New
Form of Matter Created: A Fermionic Condensate
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image credit: NIST/University of Colorado
False
color images of a condensate formed from pairs of fermion
potassium atoms. Higher areas indicate a greater density
of atoms. |
Scientists
at JILA, a joint laboratory of the National Institute of
Standards and Technology (NIST) and the University of
Colorado at Boulder (CU-Boulder) report the first observation
of a “fermionic condensate” formed from pairs
of atoms in a gas, a long-sought, novel form of matter.
Physicists hope that further research with such condensates
eventually will help unlock the mysteries of high-temperature
superconductivity, a phenomenon with the potential to improve
energy efficiency dramatically across
a broad range of applications.
The
research is described in a paper published in the Jan. 24-30
online edition of Physical Review Letters by JILA authors
Deborah S. Jin, a physicist at NIST and an adjoint associate
professor at CU-Boulder, and Markus Greiner and Cindy Regal,
a post-doctoral researcher and graduate student at CU-Boulder.
The
new work complements a previous major achievement, creation
of a “Bose-Einstein” condensate, which earned
JILA scientists Eric Cornell and Carl Wieman the Nobel
Prize in
Physics in 2001. Bose-Einstein condensates are collections
of thousands of ultracold “boson” atoms occupying
a single quantum state, that is, all the atoms are behaving
identically like a single, huge superatom.
The new
condensate is made with a different type of particle, fermions,
that are inherently difficult to coax into
a uniform quantum state.
Superconductivity,
in which currents flow without resistance or losses, involves
the
pairing of electrons, which
are also fermions. Quantum physicists are in worldwide
race
to produce
fermionic condensates from gases because they are
expected to exhibit a similar “superfluidity” similar
to that seen in superconductors, but will be much easier
to study.
“The
strength of pairing in our fermionic condensate, adjusted
for mass and density,” Jin explains, “would
correspond to a room temperature super-conductor.
This makes me optimistic that the fundamental physics
we learn through fermionic condensates
will eventually help
others design more practical superconducting materials.”
For further
details, see http://www.nist.gov/public_affairs/releases/fermi_condensate.htm.
Media
Contact:
Gail Porter,
(301) 975-3392
New
Cryogenic Refrigerator Dips Chips into a Deep Freeze
In
a major advance for cryogenics, researchers at the National
Institute of Standards and Technology (NIST) have developed
a compact, solid-state refrigerator capable of reaching
temperatures as low as 100 milliKelvin. The refrigerator
works by removing hot electrons in a manner similar to
an evaporative air-conditioner or “swamp cooler.”
When
combined with an X-ray sensor, also being developed at
NIST, the instrument will be useful in semiconductor
manufacturing
for identifying trace contaminants and in the astronomical
community for X-ray telescopes. The device can be made
in a wide range of sizes and shapes, as well as readily
integrated
with other cryogenic devices ranging in size from nano-meters
to millimeters.
A
report of the work is featured on the cover of the January
26, 2004, issue of Applied Physics Letters. “The
idea is to use a solid-state refrigerator for on-chip
cooling of
these cryogenic sensors,” says Anna M. Clark, the
report’s
lead author. “We have a working refrigerator that
reduces temperatures low enough to be used with highly
sensitive
X-ray detectors. These detectors require subKelvin temperatures
to
minimize thermal noise and maximize their resolution.”
Current
equipment capable of cooling to 100 milliKelvin is
bulky and expensive. By combining an on-chip cooler
with
an X-ray sensor, the NIST device may reduce substantially
the
weight and cost of such equipment.
The
refrigerator is made from a sandwich of nomal- metal/insulator/superconductor
junctions. When a voltage
is applied across the “sandwich,” high-energy
(hot) electrons tunnel from the normal metal through
the insulator and into the superconductor. As the hottest
electrons
leave,
the temperature of the normal metal drops dramatically.
Media
Contact:
Gail Porter, (301) 975-3392
‘Kissing’ RNA
and HIV-1: Unraveling the Details
A subtle structural change that may play a role in the molecular
machinery for making HIV-1 (the virus that causes AIDS) has
been identified by scientists from the National Institute
of Standards and Technology (NIST) and University of Maryland
working at the Center for Advanced Research in Biotechnology
(CARB). If confirmed in living cells, the mechanism, described
in the Jan. 20 online edition of Proceedings of the National
Academy of Sciences, might provide a new target for antiviral
drugs.
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NIST
research chemist John Marino places a RNA sample into
the magnet of a nuclear magnetic resonance instrument.
|
The
finding is among several to emerge recently from CARB’s
efforts to develop and validate sensitive tools for rapidly
detecting and quantifying ribonucleic acid (RNA) interactions.
RNA provides
the genetic blueprint for retroviruses such as HIV-1. CARB
scientists created a model system for tracking changes in
an RNA struc-tural
element involved in forming HIV-1 viral particles.
As
new HIV-1 viruses form and mature into infectious particles,
two strands
of RNA interact through a transient structure called
a “molecular kiss.” This structure then is packaged
into new virus particles, which undergo further maturation
after release from the infected cell. CARB scientists found
that specific
sites in the “kissing” structure acquire a proton
(a positively charged particle) at a pH close to that of
living cells. The proton’s presence alters the RNA
structure and accelerates its refolding by a protein associated
with
viral
maturation. Taken together, these observations suggest that
such a mechanism might be at work during viral infection.
To
track RNA binding and folding in real-time, the CARB scientists
developed fluorescent markers as substitutes for pieces
of the RNA. By monitoring changes in the fluorescent signal,
the scientists
could follow these reactions. The scientists also used
nuclear
magnetic resonance to identify the sites in the RNA that
acquire the proton and to characterize the resulting conformational
changes.
Media
Contact:
Laura
Ost, (301) 975-4034
Stirring
Research Provides Recipe for Nanotube Success
If
manufacturing is entering the “Golden Age” of
nanotechnology, then carbon nanotubes are the “Golden
Child.” In recent years, these tubes of graphite
many times thinner than a human hair have become a much-touted
emerging technology because of their potential ability
to add strength and other important properties to materials.
Adding
carbon nanotubes to plastics and other polymers has potential
to make automobile and airplane bodies stronger and
lighter, and textiles more tear-resistant. And because of
their electrical properties, carbon nanotubes also may
be used to
embed sensors in clothing for military and medical applications.
By one estimate, the carbon nanotube market valued at approximately
$12 million in 2002 could grow to $700 million by 2005.
One
problem, however, is the nanotubes tend to clump together
in certain applications. Just as an oil and water salad
dressing must be shaken thoroughly to mix well, carbon
nanotube formulations
must be thoroughly blended to perform their best.
In
a set of experiments reported in the Jan. 30 issue of Physical
Review Letters, researchers at the National Institute
of Standards
and Technology (NIST) have started to quantify both the
problem and the solution. The scientists used a microscope
and an “optical
flow cell” to measure the force needed to mix different
concentrations of nanotubes. Their findings suggest that
flow conditions often encountered in the processing of
carbon nanotube
suspensions can actually have the opposite effect, leading
to demixing. The effect is related directly to the long
fiber-like structure of the nanotubes. Although this
work only sets the stage
for resolving
what will
be an important technological issue, the findings give
researchers insight into how to process nanotubes more
efficiently.
Media Contact:
Scott Nance, (301) 975-5226
NIST
Neutron Researcher Wins Inaugural Society Award
J. Michael
Rowe, director of the National Institute of Standards
and Technology’s Center for Neutron Research
(NCNR), will receive the first-ever Clifford G. Shull
Award from the Neutron Scattering Society of America
(NSSA). Established in 2002 in memory of the Nobel Prize
winner of the same name, the award honors those who have
made outstanding contributions to the field of neutron
science.
In
addition to his influential scientific work, NSSA officials
said they selected Rowe to receive the
inaugural
award for being “a leader in the design of the
latest generation cold neutron sources, including the
most efficient hydrogen cold source currently operating
in the world at the NCNR” and for providing leadership
over 15 years as head of the NCNR that made the center
the “most important and widely used neutron facility
thus far developed in the United States.”
More
than 1,900 participants from academia, industry and
government conducted research last year that used
neutrons at the NCNR to probe the structure and dynamics
of materials.
Rowe
plans to retire this year after a 31-year career at NIST.
NSSA
represents more than 1,000 professionals in 26 nations.
NSSA intends to present Rowe with the
award
at its biennial
conference in June.
The
Shull award consists of a plaque and a $5,000 honorarium.
Media
Contact:
Scott Nance,
(301) 975-5226
Quick
Links
Materials
Practice Guide—The National Institute
of Standards and Technology (NIST) has published a new practice
guide, titled Data Evaluation Theory and Practice for Materials
Properties, that provides guidance on how to assess data for
reliability and consistency. The new guide represents NIST’s
first formalized methodology for the evaluation of materials
properties data. Industry will be able to use this publication
to improve efficiency by ensuring that manufacturing processes
are based on the best available data. The guide is available
online at: http://www.nist.gov/public_affairs/practiceguides/practiceguides.htm
Nanotechnology
workshop—The National Institute of Standards
and Technology (NIST) hosted more than 200 representatives of
government, academia and industry Jan. 27-29 for a “Grand
Challenge” workshop aimed at developing the equivalent
of a roadmap for metrology and instrumentation to further develop
the emerging field of nanotechnology. When will the sizable federal
investment in nanotechnology begin to deliver tangible returns?
A big part of the answer lies within the domain of instrumentation
and metrology, NIST Director Arden L. Bement Jr. told workshop
attendees.
“To
be sure, new and better measurement tools are needed to sustain
advances and discoveries in the laboratory—to distinguish
artifact from novel phenomenon, for example, and to enable
replication and verification of research results across laboratories,” he
said. “Without such tools, science will not acquire the
detailed knowledge it needs of the exotic properties and the
odd behavior of matter at the nanoscale.” For
the full text of Bement’s remarks, go to http://www.nist.gov/speeches/bement_012704.htm.
