5,557 research outputs found
Revisiting the optical -symmetric dimer
Optics has proved a fertile ground for the experimental simulation of quantum
mechanics. Most recently, optical realizations of -symmetric
quantum mechanics have been shown, both theoretically and experimentally,
opening the door to international efforts aiming at the design of practical
optical devices exploiting this symmetry. Here, we focus on the optical
-symmetric dimer, a two-waveguide coupler were the materials show
symmetric effective gain and loss, and provide a review of the linear and
nonlinear optical realizations from a symmetry based point of view. We go
beyond a simple review of the literature and show that the dimer is just the
smallest of a class of planar -waveguide couplers that are the optical
realization of Lorentz group in 2+1 dimensions. Furthermore, we provide a
formulation to describe light propagation through waveguide couplers described
by non-Hermitian mode coupling matrices based on a non-Hermitian generalization
of Ehrenfest theorem.Comment: 25 pages, 12 figure
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
Struggles and pacification in the history of american kinesiology
En este artículo estudiamos la disputa epistemológica y pedagógica sobre la kinesiología/educación física que ha tenido lugar en las universidades de Estados Unidos desde 1990 hasta la actualidad. Hemos recogido el pensamiento de una muestra amplia de autores involucrados, con el propósito de obtener una visión de conjunto de un proceso que, de acuerdo con Morrow (2006), trata de esclarecer ¿de dónde venimos?, ¿qué somos?, ¿a dónde vamos? Tras el cotejo y análisis de la documentación más relevante concluimos que el periodo 1990-2013, caracterizado por una enconada pugna de paradigmas –en la que han estado implicados humanistas, positivistas, crosdisciplinaristas y subdisciplinaristas–, ha dado como resultado el dominio del paradigma integrador de Kretchmar (2007, 2008)In this article we review the epistemological and pedagogical debate on Kinesiology and Physical Education that has been going on in the universities of the US from 1990 to the present. We have compiled the opinions of a wide sample of authors, with the intention of getting the most complete picture of a process that, according to Morrow (2006), seeks to answer the questions "where we come from, who we are, and where we are going". After comparing and analysing the most relevant documents, we conclude that the period 1990-2013, characterized by a bitter struggle between paradigms fought by humanists, positivists, cross-disciplinarists, and sub-disciplinarists, has revealed the eventual predominance of the integrative paradigm of Kretchmar (2007, 2008
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