PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News Number 750
October 19, 2005  by Phillip F. Schewe, Ben Stein
        
THE PHONON HALL EFFECT, the acoustic equivalent of the electrical Hall
effect, has been observed by physicists at the Max Planck Institut fur
Festkorperforschung (MPI) and the Centre National de la Recherche
Scientifique (CNRS) in France.  In the electrical Hall effect, when an
electrical current (consisting of free electrons moving along a material
sample) being driven by an electric field is subjected to an external
magnetic field, the charge carriers will feel a force perpendicular to both
the original current and the magnetic force, causing the electrical current
to be deflected somewhat to the side.  Thermal transport is a bit more
complicated than electrical transport.  A "current" of heat can
consist of free electrons carrying thermal energy or it can consist of
phonons, which are vibrations rippling through the lattice of atoms of the
sample.
Previously, some scientists believed that in the absence of free electrons,
a magnetically induced deflection of heat could not be possible.  The
MPI-CNRS researchers felt, however, that a magnetic deflection of phonons
was possible, and have now demonstrated it experimentally in insulating
samples of Terbium Gallium Garnet (a material often used for its magneto
optical properties) where no free charges are present. The sample was held
at a temperature of 5 K and was warmed at one side, creating the thermal
equivalent of an applied voltage. Application of a magnetic field of a few
Tesla led to an extremely small (smaller than one thousandth of a degree)
yet
detectable temperature difference.   (Strohm et al., Physical Review
Letters, 7 October 2005; text at www.aip.org/physnews/select) The same team
of MPI-CNRS scientists earlier demonstrated a kind of "photon Hall
effect"
(http://www.aip.org/pnu/1997/split/pnu349-2.htm).

DETECTING ALZHEIMER'S EARLY WITH NON-INVASIVE OPTICAL TOOLS.
Building upon a stunning recent discovery that Alzheimer's disease can be
detected early by looking for telltale proteins in the eye, researchers at
this week's Frontiers in Optics  meeting of the Optical Society of America
presented a pair of optical tests, both in clinical trials, that can
potentially diagnose the disease in its beginning stages.  Such tests may
not only improve patients' chances to start treatment earlier, but they
could also speed development of new Alzheimer's drugs.
Two years ago (Goldstein et al., Lancet, 12 April 2003), Lee Goldstein of
Harvard Medical School (LGOLDSTEIN{at}RICS.BWH.HARVARD.EDU) and his colleagues
showed that the exact same amyloid beta proteins which are a hallmark of
Alzheimer's disease are also found in the lens and its surrounding fluid. 
In those portions of the eye, the proteins form amyloid deposits similar to
those in the brain.  Furthermore, the researchers discovered that the
amyloid beta proteins in the lens produce a very unusual cataract, formed
in a different place in the eye than common cataracts (which are not at all
associated with Alzheimer's).  Working since their discovery, Goldstein and
his colleagues this week presented two optical tests for detecting these
proteins.
Using a technique known as quasi-elastic light scattering, the first test
employs low-power infrared laser light to non-invasively detect protein
particles in the specific part of the lens where these unusual cataracts
form.  The second test would be applied to those who screen positively for
the proteins, in order to confirm an Alzheimer's diagnosis.  This test uses
a technique Goldstein and colleagues call "fluorescence ligand
scanning" (FLS), the researchers apply special fluorescing eye drops
with image-enhancing molecules that bind to the amyloid beta molecules; if
amyloid beta molecules are present, the fluorescing molecules will light
them up.
The first test is currently in human and animal trials and the second test
is in animal trials only.  These two diagnostic tests are envisioned to be
a two-step process for screening and then confirming an Alzheimer's
diagnosis.  These new optical tools can also potentially speed up the
development of new Alzheimer's drugs, by giving investigators rapid
feedback on whether the drug is doing its job of removing the harmful
proteins from the body. Moreover, the researchers are using the same
technologies to develop new tests for rapidly detecting amyloid plaques
resulting from prion diseases, including mad cow, scrapie in sheep, and
Creutzfeldt-Jacob disease in humans.
(http://www.osa.org/meetings/annual/; Paper FTuBB4 at meeting, October 18, 2005.)

SUPER LENSING IN THE MID INFRARED.  Physicists at the University of Texas
have made a "super lens," a plane-shaped lens that can image a
point source of light down to a focal spot only one-eighth of a wavelength
wide; this is the first time such super lensing has been accomplished in a
functional device in the mid-infrared range of the electromagnetic
spectrum.  Historically lensing required a lens-shaped (that is,
lozenge-shaped) optical medium for bringing the diverging rays coming from
a point source into focus on the far side of the lens.  But in recent
years, researchers have found that in "negative permittivity"
materials (in which a material's response to an applied electric field is
opposite that of most normal materials), light rays can be refracted in
such a way as to focus planar waves into nearly a point, albeit over a very
truncated region, usually only a tenth or so of the wavelength of the
light.
Such near-field optics are not suitable for such applications as reading
glasses or telescopes, but have become an important technique for certain
kinds of nanoscale imaging of large biological molecules than can be
damaged by UV light.  The micron-sized Texas lens, reported at the OSA
meeting (http://www.osa.org/meetings/annual), consists of a silicon carbide
membrane in between layers of silicon oxide.  It focuses
11-micron-wavelength light, but the researchers hope to push on into the
near-infrared range soon.  Furthermore, the lensing effect seems to be
highly sensitive to the imaging wavelength and to the lens thickness. 
Gennady Shvets (gena{at}physics.utexas.edu) says that additional possible
applications of the lens include direct laser nanolithography and making
tiny antennas for mid-IR-wavelength free-space telecommunications.  (Paper
fMG2 at meeting; Lab website: www.ph.utexas.edu/~shvetsgr/)

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