Science.gov

Sample records for atomic short-range order

  1. Disentangling the intricate atomic short-range order and electronic properties in amorphous transition metal oxides.

    PubMed

    Triana, C A; Araujo, C Moyses; Ahuja, R; Niklasson, G A; Edvinsson, T

    2017-05-17

    Solid state materials with crystalline order have been well-known and characterized for almost a century while the description of disordered materials still bears significant challenges. Among these are the atomic short-range order and electronic properties of amorphous transition metal oxides [aTMOs], that have emerged as novel multifunctional materials due to their optical switching properties and high-capacity to intercalate alkali metal ions at low voltages. For decades, research on aTMOs has dealt with technological optimization. However, it remains challenging to unveil their intricate atomic short-range order. Currently, no systematic and broadly applicable methods exist to assess atomic-size structure, and since electronic localization is structure-dependent, still there are not well-established optical and electronic mechanisms for modelling the properties of aTMOs. We present state-of-the-art systematic procedures involving theory and experiment in a self-consistent computational framework to unveil the atomic short-range order and its role for the electronic properties. The scheme is applied to amorphous tungsten trioxide aWO3, which is the most studied electrochromic aTMO in spite of its unidentified atomic-size structure. Our approach provides a one-to-one matching of experimental data and corresponding model structure from which electronic properties can be directly calculated in agreement with the electronic transitions observed in the XANES spectra.

  2. Atomic short-range order and incipient long-range order in high-entropy alloys

    NASA Astrophysics Data System (ADS)

    Singh, Prashant; Smirnov, A. V.; Johnson, D. D.

    2015-06-01

    Within density-functional theory, we apply an electronic-structure-based thermodynamic theory to calculate short-ranged order (SRO) in homogeneously disordered substitutional N -component alloys, and its electronic origin. Using the geometric properties of an (N -1 ) simplex that describes the Gibbs (compositional) space, we derive the analytic transform of the SRO eigenvectors that provides a unique description of high-temperature SRO in N -component alloys and the incipient low-temperature long-range order. We apply the electronic-based thermodynamic theory and the new general analysis to ternaries (A 1 Cu-Ni-Zn and A 2 Nb-Al-Ti) for validation, and then to quinary Al-Co-Cr-Fe-Ni high-entropy alloys for predictive assessment.

  3. Atomically Resolved Short-Range Order at the Nanoscale in the Ca-Mn-O System.

    PubMed

    Mazarío-Fernández, A; Torres-Pardo, A; Varela, A; Parras, M; Martínez, J L; Fernández-Díaz, M T; Hernando, M; González-Calbet, J M

    2017-10-02

    The elucidation of the reaction mechanisms involving redox processes in functional transition-metal oxides, which usually start in areas of very few nanometers in size, is yet a challenge to be satisfactorily achieved. Atomically resolved HAADF and EELS have provided both chemical and structural information at the nanoscale, which reveal the preservation of short-range cationic order in areas of 2-3 nm length as the driving force behind the reversibility of the Ca2Mn3O8-Ca2Mn3O5 redox process. Oxygen evolution is accommodated by cationic diffusion along the Ca and Mn layers of the cation-deficient Ca2Mn3O8 delafossite related structure, whereas Mn remains octahedrally coordinated.

  4. Short-range ordering of ion-implanted nitrogen atoms in SiC-graphene

    SciTech Connect

    Willke, P.; Druga, T.; Wenderoth, M.; Amani, J. A.; Weikert, S.; Hofsäss, H.; Thakur, S.; Maiti, K.

    2014-09-15

    We perform a structural analysis of nitrogen-doped graphene on SiC(0001) prepared by ultra low-energy ion bombardment. Using scanning tunneling microscopy, we show that nitrogen atoms are incorporated almost exclusively as graphitic substitution in the graphene honeycomb lattice. With an irradiation energy of 25 eV and a fluence of approximately 5 × 10{sup 14 }cm{sup −2}, we achieve a nitrogen content of around 1%. By quantitatively comparing the position of the N-atoms in the topography measurements with simulated random distributions, we find statistically significant short-range correlations. Consequently, we are able to show that the dopants arrange preferably at lattice sites given by the 6 × 6-reconstruction of the underlying substrate. This selective incorporation is most likely triggered by adsorbate layers present during the ion bombardment. This study identifies low-energy ion irradiation as a promising method for controlled doping in epitaxial graphene.

  5. Quantitative chemical-structure evaluation using atom probe tomography: Short-range order analysis of Fe-Al.

    PubMed

    Marceau, R K W; Ceguerra, A V; Breen, A J; Raabe, D; Ringer, S P

    2015-10-01

    Short-range-order (SRO) has been quantitatively evaluated in an Fe-18Al (at%) alloy using atom probe tomography (APT) data and by calculation of the generalised multicomponent short-range order (GM-SRO) parameters, which have been determined by shell-based analysis of the three-dimensional atomic positions. The accuracy of this method with respect to limited detector efficiency and spatial resolution is tested against simulated D03 ordered data. Whilst there is minimal adverse effect from limited atom probe instrument detector efficiency, the combination of this with imperfect spatial resolution has the effect of making the data appear more randomised. The value of lattice rectification of the experimental APT data prior to GM-SRO analysis is demonstrated through improved information sensitivity.

  6. Short-range order and dynamics of atoms in liquid gallium

    SciTech Connect

    Mokshin, A. V. Khusnutdinoff, R. M.; Novikov, A. G.; Blagoveshchenskii, N. M.; Puchkov, A. V.

    2015-11-15

    The features of the microscopic structure, as well as one-particle and collective dynamics of liquid gallium in the temperature range from T = 313 to 1273 K, are studied on the p = 1.0 atm isobar. Detailed analysis of the data on diffraction of neutrons and X-rays, as well as the results of atomic dynamics simulation, lead to some conclusions about the structure. In particular, for preset conditions, gallium is in the equilibrium liquid phase showing no features of any stable local crystalline clusters. The pronounced asymmetry of the principle peak of the static structure factor and the characteristic “shoulder” in its right-hand part appearing at temperatures close to the melting point, which are clearly observed in the diffraction data, are due to the fact that the arrangement of the nearest neighbors of an arbitrary atom in the system is estimated statistically from the range of correlation length values and not by a single value as in the case of simple liquids. Compactly located dimers with a very short bond make a significant contribution to the statistics of nearest neighbors. The temperature dependence of the self-diffusion coefficient calculated from atomic dynamics simulation agrees well with the results obtained from experimental spectra of the incoherent scattering function. Interpolation of the temperature dependence of the self-diffusion coefficient on a logarithmic scale reveals two linear regions with a transition temperature of about 600 K. The spectra of the dynamic structure factor and spectral densities of the local current calculated by simulating the atomic dynamics indicate the existence of acoustic vibrations with longitudinal and transverse polarizations in liquid gallium, which is confirmed by experimental data on inelastic scattering of neutrons and X-rays. It is found that the vibrational density of states is completely reproduced by the generalized Debye model, which makes it possible to decompose the total vibrational motion into

  7. Effects of atomic short-range order on properties of the PbMg1 /3Nb2 /3O3 relaxor ferroelectric

    NASA Astrophysics Data System (ADS)

    Prosandeev, Sergey; Bellaiche, L.

    2016-11-01

    The effect of atomic short-range order on the macroscopic and microscopic properties of the prototype of relaxor ferroelectrics, that is, lead magnesium niobate Pb (Mg1 /3Nb2 /3) O3 (PMN), is studied via the combination of an annealing technique and a large-scale effective Hamiltonian method. The investigated short-range order gradually varies from the case of fully disordered solid solutions to the situation for which the first three nearest-neighboring shells of the B lattice of PMN adopt a rocksalt ordering between a sublattice made of pure Nb ions and a randomly distributed sublattice consisting of 2/3 of Mg and 1/3 of Nb. The characteristic temperatures of relaxor ferroelectrics (namely, the Burns, so-called T*, and depolarizing temperatures) significantly increase when strengthening this short-range chemical order, which is accompanied by an overall enhancement of the size of the polar nanoregions as well as of some antiferroelectric interactions. These results can be understood by the fact that chemical short-range order strongly modifies the internal electric fields felt by the Pb ions.

  8. Short range atomic migration in amorphous silicon

    SciTech Connect

    Strauß, F. Jerliu, B.; Geue, T.; Stahn, J.; Schmidt, H.

    2016-05-07

    Experiments on self-diffusion in amorphous silicon between 400 and 500 °C are presented, which were carried out by neutron reflectometry in combination with {sup 29}Si/{sup nat}Si isotope multilayers. Short range diffusion is detected on a length scale of about 2 nm, while long range diffusion is absent. Diffusivities are in the order of 10{sup −19}–10{sup −20} m{sup 2}/s and decrease with increasing annealing time, reaching an undetectable low value for long annealing times. This behavior is strongly correlated to structural relaxation and can be explained as a result of point defect annihilation. Diffusivities for short annealing times of 60 s follow the Arrhenius law with an activation enthalpy of (0.74 ± 0.21) eV, which is interpreted as the activation enthalpy of Si migration.

  9. Pressure effects on icosahedral short range order in undercooled copper

    NASA Astrophysics Data System (ADS)

    Celino, Massimo; Coppari, Federica; Di Cicco, Andrea

    2010-02-01

    There is not a wide consensus on the role played by the icosahedral short range order on the stability of undercooled simple metals. The scenario is even less clear for undercooled metals under external pressure. Classical molecular dynamics simulations are performed to explain experimental results recently obtained on liquid and undercooled liquid copper under pressure. The atomic configurations are characterized by a common neighbor analysis to reveal the icosahedral short range order and its relation with external pressure. External pressure increases the probability to find atomic bonds with icosahedral symmetry both in the liquid and in the undercooled copper.

  10. Short range order in liquid pnictides.

    PubMed

    Mayo, M; Yahel, E; Greenberg, Y; Makov, G

    2013-12-18

    Liquid pnictides have anomalous physical properties and complex radial distribution functions. The quasi-crystalline model of liquid structure is applied to interpret the three-dimensional structure of liquid pnictides. It is shown that all the column V elements can be characterized by a short range order lattice symmetry similar to that of the underlying solid, the A7 structure, which originates from a Peierls distorted simple cubic lattice. The evolution of the liquid structure down the column as well as its temperature and pressure dependence is interpreted by means of the effect of thermodynamic parameters on the Peierls distortion. Surprisingly, it is found that the Peierls effect increases with temperature and the nearest neighbour distances exhibit negative thermal expansion.

  11. New clues to the local atomic structure of short-range ordered ferric arsenate from extended X-ray absorption fine structure spectroscopy.

    PubMed

    Mikutta, Christian; Mandaliev, Petar N; Kretzschmar, Ruben

    2013-04-02

    Short-range ordered ferric arsenate (FeAsO4 · xH2O) is a secondary As precipitate frequently encountered in acid mine waste environments. Two distinct structural models have recently been proposed for this phase. The first model is based on the structure of scorodite (FeAsO4 · 2H2O) where isolated FeO6 octahedra share corners with four adjacent arsenate (AsO4) tetrahedra in a three-dimensional framework (framework model). The second model consists of single chains of corner-sharing FeO6 octahedra being bridged by AsO4 bound in a monodentate binuclear (2)C complex (chain model). In order to rigorously test the accuracy of both structural models, we synthesized ferric arsenates and analyzed their local (<6 Å) structure by As and Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. We found that both As and Fe K-edge EXAFS spectra were most compatible with isolated FeO6 octahedra being bridged by AsO4 tetrahedra (RFe-As = 3.33 ± 0.01 Å). Our shell-fit results further indicated a lack of evidence for single corner-sharing FeO6 linkages in ferric arsenate. Wavelet-transform analyses of the Fe K-edge EXAFS spectra of ferric arsenates complemented by shell fitting confirmed Fe atoms at an average distance of ∼5.3 Å, consistent with crystallographic data of scorodite and in disagreement with the chain model. A scorodite-type local structure of short-range ordered ferric arsenates provides a plausible explanation for their rapid transformation into scorodite in acid mining environments.

  12. Neutron scattering studies of short-range order, atomic displacements, and effective pair interactions in a null-matrix Ni0.5262Pt0.48 crystal

    NASA Astrophysics Data System (ADS)

    Rodriguez, J. A.; Moss, S. C.; Robertson, J. L.; Copley, J. R. D.; Neumann, D. A.; Major, J.

    2006-09-01

    The best known exception to the Heine-Sampson and Bieber-Gauthier arguments for ordering effects in transition metal alloys (similar to the Hume-Rothery rules) is a NiPt alloy, whose phase diagram is similar to that of the CuAu system. Using neutron scattering we have investigated the local atomic order in a null-matrix Ni0.5262Pt0.48 single crystal. In a null-matrix alloy, the isotopic composition is adjusted so that the average neutron scattering length vanishes ( Ni62 has a negative scattering length nearly equal in magnitude to that of Pt). Consequently, all contributions to the total scattering depending on the average lattice are suppressed. The only remaining components of the elastic scattering are the short-range order (SRO) and size effect terms. These data permit the extraction of the SRO parameters (concentration-concentration correlations) as well as the displacement parameters (concentration-displacement correlations). Using the Krivoglaz-Clapp-Moss theory, we obtain the effective pair interactions (EPIs) between near neighbors in the alloy. The results can be used by theorists to model the alloy in the context of the electronic theory of alloy phase stability, including a preliminary evaluation of the local species-dependent displacements. Our maps of V(q) , the Fourier transform of the EPIs, show very similar shapes in the experimental and reconstructed data. This is of importance when comparing to electronic structure calculations.

  13. Atomic and electronic structures of (GaN)1-x(ZnO)x alloys: the role of short-range order

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Allen, Philip

    2015-03-01

    (GaN)1-x(ZnO)x solid solution is a promising photocatalyst for efficient water splitting under visible illumination. For theoretical modeling, the special quasirandom structure (SQS) method which assumes random site occupancy is widely used. We have previously shown, with density-functional theory (DFT) total energy calculations, cluster expansion, and Monte Carlo simulations, that short-range order (SRO) is significant due to the non-isovalency. Thus it is desirable to include SRO in the construction of supercells. Inspired by the SQS method, we construct the ``special quasi-ordered structure'' (SQoS) supercells. Subsequent DFT calculations show that the atomic and electronic structures of SQS and SQoS alloys differ significantly. The SRO and (x,T) dependence of the valence band maximum stem mainly from the anti-bonding hybrids of N2p and Zn3d states. This suggests the possibility of engineering the band gap by tuning SRO. We also explore bond length distribution and bond angle variation over the composition-temperature (x,T) phase space using bond valence method (BVM). The validity of our BVM model is tested by DFT total energy calculations. Supported by DOE Grant No. DE-FG02-08ER46550.

  14. Short-Range Order in Ferroelectric Triglycine Sulphate

    NASA Astrophysics Data System (ADS)

    Hudspeth, J. M.

    The short-range order in triglycine sulphate (TGS) was investigated using x-ray and neutron diffraction techniques. Complete deuteration of TGS was required for the neutron diffraction experiments and a new method was developed to grow single crystals of fully deuterated TGS by vapour diffusion crystallisation. The long-range structure of fully deuterated TGS was refined at several temperatures from single crystal neutron diffraction data and found to be consistent with the published structure of hydrogenous TGS. The phase transition temperature was found to increase from about 322 K to about 334 K with complete deuteration. The evolution of the long-range structure with temperature was investigated using x-ray and neutron powder diffraction. All of the lattice parameters had a single cusp at the phase transition, except for the b lattice parameter, which also had a second cusp about 34 K below TC. In contrast to the lattice parameter behaviour, the unit cell volume was found to increase monotonically with temperature. The length of the hydrogen bonds between the disordered N atom on glycine 1 (G1) and the surrounding molecules was found to increase with temperature, whereas the length of the short hydrogen bond between G2 and G3 decreased slightly with temperature. This supports the suggestion that weakening of the hydrogen bonds decouples G1 from G2 and G3, allowing the system to become disordered. Except around the ferroelectric to paraelectric phase transition temperature, no abnormalities in the behaviour of any of the refined parameters were observed, suggesting that TGS only has a single phase transition. The short-range order in TGS was investigated by collecting single crystal x-ray and neutron diffuse scattering at several temperatures from well below to well above TC. Well below TC, the diffuse scattering was purely thermal diffuse scattering due to correlations of the atomic displacements. Close to the phase transition, diffuse streaks perpendicular to

  15. Difference in Icosahedral Short-Range Order in Early and Late Transition Metals Liquids

    NASA Technical Reports Server (NTRS)

    Lee, G. W.; Gangopadhyay, A. K.; Kelton, K. F.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.

    2003-01-01

    New short-range order data are presented for equilibrium and undercooled liquids of Ti and Ni. These were obtained from in-situ synchrotron x-ray diffraction measurements of electrostatically-levitated droplets. While the short-range order of liquid Ni is icosahedral, consistent with Frank's hypothesis, significantly distorted icosahedral order is observed in liquid Ti. This is the first experimental observation of distorted icosahedral short-range order in any liquid, although this has been predicted by theoretical studies on atomic clusters.

  16. Difference in Icosahedral Short-Range Order in Early and Late Transition Metal Liquids

    NASA Technical Reports Server (NTRS)

    Lee, G. W.; Gangopadbyay, A. K.; Kelton, K. F.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.

    2004-01-01

    New short-range order data are presented for equilibrium and undercooled liquids of Ti and Ni. These were obtained from in-situ synchrotron x-ray diffraction measurements of electrostatically-levitated droplets. While the short-range order of liquid Ni is icosahedral, consistent with Frank's hypothesis, significantly distorted icosahedral order is observed in liquid Ti. This is the first experimental observation of distorted icosahedral short-range order in any liquid. although this has been predicted by theoretical studies on atomic clusters.

  17. Difference in Icosahedral Short-Range Order in Early and Late Transition Metal Liquids

    NASA Technical Reports Server (NTRS)

    Lee, G. W.; Gangopadbyay, A. K.; Kelton, K. F.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.

    2004-01-01

    New short-range order data are presented for equilibrium and undercooled liquids of Ti and Ni. These were obtained from in-situ synchrotron x-ray diffraction measurements of electrostatically-levitated droplets. While the short-range order of liquid Ni is icosahedral, consistent with Frank's hypothesis, significantly distorted icosahedral order is observed in liquid Ti. This is the first experimental observation of distorted icosahedral short-range order in any liquid. although this has been predicted by theoretical studies on atomic clusters.

  18. Difference in Icosahedral Short-Range Order in Early and Late Transition Metals Liquids

    NASA Technical Reports Server (NTRS)

    Lee, G. W.; Gangopadhyay, A. K.; Kelton, K. F.; Hyers, R. W.; Rathz, T. J.; Rogers, J. R.

    2003-01-01

    New short-range order data are presented for equilibrium and undercooled liquids of Ti and Ni. These were obtained from in-situ synchrotron x-ray diffraction measurements of electrostatically-levitated droplets. While the short-range order of liquid Ni is icosahedral, consistent with Frank's hypothesis, significantly distorted icosahedral order is observed in liquid Ti. This is the first experimental observation of distorted icosahedral short-range order in any liquid, although this has been predicted by theoretical studies on atomic clusters.

  19. Amorphous photonic crystals with only short-range order.

    PubMed

    Shi, Lei; Zhang, Yafeng; Dong, Biqin; Zhan, Tianrong; Liu, Xiaohan; Zi, Jian

    2013-10-04

    Distinct from conventional photonic crystals with both short- and long-range order, amorphous photonic crystals that possess only short-range order show interesting optical responses owing to their unique structural features. Amorphous photonic crystals exhibit unique light scattering and transport, which lead to a variety of interesting phenomena such as isotropic photonic bandgaps or pseudogaps, noniridescent structural colors, and light localization. Recent experimental and theoretical advances in the study of amorphous photonic crystals are summarized, focusing on their unique optical properties, artificial fabrication, bionspiration, and potential applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Short range order in elemental liquids of column IV

    NASA Astrophysics Data System (ADS)

    Mayo, M.; Shor, S.; Yahel, E.; Makov, G.

    2015-05-01

    The short range order (SRO) in liquid elements of column IV is analysed within the quasi-crystalline model across a wide range of temperatures. It is found that l-Si, Ge, and Sn are well described with a beta-tin like SRO. In contrast, Pb retains a bcc-like SRO similar to other simple elemental liquids. However, a distinction is found between the SRO in Si and Ge and that in Sn, where the latter has a more rigid structure. This difference persists across the entire temperature range examined but is overcome in Si at pressures above 8 GPa, where the liquid structure evolves towards that of Sn.

  1. Short range order in elemental liquids of column IV.

    PubMed

    Mayo, M; Shor, S; Yahel, E; Makov, G

    2015-05-21

    The short range order (SRO) in liquid elements of column IV is analysed within the quasi-crystalline model across a wide range of temperatures. It is found that l-Si, Ge, and Sn are well described with a beta-tin like SRO. In contrast, Pb retains a bcc-like SRO similar to other simple elemental liquids. However, a distinction is found between the SRO in Si and Ge and that in Sn, where the latter has a more rigid structure. This difference persists across the entire temperature range examined but is overcome in Si at pressures above 8 GPa, where the liquid structure evolves towards that of Sn.

  2. Molecular dynamics characterization of icosahedral short range order in undercooled copper

    NASA Astrophysics Data System (ADS)

    Celino, M.

    2011-05-01

    The stability of undercooled simple metals is still an intriguing problem for materials science and technology. There is not consensus on the role played by the icosahedral short range order during undercooling. The scenario is even less clear for undercooled metals under external pressure. Extensive molecular dynamics simulations, based on an empirical tight-binding interatomic potential, are performed to explain experimental results recently obtained on liquid and undercooled liquid copper. A common neighbour analysis is used to fully characterize the icosahedral short range order in both undercooled and liquid systems. Moreover, the effect of pressure on icosahedral short range order, is addressed and rationalized. External pressure increases the probability to find atomic bonds with icosahedral symmetry both in the liquid and in the undercooled copper.

  3. Lazarevicite-type short-range ordering in ternary III-V nanowires

    NASA Astrophysics Data System (ADS)

    Schnedler, M.; Lefebvre, I.; Xu, T.; Portz, V.; Patriarche, G.; Nys, J.-P.; Plissard, S. R.; Caroff, P.; Berthe, M.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.; Grandidier, B.

    2016-11-01

    Stabilizing ordering instead of randomness in alloy semiconductor materials is a powerful means to change their physical properties. We used scanning tunneling and transmission electron microscopies to reveal the existence of an unrecognized ordering in ternary III-V materials. The lazarevicite short-range order, found in the shell of InAs1 -xSbx nanowires, is driven by the strong Sb-Sb repulsion along <110 > atomic chains during their incorporation on unreconstructed {110 } sidewalls. Its spontaneous formation under group-III-rich conditions of growth offers the prospect to broaden the limited classes of ordered structures occurring in III-V semiconductor alloys.

  4. Local Structure and Short-Range Order in a NiCoCr Solid Solution Alloy

    DOE PAGES

    Zhang, F. X.; Zhao, Shijun; Jin, Ke; ...

    2017-05-19

    Multi-element solid solution alloys are intrinsically disordered on the atomic scale, and many of their advanced properties originate from the unique local structural characteristics. We measured the local structure of a NiCoCr solid solution alloy with X-ray/neutron total scattering and extended X-ray absorption fine structure (EXAFS) techniques. The atomic pair distribution function analysis (PDF) did not exhibit distinct structural distortion. But, EXAFS analysis suggested that the Cr atoms are favorably bonded with Ni and Co in the solid solution alloys. This short-range order (SRO) plays a role in the distinct low values of electrical and thermal conductivities in Ni-based solidmore » solution alloys when Cr is incorporated. Both the long-range and local structures of the NiCoCr alloy upon Ni ion irradiation were studied and an irradiation-induced enhancement of SRO was found.« less

  5. Local Structure and Short-Range Order in a NiCoCr Solid Solution Alloy

    NASA Astrophysics Data System (ADS)

    Zhang, F. X.; Zhao, Shijun; Jin, Ke; Xue, H.; Velisa, G.; Bei, H.; Huang, R.; Ko, J. Y. P.; Pagan, D. C.; Neuefeind, J. C.; Weber, W. J.; Zhang, Yanwen

    2017-05-01

    Multielement solid solution alloys are intrinsically disordered on the atomic scale, and many of their advanced properties originate from the local structural characteristics. The local structure of a NiCoCr solid solution alloy is measured with x-ray or neutron total scattering and extended x-ray absorption fine structure (EXAFS) techniques. The atomic pair distribution function analysis does not exhibit an observable structural distortion. However, an EXAFS analysis suggests that the Cr atoms are favorably bonded with Ni and Co in the solid solution alloys. This short-range order (SRO) may make an important contribution to the low values of the electrical and thermal conductivities of the Cr-alloyed solid solutions. In addition, an EXAFS analysis of Ni ion irradiated samples reveals that the degree of SRO in NiCoCr alloys is enhanced after irradiation.

  6. Electronic transitions induced by short-range structural order in amorphous TiO2

    NASA Astrophysics Data System (ADS)

    Triana, C. A.; Araujo, C. Moyses; Ahuja, R.; Niklasson, G. A.; Edvinsson, T.

    2016-10-01

    Several promising applications of amorphous titanium dioxide, a TiO2 , have appeared recently, but the correlation between electronic properties and atomic short-range structural order is poorly understood. Herein we show that structural disorder yields local undercoordinated TiOx units which influence electronic hybridization of Ti-[4 p ] and Ti-[3 d ] orbitals with a low crystal-field splitting [E (eg) -E (t2 g) =2.4 ±0.3 eV ] . The short-range order and electronic properties of a TiO2 thin-film oxides are described through an integrated approach based on x-ray-absorption experiments and ab initio computational simulations where the energy splitting of the electronic levels in the Ti-[4 p -3 d ] manifold are analyzed. Structural disorder provides enough p -d orbital mixing for the hybridized electronic transitions from the Ti-[1 s ] core level into the [Ti -t2 g] and [Ti -eg] bands [1 s →4 p -3 d excitations], to be allowed. This yields an intense pre-edge structure in the Ti K -edge x-ray-absorption near-edge structure spectrum of a TiO2 , which is consistent with the projected density of states on the photoabsorbing Ti atoms.

  7. Short-range order and stability in Gd-Ni and Y-Ni systems

    SciTech Connect

    Colinet, C.; Pasturel, A.; Buschow, K.H.J.

    1987-11-01

    We present experimental determinations of the enthalpies of formation of various amorphous and crystalline alloys in the Gd-Ni and Y-Ni systems. For the amorphous alloys, crystallization enthalpy is studied by means of differential scanning calorimetry. The enthalpy effects observed in amorphous alloys point to the occurrence of chemical short-range order. This manifestation is analyzed using microscopic calculations of chemical short-range order based on a tight-binding Hamiltonian.

  8. Short-range order and near-field effects on optical scattering and structural coloration

    SciTech Connect

    Liew, S.F.; Forster, J.; Noh, H.; Schreck, C.F.; Saranathan, V.; Lu, X.; Yang, L.; Prum, Richard O.; O’Hern, C.S.; Dufresne, E.R.; Cao, H.

    2012-03-26

    We have investigated wavelength-dependent light scattering in biomimetic structures with short-range order. Coherent backscattering experiments are performed to measure the transport mean free path over a wide wavelength range. Overall scattering strength is reduced significantly due to short-range order and near-field effects. Our analysis explains why single scattering of light is dominant over multiple scattering in similar biological structures and is responsible for color generation.

  9. Photonic band gaps in three-dimensional network structures with short-range order

    SciTech Connect

    Liew, Seng Fatt; Noh, Heeso; Yang, Jin-Kyu; Schreck, Carl F.; Dufresne, Eric R.; O'Hern, Corey S.; Cao, Hui

    2011-12-15

    We present a systematic study of photonic band gaps (PBGs) in three-dimensional (3D) photonic amorphous structures (PASs) with short-range order. From calculations of the density of optical states (DOS) for PASs with different topologies, we find that tetrahedrally connected dielectric networks produce the largest isotropic PBGs. Local uniformity and tetrahedral order are essential to the formation of PBGs in PASs, in addition to short-range geometric order. This work demonstrates that it is possible to create broad, isotropic PBGs for vector light fields in 3D PASs without long-range order.

  10. Simultaneous occurrence of multiferroism and short-range magnetic order in DyFeO3

    DOE PAGES

    Wang, Jinchen; Liu, Juanjuan; Sheng, Jieming; ...

    2016-04-06

    In this paper, we present a combined neutron scattering and magnetization study on the multiferroic DyFeO3, which shows a very strong magnetoelectric effect. Applying magnetic field along the c axis, the weak ferromagnetic order of the Fe ions is quickly recovered from a spin reorientation transition, and the long-range antiferromagnetic order of Dy becomes a short-range one. We found that the short-range order concurs with the multiferroic phase and is responsible for its sizable hysteresis. In conclusion, our H-T phase diagram suggests that the strong magnetoelectric effect in DyFeO3 has to be understood with not only the weak ferromagnetism ofmore » Fe but also the short-range antiferromagnetic order of Dy.« less

  11. Size correlated long and short range order of ternary Co2FeGa Heusler nanoparticles

    NASA Astrophysics Data System (ADS)

    Wang, C. H.; Guo, Y. Z.; Casper, F.; Balke, B.; Fecher, G. H.; Felser, C.; Hwu, Y.

    2010-09-01

    The long and short range order of chemically prepared Co2FeGa Heusler nanoparticles with various sizes are determined by x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS) spectroscopy. Specifically, EXAFS fittings reveal the size dependent crystal structure and short range order of the Heusler type Co2FeGa nanoparticles. With decreasing particle size, the degree of L21 order in the nanoparticles decreases and the probability of B2 disorder increases simultaneously. The consequences of antisite disorder on the size correlated structure of Co2FeGa nanoparticles are also discussed.

  12. Covalent and reversible short-range electrostatic imaging in noncontact atomic force microscopy.

    PubMed

    Dieska, Peter; Stich, Ivan; Pérez, Rubén

    2003-11-21

    We present a computational study of atomic-scale image formation in noncontact atomic force microscopy on metallic surfaces. We find two imaging scenarios: (1). atomic resolution arising due to very strong covalent tip-sample interaction exhibiting striking similarity with the imaging mechanism found on semiconductor surfaces, and (2). a completely new mechanism, reversible short-range electrostatic imaging, arising due to subtle charge-transfer interactions. Contrary to the strong covalent-bond imaging, the newly identified mechanism causes only negligible surface perturbation and can account for results recently observed experimentally.

  13. Double scattering of light from Biophotonic Nanostructures with short-range order.

    PubMed

    Noh, Heeso; Liew, Seng Fatt; Saranathan, Vinodkumar; Prum, Richard O; Mochrie, Simon G J; Dufresne, Eric R; Cao, Hui

    2010-05-24

    We investigate the physical mechanism for color production by isotropic nanostructures with short-range order in bird feather barbs. While the primary peak in optical scattering spectra results from constructive interference of singly-scattered light, many species exhibit secondary peaks with distinct characteristic. Our experimental and numerical studies show that these secondary peaks result from double scattering of light by the correlated structures. Without an analog in periodic or random structures, such a phenomenon is unique for short-range ordered structures, and has been widely used by nature for non-iridescent structural coloration.

  14. Double scattering of light from Biophotonic Nanostructures with short-range order

    SciTech Connect

    Noh, Heeso; Liew, Seng Fatt; Saranathan, Vinodkumar; Prum, Richard O.; Mochrie, Simon G.J.; Dufresne, Eric R.; Cao, Hui

    2010-07-28

    We investigate the physical mechanism for color production by isotropic nanostructures with short-range order in bird feather barbs. While the primary peak in optical scattering spectra results from constructive interference of singly-scattered light, many species exhibit secondary peaks with distinct characteristic. Our experimental and numerical studies show that these secondary peaks result from double scattering of light by the correlated structures. Without an analog in periodic or random structures, such a phenomenon is unique for short-range ordered structures, and has been widely used by nature for non-iridescent structural coloration.

  15. CO Tip Functionalization Inverts Atomic Force Microscopy Contrast via Short-Range Electrostatic Forces

    NASA Astrophysics Data System (ADS)

    Schneiderbauer, Maximilian; Emmrich, Matthias; Weymouth, Alfred J.; Giessibl, Franz J.

    2014-04-01

    We investigate insulating Cu2N islands grown on Cu(100) by means of combined scanning tunneling microscopy and atomic force microscopy with two vastly different tips: a bare metal tip and a CO-terminated tip. We use scanning tunneling microscopy data as proposed by Choi, Ruggiero, and Gupta to unambiguously identify atomic positions. Atomic force microscopy images taken with the two different tips show an inverted contrast over Cu2N. The observed force contrast can be explained with an electrostatic model, where the two tips have dipole moments of opposite directions. This highlights the importance of short-range electrostatic forces in the formation of atomic contrast on polar surfaces in noncontact atomic force microscopy.

  16. CO tip functionalization inverts atomic force microscopy contrast via short-range electrostatic forces.

    PubMed

    Schneiderbauer, Maximilian; Emmrich, Matthias; Weymouth, Alfred J; Giessibl, Franz J

    2014-04-25

    We investigate insulating Cu2N islands grown on Cu(100) by means of combined scanning tunneling microscopy and atomic force microscopy with two vastly different tips: a bare metal tip and a CO-terminated tip. We use scanning tunneling microscopy data as proposed by Choi, Ruggiero, and Gupta to unambiguously identify atomic positions. Atomic force microscopy images taken with the two different tips show an inverted contrast over Cu2N. The observed force contrast can be explained with an electrostatic model, where the two tips have dipole moments of opposite directions. This highlights the importance of short-range electrostatic forces in the formation of atomic contrast on polar surfaces in noncontact atomic force microscopy.

  17. Nuclear-spin-independent short-range three-body physics in ultracold atoms.

    PubMed

    Gross, Noam; Shotan, Zav; Kokkelmans, Servaas; Khaykovich, Lev

    2010-09-03

    We investigate three-body recombination loss across a Feshbach resonance in a gas of ultracold 7Li atoms prepared in the absolute ground state and perform a comparison with previously reported results of a different nuclear-spin state [N. Gross, Phys. Rev. Lett. 103, 163202 (2009)]. We extend the previously reported universality in three-body recombination loss across a Feshbach resonance to the absolute ground state. We show that the positions and widths of recombination minima and Efimov resonances are identical for both states which indicates that the short-range physics is nuclear-spin independent.

  18. Short-range order and its effects on electrons in (GaN)(1 - x)(ZnO)x alloys

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Pedroza, Luana; Misch, Carissa; Fernandez-Serra, Maria; Allen, Philip

    2014-03-01

    Prior work by Li et al. gives ``cluster expansion'' parameters for (GaN)(1 - x)(ZnO)x alloys. From these, by Monte-Carlo calculations, large representative unit cells can be generated at any chosen temperature. We choose mainly T=1200K, typical of the temperature at which experimental samples fall out of equilibrium. The atoms are distributed on the wurtzite anion and cation sublattices with significant short-range order. A periodic supercell with 432 atoms is chosen as a compromise between accurate self-averaging and fully self-consistent and relaxed density-functional (DFT) computation. Composition- and temperature-dependent short-range order (SRO) parameters of the alloys are discussed. Entropy is related to the SRO parameters. DFT relaxation finds significant bond-length alterations. Typical Zn-O distances are larger by 10 % than Ga-N distances in the alloy, even though in pure ZnO and GaN, bond lengths are nearly equal. Electronic properties of the alloys, and in particular, the influences of short-range order and bond-length fluctuations, will be discussed. Supported by DOE Grant No. DE-FG02-08ER46550 (PBA) and DE-FG02-09ER16052 (MFS). Computer resources came from the BNL CFN under DOE Contract DE-AC02-98CH10886.

  19. Short-range order effects on the electronic properties of a binary linear chain

    NASA Astrophysics Data System (ADS)

    Rössler, Jaime; Martinez, Gaston; Kiwi, Miguel

    1980-06-01

    A new technique to treat one-dimensional binary alloys, described in tight-binding approximation, capable of incorporating short-range correlations in a simple way is presented. The method is an extension of work by Faulkner and Korringa and handles spatial correlations by restricting the number of allowed configurations in the ensemble over which averages are taken. The density of electron states thus calculated exhibits rich structure, which is known to exist but is lost in treatments which neglect local correlation effects. A detailed study of the stoichiometric case with an equal number of atoms of both chemical species is presented, including up to next-nearest-neighbor correlations.

  20. Spin-polarized photoelectron diffraction: A new probe of short-range magnetic order (invited) (abstract)

    NASA Astrophysics Data System (ADS)

    Fadley, C. S.; Sinkovic, B.; Hermsmeier, B. D.; Osterwalder, J.

    1988-04-01

    It has recently been pointed out theoretically and subsequently observed experimentally that core-level multiplet splittings can be used to yield a spin-polarized form of photoelectron diffraction (SPPD). This internally referenced source of electrons that are highly polarized with both orientations of spin thus eliminates the need for an external spin detector, permits studying both ferromagnetic and antiferromagnetic specimens, and can, in principle, detect short-range magnetic or for temperatures above the Curie or Néel temperature. In the first measurements of this type on the antiferromagnet KMnF3, an abrupt loss of short-range order at a transition temperature considerably above the bulk Néel temperature of the material was observed. More recent theoretical diffraction calculations have pointed out several ways in which SPPD should permit deriving unique information on short-range spin-order structures at and near the surfaces of magnetic materials. New experimental results have also been obtained for the antiferromagnet MnO. This paper will discuss these new developments, will review the advantages and disadvantages of SPPD, and also will consider some interesting future directions of investigation.

  1. Short range ordering and magnetostriction in Fe-Ga and other Fe alloy single crystals

    NASA Astrophysics Data System (ADS)

    Guruswamy, Sivaraman; Jayaraman, Tanjore V.; Corson, Robert P.; Garside, Gavin; Thuanboon, Swieng

    2008-12-01

    The magnetostrictive behaviors of Fe-Ga, Fe-Mo, Fe-W, and other Fe alloys have been observed to be sensitive to their thermal history. In this work, the changes in the structure with thermal history and how they correlate with the observed magnetostriction values in Fe-Ga, Fe-W, and Fe-Mo single crystals are examined. Single crystals were grown using the vertical Bridgman crystal growth technique. The magnetostriction constant (3/2)λ100 measured in (i) as-grown and air-cooled (DG) and (ii) annealed and water quenched single crystal samples of Fe-Ga and Fe-W alloys clearly indicate that annealing in the α-phase region followed by rapid quenching improves the magnetostriction values. High-resolution x-ray diffraction (XRD) studies on [100]-oriented Fe-Ga as well as other Fe alloy single crystals show (i) a diffuse scattering peak indicative of short range ordering, the extent of which depends on composition and thermal history, and (ii) (200) peak splitting and broadening indicative of the presence of long range ordered coherent second phases and associated coherency strains. A detailed examination of the XRD patterns suggests that the changes in magnetostriction with composition and thermal history are related to the local strain modulations associated with the solutes, short range order, long range ordered coherent second phases, incoherent precipitates, and other structural defects.

  2. Distinct Short-Range Order Is Inherent to Small Amorphous Calcium Carbonate Clusters (<2 nm)

    SciTech Connect

    Sun, Shengtong; Chevrier, Daniel M.; Zhang, Peng; Gebauer, Denis; Cölfen, Helmut

    2016-09-09

    Amorphous intermediate phases are vital precursors in the crystallization of many biogenic minerals. While inherent short-range orders have been found in amorphous calcium carbonates (ACCs) relating to different crystalline forms, it has never been clarified experimentally whether such orders already exist in very small clusters less than 2 nm in size. Here, we studied the stability and structure of 10,12-pentacosadiynoic acid (PCDA) protected ACC clusters with a core size of ca. 1.4 nm consisting of only seven CaCO3 units. Ligand concentration and structure are shown to be key factors in stabilizing the ACC clusters. More importantly, even in such small CaCO3 entities, a proto-calcite short-range order can be identified but with a relatively high degree of disorder that arises from the very small size of the CaCO3 core. Our findings support the notion of a structural link between prenucleation clusters, amorphous intermediates, and final crystalline polymorphs, which appears central to the understanding of polymorph selection.

  3. Bounds to Hardening by Solid Solution, Precipitation and Short Range Order in Mg Binary Alloys

    NASA Astrophysics Data System (ADS)

    Cáceres, C. H.; Abaspour, Saeideh

    Miedema's coordinates are used to rank 4 model binary alloys considering the respective values of enthalpy of formation and the tendency to developing random solid solution, precipitation, short range order (SRO) and intermetallic compounds. The terminal solid solubility generally increases whereas the tendency to order decreases with decreasing heat of formation, and hardening by near-random solid solution and/or precipitation is expected to be dominant for solutes with low tendency to order, such as Al. For solutes with an intermediate tendency to order, hence solubility, such as Zn, or to form compounds, such as Gd, SRO is predicted to dominate the hardening. For solutes whose very large heat of formation leads to very high melting point intermetallics forming congruently, such as Sb, the terminal solid solubility is too low for any solute based hardening to be feasible. Implicancies for alloy design and selection regarding solute or precipitation hardening, SRO and creep resistance are discussed.

  4. KKR-DCA Thermodynamics for Cluster Short-Range Order with Full Charge Self-Consistency

    NASA Astrophysics Data System (ADS)

    Biava, Dominic A.; Johnson, Duane D.

    The Dynamical Cluster Approximation (DCA) implemented in the Korringa-Kohn-Rostoker (KKR) electronic-structure method gives a systematically exact, course-grained theory of the electronic states of substitutionally disordered alloys, including the effects of chemical short-ranged order (SRO). We implement the KKR-DCA within density functional theory (DFT) to calculate directly the charge self-consistent electronic contributions to the alloy grand potential. The KKR-DCA is combined with the chemical entropy from the Cluster Variation Method (CVM), which when minimized predicts the SRO directly. The calculated SRO has been tested in several metallic systems with agreement to measured values. For very large clusters, the KKR-DCA can be sampled, as done within Quantum Monte Carlo, and provides the charge self-consistent thermodynamic grand potential in complex alloys with SRO at finite temperature, at the same level as done for perfect ordered alloys in other electronic-structure methods at zero Kelvin.

  5. Cascaded third-harmonic generation in a single short-range-ordered nonlinear photonic crystal.

    PubMed

    Sheng, Yan; Saltiel, Solomon M; Koynov, Kaloian

    2009-03-01

    Collinear third-harmonic generation at 526.7 nm was realized by the simultaneous phase matching of two second-order processes in a single quadratic crystal: second-harmonic generation (SHG) and sum-frequency mixing (SFM). The measured conversion efficiency was 12%. As a nonlinear medium a LiNbO(3) nonlinear photonic crystal with short-range order was used that allowed simultaneous phase matching by use of discrete reciprocal vector (for the SHG process) and continuous reciprocal vectors (for the SFM process). It was demonstrated that the third harmonic could be generated efficiently in such a crystal even if the intermediate process of SHG was not perfectly phase matched.

  6. Short range smectic order driving long range nematic order: Example of cuprates

    SciTech Connect

    Markiewicz, R. S.; Lorenzana, J.; Seibold, G.; Bansil, A.

    2016-01-27

    We present a model for describing the combined presence of nematic and ‘smectic’ or stripe-like orders seen in recent scanning tunneling microscopy (STM) experiments on cuprates. The smectic order is treated as an electronic charge density wave with an associated Peierls distortion or a ‘Pomeranchuk wave’. This primary order is restricted to nanoscale domains by disorder effects, while the secondary coupling to strain generates the nematic order with a considerably longer range. Lastly, a variety of experimental results are shown to be consistent with our theoretical predictions.

  7. Short range smectic order driving long range nematic order: example of cuprates

    PubMed Central

    Markiewicz, R. S.; Lorenzana, J.; Seibold, G.; Bansil, A.

    2016-01-01

    We present a model for describing the combined presence of nematic and ‘smectic’ or stripe-like orders seen in recent scanning tunneling microscopy (STM) experiments on cuprates. The smectic order is treated as an electronic charge density wave with an associated Peierls distortion or a ‘Pomeranchuk wave’. This primary order is restricted to nanoscale domains by disorder effects, while the secondary coupling to strain generates the nematic order with a considerably longer range. A variety of experimental results are shown to be consistent with our theoretical predictions. PMID:26813579

  8. Discriminating short-range from van der Waals forces using total force data in noncontact atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Kuhn, Stefan; Rahe, Philipp

    2014-06-01

    Noncontact atomic force microscopy (NC-AFM) features the measurement of forces with highest spatial resolution and sensitivity, resolving forces of the order of pico-Newtons with submolecular resolution. However, the measured total force is a mixture composed of various interactions. While some interactions such as electrostatic or magnetic forces can be excluded by a careful design of the experiment, the subtraction of van der Waals forces, which mainly originate from London dispersion interactions between the macroscopic tip shank and the bulk sample, remains a challenge. We present the determination of the inherently present van der Waals forces in total interaction force data from fitting a suitable model, allowing for extraction of the short-range force component. We compare the applicability of several van der Waals models based on experimental interaction data from the calcite(101¯4) surface. The feasibility to fit these models to experimental data is critically discussed. We furthermore introduce criteria to assess the transition point from pure long-range interaction to mixed short- and long-range forces based on the variance of lateral and vertical force data. This determination allows us to extract the short-range interaction forces, which remained a challenge so far in NC-AFM experiments.

  9. Reformation Capability of Short-Range Order and Their Medium-Range Connections Regulates Deformability of Bulk Metallic Glasses

    NASA Astrophysics Data System (ADS)

    Li, Congling; Wei, Yujie; Shi, Xinghua

    2015-07-01

    Metallic glasses (MGs) typically have high yield strength while low ductility, and the latter is commonly considered as the Achilles’ heel of MGs. Elucidate the mechanism for such low ductility becomes the research focus of this field. With molecular level simulations, we show the degree of short-range order (SRO) of atomic structure for brittle Fe-based glass decreases dramatically during the stretch, while mild change occurs in ductile Zr-based glass. The reformation capability for SRO and their medium-range connections is found to be the primary characteristics to differentiate the deformability between the two metallic glasses. We suspect that, in addition to the strength of networks formed by SRO structure, the reformation capability to reform SRO networks also plays the key role in regulating the ductility in metallic glasses. Our study provides important insights into the understanding about the mechanisms accounting for ductility or brittleness of bulk metallic glasses.

  10. Reformation Capability of Short-Range Order and Their Medium-Range Connections Regulates Deformability of Bulk Metallic Glasses

    PubMed Central

    Li, Congling; Wei, Yujie; Shi, Xinghua

    2015-01-01

    Metallic glasses (MGs) typically have high yield strength while low ductility, and the latter is commonly considered as the Achilles’ heel of MGs. Elucidate the mechanism for such low ductility becomes the research focus of this field. With molecular level simulations, we show the degree of short-range order (SRO) of atomic structure for brittle Fe-based glass decreases dramatically during the stretch, while mild change occurs in ductile Zr-based glass. The reformation capability for SRO and their medium-range connections is found to be the primary characteristics to differentiate the deformability between the two metallic glasses. We suspect that, in addition to the strength of networks formed by SRO structure, the reformation capability to reform SRO networks also plays the key role in regulating the ductility in metallic glasses. Our study provides important insights into the understanding about the mechanisms accounting for ductility or brittleness of bulk metallic glasses. PMID:26178316

  11. Reformation Capability of Short-Range Order and Their Medium-Range Connections Regulates Deformability of Bulk Metallic Glasses.

    PubMed

    Li, Congling; Wei, Yujie; Shi, Xinghua

    2015-07-16

    Metallic glasses (MGs) typically have high yield strength while low ductility, and the latter is commonly considered as the Achilles' heel of MGs. Elucidate the mechanism for such low ductility becomes the research focus of this field. With molecular level simulations, we show the degree of short-range order (SRO) of atomic structure for brittle Fe-based glass decreases dramatically during the stretch, while mild change occurs in ductile Zr-based glass. The reformation capability for SRO and their medium-range connections is found to be the primary characteristics to differentiate the deformability between the two metallic glasses. We suspect that, in addition to the strength of networks formed by SRO structure, the reformation capability to reform SRO networks also plays the key role in regulating the ductility in metallic glasses. Our study provides important insights into the understanding about the mechanisms accounting for ductility or brittleness of bulk metallic glasses.

  12. Short-Range-Order Mineral Physical Protection On Black Carbon Stabilization

    NASA Astrophysics Data System (ADS)

    Liang, B.; Weng, Y. T.; Wang, C. C.; Song, Y. F.; Lehmann, J.; Wang, C. H.

    2015-12-01

    Soil organic matter is one of the largest reservoirs in global carbon cycle, and black carbon (BC) represents a chemical resistant component. Black C plays an important role in global climate change. Generally considered recalcitrant due to high aromaticity, the reactive surface and functional groups of BC are crucial for carbon sequestration in soils. Mineral sorption and physical protection is an important mechanism for BC long term stabilization and sequestration in environments. Previous studies on mineral protection of BC were limited to analysis techniques in two-dimensions, for example, by SEM, TEM, and NanoSIMS. Little is known about the scope of organo-mineral association, the in-situ distribution and forms of minerals, and the ultimate interplay of BC and minerals. The aim of this study is to investigate the three-dimensional interaction of organic C and minerals in submicron scale using synchrotron-based Transmission X-ray Microcopy (TXM) and Fourier-Transform Infrared Spectroscopy (FTIR). Abundant poorly-crystallined nano-minerals particles were observed. These short-range-order (SRO) minerals also aggregate into clusters and sheets, and form envelops-like structures on the surface of BC. On top of large surface contact area, the intimate interplay between BC and minerals reinforces the stability of both organic C and minerals, resulting from chemical bonding through cation bridging and ligand exchange. The mineral protection enhances BC stabilization and sequestration and lowers its bioavailability in environment. The results suggest that mineral physical protection for BC sequestration may be more important than previous understanding.

  13. Fungal biomineralization of montmorillonite and goethite to short-range-ordered minerals

    NASA Astrophysics Data System (ADS)

    Li, Huan; Hu, Shuijin; Polizzotto, Matthew L.; Chang, Xiaoli; Shen, Qirong; Ran, Wei; Yu, Guanghui

    2016-10-01

    Highly reactive nano-scale minerals, e.g., short-range-ordered minerals (SROs) and other nanoparticles, play an important role in soil carbon (C) retention. Yet, the mechanisms that govern biomineralization from bulk minerals to highly reactive nano-scale minerals remain largely unexplored, which critically hinders our efforts toward managing nano-scale minerals for soil C retention. Here we report the results from a study that explores structural changes during Aspergillus fumigatus Z5 transformation of montmorillonite and goethite to SROs. We examined the morphology and structure of nano-scale minerals, using high-resolution transmission electron microscopy, time-resolved solid-state 27Al and 29Si NMR, and Fe K-edge X-ray absorption fine structure spectroscopy combined with two dimensional correlation spectroscopy (2D COS) analysis. Our results showed that after a 48-h cultivation of montmorillonite and goethite with Z5, new biogenic intracellular and extracellular reactive nano-scale minerals with a size of 3-5 nm became abundant. Analysis of 2D COS further suggested that montmorillonite and goethite were the precursors of the dominant biogenic nano-scale minerals. Carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectra and their deconvolution results demonstrated that during fungus Z5 growth, carboxylic C (288.4-289.1 eV) was the dominant organic group, accounting for approximately 34% and 59% in the medium and aggregates, respectively. This result suggested that high percentage of the production of organic acids during the growth of Z5 was the driving factor for structural changes during biomineralization. This is, to the best of our knowledge, the first report of the structural characterization of nano-scale minerals by 2D COS, highlighting its potential to elucidate biomineralization pathways and thus identify the precursors of nano-scale minerals.

  14. Short-range order in Fe-based metallic glasses: Wide-angle X-ray scattering studies

    SciTech Connect

    Babilas, Rafał; Hawełek, Łukasz; Burian, Andrzej

    2014-11-15

    The local atomic structure of the Fe{sub 80}B{sub 20}, Fe{sub 70}Nb{sub 10}B{sub 20} and Fe{sub 62}Nb{sub 8}B{sub 30} glasses prepared in the form of ribbons has been studied by wide-angle X-ray scattering. Structural information about the amorphous ribbons has been derived from analysis of the radial distribution functions using the least-squares curve-fitting method. The obtained structural parameters indicate that Fe–Fe, Fe–B, Fe–Nb and Nb–B contributions are involved in the near-neighbor coordination spheres. The possible similarities of the local atomic arrangement in the investigated glasses and the crystalline Fe{sub 3}B, Fe{sub 23}B{sub 6} and bcc Fe structures are also discussed. - Graphical abstract: Pair distribution functions (a) and best-fit model and experimental radial distribution functions for Fe{sub 80}B{sub 20} (b), Fe{sub 70}Nb{sub 10}B{sub 20} (c) and Fe{sub 62}Nb{sub 8}B{sub 30} (d) metallic glasses. - Highlights: • The short-range ordering in the Fe-based metallic glasses is presented. • The results of RDF function have been analyzed using the least-squares method. • The Fe–Fe, Fe–B, Fe–Nb or Nb–B contributions are involved in coordination spheres. • The structural unit is distorted triangular prism containing B, Fe or Nb atoms. • Similarities of atomic arrangement in glassy and crystalline structures are discussed.

  15. Chemical short-range order in dense random packed models. [Ni/sub 35/Ti/sub 65/; Ni/sub 35/Zr/sub 65/

    SciTech Connect

    Saw, C.K.; Schwarz, R.B.

    1987-01-01

    A dense random packed model of an amorphous alloy was used to calculate the total and partial reduced radial distribution functions, the Bhathia-Thorton number-concentration fluctuations, and the number-concentration interference functions. The model was applied to amorphous Ni/sub 35/Ti/sub 65/ using atomic radii of 1.10 and 1.58 A/sup -1/ for nickel and zirconium, respectively. Chemical short-range order was included in the model by permuting nickel-zirconium nearest-neighbors atoms pairs in response to a decrease in the alloy's enthalpy. The permutations were found to decrease in the Warren-Cowley order parameter from zero to -0.38. The increase in chemical short range order is accompanied by the appearance of a peak in the partial interference function I/sub Ni-Ni/(K) at K = 1.9 A/sup -1/. The increase in chemical short range order and the prepeak in I/sub Ni-Ni/(K) are tentatively attributed to the formation of double tetrahedra with three zirconium atoms at the base and two nickel atoms at the apexes. 18 refs., 5 figs.

  16. Icosahedral short-range order in amorphous Cu80Si20 by ab initio molecular dynamics simulation study

    SciTech Connect

    Wu, S.; Kramer, Matthew J.; Fang, Xiaowei; Wang, Shy-Guey; Wang, Cai-Zhuang; Ho, Kai-Ming; Ding, Z.J.; Chen, L.Y.

    2012-04-26

    Short-range order in liquid and amorphous structures of Cu80Si20 is studied by ab initio molecular dynamics simulations. We performed the simulations at 1140 and 300 K respectively to investigate the local structure change from liquid to amorphous. The result of structure factor in comparison with experimental data indicates that our simulation of amorphous Cu80Si20 is reliable. By using the bond-angle distribution function, Honeycutt–Andersen index, Voronoi tessellation method, and the atomistic cluster alignment method, the icosahedral short-range order in the system is revealed. Strong Cu–Si interaction was also observed.

  17. Role of Short-Range Order and Hyperuniformity in the Formation of Band Gaps in Disordered Photonic Materials

    NASA Astrophysics Data System (ADS)

    Froufe-Pérez, Luis S.; Engel, Michael; Damasceno, Pablo F.; Muller, Nicolas; Haberko, Jakub; Glotzer, Sharon C.; Scheffold, Frank

    2016-07-01

    We study photonic band gap formation in two-dimensional high-refractive-index disordered materials where the dielectric structure is derived from packing disks in real and reciprocal space. Numerical calculations of the photonic density of states demonstrate the presence of a band gap for all polarizations in both cases. We find that the band gap width is controlled by the increase in positional correlation inducing short-range order and hyperuniformity concurrently. Our findings suggest that the optimization of short-range order, in particular the tailoring of Bragg scattering at the isotropic Brillouin zone, are of key importance for designing disordered PBG materials.

  18. Short Range-Ordered Minerals: Insight into Aqueous Alteration Processes on Mars

    NASA Technical Reports Server (NTRS)

    Ming, Douglas W.; Morris, R. V.; Golden, D. C.

    2011-01-01

    Short range-ordered (SRO) aluminosilicates (e.g., allophane) and nanophase ferric oxides (npOx) are common SRO minerals derived during aqueous alteration of basaltic materials. NpOx refers to poorly crystalline or amorphous alteration products that can be any combination of superparamagnetic hematite and/or goethite, akaganeite, schwertmannite, ferrihydrite, iddingsite, and nanometer-sized ferric oxide particles that pigment palagonitic tephra. Nearly 30 years ago, SRO phases were suggested as alteration phases on Mars based on similar spectral properties for altered basaltic tephra on the slopes of Mauna Kea in Hawaii and Martian bright regions measured by Earth-based telescopes. Detailed characterization of altered basaltic tephra on Mauna Kea have identified a variety of alteration phases including allophane, npOx, hisingerite, jarosite, alunite, hematite, goethite, ferrihydrite, halloysite, kaolinite, smectite, and zeolites. The presence of npOx and other Fe-bearing minerals (jarosite, hematite, goethite) was confirmed by the M ssbauer Spectrometer onboard the Mars Exploration Rovers. Although the presence of allophane has not been definitely identified on Mars robotic missions, chemical analysis by the Spirit and Opportunity rovers and thermal infrared spectral orbital measurements suggest the presence of allophane or allophane-like phases on Mars. SRO phases form under a variety of environmental conditions on Earth ranging from cold and arid to warm and humid, including hydrothermal conditions. The formation of SRO aluminosilicates such as allophane (and crystalline halloysite) from basaltic material is controlled by several key factors including activity of water, extent of leaching, Si activity in solution, and available Al. Generally, a low leaching index (e.g., wet-dry cycles) and slightly acidic to alkaline conditions are necessary. NpOx generally form under aqueous oxidative weathering conditions, although thermal oxidative alteration may occasional be

  19. Short Range-Ordered Minerals: Insight into Aqueous Alteration Processes on Mars

    NASA Astrophysics Data System (ADS)

    Ming, D. W.; Morris, R. V.; Golden, D. C.

    2011-12-01

    Short range-ordered (SRO) aluminosilicates (e.g., allophane) and nanophase ferric oxides (npOx) are common SRO minerals derived during aqueous alteration of basaltic materials. NpOx refers to poorly crystalline or amorphous alteration products that can be any combination of superparamagnetic hematite and/or goethite, akaganeite, schwertmannite, ferrihydrite, iddingsite, and nanometer-sized ferric oxide particles that pigment palagonitic tephra. Nearly 30 years ago, SRO phases were suggested as alteration phases on Mars based on similar spectral properties for altered basaltic tephra on the slopes of Mauna Kea in Hawaii and Martian bright regions measured by Earth-based telescopes. Detailed characterization of altered basaltic tephra on Mauna Kea have identified a variety of alteration phases including allophane, npOx, hisingerite, jarosite, alunite, hematite, goethite, ferrihydrite, halloysite, kaolinite, smectite, and zeolites. The presence of npOx and other Fe-bearing minerals (jarosite, hematite, goethite) was confirmed by the Mössbauer Spectrometer onboard the Mars Exploration Rovers. Although the presence of allophane has not been definitely identified on Mars robotic missions, chemical analysis by the Spirit and Opportunity rovers and thermal infrared spectral orbital measurements suggest the presence of allophane or allophane-like phases on Mars. SRO phases form under a variety of environmental conditions on Earth ranging from cold and arid to warm and humid, including hydrothermal conditions. The formation of SRO aluminosilicates such as allophane (and crystalline halloysite) from basaltic material is controlled by several key factors including activity of water, extent of leaching, Si activity in solution, and available Al. Generally, a low leaching index (e.g., wet-dry cycles) and slightly acidic to alkaline conditions are necessary. NpOx generally form under aqueous oxidative weathering conditions, although thermal oxidative alteration may occasional be

  20. Short Range Order Signature in Crystalline and Amorphous GeSbTe Xanes Spectra

    NASA Astrophysics Data System (ADS)

    Raty, Jean-Yves; Otjacques, C. Éline; Pekoz, Rengin; Bichara, Christophe; Lordi, Vince

    2011-03-01

    A new implementation of XANES spectra calculations within DFT and PAW potentials is used to compute the XANES spectra of various amorphous and crystalline GeSbTe structures. A clear correlation between the local order, either tetrahedral or distorted octahedral, and the shape of the XANES signal is observed. These calculations provide a new interpretation of past XANES measurements, relating essentially the phase change mechanism to a moderate modification of the local environment of the Ge atoms. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work was supported by the Belgian PAI 3/42 program and the FNRS-FRFC.

  1. Quantitative description of short-range order and its influence on the electronic structure in Ag-Pd alloys.

    PubMed

    Hoffmann, M; Marmodoro, A; Ernst, A; Hergert, W; Dahl, J; Lång, J; Laukkanen, P; Punkkinen, M P J; Kokko, K

    2016-08-03

    We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the outcome of spectroscopic measurements. We aim at quantifying the degree of potential SRO with a proper parameter. The theoretical modeling is done with the Korringa-Kohn-Rostoker Green's function method. Therein, the extended multi-sublattice non-local coherent potential approximation is used to include SRO. As a model system, we use the binary solid solution Ag c Pd1-c at three representative concentrations c  =  0.25, 0.5 and 0.75. The degree of SRO is varied from local ordering to local segregation through an intermediate completely uncorrelated state. We observe some pronounced features, which change over the whole energy range of the valence bands as a function of SRO in the alloy. These spectral variations should be traceable in modern photoemission experiments.

  2. Quantitative description of short-range order and its influence on the electronic structure in Ag-Pd alloys

    NASA Astrophysics Data System (ADS)

    Hoffmann, M.; Marmodoro, A.; Ernst, A.; Hergert, W.; Dahl, J.; Lång, J.; Laukkanen, P.; Punkkinen, M. P. J.; Kokko, K.

    2016-08-01

    We investigate the effect of short-range order (SRO) on the electronic structure in alloys from the theoretical point of view using density of states (DOS) data. In particular, the interaction between the atoms at different lattice sites is affected by chemical disorder, which in turn is reflected in the fine structure of the DOS and, hence, in the outcome of spectroscopic measurements. We aim at quantifying the degree of potential SRO with a proper parameter. The theoretical modeling is done with the Korringa-Kohn-Rostoker Green’s function method. Therein, the extended multi-sublattice non-local coherent potential approximation is used to include SRO. As a model system, we use the binary solid solution Ag c Pd1-c at three representative concentrations c  =  0.25, 0.5 and 0.75. The degree of SRO is varied from local ordering to local segregation through an intermediate completely uncorrelated state. We observe some pronounced features, which change over the whole energy range of the valence bands as a function of SRO in the alloy. These spectral variations should be traceable in modern photoemission experiments.

  3. Two-electron distribution functions and short-range electron correlations of atoms and molecules by first principles T-matrix calculations.

    PubMed

    Noguchi, Yoshifumi; Ishii, Soh; Ohno, Kaoru

    2006-09-21

    The accurate first principles description of the correlations between electrons has been a topic of interest in molecular physics. We have reported in our previous paper [J. Chem. Phys. 123, 144112 (2005)] that the T matrix, which is the ladder diagrams up to the infinite order, can accurately represent the short-range electron correlations while calculating the double ionization energy spectra of atoms and molecules. In this paper, we calculate the two-electron distribution functions of real systems (Ar, CO, CO(2), and C(2)H(2)) from the eigenvalue equation associated with the Bethe-Salpeter equation for the T matrix by beginning with the local density approximation of the density functional theory and the GW approximation. We found that when the interelectron distance is very small, the Coulomb hole appears between antiparallel spin electrons due to the short-range repulsive Coulomb interaction. The resulting two-electron distribution functions clearly show the Coulomb hole.

  4. Spin-orbital short-range order on a honeycomb-based lattice.

    PubMed

    Nakatsuji, S; Kuga, K; Kimura, K; Satake, R; Katayama, N; Nishibori, E; Sawa, H; Ishii, R; Hagiwara, M; Bridges, F; Ito, T U; Higemoto, W; Karaki, Y; Halim, M; Nugroho, A A; Rodriguez-Rivera, J A; Green, M A; Broholm, C

    2012-05-04

    Frustrated magnetic materials, in which local conditions for energy minimization are incompatible because of the lattice structure, can remain disordered to the lowest temperatures. Such is the case for Ba(3)CuSb(2)O(9), which is magnetically anisotropic at the atomic scale but curiously isotropic on mesoscopic length and time scales. We find that the frustration of Wannier's Ising model on the triangular lattice is imprinted in a nanostructured honeycomb lattice of Cu(2+) ions that resists a coherent static Jahn-Teller distortion. The resulting two-dimensional random-bond spin-1/2 system on the honeycomb lattice has a broad spectrum of spin-dimer-like excitations and low-energy spin degrees of freedom that retain overall hexagonal symmetry.

  5. Key role of the short-range order on the response of the titanate pyrochlore Y2T i2O7 to irradiation

    NASA Astrophysics Data System (ADS)

    Sattonnay, G.; Cammelli, S.; Menut, D.; Sellami, N.; Grygiel, C.; Monnet, I.; Béchade, J. L.; Crocombette, J. P.; Chartier, A.; Soulié, A.; Tétot, R.; Legros, C.; Simon, P.; Miro, S.; Thomé, L.

    2016-12-01

    Ordering and disordering processes in complex oxides strongly influence their physicochemical properties when they are submitted to severe conditions, such as high temperature, high pressure, or irradiation. This paper examines the role played by the local atomic order on the structural stability of Y2T i2O7 pyrochlore submitted to ion irradiation by combining experimental and atomistic computation studies. X-ray absorption spectroscopy at the Ti K edge, molecular dynamics simulations, and calculations using a tight-binding variable-charge model show that the short-range order around Ti atoms in Y2T i2O7 is strongly modified by irradiation. Strong local distortions around Ti defects occur due to a decrease of the Ti coordination number. These local atomic rearrangements trigger the overall amorphization of the compound. These results show that the local short-range order influences the long-range structural stability of complex oxides, thus providing a key feature for the control of the functional properties of these materials.

  6. Understanding the Cu-Zn brass alloys using a short-range-order cluster model: significance of specific compositions of industrial alloys

    PubMed Central

    Hong, H. L.; Wang, Q.; Dong, C.; Liaw, Peter K.

    2014-01-01

    Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn α-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn1~6 and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1st-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys. PMID:25399835

  7. Understanding the Cu-Zn brass alloys using a short-range-order cluster model: significance of specific compositions of industrial alloys

    NASA Astrophysics Data System (ADS)

    Hong, H. L.; Wang, Q.; Dong, C.; Liaw, Peter K.

    2014-11-01

    Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn α-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn1~6 and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1st-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys.

  8. Formation and transformation of a short range ordered iron carbonate precursor

    NASA Astrophysics Data System (ADS)

    Dideriksen, Knud; Frandsen, Cathrine; Bovet, Nicolas; Wallace, Adam F.; Sel, Ozlem; Arbour, Tyler; Navrotsky, Alexandra; De Yoreo, James J.; Banfield, Jillian F.

    2015-09-01

    Fe(II)-carbonates, such as siderite, form in environments where O2 is scarce, e.g., during marine sediment diagenesis, corrosion and possibly CO2 sequestration, but little is known about their formation pathways. We show that early precipitates from carbonate solutions containing 0.1 M Fe(II) with varying pH produced broad peaks in X-ray diffraction and contained dominantly Fe and CO3 when probed with X-ray photoelectron spectroscopy. Reduced pair distribution function (PDF) analysis shows only peaks corresponding to interatomic distances below 15 Å, reflecting a material with no long range structural order. Moreover, PDF peak positions differ from those for known iron carbonates and hydroxides. Mössbauer spectra also deviate from those expected for known iron carbonates and suggest a less crystalline structure. These data show that a previously unidentified iron carbonate precursor phase formed. Its coherent scattering domains determined from PDF analysis are slightly larger than for amorphous calcium carbonate, suggesting that the precursor could be nanocrystalline. Replica exchange molecular dynamics simulations of Fe-carbonate polynuclear complexes yield PDF peak positions that agree well with those from experiments, offering the possibility that the material is a condensate of such complexes, assembled in a relatively unorganised fashion. If this is the case, the material could be nearly amorphous, rather than being composed of well defined nanocrystals. PDF measurements of samples ageing in solution coupled with refinement with the software PDFgui show that the material transforms to siderite or siderite/chukanovite mixtures within hours and that the transformation rate depends on pH. The identified Fe-carbonate precursor may potentially form during anaerobic corrosion or bacterial Fe reduction.

  9. Static and dynamic X Y -like short-range order in a frustrated magnet with exchange disorder

    NASA Astrophysics Data System (ADS)

    Ross, K. A.; Krizan, J. W.; Rodriguez-Rivera, J. A.; Cava, R. J.; Broholm, C. L.

    2016-01-01

    A single crystal of the Co2 +-based pyrochlore NaCaCo2F7 was studied by inelastic neutron scattering. This frustrated magnet with quenched exchange disorder remains in a strongly correlated paramagnetic state down to 1/60th of the Curie-Weiss temperature. Below Tf=2.4 K, diffuse elastic scattering develops and comprises 30 ±10 % of the total magnetic scattering, as expected for Jeff=1 /2 moments frozen on a time scale that exceeds ℏ /δ E =3.8 ps. The diffuse scattering is consistent with short range X Y antiferromagnetism with a correlation length of 16 Å. The momentum (Q ) dependence of the inelastic intensity indicates relaxing X Y -like antiferromagnetic clusters at energies below ˜5.5 meV, and collinear antiferromagnetic fluctuations above this energy. The relevant X Y configurations form a continuous manifold of symmetry-related states. Contrary to well-known models that produce this continuous manifold, order-by-disorder does not select an ordered state in NaCaCo2F7 despite evidence for weak (˜12 % ) exchange disorder. Instead, NaCaCo2F7 freezes into short range ordered clusters that span this manifold.

  10. Amylose Phase Composition As Analyzed By FTIR In A Temperature Ramp: Influence Of Short Range Order On The Thermodynamic Properties

    NASA Astrophysics Data System (ADS)

    Bernazzani, Paul; Delmas, Genevieve

    1998-03-01

    Amylose, a major component of starch, is one of the most important biopolymers, being mainly associated with the pharmacological and food industries. Although widely studied, a complete control and understanding of the physical properties of amylose is still lacking. It is well known that structure and phase transition are important aspects of the functionality of biopolymers since they influence physical attributes such as appearance, digestibility, water holding capacity, etc. In the past, we have studied polyethylene phase composition by DSC in a very slow temperature (T) ramp (1K/h) and have demonstrated the presence and importance of short-range order on the polymer and its characteristics. In this study, we evaluated the phase composition of potato amylose and associated the thermodynamic properties with the presence of short-range order. Two methods were correlated, DSC (in a 1K/h T-ramp) and FTIR as a function of temperature, also in a 1K/h T-ramp. The effects of the various phases on thermodynamic properties such as gelation and enzyme or chemical resistance are discussed.

  11. Temperature and composition dependence of short-range order and entropy, and statistics of bond length: the semiconductor alloy (GaN)(1-x)(ZnO)(x).

    PubMed

    Liu, Jian; Pedroza, Luana S; Misch, Carissa; Fernández-Serra, Maria V; Allen, Philip B

    2014-07-09

    We present total energy and force calculations for the (GaN)1-x(ZnO)x alloy. Site-occupancy configurations are generated from Monte Carlo (MC) simulations, on the basis of a cluster expansion model proposed in a previous study. Local atomic coordinate relaxations of surprisingly large magnitude are found via density-functional calculations using a 432-atom periodic supercell, for three representative configurations at x = 0.5. These are used to generate bond-length distributions. The configurationally averaged composition- and temperature-dependent short-range order (SRO) parameters of the alloys are discussed. The entropy is approximated in terms of pair distribution statistics and thus related to SRO parameters. This approximate entropy is compared with accurate numerical values from MC simulations. An empirical model for the dependence of the bond length on the local chemical environments is proposed.

  12. Transition from Short-Range to Long-Range Order in Lead-Bismuthate Oxide Glass Matrices

    NASA Astrophysics Data System (ADS)

    Simon, V.; Pop, R.; Simon, S.

    Glass transition and nucleation temperatures as well as densities and molar volumes of xBi2O3.yPbO (0.5<=x/y<=4) are reported. The glass transition temperature and molar volume are further analysed in terms of structural data. The obtained results indicate the occurrence of structural changes from short range to long range order induced by the heat treatment applied at 550°C, as per DTA results. These changes depend on the x/y ratio between Bi2O3 and PbO content. The compositional variation of the molar volume of untreated and heat-treated samples are evidences that both Bi2O3 and PbO play the role of network formers.

  13. Understanding the Cu-Zn brass alloys using a short-range-order cluster model: Significance of specific compositions of industrial alloys

    SciTech Connect

    Hong, H. L.; Wang, Q.; Dong, C.; Liaw, Peter K.

    2014-11-17

    Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn a-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn1,6 and [Zn-Cu12](Zn,Cu)6, which explain the a-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1st-neighbor cluster, and each cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. The revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, therefore offering a fundamental and practical method towards composition interpretations of all kinds of alloys.

  14. Understanding the Cu-Zn brass alloys using a short-range-order cluster model: Significance of specific compositions of industrial alloys

    DOE PAGES

    Hong, H. L.; Wang, Q.; Dong, C.; ...

    2014-11-17

    Metallic alloys show complex chemistries that are not yet understood so far. It has been widely accepted that behind the composition selection lies a short-range-order mechanism for solid solutions. The present paper addresses this fundamental question by examining the face-centered-cubic Cu-Zn α-brasses. A new structural approach, the cluster-plus-glue-atom model, is introduced, which suits specifically for the description of short-range-order structures in disordered systems. Two types of formulas are pointed out, [Zn-Cu12]Zn1~6 and [Zn-Cu12](Zn,Cu)6, which explain the α-brasses listed in the American Society for Testing and Materials (ASTM) specifications. In these formulas, the bracketed parts represent the 1st-neighbor cluster, and eachmore » cluster is matched with one to six 2nd-neighbor Zn atoms or with six mixed (Zn,Cu) atoms. Such a cluster-based formulism describes the 1st- and 2nd-neighbor local atomic units where the solute and solvent interactions are ideally satisfied. The Cu-Ni industrial alloys are also explained, thus proving the universality of the cluster-formula approach in understanding the alloy selections. As a result, the revelation of the composition formulas for the Cu-(Zn,Ni) industrial alloys points to the common existence of simple composition rules behind seemingly complex chemistries of industrial alloys, thus offering a fundamental and practical method towards composition interpretations of all kinds of alloys.« less

  15. Incommensurate short-range multipolar order parameter of phase II in Ce3Pd20Si6

    NASA Astrophysics Data System (ADS)

    Portnichenko, P. Y.; Paschen, S.; Prokofiev, A.; Vojta, M.; Cameron, A. S.; Mignot, J.-M.; Ivanov, A.; Inosov, D. S.

    2016-12-01

    The clathrate compound Ce3Pd20Si6 is a heavy-fermion metal that exhibits magnetically hidden order at low temperatures. Reputedly, this exotic type of magnetic ground state, known as "phase II", could be associated with the ordering of Ce 4 f quadrupolar moments. In contrast to conventional (dipolar) order, it has vanishing Bragg intensity in zero magnetic field and, as a result, has escaped direct observation by neutron scattering until now. Here we report the observation of diffuse magnetic neutron scattering induced by an application of magnetic field along either the [1 1 ¯0 ] or the [001 ] direction within phase II. The broad elastic magnetic signal that surrounds the (111) structural Bragg peak can be attributed to a short-range G -type antiferromagnetic arrangement of field-induced dipoles modulated by the underlying multipolar order on the simple-cubic sublattice of Ce ions occupying the 8 c Wyckoff site. In addition, for magnetic fields applied along the [001 ] direction, the diffuse magnetic peaks in Ce3Pd20Si6 become incommensurate, suggesting a more complex modulated structure of the underlying multipolar order that can be continuously tuned by a magnetic field.

  16. Thermal ageing and short-range ordering of Alloy 690 between 350 and 550 °C

    NASA Astrophysics Data System (ADS)

    Mouginot, Roman; Sarikka, Teemu; Heikkilä, Mikko; Ivanchenko, Mykola; Ehrnstén, Ulla; Kim, Young Suk; Kim, Sung Soo; Hänninen, Hannu

    2017-03-01

    Thermal ageing of Alloy 690 triggers an intergranular (IG) carbide precipitation and is known to promote an ordering reaction causing lattice contraction. It may affect the long-term primary water stress corrosion cracking (PWSCC) resistance of pressurized water reactor (PWR) components. Four conditions of Alloy 690 (solution annealed, cold-rolled and/or heat-treated) were aged between 350 and 550 °C for 10 000 h and characterized. Although no direct observation of ordering was made, variations in hardness and lattice parameter were attributed to the formation of short-range ordering (SRO) in all conditions with a peak level at 420 °C, consistent with the literature. Prior heat treatment induced ordering before thermal ageing. At higher temperatures, stress relaxation, recrystallization and α-Cr precipitation were observed in the cold-worked samples, while a disordering reaction was inferred in all samples based on a decrease in hardness. IG precipitation of M23C6 carbides increased with increasing ageing temperature in all conditions, as well as diffusion-induced grain boundary migration (DIGM).

  17. Special quasiordered structures: Role of short-range order in the semiconductor alloy (GaN) 1 -x(ZnO) x

    NASA Astrophysics Data System (ADS)

    Liu, Jian; Fernández-Serra, Maria V.; Allen, Philip B.

    2016-02-01

    This paper studies short-range order (SRO) in the semiconductor alloy (GaN) 1 -x(ZnO) x. Monte Carlo simulations performed on a density functional theory (DFT)-based cluster expansion model show that the heterovalent alloys exhibit strong SRO because of the energetic preference for the valence-matched nearest-neighbor Ga-N and Zn-O pairs. To represent the SRO-related structural correlations, we introduce the concept of special quasiordered structure (SQoS). Subsequent DFT calculations reveal the dramatic influence of SRO on the atomic, electronic, and vibrational properties of the (GaN) 1 -x(ZnO) x alloy. Due to the enhanced statistical presence of the energetically unfavored Zn-N bonds with the strong Zn 3 d -N 2 p repulsion, the disordered alloys exhibit much larger lattice bowing and band-gap reduction than those of the short-range ordered alloys. Lattice vibrational entropy tilts the alloy toward less SRO.

  18. Large magnetoelectric coupling in magnetically short-range ordered Bi5Ti3FeO15 film

    NASA Astrophysics Data System (ADS)

    Zhao, Hongyang; Kimura, Hideo; Cheng, Zhenxiang; Osada, Minoru; Wang, Jianli; Wang, Xiaolin; Dou, Shixue; Liu, Yan; Yu, Jianding; Matsumoto, Takao; Tohei, Tetsuya; Shibata, Naoya; Ikuhara, Yuichi

    2014-06-01

    Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi5Ti3FeO15 with high ferroelectric Curie temperature of ~1000 K. Bi5Ti3FeO15 thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at ~620 K. In Bi5Ti3FeO15 with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of ~400 mV/Oe.cm even at room temperature.

  19. Large magnetoelectric coupling in magnetically short-range ordered Bi5Ti3FeO15 film

    PubMed Central

    Zhao, Hongyang; Kimura, Hideo; Cheng, Zhenxiang; Osada, Minoru; Wang, Jianli; Wang, Xiaolin; Dou, Shixue; Liu, Yan; Yu, Jianding; Matsumoto, Takao; Tohei, Tetsuya; Shibata, Naoya; Ikuhara, Yuichi

    2014-01-01

    Multiferroic materials, which offer the possibility of manipulating the magnetic state by an electric field or vice versa, are of great current interest. However, single-phase materials with such cross-coupling properties at room temperature exist rarely in nature; new design of nano-engineered thin films with a strong magneto-electric coupling is a fundamental challenge. Here we demonstrate a robust room-temperature magneto-electric coupling in a bismuth-layer-structured ferroelectric Bi5Ti3FeO15 with high ferroelectric Curie temperature of ~1000 K. Bi5Ti3FeO15 thin films grown by pulsed laser deposition are single-phase layered perovskit with nearly (00l)-orientation. Room-temperature multiferroic behavior is demonstrated by a large modulation in magneto-polarization and magneto-dielectric responses. Local structural characterizations by transmission electron microscopy and Mössbauer spectroscopy reveal the existence of Fe-rich nanodomains, which cause a short-range magnetic ordering at ~620 K. In Bi5Ti3FeO15 with a stable ferroelectric order, the spin canting of magnetic-ion-based nanodomains via the Dzyaloshinskii-Moriya interaction might yield a robust magneto-electric coupling of ~400 mV/Oe·cm even at room temperature. PMID:24918357

  20. Modular organization of directionally tuned cells in the motor cortex: Is there a short-range order?

    NASA Astrophysics Data System (ADS)

    Amirikian, Bagrat; Georgopoulos, Apostolos P.

    2003-10-01

    We investigated the presence of short-range order (<600 μm) in the directional properties of neurons in the motor cortex of the monkey. For that purpose, we developed a quantitative method for the detection of functional cortical modules and used it to examine such potential modules formed by directionally tuned cells. In the functional domain, we labeled each cell by its preferred direction (PD) vector in 3D movement space; in the spatial domain, we used the position of the tip of the recording microelectrode as the cell's coordinate. The images produced by this method represented two orthogonal dimensions in the cortex; one was parallel ("horizontal") and the other perpendicular ("vertical") to the cortical layers. The distribution of directionally tuned cells in these dimensions was nonuniform and highly structured. Specifically, cells with similar PDs tended to segregate into vertically oriented minicolumns 50-100 μm wide and at least 500 μm high. Such minicolumns aggregated across the horizontal dimension in a secondary structure of higher order. In this structure, minicolumns with similar PDs were 200 μm apart and were interleaved with minicolumns representing nearly orthogonal PDs; in addition, nonoverlapping columns representing nearly opposite PDs were 350 μm apart.

  1. Short-range ordered photonic structures of lamellae-forming diblock copolymers for excitation-regulated fluorescence enhancement

    NASA Astrophysics Data System (ADS)

    Kim, Se Hee; Kim, Ki-Se; Char, Kookheon; Yoo, Seong Il; Sohn, Byeong-Hyeok

    2016-05-01

    Photonic crystals can be represented by periodic nanostructures with alternating refractive indices, which create artificial stop bands with the appearance of colors. In this regard, nanodomains of block copolymers and the corresponding structural colors have been intensively studied in the past. However, the practical application of photonic crystals of block copolymers has been limited to a large degree because of the presence of large defects and grain boundaries in the nanodomains of block copolymers. The present study focuses on the alternative opportunity of short-range ordered nanodomains of block copolymers for fluorescence enhancement, which also has a direct relevance to the development of fluorescence sensors or detectors. The enhancement mechanism was found to be interconnected with the excitation process rather than the alternation of the decay kinetics. In particular, we demonstrate that randomly oriented, but regular grains of lamellae of polystyrene-block-polyisoprene, PS-b-PI, diblock copolymers and their blend with PS homopolymers can behave as Bragg mirrors to induce multiple reflections of the excitation source inside the photonic structures. This process in turn significantly increases the effective absorption of the given fluorophores inside the polymeric photonic structures to amplify the fluorescence signal.Photonic crystals can be represented by periodic nanostructures with alternating refractive indices, which create artificial stop bands with the appearance of colors. In this regard, nanodomains of block copolymers and the corresponding structural colors have been intensively studied in the past. However, the practical application of photonic crystals of block copolymers has been limited to a large degree because of the presence of large defects and grain boundaries in the nanodomains of block copolymers. The present study focuses on the alternative opportunity of short-range ordered nanodomains of block copolymers for fluorescence

  2. Bona-fide method for the determination of short range order and transport properties in a ferro-aluminosilicate slag

    PubMed Central

    Karalis, Konstantinos T.; Dellis, Dimitrios; Antipas, Georgios S. E.; Xenidis, Anthimos

    2016-01-01

    The thermodynamics, structural and transport properties (density, melting point, heat capacity, thermal expansion coefficient, viscosity and electrical conductivity) of a ferro-aluminosilicate slag have been studied in the solid and liquid state (1273–2273 K) using molecular dynamics. The simulations were based on a Buckingham-type potential, which was extended here, to account for the presence of Cr and Cu. The potential was optimized by fitting pair distribution function partials to values determined by Reverse Monte Carlo modelling of X-ray and neutron diffraction experiments. The resulting short range order features and ring statistics were in tight agreement with experimental data and created consensus for the accurate prediction of transport properties. Accordingly, calculations yielded rational values both for the average heat capacity, equal to 1668.58 J/(kg·K), and for the viscosity, in the range of 4.09–87.64 cP. The potential was consistent in predicting accurate values for mass density (i.e. 2961.50 kg/m3 vs. an experimental value of 2940 kg/m3) and for electrical conductivity (5.3–233 S/m within a temperature range of 1273.15–2273.15 K). PMID:27455915

  3. Solid-state NMR and short-range order in crystalline oxides and silicates: a new tool in paramagnetic resonances.

    PubMed

    Stebbins, Jonathan F; McCarty, Ryan J; Palke, Aaron C

    2017-03-01

    Most applications of high-resolution NMR to questions of short-range order/disorder in inorganic materials have been made in systems where ions with unpaired electron spins are of negligible concentration, with structural information extracted primarily from chemical shifts, quadrupolar coupling parameters, and nuclear dipolar couplings. In some cases, however, the often-large additional resonance shifts caused by interactions between unpaired electron and nuclear spins can provide unique new structural information in materials with contents of paramagnetic cations ranging from hundreds of ppm to several per cent and even higher. In this brief review we focus on recent work on silicate, phosphate, and oxide materials with relatively low concentrations of paramagnetic ions, where spectral resolution can remain high enough to distinguish interactions between NMR-observed nuclides and one or more magnetic neighbors in different bonding configurations in the first, second, and even farther cation shells. We illustrate the types of information available, some of the limitations of this approach, and the great prospects for future experimental and theoretical work in this field. We give examples for the effects of paramagnetic transition metal, lanthanide, and actinide cation substitutions in simple oxides, pyrochlore, zircon, monazite, olivine, garnet, pyrochlores, and olivine structures.

  4. Bona-fide method for the determination of short range order and transport properties in a ferro-aluminosilicate slag

    NASA Astrophysics Data System (ADS)

    Karalis, Konstantinos T.; Dellis, Dimitrios; Antipas, Georgios S. E.; Xenidis, Anthimos

    2016-07-01

    The thermodynamics, structural and transport properties (density, melting point, heat capacity, thermal expansion coefficient, viscosity and electrical conductivity) of a ferro-aluminosilicate slag have been studied in the solid and liquid state (1273-2273 K) using molecular dynamics. The simulations were based on a Buckingham-type potential, which was extended here, to account for the presence of Cr and Cu. The potential was optimized by fitting pair distribution function partials to values determined by Reverse Monte Carlo modelling of X-ray and neutron diffraction experiments. The resulting short range order features and ring statistics were in tight agreement with experimental data and created consensus for the accurate prediction of transport properties. Accordingly, calculations yielded rational values both for the average heat capacity, equal to 1668.58 J/(kg·K), and for the viscosity, in the range of 4.09-87.64 cP. The potential was consistent in predicting accurate values for mass density (i.e. 2961.50 kg/m3 vs. an experimental value of 2940 kg/m3) and for electrical conductivity (5.3-233 S/m within a temperature range of 1273.15-2273.15 K).

  5. Interplay between Long-Range Crystal Order and Short-Range Molecular Interactions Tunes Carrier Mobility in Liquid Crystal Dyes

    PubMed Central

    2017-01-01

    We investigated the influence of molecular packing on the optical and electrical properties of the liquid crystalline dye 4,7-bis[5-(2-fluoro-4-pentyl-phenyl)-2-thienyl]-2,1,3-benzothiadiazole (FPPTB). FPPTB is crystalline at room temperature, exhibits a nematic phase at temperatures above 149 °C and is in an isotropic melt at temperatures above 230 °C. Solution processed FPPTB films were subject to thermal annealing through these phase transition temperatures and characterized with X-ray diffraction and polarized optical microscopy. Cooling FPPTB films from the nematic and isotropic phases increased crystal domain size, but also induced local structural variations in the molecular packing of crystalline FPPTB. The decrease in long-range order was correlated with an increase in short-range π–π interactions, leading to changes in molecular aggregation which persisted even when the FPPTB films were cooled to room temperature. Annealing-induced changes in molecular aggregation were confirmed with optical spectroscopy. The carrier mobility in FPPTB films increased over 2 orders of magnitude from (2.2 ± 0.4) × 10–5 cm2 V–1 s–1 in as-spun films to μ = (5.0 ± 0.8) × 10–3 cm2 V–1 s–1 in films cooled from the isotropic melt. We discuss the relationship between thermal stability and high carrier mobility values in terms of the interplay between long-range molecular order and increased π–π interactions between molecular pairs in the FPPTB film. PMID:28139915

  6. Crystal fields, disorder, and antiferromagnetic short-range order in Yb0.24Sn0.76Ru

    NASA Astrophysics Data System (ADS)

    Klimczuk, T.; Wang, C. H.; Lawrence, J. M.; Xu, Q.; Durakiewicz, T.; Ronning, F.; Llobet, A.; Trouw, F.; Kurita, N.; Tokiwa, Y.; Lee, Han-Oh; Booth, C. H.; Gardner, J. S.; Bauer, E. D.; Joyce, J. J.; Zandbergen, H. W.; Movshovich, R.; Cava, R. J.; Thompson, J. D.

    2011-08-01

    We report extensive measurements on a new compound (Yb0.24Sn0.76)Ru that crystallizes in the cubic CsCl structure. Valence-band photoemission (PES) and L3 x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb3+ is split by the crystalline electric field (CEF) into a Γ7-doublet ground state and a Γ8 quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a Γ6-excited state resides at 32 meV; however, the Γ8/Γ6 transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K there is a peak in specific heat that is too broad to represent a magnetic-phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand this peak also is too narrow to represent the Kondo effect in the Γ7-doublet ground state. On the basis of the field dependence of the specific heat, we argue that antiferromagnetic (AF) short-range order (SRO) (possibly coexisting with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.

  7. Microstrain and short-range ordering of Ca and Mg cations in pyrope-grossular garnet system

    NASA Astrophysics Data System (ADS)

    DU, W.; Clark, S. M.; Walker, D.

    2016-12-01

    Synchrotron X-ray diffraction (XRD) was used to measure the unit cell parameters of synthetic pyrope (Mg3Al2Si3O12), grossular (Ca3Al2Si3O12) and four intermediate garnet solid solutions at the Advanced Light Source, Lawrence Berkeley National Laboratory (ALS on beamline 12.2.2 at room temperature and pressure). Analysis of X-ray diffraction profiles by using Williamson-Hall plots shows that XRD peak width getting broadened with diffraction angle and the degree of the XRD peak broadening changes with garnet composition. Microstrain in the garnet structure, rather than grain size variation, is the principal reason for the observed XRD peak broadening. Garnets with compositions Py80Gr20 and Py20Gr80, close to the negligibly strained end members pyrope (Py100) and grossular (Gr100), have large microstrains, which is contrast to garnet with intermediate composition Py40Gr60, which almost has no microstrain. This compositional dependent elastic structural strain shows a complex correlation with other nonideal mixing properties along the pyrope-grossular binary, for example, excess volume, mixing enthalpy, thermal expansion etc. The observation that the two end member garnets carry almost zero microstrain indicates that the microstrain calculated from XRD peak broadening is related to the Mg-Ca substitution. A different degree of short-range ordering of Ca-Mg in dodecahedral site that develops during annealing after MA crystallization may be partly responsible for these nonideal-mixing phenomena along the pyrope-grossular join.

  8. Bound states of the spin-orbit coupled ultracold atom in a one-dimensional short-range potential

    SciTech Connect

    Jursenas, Rytis; Ruseckas, Julius

    2013-05-15

    We solve the bound state problem for the Hamiltonian with the spin-orbit and the Raman coupling included. The Hamiltonian is perturbed by a one-dimensional short-range potential V which describes the impurity scattering. In addition to the bound states obtained by considering weak solutions through the Fourier transform or by solving the eigenvalue equation on a suitable domain directly, it is shown that ordinary point-interaction representations of V lead to spin-orbit induced extra states.

  9. Simultaneous occurrence of multiferroism and short-range magnetic order in DyFeO3

    SciTech Connect

    Wang, Jinchen; Liu, Juanjuan; Sheng, Jieming; Luo, Wei; Ye, Feng; Zhao, Zhiying; Sun, Xuefeng; Danilkin, Sergey A.; Deng, Guochu; Bao, Wei

    2016-04-06

    In this paper, we present a combined neutron scattering and magnetization study on the multiferroic DyFeO3, which shows a very strong magnetoelectric effect. Applying magnetic field along the c axis, the weak ferromagnetic order of the Fe ions is quickly recovered from a spin reorientation transition, and the long-range antiferromagnetic order of Dy becomes a short-range one. We found that the short-range order concurs with the multiferroic phase and is responsible for its sizable hysteresis. In conclusion, our H-T phase diagram suggests that the strong magnetoelectric effect in DyFeO3 has to be understood with not only the weak ferromagnetism of Fe but also the short-range antiferromagnetic order of Dy.

  10. Hyperfine and X-ray investigations of amorphous Fe2Er and Fe2Ce alloys and the effect of hydrogenation on short-range order

    NASA Astrophysics Data System (ADS)

    Ghafari, M.; Keune, W.; Matsuura, M.; Schletz, K. P.

    1990-07-01

    The effect of hydrogenation on the short-range order of amorphous Fe2Er and Fe2Ce alloys has been investigated by Mössbauer, X-ray and magnetization measurements. The hydrogenation leads to drastic changes in the short-range order. The results of Mössbauer measurements show two different distributions of magnetic hyperfine fields for amorphous Fe2CeH4 alloys (a-Fe2CeH4). For a-Fe2ErH3 alloys we found drastic changes in magnetic structure, which is different from the well-known magnetic structures.

  11. Short-range surface plasmonics: Localized electron emission dynamics from a 60-nm spot on an atomically flat single-crystalline gold surface.

    PubMed

    Frank, Bettina; Kahl, Philip; Podbiel, Daniel; Spektor, Grisha; Orenstein, Meir; Fu, Liwei; Weiss, Thomas; Horn-von Hoegen, Michael; Davis, Timothy J; Meyer Zu Heringdorf, Frank-J; Giessen, Harald

    2017-07-01

    We experimentally and theoretically visualize the propagation of short-range surface plasmon polaritons using atomically flat single-crystalline gold platelets on silicon substrates. We study their excitation and subfemtosecond dynamics via normal-incidence two-photon photoemission electron microscopy. By milling a plasmonic disk and grating structure into a single-crystalline gold platelet, we observe nanofocusing of the short-range surface plasmon polariton. Localized two-photon ultrafast electron emission from a spot with a smallest dimension of 60 nm is observed. Our novel approach opens the door toward reproducible plasmonic nanofocusing devices, which do not degrade upon high light intensity or heating due to the atomically flat surface without any tips, protrusions, or holes. Our nanofoci could also be used as local emitters for ultrafast electron bunches in time-resolved electron microscopes.

  12. Stripe and Short Range Order in the Charge Density Wave of 1 T -CuxTiSe2

    NASA Astrophysics Data System (ADS)

    Novello, A. M.; Spera, M.; Scarfato, A.; Ubaldini, A.; Giannini, E.; Bowler, D. R.; Renner, Ch.

    2017-01-01

    We study the impact of Cu intercalation on the charge density wave (CDW) in 1 T -CuxTiSe2 by scanning tunneling microscopy and spectroscopy. Cu atoms, identified through density functional theory modeling, are found to intercalate randomly on the octahedral site in the van der Waals gap and to dope delocalized electrons near the Fermi level. While the CDW modulation period does not depend on Cu content, we observe the formation of charge stripe domains at low Cu content (x <0.02 ) and a breaking up of the commensurate order into 2 ×2 domains at higher Cu content. The latter shrink with increasing Cu concentration and tend to be phase shifted. These findings invalidate a proposed excitonic pairing as the primary CDW formation mechanism in this material.

  13. Short range order and stability of amorphous Ge(x)Te(100-x) alloys (12 ≤ x ≤ 44.6).

    PubMed

    Jóvári, P; Piarristeguy, A; Escalier, R; Kaban, I; Bednarčik, J; Pradel, A

    2013-05-15

    Amorphous Ge(x)Te(100-x) alloys were obtained over a broad composition range (12 ≤ x ≤ 44.6) by thermal co-evaporation. Their structure was investigated by x-ray diffraction and extended x-ray absorption fine structure measurements. Experimental datasets were fitted simultaneously by the reverse Monte Carlo simulation technique. It is concluded that Te is mostly twofold coordinated and the majority of Ge atoms have four neighbours. The number of Ge-Ge and Te-Te bonds evolves monotonically with composition. Ge-Ge bonding can be observed already at x = 24 while Te-Te bonds can be found even in Ge44.6Te55.4. The models obtained by simulation show that the structure of compositions with x > 24 should be considered as a random covalent network but there is chemical ordering for x ≤ 24, exactly in the composition range where glasses can be obtained from the melt by fast quenching. The composition dependences of some physical properties also point to the connection between chemical short range order and the stability of the amorphous phase: while the glass transition temperature and microhardness increase monotonically with the composition, the thermal stability of the amorphous films goes through a maximum around x = 20-24.

  14. Short-range order of undercooled melts of PdZr2 intermetallic compound studied by X-ray and neutron scattering experiments

    NASA Astrophysics Data System (ADS)

    Klein, S.; Holland-Moritz, D.; Herlach, D. M.; Mauro, N. A.; Kelton, K. F.

    2013-05-01

    The short-range order in undercooled melts of the intermetallic Zr2Pd glass-forming alloy is investigated by combining electrostatic levitation (ESL) with high-energy X-ray diffraction and neutron diffraction. Experimentally determined structure factors are measured and analyzed with respect to various structures of short-range order. The comparative X-ray and neutron scattering experiments allow for investigations of topological and chemical short-range order. Based on these studies, no preference of a specific short-range order is found for the liquid Zr2Pd glass-forming alloy, even in the metastable state of the deeply undercooled melt. This is in agreement with an earlier report from X-ray diffraction and molecular-dynamics studies of a Zr75.5Pd24.5 liquid, which showed a broad distribution of cluster types. The results for the Zr2Pd liquid are discussed with respect to the glass-forming ability of this melt.

  15. Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary

    DOE PAGES

    John A. Schneeloch; Xu, Zhijun; Winn, B.; ...

    2015-12-28

    We report neutron inelastic scattering experiments on single-crystal PbMg1/3Nb2/3O3 doped with 32% PbTiO3, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field E∥ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to E weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to E weakens for energy transfers 4 ≤ ℏω ≤ 9 meV. However, TA and TO phonons polarized perpendicular to E show no change. This anisotropicmore » field response is similar to that of the diffuse scattering cross section, which, as previously reported, is suppressed when polarized parallel to E but not when polarized perpendicular to E. Lastly, our findings suggest that the lattice dynamics and dynamic short-range polar correlations that give rise to the diffuse scattering are coupled.« less

  16. Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary

    SciTech Connect

    John A. Schneeloch; Xu, Zhijun; Winn, B.; Stock, C.; Gehring, P. M.; Birgeneau, R. J.; Xu, Guangyong

    2015-12-28

    We report neutron inelastic scattering experiments on single-crystal PbMg1/3Nb2/3O3 doped with 32% PbTiO3, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field E∥ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to E weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to E weakens for energy transfers 4 ≤ ℏω ≤ 9 meV. However, TA and TO phonons polarized perpendicular to E show no change. This anisotropic field response is similar to that of the diffuse scattering cross section, which, as previously reported, is suppressed when polarized parallel to E but not when polarized perpendicular to E. Lastly, our findings suggest that the lattice dynamics and dynamic short-range polar correlations that give rise to the diffuse scattering are coupled.

  17. Phonon coupling to dynamic short-range polar order in a relaxor ferroelectric near the morphotropic phase boundary

    NASA Astrophysics Data System (ADS)

    Schneeloch, John A.; Xu, Zhijun; Winn, B.; Stock, C.; Gehring, P. M.; Birgeneau, R. J.; Xu, Guangyong

    2015-12-01

    We report neutron inelastic scattering experiments on single-crystal PbMg1 /3Nb2 /3O3 doped with 32% PbTiO3, a relaxor ferroelectric that lies close to the morphotropic phase boundary. When cooled under an electric field E ∥ [001] into tetragonal and monoclinic phases, the scattering cross section from transverse acoustic (TA) phonons polarized parallel to E weakens and shifts to higher energy relative to that under zero-field-cooled conditions. Likewise, the scattering cross section from transverse optic (TO) phonons polarized parallel to E weakens for energy transfers 4 ≤ℏ ω ≤9 meV. However, TA and TO phonons polarized perpendicular to E show no change. This anisotropic field response is similar to that of the diffuse scattering cross section, which, as previously reported, is suppressed when polarized parallel to E but not when polarized perpendicular to E . Our findings suggest that the lattice dynamics and dynamic short-range polar correlations that give rise to the diffuse scattering are coupled.

  18. Observation of electronic states on Si(111)-(7 x 7) through short-range attractive force with noncontact atomic force spectroscopy.

    PubMed

    Arai, T; Tomitori, M

    2004-12-17

    We experimentally reveal that the short-range attractive force between a Si tip and a Si(111)-(7 x 7) surface is enhanced at specified bias voltages; we conduct force spectroscopy based on noncontact atomic force microscopy with changing bias voltage at a fixed separation. The spectra exhibit prominent peaks and a broad peak, which are attributed to quantum mechanical resonance as the energy levels of sample surface states are tuned to those of the tip states by shifting the Fermi level through changing bias voltage, and to the resonating states over a lowered tunneling barrier, respectively.

  19. Comparing the activity of aluminum in two B horizons developed from volcanic ash deposits in Japan, dominated by short-range ordered aluminosilicates and crystalline clay minerals, respectively

    NASA Astrophysics Data System (ADS)

    Yagasaki, Yasumi; Mulder, Jan; Okazaki, Masanori

    2006-01-01

    Mechanisms controlling the activity of free aluminum (Al) in Bw1 horizons of soils developed from volcanic ash deposits in Japan were investigated by means of acid-base titrations and kinetic studies. In a Bw1 horizon, with a high content of acid-oxalate extractable Al, soil solution reached equilibrium with short-range ordered aluminosilicates in the order of days. Relatively fast kinetics of the release and precipitation of Al and Si indicate a high reactivity of short-range ordered aluminosilicates in the soil. In the Bw1 horizon of an adjacent soil, with a high content of crystalline clay minerals like halloysite and interlayered vermiculite, solution remained well undersaturated with respect to short-range ordered aluminosilicates and aluminum hydroxide. Apparent equilibrium with respect to halloysite occurred after more than 30 days. This halloysite ( logKso0=3.74±0.02 (25 °C)) has a solubility that is less than that reported in the literature ( logKso0=4.36 (25°C)). Our findings suggest that different reactive aluminosilicates may control the activity of free Al in sub-surface horizons of volcanic ash soils with different mineralogy.

  20. Short-range order of low-coverage Ti /Al(111): Implications for hydrogen storage in complex metal hydrides

    NASA Astrophysics Data System (ADS)

    Muller, E.; Sutter, E.; Zahl, P.; Ciobanu, C. V.; Sutter, P.

    2007-04-01

    Using scanning tunneling microscopy and density functional theory, we characterize the population of low-coverage Ti atoms on Al(111) as a model surface system for transition metal doped alanate hydrogen storage compounds, such as NaAlH4. When deposited at room temperature, Ti is kinetically trapped in first-layer substitutional sites, avoids nearest-neighbor locations, and preferentially forms next-nearest-neighbor pairs, similar to a structure that has been predicted to dissociate H2 with no energy barrier. The results on this well-defined system suggest the presence of a large population of Ti-pair complexes that may catalyze the dissociative chemisorption of hydrogen in Ti-doped alanate storage materials.

  1. Short-ranged and short-lived charge-density-wave order and pseudogap features in underdoped cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Greco, Andrés; Bejas, Matías

    2011-06-01

    The pseudogap phase of high-Tc cuprates is controversially attributed to preformed pairs or to a phase which coexists and competes with superconductivity. One of the challenges is to develop theoretical and experimental studies in order to distinguish between both proposals. Very recently, researchers at Stanford have reported [M. Hashimoto , Nat. Phys.PRLTAO1745-247310.1038/nphys1632 6, 414 (2010); R.-H. He , ScienceSCIEAS0036-807510.1126/science.1198415 331, 1579 (2011)] angle-resolved photoemission spectroscopy experiments on Pb-Bi2201 supporting the point of view that the pseudogap is distinct from superconductivity and associated to a spacial symmetry breaking without long-range order. In this paper, we show that many features reported by these experiments can be described in the framework of the t-J model considering self-energy effects in the proximity to a d charge-density-wave instability.

  2. Chemical inhomogeneity, short-range order, and magnetism in the LiNiO2 -NiO solid solution.

    PubMed

    Barton, Phillip T; Premchand, Y Daniel; Chater, Philip A; Seshadri, Ram; Rosseinsky, Matthew J

    2013-10-18

    NiO:Li is an early exemplar for which hole-doping of a correlated insulator gives rise to rich and varied magnetic behavior. It is also an important system from the viewpoint of p-type transparent conducting oxides, and is representative of a large class of materials that have been used in lithium ion batteries, since the end-member compound, LiNiO2 , belongs to the class of layered cathode materials. Despite the deceptive structural and compositional simplicity of this system, a complete understanding of its complex magnetic properties has remained elusive. Here a comprehensive investigation of the solid solution Lix Ni2-x O2 , examining samples of precise stoichiometry using a combination of high-resolution synchrotron X-ray powder diffraction and SQUID magnetometry, is provided. The focus is on the interesting region between 0.40ordering temperature changes drastically with composition. The magnetism evolves from strong G-type antiferromagnetism of x=0.40 with TN =327 K to robust uncompensated magnetic order at TN =240 K when x is close to 0.7, and to glassy A-type antiferromagnetism of x=1.00 at TN =9 K. This study demonstrates this magnetic behavior is linked to the Li-Ni chemical order that develops from short- to long-range. The interfaces between ordered domains give rise to magnetic exchange bias, which manifests as a shift in the magnetization-field loop for samples with nanoscale coherence lengths (0.54

  3. Crossover scaling of apparent first-order wetting in two-dimensional systems with short-ranged forces

    NASA Astrophysics Data System (ADS)

    Parry, Andrew O.; Malijevský, Alexandr

    2016-06-01

    Recent analyses of wetting in the semi-infinite two-dimensional Ising model, extended to include both a surface coupling enhancement and a surface field, have shown that the wetting transition may be effectively first-order and that surprisingly the surface susceptibility develops a divergence described by an anomalous exponent with value γ11eff=3/2 . We reproduce these results using an interfacial Hamiltonian model making a connection with previous studies of two-dimensional wetting, and we show that they follow from the simple crossover scaling of the singular contribution to the surface free-energy, which describes the change from apparent first-order to continuous (critical) wetting due to interfacial tunneling. The crossover scaling functions are calculated explicitly within both the strong-fluctuation and intermediate-fluctuation regimes, and they determine uniquely and more generally the value of γ11eff, which is nonuniversal for the latter regime. The location and the rounding of a line of pseudo-prewetting transitions occurring above the wetting temperature and off bulk coexistence, together with the crossover scaling of the parallel correlation length, are also discussed in detail.

  4. Evidence for short-range-ordered charge stripes far above the charge-ordering transition in La1.67Sr0.33NiO4.

    PubMed

    Abeykoon, A M Milinda; Božin, Emil S; Yin, Wei-Guo; Gu, Genda; Hill, John P; Tranquada, John M; Billinge, Simon J L

    2013-08-30

    The temperature evolution of structural effects associated with charge order (CO) and spin order in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction. We report an anomalous shrinking of the c/a lattice parameter ratio that correlates with T(CO). The sign of this change can be explained by the change in interlayer Coulomb energy between the static-stripe-ordered state and the fluctuating-stripe-ordered state or the charge-disordered state. In addition, we identify a contribution to the mean-square displacements of Ni and in-plane O atoms whose width correlates quite well with the size of the pseudogap extracted from the reported optical conductivity, with a non-Debye-like component that persists below and well above T(CO). We infer that dynamic charge-stripe correlations survive to T∼2T(CO).

  5. Evidence for Short-Range-Ordered Charge Stripes Far above the Charge-Ordering Transition in La1.67Sr0.33NiO4

    NASA Astrophysics Data System (ADS)

    Abeykoon, A. M. Milinda; Božin, Emil S.; Yin, Wei-Guo; Gu, Genda; Hill, John P.; Tranquada, John M.; Billinge, Simon J. L.

    2013-08-01

    The temperature evolution of structural effects associated with charge order (CO) and spin order in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction. We report an anomalous shrinking of the c/a lattice parameter ratio that correlates with TCO. The sign of this change can be explained by the change in interlayer Coulomb energy between the static-stripe-ordered state and the fluctuating-stripe-ordered state or the charge-disordered state. In addition, we identify a contribution to the mean-square displacements of Ni and in-plane O atoms whose width correlates quite well with the size of the pseudogap extracted from the reported optical conductivity, with a non-Debye-like component that persists below and well above TCO. We infer that dynamic charge-stripe correlations survive to T˜2TCO.

  6. Evidence for Short-Range-Ordered Charge Stripes Far above the Charge-Ordering Transition in La1.67Sr0.33NiO4

    NASA Astrophysics Data System (ADS)

    Abeykoon, A. M. Milinda; Bozin, Emil S.; Yin, Wei-Guo; Gu, Genda; Hill, John P.; Tranquada, John M.; Billinge, Simon J. L.

    2015-03-01

    The temperature evolution of structural modulation associated with charge and spin order in La1.67Sr0.33NiO4 has been investigated using neutron powder diffraction. For the first time we report an anomalous shrinking of the c/a lattice parameter ratio that correlates with TCO at the temperature where long-range stacking order of charge stripes disappears. The sign of this change can be explained by the change in interlayer Coulomb energy between the static-stripe-ordered state and the fluctuating-stripe-ordered state or the charge-disordered state. In addition, we identify a contribution to the mean-square displacements of Ni and in-plane O atoms whose width correlates quite well with the size of the pseudogap extracted from the reported optical conductivity, with a non-Debye-like component that persists below and well above TCO. Local structural parameters in the atomic pair distribution function (PDF) well-agree with this result. We infer that dynamic charge-stripe correlations survive to T ~ 2TCO. This work was supported by the DOE Grant, DE- AC02-98CH10886.

  7. Spin dynamics, short range order and spin freezing in Y0.5Ca0.5BaCo4O7

    SciTech Connect

    Stewart, John Ross; Ehlers, Georg; Fouquet, Peter; Mutka, Hannu; Payen, Christophe; Lortz, Rolf

    2011-01-01

    Y0.5Ca0.5BaCo4O7 was recently introduced as a possible candidate for capturing some of the predicted classical spin kagome ground-state features. Stimulated by this conjecture, we have taken up a more complete study of the spin correlations in this compound with neutron scattering methods on a powder sample characterized with high-resolution neutron diffraction and the temperature dependence of magnetic susceptibility and specific heat. We have found that the frustrated near-neighbor magnetic correlations involve not only the kagome planes but concern the full Co sublattice, as evidenced by the analysis of the wave-vector dependence of the short-range order. We conclude from our results that the magnetic moments are located on the Co sublattice as a whole and that correlations extend beyond the two-dimensional kagome planes. We identify intriguing dynamical properties, observing high-frequency fluctuations with a Lorentzian linewidth G?20 meV at ambient temperature. On cooling a low-frequency ({approx}1 meV) dynamical component develops alongside the high-frequency fluctuations, which eventually becomes static at temperatures below T {approx} 50 K. The high-frequency response with an overall linewidth of {approx}10 meV prevails at T?2 K, coincident with a fully elastic short-range-ordered contribution.

  8. Cluster perturbation theory in Hubbard model exactly taking into account the short-range magnetic order in 2 x 2 cluster

    SciTech Connect

    Nikolaev, S. V. Ovchinnikov, S. G.

    2010-10-15

    The cluster perturbation theory is presented in the 2D Hubbard model constructed using X operators in the Hubbard-I approximation. The short-range magnetic order is taken into account by dividing the entire lattice into individual 2 x 2 clusters and solving the eigenvalue problem in an individual cluster using exact diagonalization taking into account all excited levels. The case of half-filling taking into account jumps between nearest neighbors is considered. As a result of numerical solution, a shadow zone is discovered in the quasiparticle spectrum. It is also found that a gap in the density of states in the quasiparticle spectrum at zero temperature exists for indefinitely small values of Coulomb repulsion parameter U and increases with this parameter. It is found that the presence of this gap in the spectrum is due to the formation of a short-range antiferromagnetic order. An analysis of the temperature evolution of the density of states shows that the metal-insulator transition occurs continuously. The existence of two characteristic energy scales at finite temperatures is demonstrated, the larger scale is associated with the formation of a pseudogap in the vicinity of the Fermi level, and the smaller scale is associated with the metal-insulator transition temperature. A peak in the density of states at the Fermi level, which is predicted in the dynamic mean field theory in the vicinity of the metal-insulator transition, is not observed.

  9. Defect-induced short-range-order from a spin-ice related state in deformed pyrochlore Co2(OH)3Cl

    NASA Astrophysics Data System (ADS)

    Zheng, X. G.; Hagihala, M.; Kawae, T.; Xu, C. N.

    2008-01-01

    Recently, we observed a kagome-ice-like partial ferromagnetic order with coexisting fluctuation in a deformed pyrochlore structure Co2(OH)3Cl . Here, we show that when lattice defects are present, the remaining fluctuating spins in this material further freeze at lower temperatures below Torder near TC=10K . This low-temperature transition is glasslike requiring an extremely slow relaxation process in Co2(OH)3Cl . Enhanced disorder in (Co1-xAlx)2(OH)3Cl leads to a short-range order for the fluctuating spins. This result can be considered as an interesting analogy to the low-temperature anomaly in defect-containing pure and doped water ice, especially in the light of its relevance to the problem of residual entropy in ice-water or spin-ice transition.

  10. Statistical analysis of long- and short-range forces involved in bacterial adhesion to substratum surfaces as measured using atomic force microscopy.

    PubMed

    Chen, Yun; Busscher, Henk J; van der Mei, Henny C; Norde, Willem

    2011-08-01

    Surface thermodynamic analyses of microbial adhesion using measured contact angles on solid substrata and microbial cell surfaces are widely employed to determine the nature of the adhesion forces, i.e., the interplay between Lifshitz-van der Waals and acid-base forces. While surface thermodynamic analyses are often viewed critically, atomic force microscopy (AFM) can also provide information on the nature of the adhesion forces by means of Poisson analysis of the measured forces. This review first presents a description of Poisson analysis and its underlying assumptions. The data available from the literature for different combinations of bacterial strains and substrata are then summarized, leading to the conclusion that bacterial adhesion to surfaces is generally dominated by short-range, attractive acid-base interactions, in combination with long-range, weaker Lifshitz-van der Waals forces. This is in line with the findings of surface thermodynamic analyses of bacterial adhesion. Comparison with single-molecule ligand-receptor forces from the literature suggests that the short-range-force contribution from Poisson analysis involves a discrete adhesive bacterial cell surface site rather than a single molecular force. The adhesion force arising from these cell surface sites and the number of sites available may differ from strain to strain. Force spectroscopy, however, involves the tedious task of identifying the minor peaks in the AFM retraction force-distance curve. This step can be avoided by carrying out Poisson analysis on the work of adhesion, which can also be derived from retraction force-distance curves. This newly proposed way of performing Poisson analysis confirms that multiple molecular bonds, rather than a single molecular bond, contribute to a discrete adhesive bacterial cell surface site.

  11. Short-range ordering effects on the electronic Bloch spectral function of real materials in the nonlocal coherent-potential approximation

    NASA Astrophysics Data System (ADS)

    Marmodoro, Alberto; Ernst, Arthur; Ostanin, Sergei; Sandratskii, Leonid; Trevisanutto, Paolo E.; Lathiotakis, Nektarios N.; Staunton, Julie B.

    2016-12-01

    The nonlocal coherent-potential approximation provides a systematic technique for the study of short-range ordering effects in a variety of disordered systems. In its original formulation the technique, however, shows an unwanted dependence on details in the coarse-grained effective medium construction. This is particularly evident in the study of k ⃗-resolved quantities, such as the Bloch spectral function and other non-site-diagonal observables. We remove the issue and recover fully physical results in first principles studies of real materials, by means of a resampling procedure first proposed for model tight-binding Hamiltonians. The prescription is further generalized to the case of complex unit cell compounds, with more than a single sublattice, and illustrated through examples from metallic alloys and disordered local moment simulations of paramagnetism in the prototype iron-based superconductor FeSe.

  12. Magnetic impurity doping induced spin-glass state and short-range zigzag order in the honeycomb iridate Na2IrO3.

    PubMed

    Cai, W P; Yan, Z R; Liu, R M; Qin, M H; Zeng, M; Lu, X B; Gao, X S; Liu, J-M

    2017-10-11

    Based on the modified Heisenberg-Kitaev model, the effects of magnetic substitution on the magnetic properties of the honeycomb-lattice iridate [Formula: see text] [Formula: see text] are studied using Monte Carlo simulations. It is observed that the long-range zigzag state of the original system is rather fragile and can be replaced by a spin-glass state even for small substitution, well consistent with the experimental observation in Ru-substituted samples (Mehlawat et al 2015 Phys. Rev. B 92 134412). Both the disordered Heisenberg and Kitaev interactions caused by the magnetic ion-doping are suggested to be responsible for the magnetic phase transitions in the system. More interestingly, a short-range zigzag order is suggested to survive above the freezing temperature even at high magnetic impurity doping levels.

  13. Magnetic impurity doping induced spin-glass state and short-range zigzag order in the honeycomb iridate Na2IrO3

    NASA Astrophysics Data System (ADS)

    Cai, W. P.; Yan, Z. R.; Liu, R. M.; Qin, M. H.; Zeng, M.; Lu, X. B.; Gao, X. S.; Liu, J.-M.

    2017-10-01

    Based on the modified Heisenberg–Kitaev model, the effects of magnetic substitution on the magnetic properties of the honeycomb-lattice iridate Na2 IrO3 are studied using Monte Carlo simulations. It is observed that the long-range zigzag state of the original system is rather fragile and can be replaced by a spin-glass state even for small substitution, well consistent with the experimental observation in Ru-substituted samples (Mehlawat et al 2015 Phys. Rev. B 92 134412). Both the disordered Heisenberg and Kitaev interactions caused by the magnetic ion-doping are suggested to be responsible for the magnetic phase transitions in the system. More interestingly, a short-range zigzag order is suggested to survive above the freezing temperature even at high magnetic impurity doping levels.

  14. Short-range Fundamental forces

    SciTech Connect

    Antoniadis, I; Baessler, Stefan; Buechner, M; Fedorov, General Victor; Hoedl, S.; Lambrecht, A; Nesvizhevsky, V.; Pignol, G; Reynaud, S.; Sobolev, Yu.

    2011-01-01

    We consider theoretical motivations to search for extra short-range fundamental forces as well as experiments constraining their parameters. The forces could be of two types: (1) spin-independent forces; and (2) spin-dependent axion-like forces. Different experimental techniques are sensitive in respective ranges of characteristic distances. The techniques include measurements of gravity at short distances, searches for extra interactions on top of the Casimir force, precision atomic and neutron experiments. We focus on neutron constraints, thus the range of characteristic distances considered here corresponds to the range accessible for neutron experiments.

  15. X-ray diffuse scattering measurements of chemical short-range order and lattice strains in a highly magnetostrictive Fe0.813Ga0.187alloy in an applied magnetic field

    SciTech Connect

    Du, Y.; Huang, M.; Lograsso, T. A.; McQueeney, R. J.

    2012-06-28

    The rapid growth of the magnetostriction coefficient of ferromagnetic Fe1-xGax alloys that occurs at a composition range from 0order-disorder transition. The structurally anisotropic precipitates are proposed to rotate in an applied magnetic field, thereby resulting in a large magnetoelastic response. X-ray diffuse scattering measurements sensitive to the atomic short-range ordering and lattice strain were performed on a quenched 18.7 at. % Ga alloy and show no dependence on the application of a magnetic field. This negative result sets limits on the role of nanoscale precipitates in magnetostriction.

  16. Short-range Incommensurate Magnetic Order Near the Superconducting Phase Boundary in Fe1+δTe1−xSex

    SciTech Connect

    Wen, J.; Xu, G.; Xu, Z.; Lin, Z.W.; Li, Q.; Ratcliff, W.; Gu, G.; Tranquada, J.M.

    2009-09-10

    We performed elastic neutron-scattering and magnetization measurements on Fe{sub 1.07}Te{sub 0.75}Se{sub 0.25} and FeTe{sub 0.7}Se{sub 0.3}. Short-range incommensurate magnetic order is observed in both samples. In the former sample with higher Fe content, a broad magnetic peak appears around (0.46,0,0.5) at low temperature, while in FeTe{sub 0.7}Se{sub 0.3}, the broad magnetic peak is found to be closer to the antiferromagnetic (AFM) wave vector (0.5,0,0.5). The incommensurate peaks are only observed on one side of the AFM wave vector for both samples, which can be modeled in terms of an imbalance of ferromagnetic/antiferromagnetic correlations between nearest-neighbor spins. We also find that with higher Se (and lower Fe) concentration, the magnetic order becomes weaker while the superconducting temperature and volume increase.

  17. Ab initio molecular dynamics model for density, elastic properties and short range order of Co-Fe-Ta-B metallic glass thin films.

    PubMed

    Hostert, C; Music, D; Bednarcik, J; Keckes, J; Kapaklis, V; Hjörvarsson, B; Schneider, J M

    2011-11-30

    Density, elastic modulus and the pair distribution function of Co-Fe-Ta-B metallic glasses were obtained by ab initio molecular dynamics simulations and measured for sputtered thin films using x-ray reflectivity, nanoindentation and x-ray diffraction using high energy photons. The computationally obtained density of 8.19 g cm(-3) for Co(43)Fe(20)Ta(5.5)B(31.5) and 8.42 g cm(-3) for Co(45.5)Fe(24)Ta(6)B(24.5), as well as the Young's moduli of 273 and 251 GPa, respectively, are consistent with our experiments and literature data. These data, together with the good agreement between the theoretical and the experimental pair distribution functions, indicate that the model established here is useful to describe the density, elasticity and short range order of Co-Fe-Ta-B metallic glass thin films. Irrespective of the investigated variation in chemical composition, (Co, Fe)-B cluster formation and Co-Fe interactions are identified by density-of-states analysis. Strong bonds within the structural units and between the metallic species may give rise to the comparatively large stiffness.

  18. Ab initio molecular dynamics simulations of short-range order in Zr50Cu45Al5 and Cu50Zr45Al5 metallic glasses

    DOE PAGES

    Huang, Yuxiang; Huang, Li; Wang, C. Z.; ...

    2016-02-01

    Comparative analysis between Zr-rich Zr50Cu45Al5 and Cu-rich Cu50Zr45Al5 metallic glasses (MGs) is extensively performed to locate the key structural motifs accounting for their difference of glass forming ability. Here we adopt ab initio molecular dynamics simulations to investigate the local atomic structures of Zr50Cu45Al5 and Cu50Zr45Al5 MGs. A high content of icosahedral-related (full and distorted) orders was found in both samples, while in the Zr-rich MG full icosahedrons < 0,0,12,0 > is dominant, and in the Cu-rich one the distorted icosahedral orders, especially < 0,2,8,2 > and < 0,2,8,1 >, are prominent. And the < 0,2,8,2 > polyhedra in Cu50Zr45Al5more » MG mainly originate from Al-centered clusters, while the < 0,0,12,0 > in Zr50Cu45Al5 derives from both Cu-centered clusters and Al-centered clusters. These difference may be ascribed to the atomic size difference and chemical property between Cu and Zr atoms. Lastly, the relatively large size of Zr and large negative heat of mixing between Zr and Al atoms, enhancing the packing density and stability of metallic glass system, may be responsible for the higher glass forming ability of Zr50Cu45Al5.« less

  19. Pockets of short-range transient order and restricted topological heterogeneity in the guanidine-denatured state ensemble of GED of dynamin.

    PubMed

    Chugh, Jeetender; Sharma, Shilpy; Hosur, Ramakrishna V

    2007-10-23

    The nature and variety in the denatured state of a protein, a non-native state under a given set of conditions, has been a subject of intense debate. Here, using multidimensional NMR, we have characterized the 6 M Gdn-HCl-denatured state of GED, the assembly domain of dynamin. Even under such strongly denaturing conditions, we detected the presence of conformations in slow exchange on the NMR chemical shift time scale. Although the GED oligomer as well as the SDS-denatured monomeric GED were seen to be predominantly helical [Chugh et al. (2006) FEBS J. 273, 388-397], the 6 M Gdn-HCl-denatured GED has largely beta-structural preferences. However, against such a background, we could detect the presence of a population with a short helical stretch (Arg42-Ile47) in the ensemble. The 1H-1H NOEs suggested presence of pockets of transient short-range order along the chain. Put together these segments may lead to a rather small number of interconverting topologically distinguishable ensembles. Spectral density analysis of 15N relaxation rates and {1H}-15N NOE, measured at 600 and 800 MHz, and comparison of J(0) with hydrophobic patches calculated using AABUF approach, indicated presence of four domains of slow motions. These coincided to a large extent with those showing significant Rex. Additionally, a proline residue in the connection between two of these domains seems to cause a fast hinge motion. These observations help enhance our understanding of protein denatured states, and of folding concepts, in general.

  20. Non-ideal diffusion effects, short-range ordering, and unsteady-state effects strongly influence Brownian aggregation rates in concentrated dispersions of interacting spheres.

    PubMed

    Kelkar, Aniruddha V; Franses, Elias I; Corti, David S

    2015-08-21

    Brownian aggregation rates are determined for concentrated dispersions of interacting particles with Brownian dynamics (BD) simulations and various theoretical models. Using simulation results as benchmarks, the predictions of the classical Fuchs-Smoluchowski (FS) model are shown to be quite inaccurate for concentrated dispersions. A new aggregation model is presented which provides significantly improved predictions. This model is developed on the basis of the fundamental measure theory (FMT) which is a rigorous "liquid-state" dynamic density-functional theory (DDFT) approach. It provides a major improvement of the FS model by considering short-range ordering, non-ideal diffusion, and unsteady-state effects. These were recently shown by the authors to play important roles in Brownian aggregation of hard spheres at high concentrations. Two types of interparticle interaction potentials are examined, the purely attractive van der Waals potential and the DLVO potential which includes van der Waals attraction and electrostatic double layer repulsion. For dispersions of particles with purely attractive interactions, the FS model underpredicts the aggregation rates by up to 1000 fold. In the presence of strong interparticle repulsive forces, its predictions are in fair agreement with the BD simulation results for dilute systems with particle volume fractions ϕ < < 0.1. In contrast, the predictions of the new FM-DDFT based model compare favorably with the BD simulation results, in both cases, up to ϕ = 0.3. A new quantitative measure for colloidal dispersion stability, different from the classical FS stability ratio, is proposed on the basis of aggregation half-times. Hence, a better mechanistic understanding of Brownian aggregation is obtained for concentrated dispersions of particles with either attractive or repulsive interactions, or both.

  1. Intricate Short-Range Ordering and Strongly Anisotropic Transport Properties of Li1–x Sn 2+x As2

    DOE PAGES

    Lee, Kathleen; Kaseman, Derrick; Sen, Sabyasachi; ...

    2015-02-22

    A new ternary compound, Li1-xSn2+xAs2, 0.2 < x < 0.4, was synthesized via solid-state reaction of elements. The compound crystallizes in a layered structure in the Rmore » $$\\overline{3}m$$ space group (No. 166) with Sn-As layers separated by layers of jointly occupied Li/Sn. The Sn-As layers are comprised of Sn3As3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As6 octahedron. Thorough investigations by synchrotron x-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, local Sn/Li ordering was revealed by synergistic investigations via solid-state 6,7Li NMR spectroscopy, HR-TEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions creating substantial inhomogeneity on the nanoscale. Inhomogeneous local structure has high impact on the physical properties of the synthesized compounds: local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li1-xSn2+xAs2.« less

  2. Dependency Ordering of Atomic Observables

    NASA Astrophysics Data System (ADS)

    Cīrulis, Jānis

    2015-12-01

    The notion of atomic observable was introduced by S.Gudder for effect test spaces in 1997. In this paper an observable is a σ-homomorphism from the Borel algebra on a line to some logic. Roughly, an observable on a logic is atomic, if it is completely determined by its restriction to one-element subsets of its point spectrum. In particular, every discrete observable is atomic. We study some elementary properties of such observables, and discuss a possible notion of functional dependency between them. Algebraically, a dependency is a certain preorder relation on the set of all atomic observables, which induces an order relation on the set of all maximal orthogonal subsets of the logic. Several properties, as well as characteristics in terms of the underlying logic, of these relations are stated.

  3. Short-range communication system

    NASA Technical Reports Server (NTRS)

    Alhorn, Dean C. (Inventor); Howard, David E. (Inventor); Smith, Dennis A. (Inventor)

    2012-01-01

    A short-range communication system includes an antenna, a transmitter, and a receiver. The antenna is an electrical conductor formed as a planar coil with rings thereof being uniformly spaced. The transmitter is spaced apart from the plane of the coil by a gap. An amplitude-modulated and asynchronous signal indicative of a data stream of known peak amplitude is transmitted into the gap. The receiver detects the coil's resonance and decodes same to recover the data stream.

  4. Crystal fields, disorder, and antiferromagnetic short-range order in (Yb{sub 0.24}Sn{sub 0.76})Ru

    SciTech Connect

    Klimczuk, T; Wang, C H; Lawrence, J M; Xu, Q; Durakiewicz, T; Ronning, F; Llobet, A; Trouw, F; Kurita, N; Tokiwa, Y; Lee, Han-oh; Booth, C H; Gardner, J S; Bauer, E D; Joyce, J J; Zandbergen, H W; Movshovich, R; Cava, R J; Thompson, J D

    2011-07-18

    We report extensive measurements on a new compound (Yb{sub 0.24}Sn{sub 0.76})Ru that crystallizes in the cubic CsCl structure. Valence band photoemission and L{sub 3} x-ray absorption show no divalent component in the 4f configuration of Yb. Inelastic neutron scattering (INS) indicates that the eight-fold degenerate J-multiplet of Yb{sup 3+} is split by the crystalline electric field (CEF) into a Γ{sub 7} doublet ground state and a Γ{sub 8} quartet at an excitation energy 20 meV. The magnetic susceptibility can be fit very well by this CEF scheme under the assumption that a Γ{sub 6} excited state resides at 32 meV; however, the Γ{sub 8}/Γ{sub 6} transition expected at 12 meV was not observed in the INS. The resistivity follows a Bloch-Grüneisen law shunted by a parallel resistor, as is typical of systems subject to phonon scattering with no apparent magnetic scattering. All of these properties can be understood as representing simple local moment behavior of the trivalent Yb ion. At 1 K, there is a peak in specific heat that is too broad to represent a magnetic phase transition, consistent with absence of magnetic reflections in neutron diffraction. On the other hand, this peak also is too narrow to represent the Kondo effect in the Γ{sub 7} ground state doublet. On the basis of the field-dependence of the specific heat, we argue that antiferromagnetic shortrange order (possibly co-existing with Kondo physics) occurs at low temperatures. The long-range magnetic order is suppressed because the Yb site occupancy is below the percolation threshold for this disordered compound.

  5. Magnetic properties of ultrathin discontinuous Co/Pt multilayers: Comparison with short-range ordered and isotropic CoPt3 films

    NASA Astrophysics Data System (ADS)

    Charilaou, M.; Bordel, C.; Berche, P.-E.; Maranville, B. B.; Fischer, P.; Hellman, F.

    2016-06-01

    Magnetic properties of thin Co/Pt multilayers have been investigated in order to study the dependence of magnetization M , uniaxial anisotropy Ku, and Curie temperature TC on the multilayer thickness, composition, and structure. A comparison between epitaxial submonolayer multilayers and epitaxial fcc CoPt3 alloy films with large perpendicular magnetic anisotropy (PMA) attributed to growth-induced Co clustering reveals significant differences in the temperature dependence of magnetization M (T ) , despite the presence of thin planar Co platelets in both cases. Even the thinnest discontinuous multilayered structure shows a Langevin-like M (T ) , while the alloy films with PMA show a broadened and enhanced M (T ) indicating a distribution of environments, including monolayer Co platelets separated by only 1-2 layers of Pt. These differences have been reproduced in Monte Carlo simulations, and are shown to be due to different distributions of Co-Co and Co-Pt nearest neighbors. The relatively uniform Co-Co coordination of even a discontinuous rough multilayer produces a Langevin-like M (T ) , whereas the broader distribution associated with platelets in the PMA films results in a nearly linear T dependence of M .

  6. Role of composition, bond covalency, and short-range order in the disordering of stannate pyrochlores by swift heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Tracy, Cameron L.; Shamblin, Jacob; Park, Sulgiye; Zhang, Fuxiang; Trautmann, Christina; Lang, Maik; Ewing, Rodney C.

    2016-08-01

    A2S n2O7 (A =Nd ,Sm,Gd,Er,Yb,and Y) materials with the pyrochlore structure were irradiated with 2.2 GeV Au ions to systematically investigate disordering of this system in response to dense electronic excitation. Structural modifications were characterized, over multiple length scales, by transmission electron microscopy, x-ray diffraction, and Raman spectroscopy. Transformations to amorphous and disordered phases were observed, with disordering dominating the structural response of materials with small A -site cation ionic radii. Both the disordered and amorphous phases were found to possess weberite-type local ordering, differing only in that the disordered phase exhibits a long-range, modulated arrangement of weberite-type structural units into an average defect-fluorite structure, while the amorphous phase remains fully aperiodic. Comparison with the behavior of titanate and zirconate pyrochlores showed minimal influence of the high covalency of the Sn-O bond on this phase behavior. An analytical model of damage accumulation was developed to account for simultaneous amorphization and recrystallization of the disordered phase during irradiation.

  7. Magnetic properties and magnetocaloric effect in Fe-doped La0.6Ca0.4MnO3 with short-range ferromagnetic order

    NASA Astrophysics Data System (ADS)

    Ho, T. A.; Thanh, T. D.; Ho, T. O.; Phan, M. H.; Phan, The-Long; Yu, S. C.

    2015-05-01

    The magnetic properties and magnetocaloric effect of La0.6Ca0.4Mn1-xFexO3 (x = 0-0.04) compounds fabricated by solid-state reaction have been studied. Magnetization measurements versus temperature revealed a decrease of the ferromagnetic-paramagnetic phase transition temperature (TC) with increasing Fe-doping content. The TC values determined for the samples with x = 0, 0.02 and 0.04 are about 260, 254 and 236 K, respectively. Based on magnetic-field dependences of magnetization, M(H), the magnetic entropy change (ΔSm) of the samples were calculated. Under an applied field change ΔH = 30 kOe, the maximum |ΔSmax| value decreases from 5.74 Jkg-1 K-1 for x = 0 to about 2.62 Jkg-1 K-1 for x = 0.04. These values correspond to relative cooling powers 140-180 J/kg, which are comparable to those of other manganites. Analyzing magnetic-field dependences of |ΔSm| for the samples indicates their power-law relation. Based on Banerjee's criteria and Franco's universal curves related to the magnetic-entropy change, we assess magnetic order existing in the samples.

  8. Time ordering in atomic collisions

    NASA Astrophysics Data System (ADS)

    McGuire, J. H.; Godunov, A. L.; Shakov, Kh Kh; Kaplan, L.; Burin, A.; Uskov, D.

    2007-06-01

    Time ordering constrains interactions to occur in increasing (or decreasing) order. This places a constraint on the time evolution of the system and can lead to correlations in time of different particles in a few/many body system. Unlike overall time reversal, time ordering is not a conserved symmetry of the atomic system. A number of examples of observable effects of time ordering are presented. A convenient way to describe time ordering is to define the limit of no time ordering by replacing the instantaneous interaction by its time average. This is similar to the way in which spatial correlation is defined. Like spatial correlation, time ordering is usually formulated in the interaction representation. The effects of time ordering can differ in different representations. In energy space, conjugate to time space, time ordering is imposed as the i ɛ term in the Greens' function that corresponds to an initial condition (usually incoming plane waves and outgoing scattered waves). This permits off-energy-shell (energy non- conserving) fluctuations during the collision consistent with the Uncertainty Principle.

  9. Comparison of short-range-order in liquid- and rotator-phase states of a simple molecular liquid: A reverse Monte Carlo and molecular dynamics analysis of neutron diffraction data

    SciTech Connect

    Pardo, Luis Carlos; Tamarit, Josep Lluis; Veglio, Nestor; Bermejo, Francisco Javier; Cuello, Gabriel Julio

    2007-10-01

    The short-range order (SRO) correlations in liquid- and rotator-phase states of carbon tetrachloride are revisited here. The correlation of some angular magnitudes is used to evaluate the positional and orientational correlations in the liquid as well as in the rotator phase. The results show significant similitudes in the relative position of the molecules surrounding a central one but striking differences in their relative orientations, which could explain the changes in SRO between the two phases and the puzzling behavior of the local density in the liquid and rotator phases.

  10. Spin dynamics, short-range order, and spin freezing in Y{sub 0.5}Ca{sub 0.5}BaCo{sub 4}O{sub 7}

    SciTech Connect

    Stewart, J. R.; Ehlers, G.; Mutka, H.; Fouquet, P.; Payen, C.; Lortz, R.

    2011-01-15

    Y{sub 0.5}Ca{sub 0.5}BaCo{sub 4}O{sub 7} was recently introduced as a possible candidate for capturing some of the predicted classical spin kagome ground-state features. Stimulated by this conjecture, we have taken up a more complete study of the spin correlations in this compound with neutron scattering methods on a powder sample characterized with high-resolution neutron diffraction and the temperature dependence of magnetic susceptibility and specific heat. We have found that the frustrated near-neighbor magnetic correlations involve not only the kagome planes but concern the full Co sublattice, as evidenced by the analysis of the wave-vector dependence of the short-range order. We conclude from our results that the magnetic moments are located on the Co sublattice as a whole and that correlations extend beyond the two-dimensional kagome planes. We identify intriguing dynamical properties, observing high-frequency fluctuations with a Lorentzian linewidth {Gamma}{<=}20 meV at ambient temperature. On cooling a low-frequency ({approx}1 meV) dynamical component develops alongside the high-frequency fluctuations, which eventually becomes static at temperatures below T{approx_equal}50 K. The high-frequency response with an overall linewidth of {approx}10 meV prevails at T{<=}2 K, coincident with a fully elastic short-range-ordered contribution.

  11. Evidence of a short-range incommensurate d-wave charge order from a fermionic two-loop renormalization group calculation of a 2D model with hot spots

    SciTech Connect

    Carvalho, Vanuildo S de; Freire, Hermann

    2014-09-15

    The two-loop renormalization group (RG) calculation is considerably extended here for the two-dimensional (2D) fermionic effective field theory model, which includes only the so-called “hot spots” that are connected by the spin-density-wave (SDW) ordering wavevector on a Fermi surface generated by the 2D t−t{sup ′} Hubbard model at low hole doping. We compute the Callan–Symanzik RG equation up to two loops describing the flow of the single-particle Green’s function, the corresponding spectral function, the Fermi velocity, and some of the most important order-parameter susceptibilities in the model at lower energies. As a result, we establish that–in addition to clearly dominant SDW correlations–an approximate (pseudospin) symmetry relating a short-range incommensurated-wave charge order to the d-wave superconducting order indeed emerges at lower energy scales, which is in agreement with recent works available in the literature addressing the 2D spin-fermion model. We derive implications of this possible electronic phase in the ongoing attempt to describe the phenomenology of the pseudogap regime in underdoped cuprates.

  12. Covalent bond orders and atomic anisotropies from iterated stockholder atoms.

    PubMed

    Wheatley, Richard J; Gopal, Angelica A

    2012-02-14

    Iterated stockholder atoms are produced by dividing molecular electron densities into sums of overlapping, near-spherical atomic densities. It is shown that there exists a good correlation between the overlap of the densities of two atoms and the order of the covalent bond between the atoms (as given by simple valence rules). Furthermore, iterated stockholder atoms minimise a functional of the charge density, and this functional can be expressed as a sum of atomic contributions, which are related to the deviation of the atomic densities from spherical symmetry. Since iterated stockholder atoms can be obtained uniquely from the electron density, this work gives an orbital-free method for predicting bond orders and atomic anisotropies from experimental or theoretical charge density data.

  13. Relaxor-like ferroelectric behaviour favoured by short-range B-site ordering in 10% Ba{sup 2+} substituted MgFe{sub 2}O{sub 4}

    SciTech Connect

    Chithra Lekha, P.; Ramesh, G.; Revathi, V.; Subramanian, V.

    2014-05-01

    Graphical abstract: - Highlights: • Mechanism driving polarization in MgFe{sub 2}O{sub 4} is the Maxwell–Wagner polarization. • But Raman studies confirm the existence of local P4{sub 1}22/P4{sub 3}22 symmetry in MgFe{sub 2}O{sub 4}. • Ba{sup 2+} substitution increases ferroelectric ordering, ΔT{sub m} span, and masks electronic contribution. - Abstract: Using the molten salt method, pristine and Ba{sup 2+} substituted MgFe{sub 2}O{sub 4} are prepared. The relaxor-like behaviour observed in the dielectric dispersion indicates the existence of B-site short-range ordering with the local P4{sub 1}22/P4{sub 3}22 symmetry which is confirmed by the Raman spectroscopy. The paper further analyses the origin of polarization using Maxwell–Wagner fit and Nyquist plot. This work suggests a possible way to increase the relaxor-like ferroelectric ordering, larger span of relaxation temperature (ΔT{sub m}) and the effective masking of electronic contribution by the substitution of Ba{sup 2+} ion.

  14. Short range effective potentials for ionic fluids

    NASA Astrophysics Data System (ADS)

    Clarke, J. H. R.; Smith, W.; Woodcock, L. V.

    1986-02-01

    It is shown that the structure of a simple ionic liquid, potassium chloride, can be reproduced in computer simulations using short range effective pair (SHREP) potentials of a simple form. Aside from the balance between like and unlike particle interactions, the important parameters determining the structure are the depth ɛ and the position r0 of the unlike particle pair energy minimum. The results demonstrate that the long range ordering characteristic of ionic liquids is not a consequence of the long range of Coulomb interactions. It is further shown that first order perturbation theory can be used accurately to calculate the thermodynamic properties of an ionic liquid from a corresponding reference liquid generated using a SHREP potential. These results can be generalized to explain deviations from the Reiss-Mayer-Katz corresponding states law for alkali halides and suggest an alternative scheme, effective depth reduction (EDR), based on values of ɛ for the gas phase ion pairs.

  15. Narrow resonances and short-range interactions

    NASA Astrophysics Data System (ADS)

    Gelman, Boris A.

    2009-09-01

    Narrow resonances in systems with short-range interactions are discussed in an effective field theory (EFT) framework. An effective Lagrangian is formulated in the form of a combined expansion in powers of a momentum Q≪Λ—a short-distance scale—and an energy difference δɛ=|E-ɛ0|≪ɛ0—a resonance peak energy. At leading order in the combined expansion, a two-body scattering amplitude is the sum of a smooth background term of order Q0 and a Breit-Wigner term of order Q2(δɛ)-1 which becomes dominant for δɛ≲Q3. Such an EFT is applicable to systems in which short-distance dynamics generates a low-lying quasistationary state. The EFT is generalized to describe a narrow low-lying resonance in a system of charged particles. It is shown that in the case of Coulomb repulsion, a two-body scattering amplitude at leading order in a combined expansion is the sum of a Coulomb-modified background term and a Breit-Wigner amplitude with parameters renormalized by Coulomb interactions.

  16. Narrow resonances and short-range interactions

    SciTech Connect

    Gelman, Boris A.

    2009-09-15

    Narrow resonances in systems with short-range interactions are discussed in an effective field theory (EFT) framework. An effective Lagrangian is formulated in the form of a combined expansion in powers of a momentum Q<<{lambda}--a short-distance scale--and an energy difference {delta}{epsilon}=|E-{epsilon}{sub 0}|<<{epsilon}{sub 0}--a resonance peak energy. At leading order in the combined expansion, a two-body scattering amplitude is the sum of a smooth background term of order Q{sup 0} and a Breit-Wigner term of order Q{sup 2}({delta}{epsilon}){sup -1} which becomes dominant for {delta}{epsilon} < or approx. Q{sup 3}. Such an EFT is applicable to systems in which short-distance dynamics generates a low-lying quasistationary state. The EFT is generalized to describe a narrow low-lying resonance in a system of charged particles. It is shown that in the case of Coulomb repulsion, a two-body scattering amplitude at leading order in a combined expansion is the sum of a Coulomb-modified background term and a Breit-Wigner amplitude with parameters renormalized by Coulomb interactions.

  17. Intricate Short-Range Ordering and Strongly Anisotropic Transport Properties of Li1–x Sn 2+x As2

    SciTech Connect

    Lee, Kathleen; Kaseman, Derrick; Sen, Sabyasachi; Hung, Ivan; Gan, Zhehong; Gerke, Birgit; Pöttgen, Rainer; Feygenson, Mikhail; Neuefeind, Jörg; Lebedev, Oleg I.; Kovnir, Kirill

    2015-02-22

    A new ternary compound, Li1-xSn2+xAs2, 0.2 < x < 0.4, was synthesized via solid-state reaction of elements. The compound crystallizes in a layered structure in the R$\\overline{3}m$ space group (No. 166) with Sn-As layers separated by layers of jointly occupied Li/Sn. The Sn-As layers are comprised of Sn3As3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As6 octahedron. Thorough investigations by synchrotron x-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, local Sn/Li ordering was revealed by synergistic investigations via solid-state 6,7Li NMR spectroscopy, HR-TEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions creating substantial inhomogeneity on the nanoscale. Inhomogeneous local structure has high impact on the physical properties of the synthesized compounds: local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li1-xSn2+xAs2.

  18. Optical method of atomic ordering estimation

    SciTech Connect

    Prutskij, T.; Attolini, G.

    2013-12-04

    It is well known that within metal-organic vapor-phase epitaxy (MOVPE) grown semiconductor III-V ternary alloys atomically ordered regions are spontaneously formed during the epitaxial growth. This ordering leads to bandgap reduction and to valence bands splitting, and therefore to anisotropy of the photoluminescence (PL) emission polarization. The same phenomenon occurs within quaternary semiconductor alloys. While the ordering in ternary alloys is widely studied, for quaternaries there have been only a few detailed experimental studies of it, probably because of the absence of appropriate methods of its detection. Here we propose an optical method to reveal atomic ordering within quaternary alloys by measuring the PL emission polarization.

  19. Short-Range Structure of Nuclei

    SciTech Connect

    Higinbotham, Douglas W.

    2008-10-13

    The nucleons in a nucleus can form short-range correlated pairs. A recent Jefferson Lab electron scattering experiment, where a proton was knocked-out of the nucleus with high momentum transfer and high missing momentum, has shown that in {sup 12}C the neutron-proton pairs are nearly twenty times as prevalent as proton-proton pairs and, by inference, neutron-neutron pairs. This difference between the types of pairs has been shown to be due to the short-range tensor part of the nucleon-nucleon interaction.

  20. The MOLDY short-range molecular dynamics package

    NASA Astrophysics Data System (ADS)

    Ackland, G. J.; D'Mellow, K.; Daraszewicz, S. L.; Hepburn, D. J.; Uhrin, M.; Stratford, K.

    2011-12-01

    We describe a parallelised version of the MOLDY molecular dynamics program. This Fortran code is aimed at systems which may be described by short-range potentials and specifically those which may be addressed with the embedded atom method. This includes a wide range of transition metals and alloys. MOLDY provides a range of options in terms of the molecular dynamics ensemble used and the boundary conditions which may be applied. A number of standard potentials are provided, and the modular structure of the code allows new potentials to be added easily. The code is parallelised using OpenMP and can therefore be run on shared memory systems, including modern multicore processors. Particular attention is paid to the updates required in the main force loop, where synchronisation is often required in OpenMP implementations of molecular dynamics. We examine the performance of the parallel code in detail and give some examples of applications to realistic problems, including the dynamic compression of copper and carbon migration in an iron-carbon alloy. Program summaryProgram title: MOLDY Catalogue identifier: AEJU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEJU_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License version 2 No. of lines in distributed program, including test data, etc.: 382 881 No. of bytes in distributed program, including test data, etc.: 6 705 242 Distribution format: tar.gz Programming language: Fortran 95/OpenMP Computer: Any Operating system: Any Has the code been vectorised or parallelized?: Yes. OpenMP is required for parallel execution RAM: 100 MB or more Classification: 7.7 Nature of problem: Moldy addresses the problem of many atoms (of order 10 6) interacting via a classical interatomic potential on a timescale of microseconds. It is designed for problems where statistics must be gathered over a number of equivalent runs, such as

  1. Nonperturbative short-range dynamics in TMDs

    SciTech Connect

    Weiss, Christian

    2013-05-01

    This presentation covers: deep inelastic processes and transverse momentum distributions; chiral symmetry breaking, including the physical picture, the dynamical model, and parton distributions; partonic structures, including transverse momentum distributions, coordinate space correlator, and short range correlations; and measurements of semi-inclusive deep inelastic scattering, correlations, and multi-parton processes in pp interactions.

  2. Combined Search for Lorentz Violation in Short-Range Gravity

    NASA Astrophysics Data System (ADS)

    Shao, Cheng-Gang; Tan, Yu-Jie; Tan, Wen-Hai; Yang, Shan-Qing; Luo, Jun; Tobar, Michael Edmund; Bailey, Quentin G.; Long, J. C.; Weisman, E.; Xu, Rui; Kostelecký, V. Alan

    2016-08-01

    Short-range experiments testing the gravitational inverse-square law at the submillimeter scale offer uniquely sensitive probes of Lorentz invariance. A combined analysis of results from the short-range gravity experiments HUST-2015, HUST-2011, IU-2012, and IU-2002 permits the first independent measurements of the 14 nonrelativistic coefficients for Lorentz violation in the pure-gravity sector at the level of 10-9 m2 , improving by an order of magnitude the sensitivity to numerous types of Lorentz violation involving quadratic curvature derivatives and curvature couplings.

  3. Combined Search for Lorentz Violation in Short-Range Gravity.

    PubMed

    Shao, Cheng-Gang; Tan, Yu-Jie; Tan, Wen-Hai; Yang, Shan-Qing; Luo, Jun; Tobar, Michael Edmund; Bailey, Quentin G; Long, J C; Weisman, E; Xu, Rui; Kostelecký, V Alan

    2016-08-12

    Short-range experiments testing the gravitational inverse-square law at the submillimeter scale offer uniquely sensitive probes of Lorentz invariance. A combined analysis of results from the short-range gravity experiments HUST-2015, HUST-2011, IU-2012, and IU-2002 permits the first independent measurements of the 14 nonrelativistic coefficients for Lorentz violation in the pure-gravity sector at the level of 10^{-9}  m^{2}, improving by an order of magnitude the sensitivity to numerous types of Lorentz violation involving quadratic curvature derivatives and curvature couplings.

  4. High-order-harmonic generation in atomic and molecular systems

    NASA Astrophysics Data System (ADS)

    Suárez, Noslen; Chacón, Alexis; Pérez-Hernández, Jose A.; Biegert, Jens; Lewenstein, Maciej; Ciappina, Marcelo F.

    2017-03-01

    High-order-harmonic generation (HHG) results from the interaction of ultrashort laser pulses with matter. It configures an invaluable tool to produce attosecond pulses, moreover, to extract electron structural and dynamical information of the target, i.e., atoms, molecules, and solids. In this contribution, we introduce an analytical description of atomic and molecular HHG, that extends the well-established theoretical strong-field approximation (SFA). Our approach involves two innovative aspects: (i) First, the bound-continuum and rescattering matrix elements can be analytically computed for both atomic and multicenter molecular systems, using a nonlocal short range model, but separable, potential. When compared with the standard models, these analytical derivations make possible to directly examine how the HHG spectra depend on the driven media and laser-pulse features. Furthermore, we can turn on and off contributions having distinct physical origins or corresponding to different mechanisms. This allows us to quantify their importance in the various regions of the HHG spectra. (ii) Second, as reported recently [N. Suárez et al., Phys. Rev. A 94, 043423 (2016), 10.1103/PhysRevA.94.043423], the multicenter matrix elements in our theory are free from nonphysical gauge- and coordinate-system-dependent terms; this is accomplished by adapting the coordinate system to the center from which the corresponding time-dependent wave function originates. Our SFA results are contrasted, when possible, with the direct numerical integration of the time-dependent Schrödinger equation in reduced and full dimensionality. Very good agreement is found for single and multielectronic atomic systems, modeled under the single active electron approximation, and for simple diatomic molecular systems. Interference features, ubiquitously present in every strong-field phenomenon involving a multicenter target, are also captured by our model.

  5. Short-range interaction energy for ground state H2+

    NASA Astrophysics Data System (ADS)

    Battezzati, Michele; Magnasco, Valerio

    2006-12-01

    Two of the Hermitian eigenvalue equations resulting from the separation of the three-dimensional Schroedinger equation for H2+ in spheroidals are solved perturbatively for the ground state by expanding the action in positive powers of the internuclear distance R near the united atom He+. The dispersion relations between the separation constants A and Ee are seen to have rigorous analytic solutions, the third-order equation leading to an exact expansion for the inner determinantal equation up to R10. The explicit form for the expansion coefficients is determined up to n = 10, and is seen to contain up to the third power of (γ + ln 4R) logarithmic terms. Even if the general range of validity of the short-range Rn-expansion is expected to be smaller than the corresponding long-range R-n-expansion, it is important to stress that such higher expansion coefficients are calculated exactly for the first time. These formulae give extremely accurate numerical results up to R cong 0.3a0.

  6. Coarse-grained short-range correlations

    NASA Astrophysics Data System (ADS)

    Simo, I. Ruiz; Pérez, R. Navarro; Amaro, J. E.; Ruiz Arriola, E.

    2017-05-01

    We develop a scheme to take into account the effects of short-range nucleon-nucleon correlations in the nucleon-pair wave function by solving the Bethe-Goldstone equation for a coarse-grained delta shell potential in S -wave configuration. The S -wave delta shell potential has been adjusted to reproduce the 1S0 phase shifts of the AV18 potential for this partial wave up to 2 GeV in the laboratory kinetic energy. We show that a coarse-grained potential can describe the high momentum tail of the back-to-back correlated pairs and the G matrix in momentum space. We discuss the easiness and robustness of the calculation in coordinate space and the future improvements and utilities of this model. This work suggests the possibility of using perturbation theory for describing the short-range correlations and, related to this, to substitute the G matrix by an appropriate coarse-grained potential.

  7. OMV--Short Range Vehicle Concept

    NASA Technical Reports Server (NTRS)

    1986-01-01

    In this 1986 artist's concept, the Orbital Maneuvering Vehicle (OMV), is shown without its main propulsion module. Essentially two propulsion vehicles in one, the OMV could be powered by a main propulsion module , or, in its short range vehicle configuration shown here, use its own hydrazine and cold gas thrusters. As envisioned by Marshall Space Flight Center plarners, the OMV would be a remotely-controlled free-flying space tug which would place, rendezvous, dock, and retrieve orbital payloads.

  8. OMV--Short Range Vehicle Concept

    NASA Technical Reports Server (NTRS)

    1986-01-01

    In this 1986 artist's concept, the Orbital Maneuvering Vehicle (OMV), is shown without its main propulsion module. Essentially two propulsion vehicles in one, the OMV could be powered by a main propulsion module , or, in its short range vehicle configuration shown here, use its own hydrazine and cold gas thrusters. As envisioned by Marshall Space Flight Center plarners, the OMV would be a remotely-controlled free-flying space tug which would place, rendezvous, dock, and retrieve orbital payloads.

  9. Aspects of short-range interconnect packaging

    NASA Astrophysics Data System (ADS)

    Wohlfeld, Denis; Brenner, Karl-Heinz

    2012-01-01

    In short-range interconnect applications, one question arises frequently: When should optical solutions be chosen over electrical wiring? The answer to this question of course depends on several factors like costs, performance, reliability, availability of testing equipment and knowledge about optical technologies, and last but not least, it strongly depends on the application itself. Networking in high performance computing (HPC) is one such example. With bit rates around 10 Gbit/s per channel and cable length above 2 m, the high attenuation of electrical cables leads to a clear preference of optical or active optical cables (AOC) for most planned HPC systems. For AOCs, the electro-optical conversion is realized inside the connector housing, while for purely optical cables, the conversion is done at the edge of the board. Proceeding to 25 Gbit/s and higher, attenuation and loss of signal quality become critical. Therefore, either significantly more effort has to be spent on the electrical side, or the package for conversion has to be integrated closer to the chip, thus requiring new packaging technologies. The paper provides a state of the art overview of packaging concepts for short range interconnects, it describes the main challenges of optical package integration and illustrates new concepts and trends in this research area.

  10. Short Range Correlations and the EMC Effect

    SciTech Connect

    L.B. Weinstein, E. Piasetzky, D.W. Higinbotham, J. Gomez, O. Hen, R. Shneor

    2011-02-01

    This Letter shows quantitatively that the magnitude of the EMC effect measured in electron deep inelastic scattering at intermediate xB, 0.35≤xB≤0.7, is linearly related to the short range correlation (SRC) scale factor obtained from electron inclusive scattering at xB≥1. The observed phenomenological relationship is used to extract the ratio of the deuteron to the free pn pair cross sections and F2n/F2p, the ratio of the free neutron to free proton structure functions. We speculate that the observed correlation is because both the EMC effect and SRC are dominated by the high virtuality (high momentum) nucleons in the nucleus.

  11. Calorimetric investigation of the excess entropy of mixing in analbite-sanidine solid solutions: lack of evidence for Na,K short- range order and implications for two-feldspar thermometry.

    USGS Publications Warehouse

    Haselton, H.T.; Hovis, G.L.; Hemingway, B.S.; Robie, R.A.

    1983-01-01

    Heat capacities (5-380 K) have been measured by adiabatic calorimetry for five highly disordered alkali feldspars (Ab99Or1, Ab85Or15, Ab55Or45, Ab25Or75 and Ab1Or99). The thermodynamic and mineralogical implications of the results are discussed. The new data are also combined with recent data for plagioclases in order to derive a revised expression for the two-feldspar thermometer. T calculated from the revised expression tend to be higher than previous calculations.-J.A.Z.

  12. Effect of magnetism and atomic order on static atomic displacements in the Invar alloy Fe-27 at.% Pt

    NASA Astrophysics Data System (ADS)

    Sax, C. R.; Schönfeld, B.; Ruban, A. V.

    2015-08-01

    Fe-27 at.% Pt was aged at 1123 K and quenched to room temperature (RT) to set up a state of thermal equilibrium. The local atomic arrangement was studied by diffuse x-ray scattering above (at 427 K) and below (at RT) the Curie temperature as well as at RT under a saturating magnetic field. The separated short-range order scattering remained unchanged for all three states, with maxima at 100 positions. Effective pair interaction parameters determined by the inverse Monte Carlo method gave an order-disorder transition temperature of about 1088 K, close to direct experimental findings. The species-dependent static atomic displacements for the first two shells show large differences, with a strong increase in magnitude from the state at 427 K over RT to the state under saturating magnetic field. This outcome is in agreement with an increase in atomic volume of Fe with increasing local magnetic moment. Electronic-structure calculations closely reproduce the values for the static atomic displacements in the ferromagnetic state, and predict their dependence on the atomic configuration. They also reveal a strong dependence of the magnetic exchange interactions in Fe-Pt on the atomic configuration state and lattice parameter. In particular, the increase of the Curie temperature in a random state relative to that in the ordered one is demonstrated to be related to the corresponding change of the magnetic exchange interactions due to the different local atomic chemical environment. There exists a similar strong concentration dependence of the chemical interactions as in the case of magnetic exchange interactions. Theoretical effective interactions for Fe-27 at.% Pt alloy are in good agreement with experimental results, and they also reproduce well the L1 2-A1 transition temperature.

  13. Investigation of short-range structural order in Zr69.5Cu12Ni11Al7.5 and Zr41.5Ti41.5Ni17 glasses, using X-ray absorption spectroscopy and ab initio molecular dynamics simulations.

    PubMed

    Lahiri, Debdutta; Sharma, Surinder M; Verma, Ashok K; Vishwanadh, B; Dey, G K; Schumacher, Gerhard; Scherb, Tobias; Riesemeier, Heinrich; Reinholz, Uwe; Radtke, Martin; Banerjee, S

    2014-11-01

    Short-range order has been investigated in Zr69.5Cu12Ni11Al7.5 and Zr41.5Ti41.5Ni17 metallic glasses using X-ray absorption spectroscopy and ab initio molecular dynamics simulations. While both of these alloys are good glass formers, there is a difference in their glass-forming abilities (Zr41.5Ti41.5Ni17 > Zr69.5Cu12Ni11Al7.5). This difference is explained by inciting the relative importance of strong chemical order, icosahedral content, cluster symmetry and configuration diversity.

  14. An artificial boundary approach for short-ranged interactions

    NASA Astrophysics Data System (ADS)

    Jacobs, David M.

    2016-07-01

    Real physical systems are only understood, experimentally or theoretically, to a finite resolution so in their analysis there is generally an ignorance of possible short-range phenomena. It is also well-known that the boundary conditions of wavefunctions and fields can be used to model short-range interactions when those interactions are expected, a priori. Here, a real-space approach is described wherein an artificial boundary of ignorance is imposed to explicitly exclude from analysis the region of a system wherein short-distance effects may be obscure. The (artificial) boundary conditions encode those short-distance effects by parameterizing the possible UV completions of the wavefunction. Since measurable quantities, such as spectra and cross sections, must be independent of the position of the artificial boundary, the boundary conditions must evolve with the radius of the boundary in a particular way. As examples of this approach, an analysis is performed of the non-relativistic free particle, harmonic oscillator, and Coulomb potential, and some known results for point-like (contact) interactions are recovered, however from a novel perspective. Generically, observables differ from their canonical values and symmetries are anomalously broken compared to those of idealized models. Connections are made to well-studied physical systems, such as the binding of light nuclei and cold atomic systems. This method is arguably more physically transparent and mathematically easier to use than other techniques that require the regularization and renormalization of delta-function potentials, and may offer further generalizations of practical use.

  15. Fast parallel algorithms for short-range molecular dynamics

    SciTech Connect

    Plimpton, S.

    1993-05-01

    Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a subset of atoms; the second assigns each a subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently -- those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 10,000,000 atoms on three parallel supercomputers, the nCUBE 2, Intel iPSC/860, and Intel Delta. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and the Intel Delta performs about 30 times faster than a single Y-MP processor and 12 times faster than a single C90 processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

  16. Searching for Short-Range Correlations in Carbon

    SciTech Connect

    Peter Monaghan

    2009-12-01

    A dedicated experiment to study nucleon-nucleon short-range correlations was performed in Hall A at Jefferson Lab. Measurements were made through a triple coincidence (e, e[prime]pN) reaction, with incident electrons scattered from a carbon foil target. The data showed that nucleon pairs are on the order of twenty times more likely to be neutron-proton pairs instead of a proton-proton pair. This result is consistent with observations from a previous experiment at Brookhaven National Laboratory. The experimental details are described and the results presented.

  17. Conversion properties of short-range autodyne systems

    NASA Astrophysics Data System (ADS)

    Damgov, V. N.

    1990-04-01

    An analysis is made of the conversion properties of Doppler autodyne systems (for use in short-range navigation systems) described by a third-order differential equation. Expressions are obtained for the conversion coefficients of the echo signal from a moving object as a function of the degree of regeneration and detuning of the oscillation circuit of the autodyne, the time constant of the shift circuit, the self-oscillation amplitude, the degree of nonlinearity of the active-element characteristics, and the Doppler-shift frequency.

  18. Microcanonical phase diagrams of short-range ferromagnets.

    PubMed

    Kastner, Michael; Pleimling, Michel

    2009-06-19

    A phase diagram is a graph in parameter space showing the phase boundaries of a many-particle system. Commonly, the control parameters are chosen to be those of the (generalized) canonical ensemble, such as temperature and magnetic field. However, depending on the physical situation of interest, the (generalized) microcanonical ensemble may be more appropriate, with the corresponding control parameters being energy and magnetization. We show that the phase diagram on this parameter space looks remarkably different from the canonical one. The general features of such a microcanonical phase diagram are investigated by studying two models of ferromagnets with short-range interactions. The physical consequences of the findings are discussed, including possible applications to nuclear fragmentation, adatoms on surfaces, and cold atoms in optical lattices.

  19. Transverse Effect due to Short-range Resistive Wall Wakefield

    SciTech Connect

    Juhao Wu; Alex Chao; Jean Delayen

    2007-06-18

    For accelerator designs with ultra short electron beams, beam dynamics study has to invoke the short-range wakefields. In this paper, we first obtain the short-range dipole mode resistive wall wakefield. Analytical approach is then developed to study the single bunch transverse beam dynamics due to this short-range resistive wall wake. The results are applied to the LCLS undulator.

  20. Transverse Effect Due to Short Range Resistive Wall Wakefield

    SciTech Connect

    Delayen, J.R.; Chao, Alexander Wu; Wu, J.; /SLAC

    2008-01-08

    For accelerator designs with ultra short electron beams, beam dynamics study has to invoke the short-range wakefields. In this paper, we first obtain the short-range dipole mode resistive wall wakefield. Analytical approach is then developed to study the single bunch transverse beam dynamics due to this short-range resistive wall wake. The results are applied to the LCLS undulator.

  1. Dynamic decoupling and local atomic order of a model multicomponent metallic glass-former.

    PubMed

    Kim, Jeongmin; Sung, Bong June

    2015-06-17

    The dynamics of multicomponent metallic alloys is spatially heterogeneous near glass transition. The diffusion coefficient of one component of the metallic alloys may also decouple from those of other components, i.e., the diffusion coefficient of each component depends differently on the viscosity of metallic alloys. In this work we investigate the dynamic heterogeneity and decoupling of a model system for multicomponent Pd43Cu27Ni10P20 melts by using a hard sphere model that considers the size disparity of alloys but does not take chemical effects into account. We also study how such dynamic behaviors would relate to the local atomic structure of metallic alloys. We find, from molecular dynamics simulations, that the smallest component P of multicomponent Pd43Cu27Ni10P20 melts becomes dynamically heterogeneous at a translational relaxation time scale and that the largest major component Pd forms a slow subsystem, which has been considered mainly responsible for the stabilization of amorphous state of alloys. The heterogeneous dynamics of P atoms accounts for the breakdown of Stokes-Einstein relation and also leads to the dynamic decoupling of P and Pd atoms. The dynamically heterogeneous P atoms decrease the lifetime of the local short-range atomic orders of both icosahedral and close-packed structures by orders of magnitude.

  2. Short range magnetic exchange interaction favors ferroelectricity

    PubMed Central

    Wan, Xiangang; Ding, Hang-Chen; Savrasov, Sergey Y.; Duan, Chun-Gang

    2016-01-01

    Multiferroics, where two or more ferroic order parameters coexist, is one of the hottest fields in condensed matter physics and materials science. To search multiferroics, currently most researches are focused on frustrated magnets, which usually have complicated magnetic structure and low magnetic ordering temperature. Here, we argue that actually simple interatomic magnetic exchange interaction already contains a driving force for ferroelectricity, thus providing a new microscopic mechanism for the coexistence and strong coupling between ferroelectricity and magnetism. We demonstrate this mechanism by showing that even the simplest antiferromagnetic insulator like MnO, could display a magnetically induced ferroelectricity under a biaxial strain. In addition, we show that such mechanism also exists in the most important single phase multiferroics, i.e. BiFeO3, suggesting that this mechanism is ubiquitous in systems with superexchange interaction. PMID:26956480

  3. Short-range interactions of concentrated proline in aqueous solution.

    PubMed

    Busch, Sebastian; Lorenz, Christian D; Taylor, Jonathan; Pardo, Luis Carlos; McLain, Sylvia E

    2014-12-11

    Molecular interactions for proline in a highly concentrated aqueous solution (up to 1:5 proline:water molecular ratio) have been investigated using a variety of experimental and computational techniques. Rather than the solution containing either small crystallites or large aggregates of proline, three-dimensional structural analysis reveals the presence of proline-proline dimers. These dimers appear to be formed by cyclic electrostatic interactions between CO2(-) and NH2(+) groups on neighboring proline molecules, which causes the ring motifs of proline to be roughly parallel to one another. In addition, water appears to aggregate around the electrostatic groups of the proline-proline dimers where it may in fact bridge these groups on different molecules. The observed short-range interactions for proline in solution may explain its function as a hydrotrope in vivo in which this observed dimerization might allow proline molecules to generate small pockets of a hydrophobic environment that can associate with nonpolar motifs of other molecules in solution. The results presented here emphasize the need for careful three-dimensional analysis to assess the short-range order of highly concentrated solutions.

  4. Persistent homology and many-body atomic structure for medium-range order in the glass

    NASA Astrophysics Data System (ADS)

    Nakamura, Takenobu; Hiraoka, Yasuaki; Hirata, Akihiko; Escolar, Emerson G.; Nishiura, Yasumasa

    2015-07-01

    The characterization of the medium-range (MRO) order in amorphous materials and its relation to the short-range order is discussed. A new topological approach to extract a hierarchical structure of amorphous materials is presented, which is robust against small perturbations and allows us to distinguish it from periodic or random configurations. This method is called the persistence diagram (PD) and introduces scales to many-body atomic structures to facilitate size and shape characterization. We first illustrate the representation of perfect crystalline and random structures in PDs. Then, the MRO in amorphous silica is characterized using the appropriate PD. The PD approach compresses the size of the data set significantly, to much smaller geometrical summaries, and has considerable potential for application to a wide range of materials, including complex molecular liquids, granular materials, and metallic glasses.

  5. Detection of antiferromagnetic order by cooling atoms in an optical lattice

    NASA Astrophysics Data System (ADS)

    Yang, Tsung-Lin; Teles, Rafael; Hazzard, Kaden; Hulet, Randall; Rice University Collaboration

    2016-05-01

    We have realized the Fermi-Hubbard model with fermionic 6 Li atoms in a three-dimensional compensated optical lattice. The compensated optical lattice has provided low enough temperatures to produce short-range antiferromagnetic (AF) spin correlations, which we detect via Bragg scattering of light. Previously, we reached temperatures down to 1.4 times that of the AFM phase transition, more than a factor of 2 below temperatures obtained previously in 3D optical lattices with fermions. In order to further reduce the entropy in the compensated lattice, we implement an entropy conduit - which is a single blue detuned laser beam with a waist size smaller than the overall atomic sample size. This repulsive narrow potential provides a conductive metallic path between the low entropy core and the edges of the atomic sample where atoms may be evaporated. In addition, the entropy conduit may store entropy, thus further lowering the entropy in the core. We will report on the status of these efforts to further cool atoms in the optical lattice. Work supported by ARO MURI Grant, NSF and The Welch Foundation.

  6. Very Short Range Statistical Forecasting of Automated Weather Observations.

    DTIC Science & Technology

    WEATHER FORECASTING, AUTOMATION, WEATHER , PREDICTIONS , MULTIVARIATE ANALYSIS, STATISTICS, METEOROLOGICAL DATA, SHORT RANGE(TIME), MATHEMATICAL PREDICTION, OPERATORS(MATHEMATICS), LINEAR REGRESSION ANALYSIS, MARKOV PROCESSES.

  7. 3D Short-Range Wetting and Nonlocality

    NASA Astrophysics Data System (ADS)

    Parry, A. O.; Rascón, C.; Bernardino, N. R.; Romero-Enrique, J. M.

    2008-04-01

    Analysis of a microscopic Landau-Ginzburg-Wilson model of 3D short-ranged wetting shows that correlation functions are characterized by two length scales, not one, as previously thought. This has a simple diagrammatic explanation using a nonlocal interfacial Hamiltonian and yields a thermodynamically consistent theory of wetting in keeping with exact sum rules. For critical wetting the second length serves to lower the cutoff in the spectrum of interfacial fluctuations determining the repulsion from the wall. We show how this corrects previous renormalization group predictions for fluctuation effects, based on local interfacial Hamiltonians. In particular, lowering the cutoff leads to a substantial reduction in the effective value of the wetting parameter and prevents the transition being driven first order. Quantitative comparison with Ising model simulation studies due to Binder, Landau, and co-workers is also made.

  8. Short Range Stabilization Actions: Good But Not Enough.

    ERIC Educational Resources Information Center

    Kemerer, Frank R.

    An alternative approach to achieve short-time enrollment stabilization based in part on experiences at the State University of New York, Geneseo, is described. It is suggested that a short-range effort will not be enough to assure institutional vitality in the difficult years ahead. Short-range stabilization should be followed by the integration…

  9. Emerging magnetic order in platinum atomic contacts and chains

    PubMed Central

    Strigl, Florian; Espy, Christopher; Bückle, Maximilian; Scheer, Elke; Pietsch, Torsten

    2015-01-01

    The development of atomic-scale structures revealing novel transport phenomena is a major goal of nanotechnology. Examples include chains of atoms that form while stretching a transition metal contact or the predicted formation of magnetic order in these chains, the existence of which is still debated. Here we report an experimental study of the magneto-conductance (MC) and anisotropic MC with atomic-size contacts and mono-atomic chains of the nonmagnetic metal platinum. We find a pronounced and diverse MC behaviour, the amplitude and functional dependence change when stretching the contact by subatomic distances. These findings can be interpreted as a signature of local magnetic order in the chain, which may be of particular importance for the application of atomic-sized contacts in spintronic devices of the smallest possible size. PMID:25649440

  10. Tensor interaction and short range correlations in relativistic nuclear models

    SciTech Connect

    Panda, Prafulla K.; Providencia, C.; Providencia, J. da

    2007-06-15

    Short range correlations are introduced using a Jastrow factor in a relativistic approach to the equation of state of the infinite nuclear matter in the framework of the Hartree-Fock approximation. The pion exchange, including the tensor contribution, is taken into account. It is shown that both the tensor contribution of pion exchange and short range correlations soften the equation of state. Neutron matter with correlations presents no minimum at low densities.

  11. Hard probes of short-range nucleon-nucleon correlations

    SciTech Connect

    J. Arrington, D. W. Higinbotham, G. Rosner, M. Sargsian

    2012-10-01

    The strong interaction of nucleons at short distances leads to a high-momentum component to the nuclear wave function, associated with short-range correlations between nucleons. These short-range, high-momentum structures in nuclei are one of the least well understood aspects of nuclear matter, relating to strength outside of the typical mean-field approaches to calculating the structure of nuclei. While it is difficult to study these short-range components, significant progress has been made over the last decade in determining how to cleanly isolate short-range correlations in nuclei. We have moved from asking if such structures exist, to mapping out their strength in nuclei and studying their microscopic structure. A combination of several different measurements, made possible by high-luminosity and high-energy accelerators, coupled with an improved understanding of the reaction mechanism issues involved in studying these structures, has led to significant progress, and provided significant new information on the nature of these small, highly-excited structures in nuclei. 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.

  12. Electron diffraction study of the sillenites Bi{sub 12}SiO{sub 20}, Bi{sub 25}FeO{sub 39} and Bi{sub 25}InO{sub 39}: Evidence of short-range ordering of oxygen-vacancies in the trivalent sillenites

    SciTech Connect

    Scurti, Craig A.; Arenas, D. J.; Auvray, Nicolas; Lufaso, Michael W.; Takeda, Seiji; Kohno, Hideo

    2014-08-15

    We present an electron diffraction study of three sillenites, Bi{sub 12}SiO{sub 20}, Bi{sub 25}FeO{sub 39}, and Bi{sub 25}InO{sub 39} synthesized using the solid-state method. We explore a hypothesis, inspired by optical studies in the literature, that suggests that trivalent sillenites have additional disorder not present in the tetravalent compounds. Electron diffraction patterns of Bi{sub 25}FeO{sub 39} and Bi{sub 25}InO{sub 39} show streaks that confirm deviations from the ideal sillenite structure. Multi-slice simulations of electron-diffraction patterns are presented for different perturbations to the sillenite structure - partial substitution of the M site by Bi{sup 3+}, random and ordered oxygen-vacancies, and a frozen-phonon model. Although comparison of experimental data to simulations cannot be conclusive, we consider the streaks as evidence of short-range ordered oxygen-vacancies.

  13. Real space probe of short-range interaction between Cr in a ferromagnetic semiconductor ZnCrTe.

    PubMed

    Kanazawa, Ken; Nishimura, Taku; Yoshida, Shoji; Shigekawa, Hidemi; Kuroda, Shinji

    2014-12-21

    The short-range interaction between Cr atoms was directly examined by scanning tunneling microscopy measurements on a Zn(0.95)Cr(0.05)Te film. Our measurements revealed that a Cr atom formed a localized state within the bandgap of ZnTe and this state was broadened for a pair of Cr atoms within a distance of ∼ 1 nm.

  14. Investigation of odd-order nonlinear susceptibilities in atomic vapors

    SciTech Connect

    Yan, Yaqi; Wu, Zhenkun; Si, Jinhai; Yan, Lihe; Zhang, Yiqi; Yuan, Chenzhi; Sun, Jia; Zhang, Yanpeng

    2013-06-15

    We theoretically deduce the macroscopic symmetry constraints for arbitrary odd-order nonlinear susceptibilities in homogeneous media including atomic vapors for the first time. After theoretically calculating the expressions using a semiclassical method, we demonstrate that the expressions for third- and fifth-order nonlinear susceptibilities for undressed and dressed four- and six-wave mixing (FWM and SWM) in atomic vapors satisfy the macroscopic symmetry constraints. We experimentally demonstrate consistence between the macroscopic symmetry constraints and the semiclassical expressions for atomic vapors by observing polarization control of FWM and SWM processes. The experimental results are in reasonable agreement with our theoretical calculations. -- Highlights: •The macroscopic symmetry constraints are deduced for homogeneous media including atomic vapors. •We demonstrate that odd-order nonlinear susceptibilities satisfy the constraints. •We experimentally demonstrate the deduction in part.

  15. Hidden Kekule Order of Ghost Atoms on Monolayer Graphene

    NASA Astrophysics Data System (ADS)

    Gutierrez, Christopher; Brown, Lola; Lochocki, Edward; Rosenthal, Ethan; Kim, Cheol-Joo; Ogawa, Yui; Shen, Kyle; Park, Jiwoong; Pasupathy, Abhay

    2015-03-01

    Various charge and spin ordered phases have been predicted to exist in graphene when the lattice symmetry is broken on the atomic scale. One such phase is the Kekule distortion, whereby the C-C bond symmetry is broken and the graphene unit cell is tripled. It has been proposed that when certain adatoms are placed on monolayer graphene, strong interactions can exist between them mediated by the graphene lattice. The graphene-adatom interaction can induce Kekule order in the graphene itself, and move the adatoms to produce a hidden Kekule ordering. In this talk I will discuss evidence from scanning tunneling microscopy, electron diffraction and angle resolved photoemission spectroscopy that shows the existence of this unique ordering in epitaxial graphene on copper. Interestingly, we find in this case that the Kekule order is induced by a dilute number of ``ghost atoms'' - unidentified atomic features - in the otherwise perfect copper lattice underneath monolayer graphene.

  16. μ--e+ conversion from short-range operators

    NASA Astrophysics Data System (ADS)

    Geib, Tanja; Merle, Alexander

    2017-03-01

    We present a detailed discussion of the lepton flavor and number violating conversion of bound muons into positrons. This process is a viable alternative to neutrinoless double beta decay, and, given that experiments on ordinary μ-- e- conversion are expected to improve their sensitivities by several orders of magnitude in the coming years, we can also assume the limit on μ-- e+ conversion to improve by roughly the same factor. We discuss how new physics at a high scale can lead to short-range contributions to this conversion process, and we present one explicit case in great detail (the single one for which the corresponding nuclear matrix element is presently known). The main goal of our discussion is to make the respective computation accessible to the particle physics community, so that promising models can be investigated while the nuclear physics community can simultaneously advance the computation of nuclear matrix elements. Given the progress to be expected on the experimental side, it may even be possible that lepton number violation in the e μ -sector is discovered by μ-- e+ conversion before neutrinoless double beta decay can show its existence in the e e -sector.

  17. First-Order Quantum Phase Transition for Dicke Model Induced by Atom-Atom Interaction

    NASA Astrophysics Data System (ADS)

    Zhao, Xiu-Qin; Liu, Ni; Liang, Jiu-Qing

    2017-05-01

    In this article, we use the spin coherent state transformation and the ground state variational method to theoretically calculate the ground function. In order to consider the influence of the atom-atom interaction on the extended Dicke model’s ground state properties, the mean photon number, the scaled atomic population and the average ground energy are displayed. Using the self-consistent field theory to solve the atom-atom interaction, we discover the system undergoes a first-order quantum phase transition from the normal phase to the superradiant phase, but a famous Dicke-type second-order quantum phase transition without the atom-atom interaction. Meanwhile, the atom-atom interaction makes the phase transition point shift to the lower atom-photon collective coupling strength. Supported by the National Natural Science Foundation of China under Grant Nos. 11275118, 11404198, 91430109, 61505100, 51502189, and the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi Province (STIP) under Grant No. 2014102, and the Launch of the Scientific Research of Shanxi University under Grant No. 011151801004, and the National Fundamental Fund of Personnel Training under Grant No. J1103210. The Natural Science Foundation of Shanxi Province under Grant No. 2015011008

  18. Atomically ordered solute segregation behaviour in an oxide grain boundary

    PubMed Central

    Feng, Bin; Yokoi, Tatsuya; Kumamoto, Akihito; Yoshiya, Masato; Ikuhara, Yuichi; Shibata, Naoya

    2016-01-01

    Grain boundary segregation is a critical issue in materials science because it determines the properties of individual grain boundaries and thus governs the macroscopic properties of materials. Recent progress in electron microscopy has greatly improved our understanding of grain boundary segregation phenomena down to atomistic dimensions, but solute segregation is still extremely challenging to experimentally identify at the atomic scale. Here, we report direct observations of atomic-scale yttrium solute segregation behaviours in an yttria-stabilized-zirconia grain boundary using atomic-resolution energy-dispersive X-ray spectroscopy analysis. We found that yttrium solute atoms preferentially segregate to specific atomic sites at the core of the grain boundary, forming a unique chemically-ordered structure across the grain boundary. PMID:27004614

  19. Atomically ordered solute segregation behaviour in an oxide grain boundary

    NASA Astrophysics Data System (ADS)

    Feng, Bin; Yokoi, Tatsuya; Kumamoto, Akihito; Yoshiya, Masato; Ikuhara, Yuichi; Shibata, Naoya

    2016-03-01

    Grain boundary segregation is a critical issue in materials science because it determines the properties of individual grain boundaries and thus governs the macroscopic properties of materials. Recent progress in electron microscopy has greatly improved our understanding of grain boundary segregation phenomena down to atomistic dimensions, but solute segregation is still extremely challenging to experimentally identify at the atomic scale. Here, we report direct observations of atomic-scale yttrium solute segregation behaviours in an yttria-stabilized-zirconia grain boundary using atomic-resolution energy-dispersive X-ray spectroscopy analysis. We found that yttrium solute atoms preferentially segregate to specific atomic sites at the core of the grain boundary, forming a unique chemically-ordered structure across the grain boundary.

  20. Ordered Porous Pd Octahedra Covered with Monolayer Ru Atoms.

    PubMed

    Ge, Jingjie; He, Dongsheng; Bai, Lei; You, Rui; Lu, Haiyuan; Lin, Yue; Tan, Chaoliang; Kang, Yan-Biao; Xiao, Bin; Wu, Yuen; Deng, Zhaoxiang; Huang, Weixin; Zhang, Hua; Hong, Xun; Li, Yadong

    2015-11-25

    Monolayer Ru atoms covered highly ordered porous Pd octahedra have been synthesized via the underpotential deposition and thermodynamic control. Shape evolution from concave nanocube to octahedron with six hollow cavities was observed. Using aberration-corrected high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, we provide quantitative evidence to prove that only a monolayer of Ru atoms was deposited on the surface of porous Pd octahedra. The as-prepared monolayer Ru atoms covered Pd nanostructures exhibited excellent catalytic property in terms of semihydrogenation of alkynes.

  1. Long- versus Short-Range Scattering in Doped Epitaxial Graphene.

    PubMed

    Straßer, C; Ludbrook, B M; Levy, G; Macdonald, A J; Burke, S A; Wehling, T O; Kern, K; Damascelli, A; Ast, C R

    2015-05-13

    Tuning the electronic properties of graphene by adatom deposition unavoidably introduces disorder into the system, which directly affects the single-particle excitations and electrodynamics. Using angle-resolved photoemission spectroscopy (ARPES) we trace the evolution of disorder in graphene by thallium adatom deposition and probe its effect on the electronic structure. We show that the signatures of quasiparticle scattering in the photoemission spectral function can be used to identify thallium adatoms, although charged, as efficient short-range scattering centers. Employing a self-energy model for short-range scattering, we are able to extract a δ-like scattering potential δ = -3.2 ± 1 eV. Therefore, isolated charged scattering centers do not necessarily act just as good long-range (Coulomb) scatterers but can also act as efficient short-range (δ-like) scatterers; in the case of thallium, this happens with almost equal contributions from both mechanisms.

  2. Analysis on short-range millimetre wave scattering imaging system

    NASA Astrophysics Data System (ADS)

    Zhu, Li; Li, Xing-Guo; Lou, Guo-Wei; Zhang, Chao

    2011-08-01

    A system for short-range millimetre wave(MMW) active imaging was developed, including transceiver antenna, scanning system, transceiver front-end, signal processing. A target within a few meters or even a few centimeters can be imaged. The overall structure of the imaging system and imaging method were researched. The short-range scattering imaging formula was derived from the spectral distribution shift view, which can simplify the method. Phase compensation factor was introduced to improve the imaging resolution. The relationship between the sampling frequency and scanning speed was analyzed to optimize the system parameters, which can improve image quality and system efficiency.

  3. Testing local Lorentz invariance with short-range gravity

    NASA Astrophysics Data System (ADS)

    Kostelecký, V. Alan; Mewes, Matthew

    2017-03-01

    The Newton limit of gravity is studied in the presence of Lorentz-violating gravitational operators of arbitrary mass dimension. The linearized modified Einstein equations are obtained and the perturbative solutions are constructed and characterized. We develop a formalism for data analysis in laboratory experiments testing gravity at short range and demonstrate that these tests provide unique sensitivity to deviations from local Lorentz invariance.

  4. Testing local Lorentz invariance with short-range gravity

    DOE PAGES

    Kostelecký, V. Alan; Mewes, Matthew

    2017-01-10

    The Newton limit of gravity is studied in the presence of Lorentz-violating gravitational operators of arbitrary mass dimension. The linearized modified Einstein equations are obtained and the perturbative solutions are constructed and characterized. We develop a formalism for data analysis in laboratory experiments testing gravity at short range and demonstrate that these tests provide unique sensitivity to deviations from local Lorentz invariance.

  5. Experiments of Search for Neutron Electric Dipole Moment and Spin-Dependent Short-Range Force

    NASA Astrophysics Data System (ADS)

    Zheng, Wangzhi

    It is of great importance to identify new sources of discrete symmetry violations because it can explain the baryon number asymmetry of our universe and also test the validity of various models beyond the standard model. Neutron Electric Dipole Moment (nEDM) and short-range force are such candidates for the new sources of P&T violations. A new generation nEDM experiment was proposed in USA in 2002, aiming at improving the current nEDM upperlimit by two orders of magnitude. Polarized 3He is crucial in this experiment and Duke is responsible for the 3He injection, measurements of 3He nuclear magnetic resonance (NMR) signal and some physics properties related to polarized 3He. A Monte-Carlo simulation is used to simulate the entire 3He injection process in order to study whether polarized 3He can be successfully delivered to the measurement cell. Our simulation result shows that it is achievable to maintain more than 95% polarization after 3He atoms travel through very complicated paths in the presence of non-uniform magnetic fiels. We also built an apparatus to demonstrate that the 3He precession signal can be measured under the nEDM experimental conditions using the Superconducting Quantum Interference Device (SQUID). Based on the measurement result in our lab, we project that the signal-to-noise ratio in the nEDM experiment will be at least 10. During this SQUID test, two interesting phenomena were discovered. One is the pressure dependence of the T1 of the polarized 3He which has never been reported before. The other is the discrepancy between the theoretically predicted T2 and the experimentally measured T2 of the 3He precession signal. To investigate these two interesting phenomena, two dedicated experiments were built, and two papers have been published in Physical Review A. In addition to the nEDM experiment, polarized 3He is also used in the search for the exotic short-range force. The high pressure 3He cell used in this experiment has a very thin window (

  6. Pattern formation in binary fluid mixtures induced by short-range competing interactions

    NASA Astrophysics Data System (ADS)

    Bores, Cecilia; Lomba, Enrique; Perera, Aurélien; Almarza, Noé G.

    2015-08-01

    Molecular dynamics simulations and integral equation calculations of a simple equimolar mixture of diatomic molecules and monomers interacting via attractive and repulsive short-range potentials show the existence of pattern formation (microheterogeneity), mostly due to depletion forces away from the demixing region. Effective site-site potentials extracted from the pair correlation functions using an inverse Monte Carlo approach and an integral equation inversion procedure exhibit the features characteristic of a short-range attractive and a long-range repulsive potential. When charges are incorporated into the model, this becomes a coarse grained representation of a room temperature ionic liquid, and as expected, intermediate range order becomes more pronounced and stable.

  7. Rapidly rotating boson molecules with long- or short-range repulsion: An exact diagonalization study

    SciTech Connect

    Baksmaty, Leslie O.; Yannouleas, Constantine; Landman, Uzi

    2007-02-15

    The Hamiltonian for a small number N{<=}11 of bosons in a rapidly rotating harmonic trap, interacting via a short range (contact potential) or a long range (Coulomb) interaction, is studied via an exact diagonalization in the lowest Landau level. Our analysis shows that, for both low and high fractional fillings, the bosons localize and form rotating boson molecules (RBMs) consisting of concentric polygonal rings. Focusing on systems with the number of trapped atoms sufficiently large to form multiring bosonic molecules, we find that, as a function of the rotational frequency and regardless of the type of repulsive interaction, the ground-state angular momenta grow in specific steps that coincide with the number of localized bosons on each concentric ring. Comparison of the conditional probability distributions (CPDs) for both interactions suggests that the degree of crystalline correlations appears to depend more on the fractional filling {nu} than on the range of the interaction. The RBMs behave as nonrigid rotors, i.e., the concentric rings rotate independently of each other. At filling fractions {nu}<1/2, we observe well developed crystallinity in the CPDs (two-point correlation functions). For larger filling fractions {nu}>1/2, observation of similar molecular patterns requires consideration of even higher-order correlation functions.

  8. Perturbation theory for short-range weakly-attractive potentials in one dimension

    NASA Astrophysics Data System (ADS)

    Amore, Paolo; Fernández, Francisco M.

    2017-03-01

    We have obtained the perturbative expressions up to sixth order for the energy of the bound state in a one dimensional, arbitrarily weak, short range finite well, applying a method originally developed by Gat and Rosenstein Ref. [1]. The expressions up to fifth order reproduce the results already known in the literature, while the sixth order had not been calculated before. As an illustration of our formulas we have applied them to two exactly solvable problems and to a nontrivial problem.

  9. Short-Range Correlation Models in Electronic Structure Theory

    NASA Astrophysics Data System (ADS)

    Goldey, Matthew Bryant

    Correlation methods within electronic structure theory focus on recovering the exact electron-electron interaction from the mean-field reference. For most chemical systems, including dynamic correlation, the correlation of the movement of electrons proves to be sufficient, yet exact methods for capturing dynamic correlation inherently scale polynomially with system size despite the locality of the electron cusp. This work explores a new family of methods for enhancing the locality of dynamic correlation methodologies with an aim toward improving accuracy and scalability. The introduction of range-separation into ab initio wavefunction methods produces short-range correlation methodologies, which can be supplemented with much faster approximate methods for long-range interactions. First, I examine attenuation of second-order Moller-Plesset perturbation theory (MP2) in the aug-cc-pVDZ basis. MP2 treats electron correlation at low computational cost, but suffers from basis set superposition error (BSSE) and fundamental inaccuracies in long-range contributions. The cost differential between complete basis set (CBS) and small basis MP2 restricts system sizes where BSSE can be removed. Range-separation of MP2 could yield more tractable and/or accurate forms for short- and long-range correlation. Retaining only short-range contributions proves to be effective for MP2 in the small aug-cc-pVDZ (aDZ) basis. Using one range-separation parameter within either the complementary error function (erfc) or a sum of two error functions (terfc), superior behavior is obtained versus both MP2/aDZ and MP2/CBS for inter- and intra-molecular test sets. Attenuation of the long-range helps to cancel both BSSE and intrinsic MP2 errors. Direct scaling of the MP2 correlation energy (SMP2) proves useful as well. The resulting SMP2/aDZ, MP2(erfc, aDZ), and MP2(terfc, aDZ) methods perform far better than MP2/aDZ across systems with hydrogen-bonding, dispersion, and mixed interactions at a

  10. Detecting magnetic ordering with atomic size electron probes

    SciTech Connect

    Idrobo, Juan Carlos; Rusz, Ján; Spiegelberg, Jakob; McGuire, Michael A.; Symons, Christopher T.; Vatsavai, Ranga Raju; Cantoni, Claudia; Lupini, Andrew R.

    2016-05-27

    While magnetism originates at the atomic scale, the existing spectroscopic techniques sensitive to magnetic signals only produce spectra with spatial resolution on a larger scale. However, recently, it has been theoretically argued that atomic size electron probes with customized phase distributions can detect magnetic circular dichroism. Here, we report a direct experimental real-space detection of magnetic circular dichroism in aberration-corrected scanning transmission electron microscopy (STEM). Using an atomic size-aberrated electron probe with a customized phase distribution, we reveal the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The novel experimental setup presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution.

  11. Detecting magnetic ordering with atomic size electron probes

    DOE PAGES

    Idrobo, Juan Carlos; Rusz, Ján; Spiegelberg, Jakob; ...

    2016-05-27

    While magnetism originates at the atomic scale, the existing spectroscopic techniques sensitive to magnetic signals only produce spectra with spatial resolution on a larger scale. However, recently, it has been theoretically argued that atomic size electron probes with customized phase distributions can detect magnetic circular dichroism. Here, we report a direct experimental real-space detection of magnetic circular dichroism in aberration-corrected scanning transmission electron microscopy (STEM). Using an atomic size-aberrated electron probe with a customized phase distribution, we reveal the checkerboard antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge. The novel experimental setupmore » presented here, which can easily be implemented in aberration-corrected STEM, opens new paths for probing dichroic signals in materials with unprecedented spatial resolution.« less

  12. Short-range photoassociation of LiRb

    NASA Astrophysics Data System (ADS)

    Blasing, D. B.; Stevenson, I. C.; Pérez-Ríos, J.; Elliott, D. S.; Chen, Y. P.

    2016-12-01

    We have observed short-range photoassociation of 7Li85Rb to the two lowest vibrational states of the d 3Π potential. We have also observed several a3Σ+ vibrational levels with generation rates between ˜102 and ˜103 molecules per second, resulting from the spontaneous decay of these d 3Π molecules. We observe an alternation of the peak heights in the rotational photoassociation spectrum that depends on the parity of the excited molecular state. Franck-Condon overlap calculations predict that photoassociation to higher vibrational levels of the d 3Π potential, in particular, the sixth vibrational level, should populate the lowest vibrational level of the a 3Σ+ state at a rate as high as 104 molecules per second. This work also motivates an experimental search for short-range photoassociation to other bound molecular states, such as c 3Σ+ or b 3Π , as prospects for preparing ground-state molecules.

  13. Short-Range Force Detection Using Optically Cooled Levitated Microspheres

    NASA Astrophysics Data System (ADS)

    Geraci, Andrew A.; Papp, Scott B.; Kitching, John

    2010-09-01

    We propose an experiment using optically trapped and cooled dielectric micro-spheres for the detection of short-range forces. The center-of-mass motion of a microsphere trapped in vacuum can experience extremely low dissipation and quality factors of 1012, leading to yoctonewton force sensitivity. Trapping the sphere in an optical field enables positioning at less than 1μm from a surface, a regime where exotic new forces may exist. We expect that the proposed system could advance the search for non-Newtonian gravity forces via an enhanced sensitivity of 105-107 over current experiments at the 1μm length scale. Moreover, our system may be useful for characterizing other short-range physics such as Casimir forces.

  14. Ab initio molecular dynamics simulations of short-range order in Zr50Cu45Al5 and Cu50Zr45Al5 metallic glasses

    SciTech Connect

    Huang, Yuxiang; Huang, Li; Wang, C. Z.; Kramer, M. J.; Ho, K. M.

    2016-02-01

    Comparative analysis between Zr-rich Zr50Cu45Al5 and Cu-rich Cu50Zr45Al5 metallic glasses (MGs) is extensively performed to locate the key structural motifs accounting for their difference of glass forming ability. Here we adopt ab initio molecular dynamics simulations to investigate the local atomic structures of Zr50Cu45Al5 and Cu50Zr45Al5 MGs. A high content of icosahedral-related (full and distorted) orders was found in both samples, while in the Zr-rich MG full icosahedrons < 0,0,12,0 > is dominant, and in the Cu-rich one the distorted icosahedral orders, especially < 0,2,8,2 > and < 0,2,8,1 >, are prominent. And the < 0,2,8,2 > polyhedra in Cu50Zr45Al5 MG mainly originate from Al-centered clusters, while the < 0,0,12,0 > in Zr50Cu45Al5 derives from both Cu-centered clusters and Al-centered clusters. These difference may be ascribed to the atomic size difference and chemical property between Cu and Zr atoms. Lastly, the relatively large size of Zr and large negative heat of mixing between Zr and Al atoms, enhancing the packing density and stability of metallic glass system, may be responsible for the higher glass forming ability of Zr50Cu45Al5.

  15. Short Range Correlations, Inclusive Electron-Nucleus Scattering, and Scaling

    SciTech Connect

    Day, Donal

    2008-10-13

    The presence of high momentum components in the nuclear wavefunction has been of great interest for many years. Unfortunately high momentum components, associated with the short range correlations (SRC), have been difficult to isolate unambiquously. Inclusive electron scattering cross sections in the quasielastic region have been measured over a wide range of energy and momentum transfers from very light to very heavy nuclei and the scaling analyses of these data can provide useful information on the presence of SRCs and more.

  16. Recent results on short-range gravity experiment

    NASA Astrophysics Data System (ADS)

    Hata, Maki; Akiyama, Takashi; Ikeda, Yuki; Kawamura, Hirokazu; Narita, Keigo; Ninomiya, Kazufumi; Ogawa, Naruya; Sato, Toshiaki; Seitaibashi, Etsuko; Sekiguchi, Yuta; Tsutsui, Ryosuke; Yazawa, Kazumasa; Murata, Jiro

    2009-10-01

    According to the ADD model [1], deviation from Newton's inverse square law is expected at below sub-millimeter scale. Present study is an experimental investigation of the Newton's gravitational law at a short range scale. We have developed an experimental setup using torsion balance bar, and succeeded to confirm the inverse square law at a centimeter scale. In addition, composition dependence of gravitational constant G is also tested at the centimeter scale, motivated to test the weak equivalence principle.

  17. Short-range inverse-square law experiment in space

    NASA Technical Reports Server (NTRS)

    Paik, H. J.; Moody, M. V.

    2002-01-01

    Newton's inverse-square law is a cornerstone of General Relativity. Its validity has been demonstrated to better than one part in thousand in ranges greater than 1 cm. The range below 1 mm has been left largely unexplored, due to the difficulties associated with designing sensitive short-range experiments. However, the theoretical rationale for testing Newton's law at ranges below 1 mm has become very strong recently.

  18. Effect of short range hydrodynamic on bimodal colloidal gel systems

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Jamali, Safa; Maia, Joao

    2015-03-01

    Colloidal Gels and disordered arrested systems has been studied extensively during the past decades. Although, they have found their place in multiple industries such as cosmetic, food and so on, their physical principals are still far beyond being understood. The interplay between different types of interactions from quantum scale, Van der Waals interaction, to short range interactions, depletion interaction, and long range interactions such as electrostatic double layer makes this systems challenging from simulation point of view. Many authors have implemented different simulation techniques such as molecular dynamics (MD) and Brownian dynamics (BD) to capture better picture during phase separation of colloidal system with short range attractive force. However, BD is not capable to include multi-body hydrodynamic interaction and MD is limited by the computational resources and is limited to short time and length scales. In this presentation we used Core-modified dissipative particle dynamics (CM-DPD) with modified depletion potential, as a coarse-grain model, to address the gel formation process in short ranged-attractive colloidal suspensions. Due to the possibility to include and separate short and long ranged-hydrodynamic forces in this method we studied the effect of each of those forces on the final morphology and report one of the controversial question in this field on the effect of hydrodynamics on the cluster formation process on bimodal, soft-hard colloidal mixtures.

  19. Beyond Born-Mayer: Improved models for short-range repulsion in ab initio force fields

    DOE PAGES

    Van Vleet, Mary J.; Misquitta, Alston J.; Stone, Anthony J.; ...

    2016-06-23

    Short-range repulsion within inter-molecular force fields is conventionally described by either Lennard-Jones or Born-Mayer forms. Despite their widespread use, these simple functional forms are often unable to describe the interaction energy accurately over a broad range of inter-molecular distances, thus creating challenges in the development of ab initio force fields and potentially leading to decreased accuracy and transferability. Herein, we derive a novel short-range functional form based on a simple Slater-like model of overlapping atomic densities and an iterated stockholder atom (ISA) partitioning of the molecular electron density. We demonstrate that this Slater-ISA methodology yields a more accurate, transferable, andmore » robust description of the short-range interactions at minimal additional computational cost compared to standard Lennard-Jones or Born-Mayer approaches. Lastly, we show how this methodology can be adapted to yield the standard Born-Mayer functional form while still retaining many of the advantages of the Slater-ISA approach.« less

  20. Hand-Held Units for Short-Range Wireless Biotelemetry

    NASA Technical Reports Server (NTRS)

    Miranda, Felix A.; Simons, Rainee N.

    2008-01-01

    Special-purpose hand-held radiotransceiver units have been proposed as means of short-range radio powering and interrogation of surgically implanted microelectromechanical sensors and actuators. These units are based partly on the same principles as those of the units described in "Printed Multi- Turn Loop Antennas for RF Biotelemetry" (LEW-17879-1), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 48. Like the previously reported units, these units would make it unnecessary to have wire connections between the implanted devices and the external equipment used to activate and interrogate them. Like a unit of the previously reported type, a unit of the type now proposed would include a printed-circuit antenna on a dielectric substrate. The antenna circuitry would include integrated surface-mount inductors for impedance tuning. Circuits for processing the signals transmitted and received by the antenna would be included on the substrate. During operation, the unit would be positioned near (but not in electrical contact with) a human subject, in proximity to a microelectromechanical sensor or actuator that has been surgically implanted in the subject. It has been demonstrated that significant electromagnetic coupling with an implanted device could be established at a distance of as much as 4 in. (.10 cm). During operation in the interrogation mode, the antenna of the unit would receive a radio telemetry signal transmitted by the surgically implanted device. The antenna substrate would have dimensions of approximately 3.25 by 3.75 inches (approximately 8.3 by 9.5 cm). The substrate would have a thickness of the order of 30 mils (of the order of a somewhat less than a millimeter). The substrate would be made of low-radiofrequency- loss dielectric material that could be, for example, fused quartz, alumina, or any of a number of commercially available radio-frequency dielectric composite materials. The antenna conductors would typically be made of copper or a

  1. Short range travel time geoacoustic inversion with vertical line array.

    PubMed

    Jiang, Yong-Min; Chapman, N Ross; Gerstoft, Peter

    2008-09-01

    This paper presents travel time geoacoustic inversion of broadband data collected on a vertical line array at short range of 230 m during the Shallow Water 2006 experiments. A ray-tracing method combined with a hybrid optimization algorithm that utilizes differential evolution and downhill simplex was used for the inversion of sediment properties. The ocean sound speed profile and geometric parameters were inverted prior to the sea bottom properties to account for the temporally variable ocean environment. The sediment sound speed and thickness estimates are consistent with in situ measurements and matched-field inversion results of longer-range data from the experiment.

  2. Impact of prescribed diabatic heating on short range weather forecasts

    NASA Technical Reports Server (NTRS)

    Marx, L.; Shukla, J.

    1984-01-01

    Using the 9 layer general circulation model developed at the Goddard Laboratory for Atmospheric Sciences (GLAS), several 4 to 5 day integrations were made to assess the impact that latent heating processes (supersaturation and moist convective) have on the model forecasts. In an earlier study by Shukla (1981) it was hypothesized that because of strong interaction between dynamics and moist convection, small initial errors grow very fast and make short range forecasting difficult. The purpose of this study was to examine if prescribed heating rates can improve the forecasts for a few days.

  3. Simple empirical order parameter for a first-order quantum phase transition in atomic nuclei.

    PubMed

    Bonatsos, Dennis; McCutchan, E A; Casten, R F; Casperson, R J

    2008-04-11

    A simple, empirical, easy-to-measure effective order parameter of a first-order phase transition in atomic nuclei is presented, namely, the ratio of the energies of the first excited 6+ and 0+ states, distinguishing between first- and second-order transitions, and taking on a special value in the critical region, as data in Nd-Dy show. In the large NB limit of the interacting boson approximation model, a repeating degeneracy between alternate yrast and successive 0+ states is found in the critical region around the line of a first-order phase transition, pointing to a possible underlying symmetry.

  4. Atomic-scale visualization of surface-assisted orbital order

    PubMed Central

    Kim, Howon; Yoshida, Yasuo; Lee, Chi-Cheng; Chang, Tay-Rong; Jeng, Horng-Tay; Lin, Hsin; Haga, Yoshinori; Fisk, Zachary; Hasegawa, Yukio

    2017-01-01

    Orbital-related physics attracts growing interest in condensed matter research, but direct real-space access of the orbital degree of freedom is challenging. We report a first, real-space, imaging of a surface-assisted orbital ordered structure on a cobalt-terminated surface of the well-studied heavy fermion compound CeCoIn5. Within small tip-sample distances, the cobalt atoms on a cleaved (001) surface take on dumbbell shapes alternatingly aligned in the [100] and [010] directions in scanning tunneling microscopy topographies. First-principles calculations reveal that this structure is a consequence of the staggered dxz-dyz orbital order triggered by enhanced on-site Coulomb interaction at the surface. This so far overlooked surface-assisted orbital ordering may prevail in transition metal oxides, heavy fermion superconductors, and other materials. PMID:28948229

  5. Unsupervised learning in neural networks with short range synapses

    NASA Astrophysics Data System (ADS)

    Brunnet, L. G.; Agnes, E. J.; Mizusaki, B. E. P.; Erichsen, R., Jr.

    2013-01-01

    Different areas of the brain are involved in specific aspects of the information being processed both in learning and in memory formation. For example, the hippocampus is important in the consolidation of information from short-term memory to long-term memory, while emotional memory seems to be dealt by the amygdala. On the microscopic scale the underlying structures in these areas differ in the kind of neurons involved, in their connectivity, or in their clustering degree but, at this level, learning and memory are attributed to neuronal synapses mediated by longterm potentiation and long-term depression. In this work we explore the properties of a short range synaptic connection network, a nearest neighbor lattice composed mostly by excitatory neurons and a fraction of inhibitory ones. The mechanism of synaptic modification responsible for the emergence of memory is Spike-Timing-Dependent Plasticity (STDP), a Hebbian-like rule, where potentiation/depression is acquired when causal/non-causal spikes happen in a synapse involving two neurons. The system is intended to store and recognize memories associated to spatial external inputs presented as simple geometrical forms. The synaptic modifications are continuously applied to excitatory connections, including a homeostasis rule and STDP. In this work we explore the different scenarios under which a network with short range connections can accomplish the task of storing and recognizing simple connected patterns.

  6. Predictability of short-range forecasting: a multimodel approach

    NASA Astrophysics Data System (ADS)

    García-Moya, Jose-Antonio; Callado, Alfons; Escribà, Pau; Santos, Carlos; Santos-Muñoz, Daniel; Simarro, Juan

    2011-05-01

    Numerical weather prediction (NWP) models (including mesoscale) have limitations when it comes to dealing with severe weather events because extreme weather is highly unpredictable, even in the short range. A probabilistic forecast based on an ensemble of slightly different model runs may help to address this issue. Among other ensemble techniques, Multimodel ensemble prediction systems (EPSs) are proving to be useful for adding probabilistic value to mesoscale deterministic models. A Multimodel Short Range Ensemble Prediction System (SREPS) focused on forecasting the weather up to 72 h has been developed at the Spanish Meteorological Service (AEMET). The system uses five different limited area models (LAMs), namely HIRLAM (HIRLAM Consortium), HRM (DWD), the UM (UKMO), MM5 (PSU/NCAR) and COSMO (COSMO Consortium). These models run with initial and boundary conditions provided by five different global deterministic models, namely IFS (ECMWF), UM (UKMO), GME (DWD), GFS (NCEP) and CMC (MSC). AEMET-SREPS (AE) validation on the large-scale flow, using ECMWF analysis, shows a consistent and slightly underdispersive system. For surface parameters, the system shows high skill forecasting binary events. 24-h precipitation probabilistic forecasts are verified using an up-scaling grid of observations from European high-resolution precipitation networks, and compared with ECMWF-EPS (EC).

  7. On the universality of the long-/short-range separation in multiconfigurational density-functional theory.

    PubMed

    Fromager, Emmanuel; Toulouse, Julien; Jensen, Hans Jorgen Aa

    2007-02-21

    In many cases, the dynamic correlation can be calculated quite accurately and at a fairly low computational cost in Kohn-Sham density-functional theory (KS-DFT), using current standard approximate functionals. However, in general, KS-DFT does not treat static correlation effects (near degeneracy) adequately which, on the other hand, can be described in wave-function theory (WFT), for example, with a multiconfigurational self-consistent field (MCSCF) model. It is therefore of high interest to develop a hybrid model which combines the best of both WFT and DFT approaches. The merge of WFT and DFT can be achieved by splitting the two-electron interaction into long-range and short-range parts. The long-range part is then treated by WFT and the short-range part by DFT. In this work the authors consider the so-called "erf" long-range interaction erf(micror12)/r12, which is based on the standard error function, and where mu is a free parameter which controls the range of the long-/short-range decomposition. In order to formulate a general method, they propose a recipe for the definition of an optimal microopt parameter, which is independent of the approximate short-range functional and the approximate wave function, and they discuss its universality. Calculations on a test set consisting of He, Be, Ne, Mg, H2, N2, and H2O yield microopt approximately 0.4 a.u.. A similar analysis on other types of test systems such as actinide compounds is currently in progress. Using the value of 0.4 a.u. for micro, encouraging results are obtained with the hybrid MCSCF-DFT method for the dissociation energies of H2, N2, and H2O, with both short-range local-density approximation and PBE-type functionals.

  8. Enhanced survival of short-range magnetic correlations and frustrated interactions in R3T intermetallics

    SciTech Connect

    Baranov, Nikolai; Proshkin, Aleksei; Gubkin, Andrey; Cervellino, A.; Michor, H.; Hilsher, G.; Gerasimov, E.G.; Ehlers, Georg; Frontzek, Matthias D; Podlesnyak, Andrey A

    2012-01-01

    Elastic and inelastic neutron scattering and magnetization measurements have been used to study peculiarities of the magnetic state in R{sub 3}T compounds (R=Gd, Er, Tb; T=Ni, Co) below and above magnetic ordering temperatures. A pronounced non-Brillouin shape of the magnetization curves observed in the antiferromagnetic compounds Gd{sub 3}Ni and Tb{sub 3}Ni above their magnetic ordering temperatures together with earlier reported data about the retention of the magnetic contribution to the total specific heat of Gd{sub 3}T and anomalous behavior of the electrical resistivity above magnetic ordering temperatures are ascribed to the existence of short-range magnetic correlations in the wide temperature range in the paramagnetic state. The persistence of short-range magnetic order up to temperatures greater than 5-6 times the Neel temperature has been revealed by powder neutron diffraction measurements performed for Tb{sub 3}Ni and Tb{sub 3}Co. On the other hand, results from inelastic neutron scattering show that the low temperature magnetic excitations are strongly suppressed in both Tb{sub 3}Co and Er{sub 3}Co. It is suggested that the extended short-range magnetic correlations, which turn out to be an inherent feature of R{sub 3}T type compounds, are due to the layered crystal structure and to the difference between geometrically frustrated intra-layer exchange interactions and inter-layer exchange.

  9. Magnetic ordering and anisotropy in heavy atom radicals.

    PubMed

    Winter, Stephen M; Hill, Stephen; Oakley, Richard T

    2015-03-25

    Recent developments in stable radical chemistry have afforded "heavy atom" radicals, neutral open-shell (S = 1/2) molecular species containing heavy p-block elements (S, Se), which display solid-state magnetic properties once considered exclusive to conventional metal-based magnets. These highly spin-delocalized radicals do not associate in the solid state and yet display extensive networks of close intermolecular interactions. Spin density on the heavy atoms allows for increased isotropic and spin-orbit mediated anisotropic exchange effects. Structural variations induced by chemical modification and physical pressure, coupled with ab-initio methods to estimate exchange energies, have facilitated the development of predictive structure/property relationships. These results, coupled with detailed theoretical analyses and magnetic resonance spectroscopic measurements, have provided insight into the magnetic structure of ferromagnetic and spin-canted antiferromagnetic ordered materials as well as an understanding of the importance of spin-orbit coupling contributions to magnetic hysteresis and anisotropy. Isotropic and anisotropic ferromagnetic exchange can also be enhanced indirectly by the incorporation of heavy atoms into nonspin-bearing sites, where they can contribute to multi-orbital spin-orbit coupling.

  10. Kinetic Glass Transition in a Micellar System with Short-Range Attractive Interaction

    SciTech Connect

    Mallamace, F.; Gambadauro, P.; Micali, N.; Chen, S.-H.

    2000-06-05

    We show that percolation and structural arrest transitions coexist in different regions of the phase diagram of a copolymer-micellar system and relate them to short-range intermicellar attraction. The intermediate scattering function shows a nonergodic transition along a temperature and concentration dependent line. Analyses show a logarithmic time dependence, attributed to a higher-order glass transition singularity predicted by mode-coupling theory, followed by a power law. (c) 2000 The American Physical Society.

  11. Phase diagrams of model C60 and C70 fullerenes from short-range attractive potentials.

    PubMed

    Orea, Pedro

    2009-03-14

    We report a computer-simulation study of six model fluids interacting through short-range attractive potentials in order to calculate the vapor-liquid (VL) diagrams using canonical Monte Carlo simulation. It is found that the binodal curves of these systems correctly reproduce those reported in the literature for C(60) and C(70) Girifalco potentials. Besides, we found that all coexistence curves collapse into a master curve when we rescale with their respective critical points.

  12. Short-range inverse-square law experiment in space

    NASA Astrophysics Data System (ADS)

    Paik, H.; Moody, M.; Strayer, D.

    Newton's inverse-square law is a cornerstone of General Relativity. Its validity has been demonstrated to better than one part in 103 in ranges1 cm; however, experimental challenges have left ranges1 mm largely unexplored. The theoretical rationale for testing Newton's law at short ranges has become compelling. The "strong CP problem," in the Standard Model of particle physics has led to the prediction of a new particle, called the "axion," which mediates a short-range mass- mass interaction, as well as a force between intrinsic spin and mass. The axion is also a candidate for cold dark matter. A second imp etus for testing the law at the short ranges comes from string theories where a radius of compactification, R1 μm has recently been suggested. This would imply a violation of the inverse-square law at a level of one part in 104 at a 100 μm distance. The objective our proposed Inverse-Square Law Experiment in Space (ISLES) is to perform a null test of Newton's law on ISS with a resolution of one part in 10 5 at distances ranging from 100 μm to 1 mm. Thus ISLES will be sensitive enough to detect axions with the strongest allowed coupling and test the string-theory prediction with R300 nm. This represents a dramatic improvement over existing limits. The experiment will be cooled in LTMPF, which permits superconducting magnetic levitation of the test masses in the micro-g environment. Low magnetic damping, combined with a low-noise SQUID, leads to extremely low intrinsic noise in the detector. To minimize Newtonian errors, ISLES employs a near null source, a circular disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, are suspended on the two sides of the source mass at a distance of 100 μm and are configured as a superconducting differential accelerometer. As the source position is driven sinusoidally, a violation of the inverse-square law would appear at the second harmonic as a differential acceleration signal. Direct vibration

  13. Numerical Calculations of Short-Range Wakefields of Collimators

    SciTech Connect

    Ng, Cho-Kuen

    2001-12-07

    The performance of future linear colliders are limited by the effect of short-range collimator wakefields on the beam. The beam quality is sensitive to the positioning of collimators at the end of the linac. The determination of collimator wakefields has been difficult, largely because of the scarcity of measurement data, and of the limitation of applicability of analytical results to realistic structures. In this paper, numerical methods using codes such as MAFIA are used to determine a series of tapered collimators with rectangular apertures that have been built for studies at SLAC. We will study the dependences of the wakefield on the collimator taper angle, the collimator gap as well as the bunch length. Calculations are also compared with measurements.

  14. Numerical Calculations of Short-Range Wakefields of Collimators

    NASA Astrophysics Data System (ADS)

    Ng, C. K.

    2001-12-01

    The performance of future linear colliders are limited by the effect of short-range collimator wakefields on the beam. The beam quality is sensitive to the positioning of collimators at the end of the linac. The determination of collimator wakefields has been difficult, largely because of the scarcity of measurement data, and of the limitation of applicability of analytical results to realistic structures. In this paper, numerical methods using codes such as MAFIA are used to determine a series of tapered collimators with rectangular apertures that have been built for studies at SLAC (Stanford Linear Accelerator Center). We will study the dependences of the wakefield on the collimator taper angle, the collimator gap as well as the bunch length. Calculations are also compared with measurements.

  15. Design of short-range terahertz wave passive detecting system

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Lou, Guowei; Zhu, Li; Qian, Songsong; Li, Ting

    2016-09-01

    Based on the study of radiation and transmission characteristics on THz waveband, a short-range passive detecting system is designed. The scheme originated from microwave passive detecting system. A prototype was developed following the design of key components including antennas and a harmonic mixer. The system operated at 0.36 THz. A dual-beam Cassegrain antenna was adopted for receiving signals which radiated by object and background. Local oscillator signal was generated by frequency multiplication. Harmonic mixing is adopted for reducing local oscillator signal frequency required by half. Superheterodyne technology is employed for signal acquisition. The system implemented easily. Tests and measurements were taken, which showed that the scheme was feasible and the performance of the prototype system met the design requirements.

  16. Freely cooling granular gases with short-ranged attractive potentials

    SciTech Connect

    Murphy, Eric; Subramaniam, Shankar

    2015-04-15

    We treat the case of an undriven gas of inelastic hard-spheres with short-ranged attractive potentials via an extension of the pseudo-Liouville operator formalism. New evolution equations for the granular temperature and coordination number are obtained. The granular temperature exhibits deviation from both Haff’s law and the case of long-ranged potentials. We verify this departure using soft-sphere discrete element method simulations. Excellent agreement is found for the duration of the simulation even beyond where exclusively binary collisions are expected. Simulations show the emergence of strong spatial-velocity correlations on the length scale of the last peak in the pair-correlation function but do not show strong correlations beyond this length scale. We argue that molecular chaos may remain an adequate approximation if the system is modelled as a Smoluchowski type equation with aggregation and break-up processes.

  17. Short-Range Correlations in Magnetite above the Verwey Temperature

    NASA Astrophysics Data System (ADS)

    Bosak, Alexey; Chernyshov, Dmitry; Hoesch, Moritz; Piekarz, Przemysław; Le Tacon, Mathieu; Krisch, Michael; Kozłowski, Andrzej; Oleś, Andrzej M.; Parlinski, Krzysztof

    2014-01-01

    Magnetite, Fe3O4, is the first magnetic material discovered and utilized by mankind in Ancient Greece, yet it still attracts attention due to its puzzling properties. This is largely due to the quest for a full and coherent understanding of the Verwey transition that occurs at TV=124 K and is associated with a drop of electric conductivity and a complex structural phase transition. A recent detailed analysis of the structure, based on single crystal diffraction, suggests that the electron localization pattern contains linear three-Fe-site units, the so-called trimerons. Here, we show that whatever the electron localization pattern is, it partially survives up to room temperature as short-range correlations in the high-temperature cubic phase, easily discernible by diffuse scattering. Additionally, ab initio electronic structure calculations reveal that characteristic features in these diffuse scattering patterns can be correlated with the Fermi surface topology.

  18. Short Range Photoassociation of Rb2 in a Broadband Dipole Trap

    NASA Astrophysics Data System (ADS)

    Menegatti, Carlos; Tallant, Jonathan; Marangoni, Bruno; Marcassa, Luis

    2013-05-01

    The process of photoassociation has been studied using cold trapped atomic samples for the last 20 years. Due to poor Franck-Condon overlap, a free-to-bound transition followed by spontaneous decay results in a small production of electronic ground state molecules, which are spread over several high-lying vibrational states. If the photoassociation is done at short range, deeply bound ground state molecules can be formed. In our experiment, we have performed photoassociation on trapped 85Rb atoms in a crossed broadband optical dipole trap. Our crossed beam configuration uses 40 W of power (at 1071 nm, bandwidth of 2 nm) in each beam with a 40 μm waist radius at the focus. A photoassociation laser is used and is detuned ~ - 7 cm-1 from the Rb D1 line. The resulting cold Rb2 molecules are photoionized by a pulsed dye laser. The time evolution of the molecule population indicates that the photoassociated molecules are being optically pumped by the high flux of 1071 nm photons present in the trapping beam. Optically pumping the molecules suggests deeply bound excited molecular states may be produced by photoassociation at short range by the broadband 1071 nm photons. A simple theoretical model is discussed. This work was supported by Fapesp and INCT-IQ.

  19. Brevity is prevalent in bat short-range communication.

    PubMed

    Luo, Bo; Jiang, Tinglei; Liu, Ying; Wang, Jing; Lin, Aiqing; Wei, Xuewen; Feng, Jiang

    2013-04-01

    Animal communication follows many coding schemes. Less is known about the coding strategy for signal length and rates of use in animal vocal communication. A generalized brevity (negative relation between signal length and frequency of use) is innovatively explored but remains controversial in animal vocal communication. We tested brevity for short-range social and distress sounds from four echolocating bats: adult black-bearded tomb bat Taphozous melanopogon, Mexican free-tailed bat Tadarida brasiliensis, adult greater horseshoe bat Rhinolophus ferrumequinum, and adult least horseshoe bat Rhinolophus pusillus. There was a negative association between duration and number of social but not distress calls emitted. The most frequently emitted social calls were brief, while most distress calls were long. Brevity or lengthiness was consistently selected in vocal communications for each species. Echolocating bats seem to have convergent coding strategy for communication calls. The results provide the evidence of efficient coding in bat social vocalizations, and lay the basis of future researches on the convergence for neural control on bats' communication calls.

  20. Short-range lidar for bioagent detection and classification

    NASA Astrophysics Data System (ADS)

    Hô, Nicolas; Émond, Frédéric; Babin, François; Healy, Dave; Simard, Jean-Robert; Buteau, Sylvie; McFee, John E.

    2010-04-01

    We have developed a small, relatively lightweight and efficient short range (<100 m) LIDAR instrument for remotely detecting harmful bioagents. The system is based on a pulsed, eye-safe, 355 nm laser exciting aerosols which then fluoresce with a typical spectrum. The system makes use of a novel technology for continuously monitoring for the presence of unusual concentrations of bioaerosols at a precise remote location within the monitored area, with response within seconds. Fluorescence is spectrally resolved over 32 channels capable of photon counting. Results show a sensitivity level of 40 ACPLA of Bacillus Globigii, an anthrax simulant, at a distance of 100 m (assumed worst case where 1 ppl = 1 ACPLA) considering particle sizes between 0.5 and 10 μm, with a geometric mean at 1 um. The apparatus has been tested in the field during three test and evaluation campaigns with multiple bioagents and public security products. Preliminary results show that the system is able to distinguish between harmful bioagents and naturally occurring ones. A classification algorithm was successfully tested with a single type of bioagent; experiments for daytime measurements are discussed.

  1. Exploiting orbital effects for short-range extravehicular transfers

    NASA Technical Reports Server (NTRS)

    Williams, Trevor; Baughman, David

    1993-01-01

    The problem studied in this paper is that of using Simplified Aid for Extravehicular Activity (EVA) Rescue (SAFER) to carry out efficient short-range transfers from the payload bay of the Space Shuttle Orbiter to the vicinity of the underside of the vehicle, for instance for inspection and repair of thermal tiles or umbilical doors. Trajectories are shown to exist, for the shuttle flying noise forward and belly down, that take the astronaut to the vicinity of the underside with no thrusting after the initial push-off. However, these trajectories are too slow to be of practical interest, as they take roughly an hour to execute. Additionally, they are quite sensitive to errors in the initial push-off rates. To overcome both of these difficulties, trajectories are then studied which include a single in-flight impulse of small magnitude ( in the range 0.1 - 0.4 fps). For operational simplicity, this impulse is applied towards the Orbiter at the moment when the line-of -sight of the EVA crewmember is tangential to the underside of the vehicle. These trajectories are considerably faster than the non-impulsive ones: transit times of less than 10 minutes are achievable. Furthermore, the man-in-the-loop feedback scheme used for impulse timing greatly reduces the sensitivity to initial velocity errors. Finally, similar one-impulse trajectories are also shown to exist for the Orbiter in a gravity-gradient attitiude.

  2. Short range spread-spectrum radiolocation system and method

    DOEpatents

    Smith, Stephen F.

    2003-04-29

    A short range radiolocation system and associated methods that allow the location of an item, such as equipment, containers, pallets, vehicles, or personnel, within a defined area. A small, battery powered, self-contained tag is provided to an item to be located. The tag includes a spread-spectrum transmitter that transmits a spread-spectrum code and identification information. A plurality of receivers positioned about the area receive signals from a transmitting tag. The position of the tag, and hence the item, is located by triangulation. The system employs three different ranging techniques for providing coarse, intermediate, and fine spatial position resolution. Coarse positioning information is provided by use of direct-sequence code phase transmitted as a spread-spectrum signal. Intermediate positioning information is provided by the use of a difference signal transmitted with the direct-sequence spread-spectrum code. Fine positioning information is provided by use of carrier phase measurements. An algorithm is employed to combine the three data sets to provide accurate location measurements.

  3. Differentiating between long and short range disorder in infra-red spectra: on the meaning of "crystallinity" in silica.

    PubMed

    Asscher, Yotam; Dal Sasso, Gregorio; Nodari, Luca; Angelini, Ivana; Boffa Ballaran, Tiziana; Artioli, Gilberto

    2017-08-16

    Local atomic disorder and crystallinity are structural properties that influence greatly the resulting chemical and mechanical properties of inorganic solids, and are used as indicators for different pathways of material formation. Here, these structural properties are assessed in the crystals of quartz based on particle-size-related scattering processes in transmission infra-red spectroscopy. Independent determinations of particle size distributions in the range 2-100 μm of a single crystal of quartz and defective quartz with highly anisotropic micro-crystallites show that particle sizes below the employed wavelength (approx 10 μm) exhibit asymmetric narrowing of absorption peak widths, due to scattering processes that depend on the intra-particle structural defects and long range crystallinity. In particular, we observe that the 1079 cm(-1) peak could be used to assess crystallinity, because it shows an asymmetric peak shape shift toward a higher wavelength, depending on the crystallite size. We observe that the 694 cm(-1) peak could be used to assess local atomic disorder as it does not show scattering and peak shape changes when absorption effects dominate, below 2 μm. We propose coupling particle size assessments with infra-red peak shape analysis as a method to characterize crystallinity and short range order for studying recrystallization in natural silica, as well as defectivity in many different types of silicas used for industrial and technological applications.

  4. Molecular collisions and reactive scattering in external fields: Are field-induced couplings important at short range?

    NASA Astrophysics Data System (ADS)

    Vieira, D.; Krems, R. V.; Tscherbul, T. V.

    2017-01-01

    We use accurate quantum scattering calculations to elucidate the role of short-range molecule-field interactions in atom-molecule inelastic collisions and abstraction chemical reactions at low temperatures. We consider two examples: elastic and inelastic scattering of NH(3Σ) molecules with Mg(1S) atoms in a magnetic field; reactive scattering LiF + H → Li + HF in an electric field. Our calculations suggest that, for non-reactive collision systems and abstraction chemical reactions, the molecule-field interactions cannot generally be neglected at short range because the atom-molecule potential passes through zero at short range. An important exception occurs for Zeeman transitions in atom-molecule collisions at magnetic fields ≲1000 G, for which the molecule-field couplings need only be included at large ρ outside the range of the atom-molecule interaction. Our results highlight the importance of an accurate description of ρ-dependent molecule-field interactions in quantum scattering calculations on molecular collisions and chemical reactions at low temperatures.

  5. Quantum many-body systems with short-range interactions

    NASA Astrophysics Data System (ADS)

    Yin, Jun

    In this dissertation, the central theme is evaluation of the ground energy and the first few excited energies of Bose or Fermi gas system in continuum R3 or lattice Z3 with short-range interactions. In Chapter 2 and 3, we carry out an analysis on low-dimensional behaviors of dilute Bose gas in traps. In Chapter 4 and 5, we generalize the results on the ground state energies of dilute Bose or Fermi gases in thermodynamic limit. In quantum mechanics, many-body quantum system is completely described by the Hamiltonian, which is a self-adjoint operator on a suitable Hilbert space. In proper scaling limits and parameter regimes, these three-dimensional Hamiltonians can be rigorously described by effective low-dimensional Hamiltonians or equations. In Chapter 2 we show that the Lieb-Liniger model for one-dimensional bosons with repulsive Delta function interaction can be rigorously derived from a dilute three-dimensional Bose gas with arbitrary repulsive interaction potential of finite scattering length. In Chapter 3 we prove that the two dimensional rotating Gross-Pitaevskii (GP) equation correctly describes the ground state energy and corresponding one-particle density matrix of rotating, dilute, interacting Bose gas in three dimensions in a potential that is strongly confining in one direction. Another one of the most remarkable recent developments in study of dilute Bose gases is the rigorous proofs on the leading terms of the effect of the repulsive interaction potential on the ground state energy or the free energy in the thermodynamic limit. For interacting Bose gases, in [44], Lieb and Yngvason proved the correction per volume on ground energy is 4pi aϱ2, where a is the scattering length of interaction potential and ϱ is the density. In this dissertation we generalize this result as follows, we prove that the upper bound part holds for all interaction potentials of positive scattering length, i.e., a > 0, and the lower bound part holds for some interaction

  6. Relativistic Hamiltonians and short-range structure of nuclei

    NASA Astrophysics Data System (ADS)

    Forest, Jun Lu

    1998-12-01

    This work is divided into two parts. In the first part, short-range structure of deuteron is studied using a nonrelativistic Hamiltonian. The equidensity surfaces for spin projection Ms = 0 distributions are found to be toroidal in shape, while those of Ms = ±1 have dumbbell shapes at large density. The toroidal shapes indicate that the tensor correlations have near maximal strength at the interparticle distance r < 2 fm. They provide new insights and simple explanations of the structure and electromagnetic form factors of the deuteron. In the second part, relativistic effects are studied using a relativistic Hamilionian defined as the sum of relativistic one-body kinetic energy, two- and three-body potentials and their boost corrections. Variational Monte Carlo method is used to study two kinds of relativistic effects in the binding energy of 3H and 4He. The first is due to the nonlocalities in the relativistic kinetic energy and relativistic one-pion exchange potential (OPEP) and the second is from boost interaction. The OPEP contribution is reduced by ~15% by the relativistic nonlocality, which may also have significant effects on pion exchange currents. However, almost all of this reduction is canceled by changes in the kinetic energy and other interaction terms, and the total effect of the nonlocalities on the binding energy is very small. The boost interactions, on the other hand, give repulsive contributions of ~0.4 (1.9) MeV in 3H (4He) and account for ~1/3 of the phenomenological part of the three-nucleon interaction needed in the nonrelativistic Hamiltonians.

  7. Tagging the EMC effect with Short-Range Correlated protons

    NASA Astrophysics Data System (ADS)

    Gilad, Shalev; Schmookler, Barak

    2014-09-01

    A linear correlation is observed between the slope of the typical EMC curve for 0.3 short-range correlated (SRC) nucleon pairs in nuclei. This correlation is surprising because of the vastly different energy and distance scales of EMC and SRC. A possible explanation is that the modification of the nucleon structure-functions F2(A) in the nucleus depend on the virtuality of nucleons and is pronounced for SRC nucleons that are highly virtual. We are studying this hypothesis by tagging EMC events with high-momentum protons recoiling backward to the transferred-momentum direction, which have been shown to be spectators in scattering off their SRC partners. The DIS data off several nuclei were collected during the eg2 running period using the CLAS detector at JLab. These data are being analyzed now as part of the data mining project. We shall present preliminary results of ratios of inclusive DIS A(e,e')X/d(e,e')X, semi-exclusive DIS A(e , e 'precoil)X/d(e,e'precoil)X and semi-exclusive to inclusive DIS A(e,e'precoil)X/d(e,e')X. We shall discuss these results with respect to our hypothesis that the EMC effect is related to DIS from highly virtual, SRC nucleons.

  8. Electron Diffraction Evidence for the Ordering of Excess Nickel Atoms by Relation to Stoichiometry in Nickel-Rich Beta'-Nial Formation of a Nickel-Aluminum (Ni2al) Superlattices

    NASA Technical Reports Server (NTRS)

    Reynaud, F.

    1988-01-01

    In electron diffraction patterns of nickel-rich beta-NiAl alloys, many anomalies are observed. One of these is the appearance of diffuse intensity maxima between the reflexions of the B2 structure. This is explained by the short-range ordering of the excess nickel atoms on the simple cubic sublattice occupied only by aluminum atoms in the stoichiometric, perfectly ordered NiAl alloy. After annealing Ni 37.5 atomic percent Al and Ni 37.75 atomic percent Al for 1 week at 300 and 400 C, the diffuse intensity maxima transformed into sharp superstructure reflexions. These reflexions are explained by the formation of the four possible variants of an ordered hexagonal superstructure corresponding to the Ni2Al composition. This structure is closely related to the Ni2Al3 structure (same space group) formed by the ordering of vacancies on the nickel sublattice in aluminum-rich beta-NiAl alloys.

  9. Short-range interactions in an effective field theory approach for nucleon-nucleon scattering

    SciTech Connect

    Scaldeferri, K.A.; Phillips, D.R.; Kao, C.; Cohen, T.D.

    1997-08-01

    We investigate in detail the effect of making the range of the {open_quotes}contact{close_quotes} interaction used in effective field theory (EFT) calculations of NN scattering finite. This is done in both an effective field theory with explicit pions, and one where the pions have been integrated out. In both cases we calculate NN scattering in the {sup 1}S{sub 0} channel using potentials which are second order in the EFT expansion. The contact interactions present in the EFT Lagrangian are made finite by use of a square-well regulator. We find that there is an optimal radius for this regulator, at which second-order corrections to the EFT are identically zero; for radii near optimal these second-order corrections are small. The cutoff EFT{close_quote}s which result from this procedure appear to be valid for momenta up to about 100{endash}150MeV/c. We also find that the radius of the square well cannot be reduced to zero if the theory is to reproduce both the experimental scattering length and effective range. Indeed, we show that, if the NN potential is the sum of a one-pion-exchange piece and a short-range interaction, then the short-range piece must extend out beyond 1.05 fm, regardless of its particular form. {copyright} {ital 1997} {ital The American Physical Society}

  10. Minimal mechanism leading to discontinuous phase transitions for short-range systems with absorbing states

    NASA Astrophysics Data System (ADS)

    Fiore, Carlos E.

    2014-02-01

    Motivated by recent findings, we discuss the existence of a direct and robust mechanism providing discontinuous absorbing transitions in short-range systems with single species, with no extra symmetries or conservation laws. We consider variants of the contact process, in which at least two adjacent particles (instead of one, as commonly assumed) are required to create a new species. Many interaction rules are analyzed, including distinct cluster annihilations and a modified version of the original pair contact process. Through detailed time-dependent numerical simulations, we find that for our modified models, the phase transitions are of first order, hence contrasting with their corresponding usual formulations in the literature, which are of second order. By calculating the order-parameter distributions, the obtained bimodal shapes as well as the finite-scale analysis reinforce coexisting phases and thus a discontinuous transition. These findings strongly suggest that the above particle creation requirements constitute a minimum and fundamental mechanism determining the phase coexistence in short-range contact processes.

  11. Analytic description of high-order harmonic generation by atoms in a two-color laser field

    SciTech Connect

    Frolov, M. V.; Manakov, N. L.; Silaev, A. A.; Vvedenskii, N. V.

    2010-06-15

    A closed-form analytic formula describing high-order harmonic generation (HHG) in a two-color field of frequencies {omega} and 2{omega} is derived quantum mechanically in the low-frequency (tunneling) limit for an electron bound by a short-range potential and generalized to the case of an active electron in a neutral atom. The HHG rates are presented as a product of an electron wave packet describing the ionization of an active electron and its propagation in a laser field up to the recombination event and an atom-specific cross section of the electron's photorecombination. In contrast to the case of a monochromatic laser pulse [Frolov et al., Phys. Rev. Lett. 102, 243901 (2009)], the two-color wave packet involves the interference of two terms (involving the Airy function) that describe the emission of harmonics during the first and second half-cycles of the fundamental laser cycle and give rise to the two-plateau structures in the HHG spectra. For the case of the H atom, we show that our analytic results are in good agreement with those obtained from a numerical solution of the three-dimensional time-dependent Schroedinger equation. The factorization formula is used for describing the dependence of HHG rates for inert gases on the relative phase and intensities of the {omega} and 2{omega} components of a laser field. It is shown that atomic structure (including electron correlation) effects can modify substantially the two-color HHG spectra of inert gases.

  12. Short-range magnetic correlations and spin dynamics in the paramagnetic regime of (Mn,Fe)2(P,Si)

    NASA Astrophysics Data System (ADS)

    Miao, X. F.; Caron, L.; Cedervall, J.; Gubbens, P. C. M.; Dalmas de Réotier, P.; Yaouanc, A.; Qian, F.; Wildes, A. R.; Luetkens, H.; Amato, A.; van Dijk, N. H.; Brück, E.

    2016-07-01

    The spatial and temporal correlations of magnetic moments in the paramagnetic regime of (Mn,Fe ) 2(P ,Si ) have been investigated by means of polarized neutron diffraction and muon-spin relaxation techniques. Short-range magnetic correlations are present at temperatures far above the ferromagnetic transition temperature (TC). This leads to deviations of paramagnetic susceptibility from Curie-Weiss behavior. These short-range magnetic correlations extend in space, slow down with decreasing temperature, and finally develop into long-range magnetic order at TC.

  13. Materials at Atomic Pressure

    SciTech Connect

    Hicks, Damien

    2010-06-10

    Atomic units give the scale at which quantum processes operate. As combinations of fundamental constants they concisely encapsulate qualities of the atom, e.g. atomic length and energy scales are given by the Bohr radius and the Hartree (or Rydberg) respectively. Although many of these quantities were probed in the early part of the 20th Century the atomic unit of time, at tens of attoseconds, was first probed in 2001. Today, the only atomic unit that remains to be studied experimentally is the atomic unit of pressure, at 294 Mbar (or 147 Mbar in Rydberg atomic units). This is nature’s definition of the ‘high’ in high-pressure science, and it sets the scale for new physics and chemistry. Among experimental facilities, only the NIF can attain and accurately probe atomic pressures. We propose to directly study material properties at these conditions by examining the short-range ordering of atoms using x-ray absorption fine structure spectroscopy (XAFS) of layers in spherical, ignition-type imploding shells. What happens at atomic pressures? The atomic unit of pressure represents the quantum mechanical pressure exerted by an orbiting electron to prevent collapse into the nucleus. Applying external pressure of this magnitude seriously disrupts orbitals and alters the character of the atom itself. Core electron orbitals overlap and chemical bonds are no longer constrained to occur between valence electron orbitals alone. The most direct probe of bonding requires a short-range order diagnostic such as XAFS.

  14. Atomic ordering in Au-(42 to 50) at.% Pd: A diffuse scattering and first-principles investigation

    NASA Astrophysics Data System (ADS)

    Schönfeld, B.; Sax, C. R.; Ruban, A. V.

    2012-01-01

    Atomic ordering in Au-Pd alloys was studied by diffuse x-ray scattering and first-principles methods. Diffuse scattering was done of a single crystal of Au-48 at.% Pd that was aged at 703 K for 24 days. The weakly modulated short-range-order scattering exhibits diffuse maxima with an incommensurate wave vector, which can be related to a Fermi-surface nesting mechanism. From effective pair interaction parameters determined by the inverse Monte Carlo method, a one-dimensional long-period superstructure of the CH structure, LPS1, was found for AuPd. Concurrent electronic-structure calculations of the effective cluster interaction (ECI) parameters indicated the presence of another closely related superstructure, LPS2, at 0 K. At the same time, direct first-principles calculations of the total energies of the CH structure and further one-dimensional long-period superstructures predicted the stabilization of LPS4. Although the energy differences between these structures are small and a complex behavior of the effective interactions is expected due to the Fermi-surface nesting, experimental data and theoretical results both support the stabilization of a long-period superstructure of the CH structure for AuPd at 0 K. The ECI parameters determined by the screened generalized perturbation method also predicted a ground-state structure different from Au7Pd5, previously obtained from cluster expansion calculations. Its energetic preference was confirmed by direct total-energy calculations.

  15. Stiffness instability in short-range critical wetting

    NASA Astrophysics Data System (ADS)

    Jin, Albert J.; Fisher, Michael E.

    1993-07-01

    Recent theoretical work has shown that an interface separating two fluid phases suffers changes in its (bare) effective stiffness, Σ~(l)=Σ~∞+ΔΣ~(l), when located at a distance l from a planar wall: terms varying as lke-jκl appear in ΔΣ~ (where 0<=k<=j=1,2, . . . and κ is the inverse bulk correlation length in the fluid wetting the wall). This may induce first-order wetting transitions when critical wetting had been expected. This general behavior of ΔΣ~(l) is confirmed using an integral/adsorption constraint to determine l, in place of the original crossing constraint. The exact linearized functional renormalization-group technique is used to analyze the full wetting-phase diagram as a function of T, of ω=kBTcWκ2/4πΣ~(TcW), and of q, the amplitude of the -le-2κl term in ΔΣ~. For dimensions d>3, any positive q (as generally expected) yields first-order wetting. The same is true for d=3 provided ω<1/2 but when ω>1/2 nonclassical critical behavior is still found for small q0. Detailed expressions are obtained for , ξ∥, etc., in the various critical and first-order regions. Numerical estimates show that previous Ising-model simulations probably encountered weakly first-order wetting transitions which might explain discrepancies with earlier renormalization-group predictions.

  16. Higher-order Sternheimer shieldings of the hydrogen atom

    NASA Astrophysics Data System (ADS)

    Fowler, P. W.; Steiner, E.

    Multiple perturbation theory is used to calculate the response of the electric field gradient at the nucleus of the hydrogen atom to external non-uniform fields. The parallel component of the field gradient at the nucleus in an axial field F with gradient F' and second derivative F'' has the perturbation expansion: [Enlarge Image

  17. Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations

    PubMed Central

    Eckstein, Martin; Werner, Philipp

    2016-01-01

    Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid. PMID:26883536

  18. The role of short-range magnetic correlations in the gap opening of topological Kondo insulators

    NASA Astrophysics Data System (ADS)

    Ramos, E.; Franco, R.; Silva-Valencia, J.; Foglio, M. E.; Figueira, M. S.

    2017-08-01

    In this article we investigate the effects of short-range anti-ferromagnetic correlations on the gap opening of topological Kondo insulators. We add a Heisenberg term to the periodic Anderson model at the limit of strong correlations in order to allow a small degree of hopping of the localized electrons between neighboring sites of the lattice. This new model is adequate for studying topological Kondo insulators, whose paradigmatic material is the compound SmB6 . The main finding of the article is that the short-range antiferromagnetic correlations, present in some Kondo insulators, contribute decisively to the opening of the Kondo gap in their density of states. These correlations are produced by the interaction between moments on the neighboring sites of the lattice. For simplicity, we solve the problem on a two dimensional square lattice. The starting point of the model is the 4f-Ce ions orbitals, with J=5/2 multiplet in the presence of spin-orbit coupling. We present results for the Kondo and for the antiferromagnetic correlation functions. We calculate the phase diagram of the model, and as we vary the Ef level position from the empty regime to the Kondo regime, the system develops metallic and topological Kondo insulator phases. The band structure calculated shows that the model describes a strong topological insulator.

  19. Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations

    NASA Astrophysics Data System (ADS)

    Eckstein, Martin; Werner, Philipp

    2016-02-01

    Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid.

  20. The role of short-range magnetic correlations in the gap opening of topological Kondo insulators.

    PubMed

    Ramos, E; Franco, R; Silva-Valencia, J; Foglio, M E; Figueira, M S

    2017-08-31

    In this article we investigate the effects of short-range anti-ferromagnetic correlations on the gap opening of topological Kondo insulators. We add a Heisenberg term to the periodic Anderson model at the limit of strong correlations in order to allow a small degree of hopping of the localized electrons between neighboring sites of the lattice. This new model is adequate for studying topological Kondo insulators, whose paradigmatic material is the compound [Formula: see text]. The main finding of the article is that the short-range antiferromagnetic correlations, present in some Kondo insulators, contribute decisively to the opening of the Kondo gap in their density of states. These correlations are produced by the interaction between moments on the neighboring sites of the lattice. For simplicity, we solve the problem on a two dimensional square lattice. The starting point of the model is the [Formula: see text] ions orbitals, with [Formula: see text] multiplet in the presence of spin-orbit coupling. We present results for the Kondo and for the antiferromagnetic correlation functions. We calculate the phase diagram of the model, and as we vary the [Formula: see text] level position from the empty regime to the Kondo regime, the system develops metallic and topological Kondo insulator phases. The band structure calculated shows that the model describes a strong topological insulator.

  1. Short-Range Interaction Energies and Forces Between Glucose and Silica

    NASA Astrophysics Data System (ADS)

    Kwon, K.; Kubicki, J. D.

    2002-12-01

    Many researchers have attempted to explain bacterial adhesion with DLVO theory and have had some success in describing long-range interactions. However, DLVO theory cannot properly explain the energetics of adhesion on a short-range scale (less than 1 nm). To understand short-range interactions of bacterial lipopolysaccharides (LPS) with mineral surfaces, we have calculated the structure and energetics of a glucose monomer interacting with a model silica surface (silsesquioxane). Glucose was chosen because it is the monomeric unit of the polymer Dextran which has been used as a model LPS. Silsesquioxane was selected because it is a convenient molecule that captures the most important silanol functional groups of the silica surface. Ab initio calculations were carried out with Gaussian 98 using both the HF/3-21G(d,p) and B3LYP/6-311++G(d,p) methods. The former basis set was used to generate approximations for the structure of the glucose-silsesquioxane dimer and the latter was used to calculate potential energies. A full energy minimization without any constraints was conducted to determine the most stable configuration of the dimer. Constrained energy minimizations were then conducted based on the optimized structure with the atoms of the silsesquioxane constrained. In addition, the interatomic distances between four atoms in the glucose molecule and four atoms in the silsesquioxane were also constrained to mimic the approach of the end of a LPS to a silica surface. The derivatives of the calculated potential energy were used to predict a force versus distance curve for these two molecules. The model predicts the formation of four H-bonds between the glucose and silsesquioxane that result in a minimum energy distance of approximately 2.4 Angstroms between the two molecules. The total interaction energy is close to -40 kJ/mol, which is reasonable based on experimental H-bond energies. The maximum attractive force predicted at 2.8 Angstroms is -0.24 nN, and the

  2. Search for exotic short-range interactions using paramagnetic insulators

    DOE PAGES

    Chu, Pinghan; Weisman, E.; Liu, C. -Y.; ...

    2015-05-26

    We describe a proposed experimental search for exotic spin-coupled interactions using a solid-state paramagnetic insulator. The experiment is sensitive to the net magnetization induced by the exotic interaction between the unpaired insulator electrons with a dense, nonmagnetic mass in close proximity. An existing experiment has been used to set limits on the electric dipole moment of the electron by probing the magnetization induced in a cryogenic gadolinium gallium garnet sample on application of a strong electric field. With suitable additions, including a movable source mass, this experiment can be used to explore “monopole-dipole” forces on polarized electrons with unique ormore » unprecedented sensitivity. As a result, the solid-state, nonmagnetic construction, combined with the low-noise conditions and extremely sensitive magnetometry available at cryogenic temperatures could lead to a sensitivity over 10 orders of magnitude greater than exiting limits in the range below 1 mm.« less

  3. Search for exotic short-range interactions using paramagnetic insulators

    SciTech Connect

    Chu, Pinghan; Weisman, E.; Liu, C. -Y.; Long, J. C.

    2015-05-26

    We describe a proposed experimental search for exotic spin-coupled interactions using a solid-state paramagnetic insulator. The experiment is sensitive to the net magnetization induced by the exotic interaction between the unpaired insulator electrons with a dense, nonmagnetic mass in close proximity. An existing experiment has been used to set limits on the electric dipole moment of the electron by probing the magnetization induced in a cryogenic gadolinium gallium garnet sample on application of a strong electric field. With suitable additions, including a movable source mass, this experiment can be used to explore “monopole-dipole” forces on polarized electrons with unique or unprecedented sensitivity. As a result, the solid-state, nonmagnetic construction, combined with the low-noise conditions and extremely sensitive magnetometry available at cryogenic temperatures could lead to a sensitivity over 10 orders of magnitude greater than exiting limits in the range below 1 mm.

  4. Eye safe short range standoff aerosol cloud finder.

    SciTech Connect

    Bambha, Ray P.; Schroder, Kevin L.; Reichardt, Thomas A.

    2005-02-01

    Because many solid objects, both stationary and mobile, will be present in an indoor environment, the design of an indoor aerosol cloud finding lidar (light detection and ranging) instrument presents a number of challenges. The cloud finder must be able to discriminate between these solid objects and aerosol clouds as small as 1-meter in depth in order to probe suspect clouds. While a near IR ({approx}1.5-{micro}m) laser is desirable for eye-safety, aerosol scattering cross sections are significantly lower in the near-IR than at visible or W wavelengths. The receiver must deal with a large dynamic range since the backscatter from solid object will be orders of magnitude larger than for aerosol clouds. Fast electronics with significant noise contributions will be required to obtain the necessary temporal resolution. We have developed a laboratory instrument to detect aerosol clouds in the presence of solid objects. In parallel, we have developed a lidar performance model for performing trade studies. Careful attention was paid to component details so that results obtained in this study could be applied towards the development of a practical instrument. The amplitude and temporal shape of the signal return are analyzed for discrimination of aerosol clouds in an indoor environment. We have assessed the feasibility and performance of candidate approaches for a fieldable instrument. With the near-IR PMT and a 1.5-{micro}m laser source providing 20-{micro}J pulses, we estimate a bio-aerosol detection limit of 3000 particles/l.

  5. Short Range Photoassociation of Rb2 by a high power fiber laser

    NASA Astrophysics Data System (ADS)

    Passagem, Henry; Rodriguez, Ricardo; Ventura, Paulo; Bouloufa, Nadia; Dulieu, Olivier; Marcassa, Luis

    2016-05-01

    Photoassociation has been studied using cold trapped atomic samples for the last 20 years. Due to poor Franck-Condon overlap, a free-to-bound transition followed by spontaneous decay results in a small production of electronic ground state molecules. If the photoassociation is done at short range, deeply bound ground state molecules can be formed. Optical pumping schemes can be used to populate a single state. In our experiment, we have performed trap loss spectroscopy on trapped 85 Rb atoms in a MOT using a high power fiber laser. Our single mode fiber laser (linewidth < 1 MHz) produces about 50 W, which can be tuned in the 1060-1070 nm range. Two vibrational bound states of the 0u+ potential were observed (ν = 137 and 138). The frequency positions as well as the rotational constants of these states are in good agreement with theoretical predictions. We have also measured the lifetime of a crossed optical dipole trap using such fiber laser. The lifetime on resonance is shorter than off resonance as expected. A simple theoretical model indicates that the molecules decay to deeply bound vibrational levels in the ground state. This work was supported by Fapesp and INCT-IQ.

  6. Short-range variation in a Wisconsin soilscape (USA)

    NASA Astrophysics Data System (ADS)

    Hartemink, A. E.; Gennadiyev, A. N.; Bockheim, J. G.; Bero, N.

    2017-02-01

    Here we report on the variation of a soilscape in south central Wisconsin, USA. The variation in soil properties and soil features results in four soil order (Entisols, Inceptisols, Alfisols and Mollisols). Observations were made along a 200 m transect in a field that was cultivated since 1870. Slopes ranged from 7.5% on the back slope to 0% in the lower part. The soilscape had a total relief difference of 7.0 m. The soils were studied by 41 soil pits (60 cm), 6 soil pits (125 cm), 15 soil augers (100 cm), and ground-penetrating radar imagery. The summit and shoulder consist of coarse glacial outwash (loamy sands) over limestone whereas the lower part is lacustrine sediments over coarse outwash (loams, silty loams). The A-horizon thickness ranged from 14 to 52 cm with thick A horizons at the toeslope that also had the lowest soil pH. The soil organic carbon (SOC) contents of the A horizons ranged from 11.6 to 46.9 g C kg-1, and the higher contents are in the lower part of the soilscape. SOC stocks (0-20 cm depth) ranged from 50 to 70 Mg C ha-1 on the summit and backslope, but were 80 to 95 Mg C ha-1 in the flat part of the soilscape. The lowest soybean yields (1.6 Mg ha-1) were found at the summit and the highest yield (6.3 Mg ha-1) at the lower end of the backslope. Soybean yields were correlated to the thickness of the A horizon, and every 10 cm increase in A horizon thickness yielded an extra 0.6 Mg soybeans ha-1. Analysis of spherical magnetic particles was used to estimate soil erosion rates that were highest on the backslope (16.2 Mg ha-1 yr-1) and rates of soil deposition in the lowest part of the soilscape was 18.8 Mg haP1 yr-1. It seems that there is no net soil and SOC loss within this soilscape. All in all, we found 4 soil taxonomic orders within 200 m. The variation in this soilscape was substantial and probably enhanced by 140 years of cultivation.

  7. Straightforward biodegradable nanoparticle generation through megahertz-order ultrasonic atomization

    NASA Astrophysics Data System (ADS)

    Forde, Gareth; Friend, James; Williamson, Tom

    2006-08-01

    Simple and reliable formation of biodegradable nanoparticles formed from poly-ɛ-caprolactone was achieved using 1.645MHz piston atomization of a source fluid of 0.5% w/v of the polymer dissolved in acetone; the particles were allowed to descend under gravity in air 8cm into a 1mM solution of sodium dodecyl sulfate. After centrifugation to remove surface agglomerations, a symmetric monodisperse distribution of particles ϕ 186nm (SD =5.7, n =6) was obtained with a yield of 65.2%.

  8. Draft Performance Specification for USAF Short Range Wideband Radio AN/GRC-XXX.

    DTIC Science & Technology

    1978-10-01

    assemblages. This specification establishes the requirements for the performance, design, fabrication, test, qualification and evaluation for the USAF Short Range Wideband Radio, AN/GRC- XXX . (Author)

  9. Homodyne detection of short-range Doppler radar using a forced oscillator model

    NASA Astrophysics Data System (ADS)

    Kittipute, Kunanon; Saratayon, Peerayudh; Srisook, Suthasin; Wardkein, Paramote

    2017-03-01

    This article presents the homodyne detection in a self-oscillation system, which represented by a short-range radar (SRR) circuit, that is analysed using a multi-time forced oscillator (MTFO) model. The MTFO model is based on a forced oscillation perspective with the signal and system theory, a second-order differential equation, and the multiple time variable technique. This model can also apply to analyse the homodyne phenomenon in a difference kind of the oscillation system under same method such as the self-oscillation system, and the natural oscillation system with external forced. In a free oscillation system, which forced by the external source is represented by a pendulum with an oscillating support experiment, and a modified Colpitts oscillator circuit in the UHF band with input as a Doppler signal is a representative of self-oscillation system. The MTFO model is verified with the experimental result, which well in line with the theoretical analysis.

  10. Attitude algorithm and initial alignment method for SINS applied in short-range aircraft

    NASA Astrophysics Data System (ADS)

    Zhang, Rong-Hui; He, Zhao-Cheng; You, Feng; Chen, Bo

    2017-07-01

    This paper presents an attitude solution algorithm based on the Micro-Electro-Mechanical System and quaternion method. We completed the numerical calculation and engineering practice by adopting fourth-order Runge-Kutta algorithm in the digital signal processor. The state space mathematical model of initial alignment in static base was established, and the initial alignment method based on Kalman filter was proposed. Based on the hardware in the loop simulation platform, the short-range flight simulation test and the actual flight test were carried out. The results show that the error of pitch, yaw and roll angle is fast convergent, and the fitting rate between flight simulation and flight test is more than 85%.

  11. Homodyne detection of short-range Doppler radar using a forced oscillator model

    PubMed Central

    Kittipute, Kunanon; Saratayon, Peerayudh; Srisook, Suthasin; Wardkein, Paramote

    2017-01-01

    This article presents the homodyne detection in a self-oscillation system, which represented by a short-range radar (SRR) circuit, that is analysed using a multi-time forced oscillator (MTFO) model. The MTFO model is based on a forced oscillation perspective with the signal and system theory, a second-order differential equation, and the multiple time variable technique. This model can also apply to analyse the homodyne phenomenon in a difference kind of the oscillation system under same method such as the self-oscillation system, and the natural oscillation system with external forced. In a free oscillation system, which forced by the external source is represented by a pendulum with an oscillating support experiment, and a modified Colpitts oscillator circuit in the UHF band with input as a Doppler signal is a representative of self-oscillation system. The MTFO model is verified with the experimental result, which well in line with the theoretical analysis. PMID:28252000

  12. Short-range correlations in the magnetic ground state of Na4 Ir3 O8

    NASA Astrophysics Data System (ADS)

    Dally, Rebecca; Hogan, Tom; Amato, Alex; Luetkens, Hubertus; Baines, Chris; Rodriguez-Rivera, Jose; Graf, Michael; Wilson, Stephen

    2015-03-01

    The magnetic ground state of the candidate three-dimensional quantum spin liquid Na4 Ir3O8 has been studied through bulk magnetization, muon spin relaxation and neutron scattering measurements. Na4 Ir3O8 possesses a unique hyper-Kagome lattice of Ir moments that is potentially accompanied by a novel realization of Heisenberg-Kitaev exchange. This fact combined with the absence of previously reported magnetic ordering has led to its candidacy as a three-dimensional quantum spin liquid. Our combined experimental data show that a short-range, frozen, ground state comprised of quasi-static moments develops in this material below a characteristic temperature TF = 6 K , persisting down until at least 20 mK. The expected dynamical ground state of a quantum spin liquid was not observed but rather an inhomogeneous quasi-static spin state that survives with persistent long timescale fluctuations.

  13. Null Test of Newtonian Inverse-Square-Law at Short Range: Current Status and Developments

    NASA Astrophysics Data System (ADS)

    Guan, S.; Tu, L.; Luo, J.; Shao, C.; Liu, L.

    Motivated by a variety of novel theories that predict new effects,we will test Newtonian inverse-square law (ISL) at several sub-millimeter separations using a torsion pendulum in its horizontal direction. We had tested ISL at separations ranging down to 176μ m, previous result stated that no new effects were observed. [L. C. Tu, S. G. Guan, J. Luo, C. G. Shao and L. X. Liu, Phys. Rev. Lett. 98 (2007), 201101.] On the basis of before, an improved ISL experiment (IISL) has been proposed, detecting distance will close up to 120μm and prospective result will set a constraint on Yukawa interactions with | α | ≥ 1 at 95% confidence for λ < 33 μ m, which will improve previous short-range constraints by one order at least.

  14. Short range ferromagnetic, magneto-electric, and magneto-dielectric effect in ceramic Co3TeO6

    NASA Astrophysics Data System (ADS)

    Singh, Harishchandra; Ghosh, Haranath; Chandrasekhar Rao, T. V.; Sharma, G.; Saha, J.; Patnaik, S.

    2016-01-01

    We report observation of magneto-electric and magneto-dielectric couplings along with short range ferromagnetic order in ceramic Cobalt Tellurate (Co3TeO6, CTO) using magnetic, structural, dielectric, pyroelectric, and polarization studies. DC magnetization along with dielectric constant measurements indicate a coupling between magnetic order and electrical polarization. A strong anomaly in the dielectric constant at ˜17.4 K in zero magnetic field indicates spontaneous electric polarization, consistent with a recent neutron diffraction study. Observation of weak short range ferromagnetic order at lower temperatures is attributed to the Griffiths-like ferromagnetism. Furthermore, magnetic field dependence of the ferroelectric transition follows earlier theoretical predictions, applicable to single crystal CTO. Finally, combined dielectric, pyroelectric, and polarization measurements suggest that the ground state of CTO may possess spontaneous symmetry breaking in the absence of magnetic field.

  15. Electric field induced short range to long range structural ordering and its influence on the Eu{sup +3} photoluminescence in the lead-free ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3}

    SciTech Connect

    Kalaskar, Abhijeet; Rao, Badari Narayana; Ranjan, Rajeev; Thomas, Tiju

    2015-06-28

    Eu{sup +3} was incorporated into the lattice of a lead-free ferroelectric Na{sub 1/2}Bi{sub 1/2}TiO{sub 3} (NBT) as per the nominal formula Na{sub 0.5}Bi{sub 0.5−x}Eu{sub x}TiO{sub 3}. This system was investigated with regard to the Eu{sup +3} photoluminescence (PL) and structural behaviour as a function of composition and electric field. Electric field was found to irreversibly change the features in the PL spectra and also in the x-ray diffraction patterns below the critical composition x = 0.025. Detailed analysis revealed that below the critical composition, electric field irreversibly suppresses the structural heterogeneity inherent of the host matrix NBT and brings about a long range ferroelectric state with rhombohedral (R3c) distortion. It is shown that the structural disorder on the nano-scale opens a new channel for radiative transition which manifests as a new emission line branching off from the main {sup 5}D{sub 0}→{sup 7}F{sub 0} line along with a concomitant change in the relative intensity of the other crystal field induced Stark lines with different J values. The study suggests that Eu{sup +3} luminescence can be used to probe the relative degree of field induced structural ordering in relaxor ferroelectrics and also in high performance piezoelectric alloys where electric field couples very strongly with the lattice and structural degrees of freedom.

  16. Core-excitation energy calculations with a long-range corrected hybrid exchange-correlation functional including a short-range Gaussian attenuation (LCgau-BOP).

    PubMed

    Song, Jong-Won; Watson, Mark A; Nakata, Ayako; Hirao, Kimihiko

    2008-11-14

    We report the calculations of core-excitation energies of first-row atoms using the time-dependent density functional theory (DFT) and the long-range correction (LC) scheme for exchange-correlation functionals, including LC-BOP, Coulomb-attenuated method BLYP, and our recently developed LCgau-BOP method, which includes a flexible portion of short-range Hartree-Fock (HF) exchange through the inclusion of a Gaussian function in the LC scheme. We show that the LC scheme completely fails to improve the poor accuracy of conventional generalized gradient approximation functionals, while the LCgau scheme gives an accuracy which is an order of magnitude better than BLYP and significantly better than B3LYP. A reoptimization of the two parameters controlling the inclusion of short-range HF exchange in the LCgau method enables the errors to be reduced to the order of 0.1 eV which is competitive with the best DFT methods we are aware of. This reparametrization does not affect the LC scheme and therefore maintains the high accuracy of predicted reaction barrier heights. Moreover, while there is some loss in accuracy in thermochemical predictions compared to the previously optimized LCgau-BOP, rms errors in the atomization energies over the G2 test set are found to be comparable to B3LYP. Finally, we attempt to rationalize the success of the LC and LCgau schemes in terms of the well-known self-interaction error (SIE) of conventional functionals. To estimate the role of the SIE, we examine the total energy calculations for systems with a fractional number of electrons, not only in the highest occupied molecular orbital but also in the 1s-characterized core orbital. Our conclusion is that the inclusion of short-range HF exchange in LC-type functionals can significantly alleviate the problems of the SIE in the core region. In particular, we confirm that the absence of the SIE diagnostics in the core orbital energies correlates with the accurate prediction of core

  17. STM and LEED studies of atomically ordered terraced Si(557) surfaces

    SciTech Connect

    Chaika, A. N. Bozhko, S. I.; Ionov, A. M.; Myagkov, A. N.; Abrosimov, N. V.

    2007-04-15

    We report results of LEED, STM, and photoemission studies of the atomic and electronic structure of atomically ordered terraced Si(hhm) surfaces. LEED and STM data demonstrate the possibility of fabricating atomically accurate terraced structures based on Si(557) with different periodicities depending on the thermal treatment procedure. Atomically resolved STM images reveal (7 x 7) terrace ordering and triple step structure. Comparative photoemission studies of the valence band and Si 2p core level electronic structure have been done on clean stepped surfaces with different terrace widths (namely, Si(557), Si(556)) and flat Si(111)-(7 x 7)

  18. Very-short range forecasting system for 2018 Pyeonchang Winter Olympic and Paralympic games

    NASA Astrophysics Data System (ADS)

    Nam, Ji-Eun; Park, Kyungjeen; Kim, Minyou; Kim, Changhwan; Joo, Sangwon

    2016-04-01

    The 23rd Olympic Winter and the 13th Paralympic Winter Games will be held in Pyeongchang, Republic of Korea respectively from 9 to 25 February 2018 and from 9 to 18 February 2018. The Korea Meteorological Administration (KMA) and the National Institute for Meteorological Science (NIMS) have the responsibility to provide weather information for the management of the Games and the safety of the public. NIMS will carry out a Forecast Demonstration Project (FDP) and a Research and Development Project (RDP) which will be called ICE-POP 2018. These projects will focus on intensive observation campaigns to understand severe winter weathers over the Pyeongchang region, and the research results from the RDP will be used to improve the accuracy of nowcasting and very short-range forecast systems during the Games. To support these projects, NIMS developed Very-short range Data Assimilation and Prediction System (VDAPS), which is run in real time with 1 hour cycling interval and up to 12 hour forecasts. The domain is covering Korean Peninsular and surrounding seas with 1.5km horizontal resolution. AWS, windprofiler, buoy, sonde, aircraft, scatwinds, and radar radial winds are assimilated by 3DVAR on 3km resolution inner domain. The rain rate is converted into latent heat and initialized via nudging. The visibility data are also assimilated with the addition of aerosol control variable. The experiments results show the improvement in rainfall over south sea of Korean peninsula. In order to reduce excessive rainfalls during first 2 hours due to the reduced cycling interval, the data assimilation algorithm is optimized.

  19. Short-range cytokine gradients to mimic paracrine cell interactions in vitro.

    PubMed

    Ansorge, Michael; Rastig, Nadine; Steinborn, Ralph; König, Tina; Baumann, Lars; Möller, Stephanie; Schnabelrauch, Matthias; Cross, Michael; Werner, Carsten; Beck-Sickinger, Annette G; Pompe, Tilo

    2016-02-28

    Cell fate decisions in many physiological processes, including embryogenesis, stem cell niche homeostasis and wound healing, are regulated by secretion of small signaling proteins, called cytokines, from source cells to their neighbors or into the environment. Concentration level and steepness of the resulting paracrine gradients elicit different cell responses, including proliferation, differentiation or chemotaxis. For an in-depth analysis of underlying mechanisms, in vitro models are required to mimic in vivo cytokine gradients. We set up a microparticle-based system to establish short-range cytokine gradients in a three-dimensional extracellular matrix context. To provide native binding sites for cytokines, agarose microparticles were functionalized with different glycosaminoglycans (GAG). After protein was loaded onto microparticles, its slow release was quantified by confocal microscopy and fluorescence correlation spectroscopy. Besides the model protein lysozyme, SDF-1 was used as a relevant chemokine for hematopoietic stem and progenitor cell (HSPC) chemotaxis. For both proteins we found gradients ranging up to 50μm from the microparticle surface and concentrations in the order of nM to pM in dependence on loading concentration and affinity modulation by the GAG functionalization. Directed chemotactic migration of cells from a hematopoietic cell line (FDCPmix) and primary murine HSPC (Sca-1(+) CD150(+) CD48(-)) toward the SDF-1-laden microparticles proved functional short-range gradients in a two-dimensional and three-dimensional setting over time periods of many hours. The approach has the potential to be applied to other cytokines mimicking paracrine cell-cell interactions in vitro.

  20. Multinucleon short-range correlation model for nuclear spectral functions: Theoretical framework

    NASA Astrophysics Data System (ADS)

    Artiles, Oswaldo; Sargsian, Misak M.

    2016-12-01

    We develop a theoretical approach for nuclear spectral functions at high missing momenta and removal energies based on the multinucleon short-range correlation (SRC) model. The approach is based on the effective Feynman diagrammatic method which allows us to account for the relativistic effects important in the SRC domain. In addition to two-nucleon (2N) SRC with center of mass motion we also derive the contribution of three-nucleon SRCs to the nuclear spectral functions. The latter is modeled based on the assumption that 3N SRCs are a product of two sequential short-range nucleon-nucleon (NN) interactions. This approach allows us to express the 3N SRC part of the nuclear spectral function as a convolution of two NN SRCs. Thus the knowledge of 2N SRCs allows us to model both two- and three-nucleon SRC contributions to the spectral function. The derivations of the spectral functions are based on two theoretical frameworks for evaluating covariant Feynman diagrams: In the first, referred to as virtual nucleon approximation, we reduce Feynman diagrams to the time ordered noncovariant diagrams by evaluating nucleon spectators in the SRC at their positive energy poles, neglecting explicitly the contribution from vacuum diagrams. In the second approach, referred to as light-front approximation, we formulate the boost invariant nuclear spectral function in the light-front reference frame in which case the vacuum diagrams are generally suppressed and the bound nucleon is described by its light-front variables such as momentum fraction, transverse momentum, and invariant mass.

  1. Spontaneous dimerization, critical lines, and short-range correlations in a frustrated spin-1 chain

    NASA Astrophysics Data System (ADS)

    Chepiga, Natalia; Affleck, Ian; Mila, Frédéric

    2016-11-01

    We report on a detailed investigation of the spin-1 J1-J2-J3 Heisenberg model, a frustrated model with nearest-neighbor coupling J1, next-nearest neighbor coupling J2, and a three-site interaction J3[(Si -1.Si) (Si.Si +1) +H .c . ] previously studied in [Phys. Rev. B 93, 241108(R) (2016), 10.1103/PhysRevB.93.241108]. Using density matrix renormalization group (DMRG) and exact diagonalizations, we show that the phase boundaries between the Haldane phase, the next-nearest neighbor Haldane phase, and the dimerized phase can be very accurately determined by combining the information deduced from the dimerization, the ground-state energy, the entanglement spectrum and the Berry phase. By a careful investigation of the finite-size spectrum, we also show that the transition between the next-nearest neighbor Haldane phase and the dimerized phase is in the Ising universality class all along the critical line. Furthermore, we justify the conformal embedding of the SU (2) 2 Wess-Zumino-Witten conformal field theory in terms of a boson and an Ising field, and we explicitly derive a number of consequences of this embedding for the spectrum along the SU (2) 2 transition line between the Haldane phase and the dimerized phase. We also show that the solitons along the first-order transition line between the Haldane phase and the dimerized phase carry a spin-1/2, while the domain walls between different dimerization domains inside the dimerized phase carry a spin 1. Finally, we show that short-range correlations change character in the Haldane and dimerized phases through disorder and Lifshitz lines, as well as through the development of short-range dimer correlations in the Haldane phase, leading to a remarkably rich phase diagram.

  2. General Model for Treating Short-Range Electrostatic Penetration in a Molecular Mechanics Force Field.

    PubMed

    Wang, Qiantao; Rackers, Joshua A; He, Chenfeng; Qi, Rui; Narth, Christophe; Lagardere, Louis; Gresh, Nohad; Ponder, Jay W; Piquemal, Jean-Philip; Ren, Pengyu

    2015-06-09

    Classical molecular mechanics force fields typically model interatomic electrostatic interactions with point charges or multipole expansions, which can fail for atoms in close contact due to the lack of a description of penetration effects between their electron clouds. These short-range penetration effects can be significant and are essential for accurate modeling of intermolecular interactions. In this work we report parametrization of an empirical charge-charge function previously reported (Piquemal J.-P.; J. Phys. Chem. A2003, 107, 10353) to correct for the missing penetration term in standard molecular mechanics force fields. For this purpose, we have developed a database (S101×7) of 101 unique molecular dimers, each at 7 different intermolecular distances. Electrostatic, induction/polarization, repulsion, and dispersion energies, as well as the total interaction energy for each complex in the database are calculated using the SAPT2+ method (Parker T. M.; J. Chem. Phys.2014, 140, 094106). This empirical penetration model significantly improves agreement between point multipole and quantum mechanical electrostatic energies across the set of dimers and distances, while using only a limited set of parameters for each chemical element. Given the simplicity and effectiveness of the model, we expect the electrostatic penetration correction will become a standard component of future molecular mechanics force fields.

  3. Pel promotes symmetric, short-ranged surface attachment in P. aeruginosa

    NASA Astrophysics Data System (ADS)

    Cooley, B. J.; Thatcher, Travis; Hashmi, Sara; L'Her, Guillaume; Touhami, Ahmed; Provenzano, Daniele; Gordon, Vernita

    2013-03-01

    Bacterial biofilms are surface mounted, multicellular communities of interacting bacteria that are often associated with chronic infections that resist antibiotics and damage host tissue. Bacteria in a biofilm are bound in a matrix of polymeric materials that adhere the bacteria to the surface, give the system spatial structure, and cluster the bacteria near each other. The opportunistic human pathogen Pseudomonas aeruginosa is widely studied as a model biofilm-forming organism. The polymeric matrix of P. aeruginosa strain PAO1 biofilms is dominated by two bacteria-produced extracellular polymers, Pel and Psl. We use both optical and atomic force microscopy to examine the roles of these polymers in very early biofilm development, in the hours after initial surface attachment. In agreement with other researchers, we find that Psl mediates strong attachment to a glass surface. Unexpectedly, we find that Pel promotes symmetric attachment, in the form of the rod-shaped bacteria lying flat on the surface, independently of permanent attachment to the surface. Further, the presence of Pel makes adhesion forces more short-ranged than they are with Psl alone. We suggest that these effects may result through synergistic interactions of Pel and Psl in the polymeric matrix.

  4. Long- and Short-Range Structure of Ferrimagnetic Iron-Chromium Maghemites.

    PubMed

    García-Guaderrama, Marco; Montero-Cabrera, María E; Morán, Emilio; Alario-Franco, Miguel A; Fuentes-Cobas, Luis E; Macías-Ríos, Edgar; Esparza-Ponce, Hilda E; Fuentes-Montero, María E

    2015-12-07

    Maghemite-like materials containing Fe(3+) and Cr(3+) in comparable amounts have been prepared by solution-combustion synthesis. The conditions of synthesis and the magnetic properties are described. These materials are ferrimagnetic and are much more stable than pure iron maghemite since their maghemite-hematite transformation takes place at about ∼ 700 °C instead of ∼ 300 °C, as usually reported. These materials were studied by synchrotron radiation X-ray diffraction (XRD) and by X-ray absorption fine structure (XAFS) of the K-absorption edge of two elements. High-resolution XRD patterns were processed by means of the Rietveld method. Thus, maghemites were studied by XAFS in both Fe and Cr K-edges to clarify the short-range structure of the investigated systems. Pre-edge decomposition and theoretical modeling of X-ray absorption near edge structure transitions were performed. The extended X-ray absorption fine structure (EXAFS) spectra were fitted considering the facts that the central atom of Fe is able to occupy octahedral and tetrahedral sites, each with a weight adjustment, while Cr occupies only octahedral sites. Interatomic distances were determined for x = 1, by fitting simultaneously both Fe and Cr K-edges average EXAFS spectra. The results showed that the cation vacancies tend to follow a regular pattern within the structure of the iron-chromium maghemite (FeCrO3).

  5. Second-order virial expansion for an atomic gas in a harmonic waveguide

    NASA Astrophysics Data System (ADS)

    Kristensen, Tom; Leyronas, Xavier; Pricoupenko, Ludovic

    2016-06-01

    The virial expansion for cold two-component Fermi and Bose atomic gases is considered in the presence of a waveguide and in the vicinity of a Feshbach resonance. The interaction between atoms and the coupling with the Feshbach molecules is modeled using a quantitative separable two-channel model. The scattering phase shift in an atomic waveguide is defined. This permits us to extend the Beth-Uhlenbeck formula for the second-order virial coefficient to this inhomogeneous case.

  6. Study of the effect of short ranged ordering on the magnetism in FeCr alloys

    NASA Astrophysics Data System (ADS)

    Jena, Ambika Prasad; Sanyal, Biplab; Mookerjee, Abhijit

    2014-01-01

    For the study of magnetism in systems where the local environment plays an important role, we propose a marriage between the Monte Carlo simulation and Zunger's special quasi-random structures. We apply this technique on disordered FeCr alloys and show that our estimates of the transition temperature is in good agreement with earlier experiments.

  7. Divacancies and the hydrogenation of Mg-Ti films with short range chemical order

    SciTech Connect

    Leegwater, H.; Schut, H.; Eijt, S. W. H.; Egger, W.; Baldi, A.; Dam, B.

    2010-03-22

    We obtained evidence for the partial chemical segregation of as-deposited and hydrogenated Mg{sub 1-y}Ti{sub y} films (0<=y<=0.30) into nanoscale Ti and Mg domains using positron Doppler-broadening. We exclusively monitor the hydrogenation of Mg domains, owing to the large difference in positron affinity for Mg and Ti. The electron momentum distribution broadens significantly upon transformation to the MgH{sub 2} phase over the whole compositional range. This reveals the similarity of the metal-insulator transition for rutile and fluorite MgH{sub 2}. Positron lifetime studies show the presence of divacancies in the as-deposited and hydrogenated Mg-Ti metal films. In conjunction with the relatively large local lattice relaxations we deduce to be present in fluorite MgH{sub 2}, these may be responsible for the fast hydrogen sorption kinetics in this MgH{sub 2} phase.

  8. Short-range order effect on resonance energy transfer in rigid solution

    NASA Astrophysics Data System (ADS)

    Bodunov, E. N.; Berberan-Santos, M. N.

    2004-05-01

    Resonance energy transfer by the Förster-Dexter mechanism in a rigid homogeneous medium is modeled using a hard-sphere fluid (HSF) radial distribution function. This distribution is more realistic than the commonly used uniform distribution with excluded volume (UDEV) function. For the dipole-dipole mechanism, both models yield essentially the same donor luminescence decay, except for small critical radii. For the exchange mechanism, however, the two models differ significantly. The HSF model displays a stronger "two-exponential" behavior. Also, to fit a given experimental decay, the UDEV model requires both a larger effective Bohr radius and a larger rate constant at collisional distance than the HSF model.

  9. Effect of Jahn-Teller distortion on the short range magnetic order in copper ferrite

    NASA Astrophysics Data System (ADS)

    Abdellatif, M. H.; Innocenti, Claudia; Liakos, Ioannis; Scarpellini, Alice; Marras, Sergio; Salerno, Marco

    2017-02-01

    Copper ferrite of spinel crystal structure was synthesized in the form of nano-particles using citrate-gel auto-combustion method. The sample morphology and composition were identified using scanning electron microscopy, X-ray diffraction, and X-ray spectroscopy. The latter technique reveals an inverse spinel structure with Jahn-Teller tetragonal distortion. The static magnetization was measured using vibrating sample magnetometer. Magnetic force microscopy was used in combination with the magnetization data to demonstrate the finite size effect of the magnetic spins and their casting behavior due to the introduction of copper ions in the tetrahedral magnetic sub-lattices, which results in tetragonal distorting the spinel structure of the copper ferrite. The magnetic properties of materials are a result of the collective behavior of the magnetic spins, and magnetic force microscopy can probe the collective behavior of the magnetic spins in copper ferrite, yet providing a sufficient resolution to map the effects below the micrometer size scale, such as the magnetic spin canting. A theoretical study was done to clarify the finite size effect of Jahn-Teller distortion on the magnetic properties of the material. When the particles are in the nano-scale, below the single domain size, their magnetic properties are very sensitive to their size change.

  10. Short-range order in amorphous SiO{sub x} by x ray photoelectron spectroscopy

    SciTech Connect

    Novikov, Yu. N.; Gritsenko, V. A.

    2011-07-01

    The Si 2p x ray photoelectron spectra of SiO{sub x} with a different composition of 0 {<=} x {<=} 2 have been studied experimentally and theoretically. The SiO{sub x} films were prepared by low-pressure chemical vapor deposition from SiH{sub 4} and N{sub 2}O source at 750 deg. C. Neither random bonding nor random mixture models can adequately describe the structure of these compounds. The interpretation of the experimental results is discussed according to a large scale potential fluctuation due to the spatial variation of chemical composition in SiO{sub x}.

  11. Calculation of the Short-Range Longitudinal Wakefields in the NLC Linac

    SciTech Connect

    Bane, Karl LF

    1998-11-30

    Using two frequency domain and one time domain numerical approaches, we calculate the short-range longitudinal wakefield of the NLC linac accelerating structure, and find that the results agree to approximately 5%. We show that our results are consistent with an analytical formula for the impedance at high frequencies. We, in addition, obtain through fitting a simple formula for the short-range wakefield of a linac structure that can be useful in designing linear colliders. Finally, we demonstrate that for the NLC linac cavity the effects on the short-range wake of end conditions, tapering, and rounding of the irises are small.

  12. Evidence for an unusual dynamical-arrest scenario in short-ranged colloidal systems

    NASA Astrophysics Data System (ADS)

    Foffi, G.; Dawson, K. A.; Buldyrev, S. V.; Sciortino, F.; Zaccarelli, E.; Tartaglia, P.

    2002-05-01

    Extensive molecular dynamics simulation studies of particles interacting via a short-ranged attractive square-well potential are reported. The calculated loci of constant diffusion coefficient D in the temperature-packing fraction plane show a reentrant behavior, i.e., an increase of diffusivity on cooling, confirming an important part of the high volume-fraction dynamical-arrest scenario earlier predicted by theory for particles with short-ranged potentials. The more efficient localization mechanism induced by the short-range bonding provides, on average, additional free volume as compared to the hard-sphere case and results in faster dynamics.

  13. Effect of competing short-range attraction and long-range repulsion on the dynamics of globular particle suspensions

    NASA Astrophysics Data System (ADS)

    Riest, Jonas; Naegele, Gerhard

    2015-03-01

    The dynamic clustering of globular particle suspensions exhibiting competing short-range attraction and long-range repulsion such as protein solutions has gained a lot of interest in the last years. We investigate the influence of clustering on the phase behavior, and in particular on the dynamics of globular particle systems. To this end, we explore various pair potential models by a combination of static and dynamic analytic calculation methods in conjunction with Molecular Dynamics and Monte Carlo simulations. Our results show that the cluster peak (intermediate-range-order peak) is present also in the hydrodynamic function characterizing the short-time dynamics. Moreover, an enhanced short-range attraction leads to a larger sedimentation velocity and a smaller self-diffusion coefficient. Our results are useful also for technical applications, such as in the ultrafiltration of proteins.

  14. Atomic Ordering in InGaN Alloys within Nanowire Heterostructures.

    PubMed

    Woo, Steffi Y; Bugnet, Matthieu; Nguyen, Hieu P T; Mi, Zetian; Botton, Gianluigi A

    2015-10-14

    Ternary III-nitride based nanowires (NWs) are promising for optoelectronic applications by offering advantageous design and control over composition, structure, and strain. Atomic-level chemical ordering in wurtzite InGaN alloys along the c-plane direction with a 1:1 periodicity within InGaN/GaN NW heterostructures was investigated by scanning transmission electron microscopy. Atomic-number-sensitive imaging contrast was used to simultaneously assign the In-rich and Ga-rich planes and determine the crystal polarity to differentiate unique sublattice sites. The nonrandom occupation of the c-planes in the InGaN alloys is confirmed by the occurrence of additional superlattice spots in the diffraction pattern within the ternary alloy. Compositional modulations in the ordered InGaN was further studied using atomic-resolution elemental mapping, outlining the substantial In-enrichment. Confirming the preferential site occupation of In-atoms provides experimental validation for the previous theoretical model of ordered InGaN alloys in bulk epilayers based on differences in surface site energy. Therefore, this study strongly suggests that atomic ordering in InGaN has a surface energetics-induced origin. Optimization of atomic ordering, in particular in III-nitride NW heterostructures, could be an alternative design tool toward desirable structural and compositional properties for various device applications operating at longer visible wavelengths.

  15. Short-range, overpressure-driven methane migration in coarse-grained gas hydrate reservoirs

    SciTech Connect

    Nole, Michael; Daigle, Hugh; Cook, Ann E.; Malinverno, Alberto

    2016-08-31

    Two methane migration mechanisms have been proposed for coarse-grained gas hydrate reservoirs: short-range diffusive gas migration and long-range advective fluid transport from depth. Herein we demonstrate that short-range fluid flow due to overpressure in marine sediments is a significant additional methane transport mechanism that allows hydrate to precipitate in large quantities in thick, coarse-grained hydrate reservoirs. Two-dimensional simulations demonstrate that this migration mechanism, short-range advective transport, can supply significant amounts of dissolved gas and is unencumbered by limitations of the other two end-member mechanisms. Here, short-range advective migration can increase the amount of methane delivered to sands as compared to the slow process of diffusion, yet it is not necessarily limited by effective porosity reduction as is typical of updip advection from a deep source.

  16. Short-range, overpressure-driven methane migration in coarse-grained gas hydrate reservoirs

    DOE PAGES

    Nole, Michael; Daigle, Hugh; Cook, Ann E.; ...

    2016-08-31

    Two methane migration mechanisms have been proposed for coarse-grained gas hydrate reservoirs: short-range diffusive gas migration and long-range advective fluid transport from depth. Herein we demonstrate that short-range fluid flow due to overpressure in marine sediments is a significant additional methane transport mechanism that allows hydrate to precipitate in large quantities in thick, coarse-grained hydrate reservoirs. Two-dimensional simulations demonstrate that this migration mechanism, short-range advective transport, can supply significant amounts of dissolved gas and is unencumbered by limitations of the other two end-member mechanisms. Here, short-range advective migration can increase the amount of methane delivered to sands as compared tomore » the slow process of diffusion, yet it is not necessarily limited by effective porosity reduction as is typical of updip advection from a deep source.« less

  17. Short-range, overpressure-driven methane migration in coarse-grained gas hydrate reservoirs

    SciTech Connect

    Nole, Michael; Daigle, Hugh; Cook, Ann E.; Malinverno, Alberto

    2016-08-31

    Two methane migration mechanisms have been proposed for coarse-grained gas hydrate reservoirs: short-range diffusive gas migration and long-range advective fluid transport from depth. Herein we demonstrate that short-range fluid flow due to overpressure in marine sediments is a significant additional methane transport mechanism that allows hydrate to precipitate in large quantities in thick, coarse-grained hydrate reservoirs. Two-dimensional simulations demonstrate that this migration mechanism, short-range advective transport, can supply significant amounts of dissolved gas and is unencumbered by limitations of the other two end-member mechanisms. Here, short-range advective migration can increase the amount of methane delivered to sands as compared to the slow process of diffusion, yet it is not necessarily limited by effective porosity reduction as is typical of updip advection from a deep source.

  18. Short-range, overpressure-driven methane migration in coarse-grained gas hydrate reservoirs

    NASA Astrophysics Data System (ADS)

    Nole, Michael; Daigle, Hugh; Cook, Ann E.; Malinverno, Alberto

    2016-09-01

    Two methane migration mechanisms have been proposed for coarse-grained gas hydrate reservoirs: short-range diffusive gas migration and long-range advective fluid transport from depth. Herein, we demonstrate that short-range fluid flow due to overpressure in marine sediments is a significant additional methane transport mechanism that allows hydrate to precipitate in large quantities in thick, coarse-grained hydrate reservoirs. Two-dimensional simulations demonstrate that this migration mechanism, short-range advective transport, can supply significant amounts of dissolved gas and is unencumbered by limitations of the other two end-member mechanisms. Short-range advective migration can increase the amount of methane delivered to sands as compared to the slow process of diffusion, yet it is not necessarily limited by effective porosity reduction as is typical of updip advection from a deep source.

  19. Screening methods for linear-scaling short-range hybrid calculations on CPU and GPU architectures.

    PubMed

    Beuerle, Matthias; Kussmann, Jörg; Ochsenfeld, Christian

    2017-04-14

    We present screening schemes that allow for efficient, linear-scaling short-range exchange calculations employing Gaussian basis sets for both CPU and GPU architectures. They are based on the LinK [C. Ochsenfeld et al., J. Chem. Phys. 109, 1663 (1998)] and PreLinK [J. Kussmann and C. Ochsenfeld, J. Chem. Phys. 138, 134114 (2013)] methods, but account for the decay introduced by the attenuated Coulomb operator in short-range hybrid density functionals. Furthermore, we discuss the implementation of short-range electron repulsion integrals on GPUs. The introduction of our screening methods allows for speedups of up to a factor 7.8 as compared to the underlying linear-scaling algorithm, while retaining full numerical control over the accuracy. With the increasing number of short-range hybrid functionals, our new schemes will allow for significant computational savings on CPU and GPU architectures.

  20. Screening methods for linear-scaling short-range hybrid calculations on CPU and GPU architectures

    NASA Astrophysics Data System (ADS)

    Beuerle, Matthias; Kussmann, Jörg; Ochsenfeld, Christian

    2017-04-01

    We present screening schemes that allow for efficient, linear-scaling short-range exchange calculations employing Gaussian basis sets for both CPU and GPU architectures. They are based on the LinK [C. Ochsenfeld et al., J. Chem. Phys. 109, 1663 (1998)] and PreLinK [J. Kussmann and C. Ochsenfeld, J. Chem. Phys. 138, 134114 (2013)] methods, but account for the decay introduced by the attenuated Coulomb operator in short-range hybrid density functionals. Furthermore, we discuss the implementation of short-range electron repulsion integrals on GPUs. The introduction of our screening methods allows for speedups of up to a factor 7.8 as compared to the underlying linear-scaling algorithm, while retaining full numerical control over the accuracy. With the increasing number of short-range hybrid functionals, our new schemes will allow for significant computational savings on CPU and GPU architectures.

  1. Approximants of icosahedral quasicrystals: Atomic structure, inherent defects, and superstructural ordering

    SciTech Connect

    Dmitrienko, V. E. Chizhikov, V. A.

    2006-07-15

    The structural features of approximants of icosahedral and decagonal quasicrystals and new unusual approximants (rhombohedral AlPd and cubic Al{sub 68}Pd{sub 20}Ru{sub 12}) are considered. It is shown that most approximants can be described in terms of universal local ordering of atoms, in which the nearest neighbors of each atom occupy the vertices of an almost ideal dodecahedron: the so-called dodecahedral local ordering. A set of general atomic motifs in the approximants of different orders is found for quasicrystals of different types. It is shown that the dodecahedral local ordering can be easily described by the project method, in which the basis vectors directed along icosahedral threefold axes are used. Different types of defects inherent in dodecahedral local ordering are analyzed.

  2. Toxicity to neuroblastoma cells and spheroids of benzylguanidine conjugated to radionuclides with short-range emissions.

    PubMed Central

    Cunningham, S. H.; Mairs, R. J.; Wheldon, T. E.; Welsh, P. C.; Vaidyanathan, G.; Zalutsky, M. R.

    1998-01-01

    Radiolabelled meta-iodobenzylguanidine (MIBG) is selectively taken up by tumours of neuroendocrine origin, where its cellular localization is believed to be cytoplasmic. The radiopharmaceutical [131I]MIBG is now widely used in the treatment of neuroblastoma, but other radioconjugates of benzylguanidine have been little studied. We have investigated the cytotoxic efficacy of beta, alpha and Auger electron-emitting radioconjugates in treating neuroblastoma cells grown in monolayer or spheroid culture. Using a no-carrier-added synthesis route, we produced 123I-, 125I-, 131I- and 211At-labelled benzylguanidines and compared their in vitro toxicity to the neuroblastoma cell line SK-N-BE(2c) grown in monolayer and spheroid culture. The Auger electron-emitting conjugates ([123I]MIBG and [125I]MIBG) and the alpha-emitting conjugate ([211At]MABG) were highly toxic to monolayers and small spheroids, whereas the beta-emitting conjugate [131I]MIBG was relatively ineffective. The Auger emitters were more effective than expected if the cellular localization of MIBG is cytoplasmic. As dosimetrically predicted however, [211At]MABG was found to be extremely potent in terms of both concentration of radioactivity and number of atoms ml(-1) administered. In contrast, the Auger electron emitters were ineffective in the treatment of larger spheroids, while the beta emitter showed greater efficacy. These findings suggest that short-range emitters would be well suited to the treatment of circulating tumour cells or small clumps, whereas beta emitters would be superior in the treatment of subclinical metastases or macroscopic tumours. These experimental results provide support for a clinical strategy of combinations ('cocktails') of radioconjugates in targeted radiotherapy. PMID:9649115

  3. a Field-Theoretical Investigation of 2-D Coulomb Systems with Short-Range Yukawa Repulsion.

    NASA Astrophysics Data System (ADS)

    Jargocki, Krzysztof Piotr

    The two-dimensional Coulomb gas, consisting of positive and negative charges, is an important system which, on one hand, is equivalent to the vortex sector of the planar X-Y model, and, on the other, to the sine-Gordon field theory. In most treatments the charged particles are assumed to have a repulsive hard core which prevents arbitrarily close approaches. In the present work a new regularization scheme based on a soft short-range Yukawa repulsion between the Coulomb gas particles is presented. This formulation is transcribed into a local sine-Gordon-like field theory involving two Bose fields, one the original massless sine -Gordon field corresponding to the long-range Coulomb interaction and an auxiliary massive field corresponding to the short -range Yukawa repulsion. The resulting Lagrangian is not Hermitian. Using the techniques of functional integration, an effective field theory involving the Coulomb field alone is obtained by integrating out the massive field. The resulting Lagrangian is now Hermitian. Then a generalization of Peierls' inequality is used to make a variational calculation of the ground state energy of the Coulomb system. Unlike in the pure sine-Gordon case the theory has a well-defined ground state energy for (beta)q('2) > 2 (or (beta)c('2) > 8(pi)). A new method is used to derive the Kosterlitz -Thouless renormalization group equations, starting with the original sine-Gordon-like theory. The equations are identical to those found previously by other authors. A wave function renormalization is found to be necessary in addition to the normal ordering discussed by Coleman. A fermionized version of the theory is obtained, using the dictionary provided by Kogut and Susskind, which involves two Fermi fields and an electromagnetic potential. Position -space correlation functions are calculated at the critical point. The effective potential is computed in the one -loop approximation. A nonlinear field theory with derivative couplings is found to

  4. Deciphering chemical order/disorder and material properties at the single-atom level

    DOE PAGES

    Yang, Yongsoo; Chen, Chien-Chun; Scott, M. C.; ...

    2017-02-01

    The properties and functionalities of materials are strongly influenced by the three-dimensional (3D) arrangements of atoms and defects. Correlating 3D atomic structure and chemical order/disorder with material properties is essential to understand microscopic mechanisms and engineer new materials. Here, we use iron-platinum nanoparticles as a model system to reveal chemical order/disorder and magnetic properties at the single-atom level. We also determined the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle with 22pm precision. We identified rich structural variety and chemical order/disorder including 3D grains with different compositions, orientations, anti-phase boundaries, anti-site point defects and swapmore » defects. We show for the first time that measured 3D atomic coordinates and chemical species with defects can be used as direct input for density functional theory calculations of material properties such as local magnetocrystalline anisotropy. This work not only opens the door to determining the 3D chemical order/disorder of a wide range of nanostructured materials with atomic resolution, but also promises to understand structure-property relationships at the most fundamental scale.« less

  5. Array rotation aperture synthesis for short-range imaging at millimeter wavelengths

    NASA Astrophysics Data System (ADS)

    Lucotte, B. M.; Grafulla-GonzáLez, B.; Harvey, A. R.

    2009-02-01

    Millimeter-wave interferometric synthetic aperture imagers are currently being developed for short-range applications such as concealed weapons detection. In contrast to the traditional snapshot imaging approach, we investigate the potential of mechanical scanning between the scene and the array in order to reduce the number of antennas and correlators. We assess the trade-off between this hardware reduction, the radiometric sensitivity and the imaging frame rate of the system. We show that rotational scanning achieves a more uniform coverage of the (u, v) plane than the more conventional linear scanning. We use a genetic algorithm to optimize two-dimensional arrays for maximum uniform (u, v) coverage after a rotational mechanical scan and demonstrates improvements in the array point spread function. Imaging performance is assessed with simulated millimeter-wave scenes. Results show an increased image quality is achieved with the optimized array compared with a conventional power law Y-shaped array. Finally we discuss the increased demands on system stability and calibration that the increased acquisition time of the proposed technique places.

  6. Acoustic communication in two freshwater gobies: ambient noise and short-range propagation in shallow streams.

    PubMed

    Lugli, M; Fine, M L

    2003-07-01

    Noise is an important theoretical constraint on the evolution of signal form and sensory performance. In order to determine environmental constraints on the communication of two freshwater gobies Padogobius martensii and Gobius nigricans, numerous noise spectra were measured from quiet areas and ones adjacent to waterfalls and rapids in two shallow stony streams. Propagation of goby sounds and waterfall noise was also measured. A quiet window around 100 Hz is present in many noise spectra from noisy locations. The window lies between two noise sources, a low-frequency one attributed to turbulence, and a high-frequency one (200-500 Hz) attributed to bubble noise from water breaking the surface. Ambient noise from a waterfall (frequencies below 1 kHz) attenuates as much as 30 dB between 1 and 2 m, after which values are variable without further attenuation (i.e., buried in the noise floor). Similarly, courtship sounds of P. martensii attenuate as much as 30 dB between 5 and 50 cm. Since gobies are known to court in noisy as well as quiet locations in these streams, their acoustic communication system (sounds and auditory system) must be able to cope with short-range propagation dictated by shallow depths and ambient noise in noisy locations.

  7. Observations of clustering inside oceanic bubble clouds and the effect on short-range acoustic propagation.

    PubMed

    Weber, Thomas C

    2008-11-01

    It has recently been shown [Weber, T. C. et al. (2007). "Acoustic propagation through clustered bubble clouds," IEEE J. Ocean. Eng. 32, 513-523] that gas bubble clustering plays a role in determining the acoustic field characteristics of bubbly fluids. In particular, it has been shown that clustering changes the bubble-induced attenuation as well as the ping-to-ping variability in the acoustic field. The degree to which bubble clustering exists in nature, however, is unknown. This paper describes a method for quantifying bubble clustering using a high frequency (400 kHz) multibeam sonar, and reports on observations of near-surface bubble clustering during a storm (14.6 m/s wind speed) in the Gulf of Maine. The multibeam sonar data are analyzed to estimate the pair correlation function, a measure of bubble clustering. In order to account for clustering in the mean acoustic field, a modification to the effective medium wave number is made. With this modification, the multibeam sonar observations are used to predict the effect of clustering on the attenuation of the mean field for short-range propagation (1 m) at frequencies between 10 and 350 kHz. Results for this specific case show that clustering can cause the attenuation to change by 20%-80% over this frequency range.

  8. Influence of short-range correlations in neutrino-nucleus scattering

    NASA Astrophysics Data System (ADS)

    Van Cuyck, T.; Jachowicz, N.; González-Jiménez, R.; Martini, M.; Pandey, V.; Ryckebusch, J.; Van Dessel, N.

    2016-08-01

    Background: Nuclear short-range correlations (SRCs) are corrections to mean-field wave functions connected with the short-distance behavior of the nucleon-nucleon interaction. These SRCs provide corrections to lepton-nucleus cross sections as computed in the impulse approximation (IA). Purpose: We want to investigate the influence of SRCs on the one-nucleon (1 N ) and two-nucleon (2 N ) knockout channels for muon-neutrino induced processes on a 12 target at energies relevant for contemporary measurements. Method: The model adopted in this work corrects the impulse approximation for SRCs by shifting the complexity induced by the SRCs from the wave functions to the operators. Due to the local character of the SRCs, it is argued that the expansion of these operators can be truncated at a low order. Results: The model is compared with electron-scattering data, and two-particle two-hole responses are presented for neutrino scattering. The contributions from the vector and axial-vector parts of the nuclear current as well as the central, tensor, and spin-isospin parts of the SRCs are studied. Conclusions: Nuclear SRCs affect the 1 N knockout channel and give rise to 2 N knockout. The exclusive neutrino-induced 2 N knockout cross section of SRC pairs is shown and the 2 N knockout contribution to the QE signal is calculated. The strength occurs as a broad background which extends into the dip region.

  9. Effective short-range Coulomb correction to model the aggregation behavior of ionic surfactants.

    PubMed

    Burgos-Mármol, J Javier; Solans, Conxita; Patti, Alessandro

    2016-06-21

    We present a short-range correction to the Coulomb potential to investigate the aggregation of amphiphilic molecules in aqueous solutions. The proposed modification allows to quantitatively reproduce the distribution of counterions above the critical micelle concentration (CMC) or, equivalently, the degree of ionization, α, of the micellar clusters. In particular, our theoretical framework has been applied to unveil the behavior of the cationic surfactant C24H49N2O2 (+) CH3SO4 (-), which offers a wide range of applications in the thriving and growing personal care market. A reliable and unambiguous estimation of α is essential to correctly understand many crucial features of the micellar solutions, such as their viscoelastic behavior and transport properties, in order to provide sound formulations for the above mentioned personal care solutions. We have validated our theory by performing extensive lattice Monte Carlo simulations, which show an excellent agreement with experimental observations. More specifically, our coarse-grained model is able to reproduce and predict the complex morphology of the micelles observed at equilibrium. Additionally, our simulation results disclose the existence of a transition from a monodisperse to a bidisperse size distribution of aggregates, unveiling the intriguing existence of a second CMC.

  10. Folding mechanism of a polymer chain with short-range attractions

    NASA Astrophysics Data System (ADS)

    Leitold, Christian; Dellago, Christoph

    2014-10-01

    We investigate the crystallization of a single, flexible homopolymer chain using transition path sampling. The chain consists of N identical spherical monomers evolved according to Langevin dynamics. While neighboring monomers are coupled via harmonic springs, the non-neighboring monomers interact via a hard core and a short-ranged attractive potential. For a sufficiently small interaction range λ, the system undergoes a first-order freezing transition from an expanded, disordered phase to a compact crystalline state. Using a new shooting move tailored to polymers combined with a committor analysis, we study the transition state ensemble of an N = 128 chain and search for possible reaction coordinates based on likelihood maximization. We find that typical transition states consist of a crystalline nucleus with one or more chain fragments attached to it. Furthermore, we show that the number of particles in the crystalline core is not well suited as a reaction coordinate. We then present an improved reaction coordinate, which includes information from the potential energy and the overall crystallinity of the polymer.

  11. Effective short-range Coulomb correction to model the aggregation behavior of ionic surfactants

    NASA Astrophysics Data System (ADS)

    Burgos-Mármol, J. Javier; Solans, Conxita; Patti, Alessandro

    2016-06-01

    We present a short-range correction to the Coulomb potential to investigate the aggregation of amphiphilic molecules in aqueous solutions. The proposed modification allows to quantitatively reproduce the distribution of counterions above the critical micelle concentration (CMC) or, equivalently, the degree of ionization, α, of the micellar clusters. In particular, our theoretical framework has been applied to unveil the behavior of the cationic surfactant C24H49N2O2+ CH3SO4-, which offers a wide range of applications in the thriving and growing personal care market. A reliable and unambiguous estimation of α is essential to correctly understand many crucial features of the micellar solutions, such as their viscoelastic behavior and transport properties, in order to provide sound formulations for the above mentioned personal care solutions. We have validated our theory by performing extensive lattice Monte Carlo simulations, which show an excellent agreement with experimental observations. More specifically, our coarse-grained model is able to reproduce and predict the complex morphology of the micelles observed at equilibrium. Additionally, our simulation results disclose the existence of a transition from a monodisperse to a bidisperse size distribution of aggregates, unveiling the intriguing existence of a second CMC.

  12. Multi-Nucleon Short-Range Correlation Model for Nuclear Spectral Functions.

    NASA Astrophysics Data System (ADS)

    Artiles, Oswaldo; Sargsian, Misak

    2017-01-01

    We develop a theoretical model for nuclear spectral functions at high missing momenta and energies based on the multi-nucleon short-range correlation (SRC) model aimed at probing nuclear structure at short-distances. The model is based on the effective Feynman diagram method which allows us to account for the relativistic effects in the SRC domain. We derive the contribution of two-nucleon SRC with center of mass motion, and three-nucleon SRCs to the nuclear spectral functions. The spectral functions are based on two theoretical approaches in evaluating covariant Feynman diagrams: In the first, referred to as virtual nucleon approximation, we reduce Feynman diagrams to the time ordered non-covariant diagrams by evaluating nucleon spectators on the SRC at their positive energy poles, neglecting the contribution from vacuum diagrams. In the second approach, referred to as light-front approximation, we formulate the boost invariant nuclear spectral function on the light-front reference frame, on which the vacuum diagrams are suppressed. Numerical calculations and parametrization of spectral functions and momentum distributions are presented. This work is supported by U.S. Department of Energy grant under contract DE- FG02-01ER41172.

  13. The influence of non-locality on fluctuation effects for 3D short-ranged wetting

    NASA Astrophysics Data System (ADS)

    Parry, A. O.; Romero-Enrique, J. M.; Bernardino, N. R.; Rascón, C.

    2008-12-01

    We use a non-local interfacial Hamiltonian to revisit a number of problems associated with the fluctuation theory of critical wetting transitions in three-dimensional systems with short-ranged forces. These centre around previous renormalization group predictions of strongly non-universal critical singularities and also possible fluctuation-induced first-order (stiffness-instability) behaviour, based on local interfacial models, which are not supported by extensive Monte Carlo simulations of wetting in the three-dimensional Ising model. Non-locality gives rise to long-ranged two-body interfacial interactions controlling the repulsion from the wall not modelled correctly in previous interfacial descriptions. In particular, correlation functions are characterized by two diverging parallel correlation lengths, \\xi_{\\parallel } and \\xi_{\\mathrm { NL}}\\propto \\sqrt {\\ln \\xi_\\parallel } , not one as previously thought. Mean-field, Ginzburg criterion and linear renormalization group analyses all show that some interfacial fluctuation effects are strongly damped for wavenumbers q>1/ξNL. This prevents a stiffness-instability and reduces the size of the asymptotic critical regime where non-universality can be observed. Non-universal critical singularities along the critical wetting isotherm are determined by a smaller, effective value of the wetting parameter which slowly approaches its asymptotic limit as the wetting film grows. This is confirmed by numerical simulation of a discretized version of the non-local model.

  14. Interaction of laser-cooled 87Rb atoms with higher order modes of an optical nanofibre

    NASA Astrophysics Data System (ADS)

    Kumar, Ravi; Gokhroo, Vandna; Deasy, Kieran; Maimaiti, Aili; Frawley, Mary C.; Phelan, Ciarán; Chormaic, Síle Nic

    2015-01-01

    Optical nanofibres are used to confine light to sub-wavelength regions and are very promising tools for the development of optical fibre-based quantum networks using cold, neutral atoms. To date, experimental studies on atoms near nanofibres have focussed on fundamental fibre mode interactions. In this work, we demonstrate the integration of a few-mode optical nanofibre into a magneto-optical trap for 87Rb atoms. The nanofibre, with a waist diameter of ∼700 nm, supports both the fundamental and first group of higher order modes (HOMs) and is used for atomic fluorescence and absorption studies. In general, light propagating in higher order fibre modes has a greater evanescent field extension around the waist in comparison with the fundamental mode. By exploiting this behaviour, we demonstrate that the detected signal of fluorescent photons emitted from a cloud of cold atoms centred at the nanofibre waist is larger if HOMs are also included. In particular, the signal from HOMs appears to be about six times larger than that obtained for the fundamental mode. Absorption of on-resonance, HOM probe light by the laser-cooled atoms is also observed. These advances should facilitate the realization of atom trapping schemes based on HOM interference.

  15. Temperature-modulated annealing of c-plane sapphire for long-range-ordered atomic steps

    NASA Astrophysics Data System (ADS)

    Yatsui, Takashi; Kuribara, Kazunori; Sekitani, Tsuyoshi; Someya, Takao; Yoshimoto, Mamoru

    2016-03-01

    High-quality single-crystalline sapphire is used to prepare various semiconductors because of its thermal stability. Here, we applied the tempering technique, which is well known in the production of chocolate, to prepare a sapphire substrate. Surprisingly, we successfully realised millimetre-range ordering of the atomic step of the sapphire substrate. We also obtained a sapphire atomic step with nanometre-scale uniformity in the terrace width and atomic-step height. Such sapphire substrates will find applications in the preparation of various semiconductors and devices.

  16. Scanning Transmission Electron Microscopy Using Selective High-Order Laue Zones: Three-Dimensional Atomic Ordering in Sodium Cobaltate

    NASA Astrophysics Data System (ADS)

    Huang, F.-T.; Gloter, A.; Chu, M.-W.; Chou, F. C.; Shu, G. J.; Liu, L.-K.; Chen, C. H.; Colliex, C.

    2010-09-01

    A new scanning transmission electron microscopy (STEM) imaging technique using high-order Laue zones (named HOLZ-STEM), a diffraction contrast which has been strenuously avoided or minimized in traditional STEM imaging, can be used to obtain the additional 1D periodic information along the electron propagation axis without sacrificing atomic resolution in the lateral (2D) dimension. HOLZ-STEM has been demonstrated to resolve the 3D long-range Na ordering of Na0.71CoO2. Direct evidence of spiral-like Na-trimer chains twisting along the c axis is unambiguously established in real space.

  17. Long- and Short-Range Constraints for the Structure Determination of Layered Silicates with Stacking Disorder

    SciTech Connect

    Cadars, Sylvian; Allix, mathieu; Brouwer, Darren H.; Shayib, Ramzy; Suchomel, Matthew; Garaga, Mounesha N.; Rakhmatullin, Aydar; Burton, Allen W.; Zones, Stacy I.; Massiot, Dominique; Chmelka, Bradley F.

    2014-12-23

    Layered silicates have important applications as host materials, supports for catalysis, and zeolite precursors. However, their local structures are often challenging to establish due to disorder of the sheet assemblies. We present a new protocol that combines long- and short-range structural constraints from diffraction and solid-state NMR techniques, respectively, to determine the molecular structure of layered silicates in the presence of various extents of stacking disorder. Solid-state 29Si NMR data are largely insensitive to the incomplete extent of three-dimensional (3D) crystallinity that limits the interpretation of diffraction data alone to the identification of possible unit cells and space groups. State-of-the-art NMR crystallography techniques consequently provide a simplified view of materials from which candidate framework structures can be built and evaluated based on local structural constraints, including interatomic distances, Si site numbers and multiplicities, and Si–O–Si connectivities, and refined using density functional theory. This protocol was applied to a new layered silicate material named CLS-1, of composition [Si5O11H][C9N2H15]·1.9(H2O), synthesized by using a fluoride-based protocol and cationic alkylaminopyridinium as a structure-directing agent (SDA). Despite the intrinsic complexity and partial ordering of the intersheet arrangements and organic–inorganic interactions, this led to the identification of a single space group that is compatible with both NMR and diffraction data, from which the silicate framework structure could be established,. The remarkable similarities between the layered framework structures of CLS-1, HUS-2 (Tsunoji et al. J. Mater. Chem.2012, 22, 13682), and another layered silicate material with a radically different morphology and extent of stacking order and interlayer dynamics, established by using a similar approach (Brouwer et al. J. Am. Chem. Soc.2013, 135, 5641), point to the remarkable

  18. Deciphering chemical order/disorder and material properties at the single-atom level

    NASA Astrophysics Data System (ADS)

    Yang, Yongsoo; Chen, Chien-Chun; Scott, M. C.; Ophus, Colin; Xu, Rui; Pryor, Alan; Wu, Li; Sun, Fan; Theis, Wolfgang; Zhou, Jihan; Eisenbach, Markus; Kent, Paul R. C.; Sabirianov, Renat F.; Zeng, Hao; Ercius, Peter; Miao, Jianwei

    2017-02-01

    Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling ‘real’ materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily on average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. This work combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure-property relationships at the fundamental level.

  19. Atomic Ordering Enhanced Electrocatalytic Activity of Nanoalloys for Oxygen Reduction Reaction

    SciTech Connect

    Loukrakpam, Rameshwori; Shan, Shiyao; Petkov, Valeri; Yang, Lefu; Luo, Jin; Zhong, Chuan-Jian

    2013-10-01

    For oxygen reduction reaction (ORR) over alloy electrocatalysts, the understanding of how the atomic arrangement of the metal species in the nanocatalysts is responsible for the catalytic enhancement is challenging for achieving better design and tailoring of nanoalloy catalysts. This paper reports results of an investigation of the atomic structures and the electrocatalytic activities of ternary and binary nanoalloys, aiming at revealing a fundamental insight into the unique atomic-scale structure-electrocatalytic activity relationship. PtIrCo catalyst and its binary counterparts (PtCo and PtIr) are chosen as a model system for this study. The effect of thermochemical treatment temperature on the atomic-scale structure of the catalysts was examined as a useful probe to the structure-activity correlation. The structural characterization of the binary and ternary nanoalloy catalysts was performed by combining surface sensitive techniques such as XPS and 3D atomic ordering sensitive techniques such as high-energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis (HE-XRD/PDFs) and computer simulations. The results show that the thermal treatment temperature tunes the nanoalloy’s atomic and chemical ordering in a different way depending on the chemical composition, leading to differences in the nanoalloy’s mass and specific activities. A unique structural tunability of the atomic ordering in a platinum-iridium-cobalt nanoalloy has been revealed for enhancing greatly the electrocatalytic activity toward oxygen reduction reaction, which has significant implication for rational design and nanoengineering of advanced catalysts for electrochemical energy conversion and storage.

  20. Deciphering chemical order/disorder and material properties at the single-atom level.

    PubMed

    Yang, Yongsoo; Chen, Chien-Chun; Scott, M C; Ophus, Colin; Xu, Rui; Pryor, Alan; Wu, Li; Sun, Fan; Theis, Wolfgang; Zhou, Jihan; Eisenbach, Markus; Kent, Paul R C; Sabirianov, Renat F; Zeng, Hao; Ercius, Peter; Miao, Jianwei

    2017-02-01

    Perfect crystals are rare in nature. Real materials often contain crystal defects and chemical order/disorder such as grain boundaries, dislocations, interfaces, surface reconstructions and point defects. Such disruption in periodicity strongly affects material properties and functionality. Despite rapid development of quantitative material characterization methods, correlating three-dimensional (3D) atomic arrangements of chemical order/disorder and crystal defects with material properties remains a challenge. On a parallel front, quantum mechanics calculations such as density functional theory (DFT) have progressed from the modelling of ideal bulk systems to modelling 'real' materials with dopants, dislocations, grain boundaries and interfaces; but these calculations rely heavily on average atomic models extracted from crystallography. To improve the predictive power of first-principles calculations, there is a pressing need to use atomic coordinates of real systems beyond average crystallographic measurements. Here we determine the 3D coordinates of 6,569 iron and 16,627 platinum atoms in an iron-platinum nanoparticle, and correlate chemical order/disorder and crystal defects with material properties at the single-atom level. We identify rich structural variety with unprecedented 3D detail including atomic composition, grain boundaries, anti-phase boundaries, anti-site point defects and swap defects. We show that the experimentally measured coordinates and chemical species with 22 picometre precision can be used as direct input for DFT calculations of material properties such as atomic spin and orbital magnetic moments and local magnetocrystalline anisotropy. This work combines 3D atomic structure determination of crystal defects with DFT calculations, which is expected to advance our understanding of structure-property relationships at the fundamental level.

  1. Simulating superradiance from higher-order-intensity-correlation measurements: Single atoms

    NASA Astrophysics Data System (ADS)

    Wiegner, R.; Oppel, S.; Bhatti, D.; von Zanthier, J.; Agarwal, G. S.

    2015-09-01

    Superradiance typically requires preparation of atoms in highly entangled multiparticle states, the so-called Dicke states. In this paper we discuss an alternative route where we prepare such states from initially uncorrelated atoms by a measurement process. By measuring higher-order intensity-intensity correlations we demonstrate that we can simulate the emission characteristics of Dicke superradiance by starting with atoms in the fully excited state. We describe the essence of the scheme by first investigating two excited atoms. Here we demonstrate how via Hanbury Brown and Twiss type of measurements we can produce Dicke superradiance and subradiance displayed commonly with two atoms in the single excited symmetric and antisymmetric Dicke states, respectively. We thereafter generalize the scheme to arbitrary numbers of atoms and detectors, and explain in detail the mechanism which leads to this result. The approach shows that the Hanbury Brown and Twiss type of intensity interference and the phenomenon of Dicke superradiance can be regarded as two sides of the same coin. We also present a compact result for the characteristic functional which generates all order intensity-intensity correlations.

  2. Static atomic displacements in Ni-rich Ni-Al

    NASA Astrophysics Data System (ADS)

    Schönfeld, B.; Kostorz, G.; Celino, M.; Rosato, V.

    2001-05-01

    Short-range order and static atomic displacement parameters, previously determined from diffuse neutron scattering for Ni-8.9 at.% Al equilibrated at 775 K and quenched to room temperature, were used to study lattice relaxation effects in molecular-dynamics simulations. An occupation of average lattice sites with Ni and Al atoms compatible with the short-range ordered state was taken as the starting situation. Displacement parameters obtained from the relaxation simulations and from diffuse neutron scattering show general similarity in magnitude and dependence on distance. Also, the species dependence of the displacement parameters known from diffuse X-ray scattering investigations is reproduced in magnitude.

  3. Constraints on lepton number violating short-range interactions from |ΔL| = 2 processes

    NASA Astrophysics Data System (ADS)

    Quintero, Néstor

    2017-01-01

    In this work we study the short-range contributions that induce effective lepton number violating (LNV) interactions. We obtain a full set of constraints on the effective short-range couplings from a large variety of low-energy | ΔL | = 2 processes of pseudoscalar mesons K , D ,Ds , B, and τ-lepton. These constraints provide complementary and additional information to the one obtained from the neutrinoless double-β (0 νββ) decay. As expected, the bounds on electron-electron short-range couplings are the only ones that are strongly constrained by the 0 νββ decay. Although weaker, LNV effective couplings with different flavors are not accessible to 0 νββ decay and these can be probe by the | ΔL | = 2 processes in consideration.

  4. Short-range/Long-range Integrated Target (SLIT) for Video Guidance Sensor Rendezvous and Docking

    NASA Technical Reports Server (NTRS)

    Roe, Fred D. (Inventor); Bryan, Thomas C. (Inventor)

    2009-01-01

    A laser target reflector assembly for mounting upon spacecraft having a long-range reflector array formed from a plurality of unfiltered light reflectors embedded in an array pattern upon a hemispherical reflector disposed upon a mounting plate. The reflector assembly also includes a short-range reflector array positioned upon the mounting body proximate to the long-range reflector array. The short-range reflector array includes three filtered light reflectors positioned upon extensions from the mounting body. The three filtered light reflectors retro-reflect substantially all incident light rays that are transmissive by their monochromatic filters and received by the three filtered light reflectors. In one embodiment the short-range reflector array is embedded within the hemispherical reflector,

  5. Atomic-Resolution Kinked Structure of an Alkylporphyrin on Highly Ordered Pyrolytic Graphite.

    PubMed

    Chin, Yiing; Panduwinata, Dwi; Sintic, Maxine; Sum, Tze Jing; Hush, Noel S; Crossley, Maxwell J; Reimers, Jeffrey R

    2011-01-20

    The atomic structure of the chains of an alkyl porphyrin (5,10,15,20-tetranonadecylporphyrin) self-assembled monolayer (SAM) at the solid/liquid interface of highly ordered pyrolytic graphite (HOPG) and 1-phenyloctane is resolved using calibrated scanning tunneling microscopy (STM), density functional theory (DFT) image simulations, and ONIOM-based geometry optimizations. While atomic structures are often readily determined for porphyrin SAMs, the determination of the structure of alkyl-chain connections has not previously been possible. A graphical calibration procedure is introduced, allowing accurate observation of SAM lattice parameters, and, of the many possible atomic structures modeled, only the lowest-energy structure obtained was found to predict the observed lattice parameters and image topography. Hydrogen atoms are shown to provide the conduit for the tunneling current through the alkyl chains.

  6. Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions

    SciTech Connect

    Murphy, Ryan P.; Hong, Kunlun; Wagner, Norman J.

    2016-07-28

    Dynamic arrest transitions of colloidal suspensions containing non-spherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346–2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultra-small angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. We find the adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.

  7. Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions

    DOE PAGES

    Murphy, Ryan P.; Hong, Kunlun; Wagner, Norman J.

    2016-07-28

    Dynamic arrest transitions of colloidal suspensions containing non-spherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346–2349) and temperature-dependent attractions were introduced by coating themore » calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultra-small angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. We find the adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.« less

  8. Thermoreversible Gels Composed of Colloidal Silica Rods with Short-Range Attractions

    SciTech Connect

    Murphy, Ryan P.; Hong, Kunlun; Wagner, Norman J.

    2016-07-28

    Dynamic arrest transitions of colloidal suspensions containing non-spherical particles are of interest for the design and processing of various particle technologies. To better understand the effects of particle shape anisotropy and attraction strength on gel and glass formation, we present a colloidal model system of octadecyl-coated silica rods, termed as adhesive hard rods (AHR), which enables control of rod aspect ratio and temperature-dependent interactions. The aspect ratios of silica rods were controlled by varying the initial TEOS concentration following the work of Kuijk et al. (J. Am. Chem. Soc., 2011, 133, 2346–2349) and temperature-dependent attractions were introduced by coating the calcined silica rods with an octadecyl-brush and suspending in tetradecane. The rod length and aspect ratio were found to increase with TEOS concentration as expected, while other properties such as the rod diameter, coating coverage, density, and surface roughness were nearly independent of the aspect ratio. Ultra-small angle X-ray scattering measurements revealed temperature-dependent attractions between octadecyl-coated silica rods in tetradecane, as characterized by a low-q upturn in the scattered intensity upon thermal quenching. Lastly, the rheology of a concentrated AHR suspension in tetradecane demonstrated thermoreversible gelation behavior, displaying a nearly 5 orders of magnitude change in the dynamic moduli as the temperature was cycled between 15 and 40 °C. We find the adhesive hard rod model system serves as a tunable platform to explore the combined influence of particle shape anisotropy and attraction strength on the dynamic arrest transitions in colloidal suspensions with thermoreversible, short-range attractions.

  9. Study of local atomic order in amorphous materials in a computerized transmission electron microscope.

    PubMed

    Balossier, G; Garg, R K; Bonhomme, P; Thomas, X

    1989-03-01

    Experimental results obtained by electron diffraction (ED) and extended electron energy loss fine structure (EXELFS) techniques to study the local atomic order in amorphous materials such as carbon, silicon, and its oxides are described. Potential applications of ED and EXELFS techniques and their limitations are also discussed.

  10. Electrochemical Activation of CO2 through Atomic Ordering Transformations of AuCu Nanoparticles.

    PubMed

    Kim, Dohyung; Xie, Chenlu; Becknell, Nigel; Yu, Yi; Karamad, Mohammadreza; Chan, Karen; Crumlin, Ethan J; Nørskov, Jens K; Yang, Peidong

    2017-06-21

    Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO2 to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced catalytic behavior, which is further supported by DFT analysis.

  11. Resolving all-order method convergence problems for atomic physics applications

    SciTech Connect

    Gharibnejad, H.; Derevianko, A.; Eliav, E.; Safronova, M. S.

    2011-05-15

    The development of the relativistic all-order method where all single, double, and partial triple excitations of the Dirac-Hartree-Fock wave function are included to all orders of perturbation theory led to many important results for the study of fundamental symmetries, development of atomic clocks, ultracold atom physics, and others, as well as provided recommended values of many atomic properties critically evaluated for their accuracy for a large number of monovalent systems. This approach requires iterative solutions of the linearized coupled-cluster equations leading to convergence issues in some cases where correlation corrections are particularly large or lead to an oscillating pattern. Moreover, these issues also lead to similar problems in the configuration-interaction (CI)+all-order method for many-particle systems. In this work, we have resolved most of the known convergence problems by applying two different convergence stabilizer methods, namely, reduced linear equation and direct inversion of iterative subspace. Examples are presented for B, Al, Zn{sup +}, and Yb{sup +}. Solving these convergence problems greatly expands the number of atomic species that can be treated with the all-order methods and is anticipated to facilitate many interesting future applications.

  12. 77 FR 24538 - Fukushima-Related Orders Modifying Licenses; Establishment of Atomic Safety and Licensing Board

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-24

    ... From the Federal Register Online via the Government Publishing Office NUCLEAR REGULATORY COMMISSION Fukushima-Related Orders Modifying Licenses; Establishment of Atomic Safety and Licensing Board Pursuant to delegation by the Commission dated December 29, 1972, published in the Federal Register, 37...

  13. Ordered many-electron motions in atoms and x-ray lasers. [Subpicosecond ultraviolet laser radiation

    SciTech Connect

    Rhodes, C.K.

    1986-01-01

    Subpicosecond ultraviolet laser technology is enabling the exploration of nonlinear atomic interactions with electric field strengths considerably in excess of an atomic unit. As this regime is approached, experiments studying multiple ionization, photoelectron energy spectra, and harmonically produced radiation all exhibit strong nonlinear coupling. Peak total energy transfer rates on the order of approx.2 x 10/sup -4/ W/atom have been observed at an intensity of approx.10/sup 16/ W/cm/sup 2/, and it is expected that energy transfer rates approaching approx.0.1 to 1 W/atom will occur under more extreme conditions for which the ultraviolet electric field E is significantly greater than e/a/sub 0//sup 2/. In this high intensity regime, a wide range of new nonlinear phenomena will be open to study. These will include the possibility of ordered driven motions in atoms, molecules, and plasmas, mechanisms involving collisions, and relativistic processes such as electron-positron pair production. An understanding of these physical interactions may provide a basis for the generation of stimulated emission in the x-ray range. 100 refs., 8 figs.

  14. Electronic structure of ordered and disordered alloys in the atomic-sphere approximation

    SciTech Connect

    Singh, P.P.; Gonis, A.

    1994-12-31

    Based on the idea of charge-neutral atomic spheres the authors have calculated the electronic structure of ordered and disordered Cu-Zn, Ni-Pt, and Al-Li alloys using the linear muffin-tin orbital (LMTO) method and the Korringa-Kohn-Rostoker coherent potential approximation (KKR CPA) method in the atomic-sphere approximation (ASA), respectively. The equilibrium lattice constants and the formation energies of ordered alloys obtained with the LMTO-ASA method show that the calculations done with charge-neutral atomic spheres are closer to the experimental results than the conventional equivolume atomic-sphere-type calculations. In the case of disordered alloys, the authors find that charge-neutral atomic spheres are essential for the stability of these alloys within the KKR-ASA CPA method where the Madelung type contribution is neglected. Their results clearly indicate that for disordered alloys any future implementation of a full-potential method within the single-site CPA should be carried out with charge-neutral cells rather than the Wigner-Seitz cells.

  15. Ultraviolet laser-based communication system for short-range tactical applications

    NASA Astrophysics Data System (ADS)

    Charles, Barry; Hughes, Bill; Erickson, Andrew; Wilkins, Jay; Teppo, Edward A.

    1994-06-01

    Solar blind ultraviolet communication techniques have promise to address the military's needs for short range applications where non-line-of-sight and a low probability of interception and detection is required. This paper addresses the general requirements for these systems and discusses an example system developed using a compact quadrupled Nd:YAG laser.

  16. Future directions for probing two and three nucleon short-range correlations at high energies

    SciTech Connect

    Frankfurt, Leonid; Sargsian, Misak; Strikman, Mark

    2008-10-13

    We summarize recent progress in the studies of the short-rang correlations (SRC) in nuclei in high energy electron and hadron nucleus scattering and suggest directions for the future high energy studies aimed at establishing detailed structure of two-nucleon SRCs, revealing structure of three nucleon SRC correlations and discovering non-nucleonic degrees of freedom in nuclei.

  17. Short-range NN and N. Delta. correlations in pion double charge exchange (DCX)

    SciTech Connect

    Johnson, M.B.

    1990-01-01

    I will review several important results related to the short-range nucleon-nucleon and delta-nucleon interaction that have been obtained from recent studies of pion double charge exchange in selected nuclei. 32 refs., 5 figs., 3 tabs.

  18. A generalized Poisson equation and short-range self-interaction energies.

    PubMed

    Varganov, Sergey A; Gilbert, Andrew T B; Gill, Peter M W

    2008-06-28

    We generalize the Poisson equation to attenuated Newtonian potentials. If the attenuation is at least exponential, the equation provides a local mapping between the density and its potential. We use this to derive several density functionals for the short-range self-interaction energy.

  19. Probing Short-Range Correlations in Nuclei with Neutrinos, Protons, and Electrons

    SciTech Connect

    Stephen Wood

    2007-05-30

    Experimental signatures for short-range correlations using ele ctron, proton and neutrino probes are discussed. The measurement of C12(e,e'pp) and C12(e,e'pn) indicates that correlations of np pairs dominate that of pp pairs.

  20. An x-ray setup to investigate the atomic order of confined liquids in slit geometry

    SciTech Connect

    Lippmann, M.; Ehnes, A.; Seeck, O. H.

    2014-01-15

    A setup has been designed to investigate thin films of confined liquids with the use of X-ray scattering methods. The confinement is realized between the flat culets of a pair of diamonds by positioning and orienting the lower diamond with nanometer and micro radian accuracy. We routinely achieve gaps between 5 and 50 nm at culet diameters of 200 μm. With this setup and a micro focused X-ray beam we have investigated the in-plane and the out-off-plane atomic order of benzene with atomic resolution.

  1. Higher-order spin-noise spectroscopy of atomic spins in fluctuating external fields

    SciTech Connect

    Li, Fuxiang; Crooker, S. A.; Sinitsyn, N. A.

    2016-03-09

    Here, we discuss the effect of external noisy magnetic fields on mesoscopic spin fluctuations that can be probed in semiconductors and atomic vapors by means of optical spin-noise spectroscopy. We also show that conventional arguments of the law of large numbers do not apply to spin correlations induced by external fields, namely, the magnitude of the 4th-order spin cumulant grows as ~N2 with the number N of observed spins, i.e., it is not suppressed in comparison to the 2nd-order cumulant. Moreover, this allows us to design a simple experiment to measure the 4th-order cumulant of spin fluctuations in an atomic system near thermodynamic equilibrium and develop a quantitative theory that explains all observations.

  2. Superlattice effects induced by atomic ordering on GaxIn1-xP Raman modes

    NASA Astrophysics Data System (ADS)

    Hassine, A.; Sapriel, J.; Le Berre, P.; di Forte-Poisson, M. A.; Alexandre, F.; Quillec, M.

    1996-07-01

    A polarized Raman scattering study is undertaken in order to investigate the atomic ordering in (001)-oriented Ga0.51In0.49P layers lattice matched to GaAs and preliminarily characterized by photoluminescence. The superlattice structure of trigonal symmetry which results from ordering manifests itself through phonon mode modifications. Several new modes are detected and their frequency and intensity behaviors are properly analyzed. In addition to the folded longitudinal-acoustic mode on Raman spectra, we observed the folded transverse-acoustic mode. Both folded acoustic modes display narrow lines (~10 cm-1) superposed to the disorder-induced acoustic bands DALA and DATA of the alloy. In the ``optical mode'' frequency range one clearly observes a doubling of the longitudinal GaP-type and InP-type modes, never reported before to our knowledge. The magnitude of the splitting between the two components of the LO doublet is measured precisely in the case of GaP-type modes and is an increasing function of the atomic ordering degree. So it is with intensities of the TO modes which become Raman active due to the trigonal symmetry. Finally the ``valley depth'' which had been empirically assigned as a significant parameter of the atomic ordering degree, is now precisely interpreted in the light of the whole Raman study.

  3. Confinement-induced orbital breathing, fusion, fission and re-ordering in semifilled shell atoms

    NASA Astrophysics Data System (ADS)

    Dolmatov, V. K.

    2013-05-01

    Alternate contraction and drastic expansion, i.e., ‘breathing’ of electronic subshells, the effects of the fusion of two subshells into one subshell and its subsequent fission (splitting) into the original subshells, as well as multiple alteration of the order of subshells in confined semifilled shell atoms with a progressively narrowing confinement are theoretically discovered. The confinement is represented by a repulsive penetrable spherical potential of an inner radius r0. The effects are exemplified by calculated data for confined semifilled shell atoms from the second, third and fourth rows of Mendeleev's table—Li, N, P and Cr atoms with semifilled 2s1, 2p3, 3p3 and 3d5 subshells, respectively—for the completeness of the study. The underlying physics behind the discovered effects is explained.

  4. High-order-harmonic generation from Rydberg atoms driven by plasmon-enhanced laser fields

    NASA Astrophysics Data System (ADS)

    Tikman, Y.; Yavuz, I.; Ciappina, M. F.; Chacón, A.; Altun, Z.; Lewenstein, M.

    2016-02-01

    We theoretically investigate high-order-harmonic generation (HHG) in Rydberg atoms driven by spatially inhomogeneous laser fields, induced, for instance, by plasmonic enhancement. It is well known that the laser intensity should exceed a certain threshold in order to stimulate HHG when noble gas atoms in their ground state are used as an active medium. One way to enhance the coherent light coming from a conventional laser oscillator is to take advantage of the amplification obtained by the so-called surface plasmon polaritons, created when a low-intensity laser field is focused onto a metallic nanostructure. The main limitation of this scheme is the low damage threshold of the materials employed in the nanostructure engineering. In this work we propose the use of Rydberg atoms, driven by spatially inhomogeneous, plasmon-enhanced laser fields, for HHG. We exhaustively discuss the behavior and efficiency of these systems in the generation of coherent harmonic emission. Toward this aim we numerically solve the time-dependent Schrödinger equation for an atom, with an electron initially in a highly excited n th Rydberg state, located in the vicinity of a metallic nanostructure. In this zone the electric field changes spatially on scales relevant for the dynamics of the laser-ionized electron. We first use a one-dimensional model to investigate systematically the phenomena. We then employ a more realistic situation, in which the interaction of a plasmon-enhanced laser field with a three-dimensional hydrogen atom is modeled. We discuss the scaling of the relevant input parameters with the principal quantum number n of the Rydberg state in question and demonstrate that harmonic emission can be achieved from Rydberg atoms well below the damage threshold, thus without deterioration of the geometry and properties of the metallic nanostructure.

  5. Strained lattice with persistent atomic order in Pt3Fe2 intermetallic core-shell nanocatalysts.

    PubMed

    Prabhudev, Sagar; Bugnet, Matthieu; Bock, Christina; Botton, Gianluigi A

    2013-07-23

    Fine-tuning nanocatalysts to enhance their catalytic activity and durability is crucial to commercialize proton exchange membrane fuel cells. The structural ordering and time evolution of ordered Pt3Fe2 intermetallic core-shell nanocatalysts for the oxygen reduction reaction that exhibit increased mass activity (228%) and an enhanced catalytic activity (155%) compared to Pt/C has been quantified using aberration-corrected scanning transmission electron microscopy. These catalysts were found to exhibit a static core-dynamic shell regime wherein, despite treating over 10,000 cycles, there is negligible decrease (9%) in catalytic activity and the ordered Pt3Fe2 core remained virtually intact while the Pt shell suffered a continuous enrichment. The existence of this regime was further confirmed by X-ray diffraction and the compositional analyses using energy-dispersive spectroscopy. With atomic-scale two-dimensional (2-D) surface relaxation mapping, we demonstrate that the Pt atoms on the surface are slightly relaxed with respect to bulk. The cycled nanocatalysts were found to exhibit a greater surface relaxation compared to noncycled catalysts. With 2-D lattice strain mapping, we show that the particle was about -3% strained with respect to pure Pt. While the observed enhancement in their activity is ascribed to such a strained lattice, our findings on the degradation kinetics establish that their extended catalytic durability is attributable to a sustained atomic order.

  6. Atomic-Scale Study of Cation Ordering in Potassium Tungsten Bronze Nanosheets.

    PubMed

    Li, Luying; Jiang, Fan; Tu, Fanfan; Jia, Shuangfeng; Gao, Yihua; Wang, Jianbo

    2017-09-01

    It has long been accepted that the formation of superlattices in hexagonal-based potassium tungsten bronzes is attributed to K vacancies only, together with small displacements of W cations. Here, the superlattices within potassium tungsten bronze nanosheets both structurally and spectroscopically at atomic resolution using comprehensive transmission electron microscopy techniques are studied. The multidimensional chemical analyses are realized by energy-dispersive X-ray spectroscopy, electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy, the atomic-scale structures are characterized using aberration-corrected scanning transmission electron microscopy with high-angle annular-dark-field detector. The observed superstructures are mainly attributed to small amount of W vacancies within single atomic layer, which would recover to more uniform distributions of W vacancies with lower concentrations at higher temperature. The band regions of different orientation from the matrix tend to regulate the superstructures to be pinned along the same direction, forming domains of highly ordered structures. The characterization of cation ordering and recovery processes of nanostructures from chemical and structural point of view at atomic resolution enables rational design of optoelectronic devices with controlled physical properties.

  7. Nonclassicality in an atom-molecule Bose-Einstein condensate: Higher-order squeezing, antibunching and entanglement

    NASA Astrophysics Data System (ADS)

    Giri, Sandip Kumar; Thapliyal, Kishore; Sen, Biswajit; Pathak, Anirban

    2017-01-01

    The transient quantum statistical properties of the atoms and molecules in an atom-molecule BEC system are investigated by obtaining a third-order perturbative solution of the Heisenberg's equations of motion corresponding to the Hamiltonian of the system, where two atoms can collide to form a molecule. Time dependent quantities, like two boson correlation, entanglement, squeezing, antibunching, etc., are computed, and their properties are compared. It is established that the atom-molecule BEC system is highly nonclassical as lower-order and higher-order squeezing and antibunching in pure (atomic and molecular) modes, squeezing and antibunching in compound mode, and lower-order and higher-order entanglement in compound mode can be observed in the atom-molecule BEC system. Exact numerical results are also reported and the analytic results obtained using the perturbative technique are shown to agree with the exact numerical results.

  8. Effects of Quantum Fluctuations and Short-Ranged Spin Correlations on the Magnetic Phase transitions in insulating vanadium oxide

    NASA Astrophysics Data System (ADS)

    de Silva, Theja; Ma, Michael; Zhang, Fu-Chun

    2002-03-01

    We study the magnetic phase transition of insulating vanadium oxide using the recently proposed S=2 bond model (1). In this model, the anomalous spin ordering of V_2O3 (RS) is due to a coupling of spin-spin correlations to orbitals. It was shown using single-site mean field theory (SSMFT) that the model also explains the unusual phase transition properities qualitatively (2). We use a modified MF approach to study the effects of quantum fluctuations and short range spin correlations which were neglected in the SSMFT calculation. The key results are i) Similar to SSMFT, at T=0, the ground state undergoes a transition from conventional antiferromagnetic (AS) ordering to ferro-orbital RS (FORS) ordering as the strength of the spin-orbital is increased relative to the bare spin-spin coupling. However, fluctuations tend to stabilize the FORS phase relative to the AS phase. ii) In contrast to SSMFT, which gave a weak first order transition, the paramagnetic to FORS transition is strongly first order. iii) The system can first become AS as T is lowered and then undergoes a second transition into either the FORS phase or a FO phase with short-ranged RS correlations. The last case corresponds to an orbital driven spin-Peirels transition. 1. F.Mila,R.Shiina,F.C.Zhang,A.Joshi,M.Ma,V.Anisimov, and T.M.Rice,Phys,Rev,Lett,85,1714(2000) 2. A.Joshi,M.Ma,and F.C.Zhang,Phys,Rev,Lett,86,5743(2001)

  9. Short-range Ising spin glasses: The metastate interpretation of replica symmetry breaking

    NASA Astrophysics Data System (ADS)

    Read, N.

    2014-09-01

    Parisi's formal replica-symmetry-breaking (RSB) scheme for mean-field spin glasses has long been interpreted in terms of many pure states organized ultrametrically. However, the early version of this interpretation, as applied to the short-range Edwards-Anderson model, runs into problems because as shown by Newman and Stein (NS) it does not allow for chaotic size dependence, and predicts non-self-averaging that cannot occur. NS proposed the concept of the metastate (a probability distribution over infinite-size Gibbs states in a given sample that captures the effects of chaotic size dependence) and a nonstandard interpretation of the RSB results in which the metastate is nontrivial and is responsible for what was called non-self-averaging. In this picture, each state drawn from the metastate has the ultrametric properties of the old theory, but when the state is averaged using the metastate, the resulting mixed state has little structure. This picture was constructed so as to agree both with the earlier RSB results and with rigorous results. Here we use the effective field theory of RSB, in conjunction with the rigorous definitions of pure states and the metastate in infinite-size systems, to show that the nonstandard picture follows directly from the RSB mean-field theory. In addition, the metastate-averaged state possesses power-law correlations throughout the low-temperature phase; the corresponding exponent ζ takes the value 4 according to the field theory in high dimensions d, and describes the effective fractal dimension of clusters of spins. Further, the logarithm of the number of pure states in the decomposition of the metastate-averaged state that can be distinguished if only correlations in a window of size W can be observed is of order Wd -ζ. These results extend the nonstandard picture quantitatively; we show that arguments against this scenario are inconclusive. More generally, in terms of Parisi's function q (x), if q(0)≠∫01dxq(x ), then the

  10. Contrasting accounts of direction and shape perception in short-range motion: Counterchange compared with motion energy detection.

    PubMed

    Norman, Joseph; Hock, Howard; Schöner, Gregor

    2014-07-01

    It has long been thought (e.g., Cavanagh & Mather, 1989) that first-order motion-energy extraction via space-time comparator-type models (e.g., the elaborated Reichardt detector) is sufficient to account for human performance in the short-range motion paradigm (Braddick, 1974), including the perception of reverse-phi motion when the luminance polarity of the visual elements is inverted during successive frames. Human observers' ability to discriminate motion direction and use coherent motion information to segregate a region of a random cinematogram and determine its shape was tested; they performed better in the same-, as compared with the inverted-, polarity condition. Computational analyses of short-range motion perception based on the elaborated Reichardt motion energy detector (van Santen & Sperling, 1985) predict, incorrectly, that symmetrical results will be obtained for the same- and inverted-polarity conditions. In contrast, the counterchange detector (Hock, Schöner, & Gilroy, 2009) predicts an asymmetry quite similar to that of human observers in both motion direction and shape discrimination. The further advantage of counterchange, as compared with motion energy, detection for the perception of spatial shape- and depth-from-motion is discussed.

  11. Short-range photoassociation from the inner wall of the lowest triplet potential of 85Rb2

    NASA Astrophysics Data System (ADS)

    Carollo, R. A.; Carini, J. L.; Eyler, E. E.; Gould, P. L.; Stwalley, W. C.

    2016-10-01

    Ultracold photoassociation is typically performed at large internuclear separations, where the scattering wavefunction amplitude is large and Franck-Condon overlap is maximized. Recently, work by this group and others on alkali-metal diatomics has shown that photoassociation can efficiently form molecules at short internuclear distance in both homonuclear and heteronuclear dimers. We propose that this short-range photoassociation is due to excitation near the wavefunction amplitude maximum at the inner wall of the lowest triplet potential. We show that Franck-Condon factors (FCFs) from the highest-energy bound state can almost precisely reproduce FCFs from a low-energy scattering state, and that both calculations match experimental data from the near-zero positive-energy scattering state with reasonable accuracy. We also show that the corresponding photoassociation from the inner wall of the ground-state singlet potential at much shorter internuclear distance is weaker and undetectable under our current experimental conditions. We predict from FCFs that the strongest of these weaker short-range photoassociation transitions are one order of magnitude below our current sensitivity.

  12. Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface.

    PubMed

    Li, Gang; Höpfner, Philipp; Schäfer, Jörg; Blumenstein, Christian; Meyer, Sebastian; Bostwick, Aaron; Rotenberg, Eli; Claessen, Ralph; Hanke, Werner

    2013-01-01

    Two-dimensional electron systems, as exploited for device applications, can lose their conducting properties because of local Coulomb repulsion, leading to a Mott-insulating state. In triangular geometries, any concomitant antiferromagnetic spin ordering can be prevented by geometric frustration, spurring speculations about 'melted' phases, known as spin liquid. Here we show that for a realization of a triangular electron system by epitaxial atom adsorption on a semiconductor, such spin disorder, however, does not appear. Our study compares the electron excitation spectra obtained from theoretical simulations of the correlated electron lattice with data from high-resolution photoemission. We find that an unusual row-wise antiferromagnetic spin alignment occurs that is reflected in the photoemission spectra as characteristic 'shadow bands' induced by the spin pattern. The magnetic order in a frustrated lattice of otherwise non-magnetic components emerges from longer-range electron hopping between the atoms. This finding can offer new ways of controlling magnetism on surfaces.

  13. Ordering actions for visibility. [distributed computing based on idea of atomic actions operating on data

    NASA Technical Reports Server (NTRS)

    Mckendry, M. S.

    1985-01-01

    The notion of 'atomic actions' has been considered in recent work on data integrity and reliability. It has been found that the standard database operations of 'read' and 'write' carry with them severe performance limitations. For this reason, systems are now being designed in which actions operate on 'objects' through operations with more-or-less arbitrary semantics. An object (i.e., an instance of an abstract data type) comprises data, a set of operations (procedures) to manipulate the data, and a set of invariants. An 'action' is a unit of work. It appears to be primitive to its surrounding environment, and 'atomic' to other actions. Attention is given to the conventional model of nested actions, ordering requirements, the maximum possible visibility (full visibility) for items which must be controlled by ordering constraints, item management paradigms, and requirements for blocking mechanisms which provide the required visibility.

  14. Ordering actions for visibility. [distributed computing based on idea of atomic actions operating on data

    NASA Technical Reports Server (NTRS)

    Mckendry, M. S.

    1985-01-01

    The notion of 'atomic actions' has been considered in recent work on data integrity and reliability. It has been found that the standard database operations of 'read' and 'write' carry with them severe performance limitations. For this reason, systems are now being designed in which actions operate on 'objects' through operations with more-or-less arbitrary semantics. An object (i.e., an instance of an abstract data type) comprises data, a set of operations (procedures) to manipulate the data, and a set of invariants. An 'action' is a unit of work. It appears to be primitive to its surrounding environment, and 'atomic' to other actions. Attention is given to the conventional model of nested actions, ordering requirements, the maximum possible visibility (full visibility) for items which must be controlled by ordering constraints, item management paradigms, and requirements for blocking mechanisms which provide the required visibility.

  15. Holographic reconstruction of atomic adsorption sites from fractional-order LEED spots

    NASA Astrophysics Data System (ADS)

    Saldin, D. K.; Reuter, K.; Blum, V.; Wedler, H.; Heinz, K.; Vamvakas, J. A.

    1998-03-01

    Striking 3D holographic images of atomic adsorption sites on surfaces may be reconstructed from diffuse LEED data by means of the Compensated Object and Reference-wave Reconstruction by an Energy-dependent Cartesian Transform (CORRECT) (D. K. Saldin and X. Chen, Phys. Rev. B 52), 2941 (1995); D. K. Saldin et al., Surf. Rev. Lett, in press. The fact that the input to the algorithm consists of LEED data on a Cartesian grid in reciprocal space suggests that it may be used also with data from fractional order Bragg spots from ordered surfaces. This has been demsonstrated recently (K. Reuter et al., Phys. Rev. Lett. 79), 4818 (1997) for the (3×3) reconstruction of the SiC(111) surface, where the holographic image was a crucial piece of information for solving that unknown structure. We show here that such an algorithm may even determine atomic adsorption geometries from superstructure unit cells as small as p(2×2).

  16. Short-Range Noncontact Sensors for Healthcare and Other Emerging Applications: A Review

    PubMed Central

    Gu, Changzhan

    2016-01-01

    Short-range noncontact sensors are capable of remotely detecting the precise movements of the subjects or wirelessly estimating the distance from the sensor to the subject. They find wide applications in our day lives such as noncontact vital sign detection of heart beat and respiration, sleep monitoring, occupancy sensing, and gesture sensing. In recent years, short-range noncontact sensors are attracting more and more efforts from both academia and industry due to their vast applications. Compared to other radar architectures such as pulse radar and frequency-modulated continuous-wave (FMCW) radar, Doppler radar is gaining more popularity in terms of system integration and low-power operation. This paper reviews the recent technical advances in Doppler radars for healthcare applications, including system hardware improvement, digital signal processing, and chip integration. This paper also discusses the hybrid FMCW-interferometry radars and the emerging applications and the future trends. PMID:27472330

  17. Enhanced sensitivity to Lorentz invariance violations in short-range gravity experiments

    NASA Astrophysics Data System (ADS)

    Shao, Cheng-Gang; Chen, Ya-Fen; Tan, Yu-Jie; Luo, Jun; Yang, Shan-Qing; Tobar, Michael Edmund

    2016-11-01

    Recently, first limits on putative Lorentz invariance violation coefficients in the pure gravity sector were determined by the reanalysis of short-range gravity experiments. Such experiments search for new physics at sidereal frequencies. They are not, however, designed to optimize the signal strength of a Lorentz invariance violation force; in fact the Lorentz violating signal is suppressed in the planar test mass geometry employed in those experiments. We describe a short-range torsion pendulum experiment with enhanced sensitivity to possible Lorentz violating signals. A periodic, striped test mass geometry is used to augment the signal. Careful arrangement of the phases of the striped patterns on opposite ends of the pendulum further enhances the signal while simultaneously suppressing the Newtonian background.

  18. Towards numerically accurate many-body perturbation theory: Short-range correlation effects

    SciTech Connect

    Gulans, Andris

    2014-10-28

    The example of the uniform electron gas is used for showing that the short-range electron correlation is difficult to handle numerically, while it noticeably contributes to the self-energy. Nonetheless, in condensed-matter applications studied with advanced methods, such as the GW and random-phase approximations, it is common to neglect contributions due to high-momentum (large q) transfers. Then, the short-range correlation is poorly described, which leads to inaccurate correlation energies and quasiparticle spectra. To circumvent this problem, an accurate extrapolation scheme is proposed. It is based on an analytical derivation for the uniform electron gas presented in this paper, and it provides an explanation why accurate GW quasiparticle spectra are easy to obtain for some compounds and very difficult for others.

  19. Analyses of kinetic glass transition in short-range attractive colloids based on time-convolutionless mode-coupling theory.

    PubMed

    Narumi, Takayuki; Tokuyama, Michio

    2017-03-01

    For short-range attractive colloids, the phase diagram of the kinetic glass transition is studied by time-convolutionless mode-coupling theory (TMCT). Using numerical calculations, TMCT is shown to recover all the remarkable features predicted by the mode-coupling theory for attractive colloids: the glass-liquid-glass reentrant, the glass-glass transition, and the higher-order singularities. It is also demonstrated through the comparisons with the results of molecular dynamics for the binary attractive colloids that TMCT improves the critical values of the volume fraction. In addition, a schematic model of three control parameters is investigated analytically. It is thus confirmed that TMCT can describe the glass-glass transition and higher-order singularities even in such a schematic model.

  20. Analyses of kinetic glass transition in short-range attractive colloids based on time-convolutionless mode-coupling theory

    NASA Astrophysics Data System (ADS)

    Narumi, Takayuki; Tokuyama, Michio

    2017-03-01

    For short-range attractive colloids, the phase diagram of the kinetic glass transition is studied by time-convolutionless mode-coupling theory (TMCT). Using numerical calculations, TMCT is shown to recover all the remarkable features predicted by the mode-coupling theory for attractive colloids: the glass-liquid-glass reentrant, the glass-glass transition, and the higher-order singularities. It is also demonstrated through the comparisons with the results of molecular dynamics for the binary attractive colloids that TMCT improves the critical values of the volume fraction. In addition, a schematic model of three control parameters is investigated analytically. It is thus confirmed that TMCT can describe the glass-glass transition and higher-order singularities even in such a schematic model.

  1. Direct Atomic Scale Observation of the Structure and Chemistry of Order/Disorder Interfaces

    DTIC Science & Technology

    2008-02-01

    contains color. 14. ABSTRACT The high strength of many metallic alloys, including nickel base superalloys used in aircraft jet engines, especially...tomography the atomic scale structure and chemistry across the order/disorder interface in nickel base superalloys has been determined. While, the...including nickel base superalloys used in aircraft jet engines, especially at elevated temperatures, is often attributed to the presence of homogeneously

  2. Neutrino-Nucleus Interactions and the Short-Range Structure of Nuclei

    SciTech Connect

    Cavanna, F.; Palamara, O.; Schiavilla, R.; Soderberg, M.; Wiringa, R. B.

    2015-01-08

    Improvements in theoretical modeling of Short Range structures and phenomena, and comparisons with data, will require sustained collaboration between nuclear theorists and neutrino experimentalists. The extensive history of studying this area of nuclear physics in electron- and hadron-scattering experiments, coupled with the transformative capabilities of LArTPCs to identify neutrinos, will provide a ripe opportunity for new discoveries that will further our understanding of the nucleus.

  3. Beam divergence changing mechanism for short-range inter-unmanned aerial vehicle optical communications.

    PubMed

    Heng, Kiang Huat; Zhong, Wen-De; Cheng, Tee Hiang; Liu, Ning; He, Yingjie

    2009-03-10

    The problems associated with using a single fixed beam divergence for short-range inter-unmanned aerial vehicle free-space optical communications are discussed. To overcome the problems, a beam divergence changing mechanism is proposed. Four different methods are then proposed to implement the beam divergence changing mechanism. The performance of these methods is evaluated in terms of transmission distance under adverse weather conditions. The results show that the performance is greatly improved when the beam divergence changing mechanism is used.

  4. Short-Range Guiding Can Result in the Formation of Circular Aggregates in Myxobacteria Populations

    PubMed Central

    Janulevicius, Albertas; van Loosdrecht, Mark; Picioreanu, Cristian

    2015-01-01

    Myxobacteria are social bacteria that upon starvation form multicellular fruiting bodies whose shape in different species can range from simple mounds to elaborate tree-like structures. The formation of fruiting bodies is a result of collective cell movement on a solid surface. In the course of development, groups of flexible rod-shaped cells form streams and move in circular or spiral patterns to form aggregation centers that can become sites of fruiting body formation. The mechanisms of such cell movement patterns are not well understood. It has been suggested that myxobacterial development depends on short-range contact-mediated interactions between individual cells, i.e. cell aggregation does not require long-range signaling in the population. In this study, by means of a computational mass-spring model, we investigate what types of short-range interactions between cells can result in the formation of streams and circular aggregates during myxobacterial development. We consider short-range head-to-tail guiding between individual cells, whereby movement direction of the head of one cell is affected by the nearby presence of the tail of another cell. We demonstrate that stable streams and circular aggregates can arise only when the trailing cell, in addition to being steered by the tail of the leading cell, is able to speed up to catch up with it. It is suggested that necessary head-to-tail interactions between cells can arise from physical adhesion, response to a diffusible substance or slime extruded by cells, or pulling by motility engine pili. Finally, we consider a case of long-range guiding between cells and show that circular aggregates are able to form without cells increasing speed. These findings present a possibility to discriminate between short-range and long-range guiding mechanisms in myxobacteria by experimentally measuring distribution of cell speeds in circular aggregates. PMID:25928112

  5. Improved short range forecasting by blending techniques using extrapolation and NWP model forecasts

    NASA Astrophysics Data System (ADS)

    Jang, M.; Jee, J. B.; Kim, S.; Park, J. G.

    2016-12-01

    Nowcasting and short range forecast rely more and more on "blending" techniques combining several data sources (both in situ and remote sensing observation, NWP, model output statistic data, high resolution topography, etc..) in a seamless way using lead-time-dependent weights. Developed nowcasting techniques blend extrapolation-based forecasts with numerical weather prediction (NWP)-based forecasts, heavily weighting the extrapolation forecasts at 0 3h lead times and transitioning emphasis to the NWP-based forecasts at the later lead times. Korea Meteorological Administration (KMA) employs NOAA's Local Analysis and Prediction System (LAPS) which is called KLAPS. It provides the hot-start initial condition to the very short-range forecasting system called advanced storm-scale analysis and prediction system (ASAPS) based on the Weather Research and Forecasting (WRF) model. MAPLE (McGill Algorithm for Precipitation nowcasting by Lagrangian Extrapolation) uses radar composite maps to predict the location of precipitation echoes several hours in advance (up to 6 hours) using the variational echo tracking method and a semi-Lagrangian backward advection technique. This system has been operating in real-time since June 2008, the output being used in operations by KMA's weather forecasters and hydrologists. The spatial resolution of both products are 1km. The purpose of this study is to improve the accuracy of short range forecasting using the merging method (distance, similarity) between radar-based extrapolation forecast (MAPLE) and precipitation forecast from NWP model (ASAPS). In this study, a new approach to applying different weights to blend extrapolation and model forecasts based on intensities and forecast times is applied and tested. As a result, very short range forecasts was confirmed the possibility to be improved.

  6. SHORT RANGE WAKEFIELD IN A FLAT PILLBOX CAVITY GENERATED BY A SUB-RELATIVISTIC BEAM BUNCH.

    SciTech Connect

    WANG,H.; PALMER,R.B.; GALLARDO,J.

    2001-06-18

    The short-range wakefield between two parallel conducting plates generated by a sub-relativistic beam bunch has been solved analytically by image charge method in time domain. Comparing with traditional modal analysis in frequency domain this algorithm simplifies mathematics and reveals great details of physics in electromagnetic field generation, propagation, reflection and causality. The calculated results have an excellent agreement with MAFIA and ABCI simulations in all range of beam velocities.

  7. A short-range optical wireless transmission method based on LED

    NASA Astrophysics Data System (ADS)

    Miao, Meiyuan; Chen, Ailin; Zhu, Mingxing; Li, Ping; Gao, Yingming; Zou, Nianyu

    2016-10-01

    As to electromagnetic wave interfere and only one to one transmission problem of Bluetooth, a short-range LED optical wireless transmission method is proposed to be complementary technology in this paper. Furthermore achieved image transmission through this method. The system makes C52 to be the mater controller, transmitter got data from terminals by USB and sends modulated signals with LED. Optical signal is detected by PD, through amplified, filtered with shaping wave from, and demodulated on receiver. Then send to terminals like PC and reverted back to original image. Analysis the performance from peak power and average power, power consumption of transmitter, relationship of bit error rate and modulation mode, and influence of ambient light, respectively. The results shows that image can be received accurately which uses this method. The most distant transmission distance can get to 1m with transmitter LED source of 1w, and the transfer rate is 14.4Kbit/s with OOK modulation mode on stabilization system, the ambient light effect little to LED transmission system in normal light environment. The method is a convenient to carry LED wireless short range transmission for mobile transmission equipment as a supplement of Bluetooth short-range transmission for its ISM band interfere, and the analysis method in this paper can be a reference for other similar systems. It also proves the system is feasibility for next study.

  8. Particle simulation algorithms with short-range forces in MHD and fluid flow

    SciTech Connect

    Cable, S.; Tajima, T.; Umegaki, K.

    1992-07-01

    Attempts are made to develop numerical algorithms for handling fluid flows involving liquids and liquid-gas mixtures. In these types of systems, the short-range intermolecular interactions are important enough to significantly alter behavior predicted on the basis of standard fluid mechanics and magnetohydrodynamics alone. We have constructed a particle-in-cell (PIC) code for the purpose of studying the effects of these interactions. Of the algorithms considered, the one which has been successfully implemented is based on a MHD particle code developed by Brunel et al. In the version presented here, short range forces are included in particle motion by, first, calculating the forces between individual particles and then, to prevent aliasing, interpolating these forces to the computational grid points, then interpolating the forces back to the particles. The code has been used to model a simple two-fluid Rayleigh-Taylor instability. Limitations to the accuracy of the code exist at short wavelengths, where the effects of the short-range forces would be expected to be most pronounced.

  9. Molecular positional order in langmuir-blodgett films by atomic force microscopy.

    PubMed

    Bourdieu, L; Ronsin, O; Chatenay, D

    1993-02-05

    Langmuir-Blodgett films of barium arachidate have been studied on both macroscopic and microscopic scales by atomic force microscopy. As prepared, the films exhibit a disordered hexagonal structure; molecularly resolved images in direct space establish a connection between the extent of the positional order and the presence of defects such as dislocations. Upon heating, the films reorganize into a more condensed state with a centered rectangular crystallographic arrangement; in this new state the films exhibit long-range positional order and unusual structural features, such as a height modulation of the arachidic acid molecules.

  10. Molecular Positional Order in Langmuir-Blodgett Films by Atomic Force Microscopy

    NASA Astrophysics Data System (ADS)

    Bourdieu, L.; Ronsin, O.; Chatenay, D.

    1993-02-01

    Langmuir-Blodgett films of barium arachidate have been studied on both macroscopic and microscopic scales by atomic force microscopy. As prepared, the films exhibit a disordered hexagonal structure; molecularly resolved images in direct space establish a connection between the extent of the positional order and the presence of defects such as dislocations. Upon heating, the films reorganize into a more condensed state with a centered rectangular crystallographic arrangement; in this new state the films exhibit long-range positional order and unusual structural features, such as a height modulation of the arachidic acid molecules.

  11. Accurate classical short-range forces for the study of collision cascades in Fe-Ni-Cr

    NASA Astrophysics Data System (ADS)

    Béland, Laurent Karim; Tamm, Artur; Mu, Sai; Samolyuk, German D.; Osetsky, Yuri N.; Aabloo, Alvo; Klintenberg, Mattias; Caro, Alfredo; Stoller, Roger E.

    2017-10-01

    The predictive power of a classical molecular dynamics simulation is largely determined by the physical validity of its underlying empirical potential. In the case of high-energy collision cascades, it was recently shown that correctly modeling interactions at short distances is necessary to accurately predict primary damage production. An ab initio based framework is introduced for modifying an existing embedded-atom method FeNiCr potential to handle these short-range interactions. Density functional theory is used to calculate the energetics of two atoms approaching each other, embedded in the alloy, and to calculate the equation of state of the alloy as it is compressed. The pairwise terms and the embedding terms of the potential are modified in accordance with the ab initio results. Using this reparametrized potential, collision cascades are performed in Ni50Fe50, Ni80Cr20 and Ni33Fe33Cr33. The simulations reveal that alloying Ni and NiCr to Fe reduces primary damage production, in agreement with some previous calculations. Alloying Ni and NiFe to Cr does not reduce primary damage production, in contradiction with previous calculations.

  12. Coherent cluster atomic ordering in the Fe-27Al intermetallic compound

    NASA Astrophysics Data System (ADS)

    Balagurov, A. M.; Bobrikov, I. A.; Mukhametuly, B.; Sumnikov, S. V.; Golovin, I. S.

    2016-10-01

    Neutron diffraction studies of the Fe0.735Al0.265 compound are performed in a wide temperature range (20-900°C) in order to determine its structural states and the mechanism of ordering of atoms. The combination of high-resolution diffraction and the real-time detection of diffraction spectra makes it possible to establish that, in contrast to traditional notions, the structure of this compound at room temperature is a phase with only a partially ordered arrangement of Fe and Al in a unit cell. A completely ordered phase (such as Fe3Al) is present in the form of mesoscopic ( 200Å) clusters coherently incorporated into the disordered matrix of the main phase. After the transition of the sample to a disordered state ( T> 740°C) and slow cooling to room temperature, the size of structurally ordered clusters increases to 900 Å. A high contrast in the coherent neutron scattering lengths of iron and gallium nuclei allows the accurate determination of the temperature dependence of the occupancy factors of sites by Fe and Al atoms up to a phase transition to the disordered state.

  13. Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition

    SciTech Connect

    Zhang, Yijun; Liu, Ming; Peng, Bin; Zhou, Ziyao; Chen, Xing; Yang, Shu-Ming; Jiang, Zhuang-De; Zhang, Jie; Ren, Wei; Ye, Zuo-Guang

    2016-01-27

    Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe2O3 and superparamagnetic Fe2O3with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe2O3 in a reducing atmosphere leads to the formation of the spinel Fe3O4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. Finally, the ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.

  14. Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition.

    PubMed

    Zhang, Yijun; Liu, Ming; Peng, Bin; Zhou, Ziyao; Chen, Xing; Yang, Shu-Ming; Jiang, Zhuang-De; Zhang, Jie; Ren, Wei; Ye, Zuo-Guang

    2016-01-27

    Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe2O3 and superparamagnetic Fe3O4 with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe2O3 in a reducing atmosphere leads to the formation of the spinel Fe3O4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. The ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.

  15. Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Yijun; Liu, Ming; Peng, Bin; Zhou, Ziyao; Chen, Xing; Yang, Shu-Ming; Jiang, Zhuang-De; Zhang, Jie; Ren, Wei; Ye, Zuo-Guang

    2016-01-01

    Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe2O3 and superparamagnetic Fe3O4 with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe2O3 in a reducing atmosphere leads to the formation of the spinel Fe3O4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. The ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.

  16. Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition

    DOE PAGES

    Zhang, Yijun; Liu, Ming; Peng, Bin; ...

    2016-01-27

    Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe2O3 and superparamagnetic Fe2O3with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe2O3 in a reducing atmosphere leads to the formation of the spinel Fe3O4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulatormore » transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. Finally, the ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.« less

  17. ACKS2: Atom-condensed Kohn-Sham DFT approximated to second order

    NASA Astrophysics Data System (ADS)

    Verstraelen, T.; Ayers, P. W.; Van Speybroeck, V.; Waroquier, M.

    2013-02-01

    A new polarizable force field (PFF), namely atom-condensed Kohn-Sham density functional theory approximated to second order (ACKS2), is proposed for the efficient computation of atomic charges and linear response properties of extended molecular systems. It is derived from Kohn-Sham density functional theory (KS-DFT), making use of two novel ingredients in the context of PFFs: (i) constrained atomic populations and (ii) the Legendre transform of the Kohn-Sham kinetic energy. ACKS2 is essentially an extension of the Electronegativity Equalization Method (EEM) [W. J. Mortier, S. K. Ghosh, and S. Shankar, J. Am. Chem. Soc. 108, 4315 (1986)], 10.1021/ja00275a013 in which two major EEM shortcomings are fixed: ACKS2 predicts a linear size-dependence of the dipole polarizability in the macroscopic limit and correctly describes the charge distribution when a molecule dissociates. All ACKS2 parameters are defined as atoms-in-molecules expectation values. The implementation of ACKS2 is very similar to that of EEM, with only a small increase in computational cost.

  18. Random phase approximation with second-order screened exchange for current-carrying atomic states

    NASA Astrophysics Data System (ADS)

    Zhu, Wuming; Zhang, Liang; Trickey, S. B.

    2016-12-01

    The direct random phase approximation (RPA) and RPA with second-order screened exchange (SOSEX) have been implemented with complex orbitals as a basis for treating open-shell atoms. Both RPA and RPA+SOSEX are natural implicit current density functionals because the paramagnetic current density implicitly is included through the use of complex orbitals. We confirm that inclusion of the SOSEX correction improves the total energy accuracy substantially compared to RPA, especially for smaller-Z atoms. Computational complexity makes post self-consistent-field (post-SCF) evaluation of RPA-type expressions commonplace, so orbital basis origins and properties become important. Sizable differences are found in correlation energies, total atomic energies, and ionization energies for RPA-type functionals evaluated in the post-SCF fashion with orbital sets obtained from different schemes. Reference orbitals from Kohn-Sham calculations with semi-local functionals are more suitable for RPA+SOSEX to generate accurate total energies, but reference orbitals from exact exchange (non-local) yield essentially energetically degenerate open-shell atom ground states. RPA+SOSEX correlation combined with exact exchange calculated from a hybrid reference orbital set (half the exchange calculated from exact-exchange orbitals, the other half of the exchange from orbitals optimized for the Perdew-Burke-Ernzerhof (PBE) exchange functional) gives the best overall performance. Numerical results show that the RPA-like functional with SOSEX correction can be used as a practical implicit current density functional when current effects should be included.

  19. Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition

    PubMed Central

    Zhang, Yijun; Liu, Ming; Peng, Bin; Zhou, Ziyao; Chen, Xing; Yang, Shu-Ming; Jiang, Zhuang-De; Zhang, Jie; Ren, Wei; Ye, Zuo-Guang

    2016-01-01

    Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe2O3 and superparamagnetic Fe3O4 with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe2O3 in a reducing atmosphere leads to the formation of the spinel Fe3O4 phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. The ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications. PMID:26813143

  20. The reaction of propylene with ordered and disordered oxygen atoms adsorbed on the Ag(110) surface

    NASA Astrophysics Data System (ADS)

    Ranney, Jeffrey T.; Bare, Simon R.

    1997-06-01

    The adsorption and reaction of propylene on oxygen covered Ag(110) was investigated using temperature programmed desorption spectroscopy. Propylene oxidation was compared on the oxygen reconstructed (ordered) Ag(110) surface and on the unreconstructed (disordered) oxygen dosed surface. Oxygen atoms adsorbed < 185 K do not incorporate into long silver-oxygen chains on the (110) surface and are referred to as disordered. Propylene desorbs from clean Ag(110) with an activation energy of 9.8 kcal mol -1. The desorption activation energy increases by 30% as the coverage of oxygen is increased up to 0.33 monolayers. While the desorption activation energy increase was the same on the reconstructed and unreconstructed surface, the reactivity of the adsorbed oxygen for propylene oxidation was quite different. Disordered oxygen adatoms were determined to be at least ten times more active for propylene oxidation than ordered oxygen atoms on the reconstructed surface. The decrease in activity of the oxygen atoms is attributed to the embedding of the oxygen adatoms into long silver-oxygen chains at higher temperatures. With increasing propylene coverage on the oxygen pre-covered surface the water yield increases and the yield of carbon dioxide decreases, indicating that water formation through hydrogen abstraction consumes the bulk of the oxygen at higher propylene coverages.

  1. Quantifying the Hierarchical Order in Self-Aligned Carbon Nanotubes from Atomic to Micrometer Scale.

    PubMed

    Meshot, Eric R; Zwissler, Darwin W; Bui, Ngoc; Kuykendall, Tevye R; Wang, Cheng; Hexemer, Alexander; Wu, Kuang Jen J; Fornasiero, Francesco

    2017-06-27

    Fundamental understanding of structure-property relationships in hierarchically organized nanostructures is crucial for the development of new functionality, yet quantifying structure across multiple length scales is challenging. In this work, we used nondestructive X-ray scattering to quantitatively map the multiscale structure of hierarchically self-organized carbon nanotube (CNT) "forests" across 4 orders of magnitude in length scale, from 2.0 Å to 1.5 μm. Fully resolved structural features include the graphitic honeycomb lattice and interlayer walls (atomic), CNT diameter (nano), as well as the greater CNT ensemble (meso) and large corrugations (micro). Correlating orientational order across hierarchical levels revealed a cascading decrease as we probed finer structural feature sizes with enhanced sensitivity to small-scale disorder. Furthermore, we established qualitative relationships for single-, few-, and multiwall CNT forest characteristics, showing that multiscale orientational order is directly correlated with number density spanning 10(9)-10(12) cm(-2), yet order is inversely proportional to CNT diameter, number of walls, and atomic defects. Lastly, we captured and quantified ultralow-q meridional scattering features and built a phenomenological model of the large-scale CNT forest morphology, which predicted and confirmed that these features arise due to microscale corrugations along the vertical forest direction. Providing detailed structural information at multiple length scales is important for design and synthesis of CNT materials as well as other hierarchically organized nanostructures.

  2. Atomic ordering in cubic bismuth telluride alloy phases at high pressure

    NASA Astrophysics Data System (ADS)

    Loa, I.; Bos, J.-W. G.; Downie, R. A.; Syassen, K.

    2016-06-01

    Pressure-induced transitions from ordered intermetallic phases to substitutional alloys to semi-ordered phases were studied in a series of bismuth tellurides. By using angle-dispersive x-ray diffraction, the compounds Bi4Te5 , BiTe, and Bi2Te were observed to form alloys with the disordered body-centered cubic (bcc) crystal structure upon compression to above 14-19 GPa at room temperature. The BiTe and Bi2Te alloys and the previously discovered high-pressure alloys of Bi2Te3 and Bi4Te3 were all found to show atomic ordering after gentle annealing at very moderate temperatures of ˜100 ∘C . Upon annealing, BiTe transforms from bcc to the B2 (CsCl) crystal-structure type, and the other phases adopt semi-disordered variants thereof, featuring substitutional disorder on one of the two crystallographic sites. The transition pressures and atomic volumes of the alloy phases show systematic variations across the BimTen series including the end members Bi and Te. First-principles calculations were performed to characterize the electronic structure and chemical bonding properties of B2-type BiTe and to identify the driving forces of the ordering transition. The calculated Fermi surface of B2-type BiTe has an intricate structure and is predicted to undergo three topological changes between 20 and 60 GPa.

  3. Explicitly correlated atomic orbital basis second order Møller-Plesset theory.

    PubMed

    Hollman, David S; Wilke, Jeremiah J; Schaefer, Henry F

    2013-02-14

    The scope of problems treatable by ab initio wavefunction methods has expanded greatly through the application of local approximations. In particular, atomic orbital (AO) based wavefunction methods have emerged as powerful techniques for exploiting sparsity and have been applied to biomolecules as large as 1707 atoms [S. A. Maurer, D. S. Lambrecht, D. Flaig, and C. Ochsenfeld, J. Chem. Phys. 136, 144107 (2012)]. Correlated wavefunction methods, however, converge notoriously slowly to the basis set limit and, excepting the use of large basis sets, will suffer from a severe basis set incompleteness error (BSIE). The use of larger basis sets is prohibitively expensive for AO basis methods since, for example, second-order Møller-Plesset perturbation theory (MP2) scales linearly with the number of atoms, but still scales as O(N(5)) in the number of functions per atom. Explicitly correlated F12 methods have been shown to drastically reduce BSIE for even modestly sized basis sets. In this work, we therefore explore an atomic orbital based formulation of explicitly correlated MP2-F12 theory. We present working equations for the new method, which produce results identical to the widely used molecular orbital (MO) version of MP2-F12 without resorting to a delocalized MO basis. We conclude with a discussion of several possible approaches to a priori screening of contraction terms in our method and the prospects for a linear scaling implementation of AO-MP2-F12. The discussion includes concrete examples involving noble gas dimers and linear alkane chains.

  4. Second order classical perturbation theory for atom surface scattering: Analysis of asymmetry in the angular distribution

    SciTech Connect

    Zhou, Yun Pollak, Eli; Miret-Artés, Salvador

    2014-01-14

    A second order classical perturbation theory is developed and applied to elastic atom corrugated surface scattering. The resulting theory accounts for experimentally observed asymmetry in the final angular distributions. These include qualitative features, such as reduction of the asymmetry in the intensity of the rainbow peaks with increased incidence energy as well as the asymmetry in the location of the rainbow peaks with respect to the specular scattering angle. The theory is especially applicable to “soft” corrugated potentials. Expressions for the angular distribution are derived for the exponential repulsive and Morse potential models. The theory is implemented numerically to a simplified model of the scattering of an Ar atom from a LiF(100) surface.

  5. Photoassociation of a cold-atom-molecule pair. II. Second-order perturbation approach

    SciTech Connect

    Lepers, M.; Vexiau, R.; Bouloufa, N.; Dulieu, O.; Kokoouline, V.

    2011-04-15

    The electrostatic interaction between an excited atom and a diatomic ground-state molecule in an arbitrary rovibrational level at large mutual separations is investigated with a general second-order perturbation theory, in the perspective of modeling the photoassociation between cold atoms and molecules. We find that the combination of quadrupole-quadrupole and van der Waals interactions competes with the rotational energy of the dimer, limiting the range of validity of the perturbative approach to distances larger than 100 Bohr radii. Numerical results are given for the long-range interaction between Cs and Cs{sub 2}, showing that the photoassociation is probably efficient for any Cs{sub 2} rotational energy.

  6. Phase decomposition and ordering in Ni-11.3 at.% Ti studied with atom probe tomography.

    PubMed

    Al-Kassab, T; Kompatscher, M; Kirchheim, R; Kostorz, G; Schönfeld, B

    2014-09-01

    The decomposition behavior of Ni-rich Ni-Ti was reassessed using Tomographic Atom Probe (TAP) and Laser Assisted Wide Angle Tomographic Atom Probe. Single crystalline specimens of Ni-11.3 at.% Ti were investigated, the states selected from the decomposition path were the metastable γ″ and γ' states introduced on the basis of small-angle neutron scattering (SANS) and the two-phase model for evaluation. The composition values of the precipitates in these states could not be confirmed by APT data as the interface of the ordered precipitates may not be neglected. The present results rather suggest to apply a three-phase model for the interpretation of SANS measurements, in which the width of the interface remains nearly unchanged and the L12 structure close to 3:1 stoichiometry is maintained in the core of the precipitates from the γ″ to the γ' state.

  7. Higher-order recoil corrections for singlet states of the helium atom

    NASA Astrophysics Data System (ADS)

    Patkóš, Vojtěch; Yerokhin, Vladimir A.; Pachucki, Krzysztof

    2017-01-01

    We investigate the finite nuclear mass corrections in the helium atom in order to resolve a significant disagreement between the 2 3S -2 3P and 2 3S -2 1S transition isotope shifts. These two transitions lead to discrepant results for the nuclear charge radii difference between 4He and 3He. The accurate treatment of the finite nuclear mass effects is quite complicated and requires the use of the quantum field theoretical approach. We derive the α6m2/M correction with the help of nonrelativistic QED and dimensional regularization of the three-body Coulombic system and present accurate numerical results for low-lying states. The previously reported 4 σ discrepancy in the nuclear charge radius difference between 3He and 4He from two different atomic isotope shift transitions is confirmed, which calls for verification of experimental transition frequencies.

  8. Search for spin-dependent short-range force between nucleons using optically polarized He3 gas

    NASA Astrophysics Data System (ADS)

    Zheng, W.; Gao, H.; Lalremruata, B.; Zhang, Y.; Laskaris, G.; Snow, W. M.; Fu, C. B.

    2012-02-01

    We propose a new method to detect short-range P- and T-violating interactions between nucleons, based on measuring the precession frequency shift of polarized He3 nuclei in the presence of an unpolarized mass. To maximize the sensitivity, a high-pressure He3 cell with thin glass windows (250μm) is used to minimize the distance between the mass and He3. The magnetic field fluctuation is suppressed by using the He3 gas in a different region of the cell as a magnetometer. Systematic uncertainties from the magnetic properties of the mass are suppressed by flipping both the magnetic field and spin directions. Without any magnetic shielding, our result has already reached the sensitivity of the current best limit. With improvement in uniformity and stability of the field, we can further improve the sensitivity by 2 orders of magnitude over the force range from 10-4-10-2m.

  9. Derivation of a non-local interfacial Hamiltonian for short-ranged wetting: I. Double-parabola approximation.

    PubMed

    Parry, A O; Rascón, C; Bernardino, N R; Romero-Enrique, J M

    2006-07-19

    We derive a non-local effective interfacial Hamiltonian model for short-ranged wetting phenomena using a Green's function method. The Hamiltonian is characterized by a binding potential functional and is accurate to exponentially small order in the radii of curvature of the interface and the bounding wall. The functional has an elegant diagrammatic representation in terms of planar graphs which represent different classes of tube-like fluctuations connecting the interface and wall. For the particular cases of planar, spherical and cylindrical interfacial (and wall) configurations, the binding potential functional can be evaluated exactly. More generally, the non-local functional naturally explains the origin of the effective position-dependent stiffness coefficient in the small-gradient limit.

  10. Explicit Design of FPGA-Based Coprocessors for Short-Range Force Computations in Molecular Dynamics Simulations *†

    PubMed Central

    Gu, Yongfeng; VanCourt, Tom; Herbordt, Martin C.

    2008-01-01

    FPGA-based acceleration of molecular dynamics simulations (MD) has been the subject of several recent studies. The short-range force computation, which dominates the execution time, is the primary focus. Here we combine: a high level of FPGA-specific design including cell lists, systematically determined interpolation and precision, handling of exclusion, and support for MD simulations of up to 256K particles. The target system consists of a standard PC with a 2004-era COTS FPGA board. There are several innovations: new microarchitectures for several major components, including the cell list processor and the off-chip memory controller; and a novel arithmetic mode. Extensive experimentation was required to optimize precision, interpolation order, interpolation mode, table sizes, and simulation quality. We obtain a substantial speed-up over a highly tuned production MD code. PMID:19412319

  11. Higher-order spin-noise spectroscopy of atomic spins in fluctuating external fields

    DOE PAGES

    Li, Fuxiang; Crooker, S. A.; Sinitsyn, N. A.

    2016-03-09

    Here, we discuss the effect of external noisy magnetic fields on mesoscopic spin fluctuations that can be probed in semiconductors and atomic vapors by means of optical spin-noise spectroscopy. We also show that conventional arguments of the law of large numbers do not apply to spin correlations induced by external fields, namely, the magnitude of the 4th-order spin cumulant grows as ~N2 with the number N of observed spins, i.e., it is not suppressed in comparison to the 2nd-order cumulant. Moreover, this allows us to design a simple experiment to measure the 4th-order cumulant of spin fluctuations in an atomicmore » system near thermodynamic equilibrium and develop a quantitative theory that explains all observations.« less

  12. Magnetic field and atomic order effect on the martensitic transformation of a metamagnetic alloy.

    PubMed

    Barandiaran, J M; Chernenko, V A; Cesari, E; Salas, D; Gutierrez, J; Lazpita, P

    2013-12-04

    The martensitic transformation (MT) of metamagnetic shape memory alloys is very sensitive to the applied magnetic field and atomic order. We analyze the alloy Ni50Mn34.5In15.5 in magnetic fields up to 13 T. The alloy has been prepared both in an ordered state by slow cooling, and in a disordered state by rapid quenching. In both cases the dependence of the martensitic transition temperature on the field is highly nonlinear. Such departure from linearity is due to a decrease of the entropy change at the transition, ΔS, with the applied field. This can be explained by the ordering effect of the magnetic field on the frustrated magnetic structure of the alloy in the martensitic phase. Compliance with a recent model, relying on the strong magnetoelastic interactions in these compounds, is very satisfactory.

  13. Glass fragility and atomic ordering on the intermediate and extended range.

    PubMed

    Salmon, Philip S; Barnes, Adrian C; Martin, Richard A; Cuello, Gabriel J

    2006-06-16

    The relation between the fragility of glass-forming systems, a parameter which describes many of their key physical characteristics, and atomic scale structure is investigated by using neutron diffraction to measure the topological and chemical ordering for germania, or GeO(2), which is an archetypal strong glass former. We find that the ordering for this and other tetrahedral network-forming glasses at distances greater than the nearest neighbor can be rationalized in terms of an interplay between the relative importance of two length scales. One of these is associated with an intermediate range, the other with an extended range and, with increasing glass fragility, it is the extended range ordering which dominates.

  14. Nuclear matrix element of neutrinoless double-β decay: Relativity and short-range correlations

    NASA Astrophysics Data System (ADS)

    Song, L. S.; Yao, J. M.; Ring, P.; Meng, J.

    2017-02-01

    Background:The discovery of neutrinoless double-β (0 ν β β ) decay would demonstrate the nature of neutrinos, have profound implications for our understanding of matter-antimatter mystery, and solve the mass hierarchy problem of neutrinos. The calculations for the nuclear matrix elements M0 ν of 0 ν β β decay are crucial for the interpretation of this process. Purpose: We study the effects of relativity and nucleon-nucleon short-range correlations on the nuclear matrix elements M0 ν by assuming the mechanism of exchanging light or heavy neutrinos for the 0 ν β β decay. Methods:The nuclear matrix elements M0 ν are calculated within the framework of covariant density functional theory, where the beyond-mean-field correlations are included in the nuclear wave functions by configuration mixing of both angular-momentum and particle-number projected quadrupole deformed mean-field states. Results: The nuclear matrix elements M0 ν are obtained for ten 0 ν β β -decay candidate nuclei. The impact of relativity is illustrated by adopting relativistic or nonrelativistic decay operators. The effects of short-range correlations are evaluated. Conclusions: The effects of relativity and short-range correlations play an important role in the mechanism of exchanging heavy neutrinos though the influences are marginal for light neutrinos. Combining the nuclear matrix elements M0 ν with the observed lower limits on the 0 ν β β -decay half-lives, the predicted strongest limits on the effective masses are ||<0.06 eV for light neutrinos and | |-1>3.065 ×108GeV for heavy neutrinos.

  15. Studies of some problems related to atomic ordering, molecular motion and pair distribution function

    NASA Astrophysics Data System (ADS)

    Levashov, Valentin A.

    In this thesis the results of my work on three out of four projects on which I was working during my Ph.D. under supervision of Prof. M. F. Thorpe are summarized. The first project was devoted to the study of properties of a model that was developed to reproduce the ordering of ions in layered double hydroxides. In the model two types of positive ions occupy the sites of triangular lattice. The ordering of ions is assumed to occur due to the long-range Coulomb interaction. The charge neutrality is provided by the negative background charge, which is assumed to be the same at every site of the lattice. General properties of the model in 1d and 2d were studied and the phase diagrams were obtained. The obtained results predict multiple phase separations in this system of charges that can, in particularly, affect the stability of the layered double hydroxides. Some properties of the atomic pair distribution function (PDF) were studied during my work on the second project. Traditionally PDF was used to study atomic ordering at small distances, while it was assumed that at large distances PDF is featureless. Puzzled by the observation that PDF calculated for the crystalline Ni does not decay at large distances we studied the behavior, in particularly the origin of decay, of PDF at large distances. The obtained results potentially could be used to measure the amount of imperfections in crystalline materials and to test instrumental resolution in X-ray and neutron diffraction experiments. During my work on the third project we were developing a technique that would allow accurate calculation of PDF for the flexible molecules. Since quantum mechanical calculations are complicated and computationally demanding in calculations of PDF for molecules in liquid or gaseous phases, classical methods, like molecular dynamics are usually employed. Thus, quantum mechanical effects, like zero-point atomic motion, are usually ignored. However, it is necessary to take into account the

  16. Hybrid-Mode-Assisted Long-Distance Excitation of Short-Range Surface Plasmons in a Nanotip-Enhanced Step-Index Fiber.

    PubMed

    Tuniz, Alessandro; Chemnitz, Mario; Dellith, Jan; Weidlich, Stefan; Schmidt, Markus A

    2017-02-08

    We propose and experimentally demonstrate a monolithic nanowire-enhanced fiber-based nanoprobe for the broadband delivery of light (550-730 nm) to a deep subwavelength scale using short-range surface plasmons. The geometry is formed by a step index fiber with an integrated gold nanowire in its core and a protruding gold nanotip with sub-10 nm apex radius. We present a novel coupling scheme to excite short-range surface plasmons, whereby the radially polarized hybrid mode propagating inside the nanowire section excites the plasmonic mode close to the fiber endface, which is in turn superfocused down to nanoscale dimensions at the tip apex. We show that in this all-integrated fiber-plasmonic coupling scheme the wire length can be orders of magnitude longer than the attenuation length of short-range plasmon polaritons, yielding a broadband plasmon excitation and reducing demands in fabrication. We observe that the scattered light in the far-field from the nanotip is axially polarized and preferentially excited by a radially polarized input, unambiguously revealing that it originates from a short-range plasmon propagating on the nanotip, in agreement with simulations. This novel excitation scheme will have important applications in near-field microscopy and nanophotonics and potentially offers significantly improved resolution compared to current delivery near-field probes.

  17. Unique atom hyper-kagome order in Na4Ir3O8 and in low-symmetry spinel modifications.

    PubMed

    Talanov, V M; Shirokov, V B; Talanov, M V

    2015-05-01

    Group-theoretical and thermodynamic methods of the Landau theory of phase transitions are used to investigate the hyper-kagome atomic order in structures of ordered spinels and a spinel-like Na4Ir3O8 crystal. The formation of an atom hyper-kagome sublattice in Na4Ir3O8 is described theoretically on the basis of the archetype (hypothetical parent structure/phase) concept. The archetype structure of Na4Ir3O8 has a spinel-like structure (space group Fd\\bar 3m) and composition [Na1/2Ir3/2](16d)[Na3/2](16c)O(32e)4. The critical order parameter which induces hypothetical phase transition has been stated. It is shown that the derived structure of Na4Ir3O8 is formed as a result of the displacements of Na, Ir and O atoms, and ordering of Na, Ir and O atoms, ordering dxy, dxz, dyz orbitals as well. Ordering of all atoms takes place according to the type 1:3. Ir and Na atoms form an intriguing atom order: a network of corner-shared Ir triangles called a hyper-kagome lattice. The Ir atoms form nanoclusters which are named decagons. The existence of hyper-kagome lattices in six types of ordered spinel structures is predicted theoretically. The structure mechanisms of the formation of the predicted hyper-kagome atom order in some ordered spinel phases are established. For a number of cases typical diagrams of possible crystal phase states are built in the framework of the Landau theory of phase transitions. Thermodynamical conditions of hyper-kagome order formation are discussed by means of these diagrams. The proposed theory is in accordance with experimental data.

  18. Short range ferromagnetic, magneto-electric, and magneto-dielectric effect in ceramic Co{sub 3}TeO{sub 6}

    SciTech Connect

    Singh, Harishchandra E-mail: singh85harish@rrcat.gov.in; Ghosh, Haranath; Chandrasekhar Rao, T. V.; Sharma, G.; Saha, J.; Patnaik, S.

    2016-01-28

    We report observation of magneto-electric and magneto-dielectric couplings along with short range ferromagnetic order in ceramic Cobalt Tellurate (Co{sub 3}TeO{sub 6}, CTO) using magnetic, structural, dielectric, pyroelectric, and polarization studies. DC magnetization along with dielectric constant measurements indicate a coupling between magnetic order and electrical polarization. A strong anomaly in the dielectric constant at ∼17.4 K in zero magnetic field indicates spontaneous electric polarization, consistent with a recent neutron diffraction study. Observation of weak short range ferromagnetic order at lower temperatures is attributed to the Griffiths-like ferromagnetism. Furthermore, magnetic field dependence of the ferroelectric transition follows earlier theoretical predictions, applicable to single crystal CTO. Finally, combined dielectric, pyroelectric, and polarization measurements suggest that the ground state of CTO may possess spontaneous symmetry breaking in the absence of magnetic field.

  19. Short range laser obstacle detector. [for surface vehicles using laser diode array

    NASA Technical Reports Server (NTRS)

    Kuriger, W. L. (Inventor)

    1973-01-01

    A short range obstacle detector for surface vehicles is described which utilizes an array of laser diodes. The diodes operate one at a time, with one diode for each adjacent azimuth sector. A vibrating mirror a short distance above the surface provides continuous scanning in elevation for all azimuth sectors. A diode laser is synchronized with the vibrating mirror to enable one diode laser to be fired, by pulses from a clock pulse source, a number of times during each elevation scan cycle. The time for a given pulse of light to be reflected from an obstacle and received is detected as a measure of range to the obstacle.

  20. Thermodynamic Identities and Symmetry Breaking in Short-Range Spin Glasses.

    PubMed

    Arguin, L-P; Newman, C M; Stein, D L

    2015-10-30

    We present a technique to generate relations connecting pure state weights, overlaps, and correlation functions in short-range spin glasses. These are obtained directly from the unperturbed Hamiltonian and hold for general coupling distributions. All are satisfied in phases with simple thermodynamic structure, such as the droplet-scaling and chaotic pairs pictures. If instead nontrivial mixed-state pictures hold, the relations suggest that replica symmetry is broken as described by a Derrida-Ruelle cascade, with pure state weights distributed as a Poisson-Dirichlet process.

  1. Thermodynamic Identities and Symmetry Breaking in Short-Range Spin Glasses

    NASA Astrophysics Data System (ADS)

    Arguin, L.-P.; Newman, C. M.; Stein, D. L.

    2015-10-01

    We present a technique to generate relations connecting pure state weights, overlaps, and correlation functions in short-range spin glasses. These are obtained directly from the unperturbed Hamiltonian and hold for general coupling distributions. All are satisfied in phases with simple thermodynamic structure, such as the droplet-scaling and chaotic pairs pictures. If instead nontrivial mixed-state pictures hold, the relations suggest that replica symmetry is broken as described by a Derrida-Ruelle cascade, with pure state weights distributed as a Poisson-Dirichlet process.

  2. Management challenges in a short-range low-velocity gunshot injury

    PubMed Central

    Arunkumar, K. V.; Kumar, Sanjeev; Aggarwal, Rajat; Dubey, Prajesh

    2012-01-01

    The use of firearms is becoming more prevalent in the society and hence the number of homicidal and suicidal cases. The severity of gunshot wounds varies depending on the weapons caliber and the distance of firing. Close-range, high-velocity gunshot wounds in the head and neck region can result in devastating esthetic and functional impairment. The complexity in facial skeletal anatomy cause multiple medical and surgical challenges to an operating surgeon, demanding elaborate soft and hard tissue reconstructions. Here we present the successful management of a patient shot by a low-velocity short-range pistol with basic life support measures, wound management, reconstruction, and rehabilitation. PMID:23482828

  3. Short Range Correlations in Nuclei at Large xbj through Inclusive Quasi-Elastic Electron Scattering

    SciTech Connect

    Ye, Zhihong

    2013-12-01

    The experiment, E08-014, in Hall-A at Jefferson Lab aims to study the short-range correlations (SRC) which are necessary to explain the nuclear strength absent in the mean field theory. The cross sections for 2H, 3He, 4He, 12C, 40Ca and 48Ca, were measured via inclusive quasi-elastic electron scattering from these nuclei in a Q2 range between 0.8 and 2.8 (GeV/c)2 for x>1. The cross section ratios of heavy nuclei to 2H were extracted to study two-nucleon SRC for 1

  4. Vapor-liquid surface tension of strong short-range Yukawa fluid.

    PubMed

    Odriozola, G; Bárcenas, M; Orea, P

    2011-04-21

    The thermodynamic properties of strong short-range attractive Yukawa fluids, κ = 10, 9, 8, and 7, are determined by combining the slab technique with the standard and the replica exchange Monte Carlo (REMC) methods. A good agreement was found among the coexistence curves of these systems calculated by REMC and those previously reported in the literature. However, REMC allows exploring the coexistence at lower temperatures, where dynamics turns glassy. To obtain the surface tension we employed, for both methods, a procedure that yields the pressure tensor components for discontinuous potentials. The surface tension results obtained by the standard MC and REMC techniques are in good agreement.

  5. Fluids with short-range attractions and longer-range repulsions

    NASA Astrophysics Data System (ADS)

    Truskett, Thomas

    2015-03-01

    Many complex fluids comprise particles with effective interactions that include short-range attractions and longer-range repulsions. In this talk, I explore--using a simple theoretical model--what behaviors one should expect to find in such systems, including the possibility of equilibrium ``cluster'' formation and its associated implications for dynamics near structural arrest. I also discuss how one might predict the onset of cluster formation from the static structure factor. Finally, some implications for concentrated liquid formulations of therapeutic proteins are addressed. Partial support from The Welch Foundation and the Gulf of Mexico Research Initiative.

  6. Interplay between spinodal decomposition and glass formation in proteins exhibiting short-range attractions.

    PubMed

    Cardinaux, Frédéric; Gibaud, Thomas; Stradner, Anna; Schurtenberger, Peter

    2007-09-14

    We investigate the competition between spinodal decomposition and dynamical arrest using aqueous solutions of the globular protein lysozyme as a model system for colloids with short-range attractions. We show that quenches below a temperature Ta lead to gel formation as a result of a local arrest of the protein-dense phase during spinodal decomposition. The rheological properties of these gels allow us to use centrifugation experiments to determine the local densities of both phases and to precisely locate the gel boundary and the attractive glass line close to and within the unstable region of the phase diagram.

  7. Magnitude of the prewetting boundary tension near wetting for short-range forces

    NASA Astrophysics Data System (ADS)

    Varea, C.; Robledo, A.

    1993-05-01

    We determine in a mean field approximation the spin-1/2 Ising model line tension τ along the boundary between surface states at the prewetting transition in the neighborhood of the wetting transition at bulk phase coexistence. We find very close agreement with the predictions of the interface displacement model for short-range interactions, i.e., τ increases (with a square-root dependence on the bulk external field h) towards a finite limit with diverging slope at wetting. Our findings help both in settling the discussion on the limiting value of τ and in understanding the origin of its singular behavior.

  8. Management challenges in a short-range low-velocity gunshot injury.

    PubMed

    Arunkumar, K V; Kumar, Sanjeev; Aggarwal, Rajat; Dubey, Prajesh

    2012-07-01

    The use of firearms is becoming more prevalent in the society and hence the number of homicidal and suicidal cases. The severity of gunshot wounds varies depending on the weapons caliber and the distance of firing. Close-range, high-velocity gunshot wounds in the head and neck region can result in devastating esthetic and functional impairment. The complexity in facial skeletal anatomy cause multiple medical and surgical challenges to an operating surgeon, demanding elaborate soft and hard tissue reconstructions. Here we present the successful management of a patient shot by a low-velocity short-range pistol with basic life support measures, wound management, reconstruction, and rehabilitation.

  9. The past, present, and anticipated future contributions of geosynchronous satellites to short range prediction

    NASA Technical Reports Server (NTRS)

    Shenk, W. E.; Schmidt, H. L.

    1984-01-01

    Use of geosynchronous satellites to improve the short range prediction of convective and mesoscale phenomena by measuring cloud parameters; surface temperature; and temperature and moisture profiles and gradients (in clear and partly cloudy areas) with temporal resolutions of minutes, and spatial scales ranging from 1 km (for clouds) to tens to kilometers (temperature and moisture profiles) is discussed. Improvements can be made with microwave sounding (temperature and moisture profiles in cloudy areas) and imaging (precipitation). Higher spectral resolution infrared sounding yields a 50% better vertical resolution for temperature and moisture profiles. Very high resolution imaging (infrared resolution of 1 km, visible resolution of 200 m) is advocated for convection monitoring.

  10. Short-range optical air data measurements for aircraft control using rotational Raman backscatter.

    PubMed

    Fraczek, Michael; Behrendt, Andreas; Schmitt, Nikolaus

    2013-07-15

    A first laboratory prototype of a novel concept for a short-range optical air data system for aircraft control and safety was built. The measurement methodology was introduced in [Appl. Opt. 51, 148 (2012)] and is based on techniques known from lidar detecting elastic and Raman backscatter from air. A wide range of flight-critical parameters, such as air temperature, molecular number density and pressure can be measured as well as data on atmospheric particles and humidity can be collected. In this paper, the experimental measurement performance achieved with the first laboratory prototype using 532 nm laser radiation of a pulse energy of 118 mJ is presented. Systematic measurement errors and statistical measurement uncertainties are quantified separately. The typical systematic temperature, density and pressure measurement errors obtained from the mean of 1000 averaged signal pulses are small amounting to < 0.22 K, < 0.36% and < 0.31%, respectively, for measurements at air pressures varying from 200 hPa to 950 hPa but constant air temperature of 298.95 K. The systematic measurement errors at air temperatures varying from 238 K to 308 K but constant air pressure of 946 hPa are even smaller and < 0.05 K, < 0.07% and < 0.06%, respectively. A focus is put on the system performance at different virtual flight altitudes as a function of the laser pulse energy. The virtual flight altitudes are precisely generated with a custom-made atmospheric simulation chamber system. In this context, minimum laser pulse energies and pulse numbers are experimentally determined, which are required using the measurement system, in order to meet measurement error demands for temperature and pressure specified in aviation standards. The aviation error margins limit the allowable temperature errors to 1.5 K for all measurement altitudes and the pressure errors to 0.1% for 0 m and 0.5% for 13000 m. With regard to 100-pulse-averaged temperature measurements, the pulse energy using 532 nm

  11. Rotational excitation of symmetric top molecules by collisions with atoms. II - Infinite order sudden approximation

    NASA Technical Reports Server (NTRS)

    Green, S.

    1979-01-01

    The infinite order sudden (IOS) approximation is extended to rotational excitation of symmetric tops by collisions with atoms. After development of a formalism for 'primitive' or 'one-ended' tops, proper parity-adapted linear combinations describing real rotors are considered and modifications needed for asymmetric rigid rotors are noted. The generalized spectroscopic relaxation cross sections are discussed. IOS calculations for NH3-He and H2CO-He are performed and compared with more accurate calculations, and the IOS approximation is found to provide a reasonably accurate description.

  12. Self-ordered nanoporous lattice formed by chlorine atoms on Au(111)

    NASA Astrophysics Data System (ADS)

    Cherkez, V. V.; Zheltov, V. V.; Didiot, C.; Kierren, B.; Fagot-Revurat, Y.; Malterre, D.; Andryushechkin, B. V.; Zhidomirov, G. M.; Eltsov, K. N.

    2016-01-01

    A self-ordered nanoporous lattice formed by individual chlorine atoms on the Au(111) surface has been studied with low-temperature scanning tunneling microscopy, low-energy electron diffraction, and density functional theory calculations. We have found out that room-temperature adsorption of 0.09-0.30 monolayers of chlorine on Au(111) followed by cooling below 110 K results in the spontaneous formation of a nanoporous quasihexagonal structure with a periodicity of 25-38 Å depending on the initial chlorine coverage. The driving force of the superstructure formation is attributed to the substrate-mediated elastic interaction.

  13. An all-atom simulation study of the ordering of liquid squalane near a solid surface

    NASA Astrophysics Data System (ADS)

    Tsige, Mesfin; Patnaik, Soumya S.

    2008-05-01

    An all-atom molecular dynamics study using the OPLS force field has been carried out to obtain new insights in to the orientation and ordering of liquid squalane near a solid surface. As observed in previous experiments, the squalane molecules closest to a SiO 2 substrate are found to be tightly bound with their molecular axis preferentially parallel to the interface. Unlike linear alkanes, the squalane molecules are also found to lie preferentially parallel to the liquid/vapor interface. The simulation results predict that the molecular plane orientation of the squalane molecules changes from mainly parallel to perpendicular to the substrate in going further away from the substrate.

  14. A third-order mode high frequency biosensor with atomic resolution.

    PubMed

    Cai, Hua-Lin; Yang, Yi; Chen, Xiao; Mohammad, Mohammad Ali; Ye, Tian-Xiang; Guo, Cang-Ran; Yi, Li-Ting; Zhou, Chang-Jian; Liu, Jing; Ren, Tian-Ling

    2015-09-15

    An atomic resolution ultra-high sensitivity surface acoustic wave (SAW) biosensor for DNA sequences and cells detection is proposed. Interdigitated transducers (IDTs) fabricated on LiNbO3 substrate achieve a high quality factor (Q) of over 4000 at a frequency of 6.4 GHz (third-order harmonic mode) using an optimized design and process. The biosensor shows excellent linear responses to target DNA in the range from 1 μg/ml to 1 ng/ml with a high sensitivity of 6.7 × 10(-16)g/cm(2)/Hz, hence the difference of a single hybridized DNA base can also be distinguished. With such a high mass resolution, the biosensor is capable of quantitative detection of living cancer cells. The frequency responses of single mouse mammary adenocarcinoma (EMT6) cell and mouse fibroblast (3T3) cell are studied. The interferences in the experiments show insignificant influence on the frequency shift, which verifies the high selectivity of the biosensor. The biosensor is also able to repeat the sensing ability after rough cleaning, therefore cost reduction is achieved from the recycling process in practical applications. The detection limit is defined from the noise analysis of the device, atomic resolution is realized according to the calculation, thereby initiating a potential tool for high-precision medical diagnoses and phenomena observation at the atomic-level. Copyright © 2015. Published by Elsevier B.V.

  15. Aggregation of heteropolyanions in aqueous solutions exhibiting short-range attractions and long-range repulsions

    DOE PAGES

    Bera, Mrinal K.; Qiao, Baofu; Seifert, Soenke; ...

    2015-12-15

    Charged colloids and proteins in aqueous solutions interact via short-range attractions and long-range repulsions (SALR) and exhibit complex structural phases. These include homogeneously dispersed monomers, percolated monomers, clusters, and percolated clusters. We report the structural architectures of simple charged systems in the form of spherical, Keggin-type heteropolyanions (HPAs) by small-angle X-ray scattering (SAXS) and molecular dynamics (MD) simulations. Structure factors obtained from the SAXS measurements show that the HPAs interact via SALR. Concentration and temperature dependences of the structure factors for HPAs with –3e (e is the charge of an electron) charge are consistent with a mixture of nonassociated monomersmore » and associated randomly percolated monomers, whereas those for HPAs with –4e and –5e charges exhibit only nonassociated monomers in aqueous solutions. Our experiments show that the increase in magnitude of the charge of the HPAs increases their repulsive interactions and inhibits their aggregation in aqueous solutions. MD simulations were done to reveal the atomistic scale origins of SALR between HPAs. As a result, the short-range attractions result from water or proton-mediated hydrogen bonds between neighboring HPAs, whereas the long-range repulsions are due to the distributions of ions surrounding the HPAs.« less

  16. Aggregation of heteropolyanions in aqueous solutions exhibiting short-range attractions and long-range repulsions

    SciTech Connect

    Bera, Mrinal K.; Qiao, Baofu; Seifert, Soenke; Burton-Pye, Benjamin P.; Monica Olvera de la Cruz; Antonio, Mark R.

    2015-12-15

    Charged colloids and proteins in aqueous solutions interact via short-range attractions and long-range repulsions (SALR) and exhibit complex structural phases. These include homogeneously dispersed monomers, percolated monomers, clusters, and percolated clusters. We report the structural architectures of simple charged systems in the form of spherical, Keggin-type heteropolyanions (HPAs) by small-angle X-ray scattering (SAXS) and molecular dynamics (MD) simulations. Structure factors obtained from the SAXS measurements show that the HPAs interact via SALR. Concentration and temperature dependences of the structure factors for HPAs with –3e (e is the charge of an electron) charge are consistent with a mixture of nonassociated monomers and associated randomly percolated monomers, whereas those for HPAs with –4e and –5e charges exhibit only nonassociated monomers in aqueous solutions. Our experiments show that the increase in magnitude of the charge of the HPAs increases their repulsive interactions and inhibits their aggregation in aqueous solutions. MD simulations were done to reveal the atomistic scale origins of SALR between HPAs. As a result, the short-range attractions result from water or proton-mediated hydrogen bonds between neighboring HPAs, whereas the long-range repulsions are due to the distributions of ions surrounding the HPAs.

  17. Gelation and glass transition of particles with short-range attraction induced by adsorbing microgel

    NASA Astrophysics Data System (ADS)

    Yuan, Guangcui; Luo, Junhua; Han, Charles C.

    2015-03-01

    Mixed suspensions of large hard polystyrene microsphere and small poly(N-isopropylacrylamide) microgel is used as model systems to investigate the static and viscoelastic properties of suspensions which go through liquid to gel and to glass transitions. The microgels cause short-range attraction between microspheres through bridging and depletion mechanism whose strength can be tuned by the microgel concentration. Baxter's sticky hard-sphere model is used to extract the effective inter-microsphere interaction introduced by bridging or depletion of microgels despite the fact that the physical mechanisms of bridging attraction and depletion attraction are different at a molecular level. A new state diagram of gelation and even of glass transition was constructed by taking the bridges as a short-ranged attractive interaction With the help of the well-defined bridging bonds, some controversies regarding to the interference between two origins for ergodic to\\ non-ergodic transition in condensed system, i.e. cage effect and bond effect, were clarified. This work is supported by the National Basic Research Program of China (973 Program, 2012CB821503).

  18. Passive FOG IMU for short-range missile application: from qualification toward series production

    NASA Astrophysics Data System (ADS)

    Trommer, Gert F.; Mueller, R.; Opitz, S.

    1996-11-01

    An inertial measurement unit (IMU) with angular rate, angular increment and linear acceleration measurement systems for short range missile application is described. It consists of a three axis fiber optic gyroscope (FOG) cluster, three linear vibrating beam accelerometers and an electronics device for signal evaluation and data transmission via a serial transputer link. The FOG cluster is realized by means of a passive all-fiber open loop configuration. Due to the inherent optical phase shift of 3 by 3 couplers, completely passive operation near the quadrature point is achieved without the need for a non- reciprocal optical phase modulation in the fiber loop. Basing on that concept more than 50 rugged IMUs have been built for implementation into a short range air to air missile. Verification tests for flight clearance with stresses simulating air carriage and missile free flight environments have been computed. The operation under extreme vibration and shock environments without the use of vibration isolator fixings due to very tight requirements on data time delay has been demonstrated. The first telemetered missile firings have been performed successfully. The line- setup for large quantity series production is progressing. The implementation of the workstations for the integration of the IMU is finished. The production equipment for calibration and acceptance testing of IMUs in parallel allowing for a rate of more than 150 unit per month has been installed and will be operational in autumn this year.

  19. Implementing molecular dynamics on hybrid high performance computers - short range forces

    NASA Astrophysics Data System (ADS)

    Brown, W. Michael; Wang, Peng; Plimpton, Steven J.; Tharrington, Arnold N.

    2011-04-01

    The use of accelerators such as graphics processing units (GPUs) has become popular in scientific computing applications due to their low cost, impressive floating-point capabilities, high memory bandwidth, and low electrical power requirements. Hybrid high-performance computers, machines with more than one type of floating-point processor, are now becoming more prevalent due to these advantages. In this work, we discuss several important issues in porting a large molecular dynamics code for use on parallel hybrid machines - (1) choosing a hybrid parallel decomposition that works on central processing units (CPUs) with distributed memory and accelerator cores with shared memory, (2) minimizing the amount of code that must be ported for efficient acceleration, (3) utilizing the available processing power from both multi-core CPUs and accelerators, and (4) choosing a programming model for acceleration. We present our solution to each of these issues for short-range force calculation in the molecular dynamics package LAMMPS, however, the methods can be applied in many molecular dynamics codes. Specifically, we describe algorithms for efficient short range force calculation on hybrid high-performance machines. We describe an approach for dynamic load balancing of work between CPU and accelerator cores. We describe the Geryon library that allows a single code to compile with both CUDA and OpenCL for use on a variety of accelerators. Finally, we present results on a parallel test cluster containing 32 Fermi GPUs and 180 CPU cores.

  20. Effect of atomic order on the martensitic and magnetic transformations in Ni-Mn-Ga ferromagnetic shape memory alloys.

    PubMed

    Sánchez-Alarcos, V; Pérez-Landazábal, J I; Recarte, V; Rodríguez-Velamazán, J A; Chernenko, V A

    2010-04-28

    The influence of long-range L2(1) atomic order on the martensitic and magnetic transformations of Ni-Mn-Ga shape memory alloys has been investigated. In order to correlate the structural and magnetic transformation temperatures with the atomic order, calorimetric, magnetic and neutron diffraction measurements have been performed on polycrystalline and single-crystalline alloys subjected to different thermal treatments. It is found that both transformation temperatures increase with increasing atomic order, showing exactly the same linear dependence on the degree of L2(1) atomic order. A quantitative correlation between atomic order and transformation temperatures has been established, from which the effect of atomic order on the relative stability between the structural phases has been quantified. On the other hand, the kinetics of the post-quench ordering process taking place in these alloys has been studied. It is shown that the activation energy of the ordering process agrees quite well with the activation energy of the Mn self-diffusion process.

  1. 77 FR 55466 - Environmental Impact Statement for Short Range-Projects and Update of the Real Property Master...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-10

    ... currently programmed for construction in fiscal years 2013- 2017. These projects include new office... Department of the Army Environmental Impact Statement for Short Range-Projects and Update of the Real... proposed short-range improvement projects and the proposed update of the Real Property Master Plan (RPMP...

  2. Atomic study on the ordered structure in Al melts induced by liquid/substrate interface with Ti solute

    SciTech Connect

    Zhang, H. L.; Han, Y. F. E-mail: bdsun@sjtu.edu.cn; Zhou, W.; Dai, Y. B.; Wang, J.; Sun, B. D. E-mail: bdsun@sjtu.edu.cn

    2015-01-26

    Atomic ordering in Al melts induced by liquid/substrate interface with Ti solute was investigated by ab initio molecular dynamics simulations and in-situ synchrotron X-ray diffraction. It is predicted that deformed nanoscale ordering Al layers with a rhombohedral-centered hexagonal structure (R3{sup ¯}m space group) instead of the intrinsic fcc structure (Fm3{sup ¯}m space group) form on substrate at temperature above Al liquids. With Al atoms stacking away from the interface, the ordering structure reaches a critical thickness, which inhibits the consecutive stacking of Al atoms on substrates. The locally stacking reconstruction induced by Ti atom relieves the accumulated elastic strain energy in ordered Al layers, facilitating fully heterogeneous nucleation on substrate beyond the deformed ordering Al layer around the melting point. The roles of liquid/substrate interface with Ti solute in the physical behavior of heterogeneous nucleation on substrate were discussed.

  3. Atomic self-ordering in a ring cavity with counterpropagating pump fields

    NASA Astrophysics Data System (ADS)

    Ostermann, S.; Grießer, T.; Ritsch, H.

    2015-02-01

    The collective dynamics of mobile scatterers and light in optical resonators generates complex behaviour. For strong transverse illumination a phase transition from homogeneous to crystalline particle order appears. In contrast, cold particles inside a single-side pumped ring cavity exhibit an instability towards bunching and collective acceleration called collective atomic recoil lasing (CARL). We demonstrate that by driving two orthogonally polarized counterpropagating modes of a ring resonator one realises both cases within one system. As a function of the two pump intensities the corresponding phase diagram exhibits regions in which either a generalized form of self-ordering towards a travelling density wave with constant centre-of-mass velocity or a CARL instability is formed. Time-dependent control of the cavity driving then allows to accelerate or slow down and trap a sufficiently dense beam of linearly polarizable particles.

  4. Universal relationships for the phonon spectra in BCC, FCC, and HCP crystals with a short-range interatomic interaction

    SciTech Connect

    Vaks, V. G. Zhuravlev, I. A.; Zabolotskii, A. D.

    2012-03-15

    The frequencies of the phonon branches that correspond to the vibrations of the close-packed atomic planes in bcc, fcc, and hcp crystals with short-range interatomic interaction are shown to be described by a universal relationship, which only contains two parameters for each branch, for any polarization {lambda}. These phonon branches correspond to the ({xi}, {xi}, 0) direction in bcc crystals, the ({xi}, {xi}, {xi}) direction in fcc crystals, and the (0, 0, {xi}) direction in hcp crystals. This universal relationship can only be violated by long-range interactions, namely, the interactions outside the sixth coordination shell in a bcc crystal, the fifth coordination shell in an fcc crystal, and the eleventh or tenth coordination shell in an hcp crystal. The effect of these long-range interactions for each phonon branch can be quantitatively characterized by certain parameters {Delta}{sub n{lambda}}, which are simply expressed in terms of the frequencies of three phonons of the branch. The values of these parameters are presented for all bcc, fcc, and hcp metals whose phonon spectra are measured. In most cases, the proposed relationships for the frequencies are found to be fulfilled accurate to several percent. In the cases where the {Delta}{sub n{lambda}} parameters are not small, they can give substantial information on the type and scale of long-range interaction effects in various metals.

  5. Short range shooting distance estimation using variable pressure SEM images of the surroundings of bullet holes in textiles.

    PubMed

    Hinrichs, Ruth; Frank, Paulo Ricardo Ost; Vasconcellos, M A Z

    2017-03-01

    Modifications of cotton and polyester textiles due to shots fired at short range were analyzed with a variable pressure scanning electron microscope (VP-SEM). Different mechanisms of fiber rupture as a function of fiber type and shooting distance were detected, namely fusing, melting, scorching, and mechanical breakage. To estimate the firing distance, the approximately exponential decay of GSR coverage as a function of radial distance from the entrance hole was determined from image analysis, instead of relying on chemical analysis with EDX, which is problematic in the VP-SEM. A set of backscattered electron images, with sufficient magnification to discriminate micrometer wide GSR particles, was acquired at different radial distances from the entrance hole. The atomic number contrast between the GSR particles and the organic fibers allowed to find a robust procedure to segment the micrographs into binary images, in which the white pixel count was attributed to GSR coverage. The decrease of the white pixel count followed an exponential decay, and it was found that the reciprocal of the decay constant, obtained from the least-square fitting of the coverage data, showed a linear dependence on the shooting distance.

  6. Higher-order C{sub n} dispersion coefficients for the alkali-metal atoms

    SciTech Connect

    Mitroy, J.; Bromley, M.W.J.

    2005-04-01

    The van der Waals coefficients, from C{sub 11} through to C{sub 16} resulting from second-, third-, and fourth-order perturbation theory are estimated for the alkali-metal (Li, Na, K, and Rb) atoms. The dispersion coefficients are also computed for all possible combinations of the alkali-metal atoms and hydrogen. The parameters are determined from sum rules after diagonalizing a semiempirical fixed core Hamiltonian in a large basis. Comparisons of the radial dependence of the C{sub n}/r{sup n} potentials give guidance as to the radial regions in which the various higher-order terms can be neglected. It is seen that including terms up to C{sub 10}/r{sup 10} results in a dispersion interaction that is accurate to better than 1% whenever the inter-nuclear spacing is larger than 20a{sub 0}. This level of accuracy is mainly achieved due to the fortuitous cancellation between the repulsive (C{sub 11},C{sub 13},C{sub 15}) and attractive (C{sub 12},C{sub 14},C{sub 16}) dispersion forces.

  7. Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface

    NASA Astrophysics Data System (ADS)

    Li, Gang; Höpfner, Philipp; Schäfer, Jörg; Blumenstein, Christian; Meyer, Sebastian; Bostwick, Aaron; Rotenberg, Eli; Claessen, Ralph; Hanke, Werner

    2013-03-01

    Two-dimensional electron systems, as exploited for device applications, can lose their conducting properties because of local Coulomb repulsion, leading to a Mott-insulating state. In triangular geometries, any concomitant antiferromagnetic spin ordering can be prevented by geometric frustration, spurring speculations about ‘melted’ phases, known as spin liquid. Here we show that for a realization of a triangular electron system by epitaxial atom adsorption on a semiconductor, such spin disorder, however, does not appear. Our study compares the electron excitation spectra obtained from theoretical simulations of the correlated electron lattice with data from high-resolution photoemission. We find that an unusual row-wise antiferromagnetic spin alignment occurs that is reflected in the photoemission spectra as characteristic ‘shadow bands’ induced by the spin pattern. The magnetic order in a frustrated lattice of otherwise non-magnetic components emerges from longer-range electron hopping between the atoms. This finding can offer new ways of controlling magnetism on surfaces.

  8. Transitions from order to disorder in multiple dark and multiple dark-bright soliton atomic clouds

    SciTech Connect

    Wang, Wenlong; Kevrekidis, P. G.

    2015-03-09

    We have performed a systematic study quantifying the variation of solitary wave behavior from that of an ordered cloud resembling a “crystalline” configuration to that of a disordered state that can be characterized as a soliton “gas.” As our illustrative examples, we use both one-component, as well as two-component, one-dimensional atomic gases very close to zero temperature, where in the presence of repulsive interatomic interactions and of a parabolic trap, a cloud of dark (dark-bright) solitons can form in the one- (two-) component system. We corroborate our findings through three distinct types of approaches, namely a Gross-Pitaevskii type of partial differential equation, particle-based ordinary differential equations describing the soliton dynamical system, and Monte Carlo simulations for the particle system. In addition, we define an “empirical” order parameter to characterize the order of the soliton lattices and study how this changes as a function of the strength of the “thermally” (i.e., kinetically) induced perturbations. As may be anticipated by the one-dimensional nature of our system, the transition from order to disorder is gradual without, apparently, a genuine phase transition ensuing in the intermediate regime.

  9. The influence of atomic ordering on strain relaxation during the growth of metamorphic solar cells

    NASA Astrophysics Data System (ADS)

    Norman, A. G.; France, R. M.; McMahon, W. E.; Geisz, J. F.; Romero, M. J.

    2013-11-01

    The occurrence of single variant CuPtB ordering during growth of InGaP graded buffer layer structures on offcut (001) GaAs substrates for inverted metamorphic solar cells is found to have a strong influence on strain relaxation mechanisms. Since the surface-induced CuPtB ordering is metastable in the bulk of the material, a strong preference is observed for the nucleation and glide of 60° type misfit dislocations with Burgers vectors that introduce an antiphase boundary into the ordered structure. This results in an overall epitaxial layer tilt in the opposite sense to that normally observed for the direction of substrate offcut. Furthermore, in InGaP buffer layers graded to InP, a switch in the dislocation glide plane preference back to that normally observed for the direction of substrate offcut is observed as the degree of atomic ordering falls below a critical value. This results in the nucleation and glide of new misfit dislocations resulting in an increase in the threading dislocation density that is found to have a deleterious effect on device efficiency. Understanding the materials science behind this behavior will enable the engineering of more effective, lower threading dislocation density strain relief buffer layers resulting in improved performance of subsequently grown devices.

  10. Transitions from order to disorder in multiple dark and multiple dark-bright soliton atomic clouds

    DOE PAGES

    Wang, Wenlong; Kevrekidis, P. G.

    2015-03-09

    We have performed a systematic study quantifying the variation of solitary wave behavior from that of an ordered cloud resembling a “crystalline” configuration to that of a disordered state that can be characterized as a soliton “gas.” As our illustrative examples, we use both one-component, as well as two-component, one-dimensional atomic gases very close to zero temperature, where in the presence of repulsive interatomic interactions and of a parabolic trap, a cloud of dark (dark-bright) solitons can form in the one- (two-) component system. We corroborate our findings through three distinct types of approaches, namely a Gross-Pitaevskii type of partialmore » differential equation, particle-based ordinary differential equations describing the soliton dynamical system, and Monte Carlo simulations for the particle system. In addition, we define an “empirical” order parameter to characterize the order of the soliton lattices and study how this changes as a function of the strength of the “thermally” (i.e., kinetically) induced perturbations. As may be anticipated by the one-dimensional nature of our system, the transition from order to disorder is gradual without, apparently, a genuine phase transition ensuing in the intermediate regime.« less

  11. Control of Adult Neurogenesis by Short-Range Morphogenic-Signaling Molecules.

    PubMed

    Choe, Youngshik; Pleasure, Samuel J; Mira, Helena

    2015-12-04

    Adult neurogenesis is dynamically regulated by a tangled web of local signals emanating from the neural stem cell (NSC) microenvironment. Both soluble and membrane-bound niche factors have been identified as determinants of adult neurogenesis, including morphogens. Here, we review our current understanding of the role and mechanisms of short-range morphogen ligands from the Wnt, Notch, Sonic hedgehog, and bone morphogenetic protein (BMP) families in the regulation of adult neurogenesis. These morphogens are ideally suited to fine-tune stem-cell behavior, progenitor expansion, and differentiation, thereby influencing all stages of the neurogenesis process. We discuss cross talk between their signaling pathways and highlight findings of embryonic development that provide a relevant context for understanding neurogenesis in the adult brain. We also review emerging examples showing that the web of morphogens is in fact tightly linked to the regulation of neurogenesis by diverse physiologic processes.

  12. Diffusion of electrons scattered by short-range impurities in a quantizing magnetic field

    SciTech Connect

    Andreev, S. P. Pavlova, T. V.

    2008-04-15

    Formulas for transverse diffusion and conductivity in a semiconductor are obtained for electrons scattered by neutral impurities in a quantizing magnetic field. The formulas are valid for an impurity potential of arbitrary depth. Based on Kubo's theory, calculations are performed using electron wavefunctions of the problem of single-impurity scattering in a magnetic field. The poles of the scattering amplitude correctly determine electron eigenstates and magnetic impurity states. As a result, an exact expression is found for the dependence of transverse diffusion coefficient D{sub perpendicular} on longitudinal electron energy {epsilon} due to scattering by short-range (neutral) impurities. The behavior of D{sub perpendicular} ({epsilon}) is examined over an interval of magnetic field strength for several values of impurity potential depth. The experimental observability of diffusion and conductivity using IR lasers is discussed.

  13. Short-ranged attractions in jammed liquids: how cooling can melt a glass.

    PubMed

    Geissler, Phillip L; Reichman, David R

    2005-03-01

    We demonstrate that an extended picture of kinetic constraints in glass-forming liquids is sufficient to explain dynamic anomalies observed in dense suspensions of strongly attracting colloidal particles. We augment a simple model of heterogeneous relaxation with static attractions between facilitating excitations, in a way that mimics the structural effect of short-ranged interparticle attractions. The resulting spatial correlations among facilitated and unfacilitated regions give rise to relaxation mechanisms that account for nonmonotonic dependence of relaxation times on attraction strength as well as logarithmic decay of density correlations in time. These unusual features are a simple consequence of spatial segregation of kinetic constraints, suggesting an alternative physical perspective on attractive colloids than that suggested by mode-coupling theory. Based on the behavior of our model, we predict a crossover from super-Arrhenius to Arrhenius temperature dependence as attractions become dominant at fixed packing fraction.

  14. Extended law of corresponding states in short-range square wells: a potential energy landscape study.

    PubMed

    Foffi, Giuseppe; Sciortino, Francesco

    2006-11-01

    We study the statistical properties of the potential energy landscape of a system of particles interacting via a very short-range square-well potential (of depth -u0) as a function of the range of attraction Delta to provide thermodynamic insights of the Noro and Frenkel [M. G. Noro and D. Frenkel, J. Chem. Phys. 113, 2941 (2000)] scaling. We exactly evaluate the basin free energy and show that it can be separated into a vibrational (Delta dependent) and a floppy (Delta independent) component. We also show that the partition function is a function of Deltaebetauo, explaining the equivalence of the thermodynamics for systems characterized by the same second virial coefficient. An outcome of our approach is the possibility of counting the number of floppy modes (and their entropy).

  15. Three-body problem with short-range forces: Renormalized equations and regulator-independent results

    NASA Astrophysics Data System (ADS)

    Afnan, I. R.; Phillips, Daniel R.

    2004-03-01

    We discuss effective field theory treatments of the problem of three particles interacting via short-range forces. One case of such a system is neutron-deuteron (nd) scattering at low energies. We demonstrate that in attractive channels the renormalization-group evolution of the 1+2 scattering amplitude may be complicated by the presence of eigenvalues greater than unity in the kernel. We also show that these eigenvalues can be removed from the kernel by one subtraction, resulting in an equation which is renormalization-group invariant. A unique solution for 1+2 scattering phase shifts is then obtained. We give an explicit demonstration of our procedure for both the case of three spinless bosons and the case of the doublet channel in nd scattering. After the contribution of the two-body effective range is included in the effective field theory, it gives a good description of the nd doublet phase shifts below deuteron breakup threshold.

  16. Controlling Short-Range Interactions by Tuning Surface Chemistry in HDPE/Graphene Nanoribbon Nanocomposites.

    PubMed

    Sadeghi, Soheil; Zehtab Yazdi, Alireza; Sundararaj, Uttandaraman

    2015-09-03

    Unique dispersion states of nanoparticles in polymeric matrices have the potential to create composites with enhanced mechanical, thermal, and electrical properties. The present work aims to determine the state of dispersion from the melt-state rheological behavior of nanocomposites based on carbon nanotube and graphene nanoribbon (GNR) nanomaterials. GNRs were synthesized from nitrogen-doped carbon nanotubes via a chemical route using potassium permanganate and some second acids. High-density polyethylene (HDPE)/GNR nanocomposite samples were then prepared through a solution mixing procedure. Different nanocomposite dispersion states were achieved using different GNR synthesis methods providing different surface chemistry, interparticle interactions, and internal compartments. Prolonged relaxation of flow induced molecular orientation was observed due to the presence of both carbon nanotubes and GNRs. Based on the results of this work, due to relatively weak interactions between the polymer and the nanofillers, it is expected that short-range interactions between nanofillers play the key role in the final dispersion state.

  17. Broadband short-range surface plasmon structures for absorption enhancement in organic photovoltaics.

    PubMed

    Bai, Wenli; Gan, Qiaoqiang; Song, Guofeng; Chen, Lianghui; Kafafi, Zakya; Bartoli, Filbert

    2010-11-08

    We theoretically demonstrate a polarization-independent nanopatterned ultra-thin metallic structure supporting short-range surface plasmon polariton (SRSPP) modes to improve the performance of organic solar cells. The physical mechanism and the mode distribution of the SRSPP excited in the cell device were analyzed, and reveal that the SRSPP-assisted broadband absorption enhancement peak could be tuned by tailoring the parameters of the nanopatterned metallic structure. Three-dimensional finite-difference time domain calculations show that this plasmonic structure can enhance the optical absorption of polymer-based photovoltaics by 39% to 112%, depending on the nature of the active layer (corresponding to an enhancement in short-circuit current density by 47% to 130%). These results are promising for the design of organic photovoltaics with enhanced performance.

  18. Measurement of two- and three-nucleon short-range correlation probabilities in nuclei.

    PubMed

    Egiyan, K S; Dashyan, N B; Sargsian, M M; Strikman, M I; Weinstein, L B; Adams, G; Ambrozewicz, P; Anghinolfi, M; Asavapibhop, B; Asryan, G; Avakian, H; Baghdasaryan, H; Baillie, N; Ball, J P; Baltzell, N A; Batourine, V; Battaglieri, M; Bedlinskiy, I; Bektasoglu, M; Bellis, M; Benmouna, N; Biselli, A S; Bonner, B E; Bouchigny, S; Boiarinov, S; Bradford, R; Branford, D; Brooks, W K; Bültmann, S; Burkert, V D; Bultuceanu, C; Calarco, J R; Careccia, S L; Carman, D S; Carnahan, B; Chen, S; Cole, P L; Coltharp, P; Corvisiero, P; Crabb, D; Crannell, H; Cummings, J P; De Sanctis, E; DeVita, R; Degtyarenko, P V; Denizli, H; Dennis, L; Dharmawardane, K V; Djalali, C; Dodge, G E; Donnelly, J; Doughty, D; Dragovitsch, P; Dugger, M; Dytman, S; Dzyubak, O P; Egiyan, H; Elouadrhiri, L; Empl, A; Eugenio, P; Fatemi, R; Fedotov, G; Feuerbach, R J; Forest, T A; Funsten, H; Gavalian, G; Gevorgyan, N G; Gilfoyle, G P; Giovanetti, K L; Girod, F X; Goetz, J T; Golovatch, E; Gothe, R W; Griffioen, K A; Guidal, M; Guillo, M; Guler, N; Guo, L; Gyurjyan, V; Hadjidakis, C; Hardie, J; Hersman, F W; Hicks, K; Hleiqawi, I; Holtrop, M; Hu, J; Huertas, M; Hyde-Wright, C E; Ilieva, Y; Ireland, D G; Ishkhanov, B S; Ito, M M; Jenkins, D; Jo, H S; Joo, K; Juengst, H G; Kellie, J D; Khandaker, M; Kim, K Y; Kim, K; Kim, W; Klein, A; Klein, F J; Klimenko, A; Klusman, M; Kramer, L H; Kubarovsky, V; Kuhn, J; Kuhn, S E; Kuleshov, S; Lachniet, J; Laget, J M; Langheinrich, J; Lawrence, D; Lee, T; Livingston, K; Maximon, L C; McAleer, S; McKinnon, B; McNabb, J W C; Mecking, B A; Mestayer, M D; Meyer, C A; Mibe, T; Mikhailov, K; Minehart, R; Mirazita, M; Miskimen, R; Mokeev, V; Morrow, S A; Mueller, J; Mutchler, G S; Nadel-Turonski, P; Napolitano, J; Nasseripour, R; Niccolai, S; Niculescu, G; Niculescu, I; Niczyporuk, B B; Niyazov, R A; O'Relly, G V; Osipenko, M; Ostrovidov, A I; Park, K; Pasyuk, E; Peterson, C; Pierce, J; Pivnyuk, N; Pocanic, D; Pogorelko, O; Polli, E; Pozdniakov, S; Preedom, B M; Price, J W; Prok, Y; Protopopescu, D; Qin, L M; Raue, B A; Riccardi, G; Ricco, G; Ripani, M; Ritchie, B G; Ronchetti, F; Rosner, G; Rossi, P; Rowntree, D; Rubin, P D; Sabatié, F; Salgado, C; Santoro, J P; Sapunenko, V; Schumacher, R A; Serov, V S; Sharabian, Y G; Shaw, J; Smith, E S; Smith, L C; Sober, D I; Stavinsky, A; Stepanyan, S; Stokes, B E; Stoler, P; Strauch, S; Suleiman, R; Taiuti, M; Taylor, S; Tedeschi, D J; Thompson, R; Tkabladze, A; Tkachenko, S; Todor, L; Tur, C; Ungaro, M; Vineyard, M F; Vlassov, A V; Weygand, D P; Williams, M; Wolin, E; Wood, M H; Yegneswaran, A; Yun, J; Zana, L; Zhang, J

    2006-03-03

    The ratios of inclusive electron scattering cross sections of 4He, 12C, and 56Fe to 3He have been measured at 1 < xB <. At Q2 > 1.4 GeV2, the ratios exhibit two separate plateaus, at 1.5 < xB < 2 and at xB > 2.25. This pattern is predicted by models that include 2- and 3-nucleon short-range correlations (SRC). Relative to A = 3, the per-nucleon probabilities of 3-nucleon SRC are 2.3, 3.1, and 4.4 times larger for A = 4, 12, and 56. This is the first measurement of 3-nucleon SRC probabilities in nuclei.

  19. Short-range and tensor correlations in the 16O(e,e'pn) reaction

    NASA Astrophysics Data System (ADS)

    Giusti, C.; Müther, H.; Pacati, F. D.; Stauf, M.

    1999-11-01

    The cross sections for electron-induced two-nucleon knockout reactions are evaluated for the example of the 16O(e,e'pn)14N reaction leading to discrete states in the residual nucleus 14N. These calculations account for the effects of nucleon-nucleon correlations and include the contributions of two-body meson exchange currents as the pion seagull, pion in flight, and the isobar current contribution. The effects of short-range as well as tensor correlations are calculated within the framework of the coupled cluster method employing the Argonne V14 potential as a model for a realistic nucleon-nucleon interaction. The relative importance of correlation effects as compared to the contribution of the meson exchange currents depends on the final state of the residual nucleus. The cross section leading to specific states, such as, e.g., the ground state of 14N, is rather sensitive to the details of the correlated wave function.

  20. Joint Mode Selection and Resource Allocation for Cellular Controlled Short-Range Communication in OFDMA Networks

    NASA Astrophysics Data System (ADS)

    Deng, Hui; Tao, Xiaoming; Ge, Ning; Lu, Jianhua

    This letter studies cellular controlled short-range communication in OFDMA networks. The network needs to decide when to allow direct communication between a closely located device-to-device (D2D) pair instead of conveying data from one device to the other via the base station and when not to, in addition to subchannel and power allocation. Our goal is to maximize the total network throughput while guaranteeing the rate requirements of all users. For that purpose, we formulate an optimization problem subject to subchannel and power constraints. A scheme which combines a joint mode selection and subchannel allocation algorithm based on equal power allocation with a power reallocation scheme is proposed. Simulation results show that our proposed scheme can improve the network throughput and outage probability compared with other schemes.

  1. One spatial dimensional finite volume three-body interaction for a short-range potential

    NASA Astrophysics Data System (ADS)

    Guo, Peng

    2017-03-01

    In this work, we use McGuire's model to describe scattering of three spinless identical particles in one spatial dimension; we first present analytic solutions of Faddeev's equation for scattering of three spinless particles in free space. The three particles interaction in finite volume is derived subsequently, and the quantization conditions by matching wave functions in free space and finite volume are presented in terms of two-body scattering phase shifts. The quantization conditions obtained in this work for the short-range interaction are Lüscher's formula-like and consistent with Yang's results [Phys. Rev. Lett. 19, 1312 (1967), 10.1103/PhysRevLett.19.1312].

  2. 79 GHz UWB automotive short range radar - Spectrum allocation and technology trends

    NASA Astrophysics Data System (ADS)

    Bloecher, H.-L.; Sailer, A.; Rollmann, G.; Dickmann, J.

    2009-05-01

    Automotive UWB (Ultra-Wideband) short range radar (SSR) is on the market as a key technology for novel comfort and safety systems. SiGe based 79 GHz UWB SRR will be a definite candidate for the long term substitution of the 24 GHz UWB SRR. This paper will give an overview of the finished BMBF joint project KOKON and the recently started successing project RoCC, which concentrate on the development of this technology and sensor demonstrators. In both projects, the responsibilities of Daimler AG deal with application based sensor specification, test and evaluation of realized sensor demonstrators. Recent UWB SRR frequency regulation approaches and activitites will be introduced. Furthermore, some first results of Daimler activities within RoCC will be presented, dealing with the packaging and operation of these sensors within the complex car environment.

  3. Short-range structure and thermal properties of barium tellurite glasses

    NASA Astrophysics Data System (ADS)

    Kaur, Amarjot; Khanna, Atul; Gonzàlez, Fernando

    2017-05-01

    BaO-TeO2 glasses containing 10 to 20 BaO mol% were prepared and characterized by X-ray diffraction, density measurements, differential scanning calorimetry and Raman spectroscopy. Glass density decreases with increase in BaO concentration from 10 to 20 mol%, due to replacement of heavier TeO2 by lighter BaO, however glass transition temperature (Tg) increases significantly from a value of 318°C to 327°C due to increase in average single bond enthalpy of the tellurite network. Raman studies found that glass short-range structure consists of TeO4 and TeO3 structural units and BaO modifies the network by producing the structural transformation: TeO4→ TeO3.

  4. Rapid resolution of crustal motion at short ranges with the global positioning system

    NASA Technical Reports Server (NTRS)

    Genrich, Joachim F.; Bock, Yehuda

    1992-01-01

    An analysis of GPS alignment array data collected in November 1990 and February 1991 are used to assess the temporal resolution of crustal deformation for GPS receiver systems operating as strain meters, and guidelines for achieving millimeter-level precision with short-range, kinematic-type GPS measurements are provided. Baselines between the array endpoints computed from 24 min of static observations on three consecutive days show an rms scatter of about 0.1 nm in the horizontal components and of about 0.3 mm in the vertical. They agree to within 0.2 mm with a solution calculated from measurements collected 3 mo earlier, indicating that this segment of the San Andreas fault appears to be locked at the surface over this period of time. Epoch-by-epoch solutions of array baselines with a six-satellite constellation show a multipath signature with typical amplitudes of several millimeters and periods of a few minutes.

  5. Probing short-range nucleon-nucleon interactions with an electron-ion collider

    DOE PAGES

    Miller, Gerald A.; Sievert, Matthew D.; Venugopalan, Raju

    2016-04-07

    For this research, we derive the cross section for exclusive vector meson production in high-energy deeply inelastic scattering off a deuteron target that disintegrates into a proton and a neutron carrying large relative momentum in the final state. This cross section can be expressed in terms of a novel gluon transition generalized parton distribution (T-GPD); the hard scale in the final state makes the T-GPD sensitive to the short-distance nucleon-nucleon interaction. We perform a toy model computation of this process in a perturbative framework and discuss the time scales that allow the separation of initial- and final-state dynamics in themore » T-GPD. We outline the more general computation based on the factorization suggested by the toy computation: In particular, we discuss the relative role of “pointlike” and “geometric” Fock configurations that control the parton dynamics of short-range nucleon-nucleon scattering. With the aid of exclusive J/ψ production data at the Hadron-Electron Ring Accelerator at DESY, as well as elastic nucleon-nucleon cross sections, we estimate rates for exclusive deuteron photodisintegration at a future Electron-Ion Collider (EIC). Our results, obtained using conservative estimates of EIC integrated luminosities, suggest that center-of-mass energies sNN ~12GeV2 of the neutron-proton subsystem can be accessed. We argue that the high energies of the EIC can address outstanding dynamical questions regarding the short-range quark-gluon structure of nuclear forces by providing clean gluon probes of such “knockout” exclusive reactions in light and heavy nuclei.« less

  6. Detailed study of the nuclear dependence of the EMC effect and short-range correlations

    SciTech Connect

    Arrington, J.; Daniel, A.; Day, D. B.; Fomin, N.; Gaskell, D.; Solvignon, P.

    2012-12-01

    Background: The density of the nucleus has been important in explaining the nuclear dependence of the quark distributions, also known as the EMC effect, as well as the presence of high-momentum nucleons arising from short-range correlations (SRCs). Recent measurements of both of these effects on light nuclei have shown a clear deviation from simple density-dependent models. Purpose: A better understanding of the nuclear quark distributions and short-range correlations requires a careful examination of the experimental data on these effects to constrain models that attempt to describe these phenomena. Methods: We present a detailed analysis of the nuclear dependence of the EMC effect and the contribution of SRCs in nuclei, comparing to predictions and simple scaling models based on different pictures of the underlying physics. We also make a direct, quantitative comparison of the two effects to further examine the connection between these two observables related to nuclear structure. Results: We find that, with the inclusion of the new data on light nuclei, neither of these observables can be well explained by common assumptions for the nuclear dependence. The anomalous behavior of both effects in light nuclei is consistent with the idea that the EMC effect is driven by either the presence of high-density configurations in nuclei or the large virtuality of the high-momentum nucleons associated with these configurations. Conclusions: The unexpected nuclear dependence in the measurements of the EMC effect and SRC contributions appear to suggest that the local environment of the struck nucleon is the most relevant quantity for explaining these results. The common behavior suggests a connection between the two seemingly disparate phenomena, but the data do not yet allow for a clear preference between models which aim to explain this connection.

  7. Cortical dynamics of visual motion perception: short-range and long-range apparent motion.

    PubMed

    Grossberg, S; Rudd, M E

    1992-01-01

    This article describes further evidence for a new neural network theory of biological motion perception. The theory clarifies why parallel streams V1----V2, V1----MT, and V1----V2----MT exist for static form and motion form processing among the areas V1, V2, and MT of visual cortex. The theory suggests that the static form system (Static BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast and to direction-of-motion, whereas the motion form system (Motion BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast but sensitive to direction-of-motion. The theory is used to explain classical and recent data about short-range and long-range apparent motion percepts that have not yet been explained by alternative models. These data include beta motion, split motion, gamma motion and reverse-contrast gamma motion, delta motion, and visual inertia. Also included are the transition from group motion to element motion in response to a Ternus display as the interstimulus interval (ISI) decreases; group motion in response to a reverse-contrast Ternus display even at short ISIs; speed-up of motion velocity as interflash distance increases or flash duration decreases; dependence of the transition from element motion to group motion on stimulus duration and size, various classical dependencies between flash duration, spatial separation, ISI, and motion threshold known as Korte's laws; dependence of motion strength on stimulus orientation and spatial frequency; short-range and long-range form-color interactions; and binocular interactions of flashes to different eyes.

  8. Probing short-range nucleon-nucleon interactions with an electron-ion collider

    NASA Astrophysics Data System (ADS)

    Miller, Gerald A.; Sievert, Matthew D.; Venugopalan, Raju

    2016-04-01

    We derive the cross section for exclusive vector meson production in high-energy deeply inelastic scattering off a deuteron target that disintegrates into a proton and a neutron carrying large relative momentum in the final state. This cross section can be expressed in terms of a novel gluon transition generalized parton distribution (T-GPD); the hard scale in the final state makes the T-GPD sensitive to the short-distance nucleon-nucleon interaction. We perform a toy model computation of this process in a perturbative framework and discuss the time scales that allow the separation of initial- and final-state dynamics in the T-GPD. We outline the more general computation based on the factorization suggested by the toy computation: In particular, we discuss the relative role of "pointlike" and "geometric" Fock configurations that control the parton dynamics of short-range nucleon-nucleon scattering. With the aid of exclusive J /ψ production data at the Hadron-Electron Ring Accelerator at DESY, as well as elastic nucleon-nucleon cross sections, we estimate rates for exclusive deuteron photodisintegration at a future Electron-Ion Collider (EIC). Our results, obtained using conservative estimates of EIC integrated luminosities, suggest that center-of-mass energies sNN˜12 GeV2 of the neutron-proton subsystem can be accessed. We argue that the high energies of the EIC can address outstanding dynamical questions regarding the short-range quark-gluon structure of nuclear forces by providing clean gluon probes of such "knockout" exclusive reactions in light and heavy nuclei.

  9. Searching for Short Range Correlations Using (e,e'NN) Reactions

    SciTech Connect

    Zhang, Bin

    2003-02-01

    Electron induced two nucleon knockout reactions (e,e'pp) and (e,e'np) were performed for 3He, 4He, and 12C nuclei with incident energies of 2.261 GeV and 4.461 GeV using the CLAS detector at Jefferson Lab. Events with missing momenta lower than the Fermi level and missing energies smaller than the pion threshold were studied. The residual system was assumed to be a spectator and the process was considered as a quasi-free knockout of an NN pair. The data showed that the initial momentum extends up to 800 MeV/c with considerable strength. The cross sections for 3He(e,e'pp)n were compared to the calculations of J.M. Laget. It was found that the final state interactions (FSI) and the meson exchange currents (MEC) dominate the cross sections and the short range properties of the NN pair were substantially undermined. However, the node of the S state wave function of the pp pair at around 400 MeV/c initial momentum starts to be recognizable in the 4.461 GeV data. The data and the theory suggest that with higher momentum transfers, especially in the region xBj > 1, the competing processes such as FSI and MEC will be less important and the detailed study of the short-range properties of nucleons inside nuclei will be more desirable.

  10. Short-range transport of contaminants released from e-waste recycling site in South China.

    PubMed

    Li, Huizhen; Bai, Jinmei; Li, Yetian; Cheng, Hefa; Zeng, Eddy Y; You, Jing

    2011-04-01

    The transport behaviors of a suite of contaminants released from electronic waste (e-waste) recycling operations, including polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and heavy metals, were evaluated by analyzing the contaminant residues in surface soils sampled in the surrounding area of an e-waste recycling site in South China. Concentrations of PBDEs and PCBs in the soil samples ranged from 0.565 to 2908 ng g(-1) dw and from 0.267 to 1891 ng g(-1) dw, respectively, while soil residues were 0.082-2.56, 3.22-287, and 16.3-162 μg g(-1) dw for Cd, Cu, and Pb, respectively. Concentrations of PBDEs and PCBs in soil decreased with increasing distance from the source of pollution, indicating possible PBDE and PCB contamination in the surrounding areas due to the short-range transport of these compounds from the e-waste recycling site. Although no significant difference in the short-range transport potential among PBDE and PCB congeners was observed, reductions in concentrations of the highly-brominated-BDEs and highly-chlorinated-CBs were slightly quicker than those of their less-halogen-substituted counterparts. Conversely, heavy metals showed the lowest transport potential due to their low vapor pressure, and results showed metals would remain near the pollution source instead of diffusing into the surrounding areas. Finally, mass inventories in areas near the e-waste site were 0.920, 0.134, 0.860, 4.68, 757, and 673 tons for BDE209, PBDEs (excluding BDE209), PCBs, Cd, Cu, and Pb, respectively.

  11. Probing short-range nucleon-nucleon interactions with an electron-ion collider

    SciTech Connect

    Miller, Gerald A.; Sievert, Matthew D.; Venugopalan, Raju

    2016-04-07

    For this research, we derive the cross section for exclusive vector meson production in high-energy deeply inelastic scattering off a deuteron target that disintegrates into a proton and a neutron carrying large relative momentum in the final state. This cross section can be expressed in terms of a novel gluon transition generalized parton distribution (T-GPD); the hard scale in the final state makes the T-GPD sensitive to the short-distance nucleon-nucleon interaction. We perform a toy model computation of this process in a perturbative framework and discuss the time scales that allow the separation of initial- and final-state dynamics in the T-GPD. We outline the more general computation based on the factorization suggested by the toy computation: In particular, we discuss the relative role of “pointlike” and “geometric” Fock configurations that control the parton dynamics of short-range nucleon-nucleon scattering. With the aid of exclusive J/ψ production data at the Hadron-Electron Ring Accelerator at DESY, as well as elastic nucleon-nucleon cross sections, we estimate rates for exclusive deuteron photodisintegration at a future Electron-Ion Collider (EIC). Our results, obtained using conservative estimates of EIC integrated luminosities, suggest that center-of-mass energies sNN ~12GeV2 of the neutron-proton subsystem can be accessed. We argue that the high energies of the EIC can address outstanding dynamical questions regarding the short-range quark-gluon structure of nuclear forces by providing clean gluon probes of such “knockout” exclusive reactions in light and heavy nuclei.

  12. Highly accurate evaluation of atomic three-electron integrals of lowest orders

    NASA Astrophysics Data System (ADS)

    Harris, Frank E.; Frolov, Alexei M.; Smith, Vedene H.

    2004-06-01

    Calculations of three-electron atomic systems in Hylleraas coordinates require integrals involving all the interparticle distances rij, which have usually been evaluated by introducing series expansions. For integrals with the smallest powers of rij these expansions do not converge at a satisfactory rate, leading some investigators to introduce convergence-acceleration procedures. This paper recommends the alternative of evaluating these integrals in closed form and presents stable explicit formulas for so doing. Some of the formulas are more compact versions of those in the literature; others have not been previously reported. It is also shown that finite-difference methods can be used with advantage to obtain additional low-order integrals. Sample integral values have been provided for test purposes.

  13. Safety and Mission Assurance (SMA) Automated Task Order Management System (ATOMS) Operation Manual

    NASA Technical Reports Server (NTRS)

    Wallace, Shawn; Fikes, Lou A.

    2016-01-01

    This document describes operational aspects of the ATOMS system. The information provided is limited to the functionality provided by ATOMS and does not include information provided in the contractor's proprietary financial and task management system.

  14. Nucleon momentum distributions, their spin-isospin dependence, and short-range correlations

    NASA Astrophysics Data System (ADS)

    Alvioli, M.; Ciofi degli Atti, C.; Kaptari, L. P.; Mezzetti, C. B.; Morita, H.

    2013-03-01

    The nucleon momentum distribution nA(k) for A=2, 3, 4, 16, and 40 nuclei is systematically analyzed in terms of wave functions resulting from advanced solutions of the nonrelativistic Schrödinger equation, obtained within different many-body approaches based upon different realistic bare nucleon-nucleon (NN) interactions featuring similar short-range repulsion and tensor interactions. Particular attention is paid to the separation of the momentum distributions into the mean-field and short-range correlation (SRC) contributions. It is shown that although at high values of the momentum k different approaches lead to some quantitative differences, these do not hinder the general conclusion that the high-momentum behavior (k≳1.5-2 fm-1) of all nuclei considered are very similar, exhibiting the well-known scaling behavior with the mass number A, independently of the used many-body approach and the details of the bare NN interaction. To analyze and understand the frequently addressed question concerning the relationships between the nucleus, nA(k), and the deuteron, nD(k), momentum distributions, the spin (S)-isospin (T) structure of few-nucleon systems and complex nuclei is analyzed in terms of realistic NN interactions and many-body approaches. To this end, the number of NN pairs in a given (ST) state, viz., (ST)=(10), (00), (01), and (11), and the contribution of these states to the nucleon momentum distributions are calculated. It is shown that, apart from the (00) state, which has very small effects, all other spin-isospin states contribute to the momentum distribution in a wide range of momenta. It is shown that for all nuclei considered the momentum distributions in the states T=0 and T=1 exhibit at k≳1.5-2 fm-1 very similar behaviors, which represents strong evidence of the A-independent character of SRCs. The ratio nA(k)/nD(k) is analyzed in detail, stressing that in the SRC region it always increases with the momentum and the origin of such an increase is

  15. APPLICATION OF CFD SIMULATIONS FOR SHORT-RANGE ATMOSPHERIC DISPERSION OVER OPEN FIELDS AND WITHIN ARRAYS OF BUILDINGS

    EPA Science Inventory

    Computational Fluid Dynamics (CFD) techniques are increasingly being applied to air quality modeling of short-range dispersion, especially the flow and dispersion around buildings and other geometrically complex structures. The proper application and accuracy of such CFD techniqu...

  16. EXAMPLE APPLICATION OF CFD SIMULATIONS FOR SHORT-RANGE ATMOSPHERIC DISPERSION OVER THE OPEN FIELDS OF PROJECT PRAIRIE GRASS

    EPA Science Inventory

    Computational Fluid Dynamics (CFD) techniques are increasingly being applied to air quality modeling of short-range dispersion, especially the flow and dispersion around buildings and other geometrically complex structures. The proper application and accuracy of such CFD techniqu...

  17. APPLICATION OF CFD SIMULATIONS FOR SHORT-RANGE ATMOSPHERIC DISPERSION OVER OPEN FIELDS AND WITHIN ARRAYS OF BUILDINGS

    EPA Science Inventory

    Computational Fluid Dynamics (CFD) techniques are increasingly being applied to air quality modeling of short-range dispersion, especially the flow and dispersion around buildings and other geometrically complex structures. The proper application and accuracy of such CFD techniqu...

  18. EXAMPLE APPLICATION OF CFD SIMULATIONS FOR SHORT-RANGE ATMOSPHERIC DISPERSION OVER THE OPEN FIELDS OF PROJECT PRAIRIE GRASS

    EPA Science Inventory

    Computational Fluid Dynamics (CFD) techniques are increasingly being applied to air quality modeling of short-range dispersion, especially the flow and dispersion around buildings and other geometrically complex structures. The proper application and accuracy of such CFD techniqu...

  19. Intensity-dependent atomic-phase effects in high-order harmonic generation

    NASA Astrophysics Data System (ADS)

    Peatross, J.; Meyerhofer, D. D.

    1995-11-01

    The far-field angular distributions of high-order harmonics of a 1054-nm laser, with orders ranging from the lower teens to the upper thirties, have been measured in thin, low-density Ar, Kr, and Xe targets. The 1.25-times-diffraction-limited, 1.4-ps-duration, Gaussian laser pulses were focused to intensities ranging from 3×1013 to 3×1014 W/cm2, using f/70 optics. A gas target localized the gas distribution near the laser focus to a thickness of about 1 mm at pressures as low as 0.3 Torr. The weak focusing geometry and the low gas pressures created experimental conditions for which the harmonics could be thought of as emerging from a plane at the laser focus rather than a three-dimensional volume. The far-field distributions of nearly all of the harmonics exhibit narrow central peaks surrounded by broad wings of about the same angular divergence as the emerging laser beam. The spatial wings are due to an intensity-dependent phase variation among the dipole moments of the individual target atoms. This phase variation gives rise to broad spatial interferences in the scattered light due to the radial and temporal variation of the laser intensity.

  20. The short range anion-H interaction is the driving force for crystal formation of ions in water.

    PubMed

    Alejandre, José; Chapela, Gustavo A; Bresme, Fernando; Hansen, Jean-Pierre

    2009-05-07

    The crystal formation of NaCl in water is studied by extensive molecular dynamics simulations. Ionic solutions at room temperature and various concentrations are studied using the SPC/E and TIP4P/2005 water models and seven force fields of NaCl. Most force fields of pure NaCl fail to reproduce the experimental density of the crystal, and in solution some favor dissociation at saturated conditions, while others favor crystal formation at low concentration. A new force field of NaCl is proposed, which reproduces the experimental phase diagram in the solid, liquid, and vapor regions. This force field overestimates the solubility of NaCl in water at saturation conditions when used with standard Lorentz-Berthelot combining rules for the ion-water pair potentials. It is shown that precipitation of ions is driven by the short range interaction between Cl-H pairs, a term which is generally missing in the simulation of ionic solutions. The effects of intramolecular flexibility of water on the solubility of NaCl ions are analyzed and is found to be small compared to rigid models. A flexible water model, extending the rigid SPC/E, is proposed, which incorporates Lennard-Jones interactions centered on the hydrogen atoms. This force field gives liquid-vapor coexisting densities and surface tensions in better agreement with experimental data than the rigid SPC/E model. The Cl-H, Na-O, and Cl-O pair distribution functions of the rigid and flexible models agree well with experiment. The predicted concentration dependence of the electric conductivity is in fair agreement with available experimental data.

  1. Quick-look eye-safety assessment for the short range lidar

    SciTech Connect

    Wehner, T.R.

    1998-07-02

    This is a quick-look eye-safety assessment for the Short Range (SR) lidar, a system under development for standoff biological aerosol detection in the outdoor environment. The ground-vehicle-mounted SR lidar system will scan a sector of the nearby atmosphere with a repetitively pulsed, multiple-wavelength, UV/IR laser beam. This laser is not intrinsically eye-safe, and hence the SR lidar system requires a protection system to minimize the risk of eye exposures above the ANSI-standard maximum permissible exposure within a nominal hazard zone. The nominal ocular hazard distance for the UV/IR laser itself was calculated to be 6 km. The protection system, which will include a scan-stop detector and a laser beam path interrogator, currently is conceptual only. Until the complete protection system is designed, evaluated, and tested, and a more detailed safety assessment has been performed, the eye-safety issue for the SR lidar system cannot be resolved.

  2. Evaluation of NCEP TIGGE short-range forecast for Indian summer monsoon intraseasonal oscillation

    NASA Astrophysics Data System (ADS)

    Tirkey, Snehlata; Mukhopadhyay, P.

    2016-04-01

    This study focuses on the short-range prediction of Monsoon Intraseasonal Oscillations (MISOs) using the National Centers for Environmental Prediction(NCEP) Ensemble Prediction System (EPS) data from The Observing System Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) archive. The Indian Summer Monsoon Rainfall (ISMR), which plays an important role in the socio-economic growth of the country, is highly variable and is mostly governed by the MISOs. In addition to this, deterministic forecasts of ISMR are not very reliable. Hence, a probabilistic approach at daily scale is required. Keeping this in mind, the present analysis is done by using daily forecast data for up to 7-day lead time and compared with observations. The analysis shows that the ensemble forecast well captures the variability as compared to observations even up to 7 days. The spatial characteristics and the northward propagation of MISO are observed thoroughly in the EPS. The evolution of dynamical and thermodynamical parameters such as specific humidity, moist static energy, moisture divergence, and vorticity is also captured well but show deviation from the observation from 96 h lead time onwards. The tropospheric temperature forecast captures the observed gradient but with certain bias in magnitude whereas the wind shear is simulated quite well both in pattern and magnitude. These analyses bring out the biases in TIGGE EPS forecast and also point out the possible moist processes which needs to be improved.

  3. Signal-source trackers on Infrared-based Dedicated Short-Range Communication

    NASA Astrophysics Data System (ADS)

    Lu, Po-Wen; Chen, Rongshun

    2010-03-01

    Location-based ITS applications, especially the applications based on Vehicle-to-Vehicle (V2V) communication, require the absolute or relative location information of the communicating objects. GPS receivers are often used to give the absolute locations of the objects. However, the updating rate and the resolution of GPS receivers are not sufficient for neighboring and highly mobile vehicles. This paper renders two designs, a one-dimensional IR signal-source tracker and a two-dimensional IR signal-source tracker, to estimate the location of a communicating target. By analyzing the strength of the received signal, the relative location of the target is identified once the communication data are received. The realized 1D and 2D IR signal-source tracker can give the precise location, where the repeated tests on the 2D tracker show the given locations with low deviation. Since these two tracker designs are realized with the same IR components in the Dedicated Short-Range Communication (DSRC), the communicating devices, the roadside unit (RSU) and the onboard unit (OBU), can use the 1D or 2D tracker design depending on the application to locate each other, and then to control the radiation direction for saving power, to facilitate the completeness of transactions, and to locate vehicles in V2V applications. In this work, the proposed devices are designed, realized and tested. The experimental results show that these two designs are feasible.

  4. Meta-heuristic CRPS minimization for the calibration of short-range probabilistic forecasts

    NASA Astrophysics Data System (ADS)

    Mohammadi, Seyedeh Atefeh; Rahmani, Morteza; Azadi, Majid

    2016-08-01

    This paper deals with the probabilistic short-range temperature forecasts over synoptic meteorological stations across Iran using non-homogeneous Gaussian regression (NGR). NGR creates a Gaussian forecast probability density function (PDF) from the ensemble output. The mean of the normal predictive PDF is a bias-corrected weighted average of the ensemble members and its variance is a linear function of the raw ensemble variance. The coefficients for the mean and variance are estimated by minimizing the continuous ranked probability score (CRPS) during a training period. CRPS is a scoring rule for distributional forecasts. In the paper of Gneiting et al. (Mon Weather Rev 133:1098-1118, 2005), Broyden-Fletcher-Goldfarb-Shanno (BFGS) method is used to minimize the CRPS. Since BFGS is a conventional optimization method with its own limitations, we suggest using the particle swarm optimization (PSO), a robust meta-heuristic method, to minimize the CRPS. The ensemble prediction system used in this study consists of nine different configurations of the weather research and forecasting model for 48-h forecasts of temperature during autumn and winter 2011 and 2012. The probabilistic forecasts were evaluated using several common verification scores including Brier score, attribute diagram and rank histogram. Results show that both BFGS and PSO find the optimal solution and show the same evaluation scores, but PSO can do this with a feasible random first guess and much less computational complexity.

  5. Precise long-range migration results from short-range stepwise migration during ring gland organogenesis.

    PubMed

    Sánchez-Higueras, Carlos; Hombría, James Castelli-Gair

    2016-06-01

    Many organs are specified far from the location they occupy when functional, having to migrate long distances through the heterogeneous and dynamic environment of the early embryo. We study the formation of the main Drosophila endocrine organ, the ring gland, as a new model to investigate in vivo the genetic regulation of collective cell migration. The ring gland results from the fusion of three independent gland primordia that migrate from the head towards the anterior aorta as the embryo is experiencing major morphogenetic movements. To complete their long-range migration, the glands extend filopodia moving sequentially towards a nearby intermediate target and from there to more distal ones. Thus, the apparent long-range migration is composed of several short-range migratory steps that facilitate reaching the final destination. We find that the target tissues react to the gland's proximity by sending filopodia towards it. Our finding of a succession of independent migration stages is consistent with the stepwise evolution of ring gland assembly and fits with the observed gland locations found in extant crustaceans, basal insects and flies.

  6. Long-ranged contributions to solvation free energies from theory and short-ranged models

    PubMed Central

    Remsing, Richard C.; Liu, Shule; Weeks, John D.

    2016-01-01

    Long-standing problems associated with long-ranged electrostatic interactions have plagued theory and simulation alike. Traditional lattice sum (Ewald-like) treatments of Coulomb interactions add significant overhead to computer simulations and can produce artifacts from spurious interactions between simulation cell images. These subtle issues become particularly apparent when estimating thermodynamic quantities, such as free energies of solvation in charged and polar systems, to which long-ranged Coulomb interactions typically make a large contribution. In this paper, we develop a framework for determining very accurate solvation free energies of systems with long-ranged interactions from models that interact with purely short-ranged potentials. Our approach is generally applicable and can be combined with existing computational and theoretical techniques for estimating solvation thermodynamics. We demonstrate the utility of our approach by examining the hydration thermodynamics of hydrophobic and ionic solutes and the solvation of a large, highly charged colloid that exhibits overcharging, a complex nonlinear electrostatic phenomenon whereby counterions from the solvent effectively overscreen and locally invert the integrated charge of the solvated object. PMID:26929375

  7. Predominance of short range Coulomb forces in phosphate-water interactions—a theoretical analysis

    NASA Astrophysics Data System (ADS)

    Fingerhut, Benjamin P.; Costard, Rene; Elsaesser, Thomas

    2016-09-01

    Electric forces play a key role in the interaction of negatively charged phosphate groups with the dipolar water molecules of an aqueous environment. Both fluctuation amplitudes and effective spatial range of the electric fields that fluctuate on a multitude of time scales have remained highly controversial. We employ the dimethylphosphate anion (DMP) as a fundamental building block of the phosphodiester backbone in DNA to model electric fields at the phosphate-water interface. DMP is considered to be solvated in bulk water and the fluctuating electric forces exerted on the (PO2)- moiety are calculated by combining the ab initio based effective fragment potential approach that accounts for electric fields due to static multipoles and polarization contributions due to induced dipoles, with molecular dynamics. We demonstrate that the total time-averaged electric field generated by water molecules arises to a large extent from the first water layer. The second layer contributes some 18% with noticeable contributions from induction. We further show that the solvent electric field experienced by the phosphate group is the dominant contribution to the pronounced solvatochromism of the asymmetric (PO2)- stretch vibration. Accounting for a field expansion up to quadrupoles and polarization due to induced dipoles allows us to simulate solvent induced frequency shifts and lineshapes in almost quantitative agreement to experiment. Our theoretical model strongly supports the picture of short-range electric forces that arise locally from the first and second hydration shell.

  8. Enhanced gel formation in binary mixtures of nanocolloids with tunable short-range attraction

    NASA Astrophysics Data System (ADS)

    Leheny, R.; Guo, H.; Bertrand, M.; Shendruk, T.; Ramakrishnan, S.; Harden, J.

    We report a combined experimental, theoretical, and simulation study of the phase behavior and microstructural dynamics of concentrated binary mixtures of spherical nanocolloids with a size ratio near two and with a tunable, intrinsic short-range attraction. In the absence of the attraction, the suspensions behave as well mixed, hard-sphere liquids. For sufficiently strong attraction, the suspensions undergo a gel transition. Rheometry measurements show that the fluid-gel boundary of the mixtures does not follow an ideal mixing law, but rather the gel state is stable at weaker interparticle attraction in the mixtures than in the corresponding monodisperse suspensions. X-ray photon correlation spectroscopy measurements reveal that, in contrast with depletion-driven gelation at larger size ratio, gel formation in the mixtures coincides with dynamic arrest of the smaller colloids while the larger colloids remain mobile. Molecular dynamics simulations indicate the arrest results from microphase separation that is caused by a subtle interplay of entropic and enthalpic effects and that drives the smaller particles to form dense regions.

  9. Study Of Short-Range Correlations With 6-9 GeV/c Protons

    SciTech Connect

    Watson, J. W.

    2008-10-13

    We studied the {sup 12}C(p,2p+n) reaction at beam momenta of 5.9, 8.0 and 9.0 GeV/c. For quasielastic (p,2p) events we reconstructed p{sub f}, the momentum of the knocked-out proton before the reaction;, p{sub f} was then compared (event-by-event) with p{sub n}, the measured, coincident neutron momentum. For |p{sub n}|>k{sub F} = 0.220 GeV/c(the Fermi momentum) a strong back-to-back directional correlation between p{sub f} and p{sub n} was observed, indicative of short-range n-p correlations. From these data we concluded that for nuclear protons with momenta >0.275 GeV/c, 92{+-}18% have correlated neutron partners. This result was recently corroborated by an experiment with 4.6 GeV electrons.

  10. Bond lifetime and diffusion coefficient in colloids with short-range interactions.

    PubMed

    Ndong Mintsa, E; Germain, Ph; Amokrane, S

    2015-03-01

    We use molecular dynamics simulations to study the influence of short-range structures in the interaction potential between hard-sphere-like colloidal particles. Starting from model potentials and effective potentials in binary mixtures computed from the Ornstein-Zernike equations, we investigate the influence of the range and strength of a possible tail beyond the usual core repulsion or the presence of repulsive barriers. The diffusion coefficient and mean "bond" lifetimes are used as indicators of the effect of this structure on the dynamics. The existence of correlations between the variations of these quantities with the physical parameters is discussed to assess the interpretation of dynamics slowing down in terms of long-lived bonds. We also discuss the question of a universal behaviour determined by the second virial coefficient B ((2)) and the interplay of attraction and repulsion. While the diffusion coefficient follows the B ((2)) law for purely attractive tails, this is no longer true in the presence of repulsive barriers. Furthermore, the bond lifetime shows a dependence on the physical parameters that differs from that of the diffusion coefficient. This raises the question of the precise role of bonds on the dynamics slowing down in colloidal gels.

  11. Interplay between short-range correlated disorder and Coulomb interaction in nodal-line semimetals

    NASA Astrophysics Data System (ADS)

    Wang, Yuxuan; Nandkishore, Rahul M.

    2017-09-01

    In nodal-line semimetals, Coulomb interactions and short-range correlated disorder are both marginal perturbations to the clean noninteracting Hamiltonian. We analyze their interplay using a weak-coupling renormalization group approach. In the clean case, the Coulomb interaction has been found to be marginally irrelevant, leading to Fermi liquid behavior. We extend the analysis to incorporate the effects of disorder. The nodal line structure gives rise to kinematical constraints similar to that for a two-dimensional Fermi surface, which plays a crucial role in the one-loop renormalization of the disorder couplings. For a twofold degenerate nodal loop (Weyl loop), we show that disorder flows to strong coupling along a unique fixed trajectory in the space of symmetry inequivalent disorder couplings. Along this fixed trajectory, all symmetry inequivalent disorder strengths become equal. For a fourfold degenerate nodal loop (Dirac loop), disorder also flows to strong coupling, however, the strengths of symmetry inequivalent disorder couplings remain different. We show that feedback from disorder reverses the sign of the beta function for the Coulomb interaction, causing the Coulomb interaction to flow to strong coupling as well. However, the Coulomb interaction flows to strong coupling asymptotically more slowly than disorder. Extrapolating our results to strong coupling, we conjecture that at low energies nodal line semimetals should be described by a noninteracting nonlinear sigma model. We discuss the relation of our results with possible many-body localization at zero temperatures in such materials.

  12. Effects of Diffusion Time on Short-Range Hyperpolarized 3He Diffusivity Measurements in Emphysema

    SciTech Connect

    Gierada, David S.; Woods, Jason C.; Bierhals, Andrew J.; Bartel, Seth T.; Ritter, Jon H.; Choong, Cliff K.; Das, Nitin A.; Hong, Cheng; Pilgram, Thomas K.; Chang, Yulin V.; Jacob, Rick E.; Hogg, James C.; Battafarano, Richard J.; Cooper, Joel D.; Meyers, Bryan F.; Patterson, G Alexander; Yablonskiy, Dmitriy A.; Conradi, Mark S.

    2009-09-28

    Purpose: To characterize the effect of diffusion time on short-range hyperpolarized 3He MR diffusion measurements across a wide range of emphysema severity. Materials and Methods: 3He diffusion MR imaging was performed on 19 lungs or lobes resected from 18 subjects with varying degrees of emphysema using 3 diffusion times (1.6 msec, 5 msec, and 10 msec) at constant b value. Emphysema severity was quantified as the mean apparent diffusion coefficient (ADC) and as the percentage of pixels with ADC higher than multiple thresholds from 0.30-0.55 cm2/sec (ADC index). Quantitative histology (mean linear intercept) was obtained in 10 of the lung specimens from 10 of the subjects. Results: The mean ADCs with diffusion times of 1.6, 5.0, and 10.0 msec were 0.46, 0.40, and 0.37 cm2/sec, respectively (P <0.0001, ANOVA). There was no relationship between the ADC magnitude and the effect of diffusion time on ADC values. Mean linear intercept correlated with ADC (r=0.91-0.94, P<0.001) and ADC index (r=0.78-0.92, P<0.01) at all diffusion times.

  13. Gelation of anisotropic silica colloids with thermoreversible short-range interactions

    NASA Astrophysics Data System (ADS)

    Murphy, Ryan; Wagner, Norman

    Colloidal suspensions containing anisotropic particles are widely used in particle-based technologies including pharmaceuticals, consumer products, and coatings. The rheological properties of colloidal suspensions are known to be affected by particle shape; however, the combined influence of particle shape and attraction strength is not quantitatively understood for dynamic arrest transitions such as gelation. A model system of anisotropic silica colloids with thermoreversible, short-range attractions was developed to quantify the effect of particle shape and attractions on the gelation behavior. This tunable model system aims to map a fundamental state diagram for anisotropic particle suspensions as a function of particle shape, volume fraction, and interaction strength. Macroscopic rheological properties of thermoreversible gels were explored to determine the influence of particle shape on the gel transition. Neutron and x-ray scattering methods further probed the underlying fluid and gel microstructure at various temperatures, volume fractions, and aspect ratios. Linking these fundamental macroscopic and microscopic measurements will provide practical insight into particle technologies and manufacturing processes containing anisotropic colloidal suspensions.

  14. Evaluation of NCEP TIGGE short-range forecast for Indian summer monsoon intraseasonal oscillation

    NASA Astrophysics Data System (ADS)

    Tirkey, Snehlata; Mukhopadhyay, P.

    2017-08-01

    This study focuses on the short-range prediction of Monsoon Intraseasonal Oscillations (MISOs) using the National Centers for Environmental Prediction(NCEP) Ensemble Prediction System (EPS) data from The Observing System Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) archive. The Indian Summer Monsoon Rainfall (ISMR), which plays an important role in the socio-economic growth of the country, is highly variable and is mostly governed by the MISOs. In addition to this, deterministic forecasts of ISMR are not very reliable. Hence, a probabilistic approach at daily scale is required. Keeping this in mind, the present analysis is done by using daily forecast data for up to 7-day lead time and compared with observations. The analysis shows that the ensemble forecast well captures the variability as compared to observations even up to 7 days. The spatial characteristics and the northward propagation of MISO are observed thoroughly in the EPS. The evolution of dynamical and thermodynamical parameters such as specific humidity, moist static energy, moisture divergence, and vorticity is also captured well but show deviation from the observation from 96 h lead time onwards. The tropospheric temperature forecast captures the observed gradient but with certain bias in magnitude whereas the wind shear is simulated quite well both in pattern and magnitude. These analyses bring out the biases in TIGGE EPS forecast and also point out the possible moist processes which needs to be improved.

  15. Investigation of Multiconfigurational Short-Range Density Functional Theory for Electronic Excitations in Organic Molecules.

    PubMed

    Hubert, Mickaël; Hedegård, Erik D; Jensen, Hans Jørgen Aa

    2016-05-10

    Computational methods that can accurately and effectively predict all types of electronic excitations for any molecular system are missing in the toolbox of the computational chemist. Although various Kohn-Sham density-functional methods (KS-DFT) fulfill this aim in some cases, they become inadequate when the molecule has near-degeneracies and/or low-lying double-excited states. To address these issues we have recently proposed multiconfiguration short-range density-functional theory-MC-srDFT-as a new tool in the toolbox. While initial applications for systems with multireference character and double excitations have been promising, it is nevertheless important that the accuracy of MC-srDFT is at least comparable to the best KS-DFT methods also for organic molecules that are typically of single-reference character. In this paper we therefore systematically investigate the performance of MC-srDFT for a selected benchmark set of electronic excitations of organic molecules, covering the most common types of organic chromophores. This investigation confirms the expectation that the MC-srDFT method is accurate for a broad range of excitations and comparable to accurate wave function methods such as CASPT2, NEVPT2, and the coupled cluster based CC2 and CC3.

  16. Polarizable embedding with a multiconfiguration short-range density functional theory linear response method.

    PubMed

    Hedegård, Erik Donovan; Olsen, Jógvan Magnus Haugaard; Knecht, Stefan; Kongsted, Jacob; Jensen, Hans Jørgen Aagaard

    2015-03-21

    We present here the coupling of a polarizable embedding (PE) model to the recently developed multiconfiguration short-range density functional theory method (MC-srDFT), which can treat multiconfigurational systems with a simultaneous account for dynamical and static correlation effects. PE-MC-srDFT is designed to combine efficient treatment of complicated electronic structures with inclusion of effects from the surrounding environment. The environmental effects encompass classical electrostatic interactions as well as polarization of both the quantum region and the environment. Using response theory, molecular properties such as excitation energies and oscillator strengths can be obtained. The PE-MC-srDFT method and the additional terms required for linear response have been implemented in a development version of Dalton. To benchmark the PE-MC-srDFT approach against the literature data, we have investigated the low-lying electronic excitations of acetone and uracil, both immersed in water solution. The PE-MC-srDFT results are consistent and accurate, both in terms of the calculated solvent shift and, unlike regular PE-MCSCF, also with respect to the individual absolute excitation energies. To demonstrate the capabilities of PE-MC-srDFT, we also investigated the retinylidene Schiff base chromophore embedded in the channelrhodopsin protein. While using a much more compact reference wave function in terms of active space, our PE-MC-srDFT approach yields excitation energies comparable in quality to CASSCF/CASPT2 benchmarks.

  17. Cluster formation in fluids with competing short-range and long-range interactions

    NASA Astrophysics Data System (ADS)

    Sweatman, Martin B.; Fartaria, Rui; Lue, Leo

    2014-03-01

    We investigate the low density behaviour of fluids that interact through a short-ranged attraction together with a long-ranged repulsion (SALR potential) by developing a molecular thermodynamic model. The SALR potential is a model of effective solute interactions where the solvent degrees of freedom are integrated-out. For this system, we find that clusters form for a range of interaction parameters where attractive and repulsive interactions nearly balance, similar to micelle formation in aqueous surfactant solutions. We focus on systems for which equilibrium behaviour and liquid-like clusters (i.e., droplets) are expected, and find in addition a novel coexistence between a low density cluster phase and a high density cluster phase within a very narrow range of parameters. Moreover, a simple formula for the average cluster size is developed. Based on this formula, we propose a non-classical crystal nucleation pathway whereby macroscopic crystals are formed via crystal nucleation within microscopic precursor droplets. We also perform large-scale Monte Carlo simulations, which demonstrate that the cluster fluid phase is thermodynamically stable for this system.

  18. Effects of Diffusion Time on Short-Range Hyperpolarized 3He Diffusivity Measurements in Emphysema

    PubMed Central

    Gierada, David S.; Woods, Jason C.; Bierhals, Andrew J.; Bartel, Seth T.; Ritter, Jon H.; Choong, Cliff K.; Das, Nitin A.; Hong, Cheng; Pilgram, Thomas K.; Chang, Yulin V.; Jacob, Richard E.; Hogg, James C.; Battafarano, Richard J.; Cooper, Joel D.; Meyers, Bryan F.; Patterson, G. Alexander; Yablonskiy, Dmitriy A.; Conradi, Mark S.

    2010-01-01

    Purpose To characterize the effect of diffusion time on short-range hyperpolarized 3He MR diffusion measurements across a wide range of emphysema severity. Materials and Methods 3He diffusion MR imaging was performed on 19 lungs or lobes resected from 18 subjects with varying degrees of emphysema using 3 diffusion times (1.6 msec, 5 msec, and 10 msec) at constant b value. Emphysema severity was quantified as the mean apparent diffusion coefficient (ADC) and as the percentage of pixels with ADC higher than multiple thresholds from 0.30–0.55 cm2/sec (ADC index). Quantitative histology (mean linear intercept) was obtained in 10 of the lung specimens from 10 of the subjects. Results The mean ADCs with diffusion times of 1.6, 5.0, and 10.0 msec were 0.46, 0.40, and 0.37 cm2/sec, respectively (P <0.0001, ANOVA). There was no relationship between the ADC magnitude and the effect of diffusion time on ADC values. Mean linear intercept correlated with ADC (r=0.91–0.94, P<0.001) and ADC index (r=0.78–0.92, P<0.01) at all diffusion times. Conclusion Decreases in ADC with longer diffusion time were unrelated to emphysema severity. The strong correlations between the ADC at all diffusion times tested and quantitative histology demonstrate that the ADC is a robust measure of emphysema. PMID:19787725

  19. Uracil DNA glycosylase uses DNA hopping and short-range sliding to trap extrahelical uracils.

    PubMed

    Porecha, Rishi H; Stivers, James T

    2008-08-05

    The astonishingly efficient location and excision of damaged DNA bases by DNA repair glycosylases is an especially intriguing problem in biology. One example is the enzyme uracil DNA glycosylase (UNG), which captures and excises rare extrahelical uracil bases that have emerged from the DNA base stack by spontaneous base pair breathing motions. Here, we explore the efficiency and mechanism by which UNG executes intramolecular transfer and excision of two uracil sites embedded on the same or opposite DNA strands at increasing site spacings. The efficiency of intramolecular site transfer decreased from 41 to 0% as the base pair spacing between uracil sites on the same DNA strand increased from 20 to 800 bp. The mechanism of transfer is dominated by DNA hopping between landing sites of approximately 10 bp size, over which rapid 1D scanning likely occurs. Consistent with DNA hopping, site transfer at 20- and 56-bp spacings was unaffected by whether the uracils were placed on the same or opposite strands. Thus, UNG uses hopping and 3D diffusion through bulk solution as the principal pathways for efficient patrolling of long genomic DNA sequences for damage. Short-range sliding over the range of a helical turn allows for redundant inspection of very local DNA sequences and trapping of spontaneously emerging extrahelical uracils.

  20. Statistical Short-Range Forecast Guidance for Cloud Ceilings Over the Shuttle Landing Facility

    NASA Technical Reports Server (NTRS)

    Lambert, Winifred C.

    2001-01-01

    This report describes the results of the AMU's Short-Range Statistical Forecasting task. The cloud ceiling forecast over the Shuttle Landing Facility (SLF) is a critical element in determining whether a Shuttle should land. Spaceflight Meteorology Group (SMG) forecasters find that ceilings at the SLF are challenging to forecast. The AMU was tasked to develop ceiling forecast equations to minimize the challenge. Studies in the literature that showed success in improving short-term forecasts of ceiling provided the basis for the AMU task. A 20-year record of cool-season hourly surface observations from stations in east-central Florida was used for the equation development. Two methods were used: an observations-based (OBS) method that incorporated data from all stations, and a persistence climatology (PCL) method used as the benchmark. Equations were developed for 1-, 2-, and 3-hour lead times at each hour of the day. A comparison between the two methods indicated that the OBS equations performed well and produced an improvement over the PCL equations. Therefore, the conclusion of the AMU study is that OBS equations produced more accurate forecasts than the PCL equations, and can be used in operations. They provide another tool with which to make the ceiling forecasts that are critical to safe Shuttle landings at KSC.

  1. Polarizable embedding with a multiconfiguration short-range density functional theory linear response method

    SciTech Connect

    Hedegård, Erik Donovan; Olsen, Jógvan Magnus Haugaard; Knecht, Stefan; Kongsted, Jacob Jensen, Hans Jørgen Aagaard

    2015-03-21

    We present here the coupling of a polarizable embedding (PE) model to the recently developed multiconfiguration short-range density functional theory method (MC-srDFT), which can treat multiconfigurational systems with a simultaneous account for dynamical and static correlation effects. PE-MC-srDFT is designed to combine efficient treatment of complicated electronic structures with inclusion of effects from the surrounding environment. The environmental effects encompass classical electrostatic interactions as well as polarization of both the quantum region and the environment. Using response theory, molecular properties such as excitation energies and oscillator strengths can be obtained. The PE-MC-srDFT method and the additional terms required for linear response have been implemented in a development version of DALTON. To benchmark the PE-MC-srDFT approach against the literature data, we have investigated the low-lying electronic excitations of acetone and uracil, both immersed in water solution. The PE-MC-srDFT results are consistent and accurate, both in terms of the calculated solvent shift and, unlike regular PE-MCSCF, also with respect to the individual absolute excitation energies. To demonstrate the capabilities of PE-MC-srDFT, we also investigated the retinylidene Schiff base chromophore embedded in the channelrhodopsin protein. While using a much more compact reference wave function in terms of active space, our PE-MC-srDFT approach yields excitation energies comparable in quality to CASSCF/CASPT2 benchmarks.

  2. Evidence for short range corelations from high Q{sup 2} (e,e{prime}) reactions

    SciTech Connect

    Strikman, M.I.; Frankfurt, L.L.; Sargayan, M.M.

    1994-04-01

    For many years now short-range correlations (SRC) in nuclei have been considered as an essential feature of the nuclear wave function. At high energy (e,e{prime}) reactions, where Q{sup 2} > 1 (GeV/c){sup 2}, x = Q{sup 2}/2mq{sub o} > 1 and 1 GeV > q{sub o}> 300 {approximately} 400 MeV the scattering from low momentum nucleons is kinematically suppressed and there the evidence of SRC expected to be more prominent. These reactions have been intensively investigated during the last decade or so at SLAC on both light and heavy nuclei. The above kinematics allows one to compute the cross section through the processes local in space. To explain this the authors analyse the representation of the cross section as a Fourier transform of the commutator of electromagnetic currents and see that the major contribution in the cross section is given by the region of integration.

  3. Extended Kalman Doppler tracking and model determination for multi-sensor short-range radar

    NASA Astrophysics Data System (ADS)

    Mittermaier, Thomas J.; Siart, Uwe; Eibert, Thomas F.; Bonerz, Stefan

    2016-09-01

    A tracking solution for collision avoidance in industrial machine tools based on short-range millimeter-wave radar Doppler observations is presented. At the core of the tracking algorithm there is an Extended Kalman Filter (EKF) that provides dynamic estimation and localization in real-time. The underlying sensor platform consists of several homodyne continuous wave (CW) radar modules. Based on In-phase-Quadrature (IQ) processing and down-conversion, they provide only Doppler shift information about the observed target. Localization with Doppler shift estimates is a nonlinear problem that needs to be linearized before the linear KF can be applied. The accuracy of state estimation depends highly on the introduced linearization errors, the initialization and the models that represent the true physics as well as the stochastic properties. The important issue of filter consistency is addressed and an initialization procedure based on data fitting and maximum likelihood estimation is suggested. Models for both, measurement and process noise are developed. Tracking results from typical three-dimensional courses of movement at short distances in front of a multi-sensor radar platform are presented.

  4. Cluster formation in fluids with competing short-range and long-range interactions.

    PubMed

    Sweatman, Martin B; Fartaria, Rui; Lue, Leo

    2014-03-28

    We investigate the low density behaviour of fluids that interact through a short-ranged attraction together with a long-ranged repulsion (SALR potential) by developing a molecular thermodynamic model. The SALR potential is a model of effective solute interactions where the solvent degrees of freedom are integrated-out. For this system, we find that clusters form for a range of interaction parameters where attractive and repulsive interactions nearly balance, similar to micelle formation in aqueous surfactant solutions. We focus on systems for which equilibrium behaviour and liquid-like clusters (i.e., droplets) are expected, and find in addition a novel coexistence between a low density cluster phase and a high density cluster phase within a very narrow range of parameters. Moreover, a simple formula for the average cluster size is developed. Based on this formula, we propose a non-classical crystal nucleation pathway whereby macroscopic crystals are formed via crystal nucleation within microscopic precursor droplets. We also perform large-scale Monte Carlo simulations, which demonstrate that the cluster fluid phase is thermodynamically stable for this system.

  5. Pair correlation function of short-ranged square-well fluids.

    PubMed

    Largo, J; Solana, J R; Yuste, S B; Santos, A

    2005-02-22

    We have performed extensive Monte Carlo simulations in the canonical (NVT) ensemble of the pair correlation function for square-well fluids with well widths lambda-1 ranging from 0.1 to 1.0, in units of the diameter sigma of the particles. For each one of these widths, several densities rho and temperatures T in the ranges 0.1< or =rhosigma(3)< or =0.8 and T(c)(lambda) less or approximately T less or approximately 3T(c)(lambda), where T(c)(lambda) is the critical temperature, have been considered. The simulation data are used to examine the performance of two analytical theories in predicting the structure of these fluids: the perturbation theory proposed by Tang and Lu [Y. Tang and B. C.-Y. Lu, J. Chem. Phys. 100, 3079 (1994); 100, 6665 (1994)] and the nonperturbative model proposed by two of us [S. B. Yuste and A. Santos, J. Chem. Phys. 101 2355 (1994)]. It is observed that both theories complement each other, as the latter theory works well for short ranges and/or moderate densities, while the former theory works for long ranges and high densities.

  6. Relations between short-range and long-range Ising models.

    PubMed

    Angelini, Maria Chiara; Parisi, Giorgio; Ricci-Tersenghi, Federico

    2014-06-01

    We perform a numerical study of the long-range (LR) ferromagnetic Ising model with power law decaying interactions (J∝r{-d-σ}) on both a one-dimensional chain (d=1) and a square lattice (d=2). We use advanced cluster algorithms to avoid the critical slowing down. We first check the validity of the relation connecting the critical behavior of the LR model with parameters (d,σ) to that of a short-range (SR) model in an equivalent dimension D. We then study the critical behavior of the d=2 LR model close to the lower critical σ, uncovering that the spatial correlation function decays with two different power laws: The effect of the subdominant power law is much stronger than finite-size effects and actually makes the estimate of critical exponents very subtle. By including this subdominant power law, the numerical data are consistent with the standard renormalization group (RG) prediction by Sak [Phys. Rev. B 8, 281 (1973)], thus making not necessary (and unlikely, according to Occam's razor) the recent proposal by Picco [arXiv:1207.1018] of having a new set of RG fixed points in addition to the mean-field one and the SR one.

  7. Deciphering a transcriptional regulatory code: modeling short-range repression in the Drosophila embryo.

    PubMed

    Fakhouri, Walid D; Ay, Ahmet; Sayal, Rupinder; Dresch, Jacqueline; Dayringer, Evan; Arnosti, David N

    2010-01-01

    Systems biology seeks a genomic-level interpretation of transcriptional regulatory information represented by patterns of protein-binding sites. Obtaining this information without direct experimentation is challenging; minor alterations in binding sites can have profound effects on gene expression, and underlie important aspects of disease and evolution. Quantitative modeling offers an alternative path to develop a global understanding of the transcriptional regulatory code. Recent studies have focused on endogenous regulatory sequences; however, distinct enhancers differ in many features, making it difficult to generalize to other cis-regulatory elements. We applied a systematic approach to simpler elements and present here the first quantitative analysis of short-range transcriptional repressors, which have central functions in metazoan development. Our fractional occupancy-based modeling uncovered unexpected features of these proteins' activity that allow accurate predictions of regulation by the Giant, Knirps, Krüppel, and Snail repressors, including modeling of an endogenous enhancer. This study provides essential elements of a transcriptional regulatory code that will allow extensive analysis of genomic information in Drosophila melanogaster and related organisms.

  8. Percolation transition of short-ranged square well fluids in bulk and confinement.

    PubMed

    Neitsch, Helge; Klapp, Sabine H L

    2013-02-14

    Using grand canonical Monte Carlo simulations, we investigate the percolation behavior of a square-well fluid with an ultra-short range of attraction in three dimension (3D) and in confined geometry. The latter is defined through two parallel and structureless walls (slit-pore). We focus on temperatures above the critical temperature of the (metastable) condensation transition of the 3D system. Investigating a broad range of systems sizes, we first determine the percolation thresholds, i.e., the critical packing fraction for percolation η(c). For the slit-pore systems, η(c) is found to vary with the wall separation L(z) in a continuous but non-monotonic way, η(c)(L(z)→∞)=η(c)(3D). We also report results for critical exponents of the percolation transition, specifically, the exponent ν of the correlation length ξ and the two fisher exponents τ and σ of the cluster-size distribution. These exponents are obtained from a finite-size analysis involving the cluster-size distribution and the radii of gyration distribution at the percolation threshold. Within the accuracy of our simulations, the values of the critical exponents of our 3D system are comparable to those of 3D random percolation theory. For narrow slit-pores, the estimated exponents are found to be close to those obtained from the random percolation theory in two dimensions.

  9. Long-ranged contributions to solvation free energies from theory and short-ranged models

    NASA Astrophysics Data System (ADS)

    Remsing, Richard C.; Liu, Shule; Weeks, John D.

    2016-03-01

    Long-standing problems associated with long-ranged electrostatic interactions have plagued theory and simulation alike. Traditional lattice sum (Ewald-like) treatments of Coulomb interactions add significant overhead to computer simulations and can produce artifacts from spurious interactions between simulation cell images. These subtle issues become particularly apparent when estimating thermodynamic quantities, such as free energies of solvation in charged and polar systems, to which long-ranged Coulomb interactions typically make a large contribution. In this paper, we develop a framework for determining very accurate solvation free energies of systems with long-ranged interactions from models that interact with purely short-ranged potentials. Our approach is generally applicable and can be combined with existing computational and theoretical techniques for estimating solvation thermodynamics. We demonstrate the utility of our approach by examining the hydration thermodynamics of hydrophobic and ionic solutes and the solvation of a large, highly charged colloid that exhibits overcharging, a complex nonlinear electrostatic phenomenon whereby counterions from the solvent effectively overscreen and locally invert the integrated charge of the solvated object.

  10. Cluster formation in fluids with competing short-range and long-range interactions

    SciTech Connect

    Sweatman, Martin B. Fartaria, Rui; Lue, Leo

    2014-03-28

    We investigate the low density behaviour of fluids that interact through a short-ranged attraction together with a long-ranged repulsion (SALR potential) by developing a molecular thermodynamic model. The SALR potential is a model of effective solute interactions where the solvent degrees of freedom are integrated-out. For this system, we find that clusters form for a range of interaction parameters where attractive and repulsive interactions nearly balance, similar to micelle formation in aqueous surfactant solutions. We focus on systems for which equilibrium behaviour and liquid-like clusters (i.e., droplets) are expected, and find in addition a novel coexistence between a low density cluster phase and a high density cluster phase within a very narrow range of parameters. Moreover, a simple formula for the average cluster size is developed. Based on this formula, we propose a non-classical crystal nucleation pathway whereby macroscopic crystals are formed via crystal nucleation within microscopic precursor droplets. We also perform large-scale Monte Carlo simulations, which demonstrate that the cluster fluid phase is thermodynamically stable for this system.

  11. Short-range interactions versus long-range correlations in bird flocks

    NASA Astrophysics Data System (ADS)

    Cavagna, Andrea; Del Castello, Lorenzo; Dey, Supravat; Giardina, Irene; Melillo, Stefania; Parisi, Leonardo; Viale, Massimiliano

    2015-07-01

    Bird flocks are a paradigmatic example of collective motion. One of the prominent traits of flocking is the presence of long range velocity correlations between individuals, which allow them to influence each other over the large scales, keeping a high level of group coordination. A crucial question is to understand what is the mutual interaction between birds generating such nontrivial correlations. Here we use the maximum entropy (ME) approach to infer from experimental data of natural flocks the effective interactions between individuals. Compared to previous studies, we make a significant step forward as we retrieve the full functional dependence of the interaction on distance, and find that it decays exponentially over a range of a few individuals. The fact that ME gives a short-range interaction even though its experimental input is the long-range correlation function, shows that the method is able to discriminate the relevant information encoded in such correlations and single out a minimal number of effective parameters. Finally, we show how the method can be used to capture the degree of anisotropy of mutual interactions.

  12. Range effect on percolation threshold and structural properties for short-range attractive spheres

    NASA Astrophysics Data System (ADS)

    Wei, Jiachen; Xu, Limei; Song, Fan

    2015-01-01

    Percolation or aggregation in colloidal system is important in many fields of science and technology. Using molecular dynamics simulations, we study the percolation behavior for systems consisting of spheres interacting with short-range square-well (SRSW) which mimic colloidal particles, with different interaction ranges. We specifically focus on how the interaction range affects the percolation thresholds in the supercritical region. We find that the contact percolation boundaries are strongly dependent on the interaction ranges of SRSW, especially away from the liquid-liquid critical point. However, varying the interaction ranges of SRSW does not affect much the structure along percolation boundaries especially for low packing fractions. For instance, along the percolation boundary, distributions of coordination number show convergence, and distributions of cluster size are universal for different interaction ranges considered. In addition, either the bond percolation boundaries or isolines of average bond coordination number collapse to those for Baxter sticky model on phase diagram, which confirms the extended law of corresponding states.

  13. An Energy-Harvesting Wireless-Interface SoC for Short-Range Data Communication

    NASA Astrophysics Data System (ADS)

    Mikami, Shinji; Matsuno, Tetsuro; Miyama, Masayuki; Kawaguchi, Hiroshi; Yoshimoto, Masahiko; Ono, Hiroaki

    This paper describes design and verification of a wireless-interface SoC (system-on-a-chip) for a wireless battery-less mouse with short-range data-communication capability. The SoC comprises an RF transmitter and microcontroller. The SoC, which is powered by an electric generator that exploits gyration energy by dragging the mouse, was fabricated using a TSMC 0.18-um CMOS process. The features of the SoC are the adoption of a simple FSK modulation scheme, single-end configuration on the RF transmitter, and specific microcontroller design for mouse operation. We verified that the RF transmitter can make data communication within a 1-m range at 2.17 mW, and the microcontroller consumes 0.03 mW at 1 MHz, which exhibits that the total power consumption is 2.2 mW. This is sufficiently low for the SoC to operate with energy harvesting.

  14. A UHF RFID system with on-chip-antenna tag for short range communication

    NASA Astrophysics Data System (ADS)

    Qi, Peng; Chun, Zhang; Xijin, Zhao; Zhihua, Wang

    2015-05-01

    A UHF RF identification system based on the 0.18 μm CMOS process has been developed for short range and harsh size requirement applications, which is composed of a fully integrated tag and a special reader. The whole tag chip with the antenna takes up an area of 0.36 mm2, which is smaller than other reported tags with an on-chip antenna (OCA) using the standard CMOS process. A self-defined protocol is proposed to reduce the power consumption, and minimize the size of the tag. The specialized SOC reader system consists of the RF transceiver, digital baseband, MCU and host interface. Its power consumption is about 500 mW. Measurement results show that the system's reading range is 2 mm with 20 dBm reader output power. With an inductive antenna printed on a paper substrate around the OCA tag, the reading range can be extended from several centimeters to meters, depending on the shape and size of the inductive antenna.

  15. Visualization of a short-range Wnt gradient in the intestinal stem-cell niche.

    PubMed

    Farin, Henner F; Jordens, Ingrid; Mosa, Mohammed H; Basak, Onur; Korving, Jeroen; Tauriello, Daniele V F; de Punder, Karin; Angers, Stephane; Peters, Peter J; Maurice, Madelon M; Clevers, Hans

    2016-02-18

    Mammalian Wnt proteins are believed to act as short-range signals, yet have not been previously visualized in vivo. Self-renewal, proliferation and differentiation are coordinated along a putative Wnt gradient in the intestinal crypt. Wnt3 is produced specifically by Paneth cells. Here we have generated an epitope-tagged, functional Wnt3 knock-in allele. Wnt3 covers basolateral membranes of neighbouring stem cells. In intestinal organoids, Wnt3-transfer involves direct contact between Paneth cells and stem cells. Plasma membrane localization requires surface expression of Frizzled receptors, which in turn is regulated by the transmembrane E3 ligases Rnf43/Znrf3 and their antagonists Lgr4-5/R-spondin. By manipulating Wnt3 secretion and by arresting stem-cell proliferation, we demonstrate that Wnt3 mainly travels away from its source in a cell-bound manner through cell division, and not through diffusion. We conclude that stem-cell membranes constitute a reservoir for Wnt proteins, while Frizzled receptor turnover and 'plasma membrane dilution' through cell division shape the epithelial Wnt3 gradient.

  16. Effect of long- and short-range interactions on the thermodynamics of dipolar spin ice

    NASA Astrophysics Data System (ADS)

    Shevchenko, Yuriy; Makarov, Aleksandr; Nefedev, Konstantin

    2017-02-01

    The thermodynamic properties of dipolar spin ice on square, honeycomb and shakti lattices in the long-range and short-range dipole interaction models are studied. Exact solutions for the density of states, temperature dependencies of heat capacity, and entropy are obtained for these lattices with a finite number of point dipoles by means of complete enumeration. The magnetic susceptibility and average size of the largest low-energy cluster are calculated for square spin ice by means of Wang-Landau and Metropolis methods. We show that the long-range interaction leads to a blurring of the energy spectrum for all considered lattices. The inclusion of the long-range interaction leads to a significant change in the thermodynamic behaviour. An additional peak of heat capacity appears in the case of the honeycomb lattice. The critical temperature shifts in the direction of low or high temperatures; the direction depends on the lattice geometry. The critical temperature of the phase transition of square spin ice in the long-range model with frustrated ground states is obtained with the Wang-Landau and Metropolis methods independently.

  17. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    SciTech Connect

    Antonowicz, J. Pietnoczka, A.; Pękała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-28

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  18. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    NASA Astrophysics Data System (ADS)

    Antonowicz, J.; Pietnoczka, A.; Pekała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-01

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  19. Bond order via light-induced synthetic many-body interactions of ultracold atoms in optical lattices

    NASA Astrophysics Data System (ADS)

    Caballero-Benitez, Santiago F.; Mekhov, Igor B.

    2016-11-01

    We show how bond order emerges due to light mediated synthetic interactions in ultracold atoms in optical lattices in an optical cavity. This is a consequence of the competition between both short- and long-range interactions designed by choosing the optical geometry. Light induces effective many-body interactions that modify the landscape of quantum phases supported by the typical Bose-Hubbard model. Using exact diagonalization of small system sizes in one-dimension, we present the many-body quantum phases the system can support via the interplay between the density and bond (or matter-wave coherence) interactions. We find numerical evidence to support that dimer phases due to bond order are analogous to valence bond states. Different possibilities of light-induced atomic interactions are considered that go beyond the typical atomic system with dipolar and other intrinsic interactions. This will broaden the Hamiltonian toolbox available for quantum simulation of condensed matter physics via atomic systems.

  20. Large Magnetocaloric Effect Around Room Temperature in Amorphous Fe-Gd-Zr Alloy Ribbon with Short-Range Interactions

    NASA Astrophysics Data System (ADS)

    Thanh, Tran Dang; Yen, Nguyen Hai; Duc, Nguyen Huu; Phan, The-Long; Dan, Nguyen Huy; Yu, Seong-Cho

    2016-05-01

    In this work, we present a detailed study on the magnetocaloric effect and the critical behaviors of an amorphous Fe88Gd2Zr10 alloy ribbon prepared by using a rapid quenching method. We point out that the value of maximum magnetic entropy change (|∆ S max|) of amorphous Fe88Gd2Zr10 alloy ribbon appeared at near room temperature and versus Δ H obeys a power law, |∆ S max| = a·Δ H n. In addition, all Δ S m( T, Δ H) data measured at different Δ H values are collapsed onto a universal master curve. Interestingly, M 2 versus H/ M curves prove amorphous Fe88Gd2Zr10 ribbon exhibitied a second-order magnetic phase transition. The critical exponents ( β, γ, and δ) obtained from the modified Arrott plots and the Kouvel-Fisher methods, and critical isotherm analysis are very close to those expected for the 3D-Heisenberg model, proving ferromagnetic short-range interactions exist in amorphous Fe88Gd2Zr10 ribbon.

  1. A scaling theory for the long-range to short-range crossover and an infrared duality

    NASA Astrophysics Data System (ADS)

    Behan, Connor; Rastelli, Leonardo; Rychkov, Slava; Zan, Bernardo

    2017-09-01

    We study the second-order phase transition in the d-dimensional Ising model with long-range interactions decreasing as a power of the distance 1/rd+s . For s below some known value s* , the transition is described by a conformal field theory without a local stress tensor operator, with critical exponents varying continuously as functions of s. At s=s* , the phase transition crosses over to the short-range universality class. While the location s* of this crossover has been known for 40 years, its physics has not been fully understood, the main difficulty being that the standard description of the long-range critical point is strongly coupled at the crossover. In this paper we propose another field-theoretic description which, on the contrary, is weakly coupled near the crossover. We use this description to clarify the nature of the crossover and make predictions about the critical exponents. That the same long-range critical point can be reached from two different UV descriptions provides a new example of infrared duality. Dedicated to John Cardy on the occasion of his 70th birthday.

  2. A journey from order to disorder - atom by atom transformation from graphene to a 2D carbon glass.

    PubMed

    Eder, Franz R; Kotakoski, Jani; Kaiser, Ute; Meyer, Jannik C

    2014-02-11

    One of the most interesting questions in solid state theory is the structure of glass, which has eluded researchers since the early 1900's. Since then, two competing models, the random network theory and the crystallite theory, have both gathered experimental support. Here, we present a direct, atomic-level structural analysis during a crystal-to-glass transformation, including all intermediate stages. We introduce disorder on a 2D crystal, graphene, gradually, utilizing the electron beam of a transmission electron microscope, which allows us to capture the atomic structure at each step. The change from a crystal to a glass happens suddenly, and at a surprisingly early stage. Right after the transition, the disorder manifests as a vitreous network separating individual crystallites, similar to the modern version of the crystallite theory. However, upon increasing disorder, the vitreous areas grow on the expense of the crystallites and the structure turns into a random network. Thereby, our results show that, at least in the case of a 2D structure, both of the models can be correct, and can even describe the same material at different degrees of disorder.

  3. Atomic kinetic research of ordered quantum dot growth induced by dislocation on the substrate

    NASA Astrophysics Data System (ADS)

    Zhao, Chang; Zhao, M.; Wang, Y.; Lv, A. J.; Xing, G. J.; Ma, Y. C.

    2014-01-01

    In this study, the modified effects of stress originating from the dislocation on the substrate to the semiconductor quantum dot growth are investigated by performing an event-based continuous kinetic Monte Carlo simulation, in which the contribution of the dangling bond of the atom is considered. The research results indicate that the change of binding energy initiated by the stress between the deposit atom and the substrate's atoms may significantly influence the atoms' kinetic behaviors, and on the pattern surface the atoms' kinetic effects are very sensitive to the initial condition of the substrate. In addition, the dependence of the atomic kinetics on the growth flux and temperature are also studied. The simulation results are in good qualitative agreement with those of our experiment.

  4. Importance of Achromatic Contrast in Short-Range Fruit Foraging of Primates

    PubMed Central

    Hiramatsu, Chihiro; Melin, Amanda D.; Aureli, Filippo; Schaffner, Colleen M.; Vorobyev, Misha; Matsumoto, Yoshifumi; Kawamura, Shoji

    2008-01-01

    Trichromatic primates have a ‘red-green’ chromatic channel in addition to luminance and ‘blue-yellow’ channels. It has been argued that the red-green channel evolved in primates as an adaptation for detecting reddish or yellowish objects, such as ripe fruits, against a background of foliage. However, foraging advantages to trichromatic primates remain unverified by behavioral observation of primates in their natural habitats. New World monkeys (platyrrhines) are an excellent model for this evaluation because of the highly polymorphic nature of their color vision due to allelic variation of the L-M opsin gene on the X chromosome. In this study we carried out field observations of a group of wild, frugivorous black-handed spider monkeys (Ateles geoffroyi frontatus, Gray 1842, Platyrrhini), consisting of both dichromats (n = 12) and trichromats (n = 9) in Santa Rosa National Park, Costa Rica. We determined the color vision types of individuals in this group by genotyping their L-M opsin and measured foraging efficiency of each individual for fruits located at a grasping distance. Contrary to the predicted advantage for trichromats, there was no significant difference between dichromats and trichromats in foraging efficiency and we found that the luminance contrast was the main determinant of the variation of foraging efficiency among red-green, blue-yellow and luminance contrasts. Our results suggest that luminance contrast can serve as an important cue in short-range foraging attempts despite other sensory cues that could be available. Additionally, the advantage of red-green color vision in primates may not be as salient as previously thought and needs to be evaluated in further field observations. PMID:18836576

  5. Short-Range Structure of Clouds Studied by High Resolution Photography From the Surface

    NASA Astrophysics Data System (ADS)

    Schwartz, S. E.; Huang, D.; Vladutescu, D. V.

    2015-12-01

    Clouds exhibit structures at a wide range of length scales. Passive radiometry from satellite shows structure on scales of tens to thousands of kilometers, but there is much structure at short spatial scales not resolved by satellite imagery. Here we use a commercial camera having high spatial resolution (~20 μrad) and high dynamic range (16 bits in each of three color channels) in narrow field-of-view (20 mrad, 110 mrad), zenith-looking mode from the surface, to examine clouds at the scale of centimeters to a few hundred meters, focusing on non-precipitating single-layer clouds during daytime. Up-looking photography of clouds from the surface affords the further advantage, relative to satellite imagery, of black background (space) with contributions to radiance only from blue sky (Rayleigh scattering), aerosols, and clouds, permitting reconstruction of observed radiance by radiation transfer modeling. Contrast between cloudy and cloud-free sky is enhanced in Red/(Red + Blue), RRB, image Figure 1, but no unique value of RRB distinguishes a pixel as cloud vs. cloud-free. Short-range variability is characterized by the autocorrelation length scale, which is not uncommonly as short as a few meters; longer range variability, such as cloud characteristic size, separation distance, and cloud spatial organization, is also characterized. Scene reconstruction yields the 2D distribution of cloud optical depth; spatial inhomogeneity is attributed mainly to horizontal variation in vertical motion of the air and resultant condensation or evaporation associated with upward or downward motion, respectively. Alternative approaches to calculation of the radiative influence of such clouds from the autocorrelation structure of the cloud field are examined. Figure 1. RGB image of zenith sky at New York City, May 22, 2015, (field of view 21 mrad corresponding to 56 m at cloud altitude 2.6 km) showing broken single-layer cloud; corresponding RRB image; and autocorrelation of RRB image.

  6. Are short-range forecasts of precipitation sensitive to AEW-like moist singular vector perturbations?

    NASA Astrophysics Data System (ADS)

    Cornforth, Rosalind J.; Hoskins, Brian J.

    2010-05-01

    Moist singular vectors (MSV) have been applied successfully to predicting mid-latitude storms growing in association with latent heat of condensation. Tropical cyclone sensitivity has also been assessed. There is now considerable interest in its application for singular vector computation in the tropics and tropical perturbations for the ensemble system on a wider basis than targeting tropical cyclones. Extending this approach to more general tropical weather systems, MSVs are evaluated here for understanding African easterly waves (AEWs) and associated rainfall. These are arguably, the tropical systems that exhibit dynamical organization in a manner that is most similar to extra-tropical weather systems, and yet provide the context for convection that is of great importance both in their development and their subsequent behaviour, in their impact on society and in yielding ideas on the interaction between physics and dynamics in the tropical atmosphere that may have more general relevance. The systematic errors that can plague the forecast skill in this region may be improved by process studies aimed at understanding the fundamental dynamics governing the WAM. Here we present results from a study that aims to use MSVs to build on our recently gained theoretical insights from normal mode studies of the moist AEJ-AEW system, and to learn for practical purposes, whether MSVs targeted on W. Africa could be suitable as perturbations to the ECMWF ensemble system for improving AEW prediction and associated rainfall. First results, without initial moisture perturbations, suggest MSVs may be used advantageously. Perturbations bear similar structural and energy profiles to previous idealised non-linear studies and observations. Strong sensitivities prevail in the metrics and trajectories chosen. The benefits of including initial moisture perturbations are appraised in the light of these findings with emphasis on perturbation growth mechanisms and the sensitivity of short-range

  7. Time-evolution scenarios for short-range depletion gels subjected to the gravitational stress.

    PubMed

    Secchi, Eleonora; Buzzaccaro, Stefano; Piazza, Roberto

    2014-08-07

    By exploiting photon correlation imaging and ghost particle velocimetry, two novel optical correlation techniques particularly suited to the investigation of the microscopic dynamics of spatially heterogeneous samples, we investigate the settling and restructuring dynamics of colloidal gels generated by short-ranged depletion interactions. Three distinct regions can be clearly set apart within the liquid-liquid coexistence region of the phase diagram where gel formation is observed. When depletion forces are barely sufficient to drive the system within the metastable region, an initial disordered gel hosts the rapid nucleation of crystallites, which stress the gel structure until it fully collapses, leading to the formation of a macroscopic colloidal crystal. For stronger attractive forces, two distinct scenarios are observed, depending on the particle volume fraction ϕ0 of the original suspension. At low ϕ0, the gel breaks after a short delay time into separate clusters, which rapidly settle until they compact in a denser disordered phase. The latter eventually undergoes a slow compression, which is accounted for by a poroelastic model where the microscopic gel dynamics is fully ruled by its macroscopic deformation. Yet, it is the intermediate stage between cluster settling and final compaction which displays very peculiar features, evidenced by anomalous settling profiles which are not shared, to our knowledge, by any other sedimentation processes investigated so far. For larger values of ϕ0, gel breaking is conversely suppressed, the structure undergoes a continuous compression that cannot be explained by a poroelastic model, and the microscopic dynamics is characterized by logarithmic correlation functions resembling those found for attractive glasses.

  8. Higher-order effects on uncertainties of clocks of Mg atoms in an optical lattice

    NASA Astrophysics Data System (ADS)

    Ovsiannikov, V. D.; Marmo, S. I.; Mokhnenko, S. N.; Palchikov, V. G.

    2017-01-01

    Multipole, nonlinear and anharmonic effects on the optical-lattice-based clocks of Mg atoms are evaluated theoretically. Dipole polarizabilities, hyperpolarizabilities and multipolar polarizabilities for Mg atoms are calculated in the single-electron approximation with the use of analytical presentations for the wave and Green’s functions in the modified model-potential approach. For comparison, the data are also given for atoms of the group IIb elements (Zn, Cd, Hg).

  9. Pump-probe study of atoms and small molecules with laser driven high order harmonics

    NASA Astrophysics Data System (ADS)

    Cao, Wei

    A commercially available modern laser can emit over 1015 photons within a time window of a few tens of femtoseconds (10-15second), which can be focused into a spot size of about 10 mum, resulting in a peak intensity above 1014W/cm2. This paves the way for table-top strong field physics studies such as above threshold ionization (ATI), non-sequential double ionization (NSDI), high order harmonic generation (HHG), etc.. Among these strong laser-matter interactions, high order harmonic generation, which combines many photons of the fundamental laser field into a single photon, offers a unique way to generate light sources in the vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) region. High order harmonic photons are emitted within a short time window from a few tens of femtoseconds down to a few hundreds of attoseconds (10 -18second). This highly coherent nature of HHG allows it to be synchronized with an infrared (IR) laser pulse, and the pump-probe technique can be adopted to study ultrafast dynamic processes in a quantum system. The major work of this thesis is to develop a table-top VUV(EUV) light source based on HHG, and use it to study dynamic processes in atoms and small molecules with the VUV(EUV)-pump IR-probe method. A Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) apparatus is used for momentum imaging of the interaction products. Two types of high harmonic pump pulses are generated and applied for pump-probe studies. The first one consists of several harmonics forming a short attosecond pulse train (APT) in the EUV regime (around 40 eV). We demonstrate that, (1) the auto-ionization process triggered by the EUV in cation carbon-monoxide and oxygen molecules can be modified by scanning the EUV-IR delay, (2) the phase information of quantum trajectories in bifurcated high harmonics can be extracted by performing an EUV-IR cross-correlation experiment, thus disclosing the macroscopic quantum control in HHG. The second type of high harmonic source

  10. Experimental nowcasting and short-range forecasting of severe storms at the ESSL Testbed

    NASA Astrophysics Data System (ADS)

    Groenemeijer, Pieter; Holzer, Alois M.; Pistotnik, Georg; Riemann-Campe, Kathrin

    2013-04-01

    From 4 June to 6 July 2012, the first ESSL Testbed has taken place at the Research and Training Centre of the European Severe Storms Laboratory in Wiener Neustadt, Austria. During this time, researchers and forecasters worked closely together putting new forecast supporting products to the test. The Testbed's main activity is to prepare experimental forecasts for severe weather, of which short-range forecasts and nowcasts for the following 2 hours form an important part. These nowcasts are made using new tools based on NWP, radar and satellite, as well as surface and upper-air observations. Subsequently, a verification of the forecasts is performed using the European Severe Weather Database, followed by an evaluation of forecasting tools and techniques. Inspired by the annual Spring Program at NOAA's Hazardous Weather Testbed (HWT), the ESSL Testbed has a stronger focus on forecaster training than the HWT. Given the various backgrounds of the participants, an important Testbed goal is to acquaint its participants with severe weather forecasting methods and techniques that work universally. Among the tools that were evaluated at the 2012 Testbed were visualizations of high-resolution ensemble NWP (DWD's COSMO-DE-EPS), satellite-based cloud top cooling and overshooting top detection algorithms, lightning detection, and satellite and radar-based cell-tracking algorithms (DLR's Cb-TRAM and RadTRAM, and DWD's NowcastMix). In daily "Expert Lectures", that were broadcast online to remote participants, researchers provided background information on their products and internationally renowned experts in forecasting presented their viewpoints on storm forecasting and its scientific roots. Organized by ESSL in close cooperation with the Austrian Central Institute for Meteorology and Geodynamics (ZAMG), the Testbed was supported - among others - by the German Weather Service (DWD), EUMETSAT, WMO, ECMWF, VAISALA, and the GOES-R programme, providing products for evaluation and

  11. Improvement of RAMS precipitation forecast at the short-range through lightning data assimilation

    NASA Astrophysics Data System (ADS)

    Federico, Stefano; Petracca, Marco; Panegrossi, Giulia; Dietrich, Stefano

    2017-01-01

    This study shows the application of a total lightning data assimilation technique to the RAMS (Regional Atmospheric Modeling System) forecast. The method, which can be used at high horizontal resolution, helps to initiate convection whenever flashes are observed by adding water vapour to the model grid column. The water vapour is added as a function of the flash rate, local temperature, and graupel mixing ratio. The methodology is set up to improve the short-term (3 h) precipitation forecast and can be used in real-time forecasting applications. However, results are also presented for the daily precipitation for comparison with other studies. The methodology is applied to 20 cases that occurred in fall 2012, which were characterized by widespread convection and lightning activity. For these cases a detailed dataset of hourly precipitation containing thousands of rain gauges over Italy, which is the target area of this study, is available through the HyMeX (HYdrological cycle in the Mediterranean Experiment) initiative. This dataset gives the unique opportunity to verify the precipitation forecast at the short range (3 h) and over a wide area (Italy). Results for the 27 October case study show how the methodology works and its positive impact on the 3 h precipitation forecast. In particular, the model represents better convection over the sea using the lightning data assimilation and, when convection is advected over the land, the precipitation forecast improves over the land. It is also shown that the precise location of convection by lightning data assimilation improves the precipitation forecast at fine scales (meso-β). The application of the methodology to 20 cases gives a statistically robust evaluation of the impact of the total lightning data assimilation on the model performance. Results show an improvement of all statistical scores, with the exception of the bias. The probability of detection (POD) increases by 3-5 % for the 3 h forecast and by more than 5

  12. Methane Hydrate Formation in Thick Sand Reservoirs: Long-range Gas Transport or Short-range Methane Diffusion?

    NASA Astrophysics Data System (ADS)

    You, K.; Flemings, P. B.

    2016-12-01

    We developed two 2-D numerical models to simulate hydrate formation by long range methane gas transport and short-range methane diffusion. We interpret that methane hydrates in thick sands are most likely formed by long range gas transport where methane gas is transported upward into the hydrate stability zone (HSZ) under buoyancy and locally forms hydrate to its stability limit. In short-range methane diffusion, methane is generated locally by biodegradation of organic matter in mud and diffused into bounding sands where it forms hydrate. We could not simulate enough methane transport by diffusion to account for its observed concentration in thick sands. In our models, we include the capillary effect on dissolved methane solubility and on the hydrate phase boundary, sedimentation and different compaction in sand and mud, fracture generation as well as the fully coupled multiphase flow and multicomponent transport. We apply our models to a 12 meter-thick hydrate-bearing sand layer at Walker Ridge 313, Northern Gulf of Mexico. With the long-range gas transport, hydrate saturation is greater than 90% and salinity is increased from seawater to about 8 wt.% through the entire sand. With short-range diffusion, hydrate saturation is more than 90% at the sand base and is less than 10% in the overlying section; salinity is close to seawater when sand is deposited to 800 meter below seafloor by short-range methane diffusion. With short-range diffusion, the amount of hydrate formed is much less than that interpreted from the well log data. Two transient gas layers separated by a hydrate layer are formed from short-range diffusion caused by capillary effect. This could be interpreted as a double bottom simulating reflector. This study provides further insights into different hydrate formation mechanisms, and could serve as a base to confirm the hydrate formation mechanism in fields.

  13. Increased myocardial short-range forces in a rodent model of diabetes reflect elevated content of β myosin heavy chain.

    PubMed

    Chung, Charles S; Mitov, Mihail I; Callahan, Leigh Ann; Campbell, Kenneth S

    2014-06-15

    Diastolic dysfunction is a clinically significant problem for patients with diabetes and often reflects increased ventricular stiffness. Attached cross-bridges contribute to myocardial stiffness and produce short-range forces, but it is not yet known whether these forces are altered in diabetes. In this study, we tested the hypothesis that cross-bridge-based short-range forces are increased in the streptozotocin (STZ) induced rat model of type 1 diabetes. Chemically permeabilized myocardial preparations were obtained from 12week old rats that had been injected with STZ or vehicle 4weeks earlier, and activated in solutions with pCa (=-log10[Ca(2+)]) values ranging from 9.0 to 4.5. The short-range forces elicited by controlled length changes were ∼67% greater in the samples from the diabetic rats than in the control preparations. This change was mostly due to an increased elastic limit (the length change at the peak short-range force) as opposed to increased passive muscle stiffness. The STZ-induced increase in short-ranges forces is thus unlikely to reflect changes to titin and/or collagen filaments. Gel electrophoresis showed that STZ increased the relative expression of β myosin heavy chain. This molecular mechanism can explain the increased short-ranges forces observed in the diabetic tissue if β myosin molecules remain bound between the filaments for longer durations than α molecules during imposed movements. These results suggest that interventions that decrease myosin attachment times may be useful treatments for diastolic dysfunction associated with diabetes.

  14. Impact of Short-Range Forces on Defect Production from High-Energy Collisions

    DOE PAGES

    Stoller, R. E.; Tamm, A.; Béland, L. K.; ...

    2016-04-25

    Primary radiation damage formation in solid materials typically involves collisions between atoms that have up to a few hundred keV of kinetic energy. The distance between two colliding atoms can approach 0.05 nm during these collisions. At such small atomic separations, force fields fitted to equilibrium properties tend to significantly underestimate the potential energy of the colliding dimer. To enable molecular dynamics simulations of high-energy collisions, it is common practice to use a screened Coulomb force field to describe the interactions and to smoothly join this to the equilibrium force field at a suitable interatomic spacing. But, there is nomore » accepted standard method for choosing the parameters used in the joining process, and our results prove that defect production is sensitive to how the force fields are linked. A new procedure is presented that involves the use of ab initio calculations to determine the magnitude and spatial dependence of the pair interactions at intermediate distances, along with systematic criteria for choosing the joining parameters. Results are presented for the case of nickel, which demonstrate the use and validity of the procedure.« less

  15. Impact of Short-Range Forces on Defect Production from High-Energy Collisions

    SciTech Connect

    Stoller, R. E.; Tamm, A.; Béland, L. K.; Samolyuk, G. D.; Stocks, G. M.; Caro, A.; Slipchenko, L. V.; Osetsky, Yu. N.; Aabloo, A.; Klintenberg, M.; Wang, Y.

    2016-04-25

    Primary radiation damage formation in solid materials typically involves collisions between atoms that have up to a few hundred keV of kinetic energy. The distance between two colliding atoms can approach 0.05 nm during these collisions. At such small atomic separations, force fields fitted to equilibrium properties tend to significantly underestimate the potential energy of the colliding dimer. To enable molecular dynamics simulations of high-energy collisions, it is common practice to use a screened Coulomb force field to describe the interactions and to smoothly join this to the equilibrium force field at a suitable interatomic spacing. But, there is no accepted standard method for choosing the parameters used in the joining process, and our results prove that defect production is sensitive to how the force fields are linked. A new procedure is presented that involves the use of ab initio calculations to determine the magnitude and spatial dependence of the pair interactions at intermediate distances, along with systematic criteria for choosing the joining parameters. Results are presented for the case of nickel, which demonstrate the use and validity of the procedure.

  16. Impact of Short-Range Forces on Defect Production from High-Energy Collisions

    SciTech Connect

    Stoller, R. E.; Tamm, A.; Béland, L. K.; Samolyuk, G. D.; Stocks, G. M.; Caro, A.; Slipchenko, L. V.; Osetsky, Yu. N.; Aabloo, A.; Klintenberg, M.; Wang, Y.

    2016-04-25

    Primary radiation damage formation in solid materials typically involves collisions between atoms that have up to a few hundred keV of kinetic energy. The distance between two colliding atoms can approach 0.05 nm during these collisions. At such small atomic separations, force fields fitted to equilibrium properties tend to significantly underestimate the potential energy of the colliding dimer. To enable molecular dynamics simulations of high-energy collisions, it is common practice to use a screened Coulomb force field to describe the interactions and to smoothly join this to the equilibrium force field at a suitable interatomic spacing. But, there is no accepted standard method for choosing the parameters used in the joining process, and our results prove that defect production is sensitive to how the force fields are linked. A new procedure is presented that involves the use of ab initio calculations to determine the magnitude and spatial dependence of the pair interactions at intermediate distances, along with systematic criteria for choosing the joining parameters. Results are presented for the case of nickel, which demonstrate the use and validity of the procedure.

  17. Get Your Atoms in Order--An Open-Source Implementation of a Novel and Robust Molecular Canonicalization Algorithm.

    PubMed

    Schneider, Nadine; Sayle, Roger A; Landrum, Gregory A

    2015-10-26

    Finding a canonical ordering of the atoms in a molecule is a prerequisite for generating a unique representation of the molecule. The canonicalization of a molecule is usually accomplished by applying some sort of graph relaxation algorithm, the most common of which is the Morgan algorithm. There are known issues with that algorithm that lead to noncanonical atom orderings as well as problems when it is applied to large molecules like proteins. Furthermore, each cheminformatics toolkit or software provides its own version of a canonical ordering, most based on unpublished algorithms, which also complicates the generation of a universal unique identifier for molecules. We present an alternative canonicalization approach that uses a standard stable-sorting algorithm instead of a Morgan-like index. Two new invariants that allow canonical ordering of molecules with dependent chirality as well as those with highly symmetrical cyclic graphs have been developed. The new approach proved to be robust and fast when tested on the 1.45 million compounds of the ChEMBL 20 data set in different scenarios like random renumbering of input atoms or SMILES round tripping. Our new algorithm is able to generate a canonical order of the atoms of protein molecules within a few milliseconds. The novel algorithm is implemented in the open-source cheminformatics toolkit RDKit. With this paper, we provide a reference Python implementation of the algorithm that could easily be integrated in any cheminformatics toolkit. This provides a first step toward a common standard for canonical atom ordering to generate a universal unique identifier for molecules other than InChI.

  18. Microscopic nucleon spectral function for finite nuclei featuring two- and three-nucleon short-range correlations: The model versus ab initio calculations for three-nucleon systems

    NASA Astrophysics Data System (ADS)

    Ciofi degli Atti, Claudio; Mezzetti, Chiara Benedetta; Morita, Hiko

    2017-04-01

    order of magnitude less than the effect of two-nucleon short-range correlations. Conclusions: The convolution model of the spectral function of the three-nucleon systems featuring both two- and three-nucleon short-range correlations and correctly depending upon the ab initio two-nucleon relative and center-of-mass momentum distributions provides in the correlation region a satisfactory approximation of the spectral function in a wide range of momentum and removal energy. The extension of the model to complex nuclei is expected to provide a realistic microscopic parameter-free model of the spectral function, whose properties are therefore governed by the features of realistic two-nucleon interactions and the momentum distributions in a given nucleus.

  19. Magnetic ordering and exchange interactions in structural modifications of M n3Ga alloys: Interplay of frustration, atomic order, and off-stoichiometry

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii; Ruban, Andrei V.; Mohn, Peter

    2016-05-01

    Mn-Ga alloys close to the M n3Ga stoichiometry can be synthesized in three different crystal modifications: hexagonal, tetragonal, and face-centered cubic, both in bulk and in thin-film forms. The magnetic ordering of these modifications is varying from noncollinear antiferromagnetic in the hexagonal case to ferrimagnetic order in the tetragonal one, whereas it is still unknown for the atomically disordered fcc structure. Here we study the onset of magnetic order at finite temperatures in these systems on a first-principles basis calculating the interatomic magnetic exchange interactions in the high-temperature paramagnetic regime. We employ the disordered local moment formalism and the magnetic force theorem within the framework of the local spin-density approximation and Monte Carlo simulations taking also the effects of atomic disorder in fcc alloys into account. In particular we find the origin of the stabilization of the noncollinear 3 k structure in competition between antiferromagnetic inter- and in-plane couplings of frustrated kagome planes in hexagonal M n3Ga and predict the antiferromagnetic-1 collinear order due to frustration in fcc alloys. Special attention is paid to the effects of the off-stoichiometry and the consequences of atomic disorder. We calculate the site-preference energy of Ga antisite atoms in the tetragonal structures in the range of the compositions from M n3Ga to M n2Ga and slightly beyond and confirm the earlier explanation of the effect of magnetization increase due to Ga preferentially occupying one of the Mn sites.

  20. Photoluminescence polarization anisotropy for studying long-range structural ordering within semiconductor multi-atomic alloys and organic crystals

    SciTech Connect

    Prutskij, T.; Percino, J.; Orlova, T.; Vavilova, L.

    2013-12-04

    Long-range structural ordering within multi-component semiconductor alloys and organic crystals leads to significant optical anisotropy and, in particular, to anisotropy of the photoluminescence (PL) emission. The PL emission of ternary and quaternary semiconductor alloys is polarized if there is some amount of the atomic ordering within the crystal structure. We analyze the polarization of the PL emission from the quaternary GaInAsP semiconductor alloy grown by Liquid Phase Epitaxy (LPE) and conclude that it could be caused by low degree atomic ordering within the crystal structure together with the thermal biaxial strain due to difference between the thermal expansion coefficients of the layer and the substrate. We also study the state of polarization of the PL from organic crystals in order to identify different features of the crystal PL spectrum.