April 21, 2005
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Chip-scale
Refrigerators Cool Bulk Objects
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This
colorized scanning electron micrograph shows a cube of
germanium attached to a membrane. The
four small light blue rectangles at the midpoints of the
membrane perimeter are chip-scale refrigerators that cooled
the cube and membrane to only a few hundred thousandths
of a degree above absolute zero.
Click
here to download a higher resolution version of this image.
Image credit:
N. Miller, A. Clark/NIST
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Chip-scale
refrigerators capable of reaching temperatures as low as
100 milliKelvin have been used to cool bulk objects for the
first time, researchers at the National Institute of Standards
and Technology (NIST) report. The solid-state refrigerators
have applications such as cooling cryogenic sensors in highly
sensitive instruments for semiconductor defect analysis and
astronomical research.
The work
is featured in the April 25, 2005, issue of Applied Physics
Letters.* The NIST-designed refrigerators, each 25 by 15
micrometers, are sandwiches of a normal metal, an insulator
and a superconducting metal. When a voltage is applied across
the sandwich, the hottest electrons "tunnel" from
the normal metal through the insulator to the superconductor.
The temperature in the normal metal drops dramatically and drains
electronic and vibrational energy from the objects being cooled.
The researchers used four pairs of these sandwiches to cool
the contents of a silicon nitrate membrane that was 450 micrometers
on a side and 0.4 micrometers thick. A cube of germanium 250
micrometers on a side was glued on top of the membrane. The
cube is about 11,000 times larger than the combined volume
of the refrigerators. This is roughly equivalent to having
a refrigerator the size of a person cool an object the size
of the Statue of Liberty. Both objects were cooled down to
about 200 mK, and further improvements in refrigerator performance
are possible, according to the paper.
The refrigerators are fabricated using common chip-making
lithography methods, making production and integration with
other microscale devices straightforward. The devices are much
smaller and less expensive than conventional equipment used
for cooling down to 100 mK, a target temperature for optimizing
the performance of cryogenic sensors. These sensors take advantage
of unusual phenomena that occur at very low temperatures to
detect very small differences in X-rays given off by nanometer-scale
particles, enabling users such as the semiconductor industry
to identify the particles. The work was supported in part by
the National Aeronautics and Space Administration and NIST's
Office of Microelectronics Programs.
*A.M. Clark,
N.A. Miller, A. Williams, S.T. Ruggiero, G.C. Hilton, L.R. Vale,
J.A. Beall, K.D. Irwin, J.N. Ullom. Cooling of Bulk Material
by Electron-Tunneling Refrigerators. Applied Physics Letters.
April 25, 2005.
Portable
Radiation Detectors Generally Meet Standards
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NIST
researcher Leticia Pibida uses a hand-held radiation
detection device to check the cargo of truck trailer.
©
Robert Rathe
To
receive a high-resolution version of this image, contact
Gail Porter.
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Portable
radiation detectors generally perform well enough to meet
new consensus standards but provide inaccurate readings for
certain types of radiation, according to recent tests by the
National Institute of Standards and Technology (NIST).
The results,
reported in the May issue of the journal Health Physics,*
are based on NIST tests of 31 commercial detectors, including
hand-held survey meters; electronic personal alarming detectors
(similar to pagers); and radionuclide identifiers (specialized
devices that can identify specific radioactive materials).
A number of federal, state and local agencies are using such
instruments as part of homeland security-related efforts to
detect and identify radioactive materials.
Researchers
compared the devices' exposure rate readings to NIST measurements
for different energy and intensity levels produced by NIST's
calibrated gamma ray and X-ray beam lines. The responses of
the majority of the detectors agreed with NIST-measured values,
within acceptable uncertainties, for tests with gamma rays.
This performance meets requirements established by new American
National Standards Institute (ANSI) standards, adopted by
the Department of Homeland Security (DHS) in 2004. However,
there was a large discrepancy between most detectors' readings
and the NIST values for the lowest-energy X-rays. For instance,
readings by 14 detectors were roughly 40 to 100 percent below
the NIST value. The deviations were much larger than those
stated in manufacturers' specifications.
The tests
are intended to help first responders and government agencies
make better use of existing equipment and acquire the right
equipment for emergency response, and to encourage manufacturers
to better design and characterize their instruments. The tests
were performed as part of the NIST program to support the
development of the new ANSI standards (see www.nist.gov/public_affairs/factsheet/radiation_detector_standards.htm)
as well as to support the NIST Office of Law Enforcement
Standards and DHS in testing detectors for their use by first
responders.
*L. Pibida,
R. Minniti, M. O'Brien, and M. Unterweger. Test of Radiation
Detectors used in Homeland Security Applications. Health
Physics. May. Vol. 88, Number 5. Posted online April
13, 2005.
Nanomagnets
Bend the Rules
Nanocomposite
materials seem to flout conventions of physics. In the
latest example of surprising behavior, reported*
April 15 by scientists at the National Institute of Standards
and Technology (NIST) and Brookhaven National Laboratory,
a class of nanostructured materials that are key components
of computer memories and other important technologies
undergo a previously unrecognized shift in the rate at
which magnetization changes at low temperatures.
The
team suggests that the apparent anomaly described as an “upturn” in
magnetization may be due to the quantum mechanical process
known as Bose-Einstein condensation.
They maintain that, in nanostructured magnets, energy waves
called magnons coalesce into a common ground state and, in
effect, become one. This collective identity, the researchers
say, results in magnetic behavior seemingly at odds with
a long-standing theory.
The new finding could prompt a reassessment of test methods
used to predict technologically important properties of "ferromagnetic" materials.
The results also could point the way to marked improvements
in the performance of microwave devices. Magnets are integral
to these devices, used in a variety of communication and
defense technologies.
Ferromagnets, including iron, cobalt, nickel and many tailor-made
materials, become magnetic when exposed to an external magnetic
field. As the strength of the external field increases, the
materials become more magnetic, an atomic-level, temperature-influenced
process called magnetic saturation. When the external field
is removed, ferromagnets undergo an internal restructuring
and the acquired magnetization decays, or fades, very slowly
at a rate that increases with temperature.
Determined through accelerated testing methods, the temperature
dependence of magnetic saturation and the rate of magnetization
decay are key concerns in the design of permanent magnets,
hard disks and other magnetic data storage systems.
For further
information, see www.nist.gov/public_affairs/releases/nanomagnets_bend_rules.htm.
*E. Della
Torre, L.H. Bennett, and R.E. Watson, Extension of the Bloch
T3/2 Law to Magnetic Nanostructures: Bose-Einstein
Condensation. Physical Review Letters. April 15,
2005.
Media
Contact:
Mark
Bello, mark.bello@nist.gov,
(301) 975-3776
Dogs
and Robots Share NIST Special Test Arena
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Police
Officer Michael Millsaps Jr. of the Amtrak Police Department
rewards his dog Bak for finding a hidden gun under debris
at the NIST reference test arena for urban search and
rescue and explosive ordnance disposal robots.
The
white transmitters worn by both Millsaps and Bak can be
used to track and record their movements as they proceed
through the arena. Similar transmitters are attached to
rescue robots and are used to analyze searching performance.
Photo by Gail Porter/NIST
Click
here to download a higher resolution version of this image.
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Bomb
and drug sniffing dogs are regular visitors to the National
Institute of Standards and Technology (NIST) for training, not
for emergency work. Every month as many as 10 to 20 dogs and
their handlers from federal agencies as well as from local county
and municipal police departments visit the arenas that NIST
uses to test and evaluate urban search and rescue and explosive
ordnance disposal robots.
The arenas
represent a building in various stages of collapse and provide
a robot testing site for both pre- and post-disaster
scenarios. The jumble of concrete collapsed walls and fallen
debris also offers just the right challenge to sharpen the
skills of the dogs who hunt for hidden drugs or patrol potential
terrorist targets.
Small samples
of explosive materials or narcotics are first hidden amid the
rubble. Then individual dogs, under the watchful eyes of their
handlers who are in a sense in training as well, seek out firearms,
ammunition, explosives and chemical compounds used to build
explosives or drugs such as cocaine or heroin. Once the dog
finds the "hide," he or she sits silently, at attention,
in front of the cache.
The individual
dogs are trained in locating drugs or explosives, not both.
Handlers must know why a dog is sitting, and in a real situation
whether the find is safe to pick up. Success brings a shout
of "That's my Boy," a rough, affectionate head tussle,
a brief pulling match over a toy with the handler, and then
the hunt goes on until all the hidden explosives or drugs are
found.
"A dog just wants to play," said Sergeant Rick Hawkins
of the NIH Police Department who coordinates the multi-agency
K-9 visits to NIST. "When we go home we look at our
paycheck. A dog has his toy and that's what he works for." Hawkins'
six-year-old black Labrador, Flyer, is trained to find narcotics.
The police trainers appreciate having a unique indoor facility
that challenges the dogs' skills and that is available on
a regular basis. At the same time, the NIST robotics experts
benefit from observing police techniques for systematically
searching for explosives.
In April, NIST experts helped with the 2005 RoboCup German Open
international competition in Paderborn, Germany, that used a
newly constructed version of the NIST arenas to test the performance
of the latest rescue robots.
A brief
video describing the training of both dogs and robots at the
NIST arena is available at: http://realex.nist.gov:8080/ramgen/robot2.smi.
(Requires
RealPlayer)
Audio
file for the visually impaired (Requires
RealPlayer)
Media
Contact:
John
Blair, john.blair@nist.gov, (301) 975-4261
X-Rays
Shine Light on High-Intensity Gas Lamps
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Scientists
perform a series of calculations to transform X-ray
intensity data (left, a montage of five separate images)
into an image of the spatial distribution of mercury
atoms in a high-intensity discharge lamp (right).
Blue indicates the lowest density of atoms, red the
highest.
Click
here to download a higher resolution version of this
image. |
An
X-ray technique developed by physicists at the National
Institute of Standards and Technology (NIST) is helping
to improve the design and energy efficiency of the bright
white lights often used to illuminate stadiums, roads
and many other settings.
High-intensity
gas discharge (HID) lamps produce 26 percent of the nation's
light output, but, as a result of their high energy efficiency,
consume only 17 percent of the electricity used for lighting.
Continuing improvements in energy efficiency and other
features will reduce electricity use and the negative
environmental effects of power generation. Improved efficiency
could save lots of money: HID lamps consume roughly 4
percent of U.S. electricity, equivalent to about $10 billion
annually.
The
NIST technique uses X-ray imaging to improve understanding
of the complex science underlying the HID lamp's design.
Such lamps have two electrodes in a ceramic tube that
contains small amounts of mercury and metal-halide salts.
An electric current between the electrodes heats the lamp,
vaporizing the mercury and metal-halide salts and producing
a gas of electrically charged particles, or plasma. Metal
atoms, excited by collisions with electrons in the plasma,
emit light at many different wavelengths, producing a
bright, white light.
In
the NIST technique, an HID lamp is placed in an intense
beam of X-rays. The X-rays penetrate the lamp's ceramic
housing but are partially absorbed by the mercury gas
in the lamp, casting a shadow in the beam. A special digital
camera behind the lamp captures a high-resolution, two-dimensional
image of this X-ray shadow showing the density of mercury
atoms in the discharge. From the mercury distribution,
the temperature distribution in the lamp also can be determined.
This technique has been used to quantify processes that
consume power without producing light.
Researchers
now are demonstrating that this technique can be implemented
in industrial laboratories using small-scale X-ray sources.
This project provides measurement support to universities
participating in the Advanced Light Source Research Program-II
(ALITE-II) of the Electric Power Research Institute. The
goals of the consortium are to make significant improvements
in lighting technology by combining the resources of university,
industry and government laboratories in pre-competitive
research.
*J.J.
Curry and C.J. Sansonetti. X-Ray Absorption Imaging of
High-Pressure Lighting Plasmas. IEEE Transactions
on Plasma Science. April 2005
Media
Contact:
Laura
Ost, laura.ost@nist.gov,
(301) 975-4034
Data
Effort Improves Flow Toward 'Greener' Chemistry
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Molecular
"space filling" models demonstrate
the difference in size for the positively
charged "cation" (top image) and
the negatively charged "anion"
(bottom left) that combine to form a promising
ionic liquid. It is still a mystery how
the much smaller water molecule (right)
can have such a large effect on the viscosity
of such ionic liquids.
Click
here to download a higher resolution version
of this image. |
Jeopardy
answer: Death Valley and "ionic liquids."
Correct question: Where does a little bit of
water make a whole lot of difference?
Scientists at the National Institute of Standards
and Technology (NIST) report* that flow properties
for a relatively new class of alternative solvents
called ionic liquids are extremely sensitive
to tiny amounts of water. For example, for
one of these solvents, just a 0.01 percent
increase in water dissolved into a sample,
caused a 1 percent decrease in flow resistance—a
100-fold effect. The finding should be helpful
in the design of new industrial processes such
as chemical separations that are both more
efficient and more environmentally friendly.
Ionic liquids are salts. Just like table salt,
ionic liquids consist of two components, one
positively and one negatively charged. Unlike
most simple salts, however, most of these new
solvents are liquid at room temperature.
"People
in industry are very interested in using ionic
liquids because unlike most organic solvents,
they don't evaporate and they are not flammable,"
explains NIST's Jason Widegren, lead author
on the paper.
However,
before ionic fluids can be used widely in industrial
processes, reliable property data on characteristics
like flow resistance (viscosity), density and
thermal conductivity must be collected.
The
new data help explain why reproducible measurements
of viscosity for ionic liquids have been very
difficult to achieve and published results have
differed by 30 percent or more. Even the slightest
contamination of samples with water vapor absorbed
from the air dramatically affects measurements.
The NIST group avoided these problems by carefully
drying their samples and measuring water content
both before and after each viscosity measurement.
The
NIST work is part of a larger effort, conducted
in conjunction with the International
Union of Pure and Applied Chemistry, to perform "round
robin" thermophysical property testing
on the most promising ionic fluids and make
the resulting data available to the scientific
community.
*J.
A. Widegren, A. Laesecke, and J. W. Magee. The
effect of dissolved water on the viscosities
of hydrophobic room-temperature ionic liquids.
Chemical Communications, 2005, 1610-1612.
Media
Contact:
Gail
Porter, gail.porter@nist.gov,
(301) 975-3392
Meeting
to Explore Possible Gene Expression
Consortium
The
National Institute of Standards and Technology
(NIST) will a host a meeting
on May 16, 2005, in Boulder, Colo., to
explore the possibility of creating a
NIST-industry consortium focused on gene
expression metrology.
Parallel
and closely related advances over the
last few years in the sequencing
of whole genomes and the development of
so-called gene microarrays have fueled
an explosive growth in data on genes and
their functions. Gene microarrays use thousands
or tens of thousands of short lengths of
single-strand DNA, fixed in a grid about
the size of a postage stamp, to rapidly
measure gene activity. It’s a powerful
technology, but one that has evolved rapidly,
and in advance of any underlying scientific
infrastructure to quantitatively evaluate
the quality of individual experimental
results.
As a consequence, it has become difficult
to reconcile the results of microarray
experiments at different labs using different
equipment. Lack of a gene expression measurement
infrastructure is undermining confidence
in microarray-based test results.
To address this problem, NIST is hosting
the May 16 meeting to assess industry interest
in establishing a Consortium on Gene Expression
Metrology. The consortium would develop
universal measurement methods to characterize
microarray performance, including measures
of signal-to-noise ratio, signal-to-background
ratio, dynamic range (from minimum to maximum
quantifiable amount), and selectivity/specificity.
Interested parties should contact Marc
Salit, marc.salit@nist.gov, (301) 975-3646.
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