What is "entrainment"

n. 1 Any of several processes in which a solid or liquid is put into motion by a fluid. 2 # The carrying away of droplets of liquid during violent boiling 3 # The movement of sediment in a stream of water or in a glacier 4 # The mixing of air currents 5 # The mixing of out flowing river water and underlying seawater. 6 (context biology English) The alignment of an organism's circadian rhythm to that of an external rhythm in its environment

Entrainment is the transport of fluid across an interface between two bodies of fluid by a shear induced turbulent flux.

The entrainment hypothesis was first used as a model for flow in plumes by G. I. Taylor when studying the use of oil drum fires to clear fog from aeroplane runways during World War II. It has gone on to be a common model of turbulence closure used in environmental and geophysical fluid mechanics.

Entrainment is important in turbulent jets, plumes and gravity currents and is a topic of current research.

Eductors or eductor-jet pumps are an example of entrainment. They are used onboard many ships to pump out flooded compartments: in the event of an accident, seawater is pumped to the eductor and forced through a jet, and any fluid at the inlet of the eductor is carried along to the outlet and up and out of the compartment. Eductors can pump out whatever can flow through them, including water, oil, and small pieces of wood. Another example is the pump-jet, which is used for marine propulsion. Jet pumps are also used to circulate reactor coolant in several designs of boiling water reactors.

In power generation, this phenomenon is used in steam jet air ejectors to maintain condenser vacuum by removing non-condensible gases from the condenser.

Entrainment is a phenomenon of the atmosphere which occurs when a turbulent flow captures a non-turbulent flow. It is typically used to refer to the capture of a wind flow of high moisture content, or in the case of tropical cyclones, the capture of drier air.

Detrainment is the opposite effect when the air from a convective cloud, usually at its top, is injected in the environment.

Entrainment may refer to:

• Air entrainment, the intentional creation of tiny air bubbles in concrete
• Brainwave entrainment, the practice of entraining one's brainwaves to a desired frequency
• Entrainment (biomusicology), the synchronization of organisms to an external rhythm
• Entrainment (chronobiology), the alignment of a circadian system's period and phase to the period and phase of an external rhythm
• Entrainment (engineering), the entrapment of one substance by another substance
• Entrainment (hydrodynamics), the movement of one fluid by another
• Entrainment (meteorology), a phenomenon of the atmosphere
• Entrainment (physical geography), the process by which surface sediment is incorporated into a fluid flow
• Entrainment (physics), the process whereby two interacting oscillating systems assume the same period
• Lexical entrainment, the process in conversational linguistics of the subject adopting the terms of their interlocutor

Entrainment, within the study of chronobiology, occurs when rhythmic physiological or behavioral events match their period to that of an environmental oscillation. A common example is the entrainment of circadian rhythms to the daily light–dark cycle, which ultimately is determined by the Earth's rotation. The term entrainment is justified because the biological rhythms are endogenous: They persist when the organism is isolated from periodic environmental cues. Of the several possible cues, called zeitgebers (German for 'time-givers', 'synchronizers'), which can contribute to entrainment, bright light is by far the most effective. Exercise may also play a role.

The activity/rest (sleep) cycle in animals is only one set of circadian rhythms that normally are entrained by environmental cues. In mammals, such endogenous rhythms are generated by the suprachiasmatic nuclei (SCN) of the anterior hypothalamus. Entrainment is accomplished by altering the concentration of clock components through altered gene expression and protein stability.

Circadian oscillations occur even in the cells of isolated organs, and it is believed that the master pacemaker in the mammalian brain, the SCN, coordinates the peripheral clocks. Such hierarchical relationships are not the only ones possible: Two or more oscillators may couple in order to assume the same period without either being dominant over the other(s). This situation is analogous to Huygens' pendulum clocks.

The phase of entrainment refers to the relative timing of any circadian event within the objective 24-hour day.

When good sleep hygiene is insufficient, a person's lack of synchronization to night and day can have health consequences. There is significant variation within normal chronotypes' entrainment; it is normal for humans to awaken anywhere from about 5 a.m. to 9 a.m. However, patients with DSPD, ASPD and non-24-hour sleep–wake disorder are improperly entrained to light/dark.

In physical geography, entrainment is the process by which surface sediment is incorporated into a fluid flow (such as air, water or even ice ) as part of the operation of erosion.

Entrainment in the biomusicological sense refers to the synchronization of organisms (only humans as a whole, with some particular instances of a particular animal) to an external perceived rhythm, such as human music and dance such as foot tapping.