NASA develops super-black material that absorbs light across multiple wavelength bands

ScienceDaily (Nov. 8, 2011) — NASA engineers have produced a material that absorbs on average more than 99 percent of the ultraviolet, visible, infrared, and far-infrared light that hits it -- a development that promises to open new frontiers in space technology.

The team of engineers at NASA's Goddard Space Flight Center in Greenbelt, Md., reported their findings recently at the SPIE Optics and Photonics conference, the largest interdisciplinary technical meeting in this discipline. The team has since reconfirmed the material's absorption capabilities in additional testing, said John Hagopian, who is leading the effort involving 10 Goddard technologists.

"The reflectance tests showed that our team had extended by 50 times the range of the material's absorption capabilities. Though other researchers are reporting near-perfect absorption levels mainly in the ultraviolet and visible, our material is darn near perfect across multiple wavelength bands, from the ultraviolet to the far infrared," Hagopian said. "No one else has achieved this milestone yet."

The nanotech-based coating is a thin layer of multi-walled carbon nanotubes, tiny hollow tubes made of pure carbon about 10,000 times thinner than a strand of human hair. They are positioned vertically on various substrate materials much like a shag rug. The team has grown the nanotubes on silicon, silicon nitride, titanium, and stainless steel, materials commonly used in space-based scientific instruments. (To grow carbon nanotubes, Goddard technologist Stephanie Getty applies a catalyst layer of iron to an underlayer on silicon, titanium, and other materials. She then heats the material in an oven to about 1,382 degrees Fahrenheit. While heating, the material is bathed in carbon-containing feedstock gas.)

The tests indicate that the nanotube material is especially useful for a variety of spaceflight applications where observing in multiple wavelength bands is important to scientific discovery. One such application is stray-light suppression. The tiny gaps between the tubes collect and trap background light to prevent it from reflecting off surfaces and interfering with the light that scientists actually want to measure. Because only a small fraction of light reflects off the coating, the human eye and sensitive detectors see the material as black.

In particular, the team found that the material absorbs 99.5 percent of the light in the ultraviolet and visible, dipping to 98 percent in the longer or far-infrared bands. "The advantage over other materials is that our material is from 10 to 100 times more absorbent, depending on the specific wavelength band," Hagopian said.

"We were a little surprised by the results," said Goddard engineer Manuel Quijada, who co-authored the SPIE paper and carried out the reflectance tests. "We knew it was absorbent. We just didn't think it would be this absorbent from the ultraviolet to the far infrared."

If used in detectors and other instrument components, the technology would allow scientists to gather hard-to-obtain measurements of objects so distant in the universe that astronomers no longer can see them in visible light or those in high-contrast areas, including planets in orbit around other stars, Hagopian said. Earth scientists studying the oceans and atmosphere also would benefit. More than 90 percent of the light Earth-monitoring instruments gather comes from the atmosphere, overwhelming the faint signal they are trying to retrieve.

Currently, instrument developers apply black paint to baffles and other components to help prevent stray light from ricocheting off surfaces. However, black paints absorb only 90 percent of the light that strikes it. The effect of multiple bounces makes the coating's overall advantage even larger, potentially resulting in hundreds of times less stray light.

In addition, black paints do not remain black when exposed to cryogenic temperatures. They take on a shiny, slightly silver quality, said Goddard scientist Ed Wollack, who is evaluating the carbon-nanotube material for use as a calibrator on far-infrared-sensing instruments that must operate in super-cold conditions to gather faint far-infrared signals emanating from objects in the very distant universe. If these instruments are not cold, thermal heat generated by the instrument and observatory, will swamp the faint infrared they are designed to collect.

Black materials also serve another important function on spacecraft instruments, particularly infrared-sensing instruments, added Goddard engineer Jim Tuttle. The blacker the material, the more heat it radiates away. In other words, super-black materials, like the carbon nanotube coating, can be used on devices that remove heat from instruments and radiate it away to deep space. This cools the instruments to lower temperatures, where they are more sensitive to faint signals.

To prevent the black paints from losing their absorption and radiative properties at long wavelengths, instrument developers currently use epoxies loaded with conductive metals to create a black coating. However, the mixture adds weight, always a concern for instrument developers. With the carbon-nanotube coating, however, the material is less dense and remains black without additives, and therefore is effective at absorbing light and removing heat. "This is a very promising material," Wollack said. "It's robust, lightweight, and extremely black. It is better than black paint by a long shot."

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Could a computer one day rewire itself? New nanomaterial 'steers' electric currents in multiple dimensions

ScienceDaily (Oct. 16, 2011) — Scientists at Northwestern University have developed a new nanomaterial that can "steer" electrical currents. The development could lead to a computer that can simply reconfigure its internal wiring and become an entirely different device, based on changing needs.

As electronic devices are built smaller and smaller, the materials from which the circuits are constructed begin to lose their properties and begin to be controlled by quantum mechanical phenomena. Reaching this physical barrier, many scientists have begun building circuits into multiple dimensions, such as stacking components on top of one another.

The Northwestern team has taken a fundamentally different approach. They have made reconfigurable electronic materials: materials that can rearrange themselves to meet different computational needs at different times.

"Our new steering technology allows use to direct current flow through a piece of continuous material," said Bartosz A. Grzybowski, who led the research. "Like redirecting a river, streams of electrons can be steered in multiple directions through a block of the material -- even multiple streams flowing in opposing directions at the same time."

Grzybowski is professor of chemical and biological engineering in the McCormick School of Engineering and Applied Science and professor of chemistry in the Weinberg College of Arts and Sciences.

The Northwestern material combines different aspects of silicon- and polymer-based electronics to create a new classification of electronic materials: nanoparticle-based electronics.

The study, in which the authors report making preliminary electronic components with the hybrid material, will be published online Oct. 16 by the journal Nature Nanotechnology. The research also will be published as the cover story in the November print issue of the journal.

"Besides acting as three-dimensional bridges between existing technologies, the reversible nature of this new material could allow a computer to redirect and adapt its own circuitry to what is required at a specific moment in time," said David A. Walker, an author of the study and a graduate student in Grzybowski's research group.

Imagine a single device that reconfigures itself into a resistor, a rectifier, a diode and a transistor based on signals from a computer. The multi-dimensional circuitry could be reconfigured into new electronic circuits using a varied input sequence of electrical pulses.

The hybrid material is composed of electrically conductive particles, each five nanometers in width, coated with a special positively charged chemical. (A nanometer is a billionth of a meter.) The particles are surrounded by a sea of negatively charged atoms that balance out the positive charges fixed on the particles. By applying an electrical charge across the material, the small negative atoms can be moved and reconfigured, but the relatively larger positive particles are not able to move.

By moving this sea of negative atoms around the material, regions of low and high conductance can be modulated; the result is the creation of a directed path that allows electrons to flow through the material. Old paths can be erased and new paths created by pushing and pulling the sea of negative atoms. More complex electrical components, such as diodes and transistors, can be made when multiple types of nanoparticles are used.

The title of the paper is "Dynamic Internal Gradients Control and Direct Electric Currents Within Nanostructured Materials." In addition to Grzybowski and Walker, other authors are Hideyuki Nakanishi, Paul J. Wesson, Yong Yan, Siowling Soh and Sumanth Swaminathan, from Northwestern, and Kyle J. M. Bishop, a former member of the Grzybowski research group, now with Pennsylvania State University.

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Hideyuki Nakanishi, David A. Walker, Kyle J. M. Bishop, Paul J. Wesson, Yong Yan, Siowling Soh, Sumanth Swaminathan, Bartosz A. Grzybowski. Dynamic internal gradients control and direct electric currents within nanostructured materials. Nature Nanotechnology, 2011; DOI: 10.1038/nnano.2011.165

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Giant star expels multiple dust shells, astronomers find

ScienceDaily (Sep. 27, 2011) — An international team led by KU Leuven astronomer Leen Decin discovered not less than a dozen cold dust arcs around the giant star CW Leo. The team used the sensitive PACS instrument on board the Herschel Space Observatory to detect for the first time arcs of dust far away from the star. CW Leo has expelled these shells of dust in different epochs in its life. The faintest shell we can see now was, according to the team, expelled about 16,000 years ago. In the mean time it has drifted away from the star over more than 7,000 billion kilometers.

Episodes

"Until recently, the environment of giant stars seemed homogeneous, but more and more observations indicate that this is not true," says Leen Decin. "These new Herschel images confirm that in a stunning way. We have detected a dozen arcs, puffed out by the star in the course of its life. The faintest shell we found is already at a distance of 7,000 billion kilometers from the star."

The different shells were ejected by the star with intervals of 500 to 1,700 years. The astronomers in the team believe such shells, even fainter, are also present further out, up to the violent bow shock where the expelled material of the star collides with the interstellar medium. The oldest shells have probably disappeared in the bow shock already.

Our own Sun too will turn into a red giant star, about five billion years from now, when it will inflate and condensate dust in the outer, cooling layers of its atmosphere. The episodes in CW Leo's history help astronomers understand the future of our own Sun.

Cold

Since the different shells have been travelling far away from the star by now, they are also very cold, about -248°C. The PACS instrument onboard the Herschel Space Telescope was especially designed to make images of the far-infrared light emitted by dust that cold. Thanks to the Belgian participation in the building of the PACS instrument, the team got priority access to the space telescope. Christoffel Waelkens, Co-principal investigator of the PACS instrument consortium is proud of yet another discovery by Herschel: "We had a lot of ideas for science with Herschel, but we also hoped that Herschel would surprise us with unexpected results. It has been a continuous delight since the first observations: at every opportunity nature proves to have more imagination than we have, but still presents us the phenomena so that we can understand them."

Digging in the data

Making the rings visible in the Herschel images was not trivial. Pierre Royer, instrument expert in the PACS team of the Institute of Astronomy at KU Leuven, clarifies: "The work of constantly refining the instrumental calibration and improving the data-analysis techniques really becomes rewarding when it comes to push the instrument to its limits, allowing for cutting-edge science." Also after the Herschel Launch in 2009 the PACS instrument team, including 7 scientists and engineers at KU Leuven, continued to refine the initial calibration and data analysis software.

Publication

The team published the results in the October 2011 issue of the journal Astronomy & Astrophysics.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Katholieke Universiteit Leuven.

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L. Decin, P. Royer, N. L. J. Cox, B. Vandenbussche, R. Ottensamer, J. A. D. L. Blommaert, M. A. T. Groenewegen, M. J. Barlow, T. Lim, F. Kerschbaum, T. Posch, C. Waelkens. Discovery of multiple dust shells beyond 1?arcmin in the circumstellar envelope of IRC +10216 usingHerschel/PACS. Astronomy & Astrophysics, 2011; 534: A1 DOI: 10.1051/0004-6361/201117360

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Study tests interventions targeting multiple health-related behaviors in African American couples

ScienceDaily (Apr. 25, 2011) — Interventions to promote healthy behaviors, including eating more fruits and vegetables, increasing physical activity, and participating in cancer screenings, as well as prevention of HIV/sexually transmitted diseases (STDs), appear beneficial for African-American couples who are at high risk for chronic diseases, especially if one of the individuals is living with HIV (human immunodeficiency virus).

The report is published in the April 25 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

As background information in the article, the authors write that the medications being used to treat HIV, particularly highly active antiretroviral therapy (HAART), have been so successful for many individuals that they are now living longer and are at risk for developing other chronic diseases, such as cardiovascular disease and diabetes. "The issue of comorbid chronic disease is particularly worrisome for the 48 percent of people living with HIV in 2007 who were African American," the authors note.

Nabila El-Bassel, Ph.D., and colleagues from the National Institute of Mental Health Multisite HIV/STD Prevention Trial for African-American Couples Group, tested how well an intervention would work that addressed multiple health-related behaviors in African-American heterosexual couples in which one partner was HIV-positive and the other was not. The 535 couples (1,070 participants) were randomized into two groups: 520 individuals (260 couples) participated in couple-focused HIV/STD risk reduction focusing on preventing HIV/STD transmission and acquisition and 550 individuals (275 couples) were in the individual-focused health promotion group to influence behaviors linked to the risk of cardiovascular diseases, cerebrovascular diseases, diabetes mellitus and certain cancers, including physical activity, fruit and vegetable consumption, fat consumption, breast and prostate cancer screenings and alcohol use. Both interventions consisted of eight weekly structured two-hour sessions. Participants independently reported their health behaviors at the beginning of the study, immediately after the interventions, and six to 12 months post-intervention. The average age of the participants was about 43 years and the HIV-positive partner was female in 60.4 percent of the couples.

"Health promotion intervention participants were more likely to report consuming five or more servings of fruits and vegetables daily and adhering to physical activity guidelines compared with HIV/STD intervention participants," the authors found. "In the health promotion intervention compared with the HIV/STD intervention, participants consumed fatty foods less frequently, more men received prostate cancer screening, and more women received a mammogram. Alcohol use did not differ between the intervention groups." The authors suggest that it is "possible that targeting couples enhanced efficacy. Research suggests that health promotion strategies that incorporate family members and support networks are more effective than individual-focused strategies and may be especially appropriate for African Americans."

"In conclusion, African Americans are at high risk for morbidity and mortality from chronic diseases and are less likely to report engaging in behaviors associated with reduced risk of such diseases and to detect them at an early stage. Moreover, the risk of chronic disease is of particular concern for African Americans living with HIV because HIV and its treatment with HAART are associated with increased risk. The present study revealed low rates of fruit and vegetable consumption, physical activity and cancer screening in African American individuals in HIV-serodiscordant couples. Accordingly, this study is important, demonstrating that a theory-based contextually appropriate intervention that teaches skills caused positive changes on multiple behaviors linked to chronic diseases in African American members of HIV-serodiscordant couples."

Editorial: Human Immunodeficiency Virus Is (Once Again) a Primary Care Disease

In an accompanying editorial, Mitchell H. Katz, M.D., from the Los Angeles Department of Health Services, Los Angeles, notes that "if specialty care is less needed than it used to be for HIV-infected patients, it turns out primary care is more needed. Owing to the advances in HIV treatment, our patients are no longer dying: They are aging!"

"Although serodiscordant couples are a highly specialized population, there is no reason to believe that their intervention would not work among other HIV-infected persons. Certainly, this study should encourage others to attempt group health promotion classes because, as I often tell my HIV-infected patients with diabetes, liver disease or uncontrolled hypertension, 'It's not HIV that's going to kill you.'"

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by JAMA and Archives Journals.

Journal References:

N. El-Bassel, J. B. Jemmott, J. R. Landis, W. Pequegnat, G. M. Wingood, G. E. Wyatt, S. L. Bellamy. Intervention to Influence Behaviors Linked to Risk of Chronic Diseases: A Multisite Randomized Controlled Trial With African-American HIV-Serodiscordant Heterosexual Couples. Archives of Internal Medicine, 2011; 171 (8): 728 DOI: 10.1001/archinternmed.2011.136M. H. Katz. Human Immunodeficiency Virus Is (Once Again) a Primary Care Disease. Archives of Internal Medicine, 2011; 171 (8): 719 DOI: 10.1001/archinternmed.2011.130

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