SETI bioastro: Fw: Physics News Update 616

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Date: Thu Dec 05 2002 - 13:15:50 PST

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Sent: Wednesday, December 04, 2002 2:40 PM
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Subject: Physics News Update 616

The American Institute of Physics Bulletin of Physics News
Number 616 December 4, 2002 by Phillip F. Schewe, Ben Stein, and James

ACOUSTIC MICROSCOPY. At this week's First Pan American/Iberian Meeting on
Acoustics in Cancun, researchers presented results on acoustic microscopy, a
burgeoning technique that could provide new kinds of medically useful
information on biological tissue. Unlike many other microscopy techniques,
acoustical microscopy can be performed on living tissue and even inside the
body, with the use of small ultrasound probes. And unlike optical microscopy
of biological specimens, acoustic microscopy does not require tissue
In the technique, an ultrasound probe makes contact with a tissue sample,
then yields an image based on how the tissue responds to the ultrasound.
Although the resolution of acoustical microscopy is ultimately limited to
about the cell level, rather than the molecular level (its maximum
resolution is about 0.1 microns, about a hundredth of the width of a red
blood cell), it can provide unique information on a biological tissue's
mechanical properties. For many materials, the mechanical properties have a
wider range of values than the optical properties, so the technique could
come in handy for characterizing Alzheimer's plaques, to name one example.
In principle, an acoustic microscope could also yield quick assessments on
the pathology of skin lesions, without a biopsy and long before other
techniques could provide information.
At the meeting, researchers described how acoustic microscopy is already
advancing cardiology, specifically in the area of intravascular ultrasound
(IVUS), in which a small ultrasound camera is threaded into the body to
detect artery blockage. Using a scanning acoustic microscope to gather
basic data on artery plaque, Yoshifumi Saijo of Tohoku University
( and his colleagues are helping clinicians
better interpret IVUS images. Employing knowledge from acoustical
microscopy, Ton van der Steen ( of the Erasmus
Medical Center in the Netherlands and colleagues have developed a clinical
technique called IVUS elasticity imaging, which can detect vulnerable artery
plaques, a hard-to-catch condition which kills up to 250,000 people every
year in the US alone. (Session 1pBB at the meeting; Background information
at and

internal state of an atom can change by absorbing or emitting bits of light.
In a warm gas or plasma the electrons are frequently shuttling back and
forth from one state to another. Some of these states are longer lived than
others, though, because of extenuating circumstances. For instance, many
transitions from an excited state to the ground state occur in nanoseconds,
but some can last for tens of seconds or longer. Measuring the true lifetime
of the longer-lived of these transitions is difficult for the simple reason
that even when a sample of atoms is dilute, an atom is being bumped so often
that de-excitations come about before the state decays radiatively.
When even the best laboratory vacuum on Earth is still too crowded for
making such delicate measurements, persistent scientists turn to outer
space. Tomas Brage of Lund University (Lund, Sweden), Philip Judge of the
High Altitude Observatory at NCAR (Boulder, CO), and Charles Proffitt of
the Computer Science Corporation (Baltimore, MD) resort to viewing excited
atoms in the planetary nebula NGC3918 where, amid the wreckage of a dying
star, there is enough energy to excite atoms but a density low enough (a few
1000 per cubic centimeter) that mutual pumping isn't a problem (see figure
at Using the Hubble Space
Telescope, the three scientists looked at the emissions of excited triply
ionized nitrogen atoms and observed a lifetime of 2500 seconds for one
particular hyperfine transition. Why is this state so robust? Brage
(, 46-46-222-7724) says that angular momentum can
be preserved in this transition only if, in addition to the electron
emitting an ultraviolet photon, the nucleus itself flips over. Other than
adding to basic knowledge about atomic physics, studies like these should
provide spectroscopic information for studying the deaths of stars. (Brage
et al., upcoming article in Physical Review Letters, probably 16 December.)

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