Uso del tabaco entre los jóvenes colombianos Retos para los profesionales en salud pública

Resumen El incremento en el índice del uso del tabaco y sus derivados entre los jóvenes colombianos representa un llamado para los especialistas en salud pública para que consideren el control del tabaco una prioridad en el área de prevención. El objetivo de este artículo es documentar los daños del tabaco en el cuerpo humano, el incremento del tabaquismo entre los jóvenes colombianos, y explorar el papel de los programas de prevención en la reducción de este problema. Palabra claves: Salud, juventud, tabaco, prevención. Abstract Increasing tobacco use rates among Colombian youth exemplify the need to make prevention top public health priority. The purpose of this article is to document the adverse effects of tobacco in the human body, the increases in tobacco use among Colombian youth, and to explore the role of prevention in decreasing this public health problem. Key words: Healt, young, tabacco, prevention

Phase only transmit beamforming for spectrum sharing microwave systems

This paper deals with the problem of phase-only transmit beamforming in spectrum sharing microwave systems. In contrast to sub-6 GHz schemes, general microwave systems require a large number of antennas due to its huge path loss. As a consequence, digital beamforming needs a large number of computational resources compared to analog beamforming, which only needs a single radio-frequency chain, results the less computational demanding solution. Analog schemes are usually composed by a phase shifter network whose elements transmit at a certain fixed power so that the system designer shall compute the phase values for each element given a set of directions. This approach leads to non-convex quadratic problems where the traditional semidefinite relaxation fails to deliver satisfactory outcomes. In order to solve this, we propose a nonsmooth method that behaves well in several scenarios. Numerical evaluations in different spectrum sharing scenarios, which show the performance of our method, are provided.Peer ReviewedPostprint (author's final draft

The Decade 1989-1998 in Spanish Psychology: An Analysis of Research in Statistics, Methodology, and Psychometric Theory.

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Is the DeVries-Rose to Weber Transition Empirically Possible with Sine-Wave Gratings?

Con frecuencia se ha medido la función visual a distintos niveles de iluminancia, bien determinando la agudeza visual para enrejados sinusoidales en función del nivel luminoso o bien determinando la forma en que la sensibilidad a enrejados sinusoidales cambia con la iluminancia. La primera vía de acercamiento ha revelado que la agudeza varía con la iluminancia de acuerdo con una función de dos ramas y un punto de discontinuidad en la transicion de visión escotópica a visión fotópica. Los resultados obtenidos a través de la segunda vía se han resumido aludiendo a una transición de la ley de DeVries-Rose a la de Weber, según la cual el logaritmo de la sensibilidad aumenta linealmente con pendiente 0.5 a medida que aumenta la iluminancia (para niveles bajos de iluminancia que comprenden el llamado rango de DeVries-Rose) pero luego permanece constante e invariante ante sucesivos incrementos de iluminancia (dentro del llamado rango de Weber). Aquí se evalúa la compatibilidad de los resultados obtenidos en estas dos líneas de investigación. Se parte de las restricciones empíricas impuestas por datos que revelan la forma de la superficie de sensibilidad a enrejados sinusoidales en función de la frecuencia espacial y la iluminancia, y se determina si esas restricciones son compatibles con la descripción que ofrecen las leyes de DeVries–Rose y Weber. El análisis muestra que la ley de DeVries-Rose sólo es posible empíricamente para enrejados sinusoidales de baja frecuencia.Visual functioning at various retinal illuminance levels is usually measured either by determining grating acuity as a function of light level or by determining how sensitivity to sine-wave gratings changes with retinal illuminance. The former line of research has shown that grating acuity follows a two-branch relationship with retinal illuminance, with the point of discontinuity occurring at the transition from scotopic to photopic vision. Results of the latter line of research have summarily been described as a transition from the DeVries-Rose law to Weber’s law, according to which log sensitivity increases linearly with log illuminance with a slope of 0.5 over a range of low illuminances (the DeVries-Rose range) and then levels off and does not increase with further increases of illuminance (the Weber range). This paper aims at determining the compatibility of the results of these two lines of research. We consider empirical constraints from data bearing on the shape of the surface describing contrast sensitivity to sine-wave gratings as a function of spatial frequency and illuminance simultaneously, in order to determine whether they are consistent with a summary description in terms of DeVries-Rose and Weber’s laws. Our analysis indicates that, with sine-wave gratings, the DeVries-Rose law can only hold empirically at low spatial frequencies

Does time ever fly or slow down? The difficult interpretation of psychophysical data on time perception.

Time perception is studied with subjective or semi-objective psychophysical methods. With subjective methods, observers provide quantitative estimates of duration and data depict the psychophysical function relating subjective duration to objective duration. With semi-objective methods, observers provide categorical or comparative judgments of duration and data depict the psychometric function relating the probability of a certain judgment to objective duration. Both approaches are used to study whether subjective and objective time run at the same pace or whether time flies or slows down under certain conditions. We analyze theoretical aspects affecting the interpretation of data gathered with the most widely used semi-objective methods, including single-presentation and paired-comparison methods. For this purpose, a formal model of psychophysical performance is used in which subjective duration is represented via a psychophysical function and the scalar property. This provides the timing component of the model, which is invariant across methods. A decisional component that varies across methods reflects how observers use subjective durations to make judgments and give the responses requested under each method. Application of the model shows that psychometric functions in single-presentation methods are uninterpretable because the various influences on observed performance are inextricably confounded in the data. In contrast, data gathered with paired-comparison methods permit separating out those influences. Prevalent approaches to fitting psychometric functions to data are also discussed and shown to be inconsistent with widely accepted principles of time perception, implicitly assuming instead that subjective time equals objective time and that observed differences across conditions do not reflect differences in perceived duration but criterion shifts. These analyses prompt evidence-based recommendations for best methodological practice in studies on time perception

Fitting logistic IRT models: small wonder.

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