423 research outputs found

    Quantum computation of multifractal exponents through the quantum wavelet transform

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    We study the use of the quantum wavelet transform to extract efficiently information about the multifractal exponents for multifractal quantum states. We show that, combined with quantum simulation algorithms, it enables to build quantum algorithms for multifractal exponents with a polynomial gain compared to classical simulations. Numerical results indicate that a rough estimate of fractality could be obtained exponentially fast. Our findings are relevant e.g. for quantum simulations of multifractal quantum maps and of the Anderson model at the metal-insulator transition.Comment: 9 pages, 9 figure

    Discrepancies between decoherence and the Loschmidt echo

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    The Loschmidt echo and the purity are two quantities that can provide invaluable information about the evolution of a quantum system. While the Loschmidt echo characterizes instability and sensitivity to perturbations, purity measures the loss of coherence produced by an environment coupled to the system. For classically chaotic systems both quantities display a number of -- supposedly universal -- regimes that can lead on to think of them as equivalent quantities. We study the decay of the Loschmidt echo and the purity for systems with finite dimensional Hilbert space and present numerical evidence of some fundamental differences between them.Comment: 6 pages, 3 figures. Changed title. Added 1 figure. Published version

    Quantum non-Markovian behavior at the chaos border

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    In this work we study the non-Markovian behaviour of a qubit coupled to an environment in which the corresponding classical dynamics change from integrable to chaotic. We show that in the transition region, where the dynamics has both regular islands and chaotic areas, the average non-Markovian behaviour is enhanced to values even larger than in the regular regime. This effect can be related to the non-Markovian behaviour as a function of the the initial state of the environment, where maxima are attained at the regions dividing separate areas in classical phase space, particularly at the borders between chaotic and regular regions. Moreover, we show that the fluctuations of the fidelity of the environment -- which determine the non-Markovianity measure -- give a precise image of the classical phase portrait.Comment: 23 pages, 9 figures (JPA style). Closest to published versio

    Multifractality of quantum wave packets

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    We study a version of the mathematical Ruijsenaars-Schneider model, and reinterpret it physically in order to describe the spreading with time of quantum wave packets in a system where multifractality can be tuned by varying a parameter. We compare different methods to measure the multifractality of wave packets, and identify the best one. We find the multifractality to decrease with time until it reaches an asymptotic limit, different from the mulifractality of eigenvectors, but related to it, as is the rate of the decrease. Our results could guide the study of experimental situations where multifractality is present in quantum systems.Comment: 6 pages, 4 figures, final version including a new figure (figure 1

    Ammoniacal nitrogen recovery from pig slurry using a novel hydrophobic/ hydrophilic selective membrane

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    The implementation of the circular economy paradigm in intensive pig farming requires technologies able to recover ammoniacal nitrogen from pig slurries. This research explores the feasibility of a novel hydrophobic/ hydrophilic non-porous membrane to recover ammoniacal nitrogen from pig slurry at ambient temperature and using a H2SO4 solution as trapping agent. The influence of (i) the pH of the feed solution, (ii) the volume ratio between feed and trapping solution, and (iii) the trapping solution concentration on nitrogen recovery and flux were evaluated using a synthetic solution and pig slurry. The best performance was achieved when the pH of the feed solution was controlled at 9.0, where average fluxes of 145 and 116 g N/(m2⋅day) were achieved for the synthetic solution and pig slurry after 24 h, respectively. Decreasing the feed-to-trapping volume ratio improved the recovery efficiency after 24 h from 62% to 74% for the synthetic solution and from 32% to 46% for pig slurry. However, renewing the H2SO4 concentration of the trapping solution only led to minor improvements despite the higher reagent consumption. The diffusion coefficients of NH3 and NH+4 through the membrane at pH 9.0 were (7.3 ± 0.2)⋅10-11 and (2.1 ± 0.1)⋅10-11 m2/s for the synthetic solution and (2.7 ± 0.1)⋅10-11 and (1.0 ± 0.1)⋅ 10-11 m2/s for the pig slurry, respectively. The capacity of ions to diffuse through the membrane is a distinctive feature of this membrane and allowed recovering 33% of potassium and 21% of phosphate in pig slurry after 24 h

    Decay of the classical Loschmidt echo in integrable systems

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    We study both analytically and numerically the decay of fidelity of classical motion for integrable systems. We find that the decay can exhibit two qualitatively different behaviors, namely an algebraic decay, that is due to the perturbation of the shape of the tori, or a ballistic decay, that is associated with perturbing the frequencies of the tori. The type of decay depends on initial conditions and on the shape of the perturbation but, for small enough perturbations, not on its size. We demonstrate numerically this general behavior for the cases of the twist map, the rectangular billiard, and the kicked rotor in the almost integrable regime.Comment: 8 pages, 3 figures, revte

    Kolmogorov turbulence, Anderson localization and KAM integrability

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    The conditions for emergence of Kolmogorov turbulence, and related weak wave turbulence, in finite size systems are analyzed by analytical methods and numerical simulations of simple models. The analogy between Kolmogorov energy flow from large to small spacial scales and conductivity in disordered solid state systems is proposed. It is argued that the Anderson localization can stop such an energy flow. The effects of nonlinear wave interactions on such a localization are analyzed. The results obtained for finite size system models show the existence of an effective chaos border between the Kolmogorov-Arnold-Moser (KAM) integrability at weak nonlinearity, when energy does not flow to small scales, and developed chaos regime emerging above this border with the Kolmogorov turbulent energy flow from large to small scales.Comment: 8 pages, 6 figs, EPJB style

    Informe final del proyecto elaboración y análisis de casos psicosociales por parte del alumnado

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    Projecte 2014PID-UB/048A continuación se presenta el informe final del proyecto Elaboración y análisis de casos por parte del alumnado (2014PID-UB/048). Mediante este proyecto de dos años de duración se pretendió desarrollar estrategias docentes para fomentar la adquisición de la competencia específica conocer, comprender y analizar el comportamiento por parte de los alumnos de la asignatura Psicología Social del Grado de Psicología de la Universidad de Barcelona. En esta dirección, a lo largo del primer año se planificaron, desarrollaron e implementaron actividades de aprendizaje y de evaluación basadas en la metodología de estudio de casos. A lo largo del segundo año se han realizado modificaciones en las actividades inicialmente planteadas con el fin de mejorar los procesos de aprendizaje del alumnado. Los resultados obtenidos demuestran que la elaboración y el análisis de casos por parte de los estudiantes favorecen su capacidad para comprender y analizar el comportamiento humano. Asimismo, tiene efectos positivos sobre su desempeño en el examen final de la asignatura y sobre su nivel de satisfacción con el curso

    Development of psychosocial case studies by students to improve their ability to understand and analyze human behavior

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    This study presents an active learning methodology based on the development and analysis of case studies by college students and explores its effects on academic performance and on students' capacity of understanding and analysing human behaviour. A group of 54 students who were taking the course Social Psychology at the University of Barcelona developed written stories where psychosocial concepts were represented. Results showed that participants, after developing their own case studies, improved their ability to identify and explain theoretical concepts included in case studies created by the teaching team. The proposed teaching methodology appears to enhance their ability to understand and analyse human behaviour, helping students to integrate theory with reality
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