Briefly discuss the physics involved in the process of entrainment and
what it is primarily used for in health care

Hi viv2,

Entrainment has been applied to a number of different processes,
including electrical pulses (mentioned by xarqi below), air and fluid
flow, and homeopathic health (esp. circadian rhythms).  The general
idea is that a strong action or force (be it a physical, mental, or
electical one) will influence a weaker one to "pull" it into
synchronicity.  In electricity, where the main health applications
appear to be, this is when two waves/pulses of different frequencies
become in sync with each other.  Usually the stronger wave/pulse will
force the weaker one to adapt.  You have probably experienced this
phenomenon at the theater or a concert when everyone ends up clapping
at the same time - in rhythm.  Think of how hard it is to clap off
that rhythm.  What you are experiencing is the pull of entrainment!

The American Heritage Dictionary definition of "entrain": "To pull or
draw along after itself."

I mentioned the air/fluid flow above because the EPA and NIEHS are
very interested in building design and other structures that could
cause ill-health due to entrainment or re-entrainment of wastewater
and waste air.  This happens when the intake systems are too close to
the output areas, such that the air/water that was just released is
sucked back into the system.

There is a lot of interest in the concept of entrainment as a
philosophy for holistic medicine and health.  The Cell Tech
International "Journey to Better Nutrition" discusses this in some
detail: http://www.celltech.com/BetterNutrition/entrainment.asp

However, the main health use of entrainment is in the altering of
electrical patterns in the brain.  There is some official research
being done on this, but most of the resources available on the web
appear to be alternative medicine approaches to diseases such as
ADD/ADHD, depression, and other mental health issues.

An excellent article on entrainment as used in biofeedback processes
is available from the International Council of Graphic Design
Associates (surprisingly):
Healing with Design and Communications: An Educational Approach 
by Chase A. Rogers
http://www.icograda.org/web/articles/feature-past-single.shtml?pfl=feature-single.param&op2.rf1=89.
 (also online at http://www.jyanet.com/cap/2002/0413fe0.htm)
In particular, read the section on biofeedback - I think it will
answer most of your questions.

Below are just a few of the websites that I found on the web, and
thought were interesting:

Dr. Dwight E. Nelson at the University of St. Thomas is exploring
circadian entrainment in mice
http://www.stthomas.edu/BIOL/RESEARCH/nelson-research.htm
His research seems to focus on the relationship of targeted genetic
and light-period changes to the circadian cycles of rodents. 
Entrainment in this case is referring to the "pull" of light on the
brain activity of the mice.

Hemi-Sync
http://www.hemi-syncsource.bigstep.com/generic.jhtml?pid=17
This is a product (looks kind of like headphones) that "alters states
of consciousness" by feeding an electrical/sound wave into the brain. 
The waves generated by the hemi-sync theoretically entrain the brain's
electrical pulses so that they are more rhythmic (and healthier).

Heart Rhythms and Heart Rate Variability Training
http://home.iprimus.com.au/rboon/HeartRhythmsandHRV.htm
This site discusses the entrainment of the heart's and mind's rhythms
(since they both have electrical pulses) to enhance physical
well-being.  Ms. Boon discusses biofeedback, circadian rhythms, and a
number of other concepts to support her theory of heart/brain
coherence and entrainment.

I hope you find the above sites helpful and interesting.  I found them
using the Google search engine using the following keywords:

entrainment
health
electrical
physics

Yours,

librariankt

Thank you for your work (and thanks to everyone else too!)

Hi viv2-ga: 
Sorry I am answering here. There was no other way to reach you.
This is a comment on your question "Can someone please answer these
questions. Thanks."
I am a commenter, not a Google researcher. I think that there is a
common mistake in the answer 3 that xarqui-ga gave to you. He is
referring to OSMOSIS, not to DIALYSIS (note that in osmosis, is the
water which moves through a membrane; in dialysis some of the
dissolved substances move through the membrane, see below).

He wrote:
"3: Dialysis involves the pasage of water across a semi-permeable
membrane from a region of low solute (salt or protein etc)
colcentration, to one of higher concentration."

That is the definition of OSMOSIS: see
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

"Osmosis: the movement of water molecules from an area of high
concentration to an area of low concentration."

A good definition of DIALYSIS, along some examples of applications of
dialysis in the real world, can be found at 
http://www.facstaff.bucknell.edu/mvigeant/field_guide/Dialysis-spagnola/template.html

Definition: Dialysis is the separation of solutes from a liquid
through a semiperimable membrane based on difference in diffusion
rates.

The solutes separate by passing through a membrane that behaves like a
fibre filter and separation occurs by a sieving action based on the
pore diameter and particle size (i.e. smaller molecules will diffuse
faster than larger molecules). Separation of solutes is determined by
the concentration of the molecules on either side of the membrane; the
molecules will flow from a high concentration to a lower
concentration.

In osmosis, it is only water that moves, in the following direction: 
- from a region of high water concentration to a region of lower water
concentration,
- from a more dilute solution to a more concentrated one 
- from a "weaker" solution to a "stronger" one 
- from a hypotonic to a hypertonic solution. 
http://web.ukonline.co.uk/webwise/spinneret/life/osmdia.htm

Dialysis involves the movement of some, but not all, of the dissolved
substances in a solution. The substance that moves has small
molecules, so these can pass through the pores in the membrane, but
other substances, with larger molecules, cannot escape.

This process occurs normally in the kidney. Substances with small
molecules, such as salts, glucose and urea, continuously pass out of
the blood through a membrane under pressure, but useful substances are
later reabsorbed. Waste substances are then excreted as urine.
http://web.ukonline.co.uk/webwise/spinneret/life/osmdia.htm

Regards,
Tom

My apologies.

Entrainment:
Let's see if I can getthis one right :-)
Entrainment is the spontaneous phase synchronisation of two signals
with the same, or very similar frequencies.
As it may apply to health - well - several possibilities ranging from
the operation of pacemakers, the alteration of brainwaves by music
(apparently), and the synchronisation of our normal circadian cycle
(which runs freely a little slower than daily) with the sun.
See:
http://www.bio.warwick.ac.uk/andrewM/Jo%20Selwood%20site/entrainment.htm
http://www.soundfeelings.com/products/alternative_medicine/music_therapy/entrainment.htm
http://www.schuelers.com/ChaosPsyche/part_1_13.htm