Graphene 'Invisible' to Water: How the Extreme Thinness of Graphene Enables Near-Perfect Wetting Transparency

Graphene is the thinnest material known to science. The nanomaterial is so thin, in fact, water often doesn’t even know it’s there. A new study from Rensselaer Polytechnic Institute shows how the extreme thinness of graphene enables near-perfect wetting transparency. The findings could help inform a new generation of graphene-based flexible electronic devices. Additionally, the research suggests a new type of heat pipe that uses graphene-coated copper to cool computer chips. (Credit: Rensselaer/Koratkar)

ScienceDaily (Jan. 23, 2012) — Graphene is the thinnest material known to science. The nanomaterial is so thin, in fact, water often doesn't even know it's there.

Results of the study were published in the journal Nature Materials. The findings could help inform a new generation of graphene-based flexible electronic devices. Additionally, the research suggests a new type of heat pipe that uses graphene-coated copper to cool computer chips.Engineering researchers at Rensselaer Polytechnic Institute and Rice University coated pieces of gold, copper, and silicon with a single layer of graphene, and then placed a drop of water on the coated surfaces. Surprisingly, the layer of graphene proved to have virtually no impact on the manner in which water spreads on the surfaces.

The discovery stemmed from a cross-university collaboration led by Rensselaer Professor Nikhil Koratkar and Rice Professor Pulickel Ajayan.

"We coated several different surfaces with graphene, and then put a drop of water on them to see what would happen. What we saw was a big surprise -- nothing changed. The graphene was completely transparent to the water," said Koratkar, a faculty member in the Department of Mechanical, Aerospace, and Nuclear Engineering and the Department of Materials Science and Engineering at Rensselaer. "The single layer of graphene was so thin that it did not significantly disrupt the non-bonding van der Waals forces that control the interaction of water with the solid surface. It's an exciting discovery, and is another example of the unique and extraordinary characteristics of graphene."

Results of the study are detailed in the Nature Materials paper "Wetting transparency of graphene."

Essentially an isolated layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques, graphene is single layer of carbon atoms arranged like a nanoscale chicken-wire fence. Graphene is known to have excellent mechanical properties. The material is strong and tough and because of its flexibility can evenly coat nearly any surface. Many researchers and technology leaders see graphene as an enabling material that could greatly advance the advent of flexible, paper-thin devices and displays. Used as a coating for such devices, the graphene would certainly come into contact with moisture. Understanding how graphene interacts with moisture was the impetus behind this new study.

The spreading of water on a solid surface is called wetting. Calculating wettability involves placing a drop of water on a surface, and then measuring the angle at which the droplet meets the surface. The droplet will ball up and have a high contact angle on a hydrophobic surface. Inversely, the droplet will spread out and have a low contact angle on a hydrophilic surface.

The contact angle of gold is about 77 degrees. Koratkar and Ajayan found that after coating a gold surface with a single layer of graphene, the contact angle became about 78 degrees. Similarly, the contact angle of silicon rose from roughly 32 degrees to roughly 33 degrees, and copper increased from around 85 degrees to around 86 degrees, after adding a layer of graphene.

These results surprised the researchers. Graphene is impermeable, as the tiny spaces between its linked carbon atoms are too small for water, or a single proton, or anything else to fit through. Because of this, one would expect that water would not act as if it were on gold, silicon, or copper, since the graphene coating prevents the water from directly contacting these surfaces. But the research findings clearly show how the water is able to sense the presence of the underlying surface, and spreads on those surfaces as if the graphene were not present at all.

As the researchers increased the number of layers of graphene, however, it became less transparent to the water and the contact angles jumped significantly. After adding six layers of graphene, the water no longer saw the gold, copper, or silicon and instead behaved as if it was sitting on graphite.

The reason for this perplexing behavior is subtle. Water forms chemical or hydrogen bonds with certain surfaces, while the attraction of water to other surfaces is dictated by non-bonding interactions called van der Waals forces. These non-bonding forces are not unlike a nanoscale version of gravity, Koratkar said. Similar to how gravity dictates the interaction between Earth and the sun, van der Waals forces dictate the interaction between atoms and molecules.

In the case of gold, copper, silicon, and other materials, the van der Waals forces between the surface and water droplet determine the attraction of water to the surface and dictate how water spreads on the solid surface. In general, these forces have a range of at least several nanometers. Because of the long range, these forces are not disrupted by the presence of a single-atom-thick layer of graphene between the surface and the water. In other words, the van der Waals forces are able to "look through" ultra-thin graphene coatings, Koratkar said.

If you continue to add additional layers of graphene, however, the van der Waals forces increasingly "see" the carbon coating on top of the material instead of the underlying surface material. After stacking six layers of graphene, the separation between the graphene and the surface is sufficiently large to ensure that the van der Waals forces can now no longer sense the presence of the underlying surface and instead only see the graphene coating. On surfaces where water forms hydrogen bonds with the surface, the wetting transparency effect described above does not hold because such chemical bonds cannot form through the graphene layer.

Along with conducting physical experiments, the researchers verified their findings with molecular dynamics modeling as well as classical theoretical modeling.

"We found that van der Waals forces are not disrupted by graphene. This effect is an artifact of the extreme thinness of graphene -- which is only about 0.3 nanometers thick," Koratkar said. "Nothing can rival the thinness of graphene. Because of this, graphene is the ideal material for wetting angle transparency."

"Moreover, graphene is strong and flexible, and it does not easily crack or break apart," he said. "Additionally, it is easy to coat a surface with graphene using chemical vapor deposition, and it is relatively uncomplicated to deposit uniform and homogeneous graphene coatings over large areas. Finally, graphene is chemically inert, which means a graphene coating will not oxidize away. No single material system can provide all of the above attributes that graphene is able to offer."

A practical application of this new discovery is to coat copper surfaces used in dehumidifiers. Because of its exposure to water, copper in dehumidifier systems oxidizes, which in turn decreases its ability to transfer heat and makes the entire device less efficient. Coating the copper with graphene prevents oxidation, the researchers said, and the operation of the device is unaffected because graphene does not change the way water interacts with copper. This same concept may be applied to improve the ability of heat pipes to dissipate heat from computer chips, Koratkar said.

"It's an interesting idea. The graphene doesn't cause any significant change to the wettability of copper, and at the same time it passivates the copper surface and prevents it from oxidizing," he said.

Along with Koratkar and Ajayan, co-authors of the paper are Yunfeng Shi, assistant professor in the Department of Materials Science and Engineering at Rensselaer; Rensselaer mechanical engineering graduate students Javad Rafiee, Abhay Thomas, and Fazel Yavari; Rensselaer physics graduate student Xi Mi; and Rice mechanical and materials engineering graduate student Hemtej Gullapalli.

This research was supported in part by the Advanced Energy Consortium (AEC); the National Science Foundation (NSF); and the Office of Naval Research (ONR) graphene Multidisciplinary University Research Initiative (MURI).

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The above story is reprinted from materials provided byRensselaer Polytechnic Institute (RPI), via Newswise.

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Journal Reference:

1. Javad Rafiee, Xi Mi, Hemtej Gullapalli, Abhay V. Thomas, Fazel Yavari, Yunfeng Shi, Pulickel M. Ajayan, Nikhil A. Koratkar. Wetting transparency of graphene. Nature Materials, 2012; DOI: 10.1038/NMAT3228

Scientists study 'galaxy zoo' using Google Maps and thousands of volunteers

ScienceDaily (Nov. 3, 2011) — The reddest galaxies with the largest central bulb show the largest bars -- gigantic central columns of stars and dark matter -- according to a scientific study that used Google Maps to observe the sky. A group of volunteers of more than 200,000 participants of the galaxy classification project Galaxy Zoo contributed to this research.

More than two thirds of spiral galaxies, including our own Milky Way, display a central bar that can extend for thousands of light years. These colossal elongated structures are made up of collections of stars and dark matter which are held together by gravity.

Now a team of researchers from Europe and the USA have measured the bar length of some 5000 galaxies with the help of amateur astronomers. The most precise results (those obtained for 3150 galaxies) have been published in the Monthly Notices of the Royal Astronomical Society.

The study comes under the Galaxy Zoo project, a citizen science initiative in which more than 200,000 volunteers assisted in classifying a million galaxies through images provided by the Sloan Digital Sky Survey astronomical catalogue. As for the bars, 150 amateur astronomers have recorded their observations on a webpage specifically created for this purpose. The page is currently still active despite being closed to any further data entry.

Ben Hoyle, researcher at the Institute of Cosmos Sciences (University of Barcelona, Spain) and coordinator of the study, stresses that "this webpage combines Galaxy Zoo classifications with Google Maps technology." More precisely, the team has used the Google Maps Sky interface which allows to see the sky, especially the galaxies, as seen from Earth's surface.

The redness of bars

"In this way we have compiled some 16,000 measurements of the bars of 5000 galaxies, which is a sample a hundred times greater than previous ones. We have also come to many different conclusions, such as the fact that redder galaxies, which are stopping star formation, have longer bars," says Hoyle.

In the electromagnetic spectrum, the colour red comes from older, cooler stars whereas the colour blue is linked to hotter and younger stars. The study also reveals that the bars tend to be redder than the rest of the galaxy, which indicates that they have an older stellar population.

Other conclusions indicate that those galaxies with a larger bulb (a central agglomeration of stars) have longer bars. In addition, barred galaxies are more likely to display spiral arms than unbarred galaxies.

The images provide examples of barred galaxies with spiral arms. In the first row, the arms are connected to the ring around the bar. In the second row, the arms are connected at the end of the bar and the third row shows a mixture of the two. Image: Ben Hoyle et al./Galaxy Zoo.

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Journal Reference:

Ben Hoyle, Karen. L. Masters, Robert C. Nichol, Edward M. Edmondson, Arfon M. Smith, Chris Lintott, Ryan Scranton, Steven Bamford, Kevin Schawinski, Daniel Thomas. Galaxy Zoo: bar lengths in local disc galaxies. Monthly Notices of the Royal Astronomical Society, 2011; 415 (4): 3627 DOI: 10.1111/j.1365-2966.2011.18979.x

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First-of-a-kind tension wood study broadens biofuels research

ScienceDaily (Oct. 25, 2011) — Taking a cue from Mother Nature, researchers at the Department of Energy's BioEnergy Science Center have undertaken a first-of-its-kind study of a naturally occurring phenomenon in trees to spur the development of more efficient bioenergy crops.

Tension wood, which forms naturally in hardwood trees in response to bending stress, is known to possess unique features that render it desirable as a bioenergy feedstock. Although individual elements of tension wood have been studied previously, the BESC team is the first to use a comprehensive suite of techniques to systematically characterize tension wood and link the wood's properties to sugar release. Plant sugars, known as cellulose, are fermented into alcohol for use as biofuel.

"There has been no integrated study of tension stress response that relates the molecular and biochemical properties of the wood to the amount of sugar that is released," said Oak Ridge National Laboratory's Udaya Kalluri, a co-author on the study.

The work, published in Energy & Environmental Science, describes tension wood properties including an increased number of woody cells, thicker cell walls, more crystalline forms of cellulose and lower lignin levels, all of which are desired in an biofuel crop.

"Tension wood in poplar trees has a special type of cell wall that is of interest because it is composed of more than 90 percent cellulose, whereas wood is normally composed of 40 to 55 percent cellulose," Kalluri said. "If you increase the cellulose in your feedstock material, then you can potentially extract more sugars as the quality of the wood has changed. Our study confirms this phenomenon."

The study's cohesive approach also provides a new perspective on the natural plant barriers that prevent the release of sugars necessary for biofuel production, a trait scientists term as recalcitrance.

"Recalcitrance of plants is ultimately a reflection of a series of integrated plant cell walls, components, structures and how they are put together," said co-author Arthur Ragauskas of Georgia Institute of Technology. "This paper illustrates that you need to use an holistic, integrated approach to study the totality of recalcitrance."

Using the current study as a model, the researchers are extending their investigation of tension wood down to the molecular level and hope to eventually unearth the genetic basis behind its desirable physical features. Although tension wood itself is not considered to be a viable feedstock option, insight gleaned from studying its unique physical and molecular characteristics could be used to design and select more suitably tailored bioenergy crops.

"This study exemplifies how the integrated model of BESC can bring together such unique research expertise," said BESC director Paul Gilna. "The experimental design in itself is reflective of the multidisciplinary nature of a DOE Bioenergy Research Center."

The research team also includes Georgia Institute of Technology's Marcus Foston, Chris Hubbell, Reichel Sameul, Seokwon Jung and Hu Fan; National Renewable Energy Laboratory's Robert Sykes, Shi-You Ding, Yining Zeng, Erica Gjersing and Mark Davis, and ORNL's Sara Jawdy and Gerald Tuskan.

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Journal Reference:

Marcus Foston, Christopher A. Hubbell, Reichel Samuel, Seokwon Jung, Hu Fan, Shi-You Ding, Yining Zeng, Sara Jawdy, Mark Davis, Robert Sykes, Erica Gjersing, Gerald A. Tuskan, Udaya Kalluri, Arthur J. Ragauskas. Chemical, ultrastructural and supramolecular analysis of tension wood in Populus tremula x alba as a model substrate for reduced recalcitrance. Energy & Environmental Science, 2011; DOI: 10.1039/C1EE02073K

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Science & the Public: Study recalibrates trees' carbon uptake

Finding, based on using heavy oxygen as a photosynthetic yardstick, could alter climate projections.Web edition : Wednesday, October 5th, 2011 If trees inhale faster . . . Apparent earlier underestimate of how quickly trees and other plants take in carbon for photosynthesis could have climate implications.iStockphoto

Photosynthesis appears to be somewhat speedier than conventional wisdom had suggested, a new study finds.  If true, this could mean that computer projections are at risk of overestimating the potential for forests to sop up carbon dioxide, a major greenhouse gas.

The new study did not measure photosynthesis directly. It instead deduced photosynthetic rates from subtle variations in the molecular weight of carbon dioxide molecules in air. Samples had been collected from across the globe during a 30 year period.

Some CO2 molecules tip the scales more than usual because one of their oxygen atoms has a molecular weight of 18, not 16. (The heavies pack an extra pair of neutrons.) The likelihood that an oxygen atom in CO2 will be an O18 will depend on the proportion of heavy oxygen in a region’s water, explains biogeochemist Lisa Welp of the Scripps Institution of Oceanography in La Jolla, Calif. That ratio can vary by soil moisture and weather conditions, she explains.

As plants breathe CO2 into their leaves, that CO2 will exchange its oxygen atoms with those in water, Welp notes. A substantial amount of that CO2 will eventually be released back into the air, now bearing an O18-to-O16 ratio reflective of the plant’s water.

In the September 29 Nature, Welp — and colleagues on three continents — report finding a subtle change in the proportion of CO2 molecules hosting heavy oxygen. This anomaly appeared to start in the tropics and then quickly spread across the planet. The pattern then repeats, almost in waves.

Each wave lasted about 18 months. And the start of a new wave every four years or so generally coincided with the emergence of a prolonged spell of unusually warm ocean temperatures in the Equatorial Pacific — a climatic event known as an El Niño. Explains Welp, “We find that water’s oxygen isotopes get heavier during El Niños in the tropics.”

Using the average ratio of heavy-to-normal oxygen in CO2 (linked to an El Nino event that could be timed), Welp’s group now had a means to evaluate how long it takes plants to transfer an anomalous oxygen signature into atmospheric CO2 — and then wash it away again once an El Niño ended. With this information, the researchers attempted to validate a fairly well accepted estimate of the global rate of carbon taken up by photosynthesis in plants each year —120 petagrams (peta being 1015).

Their assessment found the 120-petagram figure looked short — by about 25 to 45 percent. As to how such a revision in the rate of carbon cycling through plants might alter estimates of future long-term carbon sequestration by forests, Welp emphasizes: "We don't know yet. It's way too early to tell."

But Matthias Cuntz, a biogeochemist with the UFZ-Helmholtz Centre for Environmental Research in Leipzig, Germany, argues that in fact, carbon-storage implications of the new numbers are not that hard to fathom.

The global value for carbon sequestered long term in plant tissue each year is fairly well established at about 1.6 billion tons, he says. That’s almost 2 percent of the 120 petagram estimate. So if the carbon throughput is revised upward by 25 to 45 percent, then the amount of carbon being sequestered long term must be substantially less than 2 percent, Cuntz says – perhaps “only about 1 percent.”

In a commentary accompanying the new Nature paper, Cuntz likens the old 120-petagram figure to a “gold standard” for the annual rate at which land plants take in carbon for photosynthesis. If Welp’s team is right, he now argues, it has just put “a dent” in that gold standard.

The new estimates in the Nature paper do, however, rest on a lot of assumptions – albeit smart ones, Cuntz explains in his commentary. So the rather unexpected result that Welp and her colleagues report will certainly need confirmation.

But if the new numbers hold up, he told me, it could mean that current computer climate models rely on overly optimistic estimates about how efficiently trees can sequester carbon. “If you change photosynthesis a little, like this,” he says, “it could lead to huge differences [in projections of how climate might change in the future].”

Indeed, it would argue that reining in global warming will prove much harder than biologists had led us to expect.

Found in: Chemistry, Climate Change, Earth Science, Environment, Molecules and Science & Society

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Escaping gravity's clutches: Information could escape from black holes after all, study suggests

ScienceDaily (Aug. 11, 2011) — New research by scientists at the University of York gives a fresh perspective on the physics of black holes. Black holes are objects in space that are so massive and compact they were described by Einstein as "bending" space. Conventional thinking asserts that black holes swallow everything that gets too close and that nothing can escape, but the study by Prof. Samuel Braunstein and Dr. Manas Patra suggests that information could escape from black holes after all.

The implications could be revolutionary, suggesting that gravity may not be a fundamental force of nature.

Prof. Braunstein says: "Our results didn't need the details of a black hole's curved space geometry. That lends support to recent proposals that space, time and even gravity itself may be emergent properties within a deeper theory. Our work subtly changes those proposals, by identifying quantum information theory as the likely candidate for the source of an emergent theory of gravity."

But quantum mechanics is the theory of light and atoms, and many physicists are skeptical that it could be used to explain the slow evaporation of black holes without incorporating the effects of gravity.

The research, which appears in the latest issue of Physical Review Letters, uses the basic tenets of quantum mechanics to give a new description of information leaking from a black hole.

Prof. Braunstein says: "Our results actually extend the predictions made by well-established techniques that rely on a detailed knowledge of space time and black hole geometry."

Dr. Patra adds: "We cannot claim to have proven that escape from a black hole is truly possible, but that is the most straight-forward interpretation of our results. Indeed, our results suggest that quantum information theory will play a key role in a future theory combining quantum mechanics and gravity."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of York.

Journal Reference:

Samuel Braunstein, Manas Patra. Black Hole Evaporation Rates without Spacetime. Physical Review Letters, 2011; 107 (7) DOI: 10.1103/PhysRevLett.107.071302

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Upping the anti: Canadian researchers instrumental in game-changing antimatter study

ScienceDaily (June 5, 2011) — Science fiction is fast approaching science fact as researchers are progressing rapidly toward "bottling" antimatter.

In a paper published online in the journal Nature Physics, the ALPHA experiment at CERN, including key Canadian contributors, reports that it has succeeded in storing antimatter atoms for over 16 minutes. While carrying around bottled antimatter like in the movie "Angels and Demons" remains fundamentally far-fetched, storing antimatter for long periods of time opens up new vistas for scientists struggling to understand this elusive substance. ALPHA managed to store twice the antihydrogen (the antimatter partner to normal hydrogen) 5,000 times longer than the previous best, setting the stage, for example, to test whether antihydrogen and normal hydrogen fall the same way due to gravity.

Lead author Makoto Fujiwara, TRIUMF research scientist, University of Calgary adjunct professor, and spokesperson of the Canadian part of the ALPHA team said, "We know we have confined antihydrogen atoms for at least for 1,000 seconds. That's almost as long as one period in hockey! This is potentially a game changer in antimatter research."

Antimatter remains one of the biggest mysteries of science. At the Big Bang, matter and antimatter should have been produced equally, but since they destroy each other upon contact, eventually nothing should have remained but pure energy (light). However, all observations suggest that only the antimatter has vanished. To figure out what happened to "the lost half of the universe," scientists are eager to determine if, as predicted, the laws of physics are the same for both matter and antimatter. ALPHA uses an analogue of a very well-known system in physics, the hydrogen atom (one electron orbiting one proton), and testing whether its antimatter twin, antihydrogen (an antielectron orbiting an antiproton), behaves the same. But to study something one must hold onto it long enough.

Fujiwara asks, "Does antimatter shine in the same colour as matter? Does it experience the gravity in the same way as matter?" These are still very difficult experiments, and they will take long and hard work, but this new result is a very important step. Now experiments will be about 10,000 times less difficult than before!" Explained ALPHA spokesperson Jeffrey Hangst of Aarhus University, "This would provide the first-ever look inside the structure of antihydrogen -- element 1 on the anti-periodic table."

Antihydrogen atoms were first made in large quantities at CERN eight years ago, but can't be stored conventionally since antiatoms touching the ordinary-matter walls of a bottle would instantly annihilate. The ALPHA collaboration succeeded by developing a sophisticated "magnetic bottle" using a state-of-the-art superconducting magnet to suspend the antiatoms away from the walls, last year demonstrating definitive proof of antihydrogen atom capture for about a tenth of a second, likely the first contained antiatoms in the history of the universe.

Canadian scientists have been playing leading roles in the antihydrogen detection and data analysis aspects of the project. The next step for ALPHA is to start performing measurements on bottled antihydrogen, and this is due to get underway later this year. The first step is to illuminate the trapped anti-atoms with microwaves to determine if they absorb exactly the same frequencies (or energies) as their matter twins.

"I've always liked hydrogen atoms," said Walter Hardy of the University of British Columbia a leading expert in atomic hydrogen studies. "It's ironic that we are now trying to measure the same properties of antihydrogen that I measured many years ago on regular hydrogen. It is a crucial comparison, though, and will tell us if we truly understand the relationship between matter and antimatter. "

Support for ALPHA-Canada and its research came from NSERC (National Science and Engineering Research Council, TRIUMF, AIF (Alberta Ingenuity Fund), the Killam Trust, and FQRNT (Le Fonds québécois de la recherche sur la nature et les technologies).

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by TRIUMF (Canada's National Laboratory for Particle and Nuclear Physics).

Journal Reference:

ALPHA Collaboration: G. B. Andresen, M. D. Ashkezari, M. Baquero-Ruiz, W. Bertsche, P. D. Bowe, E. Butler, C. L. Cesar, M. Charlton, A. Deller, S. Eriksson, J. Fajans, T. Friesen, M. C. Fujiwara, D. R. Gill, A. Gutierrez, J. S. Hangst, W. N. Hardy, R. S. Hayano, M. E. Hayden, A. J. Humphries, R. Hydomako, S. Jonsell, S. L. Kemp, L. Kurchaninov, N. Madsen, S. Menary, P. Nolan, K. Olchanski, A. Olin, P. Pusa, C. Ø. Rasmussen, F. Robicheaux, E. Sarid, D. M. Silveira, C. So, J. W. Storey, R. I. Thompson, D. P. van der Werf, J. S. Wurtele, Y. Yamazaki. Confinement of antihydrogen for 1,000 seconds. Nature Physics, 2011; DOI: 10.1038/nphys2025

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Astrophysicists use X-ray fingerprints to study eating habits of giant black holes

ScienceDaily (June 7, 2011) — By studying the X-rays emitted when superheated gases plunge into distant and massive black holes, astrophysicists at the Georgia Institute of Technology have provided an important test of a long-standing theory that describes the extreme physics occurring when matter spirals into these massive objects.

Matter falling into black holes emits tremendous amounts of energy which can escape as visible light, ultraviolet light and X-rays. This energy can also drive outflows of gas and dust far from the black hole, affecting the growth and evolution of galaxies containing the black holes. Understanding the complex processes that occur in these active galactic nuclei is vital to theories describing the formation of galaxies such as the Milky Way, and is therefore the subject of intense research.

Though light cannot escape from black holes themselves, black holes with accretion disks -- which are swirling clouds of matter about to enter the black hole -- are among the most luminous objects in galaxies. By studying how the radiation and accretion disk interact, astrophysicists can learn much about the extreme gravitational fields, magnetic forces and radiation processes close to these black holes.

"We reviewed data collected from space telescopes over the past few years and found that the more rapidly a black hole was gobbling up material, the more highly ionized the accretion disk was," said David Ballantyne, an assistant professor in Georgia Tech's School of Physics. "The simple theory of accretion disks predicts this, but the relationship we saw between the ionization and rate of accretion was different from what the theory predicted."

The large difference between the observed and theoretical relationships -- a linear dependence on the rate of accretion as opposed to a cubic dependence -- is not surprising for a phenomenon that can't exactly be tested under controlled laboratory conditions. In a paper published online June 3 in The Astrophysical Journal, Ballantyne describes the research and speculates about possible reasons for the difference between observations and theory. The research, which will appear in the Journal's June 20 issue, was supported in part by the National Science Foundation (NSF).

"As in many areas of science, especially astronomy, we end up needing more data -- many more high-quality observations to better define this relationship," he added.

Astrophysicists don't have a detailed understanding of how the accretion process works, why black holes grow at different rates -- or what makes them stop growing. These questions are important because the growth of active galactic nuclei -- the black holes and their surrounding accretion disks -- has broader effects on the galaxies of which they are part.

"The rapid accretion phase releases a lot of energy, not only in radiation, but also in outflows that drive gas out of a galaxy, which can shut off star formation and hold back the growth of the galaxy," said Ballantyne, a scientist in Georgia Tech's Center for Relativistic Astrophysics. "We could potentially learn something fundamental about the flow of energy through the accretion disk very close to the black hole. We could learn about the viscosity of this matter and how efficiently radiation transport takes place. These are very important questions in astrophysics."

X-rays are believed to originate from innermost portion of active galactic nuclei. As they pass through matter on its way into the black hole, the X-rays are altered by the materials in ways that astrophysicists can measure. In their study, Ballantyne and his collaborators were interested in studying the ionization state of the matter -- which is related to the illumination -- and were able to do so by analyzing the "fingerprint" the ionization left on the X-rays.

"From laboratory work, we understand the physics of how gas interacts with X-ray radiation because that's basically an atomic physics problem," he explained. "We can model what these fingerprints might look like on the X-rays, and compare that to the actual data to help us understand what's going on."

Because of their high energy and short wavelength, X-rays pass through many materials, such as human bodies, with little attenuation. This makes them ideal for examining processes in active galactic nuclei. Longer wavelengths, such as ultraviolet and visible light, are absorbed by intergalactic dust, or are difficult to distinguish from light originating in stars. However, X-rays do get absorbed by dense objects, such as bones -- and crucially for this study -- accretion disks.

Ballantyne and his collaborators Jon McDuffie and John Rusin studied ten X-ray observations reported by other scientists from eight different active galactic nuclei. The observations were made using such space telescopes as Chandra and XMM.

To be useful, they used only measurements of X-ray emissions from the innermost and hottest portion of the accretion disk, and only where the mass of the black holes -- which range from a million to a billion times the size of our sun -- had high quality estimates.

In pursuing the study, Ballantyne hopes to maintain the involvement of Rusin, a student from South Cobb High School in Marietta, near Atlanta. Rusin became involved when he contacted Georgia Tech to inquire about astrophysics projects.

"He helped us with data acquisition and was a really big help," said Ballantyne. "I treated him just like an undergraduate student. I'm pleased to know that he has decided to attend Georgia Tech."

The next step in the research will be to gather additional information from other studies of active galactic nuclei to see if the linear relationship Ballantyne's group measured holds up. The work may also lead to other techniques for learning about black holes and the accretion process.

"Black holes themselves are very simple, but what goes on around them can be very complex," Ballantyne said. "There is still a lot to be learned about how black holes get fueled, and how some accrete slowly while others grow rapidly. The astrophysics of black holes is actually very important in determining what our universe looks like."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Georgia Institute of Technology Research News. The original article was written by John Toon.

Journal Reference:

D. R. Ballantyne, J. R. McDuffie, J. S. Rusin. A Correlation between the Ionization State of the Inner Accretion Disk and the Eddington Ratio of Active Galactic Nuclei. The Astrophysical Journal, 2011; 734 (2): 112 DOI: 10.1088/0004-637X/734/2/112

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Study evaluates relationship of urinary sodium with health outcomes

ScienceDaily (May 3, 2011) — In a study conducted to examine the health outcomes related to salt intake, as gauged by the amount of sodium excreted in the urine, lower sodium excretion was associated with an increased risk of cardiovascular death, while higher sodium excretion did not correspond with increased risk of hypertension or cardiovascular disease complications, according to a study in the May 4 issue of JAMA.

"Extrapolations from observational studies and short-term intervention trials suggest that population-wide moderation of salt intake might reduce cardiovascular events," according to background information in the article. "The assumption that lower salt intake would in the long run lower blood pressure, to our knowledge, has not yet been confirmed in longitudinal population-based studies."

Katarzyna Stolarz-Skrzypek, M.D., Ph.D., of the University of Leuven, Belgium, and colleagues examined the incidence of death, illness and hypertension in relation to measures of urinary sodium excretion. The study included 3,681 participants without cardiovascular disease (CVD) at the beginning of the study. Of these, 2,096 had normal blood pressure at baseline and 1,499 had blood pressure and sodium excretion measured at baseline and last follow-up (2005-2008).

The researches found that among 3,681 participants followed up for a median (midpoint) 7.9 years, cardiovascular deaths decreased across increasing tertiles (one of three groups) of 24-hour urinary sodium: from 50 deaths in the low (death rate, 4.1 percent), 24 deaths in the medium, (death rate, 1.9 percent) and 10 deaths in the high tertile (death rate, 0.8 percent). Analysis indicated that the risk of cardiovascular mortality was significantly elevated in the low tertile with a significant inverse association between cardiovascular mortality and tertile of sodium excretion. Baseline sodium excretion predicted neither total mortality nor fatal combined with nonfatal CVD events.

Among 2,096 participants followed up for 6.5 years, increasing tertiles of 24-hour urinary sodium were not associated with incidence of hypertension. In the entire hypertension cohort, across increasing tertiles of urinary sodium, the numbers of new cases of hypertension were 187 (27.0 percent) in the low, 190 (26.6 percent) in the medium, and 175 (25.4 percent) in the high sodium excretion group.

Among 1,499 participants followed up for 6.1 years, in multivariable-adjusted analyses, a 100-mmol increase in sodium excretion was associated with 1.71 mm Hg increase in systolic blood pressure but no change in diastolic BP.

"The associations between systolic pressure and sodium excretion did not translate into less morbidity or improved survival. On the contrary, low sodium excretion predicted higher cardiovascular mortality. Taken together, our current findings refute the estimates of computer models of lives saved and health care costs reduced with lower salt intake. They do also not support the current recommendations of a generalized and indiscriminate reduction of salt intake at the population level. However, they do not negate the blood pressure-lowering effects of a dietary salt reduction in hypertensive patients," the authors conclude.

Story Source:

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

Journal Reference:

Katarzyna Stolarz-Skrzypek, Tatiana Kuznetsova, Lutgarde Thijs, Valérie Tikhonoff, Jitka Seidlerová, Tom Richart, Yu Jin, Agnieszka Olszanecka, Sofia Malyutina, Edoardo Casiglia, Jan Filipovský, Kalina Kawecka-Jaszcz, Yuri Nikitin, Jan A. Staessen, for the European Project on Genes in Hypertension (EPOGH) Investigators. Fatal and Nonfatal Outcomes, Incidence of Hypertension, and Blood Pressure Changes in Relation to Urinary Sodium Excretion. JAMA, 2011; 305 (17): 1777-1785 DOI: 10.1001/jama.2011.574

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Increasing the number of family physicians reduces hospital readmissions, study suggests

ScienceDaily (May 3, 2011) — Boston- Researchers from Boston University School of Medicine and Boston Medical Center have found that by adding one family physician per 1,000, or 100 per 100,000, could reduce hospital readmission costs by $579 million per year, or 83 percent of the Patient Protection and Affordable Care Act (ACA) target.

These findings currently appear on the website of the "Robert Graham Center," a primary care think tank.

Growth of family physicians has fallen over the last decade due to payment disparities and other strong incentives for subspecialization, and lack of accountability of teaching hospitals for producing the physicians the country needs.

The Patient Protection and Affordable Care Act (ACA) seeks to improve healthcare quality and reduce costs. One provision targets a decrease in hospital readmissions to save $710 million annually. It is believed that timely management of fragile patients in primary care after discharge may reduce readmission.

The researchers used data from the Hospital Compare database, which included readmission rates for pneumonia, heart attack and heart failure, for 4,459 hospitals as well as the Area Source File that contains data for physicians per population at the county level. Combined, readmissions for pneumonia, heart attack and heart failure in 2005 accounted for 15.7 percent of all readmissions and numbered 74,419, 20,866 and 90,273, respectively; corresponding Medicare expenditures were $533, $136 and $590 million, respectively.

"Using these data, we found that 30-day readmission rates for all three diagnoses decrease as the number of family physicians increases," said senior author Brian Jack, MD, an associate professor and vice chair for Academic Affairs in the Department of Family Medicine at Boston University School of Medicine/Boston Medical Center. "Conversely, increased numbers of physicians in all other major specialties, including general internal medicine, is associated with increased risk of readmission," he added.

According to Jack this work demonstrates tremendous cost savings from an adequate family physician work force.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Boston University Medical Center, via EurekAlert!, a service of AAAS.

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Study examines changes in medical students’ views about internal medicine careers

ScienceDaily (Apr. 25, 2011) — Compared with 1990, more medical students in 2007 viewed internal medicine as a potentially meaningful career; however, the majority of students are choosing other specialties, according to a report in the April 25 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

"The United States faces a troubling shortage in its primary care medical workforce," the authors write as background information in the article. "According to the Institute of Medicine, the United States is not prepared to meet the health care needs of the growing number of older adults."

Mark D. Schwartz, M.D., of the New York University School of Medicine, and colleagues examined data collected during two previous national studies of senior medical students that addressed student characteristics, specialties chosen and perceptions of internal medicine among other questions. The 1990 survey included 1,244 students at 16 schools and the 2007 survey included 1,177 students at 11 schools.

The two groups of students were of similar age, marital status and parental status. Compared with the 1990 survey group, the 2007 survey group included more women (52 percent vs. 37 percent) and students reporting more educational debt, with an average of $101,000 compared with $63,000 in 1990.

The proportion of students planning careers in internal medicine (combining all types of internal medicine including subspecialty and medicine-pediatrics) was similar in 1990 and 2007 (24 percent and 23 percent respectively); however, the percentage of students planning general internal medicine training declined from 9 percent in 1990 to 2 percent in 2007.

Additionally, the appeal of being a primary care physician as an influence toward internal medicine declined from 57 percent in 1990 to 33 percent in 2007. Although most students in both cohorts were attracted toward careers in internal medicine by the "esteem" offered by the specialty (68 percent of students in 1990 and 82 percent in 2007), some students were less attracted to internal medicine by the "types of patients cared for by internists." Students in 1990 and in 2007 also felt that workload and stress are greater in internal medicine that in other fields.

"To rebuild the generalist physician workforce, improving students' experience of internal medicine in medical school is no longer sufficient," the authors conclude. "Bolder reform will be required to improve the educational pipeline, practice and payment of generalist internal medicine physicians."

Story Source:

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

Journal Reference:

M. D. Schwartz, S. Durning, M. Linzer, K. E. Hauer. Changes in Medical Students' Views of Internal Medicine Careers From 1990 to 2007. Archives of Internal Medicine, 2011; 171 (8): 744 DOI: 10.1001/archinternmed.2011.139

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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.'"

Story Source:

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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Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

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