6,372 research outputs found

    Parametric Competition in non-autonomous Hamiltonian Systems

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    In this work we use the formalism of chord functions (\emph{i.e.} characteristic functions) to analytically solve quadratic non-autonomous Hamiltonians coupled to a reservoir composed by an infinity set of oscillators, with Gaussian initial state. We analytically obtain a solution for the characteristic function under dissipation, and therefore for the determinant of the covariance matrix and the von Neumann entropy, where the latter is the physical quantity of interest. We study in details two examples that are known to show dynamical squeezing and instability effects: the inverted harmonic oscillator and an oscillator with time dependent frequency. We show that it will appear in both cases a clear competition between instability and dissipation. If the dissipation is small when compared to the instability, the squeezing generation is dominant and one can see an increasing in the von Neumann entropy. When the dissipation is large enough, the dynamical squeezing generation in one of the quadratures is retained, thence the growth in the von Neumann entropy is contained


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    QUAIS OS PROCEDIMENTOS ADOPTADOS PELO TERAPEUTA DA FALA NA REABILITA√á√ÉO/HABILITA√á√ÉO DA PESSOA SUBMETIDA A CORDECTOMIA ENDOSC√ďPICA? Joana Guimar√£es1, Paula Faria2 1Curso de Licenciatura em Terapia da Fala, 2ESTSP/IPP. Escola Superior de Tecnologias da Sa√ļde do Porto, Instituto Polit√©cnico do Porto (ESTSP/IPP), Porto. Hospital de Santo Ant√≥nio, Centro Hospitalar do Porto (HSA/CHP), Porto. Introdu√ß√£o O tratamento do carcinoma gl√≥tico envolve a ressec√ß√£o de estruturas anat√≥micas, o que se repercute, em maior ou menor grau, em termos fisiol√≥gicos. No caso de uma cordectomia, as principais altera√ß√Ķes s√£o verificadas ao n√≠vel da qualidade vocal da pessoa e, dependendo da t√©cnica adoptada e das estruturas ressecadas, podem igualmente ser verificadas altera√ß√Ķes ao n√≠vel da degluti√ß√£o, aspectos justificativos do acompanhamento ao n√≠vel da Terapia da Fala. Objectivos Este estudo pretende averiguar quais os procedimentos adoptados pelo Terapeuta da Fala na reabalita√ß√£o/habilita√ß√£o da pessoa submetida a cordectomia endosc√≥pica a laser de di√≥xido de carbono (CO2) com base nos que s√£o adoptados no processo interventivo p√≥s-cordectomia endosc√≥pica instrumental. Material e M√©todos Para tal foi realizada uma entrevista ao Terapeuta da Fala do servi√ßo de Otorrinolaringologia do Hospital de Santo Ant√≥nio, bem como foram recolhidos dados dos processos cl√≠nicos de dois sujeitos relativamente √† anamnese, √†s avalia√ß√Ķes e √† interven√ß√£o ao n√≠vel da Terapia da Fala. Resultados Os resultados deste estudo revelaram que os procedimentos adoptados na reabalita√ß√£o/habilita√ß√£o da pessoa submetida a cordectomia endosc√≥pica a laser de CO2 ou √† t√©cnica instrumental s√£o semelhantes, diferindo principalmente devido a quest√Ķes individuais de cada sujeito e n√£o tanto ao procedimento cir√ļrgico adoptado. Apresentador: Joana Daniela Pereira Guimar√£es, Aluna do Curso de Licenciatura em Terapia da Fala, ESTSP/IPP. [email protected]

    Controlling high-harmonic generation and above-threshold ionization with an attosecond-pulse train

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    We perform a detailed analysis of how high-order harmonic generation (HHG) and above-threshold ionization (ATI) can be controlled by a time-delayed attosecond-pulse train superposed to a strong, near-infrared laser field. In particular we show that the high-harmonic and photoelectron intensities, the high-harmonic plateau structure and cutoff energies, and the ATI angular distributions can be manipulated by changing this delay. This is a direct consequence of the fact that the attosecond pulse train can be employed as a tool for constraining the instant an electronic wave packet is ejected in the continuum. A change in such initial conditions strongly affects its subsequent motion in the laser field, and thus HHG and ATI. In our studies, we employ the Strong-Field Approximation and explain the features observed in terms of interference effects between various electron quantum orbits. Our results are in agreement with recent experimental findings and theoretical studies employing purely numerical methods.Comment: 10 pages revtex and 6 figures (eps files

    Low redshift constraints on energy-momentum-powered gravity models

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    There has been recent interest in the cosmological consequences of energy-momentum-powered gravity models, in which the matter side of Einstein's equations is modified by the addition of a term proportional to some power, nn, of the energy-momentum tensor, in addition to the canonical linear term. In this work we treat these models as phenomenological extensions of the standard őõ\LambdaCDM, containing both matter and a cosmological constant. We also quantitatively constrain the additional model parameters using low redshift background cosmology data that are specifically from Type Ia supernovas and Hubble parameter measurements. We start by studying specific cases of these models with fixed values of n,n, which lead to an analytic expression for the Friedmann equation; we discuss both their current constraints and how the models may be further constrained by future observations of Type Ia supernovas for WFIRST complemented by measurements of the redshift drift by the ELT. We then consider and constrain a more extended parameter space, allowing nn to be a free parameter and considering scenarios with and without a cosmological constant. These models do not solve the cosmological constant problem per se. Nonetheless these models can phenomenologically lead to a recent accelerating universe without a cosmological constant at the cost of having a preferred matter density of around ő©M‚ąľ0.4\Omega_M\sim0.4 instead of the usual ő©M‚ąľ0.3\Omega_M\sim0.3. Finally we also briefly constrain scenarios without a cosmological constant, where the single component has a constant equation of state which needs not be that of matter; we provide an illustrative comparison of this model with a more standard dynamical dark energy model with a constant equation of state.Comment: 13+2 pages, 12+1 figures; A&A (in press

    Local dynamics in high-order harmonic generation using Bohmian trajectories

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    We investigate high-order harmonic generation from a Bohmian-mechanical perspective, and find that the innermost part of the core, represented by a single Bohmian trajectory, leads to the main contributions to the high-harmonic spectra. Using time-frequency analysis, we associate this central Bohmian trajectory to an ensemble of unbound classical trajectories leaving and returning to the core, in agreement with the three step model. In the Bohmian scenario, this physical picture builds up non-locally near the core via the quantum mechanical phase of the wavefunction. This implies that the flow of the wavefunction far from the core alters the central Bohmian trajectory. We also show how this phase degrades in time for the peripheral Bohmian trajectories as they leave the core region.Comment: 7 pages, 3 figures; the manuscript has been considerably extended and modified with regard to the previous version
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