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Oak Ridge, TN, United States

Oak Ridge National Laboratory is a multiprogram science and technology national laboratory managed for the United States Department of Energy by UT-Battelle. ORNL is the largest science andenergy national laboratory in the Department of Energysystem by acreage. ORNL is located in Oak Ridge, Tennessee, near Knoxville. ORNL's scientific programs focus on materials,neutron science, energy, high-performance computing,systems biology and national security.ORNL partners with the state of Tennessee, universities and industries to solve challenges in energy, advanced materials, manufacturing, security and physics.The laboratory is home to several of the world's top supercomputers including the world's second most powerful supercomputer ranked by the TOP500, Titan, and is a leading neutron science and nuclear energy research facility that includes the Spallation Neutron Source and High Flux Isotope Reactor. ORNL hosts the Center for Nanophase Materials science, the BioEnergy Science Center, and the Consortium for Advanced Simulation of Light-Water Reactors. Wikipedia.

Lin Z.,Zhejiang University | Liang C.,Oak Ridge National Laboratory
Journal of Materials Chemistry A | Year: 2015

Lithium-sulfur (Li-S) batteries supply a theoretical specific energy 5 times higher than that of lithium-ion batteries (2500 vs. ∼500 W h kg-1). However, the insulating properties and polysulfide shuttle effects of the sulfur cathode and safety concerns of the lithium anode in liquid electrolytes are still key limitations to practical use of traditional Li-S batteries. In this review, we start with a brief discussion on fundamentals of Li-S batteries and key challenges associated with conventional liquid cells. We then introduce the most recent progress in liquid systems, including sulfur positive electrodes, lithium negative electrodes, and electrolytes and binders. We discuss the significance of investigating electrode reaction mechanisms in liquid cells using in situ techniques to monitor the compositional and morphological changes. We also discuss the importance of this game-changing shift, moving from traditional liquid cells to recently developed solid cells, with positive advances in both solid electrolytes and electrode materials. Finally, the opportunities and perspectives for future research on Li-S batteries are presented. © The Royal Society of Chemistry 2015.

Cho K.T.,Lawrence Berkeley National Laboratory | Mench M.M.,University of Tennessee at Knoxville | Mench M.M.,Oak Ridge National Laboratory
Physical Chemistry Chemical Physics | Year: 2012

In this study, the high resolution hydrogen-deuterium contrast radiography method was applied to elucidate the impact of the micro-porous layer (MPL) on water distribution in the porous fuel cell media. At the steady state, deuterium replaced hydrogen in the anode stream, and the large difference in neutron attenuation of the D 2O produced at the cathode was used to track the produced water. It was found that the water content peaked in the cathode-side diffusion media (DM) for the cell without MPL, but with an MPL on the anode and cathode DM, the peak water amount was pushed toward the anode, resulting in a relatively flattened water profile through components and demonstrating a liquid barrier effect. Additionally, the dynamic water behavior in diffusion media was analyzed to understand the effect of a MPL and operating conditions. The water content in the DM changed with applied current, although there is a significant amount of residual liquid content that does not appear to be part of capillary channels. The effect of the MPL on irreducible saturation in DM and cell performance was also investigated. This journal is © the Owner Societies 2012.

Humble T.S.,Oak Ridge National Laboratory
IEEE Communications Magazine | Year: 2013

The physical layer describes how communication signals are encoded and transmitted across a channel. Physical security often requires either restricting access to the channel or performing periodic manual inspections. In this tutorial, we describe how the field of quantum communication offers new techniques for securing the physical layer. We describe the use of quantum seals as a unique way to test the integrity and authenticity of a communication channel and to provide security for the physical layer. We present the theoretical and physical underpinnings of quantum seals including the quantum optical encoding used at the transmitter and the test for non-locality used at the receiver. We describe how the envisioned quantum physical sublayer senses tampering and how coordination with higher protocol layers allows quantum seals to influence secure routing or tailor data management methods. We conclude by discussing challenges in the development of quantum seals, the overlap with existing quantum key distribution cryptographic services, and the relevance of a quantum physical sublayer to the future of communication security. © 1979-2012 IEEE.

Garten C.T.,Oak Ridge National Laboratory
Geoderma | Year: 2011

The aim of this study was to compare the turnover time of labile soil carbon (C), in relation to temperature and soil texture, in several forest ecosystems that are representative of large areas of North America. Carbon and nitrogen (N) stocks, and C:N ratios, were measured in the forest floor, mineral soil, and two mineral soil fractions (particulate and mineral-associated organic matter, POM and MOM, respectively) at five AmeriFlux sites along a latitudinal gradient in the eastern United States. Sampling at four sites was replicated over two consecutive years. With one exception, forest floor and mineral soil C stocks increased from warm, southern sites (with fine-textured soils) to cool, northern sites (with more coarse-textured soils). The exception was a northern site, with less than 10% silt-clay content, that had a soil organic C stock similar to the southern sites. A two-compartment model was used to calculate the turnover time of labile soil organic C (MRT U) and the annual transfer of labile C to stable C (k 2) at each site. Moving from south to north, MRT U increased from approximately 5 to 14years. Carbon-13 enrichment factors (ε), that described the rate of change in δ 13C through the soil profile, were associated with soil C turnover times. Consistent with its role in stabilization of soil organic C, silt-clay content was positively correlated (r=0.91; P≤0.001) with parameter k 2. Latitudinal differences in the storage and turnover of soil C were related to mean annual temperature (MAT, °C), but soil texture superseded temperature when there was too little silt and clay to stabilize labile soil C and protect it from decomposition. Each site had a relatively high proportion of labile soil C (nearly 50% to a depth of 20cm). Depending on unknown temperature sensitivities, large labile pools of forest soil C are at risk of decomposition in a warming climate, and losses could be disproportionately higher from coarse textured forest soils. © 2011 Elsevier B.V..

Jackson P.,CSIRO | Beste A.,Oak Ridge National Laboratory | Attalla M.I.,CSIRO
Physical Chemistry Chemical Physics | Year: 2012

Twenty-five transition structures (TS's) for CO 2 fixation by up to four base molecules (ammonia or ammonia + water) were located using M06-2X/6-311++G(d,p). All lead to either carbamate (NH 2CO 2 -) or bicarbonate (HCO 3 -) products. Single-point energies at CCSD(T)/maug-cc-pVTZ//M06-2X/6-311++G(d,p) were added to SM8/M06-2X/6-311++G(d,p) energies to obtain best-estimate aqueous activation energies. All theories agree that: (i) NH 2CO 2 - formation has a lower free energy of activation (best est. 44-45 kJ mol -1) than HCO 3 - formation (best est. 86 kJ mol -1), and (ii) free energies of activation for CO 2 fixation are lowered when an ammonia molecule accepts the proton from the nucleophilic base. The theory also supports a key role for ammonium ions in the observed decomposition of NH 2CO 2 - near pH 9. © 2012 the Owner Societies.

Thomas J.,Oak Ridge National Laboratory
SAE International Journal of Passenger Cars - Mechanical Systems | Year: 2014

Vehicle manufacturers among others are putting great emphasis on improving fuel economy (FE) of light-duty vehicles in the U.S. market, with significant FE gains being realized in recent years. The U.S. Environmental Protection Agency (EPA) data indicates that the aggregate FE of vehicles produced for the U.S. market has improved by over 20% from model year (MY) 2005 to 2013. This steep climb in FE includes changes in vehicle choice, improvements in engine and transmission technology, and reducing aerodynamic drag, rolling resistance, and parasitic losses. The powertrain related improvements focus on optimizing in-use efficiency of the transmission and engine as a system, and may make use of what is termed downsizing and/or downspeeding. This study quantifies recent improvements in powertrain efficiency, viewed separately from other vehicle alterations and attributes (noting that most vehicle changes are not completely independent). A methodology is outlined to estimate powertrain efficiency for the U.S city and highway cycle tests using data from the EPA vehicle database. Comparisons of common conventional gasoline powertrains for similar MY 2005 and 2013 vehicles are presented, along with results for late-model hybrid electric vehicles, the Nissan Leaf and the Chevy Volt. © 2014 SAE International. All rights reserved.

Chen H.,University of Tennessee at Knoxville | Peet J.,Konarka Technologies | Hu S.,University of Tennessee at Knoxville | Azoulay J.,University of California at Santa Barbara | And 3 more authors.
Advanced Functional Materials | Year: 2014

This manuscript reports the mixing behavior, interdiffusion, and depth profile of 1-[3-(methoxycarbonyl)propyl]-1-phenyl-[6,6]C61 (PCBM):low-bandgap (LBG) polymer thin films that are formed by thermally annealing initial bilayers. The extent of mixing of PCBM is higher in polymers that include the 2,1,3-benzothiadiazole (BT) unit than in polymers that incorporate the 2,1,3-benzooxadiazole (BO) unit. This difference is ascribed to the enhanced mixing behavior of PCBM with the benzothiadiazole functionality than with benzooxadiazole functionality, which is attributed to preferred intermolecular interactions. The increased polymer/fullerene mixing is found to be crucial for optimal device performance. A decrease of polymer/fullerene mixing reduces the donor/acceptor interface, which lowers the probability of exciton dissociation and charge generation. Moreover, low PCBM mixing provides limited pathways for electron transport out of a miscible region, due to long distances between adjacent PCBM in such a miscible phase. This inhibits electron transport and increases the recombination of free charge carriers, resulting in a decrease in short circuit current and device performance. These results further exemplify the importance of the thermodynamic mixing behavior of the polymer:fullerene pair in designing next-generation conjugated polymers for organic photovoltaic (OPV) applications, as this controls the final morphology of the OPV active layer. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gruene T.,University of Gottingen | Hahn H.W.,University of Gottingen | Luebben A.V.,University of Gottingen | Meilleur F.,North Carolina State University | And 2 more authors.
Journal of Applied Crystallography | Year: 2014

Some of the improvements in SHELX2013 make SHELXL convenient to use for refinement of macromolecular structures against neutron data without the support of X-ray data. The new NEUT instruction adjusts the behaviour of the SFAC instruction as well as the default bond lengths of the AFIX instructions. This work presents a protocol on how to use SHELXL for refinement of protein structures against neutron data. It includes restraints extending the Engh & Huber [Acta Cryst. (1991), A47, 392-400] restraints to H atoms and discusses several of the features of SHELXL that make the program particularly useful for the investigation of H atoms with neutron diffraction. SHELXL2013 is already adequate for the refinement of small molecules against neutron data, but there is still room for improvement, like the introduction of chain IDs for the refinement of macromolecular structures. © 2014 International Union of Crystallography.

Terentyev D.,Belgian Institute for Nuclear Sciences | Osetsky Yu.N.,Oak Ridge National Laboratory | Bacon D.J.,University of Liverpool
Scripta Materialia | Year: 2010

Molecular dynamics simulation was used to investigate reactions of a frac(1, 2) 〈 1 1 1 〉 {1 1 0} edge dislocation with interstitial dislocation loops of frac(1, 2) 〈 1 1 1 〉 and 〈1 0 0〉 type in a model of iron. Whether loops are strong or weak obstacles depends not only on loop size and type, but also on temperature and dislocation velocity. These parameters determine whether a loop is absorbed on the dislocation or left behind as it glides away. Absorption requires glide of a reaction segment over the loop surface and cross-slip of dipole dislocation arms attached to the ends of the segment: these mechanisms depend on temperature and strain rate, as discussed here. © 2010 Acta Materialia Inc.

Urano D.,University of North Carolina at Chapel Hill | Chen J.-G.,Oak Ridge National Laboratory | Botella J.R.,University of Queensland | Jones A.M.,University of North Carolina at Chapel Hill
Open Biology | Year: 2013

In animals, heterotrimeric G proteins, comprising a-, b-and g-subunits, perceive extracellular stimuli through cell surface receptors, and transmit signals to ion channels, enzymes and other effector proteins to affect numerous cellular behaviours. In plants, G proteins have structural similarities to the corresponding molecules in animals but transmit signals by atypical mechanisms and effector proteins to control growth, cell proliferation, defence, stomate movements, channel regulation, sugar sensing and some hormonal responses. In this review, we summarize the current knowledge on the molecular regulation of plant G proteins, their effectors and the physiological functions studied mainly in two model organisms: Arabidopsis thaliana and rice (Oryza sativa). We also look at recent progress on structural analyses, systems biology and evolutionary studies. © 2013 The Authors.

Wilbanks T.J.,Oak Ridge National Laboratory
Energy Economics | Year: 2011

Reducing risks of severe climate change in the latter part of the 20th Century is likely to require not only incremental improvements in known energy technologies, but the discovery of transformational new energy technologies. This paper reviews current knowledge about both demand and supply aspects of the challenge of accelerating transformational change, considering both economic and policy incentives, including targeted government funding of research and development, and several other schools of thought about drivers of scientific discovery and innovation. © 2011 Elsevier B.V.

Williams M.L.,Oak Ridge National Laboratory
Nuclear Technology | Year: 2011

SCALE 6 includes several problem-independent multigroup (MG) libraries that were processed from the evaluated nuclear data file ENDF/B using a generic flux spectrum. The library data must be self-shielded and corrected for problem-specific spectral effects for use in MG neutron transport calculations. SCALE 6 computes problem-dependent MG cross sections through a combination of the conventional Bondarenko shielding-factor method and a deterministic continuous-energy (CE) calculation of the fine-structure spectra in the resolved resonance and thermal energy ranges. The CE calculation can be performed using an infinite medium approximation, a simplified two-region method for lattices, or a one-dimensional discrete ordinates transport calculation with pointwise (PW) cross-section data. This paper describes the SCALE-resonance self-shielding methodologies, including the deterministic calculation of the CE flux spectra using PW nuclear data and the method for using CE spectra to produce problem-specific MG cross sections for various configurations (including doubly heterogeneous lattices). It also presents results of verification and validation studies.

Zhao X.,Oak Ridge National Laboratory
Journal of Physical Chemistry C | Year: 2011

Molecular dynamics simulations were performed to study the interaction of double-stranded DNA segments with the surfaces of graphene and carbon nanotube arrays in aqueous solution. Several different kinds of self-assembly phenomena were observed. First, it is found that a DNA segment can Eostand up on the carbon surfaces with its helix axis perpendicular to the surfaces of graphene or nanotube arrays to form a forestlike structure. Second, a DNA segment can also lie on the carbon surface with its axis parallel to the surface if both of its ends can form stable structure with the carbon surfaces. In the latter case, the ending basepairs of the DNA are broken due to severe deformations. Third, it is observed that short DNA segments can concatenate to each other to form a longer DNA when they are placed in the grooves of nanotube bundles. The self-assembly observed in this study usually happens in less than 50 ns. Exploration on the molecular details and self-assembly mechanism indicates the primary driving force is the π stacking interaction between the ending basepairs of DNA and the carbon rings. This study confirms the dominant role of hydrophobic π stacking in the interaction between nucleotides and carbon-based nanosurfaces in aqueous environment. © 2011 American Chemical Society.

Wang S.,Northeast Normal University | Chen J.-G.,Oak Ridge National Laboratory
Frontiers in Plant Science | Year: 2014

MYB transcription factors regulate multiple aspects of plant growth and development. Among the large family of MYB transcription factors, single-repeat R3 MYBs are characterized by their short sequence (<120 amino acids) consisting largely of the single MYB DNA-binding repeat. In the model plant Arabidopsis, R3 MYBs mediate lateral inhibition during epidermal patterning and are best characterized for their regulatory roles in trichome and root hair development. R3 MYBs act as negative regulators for trichome formation but as positive regulators for root hair development. In this article, we provide a comprehensive review on the role of R3 MYBs in the regulation of cell type specification in the model plant Arabidopsis. © 2014 Wang and Chen.

Marquis E.A.,University of Oxford | Yahya N.A.,University of Oxford | Larson D.J.,Cameca Instruments Inc. | Miller M.K.,Oak Ridge National Laboratory | Todd R.I.,University of Oxford
Materials Today | Year: 2010

The ability to probe the three-dimensional atomic structure of materials is an essential tool for material design and failure analysis. Atom-probe tomography has proven very powerful to analyze the detailed structure and chemistry of metallic alloys and semiconductor structures while ceramic materials have remained outside its standard purview. In the current work, we demonstrate that bulk alumina can be quantitatively analyzed and microstructural features observed. The analysis of grain boundary carbon segregation - barely achievable by electron microscopy - opens the possibility of understanding the mechanistic effects of dopants on mechanical properties, fracture and wear properties of bulk oxides. © 2010 Elsevier Ltd.

Hendricks T.R.,Oak Ridge National Laboratory | Wang W.,Michigan State University | Lee I.,Michigan State University
Soft Matter | Year: 2010

Wrinkling is a common everyday occurrence. Over the last decade wrinkling in thin films has become an interesting topic. Nearly all studies to date have focused on the underlying physics or how the wrinkles can be used for a specific application. With more and more devices being created from stacked materials, a need for ways to prevent buckling has arisen. In this article we highlight the prevention of wrinkling in nanoscale thin films. © 2010 The Royal Society of Chemistry.

Daidone I.,University of LAquila | Di Nola A.,University of Rome La Sapienza | Smith J.C.,Oak Ridge National Laboratory
Biophysical Journal | Year: 2011

Prion proteins become pathogenic through misfolding. Here, we characterize the folding of a peptide consisting of residues 109-122 of the Syrian hamster prion protein (the H1 peptide) and of a more amyloidogenic A117V point mutant that leads in humans to an inheritable form of the Gerstmann-Sträussler- Scheinker syndrome. Atomistic molecular dynamics simulations are performed for 2.5 μs. Both peptides lose their a-helical starting conformations and assume a β-hairpin that is structurally similar in both systems. In each simulation several unfolding/refolding events occur, leading to convergence of the thermodynamics of the conformational states to within 1 kJ/mol. The similar stability of the β-hairpin relative to the unfolded state is observed in the two peptides. However, substantial differences are found between the two unfolded states. A local minimum is found within the free energy unfolded basin of the A117V mutant populated by misfolded collapsed conformations of comparable stability to the β-hairpin state, consistent with increased amyloidogenicity. This population, in which V117 stabilizes a hydrophobic core, is absent in the wild-type peptide. These results are supported by simulations of oligomers showing a slightly higher stability of the associated structures and a lower barrier to association for the mutated peptide. Hence, a single point mutation carrying only two additional methyl groups is here shown to be responsible for rather dramatic differences of structuring within the unfolded (misfolded) state. © 2011 by the Biophysical Society.

Mobini M.,University of British Columbia | Sowlati T.,University of British Columbia | Sokhansanj S.,University of British Columbia | Sokhansanj S.,Oak Ridge National Laboratory
Applied Energy | Year: 2011

This study investigates the logistics of supplying forest biomass to a potential power plant. Due to the complexities in such a supply logistics system, a simulation model based on the framework of Integrated Biomass Supply Analysis and Logistics (IBSAL) is developed in this study to evaluate the cost of delivered forest biomass, the equilibrium moisture content, and carbon emissions from the logistics operations. The model is applied to a proposed case of 300MW power plant in Quesnel, BC, Canada. The results show that the biomass demand of the power plant would not be met every year. The weighted average cost of delivered biomass to the gate of the power plant is about C$ 90 per dry tonne. Estimates of equilibrium moisture content of delivered biomass and CO2 emissions resulted from the processes are also provided. © 2010 Elsevier Ltd.

Naguib M.,Oak Ridge National Laboratory | Gogotsi Y.,Drexel University
Accounts of Chemical Research | Year: 2015

CONSPECTUS: Two-dimensional (2D) materials have attracted much attention in the past decade. They offer high specific surface area, as well as electronic structure and properties that differ from their bulk counterparts due to the low dimensionality. Graphene is the best known and the most studied 2D material, but metal oxides and hydroxides (including clays), dichalcogenides, boron nitride (BN), and other materials that are one or several atoms thick are receiving increasing attention. They may deliver a combination of properties that cannot be provided by other materials. The most common synthesis approach in general is by reacting different elements or compounds to form a new compound. However, this approach does not necessarily work well for low-dimensional structures, since it favors formation of energetically preferred 3D (bulk) solids. Many 2D materials are produced by exfoliation of van der Waals solids, such as graphite or MoS2, breaking large particles into 2D layers. However, these approaches are not universal; for example, 2D transition metal carbides cannot be produced by any of them. An alternative but less studied way of material synthesis is the selective extraction process, which is based on the difference in reactivity and stability between the different components (elements or structural units) of the original material. It can be achieved using thermal, chemical, or electrochemical processes. Many 2D materials have been synthesized using selective extraction, such as graphene from SiC, transition metal oxides (TMO) from layered 3D salts, and transition metal carbides or carbonitrides (MXenes) from MAX phases. Selective extraction synthesis is critically important when the bonds between the building blocks of the material are too strong (e.g., in carbides) to be broken mechanically in order to form nanostructures. Unlike extractive metallurgy, where the extracted metal is the goal of the process, selective extraction of one or more elements from the precursor materials releases 2D structures. In this Account, in addition to graphene and TMO, we focused on MXenes as an example for the use of selective extraction synthesis to produce novel 2D materials. About 10 new carbides and carbonitrides of transition metals have been produced by this method in the past 3 years. They off er an unusual combination of metallic conductivity and hydrophilicity and show very attractive electrochemical properties. We hope that this Account will encourage researchers to extend the use of selective extraction to other layered material systems that in turn will result in expanding the world of nanomaterials in general and 2D materials in particular, generating new materials that cannot be produced by other means. (Figure Presented). © 2014 American Chemical Society.

Zhao J.,University of California at Berkeley | Zhao J.,Miller Institute for Basic Research in Science | Cao H.,Oak Ridge National Laboratory | Bourret-Courchesne E.,Lawrence Berkeley National Laboratory | And 3 more authors.
Physical Review Letters | Year: 2012

The recently discovered K-Fe-Se high-temperature superconductor has caused heated debate regarding the nature of its parent compound. Transport, angle-resolved photoemission spectroscopy, and STM measurements have suggested that its parent compound could be insulating, semiconducting, or even metallic. Because the magnetic ground states associated with these different phases have not yet been identified and the relationship between magnetism and superconductivity is not fully understood, the real parent compound of this system remains elusive. Here, we report neutron-diffraction experiments that reveal a semiconducting antiferromagnetic (AFM) phase with rhombus iron vacancy order. The magnetic order of the semiconducting phase is the same as the stripe AFM order of the iron pnictide parent compounds. Moreover, while the √5×√5 block AFM phase coexists with superconductivity, the stripe AFM order is suppressed by it. This leads us to conjecture that the new semiconducting magnetic ordered phase is the true parent phase of this superconductor. © 2012 American Physical Society.

Zeng H.,University of Hong Kong | Dai J.,South University of Science and Technology of China | Yao W.,University of Hong Kong | Xiao D.,Oak Ridge National Laboratory | Cui X.,University of Hong Kong
Nature Nanotechnology | Year: 2012

Most electronic devices exploit the electric charge of electrons, but it is also possible to build devices that rely on other properties of electrons. Spintronic devices, for example, make use of the spin of electrons. Valleytronics is a more recent development that relies on the fact that the conduction bands of some materials have two or more minima at equal energies but at different positions in momentum space. To make a valleytronic device it is necessary to control the number of electrons in these valleys, thereby producing a valley polarization. Single-layer MoS 2 is a promising material for valleytronics because both the conduction and valence band edges have two energy-degenerate valleys at the corners of the first Brillouin zone. Here, we demonstrate that optical pumping with circularly polarized light can achieve a valley polarization of 30% in pristine monolayer MoS 2. Our results, and similar results by Mak et al., demonstrate the viability of optical valley control and valley-based electronic and optoelectronic applications in MoS 2 monolayers. © 2012 Macmillan Publishers Limited. All rights reserved.

Norman M.R.,Oak Ridge National Laboratory
Journal of Computational Physics | Year: 2013

We detail several algorithmic changes to the ADER Multi-Moment Finite-Volume Methods (ADER. +. MMFV) of Norman and Finkel (2012) [2]. The DT recurrence relations are improved, flux and source term differential transforms are saved, each are expanded as polynomials, quadrature is removed from the algorithm, integration is performed analytically, and a different Riemann solver admitting direct use of time-averaged fluxes is used. These algorithmic changes were implemented and tested, and smooth 1-D shallow water experiments confirm the same or slightly better accuracy as well as 2-3× lower runtimes compared to Norman and Finkel (2012) [2]. © 2013 Elsevier Inc.

Gilbert M.R.,EURATOM | Schuck P.,Oak Ridge National Laboratory | Sadigh B.,Lawrence Livermore National Laboratory | Marian J.,Lawrence Livermore National Laboratory
Physical Review Letters | Year: 2013

In body-centered-cubic (bcc) crystals, 1/ 2âŸ̈111⟩ screw dislocations exhibit high intrinsic lattice friction as a consequence of their nonplanar core structure, which results in a periodic energy landscape known as the Peierls potential UP. The main features determining plastic flow, including its stress and temperature dependences, can be derived directly from this potential, hence its importance. In this Letter, we use thermodynamic integration to provide a full thermodynamic extension of UP for bcc Fe. We compute the Peierls free energy path as a function of stress and temperature and show that the critical stress vanishes at 700 K, supplying the qualitative elements that explain plastic behavior in the athermal limit. © 2013 American Physical Society.

Suresh A.K.,Biosciences Division | Pelletier D.A.,Biosciences Division | Morrell-Falvey J.L.,Biosciences Division | Doktycz M.J.,Biosciences Division | Doktycz M.J.,Oak Ridge National Laboratory
Langmuir | Year: 2012

Due to their unique antimicrobial properties silver nanocrystallites have garnered substantial attention and are used extensively for biomedical applications as an additive to wound dressings, surgical instruments and bone substitute materials. They are also released into unintended locations such as the environment or biosphere. Therefore it is imperative to understand the potential interactions, fate and transport of nanoparticles with environmental biotic systems. Numerous factors including the composition, size, shape, surface charge, and capping molecule of nanoparticles are known to influence cell cytotoxicity. Our results demonstrate that the physical/chemical properties of the silver nanoparticles including surface charge, differential binding and aggregation potential, which are influenced by the surface coatings, are a major determining factor in eliciting cytotoxicity and in dictating potential cellular interactions. In the present investigation, silver nanocrystallites with nearly uniform size and shape distribution but with different surface coatings, imparting overall high negativity to high positivity, were synthesized. These nanoparticles included poly(diallyldimethylammonium) chloride-Ag, biogenic-Ag, colloidal-Ag (uncoated), and oleate-Ag with zeta potentials +45 ± 5, -12 ± 2, -42 ± 5, and -45 ± 5 mV, respectively; the particles were purified and thoroughly characterized so as to avoid false cytotoxicity interpretations. A systematic investigation on the cytotoxic effects, cellular response, and membrane damage caused by these four different silver nanoparticles was carried out using multiple toxicity measurements on mouse macrophage (RAW-264.7) and lung epithelial (C-10) cell lines. Our results clearly indicate that the cytotoxicity was dependent on various factors such as surface charge and coating materials used in the synthesis, particle aggregation, and the cell-type for the different silver nanoparticles that were investigated. Poly(diallyldimethylammonium)-coated Ag nanoparticles were found to be the most toxic, followed by biogenic-Ag and oleate-Ag nanoparticles, whereas uncoated or colloidal silver nanoparticles were found to be the least toxic to both macrophage and lung epithelial cells. Also, based on our cytotoxicity interpretations, lung epithelial cells were found to be more resistant to the silver nanoparticles than the macrophage cells, regardless of the surface coating. © 2012 American Chemical Society.

Ryon M.G.,Oak Ridge National Laboratory
Environmental Management | Year: 2011

The long-term recovery process for fish communities in a warm water stream in East Tennessee was studied using quantitative measurements over 20 years. The stream receives effluents from a U. S. Department of Energy (DOE) facility, but since 1985 these effluents have been greatly reduced, eliminated, or diluted as part of a substantial long-term pollution abatement program. The resulting changes in water quantity and quality led to a recovery of the fish communities, evidenced by significant changes in species richness, abundance (density and biomass), and community composition (e.g., number of fish species sensitive to stress). The fish community changes occurred over a spatial gradient (downstream from the headwater release zone nearest the DOE facility) and temporally, at multiple sampling locations in the stream. Changes in measured parameters were associated with specific remedial actions and the intervening steps within the recovery process are discussed with regard to changes in treatment processes. © 2010 Springer Science+Business Media, LLC (outside the USA).

Beltrami D.,Chimie Paristech | Beltrami D.,AREVA | Cote G.,Chimie Paristech | Mokhtari H.,AREVA | And 3 more authors.
Chemical Reviews | Year: 2014

Uranium is mainly used as fuel for the production of nuclear energy as harnessed in generating electricity in many countries such as the United States, France, UK, Japan, India, China, and others. To a lesser extent, uranium is also used in reactors for propulsion of naval vessels, for basic and applied research, and for production of radioisotopes for multiple applications such as the treatment of cancer or for medical imaging. The loaded extraction solvent is fed into the stripping step where the metal is back-extracted into an appropriate aqueous solution, thereby achieving concentration of the uranium and purification from other metals in the initial leachate. In certain cases, other valuable metals such as molybdenum and vanadium can be coextracted and recovered as valuable byproducts. In all cases, uranium is precipitated from the resulting strip solutions as convenient salts such as ammonium diuranate, collectively called yellow cake.

Izatt R.M.,IBC Advanced Technologies Inc. | Izatt R.M.,Brigham Young University | Izatt S.R.,IBC Advanced Technologies Inc. | Bruening R.L.,IBC Advanced Technologies Inc. | And 2 more authors.
Chemical Society Reviews | Year: 2014

Achievement of sustainability in metal life cycles from mining of virgin ore to consumer and industrial devices to end-of-life products requires greatly increased recycling rates and improved processing of metals using conventional and green chemistry technologies. Electronic and other high-tech products containing precious, toxic, and specialty metals usually have short lifetimes and low recycling rates. Products containing these metals generally are incinerated, discarded as waste in landfills, or dismantled in informal recycling using crude and environmentally irresponsible procedures. Low recycling rates of metals coupled with increasing demand for high-tech products containing them necessitate increased mining with attendant environmental, health, energy, water, and carbon-footprint consequences. In this tutorial review, challenges to achieving metal sustainability, including projected use of urban mining, in present high-tech society are presented; health, environmental, and economic incentives for various government, industry, and public stakeholders to improve metal sustainability are discussed; a case for technical improvements, including use of molecular recognition, in selective metal separation technology, especially for metal recovery from dilute feed stocks is given; and global consequences of continuing on the present path are examined. This journal is © the Partner Organisations 2014.

Custelcean R.,Oak Ridge National Laboratory
Chemical Society Reviews | Year: 2014

The ability of cationic coordination cages to act as anion receptors is reviewed, with an emphasis on the anion encapsulation chemistry and the dynamics of cage assembly, anion exchange, and other anion-induced structural transformations. The first part of the review describes various examples of anion-encapsulating coordination cages, categorized on the basis of their M xLy stoichiometry (M = metal cation; L = organic ligand). The second part deals with the dynamic aspects of anion encapsulation, including the kinetics and mechanism of anion binding, release, and exchange, as well as the structural evolution of the coordination complexes involved. © The Royal Society of Chemistry.

Su X.,Brown University | Wu Q.,Helmholtz Institute Ulm | Li J.,Oak Ridge National Laboratory | Xiao X.,General Motors | And 4 more authors.
Advanced Energy Materials | Year: 2014

There are growing concerns over the environmental, climate, and health impacts caused by using non-renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium-ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid-electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described. The most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in lithium ion batteries (LIBs) are summarized. The synthetic routes, electrochemical performance, and underlying reaction mechanisms of these nanomaterials are described and the advantages and limitations using nanostructured silicon in LIBs are also discussed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mittal S.,Oak Ridge National Laboratory
Sustainable Computing: Informatics and Systems | Year: 2014

Modern processors are using increasingly larger sized on-chip caches. Also, with each CMOS technology generation, there has been a significant increase in their leakage energy consumption. For this reason, cache power management has become a crucial research issue in modern processor design. To address this challenge and also meet the goals of sustainable computing, researchers have proposed several techniques for improving energy efficiency of cache architectures. This paper surveys recent architectural techniques for improving cache power efficiency and also presents a classification of these techniques based on their characteristics. For providing an application perspective, this paper also reviews several real-world processor chips that employ cache energy saving techniques. The aim of this survey is to enable engineers and researchers to get insights into the techniques for improving cache power efficiency and motivate them to invent novel solutions for enabling low-power operation of caches. © 2013 Elsevier Inc. All rights reserved.

Rosson T.E.,Vanderbilt University | Claiborne S.M.,Vanderbilt University | McBride J.R.,Vanderbilt University | Stratton B.S.,Vanderbilt University | And 2 more authors.
Journal of the American Chemical Society | Year: 2012

A simple treatment method using formic acid has been found to increase the fluorescence quantum yield of ultrasmall white light-emitting CdSe nanocrystals from 8% to 45%. Brighter white-light emission occurs with other carboxylic acids as well, and the magnitude of the quantum yield enhancement is shown to be dependent on the alkyl chain length. Additionally, the nanocrystal luminescence remains enhanced relative to the untreated nanocrystals over several days. This brightened emission opens the possibility for even further quantum yield improvement and potential for use of these white-light nanocrystals in solid-state lighting applications. © 2012 American Chemical Society.

Mefford J.T.,University of Texas at Austin | Hardin W.G.,University of Texas at Austin | Dai S.,Oak Ridge National Laboratory | Johnston K.P.,University of Texas at Austin | Stevenson K.J.,University of Texas at Austin
Nature Materials | Year: 2014

Perovskite oxides have attracted significant attention as energy conversion materials for metal-air battery and solid-oxide fuel-cell electrodes owing to their unique physical and electronic properties. Amongst these unique properties is the structural stability of the cation array in perovskites that can accommodate mobile oxygen ions under electrical polarization. Despite oxygen ion mobility and vacancies having been shown to play an important role in catalysis, their role in charge storage has yet to be explored. Herein we investigate the mechanism of oxygen-vacancy-mediated redox pseudocapacitance for a nanostructured lanthanum-based perovskite, LaMnO 3. This is the first example of anion-based intercalation pseudocapacitance as well as the first time oxygen intercalation has been exploited for fast energy storage. Whereas previous pseudocapacitor and rechargeable battery charge storage studies have focused on cation intercalation, the anion-based mechanism presented here offers a new paradigm for electrochemical energy storage. © 2014 Macmillan Publishers Limited. All rights reserved.

Stack A.G.,Oak Ridge National Laboratory | Raiteri P.,Curtin University Australia | Gale J.D.,Curtin University Australia
Journal of the American Chemical Society | Year: 2012

Mineral growth and dissolution are often treated as occurring via a single reversible process that governs the rate of reaction. We show that multiple distinct intermediate states can occur during both growth and dissolution. Specifically, we used metadynamics, a method for efficiently exploring the free-energy landscape of a system, coupled to umbrella sampling and reactive flux calculations to examine the mechanism and rates of attachment and detachment of a barium ion onto a stepped barite (BaSO 4) surface. The activation energies calculated for the rate-limiting reactions, which are different for attachment and detachment, precisely match those measured experimentally during both growth and dissolution. These results can potentially explain anomalous non-steady-state mineral reaction rates observed experimentally and will enable the design of more efficient growth inhibitors and facilitate an understanding of the effect of impurities. © 2011 American Chemical Society.

Gao Y.,University of Tennessee at Knoxville | Gao Y.,Oak Ridge National Laboratory
Journal of the Mechanics and Physics of Solids | Year: 2010

Stickslip behavior observed from nanoscale asperity friction experiments are often modeled by the one-degree-of-freedom Tomlinson model, which is unable to explain the effects of lattice structure and interface defects, or by molecular simulations which suffer temporal limitations in modeling the velocity- and temperature-dependent frictional behavior. A Peierls-type model developed in this work views the atomic frictional process as the initiation and gliding passage of dislocations with diffused cores on the interface. As a consequence of loss-of-ellipticity instability, the occurrence of stickslip behavior relies on the interaction among interface slip field, contact stress fields, and existing defects. The friction stress for commensurate interface under large contact area can be approximated from the Rice model of screw-dislocation nucleation from a planar crack tip. The spatially inhomogeneous nature of rate-limiting processes and the coupling effects between contact size and interface incommensurability are successfully determined, which cannot otherwise be tackled in the Tomlinsonmodel. © 2010 Elsevier Ltd. All rights reserved.

Kabirian F.,University of Maryland Baltimore County | Khan A.S.,University of Maryland Baltimore County | Pandey A.,University of Maryland Baltimore County | Pandey A.,Oak Ridge National Laboratory
International Journal of Plasticity | Year: 2014

Uniaxial tension and compression tests, at both quasi-static and dynamic ranges of loadings, are utilized to study the thermo-mechanical response of an AA5182-O sheet. The strain rate at quasi-static regime ranges from 10 -4 to 100 (s-1) and at dynamic loading is chosen to be around 3500 (s-1). Measurements are reported at temperatures of 296 K, 338 K, 373 K, 423 K, and 473 K. While at temperatures lower than the critical temperature of Tc, the flow stress decreases with increase of strain rate during quasi-static loading; above this temperature, the measured response shows positive strain rate sensitivity at the same strain rate range. In contrast, significant positive strain rate sensitivity prevails at dynamic loading over the whole range of temperature. A constitutive model is proposed to predict the stress-strain response of the alloy over the studied strain rate and temperature ranges. The developed model is also calibrated for another AA5xxx alloy series, AA5754-O, to evaluate the capability of the developed model in capturing transition from negative to positive strain rate sensitivity. © 2013 Elsevier Ltd. All rights reserved.

Leggett R.W.,Oak Ridge National Laboratory
Science of the Total Environment | Year: 2011

The International Commission on Radiological Protection (ICRP) is updating its biokinetic models used to derive dose coefficients and assess bioassay data for intake of radionuclides. This paper reviews biokinetic data for manganese and proposes a biokinetic model for systemic manganese in adult humans. The proposed model provides a more detailed and physiologically meaningful description of the behavior of absorbed manganese in the body than the current ICRP model. The proposed model and current ICRP model yield broadly similar estimates of dose per unit activity of inhaled or ingested radio-manganese but differ substantially with regard to interpretation of bioassay data. The model is intended primarily for use in radiation protection but can also serve as a baseline model for evaluation of potentially excessive intakes of stable manganese in occupational settings. © 2011 Elsevier B.V.

Bowman S.M.,Oak Ridge National Laboratory
Nuclear Technology | Year: 2011

Version 6 of the Standardized Computer Analyses for Licensing Evaluation (SCALE) computer software system developed at Oak Ridge National Laboratory, released in February 2009, contains significant new capabilities and data for nuclear safety analysis and marks an important update for this software package, which is used worldwide. This paper highlights the capabilities of the SCALE system, including continuous-energy flux calculations for processing multigroup problemdependent cross sections, ENDF/B-VII continuousenergy and multigroup nuclear cross-section data,. continuous-energy Monte Carlo criticality safety calculations, Monte Carlo radiation shielding analyses with automated three-dimensional variance reduction techniques, one- and three-dimensional sensitivity and uncertainty analyses for criticality safety evaluations, two- and three-dimensional lattice physics depletion analyses, fast and accurate source terms and decay heat calculations, automated burnup credit analyses with loading curve search, and integrated three-dimensional criticality accident alarm system analyses using coupled Monte Carlo criticality and shielding calculations.

Peplow D.E.,Oak Ridge National Laboratory
Nuclear Technology | Year: 2011

Monte Carlo shielding analysis capabilities in SCALE 6 are centered on the Consistent Adjoint Driven Importance Sampling (CADIS) methodology. CADIS is used to create an importance map for space/energy weight windows as well as a biased source distribution. New to SCALE 6 are the Monaco functional module, a multi-group fixed-source Monte Carlo transport code, and the Monaco with Automated Variance Reduction using Importance Calculations (MAVRIC) sequence. MAVRIC uses the Denovo code (also new to SCALE 6) to compute coarse-mesh discrete ordinates solutions that are used by CADIS to form an importance map and biased source distribution for the Monaco Monte Carlo code. MAVRIC allows the user to optimize the Monaco calculation for a specific tally using the CADIS method with little extra input compared with a standard Monte Carlo calculation. When computing several tallies at once or a mesh tally over a large volume of space, an extension of the CADIS method called FW-CADIS can be used to help the Monte Carlo simulation spread particles over phase space to obtain more uniform relative uncertainties.

Habenicht B.F.,Oak Ridge National Laboratory | Prezhdo O.V.,University of Rochester
Journal of the American Chemical Society | Year: 2012

Motivated by recent experiments (J. Am. Chem. Soc. 2011, 133, 17156), we used nonadiabatic (NA) molecular dynamics implemented within ab initio time-domain density functional theory to investigate the evolution of the excited electronic singlet and triplet states in the (6,4) carbon nanotube (CNT). The simulation simultaneously included the NA electron-phonon interaction and the spin-orbit (SO) interaction and focused on the intersystem crossing (ISC) from the first excited singlet state (S 1) to the triplet state (T 1) and subsequent relaxation to the ground electronic state (S 0). For the first time, the state-of-the-art methodology (Phys. Rev. Lett. 2005, 95, 163001; Phys. Rev. Lett. 2008, 100, 197402) has been advanced to include triplet states. The S 1-T 1 ISC was calculated to occur within tens of picoseconds, in agreement with the experimental data. This time scale is on the same order as the S 1-S 0 nonradiative decay time obtained previously for the (6,4) CNT. The homogeneous phosphorescence line width, which can be measured in single-molecule experiments, was predicted to be on the order of 10 meV at room temperature. This value is similar to the fluorescence line widths of CNTs suspended in air. The NA electron-phonon and SO couplings were found to be on the order of 1 meV; however, the former fluctuates much more than the latter, causing the ISC rate to be limited by the SO interaction rather than NA interaction. The electronic energy lost nonradiatively during ISC is deposited into high-frequency optical phonons of the CNT arising from C-C stretching motions. The calculations indicate that ISC can contribute to the nonradiative energy losses and low photoluminescence quantum yields observed in semiconducting CNTs. © 2012 American Chemical Society.

Cooper V.R.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Density functional theory is used to explore the electronic reconstruction at III-III/I-V heterointerfaces. It is demonstrated that due to large B-cation valence differences, a δ-doped, two-dimensional electron gas (2DEG) can be created with an increased intrinsic carrier limit, resulting in interfacial charge densities twice that of prototypical LaTiO 3/SrTiO 3. Observed decreases in band effective masses suggest enhancements in carrier mobilities. Unprecedented agreement with recent experiments highlights the fact that it is the electronic structure of the bulk component material that defines the properties of oxide 2DEGs. These geometries provide a more tunable platform through which the underlying physics of electron confinement can be thoroughly examined and thus have implications for modern device applications. © 2012 American Physical Society.

Haraldsen J.T.,Los Alamos National Laboratory | Fishman R.S.,Oak Ridge National Laboratory | Brown G.,Florida State University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We evaluate the spin-wave spectra for the high-field phases of the frustrated triangular lattice antiferromagnet with a focus on the observed high-magnetic-field phases of CuFeO 2. After determining the appropriate magnetic ground state using a combination of Monte Carlo simulations and variational methods for a two-dimensional triangular lattice, we evaluate the spin excitation frequencies and intensities using a rotational Holstein-Primakoff expansion for both the collinear and noncollinear states. These predictions should help experimentalists to identify the magnetic ground states of CuFeO 2 and other triangular-lattice antiferromagnets using inelastic neutron scattering. © 2012 American Physical Society.

Jayasekera T.,North Carolina State University | Kong B.D.,North Carolina State University | Kim K.W.,North Carolina State University | Buongiorno Nardelli M.,North Carolina State University | Buongiorno Nardelli M.,Oak Ridge National Laboratory
Physical Review Letters | Year: 2010

Using calculations from first principles we show how specific interface modifications can lead to a fine-tuning of the doping and band alignment in epitaxial graphene on SiC. Upon different choices of dopants, we demonstrate that one can achieve a variation of the valence band offset between the graphene Dirac point and the valence band edge of SiC up to 1.5 eV. Finally, via appropriate magnetic doping one can induce a half-metallic behavior in the first graphene monolayer. These results clearly establish the potential for graphene utilization in innovative electronic and spintronic devices. © 2010 The American Physical Society.

Kardol P.,Oak Ridge National Laboratory | Kardol P.,University of Tennessee at Knoxville | Cregger M.A.,University of Tennessee at Knoxville | Campanv C.E.,University of Tennessee at Knoxville | Classen A.T.,University of Tennessee at Knoxville
Ecology | Year: 2010

Feedbacks of terrestrial ecosystems to atmospheric and climate change depend on soil ecosystem dynamics. Soil ecosystems can directly and indirectly respond to climate change. For example, warming directly alters microbial communities by increasing their activity. Climate change may also alter plant community composition, thus indirectly altering the soil communities that depend on their inputs. To better understand how climate change may directly and indirectly alter soil ecosystem functioning, we investigated old-field plant community and soil ecosystem responses to single and combined effects of elevated [CO2], warming, and precipitation in Tennessee (USA). Specifically, we collected soils at the plot level (plant community soils) and beneath dominant plant species (plant-specific soils). We used microbial enzyme activities and soil nematodes as indicators for soil ecosystem functioning. Our study resulted in two main findings: (1) Overall, while there were some interactions, water, relative to increases in [CO2] and warming, had the largest impact on plant community composition, soil enzyme activity, and soil nematodes. Multiple climate-change factors can interact to shape ecosystems, but in our study, those interactions were largely driven by changes in water. (2) Indirect effects of climate change, via changes in plant communities, had a significant impact on soil ecosystem functioning, and this impact was not obvious when looking at plant community soils. Climate-change effects on enzyme activities and soil nematode abundance and community structure strongly differed between plant community soils and plant-specific soils, but also within plant-specific soils. These results indicate that accurate assessments of climate-change impacts on soil ecosystem functioning require incorporating the concurrent changes in plant function and plant community composition. Climate-change-induced shifts in plant community composition will likely modify or counteract the direct impact of atmospheric and climate change on soil ecosystem functioning, and hence, these indirect effects should be taken into account when predicting the manner in which global change will alter ecosystem functioning. © 2010 by the Ecological Society of America.

Lin Z.,Oak Ridge National Laboratory
SAE International Journal of Alternative Powertrains | Year: 2012

To provide useful information for automakers to design successful plug-in hybrid electric vehicle (PHEV) products and for energy and environmental analysts to understand the social impact of PHEVs, this paper addresses the question of how many of the U.S. consumers, if buying a PHEV, would prefer what electric ranges. The Market-oriented Optimal Range for PHEV (MOR-PHEV) model is developed to optimize the PHEV electric range for each of 36,664 sampled individuals representing U.S. new vehicle drivers. The optimization objective is the minimization of the sum of costs on battery, gasoline, electricity and refueling hassle. Assuming no battery subsidy, the empirical results suggest that: 1) the optimal PHEV electric range approximates two thirds of one's typical daily driving distance in the near term, defined as 450/kWh battery delivered price and 4/gallon gasoline price. 2) PHEVs are not ready to directly compete with HEVs at today's situation, defined by the 600/kWh battery delivered price and the 3-4/gallon gasoline price, but can do so in the near term. 3) PHEV 10s will be favored by the market over longer-range PHEVs in the near term, but longer-range PHEVs can dominate the PHEV market if gasoline prices reach as high as 5-6 per gallon and/or battery delivered prices reach as low as 150-300/kWh. 4) PHEVs can become much more attractive against HEVs in the near term if the electric range can be extended by only 10% with multiple charges per day, possible with improved charging infrastructure or adapted charging behavior. 5) the impact of a 100/kWh decrease in battery delivered prices on the competiveness of PHEVs against HEVs can be offset by about 1.25/gallon decrease in gasoline prices, or about ¢7/kWh increase in electricity prices. This also means that the impact of a 1/gallon decrease in gasoline prices can be offset by about ¢5/kWh decrease in electricity prices.

Fishman R.S.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Quantum spin fluctuations are investigated for the distorted incommensurate spiral state of a geometrically frustrated triangular-lattice antiferromagnet. With increasing easy axis anisotropy, the average reduction of the spin amplitude by quantum fluctuations is suppressed but the spiral also becomes more distorted. Quantum fluctuations enhance both the wave vector of the distorted spiral and the critical anisotropy above which it undergoes a first-order transition into a collinear state. An experimental technique is proposed to isolate the effects of quantum fluctuations from the classical distortion of the spiral. This analysis is applied to the elliptical spiral state of doped CuFeO 2. © 2012 American Physical Society.

Fishman R.S.,Oak Ridge National Laboratory | Brown G.,Florida State University | Haraldsen J.T.,Los Alamos National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

Monte-Carlo and variational calculations are used to revise the phase diagram of the magnetically frustrated material CuFeO 2. For fields 50

Yu Y.,National University of Singapore | Luo Z.,National University of Singapore | Chevrier D.M.,Dalhousie University | Leong D.T.,National University of Singapore | And 3 more authors.
Journal of the American Chemical Society | Year: 2014

The luminescence property of thiolated gold nanoclusters (Au NCs) is thought to involve the Au(I)-thiolate motifs on the NC surface; however, this hypothesis remains largely unexplored because of the lack of precise molecular composition and structural information of highly luminescent Au NCs. Here we report a new red-emitting thiolated Au NC, which has a precise molecular formula of Au22(SR)18 and exhibits intense luminescence. Interestingly, this new Au22(SR)18 species shows distinctively different absorption and emission features from the previously reported Au22(SR)16, Au22(SR)17, and Au25(SR)18. In stark contrast, Au22(SR) 18 luminesces intensely at ∼665 nm with a high quantum yield of ∼8%, while the other three Au NCs show very weak luminescence. Our results indicate that the luminescence of Au22(SR)18 originates from the long Au(I)-thiolate motifs on the NC surface via the aggregation-induced emission pathway. Structure prediction by density functional theory suggests that Au22(SR)18 has two RS-[Au-SR] 3 and two RS-[Au-SR]4 motifs, interlocked and capping on a prolate Au8 core. This predicted structure is further verified experimentally by Au L3-edge X-ray absorption fine structure analysis. © 2014 American Chemical Society.

Grice W.P.,Oak Ridge National Laboratory
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

A complete Bell-state measurement is not possible using only linear-optic elements, and most schemes achieve a success rate of no more than 50%, distinguishing, for example, two of the four Bell states but returning degenerate results for the other two. It is shown here that the introduction of a pair of ancillary entangled photons improves the success rate to 75%. More generally, the addition of 2N-2 ancillary photons yields a linear-optic Bell-state measurement with a success rate of 1-1/2N. © 2011 American Physical Society.

Engelmann C.,Oak Ridge National Laboratory
Future Generation Computer Systems | Year: 2014

As supercomputers scale to 1000 PFlop/s over the next decade, investigating the performance of parallel applications at scale on future architectures and the performance impact of different architecture choices for high-performance computing (HPC) hardware/software co-design is crucial. This paper summarizes recent efforts in designing and implementing a novel HPC hardware/software co-design toolkit. The presented Extreme-scale Simulator (xSim) permits running an HPC application in a controlled environment with millions of concurrent execution threads while observing its performance in a simulated extreme-scale HPC system using architectural models and virtual timing. This paper demonstrates the capabilities and usefulness of the xSim performance investigation toolkit, such as its scalability to 227 simulated Message Passing Interface (MPI) ranks on 960 real processor cores, the capability to evaluate the performance of different MPI collective communication algorithms, and the ability to evaluate the performance of a basic Monte Carlo application with different architectural parameters. © 2013 Elsevier B.V. All rights reserved.

Gao C.,Xian University of Science and Technology | Gao C.,University of California at Riverside | Hu Y.,Argonne National Laboratory | Wang M.,University of California at Riverside | And 2 more authors.
Journal of the American Chemical Society | Year: 2014

We report that fully alloyed Ag/Au nanospheres with high compositional homogeneity ensured by annealing at elevated temperatures show large extinction cross sections, extremely narrow bandwidths, and remarkable stability in harsh chemical environments. Nanostructures of Ag are known to have much stronger surface plasmon resonance than Au, but their applications in many areas have been very limited by their poor chemical stability against nonideal chemical environments. Here we address this issue by producing fully alloyed Ag/Au nanospheres through a surface-protected annealing process. A critical temperature has been found to be around 930 °C, below which the resulting alloy nanospheres, although significantly more stable than pure silver nanoparticles, can still gradually decay upon extended exposure to a harsh etchant. Nanospheres annealed above the critical temperature show a homogeneous distribution of Ag and Au, minimal crystallographic defects, and the absence of structural and compositional interfaces, which account for the extremely narrow bandwidths of the surface plasmon resonance and may enable many plasmonic applications with high performance and long lifetime, especially for those involving corrosive species. © 2014 American Chemical Society.

Singh D.J.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

SrRu2O6 is a layered honeycomb-lattice material with an extraordinarily high magnetic ordering temperature. We investigated this material using density functional calculations. We find that the energy scales for moment formation and ordering are similar and high. Additionally, we find that the magnetic anisotropy is high and favors moments oriented along the c axis. This provides an explanation for the exceptionally high ordering temperature. Finally, the compound is found to be semiconducting at the bare density functional level, even without magnetic order. Experimental consequences of this scenario for the high ordering temperature are discussed. © 2015 American Physical Society.

Edwards R.E.,University of Tennessee at Knoxville | New J.,Oak Ridge National Laboratory | Parker L.E.,University of Tennessee at Knoxville
Energy and Buildings | Year: 2012

Traditional whole building energy modeling suffers from several factors, including the large number of inputs required for building characterization, simplifying assumptions, and the gap between the as-designed and as-built building. Prior work has attempted to mitigate these problems by using sensor-based machine learning approaches to statistically model energy consumption, applying the techniques primarily to commercial building data, which makes use of hourly consumption data. It is unclear, however, whether these techniques can translate to residential buildings, since the energy usage patterns may vary significantly. Until now, most residential modeling research only had access to monthly electrical consumption data. In this article, we report on the evaluation of seven different machine learning algorithms applied to a new residential data set that contains sensor measurements collected every 15 min, with the objective of determining which techniques are most successful for predicting next hour residential building consumption. We first validate each learner's correctness on the ASHRAE Great Energy Prediction Shootout, confirming existing conclusions that Neural Network-based methods perform best on commercial buildings. However, our additional results show that these methods perform poorly on residential data, and that Least Squares Support Vector Machines perform best - a technique not previously applied to this domain. © 2012 Elsevier B.V. All rights reserved.

Xu L.,Stevens Institute of Technology | Ankner J.F.,Oak Ridge National Laboratory | Sukhishvili S.A.,Stevens Institute of Technology
Macromolecules | Year: 2011

Using a series of polycations synthesized by atom transfer radical polymerization (ATRP), we investigate the effects of the polymer charge density and hydrophobicity on salt-induced interdiffusion of polymer layers within polyelectrolyte multilayer (PEM) films. Polycations with two distinct hydrophobicities and various quaternization degrees (QPDMA and QPDEA) were derived from parent polymers of matched molecular weights-poly(2-(dimethylamino) ethyl methacrylate) (PDMA) and poly(2-(diethylamino)ethyl methacrylate) (PDEA)-by quaternization with either methyl or ethyl sulfate. Multilayers of these polycations with polystyrenesulfonate (PSS) were assembled in low-salt conditions and annealed in NaCl solutions to induce layer intermixing. As revealed by neutron reflectometry (NR), polycations with lower charge density resulted in a faster decay of film structure with distance from the substrate. Interestingly, when comparing polymer mobility in QPDEA/PSS and QPDMA/PSS films, layer intermixing was faster in the case of more hydrophobic QPDEA as compared to QPDMA because of the weaker ionic pairing (due to the presence of a bulky ethyl spacer) between QPDEA and PSS. © 2011 American Chemical Society.

Russell L.B.,Oak Ridge National Laboratory
Mutation Research - Reviews in Mutation Research | Year: 2013

The large mouse genetics program at the Oak Ridge National Laboratory (ORNL) is often remembered chiefly for the germ-cell mutation-rate data it generated and their uses in estimating the risk of heritable radiation damage. In fact, it soon became a multi-faceted research effort that, over a period of almost 60 years, generated a wealth of information in the areas of mammalian mutagenesis, basic genetics (later enriched by molecular techniques), cytogenetics, reproductive biology, biochemistry of germ cells, and teratology. Research in the area of germ-cell mutagenesis explored the important physical and biological factors that affect the frequency and nature of induced mutations and made several unexpected discoveries, such as the major importance of the perigametic interval (the zygote stage) for the origin of spontaneous mutations and for the sensitivity to induced genetic change. Of practical value was the discovery that ethylnitrosourea was a supermutagen for point mutations, making high-efficiency mutagenesis in the mouse feasible worldwide. Teratogenesis findings resulted in recommendations still generally accepted in radiological practice. Studies supporting the mutagenesis research added whole bodies of information about mammalian germ-cell development and about molecular targets in germ cells. The early decision to not merely count but propagate genetic variants of all sorts made possible further discoveries, such as the Y-chromosome's importance in mammalian sex determination and the identification of rare X-autosome translocations, which, in turn, led to the formulation of the single-active-X hypothesis and provided tools for studies of functional mosaicism for autosomal genes, male sterility, and chromosome-pairing mechanism. Extensive genetic and then molecular analyses of large numbers of induced specific-locus mutants resulted in fine-structure physical and correlated functional mapping of significant portions of the mouse genome and constituted a valuable source of mouse models for human genetic disorders. © 2013 Elsevier B.V.

Zhang Q.,University of California at Riverside | Lima D.Q.,University of California at Riverside | Lee I.,University of California at Riverside | Zaera F.,University of California at Riverside | And 2 more authors.
Angewandte Chemie - International Edition | Year: 2011

Nicely decorated: A sandwich-structured photocatalyst shows an excellent performance in degradation reactions of a number of organic compounds under UV, visible light, and direct sunlight (see picture). The catalyst was synthesized by a combination of nonmetal doping and plasmonic metal decoration of TiO 2 nanocrystals, which improves visible-light activity and enhances light harvesting and charge separation, respectively. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sun C.,University of Queensland | Smith S.C.,Oak Ridge National Laboratory
Journal of Physical Chemistry C | Year: 2012

The adsorption of gold clusters (Au n, n = 1-10) on the minority surface, (001), of anatase titanium dioxide (TiO 2) has been studied in the framework of density functional theory. Various adsorption geometries of gold (Au) clusters on clean, unreconstructed TiO 2(001) have been investigated. It is found the adsorption of gold on TiO 2(001) is much stronger than that on the majority surface, (101). Due to the strong interfacial bonding, the valence electrons of gold have been highly delocalized and dominate the highest occupied frontier orbitals of Au/TiO 2(001). Consequently, it is predicted that the support of TiO 2(001) may offer better catalysis performance than conventionally used TiO 2(101). © 2012 American Chemical Society.

Malikopoulos A.A.,Oak Ridge National Laboratory
Proceedings of the American Control Conference | Year: 2013

Increasing demand for improving fuel economy and reducing emissions has stimulated significant research and investment in hybrid propulsion systems. In this paper, we address the problem of optimizing online the supervisory control in a series hybrid configuration by modeling its operation as a controlled Markov chain using the average cost criterion. We treat the stochastic optimal control problem as a dual constrained optimization problem. We show that the control policy that yields higher probability distribution to the states with low cost and lower probability distribution to the states with high cost is an optimal control policy, defined as an equilibrium control policy. We demonstrate the effectiveness of the efficiency of the proposed controller in a series hybrid configuration and compare it with a thermostat-type controller. © 2013 AACC American Automatic Control Council.

Mittal S.,Iowa State University | Vetter J.S.,Oak Ridge National Laboratory
ACM Computing Surveys | Year: 2014

Recent years have witnessed phenomenal growth in the computational capabilities and applications of GPUs. However, this trend has also led to a dramatic increase in their power consumption. This article surveys research works on analyzing and improving energy efficiency of GPUs. It also provides a classification of these techniques on the basis of their main research idea. Further, it attempts to synthesize research works that compare the energy efficiency of GPUs with other computing systems (e.g., FPGAs and CPUs). The aim of this survey is to provide researchers with knowledge of the state of the art in GPU power management and motivate them to architect highly energy-efficient GPUs of tomorrow. © 2014 ACM.

Dash A.,Bhabha Atomic Research Center | Knapp Jr. F.F.,Oak Ridge National Laboratory | Pillai M.R.A.,Bhabha Atomic Research Center
Current Radiopharmaceuticals | Year: 2013

Radionuclide therapy (RNT) based on the concept of delivering cytotoxic levels of radiation to disease sites is one of the rapidly growing fields of nuclear medicine. Unlike conventional external beam therapy, RNT targets diseases at the cellular level rather than on a gross anatomical level. This concept is a blend of a tracer moiety that mediates a site specific accumulation followed by induction of cytotoxicity with the short-range biological effectiveness of particulate radiations. Knowledge of the biochemical reactions taking place at cellular levels has stimulated the development of sophisticated molecular carriers, catalyzing a shift towards using more specific targeting radiolabelled agents. There is also improved understanding of factors of importance for choice of appropriate radionuclides based on availability, the types of emissions, linear energy transfer (LET), and physical half-life. This article discusses the applications of radionuclide therapy for treatment of cancer as well as other diseases. The primary objective of this review is to provide an overview on the role of radionuclide therapy in the treatment of different diseases such as polycythaemia, thyroid malignancies, metastatic bone pain, radiation synovectomy, hepatocellular carcinoma (HCC), neuroendocrine tumors (NETs), non-Hodgkin's lymphoma (NHL) and others. In addition, recent developments on the systematic approach in designing treatment regimens as well as recent progress, challenges and future perspectives are discussed. An examination of the progress of radionuclide therapy indicates that although a rapid stride has been made for treating hematological tumors, the development for treating solid tumors has, so far, been limited. However, the emergence of novel tumor-specific targeting agents coupled with successful characterization of new target structures would be expected to pave the way for future treatment for such tumors. © 2013 Bentham Science Publishers.

Ghosh S.,Indian Institute of Technology Bombay | Das D.,Temple University | Kao S.-C.,Oak Ridge National Laboratory | Ganguly A.R.,Northeastern University
Nature Climate Change | Year: 2012

Recent studies disagree on how rainfall extremes over India have changed in space and time over the past half century, as well as on whether the changes observed are due to global warming or regional urbanization. Although a uniform and consistent decrease in moderate rainfall has been reported, a lack of agreement about trends in heavy rainfall may be due in part to differences in the characterization and spatial averaging of extremes. Here we use extreme value theory to examine trends in Indian rainfall over the past half century in the context of long-term, low-frequency variability. We show that when generalized extreme value theory is applied to annual maximum rainfall over India, no statistically significant spatially uniform trends are observed, in agreement with previous studies using different approaches. Furthermore, our spaceĝ€"time regression analysis of the return levels points to increasing spatial variability of rainfall extremes over India. Our findings highlight the need for systematic examination of global versus regional drivers of trends in Indian rainfall extremes, and may help to inform flood hazard preparedness and water resource management in the region. © 2012 Macmillan Publishers Limited. All rights reserved.

Awes T.C.,Oak Ridge National Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2010

ALICE is the general purpose experiment at the LHC dedicated to the study of heavy-ion collisions. The electromagnetic calorimeter (EMCal) is a late addition to the ALICE suite of detectors with first modules installed in ALICE this year. The EMCal is designed to trigger on high energy gamma-rays and jets, and to enhance the capabilities of ALICE for these measurements. The EMCal is a Pb/scintillator sampling shish-kebab type calorimeter. The EMCal construction, readout, and performance in beam tests at the CERN SPS and PS are described. © 2009 Elsevier B.V. All rights reserved.

Singh D.J.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We report electronic structure calculations for the layered centrosymmetric superconductor LaNiGa 2, which has been identified as having a possible triplet state based on evidence for time reversal symmetry breaking. The Fermi surface has several large sheets and is only moderately anisotropic, so that the material is best described as a three-dimensional metal. These include sections that are open in the in-plane direction as well as a section that approaches the zone center. The density of states is high and primarily derived from Ga p states, which hybridize with Ni d states. Comparing with experimental specific heat data, we infer a superconducting λ≤0.55, which implies that this is a weak to intermediate coupling material. However, the Ni occurs in a nominal d10 configuration in this material, which places the compound far from magnetism. Implications of these results for superconductivity are discussed. © 2012 American Physical Society.

Savara A.,Oak Ridge National Laboratory | Weitz E.,Northwestern University
Annual Review of Physical Chemistry | Year: 2014

Infrared spectroscopy has a long history as a tool for the identification of chemical compounds. More recently, various implementations of infrared spectroscopy have been successfully applied to studies of heterogeneous catalytic reactions with the objective of identifying intermediates and determining catalytic reaction mechanisms. We discuss selective applications of these techniques with a focus on several heterogeneous catalytic reactions, including hydrogenation, deNOx, water-gas shift, and reverse-water-gas shift. The utility of using isotopic substitutions and other techniques in tandem with infrared spectroscopy is discussed. We comment on the modes of implementation and the advantages and disadvantages of the various infrared techniques. We also note future trends and the role of computational calculations in such studies. The infrared techniques considered are transmission Fourier transform infrared spectroscopy, infrared reflection-absorption spectroscopy, polarization- modulation infrared reflection-absorption spectroscopy, sum-frequency generation, diffuse reflectance infrared Fourier transform spectroscopy, attenuated total reflectance, infrared emission spectroscopy, photoacoustic infrared spectroscopy, and surface-enhanced infrared absorption spectroscopy. Copyright © 2014 by Annual Reviews.

Dmowski W.,University of Tennessee at Knoxville | Iwashita T.,University of Tennessee at Knoxville | Chuang C.-P.,University of Tennessee at Knoxville | Almer J.,Argonne National Laboratory | And 2 more authors.
Physical Review Letters | Year: 2010

When a stress is applied on a metallic glass it deforms following Hook's law. Therefore it may appear obvious that a metallic glass deforms elastically. Using x-ray diffraction and anisotropic pair-density function analysis we show that only about 34 in volume fraction of metallic glasses deforms elastically, whereas the rest of the volume is anelastic and in the experimental time scale deform without resistance. We suggest that this anelastic portion represents residual liquidity in the glassy state. Many theories, such as the free-volume theory, assume the density of defects in the glassy state to be of the order of 1%, but this result shows that it is as much as a quarter.

Ye L.,Fudan University | Tian Y.,Fudan University | Jin X.,Fudan University | Xiao D.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The unusual temperature dependence of the anomalous Hall effect (AHE) in Ni is investigated by an experimental approach which enables us to extract the intrinsic anomalous Hall conductivity over the whole temperature range. In stark contrast to the existing literature, the intrinsic contribution in Ni is found to be strongly temperature dependent between 5 and 150 K, where the corresponding magnetization remains almost unchanged. This pronounced temperature dependence, a cause of the long-standing confusion concerning the physical origin of the AHE in Ni, is likely due to the existence of small band gaps caused by the spin-orbit coupling at the Fermi level. Our result helps pave the way for the general claim of the Berry-phase interpretation for the AHE, and also points out another mechanism for the temperature dependence of the AHE. © 2012 American Physical Society.

Lee C.-C.,Rice University | Sun Y.,Rice University | Qian S.,Oak Ridge National Laboratory | Huang H.W.,Rice University
Biophysical Journal | Year: 2011

Human LL-37 is a multifunctional cathelicidin peptide that has shown a wide spectrum of antimicrobial activity by permeabilizing microbial membranes similar to other antimicrobial peptides; however, its molecular mechanism has not been clarified. Two independent experiments revealed LL-37 bound to membranes in the α-helical form with the axis lying in the plane of membrane. This led to the conclusion that membrane permeabilization by LL-37 is a nonpore carpet-like mechanism of action. Here we report the detection of transmembrane pores induced by LL-37. The pore formation coincided with LL-37 helices aligning approximately normal to the plane of the membrane. We observed an unusual phenomenon of LL-37 embedded in stacked membranes, which are commonly used in peptide orientation studies. The membrane-bound LL-37 was found in the normal orientation only when the membrane spacing in the multilayers exceeded its fully hydrated value. This was achieved by swelling the stacked membranes with excessive water to a swollen state. The transmembrane pores were detected and investigated in swollen states by means of oriented circular dichroism, neutron in-plane scattering, and x-ray lamellar diffraction. The results are consistent with the effect of LL-37 on giant unilamellar vesicles. The detected pores had a water channel of radius 23-33 Å. The molecular mechanism of pore formation by LL-37 is consistent with the two-state model exhibited by magainin and other small pore-forming peptides. The discovery that peptide-membrane interactions in swollen states are different from those in less hydrated states may have implications for other large membrane-active peptides and proteins studied in stacked membranes. © 2011 by the Biophysical Society.

Ghattyvenkatakrishna P.K.,Oak Ridge National Laboratory | Carri G.A.,University of Akron
European Physical Journal E | Year: 2013

We present a Molecular Dynamics simulation study of the effect of trehalose concentration on the structure and dynamics of individual proteins immersed in trehalose/water mixtures. Hen egg-white Lysozyme is used in this study and trehalose concentrations of 0%, 10%, 20%, 30% and 100% by weight are explored. Surprisingly, we have found that changes in trehalose concentration do not change the global structural characteristics of the protein as measured by standard quantities like the mean square deviation, radius of gyration, solvent accessible surface area, inertia tensor and asphericity. Only in the limit of pure trehalose these metrics change significantly. Specifically, we found that the protein is compressed by 2% when immersed in pure trehalose. At the amino acid level there is noticeable rearrangement of the surface residues due to the change in polarity of the surrounding environment with the addition of trehalose. From a dynamic perspective, our computation of the Incoherent Intermediate Scattering Function shows that the protein slows down with increasing trehalose concentration; however, this slowdown is not monotonic. Finally, we also report in-depth results for the hydration layer around the protein including its structure, hydrogen-bonding characteristics and dynamic behavior at different length scales. © 2013 The Author(s).

Abou-Hanna J.,Bradley University | McGreevy T.E.,Oak Ridge National Laboratory
International Journal of Pressure Vessels and Piping | Year: 2011

Two effective approaches for obtaining ratchet boundaries of a structure undergoing cyclic loads are presented. The approaches use limit analysis of a structure whose yield surface is modified according to the cyclic load. In the first approach, Uniform Modified Yield (UMY) surface is used. UMY approach reduces the Mises-based cylindrical yield surface by Mises stress of the cyclic stress amplitude. UMY method was slightly conservative, and sometimes overly conservative, especially at high ratio of cyclic load to primary steady load. Conservatism, caused by the assumption that the modified yield surface remains isotropic, is eliminated by considering anisotropic Load Dependent Yield Modification approach, LDYM. This approach reduces yield strength based on relative orientation of steady primary and cyclic stress tensors. This work assumed elastic perfect plastic material behavior, with no strain hardening for both original and modified yield surfaces. Ratchet boundaries of several structures, published in literature, were obtained using UMY and LDYM approaches and verified against published data and results of conventional methods. Numerical procedures for UMY and LDYM approaches are extremely fast relative to conventional numerical schemes, and are not restricted by complex geometry or loading. © 2010 Elsevier Ltd.

Nicolai A.,Rensselaer Polytechnic Institute | Sumpter B.G.,Oak Ridge National Laboratory | Meunier V.,Rensselaer Polytechnic Institute
Physical Chemistry Chemical Physics | Year: 2014

The performance of graphene oxide framework (GOF) membranes for water desalination is assessed using classical molecular dynamics (MD) simulations. The coupling between water permeability and salt rejection of GOF membranes is studied as a function of linker concentration n, thickness h and applied pressure ΔP. The simulations reveal that water permeability in GOF-(n,h) membranes can be tuned from ∼5 (n = 32 and h = 6.5 nm) to 400 L cm -2 day-1 MPa-1 (n = 64 and h = 2.5 nm) and follows a Cnh-αn law. For a given pore size (n = 16 or 32), water permeability of GOF membranes increases when the pore spacing decreases, whereas for a given pore spacing (n = 32 or 64), water permeability increases by up to two orders of magnitude when the pore size increases. Furthermore, for linker concentrations n ≤ 32, the high water permeability corresponds to a 100% salt rejection, elevating this type of GOF membrane as an ideal candidate for water desalination. Compared to experimental performance of reverse osmosis membranes, our calculations suggest that under the same conditions of applied pressure and characteristics of membranes (ΔP ∼ 10 MPa and h ∼ 100 nm), one can expect a perfect salt rejection coupled to a water permeability two orders of magnitude higher than existing technologies, i.e., from a few cL cm-2 day-1 MPa-1 to a few L cm-2 day-1 MPa -1.© 2014 the Owner Societies.

Terentyev D.A.,Belgian Institute for Nuclear Sciences | Osetsky Yu.N.,Oak Ridge National Laboratory | Bacon D.J.,University of Liverpool
Acta Materialia | Year: 2010

Dislocation segments with Burgers vector b = 〈1 0 0〉 are formed during deformation of body-centred-cubic (bcc) metals by the interaction between dislocations with b = 1/2〈1 1 1〉. Such segments are also created by reactions between dislocations and dislocation loops in irradiated bcc metals. The obstacle resistance produced by these segments on gliding dislocations is controlled by their mobility, which is determined in turn by the atomic structure of their cores. The core structure of a straight 〈1 0 0〉 edge dislocation is investigated here by atomic-scale computer simulation for α-iron using three different interatomic potentials. At low temperature the dislocation has a non-planar core consisting of two 1/2〈1 1 1〉 fractional dislocations with atomic disregistry spread on planes inclined to the main glide plane. Increasing temperature modifies this core structure and so reduces the critical applied shear stress for glide of the 〈1 0 0〉 dislocation. It is concluded that the response of the 〈1 0 0〉 edge dislocation to temperature or applied stress determines specific reaction pathways occurring between a moving dislocation and 1/2〈1 1 1〉 dislocation loops. The implications of this for plastic flow in unirradiated and irradiated ferritic materials are discussed and demonstrated by examples. © 2009 Acta Materialia Inc.

Pint B.A.,Oak Ridge National Laboratory
Materials Science Forum | Year: 2011

Alumina-forming alloys have been studied for over 50 years and are now needed for high efficiency power generation applications operating at higher temperatures. Especially in the presence of water vapor, alumina-forming alloys outperform conventional chromia-forming alloys above 1000°C. However, alloy mechanical behavior is a significant issue and alumina-forming alloy development has been limited. The opportunity for alloy development is discussed as well as the factors that limit oxidation resistance, including alloy thermal expansion and optimizing reactive element additions. Finally, lifetime modeling is discussed for thick section components together with the need to address performance in more complex environments. © (2011) Trans Tech Publications.

Martin M.J.,Oak Ridge National Laboratory
Nuclear Data Sheets | Year: 2013

Detailed level schemes, decay schemes, and the experimental data on which they are based are presented for all nuclei with mass number A=152. The experimental data are evaluated; inconsistencies and discrepancies are noted; and adopted values for level and γ-ray energies, γ intensities, as well as for other nuclear properties are given. This evaluation replaces the A=152 evaluation published by Agda Artna-Cohen in Nuclear Data Sheets 79, 1 (1996) and the evaluation for 152Dy prepared by Balraj Singh and published in Nuclear Data Sheets 95, 995 (2002). © 2013 Elsevier Inc.

Dagotto E.,University of Tennessee at Knoxville | Dagotto E.,Oak Ridge National Laboratory
Reviews of Modern Physics | Year: 2013

The iron-based superconductors that contain FeAs layers as the fundamental building block in the crystal structures have been rationalized in the past using ideas based on the Fermi surface nesting of hole and electron pockets when in the presence of weak Hubbard U interactions. This approach seemed appropriate considering the small values of the magnetic moments in the parent compounds and the clear evidence based on photoemission experiments of the required electron and hole pockets. However, recent results in the context of alkali metal iron selenides, with generic chemical composition A xFe2-ySe2 (A=alkali metal element), have challenged those previous ideas since at particular compositions y the low-temperature ground states are insulating and display antiferromagnetic order with large iron magnetic moments. Moreover, angle-resolved photoemission studies have revealed the absence of hole pockets at the Fermi level in these materials. The present status of this exciting area of research, with the potential to alter conceptually our understanding of the iron-based superconductors, is here reviewed, covering both experimental and theoretical investigations. Other recent related developments are also briefly reviewed, such as the study of selenide two-leg ladders and the discovery of superconductivity in a single layer of FeSe. The conceptual issues considered established for the alkali metal iron selenides, as well as several issues that still require further work, are discussed. © 2013 American Physical Society.

Sridharan H.,Oak Ridge National Laboratory | Qiu F.,University of Texas at Dallas
Geographical Analysis | Year: 2013

Dasymetric areal interpolation is the process by which data are transferred from a spatial unit system for which they are available (source units) to another system for which they are required (target units) with the aid of ancillary information (control units). We propose a spatially disaggregated areal interpolation model for population data using light detection and ranging (LiDAR)-derived building volumes as an ancillary variable. Innovative methods are proposed for model initialization, iterative regression and adjustment, and stopping criteria to deal effectively with control units of unequal size. The model is derived and applied at the control unit level to minimize the modifiable areal unit problem, and an iterative adjustment process is utilized to overcome the spatial heterogeneity problem encountered in earlier approaches. The use of building volume to disaggregate the population into finer scales ensures maximum correspondence with the unit at which the original population data were collected and models not only the horizontal but also the vertical population distribution. A case study for Round Rock, Texas, demonstrates that the proposed spatially disaggregated model using LiDAR-derived building volumes outperforms earlier areal interpolation models using traditional area- and length-based ancillary variables. © 2013 The Ohio State University.

Liang J.F.,Oak Ridge National Laboratory
Acta Physica Polonica B | Year: 2013

The reaccelerated fission-fragment beams at HRIBF provide a unique opportunity for studying the mechanisms of fusion involving nuclei with large neutron excess. The fusion excitation functions for neutron-rich radioactive 132Sn incident on 40Ca and 58Ni targets have been measured to explore the role of transfer couplings in sub-barrier fusion enhancement. Evaporation residue cross sections for 124;126;127;128Sn+64Ni were measured to study the dependence of fusion probability on neutron excess.

Callen J.D.,University of Wisconsin - Madison | Canik J.M.,Oak Ridge National Laboratory | Smith S.P.,General Atomics
Physical Review Letters | Year: 2012

Predictions are developed for gradients and profiles of the electron density and temperature in tokamak H-mode pedestals that are in transport quasiequilibrium. They are based on assuming paleoclassical processes provide the irreducible minimum radial plasma transport and dominate in the steep gradient regions of pedestals. The predictions agree (within a factor of about two) with properties of a number of pedestal experimental results. © 2012 American Physical Society.

Zhang X.F.,Northeastern University China | Guo J.J.,Oak Ridge National Laboratory | Qin G.W.,Northeastern University China
Applied Physics Letters | Year: 2014

The usually utilized electromagnetic absorbers are fabricated by randomly dispersed fillers in polymer matrix, which limit the construction of multiple interfaces, thus influencing the optimization of absorption efficiency. In this Letter, the core/shell heterogeneous nanocapsules are chemically modified and subsequently conjugated on the micrometre-scale polymer units, forming a micro/nano-hybrided absorbent. Such a system creates multiple interfaces at sub-nanoscalc, thus producing enhanced dielectric loss phenomena and resulting in an absorption efficiency of more than 90% over 2-18 GHz. The present study provides an effective concept to optimize the electromagnetic coupling and has important implications in the development of electromagnetic absorption materials. ©2014 AIP Publishing LLC.

Chen J.,Brookhaven National Laboratory | Bai J.,Oak Ridge National Laboratory | Chen H.,New Jersey Institute of Technology | Graetz J.,Brookhaven National Laboratory
Journal of Physical Chemistry Letters | Year: 2011

The development of high capacity, safe lithium battery materials requires new tools to better understand how reaction conditions affect nucleation and crystallization, particle size, morphology, and defects. We present a general approach for studying the synthesis of Li battery electrode materials in real time. The formation of LiFePO4 was investigated by time-resolved in situ synchrotron X-ray diffraction under hydrothermal conditions, and the reaction kinetics were determined by changes of the Bragg reflections. We provide the first evidence in support of a dissolution-reprecipitation process for the formation of LiFePO4, which occurs at temperatures as low as 105 °C and appears to be a three-dimensional diffusion-controlled process. Lattice parameters and their evolution were monitored in situ, as well as the formation of antisite defects and their subsequent elimination under various synthesis conditions. The ability to characterize and tailor synthesis reactions in situ is essential for rapid optimization of the synthesis procedures and, ultimately, the development of new battery electrodes. © 2011 American Chemical Society.

Borole A.P.,Oak Ridge National Laboratory
Biofuels, Bioproducts and Biorefining | Year: 2011

Improving biofuel yield and water reuse are two important issues in the further development of biorefineries. An alternative to the typical combustion-based approach to handle residual organics stream by implementation of bioelectrochemical systems such as microbial fuel cells (MFCs) and/or microbial electrolysis cells (MECs) to improve energy recovery from biomass is presented. The potential advantages of this alternative scheme in a biorefinery include minimization of heat loss and generation of a higher-value product: electricity (in MFC) or hydrogen (MEC). The need for 5-15 gallons of water per gallon of ethanol can be reduced significantly via recycling of water after MEC treatment. Removal of inhibitory byproducts such as furans, phenolics, and acetate in MFC/MECs to generate energy, thus, has dual advantages: improvements in energy efficiency and ability to recycle water. Conversion of the sugar- and lignin-degradation products to hydrogen is synergistic with biorefinery hydrogen requirements for upgrading Fischer-Tropsch (F-T) liquids and other byproducts to high-octane fuels and/or high-value products. Some of these products include sorbitol, succinic acid, furan and levulinate derivatives, glycols, polyols, 1,4-butenadiol, phenolics polymers, etc. Potential process alternatives utilizing MECs in biorefineries capable of improving energy efficiency by up to 30% are discussed. Published in 2011 by John Wiley & Sons, Ltd. © 2011 Society of Chemical Industry and John Wiley & Sons, Ltd.

Calkins J.O.,University of Georgia | Umasankar Y.,University of Georgia | O'Neill H.,Oak Ridge National Laboratory | Ramasamy R.P.,University of Georgia
Energy and Environmental Science | Year: 2013

Spinach thylakoids were immobilized onto multiwalled carbon nanotubes using a molecular tethering chemistry. The resulting thylakoid-carbon nanotube composites showed high photo-electrochemical activity under illumination. Multiple membrane proteins have been observed to participate in direct electron transfer with the electrode, resulting in the generation of photocurrents, the first of its kind reported for natural photosynthetic systems. Upon inclusion of a mediator, the photo-activity was enhanced. The major contributor to the photocurrent was the light-induced water oxidation reaction at the photosystem II complex. The thylakoid-MWNT composite electrode yielded a maximum current density of 68 μA cm-2 and a steady state current density of 38 μA cm-2, which are two orders of magnitude larger than previously reported for similar systems. The high electrochemical activity of the thylakoid-MWNT composites has significant implications for both photosynthetic energy conversion and photofuel production applications. A fuel cell type photosynthetic electrochemical cell developed using a thylakoid-MWNT composite anode and laccase cathode produced a maximum power density of 5.3 μW cm -2, comparable to that of enzymatic fuel cells. The carbon based nanostructured electrode has the potential to serve as an excellent immobilization support for photosynthetic electrochemistry based on the molecular tethering approach as demonstrated in this work. © 2013 The Royal Society of Chemistry.

Dai P.,University of Tennessee at Knoxville | Dai P.,CAS Institute of Physics | Hu J.,CAS Institute of Physics | Hu J.,Purdue University | And 2 more authors.
Nature Physics | Year: 2012

High-temperature superconductivity in the iron-based materials emerges from, or sometimes coexists with, their metallic or insulating parent compound states. This is surprising, as these undoped states exhibit dramatically different antiferromagnetic spin arrangements and Néel temperatures. Although there is a general consensus that magnetic interactions are important for superconductivity, much remains unknown concerning the microscopic origin of the magnetic states. In this review, we summarize the progress in this area, focusing on recent experimental and theoretical results, and their microscopic implications. We conclude that the parent compounds are in a state that is more complex than that implied by a simple Fermi surface nesting scenario, and a dual description including both itinerant and localized degrees of freedom is needed to properly describe these fascinating materials. © 2012 Macmillan Publishers Limited.

Staruch M.,University of Connecticut | Cantoni C.,Oak Ridge National Laboratory | Jain M.,University of Connecticut
Applied Physics Letters | Year: 2013

La, Sr, Mn, and Mg precursors were mixed in stoichiometric ratio 0.67/0.33/1/x with solvent and were spin-coated onto (001) LaAlO3 substrates. X-ray diffraction and elemental mapping of these films indicate that for small addition of Mg precursor, Mg2+ acts as a dopant in La 0.67Sr0.33MnO3 phase and for higher concentrations, MgO phase separates out. Curie temperature and metal-insulator transition temperature systematically decrease with increasing molar concentration of Mg(O). Low-field magnetoresistance of films significantly enhanced by Mg addition and for the highest amount of Mg at 10 K, values were -35.5% and -83.2% with 0.5 T and 3 T applied fields, respectively. © 2013 American Institute of Physics.

Du M.-H.,Oak Ridge National Laboratory
Applied Physics Letters | Year: 2013

Ionic conductivity due to vacancy diffusion and the resulting polarization phenomenon are major challenges to the development of TlBr radiation detector. It had been proposed that impurity doping of TlBr can suppress the ionic conductivity because the impurities can getter vacancies to form neutral complexes. This paper shows that the isolated vacancies can maintain their equilibrium concentrations even at room temperature, rendering any gettering methods ineffective. The main effect of doping is to change the Fermi level and consequently the vacancy concentration. The minimal ionic conductivity is reached at the donor concentration of [D+] = 4 × 10 16 cm-3. © 2013 American Institute of Physics.

Liu M.,General Motors | Song G.-L.,Oak Ridge National Laboratory
Corrosion Science | Year: 2013

In the present study, the corrosion behavior of AXJ530 magnesium alloy with different iron and manganese contents is investigated in 3.5. wt% sodium chloride solution in order to tailor the tolerance limit of Fe impurity in the magnesium alloy. Through a comprehensive phase diagram calculation and corrosion evaluation, the mechanisms for the tolerance limit of Fe in magnesium alloys are discussed. The study adds a new dimension to controlling the Mg alloy impurity in terms of alloying composition design and casting conditions. © 2013 Elsevier Ltd.

Mittal S.,Oak Ridge National Laboratory
ACM Computing Surveys | Year: 2016

Approximate computing trades off computation quality with effort expended, and as rising performance demands confront plateauing resource budgets, approximate computing has become not merely attractive, but even imperative. In this article, we present a survey of techniques for approximate computing (AC). We discuss strategies for finding approximable program portions and monitoring output quality, techniques for using AC in different processing units (e.g., CPU, GPU, and FPGA), processor components, memory technologies, and so forth, as well as programming frameworks for AC. We classify these techniques based on several key characteristics to emphasize their similarities and differences. The aim of this article is to provide insights to researchers into working of AC techniques and inspire more efforts in this area to make AC the mainstream computing approach in future systems. © 2016 ACM.

Numerical simulation can be key to the understanding of the multidimensional nature of transient detonation waves. However, the accurate approximation of realistic detonations is demanding as a wide range of scales needs to be resolved. This paper describes a successful solution strategy that utilizes logically rectangular dynamically adaptive meshes. The hydrodynamic transport scheme and the treatment of the nonequilibrium reaction terms are sketched. A ghost fluid approach is integrated into the method to allow for embedded geometrically complex boundaries. Large-scale parallel simulations of unstable detonation structures of Chapman-Jouguet detonations in low-pressure hydrogen-oxygen-argon mixtures demonstrate the efficiency of the described techniques in practice. In particular, computations of regular cellular structures in two and three space dimensions and their development under transient conditions, that is, under diffraction and for propagation through bends are presented. Some of the observed patterns are classified by shock polar analysis, and a diagram of the transition boundaries between possible Mach reflection structures is constructed. Copyright © 2011 Ralf Deiterding.

Ma Z.,Fudan University | Dai S.,Oak Ridge National Laboratory
ACS Catalysis | Year: 2011

Small gold nanoparticles dispersed on certain oxide supports exhibit unprecedented catalytic activities in low-temperature CO oxidation, and gold catalysts show a great potential for selective oxidation or hydrogenation of organic substrates. Nevertheless, most gold catalysts (e.g., Au/TiO2, Au/Al2O3, Au/Fe2O3, Au/SiO 2, Au/CeO2) have been prepared by loading gold on unmodified or modified solid supports through traditional synthesis methodologies (e.g., deposition precipitation, wet impregnation), therefore having simple metal-on-support structures and metal-support interactions. The current Perspective highlights some recent progress in the design of novel structured gold nanocatalysts, including unsupported or supported core-shell or yolk-shell structures, gold nanoparticles encapsulated in an inorganic matrix, postmodified gold catalysts, gold-based alloy catalysts, and gold catalysts with additional interfacial sites (or metal oxide components) carried to supports or formed in situ on supports. The objective of most of these studies was to demonstrate synthetic protocols by testing the catalytic performance of the prepared catalysts in simple probe reactions, and the focus was more on materials synthesis than on catalytic reactions or reaction mechanisms. These novel structured gold catalysts will certainly bring new opportunities for studying their performance in various catalytic reactions, the nature of active sites, reaction mechanisms, and correlations between structure and catalytic properties. © 2011 American Chemical Society.

Sumpter B.G.,Oak Ridge National Laboratory | Liang L.,Rensselaer Polytechnic Institute | Nicolai A.,Rensselaer Polytechnic Institute | Meunier V.,Rensselaer Polytechnic Institute
Accounts of Chemical Research | Year: 2014

The vital importance of energy to society continues to demand a relentless pursuit of energy responsive materials that can bridge fundamental chemical structures at the molecular level and achieve improved functionality and performance. This demand can potentially be realized by harnessing the power of self-assembly, a spontaneous process where molecules or much larger entities form ordered aggregates as a consequence of predominately noncovalent (weak) interactions. Self-assembly is the key to bottom-up design of molecular devices, because the nearly atomic-level control is very difficult to realize in a top-down, for example, lithographic, approach. However, while function in simple systems such as single crystals can often be evaluated a priori, predicting the function of the great variety of self-assembled molecular architectures is complicated by the lack of understanding and control over nanoscale interactions, mesoscale architectures, and macroscale order. To establish a foundation toward delivering practical solutions, it is critical to develop an understanding of the chemical and physical mechanisms responsible for the self-assembly of molecular and hybrid materials on various support substrates.Typical molecular self-assembly involves noncovalent intermolecular and substrate-molecule interactions. These interactions remain poorly understood, due to the combination of many-body interactions compounded by local or collective influences from the substrate atomic lattice and electronic structure. Progress toward unraveling the underlying physicochemical processes that control the structure and macroscopic physical, chemical, mechanical, electrical, and transport properties of materials increasingly requires tight integration of theory, modeling, and simulation with precision synthesis, advanced experimental characterization, and device measurements. Theory, modeling, and simulation can accelerate the process of materials understanding and design by providing atomic level understanding of the underlying physicochemical phenomena (illuminating connections between experiments). It can also provide the ability to explore new materials and conditions before they are realized in the laboratory. With tight integration and feedback with experiment, it becomes feasible to identify promising materials or processes for targeted energy applications.In this Account, we highlight recent advances and success in using an integrated approach based on electronic structure simulations and scanning probe microscopy techniques to study and design functional materials formed from the self-assembly of molecules into supramolecular or polymeric architectures on substrates. © 2014 American Chemical Society.

Li C.,North Carolina State University | Yu Y.,North Carolina State University | Chi M.,Oak Ridge National Laboratory | Cao L.,North Carolina State University
Nano Letters | Year: 2013

We demonstrate synthesis of a new type of heterostructures that comprise two-dimensional (2D) nanosheets (NSs) epitaxially grown at one-dimensional (1D) nanowires (NWs). The synthesis involves materials with a graphite-like layered structure in which covalently bonded layers are held by weak van der Waals forces. GeS was used as a prototype material in this work. The synthesis also involves a seeded-growth process, where GeS NWs are grown first as seeds followed by a seeded growth of NSs at the pre-grown NWs. We observe that exposing the pre-grown NWs to air prior to the seeded growth is critical for the formation of NSs to yield NS-NW heterostructures. Our experimental results suggest that this might be due to a mild oxidation at the NW surface caused by the air exposure, which could subsequently facilitate the nucleation of NSs at the NWs. It also suggests that the surface oxidation needs to be controlled in a proper range in order to achieve optimized NS growths. We believe that this synthetic strategy may generally apply to the growth of NS-NW heterostructures of other layered chalcogenide materials. NS-NW heterostructures provide capabilities to monolithically integrate the functionality of 1D NWs and 2D NSs into a 3D space. It holds great potential in applications that request complex nanomaterials with multiple functionality, high surface area, and efficient charge transport, such as energy storage, chemical sensing, solar energy conversion, and 3D electric and photonic devices. © 2013 American Chemical Society.

Rubin J.,University of Maine, United States | Leiby P.N.,Oak Ridge National Laboratory
Energy Policy | Year: 2013

This research examines the economic implications of different designs for a national low carbon fuel standard (NLCFS) for the road transportation sector. A NLCFS based on the average Carbon Intensity (CI) of all fuels sold generates an incentive for fuel suppliers to reduce the measured CI of their fuels. The economic impacts are determined by the availability of low carbon fuels, estimates of which can vary widely. Also important are the compliance path, reference level CI, and the design of the credit system, particularly the opportunities for trading and banking. To quantitatively examine the implications of a NLCFS, we created the Transportation Regulation and Credit Trading (TRACT) Model. With TRACT, we model a NLCFS credit trading system among profit maximizing fuel suppliers for light- and heavy-duty vehicle fuel use for the United States from 2012 to 2030. We find that credit trading across gasoline and diesel fuel markets can lower the average costs of carbon reductions by an insignificant amount to 98% depending on forecasts of biofuel supplies and carbon intensities. Adding banking of credits on top of trading can further lower the average cost of carbon reductions by 5%-9% and greatly reduce year-to-year fluctuations in credit prices. © 2012 Elsevier Ltd.

Mittal S.,Oak Ridge National Laboratory
ACM Computing Surveys | Year: 2016

To meet the needs of a diverse range of workloads, asymmetric multicore processors (AMPs) have been proposed, which feature cores of different microarchitecture or ISAs. However, given the diversity inherent in their design and application scenarios, several challenges need to be addressed to effectively architect AMPs and leverage their potential in optimizing both sequential and parallel performance. Several recent techniques address these challenges. In this article, we present a survey of architectural and system-level techniques proposed for designing and managing AMPs. By classifying the techniques on several key characteristics, we underscore their similarities and differences. We clarify the terminology used in this research field and identify challenges that are worthy of future investigation. We hope that more than just synthesizing the existing work on AMPs, the contribution of this survey will be to spark novel ideas for architecting future AMPs that can make a definite impact on the landscape of next-generation computing systems. © 2016 ACM.

Ding J.,Johns Hopkins University | Cheng Y.-Q.,Oak Ridge National Laboratory | Ma E.,Johns Hopkins University
Acta Materialia | Year: 2014

Extensive molecular dynamics simulations were carried out to monitor the development of icosahedral order in Cu64Zr34 liquid and metallic glass (MG). This study illustrates that at this Cu-rich Cu-Zr alloy composition, Cu-centered full icosahedra constitute the dominant and characteristic short-range-ordered coordination motif. The results for this model liquid/glass address five questions regarding the ordering of Cu-centered coordination polyhedral towards full icosahedra, including: (i) its evolution and extent during prolonged structural relaxation; (ii) the resulting reduction in potential energy and slowing-down of dynamics; (iii) the accompanying preference of a particular type of Zr-centered Kasper coordination polyhedra; (iv) the evolution and conversion of polyhedral connection schemes in the medium range; and (v) the formation and percolation of networks formed by interpenetrating connection of icosahedra to constitute a stiff backbone over extended range. Five related issues are also clarified, to: (i) differentiate full-icosahedra-based ordering from the generally favorable fivefold bonds; (ii) compare the Cu-based perspective with a Zr-centric view; (iii) systematically list the rationales behind focusing on icosahedral order for explaining the Cu64Zr34 MG/liquid properties; (iv) discuss other non-icosahedral ordering varieties; and (v) comment on the most liquid-like local environments. Taken together, the ten issues addressed set the stage for understanding structure-property relations in a category of amorphous alloys that can be characterized based on full-icosahedral ordering. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Tsetseris L.,National Technical University of Athens | Tsetseris L.,Vanderbilt University | Pantelides S.T.,Vanderbilt University | Pantelides S.T.,Oak Ridge National Laboratory
Carbon | Year: 2014

Graphene is generally thought to be a perfect membrane that can block completely the penetration of impurities and molecules. Here we use density-functional theory calculations to examine this property with respect to prototype atomic species. We find that hydrogen and oxygen atoms have, indeed, prohibitively large barriers (4.2 eV and 5.5 eV) for permeation through a defect-free graphene layer.We also find, however, that boron permeation occurs by an intricate bond switching synergistic process with an activation energy of only 1.3 eV, indicating easy B penetration upon moderate annealing. Nitrogen permeation has an intermediate activation energy of 3.2 eV. The results show that by controlling annealing conditions, pristine graphene could allow the selective passage of atoms. © 2013 Elsevier Ltd. All rights reserved.

Savara A.,Oak Ridge National Laboratory
Surface Science | Year: 2016

A method has been developed for finding improved fits during simulation and fitting of data from complex reaction network temperature programmed reactions (CRN-TPR). It was found that simulation and fitting of CRN-TPR presents additional challenges relative to simulation and fitting of simpler TPR systems. The method used here can enable checking the plausibility of proposed chemical mechanisms and kinetic models. The most important finding was that when choosing an objective function, use of an objective function that is based on integrated production provides more utility in finding improved fits when compared to an objective function based on the rate of production. The response surface produced by using the integrated production is monotonic, suppresses effects from experimental noise, requires fewer points to capture the response behavior, and can be simulated numerically with smaller errors. For CRN-TPR, there is increased importance (relative to simple reaction network TPR) in resolving of peaks prior to fitting, as well as from weighting of experimental data points. Using an implicit ordinary differential equation solver was found to be inadequate for simulating CRN-TPR. The method employed here was capable of attaining improved fits in simulation and fitting of CRN-TPR when starting with a postulated mechanism and physically realistic initial guesses for the kinetic parameters. © 2016

Greer A.L.,University of Cambridge | Greer A.L.,Tohoku University | Cheng Y.Q.,Oak Ridge National Laboratory | Ma E.,Johns Hopkins University
Materials Science and Engineering R: Reports | Year: 2013

Shear-banding is a ubiquitous plastic-deformation mode in materials. In metallic glasses, shear bands are particularly important as they play the decisive role in controlling plasticity and failure at room temperature. While there have been several reviews on the general mechanical properties of metallic glasses, a pressing need remains for an overview focused exclusively on shear bands, which have received tremendous attention in the past several years. This article attempts to provide a comprehensive and up-to-date review on the rapid progress achieved very recently on this subject. We describe the shear bands from the inside out, and treat key materials-science issues of general interest, including the initiation of shear localization starting from shear transformations, the temperature and velocity reached in the propagating or sliding band, the structural evolution inside the shear-band material, and the parameters that strongly influence shear-banding. Several new discoveries and concepts, such as stick-slip cold shear-banding and strength/plasticity enhancement at sub-micrometer sample sizes, will also be highlighted. The understanding built-up from these accounts will be used to explain the successful control of shear bands achieved so far in the laboratory. The review also identifies a number of key remaining questions to be answered, and presents an outlook for the field. © 2013 Elsevier B.V. All rights reserved.

Samayam I.P.,University of Toledo | Hanson B.L.,University of Toledo | Langan P.,Oak Ridge National Laboratory | Schall C.A.,University of Toledo
Biomacromolecules | Year: 2011

The effects of varying ionic liquid pretreatment parameters on various sources of lignocellulosic biomass have been studied using X-ray powder diffraction, X-ray fiber diffraction, and compositional analysis. Comparative enzymatic hydrolysis and sugar analysis were used to relate the observed changes in cellulose structure to biomass digestibility. In this study, the factor most clearly associated with enhanced biomass hydrolysis is the conversion of cellulose fibers from the cellulose I to the cellulose II crystal phase. © 2011 American Chemical Society.

Mamontov E.,Oak Ridge National Laboratory
Journal of Physical Chemistry B | Year: 2013

At sufficiently high temperatures, the center-of-mass microscopic diffusion dynamics of liquids is characterized by a single component, often with weak temperature dependence. In this regime, the effective cage made by the neighbor particles cannot be sustained and readily breaks down, enabling long-range diffusion. As the temperature is decreased, the cage relaxation becomes impeded, leading to a higher viscosity with more pronounced temperature dependence. On the microscopic scale, the sustained caging effect leads to a separation between a faster in-cage relaxation component and a slower cage-breaking relaxation component. The evidence for the separate dynamic components, as opposed to a single stretched component, is provided by quasielastic neutron scattering experiments. We use a simple method to evaluate the extent of the dynamic components separation as a function of temperature in a group of related aromatic molecular liquids. We find that, regardless of the glass-forming capabilities or lack thereof, progressively more pronounced separation between the in-cage and cage-breaking dynamic components develops on cooling down as the ratio of Tb/T, where Tb is the boiling temperature, increases. This reflects the microscopic mechanism behind the empirical rule for the glass forming capability based on the ratio of boiling and melting temperatures, Tb/Tm. When a liquid's Tb/T m happens to be high, the liquid can readily be supercooled below its Tm because the liquid's microscopic relaxation dynamics is already impeded at Tm, as evidenced by a sustained caging effect manifested through the separation of the in-cage and cage-breaking dynamic components. Our findings suggest certain universality in the temperature dependence of the microscopic diffusion dynamics in molecular liquids, regardless of their glass-forming capabilities. Unless the insufficiently low (with respect to Tb) melting temperature, Tm, intervenes and makes crystallization thermodynamically favorable when cage-breaking is still unimpeded and the structural relaxation is fast, the liquid is likely to become supercooled. The propensity to supercooling and eventually forming a glass is thus determined by a purely thermodynamic factor, Tb/Tm. © 2013 American Chemical Society.

Singh D.J.,Oak Ridge National Laboratory
PLoS ONE | Year: 2015

We report the electronic structure and related properties of the superconductor Ta2PdSe5 as determined from density functional calculations. The Fermi surface has two disconnected sheets, both derived from bands of primarily chalcogenide p states. These are a corrugated hole cylinder and a heavier complex shaped electron sheet. The sheets contain 0.048 holes and a compensating number of electrons per formula unit, making the material a semimetallic superconductor. The results support the presence of two band superconductivity, although a discrepancy in the specific heat is noted. This discrepancy is discussed as a possible consequence of Pd deficiency in samples. © 2015 David Joseph Singh.

Conley H.J.,Vanderbilt University | Wang B.,Vanderbilt University | Ziegler J.I.,Vanderbilt University | Haglund R.F.,Vanderbilt University | And 3 more authors.
Nano Letters | Year: 2013

We report the influence of uniaxial tensile mechanical strain in the range 0-2.2% on the phonon spectra and bandstructures of monolayer and bilayer molybdenum disulfide (MoS2) two-dimensional crystals. First, we employ Raman spectroscopy to observe phonon softening with increased strain, breaking the degeneracy in the E′ Raman mode of MoS2, and extract a Grüneisen parameter of ∼1.06. Second, using photoluminescence spectroscopy we measure a decrease in the optical band gap of MoS2 that is approximately linear with strain, ∼45 meV/% strain for monolayer MoS2 and ∼120 meV/% strain for bilayer MoS2. Third, we observe a pronounced strain-induced decrease in the photoluminescence intensity of monolayer MoS2 that is indicative of the direct-to-indirect transition of the character of the optical band gap of this material at applied strain of ∼1%. These observations constitute a demonstration of strain engineering the band structure in the emergent class of two-dimensional crystals, transition-metal dichalcogenides. © 2013 American Chemical Society.

Banerjee A.,Oak Ridge National Laboratory
Nature Materials | Year: 2016

Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. Whereas their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting owing to the emergence of fundamentally new excitations such as Majorana fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. These we report here for a ruthenium-based material, α-RuCl3, continuing a major search (so far concentrated on iridium materials) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisite strong spin–orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly two-dimensional nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl3 as a prime candidate for fractionalized Kitaev physics. © 2016 Nature Publishing Group

The interaction of proteins with aqueous solutions of ionic liquids (ILs) has attracted considerable recent attention owing to the challenges of finding biocompatible water-free ILs. These systems remain of great interest because of the potential for using ILs as designer solvents for biocatalytic processes. Increasing evidence demonstrates that aqueous solutions of water-miscible ILs, such as the well-studied 1-alkyl-3-methylimidazolium ILs, disrupt the native fold of proteins and can drive the formation of non-native aggregates that could negatively impact catalytic function. Here, we present a study comparing the thermal unfolding of human serum albumin (HSA) in a 1 M solution of the protein denaturant guanidine hydrochloride with two 1 M aqueous solutions of 1-butyl-3-methylimidazolium ILs, namely the chloride and the acetate. Small-angle neutron scattering (SANS) measurements found qualitative agreement between the thermally driven unfolding process for the three denaturants, as well as with a Tris buffer solution. HSA irreversibly aggregates and unfolds in the three denaturant solutions upon heating to temperatures below that required to drive the same process in a simple Tris buffer solution. The results reveal subtle differences in the interaction of the ILs and guanidine hydrochloride with the protein, although the final states of the protein were similar in all cases. The results indicate that the ions of water-miscible ILs and guanidine hydrochloride have specific roles in disrupting protein structure and driving aggregation. The experimental approach employed has the potential to provide new insights into protein interactions with ionic liquids that may aid in the search for more biocompatible ionic liquids. © 2013 American Chemical Society.

Okamoto S.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

We investigate the spin injection and the spin transport in paramagnetic insulators described by simple Heisenberg interactions using auxiliary particle methods. Some of these methods allow access to both paramagnetic states above magnetic transition temperatures and magnetic states at low temperatures. It is predicted that the spin injection at an interface with a normal metal is rather insensitive to temperatures above the magnetic transition temperature. On the other hand below the transition temperature, it decreases monotonically and disappears at zero temperature. We also analyze the bulk spin conductance. It is shown that the conductance becomes zero at zero temperature as predicted by linear spin wave theory but increases with temperature and is maximized around the magnetic transition temperature. These findings suggest that the compromise between the two effects determines the optimal temperature for spintronics applications utilizing magnetic insulators. © 2016 American Physical Society.

Del-Castillo-Negrete D.,Oak Ridge National Laboratory
Nonlinear Processes in Geophysics | Year: 2010

A review of non-diffusive transport in fluids and plasmas is presented. In the fluid context, non-diffusive chaotic transport by Rossby waves in zonal flows is studied following a Lagrangian approach. In the plasma physics context the problem of interest is test particle transport in pressure-gradient-driven plasma turbulence. In both systems the probability density function (PDF) of particle displacements is strongly non-Gaussian and the statistical moments exhibit super-diffusive anomalous scaling. Fractional diffusion models are proposed and tested in the quantitative description of the non-diffusive Lagrangian statistics of the fluid and plasma problems. Also, fractional diffusion operators are used to construct non-local transport models exhibiting up-hill transport, multivalued flux-gradient relations, fast pulse propagation phenomena, and "tunneling" of perturbations across transport barriers. © 2010 Author(s).

Gao Z.,Oak Ridge National Laboratory
Energy Conversion and Management | Year: 2010

This paper discusses the strategy of improving the efficiency of air-source heat pumps by adding a small amount of heat to the sensor of the thermostatic expansion valve (TXV). TXV heating retards the closing of the valve and boosts energy efficiency in heating mode. Test results demonstrate that appropriate TXV heating achieves an improvement in coefficient of performance (COP) and thermal comfort. The required heating power is no more than 40 W and the additional equipment cost is less than $20 at manufacturer cost (2006). Thus, the strategy of TXV heating is both technologically practical and low cost. © 2009 Elsevier Ltd.

Du A.,University of Queensland | Sanvito S.,Trinity College Dublin | Smith S.C.,Oak Ridge National Laboratory
Physical Review Letters | Year: 2012

Transition metal-free magnetism and half-metallicity recently has been the subject of intense research activity due to its potential in spintronics application. Here we, for the first time, demonstrate via density functional theory that the most recently experimentally realized graphitic carbon nitride (g-C 4N 3) displays a ferromagnetic ground state. Furthermore, this novel material is predicted to possess an intrinsic half-metallicity never reported to date. Our results highlight a new promising material toward realistic metal-free spintronics application. © 2012 American Physical Society.

Osetsky Y.N.,Oak Ridge National Laboratory | Yip S.,Massachusetts Institute of Technology
Physical Review Letters | Year: 2012

The strain-rate response of flow stress in a plastically deforming crystal is formulated through a stress-sensitive dislocation mobility model that can be evaluated by atomistic simulation. For the flow stress of a model crystal of bcc Fe containing a 12-111 screw dislocation, this approach describes naturally a non-Arrhenius upturn at high strain rate, an experimentally established transitional behavior for which the underlying mechanism has not been clarified. Implications of our findings regarding the previous explanations of strain-rate effects on flow stress are discussed. © 2012 American Physical Society.

Cheng M.-D.,Oak Ridge National Laboratory | Corporan E.,Air Force Research Lab
Atmospheric Environment | Year: 2010

Aircraft emissions contribute to the increased atmospheric burden of particulate matter (PM) that plays an important role in air quality, human health, visibility, contrail formation and climate change. Sampling and measurement of modern aircraft emissions at the engine exhaust plane (EEP) for engine and fuel certification remains challenging, as no agency-certified method is available. In this paper we summarize the results of three recent field studies devoted to investigate the consistency and applicability of " extractive" and " optical remote-sensing" (ORS) technologies in the sampling and measurement of gaseous and PM emitted by a number of military aircraft engines. Three classes of military engines were investigated; these include T56, TF33, and T700 & T701C types of engines, which consume 70-80% of the military aviation fuel each year. JP-8 and Fischer-Tropsch (FT)-derived paraffinic fuels were used to study the effect of fuels. It was found that non-volatile particles in the engine emissions were in the 20. nm range for the low power condition of new helicopter engines to 80. nm for the high power condition of legacy engines. Elemental analysis indicated little metals were present on particles, while most of the materials on the exhaust particles were carbon and sulfate based. Alkanes, carbon monoxide, carbon dioxide, nitrogen oxides, sulfur dioxide, formaldehyde, ethylene, acetylene and propylene were detected. The last five species were most noticeable only under low engine power. The emission indices calculated based on the ORS data deviate significantly from those based on the extractive data. Nevertheless, the ORS techniques were useful in the sense that it provided non-intrusive real-time detection of species in the exhaust plume, which warrants further development. The results obtained in this program help validate sampling methodology and measurement techniques used for non-volatile PM aircraft emissions as described in the SAE AIR6037 (2009). © 2010 Elsevier Ltd.

Pennycook S.J.,Oak Ridge National Laboratory
Ultramicroscopy | Year: 2012

This review covers the development of scanning transmission electron microscopy from the innovations of Albert Crewe to the two-dimensional spectrum imaging in the era of aberration correction. It traces the key events along the path, the first atomic resolution Z-contrast imaging of individual atoms, the realization of incoherent imaging in crystals and the role of dynamical diffraction, simultaneous, atomic resolution electron energy loss spectroscopy, and finally the tremendous impact of the successful correction of lens aberrations, not just in terms of resolution but also in single atom sensitivity. © 2012 Elsevier B.V.

Koshelkin A.V.,National Research Nuclear University MEPhI | Wong C.-Y.,Oak Ridge National Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We show from the action integral that in the special environment of a flux tube, QCD4 in (3+1) dimensional space-time can be approximately compactified into QCD2 in (1+1) dimensional space-time. In such a process, we find out how the coupling constant g2D in QCD2 is related to the coupling constant g4D in QCD4. We show how the quark and the gluon in QCD2 acquire contributions to their masses arising from their confinement within the tube and how all these quantities depend on the excitation of the partons in the transverse degrees of freedom. The compactification facilitates the investigation of some dynamical problems in QCD4 in the simpler dynamics of QCD2 where the variation of the gluon fields leads to a bound state. © 2012 American Physical Society.

Feng G.,Vanderbilt University | Cummings P.T.,Vanderbilt University | Cummings P.T.,Oak Ridge National Laboratory
Journal of Physical Chemistry Letters | Year: 2011

Supercapacitors composed of slit-shaped micropores ranging in size from 0.67 to 1.8 nm in a room-temperature ionic liquid were studied to investigate the dependence of capacitance (C) on the pore size (d) using molecular dynamics simulations. The capacitance versus pore size (i.e., the C-d curve) was found to exhibit two peaks located at 0.7 and 1.4 nm, respectively. Specifically, as the pore shrinks from 1.0 to 0.7 nm, the capacitance of the micropore increases anomalously, in good agreement with experimental observations. We report herein that the second peak within 1.0 to 1.8 nm is a new feature of the C-d curve. Furthermore, by analogy to the wave interference, we demonstrate that the interference of two electrical double layers near each slit wall does not only explain the entire C-d curve, including the anomalous character, but also predicts the oscillatory behavior of C-d curve beyond 1.8 nm. © 2011 American Chemical Society.

Mullins D.R.,Oak Ridge National Laboratory
Surface Science | Year: 2016

The adsorption and reactions of CO adsorbed on Rh particles deposited on K-covered CeO2(111) were studied by temperature programmed desorption and photoelectron spectroscopy. K deposited on CeO2(111) forms a KOX over-layer by extracting O from the ceria and partially reducing some of the Ce4+ to Ce3+. CO does not adsorb on the KOX/ CeO2-X(111) surface in the absence of Rh particles. CO adsorbed on Rh/K/CeO2(111) adsorbs molecularly on the Rh at 200K. As the surface is heated the CO spills-over and reacts with the KOX to form carbonate. The carbonate decomposes at elevated temperature to produce CO and CO2. The carbonate stabilizes the KOX so that K desorbs at a higher temperature than it would in the absence of CO. When the Rh and K deposition are reversed so that K is deposited on both the Rh and the CeO2(111), CO adsorbs as CO2 - at 200K. The CO2 - decomposes below 350K to produce gas phase CO and adsorbed CO3 2- and CO. The CO is stabilized by the K on the Rh and desorbs above 540K. The carbonate decomposes into gas phase CO and CO2. © 2016 Elsevier B.V.

Accurately predicting the fuel savings that can be achieved with the implementation of various technologies developed for fuel efficiency can be very challenging, particularly when considering combinations of technologies. Differences in the usage of highway vehicles can strongly influence the benefits realized with any given technology, which makes generalizations about fuel savings inappropriate for different vehicle applications. A model has been developed to estimate the potential for reducing fuel consumption when advanced efficiency technologies, or combinations of these technologies, are employed on highway vehicles, particularly medium- and heavy-duty trucks. The approach is based on a tractive energy analysis applied to drive cycles representative of the vehicle usage, and the analysis specifically accounts for individual energy loss factors that characterize the technologies of interest. This tractive energy evaluation is demonstrated by analyzing measured drive cycles from a long-haul trucking fleet and the results of an assessment of the fuel savings potential for combinations of technologies are presented. The results of this research will enable more reliable estimates of the fuel savings benefits that can be realized with particular technologies and technology combinations for individual trucking applications so that decision makers can make informed investment decisions for the implementation of advanced efficiency technologies.

This research develops then merges two separate models to simulate electric vehicle diffusion through recreation of the Boston metropolitan statistical area vehicle market place. The first model is a mixed (random parameters) logistic regression applied to data from the US Department of Transportation's 2009 National Household Travel Survey. The second, agent-based model simulates social network interactions through which agents' vehicle choice sets are endogenously determined. Parameters from the first model are applied to the choice sets determined in the second. Results indicate that electric vehicles as a percentages of vehicle stock range from 1% to 22% in the Boston metropolitan statistical area in the year 2030, percentages being highly dependent on scenario specifications. A lower price is the main source of competitive advantage for vehicles but other characteristics, such as vehicle classification and range, are demonstrated to influence consumer choice. Government financial incentive availability leads to greater market shares in the beginning years and helps to spread diffusion in later years due to an increased base of initial adopters. Although seen as a potential hindrance to EV diffusion, battery cost scenarios have relatively small impacts on EV diffusion in comparison to policy, range, miles per gallon (MPG), and vehicle miles travelled (VMT) as a percentage of range assumptions. Pessimistic range assumptions decrease overall PHEV and BEV percentages of vehicle stock by 50% and 30%, respectively, relative to the EPA-estimated range scenarios. Fuel cost scenarios do not considerably alter estimated BEV and PHEV stock but increase the ratio of car stock to light truck stock in the internal combustion engine (ICE) vehicle spectrum. Specifically, cars are estimated at 55% of ICE vehicle stock in the default fuel price scenario but increase to 62% of ICE vehicle stock in the high world oil price scenario, with LTs covering the appropriate differences. © JASSS.

Chu S.H.,Agency for Science, Technology and Research Singapore | Singh D.J.,Oak Ridge National Laboratory | Wang J.,National University of Singapore | Li E.-P.,Agency for Science, Technology and Research Singapore | Ong K.P.,Agency for Science, Technology and Research Singapore
Laser and Photonics Reviews | Year: 2012

First principles calculations of electronic and optical properties of multiferroic oxide BiFeO 3 are used in combination with a plasmonic device model of optical switch to show that a BiFeO 3 based device can have much better performance than devices based on existing materials. This arises from the combination of octahedral tilts, ferroelectricity and G-type antiferromagnetism in BiFeO 3 leading to a strong dependence of the optical refractive indices on the orientation with respect to the polarization. A prototype of a plasmonic resonator with an R-BFO thin film layer is used as an example and shows excellent switch and modulation responses. The proposed approach provides potential opportunities to develop high performance nanophotonic devices for optical communication. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical intuition suggests that the stabilization of a carbon-centered free radical by a substituent X would be the greatest for a prim and least for a more stable tert radical because of "saturation". However, analysis of a comprehensive recent set of bond dissociation energies computed by Coote and co-workers (Phys. Chem. Chem. Phys. 2010, 12, 9597) and transformed into radical stabilization energies (RSE) suggests that this supposition is often violated. The RSE for a given X depends not only on the nature of X but also on the ordinality (i.e., prim, sec, or tert) of the radical onto which it is substituted. For substituents that stabilize by electron delocalization but also contain electron-withdrawing centers, such as the carbonyl function, the stabilization of XCMe2• compared with HCMe2• is greater than that for XCH2• compared with HCH2•. However, for substituents that stabilize by lone-pair electron donation, such as N or O centers, the order is strongly reversed. This contrast can be qualitatively rationalized by considering charge-separated VB contributors to the radical structure (R2C+-X-• and R 2C--X+•) and the contrasting effects of methyl substituents on them. This conclusion is not dependent on the particular definition used for RSE. © 2010 American Chemical Society.

Pennycook S.J.,Oak Ridge National Laboratory | Colliex C.,University Paris - Sud
MRS Bulletin | Year: 2012

In the scanning transmission electron microscope, multiple signals can be simultaneously collected, including the transmitted and scattered electron signals (bright field and annular dark field or Z-contrast images), along with spectroscopic signals such as inelastically scattered electrons and emitted photons. In the last few years, the successful development of aberration correctors for the electron microscope has transformed the field of electron microscopy, opening up new possibilities for correlating structure to functionality. Aberration correction not only allows for enhanced structural resolution with incident probes into the sub-Ãngstrom range, but can also provide greater probe currents to facilitate mapping of intrinsically weak spectroscopic signals at the nanoscale or even the atomic level. In this issue of MRS Bulletin, we illustrate the power of the new generation of electron microscopes with a combination of imaging and spectroscopy. We show the mapping of elemental distributions at atomic resolution and also the mapping of electronic and optical properties at unprecedented spatial resolution, with applications ranging from graphene to plasmonic nanostructures, and oxide interfaces to biology. © 2012 Materials Research Society.

Jiang D.-E.,Oak Ridge National Laboratory
Chemistry - A European Journal | Year: 2011

Survival of the fittest: A profound connection has been found between the structures of thiolated gold clusters and the combinatorial problem of pairing up dots on a surface. The bridge is the concept of staple fitness: the fittest combination corresponds to the experimental structure. This connection has been demonstrated for both Au 25(SR) 18 and Au 38(SR) 24 (-SR being a thiolate group) and applied to predict a promising structure for the recently synthesized Au 19(SR) 13. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wang B.,Vanderbilt University | Puzyrev Y.,Vanderbilt University | Pantelides S.T.,Vanderbilt University | Pantelides S.T.,Oak Ridge National Laboratory
Carbon | Year: 2011

Grain boundaries dominate the property of polycrystalline graphene. We report first-principles calculations and classical molecular dynamics simulations that reveal enhanced defect reactivity induced by an inhomogeneous strain field at grain boundaries. Strained carbon bonds located at heptagons and pentagons can accumulate interstitials and single vacancies, respectively. We find that recombination of vacancies and interstitials can occur locally at grain boundaries, which serve as effective sinks, resulting in efficient annealing of defects. The enhanced defect reactivity indicates that grain boundaries may be manipulated by point defects. © 2011 Elsevier Ltd. All rights reserved.

Sen S.,Oak Ridge National Laboratory
ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings | Year: 2013

We propose an algorithm to directly synthesize in time-domain a constant-envelope transmit waveform that achieves the optimal performance in detecting an extended target in the presence of signal-dependent interference. This approach is in contrast to the traditional indirect methods that synthesize the transmit signal following the computation of the optimal energy spectral density. Additionally, we aim to maintain a good autocorrelation property of the designed signal. Therefore, our waveform design technique solves a bi-objective optimization problem in order to simultaneously improve the detection and autocorrelation performances, which are in general conflicting in nature. We demonstrate this compromising characteristics of the detection and autocorrelation performances with numerical examples. Furthermore, in the absence of the autocorrelation criterion, our designed signal is shown to achieve a near-optimum detection performance. © 2013 IEEE.

Fishman R.S.,Oak Ridge National Laboratory
Physical Review Letters | Year: 2011

The magnetic phase diagram of a geometrically frustrated triangular-lattice antiferromagnet is evaluated as a function of magnetic field and anisotropy using a trial spin state built from harmonics of a fundamental ordering wave vector. A noncollinear incommensurate state, observed to be chiral and ferroelectric in CuFeO 2, appears above a collinear state with 4 sublattices (SLs). The apparent absence of multiferroic behavior for predicted chiral, noncollinear 5-SL states poses a challenge to theories of the ferroelectric coupling in CuFeO 2. © 2011 American Physical Society.

Toth G.I.,Hungarian Academy of Sciences | Morris J.R.,Oak Ridge National Laboratory | Granasy L.,Hungarian Academy of Sciences | Granasy L.,Brunel University
Physical Review Letters | Year: 2011

We address crystal nucleation and fcc-bcc phase selection in alloys using a multiphase field model that relies on Ginzburg-Landau free energies of the liquid-fcc, liquid-bcc, and fcc-bcc subsystems, and determine the properties of the nuclei as a function of composition, temperature, and structure. With a realistic choice for the free energy of the fcc-bcc interface, the model predicts well the fcc-bcc phase-selection boundary in the Fe-Ni system. © 2011 American Physical Society.

Savara A.,Oak Ridge National Laboratory
Journal of Physical Chemistry C | Year: 2013

Standard states are utilized to compare thermodynamic data obtained from different experiments and calculations, and this ability to compare thermodynamic data plays an important role in science and society. For molecules adsorbed on surfaces, there are currently no universally accepted standard states. Here, standard states are proposed for the different types of molecular adsorbate phases, with the intent to enable physical insight to be gained by tabulating experimental/calculated values, such that comparison between different systems and existing societal tabulations of chemical standard state tabulated values can be done directly. A "density based" standard state is proposed for 2D gases, and a "relative coverage based" standard state is proposed for immobile adsorbates and nonislanding 2D liquids. These units are chosen based upon the units which the activity depends on. The standard states recommended here are chosen due to the entropies associated with them, such that physical insight can be gained by direct comparison to existing tabulated data. For 2D gases adsorbed on solid surfaces, the recommended standard state is σ = 1.39 × 10-7 mol m-2. For immobile adsorbates and nonislanding liquid states on solid surfaces, the recommended standard state is θA = 0.5 (which implies a standard state for the surface sites of of θS = 1 - θA = 0.5). With the standard states recommended here, tabulated values at a common temperature are expected to display the following approximate hierarchy for decreasing entropy: 3D gas > 2D gas > liquid > surface liquid > solid > lattice confined. Recommended standard states are also provided in the Supporting Information for cases with dissociative adsorption. © 2013 American Chemical Society.

Lopez-Bezanilla A.,Oak Ridge National Laboratory
Journal of Physical Chemistry C | Year: 2013

We present a study on the quantum transport properties of chemically functionalized metallic double-walled carbon nanotubes (DWNTs) with lengths reaching the micrometer scale. First-principles calculations evidence that, for coaxial tubes separated by the typical graphitic van der Waals bond distance, the chemical modification of the outer wall with sp3-type defects affects the electronic structure of both the outer and the inner tube, which reduces significantly the charge transport capability of the DWNTs. For larger spacing between sidewalls, the conductivity of the outer wall decreases with increasing functional group coverage density, while charge transport in the inner tube is equivalent to that of a pristine nanotube. Additionally, [2 + 1] cycloaddition of CCl2 onto the outer DWNT sidewall barely affects the hyperconjugated π-network of the double wall, and charge transport remains in the quasi-ballistic regime. These results indicate an efficient route for tailoring electronic transport in DWNTs provided inner shell geometry and grafted functional groups are properly chosen. © 2013 American Chemical Society.

Neary V.S.,Sandia National Laboratories | Gunawan B.,Oak Ridge National Laboratory | Sale D.C.,University of Washington
Renewable and Sustainable Energy Reviews | Year: 2013

Marine and hydrokinetic technologies, which convert kinetic energy from currents in open-channel flows to electricity, require inflow characteristics (e.g. mean velocity and turbulence intensity profiles) for their siting, design, and evaluation. The present study reviews mean velocity and turbulence intensity profiles reported in the literature for open-channel flows to gain a better understanding of the range of current magnitudes and longitudinal turbulence intensities that these technologies may be exposed to. We compare 47 measured vertical profiles of mean current velocity and longitudinal turbulence intensity (normalized by the shear velocity) that have been reported for medium-large rivers, a large canal, and laboratory flumes with classical models developed for turbulent flat plate boundary layer flows. The comparison suggests that a power law (with exponent, 1/a=1/6) and a semi-theoretical exponential decay model can be used to provide first-order approximations of the mean velocity and turbulence intensity profiles in rivers suitable for current energy conversion. Over the design life of a current energy converter, these models can be applied to examine the effects of large spatiotemporal variations of river flow depth on inflow conditions acting over the energy capture area. Significant engineering implications on current energy converter structural loads, annual energy production, and cost of energy arise due to these spatiotemporal variations in the mean velocity, turbulence intensity, hydrodynamic force, and available power over the energy capture area. © 2013 Elsevier Ltd. All rights reserved.

Hammond G.E.,Sandia National Laboratories | Lichtner P.C.,OFM Research | Mills R.T.,Oak Ridge National Laboratory | Mills R.T.,University of Tennessee at Knoxville
Water Resources Research | Year: 2014

To better inform the subsurface scientist on the expected performance of parallel simulators, this work investigates performance of the reactive multiphase flow and multicomponent biogeochemical transport code PFLOTRAN as it is applied to several realistic modeling scenarios run on the Jaguar supercomputer. After a brief introduction to the code's parallel layout and code design, PFLOTRAN's parallel performance (measured through strong and weak scalability analyses) is evaluated in the context of conceptual model layout, software and algorithmic design, and known hardware limitations. PFLOTRAN scales well (with regard to strong scaling) for three realistic problem scenarios: (1) in situ leaching of copper from a mineral ore deposit within a 5-spot flow regime, (2) transient flow and solute transport within a regional doublet, and (3) a real-world problem involving uranium surface complexation within a heterogeneous and extremely dynamic variably saturated flow field. Weak scalability is discussed in detail for the regional doublet problem, and several difficulties with its interpretation are noted. Key Points Scientists must better understand the benefit of high-performance computing PFLOTRAN's scalability is exceptional on multiple realistic subsurface problems Understanding PFLOTRAN's scalability better educates on expected performance ©2013. The Authors. Water Resources Research published by Wiley on behalf of the American Geophysical Union.

Jager H.I.,Oak Ridge National Laboratory
Ecological Modelling | Year: 2014

Using models to represent relationships between flow and fishes has important practical applications for managing reservoir releases. Attempts to model such relationships often neglect indirect mechanisms by which flow influences fish. For example, growth of salmon juveniles is measurably faster when flows inundate floodplain and promote higher production of invertebrate prey, but out-of-channel flows have not yet been incorporated into models. The QUANTUS model developed here represents indirect linkages between flow and freshwater survival, mediated by temperature and prey availability, for fall Chinook salmon (Oncorhynchus tshawytscha). Quantiles of spawning time and place were used to define cohorts of salmon in a regulated Central Valley, California river. Survival of these quantile-cohorts was simulated through incubation, juvenile growth, and eventual downstream migration. A genetic algorithm was used to optimize the seasonal timing of pulse flows. Simulated survival was highest for flow regimes that provided a modest, temperature-moderating pulse flow in early summer and, for wetter years, a second, larger pulse of over-bank flow in late winter. For many rivers of the Pacific coast that support fall Chinook salmon, the thermal window of opportunity for spawning and rearing is narrow. Optimized flows made the most of this window by providing access to accelerated juvenile growth and early survival in floodplain habitat, a result that should be verified with field experiments. Timing of optimized pulse flows differed in some respects from the region's natural hydrograph, dominated by spring runoff. This suggests that understanding the mechanisms by which flow influences fishes can be important when shaping flows in the changed context of a regulated river. © 2013 Elsevier B.V.

Eblen J.D.,Oak Ridge National Laboratory
BMC bioinformatics | Year: 2012

The maximum clique enumeration (MCE) problem asks that we identify all maximum cliques in a finite, simple graph. MCE is closely related to two other well-known and widely-studied problems: the maximum clique optimization problem, which asks us to determine the size of a largest clique, and the maximal clique enumeration problem, which asks that we compile a listing of all maximal cliques. Naturally, these three problems are NP-hard, given that they subsume the classic version of the NP-complete clique decision problem. MCE can be solved in principle with standard enumeration methods due to Bron, Kerbosch, Kose and others. Unfortunately, these techniques are ill-suited to graphs encountered in our applications. We must solve MCE on instances deeply seeded in data mining and computational biology, where high-throughput data capture often creates graphs of extreme size and density. MCE can also be solved in principle using more modern algorithms based in part on vertex cover and the theory of fixed-parameter tractability (FPT). While FPT is an improvement, these algorithms too can fail to scale sufficiently well as the sizes and densities of our datasets grow. An extensive testbed of benchmark graphs are created using publicly available transcriptomic datasets from the Gene Expression Omnibus (GEO). Empirical testing reveals crucial but latent features of such high-throughput biological data. In turn, it is shown that these features distinguish real data from random data intended to reproduce salient topological features. In particular, with real data there tends to be an unusually high degree of maximum clique overlap. Armed with this knowledge, novel decomposition strategies are tuned to the data and coupled with the best FPT MCE implementations. Several algorithmic improvements to MCE are made which progressively decrease the run time on graphs in the testbed. Frequently the final runtime improvement is several orders of magnitude. As a result, instances which were once prohibitively time-consuming to solve are brought into the domain of realistic feasibility.

Lee E.-S.,University of Texas at Austin | Huq A.,Oak Ridge National Laboratory | Manthiram A.,University of Texas at Austin
Journal of Power Sources | Year: 2013

The effect of synthesis temperature on the structural and electrochemical characteristics of the layered-spinel composite cathode system xLi[Li 0.2Mn0.6Ni0.2]O2-(1 - x)Li[Mn 1.5Ni0.5]O4 (0 ≤ x ≤ 1) has been investigated. With a joint neutron diffraction (ND) and X-ray diffraction (XRD) Rietveld refinement method, the composition and weight percent variations of the layered and spinel phases in this composite cathode system have been obtained as a function of x and synthesis temperature. While no significant composition and weight percent variations are found with the synthesis temperature, the electrochemical characteristics of both the layered and spinel phases in the composites are significantly affected by the synthesis temperature. In contrast to the layered sample (x = 1), the capacity of the layered phase in the composites increases with decreasing synthesis temperature due to an increase in surface area. Conversely, the effect of synthesis temperature on the spinel phase is similar in both the spinel sample (x = 0) and the composite samples. However, the lower synthesis temperature increases the cation ordering in the 16d octahedral sites of the spinel phase, which changes the voltage profiles below 3 V due to the decrease in the lattice distortion during lithium ion insertion into the empty 16c octahedral sites. © 2013 Elsevier B.V. All rights reserved.

Gao C.,University of California at Riverside | Lu Z.,University of California at Riverside | Liu Y.,University of California at Riverside | Zhang Q.,University of California at Riverside | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2012

An SPR biosensor was developed by employing highly stable Au-protected Ag nanoplates (NP) as enhancers (see picture). Superior performance was achieved by depositing a thin and uniform coating of Au on the Ag surface while minimizing disruptive galvanic replacement and retaining the strong surface plasmon resonance (SPR) of the silver nanoplates. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Czarnecki O.,Humboldt University of Berlin | Czarnecki O.,Oak Ridge National Laboratory | Grimm B.,Humboldt University of Berlin
Journal of Experimental Botany | Year: 2012

The tetrapyrrole biosynthetic pathway provides the vital cofactors and pigments for photoautotrophic growth (chlorophyll), several essential redox reactions in electron transport chains (haem), N-and S-assimilation (sirohaem), and photomorphogenic processes (phytochromobilin). While the biochemistry of the pathway is well understood and almost all genes encoding enzymes of tetrapyrrole biosynthesis have been identified in plants, the post-translational control and organization of the pathway remains to be clarified. Post-translational mechanisms controlling metabolic activities are of particular interest since tetrapyrrole biosynthesis needs adaptation to environmental challenges. This review surveys post-translational mechanisms that have been reported to modulate metabolic activities and organization of the tetrapyrrole biosynthesis pathway. © 2011 The Author.

Menestrina J.,University of California at Irvine | Yang C.,University of California at Irvine | Schiel M.,University of California at Irvine | Vlassiouk I.,Oak Ridge National Laboratory | Siwy Z.S.,University of California at Irvine
Journal of Physical Chemistry C | Year: 2014

We study the effect of electrolyte concentration on the shape of ion current pulses in resistive-pulse sensing. We show that electrokinetic passage of several hundred nanometers in diameter charged polystyrene particles through a micropore leads to formation of current increase when the particles exit the pore. The particle entrance, as reported before, causes formation of the current decrease, which is a measure of the particle size. Formation of the double peak, i.e., current decrease followed by a current increase, is especially pronounced if the resistive-pulse experiments are carried out in KCl concentrations below 200 mM. In order to explain the pulse shape, experiments were designed in which the particles passed through the pore only by either electroosmosis or electrophoresis. The presented experiments and modeling indicate that while both electroosmosis and electrophoresis affect the ion current pulse, formation of the positive peak is mainly determined by the latter effect and the charged state of the particle. The importance of the findings for resistive-pulse analysis is discussed. © 2014 American Chemical Society.

Qu M.,Purdue University | Abdelaziz O.,Oak Ridge National Laboratory | Yin H.,Nanjing Southeast University
Energy Conversion and Management | Year: 2014

Conventional natural gas-fired boilers exhaust flue gas direct to the atmosphere at 150-200 °C, which, at such temperatures, contains large amount of energy and results in relatively low thermal efficiency ranging from 70% to 80%. Although condensing boilers for recovering the heat in the flue gas have been developed over the past 40 years, their present market share is still less than 25%. The major reason for this relatively slow acceptance is the limited improvement in the thermal efficiency of condensing boilers. In the condensing boiler, the temperature of the hot water return at the range of 50-60 °C, which is used to cool the flue gas, is very close to the dew point of the water vapor in the flue gas. Therefore, the latent heat, the majority of the waste heat in the flue gas, which is contained in the water vapor, cannot be recovered. This paper presents a new approach to improve boiler thermal efficiency by integrating absorption heat pumps with natural gas boilers for waste heat recovery (HRAHP). Three configurations of HRAHPs are introduced and discussed. The three configurations are modeled in detail to illustrate the significant thermal efficiency improvement they attain. Further, for conceptual proof and validation, an existing hot water-driven absorption chiller is operated as a heat pump at operating conditions similar to one of the devised configurations. An overall system performance and economic analysis are provided for decision-making and as evidence of the potential benefits. These three configurations of HRAHP provide a pathway to achieving realistic high-efficiency natural gas boilers for applications with process fluid return temperatures higher than or close to the dew point of the water vapor in the flue gas. © 2014 Elsevier Ltd. All rights reserved.

Bansal D.G.,Oak Ridge National Laboratory | Streator J.L.,Georgia Institute of Technology
Wear | Year: 2012

This study considers the approaches of Blok and Jaeger for the estimation of maximum and average temperatures in sliding elliptical contacts with both uniform and semi-ellipsoidal (Hertzian) heat distributions. The accuracy of each of these methods, which are based on single-point temperature matching between contacting bodies, is assessed relative to a numerical solution of the heat partition problem developed in a previous work, which imposed temperature matching at all nodal points. Comparisons are made for a wide range of Peclet numbers, as well as for moderate ranges of thermal conductivity ratio and elliptical ratio. It is found that the application of Blok's hypothesis yields remarkably accurate predictions of the maximum interfacial temperature, with typical errors less than 3%, whereas the hypothesis of Jaeger leads to predictions of the average interfacial temperature that have typical errors of around 6%. The authors also assess the accuracy of approximate formula developed by Tian and Kennedy to predict the maximum temperature at the interface for the case of sliding circular contacts and find the error to be no more than 2.6% for the full range of Peclet number. Further, the authors of the current study use fundamental heat source solutions developed by Tian and Kennedy to arrive at formulae for average temperature rise for circular contacts that are analogous to the Tian and Kennedy maximum temperature rise formulae. It is found that the formulae for computing the average interfacial temperature rise are also quite accurate, but have slightly more error than the maximum temperature rise formulae. Finally, in the present work, extensions are suggested to the maximum and average temperature rise formulae of Tian and Kennedy to include the effects of elliptical contact geometry. It is found that these formulae are at least 91% accurate for elliptical ratios between 0.4 and 5.0. © 2011 Elsevier B.V.

Melnykov V.,University of Alabama | Chen W.-C.,Oak Ridge National Laboratory | Maitra R.,Iowa State University
Journal of Statistical Software | Year: 2012

The R package MixSim is a new tool that allows simulating mixtures of Gaussian distributions with different levels of overlap between mixture components. Pairwise overlap, defined as a sum of two misclassification probabilities, measures the degree of interaction between components and can be readily employed to control the clustering complexity of datasets simulated from mixtures. These datasets can then be used for systematic performance investigation of clustering and finite mixture modeling algorithms. Among other capabilities of MixSim, there are computing the exact overlap for Gaussian mixtures, simulating Gaussian and non-Gaussian data, simulating outliers and noise variables, calculating various measures of agreement between two partitionings, and constructing parallel distribution plots for the graphical display of finite mixture models. All features of the package are illustrated in great detail. The utility of the package is highlighted through a small comparison study of several popular clustering algorithms.

Shue C.A.,Oak Ridge National Laboratory | Kalafut A.J.,Grand Valley State University | Gupta M.,Indiana University Bloomington
IEEE/ACM Transactions on Networking | Year: 2012

While many attacks are distributed across botnets, investigators and network operators have recently identified malicious networks through high profile autonomous system (AS) depeerings and network shutdowns. In this paper, we explore whether some ASs indeed are safe havens for malicious activity. We look for ISPs and ASs that exhibit disproportionately high malicious behavior using 10 popular blacklists, plus local spam data, and extensive DNS resolutions based on the contents of the blacklists. We find that some ASs have over 80% of their routable IP address space blacklisted. Yet others account for large fractions of blacklisted IP addresses. Several ASs regularly peer with ASs associated with significant malicious activity. We also find that malicious ASs as a whole differ from benign ones in other properties not obviously related to their malicious activities, such as more frequent connectivity changes with their BGP peers. Overall, we conclude that examining malicious activity at AS granularity can unearth networks with lax security or those that harbor cybercrime. © 2011 IEEE.

Zhao H.,Savannah State University | Baker G.A.,Oak Ridge National Laboratory | Cowins J.V.,Savannah State University
Biotechnology Progress | Year: 2010

The pretreatment of cellulose using ionic liquids (ILs) has been shown to be an effective method for improving the enzymatic hydrolysis of cellulose; this technique affords a fast and complete saccharification of cellulose into reducing sugars (Dadi et al., Biotechnol Bioeng. 2006; 95:904-910; Liu and Chen, Chinese Sci Bull. 2006; 51:2432-2436; Zhao et al., J Biotechnol. 2009; 139:47-54). Motivated by these advances, this study examines the effect of IL-pretreatment on the enzymatic hydrolysis of purified xylan (as a model system of hemicellulose) and switchgrass (as a real lignocellulose). The IL-pretreatment resulted in no improvement in the hydrolysis of xylan. The likely reason is that pure xylan has a low degree of polymerization (DP), and is readily biodegraded even without any pretreatment. However, in real cellulosic materials (such as switchgrass), xylan is entrapped within the cellulosic matrix, and cannot be conveniently accessed by enzymes. Our data demonstrate that the IL-pretreatment of switchgrass significantly improved the enzymatic saccharification of both cellulose (96% D-glucose yield in 24 h) and xylan (63% D-xylose yield in 24 h). The compositional analysis of switchgrass suggests a lower lignin content after IL-pretreatment. In addition, the infrared spectrum of regenerated switchgrass indicates a lower substrate crystallinity, whereas the enzyme adsorption isotherm further implies that the regenerated substrate is more accessible to enzymes. This study has further confirmed that IL-pretreatment is an effective tool in enhancing the enzymatic hydrolysis of cellulosic biomass, and allowing a more complete saccharification. © 2009 American Institute of Chemical Engineers.

Bansal P.,University of Auckland | Bansal P.,Oak Ridge National Laboratory
Applied Thermal Engineering | Year: 2012

Carbon dioxide (CO 2) has emerged as one of the most promising and preferred refrigerants for low temperature refrigeration systems in the food and refrigeration industry and/or recreational activities. In recent times, the widespread use of CO 2 refrigerant, particularly in supermarkets, has proved commercially attractive worldwide. Some of the designs that are most commonly used in industry include cascade, transcritical and transcritical booster, while many other interesting designs and variations are also being consistently used for specific situations. This paper presents the holistic view of the fundamentals and application of CO 2 refrigerant in low temperature refrigeration systems, along with some discussion on its benign properties, thermodynamic analysis, the challenges, the need for fundamental research and design of novel systems for its continuing dominance in the refrigeration industry.© 2011 Elsevier Ltd. All rights reserved.

Croft S.,Oak Ridge National Laboratory | Henzlova D.,Los Alamos National Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

Physically small, lightly encapsulated, radionuclide sources containing 252Cf are widely used for a vast variety of industrial, medical, educational and research applications requiring a convenient source of neutrons. For many quantitative applications, such as detector efficiency calibrations, the absolute strength of the neutron emission is needed. In this work we show how, by using a neutron multiplicity counter the neutron emission rate can be obtained with high accuracy. This provides an independent and alternative way to create reference sources in-house for laboratories such as ours engaged in international safeguards metrology. The method makes use of the unique and well known properties of the 252Cf spontaneous fission system and applies advanced neutron correlation counting methods. We lay out the foundation of the method and demonstrate it experimentally. We show that accuracy comparable to the best methods currently used by national bodies to certify neutron source strengths is possible. © 2013 Elsevier B.V. All rights reserved.

Okamoto S.,Oak Ridge National Laboratory
Physical Review Letters | Year: 2013

The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the d orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for t2g systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed. © 2013 American Physical Society.

Muroga T.,Japan National Institute for Fusion Science | Pint B.A.,Oak Ridge National Laboratory
Fusion Engineering and Design | Year: 2010

This paper overviews the recent progress in the development of insulator coating for liquid Li blanket. Insulator coating for mitigating the MHD pressure drop is the key issue for self-cooled liquid lithium blankets with V-alloy structures. Recent efforts are focused on developing Er2O3 and Y2O3 coatings with various physical and chemical coating technologies. Because of low allowance of the crack areal fraction for the single-layer coating, the in situ healing and the two-layer coating with metallic overlayer have also been investigated. Recent mono-metallic loop experiments with high impurity control showed high stability of V and V-alloy overlayer covering the ceramic coating on V-4Cr-4Ti substrate in flowing Li at 700°C. The development of fabrication technology for the two-layer coating on large and complex shaped surfaces will be the next necessary step. The studies on the effects of radiation on the coating (resistivity, microstructure, mechanical properties and compatibility) need to be enhanced. © 2010 Elsevier B.V. All rights reserved.

Jagadamma S.,Oak Ridge National Laboratory | Lal R.,Ohio State University
Biology and Fertility of Soils | Year: 2010

Soil organic carbon (SOC) is distributed heterogeneously among different-sized primary particles and aggregates. Further, the SOC associated with different physical fractions respond differently to managements. Therefore, this study was conducted with the objective to quantify the SOC associated with all the three structural levels of SOC (particulate organic matter, soil separates and aggregate-size fractions) as influenced by long-term change in management. The study also aims at reevaluating the concept that the SOC sink capacity of individual size-fractions is limited. Long-term tillage and crop rotation effects on distribution of SOC among fractions were compared with soil from adjacent undisturbed area under native vegetation for the mixed, mesic, Typic Fragiudalf of Wooster, OH. Forty five years of no-till (NT) management resulted in more SOC accumulation in soil surface (0-7.5 cm) than in chisel tillage and plow tillage (PT) treatments. However, PT at this site resulted in a redistribution of SOC from surface to deeper soil layers. The soils under continuous corn accumulated significantly more SOC than those under corn-soybean rotation at 7.5-45 cm depth. Although soil texture was dominated by the silt-sized particles, most of the SOC pool was associated with the clay fraction. Compared to PT, the NT treatment resulted in (i) significantly higher proportion of large macroaggregates (>2,000 μm) and (ii) 1.5-2.8 times higher SOC concentrations in all aggregate-size classes. A comparative evaluation using radar graphs indicated that among the physical fractions, the SOC associated with sand and silt fractions quickly changed with a land use conversion from native vegetation to agricultural crops. A key finding of this study is the assessment of SOC sink capacity of individual fractions, which revealed that the clay fraction of agricultural soils continues to accumulate more SOC, albeit at a slower rate, with progressive increase in total SOC concentration. However, the clay fraction of soil under native woodlot showed an indication for SOC saturation. The data presented in this study from all the three structural levels of SOC would be helpful for refining the conceptual pool definitions of the current soil organic matter prediction models. © 2010 Springer-Verlag.

Wang J.G.,Oak Ridge National Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2013

The SNS accumulator ring employs 32 electro-magnetic dipoles to bend proton beams. The dipoles are typical sector magnets with relatively large aperture and short length. Thus, how to correctly treat magnetic fringe fields in the devices remains as a question. We have performed 3D computer simulations to study magnetic field distributions in the dipoles. Further, we have analyzed particle optics based on the space-dependent curvature and focusing functions in the magnets. The effect of magnetic fringe fields on the particle motion, especially the focusing/defocusing and dispersion, is investigated. The lens parameters, including the second-order aberrations, are derived and compared with the design hard-edge parameters used in the ring lattice calculations. © 2013 Elsevier B.V.

Curtarolo S.,Duke University | Hart G.L.W.,Duke University | Hart G.L.W.,Brigham Young University | Nardelli M.B.,Duke University | And 8 more authors.
Nature Materials | Year: 2013

High-throughput computational materials design is an emerging area of materials science. By combining advanced thermodynamic and electronic-structure methods with intelligent data mining and database construction, and exploiting the power of current supercomputer architectures, scientists generate, manage and analyse enormous data repositories for the discovery of novel materials. In this Review we provide a current snapshot of this rapidly evolving field, and highlight the challenges and opportunities that lie ahead. © 2013 Macmillan Publishers Limited. All rights reserved.

Keiber T.,University of California at Santa Cruz | Bridges F.,University of California at Santa Cruz | Sales B.C.,Oak Ridge National Laboratory
Physical Review Letters | Year: 2013

PbTe is a well-known thermoelectric material. Recent x-ray total scattering studies suggest that Pb moves off center along 100 in PbTe, by ∼0.2 Å at 300 K, producing a split Pb-Te pair distribution. We present an extended x-ray absorption fine structure spectroscopy (EXAFS) study of PbTe (and Tl doped PbTe) to determine if Pb or Te is off center. EXAFS provides sensitive r- or k-space phase information which can differentiate between a split peak for the Pb-Te distribution (indicative of off-center Pb) and a thermally broadened peak. We find no evidence for a split peak for Pb-Te or Te-Pb. At 300 K, the vibration amplitude for Pb-Te (or Te-Pb) is large; this thermally induced disorder is indicative of weak bonds, and the large disorder is consistent with the low thermal conductivity at 300 K. We also find evidence of an anharmonic potential for the nearest Pb-Te bonds, consistent with the overall anharmonicity found for the phonon modes. This effect is modeled by a "skew" factor (C3) which significantly improves the fit of the Pb-Te and Te-Pb peaks for the high temperature EXAFS data; C3 becomes significant above approximately 150-200 K. The consequences of these results will be discussed. Published by the American Physical Society.

Woo S.-J.,KAIST | Lee E.-S.,KAIST | Yoon M.,Oak Ridge National Laboratory | Kim Y.-H.,KAIST
Physical Review Letters | Year: 2013

It has been widely accepted that enhanced dihydrogen adsorption is required for room-temperature hydrogen storage on nanostructured porous materials. Here we report, based on results of first-principles total energy and vibrational spectrum calculations, finite-temperature adsorption and desorption thermodynamics of hydrogen molecules that are adsorbed on the metal center of metal-porphyrin-incorporated graphene. We have revealed that the room-temperature hydrogen storage is achievable not only with the enhanced adsorption enthalpy, but also with soft-mode driven vibrational entropy of the adsorbed dihydrogen molecule. The soft vibration modes mostly result from multiple orbital coupling between the hydrogen molecule and the buckled metal center, for example, in Ca-porphyrin-incorporated graphene. Our study suggests that the current design strategy for room-temperature hydrogen storage materials should be modified with explicitly taking the finite-temperature vibration thermodynamics into account. © 2013 American Physical Society.

Kao S.-C.,Oak Ridge National Laboratory | Govindaraju R.S.,Purdue University
Journal of Hydrology | Year: 2010

Current drought information is based on indices that do not capture the joint behaviors of hydrologic variables. To address this limitation, the potential of copulas in characterizing droughts from multiple variables is explored in this study. Starting from the standardized index (SI) algorithm, a modified index accounting for seasonality is proposed for precipitation and streamflow marginals. Utilizing Indiana stations with long-term observations (a minimum of 80 years for precipitation and 50 years for streamflow), the dependence structures of precipitation and streamflow marginals with various window sizes from 1- to 12-months are constructed from empirical copulas. A joint deficit index (JDI) is defined by using the distribution function of copulas. This index provides a probability-based description of the overall drought status. Not only is the proposed JDI able to reflect both emerging and prolonged droughts in a timely manner, it also allows a month-by-month drought assessment such that the required amount of precipitation for achieving normal conditions in future can be computed. The use of JDI is generalizable to other hydrologic variables as evidenced by similar drought severities gleaned from JDIs constructed separately from precipitation and streamflow data. JDI further allows the construction of an inter-variable drought index, where the entire dependence structure of precipitation and streamflow marginals is preserved. © 2009 Elsevier B.V. All rights reserved.

Sen S.,Oak Ridge National Laboratory
IEEE Sensors Journal | Year: 2014

We propose to design a peak-to-average power ratio (PAPR) constrained transmit waveform that achieves the optimal performance (following the Neyman-Pearson lemma) in detecting a target in the presence of signal-dependent interference. The direct time-domain approach allows straightforward characterizations of the correlation and PAPR properties of the designed signals, which are critically important to analyze the system performance in the presence of multiple targets and to assess the transmitter power-utilization, respectively. Therefore, instead of designing a transmit signal only for the optimal detection performance, we solve a biobjective Pareto-optimization problem, subjecting to the PAPR and total energy constraints, in order to simultaneously optimize the detection and cross-correlation performances. With extensive numerical examples, we demonstrate that PAPR-constrained signals produce nearly optimum detection performance even with a strict PAPR requirement, and also highlight the conflicting behavior of the detection and correlation performances. © 2014 IEEE.

Preston B.L.,Oak Ridge National Laboratory
Global Environmental Change | Year: 2013

Despite improvements in disaster risk management in the United States, a trend toward increasing economic losses from extreme weather events has been observed. This trend has been attributed to growth in socioeconomic exposure to extremes, a process characterized by strong path dependence. To understand the influence of path dependence on past and future losses, an index of potential socioeconomic exposure was developed at the U.S. county level based upon population size and inflation-adjusted wealth proxies. Since 1960, exposure has increased preferentially in the U.S. Southeast (particularly coastal and urban counties) and Southwest relative to the Great Plains and Northeast. Projected changes in exposure from 2009 to 2054 based upon scenarios of future demographic and economic change suggest a long-term commitment to increasing, but spatially heterogeneous, exposure to extremes, independent of climate change. The implications of this path dependence are examined in the context of several natural hazards. Using methods previously reported in the literature, annualized county-level losses from 1960 to 2008 for five climate-related natural hazards were normalized to 2009 values and then scaled based upon projected changes in exposure and two different estimates of the exposure elasticity of losses. Results indicate that losses from extreme events will grow by a factor of 1.3-1.7 and 1.8-3.9 by 2025 and 2050, respectively, with the exposure elasticity representing a major source of uncertainty. The implications of increasing physical vulnerability to extreme weather events for investments in disaster risk management are ultimately contingent upon the normative values of societal actors. © 2013 Elsevier Ltd.

Larson B.C.,Oak Ridge National Laboratory | Levine L.E.,U.S. National Institute of Standards and Technology
Journal of Applied Crystallography | Year: 2013

The ability to study the structure, microstructure and evolution of materials with increasing spatial resolution is fundamental to achieving a full understanding of the underlying science of materials. Polychromatic three-dimensional X-ray microscopy (3DXM) is a recently developed nondestructive diffraction technique that enables crystallographic phase identification, determination of local crystal orientations, grain morphologies, grain interface types and orientations, and in favorable cases direct determination of the deviatoric elastic strain tensor with submicrometre spatial resolution in all three dimensions. With the added capability of an energy-scanning incident beam monochromator, the determination of absolute lattice parameters is enabled, allowing specification of the complete elastic strain tensor with three-dimensional spatial resolution. The methods associated with 3DXM are described and key applications of 3DXM are discussed, including studies of deformation in single-crystal and polycrystalline metals and semiconductors, indentation deformation, thermal grain growth in polycrystalline aluminium, the metal-insulator transition in nanoplatelet VO2, interface strengths in metal-matrix composites, high-pressure science, Sn whisker growth, and electromigration processes. Finally, the outlook for future developments associated with this technique is described. © 2013 International Union of Crystallography.

Bansal D.G.,Oak Ridge National Laboratory | Streator J.L.,Georgia Institute of Technology
Acta Materialia | Year: 2011

Electrical contact resistance affects the performance of electrical switches and other current-carrying interfaces. This study investigates the behavior of electrical contact resistance for copper-copper and aluminum-aluminum sphere-on-flat contact as a function of current through the interface. It is observed that the contact resistance may either increase or decrease with increasing current, depending on the current level as well as the current history. At low current levels the voltage drop across the interface increases initially with increasing current until it saturates. The voltage level remains nearly constant even if the current is increased beyond the value corresponding to saturation. Hereafter any subsequent decrease in current yields a corresponding decrease in voltage, so that the associated current cycle shows substantial hysteresis. However, subsequent cycles of current are reversible so long as the voltage remains below the saturation point. Analyses of the results suggest that the mechanism of viscoplastic creep is responsible for the voltage saturation phenomenon. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Zaliznyak I.A.,Brookhaven National Laboratory | Xu Z.,Brookhaven National Laboratory | Tranquada J.M.,Brookhaven National Laboratory | Gu G.,Brookhaven National Laboratory | And 2 more authors.
Physical Review Letters | Year: 2011

Our inelastic neutron scattering study of spin excitations in iron telluride reveals remarkable thermal evolution of the collective magnetism. In the temperature range relevant for the superconductivity in FeTe 1-xSex materials, where the local-moment behavior is dominated by liquidlike correlations of emergent spin plaquettes, we observe unusual, marked increase of magnetic fluctuations upon heating. The effective spin per Fe at T10K, in the phase with weak antiferromagnetic order, corresponds to S1, consistent with the recent analyses that emphasize importance of Hund's coupling. However, it grows to S3/2 in the high-T disordered phase, suggestive of the Kondo-type behavior, where local magnetic moments are entangled with the itinerant electrons. © 2011 American Physical Society.

Sen S.,Oak Ridge National Laboratory
IEEE Transactions on Signal Processing | Year: 2013

We propose a sparsity-based space-time adaptive processing (STAP) algorithm to detect a slowly-moving target using an orthogonal frequency division multiplexing (OFDM) radar. We observe that the target and interference spectra are inherently sparse in the spatio-temporal domain. Hence, we exploit that sparsity to develop an efficient STAP technique that utilizes considerably lesser number of secondary data and produces an equivalent performance as the other existing STAP techniques. In addition, the use of an OFDM signal increases the frequency diversity of our system, as different scattering centers of a target resonate at different frequencies, and thus improves the target detectability. First, we formulate a realistic sparse-measurement model for an OFDM radar considering both the clutter and jammer as the interfering sources. Then, we apply a residual sparse-recovery technique based on the LASSO estimator to estimate the target and interference covariance matrices, and subsequently compute the optimal STAP-filter weights. Our numerical results demonstrate a comparative performance analysis of the proposed sparse-STAP algorithm with four other existing STAP methods. Furthermore, we discover that the OFDM-STAP filter-weights are adaptable to the frequency-variabilities of the target and interference responses, in addition to the spatio-temporal variabilities. Hence, by better utilizing the frequency variabilities, we propose an adaptive OFDM-waveform design technique, and consequently gain a significant amount of STAP-performance improvement. © 1991-2012 IEEE.

Custelcean R.,Oak Ridge National Laboratory
Chemical Communications | Year: 2013

The persistent ability of tripodal TREN-based tris-urea receptors (TREN = tris(2-aminoethyl)amine) to self-assemble with a variety of oxoanions into dimeric capsules upon crystallization is reviewed. The capsule crystallization allows for charge-, shape-, and size-selective encapsulation of tetrahedral XO4 n- anions (n = 2,3), and provides an effective way to separate these anions from competitive aqueous environments. © 2013 The Royal Society of Chemistry.

Stack A.G.,Oak Ridge National Laboratory
Greenhouse Gases: Science and Technology | Year: 2014

The long-term success of carbon sequestration lies in part on the ability to trap carbon dioxide as a carbonate mineral phase. As such, the ability to predict the extent of carbonate mineral precipitation over the lifetime of a proposed geologic sequestration site will be necessary. In this review, different methods of predicting the growth of carbonate minerals, particularly calcite, and their disadvantages and advantages are summarized. Starting from a simple description of the solution saturation state, more advanced affinity-based models are described that comprise the status quo. In these, the reaction rate is measured by the difference in concentration from an equilibrium value or the Gibbs Free Energy of reaction. It is shown that these models fail to capture some important aspects of carbonate mineral growth rates. Next-generation models in development are those that reflect the processes that occur on a mineral surface while it is growing, not just the concentration of dissolved species. While incomplete, these process-based models are already addressing some long-standing questions in geochemistry and are enhancing the accuracy and robustness of the predictive ability for calcite precipitation. Lastly, the importance of the step density, analogous to the reactive site density in a natural sample, is shown. The factors that may influence the step density are described and the potentially complex relationship between step density and solution conditions is presented. While still in development, these models suggest that many of the historical problems in quantitative prediction of mineral growth and dissolution reactions can be resolved. © 2014 Society of Chemical Industry and John Wiley & Sons, Ltd.

Wong C.-Y.,Oak Ridge National Laboratory | Wilk G.,National Center for Nuclear Research
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Phenomenological Tsallis fits to the CMS, ATLAS, and ALICE transverse momentum spectra of hadrons for pp collisions at LHC were recently found to extend over a large range of the transverse momentum. We investigate whether the few degrees of freedom in the Tsallis parametrization may arise from the relativistic parton-parton hard-scattering and related processes. The effects of the multiple hard-scattering and parton showering processes on the power law are discussed. We find empirically that whereas the transverse spectra of both hadrons and jets exhibit power-law behavior of 1/pTn at high pT, the power indices n for hadrons are systematically greater than those for jets, for which n∼4-5. © 2013 American Physical Society.

Dow K.,University of South Carolina | Berkhout F.,Kings College London | Preston B.L.,Oak Ridge National Laboratory
Current Opinion in Environmental Sustainability | Year: 2013

As attention to adaptation to climate change increases, there is a growing call for adaptation approaches that focus on risk management. There is also greater recognition that the rate and magnitude of climate variability and change may exceed the limits to adaptation of socio-ecological systems. We offer an actor-centered, risk-based definition for adaptation limits in social systems. Specifically, we frame adaptation limits as the point at which an actor's objectives cannot be secured from intolerable risks through adaptive actions. These limits are significant because exceeding a limit will either result in intolerable losses on the affected actor or system, or precipitate a discontinuous (or transformational) change of behavior by actors. Such discontinuities in behavior have implications for the distribution of risks, with potentially significant governance consequences. We further argue that some adaptation limits are dynamic through time. We conclude with recommendations for further research into adaptation limits and challenges to risk governance. © 2013 Elsevier B.V.

Godec A.,Slovenian National Institute of Chemistry | Smith J.C.,Oak Ridge National Laboratory | Smith J.C.,University of Tennessee at Knoxville | Merzel F.,Slovenian National Institute of Chemistry
Physical Review Letters | Year: 2011

Monte Carlo simulations of a small model solute in an aqueous solution are used to examine the effects of solute polarity on hydration structure. A judicious definition of the orientational order parameter leads to reinterpretation of the conventional picture of hydration. As the solute varies from hydrophobic to hydrophilic the ordered first shell water simultaneously fractionates into a more highly ordered and a more disordered component. The hydrogen-bond network rearranges such that the more ordered component relaxes to configurations of optimal intermolecular angles, the other fraction being released from the network. © 2011 American Physical Society.

Yueh K.,EPRI | Terrani K.A.,Oak Ridge National Laboratory
Journal of Nuclear Materials | Year: 2014

The feasibility of using SiCf-SiCm composites in light water reactor (LWR) fuel designs was evaluated. The evaluation was motivated by the desire to improve fuel performance under normal and accident conditions. The Fukushima accident once again highlighted the need for improved fuel materials that can maintain fuel integrity to higher temperatures for longer periods of time. The review identified many benefits as well as issues in using the material. Issues perceived as presenting the biggest challenges to the concept were identified to be flux gradient induced differential volumetric swelling, fragmentation and thermal shock resistance. The oxidation of silicon and its release into the coolant as silica has been identified as an issue because existing plant systems have limited ability for its removal. Detailed evaluation using available literature data and testing as part of this evaluation effort have eliminated most of the major concerns. The evaluation identified Boiling Water Reactor (BWR) channel, BWR fuel water tube, and Pressurized Water Reactor (PWR) guide tube as feasible applications for SiC composite. A program has been initiated to resolve some of the remaining issues and to generate physical property data to support the design of commercial fuel components. © 2014 Elsevier B.V. All rights reserved.

Kilina S.V.,North Dakota State University | Neukirch A.J.,University of Rochester | Habenicht B.F.,Oak Ridge National Laboratory | Kilin D.S.,University of South Dakota | Prezhdo O.V.,University of Rochester
Physical Review Letters | Year: 2013

Quantum confinement can dramatically slow down electron-phonon relaxation in nanoclusters. Known as the phonon bottleneck, the effect remains elusive. Using a state-of-the-art time-domain ab initio approach, we model the observed bottleneck in CdSe quantum dots and show that it occurs under quantum Zeno conditions. Decoherence in the electronic subsystem, induced by elastic electron-phonon scattering, should be significantly faster than inelastic scattering. Achieved with multiphonon relaxation, the phonon bottleneck is broken by Auger processes and structural defects, rationalizing experimental difficulties. © 2013 American Physical Society.

Greene S.R.,Oak Ridge National Laboratory
Transactions of the American Nuclear Society | Year: 2010

The results of this analysis indicate that fluoride salt-cooled high temperature reactors are an extraordinarily-promising class of reactor concepts, and that development of these reactor systems has strong potential to enable four of the Five Imperatives of Nuclear Energy.

Sun P.,University of California at Berkeley | Siddiqi G.,University of California at Berkeley | Chi M.,Oak Ridge National Laboratory | Bell A.T.,University of California at Berkeley
Journal of Catalysis | Year: 2010

A novel approach is described for preparing Ga-promoted Pt particles for the dehydrogenation of light alkanes to alkenes. The modifying element, Ga, was introduced by transference from the support, a calcined Mg(Ga)(Al)O hydrotalcite-like material. Pt nanoparticles were dispersed onto the calcined Mg(Ga)(Al)O starting from an organometallic precursor, followed by reduction. The formation of PtGa alloy particles is dependent on reduction temperature. Reduction at 723 K produces mainly metallic Pt particles. The average diameter of the Pt nanoparticles increased from 1.4 nm to 2.2 nm with increasing Ga content, and decreasing Al content of the support, demonstrating the importance of support Al atoms in stabilizing the dispersion of Pt. After reduction at 773-873 K, PtGa alloys were observed. It is proposed that at high reduction temperatures, H atoms formed on the surface of the metal particles spill over onto the support where they reduce Ga 3+ cation to atomic Ga, which then interacts with the supported Pt to form PtGa alloys. The activity, selectivity and stability of Pt/Mg(Ga)(Al)O catalysts for ethane and propane dehydrogenation are described in the second part of this study (G. Siddiqi, P. Sun, V. Galvita, A.T. Bell, Journal of catalysis (2010), doi:10.1016/j.jcat. 2010.06.016 [40]). © 2010 Elsevier Inc. All rights reserved.

Xiao H.Y.,University of Tennessee at Knoxville | Weber W.J.,University of Tennessee at Knoxville | Weber W.J.,Oak Ridge National Laboratory
Journal of Physical Chemistry B | Year: 2011

A local-density approximation with the Hubbard U correction (LDAU) method has been employed to investigate oxygen vacancy formation and migration in CeαTh1-αO2. The addition of CeO2 into ThO2 significantly decreases the oxygen vacancy formation and migration energies. ThO2 containing 50% CeO2 exhibits the lowest calculated formation energy, 3.7 eV, and the lowest calculated migration energy, 0.2 eV, occurs for a CeO2 content of 75%, suggesting that introducing CeO2 into ThO2 promotes the formation of mobile oxygen vacancies. If the ceria content is less than about 35%, the reduced Ce α Th1-α O2 becomes antiferromagnetic (AFM), whereas the ferromagnetic (FM) state dominates for α values above about 35%, which may allow the tailoring of magnetic properties by varying the CeO2 content. © 2011 American Chemical Society.

Proksch R.,Asylum Research | Kalinin S.V.,Oak Ridge National Laboratory
Nanotechnology | Year: 2010

Local dissipation measurements by scanning probe microscopy have attracted increasing interest as a method for probing energy losses and hysteretic phenomena due to magnetic, electrical, and structural transformations at the tip-surface junction. One challenge of this technique is the lack of a standard for ensuring quantification of the dissipation signal. In the following, we explored magnetic dissipation imaging of an yttrium-iron garnet (YIG) sample, using a number of similar but not identical cantilever probes. Typical frequency-dependent dispersion of the actuator-probe assembly commonly approached ±1 part in 103 Hz-1, much larger than the minimum detectable level of ±1 part in 105 Hz -1. This cantilever-dependent behavior results in a strong crosstalk between the conservative (frequency) and dissipative channels. This crosstalk was very apparent in the YIG dissipation images and in fact should be an inherent feature of single-frequency heterodyne detection schemes. It may also be a common effect in other dissipation imaging, even down to the atomic level, and in particular may be a significant issue when there are correlations between the conservative and dissipative components. On the other hand, we present a simple method for correcting for this effect. This correction technique resulted in self-consistent results for the YIG dissipation measurements and would presumably be effective for other systems as well. © 2010 IOP Publishing Ltd.

Chang J.C.,Vanderbilt University | Rosenthal S.J.,Vanderbilt University | Rosenthal S.J.,Oak Ridge National Laboratory
ACS Chemical Neuroscience | Year: 2012

Lipid rafts are cholesterol-enriched subdomains in the plasma membrane that have been reported to act as a platform to facilitate neuronal signaling; however, they are suspected to have a very short lifetime, up to only a few seconds, which calls into question their roles in biological signaling. To better understand their diffusion dynamics and membrane compartmentalization, we labeled lipid raft constituent ganglioside GM1 with single quantum dots through the connection of cholera toxin B subunit, a protein that binds specifically to GM1. Diffusion measurements revealed that single quantum dot-labeled GM1 ganglioside complexes undergo slow, confined lateral diffusion with a diffusion coefficient of ∼7.87 × 10-2 μm2/s and a confinement domain about 200 nm in size. Further analysis of their trajectories showed lateral confinement persisting on the order of tens of seconds, comparable to the time scales of the majority of cellular signaling and biological reactions. Hence, our results provide further evidence in support of the putative function of lipid rafts as signaling platforms. © 2012 American Chemical Society.

Parish C.M.,Oak Ridge National Laboratory
Advances in Imaging and Electron Physics | Year: 2011

A modern STEM-EDS spectrum imaging system can quickly and easily collect huge quantities of data. Then the challenge to the analyst is how to turn a large, often noisy, dataset into insight to the materials science and engineering problem at hand. This review discussed the application of MVSA methods, primarily PCA and MCR, to address this question. MVSA methods are generally used to either (1) perform noise filtering on the raw data or (2) provide a reduced-rank, and more interpretable, description of the raw data. However, neither application is straightforward in the general case. PCA and PCA followed by further manipulations can provide both noise-filtering and qualitative interpretations of the data, but effects such as a matrix phase fully surrounding precipitates can lead to significant ambiguities in the quantitative application of score images or loading spectra. MCR-based techniques have the potential to address these ambiguities, but much more work is needed. MCR methods are also subject to subtle artifacts that must be carefully considered. Experimental parameters such as signal level, detector resolution, and phases present in the SI data can significantly affect both the quantitative and qualitative results of MVSA computations, and precautions such as ensuring that the rank of the sample and the pseudo-rank of the MVSA results match, are important to ensure useful MVSA applications. This is also an area of ongoing research.

Egami T.,University of Tennessee at Knoxville | Egami T.,Oak Ridge National Laboratory
Progress in Materials Science | Year: 2011

The birth and subsequent development of the concept of the atomic level stresses are reviewed, and its future is discussed. Initially it was conceived as a means of describing the local structure in metallic glasses. It gradually became evident that its capacity is beyond the initial expectation. It appears that this concept is a powerful tool in understanding diverse phenomena in strongly disordered systems, such as the atomic dynamics in liquids, glass transition, mechanical failure and structural relaxation. This concept also has a potential to bridge distinct fields of glass research beyond metallic glasses, including colloids, molecular liquids, granular matter and other materials. © 2011 Elsevier Ltd. All rights reserved.

Vass A.A.,Oak Ridge National Laboratory
Forensic Science International | Year: 2012

This study, the third of a series on the odor signature of human decomposition, reports on the intermittent nature of chemical evolution from decomposing human remains, and focuses primarily on headspace analysis from soil associated with older human remains (10-60+ years) from different environments around the globe. Fifty grams of soil were collected in 40. mL glass vials with polypropylene sealed lids from soil above known or suspected graves and from subsurface chemical plumes associated with human decompositional events. One hundred eighty six separate samples were analyzed using gas chromatography-mass spectrometry (GC-MS). After comparison to relevant soil controls, approximately fifty volatile chemical compounds were identified as being associated with human remains. This manuscript reports these findings and identifies when and where they are most likely to be detected showing an overall decrease in cyclic and halogenated compounds and an increase in aldehydes and alkanes as time progresses. This research identifies the " odor signatures" unique to the decomposition of human remains with projected ramifications on cadaver dog training procedures and in the development of field portable analytical instruments which can be used to locate human remains in shallow burial sites. © 2012 Elsevier Ireland Ltd.

Hudiburg T.W.,University of Illinois at Urbana - Champaign | Law B.E.,Oregon State University | Thornton P.E.,Oak Ridge National Laboratory
Biogeosciences | Year: 2013

Ecosystem process models are important tools for determining the interactive effects of global change and disturbance on forest carbon dynamics. Here we evaluated and improved terrestrial carbon cycling simulated by the Community Land Model (CLM4), the land model portion of the Community Earth System Model (CESM1.0.4). Our analysis was conducted primarily in Oregon forests using FLUXNET and forest inventory data for the period 2001-2006. We go beyond prior modeling studies in the region by incorporating regional variation in physiological parameters from >100 independent field sites in the region. We also compare spatial patterns of simulated forest carbon stocks and net primary production (NPP) at 15 km resolution using data collected from federal forest inventory plots (FIA) from >3000 plots in the study region. Finally, we evaluate simulated gross primary production (GPP) with FLUXNET eddy covariance tower data at wet and dry sites in the region. We improved model estimates by making modifications to CLM4 to allow physiological parameters (e.g., foliage carbon to nitrogen ratios and specific leaf area), mortality rate, biological nitrogen fixation, and wood allocation to vary spatially by plant functional type (PFT) within an ecoregion based on field plot data in the region. Prior to modifications, default parameters resulted in underestimation of stem biomass in all forested ecoregions except the Blue Mountains and annual NPP was both over-and underestimated. After modifications, model estimates of mean NPP fell within the observed range of uncertainty in all ecoregions (two-sided P value Combining double low line 0.8), and the underestimation of stem biomass was reduced. This was an improvement from the default configuration by 50% for stem biomass and 30% for NPP. At the tower sites, modeled monthly GPP fell within the observed range of uncertainty at both sites for the majority of the year, however summer GPP was underestimated at the Metolius semi-arid pine site and spring GPP was overestimated at the Campbell River mesic Douglas-fir site, indicating GPP may be an area for further improvement. The low bias in summer maximum GPP at the semi-arid site could be due to seasonal response of Vcmax to temperature and precipitation while overestimated spring values at the mesic site could be due to response of Vcmax to temperature and day length. © Author(s) 2013.

Keene J.D.,Vanderbilt University | McBride J.R.,Vanderbilt University | Orfield N.J.,Vanderbilt University | Rosenthal S.J.,Vanderbilt University | Rosenthal S.J.,Oak Ridge National Laboratory
ACS Nano | Year: 2014

Interaction of charge carriers with the surface of semiconductor nanocrystals plays an integral role in determining the ultimate fate of the excited state. The surface contains a dynamic ensemble of trap states that can localize excited charges, preventing radiative recombination and reducing fluorescence quantum yields. Here we report quasi-type-II band alignment in graded alloy CdSxSe1-x nanocrystals revealed by femtosecond fluorescence upconversion spectroscopy. Graded alloy CdSxSe1-x quantum dots are a compositionally inhomogeneous nano-heterostructure designed to decouple the exciton from the nanocrystal surface. The large valence band offset between the CdSe-rich core and CdS-rich shell separates the excited hole from the surface by confining it to the core of the nanocrystal. The small conduction band offset, however, allows the electron to delocalize throughout the entire nanocrystal and maintain overlap with the surface. Indeed, the ultrafast charge carrier dynamics reveal that the fast 1-3 ps hole-trapping process is fully eliminated with increasing sulfur composition and the decay constant for electron trapping (∼20-25 ps) shows a slight increase. These findings demonstrate progress toward highly efficient nanocrystal fluorophores that are independent of their surface chemistry to ultimately enable their incorporation into a diverse range of applications without experiencing adverse effects arising from dissimilar environments. © 2014 American Chemical Society.

Shin N.,Georgia Institute of Technology | Chi M.,Oak Ridge National Laboratory | Filler M.A.,Georgia Institute of Technology
ACS Nano | Year: 2014

Semiconductor nanowire kinking superstructures, particularly those with long-range structural coherence, remain difficult to fabricate. Here, we combine high-resolution electron microscopy with operando infrared spectroscopy to show why this is the case for Si nanowires and, in doing so, reveal the interplay between defect propagation and surface chemistry during 〈211〉 - 〈111〉 and 〈211〉 - 〈211〉 kinking. Our experiments show that adsorbed hydrogen atoms are responsible for selecting 〈211〉-oriented growth and indicate that a twin boundary imparts structural coherence. The twin boundary, only continuous at 〈211〉 - 〈211〉 kinks, reduces the symmetry of the trijunction and limits the number of degenerate directions available to the nanowire. These findings constitute a general approach for rationally engineering kinking superstructures and also provide important insight into the role of surface chemical bonding during vapor-liquid-solid synthesis. © 2014 American Chemical Society.

Hayes D.,Oak Ridge National Laboratory | Turner D.,Oregon State University
Eos | Year: 2012

The global land-based carbon dioxide (CO 2) sink can be derived from the difference between fossil fuel emissions and the sum of estimated increases of CO 2 in the atmosphere and in the ocean [Houghton, 2010]. For the purposes of developing policy to limit CO 2 emissions, it is necessary to refine scientific understanding of the land CO 2 flux in terms of its spatial and temporal patterns, as well as the underlying drivers. Net ecosystem exchange (NEE) is the commonly used measure of the land flux and is defined as the net vertical exchange of CO 2 between a specified horizontal surface and the atmosphere above it over a given period of time. NEE estimates are reported from the atmospheric perspective, such that a positive value represents emissions (a land source) and a negative value represents removals (a land sink). This term represents a seemingly simple concept, and it was given a clear definition as one of the key carbon cycle variables by Chapin et al. [2006]. However, considerable confusion still arises around its usage, and the ambiguity is traceable primarily to the suite of different approaches used to estimate it. © 2012. American Geophysical Union. All Rights Reserved.

Poutsma M.L.,Oak Ridge National Laboratory
Journal of Physical Chemistry A | Year: 2013

Empirical structure-reactivity correlations are developed for log k 298, the gas-phase rate constants for the reaction (Cl • + HCR3 → ClH + CR3 •). It has long been recognized that correlation with ΔrH is weak. The poor performance of the linear Evans-Polanyi formulation is illustrated and was little improved by adding a quadratic term, for example, by making its slope smoothly dependent on ΔrH [η ≡ (ΔrH - ΔrHmin)/ (ΔrHmax - ΔrHmin)]. The "polar effect" (δ-Cl - -H - -CR3 δ+)⧧ has also been long discussed, but there is no formalization of this dependence based on widely available independent variable(s). Using the sum of Hammett constants for the R substituents also gave at best modest correlations, either for σpara or for its dissection into F (field/inductive) and R (resonance) effects. Much greater success was achieved by combining these approaches with the preferred independent variable set being either [(ΔrH)2, ΔrH, ΣF, and ΣR] or [η, ΔrH, ΣF, and ΣR]. For 64 rate constants that span 7 orders of magnitude, these correlation formulations give r2 > 0.87 and a mean unsigned deviation of <0.5 log k units, with even better performance if primary, secondary, and tertiary reaction centers are treated separately. © 2013 American Chemical Society.

Singh D.J.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We report calculations of the electronic structure and magnetic properties of YFe2Ge2 and discuss the results in terms of the observed superconductivity near magnetism. We find that YFe2Ge2 is a material near a magnetic quantum critical point based on comparison of standard density functional results that predict magnetism with experiment. The band structure and Fermi surfaces are very three dimensional and higher conductivity is predicted in the c-axis direction. The magnetism is of Stoner type and is predominately from an in-plane ferromagnetic tendency. The interlayer coupling is weak giving a perhaps two dimensional character to the magnetism, which is in contrast to the conductivity and may be important for suppressing the ordering tendency. This is compatible with a triplet superconducting state mediated by spin fluctuations. © 2014 American Physical Society.

Garten Jr. C.T.,Oak Ridge National Laboratory
Bioenergy Research | Year: 2012

A multi-compartment model was developed to summarize existing data and predict soil carbon sequestration beneath switchgrass (Panicum virgatum) in the southeastern USA. Soil carbon sequestration is an important part of sustainable switchgrass production for bioenergy because soil organic matter promotes water retention, nutrient supply, and soil properties that minimize erosion. A literature review was undertaken for the purpose of model parameterization. A sensitivity analysis of the model indicated that predictions of soil carbon sequestration were affected most by changes in aboveground biomass production, the ratio of belowground-to-aboveground biomass production, and mean annual temperature. Simulations indicated that the annual rate of soil carbon sequestration approached steady state after a decade of switchgrass growth while predicted mineral soil carbon stocks were still increasing. A model-based experiment was performed to predict rates of soil carbon sequestration at different levels of nitrogen fertilization and initial soil carbon stocks (to a 30-cm depth). At a mean annual temperature of 13°C, the predicted rate of soil carbon sequestration varied from -28 to 114 g C m -2 year -1 (after 30 years) and was greater than zero in 11 of 12 simulations that varied initial surface soil carbon stocks from 1 to 5 kg C m -2 and nitrogen fertilization from 0 to 18 g N m -2 year -1. The modeling indicated that more research is needed on the process of biomass allocation and on nitrogen loss from mature plantations, respectively, to improve our understanding of carbon and nitrogen dynamics in switchgrass agriculture. © 2011 Springer Science+Business Media, LLC. (outside the USA).

Pint B.A.,Oak Ridge National Laboratory
JOM | Year: 2013

Fossil fuels have historically represented two-thirds of all electricity generation in the United States and are projected to continue to play a similar role despite historically low projected growth rates in electricity demand and the recent dramatic shift from coal to more natural gas usage. Economic and environmental drivers will require more reliable and efficient fossil fuel generation systems in the future, likely with new system designs, higher operating temperatures, and more aggressive environments. Some of the current corrosion issues in power plants are reviewed along with research on materials solutions for systems envisioned for the near future, such as coal gasification and oxy-fired coal boilers. © 2013 TMS.

Nickels J.D.,University of Texas at Austin | Nickels J.D.,Oak Ridge National Laboratory | Schmidt C.E.,University of Texas at Austin
Journal of Biomedical Materials Research - Part A | Year: 2013

A novel strategy for affinity-based surface modification of the conducting polymer, polypyrrole, (PPy), has been developed. A 12-amino acid peptide (THRTSTLDYFVI, hereafter denoted T59) was previously identified via the phage display technique. This peptide noncovalently binds to the chlorine-doped conducting polymer polypyrrole (PPyCl). Studies have previously shown that conductive polymers have promising application in neural electrodes, sensors, and for improving regeneration and healing of peripheral nerves and other tissues. Thus, the strong and specific attachment of bioactive molecules to the surface of PPy using the T59 affinity peptide is an exciting new approach to enhance the bioactivity of electrically active materials for various biomedical applications. We demonstrate this by using T59 as a tether to modify PPyCl with the laminin fragment IKVAV to enhance cell interactions, as well as with the so-called stealth molecule poly(ethylene glycol; PEG) to decrease cell interactions. Using these two modification strategies, we were able to control cell attachment and neurite extension on the PPy surface, which is critical for different applications (i.e., the goal for tissue regeneration is to enhance cell interactions, whereas the goal for electrode and sensor applications is to reduce glial cell interactions and thus decrease scarring). Significantly, the conductivity of the PPyCl surface was unaffected by this surface modification technique, which is not the case with other methods that have been explored to surface modify conducting polymers. Finally, using subcutaneous implants, we confirmed that the PPyCl treated with the T59 peptide did not react in vivo differently than untreated PPyCl. © 2012 Wiley Periodicals, Inc.

Wu X.,University of Tennessee at Knoxville | Wang S.,University of Tennessee at Knoxville | Wang S.,Oak Ridge National Laboratory
Advanced Healthcare Materials | Year: 2013

Biomimetic, self-assembled calcium carbonate (CaCO3) concentric microgrooves with groove widths of 5.0 and 10 μm were fabricated through simply controlling incubation temperature. Mouse pre-osteoblastic MC3T3-E1 cells were cultured on flat and microgrooved substrates of CaCO3 and their adhesion, spreading, proliferation, alkaline phosphatase activity, and calcium content were remarkably enhanced by the microgrooves, in particular, the narrower ones. Furthermore, focal adhesions and actin filaments of MC3T3-E1 cells could be aligned on both 5.0-μm and 10-μm-wide CaCO3 grooves. Compared with the original round nuclei on the flat substrates and expanded round nuclei on the narrower microgrooves, the MC3T3-E1 cell nuclei on 10-μm-wide CaCO3 grooves demonstrated preferred entrapment in the grooves and significant alignment with a smaller area after two-day culture. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zhao Q.,Samuel Roberts Noble Foundation | Dixon R.A.,University of North Texas | Dixon R.A.,Oak Ridge National Laboratory
Annual Review of Phytopathology | Year: 2014

The individual sugars found within the major classes of plant cell wall polymers are dietary components of herbivores and are targeted for release in industrial processes for fermentation to liquid biofuels. With a growing understanding of the biosynthesis of the complex cell wall polymers, genetic modification strategies are being developed to target the cell wall to improve the digestibility of forage crops and to render lignocellulose less recalcitrant for bioprocessing. This raises concerns as to whether altering cell wall properties to improve biomass processing traits may inadvertently make plants more susceptible to diseases and pests. Here, we review the impacts of cell wall modification on plant defense, as assessed from studies in model plants utilizing mutants or transgenic modification and in crop plants specifically engineered for improved biomass or bioenergy traits. Such studies reveal that cell wall modifications can indeed have unintended impacts on plant defense, but these are not always negative. ©2014 by Annual Reviews. All rights reserved.

Singh D.J.,Oak Ridge National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Ta4Pd3Te16 is a recently discovered superconductor that has been suggested to be an unconventional superconductor near magnetism. We report electronic structure calculations showing that despite the layered crystal structure the material is an anisotropic three-dimensional (3D) metal. The Fermi surface contains prominent one-dimensional (1D) and two-dimensional (2D) features, including nested 1D sheets, a 2D cylindrical section, and a 3D sheet. The electronic states that make up the Fermi surface are mostly derived from Te p states with small Ta d and Pd d contributions. This places the compound far from magnetic instabilities. The results are discussed in terms of multiband superconductivity. © 2014 American Physical Society.

Kumara C.,University of Mississippi | Zuo X.,Argonne National Laboratory | Cullen D.A.,Oak Ridge National Laboratory | Dass A.,University of Mississippi
ACS Nano | Year: 2014

Obtaining monodisperse nanocrystals and determining their composition to the atomic level and their atomic structure is highly desirable but is generally lacking. Here, we report the discovery and comprehensive characterization of a 2.9 nm plasmonic nanocrystal with a composition of Au 940±20(SCH2CH2Ph) 160±4, which is the largest mass spectrometrically characterized gold thiolate nanoparticle produced to date. The compositional assignment has been made using electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry (MS). The MS results show an unprecedented size monodispersity, where the number of Au atoms varies by only 40 atoms (940 ± 20). The mass spectrometrically determined composition and size are supported by aberration-corrected scanning transmission electron microscopy (STEM) and synchrotron-based methods such as atomic pair distribution function (PDF) and small-angle X-ray scattering (SAXS). Lower-resolution STEM images show an ensemble of particles-1000s per frame-visually demonstrating monodispersity. Modeling of SAXS data on statistically significant nanoparticle population-approximately 1012 individual nanoparticles-shows that the diameter is 3.0 ± 0.2 nm, supporting mass spectrometry and electron microscopy results on monodispersity. Atomic PDF based on high-energy X-ray diffraction experiments shows decent match with either a Marks decahedral or truncated octahedral structure. Atomic resolution STEM images of single particles and their fast Fourier transform suggest face-centered cubic arrangement. UV-visible spectroscopy data show that Faradaurate-940 supports a surface plasmon resonance peak at ̃505 nm. These monodisperse plasmonic nanoparticles minimize averaging effects and have potential application in solar cells, nano-optical devices, catalysis, and drug delivery. © 2014 American Chemical Society.

Chandola V.,Oak Ridge National Laboratory | Banerjee A.,University of Minnesota | Kumar V.,University of Minnesota
IEEE Transactions on Knowledge and Data Engineering | Year: 2012

This survey attempts to provide a comprehensive and structured overview of the existing research for the problem of detecting anomalies in discrete/symbolic sequences. The objective is to provide a global understanding of the sequence anomaly detection problem and how existing techniques relate to each other. The key contribution of this survey is the classification of the existing research into three distinct categories, based on the problem formulation that they are trying to solve. These problem formulations are: 1) identifying anomalous sequences with respect to a database of normal sequences; 2) identifying an anomalous subsequence within a long sequence; and 3) identifying a pattern in a sequence whose frequency of occurrence is anomalous. We show how each of these problem formulations is characteristically distinct from each other and discuss their relevance in various application domains. We review techniques from many disparate and disconnected application domains that address each of these formulations. Within each problem formulation, we group techniques into categories based on the nature of the underlying algorithm. For each category, we provide a basic anomaly detection technique, and show how the existing techniques are variants of the basic technique. This approach shows how different techniques within a category are related or different from each other. Our categorization reveals new variants and combinations that have not been investigated before for anomaly detection. We also provide a discussion of relative strengths and weaknesses of different techniques. We show how techniques developed for one problem formulation can be adapted to solve a different formulation, thereby providing several novel adaptations to solve the different problem formulations. We also highlight the applicability of the techniques that handle discrete sequences to other related areas such as online anomaly detection and time series anomaly detection. © 2012 IEEE.

BACKGROUND: Zymomonas mobilis produces near theoretical yields of ethanol and recombinant strains are candidate industrial microorganisms. To date, few studies have examined its responses to various stresses at the gene level. Hfq is a conserved bacterial member of the Sm-like family of RNA-binding proteins, coordinating a broad array of responses including multiple stress responses. In a previous study, we observed Z. mobilis ZM4 gene ZMO0347 showed higher expression under anaerobic, stationary phase compared to that of aerobic, stationary conditions. RESULTS: We generated a Z. mobilis hfq insertion mutant AcRIM0347 in an acetate tolerant strain (AcR) background and investigated its role in model lignocellulosic pretreatment inhibitors including acetate, vanillin, furfural and hydroxymethylfurfural (HMF). Saccharomyces cerevisiae Lsm protein (Hfq homologue) mutants and Lsm protein overexpression strains were also assayed for their inhibitor phenotypes. Our results indicated that all the pretreatment inhibitors tested in this study had a detrimental effect on both Z. mobilis and S. cerevisiae, and vanillin had the most inhibitory effect followed by furfural and then HMF for both Z. mobilis and S. cerevisiae. AcRIM0347 was more sensitive than the parental strain to the inhibitors and had an increased lag phase duration and/or slower growth depending upon the conditions. The hfq mutation in AcRIM0347 was complemented partially by trans-acting hfq gene expression. We also assayed growth phenotypes for S. cerevisiae Lsm protein mutant and overexpression phenotypes. Lsm1, 6, and 7 mutants showed reduced tolerance to acetate and other pretreatment inhibitors. S. cerevisiae Lsm protein overexpression strains showed increased acetate and HMF resistance as compared to the wild-type, while the overexpression strains showed greater inhibition under vanillin stress conditions. CONCLUSIONS: We have shown the utility of the pKNOCK suicide plasmid for mutant construction in Z. mobilis, and constructed a Gateway compatible expression plasmid for use in Z. mobilis for the first time. We have also used genetics to show Z. mobilis Hfq and S. cerevisiae Lsm proteins play important roles in resisting multiple, important industrially relevant inhibitors. The conserved nature of this global regulator offers the potential to apply insights from these fundamental studies for further industrial strain development.

Mukherjee P.P.,Los Alamos National Laboratory | Mukherjee P.P.,Oak Ridge National Laboratory | Kang Q.,Los Alamos National Laboratory | Wang C.-Y.,Pennsylvania State University
Energy and Environmental Science | Year: 2011

Recent years have witnessed an explosion of research and development efforts in the area of polymer electrolyte fuel cells (PEFC), perceived as the next generation clean energy source for automotive, portable and stationary applications. Despite significant progress, a pivotal performance/durability limitation in PEFCs centers on two-phase transport and mass transport loss originating from suboptimal liquid water transport and flooding phenomena. Liquid water blocks the porous pathways in the gas diffusion layer (GDL) and the catalyst layer (CL), thus hindering oxygen transport from the flow field to the electrochemically actives sites in the catalyst layer. Different approaches have been examined to model the underlying transport mechanisms in the PEFC with different levels of complexities. Due to the macroscopic nature, these two-phase models fail to resolve the underlying structural influence on the transport and performance. Mesoscopic modeling at the pore-scale offers great promise in elucidating the underlying structure-transport-performance interlinks in the PEFC porous components. In this article, a systematic review of the recent progress and prospects of pore-scale modeling in the context of two-phase transport in the PEFC is presented. Specifically, the efficacy of lattice Boltzmann (LB), pore morphology (PM) and pore network (PN) models coupled with realistic delineation of microstructures in fostering enhanced insight into the underlying liquid water transport in the PEFC GDL and CL is highlighted. © 2011 The Royal Society of Chemistry.

Mamontov E.,Oak Ridge National Laboratory
Chemical Physics Letters | Year: 2012

Using quasielastic neutron scattering, we compare dynamics in single-element liquids, glass-forming selenium and non glass-forming gallium. There is a single jump-diffusion process in gallium, whereas in selenium there is also a faster, spatially localized process. The fast and slow processes describe β- and α-relaxation, respectively. We then analyze an archetypical glass-former, glycerol, to show that the two-component fit, with β- and α-relaxations explicitly separated, yields the correct value for the translational diffusion coefficient and provides information on the spatial localization of the β-relaxation that is not experimentally accessible otherwise. © 2012 Elsevier B.V. All rights reserved.

Iwuchukwu I.J.,University of Tennessee at Knoxville | Vaughn M.,University of Tennessee at Knoxville | Myers N.,University of Tennessee at Knoxville | O'Neill H.,University of Tennessee at Knoxville | And 3 more authors.
Nature Nanotechnology | Year: 2010

There is considerable interest in making use of solar energy through photosynthesis to create alternative forms of fuel. Here, we show that photosystem I from a thermophilic bacterium and cytochrome-c 6 can, in combination with a platinum catalyst, generate a stable supply of hydrogen in vitro upon illumination. The self-organized platinization of the photosystem I nanoparticles allows electron transport from sodium ascorbate to photosystem I via cytochrome-c 6 and finally to the platinum catalyst, where hydrogen gas is formed. Our system produces hydrogen at temperatures up to 55°C and is temporally stable for >85 days with no decrease in hydrogen yield when tested intermittently. The maximum yield is ∼5.5μmol H 2 h-1 mg-1 chlorophyll and is estimated to be ∼25-fold greater than current biomass-to-fuel strategies. Future work will further improve this yield by increasing the kinetics of electron transfer, extending the spectral response and replacing the platinum catalyst with a renewable hydrogenase. © 2010 Macmillan Publishers Limited. All rights reserved.

Malikopoulos A.A.,Oak Ridge National Laboratory
IEEE Transactions on Intelligent Transportation Systems | Year: 2014

The growing necessity for environmentally benign hybrid propulsion systems has led to the development of advanced power management control algorithms to maximize fuel economy and minimize pollutant emissions. This paper surveys the control algorithms for hybrid electric vehicles (HEVs) and plug-in HEVs (PHEVs) that have been reported in the literature to date. The exposition ranges from parallel, series, and power split HEVs and PHEVs and includes a classification of the algorithms in terms of their implementation and the chronological order of their appearance. Remaining challenges and potential future research directions are also discussed. © 2000-2011 IEEE.

Pint B.A.,Oak Ridge National Laboratory
Journal of Nuclear Materials | Year: 2011

To inhibit the dissolution and mass transfer of ferritic-martensitic steels in Pb-Li above 500 °C, the behavior of Al-rich diffusion coatings was explored in isothermal capsule exposures. After 1 kh at 600 °C or 700 °C, thin (∼40 μm) coatings made by chemical vapor deposition significantly reduced the mass loss of commercial Fe-9Cr-2 W substrates. At both temperatures, the surface reaction product was LiAlO 2 but at 700 °C a significant Al depletion occurred in the coating reducing the surface Al content from ∼18 at.% to <9%. Several strategies were explored to reduce the Al depletion from the coating including pre-oxidizing the coating before Pb-Li exposure and exposure to pure Pb. In each case, the Al loss was similar, suggesting that Al is being lost to the liquid metal despite the formation of an external oxide layer. Thicker coatings or Al alloy additions are potential solutions for operation at >600 °C. © 2011 Elsevier B.V. All rights reserved.

Singh D.J.,Oak Ridge National Laboratory
Science of Advanced Materials | Year: 2011

There is no known fundamental limit to the performance of thermoelectric materials as characterized by the dimensionless figure of merit, ZT, and in fact there has been significant recent progress in improving the performance of practical materials. Here we discuss some of the issues involved in improving ZT starting from transport theory, with particular emphasis on recent results on IV-VI chalcogenides and filled skutterudites. © 2011 American Scientific Publishers.

Blazevski D.,ETH Zurich | Del-Castillo-Negrete D.,Oak Ridge National Laboratory
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

A study of anisotropic heat transport in reversed shear (nonmonotonic q-profile) magnetic fields is presented. The approach is based on a recently proposed Lagrangian-Green's function method that allows an efficient and accurate integration of the parallel (i.e., along the magnetic field) heat transport equation. The magnetic field lines are described by a nontwist Hamiltonian system, known to exhibit separatrix reconnection and robust shearless (dq/dr=0) transport barriers. The changes in the magnetic field topology due to separatrix reconnection lead to bifurcations in the equilibrium temperature distribution. For perturbations of moderate amplitudes, magnetic chaos is restricted to bands flanking the shearless region. As a result, the temperature flattens in the chaotic bands and develops a very sharp radial gradient at the shearless region. For perturbations with larger amplitude, shearless Cantori (i.e., critical magnetic surfaces located at the minimum of the q profile) give rise to anomalous temperature relaxation involving widely different time scales. The first stage consists of the relatively fast flattening of the radial temperature profile in the chaotic bands with negligible flux across the shearless region that, for practical purposes, on a short time scale acts as an effective transport barrier despite the lack of magnetic flux surfaces. In the long-time scale, heat starts to flow across the shearless region, albeit at a comparatively low rate. The transport of a narrow temperature pulse centered at the reversed shear region exhibits weak self-similar scaling with non-Gaussian scaling functions indicating that transport at this scale cannot be modeled as a diffusive process with a constant diffusivity. Evidence of nonlocal effective radial transport is provided by the existence of regions with nonzero heat flux and zero temperature gradient. Parametric flux-gradient plots exhibit multivalued loops that question the applicability of the Fourier-Fick's prescription even in the presence of a finite pinch velocity. © 2013 American Physical Society.

Graham D.E.,Oak Ridge National Laboratory | Graham D.E.,University of Tennessee at Knoxville
Molecular Microbiology | Year: 2010

Hepatotoxic aflatoxins have found a worthy adversary in two new families of bacterial oxidoreductases. These enzymes use the reduced coenzyme F420 to initiate the degradation of furanocoumarin compounds, including the major mycotoxin products of Aspergillus flavus. Along with pyridoxal 5'-phosphate synthases and aryl nitroreductases, these proteins form a large and versatile superfamily of flavin and deazaflavin-dependent oxidoreductases. F420-dependent members of this family appear to share a common mechanism of hydride transfer from the reduced, low-potential deazaflavin to the electron-deficient ring systems of their substrates. © 2010 Blackwell Publishing Ltd.

Beste A.,Bethel University | Buchanan III A.C.,Oak Ridge National Laboratory
Chemical Physics Letters | Year: 2012

Employing kinetic Monte Carlo, we simulated the radical chain propagation of the pyrolysis of phenethyl phenyl ether (PPE), which serves as a model compound for the β-O-4 linkage in lignin. The input rate constants were obtained with transition state theory based on density functional calculations. Pre- and postcomplexes for hydrogen abstraction and β-scission reactions were included assuming thermal equilibrium. Individual rate constants compare well with experimental estimates. The calculated overall α/β-product selectivity is qualitatively in agreement with experiment. The simulation revealed that the carbon-carbon phenyl shift reaction for the β-PPE radical is part of the pyrolysis mechanism. © 2012 Elsevier B.V. All rights reserved.

Zinkle S.J.,Oak Ridge National Laboratory | Ghoniem N.M.,University of California at Los Angeles
Journal of Nuclear Materials | Year: 2011

We present an overview of key aspects for development of steels for fission and fusion energy applications, by linking material fabrication to thermo-mechanical properties through a physical understanding of microstructure evolution. Numerous design constraints (e.g. reduced activation, low ductile-brittle transition temperature, low neutron-induced swelling, good creep resistance, and weldability) need to be considered, which in turn can be controlled through material composition and processing techniques. Recent progress in the development of high-performance steels for fossil and fusion energy systems is summarized, along with progress in multiscale modeling of mechanical behavior in metals. Prospects for future design of optimum structural steels in nuclear applications by utilization of the hierarchy of multiscale experimental and computational strategies are briefly described. © 2011 Elsevier B.V. All rights reserved.

Sefat A.S.,Oak Ridge National Laboratory
Current Opinion in Solid State and Materials Science | Year: 2013

Exploratory synthesis efforts for iron-based superconductors (FeSCs) have been driven by hopes of improving superconducting critical temperatures (T Cs), providing high-quality samples for in-depth studies of intrinsic properties, and exploring potential superconductivity in similar families of materials. This manuscript summarizes the synthesis routes that are used for producing FeSC and their undoped parents, in single crystal and polycrystalline forms. A few of the materials challenges are summarized. © 2013 Elsevier Ltd. All rights reserved.

Zinkle S.J.,Oak Ridge National Laboratory | Was G.S.,University of Michigan
Acta Materialia | Year: 2013

Nuclear power currently provides about 13% of electrical power worldwide, and has emerged as a reliable baseload source of electricity. A number of materials challenges must be successfully resolved for nuclear energy to continue to make further improvements in reliability, safety and economics. The operating environment for materials in current and proposed future nuclear energy systems is summarized, along with a description of materials used for the main operating components. Materials challenges associated with power uprates and extensions of the operating lifetimes of reactors are described. The three major materials challenges for the current and next generation of water-cooled fission reactors are centered on two structural materials aging degradation issues (corrosion and stress corrosion cracking of structural materials and neutron-induced embrittlement of reactor pressure vessels), along with improved fuel system reliability and accident tolerance issues. The major corrosion and stress corrosion cracking degradation mechanisms for light-water reactors are reviewed. The materials degradation issues for the Zr alloy-clad UO2 fuel system currently utilized in the majority of commercial nuclear power plants are discussed for normal and off-normal operating conditions. Looking to proposed future (Generation IV) fission and fusion energy systems, there are five key bulk radiation degradation effects (low temperature radiation hardening and embrittlement; radiation-induced and -modified solute segregation and phase stability; irradiation creep; void swelling; and high-temperature helium embrittlement) and a multitude of corrosion and stress corrosion cracking effects (including irradiation-assisted phenomena) that can have a major impact on the performance of structural materials. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Si W.,Brookhaven National Laboratory | Han S.J.,Brookhaven National Laboratory | Shi X.,Brookhaven National Laboratory | Ehrlich S.N.,Brookhaven National Laboratory | And 3 more authors.
Nature Communications | Year: 2013

Although high-temperature superconductor cuprates have been discovered for more than 25 years, superconductors for high-field application are still based on low-temperature superconductors, such as Nb 3 Sn. The high anisotropies, brittle textures and high manufacturing costs limit the applicability of the cuprates. Here we demonstrate that the iron superconductors, without most of the drawbacks of the cuprates, have a superior high-field performance over low-temperature superconductors at 4.2 K. With a CeO 2 buffer, critical current densities >10 6 A cm-2 were observed in iron-chalcogenide FeSe 0.5 Te 0.5 films grown on single-crystalline and coated conductor substrates. These films are capable of carrying critical current densities exceeding 10 5 A cm-2 under 30 tesla magnetic fields, which are much higher than those of low-temperature superconductors. High critical current densities, low magnetic field anisotropies and relatively strong grain coupling make iron-chalcogenide-coated conductors particularly attractive for high-field applications at liquid helium temperatures. © & 2013 Macmillan Publishers Limited.

De Kruif C.G.,NIZO food research | De Kruif C.G.,University Utrecht | Huppertz T.,NIZO food research | Urban V.S.,Oak Ridge National Laboratory | Petukhov A.V.,University Utrecht
Advances in Colloid and Interface Science | Year: 2012

The internal structure of casein micelles was studied by calculating the small-angle neutron and X-ray scattering and static light scattering spectrum (SANS, SAXS, SLS) as a function of the scattering contrast and composition. We predicted experimental SANS, SAXS, SLS spectra self consistently using independently determined parameters for composition size, polydispersity, density and voluminosity. The internal structure of the casein micelles, i.e. how the various components are distributed within the casein micelle, was modeled according to three different models advocated in the literature; i.e. the classical sub-micelle model, the nanocluster model and the dual binding model. In this paper we present the essential features of these models and combine new and old experimental SANS, SAXS, SLS and DLS scattering data with new calculations that predict the spectra. Further evidence on micellar substructure was obtained by internally cross linking the casein micelles using transglutaminase, which led to casein nanogel particles. In contrast to native casein micelles, the nanogel particles were stable in 6 M urea and after sequestering the calcium using trisodium citrate. The changed scattering properties were again predicted self consistently. An important result is that the radius of gyration is independent of contrast, indicating that the mass distribution within a casein micelle is homogeneous. Experimental contrast is predicted quite well leading to a match point at a D 2O volume fraction of 0.41 ratio in SANS. Using SANS and SAXS model calculations it is concluded that only the nanocluster model is capable of accounting for the experimental scattering contrast variation data. All features and trends are predicted self consistently, among which the 'famous' shoulder at a wave vector value Q = 0.35 nm -1 In the nanocluster model, the casein micelle is considered as a (homogeneous) matrix of caseins in which the colloidal calcium phosphate (CCP) nanoclusters are dispersed as very small (about 2 nm) "cherry stones" at an average distance of 18.6 nm. Attached to the surface of the nanoclusters are the centers of phosphorylation (3-5 nearby phosphorylated amino acid residues) of the caseins. The tails of the caseins, much larger than the CCP clusters, then associate to form a protein matrix, which can be viewed as polymer mesh with density fluctuations at the 2 nm scale. The association of the tails is driven by a collection of weak interactions. We explicitly use weak interactions as a collective term for hydrophobic interactions, hydrogen bonding, ion bonding, weak electrostatic Van der Waals attraction and other factors (but not the strong calcium phosphate interaction) leading to self association. The association is highly cooperative and originates in the weak interactions. It is the cooperativety that leads to a stable casein micelle. Invariably, κ-casein is thought to limit the process of self association leading to stabilization of the native casein micelle. © 2012 Elsevier B.V.

Leggett R.W.,Oak Ridge National Laboratory
Science of the Total Environment | Year: 2012

The physiology of the essential trace element zinc has been studied extensively in human subjects using kinetic analysis of time-dependent measurements of administered zinc tracers. A number of biokinetic models describing zinc exchange between plasma and tissues and endogenous excretion of zinc have been derived as fits to data for specific study groups. More rudimentary biokinetic models for zinc have been developed to estimate radiation doses from internally deposited radioisotopes of zinc. The latter models are designed to provide broadly accurate estimates of cumulative decays of zinc radioisotopes in tissues and are not intended as realistic descriptions of the directions of movement of zinc in the body. This paper reviews biokinetic data for zinc and proposes a physiologically meaningful biokinetic model for systemic zinc for use in radiation protection. The proposed model bears some resemblance to zinc models developed in physiological studies but depicts a finer division of systemic zinc and is based on a broader spectrum of data than previous models. The proposed model and the model for zinc currently recommended by the International Commission on Radiological Protection yield reasonably similar estimates of total-body retention and effective dose for internally deposited radioisotopes of zinc but much different systemic distributions of activity and much different dose estimates for some individual tissues, particularly the liver. © 2011 Elsevier B.V.

Robinson S.A.,University of Wollongong | Erickson D.J.,Oak Ridge National Laboratory
Global Change Biology | Year: 2015

Climate scientists have concluded that stratospheric ozone depletion has been a major driver of Southern Hemisphere climate processes since about 1980. The implications of these observed and modelled changes in climate are likely to be far more pervasive for both terrestrial and marine ecosystems than the increase in ultraviolet-B radiation due to ozone depletion; however, they have been largely overlooked in the biological literature. Here, we synthesize the current understanding of how ozone depletion has impacted Southern Hemisphere climate and highlight the relatively few documented impacts on terrestrial and marine ecosystems. Reviewing the climate literature, we present examples of how ozone depletion changes atmospheric and oceanic circulation, with an emphasis on how these alterations in the physical climate system affect Southern Hemisphere weather, especially over the summer season (December-February). These potentially include increased incidence of extreme events, resulting in costly floods, drought, wildfires and serious environmental damage. The ecosystem impacts documented so far include changes to growth rates of South American and New Zealand trees, decreased growth of Antarctic mosses and changing biodiversity in Antarctic lakes. The objective of this synthesis was to stimulate the ecological community to look beyond ultraviolet-B radiation when considering the impacts of ozone depletion. Such widespread changes in Southern Hemisphere climate are likely to have had as much or more impact on natural ecosystems and food production over the past few decades, than the increased ultraviolet radiation due to ozone depletion. Copyright © 2015 John Wiley & Sons Ltd212 February 2015 10.1111/gcb.12739 Research Review Review Articles © 2014 John Wiley & Sons Ltd.

Rathmell A.R.,Duke University | Nguyen M.,Duke University | Chi M.,Oak Ridge National Laboratory | Wiley B.J.,Duke University
Nano Letters | Year: 2012

Nanowires of copper can be coated from liquids to create flexible, transparent conducting films that can potentially replace the dominant transparent conductor, indium tin oxide, in displays, solar cells, organic light-emitting diodes, and electrochromic windows. One issue with these nanowire films is that copper is prone to oxidation. It was hypothesized that the resistance to oxidation could be improved by coating copper nanowires with nickel. This work demonstrates a method for synthesizing copper nanowires with nickel shells as well as the properties of cupronickel nanowires in transparent conducting films. Time- and temperature-dependent sheet resistance measurements indicate that the sheet resistance of copper and silver nanowire films will double after 3 and 36 months at room temperature, respectively. In contrast, the sheet resistance of cupronickel nanowires containing 20 mol % nickel will double in about 400 years. Coating copper nanowires to a ratio of 2:1 Cu:Ni gave them a neutral gray color, making them more suitable for use in displays and electrochromic windows. These properties, and the fact that copper and nickel are 1000 times more abundant than indium or silver, make cupronickel nanowires a promising alternative for the sustainable, efficient production of transparent conductors. © 2012 American Chemical Society.

Leggett R.W.,Oak Ridge National Laboratory
Radiation Research | Year: 2010

This paper summarizes the biokinetic database for iodine in the human body and proposes a biokinetic model for systemic iodine for use in dose assessments for internally deposited radioiodine. The model consolidates and extends existing physiological systems models describing three subsystems of the iodine cycle in the body: circulating inorganic iodide, thyroidal iodine (trapping and organic binding of iodide and synthesis, storage and secretion of thyroid hormones), and extrathyroidal organic iodine. Thyroidal uptake of inorganic iodide is described as a function of stable iodine intake (Y, g day -1) and thyroidal secretion of hormonal iodine (S, g day -1). Baseline parameter values are developed for reference adults with typical iodine intake. Compared with the current systemic biokinetic model of the International Commission on Radiological Protection (ICRP) for occupational intake of radioiodine, the proposed model predicts higher absorbed doses to the thyroid per unit uptake to blood for very short-lived iodine isotopes, similar absorbed doses to thyroid for iodine isotopes with half-life of at least a few hours, and substantially higher estimates of absorbed dose to stomach wall, salivary gland and kidneys for most iodine isotopes. Absorbed dose estimates for intravenous administration of radioiodine-labeled thyroid hormones based on the proposed model differ substantially in some cases from current ICRP values. © 2010 by Radiation Research Society.

Xing Y.,Oak Ridge National Laboratory | Xing Y.,University of Tennessee at Knoxville
Journal of Computational Physics | Year: 2013

Hyperbolic conservation laws with source terms often admit steady state solutions where the fluxes and source terms balance each other. To capture this balance and near-equilibrium solutions, well-balanced methods have been introduced and performed well in many numerical tests. Shallow water equations have been extensively investigated as a prototype example. In this paper, we develop well-balanced discontinuous Galerkin methods for the shallow water system, which preserve not only the still water at rest steady state, but also the more general moving water equilibrium. The key idea is the recovery of well-balanced states, a special source term approximation, and the approximation of the numerical fluxes based on a generalized hydrostatic reconstruction. We also study the extension of the positivity-preserving limiter presented in [40] in this framework. Numerical examples are provided at the end to verify the well-balanced property and good resolution for smooth and discontinuous solutions. © 2013 Elsevier Inc.

Terentyev D.,Belgian Institute for Nuclear Sciences | Bergner F.,Helmholtz Center Dresden | Osetsky Y.,Oak Ridge National Laboratory
Acta Materialia | Year: 2013

The effect of chromium on iron hardening via segregation on dislocation loops was studied by atomic scale computer modeling. A combination of Monte Carlo and molecular dynamics techniques together with the recently determined Fe-Cr interatomic potentials fitted to ab initio data was used to investigate Cr segregation on 1/2〈1 1 1〉 interstitial dislocation loops and its impact on the interaction with moving dislocations. The Monte Carlo results reveal that Cr atoms segregate to the loop tensile strain region and dissolve well above the temperature corresponding to the solubility limit. The molecular dynamics results demonstrated that local micro-chemical changes near the loop reduce its mobility and increase the strength. The stress to move a dislocation through the array of Cr "decorated" loops increases due to modification of the dislocation-loop interaction mechanism. A possible explanation for a number of experimental observations being dependent on the radiation dose and for Cr concentration effects on the yield stress is given on the basis of the modeling results. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Feng G.,Vanderbilt University | Li S.,Vanderbilt University | Presser V.,Leibniz Institute for New Materials | Cummings P.T.,Vanderbilt University | Cummings P.T.,Oak Ridge National Laboratory
Journal of Physical Chemistry Letters | Year: 2013

The performance of supercapacitors is determined by the electrical double layers (EDLs) formed at electrolyte/electrode interfaces. To understand the energy storage mechanism underlying supercapacitors, molecular dynamics (MD) simulations were used to study the capacitive behavior of carbon-based supercapacitors with room-temperature ionic liquid (RTIL) electrolytes. The performance of porous supercapacitors was found to be correlated with the ion/pore size and applied voltage. Supercapacitors composed of RTILs on the outer, positively curved surfaces of onion-like carbons (OLCs) or carbon nanotubes (CNTs) exhibited significant effects on capacitance and the distinctive feature that differential capacitance varies only weakly with voltage. Investigations of temperature influence revealed a positive temperature dependence of capacitance for OLC-based supercapacitors and a weak dependence of capacitance on temperature for CNT-based supercapacitors, in line with experimental observations. Molecular insights into RTIL-based supercapacitors, reviewed in this Perspective, could facilitate the design and development of a new generation of energy storage devices. © 2013 American Chemical Society.

Wietfeldt F.E.,Tulane University | Greene G.L.,University of Tennessee at Knoxville | Greene G.L.,Oak Ridge National Laboratory
Reviews of Modern Physics | Year: 2011

The decay of the free neutron into a proton, electron, and antineutrino is the prototype semileptonic weak decay and is the simplest example of nuclear beta decay. It played a key role in the early Universe as it determined the ratio of neutrons to protons during the era of primordial light element nucleosynthesis. Neutron decay is physically related to important processes in solar physics and neutrino detection. The mean neutron lifetime has been the subject of more than 20 major experiments done, using a variety of methods, between 1950 and the present. The most precise recent measurements have stated accuracies approaching 0.1%, but are not in good agreement as they differ by as much as 5σ using quoted uncertainties. The history of neutron lifetime measurements is reviewed and the different methods used are described, giving important examples of each. The discrepancies and some systematic issues in the experiments that may be responsible are discussed, and it is shown by means of global averages that the neutron lifetime is likely to lie in the range of 880-884 s. Plans and prospects for future experiments are considered that will address these systematic issues and improve our knowledge of the neutron lifetime. © 2011 American Physical Society.

Jiang D.-E.,Oak Ridge National Laboratory | Meng D.,University of California at Riverside | Wu J.,University of California at Riverside
Chemical Physics Letters | Year: 2011

The differential capacitance of electric double layers in ionic liquids and its correlation with the surface charge density, ion size and concentration are studied within the framework of the classical density functional theory (DFT). As prescribed by previous analytical theories, DFT is able to reproduce the transition in the differential capacitance versus the surface potential curve from the 'camel' shape to the 'bell' shape when the ionic density increases. However, DFT predicts alternating layers of cations and anions at the charged surface that cannot be described by the classical Gouy-Chapman-Stern model and its modifications. © 2011 Elsevier B.V. All rights reserved.

Maier T.A.,Oak Ridge National Laboratory | Scalapino D.J.,University of California at Santa Barbara
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Here we calculate the pairing interaction and the k dependence of the gap function associated with the nematic charge fluctuations of a CuO2 model. We find that the nematic pairing interaction is attractive for small momentum transfer and that it gives rise to d-wave pairing. As the doping p approaches a quantum critical point, the strength of this pairing increases and higher d-wave harmonics contribute to the k dependence of the superconducting gap function, reflecting the longer range nature of the nematic fluctuations. © 2014 American Physical Society.

Sen S.,Oak Ridge National Laboratory
IEEE Journal on Selected Topics in Signal Processing | Year: 2015

We develop space-time adaptive processing (STAP) methods by leveraging the advantages of sparse signal processing techniques in order to detect a slowly-moving target. We observe that the inherent sparse characteristics of a STAP problem can be formulated as the low-rankness of clutter covariance matrix when compared to the total adaptive degrees-of-freedom, and also as the sparse interference spectrum on the spatio-temporal domain. By exploiting these sparse properties, we propose two approaches for estimating the interference covariance matrix. In the first approach, we consider a constrained matrix rank minimization problem (RMP) to decompose the sample covariance matrix into a low-rank positive semidefinite and a diagonal matrix. The solution of RMP is obtained by applying the trace minimization technique and the singular value decomposition with matrix shrinkage operator. Our second approach deals with the atomic norm minimization problem to recover the clutter response-vector that has a sparse support on the spatio-temporal plane. We use convex relaxation based standard sparse-recovery techniques to find the solutions. With extensive numerical examples, we demonstrate the performances of proposed STAP approaches with respect to both the ideal and practical scenarios, involving Doppler-ambiguous clutter ridges, spatial and temporal decorrelation effects. The low-rank matrix decomposition based solution requires secondary measurements as many as twice the clutter rank to attain a near-ideal STAP performance; whereas the spatio-temporal sparsity based approach needs a considerably small number of secondary data. © 2015 IEEE.

Diffenbaugh N.S.,Stanford University | Scherer M.,Stanford University | Ashfaq M.,Oak Ridge National Laboratory
Nature Climate Change | Year: 2013

Snow accumulation is critical for water availability in the Northern Hemisphere, raising concern that global warming could have important impacts on natural and human systems in snow-dependent regions. Although regional hydrologic changes have been observed (for example, refs,), the time of emergence of extreme changes in snow accumulation and melt remains a key unknown for assessing climate-change impacts. We find that the CMIP5 global climate model ensemble exhibits an imminent shift towards low snow years in the Northern Hemisphere, with areas of western North America, northeastern Europe and the Greater Himalaya showing the strongest emergence during the near-term decades and at 2C global warming. The occurrence of extremely low snow years becomes widespread by the late twenty-first century, as do the occurrences of extremely high early-season snowmelt and runoff (implying increasing flood risk), and extremely low late-season snowmelt and runoff (implying increasing water stress). Our results suggest that many snow-dependent regions of the Northern Hemisphere are likely to experience increasing stress from low snow years within the next three decades, and from extreme changes in snow-dominated water resources if global warming exceeds 2C above the pre-industrial baseline. © 2013 Macmillan Publishers Limited. All rights reserved.

Palmer D.A.,Oak Ridge National Laboratory
Journal of Solution Chemistry | Year: 2011

The equilibrium solubility of crystalline cuprous oxide, cuprite, was measured in liquid water and steam using two flow-through reactors and a conventional batch autoclave. These measurements were carried out from 20 to 400 °C. Different batches of pretreated cuprite were thoroughly characterized prior to and following each set of experiments. Metallic copper beads were added to the inlet end of the reactors and to the solid charge in the autoclave to preserve the Cu(I) oxidation state, although one series of experiments produced some results which were only compatible with CuO(cr) as the solubility limiting phase. Comparison of the solubility data for Cu2O(cr) in aqueous solution with those from the only available high-temperature dataset (Var'yash, Geochem. Int. 26:80-90, 1989) showed that in near-neutral solutions the new data are lower by about four orders of magnitude at 350 °C. Moreover, the dominant species in solution at temperatures ≥100 °C were found to be only Cu+ and Cu(OH)- 2 with Cu(OH)0 occurring over a narrow pH range at ≤75 °C rather than the reverse trend reported previously. Solubility equations were developed as a function of temperature and pH, based on these new results, which showed increased solubility with temperature in acidic and basic solutions. The solubility of Cu2O(cr) in steam decreased slightly with temperature and as expected increased with increasing pressure to supercritical conditions where limited, compatible data were available in the literature. The solubility at subcritical conditions was on the order of one to several parts per billion, ppb. A simple empirical fit was derived for the solubility in steam as a function of temperature and pressure. © Springer Science+Business Media, LLC (Outside the U.S.) 2011.

Rosenthal S.J.,Vanderbilt University | Rosenthal S.J.,Oak Ridge National Laboratory | Chang J.C.,Vanderbilt University | Kovtun O.,Vanderbilt University | And 2 more authors.
Chemistry and Biology | Year: 2011

Semiconductor quantum dots are quickly becoming a critical diagnostic tool for discerning cellular function at the molecular level. Their high brightness, long-lasting, size-tunable, and narrow luminescence set them apart from conventional fluorescence dyes. Quantum dots are being developed for a variety of biologically oriented applications, including fluorescent assays for drug discovery, disease detection, single protein tracking, and intracellular reporting. This review introduces the science behind quantum dots and describes how they are made biologically compatible. Several applications are also included, illustrating strategies toward target specificity, and are followed by a discussion on the limitations of quantum dot approaches. The article is concluded with a look at the future direction of quantum dots. © 2011 Elsevier Ltd. All rights reserved.

Villa A.,University of Milan | Veith G.M.,Oak Ridge National Laboratory | Prati L.,University of Milan
Angewandte Chemie - International Edition | Year: 2010

(Figure Presented) Skip the bases! H-mordenite-supported PtAu nanoparticles are highly active and selective in the oxidation of glycerol under acidic conditions, which allows the direct preparation of free acids (see picture). The high selectivity for C3 compounds results from the negligible formation of H2O2, in contrast to PtAu nanoparticles supported on activated carbon. © 2010 Wiley-VCH Verlag GmbH &. Co. KGaA, Weinheim.

Afonine P.V.,Lawrence Berkeley National Laboratory | Moriarty N.W.,Lawrence Berkeley National Laboratory | Mustyakimov M.,Oak Ridge National Laboratory | Sobolev O.V.,Lawrence Berkeley National Laboratory | And 6 more authors.
Acta Crystallographica Section D: Biological Crystallography | Year: 2015

A method is presented that modifies a 2mFobs - D Fmodel σA-weighted map such that the resulting map can strengthen a weak signal, if present, and can reduce model bias and noise. The method consists of first randomizing the starting map and filling in missing reflections using multiple metho