Spring and latch dynamics can act as control pathways in ultrafast systems.

Ultrafast movements propelled by springs and released by latches are thought limited to energetic adjustments prior to movement, and seemingly cannot adjust once movement begins. Even so, across the tree of life, ultrafast organisms navigate dynamic environments and generate a range of movements, suggesting unrecognized capabilities for control. We develop a framework of control pathways leveraging the non-linear dynamics of spring-propelled, latch-released systems. We analytically model spring dynamics and develop reduced-parameter models of latch dynamics to quantify how they can be tuned internally or through changing external environments. Using Lagrangian mechanics, we test feedforward and feedback control implementation via spring and latch dynamics. We establish through empirically-informed modeling that ultrafast movement can be controllably varied during latch release and spring propulsion. A deeper understanding of the interconnection between multiple control pathways, and the tunability of each control pathway, in ultrafast biomechanical systems presented here has the potential to expand the capabilities of synthetic ultra-fast systems and provides a new framework to understand the behaviors of fast organisms subject to perturbations and environmental non-idealities.

Priapism in children with leukemia.

A case of priapism in a child with chronic granulocytic leukemia is presented, and the English literature is reviewed. While common in adult leukemia patients, priapism is rare in children with these neoplasms. Sludging of blood in the corpora cavernosa is almost universally accepted as the mechanism behind the development of painful and persistent erection in these patients. Permanent fibrosis of the cavernosal tissue may not occur in leukemic priapism as it does in other than chronic granulocytic leukemia. Therapy directed toward the priapism is almost uniformly unsuccessful. However, the painful erection will resolve spontaneously in a matter of days with proper treatment of the leukemic process.