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Summary1. The time course and concentration-response relationship of amylase release from pieces of guinea-pig pancreas in vitro in response to bethanechol and pancreozymin was determined. 2. Removal of Ca++ from the medium had no effect on basal amylase release but abolished the stimulating effect on release of bethanechol. 3. Elevation of the concentration of Mg++ in the medium increased basal amylase release and reduced the response to bethanechol. 4. Elevation of the concentration of K+ in the medium increased amylase release; this effect was blocked by a concentration of atropine which blocked also the response to bethanechol. 5. Cyclic AMP, dibutyryl cyclic AMP and theophylline failed to stimulate amylase release. Pancreatic cyclic AMP concentrations were found not to be increased by bethanechol, pancreozymin or an elevated concentration of K+ in the medium. 6. Colchicine had no effect on basal amylase release or the response to bethanechol or pancreozymin. 7. It is concluded that the coupling of stimulus to secretion involves ionic control but that neither cyclic AMP production nor microtubular mechanisms play a major role in controlling exocytosis in the pancreatic acinar cell. These findings are discussed in relation to the stimulus-secretion coupling processes in other cells.

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Nowadays, a variety of civil, aeronautic or mechanical engineering structures need regular inspections. While nondestructive testing has become state of the art, there is a trend towards online testing on demand using built-in sensors. A vast amount of in-service monitoring, as part of structural health monitoring, uses piezoelectric elements. Their deployment requires a control of the sensor performance in order to prevent false alarm. Several kinds of damage can influence the sensor performance, for example, degradation of piezoceramic or adhesive, debonding or breakage of the element. Therefore, this paper aims to detect damage of circular piezoelectric elements and their bonding layers during in-service monitoring. For this purpose, a local method, using the coupled electro-mechanical admittance, is proposed. However, changing environmental and operational conditions such as temperature have an effect on the measured quantities, masking the damage. To cope with this, the dynamic behaviour of an attached piezoelectric element including temperature trends is modelled to enable physics-based temperature compensation. This novel combination of an improved analytical model, updated according to impedance measurements, realizes a method less dependent on experimental baseline data, than the sole comparison of experimental data, established in many monitoring systems. By comparison with experimentally obtained electro-mechanical susceptance the physical model of circular piezoelectric elements is validated. The feasibility of the proposed method is presented employing experimental data of piezoelectric elements mounted on aluminium coupons, partly damaged with degradation and sensor breakage. The application produces promising results, detecting the created defects.