Laser ultrasonics system for measurement of speed of sound in gases

In this work we developed a setup to measure the speed of sound in gases using a laser ultrasonics system. The mentioned setup is an all optical system composed by a Q-switched Nd:YAG laser to generate the sound waves, and a fiber optical microphone to detect them. The Nd:YAG provided a laser pulse of approximately 420 mJ energy and 9 ns of pulse width, at the wavelength of 1064 nm. The pulsed laser beam, focused by a positive lens, was used to generate an electrical breakdown (in the gas) which, in turn, generates an sound wave that traveled through a determined distance and reached the fiber optical microphone. The resulting signal was acquired in an oscilloscope and the time difference between the optical pulse and the arrival of the sound waves was used to calculate the speed of sound, since the distance was known. The system was initially tested to measure the speed of sound in air, at room pressure and temperature and it presented results in agreement with the theory, showing to be suitable to measure the speed of sound in gases. © 2012 American Institute of Physics.

Guatemala: proyecciones de poblacion por sexo y edad. 1965-1980

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Panamá: el descenso de la fecundidad según variables socioeconómicas y geográficas 1965-1977

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La mortalidad en los primeros años de vida en países de la América Latina: Chile, 1965-1966

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Colombia: proyeccion de la poblacion economicamente activa, por sexo y grupos quinquenales de edades y de la residencia en cabeceras municipales, a traves de una representacion matricial, para el periodo 1965-1980

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Colombia: el crecimiento de la poblacion 1950-1965. Perspectivas e implicaciones sobre los requerimientos de profesores en el sector de educacion infantil y primaria, 1965-1985

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Colombia: la mortalidad por secciones politico-administrativas, 1963-1965

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Trayectorias de especialización tecnológica: una visión global del intercambio mundial 1965-1987

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Sound pressure level in a municipal preschool

Aim: To evaluate the sound pressure level to which preschool students are exposed. Method: This was a prospective, quantitative, nonexperimental, and descriptive study. To achieve the aim of the study we used an audio dosimeter. The sound pressure level (SPL) measurements were obtained for 2 age based classrooms. Preschool I and II. The measurements were obtained over 4 days in 8-hour sessions, totaling 1920 minutes. Results: Compared with established standards, the SPL measured ranged from 40.6 dB (A) to 105.8 dB (A). The frequency spectrum of the SPL was concentrated in the frequency range between 500 Hz and 4000 Hz. The older children produced higher SPLs than the younger ones, and the levels varied according to the activity performed. Painting and writing were the quietest activities, while free activities period and games were the noisiest. Conclusion: The SPLs measured at the preschool were higher and exceeded the maximum permitted level according to the reference standards. Therefore, the implementation of actions that aim to minimize the negative impact of noise in this environment is essential.