Revisiting the optical PTPT-symmetric dimer

Optics has proved a fertile ground for the experimental simulation of quantum mechanics. Most recently, optical realizations of $\mathcal{PT}$-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 $\mathcal{PT}$-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 $N$-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

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

Hipotiroidismo subclínico y factores de riesgo cardiovascular

Objetivo: Conocer la prevalencia del hipotiroidismo subclínico en la población general de un centro de salud urbano y describir las características clínicas y factores de riesgo cardiovascular de los pacientes con hipotiroidismo subclínico. Métodos: Se realizó un estudio observacional descriptivo, transversal, retrospectivo, revisando las historias clínicas de los pacientes incluidos en la muestra desde junio de 2005 hasta julio de 2007. Se analizaron las siguientes variables; Datos generales: edad y sexo. Antecedentes familiares: patología tiroidea y otras enfermedades. Antecedentes personales: cardiovasculares, pulmonares, enfermedades autoinmunes, alteraciones gineco-obstétricas, diabetes, hipertensión (HT), dislipemia, obesidad, alteraciones psiquiátricas y hematológicas. Datos de laboratorio: niveles de TSH, niveles de T4 libre,presencia de anticuerpos antiperoxidasa, niveles de colesterol total y sus fracciones. Resultados: La prevalencia de la muestra de 100 pacientes recogida durante 8 meses fue de 3,8% de la población general mayor de 14 años, de la cual 79 eran mujeres y 21 eran hombres. El 13% eran diabéticos tipo 2, 23% tenían HT y un 40% tenían dislipemia. Sobrepeso y obesidad estaban presentes en un 26%. El nivel medio de TSH fue 6.92 ± 2,29 U/ml y el nivel medio de T4 libre fue 1,16 ± 0,16 ng/ml. Conclusiones: La prevalencia del hipotiroidismo subclínico fue 3,8%. sobre todo en mujeres con una edad media de 46 años. La incidencia de factores de riesgo cardiovascular en los sujetos estudiados es mayor en DM (13%), similar a la población general en cuanto a la dislipemia (40%) y obesidad (20%) y menor en HTA (23%). En nuestro estudio no se observa una pauta común en el manejo del hipotiroidismo subclínico, siendo necesaria la implementación y promoción de guías de actuación en Atención PrimariaObjective: To determine the prevalence of subclinical hypothyroidism in the general population of an urban health center and describe the clinical characteristics and cardiovascular risk factors in patients with subclinical hypothyroidism. Methods: An observational study, retrospective, reviewing the medical histories of patients sampled from June 2005 until July 2007. We analyzed the following variables; facts: age and sex. Family history thyroid disease and other diseases. Personal history: cardiovascular pulmonary autoimmune, alterations gynecology obstetric diabetes, hypertension (HT) dislipemia, obesity, psychiatric alterations and haematological. Laboratory data: novel TSH, free T4, antiperoxidase antibodies, total cholesterol and its fractions. Results: The prevalence of the sample of 100 patients collected over 8 months was 3.8% in the general population over 14 years, of which 79 were women and 21 were men. 13% were type 2 diabetics, 23% had HT and 40% had dyslipidemia. Overweight and obesity were present in 26%. The average level of TSH was 6.92 ± 2.29 U/ml and the average level of free T4 was 1.16 ± 0.16 ng/ml. Conclusions: Prevalence subclinical hypothyroidism was 3.8%. especially in women with a mean age of 46. The incidence of cardiovascular risk factors in the subjects studied is higher in DM (13%), similar to general population in terms of dyslipidemia (40%) and obesity (23%) and lowest in hypertension (23%). In our study we observed a common pattern in the management of subclinical hypothyroidism, requiring the implementation and promotion of practice guidelines in primary car

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