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Archive for the ‘Scientific Highlights’ Category

‘Repulsive’ quantum magnet

Neutron measurements at Oak Ridge National Laboratory’s Spallation Neutron Source are giving physicists new insight into the behavior of quantum magnets. A research team led by Young-June Kim from the University of Toronto used neutron spectroscopy to observe a novel type of energy band repulsion in a magnetic insulator. The study adds to scientists’ understanding of quasiparticles, a theoretical concept that describes many particle interactions inside a material.

This work was conducted at SEQUOIA, SNS beam line 17. The team’s results are published in Nature Physics.

NIST, UC Davis Scientists Float New Approach to Creating Computer Memory

What can skyrmions do for you? These ghostly quantum rings, heretofore glimpsed only under extreme laboratory conditions, just might be the basis for a new type of computer memory that never loses its grip on the data it stores. Now, thanks to a research team including scientists from the National Institute of Standards and Technology (NIST),* the exotic ring-shaped magnetic effects have been coaxed out of the physicist’s deepfreeze with a straightforward method that creates magnetic skyrmions under ambient room conditions. The achievement brings skyrmions a step closer for use in real-world data storage as well as other novel magnetic and electronic technologies.

It took a trip to NIST to confirm the skyrmions’ existence. Creating them involves placing arrays of tiny magnetized cobalt disks atop a thin film made of cobalt and palladium; the NIST Center for Neutron Research (NCNR) had just developed a state-of-art polarized neutron reflectometer that was well suited to study their lab results. Working with NCNR scientists, the team used neutrons to see through the disk to spot the skyrmions underneath. The team also captured images of the whirling configurations in the disk array at NIST’s Center for Nanoscale Science and Technology (CNST) and Lawrence Berkeley Laboratory. This work was published in Nature Communications.

Read the full story here.

Neutron Beams Reveal How Two Potential Pieces of Parkinson’s Puzzle Fit

To understand diseases like Parkinson’s, the tiniest of puzzles may hold big answers. That’s why a team including scientists from the National Institute of Standards and Technology (NIST) have determined* how two potentially key pieces of the Parkinson’s puzzle fit together, in an effort to reveal how the still poorly understood illness develops and affects its victims.

This puzzle is a tough one because its pieces are not only microscopic but three-dimensional, and can even change shape. The pieces are protein molecules whose lengthy names are abbreviated as GCase and α-syn. The two proteins wrap around each other and take on a complicated shape before attaching themselves to the membrane surface inside a neural cell in a victim’s brain.

To get a better handle on how these proteins operate in the body, the team—which also included scientists from the National Institutes of Health (NIH) and Carnegie Mellon University—came to the NIST Center for Neutron Research (NCNR) to get a picture of how the two proteins combine into a single unit called a complex that interacts with cell membranes. Using techniques including neutron reflectometry, the team teased out the first-ever structural picture of the GCase/α-syn complex, including their shape change. This work was published in Journal of Biological Chemistry.

Read the full story here.

Unlocking Enzyme Synthesis of Rare Sugars to Create Drugs with Fewer Side Effects

In a paper published in Structure, a team led by the U.S. Department of Energy’s Oak Ridge National Laboratory reported the pioneering use of neutron and X-ray crystallography and high performance computing to study how the enzyme D-xylose isomerase, or XI, can cause a biochemical reaction in natural sugar to produce rare sugars. Unlike drugs made from natural sugar compounds, drugs made from rare sugars do not interfere with cellular processes. As a result, rare sugars have important commercial and biomedical applications as precursors for the synthesis of different antiviral and anti-cancer drugs with fewer side effects. Using X-ray and neutron crystallography combined with theoretical calculations, the team figured out how the enzyme isomerizes L-arabinose into the rare sugar L-ribulose and then epimerizes the latter into another rare sugar L-ribose. Importantly, L-ribose is the enantiomer, a mirror image, of the ubiquitous D-ribose that is a building block of DNA and RNA.

Langan , A.K. Sangha, T. Wymore, J.M. Parks, Z.K. Yang, B.L. Hanson, Z. Fisher, S.A. Mason, M.P. Blakeley, V.T. Forsyth, J.P. Glusker, H.L. Carrell, J.C. Smith, D.A. Keen, D.E. Graham, A. Kovalevsky. “L-Arabinose Binding, Isomerization, and Epimerization by D-Xylose Isomerase: X-Ray/Neutron Crystallographic and Molecular Simulation Study,” Structure. 22:9 (2014): 1287–1300. http://dx.doi.org/10.1016/j.str.2014.07.002

Improving Plant-based Battery with Neutrons, Simulation

A team from Oak Ridge National Laboratory and the University of Tennessee studied carbon fibers made from lignin, a woody plant polymer known as, and found a mixture of perfectly spherical nanoscale crystallites distributed within a fibrous matrix. They found the lignin fiber’s unique structure could make it useful as a battery anode, potentially improving upon graphitic materials found in most lithium-ion batteries. Lignin, a low-cost byproduct of the pulp, paper and biofuels industries, could be transformed into a cheaper version of highly engineered graphite through a simple and industrially scalable manufacturing process. The team ran neutron scattering experiments at ORNL’s Spallation Neutron Source (SNS) to analyze how lignin-based fiber samples reacted with lithium. Using neutron data, they developed computational models and ran simulations on supercomputers including the Oak Ridge Leadership Computing Facility’s (OLCF) Titan, supported by DOE’s Office of Science, and UT’s Kraken, supported by the National Science Foundation. The team detailed its approach in the Journal of Applied Crystallography. The initial combination of neutron experiments and simulation gave the UT-ORNL team a first glimpse into how the material’s structure affects its overall performance. Now that they have confirmed their model’s accuracy, the researchers plan on applying the technique to how the material’s structure changes with and without added lithium, mimicking the charging and discharging cycles of a real battery.

N.W. McNutt, O. Rios, M. Feygenson, T.  E. Proffen and D. J. Keffer. “Structural analysis of lignin-derived carbon composite anodes,” Journal of Applied Crystallography. 47:5 (2014): 1577-1584. http://journals.iucr.org/j/issues/2014/05/00/pd5045/index.html

Study compares structures of Huntington’s disease protein

Neutron scattering research at the Department of Energy’s Oak Ridge National Laboratory has revealed clear structural differences in the normal and pathological forms of a protein involved in Huntington’s disease. Huntington’s disease, an incurable neurodegenerative disorder, starts as a genetic mutation that leads to an overabundance of “huntingtin” protein fragments, which form clumps in the brain. Valerie Berthelier of the University of Tennessee Graduate School of Medicine, who co-led the study published in Biophysical Journal with ORNL’s Chris Stanley, said the goal was to establish a baseline understanding of huntingtin’s structure in order to eventually determine the true structural basis of Huntington’s disease. The study’s results showed key differences in the ways mutant and normal huntingtin proteins take shape. The disease protein, for instance, initially forms aggregates of one to two peptides, whereas the normal version makes bigger aggregates, gathering seven or eight peptides together. These data on the very early stages of protein aggregate formation support a growing focus of the research in the amyloid field. Amyloid disorders, such as Parkinson’s, Alzheimer’s and Huntington’s, all involve protein aggregation phenomena leading to a disease.

Perevozchikova, Tatiana et al. “Investigating the Structural Impact of the Glutamine Repeat in Huntingtin Assembly,” Biophysical Journal. 107:2 (2014): 411 – 421. http://www.cell.com/biophysj/abstract/S0006-3495(14)00602-X

Neutrons Explore the Quantum Nature of Magnetically Frustrated Systems

Neutron scattering and heat capacity techniques were used to investigate two frustrated magnets with similar structure, but different sized spins (S).The research team, led by McMaster University, found the molybdate pyrochlore oxide material, Lu2Mo2O7 (S=1) undergoes a transition to a spin glass ground state, while the oxynitride Lu2Mo2O5N2 (S=1/2) possesses a quantum spin liquid ground state. The smaller spin of the oxynitride is subjected to larger quantum fluctuations that favor a quantum spin liquid state. The preparation of oxynitride samples makes it possible to study magnetic frustration for different spin magnitudes without changing the magnetic lattice. Inelastic neutron scattering conducted at the Cold Neutron Chopper Spectrometer (CNCS) instrument at the Spallation Neutron Source of the Oak Ridge National Laboratory was used to probe the length and energy scales of spin fluctuations.

L. Clark, G. J. Nilsen, E. Kermarrec, G. Ehlers, K. S. Knight, A. Harrison, J. P. Attfield and B. D. Gaulin. “From Spin Glass to Quantum Spin Liquid Ground States in Molybdate Pyrochlores.” Phys. Rev. Lett. 113 (2014): 117201. http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.117201

Unlocking Enzyme Synthesis of Rare Sugars to Create Drugs with Fewer Side Effects

A team led by the U.S. Department of Energy’s Oak Ridge National Laboratory has unlocked the enzymatic synthesis process of rare sugars, which are useful in developing drugs with low side effects using a process more friendly to the environment.

Neutrons Reveal Structural Tunability of Magnetic Exchange Couplings

Inelastic neutron scattering experiments reveal that the effective magnetic exchange couplings in NaFeAs are smaller and more isotropic than those in the heavily studied AFe2As2 family. These results provide evidence that the energy scale of the magnetic excitations, which are thought to influence the superconducting transition temperature, is controlled by the position of As atoms above the Fe layers.

Spin waves, measured using the ARCS chopper spectrometer at SNS, were studied in the antiferromagnetic ordered phase of NaFeAs, the parent compound of NaFe1−x CoxAs family of iron pnictide superconductors. NaFeAs was chosen because it has weak AF ordered moment, low superconducting transition temperature, and large As height, significantly different from AFe2As2.

C. Zhang, L.W. Harriger, Z. Yin, W. Lv, M. Wang, G. Tan, Y. Song, D. L. Abernathy, W. Tian, T. Egami, K. Haule, G. Kotliar, and P. Dai, “Effect of Pnictogen Height on Spin Waves in Iron Pnictides”. Phys. Rev. Lett. 112 (2014): 217202. http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.217202

Spatiotemporal stress and structure evolution in dynamically sheared polymer-like micellar solutions

The complex, nonlinear flow behavior of soft materials transcends industrial applications, smart material design and non-equilibrium thermodynamics. A long-standing, fundamental challenge in soft-matter science is establishing a quantitative connection between the deformation field, local microstructure and macroscopic dynamic flow properties i.e., the rheology. Here, a new experimental method is developed using simultaneous small angle neutron scattering (SANS) and nonlinear oscillatory shear rheometry to investigate the spatiotemporal microstructure evolution of a polymer-like micellar (PLM) solution. We demonstrate the novelty of nonlinear oscillatory shear experimental methods to create and interrogate metastable material states. These include a precursory state to the shear banded condition as well as a disentangled, low viscosity state with an inhomogeneous supra-molecular microstructure flowing at high shear rates. This new experimental evidence provides insight into the complexities of the shear banding phenomenon often observed in sheared complex fluids and provides valuable data for quantitatively testing non-equilibrium theory.

A. Kate Gurnon, Carlos R. Lopez-Barron, Aaron P. R. Eberle, Lionel Porcar and Norman J. Wagner, Soft Matter, 2014,10, 2889-2898
DOI:10.1039/c3sm53113a