Mass concrete sections and the maturity concept

The 28 day strength of concrete cylinders cured under standard laboratory conditions can now be reliably predicted at early ages by use of (a) the Modified Boiling Test or (b) the Autogenous Curing Test. The availability of early strength indicators for concrete can be used to great advantage during construction provided these strengths can be related to the strength of the structural elements.To permit an estimate to be made of the strength of in-place concrete on structures appurtenant to the Welland Channel By-pass, the temperature rise of the structural elements was monitored with an automatic 16 point recording potentiometer. The time temperature curve of the in-place concrete was compared to that of 6 in. by 12 in. (150 mm by 300 mm) concrete cylinders taken during casting of the structure and cured autogenously for 48 h, thus permitting an estimate of the in-place concrete strength to be made from the results of the 48 h autogenous strengths.On the basis of the in-place concrete strength estimates, decisions were made regarding the application of post tensioning forces and/or the removal of formwork and supporting shoring.

Freezing Point Determination in Immature Stages of Insects

Conventional and modified methods of obtaining supercooling points of immature stages of insects have been utilized in studies of the cold-hardiness of the European pine shoot moth and the European pinesawfly. A method has been developed to permit visual observation of the freezing process of more than one specimen at a time. A freezing chamber consisting of a hole one inch in depth and one-half inch in diameter is located in the upper end of an aluminum rod partially submerged in a dry ice-alcohol mixture. A small filter paper disc, used as the insect platform, rests upon a #40 copper-constantan thermocouple located near the base of the freezing chamber. The thermocouple enters the chamber through a hole in the wall after several circuits around the circumference of the rod to prevent temperature anomalies attributable to thermal conduction within the wire. The thermocouple is connected to a sensitive recording potentiometer. The wall of the freezing chamber is blackened to prevent reflection of light from obscuring the view of the freezing process, through a binocular microscope mounted above the freezing chamber. The moment of freezing is readily recorded on the temperature trace provided by the potentiometer. At a cooling rate of approximately 5°F. per minute, a correction factor of 2.5°F. must be added to the indicated freezing point to obtain the actual temperature at the surface of the platform. When this correction is applied, the results provide data applicable to statistical analysis of freezing point determinations.

NOTE ON A MULTI-CHANNEL INTEGRATOR FOR A RECORDING POTENTIOMETER

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Potential difference across the pyloric antrum

Previous work has shown the presence of a potential difference (PD) across the fundic portion of the stomach and a smaller PD across the pyloric antrum. All of the reported measurements on the pylorus have been performed with in vitro techniques. The magnitude of the PD across the pyloric antrum was determined when its blood supply was intact. Isoelectric electrodes were placed opposite each other across the wall with isotonic saline agar making contact with the surfaces. The PD's were measured with a recording potentiometer. The average PD (mucosa negative) across the fundus, pyloric antrum and duodenum was 64 mv, 48 mv and 11 mv, respectively. There was a steep gradient of PD at the duodenal-pyloric junction. The PD of the pylorus arises from its own inherent electromotive forces. The PD like that of the fundus declines rapidly following interruption of the blood supply. The injection of Mecholyl results in a reversible decrease in the fundic potential and relatively little change in the pyloric PD.