Metabolic fate of DHA from regio- and stereospecific positions of triacylglycerols in a long-term feeding trial in rats.

This study investigated the impact of regio- and stereospecific position of docosahexaenoic acid (DHA) in dietary triacylglycerols (TAGs) on the fatty acid composition of tissues and organs in rats. Four-week feeding with TAGs containing DHA in sn-1, 2, or 3 position and palmitic acid in the remaining positions at a daily dosage of 500 mg TAG/kg body weight significantly increased the DHA content in all organs and tissues in rats, except in the brain, where the change in DHA level was not statistically significant. The group fed sn-1 DHA showed a significantly higher content of DHA in the plasma TAG than the group fed sn-3 DHA. The sn-3 DHA group had higher levels of DHA in the visceral fat compared to the sn-1, sn-2, as well as all other groups. This is the first study showing that DHA from sn-1 and sn-3 positions of dietary TAGs have differential accumulation in tissues. The new findings improved the current knowledge on the significance of TAG isomeric structure for the bioavailability and metabolic fate of DHA.

A Frequency-Dependent Dynamic Electric-Mechanical Network for Thin-Wafer Piezoelectric Transducers Polarized in the Thickness Direction: Physical Model and Experimental Confirmation.

This paper is concerned with electric-acoustic/acoustic-electric conversions of thin-wafer piezoelectric transducers polarized in the thickness direction. By introducing two mechanical components with frequency-dependent values, i.e., radiation resistance and radiation mass, into the equivalent circuit of the thin-wafer piezoelectric transducer, we established a frequency-dependent dynamic mechanic-electric equivalent network with four terminals for an arbitrary given frequency, an enhancement from the conventional circuit networks. We derived the analytic expressions of its electric-acoustic and acoustic-electric conversion impulse responses using the four-terminal equivalent circuit to replace the traditional six-terminal equivalent circuit for a thin-wafer transducer with harmonic vibrational motion. For multifrequency electrical/acoustic signals acting on the transducer, we established parallel electric-acoustic/acoustic-electric conversion transmission networks. These two transmission network models have simple structures and clear physical and mathematical descriptions of thin-wafer transducers for electric-acoustic/acoustic-electric conversion when excited by a multifrequency electric/acoustic signal wavelet. The calculated results showed that the transducer's center frequency shift relates to its mechanical load and vibration state. The method reported in this paper can be applied to conventional-sized and small-sized piezoelectric transducers with universal applicability.

Physical Characteristics of and Transient Response from Thin Cylindrical Piezoelectric Transducers Used in a Petroleum Logging Tool.

We report on a transient response model of thin cylindrical piezoelectric transducers used in the petroleum logging tools, parallel to a recently established transient response model of thin spherical-shell transducers. Established on a series of parallel-connected equivalent-circuits, this model provides insightful information on the physical characteristics of the thin cylindrical piezoelectric transducers, i.e., the transient response, center-frequency, and directivity of the transducer. We have developed a measurement system corresponding to the new model to provide a state-of-the-art comparison between theory and experiment. We found that the measured results were in good agreement with those of theoretical calculations.