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News Article | October 5, 2016
Site: www.nature.com

Recently discovered Dirac and Weyl semimetals3, 4, 5, 6, 7, 8, 9, 10 host topologically protected degeneracy of four and two electronic bands, respectively, at isolated points in the Brillouin zone close to the Fermi level (E )2, 4, 19. The low-energy excitations in these materials are described by Dirac or Weyl Hamiltonians, as appropriate, of the relativistic quantum field theory, leading to the realization of the chiral anomaly20, 21 and topological surface Fermi arcs3, 9, 10. Owing to weaker symmetry constraints, condensed matter systems can realize quasiparticles that have no analogues in high-energy theories11, 12, 13, 14, 15, 16, 17, 18, hosting new physical phenomena. For example, in the presence of spin–orbit coupling, a valence and a conduction band with different mirror eigenvalues can touch along lines in mirror-invariant planes of the Brillouin zone, forming a so-called accidental nodal loop (ANL). The ANL materials are predicted to host special ‘drumhead’ surface states18, which were argued to provide a route to higher-temperature superconductivity22, 23. The spectrum of a nodal-chain fermion described here is illustrated in Fig. 1. The nodal chain consists of nodal loops, which are distinct from ANLs in that they are guaranteed to appear in the vicinity of the Fermi level (E ) in certain non-centrosymmetric materials provided that their crystal structure has a non-symmorphic glide-plane symmetry g = {σ|t}, formed by a reflection σ, followed by a translation by a fraction of a primitive lattice vector, t. For several space groups listed in Fig. 1, such non-symmorphic nodal loops (NSNLs) appear on mutually orthogonal high-symmetry planes, touching each other at isolated points on a high-symmetry axis. Thus, a chain of double degeneracy is formed that goes across the entire Brillouin zone. We first describe the building blocks of nodal chains—NSNLs. For spin–orbit coupled systems, , where k is the electron momentum and t is the in-plane component of t; consequently, the possible eigenvalues of g are , which are k-dependent whenever t ≠ 0 (ref. 24). The relation Γ · t  = 0 (mod π/2) holds for any of the four in-plane time-reversal invariant momenta (TRIMs) Γ , defined as Γ  = −Γ  + G, with G a reciprocal lattice vector (see Supplementary Information). This definition makes it possible for the two TRIMs Γ to satisfy so that the glide eigenvalues η (k) are ±i at k = Γ and ±1 at k = Γ . Hence, along any in-plane path p that connects Γ to Γ , the glide eigenvalues η (k) must smoothly evolve from (+i, −i) to (+1, −1), as illustrated in Fig. 2a. However, in time-reversal-symmetric (Θ-symmetric) systems (see Supplementary Information for a generalization to antiferromagnetic systems), the bands form Kramers pairs, which are degenerate at TRIMs and carry complex-conjugate eigenvalues. Because the eigenvalues are no longer complex conjugates at Γ , they belong to different Kramers doublets, meaning that there are several Kramers pairs that switch partners along p, as shown in Fig. 2b. This argument holds for any in-plane path p, and so there exists a nodal loop (the NSNL) separating the two TRIMs, shown as a red loop in Fig. 2a. A similar glide-plane argument plays a crucial role in realizing the hour-glass fermions12 on the surfaces of certain insulators, but here we describe a three-dimensional metallic bulk excitation. The illustration in Fig. 2b shows that NSNLs appear in materials in which bands come in quadruplets. Therefore, the NSNL is formed between valence and conduction bands whenever the number of electrons per unit cell is irrespective of all further material details. (Material examples of NSNLs formed by valence or conduction bands, and the ways in which NSNLs can be tuned to E , are discussed in Supplementary Information.) The topological characterization and the existence of the drumhead surface states18 is similar for ANLs and NSNLs (see Supplementary Information). Despite this similarity, we argue that low-energy excitations produced by ANLs and NSNLs are intrinsically distinct. Unlike ANLs, NSNLs are enforced by the symmetry of the underlying crystal structure. Moreover, NSNLs in Θ-symmetric, non-centrosymmetric systems always enclose a TRIM, and so a single nodal loop contains a time-reversed image of each Bloch state in addition to the state itself. In fact, if inversion-symmetry-breaking terms are smoothly tuned to zero in a NSNL Hamiltonian, then the NSNL shrinks into a Dirac point4, 19 (see Supplementary Information). This feature has immediate consequences in electron transport. In particular, as outlined in Supplementary Information, application of a magnetic field in the direction orthogonal to the NSNL results in field-driven topological phase transitions. We find that the Landau levels of the conduction and valence bands touch at certain values B of the magnetic field, resulting in pumping of charge (equivalent to e/2 per area covered by a magnetic flux quantum, where e is the elementary charge) to the surface of the sample that is parallel to the plane of the NSNL. Hence, a step change in the Hall response of the metallic surface state is expected for magnetic field values B . The response of the NSNLs to the mirror-symmetry-breaking, in-plane magnetic field is distinct from that of the ANLs. Although the Landau spectrum is gapped25 for ANLs, it is always gapless for NSNLs. The crossing of the two Landau levels is protected by the product symmetry that survives the application of the in-plane field. The gapless structure of the Landau levels suggests unusual transport properties for materials hosting NSNLs when an electric field is aligned with the in-plane magnetic field, similar to case of the chiral anomaly in Weyl and Dirac semimetals20, 21. This dependence of the response on the direction of the magnetic field distinguishes NSNLs from all other known topological excitations. Having established the NSNLs, we can now address systems with two glide planes. Such systems can accommodate nodal chains formed by a pair of touching NSNLs located in mutually orthogonal planes, while the bands at the touching point are still only doubly degenerate. The criteria for the occurrence of a nodal chain are: (1) the system has to be symmetric under two inequivalent glide planes g  = {σ |t } such that the criterion of equation (1) is fulfilled for the two TRIMs Γ , which are located on the intersection of the two glide-invariant planes, for both translation vectors t ; and (2) the two bands forming the chain must belong to two-dimensional representations at Γ , which split into one-dimensional representations on the high-symmetry line connecting Γ and Γ . Out of the 230 space groups26, those satisfying the above criteria for two mutually orthogonal glide planes are listed in Fig. 1. The space group number 110 (I4 cd) is discussed separately in Supplementary Information. In all the cases shown in Fig. 1, we find that at least one additional point of fourfold degeneracy, formed by two Weyl points of opposite chirality, is present at a high-symmetry point on the boundary of the Brillouin zone. A nodal chain represents a new topological excitation, distinct from a collection of NSNLs. To see this, first note that the two NSNLs that form a nodal chain cannot be separated. The argument provided above for the appearance of the NSNL guarantees that there must be an odd number of band crossings along the high-symmetry line connecting Γ and Γ . The non-trivial transport properties of the nodal chain can be inferred from the above analysis of NSNLs in magnetic fields (a detailed study of the transport properties will be reported elsewhere (T.B., Q.S.W., A.A.S., manuscript in preparation)), suggesting several distinct scenarios for the Landau-level spectrum. Here we proceed with the analysis of the topological surface states of nodal chains that we illustrate using a particular real material example. We found the nodal-chain state in iridium tetrafluoride (IrF ). The orthorhombic crystal structure of this compound belongs to space group number 43 (Fdd2). The primitive unit cell contains two formula units27 so that the number of electrons satisfies equation (2). Each iridium site is surrounded by an octahedron of six fluorine atoms, four of which are shared with the neighbouring octahedra. The octahedra form a bipartite lattice as shown in Fig. 3a, b (see Supplementary Information for a detailed description of the crystal structure). The space group contains two mutually orthogonal glide planes: g and g , formed by a reflection about the (100) and (010) plane, respectively, followed by a translation of (1/4, 1/4, 1/4) in the reduced coordinates. Possible antiferromagnetic ordering with a Néel temperature of less than about 100 K was reported for IrF in magnetic susceptibility measurements27. A paramagnetic phase is expected to occur at temperatures above the Néel temperature, which are still accessible for angle-resolved photoemission spectroscopy (ARPES). We first discuss the paramagnetic phase, in which the crystal symmetries and band filling guarantee the presence of a nodal chain corresponding to the bottom left scenario in Fig. 1. To study paramagnetic IrF we performed first-principles calculations as detailed in Supplementary Information. The obtained band structure is shown in Fig. 3c. We indeed find a nodal chain, plotted in Fig. 4a, consisting of two NSNLs in the (100) and (010) planes. Both NSNLs cross the chemical potential four times, resulting in topologically protected touching points between electron and hole pockets (arrows in Fig. 3d). Similar touchings of carrier pockets, although of different topological origin, were predicted for type-II Weyl semimetals11 and ANLs16, 18, 23. These Fermi-surface touching points can be probed using soft X-ray ARPES, and have been argued to be important for potential higher-temperature superconducting phases22, 23, 28. The nodal chain produces non-trivial topological surface states on the (100) surface of IrF , as shown in Fig. 3e, f. The projection of the (010) NSNL ((100) NSNL) onto the surface Brillouin zone is a line (oval), shown dashed in Fig. 3f. Fermi arcs arise from the touching points of the Fermi pockets. For the projection of the (100) NSNL (region 1 in Fig. 3h), a single such arc produced by the drumhead state emerges from the touching point. However, the touching points that appear on a linear projection of the (010) NSNL produce two Fermi arcs, consistent with the fact that there are two such Fermi pocket touchings that project onto the same point in the surface Brillouin zone. The arcs originating on different NSNLs are connected either directly or through a carrier pocket. Moreover, the invariant computed along the gapped, Θ-symmetric plane projected onto the magenta path in Fig. 3f is non-trivial. Hence, the path corresponds to an edge of a two-dimensional topological insulator, and has to host an odd number of Kramers pairs of edge states29. In accord with the observed connectivity of Fermi arcs, there is a single Kramers pair of such edge states (see Supplementary Information). To understand why both Fermi arcs of the (010) NSNL appear on the same side of its projection onto the (100) surface, we need to expose the approximate chiral symmetry that is present in the material. We constructed a tight-binding model for the pseudospin-1/2 orbitals located on the iridium sites that represent the two sublattices of the IrF structure, and fitted the parameters to reproduce the first-principles results (see Supplementary Information). We found that the avoided crossing along the Z–Γ line in Fig. 3c originates from the hoppings within the sublattices. The amplitudes of these hoppings are more than three times smaller than those of the inter-sublattice hoppings, meaning that there exists a weakly broken chiral symmetry in IrF , relating the two sublattices of the crystal structure. The chiral symmetry can be restored in the model by setting the intra-sublattice hoppings to zero. The corresponding band structure is shown in Fig. 3c, and it can be seen that the gap along the Z–Γ line now vanishes, and an additional nodal loop appears. It connects to the nodal chain, thus creating a nodal net, shown in Fig. 4. The projection of the additional nodal loop onto the (100) surface is shown in green in Fig. 3h. Endowed with the chiral symmetry, the Hamiltonian allows for an additional topological classification (see Supplementary Information), which predicts two/one/zero surface modes to exist in the regions labelled 2/1/0 in Fig. 3h. In the presence of the chiral symmetry, all these regions are topologically distinct and separated by nodal loops. When the chiral symmetry is weakly broken in real IrF , only the parity of the number of surface states remains topologically protected and the additional nodal loop becomes gapped. However, because the breaking of the chiral symmetry is weak, the location of surface modes in the surface Brillouin zone of IrF is inherited from the chiral-symmetric structure. The possible antiferromagnetic ordering in IrF at low temperatures preserves the nodal-chain structure if the magnetic moment is aligned with the [001] axis. In fact, the nodal chain survives weak breaking of time-reversal symmetry, but not the breaking of glide planes. We also looked for other possible nodal chain candidates. Several reports27, 30 of stable XY crystals (X = Ir, Ta, Re; Y = F, Cl, Br, I) with lattices formed of octahedra, similar to the IrF lattice, exist, but with only fragmentary crystallographic data. Assuming these compounds crystallize in the same space group as IrF , we carried out an exhaustive first-principles study and found nodal chains in each of them (see Supplementary Information). We find that the particular shape of the chain and its position relative to the Fermi level depend on the lattice constants of the unit cell, suggesting the possibility of fine tuning with uniaxial or hydrostatic strains. The prediction of the new nodal-chain state of matter in the IrF class of materials opens up avenues for further study of novel physical properties associated with these compounds. The presence of both strongly and weakly correlated compounds in this family enables the interplay between the nodal-chain topology and electron–electron interactions, as well as magnetism, to be studied. The application of strains that break one of the glide planes in these compounds provides a route for a similar study of the NSNL phase, as well as for experimental probing of the anomalous magnetoelectric response predicted here for NSNLs.


News Article | December 20, 2016
Site: www.eurekalert.org

Scientists at Washington University School of Medicine in St. Louis have detailed the structure of a molecule that has been implicated in Alzheimer's disease. Knowing the shape of the molecule -- and how that shape may be disrupted by certain genetic mutations -- can help in understanding how Alzheimer's and other neurodegenerative diseases develop and how to prevent and treat them. The study is published Dec. 20 in the journal eLife. The idea that the molecule TREM2 is involved in cognitive decline -- the hallmark of neurodegenerative diseases, including Alzheimer's -- has gained considerable support in recent years. Past studies have demonstrated that certain mutations that alter the structure of TREM2 are associated with an increased risk of developing late-onset Alzheimer's, frontal temporal dementia, Parkinson's disease and sporadic amyotrophic lateral sclerosis (ALS). Other TREM2 mutations are linked to Nasu-Hakola disease, a rare inherited condition that causes progressive dementia and death in most patients by age 50. "We don't know exactly what dysfunctional TREM2 does to contribute to neurodegeneration, but we know inflammation is the common thread in all these conditions," said senior author Thomas J. Brett, PhD, an assistant professor of medicine. "Our study looked at these mutations in TREM2 and asked what they do to the structure of the protein itself, and how that might impact its function. If we can understand that, we can begin to look for ways to correct it." The analysis of TREM2 structure, completed by first author, Daniel L. Kober, a doctoral student in Brett's lab, revealed that the mutations associated with Alzheimer's alter the surface of the protein, while those linked to Nasu-Hakola influence the "guts" of the protein. The difference in location could explain the severity of Nasu-Hakula, in which signs of dementia begin in young adulthood. The internal mutations totally disrupt the structure of TREM2, resulting in fewer TREM2 molecules. The surface mutations, in contrast, leave TREM2 intact but likely make it harder for the molecule to connect to proteins or send signals as normal TREM2 molecules would. TREM2 lies on the surface of immune cells called microglia, which are thought to be important "housekeeping" cells. Via a process called phagocytosis, such cells are responsible for engulfing and cleaning up cellular waste, including the amyloid beta that is known to accumulate in Alzheimer's disease. If the microglia lack TREM2, or the TREM2 that is present doesn't function properly, the cellular housekeepers can't perform their cleanup tasks. "Exactly what TREM2 does is still an open question," Brett said. "We know mice without TREM2 have defects in microglia, which are important in maintaining healthy brain biology. Now that we have these structures, we can study how TREM2 works, or doesn't work, in these neurodegenerative diseases." TREM2 also has been implicated in other inflammatory conditions, including chronic obstructive pulmonary disease and stroke, making the structure of TREM2 important for understanding chronic and degenerative diseases throughout the body, he added. This work was supported by the National Institutes of Health (NIH), grant numbers R01-HL119813, R01-AG044546, R01-AG051485, R01-HL120153, R01-HL121791, K01-AG046374, T32-GM007067, K08-HL121168, and P50-AG005681-30.1; the Burroughs-Wellcome Fund; the Alzheimer's Association, grant number AARG-16-441560; and the American Heart Association, grant number PRE22110004. Results were derived from work performed at Argonne National Laboratory (ANL) Structural Biology Center. ANL is operated by U. Chicago Argonne, LLC, for the U.S. DOE, Office of Biological and Environmental Research, supported by grant number DE-AC02-06CH11357. Kober DL, Alexander-Brett JM, Karch CM, Cruchaga C, Colonna M, Holtzman MJ, Brett TJ. Neurodegenerative disease mutations in TREM2 reveal a functional surface and distinct loss-of-function mechanisms. eLife. Dec. 20, 2016. Washington University School of Medicine's 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient-care institutions in the nation, currently ranked sixth in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.


News Article | September 8, 2016
Site: www.greencarcongress.com

« Volkswagen Group & Anhui Jianghuai Automobile (JAC) jointly to develop EVs in China; new JV focused on NEVs | Main | Solaris Bus to offer BAE Systems hybrid electric drive on its vehicles » The Department of Energy’s Exascale Computing Project (ECP) announced its first round of funding with the selection of 15 application development proposals for full funding and seven proposals for seed funding, representing teams from 45 research and academic organizations. The awards, totaling $39.8 million, target advanced modeling and simulation solutions to specific challenges supporting key DOE missions in science, clean energy and national security, as well as collaborations such as the Precision Medicine Initiative with the National Institutes of Health’s National Cancer Institute. Exascale refers to high-performance computing systems capable of at least a billion billion calculations per second, or a factor of 50 to 100 times faster than the nation’s most powerful supercomputers in use today. The application efforts will help guide DOE’s development of a U.S. exascale ecosystem as part of President Obama’s National Strategic Computing Initiative (NSCI). DOE, the Department of Defense and the National Science Foundation have been designated as NSCI lead agencies, and ECP is the primary DOE contribution to the initiative. The ECP’s multi-year mission is to maximize the benefits of high performance computing (HPC) for US economic competitiveness, national security and scientific discovery. In addition to applications, the DOE project addresses hardware, software, platforms and workforce development needs critical to the effective development and deployment of future exascale systems. First-round funding (see list below) includes a broad set of modeling and simulation applications with a focus on portability, usability and scalability. A key consideration in the selection process was each team’s emphasis on co-design of the applications with the ECP’s ongoing development of hardware, software and computational capabilities, including physical models, algorithms, scalability and overall performance. Projects will be funded in the following strategic areas: energy security, economic security, scientific discovery, climate and environmental science, and healthcare. Leadership of the Exascale Computing Project comes from six DOE national laboratories: The Office of Science’s Argonne, Lawrence Berkeley, and Oak Ridge national labs, and NNSA’s Los Alamos, Lawrence Livermore, and Sandia national labs. The full list of application development awards follows: Full Funding: Computing the Sky at Extreme Scales, Salman Habib (ANL) with LANL, LBNL Exascale Deep Learning and Simulation Enabled Precision Medicine for Cancer, Rick Stevens (ANL) with LANL, LLNL, ORNL, NIH/NCI Exascale Lattice Gauge Theory Opportunities and Requirements for Nuclear and High Energy Physics, Paul Mackenzie (FNAL) with BNL, TJNAF, Boston University, Columbia University, University of Utah, Indiana University, UIUC, Stony Brook, College of William & Mary Molecular Dynamics at the Exascale: Spanning the Accuracy, Length and Time Scales for Critical Problems in Materials Science, Arthur Voter (LANL) with SNL, University of Tennessee An Exascale Subsurface Simulator of Coupled Flow, Transport, Reactions and Mechanics, Carl Steefel (LBNL) with LLNL, NETL QMCPACK: A Framework for Predictive and Systematically Improvable Quantum- Mechanics Based Simulations of Materials, Paul Kent (ORNL) with ANL, LLNL, SNL, Stone Ridge Technology, Intel, Nvidia Coupled Monte Carlo Neutronics and Fluid Flow Simulation of Small Modular Reactors, Thomas Evans (ORNL, PI) with ANL, INL, MIT NWChemEx: Tackling Chemical, Materials and Biomolecular Challenges in the Exascale Era, T. H. Dunning, Jr. (PNNL), with Ames, ANL, BNL, LBNL, ORNL, PNNL, Virginia Tech High-Fidelity Whole Device Modeling of Magnetically Confined Fusion Plasma, Amitava Bhattacharjee (PPPL) with ANL, ORNL, LLNL, Rutgers, UCLA, University of Colorado Data Analytics at the Exascale for Free Electron Lasers, Amedeo Perazzo (SLAC) with LANL, LBNL, Stanford Transforming Combustion Science and Technology with Exascale Simulations, Jackie Chen (SNL) with LBNL, NREL, ORNL, University of Connecticut Cloud-Resolving Climate Modeling of the Earth's Water Cycle, Mark Taylor (SNL) with ANL, LANL, LLNL, ORNL, PNNL, UCI, CSU The ECP is a collaborative effort of two DOE organizations: the Office of Science and the National Nuclear Security Administration. As part of President Obama’s National Strategic Computing initiative, ECP was established to develop a capable exascale ecosystem, encompassing applications, system software, hardware technologies and architectures, and workforce development to meet the scientific and national security mission needs of DOE in the mid-2020s timeframe.


« Honda begins sales of Clarity Fuel Cell in Japan; targeting 200 units first year | Main | UQM receives new follow-on order from Proterra to support increased demand for electric buses » The US Department of Energy (DOE) selected 33 small businesses to work directly with DOE national labs to accelerate the commercialization of new clean energy technologies. The department’s Office of Energy Efficiency and Renewable Energy is investing nearly $6.7 million under Round 1 of the new Small Business Vouchers (SBV) pilot. For Round 1, the small businesses and laboratories will collaborate on advancing a number of clean energy technologies, including water, wind, bioenergy, solar, buildings, vehicles, fuel cells, geothermal technologies, and advanced manufacturing. The selected small businesses will work with scientists at nine department laboratories: Oak Ridge National Laboratory (ORNL); National Renewable Energy Laboratory (NREL); Lawrence Berkeley National Laboratory (LBNL); Sandia National Laboratories (SNL); Pacific Northwest National Laboratory (PNNL); Idaho National Laboratory (INL); Los Alamos National Laboratory (LANL); Argonne National Laboratory (ANL); and Lawrence Livermore National Laboratory (LLNL). SBV is a collaborative, national effort that provides $20 million for US companies to help improve industry awareness of national laboratory capabilities and provide small and mid-size businesses access to the resources available within the national laboratory system. Vouchers range from $50,000-300,000. The companies were competitively chosen from a pool of hundreds of applications. Almost 40% of the businesses represent new DOE-industry partnerships and relationships with the national labs. Building on the tremendous response of Round 1, the department also has begun accepting applications for Round 2 of the SBV pilot. A total of $13 million worth of funding remains; over the course of the year, up to 100 vouchers will be awarded.


News Article | March 2, 2017
Site: phys.org

This single finding led to a worldwide investigation that's spanned a century. While it resolved one scientific debate, it created many more. The Department of Energy's Office of Science and its predecessors have spent decades supporting scientists investigating the mystery of why superconductivity occurs under a variety of circumstances. The answer to this question holds major opportunities for scientific and technological development. About six percent of all electricity distributed in the U.S. is lost in transmission and distribution. Because superconductors don't lose current as they conduct electricity, they could enable ultra-efficient power grids and incredibly fast computer chips. Winding them into coils produces magnetic fields that could be used for highly-efficient generators and high-speed magnetic levitation trains. Unfortunately, technical challenges with both traditional and "high temperature" superconductors restrict their use. "To the extent that Tesla and Edison introducing the use of electricity revolutionized our society, ambient superconductivity would revolutionize it once again," said J.C. Séamus Davis, a physicist who works with the Center for Emergent Superconductivity, a DOE Energy Frontier Research Center. The How and Why of Superconductivity Kamerlingh Onnes' discovery set off a flurry of activity. Despite his grand visions, most of what scientists found only reinforced superconductors' limitations. One of the first big breakthroughs came nearly half a century after Kamerlingh Onnes' initial finding. While most researchers thought superconductivity and magnetism couldn't co-exist, Alexei A. Abrikosov proposed "Type II" superconductors that can tolerate magnetic fields in 1952. Abrikosov continued his research at DOE's Argonne National Laboratory (ANL) and later won the Nobel Prize in Physics for his contributions. The next big leap came in 1957, when John Bardeen, Leon Cooper, and John Robert Schrieffer proposed the first theory of why superconductivity occurs. Their theory, made possible by the support of DOE's predecessor, the Atomic Energy Commission, also won them the Nobel Prize in physics. Their theory contrasts how some metals work under normal conditions with how they act at extremely low temperatures. Normally, atoms are packed together in metals, forming regular lattices. Similar to the spokes and rods of Tinkertoys, the metals' positively charged ions are bonded together. In contrast, negatively charged free electrons (electrons not tied to an ion) move independently through the lattice. But at extremely low temperatures, the relationship between the electrons and the surrounding lattice changes. A common view is that the electrons' negative charges weakly attract positive ions. Like someone tugging the middle of a rubber band, this weak attraction slightly pulls positive ions out of place in the lattice. Even though the original electron has already passed by, the now displaced positive ions then slightly attract other electrons. At near absolute zero, attraction from the positive ions causes electrons to follow the path of the ones in front of them. Instead of travelling independently, they couple into pairs. These pairs flow easily through metal without resistance, causing superconductivity. Unfortunately, all of the superconductors that scientists had found only functioned near absolute zero, the coldest theoretically possible temperature. But in 1986, Georg Bednorz and K. Alex Müller at IBM discovered copper-based materials that become superconducting at 35 K (-396 F). Other scientists boosted these materials' superconducting temperature to close to 150 K (-190 F), enabling researchers to use fairly common liquid nitrogen to cool them. In the last decade, researchers in Japan and Germany discovered two more categories of high-temperature superconductors. Iron-based superconductors exist in similar conditions to copper-based ones, while hydrogen-based ones only exist at pressures more than a million times that of Earth's atmosphere. But interactions between the electron pairs and ions in the metal lattice that Bardeen, Cooper, and Schrieffer described couldn't explain what was happening in copper and iron-based high temperature superconductors. "We were thrown into a quandary," said Peter Johnson, a physicist at Brookhaven National Laboratory (BNL) and director of its Center for Emergent Superconductivity. "These new materials challenged all of our existing ideas on where to look for new superconductors." In addition to being scientifically intriguing, this conundrum opened up a new realm of potential applications. Unfortunately, industry can only use "high-temperature" superconductors for highly specialized applications. They are still too complex and expensive to use in everyday situations. However, figuring out what makes them different from traditional ones may be essential to developing superconductors that work at room temperature. Because they wouldn't require cooling equipment and could be easier to work with, room temperature superconductors could be cheaper and more practical than those available today. Several sets of experiments supported by the Office of Science are getting us closer to finding out what, if anything, high-temperature superconductors have in common. Evidence suggests that magnetic interactions between electrons may be essential to why high-temperature superconductivity occurs. All electrons have a spin, creating two magnetic poles. As a result, electrons can act like tiny refrigerator magnets. Under normal conditions, these poles aren't oriented in a particular way and don't interact. However, copper and iron-based superconductors are different. In these materials, the spins on adjacent iron sites have north and south poles that alternate directions – oriented north, south, north, south and so on. One project supported by the Center for Emergent Superconductivity examined how the ordering of these magnetic poles affected their interactions. Scientists theorized that because magnetic poles were already pointing in opposite directions, it would be easier than usual for electrons to pair up. To test this theory, they correlated both the strength of bonds between electrons (the strength of the electron pairs) and the direction of their magnetism. With this technique, they provided significant experimental evidence of the relationship between superconductivity and magnetic interactions. Other experiments at a number of DOE's national laboratories have further reinforced this theory. These observations met scientists' expectations of what should occur if superconductivity and magnetism are connected. Researchers at ANL observed an iron-based superconductor go through multiple phases before reaching a superconducting state. As scientists cooled the material, iron atoms went from a square structure to a rectangular one and then back to a square one. Along the way, there was a major change in the electrons' magnetic poles. While they were originally random, they assumed a specific order right before reaching superconductivity. At DOE's Ames Laboratory, researchers found that adding or removing electrons from an iron-based superconducting material changed the direction in which electricity flowed more easily. Researchers at BNL observed that superconductivity and magnetism not only co-exist, but actually fluctuate together in a regular pattern. Unfortunately, electron interactions' complex nature makes it difficult to pinpoint exactly what role they play in superconductivity. Research at BNL found that as scientists cooled an iron-based material, the electron spins' directions and their relationship with each other changed rapidly. The electrons swapped partners right before the material became superconducting. Similarly, research at ANL has showed that electrons in iron-based superconductors produce "waves" of magnetism. Because some of the magnetic waves cancel each other out, only half of the atoms demonstrate magnetism at any one time. These findings are providing new insight into why superconductors behave the way they do. Research has answered many questions about them, only to bring up new ones. While laboratories have come a long way from Kamerlingh Onnes' hand-blown equipment, scientists continue to debate many aspects of these unique materials. Explore further: Electron spin could be the key to high-temperature superconductivity


« Volvo Cars to launch UK’s largest autonomous driving trial | Main | Onboard Dynamics receives $3M from ARPA-E, others for innovative CNG refueling technology » Volkswagen is working with partners from industry and science on the German Federal Ministry for Economic Affairs and Energy’s SLAM research project (Schnellladenetz für Achsen und Metropolen, Fast charging network for road axes and metropolitan areas). The SLAM project has a total budget of €12.9 million (US$14.6 million) and will receive support from the Federal Ministry for Economic Affairs and Energy to the extent of €8.7 million (US$9.8 million) by August 2017. The German government designated SLAM as one of seven “flagship projects in electric mobility”. A central component of SLAM is the “Golden Test Device” prototype co-developed by Volkswagen which will be unveiled at the Hannover Messe industrial trade show. The Golden Test Device is a standardized testing device to check quickly and cost-effectively the compatibility of new electric vehicles and charging stations produced by different manufacturers. A further aim is to provide an internationally accepted testing reference for connecting electric vehicles to charging stations. Volkswagen will be showing a prototype of the device at the joint stand of the United States Department of Energy/ANL and the Joint Research Centre of the European Commission at the Hannover Messe. Volkswagen took into account all the technical requirements for vehicles and charging stations and defined various test scenarios in collaboration with national and international partners to develop the device. SLAM’s mission includes setting up a fund-based research network of up to 600 fast-charging stations to collect basic data for the research and analysis of suitable charging infrastructures according to the CCS-DC standard (combined charging system). This includes simulation and location scenarios to forecast demand for new charging stations, developing business models for site operators and a uniform access and billing system. SLAM includes the development of CCS to support charging at more than 150 kW and also takes into account conditions for private investors. Volkswagen’s project partners are the BMW Group, Daimler AG, Porsche AG, Deutscher Genossenschaftsverlag, EnBW, the RWTH Aachen University and the Institute of Human Factors and Technology Management (IAT, Stuttgart).


News Article | February 15, 2017
Site: cerncourier.com

Designing and building the advanced accelerator structures for CERN’s High-Luminosity LHC is a major challenge that requires international collaboration. Paola Catapano tours two labs in the US that are helping to develop superconducting focusing magnets and crab cavities for the project. Inside the IB3 Tech Building at Fermilab on the outskirts of Chicago, a heavy-duty machine several metres long slowly winds a flat superconducting cable. Watching the bespoke coil winder – called the Spirex and manufactured by Italian firm SELVA – in action, and the meticulous attention to detail from the coil’s specialist operators, is mesmerising. Their task is to fabricate the precision coils that will form the core of novel magnets for CERN’s High-Luminosity LHC (HL-LHC) project, scheduled to begin operation in the early 2020s. “It has to make 50 turns in total, 22 on the inner layer and 28 on the outer,” explains Fred Nobrega, of Fermilab’s magnet-systems department. The main challenge is the niobium-tin (Nb Sn) material, he says. “Bend it and it breaks like spaghetti.” The HL-LHC magnets will be built from Nb Sn, a new conductor used for the first time in an accelerator. Unlike copper, however,  Nb Sn is extremely brittle. Winding turns around the ends of the coil is particularly difficult, says Nobrega, and new chemical and heat treatments are being developed in the current R&D phase of the project at Fermilab to address this issue. The aim is to move from the prototype stage directly to the mass production of 45 long coils that are uniform and of high quality. A further 45 coils will be manufactured more than 1000 km away at Brookhaven National Laboratory (BNL). The HL-LHC relies on a number of innovative magnet and accelerating technologies, most of which are not available off-the-shelf. Key to the new accelerator configuration are powerful superconducting dipole and quadrupole magnets with field strengths of 11 and 12 T, respectively (for comparison, the superconducting niobium-titanium dipoles that guide protons around the existing LHC have fields of around 8.3 T. The new quadrupoles will be installed on either side of the LHC collision points to increase the total number of proton–proton collisions by a factor 10, therefore boosting the chances of a discovery. Although the project requires modifications to just 5% of the current LHC configuration (see article on p28), each one of the HL-LHC’s key innovative technologies pose exceptional challenges that involve several institutes around the world. Fermilab has a glorious history in superconductivity. It was here that the first large superconducting magnet accelerator was built, for example. “But more than that, it was shown that [superconducting magnets] could be reliably employed in a collider experiment for hours and hours of stable beams,” says physicist Giorgio Bellettini, who was spokesperson of the CDF experiment at Fermilab’s Tevatron collider during the mid-1990s at the time the top quark was discovered there. “The LHC experience is built upon this previous large endeavour.” The plan is to develop and build half of the focusing magnets for the HL-LHC in the US. These have the specific project labels Q1 and Q3, and are a collaboration between three laboratories: Fermilab, BNL and Lawrence Berkeley National Laboratory in California. Nb Sn technology, whose development has been supported by the US Department of Energy, was not applicable to accelerator magnets until around a decade ago. Now, Nb Sn magnets are the technology of choice. The prototypes being developed here are 4 m long, and once assembled with the surrounding “cold mass” to keep them below the superconducting operational temperature of Nb Sn, they will grow to around twice this length. The innovative feature of these magnets is their very large aperture – 150 mm in diameter – which is necessary to focus the proton beams more tightly in the interaction points. It also allows greater control of the stress on the magnets and the coils induced by the large magnetic field, explains Giorgio Apollinari, who joined Fermilab in the early days and is now director of the US LHC Accelerator Research Program (LARP). No magnet today can achieve fields of 12 T with such a big opening, which is three times larger than that of the existing LHC dipoles. This is a new development introduced by the LARP team, explains Apollinari, and it took several years to go from 70, then 90 to 120 and now 150 mm required by the HL-LHC. “And then you have to have all the infrastructure necessary to build the magnets, test the magnets, make sure they work, measure the field quality and hopefully send them to CERN for installation in the beamline in 2025.” Fermilab and the other LARP laboratories have successfully built 1 m-long short models to demonstrate that the technology meets the technical requirements, and the components are working exactly as expected. Now the teams are building longer prototypes with the correct length, aperture and all other design features. The next step is to build a full prototype with four coils, to complete the quadrupole configuration of the magnets, this coming spring. Similar magnets are being prototyped at CERN with a more ambitious length of 7.5 m. The final product from the US will be a 60 cm-diameter 4 m-long basic magnet containing a hole for the HL-LHC beam pipe. Twenty of these structures will be built in total, 10 in the US and 10 at CERN, of which 16 will be installed and the rest kept as spares. “This is collaboration in physics at its best,” explains Apollinari. “Everybody is trying to go faster, but we are looking at what each other does openly and learning from each other.” Over at Fermilab’s sister laboratory, Argonne National Laboratory (ANL) some 40 km away, the other substantial part of the US contribution to the HL-LHC project is gathering pace. This involves novel “crab”-cavity technology, which is needed both to increase the luminosity and reduce so-called beam–beam parasitic effects that limit the collision efficiency of the accelerator. Unlike standard radiofrequency cavities, which accelerate charged particles in the direction along their path, crab cavities provide a transverse deflection of the beam which causes it to rotate. The cavities are made from pure niobium and therefore require strict control from contamination via chemical processing. ANL specialises in superconducting cavities with a wide range of geometries, and a joint facility for the chemical processing of cavities is in place. ANL’s extensive experience with superconducting cavities includes the Argonne Tandem Linac Accelerator System (ATLAS). Built and operated by the physics division, this is the world’s first superconducting linear accelerator for heavy ions, working at energies in the vicinity of the Coulomb barrier to study the properties of the nucleus. It is for this machine that niobium was used for the first time in an accelerator, in 1977, and for which “quarter-wave” superconducting cavities were developed. “We developed superconducting cavities for a whole variety of projects, for the ATLAS accelerator, Fermilab, BNL, SLAC and of course for the HL-LHC at CERN,” says ANL accelerator scientist Michael Kelly. We meet in the lobby of the ANL physics division, next to a piece of the laboratory’s history: Enrico Fermi’s original “chopper”, a mechanical rotating shutter to select neutrons built in 1947 as part of ANL’s original nuclear-physics programme. “Today we process crab cavities for the HL-LHC, trying to achieve the highest possible accelerating or crabbing voltages, by making a very very clean surface on the cavity,” he explains. ANL’s chemical processing facility has recently been enlarged to accommodate new buffer chemical polishing and electro-polishing rooms. Wearing a complete set of clean-room garments as we enter the facility, electronic engineer Brent Stone explains the importance of surface processing. “A feature of niobium is that a damaged layer is formed as it is mined from the ground and goes through all different processes, so when the niobium is transformed into cavities we need to remove a 120–150 μm-thick damaged layer,” he says. “Inside these layers you can have inclusions that may affect their performance and it is critical to remove them.” Several steps, and journeys, are required to process the cavities. After the application of acids to remove material from the surface, the cavities undergo two cycles in ultrasonic tanks before being rinsed at high pressure and returned to Fermilab to be degassed in vacuum at high temperatures. They are then taken back to ANL for final chemical treatment, cleaning and assembly in the clean room. Finally, the cavities processed at Argonne are sent to BNL were they are cooled down to liquid-helium temperatures to test if they meet the crabbing voltage required for the HL-LHC. “One of the cavities processed has just very easily achieved its design goal,” says Kelly proudly, before we take leave of the laboratory. The crab cavities are less advanced than the magnets for the HL-LHC, both at CERN and at Fermilab. But efforts are progressing on schedule on both sides of the Atlantic. Two different designs have been developed for the HL-LHC interaction points: vertical plane for ATLAS and horizontal plane for CMS. Both cavity designs originated from LARP, the LHC accelerator R&D programme created by the DOE in 2005 while the LHC was nearing its completion. “Without that foresight we wouldn’t have the HL-LHC today,” says Apollinari.


News Article | January 19, 2016
Site: www.theenergycollective.com

The Department of Energy (DOE) announced it will fund up to $220 million of R&D projects to modernize America’s aging power grid infrastructure over the next three years. Accompanying this, DOE released its ¨Grid Modernization Multi-Year Program Plan¨ (MYPP), a strategic blueprint that informs and guides a national R&D agenda involving a consortium of DOE National Laboratories. The Grid Modernization Laboratory Consortium (GMLC) is made up of 14 DOE National Laboratories and dozens of industry, academia, and state and local government agency partners across the country, according to a DOE news release. DOE is providing funding for an initial set of 88 grid modernization projects. While a few focus specifically on microgrids, many, if not all, of them will advance development of power technologies that could be of use to microgrid project developers, utilities and other relevant stakeholders. In addition to the recently established Microgrid System Laboratory, the Grid Modernization Program reflects the potential for a distributed, smarter energy system to meet national energy objectives such as decarbonization, energy independence, and resilience from storms and terrorist attacks. Enhancing the security, reliability and resiliency of U.S. grid infrastructure and reducing carbon emissions are among the main objectives of DOE’s grid modernization plan and the new R&D funding, Energy Secretary Ernest Moniz explained. “Modernizing the U.S. electrical grid is essential to reducing carbon emissions, creating safeguards against attacks on our infrastructure, and keeping the lights on,” Secretary Moniz was quoted as saying. ¨This public-private partnership between our National Laboratories, industry, academia, and state and local government agencies will help us further strengthen our ongoing efforts to improve our electrical infrastructure so that it is prepared to respond to the nation’s energy needs for decades to come.” A full list of the Grid Modernization Initiative projects, participating laboratories and partners, as well as additional information is available on DOE’s website. Among them, UPS, Waste Management, Burns McDonnell, Harshaw Trane, LG&E and the State of Kentucky will carry out a 2-year, $1 million ¨Industrial Microgrid Analysis and Design for Energy Security and Resiliency.¨ Also directed specifically at advancing microgrid technology, Alaska state agencies, universities and Intelligent Energy systems have banded together to form the Alaska Microgrid Partnership, which is to develop a programmatic approach and framework that provides the basis for stakeholders to reduce diesel fuel consumption in remote microgrids by at least 50 percent and improve system reliability, security and resiliency without increasing system lifecycle costs. The DOE National Renewable Energy Laboratory (NREL) is participating in 44 of the 88 initial grid modernization R&D projects. GMLC co-chair and NREL Associate Laboratory Director Bryan Hannegan highlighted how GMLC illustrates a promising new approach to leveraging the resources of DOE National Labs, academic researchers and private sector power industry participants. “The Grid Modernization Laboratory Consortium is a new way of efficiently leveraging the strengths and capabilities of America’s national laboratories to deploy new concepts and technologies that will make the grid cleaner, more productive, and more secure,¨ Hannegan stated. ¨The projects announced today are an important first step towards achieving the DOE vision of a modernized grid for the nation.” DOE has invested more than $4.5 billion in grid modernization and smart grid projects via American Recovery & Reinvestment Act funding. Those investments are paying dividends in communities throughout the nation, reducing electricity costs while at the same time improving efficiency, reliability, resiliency and security, DOE highlights. ¨In Tennessee, for example, as a result of Chattanooga’s Smart Grid Investment Grant (SGIG) project, reliability increased by 45 percent. In Georgia, an electric cooperative deployed advanced metering infrastructure under the SGIG program, and reduced its operational costs by 65 percent. Service is restored faster after weather-related grid outages and emissions have been reduced. In addition, consumers are now able to better manage their own consumption, saving money and electricity.¨ Microgrid Projects Project 8: Industrial Microgrid Analysis and Design for Energy Security and Resiliency Investigation, development, and analysis of the risks, costs, and benefits of a microgrid utilizing renewable energy systems at the UPS WorldPort and Centennial Hub facilities. Develop a roadmap to help industries evaluate microgrid adoption by defining institutional and regulatory challenges associated with development of industrial-based resilient systems. Deliver to stakeholders an integrated distributed resource planning and optimization platform, hosted online, able to identify meaningful behind-the-meter DER adoption patterns, potential microgrid sites and demand-side resources, and evaluate the impacts of high renewable penetration feeders on the distribution and transmission grid. Partners: ANL, BNL, LBNL, LLNL, NREL, SLAC, California PUC, Pacific Gas and Electric (PG&E), Southern California Ediso (SCE), Metropolitan Council of Governments, New York State Energy Research and Development Authority (NYSERDA) Improve physical security of the Idaho Falls distribution system by testing smart reconfiguration, intelligent DR utilizing loads as a resource, controlled islanding, black start procedures for emergency service, and resynchronization in the presence of DERs. Develop a design basis framework and programmatic approach to assist stakeholders in their efforts to reduce diesel fuel consumption by at least 50% in Alaska’s remote microgrids without increasing system lifecycle costs, while improving overall system reliability, security, and resilience. Three campuses (PNNL, UW and WSU) will develop and test a range of tranactive control activities on each of the 3 campuses.  They will also develop the ability to coordinate across these three campuses to provide coordinated services to the PNW power system and their serving distribution utilities based upon the transactive response of key loads on the campuses.  The UW will emphasize energy storage and coordination for peak management and provision of flexibility.  The WSU campus will leverage its microgrid and major campus loads and thermal storage to deliver transactive response.  And PNNL will advance controls in its new SEB grid building and other campus loads to help the City of Richland better manage it’s demand limits.  OE and BTO collaborated in the design and cost share of the project. The post DOE Announces Grid Modernization R&D Projects, Partners, and Funding appeared first on Microgrid Media.


News Article | October 31, 2016
Site: www.businesswire.com

NEW YORK--(BUSINESS WIRE)--As losses for U.S. auto ABS continue their steady climb, some lenders are responding by holding the line on underwriting quality, according to the latest monthly auto loan ABS index from Fitch Ratings. Prime and subprime auto loan ABS annualized net losses (ANL) have increased in each of the last three months. Prime annualized net losses hit 0.70%, the highest rate since early 2011, while subprime ANL crossed the 9% mark for the second time in 2016. U.S. auto loan ABS


News Article | December 1, 2016
Site: www.businesswire.com

NEW YORK--(BUSINESS WIRE)--Losses fell for U.S. prime auto ABS while subprime losses continued their slow climb last month, according to the latest monthly index results from Fitch Ratings. Prime auto loan ABS annualized net losses (ANL) declined on a monthly basis in October, while subprime losses rose 32 bps to 9.61%. Subprime ANL remain within levels recorded earlier this year. Prime 60+ day delinquencies declined to 0.68% in October, improving 2.7% month-over-month (MOM). The rate last mont

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