Thermal phase diagrams of columnar liquid crystals

In order to understand the possible sequence of transitions from the disordered columnar phase to the helical phase in hexa(hexylthio)triphenylene (HHTT), we study a three-dimensional planar model with octupolar interactions inscribed on a triangular lattice of columns. We obtain thermal phase diagrams using a mean-field approximation and Monte Carlo simulations. These two approaches give similar results, namely, in the quasi one-dimensional regime, as the temperature is lowered, the columns order with a linear polarization, whereas helical phases develop at lower temperatures. The helicity patterns of the helical phases are determined by the exact nature of the frustration in the system, itself related to the octupolar nature of the molecules.Comment: 12 pages, 9 figures, ReVTe

Innovación en Cartografía y Fotointerpretación digital: retos y resultados

En los últimos años la Cartografía ha experimentado profundos cambios gracias al uso de la informática. Actualmente, los procesos cartográficos pueden realizarse con ordenadores pero su incorporación a las aulas universitarias ha sido muy dispar debido a los elevados costes o a la falta de formación específica del profesorado. “Cartografía y Fotointerpretación” es una asignatura obligatoria de primer ciclo que se imparte en las licenciaturas de Geografía y de Ciencias Ambientales de la Universidad Autónoma de Barcelona. Dentro de los principales retos de la asignatura fruto de los cambios tecnológicos comentados o a consecuencia del proceso de convergencia al EEES, la transformación de las prácticas en formato analógico (en papel) a formato digital (con ordenador) aparece como uno de los requisitos de obligado cumplimiento. El proyecto de innovación presentado tiene como objetivo profundizar en esta transformación y se basa en los siguientes bloques: 1. Uso de un programa informático gratuito, MiraMon, muy útil por los siguientes motivos: es un programa de prestaciones totalmente profesionales pero gratuito para el alumnado; es un de fácil manejo; y es capaz de leer un elevado número de formatos. 2. Las prácticas se realizan en las aulas con recursos informáticos, con un doble objetivo: captación desde Internet del material digital necesario y almacenamiento de los resultados en una carpeta de acceso exclusivo para el alumno. 3. Espacio de consulta y atención al alumno. En el Campus Virtual, los alumnos tienen acceso al material didáctico y pueden consultar cualquier duda directamente con el profesor. Los resultados han sido, hasta la fecha, muy positivos, produciéndose, además, un estimable ahorro de papelSIN FINANCIACIÓNNo data 200

Design of an Adaptive Fuzzy Control System for Dual Star Induction Motor Drives

In this paper, a new control stra¬tegy is deve¬loped; an adaptive fuzzy controller based on Lyapunov's stability theory (AFLC) recalculates the real-time PI-fuzzy gains and combines the advantages of two robust techniques i.e. the fuzzy logic control and the adaptive one. For the new adaptive fuzzy control, we followed two steps: in the first one, a PI-fuzzy controller is designed, in the second step, the gains of a fuzzy regulator are determined. Extensive simulation results are presented to validate the proposed technique. The system is tested at different speeds and a very satisfactory performance has been achieved

Automatic and improved radiometric correction of Landsat imagery using reference values from MODIS surface reflectance images

AbstractRadiometric correction is a prerequisite for generating high-quality scientific data, making it possible to discriminate between product artefacts and real changes in Earth processes as well as accurately produce land cover maps and detect changes. This work contributes to the automatic generation of surface reflectance products for Landsat satellite series. Surface reflectances are generated by a new approach developed from a previous simplified radiometric (atmospheric+topographic) correction model. The proposed model keeps the core of the old model (incidence angles and cast-shadows through a digital elevation model [DEM], Earth–Sun distance, etc.) and adds new characteristics to enhance and automatize ground reflectance retrieval. The new model includes the following new features: (1) A fitting model based on reference values from pseudoinvariant areas that have been automatically extracted from existing reflectance products (Terra MODIS MOD09GA) that were selected also automatically by applying quality criteria that include a geostatistical pattern model. This guarantees the consistency of the internal and external series, making it unnecessary to provide extra atmospheric data for the acquisition date and time, dark objects or dense vegetation. (2) A spatial model for atmospheric optical depth that uses detailed DEM and MODTRAN simulations. (3) It is designed so that large time-series of images can be processed automatically to produce consistent Landsat surface reflectance time-series. (4) The approach can handle most images, acquired now or in the past, regardless of the processing system, with the exception of those with extremely high cloud coverage. The new methodology has been successfully applied to a series of near 300 images of the same area including MSS, TM and ETM+ imagery as well as to different formats and processing systems (LPGS and NLAPS from the USGS; CEOS from ESA) for different degrees of cloud coverage (up to 60%) and SLC-off. Reflectance products have been validated with some example applications: time series robustness (for a pixel in a pseudoinvariant area, deviations are only 1.04% on average along the series), spectral signatures generation (visually coherent with the MODIS ones, but more similar between dates), and classification (up to 4 percent points better than those obtained with the original manual method or the CDR products). In conclusion, this new approach, that could also be applied to other sensors with similar band configurations, offers a fully automatic and reasonably good procedure for the new era of long time-series of spatially detailed global remote sensing data