A Hybrid Segmentation and D-bar Method for Electrical Impedance Tomography

The Regularized D-bar method for Electrical Impedance Tomography provides a rigorous mathematical approach for solving the full nonlinear inverse problem directly, i.e. without iterations. It is based on a low-pass filtering in the (nonlinear) frequency domain. However, the resulting D-bar reconstructions are inherently smoothed leading to a loss of edge distinction. In this paper, a novel approach that combines the rigor of the D-bar approach with the edge-preserving nature of Total Variation regularization is presented. The method also includes a data-driven contrast adjustment technique guided by the key functions (CGO solutions) of the D-bar method. The new TV-Enhanced D-bar Method produces reconstructions with sharper edges and improved contrast while still solving the full nonlinear problem. This is achieved by using the TV-induced edges to increase the truncation radius of the scattering data in the nonlinear frequency domain thereby increasing the radius of the low pass filter. The algorithm is tested on numerically simulated noisy EIT data and demonstrates significant improvements in edge preservation and contrast which can be highly valuable for absolute EIT imaging

Adaptive Vectorial Filter for Grid Synchronization of Power Converters Under Unbalanced and/or Distorted Grid Conditions

This paper presents a new synchronization scheme for detecting multiple positive-/negative-sequence frequency harmonics in three-phase systems for grid-connected power converters. The proposed technique is called MAVF-FLL because it is based on the use of multiple adaptive vectorial filters (AVFs) working together inside a harmonic decoupling network, resting on a frequency-locked loop (FLL) which makes the system frequency adaptive. The method uses the vectorial properties of the three-phase input signal in the αβ reference frame in order to obtain the different harmonic components. The MAVF-FLL is fully designed and analyzed, addressing the tuning procedure in order to obtain the desired and predefined performance. The proposed algorithm is evaluated by both simulation and experimental results, demonstrating its ability to perform as required for detecting different harmonic components under a highly unbalanced and distorted input grid voltage

Analysis of the power balance In the cells of a multilevel cascaded H-Bridge converter

Multilevel cascaded H-Bridge converters (CHB) have been presented as a good solution for high power applications. In this way, several control and modulation techniques have been proposed for this power converter topology. In this paper the steady state power balance in the cells of the single phase two cell CHB is studied. The capability to be supplied with active power from the grid or to deliver active power to the grid in each cell is analyzed according to the dc-link voltages and the desired ac output voltage value. Limits of the maximum and minimum input active power for stable operation of the CHB are addressed. Simulation results are shown to validate the presented analysis

Development and Experimental Validation of a Dynamic Model for a Fresnel Solar Collector

this paper presents a lumped parameter dynamic model of a Fresnel collector field of a solar refrigeration plant. The plant is located in the Escuela Superior de Ingenieros of the University of Seville. The dynamic model parameter model developed can be used as a control model or as a simulation tool to test controllers. The lumped parameters have been determined by using real data from the plant in different operating conditions. The model has been validated against a data validation set obtained from the plant. The model has shown to reproduce the system behavior with a good compromise in accuracy and model complexity

Estudios sobre Agricultura y conocimiento tradicional en México

La agricultura es una de las actividades importantes para las comunidades rurales en México. Diversas situaciones impactan directamente a los campesinos y sus sistemas agrícolas. Por ejemplo, los productores con agricultura de temporal, son los menos favorecidos con determinadas políticas internacionales como el Tratado de Libre Comercio (TLC), cuyo potencial productivo se ha reducido a niveles de 1.2 por ciento. En las últimas dos décadas se ha dado fuerte impulso a los cultivos comerciales como hortalizas, frutas y flores ocasionando impactos a los productores rurales (Escalante et al. 2007 y 2008). Los campesinos en México se han enfrentado a diferentes situaciones complejas como los impactos de la modernización del sector agropecuario, los proyectos de desarrollo, la expansión de la industria y las áreas urbanas sobre las rurales y los procesos de mundialización de la economía (González 2007). Ante la situación que atraviesa el sector agrícola, es de vital importancia reconsiderar los sistemas agrícolas tradicionales que practican los campesinos. Los estudio sobre agricultura tradicional mexicana han demostrado la diversidad de sistemas que los campesinos han practicado durante cientos de años. Algunos estudios evidencian la historia del control del agua, la tecnología de riego, el manejo de las plantas, la intensificación del uso del suelo, las formas de organización sociopolítica, el mercado y los tipos de asentamientos humanos (Donkin 1979; Palerm 1980; Palerm y Wolf 1980; Doolittle 2004). Otros estudio más específicos se relacionan con el control de procesos erosivos del suelo, el manejo del suelo, la biodiversidad, el conocimiento ecológico tradicional, las estrategias y manejo de agua de riego y de humedales (González 1992; Maimone et al. 2006; Ocampo y Escobedo 2006; Miranda et al. 2009; Pérez 2014). Por consiguiente, el objetivo de este trabajo es presentar cinco estudios de caso que abordan el estudio de la agricultura y el conocimiento tradicional en México, indicando las diferentes temáticas en cuanto al uso y manejo de la agricultura, los suelos, las plantas y la fauna