118 research outputs found
Gain modulation of synaptic inputs by network state in auditory cortex in vivo
The cortical network recurrent circuitry generates spontaneous activity organized into Up (active) and Down (quiescent) states during slow-wave sleep or anesthesia. These different states of cortical activation gain modulate synaptic transmission. However, the reported modulation that Up states impose on synaptic inputs is disparate in the literature, including both increases and decreases of responsiveness. Here, we tested the hypothesis that such disparate observations may depend on the intensity of the stimulation. By means of intracellular recordings, we studied synaptic transmission during Up and Down states in rat auditory cortex in vivo. Synaptic potentials were evoked either by auditory or electrical (thalamocortical, intracortical) stimulation while randomly varying the intensity of the stimulus. Synaptic potentials evoked by the same stimulus intensity were compared in Up/Down states. Up states had a scaling effect on the stimulus-evoked synaptic responses: the amplitude of weaker responses was potentiated whereas that of larger responses was maintained or decreased with respect to the amplitude during Down states. We used a computational model to explore the potential mechanisms explaining this nontrivial stimulus–response relationship. During Up/Down states, there is different excitability in the network and the neuronal conductance varies. We demonstrate that the competition between presynaptic recruitment and the changing conductance might be the central mechanism explaining the experimentally observed stimulus–response relationships. We conclude that the effect that cortical network activation has on synaptic transmission is not constant but contingent on the strength of the stimulation, with a larger modulation for stimuli involving both thalamic and cortical networks.Fil: Reig, Ramon. Institut d'Investigacions Biomèdiques August Pi i Sunyer; España. Karolinska Huddinge Hospital. Karolinska Institutet; SueciaFil: Zerlaut, Yann. Centre National de la Recherche Scientifique; Francia. Unité de Neurosciences, Information et Complexité; FranciaFil: Vergara, Ramiro Oscar. Institut d'Investigacions Biomèdiques August Pi i Sunyer; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Acústica y Percepción Sonora; ArgentinaFil: Destexhe, Alain. Centre National de la Recherche Scientifique; Francia. Unité de Neurosciences, Information et Complexité; FranciaFil: Sánchez Vives, María V.. Institut d'Investigacions Biomèdiques August Pi i Sunyer; España. Institució Catalana de Recerca i Estudis Avancats; Españ
Image registration techniques with multiresolution analysis in satellite oceanography
En aquest article es fa una descripció dels procediments realitzats per enregistrar dues imatges geomètricament, de forma automàtica, si es pren la primera com a imatge de referència. Es comparen els resultats obtinguts mitjançant tres
mètodes. El primer mètode és el d’enregistrament clàssic en domini espacial maximitzant la correlació creuada (MCC)[1]. El segon mètode es basa en aplicar l’enregistrament MCC conjuntament amb un anàlisi multiescala a partir de
transformades wavelet [2]. El tercer mètode és una variant de l’anterior que es situa a mig camí dels dos. Per cada un dels mètodes s’obté una estimació dels coeficients de la transformació que relaciona les dues imatges. A continuació
es transforma per cada cas la segona imatge i es georeferencia respecte la primera. I per acabar es proposen unes mesures quantitatives que permeten discutir i comparar els resultats obtinguts amb cada mètode.In this paper we present processing techniques for automated image-to-image geometrical registration. One reference image is used to register the working image. Three methods are used. The first method is the classical image registration method using the maximum cross-correlation (MCC) in the spatial domain [1]. The second method is based on MCC and multiscale analysis through wavelet multiresolution techniques [2]. The third one is a fusion of the two previous methods. For each technique the transformation coefficients relating both images are estimated. Finally, the second image is transformed and georeferenced to the first one. In the conclusion, a proposal of quantitative parameters leads to a final discussion on the results.En este artículo se describen los procedimientos realizados para registrar geométricamente dos imágenes de forma automática si se toma la primera como imagen de referencia. Se comparan los resultados obtenidos mediante tres métodos. El primero es el método clásico para registrar dos imágenes en el dominio espacial maximizando la correlación cruzada (MCC) [1]. En el segundo se trata de aplicar de forma conjunta técnicas de análisis multiescalar, basadas en las transformaciones wavelet y el método MCC [2]. El tercero es una variación del segundo situada a medio camino de los dos métodos anteriores. Para cada método se obtiene una estimación de los coeficientes de la transformación que relaciona las dos imágenes. A continuación, se transforma la segunda imagen que se georreferencia respecto a la primera para cada caso. Para finalizar se proponen unas medidas cuantitativas que nos permiten discutir y comparar los resultados obtenidos en cada uno de los método
Features extraction based on the Discrete Hartley Transform for closed contour
In this paper the authors propose a new closed contour descriptor that could be seen as a Feature Extractor of closed
contours based on the Discrete Hartley Transform (DHT), its main characteristic is that uses only half of the coefficients required
by Elliptical Fourier Descriptors (EFD) to obtain a contour approximation with similar error measure. The proposed closed contour
descriptor provides an excellent capability of information compression useful for a great number of AI applications. Moreover
it can provide scale, position and rotation invariance, and last but not least it has the advantage that both the parameterization
and the reconstructed shape from the compressed set can be computed very efficiently by the fast Discrete Hartley Transform
(DHT) algorithm. This Feature Extractor could be useful when the application claims for reversible features and when the user
needs and easy measure of the quality for a given level of compression, scalable from low to very high quality
Improving Pitch Tracking Performance in Hard Noise Conditions by a Preprocessing Based on Mathematical Morphology
In this paper we show how a nonlinear preprocessing of speech
signal -with high noise- based on morphological filters improves the
performance of robust algorithms for pitch tracking (RAPT). This result
happens for a very simple morphological filter. More sophisticated ones could
even improve such results. Mathematical morphology is widely used in image
processing and has a great amount of applications. Almost all its formulations
derived in the two-dimensional framework are easily reformulated to be
adapted to one-dimensional contex
Exploring Non-linear Transformations for an Entropybased Voice Activity Detector
In this paper we explore the use of non-linear transformations in
order to improve the performance of an entropy based voice activity detector
(VAD). The idea of using a non-linear transformation comes from some
previous work done in speech linear prediction (LPC) field based in source
separation techniques, where the score function was added into the classical
equations in order to take into account the real distribution of the signal. We
explore the possibility of estimating the entropy of frames after calculating its
score function, instead of using original frames. We observe that if signal is
clean, estimated entropy is essentially the same; but if signal is noisy
transformed frames (with score function) are able to give different entropy if
the frame is voiced against unvoiced ones. Experimental results show that this
fact permits to detect voice activity under high noise, where simple entropy
method fails
Satellite image georegistration from coast-line codification
This paper presents a contour-based approach for automatic image
registration in satellite oceanography. Accurate image georegistration
is an essential step to increase the eff ectiveness of all the image
processing methods that aggregate information from diff erent
sources, i.e. applying data fusion techniques. In our approach the images
description is based on main contours extracted from coast-line.
Each contour is codifi ed by a modifi ed chain-code, and the result is
a discrete value sequence. The classical registration techniques were
area-based, and the registration was done in a 2D domain (spatial
and/or transformed); this approach is feature-based, and the registration
is done in a 1D domain (discrete sequences). This new technique
improves the registration results. It allows the registration of multimodal
images, and the registration when there are occlusions and
gaps in the images (i.e. due to clouds), or the registration on images
with moderate perspective changes. Finally, it has to be pointed out
that the proposed contour-matching technique assumes that a reference
image, containing the coastlines of the input image geographical
area, is available
Orbital X-Ray Variability of the Microquasar LS 5039
The properties of the orbit and the donor star in the high mass X-ray binary
microquasar LS 5039 indicate that accretion processes should mainly occur via a
radiatively driven wind. In such a scenario, significant X-ray variability
would be expected due to the eccentricity of the orbit. The source has been
observed at X-rays by several missions, although with a poor coverage that
prevents to reach any conclusion about orbital variability. Therefore, we
conducted RossiXTE observations of the microquasar system LS 5039 covering a
full orbital period of 4 days. Individual observations are well fitted with an
absorbed power-law plus a Gaussian at 6.7 keV, to account for iron line
emission that is probably a diffuse background feature. In addition, we have
taken into account that the continuum is also affected by significant diffuse
background contamination. Our results show moderate power-law flux variations
on timescales of days, as well as the presence of miniflares on shorter
timescales. The new orbital ephemeris of the system recently obtained by
Casares et al. have allowed us to show, for the first time, that an increase of
emission is seen close to the periastron passage, as expected in an accretion
scenario. Moreover, the detected orbital variability is a factor of ~4 smaller
than the one expected by using a simple wind accretion model, and we suggest
that an accretion disk around the compact object could be responsible for this
discrepancy. On the other hand, significant changes in the photon index are
also observed clearly anti-correlated with the flux variations. We interpret
the overall X-ray spectral characteristics of LS 5039 in the context of X-ray
radiation produced by inverse Compton and/or synchrotron processes in the jet
of this microquasar.Comment: published in Astrophysical Journal, submission format (real number of
pages: 7, 4 figures
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