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Time
Got a Second?
Nothing Counts Them Better Than New NIST Clock
There’s
an old joke that says a man with one watch always knows what time
it is while a man with two watches is never sure. Now, everyone
in the United States can be certain that his or her time is accurate
to one second in nearly 20 million years, thanks to the startup
of NIST F-1, the new cesium atomic clock at NIST’s
Boulder, Colo., laboratories.
F-1
began its role as the nation’s primary frequency standard in December
by making its first contribution to an international pool of atomic
clocks used to define Coordinated Universal Time, the official
world time.
NIST
F-1 shares the distinction of being the world’s most accurate
clock with a similar device in Paris. It is approximately three
times more accurate than its predecessor, NIST-7, also located
at the Boulder facility. NIST-7 has been in service since 1993
and is among the best time standards in the world.
NIST
F-1 is referred to as a fountain
clock because it uses a fountain-like movement of atoms to
obtain its improved reckoning of time. First, a gas of cesium
atoms is introduced into the clock’s vacuum chamber. Six infrared
laser beams gently push the atoms together into a ball. In the
process of creating this ball, the lasers slow down the movement
of the atoms and cool them to near absolute zero.
Two
vertical lasers are used to gently toss the ball upward (the “fountain”
action), and then all of the lasers are turned off. This little
push is just enough to loft the ball about a meter high through
a microwave-filled cavity. Under the influence of gravity, the
ball then falls back down. As the atoms interact with the microwave
signal—depending on the frequency of that signal—their atomic
states might be altered. The entire round trip for the ball of
atoms takes about a second.
At
the finish point, another laser is directed at the atoms. Only
those whose atomic states are altered by the microwaves are induced
to emit light. The emitted photons (tiny packets of light) are
measured by a detector. This procedure is repeated many times
while the microwave energy is tuned to different frequencies.
Eventually, a frequency is achieved that alters the states of
most of the cesium atoms and maximizes their fluorescence. This
frequency is the natural resonance frequency for the cesium atom—the
characteristic that defines the second.
More
information, including graphics, photos, fact sheets and a downloadable
video (with an animation and B-roll footage), is available on
the World Wide Web at www.nist.gov/fountainclock.
Media
Contact:
Fred
McGehan (Boulder), (303) 497-3246 
Optoelectronics
Kaleidoscope
Is Model for Optical Tunnel-Trap Detector
Remember
when you were a kid looking through a kaleidoscope? These days,
you’d probably say that while the rotating, changing patterns
were pretty, there wasn’t any practical science involved. Not
so fast, say researchers at NIST’s
Boulder, Colo., laboratories.
The
principle of the kaleidoscope is the model for a new, NIST-developed
instrument used as a transfer standard for laser power measurements.
Called an optical-trap detector, it is a triangular tube with
two relatively inexpensive photodiodes on each side in the place
of a kaleidoscope’s mirrors. Where the mirrors would trap light
and reflect it back and forth to create images, the photodiodes
either absorb the laser light or reflect it to the other diodes
for absorbtion. With each absorbtion, the photons are converted
to electrical energy and a measure of laser power is made.
One
version of the detector incorporates six 10-millimeter by 10-millimeter
square silicon photodiodes in a detector having a 7-millimeter
diameter aperture; it has an efficiency greater than 99 percent.
Another version incorporates six 18-millimeter by 18-millimeter
square photodiodes in a detector having a 12-millimeter diameter
aperture; it has an even greater efficiency, with variations that
are less than 0.05 percent. The NIST researchers hope to continue
their work in order to develop simpler trap designs with fewer
diodes and larger fields of view.
Copies
of a paper (54-99) discussing the design and fabrication of the
detector are available from Sarabeth
Harris, MC104, NIST, Boulder, Colo. 80303-3337; (303) 497-3237.
Technical details are available from John
Lehman, MC815.01, NIST, Boulder, Colo. 80303-3337; (303) 497-3654.
Media
Contact:
Fred
McGehan (Boulder), (303) 497-3246
Buildings
Housing Technology
Grants Now Available from PATH
In
conjunction with the Department of Housing and Urban Development’s
Partnership for Advancing Technology in Housing, NIST’s
Building and Fire Research Laboratory is offering financial
assistance to private-sector organizations that want to develop
innovative housing technologies.
The
program anticipates making between five and 10 cooperative agreements
ranging from $50,000 to $200,000 each. Private-sector organizations
that participate are required to fund at least 30 percent of the
total proposed project value. The program is designed to accelerate
development of technologies and have a measurable result within
18 months. Proposals will be accepted in the following seven areas:
(1) labor-saving processes for housing to reduce cycle time, enhance
worker safety and simplify construction processes; (2) advanced
materials and systems for structural integrity; (3) advanced and
innovative foundation systems for all types of soil conditions;
(4) advanced materials and systems for the building envelope to
control moisture in walls or control infestation by termites and
other insects; (5) new or innovative methods incorporating traditional
exterior finishes with advanced framing systems; (6) advanced
materials and systems for interior finishes; and (7) advanced
materials and systems for home function and operation.
The
deadline for submitting applications is Feb. 7, 2000.
More
information is available in the Dec. 7, 1999, Federal Register,
which can be accessed online at www.access.gpo.gov/su_docs/aces/aces140.html.
An application kit is available from Alexander
Phillips, (301) 975-6069. Potential applicants who have technical
questions may contact James Hill,
(301) 975-5901.
Media
Contacts:
Philip
Bulman, (301) 975-5661
John
Blair (HUD), (202) 708-4277 ext. 106
Proteins
NIST Physicists
Develop New Tool to Validate Protein Modeling
Proteins
intrigue industry for their potential applications in designing
new pharmaceuticals, improving agriculture and processing food,
chemical and materials. They also are large and highly complex
molecules that present difficult puzzles to the biochemists who
try to understand and define their structures. Now, NIST physicists
have a new tool that could help solve protein structures by verifying
the accuracy of protein modeling software.
One
of the problems in deciphering protein structures is the large
number of possible spatial orientations that atoms can occupy
when bonded together, much as a chain of beads can be twisted
or rotated into numerous positions. In fact, the number of possible
conformations of a long chain of atoms is so great that current
computer speed is not fast enough to calculate all of them.
Using
a NIST-developed Fourier transform microwave spectrometer, NIST
physicists Richard Suenram and Gerald Fraser have determined several
conformational isomers of small alkene molecules ranging in size
from five to 12 carbon atoms. Since the bonds in these chains
are similar to the bonds in protein molecules, software designers
could use the NIST data to verify the accuracy of their protein
modeling algorithms. The advantage of the NIST Fourier transform
microwave spectrometer is its ability to resolve different conformers
of the same molecule very clearly. For example, the NIST instrument
has identified 15 conformers of 1-octene, an 8-carbon chain, more
than have been observed experimentally ever before.
The
NIST alkene data represent the first large experimental conformational
data set that protein modelers and software designers can use
as a check on the accuracy of their methods and codes.
Media
Contact:
Linda
Joy, (301) 975-4403
Chemistry
‘Return
of the Cryogenics Database’ Now Playing at NIST
NIST,
along with the Chemical Propulsion Information Agency, Columbia,
Md., and Technology Applications Inc., Boulder, Colo., has reconstructed
and updated the database of the former National Bureau of Standards
Cryogenic Data Center. The center, which housed on a mainframe
computer a bibliography of cryogenic literature and thermophysical
property data that covered 100 years, was discontinued in the
early 1980s.
After
a 1997 survey showed there was substantial interest by industry
and government researchers in a revived database, the three organizations
created a Cryogenic Information Technology Database, available
on CD-ROM with over 133,000 document citations. The CD-ROM is
planned for semi-annual release with additional citations from
current literature. A specialized technical staff has been trained
to establish a clearinghouse of cryogenic information, acquire
hard copies of documents, store computerized records of bibliographic
data for retrieval and update the record base continuously. The
goal is to establish an information center capable of providing
technical analyses, state-of-the-art reviews, enhanced fluid and
material property software routines, current-awareness services
and Internet accessibility. In other words, the renewed database
is a one-stop resource for cryogenic documents and technical data.
Information
on the Cryogenic Technology Database is available from Eric
D. Marquardt, NIST, MS 838, Boulder, Colo. 80303-3337; (303)
497-5467. A paper (no. 52- 99) outlining the database program
is available from Sarabeth
Harris, MC 104, NIST, Boulder, Colo. 80303-3337; (303) 497-3237.
Media
Contact:
Fred
McGehan (Boulder), (303) 497-3246
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