Time filter

Source Type

Lemont, IL, United States

Matveev K.A.,Argonne National Laboratory | Andreev A.V.,University of Washington | Pustilnik M.,Georgia Institute of Technology
Physical Review Letters | Year: 2010

Equilibration of a one-dimensional system of interacting electrons requires processes that change the numbers of left- and right-moving particles. At low temperatures such processes are strongly suppressed, resulting in slow relaxation towards equilibrium. We study this phenomenon in the case of spinless electrons with strong long-range repulsion, when the electrons form a one-dimensional Wigner crystal. We find the relaxation rate by accounting for the umklapp scattering of phonons in the crystal. For the integrable model of particles with inverse-square repulsion, the relaxation rate vanishes. © 2010 The American Physical Society.

Ratchford D.,University of Texas at Austin | Shafiei F.,University of Texas at Austin | Kim S.,University of Texas at Austin | Gray S.K.,Argonne National Laboratory | Li X.,University of Texas at Austin
Nano Letters | Year: 2011

Using atomic force microscopy nanomanipulation, we position a single Au nanoparticle near a CdSe/ZnS quantum dot to construct a hybrid nanostructure with variable geometry. The coupling between the two particles is varied in a systematic and reversible manner. The photoluminescence lifetime and blinking of the same quantum dot are measured before and after assembly of the structure. In some hybrid structures, the total lifetime is reduced from about 30 ns to well below 1 ns. This dramatic change in lifetime is accompanied by the disappearance of blinking as the nonradiative energy transfer from the CdSe/ZnS quantum dot to the Au nanoparticle becomes the dominant decay channel. Both total lifetime and photoluminescence intensity changes are well described by simple analytical calculations. © 2011 American Chemical Society.

Das S.,Purdue University | Das S.,Argonne National Laboratory | Appenzeller J.,Purdue University
Applied Physics Letters | Year: 2013

One of the most relevant features that a semiconducting channel material can offer when used in a field-effect transistor (FET) layout is its capability to enable both electron transport in the conduction band and hole transport in the valence band. In this way, complementary metal-oxide-semiconductor type applications become feasible once similar electron and hole drive current densities are achieved, and the threshold voltages are properly adjusted. In this article, we demonstrate pronounced ambipolar device characteristics of multilayer WSe2 FETs using different contact electrodes. Our study reveals that nickel electrodes facilitate electron injection while palladium electrodes are more efficient for hole injection. We also show, as an interesting demonstration, that by using nickel as the source contact electrode and palladium as the drain contact electrode, ambipolar device characteristics with similar on-state performance for both the electron and the hole branch can be achieved in WSe2 FETs. Finally, we discuss a unique technique based on the asymmetry in the ambipolar device characteristics to extract the Schottky barrier heights for such metal to WSe2 contacts. © 2013 AIP Publishing LLC.

Ungaro C.,University of Virginia | Gray S.K.,Argonne National Laboratory | Gupta M.C.,University of Virginia
Applied Physics Letters | Year: 2013

The viability of micro/nano textured tungsten as an efficient solar absorber is explored via computational electrodynamics simulations. Pseudo-random structures are investigated, along with the effects of protective oxide coatings. These structures show extremely high absorption across the solar spectrum along with relaxed requirements for manufacturing, allowing them to be applied for power generation. © 2013 AIP Publishing LLC.

Biswas K.,Northwestern University | He J.,Northwestern University | Zhang Q.,Northwestern University | Wang G.,University of Michigan | And 4 more authors.
Nature Chemistry | Year: 2011

Thermoelectric materials can directly generate electrical power from waste heat but the challenge is in designing efficient, stable and inexpensive systems. Nanostructuring in bulk materials dramatically reduces the thermal conductivity but simultaneously increases the charge carrier scattering, which has a detrimental effect on the carrier mobility. We have experimentally achieved concurrent phonon blocking and charge transmitting via the endotaxial placement of nanocrystals in a thermoelectric material host. Endotaxially arranged SrTe nanocrystals at concentrations as low as 2% were incorporated in a PbTe matrix doped with Na 2 Te. This effectively inhibits the heat flow in the system but does not affect the hole mobility, allowing a large power factor to be achieved. The crystallographic alignment of SrTe and PbTe lattices decouples phonon and electron transport and this allows the system to reach a thermoelectric figure of merit of 1.7 at ∼800 K. © 2011 Macmillan Publishers Limited. All rights reserved.

Heinonen O.G.,Recording Heads Operation | Heinonen O.G.,Argonne National Laboratory | Stokes S.W.,Recording Heads Operation | Yi J.Y.,Recording Heads Operation
Physical Review Letters | Year: 2010

A steady-state electrical current flowing in a magnetic heterostructure can exert a torque on the magnetization, and provides a means to control magnetization states and dynamics in spintronics structures. However, some components of the torque are difficult to measure and to calculate. We have determined the perpendicular spin torque in MgO magnetic tunnel junctions by measuring their lowest ferromagnetic resonance frequency and find that it decreases linearly with increasing bias voltage. Micromagnetic modeling shows that this decrease is caused by the perpendicular component of spin torque. We obtain a quantitative value for the perpendicular spin torque effective field as a function of bias voltage, and show that this effective field is a linear function in bias voltage and approximately equal in magnitude to the in-plane spin torque effective field. © 2010 The American Physical Society.

Dauter Z.,Argonne National Laboratory
Acta Crystallographica Section D: Biological Crystallography | Year: 2010

Diffraction data collection is the last experimental stage in structural crystallography. It has several technical and theor-etical aspects and a compromise usually has to be found between various parameters in order to achieve optimal data quality. The influence and importance of various experimental parameters and their consequences are discussed in the context of different data applications, such as molecular replacement, anomalous phasing, high-resolution refinement or searching for ligands.

Armatas G.S.,Northwestern University | Armatas G.S.,University of Crete | Kanatzidis M.G.,Northwestern University | Kanatzidis M.G.,Argonne National Laboratory
Nano Letters | Year: 2010

A series of hexagonal mesoporous germanium semiconductors with tunable wall thickness is reported. These nanostructures possess uniform pores of 3.1-3.2 nm, wall thicknesses from 1.3 to 2.2 nm, and large internal BET surface area in the range of 404-451 m2/g. The porous Ge framework of these materials is assembled from the templated oxidative self-polymerization of (Ge 9)4- Zintl clusters. Total X-ray scattering analysis supports a model of interconnected deltahedral (Ge9)-cluster forming the framework and X-ray photoelectron spectroscopy indicates nearly zero-valence Ge atoms. We show the controllable tuning of the pore wall thickness and its impact on the energy band gap which increases systematically with diminishing wall thickness. Furthermore, there is room temperature photoluminescence emission which shifts correspondingly from 672 to 640 nm. The emission signal can be quenched via energy transfer with organic molecules such as pyridine diffusing into the pores. © 2010 American Chemical Society.

Meral C.,University of California at Berkeley | Benmore C.J.,Argonne National Laboratory | Monteiro P.J.M.,University of California at Berkeley
Cement and Concrete Research | Year: 2011

Significant progress was achieved with the application of Rietveld method to characterize the crystalline phases in portland cement paste. However, to obtain detailed information on the amorphous or poorly crystalline phases, it is necessary to analyze the total scattering data. The pair distribution function (PDF) method has been successfully used in the study of liquids and amorphous solids. The method takes the Sine Fourier transform of the measured structure factor over a wide momentum transfer range, providing a direct measure of the probability of finding an atom surrounding a central atom at a radial distance away. The obtained experimental characteristic distances can be also used to validate the predictions by the theoretical models, such as, molecular dynamics, ab initio simulations and density functional theory. The paper summarizes recent results of PDF analysis on silica fume, rice husk ash, fly ash, ASR gel, C-S-H and geopolymers. © 2011 Elsevier Ltd. All rights reserved.

Rozhkova E.A.,Argonne National Laboratory
Advanced Materials | Year: 2011

This article reports on recent progress in the development of advanced nanoscale photoreactive, magnetic and multifunctional materials applicable to brain cancer diagnostics, imaging, and therapy, with an emphasis on the latest contributions and the novelty of the approach, along with the most promising emergent trends. This article reports on recent progress in the development of advanced nanoscale photoreactive, magnetic and multifunctional materials applicable to brain cancer diagnostics, imaging, and therapy, with an emphasis on the latest contributions and the novelty of the approach, along with the most promising emergent trends. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Arrington J.,Argonne National Laboratory | Higinbotham D.W.,Jefferson Lab | Rosner G.,University of Glasgow | Sargsian M.,Florida International University
Progress in Particle and Nuclear Physics | Year: 2012

One of the primary goals of nuclear physics is providing a complete description of the structure of atomic nuclei. While mean-field calculations provide detailed information on the nuclear shell structure for a wide range of nuclei, they do not capture the complete structure of nuclei, in particular the impact of small, dense structures in nuclei. The strong, short-range component of the nucleonnucleon potential yields hard interactions between nucleons which are close together, generating a high-momentum tail to the nucleon momentum distribution, with momenta well in excess of the Fermi momentum. This high-momentum component of the nuclear wave-function is one of the most poorly understood parts of nuclear structure. Utilizing high-energy probes, we can isolate scattering from high-momentum nucleons, and use these measurements to examine the structure and impact of short-range nucleonnucleon correlations. Over the last decade we have moved from looking for evidence of such short-range structures to mapping out their strength in nuclei and examining their isospin structure. This has been made possible by high-luminosity and high-energy accelerators, coupled with an improved understanding of the reaction mechanism issues involved in studying these structures. We review the general issues related to short-range correlations, survey recent experiments aimed at probing these short-range structures, and lay out future possibilities to further these studies. © 2012 Elsevier B.V. All rights reserved.

Freeman S.J.,University of Manchester | Schiffer J.P.,Argonne National Laboratory
Journal of Physics G: Nuclear and Particle Physics | Year: 2012

The discovery that neutrinos have finite rest mass has led to renewed interest in neutrinoless double beta decay. The development of large-scale experiments to search for neutrinoless double beta decay has increased the probability of a credible observation of the process in the near future. The reliability of calculations of the associated nuclear matrix elements is likely soon to become a critical issue. In this paper experimental techniques that access properties of the ground-state wave functions of double-beta-decay candidates, the occupancies of valence single-particle orbitals and pairing correlations, are summarized and the experimental data for candidate nuclei are reviewed. The results are discussed in relation to questions concerning which aspects of nuclear structure may play an important role in determining the nuclear matrix elements for neutrinoless double beta decay. © 2012 IOP Publishing Ltd.

Holt R.J.,Argonne National Laboratory | Gilman R.,Rutgers University
Reports on Progress in Physics | Year: 2012

We provide a perspective on studies aimed at observing the transition between hadronic and quark-gluonic descriptions of reactions involving light nuclei. We begin by summarizing the results for relatively simple reactions such as the pion form factor and the neutral pion transition form factor as well as that for the nucleon and end with exclusive photoreactions in our simplest nuclei. A particular focus will be on reactions involving the deuteron. It is noted that a firm understanding of these issues is essential for unravelling important structure information from processes such as deeply virtual Compton scattering as well as deeply virtual meson production. The connection to exotic phenomena such as color transparency will be discussed. A number of outstanding challenges will require new experiments at modern facilities on the horizon as well as further theoretical developments. © 2012 IOP Publishing Ltd.

Cheng X.M.,Bryn Mawr College | Keavney D.J.,Argonne National Laboratory
Reports on Progress in Physics | Year: 2012

As interest in magnetic devices has increased over the last 20 years, research into nanomagnetism has experienced a corresponding growth. Device applications from magnetic storage to magnetic logic have compelled interest in the influence of geometry and finite size on magnetism and magnetic excitations, in particular where the smallest dimensions reach the important magnetic interaction length scales. The dynamical behavior of nanoscale magnets is an especially important subset of research, as these phenomena are both critical for device physics and profoundly influenced by finite size. At the same time, nanoscale systems offer unique geometries to promote and study model systems, such as magnetic vortices, leading to new fundamental insights into magnetization dynamics. A wide array of experimental and computational techniques have been applied to these problems. Among these, imaging techniques that provide real-space information on the magnetic order are particularly useful. X-ray microscopy offers several advantages over scanning probe or optical techniques, such as high spatial resolution, element specificity and the possibility for high time resolution. Here, we review recent contributions using static and time-resolved x-ray photoemission electron microscopy to nanomagnetism research. © 2012 IOP Publishing Ltd.

Lin X.-M.,Argonne National Laboratory
Nano Letters | Year: 2010

Critical photonic, electronic, and magnetic applications of two-dimensional nanocrystal superlattices often require nanostructures in perfect single-crystal phases with long-range order and limited defects. Here we discovered a crystalline phase with quasi long range positional order for two-dimensional nanocrystal superlattice domains self-assembled at the liquid-air interface during droplet evaporation, using in situ time-resolved X-ray scattering along with rigorous theories on two dimensional crystal structures. Surprisingly, it was observed that drying these superlattice domains preserved only an orientational order but not a longrange positional order, also supported by quantitative analysis of transmission electron microscopy images. © 2010 American Chemical Society.

Paracchino A.,Ecole Polytechnique Federale de Lausanne | Brauer J.C.,Ecole Polytechnique Federale de Lausanne | Moser J.-E.,Ecole Polytechnique Federale de Lausanne | Thimsen E.,Argonne National Laboratory | Graetzel M.,Ecole Polytechnique Federale de Lausanne
Journal of Physical Chemistry C | Year: 2012

We present a systematic study on the effects of electrodeposition parameters on the photoelectrochemical properties of Cu 2O. The influence of deposition variables (temperature, pH, and deposition current density) on conductivity has been widely explored in the past for this semiconductor, but the optimization of the electrodeposition process for the photoelectrochemical response in aqueous solutions under AM 1.5 illumination has received far less attention. In this work, we analyze the photoactivity of Cu 2O films deposited at different conditions and correlate the photoresponse to morphology, film orientation, and electrical properties. The photoelectrochemical response was measured by linear sweep voltammetry under chopped simulated AM 1.5 illumination. The highest photocurrent obtained was â̂'2.4 mA cm -2 at 0.25 V vs RHE for a film thickness of 1.3 μm. This is the highest reported value reached so far for this material in an aqueous electrolyte under AM 1.5 illumination. The optical and electrical properties of the most photoactive electrode were investigated by UV-vis spectroscopy and electrochemical impedance, while the minority carrier lifetime and diffusion length were measured by optical-pump THz-probe spectroscopy. © 2012 American Chemical Society.

Arrington J.,Argonne National Laboratory
Journal of Physics G: Nuclear and Particle Physics | Year: 2013

Multi-photon exchange contributions are important in extracting the proton charge radius from elastic electron-proton scattering. So far, only diagrams associated with the exchange of a second photon have been evaluated. At the low Q2 values relevant to the radius extraction, and especially the very low Q2 region to be probed by proposed measurements, higher order contributions may become important. We evaluate these corrections in the Effective Momentum Approximation, which includes the Coulomb interaction to all orders, and find small corrections with a strong Q2 dependence at low Q2 and large scattering angles. This suggests that the higher order terms may be important in the evaluation of the proton magnetic radius. © 2013 IOP Publishing Ltd.

Martiny A.C.,University of California at Irvine | Treseder K.,University of California at Irvine | Pusch G.,Argonne National Laboratory
ISME Journal | Year: 2013

A central question in biology is how biodiversity influences ecosystem functioning. Underlying this is the relationship between organismal phylogeny and the presence of specific functional traits. The relationship is complicated by gene loss and convergent evolution, resulting in the polyphyletic distribution of many traits. In microorganisms, lateral gene transfer can further distort the linkage between phylogeny and the presence of specific functional traits. To identify the phylogenetic conservation of specific traits in microorganisms, we developed a new phylogenetic metric -consenTRAIT -to estimate the clade depth where organisms share a trait. We then analyzed the distribution of 89 functional traits across a broad range of Bacteria and Archaea using genotypic and phenotypic data. A total of 93% of the traits were significantly non-randomly distributed, which suggested that vertical inheritance was generally important for the phylogenetic dispersion of functional traits in microorganisms. Further, traits in microbes were associated with a continuum of trait depths (τ D), ranging from a few deep to many shallow clades (average τ D: 0.101-0.0011 rRNA sequence dissimilarity). Next, we demonstrated that the dispersion and the depth of clades that contain a trait is correlated with the trait's complexity. Specifically, complex traits encoded by many genes like photosynthesis and methanogenesis were found in a few deep clusters, whereas the ability to use simple carbon substrates was highly phylogenetically dispersed. On the basis of these results, we propose a framework for predicting the phylogenetic conservatism of functional traits depending on the complexity of the trait. This framework enables predicting how variation in microbial composition may affect microbially-mediated ecosystem processes as well as linking phylogenetic and trait-based patterns of biogeography. © 2013 International Society for Microbial Ecology All rights reserved.

Singh S.,University of Wisconsin - Madison | Ediger M.D.,University of Wisconsin - Madison | De Pablo J.J.,University of Wisconsin - Madison | De Pablo J.J.,University of Chicago | De Pablo J.J.,Argonne National Laboratory
Nature Materials | Year: 2013

Glasses are generally prepared by cooling from the liquid phase, and their properties depend on their thermal history. Recent experiments indicate that glasses prepared by vapour deposition onto a substrate can exhibit remarkable stability, and might correspond to equilibrium states that could hitherto be reached only by glasses aged for thousands of years. Here we create ultrastable glasses by means of a computer-simulation process that mimics physical vapour deposition. These stable glasses have, far below the conventional glass-transition temperature, the properties expected for the equilibrium supercooled liquid state, and optimal stability is attained when deposition occurs at the Kauzmann temperature. We also show that the glasses' extraordinary stability is associated with distinct structural motifs, in particular the abundance of regular Voronoi polyhedra and the relative lack of irregular polyhedra. © 2013 Macmillan Publishers Limited.

Iski E.V.,Center for Nanoscale Materials | Yitamben E.N.,Center for Nanoscale Materials | Gao L.,California State University, Northridge | Guisinger N.P.,Argonne National Laboratory
Advanced Functional Materials | Year: 2013

Graphene is nature's ideal two-dimensional conductor and is comprised of a single sheet of hexagonally packed carbon atoms. Since the first electrical measurements made on graphene, researchers have been trying to exploit the unique properties of this material for a variety of applications that span numerous scientific and engineering disciplines. In order to fully realize the potential of graphene, large scale synthesis of high quality graphene and the ability to control the electronic properties of this material on a nanometer length-scale are necessary and remain key challenges. This article will review the efforts at the Center for Nanoscale Materials that focus on the atomic-scale characterization and modification of graphene via scanning tunneling microscopy and its synthesis on various materials (SiC, Cu(111), Cu foil, etc.). These fundamental studies explore growth dynamics, film quality, and the role of defects. The chemical modification of graphene following exposure to atomic hydrogen will also be covered, while additional emphasis will be made on graphene's unique structural properties. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Esbensen H.,Argonne National Laboratory
Physical Review C - Nuclear Physics | Year: 2010

The complete fusion of Be9 with Sm144 and Pb208 targets is calculated in the coupled-channels approach. The calculations include couplings among the 3/2-, 5/2-, and 7/2- states in the K=3/2 ground-state rotational band of Be9. It is shown that the B(E2) values for the excitation of these states are accurately described in the rotor model. The interaction of the strongly deformed Be9 nucleus with a spherical target is calculated using the double-folding technique and the effective M3Y interaction, which is supplemented with a repulsive term that is adjusted to optimize the fit to the data for the Sm144 target. The complete fusion is described by ingoing-wave boundary conditions. The decay of the unbound excited states in Be9 is considered explicitly in the calculations by using complex excitation energies. The model gives an excellent account of the complete fusion (CF) data for Be9+Sm144, and the cross sections for the decay of the excited states are in surprisingly good agreement with the incomplete fusion (ICF) data. Similar calculations for Be9+Pb208 explain the total fusion data at high energies but fail to explain the CF data, which are suppressed by 20%, and the calculated cross section for the decay of excited states is a factor of 3 smaller than the ICF data at high energies. Possible reasons for these discrepancies are discussed. © 2010 The American Physical Society.

Kuzmenko I.,Argonne National Laboratory
Physical Review Letters | Year: 2010

We report a structural study of cholesterol-DPPC (1,2-dipalmitoyl-sn- glycero-3-phophocholine) monolayers using x-ray reflectivity and grazing incidence x-ray diffraction. Reflectivity reveals that the vertical position of cholesterol relative to phospholipids strongly depends on its mole fraction (χCHOL). Moreover, we find that at a broad range of χCHOL cholesterol and DPPC form alloylike mixed domains of short-range order and the same stoichiometry as that of the film. Based on the data presented, we propose a new model of cholesterol-phospholipid organization in mixed monolayers. © 2010 The American Physical Society.

Nakhmanson S.M.,Argonne National Laboratory | Naumov I.,Hewlett - Packard
Physical Review Letters | Year: 2010

With the help of first-principles-based computational techniques, we demonstrate that Goldstone-like states can be artificially induced in a layered-perovskite ferroelectric compound with frustrated polarization, resulting in the emergence of a variety of interesting physical properties that include large, tunable dielectric constants and an ability to easily form vortex polar states in a nanodot geometry. In a similar fashion to the well-known perovskite materials with morphotropic phase boundaries (MPBs), these states manifest themselves as polarization rotations with almost no energy penalty, suggesting that the existence of an MPB is actually yet another manifestation of the Goldstone theorem in solids. © 2010 The American Physical Society.

Koshelev A.E.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

The s± state in which the order parameter has different signs in different bands is a leading candidate for the superconducting state in the iron-based superconductors. We investigate a Josephson junction between s and s± superconductors within microscopic theory. Frustration, caused by interaction of the s-wave gap parameter with the opposite-sign gaps of the s± superconductor, leads to nontrivial phase diagram. When the partial Josephson coupling energy between the s-wave superconductor and one of the s± bands dominates, s-wave gap parameter aligns with the order parameter in this band. In this case, the partial Josephson energies have different signs corresponding to signs of the gap parameters. In the case of strong frustration, corresponding to almost complete compensation of the total Josephson energy, a nontrivial time-reversal-symmetry breaking (TRSB) state realizes. In this state, all gap parameters become essentially complex. As a consequence, this state provides realization for so-called -junction with finite phase difference in the ground state. The width of the TRSB state region is determined by the second harmonic in Josephson current, sin(2), which appears in the second order with respect to the boundary transparency. Using the microscopic theory, we establish a range of parameters where different states are realized. Our analysis shows insufficiency of the simple phenomenological approach for treatment of this problem. © 2012 American Physical Society.

Van Wezel J.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

It was recently discovered that in spite of the scalar nature of its order parameter, the charge order in 1T-TiSe 2 can be chiral. This is made possible by the emergence of orbital order in conjunction with the charge-density modulations. Here we show that a closely related charge and orbital ordered state arises in 2H-TaS 2. In both materials, the microscopic mechanism driving the transition is based on the interaction between three differently polarized displacement waves. The relative phase shifts between these waves lead both to the formation of orbital order and to the breakdown of inversion symmetry. In contrast to 1T-TiSe 2, however, the presence of a mirror plane in the lattice of 2H-TaS 2 prevents the distorted structure in this material from being chiral, and a polar charge and orbital ordered state arises instead. It is stressed that bulk experiments are indispensable in differentiating between the chiral and polar phases. © 2012 American Physical Society.

Matveev K.A.,Argonne National Laboratory | Andreev A.V.,University of Washington
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We study how a Luttinger liquid of spinless particles in one dimension approaches thermal equilibrium. Full equilibration requires processes of backscattering of excitations, which occur at energies of the order of the bandwidth. Such processes are not accounted for by the Luttinger-liquid theory. We treat the high-energy excitations as mobile impurities and derive an expression for the equilibration rate in terms of their spectrum. Our results apply at any interaction strength. © 2012 American Physical Society.

Warren S.C.,Ecole Polytechnique Federale de Lausanne | Warren S.C.,Equilibrium Energy | Thimsen E.,Ecole Polytechnique Federale de Lausanne | Thimsen E.,Argonne National Laboratory
Energy and Environmental Science | Year: 2012

The study of the optoelectronic effects of plasmonic metal nanoparticles on semiconductors has led to compelling evidence for plasmon-enhanced water splitting. We review the relevant physics, device geometries, and research progress in this area. We focus on localized surface plasmons and their effects on semiconductors, particularly in terms of energy transfer, scattering, and hot electron transfer. © 2011 The Royal Society of Chemistry.

Van Wezel J.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In their publication, Ishioka discuss the recently discovered chiral charge-density wave state in 1T-TiSe2 in terms of a parameter H CDW, whose sign is suggested to correspond to the handedness of the chiral order. Here, we point out that HCDW, as defined by Ishioka, cannot be used to characterize chirality in that way. An alternative measure of chirality for the specific case of 1T-TiSe2 is suggested. © 2012 American Physical Society.

Shade A.,Yale University | Gregory Caporaso J.,Northern Arizona University | Gregory Caporaso J.,Argonne National Laboratory | Handelsman J.,Yale University | And 3 more authors.
ISME Journal | Year: 2013

Ecologists have long studied the temporal dynamics of plant and animal communities with much less attention paid to the temporal dynamics exhibited by microbial communities. As a result, we do not know if overarching temporal trends exist for microbial communities or if changes in microbial communities are generally predictable with time. Using microbial time series assessed via high-throughput sequencing, we conducted a meta-analysis of temporal dynamics in microbial communities, including 76 sites representing air, aquatic, soil, brewery wastewater treatment, human- and plant-associated microbial biomes. We found that temporal variability in both within- and between-community diversity was consistent among microbial communities from similar environments. Community structure changed systematically with time in less than half of the cases, and the highest rates of change were observed within ranges of 1 day to 1 month for all communities examined. Microbial communities exhibited species-time relationships (STRs), which describe the accumulation of new taxa to a community, similar to those observed previously for plant and animal communities, suggesting that STRs are remarkably consistent across a broad range of taxa. These results highlight that a continued integration of microbial ecology into the broader field of ecology will provide new insight into the temporal patterns of microbial and 'macro'-bial communities alike. © 2013 International Society for Microbial Ecology. All rights reserved.

Lin F.P.-J.,Old Dominion University | Lin F.P.-J.,Argonne National Laboratory | Gurevich A.,Old Dominion University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We consider the effect of nonmagnetic and magnetic impurities on the superheating field H s in a type-II superconductor. We solved the Eilenberger equations, which take into account the nonlinear pairbreaking of Meissner screening currents, and calculated H s(T) for arbitrary temperatures and impurity concentrations in a single-band s-wave superconductor with a large Ginzburg-Landau parameter. At low temperatures, nonmagnetic impurities suppress a weak maximum in H s(T), which has been predicted for the clean limit, resulting, instead, in a maximum of H s as a function of impurity concentration in a moderately clean limit. It is shown that nonmagnetic impurities weakly affect H s even in the dirty limit, while magnetic impurities suppress both H s and the critical temperature T c. The density of quasiparticles states N(ε) is strongly affected by an interplay of impurity scattering and current pairbreaking. We show that a clean superconductor at H=H s is in a gapless state, but a quasiparticle gap ε g in N(ε) at H=H s appears as the concentration of nonmagnetic impurities increases. As the nonmagnetic scattering rate α increases above α c=0.36, the quasiparticle gap ε g(α) at H=H s increases, approaching ε g0.32Δ 0 in the dirty limit α 1, where Δ 0 is the superconducting gap parameter at zero field. The effects of impurities on H s can be essential for the nonlinear surface resistance and superconductivity breakdown by strong RF fields. © 2012 American Physical Society.

Kharitonov M.,Argonne National Laboratory | Kharitonov M.,Rutgers University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We develop a theory of the correlated magnetically ordered insulating state at the edge of a two-dimensional topological insulator. We demonstrate that the gapped spin-polarized state, induced by the application of the magnetic field B, is naturally facilitated by electron interactions, which drive the critical easy-plane ferromagnetic correlations in the helical liquid. As the key manifestation, the gap Δ in the spectrum of collective excitations, which carry both spin and charge, is enhanced and exhibits a scaling dependence ΔA¢EAB1 /(2 -K ), controlled by the Luttinger liquid parameter K. This scaling dependence could be probed through the activation behavior G∼(e2/h)exp(-Δ/T) of the longitudinal conductance of a Hall-bar device at lower temperatures, providing a straightforward way to extract the parameter K experimentally. Our findings thus suggest that the signatures of the interaction-driven quantum criticality of the helical liquid could be revealed already in a standard Hall-bar measurement. © 2012 American Physical Society.

Huang X.R.,Argonne National Laboratory
Journal of Applied Crystallography | Year: 2010

LauePt is a robust and extremely easy-to-use Windows application for accurately simulating, indexing and analyzing white-beam X-ray diffraction Laue patterns of any crystals under arbitrary diffraction geometry. This program has a user-friendly graphic interface and can be conveniently used by nonspecialists with little X-ray diffraction or crystallography knowledge. Its wide range of applications include (1) determination of single-crystal orientation with the Laue method, (2) white-beam topography, (3) white-beam microdiffraction, (4) X-ray studies of twinning, domains and heterostructures, (5) verification or determination of crystal structures from white-beam diffraction, and (6) teaching of X-ray crystallography. © 2010 International Union of Crystallography Printed in Singapore - all rights reserved.

Bonatsos D.,Greek National Center For Scientific Research | McCutchan E.A.,Argonne National Laboratory | Casten R.F.,Yale University
Physical Review Letters | Year: 2010

The first example of an empirically manifested quasidynamical symmetry trajectory in the interior of the symmetry triangle of the interacting boson approximation model is identified for large boson numbers. Along this curve, extending from SU(3) to near the critical line of the first order phase transition, spectra exhibit nearly the same degeneracies that characterize the low energy levels of SU(3). This trajectory also lies close to the Alhassid-Whelan arc of regularity, the unique interior region of regular behavior connecting the SU(3) and U(5) vertices, thus offering a possible symmetry-based interpretation of that narrow zone of regularity amidst regions of more chaotic spectra. © 2010 The American Physical Society.

Tao Y.,Stanford University | Cheung L.S.,Carnegie Institution for Science | Li S.,Stanford University | Li S.,Sichuan University | And 6 more authors.
Nature | Year: 2015

Eukaryotes rely on efficient distribution of energy and carbon skeletons between organs in the form of sugars. Glucose in animals and sucrose in plants serve as the dominant distribution forms. Cellular sugar uptake and release require vesicular and/or plasma membrane transport proteins. Humans and plants use proteins from three superfamilies for sugar translocation: the major facilitator superfamily (MFS), the sodium solute symporter family (SSF; only in the animal kingdom), and SWEETs. SWEETs carry mono- and disaccharides across vacuolar or plasma membranes. Plant SWEETs play key roles in sugar translocation between compartments, cells, and organs, notably in nectar secretion, phloem loading for long distance translocation, pollen nutrition, and seed filling. Plant SWEETs cause pathogen susceptibility possibly by sugar leakage from infected cells. The vacuolar Arabidopsis thaliana AtSWEET2 sequesters sugars in root vacuoles; loss-of-function mutants show increased susceptibility to Pythium infection. Here we show that its orthologue, the vacuolar glucose transporter OsSWEET2b from rice (Oryza sativa), consists of an asymmetrical pair of triple-helix bundles, connected by an inversion linker transmembrane helix (TM4) to create the translocation pathway. Structural and biochemical analyses show OsSWEET2b in an apparent inward (cytosolic) open state forming homomeric trimers. TM4 tightly interacts with the first triple-helix bundle within a protomer and mediates key contacts among protomers. Structure-guided mutagenesis of the close paralogue SWEET1 from Arabidopsis identified key residues in substrate translocation and protomer crosstalk. Insights into the structure-function relationship of SWEETs are valuable for understanding the transport mechanism of eukaryotic SWEETs and may be useful for engineering sugar flux. ©2015 Macmillan Publishers Limited. All rights reserved.

Ilavsky J.,Argonne National Laboratory
Journal of Applied Crystallography | Year: 2012

Nika is an Igor Pro-based package for correction, calibration and reduction of two-dimensional area-detector data into one-dimensional data (lineouts). It is free (although the user needs a paid license for Igor Pro), open source and highly flexible. While typically used for small-angle X-ray scattering (SAXS) data, it can also be used for grazing-incidence SAXS data, wide-angle diffraction data and even small-angle neutron scattering data. It has been widely available to the user community since about 2005, and it is currently used at the SAXS instruments of selected large-scale facilities as their main data reduction package. It is, however, also suitable for desktop instruments when the manufacturers software is not available or appropriate. Since it is distributed as source code, it can be scrutinized, verified and modified by users to suit their needs. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.

Latta D.E.,Argonne National Laboratory | Gorski C.A.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Scherer M.M.,University of Iowa
Biochemical Society Transactions | Year: 2012

Recent work has indicated that iron (oxyhydr-)oxides are capable of structurally incorporating and releasing metals and nutrients as a result of Fe2+-induced iron oxide recrystallization. In the present paper, we briefly review the current literature examining the mechanisms by which iron oxides recrystallize and summarize how recrystallization affects metal incorporation and release. We also provide new experimental evidence for the Fe2+-induced release of structural manganese from manganese-doped goethite. Currently, the exact mechanism(s) for Fe2+-induced recrystallization remain elusive, although they are likely to be both oxide- and metal-dependent. We conclude by discussing some future research directions for Fe2+-catalysed iron oxide recrystallization. ©The Authors Journal compilation ©2012 Biochemical Society.

Zador J.,Sandia National Laboratories | Miller J.A.,Argonne National Laboratory
Proceedings of the Combustion Institute | Year: 2013

Unimolecular pressure- and temperature-dependent decomposition rate coefficients of radicals derived from n- and i-propanol by H-atom abstraction are calculated using a time-dependent master equation in the 300-2000 K temperature range. The calculations are based on a C3H7O potential energy surface, which was previously tested successfully for the propene + OH reaction. All rate coefficients are obtained with internal consistency with particular attention paid to shallow wells. After minor adjustments very good agreement with the few available experimental results is obtained. Several interesting pathways are uncovered, such as the catalytic dehydration, well-skipping reactions and reactions forming enols. The results of the calculations can be readily used in CHEMKIN simulations or to assess important channels for higher alcohols. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Baryshev S.V.,Argonne National Laboratory
Journal of visualized experiments : JoVE | Year: 2013

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed. In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens. Specifically, we will discuss: i. Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion. ii. Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions. iii. Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests. Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

Ruscic B.,Argonne National Laboratory | Ruscic B.,University of Chicago
International Journal of Quantum Chemistry | Year: 2014

The accepted convention for expressing uncertainties of thermochemical quantities, followed by virtually all thermochemical tabulations, is to provide earnest estimates of 95% confidence intervals. Theoretical studies frequently ignore this convention, and, instead, provide the mean absolute deviation, which underestimates the recommended thermochemical uncertainty by a factor of 2.5-3.5 or even more, and thus may vitiate claims that "chemical accuracy" (ability to predict thermochemical quantities within ±1 kcal/mol) has been achieved. Furthermore, copropagating underestimated uncertainties for theoretical values with uncertainties found in thermochemical compilations produces invalid uncertainties for reaction enthalpies. Two groups of procedures for determining the accuracy of computed thermochemical quantities are outlined: one relying on estimates that are based on experience, the other on benchmarking. Benchmarking procedures require a source of thermochemical data that is as accurate and reliable as possible. The role of Active Thermochemical Tables in benchmarking state-of-the-art electronic structure methods is discussed. © Published 2014.

Wilson R.E.,Argonne National Laboratory
Radiochimica Acta | Year: 2014

The retrieval and purification of a macroscopic aged sample of protactinium-231 is described. The 231Pa was separated from its decay daughters using a precipitation based method. The method exploits the hydrolytic behavior and insolubility of protactinium rather than attempting to avoid it by way of concentrated hydrofluoric and sulfuric acids, which have been shown to vitiate separations using ion-exchange and solvent extraction based methods. Based on alpha spectrometry the sourcewas previously separated in 1959-1960, consistent with the Harwell Pa separations program. The method described here achieved 98% recovery of the 231Pa with a final alpharadiopurity of 93.75% in contrast to the 20.25% radiopurity of the starting material.

Holby E.F.,University of Wisconsin - Madison | Greeley J.,Argonne National Laboratory | Morgan D.,University of Wisconsin - Madison
Journal of Physical Chemistry C | Year: 2012

Oxygen adsorption on Pt(111) has many implications for a wide range of technologies including PEM fuel cells. Using DFT, we have calculated the stable phases for oxygen on Pt(111) surfaces up to one monolayer of oxygen coverage. Our predicted stable phases are consistent with electrochemical measurements and are in agreement with Temkin/Frumkin isotherm conditions. We predict a new phase at one monolayer that suggests a simple mechanism for oxygen place-exchange to subsurface positions. Analysis of the phase diagram provides a possible explanation for the hysteresis observed in Pt cyclic voltammograms in aqueous environments. © 2012 American Chemical Society.

Myung S.-T.,Iwate University | Amine K.,Argonne National Laboratory | Sun Y.-K.,Hanyang University
Journal of Materials Chemistry | Year: 2010

The present concern with global warming urgently requires a large increase in the energy share provided by green, renewable energy sources, as well as massive commercialization of sustainable vehicles. The widespread availability of reliable energy storage systems and highly efficient lithium batteries can, in principle, meet this need. For example, many individuals already own at least one lithium-ion battery portable device, such as a cellular phone, MP3 player, digital camera, or laptop computer. Hybrid electric vehicles and full electric vehicles will sooner or later be marketed with lithium-ion batteries. However, to acquire an established role in the commercial sector, lithium-ion batteries must be improved with regard to energy density, cost, and particularly, safety. Further development of electrode materials, especially the cathode active materials, is important to satisfy the above requirements. The easiest route to cathode improvement is to modify the cathode surface. This article describes recent advances in cathode active materials with surface modification from the nano-to microscale. © 2010 The Royal Society of Chemistry.

Kryvohuz M.,Argonne National Laboratory
Journal of Chemical Physics | Year: 2013

Expressions for reaction rate constants in multidimensional chemical systems are derived by applying semiclassical approximation to the quantum path integrals of the ImF formulation of reaction rate theory. First, the transverse degrees of freedom orthogonal to the reaction coordinate are treated within the steepest descent approximation, after which the semiclassical approximation is applied to the remaining reaction coordinate. Thus derived, the semiclassical expressions account for the multidimensional nature of quantum effects and accurately incorporate nuclear quantum effects such as multidimensional tunneling and zero point energies. The obtained expressions are applicable in the broad temperature range from the deep tunneling to high-temperature regimes. The present paper provides derivation of the semiclassical instanton expressions proposed by Kryvohuz [J. Chem. Phys. 134, 114103 (2011)]10.1063/1.3565425. © 2013 AIP Publishing LLC.

Guffey M.J.,James Franck Institute | Scherer N.F.,James Franck Institute | Scherer N.F.,Argonne National Laboratory
Nano Letters | Year: 2010

The fabrication of nanoscale devices would be greatly enhanced by "nanomanipulators" that can position single and few objects rapidly with nanometer precision and without mechanical damage. Here, we demonstrate the feasibility and precision of an optical laser tweezer, or optical trap, approach to place single gold (Au) nanoparticles on surfaces with high precision (approximately 100 nm standard deviation). The error in the deposition process is rather small but is determined to be larger than the thermal fluctuations of single nanoparticles within the optical trap. Furthermore, areas of tens of square micrometers could be patterned in a matter of minutes. Since the method does not rely on lithography, scanning probes or a specialized surface, it is versatile and compatible with a variety of systems. We discuss active feedback methods to improve positioning accuracy and the potential for multiplexing and automation. © 2010 American Chemical Society.

Thimmapuram P.R.,Argonne National Laboratory | Kim J.,Gachon University
IEEE Transactions on Smart Grid | Year: 2013

Automated Metering Infrastructure (AMI) is a technology that would allow consumers to exhibit price elasticity of demand under smart-grid environments. The market power of the generation and transmission companies can be mitigated when consumers respond to price signals. Such responses by consumers can also result in reductions in price spikes, consumer energy bills, and emissions of greenhouse gases and other pollutants. In this paper, we use the Electricity Market Complex Adaptive System (EMCAS), an agent-based model that simulates restructured electricity markets, to explore the impact of consumers' price elasticity of demand on the performance of the electricity market. An 11-node test network with eight generation companies and five aggregated consumers is simulated for a period of one month. Results are provided and discussed for a case study based on the Korean power system. © 2012 IEEE.

Padilha L.A.,Los Alamos National Laboratory | Bae W.K.,Los Alamos National Laboratory | Klimov V.I.,Los Alamos National Laboratory | Pietryga J.M.,Los Alamos National Laboratory | And 2 more authors.
Nano Letters | Year: 2013

Using a combination of transient photoluminescence and transient cathodoluminescence (trCL) we, for the first time, identify and quantify the distribution of electronic excitations in colloidal semiconductor nanocrystals (NCs) under high-energy excitation. Specifically, we compare the temporally and spectrally resolved radiative recombination produced following excitation with 3.1 eV, subpicosecond photon pulses, or with ionizing radiation in the form of 20 keV picosecond electron pulses. Using this approach, we derive excitation branching ratios produced in the scenario of energetic excitation of NCs typical of X-ray, neutron, or gamma-ray detectors. Resultant trCL spectra and dynamics for CdSe NCs indicate that all observable emission can be attributed to recombination between states within the quantum-confined nanostructure with particularly significant yields of trions and multiexcitons produced by carrier multiplication. Our observations offer direct insight into the transduction of atomic excitation into quantum-confined states within NCs, explain that the root cause of poor performance in previous scintillation studies arises from efficient nonradiative Auger recombination, and suggest routes for improved detector materials. © 2013 American Chemical Society.

Morrissey D.E.,TRIUMF Laboratory Particle and Nuclear Physics | Morrissey D.E.,Jefferson Lab | Plehn T.,University of Heidelberg | Tait T.M.P.,University of California at Irvine | And 2 more authors.
Physics Reports | Year: 2012

With the LHC up and running, the focus of experimental and theoretical high energy physics will soon turn to an interpretation of LHC data in terms of the physics of electroweak symmetry breaking and the TeV scale. We present here a broad review of models for new TeV-scale physics and their LHC signatures. In addition, we discuss possible new physics signatures and describe how they can be linked to specific models of physics beyond the Standard Model. Finally, we illustrate how the LHC era could culminate in a detailed understanding of the underlying principles of TeV-scale physics. © 2012 Elsevier B.V.

Li X.,University of Georgia | Budai J.D.,Oak Ridge National Laboratory | Liu F.,University of Georgia | Howe J.Y.,Oak Ridge National Laboratory | And 6 more authors.
Light: Science and Applications | Year: 2013

Phosphor-converted white light-emitting diodes for indoor illumination need to be warm-white (i.e., correlated color temperature,<4000 K) with good color rendition (i.e., color rendering index >.80). However, no single-phosphor, single-emitting-center-converted white light-emitting diodes can simultaneously satisfy the color temperature and rendition requirements due to the lack of sufficient red spectral component in the phosphors' emission spectrum. Here, we report a new yellow Ba0.93Eu0.07Al 2O4 phosphor that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component. Warm-white emissions with correlated color temperature <4000 K and color rendering index >80 were readily achieved when combining the Ba0.93Eu0.07Al2O4 phosphor with a blue light-emitting diode (440-470 nm). This study demonstrates that warm-white light-emitting diodes with high color rendition (i.e., color rendering index .80) can be achieved based on single-phosphor, single-emitting-center conversion. © 2013 CIOMP. All rights reserved.

Hoffmann A.,Argonne National Laboratory | Schultheiss H.,Helmholtz Center Dresden
Current Opinion in Solid State and Materials Science | Year: 2015

Magnetic interactions give rise to a surprising amount of complexity due to the fact that both static and dynamic magnetic properties are governed by competing short-range exchange interactions and long-range dipolar coupling. Even though the underlying dynamical equations are well established, the connection of magnetization dynamics to other degrees of freedom, such as optical excitations, charge and heat flow, or mechanical motion, make magnetism a mesoscale research problem that is still wide open for exploration. Synthesizing magnetic materials and heterostructures with tailored properties will allow to take advantage of magnetic interactions spanning many length-scales, which can be probed with advanced spectroscopy and microscopy and modeled with multi-scale simulations. This review highlights some of the current basic research topics in mesoscale magnetism, which beyond their fundamental science impact are also expected to influence applications ranging from information technologies to magnetism based energy conversion. © 2015 Elsevier Ltd. All rights reserved.

Yuan D.,Texas A&M University | Lu W.,Texas A&M University | Zhao D.,Argonne National Laboratory | Zhou H.-C.,Texas A&M University
Advanced Materials | Year: 2011

Highly stable porous polymer networks (PPNs) are synthesized through Yamamoto homocoupling reaction between tetrahedral monomers. Among those polymers, PPN-4 shows exceptionally high Langmuir surface area of 10063 m 2 g -1 (SA BET: 6461 m 2 g -1). It also exhibits ultra-high hydrogen (158 mg g -1), methane (389 mg g -1), and carbon dioxide (2121 mg g -1) storage capacities. These properties make it a perfect adsorbent for clean energy applications. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sun Y.,Argonne National Laboratory
Nanoscale | Year: 2011

Silver (Ag) nanowires with chemically clean surfaces have been directly grown on semi-insulating gallium arsenide (GaAs) wafers through a simple solution/solid interfacial reaction (SSIR) between the GaAs wafers themselves and aqueous solutions of silver nitrate (AgNO 3) at room temperature. The success in synthesis of Ag nanowires mainly benefits from the low concentration of surface electrons in the semi-insulating GaAs wafers that can lead to the formation of a low-density of nuclei that facilitate their anisotropic growth into nanowires. The resulting Ag nanowires exhibit rough surfaces and reasonably good electric conductivity. These characteristics are beneficial to sensing applications based on single-nanowire surface-enhanced Raman scattering (SERS) and possible surface-adsorption-induced conductivity variation. © 2011 The Royal Society of Chemistry.

Smither R.K.,Argonne National Laboratory
Review of Scientific Instruments | Year: 2014

This paper follows the development of crystal diffraction lenses designed to focus energetic photons. It begins with the search for a solution to the astrophysics problem of how to detect weak astrophysics sources of gamma rays and x-rays. This led to the basic designs for a lens and to the understanding of basic limitations of lens design. The discussion of the development of crystal diffraction lenses is divided into two parts: lenses using crystals with mosaic structure, and lenses that use crystals with curved crystal planes. This second group divides into two sub-groups: (1) Curved crystals that are used to increase the acceptance angle of the diffraction of a monochromatic beam and to increase the energy bandwidth of the diffraction. (2) Curved crystals used to focus gamma ray beams. The paper describes how these two types of crystals affect the design of the corresponding crystal lenses in different fields: astrophysics, medical imaging, detection of weak, distant, gamma-ray sources, etc. The designs of crystal lenses for these applications are given in enough detail to allow the reader to design a lens for his own application. © 2014 AIP Publishing LLC.

Ivankin A.,Illinois Institute of Technology | Kuzmenko I.,Argonne National Laboratory | Gidalevitz D.,Illinois Institute of Technology
Physical Review Letters | Year: 2012

Biomembranes undergo extensive shape changes as they perform vital cellular functions. The mechanisms by which lipids and proteins control membrane curvature remain unclear. We use x-ray reflectivity, grazing incidence x-ray diffraction, and epifluorescence microscopy to study binding of HIV-1 glycoprotein gp41's membrane-bending domain to DPPC/cholesterol monolayers of various compositions at the air-liquid interface. The results offer a new insight into how membrane curvature could be regulated by cholesterol during fusion of the viral lipid envelope and the host cell membranes. © 2012 American Physical Society.

Picon A.,University of Colorado at Boulder | Picon A.,Argonne National Laboratory | Jaron-Becker A.,University of Colorado at Boulder | Becker A.,University of Colorado at Boulder
Physical Review Letters | Year: 2012

We study vibrational excitations, dissociation, and ionization of H2+ in few-cycle laser pulses over a broad wavelength regime. Our results of numerical simulations supported by model calculations show a many orders-of-magnitude enhancement of vibrational excitation and dissociation (over ionization) of the molecular ion at infrared wavelengths. The enhancement occurs without any chirping of the pulse, which was previously applied to take account of the anharmonicity of the molecular vibrations. The effect is related to strong-field two- and higher-order photon transitions between different vibrational states. © 2012 American Physical Society.

Savary L.,University of California at Santa Barbara | Ross K.A.,McMaster University | Gaulin B.D.,McMaster University | Gaulin B.D.,Canadian Institute for Advanced Research | And 3 more authors.
Physical Review Letters | Year: 2012

Here we establish the systematic existence of a U(1) degeneracy of all symmetry-allowed Hamiltonians quadratic in the spins on the pyrochlore lattice, at the mean-field level. By extracting the Hamiltonian of Er 2Ti 2O 7 from inelastic neutron scattering measurements, we then show that the U(1)-degenerate states of Er 2Ti 2O 7 are its classical ground states, and unambiguously show that quantum fluctuations break the degeneracy in a way which is confirmed by experiment. The degree of symmetry protection of the classical U(1) degeneracy in Er 2Ti 2O 7 is unprecedented in other materials. As a consequence, our observation of order by disorder is unusually definitive. We provide further verifiable consequences of this phenomenon, and several additional comparisons between theory and experiment. © 2012 American Physical Society.

Huang L.,University of Chicago | Roux B.,University of Chicago | Roux B.,Argonne National Laboratory
Journal of Chemical Theory and Computation | Year: 2013

Classical molecular dynamics (MD) simulations based on atomistic models are increasingly used to study a wide range of biological systems. A prerequisite for meaningful results from such simulations is an accurate molecular mechanical force field. Most biomolecular simulations are currently based on the widely used AMBER and CHARMM force fields, which were parametrized and optimized to cover a small set of basic compounds corresponding to the natural amino acids and nucleic acid bases. Atomic models of additional compounds are commonly generated by analogy to the parameter set of a given force field. While this procedure yields models that are internally consistent, the accuracy of the resulting models can be limited. In this work, we propose a method, general automated atomic model parameterization (GAAMP), for generating automatically the parameters of atomic models of small molecules using the results from ab initio quantum mechanical (QM) calculations as target data. Force fields that were previously developed for a wide range of model compounds serve as initial guesses, although any of the final parameter can be optimized. The electrostatic parameters (partial charges, polarizabilities, and shielding) are optimized on the basis of QM electrostatic potential (ESP) and, if applicable, the interaction energies between the compound and water molecules. The soft dihedrals are automatically identified and parametrized by targeting QM dihedral scans as well as the energies of stable conformers. To validate the approach, the solvation free energy is calculated for more than 200 small molecules and MD simulations of three different proteins are carried out. © 2013 American Chemical Society.

Clark J.N.,University College London | Huang X.,University College London | Harder R.,Argonne National Laboratory | Robinson I.K.,University College London | Robinson I.K.,Research Complex at Harwell
Nature Communications | Year: 2012

The wave properties of light, particularly its coherence, are responsible for interference effects, which can be exploited in powerful imaging applications. Coherent diffractive imaging relies heavily on coherence and has recently experienced rapid growth. Coherent diffractive imaging recovers an object from its diffraction pattern by computational phasing with the potential of wavelength-limited resolution. Diminished coherence results in reconstructions that suffer from artefacts or fail completely. Here we demonstrate ab initio phasing of partially coherent diffraction patterns in three dimensions, while simultaneously determining the coherence properties of the illuminating wavefield. Both the dramatic improvements in image interpretability and the three-dimensional evaluation of the coherence will have broad implications for quantitative imaging of nanostructures and wavefield characterization with X-rays and electrons. © 2012 Macmillan Publishers Limited. All rights reserved.

Aranson I.S.,Argonne National Laboratory | Aranson I.S.,Northwestern University
Physics-Uspekhi | Year: 2013

A colloidal suspension is a heterogeneous fluid containing solid microscopic particles. Colloids play an important role in our everyday life, from food and pharmaceutical industries to medicine and nontechnology. It is useful to distinguish two major classes of colloidal suspensions: equilibrium and active, i.e., maintained out of thermodynamic equilibrium by external electric or magnetic fields, light, chemical reactions, or hydrodynamic shear flow. While the properties of equilibrium colloidal suspensions are fairly well understood, active colloids pose a formidable challenge, and the research is in its early exploratory stage. One of the most remarkable properties of active colloids is the possibility of dynamic self-assembly, a natural tendency of simple building blocks to organize into complex functional architectures. Examples range from tunable, self-healing colloidal crystals and membranes to self-assembled microswimmers and robots. Active colloidal suspensions may exhibit material properties not present in their equilibrium counterparts, e.g., reduced viscosity and enhanced self-diffusivity, etc. This study surveys the most recent developments in the physics of active colloids, both in synthetic and living systems, with the aim of elucidation of the fundamental physical mechanisms governing self-assembly and collective behavior. © 2013 Uspekhi Fizicheskikh Nauk, Russian Academy of Sciences.

Lange A.W.,Argonne National Laboratory | Voth G.A.,James Franck Institute
Journal of Chemical Theory and Computation | Year: 2013

We introduce a multistate framework for Fragment Molecular Orbital (FMO) quantum mechanical calculations and implement it in the context of protonated water clusters. The purpose of the framework is to address issues of nonuniqueness and dynamic fragmentation in FMO as well as other related fragment methods. We demonstrate that our new approach, Fragment Molecular Orbital Multistate Reactive Molecular Dynamics (FMO-MS-RMD), can improve energetic accuracy and yield stable molecular dynamics for small protonated water clusters undergoing proton transfer reactions. © 2013 American Chemical Society.

Porubsky P.R.,University of Kansas | Battaile K.P.,Argonne National Laboratory | Scott E.E.,University of Kansas
Journal of Biological Chemistry | Year: 2010

Human microsomal cytochrome P450 (CYP) 2E1 is widely known for its ability to oxidize >70 different, mostly compact, low molecular weight drugs and other xenobiotic compounds. In addition CYP2E1 oxidizes much larger C9-C20 fatty acids that can serve as endogenous signaling molecules. Previously structures of CYP2E1 with small molecules revealed a small, compact CYP2E1 active site, which would be insufficient to accommodate medium and long chain fatty acids without conformational changes in the protein. In the current work we have determined how CYP2E1 can accommodate a series of fatty acid analogs by cocrystallizing CYP2E1 with ω-imidazolyl-octanoic fatty acid, ω-imidazolyl-decanoic fatty acid, and ω-imidazolyldodecanoic fatty acid. In each structure direct coordination of the imidazole nitrogen to the heme iron mimics the position required for native fatty acid substrates to yield the ω-1 hydroxylated metabolites that predominate experimentally. In each case rotation of a single Phe298 side chain merges the active site with an adjacent void, significantly altering the active site size and topology to accommodate fatty acids. The binding of these fatty acid ligands is directly opposite the channel to the protein surface and the binding observed for fatty acids in the bacterial cytochrome P450 BM3 (CYP102A1) from Bacillus megaterium. Instead of the BM3-like binding mode in the CYP2E1 channel, these structures reveal interactions between the fatty acid carboxylates and several residues in the F, G, and B′ helices at successive distances from the active site.

Wu W.,Rutgers University | Horibe Y.,Rutgers University | Lee N.,Rutgers University | Cheong S.-W.,Rutgers University | Guest J.R.,Argonne National Laboratory
Physical Review Letters | Year: 2012

We report on the observation of nanoscale conduction at ferroelectric domain walls in hexagonal HoMnO 3 protected by the topology of multiferroic vortices using in situ conductive atomic force microscopy, piezoresponse force microscopy, and Kelvin-probe force microscopy at low temperatures. In addition to previously observed Schottky-like rectification at low bias, conductance spectra reveal that negatively charged tail-to-tail walls exhibit enhanced conduction at high forward bias, while positively charged head-to-head walls exhibit suppressed conduction at high reverse bias. Our results pave the way for understanding the semiconducting properties of the domains and domain walls in small-gap ferroelectrics. © 2012 American Physical Society.

Aranson I.S.,Argonne National Laboratory | Aranson I.S.,Northwestern University
Comptes Rendus Physique | Year: 2013

Colloidal suspensions, heterogeneous fluids containing solid microscopic particles, play an important role in our everyday life, from food and pharmaceutical industries to medicine and nanotechnology. Colloidal suspensions can be divided in two major classes: equilibrium, and active, i.e. maintained out of thermodynamic equilibrium by external electric or magnetic fields, light, chemical reactions, or hydrodynamic shear flow. While the properties of equilibrium colloidal suspensions are fairly well understood, out-of-equilibrium colloids pose a formidable challenge and the research is in its early exploratory stage. The possibility of dynamic self-assembly, a natural tendency of simple building blocks to organize into complex functional architectures, is one of the most remarkable properties of out-of-equilibrium colloids. Examples range from tunable, self-healing colloidal crystals and membranes to self-assembled microswimmers and robots. In contrast to their equilibrium counterparts, out-of-equilibrium colloidal suspensions may exhibit novel material properties, e.g. reduced viscosity, enhanced self-diffusivity, etc. This work reviews recent developments in the field of self-assembly and collective behavior of out-of-equilibrium colloids, with the focus on the fundamental physical mechanisms. © 2013 Académie des sciences.

Yurkovetskiy L.,University of Chicago | Burrows M.,University of Chicago | Khan A.,University of Chicago | Graham L.,University of Chicago | And 6 more authors.
Immunity | Year: 2013

Gender bias and the role of sex hormones in autoimmune diseases are well established. In specific pathogen-free nonobese diabetic (NOD) mice, females have 1.3-4.4 times higher incidence of type 1 diabetes (T1D). Germ-free (GF) mice lost the gender bias (female-to-male ratio 1.1-1.2). Gut microbiota differed in males and females, a trend reversed by male castration, confirming that androgens influence gut microbiota. Colonization of GF NOD mice with defined microbiota revealed that some, but not all, lineages overrepresented in male mice supported a gender bias in T1D. Although protection of males did not correlate with blood androgen concentration, hormone-supported expansion of selected microbial lineages may work as a positive-feedback mechanism contributing to the sexual dimorphism of autoimmune diseases. Gene-expression analysis suggested pathways involved in protection of males from T1D by microbiota. Our results favor a two-signal model of gender bias, in which hormones and microbes together trigger protective pathways. © 2013 Elsevier Inc.

Upadhye A.,Argonne National Laboratory | Hu W.,University of Chicago | Khoury J.,University of Pennsylvania
Physical Review Letters | Year: 2012

Chameleon scalar fields are dark-energy candidates which suppress fifth forces in high density regions of the Universe by becoming massive. We consider chameleon models as effective field theories and estimate quantum corrections to their potentials. Requiring that quantum corrections be small, so as to allow reliable predictions of fifth forces, leads to an upper bound m<0.0073(ρ/10gcm -3)1 /3eV for gravitational-strength coupling whereas fifth force experiments place a lower bound of m>0.0042eV. An improvement of less than a factor of two in the range of fifth force experiments could test all classical chameleon field theories whose quantum corrections are well controlled and couple to matter with nearly gravitational strength regardless of the specific form of the chameleon potential. © 2012 American Physical Society.

Liu S.,Fuzhou University | Tang Z.-R.,Fuzhou University | Sun Y.,Argonne National Laboratory | Colmenares J.C.,Polish Academy of Sciences | Xu Y.-J.,Fuzhou University
Chemical Society Reviews | Year: 2015

The severe consequences of fossil fuel consumption have resulted in a need for alternative sustainable sources of energy. Conversion and storage of solar energy via a renewable method, such as photocatalysis, holds great promise as such an alternative. One-dimensional (1D) nanostructures have gained attention in solar energy conversion because they have a long axis to absorb incident sunlight yet a short radial distance for separation of photogenerated charge carriers. In particular, well-ordered spatially high dimensional architectures based on 1D nanostructures with well-defined facets or anisotropic shapes offer an exciting opportunity for bridging the gap between 1D nanostructures and the micro and macro world, providing a platform for integration of nanostructures on a larger and more manageable scale into high-performance solar energy conversion applications. In this review, we focus on the progress of photocatalytic solar energy conversion over controlled one-dimension-based spatially ordered architecture hybrids. Assembly and classification of these novel architectures are summarized, and we discuss the opportunity and future direction of integration of 1D materials into high-dimensional, spatially organized architectures, with a perspective toward improved collective performance in various artificial photoredox applications. This journal is © The Royal Society of Chemistry.

Chopra O.K.,Argonne National Laboratory | Rao A.S.,U.S. Nuclear Regulatory Commission
Journal of Nuclear Materials | Year: 2011

Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels because of their relatively high strength, ductility, and fracture toughness. However, exposure to neutron irradiation for extended periods not only changes the microstructure and microchemistry of these steels, but also degrades their fracture properties. The existing data on irradiated austenitic SSs are reviewed to determine the effects of key parameters such as material type and condition and irradiation temperature, dose, and dose rate on neutron embrittlement. Differences in the radiation-induced degradation of fracture properties between LWR and fast-reactor irradiations are also discussed. The results are used to (a) define a threshold fluence above which irradiation effects on fracture toughness of the material are significant, (b) evaluate the potential of neutron embrittlement under LWR operating conditions, and (c) assess the potential effects of voids on fracture toughness. © 2011 Elsevier B.V. All rights reserved.

Huang X.-R.,Argonne National Laboratory | Peng R.-W.,Nanjing University | Fan R.-H.,Nanjing University
Physical Review Letters | Year: 2010

From first-principles computations we reveal that metallic gratings consisting of narrow slits may become transparent for extremely broad bandwidths under oblique incidence. This phenomenon can be explained by a concrete picture in which the incident wave drives free electrons on the conducting surfaces and part of the slit walls to form spoof surface plasmons (SSPs). The SSPs then propagate on the slit walls but are abruptly discontinued by the bottom edges to form oscillating charges that emit the transmitted wave. This picture explicitly demonstrates the conversion between light and SSPs and indicates clear guidelines for enhancing SSP excitation and propagation. Making structured metals transparent may lead to a variety of applications. © 2010 The American Physical Society.

Norman M.R.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

Recent experiments have addressed the nature of the charge order seen in underdoped cuprates. Here I show that x-ray absorption and linear dichroism are excellent probes of such order. Ab initio calculations reveal that a d-wave charge density wave order involving the oxygen ions is a much better description of the data than alternate models. © 2015 American Physical Society.

Ong Q.K.,Purdue University | Lin X.-M.,Argonne National Laboratory | Wei A.,Purdue University
Journal of Physical Chemistry C | Year: 2011

Core-shell Fe@Fe 3O 4 nanoparticles exhibit substantial exchange bias at low temperatures, mediated by unidirectionally aligned moments at the core-shell interface. These spins are frozen into magnetic alignment with field cooling and are depinned in a temperature-dependent manner. The population of such frozen spins has a direct impact on both coercivity (H C) and the exchange-bias field (H E), which are modulated by external physical parameters such as the strength of the applied cooling field and the cycling history of magnetic field sweeps (training effect). Aging of the core-shell nanoparticles under ambient conditions results in a gradual decrease in magnetization but overall retention of H C and H E, as well as a large increase in the population of frozen spins. These changes are accompanied by a structural evolution from well-defined core-shell structures to particles containing multiple voids, attributable to the Kirkendall effect. Energy-filtered and high-resolution transmission electron microscopy both indicate further oxidation of the shell layer, but the Fe core is remarkably well preserved. The increase in frozen spin population with age is responsible for the overall retention of exchange bias, despite void formation and other oxidation-dependent changes. The exchange-bias field becomes negligible upon deliberate oxidation of Fe@Fe 3O 4 nanoparticles into yolk-shell particles, with a nearly complete physical separation of core and shell. © 2011 American Chemical Society.

Chopra O.K.,Argonne National Laboratory | Rao A.S.,U.S. Nuclear Regulatory Commission
Journal of Nuclear Materials | Year: 2011

Austenitic stainless steels (SSs) are used extensively as structural alloys in the internal components of light water reactor (LWR) pressure vessels because of their relatively high strength, ductility, and fracture toughness. However, exposure to neutron irradiation for extended periods changes the microstructure (radiation hardening) and microchemistry (radiation-induced segregation) of these steels, and degrades their fracture properties. Irradiation-assisted stress corrosion cracking (IASCC) is another degradation process that affects LWR internal components exposed to neutron radiation. The existing data on irradiated austenitic SSs were reviewed to evaluate the effects of key parameters such as material composition, irradiation dose, and water chemistry on IASCC susceptibility and crack growth rates of these materials in LWR environments. The significance of microstructural and microchemistry changes in the material on IASCC susceptibility is also discussed. The results are used to determine (a) the threshold fluence for IASCC and (b) the disposition curves for cyclic and IASCC growth rates for irradiated SSs in LWR environments. © 2010 Elsevier B.V. All rights reserved.

Vaughey J.T.,Argonne National Laboratory | Liu G.,Lawrence Berkeley National Laboratory | Zhang J.-G.,Pacific Northwest National Laboratory
MRS Bulletin | Year: 2014

The success of high capacity energy storage systems based on lithium (Li) batteries relies on the realization of the promise of Li-metal anodes. Li metal has many advantageous properties, including an extremely high theoretical specific capacity (3860 mAh g-1), the lowest electrochemical potential (-3.040 V versus standard hydrogen electrode), and low density (0.59 g cm-3), which, all together, make it a very desirable electrode for energy storage devices. However, while primary Li batteries are used for numerous commercial applications, rechargeable Li-metal batteries that utilize Li-metal anodes have not been as successful. This article discusses the properties of Li metal in the absence of surface stabilization, as well as three different approaches currently under investigation for stabilizing the surface of Li metal to control its reactivity within the electrochemical environment of a Li-based battery. © 2014 Materials Research Society.

Guzman-Verri G.G.,Argonne National Laboratory
MRS Bulletin | Year: 2014

This article reviews silicene, a relatively new allotrope of silicon, which can also be viewed as the silicon version of graphene. Graphene is a two-dimensional material with unique electronic properties qualitatively different from those of standard semiconductors such as silicon. While many other two-dimensional materials are now being studied, our focus here is solely on silicene. We first discuss its synthesis and the challenges presented. Next, a survey of some of its physical properties is provided. Silicene shares many of the fascinating properties of graphene, such as the so-called Dirac electronic dispersion. The slightly different structure, however, leads to a few major differences compared to graphene, such as the ability to open a bandgap in the presence of an electric field or on a substrate, a key property for digital electronics applications. We conclude with a brief survey of some of the potential applications of silicene. © 2014 Materials Research Society.

Han J.,Argonne National Laboratory | Papalambros P.Y.,University of Michigan
Journal of Mechanical Design, Transactions of the ASME | Year: 2010

Decomposition-based strategies, such as analytical target cascading (ATC), are often employed in design optimization of complex systems. Achieving convergence and computational efficiency in the coordination strategy that solves the partitioned problem is a key challenge. A new convergent strategy is proposed for ATC that coordinates interactions among subproblems using sequential linearizations. The linearity of subproblems is maintained using infinity norms to measure deviations between targets and responses. A subproblem suspension strategy is used to suspend temporarily inclusion of subproblems that do not need significant redesign, based on trust region and target value step size. An individual subproblem trust region method is introduced for faster convergence. The proposed strategy is intended for use in design optimization problems where sequential linearizations are typically effective, such as problems with extensive monotonicities, a large number of constraints relative to variables, and propagation of probabilities with normal distributions. Experiments with test problems show that, relative to standard ATC coordination, the number of subproblem evaluations is reduced considerably while the solution accuracy depends on the degree of monotonicity and nonlinearity. Copyright © 2010 by ASME.

Gaines L.,Argonne National Laboratory
Sustainable Materials and Technologies | Year: 2014

This paper looks ahead, beyond the projected large-scale market penetration of vehicles containing advanced batteries, to the time when the spent batteries will be ready for final disposition. It describes a working system for recycling, using lead-acid battery recycling as a model. Recycling of automotive lithium-ion (Li-ion) batteries is more complicated and not yet established because few end-of-life batteries will need recycling for another decade. There is thus the opportunity now to obviate some of the technical, economic, and institutional roadblocks that might arise. The paper considers what actions can be started now to avoid the impediments to recycling and ensure that economical and sustainable options are available at the end of the batteries' useful life. © 2014 The Author.

Degottardi W.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Boundary conformal field theory is brought to bear on the study of topological insulating phases of non-Abelian anyonic chains. These phases display protected anyonic end modes. We consider spin-1/2 su(2)k chains at any level k, focusing on the most prominent examples: the case k=2 describes Ising anyons (equivalent to Majorana fermions) and k=3 corresponds to Fibonacci anyons. The method we develop is quite general and rests on a deep connection between boundary conformal field theory and topological symmetry. This method tightly constrains the nature of the topological insulating phases of these chains for general k. Emergent anyons which arise at domain walls are shown to have the same braiding properties as the physical quasiparticles. This suggests a "solid-state" topological quantum computation scheme in which emergent anyons are braided by tuning the couplings of non-Abelian quasiparticles in a fixed network. © 2014 American Physical Society.

Norman M.R.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

Recently, a general formalism was presented for gyrotropic, ferroelectric, and multipolar order in spin-orbit coupled metals induced by spin-spin interactions. Here, I point out that the resulting order parameters are equivalent to expectation values of operators that determine natural circular dichroic signals in optical and x-ray absorption. Some general properties of these operator equivalents and the resulting dichroisms are mentioned, and I list several material examples in this connection, including Weyl semimetals. The particular case of the tensor order in the pyrochlore superconductor Cd2Re2O7 is treated in more detail, including calculations of the x-ray absorption and circular dichroism at the O K edge. © 2015 American Physical Society.

Mishra V.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

The majority of unconventional superconductors has close proximity to a magnetic phase. In many cases, the magnetic phase coexists with superconductivity in some fraction of the phase diagram. The response of these two competing phases to disorder can be used as a tool to gain a better understanding of these complex systems. Here I consider the effect of disorder on a multiband superconductor appropriate for the ferro-pnictide superconductors. I consider both interband and intraband scattering for a two-band model consisting of a hole pocket and an electron pocket. The scattering from pointlike impurities is treated within the self-consistent Born approximation. I calculate the effect of disorder on the transition temperature to the superconducting state. The influence of impurity scattering on the low-energy excitation spectrum in the superconducting state is also studied for different kinds of gap structures. © 2015 American Physical Society.

Wang Z.,Georgia Institute of Technology | Begovic M.,Georgia Institute of Technology | Wang J.,Argonne National Laboratory
IEEE Transactions on Smart Grid | Year: 2014

This paper aims to develop a novel method to evaluate Conservation Voltage Reduction (CVR) effects. A multistage Support Vector Regression (MSVR)-based model is proposed to estimate the load without voltage reduction during the CVR period. The first stage is to select a set of load profiles that are close to the profile under estimation by a Euclidian distance-based index; the second stage is to train the SVR prediction model using the pre-selected profiles; the third stage is to re-select the estimated profiles to minimize the impacts of estimation errors on CVR factor calculation. Compared with previous efforts to analyze the CVR outcome, this MSVR-based technique does not depend on selections of control groups or assumptions of any linear relationship between the load and its impact factors. In order to deal with the variability of CVR performances, a stochastic framework is proposed to assist utilities in selecting target feeders. The proposed method has been applied to evaluate CVR effects of practical voltage reduction tests and shown to be accurate and effective. © 2010-2012 IEEE.

Wang Z.,Georgia Institute of Technology | Wang J.,Argonne National Laboratory
IEEE Transactions on Power Systems | Year: 2014

Conservation voltage reduction (CVR) is widely adopted by utilities for peak demand reduction and energy savings through reducing the voltage level of the electrical distribution system. This paper presents an in-depth review on implementing and assessing CVR. The methodologies to quantify CVR effects are categorized into comparison-based, regression-based, synthesis-based and simulation-based methods. The implementation strategies for voltage reduction are classified into open-loop and closed-loop methods. The impacts of emerging smart-grid technologies on CVR are also discussed. The paper can provide researchers and utility engineers with further insights into the state of the art, technical barriers and future research directions of CVR technologies. © 2013 IEEE.

Lu L.,James Franck Institute | Xu T.,James Franck Institute | Chen W.,Argonne National Laboratory | Chen W.,University of Chicago | And 6 more authors.
Nano Letters | Year: 2013

This paper reports an improved solar cell performance of 8.6% by incorporation of N-doped multiwall carbon nanotubes (N-MCNTs) into BHJ solar cells composed of PTB7 and PC71BM. It was demonstrated for the first time that incorporation of N-MCNTs leads to not only increased nanocrystallite sizes but also smaller phase-separated domain sizes of both PTB7 copolymers and PC71BM from X-ray scattering study. The results show that N-MCNTs could serve as both exciton dissociation centers and charge transfer channels. The enhanced charge dissociation probabilities and effective charge carrier lifetime in the active layer material offer evidence to support the conclusion that N-MCNTs facilitated charge separation and transport. © 2013 American Chemical Society.

Wang J.,Argonne National Laboratory
IEEE Transactions on Power Systems | Year: 2014

For robust unit commitment problems addressing load, renewable energy generation, and demand response uncertainties, constructing a proper uncertainty set plays an important role in determining the conservativeness of the model. In this letter, we discuss different approaches to construct uncertainty sets based on historical data, with the purpose of reducing the conservativeness while maintaining the same level of robustness of the solution. © 2013 IEEE.

Wang Z.,Georgia Institute of Technology | Wang J.,Argonne National Laboratory
IEEE Transactions on Power Systems | Year: 2014

This paper presents a time-varying stochastic technique to assess conservation voltage reduction (CVR) effects based on load modeling. A time-varying exponential load model is developed to represent voltage dependences of loads. The recursive least square (RLS) method is applied to identify model parameters in a recursive way. CVR factors can be calculated using the identified model parameters. The time-varying stochastic model for CVR effects can then be constructed by the Kolmogorov-Smirnov (K-S) test. The proposed CVR assessment method is applied to one-year measurement data from a utility company. The calculated CVR factors are verified by a Euclidian distance-based comparison method. Stochastic models of CVR effects in each time window are constructed. Compared with previous efforts on assessing CVR effects, the proposed method does not require control groups or assumptions of linear relationships between the load and its impact factors. The probabilistic nature of CVR effects is also fully considered. © 2014 IEEE.

Sinha S.K.,University of California at San Diego | Jiang Z.,Argonne National Laboratory | Lurio L.B.,Northern Illinois University
Advanced Materials | Year: 2014

The technique of X-ray Photon Correlation Spectroscopy (XPCS) is reviewed as a method for studying the relatively slow dynamics of materials on time scales ranging from microseconds to thousands of seconds and length scales ranging from microns down to nanometers. We focus on the application of this technique to study dynamical fluctuations of surfaces, interfaces and thin films. We first discuss instrumental issues such as the effects of partial coherence (or alternatively finite instrumental resolution) and optimization of signal-to-noise ratios in the experiments. We then review what has been learned from recent XPCS studies of capillary wave fluctuations on liquid surfaces and polymer films, of nanoparticles used as probes to study the interior dynamics of polymer films, of liquid crystals and multilamellar surfactant films, and of metal surfaces, and magnetic domain wall fluctuations in antiferromagnets. We then discuss studies of non-equilibrium dynamics described by 2-time correlation functions. Finally, we briefly speculate on possible future XPCS experiments at new synchrotron sources currently under development including studies of dynamics on time scales down to femtoseconds. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cooper D.R.,McGill University | Dimitrijevic N.M.,Argonne National Laboratory | Nadeau J.L.,McGill University
Nanoscale | Year: 2010

CdSe/ZnS quantum dots (QDs) conjugated to biomolecules that can act as electron donors are said to be "photosensitized": that is, they are able to oxidize or reduce molecules whose redox potential lies inside their band edges, in particular molecular oxygen and water. This leads to the formation of reactive oxygen species (ROS) and phototoxicity. In this work, we quantify the generation of different forms of ROS from as-synthesized QDs in toluene; water-solubilized, unconjugated QDs; QDs conjugated to the neurotransmitter dopamine; and dopamine alone. Results of indirect fluorescent ROS assays, both in solution and inside cells, are compared with those of spin-trap electron paramagnetic resonance spectroscopy (EPR). The effect of these particles on the metabolism of mammalian cells is shown to be dependent upon light exposure and proportional to the amount of ROS generated. © The Royal Society of Chemistry 2010.

Pelton M.,Argonne National Laboratory | Tang Y.,Ecole Polytechnique Federale de Lausanne | Bakr O.M.,King Abdullah University of Science and Technology | Stellacci F.,Ecole Polytechnique Federale de Lausanne
Journal of the American Chemical Society | Year: 2012

Recently developed synthesis methods allow for the production of atomically monodisperse clusters of silver atoms stabilized in solution by aromatic thiol ligands, which exhibit intense absorption peaks throughout the visible and near-IR spectral regions. Here we investigated the time-dependent optical properties of these clusters. We observed two kinetic processes following ultrafast laser excitation of any of the absorption peaks: a rapid decay, with a time constant of 1 ps or less, and a slow decay, with a time constant that can be longer than 300 ns. Both time constants decrease as the polarity of the solvent increases, indicating that the two processes correspond to the formation and recombination, respectively, of a charge-separated state. The long lifetime of this state and the broad optical absorption spectrum mean that the ligand-stabilized silver clusters are promising materials for solar energy harvesting. © 2012 American Chemical Society.

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.

Shenai K.,Argonne National Laboratory
IEEE Power Electronics Magazine | Year: 2014

To enable the rapidly emerging and imminent energy economy, high-voltage (HV) and high-current robust power electronic modules (PEMs) are needed at low cost. PEMs typically consist of a number of semiconductor power switches and driver chips; intelligent power modules often contain sensing and protection circuitry. In the entire supply chain of power electronics systems-from materials to end-user applications, including the original equipment manufacturers (OEMs)-the PEM is the key building block, as it forms the heart of a power electronic system. The performance, cost, and durability of the entire power electronic system critically hinge on those of the PEM. In addition, major business opportunities in power electronics are often enabled by the advances in power semiconductor devices. One such opportunity currently available to the power electronics community has been created by the advances in wide-bandgap (WBG) power switching devices, which were first introduced by Shenai et al. in the 1980s [1]. © 2014 IEEE.

Schunck N.,Lawrence Livermore National Laboratory | Duke D.,University of Leeds | Carr H.,University of Leeds | Knoll A.,Argonne National Laboratory
Physical Review C - Nuclear Physics | Year: 2014

Eighty years after its experimental discovery, a description of induced nuclear fission based solely on the interactions between neutrons and protons and quantum many-body methods still poses formidable challenges. The goal of this paper is to contribute to the development of a predictive microscopic framework for the accurate calculation of static properties of fission fragments for hot fission and thermal or slow neutrons. To this end, we focus on the Pu239(n,f) reaction and employ nuclear density functional theory with Skyrme energy densities. Potential energy surfaces are computed at the Hartree-Fock-Bogoliubov approximation with up to five collective variables. We find that the triaxial degree of freedom plays an important role, both near the fission barrier and at scission. The impact of the parametrization of the Skyrme energy density and the role of pairing correlations on deformation properties from the ground state up to scission are also quantified. We introduce a general template for the quantitative description of fission fragment properties. It is based on the careful analysis of scission configurations, using both advanced topological methods and recently proposed quantum many-body techniques. We conclude that an accurate prediction of fission fragment properties at low incident neutron energies, although technologically demanding, should be within the reach of current nuclear density functional theory. © 2014 American Physical Society.

De Jonge M.D.,Australian Synchrotron | Vogt S.,Argonne National Laboratory
Current Opinion in Structural Biology | Year: 2010

Hard X-ray fluorescence microscopy is well-suited to in-situ investigations of trace metal distributions within whole, unstained, biological tissue, with sub-parts-per-million detection achievable in whole cells. The high penetration of X-rays indicates the use of X-ray fluorescence tomography for structural visualization, and recent measurements have realised sub-500-nm tomography on a 10-μm cell. Limitations of present approaches impact the duration of an experiment and imaging fidelity. Developments in X-ray resolution, detector speed, cryogenic environments, and the incorporation of auxiliary signals are being pursued within the synchrotron community. Several complementary approaches to X-ray fluorescence tomography will be routinely available to the biologist in the near future. We discuss these approaches and review applications of biological relevance. © 2010 Elsevier Ltd.

Tzanos C.P.,Argonne National Laboratory
Nuclear Technology | Year: 2011

In liquid-metal flows, the predictions of the Nusselt number (heat transfer) by Reynolds-averaged NavierStokes models of turbulence that use the assumption of a constant turbulent Prandtl number can be significantly off. Heat transfer analyses were performed with a number of turbulence models for flows in a triangular rod bundle and in a pipe, and model predictions were compared with experimental data. Emphasis was placed on the low Reynolds (low-Re) number k-e model that resolves the boundary layer and does not use &qute; logarithmic wall functions.&qute; The high Reynolds (high-Re) number k-ε model underpredicts the Nusselt number up to 30%, while the low-Re number model overpredicts it up to 34%. For high Peclet number values, the low-Re number model provides better predictions than the high-Re num-ber model. For Peclet numbers higher than 1500, the predictions of the Reynolds stress model (RSM) are in very good agreement with experimental measurements, but for lower Peclet number values its predictions are significantly off. A relationship was developed that expresses the turbulent Prandtl number as a function of the ratio of the turbulent viscosity to the molecular viscosity. With this modified turbulent Prandtl number, for the flow in the rod bundle the predictions of the low-Re number model are well within the spread of the experimental measurements. For pipe flow, the model predictions are not as sensitive to the correction of the turbulent Prandtl number as they are in the case of the flow in a bundle. The modified low-Re number model underpredicts the limited experimental data by 4%.

Amine K.,Argonne National Laboratory | Kanno R.,Tokyo Institute of Technology | Tzeng Y.,National Cheng Kung University
MRS Bulletin | Year: 2014

This issue contains assessments of battery performance involving complex, interrelated physical and chemical processes between electrode materials and electrolytes. Transformational changes in battery technologies are critically needed to enable the effective use of renewable energy sources such as solar and wind to allow for the expansion of hybrid electric vehicles (HEVs) to plug-in HEVs and pure-electric vehicles. For these applications, batteries must store more energy per unit volume and weight, and they must be capable of undergoing many thousands of charge-discharge cycles. The articles in this theme issue present details of several growing interest areas, including high-energy cathode and anode materials for rechargeable Li-ion batteries and challenges of Li metal as an anode material for Li batteries. They also address the recent progress in systems beyond Li ion, including Li-S and Li-air batteries, which represent possible next-generation batteries for electrical vehicles. One article reviews the recent understanding and new strategies and materials for rechargeable Mg batteries. The knowledge presented in these articles is anticipated to catalyze the design of new multifunctional materials that can be tailored to provide the optimal performance required for future electrical energy storage applications. © 2014 Materials Research Society.

He J.,Northwestern University | Girard S.N.,Northwestern University | Kanatzidis M.G.,Northwestern University | Kanatzidis M.G.,Argonne National Laboratory | Dravid V.P.,Northwestern University
Advanced Functional Materials | Year: 2010

The reduction of thermal conductivity, and a comprehensive understanding of the microstructural constituents that cause this reduction, represent some of the important challenges for the further development of thermoelectric materials with improved figure of merit. Model PbTe-based thermoelectric materials that exhibit very low lattice thermal conductivity have been chosen for this microstructure-thermal conductivity correlation study. The nominal PbTe 0-7S0.3 composition spinodally decomposes into two phases: PbTe and PbS. Orderly misfit dislocations, incomplete relaxed strain, and structuremodulated contrast rather than composition-modulated contrast are observed at the boundaries between the two phases. Furthermore, the samples also contain regularly shaped nanometer-scale precipitates. The theoretical calculations of the lattice thermal conductivity of the PbTe0.7S 0.3 material, based on transmission electron microscopy observations, closely aligns with experimental measurements of the thermal conductivity of a very low value, ∼8Wm-1 K-1 at room temperature, approximately 35% and 30% of the value of the lattice thermal conductivity of either PbTe and PbS, respectively. It is shown that phase boundaries, interfacial dislocations, and nanometer-scale precipitates play an important role in enhancing phonon scattering and, therefore, in reducing the lattice thermal conductivity. ©2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Sliwiak J.,Polish Academy of Sciences | Jaskolski M.,Polish Academy of Sciences | Jaskolski M.,Adam Mickiewicz University | Dauter Z.,Argonne National Laboratory | And 2 more authors.
Acta Crystallographica Section D: Biological Crystallography | Year: 2014

Translational noncrystallographic symmetry (tNCS) is a pathology of protein crystals in which multiple copies of a molecule or assembly are found in similar orientations. Structure solution is problematic because this breaks the assumptions used in current likelihood-based methods. To cope with such cases, new likelihood approaches have been developed and implemented in Phaser to account for the statistical effects of tNCS in molecular replacement. Using these new approaches, it was possible to solve the crystal structure of a protein exhibiting an extreme form of this pathology with seven tetrameric assemblies arrayed along the c axis. To resolve space-group ambiguities caused by tetartohedral twinning, the structure was initially solved by placing 56 copies of the monomer in space group P1 and using the symmetry of the solution to define the true space group, C2. The resulting structure of Hyp-1, a pathogenesis-related class 10 (PR-10) protein from the medicinal herb St John's wort, reveals the binding modes of the fluorescent probe 8-anilino-1-naphthalene sulfonate (ANS), providing insight into the function of the protein in binding or storing hydrophobic ligands. © 2014 International Union of Crystallography.

Abhishek K.,Enterprise Optimization | Leyffer S.,Argonne National Laboratory | Linderoth J.,University of Wisconsin - Madison
INFORMS Journal on Computing | Year: 2010

We describe a new solver for convex mixed-integer nonlinear programs (MINLPs) that implements a linearization-based algorithm. The solver is based on an algorithm of Quesada and Grossmann [Quesada, I., I. E. Grossmann. 1992. An LP/NLP based branch-and-bound algorithm for convex MINLP optimization problems. Comput. Chemical Engrg. 16(10-11) 937-947] that avoids the complete re-solution of a master mixed-integer linear program (MILP) by adding new linearizations at open nodes of the branch-and-bound tree whenever an integer solution is found. The new solver, FilMINT, combines the MINTO branch-and-cut framework for MILP with filterSQP to solve the nonlinear programs that arise as subproblems in the algorithm. The MINTO framework allows us to easily employ cutting planes, primal heuristics, and other well-known MILP enhancements for MINLPs. We present detailed computational experiments that show the benefit of such advanced MILP techniques. We offer new suggestions for generating and managing linearizations that are shown to be efficient on a wide range of MINLPs. By carefully incorporating and tuning all these enhancements, an effective solver for convex MINLPs is constructed. © 2010 INFORMS.

Yang Y.,Northwestern University | Wang J.,Argonne National Laboratory | Motter A.E.,Northwestern University
Physical Review Letters | Year: 2012

In the modeling, monitoring, and control of complex networks, a fundamental problem concerns the comprehensive determination of the state of the system from limited measurements. Using power grids as example networks, we show that this problem leads to a new type of percolation transition, here termed a network observability transition, which we solve analytically for the configuration model. We also demonstrate a dual role of the network's community structure, which both facilitates optimal measurement placement and renders the networks substantially more sensitive to "observability attacks." Aside from their immediate implications for the development of smart grids, these results provide insights into decentralized biological, social, and technological networks. © 2012 American Physical Society.

Bansal D.G.,Oak Ridge National Laboratory | Eryilmaz O.L.,Argonne National Laboratory | Blau P.J.,Oak Ridge National Laboratory
Wear | Year: 2011

The fuel efficiency of ground vehicles, like heavy trucks, can be improved by reducing engine weight. While primarily known for its use in aerospace structures, titanium alloy Ti-6Al-4V has the potential to replace heavier steel in certain friction and wear-critical diesel engine components like connecting rods, intake valves, movable turbocharger vanes, and pistons. While Ti-6Al-4V exhibits excellent corrosion resistance, good fatigue strength, and acceptable fracture toughness, it has poor sliding characteristics. Titanium alloys have a propensity to fail by galling, and often exhibit high and unstable friction coefficients. In the current work, selected surface engineering techniques were compared to determine which best enhance the tribological performance of Ti-6Al-4V alloy and another alloy, 60Ni-40Ti. Candidate treatments included diffusion treatments, hard coatings (TiN and CrN), a soft coating (Cu-Ni-In), titanium-matrix TiB2 in situ-formed composite, and shot peening. Diffusion treatments included oxygen diffusion, nitriding, and carburizing. In addition to studying the effects of individual surface engineering approaches, some were combined in an attempt to maximize their effects, but at the same time retain the mechanical properties of the titanium alloy achieved by proper heat treatment. Both dry and lubricated friction and wear tests were conducted using ASTM G133 (linearly reciprocating ball-on-flat). The ball specimens were AISI 52100 bearing steel. Lubricated tests were performed in engine-conditioned diesel engine oil. Test coupons were characterized using microindentation, stylus and optical interferometry, and metallographic examination. Surface engineering methods significantly improved the wear performance of Ti-6Al-4V alloy, but their relative rankings varied significantly between oil-lubricated and non-lubricated conditions. © 2011 Elsevier B.V.

Kim T.-J.,Pusan National University | Kwon G.,Argonne National Laboratory | Kim Y.-T.,Pusan National University
Chemical Communications | Year: 2014

We report an anomalous phenomenon in Pt supported on thiolated multi-walled carbon nanotubes (Pt-S-MWNT): oxygen reduction reaction (ORR) activity increases with accelerated durability test (ADT) cycles. Sub-nanometer-sized Pt clusters on S-MWNT were gradually agglomerated to an optimal size with ADT cycles, and finally showed increased ORR activity after the ADT. This journal is © The Royal Society of Chemistry 2014.

Ungaro C.,University of Virginia | Gray S.K.,Argonne National Laboratory | Gupta M.C.,University of Virginia
Optics Letters | Year: 2014

This Letter presents a highly efficient emitter structure for solar thermophotovoltaic systems. The structure consists of a graded index on tungsten, shows a spectral efficiency of 59%, or 70% with the use of a back reflector, and is compared to other state-of-the-art emitter structures. The effects of different structures and periodicities on the efficiency of the emitter are explored, as well as the effect of a protective oxide coating. The causes of the antireflection properties of these structures are also explored. © 2014 Optical Society of America.

Talamo A.,Argonne National Laboratory
Journal of Computational Physics | Year: 2013

This study presents three numerical algorithms to solve the time dependent neutron transport equation by the method of the characteristics. The algorithms have been developed taking into account delayed neutrons and they have been implemented into the novel MCART code, which solves the neutron transport equation for two-dimensional geometry and an arbitrary number of energy groups. The MCART code uses regular mesh for the representation of the spatial domain, it models up-scattering, and takes advantage of OPENMP and OPENGL algorithms for parallel computing and plotting, respectively. The code has been benchmarked with the multiplication factor results of a Boiling Water Reactor, with the analytical results for a prompt jump transient in an infinite medium, and with PARTISN and TDTORT results for cross section and source transients. The numerical simulations have shown that only two numerical algorithms are stable for small time steps. © 2012 Elsevier Inc.

Benmore C.J.,Argonne National Laboratory | Benmore C.J.,Arizona State University | Izdebski T.,Arizona State University | Yarger J.L.,Arizona State University
Physical Review Letters | Year: 2012

Total x-ray scattering measurements of spider dragline silk fibers from Nephila clavipes, Argiope aurantia, and Latrodectus hesperus all yield similar structure factors, with only small variations between the different species. Wide-angle x-ray scattering from fibers orientated perpendicular to the beam shows a high degree of anisotropy, and differential pair distribution functions obtained by integrating over wedges of the equatorial and meridian planes indicate that, on average, the majority (95%) of the atom-atom correlations do not extend beyond 1 nm. Futhermore, the atom-atom correlations between 1 and 3 nm are not associated with the most intense diffraction peaks at Q=1-2Å -1. Disordered molecular orientations along the fiber axis are consistent with proteins in similar structural arrangements to those in the equatorial plane, which may be associated with the silk's greater flexibility in this direction. © 2012 American Physical Society.

Becker S.,Argonne National Laboratory | Weinzierl S.,Johannes Gutenberg University Mainz
European Physical Journal C | Year: 2013

We present a method to construct a suitable contour deformation in loop momentum space for multi-loop integrals. This contour deformation can be used to perform the integration for multi-loop integrals numerically. The integration can be performed directly in loop momentum space without the introduction of Feynman or Schwinger parameters. The method can be applied to finite multi-loop integrals and to divergent multi-loop integrals with suitable subtraction terms. The algorithm extends techniques from the one-loop case to the multi-loop case. Examples at two and three loops are discussed explicitly. © 2013 Springer-Verlag Berlin Heidelberg and Società Italiana di Fisica.

Ithurria S.,University of Chicago | Talapin D.V.,University of Chicago | Talapin D.V.,Argonne National Laboratory
Journal of the American Chemical Society | Year: 2012

Atomic layer deposition (ALD) is widely used for gas-phase deposition of high-quality dielectric, semiconducting, or metallic films on various substrates. In this contribution we propose the concept of colloidal ALD (c-ALD) for synthesis of colloidal nanostructures. During the c-ALD process, either nanoparticles or molecular precursors are sequentially transferred between polar and nonpolar phases to prevent accumulation of unreacted precursors and byproducts in the reaction mixture. We show that binding of inorganic ligands (e.g., S2-) to the nanocrystal surface can be used as a half-reaction in c-ALD process. The utility of this approach has been demonstrated by growing CdS layers on colloidal CdSe nanocrystals, nanoplatelets, and CdS nanorods. The CdS/CdSe/CdS nanoplatelets represent a new example of colloidal nanoheterostructures with mixed confinement regimes for electrons and holes. In these materials holes are confined to a thin (∼1.8 nm) two-dimensional CdSe quantum well, while the electron confinement can be gradually relaxed in all three dimensions by growing epitaxial CdS layers on both sides of the quantum well. The relaxation of the electron confinement energy caused a shift of the emission band from 510 to 665 nm with unusually small inhomogeneous broadening of the emission spectra. © 2012 American Chemical Society.

Von Dreele R.B.,Argonne National Laboratory
Journal of Applied Crystallography | Year: 2014

The General Structure Analysis System II (GSAS-II) now contains modules for the analysis of small-angle X-ray scattering data. This includes processing of two-dimensional images to create corrected one-dimensional patterns, analysis via maximum entropy or total nonnegative least-squares methods of the size distribution, assuming polydispersity, in the dilute limit, and modeling of the one-dimensional data with combinations of Guinier/Porod, Porod, both dilute and condensed populations of scattering objects, and Bragg scattering components; slit smearing corrections can be applied where needed. GSAS-II can apply these modeling tools over a sequence of data collected while some experimental condition is varied. This sequential refinement result can then be subjected to a post refinement analysis to determine global parameters encompassing the entire experiment. © 2014 International Union of Crystallography.

Benioff P.,Argonne National Laboratory
International Journal of Theoretical Physics | Year: 2011

One way of describing gauge theories in physics is to assign a vector space V̄ x to each space time point x. For each x the field ψ takes values ψ(x) in V̄ x. The freedom to choose a basis in each V̄ x introduces gauge group operators and their Lie algebra representations to define parallel transformations between vector spaces. This paper is an exploration of the extension of these ideas to include the underlying scalar complex number fields. Here a Hilbert space, H̄ x, as an example of V̄ x, and a complex number field, C̄ x, are associated with each space time point. The freedom to choose a basis in H̄ x is expanded to include the freedom to choose complex number fields. This expansion is based on the discovery that there exist representations of complex (and other) number systems that differ by arbitrary scale factors. Compensating changes must be made in the basic field operations so that the relevant axioms are satisfied. This results in the presence of a new real valued gauge field A(x). Inclusion of A(x) into covariant derivatives in Lagrangians results in the description of A(x) as a gauge boson for which mass is optional. The great accuracy of QED suggests that the coupling constant of A(x) to matter fields is very small compared to the fine structure constant. Other physical properties of A(x) are not known at present. © 2011 Springer Science+Business Media, LLC.

Dauter Z.,Argonne National Laboratory
Acta Crystallographica Section D: Biological Crystallography | Year: 2013

There are currently no rules for a unified, standard way of placing macromolecular structures in the crystal lattice. An analysis of all possible symmetry-equivalent representations of molecular structures in various space groups leads to the concept of the anti-Cheshire symmetry and suggests that the center of a unique structural motif can always be placed within the selected asymmetric unit of the anti-Cheshire cell. The placement of structures according to this suggestion will ensure uniformity of presentation of all structurally equivalent Protein Data Bank models and will therefore diminish the possibility of confusing less crystallographically knowledgeable users of the PDB. The anti-Cheshire cells and their asymmetric units are defined and tabulated for all 65 space groups relevant to macromolecular crystallography that exhibit only rotational symmetry operations. © 2013 International Union of Crystallography Printed in Singapore - all rights reserved.

Lee T.-W.,Louisiana State University | Gray S.K.,Argonne National Laboratory
Optics Express | Year: 2010

We show, based on theoretical analysis and realistic simulations, how a grating embedded in a dielectric substrate can excite surface plasmon polaritons (SPPs) on the top side of a flat metal film far removed from the grating. This remote SPP excitation is characterized by a narrow spectral bandwidth and a high near-field intensity relative to the standard approach for exciting SPPs. The simplicity of the structure and the fact that it requires only normally incident light should make it relevant to the many applications that benefit from high quality SPPs on a flat metal film. © 2010 Optical Society of America.

Kannan A.,Argonne National Laboratory | Shanbhag U.V.,Pennsylvania State University
SIAM Journal on Optimization | Year: 2012

We consider the development of single-timescale schemes for the distributed computation of equilibria associated with Nash games in which each player solves a convex program. Equilibria associated with such games are wholly captured by the solution set of a variational inequality. Our focus is on a class of games, termed monotone Nash games, that lead to monotone variational inequalities. Distributed extensions of standard approaches for solving such variational problems are characterized by two challenges: (1) Unless suitable assumptions (such as strong monotonicity) are imposed on the mapping arising in the specification of the variational inequality, iterative methods often require the solution of a sequence of regularized problems, a naturally two-timescale process that is harder to implement in practice. (2) Additionally, algorithm parameters for all players (such as steplengths and regularization parameters) have to be chosen centrally and communicated to all players; importantly, these parameters cannot be independently chosen by a player. Motivated by these shortcomings, we present two practically implementable distributed regularization schemes that work on a single timescale; specifically, each scheme requires precisely one gradient or projection step at every iteration. Of these, the first is an iterative Tikhonov regularization (ITR) scheme, while the second is an analogously constructed iterative proximal-point (IPP) method. Both schemes are characterized by the property that the regularization/centering parameter are updated after every iteration, rather than when one has approximately solved the regularized problem. To aid in distributed settings requiring limited coordination across players, the schemes allow players to select their parameters independently and do not insist on central prescription of such parameters. We conclude with an application of these schemes on a networked Cournot game with nonlinear prices. © 2012 Society for Industrial and Applied Mathematics.

Segovia J.,University of Salamanca | Roberts C.D.,Argonne National Laboratory | Schmidt S.M.,Julich Research Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2015

Analyses of the three valence-quark bound-state problem in relativistic quantum field theory predict that the nucleon may be understood primarily as a Borromean bound-state, in which binding arises mainly from two separate effects. One originates in non-Abelian facets of QCD that are expressed in the strong running coupling and generate confined but strongly-correlated colour-antitriplet diquark clusters in both the scalar-isoscalar and pseudovector-isotriplet channels. That attraction is magnified by quark exchange associated with diquark breakup and reformation. Diquark clustering is driven by the same mechanism which dynamically breaks chiral symmetry in the Standard Model. It has numerous observable consequences, the complete elucidation of which requires a framework that also simultaneously expresses the running of the coupling and masses in the strong interaction. Planned experiments are capable of validating this picture. © 2015 Argonne National Laboratory and The Authors.

Resolution in transmission electron microscopy (TEM) now is limited by the properties of specimens, rather than by those of instrumentation. The long-standing difficulties in obtaining truly high-resolution structure from biological macromolecules with TEM demand the development, testing, and application of new ideas and unconventional approaches. This review concisely describes some new concepts and innovative methodologies for TEM that deal with unsolved problems in the preparation and preservation of macromolecular specimens. The selected topics include use of better support films, a more protective multi-component matrix surrounding specimens for cryo-TEM and negative staining, and, several quite different changes in microscopy and micrography that should decrease the effects of electron radiation damage; all these practical approaches are non-traditional, but have promise to advance resolution for specimens of biological macromolecules beyond its present level of 3-10. Å (0.3-1.0. nm). The result of achieving truly high resolution will be a fulfillment of the still unrealized potential of transmission electron microscopy for directly revealing the structure of biological macromolecules down to the atomic level. © 2010.

Bouchard C.,Ohio State University | Lepage G.P.,Cornell University | Monahan C.,College of William and Mary | Na H.,Argonne National Laboratory | Shigemitsu J.,Ohio State University
Physical Review Letters | Year: 2013

We calculate, for the first time using unquenched lattice QCD form factors, the standard model differential branching fractions dB/ dq2(B→Kℓ+ℓ-) for ℓ=e, μ, τ and compare with experimental measurements by Belle, BABAR, CDF, and LHCb. We report on B(B→Kℓ+ℓ-) in q2 bins used by experiment and predict B(B→Kτ+τ-)=(1.41±0.15) ×10-7. We also calculate the ratio of branching fractions Reμ=1.00029(69) and predict Rℓτ=1.176(40), for ℓ=e, μ. Finally, we calculate the "flat term" in the angular distribution of the differential decay rate FHe,μ,τ in experimentally motivated q2 bins. © 2013 American Physical Society.

Hohensee M.A.,University of California at Berkeley | Muller H.,University of California at Berkeley | Wiringa R.B.,Argonne National Laboratory
Physical Review Letters | Year: 2013

We consider the role of the internal kinetic energy of bound systems of matter in tests of the Einstein equivalence principle. Using the gravitational sector of the standard model extension, we show that stringent limits on equivalence principle violations in antimatter can be indirectly obtained from tests using bound systems of normal matter. We estimate the bound kinetic energy of nucleons in a range of light atomic species using Green's function Monte Carlo calculations, and for heavier species using a Woods-Saxon model. We survey the sensitivities of existing and planned experimental tests of the equivalence principle, and report new constraints at the level of between a few parts in 106 and parts in 108 on violations of the equivalence principle for matter and antimatter. © 2013 American Physical Society.

Rajh T.,Argonne National Laboratory
Methods in molecular biology (Clifton, N.J.) | Year: 2011

Semiconductor photocatalysis using nanoparticulate TiO(2) has proven to be a promising technology for use in catalytic reactions, in the cleanup of water contaminated with hazardous industrial by-products, and in nanocrystalline solar cells as a photoactive material. Metal oxide semiconductor colloids are of considerable interest because of their photocatalytic properties. The coordination sphere of the surface metal atoms is incomplete and thus traps light-induced charges, but also exhibits high affinity for oxygen-containing ligands and gives the opportunity for chemical modification. We use enediol linkers, such as dopamine and its analogs, to bridge the semiconductors to biomolecules such as DNA or proteins. Nanobio hybrids that combine the physical robustness and chemical reactivity of nanoscale metal oxides with the molecular recognition and selectivity of biomolecules were developed. Control of chemical processes within living cells was achieved using TiO(2) nanocomposites in order to develop new tools for advanced nanotherapeutics. Here, we describe general experimental approaches for synthesis and characterization of high crystallinity, water soluble 5 nm TiO(2) particles and their nanobio composites, methods of cellular sample preparation for advanced Synchrotron-based imaging of nanoparticles in single cell X-ray fluorescence, and a detailed experimental setup for application of the high-performance TiO(2)-based nanobio photocatalyst for targeted lysis of cancerous or other disordered cells.

Gidalevitz T.,Drexel University | Stevens F.,Argonne National Laboratory | Argon Y.,Childrens Hospital of Philadelphia | Argon Y.,University of Pennsylvania
Biochimica et Biophysica Acta - Molecular Cell Research | Year: 2013

The endoplasmic reticulum is a major compartment of protein biogenesis in the cell, dedicated to production of secretory, membrane and organelle proteins. The secretome has distinct structural and post-translational characteristics, since folding in the ER occurs in an environment that is distinct in terms of its ionic composition, dynamics and requirements for quality control. The folding machinery in the ER therefore includes chaperones and folding enzymes that introduce, monitor and react to disulfide bonds, glycans, and fluctuations of luminal calcium. We describe the major chaperone networks in the lumen and discuss how they have distinct modes of operation that enable cells to accomplish highly efficient production of the secretome. This article is part of a Special Issue entitled: Functional and structural diversity of endoplasmic reticulum. © 2013 Elsevier B.V.

Stan L.,Argonne National Laboratory
Nano Letters | Year: 2016

The field of oxide electronics has benefited from the wide spectrum of functionalities available to the ABO3 perovskites, and researchers are now employing defect engineering in single crystalline heterostructures to tailor properties. However, bulk oxide single crystals are not conducive to many types of applications, particularly those requiring mechanical flexibility. Here, we demonstrate the realization of an all-oxide, single-crystalline nanomembrane heterostructure. With a surface-to-volume ratio of 2 × 107, the nanomembranes are fully flexible and can be readily transferred to other materials for handling purposes or for new materials integration schemes. Using in situ synchrotron X-ray scattering, we find that the nanomembranes can bond to other host substrates near room temperature and demonstrate coupling between surface reactivity and electromechanical properties in ferroelectric nanomembrane systems. The synthesis technique described here represents a significant advancement in materials integration and provides a new platform for the development of flexible oxide electronics. © 2015 American Chemical Society.

Chen J.,Argonne National Laboratory | Burer S.,University of Iowa
Mathematical Programming Computation | Year: 2012

Nonconvex quadratic programming (QP) is an NP-hard problem that optimizes a general quadratic function over linear constraints. This paper introduces a new global optimization algorithm for this problem, which combines two ideas from the literature-finite branching based on the first-order KKT conditions and polyhedral-semidefinite relaxations of completely positive (or copositive) programs. Through a series of computational experiments comparing the new algorithm with existing codes on a diverse set of test instances, we demonstrate that the new algorithm is an attractive method for globally solving nonconvex QP. © 2011 Springer and Mathematical Optimization Society.

Elcock D.,Argonne National Laboratory
Journal of the American Water Resources Association | Year: 2010

Elcock, Deborah, 2010. Future U.S. Water Consumption: The Role of Energy Production. Journal of the American Water Resources Association (JAWRA) 46(3):447-460. DOI: 10.1111/j.1752-1688.2009.00413.x. Abstract: This study investigates how meeting domestic energy production targets for both fossil and renewable fuels may affect future water demand. It combines projections of energy production developed by the U.S. Department of Energy with estimates of water consumption on a per-unit basis (water-consumption coefficients) for coal, oil, gas, and biofuels production, to estimate and compare the domestic freshwater consumed. Although total domestic freshwater consumption is expected to increase by nearly 7% between 2005 and 2030, water consumed for energy production is expected to increase by nearly 70%, and water consumed for biofuels (biodiesel and ethanol) production is expected to increase by almost 250%. By 2030, water consumed in the production of biofuels is projected to account for nearly half of the total amount of water consumed in the production of all energy fuels. Most of this is for irrigation, and the West North Central Region is projected to consume most of this water in 2030. These findings identify an important potential future conflict between renewable energy production and water availability that warrants further investigation and action to ensure that future domestic energy demand can be met in an economically efficient and environmentally sustainable manner. © 2010 UChicago Argonne, LLC, Operator of Argonne National Laboratory.

Brown M.A.,Oregon State University | Paulenova A.,Oregon State University | Gelis A.V.,Argonne National Laboratory
Inorganic Chemistry | Year: 2012

Aqueous complexation of Th(IV), U(IV), Np(IV), Pu(III/IV), and Ce(III/IV) with DTPA was studied by potentiometry, absorption spectrophotometry, and cyclic voltammetry at 1 M ionic strength and 25 °C. The stability constants for the 1:1 complex of each trivalent and tetravalent metal were calculated. From the potentiometric data, we report stability constant values for Ce(III)DTPA, Ce(III)HDTPA, and Th(IV)DTPA of log β101 = 20.01 ± 0.02, log β111 = 22.0 ± 0.2, and log β101 = 29.6 ± 1, respectively. From the absorption spectrophotometry data, we report stability constant values for U(IV)DTPA, Np(IV)DTPA, and Pu(IV)DTPA of log β101 = 31.8 ± 0.1, 32.3 ± 0.1, and 33.67 ± 0.02, respectively. From the cyclic voltammetry data, we report stability constant values for Ce(IV) and Pu(III) of log β101 = 34.04 ± 0.04 and 20.58 ± 0.04, respectively. The values obtained in this work are compared and discussed with respect to the ionic radius of each cationic metal. © 2012 American Chemical Society.

Gopalakrishnan S.,Harvard University | Martin I.,Argonne National Laboratory | Demler E.A.,Harvard University
Physical Review Letters | Year: 2013

We study quasi-two-dimensional dipolar Bose gases in which the bosons experience a Rashba spin-orbit coupling. We show that the degenerate dispersion minimum due to the spin-orbit coupling, combined with the long-range dipolar interaction, can stabilize a number of quantum crystalline and quasicrystalline ground states. Coupling the bosons to a fermionic species can further stabilize these phases. We estimate that the crystalline and quasicrystalline phases should be detectable in realistic dipolar condensates, e.g., dysprosium, and discuss their symmetries and excitations. © 2013 American Physical Society.

Wilson R.E.,Argonne National Laboratory
Inorganic Chemistry | Year: 2011

The chemistry of tetravalent Pu with sulfate is explored in a series of single-crystal X-ray diffraction studies of the alkali metal plutonium sulfate compounds. Five new structures of Pu(IV) sulfates are presented including the structure for the α-phase of Pu(SO4)2(H 2O)4, Na10Pu2(SO4) 9(H2O)4, K8Pu2(SO 4)8(H2O)5, Rb8Pu 2(SO4)8(H2O)4, and Cs4Pu(SO4)4(H2O)2. Changes in structure and stoichiometry are seen down the alkali-metal series despite identical reaction conditions for each of the complexes. Comparison to the other known An(IV) sulfates, Group IV sulfates, and Ce(IV) reveals limited similarity in stoichiometry and structure across the actinide series and their homologues. Marked color changes are observed down the series indicating strong interactions between the plutonium ions and the ligands in these complexes. © 2011 American Chemical Society.

Holmberg K.,VTT Technical Research Center of Finland | Andersson P.,VTT Technical Research Center of Finland | Erdemir A.,Argonne National Laboratory
Tribology International | Year: 2012

This study presents calculations on the global fuel energy consumption used to overcome friction in passenger cars in terms of friction in the engine, transmission, tires, and brakes. Friction in tribocontacts was estimated according to prevailing contact mechanisms such as elastohydrodynamic, hydrodynamic, mixed, and boundary lubrication. Coefficients of friction in the tribocontacts were estimated based on available information in the literature on the average passenger car in use today, a car with today's advanced commercial tribological technology, a car with today's best advanced technology based upon recent research and development, and a car with the best technology forecasted in the next 10 years. The following conclusions were reached: In passenger cars, one-third of the fuel energy is used to overcome friction in the engine, transmission, tires, and brakes. The direct frictional losses, with braking friction excluded, are 28% of the fuel energy. In total, 21.5% of the fuel energy is used to move the car.Worldwide, 208,000 million liters of fuel (gasoline and diesel) was used in 2009 to overcome friction in passenger cars. This equals 360 million tonne oil equivalent per year (Mtoe/a) or 7.3 million TJ/a. Reductions in frictional losses will lead to a threefold improvement in fuel economy as it will reduce both the exhaust and cooling losses also at the same ratio.Globally, one passenger car uses on average of 340 l of fuel per year to overcome friction, which would cost 510 euros according to the average European gas price in 2011 and corresponds to an average driving distance of 13,000 km/a.By taking advantage of new technology for friction reduction in passenger cars, friction losses could be reduced by 18% in the short term (510 years) and by 61% in the long term (1525 years). This would equal worldwide economic savings of 174,000 million euros and 576,000 million euros, respectively; fuel savings of 117,000 million and 385,000 million liters, respectively; and CO 2 emission reduction of 290 million and 960 million tonnes, respectively.The friction-related energy losses in an electric car are estimated to be only about half those of an internal combustion passenger car. Potential actions to reduce friction in passenger cars include the use of advanced coatings and surface texturing technology on engine and transmission components, new low-viscosity and low-shear lubricants and additives, and tire designs that reduce rolling friction. © 2011 Elsevier Ltd. All rights reserved.

Morelock C.R.,Georgia Institute of Technology | Suchomel M.R.,Argonne National Laboratory | Wilkinson A.P.,Georgia Institute of Technology
Journal of Applied Crystallography | Year: 2013

GE-7031 varnish, a commonly used low-temperature adhesive and electrical insulator owing to its high thermal conductivity and mechanical strength at low temperatures, was used as a sample matrix for low-temperature powder X-ray diffraction measurements of the negative thermal expansion (NTE) material ScF3. When ScF3 powder was mixed with GE-7031 varnish, an unexpected cubic to rhombohedral phase transition in the ScF3 sample was observed at ∼50K, and it exhibited smaller low-temperature unit-cell volumes than samples without the varnish matrix. Experimental observations and quantitative estimates suggest that these anomalies are the result of stress induced by a thermal expansion mismatch between the varnish matrix (large positive coefficient of thermal expansion, CTE) and ScF3 (quite large negative CTE). The use of GE-7031 varnish as a sample matrix for low-temperature measurements should be approached with caution if a large thermal expansion mismatch is expected. © 2013 International Union of Crystallography.

Finney L.,Argonne National Laboratory
Expert Review of Proteomics | Year: 2014

Metals are essential cofactors, utilized in many critical cellular processes. For example, zinc is important in insulin biosynthesis and may play a role in Alzheimer's disease, but much of how the zinc-mediated process remains unknown. Knowing which metal is in which protein at a given point in time would lead to new insights into how metals work in biological systems. New tools are being developed to investigate the biochemistry and cell biology of metals, with potential for biomedical applications. In this report, we consider the promise and limitations of metalloproteins detection techniques. We provide a brief overview of the techniques available and a discussion of the technical challenges to biomedical applications, with particular focus on what must be overcome for the potential of these approaches to be achieved. © 2014 Informa UK, Ltd.

Lu J.,Northwestern University | Stair P.C.,Northwestern University | Stair P.C.,Argonne National Laboratory
Angewandte Chemie - International Edition | Year: 2010

[Figure Presented] Sheltered growth: A novel atomic layer deposition (ALD) method to synthesize highly uniform ultrafine supported metal nanoparticles is described. The ALD process includes growing protected metal nanoparticles and new support layers simultaneously at low temperature. In the final stage, the activation of the metal nanoparticles can be achieved by removing the protective ligands through calcination or reduction at elevated temperature (see picture).© 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Chan R.T.,University of California at San Diego | Robart A.R.,University of California at San Diego | Rajashankar K.R.,Argonne National Laboratory | Pyle A.M.,Yale University | And 2 more authors.
Nature Structural and Molecular Biology | Year: 2012

Group II introns are self-splicing catalytic RNAs that are thought to be ancestral to the spliceosome. Here we report the 3.65-Åcrystal structure of the group II intron from Oceanobacillus iheyensis in the pre-catalytic state. The structure reveals the conformation of the 5′2 splice site in the catalytic core and represents the first structure of an intron prior to the first step of splicing. © 2012 Nature America,inc. All Right Reserved.

Kalinin S.V.,Oak Ridge National Laboratory | Borisevich A.,Oak Ridge National Laboratory | Fong D.,Argonne National Laboratory
ACS Nano | Year: 2012

Novel physical functionality enabled by nanoscale control of materials has been the target of intense scientific exploration and interest for the last two decades, leading directly to the explosive growth of nanoscience and nanotechnology. However, this transition to nanometer scales also blurs the boundary between classical physical and electrochemical phenomena, due to smaller transport lengths, larger chemical and electrostatic potential gradients, and higher surface/volume ratios. While well-recognized for many decades in areas such as ferroelectricity, these phenomena remained largely outside the realm of condensed matter physics studies. Here, we offer a perspective on the role of electrochemical phenomena in the nanoscale physics of correlated oxides and summarize the challenges for local characterization of these behaviors. © 2012 American Chemical Society.

Ding N.,Northwestern University | Kanatzidis M.G.,Northwestern University | Kanatzidis M.G.,Argonne National Laboratory
Nature Chemistry | Year: 2010

The selective capture of Cs+ from solution is relevant to the remediation of nuclear waste and remains a significant challenge. Here we describe a new framework composed of [(CH3)2 NH 2]+ and [Ga2 Sb2 S7] 2- layers, which are perforated with holes. Shape selectivity couples with framework flexibility, allowing the compound to respond to the ion-exchange process. The size, shape and flexibility of the holes allow Cs+ ions in an aqueous solution to selectively pass through and enter the material via an ion-exchange process. Following capture, the structure dynamically closes its holes in a manner reminiscent of a Venus flytrap, which prevents the Cs + ions from leaching out. This process has useful implications in the separation science of Cs as it relates to the clean-up of nuclear waste. The dynamic response we describe here provides important insights for designing new materials for the selective removal of difficult-to-capture ions. © 2010 Macmillan Publishers Limited.

Akey D.L.,University of Michigan | Brown W.C.,University of Michigan | Konwerski J.R.,University of Michigan | Ogata C.M.,Argonne National Laboratory | Smith J.L.,University of Michigan
Acta Crystallographica Section D: Biological Crystallography | Year: 2014

An emergent challenge in macromolecular crystallography is the identification of the substructure from native anomalous scatterers in crystals that diffract to low to moderate resolution. Increasing the multiplicity of data sets has been shown to make previously intractable phasing problems solvable and to increase the useful resolution in model refinement. For the West Nile virus nonstructural protein 1 (NS1), a protein of novel fold, the utility of exceptionally high multiplicity data is demonstrated both in solving the crystal structure from the anomalous scattering of the native S atoms and in extending the useful limits of resolution during refinement. A high-multiplicity data set from 18 crystals had sufficient anomalous signal to identify sulfur sites using data to 5.2Å resolution. Phases calculated to 4.5Å resolution and extended to 3.0Å resolution were of sufficient quality for automated building of three-quarters of the final structure. Crystallographic refinement to 2.9Å resolution proceeded smoothly, justifying the increase in resolution that was made possible by combining multiple data sets. The identification and exclusion of data from outlier crystals is shown to result in more robust substructure determination. © 2014 International Union of Crystallography.

Burke J.E.,University of Wisconsin - Madison | Sashital D.G.,University of Wisconsin - Madison | Sashital D.G.,University of California at Berkeley | Zuo X.,Argonne National Laboratory | And 2 more authors.
RNA | Year: 2012

The U2/U6 snRNA complex is a conserved and essential component of the active spliceosome that interacts with the pre-mRNA substrate and essential protein splicing factors to promote splicing catalysis. Here we have elucidated the solution structure of a 111-nucleotide U2/U6 complex using an approach that integrates SAXS, NMR, and molecular modeling. The U2/U6 structure contains a three-helix junction that forms an extended "Y" shape. The U6 internal stem-loop (ISL) forms a continuous stack with U2/U6 Helices Ib, Ia, and III. The coaxial stacking of Helix Ib on the U6 ISL is a configuration that is similar to the Domain V structure in group II introns. Interestingly, essential features of the complex-including the U80 metal binding site, AGC triad, and pre-mRNA recognition sites-localize to one face of the molecule. This observation suggests that the U2/U6 structure is well-suited for orienting substrate and cofactors during splicing catalysis. Published by Cold Spring Harbor Laboratory Press. Copyright ©2012 RNA Society.

Tasora A.,University of Parma | Anitescu M.,Argonne National Laboratory
Meccanica | Year: 2013

In this work (also, preprint ANL/MCS-P3020-0812, Argonne National Laboratory) we introduce a complementarity-based rolling friction model to characterize dissipative phenomena at the interface between moving parts. Since the formulation is based on differential inclusions, the model fits well in the context of nonsmooth dynamics, and it does not require short integration timesteps. The method encompasses a rolling resistance limit for static cases, similar to what happens for sliding friction; this is a simple yet efficient approach to problems involving transitions from rolling to resting, and vice-versa. We propose a convex relaxation of the formulation in order to achieve algorithmic robustness and stability; moreover, we show the side effects of the convexification. A natural application of the model is the dynamics of granular materials, because of the high computational efficiency and the need for only a small set of parameters. In particular, when used as a micromechanical model for rolling resistance between granular particles, the model can provide an alternative way to capture the effect of irregular shapes. Other applications can be related to real-time simulations of rolling parts in bearing and guideways, as shown in examples. © 2013 Springer Science+Business Media Dordrecht.

Akhter S.,San Diego State University | Aziz R.K.,San Diego State University | Aziz R.K.,Cairo University | Edwards R.A.,San Diego State University | Edwards R.A.,Argonne National Laboratory
Nucleic Acids Research | Year: 2012

Prophages are phages in lysogeny that are integrated into, and replicated as part of, the host bacterial genome. These mobile elements can have tremendous impact on their bacterial hosts' genomes and phenotypes, which may lead to strain emergence and diversification, increased virulence or antibiotic resistance. However, finding prophages in microbial genomes remains a problem with no definitive solution. The majority of existing tools rely on detecting genomic regions enriched in protein-coding genes with known phage homologs, which hinders the de novo discovery of phage regions. In this study, a weighted phage detection algorithm, PhiSpy was developed based on seven distinctive characteristics of prophages, i.e. protein length, transcription strand directionality, customized AT and GC skew, the abundance of unique phage words, phage insertion points and the similarity of phage proteins. The first five characteristics are capable of identifying prophages without any sequence similarity with known phage genes. PhiSpy locates prophages by ranking genomic regions enriched in distinctive phage traits, which leads to the successful prediction of 94 of prophages in 50 complete bacterial genomes with a 6false-negative rate and a 0.66false-positive rate. © 2012 The Author(s).

Ellis R.J.,Argonne National Laboratory
Journal of Physical Chemistry B | Year: 2014

The solvent extraction of an ionizable solute (H3PO4) from water into a water-in-oil microemulsion, and subsequent organic phase splitting (known as third phase formation), has been recast as a critical phenomenon by linking system structure to solute concentration via a critical exponent. The transuranic extraction (TRUEX) system was investigated by extracting increasing concentrations of H3PO4 into a microemulsion - consisting of two extractant amphiphiles (CMPO and TBP) and water in n-dodecane - and taking small-angle X-ray scattering (SAXS) measurements from the resulting solutions. The H3PO4 concentration at which phase splitting occurred was defined as the critical concentration (XC), and this was related to the precritical concentrations (X) by the reduced parameter ε = (XC - X)/X C. The scattering intensity at the zero angle I(0), relating to the interaction between reverse micellar aggregates, conformed to the relation I(0) = I0ε-γ, with critical exponent γ = 2.20. To check γ, SAXS measurements were taken from the organic phase in situ with variable temperature through the point at which third phase formation initiates (the critical temperature), giving I(0) = I0t -γ, where t = (T - TC)/TC and T C and T are the critical and precritical temperatures, with critical exponent γ = 2.55. These γ values suggest third phase formation is a universal phenomenon manifest from a critical double point. Thus, solvent extraction is reduced to its fundamental physical roots where the system is not defined by detailed analysis of metrical properties but by linking the fundamental order to thermodynamic parameters via an exponent, working toward a more predictive understanding of third phase formation. © 2013 American Chemical Society.

Gopalakrishnan S.,Harvard University | Martin I.,Argonne National Laboratory | Demler E.A.,Harvard University
Physical Review Letters | Year: 2014

A Reply to the Comments by M. Sandbrink et al. and R. Lifshitz. © 2014 American Physical Society.

Smith D.H.,Ohio State University | Braaten E.,Ohio State University | Kang D.,Massachusetts Institute of Technology | Platter L.,Argonne National Laboratory | Platter L.,Chalmers University of Technology
Physical Review Letters | Year: 2014

In a recent experiment with ultracold trapped Rb85 atoms, Makotyn et al. studied a quantum-degenerate Bose gas in the unitary limit where its scattering length is infinitely large. We show that the observed momentum distributions are compatible with a universal relation that expresses the high-momentum tail in terms of the two-body contact C2 and the three-body contact C3. We determine the contact densities for the unitary Bose gas with number density n to be C2≈20n4/3 and C3≈2n5/3. We also show that the observed atom loss rate is compatible with that from 3-atom inelastic collisions, which gives a contribution proportional to C3, but the loss rate is not compatible with that from 2-atom inelastic collisions, which gives a contribution proportional to C2. We point out that the contacts C2 and C3 could be measured independently by using the virial theorem near and at unitarity, respectively. © 2014 American Physical Society.

Hessel C.M.,Institute of Chemical Technology | P. Pattani V.,University of Texas at Austin | Rasch M.,Institute of Chemical Technology | Panthani M.G.,Institute of Chemical Technology | And 3 more authors.
Nano Letters | Year: 2011

Ligand-stabilized copper selenide (Cu2-xSe) nanocrystals, approximately 16 nm in diameter, were synthesized by a colloidal hot injection method and coated with amphiphilic polymer. The nanocrystals readily disperse in water and exhibit strong near-infrared (NIR) optical absorption with a high molar extinction coefficient of 7.7 Cu 107 cm- 1 M -1 at 980 nm. When excited with 800 nm light, the Cu2-xSe nanocrystals produce significant photothermal heating with a photothermal transduction efficiency of 22%, comparable to nanorods and nanoshells of gold (Au). In vitro photothermal heating of Cu2-xSe nanocrystals in the presence of human colorectal cancer cell (HCT-116) led to cell destruction after 5 min of laser irradiation at 33 W/cm2, demonstrating the viabilitiy of Cu2-xSe nanocrystals for photothermal therapy applications. © 2011 American Chemical Society.

Pineda A.,Autonomous University of Barcelona | Segovia J.,Argonne National Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We compute the magnetic dipole transitions between low-lying heavy quarkonium states in a model-independent way. We use the weak-coupling version of the effective field theory named potential nonrelativistic QCD, with the static potential exactly incorporated in the leading order Hamiltonian. The precision we reach is kγ3/m2×O(αs2,v2) and kγ3/m2×O(v4) for the allowed and forbidden transitions, respectively, where kγ is the photon energy. We also resum the large logarithms associated with the heavy quark mass scale. The specific transitions considered in this paper are the following: Υ(1S) →ηb(1S)γ, J/ψ(1S)→ηc(1S) γ, hb(1P)→χb0,1(1P)γ, χb2(1P)→hb(1P)γ, Υ(2S) →ηb(2S)γ, Υ(2S)→ηb(1S)γ and ηb(2S)→Υ(1S)γ. The effect of the new power counting is found to be large, and the exact treatment of the soft logarithms of the static potential makes the factorization scale dependence much smaller. The convergence for the bb̄ ground state is quite good, and also quite reasonable for the cc̄ ground state and the bb̄ 1P state. For all of them we give solid predictions. For the 2S decays the situation is less conclusive, yet our results are perfectly consistent with existing data, as the previous disagreement with experiment for the Υ(2S) →ηb(1S)γ decay fades away. We also compute some expectation values like the electromagnetic radius, or. We find to be nicely convergent in all cases, whereas the convergence of is typically worse. © 2013 American Physical Society.

Zhang N.,Fuzhou University | Yang M.-Q.,Fuzhou University | Liu S.,Fuzhou University | Sun Y.,Argonne National Laboratory | Xu Y.-J.,Fuzhou University
Chemical Reviews | Year: 2015

A review of graphene-based photocatalysis, which has covered a systematic understanding of the multifarious roles of graphene in boosting the photocatalytic performance, is discussed. To fabricate smart graphene-based composite photocatalysts, it is necessary and still challenging to rationally design graphene-based composites from a system-level engineering consideration, which in analogy to biological systems in nature requires a collective integration of the individual components, interface composition, and fine control of material structure and morphology at the nanoscale. In particular, interface engineering by the combination of tailored individual components that afford special interfacial interaction such as p-n junctions, heterojunctions, and Zscheme systems would be an effective strategy for improving the photoactivity of graphene-based composites because it predominantly determines the microscopic transfer pathway of charge carriers, the efficiency of the separation and transfer of charge carriers, and thus the photoactivity. While it is well recognized that graphene-based composites are feasible for boosting photocatalysis, more attention should be paid to the design of graphene-based composites by a system-level method and, particularly, to an in-depth fundamental understanding of the pathway and dynamics of charge carrier transfer associated with such composites by the joint cooperation between experiment and theory.

Gao J.,Southern Methodist University | Gao J.,Argonne National Laboratory | Zhu H.X.,SLAC
Physical Review Letters | Year: 2014

We report on a complete calculation of electroweak production of top-quark pairs in e+e- annihilation at next-to-next-to-leading order in quantum chromodynamics. Our setup is fully differential in phase space and can be used to calculate any infrared-safe observable. Especially we calculated the next-to-next-to-leading-order corrections to the top-quark forward-backward asymmetry and found sizable effects. Our results show a large reduction of the theoretical uncertainties in predictions of the forward-backward asymmetry, and allow for a precision determination of the top-quark electroweak couplings at future e+e- colliders. © 2014 American Physical Society.

Srivastava S.,Cornell University | Archer L.A.,Cornell University | Narayanan S.,Argonne National Laboratory
Physical Review Letters | Year: 2013

Anomalous trends in nanoparticle correlation and motion are reported in soft nanoparticle suspensions using static and dynamic x-ray scattering measurements. Contrary to normal expectations, we find that particle-particle correlations decrease and particle dynamics become faster as volume fraction rises above a critical particle loading associated with overlap. Our observations bear many similarities to the cascade of structural and transport anomalies reported for complex, network forming molecular fluids such as water, and are argued to share similar physical origins. © 2013 American Physical Society.

Marcus G.,Lawrence Berkeley National Laboratory | Marcus G.,SLAC | Penn G.,Lawrence Berkeley National Laboratory | Zholents A.A.,Argonne National Laboratory
Physical Review Letters | Year: 2014

We present the design of a single-pass free-electron laser amplifier suitable for enabling four-wave mixing x-ray spectroscopic investigations. The production of longitudinally coherent, single-spike pulses of light from a single electron beam in this scenario relies on a process of selective amplification where a strong undulator taper compensates for a large energy chirp only for a short region of the electron beam. This proposed scheme offers improved flexibility of operation and allows for independent control of the color, timing, and angle of incidence of the individual pulses of light at an end user station. Detailed numerical simulations are used to illustrate the more impressive characteristics of this scheme. © 2014 American Physical Society.

Hernandez-Garcia C.,University of Salamanca | Hernandez-Garcia C.,University of Colorado at Boulder | Picon A.,Argonne National Laboratory | San Roman J.,University of Salamanca | Plaja L.,University of Salamanca
Physical Review Letters | Year: 2013

We present a theoretical study of high-order harmonic generation (HHG) and propagation driven by an infrared field carrying orbital angular momentum (OAM). Our calculations unveil the following relevant phenomena: extreme-ultraviolet harmonic vortices are generated and survive to the propagation effects, vortices transport high-OAM multiples of the corresponding OAM of the driving field and, finally, the different harmonic vortices are emitted with similar divergence. We also show the possibility of combining OAM and HHG phase locking to produce attosecond pulses with helical pulse structure. © 2013 American Physical Society.

Gerard D.,University of Technology of Troyes | Gray S.K.,Argonne National Laboratory
Journal of Physics D: Applied Physics | Year: 2015

We present an overview of 'aluminium plasmonics', i.e. the study of both fundamental and practical aspects of surface plasmon excitations in aluminium structures, in particular thin films and metal nanoparticles. After a brief introduction noting both some recent and historical contributions to aluminium plasmonics, we discuss the optical properties of aluminium and aluminium nanostructures and highlight a few selected studies in a host of areas ranging from fluorescence to data storage. © 2015 IOP Publishing Ltd.

Low I.,Argonne National Laboratory | Low I.,Northwestern University | Low I.,University of California at Santa Barbara
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Current searches for direct production of scalar top quarks, or stops, in supersymmetry focus on their decays into bW+χ Ëœ0 by way of tχËœ0 and bχËœ+. While the polarization of the top quark depends on the stop mixing, the chargino turns out to be fully polarized when the bottom Yukawa coupling can be neglected relative to the top Yukawa coupling. We compute the energy and angular spectra of the charged lepton in the chargino channel, which could serve as the spin analyzer of the chargino. In addition, we demonstrate the top polarization could have a significant impact on the selection efficiencies in direct stop samples at the LHC, while the effect from the chargino polarization is less pronounced. Two observables in the laboratory frame, the opening angle between the charged lepton and the b quark and the energy of the b quark, are also proposed to optimize searches in the chargino channel versus the top channel. © 2013 American Physical Society.

Ament L.J.P.,Leiden University | Van Veenendaal M.,Argonne National Laboratory | Van Veenendaal M.,Northern Illinois University | Devereaux T.P.,SLAC | And 2 more authors.
Reviews of Modern Physics | Year: 2011

In the past decade, resonant inelastic x-ray scattering (RIXS) has made remarkable progress as a spectroscopic technique. This is a direct result of the availability of high-brilliance synchrotron x-ray radiation sources and of advanced photon detection instrumentation. The technique's unique capability to probe elementary excitations in complex materials by measuring their energy, momentum, and polarization dependence has brought RIXS to the forefront of experimental photon science. Both the experimental and theoretical RIXS investigations of the past decade are reviewed, focusing on those determining the low-energy charge, spin, orbital, and lattice excitations of solids. The fundamentals of RIXS as an experimental method are presented and then the theoretical state of affairs, its recent developments, and the different (approximate) methods to compute the dynamical RIXS response are reviewed. The last decade's body of experimental RIXS data and its interpretation is surveyed, with an emphasis on RIXS studies of correlated electron systems, especially transition-metal compounds. Finally, the promise that RIXS holds for the near future is discussed, particularly in view of the advent of x-ray laser photon sources. © 2011 American Physical Society.

Bouchard C.,Ohio State University | Lepage G.P.,Cornell University | Monahan C.,College of William and Mary | Na H.,Argonne National Laboratory | Shigemitsu J.,Ohio State University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

We calculate, for the first time using unquenched lattice QCD, form factors for the rare decay B→Kℓ+ℓ- in and beyond the Standard Model. Our lattice QCD calculation utilizes a nonrelativistic QCD formulation for the b valence quarks and the highly improved staggered quark formulation for the light valence quarks. We employ the MILC 2+1 asqtad ensembles. The form factor results, based on the z expansion, are valid over the full kinematic range of q2. We construct the ratios f0/f+ and fT/f+, which are useful in constraining new physics and verifying effective theory form factor symmetry relations. We also discuss the calculation of Standard Model observables. © 2013 American Physical Society.

Rondinelli J.M.,Argonne National Laboratory | Rondinelli J.M.,Drexel University | Coh S.,Rutgers University
Physical Review Letters | Year: 2011

Using first-principles density functional theory calculations, we discover an anomalously large biaxial strain-induced octahedral rotation axis reorientation in orthorhombic perovskites with tendency towards rhombohedral symmetry. The transition between crystallographically equivalent (isosymmetric) structures with different octahedral rotation magnitudes originates from strong strain-octahedral rotation coupling available to perovskites and the energetic hierarchy among competing octahedral tilt patterns. By elucidating these criteria, we suggest many functional perovskites would exhibit the transition in thin film form, thus offering a new landscape in which to tailor highly anisotropic electronic responses. © 2011 American Physical Society.

Matveev K.A.,Argonne National Laboratory | Andreev A.V.,University of Washington
Physical Review Letters | Year: 2011

Luttinger liquid theory describes one-dimensional electron systems in terms of noninteracting bosonic excitations. In this approximation thermal excitations are decoupled from the current flowing through a quantum wire, and the conductance is quantized. We show that relaxation processes not captured by the Luttinger liquid theory lead to equilibration of the excitations with the current and give rise to a temperature-dependent correction to the conductance. In long wires, the magnitude of the correction is expressed in terms of the velocities of bosonic excitations. In shorter wires it is controlled by the relaxation rate. © 2011 American Physical Society.

Bodwin G.,Argonne National Laboratory | Petriello F.,Northwestern University | Stoynev S.,Northwestern University | Velasco M.,Northwestern University
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

In this paper we discuss decays of the Higgs boson to quarkonia in association with a photon. We identify a new mechanism for producing such final states in Higgs decays that leads to predictions for the decay rates that differ by an order of magnitude from previous estimates. Although the branching ratios for these processes are still small, the processes are experimentally clean, and the H→J/ψγ decay should be observable at a 14 TeV LHC. We point out that quantum interference between two different production mechanisms makes the decay rates sensitive to the HQ̄Q couplings. Consequently, measurements of the H→J/ψγ decay rate would allow one to probe the Higgs-charm coupling directly at the LHC. We discuss the experimental prospects for the observation of these decays and for the direct measurement of the Hc̄c coupling. © 2013 American Physical Society.

Bahn C.B.,Argonne National Laboratory
Nuclear Engineering and Technology | Year: 2013

Industry-or regulatory-sponsored research activities on the resolution of Generic Safety Issue (GSI)-191 were reviewed, especially on the chemical effects. Potential chemical effects on the head loss across the debris-loaded sump strainer under a post-accident condition were experimentally evidenced by small-scale bench tests, integrated chemical effects test (ICET), and vertical loop head loss tests. Three main chemical precipitates were identified by WCAP-16530-NP: calcium phosphate, aluminum oxyhydroxide, and sodium aluminum silicate. The former two precipitates were also identified as major chemical precipitates by the ICETs. The assumption that all released calcium would form precipitates is reasonable. CalSil insulation needs to be minimized especially in a plant using trisodium phosphate buffer. The assumption that all released aluminum would form precipitates appears highly conservative because ICETs and other studies suggest substantial solubility of aluminum at high temperature and inhibition of aluminum corrosion by silicate or phosphate. The industry-proposed chemical surrogates are quite effective in increasing the head loss across the debris-loaded bed and more effective than the prototypical aluminum hydroxide precipitates generated by in-situ aluminum corrosion. There appears to be some unresolved potential issues related to GSI-191 chemical effects as identified in NUREG/CR-6988. The United States Nuclear Regulatory Commission, however, concluded that the implications of these issues are either not generically significant or are appropriately addressed, although several issues associated with downstream in-vessel effects remain.

Chen Y.,Argonne National Laboratory
Nuclear Engineering and Technology | Year: 2013

High-Cr martensitic steel HT-9 is one of the candidate materials for advanced nuclear energy systems. Thanks to its excellent thermal conductivity and irradiation resistance, ferritic/martensitic steels such as HT-9 are considered for in-core applications of advanced nuclear reactors. The harsh neutron irradiation environments at the reactor core region pose a unique challenge for structural and cladding materials. Microstructural and microchemical changes resulting from displacement damage are anticipated for structural materials after prolonged neutron exposure. Consequently, various irradiation effects on the service performance of in-core materials need to be understood. In this work, the fundamentals of radiation damage and irradiation effects of the HT-9 martensitic steel are reviewed. The objective of this paper is to provide a background introduction of displacement damage, microstructural evolution, and subsequent effects on mechanical properties of the HT-9 martensitic steel under neutron irradiations. Mechanical test results of the irradiated HT-9 steel obtained from previous fast reactor and fusion programs are summarized along with the information of irradiated microstructure. This review can serve as a starting point for additional investigations on the in-core applications of ferritic/martensitic steels in advanced nuclear reactors.

Micklitz T.,Free University of Berlin | Levchenko A.,Argonne National Laboratory | Levchenko A.,Michigan State University
Physical Review Letters | Year: 2011

We study the problem of energy relaxation in a one-dimensional electron system. The leading thermalization mechanism is due to three-particle collisions. We show that for the case of spinless electrons in a single channel quantum wire the corresponding collision integral can be transformed into an exactly solvable problem. The latter is known as the Schrödinger equation for a quantum particle moving in a Pöschl-Teller potential. The spectrum for the resulting eigenvalue problem allows for bound-state solutions, which can be identified with the zero modes of the collision integral, and a continuum of propagating modes, which are separated by a gap from the bound states. The inverse gap gives the time scale at which counterpropagating electrons thermalize. © 2011 American Physical Society.

Paracchino A.,Ecole Polytechnique Federale de Lausanne | Laporte V.,Ecole Polytechnique Federale de Lausanne | Sivula K.,Ecole Polytechnique Federale de Lausanne | Gratzel M.,Ecole Polytechnique Federale de Lausanne | And 2 more authors.
Nature Materials | Year: 2011

A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H2 production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm-2 at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%. © 2011 Macmillan Publishers Limited. All rights reserved.

Littlewood P.,Argonne National Laboratory | Littlewood P.,James Franck Institute
Nature Materials | Year: 2011

Studies have shown that X-ray illumination can be used to control the arrangement of oxygen atoms in cuprate superconductors, allowing the writing of regions of robust high-transition-temperature superconductivity. Optimal superconductivity occurs when conditions are such that the phase percolates into a fractal network. It is also found that above 370 K this phase becomes disordered, so that if a sample is heated above this temperature and then quenched to low temperature, it has a poor superconducting order. Poccia et al. observed nucleation and growth of the ordered domains and a recovery of a robust high state and found that the timescale for the growth with X-ray intensity makes it clear that X-ray illumination is the source, indeed photo-switching of phase transitions is known elsewhere in oxides. The cuprates, as exemplars of transition metal oxides in general, to demonstrate their multiphase complexity that is found to provide many avenues to control functionalities.

Oh S.-M.,Hanyang University | Myung S.-T.,Sejong University | Park J.B.,Hanyang University | Scrosati B.,Hanyang University | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2012

A new coat: LiMn 1-xFe xPO 4 materials with a LiFePO 4 outer layer of varying thickness and a LiMn 0.85Fe 0.15PO 4 bulk were prepared. The physical characteristics such as tap density, porosity, and spherical morphology were fine-tuned. The double-structured micron-sized LiMn 0.85Fe 0.15PO 4/LiFePO 4 material (see picture) shows properties which make this material an ideal candidate for rechargeable lithium batteries. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Han M.J.,Columbia University | Han M.J.,Argonne National Laboratory | Wang X.,University of Maryland University College | Marianetti C.A.,Columbia University | Millis A.J.,Columbia University
Physical Review Letters | Year: 2011

Dynamical mean-field methods are used to calculate the phase diagram, many-body density of states, relative orbital occupancy, and Fermi-surface shape for a realistic model of LaNiO3-based superlattices. The model is derived from density-functional band calculations and includes oxygen orbitals. The combination of the on-site Hunds interaction and charge transfer between the transition metal and the oxygen orbitals is found to reduce the orbital polarization far below the levels predicted either by band-structure calculations or by many-body analyses of Hubbard-type models which do not explicitly include the oxygen orbitals. The findings indicate that heterostructuring is unlikely to produce one band-model physics and demonstrate the fundamental inadequacy of modeling the physics of late transition-metal oxides with Hubbard-like models. © 2011 American Physical Society.

Liu M.,Northeastern University | Liu M.,Argonne National Laboratory | Lou J.,Northeastern University | Li S.,Northeastern University | Sun N.X.,Northeastern University
Advanced Functional Materials | Year: 2011

The coexistence of electrical polarization and magnetization in multiferroic materials provides great opportunities for novel information storage systems. In particular, magnetoelectric (ME) effect can be realized in multiferroic composites consisting of both ferromagnetic and ferroelectric phases through a strain mediated interaction, which offers the possibility of electric field (E-field) manipulation of magnetic properties or vice versa, and enables novel multiferroic devices such as magnetoelectric random access memories (MERAMs). These MERAMs combine the advantages of FeRAMs (ferroelectric random access memories) and MRAMs (magnetic random access memories), which are non-volatile magnetic bits switchable by electric field (E-field). However, it has been challenging to realize 180° deterministic switching of magnetization by E-field, on which most magnetic memories are based. Here we show E-field modulating exchange bias and for the first time realization of near 180° dynamic magnetization switching at room temperature in novel AFM (antiferromagnetic)/FM (ferromagnetic)/FE (ferroelectric) multiferroic heterostructures of FeMn/Ni80Fe20/FeGaB/PZN-PT (lead zinc niobate-lead titanate). Through competition between the E-field induced uniaxial anisotropy and unidirectional anisotropy, large E-field-induced exchange bias field-shift up to Δ Hex Hex = 218 and near 180° deterministic magnetization switching were demonstrated in the exchange-coupled multiferroic system of FeMn/Ni80Fe20/FeGaB/PZN-PT. This E-field tunable exchange bias and near 180° deterministic magnetization switching at room temperature in AFM/FM/FE multiferroic heterostructures paves a new way for MERAMs and other memory technologies. Electric field modulating exchange bias and near 180° dynamic magnetization switching at room temperature were demonstrated in novel AFM (antiferromagnetic)/FM(ferromagnetic) /FE(ferroelectric) multiferroic heterostructures of FeMn/Ni80Fe 20/FeGaB/PZN-PT. Through competition between E-field induced uniaxial anisotropy and unidirectional anisotropy, large E-field induced exchange bias field shift up to Δ Hex = 42Oe and near 180° deterministic magnetization switching were achieved, which would pave a new way for magnetoelectric random access memories and other memory technologies. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chard K.,Argonne National Laboratory | Bubendorfer K.,Victoria University of Wellington
IEEE Transactions on Parallel and Distributed Systems | Year: 2013

Utility computing models have long been the focus of academic research, and with the recent success of commercial cloud providers, computation and storage is finally being realized as the fifth utility. Computational economies are often proposed as an efficient means of resource allocation, however adoption has been limited due to a lack of performance and high overheads. In this paper, we address the performance limitations of existing economic allocation models by defining strategies to reduce the failure and reallocation rate, increase occupancy and thereby increase the obtainable utilization of the system. The high-performance resource utilization strategies presented can be used by market participants without requiring dramatic changes to the allocation protocol. The strategies considered include overbooking, advanced reservation, just-in-time bidding, and using substitute providers for service delivery. The proposed strategies have been implemented in a distributed metascheduler and evaluated with respect to Grid and cloud deployments. Several diverse synthetic workloads have been used to quantity both the performance benefits and economic implications of these strategies. © 2012 IEEE.

Jun Y.-S.,Washington University in St. Louis | Lee B.,Argonne National Laboratory | Waychunas G.A.,Lawrence Berkeley National Laboratory
Environmental Science and Technology | Year: 2010

The early development of nanoparticles at mineral-water interfaces exerts crucial influences on the sequestration and transport of aqueous toxic species originating from both natural and anthropogenic sources. Homogeneous and heterogeneous nucleation often occur simultaneously, making it difficult to sort out whether toxic species are transported as free species, sorbed on nanoparticle surfaces, or trapped between aggregated nanoparticles. Here, using a newly developed X-ray scattering setup, we show how homogeneous nucleation and growth can be quantitatively separated from heterogeneous processes under aqueous conditions in real-time. Under conditions found in acid-mine-drainage (at pH 3.6 and [Fe3+] = 10-4 M), heterogeneous nucleation of iron oxide nanoparticles on quartz dominated homogeneous nucleation by a factor of 192 (by particle volume). The smallest heterogeneously formed nanoparticles had radii of 1.7 ± 0.5 nm, significantly smaller than the size estimated using classical nucleation theory (CNT). Based on the data, the dominant nucleation and growth mechanisms of iron oxide nanoparticles depending on ionic strength were presented. Our findings have implications for the formation and transport of nanoparticles, and thus toxins, in both environmental and biological systems. © 2010 American Chemical Society.

Pepin C.,CEA Saclay Nuclear Research Center | Pepin C.,Federal University of Rio Grande do Norte | Norman M.R.,Argonne National Laboratory | Burdin S.,University of Bordeaux 1 | Ferraz A.,Federal University of Rio Grande do Norte
Physical Review Letters | Year: 2011

We argue that near a Kondo breakdown critical point, a spin liquid with spatial modulations can form. Unlike its uniform counterpart, we find that this occurs via a second order phase transition. The amount of entropy quenched when ordering is of the same magnitude as for an antiferromagnet. Moreover, the two states are competitive, and at low temperatures are separated by a first order phase transition. The modulated spin liquid we find breaks Z4 symmetry, as recently seen in the hidden order phase of URu2Si 2. Based on this, we suggest that the modulated spin liquid is a viable candidate for this unique phase of matter. © 2011 American Physical Society.

Yang C.,Tufts University | Manocchi A.K.,Tufts University | Lee B.,Argonne National Laboratory | Yi H.,Tufts University
Journal of Materials Chemistry | Year: 2011

We demonstrate and thoroughly examine tobacco mosaic virus (TMV)-templated palladium (Pd) nanocatalysts for the ligand-free Suzuki coupling reaction under mild conditions. The surface-assembled TMV templates allow for facile catalyst synthesis under mild aqueous conditions that leads to high Pd surface loading and stability. Further, the chip-based format enables simple catalyst separation and reuse as well as facile product recovery. Reaction condition studies demonstrated that the solvent ratio played an important role in the selectivity of the Suzuki reaction, and that a higher water/acetonitrile ratio significantly facilitated the cross-coupling pathway. We envision that our viral template-based bottom-up assembly approach can be readily extended to other biotemplates, metal catalysts and organic reaction systems. © The Royal Society of Chemistry.

Gandolfi S.,Los Alamos National Laboratory | Carlson J.,Los Alamos National Laboratory | Pieper S.C.,Argonne National Laboratory
Physical Review Letters | Year: 2011

The properties of inhomogeneous neutron matter are crucial to the physics of neutron-rich nuclei and the crust of neutron stars. Advances in computational techniques now allow us to accurately determine the binding energies and densities of many neutrons interacting via realistic microscopic interactions and confined in external fields. We perform calculations for different external fields and across several shells to place important constraints on inhomogeneous neutron matter, and hence the large isospin limit of the nuclear energy density functionals that are used to predict properties of heavy nuclei and neutron star crusts. We find important differences between microscopic calculations and current density functionals; in particular, the isovector gradient terms are significantly more repulsive than in traditional models, and the spin-orbit and pairing forces are comparatively weaker. © 2011 The American Physical Society.

Nie M.,University of Rhode Island | Chalasani D.,University of Rhode Island | Abraham D.P.,Argonne National Laboratory | Chen Y.,University of Rhode Island | And 2 more authors.
Journal of Physical Chemistry C | Year: 2013

The surface reactions of electrolytes with the graphitic anode of lithium ion batteries have been investigated. The investigation utilizes two novel techniques, which are enabled by the use of binder-free graphite anodes. The first method, transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy, allows straightforward analysis of the graphite solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance (NMR) spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Cells were cycled with LiPF6 and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and EC/EMC blends. This unique combination of techniques establishes that for EC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick after the first full lithiation cycle, and predominantly contains lithium ethylene dicarbonate (LEDC) and LiF. In cells containing EMC/LiPF6 electrolytes, the graphite SEI is nonuniform, ∼10-20 nm thick, and contains lithium ethyl carbonate (LEC), lithium methyl carbonate (LMC), and LiF. In cells containing EC/EMC/LiPF6 electrolytes, the graphite SEI is ∼50 nm thick, and predominantly contains LEDC, LMC, and LiF. © 2013 American Chemical Society.

Schmieder R.,San Diego State University | Lim Y.W.,San Diego State University | Edwards R.,San Diego State University | Edwards R.,Argonne National Laboratory
Bioinformatics | Year: 2012

Here, we present riboPicker, a robust framework for the rapid, automated identification and removal of ribosomal RNA sequences from metatranscriptomic datasets. The results can be exported for subsequent analysis, and the databases used for the web-based version are updated on a regular basis. riboPicker categorizes rRNA-like sequences and provides graphical visualizations and tabular outputs of ribosomal coverage, alignment results and taxonomic classifications. © The Author(s) 2011. Published by Oxford University Press. All rights reserved.

Young R.D.,Argonne National Laboratory | Thomas A.W.,University of Adelaide
Nuclear Physics A | Year: 2010

It has proven a significant challenge to experiment and phenomenology to extract a precise values of the nucleon sigma terms. This difficulty opens the window for lattice QCD simulations to lead the field in resolving this aspect of nucleon structure. Here we report on recent advances in the extraction of nucleon sigma terms in lattice QCD. In particular, the strangeness component is now being resolved to a precision that far surpasses best phenomenological estimates. © 2010 Elsevier B.V.

Hla S.W.,Argonne National Laboratory | Hla S.W.,Ohio University
Reports on Progress in Physics | Year: 2014

Atomic manipulation using a scanning tunneling microscope (STM) tip enables the construction of quantum structures on an atom-by-atom basis, as well as the investigation of the electronic and dynamical properties of individual atoms on a one-atom-at-a-time basis. An STM is not only an instrument that is used to 'see' individual atoms by means of imaging, but is also a tool that is used to 'touch' and 'take' the atoms, or to 'hear' their movements. Therefore, the STM can be considered as the 'eyes', 'hands' and 'ears' of the scientists, connecting our macroscopic world to the exciting atomic world. In this article, various STM atom manipulation schemes and their example applications are described. The future directions of atomic level assembly on surfaces using scanning probe tips are also discussed. © 2014 IOP Publishing Ltd.

Esbensen H.,Argonne National Laboratory | Stefanini A.M.,National Institute of Nuclear Physics, Italy
Physical Review C - Nuclear Physics | Year: 2014

Fusion data for 48Ca+90,96Zr are analyzed by coupled-channels calculations that are based on the M3Y+repulsion, double-folding potential. By applying a previously determined nuclear density of Ca48, the neutron densities of the zirconium isotopes are adjusted to optimize the fit to the fusion data, whereas the proton densities are determined by electron-scattering experiments. It is shown that the fusion data can be explained fairly well by including couplings to one- and two-phonon excitations of the reacting nuclei and to one- and two-nucleon transfer reactions but there is also some sensitivity to multiphonon excitations. The neutron skin thicknesses extracted for the two zirconium isotopes are consistent with antiproton measurements. The densities of the zirconium isotopes are used together with the previously determined nuclear density of Ca40 to calculate the M3Y+repulsion potentials and predict the fusion cross sections of 40Ca+90,96Zr. The predicted cross sections for 40Ca+90Zr are in reasonable agreement with the data when the influence of multiphonon excitations and a modest transfer is considered. The prediction of the 40Ca+96Zr fusion cross section, on the other hand, is poor and underpredicts the data by 30% to 40%. Although couplings to transfer channels with positive Q values were expected to play an important role, they are not able to explain the data, primarily because the predicted Coulomb barrier is about 1.5 MeV too high. Possible reasons for this failure are discussed. © 2014 American Physical Society.

Heald S.M.,Argonne National Laboratory
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

Recently, beamline 20-BM has been upgraded with new optics. A large bent cylindrical focusing mirror has been installed to provide an intense focused beam. It is designed to operate over the energy range 2.730 keV, and features a novel Al 2O 3/Pt coating. When operated near 2.6 mrad, the Pt coating provides good reflectivity up to 30 keV. The Al 2O 3 overlayer minimizes the influence of the Pt M and L edges. The second upgrade that is in progress is the development of longer KB mirrors. A prototype bender has achieved a focus of about 2.5 μm using a 300 mm long mirror. Analysis of the focal spot indicates that the size is dominated by the slope errors of the mirror, and can be further reduced if these are minimized by better mirrors or by using differential coating methods. © 2011 Elsevier B.V. All rights reserved.

Oh S.-M.,Hanyang University | Oh S.-W.,Hanyang University | Yoon C.-S.,Hanyang University | Scrosati B.,University of Rome La Sapienza | And 2 more authors.
Advanced Functional Materials | Year: 2010

A cathode material of an electrically conducting carbon-LiMnPO4 nanocomposite is synthesized by ultrasonic spray pyrolysis followed by ball milling. The effect of the carbon content on the physicochemical and electrochemical properties of this material is extensively studied. A LiMnPO4 electrode with 30 wt% acetylene black (AB) carbon exhibits an excellent rate capability and good cycle life in cell tests at 55 and 25 ° C. This electrode delivers a discharge capacity of 158 mAh g -1 at 1/20 C, 126 mAh g-1 at 1 C, and 107 mAh g -1 at 2 C rate, which are the highest capacities reported so far for this type of electrode. Transmission electron microscopy and Mn dissolution results confi rm that the carbon particles surrounding the LiMnPO4 protect the electrode from HF attack, and thus lead to a reduction of the Mn dissolution that usually occurs with this electrode. The improved electrochemical properties of the C-LiMnPO4 electrode are also verifi ed by electrochemical impedance spectroscopy. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Jiang C.,University of Chicago | Lee J.-S.,University of Chicago | Talapin D.V.,University of Chicago | Talapin D.V.,Argonne National Laboratory
Journal of the American Chemical Society | Year: 2012

We report a new platform for design of soluble precursors for CuInSe 2 (CIS), Cu(In 1-xGa x)Se 2 (CIGS), and Cu 2ZnSn(S,Se) 4 (CZTS) phases for thin-film potovoltaics. To form these complex phases, we used colloidal nanocrystals (NCs) with metal chalcogenide complexes (MCCs) as surface ligands. The MCC ligands both provided colloidal stability and represented essential components of target phase. To obtain soluble precursors for CuInSe 2, we used Cu 2-xSe NCs capped with In 2Se 4 2- MCC surface ligands or CuInSe 2 NCs capped with {In 2Cu 2Se 4S 3} 3- MCCs. A mixture of Cu 2-xSe and ZnS NCs, both capped with Sn 2S 6 4- or Sn 2Se 6 4- ligands was used for solution deposition of CZTS films. Upon thermal annealing, the inorganic ligands reacted with NC cores forming well-crystallized pure ternary and quaternary phases. Solution-processed CIS and CZTS films featured large grain size and high phase purity, confirming the prospects of this approach for practical applications. © 2012 American Chemical Society.

Kanatzidis M.G.,Northwestern University | Kanatzidis M.G.,Argonne National Laboratory
Chemistry of Materials | Year: 2010

This review discusses recent developments and current research in bulk thermoelectric materials in which nanostructuring is a key aspect affecting thermoelectric performance. Systems based on PbTe, AgPbmSbTe 2+m, NaPbMSbTe2+m Bi2Te3 and Si are given particular emphasis. To date the dramatic enhancements in figure of merit in bulk nanostructured materials come from very large reductions in lattice thermal conductivity rather than improvement in power factors. A discussion of future possible strategies is aimed at enhancing the thermoelectric figure of merit of these materials. © 2009 American Chemical Society.

Boughezal R.,Argonne National Laboratory | Gehrmann-De Ridder A.,ETH Zurich | Ritzmann M.,ETH Zurich
Journal of High Energy Physics | Year: 2011

The antenna subtraction formalism allows to calculate QCD corrections to jet observables. Within this formalism, the subtraction terms are constructed using antenna functions describing all unresolved radiation between a pair of hard radiator partons. In this paper, we focus on the subtraction terms for double real radiation contributions to jet observables in hadron-hadron collisions evaluated at NNLO. An essential ingredient to these subtraction terms are the four-parton antenna functions with both radiators in the initial state. We outline the construction of the double real subtraction terms, classify all relevant antenna functions and describe their integration over the relevant antenna phase space. For the initial-initial antenna functions with two quark flavours, we derive the phase space master integrals and obtain the integrated antennae. © SISSA 2011.

Arrington J.,Argonne National Laboratory
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

In a recent paper, Hagelstein and Pascalutsa [F. Hagelstein and V. Pascalutsa, Phys. Rev. A 91, 040502 (2015)PLRAAN1050-294710.1103/PhysRevA.91.040502] examine the error associated with an expansion of proton structure corrections to the Lamb shift in terms of moments of the charge distribution. They propose a small modification to a conventional parametrization of the proton's charge form factor and show that this can resolve the proton radius puzzle. However, while the size of the bump they add to the form factor is small, it is large compared to the total proton structure effects in the initial parametrization, yielding a final form factor that is unphysical. Reducing their modification to the point where the resulting form factor is physical does not allow for a resolution of the radius puzzle. © 2016 American Physical Society.

Holder G.P.,McGill University | Nollett K.M.,Argonne National Laboratory | Van Engelen A.,McGill University
Astrophysical Journal | Year: 2010

The fraction of matter that is in the form of baryons or dark matter could have spatial fluctuations in the form of baryon-dark matter isocurvature fluctuations. We use big bang nucleosynthesis calculations compared with observed light-element abundances as well as galaxy cluster gas fractions to constrain cosmological variations in the baryon fraction. Light-element abundances constrain spatial variations to be less than 26%-27%, while a sample of "relaxed" galaxy clusters shows spatial variations in gas fractions less than 8%. Larger spatial variations could cause differential screening of the primary cosmic microwave background (CMB) anisotropies, leading to asymmetries in the fluctuations, and ease some tension with the halo-star 7Li abundance. We also show that fluctuations within our allowed bounds can lead to "B-mode" CMB polarization anisotropies at a non-negligible level. © 2010. The American Astronomical Society. All rights reserved.

Rahmani A.,Los Alamos National Laboratory | Muniz R.A.,Los Alamos National Laboratory | Muniz R.A.,Federal University of Rio Grande do Norte | Martin I.,Los Alamos National Laboratory | Martin I.,Argonne National Laboratory
Physical Review X | Year: 2014

Strongly correlated fractional quantum Hall liquids support fractional excitations, which can be understood in terms of adiabatic flux insertion arguments. A second route to fractionalization is through the coupling of weakly interacting electrons to topologically nontrivial backgrounds such as in polyacetylene. Here, we demonstrate that electronic fractionalization combining features of both these mechanisms occurs in noncoplanar itinerant magnetic systems, where integer quantum Hall physics arises from the coupling of electrons to the magnetic background. The topologically stable magnetic vortices in such systems carry fractional (in general, irrational) electronic quantum numbers and exhibit Abelian anyonic statistics. We analyze the properties of these topological defects by mapping the distortions of the magnetic texture onto effective non-Abelian vector potentials. We support our analytical results with extensive numerical calculations.

Shade A.,Michigan State University | Gilbert J.A.,Argonne National Laboratory | Gilbert J.A.,University of Chicago | Gilbert J.A.,National Oceanic and Atmospheric Administration | Gilbert J.A.,Zhejiang University
Trends in Microbiology | Year: 2015

Recently, conditionally rare taxa (CRTs) - those taxa that are typically in very low abundance but occasionally achieve prevalence - were shown to contribute to patterns of microbial diversity because their collective dynamics explained a large proportion of temporal variability in microbial community structure. Here the benefits and challenges of characterizing the presence and interpreting the role of CRTs are further explored, along with questions about CRT ecology. We also introduce a conceptual model for thinking about microbial taxa as dynamic components along the dimensions of occurrence and abundance. Accounting for CRTs in interpretations of microbial ecological dynamics is essential if we are to understand community stability and ecoevolutionary interactions. © 2015 Elsevier Ltd.

Ungaro C.,University of Virginia | Gray S.K.,Argonne National Laboratory | Gupta M.C.,University of Virginia
Optics Express | Year: 2015

This paper presents results on a highly efficient experimental solar thermophotovoltaic (STPV) system using simulated solar energy. An overall power conversion efficiency of 6.2% was recorded under solar simulation. This was matched with a thermodynamic model, and the losses within the system, as well as a path forward to mitigate these losses, have been investigated. The system consists of a planar, tungsten absorbing/emitting structure with an anti-reflection layer coated laser-microtextured absorbing surface and single-layer dielectric coated emitting surface. A GaSb PV cell was used to capture the emitted radiation and convert it into electrical energy. This simple structure is both easy to fabricate and temperature stable, and contains no moving parts or heat exchange fluids. © 2015 Optical Society of America.

Rest J.,Argonne National Laboratory
Journal of Nuclear Materials | Year: 2010

A multi-atom gas-bubble nucleation mechanism in uranium-alloy nuclear fuel operating in the high-temperature equilibrium gamma phase is proposed based on interpretation of measured intragranular bubble-size distribution data. This model is contrasted with the conventional two-atom nucleation mechanism within the context of a mechanistic calculation of the fission-gas bubble-size distribution. The results of the analysis enable the calculation of safety margins for unrestrained fuel swelling. These safety margins contain an uncertainty primarily tied to uncertainties in the values of the volume and Xe diffusion coefficients. © 2010 Elsevier B.V. All rights reserved.

Laboratory studies show that introduction of fresh and easily decomposable organic carbon (OC) into soil-water systems can stimulate the decomposition of soil OC (SOC) via priming effects in temperate forests, shrublands, grasslands, and agro-ecosystems. However, priming effects are still not well understood in the field setting for temperate ecosystems and virtually nothing is known about priming effects (e.g., existence, frequency, and magnitude) in boreal ecosystems. In this study, a coupled dissolved OC (DOC) transport and microbial biomass dynamics model was developed to simultaneously simulate co-occurring hydrological, physical, and biological processes and their interactions in soil pore-water systems. The developed model was then used to examine the importance of priming effects in two black spruce forest soils, with and without underlying permafrost. Our simulations showed that priming effects were strongly controlled by the frequency and intensity of DOC input, with greater priming effects associated with greater DOC inputs. Sensitivity analyses indicated that priming effects were most sensitive to variations in the quality of SOC, followed by variations in microbial biomass dynamics (i.e., microbial death and maintenance respiration), highlighting the urgent need to better discern these key parameters in future experiments and to consider these dynamics in existing ecosystem models. Water movement carries DOC to deep soil layers that have high SOC stocks in boreal soils. Thus, greater priming effects were predicted for the site with favorable water movement than for the site with limited water flow, suggesting that priming effects might be accelerated for sites where permafrost degradation leads to the formation of dry thermokarst.

Chang L.,University of Adelaide | Mezrag C.,CEA Saclay Nuclear Research Center | Moutarde H.,CEA Saclay Nuclear Research Center | Roberts C.D.,Argonne National Laboratory | And 2 more authors.
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

The impulse-approximation expression used hitherto to define the pion's valence-quark distribution function is flawed because it omits contributions from the gluons which bind quarks into the pion. A corrected leading-order expression produces the model-independent result that quarks dressed via the rainbow-ladder truncation, or any practical analogue, carry all the pion's light-front momentum at a characteristic hadronic scale. Corrections to the leading contribution may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea-quarks. Working with available empirical information, we use an algebraic model to express the principal impact of both classes of corrections. This enables a realistic comparison with experiment that allows us to highlight the basic features of the pion's measurable valence-quark distribution, qπ(x); namely, at a characteristic hadronic scale, qπ(x) ~ (1 -x)2 for x ≳ 0.85; and the valence-quarks carry approximately two-thirds of the pion's light-front momentum. © 2014 Elsevier B.V.

Norman M.R.,Argonne National Laboratory
Reports on Progress in Physics | Year: 2016

Since the announcement in 2011 of the Materials Genome Initiative by the Obama administration, much attention has been given to the subject of materials design to accelerate the discovery of new materials that could have technological implications. Although having its biggest impact for more applied materials like batteries, there is increasing interest in applying these ideas to predict new superconductors. This is obviously a challenge, given that superconductivity is a many body phenomenon, with whole classes of known superconductors lacking a quantitative theory. Given this caveat, various efforts to formulate materials design principles for superconductors are reviewed here, with a focus on surveying the periodic table in an attempt to identify cuprate analogues. © 2016 IOP Publishing Ltd.

You F.,Carnegie Mellon University | You F.,Argonne National Laboratory | Grossmann I.E.,Carnegie Mellon University
AIChE Journal | Year: 2011

We address in this article the mid-term planning of chemical complexes with integration of stochastic inventory management under supply and demand uncertainty. By using the guaranteed service approach to model time delays in the flows inside the network, we capture the stochastic nature of the supply and demand variations, and develop an equivalent deterministic optimization model to minimize the production, feedstock purchase, cycle inventory, and safety stock costs. The model determines the optimal purchases of the feedstocks, production levels of the processes, sales of final products, and safety stock levels of all the chemicals. We formulate the model as a mixed-integer nonlinear program with a nonconvex objective function and nonconvex constraints. To solve the global optimization problem with modest computational times, we exploit some model properties and develop a tailored branch-and-refine algorithm based on successive piecewise linear approximation. Five industrial-scale examples with up to 38 processes and 28 chemicals are presented to illustrate the application of the model and the performance of the proposed algorithm. Copyright © 2010 American Institute of Chemical Engineers (AIChE).

Complexity, wide size ranges, and anisotropy are attributes that can describe porous microstructures of thermally sprayed deposits, which present especially difficult challenges for characterization techniques. A number of different methods have been utilized and found to be useful while having significant limitations. Therefore, scientists and engineers need to understand the advantages, limitations, and disadvantages of each technique. This very short review attempts to present a wide range of characterization tools-from frequently employed optical and scanning electron imaging techniques, through intrusion porosimetry, to lesser-used x-ray and neutron imaging and scattering techniques. It will be shown that no technique in itself is sufficient and that a properly selected combination of techniques is necessary to get a sufficiently complex characterization method. A really powerful and capable characterization protocol may need to combine fast and accessible ("in-house") tools with sparingly applied advanced scattering and imaging techniques. Such a combination of techniques can then be utilized to research the processing-microstructure-properties relationships as well as to provide sufficient data for development of successful models. © 2009 ASM International.

Sun Y.,Argonne National Laboratory
Advanced Functional Materials | Year: 2010

Growth of anisotropic metal nanostructures with well-defined shapes on large-area semiconductor substrates represents a challenge to synthesize hybrid materials with complex functionalities. This Feature Article highlights the approach recently developed in our group for growing nanoplates made of noble metals (e.g., Ag, Pd, Au/Ag alloy) on semiconductor wafers (e.g., GaAs and Si), which are widely used in the semiconductor industry. In the typical syntheses, only the semiconductor wafers and pure aqueous solutions of metal precursors are involved in the reaction. The absence of surfactant molecules, organic solvents, catalysts, etc. in the syntheses makes this strategy suitable for the formation of metal/semiconductor hybrid materials with clean metal/semiconductor interfaces. The mechanism for the selective growth of metal nanoplates on semiconductor substrates is extensively discussed. The as-grown metal nanoplates protrude out of the substrates to expose most of their surface areas to the surrounding environment, leading to be favorable for some applications, such as catalysis and surface-enhanced Raman scattering. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Jasper A.W.,Sandia National Laboratories | Miller J.A.,Argonne National Laboratory
Combustion and Flame | Year: 2014

Lennard-Jones parameters for use in combustion modeling, as transport parameters and in pressure-dependent rate-coefficient calculations as collision rate parameters, are calculated from accurate full-dimensional intermolecular potentials. Several first-principles theoretical methods are considered. In the simplest approach, the intermolecular potential is spherically averaged and used to determine Lennard-Jones parameters. This method works well for small species, but it is not suitable for larger species due to unphysical averaging over the repulsive wall. Another method considered is based on full-dimensional trajectory calculations of binary collisions. This method is found to be very accurate, predicting Lennard-Jones collision rates within ~10% of those obtained via tabulated (experimentally-based) Lennard-Jones parameters. Finally, a computationally efficient method is presented based on one-dimensional minimizations averaged over the colliding partners' relative orientations. This method is shown to be both accurate and efficient. The good accuracy of the latter two approaches is shown to be a result of their explicit treatment of anisotropy. The effects of finite temperature vibrations and multiple conformers are quantified and are shown to be small. The choice of potential energy surface has a somewhat larger effect, and strategies based both on efficient semiempirical methods and on first-principles direct dynamics are considered. Overall, 75 systems are considered, including seven baths, targets as large as heptane, both molecules and radicals, and both hydrocarbons and oxygenates. © 2013 The Combustion Institute.

Hsu Y.-K.,National Dong Hwa University | Yu C.-H.,National Dong Hwa University | Chen Y.-C.,National Taiwan University | Lin Y.-G.,Argonne National Laboratory
Journal of Power Sources | Year: 2013

The direct-grown and coral-like p-type Cu2O nanostructural film on copper foil is successfully fabricated via a facile and cost-effective template route through transformation of Cu(OH)2 nanowires for photoelectrochemical (PEC) hydrogen generation. The dense Cu2O nanocoral electrode thermally transfers from Cu(OH)2 nanowires by means of the dehydrate and deoxidization processes under nitrogen atmosphere. Mott-Schottky plot shows the flat-band potential of the coral-like Cu 2O nanostructural film to be -0.1 V and a hole concentration of 8.2 × 1019 cm-3. Direct band gap of 2.08 eV in Cu 2O film is determined via incident photon-to-electron conversion efficiency measurement. Significantly, this Cu2O nanocoral photocathode exhibits remarkable photocurrent of -1.3 mA cm-2 at a potential of -0.6 V vs Ag/AgCl, corresponding to the solar conversion efficiency of 1.47%. These results demonstrate the great potential of Cu2O nanocoral film in solar hydrogen applications. © 2013 Elsevier B.V. All rights reserved.

Rowland C.E.,Northwestern University | Schaller R.D.,Northwestern University | Schaller R.D.,Argonne National Laboratory
Journal of Physical Chemistry C | Year: 2013

The tens-of-percent photoluminescence (PL) quantum yields routinely obtained for colloidally prepared CdSe semiconductor nanocrystals (NCs) decrease substantially with temperature elevation. While such PL efficiency loss has direct consequences for applications ranging from light-emitting diodes and lasers to photovoltaics under solar concentration, the origin of this loss is currently not established, hindering synthetic efforts to design materials with robust performance. Here, for the first time, we utilize transient absorption and ultrafast PL in addition to static PL and time-correlated single photon counting, to characterize CdSe core-only and CdSe/ZnS core/shell NCs up to temperatures as high as 800 K. For multiple particle sizes, loss of PL efficiency as a function of temperature elevation is more severe and less reversible for core-only NCs than for core/shell NCs. Ultrafast measurements performed at elevated sample temperatures indicate that thermally activated trapping of individual carriers dominates the nonradiative loss of excitons. Through a combination of spectroscopic techniques, we identify the primary carrier loss process as hole trapping in particular. These findings support the notion that extrinsic trapping effects out-compete intrinsic exciton deactivation at high temperature and point to realizable improvements in thermally robust optoelectronic performance. © 2013 American Chemical Society.

Kim A.M.,Northwestern University | Vogt S.,Argonne National Laboratory | O'Halloran T.V.,Northwestern University | Woodruff T.K.,Northwestern University
Nature Chemical Biology | Year: 2010

Cellular metal ion fluxes are known in alkali and alkaline earth metals but are not well documented in transition metals. Here we describe major changes in the zinc physiology of the mammalian oocyte as it matures and initiates embryonic development. Single-cell elemental analysis of mouse oocytes by synchrotron-based X-ray fluorescence microscopy (XFM) revealed a 50% increase in total zinc content within the 12ĝ€"14-h period of meiotic maturation. Perturbation of zinc homeostasis with a cell-permeable small-molecule chelator blocked meiotic progression past telophase I. Zinc supplementation rescued this phenotype when administered before this meiotic block. However, after telophase arrest, zinc triggered parthenogenesis, suggesting that exit from this meiotic step is tightly regulated by the availability of a zinc-dependent signal. These results implicate the zinc bolus acquired during meiotic maturation as an important part of the maternal legacy to the embryo. © 2010 Nature America, Inc. All rights reserved.

Chapman K.W.,Argonne National Laboratory
MRS Bulletin | Year: 2016

Our energy needs drive widespread materials research. Advances in materials characterization are critical to this research effort. Using new characterization tools that allow us to probe the atomic structure of energy materials in situ as they operate, we can identify how their structure is linked to their functional properties and performance. These fundamental insights serve as a roadmap to enhance performance in the next generation of advanced materials. In the last decade, developments in synchrotron instrumentation have made the pair distribution function (PDF) method and operando X-ray studies more readily accessible tools capable of providing valuable insights into complex materials systems. Here, the emergence of the PDF method as a versatile structure characterization tool and the further enhancement of this method through developments in operando capabilities and multivariate data analytics are described. These advances in materials characterization are demonstrated by several highlighted studies focused on energy storage in batteries. © 2016 Materials Research Society.

Nie M.,University of Rhode Island | Abraham D.P.,Argonne National Laboratory | Chen Y.,University of Rhode Island | Bose A.,University of Rhode Island | Lucht B.L.,University of Rhode Island
Journal of Physical Chemistry C | Year: 2013

The surface reactions of electrolytes with a silicon anode in lithium ion cells have been investigated. The investigation utilizes two novel techniques that are enabled by the use of binder-free silicon (BF-Si) nanoparticle anodes. The first method, transmission electron microscopy with energy dispersive X-ray spectroscopy, allows straightforward analysis of the BF-Si solid electrolyte interphase (SEI). The second method utilizes multi-nuclear magnetic resonance spectroscopy of D2O extracts from the cycled anodes. The TEM and NMR data are complemented by XPS and FTIR data, which are routinely used for SEI studies. Coin cells (BF-Si/Li) were cycled in electrolytes containing LiPF 6 salt and ethylene carbonate or fluoroethylene carbonate solvent. Capacity retention was significantly better for cells cycled with LiPF 6/FEC electrolyte than for cells cycled with LiPF6/EC electrolyte. Our unique combination of techniques establishes that for LiPF 6/EC electrolyte the BF-Si SEI continuously grows during the first 20 cycles and the SEI becomes integrated with the BF-Si nanoparticles. The SEI predominantly contains lithium ethylene dicarbonate, LiF, and Li xSiOy. BF-Si electrodes cycled with LiPF6/FEC electrolyte have a different behavior; the BF-Si nanoparticles remain relatively distinct from the SEI. The SEI predominantly contains LiF, Li xSiOy, and an insoluble polymeric species. © 2013 American Chemical Society.

Lopez-Bezanilla A.,Argonne National Laboratory
Journal of Physical Chemistry C | Year: 2014

A first-principles investigation of the electronic and quantum transport properties of double-walled carbon nanotubes doped with nitrogen and boron atoms is presented. Concentric nanotube sidewalls separated by the typical graphitic van der Waals bond distance are found to strongly interact upon incorporation of doping atoms in the hexagonal networks. The local perturbation caused by the doping atoms extends over both shells due to a hybridization of their electronic states, yielding a reduction of the backscattering efficiency as compared with two independent single-walled nanotubes. A multiscale approach for the study of transport properties of micrometer-long double-walled carbon nanotubes demonstrates that transitions from the ballistic to the localized regime can occur depending on the type of doping and the energy of the charge carrier. These results shed light on the quantum mechanism by which B and N doping represent an efficient method to create mobility gaps in metallic concentric carbon nanotubes. © 2014 American Chemical Society.

Son S.-K.,German Electron Synchrotron | Young L.,Argonne National Laboratory | Santra R.,German Electron Synchrotron | Santra R.,University of Hamburg
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

X-ray free-electron lasers (FELs) are promising tools for structural determination of macromolecules via coherent x-ray scattering. During ultrashort and ultraintense x-ray pulses with an atomic-scale wavelength, samples are subject to radiation damage and possibly become highly ionized, which may influence the quality of x-ray scattering patterns. We develop a toolkit to treat detailed ionization, relaxation, and scattering dynamics for an atom within a consistent theoretical framework. The coherent x-ray scattering problem including radiation damage is investigated as a function of x-ray FEL parameters such as pulse length, fluence, and photon energy. We find that the x-ray scattering intensity saturates at a fluence of ∼107 photon/Å2 per pulse but can be maximized by using a pulse duration much shorter than the time scales involved in the relaxation of the inner-shell vacancy states created. Under these conditions, both inner-shell electrons in a carbon atom are removed, and the resulting hollow atom gives rise to a scattering pattern with little loss of quality for a spatial resolution >1 Å. Our numerical results predict that in order to scatter from a carbon atom 0.1 photon per x-ray pulse, within a spatial resolution of 1.7 Å, a fluence of 1×107 photons/Å2 per pulse is required at a pulse length of 1 fs and a photon energy of 12 keV. By using a pulse length of a few hundred attoseconds, one can suppress even secondary ionization processes in extended systems. The present results suggest that high-brightness attosecond x-ray FELs would be ideal for single-shot imaging of individual macromolecules. © 2011 American Physical Society.

Lopez-Bezanilla A.,Argonne National Laboratory
Journal of Physical Chemistry C | Year: 2014

A numerical study of electronic transport properties of doped silicene is presented. By means of ab initio calculations, a self-consistent scattering potential is derived for boron, nitrogen, aluminum, and phosphorus substitutions in silicene, and the quantum-mechanical Landauer-Büttiker approach is used to evaluate the conductivities of doped silicene ribbons with various impurity concentrations. An individual defect introduces asymmetric electron-hole conductivities that depend on both the type of doping and the position of the foreign atom with respect to the edges. Quantum interference effects at zero temperature are modeled to show that randomly distributed defects over 1 μm long and realistically wide silicon nanoribbons widen the intrinsic electronic gap that arises from quantum confinement. Mobility gaps created at low doping rates may lead to greater efficiency in the design of new silicon-based devices, providing the ability for suitable control of silicon ribbons band gap. © 2014 American Chemical Society.

Gray S.K.,Argonne National Laboratory
Journal of Physical Chemistry C | Year: 2013

Plasmonic structures, or systems generally containing nanostructured metallic components allowing for the exploitation of surface plasmon resonances, continue to draw much experimental and theoretical interest. This is due to the ability of surface plasmons to capture, concentrate, and propagate optical energy. This Feature Article discusses the basic theoretical principles and computational modeling of such structures. A variety of illustrations are also given, including optical transmission by nanohole arrays in thin metal films, remote-grating generation of narrow band plasmons, the excitation of dark modes in bipyramidal nanoparticles, optical transparencies in nanoparticle-quantum dot systems, and the size dependence of surface plasmon resonances in the limit of very small particle sizes. © 2012 American Chemical Society.

Reimer P.E.,Argonne National Laboratory
Nuovo Cimento della Societa Italiana di Fisica C | Year: 2012

Measurements of parity violation in electron scattering have provided a wealth of information on the nucleon, the nucleus and the electroweak interaction. Many of these measurement have been at relatively low four-momentum exchange (Q). The upgrade of the CEBAF beam energy at Thomas Jefferson National Accelerator Facility (JLab) to a maximum of 12 GeV will expand the kinematics in which PVES measurements can be made to include significantly more of the deep inelastic scattering (DIS) region. To take advantage of this, a new spectrometer, named SoLID, has been proposed. Measurements in the DIS region will provide new information on a variety of topics, including charge symmetry violation, higher twist contributions to proton structure and electroweak coupling constants. To differentiate between these effects, measurements with the SoLID spectrometer will simultaneously cover a large kinematic range in both xBj and Q2. © Società Italiana di Fisica.

Morin A.,Harvard University | Urban J.,University of California at Berkeley | Adams P.D.,Lawrence Berkeley National Laboratory | Foster I.,Argonne National Laboratory | And 3 more authors.
Science | Year: 2012

Funders, publishers, and research institutions must act to ensure that research computer code is made widely available.

Sun Y.,Argonne National Laboratory
Journal of Physical Chemistry C | Year: 2010

Direct synthesis of Ag nanoplates on GaAs wafers has been developed in our group through a simple solution/ solid interfacial reaction (SSIR) strategy, in which aqueous solutions of pure AgNO3 react with the GaAs wafers at room temperature [J. Phys. Chem. C 2009, 113, 6061; 2008, 112, 8928; Chem. Mater. 2007, 19, 5845]. However, a number of questions are still not clear yet regarding the roles of different possible pathways for reducing Ag+ ions in the growth of Ag nanoplates. In this article, we try to answer these remaining questions by specifically designing experiments and extracting direct evidence from systematic characterizations of different samples. It is conclusive that growth of high-quality Ag nanoplates on GaAs wafers is ascribed to the good separation between nucleation and growth steps, which are driven by two different reduction pathways. At the nucleation step, fast reduction of Ag+ ions with a high concentration of surface electrons is crucial for the formation of Ag nuclei with multiple (111) twin planes parallel to each other, and remaining the environment of a high concentration of surface electrons for a period long enough is also important to develop the Ag nuclei into stable seeds. At the growth step, a hole injection process is mainly responsible for reduction of Ag+ ions to enlarge the stable seeds into Ag nanoplates with controlled sizes by tuning the growth time. The paralleled multiple (111) twin planes provide a crystalline confinement to guide the growth of the seeds into nanoplates. © 2010 American Chemical Society.

Weber F.,Argonne National Laboratory | Pintschovius L.,Karlsruhe Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

Superconductivity-induced changes in phonon lineshapes in niobium have been reinvestigated by high-resolution inelastic neutron scattering. We show that the changes go beyond a simple change in lifetime and frequency when the phonon frequency is close to the superconducting energy gap 2Δ. The observed lineshapes in elemental niobium are qualitatively similar to those found previously in borocarbide superconductors and agree very well with those predicted by the theory of Allen [Phys. Rev. B 56, 5552 (1997)]10.1103/PhysRevB. 56.5552. Our results indicate that the peculiar phonon lineshapes in the superconducting state predicted by the theory of Allen [Phys. Rev. B 56, 5552 (1997)]10.1103/PhysRevB.56.5552 are a general phenomenon and not restricted to a particular class of compounds. © 2010 The American Physical Society.

Narayan R.J.,North Carolina State University | Boehm R.D.,North Carolina State University | Sumant A.V.,Argonne National Laboratory
Materials Today | Year: 2011

Diamond has been considered for use in several medical applications due to its unique mechanical, chemical, optical, and biological properties. In this paper, methods for preparing synthetic diamond surfaces and particles are described. In addition, recent developments involving the use of diamond in prostheses, sensing, imaging, and drug delivery applications are reviewed. These developments suggest that diamond-containing structures will provide significant improvements in the diagnosis and treatment of medical conditions over the coming years. © 2011 Elsevier Ltd.

Zhang F.,U.S. National Institute of Standards and Technology | Zhang F.,Northern Illinois University | Ilavsky J.,Argonne National Laboratory
Polymer Reviews | Year: 2010

Ultra-small-angle X-ray scattering (USAXS) is capable of probing structural inhomogeneities in the size range of 1 to 1000 nm. Recent developments of X-ray sources and optics make USAXS increasingly relevant to polymer research. In this review, we examine the current technical state of USAXS instrumentation, and briefly introduce the method of data reduction and analysis. We emphasize USAXS's application in areas such as polymer nanocomposites, polymer gels and solutions, polymer blends, polymer micelles and microemulsions, and colloidal sciences. Finally, we predict more USAXS studies on polymeric systems, especially those with large-scale structures or hierarchical microstructures.

Sun Y.,Argonne National Laboratory
Journal of Physical Chemistry C | Year: 2010

A two-step approach has been developed to synthesize AgCl nanowires decorated with Au nanoparticles by using Ag nanowires as chemical templates. In the first step, the Ag nanowires are oxidized with FeCl3 followed by a simultaneous precipitation reaction between Ag+ and Cl- ions at room temperature, resulting in conversion of the Ag nanowires to AgCl nanowires as well as reduction of Fe3+ to Fe2+ ions. In the second step, the Fe2+ ions generated in the first step reduce Au precursors (e.g., NaAuCl4) to deposit Au nanoparticles on the surfaces of the AgCl nanowires, resulting in the formation of AgCl:Au composite nanowires. Because of strong surface plasmon resonance and chemical inertness of Au nanoparticles, the as-synthesized AgCl:Au nanowires exhibit enhanced absorption coefficient in the visible region and enhanced chemical stability to prevent them from degradation and aggregation. These unique properties enable the AgCl:Au nanowires to be used as a class of promising plasmonic photocatalysts driven by visible light. Preliminary results demonstrate these composite nanowires can efficiently decompose organics, such as methylene blue molecules, under illumination of white light. Copyright © 2010 American Chemical Society.

Schmieder R.,San Diego State University | Edwards R.,San Diego State University | Edwards R.,Argonne National Laboratory
PLoS ONE | Year: 2011

High-throughput sequencing technologies have strongly impacted microbiology, providing a rapid and cost-effective way of generating draft genomes and exploring microbial diversity. However, sequences obtained from impure nucleic acid preparations may contain DNA from sources other than the sample. Those sequence contaminations are a serious concern to the quality of the data used for downstream analysis, causing misassembly of sequence contigs and erroneous conclusions. Therefore, the removal of sequence contaminants is a necessary and required step for all sequencing projects. We developed DeconSeq, a robust framework for the rapid, automated identification and removal of sequence contamination in longer-read datasets (> 150 bp mean read length). DeconSeq is publicly available as standalone and web-based versions. The results can be exported for subsequent analysis, and the databases used for the web-based version are automatically updated on a regular basis. DeconSeq categorizes possible contamination sequences, eliminates redundant hits with higher similarity to non-contaminant genomes, and provides graphical visualizations of the alignment results and classifications. Using DeconSeq, we conducted an analysis of possible human DNA contamination in 202 previously published microbial and viral metagenomes and found possible contamination in 145 (72%) metagenomes with as high as 64% contaminating sequences. This new framework allows scientists to automatically detect and efficiently remove unwanted sequence contamination from their datasets while eliminating critical limitations of current methods. DeconSeq's web interface is simple and user-friendly. The standalone version allows offline analysis and integration into existing data processing pipelines. DeconSeq's results reveal whether the sequencing experiment has succeeded, whether the correct sample was sequenced, and whether the sample contains any sequence contamination from DNA preparation or host. In addition, the analysis of 202 metagenomes demonstrated significant contamination of the non-human associated metagenomes, suggesting that this method is appropriate for screening all metagenomes. DeconSeq is available at http://deconseq.sourceforge.net/. © 2011 Schmieder, Edwards.

Klahr B.M.,Michigan State University | Martinson A.B.F.,Argonne National Laboratory | Hamann T.W.,Michigan State University
Langmuir | Year: 2011

Atomic layer deposition was used to grow conformal thin films of hematite with controlled thickness on transparent conductive oxide substrates. The hematite films were incorporated as photoelectrodes in regenerative photoelectrochemical cells employing an aqueous [Fe(CN)6] 4- electrolyte. Steady state current density versus applied potential measurements under monochromatic and simulated solar illumination were used to probe the photoelectrochemical properties of the hematite electrodes as a function of film thickness. Combining the photoelectrochemical results with careful optical measurements allowed us to determine an optimal thickness for a hematite electrode of ∼20 nm. Mott-Schottky analysis of differential capacitance measurements indicated a depletion region of ∼17 nm. Thus, only charge carriers generated in the depletion region were found to contribute to the photocurrent. © 2010 American Chemical Society.

Chan H.,University of Illinois at Chicago | Demortiere A.,University Pierre and Marie Curie | Demortiere A.,Argonne National Laboratory | Vukovic L.,University of Illinois at Chicago | And 2 more authors.
ACS Nano | Year: 2012

We explore microscopic principles governing the self-assembly of colloidal octylamine-coated platinum nanocubes solvated in toluene. Our experiments show that regular nanocubes with an edge length of l RC = 5.5 nm form supercrystals with simple cubic packing, while slightly truncated nanocubes with an edge length of l TC = 4.7 nm tend to arrange in fcc packing. We model by averaged force fields and atomistic molecular dynamics simulations the coupling forces between these nanocrystals. Our detailed analysis shows that the fcc packing, which for cubes has a lower density than simple cubic packing, is favored by the truncated nanocubes due to their Coulombic coupling by multipolar electrostatic fields, formed during charge transfer between the octylamine ligands and the Pt cores. © 2012 American Chemical Society.

Aithal S.M.,Argonne National Laboratory
Applied Energy | Year: 2010

A fast, physics-based model to predict the temporal evolution of NOx in diesel engines is investigated using finite-rate chemical kinetics. The temporal variation of temperature required for the computation of the reaction rate constants is obtained from the solution of the energy equation. NOx formation is modeled by using a six step mechanism with eight species instead of the traditional equilibrium calculations based on the Zeldovich mechanism. Fuel combustion chemistry is modeled by a single-step global reaction. Effects of various stages of combustion on NOx formation is included using a phenomenological burning rate model. The effects of composition and temperature on the thermophysical properties of the working fluid are included in the computations. Comparison with measured single-cylinder engine-out NO shows good agreement with experimental data. The validated model is then used to demonstrate the impact of various operating parameters such as injection timing and EGR on engine-out NOx. This fast, robust model has potential applications in model-based real-time control strategies seeking to reduce feed gas NOx emissions from diesel engines. © 2010 Elsevier Ltd.

Micklitz T.,Free University of Berlin | Norman M.R.,Argonne National Laboratory
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We derive the spin Hamiltonian for the quantum spin liquid Na 4Ir3O8, and then estimate the direct and superexchange contributions between near neighbor iridium ions using a tight-binding parametrization of the electronic structure. We find a magnitude of the exchange interaction comparable to experiment for a reasonable value of the on-site Coulomb repulsion. For one of the two tight-binding parametrizations we have studied, the direct exchange term, which is isotropic, dominates the total exchange. This provides support for those theories proposed to describe this quantum spin liquid that assume an isotropic Heisenberg model. © 2010 The American Physical Society.

Talamo A.,Argonne National Laboratory
Nuclear Engineering and Design | Year: 2010

In high temperature reactors, burnable absorbers are utilized to manage the excess reactivity at the early stage of the fuel cycle. In this paper QUADRISO particles are proposed to manage the initial excess reactivity of high temperature reactors. The QUADRISO concept synergistically couples the decrease of the burnable poison with the decrease of the fissile materials at the fuel particle level. This mechanism is set up by introducing a burnable poison layer around the fuel kernel in ordinary TRISO particles or by mixing the burnable poison with any of the TRISO coated layers. At the beginning of life, the initial excess reactivity is small because some neutrons are absorbed in the burnable poison and they are prevented from entering the fuel kernel. At the end of life, when the absorber is almost depleted, more neutrons stream into the fuel kernel of QUADRISO particles causing fission reactions. The mechanism has been applied to a prismatic high temperature reactor with europium or erbium burnable absorbers, showing a significant reduction in the initial excess reactivity of the core.

Marsh G.E.,Argonne National Laboratory
International Journal of Astrobiology | Year: 2013

It has been argued that the limited set of proteins used by life as we know could not have arisen by the process of Darwinian selection from all possible proteins. This probabilistic argument has a number of implicit assumptions that may not be warranted. A variety of considerations are presented to show that the number of amino acid sequences that need to have been sampled during the evolution of proteins is far smaller than assumed by the argument. © 2012 Cambridge University Press.

Liu X.,University of Cambridge | Liu X.,Solar Energy Research Institute of Singapore | Coxon P.R.,University of Cambridge | Peters M.,Solar Energy Research Institute of Singapore | And 4 more authors.
Energy and Environmental Science | Year: 2014

Black silicon (BSi) represents a very active research area in renewable energy materials. The rise of BSi as a focus of study for its fundamental properties and potentially lucrative practical applications is shown by several recent results ranging from solar cells and light-emitting devices to antibacterial coatings and gas-sensors. In this paper, the common BSi fabrication techniques are first reviewed, including electrochemical HF etching, stain etching, metal-assisted chemical etching, reactive ion etching, laser irradiation and the molten salt Fray-Farthing-Chen-Cambridge (FFC-Cambridge) process. The utilization of BSi as an anti-reflection coating in solar cells is then critically examined and appraised, based upon strategies towards higher efficiency renewable solar energy modules. Methods of incorporating BSi in advanced solar cell architectures and the production of ultra-thin and flexible BSi wafers are also surveyed. Particular attention is given to routes leading to passivated BSi surfaces, which are essential for improving the electrical properties of any devices incorporating BSi, with a special focus on atomic layer deposition of Al2O3. Finally, three potential research directions worth exploring for practical solar cell applications are highlighted, namely, encapsulation effects, the development of micro-nano dual-scale BSi, and the incorporation of BSi into thin solar cells. It is intended that this paper will serve as a useful introduction to this novel material and its properties, and provide a general overview of recent progress in research currently being undertaken for renewable energy applications. © The Royal Society of Chemistry 2014.

Atesin A.C.,Northwestern University | Ray N.A.,Northwestern University | Stair P.C.,Northwestern University | Stair P.C.,Argonne National Laboratory | Marks T.J.,Northwestern University
Journal of the American Chemical Society | Year: 2012

Selective hydrogenolysis of cyclic and linear ether C-O bonds is accomplished by a tandem catalytic system consisting of lanthanide triflates and sinter-resistant supported palladium nanoparticles in an ionic liquid. The lanthanide triflates catalyze endothermic dehydroalkoxylation, while the palladium nanoparticles hydrogenate the resulting intermediate alkenols to afford saturated alkanols with high overall selectivity. The catalytic C-O hydrogenolysis is shown to have significant scope, and the C-O bond cleavage is turnover-limiting. © 2012 American Chemical Society.

Gao J.,Argonne National Laboratory | Zhang H.,University of California at Santa Barbara | Zhu H.X.,Massachusetts Institute of Technology
European Physical Journal C | Year: 2016

Recently, ATLAS and CMS collaborations reported an excess in the measurement of diphoton events, which can be explained by a new resonance with a mass around 750 GeV. In this work, we explored the possibility of identifying if the hypothetical new resonance is produced through gluon–gluon fusion or quark–antiquark annihilation, or tagging the beam. Three different observables for beam tagging, namely the rapidity and transverse-momentum distribution of the diphoton, and one tagged bottom-jet cross section, are proposed. Combining the information gained from these observables, a clear distinction of the production mechanism for the diphoton resonance is promising. © 2016, The Author(s).

Schmieder R.,San Diego State University | Edwards R.,San Diego State University | Edwards R.,Argonne National Laboratory
Future Microbiology | Year: 2012

The consequences of bacterial infections have been curtailed by the introduction of a wide range of antibiotics. However, infections continue to be a leading cause of mortality, in part due to the evolution and acquisition of antibiotic-resistance genes. Antibiotic misuse and overprescription have created a driving force influencing the selection of resistance. Despite the problem of antibiotic resistance in infectious bacteria, little is known about the diversity, distribution and origins of resistance genes, especially for the unculturable majority of environmental bacteria. Functional and sequence-based metagenomics have been used for the discovery of novel resistance determinants and the improved understanding of antibiotic-resistance mechanisms in clinical and natural environments. This review discusses recent findings and future challenges in the study of antibiotic resistance through metagenomic approaches.

Sinclair W.K.,Argonne National Laboratory
Radiation Research | Year: 2012

Various radiation responses in mammalian cells depend on the position of the cell within its generation cycle (that is, its age) at the time of irradiation. Studies have most often been made by irradiating synchronized populations of cells in vitro. Results in different cell lines are not easy to compare, but an attempt has been made here to point out similarities and differences with regard to cell killing and division delay. In general, survival data obtained so far show that, in cells with a short G1, cells are most sensitive in mitosis and in G2, less sensitive in G1, and least sensitive during the latter part of the S period. In cells with a long G 1, in addition to the above, there is usually a resistant phase early in G1 followed by a sensitive stage near its end. (The latter may be as sensitive as mitosis.) Exceptions to the above, especially in some L cell sublines, have been noted, and a possible explanation is given. In Chinese hamster cells, maximum survival after irradiation occurs during S, but it does not coincide with the time of the maximum rate of DNA synthesis or with the time of the maximum number of cells in DNA synthesis, and changes in survival also occur in cells inhibited from synthesizing DNA. Rather, survival depends on the position the cell has reached in the cycle at that time, which involves not only DNA synthesis but other processes as well. Survival is not completely correlated with DNA synthesis, since halting DNA synthesis just before or just after irradiation only slightly affects survival at its maximum. Division delay exhibits a pattern of response which is similar in most cell lines. Delay is considerable for cells irradiated in mitosis, is small for cells in G 1, increases to a maximum for cells during S, and declines for cells in G2. L cells or human kidney cells may have a longer delay for cells irradiated in G2 than for those irradiated in S. The results can be explained in terms of a two-component model of division delay. One component results from the prolongation of the S period due to the reduced rate of DNA synthesis, and the other, a block in G2, is independent of DNA synthesis. The proportion of the two components may vary in different cell lines. © 2012 by Radiation Research Society. All rights of reproduction in any form reserved.