Using a pulse reflection technique an ultrasonic system has been
developed to monitor in situ the coagulation process of rennetted milk. The
velocity and attenuation of ultrasonic waves through coagulating milk were
continuously monitored. The observed changes in ultrasonic velocity during
coagulation were used to predict the coagulation time. The coagulation time is
indicative of the transition from the enzymatic phase to the physicochemical
phase. The determination of coagulation time has a decisive role in
determining the qualities of the end product in cheesemaking.
The performance of unhydrogenated soybean oil (USBO) and partially hydrogenated soybean oil (PHSBO) was evaluated by comparing their frying stability. Ultrasonic velocity was used to evaluate the oils. Measurements of free fatty acids (FFA) and total polar compounds (TPC) are typical indexes of oil degradation. Oils were heated at 180 °C for periods of 8 h per day for 4 consecutive days. The results from the ultrasonic analyses show different influences of thermo-oxidation on USBO and PHSBO. The ultrasonic measurements had strong correlations with chemical changes. Consequently, the ultrasonic method is useful to obtain information on the quality of the used frying oils.<br><br>La eficacia de aceites de soja sin hidrogenar (USBO) y aceites de soja parcialmente hidrogenado (PHSBO) fue evaluada por comparación de sus estabilidades de fritura. La velocidad ultrasónica fue usada para evaluar los aceites. La medida de ácidos grasos libres (FFA) y compuestos polares (TPC) son típicos índices de degradación de aceites. Los aceites fueron calentados a 180 °C en periodos de 8 h por día durante 4 días consecutivos. Los resultados del análisis ultrasónico muestran diferentes influencias de termooxidación en USBO y PHSBO. Las medidas ultrasónicas tuvieron una fuerte correlación con cambios químicos. Consecuentemente, el método ultrasónico es útil para obtener información en la calidad de aceites de fritura usados
A non-invasive ultrasonic method was used to control the change in physical properties of milk gel and the syneresis, which is an essential step in the manufacture of cheese. The velocity and the attenuation were recorded for ten hours. They provide a good indicator of syneresis occurring. The firmness of the milk gel increases with the variation in velocity (ΔV). The effects of the temperature, calcium chloride and rennet concentration on the syneresis were studied.
This paper presents a study of the group velocity dispersion of some circumferential waves propagating around an elastic tube. The dispersive character of the circumferential waves is theoretically known, but the experimental measurement of the group velocity in a dispersive medium is still a complex operation. We have determined the characteristics of the circumferential wave dispersion for aluminium and steel tubes using a time-frequency representation. Among these time-frequency techniques, the Wigner-Ville distribution (WVD) is used here for its interesting properties in terms of acoustic applications. The WVD is applied to the analysis of the dispersion of S0 symmetric and A1 antisymmetric circumferential waves propagating around a tube with a radii ratio equal to 0.95 (internal radius:external radius). This allowed us to determine their group velocities and reduced cutoff frequencies. The results obtained are in good agreement with the calculated values using the proper modes theory.
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