A train is approaching a signal tower at a speed of 40m/s. The train engineer sounds the 1000-Hz whistle, while a switchman in t
he tower responds by sounding 1200-Hz siren. THe air still and the speed is 340m/s. What is the frequency of the train whistle tone that is heard by the switchman? 300/340x1000Hz
380/340x1000Hz
340/300x1000Hz
1000Hz
340/380x1000Hz
New research reveals that glycans -- branched sugar molecules found in mucus -- can prevent bacteria from communicating with each other and forming infectious biofilms, effectively rendering the microbes harmless.