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In This Issue...
Terracotta and Cement Roofs Vulnerable in Wildfires, NIST Study Finds
Although made of fire-resistant materials, terracotta and cement roof tiles are vulnerable to penetration by windblown embers generated in wildfires, according to new research findings* from the National Institute of Standards and Technology (NIST).
In scoping experiments conducted in the Fire Research Wind Tunnel Facility at Japan's Building Research Institute, NIST fire scientist Samuel Manzello found that the embers—or firebrands—infiltrated gaps between certain types of roofing tiles and, once trapped, proceeded to melt the underlayment below.
Of the four roof styles studied, the flat tile terracotta roofing assembly performed best probably due to its interlocking design. For these tiles, the firebrands were observed to become trapped within the interlocking sections of the tiles and, as a result, the firebrands did not penetrate past the tiles towards the underlayment.
Manzello cautions, however, against a false sense of security with this type of roofing assembly.
"Over time, gaps can develop in roofing assemblies due to settling of the structure, aging of the materials, earthquakes or other causes," he says. In an earlier study,** Manzello and colleagues simulated this effect and observed greatly reduced performance of ceramic roofing assemblies as compared to well-aligned Spanish tile roofing assemblies.
This infiltration of embers through gaps, he explains, ultimately could lead to ignition of materials in an attic space immediately below.
The research findings suggest that one potential approach to reducing wildfire risks would be to install continuous, fire-resistant underlayments. This hypothesis, Manzello says, requires further investigation.
In the new research, Manzello studied roof assemblies made of flat and profiled (wave-like) cement and terracotta tiles. The assemblies were exposed to firebrand showers generated by the NIST-developed firebrand generator. Devised by Manzello, the generator, or NIST Dragon, is a two-meter tall, goose-neck-shaped apparatus that breathes in wood chips and exhales firebrands at a controlled rate.*** The novel device supports NIST's program to improve the fire-resistance or hardening of structures in the wildland-urban interface (WUI), with the ultimate aim of reducing property damage and the threat to life safety associated with WUI fires.
*S.L. Manzello, The Performance of Concrete Tile and Terracotta Tile Roofing Assemblies Exposed to Wind-Driven Firebrand Showers, (NIST Technical Note 1794) March 2013. Available at: http://dx.doi.org/10.6028/NIST.TN.1794.
** S.L, Manzello, Y. Hayashi, Y. Yoneki and Y.Yamamoto, Quantifying the vulnerabilities of ceramic tile roofing assemblies to ignition during a firebrand attack. Fire Safety Journal 45 (2010), pp. 35-43.
*** See the Sept. 27, 2011 Tech Beat item, "In Unique Fire Tests, Outdoor Decks Will Be Under Firebrand Attack" at www.nist.gov/public_affairs/tech-beat/tb20110927.cfm#fire.
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Innovation in Spectroscopy Could Improve Greenhouse Gas Detection
Detecting greenhouse gases in the atmosphere could soon become far easier with the help of an innovative technique* developed by a team at the National Institute of Standards and Technology (NIST), where scientists have overcome an issue preventing the effective use of lasers to rapidly scan samples.
The team, which recently published its findings in the journal Nature Photonics, says the technique also could work for other jobs that require gas detection, including the search for hidden explosives and monitoring chemical processes in industry and the environment.
Searching for faint whiffs of an unusual gas mixed in the air is called "trace gas sensing." By far, the most common method is spectroscopy—identifying gas molecules by the unique set of frequencies of light that each absorbs. The telltale pattern of dark lines in a spectrum indicates which gases are present in the mix. Accurately measuring the concentrations of relatively low-concentration gases, however, requires a lot of light, generated by a laser that can be tuned to different colors. Until now, tuning a laser to shine in a wide enough range of colors typically has required a mechanical device to change the frequency, but all the available methods adjust the laser too slowly to obtain meaningful snapshots of the turbulent atmosphere.
"One of the major goals in climate science is to combine a wide variety of high-accuracy atmospheric measurements, including ground-based, aircraft and satellite missions, in order to fully understand the carbon cycle," says the research team's David Long, a scientist in NIST's Chemical Sciences Division. "The technology we've developed is general enough to be applicable for each of these platforms. The high speed of the technique allows for very accurate measurements of atmospheric gases at rates which are faster than atmospheric changes in temperature and pressure due to turbulence."
The team found a solution using electronics that permit fast and discrete changes in frequency. The components—called an electro-optic modulator and an optical resonator—work together to alter the laser so that its light shines in a number of different frequencies, and then to filter these frequencies so that the laser only shines in one color at any given instant. The new method allows a wide range of different frequencies to pass through a gas sample in a few milliseconds or less, with the added benefit of providing a clearer and more accurate resulting spectrum than the previous "slow scan" methods could.
Long says that the Nature Photonics paper details the use of the technique in a controlled laboratory environment using a small sample chamber for ground-based measurements, but that the team has submitted other papers with data indicating the technique also could work at great distances—potentially allowing a scanner to be mounted on a vehicle, an aircraft or a satellite. The team also has applied for a patent on its work, he says.
*G.-W. Truong, K.O. Douglass, S.E. Maxwell, R.D. van Zee, D.F. Plusquellic, J.T. Hodges and D.A. Long. Frequency-agile, rapid scanning spectroscopy. Nature Photonics, DOI: 10.1038/NPHOTON.2013.98, April 28, 2013.
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Squishy Hydrogels May Be the Ticket for Studying Biological Effects of Nanoparticles
A class of water-loving, jelly-like materials with uses ranges ranging from the mundane, such as superabsorbent diaper liners, to the sophisticated, such as soft contact lenses, could be tapped for a new line of serious work: testing the biological effects of nanoparticles now being eyed for a large variety of uses.
New research* by scientists at the National Institute of Standards and Technology (NIST) demonstrates that three-dimensional scaffolds made with cells and supporting materials known as hydrogels can serve as life-like measurement platforms for evaluating how tiny engineered materials interact with cells and tissues. Their proof-of-concept study suggests that hydrogel tissue scaffolds can be a "powerful bridge" between current laboratory tests and tests that use animal models.
Today, laboratory tests of nanoparticles usually entail exposing a two-dimensional layer of cells to the material of interest. Besides being questionable substitutes for the complex cellular frameworks that make up tissues and organs inside the body, these tests can yield conflicting results, explains analytical chemist Elisabeth Mansfield, lead researcher on the new NIST study.
"Our study shows that hydrogel-based, tissue-engineering scaffolds can provide more realistic environments to study nanoparticle-influenced cell biology over extended periods," she says. Importantly, the NIST research shows that studies employing the scaffold do not require exposing cells to nanoparticles in doses that exceed normal exposure levels.
Hydrogels are networks of stringy, branching polymer molecules with ends that latch onto water molecules—so much so that 99.9 percent of a hydrogel may consist of water. Depending on the spacing between the strands (the so-called mesh size) and other factors, hydrogels can support and promote the growth and differentiation of cell populations.
While hydrogels occur naturally—an example is cartilage—the NIST team chose to craft its own, giving them control over the mesh size in the scaffolds they created.
In their experiment, the team used polyethylene glycol—a common polymer used in skin creams, toothpaste, lubricants and other products—to create three hydrogels with different mesh sizes. One set of hydrogels was populated with rat cells containing ultrasmall semiconducting materials known as quantum dots. When exposed to light, quantum dots emit strong fluorescent signals that enabled the researchers to track the fate of treated cells in the synthetic scaffolds.
Results were compared with those for similarly treated cells grown in a single layer on a substrate, akin to standard laboratory toxicology tests.
The NIST researchers found that cells diffused through the hydrogel scaffold, forming a persisting tissue-like structure. Quantum dots attached to cell membranes and, over time, were absorbed into the cells.
Three-dimensional scaffolds often are used to test cells for multi-week experiments, and NIST researchers found quantum dots can be detected for four or more days inside the scaffold.
As significant, cells that populated the hydrogel scaffolds were exposed to lower levels of quantum dots, yielding a more representative scenario for evaluating biological effects.
The NIST team concludes that, compared with conventional cell cultures, hydrogel scaffolds provide a more realistic, longer-lived biological environment for studying how engineering nanoparticles interact with cells. In addition, the scaffolds will accommodate studies of how these interactions evolve over time and of how the physical features of nanoparticles may change.
*E. Mansfield, T.L. Oreskovic, N.S. Rentz, and K.M. Jeerage, Three-dimensional hydrogel constructs for exposing cells to nanoparticles. Nanotoxicology, 2013; Early Online. DOI: 10.3109/17435390.2013.790998.
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NIST Demonstrates Significant Improvement in the Performance of Solar-Powered Hydrogen Generation
Using a powerful combination of microanalytic techniques that simultaneously image photoelectric current and chemical reaction rates across a surface on a micrometer scale, researchers at the National Institute of Standards and Technology (NIST) have shed new light on what may become a cost-effective way to generate hydrogen gas directly from water and sunlight.*
Their quarry is a potentially efficient, cost-effective, photoelectrochemical (PEC) cell—essentially a solar cell that produces hydrogen gas instead of electric current. "A major challenge with solar energy is dealing with solar intermittency," says NIST chemical engineer Daniel Esposito. "We demand energy constantly, but the sun's not always going to be shining, so there's an important need to convert solar energy into a form we can use when the sun's not out. For large-scale energy storage or transportation, hydrogen has a lot of benefits."
At its simplest, a PEC cell contains a semiconducting photoelectrode that absorbs photons and converts them into energetic electrons, which are used to facilitate chemical reactions that split water molecules into hydrogen and oxygen gases. It's not that easy. The best PEC cell has been demonstrated with an efficiency around 12.5 percent,** says Esposito. But, "it's been estimated that such a cell would be extremely expensive—thousands of dollars per square meter—and they also had issues with stability," he says. One big problem is that the semiconductors used to achieve the best conversion efficiency also tend to be highly susceptible to corrosion by the cell's water-based electrolyte. A PEC electrode that is efficient, stable and economical to produce has been elusive.
The NIST team's proposed solution is a silicon-based device using a metal-insulator-semiconductor (MIS) design that can overcome the efficiency/stability trade-off. The key is to deposit a very thin, but very uniform, layer of silicon dioxide—an insulator—on top of the semiconductor—silicon—that is well-suited for doing the photon-gathering work. On top of that is a polka-dot array of tiny electrodes consisting of platinum-covered titanium. The stable oxide layer protects the semiconductor from the electrolyte, but it's thin enough and transparent enough that the photons will travel through it to the semiconductor, and the photo-generated electrons will "tunnel" in the opposite direction to reach the electrodes, where the platinum catalyzes the reaction that produces hydrogen.
The MIS device requires good production controls—the oxide layer in particular has to be deposited precisely—but Esposito notes that they used fabrication techniques that are standard in the electronics industry, which has decades of experience in building low-cost, silicon-based devices.
To study the system in detail, the NIST team scanned the surface of the device with a laser beam, illuminating only a small portion at a time to record photocurrent with micrometer resolution. In tandem with the beam, they also tracked an "ultramicroelectrode" across the surface to measure the rate of molecular hydrogen generation, the chemical half of the reaction.*** The combination allowed them to observe two bonus effects of the MIS photoelectrode design: a secondary mechanism for hydrogen generation caused by the channeling of electrons through the oxide layer, and a more efficient transport of electrons to the reaction site than predicted.
The NIST team calculates an efficiency of 2.9 percent for their device, which also exhibits excellent stability during operation. While this efficiency is far lower than more costly designs, they note that it is 15 times better than previously reported results for similar silicon-based MIS devices, and the new data from their microanalysis of the system points towards several potential routes to improving performance. The detailed results are found in Nature Materials.
* D.V. Esposito, I. Levin, T.P. Moffat and A.A. Talin. H2 evolution at Si-based metal–insulator–semiconductor photoelectrodes enhanced by inversion channel charge collection and H spillover. Nature Materials. Published online, May 5, 2013. doi:10.1038/nmat3626.
** In the 90s by the U.S. Department of Energy's National Renewable Energy Laboratory.
*** Technically, scanning photocurrent microscopy (SPCM) and scanning electrochemical microscopy (SECM).
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New Report Identifies Strategies to Achieve Net-Zero Energy Homes
Chances are you know how many miles your car logs for each gallon or tankful of gas, but you probably have only a foggy idea of how much energy your house consumes, even though home energy expenditures often account for a larger share of the household budget.
This disparity in useful energy data is just one of several information gaps that must be bridged as the United States transitions towards residences that generate as much energy as they use over the course of a year—so-called net-zero houses.
Gaps—and strategies to overcome them—are summarized in Strategies to Achieve Net-Zero Energy Homes: A Framework for Future Guidelines, a new publication* from the National Institute of Standards and Technology (NIST) based on the discussions at a 2011 workshop convened by the agency.
One such strategy, proffered by experts who attended the workshop, is to require that energy costs be listed in all real-estate transactions.
"This means incorporating energy in the appraisal process, and the valuation of principal, interest, taxes, and insurance (PITI), so that it incorporates energy cost considerations to become the valuation of principal, interest, taxes, insurance, and energy cost considerations (PITIE)," the report says.
The report breaks out three categories of challenges: design, technology and equipment, and the needs and behaviors of homeowners and the building industry.
With regard to design, one workshop recommendation is to establish a scoring system for new and used homes so that prospective buyers can "compare energy, durability, indoor air quality, accessibility, and other factors relative to their needs."
In net-zero energy homes, energy loads will be substantially lower than current heating and cooling equipment is built to deliver and existing product performance standards are designed to test. According to the report, manufacturers will need new guidelines and underlying data that will help them size their equipment offerings appropriately and align performance with the conditions and requirements of net-zero energy homes.
The behaviors and requirements of homeowners and builders may provide the most complex set of challenges. One clear need, the report says, is to help designers, builders and occupants understand how best to collect and analyze home energy data.
"Consumers require information that is useful, timely and understandable to be able to make the energy purchase and consumption decisions necessary to achieve net-zero energy for new and existing homes," the report says.
To obtain the 41-page summary report, go to: www.nist.gov/manuscript-publication-search.cfm?pub_id=911717 or http://dx.doi.org/10.6028/NIST.SP.1140.
* N.A. McNabb. Strategies to Achieve Net-Zero Energy Homes: A Framework for Future Guidelines Workshop Summary Report. NIST Special Publication 1140, April 2013. http://dx.doi.org/10.6028/NIST.SP.1140
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FLC Names Zielinski National Chair, Honors Satterfield with STEM Award
The Federal Laboratory Consortium for Technology Transfer (FLC), the nationwide network that promotes and strengthens technology transfer from its membership of 300 federal laboratories and centers, recently honored two officials from the National Institute of Standards and Technology (NIST).
Paul Zielinski, director of NIST’s Technology Partnerships Office, has been elected for a two-year term as the FLC national chair, starting in October 2013. In this position, Zielinski will serve as the organization’s chief executive, head its executive board and executive committee, and be responsible for leading activities that advance FLC’s mission to “create an environment that adds value to and supports the technology transfer efforts of its members and potential partners.”
The FLC also recently announced that Mary Satterfield, scientific advisor to the director of NIST’s Materials Measurement Laboratory, has been named as a winner of the 2013 STEM Award. The award “recognizes the efforts of an FLC laboratory employee (or team) that has demonstrated outstanding work in support of science, technology, engineering and mathematics (STEM) education during the past year.” At NIST, Satterfield has led the development and operation of the agency’s Summer Institute for Middle School Science Teachers, a two-week workshop for science teachers in Grades 6-8 with hands-on activities, lectures, tours and visits with scientists.
For more information on the FLC, go to www.federallabs.org.
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Five at NIST Honored with Flemming Awards
The Trachtenberg School of Public Policy and Public Administration at The George Washington University has announced that five researchers at the National Institute of Standards and Technology (NIST) are among 13 federal employees being honored with 2012 Arthur S. Flemming Awards.
Gretchen Campbell (Physical Measurement Laboratory, Quantum Measurement Division) is being honored for her pioneering accomplishments in the emerging field of atomtronics, in which ultracold atoms are manipulated to make "atom circuits" in analogy to electrical circuits.
Kathryn Beers (Materials Measurement Laboratory, Materials Science and Engineering Division) is being honored for her contributions to controlled polymer synthesis, microfluidic technology for the production and analysis of new materials and creative approaches to advance green polymer chemistry.
Michal Chojnacky (Physical Measurement Laboratory, Sensor Science Division) is being honored for her work in applying research in temperature measurement to public health clinics and primary care physician offices to help ensure the potency of over $3.6 billion dollars of vaccines distributed each year through programs administered by the CDC.
Leticia Pibida (Physical Measurement Laboratory, Radiation and Biomolecular Physics Division) is being honored "for her tireless efforts … to ensure that the Nation's security and first response communities have the radiation detection equipment they need, designed to the highest standards and for the intended users, in their continuing efforts to guard the nation against radiological and nuclear threats on U.S. soil.
Joel Ullom (Physical Measurement Laboratory, Quantum Electronics and Photonics Division) is being recognized for his work in developing and deploying "a revolutionary new type of high-resolution radiation detector to solve important national measurement problems related to nuclear nonproliferation, nuclear forensics, and advanced materials analysis."
In a speech before the Washington, D.C., Downtown Jaycees in the late 1940s, Dr. Arthur S. Flemming suggested that the group create an award to recognize exceptional young employees within the federal government. Flemming felt that a chapter in the nation's capital was in the perfect position to educate the public about the contributions young civil servants make to America.
In 1948, the Downtown Jaycees established and presented the first Flemming Awards. Since 1998, the awards have been administered by The George Washington University, which will present the awards at a ceremony on June 10, 2013. The full citations for the Flemming award winners are at http://flemming.gwu.edu/.
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NIST Fire Protection Engineer Named Service to America Finalist
Daniel Madrzykowski, a National Institute of Standards and Technology (NIST) fire protection engineer with a 25-year track record of conducting research that saves lives and improves the effectiveness of fire-fighting techniques, has been named as a finalist for the 2013 Service to America Medals.
The awards are presented annually by the nonprofit, nonpartisan Partnership for Public Service to celebrate excellence in the federal civil service. Honorees are chosen on the basis of their commitment and innovation, as well as the impact of their work on addressing the needs of the nation.
A registered professional engineer, Madrzykowski has conducted studies on fire suppressants, gas and oil well fires, the effects of sprinkler systems on temperature and toxic concentrations of fire gases, fire incident simulations, and an array of innovative fire-fighting methods. His research often is carried out in cooperation with fire departments across the nation during “live burns” of abandoned homes and buildings.
To read about the research being conducted by the NIST Fire Fighting Technology Group, which Madrzykowski currently leads, go to: www.nist.gov/fire
The 2013 finalists are contenders for eight Service to America Medals, including Federal Employee of the Year. Medal recipients will be announced on October 3, 2013, at the Andrew Mellon Auditorium in Washington, D.C. Read more about the finalists at http://servicetoamericamedals.org/SAM/finalists/index.shtml.
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