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  • richardmitnick 8:49 am on April 2, 2015 Permalink | Reply
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    From SLAC: “Scientists Track Ultrafast Creation of a Catalyst with X-ray Laser” 


    SLAC Lab

    April 1, 2015

    Chemical Transformations Driven by Light Provide Key Insight to Steps in Solar-energy Conversion

    1
    This artistic rendering shows an iron-centered molecule that is severed by laser light (upper left). Within hundreds of femtoseconds, or quadrillionths of a second, a molecule of ethanol from a solvent rushes in (bottom right) to bond with the iron-centered molecule. (SLAC National Accelerator Laboratory)

    An international team has for the first time precisely tracked the surprisingly rapid process by which light rearranges the outermost electrons of a metal compound and turns it into an active catalyst – a substance that promotes chemical reactions.

    The results, published April 1 in Nature, could help in the effort to develop novel catalysts to efficiently produce fuel using sunlight. The research was performed with an X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory.

    “We were able to determine how light rearranges the outermost electrons of the compound on timescales down to a few hundred femtoseconds, or quadrillionths of a second,” said Philippe Wernet, a scientist at Helmholtz-Zentrum Berlin for Materials and Energy who led the experiment.

    Researchers hope that learning these details will allow them to develop rules for predicting and controlling the short-lived early steps in important reactions, including the ones plants use to turn sunlight and water into fuel during photosynthesis. Scientists are seeking to replicate these natural processes to produce hydrogen fuel from sunlight and water, for example, and to master the chemistry required to produce other renewable fuels.

    “The eventual goal is to design chemical reactions that behave exactly the way you want them to,” Wernet said.

    In the experiment at SLAC’s Linac Coherent Light Source, a DOE Office of Science User Facility, the scientists studied a yellowish fluid called iron pentacarbonyl, which consists of carbon monoxide “spurs” surrounding a central iron atom. It is a basic building block for more complex compounds and also provides a simple model for studying light-induced chemical reactions.

    SLAC LCLS Inside
    LCLS

    Researchers had known that exposing this iron compound to light can cleave off one of the five carbon monoxide spurs, causing the molecule’s remaining electrons to rearrange. The arrangement of the outermost electrons determines the molecule’s reactivity – including whether it might make a good catalyst – and also informs how reactions unfold.

    What wasn’t well understood was just how quickly this light-triggered transformation occurs and which short-lived intermediate states the molecule goes through on its way to becoming a stable product.

    At LCLS, the scientists struck a thin stream of the iron compound, which was mixed into an ethanol solvent, with pulses of optical laser light to break up the iron-centered molecules. Just hundreds of femtoseconds later, an ultrabright X-ray pulse probed the molecules’ transformation, which was recorded with sensitive detectors.

    By varying the arrival time of the X-ray pulses, they tracked the rearrangements of the outermost electrons during the molecular transformations.

    Roughly half of the severed molecules enter a chemically reactive state in which their outermost electrons are prone to binding other molecules. As a consequence, they either reconnect with the severed part or bond with an ethanol molecule to form a new compound. In other cases the outermost electrons in the molecule stabilize themselves in a configuration that makes the molecule non-reactive. All of these changes were observed within the time it takes light to travel a few thousandths of an inch.

    “To see this happen so quickly was extremely surprising,” Wernet said.

    Several years’ worth of data analysis and theoretical work were integral to the study, he said. The next step is to move on from model compounds to LCLS studies of the actual molecules used to make solar fuels.

    “This was a really exciting experiment, as it was the first time we used the LCLS to study chemistry in a liquid compound,” said Josh Turner, a SLAC staff scientist who participated in the experiment. “The LCLS is unique in the world in its ability to resolve these types of ultrafast processes in the right energy range for this compound.”

    SLAC’s Kelly Gaffney, a chemist who contributed expertise in how the changing arrangement of electrons steered the chemical reactions, said, “This work helps set the stage for future studies at LCLS and shows how cooperation across different research areas at SLAC enables broader and better science.”

    In addition to researchers from Helmholtz-Zentrum Berlin for Materials and Energy and LCLS, other scientists who assisted in the study were from: SLAC’s Stanford Synchrotron Radiation Lightsource; the SLAC and Stanford PULSE Institute; University of Potsdam, Max Planck Institute for Biophysical Chemistry, Goettingen University and DESY lab in Germany; Stockholm University and MAX-lab in in Sweden; Utrecht University in the Netherlands; Paul Scherrer Institute in Switzerland; and the University of Pennsylvania.

    This work was supported by the Volkswagen Foundation, the Swedish Research Council, the Carl Tryggers Foundation, the Magnus Bergvall Foundation, Collaborative Research Centers of the German Science Foundation and the Helmholtz Virtual Institute “Dynamic Pathways in Multidimensional Landscapes,” and the U.S. Department of Energy Office of Science.

    See the full article here.

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    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 12:03 pm on March 24, 2015 Permalink | Reply
    Tags: , SLAC LCLS, Warm Dense Matter,   

    From SLAC: “Experiment Provides the Best Look Yet at ‘Warm Dense Matter’ at Cores of Giant Planets” 


    SLAC Lab

    March 23, 2015

    Shock Wave Experiment at SLAC’s X-ray Laser Tracks Formation of a Mysterious Type of Matter

    In an experiment at the Department of Energy’s SLAC National Accelerator Laboratory, scientists precisely measured the temperature and structure of aluminum as it transitions into a superhot, highly compressed concoction known as “warm dense matter.”

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    This illustration shows a cutaway view of Jupiter, which is believed to contain “warm dense matter” at its core. A study at SLAC’s Linac Coherent Light Source X-ray laser has provided the most detailed measurements yet of a material’s temperature and compression as it transitions into this exotic state of matter. (SLAC National Accelerator Laboratory)

    Warm dense matter is the stuff believed to be at the cores of giant gas planets in our solar system and some of the newly observed “exoplanets” that orbit distant suns, which can be many times more massive than Jupiter. Their otherworldly properties, which stretch our understanding of planetary formation, have excited new interest in studies of this exotic state of matter.

    The results of the SLAC study, published March 23 in Nature Photonics, could also lead to a greater understanding of how to produce and control nuclear fusion, which scientists hope to harness as a new source of energy.

    “The heating and compression of warm dense matter has never been measured before in a laboratory with such precise timing,” says Siegfried Glenzer, a distinguished staff scientist who is part of the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC. “We have shown the detailed steps of how a solid hit by powerful lasers becomes a compressed solid and a dense plasma at the same time. This is a step on the path toward creating fusion in the lab.”


    This video describes how scientists at SLAC created and precisely measured the temperature and compression in “warm dense matter,” an exotic state that is believed to exist at the core of giant planets like Jupiter. (SLAC National Accelerator Laboratory)

    A team led by Glenzer used laser light to compress ultrathin aluminum foil samples to a pressure more than 4,500 times higher than the deepest ocean depths and superheat it to 20,000 kelvins – about four times hotter than the surface of the sun. SLAC’s Linac Coherent Light Source X-ray laser, a DOE Office of Science User Facility, then precisely measured the foil’s properties as it transformed into warm dense matter and then into a plasma – a very hot gas of electrons and supercharged atoms.

    SLAC LCLSII
    SLAC LCLS Inside
    LCLS

    Warm dense matter remains largely mysterious because it is difficult to create and study in a laboratory, can exhibit properties of several types of matter and occupies a middle ground between solid and plasma. Our own sun is an example of a self-sustaining plasma, and plasmas have also been harnessed in some TV displays.

    While warm dense matter is believed to exist in a stable state at the heart of giant planets, in a laboratory it lasts just billionths of a second. Scientists have relied largely on computer simulations, driven by scientific theories, to help explain how a solid, when shocked with powerful lasers, transforms into a plasma.

    LCLS, with its complement of high-power lasers, is uniquely suited to creating and studying matter at the extremes. Its ultrabright X-ray pulses are measured in femtoseconds, or quadrillionths of a second, so it works like an ultra-high-speed X-ray camera to illuminate and record the properties of the most fleeting phenomena in atomic-scale detail.

    In this experiment, researchers used a high-power optical laser at LCLS’s Matter in Extreme Conditions experimental station to fire separate beams of green laser light simultaneously at both sides of coated, ultrathin aluminum foil samples, each just half the width of an average human hair. The lasers produced shock waves in the material that converged to create extreme temperatures and pressures.

    3
    Scientists prepare for an experiment at SLAC’s Matter in Extreme Conditions (MEC) station, part of the Linac Coherent Light Source X-ray laser. They used this MEC station to create and measure the properties of ultrathin sheets of superheated aluminum as it transitioned into warm dense matter, an exotic state of matter.(SLAC National Accelerator Laboratory)

    Researchers struck the samples with X-rays just nanoseconds later, and varied the arrival time of the X-rays to essentially make a series of snapshots of warm dense matter formation. The team used a technique known as small angle X-ray scattering to measure the internal structure of the material, capturing its brief transition into the warm dense state.

    “This early work with aluminum is a first stepping stone toward other problems we really need to solve,” Glenzer said, such as how hydrogen behaves under similar conditions. Hydrogen, which makes up about 75 percent of the visible mass of the universe, plays a central role in fusion, the process that powers stars. A better understanding of how hydrogen transitions into warm dense matter could help settle debates over conflicting theories on this transition and help unlock the secrets of fusion energy.

    “I think LCLS can help to resolve the hydrogen ‘controversy,’ in upcoming experiments,” Glenzer said.

    Participants in the research included scientists at SLAC, University of California Berkeley, Lawrence Livermore National Laboratory and General Atomics; QuantumWise A/S in Denmark; AWE plc, University of Warwick and University of Oxford in the U.K.; and the Max Planck Institute for the Physics of Complex Systems, Institute for Optics and Quantum Electronics, Friedrich-Schiller-University and GSI Helmholtz Center for Heavy Ion Research in Germany.

    The work was supported by the DOE Office of Science, Fusion Energy Science; the DOE Office of Basic Energy Sciences, Materials Sciences and Engineering Division; Lawrence Livermore National Laboratory; a Laboratory Directed Research and Development grant; and the Peter-Paul-Ewald Fellowship of the VolkswagenStiftung.

    See the full article here.

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    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 8:41 am on March 19, 2015 Permalink | Reply
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    From SLAC: “Scientists Watch Quantum Dots ‘Breathe’ in Response to Stress” 


    SLAC Lab

    March 18, 2015

    Nanocrystal Study at SLAC’s X-ray Laser Could Aid in the Design of New Materials

    1
    In this illustration, intense X-rays produced at SLAC’s Linac Coherent Light Source strike nanocrystals of a semiconductor material. Scientists used the X-rays to study an ultrafast “breathing” response in the crystals induced quadrillionths of a second earlier by laser light. (SLAC National Accelerator Laboratory)

    Researchers at the Department of Energy’s SLAC National Accelerator Laboratory watched nanoscale semiconductor crystals expand and shrink in response to powerful pulses of laser light. This ultrafast “breathing” provides new insight about how such tiny structures change shape as they start to melt – information that can help guide researchers in tailoring their use for a range of applications.

    In the experiment using SLAC’s Linac Coherent Light Source (LCLS) X-ray laser, a DOE Office of Science User Facility, researchers first exposed the nanocrystals to a burst of laser light, followed closely by an ultrabright X-ray pulse that recorded the resulting structural changes in atomic-scale detail at the onset of melting.

    SLAC LCLS Inside
    LCLS

    “This is the first time we could measure the details of how these ultrasmall materials react when strained to their limits,” said Aaron Lindenberg, an assistant professor at SLAC and Stanford who led the experiment. The results were published March 12 in Nature Communications.

    Getting to Know Quantum Dots

    The crystals studied at SLAC are known as “quantum dots” because they display unique traits at the nanoscale that defy the classical physics governing their properties at larger scales. The crystals can be tuned by changing their size and shape to emit specific colors of light, for example.

    So scientists have worked to incorporate them in solar panels to make them more efficient and in computer displays to improve resolution while consuming less battery power. These materials have also been studied for potential use in batteries and fuel cells and for targeted drug delivery.

    Scientists have also discovered that these and other nanomaterials, which may contain just tens or hundreds of atoms, can be far more damage-resistant than larger bits of the same materials because they exhibit a more perfect crystal structure at the tiniest scales. This property could prove useful in battery components, for example, as smaller particles may be able to withstand more charging cycles than larger ones before degrading.

    A Surprise in the ‘Breathing’ of Tiny Spheres and Nanowires

    In the LCLS experiment, researchers studied spheres and nanowires made of cadmium sulfide and cadmium selenide that were just 3 to 5 nanometers, or billionths of a meter, across. The nanowires were up to 25 nanometers long. By comparison, amino acids – the building blocks of proteins – are about 1 nanometer in length, and individual atoms are measured in tenths of nanometers.

    By examining the nanocrystals from many different angles with X-ray pulses, researchers reconstructed how they change shape when hit with an optical laser pulse. They were surprised to see the spheres and nanowires expand in width by about 1 percent and then quickly contract within femtoseconds, or quadrillionths of a second. They also found that the nanowires don’t expand in length, and showed that the way the crystals respond to strain was coupled to how their structure melts.

    In an earlier, separate study, another team of researchers had used LCLS to explore the response of larger gold particles on longer timescales.

    “In the future, we want to extend these experiments to more complex and technologically relevant nanostructures, and also to enable X-ray exploration of nanoscale devices while they are operating,” Lindenberg said. “Knowing how materials change under strain can be used together with simulations to design new materials with novel properties.”

    Participating researchers were from SLAC, Stanford and two of their joint institutes, the Stanford Institute for Materials and Energy Sciences (SIMES) and Stanford PULSE Institute; University of California, Berkeley; University of Duisburg-Essen in Germany; and Argonne National Laboratory. The work was supported by the DOE Office of Science and the German Research Council.

    See the full article here.

    Please help promote STEM in your local schools.

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    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 5:32 pm on February 13, 2015 Permalink | Reply
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    From SLAC: “Scientists Get First Glimpse of a Chemical Bond Being Born” 


    SLAC Lab

    February 12, 2015

    Scientists have used an X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory to get the first glimpse of the transition state where two atoms begin to form a weak bond on the way to becoming a molecule.

    1
    This illustration shows atoms forming a tentative bond, a moment captured for the first time in experiments with an X-ray laser at SLAC National Accelerator Laboratory. The reactants are a carbon monoxide molecule, left, made of a carbon atom (black) and an oxygen atom (red), and a single atom of oxygen, just to the right of it. They are attached to the surface of a ruthenium catalyst, which holds them close to each other so they can react more easily. When hit with an optical laser pulse, the reactants vibrate and bump into each other, and the carbon atom forms a transitional bond with the lone oxygen, center. The resulting carbon dioxide molecule detaches and floats away, upper right. The Linac Coherent Light Source (LCLS) X-ray laser probed the reaction as it proceeded and allowed the movie to be created. (SLAC National Accelerator Laboratory)

    This fundamental advance, reported Feb. 12 in Science Express and long thought impossible, will have a profound impact on the understanding of how chemical reactions take place and on efforts to design reactions that generate energy, create new products and fertilize crops more efficiently.

    “This is the very core of all chemistry. It’s what we consider a Holy Grail, because it controls chemical reactivity,” said Anders Nilsson, a professor at the SLAC/Stanford SUNCAT Center for Interface Science and Catalysis and at Stockholm University who led the research. “But because so few molecules inhabit this transition state at any given moment, no one thought we’d ever be able to see it.”


    Anders Nilsson, a professor at SLAC and at Stockholm University, explains how scientists used an X-ray laser to watch atoms form a tentative bond, and why that’s important.

    The experiments took place at SLAC’s Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility. Its brilliant, strobe-like X-ray laser pulses are short enough to illuminate atoms and molecules and fast enough to watch chemical reactions unfold in a way never possible before.

    Researchers used LCLS to study the same reaction that neutralizes carbon monoxide (CO) from car exhaust in a catalytic converter. The reaction takes place on the surface of a catalyst, which grabs CO and oxygen atoms and holds them next to each other so they pair up more easily to form carbon dioxide.

    In the SLAC experiments, researchers attached CO and oxygen atoms to the surface of a ruthenium catalyst and got reactions going with a pulse from an optical laser. The pulse heated the catalyst to 2,000 kelvins – more than 3,000 degrees Fahrenheit – and set the attached chemicals vibrating, greatly increasing the chance that they would knock into each other and connect.

    The team was able to observe this process with X-ray laser pulses from LCLS, which detected changes in the arrangement of the atoms’ electrons – subtle signs of bond formation – that occurred in mere femtoseconds, or quadrillionths of a second.

    “First the oxygen atoms get activated, and a little later the carbon monoxide gets activated,” Nilsson said. “They start to vibrate, move around a little bit. Then, after about a trillionth of a second, they start to collide and form these transition states.”

    ‘Rolling Marbles Uphill’

    The researchers were surprised to see so many of the reactants enter the transition state – and equally surprised to discover that only a small fraction of them go on to form stable carbon dioxide. The rest break apart again.

    “It’s as if you are rolling marbles up a hill, and most of the marbles that make it to the top roll back down again,” Nilsson said. “What we are seeing is that many attempts are made, but very few reactions continue to the final product. We have a lot to do to understand in detail what we have seen here.”

    Theory played a key role in the experiments, allowing the team to predict what would happen and get a good idea of what to look for. “This is a super-interesting avenue for theoretical chemists. It’s going to open up a completely new field,” said report co-author Frank Abild-Pedersen of SLAC and SUNCAT.

    A team led by Associate Professor Henrik Öström at Stockholm University did initial studies of how to trigger the reactions with the optical laser. Theoretical spectra were computed under the leadership of Stockholm Professor Lars G.M. Pettersson, a longtime collaborator with Nilsson.

    Preliminary experiments at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), another DOE Office of Science User Facility, also proved crucial. Led by SSRL’s Hirohito Ogasawara and SUNCAT’s Jerry LaRue, they measured the characteristics of the chemical reactants with an intense X-ray beam so researchers would be sure to identify everything correctly at the LCLS, where beam time is much more scarce. “Without SSRL this would not have worked,” Nilsson said.

    The team is already starting to measure transition states in other catalytic reactions that generate chemicals important to industry.

    “This is extremely important, as it provides insight into the scientific basis for rules that allow us to design new catalysts,” said SUNCAT Director and co-author Jens Nørskov.

    Researchers from LCLS, Helmholtz-Zentrum Berlin for Materials and Energy, University of Hamburg, Center for Free Electron Laser Science, University of Potsdam, Fritz-Haber Institute of the Max Planck Society, DESY and University of Liverpool also contributed to the research. The research was funded by the DOE Office of Science, the Swedish National Research Council, the Knut and Alice Wallenberg Foundation, the Volkswagen Foundation and the German Research Foundation (DFG) Center for Ultrafast Imaging.

    See the full article here.

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    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 2:37 pm on February 3, 2015 Permalink | Reply
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    From SLAC: “5 Ways to Put Tiny Targets in Front of an X-ray Laser” 


    SLAC Lab

    February 2, 2015

    Scientists Have Assembled an Exotic Toolbox for Experiments that Tap into the Brightest X-Rays on the Planet

    X-ray devices have long been used to see the inner structure of things, from bone breaks in the human body to the contents of luggage at airport security checkpoints. But to see life’s chemistry and exotic materials at the scale of individual atoms, you need a far more powerful X-ray device.

    Enter the Linac Coherent Light Source (LCLS) X-ray laser at the Department of Energy’s SLAC National Accelerator Laboratory. This mile-long machine, a DOE Office of Science User Facility that opened in 2009, merges decades of particle accelerator know-how with cutting-edge X-ray and laser technology.

    SLAC LCLS
    SLAC LCLS Inside
    LCLS at SLAC

    Its unique X-ray laser pulses, a billion times brighter than any previous X-ray source on the planet, are the “ammo” in a high-tech shooting gallery with tiny samples as targets. With each direct X-ray hit comes an opportunity to unlock secrets hidden in the molecular structure of the sample.

    But it’s a whole lot harder than scoring bull’s-eyes on ducks at a carnival booth. At LCLS, the X-ray ammo is traveling at the speed of light, can be focused to a spot more than a million times smaller than a bullet, and the targets can be more than 10,000 times smaller than the typical shooting-gallery duck.

    Pulses last just quadrillionths of seconds, about the time it takes light to travel the breadth of a human hair. They’re fired 120 times per second, and in many cases have to hit tiny samples that are tumbling randomly so you can’t tell which way they’re facing when they’re hit. Each pulse can damage or destroy its target, so there are no second chances.

    Raising the stakes even higher, your targets may have taken a lot of time, effort and money to produce, you may need millions of direct hits to get conclusive results for your experiment and you have only a limited time to do that. Missed shots can be the difference between discovery and disappointment.

    To maximize the odds of success, SLAC researchers adapt techniques from other applications and invent new ways to precisely align, time and refresh samples, whether liquid, gas or solid, so they reliably connect with laser pulses. Here’s a look at five important techniques:
    1. Drop-on-Demand Systems
    1

    Like a dripping water faucet but with more complex physics behind it, a “drop on demand” system provides a precisely measured and timed supply of tiny liquid droplets containing whole or dissolved samples.

    Some of these systems in development borrow from inkjet printer technology developed in the 1970s. They can use “piezoelectric” crystals (see above), which change shape in response to electric current to precisely push out streams or droplets of liquid, or they can do this with acoustic waves or other applied pressure.

    2. Simple Liquid Jets
    2

    Jets are like mini squirt guns streaming samples of liquid or gel into the X-ray pulses. They’re often used to study delicate, nanoscale samples such as crystallized proteins, which offer an ideal X-ray window into a protein’s atomic structure.

    The jet’s nozzle can be shaped to produce a stream of the desired thickness – for instance, to accommodate crystals of a certain size. If the nozzle is too narrow, the samples can quickly clog it. And if the stream is too thick, the liquid solution can interfere with the quality of the crystal images.

    The simplest type of liquid jet, called a Rayleigh jet (see above), produces a stream as wide as its nozzle, and can also produce a flow of droplets for experiments.

    3. Virtual Nozzle Jets
    3
    A more complex jet, popular in LCLS experiments involving crystals, uses a flow of gas around the nozzle to further squeeze and narrow the liquid or gel stream. This design, called a “gas dynamic virtual nozzle” or “flow focusing” jet (see above), can create unbroken streams of liquid just millionths of an inch wide.

    Read about an experiment that used a “virtual nozzle” liquid jet.

    4. Aerosol Jets
    4

    If you want to reduce the amount of liquid surrounding samples – as you might when studying living viruses, cells or cell components – you can spray them from an aerosol jet, which produces a fine mist like the one from a perfume bottle. These aerosols may be propelled by gases or produced by electric currents that break sample-containing liquid into sprays of tiny droplets.

    Another sophisticated tool that’s been customized for LCLS is the aerodynamic lens system (see above). It uses streams of gas and a series of gun-like chambers to produce very narrow streams of liquid and a more regular spacing of samples. This allows researchers to deliberately hit and study individual particles.

    Read about an experiment that used an aerosol jet.

    5. Translation Stages
    5

    Researchers can study the properties of materials, such as the strength of exotic metals exposed to extreme temperatures and pressures, with motorized platforms called translation stages (see above) that rapidly move samples in a gridded pattern to continually expose fresh sections to the X-ray laser pulses.

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    This illustration shows a cutaway view of a type of sample system used at the Linac Coherent Light Source X-ray laser that jets samples in a superthin liquid or gel stream into its X-ray pulses. This system is known as a gas dynamic virtual nozzle. (SLAC National Accelerator Laboratory)

    While this method was in use prior to LCLS, it had to be customized to match the high repetition rate of LCLS pulses.

    See the full article here.

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    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 7:51 pm on December 4, 2014 Permalink | Reply
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    From SLAC: “Rattled Atoms Mimic High-temperature Superconductivity” 


    SLAC Lab

    December 4, 2014

    X-ray Laser Experiment Provides First Look at Changes in Atomic Structure that Support Superconductivity

    An experiment at the Department of Energy’s SLAC National Accelerator Laboratory provided the first fleeting glimpse of the atomic structure of a material as it entered a state resembling room-temperature superconductivity – a long-sought phenomenon in which materials might conduct electricity with 100 percent efficiency under everyday conditions.

    a
    In a high-temperature superconducting material known as YBCO, light from a laser causes oxygen atoms (red) to vibrate between layers of copper oxide that are just two molecules thick. (The copper atoms are shown in blue.) This jars atoms in those layers out of their normal positions in a way that likely favors superconductivity. In this short-lived state, the distance between copper oxide planes within a layer increases, while the distance between the layers decreases. (Jörg Harms/Max Planck Institute for the Structure and Dynamics of Matter)

    Researchers used a specific wavelength of laser light to rattle the atomic structure of a material called yttrium barium copper oxide, or YBCO. Then they probed the resulting changes in the structure with an X-ray laser beam from the Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility.

    SLAC LCLS
    SLAC LCLS Inside
    LCLS at SLAC

    They discovered that the initial exposure to laser light triggered specific shifts in copper and oxygen atoms that squeezed and stretched the distances between them, creating a temporary alignment that exhibited signs of superconductivity for a few trillionths of a second at well above room temperature – up to 60 degrees Celsius (140 degrees Fahrenheit). The scientists coupled data from the experiment with theory to show how these changes in atomic positions allow a transfer of electrons that drives the superconductivity.

    New Views of Atoms in Motion

    “This is a highly interesting state, even though it only exists for a short period of time,” said Roman Mankowsky of the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany, who was lead author of a report on the experiment in the Dec. 4 print issue of Nature. “When the laser excites the material, it shifts the atoms and changes the structure. We hope these results will ultimately help in the design of new materials to enhance superconductivity.”

    Sustaining such a state at room temperature would revolutionize many fields, making the electrical grid more efficient and enabling more powerful and compact computers. Traditional superconductors operate only at temperatures close to absolute zero. YBCO is one of a handful of materials discovered since 1986 that superconduct at somewhat higher temperatures; but they still have to be chilled to at least minus 135 degrees Celsius in order to sustain superconductivity, and scientists still don’t know what allows these so-called high-temperature superconductors to carry electricity with zero resistance.

    A Powerful Tool for Exploring Superconductivity

    Josh Turner, a SLAC staff scientist who has led other studies of YBCO at the LCLS, said powerful tools such as X-ray lasers have excited new interest in superconductor research by allowing researchers to isolate a specific property that they want to learn more about. This is important because high-temperature superconductors can exhibit a tangle of magnetic, electronic and structural properties that may compete or cooperate as the material moves toward a superconducting state. For example, another recently published LCLS study found that exciting YBCO with the same optical laser light disrupts an electronic order that competes with superconductivity.

    “What LCLS is now showing us is how these different properties change over short times,” Turner said. “We can actually see how the electrons or atoms are moving.”

    Mankowsky said future experiments at LCLS could try to sustain the superconducting state for longer periods, use a combination of experimental techniques to study how other properties evolve in the transition into the superconducting state and explore whether the same structural changes are at work in other high-temperature superconductors.

    Researchers from the National Center for Scientific Research in France, Paul Scherrer Institute in Switzerland, Max Planck Institute for Solid State Research in Germany, Swiss Federal Institute of Technology, College of France, University of Geneva, Oxford University in the United Kingdom, the Center for Free-Electron Laser Science in Germany, and University of Hamburg in Germany also participated in the study. The work was supported by the European Research Council, German Science Foundation, Swiss National Superconducting Center and Swiss National Science Foundation.

    See the full article here.

    Please help promote STEM in your local schools.

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    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 4:24 pm on December 4, 2014 Permalink | Reply
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    From SLAC: “X-ray Laser Reveals How Bacterial Protein Morphs in Response to Light” 


    SLAC Lab

    December 4, 2014

    A Series of Super-Sharp Snapshots Demonstrates a New Tool for Tracking Life’s Chemistry

    Human biology is a massive collection of chemical reactions, from the intricate signaling network that powers our brain activity to the body’s immune response to viruses and the way our eyes adjust to sunlight. All involve proteins, known as the molecules of life; and scientists have been steadily moving toward their ultimate goal of following these life-essential reactions step by step in real time, at the scale of atoms and electrons.

    Now, researchers have captured the highest-resolution snapshots ever taken with an X-ray laser that show changes in a protein’s structure over time, revealing how a key protein in a photosynthetic bacterium changes shape when hit by light. They achieved a resolution of 1.6 angstroms, equivalent to the radius of a single tin atom.

    m
    This illustration depicts an experiment at SLAC that revealed how a protein from photosynthetic bacteria changes shape in response to light. Samples of the crystallized protein (right), called photoactive yellow protein or PYP, were jetted into the path of SLAC’s LCLS X-ray laser beam (fiery beam from bottom left). The crystallized proteins had been exposed to blue light (coming from left) to trigger shape changes. Diffraction patterns created when the X-ray laser hit the crystals allowed scientists to recreate the 3-D structure of the protein (center) and determine how light exposure changes its shape. (SLAC National Accelerator Laboratory)

    “These results establish that we can use this same method with all kinds of biological molecules, including medically and pharmaceutically important proteins,” said Marius Schmidt, a biophysicist at the University of Wisconsin-Milwaukee who led the experiment at the Department of Energy’s SLAC National Accelerator Laboratory. There is particular interest in exploring the fastest steps of chemical reactions driven by enzymes — proteins that act as the body’s natural catalysts, he said: “We are on the verge of opening up a whole new unexplored territory in biology, where we can study small but important reactions at ultrafast timescales.”

    The results, detailed in a report published online Dec. 4 in Science, have exciting implications for research on some of the most pressing challenges in life sciences, which include understanding biology at its smallest scale and making movies that show biological molecules in motion.

    A New Way to Study Shape-shifting Proteins

    The experiment took place at SLAC’s Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility. LCLS’s X-ray laser pulses, which are about a billion times brighter than X-rays from synchrotrons, allowed researchers to see atomic-scale details of how the bacterial protein changes within millionths of a second after it’s exposed to light.

    SLAC LCLS
    SLAC LCLS Inside
    LCLS at SLAC

    “This experiment marks the first time LCLS has been used to directly observe a protein’s structural change as it happens. It opens the door to reaching even faster time scales,” said Sébastien Boutet, a SLAC staff scientist who oversees the experimental station used in the study. LCLS’s pulses, measured in quadrillionths of a second, work like a super-speed camera to record ultrafast changes, and snapshots taken at different points in time can be compiled into detailed movies.

    The protein the researchers studied, found in purple bacteria and known as PYP for “photoactive yellow protein,” functions much like a bacterial eye in sensing blue light. The mechanism is very similar to that of other receptors in biology, including receptors in the human eye. “Though the chemicals are different, it’s the same kind of reaction,” said Schmidt, who has studied PYP since 2001. Proving the technique works with a well-studied protein like PYP sets the stage to study more complex and biologically important molecules at LCLS, he said.

    Chemistry on the Fly

    In the LCLS experiment, researchers prepared crystallized samples of the protein, and exposed the crystals, each about 2 millionths of a meter long, to blue laser light before jetting them into the LCLS X-ray beam.

    The X-rays produced patterns as they struck the crystals, which were used to reconstruct the 3-D structures of the proteins. Researchers compared the structures of the proteins that had been exposed to light to those that had not to identify light-induced structural changes.

    “In the future we plan to study all sorts of enzymes and other proteins using this same technique,” Schmidt said. “This study shows that the molecular details of life’s chemistry can be followed using X-ray laser crystallography, which puts some of biology’s most sought-after goals within reach.”

    Researchers from the University of Wisconsin-Milwaukee and SLAC were joined by researchers from Arizona State University; Lawrence Livermore National Laboratory; University of Hamburg and DESY in Hamburg, Germany; State University of New York, Buffalo; University of Chicago; and Imperial College in London. The work was supported by the National Science Foundation, National Institutes of Health and Lawrence Livermore National Laboratory.

    See the full article here.

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  • richardmitnick 8:22 pm on December 3, 2014 Permalink | Reply
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    From SLAC: “SLAC, RadiaBeam Build New Tool to Tweak Rainbows of X-ray Laser Light” 


    SLAC Lab

    December 3, 2014

    ‘Dechirper’ Will Give Scientists More Control Over ‘Color Spectrum’ of LCLS X-ray Pulses

    The Department of Energy’s SLAC National Accelerator Laboratory has teamed up with Santa Monica-based RadiaBeam Systems to develop a device known as a dechirper, which will provide a new way of adjusting the range of energies within single pulses from SLAC’s X-ray laser.

    d
    Design drawing of the outer structure of a dechirper that will be used to tweak the “color range” of light pulses from SLAC’s X-ray laser, LCLS. Two dechirpers will be lined up in front of the LCLS undulator—a magnetic structure that generates ultrabright, ultrafast X-rays from bunches of electrons. (RadiaBeam Systems)

    i
    The inside of the dechirper consists of two parallel, 2-meter-long, flat aluminum rails. Electron bunches will travel through a variable gap between the rails at nearly the speed of light. (RadiaBeam Systems)

    r
    The aluminum rails have comb-like grooves that are half a millimeter deep and a quarter millimeter wide. The electron bunches “sense” the grooves, leading to a change in the energy spread of the X-rays they produce. (RadiaBeam Systems)

    “For many experiments it is important to use a specific X-ray energy so that we can study specific chemical elements in our samples,” says LCLS scientist William Schlotter. “The narrower the energy bandwidth, the more precisely we can study those elements.”

    Tweaking the ‘Color Spectrum’ of X-ray Pulses

    LCLS generates ultrabright and ultrashort X-ray pulses from packets of electrons that travel through a magnetic structure, called an undulator, at almost the speed of light. The properties of the electron bunches determine the characteristics of the X-ray light that they produce.

    un
    Working of the undulator. 1: magnets, 2: electron beam entering from the upper left, 3: synchrotron radiation exiting to the lower right

    Many experiments demand X-ray pulses that last only a few quadrillionths of a second, but it is difficult to make electron bunches this short. Therefore, scientists have turned to nature and adopted a solution reminiscent of a bird’s chirp. They create a spread of energies in the electron bunch, with the tail having more energy than the head. When electron bunches pass through another magnetic device known as a chicane, this so-called “energy chirp” allows lagging electrons in the tail to catch up with the ones in the head, creating shorter electron bunches, and thus shorter X-ray pulses.

    However, since the chirp consists of a spectrum of energies, the X-rays also have multiple energies—a rainbow of X-ray “colors” known as the energy bandwidth. Depending on the type of experiment, this can be an advantage or disadvantage, and researchers would like to have new tools to adjust the energy bandwidth to match their needs.

    As the name suggests, the dechirper’s primary task will be to minimize the chirp, i.e. to make pulses with a smaller spread in X-ray energies. Additionally, the dechirper can do the opposite and make X-ray pulses with a broader energy spectrum. In fact, many users have had a desire for a wider bandwidth since LCLS started operations in 2009, as LCLS scientist Sébastien Boutet points out.

    Precision Tool to Manipulate Electron Bunches

    SLAC scientists first proposed the idea for a dechirper in 2012 and, together with researchers from Lawrence Berkeley National Laboratory, demonstrated its feasibility in a test experiment at the Pohang Accelerator Laboratory in South Korea.

    The LCLS device, whose final design review will take place on Dec. 4, will consist of two flat, parallel aluminum rails, each 2 meters long, with comb-like grooves that are half a millimeter deep and a quarter millimeter wide. Two of these devices will be lined up in front of the undulator, with the electron beam traveling through the gap between the rails.

    Even though the electron bunches will not touch the rails, they will “sense” the grooves. These “bumps” along the electrons’ flight path will create a wake at the tail of the bunch, similar to the wake behind a boat gliding over water. “In this process, the tail loses energy while the front stays the same,” explains accelerator physicist Richard Iverson, the project lead at SLAC, where the technical requirements for the dechirper were specified.

    Varying the gap between the rails changes the effect on the electrons, allowing scientists to adjust the chirp of the electron bunches and, consequently, the energy bandwidth of the X-ray pulses generated in the undulator.

    What may sound like a relatively simple setup poses significant challenges for the manufacturing process. “The dechirper’s grooves are only as wide as three or four human hairs,” says project manager Marcos Ruelas at RadiaBeam, where the device is being designed and constructed. “Moreover, the rails must be very flat and smooth. Over the entire length of 4 meters, their height can only differ by 50 micrometers.” To meet these requirements, each 2-meter rail will be manufactured in four smaller blocks.

    The new device is expected to be installed at SLAC in August 2015. It will not only start providing LCLS users with more flexibility for their experiments, but will also become the test bed for dechirpers at SLAC’s next-generation LCLS-II facility and other X-ray lasers worldwide.

    Other key personnel of the project include Karl Bane, Paul Emma, Timothy Maxwell, Zhirong Huang, Gennady Stupakov and Zhen Zhang from SLAC’s Accelerator Directorate, as well as RadiaBeam’s Pedro Frigola, Mark Harrison and David Martin.

    See the full article here.

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  • richardmitnick 4:40 pm on November 21, 2014 Permalink | Reply
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    From SLAC: “Robotics Meet X-ray Lasers in Cutting-edge Biology Studies” 


    SLAC Lab

    November 21, 2014

    Platform Brings Speed, Precision in Determining 3-D Structure of Challenging Biological Molecules

    Scientists at the Department of Energy’s SLAC National Accelerator Laboratory are combining the speed and precision of robots with one of the brightest X-ray lasers on the planet for pioneering studies of proteins important to biology and drug discovery.

    The new system uses robotics and other automated components to precisely maneuver delicate samples for study with the X-ray laser pulses at SLAC’s Linac Coherent Light Source (LCLS). This will speed efforts to map the 3-D structures of nanoscale crystallized proteins, which are important for designing targeted drugs and synthesizing natural systems and processes.

    s
    This illustration shows an experimental setup used in crystallography experiments at SLAC’s Linac Coherent Light Source X-ray laser. The drum-shaped container at left stores supercooled crystal samples that are fetched by a robotic arm and delivered to another device, called a goniometer. The goniometer moves individual crystals through the X-ray beam, which travels from the pipe at upper left toward the lower right. A detector, right, captures X-ray diffraction patterns produced as the X-rays pass through the crystal samples. (SLAC National Accelerator Laboratory)

    i
    Equipment used in a highly automated X-ray crystallography system at SLAC’s Linac Coherent Light Source X-ray laser. The metal drum at lower left contains liquid nitrogen for cooling crystallized samples studied with LCLS’s intense X-ray pulses. (SLAC National Accelerator Laboratory)

    SLAC LCLS
    SLAC LCLS

    A New Way to Study Biology

    “This is an efficient, highly reliable and automated way to obtain high-resolution 3-D structural information from small sizes and volumes of samples, and from samples that are too delicate to study using other X-ray sources and techniques,” said Aina Cohen, who oversaw the development of the platform in collaboration with staff at LCLS and at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), both DOE Office of Science User Facilities.

    SLAC SSRL
    SLAC SSRL

    She is co-leader of the Macromolecular Crystallography group in the Structural Molecular Biology (SMB) program at SSRL, which has used robotic sample-handling systems to run remote-controlled experiments for a decade.

    The new setup at LCLS is described in the Oct. 31 edition of Proceedings of the National Academy of Sciences. It includes a modified version of a “goniometer,” a sample-handling device in use at SSRL and many other synchrotrons, as well as a custom version of an SSRL-designed software package that pinpoints the position of crystals in arrays of samples.

    LCLS, with X-ray pulses a billion times brighter than more conventional sources, has already allowed scientists to explore biological samples too small or fragile to study in detail with other tools. The new system provides added flexibility in the type of samples and sample-holders that can be used in experiments.

    Rather than injecting millions of tiny, randomly tumbling crystallized samples into the path of the pulses in a thin liquid stream – common in biology experiments at LCLS – the goniometer-based system places crystals one at a time into the X-ray pulses. This greatly reduces the number of crystals needed for structural studies on rare and important samples that require a more controlled approach.

    Early Successes

    “This system adapts common synchrotron techniques for use at LCLS, which is very important,” said Henrik Lemke, staff scientist at LCLS. “There is a large community of scientists who are familiar with the goniometer technique.”

    The system has already been used to provide a complete picture of a protein’s structure in about 30 minutes using only five crystallized samples of an enzyme, moved one at a time into the X-rays for a sequence of atomic-scale “snapshots.”

    It has also helped to determine the atomic-scale structures of an oxygen-binding protein found in muscles, and another protein that regulates heart and other muscle and organ functions.

    “We have shown that this system works, and we can further automate it,” Cohen said. “Our goal is to make it easy for everyone to use.”

    Many biological experiments at LCLS are conducted in air-tight chambers. The new setup is designed to work in the open air and can also be used to study room-temperature samples, although most of the samples used in the system so far have been deeply chilled to preserve their structure. One goal is to speed up the system so it delivers samples and measures the resulting diffraction patterns as fast as possible, ideally as fast as LCLS delivers pulses: 120 times a second.

    The goniometer setup is the latest addition to a large toolkit of systems that deliver a variety of samples to the LCLS beam, and a new experimental station called MFX that is planned at LCLS will incorporate a permanent version.

    Team Effort

    Developed through a collaboration of SSRL’s Structural Molecular Biology program and the Stanford University School of Medicine, the LCLS goniometer system reflects increasing cooperation in the science of SSRL and LCLS, Cohen said, drawing upon key areas of expertise for SSRL and the unique capabilities of LCLS. “The combined effort of staff at both experimental facilities was key in this success,” she said.

    In addition to staff at SLAC’s SSRL and LCLS and at Stanford University’s School of Medicine, researchers from SLAC’s Photon Science Directorate, the University of Pittsburgh School of Medicine, Howard Hughes Medical Institute, Montana State University, Lawrence Berkeley National Laboratory and the University of California, San Francisco also participated in this effort.

    The work was supported by the Department of Energy Office of Basic Energy Sciences, the SSRL Structural Molecular Biology Program via the DOE Office of Biological and Environmental Research, and the Biomedical Technology Research Resources program at the National Institute of General Medical Sciences, National Institutes of Health.

    See the full article here.

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  • richardmitnick 7:25 pm on November 17, 2014 Permalink | Reply
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    From SLAC: “SLAC X-ray Laser Brings Key Cell Structures into Focus” 


    SLAC Lab

    November 17, 2014

    Experiment is Important Step Toward Atomic-Scale Imaging of Intact Biological Particles

    Scientists have made high-resolution X-ray laser images of an intact cellular structure much faster and more efficiently than ever possible before. The results are an important step toward atomic-scale imaging of intact biological particles, including viruses and bacteria.

    The technique was demonstrated at the Linac Coherent Light Source (LCLS) at the Department of Energy’s SLAC National Accelerator Laboratory and reported in the Nov. 17 issue of Nature Photonics.

    art
    A 20-sided structure from a bacterial cell, called a carboxysome, is struck by an X-ray pulse (purple) at SLAC’s Linac Coherent Light Source. (SLAC National Accelerator Laboratory)

    An international team of scientists used LCLS, a DOE Office of Science User Facility, to produce tens of thousands of high-resolution images of the tiniest individual biological particles yet studied there – 20-sided structures called carboxysomes that are found in some bacterial cells and play a major role in Earth’s life-sustaining carbon cycle. Although these structures have been studied for years, much remains unknown about their inner workings.

    New Views of Bacteria’s Carbon-conversion Engines

    “In an experiment lasting only 12 minutes, we collected many high-quality images using a very small amount of sample,” said Janos Hajdu, a professor of biophysics at Uppsala University in Sweden, which led the research. “In the future you could conceivably get results within minutes that used to take five days for certain types of samples. We showed that with the right type of instruments and detectors, you can increase the throughput of X-ray lasers by a huge amount.”

    The results bolster the aims of the LCLS Single-Particle Imaging initiative, formally launched at SLAC in October in cooperation with the international scientific community, said Christoph Bostedt, a SLAC senior staff scientist who leads the initiative with staff scientist Andy Aquila. The initiative is working toward atomic-scale imaging for many types of biological samples by identifying and addressing technical challenges at LCLS.

    “As this work demonstrates, we are already achieving imaging of single particles today, and we are working to improve upon these capabilities,” Aquila said.

    Bostedt added, “We will tackle these hurdles by working with the community. LCLS managers have committed to support this effort with dedicated experimental time.”

    Biology ‘On the Fly’

    Carboxysomes are microscopic workhorses inside cyanobacteria, which carry out photosynthesis. They pull in carbon dioxide from their surroundings and use an enzyme to convert it to forms that other living things can use. An estimated 40 percent of the organic carbon on Earth was made in these cell structures. “A better understanding of the structure and function of these cell organelles could benefit carbon-cycle research,” said Dirk Hasse of Uppsala University, one of the paper’s lead authors.

    Because they vary in size from about 90 to 140 nanometers, or billionths of a meter, in diameter, it is difficult to crystallize these tiny structures for conventional X-ray studies of their structure.

    A 2011 study by members of the same international team had studied samples of a giant virus, called Mimivirus, using a similar experimental technique that jets samples in a finely focused aerosol spray into the path of the X-ray pulses.

    In the latest study they were able to achieve better resolution, showing features as small as 18 nanometers.

    The scientists said a new design for the “aerosol injector” that shot the samples in a thin stream toward the X-ray pulses was among the key improvements that allowed them to achieve higher-resolution images. They also improved data-analysis tools that automatically sorted the 70,000 images they collected and assembled them into distinct groups. These advances lay the foundation for accurate, high-throughput structure determination for individual biological samples and other types of samples.

    The resolution achieved in this first experiment was not high enough to reveal the interior of the carboxysomes, though the team said that upgrades to higher intensity and a narrower focus of LCLS X-rays could allow far more detailed explorations of many biological samples in this size range, including small viruses. “We haven’t yet reached the limits,” said Filipe Maia of Uppsala University, who participated in the study.

    Pushing the Limits

    Max Hantke of Uppsala University, a lead author of the study, said the ultrashort pulses of X-ray lasers offer important advantages over instruments like electron microscopes that are used to study biological samples.

    For example, the X-ray laser can be used to track ultrafast processes, such as how biological samples respond to pulses of light over time. “These types of experiments are not possible with other methods,” Hantke said.

    In addition to scientists from Uppsala University and SLAC, other researchers who participated in the study were from Lawrence Berkeley National Laboratory; Kansas State University; the National University of Singapore; the University of Melbourne in Australia; University of Rome in Italy; and DESY laboratory, PNSensor, Max Planck Institute for Extraterrestrial Physics and European XFEL, all in Germany.

    This work was supported by the Swedish Research Council, the Knut and Alice Wallenberg Foundation, the European Research Council, the Röntgen-Ångström Cluster, and Stiftelsen Olle Engkvist Byggmästare. The CAMP instrument used in the experiment was funded by the Max Planck Society.

    See the full article here.

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