Mesoscopic modelling of the interaction of infrared lasers with composite materials: an application to dental enamel

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 distribution. We apply them to the specific case of human dental enamel, a material which has nanometer scale pores containing water/organic, and predict the maximum temperature reached after a single 0.35 μs laser pulse of sub-ablative fluence by two lasers: Er:YAG (2.9 μm) and CO2 (10.6 μm). For the Er:YAG laser, the results imply a strong dependence of the maximum temperature reached at the pore on the area-to-volume ratio of the pore, whereas there is little such dependence for CO2 lasers. Thus, CO2 lasers may produce more reproducible results than Er:YAG lasers when it comes to enamel ablation, which may be of significant interest during clinical practice. More generally, when ablating composite materials by infrared lasers researchers should account for the material’s microstructure and composition when designing experiments or interpreting results, since a more simplistic continuum approach may not be sufficient to explain differences observed during ablation of materials with similar optical properties or of the same material but using different wavelengths

Mesoscopic modelling of enamel interaction with mid-infrared sub-ablative laser pulses

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 sub-ablative 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 (two orders of magnitude) stress values occur in models with homogeneously distributed water than in models with 0.27 vol.% water located in pores or 4 vol.% in layers. The amount of water in enamel has a strong influence on the stress distribution, but not on the maximum stress values reached. However, different water contents do not influence the temperature distribution in enamel. These results suggest that adequate modelling of the ablation mechanisms in enamel, as in other highly inhomogeneous materials, must include their structure at the mesoscopic scale

Entanglement of Remote Spins with Unequal Coupling to an Optically Active Mediator

We demonstrate that two remote qubits can be entangled through an optically active intermediary even if the coupling strengths between mediator and qubits are different. This is true for a broad class of interactions. We consider two contrasting scenarios. First, we extend the analysis of a previously studied gate operation which relies on pulsed, dynamical control of the optical state and which may be performed quickly. We show that remote spins can be entangled in this case even when the intermediary coupling strengths are unequal. Second, we propose an alternative adiabatic control procedure, and find that the system requirements become even less restrictive in this case. The scheme could be tested immediately in a range of systems including molecules, quantum dots, or defects in crystals.Comment: 16 pages, 9 figure

System among the corticosteroids: specificity and molecular dynamics.

Fil: Brookes, Jennifer C.. University College London; Estados UnidosFil: Galigniana, Mario Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental (i); ArgentinaFil: Harker, Anthony H.. University College London; Estados UnidosFil: Stoneham, A. Marshall. University College London; Estados UnidosFil: Vinson, Gavin P.. Queen Mary University of London; Reino Unid

A new model for magnetoreception

Certain migratory birds can sense the earth's magnetic field. The nature of this process is not yet properly understood. Here we offer a simple explanation according to which birds literally `see' the local magnetic field: Our model relates the well-established radical pair hypothesis to the phenomenon of Haidinger's brush, a capacity to see the polarisation of light. This new picture explains recent surprising experimental data indicating long lifetimes for the radical pair. Moreover there is a clear evolutionary path toward this field sensing mechanism: it is an enhancement of a weak effect that may be present in many species.Comment: 8 pages, 5 figures, version of final published pape