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.
Today you can get ultrasonic systems with frequencies ranging from 20 to 950 kHz, which one to choose depends on what your cleaning job is, what type of soil is to be removed and how clean your part needs to be. In reality, most systems to day incorporate more than one frequency of ultrasonics.ny ultrasonic tank will clean a part. The determining factor is how clean do you want the part. If you are looking for a level of cleanliness such as laser parts or semiconductor wafers you need to take additional steps. The most common ultrasonic cleaning process consists of 5 steps.