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Benefits in cost and reduced discomfort of new techniques of minimally invasive...
Vila Verde, A.; Ramos, Marta M. D.; Stoneham, A. M.The concept of minimally invasive dentistry is appealing to more and more dentists. Patients share this enthusiasm. Three basic principles underlie minimally invasive dentistry: prevention of dental caries, less intrusive treatment for early lesions, and conservation of tissue when deeper lesions are restored. Together, these principles improve patient well-being by prolonging the life of teeth and by reducing ...
The role of mesoscopic modelling in understanding the response of dental enamel...
Vila Verde, A.; Ramos, Marta M. D.; Stoneham, A. M.Human dental enamel has a porous mesostructure at the nanometre to micrometer scales that affects its thermal and mechanical properties relevant to laser treatment. We exploit finite element models to investigate the response of this mesostructured enamel to mid infrared lasers (CO2 at 10.6 mm and Er:YAG at 2.94 mm). Our models might easily be adapted to investigate ablation of other brittle composite materials...
Effect of molecular properties on the performance of polymer light-emitting diodes
Ramos, Marta M. D.; Almeida, A. M.; Correia, Helena M. G.; Ribeiro, R. M.; Stoneham, A. M.The performance of a single layer polymer light-emitting diode depends on several interdependent factors, although recombination between electrons and holes within the polymer layer is believed to play an important role. Our aim is to carry out computer experiments in which bipolar charge carriers are injected in polymer networks made of poly(p-phenylene vinylene) chains randomly oriented. In these simulations,...
Mesoscopic modelling of enamel interaction with mid-infrared sub-ablative laser...
Vila Verde, A.; Ramos, Marta M. D.; Ribeiro, R. M.; Stoneham, A. M.Using a finite element approach the authors model the influence of enamel's microstructure and water distribution on the temperature and stress at the centre of the laser spot, for a CO2 laser working at 10.6 μm, with 0.35 μs pulse duration and subablative intensity. The authors found that the distribution of water in enamel significantly influences the stress generated at the end of one laser pulse: much lower...
Mesoscopic modelling of the interaction of infrared lasers with composite mater...
Vila Verde, A.; Ramos, Marta M. D.; Stoneham, A. M.; Ribeiro, R. M.The mesostructure and composition of composite materials determine their mechanical, optical and thermal properties and, consequently, their response to incident radiation. We have developed general finite element models of porous composite materials under infrared radiation to examine the influence of pore size on one of the determining parameters of the stress distribution in the material: the temperature dis...
Modelling of the human enamel laser ablation process at the mesoscopic scale
Vila Verde, A.; Ramos, Marta M. D.; Ribeiro, R. M.; Stoneham, A. M.Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER). ; A mesoscopic simulation of the process of human enamel laser ablation by Er:YAG and CO2 lasers is being developed using the finite element method, taking into account the complex structure and chemical composition of this material. A geometric model that allows studying in detail the temperature, stress and displacement distributio...
Mesoscopic study of the electronic properties of thin polymer films
Ribeiro, R. M.; Ramos, Marta M. D.; Almeida, A. M.; Correia, Helena M. G.; Silva, Jaime; Stoneham, A. M.Conjugated polymers are very interesting for light emitting diodes. Further improvement in device performance requires a better understanding on the correlation between the polymer structure and device characteristics. A mesoscopic study using a generalised Monte Carlo method of bipolar charge transport in thin poly(p-phenylene-vinylene) (PPV) films is presented in this paper. We show that energy and spatial mo...
Understanding electron flow in conducting polymer films : injection, mobility, ...
Stoneham, A. M.; Ramos, Marta M. D.; Almeida, A. M.; Correia, Helena M. G.; Ribeiro, R. M.; Ness, H.; Fisher, A. J.We survey the current state of models for electronic processes in conducting polymer devices, especially light-emitting diodes. We pay special attention to several processes that have been somewhat neglected in the previous literature: charge injection from electrodes into a polymer sample, mobility of charge-or energy-carrying defects within a single molecule and (more briefly) transfer of carriers between mol...
Charge and the unexpected : solid state processes involving charged species
Stoneham, A. M.; Harker, A. H.; Ramos, Marta M. D.We explore links between performance under electrical stress and the way in which charge is localised in two contrasted systems. Both systems are arnorphous. In one case inhomogeneity which plays a role; for the other, it is topology. For silicon dioxide, the gate dielectric of microelectronics, we show that the charge state of the oxidising species (mobile atomic or molecular oxygen) is critical for ultra-thin...
Mesoscopic modelling of conducting and semiconducting polymers
Stoneham, A. M.; Ramos, Marta M. D.We present generalized Monte Carlo calculations to assess the effects of texture and related key factors on the properties of polymer-based light emitting diodes. We, describe one class of mesoscopic model giving specific realizations of the polymer network. The model, with simple physically based rules, shows the effects of polymer structural order on current flow, trapping and radiative and non-radiative char...
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