Each case of communicable disease is the result of an orderly progression in. a series of events. This series of events may be described as a three-link chain, each. link representing a factor essential to the transmission of disease. These links (figure 1-1) are: (1) The source of the disease (reservoir) (2) The means by which the disease may be transmitted (mode of.
Radio Waves. Radio waves are a type of electromagnetic (EM) radiation with wavelengths in the electromagnetic spectrum longer than infrared light . They have have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves, radio waves travel at the speed of light. Naturally occurring radio waves are made by lightning or by astronomical objects.
Rayleigh waves, also called ground roll, travel like ocean waves over the surface of the Earth, moving the ground surface up and down. They cause most of the shaking at the ground surface during an earthquake. Love waves are fast and move the ground from side to side. Body waves travel through the Earth. P-waves are the fastest type of seismic wave. As P-waves travel, the surrounding rock is repeatedly compressed and then stretched.