Transitional-turbulent spots and turbulent-turbulent spots in boundary layers.

Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a [Formula: see text] vortex and then, a hairpin packet. Long streak meandering does occur but usually when a streak is infected by a nearby existing transitional-turbulent spot.

Methylphenidate improves aspects of executive function in African American children with ADHD.

Objective: The undertreatment of ethnic minority children with ADHD prompted a study on the effects of methylphenidate (MPH) on the executive functions of African American children with ADHD.

Method: Nineteen African American children with ADHD are tested on the Tower of Hanoi (TOH) and the Paired Associates Learning Task (PAL) in a double-blind crossover acute challenge of MPH and placebo.

Results: Under MPH, TOH rule breaks decrease, especially in the second testing session, and TOH planning time increases, particularly for incorrect solutions; PAL recall in the final learning trial improves with MPH.