A total of 227, or roughly one out of every five teachers who reported to city schools for the first day of school last year, were no longer teaching in the system on Sept. 5, when the schools kicked off the 2006-07 school year. More than half of those -- 138 -- had resigned or left of their own will, and 46 retired.
Ultrasound and Arthropod Pest Control (2001), an extensive Kansas State University study, confirmed that ultrasonic sound devices do have both a repellent effect as well as reduces mating and reproduction of insects. However, the results were mixed, and ultrasonic sound had little or no effect on some pests.ome animals, such as bats, dogs, and rodents, can hear well into the ultrasonic range. Some insects, such as grasshoppers and locusts, can detect frequencies from 50,000 Hz to 100,000 Hz, and lacewings and moths can detect ultrasound as high as 240,000 Hz produced by insect-hunting bats.
The claim is that these devices drive pests out of a room, or structure, by a combination of electromagnetic, sonic and/or ultrasonic energy. The idea is that the high energy waves are repellent to the various pests -- everything from cockroaches to mice.ome claim to repel insects, spiders, and rodents by ultrasonic, or very high pitched, sound. Others claim to produce an electromagnetic field that is repellent while newer devices add ionic air cleaning.