Some discrete approaches to continuum economies

Given the preferences of the agents of a continuum economy, we define the average and unanimous preference. This allow us to consider several sequences of economies, in which only a finite number of different agents' characteristics can be distinguished. We obtain approximation results for the core of these economies

Peer Victimization in Overweight Adolescents and Its Effect on Their Self-Esteem and Peer Difficulties

This study has three objectives: to examine whether adolescents who perceive themselves as overweight differ from others in terms of offline victimization at school, cybervictimization, self-esteem, and difficulties relating to peers; to examine the possible effects of offline and cybervictimization on self-esteem and difficulties relating to peers; and to examine the possible moderating role of perceiving oneself as overweight on those effects. Previously validated questionnaires were applied to a sample of 3145 adolescents in Asturias (Spain). Descriptive, inferential, correlational, and structural equation analyses were performed. Adolescents who perceived themselves as overweight reported being victims of both offline victimization and most forms of cybervictimization to a greater extent than those who did not perceive themselves as overweight. They also reported lower self-esteem and more peer difficulties (shyness or social anxiety). In both groups of adolescents, victimization and cybervictimization were correlated with each other, both types of victimization had direct, negative effects on self-esteem, and self-esteem in turn had a direct, negative effect on peer difficulties. Furthermore, offline victimization had a direct, positive effect on peer difficulties. Perceiving oneself as overweight moderated the effect of self-esteem on peer difficulties. In adolescents perceiving themselves as overweight, low self-esteem was a stronger risk factor of peer difficulties than in the rest of the adolescents. With high overall self-esteem there were no significant differences in peer difficulties between the adolescents perceiving themselves as overweight and the rest of the adolescents

Contribution to the Development of Electronic Devices Based on Zn3N2 Thin Films, and ZnO and GaAs Nanowires

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Aplicada. Fecha de lectura: 16-07-201

Study of coliforms and Clostridium bacteria inactivation in wastewaters by a pilot photolysis process and by the maturation lagoons of a low-cost nature-based WWTP

[EN] The inactivation processes of coliform bacteria (total and fecal) and sulphito-reducing Clostridium bacteria (vegetative species and spores) in water maturation lagoon of a low-cost nature-based wastewater treatment plant using constructed wetlands and through processes of photolysis in a pilot photoreactor have been comparatively studied. The diferent inactivation mechanisms by photolysis of these bacteria have been studied following the criteria of diferent statistical and kinetic models. Clostridium disinfection treatments ft models in which two types of bacteria populations coexist, one sensitive (vegetative species) and the other (spores) resistant to the treatment, the sensitive one (94%) with an inactivation rate of k=0.24±0.07 min−1 and the resistant one (6%) with k=0.11±0.05 min−1. Total coliform photolytic disinfection also shows two populations with diferent physiological state. The time required to reduce the frst logarithmic decimal cycle of the diferent types of bacteria (physiological states) are δ1=4.2±0.9 and δ2=8.3±1.1 min, respectively. For fecal coliform photolytic disinfection, only bacteria population, with k=1.15±0.19 min−1, is found. The results obtained confrm the photolytic disinfection processes and maturation lagoon are efective systems for Clostridia bacteria removal after water treatment by nature-based systems. Total removal of coliform bacteria is not achieved by maturation lagoons, but their reduction is signifcant using low doses of cumulative radiation.Publicación en abierto financiada por el Consorcio de Bibliotecas Universitarias de Castilla y León (BUCLE), con cargo al Programa Operativo 2014ES16RFOP009 FEDER 2014-2020 DE CASTILLA Y LEÓN, Actuación:20007-CL - Apoyo Consorcio BUCLE

A novel growth method to improve the quality of GaAs nanowires grown by Ga-assisted chemical beam epitaxy

The successful synthesis of high crystalline quality and high aspect ratio GaAs nanowires (NWs) with a uniform diameter is needed to develop advanced applications beyond the limits established by thin film and bulk material properties. Vertically aligned GaAs NWs have been extensively grown by Ga-assisted vapor–liquid–solid (VLS) mechanism on Si(111) substrates, and they have been used as building blocks in photovoltaics, optoelectronics, electronics, and so forth. However, the nucleation of parasitic species such as traces and nanocrystals on the Si substrate surface during the NW growth could affect significantly the controlled nucleation of those NWs, and therefore the resulting performance of NW-based devices. Preventing the nucleation of parasitic species on the Si substrate is a matter of interest, because they could act as traps for gaseous precursors and/or chemical elements during VLS growth, drastically reducing the maximum length of grown NWs, affecting their morphology and structure, and reducing the NW density along the Si substrate surface. This work presents a novel and easy to develop growth method (i.e., without using advanced nanolithography techniques) to prevent the nucleation of parasitic species, while preserving the quality of GaAs NWs even for long duration growths. GaAs NWs are grown by Ga-assisted chemical beam epitaxy on oxidized Si(111) substrates using triethylgallium and tertiarybutylarsine precursors by a two-step-based growth method presented here; this method includes a growth interruption for an oxidation on air between both steps of growth, reducing the nucleation of parasitic crystals on the thicker SiOx capping layer during the second and longer growth step. VLS conditions are preserved overtime, resulting in a stable NW growth rate of around 6 μm/h for growth times up to 1 h. Resulting GaAs NWs have a high aspect ratio of 85 and average radius of 35 nm. We also report on the existence of characteristic reflection high-energy electron diffraction patterns associated with the epitaxial growth of GaAs NWs on Si(111) substrates, which have been analyzed and compared to the morphological characterization of GaAs NWs grown for different times under different conditions

Object Tracking from Unstabilized Platforms by Particle Filtering with Embedded Camera Ego Motion

Visual tracking with moving cameras is a challenging task. The global motion induced by the moving camera moves the target object outside the expected search area, according to the object dynamics. The typical approach is to use a registration algorithm to compensate the camera motion. However, in situations involving several moving objects, and backgrounds highly affected by the aperture problem, image registration quality may be very low, decreasing dramatically the performance of the tracking. In this work, a novel approach is proposed to successfully tackle the tracking with moving cameras in complex situations, which involve several independent moving objects. The key idea is to compute several hypotheses for the camera motion, instead of estimating deterministically only one. These hypotheses are combined with the object dynamics in a Particle Filter framework to predict the most probable object locations. Then, each hypothetical object location is evaluated by the measurement model using a spatiogram, which is a region descriptor based on color and spatial distributions. Experimental results show that the proposed strategy allows to accurately track an object in complex situations affected by strong ego motion

Robust automatic target tracking based on a Bayesian ego-motion compensation framework for airborne FLIR imagery

Automatic target tracking in airborne FLIR imagery is currently a challenge due to the camera ego-motion. This phenomenon distorts the spatio-temporal correlation of the video sequence, which dramatically reduces the tracking performance. Several works address this problem using ego-motion compensation strategies. They use a deterministic approach to compensate the camera motion assuming a specific model of geometric transformation. However, in real sequences a specific geometric transformation can not accurately describe the camera ego-motion for the whole sequence, and as consequence of this, the performance of the tracking stage can significantly decrease, even completely fail. The optimum transformation for each pair of consecutive frames depends on the relative depth of the elements that compose the scene, and their degree of texturization. In this work, a novel Particle Filter framework is proposed to efficiently manage several hypothesis of geometric transformations: Euclidean, affine, and projective. Each type of transformation is used to compute candidate locations of the object in the current frame. Then, each candidate is evaluated by the measurement model of the Particle Filter using the appearance information. This approach is able to adapt to different camera ego-motion conditions, and thus to satisfactorily perform the tracking. The proposed strategy has been tested on the AMCOM FLIR dataset, showing a high efficiency in the tracking of different types of targets in real working conditions

Automatic Feature-Based Stabilization of Video with Intentional Motion through a Particle Filter

Video sequences acquired by a camera mounted on a hand held device or a mobile platform are affected by unwanted shakes and jitters. In this situation, the performance of video applications, such us motion segmentation and tracking, might dramatically be decreased. Several digital video stabilization approaches have been proposed to overcome this problem. However, they are mainly based on motion estimation techniques that are prone to errors, and thus affecting the stabilization performance. On the other hand, these techniques can only obtain a successfully stabilization if the intentional camera motion is smooth, since they incorrectly filter abrupt changes in the intentional motion. In this paper a novel video stabilization technique that overcomes the aforementioned problems is presented. The motion is estimated by means of a sophisticated feature-based technique that is robust to errors, which could bias the estimation. The unwanted camera motion is filtered, while the intentional motion is successfully preserved thanks to a Particle Filter framework that is able to deal with abrupt changes in the intentional motion. The obtained results confirm the effectiveness of the proposed algorith

Aerial moving target detection based on motion vector field analysis

An efficient automatic detection strategy for aerial moving targets in airborne forward-looking infrared (FLIR) imagery is presented in this paper. Airborne cameras induce a global motion over all objects in the image, that invalidates motion-based segmentation techniques for static cameras. To overcome this drawback, previous works compensate the camera ego-motion. However, this approach is too much dependent on the quality of the ego-motion compensation, tending towards an over-detection. In this work, the proposed strategy estimates a robust motion vector field, free of erroneous vectors. Motion vectors are classified into different independent moving objects, corresponding to background objects and aerial targets. The aerial targets are directly segmented using their associated motion vectors. This detection strategy has a low computational cost, since no compensation process or motion-based technique needs to be applied. Excellent results have been obtained over real FLIR sequences

La gestión de la liquidez del Banco Central Europeo durante la crisis financiera: 2008-2009

Después de la quiebra de Lehman Brothers, en septiembre de 2008, hubo gran tensión en los mercados financieros. En los mercados de dinero, el Eurosistema tuvo que adoptar medidas que ofrezcan liquidez a los bancos a fin de evitar el colapso del mercado interbancario. En este trabajo se analizan los cambios en las formas de inyectar liquidez en el sistema, en un contexto de grave crisis económica y financiera. Con la disminución de las tasas de interés, se había producido una transformación radical entre octubre de 2008 y mediados de 2009. Las operaciones de financiación a más largo plazo alcanzaron la primera posición, la eliminación de las operaciones principales de financiación, mientras que se amplió la lista de valores como garantía, y un número cada vez mayor de bancos recurrieron a las subastas de liquidez. Si el BCE decide limitar las subastas de financiación a más largo plazo, adaptándolas a su procedimiento habitual de la política monetaria, que será de gran interés el análisis de la deuda actual de los bancos con respecto al BCE.After the bankruptcy of Lehman Brothers, in September 2008, there was huge stress in the financial markets. In the money markets, the Eurosystem had to adopt measures providing liquidity to banks in order to avoid the collapse of the interbank market. In this work we analyze the changes in the ways of injecting liquidity in the system, within a context of serious economic and financial crisis. With decreasing interest rates, there had been a radical transformation between October 2008 and mid 2009. The longer-term refinancing operations reached the first position, removing the main refinancing operations, while was enlarged the list of securities as collateral, and an increasing number of banks resorted to liquidity auctions. If the ECB decides to limit longer-term financing auctions, adapting them to its usual monetary policy procedure, it will be of great interest the analysis of the current debt of the banks with respect to the ECB.notPeerReviewe