1. A pattern of slow brain waves (alpha waves) in normal people at rest with closed eyes, thought by some to be associated with an alert but daydreaming mind.
2. The normal brainwave in the electroencephalogram of a person who is awake but relaxed.
3. A pattern of smooth, regular electrical oscillations in the human brain that occur when a person is awake and relaxed.

As recorded by the electroencephalograph, alpha waves have a frequency of 8 to 13 hertz.

A type of biofeedback when alpha brain waves (7.5-13.5 cps) are characteristic of relaxed and peaceful wakefulness or the alpha state.

In alpha biofeedback training, the subject receives information on his or her EEG as a means of achieving a state of relaxation.

In one technique, a tone sounds in the absence of alpha waves and disappears when the subject produces alpha waves.

In electroencephalography, rhythmic oscillations in electric potential occurring at an average rate of 10 per second.

A radio wave that is propagated by reflection through the atmosphere by reflections and refractions occurring in the atmosphere: Atmospheric radio waves may include either the ionospheric wave or the tropospheric wave, or both of them.

1. A pattern of electrical waves in the brain of someone who is awake and active.
2. In electroencephalography, a rapid rhythm usually of low voltage, which can be recorded in the motor areas of the brain and sometimes in the frontal regions; especially, during states of stress or anxiety or after the administration of certain drugs such as barbiturates.
3. The second most common waveform occurring in electroencephalograms of the adult brain, characteristically having a frequency from 13 to 30 cycles per second.

It is associated with an alert waking state but can also occur as a sign of anxiety or apprehension.

1. A zone of combustion which travels along a narrow path through a burning substance.
2. A zone of burning propagated or transmitted through a combustible medium.
3. The zoned, reacting, gaseous material formed when an explosive mixture is ignited.

One of the high-amplitude, slow, and regular brain waves that characterize the stages of deep sleep: The delta waves are "deep-sleep waves" that are associated with a dreamless state from which an individual is not easily aroused.

1. A circuit that passes selected frequencies of alternating currents while weakening other frequencies.
2. A network that transmits alternating currents of desired frequencies while substantially attenuating all other frequencies.

A transverse electric wave, transverse electromagnetic wave, or transverse magnetic wave.

A transverse electric wave and a transverse magnetic wave are electromagnetic waves in which the magnetic field vectors are every where perpendicular to the directions of propagation.

1. An intense electromagnetic wave resulting from the coincidence of several waves of different velocities in a nonlinear dispersive medium.
2. An electromagnetic wave of significant intensity that results when waves with different intensities propagate with different velocities in a nonlinear optical medium, and faster-traveling waves from a pulse of light catch up with preceding, slower traveling waves.

1. An oscillation of the electric or magnetic field associated with the propagation of electromagnetic radiation.
2. A wave which consists of both electric and magnetic variation.
3. A wave of electromagnetic radiation generated by the oscillation of a charged particle and characterized by periodic variations of electric and magnetic fields.
4. A wave of energy made up of an electric and a magnetic field which is generated when an electric charge oscillates or is accelerated.

Light waves and radio waves are electromagnetic waves, according to their frequencies and wavelengths.

The primary kinds of electromagnetic waves, ranging from the longest to the shortest wave length, are long radio waves, short radio waves, infrared rays, visible light, ultraviolet light, X-rays, and gamma rays.

1. A device that allows electromagnetic waves of certain frequencies to pass while effectively attenuating (weakening) others.
2. Any device to transmit electromagnetic waves of desired frequencies while substantially reducing the strength of all of the other frequencies.

1. A circularly polarized wave found in a plasma that runs parallel to the magnetic field produced by electric currents outside the plasma.
2. A wave in a plasma that moves parallel to the magnetic field produced by currents outside the plasma at frequencies less than that of the electron cyclotron resonance, and which is circularly polarized, rotating in the same sense as electrons in the plasma; responsible for whistlers.

A whistler is defined as an effect that occurs when a plasma disturbance, caused by a lightning discharge, travels out along lines of magnetic force of the earth's field and is reflected back to its origin from a magnetic point on the earth's surface.

The de Broglie wave, or probability amplitude wave (amount by which a voltage or current changes from zero or an average value), associated with an electron.

A function of the spin orientation and position of one or more electrons, specifying the dynamical state of the electrons.

The square of the function's modulus gives the probability per unit volume of finding electrons at a given position.

1. An electron tube which has mutually interacting streams of electrons with different velocities that cause a signal modulation to change progressively along the length of the electron streams.
2. An electron tube in which stream of electrons having different velocities interact and cause a progressive change in signal modulation along their length.

The wave motion of a plasma (an electrically conductive fluid) in which restoring forces are primarily electrostatic.

A longitudinal compression wave in the ion density of a plasma: An ion-acoustic wave can take place at high electron temperatures and low frequencies, and is effected by a combination of ion inertia and electron pressure.

1. A radio signal transmitted into the sky and reflected back down to earth from the ionosphere.
2. A radio wave that travels upward into space and may or may not be returned to earth by reflection from the ionosphere.
3. A radio wave that is transmitted around the curved surface of the earth by being reflected back to earth by the ionosphere.

A low-voltage occipital wave recorded by electroencephalography during visual activity.

An elastic wave generated by an impulse such as an earthquake or an explosion. Seismic waves may travel either along or near the earth's surface ("Rayleigh" and "Love" waves) or through the earth's interior ("P" and "S" waves).

Waves of Destruction

Earthquakes are said to radiate destruction much like bomb blasts in that seismic waves burst from the underground hypocenter (the point within the earth where an earthquake rupture starts; also known as the focus).

Surface waves consist of heaving waves produced by P and S waves. The P wave is the fastest wave which is generated by the fault rupture and it compresses and stretches the rock area. The S wave is slower but often the more destructive wave as it shakes rock from side to side.

• P waves, which compress and stretch rock, deliver the quake's initial thrust.
• Slower and often more destructive S waves follow, slithering side to side.
• S waves tear buildings off foundations and can churn wet soils into a mixture that acts like quicksand, causing buildings to tilt.
• At ground level, P and S waves produce surface waves that can flatten bridges, crack windows, or simply pass unnoticed.
• Eventually the waves weaken as they roll away from the hypocenter; but the seismic echoes of powerful quakes can resonate across and around the globe

A "Rayleigh wave" is a seismic surface wave causing the ground to shake in an elliptical motion, with no transverse, or perpendicular, motion.

A "Love wave" is a surface wave having a horizontal motion that is transverse (or perpendicular) to the direction the wave is traveling.

A wave generated from a point source; such as, that generated by an underground explosion.

Typical seismic sources; such as, vibrators and air-gun arrays emit elastic waves that are assumed to be spherical waves.

A technology used for automatic identification in which low power microwave radio frequency signals are converted to ultrasonic acoustic signals by a piezoelectric crystalline material in the transponder: Surface acoustic waves were first described by Lord Rayleigh in 1885.

Variations in the reflected signal can be used to provide a unique identity.

SAW appliances are applied in television and radio.

1. A pattern of brain waves having a regular frequency of 4 to 7 cycles per second as recorded by an electroencephalograph, observed during various states of light sleep or arousal.

It occurs naturally in children up to about 12 years of age, but it is considered abnormal in adults.

2. The normal brainwave in the encephalogram of a person who is awake but relaxed and drowsy.

It occurs with low frequency and low amplitude.

3. A relatively high amplitude brain wave pattern between approximately 4 and 9 hertz that is characteristic; especially, of the hippocampus but occurs in many regions of the brain including the cortex.

An electrically operated instrument that indicates voltage standing-wave ratios and is calibrated in voltage ratios.

The ratio of the amplitude of the electric field or voltage at a voltage minimum to that at an adjacent maximum in a stationary-wave system; as in a waveguide, coaxial cable, or other transmission line.