6,751 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
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
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