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  • richardmitnick 12:59 pm on September 9, 2014 Permalink | Reply
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    From SLAC: “Buckyballs and Diamondoids Join Forces in Tiny Electronic Gadget” 


    SLAC Lab

    September 9, 2014
    Press Office Contact: Andrew Gordon, agordon@slac.stanford.edu, (650) 926-2282

    Scientists Craft Two Exotic Forms of Carbon into a Molecule for Steering Electron Flow

    Scientists have married two unconventional forms of carbon – one shaped like a soccer ball, the other a tiny diamond – to make a molecule that conducts electricity in only one direction. This tiny electronic component, known as a rectifier, could play a key role in shrinking chip components down to the size of molecules to enable faster, more powerful devices.

    dd
    An international team led by researchers at SLAC National Accelerator Laboratory and Stanford University joined two offbeat carbon molecules – diamondoids, the square cages at left, and buckyballs, the soccer-ball shapes at right – to create “buckydiamondoids,” center. These hybrid molecules function as rectifiers, conducting electrons in only one direction, and could help pave the way to molecular electronic devices. (Manoharan Lab/Stanford University)

    “We wanted to see what new, emergent properties might come out when you put these two ingredients together to create a ‘buckydiamondoid,’” said Hari Manoharan of the Stanford Institute for Materials and Energy Sciences (SIMES) at the Department of Energy’s SLAC National Accelerator Laboratory. “What we got was a basically a one-way valve for conducting electricity – clearly more than the sum of its parts.”

    The research team, which included scientists from Stanford University, Belgium, Germany and Ukraine, reported its results September 9, 2014, in Nature Communications.

    Two Offbeat Carbon Characters Meet Up

    Many electronic circuits have three basic components: a material that conducts electrons; rectifiers, which commonly take the form of diodes, to steer that flow in a single direction; and transistors to switch the flow on and off. Scientists combined two offbeat ingredients – buckyballs and diamondoids – to create the new diode-like component.

    Buckyballs – short for buckminsterfullerenes – are hollow carbon spheres whose 1985 discovery earned three scientists a Nobel Prize in chemistry. Diamondoids are tiny carbon cages bonded together as they are in diamonds, but weighing less than a billionth of a billionth of a carat. Both are subjects of a lot of research aimed at understanding their properties and finding ways to use them.

    In 2007, a team led by researchers from SLAC and Stanford discovered that a single layer of diamondoids on a metal surface can efficiently emit a beam of electrons. Manoharan and his colleagues wondered: What would happen if they paired an electron-emitting diamondoid with another molecule that likes to grab electrons? Buckyballs are just that sort of electron-grabbing molecule.

    A Very Small Valve for Channeling Electron Flow

    For this study, diamondoids were produced in the SLAC laboratory of SIMES researchers Jeremy Dahl and Robert Carlson, who are world experts in extracting the tiny diamonds from petroleum. They were then shipped to Germany, where chemists at Justus-Liebig University figured out how to attach them to buckyballs.

    The resulting buckydiamondoids, which are just a few nanometers long, were tested in SIMES laboratories at Stanford. A team led by graduate student Jason Randel and postdoctoral researcher Francis Niestemski used a scanning tunneling microscope to make images of the hybrid molecules and measure their electronic behavior. They discovered the hybrid is an excellent rectifier: The electrical current flowing through the molecule was up to 50 times stronger in one direction, from electron-spitting diamondoid to electron-catching buckyball, than in the opposite direction. This is something neither component can do on its own.

    ball
    An image made with a scanning tunneling microscope shows hybrid buckydiamondoid molecules on a gold surface. The buckyball end of each molecule is attached to the surface, with the diamondoid end sticking up; both are clearly visible. The area shown here is 5 nanometers on a side. (H. Manoharan et al, Nature Communications)

    image
    Illustration of a buckydiamondoid molecule under a scanning tunneling microscope (STM). The sharp metallic tip of the STM ends in a single atom; as it scans over a sample, electrons tunnel from the tip into the sample. In this study the STM made images of the buckydiamondoids and probed their electronic properties. (SLAC National Accelerator Laboratory)

    While this is not the first molecular rectifier ever invented, it’s the first one made from just carbon and hydrogen, a simplicity researchers find appealing, said Manoharan, who is an associate professor of physics at Stanford. The next step, he said, is to see if transistors can be constructed from the same basic ingredients.

    “Buckyballs are easy to make – they can be isolated from soot – and the type of diamondoid we used here, which consists of two tiny cages, can be purchased commercially,” he said. “And now that our colleagues in Germany have figured out how to bind them together, others can follow the recipe. So while our research was aimed at gaining fundamental insights about a novel hybrid molecule, it could lead to advances that help make molecular electronics a reality.”

    Other research collaborators came from the Catholic University of Louvain in Belgium and Kiev Polytechnic Institute in Ukraine. The primary funding for the work came from the U.S. Department of Energy 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.
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  • richardmitnick 4:37 pm on August 12, 2014 Permalink | Reply
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    From SLAC Lab: “Construction of Large Synoptic Survey Telescope to Begin” 


    SLAC Lab

    August 4, 2014

    LSST Will Capture Unprecedented View of Night Sky

    LSST Telescope

    On August 1, 2014, the National Science Foundation (NSF) announced an award to the Association of Universities for Research in Astronomy (AURA) to manage construction of the Large Synoptic Survey Telescope (LSST); with this announcement, construction of the LSST observatory can begin.

    When the LSST observatory starts surveying the entire visible southern sky from a Chilean mountaintop in October 2022, it will produce a unique view of the universe—the widest and fastest views of the night sky ever observed. LSST’s vast public archive of data will dramatically advance knowledge of the dark energy and dark matter that make up much of the universe, as well as galaxy formation and potentially hazardous asteroids. The LSST is expected to see “engineering first light” by 2020.

    LSST Camera
    SLAC is leading the construction of the 3,200-megapixel LSST camera, which will be the size of a small car and will weigh more than 3 tons. The digital camera will be the largest ever built for astronomy, allowing LSST to create an unprecedented public archive of data – about 6 million gigabytes per year, the equivalent of shooting roughly 800,000 images with a regular eight-megapixel digital camera every night. (SLAC National Accelerator Laboratory)

    LSST is an NSF and DOE partnership. NSF is responsible for the telescope and site, education and outreach, and the data management system, and DOE is providing the camera and related instrumentation. The National Research Council’s Astronomy and Astrophysics decadal survey ranked the LSST as the top new ground-based priority for the field in its 2010 report “New Worlds, New Horizons.”

    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.
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  • richardmitnick 8:45 pm on August 5, 2014 Permalink | Reply
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    From SLAC: “Rebooted Muon Experiment Tests Detector Design at SLAC” 


    SLAC Lab

    August 5, 2014
    Last year, a monster magnet set out from Brookhaven National Lab on an epic, 35-day trek by land and sea to its new home at Fermilab, where it will serve as the heart of a search for evidence of new subatomic particles. Last month, with much less fanfare, researchers came to the End Station Test Beam (ESTB) facility at the Department of Energy’s SLAC National Accelerator Laboratory to test the eyes and nerves of the same experiment: a cutting-edge design for a new detector.

    mag
    Muon g-2 magnet to be transported to Fermilab.

    The goal of the experiment, called Muon g-2 (pronounced gee-minus-two), is to precisely measure a property of muons by studying the way their spins precess, or wobble like a slowing top, in the grip of a powerful magnet. Researchers can track this spin by observing the muon’s decay into electrons, their lighter, longer-lived siblings.

    In the experiment’s original incarnation at Brookhaven, researchers discovered the spin rate is a tiny bit different from what theory says it should be – a difference that could indicate the influence of unknown virtual particles that pop into existence from the vacuum, affect the muons, and disappear once more.

    However, the researchers at Brookhaven weren’t able to measure the property precisely enough to know for sure. That prompted the relocation of the experiment – including the headline-grabbing move of the giant ring magnet – to Fermilab, with its more powerful muon beam.

    More Muons = More Data

    To take advantage of more muons, and thus more data, a team led by University of Washington physicist David Hertzog developed a new detector design for the experiment, a novel combination of lead-fluoride crystals and silicon photomultiplier chips that they hope will capture more information about the escaping electrons.

    Hertzog and his colleagues brought some of the crystals and silicon chips to SLAC’s ESTB facility, where electrons from the linear accelerator could stand in for the results of muon decays – but controlled and easily tracked muon decays, unlike what the detectors will face during the actual experiment.

    “These detectors will need to catch a tremendous number of muon decays, pinpointing their times and the energies of the electrons,” Hertzog said. “The electrons at ESTB can be delivered one at a time and with known energies, so we can see how the crystals and silicon photomultipliers respond.”

    The tests at ESTB have been much more low-key than the magnet’s 3200-mile trek, but Hertzog said his team can also look back at a successful venture.

    “This experiment has been really enjoyable,” Hertzog said. “We’ve got good data and our system seems to be working well.”

    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.
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  • richardmitnick 9:45 pm on July 31, 2014 Permalink | Reply
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    From SLAC Lab: “Despite Extensive Analysis, Fermi Bubbles Defy Explanation” 


    SLAC Lab

    July 31, 2014

    Scientists from Stanford and the Department of Energy’s SLAC National Accelerator Laboratory have analyzed more than four years of data from NASA’s Fermi Gamma-ray Space Telescope, along with data from other experiments, to create the most detailed portrait yet of two towering bubbles that stretch tens of thousands of light-years above and below our galaxy.

    https://www6.slac.stanford.edu/sites/www6.slac.stanford.edu/files/styles/lightbox_large_image/public/images/Fermi_bubbles-ST.jpg
    This artist’s representation shows the Fermi bubbles towering above and below the galaxy. (NASA’s Goddard Space Flight Center)

    NASA Fermi Telescope
    NASA/Fermi

    The bubbles, which shine most brightly in energetic gamma rays, were discovered almost four years ago by a team of Harvard astrophysicists led by Douglas Finkbeiner who combed through data from Fermi’s main instrument, the Large Area Telescope.

    NASA Fermi LAT Large Area Telescope
    NASA/Fermi LAT

    The new portrait, described in a paper that has been accepted for publication in The Astrophysical Journal, reveals several puzzling features, said Dmitry Malyshev, a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology who co-led on the analysis.

    For example, the outlines of the bubbles are quite sharp, and the bubbles themselves glow in nearly uniform gamma rays over their colossal surfaces, like two 30,000-light-year-tall incandescent bulbs screwed into the center of the galaxy.

    Their size is another puzzle. The farthest reaches of the Fermi bubbles boast some of the highest energy gamma rays, but there’s no discernable cause for them that far from the galaxy.

    Finally, although the parts of the bubbles closest to the galactic plane shine in microwaves as well as gamma rays, about two-thirds of the way out the microwaves fade and only gamma rays are detectable. Not only is this different from other galactic bubbles, but it makes the researchers’ work that much more challenging, said Malyshev’s co-lead, KIPAC postdoctoral researcher Anna Franckowiak.

    two
    KIPAC researchers Dmitry Malyshev (left) and Anna Franckowiak with the magazine issues that contain the articles about the Fermi bubbles they co-authored for the general public. Malyshev’s is in the July 2014 issue of Scientific American, while Franckowiak’s article is in the July 2014 issue of Physics Today. (SLAC National Accelerator Laboratory)

    “Since the Fermi bubbles have no known counterparts in other wavelengths in areas high above the galactic plane, all we have to go on for clues are the gamma rays themselves,” she said.

    What Blew The Bubbles?

    Soon after the initial discovery theorists jumped in, offering several explanations for the bubbles’ origins. For example, they could have been created by huge jets of accelerated matter blasting out from the supermassive black hole at the center of our galaxy. Or they could have been formed by a population of giant stars, born from the plentiful gas surrounding the black hole, all exploding as supernovae at roughly the same time.

    “There are several models that explain them, but none of the models is perfect,” Malyshev said. “The bubbles are rather mysterious.”

    Creating the portrait wasn’t easy.

    “It’s very tricky to model,” said Franckowiak. “We had to remove all the foreground gamma-ray emissions from the data before we could clearly see the bubbles.”

    From the vantage point of most Earth-bound telescopes, all but the highest-energy gamma rays are completely screened out by our atmosphere. It wasn’t until the era of orbiting gamma-ray observatories like Fermi that scientists discovered how common extra-terrestrial gamma rays really are. Pulsars, supermassive black holes in other galaxies and supernovae are all gamma rays point sources, like distant stars are point sources of visible light, and all those gamma rays had to be scrubbed from the Fermi data. Hardest to remove were the galactic diffuse emissions, a gamma ray fog that fills the galaxy from cosmic rays interacting with interstellar particles.

    “Subtracting all those contributions didn’t subtract the bubbles,” Franckowiak said. “The bubbles do exist and their properties are robust.” In other words, the bubbles don’t disappear when other gamma-ray sources are pulled out of the Fermi data – in fact, they stand out quite clearly.

    Franckowiak says more data is necessary before they can narrow down the origin of the bubbles any further.

    “What would be very interesting would be to get a better view of them closer to the galactic center,” she said, “but the galactic gamma ray emissions are so bright we’d need to get a lot better at being able to subtract them.”

    Fermi is continuing to gather the data Franckowiak wants, but for now, both researchers said, there are a lot of open questions.

    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.
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  • richardmitnick 11:02 pm on July 16, 2014 Permalink | Reply
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    From SLAC Lab: “Antimatter Once More Flowing to Experiments at SLAC” 


    SLAC Lab

    July 16, 2014
    No Writer Credit

    Following an absence of six years, beams of positrons – the antimatter twins of electrons – are once more streaming through the linear accelerator to waiting experiments at the Department of Energy’s SLAC National Accelerator Laboratory.

    SLAC Linac 2
    SLAC 1.9 mile (3 kilometer) long Klystron Gallery

    Positrons were last seen at SLAC during a particle physics experiment called BaBar, which studied electron-positron collisions. Because matter and antimatter annihilate into a flash of pure energy when they collide, the particles born from these collisions are easier to track than particles resulting from proton-proton collisions.

    When BaBar stopped taking data in 2008, the equipment to create the positrons was left in place. Then SLAC opened the Facility for Advanced Accelerator Experimental Tests (FACET) in 2012, where researchers can explore cutting-edge technologies to power the next generation of accelerators – including accelerators that send matter smashing into antimatter. Positrons were a necessary addition to the FACET toolbox.

    SLAC FACET

    SLAC FACET Line

    facet box
    The instruments at the heart of the Facility for Advanced Accelerator Experimental Tests, such as the plasma oven seen here, can now experiment on positrons. (Matt Beardsley/SLAC National Accelerator Laboratory)

    Beginning in March, a cross-lab team led by SLAC accelerator physicists Jerry Yocky and Nate Lipkowitz started getting the equipment up and running again. By June, the final push began.

    “A lot of people had to work really hard, but it was fun and exciting to bring them back,” Yocky said. “SLAC is unique. We make the most positrons anywhere, plus our linac can accelerate them to the highest energy available anywhere in the world today.”

    Three experiments were able to use the positron beam before FACET shut down for maintenance and upgrades in early July.

    Ioan Tudosa, a member of the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC, exposed magnetic materials to the positron beam. The experiment was a continuation of previous work at FACET on ultrafast magnetic switching. “We don’t expect a very different result from previous experiments with electrons, but surprises can occur,” he said.

    Stanford graduate student Spencer Gessner has been working on ways to accelerate both electrons and positrons in clouds of hot, ionized gas called plasmas. “We saw definite acceleration of the positrons in the plasma,” he said. “When you add that to the acceleration we’ve already seen from electrons in the plasma, I think we’ve really taken our first steps toward compact accelerators that are still powerful enough for electron-positron colliders.”

    Gessner is also exploring “hollow channel” plasma acceleration, in which a laser drills through neutral gas, forming a tunnel with walls of plasma. Theory suggests both electron and positron beams can be accelerated through such tubes, and, said Gessner, the research team was able to begin exploring how the positron beam and the tube interacted.

    “It’s step zero for hollow channel experiments, but it’s a big step zero,” he said.

    spot
    This image shows a cross-section of a plasma-walled channel (orange ring) with a positron bunch (bright dot) making a bull’s eye in the center. (E200 Collaboration)

    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.
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  • richardmitnick 11:43 am on July 15, 2014 Permalink | Reply
    Tags: , , , , KEK Laboratory, , SLAC National Accelerator Lab   

    From interactions.org: “KEK: 50 years from the discovery of ‘CP-violation'” 

    Interactionsdotorg

    11 July 2014
    Professor Yoshihide Sakai
    Co-spokesperson, the Belle Collaboration
    The High Energy Accelerator Research Organization

    Public Relations Office, High Energy Accelerator Research Organization (KEK), Japan
    Saeko Okada
    Senior Press Officer, Public Relations Office, KEK
    TEL: +81-29-879-6046
    FAX: +81-29-879-6049
    E-mail: press@kek.jp

    Belle and Babar complete a joint book on their experimental work to prove the Kobayashi-Maskawa theory of CP-violation

    The joint publication was completed last month. To celebrate this achievement, the first special editions of the book are presented to Drs. Cronin, Kobayashi and Maskawa today at the 50 Years of CP Violation conference held in London.

    In 1993 the SLAC National Accelerator Laboratory in California and the KEK laboratory near Tokyo in Japan embarked on a quest to understand the nature of CP violation, a tiny difference between matter and antimatter that is vital for our existence. This effect was discovered in the decay of a particle called a kaon in 1964. These kaons exhibited strange behaviour compared with other particles studied at the time, and we now refer to the quark that causes that behaviour as a strange (or just s) quark. The amount of CP violation in kaon decays is insufficient to explain how the universe came to be dominated by matter.

    SLAC Campus
    SLAC National Accelerator Lab

    KEK lab
    KEK

    SLAC and KEK constructed so called B Factories, which are particle accelerators and detectors to produce a large number of Bottom (or Beauty) particles, which contain b quarks, and study CP violation. The B Factory mission was to explore the phenomenon of CP violation in these particles. Twenty-one years on, these two international collaborations have come to the end of a global collaborative project: one that has produced a weighty tome over 900 pages in length, detailing all aspects of the Physics of the B Factories and their detectors: BaBar and Belle. The physics harvest from the international collaborations that run BaBar and Belle have included many notable discoveries including: CP violation in B decays, first studies of some very rare B decays, and a host of new particles. The breakthroughs have continued more recently with the determination of mixing in neutral charm mesons. This discovery paves the way for the next generation of experiments to search for certain types of CP violation in the decay of charm mesons. Almost a thousand papers have been published by these two experiments during their lifetime.

    The original flagship measurements of the B Factories were found to be consistent with the Cabibbo-Kobayashi-Maskawa matrix description of CP violation. This provides the Standard Model of particle physics with a description of CP violation as predicted by Kobayashi and Maskawa in 1972.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The B Factory confirmation of the Kobayashi-Maskawa mechanism was quickly followed by Kobayashi and Maskawa sharing a Nobel Prize (in 2008) for their insightful work. The Cabibbo-Kobayashi-Maskawa matrix is now known to provide the leading description of CP violation. However, while this was an important step forward for the field, the amount of CP violation in the Standard Model remains about a billion times too small to explain the matter-dominated universe that we live in. As a result the focus of the field has turned from understanding how nature behaves to the much more subtle task of trying to understand if there are small deviations from this leading description that have been missed so far.

    A new book has been written as a collaboration between the two teams of physicists working on BaBar and Belle, with the help of the theory community. This is envisioned to be a pedagogical resource for the next generation of experimentalists to work in this field. Preparations started in 2008 and the concept was solidified through a number of international meetings over the past six years. This effort brought together experts from the global flavour physics communities from four continents. The KEK B Factory is in the process of being upgraded and should recommence data taking as a “Super B Factory” with a physics programme resuming in 2016. A decade from now someone will surely need to write a book on the Physics of the Super B Factory.


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  • richardmitnick 4:05 pm on July 10, 2014 Permalink | Reply
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    From SLAC: “Uncertainty Gives Scientists New Confidence in Search for Novel Materials “ 


    SLAC Lab

    July 10, 2014
    Andrew Gordon, agordon@slac.stanford.edu, (650) 926-2282

    Scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have found a way to estimate uncertainties in computer calculations that are widely used to speed the search for new materials for industry, electronics, energy, drug design and a host of other applications. The technique, reported in the July 11 issue of Science, should quickly be adopted in studies that produce some 30,000 scientific papers per year.

    “Over the past 10 years our ability to calculate the properties of materials and chemicals, such as reactivity and mechanical strength, has increased enormously. It’s totally exploded,” said Jens Nørskov, a professor at SLAC and Stanford and director of the SUNCAT Center for Interface Science and Catalysis, who led the research.

    “As more and more researchers use computer simulations to predict which materials have the interesting properties we’re looking for – part of a process called ‘materials by design’ ­– knowing the probability for error in these calculations is essential,” he said. “It tells us exactly how much confidence we can put in our results.”

    Nørskov and his colleagues have been at the forefront of developing this approach, using it to find better and cheaper catalysts to speed ammonia synthesis and generate hydrogen gas for fuel, among other things. But the technique they describe in the paper can be broadly applied to all kinds of scientific studies.

    graph
    This image shows the results of calculations aimed at determining which of six chemical elements would make the best catalyst for promoting an ammonia synthesis reaction. Researchers at SLAC and Stanford used Density Functional Theory (DFT) to calculate the strength of the bond between nitrogen atoms and the surfaces of the catalysts. The bond strength, plotted on the horizontal axis, is a key factor in determining the reaction speed, plotted on the vertical axis. Based on thousands of these calculations, which yielded a range of results (colored dots) that reveal the uncertainty involved, researchers estimated an 80 percent chance that ruthenium (Ru, in red) will be a better catalyst than iron (Fe, in orange.) (Andrew Medford and Aleksandra Vojvodic/SUNCAT, Callie Cullum)

    Speeding the Material Design Cycle

    The set of calculations involved in this study is known as DFT, for Density Functional Theory. It predicts bond energies between atoms based on the principles of quantum mechanics. DFT calculations allow scientists to predict hundreds of chemical and materials properties, from the electronic structures of compounds to density, hardness, optical properties and reactivity.

    Because researchers use approximations to simplify the calculations – otherwise they’d take too much computer time – each of these calculated material properties could be off by a fairly wide margin.

    To estimate the size of those errors, the team applied a statistical method: They calculated each property thousands of times, each time tweaking one of the variables to produce slightly different results. That variation in results represents the possible range of error.

    “Even with the estimated uncertainties included, when we compared the calculated properties of different materials we were able to see clear trends,” said Andrew J. Medford, a graduate student with SUNCAT and first author of the study. “We could predict, for instance, that ruthenium would be a better catalyst for synthesizing ammonia than cobalt or nickel, and say what the likelihood is of our prediction being right.”

    An Essential New Tool for Thousands of Studies

    DFT calculations are used in the materials genome initiative to search through millions of solids and compounds, and also widely used in drug design, said Kieron Burke, a professor of chemistry and physics at the University of California-Irvine who was not involved in the study.

    “There were roughly 30,000 papers published last year using DFT,” he said. “I believe the technique they’ve developed will become absolutely necessary for these kinds of calculations in all fields in a very short period of time.”

    Thomas Bligaard, a senior staff scientist in charge of theoretical method development at SUNCAT, said the team has a lot of work ahead in implementing these ideas, especially in calculations attempting to make predictions of new phenomena or new functional materials.

    Other researchers involved in the study were Jess Wellendorff, Aleksandra Vojvodic, Felix Studt, and Frank Abild-Pedersen of SUNCAT and Karsten W. Jacobsen of the Technical University of Denmark. Funding for the research came from the DOE 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.
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  • richardmitnick 6:07 pm on June 23, 2014 Permalink | Reply
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    From SLAC Lab: “Scientists Use X-rays to Look at How DNA Protects Itself from UV Light” 


    SLAC Lab

    June 23, 2014
    Andrew Gordon, agordon@slac.stanford.edu, (650) 926-2282

    The molecular building blocks that make up DNA absorb ultraviolet light so strongly that sunlight should deactivate them – yet it does not. Now scientists have made detailed observations of a “relaxation response” that protects these molecules, and the genetic information they encode, from UV damage.

    The experiment at the Department of Energy’s SLAC National Accelerator Laboratory focused on thymine, one of four DNA building blocks. Researchers hit thymine with a short pulse of ultraviolet light and used a powerful X-ray laser to watch the molecule’s response: A single chemical bond stretched and snapped back into place within 200 quadrillionths of a second, setting off a wave of vibrations that harmlessly dissipated the destructive UV energy.

    The international research team reported the results June 23 in Nature Communications.

    While protecting the genetic information encoded in DNA is vitally important, the significance of this result goes far beyond DNA chemistry, said Philip Bucksbaum, director of the Stanford PULSE Institute and a co-author of the report.

    “The new tool the team developed for this study provides a new window on the motion of electrons that control all of chemistry,” he said. “We think this will enhance the value and impact of X-ray free-electron lasers for important problems in biology, chemistry and physics.”

    Light Becomes Heat

    Researchers had noticed years ago that thymine seemed resistant to damage from UV rays in sunlight, which cause sunburn and skin cancer. Theorists proposed that thymine got rid of the UV energy by quickly shifting shape. But they differed on the details, and previous experiments could not resolve what was happening.

    The SLAC experiment took place at the Linac Coherent Light Source (LCLS), a DOE Office of Science user facility, whose bright, ultrashort X-ray laser pulses can see changes taking place at the level of individual atoms in quadrillionths of a second.

    Scientists turned thymine into a gas and hit it with two pulses of light in rapid succession: first UV, to trigger the protective relaxation response, and then X-rays, to detect and measure the response.

    “As soon as the thymine swallows the light, the energy is funneled as quickly as possible into heat, rather than into making or breaking chemical bonds,” said Markus Guehr, a DOE Early Career Program recipient and senior staff scientist at PULSE who led the study. “It’s like a system of balls connected by springs; when you elongate that one bond between two atoms and let it loose, the whole molecule starts to tremble.”

    Ejected Electrons Signal Changes

    The X-rays measured the relaxation response indirectly by stripping away some of the innermost electrons from atoms in the thymine molecule. This sets off a process known as Auger decay that ultimately ejects other electrons. The ejected electrons fly into a detector, carrying information about the nature and state of their home atoms.

    By comparing the speeds of the ejected electrons before and after thymine was hit with UV, the researchers were able to pinpoint rapid changes in a single carbon-oxygen bond: It stretched when hit with UV light and shortened 200 quadrillionths of a second later, setting off vibrations that continued for billionths of a second.

    “This is the first time we’ve been able to distinguish between two fundamental responses in the molecule – movements of the atomic nuclei and changes in the distribution of electrons – and time them within a few quadrillionths of a second,” said the paper’s first author, Brian McFarland, a postdoctoral researcher who has since moved from SLAC to Los Alamos National Laboratory.

    Guehr said the team plans more experiments to further explore the protective relaxation response and extend the new method, called time-resolved Auger spectroscopy, into other scientific realms.

    In addition to the Stanford PULSE Institute, which is a joint institute of SLAC and Stanford University, the study included researchers from LCLS, Stanford, the University of Perugia in Italy, Lawrence Berkeley National Laboratory, the University of Connecticut, Western Michigan University, the University of Gothenburg in Sweden, and UNIST in South Korea. Parts of the research were carried out at Berkeley Lab’s Advanced Light Source, a DOE Office of Science user facility. The work was funded by the DOE Office of Science, the Swedish Research Council, the Göran Gustafsson Foundation and the Knut and Alice Wallenberg Foundation.

    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.
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  • richardmitnick 1:08 pm on June 18, 2014 Permalink | Reply
    Tags: , SLAC National Accelerator Lab,   

    From SLAC Lab: “Scientists Take First Dip into Water’s Mysterious ‘No Man’s Land’” 


    SLAC Lab

    June 18, 2014
    Andy Freeberg, afreeberg@slac.stanford.edu, (650) 926-4359

    Scientists at the Department of Energy’s SLAC National Accelerator Laboratory have made the first structural observations of liquid water at temperatures down to minus 51 degrees Fahrenheit, within an elusive “no man’s land” where water’s strange properties are super-amplified.

    The research, made possible by SLAC’s Linac Coherent Light Source (LCLS) X-ray laser and reported June 18 in Nature, opens a new window for exploring liquid water in these exotic conditions, and promises to improve our understanding of its unique properties at the more natural temperatures and states that are relevant to global ocean currents, climate and biology.

    Scientists have known for some time that water can remain liquid at extremely cold temperatures, but they’ve never before been able to examine its molecular structure in this zone.

    “Water is not only essential for life as we know it, but it also has very strange properties compared to most other liquids,” said Anders Nilsson, deputy director of the SUNCAT Center for Interface Science and Catalysis, a joint SLAC/Stanford institute, and leader of the research. “Now, thanks to LCLS, we have finally been able to enter this cold zone that should provide new information about the unique nature of water.”

    Not Your Typical Liquid

    Despite its simple molecular structure, water has many weird traits: Its solid form is less dense than its liquid form, which is why ice floats; it can absorb a large amount of heat, which is carried long distances by ocean currents and has a profound impact on climate; and its peculiar density profile prevents oceans and lakes from freezing solid all the way to the bottom, allowing fish to survive the winter.

    These traits are amplified when purified water is supercooled. When water is very pure, with nothing to seed the formation of ice crystals, it can remain liquid at much lower temperatures than normal. The temperature range of water from about minus 42 to minus 172 degrees (see diagram) has been dubbed no man’s land. For decades scientists have sought to better explore what happens to water molecules at temperatures below minus 42 degrees, but they had to rely largely on theory and modeling.

    graph
    This diagram illustrates the rough boundaries of “no man’s land,” a temperature region where supercooled water is difficult to study because of rapid ice formation. Using SLAC’s Linac Coherent Light Source, scientists dipped down to minus 51 degrees Fahrenheit and made the first structural measurements of liquid water in this mysterious region, where water’s unusual properties are amplified. (Greg Stewart/SLAC, Ultrafast Chemical Physics Group/University of Glasgow, Scotland)

    Femtosecond Shutter Speeds

    Now the LCLS, with X-ray laser pulses just quadrillionths of a second long, allows researchers to capture rapid-fire snapshots showing the detailed molecular structure of water in this mysterious zone the instant before it freezes. The research showed that water’s molecular structure transforms continuously as it enters this realm, and with further cooling the structural changes accelerate more dramatically than theoretical models had predicted.

    For this experiment, researchers produced a steady flow of tiny water droplets in a vacuum chamber. As the drops traveled toward the laser beam, some of their liquid rapidly evaporated, supercooling the remaining liquid. (The same process cools us when we sweat.) By adjusting the distance the droplets traveled, the researchers were able to fine-tune the temperatures they reached on arrival at the X-ray laser beam.

    Colder Still

    Nilsson’s team hopes to dive to even colder temperatures where water morphs into a glassy, non-crystalline solid. They also want to determine whether supercooled water reaches a critical point where its unusual properties peak, and to pinpoint the temperature at which this occurs.

    “Our dream is to follow these dynamics as far as we can,” Nilsson said. “Eventually our understanding of what’s happening here in no man’s land will help us fundamentally understand water in all conditions.”

    Scientists at SLAC’s Linac Coherent Light Source, Stanford Synchrotron Radiation Lightsource and Stanford PULSE Institute; Stockholm University; Germany’s DESY laboratory; the Helmholtz Center for Materials and Energy in Germany; and Stony Brook University in New York also contributed to the research. The work was partially funded by the U.S. Department of Energy Office of Science, the SLAC Laboratory Directed Research and Development Program and the Swedish Research Council.

    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.
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  • richardmitnick 4:06 am on June 7, 2014 Permalink | Reply
    Tags: , , SLAC National Accelerator Lab   

    From SLAC Lab: “A New Way to Create Compact Light Sources” 


    SLAC Lab

    June 6, 2014
    Glenn Roberts Jr.

    SLAC scientists have found a new way to produce bright pulses of light from accelerated electrons that could shrink “light source” technology used around the world since the 1970s to examine details of atoms and chemical reactions.

    Traditionally this light is created by wiggling accelerated electrons with heavy magnets in a device called an undulator. Undulators currently produce bright X-ray pulses for experiments at dozens of sites, including SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL) and Linac Coherent Light Source (LCLS) free-electron X-ray laser. The new approach replaces the magnets with microwaves, and designers say it could be scaled to produce X-ray light.

    “This is a radical new design that can be used to create light sources that are more compact than can be achieved using a conventional undulator,” said Sami Tantawi, a SLAC particle physics and astrophysics professor who led the development effort.

    The microwave undulator can produce shorter wavelengths of light – using less driving energy from electrons than conventional undulators. This means the accelerator that feeds it electrons can shrink considerably, Tantawi said.

    A Step Toward Tabletop X-ray Lasers

    “This brings us much closer to the dream of a tabletop X-ray free-electron laser,” Tantawi said. “We have proved, in principle, that this is possible.”

    Electrons beamed into the undulator encounter rapidly alternating high-power microwave fields that cause the electrons to wiggle, emitting light at specific wavelengths. The wavelength and other properties of this light can be precisely tuned to suit many different types of experiments by adjusting the energy of the electrons and the microwave power.

    Tantawi said, “Because it doesn’t have any moving parts, the microwave undulator is amenable to scaling down to very short wavelengths.” Increasing its length and supplying more electron energy could allow it to produce X-ray pulses like those generated by the LCLS X-ray laser. Its scalability and rapid tuning sets it apart from other next-generation undulators, he noted.

    A Next-generation Source of Highly Tunable Light

    The new device, featured on the cover of the April 25 edition of Physical Review Letters, could be used to provide more highly tailored light pulses that open new realms of experimental possibilities, particularly for studies of materials with exotic properties. It could be incorporated into next-generation lasers, synchrotrons and particle colliders and installed in existing facilities, such as SLAC’s LCLS and SSRL.

    Also, Tantawi said he would like to pursue a superconducting version of the undulator that would require supercooling in order to produce a more continuous stream of light for experiments.

    “This technology has vast potential to dynamically control the properties of the light for use in many scientific experiments,” Muhammad Shumail, a PhD student who is writing his thesis about the undulator, said.

    ms
    Muhammad Shumail, a PhD student, inspects the microwave undulator that he worked to design and build. (Fabricio Sousa/SLAC)

    With further miniaturization, it is conceivable that the microwave undulator could serve as a portable medical imaging source, Tantawi said. “The next step of the research is to really make this technology more available.”

    SLAC technologist Gordon Bowden said building the prototype device was challenging, requiring specialized tools to cut a series of tiny ribs from the inside of the copper pipe the undulator is made of. The ends of the device had to be precisely tapered to better trap the microwave energy in the device.

    “No conventional undulator has the agility that this device can offer,” Bowden said. “The unique properties of the light that emerges from the undulator are due to the precise comb-like pattern of the microwave fields trapped inside,” he said.

    Unique Expertise

    Tantawi said SLAC’s historic and unique expertise in accelerators and microwave technology was well-suited to the development of the new device. “This is one of the few places on the planet we could have built this,” he said. The first magnetic undulator was built by Stanford researchers in the 1950s.

    device
    This microwave undulator, designed and built at SLAC, uses microwave power and electrons to produce shorter-wavelength pulses, and is highly tunable compared to conventional undulators that use magnets. (Glenn Roberts Jr./SLAC)

    The pursuit of the microwave undulator was inspired by Tantawi’s conversations with X-ray free-electron laser pioneer Claudio Pellegrini and by Joachim Stöhr, SLAC photon science professor, and the design stemmed from his work on a similar design for an antenna that could be used to explore the so-called cosmic microwave background radiation, which is believed to hold clues to the earliest origins of the universe.

    Also participating in the microwave undulator project: Jeffrey Neilson, Chao Chang, Erik Hemsing and Michael Dunning. The project was funded by the U.S. Department of Energy and the Defense Advanced Research Projects Agency AXiS program.

    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.
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