Comparative study of models of impedance boundary conditions in acoustic problems

En este artículo se presentan distintas soluciones para la implementación numérica de condiciones de contorno de impedancia (reactancia local) en problemas acústicos. Para ello se analizan 2 tipos de ecuaciones: las ecuaciones de Euler y la ecuación de ondas, y se estudian diferentes soluciones para los contornos tanto en algoritmos de diferencias finitas en el dominio del tiempo (FDTD) como en algoritmos pseudo-espectrales en el dominio del tiempo (PSTD). El análisis de las distintas propuestas numéricas existentes en la literatura se realiza mediante exhaustivos experimentos numéricos que permiten estudiar el comportamiento absorbente de las distintas condiciones de contorno en función de la frecuencia y del ángulo de las ondas incidentes. Este novedoso estudio comparativo permite al ingenierio acústico escoger el modelo numérico que más se adapte a sus necesidades.In this paper, different implementations of numerical locally reacting boundary conditions are studied for acoustic problems. In this comparative study we analyze two types of equations, the Euler equations and the wave equation. We also analyze both finite-differences time-domain (FDTD) algorithms, and pseudo-spectral time domain (PSTD) numerical schemes. We compare different numerical implementations existing in the literature by means of exhaustive numerical experiments. These numerical experiments allow for the study of the absorbing properties of the different schemes as a function of the frequency and the angle of the incident sound waves. This novel comparative study will help the acoustic engineer in order to choose the proper numerical scheme for his/her simulations.Peer Reviewe

Relativistic Positioning Systems: The Emission Coordinates

This paper introduces some general properties of the gravitational metric and the natural basis of vectors and covectors in 4-dimensional emission coordinates. Emission coordinates are a class of space-time coordinates defined and generated by 4 emitters (satellites) broadcasting their proper time by means of electromagnetic signals. They are a constitutive ingredient of the simplest conceivable relativistic positioning systems. Their study is aimed to develop a theory of these positioning systems, based on the framework and concepts of general relativity, as opposed to introducing `relativistic effects' in a classical framework. In particular, we characterize the causal character of the coordinate vectors, covectors and 2-planes, which are of an unusual type. We obtain the inequality conditions for the contravariant metric to be Lorentzian, and the non-trivial and unexpected identities satisfied by the angles formed by each pair of natural vectors. We also prove that the metric can be naturally split in such a way that there appear 2 parameters (scalar functions) dependent exclusively on the trajectory of the emitters, hence independent of the time broadcast, and 4 parameters, one for each emitter, scaling linearly with the time broadcast by the corresponding satellite, hence independent of the others.Comment: 13 pages, 3 figures. Only format changed for a new submission. Submitted to Class. Quantum Gra

Erratum to “Comparative study of models of impedance boundary conditions in acoustic problems”

Peer Reviewe

Erratum to “Comparative study of models of impedance boundary conditions in acoustic problems”

Peer Reviewe

Ecotypic Adaptation of Medicago Polymorpha along a Gradient in Central Chile: Growth and Seed Production

Relative growth rate, total dry weight and seed yield on 19 accessions of burr medic (Medicago polymorpha L.) from different bioclimatic conditions, were assessed at Cauquenes (35°58’;72°17’W) in the subhumid mediterranean region. The accessions were sown in microplots over raised beds during two years (1991 and 1992), and swards cut periodically at 2, 6 and 10 cm height. There were significant differences between accessions in both total dry weight and seed yield (P \u3c 0.001, Table 1), but the interaction between accessions and height of cutting was not significant (P \u3e 0.05). Total dry weight was positive correlated with days to flowering (r2 = 0.81; P \u3e 0.01)

Indomethacin decreases viscosity of gallbladder bile in patients with cholesterol gallstone disease

There is experimental evidence that inhibition of cyclooxygenase with nonsteroidal anti-inflammatory drugs may decrease cholesterol gall-stone formation and mitigate biliary pain in gall-stone patients. The mechanisms by which NSAIDs exert these effect are unclear. In a prospective, controlled clinical trial we examined the effects of oral indomethacin on the composition of human gall-bladder bile. The study included 28 patients with symptomatic cholesterol or mixed gallstones. Of these, 8 were treated with 3 × 25 mg indomethacin daily for 7 days prior to elective cholecystectomy while 20 received no treatment and served as controls. Bile and tissue samples from the gallbladder were obtained during cholecystectomy. Indomethacin tissue levels in the gallbladder mucosa, as assessed by HPLC, were 1.05±0.4 ng/mg wet weight, a concentration known to inhibit effectively cyclooxygenase activity. Nevertheless, no differences between the treated and untreated groups were found in the concentrations of biliary mucus glycoprotein (0.94±0.27 versus 0.93±0.32 mg/ml) or total protein (5.8±0.9 versus 6.4±1.3 mg/ml), cholesterol saturation (1.3±0.2 versus 1.5±0.2), or nucleation time (2.0±3.0 versus 1.5±2.0 days). However, biliary viscosity, measured using a low-shear rotation viscosimeter, was significantly lower in patients receiving indomethacin treatment (2.9±0.6 versus 5.6±1.2 mPa.s; P < 0.02). In conclusion, in man oral indomethacin decreases bile viscosity without alteration of bile lithogenicity or biliary mucus glycoprotein content. Since mucus glycoproteins are major determinants of bile viscosity, an alteration in mucin macromolecular composition may conceivably cause the indomethacin-induced decrease in biliary viscosity and explain the beneficial effects of nonsteroidal anti-inflammatory drugs in gallstone disease

Inicio de una investigación de diseño sobre el desarrollo de competencias numéricas con niños de 4 años

En esta investigación de diseño sobre el desarrollo de competencias numéricas, describimos el comienzo de un taller de resolución de problemas con niños de 4 y 5 años. Aspiramos a lograr una complementariedad metodológica al incorporar, dentro de la investigación de diseño, el uso del Test de Competencia Matemática Básica (TEMA-3). Con él pretendemos evaluar el desarrollo de las competencias numéricas de los niños durante el curso. Además, dado que uno de los objetivos de la investigación es el desarrollo del currículo de Educación Infantil, a través de la elaboración del taller, deseamos valorar la idoneidad del TEMA-3 para un posible estudio posterior sobre la eficiencia de la intervención a través del taller