1,177 research outputs found

    Quantum correlations in continuos-time quantum walks of two indistinguishable particles

    Full text link
    We evaluate the degree of quantum correlation between two fermions (bosons) subject to continuous time quantum walks in a one-dimensional ring lattice with periodic boundary conditions. In our approach, no particle-particle interaction is considered. We show that the interference effects due to exchange symmetry can result into the appearance of non-classical correlations. The role played onto the appearance of quantum correlations by the quantum statistics of the particles, the boundary conditions, and the partition of the system is widely investigated. Quantum correlations also been investigated in a model mimicking the ballistic evolution of two indistinguishable particles in a 1D continuous space structure. Our results are consistent with recent quantum optics and electron quantum optics experiments where the showing up of two-particle non-classical correlations has been observed even in the absence of mutual interaction between the particles.Comment: 12 pages, 5 figure

    Factores auto-percibidos de eficiencia grupal en una comunidad lúdica on-line

    Get PDF
    Setenes Jornades de Foment de la Investigació de la FCHS (Any 2001-2002

    Efectos de tempo y modo sobre el contenido emocional de la música

    Get PDF
    Novenes Jornades de Foment de la Investigació de la FCHS (Any 2003-2004)La relación entre música y emociones es evidente (Juslin & Sloboda, 2001), pero el acercamiento efectuado por la psicología se ha centrado casi siempre en “gestalt” musicales antes que en los parámetros de la música misma hasta fechas muy recientes. En el marco de esta indagación psicológica de la influencia de los parámetros musicales sobre las emociones humanas, se propone una primera exploración con cuatro condiciones experimentales, fruto de la modificación de una melodía neutra en dos factores – tempo y modo, cada uno dividido en dos niveles. Se recogieron los juicios sobre el contenido emocional de cada una de las cuatro melodías mediante una página web programada a propósito, teniendo que puntuar cada melodía en cuatro emociones básicas mediante una escala tipo Likert de cinco puntos. Los resultados parecen apoyar una teoría paramétrica de la influencia de la música sobre las emociones

    Non-Markovian continuous-time quantum walks on lattices with dynamical noise

    Get PDF
    We address the dynamics of continuous-time quantum walks on one-dimensional disordered lattices inducing dynamical noise in the system. Noise is described as time-dependent fluctuations of the tunneling amplitudes between adjacent sites, and attention is focused on non-Gaussian telegraph noise, going beyond the usual assumption of fast Gaussian noise. We observe the emergence of two different dynamical behaviors for the walker, corresponding to two opposite noise regimes: slow noise (i.e. strong coupling with the environment) confines the walker into few lattice nodes, while fast noise (weak coupling) induces a transition between quantum and classical diffusion over the lattice. A phase transition between the two dynamical regimes may be observed by tuning the ratio between the autocorrelation time of the noise and the coupling between the walker and the external environment generating the noise. We also address the non-Markovianity of the quantum map by assessing its memory effects, as well as evaluating the information backflow to the system. Our results suggest that the non-Markovian character of the evolution is linked to the dynamical behavior in the slow noise regime, and that fast noise induces a Markovian dynamics for the walker.Comment: 10 pages, 8 figure

    What is the relative contribution of biological and psychosocial factors to the generation of hypoxia headache?

    Get PDF
    ABSTRACTBackground: The biopsychosocial model claims that illness is generated by both biological and psychosocial factors. Accordingly, several studies have shown that both factors contribute to the generation of pain.Aims: The aim of the present study is to manipulate biological, psychological, and social factors in hypobaric hypoxia headache in order to understand their relative contribution to the generation of headache pain.Methods: Healthy subjects were subdivided into three groups and brought to our high-altitude labs for the assessment of hypoxia-induced headache, blood oxygen saturation (SO2), prostaglandins, and cortisol during the first 24 h after arrival. The first group did not undergo any manipulation. The second group (negative expectation) was told that severe headache would occur if SO2 dropped to less than 80% and their oximeters were set to display a saturation of 75%, even though real SO2 was much higher. The third group (negative expectation and social interaction) underwent the same ..

    Statistical Study of the Unfolding of Multimodular Proteins and their Energy Landscape by Atomic Force Microscopy

    Get PDF
    The aim of the present thesis is to investigate several aspects of: the proteins mechanics, interprotein interactions and to study also new techniques, theoretical and technical, to obtain and analyze the force spectroscopy experiments. The first section is dedicated to the statistical properties of the unfolding forces in a chain of homomeric multimodular proteins. The basic idea of this kind of statistic is to divide the peaks observed in a force extension curve in separate groups and then analyze these groups considering their position in the force curves. In fact in a multimodular homomeric protein the unfolding force is related to the number of not yet unfolded modules (we call it "N"). Such effect yields to a linear dependence of the most probable unfolding force of a peak on ln(N). We demonstrate how such dependence can be used to extract the kinetic parameters and how, ignoring it, could lead to significant errors. Following this topic we continue with non kinetic methods that, using the resampling from the rupture forces of any peak, could reconstruct the rupture forces for all the other peaks in a chain. Then a discussion about the Monte Carlo simulation for protein pulling is present. In fact a theoretical framework for such methodology has to be introduced to understand the various simulations done. In this chapter we also introduce a methodology to study the ligand receptor interactions when we directly functionalize the AFM tip and the substrate. In fact, in many of our experiments, we see a "cloud of points" in the force vs loading rate graph. We have modeled a system composed by "N" parallel springs, and studying the distribution of forces obtained in the force vs loading rate graph we have establish a procedure to restore the kinetic parameters used. Such procedure has then been used to discuss real experiments similar to biotin-avidin interaction. In the following chapter we discuss a first order approximation of the Bell-Evans model where a more explicit form of the potential is considered. In particular the dependence of the curvature of the potential on the applied force at the minimum and at the metastable state is considered. In the well known Bell-Evans model the prefactors of the transition rate are fixed at any force, however this is not what happen in nature, where the prefactors (that are the second local derivative of the interacting energy with respect to the reaction coordinate in its minimum and maximum) depend on the force applied. The results obtained with the force spectroscopy of the Laminin-binding-protein are discussed, in particular this protein showed a phase transition when the pH was changed. The behavior of this protein changes, from a normal WLC behavior to a plateau behavior. The analysis of the force spectroscopy curves shows a distribution of length where the maximum of the first prominent peak correspond to the full length of the protein. However, length that could be associated with dimers and trymers are also present in this distribution. Later a new approach to study the lock and key mechanism, using "handles" with a specific force extension pattern, is introduced. In particular handles of (I27)3 and (I27–SNase)3 were biochemically attached to: strept-actin molecules, biotin molecules, RNase and Angiogenin. The main idea is to have a system composed by "handle-(molecule A)-(molecule B)-handle" where the handles are covalently attached to the respective molecules and the two molecules "A and B" are attached by secondary bonds. This approach allows a better recognition of the protein-protein interaction enabling us to filter out spurious events. Doing a statistic on the rupture forces and comparing this with the statistic of the detachments of the system of the bare handles, we are able to extract the information of the interaction between the molecule A and B. The two last chapters are of more preliminary character that the previous part of the thesis. A section is dedicated to the estimation of effective mass and viscous drag of the cantilevers studied by autocorrelation and noise power spectrum. Usually the noise power spectrum method is the most used, however the autocorrelation should give approximately the same information. The parameters obtained are important in high frequency modulation techniques. In fact, they are needed to interpret the results. The results of these two methods show a good agreement in the estimation of the mass and the viscous drag of the various cantilever used. Afterwards a chapter is dedicated to the discussion of the force spectroscopy experiments using a low frequency modulation of the cantilever base. Such experiments allow us to record the phase and the amplitude shift of the modulation signal used. Using the amplitude channel we managed to restore the static force signal with a lower level of noise. Moreover these signals give us direct information about the dynamic stiffness and the lose of energy in the system, information that, using the standard technique would be difficult (or even impossible) to obtain
    • …