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.
Electronic mouse repellents operate under the idea of using high-frequency sounds to drive mice away from food sources and nesting grounds within human homes. Sonic or ultrasonic devices have been touted as repellents for everything from roaches to insects to rodents, specifically rats and mice.There are multiple brands of these electric devices that are said to emit either a sonic or ultrasonic wave, which these pests allegedly find irritating.ome are sold specifically to repel rodents. However, there is little data that these devices repel insects or are effective in rodent control. Rats and mice emit high-pitched sounds and may communicate using these sounds. Devices that use sound that humans can hear typically have no effect on the rodents.