7,771 research outputs found

    An analytically solvable model of probabilistic network dynamics

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    We present a simple model of network dynamics that can be solved analytically for uniform networks. We obtain the dynamics of response of the system to perturbations. The analytical solution is an excellent approximation for random networks. A comparison with the scale-free network, though qualitatively similar, shows the effect of distinct topology.Comment: 4 pages, 1 figur

    Chaos in one-dimensional lattices under intense laser fields

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    A model is investigated where a monochromatic, spatially homogeneous laser field interacts with an electron in a one-dimensional periodic lattice. The classical Hamiltonian is presented and the technique of stroboscopic maps is used to study the dynamical behavior of the model. The electron motion is found to be completely regular only for small field amplitudes, developing a larger chaotic region as the amplitude increases. The quantum counterpart of the classical Hamiltonian is derived. Exact numerical diagonalizations show the existence of universal, random-matrix fluctuations in the electronic energy bands dressed by the laser field. A detailed analysis of the classical phase space is compatible with the statistical spectral analysis of the quantum model. The application of this model to describe transport and optical absorption in semiconductor superlattices submitted to intense infrared laser radiation is proposed.Comment: 9 pages, RevTex 3.0, EPSF (6 figures), to appear in Europhys. J.

    Kondo effect in transport through molecules adsorbed on metal surfaces: from Fano dips to Kondo peaks

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    The Kondo effect observed in recent STM experiments on transport through CoPc and TBrPP-Co molecules adsorbed on Au(111) and Cu(111) surfaces, respectively, is discussed within the framework of a simple model (Phys. Rev. Lett. {\bf 97}, 076806 (2006)). It is shown that, in the Kondo regime and by varying the adequate model parameters, it is possible to produce a crossover from a conductance Kondo peak (CoPc) to a conductance Fano dip (TBrPP-Co). In the case of TBrPP-Co/Cu(111) we show that the model reproduces the changes in the shape of the Fano dip, the raising of the Kondo temperature and shifting to higher energies of the dip minimum when the number of nearest neighbors molecules is lowered. These features are in line with experimental observations indicating that our simple model contains the essential physics underlying the transport properties of such complex molecules.Comment: 4 pages, 3 figures, submitted to PR

    Distinct magnetic signatures of fractional vortex configurations in multiband superconductors

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    Vortices carrying fractions of a flux quantum are predicted to exist in multiband superconductors, where vortex core can split between multiple band-specific components of the superconducting condensate. Using the two-component Ginzburg-Landau model, we examine such vortex configurations in a two-band superconducting slab in parallel magnetic field. The fractional vortices appear due to the band-selective vortex penetration caused by different thresholds for vortex entry within each band-condensate, and stabilize near the edges of the sample. We show that the resulting fractional vortex configurations leave distinct fingerprints in the static measurements of the magnetization, as well as in ac dynamic measurements of the magnetic susceptibility, both of which can be readily used for the detection of these fascinating vortex states in several existing multiband superconductors.Comment: 5 pages, 4 figure

    Energy transfer dynamics and thermalization of two oscillators interacting via chaos

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    We consider the classical dynamics of two particles moving in harmonic potential wells and interacting with the same external environment (HE), consisting of N non-interacting chaotic systems. The parameters are set so that when either particle is separately placed in contact with the environment, a dissipative behavior is observed. When both particles are simultaneously in contact with HE an indirect coupling between them is observed only if the particles are in near resonance. We study the equilibrium properties of the system considering ensemble averages for the case N=1 and single trajectory dynamics for N large. In both cases, the particles and the environment reach an equilibrium configuration at long times, but only for large N a temperature can be assigned to the system.Comment: 8 pages, 6 figure

    Analysis of structure withdissipator spectra under design and control

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    Las estructuras de Quito, Ecuador, son diseñadas para el espectro de la norma ecuatoriana de 2015, o para el hallado en la microzonificación de la ciudad de 2012. Estos espectros consideran en forma macro las fallas ciegas inversas sobre las que se halla la ciudad. En este artículo se destaca la importancia de verificar el diseño para los espectros de control que fueron desarrollados mediante métodos determinísticos para Quito en el 2015, los mismos que consideran la generación de sismos en las fallas ciegas. En el artículo se presentan dos modelos de plasticidad extendida para los elementos estructurales y un modelo de plasticidad para los disipadores ADAS o TADAS. Luego se indica con cierto detalle la técnica del pushover multimodal y el método del espectro de capacidad con el cual se halla el punto de capacidad de una estructura que fue inicialmente calculada para los espectros de diseño. Dicha estructura ha sido reforzada con disipadores ADAS para que no colapse ante el espectro de control que tiene ordenadas más altas que el espectro de diseño.The structures of Quito, Ecuador, are designed for the spectrum of the Ecuadorian code of 2015, or using the study of microzoning of the city of 2012. These spectra consider in general the effect of the blind reverse faults belonging to the city area. In this article, it is pointed out the importance of checking the design for the deterministic control spectra developed for Quito in 2015 based on earthquakes simulated in the blinds faults. In this paper we considered two models of extended plasticity for the structural elements and one model of plasticity for the ADAS and TADAS devices. Then, the technique of multimodal pushover is described, as well as the method of the capacity spectrum used to calculate the performance point of the structure. This structure was initially calculated by using design spectra and it had to be reinforced with ADAS devices in order to avoid its collapse for the control spectrum which has higher ordinates than the design one.Peer Reviewe

    The Tchebyshev transforms of the first and second kind

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    We give an in-depth study of the Tchebyshev transforms of the first and second kind of a poset, recently discovered by Hetyei. The Tchebyshev transform (of the first kind) preserves desirable combinatorial properties, including Eulerianess (due to Hetyei) and EL-shellability. It is also a linear transformation on flag vectors. When restricted to Eulerian posets, it corresponds to the Billera, Ehrenborg and Readdy omega map of oriented matroids. One consequence is that nonnegativity of the cd-index is maintained. The Tchebyshev transform of the second kind is a Hopf algebra endomorphism on the space of quasisymmetric functions QSym. It coincides with Stembridge's peak enumerator for Eulerian posets, but differs for general posets. The complete spectrum is determined, generalizing work of Billera, Hsiao and van Willigenburg. The type B quasisymmetric function of a poset is introduced. Like Ehrenborg's classical quasisymmetric function of a poset, this map is a comodule morphism with respect to the quasisymmetric functions QSym. Similarities among the omega map, Ehrenborg's r-signed Birkhoff transform, and the Tchebyshev transforms motivate a general study of chain maps. One such occurrence, the chain map of the second kind, is a Hopf algebra endomorphism on the quasisymmetric functions QSym and is an instance of Aguiar, Bergeron and Sottile's result on the terminal object in the category of combinatorial Hopf algebras. In contrast, the chain map of the first kind is both an algebra map and a comodule endomorphism on the type B quasisymmetric functions BQSym.Comment: 33 page

    A conjugate for the Bargmann representation

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    In the Bargmann representation of quantum mechanics, physical states are mapped into entire functions of a complex variable z*, whereas the creation and annihilation operators a^†\hat{a}^\dagger and a^\hat{a} play the role of multiplication and differentiation with respect to z*, respectively. In this paper we propose an alternative representation of quantum states, conjugate to the Bargmann representation, where the roles of a^†\hat{a}^\dagger and a^\hat{a} are reversed, much like the roles of the position and momentum operators in their respective representations. We derive expressions for the inner product that maintain the usual notion of distance between states in the Hilbert space. Applications to simple systems and to the calculation of semiclassical propagators are presented.Comment: 15 page

    Modelling patterns in continuous streams of data

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    The untapped source of information, extracted from the increasing number of sensors, can be explored to improve and optimize several systems. Yet, hand in hand with this growth goes the increasing difficulty to manage and organize all this new information. The lack of a standard context representation scheme is one of the main struggles in this research area, conventional methods for extracting knowledge from data rely on a standard representation or a priori relation. Which may not be feasible for IoT and M2M scenarios, with this in mind we propose a stream characterization model which aims to provide the foundations for a novel stream similarity metric. Complementing previous work on context organization, we aim to provide an automatic stream organizational model without enforcing specific representations. In this paper we extend our work on stream characterization and devise a novel similarity metho
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