Towards high-level execution primitives for and-parallelism: preliminary results

Most implementations of parallel logic programming rely on complex low-level machinery which is arguably difflcult to implement and modify. We explore an alternative approach aimed at taming that complexity by raising core parts of the implementation to the source language level for the particular case of and-parallelism. Therefore, we handle a signiflcant portion of the parallel implementation mechanism at the Prolog level with the help of a comparatively small number of concurrency-related primitives which take care of lower-level tasks such as locking, thread management, stack set management, etc. The approach does not eliminate altogether modiflcations to the abstract machine, but it does greatly simplify them and it also facilitates experimenting with different alternatives. We show how this approach allows implementing both restricted and unrestricted (i.e., non fork-join) parallelism. Preliminary experiments show that the amount of performance sacriflced is reasonable, although granularity control is required in some cases. Also, we observe that the availability of unrestricted parallelism contributes to better observed speedups.

Terapia por láser de baja potencia: consideraciones óptico-físicas y biológicas determinantes en su aplicación clínica.

Objetivos : Analizar la distribución de energía en un tejido cuando se emplea terapia por láser de baja potencia y estudiar las especificaciones mínimas de equipos de terapia láser para estimar la dosis. Material y métodos: Se ha empleado el método de Monte Carlo para obtener la distribución de energía absorbida por la piel para dos tipos de láser y la teoría de la difusión para estimar la longitud de penetración y el recorrido libre medio. Se ha estudiado la variación de esa distribución en función de la raza (caucásico, asiático, afroamericano) y para dos localizaciones anatómicas distintas. Se ha analizado la información facilitada por diversos fabricantes de equipos comerciales para determinar si es necesario adaptar la dosimetría recomendada. Resultados: La radiación láser infrarroja (810nm) se absorbe mayoritariamente en un espesor de piel de 1,9±0,2mm para caucásicos, entre 1,73±0,08mm (volar del antebrazo) y 1,80±0,11mm (palma) para asiáticos y entre 1,25±0,09mm (volar del antebrazo) y 1,65±0,2mm (palma) para afroamericanos. El recorrido libre medio de la luz siempre es menor que 0,69±0,09mm. Para los equipos comerciales analizados la única característica geométrica del haz láser que se menciona es la superficie que oscila entre 0,08 y 1cm2, pero no se especifica cómo es la distribución de energía, la divergencia del haz, forma de la sección transversal, etc. Conclusiones:Dependiendo del equipo de terapia por láser de baja potencia utilizado, el tipo de paciente y la zona a tratar, el clínico debe adaptar las dosis recomendadas. Abstract: Objectives: To analyze the distribution of energy deposited in a tissue when this is irradiated with a low power laser and to study the minimum characteristics that manufacturers of low power laser therapy equipments should include to estimate the dosage. Material and methods: Monte Carlo simulation was performed to determine the absorption location of the laser energy. The diffusion theory was used to estimate penetration depth and mean free path. Variation of this distribution was studied based on three different skin types (Caucasians, Asians and Afroamericans) and for two different anatomic locations: palm and volar forearm. Information given by several manufactures of low power laser therapy equipments has been analyzed. Results: Infrared (810 nm) laser radiation is mainly absorbed in a skin layer of thickness 1.9±0.2mm for Caucasians, from 1.73±0.08mm (volar forearm) to 1.80±0.11mm (palm) for Asians, and from 1.25±0.09mm (volar forearm) to 1.65±0.2mm (palm) for Afroamericans. The light mean free path is lower than 0.69±0.09mm for all cases. The laser beam characteristics (beam shape, energy distribution on a transversal section, divergence, incidence angle,etc.) are not usually specified by the manufacturers. Only beam size (ranging from 0.08 to 1cm2) is given in some cases. Discussion and conclusions: Depending on the low power laser therapy equipment, on the patient and on the anatomic area to be treated, the staff should adapt the recommended dosage for each individual case.