Aprendizaje con la internet: una aproximación critica

En los últimos años, la Internet ha experimentado un crecimiento espectacular y los responsables de la educación de los países desarrollados preconizan su incorporación a todos los niveles de enseñanza. Este articulo propone una reflexión sobre la Internet desde perspectivas que incluyen el análisis de sus implicaciones socioeconómicas y la descripción de las teorías de aprendizaje y resultados de investigación que sustentan su aplicación en el terreno educativo. Él articulo igualmente invita a la consideración de los factores coyunturales que pueden determinar el éxito de tal aplicación

Tecnologías de telecomunicación y educación a distancia en los estados unidos (EE.UU.)

Este artículo pretende describir el uso y las implicaciones de las tecnologías de telecomunicación en la enseñanza a distancia norteamericana. Se ofrece un descripción de la oferta y la demanda de la programación por satélite y cable, las posibles causas del aumento de cursos a distancia en universidades y los contenidos de algunos programas, varias propuestas conceptuales sobre diseños de cursos, y modelos de enseñanza y transmisión en educación a distancia electrónica. Se realiza un examen de la literatura sobre la efectividad instruccional de las tecnologías de telecomunicación y sobre los papeles del profesor a distancia y del tutor. Se discute también el futuro de las tecnologías de telecomunicación

Coarse-grained approach to amorphous and anisotropic materials in kinetic Monte Carlo thin-film growth simulations: A case study of TiO₂ and ZnO by plasma-enhanced chemical vapor deposition

The growth of TiO₂ and ZnO thin films is studied by means of coarse-grained kinetic Monte Carlo simulations under conditions typically encountered in plasma-enhanced chemical vapor deposition experiments. The basis of our approach is known to work well to simulate the growth of amorphous materials using cubic grids and is extended here to reproduce not only the morphological characteristics and scaling properties of amorphous TiO₂ but also the growth of polycrystalline ZnO with a good approximation, including the evolution of the film texture during growth and its dependence on experimental conditions. The results of the simulations have been compared with available experimental data obtained by X-ray diffraction, analysis of the texture coefficients, atomic force microscopy, and scanning electron microscopy

Laser induced enhancement of dichroism in supported silver nanoparticles deposited by evaporation at glancing angles

were deposited on flat substrates by physical vapor deposition in a glancing angle configuration. The particles were characterized by scanning electron microscopy and atomic force microscopy and their optical properties examined by UV–vis absorption spectroscopy using linearly polarized light. It was found that, depending on the amount of deposited silver and the evaporation angle, part of the ‘as-prepared’ samples present NPs characterized by an anisotropic shape and a polarization dependent SPR absorption and different colors when using polarized white light at 0 and 90 . Low-power irradiation of these materials with an infrared Nd-YAG nanosecond laser in ambient conditions produced an enhancement in such dichroism. At higher powers, the dichroism was lost and the SPR bands shifted to lower wavelengths as a result of the reshaping of the silver NPs in the form of spheres. The possible factors contributing to the observed changes in dichroism are discussed

Superhydrophobic supported Ag-NPs@ZnO-nanorods with photoactivity in the visible range

In this article we present a new type of 1D nanostructures consisting of supported hollow ZnO nanorods (NRs) decorated with Ag nanoparticles (NPs). The 3D reconstruction by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) electron tomography reveals that the Ag NPs are distributed along the hollow interior of the ZnO NRs. Supported and vertically aligned Ag-NPs@ZnO-NRs grow at low temperature (135 °C) by plasma enhanced chemical vapour deposition on heterostructured substrates fabricated by sputtered deposition of silver on flat surfaces of Si wafers, quartz slides or ITO. The growth mechanisms of these structures and their wetting behavior before and after visible light irradiation are critically discussed. The as prepared surfaces are superhydrophobic with water contact angles higher than 150°. These surfaces turn into superhydrophilic with water contact angles lower than 10° after prolonged irradiation under both visible and UV light. The evolution rate of the wetting angle and its dependence on the light characteristics are related to the nanostructure and the presence of silver embedded within the ZnO NRs. ÂEuropean Union NMP3-CT-2006- 032583Ministerio de Ciencia e Innovación MAT2010-21228, MAT2010-18447, CSD2008-00023Junta de Andalucía P09-TEP-5283, CTS-518

Mechanically switchable wetting petal effect in self‐patterned nanocolumnar films on poly(Dimethylsiloxane)

Switchable mechanically induced changes in the wetting behavior of surfaces are of para-mount importance for advanced microfluidic, self‐cleaning and biomedical applications. In this work we show that the well‐known polydimethylsiloxane (PDMS) elastomer develops self‐patterning when it is coated with nanostructured TiO2 films prepared by physical vapor deposition at glancing angles and subsequently subjected to a mechanical deformation. Thus, unlike the disordered wrinkled surfaces typically created by deformation of the bare elastomer, well‐ordered and aligned micro‐scaled grooves form on TiO2/PDMS after the first post‐deposition bending or stretching event. These regularly patterned surfaces can be reversibly modified by mechanical deformation, thereby inducing a switchable and reversible wetting petal effect and the sliding of liquid droplets. When performed in a dynamic way, this mechanical actuation produces a unique capacity of liquid droplets (water and diiodomethane) transport and tweezing, this latter through their selective capture and release depending on their volume and chemical characteristics. Scanning electron and atomic force microscopy studies of the strained samples showed that a dual‐scale rough-ness, a parallel alignment of patterned grooves and their reversible widening upon deformation, are critical factors controlling this singular sliding behavior and the possibility to tailor their response by the appropriate manufacturing of surface structures.European Union 899352Ministerio de Ciencia e Innovación PID2019- 110430GB-C21, PID2019-109603RA-I0, MAT2013-40852-R, MAT2013- 42900-PMinisterio de Economía y Competitividad 201560E055Junta de Andalucía AT17-6079, P18-RT-348

Enhancement of visible light-induced surface photo-activity of nanostructured N¿TiO2 thin films modified by ion implantation

This work reports the morphological and chemical modifications induced in TiO2 thin films by bombardment with high energy N+ ions at different temperatures and their different photo-activity responses after implantation under visible and UV light illumination. When implanted samples are illuminated with visible light, no dye photo-decolouration takes place despite that light transformed the surfaces from hydrophobic to hydrophilic. In agreement with the Wenzel model of wetting, correlation is found between visible light photo-activity and film morphology. We conclude that the photo-activity response can be separated into shallow and Schottky barrier photo-activity, this latter involving a thicker layer of materialMinisterio de Ciencia e Innovación CONSOLIDER CSD2008-00023 MAT2010-21228 MAT2010-1844

Wetting Angles on Illuminated Ta2O5 Thin Films with Controlled Nanostructure

Ta2O5 thin films with different nanostructure and surface roughness have been prepared by electron evaporation at different angles between the evaporation source and the substrates. Large variation of refraction indexes (n) from 1.40 to 1.80 were obtained by changing the geometry of evaporation and/or by annealing the evaporated films at increasing temperatures up to 1000 °C to make them crystalline. Very flat and compact thin films (n ) 2.02) were also obtained by assisting the growth by bombardment with O2 + ions of 800 eV kinetic energy. A similar correlation has been found between the wetting contact angle of water and the roughness of the films for the evaporated and evaporated + annealed samples, irrespective of their procedure of preparation and other microstructural characteristics. When the films were illuminated with UV light of h > Eg ) 4.2 eV (Eg, band gap energy of Ta2O5), their surface became superhydrophilic (contact angle < 10°) in a way quite similar to those reported for illuminated TiO2 thin films. The rate of transformation into the superhydrophilic state was smaller for the crystalline than for the amorphous films, suggesting that in Ta2O5 the size of crystal domains at the surface is an important parameter for the control of this kinetics. Changes in the water contact angle on films illuminated with visible light were also found when they were subjected to implantation with N2 + ions of 800 eV kinetic energy. The origin of this photoactivity is discussed in terms of the electronic band gap states associated with the nitrogen-implanted atoms. The possibility of preparing antireflective and self-cleaning coatings of Ta2O5 is discussed

Vacuum template synthesis of multifunctional nanotubes with tailored nanostructured walls

A three-step vacuum procedure for the fabrication of vertical TiO2 and ZnO nanotubes with three dimensional walls is presented. The method combines physical vapor deposition of small-molecules, plasma enhanced chemical vapor deposition of inorganic functional thin films and layers and a postannealing process in vacuum in order to remove the organic template. As a result, an ample variety of inorganic nanotubes are made with tunable length, hole dimensions and shapes and tailored wall composition, microstructure, porosity and structure. The fabrication of multishell nanotubes combining different semiconducting oxides and metal nanoparticles is as well explored. This method provides a feasible and reproducible route for the fabrication of high density arrays of vertically alligned nanotubes on processable substrates. The emptying mechanism and microstructure of the nanotubes have been elucidated through SEM, STEM, HAADF-STEM tomography and energy dispersive X-ray spectroscopy. In this article, as a proof of concept, it is presented the straightforward integration of ZnO nanotubes as photoanode in a photovoltaic cell and as a photonic oxygen gas sensorJunta de Andalucia TEP8067 FQM-6900 FQM 1851 P12-FQM-2265España Mineco CONSOLIDER-CSD 2008-00023 MAT2013-40852-R MAT2013-42900-P MAT2013-47192-C3-3-R RECUPERA 2020Unión Europea FP/2007-2013 312483 - ESTEEM2 291522 - 3DIMAGE REGPOT-CT-2011-285895-Al-NANOFUNC

Anisotropic in-plane conductivity and dichroic gold plasmon resonance in plasma assisted ITO thin films e-beam evaporated at oblique angles

ITO thin films have been prepared by electron beam evaporation at oblique angles (OA), directly and while assisting their growth with a downstream plasma. The films microstructure, characterized by scanning electron microscopy, atomic force microscopy and glancing incidence small angle X-ray scattering, consisted of tilted and separated nanostructures. In the plasma 2 assisted films, the tilting angle decreased and the nanocolumns became associated in the form of bundles along the direction perpendicular to the flux of evaporated material. The annealed films presented different in-depth and sheet resistivity as confirmed by scanning conductivity measurements taken for the individual nanocolumns. In addition, for the plasma assisted thin films, two different sheet resistance values were determined by measuring along the nanocolumn bundles or along the perpendicular direction. This in-plane anisotropy induces the electrochemical deposition of elongated gold nanostructures. The obtained Au-ITO composite thin films were characterized by anisotropic plasmon resonance absorption and a dichroic behavior when examined with linearly polarized light