A constant-frequency ultrasonic phase method for monitoring imperfect adherent/adhesive interfaces.

A primary mechanism of adhesive bond failure is a degradation of the adherent/adhesive interfacial stiffness from unwanted contamination or exposure to those environmental factors, which reduce adhesion quality. Substantial research has been conducted on the assessment of adhesively bonded structures and the detection of "kissing" bonds. Advanced ultrasonic assessment methods to interrogate bonded joints and measure interfacial stiffness using a distributed spring interface model have been developed.

Swept-frequency ultrasonic phase evaluation of adhesive bonding in tri-layer structures.

As modern aerospace and automotive designs continually strive for higher performance, and thus rely on advanced composite structures where adhesive bonding is a preferred method of joining, the need for a robust quantitative nondestructive bond strength measurement method has increased. As such, advanced nondestructive evaluation methods have been researched for increased sensitivity to weak interfacial bonding and ultimately to detect "kissing" bonds. In this work, a phase-based method for interrogating bonded joints and detecting weak adhesion is developed by using swept-frequency phase measurements of ultrasonic waves reflected from an adhesive joint and modeling adhesive interfaces as a distributed spring system.

A digital, constant-frequency pulsed phase-locked-loop instrument for real-time, absolute ultrasonic phase measurements.

A digitally controlled instrument for conducting single-frequency and swept-frequency ultrasonic phase measurements has been developed based on a constant-frequency pulsed phase-locked-loop (CFPPLL) design. This instrument uses a pair of direct digital synthesizers to generate an ultrasonically transceived tone-burst and an internal reference wave for phase comparison. Real-time, constant-frequency phase tracking in an interrogated specimen is possible with a resolution of 0.

Rabbit gut-associated lymphoid tissue. Major pathway for thoracic duct lymphocyte circulation.

The demonstration of a preponderance of T cells in the thoracic duct lymph of rabbits prompted us to initiate cytokinetic studies using both uridine- and thymidine-labeled thoracic duct lymphocytes (TDL). Rabbits received intravenous injections of 8 to 11 X 10(8) autologous or allogeneic TDL, 95 per cent of which had incorporated 3H-uridine during a 1-hour in vitro incubation. Autoradiographs of tissues collected 24 hours after injection of TDL failed to demonstrate any trapping of label in liver or in vivo reutilization of 3H-uridine.