37,818 research outputs found

    Optical binding in nanoparticle assembly: Potential energy landscapes

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    Optical binding is an optomechanical effect exhibited by systems of micro- and nanoparticles, suitably irradiated with off-resonance laser light. Physically distinct from standing-wave and other forms of holographic optical traps, the phenomenon arises as a result of an interparticle coupling with individual radiation modes, leading to optically induced modifications to Casmir-Polder interactions. To better understand how this mechanism leads to the observed assemblies and formation of patterns in nanoparticles, we develop a theory in terms of optically induced energy landscapes exhibiting the three-dimensional form of the potential energy field. It is shown in detail that the positioning and magnitude of local energy maxima and minima depend on the configuration of each particle pair, with regards to the polarization and wave vector of the laser light. The analysis reveals how the positioning of local minima determines the energetically most favorable locations for the addition of a third particle to each equilibrium pair. It is also demonstrated how the result of such an addition subtly modifies the energy landscape that will, in turn, determine the optimum location for further particle additions. As such, this development represents a rigorous and general formulation of the theory, paving the way toward full comprehension of nanoparticle assembly based on optical binding

    The neural correlates of phonological short-term memory: A repetitive transcranial magnetic stimulation study

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    Neuropsychological reports and activation studies by means of positron emission tomography anti functional magnetic resonance imaging have suggested that the neural correlates of phonological short-term memory are located in the left hemisphere, with Brodmann's area (BA) 40 being, responsible for short-term storage and BA 44 for articulatory rehearsal. However, a careful review of the literature on the role of left BA 40 shows that the data are equivocal. We tested We hypotheses by means of repetitive transcranial magnetic stimulation (rTMS). Participants performed four tasks: two phonological judgements, thought to require only articulatory rehearsal Without the contribution of short-term storage digit span, which involves both short-term storage and articudlatory rehearsal: and a pattern span, this last heing the control task. The sites of stimulation were left BA 40. left BA 44 anti the electrode location V-W plus a baseline without TMS. Reaction times increased and accuracy decreased in the case of the phonological judgement and digit span after stimulation of both left sites, suggesting that BA 40, in addition to BA 44. is involved in phonological judgements. Possible explanations are discussed, namely, the possibility that (i) the neural correlates of rehearsal are not limited to BA and (ii) phonological judgements invlove processes other than rehearsal. We also consider the effects of using different tasks and responses to resolve some of the descrepancies in the literature

    Gamma-ray flares from black hole coronae

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    We present results of a study of non-thermal, time-dependent particle injection in a corona around an accreting black hole. We model the spectral energy distribution of high-energy flares in this scenario. We consider particle interactions with magnetic, photon and matter fields in the black hole magnetosphere. Transport equations are solved for all species of particles and the electromagnetic output is predicted. Photon annihilation is taken into account for the case of systems with early-type donor stars.Comment: 7 pages, 7 figures. Accepted for publication in the Proceedings of the 25th Texas Symposium on Relativistic Astrophysics, held in Heidelberg, December 06-10, 201

    Resonance damping and optical susceptibilities

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    Core-crust transition pressure for relativistic slowly rotating neutron stars

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    We study the influence of core-\textit{crust} transition pressure changes on the general dynamical properties of neutron star configurations. First we study the matching conditions in core-\textit{crust} transition pressure region, where phase transitions in the equation of state causes energy density jumps. Then using a surface \textit{crust} approximation, we can construct configurations where the matter is described by the equation of state of the core of the star and the core-\textit{crust} transition pressure. We will consider neutron stars in the slow rotation limit, considering perturbation theory up to second order in the angular velocity so that the deformation of the star is also taken into account. The junction determines the parameters of the star such as total mass, angular and quadrupolar momentum.Comment: 4 pages, 1 figur
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