Number 285, September 9, 1996 by Phillip F. Schewe and Ben Stein
A 3-DIMENSIONAL, FULL-COLOR SOLID-STATE DISPLAY has been created by
a team of scientists at Stanford, IBM-Almaden, and SDL Corp. in San Jose.
Elizabeth Downing and her colleagues shine a pair of infrared lasers into
a sugar-cube-sized piece of heavy metal fluoride glass. The criss-crossing
laser beams are aimed at individual volume elements (voxels) in the transparent
cube. Doped with rare-earth atoms, the tiny voxels sequentially absorb
the pair of infrared photons and then emit single visible-light photons.
By scanning the beams through plane after plane (which fluoresce in succession
at blue, green, or red wavelengths), a full-color, 3-dimensional image
can be created. Like the 2D image cast on a television picture screen,
the 3D image persists in the viewer's perception because it is refreshed
30 to 60 times every second. So far only wire-frame figures or simple shapes
can be rendered. Unlike holographic, stereoscopic, or virtual-reality displays,
Downing's device requires no special viewing equipment and does not restrict
the angle of viewing. What keeps this technique of 3D imaging from being
applied any time soon to medical imaging or computer-assisted design is
the relatively small size of the cube and the enormous data load needed
to specify the image. (Elizabeth Downing et al., Science, 30 August 1996;
an accompanying picture can be viewed on the Web at /png/)
BRAIDS PLAITED BY MAGNETIC HOLES . The study of braids and knots is important
for both mathematics (where it is a subfield of topology) and for quantum
physics, where it is used to describe the interactions of particles in
an abstract multidimensional phase space. Now physicists at the Institute
of Energy Technology in Norway (Geir Helgesen, geirh@ife.no) have demonstrated
a practical way to investigate complicated braids using tiny beads confined
between two plates and subjected to complex magnetic fields. The motion
of these beads constitutes a three-dimensional braid if you consider time
as a third spatial dimension; a sequence of photos of the beads at regular
intervals is assembled into a plait-like trajectory not unlike the smoke
trails used in wind-tunnel experiments, except that in this case the observed
braid topology can reveal information about the magnetic fields pushing
the beads around. The researchers expect that the behavior of the beads
(actually non-magnetic spheres immersed in a ferrofluid) can be used as
a simple experimental tool for modeling complex interactions in quantum
field theory or chaos theory. (P. Pieranski et al., Physical Review Letters,
19 August 1996.)
THE PROSPECT OF ORGANIC ELECTRONIC DEVICES , mass produced on huge, cheap,
lightweight, flexible sheets, has been hampered by the fact that certain
components, such as organic LEDs, tend to burn out prematurely; the problem
stems mostly from hotspots which develop in the vicinity of undesired impurities.
Recently, however, research in a number of labs, such as Kodak and UC Santa
Barbara, has mitigated the impurity problem and device lifetimes of thousands
of hours have been achieved. Furthermore, full-color displays are possible
with organic LEDs; the Pioneer Electronic Corp. in Saitama, Japan has developed
a system with 16,000 picture elements (and a lifetime of 5000 hours) based
on blue-light emitting diodes. Now researchers are working on improving
device efficiency, the rate of light out to the electricity in. (Science,
16 August 1996.)
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