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  • richardmitnick 8:23 am on April 17, 2014 Permalink | Reply
    Tags: Applied Research & Technology, , ,   

    From Caltech: “Made-to-Order Materials” 

    Caltech Logo
    Caltech

    09/05/2013
    Kimm Fesenmaier

    Caltech engineers focus on the nano to create strong, lightweight materials

    The lightweight skeletons of organisms such as sea sponges display a strength that far exceeds that of manmade products constructed from similar materials. Scientists have long suspected that the difference has to do with the hierarchical architecture of the biological materials—the way the silica-based skeletons are built up from different structural elements, some of which are measured on the scale of billionths of meters, or nanometers. Now engineers at the California Institute of Technology (Caltech) have mimicked such a structure by creating nanostructured, hollow ceramic scaffolds, and have found that the small building blocks, or unit cells, do indeed display remarkable strength and resistance to failure despite being more than 85 percent air.

    mat
    Three-dimensional, hollow titanium nitride nanotruss with tessellated octahedral geometry. Each unit cell is on the order of 10 microns, each strut length within the unit cell is about three to five microns, the diameter of each strut is less than one micron, and the thickness of titanium nitride is roughly 75 nanometers.Credit: Dongchan Jang and Lucas Meza

    “Inspired, in part, by hard biological materials and by earlier work by Toby Schaedler and a team from HRL Laboratories, Caltech, and UC Irvine on the fabrication of extremely lightweight microtrusses, we designed architectures with building blocks that are less than five microns long, meaning that they are not resolvable by the human eye,” says Julia R. Greer, professor of materials science and mechanics at Caltech. “Constructing these architectures out of materials with nanometer dimensions has enabled us to decouple the materials’ strength from their density and to fabricate so-called structural metamaterials which are very stiff yet extremely lightweight.

    “At the nanometer scale, solids have been shown to exhibit mechanical properties that differ substantially from those displayed by the same materials at larger scales. For example, Greer’s group has shown previously that at the nanoscale, some metals are about 50 times stronger than usual, and some amorphous materials become ductile rather than brittle. “We are capitalizing on these size effects and using them to make real, three-dimensional structures,” Greer says.

    In an advance online publication of the journal Nature Materials, Greer and her students describe how the new structures were made and responded to applied forces.

    The largest structure the team has fabricated thus far using the new method is a one-millimeter cube. Compression tests on the the entire structure indicate that not only the individual unit cells but also the complete architecture can be endowed with unusually high strength, depending on the material, which suggests that the general fabrication technique the researchers developed could be used to produce lightweight, mechanically robust small-scale components such as batteries, interfaces, catalysts, and implantable biomedical devices.

    Greer says the work could fundamentally shift the way people think about the creation of materials. “With this approach, we can really start thinking about designing materials backward,” she says. “I can start with a property and say that I want something that has this strength or this thermal conductivity, for example. Then I can design the optimal architecture with the optimal material at the relevant size and end up with the material I wanted.”

    The team first digitally designed a lattice structure featuring repeating octahedral unit cells—a design that mimics the type of periodic lattice structure seen in diatoms. Next, the researchers used a technique called two-photon lithography to turn that design into a three-dimensional polymer lattice. Then they uniformly coated that polymer lattice with thin layers of the ceramic material titanium nitride (TiN) and removed the polymer core, leaving a ceramic nanolattice. The lattice is constructed of hollow struts with walls no thicker than 75 nanometers.

    “We are now able to design exactly the structure that we want to replicate and then process it in such a way that it’s made out of almost any material class we’d like—for example, metals, ceramics, or semiconductors—at the right dimensions,” Greer says.

    In a second paper, scheduled for publication in the journal Advanced Engineering Materials, Greer’s group demonstrates that similar nanostructured lattices could be made from gold rather than a ceramic. “Basically, once you’ve created the scaffold, you can use whatever technique will allow you to deposit a uniform layer of material on top of it,” Greer says.

    In the Nature Materials work, the team tested the individual octahedral cells of the final ceramic lattice and found that they had an unusually high tensile strength. Despite being repeatedly subjected to stress, the lattice cells did not break, whereas a much larger, solid piece of TiN would break at much lower stresses. Typical ceramics fail because of flaws—the imperfections, such as holes and voids, that they contain. “We believe the greater strength of these nanostructured materials comes from the fact that when samples become sufficiently small, their potential flaws also become very small, and the probability of finding a weak flaw within them becomes very low,” Greer says. So although structural mechanics would predict that a cellular structure made of TiN would be weak because it has very thin walls, she says, “we can effectively trick this law by reducing the thickness or the size of the material and by tuning its microstructure, or atomic configurations.”

    Additional coauthors on the Nature Materials paper, Fabrication and Deformation of Three-Dimensional Hollow Ceramic Nanostructures, are Dongchan Jang, who recently completed a postdoctoral fellowship in Greer’s lab, Caltech graduate student Lucas Meza, and Frank Greer, formerly of the Jet Propulsion Laboratory (JPL). The work was supported by funding from the Dow-Resnick Innovation Fund at Caltech, DARPA’s Materials with Controlled Microstructural Architecture program, and the Army Research Office through the Institute for Collaborative Biotechnologies at Caltech. Some of the work was carried out at JPL under a contract with NASA, and the Kavli Nanoscience Institute at Caltech provided support and infrastructure.

    The lead author on the Advanced Engineering Materials paper, Design and Fabrication of Hollow Rigid Nanolattices Via Two-Photon Lithography, is Caltech graduate student Lauren Montemayor. Meza is a coauthor. In addition to support from the Dow-Resnick Innovation Fund, this work received funding from an NSF Graduate Research Fellowship.

    See the full article here.

    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”


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  • richardmitnick 10:10 pm on April 16, 2014 Permalink | Reply
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    From SLAC Lab: “Scientists Capture Ultrafast Snapshots of Light-driven Superconductivity” 

    April 16, 2014
    No Writer Credit

    A new study pins down a major factor behind the appearance of superconductivity – the ability to conduct electricity with 100 percent efficiency – in a promising copper-oxide material.

    Scientists used carefully timed pairs of laser pulses at SLAC National Accelerator Laboratory’s Linac Coherent Light Source (LCLS) to trigger superconductivity in the material and immediately take X-ray snapshots of its atomic and electronic behavior as superconductivity emerged.

    und
    The Undulator Hall at SLAC’s Linac Coherent Light Source X-ray laser. (Brad Plummer/SLAC)

    They discovered that so-called “charge stripes” of increased electrical charge melted away as superconductivity appeared. Further, the results help rule out the theory that shifts in the material’s atomic lattice hinder the onset of superconductivity.

    Armed with this new understanding, scientists may be able to develop new techniques to eliminate these charge stripes and help pave the way for room-temperature superconductivity, often considered the holy grail of condensed matter physics. The demonstrated ability to rapidly switch between the insulating and superconducting states could also prove useful in advanced electronics and computation.

    The results, from a collaboration led by scientists from the Max Planck Institute for the Structure and Dynamics of Matter in Germany and the U.S. Department of Energy’s SLAC and Brookhaven national laboratories, were published online April 16, 2014, in the journal Physical Review Letters.

    “The very short timescales and the need for high spatial resolution made this experiment extraordinarily challenging,” said co-author Michael Först, a scientist at the Max Planck Institute. “Now, using femtosecond X-ray pulses, we found a way to capture the quadrillionths-of-a-second dynamics of the charges and the crystal lattice. We’ve broken new ground in understanding light-induced superconductivity.”

    Josh Turner, an LCLS staff scientist, said, “This represents a very important result in the field of superconductivity using LCLS. It demonstrates how we can unravel different types of complex mechanisms in superconductivity that have, up until now, been inseparable.”

    He added, “To make this measurement, we had to push the limits of our current capabilities. We had to measure a very weak, barely detectable signal with state-of-the-art detectors, and we had to tune the number of X-rays in each laser pulse to see the signal from the stripes without destroying the sample.”

    Ripples in Quantum Sand

    The compound used in this study was a layered material consisting of lanthanum, barium, copper, and oxygen grown at Brookhaven Lab by physicist Genda Gu. Each copper oxide layer contained the crucial charge stripes.

    man
    Physicist Genda Gu in the Brookhaven Lab facility where the copper-oxide materials were grown for this study.

    “Imagine these stripes as ripples frozen in the sand,” said John Hill, a Brookhaven Lab physicist and coauthor on the study. “Each layer has all the ripples going in one direction, but in the neighboring layers they run crosswise. From above, this looks like strings in a pile of tennis racquets. We believe that this pattern prevents each layer from talking to the next, thus frustrating superconductivity.”

    To excite the material and push it into the superconducting phase, the scientists used mid-infrared laser pulses to “melt” those frozen ripples. These pulses had previously been shown to induce superconductivity in a related compound at a frigid 10 Kelvin (minus 442 degrees Fahrenheit).

    “The charge stripes disappeared immediately,” Hill said. “But specific distortions in the crystal lattice, which had been thought to stabilize these stripes, lingered much longer. This shows that only the charge stripes inhibit superconductivity.”

    Stroboscopic Snapshots

    To capture these stripes in action, the collaboration turned to SLAC’s LCLS X-ray laser, which works like a camera with a shutter speed faster than 100 femtoseconds, or quadrillionths of a second, and provides atomic-scale image resolution. LCLS uses a section of SLAC’s 2-mile-long linear accelerator to generate the electrons that give off X-ray light.

    Researchers used the so-called “pump-probe” approach: an optical laser pulse strikes and excites (pumps) the lattice and an ultrabright X-ray laser pulse is carefully synchronized to follow within femtoseconds and measure (probe) the lattice and stripe configurations. Each round of tests results in some 20,000 X-ray snapshots of the changing lattice and charge stripes, a bit like a strobe light rapidly illuminating the process.

    To measure the changes with high spatial resolution, the team used a technique called resonant soft X-ray diffraction. The LCLS X-rays strike and scatter off the crystal into the detector, carrying time-stamped signatures of the material’s charge and lattice structure that the physicists then used to reconstruct the rise and fall of superconducting conditions.

    “By carefully choosing a very particular X-ray energy, we are able to emphasize the scattering from the charge stripes,” said Brookhaven Lab physicist Stuart Wilkins, another co-author on the study. “This allows us to single out a very weak signal from the background.”

    Toward Superior Superconductors

    The X-ray scattering measurements revealed that the lattice distortion persists for more than 10 picoseconds (trillionths of a second) – long after the charge stripes melted and superconductivity appeared, which happened in less than 400 femtoseconds. Slight as it may sound, those extra trillionths of a second make a huge difference.

    “The findings suggest that the relatively weak and long-lasting lattice shifts do not play an essential role in the presence of superconductivity,” Hill said. “We can now narrow our focus on the stripes to further pin down the underlying mechanism and potentially engineer superior materials.”

    Andrea Cavalleri, director of the Max Planck Institute, said, “Light-induced superconductivity was only recently discovered, and we’re already seeing fascinating implications for understanding it and going to higher temperatures. In fact, we have observed the signature of light-induced superconductivity in materials all the way up to 300 Kelvin (80 degrees Fahrenheit) – that’s really a significant breakthrough that warrants much deeper investigations.”

    Other collaborators on this research include the University of Groningen, the University of Oxford, Diamond Light Source, the Lawrence Berkeley National Laboratory, Stanford University, the European XFEL, the University of Hamburg and the Center for Free-Electron Laser Science.

    The research conducted at the Soft X-ray Materials Science (SXR) experimental station at SLAC’s LCLS – a DOE Office of Science user facility – was funded by Stanford University, Lawrence Berkeley National Laboratory, the University of Hamburg and the Center for Free-Electron Laser Science (CFEL). Work performed at Brookhaven Lab was supported by the DOE’s Office of Science.

    See the full article here.

    SLAC Campus
    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
    i1


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  • richardmitnick 4:20 pm on April 16, 2014 Permalink | Reply
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    From M.I.T.: “Engineers design ‘living materials’” 

    March 23, 2014
    Anne Trafton, MIT News Office

    Hybrid materials combine bacterial cells with nonliving elements that can conduct electricity or emit light.

    Inspired by natural materials such as bone — a matrix of minerals and other substances, including living cells — MIT engineers have coaxed bacterial cells to produce biofilms that can incorporate nonliving materials, such as gold nanoparticles and quantum dots.

    cell
    An artist’s rendering of a bacterial cell engineered to produce amyloid nanofibers that incorporate particles such as quantum dots (red and green spheres) or gold nanoparticles.Image: Yan Liang

    These “living materials” combine the advantages of live cells, which respond to their environment, produce complex biological molecules, and span multiple length scales, with the benefits of nonliving materials, which add functions such as conducting electricity or emitting light.

    The new materials represent a simple demonstration of the power of this approach, which could one day be used to design more complex devices such as solar cells, self-healing materials, or diagnostic sensors, says Timothy Lu, an assistant professor of electrical engineering and biological engineering. Lu is the senior author of a paper describing the living functional materials in the March 23 issue of Nature Materials.

    “Our idea is to put the living and the nonliving worlds together to make hybrid materials that have living cells in them and are functional,” Lu says. “It’s an interesting way of thinking about materials synthesis, which is very different from what people do now, which is usually a top-down approach.”

    The paper’s lead author is Allen Chen, an MIT-Harvard MD-PhD student. Other authors are postdocs Zhengtao Deng, Amanda Billings, Urartu Seker, and Bijan Zakeri; recent MIT graduate Michelle Lu; and graduate student Robert Citorik.

    Self-assembling materials

    Lu and his colleagues chose to work with the bacterium E. coli because it naturally produces biofilms that contain so-called “curli fibers” — amyloid proteins that help E. coli attach to surfaces. Each curli fiber is made from a repeating chain of identical protein subunits called CsgA, which can be modified by adding protein fragments called peptides. These peptides can capture nonliving materials such as gold nanoparticles, incorporating them into the biofilms.

    By programming cells to produce different types of curli fibers under certain conditions, the researchers were able to control the biofilms’ properties and create gold nanowires, conducting biofilms, and films studded with quantum dots, or tiny crystals that exhibit quantum mechanical properties. They also engineered the cells so they could communicate with each other and change the composition of the biofilm over time.

    First, the MIT team disabled the bacterial cells’ natural ability to produce CsgA, then replaced it with an engineered genetic circuit that produces CsgA but only under certain conditions — specifically, when a molecule called AHL is present. This puts control of curli fiber production in the hands of the researchers, who can adjust the amount of AHL in the cells’ environment. When AHL is present, the cells secrete CsgA, which forms curli fibers that coalesce into a biofilm, coating the surface where the bacteria are growing.

    The researchers then engineered E. coli cells to produce CsgA tagged with peptides composed of clusters of the amino acid histidine, but only when a molecule called aTc is present. The two types of engineered cells can be grown together in a colony, allowing researchers to control the material composition of the biofilm by varying the amounts of AHL and aTc in the environment. If both are present, the film will contain a mix of tagged and untagged fibers. If gold nanoparticles are added to the environment, the histidine tags will grab onto them, creating rows of gold nanowires, and a network that conducts electricity.

    ‘Cells that talk to each other’

    The researchers also demonstrated that the cells can coordinate with each other to control the composition of the biofilm. They designed cells that produce untagged CsgA and also AHL, which then stimulates other cells to start producing histidine-tagged CsgA.

    “It’s a really simple system but what happens over time is you get curli that’s increasingly labeled by gold particles. It shows that indeed you can make cells that talk to each other and they can change the composition of the material over time,” Lu says. “Ultimately, we hope to emulate how natural systems, like bone, form. No one tells bone what to do, but it generates a material in response to environmental signals.”

    To add quantum dots to the curli fibers, the researchers engineered cells that produce curli fibers along with a different peptide tag, called SpyTag, which binds to quantum dots that are coated with SpyCatcher, a protein that is SpyTag’s partner. These cells can be grown along with the bacteria that produce histidine-tagged fibers, resulting in a material that contains both quantum dots and gold nanoparticles.

    These hybrid materials could be worth exploring for use in energy applications such as batteries and solar cells, Lu says. The researchers are also interested in coating the biofilms with enzymes that catalyze the breakdown of cellulose, which could be useful for converting agricultural waste to biofuels. Other potential applications include diagnostic devices and scaffolds for tissue engineering.

    “I think this is really fantastic work that represents a great integration of synthetic biology and materials engineering,” says Lingchong You, an associate professor of biomedical engineering at Duke University who was not part of the research team.

    The research was funded by the Office of Naval Research, the Army Research Office, the National Science Foundation, the Hertz Foundation, the Department of Defense, the National Institutes of Health, and the Presidential Early Career Award for Scientists and Engineers.

    See the full article here.


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  • richardmitnick 4:03 pm on April 16, 2014 Permalink | Reply
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    From M.I.T.: “Tiny particles may pose big risk” 

    April 8, 2014
    Anne Trafton | MIT News Office

    Thousands of consumer products — including cosmetics, sunscreens, and clothing — contain nanoparticles added by manufacturers to improve texture, kill microbes, or enhance shelf life, among other purposes. However, several studies have shown that some of these engineered nanoparticles can be toxic to cells.

    cells
    Illustration: Christine Daniloff/MIT

    A new study from MIT and the Harvard School of Public Health (HSPH) suggests that certain nanoparticles can also harm DNA. This research was led by Bevin Engelward, a professor of biological engineering at MIT, and associate professor Philip Demokritou, director of HSPH’s Center for Nanotechnology and Nanotoxicology.

    The researchers found that zinc oxide nanoparticles, often used in sunscreen to block ultraviolet rays, significantly damage DNA. Nanoscale silver, which has been added to toys, toothpaste, clothing, and other products for its antimicrobial properties, also produces substantial DNA damage, they found.

    The findings, published in a recent issue of the journal ACS Nano, relied on a high-speed screening technology to analyze DNA damage. This approach makes it possible to study nanoparticles’ potential hazards at a much faster rate and larger scale than previously possible.

    The Food and Drug Administration does not require manufacturers to test nanoscale additives for a given material if the bulk material has already been shown to be safe. However, there is evidence that the nanoparticle form of some of these materials may be unsafe: Due to their immensely small size, these materials may exhibit different physical, chemical, and biological properties, and penetrate cells more easily.

    “The problem is that if a nanoparticle is made out of something that’s deemed a safe material, it’s typically considered safe. There are people out there who are concerned, but it’s a tough battle because once these things go into production, it’s very hard to undo,” Engelward says.

    The researchers focused on five types of engineered nanoparticles — silver, zinc oxide, iron oxide, cerium oxide, and silicon dioxide (also known as amorphous silica) — that are used industrially. Some of these nanomaterials can produce free radicals called reactive oxygen species, which can alter DNA. Once these particles get into the body, they may accumulate in tissues, causing more damage.

    “It’s essential to monitor and evaluate the toxicity or the hazards that these materials may possess. There are so many variations of these materials, in different sizes and shapes, and they’re being incorporated into so many products,” says Christa Watson, a postdoc at HSPH and the paper’s lead author. “This toxicological screening platform gives us a standardized method to assess the engineered nanomaterials that are being developed and used at present.”

    The researchers hope that this screening technology could also be used to help design safer forms of nanoparticles; they are already working with partners in industry to engineer safer UV-blocking nanoparticles. Demokritou’s lab recently showed that coating zinc oxide particles with a nanothin layer of amorphous silica can reduce the particles’ ability to damage DNA.

    Rapid analysis

    Until now, most studies of nanoparticle toxicity have focused on cell survival after exposure. Very few have examined genotoxicity, or the ability to damage DNA — a phenomenon that may not necessarily kill a cell, but one that can lead to cancerous mutations if the damage is not repaired.

    A common way to study DNA damage in cells is the so-called “comet assay,” named for the comet-shaped smear that damaged DNA forms during the test. The procedure is based on gel electrophoresis, a test in which an electric field is applied to DNA placed in a matrix, forcing the DNA to move across the gel. During electrophoresis, damaged DNA travels farther than undamaged DNA, producing a comet-tail shape.

    Measuring how far the DNA can travel reveals how much DNA damage has occurred. This procedure is very sensitive, but also very tedious.

    In 2010, Engelward and MIT professor Sangeeta Bhatia developed a much more rapid version of the comet assay, known as the CometChip. Using microfabrication technology, single cells can be trapped in tiny microwells within the matrix. This approach makes it possible to process as many as 1,000 samples in the time that it used to take to process just 30 samples — allowing researchers to test dozens of experimental conditions at a time, which can be analyzed using imaging software.

    Wolfgang Kreyling, an epidemiologist at the German Research Center for Environmental Health who was not involved in the study, says this technology should help toxicologists catch up to the rapid rate of deployment of engineered nanoparticles (ENPs).

    “High-throughput screening platforms are desperately needed,” Kreyling says. “The proposed approach will be not only an important tool for nanotoxicologists developing high-throughput screening strategies for the assessment of possible adverse health effects associated with ENPs, but also of great importance for material scientists working on the development of novel ENPs and safer-by-design approaches.”

    Using the CometChip, the MIT and HSPH researchers tested the nanoparticles’ effects on two types of cells that are commonly used for toxicity studies: a type of human blood cells called lymphoblastoids, and an immortalized line of Chinese hamster ovary cells.

    Zinc oxide and silver produced the greatest DNA damage in both cell lines. At a concentration of 10 micrograms per milliliter — a dose not high enough to kill all of the cells — these generated a large number of single-stranded DNA breaks.

    Silicon dioxide, which is commonly added during food and drug production, generated very low levels of DNA damage. Iron oxide and cerium oxide also showed low genotoxicity.

    How much is too much?

    More studies are needed to determine how much exposure to metal oxide nanoparticles could be unsafe for humans, the researchers say.

    “The biggest challenge we have as people concerned with exposure biology is deciding when is something dangerous and when is it not, based on the dose level. At low levels, probably these things are fine,” Engelward says. “The question is: At what level does it become problematic, and how long will it take for us to notice?”

    One of the areas of greatest concern is occupational exposure to nanoparticles, the researchers say. Children and fetuses are also potentially at greater risk because their cells divide more often, making them more vulnerable to DNA damage.

    The most common routes that engineered nanoparticles follow into the body are through the skin, lungs, and stomach, so the researchers are now investigating nanoparticle genotoxicity on those cell types. They are also studying the effects of other engineered nanoparticles, including metal oxides used in printer and photocopier toner, which can become airborne and enter the lungs.

    The research was funded by MIT’s Center for Environmental Health Sciences, the National Institute of Environmental Health Sciences, the National Science Foundation, and the National Institutes of Health. Other authors of the study are MIT graduate student Jing Ge, Harvard graduate student Joel Cohen, and Harvard postdoc Georgios Pyrgiotakis.

    See the full article here.


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  • richardmitnick 12:54 pm on April 16, 2014 Permalink | Reply
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    From M.I.T.: “Excitons observed in action for the first time” 

    April 16, 2014
    David L. Chandler | MIT News Office

    Technique developed at MIT reveals the motion of energy-carrying quasiparticles in solid material.

    A quasiparticle called an exciton — responsible for the transfer of energy within devices such as solar cells, LEDs, and semiconductor circuits — has been understood theoretically for decades. But exciton movement within materials has never been directly observed.

    Now scientists at MIT and the City University of New York have achieved that feat, imaging excitons’ motions directly. This could enable research leading to significant advances in electronics, they say, as well as a better understanding of natural energy-transfer processes, such as photosynthesis.

    graph
    Diagram of an exciton within a tetracene crystal, used in these experiments, shows the line across which data was collected. That data, plotted below as a function of both position (horizontal axis) and time (vertical axis) provides the most detailed information ever obtained on how excitons move through the material. Illustration courtesy of the researchers

    The research is described this week in the journal Nature Communications, in a paper co-authored by MIT postdocs Gleb Akselrod and Parag Deotare, professors Vladimir Bulovic and Marc Baldo, and four others.

    “This is the first direct observation of exciton diffusion processes,” Bulovic says, “showing that crystal structure can dramatically affect the diffusion process.”

    “Excitons are at the heart of devices that are relevant to modern technology,” Akselrod explains: The particles determine how energy moves at the nanoscale. “The efficiency of devices such as photovoltaics and LEDs depends on how well excitons move within the material,” he adds.

    An exciton, which travels through matter as though it were a particle, pairs an electron, which carries a negative charge, with a place where an electron has been removed, known as a hole. Overall, it has a neutral charge, but it can carry energy. For example, in a solar cell, an incoming photon may strike an electron, kicking it to a higher energy level. That higher energy is propagated through the material as an exciton: The particles themselves don’t move, but the boosted energy gets passed along from one to another.

    While it was previously possible to determine how fast, on average, excitons could move between two points, “we really didn’t have any information about how they got there,” Akselrod says. Such information is essential to understanding which aspects of a material’s structure — for example, the degree of molecular order or disorder — might facilitate or slow that motion.

    “People always assumed certain behavior of the excitons,” Deotare says. Now, using this new technique — which combines optical microscopy with the use of particular organic compounds that make the energy of excitons visible — “we can directly say what kind of behavior the excitons were moving around with.” This advance provided the researchers with the ability to observe which of two possible kinds of “hopping” motion was actually taking place.

    “This allows us to see new things,” Deotare says, making it possible to demonstrate that the nanoscale structure of a material determines how quickly excitons get trapped as they move through it.

    For some applications, such as LEDs, Deotare says, it is desirable to maximize this trapping, so that energy is not lost to leakage; for other uses, such as solar cells, it is essential to minimize the trapping. The new technique should allow researchers to determine which factors are most important in increasing or decreasing this trapping.

    “We showed how energy flow is impeded by disorder, which is the defining characteristic of most materials for low-cost solar cells and LEDs,” Baldo says.

    While these experiments were carried out using a material called tetracene — a well-studied archetype of a molecular crystal — the researchers say that the method should be applicable to almost any crystalline or thin-film material. They expect it to be widely adopted by researchers in academia and industry.

    “It’s a very simple technique, once people learn about it,” Akselrod says, “and the equipment required is not that expensive.”

    Exciton diffusion is also a basic mechanism underlying photosynthesis: Plants absorb energy from photons, and this energy is transferred by excitons to areas where it can be stored in chemical form for later use in supporting the plant’s metabolism. The new method might provide an additional tool for studying some aspects of this process, the team says.

    David Lidzey, a professor of physics and astronomy at the University of Sheffield who was not involved in this work, calls the research “a really impressive demonstration of a direct measurement of the diffusion of triplet excitons and their eventual trapping.” He adds, “Exciton diffusion and transport are important processes in solar-cell devices, so understanding what limits these may well help the design of better materials, or the development of better ways to process materials so that energy losses during exciton migration are limited.”

    The work was supported by the U.S. Department of Energy and by the National Science Foundation, and used facilities of the Eni-MIT Solar Frontiers Center.

    See the full article here.


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  • richardmitnick 6:41 pm on April 9, 2014 Permalink | Reply
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    From M.I.T.: “New ‘switch’ could power quantum computing” 

    April 9, 2014
    Peter Dizikes | MIT News Office

    A light lattice that traps atoms may help scientists build networks of quantum information transmitters.

    Using a laser to place individual rubidium atoms near the surface of a lattice of light, scientists at MIT and Harvard University have developed a new method for connecting particles — one that could help in the development of powerful quantum computing systems.

    qc

    The new technique, described in a paper published today in the journal Nature, allows researchers to couple a lone atom of rubidium, a metal, with a single photon, or light particle. This allows both the atom and photon to switch the quantum state of the other particle, providing a mechanism through which quantum-level computing operations could take place.

    Moreover, the scientists believe their technique will allow them to increase the number of useful interactions occurring within a small space, thus scaling up the amount of quantum computing processing available.

    “This is a major advance of this system,” says Vladan Vuletić, a professor in MIT’s Department of Physics and Research Laboratory for Electronics (RLE), and a co-author of the paper. “We have demonstrated basically an atom can switch the phase of a photon. And the photon can switch the phase of an atom.”

    That is, photons can have two polarization states, and interaction with the atom can change the photon from one state to another; conversely, interaction with the photon can change the atom’s phase, which is equivalent to changing the quantum state of the atom from its “ground” state to its “excited” state. In this way the atom-photon coupling can serve as a quantum switch to transmit information — the equivalent of a transistor in a classical computing system. And by placing many atoms within the same field of light, the researchers may be able to build networks that can process quantum information more effectively.

    “You can now imagine having several atoms placed there, to make several of these devices — which are only a few hundred nanometers thick, 1,000 times thinner than a human hair — and couple them together to make them exchange information,” Vuletić adds.

    Using a photonic cavity

    Quantum computing could enable the rapid performance of calculations by taking advantage of the distinctive quantum-level properties of particles. Some particles can be in a condition of superposition, appearing to exist in two places at the same time. Particles in superposition, known as qubits, could thus contain more information than particles at classical scales, and allow for faster computing.

    However, researchers are in the early stages of determining which materials best allow for quantum-scale computing. The MIT and Harvard researchers have been examining photons as a candidate material, since photons rarely interact with other particles. For this reason, an optical quantum computing system, using photons, could be harder to knock out of its delicate alignment. But since photons rarely interact with other bits of matter, they are difficult to manipulate in the first place.

    In this case, the researchers used a laser to place a rubidium atom very close to the surface of a photonic crystal cavity, a structure of light. The atoms were placed no more than 100 or 200 nanometers — less than a wavelength of light — from the edge of the cavity. At such small distances, there is a strong attractive force between the atom and the surface of the light field, which the researchers used to trap the atom in place.

    Other methods of producing a similar outcome have been considered before — such as, in effect, dropping atoms into the light and then finding and trapping them. But the researchers found that they had greater control over the particles this way.

    “In some sense, it was a big surprise how simple this solution was compared to the different techniques you might envision of getting the atoms there,” Vuletić says.

    The result is what he calls a “hybrid quantum system,” where individual atoms are coupled to microscopic fabricated devices, and in which atoms and photons can be controlled in productive ways. The researchers also found that the new device serves as a kind of router separating photons from each other.

    “The idea is to combine different things that have different strengths and weaknesses in such a way to generate something new,” Vuletić says, adding: “This is an advance in technology. Of course, whether this will be the technology remains to be seen.”

    ‘Still amazing’ to hold onto one atom

    The paper, Nanophotonic quantum phase switch with a single atom, is co-authored by Vuletić; Tobias Tiecke, a postdoc affiliated with both RLE and Harvard; Harvard professor of physics Mikhail Lukin; Harvard postdoc Nathalie de Leon; and Harvard graduate students Jeff Thompson and Bo Liu.

    The collaboration between the MIT and Harvard researchers is one of two advances in the field described in the current issue of Nature. Researchers at the Max Planck Institute of Quantum Optics in Germany have concurrently developed a new method of producing atom-photon interactions using mirrors, forming quantum gates, which change the direction of motion or polarization of photons.

    “The Harvard/MIT experiment is a masterpiece of quantum nonlinear optics, demonstrating impressively the preponderance of single atoms over many atoms for the control of quantum light fields,” says Gerhard Rempe, a professor at the Max Planck Institute of Quantum Optics who helped lead the German team’s new research, and who has read the paper by the U.S.-based team. “The coherent manipulation of an atom coupled to a photonic crystal resonator constitutes a breakthrough and complements our own work … with an atom in a dielectric mirror resonator.”

    Rempe adds that he thinks both techniques will be regarded as notable “achievements on our way toward a robust quantum technology with stationary atoms and flying photons.”

    If the research techniques seem a bit futuristic, Vuletić says that even as an experienced researcher in the field, he remains slightly awed by the tools at his disposal.

    “For me what is still amazing, after working in this for 20 years,” Vuletić reflects, “is that we can hold onto a single atom, we can see it, we can move it around, we can prepare quantum superpositions of atoms, we can detect them one by one.”

    Funding for the research was provided in part by the National Science Foundation, the MIT-Harvard Center for Ultracold Atoms, the Natural Sciences and Engineering Research Council of Canada, the Air Force Office of Scientific Research, and the Packard Foundation.

    See the full article here.


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  • richardmitnick 7:09 pm on April 3, 2014 Permalink | Reply
    Tags: Applied Research & Technology, , ,   

    From ISOLDE at CERN: “ISOLDE sheds light on dying stars” 

    CERN New Masthead

    CERN ISOLDE New
    ISOLDE

    3 Apr 2014
    Dan Noyes

    What happens inside a dying star? A recent experiment at CERN’s REX accelerator offers clues that could help astrophysicists to recalculate the ages of some of the largest explosions in the universe.

    CERN REX post accelerator
    REX post-accelerator

    Core-collapse supernovae are spectacular stellar explosions that can briefly outshine an entire galaxy. They occur when massive stars – stars that are more than eight times as massive as our sun – collapse upon themselves. Huge amounts of matter and energy are ejected into space during these events. The cores of such stars then rapidly collapse and go on to form a neutron star or a black hole.

    TII
    Date 6 January 2014, 16:15:00
    Source http://www.eso.org/public/images/eso1401a/
    Author ALMA (ESO/NAOJ/NRAO)/A. Angelich. Visible light image: the NASA/ESA Hubble Space Telescope. X-Ray image: The NASA Chandra X-Ray Observatory
    The expanding remnant of SN 1987A, a Type II-P supernova in the Large Magellanic Cloud. NASA image.

    The sequence of events in the first few seconds of a massive star collapsing is well understood. Elements in and around the core are broken down by high-energy photons into free protons, neutrons and alpha particles. Bursts of neutrinos follow. But modelling what happens next remains a challenge for astrophysicists.

    Optical telescopes offer little detail on the explosion mechanism. Gamma ray observatories, by contrast, offer tantalising clues, notably in the gamma rays produced by titanium-44 , an isotope of titanium created naturally in supernovae, which can be detected as it is ejected from the dying stars. The amount of the isotope ejected from the supernovae can tell astrophysicists about how it exploded.

    compton
    The Compton Gamma Ray Observatory (CGRO) was a space observatory detecting light from 20 KeV to 30 GeV in Earth orbit from 1991 to 2000. It featured four main telescopes in one spacecraft covering x-rays and gamma-rays, including various specialized sub-instruments and detectors. Following 14 years of effort, the observatory was launched from Space Shuttle Atlantis during STS-37 on 5 April 1991, and operated until its deorbit on 4 June 2000. CGRO was part of NASA’s Great Observatories series, along with the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope. It was the second of the NASA “Great Observatories” to be launched to space, following the Hubble Space Telescope. CGRO was an international collaboration and additional contributions came from the European Space Agency and various Universities, as well as the U.S. Naval Research Laboratory.

    Two of the best of the ground based Optical observatories
    Keck Observatory
    Keck

    ESO VLT
    ESO VLT

    By understanding the behavior of titanium-44 at energies similar to those at the core a collapsing star, researchers at CERN hope to offer some insight into the mechanisms of core-collapse supernovae.

    In a paper published in March, they reported on an experiment that used titanium-44 harvested from waste accelerator parts at the Paul Scherrer Institute (PSI) in Switzerland.

    At the ISOLDE facility at CERN, the REX team accelerated a beam of titanium-44 into a chamber of helium gas and observed the resulting collisions between the isotope and the helium atoms. The measurements – which mimic reactions occurring in the silicon-rich region just above the exploding core of a supernova – indicated that more of the isotope is ejected from core collapse supernovae than has previously been thought.

    Astrophysicists can use the new data to recalculate the ages of supernovae.

    See the full article here.

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries


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  • richardmitnick 2:09 pm on April 2, 2014 Permalink | Reply
    Tags: , Applied Research & Technology, ,   

    From Ames Lab: “Ames Lab researchers show polymer-coated nanocubes form complex structures” 

    AmesLabII
    Ames Laboratory

    March 21, 2014
    Alex Travesset, Materials Sciences and Engineering, 515-294-7191
    Kerry Gibson, Public Affairs, 515-294-1405

    Nanoparticles assembled in new ways hold the promise of a wave of new high-tech materials that could offer high strength, enhanced magnetic properties, light reflectivity or absorption, use as catalysts and much more. Scientists at the U.S. Department of Energy’s Ames Laboratory have developed a theoretical model to explore the effect of polymer coatings, including DNA, for self-assembly of nanocubes into so-called superlattices.

    What makes the work by Ames Laboratory physicist Alex Travesset and graduate assistant Chris Knorowski significant is that they have characterized how these nanocubes form crystalline and liquid crystalline structures. Their work was published in the Journal of the American Chemical Society and mentioned in an Editor’s Choice article in the January 31 issue of Science.

    ns
    Using numerical simulations, Ames Lab researchers found that “hairy” (f-star) or DNA grafted on nanocubes provided a general framework to direct the self-assembly into phases with crystalline, liquid crystalline, rotator, or noncrystalline phases with both long-range positional and orientational order.

    “Spherical nanoparticles, are isotropic so they can align in any direction,” Travesset explains. “Nanocubes are different. They are anisotropic, so they display orientational order. They will only stack together if the faces orient in certain ways.”

    “From a more applied point of view, cubes can pack together more efficiently than spheres; in configurations that do not leave any gaps,” he adds, “so they are of interest in areas such as catalysis where you want to maximize contact area.”

    To date scientists had only considered theoretical systems that consist of hard nanocubes. However, by coating nanocubes with strands of polymer, the structures that form are bound together so that they can be extracted and studied in laboratory environments. The nanocubes can be metallic, gold or silver, or made of semiconducting material.

    Travesset’s theoretical model uses both a general polymer and DNA. While both resulted in assembly of nanocubes into complex crystalline structures, the DNA system allows control of self-assembly by hybridization of complementary base pairs.

    “With DNA, you can encode information about which cubes are going to assemble with which other cubes,” Travesset said. “It gives you a more precise way to target relevant self-assembled structures.”

    “Because the system can be polymerized in water, the assembled structure can be extracted and used in dry environments,” Travesset said. “And these complex structures provide much more opportunity for applications and systems than simple hard cubes allow. We hope these systems will lead to further experimentation.”

    The research is funded by the DOE’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

    See the full article here.

    Ames Laboratory is a government-owned, contractor-operated research facility of the U.S. Department of Energy that is run by Iowa State University.

    For more than 60 years, the Ames Laboratory has sought solutions to energy-related problems through the exploration of chemical, engineering, materials, mathematical and physical sciences. Established in the 1940s with the successful development of the most efficient process to produce high-quality uranium metal for atomic energy, the Lab now pursues a broad range of scientific priorities.

    Ames Laboratory shares a close working relationship with Iowa State University’s Institute for Physical Research and Technology, or IPRT, a network of scientific research centers at Iowa State University, Ames, Iowa.

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  • richardmitnick 9:08 pm on March 31, 2014 Permalink | Reply
    Tags: Applied Research & Technology, , , , , ,   

    From Argonne Lab via PPPL: “Plasma Turbulence Simulations Reveal Promising Insight for Fusion Energy” 

    March 31, 2014
    By Argonne National Laboratory

    With the potential to provide clean, safe, and abundant energy, nuclear fusion has been called the “holy grail” of energy production. But harnessing energy from fusion, the process that powers the sun, has proven to be an extremely difficult challenge.

    turb
    Simulation of microturbulence in a tokamak fusion device. (Credit: Chad Jones and Kwan-Liu Ma, University of California, Davis; Stephane Ethier, Princeton Plasma Physics Laboratory)

    Scientists have been working to accomplish efficient, self-sustaining fusion reactions for decades, and significant research and development efforts continue in several countries today.

    For one such effort, researchers from the Princeton Plasma Physics Laboratory (PPPL), a DOE collaborative national center for fusion and plasma research in New Jersey, are running large-scale simulations at the Argonne Leadership Computing Facility (ALCF) to shed light on the complex physics of fusion energy. Their most recent simulations on Mira, the ALCF’s 10-petaflops Blue Gene/Q supercomputer, revealed that turbulent losses in the plasma are not as large as previously estimated.

    MIRA

    Good news

    This is good news for the fusion research community as plasma turbulence presents a major obstacle to attaining an efficient fusion reactor in which light atomic nuclei fuse together and produce energy. The balance between fusion energy production and the heat losses associated with plasma turbulence can ultimately determine the size and cost of an actual reactor.

    “Understanding and possibly controlling the underlying physical processes is key to achieving the efficiency needed to ensure the practicality of future fusion reactors,” said William Tang, PPPL principal research physicist and project lead.

    Tang’s work at the ALCF is focused on advancing the development of magnetically confined fusion energy systems, especially ITER, a multi-billion dollar international burning plasma experiment supported by seven governments including the United States.

    Currently under construction in France, ITER will be the world’s largest tokamak system, a device that uses strong magnetic fields to contain the burning plasma in a doughnut-shaped vacuum vessel. In tokamaks, unavoidable variations in the plasma’s ion temperature drive microturbulence, which can significantly increase the transport rate of heat, particles, and momentum across the confining magnetic field.

    “Simulating tokamaks of ITER’s physical size could not be done with sufficient accuracy until supercomputers as powerful as Mira became available,” said Tang.

    To prepare for the architecture and scale of Mira, Tim Williams of the ALCF worked with Tang and colleagues to benchmark and optimize their Gyrokinetic Toroidal Code – Princeton (GTC-P) on the ALCF’s new supercomputer. This allowed the research team to perform the first simulations of multiscale tokamak plasmas with very high phase-space resolution and long temporal duration. They are simulating a sequence of tokamak sizes up to and beyond the scale of ITER to validate the turbulent losses for large-scale fusion energy systems.

    Decades of experiments

    Decades of experimental measurements and theoretical estimates have shown turbulent losses to increase as the size of the experiment increases; this phenomenon occurs in the so-called Bohm regime. However, when tokamaks reach a certain size, it has been predicted that there will be a turnover point into a Gyro-Bohm regime, where the losses level off and become independent of size. For ITER and other future burning plasma experiments, it is important that the systems operate in this Gyro-Bohm regime.

    The recent simulations on Mira led the PPPL researchers to discover that the magnitude of turbulent losses in the Gyro-Bohm regime is up to 50% lower than indicated by earlier simulations carried out at much lower resolution and significantly shorter duration. The team also found that transition from the Bohm regime to the Gyro-Bohm regime is much more gradual as the plasma size increases. With a clearer picture of the shape of the transition curve, scientists can better understand the basic plasma physics involved in this phenomenon.

    “Determining how turbulent transport and associated confinement characteristics will scale to the much larger ITER-scale plasmas is of great interest to the fusion research community,” said Tang. “The results will help accelerate progress in worldwide efforts to harness the power of nuclear fusion as an alternative to fossil fuels.”

    This project has received computing time at the ALCF through DOE’s Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. The effort was also awarded pre-production time on Mira through the ALCF’s Early Science Program, which allowed researchers to pursue science goals while preparing their GTC-P code for Mira.

    See the full article here.

    Princeton Plasma Physics Laboratory is a U.S. Department of Energy national laboratory managed by Princeton University.


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  • richardmitnick 1:11 pm on March 31, 2014 Permalink | Reply
    Tags: , Applied Research & Technology, ,   

    From Ames Lab: “Ultra-fast laser spectroscopy lights way to understanding new materials” 

    AmesLabII
    Ames Laboratory

    Feb. 28, 2014
    Jigang Wang, Material Sciences and Engineering, 515-294-5630
    Breehan Gerleman Lucchesi, Public Affairs, 515-294-9750

    Scientists at the U.S. Department of Energy’s Ames Laboratory are revealing the mysteries of new materials using ultra-fast laser spectroscopy, similar to high-speed photography where many quick images reveal subtle movements and changes inside the materials. Seeing these dynamics is one emerging strategy to better understanding how new materials work, so that we can use them to enable new energy technologies.

    Physicist Jigang Wang and his colleagues recently used ultra-fast laser spectroscopy to examine and explain the mysterious electronic properties of iron-based superconductors. Results appeared in Nature Communications this month.

    Superconductors are materials that, when cooled below a certain temperature, display zero electrical resistance, a property that could someday make possible lossless electrical distribution. Superconductors start in a “normal” often magnetic state and then transition to a superconducting state when they are cooled to a certain temperature.

    What is still a mystery is what goes on in materials as they transform from normal to superconducting. And this “messy middle” area of superconducting materials’ behavior holds richer information about the why and how of superconductivity than do the stable areas.

    fast
    Ames Laboratory scientists use ultra-fast laser spectroscopy to “see” tiny actions in real time in
    materials. Scientists apply a pulse laser to a sample to excite the material. Some of the laser light
    is absorbed by the material, but the light that passes through or reflected from the material can be
    used to take super-fast “snapshots” of what is going on in the material following the laser pulse.

    “The stable states of materials aren’t quite as interesting as the crossover region when comes to understanding materials’ mechanisms because everything is settled and there’s not a lot of action. But, in this crossover region to superconductivity, we can study the dynamics, see what goes where and when, and this information will tell us a lot about the interplay between superconductivity and magnetism,” said Wang, who is also an associate professor of physics and astronomy at Iowa State University.

    But the challenges is that in the crossover region, all the different sets of materials properties that scientists examine, like its magnetic order and electronic order, are all coupled. In other words, when there’s a change to one set of properties, it changes all the others. So, it’s really difficult to trace what individual changes and properties are dominant.

    The complexity of this coupled state has been studied by groundbreaking work by research groups at Ames Laboratory over the past five years. Paul Canfield, an Ames Laboratory scientist and expert in designing and developing iron-based superconductor materials, created and characterized a very high quality single crystal used in this investigation. These high-quality single crystals had been exceptionally well characterized by other techniques and were essentially “waiting for their close up” under Wang’s ultra-fast spot-light.

    Wang and the team used ultra-fast laser spectroscopy to “see” the tiny actions in materials. In ultra-fast laser spectroscopy, scientists apply a pulsed laser to a materials sample to excite particles within the sample. Some of the laser light is absorbed by the material, but the light that passes through the material can be used to take super-fast “snapshots” of what is going on in the material following the laser pulse and then replayed afterward like a stop-action movie.

    The technique is especially well suited to understanding the crossover region of iron-arsenide based superconductors materials because the laser excitation alters the material so that different properties of the material are distinguishable from each other in time, even the most subtle evolutions in the materials’ properties.

    “Ultra-fast laser spectroscopy is a new experimental tool to study dynamic, emergent behavior in complex materials such as these iron-based superconductors,” said Wang. “Specifically, we answered the pressing question of whether an electronically-driven nematic order exists as an independent phase in iron-based superconductors, as these materials go from a magnetic normal state to superconducting state. The answer is yes. This is important to our overall understanding of how superconductors emerge in this type of materials.”

    Aaron Patz and Tianqi Li collaborated on the laser spectroscopy work. Sheng Ran, Sergey L. Bud’ko and Paul Canfield collaborated on sample development at Ames Laboratory and Iowa State University. Rafael M. Fernandes at the University of Minnesota, Joerg Schmalian, formerly of Ames Laboratory and now at Karlsruhe Institute of Technology and Ilias E. Perakis at University of Crete, Greece collaborated on the simulation work.

    Wang, Patz, Li, Ran, Bud’ko and Canfield’s work at Ames Laboratory was supported by the U.S. Department of Energy’s Office of Science, (sample preparation and characterization). Wang’s work on pnictide superconductors is supported by Ames Laboratory’s Laboratory Directed Research and Development (LDRD) funding (femtosecond laser spectroscopy).

    DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

    See the full article here.

    Ames Laboratory is a government-owned, contractor-operated research facility of the U.S. Department of Energy that is run by Iowa State University.

    For more than 60 years, the Ames Laboratory has sought solutions to energy-related problems through the exploration of chemical, engineering, materials, mathematical and physical sciences. Established in the 1940s with the successful development of the most efficient process to produce high-quality uranium metal for atomic energy, the Lab now pursues a broad range of scientific priorities.

    Ames Laboratory shares a close working relationship with Iowa State University’s Institute for Physical Research and Technology, or IPRT, a network of scientific research centers at Iowa State University, Ames, Iowa.

    DOE Banner


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