A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance
of a vibrating crystal of piezoelectric material to create an electrical signal with a precise
frequency.
This frequency is commonly used to keep track of time, as in quartz wristwatches, to
provide a stable clock signal for digital integrated circuits, and to stabilize frequencies
for radio transmitters and receivers. The most common type of piezoelectric resonator
used is the quartz crystal, so oscillator circuits incorporating them became known as
crystal oscillators, but other piezoelectric materials including polycrystalline ceramics
are used in similar circuits.
George Washington Carver (1860s – 1943), was an American botanist and
inventor. He became well-known to the public due to his active promotion of
alternative crops to cotton and methods to prevent soil depletion.
While a professor at Tuskegee Insitutute, Carver developed techniques to improve soils
depleted by repeated plantings of cotton. He wanted poor farmers to grow alternative
crops, such as peanuts and sweet potatoes, as a source of their own food and to improve
their quality of life. The most popular of his 44 practical bulletins for farmers contained
105 food recipes using peanuts. Although he spent years developing and promoting
numerous products made from peanuts; none became commercially successful.
A Yagi–Uda antenna, commonly known as a Yagi antenna, is a directional antenna
consisting of multiple parallel elements in a line, usually half-wave dipoles made of metal
rods.
Yagi–Uda antennas consist of a single driven element connected to the transmitter or
receiver with a cable, and additional elements which are not connected to the
transmitter or receiver: a so-called reflector and one or more directors. It was invented
in 1926 by Shintaro Uda of Tohoku Imperial University, Japan, and (with a lesser role
played by his colleague) Hidetsugu Yagi.
Penicillin is a common antibiotic, used to treat bacterial infections. It was one of the
first to be discovered, and worked well against staphylococci and streptococci. Many
strains of bacteria are now resistant. Chemists keep changing part of its structure in the
effort to keep it working against the bacteria.
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