Affective video and problem solving within a Web-environment

Currently there is a growing interest in Web-based multimedia learning environments, particularly those making use of asynchronous streaming video. This interest motivates renewed attention to properties of video for educational purposes. A typical property of video is its emotion-evoking potential. Research by Isen, Daubman, and Nowicki (1987), Kaufmann and Vosburg (1997) and by Vosburg (1998) on video-evoked positive or negative mood states inspired a research project on the didactical functionality of emotion-evoking video materials in relationship to (educational) problem solving tasks within a Web-based environment. The results show that the video materials that were used in the experiment induced the expected positive or negative mood. Differential effects of positive or negative mood for problem solving tasks, however, were not observed. This outcome is discussed in the context of the findings of the above-mentioned authors

Video outside versus video inside the web: do media setting and image size have an impact on the emotion-evoking potential of video?

To explore the educational potential of video-evoked affective responses in a Web-based environment, the question was raised whether video in a Web-based environment is experienced differently from video in a traditional context. An experiment was conducted that studied the affect-evoking power of video segments in a window on a computer screen compared to presenting the same video materials on a television monitor. The study first demonstrates that affect-evoking power of video exists. Although not always significant, the results who that selected positive and negative video clips induce positive or negative affective responses and mood changes in participants, in a Web-based environment as well as in a television environment. Smaller window sizes, however, may do less well

Light dynamics in glass-vanadium dioxide nanocomposite waveguides with thermal nonlinearity

We address the propagation of laser beams in Si02-VO2 nanocomposite waveguides with thermo-optical nonlinearity. We show that the large modifications of the absorption coefficient as well as notable changes of refractive index of VO2 nanoparticles embedded into the SiO2 host media that accompany the semiconductor-to-metal phase transition may lead to optical limiting in the near-infrared wave range.Comment: 13 pages, 3 figures, to appear in Optics Letter

Ultrafast changes in lattice symmetry probed by coherent phonons

The electronic and structural properties of a material are strongly determined by its symmetry. Changing the symmetry via a photoinduced phase transition offers new ways to manipulate material properties on ultrafast timescales. However, in order to identify when and how fast these phase transitions occur, methods that can probe the symmetry change in the time domain are required. We show that a time-dependent change in the coherent phonon spectrum can probe a change in symmetry of the lattice potential, thus providing an all-optical probe of structural transitions. We examine the photoinduced structural phase transition in VO2 and show that, above the phase transition threshold, photoexcitation completely changes the lattice potential on an ultrafast timescale. The loss of the equilibrium-phase phonon modes occurs promptly, indicating a non-thermal pathway for the photoinduced phase transition, where a strong perturbation to the lattice potential changes its symmetry before ionic rearrangement has occurred.Comment: 14 pages 4 figure

Phonon confinement and substitutional disorder in Cd1-xZnxS Nanocrystals

1LO optical phonons in free-standing mixed Cd1-xZnxS nanocrystals, synthesized using chemical precipitation, are investigated using Raman spectroscopy. As expected for the nanocrystals, the 1-LO modes are found to appear at slightly lower wavenumbers than those in the bulk mixed crystals and exhibit one mode behavior. On the other hand, the line broadening is found to be much more than that can be accounted on the basis of phonon confinement. From the detailed line shape analysis it turns out that the substitutional disorder in the mixed crystals contributes much more to the line broadening than the phonon confinement. The linewidth arising from these mechanisms are also extracted from the analysis.Comment: 15 Pages,8 Figures, Accepted in J. Raman Spectroscop

Metal-insulator transition in vanadium dioxide nanobeams: probing sub-domain properties of strongly correlated materials

Many strongly correlated electronic materials, including high-temperature superconductors, colossal magnetoresistance and metal-insulator-transition (MIT) materials, are inhomogeneous on a microscopic scale as a result of domain structure or compositional variations. An important potential advantage of nanoscale samples is that they exhibit the homogeneous properties, which can differ greatly from those of the bulk. We demonstrate this principle using vanadium dioxide, which has domain structure associated with its dramatic MIT at 68 degrees C. Our studies of single-domain vanadium dioxide nanobeams reveal new aspects of this famous MIT, including supercooling of the metallic phase by 50 degrees C; an activation energy in the insulating phase consistent with the optical gap; and a connection between the transition and the equilibrium carrier density in the insulating phase. Our devices also provide a nanomechanical method of determining the transition temperature, enable measurements on individual metal-insulator interphase walls, and allow general investigations of a phase transition in quasi-one-dimensional geometry.Comment: 9 pages, 3 figures, original submitted in June 200

Optical Properties of Correlated Materials -- or Why Intelligent Windows may look Dirty

Materials with strong electronic Coulomb correlations play an increasing role in modern materials applications. "Thermochromic" systems, which exhibit thermally induced changes in their optical response, provide a particularly interesting case. The optical switching associated with the metal-insulator transition of vanadium dioxide, for example, has been proposed for use in numerous applications, ranging from anti-laser shields to "intelligent" windows, which selectively filter radiative heat in hot weather conditions. Are present-day electronic structure techniques able to describe, or -- eventually even predict -- such a kind of behavior ? How far are we from materials design using correlated oxides ? These are the central questions we try to address in this article. We review recent attempts of calculating optical properties of correlated materials within dynamical mean field theory, and summarize results for vanadium dioxide obtained within a novel scheme aiming at particularly simple and efficient calculations of optical transition matrix elements within localized basis sets. Finally, by optimizing the geometry of "intelligent windows", we argue that this kind of technique can in principle be used to provide guidance for experiments, thus giving a rather optimistic answer to the above questions.Comment: 11 pages, 4 figures, Phys. Status Solidi B 246, in print (2009), also available as psi-k Scientific Highlight of the Month, no. 88, August 2008, http://www.psi-k.org/newsletters/News_88/Highlight_88.pd

Ict-toepassingen met gevoel dragen bij aan leren (ICT applications with feelings contribute to learning)

Onze cultuur wordt gedomineerd door bewegende beelden. Deze beelden worden steeds affectiever. Dankzij ict-toepassingen wordt dit audiovisueel materiaal in de klas gebruikt. Ondanks het grote aanbod, ervaren leraren een gebrek aan bruikbaar digitaal materiaal. Dit essay probeert een oplossing te zoeken voor dat probleem