From: LARRY KLAES (ljk4@msn.com)
Date: Thu Apr 11 2002 - 22:33:20 PDT
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Sent: Friday, April 12, 2002 12:46 AM
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Subject: Update 584
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 584 April 9, 2002 by Phillip F. Schewe, Ben Stein, and
James Riordon
INFANT RESPIRATORY DISEASE. Afflicting 10% of all
premature infants, respiratory distress syndrome (RDS) results
from a lack of pulmonary surfactant, a molecular substance that
helps the lung's alveoli (air sacs) do their job of extracting carbon
dioxide from the blood and replacing it with oxygen. The
surfactant prevents the lung's alveoli from collapsing and helps
keep them properly inflated by reducing their surface tension. The
absence of surfactant prevents the alveoli from functioning
properly. In an in-vitro study that may improve treatment of this
sometimes fatal condition, UC-Santa Barbara researchers (Joseph
Zasadzinski, 805-893-4769, gorilla@engineering.ucsb.edu)
measured the viscosity in single-molecule layers of human lung
surfactant lipids similar to those used to treat premature infants
with RDS. The viscosity of the single-molecule layer determines
how quickly the lipids spread over the surface of an air sac.
The researchers found that the single-molecule layers consisted
of islands of two-dimensional lipid crystals (a solid-like sheet of
lipids arranged in a repeating pattern) floating in a continuous sea
of lipids in a more liquid-like state. The relative fractions of area
taken up by crystals and liquids change during the breathing cycle,
as inhalation and exhalation changes the amount of surface area on
which the surfactant can spread. The researchers found that the
viscosity of the single-molecule layer depends greatly on this
relative fraction of crystals and liquids. Below a critical fraction of
crystals, the molecule layer behaves like a liquid, with a low
viscosity and low resistance to spreading. However, as a critical
fraction of crystals is attained, the viscosity changes abruptly and
the single-molecule layer becomes completely rigid and immobile.
Changing the lipid composition can alter the fraction of crystals
in the molecule layer, so it is possible to engineer the surfactant to
have the proper viscosity. The researchers believe that the rapid
transition from liquid to almost rigid is important to keeping the
alveoli open at the end of exhalation, when surface tension forces
would like to empty them completely. These findings should help
researchers formulate better replacement surfactants for treatment
of premature infants with RDS. (Ding et al., Physical Review
Letters, 22 April 2002; text at
http://www.aip.org/physnews/select.)
DIMMING SUPERNOVAS WITHOUT COSMIC
ACCELERATION. Several years ago two different studies of
distant supernovas seemed to suggest that the expansion of the
universe was not slowing but actually accelerating (go to
www.aip.org/physnews/update and see Update 361). One
implication of this would be the existence of some kind of anti-
gravity or "dark energy" responsible for counteracting the mutual
gravitational attractiveness thought to be operating among all the
galaxies. But could there be another explanation for the observed
dimness of distant supernovas? Scientists from Los Alamos and
Stanford say yes, there is. John Terning
(terning@particle.lanl.gov, 505-665-0437), Csaba Csaki, and
Nemanja say that the dimness might arise when photons from the
supernovas turn into axions on their way to Earth. Axions are
hypothetical particles which are thought to account for some of the
asymmetries between left-handed and right-handed things in the
universe. The occasional transformation of a photon into an axion
and back again would be analogous to the oscillation of one
neutrino species into another and back again; in the oscillation
process at least one of the species must have some mass. The
axions would probably have a very low mass, something like 10^-
16 eV. Terning says that the axion hypothesis nicely recreates the
observed supernova luminosity actually observed. A direct search
for axions is underway at the CERN Axion Solar Telescope
(CAST), http://axnd02.cern.ch/CAST/). (Csaki et al., Physical
Review Letters, 22 April 2002; text at
www.aip.org/physnews/select; see also
http://t8web.lanl.gov/people/terning/axion.html)
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