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In This Issue...
New Explanation for Key Step in Anthrax Infection Proposed by NIST and USAMRIID
A new hypothesis concerning a crucial step in the anthrax infection process has been advanced by scientists at the National Institute of Standards and Technology (NIST) and the U.S. Army Medical Research Institute for Infectious Diseases (USAMRIID) at Fort Detrick, Md.
The research teams have explored the behavior of the toxins that rapidly overwhelm the body as the often-fatal disease progresses. Their findings suggest a new possible mechanism by which anthrax bacteria deliver the protein molecules that poison victims. Anthrax is easily weaponized; the findings could help lead to a more effective cure.
Anthrax bacteria kill by releasing three toxins that work in concert to destroy cells. One toxin, called PA, attaches to the cell membrane, where its surface serves as a sort of landing pad for the other two toxins, called LF and EF. Once several molecules of LF and EF have latched onto PA, the cell membrane tries to destroy these unwanted hangers-on by wrapping them up in an "endosome," a small bubble of membrane that gets pinched off and moved into the cell's interior. There, the cell attempts to destroy its contents by a process that includes making the interior of the endosome more acidic. But before the cell can fully carry out its plan, the LF and EF escape from the endosome and wreak havoc in the cell's interior. The question is: how do these toxins escape?
"A recent hypothesis is that LF and EF completely unfold and then squeeze through the narrow hole that PA forms in the endosomal membrane," says NIST physical scientist John Kasianowicz. "However, the results don't conclusively show that LF and EF are completely transported through the pore or whether the proteins refold into functional enzymes once they reach the other side. So, we decided to look at other possible explanations."**
The NIST/USAMRIID team explored the behavior of full-length toxins using an artificial membrane that mimics a cell's exterior. They put the toxins mixed in salt water on one side of this barrier and slowly rendered this fluid more acidic, resembling conditions within an endosome. But the change in chemistry apparently altered the physical characteristics of the LF and EF toxins, because it caused them to bind irreversibly to the PA pore, creating a "complex" of multiple toxins. This result alone suggested it would be difficult, if not impossible, for LF and EF to thread through the pore.
In addition, the team discovered that the bound toxins tend to rupture membranes. This finding led them to suggest that perhaps it is complexes of LF or EF bound to PA that gets into cells, and that these complexes are the active toxins inside cells.
Kasianowicz says this new hypothesis could explain previous experimental results, in which the complex was found in the blood of animals that died of anthrax. But he emphasizes that the matter is not yet settled.
"We don't know enough to choose between these theories—and in fact it's possible that the toxins escape the endosome by more than one mechanism," he says. "But it's important that we better understand this step in the process to thwart anthrax more effectively."
*B.J. Nablo, R.G. Panchal, S. Bavari, T.L. Nguyen, R. Gussio, W. Ribot, A. Friedlander, D. Chabot, J.E. Reiner, J.W.F. Robertson, A. Balijepalli, K.M. Halverson and J.J. Kasianowicz. Anthrax toxin-induced rupture of artificial lipid bilayer membranes. Journal of Chemical Physics, Aug. 8, 2013 (Vol.139, Issue 6), DOI: 10.1063/1.4816467
**Edited on Aug. 28, 2013 to correct quote.
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JILA Researchers Discover Atomic Clock Can Simulate Quantum Magnetism
Researchers at JILA have for the first time used an atomic clock as a quantum simulator, mimicking the behavior of a different, more complex quantum system.*
Atomic clocks now join a growing list of physical systems that can be used for modeling and perhaps eventually explaining the quantum mechanical behavior of exotic materials such as high-temperature superconductors, which conduct electricity without resistance. All but the smallest, most trivial quantum systems are too complicated to simulate on classical computers, hence the interest in quantum simulators. Sharing some of the features of experimental quantum computers—a hot research topic—quantum simulators are "special purpose" devices designed to provide insight into specific challenging problems.
JILA is operated jointly by the National Institute of Standards and Technology (NIST) and the University of Colorado Boulder.
As described in the Aug. 9 issue of Science, the JILA experiment was performed with an atomic clock made of about 2,000 neutral strontium atoms trapped in intersecting laser beams. The researchers were surprised to discover that, under certain conditions, the clock atoms interact like atoms in magnetic materials.
"This was completely unexpected," JILA/NIST Fellow Jun Ye says. "We were not looking for this at all, we were just naively trying to understand the particle interactions as part of our effort to further improve the clock. We were pleasantly surprised to find we can now use a clock as a powerful quantum apparatus to study magnetic spin interactions."
The strontium clock atoms are arranged like a stack of 100 pancakes, each containing about 20 atoms. Normally the atoms react individually to red laser pulses, switching between two energy levels. But researchers discovered the atoms also can interact with each other, first in pairs and eventually all together. Until now researchers were trying to eliminate these interactions, which are undesirable in atomic clocks** but they can turn into a powerful feature for a quantum simulator.
Strontium atoms have two energy levels used for clock purposes, each with a particular configuration of electrons. In the JILA simulation, all the atoms start out at the same energy level with the same electron configuration, also called a spin-down state. A quick pulse from a very stable red laser places all the atoms in a "superposition" of spins pointing both up and down at the same time. The possibility of superposition is one of the most notable features of the quantum world. When the laser is turned off, the atoms start to interact. One second later another pulse from the same laser hits the atoms to prepare them for collective spin measurement, and then a different laser measures, based on any detected fluorescence, the final spin states of all the atoms.
In the world of classical physics such measurements would have definite results, without any "noise," or uncertainty. However, in the quantum world a spin measurement usually has a random amount of noise. In the JILA experiment, correlations appear over time between the noise patterns of some of the atoms' spins. Ye says these correlations suggest the atoms become entangled, another unusual quantum feature that links the properties of separated particles. JILA researchers have not yet performed the definitive test proving entanglement, however.
JILA theorist Ana Maria Rey helped to explain what Ye's experimental team observed. For small numbers of particles, about 30 atoms, Rey calculated that the clock atom interactions obey mathematical formulas similar to those describing the behavior of electrons in magnetic materials. But if more atoms are included, classical calculations would not keep up with the experimental results. In the future the JILA team hopes to perform more complicated simulations while continuing to develop a theory explaining the findings.
The atomic clock joins a growing list of quantum simulators demonstrated recently at NIST*** and elsewhere.
The JILA research is supported by NIST, the Defense Advanced Research Projects Agency, Air Force Office of Scientific Research, National Science Foundation, and Army Research Office.
*M.J. Martin, M. Bishof, M.D. Swallows, X. Zhang, C. Benko, J. von-Stecher, A.V. Gorshkov, A.M. Rey and J. Ye. 2013. A quantum many-body spin system in an optical lattice clock. Science. August 9.
**See 2009 NIST news release, "JILA/NIST Scientists Get a Grip on Colliding Fermions to Enhance Atomic Clock Accuracy," at www.nist.gov/pml/div689/fermions_041609.cfm.
***See 2012 NIST Tech Beat article, "NIST Physicists Benchmark Quantum Simulator with Hundreds of Qubits," at www.nist.gov/pml/div688/qubits-042512.cfm.
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NIST Study Advances Use of Iris Images as a Long-Term Form of Identification
A new report* by biometric researchers at the National Institute of Standards and Technology (NIST) uses data from thousands of frequent travelers enrolled in an iris recognition program to determine that no consistent change occurs in the distinguishing texture of their irises for at least a decade. These findings inform identity program administrators on how often iris images need to be recaptured to maintain accuracy.
For decades, researchers seeking biometric identifiers other than fingerprints believed that irises were a strong biometric because their one-of-a-kind texture meets the stability and uniqueness requirements for biometrics. However, recent research has questioned that belief. A study of 217 subjects over a three-year period found that the recognition of the subjects' irises became increasingly difficult, consistent with an aging effect.**
To learn more, NIST biometric researchers used several methods to evaluate iris stability.
Researchers first examined anonymous data from millions of transactions from NEXUS, a joint Canadian and American program used by frequent travelers to move quickly across the Canadian border. As part of NEXUS, members' irises are enrolled into the system with an iris camera and their irises are scanned and matched to system files when they travel across the border. NIST researchers also examined a larger, but less well-controlled set of anonymous statistics collected over a six-year period.
In both large-population studies, NIST researchers found no evidence of a widespread aging effect, said Biometric Testing Project Leader Patrick Grother. A NIST computer model estimates that iris recognition of average people will typically be useable for decades after the initial enrollment.
"In our iris aging study we used a mixed effects regression model, for its ability to capture population-wide aging and individual-specific aging, and to estimate the aging rate over decades," said Grother. "We hope these methods will be applicable to other biometric aging studies such as face aging because of their ability to represent variation across individuals who appear in a biometric system irregularly."
NIST researchers then reanalyzed the images from the earlier studies of 217 subjects that evaluated the population-wide aspect. Those studies reported an increase in false rejection rates over time—that is, the original, enrolled images taken in the first year of the study did not match those taken later. While the rejection numbers were high, the results did not necessarily demonstrate that the iris texture itself was changing. In fact, a study by another research team identified pupil dilation as the primary cause behind the false rejection rates.*** This prompted the NIST team to consider the issue.
NIST researchers showed that dilation in the original pool of subjects increased in the second year of the test and decreased the next, but was not able to determine why. When they accounted for the dilation effect, researchers did not observe a change in the texture or aging effect. Some iris cameras normalize dilation by using shielding or by varying the illumination.
NIST established the Iris Exchange (IREX) program in 2008 to give quantitative support to iris recognition standardization, development and deployment. Sponsors for this research include the Criminal Justice Information Systems Division of the Federal Bureau of Investigation, the Office of Biometric Identity Management in the Department of Homeland Security (DHS) and the DHS Science and Technology Directorate.
*The NIST results are reported in IREX VI – Temporal Stability of Iris Recognition Accuracy, NIST Interagency Report 7948, at www.nist.gov/manuscript-publication-search.cfm?pub_id=913900.
**S. Fenker and K.W. Bowyer. Experimental evidence of a template aging effect in iris biometrics. IEEE Computer Society Workshop on Applications of Computer Vision, November 2012.
***M. Fairhurst and M. Erbilek. Analysis of physical ageing effects in iris biometrics. IET Computer Vision, 5(6):358–366, 2011. ww.ietdl.org.
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Two Updated Guides Provide Latest NIST Recommendations for System Patches, Malware Avoidance
The National Institute of Standards and Technology (NIST) has updated two of its series of computer security guides to help computer system managers protect their systems from hackers and malware. Vulnerabilities in software and firmware are the easiest ways to attack a system, and the two revised publications approach the problem by providing new guidance for software patching and warding off malware.
A common method to avoid attacks is to "patch" the vulnerabilities as soon as possible after the software company develops a piece of repair software—a patch—for the problem. Patch management is the process of identifying, acquiring, installing and verifying patches for products and systems.
The earlier guidance on patching, Creating a Patch and Vulnerability Management Program, was written when patching was a manual process. The revision, Guide to Enterprise Patch Management Technologies,* is designed for agencies that take advantage of automated patch management systems such as those based on NIST's Security Content Automation Protocol (SCAP).
Guide to Enterprise Patch Management Technologies explains the technology basics and covers metrics for assessing the technologies' effectiveness.
The second security document provides guidance to protect computer systems from malware—malicious code. Malware is the most common external threat to most systems and can cause widespread damage and disruption.
NIST's Guide to Malware Incident Prevention and Handling for Desktops and Laptops** was updated to help agencies protect against modern malware attacks that are more difficult to detect and eradicate than when the last version was published in 2005. The new guidance reflects the growing use of social engineering and the harvesting of social networking information for targeting attacks.
The new malware guide provides information on how to modernize an organization's malware incident prevention measures and suggests recommendations to enhance an organization's existing incident response capability to handle modern malware.
*Guide to Enterprise Patch Management Technologies (NIST Special Publication 800-40, Revision 3) is available at: http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-40r3.pdf .
**Guide to Malware Incident Prevention and Handling for Desktops and Laptops (Special Publication 800-83 Revision 1) can be found at: http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-83r1.pdf.
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Two NIST Standards Experts Are Honored With 2013 ANSI Leadership and Service Awards
The American National Standards Institute (ANSI) has recognized two staff members from the National Institute of Standards and Technology (NIST) for their significant contributions to national and international standardization activities, as well as ongoing commitment to their industry, their nation and the enhancement of the global voluntary consensus standards system.
Biometric Testing Project Leader Patrick Grother, of NIST’s Information Technology Laboratory, will receive the Edward Lohse Information Technology Medal, which recognizes outstanding effort to foster cooperation among the bodies involved in global IT standardization. Grother has supported biometrics standardization, particularly with respect to standards for biometric data interchange and testing performance of biometric technologies.
Deputy Standards Liaison Elaine Newton, also in NIST’s Information Technology Laboratory, has been named one of three recipients of the Next Generation Award, which is presented to outstanding members who have been engaged with the association for less than eight years. Newton is being honored for demonstrating vision, leadership, dedication and significant contributions to standards activities since 2006.
The awards will be presented October 2, 2013, during World Standards Week 2013.
ANSI is a private, nonprofit organization whose mission is to enhance U.S. global competitiveness and the American quality of life by promoting, facilitating and safeguarding the integrity of the voluntary standardization and conformity assessment system. The organization is the official U.S representative to the International Organization for Standardization.
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