Intrinsic leakage and adsorption currents associated with the electrocaloric effect in multilayer capacitors

During the last few years, the increasing demand of energy for refrigeration applications has relived the interest of the scientific community in the study of alternative methods to the traditional gas-based refrigeration. Within this framework, the use of solid state refrigeration based on the electrocaloric effect reveals itself as one of the most promising technologies. In this work, we analyze how the temperature change associated with the electrocaloric effect shows a correlation with the electrical properties of a commercial multilayer capacitor. In that sense we established a clear relation between the adsorption currents and the temperature change produced by the electrocaloric effect. Additionally, intrinsic leakage currents are responsible for the sample heating due to the Joule effect. These well distinguished contributions can be useful during the design of solid state refrigeration devices based on the electrocaloric effect.Comment: Acepted to be published in Applied Physics Letter

Nonlinear Schr\"odinger Equation with Spatio-Temporal Perturbations

We investigate the dynamics of solitons of the cubic Nonlinear Schr\"odinger Equation (NLSE) with the following perturbations: non-parametric spatio-temporal driving of the form $f(x,t) = a \exp[i K(t) x]$, damping, and a linear term which serves to stabilize the driven soliton. Using the time evolution of norm, momentum and energy, or, alternatively, a Lagrangian approach, we develop a Collective-Coordinate-Theory which yields a set of ODEs for our four collective coordinates. These ODEs are solved analytically and numerically for the case of a constant, spatially periodic force $f(x)$. The soliton position exhibits oscillations around a mean trajectory with constant velocity. This means that the soliton performs, on the average, a unidirectional motion although the spatial average of the force vanishes. The amplitude of the oscillations is much smaller than the period of $f(x)$. In order to find out for which regions the above solutions are stable, we calculate the time evolution of the soliton momentum $P(t)$ and soliton velocity $V(t)$: This is a parameter representation of a curve $P(V)$ which is visited by the soliton while time evolves. Our conjecture is that the soliton becomes unstable, if this curve has a branch with negative slope. This conjecture is fully confirmed by our simulations for the perturbed NLSE. Moreover, this curve also yields a good estimate for the soliton lifetime: the soliton lives longer, the shorter the branch with negative slope is.Comment: 21 figure

Energy Flow Puzzle of Soliton Ratchets

We study the mechanism of directed energy transport for soliton ratchets. The energy flow appears due to the progressive motion of a soliton (kink) which is an energy carrier. However, the energy current formed by internal system deformations (the total field momentum) is zero. We solve the underlying puzzle by showing that the energy flow is realized via an {\it inhomogeneous} energy exchange between the system and the external ac driving. Internal kink modes are unambiguously shown to be crucial for that transport process to take place. We also discuss effects of spatial discretization and combination of ac and dc external drivings.Comment: 4 pages, 3 figures, submitted to PR

When Does Output Feedback Enlarge the Capacity of the Interference Channel?

In this paper, the benefits of channel-output feedback in the Gaussian interference channel (G-IC) are studied under the effect of additive Gaussian noise. Using a linear deterministic (LD) model, the signal to noise ratios (SNRs) in the feedback links beyond which feedback plays a significant role in terms of increasing the individual rates or the sum-rate are approximated. The relevance of this work lies on the fact that it identifies the feedback SNRs for which in any G-IC one of the following statements is true: (a) feedback does not enlarge the capacity region; (b) feedback enlarges the capacity region and the sum-rate is greater than the largest sum-rate without feedback; and (c) feedback enlarges the capacity region but no significant improvement is observed in the sum-rate

Equilibrium tuned by a magnetic field in phase separated manganite

We present magnetic and transport measurements on La5/8-yPryCa3/8MnO3 with y = 0.3, a manganite compound exhibiting intrinsic multiphase coexistence of sub-micrometric ferromagnetic and antiferromagnetic charge ordered regions. Time relaxation effects between 60 and 120K, and the obtained magnetic and resistive viscosities, unveils the dynamic nature of the phase separated state. An experimental procedure based on the derivative of the time relaxation after the application and removal of a magnetic field enables the determination of the otherwise unreachable equilibrium state of the phase separated system. With this procedure the equilibrium phase fraction for zero field as a function of temperature is obtained. The presented results allow a correlation between the distance of the system to the equilibrium state and its relaxation behavior.Comment: 13 pages, 5 figures. Submited to Journal of Physics: Condensed Matte

APPLICATIONS OF VORONOI AND DELAUNAY DIAGRAMS IN THE SOLUTION OF THE GEODETIC BOUNDARY VALUE PROBLEM

Voronoi and Delaunay structures are presented as discretization tools to be used innumerical surface integration aiming the computation of geodetic problemssolutions, when under the integral there is a non-analytical function (e. g., gravityanomaly and height). In the Voronoi approach, the target area is partitioned intopolygons which contain the observed point and no interpolation is necessary, onlythe original data is used. In the Delaunay approach, the observed points are verticesof triangular cells and the value for a cell is interpolated for its barycenter. If theamount and distribution of the observed points are adequate, gridding operation isnot required and the numerical surface integration is carried out by point-wise. Evenwhen the amount and distribution of the observed points are not enough, thestructures of Voronoi and Delaunay can combine grid with observed points in orderto preserve the integrity of the original information. Both schemes are applied to thecomputation of the Stokes’ integral, the terrain correction, the indirect effect and thegradient of the gravity anomaly, in the State of Rio de Janeiro, Brazil area

Soliton ratchets

The mechanism underlying the soliton ratchet, both in absence and in presence of noise, is investigated. We show the existence of an asymmetric internal mode on the soliton profile which couples, trough the damping in the system, to the soliton translational mode. Effective soliton transport is achieved when the internal mode and the external force are phase locked. We use as working model a generalized double sine-Gordon equation. The phenomenon is expected to be valid for generic soliton systems.Comment: 4 pages, 4 figure

Estimación de la pose humana 2D en imágenes estéreo

La Estimación de la Pose Humana es el proceso de obtener la configuración espacial de las partes del cuerpo en imágenes. Frente a los métodos monoculares, que recuperan la pose a partir de una sola imagen, los métodos estéreo usan un par de imágenes para realizar el proceso, siendo capaces de aprovechar la redundancia de información y así mejorar la precisión. Este trabajo de Tesis se centra en adaptar técnicas monoculares de estimación de la pose ya existentes para que sean capaces de aprovechar las ventajas del uso de información estéreo. La primera contribución de esta tesis es una nueva técnica para estimar la pose 2D de personas en imágenes estéreo basado en una restricción de similitud que permite la colaboración entre dos estimadores de pose. Nuestra propuesta mejora la precisión de las poses estimadas en comparación con técnicas monoculares de estimación de la pose ejecutadas de forma independiente en cada vista de la imagen estéreo. La segunda contribución es una base de datos para el problema de la estimación de la pose humana en imágenes estéreo. Para validar experimentalmente nuestras propuestas, hemos creado una nueva base de datos anotada de 630 imágenes estéreo que muestran personas en entornos diferentes, con ropa variada y diversa iluminación. La base de datos muestra a las personas en posición vertical con una gran variedad de poses de brazos que cubren todo el espacio de posibles configuraciones de poses. La tercera contribución es un nuevo método para estimar la pose 2D de personas en secuencias de video estéreo. El método comienza con una reducción de las posibles localizaciones de las partes del cuerpo usando información de color y de disparidad. A continuación, se utiliza información a priori para la localización de las partes del cuerpo más estructuradas. Por último, un método de recombinación de partes del cuerpo se aplica en la secuencia estéreo para obtener la mejor configuración de las partes del cuerpo. Los experimentos demuestran que la propuesta consigue mejores resultados que el actual estado del arte.Human Pose Estimation (HPE) is the task of obtaining the spatial con guration of human body parts from images. Methods recovering the human pose from a single image are called monocular approaches while those using image pairs are called stereo approaches. Stereo images provide extra information that can be employed to improve the results obtained by monocular approaches. This Thesis considers the problem of 2D human pose estimation on stereo images. To this end, three contributions are provided. The rst contribution of this thesis is a new technique to automatically detect and estimate the 2D pose of humans in stereo images. The proposed method is based on a similarity constraint that promotes a collaboration between two pose estimators. We show experimentally that our proposal improves the accuracy of the estimated poses when compared to standard HPE techniques running independently on each image. The second contribution is a dataset for the problem of human pose estimation in stereo image. To experimentally validate our approach, we have created a new annotated dataset of 630 stereo image from stereo videos depicting people in di erent backgrounds, clothing, lighting or locations in the image frames. The dataset contains upright people in a great variety of arms poses, covering the space of possible con gurations quite uniformly. The third contribution is a new method to estimate the 2D pose of humans in stereo videos sequences. The proposed pipeline starts by constraining the posible location of body joints by exploiting color and disparity information, and adding location priors to the most structured joints. Finally, a body limb recombination method is applied along the stereo sequence to obtain the best con guration of the body joints. The experiments show that our method obtains better average results than the state-of-the-art

Redes de sensores inalámbricos: ampliación de red de sensores de monitoreo ambiental del iteso. Drones para fotogrametría: utilizacion de vehiculos no tripulados para fotogrametría; generación de ortofoto

Dentro del proyecto de aplicación profesional “Vida digital” se trabajó en dos áreas de aplicación de ciudades inteligentes las cuales están conformadas por una red de sensores de monitoreo ambiental y el uso de drones para creación de ortofotos y hacer análisis de estas. En la parte de sensores se compararon dos marcas diferentes de sensores de monitoreo de bajo costo que fueron Kunak y Libelium para determinar la que se acercara más a las mediciones hechas por el Sistema de Monitoreo Ambiental de Jalisco (SIMAJ). Se obtuvieron datos de gran importancia para determinar el funcionamiento de estos sin embargo se necesita realizar más pruebas con los sensores en el mismo lugar para emitir una opinión final. En la parte de drones para fotogrametría, se tomaron fotografías con un vehículo no tripulado y se procesaron para generar una sola ortofoto, esta misma se analizó y se determinó que había mejoras para hacer en el momento de capturarlas por lo que se hizo el análisis espacial con las existentes y se hizo la recomendación de modificar los parámetros de toma de fotografías para mejorar la calidad de estas.ITESO, A.C