Fire ant rafts elongate under fluid flows.

Fire ants survive flash floods by linking their bodies together to build waterproof rafts. Most studies of fire ant rafts consider static water conditions, but here, we consider the influence of flow. In particular, when floating on shallow water, the raft can run aground on vegetation, generating stresses in the raft as the water continues to flow around it. In this combined experimental and numerical study, we film the 10 h response of a fire ant raft caught on an anchor and subjected to water flows of 6 cm s-1. In this situation, ant rafts elongate from circular to more streamlined shapes, doubling in aspect ratio before eventually contracting back into smaller circular shapes as they enter dormancy. Ants in upstream regions of the raft exhibit less exploration activity than those downstream, suggesting that ants migrate to areas of lower fluid stress. While the raft is rough, hydrophobic, and heterogeneous in height, we may gain some insight by performing both fluid-structure interaction and agent based simulations on smooth rafts. Elongation to the degree observed is associated with a 48% drag reduction. Moreover, a purely elastic raft does not elongate, but conversely increases its bluff body cross-sectional area. We conclude that ant raftsmust reconfigure to generate the elongated shape observed. This work may provide insights into designing intelligent robotic swarms that can adapt to fluid flows.

Changes in Tongue Area, Pharyngeal Area, and Pharyngeal Airway Velocity after Correction of Mandibular Prognathism.

This study aimed to investigate the correlation between the amount of mandibular setback, and the related changes of the tongue area, pharyngeal area, and pharyngeal airflow velocity. Twenty-five patients treated for mandibular prognathism, and serial cephalograms were obtained (T1: preoperation, T2: more than one year postoperation). The postoperative area of the tongue, pharyngeal airway space, and pharyngeal airflow velocity were investigated. Statistical analysis was performed with the Student t-test and Pearson correlation. The amount of mandible setback was significant after surgery (12.8 mm; p < 0.001). The pharyngeal area was significantly reduced 115.5 mm2 (p = 0.046). There was a slight reduction of the tongue area (43.2 mm2; p = 0.305) and an increase of pharyngeal airflow velocity (0.3 m/s; p = 0.133). The Pearson correlation coefficient test showed no statistical significance among the amount of horizontal setback and vertical movement of the mandible, such as the reductions in the tongue area, the pharyngeal airway space, and the increase in pharyngeal airflow velocity. Larger amounts of mandibular setback caused a significant reduction of pharyngeal airway area, but without significant changes of the tongue area and pharyngeal airflow velocity.