Ultrasonic irradiation enhanced cell nucleation : An effective approach to microcellular foams of both high cell density and expansion ratio
In this work, ultrasonic irradiation (UI) was used as the external energy source to assist polystyrene foaming process by using supercritical CO2 as the physical blowing agent. It is shown that by introducing the UI at the very start of foaming, the resultant polymer foam exhibited significant and concurrent increase in cell density, i.e., three orders of magnitude, and expansion ratio, i.e., 1–3 times, compared to those without UI. Further experiments indicate that the enhanced cell nucleation induced by UI was the main reason for this unique phenomenon. This method also provided new insight into the mechanism of cell nucleation.
Ethological communication permits the exchange of context-specific information among mammals. In recent literature, many investigations have been performed on behavioral responses but little is known about neurophysiological pattern activation. In this study we investigated neuron patterns in response to ultrasound vocalizations, mapping the auditory cortex in order to find the specific activation area which best fits with perceived vocalization in rats. Receptive fields were directly reached through implanted electrodes in order to record the ultrasound information into the auditory system, bypassing sense organs. Techniques based on Principal Component Analysis and statistical analysis were used to investigate the tonotopic organization exploiting local field-potential classifications. The results, according to the sensitivity index, identified two tonotopic fields with a gradient from high-to-low best frequency using unsupervised classification algorithm.