An experimental and theoretical phenomenological study of accelerating–decelerating bubbles, condensing in an immiscible liquid, was conducted. The system consisted of a column of water, and bubbles of freon-113, 4–5×10−3 m in diameter. Shadowgraphing of the process has illustrated the wake formation behind the bubble, wake shedding, forward movement of vortices, and envelopment of the decelerating bubble in its wake. The bubble size, shape, and path were videotaped and analyzed for the collapse rate, and the instantaneous position. The visualized hydrodynamic phenomena provided a phenomenological basis for the theoretical formulations. The theoretical model postulated an eccentrically positioned vapor sphere in the collapsing bubble, a boundary layer and wake over the accelerating bubble, and a concentric vorticular envelope around the decelerating bubble. The theoretical–phenomenological predictions compared well with experiment.
The increased usage of new technologies in combat requires measuring tools and guidelines that will enable maximal compatibility between technology and users' needs. Specifically, using video feeds retrieved by dismounted soldiers from different types of unmanned aerial vehicles (UAVs) may affect the efficiency level of using such machines. This work follows our previous studies on the type (e.g. size) of displays required by dismounted soldiers to process video feed from UAVs. Twenty two former infantry soldiers with no experience using UAV video feed participated. Three displays were examined using two video feed types (MALE and Mini UAVs) in four different task types (description, direction, orientation, and response). Performance and subjective data were collected. Results show no effect (only some trends) for display type, but significant effect for the interaction between video feed type and task type and display type.
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