.comment-link {margin-left:.6em;}

2Physics Quote:
"Lasers are light sources with well-defined and well-manageable properties, making them an ideal tool for scientific research. Nevertheless, at some points the inherent (quasi-) monochromaticity of lasers is a drawback. Using a convenient converting phosphor can produce a broad spectrum but also results in a loss of the desired laser properties, in particular the high degree of directionality. To generate true white light while retaining this directionality, one can resort to nonlinear effects like soliton formation."
-- Nils W. Rosemann, Jens P. Eu├čner, Andreas Beyer, Stephan W. Koch, Kerstin Volz, Stefanie Dehnen, Sangam Chatterjee
(Read Full Article: "Nonlinear Medium for Efficient Steady-State Directional White-Light Generation"
)

Sunday, September 25, 2005

Force & Matter Wave

Background of this report:
What is matter wave? The idea that atoms behave as waves as well as particles
goes back to 1924. They're called "de Broglie waves" for early 20th-century French
quantum physicist Prince Louis-Victor de Brogli, who first proposed the concept of
atom waves. Physicists have grappled with the dual wave-particle nature of atoms
for decades and, in the 1990s, they began chilling atoms to near absolute zero and
studying the wave properties of atoms in detail. The de Broglie wavelength is Planck
Constant [6.626X10^(-34) Joule-sec] divided by the momentum (mass X velocity)
of a particle.
What is van der Waals force? All atoms and molecules exhibit weak, short-
range interactions for one another. These forces are responsible for the condensation
of gases into liquids and the freezing of liquids into solids despite the absense of ionic,
covalent or metallic bonding mechanisms. The familiar aspects of behavior of matter
in bulk such as friction, surface tension, viscosity, adhesion, cohesion and so on also
arise from vander Waals forces. The van der Waals attraction between 2 molecules
at distance 'd' apart is proportional to 1/d^7 (^ stands for 'to the power of') and so is
significant only for molecules very close together.

Report: University of Arizona physicists
have directly measured how close
speeding atoms can come to a surface
before the atoms' wavelengths change.
This is a first, fundamental measurement
that confirms the idea that the wave of
a fast-moving atom shortens and
lengthens depending on its distance
from a surface, an idea first proposed by
pioneering quantum physicists in the late
1920s.

UA optical sciences doctoral candidate
John D. Perreault (right in picture) and
UA assistant professor of physics
Alexander D. Cronin (left in picture)
report the experiment in the Sept. 23
Physical Review Letters. You can read
the paper here.

Perreault and Cronin found that atoms
closer than 25 nanometers to a surface
are very strongly attracted to the
surface because of the van der Waals
interaction -- so strongly that the atoms are accelerated with the force of a million g's.
A "g" is a term for acceleration any object on earth feels due to gravity (about 9.8 meter/second^2). A roller coaster rider might feel 3 to 4 g's for brief moments during
a ride. Fighter pilots can experience accelerations of up to 8 g for brief periods during
tactical maneuvers, but can black out if subjected to 4 to 6 g's for more than a few
seconds.

The measurement tells nanotechnologists how small they can make extremely tiny
devices before a microscopic force between atoms and surfaces, called van der Waals
interaction, becomes a concern. The result is important both for nanotechnology,
where the goal is to make devices as small as a few tens of billionths of a meter, and
for atom optics, where the goal is to use the wave nature of atoms to make more
precise sensors and study quantum mechanics.

Source of report: Univ of Arizona Original news release

Labels: ,


2 Comments:

At 7:16 PM, Anonymous Anonymous said...

"Blogs Get People Excited," Media Anti-Censorship Handbook Warns
"Blogs get people excited. Or else they disturb and worry them. Some people distrust them.
While I was surfing I discovered your blog! If you are interested, stop by my alimta mesothelioma pemetrexed treatment related site. You may find it of interest.

 
At 9:12 PM, Blogger Steve Austin said...

Enjoyable blog. Please check out my washington mesothelioma lawyer. It is all about washington mesothelioma lawyer.

 

Post a Comment

Links to this post:

Create a Link