A new low-turbulence wind tunnel for animal and small vehicle flight experiments

Our understanding of animal flight benefits greatly from specialized wind tunnels designed for flying animals. Existing facilities can simulate laminar flow during straight, ascending and descending flight, as well as at different altitudes. However, the atmosphere in which animals fly is even more complex. Flow can be laminar and quiet at high altitudes but highly turbulent near the ground, and gusts can rapidly change wind speed. To study flight in both laminar and turbulent environments, a multi-purpose wind tunnel for studying animal and small vehicle flight was built at Stanford University. The tunnel is closed-circuit and can produce airspeeds up to 50 m s^-1 in a rectangular test section that is 1.0 m wide, 0.82 m tall and 1.73 m long. Seamless honeycomb and screens in the airline together with a carefully designed contraction reduce centreline turbulence intensities to less than or equal to 0.030% at all operating speeds. A large diameter fan and specialized acoustic treatment allow the tunnel to operate at low noise levels of 76.4 dB at 20 m s^-1. To simulate high turbulence, an active turbulence grid can increase turbulence intensities up to 45%. Finally, an open jet configuration enables stereo high-speed fluoroscopy for studying musculoskeletal control in turbulent flow.

Preliminary evaluation of a technique for inhibiting intimal hyperplasia: implantation of a resorbable luminal collagen membrane

Pharmacologic control of intimal hyperplasia has been attempted through oral and intravenous administration of smooth muscle cell inhibitors. We report a more direct method of altering arterial healing using a novel bioresorbable membrane that can be applied to the lumen of an artery or anastomosis following endarterectomy or vascular reconstruction. Following a standard balloon injury, the infrarenal aortas of 3 kg female New Zealand white rabbits were opened and a thin membrane composed of collagen/chondroitin 6-sulfate copolymer was sutured to the posterior wall of each artery. Animals were killed at intervals of up to 3 months. All arteries remained patent. By 24 hours the membrane had become infiltrated with fibrin and red blood cells. An inflammatory response ensued and by 8 days the membrane was filled with mononuclear cells. At 3 months only a small remnant of the membrane remained. Intimal hyperplasia developed throughout the injured aorta. However, the hyperplastic response beneath the membrane was no greater than that observed in the adjacent injured aorta. A bioresorbable membrane can be sutured into the lumen of a small-diameter vessel without inducing thrombosis and without locally increasing intimal hyperplasia. A prosthesis of this type might be used to deliver inhibitors of smooth muscle cell proliferation and migration to the injured arterial wall.