In This Issue...
NIST Study Suggests Ways to Improve Common Furniture Fire Test
The bench-scale test widely used to evaluate whether a burning cigarette will ignite upholstered furniture may underestimate the tendency of component materials to smolder when these materials are used in sofas and chairs supported by springs or cloth, National Institute of Standards and Technology (NIST) and American University researchers report in a new study.*
The study comes as regulations and methods for evaluating the likelihood that soft-furniture materials will ignite are undergoing scrutiny. In November 2013, California removed an open-flame test from its furniture flammability testing law—the de facto national standard since no national regulation currently exists—and now relies solely on the so-called cigarette-smoldering-ignition test.
The new research identifies changes to this test that might make it more realistic—representative of a "near-worst-case scenario." The modifications, the researchers write, would make the test more consistent and, therefore, more useful for identifying "upholstery materials most likely to prevent smoldering ignition."
In the same article, the research team reports guidelines for making a reproducible reference foam for furniture flammability testing—a challenging, long standing priority of standards developers, regulators and fire researchers. Such a standardized foam would help in comparing flammability data from different laboratories.
In the current setup for the test, two fabric-covered foam pieces are positioned like seat and back cushions on a small solid wood support structure. A lit standard reference cigarette (one certified by NIST to burn consistently) is placed in the crevice formed by the two pieces. To pass, a fabric covering or barrier material under test must prevent the burning cigarette from igniting the underlying foam so that it does not smolder on its own, even after the cigarette self-extinguishes.
The researchers found that directly placing the test samples on top of the wooden support impedes air flow and, as a consequence, inhibits smoldering. They point out that the arrangement is not representative of furniture with cushions that rest on air-permeable substrates such as springs or cloth, which allows air to circulate and promotes smoldering.
The team introduced gaps between the foam samples and the underlying wood, permitting air flow. The adjustment increased—by up to threefold—the rate at which smoldering spread in the foam. It also generated significantly higher smoldering temperatures in the foam—as much as 400 degrees Celsius higher.
"Because it inhibits air flow, the current test apparatus may diminish the propensity for smoldering ignition," explains NIST's Rick Davis. "Creating gaps to increase air flow, and the other modifications we are suggesting—especially adoption of a reference foam—will enable more consistent smoldering behavior and help to minimize other causes of inconsistent flammability test results."
Either overlooked or considered unavoidable, differences in foam samples can be a significant source of ambiguity in flammability test results. Whether a lit cigarette burning on, say, a fabric covering initiates self-sustained smoldering in the underlying foam depends on whether the heat produced exceeds the heat lost. Both heat generated and heat loss are affected by the foam's internal physical structure, as well as other factors.
So, identical swatches of furniture fabric might pass one lab's cigarette-smoldering-ignition test and fail another's because the foam samples were not uniform.
The researchers' guidelines for making a standard reference foam focus on achieving uniformly sized pores, or open cells, that are arrayed throughout the material's internal, Swiss-cheese-like interior. Their experiments indicate that, for a given formulation, samples with same-sized open cells will smolder similarly.
The team found that the process for making polyurethane foams with a network-like, open-cell structure can be controlled sufficiently to minimize differences in cell size so that smoldering behavior is consistent across test samples. In fact, they say, the average cell size can be "easily tuned" so that the sample mimics the smoldering intensity observed in foams used in actual upholstered furniture.
Nationwide, fires in which upholstered furniture is the first item ignited account for about 6,700 home fires annually and result in 480 civilian deaths, or almost 20 percent of home fire deaths between 2006 and 2010, according to the National Fire Protection Association.
The Consumer Product Safety Commission provided financial and technical support for this research.
*M. Zammarano, S. Matko, W.M. Pitts, D.M. Fox and R.D. Davis. Towards a reference polyurethane foam and bench scale test for assessing smoldering in upholstered furniture. Polymer Degradation and Stability (2014), doi: 10.1016/j.polymdegradstab.2013.12.010.
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Clever NIST/JPL Technology Decodes More Information from Single Photons
It's not quite Star Trek communications—yet. But long-distance communications in space may be easier now that researchers at the National Institute of Standards and Technology (NIST) and Jet Propulsion Laboratory (JPL) have designed a clever detector array that can extract more information than usual from single particles of light.
Described in a new paper,* the NIST/JPL array-on-a-chip easily identifies the position of the exact detector in a multi-detector system that absorbs an incoming infrared light particle, or photon. That's the norm for digital photography cameras, of course, but a significant improvement in these astonishingly sensitive detectors that can register a single photon. The new device also records the signal timing, as these particular single-photon detectors have always done.
The technology could be useful in optical communications in space. Lasers can transmit only very low light levels across vast distances, so signals need to contain as much information as possible.
One solution is "pulse position modulation" in which a photon is transmitted at different times and positions to encode more than the usual one bit of information. If a light source transmitted photons slightly to the left/right and up/down, for instance, then the new NIST/JPL detector array circuit could decipher the two bits of information encoded in the spatial position of the photon. Additional bits of information could be encoded by using the arrival time of the photon.
The same NIST/JPL collaboration recently produced detector arrays for the first demonstration of two-way laser communications outside Earth's orbit using the timing version of pulse position modulation.** The new NIST/JPL paper shows how to make an even larger array of detectors for future communications systems.
The new technology uses superconducting nanowire single-photon detectors. The current design can count tens of millions of photons per second but the researchers say it could be scaled up to a system capable of counting of nearly a billion photons per second with low dark (false) counts. The key innovation enabling the latest device was NIST's 2011 introduction of a new detector material, tungsten-silicide, which boosted efficiency, the ability to generate an electrical signal for each arriving photon.*** Detector efficiency now exceeds 90 percent. Other materials are less efficient and would be more difficult to incorporate into complex circuits.
The detectors superconduct at cryogenic temperatures (about minus 270 °C or minus 454 °F), and cooling needs set a limit on wiring complexity. The NIST/JPL scheme requires only twice as many wires (2N) as the number of detectors on one side of a square array (N x N), greatly reducing cooling loads compared to a one-wire-per-detector approach while maintaining high timing accuracy. NIST researchers demonstrated the scheme for a four-detector array with four wires and are now working on a 64-detector array with 16 wires.
In the circuit, each detector is located in a specific column and row of the square array. Each detector acts like an electrical switch. When the detector is in the superconducting state, the switch is closed and the current is equally distributed among all detectors in that column. When a detector absorbs a photon, the switch opens, temporarily diverting the current to an amplifier for the affected column while reducing the signal through the affected row. As a result, the circuit generates a voltage spike in the column readout and a voltage dip in the row readout. The active detector is at the intersection of the active column and row.
The research was supported by the Defense Advanced Research Projects Agency.
*V.B. Verma, R. Horansky, F. Marsili, J.A. Stern, M.D. Shaw, A.E. Lita, R.P. Mirin and S.W. Nam. A four-pixel single-photon pulse position camera fabricated from WSi superconducting nanowire single photon detectors. Applied Physics Letters 104, 051115. DOI: 10.1063/1.4864075. Posted online Feb. 4, 2014.
**See Oct. 28, 2013, National Aeronautics and Space Administration news release, "Historic Demonstration Proves Laser Communication Possible," at www.nasa.gov/content/goddard/historic-demonstration-proves-laser-communication-possible/#.Um62W3Dkvv2.
***See 2011 NIST Tech Beat article, "Key Ingredient: Change in Material Boosts Prospects of Ultrafast Single-photon
(Top) The same basic cell type grown on two different bio scaffolds (collagen gel and a grid-like scaffold made of a biocompatible polymer) adopts significantly different shapes. The superimposed ellipsoids are calculated from the dimensions of each cell. (Bottom) Plotting the characteristic ellipsoids for each cell by how round they are in the two major cross sections reveals that cells tend to different shapes on different scaffolds--spheres at one extreme, long narrow rods at another.
Credit: Farooque, Camp, Simon/NIST
With the notable exception of Flat Stanley, we all live, and are shaped by, a 3-dimensional world. Biologists have accepted that this dimensional outlook is just as important to growing cells. A key challenge in tissue engineering—the engineering of living cells to grow into replacement or repair tissues such as bone, heart muscle, blood vessels or cartilage—is creating 3-D scaffolds to support the cells as they grow and provide an appropriate environment so that they develop into viable tissue.**
This, says NIST materials scientist Carl Simon, has led to a large and rapidly expanding collection of possible 3D scaffolds, ranging from relatively simple gels made of collagen, the body's natural structural matrix, to structured or unstructured arrangements of polymer fibers, hydrogels and many more.
"What we're trying to measure," Simon explains, "is 'what is 3D in this context?' Presumably, a scaffold provides some sort of microenvironment—a niche that allows a cell to adopt the normal 3D morphology that it would have in the body. But you can't measure the niche because that's sort of an amorphous, ill-defined concept. So, we decided to measure cell shape and see how that changes, if it becomes more 3D in the scaffold."
The NIST team made painstaking measurements of individual cells in a variety of typical scaffolds using a confocal microscope, an instrument that can make highly detailed, 3-dimensional images of a target, albeit with very lengthy exposure times. They then used a mathematical technique—"gyration tensors"—to reduce each cell's shape to a characteristic ellipsoid. Ellipsoids can range in shape from points or spheres to flat ellipses or elongated sticks to something like an American football.
Analyzing the ellipsoid collection allowed them to categorize average cell shapes by scaffold. Cells in collagen gels and some fiber scaffolds, for example, tend toward a 1-dimensional rod shape. Other scaffolds promoted 2-dimensional disks, while a synthetic gel using a material called PEGTM* seems to encourage spheres.
"This technique," says Simon, "gives you a way to compare these different scaffolds. There are hundreds of scaffolds being advanced. It's hard to know how they differ with respect to cell morphology. By looking at the cell shape in 3D with this approach, you can compare them. You can say this one makes the cells more 3-dimensional, or this one makes the cells more like they would develop in collagen, depending on what you want. "
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Researchers at the National Institute of Standards and Technology (NIST) have developed a new method for accurately measuring a key process governing a wide variety of cellular functions that may become the basis for a "health checkup" for living cells.
NMR data showing the levels of reduced glutathione (GSH) and oxidized glutathione (GSSG) over time in yeast cells at rest (top) and under oxidative stress (bottom). The cells at rest have almost no GSSG (dark blue shades) but it spikes briefly when they are stressed, while GSH declines. This type of analysis may one day help to measure cell health.
The NIST technique measures changes in a living cell's internal redox (reduction-oxidation) potential, a chemistry concept that expresses the favorability of reactions in which molecules or atoms either gain or lose electrons. Redox reactions are important to cell chemistry because they regulate many genes and the proteins they produce. An accurate measure of redox potential can provide insight into how well these genes are working, and in turn, whether or not the activities they control—such as differentiation and growth—are functioning normally.
To assess this, scientists customarily measure the levels of both the reduced (electrons added) and oxidized (electrons lost) forms of glutathione, a peptide the cell uses as an antioxidant. Glutathione in cells is found predominately in the reduced state, known as GSH, but some gets converted to the oxidized form, known as GSSG. A high amount of GSSG indicates a cell has suffered oxidative stress, a process believed to contribute to cell aging, breakdown, malfunction (such as cancer) and eventual death.
Unfortunately, traditional methods of obtaining this data are akin to an autopsy. The only way to measure the relative amounts of GSH and GSSG within a cell has been to rupture its membrane—killing it—and then examine the released contents.
The NIST team developed a way to measure GSH and GSSG levels in living cells in real time using nuclear magnetic resonance (NMR)spectroscopy, a technique that images individual molecules similar to how doctors use magnetic resonance imaging (MRI) to noninvasively view organs. "NMR has been shown in recent years to be a powerful tool for studying metabolites as they operate in living cells, so we felt it could work well as a noninvasive way to do the same for GSH and GSSG," says NIST research chemist Vytas Reipa.
In their proof-of-concept experiment,* the NIST researchers grew a mutant strain of yeast cells that could not manufacture their own glutathione in a medium containing the peptide tagged with a nitrogen isotope. This ensured that the only glutathione available in the cells would be detectable using NMR during its conversion from GSH to GSSG.
GSH and GSSG levels were measured by NMR for both cells at rest and under oxidative stress, and then used to calculate the changing intracellular redox potentials over time. The results showed, for the first time ever, that redox potential can serve as an indicator of how cells perform in response to oxidation in real time.
"We know that when oxidation tips the balance toward too much GSSG, we get a redox potential shifted more to the positive than it should be," Reipa explains. "A healthy cell compensates by reversing the process and when that happens, the redox potential shifts back to its original value. A sick cell, on the other hand, does not compensate and the value stays positive. Therefore, an accurate in-cell measurement of redox potential could one day help us determine how well cells can recover from oxidative stress and, as a result, give us a picture of the cell's overall health."
Currently, the NIST researchers are exploring other NMR-detectable peptides involved in reduction and oxidation processes to conduct studies with mammalian cells.
The NMR spectroscopy in this experiment was conducted at NIST's Gaithersburg, Md., facility in collaboration with NIST scientists at the Hollings Marine Laboratory (HML) in Charleston, S.C., and the Institute for Bioscience and Biotechnology Research (IBBR) in Rockville, Md.
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The National Institute of Standards and Technology's (NIST) Hollings Manufacturing Extension Partnership (MEP) has announced two funding awards that will support small and mid-sized manufacturers in Nebraska and Alaska.
The University of Alaska Anchorage will evaluate the technical needs of small and mid-sized manufacturers in Alaska on behalf of NIST's Manufacturing Extension Partnership.
Credit: Courtesy University of Alaska Anchorage
Following a competition open to U.S.-based nonprofit organizations, the University of Nebraska-Lincoln has been awarded a cooperative agreement and $600,000 to host an MEP center. The funding represents half of the center's operating funds for one year; it must provide matching funds from nonfederal sources. Centers may apply for an annual award renewal, but the mandatory cost-share increases after the third renewal, up to a maximum two-thirds of the center's budget for year five and beyond. The center will become part of the national MEP system, comprising more than 400 centers and field offices throughout the United States and Puerto Rico.
MEP centers provide services that help manufacturing firms enhance their productivity, innovative capacity and technological performance, which strengthens America's global competitiveness. According to the National Association of Manufacturers, in 2012, Nebraska manufacturers accounted for 12.5 percent of the state's total output, employing 9.6 percent of the workforce. Compensation for manufacturing jobs that year was $12,000 higher on average than for the state's other nonfarm employees.
NIST also has awarded $150,000 to the University of Alaska Anchorage as a State Technology Extension Assistance Project. The funding supports efforts to assess the technical needs of small and mid-sized manufacturers in Alaska, as the state seeks to diversify its manufacturing base. This effort may lead to the future creation of an MEP center in the state. For every one dollar of federal investment, the MEP generates nearly $19 in new sales growth and $21 in new client investment. This translates into $2.2 billion in new sales annually. For every $1,978 of federal investment, MEP creates or retains one manufacturing job.
To learn more about MEP, visit www.nist.gov/mep.
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A workshop aimed at improving federal cryptographic key management systems will be held at the National Institute of Standards and Technology (NIST)'s Gaithersburg, Md., campus on March 4-5, 2014.
The workshop will focus on discussing a draft NIST Special Publication that will establish specific requirements for federal organizations desiring to use or operate a cryptographic key management system. Protecting sensitive electronic information requires cryptographic algorithms that depend on "keys," the cryptographic equivalent of a password. Effectively managing the secure use and distribution of these keys is considered one of the most difficult aspects of cryptographic technology.
This draft publication up for discussion, SP 800-152 ("A Profile for U.S. Federal CKMS"), is based on the requirements in SP 800-130 ("A Framework for Designing Cryptographic Key Management Systems"), and is available for public comment at http://csrc.nist.gov/publications/PubsDrafts.html#SP-800-152.
Registration is required by Feb. 25 for permission to enter the NIST campus. Visit https://www-s.nist.gov/CRS/conf_disclosure.cfm?conf_id=6671 to register; onsite registration is not available. The conference also will be webcast, and registration is not required for viewing.
More information is available at http://www.nist.gov/itl/csd/ct/ckm_workshop2014.cfm.
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