Thermoelectric relations in the conformal limit in Dirac and Weyl semimetals

In the Fermi liquid description of metals, electrical and thermoelectric transport coefficients are linked by robust relations which can be challenged by strong interactions or when the electron liquid enters a different regime. These relations have been very powerful in the characterisation of novel materials. We show that Dirac and Weyl semimetals at zero doping and zero temperature (the conformal limit) have a very singular behavior due to a quantum anomaly. Away from this point, a Mott relation can be established

Bistable and dynamic states of parametrically excited ultrasound in a fluid-filled cavity

In this paper we have considered the problem of parametric sound generation in an acoustic resonator flled with a fluid, taking explicitely into account the influence of the nonlinearly generated second harmonic. A simple model is presented, and its stationary solutions obtained. The main feature of these solutions is the appearance of bistable states of the fundamental field resulting from the coupling to the second harmonic. An experimental setup was designed to check the predictions of the theory. The results are consistent with the predicted values for the mode amplitudes and parametric thresholds. At higher driving values a self-modulation of the amplitudes is observed. We identify this phenomenon with a secondary instability previously reported in the frame of the theoretical model.Comment: 5 figures. Submitted to JAS

Nondiffractive sonic crystals

We predict theoretically the nondiffractive propagation of sonic waves in periodic acoustic media (sonic crystals), by expansion into a set of plane waves (Bloch mode expansion), and by finite difference time domain calculations of finite beams. We also give analytical evaluations of the parameters for nondiffractive propagation, as well as the minimum size of the nondiffractively propagating acoustic beams.Comment: 7 figures, submitted to J. Acoust. Soc. A

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

Theory of quantum fluctuations of optical dissipative structures and its application to the squeezing properties of bright cavity solitons

We present a method for the study of quantum fluctuations of dissipative structures forming in nonlinear optical cavities, which we illustrate in the case of a degenerate, type I optical parametric oscillator. The method consists in (i) taking into account explicitly, through a collective variable description, the drift of the dissipative structure caused by the quantum noise, and (ii) expanding the remaining -internal- fluctuations in the biorthonormal basis associated to the linear operator governing the evolution of fluctuations in the linearized Langevin equations. We obtain general expressions for the squeezing and intensity fluctuations spectra. Then we theoretically study the squeezing properties of a special dissipative structure, namely, the bright cavity soliton. After reviewing our previous result that in the linear approximation there is a perfectly squeezed mode irrespectively of the values of the system parameters, we consider squeezing at the bifurcation points, and the squeezing detection with a plane--wave local oscillator field, taking also into account the effect of the detector size on the level of detectable squeezing.Comment: 10 figure

Revista Ciencias y Humanidades (Vol. II no. 2 ene-jun 2016)

La revista tiene como objetivo la difusión de material académico de corte investigativo relacionado con las disciplinas sociales y humanas; teniendo cabida en sus páginas: la educación y la pedagogía, la historia, la antropología y etnografía, la sociología, psicología, lingüística, el análisis y la crítica literaria, economía, política, geografía humana, psicoanálisis, la filosofía, la estética y las artes. El contenido de la revista está dirigido a estudiantes y profesionales dedicados a la investigación o interesados en el conocimiento de los resultados investigativos en las disciplinas ya mencionadas. El articulado de esta publicación es íntegramente inédito. La revista Ciencias y Humanidades no condiciona a los autores a una línea o postura ideológica. Es así como los resultados de investigaciones, las reseñas, traducciones, entrevistas, análisis, y todo el material que impregna las páginas de esta publicación está terciado por un aroma a libertad desde los cimientos plantados por la ilustración y la modernidadContenido La prensa literaria colombiana: La lucha por las reglas del juego en el campo literario nacional. 1836 1865. Laura Sánchez Guerra. 9-26 Temporalité, consommation et individualité : une approche critique. Juan Diego González Rúa. Fernando Pessoa y la negación de la acción a través de la literatura del desasosiego. Mauricio Calle Zapata. 81-99 Narrativa filosófica o filosofía estetizada: rasgos del humanismo alemán en la obra de Jorge Luis Borges. Juan Carlos Herrera Ruíz. 101-114 Paraíso prohibido. Imágenes dialécticas en la construcción del Estado del Interior. Fernando Londoño. 115-133 Centro de Estudios en Ciencias y Humanidades Federico Guillermo García Arjona, Mauricio Calle Zapata, Rosa María Moreno Cardona, Fernando Londoño, Myriam Verónica Pérez Carvajal, Mauricio García Echeverri y el Dr. Federico García Posada. 135-14

Quantum squeezing of optical dissipative structures

We show that any optical dissipative structure supported by degenerate optical parametric oscillators contains a special transverse mode that is free from quantum fluctuations when measured in a balanced homodyne detection experiment. The phenomenon is not critical as it is independent of the system parameters and, in particular, of the existence of bifurcations. This result is a consequence of the spatial symmetry breaking introduced by the dissipative structure. Effects that could degrade the squeezing level are considered.Comment: 4 pages and a half, 1 fugure. Version to appear in Europhysics Letter