Close range photogrammetry in the survey of the coastal area geoecological conditions (on the example of Portugal)

Close range digital photogrammetry, which involves the application of unmanned aerial vehicle (UAV), has been used in a growing number of diverse applications across different scientific disciplines. Our objective was to use the mentioned method in the survey of the contemporary geoecological conditions of the coastal area on the example of Portuguese northwest coastal zone. The coastal zone can be subdivided into two geomorphological sectors: Sector 1, between the Minho River and the town of Espinho, where the coastal segments consist of estuaries, sandy and shingle beaches with rocky outcrops, and Holocene dune systems. The estuaries and the foredunes in particular are very degraded by human activities; and Sector 2, between Espinho and the Mondego Cape, where coastal lagoons and Holocene dune systems occur. We chose two beaches for surveying – Aguçadoura and Ramalha to which the drone swinglet CAM took the photos. We used the ground control software eMotion 2 to plan the flights over the study area and controlled the drone’s trajectory during flight. After processing the obtained images in the program of AgisoftPhotoscanPro, we generated the 2D orthophotos and 3D digital elevation models (DEM) of the research sections. At this stage of study we derived the above product without using the ground control points, or we used only the camera GPS data. Based on these models the compilation of the large-scale maps of high resolution (1cm-5cm) will be possible in the GISs for monitoring and management of the geoecological state of the mentioned beaches in case to precise the x, y and z values of the models with the geodetic device of Differential GPSs in the selected ground control points (GCP).We are grateful to the European Commission ERASMUS-MUNDUS Action-2 ELECTRA program and the Earth Sciences Centre of the University of Minho (Braga, Portugal) in supporting us to conduct the field works and research.info:eu-repo/semantics/publishedVersio

PYROELECTRIC PROPERTIES OF CHIRAL SMECTIC PHASES

On a mesuré la réponse pyroélectrique des cristaux liquides ferroélectriques (L-p-décyloxy-, L-p-nonyloxybenzilidène p'-amino cinnamate de méthyl-2 butyle et mélange) à des impulsions thermiques de durées de 2 x 10-4 et 3 x 10-8 s. A partir des données obtenues on a calculé les variations du coefficient pyroélectrique γ(T) en fonction de la température. La dispersion de γ et de la polarisation spontanée Ps en fonction de la fréquence a été obtenue et est en accord avec les mesures de dispersion de la susceptibilité diélectrique pour des fréquences dans la gamme 104-2 x 105 Hz. On a mesuré le temps de relaxation de la polarisation spontanée (τ) et on a trouvé une divergence de τ près de la température de transition smectique C-smectique A. On a aussi montré que des impuretés dipolaires ont une influence visible sur les valeurs de γmax et de Pmaxs pour les cristaux étudiés.The temperature dependences of the pyroelectric coefficient γ(T) of ferroelectric liquid crystalline L-p-decyloxy- and L-p-nonyloxybenzylidene-p'-amino-2-methylbutylcinnamate and their mixture were calculated from the measurements of their responses to heat pulses with durations of 2 x 10-4 and 3 x 10-8 s. The frequency dispersion of γ and the spontaneous polarization Ps was discovered which is consistent with the corresponding dispersion of dielectric permittivity over a frequency range 104-2 x 105 Hz. The direct measurements of the relaxation time for spontaneous polarization (τ) were performed and sharp increase in τ near the SmC-SmA phase transition was observed. The effect of dipolar admixtures on γmax and Pmaxs was also discussed

VISCOSITY OF NEMATIC-CHIRAL MIXTURES AND THEIR ELECTROOPTICAL CHARACTERISTICS

On a étudié la dépendance en température et en concentration de la viscosité de mélanges de cristaux liquides nématiques et de corps non mésomorphes optiquement actifs : les L-menthylchloracetate, l-menthylbenzoate et l-menthyloxalate. On a montré que l'augmentation de la viscosité pour de faibles concentrations d'additifs (Cm < 3 %) est due à la variation de la structure (formation de la phase cholestérique), tandis que l'influence de facteurs géométriques spécifiques aux molécules d'additif se manifeste à des concentrations élevées. Le temps de montée et le seuil de tension de l'instabilité électro-hydrodynamique ont été déterminés. L'augmentation de la viscosité entraîne un accroissement du temps de montée et les seuils de tension croissent lorsque le pas de l'hélice décroît.We have measured the viscosity in mixtures of nematics and optically active non mesomorphic compounds both as a function of temperature and concentration. L-menthylchloracetate, l-menthylbenzoate and l-menthyloxalate have been used as additives. We show that the increase of the viscosity at low additive concentration (Cm < 3 %) is due to a general structure change (formation of a cholesteric phase), whereas the specific geometry of the molecules has a remarked influence at higher concentrations. The time of onset and the voltage threshold for electrohydrodynamic instabilities have also been determined. The rise in viscosity is accompanied by a corresponding rise in onset time and the voltage threshold increases with increased helicity