Ultradiscrete kinks with supersonic speed in a layered crystal with realistic potentials

We develop a dynamical model of the propagating nonlinear localized excitations, supersonic kinks, in the cation layer in a silicate mica crystal. We start from purely electrostatic Coulomb interaction and add the Ziegler-Biersack-Littmark short-range repulsive potential and the periodic potential produced by other atoms of the lattice. This approach allows the construction of supersonic kinks which can propagate in the lattice within a large range of energies and velocities. The interparticle distances in the lattice kinks with high energy are physically reasonable values. The introduction of the periodic lattice potential results in the important feature that the kinks propagate with a single velocity and a single energy which are independent on the excitation conditions. The found kinks are ultra-discrete and can be described with the "magic wave number" $q\simeq 2\pi/3a$, which was previously revealed in the nonlinear sinusoidal waves and supersonic kinks in the Fermi-Pasta-Ulam lattice. The extreme discreteness of the supersonic kinks, with basically two particles moving at the same time, allows the interpretation of their double-kink structure. The energy of the supersonic kinks is between the possible source of $^{40}$K recoil in beta decay and the energy necessary for the ejection of an atom at the border as has been found experimentally.Comment: 14 pages, 15 figure

Estudio de los impactos ambientales de los cruces de gasoductos con ríos vadeables

El río Cigüela y su afluente Valdepineda (Cuenca, España) fueron afectados por el cruce de un gasoducto, en Diciembre de 2001, mediante la técnica convencional "cruce subálveo" que consta de tres fases: instalación de la pista de trabajo, apertura de zanja y rehabilitación. Con el objetivo de evaluar el impacto de las distintas etapas de la obra en el medio acuático, se está llevando a cabo un estudio que se centra en el efecto de los sólidos en suspensión en las comunidades macrobentónicas e ícticas. Se presentan los resultados preliminares obtenidos en la fase de apertura de zanja, donde se observa un valor muy elevado de movilización de sólidos en suspensión (hasta 5000 mg/l), alcanzando las mayores concentraciones en los 100 primeros metros aguas abajo del punto de cruce. Estos sólidos en suspensión podrían ser la causa del aumento significativo de la sedimentación de las partículas de tamaño comprendido entre 50-250 μm y 250-500 μm en los 30 primeros metros aguas abajo del punto de cruce. Por otro lado, no se han observado diferencias en el valor del índice BMWP' en las distintas estaciones de muestreo. Sin embargo, en la fase de rehabilitación, se encuentra una diferencia significativa en la frecuencia de distribución de algunas de las especies de peces presentes en el río, además se observa un claro efecto barrera para la ictiofauna al eliminar la pista de trabajo.The Cigüela River and its tributary, Valdepineda (Cuenca, España) were affected by the crossing of a natural gas pipeline, in December 2001, by means of the conventional technique "open-cut water crossing" that consists of three different works: installation of the right-of-way, excavation and backfill of the pipeline trench, and restoration. In order to assess the impacts of these different activities on the aquatic environment, we are carrying out a study that is focused on the effects of suspended solids in the benthic and fish communities. Preliminary results of this study are presented on the excavation and backfill of the pipeline trench, that indicate that a very high value of suspended solids mobilisation is observed (up to 5000 mg/l), reaching the higher concentrations in the first 100 meters downstream of the crossing site. These suspended solids might be responsible for the significant increase in the sedimentation of the particles of sizes 50-250 μm and 250-500 μm in the 30 first meters downstream of the crossing site. On the other hand, we have not found differences in the values of the BMWP' index at the different sampling sites. Nevertheless, in the restoration phase , there is a significant difference in the distribution frequency of some fish species that appear in the river and also a clear barrier effect is observed for fishes when eliminating the right-of-way

Nonlinear waves in a chain of magnetically coupled pendula

A motivation for the study of reduced models like one-dimensional systems in Solid State Physics is the complexity of the full problem. In recent years our group has studied theoretically, numerically and experimentally wave propagation in lattices of nonlinearly coupled oscillators. Here, we present the dynamics of magnetically coupled pendula lattices. These macroscopic systems can model the dynamical processes of matter or layered systems. We report the results obtained for harmonic wave propagation in these media, and the different regimes of mode conversion into higher harmonics strongly influenced by dispersion and discreteness, including the phenomenon of acoustic dilatation of the chain, as well as some results on the propagation of localized waves i.e., solitons and kinks.Generalitat Valenciana APOSTD/2017/042Umiversitat Politècnica de València PAID-01-14Ministerio de Economía y Competitividad (MINECO), Spain FIS2015-65998-C2-2-PJunta de Andalucía 2017/FQM-28

Self-organization of ultrasound in viscous fluids

We report the theoretical and experimental demonstration of pattern formation in acoustics. The system is an acoustic resonator containing a viscous fluid. When the system is driven by an external periodic force, the ultrasonic field inside the cavity experiences different pattern-forming instabilities leading to the emergence of periodic structures. The system is also shown to possess bistable regimes, in which localized states of the ultrasonic field develop. The thermal nonlinearity in the viscous fluid, together with the far-from-equilibrium conditions, are is the responsible of the observed effects

Self-pulsing dynamics of ultrasound in a magnetoacoustic resonator

A theoretical model of parametric magnetostrictive generator of ultrasound is considered, taking into account magnetic and magnetoacoustic nonlinearities. The stability and temporal dynamics of the system is analized with standard techniques revealing that, for a given set of parameters, the model presents a homoclinic or saddle--loop bifurcation, which predicts that the ultrasound is emitted in the form of pulses or spikes with arbitrarily low frequency.Comment: 5 pages, 5 figure

Excitability in a nonlinear magnetoacoustic resonator

We report a nonlinear acoustic system displaying excitability. The considered system is a magnetostrictive material where acoustic waves are parametrically generated. For a set of parameters, the system presents homoclinic and heteroclinic dynamics, whose boundaries define a excitability domain. The excitable behaviour is characterized by analyzing the response of the system to different external stimuli. Single spiking and bursting regimes have been identified.Comment: 4 pages, 5 figure