Manufacturing method paves way for commercially viable quantum dot-based LEDs
August 31, 2011
University of Florida researchers may help resolve the public debate over America’s future light source of choice: Edison’s incandescent bulb or the more energy efficient compact fluorescent lamp.
It could be neither.
Instead, America’s future lighting needs may be supplied by a new breed of light emitting diode, or LED, that conjures light from the invisible world of quantum dots. According to an article in the current online issue of the journal Nature Photonics, moving a QD LED from the lab to market is a step closer to reality thanks to a new manufacturing process pioneered by two research teams in UF’s department of materials science and engineering.
“Our work paves the way to manufacture efficient and stable quantum dot-based LEDs with really low cost, which is very important if we want to see wide-spread commercial use of these LEDs in large-area, full-color flat-panel displays or as solid-state lighting sources to replace the existing incandescent and fluorescent lights,” said Jiangeng Xue, the research leader and an associate professor of material science and engineering “Manufacturing costs will be significantly reduced for these solution-processed devices, compared to the conventional way of making semiconductor LED devices.”
A significant part of the research carried out by Xue’s team focused on improving existing organic LEDs. These semiconductors are multilayered structures made up of paper thin organic materials, such as polymer plastics, used to light up display systems in computer monitors, television screens, as well as smaller devices such as MP3 players, mobile phones, watches, and other handheld electronic devices. OLEDs are also becoming more popular with manufacturers because they use less power and generate crisper, brighter images than those produced by conventional LCDs (liquid crystal displays). Ultra-thin OLED panels are also used as replacements for traditional light bulbs and may be the next big thing in 3-D imaging.
Complementing Xue’s team is another headed by Paul Holloway, distinguished professor of materials science and engineering at UF, which delved into quantum dots, or QDs. These nano-particles are tiny crystals just a few nanometers (billionths of a meter) wide, comprised of a combination of sulfur, zinc, selenium and cadmium atoms. When excited by electricity, QDs emit an array of colored light. The individual colors vary depending on the size of the dots. Tuning, or “adjusting,” the colors is achieved by controlling the size of the QDs during the synthetic process.
By integrating the work of both teams, researchers created a high-performance hybrid LED, comprised of both organic and QD-based layers. Until recently, however, engineers at UF and elsewhere have been vexed by a manufacturing problem that hindered commercial development. An industrial process known as vacuum deposition is the common way to put the necessary organic molecules in place to carry electricity into the QDs. However, a different manufacturing process called spin-coating, is used to create a very thin layer of QDs. Having to use two separate processes slows down production and drives up manufacturing costs.
According to the Nature Photonics article, UF researchers overcame this obstacle with a patented device structure that allows for depositing all the particles and molecules needed onto the LED entirely with spin-coating. Such a device structure also yields significantly improved device efficiency and lifetime compared to previously reported QD-based LED devices.
Spin-coating may not be the final manufacturing solution, however.
“In terms of actual product manufacturing, there are many other high through-put, continuous “roll-to-roll” printing or coating processes that we could use to fabricate large area displays or lighting devices,” Xue said. “That will remain as a future research and development topic for the university and a start-up company, NanoPhotonica, that has licensed the technology and is in the midst of a technology development program to capitalize on the manufacturing breakthrough.”
Other co-authors of this article are Lei Qian and Ying Zheng, two postdoctoral fellows who worked with the professors on this research. The UF research teams received funding from the Army Research Office, the U.S. Department of Energy, and the Florida Energy Systems Consortium.
Contact: Jiangeng Xue
jxue@msc.ufl.edu
352-846-3775
University of Florida
The star that should not exist
August 31, 2011
A faint star in the constellation of Leo (The Lion), called SDSS J102915+172927 [1], has been found to have the lowest amount of elements heavier than helium (what astronomers call “metals”) of all stars yet studied. It has a mass smaller than that of the Sun and is probably more than 13 billion years old.
“A widely accepted theory predicts that stars like this, with low mass and extremely low quantities of metals, shouldn’t exist because the clouds of material from which they formed could never have condensed,” [2] said Elisabetta Caffau (Zentrum fur Astronomie der Universitat Heidelberg, Germany and Observatoire de Paris, France), lead author of the paper. “It was surprising to find, for the first time, a star in this ‘forbidden zone’, and it means we may have to revisit some of the star formation models.”
The team analysed the properties of the star using the X-shooter and UVES instruments on the VLT [3]. This allowed them to measure how abundant the various chemical elements were in the star. They found that the proportion of metals in SDSS J102915+172927 is more than 20 000 times smaller than that of the Sun [4][5].
“The star is faint, and so metal-poor that we could only detect the signature of one element heavier than helium – calcium – in our first observations,” said Piercarlo Bonifacio (Observatoire de Paris, France), who supervised the project. “We had to ask for additional telescope time from ESO’s Director General to study the star’s light in even more detail, and with a long exposure time, to try to find other metals.”
Cosmologists believe that the lightest chemical elements – hydrogen and helium – were created shortly after the Big Bang, together with some lithium [6], while almost all other elements were formed later in stars. Supernova explosions spread the stellar material into the interstellar medium, making it richer in metals. New stars form from this enriched medium so they have higher amounts of metals in their composition than the older stars. Therefore, the proportion of metals in a star tells us how old it is.
“The star we have studied is extremely metal-poor, meaning it is very primitive. It could be one of the oldest stars ever found,” adds Lorenzo Monaco (ESO, Chile), also involved in the study.
Also very surprising was the lack of lithium in SDSS J102915+172927. Such an old star should have a composition similar to that of the Universe shortly after the Big Bang, with a few more metals in it. But the team found that the proportion of lithium in the star was at least fifty times less than expected in the material produced by the Big Bang.
“It is a mystery how the lithium that formed just after the beginning of the Universe was destroyed in this star.” Bonifacio added.
The researchers also point out that this freakish star is probably not unique. “We have identified several more candidate stars that might have metal levels similar to, or even lower than, those in SDSS J102915+172927. We are now planning to observe them with the VLT to see if this is the case,” concludes Caffau.
Notes
[1] The star is catalogued in the Sloan Digital Sky Survey or SDSS. The numbers refer to the object’s position in the sky.
[2] Widely accepted star formation theories state that stars with a mass as low as SDSS J102915+172927 (about 0.8 solar masses or less) could only have formed after supernova explosions enriched the interstellar medium above a critical value. This is because the heavier elements act as “cooling agents”, helping to radiate away the heat of gas clouds in this medium, which can then collapse to form stars. Without these metals, the pressure due to heating would be too strong, and the gravity of the cloud would be too weak to overcome it and make the cloud collapse. One theory in particular identifies carbon and oxygen as the main cooling agents, and in SDSS J102915+172927 the amount of carbon is lower than the minimum deemed necessary for this cooling to be effective.
[3] X-shooter (http://www.eso.org/public/news/eso0920/) and UVES (http://www.eso.org/sci/facilities/paranal/instruments/uves/) are VLT spectrographs – instruments used to separate the light from celestial objects into its component colours and allow detailed analysis of the chemical composition. X-shooter can capture a very wide range of wavelengths in the spectrum of an object in one shot (from the ultraviolet to the near-infrared). UVES is the Ultraviolet and Visual Echelle Spectrograph, a high-resolution optical instrument.
[4] The star HE 1327-2326, discovered in 2005, has the lowest known iron abundance, but it is rich in carbon. The star now analysed has the lowest proportion of metals when all chemical elements heavier than helium are considered.
[5] ESO telescopes have been deeply involved in many of the discoveries of the most metal-poor stars. Some of the earlier results were reported in eso0228 (http://www.eso.org/public/news/eso0920/) and eso0723 (http://www.eso.org/public/news/eso0723/) and the new discovery shows that observations with ESO telescopes have let astronomers make a further step closer to finding the first generation of stars.
[6] Primordial nucleosynthesis refers to the production of chemical elements with more than one proton a few moments after the Big Bang. This production happened in a very short time, allowing only hydrogen, helium and lithium to form, but no heavier elements. The Big Bang theory predicts, and observations confirm, that the primordial matter was composed of about 75% (by mass) of hydrogen, 25% of helium, and trace amounts of lithium.
More information
This research was presented in a paper, “An extremely primitive halo star”, by Caffau et al. to appear in the 1 September 2011 issue of the journal Nature.
The team is composed of Elisabetta Caffau (Zentrum fur Astronomie der Universitat Heidelberg [ZAH], Germany and GEPI – Observatoire de Paris, Universite Paris Diderot, CNRS, France [GEPI]), Piercarlo Bonifacio (GEPI), Patrick François (GEPI and Universite de Picardie Jules Verne, Amiens, France), Luca Sbordone (ZAH, Max-Planck Institut fur Astrophysik, Garching, Germany, and GEPI), Lorenzo Monaco (ESO, Chile), Monique Spite (GEPI), François Spite (GEPI), Hans-G. Ludwig (ZAH and GEPI), Roger Cayrel (GEPI), Simone Zaggia (INAF, Osservatorio Astronomico di Padova, Italy), François Hammer (GEPI), Sofia Randich (INAF, Osservatorio Astrofisico di Arcetri, Firenze, Italy), Paolo Molaro (INAF, Osservatorio Astronomico di Trieste, Italy), and Vanessa Hill (Universite de Nice-Sophia Antipolis, Observatoire de la Cote d’Azur, CNRS, Laboratoire Cassiopee, Nice, France).
ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Links
Research paper:
http://www.eso.org/public/archives/releases/sciencepapers/eso1132/eso1132.pdf
Photos of the VLT:
http://www.eso.org/public/images/archive/category/paranal/
Contact: Richard Hook
rhook@eso.org
49-893-200-6655
ESO
Mobile phone data help track populations during disasters
August 31, 2011
Mobile phone positioning data can be used to monitor population movements during disasters and outbreaks, according to a study published in this week’s PLoS Medicine. The study, conducted by Linus Bengtsson and colleagues from the Karolinska Institute, Sweden and Columbia University, USA, finds that reports on the location of populations affected and in need of assistance can be generated within hours of receiving data.
Population movements after disasters make it difficult to deliver essential relief assistance to the right places and at the right scale. In this geospatial analysis, Bengtsson and colleagues investigate whether position data from mobile phone SIMs (subscriber identity modules) can be used to estimate the magnitude and trends of population movements. The authors collaborated with Digicel, the largest mobile phone operator in Haiti, to retrospectively follow the positions of 1.9 million SIMs in Haiti before and after the January 2010 earthquake, and found that the estimates of population movements using SIM cards were more accurate than ad hoc estimates generated immediately after the earthquake. The authors then tracked population movements by SIM positioning during the first few days of the cholera outbreak that occurred following the earthquake, showing that these estimates of population movements could be generated within 12 hours of receiving SIM positioning data.
Their findings show that routinely collected data on the movements of active SIM cards in a disaster-affected nation can provide estimates of the magnitude, distribution, and trends in population displacement, and that the method can be used for close to real-time monitoring of population movements during an infectious disease outbreak. Results of the study also suggest that this method could provide estimates on area-specific population sizes and could lead to important improvements in the allocation of relief supplies.
The authors say: “We recommend establishing relations with mobile phone operators prior to emergencies as well as implementing and further evaluating the method during future disasters.”
However, this approach may not be effective in all situations, since disasters can destroy mobile phone towers and some areas have sparse network coverage. Additionally, mobile use may be lower in some population groups such as children or the elderly.
In an accompanying perspective article, Peter Gething of the University of Oxford, United Kingdom and Andrew Tatem from the University of Florida, USA, both uninvolved in the study, discuss the potential impact of mobile phone positioning data on responses to disaster. They highlight challenges that must be addressed if use of this technology for disaster response planning is to develop, including how to assess cross-border population movements and the need for protocols to protect the privacy of data, saying: “Bengtsson and colleagues have demonstrated a valuable proof-of-concept of the use of phone data in disaster response, but substantial further work will likely be required before operational usage becomes common.”
Gething and Tatem continue: “While millions continue to be adversely affected by natural disasters, in an increasingly connected world where mobile phone ownership is becoming ubiquitous, these data will likely become a valuable component of the disaster response toolbox. Bengtsson and colleagues have taken the first step towards this full potential being realised.”
Funding: The Swedish National Board of Health and Welfare (www.sos.se) supported the project financially. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Citation: Bengtsson L, Lu X, Thorson A, Garfield R, von Schreeb J (2011) Improved Response to Disasters and Outbreaks by Tracking Population Movements with Mobile Phone Network Data: A Post-Earthquake Geospatial Study in Haiti. PLoS Med 8(8): e1001083. doi:10.1371/journal.pmed.1001083
Perspective by Peter Gething and Andrew Tatem
Funding: PWG is supported by a Senior Research Fellowship from the Wellcome Trust held by Dr Simon Hay #079091). AJT is supported by a grant from the Bill and Melinda Gates Foundation (#49446). PWG and AJT acknowledge support from the RAPIDD program of the Science & Technology Directorate, Department of Homeland Security, and the Fogarty International Center, National Institutes of Health. This work forms part of the output of the Malaria Atlas Project (MAP, http://www.map.ox.ac.uk/), principally funded by the Wellcome Trust (http://www.wellcome.ac.uk/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
Citation: Gething PW, Tatem AJ (2011) Can Mobile Phone Data Improve Emergency Response to Natural Disasters? PLoS Med 8(8): e1001085. doi:10.1371/journal.pmed.1001085
http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1001085
Contact: Clare Weaver
press@plos.org
44-122-344-2834
Public Library of Science
New tests for ‘legal marijuana,’ ‘bath salts’ and other emerging designer drugs
August 31, 2011
Scientists today reported development of much needed new tests to help cope with a wave of deaths, emergency room visits and other problems from a new genre of designer drugs sold legally in stores and online that mimic the effects of cocaine, ecstasy and marijuana. They spoke at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), being held here this week.
The reports, among more than 7,500 on the ACS agenda, focus on drugs sold as “bath salts,” “plant food,” “incense” and other products with colorful names, such as “Ivory Wave,” “Red Dove” and “legal marijuana.” They provide users with a high, but many have not yet been made illegal and are undetectable with current drug tests. In one presentation on these “legal highs,” a United Kingdom researcher reported a new method to trace the source of the substances in “bath salts.” In the other, a U.S. researcher discussed the challenges facing law enforcement and policy makers in regulating synthetic versions of marijuana.
Oliver Sutcliffe, Ph.D., and his collaborators reported the successful use of a method called isotope ratio mass spectrometry (IRMS) to determine who is making bath salts – drugs that can cause euphoria, paranoia, anxiety and hallucinations when snorted, smoked or injected – and which chemical companies supplied the raw materials. He and his co-workers are based at the University of Strathclyde and the James Hutton Institute in the U.K.
“With the new method, we could work backwards and trace the substances back to the starting materials,” said Sutcliffe. IRMS measures the relative amounts of an element’s different forms, or isotopic ratio. “This method was successful because the isotopic ratio of the starting material is transferred like a fingerprint through the synthesis,” he explained.
“Bath salts” first garnered major media attention in the U.K. in early 2010, and then became a problem in the U.S. These products are not in the supermarket soap aisle – they are sold on the Internet, on the street and in stores that sell drug paraphernalia. They are sold in small individual bags for as low as $20 each for the real purpose of providing a cheap, legal high.
The powders often contain mephedrone, which is a synthetic compound, structurally related to methcathinone, which is found in Khat – a plant that is illegal in many countries, including the U.K. and the U.S. Usually, that would mean that these compounds (and derivatives thereof) would be illegal in those countries too, but because the bath salts are labeled “not for human consumption,” they get around this restriction and other legislation governing the supply of medicines for human use. However, Florida and Louisiana – two hotspots of bath salts abuse – specifically banned the substances. U.K. officials banned the import of bath salts, which may lead some in the drug trade to set up clandestine labs on U.K. soil, said Sutcliffe. The new method provides law enforcement with a tool to track down these bath salts manufacturers.
In previous work, Sutcliffe developed the first pure reference standard for mephedrone, as well as the first reliable liquid chromatography test for the substance, which could be easily run in a typical law enforcement lab. The team is also developing a color-change test kit for mephedrone, which he estimates may be available by the end of the year.
In another presentation, Robert Lantz, Ph.D., from the Rocky Mountain Instrumental Laboratories, described another high that is legal in most of the U.S. – synthetic cannabinoids marketed as incense, a spice product or “legal marijuana” that give a high similar to marijuana without showing up in conventional drug tests.
“We can detect synthetic cannabinoids with modern analytical chemistry techniques, such as liquid or gas chromatography coupled to mass spectrometry, but these assays are too expensive for the 5,000-10,000 urine samples that most drug testing labs receive each day,” said Lantz. Most labs screen for drugs with less expensive antibody assays, but because the structures of these substances are so dissimilar, different antibodies would likely be required for many of them, driving up the cost of a more comprehensive test.
Synthetic cannabinoid abuse rose sharply in 2010, according to U.S. poison control centers, up to 2,863 compared to only 14 in 2009. About 200 synthetic cannabinoids exist, but the U.S. Drug Enforcement Agency (DEA) banned only five of those. A handful of states, such as Washington, Georgia and Colorado, banned five of them, but they are not always the same five that the DEA banned. “The states banned several specific compounds without a particular basis for their choices,” Lantz pointed out.
Colorado recently passed a law banning any substance that binds to a cannabinoid receptor in the human body. “The bill was well-intentioned, but technically, the new law not only covers synthetic cannabinoids, but also endocannabinoids, which are naturally occurring substances that the human body produces to regulate many normal processes,” said Lantz.
The American Chemical Society is a non-profit organization chartered by the U.S. Congress. With more than 163,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio.
To automatically receive news releases from the American Chemical Society contact newsroom@acs.org.
ABSTRACTS:
Dr. Sutcliffe:
The increase in the global abuse of synthetic cathinones has given rise to significant legal and analytical challenges in their identification and quantification – thus rapid methods of testing (especially in the field) are urgently required. This paper presents synthesis; characterisation; validated presumptive and quantitative methods for these substances (both in pure and adulterated samples) and a rapid, novel NMR screening technique for street samples containing components which cannot normally be detected using standard chromatographic methods.
Dr. Lantz:
There is no end to human ingenuity. Unfortunately, this phrase even provides to be true when it comes to methods and means of getting high. Synthetic Cannabinoids, such as JWH-018 which is only one of many such substances (which is currently marketed as K2), and other substances such as Methylone (MDPV) and Mephedrone (which is currently marketed as “Bath Salts” or “Plant Food” respectively) present unique analytical chemistry challenges from a chromatographic point-of-view. Related challenges in terms of quantitation of these substances still exist. In the rush to make illegal and prosecute the possession and use of these substances, errors related the qualitative and quantitative reporting of these compounds can occur. This presentation will examine these challenges that exist and what lies ahead.
Contact: Michael Bernstein
m_bernstein@acs.org
303-228-8532 (Aug. 25-Sept. 1)
202-872-6042 (Before Aug. 25)
Michael Woods
m_woods@acs.org
303-228-8532 (Aug. 25-Sept. 1)
202-872-6293 (Before Aug. 25)
Localizing language in the brain
August 30, 2011
New research from MIT suggests that there are parts of our brain dedicated to language and only language, a finding that marks a major advance in the search for brain regions specialized for sophisticated mental functions.
Functional specificity, as it’s known to cognitive scientists, refers to the idea that discrete parts of the brain handle distinct tasks. Scientists have long known that functional specificity exists in certain domains: In the motor system, for example, there is one patch of neurons that controls the fingers of your left hand, and another that controls your tongue. But what about more complex functions such as recognizing faces, using language or doing math? Are there special brain regions for those activities, or do they use general-purpose areas that serve whatever task is at hand?
Language, a cognitive skill that is both unique to humans and universal to all human cultures, “seems like one of the first places one would look” for this kind of specificity, says Evelina Fedorenko, a research scientist in MIT’s Department of Brain and Cognitive Sciences and first author of the new study. But data from neuroimaging – especially functional magnetic resonance imaging (fMRI), which measures brain activity associated with cognitive tasks – has been frustratingly inconclusive. Though studies have largely converged on several areas important for language, it’s been hard to say whether those areas are exclusive to language. Many experiments have found that non-language tasks seemingly activate the same areas: Arithmetic, working memory and music are some of the most common culprits.
But according to Fedorenko and her co-authors – Nancy Kanwisher, the Walter A. Rosenblith Professor of Cognitive Neuroscience, and undergraduate student Michael Behr – this apparent overlap may simply be due to flaws in methodology, i.e., how fMRI data is traditionally gathered and analyzed. In their new study, published in this week’s Proceedings of the National Academy of Sciences, they used an innovative technique they’ve been developing over the past few years; the new method yielded evidence that there are, in fact, bits of the brain that do language and nothing else.
Forget the forest, it’s all in the trees
fMRI studies of language are typically done by group analysis, meaning that researchers test 10, 20 or even 50 subjects, then average data together onto a common brain space to search for regions that are active across brains.
But Fedorenko says this is not an ideal way to do things, mainly because the fine-grained anatomical differences between brains can cause data “smearing,” making it look as if one region is active in two different tasks when in reality, the tasks activate two neighboring – but not overlapping – regions in each individual subject.
By way of analogy, she says, imagine taking pictures of 10 people’s faces and overlaying them, one on top of another, to achieve some sort of average face. While the resulting image would certainly look like a face, when you compared it back to the original pictures, it would not line up perfectly with any of them. That’s because there is natural variation in our features – the size of our foreheads, the width of our noses, the distance between our eyes.
It’s the same way for brains. “Brains are different in their folding patterns, and where exactly the different functional areas fall relative to these patterns,” Fedorenko says. “The general layout is similar, but there isn’t fine-grained matching.” So, she says, analyzing data by “aligning brains in some common space is just never going to be quite right.”
Ideally, then, data would be analyzed for each subject individually; that is, patterns of activity in one brain would only ever be compared to patterns of activity from that same brain. To do this, the researchers spend the first 10 to 15 minutes of each fMRI scan having their subject do a fairly sophisticated language task while tracking brain activity. This way, they establish where the language areas lie in that individual subject, so that later, when the subject performs other cognitive tasks, they can compare those activation patterns to the ones elicited by language.
A linguistic game of ‘Where’s Waldo?’
This methodology is exactly what allows Fedorenko, Behr and Kanwisher to see if there are areas truly specific to language. After having their subjects perform the initial language task, which they call a “functional localizer,” they had each one do a subset of seven other experiments: one on exact arithmetic, two on working memory, three on cognitive control and one on music, since these are the functions “most commonly argued to share neural machinery with language,” Fedorenko says.
Out of the nine regions they analyzed – four in the left frontal lobe, including the region known as Broca’s area, and five further back in the left hemisphere – eight uniquely supported language, showing no significant activation for any of the seven other tasks. These findings indicate a “striking degree of functional specificity for language,” as the researchers report in their paper.
Future studies will test the newly identified language areas with even more non-language tasks to see if their functional specificity holds up; the researchers also plan to delve deeper into these areas to discover which particular linguistic jobs each is responsible for.
Fedorenko says the results don’t imply that every cognitive function has its own dedicated piece of cortex; after all, we’re able to learn new skills, so there must be some parts of the brain that are both high-level and functionally flexible. Still, she says, the results give hope to researchers looking to draw some distinctions within in the human cortex: “Brain regions that do related things may be nearby [but] it’s not just all one big mushy multifunctional thing in there.”
Contact: Caroline McCall
cmccall5@mit.edu
Massachusetts Institute of Technology
Graphene’s shining light could lead to super-fast Internet
August 30, 2011
Writing in the journal Nature Communications, a collaboration between the Universities of Manchester and Cambridge, which includes Nobel Prize winning scientists Professor Andre Geim and Professor Kostya Novoselov, has discovered a crucial recipe for improving characteristics of graphene devices for use as photodetectors in future high-speed optical communications.
By combining graphene with metallic nanostructures, they show a twentyfold enhancement in harvesting light by graphene, which paves the way for advances in high-speed internet and other communications.
By putting two closely-spaced metallic wires on top of graphene and shining light on this structure, researchers previously showed that this generates electric power. This simple device presents an elementary solar cell.
More importantly for applications, such graphene devices can be incredibly fast, tens and potentially hundred times faster than communication rates in the fastest internet cables, which is due to the unique nature of electrons in graphene, their high mobility and high velocity.
The major stumbling block towards practical applications for these otherwise very promising devices has so far been their low efficiency. The problem is that graphene – the thinnest material in the world – absorbs little light, approximately only 3%, with the rest going through without contributing to the electrical power.
The Manchester researchers have solved the problems by combining graphene with tiny metallic structures, specially arranged on top of graphene.
These so-called plasmonic nanostructures have dramatically enhanced the optical electric field felt by graphene and effectively concentrated light within the one-atom-thick carbon layer.
By using the plasmonic enhancement, the light-harvesting performance of graphene was boosted by twenty times, without sacrificing any of its speed. The future efficiency can be improved even further.
Dr Alexander Grigorenko, an expert in plasmonics and a leading member of the team, said: “Graphene seems a natural companion for plasmonics. We expected that plasmonic nanostructures could improve the efficiency of graphene-based devices but it has come as a pleasant surprise that the improvements can be so dramatic.”
Professor Novoselov added: “The technology of graphene production matures day-by-day, which has an immediate impact both on the type of exciting physics which we find in this material, and on the feasibility and the range of possible applications.
“Many leading electronics companies consider graphene for the next generation of devices. This work certainly boosts graphene’s chances even further.”
Professor Andrea Ferrari, from the Cambridge Engineering Department, who lead the Cambridge effort in the collaboration, said “So far, the main focus of graphene research has been on fundamental physics and electronic devices.
“These results show its great potential in the fields of photonics and optoelectronics, where the combination of its unique optical and electronic properties with plasmonic nanostructures, can be fully exploited, even in the absence of a bandgap, in a variety of useful devices, such as solar cells and photodetectors”
Graphene is a novel two-dimensional material which can be seen as a monolayer of carbon atoms arranged in a hexagonal lattice.
It is a wonder material that possesses a large number of unique properties and is currently considered in many new technologies.
The world’s thinnest material was discovered at The University of Manchester in 2004, which was acknowledged by the 2010 Nobel Prize in Physics awarded to Geim and Novoselov for their “groundbreaking experiments regarding the two-dimensional material graphene”.
Contact: Daniel Cochlin
daniel.cochlin@manchester.ac.uk
44-161-275-8387
University of Manchester
Novel alloy could produce hydrogen fuel from sunlight
August 30, 2011
Scientists from the University of Kentucky and the University of Louisville have determined that an inexpensive semiconductor material can be “tweaked” to generate hydrogen from water using sunlight.
The research, funded by the U.S. Department of Energy, was led by Professors Madhu Menon and R. Michael Sheetz at the UK Center for Computational Sciences, and Professor Mahendra Sunkara and graduate student Chandrashekhar Pendyala at the UofL Conn Center for Renewable Energy Research. Their findings were published Aug. 1 in the Physical Review Journal (Phys Rev B 84, 075304).
The researchers say their findings are a triumph for computational sciences, one that could potentially have profound implications for the future of solar energy.
Using state-of-the-art theoretical computations, the UK-UofL team demonstrated that an alloy formed by a 2 percent substitution of antimony (Sb) in gallium nitride (GaN) has the right electrical properties to enable solar light energy to split water molecules into hydrogen and oxygen, a process known as photoelectrochemical (PEC) water splitting. When the alloy is immersed in water and exposed to sunlight, the chemical bond between the hydrogen and oxygen molecules in water is broken. The hydrogen can then be collected.
“Previous research on PEC has focused on complex materials,” Menon said. “We decided to go against the conventional wisdom and start with some easy-to-produce materials, even if they lacked the right arrangement of electrons to meet PEC criteria. Our goal was to see if a minimal ‘tweaking’ of the electronic arrangement in these materials would accomplish the desired results.”
Gallium nitride is a semiconductor that has been in widespread use to make bright-light LEDs since the 1990s. Antimony is a metalloid element that has been in increased demand in recent years for applications in microelectronics. The GaN-Sb alloy is the first simple, easy-to-produce material to be considered a candidate for PEC water splitting. The alloy functions as a catalyst in the PEC reaction, meaning that it is not consumed and may be reused indefinitely. UofL and UK researchers are currently working toward producing the alloy and testing its ability to convert solar energy to hydrogen.
Hydrogen has long been touted as a likely key component in the transition to cleaner energy sources. It can be used in fuel cells to generate electricity, burned to produce heat, and utilized in internal-combustion engines to power vehicles. When combusted, hydrogen combines with oxygen to form water vapor as its only waste product. Hydrogen also has wide-ranging applications in science and industry.
Because pure hydrogen gas is not found in free abundance on Earth, it must be manufactured by unlocking it from other compounds. Thus, hydrogen is not considered an energy source, but rather an “energy carrier.” Currently, it takes a large amount of electricity to generate hydrogen by water splitting. As a consequence, most of the hydrogen manufactured today is derived from non-renewable sources such as coal and natural gas.
Sunkara says the GaN-Sb alloy has the potential to convert solar energy into an economical, carbon-free source for hydrogen.
“Hydrogen production now involves a large amount of CO2 emissions,” Sunkara said. “Once this alloy material is widely available, it could conceivably be used to make zero-emissions fuel for powering homes and cars and to heat homes.”
Menon says the research should attract the interest of other scientists across a variety of disciplines.
“Photocatalysis is currently one of the hottest topics in science,” Menon said. “We expect the present work to have a wide appeal in the community spanning chemistry, physics and engineering.”
For more information, please contact Keith Hautala at the University of Kentucky at (859) 323-2396 or keith.hautala@uky.edu. At the University of Louisville, please contact Judy Hughes at (502) 852-6171 or judy.hughes@louisville.edu.
Contact: Keith Hautala
keith.hautala@uky.edu
859-323-2396
University of Kentucky
August 30, 2011
Even after many decades of studying ozone and its loss from our atmosphere miles above the Earth, plenty of mysteries and surprises remain, including an unexpected loss of ozone over the Arctic this past winter, an authority on the topic said here today. She also discussed chemistry and climate change, including some proposed ideas to “geoengineer” the Earth’s climate to slow down or reverse global warming. The talk happened at the 242nd National Meeting & Exposition of the American Chemical Society (ACS), being held this week. In a Kavli Foundation Innovations in Chemistry Lecture, Susan Solomon, Ph.D., of the University of Colorado, Boulder, said that the combined efforts of scientists, the public, industry and policy makers to stop ozone depletion is one of science’s greatest success stories, but unanswered questions remain. And ozone is still disappearing. “We’re no longer producing the primary chemicals – chlorofluorocarbons (CFCs) – that caused the problem, but CFCs have very long lifetimes in our atmosphere, and so we’ll have ozone depletion for several more decades,” said Solomon. “There are still some remarkable mysteries regarding exactly how these chlorine compounds behave in Antarctica – and it’s amazing that we still have much to learn, even after studying ozone for so long.” The ozone layer is crucial to life on Earth, forming a protective shield high in the atmosphere that blocks potentially harmful ultraviolet rays in sunlight. Scientists have known since 1930 that ozone forms and decomposes through chemical processes. The first hints that human activity threatened the ozone layer emerged in the 1970s, and included one warning from Paul Crutzen, Ph.D., that agricultural fertilizers might reduce ozone levels. Another hint was from F. Sherwood Rowland, Ph.D., and Mario Molina, Ph.D., who described how CFCs in aerosol spray cans and other products could destroy the ozone layer. The three shared a 1995 Nobel Prize in Chemistry for that research. In 1985, British scientists discovered a “hole,” a completely unexpected area of intense ozone depletion over Antarctica. Solomon’s 1986 expedition to Antarctica provided some of the clinching evidence that underpinned a global ban on CFCs and certain other ozone-depleting gases. Evidence suggests that the ozone depletion has stopped getting worse. “Ozone can be thought of as a patient in remission, but it’s too early to declare recovery,” said Solomon. And surprises, such as last winter’s loss of 40% of the ozone over the Arctic still occur due to the extremely long lifetimes of ozone-destroying substances released years ago before the ban. Solomon also took listeners on a tour of gases and aerosols that affect climate change and described how these substances can contribute to global warming. “On the thousand-year timescale, carbon dioxide is by far the most important greenhouse gas produced by humans, but there are some other interesting – though much less abundant – gases such as perfluorinated compounds that also last thousands of years and similarly affect our climate for millennia,” said Solomon. Increases in atmospheric “greenhouse gases” such as carbon dioxide trap heat in the atmosphere, causing the Earth’s temperature to creep upward. Global warming is causing ocean levels to rise and could lead some regions to become dry “dust bowls.” Dealing with global warming has prompted a lot of interesting research on how to reduce greenhouse gas emissions, how to adapt to a changing climate and on the possibility of ‘geoengineering’ to cool the climate. “Recent studies on ‘geoengineering’ the Earth’s climate involve stratospheric particles of different sorts,” she said. “Most of these schemes involve sulfate particles, but other types have been proposed.” The talk took place on Monday, August 29, from 5:30 to 6:30 p.m., Mountain time in the Wells Fargo Theater at the Colorado Convention Center. Sponsored by The Kavli Foundation, a philanthropic organization that supports basic scientific research, the lectures are designed to address the urgent need for vigorous, “outside the box” thinking by scientists as they tackle the world’s mounting challenges, including climate change, emerging diseases, and water and energy shortages. “We are dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research, and supporting scientists and their work,” said Kavli Foundation President Robert W. Conn in a statement. “The Kavli Foundation Innovations in Chemistry Lecture program at the ACS national meetings fits perfectly with our commitment to support groundbreaking discovery and promote public understanding.” The Kavli lectures debuted at the Anaheim meeting in March during this International Year of Chemistry and will continue through 2013. They will address the urgent need for vigorous, new, “outside-the-box”- thinking, as scientists tackle many of the world’s mounting challenges like climate change, emerging diseases, and water and energy shortages. The Kavli Foundation, an internationally recognized philanthropic organization known for its support of basic scientific innovation, agreed to sponsor the lectures in conjunction with ACS in 2010. ### The American Chemical Society is a non-profit organization chartered by the U.S. Congress. With more than 163,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio. To automatically receive news releases from the American Chemical Society contact newsroom@acs.org. ABSTRACT: The discovery of the Antarctic ozone hole shocked the scientific world when it was discovered in 1985, and research provided the underpinning for a landmark global agreement to mitigate the emissions of ozone-depleting chlorofluorocarbons and bromocarbons that were responsible. The ozone hole was linked to chemical processes occurring on surfaces of particulate matter in the cold Antarctic stratosphere, underscoring the effectiveness of surfaces in driving chemical phenomena in planetary atmospheres. However it is remarkable that key scientific questions remain today regarding exactly which types of cold liquid and solid icy surfaces contribute to the observed ozone losses, demonstrating the complexity of the chemistry, and the importance of continuing research. Both the understanding of ozone depletion and the enduring challenge of detailed surface chemistry will be reviewed in this talk. Chemical phenomena involving stratospheric surfaces are also important for some proposed schemes for deliberate engineering that may be able to cool the Earth’s climate. But the understanding of key aspects of the particle physics and chemistry relevant to these phenomena also poses major challenges, and there have been surprises in evaluating how much human addition of precursor gases would form surfaces that might engineer a controlled and quantifiable change in our climate. Finally, the suite of greenhouse gases and aerosols that are contributing to anthropogenic climate change will be reviewed, with a view towards comparing and contrasting the major chemical phenomena and challenges relevant to each.
Contact: Michael Bernstein
m_bernstein@acs.org
303-228-8532 (Aug. 25-Sept. 1)
202-872-6042 (Before Aug. 25)
Michael Woods
m_woods@acs.org
303-228-8532 (Aug. 25-Sept. 1)
202-872-6293 (Before Aug. 25)
It’s official — chocolate linked to heart health
August 29, 2011
High levels of chocolate consumption might be associated with a one third reduction in the risk of developing heart disease, finds a study published on bmj.com today.
The findings confirm results of existing studies that generally agree on a potential beneficial link between chocolate consumption and heart health. However, the authors stress that further studies are now needed to test whether chocolate actually causes this reduction or if it can be explained by some other unmeasured (confounding) factor.
The findings will be presented at the European Society of Cardiology Congress in Paris at 10:10 hrs (Paris time) / 09:10 hrs (UK time) Monday 29 August 2011.
The World Health Organisation predicts that by 2030, nearly 23.6 million people will die from heart disease. However, lifestyle and diet are key factors in preventing heart disease, says the paper.
A number of recent studies have shown that eating chocolate has a positive influence on human health due to its antioxidant and anti-inflammatory properties. This includes reducing blood pressure and improving insulin sensitivity (a stage in the development of diabetes).
However, the evidence about how eating chocolate affects your heart still remains unclear. So, Dr Oscar Franco and colleagues from the University of Cambridge carried out a large scale review of the existing evidence to evaluate the effects of eating chocolate on cardiovascular events like heart attack and stroke.
They analysed the results of seven studies, involving over 100,000 participants with and without existing heart disease. For each study, they compared the group with the highest chocolate consumption against the group with the lowest consumption. Differences in study design and quality were also taken into account to minimise bias.
Five studies reported a beneficial link between higher levels of chocolate consumption and the risk of cardiovascular events and they found that the “highest levels of chocolate consumption were associated with a 37% reduction in cardiovascular disease and a 29% reduction in stroke compared with lowest levels.” No significant reduction was found in relation to heart failure.
The studies did not differentiate between dark or milk chocolate and included consumption of chocolate bars, drinks, biscuits and desserts.
The authors say the findings need to be interpreted with caution, in particular because commercially available chocolate is very calorific (around 500 calories for every 100 grams) and eating too much of it could in itself lead to weight gain, risk of diabetes and heart disease.
However, they conclude that, given the health benefits of eating chocolate, initiatives to reduce the current fat and sugar content in most chocolate products should be explored.
Contact: Jacqueline Partarrieu
press@escardio.org
33-633-473-335
European Society of Cardiology
Astrophysicists report first simulation to create a Milky Way-like galaxy
August 29, 2011
After nine months of number-crunching on a powerful supercomputer, a beautiful spiral galaxy matching our own Milky Way emerged from a computer simulation of the physics involved in galaxy formation and evolution. The simulation by researchers at the University of California, Santa Cruz, and the Institute for Theoretical Physics in Zurich solves a longstanding problem that had led some to question the prevailing cosmological model of the universe.
“Previous efforts to form a massive disk galaxy like the Milky Way had failed, because the simulated galaxies ended up with huge central bulges compared to the size of the disk,” said Javiera Guedes, a graduate student in astronomy and astrophysics at UC Santa Cruz and first author of a paper on the new simulation, called “Eris.” The paper has been accepted for publication in the Astrophysical Journal.
The Eris galaxy is a massive spiral galaxy with a central “bar” of bright stars and other structural properties consistent with galaxies like the Milky Way. Its brightness profile, bulge-to-disk ratio, stellar content, and other key features are all within the range of observations of the Milky Way and other galaxies of the same type. “We dissected the galaxy in many different ways to confirm that it fits with observations,” Guedes said.
According to coauthor Piero Madau, professor of astronomy and astrophysics at UC Santa Cruz, the project required a large investment of supercomputer time, including 1.4 million processor-hours on NASA’s state-of-the-art Pleiades supercomputer, plus additional supporting simulations on supercomputers at UCSC and the Swiss National Supercomputing Center. “We took some risk spending a huge amount of supercomputer time to simulate a single galaxy with extra-high resolution,” Madau said.
The results support the prevailing “cold dark matter” theory, in which the evolution of structure in the universe is driven by the gravitational interactions of dark matter (“dark” because it can’t be seen, and “cold” because the particles are moving slowly). Gravity acted initially on slight density fluctuations present shortly after the Big Bang, pulling together the first clumps of dark matter, which grew into larger and larger clumps through the hierarchical merging of smaller progenitors. The ordinary matter that forms stars and planets (less than 20 percent of the matter in the universe) has fallen into the “gravitational wells” created by large clumps of dark matter, giving rise to galaxies in the centers of dark matter halos.
For the past 20 years, however, efforts to reproduce this process in computer simulations have failed to generate massive disk galaxies that look anything like the Milky Way, with its spiral arms in a large flat disk around a small central bulge made up of old stars. A realistic simulation of star formation was the key to Eris’s success, Madau said.
“Star formation in real galaxies occurs in a clustered fashion, and to reproduce that out of a cosmological simulation is hard,” Madau said. “This is the first simulation that is able to resolve the high-density clouds of gas where star formation occurs, and the result is a Milky Way type of galaxy with a small bulge and a big disk. It shows that the cold dark matter scenario, where dark matter provides the scaffolding for galaxy formation, is able to generate realistic disk-dominated galaxies.”
To perform the Eris simulation, the researchers began with a low-resolution simulation of dark matter evolving to form the haloes that host present-day galaxies. Then they chose a halo with an appropriate mass and merger history to host a galaxy like the Milky Way and “rewound the tape” back to the initial conditions. Zooming in on the small region that evolved into the chosen halo, they added gas particles and greatly increased the resolution of the simulation. High resolution means tracking the interactions of a huge number of particles.
“The simulation follows the interactions of more than 60 million particles of dark matter and gas. A lot of physics goes into the code–gravity and hydrodynamics, star formation and supernova explosions–and this is the highest resolution cosmological simulation ever done this way,” said Guedes, who is currently a postdoctoral researcher at the Swiss Federal Institute of Technology in Zurich (ETH Zurich).
The high resolution allowed for a more precise recipe for star formation. In a low-resolution simulation, with gas densities averaged out over relatively large areas, the threshold density for star formation has to be set so low that stars tend to form in diffuse gas throughout the galaxy. In the Eris simulation, the star-formation threshold allowed stars to form only in high-density regions, resulting in a more realistic distribution of stars.
An important consequence is that when stars explode as supernovae within these localized, high-density regions, the energy injected into the interstellar medium blows a lot of gas out of the galaxy. “Supernovae produce outflows of gas from the inner part of the galaxy where it would otherwise form more stars and make a large bulge,” Madau said. “Clustered star formation and energy injection from supernovae are making the difference in this simulation.”
In addition to Madau and Guedes, the coauthors of the paper are Simone Callegari and Lucio Mayer of the Institute for Theoretical Physics in Zurich. This research was funded by NASA, the U.S. National Science Foundation, the Swiss National Science Foundation, and an ARCS Foundation fellowship to Guedes.
Contact: Tim Stephens
stephens@ucsc.edu
831-459-2495
University of California – Santa Cruz