34 research outputs found
Nonlinear Breathing-like Localized Modes in C60 Nanocrystals
We study the dynamics of nanocrystals composed of C60 fullerene molecules. We
demonstrate that such structures can support long-lived strongly localized
nonlinear oscillatory modes, which resemble discrete breathers in simple
lattices. We reveal that at room temperatures the lifetime of such nonlinear
localized modes may exceed tens of picoseconds; this suggests that C60
nanoclusters should demonstrate anomalously slow thermal relaxation when the
temperature gradient decays in accord to a power law, thus violating the
Cattaneo-Vernotte law of thermal conductivity.Comment: 6 pages, 6 figure
Discapacidad visual y orientación urbana. Estudio piloto sobre planos táctiles producidos en Impresión 3D
[EN] This article presents a pilot study conducted in Barcelona with blind and visually-impaired people. The aim was to
analyze the use and efficacy of tactile maps produced by means of 3D printing. For this purpose, structured interviews were
used, along with direct observation, the creation of cognitive maps and tasks with prototypes. The aim has been to examine
the instrumental and communicative value of these products in terms of interpreting, memorizing and understanding a
certain urban route, comparing this with experience in situ, focusing on the difficulties faced by the visually disabled when
visiting new places. Findings show the utility of this type of technique in aiding visually disabled users to memorize routes.
As a limitation, this study shows that tactile maps are not wholly efficient since they require verbal support, which makes
it hard for them to be used autonomously.[ES] El trabajo aquí expuesto presenta un estudio piloto llevado a cabo en Barcelona con personas invidentes y deficientes
visuales. El objetivo del mismo ha sido analizar el uso y la eficacia de los planos táctiles producidos mediante Impresión en
3D. Para ello se han empleado entrevistas estructuradas, observación directa, realización de mapas cognitivos y tareas con
prototipos. De esta manera se ha tratado deprofundizar en elvalor instrumentalycomunicativo de estosproductos a la hora
de interpretar, memorizar y comprender un determinado recorrido urbano, contrastándolo con la experiencia in situ, atendiendo a las dificultades que este tipo de personas presentan a la hora de visitar nuevos lugares. Los resultados obtenidos
demuestran la utilidad de este tipo de técnica para memorizar recorridos por parte de este tipo de usuarios. Como limitación,
el estudio muestra que los planos táctiles no resultan del todo eficientes pues precisan de apoyo verbal, hecho que dificulta su
uso autónomo.This research has been funded by the Spanish Ministry of Science and Innovation as part of the National Fundamental Research Programme, the National R&D/Innovation Plan, within the project “Study and design of
orientation elements, communication support and other accessories to improve accessibility in different spheres of interpreting natural and/or built heritage’ (DPI2008-03981/DPI). The authors would also like particularly to thank the following for their selfless collaboration: the ONCE Educational Resources Centre in Barcelona and staff from the Disabled Service Programme at the Universitat Politècnica de Catalunya. The study was also carried out as part of the Research Staff Mobility Programme at Universitat Jaume I (E-2010-32) funded by the Caixa Castelló-Bancaixa Foundation.Gual Ortí, J.; Puyuelo Cazorla, M.; Lloveras, J.; Merino Sanjuan, L. (2012). Visual Impairment and urban orientation. Pilot study with tactile maps produced through 3D Printing. Psyecology. 3(2):239-250. https://doi.org/10.1174/217119712800337747S2392503
Theory of coherent phonons in carbon nanotubes and graphene nanoribbons
We survey our recent theoretical studies on the generation and detection of coherent radial
breathing mode (RBM) phonons in single-walled carbon nanotubes and coherent radial
breathing like mode (RBLM) phonons in graphene nanoribbons. We present a microscopic
theory for the electronic states, phonon modes, optical matrix elements and electronヨphonon
interaction matrix elements that allows us to calculate the coherent phonon spectrum. An
extended tight-binding (ETB) model has been used for the electronic structure and a valence
force field (VFF) model has been used for the phonon modes. The coherent phonon
amplitudes satisfy a driven oscillator equation with the driving term depending on the
photoexcited carrier density. We discuss the dependence of the coherent phonon spectrum on
the nanotube chirality and type, and also on the graphene nanoribbon mod number and class
(armchair versus zigzag). We compare these results with a simpler effective mass theory
where reasonable agreement with the main features of the coherent phonon spectrum is found.
In particular, the effective mass theory helps us to understand the initial phase of the coherent
phonon oscillations for a given nanotube chirality and type. We compare these results to two
different experiments for nanotubes: (i) micelle suspended tubes and (ii) aligned nanotube
films. In the case of graphene nanoribbons, there are no experimental observations to date. We
also discuss, based on the evaluation of the electronヨphonon interaction matrix elements, the
initial phase of the coherent phonon amplitude and its dependence on the chirality and type.
Finally, we discuss previously unpublished results for coherent phonon amplitudes in zigzag
nanoribbons obtained using an effective mass theory
Managing design to sharpen effectiveness
Part of the Business & Design ProgrammeAvailable from British Library Document Supply Centre- DSC:q95/26234 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo