Using Particle Velocity Sensors In Impedance Tube Measurements

Particle velocity sensors have been developed some years ago, but have not been fully exploited yet. A signal that is proportional to the particle velocity can be very useful in many applications. Current particle velocity sensors have a sensitivity that is highly dependent on frequency and are limited in frequency range. Thus, calibration is more elaborate, and must be integrated into the acoustical measurement procedure. An example is the impedance tube, where there are advantages in using a velocity sensor combined with a microphone (P-U technique). In this paper, the calibration procedures for the P-U and U-U techniques are explained in detail and the expressions for computing the absorption coefficient with the impedance tube using both techniques are reviewed. Both a single particle velocity sensor and a combined pressure/velocity sensor are used in the experiments. Experimental issues such as measurement noise, dynamic range, frequency range, and signal processing are discussed.33893396De Bree, H.-E., An Overview on Microflown Technology (2003) Acta Acustica, 89, pp. 163-172Fahy, F.J., (2001) Foundations of Engineering Acoustics, , Academic PressKinsler, L.E., Frey, A.R., Coppens, A.B., Sandres, J.V., (1982) Fundamentals of Acoustics, , WileyDe Bree, H.-E., A novel technique for measuring the reflection coefficient of sound absorbing materials (2000) ISMA, 25Microflown Tecnology (2003) User Manual and Datashee

Atividade respiratória e produção de etileno em laranja ‘Pêra’ submetida a níveis de processamento mínimo e temperaturas de armazenamento Respiratory activity and ethylene production in ‘Pera’ orange submitted to different levels of processing and storage temperature

O objetivo deste trabalho foi avaliar o efeito de diferentes níveis de processamento e temperaturas de armazenamento na atividade respiratória e na produção de etileno de laranja 'Pêra' minimamente processada. O experimento foi realizado em duas etapas. Na primeira, as laranjas lavadas, sanificadas e resfriadas foram submetidas aos processamentos: a) segmentos; b) inteiras sem albedo; c) inteiras com albedo; d) intactas (controle). As laranjas minimamente processadas foram armazenadas a 6ºC. Na segunda etapa, as laranjas sem albedo foram armazenadas a 1; 11; 21 e 31ºC. A atividade respiratória e a produção de etileno eram determinadas imediatamente após o processamento; a cada hora, durante 10 horas, e a cada 24 horas, durante sete dias. O delineamento utilizado foi o inteiramente casualizado, com seis repetições por tratamento. O processamento interferiu na atividade respiratória, que foi maior imediatamente após o descascamento e a separação dos segmentos. O processamento das laranjas na forma inteira, com ou sem albedo, afetou a atividade respiratória das mesmas somente nas primeiras horas após o processamento. Durante todo período de armazenamento, a atividade respiratória das laranjas a 1º e 11ºC não diferiu entre si, sendo inferior à das laranjas a 21º e 31ºC. O etileno foi detectado apenas nos frutos mantidos a 21º e 31ºC. Os quocientes de temperatura, após a estabilização, eram 1,73 para 1-11ºC, 2,11 para 11-21ºC, e 1,54 para 21-31ºC. A atividade respiratória das laranjas foi influenciada pelos níveis de processamento e pela temperatura de armazenamento.<br>The present work was aimed at evaluating the effect of different processing levels and storage temperatures on the respiratory activity and the ethylene production of minimally processed 'Pera' orange. The study was carried out in two stages. The first consisted of submitting the oranges previously washed, sanitized and chilled to the following processing: a) segments; b) whole without albedo; c) whole with albedo; d) intact (control). The minimally processed oranges were stored at 6ºC. In the second stage oranges without albedo were stored at 1, 11, 21 and 31ºC. The respiratory activity and ethylene production were determined immediately after the closure of the jars, at every hour for 10 hours and at every 24 hours for 7 days. The statistical design was completely randomized with six replicates per treatment. Processing influenced the respiratory activity at greater rates immediately after peeling and segments separation. The processing of oranges, in form with or without albedo affected the respiratory activity only during the first hours after processing. During all storage period, the respiratory activities of oranges at 1º and 11ºC did not differ between them, and were lower than oranges at 21º and 31ºC. Ethylene was only detected in fruits stored at 21º and 31ºC. The temperature quotients after stabilization were 1.73 for 1-11ºC; 2.11 for 11-21ºC and 1.54 for 21-31ºC. The respiratory activity of oranges was influenced by the processing levels and by the storage temperature