1/fα1/f^\alpha noise and integrable systems

An innovative test for detecting quantum chaos based on the analysis of the spectral fluctuations regarded as a time series has been recently proposed. According to this test, the fluctuations of a fully chaotic system should exhibit 1/f noise, whereas for an integrable system this noise should obey the 1/f^2 power law. In this letter, we show that there is a family of well-known integrable systems, namely spin chains of Haldane-Shastry type, whose spectral fluctuations decay instead as 1/f^4. We present a simple theoretical justification of this fact, and propose an alternative characterization of quantum chaos versus integrability formulated directly in terms of the power spectrum of the spacings of the unfolded spectrum.Comment: 5 pages, 3 figures, RevTe

Glassy dynamics, aging and thermally activated avalanches in interface pinning at finite temperatures

We study numerically the out-of-equilibrium dynamics of interfaces at finite temperatures when driven well below the zero-temperature depinning threshold. We go further than previous analysis by including the most relevant non-equilibrium correction to the elastic Hamiltonian. We find that the relaxation dynamics towards the steady-state shows glassy behavior, aging and violation of the fluctuation-dissipation theorem. The interface roughness exponent alpha approx 0.7 is found to be robust to temperature changes. We also study the instantaneous velocity signal in the low temperature regime and find long-range temporal correlations. We argue 1/f-noise arises from the merging of local thermally-activated avalanches of depinning events.Comment: 4 pages, 4 figure

High-cadence spectroscopy of M-dwarfs – II. Searching for stellar pulsations with HARPS

Stellar oscillations appear all across the Hertzsprung–Russell diagram. Recent theoretical studies support their existence also in the atmosphere of M dwarfs. These studies predict for them short periodicities ranging from 20 min to 3 h. Our Cool Tiny Beats (CTB) programme aims at finding these oscillations for the very first time. With this goal, CTB explores the short time domain of M dwarfs using radial velocity data from the High Accuracy Radial velocity Planet Searcher (HARPS)-European Southern Observatory and HARPS-N high-precision spectrographs. Here we present the results for the two most long-term stable targets observed to date with CTB, GJ 588 and GJ 699 (i.e. Barnard's star). In the first part of this work we detail the correction of several instrumental effects. These corrections are especially relevant when searching for subnight signals. Results show no significant signals in the range where M dwarfs pulsations were predicted. However, we estimate that stellar pulsations with amplitudes larger than ∼0.5 m s−1 can be detected with a 90 per cent completeness with our observations. This result, along with the excess of power regions detected in the periodograms, opens the possibility of non-resolved very low amplitude pulsation signals. Next generation more precise instrumentation would be required to detect such oscillations. However, the possibility of detecting pulsating M-dwarf stars with larger amplitudes is feasible due to the short size of the analysed sample. This motivates the need for completeness of the CTB survey

Super-roughening versus intrinsic anomalous scaling of surfaces

In this paper we study kinetically rough surfaces which display anomalous scaling in their local properties such as roughness, or height-height correlation function. By studying the power spectrum of the surface and its relation to the height-height correlation, we distinguish two independent causes for anomalous scaling. One is super-roughening (global roughness exponent larger than or equal to one), even if the spectrum behaves non anomalously. Another cause is what we term an intrinsically anomalous spectrum, in whose scaling an independent exponent exists, which induces different scaling properties for small and large length scales (that is, the surface is not self-affine). In this case, the surface does not need to be super-rough in order to display anomalous scaling. In both cases, we show how to extract the independent exponents and scaling relations from the correlation functions, and we illustrate our analysis with two exactly solvable examples. One is the simplest linear equation for molecular beam epitaxy , well known to display anomalous scaling due to super-roughening. The second example is a random diffusion equation, which features anomalous scaling independent of the value of the global roughness exponent below or above one.Comment: 9 pages, 6 figures, Revtex (uses epsfig), Phys. Rev. E, submitte

Variations in the basic biokinematic pattern in three breeds of horses at the hand-led walk

In this study the lineal and temporal parameters of the stride of andalusian (n=10), angloarabian (n=6) and arabian (n=7) mature horses were compared at the walk. The speeds were similar in the three breeds (1.63±0.10 m/s), for what the Archivos de zootecnia vol. 48, núm. 183, p. 328. GALISTEO ET AL. statistical comparisons were carried out by an analysis of the variance, and a means comparison test (Tukey test). The stride lenght was shorter in arabians and andalusians than in angloarabians, while the overtracking lenght was bigger in the arabians. The duration of the forelimb cycle was bigger in angloarabians due to a bigger duration in this breed of the stance phase. The midstace position (expressed as a percentaje of the stride duration) differed among the three breeds, indicating that each one shows times of braking and propulsion of the forelimb different to the other ones; but not in the instant in which the hoof reaches the highest point in its trajectory. In the hind limb the differences were much less marked, since small differences were detected in the duration of the cycle between arabians and angloarabians, while the stride duration was longer in andalusians and angloarabians than in the Arabians; the braking and propulsion phases (determined by the position along the stride of the midstance position) didn’t differ among breeds, the same with the instant in which the hindhoof reach the highest point in its trajectory. It can be concluded that marked differences exist between equine breeds in the lineal parameters of the stride at the walk, and the temporal parameters of the forelimb, while in the hind limb are less marked, probably because this member is functionally committed in the propulsion of the horse.En este estudio se compararon los parámetros lineales y temporales del tranco de paso de caballos adultos de Pura Raza Española (n=10), Angloárabe (n=6) y Árabe (n=7). Las velocidades fueron similares en las tres razas (1,63±0,10 m/s), por lo que las comparaciones estadísticas se realizaron mediante un análisis de la varianza y un test de comparación de medias (Test de Tukey). La amplitud de tranco fue más corta en Árabes y Españoles que en Angloárabes, mientras que la longitud de sobrehuella fue mayor en los Árabes. La duración del ciclo del miembro torácico fue mayor en Angloárabes debido a una mayor duración en esta raza de la fase de apoyo. La posición de apoyo medio (expresada porcentualmente a la duración total del ciclo) difirió entre las tres razas, indicando que cada raza presenta tiempos de frenada y propulsión del miembro torácico diferentes a las demás; no así en el instante en el que el casco alcanza el punto más alto de su trayectoria. En el miembro pelviano las diferencias fueron mucho menos marcadas, ya que se detectaron pequeñas diferencias en la duración del ciclo entre Árabes y Angloárabes, mientras que la duración del tranco fue mayor en Españoles y Angloárabes que en los Árabes; los tiempos de frenada y propulsión (determinada por la posición a lo largo del tranco del apoyo medio) no difirió entre razas, lo mismo que el instante en que el casco pelviano se encuentra en el punto más alto de su trayectoria. Se puede concluir que existen marcadas diferencias entre razas equinas en los parámetros lineales del tranco al paso, al igual que sucede con los parámetros temporales del miembro torácico, mientras que en el pelviano son menos marcadas, probablemente porque este miembro está funcionalmente más comprometido que el torácico en la propulsión del caballo

Exchange operator formalism for N-body spin models with near-neighbors interactions

We present a detailed analysis of the spin models with near-neighbors interactions constructed in our previous paper [Phys. Lett. B 605 (2005) 214] by a suitable generalization of the exchange operator formalism. We provide a complete description of a certain flag of finite-dimensional spaces of spin functions preserved by the Hamiltonian of each model. By explicitly diagonalizing the Hamiltonian in the latter spaces, we compute several infinite families of eigenfunctions of the above models in closed form in terms of generalized Laguerre and Jacobi polynomials.Comment: RevTeX, 31 pages, no figures; important additional conten