From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Dec 30 2003 - 09:00:40 PST
----- Original Message -----
From: physnews_at_aip.org
Sent: Tuesday, December 30, 2003 11:50 AM
To: ljk4_at_MSN.COM
Subject: Physics News Update 667
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 667 December 30, 2003 by Phillip F. Schewe, Ben Stein, and
James Riordon
WORLD'S FIRST LIGHT EMITTING TRANSISTOR. Researchers at the
University of Illinois at Urbana-Champaign have developed the
world's first light emitting transistor (LET). Unlike conventional
transistors, which include an electrical input port and an
electrical output port, the new LET also has an infrared optical
output port (see image at http://www.aip.org/mgr/png/2003/210.htm).
The LET is built of indium gallium phosphide and gallium arsenide,
rather than the silicon and germanium used in many conventional
transistors. Although the LET produces light in essentially the same
way that light emitting diodes (LEDs) operate, the transistor can
modulate light at much higher speeds. To date, the researchers (N.
Holonyak, Jr., blpayne_at_.uiuc.edu, 217-333-4149) have managed to
modulate the optical LET output at a frequency of one megahertz, but
much higher speeds are theoretically possible. Although it's too
early to predict the various applications for LETs, the hybrid
device should help integrate electrical and optical circuitry
designs with one convenient, high speed package. It is only fitting
that the research team that developed the LET include the inventor
of the first visible LED (Holonyak) and the developer of the world's
fastest bipolar transistor (Feng). (M. Feng et al., Applied Physics
Letters, 5 January 2004)
GLIAL CELLS AND EPILEPSY: is there a connection? Neurons are not
the only cells in the brain. In fact, 90% of brain matter consists
of glial cells. Astrocytes, the most common glial cell type, don't
have enough sodium channels to carry on the active electro-chemical
signaling characteristic of neurons, but they can communicate with
other cells through the diffusion of messenger molecules.
Furthermore, astrocytes can partially or wholly enwrap neuronal
synapses, the message sending or receiving ends of the neuron. This
facilitates neutron-astrocyte interactions, and even neuron-neuron
communications via astrocytes. Formerly glia were thought to play
a passive role in the nervous system---cleaning up the potassium
needed in the neural firing mechanism. But increasingly scientists
believe that glia play a more active role in enhancing or inhibiting
action in the synapse.
Suhita Nadkarni and Peter Jung at Ohio University believe that glia
participate in the making of epilepsy. There is no accepted theory
of epilepsy; does it arise from neurons talking in synchrony or is
it a sort of "thunderstorm" of spontaneous activity among neurons?
Jung argues that under some conditions the neuron might "listen" so
much to its astrocyte environment (by an overexpression of of
certain receptor molecules) that it enters into a bistable state;
even in the absence of outside (normal) stimulation the neuron could
fire indiscriminately in the manner characteristic of epilepsy. It
is therefore necessary to undertake a sort of electrical engineering
study of neural-glial circuitry. Jung, a physicist (presently at
the Kavli Institute for Theoretical Physics at UC Santa Barbara,
805-893-7333, jungp_at_kitp.ucsb.edu), has demonstrated some of this
glial-neural behavior in computer simulations and is working with
neuro-biologists who might shortly put the model to an experimental
test. (Physical Review Letters, upcoming article)
IMPROVED TANDEM ORGANIC LEDs. Stacking organic light emitting
diodes (OLEDs) leads to brighter, stabler, longer lived light
sources than individual OLEDs. Unfortunately, the metal layers
typically used to connect the individual elements are not very
transparent, reducing the resulting brightness of underlying OLEDs
in a tandem configuration. Researchers in the Display Technology
Laboratory at Eastman Kodak Company have now managed to stack OLEDs
that are connected through optically transparent, organic
semiconductor materials. The improvement in brightness in the new,
tandem OLED is essentially linearly related to the number of
individual light emitting segments included in the device, that is,
a three-segment tandem OLED is roughly three times as bright as a
conventional OLED. High brightness, high efficiency tandem OLEDs
could lead to brighter TV's and computer screens. They could also
make it easier to read cell phone displays in bright sunlight, which
often renders existing cell phone displays unintelligible. The
researchers (contact: L. S. Liao, liang-sheng.liao_at_kodak.com)
propose that tandem OLEDs may also be useful as lighting sources for
liquid crystal display backlighting or as solid-state room lights.
In addition, varying the number of units in a tandem OLED stack
changes the operating voltage, allowing the possibility of
tailoring the devices to match different electrical sources, such as
household 110 volt systems. Conventional LED lighting, on the other
hand, typically requires transformers to adjust power sources to
meet the lighting element's electrical specifications. (L. S. Liao
et al., Applied Physics Letters, 5 January 2004 )
***********
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