2,006 research outputs found
Phase-sensitive correlation optical time-domain reflectometer using quantum phase noise of laser light
Abstract: We propose and experimentally demonstrate a simple approach to realize a phase-sensitive correlation optical time-domain reflectometer (OTDR) suitable for detection and localization of dynamic perturbations along a single-mode optical fiber. It is based on the quantum phase fluctuations of a coherent light emitted by a telecom DFB diode laser. Truly random probe signals are generated by an interferometer with the optical path difference exceeding the coherence length of the laser light. Speckle-like OTDR traces were obtained by calculating cross-correlation functions between the probe light and the light intensity signals returned back from the sensing fiber. Perturbations are detected and localized by monitoring time variations of correlation amplitude along the fiber length. Results of proof-of-concept experimental testing are presented
Goodness-of-Fit Tests to study the Gaussianity of the MAXIMA data
Goodness-of-Fit tests, including Smooth ones, are introduced and applied to
detect non-Gaussianity in Cosmic Microwave Background simulations. We study the
power of three different tests: the Shapiro-Francia test (1972), the
uncategorised smooth test developed by Rayner and Best(1990) and the Neyman's
Smooth Goodness-of-fit test for composite hypotheses (Thomas and Pierce 1979).
The Smooth Goodness-of-Fit tests are designed to be sensitive to the presence
of ``smooth'' deviations from a given distribution. We study the power of these
tests based on the discrimination between Gaussian and non-Gaussian
simulations. Non-Gaussian cases are simulated using the Edgeworth expansion and
assuming pixel-to-pixel independence. Results show these tests behave similarly
and are more powerful than tests directly based on cumulants of order 3, 4, 5
and 6. We have applied these tests to the released MAXIMA data. The applied
tests are built to be powerful against detecting deviations from univariate
Gaussianity. The Cholesky matrix corresponding to signal (based on an assumed
cosmological model) plus noise is used to decorrelate the observations previous
to the analysis. Results indicate that the MAXIMA data are compatible with
Gaussianity.Comment: MNRAS, in pres
A retrospective analysis of colorectal serrated lesions from 2005 to 2014 in a single center: importance of the establishment of diagnostic patterns
sem informaçãoSerrated colorectal lesions are increasingly recognized as an important process in the development of colorectal cancer. Endoscopic and histological diagnosis may be difficult, and knowledge of the serrated lesions is important for the establishment of stsem informaçãosem informaçãosem informaçã
A column-store meets the point clouds
Dealing with LIDAR data in the context of database management
systems calls for a re-assessment of their functionality, performance,
and storage/processing limitations. The territory for efficient and
scalable processing of LIDAR repositories using GIS enabled database
systems is still largely unexplored. Bringing together hard core
database management experts and GIS application developers is a
sine qua non to advance the state of the art. In particular to assess
the relative merits of both traditional row-based database engines
and the modern column-oriented database engines
Incorporating Biotic Information in Species Distribution Models: A Coregionalized Approach
In this work, we discuss the use of a methodological approach for modelling spatial
relationships among species by means of a Bayesian spatial coregionalized model. Inference and
prediction is performed using the integrated nested Laplace approximation methodology to reduce
the computational burden. We illustrate the performance of the coregionalized model in species
interaction scenarios using both simulated and real data. The simulation demonstrates the better
predictive performance of the coregionalized model with respect to the univariate models. The case
study focus on the spatial distribution of a prey species, the European anchovy (Engraulis encrasicolus),
and one of its predator species, the European hake (Merluccius merluccius), in the Mediterranean sea.
The results indicate that European hake and anchovy are positively associated, resulting in improved
model predictions using the coregionalized model.Postprin
Benchmarking and improving point cloud data management in MonetDB
The popularity, availability and sizes of point cloud data sets are increasing, thus raising interesting data
management and processing challenges. Various software solutions are available for the management of
point cloud data. A benchmark for point cloud data management systems was defined and it was executed
for several solutions. In this paper we focus on the solutions based on the column-store MonetDB, the
generic out-of-the-box approach is compared with two alternative approaches that exploit the spatial
coherence of the data to improve the data access and to minimize the storage requirement
The Scale of Cosmic Isotropy
The most fundamental premise to the standard model of the universe, the
Cosmological Principle (CP), states that the large-scale properties of the
universe are the same in all directions and at all comoving positions.
Demonstrating this theoretical hypothesis has proven to be a formidable
challenge. The cross-over scale R_{iso} above which the galaxy distribution
becomes statistically isotropic is vaguely defined and poorly (if not at all)
quantified. Here we report on a formalism that allows us to provide an
unambiguous operational definition and an estimate of R_{iso}. We apply the
method to galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7,
finding that R_{iso}\sim 150h^{-1} Mpc. Besides providing a consistency test of
the Copernican principle, this result is in agreement with predictions based on
numerical simulations of the spatial distribution of galaxies in cold dark
matter dominated cosmological models.Comment: 15 pages, 4 figures, accepted by JCAP. The text matches the published
versio
Indirect Dark Matter Detection from Dwarf Satellites: Joint Expectations from Astrophysics and Supersymmetry
We present a general methodology for determining the gamma-ray flux from
annihilation of dark matter particles in Milky Way satellite galaxies, focusing
on two promising satellites as examples: Segue 1 and Draco. We use the
SuperBayeS code to explore the best-fitting regions of the Constrained Minimal
Supersymmetric Standard Model (CMSSM) parameter space, and an independent MCMC
analysis of the dark matter halo properties of the satellites using published
radial velocities. We present a formalism for determining the boost from halo
substructure in these galaxies and show that its value depends strongly on the
extrapolation of the concentration-mass (c(M)) relation for CDM subhalos down
to the minimum possible mass. We show that the preferred region for this
minimum halo mass within the CMSSM with neutralino dark matter is ~10^-9-10^-6
solar masses. For the boost model where the observed power-law c(M) relation is
extrapolated down to the minimum halo mass we find average boosts of about 20,
while the Bullock et al (2001) c(M) model results in boosts of order unity. We
estimate that for the power-law c(M) boost model and photon energies greater
than a GeV, the Fermi space-telescope has about 20% chance of detecting a dark
matter annihilation signal from Draco with signal-to-noise greater than 3 after
about 5 years of observation
Electrical transport studies of quench condensed Bi films at the initial stage of film growth: Structural transition and the possible formation of electron droplets
The electrical transport properties of amorphous Bi films prepared by
sequential quench deposition have been studied in situ. A
superconductor-insulator (S-I) transition was observed as the film was made
increasingly thicker, consistent with previous studies. Unexpected behavior was
found at the initial stage of film growth, a regime not explored in detail
prior to the present work. As the temperature was lowered, a positive
temperature coefficient of resistance (dR/dT > 0) emerged, with the resistance
reaching a minimum before the dR/dT became negative again. This behavior was
accompanied by a non-linear and asymmetric I-V characteristic. As the film
became thicker, conventional variable-range hopping (VRH) was recovered. We
attribute the observed crossover in the electrical transport properties to an
amorphous to granular structural transition. The positive dR/dT found in the
amorphous phase of Bi formed at the initial stage of film growth was
qualitatively explained by the formation of metallic droplets within the
electron glass.Comment: 7 pages, 6 figure
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