SETI bioastro: Fw: update.577

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Date: Fri Feb 22 2002 - 23:52:35 PST

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Subject: update.577

The American Institute of Physics Bulletin of Physics News
Number 577 February 20, 2002 by Phillip F. Schewe, Ben Stein,
and James Riordon

COLD ANTIHYDROGEN ATOMS might have been made, for
the first time, in an experiment at the CERN lab, where positrons
and antiprotons are brought together in a bottle made of electric
and magnetic fields. Nature allows the existence of antiparticles
but hasn't seen fit to make a lot of them. Modest amounts of
antiprotons show up in cosmic ray showers, and positrons
(antielectrons) are forged in certain high-energy regions of the sky
such as galactic nuclei. But if larger forms of anti-matter like anti-
atoms, anti-stars, and anti-galaxies were plentiful in the visible part
of the universe then we would see the catastrophic gamma ray
glare from places where matter brushes up against antimatter.
Such radiation has not been seen and scientists must make their
own anti-atoms artificially. Making antihydrogen is difficult,
however, because positrons and antiprotons, even when they can
be marshaled and brought near each other, are usually going past
each other too quickly for neutral atoms to form. A few years ago
a dozen or so hot antihydrogen atoms were made on the fly amid
violent scattering interactions at CERN and Fermilab (Updates
253, 297). These did not dally long enough to be studied, but
instead expired quickly when they crashed into detectors that
established the antihydrogen's brief existence.
    At CERN several experiments are devoted to making cold anti-
atoms in a controlled environment amenable to detailed studies.
The main goal here is to determine whether the laws of physics
(gravity, quantum mechanics, relativity, etc.) apply to anti-atoms
the same as they do to regular atoms. At this week's meeting of
the American Association for the Advancement of Science
(AAAS) in Boston, Gerald Gabrielse of Harvard, spokesperson for
the Antihydrogen Trap collaboration (ATRAP: website at, reported new results. In his
experiment 6-MeV antiprotons (themselves made by smashing a
beam of protons into a target) are slowed by a factor of 10 billion
(to an equivalent temperature of 4 K), partly by mixing them with
cold electrons, and then collected in a trap. Positrons from the
decay of sodium-22 nuclei are cooled and collected at the other
end of the device. Eventually about 300,000 positrons are
electrically nudged into the vicinity of about 50,000 antiprotons.
     Gabrielse believes that what sits in his trap isn't entirely a
neutral plasma consisting of coincident positron and antiproton
clouds, and that cold antihydrogen atoms might have formed.
More diagnostic equipment being installed now may settle the
issue in the coming months. A larger version of the ATRAP
apparatus, which might be in operation as early as this fall, should
allow the researchers to introduce some lasers for the purpose of
studying the spectroscopy of prospective anti-hydrogen atoms in
the trap.

Ultrasound is one of the primary tools available for diagnosing
breast lesions, but the final word on the malignancy of a particular
lesion generally requires a biopsy or other invasive technique.
Recently, some researchers have begun developing methods to
classify lesions based on their appearance in ultrasound scans.
Now a group at the University of Chicago (Maryellen Giger, 773-
702-6778, is taking such schemes one
step further by attempting to automate lesion classification with
computer-aided diagnosis (CAD). Clues to a lesion's malignancy
lie in its shape, texture, and the sharpness of its boarder, as well as
its response to the acoustic signals emitted by ultrasound
machines. None of these features alone characterize a given lesion,
therefore both humans and computers must consider multiple
characteristics to make a diagnosis. To test their CAD method, the
researchers studied 400 breast lesion cases that were each
documented with one to six ultrasound images. The method
correctly identified 95% of the malignant lesions and 60% of the
benign lesions.
    In a study presented at the 2001 meeting of the Radiological
Society of North America, the researcher group compared their
CAD method to human diagnostic skills. Although imperfect, the
computer's performance was marginally better than radiologists
who studied the same cases, and only slightly worse than a
comparison group of expert mammographers. In the study, both
community radiographers (who routinely interpret breast images,
but are not experts) and mammography experts improved their
accuracy when they were given access to the CAD data. In fact,
radiologists aided by the CAD system performed as well as the
expert mammographers performed without the aid. Although
some lesions stymie human experts and CAD systems alike when
they rely solely on ultrasound data, advances in computer-aided
diagnosis promise to help reduce the need for biopsies and other
procedures that are frequently both expensive and traumatic. (K.
Horsch, M. L. Giger, L. A. Venta, C. J. Vyborny, Medical Physics,
February 2002)

Physicists at Caltech have created a laser that accomplishes a
highly efficient buildup of coherent light in a small space. Light is
sent from an optical fiber into a 70-micron silica sphere. Here the
light races around the edge of the sphere in a "whispering gallery"
mode. The building up of light within the sphere is characterized
by a parameter referred to as the quality (or Q) value, and in this
case it is several hundred million, a record. The input light can
build up to such an extent that a distortion in the silica glass comes
about, and this engenders light emission. This is an example of a
Raman laser, one which achieves amplification of light by way of
a nonlinear response (the Raman effect) to an intense exciting
field. The advantage of Raman lasers is that they are tunable and
can be used as pumps for other lasers. The disadvantage is that
Raman lasers normally need a high-power input to work at all. But
the Caltech result achieves this end at power levels (tens of
microwatts) 1000 times less than other Raman lasers, and in a
much smaller package. Besides offering tunable microlasing
capabilities, the nonlinear properties of light in the silica
microspheres offer new ways of
studying quantum optics. (Spillane et al., Nature, 7 February
2002; contact Kerry Vahala, 626-395-2144,

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