Magnetic field induced control of breather dynamics in a single plaquette of Josephson junctions

We present a theoretical study of inhomogeneous dynamic (resistive) states in a single plaquette consisting of three Josephson junctions. Resonant interactions of such a breather state with electromagnetic oscillations manifest themselves by resonant current steps and voltage jumps in the current-voltage characteristics. An externally applied magnetic field leads to a variation of the relative shift between the Josephson current oscillations of two resistive junctions. By making use of the rotation wave approximation analysis and direct numerical simulations we show that this effect allows to effectively control the breather instabilities, e. g. to increase (decrease) the height of the resonant steps and to suppress the voltage jumps in the current-voltage characteristics.Comment: 4 pages, 3 figure

Spontaneous creation of discrete breathers in Josephson arrays

We report on the experimental generation of discrete breather states (intrinsic localized modes) in frustrated Josephson arrays. Our experiments indicate the formation of discrete breathers during the transition from the static to the dynamic (whirling) system state, induced by a uniform external current. Moreover, spatially extended resonant states, driven by a uniform current, are observed to evolve into localized breather states. Experiments were performed on single Josephson plaquettes as well as open-ended Josephson ladders with 10 and 20 cells. We interpret the breather formation as the result of the penetration of vortices into the system.Comment: 5 pages, 5 figure

Instabilities in Josephson Ladders with Current Induced Magnetic Fields

We report on a theoretical analysis, consisting of both numerical and analytic work, of the stability of synchronization of a ladder array of Josephson junctions under the influence of current induced magnetic fields. Surprisingly, we find that as the ratio of the mutual to self inductance of the cells of the array is increased a region of unstable behavior occurs followed by reentrant stable synchronization. Analytic work tells us that in order to understand fully the cause of the observed instabilities the behavior of the vertical junctions, sometimes ignored in analytic analyses of ladder arrays, must be taken into account.Comment: RevTeX, 4 pages, 3 figure

Discrete breathers in dissipative lattices

We study the properties of discrete breathers, also known as intrinsic localized modes, in the one-dimensional Frenkel-Kontorova lattice of oscillators subject to damping and external force. The system is studied in the whole range of values of the coupling parameter, from C=0 (uncoupled limit) up to values close to the continuum limit (forced and damped sine-Gordon model). As this parameter is varied, the existence of different bifurcations is investigated numerically. Using Floquet spectral analysis, we give a complete characterization of the most relevant bifurcations, and we find (spatial) symmetry-breaking bifurcations which are linked to breather mobility, just as it was found in Hamiltonian systems by other authors. In this way moving breathers are shown to exist even at remarkably high levels of discreteness. We study mobile breathers and characterize them in terms of the phonon radiation they emit, which explains successfully the way in which they interact. For instance, it is possible to form ``bound states'' of moving breathers, through the interaction of their phonon tails. Over all, both stationary and moving breathers are found to be generic localized states over large values of $C$, and they are shown to be robust against low temperature fluctuations.Comment: To be published in Physical Review

Row-switched states in two-dimensional underdamped Josephson junction arrays

When magnetic flux moves across layered or granular superconductor structures, the passage of vortices can take place along channels which develop finite voltage, while the rest of the material remains in the zero-voltage state. We present analytical studies of an example of such mixed dynamics: the row-switched (RS) states in underdamped two-dimensional Josephson arrays, driven by a uniform DC current under external magnetic field but neglecting self-fields. The governing equations are cast into a compact differential-algebraic system which describes the dynamics of an assembly of Josephson oscillators coupled through the mesh current. We carry out a formal perturbation expansion, and obtain the DC and AC spatial distributions of the junction phases and induced circulating currents. We also estimate the interval of the driving current in which a given RS state is stable. All these analytical predictions compare well with our numerics. We then combine these results to deduce the parameter region (in the damping coefficient versus magnetic field plane) where RS states can exist.Comment: latex, 48 pages, 15 figs using psfi

Nonlinear Localization in Metamaterials

Metamaterials, i.e., artificially structured ("synthetic") media comprising weakly coupled discrete elements, exhibit extraordinary properties and they hold a great promise for novel applications including super-resolution imaging, cloaking, hyperlensing, and optical transformation. Nonlinearity adds a new degree of freedom for metamaterial design that allows for tuneability and multistability, properties that may offer altogether new functionalities and electromagnetic characteristics. The combination of discreteness and nonlinearity may lead to intrinsic localization of the type of discrete breather in metallic, SQUID-based, and ${\cal PT}-$symmetric metamaterials. We review recent results demonstrating the generic appearance of breather excitations in these systems resulting from power-balance between intrinsic losses and input power, either by proper initialization or by purely dynamical procedures. Breather properties peculiar to each particular system are identified and discussed. Recent progress in the fabrication of low-loss, active and superconducting metamaterials, makes the experimental observation of breathers in principle possible with the proposed dynamical procedures.Comment: 19 pages, 14 figures, Invited (Review) Chapte

The qualification of collective absolutes and the individuality of persons and events in mid-nineteenth-century Spain

This article argues, on the basis of intellectual, literary, and art history, against the view that mid-nineteenth-century notions of individuality in Spain were products of a social structure based around a bourgeoisie, or, in other accounts, based around a failed effort to establish a bourgeoisie. Instead, it argues that an emphasis on individuality could take radically different forms, that there was no core shared idea of 'individuality'. The article argues that the key motivating factor in these varying notions of individuality was a conflict between and concerning different factions within an oligarchic elite over the future of that elite

Discrete breathers in ϕ4\phi^4 and related models

We touch upon the wide topic of discrete breather formation with a special emphasis on the the $\phi^4$ model. We start by introducing the model and discussing some of the application areas/motivational aspects of exploring time periodic, spatially localized structures, such as the discrete breathers. Our main emphasis is on the existence, and especially on the stability features of such solutions. We explore their spectral stability numerically, as well as in special limits (such as the vicinity of the so-called anti-continuum limit of vanishing coupling) analytically. We also provide and explore a simple, yet powerful stability criterion involving the sign of the derivative of the energy vs. frequency dependence of such solutions. We then turn our attention to nonlinear stability, bringing forth the importance of a topological notion, namely the Krein signature. Furthermore, we briefly touch upon linearly and nonlinearly unstable dynamics of such states. Some special aspects/extensions of such structures are only touched upon, including moving breathers and dissipative variations of the model and some possibilities for future work are highlighted

Evaluación del Nivel Lector.: Manual Técnico del Tests de Eficacia Lectora (TECLE)

Comentario a cargo de la Prof. Dra. Lilian R. DasetDepartamento de Ciencias Cognitivas y de la Salud.Facultad de Psicología.Universidad Católica del Urugua