeV.
HAWC is located in Mexico at a latitude of 19 degree North and was completed
in March 2015. Here, we present the 2HWC catalog, which is the result of the
first source search realized with the complete HAWC detector. Realized with 507
days of data and represents the most sensitive TeV survey to date for such a
large fraction of the sky. A total of 39 sources were detected, with an
expected contamination of 0.5 due to background fluctuation. Out of these
sources, 16 are more than one degree away from any previously reported TeV
source. The source list, including the position measurement, spectrum
measurement, and uncertainties, is reported. Seven of the detected sources may
be associated with pulsar wind nebulae, two with supernova remnants, two with
blazars, and the remaining 23 have no firm identification yet.Comment: Submitted 2017/02/09 to the Astrophysical Journa
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