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Stable Polymer Nanotubes May Have a Biotech Future
Scientists at the National Institute of Standards and Technology (NIST) have created polymer nanotubes that are unusually long (about 1 centimeter) as well as stable enough to maintain their shape indefinitely. Described in a new paper in Proceedings of the National Academy of Sciences,* the NIST nanotubes may have biotechnology applications as channels for tiny volumes of chemicals in nanofluidic reactor devices, for example, or as the “world’s smallest hypodermic needles” for injecting molecules one at a time.Carbon nanotubes are of keen interest in nanotechnology research, especially for making ultrastrong fibers and other structures. Nanotubes made from other materials are used for transport in biochemical applications, but are typically fragile and usually collapse within a few hours. The NIST team developed processes for extending the shelf life of polymer nanotubes—considered essential for commercial applications—and forming sturdy nanotube network structures.
First the researchers made tiny, fluid-filled spherical containers with bi-layer membranes consisting of polymers with one end that likes water and one end that does not. (These fluid-filled containers are a spin-off of liposomes, artificial cells with fatty membranes used in cosmetics and for drug delivery.) The researchers made the membranes stretchy by adding a soap-like fluid to change the polymer membranes’ mechanical properties. Then they used “optical tweezers” (highly focused infrared lasers) or tiny droppers called micropipettes to pull on the elastic membranes to form long, double-walled tubes that are less than 100 nanometers in diameter. (View a movie of this process. (Requires Quicktime--download free).)
A chemical was added to break bonds between atoms in one section of the polymers and induce new bonds to form between the two different sections, forming a rigid “cross-linked” membrane. The nanotubes are then snipped free from the parent cell with an “optical scalpel” (highly focused ultraviolet laser pulse). The nanotubes maintain their shape even after several weeks of storage, and can be removed from the liquid solution and placed on a dry surface or in a different container. The optical tweezers can be used to custom build nanotube network structures. The work was supported in part by the Office of Naval Research.
*J.E. Reiner, J.M. Wells, R.B. Kishore, C. Pfefferkorn, and K. Helmerson. 2006. Stable and robust polymer nanotubes stretched from polymersomes. Proceedings of the National Academy of Sciences. Published online Jan. 23, 2006.
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NIST Issues Final Federal Biometric Specs
The National Institute of Standards and Technology (NIST) yesterday issued the final publication describing how biometrics should be stored on Personal Identity Verification (PIV) cards. These cards will be required for all federal employees and contractors beginning in October 2006.
NIST Special Publication 800-76, Biometric Data Specification for Personal Identity Verification, contains specifications for acquiring, formatting, and storing fingerprint images and templates; for collecting and formatting facial images; and specifications for biometric devices used to collect and read fingerprint images. The publication specifies that two fingerprints be stored on the card as “minutia templates,” mathematical representations of fingerprint images.
In August 2004, the President issued Homeland Security Presidential Directive 12 calling for a mandatory, government-wide personal identification card that all federal government departments and agencies will issue to their employees and contractors requiring access to federal facilities and systems.
Federal Information Processing Standard 201, Personal Identity Verification for Federal Employees and Contractors, approved by Commerce Secretary Carlos Gutierrez on Feb. 25, 2005, specifies the technical and operational requirements for the PIV system and cards. NIST Special Publication 800-76 is a companion document to FIPS 201 describing how the standard will be implemented.
For a copy of SP 800-76 and more information on PIV, see http://csrc.nist.gov/groups/SNS/piv/.
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Fire Panel Changes Offer Real-Time Fire Status Data
Fire panels, or “annunciators,” are electronic devices that display data on building conditions in one easily accessible location. When used by first responders during emergencies, the devices can save lives. In December 2005, the National Electrical Manufacturing Association (NEMA) released a comprehensive standard* that promises to make future annunciators even more useful decision-making tools to fire fighters at the scene, to commanders back at headquarters, or to building and emergency personnel rushing to a fire.
Developed with the help of the National Institute of Standards and Technology (NIST) and the U.S. fire alarm industry, the standard offers greater uniformity in design, operation and arrangement of fire panels, common symbols denoting fire-related building conditions, and equipment specifications concerning wireless and remote applications. The standardization effort should make real-time information of value clearly and quickly available for processing, planning and response. For instance, agreement on how to unambiguously represent conditions such as biochemical hazards or the locations of smoke vents and elevators should make the fire panels and related equipment much better tools for rapid decision-making. Similar display and message symbols also should save time and training funds currently needed to teach fire fighters to understand dissimilar fire panel systems. Finally, standardization is considered necessary for parallel efforts in the first responder community to develop a capability to transmit relevant, easy-to-understand building and fire emergency information to fire fighters prior to their arrival on the scene.
In a related development, NIST released proceedings of a July 26, 2005, workshop** held at its Gaithersburg, Md., campus in which fire safety personnel used laptops to simulate and to evaluate the usefulness of transmitting real-time fire panel data to dispatch centers and to officers at the scene monitoring fire fighters during an emergency. Participants considered four scenarios: (1) a hospital fire; (2) arson in a third-floor laboratory building room; (3) fire on the second floor of a two-story single family dwelling; and (4) an emergency medical call inside a large shopping mall. The final report lists almost 100 recommendations for improvements of current displays, ranging from suggestions for different colors for various fire conditions, better depiction of evacuation stairwell size, and even off-site screen printout capability.
*A copy of the NEMA annunciator standard, SB 30-2005 (Fire Service Annunciator and Interface), is available for purchase at http://www.nema.org/stds/sb30.cfm.
**NIST’s Workshop on the Evaluation of a Tactical Decision Aid Display (NISTIR 7268) is available at http://fire.nist.gov/bfrlpubs/fire05/PDF/f05105.pdf (.pdf; download Acrobat Reader). The Department of Justice Community Oriented Policing Service (COPS) sponsored the workshop via the NIST Office of Law Enforcement Standards (OLES).
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New Design for Transistors Powered by Single Electrons
Scientists have demonstrated the first reproducible, controllable silicon transistors that are turned on and off by the motion of individual electrons. The experimental devices, designed and fabricated at NTT Corp. of Japan and tested at NIST, may have applications in low-power nanoelectronics, particularly as next-generation integrated circuits for logic operations (as opposed to simpler memory tasks).
The transistors, described in the Jan. 30, 2006, issue of Applied Physics Letters,* are based on the principle that as device sizes shrink to the nanometer range, the amount of energy required to move a single electron increases significantly. This makes it possible to control individual electron motion and current flow by manipulating the voltage applied to barriers, or "gates," in the electrical circuit. At negative voltage, the transistor is off; at higher voltage, the transistor is turned on and individual electrons file through the circuit, as opposed to thousands at a time in a conventional device.
This type of innovative transistor, called a "single-electron tunneling" (SET) device, is typically made with a metal “wire” interrupted by insulating barriers that offer a rigid, narrow range of control over electron flow. Silicon devices, by contrast, have barriers that are electrically "tunable" over a wider operating range, offering finer, more flexible control of the transistor’s on/off switch. Particular voltage levels are applied across the barriers, to manipulate charge, as a means of encouraging or impeding electron flow. Silicon-based devices also allow fabrication using standard semiconductor technology. Until now, however, no silicon SET transistor designs have been reported that are reproducible and controllable.
The NIST/NTT team made five uniform, working silicon transistors with tunable barriers. Each device consists of a silicon channel 360 nanometers (nm) long and 30 nm wide, with three gates crossing the channel. The gates have two levels; the upper level turns the current on and off, while the lower level controls electron flow in small local areas. The team was able to tune gate conductance properties over a wide range, by more than three orders of magnitude.This work was partly supported by the Japan Society for the Promotion of Science.
*A. Fujiwara, H. Inokawa, K. Yamazaki, H. Namatsu, Y. Takahashi, N.M. Zimmerman, and S.B. Martin. 2006. Single electron tunneling transistor with tunable barriers using silicon nanowire MOSFET. Applied Physics Letters. Jan. 30.
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Enhanced LIDAR Improves Range, Vibration Measures
Scientists at the National Institute of Standards and Technology (NIST) have demonstrated the use of an ultrafast laser “frequency comb” system for improved remote measurements of distance and vibration. The technology, described in a forthcoming issue of Optics Letters,* may have applications in automated manufacturing or defense systems because it enables unusually precise characterization of the range profile and motion of a surface.
The NIST laboratory system is an adaptation of light detection and ranging (LIDAR), which transmits light through the air to a target and analyzes the weak reflected signal to measure the distance, or range, to the target and other parameters. The NIST system uses an infrared laser that emits a continuous train of very brief, closely spaced pulses of light of many colors, or frequencies. An analysis of the frequencies reveals a very fine “comb” of evenly spaced teeth. The short pulse length (quadrillionths of a second, or millionths of a billionth of a second) creates a wide range of comb frequencies, enabling more accurate range measurements; the inherent stability of the laser creates fine comb teeth, enabling very precise vibration measurements.
The frequency comb serves as both the light source and as a precise ruler for measuring the reflected signal. NIST-developed software analyzes the intensity of the reflected signal to measure distance to the target, and analyzes the frequency (or Doppler) shift to measure vibration. The most unusual aspect of the system is the way it resolves common problems with signal “noise” and dispersion of light by the atmosphere into longer pulses (with different colors of light traveling at different speeds). The reflected light that is detected is divided into a number of different color bands for computer processing. Measurements are averaged across the channels, effectively multiplying the precision of the result by the number of channels.
The system was used to determine the distance to, and vibration of, a rotating disk located on the far side of the laboratory. Experiments were conducted under a variety of conditions. For example, with the reflected light transmitted over an extended distance (partly through 1 kilometer of optical fiber wrapped around a spool), the NIST system could measure a 45-micrometer displacement across the disk surface at a range of 1 km thanks to the signal processing method. Conventional LIDAR would have failed at that distance due to dispersion of the reflected light within the fiber, according to the paper.
* W.C. Swann and N.R. Newbury. 2006. Frequency-resolved coherent LIDAR using a femtosecond fiber laser. Optics Letters. Scheduled for the March 15 issue. Posted online Nov. 23, 2005.
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