Optically Induced Reorientation in Nematic Cylindrical Structures

Cyclindrical structures of nematics give rise to several opto-optical effects related to molecular reorientation. One of these effects is the formation of diffraction ring patterns similar to the ones observed in planar cells, but differing in shape. Another effect has been observed, namely a quasi-chaotic motion of rings with a very large angular spread; this motion can be obtained using a cw laser and high power densities. The phenomenon could be attributed to thermal motion, however, there are some features that cannot be explained by a purely thermal effect, e.g., a wavelength dependence of the threshold and the frequencies of the ring motion

La luz portadora de información: las fibras ópticas

La electricidad y la electrónica han sido, habitualmente, los elementos bási­cos para el desarrollo de las comunicaciones a través de medios guiados. Desde el viejo telégrafo hasta los modernos sistemas de transmisión de televisión por cable, todas las técnicas empleadas han tenido en común el envío de una señal eléctrica a través de un elemento con­ductor. De igual manera a como llega la electricidad a los hogares, por medio de un cable metálico, el teléfono, el télex, el facsímil... todos ellos emplean una técni­ca en cierta manera análoga: una corriente eléctrica, llevando con ella la información deseada, accede a un equipo capaz de convertirla en señal reconocible por el usuario. En ocasiones, cuan­do la frecuencia de la señal transmitida es lo suficientemente alta, puede no ser una corriente eléctrica análoga a la empleada, por ejemplo, para alimentar los electrodomésticos convencionales. En esas circunstancias la información es transportada por un campo electromag­nético y el medio por el que se desplaza puede ser una guía metálica hueca. Pero todos los elementos que la rodean siguen estando basados en conceptos derivados del manejo de corrientes eléc­tricas y en su procesado mediante técni­cas, en general, electrónicas

Experimental measurements of the scattered-light polarization from different liquid flows

An experimental system designed to measure very low optical powers, of the order of a few picowatts, is presented. Its main aid is to detect the polarisation state of scattered light from a fluid flow, in different angular directions with respect to the longitudinal axis of the flow. A laser beam incident linearly polarized crosses the fluid flow orthogonally. The scattered light is detected by means of a photodetector situated behind a lineal polarizer whose orientation can be rotated. The outgoing electrical signal is amplified by means of a Mode-lockin amplifier and is digitally processed

Optically Induced Modulation of a Laser Beam in Nematic Liquid Crystals Structures

In this paper we report the experimental results obtained when an He-Ne laser beam crosses an MBBA homeotropic sandwich structure and is modulated by the influence of another laser beam, in our case an Ar+ laser, crossing through the same region. We extend some results previously reported by us1 2 concerning the influence of the ratio of the diameters of the laser beams on the modulation characteristics. A theoretical model, based on the one reported in Ref6 , shows good agreement with the experimental results. If the Ar+ laser is intensity chopped, the resulting He-Ne diffracted image is also intensity modulated. The highest frequency observed has been 500 p. p. s

A Tylosaurine Mosasauridae (Squamata) from the Late Cretaceous of the Basque-Cantabrian Region

An isolated mosasaurid tooth from the Campanian of Alava (Basque Country), previously referred to as cf. Mosasaurus sp., is here reattributed to a tylosaurine. It may belong to Tylosaurus, a nearly cosmopolitan genus known from the Santonian-Maastrichtian. This is the first occurrence of a tylosaurine mosasaurid in the Iberian Peninsula. Moreover, it corresponds to the southernmost occurrence of this clade in the northern margin of the Mediterranean Tethys. ylosaurinae fossils are known from North America, Europe, New Zealand, Antarctica, Africa and Asia, but remain unknown from the southern Mediterranean Tethyan margin and from tropical palaeolatitudes.Un diente aislado de mosasaurio procedente del Campaniense de Álava (País Vasco), previamente asignado a cf. Mosasaurus sp., se atribuye en este trabajo a un tilosaurino. Podría pertenecer a Tylosaurus, un género cuasi cosmopolita del Santoniense-Maastrichtiense. Es la primera cita de un mosasáurido tilosaurino en la Península Ibérica. Además, se trata del registro más meridional de este clado en el margen norte del Tetis mediterráneo. Los Tylosaurinae están representados por fósiles en Norteamérica, Europa, Nueva Zelanda, Antártida, África y Asia, pero carecen de registro en el margen sur del Tetis mediterráneo y en paleolatitudes tropicales

Multiple primary and secondary sources for chemically similar obsidians from the area of portada covunco, west-central Neuquén, Argentina

In west-central Neuquén Province, Argentina, in the area around Estancia Llamuco, west of Zapala, south of Las Lajas and north-east of Lago Aluminé, there are multiple primary and secondary sources of obsidian. Primary sources occur within the south-east extension of the Plio-Quaternary volcanic chain that runs from Copahue volcano through Pino Hachado. Secondary sources include river-bed gravels within the valleys of Arroyo Cochicó Grande and Río Kilca as far south as where this river joins with Río Aluminé, and the Quaternary fluvial-glacial sediments cut by the valley of Río Covunco as far east as Portada Covunco. Visually variable obsidians from these two secondary sources include homogeneous black and grey-translucent types, porphyritic and banded types, and an abundant quantity of oxidized red and black obsidian. However, all these visually distinct obsidians have similar and unique chemistry, with Ba between 220 and 340ppm, different from any other obsidians previously reported from Neuquén, which all have Ba>500ppm, as do obsidians from sources to the north in Mendoza and to the west in Chile. This chemical distinctive obsidian has been exploited and transported over a wide area, beginning prior to 4000 bp, and occurs in local archaeological sites, as well as sites ≥ 300km to the north-east in La Pampa Province, ~430km to the south in Chubut Province, and >75km to the west across the Andean drainage divide in Chile.Fil: Stern, C. R.. State University of Colorado at Boulder; Estados UnidosFil: Pereda, I.. No especifíca;Fil: Aguerre, Ana Margarita. Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Arqueología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Synchronizing chaotic optically-programmable digital circuits

In this paper an approach to the synchronization of chaotic circuits has been reported. It is based on an optically programmable logic cell and the signals involved are fully digital. It is based on the reception of the same input signal on sender and receiver and from this approach, with a posterior correlation between both outputs, an identical chaotic output is obtained in both systems. No conversion from analog to digital signals is needed. The model here presented is based on a computer simulation

Impact of Surface Treatment on the Corrosion Resistance of ASTM F138-F139 Stainless Steel for Biomedical Applications

AbstractAISI 316 LVM stainless steel type considered in ASTM F138 and F139 standards for implant devices is widely used, in particular for orthopedic surgery, because it combines good biofunctionality and acceptable biocompatibility at low costs. Adequate interaction of these materials with the human body and its capability to reach the desired service level are determined by the surface preparation. The goal of the present work is to relate the surface roughness parameters with the localized corrosion resistance of AISI 316 LVM stainless steel grit blasted for different times and passivated with nitric acid. At intermediate blasting times the roughness parameters attain an extreme value and this surface condition corresponds with the maximum pitting corrosion resistance

A model of the mammalian retina and the visual cortex. Disorders of vision

A model of the mammalian retina and the behavior of the first layers in the visual cortex is reported. The building blocks are optically programmable logic cells. A model of the retina, similar to the one reported by Dowling (1987) is presented. From the model of the visual cortex obtained, some types of symmetries and asymmetries are possible to be detecte