Self-Consistent Screening Approximation for Flexible Membranes: Application to Graphene

Crystalline membranes at finite temperatures have an anomalous behavior of the bending rigidity that makes them more rigid in the long wavelength limit. This issue is particularly relevant for applications of graphene in nano- and micro-electromechanical systems. We calculate numerically the height-height correlation function $G(q)$ of crystalline two-dimensional membranes, determining the renormalized bending rigidity, in the range of wavevectors $q$ from $10^{-7}$ \AA$^{-1}$ till 10 \AA$^{-1}$ in the self-consistent screening approximation (SCSA). For parameters appropriate to graphene, the calculated correlation function agrees reasonably with the results of atomistic Monte Carlo simulations for this material within the range of $q$ from $10^{-2}$ \AA$^{-1}$ till 1 \AA$^{-1}$. In the limit $q\rightarrow 0$ our data for the exponent $\eta$ of the renormalized bending rigidity $\kappa_R(q)\propto q^{-\eta}$ is compatible with the previously known analytical results for the SCSA $\eta\simeq 0.82$. However, this limit appears to be reached only for $q<10^{-5}$ \AA$^{-1}$ whereas at intermediate $q$ the behavior of $G(q)$ cannot be described by a single exponent.Comment: 5 pages, 4 figure

Spontaneous symmetry breaking as a resource for noncritically squeezed light

In the last years we have proposed the use of the mechanism of spontaneous symmetry breaking with the purpose of generating perfect quadrature squeezing. Here we review previous work dealing with spatial (translational and rotational) symmetries, both on optical parametric oscillators and four-wave mixing cavities, as well as present new results. We then extend the phenomenon to the polarization state of the signal field, hence introducing spontaneous polarization symmetry breaking. Finally we propose a Jaynes-Cummings model in which the phenomenon can be investigated at the single-photon-pair level in a non-dissipative case, with the purpose of understanding it from a most fundamental point of view.Comment: Review for the proceedings of SPIE Photonics Europe. 11 pages, 5 figures

Suppression of anharmonicities in crystalline membranes by external strain

In practice, physical membranes are exposed to a certain amount of external strain (tension or compression), due to the environment where they are placed. As a result, the behavior of the phonon modes of the membrane is modified. We show that anharmonic effects in stiff two-dimensional membranes are highly suppressed under the application of tension. For this, we consider the anharmonic coupling between bending and stretching modes in the self-consistent screening approximation (SCSA), and compare the obtained height-height correlation function in the SCSA to the corresponding harmonic propagator. The elasticity theory results are compared to atomistic Monte Carlo simulations for a graphene membrane under tension. We find that, while rather high values of strain are needed to avoid anharmonicity in soft membranes, strain fields less than 1% are enough to suppress all the anharmonic effects in stiff membranes, as graphene.Comment: 7 pages, 6 figure

Squeezing spectra from s-ordered quasiprobability distributions. Application to dispersive optical bistability

It is well known that the squeezing spectrum of the field exiting a nonlinear cavity can be directly obtained from the fluctuation spectrum of normally ordered products of creation and annihilation operators of the cavity mode. In this article we show that the output field squeezing spectrum can be derived also by combining the fluctuation spectra of any pair of s-ordered products of creation and annihilation operators. The interesting result is that the spectrum obtained in this way from the linearized Langevin equations is exact, and this occurs in spite of the fact that no s-ordered quasiprobability distribution verifies a true Fokker-Planck equation, i.e., the Langevin equations used for deriving the squeezing spectrum are not exact. The (linearized) intracavity squeezing obtained from any s-ordered distribution is also exact. These results are exemplified in the problem of dispersive optical bistability.Comment: 15 pages, no figures, to be published in Journal of Modern Optic

Aspectos semióticos en el lenguaje visual de la hibridación arquitectónica chino-europea

This article analyses some concepts related to the architectural sign and presents itself a semiotic reading of one of the most important works of art of the architecture in Qing dynasty (18th Century): the Yuanying Guan (View of the Distant Sea) pavilion. Semiotic structures were employed to interpret the expression of architectural forms and formulate a subsequent understanding of these forms by turning each element into a communication tool.Este artículo analiza conceptos relacionados con el signo arquitectónico, y presenta una reflexión sobre aspectos semióticos del lenguaje visual de una de las obras de arte más importantes de la arquitectura en la dinastía Qing (S. XVIII): el Palacio Yuanying Guan (Vistas a un Mar distante). Se han utilizado conceptos y estructuras semióticas para interpretar la expresión de sus formas arquitectónicas y formular una comprensión posterior de dichas formas, convirtiendo cada elemento en una herramienta de comunicación.This article analyses some concepts related to the architectural sign and presents itself a semiotic reading of one of the most important works of art of the architecture in Qing dynasty (18th Century): the Yuanying Guan (View of the Distant Sea) pavilion. Semiotic structures were employed to interpret the expression of architectural forms and formulate a subsequent understanding of these forms by turning each element into a communication tool

Low-intensity resistance exercise training increases lower limb force in healthy retirees

INTRODUCTION: Aging is associated with decreasing muscle strength. Older people who have never done resistance work in a gym require gradual training programs to help them increasing confidence on this type of training. The use of low intensity resistance exercise with slow movements and tonic force improvement has been proposed as an effective method to increase muscular strength. There is little literature on the effect of intensity training on 30% of one repetition maximum (RM). PURPOSE: To establish the changes in the strength of upper and lower limb force after participating in a 10 week low-intensity resistance exercise for a group of healthy retirees aged between 50 and 70 years. METHODS: Quasi-experimental design, with two measurements. Fifty-eight participants were separated into two groups according to their available schedule. The experimental group received low-intensity resistance training for ten weeks, three times a week, with an intensity of 30 to 60% RM. The control group received no training. Physical tests applied to both groups were: handgrip strength with digital dynamometer, Short Physical Performance Battery (SPPB) and 8-Foot up and go test (FUGT).RESULTS: Forty nine participants completed the study (total dropout rate was 16%) from which 57% were women. Participants in the experimental group (n = 31) had improvements in SPPB and FUGT tests (p \u3c.05). Without changes in handgrip strength. On the other hand, any changes were observed in the control group. CONCLUSION: The results indicate that a low-intensity resistance training (30% 1RM) is a useful method to increase muscle strength of lower limbs in healthy older adults. Due to the interference effect of training, more time is required to observe changes in the dynamic strength of the upper limbs. This type of training program is useful for promoting functionality in older adults reluctant to resistance training

Effects of smoking on vital capacity in healthy students

INTRODUCTION: Although the tobacco consumption has been reported to obstruct the effects of physical culture in young adults, there are few reports that include physical and laboratory evidence of this. Health education appears not to prevent impairment of the vital capacity associated with tobacco consumption. PURPOSE: The purpose of this study was estimate the effect of tobacco consumption on vital capacity after four months of participation in a theoretical-practical program on movement fundamentals.METHODS: Preexperimental design of two measurements. Lung function and a physical test were performed on seventeen healthy students. Course-Navette test was carried out to estimate vital capacity (heart rate at rest, maximum heart rate, physical level, VO2 max, distance and average speed). Forced expiratory volume in one second (FEV1) was measured by Welch Allyn Schiller spirometer. The sample was divided on the consumption of cigarettes (12 consumers vs. 5 abstainers). T-tests were used to evaluate the differences between groups. RESULTS: Participants were men of 20.94 years (SD = 2.69, 18-19 years) with normal body complexion (Body mass index = 24.51 kg/m 2 (SD = 1.69). There were no baseline differences between groups regarding age or body composition (p \u3e .05). Differences in all parameters related to vital capacity were observed in the abstainers group (p \u3c .01), except for maximal heart rate and resting heart rate (p \u3e .05). The smokers group decreased their results in both tests but without significant differences. CONCLUSION: Tobacco consumption affected the vital capacity of young adults despite the participation in theoretical-practical program of fundamentals of the movement. Tobacco abstinence coupled with participation in an educational program increased vital capacity measured with a physical and a laboratory test

Brownian Carnot engine

The Carnot cycle imposes a fundamental upper limit to the efficiency of a macroscopic motor operating between two thermal baths. However, this bound needs to be reinterpreted at microscopic scales, where molecular bio-motors and some artificial micro-engines operate. As described by stochastic thermodynamics, energy transfers in microscopic systems are random and thermal fluctuations induce transient decreases of entropy, allowing for possible violations of the Carnot limit. Despite its potential relevance for the development of a thermodynamics of small systems, an experimental study of microscopic Carnot engines is still lacking. Here we report on an experimental realization of a Carnot engine with a single optically trapped Brownian particle as working substance. We present an exhaustive study of the energetics of the engine and analyze the fluctuations of the finite-time efficiency, showing that the Carnot bound can be surpassed for a small number of non-equilibrium cycles. As its macroscopic counterpart, the energetics of our Carnot device exhibits basic properties that one would expect to observe in any microscopic energy transducer operating with baths at different temperatures. Our results characterize the sources of irreversibility in the engine and the statistical properties of the efficiency -an insight that could inspire novel strategies in the design of efficient nano-motors.Comment: 7 pages, 7 figure