Bladder outlet obstruction at the level of the urethra. It occurs in approximately 1 in every 5000 to 8000 live births and only occurs in males. Since PUV always affects both sides of the urinary tract, patients with posterior urethral valves are at the greatest risk for developing chronic kidney disease and end-stage renal disease due to obstructive uropathy. A ureterocele is a cystic dilation of the end of the ureter that can occur in the bladder and/or in the urethra. It occurs in approximately 1 in every 5000 live births, is most commonly seen in females and involves both ides of the
Ludwieg tube Ludwieg tube A Ludwieg tube is a cheap and efficient way of producing supersonic flow. Mach numbers up to 4 in air are easily obtained without any additional heating of the flow. With heating, Mach numbers of up to 11 can be reached. A Ludwieg tube is a wind tunnel that produces supersonic flow for short periods of time. A large evacuated dump tank is separated from the downstream end of a convergent-divergent nozzle by a diaphragm or fast acting valve. The upstream end of the nozzle connects to a long cylindrical tube, whose cross-sectional area is significantly larger than