Sound amplification by stimulated emission of radiation phenomenon, known as the Larsen effect, is the result of a positive feedback. In general, every oscillator consists of three main parts. These are the power source or pump, the amplifier and the positive feedback leading to the output. The corresponding parts in a SASER device are the excitation or pumping mechanism, the active (amplifying) medium, and the feedback leading to acoustic radiation. Pumping can be performed, for instance, with an alternating electric field or with some mechanical vibrations of resonators. The active medium should be a material in which sound amplification can be induced. An example of a feedback
A Changed Man and Other Tales A Changed Man and Other Tales A Changed Man and Other Tales is a collection of twelve tales written by Thomas Hardy. The collection was originally published in book form in 1913, although all of the tales had been previously published in newspapers or magazines from 1881 to 1900. There are eleven short stories and a novella "The Romantic Adventures of a Milkmaid". At the end of the book there is a map of the imaginary Wessex of Hardy's novels and poems. Six of the stories were published before 1891 and therefore lacked international copyright protection when the collection began