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Sample records for anisotropic lattice fields

  1. SU(3) lattice gauge autocorrelations with anisotropic action

    NASA Astrophysics Data System (ADS)

    Draper, Terrence; Nenkov, Constantine; Peardon, Mike

    1997-02-01

    We report results of autocorrelation measurements in pure SU(3) lattice gauge theory. The computations are performed on the CONVEX SPP1200 parallel platform within the CANOPY programming environment. The focus of our analysis is on typical autocorrelation times and optimization of the mixing ratio between overrelaxation and pseudo-heatbath sweeps for generating gauge field configurations. We study second order tadpole-improved approximation of the Wilson action in the gluon sector, which offers the advantage on smaller lattices (8 3 × 16 and 6 3 × 12 - 30). We also make use of anisotropic lattices, with temporal lattice spacing smaller than the spatial spacing, which prove useful for calculating noisy correlation functions with large spatial lattice discretization (of the order of 0.4 fm).

  2. Lattice-Boltzmann hydrodynamics of anisotropic active matter

    NASA Astrophysics Data System (ADS)

    de Graaf, Joost; Menke, Henri; Mathijssen, Arnold J. T. M.; Fabritius, Marc; Holm, Christian; Shendruk, Tyler N.

    2016-04-01

    A plethora of active matter models exist that describe the behavior of self-propelled particles (or swimmers), both with and without hydrodynamics. However, there are few studies that consider shape-anisotropic swimmers and include hydrodynamic interactions. Here, we introduce a simple method to simulate self-propelled colloids interacting hydrodynamically in a viscous medium using the lattice-Boltzmann technique. Our model is based on raspberry-type viscous coupling and a force/counter-force formalism, which ensures that the system is force free. We consider several anisotropic shapes and characterize their hydrodynamic multipolar flow field. We demonstrate that shape-anisotropy can lead to the presence of a strong quadrupole and octupole moments, in addition to the principle dipole moment. The ability to simulate and characterize these higher-order moments will prove crucial for understanding the behavior of model swimmers in confining geometries.

  3. Lattice-Boltzmann hydrodynamics of anisotropic active matter.

    PubMed

    de Graaf, Joost; Menke, Henri; Mathijssen, Arnold J T M; Fabritius, Marc; Holm, Christian; Shendruk, Tyler N

    2016-04-01

    A plethora of active matter models exist that describe the behavior of self-propelled particles (or swimmers), both with and without hydrodynamics. However, there are few studies that consider shape-anisotropic swimmers and include hydrodynamic interactions. Here, we introduce a simple method to simulate self-propelled colloids interacting hydrodynamically in a viscous medium using the lattice-Boltzmann technique. Our model is based on raspberry-type viscous coupling and a force/counter-force formalism, which ensures that the system is force free. We consider several anisotropic shapes and characterize their hydrodynamic multipolar flow field. We demonstrate that shape-anisotropy can lead to the presence of a strong quadrupole and octupole moments, in addition to the principle dipole moment. The ability to simulate and characterize these higher-order moments will prove crucial for understanding the behavior of model swimmers in confining geometries. PMID:27059561

  4. Strongly interacting particles on an anisotropic kagome lattice

    NASA Astrophysics Data System (ADS)

    Hotta, Chisa; Pollmann, Frank

    2009-01-01

    We study a model of strongly interacting spinless fermions and hard-core bosons on an anisotropic kagome lattice near 2/3-filling. Our main focus lies on the strongly anisotropic case in which the nearest-neighbor repulsions V and V' are large compared to the hopping amplitudes |t| and |t'|. When t = t' = 0, the system has a charge ordered insulating ground state where the charges align in striped configurations. Doping one electron or hole into the ground state yields an anisotropic metal at V' > V, where the particle fractionalizes along the V'-bonds while propagates along the V-bonds in a one-body like manner. The sixth order ring exchange processes around the hexagonal unit of the lattice play a crucial role in forming a bound state of fractional charges.

  5. Glueball Spectrum and Matrix Elements on Anisotropic Lattices

    SciTech Connect

    Y. Chen; A. Alexandru; S.J. Dong; T. Draper; I. Horvath; F.X. Lee; K.F. Liu; N. Mathur; C. Morningstar; M. Peardon; S. Tamhankar; B.L. Young; J.B. Zhang

    2006-01-01

    The glueball-to-vacuum matrix elements of local gluonic operators in scalar, tensor, and pseudoscalar channels are investigated numerically on several anisotropic lattices with the spatial lattice spacing ranging from 0.1fm - 0.2fm. These matrix elements are needed to predict the glueball branching ratios in J/{psi} radiative decays which will help identify the glueball states in experiments. Two types of improved local gluonic operators are constructed for a self-consistent check and the finite volume effects are studied. We find that lattice spacing dependence of our results is very weak and the continuum limits are reliably extrapolated, as a result of improvement of the lattice gauge action and local operators. We also give updated glueball masses with various quantum numbers.

  6. Dipolar matter-wave solitons in two-dimensional anisotropic discrete lattices

    NASA Astrophysics Data System (ADS)

    Chen, Huaiyu; Liu, Yan; Zhang, Qiang; Shi, Yuhan; Pang, Wei; Li, Yongyao

    2016-05-01

    We numerically demonstrate two-dimensional (2D) matter-wave solitons in the disk-shaped dipolar Bose-Einstein condensates (BECs) trapped in strongly anisotropic optical lattices (OLs) in a disk's plane. The considered OLs are square lattices which can be formed by interfering two pairs of plane waves with different intensities. The hopping rates of the condensates between two adjacent lattices in the orthogonal directions are different, which gives rise to a linearly anisotropic system. We find that when the polarized orientation of the dipoles is parallel to disk's plane with the same direction, the combined effects of the linearly anisotropy and the nonlocal nonlinear anisotropy strongly influence the formations, as well as the dynamics of the lattice solitons. Particularly, the isotropy-pattern solitons (IPSs) are found when these combined effects reach a balance. Motion, collision, and rotation of the IPSs are also studied in detail by means of systematic simulations. We further find that these IPSs can move freely in the 2D anisotropic discrete system, hence giving rise to an anisotropic effective mass. Four types of collisions between the IPSs are identified. By rotating an external magnetic field up to a critical angular velocity, the IPSs can still remain localized and play as a breather. Finally, the influences from the combined effects between the linear and the nonlocal nonlinear anisotropy with consideration of the contact and/or local nonlinearity are discussed too.

  7. Measuring the aspect ratio renormalization of anisotropic-lattice gluons

    SciTech Connect

    Alford, M.; Drummond, I. T.; Horgan, R. R.; Shanahan, H.; Peardon, M.

    2001-04-01

    Using tadpole-improved actions we investigate the consistency between different methods of measuring the aspect ratio renormalization of anisotropic-lattice gluons for bare aspect ratios {chi}{sub 0}=4,6,10 and inverse lattice spacing in the range a{sub s}{sup -1}=660--840 MeV. The tadpole corrections to the action, which are established self-consistently, are defined for two cases, mean link tadpoles in the Landau gauge and gauge invariant mean plaquette tadpoles. Parameters in the latter case exhibited no dependence on the spatial lattice size L, while in the former, parameters showed only a weak dependence on L easily extrapolated to L={infinity}. The renormalized anisotropy {chi}{sub R} was measured using both the torelon dispersion relation and the sideways potential method. There is general agreement between these approaches, but there are discrepancies which are evidence for the presence of lattice artifact contributions. For the torelon these are estimated to be O({alpha}{sub S}a{sub s}{sup 2}/R{sup 2}), where R is the flux-tube radius. We also present some new data that suggest that rotational invariance is established more accurately for the mean-link action than the plaquette action.

  8. Vortex-lattice pinning and critical current density in anisotropic high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Li, Yingxu; Li, Xiangyu; Kang, Guozheng; Gao, Yuanwen

    2016-10-01

    The anisotropy of critical current density is an impressive manifestation in the physics of high-temperature superconductors. We develop an analytical characterization of anisotropic flux-lattice pinning and critical current density in a system of random point defects. The effect of superconducting anisotropy on the pinning force and critical current density is formulated. The in-plane/out-of-plane anisotropy and microscopic characteristic lengths are incorporated in the field and angular dependence of the critical current density. This is helpful in understanding the physical essence of the scaling behavior in the experiments for critical current anisotropy. We discuss the role of strong and weak point defects in the anisotropic flux-lattice pinning. Relevance of the theory to the critical-state model is dictated as well.

  9. Lattice QCD in Background Fields

    SciTech Connect

    William Detmold, Brian Tiburzi, Andre Walker-Loud

    2009-06-01

    Electromagnetic properties of hadrons can be computed by lattice simulations of QCD in background fields. We demonstrate new techniques for the investigation of charged hadron properties in electric fields. Our current calculations employ large electric fields, motivating us to analyze chiral dynamics in strong QED backgrounds, and subsequently uncover surprising non-perturbative effects present at finite volume.

  10. Scalar field in the anisotropic universe

    SciTech Connect

    Kim, Hyeong-Chan; Minamitsuji, Masato

    2010-04-15

    We discuss the primordial spectrum of a massless and minimally coupled scalar field, produced during the initial anisotropic epoch before the onset of inflation. We consider two models of the anisotropic cosmology, the (planar) Kasner-de Sitter solution (Bianchi I) and the Taub-NUT-de Sitter solution (Bianchi IX), where the 3-space geometry is initially anisotropic, followed by the de Sitter phase due to the presence of a positive cosmological constant. We discuss the behavior of a quantized, massless and minimally coupled scalar field in the anisotropic stage. This scalar field is not the inflaton and hence does not contribute to the background dynamics. We focus on the quantization procedure and evolution in the preinflationary anisotropic background. Also, in this paper for simplicity the metric perturbations are not taken into account. The initial condition is set by the requirement that the scalar field is initially in an adiabatic state. Usually, in a quantum harmonic oscillator system, an adiabatic process implies the one where the potential changes slowly enough compared to its size, and the time evolution can be obtained from the zeroth order WKB approximation. In our case, such a vacuum state exists only for limited solutions of the anisotropic universe, whose spacetime structure is regular in the initial times. In this paper, we call our adiabatic vacuum state the anisotropic vacuum. In the Kasner-de Sitter model, for one branch of planar solutions there is an anisotropic vacuum unless k{sub 3{ne}}0, where k{sub 3} is the comoving momentum along the third direction, while in the other branch there is no anisotropic vacuum state. In the first branch, for the moderate modes, k{sub 3{approx}}k, where k is the total comoving momentum, the scalar power spectrum has an oscillatory behavior and its direction dependence is suppressed. For the planar modes, k{sub 3}<

  11. Symmetry analysis for anisotropic field theories

    SciTech Connect

    Parra, Lorena; Vergara, J. David

    2012-08-24

    The purpose of this paper is to study with the help of Noether's theorem the symmetries of anisotropic actions for arbitrary fields which generally depend on higher order spatial derivatives, and to find the corresponding current densities and the Noether charges. We study in particular scale invariance and consider the cases of higher derivative extensions of the scalar field, electrodynamics and Chern-Simons theory.

  12. Lifting mean field degeneracies in anisotropic spin systems

    NASA Astrophysics Data System (ADS)

    Sizyuk, Yuriy; Perkins, Natalia; Wolfle, Peter

    We propose a method for calculating the fluctuation contribution to the free energy of anisotropic spin systems with generic bilinear superexchange magnetic Hamiltonian based on the Hubbard-Stratonovich transformation. We show that this contribution splits the set of mean field degenerate states with rotational symmetry, and chooses states with the order parameter directed along lattice symmetric directions as the true ground states. We consider the simple example of Heisenberg-compass model on cubic lattice to show that depending on the relative strength of the compass and Heisenberg interactions the spontaneous magnetization is pinned to either one of the cubic directions or one of the cubic body diagonals with a intermediate phase in between where the minima and maxima of the free energy interchange. DMR-1005932, DMR-1511768, and NSF PHY11-25915.

  13. Momentum transport in strongly coupled anisotropic plasmas in the presence of strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Finazzo, Stefano Ivo; Critelli, Renato; Rougemont, Romulo; Noronha, Jorge

    2016-09-01

    We present a holographic perspective on momentum transport in strongly coupled, anisotropic non-Abelian plasmas in the presence of strong magnetic fields. We compute the anisotropic heavy quark drag forces and Langevin diffusion coefficients and also the anisotropic shear viscosities for two different holographic models, namely, a top-down deformation of strongly coupled N =4 super-Yang-Mills theory triggered by an external Abelian magnetic field, and a bottom-up Einstein-Maxwell-dilaton (EMD) model which is able to provide a quantitative description of lattice QCD thermodynamics with (2 +1 ) flavors at both zero and nonzero magnetic fields. We find that, in general, energy loss and momentum diffusion through strongly coupled anisotropic plasmas are enhanced by a magnetic field being larger in transverse directions than in the direction parallel to the magnetic field. Moreover, the anisotropic shear viscosity coefficient is smaller in the direction of the magnetic field than in the plane perpendicular to the field, which indicates that strongly coupled anisotropic plasmas become closer to the perfect fluid limit along the magnetic field. We also present, in the context of the EMD model, holographic predictions for the entropy density and the crossover critical temperature in a wider region of the (T , B ) phase diagram that has not yet been covered by lattice simulations. Our results for the transport coefficients in the phenomenologically realistic magnetic EMD model could be readily used as inputs in numerical codes for magnetohydrodynamics.

  14. Lattice-mismatch-induced twinning for seeded growth of anisotropic nanostructures.

    PubMed

    Wang, Zhenni; Chen, Zhengzheng; Zhang, Hui; Zhang, Zhaorui; Wu, Haijun; Jin, Mingshang; Wu, Chao; Yang, Deren; Yin, Yadong

    2015-03-24

    Synthesis of anisotropic nanostructures from materials with isotropic crystal structures often requires the use of seeds containing twin planes to break the crystalline symmetry and promote the preferential anisotropic growth. Controlling twinning in seeds is therefore critically important for high-yield synthesis of many anisotropic nanostructures. Here, we demonstrate a unique strategy to induce twinning in metal nanostructures for anisotropic growth by taking advantage of the large lattice mismatch between two metals. By using Au-Cu as an example, we show, both theoretically and experimentally, that deposition of Cu to the surface of single-crystalline Au seeds can build up strain energy, which effectively induces the formation of twin planes. Subsequent seeded growth allows the production of Cu nanorods with high shape anisotropy that is unachievable without the use of Au seeds. This work provides an effective strategy for the preparation of anisotropic metal nanostructures. PMID:25744113

  15. Edge states in a honeycomb lattice: effects of anisotropic hopping and mixed edges

    SciTech Connect

    Dahal, Hari P; Balatsky, Alexander V; Sinistsyn, N A; Hu, Zi - Xiang; Yang, Kun

    2008-01-01

    We study the edge states in graphene in the presence of a magnetic field perpendicular to the plane of the lattice. Most of the work done so far discusses the edge states in either zigzag or armchair edge graphene considering an isotropic electron hopping. In practice, graphene can have a mixture of armchair and zigzag edges and the electron hopping can be anisotropic, which is the subject of this article. We predict that the mixed edges smear the enhanced local density of states (LDOS) at E=0 of the zigzag edge and, on the other hand, the anisotropic hopping gives rise to the enhanced LDOS at E=0 in the armchair edge. The behavior of the LDOS can be studied using scanning tunneling microscopy (STM) experiments. We suggest that care must be taken while interpreting the STM data, because the clear distinction between the zigzag edge (enhanced LDOS at E=0) and armchair edge (suppressed LDOS at E=0) can be lost if the hopping is not isotropic and if the edges are mixed.

  16. High Statistics Analysis using Anisotropic Clover Lattices: (III) Baryon-Baryon Interactions

    SciTech Connect

    Silas Beane; Detmold, William; Lin, Huey-Wen; Luu, Thomas C.; Orginos, Kostas; Savage, Martin; Torok, Aaron M.; Walker-Loud, Andre

    2010-03-01

    Low-energy baryon-baryon interactions are calculated in a high-statistics lattice QCD study on a single ensemble of anisotropic clover gauge-field configurations at a pion mass of m_pi ~ 390 MeV, a spatial volume of L^3 ~ (2.5 fm)^3, and a spatial lattice spacing of b ~ 0.123 fm. Luscher’s method is used to extract nucleon-nucleon, hyperon-nucleon and hyperon-hyperon scattering phase shifts at one momentum from the one- and two-baryon ground-state energies in the lattice volume. The N-Sigma interactions are found to be highly spin-dependent, and the interaction in the ^3 S _1 channel is found to be strong. In contrast, the N-Lambda interactions are found to be spin-independent, within the uncertainties of the calculation, consistent with the absence of one-pion-exchange. The only channel for which a negative energy-shift is found is Lambda-Lambda, indicating that the Lambda-Lambda interaction is attractive, as anticipated from model-dependent discussions regarding the H-dibaryon. The NN scattering lengths are found to be small, clearly indicating the absence of any fine-tuning in the NN-sector at this pion mass. This is consistent with our previous Lattice QCD calculation of the NN interactions. The behavior of the signal-to-noise ratio in the baryon-baryon correlation functions, and in the ratio of correlation functions that yields the ground-state energy splitting

  17. High statistics analysis using anisotropic clover lattices: III. Baryon-baryon interactions

    SciTech Connect

    Beane, Silas R.; Detmold, William; Orginos, Kostas; Lin, Huey-Wen; Savage, Martin J.; Luu, Thomas C.; Torok, Aaron; Walker-Loud, Andre

    2010-03-01

    Low-energy baryon-baryon interactions are calculated in a high-statistics lattice QCD study on a single ensemble of anisotropic-clover gauge-field configurations at a pion mass of m{sub {pi}{approx}3}90 MeV, a spatial volume of L{sup 3{approx}}(2.5 fm){sup 3}, and a spatial lattice spacing of b{approx}0.123 fm. Luescher's method is used to extract nucleon-nucleon, hyperon-nucleon, and hyperon-hyperon scattering phase shifts at one momentum from the one- and two-baryon ground-state energies in the lattice volume. The isospin-3/2 N{Sigma} interactions are found to be highly spin dependent, and the interaction in the {sup 3}S{sub 1} channel is found to be strong. In contrast, the N{Lambda} interactions are found to be spin independent, within the uncertainties of the calculation, consistent with the absence of one-pion exchange. The only channel for which a negative energy shift is found is {Lambda}{Lambda}, indicating that the {Lambda}{Lambda} interaction is attractive, as anticipated from model-dependent discussions regarding the H dibaryon. The nucleon-nucleon (NN) scattering lengths are found to be small, clearly indicating the absence of any fine-tuning in the NN sector at this pion mass. This is consistent with our previous lattice QCD calculation of NN interactions. The behavior of the signal-to-noise ratio in the baryon-baryon correlation functions, and in the ratio of correlation functions that yields the ground-state energy splitting is explored. In particular, focus is placed on the window of time slices for which the signal-to-noise ratio does not degrade exponentially, as this provides the opportunity to extract quantitative information about multibaryon systems.

  18. High statistics analysis using anisotropic clover lattices: (III) Baryon-baryon interactions

    SciTech Connect

    Beane, S; Detmold, W; Lin, H; Luu, T; Orginos, K; Savage, M; Torok, A; Walker-Loud, A

    2010-01-19

    Low-energy baryon-baryon interactions are calculated in a high-statistics lattice QCD study on a single ensemble of anisotropic clover gauge-field configurations at a pion mass of m{sub {pi}} {approx} 390 MeV, a spatial volume of L{sup 3} {approx} (2.5 fm){sup 3}, and a spatial lattice spacing of b {approx} 0.123 fm. Luescher's method is used to extract nucleon-nucleon, hyperon-nucleon and hyperon-hyperon scattering phase shifts at one momentum from the one- and two-baryon ground-state energies in the lattice volume. The isospin-3/2 N{Sigma} interactions are found to be highly spin-dependent, and the interaction in the {sup 3}S{sub 1} channel is found to be strong. In contrast, the N{Lambda} interactions are found to be spin-independent, within the uncertainties of the calculation, consistent with the absence of one-pion-exchange. The only channel for which a negative energy-shift is found is {Lambda}{Lambda}, indicating that the {Lambda}{Lambda} interaction is attractive, as anticipated from model-dependent discussions regarding the H-dibaryon. The NN scattering lengths are found to be small, clearly indicating the absence of any fine-tuning in the NN-sector at this pion mass. This is consistent with our previous Lattice QCD calculation of NN interactions. The behavior of the signal-to-noise ratio in the baryon-baryon correlation functions, and in the ratio of correlation functions that yields the ground-state energy splitting is explored. In particular, focus is placed on the window of time slices for which the signal-to-noise ratio does not degrade exponentially, as this provides the opportunity to extract quantitative information about multi-baryon systems.

  19. High Statistics Analysis using Anisotropic Clover Lattices: (IV) The Volume Dependence of the Light Hadron Masses

    SciTech Connect

    Beane, S R; Detmold, W; Lin, H W; Luu, T C; Orginos, K; Parreno, A; Savage, M J; Torok, A; Walker-Loud, A

    2011-07-01

    The volume dependence of the octet baryon masses and relations among them are explored with Lattice QCD. Calculations are performed with nf = 2 + 1 clover fermion discretization in four lattice volumes, with spatial extent L ? 2.0, 2.5, 3.0 and 4.0 fm, with an anisotropic lattice spacing of b_s ? 0.123 fm in the spatial direction, and b_t = b_s/3.5 in the time direction, and at a pion mass of m_\\pi ? 390 MeV. The typical precision of the ground-state baryon mass determination is lattice gauge-field configurations. Finally, the volume dependence of the pion and kaon masses are analyzed with two-flavor and three-flavor chiral perturbation theory.

  20. Anisotropic peak effect due to structural phase transition in the vortex lattice

    NASA Astrophysics Data System (ADS)

    Rosenstein, Baruch; Knigavko, Anton

    2000-05-01

    The recently observed new peak effect in YBCO is explained by softening of the vortex lattice (VL) due to a structural phase transition in the VL. At this transition, square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with softening of shear modes at melting, in this case the relevant mode is the point. The squash mode is highly anisotropic and we point out some peculiar effects associated with this feature.

  1. Noncollinear and noncoplanar magnetic order in the extended Hubbard model on anisotropic triangular lattice

    NASA Astrophysics Data System (ADS)

    Pasrija, Kanika; Kumar, Sanjeev

    2016-05-01

    Motivated by the importance of noncollinear and noncoplanar magnetic phases in determining various electrical properties in magnets, we investigate the magnetic phase diagram of the extended Hubbard model on an anisotropic triangular lattice. We map out the ground-state phase diagram within a mean-field scheme that treats collinear, noncollinear, and noncoplanar phases on equal footing. In addition to the standard ferromagnet and 120∘ antiferromagnet states, we find the four-sublattice flux, the 3Q noncoplanar, and the noncollinear charge-ordered states to be stable at specific values of filling fraction n . Inclusion of a nearest-neighbor Coulomb repulsion leads to intriguing spin-charge-ordered phases. The most notable of these are the collinear and noncollinear magnetic states at n =2 /3 , which occur together with a pinball-liquid-like charge order. Our results demonstrate that the elementary single-orbital extended Hubbard model on a triangular lattice hosts unconventional spin-charge ordered phases, which are similar to those reported in more complex and material-specific electronic Hamiltonians.

  2. High Statistics Analysis using Anisotropic Clover Lattices: (I) Single Hadron Correlation Functions

    SciTech Connect

    Detmold, Will; Detmold, William; Orginos, Konstantinos; R. Beane, Silas; C. Luu, Thomas; Parreno, Assumpta; J. Savage, Martin; Torok, Aaron; Walker-Loud, Andre

    2009-01-01

    We present the results of high-statistics calculations of correlation functions generated with single-baryon interpolating operators on an ensemble of dynamical anisotropic gauge-field configurations generated by the Hadron Spectrum Collaboration using a tadpole-improved clover fermion action and Symanzik-improved gauge action. A total of $\\Nprops$ sets of measurements are made using $\\Ncfgs$ gauge configurations of size $20^3\\times 128$ with an anisotropy parameter $\\xi= b_s/b_t = 3.5$, a spatial lattice spacing of $b_s=0.1227\\pm 0.0008~{\\rm fm}$, and pion mass of $\\mpi\\sim 390~{\\rm MeV}$. Ground state baryons masses are extracted with fully quantified uncertainties that are at or below the $\\sim 0.2\\%$-level in lattice units. The lowest-lying negative-parity states are also extracted albeit with a somewhat lower level of precision. In the case of the nucleon, this negative-parity state is above the $N\\pi$ threshold and, therefore, the isos

  3. Photorefractive writing and probing of anisotropic linear and nonlinear lattices

    NASA Astrophysics Data System (ADS)

    Allio, Raphaël; Guzmán-Silva, Diego; Cantillano, Camilo; Morales-Inostroza, Luis; Lopez-Gonzalez, Dany; Etcheverry, Sebastián; Vicencio, Rodrigo A.; Armijo, Julien

    2015-02-01

    We study experimentally the writing of one- and two-dimensional photorefractive lattices, focusing on the often overlooked transient regime. Our measurements agree well with theory, in particular concerning the ratio of the drift to diffusion terms. We then study the transverse dynamics of coherent waves propagating in the lattices, in a few novel and simple configurations. For defocusing linear waves with broad transverse spectrum, we remark that both the intensity distributions in real space (‘discrete diffraction’) and Fourier space (‘Brillouin zone spectroscopy’) reflect the Bragg planes and band structure. For nonlinear waves, we observe modulational instability and discrete solitons formation in time domain. We discuss also the non-ideal effects inherent to the photo-induction technique: anisotropy, residual nonlinearity, diffusive term, non-stationarity.

  4. Melting of the Abrikosov flux lattice in anisotropic superconductors

    NASA Technical Reports Server (NTRS)

    Beck, R. G.; Farrell, D. E.; Rice, J. P.; Ginsberg, D. M.; Kogan, V. G.

    1992-01-01

    It has been proposed that the Abrikosov flux lattice in high-Tc superconductors is melted over a significant fraction of the phase diagram. A thermodynamic argument is provided which establishes that the angular dependence of the melting temperature is controlled by the superconducting mass anisotropy. Using a low-frequency torsional-oscillator technique, this relationship has been tested in untwinned single-crystal YBa2Cu3O(7-delta). The results offer decisive support for the melting proposal.

  5. Far field expansion for anisotropic wave equations

    NASA Technical Reports Server (NTRS)

    Hariharan, S. I.; Hagstrom, Thomas

    1989-01-01

    A necessary ingredient for the numerical simulation of many time dependent phenomena in acoustics and aerodynamics is the imposition of accurate radiation conditions at artificial boundaries. The asymptotic analysis of propagating waves provides a rational approach to the development of such conditions. A far field asymptotic expansion of solutions of anisotropic wave equations is derived. This generalizes the well known Friedlander expansion for the standard wave operator. The expansion is used to derive a hierarchy of radiation conditions of increasing accuracy. Two numerical experiments are given to illustrate the utility of this approach. The first application is the study of unsteady vortical disturbances impinging on a flat plate; the second is the simulation of inviscid flow past an impulsively started cylinder.

  6. High Statistics Analysis using Anisotropic Clover Lattices: (I) Single Hadron Correlation Functions

    SciTech Connect

    Will Detmold,Konstantinos Orginos,Silas R. Beane,Will Detmold,William Detmold,Thomas C. Luu,Konstantinos Orginos,Assumpta Parreno,Martin J. Savage,Aaron Torok,Andre Walker-Loud

    2009-06-01

    We present the results of high-statistics calculations of correlation functions generated with single-baryon interpolating operators on an ensemble of dynamical anisotropic gauge-field configurations generated by the Hadron Spectrum Collaboration using a tadpole-improved clover fermion action and Symanzik-improved gauge action. A total of 292,500 sets of measurements are made using 1194 gauge configurations of size 20^3 x 128 with an anisotropy parameter \\xi= b_s/b_t = 3.5, a spatial lattice spacing of b_s=0.1227\\pm 0.0008 fm, and pion mass of m_\\pi ~ 390 MeV. Ground state baryon masses are extracted with fully quantified uncertainties that are at or below the ~0.2%-level in lattice units. The lowest-lying negative-parity states are also extracted albeit with a somewhat lower level of precision. In the case of the nucleon, this negative-parity state is above the N\\pi threshold and, therefore, the isospin-1/2 \\pi N s-wave scattering phase-shift can be extracted using Luescher's method. The disconnected contributions to this process are included indirectly in the gauge-field configurations and do not require additional calculations. The signal-to-noise ratio in the various correlation functions is explored and is found to degrade exponentially faster than naive expectations on many time-slices. This is due to backward propagating states arising from the anti-periodic boundary conditions imposed on the quark-propagators in the time-direction. We explore how best to distribute computational resources between configuration generation and propagator measurements in order to optimize the extraction of single baryon observables.

  7. High Statistics Analysis using Anisotropic Clover Lattices: (I) Single Hadron Correlation Functions

    SciTech Connect

    Beane, S; Detmold, W; Luu, T; Orginos, K; Parreno, A; Savage, M; Torok, A; Walker-Loud, A

    2009-03-23

    We present the results of high-statistics calculations of correlation functions generated with single-baryon interpolating operators on an ensemble of dynamical anisotropic gauge-field configurations generated by the Hadron Spectrum Collaboration using a tadpole-improved clover fermion action and Symanzik-improved gauge action. A total of 292, 500 sets of measurements are made using 1194 gauge configurations of size 20{sup 3} x 128 with an anisotropy parameter {zeta} = b{sub s}/b{sub t} = 3.5, a spatial lattice spacing of b{sub s} = 0.1227 {+-} 0.0008 fm, and pion mass of M{sub {pi}} {approx} 390 MeV. Ground state baryons masses are extracted with fully quantified uncertainties that are at or below the {approx} 0.2%-level in lattice units. The lowest-lying negative-parity states are also extracted albeit with a somewhat lower level of precision. In the case of the nucleon, this negative-parity state is above the N{pi} threshold and, therefore, the isospin-1/2 {pi}N s-wave scattering phase-shift can be extracted using Luescher's method. The disconnected contributions to this process are included indirectly in the gauge-field configurations and do not require additional calculations. The signal-to-noise ratio in the various correlation functions is explored and is found to degrade exponentially faster than naive expectations on many time-slices. This is due to backward propagating states arising from the anti-periodic boundary conditions imposed on the quark-propagators in the time-direction. We explore how best to distribute computational resources between configuration generation and propagator measurements in order to optimize the extraction of single baryon observables.

  8. High statistics analysis using anisotropic clover lattices: Single hadron correlation functions

    SciTech Connect

    Beane, Silas R.; Torok, Aaron; Detmold, William; Orginos, Kostas; Luu, Thomas C.; Parreno, Assumpta; Savage, Martin J.; Walker-Loud, Andre

    2009-06-01

    We present the results of high-statistics calculations of correlation functions generated with single-baryon interpolating operators on an ensemble of dynamical anisotropic gauge-field configurations generated by the Hadron Spectrum Collaboration using a tadpole-improved clover fermion action and Symanzik-improved gauge action. A total of 292, 500 sets of measurements are made using 1194 gauge configurations of size 20{sup 3}x128 with an anisotropy parameter {xi}=b{sub s}/b{sub t}=3.5, a spatial lattice spacing of b{sub s}=0.1227{+-}0.0008 fm, and pion mass of M{sub {pi}}{approx}390 MeV. Ground state baryon masses are extracted with fully quantified uncertainties that are at or below the {approx}0.2%-level in lattice units. The lowest-lying negative-parity states are also extracted albeit with a somewhat lower level of precision. In the case of the nucleon, this negative-parity state is above the N{pi} threshold and, therefore, the isospin-(1/2) {pi}N s-wave scattering phase-shift can be extracted using Luescher's method. The disconnected contributions to this process are included indirectly in the gauge-field configurations and do not require additional calculations. The signal-to-noise ratio in the various correlation functions is explored and is found to degrade exponentially faster than naive expectations on many time slices. This is due to backward propagating states arising from the antiperiodic boundary conditions imposed on the quark propagators in the time direction. We explore how best to distribute computational resources between configuration generation and propagator measurements in order to optimize the extraction of single baryon observables.

  9. Discrete solitons and vortices in anisotropic hexagonal and honeycomb lattices

    NASA Astrophysics Data System (ADS)

    Hoq, Q. E.; Kevrekidis, P. G.; Bishop, A. R.

    2016-02-01

    In the present work, we consider the self-focusing discrete nonlinear Schrödinger equation on hexagonal and honeycomb lattice geometries. Our emphasis is on the study of the effects of anisotropy, motivated by the tunability afforded in recent optical and atomic physics experiments. We find that multi-soliton and discrete vortex states undergo destabilizing bifurcations as the relevant anisotropy control parameter is varied. We quantify these bifurcations by means of explicit analytical calculations of the solutions, as well as of their spectral linearization eigenvalues. Finally, we corroborate the relevant stability picture through direct numerical computations. In the latter, we observe the prototypical manifestation of these instabilities to be the spontaneous rearrangement of the solution, for larger values of the coupling, into localized waveforms typically centered over fewer sites than the original unstable structure. For weak coupling, the instability appears to result in a robust breathing of the relevant waveforms.

  10. Anisotropic lattice thermal conductivity in chiral tellurium from first principles

    SciTech Connect

    Peng, Hua; Kioussis, Nicholas; Stewart, Derek A.

    2015-12-21

    Using ab initio based calculations, we have calculated the intrinsic lattice thermal conductivity of chiral tellurium. We show that the interplay between the strong covalent intrachain and weak van der Waals interchain interactions gives rise to the phonon band gap between the lower and higher optical phonon branches. The underlying mechanism of the large anisotropy of the thermal conductivity is the anisotropy of the phonon group velocities and of the anharmonic interatomic force constants (IFCs), where large interchain anharmonic IFCs are associated with the lone electron pairs. We predict that tellurium has a large three-phonon scattering phase space that results in low thermal conductivity. The thermal conductivity anisotropy decreases under applied hydrostatic pressure.

  11. Discrete solitons and vortices in anisotropic hexagonal and honeycomb lattices

    DOE PAGESBeta

    Hoq, Q. E.; Kevrekidis, P. G.; Bishop, A. R.

    2016-01-14

    We consider the self-focusing discrete nonlinear Schrödinger equation on hexagonal and honeycomb lattice geometries. Our emphasis is on the study of the effects of anisotropy, motivated by the tunability afforded in recent optical and atomic physics experiments. We find that multi-soliton and discrete vortex states undergo destabilizing bifurcations as the relevant anisotropy control parameter is varied. Furthermore, we quantify these bifurcations by means of explicit analytical calculations of the solutions, as well as of their spectral linearization eigenvalues. Finally, we corroborate the relevant stability picture through direct numerical computations. In the latter, we observe the prototypical manifestation of these instabilitiesmore » to be the spontaneous rearrangement of the solution, for larger values of the coupling, into localized waveforms typically centered over fewer sites than the original unstable structure. In weak coupling, the instability appears to result in a robust breathing of the relevant waveforms.« less

  12. Anisotropic intrinsic lattice thermal conductivity of phosphorene from first principles.

    PubMed

    Qin, Guangzhao; Yan, Qing-Bo; Qin, Zhenzhen; Yue, Sheng-Ying; Hu, Ming; Su, Gang

    2015-02-21

    Phosphorene, the single layer counterpart of black phosphorus, is a novel two-dimensional semiconductor with high carrier mobility and a large fundamental direct band gap, which has attracted tremendous interest recently. Its potential applications in nano-electronics and thermoelectrics call for fundamental study of the phonon transport. Here, we calculate the intrinsic lattice thermal conductivity of phosphorene by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations. The thermal conductivity of phosphorene at 300 K is 30.15 W m(-1) K(-1) (zigzag) and 13.65 W m(-1) K(-1) (armchair), showing an obvious anisotropy along different directions. The calculated thermal conductivity fits perfectly to the inverse relationship with temperature when the temperature is higher than Debye temperature (ΘD = 278.66 K). In comparison to graphene, the minor contribution around 5% of the ZA mode is responsible for the low thermal conductivity of phosphorene. In addition, the representative mean free path (MFP), a critical size for phonon transport, is also obtained.

  13. Formation of Bragg band gaps in anisotropic phononic crystals analyzed with the empty lattice model

    DOE PAGESBeta

    Wang, Yan -Feng; Maznev, Alexei; Laude, Vincent

    2016-05-11

    Bragg band gaps of phononic crystals generally, but not always, open at Brillouin zone boundaries. The commonly accepted explanation stems from the empty lattice model: assuming a small material contrast between the constituents of the unit cell, avoided crossings in the phononic band structure appear at frequencies and wavenumbers corresponding to band intersections; for scalar waves the lowest intersections coincide with boundaries of the first Brillouin zone. However, if a phononic crystal contains elastically anisotropic materials, its overall symmetry is not dictated solely by the lattice symmetry. We construct an empty lattice model for phononic crystals made of isotropic andmore » anisotropic materials, based on their slowness curves. We find that, in the anisotropic case, avoided crossings generally do not appear at the boundaries of traditionally defined Brillouin zones. Furthermore, the Bragg "planes" which give rise to phononic band gaps, are generally not flat planes but curved surfaces. Lastly, the same is found to be the case for avoided crossings between shear (transverse) and longitudinal bands in the isotropic case.« less

  14. Simulation study of anisotropic random sequential adsorption of extended objects on a triangular lattice

    NASA Astrophysics Data System (ADS)

    Budinski-Petković, Lj.; Lončarević, I.; Jakšić, Z. M.; Vrhovac, S. B.; Švrakić, N. M.

    2011-11-01

    The properties of the anisotropic random sequential adsorption (RSA) of objects of various shapes on a two-dimensional triangular lattice are studied numerically by means of Monte Carlo simulations. The depositing objects are formed by self-avoiding lattice steps, whereby the first step determines the orientation of the object. Anisotropy is introduced by positing unequal probabilities for orientation of depositing objects along different directions of the lattice. This probability is equal p or (1-p)/2, depending on whether the randomly chosen orientation is horizontal or not, respectively. Approach of the coverage θ(t) to the jamming limit θjam is found to be exponential θjam-θ(t)∝exp(-t/σ), for all probabilities p. It was shown that the relaxation time σ increases with the degree of anisotropy in the case of elongated and asymmetrical shapes. However, for rounded and symmetrical shapes, values of σ and θjam are not affected by the presence of anisotropy. We finally analyze the properties of the anisotropic RSA of polydisperse mixtures of k-mers. Strong dependencies of the parameter σ and the jamming coverage θjam on the degree of anisotropy are obtained. It is found that anisotropic constraints lead to the increased contribution of the longer k-mers in the total coverage fraction of the mixture.

  15. Artificial Staggered Magnetic Field for Ultracold Atoms in Optical Lattices

    NASA Astrophysics Data System (ADS)

    Morais Smith, Cristiane

    2011-03-01

    Uniform magnetic fields are ubiquitous in nature, but this is not the case for staggered magnetic fields. In this talk, I will discuss an experimental set-up for cold atoms recently proposed by us, which allows for the realization of a ``staggered gauge field'' in a 2D square optical lattice. If the lattice is loaded with bosons, it may be described by an effective Bose-Hubbard Hamiltonian, with complex and anisotropic hopping coefficients. A very rich phase diagram emerges: besides the usual Mott-insulator and zero-momentum condensate, a new phase with a finite momentum condensate becomes the ground-state at strong gauge fields. By using the technique of Feshbach resonance, the dynamics of a coherent superposition of a vortex-carrying atomic condensate and a conventional zero-momentum molecular condensate can also be studied within the same scheme. On the other hand, if the lattice is loaded with fermions, a highly tunable, graphene-like band structure can be realized, without requiring the honeycomb lattice symmetry. When the system is loaded with a mixture of bosons and two-species fermions, several features of the high-Tc phase diagram can be reproduced. A dome-shaped unconventional superconducting region arises, surrounded by a non-Fermi liquid and a Fermi liquid at low and high doping, respectively. We acknowledge financial support from the Netherlands Organization for Scientific Research (NWO).

  16. Working Group Report: Lattice Field Theory

    SciTech Connect

    Blum, T.; et al.,

    2013-10-22

    This is the report of the Computing Frontier working group on Lattice Field Theory prepared for the proceedings of the 2013 Community Summer Study ("Snowmass"). We present the future computing needs and plans of the U.S. lattice gauge theory community and argue that continued support of the U.S. (and worldwide) lattice-QCD effort is essential to fully capitalize on the enormous investment in the high-energy physics experimental program. We first summarize the dramatic progress of numerical lattice-QCD simulations in the past decade, with some emphasis on calculations carried out under the auspices of the U.S. Lattice-QCD Collaboration, and describe a broad program of lattice-QCD calculations that will be relevant for future experiments at the intensity and energy frontiers. We then present details of the computational hardware and software resources needed to undertake these calculations.

  17. High Statistics Analysis using Anisotropic Clover Lattices: (II) Three-Baryon Systems

    SciTech Connect

    Beane, S; Detmold, W; Luu, T; Orginos, K; Parreno, A; Savage, M; Torok, A; Walker-Loud, A

    2009-05-05

    We present the results of an exploratory Lattice QCD calculation of three-baryon systems through a high-statistics study of one ensemble of anisotropic clover gauge-field configurations with a pion mass of m{sub {pi}} {approx} 390 MeV. Because of the computational cost of the necessary contractions, we focus on correlation functions generated by interpolating-operators with the quantum numbers of the {Xi}{sup 0}{Xi}{sup 0}n system, one of the least demanding three baryon systems in terms of the number of contractions. We find that the ground state of this system has an energy of E{sub {Xi}{sup 0}{Xi}{sup 0}n} = 3877.9 {+-} 6.9 {+-} 9.2 {+-} 3.3 MeV corresponding to an energy-shift due to interactions of {delta}E{sub {Xi}{sup 0}{Xi}{sup 0}n} = E{sub {Xi}{sup 0}{Xi}{sup 0}n} - 2M{sub {Xi}{sup 0}} - M{sub n} = 4.6 {+-} 5.0 {+-} 7.9 {+-} 4.2 MeV. There are a significant number of time-slices in the three-baryon correlation function for which the signal-to-noise ratio is only slowly degrading with time. This is in contrast to the exponential degradation of the signal-to-noise ratio that is observed at larger times, and is due to the suppressed overlap of the source and sink interpolating-operators that are associated with the variance of the three-baryon correlation function onto the lightest eigenstates in the lattice volume (mesonic systems). As one of the motivations for this area of exploration is the calculation of the structure and reactions of light nuclei, we also present initial results for a system with the quantum numbers of the triton (pnn). This present work establishes a path to multi-baryon systems, and shows that Lattice QCD calculations of the properties and interactions of systems containing four and five baryons are now within sight.

  18. High Statistics Analysis using Anisotropic Clover Lattices: (II) Three-Baryon Systems

    SciTech Connect

    Andre Walker-Loud, Will Detmold, William Detmold, Aaron Torok, Konstantinos Orginos, Silas Beane, Tom Luu, Martin Savage, Assumpta Parreno

    2009-10-01

    We present the results of an exploratory Lattice QCD calculation of three-baryon systems through a high-statistics study of one ensemble of anisotropic clover gauge-field configurations with a pion mass of m_\\pi ~ 390 MeV. Because of the computational cost of the necessary contractions, we focus on correlation functions generated by interpolating-operators with the quantum numbers of the $\\Xi^0\\Xi^0 n$ system, one of the least demanding three baryon systems in terms of the number of contractions. We find that the ground state of this system has an energy of E_{\\Xi^0\\Xi^0n}= 3877.9\\pm 6.9\\pm 9.2\\pm3.3 MeV corresponding to an energy-shift due to interactions of \\delta E_{\\Xi^0\\Xi^0n}=E_{\\Xi^0\\Xi^0n}-2M_{\\Xi^0} -M_n=4.6\\pm 5.0\\pm 7.9\\pm 4.2 MeV. There are a significant number of time-slices in the three-baryon correlation function for which the signal-to-noise ratio is only slowly degrading with time. This is in contrast to the exponential degradation of the signal-to-noise ratio that is observed at larger times, and is due to the suppressed overlap of the source and sink interpolating-operators that are associated with the variance of the three-baryon correlation function onto the lightest eigenstates in the lattice volume (mesonic systems). As one of the motivations for this area of exploration is the calculation of the structure and reactions of light nuclei, we also present initial results for a system with the quantum numbers of the triton (pnn). This present work establishes a path to multi-baryon systems, and shows that Lattice QCD calculations of the properties and interactions of systems containing four and five baryons are now within sight.

  19. High statistics analysis using anisotropic clover lattices. II. Three-baryon systems

    SciTech Connect

    Beane, Silas R.; Torok, Aaron; Detmold, William; Orginos, Kostas; Luu, Thomas C.; Parreno, Assumpta; Savage, Martin J.; Walker-Loud, Andre

    2009-10-01

    We present the results of an exploratory lattice QCD calculation of three-baryon systems through a high statistics study of one ensemble of anisotropic clover gauge-field configurations with a pion mass of m{sub {pi}}{approx}390 MeV. Because of the computational cost of the necessary contractions, we focus on correlation functions generated by interpolating operators with the quantum numbers of the {xi}{sup 0}{xi}{sup 0}n system, one of the least demanding three-baryon systems in terms of the number of contractions. We find that the ground state of this system has an energy of E{sub {xi}{sup 0}}{sub {xi}{sup 0}}{sub n}=3877.9{+-}6.9{+-}9.2{+-}3.3 MeV corresponding to an energy shift due to interactions of {delta}E{sub {xi}{sup 0}}{sub {xi}{sup 0}}{sub n}=E{sub {xi}{sup 0}}{sub {xi}{sup 0}}{sub n}-2M{sub {xi}{sup 0}}-M{sub n}=4.6{+-}5.0{+-}7.9{+-}4.2 MeV. There are a significant number of time slices in the three-baryon correlation function for which the signal-to-noise ratio is only slowly degrading with time. This is in contrast to the exponential degradation of the signal-to-noise ratio that is observed at larger times, and is due to the suppressed overlap of the source and sink interpolating operators that are associated with the variance of the three-baryon correlation function onto the lightest eigenstates in the lattice volume (mesonic systems). As one of the motivations for this area of exploration is the calculation of the structure and reactions of light nuclei, we also present initial results for a system with the quantum numbers of the triton (pnn). This present work establishes a path to multibaryon systems, and shows that lattice QCD calculations of the properties and interactions of systems containing four and five baryons are now within sight.

  20. Lattice fields and strong interactions

    SciTech Connect

    Creutz, M.

    1989-06-01

    I review the lattice formulation of gauge theories and the use of numerical methods to investigate nonperturbative phenomena. These methods are directly applicable to studying hadronic matter at high temperatures. Considerable recent progress has been made in numerical algorithms for including dynamical fermions in such calculations. Dealing with a nonvanishing baryon density adds new unsolved challenges. 33 refs.

  1. Parafermionic conformal field theory on the lattice

    NASA Astrophysics Data System (ADS)

    Mong, Roger S. K.; Clarke, David J.; Alicea, Jason; Lindner, Netanel H.; Fendley, Paul

    2014-11-01

    Finding the precise correspondence between lattice operators and the continuum fields that describe their long-distance properties is a largely open problem for strongly interacting critical points. Here, we solve this problem essentially completely in the case of the three-state Potts model, which exhibits a phase transition described by a strongly interacting ‘parafermion’ conformal field theory. Using symmetry arguments, insights from integrability, and extensive simulations, we construct lattice analogues of nearly all the relevant and marginal physical fields governing this transition. This construction includes chiral fields such as the parafermion. Along the way we also clarify the structure of operator product expansions between order and disorder fields, which we confirm numerically. Our results both suggest a systematic methodology for attacking non-free field theories on the lattice and find broader applications in the pursuit of exotic topologically ordered phases of matter.

  2. Surface Diffusion Directed Growth of Anisotropic Graphene Domains on Different Copper Lattices

    PubMed Central

    Jung, Da Hee; Kang, Cheong; Nam, Ji Eun; Jeong, Heekyung; Lee, Jin Seok

    2016-01-01

    Anisotropic graphene domains are of significant interest since the electronic properties of pristine graphene strongly depend on its size, shape, and edge structures. In this work, considering that the growth of graphene domains is governable by the dynamics of the graphene-substrate interface during growth, we investigated the shape and defects of graphene domains grown on copper lattices with different indices by chemical vapor deposition of methane at either low pressure or atmospheric pressure. Computational modeling identified that the crystallographic orientation of copper strongly influences the shape of the graphene at low pressure, yet does not play a critical role at atmospheric pressure. Moreover, the defects that have been previously observed in the center of four-lobed graphene domains grown under low pressure conditions were demonstrated for the first time to be caused by a lattice mismatch between graphene and the copper substrate. PMID:26883174

  3. Phase structure of the anisotropic antiferromagnetic Heisenberg model on a layered triangular lattice: Spiral state and deconfined spin liquid

    SciTech Connect

    Nakane, Kazuya; Kamijo, Takeshi; Ichinose, Ikuo

    2011-02-01

    In the present paper, we study a spin-1/2 antiferromagnetic (AF) Heisenberg model on layered anisotropic triangular lattice and obtain its phase structure. We use the Schwinger bosons for representing spin operators and also a coherent-state path integral for calculating physical quantities. Finite-temperature properties of the system are investigated by means of the numerical Monte-Carlo simulations. A detailed phase diagram of the system is obtained by calculating internal energy, specific heat, spin correlation functions, etc. There are AF Neel, paramagnetic, and spiral states. Turning on the plaquette term (i.e., the Maxwell term on a lattice) of an emergent U(1) gauge field that flips a pair of parallel spin-singlet bonds, we found that there appears a phase that is regarded as a deconfined spin-liquid state, though 'transition' to this phase from the paramagnetic phase is not of second order but a crossover. In that phase, the emergent gauge boson is a physical gapless excitation coupled with spinons. These results support our previous study on an AF Heisenberg model on a triangular lattice at vanishing temperature.

  4. Electric double layer of anisotropic dielectric colloids under electric fields

    NASA Astrophysics Data System (ADS)

    Han, M.; Wu, H.; Luijten, E.

    2016-07-01

    Anisotropic colloidal particles constitute an important class of building blocks for self-assembly directed by electrical fields. The aggregation of these building blocks is driven by induced dipole moments, which arise from an interplay between dielectric effects and the electric double layer. For particles that are anisotropic in shape, charge distribution, and dielectric properties, calculation of the electric double layer requires coupling of the ionic dynamics to a Poisson solver. We apply recently proposed methods to solve this problem for experimentally employed colloids in static and time-dependent electric fields. This allows us to predict the effects of field strength and frequency on the colloidal properties.

  5. Field induced anisotropic cooperativity in a magnetic colloidal glass

    NASA Astrophysics Data System (ADS)

    Wandersman, E.; Chushkin, Y.; Dubois, E.; Dupuis, V.; Robert, A.; Perzynski, R.

    The translational dynamics in a repulsive colloidal glass-former is probed by time-resolved X-ray Photon Correlation Spectroscopy. In this dense dispersion of charge-stabilized and magnetic nanoparticles, the interaction potential can be tuned, from quasi-isotropic to anisotropic by applying an external magnetic field. Structural and dynamical anisotropies are reported on interparticle lengthscales associated with highly anisotropic cooperativity, almost two orders of magnitude larger in the field direction than in the perpendicular direction and in zero field.

  6. Cluster Mott insulators and two Curie-Weiss regimes on an anisotropic kagome lattice

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Kee, Hae-Young; Kim, Yong Baek

    2016-06-01

    Motivated by recent experiments on the quantum-spin-liquid candidate material LiZn2Mo3O8 , we study a single-band extended Hubbard model on an anisotropic kagome lattice with the 1/6 electron filling. Due to the partial filling of the lattice, the intersite repulsive interaction is necessary to generate Mott insulators, where electrons are localized in clusters rather than at lattice sites. It is shown that these cluster Mott insulators are generally U(1) quantum spin liquids with spinon Fermi surfaces. The nature of charge excitations in cluster Mott insulators can be quite different from conventional Mott insulator and we show that there exists a cluster Mott insulator where charge fluctuations around the hexagonal cluster induce a plaquette charge order (PCO). The spinon excitation spectrum in this spin-liquid cluster Mott insulator is reconstructed due to the PCO so that only 1/3 of the total spinon excitations are magnetically active. Based on these results, we propose that the two Curie-Weiss regimes of the spin susceptibility in LiZn2Mo3O8 may be explained by finite-temperature properties of the cluster Mott insulator with the PCO as well as fractionalized spinon excitations. Existing and possible future experiments on LiZn2Mo3O8 , and other Mo-based cluster magnets are discussed in light of these theoretical predictions.

  7. Artificial staggered magnetic field for ultracold atoms in optical lattices

    SciTech Connect

    Lim, Lih-King; Smith, C. Morais; Hemmerich, Andreas

    2010-02-15

    A time-dependent optical lattice with staggered particle current in the tight-binding regime was considered that can be described by a time-independent effective lattice model with an artificial staggered magnetic field. The low-energy description of a single-component fermion in this lattice at half-filling is provided by two copies of ideal two-dimensional massless Dirac fermions. The Dirac cones are generally anisotropic and can be tuned by the external staggered flux {phi}. For bosons, the staggered flux modifies the single-particle spectrum such that in the weak coupling limit, depending on the flux {phi}, distinct superfluid phases are realized. Their properties are discussed, the nature of the phase transitions between them is established, and Bogoliubov theory is used to determine their excitation spectra. Then the generalized superfluid-Mott-insulator transition is studied in the presence of the staggered flux and the complete phase diagram is established. Finally, the momentum distribution of the distinct superfluid phases is obtained, which provides a clear experimental signature of each phase in ballistic expansion experiments.

  8. Topological spin liquids in the ruby lattice with anisotropic Kitaev interactions

    NASA Astrophysics Data System (ADS)

    Jahromi, Saeed S.; Kargarian, Mehdi; Masoudi, S. Farhad; Langari, Abdollah

    2016-09-01

    The ruby lattice is a four-valent lattice interpolating between honeycomb and triangular lattices. In this work we investigate the topological spin-liquid phases of a spin Hamiltonian with Kitaev interactions on the ruby lattice using exact diagonalization and perturbative methods. The latter interactions combined with the structure of the lattice yield a model with Z2×Z2 gauge symmetry. We mapped out the phase diagram of the model and found gapped and gapless spin-liquid phases. While the low-energy sector of the gapped phase corresponds to the well-known topological color code model on a honeycomb lattice, the low-energy sector of the gapless phases is described by an effective spin model with three-body interactions on a triangular lattice. A gap is opened in the spectrum in small magnetic fields, where we showed that the ground state has a finite topological entanglement entropy. We argue that the gapped phases could be possibly described by exotic excitations, and their corresponding spectrum is richer than the Ising phase of the Kitaev model.

  9. Integrated digital inverters based on two-dimensional anisotropic ReS₂ field-effect transistors

    DOE PAGESBeta

    Liu, Erfu; Fu, Yajun; Wang, Yaojia; Feng, Yanqing; Liu, Huimei; Wan, Xiangang; Zhou, Wei; Wang, Baigeng; Shao, Lubin; Ho, Ching -Hwa; et al

    2015-05-07

    Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS₂) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS₂ field-effect transistors, which exhibit competitive performance with large current on/off ratios (~10⁷) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconductingmore » materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS₂ anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications.« less

  10. Integrated digital inverters based on two-dimensional anisotropic ReS₂ field-effect transistors

    SciTech Connect

    Liu, Erfu; Fu, Yajun; Wang, Yaojia; Feng, Yanqing; Liu, Huimei; Wan, Xiangang; Zhou, Wei; Wang, Baigeng; Shao, Lubin; Ho, Ching -Hwa; Huang, Ying -Sheng; Cao, Zhengyi; Wang, Laiguo; Li, Aidong; Zeng, Junwen; Song, Fengqi; Wang, Xinran; Shi, Yi; Yuan, Hongtao; Hwang, Harold Y.; Cui, Yi; Miao, Feng; Xing, Dingyu

    2015-05-07

    Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS₂) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS₂ field-effect transistors, which exhibit competitive performance with large current on/off ratios (~10⁷) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconducting materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS₂ anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications.

  11. Spin transport in the frustrated anisotropic two-dimensional ferromagnet in the square lattice

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2016-08-01

    We use the SU(3) Schwinger boson formalism together with the Kubo theory of the linear response to study the spin transport in the two-dimensional S=1 frustrated anisotropic Heisenberg ferromagnet in a square lattice with easy-plane single-ion anisotropy and considering the second-neighbor interaction in the diagonal and the third-neighbor interaction (J1-J2-J3 model). The AC spin conductivity σreg(ω) is determined for several values of the critical single-ion parameter D, and the frustration parameters J2 and J3. We have calculated the dynamic structure factor too, S(q → , ω), for this model and obtained a behaviour exponentially decreasing for the damping Γq with the decreasing of q = | q → | towards q → 0.

  12. Spin superfluidity in the anisotropic XY model in the triangular lattice

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2016-07-01

    We use the SU(3) Schwinger's boson theory to study the spin transport properties in the two-dimensional anisotropic frustrated Heisenberg model in the triangular lattice at T=0. We have investigated the behavior of the spin conductivity for this model which presents an single-ion anisotropy. We study the spin transport in the Bose-Einstein condensation regime where we have that the tz bosons are condensed and the following condition is valid: = < tz† > = t . Our results show a metallic spin transport for ω > 0 and a superfluid spin transport in the limit of DC conductivity, ω → 0 , where σ(ω) tends to infinity in this limit of ω.

  13. Spin conductivity of the two-dimensional anisotropic frustrated Heisenberg model in the honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2016-07-01

    We use the SU(3) Schwinger's boson theory to study the spin transport properties of the two-dimensional anisotropic frustrated Heisenberg model in a honeycomb lattice at T=0. We have investigated the behavior of the spin conductivity for this model which presents a single-ion anisotropy and J1 and J2 exchange interactions. We study the spin transport in the Bose-Einstein condensation regime where we have that the tz bosons are condensed and the following condition is valid: = < tz† > = t. Our results show a metallic spin transport for ω > 0 and a superconductor spin transport in the limit of DC conductivity, ω → 0, where σ(ω) tends to infinity in this limit of ω.

  14. A quantum fidelity study of the anisotropic next-nearest-neighbour triangular lattice Heisenberg model

    NASA Astrophysics Data System (ADS)

    Thesberg, Mischa; Sørensen, Erik S.

    2014-10-01

    Ground- and excited-state quantum fidelities in combination with generalized quantum fidelity susceptibilites, obtained from exact diagonalizations, are used to explore the phase diagram of the anisotropic next-nearest-neighbour triangular Heisenberg model. Specifically, the J‧ - J2 plane of this model, which connects the J1 - J2 chain and the anisotropic triangular lattice Heisenberg model, is explored using these quantities. Through the use of a quantum fidelity associated with the first excited-state, in addition to the conventional ground-state fidelity, the BKT-type transition and Majumdar-Ghosh point of the J1 - J2 chain (J‧ = 0) are found to extend into the J‧ - J2 plane and connect with points on the J2 = 0 axis thereby forming bounded regions in the phase diagram. These bounded regions are then explored through the generalized quantum fidelity susceptibilities χρ, χ120\\circ , χD and χCAF which are associated with the spin stiffness, 120° spiral order parameter, dimer order parameter and collinear antiferromagnetic order parameter respectively. These quantities are believed to be extremely sensitive to the underlying phase and are thus well suited for finite-size studies. Analysis of the fidelity susceptibilities suggests that the J‧, J2 ≪ J phase of the anisotropic triangular model is either a collinear antiferromagnet or possibly a gapless disordered phase that is directly connected to the Luttinger phase of the J1 - J2 chain. Furthermore, the outer region is dominated by incommensurate spiral physics as well as dimer order.

  15. Anomalies, gauge field topology, and the lattice

    SciTech Connect

    Creutz, Michael

    2011-04-15

    Motivated by the connection between gauge field topology and the axial anomaly in fermion currents, I suggest that the fourth power of the naive Dirac operator can provide a natural method to define a local lattice measure of topological charge. For smooth gauge fields this reduces to the usual topological density. For typical gauge field configurations in a numerical simulation, however, quantum fluctuations dominate, and the sum of this density over the system does not generally give an integer winding. On cooling with respect to the Wilson gauge action, instanton like structures do emerge. As cooling proceeds, these objects tend shrink and finally 'fall through the lattice.' Modifying the action can block the shrinking at the expense of a loss of reflection positivity. The cooling procedure is highly sensitive to the details of the initial steps, suggesting that quantum fluctuations induce a small but fundamental ambiguity in the definition of topological susceptibility.

  16. Anisotropic inflation from charged scalar fields

    SciTech Connect

    Emami, Razieh; Firouzjahi, Hassan; Movahed, S.M. Sadegh; Zarei, Moslem E-mail: firouz@ipm.ir E-mail: m.zarei@cc.iut.ac.ir

    2011-02-01

    We consider models of inflation with U(1) gauge fields and charged scalar fields including symmetry breaking potential, chaotic inflation and hybrid inflation. We show that there exist attractor solutions where the anisotropies produced during inflation becomes comparable to the slow-roll parameters. In the models where the inflaton field is a charged scalar field the gauge field becomes highly oscillatory at the end of inflation ending inflation quickly. Furthermore, in charged hybrid inflation the onset of waterfall phase transition at the end of inflation is affected significantly by the evolution of the background gauge field. Rapid oscillations of the gauge field and its coupling to inflaton can have interesting effects on preheating and non-Gaussianities.

  17. Anisotropic thermal conduction with magnetic fields in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Arth, Alexander; Dolag, Klaus; Beck, Alexander; Petkova, Margarita; Lesch, Harald

    2015-08-01

    Magnetic fields play an important role for the propagation and diffusion of charged particles, which are responsible for thermal conduction. In this poster, we present an implementation of thermal conduction including the anisotropic effects of magnetic fields for smoothed particle hydrodynamics (SPH). The anisotropic thermal conduction is mainly proceeding parallel to magnetic fields and suppressed perpendicular to the fields. We derive the SPH formalism for the anisotropic heat transport and solve the corresponding equation with an implicit conjugate gradient scheme. We discuss several issues of unphysical heat transport in the cases of extreme ansiotropies or unmagnetized regions and present possible numerical workarounds. We implement our algorithm into the cosmological simulation code GADGET and study its behaviour in several test cases. In general, we reproduce the analytical solutions of our idealised test problems, and obtain good results in cosmological simulations of galaxy cluster formations. Within galaxy clusters, the anisotropic conduction produces a net heat transport similar to an isotropic Spitzer conduction model with low efficiency. In contrast to isotropic conduction our new formalism allows small-scale structure in the temperature distribution to remain stable, because of their decoupling caused by magnetic field lines. Compared to observations, strong isotropic conduction leads to an oversmoothed temperature distribution within clusters, while the results obtained with anisotropic thermal conduction reproduce the observed temperature fluctuations well. A proper treatment of heat transport is crucial especially in the outskirts of clusters and also in high density regions. It's connection to the local dynamical state of the cluster also might contribute to the observed bimodal distribution of cool core and non cool core clusters. Our new scheme significantly advances the modelling of thermal conduction in numerical simulations and overall gives

  18. Anisotropic Upper Critical Field of Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    Huang, Ruiqi; She, Weilong

    2016-09-01

    The upper critical field and its anisotropy are the easiest properties to examine in the research of iron-based superconductors. Based on warped cylindrical Fermi surface models, we investigate the temperature and angle dependence of the upper critical field in detail by employing the quasi-classical formalism of the Werthamer-Helfand-Hohenberg (WHH) theory. Our numerical results reveal the anisotropy of the upper critical field, which may be caused by an anisotropic gap function (e.g., d-wave pairing) or an anisotropic Fermi surface, respectively. Further, according to our analysis, this anisotropy can be modulated by the deformation of the Fermi surface and will be strongly suppressed by the Pauli paramagnetic effect.

  19. Graphene, Lattice Field Theory and Symmetries

    SciTech Connect

    Drissi, L. B.; Bousmina, M.; Saidi, E. H.

    2011-02-15

    Borrowing ideas from tight binding model, we propose a board class of lattice field models that are classified by non simply laced Lie algebras. In the case of A{sub N-1{approx_equal}}su(N) series, we show that the couplings between the quantum states living at the first nearest neighbor sites of the lattice L{sub suN} are governed by the complex fundamental representations N-bar and N of su(N) and the second nearest neighbor interactions are described by its adjoint N-bar x N. The lattice models associated with the leading su(2), su(3), and su(4) cases are explicitly studied and their fermionic field realizations are given. It is also shown that the su(2) and su(3) models describe the electronic properties of the acetylene chain and the graphene, respectively. It is established as well that the energy dispersion of the first nearest neighbor couplings is completely determined by the A{sub N} roots {alpha} through the typical dependence N/2+{Sigma}{sub roots} cos(k.{alpha} with k the wave vector.Other features such as the SO(2N) extension and other applications are also discussed.

  20. Electric and magnetic fields from two-dimensional anisotropic bisyncytia.

    PubMed Central

    Sepulveda, N G; Wikswo, J P

    1987-01-01

    Cardiac tissue can be considered macroscopically as a bidomain, anisotropic conductor in which simple depolarization wavefronts produce complex current distributions. Since such distributions may be difficult to measure using electrical techniques, we have developed a mathematical model to determine the feasibility of magnetic localization of these currents. By applying the finite element method to an idealized two-dimensional bisyncytium with anisotropic conductivities, we have calculated the intracellular and extracellular potentials, the current distributions, and the magnetic fields for a circular depolarization wavefront. The calculated magnetic field 1 mm from the tissue is well within the sensitivity of a SQUID magnetometer. Our results show that complex bisyncytial current patterns can be studied magnetically, and these studies should provide valuable insight regarding the electrical anisotropy of cardiac tissue. PMID:3580484

  1. Electromagnetic polarizabilities: Lattice QCD in background fields

    SciTech Connect

    W. Detmold, B.C. Tiburzi, A. Walker-Loud

    2012-04-01

    Chiral perturbation theory makes definitive predictions for the extrinsic behavior of hadrons in external electric and magnetic fields. Near the chiral limit, the electric and magnetic polarizabilities of pions, kaons, and nucleons are determined in terms of a few well-known parameters. In this limit, hadrons become quantum mechanically diffuse as polarizabilities scale with the inverse square-root of the quark mass. In some cases, however, such predictions from chiral perturbation theory have not compared well with experimental data. Ultimately we must turn to first principles numerical simulations of QCD to determine properties of hadrons, and confront the predictions of chiral perturbation theory. To address the electromagnetic polarizabilities, we utilize the background field technique. Restricting our attention to calculations in background electric fields, we demonstrate new techniques to determine electric polarizabilities and baryon magnetic moments for both charged and neutral states. As we can study the quark mass dependence of observables with lattice QCD, the lattice will provide a crucial test of our understanding of low-energy QCD, which will be timely in light of ongoing experiments, such as at COMPASS and HI gamma S.

  2. Anisotropic lattice expansion of three-dimensional colloidal crystals and its impact on hypersonic phonon band gaps.

    PubMed

    Wu, Songtao; Zhu, Gaohua; Zhang, Jin S; Banerjee, Debasish; Bass, Jay D; Ling, Chen; Yano, Kazuhisa

    2014-05-21

    We report anisotropic expansion of self-assembled colloidal polystyrene-poly(dimethylsiloxane) crystals and its impact on the phonon band structure at hypersonic frequencies. The structural expansion was achieved by a multistep infiltration-polymerization process. Such a process expands the interplanar lattice distance 17% after 8 cycles whereas the in-plane distance remains unaffected. The variation of hypersonic phonon band structure induced by the anisotropic lattice expansion was recorded by Brillouin measurements. In the sample before expansion, a phononic band gap between 3.7 and 4.4 GHz is observed; after 17% structural expansion, the gap is shifted to a lower frequency between 3.5 and 4.0 GHz. This study offers a facile approach to control the macroscopic structure of colloidal crystals with great potential in designing tunable phononic devices.

  3. Extracting Nucleon Magnetic Moments and Electric Polarizabilities from Lattice QCD in Background Electric Fields

    SciTech Connect

    William Detmold; Tiburzi, Brian C.; Walker-Loud, Andre

    2010-03-01

    Nucleon properties are investigated in background electric fields. As the magnetic moments of baryons affect their relativistic propagation in constant electric fields, electric polarizabilities cannot be determined without knowledge of magnetic moments. We devise combinations of baryon two-point functions in external electric fields to isolate both observables. Using an ensemble of anisotropic gauge configurations with dynamical clover fermions, we demonstrate how magnetic moments and electric polarizabilities can be determined from lattice QCD simulations in background electric fields. We obtain results for both the neutron and proton. Our study is currently limited to electrically neutral sea quarks.

  4. Magnetic-Field-Induced Insulator-Conductor Transition in SU(2) Quenched Lattice Gauge Theory

    SciTech Connect

    Buividovich, P.V.; Kharzeev, D.; Chernodub, M.N., Kalaydzhyan, T., Luschevskaya, E.V., and M.I. Polikarpov

    2010-09-24

    We study the correlator of two vector currents in quenched SU(2) lattice gauge theory with a chirally invariant lattice Dirac operator with a constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of a magnetic field, while for other components the correlation length slightly decreases. We apply the maximal entropy method to extract the corresponding spectral function. In the limit of zero frequency this spectral function yields the electric conductivity of quenched theory. We find that in the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field.

  5. Magnetic-field-induced insulator-conductor transition in SU(2) quenched lattice gauge theory.

    PubMed

    Buividovich, P V; Chernodub, M N; Kharzeev, D E; Kalaydzhyan, T; Luschevskaya, E V; Polikarpov, M I

    2010-09-24

    We study the correlator of two vector currents in quenched SU(2) lattice gauge theory with a chirally invariant lattice Dirac operator with a constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of a magnetic field, while for other components the correlation length slightly decreases. We apply the maximal entropy method to extract the corresponding spectral function. In the limit of zero frequency this spectral function yields the electric conductivity of quenched theory. We find that in the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field. PMID:21230764

  6. Effective field theory for lattice nuclei.

    PubMed

    Barnea, N; Contessi, L; Gazit, D; Pederiva, F; van Kolck, U

    2015-02-01

    We show how nuclear effective field theory (EFT) and ab initio nuclear-structure methods can turn input from lattice quantum chromodynamics (LQCD) into predictions for the properties of nuclei. We argue that pionless EFT is the appropriate theory to describe the light nuclei obtained in LQCD simulations carried out at pion masses heavier than the physical pion mass. We solve the EFT using the effective-interaction hyperspherical harmonics and auxiliary-field diffusion Monte Carlo methods. Fitting the three leading-order EFT parameters to the deuteron, dineutron, and triton LQCD energies at m_{π}≈800  MeV, we reproduce the corresponding alpha-particle binding and predict the binding energies of mass-5 and mass-6 ground states. PMID:25699436

  7. Lattice-based flow field modeling.

    PubMed

    Wei, Xiaoming; Zhao, Ye; Fan, Zhe; Li, Wei; Qiu, Feng; Yoakum-Stover, Suzanne; Kaufman, Arie E

    2004-01-01

    We present an approach for simulating the natural dynamics that emerge from the interaction between a flow field and immersed objects. We model the flow field using the Lattice Boltzmann Model (LBM) with boundary conditions appropriate for moving objects and accelerate the computation on commodity graphics hardware (GPU) to achieve real-time performance. The boundary conditions mediate the exchange of momentum between the flow field and the moving objects resulting in forces exerted by the flow on the objects as well as the back-coupling on the flow. We demonstrate our approach using soap bubbles and a feather. The soap bubbles illustrate Fresnel reflection, reveal the dynamics of the unseen flow field in which they travel, and display spherical harmonics in their undulations. Our simulation allows the user to directly interact with the flow field to influence the dynamics in real time. The free feather flutters and gyrates in response to lift and drag forces created by its motion relative to the flow. Vortices are created as the free feather falls in an otherwise quiescent flow. PMID:15527053

  8. Instability of anisotropic cosmological solutions supported by vector fields.

    PubMed

    Himmetoglu, Burak; Contaldi, Carlo R; Peloso, Marco

    2009-03-20

    Models with vector fields acquiring a nonvanishing vacuum expectation value along one spatial direction have been proposed to sustain a prolonged stage of anisotropic accelerated expansion. Such models have been used for realizations of early time inflation, with a possible relation to the large scale cosmic microwave background anomalies, or of the late time dark energy. We show that, quite generally, the concrete realizations proposed so far are plagued by instabilities (either ghosts or unstable growth of the linearized perturbations) which can be ultimately related to the longitudinal vector polarization present in them. Phenomenological results based on these models are therefore unreliable.

  9. Anisotropic pair superfluidity of trapped two-component Bose gases in an optical lattice

    NASA Astrophysics Data System (ADS)

    Li, Yongqiang; He, Liang; Hofstetter, Walter

    2013-09-01

    We theoretically investigate the pair-superfluid phase of two-component ultracold gases with attractive inter-species interactions in an optical lattice. We establish the phase diagram for filling n = 1 at zero and finite temperatures, by applying bosonic dynamical mean-field theory, and observe stable pair-superfluid and charge-density wave quantum phases for asymmetric hopping of the two species. While the pair superfluid is found to be robust in the presence of a harmonic trap, we observe that it is destroyed already by a small population imbalance of the two species.

  10. Paramagnetic relaxation in anisotropic materials in zero and weak constant fields

    SciTech Connect

    Fokina, N. P.; Khalvashi, E. Kh.; Khutsishvili, K. O.

    2014-12-21

    Paramagnetic relaxation in strongly anisotropic materials is analytically investigated in zero and weak constant magnetic fields. The objectives of the microscopic analytical investigation are (i) the weak-field electron paramagnetic resonance (EPR) linewidth and (ii) the electron spin relaxation rates given by a calorimetric Gorter type experiment in the zero constant field at the arbitrary low-frequency field directions, respectively, to the sample crystallographic axes. The EPR linewidth is calculated under the suggestion of its spin-phonon nature at the one-phonon mechanism of the spin-lattice relaxation in the case of the strong isotropic exchange interaction for the arbitrary direction Z of the constant magnetic field. The EPR linewidth is presented as the half sum of the zero-field relaxation rates, measured by the Gorter experiment with the low-frequency field oriented along the X, Y axes. With the help of the macroscopic consideration, it is shown that the zero-field relaxation rates describe the relaxation of the X and Y magnetization components in a zero or weak constant magnetic field. The relaxation rates of the magnetizations created along a,b,c crystallographic axes by a low-frequency field in a Gorter type experiment follow the obtained expressions in the particular cases and are in the experimentally confirmed relations with the EPR linewidth.

  11. Subsurface Stress Fields in FCC Single Crystal Anisotropic Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Knudsen, Erik; Swanson, Gregory R.; Duke, Gregory; Ham-Battista, Gilda

    2004-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent high cycle fatigue (HCF) failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and non-crystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is presented for evaluating the subsurface stresses in the elastic half-space, based on the adaptation of a stress function method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis (FEA). Effects of crystal orientation on stress response and fatigue life are examined. Obtaining accurate subsurface stress results for anisotropic single crystal contact problems require extremely refined three-dimensional (3-D) finite element grids, especially in the edge of contact region. Obtaining resolved shear stresses (RSS) on the principal slip planes also involves

  12. Field dependent spin transport of anisotropic Heisenberg chain

    NASA Astrophysics Data System (ADS)

    Rezania, H.

    2016-04-01

    We have addressed the static spin conductivity and spin Drude weight of one-dimensional spin-1/2 anisotropic antiferromagnetic Heisenberg chain in the finite magnetic field. We have investigated the behavior of transport properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on the spin transport properties has also been studied via the bosonic model by Green's function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the spin conductivity and spin Drude weight in the gapped field induced spin-polarized phase for various magnetic field and anisotropy parameters. Furthermore we have studied the magnetic field dependence of static spin conductivity and Drude weight for various anisotropy parameters. Our results show the regular part of spin conductivity vanishes in isotropic case however Drude weight has a finite non-zero value and the system exhibits ballistic transport properties. We also find the peak in the static spin conductivity factor moves to higher temperature upon increasing the magnetic field at fixed anisotropy. The static spin conductivity is found to be monotonically decreasing with magnetic field due to increase of energy gap in the excitation spectrum. Furthermore we have studied the temperature dependence of spin Drude weight for different magnetic field and various anisotropy parameters.

  13. Anisotropic electric-field-enhanced electron emission from deep-level defects in GaAs

    NASA Astrophysics Data System (ADS)

    Tsarova, Tatsiana; Wosinski, Tadeusz; Makosa, Andrzej; Tkaczyk, Zbigniew

    2009-10-01

    Strongly anisotropic electric-field enhancements of the thermal emission rates of electrons from the EL3 and EL5 deep-level defects in n-type GaAs crystal have been revealed with the double-correlation deep-level transient spectroscopy. The results, analysed by taking into account both the Poole-Frenkel and phonon-assisted tunnel effects, evidence a strong coupling of the defects to the lattice vibronic modes. The defect potential anisotropy of EL3 is consistent with the defect identification as an off-centre substitutional oxygen on the arsenic site. The revealed surprising break-down of the emission-rate enhancement, for the electric field applied along the lang1 0 0rang crystallographic direction, is interpreted as resulting from a possible reorientation of the EL3 defect, owing to a jump of the oxygen ion into a neighbouring lattice site, driven by a strong electric field. On the other hand, a close pair divacancy complex is suggested to be responsible for the EL5 defect.

  14. Subsurface Stress Fields In Single Crystal (Anisotropic) Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.; Knudsen, Erik C.; Duke, Greg; Battista, Gilda; Swanson, Greg

    2004-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and alternating stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. This paper presents analytical and numerical techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts. The subsurface stress results are required for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades. An analytical procedure is , presented, for evaluating the subsurface stresses in the elastic half-space, using a complex potential method outlined by Lekhnitskii. Numerical results are presented for cylindrical and spherical anisotropic contacts, using finite element analysis. Effects of crystal orientation on stress response and fatigue life are examined.

  15. Integrated digital inverters based on two-dimensional anisotropic ReS2 field-effect transistors

    PubMed Central

    Liu, Erfu; Fu, Yajun; Wang, Yaojia; Feng, Yanqing; Liu, Huimei; Wan, Xiangang; Zhou, Wei; Wang, Baigeng; Shao, Lubin; Ho, Ching-Hwa; Huang, Ying-Sheng; Cao, Zhengyi; Wang, Laiguo; Li, Aidong; Zeng, Junwen; Song, Fengqi; Wang, Xinran; Shi, Yi; Yuan, Hongtao; Hwang, Harold Y.; Cui, Yi; Miao, Feng; Xing, Dingyu

    2015-01-01

    Semiconducting two-dimensional transition metal dichalcogenides are emerging as top candidates for post-silicon electronics. While most of them exhibit isotropic behaviour, lowering the lattice symmetry could induce anisotropic properties, which are both scientifically interesting and potentially useful. Here we present atomically thin rhenium disulfide (ReS2) flakes with unique distorted 1T structure, which exhibit in-plane anisotropic properties. We fabricated monolayer and few-layer ReS2 field-effect transistors, which exhibit competitive performance with large current on/off ratios (∼107) and low subthreshold swings (100 mV per decade). The observed anisotropic ratio along two principle axes reaches 3.1, which is the highest among all known two-dimensional semiconducting materials. Furthermore, we successfully demonstrated an integrated digital inverter with good performance by utilizing two ReS2 anisotropic field-effect transistors, suggesting the promising implementation of large-scale two-dimensional logic circuits. Our results underscore the unique properties of two-dimensional semiconducting materials with low crystal symmetry for future electronic applications. PMID:25947630

  16. Anisotropic Peak Effect due to Structural Phase Transition in the Vortex Lattice

    NASA Astrophysics Data System (ADS)

    Rosenstein, Baruch; Knigavko, Anton

    1999-07-01

    It is shown that the recently observed new peak effect in YBCO could be explained by the softening of the vortex lattice due to a structural phase transition in the vortex lattice. At this transition square lattice transforms into a distorted hexagonal one. While conventional peak effect is associated with the softening of shear modes (elastic modulus c66 vanishes) at melting, in this case the relevant mode is ``squash'' mode ( c11+c22-2c12 vanishes).

  17. Fernique-type inequalities and moduli of continuity for anisotropic Gaussian random fields.

    PubMed

    Meerschaert, Mark M; Wang, Wensheng; Xiao, Yimin

    2012-08-01

    This paper is concerned with sample path properties of anisotropic Gaussian random fields. We establish Fernique-type inequalities and utilize them to study the global and local moduli of continuity for anisotropic Gaussian random fields. Applications to fractional Brownian sheets and to the solutions of stochastic partial differential equations are investigated.

  18. Fernique-type inequalities and moduli of continuity for anisotropic Gaussian random fields

    PubMed Central

    Meerschaert, Mark M.; Wang, Wensheng; Xiao, Yimin

    2013-01-01

    This paper is concerned with sample path properties of anisotropic Gaussian random fields. We establish Fernique-type inequalities and utilize them to study the global and local moduli of continuity for anisotropic Gaussian random fields. Applications to fractional Brownian sheets and to the solutions of stochastic partial differential equations are investigated. PMID:24825922

  19. YANG-MILLS FIELDS AND THE LATTICE.

    SciTech Connect

    CREUTZ,M.

    2004-05-18

    The Yang-Mills theory lies at the heart of our understanding of elementary particle interactions. For the strong nuclear forces, we must understand this theory in the strong coupling regime. The primary technique for this is the lattice. While basically an ultraviolet regulator, the lattice avoids the use of a perturbative expansion. I discuss some of the historical circumstances that drove us to this approach, which has had immense success, convincingly demonstrating quark confinement and obtaining crucial properties of the strong interactions from first principles.

  20. Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material.

    PubMed

    Makino, Kotaro; Saito, Yuta; Fons, Paul; Kolobov, Alexander V; Nakano, Takashi; Tominaga, Junji; Hase, Muneaki

    2016-01-01

    Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c-axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c-axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics. PMID:26805401

  1. Local spectrum analysis of field propagation in an anisotropic medium. Part I. Time-harmonic fields

    NASA Astrophysics Data System (ADS)

    Tinkelman, Igor; Melamed, Timor

    2005-06-01

    The phase-space beam summation is a general analytical framework for local analysis and modeling of radiation from extended source distributions. In this formulation, the field is expressed as a superposition of beam propagators that emanate from all points in the source domain and in all directions. In this Part I of a two-part investigation, the theory is extended to include propagation in anisotropic medium characterized by a generic wave-number profile for time-harmonic fields; in a companion paper [J. Opt. Soc. Am. A22, 1208 (2005)], the theory is extended to time-dependent fields. The propagation characteristics of the beam propagators in a homogeneous anisotropic medium are considered. With use of Gaussian windows for the local processing of either ordinary or extraordinary electromagnetic field distributions, the field is represented by a phase-space spectral distribution in which the propagating elements are Gaussian beams that are formulated by using Gaussian plane-wave spectral distributions over the extended source plane. By applying saddle-point asymptotics, we extract the Gaussian beam phenomenology in the anisotropic environment. The resulting field is parameterized in terms of the spatial evolution of the beam curvature, beam width, etc., which are mapped to local geometrical properties of the generic wave-number profile. The general results are applied to the special case of uniaxial crystal, and it is found that the asymptotics for the Gaussian beam propagators, as well as the physical phenomenology attached, perform remarkably well.

  2. Deformation fields near a steady fatigue crack with anisotropic plasticity

    SciTech Connect

    Gao, Yanfei

    2015-11-30

    In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth and the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.

  3. Deformation fields near a steady fatigue crack with anisotropic plasticity

    DOE PAGESBeta

    Gao, Yanfei

    2015-11-30

    In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

  4. Subsurface Stress Fields in Single Crystal (Anisotropic) Contacts

    NASA Technical Reports Server (NTRS)

    Arakere, Nagaraj K.

    2003-01-01

    Single crystal superalloy turbine blades used in high pressure turbomachinery are subject to conditions of high temperature, triaxial steady and fatigue stresses, fretting stresses in the blade attachment and damper contact locations, and exposure to high-pressure hydrogen. The blades are also subjected to extreme variations in temperature during start-up and shutdown transients. The most prevalent HCF failure modes observed in these blades during operation include crystallographic crack initiation/propagation on octahedral planes, and noncrystallographic initiation with crystallographic growth. Numerous cases of crack initiation and crack propagation at the blade leading edge tip, blade attachment regions, and damper contact locations have been documented. Understanding crack initiation/propagation under mixed-mode loading conditions is critical for establishing a systematic procedure for evaluating HCF life of single crystal turbine blades. Techniques for evaluating two and three dimensional subsurface stress fields in anisotropic contacts are presented in this report. Figure 1 shows typical damper contact locations in a turbine blade. The subsurface stress results are used for evaluating contact fatigue life at damper contacts and dovetail attachment regions in single crystal nickel-base superalloy turbine blades.

  5. Emergence of anisotropic heavy fermions in antiferromagnetic Kondo lattice CeIn3 revealed by photoemission

    NASA Astrophysics Data System (ADS)

    Zhang, Yun; Lu, Haiyan; Zhu, Xiegang; Tan, Shiyong; Chen, Qiuyun; Feng, Wei; Xie, Donghua; Luo, Lizhu; Zhang, Wen; Lai, Xinchun; Donglai Feng Team; Huiqiu Yuan Team

    One basic concept in heavy fermions systems is the entanglement of localized spin state and itinerant electron state. It can be tuned by two competitive intrinsic mechanisms, Kondo effect and Ruderman-Kittel-Kasuya-Yosida interaction, with external disturbances. The key issue regarding heavy fermions properties is how the two mechanisms work in the same phase region. To investigate the relation of the two mechanisms, the cubic antiferromagnetic heavy fermions compound CeIn3 was investigated by soft x-ray angle resolved photoemission spectroscopy. The hybridization between f electrons and conduction bands in the paramagnetic state was observed directly, providing compelling evidence for Kondo screening scenario and coexistence of two mechanisms. The hybridization strength shows slight and regular anisotropy in K space, implying that the two mechanisms are competitive and anisotropic. This work illuminates the concomitant and competitive relation between the two mechanisms and supplies some evidences for the anisotropic superconductivity of CeIn3

  6. An analytical model of anisotropic low-field electron mobility in wurtzite indium nitride

    NASA Astrophysics Data System (ADS)

    Wang, Shulong; Liu, Hongxia; Song, Xin; Guo, Yulong; Yang, Zhaonian

    2014-03-01

    This paper presents a theoretical analysis of anisotropic transport properties and develops an anisotropic low-field electron analytical mobility model for wurtzite indium nitride (InN). For the different effective masses in the Γ-A and Γ-M directions of the lowest valley, both the transient and steady state transport behaviors of wurtzite InN show different transport characteristics in the two directions. From the relationship between velocity and electric field, the difference is more obvious when the electric field is low in the two directions. To make an accurate description of the anisotropic transport properties under low field, for the first time, we present an analytical model of anisotropic low-field electron mobility in wurtzite InN. The effects of different ionized impurity scattering models on the low-field mobility calculated by Monte Carlo method (Conwell-Weisskopf and Brooks-Herring method) are also considered.

  7. Magnetic Field Control of the Quantum Chaotic Dynamics of Hydrogen Analogs in an Anisotropic Crystal Field

    SciTech Connect

    Zhou Weihang; Chen Zhanghai; Zhang Bo; Yu, C. H.; Lu Wei; Shen, S. C.

    2010-07-09

    We report magnetic field control of the quantum chaotic dynamics of hydrogen analogues in an anisotropic solid state environment. The chaoticity of the system dynamics was quantified by means of energy level statistics. We analyzed the magnetic field dependence of the statistical distribution of the impurity energy levels and found a smooth transition between the Poisson limit and the Wigner limit, i.e., transition between regular Poisson and fully chaotic Wigner dynamics. The effect of the crystal field anisotropy on the quantum chaotic dynamics, which manifests itself in characteristic transitions between regularity and chaos for different field orientations, was demonstrated.

  8. Magnetic phase diagram of a spatially anisotropic, frustrated spin-¹/₂ Heisenberg antiferromagnet on a stacked square lattice.

    PubMed

    Majumdar, Kingshuk

    2011-02-01

    The magnetic phase diagram of a spatially anisotropic, frustrated spin-[Formula: see text] Heisenberg antiferromagnet on a stacked square lattice is investigated using a second-order spin-wave expansion. The effects of interlayer coupling and the spatial anisotropy on the magnetic ordering of two ordered ground states are explicitly studied. It is shown that with increase in next nearest neighbor frustration the second-order corrections play a significant role in stabilizing the magnetization. We obtain two ordered magnetic phases (Néel and stripe) separated by a paramagnetic disordered phase. Within the second-order spin-wave expansion we find that the width of the disordered phase diminishes with increase in the interlayer coupling or with decrease in spatial anisotropy but it does not disappear. Our obtained phase diagram differs significantly from the phase diagram obtained using linear spin-wave theory.

  9. Frustrated electrons on a spatially anisotropic triangular lattice: Emergent competition of charge orders and exotic disorders due to thermal fluctuations

    NASA Astrophysics Data System (ADS)

    Yoshida, Tempei; Hotta, Chisa

    2014-12-01

    We study the interplay of correlation and thermal fluctuation in a system consisting of two species of classical particles with up and down spin on a geometrically frustrated anisotropic triangular lattice, described by an extended four-state Potts model. The model corresponds to the strong coupling limit of the extended Hubbard model at quarter-filling, which is known to host several competing charge ordered phases as well as an exotic quantum state called pinball liquid. The frustrated intersite Coulomb interactions together with the on-site Coulomb interaction generate macroscopically degenerate manifolds of low-energy states. They compete entropically at finite temperature and two characteristic states emerge; a threefold periodic charge ordered state and a quasi-one-dimensionally disordered state called "good defect state" characterized by the systematic generation of ferroelectric bonds. The two states show good correspondence with the threefold charge order and the pinball liquid in the extended Hubbard model, and are separated by the partial Mott transition taking place on one of the three sublattices of the triangular lattice.

  10. Effects of Electromagnetic Field on the Dynamics of Bianchi Type VI0 Universe with Anisotropic Dark Energy

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Zubair, M.

    Spatially homogeneous and anisotropic Bianchi type VI0 cosmological models with cosmological constant are investigated in the presence of anisotropic dark energy. We examine the effects of electromagnetic field on the dynamics of the universe and anisotropic behavior of dark energy. The law of variation of the mean Hubble parameter is used to find exact solutions of the Einstein field equations. We find that electromagnetic field promotes anisotropic behavior of dark energy which becomes isotropic for future evolution. It is concluded that the isotropic behavior of the universe model is seen even in the presence of electromagnetic field and anisotropic fluid.

  11. Fermion bag approach to lattice field theories

    SciTech Connect

    Chandrasekharan, Shailesh

    2010-07-15

    We propose a new approach to the fermion sign problem in systems where there is a coupling U such that when it is infinite the fermions are paired into bosons, and there is no fermion permutation sign to worry about. We argue that as U becomes finite, fermions are liberated but are naturally confined to regions which we refer to as fermion bags. The fermion sign problem is then confined to these bags and may be solved using the determinantal trick. In the parameter regime where the fermion bags are small and their typical size does not grow with the system size, construction of Monte Carlo methods that are far more efficient than conventional algorithms should be possible. In the region where the fermion bags grow with system size, the fermion bag approach continues to provide an alternative approach to the problem but may lose its main advantage in terms of efficiency. The fermion bag approach also provides new insights and solutions to sign problems. A natural solution to the ''silver blaze problem'' also emerges. Using the three-dimensional massless lattice Thirring model as an example, we introduce the fermion bag approach and demonstrate some of these features. We compute the critical exponents at the quantum phase transition and find {nu}=0.87(2) and {eta}=0.62(2).

  12. Tight-binding lattices with an oscillating imaginary gauge field

    NASA Astrophysics Data System (ADS)

    Longhi, Stefano

    2016-08-01

    We consider non-Hermitian dynamics of a quantum particle hopping on a one-dimensional tight-binding lattice made of N sites with asymmetric hopping rates induced by a time-periodic oscillating imaginary gauge field. A deeply different behavior is found depending on the lattice topology. While in a linear chain (open boundary conditions) an oscillating field can lead to a complex quasienergy spectrum via a multiple parametric resonance; in a ring topology (Born-von Karman periodic boundary conditions) an entirely real quasienergy spectrum can be found and the dynamics is pseudo-Hermitian. In the large-N limit, parametric instability and pseudo-Hermitian dynamics in the two different lattice topologies are physically explained on the basis of a simple picture of wave-packet propagation.

  13. Local spectrum analysis of field propagation in an anisotropic medium. Part II. Time-dependent fields

    NASA Astrophysics Data System (ADS)

    Tinkelman, Igor; Melamed, Timor

    2005-06-01

    In Part I of this two-part investigation [J. Opt. Soc. Am. A22, 1200 (2005)], we presented a theory for phase-space propagation of time-harmonic electromagnetic fields in an anisotropic medium characterized by a generic wave-number profile. In this Part II, these investigations are extended to transient fields, setting a general analytical framework for local analysis and modeling of radiation from time-dependent extended-source distributions. In this formulation the field is expressed as a superposition of pulsed-beam propagators that emanate from all space-time points in the source domain and in all directions. Using time-dependent quadratic-Lorentzian windows, we represent the field by a phase-space spectral distribution in which the propagating elements are pulsed beams, which are formulated by a transient plane-wave spectrum over the extended-source plane. By applying saddle-point asymptotics, we extract the beam phenomenology in the anisotropic environment resulting from short-pulsed processing. Finally, the general results are applied to the special case of uniaxial crystal and compared with a reference solution.

  14. Local spectrum analysis of field propagation in an anisotropic medium. Part II. Time-dependent fields.

    PubMed

    Tinkelman, Igor; Melamed, Timor

    2005-06-01

    In Part I of this two-part investigation [J. Opt. Soc. Am. A 22, 1200 (2005)], we presented a theory for phase-space propagation of time-harmonic electromagnetic fields in an anisotropic medium characterized by a generic wave-number profile. In this Part II, these investigations are extended to transient fields, setting a general analytical framework for local analysis and modeling of radiation from time-dependent extended-source distributions. In this formulation the field is expressed as a superposition of pulsed-beam propagators that emanate from all space-time points in the source domain and in all directions. Using time-dependent quadratic-Lorentzian windows, we represent the field by a phase-space spectral distribution in which the propagating elements are pulsed beams, which are formulated by a transient plane-wave spectrum over the extended-source plane. By applying saddle-point asymptotics, we extract the beam phenomenology in the anisotropic environment resulting from short-pulsed processing. Finally, the general results are applied to the special case of uniaxial crystal and compared with a reference solution.

  15. Phase transition of anisotropic frustrated Heisenberg model on the square lattice.

    PubMed

    Hu, Ai-Yuan; Wang, Huai-Yu

    2016-01-01

    We have investigated the J_{1}-J_{2} Heisenberg model with exchange anisotropy on a square lattice and focused on possible AF1-AF2 phase transition below the Néel point and its dependence on the exchange anisotropy, where AF1 and AF2 represent Néel state and collinear state, respectively. We use the double-time Green's-function method and adopt the random-phase approximation. The less the exchange anisotropy, the stronger the quantum fluctuation of the system will be. Both the Néel state and collinear state can exist and have the same Néel temperature for arbitrary anisotropy and spin quantum number S when J_{2}/J_{1}=0.5. Under such parameters, the calculated free energies show that there may occur a first-order phase transition between the Néel state and collinear state for an arbitrary S when anisotropy is not strong. PMID:26871025

  16. Flow and dispersion in anisotropic porous media: A lattice-Boltzmann study

    NASA Astrophysics Data System (ADS)

    Maggiolo, D.; Picano, F.; Guarnieri, M.

    2016-10-01

    Given their capability of spreading active chemical species and collecting electricity, porous media made of carbon fibers are extensively used as diffusion layers in energy storage systems, such as redox flow batteries. In spite of this, the dispersion dynamics of species inside porous media is still not well understood and often lends itself to different interpretations. Actually, the microscopic design of efficient porous media, which can potentially and effectively improve the performances of flow batteries, is still an open challenge. The present study aims to investigate the effect of fibrous media micro-structure on dispersion, in particular the effect of fiber orientation on drag and dispersion dynamics. Several lattice-Boltzmann simulations of flows through differently oriented fibrous media coupled with Lagrangian simulations of particle tracers have been performed. Results show that orienting fibers preferentially along the streamwise direction minimizes the drag and maximizes the dispersion, which is the most desirable condition for diffusion layers in flow batteries' applications.

  17. Low field induced giant anisotropic magnetocaloric effect in DyFeO3 single crystal

    NASA Astrophysics Data System (ADS)

    Ya-Jiao, Ke; Xiang-Qun, Zhang; Heng, Ge; Yue, Ma; Zhao-Hua, Cheng

    2015-03-01

    We have investigated the anisotropic magnetocaloric effect and the rotating field magnetic entropy in DyFeO3 single crystal. A giant rotating field entropy change of was achieved from b axis to c axis in bc plane at 5 K for a low field change of 20 kOe. The large anisotropic magnetic entropy change is mainly accounted for the 4f electron of rare-earth Dy3 + ion. The large value of rotating field entropy change, together with large refrigeration capacity and negligible hysteresis, suggests that the multiferroic ferrite DyFeO3 singlecrystal could be a potential material for anisotropic magnetic refrigeration at low field, which can be realized in the practical application around liquid helium temperature region. Project supported by the National Basic Research Program of China (Grant Nos. 2010CB934202, 2011CB921801, and 2012CB933102) and the National Natural Science Foundation of China (Grant Nos. 11174351, 11274360, and 11034004).

  18. Fractional flux lattice and the anyon mean-field approximation

    SciTech Connect

    Pryor, C. )

    1991-12-01

    The anyon mean-field approximation (MFA) is tested by computing the band structure of a charged particle in an infinite two-dimensional square lattice of infinitesimal flux tubes. The band structure and density of states are compared with the MFA and found to be in agreement for {Phi}=1/{ital n}, with {ital n}{gt}3. For {Phi}=1/2 and 1/3, there is no gap, unlike the MFA which predicts a gap. For {Phi}={ital m}/{ital n} (with {ital m}{gt}1), there is a gap, opening up the possibility that a superfluid may form for any rational value of the statistical parameter. A physical realization of the {Phi}=1/2 flux lattice is proposed and a connection between the {Phi}={ital m}/{ital n} lattice and the fractional quantum Hall effect is discussed.

  19. Metal-oxide-semiconductor field effect nanostructure spin lattice devices

    NASA Astrophysics Data System (ADS)

    Yang, Jun

    This dissertation explored and developed technologies for silicon based spin lattice devices. Spin lattices are artificial electron spin systems with a periodic structure having one to a few electrons at each site. They are expected to have various magnetic and even superconducting properties when structured at an optimal scale with a specific number i of electrons. Silicon turns out to be a very good material choice in realizing spin lattices. A metal-oxide-semiconductor field-effect nanostructure (MOSFENS) device, which is closely related to a MOS transistor but with a nanostructured oxide-semiconductor interface, can define the spin lattices potential at the interface and alter the occupation i with the gate electrode potential to change the magnetic phase. The MOSFENS spin lattices engineering challenge addressed in this work has come from the practical difficulty of process integration in modifying a transistor fabrication process to accommodate the interface patterning requirements. Two distinct design choices for the fabrication sequences that create the nanostructure have been examined. Patterning the silicon surface before the MOS gate stack layers gives a "nanostructure first" process, and patterning the interface after forming the gate stack gives a "nanostructure last process." Both processes take advantage of a nano-LOCOS (nano-local oxidation of silicon) invention developed in this work. The nano-LOCOS process plays a central role in defining a clean, sharp confining potential for the spin lattice electrons. The MOSFENS process required a basic transistor fabrication process that can accommodate the nanostructures. The process developed for this purpose has a gate stack with a 15 nm polysilicon gate electrode and a 3 nm thermal gate oxide on a p-type silicon substrate. The measured threshold voltage is 0.25 V. Device processes were examined for either isolating the devices with windows in the field oxide or with mesas defined by the etched trenches

  20. Features of the electric-field distribution in anisotropic semiconductor wafers in a transverse magnetic field

    SciTech Connect

    Filippov, V. V.; Bormontov, E. N.

    2013-07-15

    A macroscopic model of the Hall effects and magnetoresistance in anisotropic semiconductor wafers is developed. The results obtained by solving the electrodynamic boundary problem allow the potential and eddy currents in anisotropic semiconductors to be calculated at different current-contact locations, depending on the parameters of the sample material's anisotropy. The results of this study are of great practical importance for investigating the physical properties of anisotropic semiconductors and simulating the electron-transport phenomena in devices based on anisotropic semiconductors.

  1. Uniaxial magnetic anisotropy induced low field anomalous anisotropic magnetoresistance in manganite thin films

    NASA Astrophysics Data System (ADS)

    Liao, Zhaoliang; Huijben, Mark; Koster, Gertjan; Rijnders, Guus

    2014-09-01

    La2/3Sr1/3MnO3 films with uniaxial magnetic anisotropy were coherently grown on NdGaO3 (110) substrates. The uniaxial anisotropy has strong effect on magnetoresistance (MR). A positive MR was observed when the current is along magnetic easy axis under the current-field perpendicular geometry. In contrast, no positive MR is observed when current is along the magnetic hard axis regardless of the field direction. Our analysis indicates that the anomalous anisotropic MR effect arises from the uniaxial magnetic anisotropy caused stripe domains which contribute to strong anisotropic domain wall resistivity.

  2. Bogoliubov transformations and fermion condensates in lattice field theories

    SciTech Connect

    Caracciolo, Sergio Palumbo, Fabrizio Viola, Giovanni

    2009-03-15

    We apply generalized Bogoliubov transformations to the transfer matrix of relativistic field theories regularized on a lattice. We derive the conditions these transformations must satisfy to factorize the transfer matrix into two terms which propagate fermions and antifermions separately, and we solve the relative equations under some conditions. We relate these equations to the saddle point approximation of a recent bosonization method and to the Foldy-Wouthuysen transformations which separate positive from negative energy states in the Dirac Hamiltonian.

  3. Gravitational field calculations on a dynamic lattice by distributed computing.

    NASA Astrophysics Data System (ADS)

    Mähönen, P.; Punkka, V.

    A new method of calculating numerically time evolution of a gravitational field in general relativity is introduced. Vierbein (tetrad) formalism, dynamic lattice and massively parallelized computation are suggested as they are expected to speed up the calculations considerably and facilitate the solution of problems previously considered too hard to be solved, such as the time evolution of a system consisting of two or more black holes or the structure of worm holes.

  4. Gravitation Field Calculations on a Dynamic Lattice by Distributed Computing

    NASA Astrophysics Data System (ADS)

    Mähönen, Petri; Punkka, Veikko

    A new method of calculating numerically time evolution of a gravitational field in General Relatity is introduced. Vierbein (tetrad) formalism, dynamic lattice and massively parallelized computation are suggested as they are expected to speed up the calculations considerably and facilitate the solution of problems previously considered too hard to be solved, such as the time evolution of a system consisting of two or more black holes or the structure of worm holes.

  5. DDFT calibration and investigation of an anisotropic phase-field crystal model.

    PubMed

    Choudhary, Muhammad Ajmal; Li, Daming; Emmerich, Heike; Löwen, Hartmut

    2011-07-01

    The anisotropic phase-field crystal model recently proposed and used by Prieler et al (2009 J. Phys.: Condens. Matter 21 464110) is derived from microscopic density functional theory for anisotropic particles with fixed orientation. Its morphology diagram is also explored. In particular we have investigated the influence of anisotropy and undercooling on the process of nucleation and microstructure formation from the atomic to the microscale. To that end numerical simulations were performed varying those dimensionless parameters which represent anisotropy and undercooling in our anisotropic phase-field crystal model. The results from these numerical simulations are summarized in terms of a morphology diagram of the stable state phases. These stable phases are also investigated with respect to their kinetics and characteristic morphological features.

  6. Anisotropic Surface State Mediated RKKY Interaction Between Adatoms on a Hexagonal Lattice

    NASA Astrophysics Data System (ADS)

    Einstein, Theodore; Patrone, Paul

    2012-02-01

    Motivated by recent numerical studies of Ag on Pt(111), we derive a far-field expression for the RKKY interaction mediated by surface states on a (111) FCC surface, considering the effect of anisotropy in the Fermi edge. The main contribution to the interaction comes from electrons whose Fermi velocity vF is parallel to the vector R connecting the interacting adatoms; we show that in general, the corresponding Fermi wave-vector kF is not parallel to R. The interaction is oscillatory; the amplitude and wavelength of oscillations have angular dependence arising from the anisotropy of the surface state band structure. The wavelength, in particular, is determined by the component of the aforementioned kF that is parallel to R. Our analysis is easily generalized to other systems. For Ag on Pt(111), our results indicate that the RKKY interaction between pairs of adatoms should be nearly isotropic and so cannot account for the anisotropy found in the studies motivating our work.

  7. Approaches to the sign problem in lattice field theory

    NASA Astrophysics Data System (ADS)

    Gattringer, Christof; Langfeld, Kurt

    2016-08-01

    Quantum field theories (QFTs) at finite densities of matter generically involve complex actions. Standard Monte Carlo simulations based upon importance sampling, which have been producing quantitative first principle results in particle physics for almost forty years, cannot be applied in this case. Various strategies to overcome this so-called sign problem or complex action problem were proposed during the last thirty years. We here review the sign problem in lattice field theories, focusing on two more recent methods: dualization to worldline type of representations and the density-of-states approach.

  8. Electric field modulation of tunneling anisotropic magnetoresistance in tunnel junctions with antiferromagnetic electrodes

    NASA Astrophysics Data System (ADS)

    Goto, Minori; Nawaoka, Kohei; Miwa, Shinji; Hatanaka, Shohei; Mizuochi, Norikazu; Suzuki, Yoshishige

    2016-08-01

    We present electric field modulation of tunneling anisotropic magnetoresistance (TAMR) in MnIr|MgO|Ta tunnel junctions. TAMR enables direct observation of the antiferromagnetic spin direction at the MnIr|MgO interface. We found that the shape of magnetoresistance (MR) curve can be modulated by an electric field, which can be explained by electric field modulation of the interfacial magnetic anisotropy at MnIr|MgO.

  9. Electric field obtained from an elliptic critical-state model for anisotropic type-II superconductors

    NASA Astrophysics Data System (ADS)

    Romero-Salazar, C.; Hernández-Flores, O. A.

    2016-02-01

    The conventional elliptic critical-state models (ECSM) establish that the electric field vector is zero when it flows a critical current density in a type-II superconductor. This proposal incorporates a finite electric field on the ECSM to study samples with anisotropic-current-carrying capacity. Our theoretical scheme has the advantage of being able to dispense of a material law which drives the electric field magnitude, however, it does not consider the magnetic history of the superconductor.

  10. The 30th International Symposium on Lattice Field Theory

    NASA Astrophysics Data System (ADS)

    Kamleh, Waseem; Leinweber, Derek; Mahbub, Selim; Matevosyan, Hrayr; Thomas, Anthony; Williams, Anthony; Young, Ross; Zanotti, James

    Lattice 2012, the 30th International Symposium on Lattice Field Theory was held in Cairns, Australia from Sunday the 24th of June to Friday the 29th June 2012. It was held at the Cairns Convention Centre, providing world-class facilities in a beautiful location. Fine weather and easy access to world heritage attractions including the Great Barrier Reef and the Wet Tropics Rainforests made for an extraordinary experience. The conference was organised by the Special Research Centre for the Subatomic Structure of Matter (CSSM) in the School of Chemistry & Physics at the University of Adelaide. More than 285 participants from around the world attended the symposium. The scientific program contained 22 plenary talks and 248 parallel contributions including posters. Most of these are recorded in this proceedings. For 30 years, the Lattice meeting has provided researchers from around the world with an annual forum at which to disseminate and discuss ideas, developments and opportunities in the study of relativistic quantum fields regulated on a spacetime lattice. It fosters the exchange of ideas, networking, and builds relationships between researchers that are essential in facilitating rapid progress and the creation of new knowledge. The program included plenary talks, parallel talks and poster presentations on Algorithms and machines, Applications beyond QCD, Chiral symmetry, Hadron spectroscopy and interactions, Hadron structure, Nonzero temperature and density, Standard model parameters and renormalization, Theoretical developments, Vacuum structure and confinement and Weak decays and matrix elements. The International Advisory Committee provided excellent guidance in planning the scientific program of the conference and we thank the Committee for their important contributions. Thanks also to our presenters for the time and effort they put into preparing their talks and their proceedings. Many thanks to our Conference Secretariat, Sharon Johnson, Silvana Santucci

  11. Long-range interactions in lattice field theory

    SciTech Connect

    Rabin, J.M.

    1981-06-01

    Lattice quantum field theories containing fermions can be formulated in a chirally invariant way provided long-range interactions are introduced. It is established that in weak-coupling perturbation theory such a lattice theory is renormalizable when the corresponding continuum theory is, and that the continuum theory is indeed recovered in the perturbative continuum limit. In the strong-coupling limit of these theories one is led to study an effective Hamiltonian describing a Heisenberg antiferromagnet with long-range interactions. Block-spin renormalization group methods are used to find a critical rate of falloff of the interactions, approximately as inverse distance squared, which separates a nearest-neighbor-antiferromagnetic phase from a phase displaying identifiable long-range effects. A duality-type symmetry is present in some block-spin calculations.

  12. The XXV International Symposium on Lattice Field Theory

    NASA Astrophysics Data System (ADS)

    Bali; Braun, Gunnar; Gattring, Vladimir; Göckeler, Christof; Schäfer, Meinulf; Weisz, Andreas; Wettig, Peter; Tilo

    Lattice 2007, the XXV International Symposium on Lattice Field Theory, was held from July 30 to August 4, 2007 at the University of Regensburg, Germany. The scientific program contained 24 plenary session talks and 338 parallel session contributions (talks and posters). The conference topics included: algorithms and machines; applications beyond QCD; chiral symmetry; hadron spectroscopy; hadron structure; nonzero temperature and density; standard model parameters and renormalization; theoretical developments; vacuum structure and confinement; weak decays and matrix elements. We gratefully acknowledge financial support by the following companies and institutions, which was essential for the success of the conference: Bull, Eurotech, IBM, Intel, Sun, DESY, GSI, FZ Jülich, Vielberth Foundation, Kneitinger.Editorial Board:Gunnar Bali, Vladimir Braun, Christof Gattringer (chairman), Meinulf Göckeler, Andreas Schäfer, Peter Weisz, Tilo Wettig

  13. Multi-band near-field radiative heat transfer between two anisotropic fishnet metamaterials

    NASA Astrophysics Data System (ADS)

    Bai, Yang; Jiang, Yongyuan; Liu, Linhua

    2015-06-01

    We study the near-field radiative heat transfer between two metal-insulator-metal sandwiched-like fishnet metamaterials (FMMs) by fluctuation electrodynamics. Results show that multi-band heat flux between the fishnet metamaterials is achieved, which is attributed to the thermally excited surface modes within the FMM. Apart from the electric response mode of the near-field heat flux, magnetic modes are also existed, which are related with the excitations of the surface plasmon polaritons (SPPs) propagating on the outer surface of metal (external SPPs) and along the inner metal-dielectric interface (internal SPPs). Moreover, we show that the electromagnetic parameters of this anisotropic fishnet metamaterial depend on the angles θ of the incident light when heating the fishnet metamaterial, and thus the overall effect of the anisotropic FMM parameters is considered to predict the near-field radiative heat transfer. Different external-SPPs and internal-SPPs modes are excited at different frequencies which is attributed to the anisotropic electromagnetic response of FMM, which open new frequency channels of the near-field radiative heat transfer. This kind of anisotropic metamaterial should assist in thermal management in nanoscale.

  14. Formation of temperature fields in doped anisotropic crystals under spatially inhomogeneous light beams passing through them

    SciTech Connect

    Zaitseva, E. V.; Markelov, A. S.; Trushin, V. N. Chuprunov, E. V.

    2013-12-15

    The features of formation of thermal fields in potassium dihydrophosphate crystal doped with potassium permanganate under a 532-nm laser beam passing through it have been investigated. Data on the influence of birefringence on the temperature distribution in an anisotropic crystal whose surface is illuminated by a spatially modulated light beam are presented.

  15. The unique effect of in-plane anisotropic strain in the magnetization control by electric field

    NASA Astrophysics Data System (ADS)

    Zhao, Y. Y.; Wang, J.; Hu, F. X.; Liu, Y.; Kuang, H.; Wu, R. R.; Sun, J. R.; Shen, B. G.

    2016-05-01

    The electric field control of magnetization in both (100)- and (011)-Pr0.7Sr0.3MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3(PSMO/PMN-PT) heterostructures were investigated. It was found that the in-plane isotropic strain induced by electric field only slightly reduces the magnetization at low temperature in (100)-PSMO/PMN-PT film. On the other hand, for (011)-PSMO/PMN-PT film, the in-plane anisotropic strain results in in-plane anisotropic, nonvolatile change of magnetization at low-temperature. The magnetization, remanence and coercivity along in-plane [100] direction are suppressed by the electric field while the ones along [01-1] direction are enhanced, which is ascribed to the extra effective magnetic anisotropy induced by the electric field via anisotropic piezostrains. More interestingly, such anisotropic modulation behaviors are nonvolatile, demonstrating a memory effect.

  16. Toward a realistic low-field SSC lattice

    SciTech Connect

    Heifets, S.

    1985-10-01

    Three six-fold lattices for 3 T superferric SSC have been generated at TAC. The program based on the first order canonical transformation was used to compare lattices. On this basis the realistic race-track lattices were generated.

  17. The effect of magnetic field on the susceptibility maximum in the spatially anisotropic Heisenberg antiferromagnet

    NASA Astrophysics Data System (ADS)

    Xiang, Ying; Chen, Yuan; Chen, Qi-Zhou; Zhang, Jun; Liu, Yi-Kun

    2008-12-01

    The effect of magnetic field h on the longitudinal susceptibility in a spin S=1/2 exchange anisotropic three-dimensional Heisenberg antiferromagnet, is studied by the double-time Green's function method within Tyablikov approximation. The calculation results indicated that the height χ(Tm) and position Tm of the maximum of the longitudinal susceptibility display different behaviors related to the magnetic fields and exchange anisotropic parameters. These behaviors are very different from that in the exchange anisotropic Heisenberg ferromagnet in the magnetic field. The results are: (1) When the field h is weak, in a antiferromagnet, the height χ(Tm) is a constant χ0 which is independent of field and exchange anisotropy, but the position Tm is only a function of the exchange anisotropy. While in a ferromagnet, both χ(Tm) and Tm are a function of field and the exchange anisotropy. (2) When the field h is strong, in a antiferromagnet, χ(Tm) becomes dependent of field and the exchange anisotropy, and χ(Tm) and Tm are fitted satisfactory to power laws: χ(Tm)-χ0∝hd and TN-Tm∝hc, respectively. Here TN is the Neel temperature. On the contrary, in a ferromagnet, χ(Tm) and Tm are fitted to power laws: χ(Tm)∝h and Tm-Tc∝h, where Tc is the Curie temperature. The above results are very useful in studying the magnetic property of coordination polymers.

  18. Field-induced decays in XXZ triangular-lattice antiferromagnets

    NASA Astrophysics Data System (ADS)

    Maksimov, P. A.; Zhitomirsky, M. E.; Chernyshev, A. L.

    2016-10-01

    We investigate field-induced transformations in the dynamical response of the XXZ model on the triangular lattice that are associated with the anharmonic magnon coupling and decay phenomena. Detailed theoretical predictions are made for Ba3CoSb2O9 , which provides a close realization of the spin-1/2 XXZ model. We demonstrate that dramatic modifications in the magnon spectrum must occur in low out-of-plane fields that are easily achievable for this material. The hallmark of the effect is a coexistence of the clearly distinct well-defined magnon excitations with significantly broadened ones in different regions of the k -ω space. The field-induced decays are generic for this class of models and become more prominent at larger anisotropies and in higher fields.

  19. Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Turner, L.

    1981-01-01

    A strong external dc magnetic field introduces a basic anisotropy into incompressible magnetohydrodynamic turbulence. The modifications that this is likely to produce in the properties of the turbulence are explored for the high Reynolds number case. The conclusion is reached that the turbulent spectrum splits into two parts: an essentially two dimensional spectrum with both the velocity field and magnetic fluctuations perpendicular to the dc magnetic field, and a generally weaker and more nearly isotropic spectrum of Alfven waves. A minimal characterization of the spectral density tensors is given. Similarities to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrotor Tokamak are remarked upon, as are certain implications for the Belcher and Davis measurements of magnetohydrodynamic turbulence in the solar wind.

  20. Atomistically enabled nonsingular anisotropic elastic representation of near-core dislocation stress fields in α -iron

    NASA Astrophysics Data System (ADS)

    Seif, Dariush; Po, Giacomo; Mrovec, Matous; Lazar, Markus; Elsässer, Christian; Gumbsch, Peter

    2015-05-01

    The stress fields of dislocations predicted by classical elasticity are known to be unrealistically large approaching the dislocation core, due to the singular nature of the theory. While in many cases this is remedied with the approximation of an effective core radius, inside which ad hoc regularizations are implemented, such approximations lead to a compromise in the accuracy of the calculations. In this work an anisotropic nonsingular elastic representation of dislocation fields is developed to accurately represent the near-core stresses of dislocations in α -iron. The regularized stress field is enabled through the use of a nonsingular Green's tensor function of Helmholtz-type gradient anisotropic elasticity, which requires only a single characteristic length parameter in addition to the material's elastic constants. Using a magnetic bond-order potential to model atomic interactions in iron, molecular statics calculations are performed, and an optimization procedure is developed to extract the required length parameter. Results show the method can accurately replicate the magnitude and decay of the near-core dislocation stresses even for atoms belonging to the core itself. Comparisons with the singular isotropic and anisotropic theories show the nonsingular anisotropic theory leads to a substantially more accurate representation of the stresses of both screw and edge dislocations near the core, in some cases showing improvements in accuracy of up to an order of magnitude. The spatial extent of the region in which the singular and nonsingular stress differ substantially is also discussed. The general procedure we describe may in principle be applied to accurately model the near-core dislocation stresses of any arbitrarily shaped dislocation in anisotropic cubic media.

  1. Assessing the Structure of Isotropic and Anisotropic Turbulent Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Fatuzzo, Marco; Holden, Lisa; Grayson, Lindsay; Wallace, Kirk

    2016-10-01

    Turbulent magnetic fields permeate our universe, impacting a wide range of astronomical phenomena across all cosmic scales. A clear example is the magnetic field that threads the interstellar medium (ISM), which impacts the motion of cosmic rays through that medium. Understanding the structure of magnetic turbulence within the ISM and how it relates to the physical quantities that characterize it can thus inform our analysis of particle transport within these regions. Toward that end, we probe the structure of magentic turbulence through the use of Lyapunov exponents for a suite of isotropic and nonisotropic Alfvénic turbulence profiles. Our results provide a means of calculating a “turbulence lengthscale” that can then be connected to how cosmic rays propagate through magentically turbulent environments, and we perform such an analysis for molecular cloud environments.

  2. Intentional anisotropic strain relaxation in ( 11 2 ¯ 2) oriented Al1-xInxN one-dimensionally lattice matched to GaN

    NASA Astrophysics Data System (ADS)

    Buß, E. R.; Rossow, U.; Bremers, H.; Meisch, T.; Caliebe, M.; Scholz, F.; Hangleiter, A.

    2014-09-01

    We report on ( 11 2 ¯ 2) oriented Al1-xInxN grown by low pressure metal organic vapor phase epitaxy on ( 11 2 ¯ 2) GaN templates on patterned r-plane sapphire. The indium incorporation efficiency as well as the growth rate of ( 11 2 ¯ 2) oriented layers are similar to c-plane oriented Al1-xInxN layers. Deposition of thick Al1-xInxN layers does not lead to additional roughening like in case of c-plane oriented Al1-xInxN. Independent of the thickness, the degree of relaxation of layers lattice matched in m-direction is in the range of 33%-45% in [ 11 2 ¯ 3 ¯]-direction. Associated with the relaxation in [ 11 2 ¯ 3 ¯]-direction, there is a tilt of the Al1-xInxN layers around the [ 1 1 ¯ 00] axis due to slip of threading dislocations on the basal (0001)-plane. Relaxation in m-direction is not observable for layers lattice matched in [ 11 2 ¯ 3 ¯] direction. The possibility to adjust the lattice parameter of AlInN in [ 11 2 ¯ 3 ¯] direction without changing the lattice parameter in m-direction by anisotropic strain relaxation opens up opportunities for subsequent growth of optically active structures. One possibility is to form relaxed buffer layers for GaInN quantum well structures.

  3. Effective field theory of thermal Casimir interactions between anisotropic particles.

    PubMed

    Haussman, Robert C; Deserno, Markus

    2014-06-01

    We employ an effective field theory (EFT) approach to study thermal Casimir interactions between objects bound to a fluctuating fluid surface or interface dominated by surface tension, with a focus on the effects of particle anisotropy. The EFT prescription disentangles the constraints imposed by the particles' boundaries from the calculation of the interaction free energy by constructing an equivalent point particle description. The finite-size information is captured in a derivative expansion that encodes the particles' response to external fields. The coefficients of the expansion terms correspond to generalized tensorial polarizabilities and are found by matching the results of a linear response boundary value problem computed in both the full and effective theories. We demonstrate the versatility of the EFT approach by constructing the general effective Hamiltonian for a collection of particles of arbitrary shapes. Taking advantage of the conformal symmetry of the Hamiltonian, we discuss a straightforward conformal mapping procedure to systematically determine the polarizabilities and derive a complete description for elliptical particles. We compute the pairwise interaction energies to several orders for nonidentical ellipses as well as their leading-order triplet interactions and discuss the resulting preferred pair and multibody configurations. Furthermore, we elaborate on the complications that arise with pinned particle boundary conditions and show that the powerlike corrections expected from dimensional analysis are exponentially suppressed by the leading-order interaction energies. PMID:25019720

  4. Broken symmetry approach to density functional calculation of zero field splittings including anisotropic exchange interactions

    SciTech Connect

    Kessler, Eva M. V.; Schmitt, Sebastian; Wüllen, Christoph van

    2013-11-14

    The broken symmetry approach to the calculation of zero field splittings (or magnetic anisotropies) of multinuclear transition metal complexes is further developed. A procedure is suggested how to extract spin Hamiltonian parameters for anisotropic exchange from a set of broken symmetry density functional calculations. For isotropic exchange coupling constants J{sub ij}, the established procedure is retrieved, and anisotropic (or pseudodipolar) exchange coupling tensors D{sub ij} are obtained analogously. This procedure only yields the sum of the individual single-ion zero field splitting tensors D{sub i}. Therefore, a procedure based on localized orbitals has been developed to extract the individual single-ion contributions. With spin Hamiltonian parameters at hand, the zero field splittings of the individual spin multiplets are calculated by an exact diagonalization of the isotropic part, followed by a spin projection done numerically. The method is applied to the binuclear cation [LCr(OH){sub 3}CrL]{sup 3+} (L = 1,4,7-trimethyl-1,4,7-triazanonane) for which experimental zero field splittings for all low-energy spin states are known, and to the single-molecule magnet [Fe{sub 4}(CH{sub 3}C(CH{sub 2}O){sub 3}){sub 2}(dpm){sub 6}] (Hdpm = 2,2,6,6-tetramethylheptane-3,5-dione). In both these 3d compounds, the single-ion tensors mainly come from the spin-orbit interaction. Anisotropic exchange is dominated by the spin-dipolar interaction only for the chromium compound. Despite the rather small isotropic exchange couplings in the iron compound, spin-orbit and spin-dipolar contributions to anisotropic exchange are of similar size here.

  5. Anisotropic field-of-view shapes for improved PROPELLER imaging☆

    PubMed Central

    Larson, Peder E.Z.; Lustig, Michael S.; Nishimura, Dwight G.

    2010-01-01

    The Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction (PROPELLER) method for magnetic resonance imaging data acquisition and reconstruction has the highly desirable property of being able to correct for motion during the scan, making it especially useful for imaging pediatric or uncooperative patients and diffusion imaging. This method nominally supports a circular field of view (FOV), but tailoring the FOV for noncircular shapes results in more efficient, shorter scans. This article presents new algorithms for tailoring PROPELLER acquisitions to the desired FOV shape and size that are flexible and precise. The FOV design also allows for rotational motion which provides better motion correction and reduced aliasing artifacts. Some possible FOV shapes demonstrated are ellipses, ovals and rectangles, and any convex, pi-symmetric shape can be designed. Standard PROPELLER reconstruction is used with minor modifications, and results with simulated motion presented confirm the effectiveness of the motion correction with these modified FOV shapes. These new acquisition design algorithms are simple and fast enough to be computed for each individual scan. Also presented are algorithms for further scan time reductions in PROPELLER echo-planar imaging (EPI) acquisitions by varying the sample spacing in two directions within each blade. PMID:18818039

  6. Lattice simulations of real-time quantum fields

    NASA Astrophysics Data System (ADS)

    Berges, J.; Borsányi, Sz.; Sexty, D.; Stamatescu, I.-O.

    2007-02-01

    We investigate lattice simulations of scalar and non-Abelian gauge fields in Minkowski space-time. For SU(2) gauge-theory expectation values of link variables in 3+1 dimensions are constructed by a stochastic process in an additional (5th) “Langevin-time.” A sufficiently small Langevin step size and the use of a tilted real-time contour leads to converging results in general. All fixed point solutions are shown to fulfil the infinite hierarchy of Dyson-Schwinger identities, however, they are not unique without further constraints. For the non-Abelian gauge theory the thermal equilibrium fixed point is only approached at intermediate Langevin-times. It becomes more stable if the complex time path is deformed towards Euclidean space-time. We analyze this behavior further using the real-time evolution of a quantum anharmonic oscillator, which is alternatively solved by diagonalizing its Hamiltonian. Without further optimization stochastic quantization can give accurate descriptions if the real-time extent of the lattice is small on the scale of the inverse temperature.

  7. Electromagnetic field quantization in an anisotropic magnetodielectric medium with spatial temporal dispersion

    NASA Astrophysics Data System (ADS)

    Amooshahi, M.; Kheirandish, F.

    2008-07-01

    By modeling a linear, anisotropic and inhomogeneous magnetodielectric medium with two independent sets of harmonic oscillators, the electromagnetic field is quantized in such a medium. The electric and magnetic polarizations of the medium are expressed as linear combinations of the ladder operators of the harmonic oscillators modeling the magnetodielectric medium. Maxwell and the constitutive equations of the medium are obtained as the Heisenberg equations of the total system. The electric and magnetic susceptibility tensors of the medium are obtained in terms of the tensors coupling the medium with the electromagnetic field. The explicit forms of the electromagnetic field operators are obtained for a translationally invariant medium.

  8. Magnetic field effects on viscous fingering of a ferrofluid in an anisotropic Hele-Shaw cell

    NASA Astrophysics Data System (ADS)

    Ballou, R.; Molho, P.

    2005-12-01

    When a viscous fluid is pushed into a more viscous one in a Hele-Shaw cell, the interface between the two fluids may become unstable, leading to fingering and ramified patterns. Anisotropy can be introduced by engraving a grid in one plate of the cell, allowing one to obtain dendritic patterns. The use of a ferrofluid as one of the viscous fluid is a way to introduce magnetism in the problem, especially the magnetic field as a control parameter. Magnetic field effects on viscous fingering of ferrofluids have already been studied: in a rectangular Hele-Shaw cell, a magnetic field applied in the cell plane is stabilizing when parallel to the interface between the two fluids and destabilizing when normal to the interface. A magnetic field perpendicular to the plane of a radial Hele-Shaw cell has the same destabilizing effect as the pressure. We have studied the effect of a magnetic field, normal to and in the plane of anisotropic radial Hele-Shaw cells te{5}, to characterize the competing effects of hydrodynamics, magnetic field and dipolar energy, and anisotropy. Here we study more precisely the effect of a magnetic field normal to a radial anisotropic Hele-Shaw cell. Figs 8, Refs 9.

  9. Evaluation of three-dimensional anisotropic head model for mapping realistic electromagnetic fields of brain tissues

    NASA Astrophysics Data System (ADS)

    Jeong, Woo Chul; Wi, Hun; Sajib, Saurav Z. K.; Oh, Tong In; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2015-08-01

    Electromagnetic fields provide fundamental data for the imaging of electrical tissue properties, such as conductivity and permittivity, in recent magnetic resonance (MR)-based tissue property mapping. The induced voltage, current density, and magnetic flux density caused by externally injected current are critical factors for determining the image quality of electrical tissue conductivity. As a useful tool to identify bio-electromagnetic phenomena, precise approaches are required to understand the exact responses inside the human body subject to an injected currents. In this study, we provide the numerical simulation results of electromagnetic field mapping of brain tissues using a MR-based conductivity imaging method. First, we implemented a realistic three-dimensional human anisotropic head model using high-resolution anatomical and diffusion tensor MR images. The voltage, current density, and magnetic flux density of brain tissues were imaged by injecting 1 mA of current through pairs of electrodes on the surface of our head model. The current density map of anisotropic brain tissues was calculated from the measured magnetic flux density based on the linear relationship between the water diffusion tensor and the electrical conductivity tensor. Comparing the current density to the previous isotropic model, the anisotropic model clearly showed the differences between the brain tissues. This originates from the enhanced signals by the inherent conductivity contrast as well as the actual tissue condition resulting from the injected currents.

  10. Alignment of two-point statistics with respect to mean deformation field in anisotropic turbulent flows

    NASA Astrophysics Data System (ADS)

    Morshed, Khandakar; Dasi, Lakshmi

    2013-11-01

    We study the variations in two-point correlation functions and second-order structure functions in the strongly anisotropic turbulent flow past a backward facing step. Time-resolved particle image velocimetry measurements were performed in a stationary turbulent flow past a backward facing step at Reynolds numbers 13,600, 9,000, and 5,500 based on the maximum velocity and step size. Measurements revealed a strongly anisotropic large-scale flow with an intense turbulent free-shear layer downstream of the step. Comparison among local two-point correlation functions and second-order structure functions at varying locations within the measurement domain reveals a mechanistic relationship between the magnitude of mean flow deformation field and the spatial organization of the two-point statistics in 360 degrees. It is shown that the local spatial variation in rms velocity significantly induces local anisotropy at arbitrarily small length scales.

  11. Band structure engineering via piezoelectric fields in strained anisotropic CdSe/CdS nanocrystals

    PubMed Central

    Christodoulou, Sotirios; Rajadell, Fernando; Casu, Alberto; Vaccaro, Gianfranco; Grim, Joel Q.; Genovese, Alessandro; Manna, Liberato; Climente, Juan I.; Meinardi, Francesco; Rainò, Gabriele; Stöferle, Thilo; Mahrt, Rainer F.; Planelles, Josep; Brovelli, Sergio; Moreels, Iwan

    2015-01-01

    Strain in colloidal heteronanocrystals with non-centrosymmetric lattices presents a unique opportunity for controlling optoelectronic properties and adds a new degree of freedom to existing wavefunction engineering and doping paradigms. We synthesized wurtzite CdSe nanorods embedded in a thick CdS shell, hereby exploiting the large lattice mismatch between the two domains to generate a compressive strain of the CdSe core and a strong piezoelectric potential along its c-axis. Efficient charge separation results in an indirect ground-state transition with a lifetime of several microseconds, almost one order of magnitude longer than any other CdSe/CdS nanocrystal. Higher excited states recombine radiatively in the nanosecond time range, due to increasingly overlapping excited-state orbitals. k̇p calculations confirm the importance of the anisotropic shape and crystal structure in the buildup of the piezoelectric potential. Strain engineering thus presents an efficient approach to highly tunable single- and multiexciton interactions, driven by a dedicated core/shell nanocrystal design. PMID:26219691

  12. Band structure engineering via piezoelectric fields in strained anisotropic CdSe/CdS nanocrystals.

    PubMed

    Christodoulou, Sotirios; Rajadell, Fernando; Casu, Alberto; Vaccaro, Gianfranco; Grim, Joel Q; Genovese, Alessandro; Manna, Liberato; Climente, Juan I; Meinardi, Francesco; Rainò, Gabriele; Stöferle, Thilo; Mahrt, Rainer F; Planelles, Josep; Brovelli, Sergio; Moreels, Iwan

    2015-07-29

    Strain in colloidal heteronanocrystals with non-centrosymmetric lattices presents a unique opportunity for controlling optoelectronic properties and adds a new degree of freedom to existing wavefunction engineering and doping paradigms. We synthesized wurtzite CdSe nanorods embedded in a thick CdS shell, hereby exploiting the large lattice mismatch between the two domains to generate a compressive strain of the CdSe core and a strong piezoelectric potential along its c-axis. Efficient charge separation results in an indirect ground-state transition with a lifetime of several microseconds, almost one order of magnitude longer than any other CdSe/CdS nanocrystal. Higher excited states recombine radiatively in the nanosecond time range, due to increasingly overlapping excited-state orbitals. k˙p calculations confirm the importance of the anisotropic shape and crystal structure in the buildup of the piezoelectric potential. Strain engineering thus presents an efficient approach to highly tunable single- and multiexciton interactions, driven by a dedicated core/shell nanocrystal design.

  13. Perturbative treatment of lattice dynamics in finite electric fields

    NASA Astrophysics Data System (ADS)

    Wang, Xinjie; Souza, Ivo; Vanderbilt, David

    2004-03-01

    The methods of density-functional perturbation theory have been shown to be very powerful for realistic calculations of lattice-vibrational, dielectric, elastic, and other response properties of crystals.(S. Baroni et al.), Rev. Mod. Phys. 73, 515 (2001). Recently, a total-energy method for insulators in nonzero electric fields has been proposed.(I. Souza, J. Íñiguez, and D. Vanderbilt, Phys. Rev. Lett. 89), 117602 (2002). However, the perturbative computation of response properties under a dc bias field has not previously been addressed. Here, perturbation theory is applied to a variational total-energy functional in the presence of a static, homogeneous electric field. An analytic expression is derived for the second derivative with respect to the phonon perturbation using the 2n+1 theorem. The expression is variational with respect to the first-order Bloch-like states, and can be minimized using standard conjugate-gradients methods. We implement the method in the ABINIT code and perform illustrative calculations of the interatomic force constant matrix of III-V semiconductors.

  14. QCD on the Lattice: The Central Role of Effective Field Theory

    NASA Astrophysics Data System (ADS)

    El-Khadra, Aida X.

    Nonperturbative QCD effects are ubiquitous and affect not just processes studied in particle and nuclear physics, but also in astrophysics and cosmology. Lattice field theory is a general quantitative tool for the study of nonperturbative phenomena and has provided us with much insight into nonperturbative QCD effects. In these lectures I present an introduction to lattice QCD with emphasis on the methods used for calculations relevant to quark flavor physics. In lattice QCD, quantitative control over systematic errors is made possible with the use of effective field theories. I briefly review how the effective field theories arise and their relation to the sources of systematic error in lattice QCD.

  15. Anisotropic stark effect and electric-field noise suppression for phosphorus donor qubits in silicon.

    PubMed

    Sigillito, A J; Tyryshkin, A M; Lyon, S A

    2015-05-29

    We report the use of novel, capacitively terminated coplanar waveguide resonators to measure the quadratic Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift depending on electric and magnetic field orientations relative to the Si crystal. By measuring the linear Stark effect, we estimate the effective electric field due to strain in our samples. We show that in the presence of this strain, electric-field sources of decoherence can be non-negligible. Using our measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. We discuss the limitations of these noise-suppression points due to random distributions of strain and propose a method for overcoming them. PMID:26066457

  16. Fields induced by three-dimensional dislocation loops in anisotropic magneto-electro-elastic bimaterials

    NASA Astrophysics Data System (ADS)

    Han, Xueli; Pan, Ernie; Sangghaleh, Ali

    2013-08-01

    The coupled elastic, electric and magnetic fields produced by an arbitrarily shaped three-dimensional dislocation loop in general anisotropic magneto-electro-elastic (MEE) bimaterials are derived. First, we develop line-integral expressions for the fields induced by a general dislocation loop. Then, we obtain analytical solutions for the fields, including the extended Peach-Koehler force, due to some useful dislocation segments such as straight line and elliptic arc. The present solutions contain the piezoelectric, piezomagnetic and purely elastic solutions as special cases. As numerical examples, the fields induced by a square and an elliptic dislocation loop in MEE bimaterials are studied. Our numerical results show the coupling effects among different fields, along with various interesting features associated with the dislocation and interface.

  17. Anisotropic stark effect and electric-field noise suppression for phosphorus donor qubits in silicon.

    PubMed

    Sigillito, A J; Tyryshkin, A M; Lyon, S A

    2015-05-29

    We report the use of novel, capacitively terminated coplanar waveguide resonators to measure the quadratic Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift depending on electric and magnetic field orientations relative to the Si crystal. By measuring the linear Stark effect, we estimate the effective electric field due to strain in our samples. We show that in the presence of this strain, electric-field sources of decoherence can be non-negligible. Using our measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. We discuss the limitations of these noise-suppression points due to random distributions of strain and propose a method for overcoming them.

  18. 11B and 27Al NMR spin-lattice relaxation and Knight shift of Mg1-xAlxB2: Evidence for an anisotropic Fermi surface

    NASA Astrophysics Data System (ADS)

    Papavassiliou, G.; Pissas, M.; Karayanni, M.; Fardis, M.; Koutandos, S.; Prassides, K.

    2002-10-01

    We report a detailed study of the 11B and 27Al NMR spin-lattice relaxation rates (1/T1) and the 27Al Knight shift (K) in Mg1-xAlxB2, 0<=x<=1. The evolution of (1/T1T) and K with x is in excellent agreement with the prediction of ab initio calculations of a highly anisotropic Fermi surface, consisting mainly of hole-type two-dimensional (2D) cylindrical sheets from bonding 2px,y boron orbitals. The density of states at the Fermi level also decreases sharply on Al doping and the 2D sheets collapse at x~0.55, where the superconducting phase disappears.

  19. Studies on Highly Anisotropic Conductors and Superconductors in High Magnetic Fields and Low Temperatures.

    NASA Astrophysics Data System (ADS)

    Yu, Rangchen

    1990-08-01

    Transport properties in high magnetic field and low temperature have been studied in a number of highly anisotropic organic superconductors and high Tc cuprate superconductors. The magnetothermopower of (TMTSF)_2 ClO_4 has been systematically studied in high field and low temperature through the entire range of magnetic field induced spin-density-wave (FISDW) transitions. Our data provide strong evidence of the collective nature of the extremely stable state between 8 to 25 Tesla resembling the 1/3 fractional quantized Hall effect. A new phase transition into a semiconducting state at 2.6K in field of 30 Tesla has been identified. The FISDW phase diagram in the field range of 15-18 Tesla has been studied in detail to sort out the relationship between the "fast oscillations (FO)" and the reentrant FISDW. Our experiment show that there are no oscillations in the phase boundary correlated to the FO, in contrast to a theory proposed by Lebed and Bak which claimed that the reentrance of FISDW and FO are due to oscillations in the FISDW phase boundary resulting from the competition of two SDW modes originated from the anion ordering gap. Transport properties of the high T_ c superconductors are systematically studied. The temperature and carrier concentration dependence of the thermopower suggested that the cuprates were strongly correlated systems. The thermopower of La_{1.85 }Sr_{0.15}CuO _4 in strong magnetic field was studied to test the correlated hopping model. We find that thermopower of La_{1.85}Sr_{0.15 }CuO_4 is independent of magnetic field in field up to 30 Tesla and temperature down to 40K. Our results question the validity of this model, and lends support to the theories of carriers without spin, or of strong spin exchange interactions. The dimensionality of superconductivity of YBa _2Cu_3O _7 and Bi_{2.2} Sr_{1.9}CaCu _2O_{8+x} was studied by the orientational dependence of the critical field. While the critical field of YBa_2 Cu_3O_7 can be described by

  20. Anisotropic high-field terahertz response of free-standing carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Lee, Byounghwak; Mousavian, Ali; Paul, Michael J.; Thompson, Zachary J.; Stickel, Andrew D.; McCuen, Dalton R.; Jang, Eui Yun; Kim, Yong Hyup; Kyoung, Jisoo; Kim, Dai-Sik; Lee, Yun-Shik

    2016-06-01

    We demonstrate that unidirectionally aligned, free-standing multi-walled carbon nanotubes (CNTs) exhibit highly anisotropic linear and nonlinear terahertz (THz) responses. For the polarization parallel to the CNT axis, strong THz pulses induce nonlinear absorption in the quasi-one-dimensional conducting media, while no nonlinear effect is observed in the perpendicular polarization configuration. Time-resolved measurements of transmitted THz pulses and a theoretical analysis of the data reveal that intense THz fields enhance permittivity in carbon nanotubes by generating charge carriers.

  1. Adaptive Phase-Field Modeling of Anisotropic Wetting with Line Tension at the Triple Junction.

    PubMed

    Yeh, S Y; Lan, C W

    2015-09-01

    Line tension could affect the contact angle at triple junction, especially in micro- to nanoscale wetting. We have developed an adaptive phase-field model to consider the line tension quantitatively. This model is coupled to the smoothed boundary method for treating the contact line with the solid phase, while the volume constraint is imposed. Our calculated contact angles are in good agreement with the modified Young's equation. Further examples are illustrated for the anisotropic wetting on hydrophilic/hydrophobic stripes and rectangular grooves.

  2. Wavelet variance analysis for random fields on a regular lattice.

    PubMed

    Mondal, Debashis; Percival, Donald B

    2012-02-01

    There has been considerable recent interest in using wavelets to analyze time series and images that can be regarded as realizations of certain 1-D and 2-D stochastic processes on a regular lattice. Wavelets give rise to the concept of the wavelet variance (or wavelet power spectrum), which decomposes the variance of a stochastic process on a scale-by-scale basis. The wavelet variance has been applied to a variety of time series, and a statistical theory for estimators of this variance has been developed. While there have been applications of the wavelet variance in the 2-D context (in particular, in works by Unser in 1995 on wavelet-based texture analysis for images and by Lark and Webster in 2004 on analysis of soil properties), a formal statistical theory for such analysis has been lacking. In this paper, we develop the statistical theory by generalizing and extending some of the approaches developed for time series, thus leading to a large-sample theory for estimators of 2-D wavelet variances. We apply our theory to simulated data from Gaussian random fields with exponential covariances and from fractional Brownian surfaces. We demonstrate that the wavelet variance is potentially useful for texture discrimination. We also use our methodology to analyze images of four types of clouds observed over the southeast Pacific Ocean.

  3. Measurements of the anisotropic irreversibility field in the electron-doped high-Tc superconductor Pr2-xCexCuO4-y

    NASA Astrophysics Data System (ADS)

    Wu, Guoqing; Clark, W. G.; Brown, S. E.; Greene, R. L.; Balci, H.; Reyes, A. P.; Kuhns, P.; Moulton, W. G.

    2008-03-01

    We report measurements of the irreversibility field (Hirf) in single crystals of the electron-doped high-Tc superconductor (HTSC) Pr2-xCexCuO4-y (x = 0.15 and 0.17) with an applied magnetic field (B0) up to 28 T, using the method of the shift in a nuclear magnetic resonance (NMR) probe circuit resonance frequency (f) caused by the susceptibility of the sample. It is observed that Hirf is highly anisotropic, and that as the temperature T -> 0 the upper critical field [Hc2, c(T -> 0)] at B0 c is far less than the Pauli limit and very different from that at B0 c. A phase diagram that involves the vortex solid and/or vortex liquid states depending on the alignment of B0 relative to the lattice c-axis is proposed, and the obtained anisotropic Hc2 character along with the evaluated zero T coherence length [ξab(c)(T -> 0)] and penetration depth [λab(c)( T -> 0)] at B0 ab(c) is compared with that of hole-doped HTSCs. This work is supported at UCLA by NSF Grants DMR-0334869 (WGC) and 0520552 (SEB), at U. Maryland by 0352735 (RLG), and NHMFL by 0084173 and the State of Florida.

  4. Phase field approach with anisotropic interface energy and interface stresses: Large strain formulation

    NASA Astrophysics Data System (ADS)

    Levitas, Valery I.; Warren, James A.

    2016-06-01

    A thermodynamically consistent, large-strain, multi-phase field approach (with consequent interface stresses) is generalized for the case with anisotropic interface (gradient) energy (e.g. an energy density that depends both on the magnitude and direction of the gradients in the phase fields). Such a generalization, if done in the "usual" manner, yields a theory that can be shown to be manifestly unphysical. These theories consider the gradient energy as anisotropic in the deformed configuration, and, due to this supposition, several fundamental contradictions arise. First, the Cauchy stress tensor is non-symmetric and, consequently, violates the moment of momentum principle, in essence the Herring (thermodynamic) torque is imparting an unphysical angular momentum to the system. In addition, this non-symmetric stress implies a violation of the principle of material objectivity. These problems in the formulation can be resolved by insisting that the gradient energy is an isotropic function of the gradient of the order parameters in the deformed configuration, but depends on the direction of the gradient of the order parameters (is anisotropic) in the undeformed configuration. We find that for a propagating nonequilibrium interface, the structural part of the interfacial Cauchy stress is symmetric and reduces to a biaxial tension with the magnitude equal to the temperature- and orientation-dependent interface energy. Ginzburg-Landau equations for the evolution of the order parameters and temperature evolution equation, as well as the boundary conditions for the order parameters are derived. Small strain simplifications are presented. Remarkably, this anisotropy yields a first order correction in the Ginzburg-Landau equation for small strains, which has been neglected in prior works. The next strain-related term is third order. For concreteness, specific orientation dependencies of the gradient energy coefficients are examined, using published molecular dynamics

  5. Quantum magnetism of spinor bosons in optical lattices with synthetic non-Abelian gauge fields

    NASA Astrophysics Data System (ADS)

    Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming

    2015-10-01

    We study quantum magnetism of interacting spinor bosons at integer fillings hopping in a square lattice in the presence of non-Abelian gauge fields. In the strong-coupling limit, this leads to the rotated ferromagnetic Heisenberg model, which is a new class of quantum spin model. We introduce Wilson loops to characterize frustrations and gauge equivalent classes. For a special equivalent class, we identify a spin-orbital entangled commensurate ground state. It supports not only commensurate magnons, but also a gapped elementary excitation: incommensurate magnons with two gap minima continuously tuned by the spin-orbit coupling (SOC) strength. At low temperatures, these magnons lead to dramatic effects in many physical quantities such as density of states, specific heat, magnetization, uniform susceptibility, staggered susceptibility, and various spin-correlation functions. The commensurate magnons lead to a pinned central peak in the angle-resolved light or atom Bragg spectroscopy. However, the incommensurate magnons split it into two located at their two gap minima. At high temperatures, the transverse spin-structure factors depend on the SOC strength explicitly. The whole set of Wilson loops can be mapped out by measuring the specific heat at the corresponding orders in the high-temperature expansion. We argue that one gauge may be realized in current experiments and other gauges may also be realized in future experiments. The results achieved along the exact solvable line sets up the stage to investigate dramatic effects when tuning away from it by various means. We sketch the crucial roles to be played by these magnons at other equivalent classes, with spin anisotropic interactions and in the presence of finite magnetic fields. Various experimental detections of these phenomena are discussed.

  6. Low beta equilibrium and stability for anisotropic pressure closed field line plasma confinement systems

    SciTech Connect

    Pastukhov, V.P.; Ilgisonis, V.I.; Subbotin, A.A.

    1994-05-01

    General formalism is developed to analyze the equilibrium and stability of low beta anisotropic pressure plasmas confined in closed field line magnetic systems. The formalism allows one to consider rather general magnetic systems with nonuniform axis curvature and longitudinal profiles of toroidal and multipole poloidal field. It also allows having a strong pressure anisotropy corresponding to enhanced plasma pressure in mirror cells of the system. As an example of such a system the authors consider the recently proposed linked mirror neutron source (LMNS). Application of the above formalism to the LMNS analysis confirms most of the preliminary results, however, they obtain a considerable reduction of mirror cell axis curvature and an appreciable ellipticity of plasma cross-section in the mirror cell midplane. They have also optimized the longitudinal pressure and magnetic field distribution.

  7. Locating earthquakes in west Texas oil fields using 3-D anisotropic velocity models

    SciTech Connect

    Hua, Fa; Doser, D.; Baker, M. . Dept. of Geological Sciences)

    1993-02-01

    Earthquakes within the War-Wink gas field, Ward County, Texas, that have been located with a 1-D velocity model occur near the edges and top of a naturally occurring overpressured zone. Because the War-Wink field is a structurally controlled anticline with significant velocity anisotropy associated with the overpressured zone and finely layered evaporites, the authors have attempted to re-locate earthquakes using a 3-D anisotropic velocity model. Preliminary results with this model give the unsatisfactory result that many earthquakes previously located at the top of the overpressured zone (3-3.5 km) moved into the evaporites (1-1.5 km) above the field. They believe that this result could be caused by: (1) aliasing the velocity model; or (2) problems in determining the correct location minima when several minima exist. They are currently attempting to determine which of these causes is more likely for the unsatisfactory result observed.

  8. Silicon Needles Fabricated by Highly Selective Anisotropic Dry Etching and Their Field Emission Current Characteristics

    NASA Astrophysics Data System (ADS)

    Kanechika, Masakazu; Mitsushima, Yasuichi

    2000-12-01

    A new process to fabricate a silicon needle, whose tip radius is about 5 nm and aspect ratio is about 7, was developed. The silicon needles were fabricated by highly selective anisotropic dry etching. The etching mask was oxygen precipitation, which was formed by nitrogen ion implantation and the subsequent oxidation. The process is simple enough to be integrated with complementary metal-oxide-semiconductor (CMOS) circuits. The density of the silicon needle can be controlled by adjusting the dose for nitrogen ion implantation. The position of the silicon needle can be controlled by adjusting the position for nitrogen ion implantation, because silicon needles are formed only in the nitrogen ion implantation area. Furthermore, using these silicon needles as micro emitters, a field emission diode was fabricated. The Fowler-Nordheim plot shows that the field around the tip of the silicon needles was highly enhanced.

  9. Green's function of a free massive scalar field on the lattice

    SciTech Connect

    Borasoy, B.; Krebs, H.

    2005-09-01

    We propose a method to calculate the Green's function of a free massive scalar field on the lattice numerically to very high precision. For masses m<2 (in lattice units) the massive Green's function can be expressed recursively in terms of the massless Green's function and just two additional mass-independent constants.

  10. Variational methods in supersymmetric lattice field theory: The vacuum sector

    SciTech Connect

    Duncan, A.; Meyer-Ortmanns, H.; Roskies, R.

    1987-12-15

    The application of variational methods to the computation of the spectrum in supersymmetric lattice theories is considered, with special attention to O(N) supersymmetric sigma models. Substantial cancellations are found between bosonic and fermionic contributions even in approximate Ansa$uml: tze for the vacuum wave function. The nonlinear limit of the linear sigma model is studied in detail, and it is shown how to construct an appropriate non-Gaussian vacuum wave function for the nonlinear model. The vacuum energy is shown to be of order unity in lattice units in the latter case, after infinite cancellations.

  11. Tensor spherical harmonics theories on the exact nature of the elastic fields of a spherically anisotropic multi-inhomogeneous inclusion

    NASA Astrophysics Data System (ADS)

    Shodja, H. M.; Khorshidi, A.

    2013-04-01

    Eshelby's theories on the nature of the disturbance strains due to polynomial eigenstrains inside an isotropic ellipsoidal inclusion, and the form of homogenizing eigenstrains corresponding to remote polynomial loadings in the equivalent inclusion method (EIM) are not valid for spherically anisotropic inclusions and inhomogeneities. Materials with spherically anisotropic behavior are frequently encountered in nature, for example, some graphite particles or polyethylene spherulites. Moreover, multi-inclusions/inhomogeneities/inhomogeneous inclusions have abundant engineering and scientific applications and their exact theoretical treatment would be of great value. The present work is devoted to the development of a mathematical framework for the exact treatment of a spherical multi-inhomogeneous inclusion with spherically anisotropic constituents embedded in an unbounded isotropic matrix. The formulations herein are based on tensor spherical harmonics having orthogonality and completeness properties. For polynomial eigenstrain field and remote applied loading, several theorems on the exact closed-form expressions of the elastic fields associated with the matrix and all the phases of the inhomogeneous inclusion are stated and proved. Several classes of impotent eigenstrain fields associated to a generally anisotropic inclusion as well as isotropic and spherically anisotropic multi-inclusions are also introduced. The presented theories are useful for obtaining highly accurate solutions of desired accuracy when the constituent phases of the multi-inhomogeneous inclusion are made of functionally graded materials (FGMs).

  12. Ultrasonic field profile evaluation in acoustically inhomogeneous anisotropic materials using 2D ray tracing model: Numerical and experimental comparison.

    PubMed

    Kolkoori, S R; Rahman, M-U; Chinta, P K; Ktreutzbruck, M; Rethmeier, M; Prager, J

    2013-02-01

    Ultrasound propagation in inhomogeneous anisotropic materials is difficult to examine because of the directional dependency of elastic properties. Simulation tools play an important role in developing advanced reliable ultrasonic non destructive testing techniques for the inspection of anisotropic materials particularly austenitic cladded materials, austenitic welds and dissimilar welds. In this contribution we present an adapted 2D ray tracing model for evaluating ultrasonic wave fields quantitatively in inhomogeneous anisotropic materials. Inhomogeneity in the anisotropic material is represented by discretizing into several homogeneous layers. According to ray tracing model, ultrasonic ray paths are traced during its energy propagation through various discretized layers of the material and at each interface the problem of reflection and transmission is solved. The presented algorithm evaluates the transducer excited ultrasonic fields accurately by taking into account the directivity of the transducer, divergence of the ray bundle, density of rays and phase relations as well as transmission coefficients. The ray tracing model is able to calculate the ultrasonic wave fields generated by a point source as well as a finite dimension transducer. The ray tracing model results are validated quantitatively with the results obtained from 2D Elastodynamic Finite Integration Technique (EFIT) on several configurations generally occurring in the ultrasonic non destructive testing of anisotropic materials. Finally, the quantitative comparison of ray tracing model results with experiments on 32mm thick austenitic weld material and 62mm thick austenitic cladded material is discussed.

  13. Theory and simulation of anisotropic pair correlations in ferrofluids in magnetic fields

    NASA Astrophysics Data System (ADS)

    Elfimova, Ekaterina A.; Ivanov, Alexey O.; Camp, Philip J.

    2012-05-01

    Anisotropic pair correlations in ferrofluids exposed to magnetic fields are studied using a combination of statistical-mechanical theory and computer simulations. A simple dipolar hard-sphere model of the magnetic colloidal particles is studied in detail. A virial-expansion theory is constructed for the pair distribution function (PDF) which depends not only on the length of the pair separation vector, but also on its orientation with respect to the field. A detailed comparison is made between the theoretical predictions and accurate simulation data, and it is found that the theory works well for realistic values of the dipolar coupling constant (λ = 1), volume fraction (φ ⩽ 0.1), and magnetic field strength. The structure factor is computed for wavevectors either parallel or perpendicular to the field. The comparison between theory and simulation is generally very good with realistic ferrofluid parameters. For both the PDF and the structure factor, there are some deviations between theory and simulation at uncommonly high dipolar coupling constants, and with very strong magnetic fields. In particular, the theory is less successful at predicting the behavior of the structure factors at very low wavevectors, and perpendicular Gaussian density fluctuations arising from strongly correlated pairs of magnetic particles. Overall, though, the theory provides reliable predictions for the nature and degree of pair correlations in ferrofluids in magnetic fields, and hence should be of use in the design of functional magnetic materials.

  14. Magnetic-Field-Assisted Assembly of Anisotropic Superstructures by Iron Oxide Nanoparticles and Their Enhanced Magnetism.

    PubMed

    Jiang, Chengpeng; Leung, Chi Wah; Pong, Philip W T

    2016-12-01

    Magnetic nanoparticle superstructures with controlled magnetic alignment and desired structural anisotropy hold promise for applications in data storage and energy storage. Assembly of monodisperse magnetic nanoparticles under a magnetic field could lead to highly ordered superstructures, providing distinctive magnetic properties. In this work, a low-cost fabrication technique was demonstrated to assemble sub-20-nm iron oxide nanoparticles into crystalline superstructures under an in-plane magnetic field. The gradient of the applied magnetic field contributes to the anisotropic formation of micron-sized superstructures. The magnitude of the applied magnetic field promotes the alignment of magnetic moments of the nanoparticles. The strong dipole-dipole interactions between the neighboring nanoparticles lead to a close-packed pattern as an energetically favorable configuration. Rod-shaped and spindle-shaped superstructures with uniform size and controlled spacing were obtained using spherical and polyhedral nanoparticles, respectively. The arrangement and alignment of the superstructures can be tuned by changing the experimental conditions. The two types of superstructures both show enhancement of coercivity and saturation magnetization along the applied field direction, which is presumably associated with the magnetic anisotropy and magnetic dipole interactions of the constituent nanoparticles and the increased shape anisotropy of the superstructures. Our results show that the magnetic-field-assisted assembly technique could be used for fabricating nanomaterial-based structures with controlled geometric dimensions and enhanced magnetic properties for magnetic and energy storage applications.

  15. Theory and simulation of anisotropic pair correlations in ferrofluids in magnetic fields.

    PubMed

    Elfimova, Ekaterina A; Ivanov, Alexey O; Camp, Philip J

    2012-05-21

    Anisotropic pair correlations in ferrofluids exposed to magnetic fields are studied using a combination of statistical-mechanical theory and computer simulations. A simple dipolar hard-sphere model of the magnetic colloidal particles is studied in detail. A virial-expansion theory is constructed for the pair distribution function (PDF) which depends not only on the length of the pair separation vector, but also on its orientation with respect to the field. A detailed comparison is made between the theoretical predictions and accurate simulation data, and it is found that the theory works well for realistic values of the dipolar coupling constant (λ = 1), volume fraction (φ ≤ 0.1), and magnetic field strength. The structure factor is computed for wavevectors either parallel or perpendicular to the field. The comparison between theory and simulation is generally very good with realistic ferrofluid parameters. For both the PDF and the structure factor, there are some deviations between theory and simulation at uncommonly high dipolar coupling constants, and with very strong magnetic fields. In particular, the theory is less successful at predicting the behavior of the structure factors at very low wavevectors, and perpendicular Gaussian density fluctuations arising from strongly correlated pairs of magnetic particles. Overall, though, the theory provides reliable predictions for the nature and degree of pair correlations in ferrofluids in magnetic fields, and hence should be of use in the design of functional magnetic materials. PMID:22612098

  16. Charmonium excited state spectrum in lattice QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards

    2008-02-01

    Working with a large basis of covariant derivative-based meson interpolating fields we demonstrate the feasibility of reliably extracting multiple excited states using a variational method. The study is performed on quenched anisotropic lattices with clover quarks at the charm mass. We demonstrate how a knowledge of the continuum limit of a lattice interpolating field can give additional spin-assignment information, even at a single lattice spacing, via the overlap factors of interpolating field and state. Excited state masses are systematically high with respect to quark potential model predictions and, where they exist, experimental states. We conclude that this is most likely a result of the quenched approximation.

  17. A GENERALIZED DIFFUSION TENSOR FOR FULLY ANISOTROPIC DIFFUSION OF ENERGETIC PARTICLES IN THE HELIOSPHERIC MAGNETIC FIELD

    SciTech Connect

    Effenberger, F.; Fichtner, H.; Scherer, K.; Barra, S.; Kleimann, J.; Strauss, R. D.

    2012-05-10

    The spatial diffusion of cosmic rays in turbulent magnetic fields can, in the most general case, be fully anisotropic, i.e., one has to distinguish three diffusion axes in a local, field-aligned frame. We reexamine the transformation for the diffusion tensor from this local to a global frame, in which the Parker transport equation for energetic particles is usually formulated and solved. Particularly, we generalize the transformation formulae to allow for an explicit choice of two principal local perpendicular diffusion axes. This generalization includes the 'traditional' diffusion tensor in the special case of isotropic perpendicular diffusion. For the local frame, we describe the motivation for the choice of the Frenet-Serret trihedron, which is related to the intrinsic magnetic field geometry. We directly compare the old and the new tensor elements for two heliospheric magnetic field configurations, namely the hybrid Fisk and Parker fields. Subsequently, we examine the significance of the different formulations for the diffusion tensor in a standard three-dimensional model for the modulation of galactic protons. For this, we utilize a numerical code to evaluate a system of stochastic differential equations equivalent to the Parker transport equation and present the resulting modulated spectra. The computed differential fluxes based on the new tensor formulation deviate from those obtained with the 'traditional' one (only valid for isotropic perpendicular diffusion) by up to 60% for energies below a few hundred MeV depending on heliocentric distance.

  18. Stable anisotropic plasma confinement in magnetic configurations with convex-concave field lines

    NASA Astrophysics Data System (ADS)

    Tsventoukh, M. M.

    2014-02-01

    It is shown that a combination of the convex and the concave part of a field line provides a strong stabilizing action against convective (flute-interchange) plasma instability (Tsventoukh 2011 Nucl. Fusion 51 112002). This results in internal peaking of the stable plasma pressure profile that is calculated from the collisionless kinetic stability criterion for any magnetic confinement system with combination of mirrors and cusps. Connection of the convex and concave field line parts results in a reduction of the space charge that drives the unstable E × B motion, as there is an opposite direction of the particle drift in a non-uniform field at convex and concave field lines. The pressure peaking arises at the minimum of the second adiabatic invariant J that takes place at the ‘middle’ of a tandem mirror-cusp transverse cross-section. The position of the minimum in J varies with the particle pitch angle that results in a shift of the peaking position depending on plasma anisotropy. This allows one to improve a stable peaked pressure profile at a convex-concave field by changing the plasma anisotropy over the trap cross-section. Examples of such anisotropic distribution functions are found that give an additional substantial enhancement in the maximal central pressure. Furthermore, the shape of new calculated stable profiles has a wide central plasma layer instead of a narrow peak.

  19. Application of Anisotropic Conductive Film to Fabrication of Molybdenum Field Emitter Arrays Using Transfer Mold Technique

    NASA Astrophysics Data System (ADS)

    Cho, Eou Sik; Ahn, Min Hyung; Kwon, Sang Jik

    2008-08-01

    In the fabrication of molybdenum field emitter arrays (Mo FEA) by the transfer mold technique, anisotropic conductive film (ACF) was applied to the bond between the inverted mold structure and the transferred glass substrate. Without any electrical treatment of electrostatic bonding, the inverted mold was successfully bonded to an indium tin oxide (ITO) glass substrate under optimized thermal and pressure conditions. No additional conductive layers were used in the bonding process, and the bonded ACF was not chemically affected in the wet-etch process of the silicon inverted mold structure. The fabricated Mo FEA was structurally and electrically investigated and an anode current of 10 nA per emitter was obtained at a gate bias of 94 V. The results demonstrate the possibility of selective conduction in the fabrication of transfer mold FEA using ACF bonding.

  20. Effective field theory as the bridge between lattice QCD and nuclear physics

    SciTech Connect

    Kaplan, David B.

    2007-02-27

    A confluence of theoretical and technological developments are beginning to make possible contributions to nuclear physics from lattice QCD. Effective field theory plays a critical role in these advances. I give several examples.

  1. 31st International Symposium on Lattice Field Theory

    NASA Astrophysics Data System (ADS)

    The annual lattice symposium brings together a global community of researchers from theoretical particle physics and beyond, who employ numerical and computational methods to study the properties of strongly interacting physical systems, above all Quantum Chromodynamics (QCD), the theory describing the interactions of quarks and gluons. Topics include studies of the spectrum and structure of hadrons, lattice studies of matter under extreme conditions, hadronic contributions to weak decay amplitudes, as well as recent developments in simulation algorithms and computer hardware. The 2013 conference in Mainz was attended by over 500 participants from all over the globe, making it the biggest in this series so far. This proceedings volume is dedicated to the memory of Nobel Laureate Kenneth G. Wilson (June 8, 1936 - June 15, 2013).

  2. Magnetic-field-driven crack formation in an evaporated anisotropic colloidal assembly

    NASA Astrophysics Data System (ADS)

    Lama, Hisay; Dugyala, Venkateshwar Rao; Basavaraj, Madivala G.; Satapathy, Dillip K.

    2016-07-01

    We report the effect of applied magnetic field on the morphology of cracks formed after evaporation of a colloidal suspension consisting of shape-anisotropic ellipsoidal particles on a glass substrate. The evaporation experiments are performed in sessile drop configuration, which usually leads to accumulation of particles at the drop boundaries, commonly known as the "coffee-ring effect." The coffee-ring-like deposits that accompany cracks are formed in the presence as well as in the absence of magnetic field. However, the crack patterns formed in both cases are found to differ markedly. The direction of cracks in the presence of the magnetic field is found to be governed by the orientation of particles and not solely by the magnetic field direction. Our experimental results show that at the vicinity of cracks the particles are ordered and oriented with their long-axis parallel to crack direction. In addition, we observe that the crack spacing in general increases with the height of the particulate film.

  3. Explaining anisotropic macroseismic fields in terms of fault zone attenuation-A simple model

    NASA Astrophysics Data System (ADS)

    Sovic, Ivica; Sariri, Kristina

    2016-06-01

    In this work, we present a simple model of anisotropic macroseismic field based on the assumption that local and regional geological structures change the shape of the isotropic macroseismic field (as expected in 1D media). Local geological structures, like water saturated stratified media, may increase intensity level by multiple reflections, constructive interference and resonant effects, but inelastic attenuation, significantly stronger in water-saturated soils, as well as destructive interference, may decrease intensities. On the other hand, large geological structures like seismotectonically active fault zones decrease intensities due to energy redistribution and inelastic attenuation. This model has been developed for the Karst region of the Outer Dinarides where site effects may be neglected because of specific building construction. Neglecting of site effects simplifies the model, so we just need a map of seismically active faults acting as modulator of macroseismic field. In order to demonstrate how the model works, we have calculated the standard error for 10 earthquakes and the macroseismic fields for three of them with epicenters in the Outer Dinarides and compared the model to empiric isoseismals.

  4. Magnetic-field-driven crack formation in an evaporated anisotropic colloidal assembly.

    PubMed

    Lama, Hisay; Dugyala, Venkateshwar Rao; Basavaraj, Madivala G; Satapathy, Dillip K

    2016-07-01

    We report the effect of applied magnetic field on the morphology of cracks formed after evaporation of a colloidal suspension consisting of shape-anisotropic ellipsoidal particles on a glass substrate. The evaporation experiments are performed in sessile drop configuration, which usually leads to accumulation of particles at the drop boundaries, commonly known as the "coffee-ring effect." The coffee-ring-like deposits that accompany cracks are formed in the presence as well as in the absence of magnetic field. However, the crack patterns formed in both cases are found to differ markedly. The direction of cracks in the presence of the magnetic field is found to be governed by the orientation of particles and not solely by the magnetic field direction. Our experimental results show that at the vicinity of cracks the particles are ordered and oriented with their long-axis parallel to crack direction. In addition, we observe that the crack spacing in general increases with the height of the particulate film. PMID:27575190

  5. Ab initio nuclear structure from lattice effective field theory

    SciTech Connect

    Lee, Dean

    2014-11-11

    This proceedings article reviews recent results by the Nuclear Lattice EFT Collaboration on an excited state of the {sup 12}C nucleus known as the Hoyle state. The Hoyle state plays a key role in the production of carbon via the triple-alpha reaction in red giant stars. We discuss the structure of low-lying states of {sup 12}C as well as the dependence of the triple-alpha reaction on the masses of the light quarks.

  6. Dipole-field sums and Lorentz factors for orthorhombic lattices, and implications for polarizable molecules

    NASA Technical Reports Server (NTRS)

    Purvis, C. K.; Taylor, P. L.

    1982-01-01

    A method for computing the Lorentz tensor components in single crystals via rapidly convergent sums of Bessels functions is developed using the relationship between dipole-field sums and the tensor components. The Lorentz factors for simple, body-centered, and base-centered orthorhombic lattices are computed using this method, and the derivative Lorentz factors for simple orthorhombic lattices are also determined. Both the Lorentz factors and their derivatives are shown to be very sensitive to a lattice structure. The equivalent of the Clausius-Mossotti relation for general orthorhombic lattices is derived using the Lorentz-factor formalism, and the permanent molecular dipole moment is related to crystal polarization for the case of a ferroelectric of polarizable point dipoles. It is concluded that the polarization enhancement due to self-polarization familiar from classical theory may actually be a reduction in consequences of negative Lorentz factors in one or two lattice directions for noncubic crystals.

  7. Realization of uniform synthetic magnetic fields by periodically shaking an optical square lattice

    NASA Astrophysics Data System (ADS)

    Creffield, C. E.; Pieplow, G.; Sols, F.; Goldman, N.

    2016-09-01

    Shaking a lattice system, by modulating the location of its sites periodically in time, is a powerful method to create effective magnetic fields in engineered quantum systems, such as cold gases trapped in optical lattices. However, such schemes are typically associated with space-dependent effective masses (tunneling amplitudes) and non-uniform flux patterns. In this work we investigate this phenomenon theoretically, by computing the effective Hamiltonians and quasienergy spectra associated with several kinds of lattice-shaking protocols. A detailed comparison with a method based on moving lattices, which are added on top of a main static optical lattice, is provided. This study allows the identification of novel shaking schemes, which simultaneously provide uniform effective mass and magnetic flux, with direct implications for cold-atom experiments and photonics.

  8. SU(3) Landau gauge gluon and ghost propagators using the logarithmic lattice gluon field definition

    SciTech Connect

    Ilgenfritz, Ernst-Michael; Menz, Christoph; Mueller-Preussker, Michael; Schiller, Arwed; Sternbeck, Andre

    2011-03-01

    We study the Landau gauge gluon and ghost propagators of SU(3) gauge theory, employing the logarithmic definition for the lattice gluon fields and implementing the corresponding form of the Faddeev-Popov matrix. This is necessary in order to consistently compare lattice data for the bare propagators with that of higher-loop numerical stochastic perturbation theory. In this paper we provide such a comparison, and introduce what is needed for an efficient lattice study. When comparing our data for the logarithmic definition to that of the standard lattice Landau gauge we clearly see the propagators to be multiplicatively related. The data of the associated ghost-gluon coupling matches up almost completely. For the explored lattice spacings and sizes discretization artifacts, finite size, and Gribov-copy effects are small. At weak coupling and large momentum, the bare propagators and the ghost-gluon coupling are seen to be approached by those of higher-order numerical stochastic perturbation theory.

  9. Hamiltonian Effective Field Theory Study of the N*(1535 ) Resonance in Lattice QCD

    NASA Astrophysics Data System (ADS)

    Liu, Zhan-Wei; Kamleh, Waseem; Leinweber, Derek B.; Stokes, Finn M.; Thomas, Anthony W.; Wu, Jia-Jun

    2016-02-01

    Drawing on experimental data for baryon resonances, Hamiltonian effective field theory (HEFT) is used to predict the positions of the finite-volume energy levels to be observed in lattice QCD simulations of the lowest-lying JP=1 /2- nucleon excitation. In the initial analysis, the phenomenological parameters of the Hamiltonian model are constrained by experiment and the finite-volume eigenstate energies are a prediction of the model. The agreement between HEFT predictions and lattice QCD results obtained on volumes with spatial lengths of 2 and 3 fm is excellent. These lattice results also admit a more conventional analysis where the low-energy coefficients are constrained by lattice QCD results, enabling a determination of resonance properties from lattice QCD itself. Finally, the role and importance of various components of the Hamiltonian model are examined.

  10. Automatic NMO Correction and Full Common Depth Point NMO Velocity Field Estimation in Anisotropic Media

    NASA Astrophysics Data System (ADS)

    Sedek, Mohamed; Gross, Lutz; Tyson, Stephen

    2016-07-01

    We present a new computational method of automatic normal moveout (NMO) correction that not only accurately flattens and corrects the far offset data, but simultaneously provides NMO velocity (v_nmo ) for each individual seismic trace. The method is based on a predefined number of NMO velocity sweeps using linear vertical interpolation of different NMO velocities at each seismic trace. At each sweep, we measure the semblance between the zero offset trace (pilot trace) and the next seismic trace using a trace-by-trace rather than sample-by-sample based semblance measure; then after all the sweeps are done, the one with the maximum semblance value is chosen, which is assumed to be the most suitable NMO velocity trace that accurately flattens seismic reflection events. Other traces follow the same process, and a final velocity field is then extracted. Isotropic, anisotropic and lateral heterogenous synthetic geological models were built to test the method. A range of synthetic background noise, ranging from 10 to 30 %, was applied to the models. In addition, the method was tested on Hess's VTI (vertical transverse isotropy) model. Furthermore, we tested our method on a real pre-stack seismic CDP gathered from a gas field in Alaska. The results from the presented examples show an excellent NMO correction and extracted a reasonably accurate NMO velocity field.

  11. Quantum Field Theories on the Lattice : Concepts behind their Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Bietenholz, Wolfgang

    2011-09-01

    We review the basic ideas behind numerical simulations of quantum field theory, which lead to non-perturbative results in particle physics. We first sketch the functional integral formulation of quantum mechanics, its transition to Euclidean time and the link to statistical mechanics. Then we proceed to quantum field theory in the lattice regularization, and its applications to scalar fields, gauge fields and fermions. In particular we address the treatment of chiral symmetry. At last we describe the formulation of lattice QCD and comment on simulations and results.

  12. Transient 3D elastodynamic field in an embedded multilayered anisotropic plate.

    PubMed

    Mora, Pierric; Ducasse, Eric; Deschamps, Marc

    2016-07-01

    The aim of this paper is to study the ultrasonic response to a transient source that radiates ultrasonic waves in a 3D embedded multilayered anisotropic and dissipative plate. The source can be inside the plate or outside, in a fluid loading the plate for example. In the context of Non-Destructive Testing applied to composite materials, our goal is to create a robust algorithm to calculate ultrasonic field, irrespective of the source and receiver positions. The principle of the method described in this paper is well-established. This method is based on time analysis using the Laplace transform. In the present work, it has been customized for computing ultrasonic source interactions with multilayered dissipative anisotropic plates. The fields are transformed in the 2D Fourier wave-vector domain for the space variables related to the plate surface, and they are expressed in the partial-wave basis. Surprisingly, this method has been very little used in the ultrasonic community, while it is a useful tool which complements the much used technique based on generalized Lamb wave decomposition. By avoiding mode analysis - which can be problematic in some cases - exact numerical calculations (i.e., approximations by truncating infinite series that may be poorly convergent are not needed) can be made in a relatively short time for immersed plates and viscoelastic layers. Even for 3D cases, numerical costs are relatively low. Special attention is given to separate up- and down-going waves, which is a simple matter when using the Laplace transform. Numerical results show the effectiveness of this method. Three examples are presented here to investigate the quality of the model and the robustness of the algorithm: first, a comparison of experiment and simulation for a monolayer carbon-epoxy plate, where the diffracted field is due to a source located on the first free surface of the sample, for both dissipative and non-dissipative cases; second, the basic configuration of an

  13. Robust computation of dipole electromagnetic fields in arbitrarily anisotropic, planar-stratified environments.

    PubMed

    Sainath, Kamalesh; Teixeira, Fernando L; Donderici, Burkay

    2014-01-01

    We develop a general-purpose formulation, based on two-dimensional spectral integrals, for computing electromagnetic fields produced by arbitrarily oriented dipoles in planar-stratified environments, where each layer may exhibit arbitrary and independent anisotropy in both its (complex) permittivity and permeability tensors. Among the salient features of our formulation are (i) computation of eigenmodes (characteristic plane waves) supported in arbitrarily anisotropic media in a numerically robust fashion, (ii) implementation of an hp-adaptive refinement for the numerical integration to evaluate the radiation and weakly evanescent spectra contributions, and (iii) development of an adaptive extension of an integral convergence acceleration technique to compute the strongly evanescent spectrum contribution. While other semianalytic techniques exist to solve this problem, none have full applicability to media exhibiting arbitrary double anisotropies in each layer, where one must account for the whole range of possible phenomena (e.g., mode coupling at interfaces and nonreciprocal mode propagation). Brute-force numerical methods can tackle this problem but only at a much higher computational cost. The present formulation provides an efficient and robust technique for field computation in arbitrary planar-stratified environments. We demonstrate the formulation for a number of problems related to geophysical exploration.

  14. Internal Radiation Field in the Nonlinear Transfer Problem for a One-Dimensional Anisotropic Medium. II

    NASA Astrophysics Data System (ADS)

    Pikichyan, H. V.

    2016-06-01

    It is shown that for the nonlinear boundary value problem of determining the radiation field inside a one-dimensional anisotropic medium illuminated from outside at its boundaries on both sides, the formulas for adding layers in semilinear systems of differential equations for radiative transfer, invariant embedding, and total Ambartsumyan invariance can be used to reduce the equations for the problem to separable equations with initial conditions. The fields travelling to the left and right are thereby found independently of one another. In addition, when one of them has been determined, the other can be found directly using an explicit expression. A general equivalence property of operators with respect to a certain mathematical form, expression, or functional is formulated mathematically. New equations, referred to as kinetic equations of equivalency, are derived from the mutual equivalence of the differential operators of the Boltzmann kinetic equation (the equations of radiative transfer) and the functional equation of the Ambartsumian's complete invariance. Besides separability, these new equations also have the property of linearity. Formulas are also introduced for special problems of single sided illumination of a medium that in this case serve as supplementary information in the initial conditions for formulating Cauchy problems.

  15. Lattices for a high-field 30 TeV hadron collider

    SciTech Connect

    Peggs, S.; Dell, F.; Harrison, M.; Syphers, M.; Tepikian, S.

    1996-12-01

    Long arc cells would lead to major cost savings in a high field high T{sub c} hadron collider, operating in the regime of significant synchrotron radiation. Two such lattices, with half cell lengths of 110 and 260 m, are compared. Both allow flexible tuning, and have large dynamic apertures when dominated by chromatic sextupoles. Lattices with longer cells are much more sensitive to systematic magnet errors, which are expected to dominate.

  16. A field proof-of-concept of tomographic slug tests in an anisotropic littoral aquifer

    NASA Astrophysics Data System (ADS)

    Paradis, Daniel; Gloaguen, Erwan; Lefebvre, René; Giroux, Bernard

    2016-05-01

    Hydraulic tomography is increasingly recognized as a characterization approach that can image pathways or barriers to flow as well as their connectivity. In this study, we assess the performance of a transient analysis of tomographic slug test head data in estimating heterogeneity in horizontal hydraulic conductivity (Kh), hydraulic conductivity anisotropy (the ratio between vertical and horizontal hydraulic conductivity - Kv/Kh) and specific storage (Ss) under actual field conditions. The tomographic experiment was carried out between two wells in a moderately heterogeneous and highly anisotropic silt and sand littoral aquifer. In this field proof-of-concept, the inversion of the two-dimensional (2D) head dataset was computed with a 2D radial flow algorithm that considers Kh, Kv/Kh, Ss and wellbore storage effects. This study demonstrated that a transient analysis of tomographic slug tests is able to capture the key features of the littoral environment of the test: the vertical profiles of Kh and Kv are indeed in agreement with those from other field and laboratory tests, and Ss values exhibit physically plausible profiles. Furthermore, the simulation of independent inter-well hydraulic tests (slug and pumping tests screened over the entire aquifer) using resolved Kh, Kv/Kh and Ss tomograms produce responses very close to field observations. This study demonstrates that the effects of fine scale heterogeneity that induces K-anisotropy at larger scales can be captured through a transient analysis of tomographic slug tests, which are very difficult to quantify otherwise with conventional hydraulic tests, thus allowing a better representation of properties controlling flow and transport in aquifer systems.

  17. Local and nonlocal anisotropic transport in reversed shear magnetic fields: shearless Cantori and nondiffusive transport.

    PubMed

    Blazevski, Daniel; del-Castillo-Negrete, Diego

    2013-06-01

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

  18. A novel quark-field creation operator construction for hadronic physics in lattice QCD

    SciTech Connect

    Michael Peardon, Jozef Dudek, Robert Edwards, Huey-Wen Lin, David Richards, John Bulava, Colin Morningstar, Keisuke Juge

    2009-09-01

    A new quark-field smearing algorithm is defined which enables efficient calculations of a broad range of hadron correlation functions. The technique applies a low-rank operator to define smooth fields, that are to be used in hadron creation operators. The resulting space of smooth fields is small enough that all elements of the reduced quark propagator can be computed exactly at reasonable computational cost. Correlations between arbitrary sources, including multi-hadron operators can be computed {\\em a posteriori} without requiring new lattice Dirac operator inversions. The method is tested on realistic lattice sizes with light dynamical quarks.

  19. Spin-glass attractor on tridimensional hierarchical lattices in the presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Salmon, Octavio R.; Nobre, Fernando D.

    2009-05-01

    A nearest-neighbor-interaction Ising spin glass, in the presence of an external magnetic field, is studied on different hierarchical lattices that approach the cubic lattice. The magnetic field is considered as uniform or random (following either a bimodal or a Gaussian probability distribution). In all cases, a spin-glass attractor is found, in the plane magnetic field versus temperature, associated with a low-temperature phase. The physical consequences of this attractor are discussed, in view of the present scenario of the spin-glass problem.

  20. Influence of magnetic field on the orientation of anisotropic magnetic particles at liquid interfaces.

    PubMed

    Newton, Bethany J; Brakke, Kenneth A; Buzza, D Martin A

    2014-12-21

    We study theoretically the influence of an external magnetic field on the orientation of an ellipsoidal magnetic particle adsorbed at a liquid interface. Using the finite element program Surface Evolver, we calculate the equilibrium meniscus shape around the ellipsoidal particle and its equilibrium tilt angle with respect to the undeformed interface θt when a magnetic field B is applied perpendicular to the interface. We find that as we increase field strength, θt increases and at a critical magnetic field Bc1 and tilt angle θc1, the particle undergoes a discontinuous transition to the 'perpendicular' orientation (θt = 90°). Our results agree qualitatively with the simplified theory of Bresme and Faraudo [F. Bresme and J. Faraudo, J. Phys.: Condens. Matter, 2007, 19, 375110] which assumes that the liquid interface is flat, while they agree quantitatively with recent lattice-Boltzmann simulations of Davies et al. [G. Davies et al., Soft Matter, 2014, 10, 6742] which account for the deformation of the liquid meniscus. We also show for the first time that upon reducing the external magnetic field, at a critical magnetic field Bc2 < Bc1, the particle undergoes a second discontinuous transition from the perpendicular orientation to a finite tilt angle θc2 < θc1. In other words, for micron-sized particles where the thermal energy kBT is negligible compared to the interfacial energy, the tilt angle vs. magnetic field curve exhibits hysteresis behaviour. Due to the higher degree of accuracy of the Surface Evolver method, we are able to analyse the behaviour of the particles near these orientational transitions accurately and study how the critical quantities Bc1, Bc2, θc1 and θc2 vary with particle aspect ratio and contact angle.

  1. Viscous flux motion in anisotropic type-II superconductors in low fields

    SciTech Connect

    Hao, Zhidong; Clem, J.R. Iowa State Univ. of Science and Technology, Ames, IA . Dept. of Physics)

    1990-01-01

    The Bardeen-Stephen model of viscous flux motion in isotropic Type-II superconductors is extended to the anisotropic case characterized by a phenomenological effective mass tensor m{sub ij}. When the magnetic field is low and the vortex lines are aligned along one of the three principal axes, simple expressions for the viscosity tensor {eta}{sub ij} of the viscous flux motion are obtained as functions of m{sub ij} and the normal state conductivity tensor {sigma}{sub ij} for temperature T close to the critical temperature {Tc}. For the high-temperature oxide superconductors the theory predicts that {eta}{sub b}{sup (a)}:{eta}{sub b}{sup (c)}:{eta}{sub c}{sup (a)} {approx} 1:4{gamma}:3{gamma}{sup 2}, where {eta}{sub i}{sup (j)} is the viscosity for the motion along the i-axis of a vortex parallel to the j-axis and {gamma} = {radical}m{sub c}/m{sub a} is the anisotropy parameter (m{sub i}, i = a,b,c, are the principal values of the mass tensor satisfying m{sub a} {approx} m{sub b} {much lt} m{sub c}). 9 refs., 1 fig.

  2. A NUMERICAL TREATMENT OF ANISOTROPIC RADIATION FIELDS COUPLED WITH RELATIVISTIC RESISTIVE MAGNETOFLUIDS

    SciTech Connect

    Takahashi, Hiroyuki R.; Ohsuga, Ken

    2013-08-01

    We develop a numerical scheme for solving fully special relativistic, resistive radiation magnetohydrodynamics. Our code guarantees conservation of total mass, momentum, and energy. The radiation energy density and the radiation flux are consistently updated using the M-1 closure method, which can resolve an anisotropic radiation field, in contrast to the Eddington approximation, as well as the flux-limited diffusion approximation. For the resistive part, we adopt a simple form of Ohm's law. The advection terms are explicitly solved with an approximate Riemann solver, mainly the Harten-Lax-van Leer scheme; the HLLC and HLLD schemes are also solved for some tests. The source terms, which describe the gas-radiation interaction and the magnetic energy dissipation, are implicitly integrated, relaxing the Courant-Friedrichs-Lewy condition even in an optically thick regime or a large magnetic Reynolds number regime. Although we need to invert 4 Multiplication-Sign 4 matrices (for the gas-radiation interaction) and 3 Multiplication-Sign 3 matrices (for the magnetic energy dissipation) at each grid point for implicit integration, they are obtained analytically without preventing massive parallel computing. We show that our code gives reasonable outcomes in numerical tests for ideal magnetohydrodynamics, propagating radiation, and radiation hydrodynamics. We also applied our resistive code to the relativistic Petschek-type magnetic reconnection, revealing the reduction of the reconnection rate via radiation drag.

  3. Lattice Study of Magnetic Catalysis in Graphene Effective Field Theory

    NASA Astrophysics Data System (ADS)

    Winterowd, Christopher; Detar, Carleton; Zafeiropoulos, Savvas

    2016-03-01

    The discovery of graphene ranks as one of the most important developments in condensed matter physics in recent years. As a strongly interacting system whose low-energy excitations are described by the Dirac equation, graphene has many similarities with other strongly interacting field theories, particularly quantum chromodynamics (QCD). Graphene, along with other relativistic field theories, have been predicted to exhibit spontaneous symmetry breaking (SSB) when an external magnetic field is present. Using nonperturbative methods developed to study QCD, we study the low-energy effective field theory (EFT) of graphene subject to an external magnetic field. We find strong evidence supporting the existence of SSB at zero-temperature and characterize the dependence of the chiral condensate on the external magnetic field. We also present results for the mass of the Nambu-Goldstone boson and the dynamically generated quasiparticle mass that result from the SSB.

  4. Negative refraction of ultra-cold atoms in optical lattices with nonuniform artificial gauge fields

    NASA Astrophysics Data System (ADS)

    Zhang, Ai-Xia; Xue, Ju-Kui

    2016-07-01

    We theoretically study the reflection and refraction of ultra-cold atoms in optical lattices exposed to a nonuniform artificial magnetic field. The introduction of the nonuniform artificial magnetic field to the optical lattice for suitable designer magnetic potential barrier can lead to a series of intriguing reflection and refraction phenomena of atoms, including reflection, positive refraction, negative refraction and atomic matter wave splitting. Both the occurrence and the distribution of these reflection and refraction scenarios can be coherently controlled by the nonuniform artificial magnetic field. In particular, the regions close to the boundary of reflection demonstrate two more interesting propagation modes, i.e., a reflected branch of atoms comprising a positive or negative refracted branch of atoms with almost same atom population will be excited simultaneously at the magnetic potential barrier. The results can be a guide for the coherent control of the matter waves in optical lattices and the design of new atom optics devices.

  5. Vortex Formation of Rotating Bose-Einstein Condensates in Synthetic Magnetic Field with Optical Lattice

    NASA Astrophysics Data System (ADS)

    Zhao, Qiang

    2016-02-01

    Motivated by recent experiments carried out by Spielman's group at NIST, we study the vortex formation in a rotating Bose-Einstein condensate in synthetic magnetic field confined in a harmonic potential combined with an optical lattice. We obtain numerical solutions of the two-dimensional Gross-Pitaevskii equation and compare the vortex formation by synthetic magnetic field method with those by rotating frame method. We conclude that a large angular momentum indeed can be created in the presence of the optical lattice. However, it is still more difficult to rotate the condensate by the synthetic magnetic field than by the rotating frame even if the optical lattice is added, and the chemical potential and energy remain almost unchanged by increasing rotational frequency.

  6. Vortex dynamics in anisotropic traps

    SciTech Connect

    McEndoo, S.; Busch, Th.

    2010-07-15

    We investigate the dynamics of linear vortex lattices in anisotropic traps in two dimensions and show that the interplay between the rotation and the anisotropy leads to a rich but highly regular dynamics.

  7. Ordering classification of columnar lattices formed in magnetic fluid subjected to perpendicular fields

    NASA Astrophysics Data System (ADS)

    Jiang, I. M.; Wang, C. Y.; Tsai, M. S.; Horng, H. E.; Hong, C. Y.

    2001-07-01

    When the thin film of high-quality magnetic fluid is subjected to a perpendicular magnetic field, a separation of particles from the liquid matrix will occur, leading to a phase transition with a phase that is concentrated in particles separating from a dilute phase. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. We have explored the field-induced lattices with optical microscopy, digital imaging and computer-video techniques in this study, to classify the ordering property in terms of bond-orientation order.

  8. Third and higher order NFPA twisted constructions of conformal field theories from lattices

    NASA Astrophysics Data System (ADS)

    Montague, P. S.

    1995-02-01

    We investigate orbifold constructions of conformal field theories from lattices by no-fixed-point automorphisms (NFPAs) Zp for p prime, p > 2, concentrating on the case p = 3. Explicit expressions are given for most of the relevant vertex operators, and we consider the locality relations necessary for these to define a consistent conformal field theory. A relation to constructions of lattices from codes, analogous to that found in earlier work in the p = 2 case which led to a generalisation of the triality structure of the Monster module, is also demonstrated.

  9. Observation of exceptional points in reconfigurable non-Hermitian vector-field holographic lattices

    PubMed Central

    Hahn, Choloong; Choi, Youngsun; Yoon, Jae Woong; Song, Seok Ho; Oh, Cha Hwan; Berini, Pierre

    2016-01-01

    Recently, synthetic optical materials represented via non-Hermitian Hamiltonians have attracted significant attention because of their nonorthogonal eigensystems, enabling unidirectionality, nonreciprocity and unconventional beam dynamics. Such systems demand carefully configured complex optical potentials to create skewed vector spaces with a desired metric distortion. In this paper, we report optically generated non-Hermitian photonic lattices with versatile control of real and imaginary sub-lattices. In the proposed method, such lattices are generated by vector-field holographic interference of two elliptically polarized pump beams on azobenzene-doped polymer thin films. We experimentally observe violation of Friedel's law of diffraction, indicating the onset of complex lattice formation. We further create an exact parity-time symmetric lattice to demonstrate totally asymmetric diffraction at the spontaneous symmetry-breaking threshold, referred to as an exceptional point. On this basis, we provide the experimental demonstration of reconfigurable non-Hermitian photonic lattices in the optical domain and observe the purest exceptional point ever reported to date. PMID:27425577

  10. Observation of exceptional points in reconfigurable non-Hermitian vector-field holographic lattices

    NASA Astrophysics Data System (ADS)

    Hahn, Choloong; Choi, Youngsun; Yoon, Jae Woong; Song, Seok Ho; Oh, Cha Hwan; Berini, Pierre

    2016-07-01

    Recently, synthetic optical materials represented via non-Hermitian Hamiltonians have attracted significant attention because of their nonorthogonal eigensystems, enabling unidirectionality, nonreciprocity and unconventional beam dynamics. Such systems demand carefully configured complex optical potentials to create skewed vector spaces with a desired metric distortion. In this paper, we report optically generated non-Hermitian photonic lattices with versatile control of real and imaginary sub-lattices. In the proposed method, such lattices are generated by vector-field holographic interference of two elliptically polarized pump beams on azobenzene-doped polymer thin films. We experimentally observe violation of Friedel's law of diffraction, indicating the onset of complex lattice formation. We further create an exact parity-time symmetric lattice to demonstrate totally asymmetric diffraction at the spontaneous symmetry-breaking threshold, referred to as an exceptional point. On this basis, we provide the experimental demonstration of reconfigurable non-Hermitian photonic lattices in the optical domain and observe the purest exceptional point ever reported to date.

  11. Observation of exceptional points in reconfigurable non-Hermitian vector-field holographic lattices.

    PubMed

    Hahn, Choloong; Choi, Youngsun; Yoon, Jae Woong; Song, Seok Ho; Oh, Cha Hwan; Berini, Pierre

    2016-01-01

    Recently, synthetic optical materials represented via non-Hermitian Hamiltonians have attracted significant attention because of their nonorthogonal eigensystems, enabling unidirectionality, nonreciprocity and unconventional beam dynamics. Such systems demand carefully configured complex optical potentials to create skewed vector spaces with a desired metric distortion. In this paper, we report optically generated non-Hermitian photonic lattices with versatile control of real and imaginary sub-lattices. In the proposed method, such lattices are generated by vector-field holographic interference of two elliptically polarized pump beams on azobenzene-doped polymer thin films. We experimentally observe violation of Friedel's law of diffraction, indicating the onset of complex lattice formation. We further create an exact parity-time symmetric lattice to demonstrate totally asymmetric diffraction at the spontaneous symmetry-breaking threshold, referred to as an exceptional point. On this basis, we provide the experimental demonstration of reconfigurable non-Hermitian photonic lattices in the optical domain and observe the purest exceptional point ever reported to date. PMID:27425577

  12. Investigation of low field dielectric properties of anisotropic porous Pb(Zr,Ti)O3 ceramics: Experiment and modeling

    NASA Astrophysics Data System (ADS)

    Olariu, C. S.; Padurariu, L.; Stanculescu, R.; Baldisserri, C.; Galassi, C.; Mitoseriu, L.

    2013-12-01

    Anisotropic porous Pb(Zr,Ti)O3 ceramics with various porosity degrees have been studied in order to determine the role of the pore shape and orientation on the low-field dielectric properties. Ceramic samples with formula Pb(Zr0.52Ti0.48)0.976Nb0.024O3 with different porosity degrees (dense, 10%, 20%, 40% vol.) have been prepared by solid state reaction. Taking into consideration the shape and orientation of the pore inclusions, the dielectric properties of porous ceramics have been described by using adapted mixing rules models. Rigorous bounds, derived on the basis on Variational Principle, were used to frame dielectric properties of porous composites. The finite element method (FEM) was additionally used to simulate the dielectric response of the porous composites under various applied fields. Among the few effective medium approximation models adapted for anisotropic oriented inclusions, the best results were obtained in case of needle-like shape inclusions (which do not correspond to the real shape of microstructure inclusions). The general case of Wiener bounds limited well the dielectric properties of anisotropic porous composites in case of parallel orientation. Among the theoretical approaches, FEM technique allowed to simulate the distribution of potential and electric field inside composites and provided a very good agreement between the computed permittivity values and experimental ones.

  13. Nonequilibrium Dynamical Mean-Field Theory for Bosonic Lattice Models

    NASA Astrophysics Data System (ADS)

    Strand, Hugo U. R.; Eckstein, Martin; Werner, Philipp

    2015-01-01

    We develop the nonequilibrium extension of bosonic dynamical mean-field theory and a Nambu real-time strong-coupling perturbative impurity solver. In contrast to Gutzwiller mean-field theory and strong-coupling perturbative approaches, nonequilibrium bosonic dynamical mean-field theory captures not only dynamical transitions but also damping and thermalization effects at finite temperature. We apply the formalism to quenches in the Bose-Hubbard model, starting from both the normal and the Bose-condensed phases. Depending on the parameter regime, one observes qualitatively different dynamical properties, such as rapid thermalization, trapping in metastable superfluid or normal states, as well as long-lived or strongly damped amplitude oscillations. We summarize our results in nonequilibrium "phase diagrams" that map out the different dynamical regimes.

  14. Color fields computed in SU(3) lattice QCD for the static tetraquark system

    NASA Astrophysics Data System (ADS)

    Cardoso, Nuno; Cardoso, Marco; Bicudo, Pedro

    2011-09-01

    The color fields created by the static tetraquark system are computed in quenched SU(3) lattice QCD, in a 243×48 lattice at β=6.2 corresponding to a lattice spacing a=0.07261(85)fm. We find that the tetraquark color fields are well described by a double-Y, or butterfly, shaped flux tube. The two flux-tube junction points are compatible with Fermat points minimizing the total flux-tube length. We also compare the diquark-diantiquark central flux-tube profile in the tetraquark with the quark-antiquark fundamental flux-tube profile in the meson, and they match, thus showing that the tetraquark flux tubes are composed of fundamental flux tubes.

  15. Color fields of the static pentaquark system computed in SU(3) lattice QCD

    NASA Astrophysics Data System (ADS)

    Cardoso, Nuno; Bicudo, Pedro

    2013-02-01

    We compute the color fields of SU(3) lattice QCD created by static pentaquark systems, in a 243×48 lattice at β=6.2 corresponding to a lattice spacing a=0.07261(85)fm. We find that the pentaquark color fields are well described by a multi-Y-type shaped flux tube. The flux tube junction points are compatible with Fermat-Steiner points minimizing the total flux tube length. We also compare the pentaquark flux tube profile with the diquark-diantiquark central flux tube profile in the tetraquark and the quark-antiquark fundamental flux tube profile in the meson, and they match, thus showing that the pentaquark flux tubes are composed of fundamental flux tubes.

  16. The topological quantum phase transitions in Lieb lattice driven by the Rashba SOC and exchange field

    NASA Astrophysics Data System (ADS)

    Wang, Rui; Qiao, Qian; Wang, Bin; Ding, Xiu-Huan; Zhang, Yi-Fu

    2016-09-01

    The quantum spin Hall (QSH) effect and the quantum anomalous Hall (QAH) effect in Lieb lattice are investigated in the presence of both Rashba spin-orbit coupling (SOC) and uniform exchange field. The Lieb lattice has a simple cubic symmetry, which is characterized by the single Dirac-cone per Brillouin zone and the middle flat band in the band structure. The intrinsic SOC is essentially needed to open the full energy gap in the bulk. The QSH effect could survive even in the presence of the exchange field. In terms of the first Chern number and the spin Chern number, we study the topological nature and the topological phase transition from the time-reversal symmetry broken QSH effect to the QAH effect. For Lieb lattice ribbons, the energy spectrum and the wave-function distributions are obtained numerically, where the helical edge states and the chiral edge states reveal the non-trivial topological QSH and QAH properties, respectively.

  17. Quantum Fisher information for periodic and quasiperiodic anisotropic XY chains in a transverse field

    NASA Astrophysics Data System (ADS)

    Liu, X. M.; Du, Z. Z.; Liu, J.-M.

    2016-04-01

    In this work, the concept of quantum Fisher information (QFI) is used to characterize the quantum transitions and factorization transitions in one-dimensional anisotropic XY models with periodic coupling interaction and quasiperiodic one. For the periodic-two model, it is found that the Ising transition and anisotropic transition can be distinctively illustrated by the evolution of QFI and its first-order derivatives, confirmed additionally by the scaling behavior. For the quasiperiodic Fibonacci chain, the number of quantum phase transitions increases from one to the lth Fibonacci number Fl when the anisotropic parameter γ approaches zero. The phase diagram for the approximant Fl=8 is derived as an example. In addition, the factorization transition in the two models can be marked by the correlation quantity defined from the QFI. The present work demonstrates the implication of the QFI as a general fingerprint to characterize the quantum transitions and factorization transitions.

  18. Lattice Models for Granular-Like Velocity Fields: Hydrodynamic Description

    NASA Astrophysics Data System (ADS)

    Manacorda, Alessandro; Plata, Carlos A.; Lasanta, Antonio; Puglisi, Andrea; Prados, Antonio

    2016-08-01

    A recently introduced model describing—on a 1d lattice—the velocity field of a granular fluid is discussed in detail. The dynamics of the velocity field occurs through next-neighbours inelastic collisions which conserve momentum but dissipate energy. The dynamics is described through the corresponding Master Equation for the time evolution of the probability distribution. In the continuum limit, equations for the average velocity and temperature fields with fluctuating currents are derived, which are analogous to hydrodynamic equations of granular fluids when restricted to the shear modes. Therefore, the homogeneous cooling state, with its linear instability, and other relevant regimes such as the uniform shear flow and the Couette flow states are described. The evolution in time and space of the single particle probability distribution, in all those regimes, is also discussed, showing that the local equilibrium is not valid in general. The noise for the momentum and energy currents, which are correlated, are white and Gaussian. The same is true for the noise of the energy sink, which is usually negligible.

  19. Implementation of general background electromagnetic fields on a periodic hypercubic lattice

    NASA Astrophysics Data System (ADS)

    Davoudi, Zohreh; Detmold, William

    2015-10-01

    Nonuniform background electromagnetic fields, once implemented in lattice quantum chromodynamics calculations of hadronic systems, provide a means to constrain a large class of electromagnetic properties of hadrons and nuclei, from their higher electromagnetic moments and charge radii to their electromagnetic form factors. We show how nonuniform fields can be constructed on a periodic hypercubic lattice under certain conditions and determine the precise form of the background U (1 ) gauge links that must be imposed on the quantum chromodynamics gauge-field configurations to maintain periodicity. Once supplemented by a set of quantization conditions on the background-field parameters, this construction guarantees that no nonuniformity occurs in the hadronic correlation functions across the boundary of the lattice. The special cases of uniform electric and magnetic fields, a nonuniform electric field that varies linearly in one spatial coordinate (relevant to the determination of quadruple moment and charge radii), nonuniform electric and magnetic fields with given temporal and spatial dependences (relevant to the determination of nucleon spin polarizabilities) and plane-wave electromagnetic fields (relevant to the determination of electromagnetic form factors) are discussed explicitly.

  20. Realization of the Harper Hamiltonian with Artificial Gauge Fields in Optical Lattices

    NASA Astrophysics Data System (ADS)

    Miyake, Hirokazu; Siviloglou, Georgios; Kennedy, Colin; Burton, William Cody; Ketterle, Wolfgang

    2014-03-01

    Systems of charged particles in magnetic fields have led to many discoveries in science-such as the integer and fractional quantum Hall effects-and have become important paradigms of quantum many-body physics. We have proposed and implemented a scheme which realizes the Harper Hamiltonian, a lattice model for charged particles in magnetic fields, whose energy spectrum is the fractal Hofstadter butterfly. We experimentally realize this Hamiltonian for ultracold, charge neutral bosonic particles of 87Rb in a two-dimensional optical lattice by creating an artificial gauge field using laser-assisted tunneling and a potential energy gradient provided by gravity. Laser-assisted tunneling processes are characterized by studying the expansion of the atoms in the lattice. Furthermore, this scheme can be extended to realize spin-orbit coupling and the spin Hall effect for neutral atoms in optical lattices by modifying the motion of atoms in a spin-dependent way by laser recoil and Zeeman shifts created with a magnetic field gradient. Major advantages of our scheme are that it does not rely on near-resonant laser light to couple different spin states and should work even for fermionic particles. Our work is a step towards studying novel topological phenomena with ultracold atoms. Currently at the RAND Corporation.

  1. Boundary-field-driven control of discontinuous phase transitions on hyperbolic lattices

    NASA Astrophysics Data System (ADS)

    Lee, Yoju; Verstraete, Frank; Gendiar, Andrej

    2016-08-01

    The multistate Potts models on two-dimensional hyperbolic lattices are studied with respect to various boundary effects. The free energy is numerically calculated using the corner transfer matrix renormalization group method. We analyze phase transitions of the Potts models in the thermodynamic limit with respect to contracted boundary layers. A false phase transition is present even if a couple of the boundary layers are contracted. Its significance weakens, as the number of the contracted boundary layers increases, until the correct phase transition (deep inside the bulk) prevails over the false one. For this purpose, we derive a thermodynamic quantity, the so-called bulk excess free energy, which depends on the contracted boundary layers and memorizes additional boundary effects. In particular, the magnetic field is imposed on the outermost boundary layer. While the boundary magnetic field does not affect the second-order phase transition in the bulk if suppressing all the boundary effects on the hyperbolic lattices, the first-order (discontinuous) phase transition is significantly sensitive to the boundary magnetic field. Contrary to the phase transition on the Euclidean lattices, the discontinuous phase transition on the hyperbolic lattices can be continuously controlled (within a certain temperature coexistence region) by varying the boundary magnetic field.

  2. Boundary-field-driven control of discontinuous phase transitions on hyperbolic lattices.

    PubMed

    Lee, Yoju; Verstraete, Frank; Gendiar, Andrej

    2016-08-01

    The multistate Potts models on two-dimensional hyperbolic lattices are studied with respect to various boundary effects. The free energy is numerically calculated using the corner transfer matrix renormalization group method. We analyze phase transitions of the Potts models in the thermodynamic limit with respect to contracted boundary layers. A false phase transition is present even if a couple of the boundary layers are contracted. Its significance weakens, as the number of the contracted boundary layers increases, until the correct phase transition (deep inside the bulk) prevails over the false one. For this purpose, we derive a thermodynamic quantity, the so-called bulk excess free energy, which depends on the contracted boundary layers and memorizes additional boundary effects. In particular, the magnetic field is imposed on the outermost boundary layer. While the boundary magnetic field does not affect the second-order phase transition in the bulk if suppressing all the boundary effects on the hyperbolic lattices, the first-order (discontinuous) phase transition is significantly sensitive to the boundary magnetic field. Contrary to the phase transition on the Euclidean lattices, the discontinuous phase transition on the hyperbolic lattices can be continuously controlled (within a certain temperature coexistence region) by varying the boundary magnetic field. PMID:27627272

  3. Lattice Effective Field Theory Calculations for A=3, 4, 6, 12 Nuclei

    SciTech Connect

    Epelbaum, Evgeny; Krebs, Hermann; Lee, Dean; Meissner, Ulf-G.

    2010-04-09

    We present lattice results for the ground state energies of tritium, helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our analysis includes isospin breaking, Coulomb effects, and interactions up to next-to-next-to-leading order in chiral effective field theory.

  4. Experimental Realization of Strong Effective Magnetic Fields in an Optical Lattice

    SciTech Connect

    Aidelsburger, M.; Atala, M.; Trotzky, S.; Chen, Y.-A.; Bloch, I.; Nascimbene, S.

    2011-12-16

    We use Raman-assisted tunneling in an optical superlattice to generate large tunable effective magnetic fields for ultracold atoms. When hopping in the lattice, the accumulated phase shift by an atom is equivalent to the Aharonov-Bohm phase of a charged particle exposed to a staggered magnetic field of large magnitude, on the order of 1 flux quantum per plaquette. We study the ground state of this system and observe that the frustration induced by the magnetic field can lead to a degenerate ground state for noninteracting particles. We provide a measurement of the local phase acquired from Raman-induced tunneling, demonstrating time-reversal symmetry breaking of the underlying Hamiltonian. Furthermore, the quantum cyclotron orbit of single atoms in the lattice exposed to the magnetic field is directly revealed.

  5. Simulation study on light propagation in an anisotropic turbulence field of entrainment zone.

    PubMed

    Yuan, Renmin; Sun, Jianning; Luo, Tao; Wu, Xuping; Wang, Chen; Fu, Yunfei

    2014-06-01

    The convective atmospheric boundary layer was modeled in the water tank. In the entrainment zone (EZ), which is at the top of the convective boundary layer (CBL), the turbulence is anisotropic. An anisotropy coefficient was introduced in the presented anisotropic turbulence model. A laser beam was set to horizontally go through the EZ modeled in the water tank. The image of two-dimensional (2D) light intensity fluctuation was formed on the receiving plate perpendicular to the light path and was recorded by the CCD. The spatial spectra of both horizontal and vertical light intensity fluctuations were analyzed. Results indicate that the light intensity fluctuation in the EZ exhibits strong anisotropic characteristics. Numerical simulation shows there is a linear relationship between the anisotropy coefficients and the ratio of horizontal to vertical fluctuation spectra peak wavelength. By using the measured temperature fluctuations along the light path at different heights, together with the relationship between temperature and refractive index, the one-dimensional (1D) refractive index fluctuation spectra were derived. The anisotropy coefficients were estimated from the 2D light intensity fluctuation spectra modeled by the water tank. Then the turbulence parameters can be obtained using the 1D refractive index fluctuation spectra and the corresponding anisotropy coefficients. These parameters were used in numerical simulation of light propagation. The results of numerical simulations show this approach can reproduce the anisotropic features of light intensity fluctuations in the EZ modeled by the water tank experiment.

  6. Numerical study of renormalization group flows of nuclear effective field theory without pions on a lattice

    NASA Astrophysics Data System (ADS)

    Harada, Koji; Sasabe, Satoru; Yahiro, Masanobu

    2016-08-01

    We formulate the next-to-leading-order nuclear effective field theory without pions in the two-nucleon sector on a spatial lattice and investigate nonperturbative renormalization group flows in the strong-coupling region by diagonalizing the Hamiltonian numerically. The cutoff (proportional to the inverse of the lattice constant) dependence of the coupling constants is obtained by changing the lattice constant with the binding energy and the asymptotic normalization constant for the ground state being fixed. We argue that the critical line can be obtained by looking at the finite-size dependence of the ground-state energy. We determine the relevant operator and locate the nontrivial fixed point, as well as the physical flow line corresponding to the deuteron in the two-dimensional plane of dimensionless coupling constants. It turns out that the location of the nontrivial fixed point is very close to the one obtained by the corresponding analytic calculation, but the relevant operator is quite different.

  7. Orbital magnetism of ultracold fermionic gases in a lattice: Dynamical mean-field approach

    NASA Astrophysics Data System (ADS)

    Cichy, Agnieszka; Sotnikov, Andrii

    2016-05-01

    We study finite-temperature properties of ultracold four-component mixtures of alkaline-earth-metal-like atoms in optical lattices that can be effectively described by the two-band spin-1 /2 Hubbard model including Hund's exchange coupling term. Our main goal is to investigate the effect of exchange interactions on finite-temperature magnetic phases for a wide range of lattice fillings. We use the dynamical mean-field theory approach and its real-space generalization to obtain finite-temperature phase diagrams including transitions to magnetically ordered phases. It allows to determine optimal experimental regimes for approaching long-range ferromagnetic ordering in ultracold gases. We also calculate the entropy in the vicinity of magnetically ordered phases, which provides quantitative predictions for ongoing and future experiments aiming at approaching and studying long-range ordered states in optical lattices.

  8. Observation of a magnetic field dependence of the lattice thermal conductivity

    NASA Astrophysics Data System (ADS)

    Jin, Hyungyu; Restrepo, Oscar; Antolin, Nikolas; Windl, Wolfgang; Barnes, Stewart; Heremans, Joseph

    2014-03-01

    Can phonons respond to magnetic fields? From the simple point of view of the classical lattice vibrations, there is no clue that phonons possess any magnetic characteristics. Here, we report for the first time that the lattice thermal conductivity can show a response to an external magnetic field in a non-magnetic semiconductor crystal. We observe a magnetic field dependence of the lattice thermal conductivity in a high quality 2x1015 Te doped single crystal of InSb. The electronic contribution is over 106 times smaller than the lattice. The effect is observed in the temperature regime where the Umklapp processes start appearing, and still mainly involve phonons with long mean free paths. A special thermal design is employed to obtain a high accuracy heat flux measurement. Detailed experimental procedures and results are presented along with a brief discussion about possible origins of the effect. HJ and JPH are supported by AFOSR MURI ``Cryogenic Peltier Cooling'' Contract #FA9550-10-1-0533; ODR and WW are supported by the Center for Emergent Materials, an NSF MRSEC at The Ohio State University (Grant DMR-0820414).

  9. Gaseous bubble oscillations in anisotropic non-Newtonian fluids under influence of high-frequency acoustic field

    NASA Astrophysics Data System (ADS)

    Golykh, R. N.

    2016-06-01

    Progress of technology and medicine dictates the ever-increasing requirements (heat resistance, corrosion resistance, strength properties, impregnating ability, etc.) for non-Newtonian fluids and materials produced on their basis (epoxy resin, coating materials, liquid crystals, etc.). Materials with improved properties obtaining is possible by modification of their physicochemical structure. One of the most promising approaches to the restructuring of non-Newtonian fluids is cavitation generated by high-frequency acoustic vibrations. The efficiency of cavitation in non-Newtonian fluid is determined by dynamics of gaseous bubble. Today, bubble dynamics in isotropic non-Newtonian fluids, in which cavitation bubble shape remains spherical, is most full investigated, because the problem reduces to ordinary differential equation for spherical bubble radius. However, gaseous bubble in anisotropic fluids which are most wide kind of non-Newtonian fluids (due to orientation of macromolecules) deviates from spherical shape due to viscosity dependence on shear rate direction. Therefore, the paper presents the mathematical model of gaseous bubble dynamics in anisotropic non-Newtonian fluids. The model is based on general equations for anisotropic non-Newtonian fluid flow. The equations are solved by asymptotic decomposition of fluid flow parameters. It allowed evaluating bubble size and shape evolution depending on rheological properties of liquid and acoustic field characteristics.

  10. Multistable particle-field dynamics in cavity-generated optical lattices

    NASA Astrophysics Data System (ADS)

    Winterauer, Dominik J.; Niedenzu, Wolfgang; Ritsch, Helmut

    2015-05-01

    Polarizable particles trapped in a resonator-sustained optical-lattice potential generate strong position-dependent backaction on the intracavity field. In the quantum regime, particles in different energy bands are connected to different intracavity light intensities and optical-lattice depths. This generates a highly nonlinear coupled particle-field dynamics. For a given pump strength and detuning, a factorizing mean-field approach predicts several self-consistent stationary solutions of strongly distinct photon numbers and motional states. Quantum Monte Carlo wave-function simulations of the master equation confirm these predictions and reveal complex multimodal photon-number and particle-momentum distributions. Using larger nanoparticles in such a setup thus constitutes a well-controllable playground to study nonlinear quantum dynamics and the buildup of macroscopic quantum superpositions at the quantum-classical boundary.

  11. Transition to and from the skyrmion lattice phase by electric fields in a magnetoelectric compound.

    PubMed

    Okamura, Y; Kagawa, F; Seki, S; Tokura, Y

    2016-01-01

    Dissipation-less electric control of magnetic state variable is an important target of contemporary spintronics. The non-volatile control of magnetic skyrmions, nanometre-sized spin-swirling objects, with electric fields may exemplify this goal. The skyrmion-hosting magnetoelectric chiral magnet Cu2OSeO3 provides a unique platform for the implementation of such control; however, the hysteresis that accompanies the first-order transition associated with the skyrmion phase is negligibly narrow in practice. Here we demonstrate another method that functions irrespective of the transition boundary. Combination of magnetic-susceptibility measurements and microwave spectroscopy reveals that although the metastable skyrmion lattice is normally hidden behind a more thermodynamically stable conical phase, it emerges under electric fields and persists down to the lowest temperature. Once created, this metastable skyrmion lattice remains without electric fields, establishing a bistability distinct from the transition hysteresis. This bistability thus enables non-volatile electric-field control of the skyrmion lattice even in temperature/magnetic-field regions far from the transition boundary. PMID:27580648

  12. Transition to and from the skyrmion lattice phase by electric fields in a magnetoelectric compound

    NASA Astrophysics Data System (ADS)

    Okamura, Y.; Kagawa, F.; Seki, S.; Tokura, Y.

    2016-09-01

    Dissipation-less electric control of magnetic state variable is an important target of contemporary spintronics. The non-volatile control of magnetic skyrmions, nanometre-sized spin-swirling objects, with electric fields may exemplify this goal. The skyrmion-hosting magnetoelectric chiral magnet Cu2OSeO3 provides a unique platform for the implementation of such control; however, the hysteresis that accompanies the first-order transition associated with the skyrmion phase is negligibly narrow in practice. Here we demonstrate another method that functions irrespective of the transition boundary. Combination of magnetic-susceptibility measurements and microwave spectroscopy reveals that although the metastable skyrmion lattice is normally hidden behind a more thermodynamically stable conical phase, it emerges under electric fields and persists down to the lowest temperature. Once created, this metastable skyrmion lattice remains without electric fields, establishing a bistability distinct from the transition hysteresis. This bistability thus enables non-volatile electric-field control of the skyrmion lattice even in temperature/magnetic-field regions far from the transition boundary.

  13. Transition to and from the skyrmion lattice phase by electric fields in a magnetoelectric compound

    PubMed Central

    Okamura, Y.; Kagawa, F.; Seki, S.; Tokura, Y.

    2016-01-01

    Dissipation-less electric control of magnetic state variable is an important target of contemporary spintronics. The non-volatile control of magnetic skyrmions, nanometre-sized spin-swirling objects, with electric fields may exemplify this goal. The skyrmion-hosting magnetoelectric chiral magnet Cu2OSeO3 provides a unique platform for the implementation of such control; however, the hysteresis that accompanies the first-order transition associated with the skyrmion phase is negligibly narrow in practice. Here we demonstrate another method that functions irrespective of the transition boundary. Combination of magnetic-susceptibility measurements and microwave spectroscopy reveals that although the metastable skyrmion lattice is normally hidden behind a more thermodynamically stable conical phase, it emerges under electric fields and persists down to the lowest temperature. Once created, this metastable skyrmion lattice remains without electric fields, establishing a bistability distinct from the transition hysteresis. This bistability thus enables non-volatile electric-field control of the skyrmion lattice even in temperature/magnetic-field regions far from the transition boundary. PMID:27580648

  14. A mean-field study of the Hubbard model on the kagome lattice

    NASA Astrophysics Data System (ADS)

    Enjalran, Matthew

    The experimental work on the herbertsmithite compound, ZnCu3(OH)6Cl2, almost a decade ago ignited intense interest in the field of frustrated magnetism because it represented the best material realization of a spin- 1 / 2 Heisenberg antiferromagnet (AFM) on the kagome lattice and its ground state was a gapless spin liquid. Many theoretical and numerical studies of the quantum Heisenberg AFM on the kagome lattice have been performed since and have coalesced around the general consensus of a small gapped spin liquid ground state for the model. Although there is not currently a metallic kagome material system, the work on ZnCu3(OH)6Cl2 has motivated theoretical and numerical investigations of itinerant electrons on the kagome lattice. We contribute to this pursuit by studying the single band Hubbard model on the kagome lattice, where the frustration can be tuned by adjusting the hopping along different bonds, t1 and t2; however, we are mainly interested in the isotropic limit, t1 =t2 = t . We report preliminary results on the low temperature correlations in the half filled model as a function of frustration and interaction strength in the mean-field, Hartree-Fock, limit. CSU Research Grant.

  15. Noncircular skyrmion and its anisotropic response in thin films of chiral magnets under a tilted magnetic field

    DOE PAGESBeta

    Lin, Shi-Zeng; Saxena, Avadh

    2015-11-03

    Here we study the equilibrium and dynamical properties of skyrmions in thin films of chiral magnets with oblique magnetic field. The shape of an individual skyrmion is non-circular and the skyrmion density decreases with the tilt angle from the normal of films. As a result, the interaction between two skyrmions depends on the relative angle between them in addition to their separation. The triangular lattice of skyrmions under a perpendicular magnetic field is distorted into a centered rectangular lattice for a tilted magnetic field. For a low skyrmion density, skyrmions form a chain like structure. Lastly, the dynamical response ofmore » the non-circular skyrmions depends on the direction of external currents.« less

  16. Noncircular skyrmion and its anisotropic response in thin films of chiral magnets under a tilted magnetic field

    SciTech Connect

    Lin, Shi-Zeng; Saxena, Avadh

    2015-11-03

    Here we study the equilibrium and dynamical properties of skyrmions in thin films of chiral magnets with oblique magnetic field. The shape of an individual skyrmion is non-circular and the skyrmion density decreases with the tilt angle from the normal of films. As a result, the interaction between two skyrmions depends on the relative angle between them in addition to their separation. The triangular lattice of skyrmions under a perpendicular magnetic field is distorted into a centered rectangular lattice for a tilted magnetic field. For a low skyrmion density, skyrmions form a chain like structure. Lastly, the dynamical response of the non-circular skyrmions depends on the direction of external currents.

  17. Anisotropic viscosity and fabric evolution from laboratory experiments and field observations

    NASA Astrophysics Data System (ADS)

    Hansen, Lars; Warren, Jessica; Zimmerman, Mark; Kohlstedt, David; Skemer, Philip; Hirth, Greg

    2013-04-01

    Crystallographic alignment of grains during solid-state deformation imparts anisotropic material properties to the bulk rock, which results in significant macroscopic anisotropy in viscosity. The majority of previous laboratory studies on geological materials have performed experiments on relatively untextured samples, making it difficult to quantify the magnitude of anisotropy. Here we present results of laboratory deformation experiments that first produce strong crystallographic fabrics and then test the viscosity of these textured aggregates in multiple stress states. Our results are used in a model for shear zone evolution to reproduce field measurements of strain variation across a natural shear zone. Two sets of deformation experiments were performed in a gas-medium apparatus at 1473 K and 300 MPa confining pressure. In the first set of experiments (Hansen et al., Nature, 2012), large-strain torsion imparts a fabric in which the dominant [100] orientation is parallel to the shear direction and the dominant [010] orientation is normal to the shear plane, typical of a fabric due to shear on the (010)[100] slip system. Subsequent tension parallel to the initial torsion axis occurs with most grains having unfavorable orientations for slip on available slip systems. In the second set of experiments, samples were initially deformed in tension and subsequently deformed in torsion, with the torsion axis parallel to the initial tensional load. Tension imparts a fabric in which the dominant [100] orientation is parallel to the tension direction, with girdles of [010] and [001] axes. Subsequent torsion occurs with some grains having favorable orientations for (100)[001] slip and other grains having unfavorable orientations for slip on available slip systems. Electron-backscatter diffraction maps of axial sections of samples reveal that the crystallographic fabric reorients into a more favorable orientation at a shear strain of ~1.5. In both sets of experiments the

  18. Monogamy of entanglement and improved mean-field ansatz for spin lattices

    NASA Astrophysics Data System (ADS)

    Osterloh, Andreas; Schützhold, Ralf

    2015-03-01

    We consider rather general spin-1 /2 lattices with large coordination numbers Z . Based on the monogamy of entanglement and other properties of the concurrence C , we derive rigorous bounds for the entanglement between neighboring spins, such as C ≤1 /√{Z } , which show that C decreases for large Z . In addition, we demonstrate that the concurrence C measures the deviation from mean-field behavior and can only vanish if the mean-field ansatz yields an exact ground state of the Hamiltonian. Motivated by these findings, we propose an improved mean-field ansatz by adding entanglement.

  19. Spin-lattice dynamics simulation of external field effect on magnetic order of ferromagnetic iron

    SciTech Connect

    Chui, C. P.; Zhou, Yan

    2014-03-15

    Modeling of field-induced magnetization in ferromagnetic materials has been an active topic in the last dozen years, yet a dynamic treatment of distance-dependent exchange integral has been lacking. In view of that, we employ spin-lattice dynamics (SLD) simulations to study the external field effect on magnetic order of ferromagnetic iron. Our results show that an external field can increase the inflection point of the temperature. Also the model provides a better description of the effect of spin correlation in response to an external field than the mean-field theory. An external field has a more prominent effect on the long range magnetic order than on the short range counterpart. Furthermore, an external field allows the magnon dispersion curves and the uniform precession modes to exhibit magnetic order variation from their temperature dependence.

  20. Analogue of Rashba pseudo-spin-orbit coupling in photonic lattices by gauge field engineering

    NASA Astrophysics Data System (ADS)

    Plotnik, Y.; Bandres, M. A.; Stützer, S.; Lumer, Y.; Rechtsman, M. C.; Szameit, A.; Segev, M.

    2016-07-01

    We present, theoretically and experimentally, the observation of the Rashba effect in photonic lattices, where the effect is brought about by an artificial gauge field, induced by the geometry of the system. In doing that, we demonstrate a particular form of coupling between pseudospin and momentum, resulting in spin-dependent shifts in the spectrum. Our system consists of two coupled, oppositely tilted waveguide arrays, where the evolution of an optical beam allows for probing the dynamics of the evolving wave packets, and the formation of spectral splitting. We show that the Rashba effect can be amplified or decreased through optical nonlinear effects, which correspond to mean-field interactions in various systems such as cold-atom lattices and exciton-polariton condensates.

  1. Clebsch-Gordan construction of lattice interpolating fields for excited baryons

    SciTech Connect

    S. Basak; R. Edwards; G. Fleming; U. Heller; C. Morningstar; D. Richards; I. Sato; S. Wallace

    2005-08-01

    Large sets of baryon interpolating field operators are developed for use in lattice QCD studies of baryons with zero momentum. Operators are classified according to the double-valued irreducible representations of the octahedral group. At first, three-quark smeared, local operators are constructed for each isospin and strangeness and they are classified according to their symmetry with respect to exchange of Dirac indices. Nonlocal baryon operators are formulated in a second step as direct products of the spinor structures of smeared, local operators together with gauge-covariant lattice displacements of one or more of the smeared quark fields. Linear combinations of direct products of spinorial and spatial irreducible representations are then formed with appropriate Clebsch-Gordan coefficients of the octahedral group. The construction attempts to maintain maximal overlap with the continuum SU(2) group in order to provide a physically interpretable basis. Nonlocal operators provide direct couplings to states that have nonzero orbital angular momentum.

  2. Clebsch-Gordan construction of lattice interpolated fields for excited baryons

    SciTech Connect

    Basak, Subhasish; Sato, Ikuro; Wallace, Stephen J.; Edwards, Robert; Richards, David; Fleming, George T.; Heller, Urs M.; Morningstar, Colin

    2005-10-01

    Large sets of baryon interpolating field operators are developed for use in lattice QCD studies of baryons with zero momentum. Operators are classified according to the double-valued irreducible representations of the octahedral group. At first, three-quark smeared, local operators are constructed for each isospin and strangeness and they are classified according to their symmetry with respect to exchange of Dirac indices. Nonlocal baryon operators are formulated in a second step as direct products of the spinor structures of smeared, local operators together with gauge-covariant lattice displacements of one or more of the smeared quark fields. Linear combinations of direct products of spinorial and spatial irreducible representations are then formed with appropriate Clebsch-Gordan coefficients of the octahedral group. The construction attempts to maintain maximal overlap with the continuum SU(2) group in order to provide a physically interpretable basis. Nonlocal operators provide direct couplings to states that have nonzero orbital angular momentum.

  3. Anisotropic contributions to the Sn119 transferred hyperfine fields in RMn6Sn6-xXx ( R=Y,Tb,Er ; X=In,Ga )

    NASA Astrophysics Data System (ADS)

    Perry, Laura K.; Ryan, D. H.; Venturini, G.

    2007-04-01

    The anisotropic contribution to the transferred hyperfine fields in YMn6Sn5.42In0.58 has been isolated using a field-driven moment rotation from the ab plane to the c axis in a single crystal. We find that at 12K , the anisotropic contribution is between 3% and 4% of the total field for the Sn2c and Sn2d sites, while it accounts for nearly one-third of the observed field at the Sn2e site. Comparison with data from RMn6Sn6-xXx ( R=Tb,Er ; X=Ga,In ) compounds containing magnetic rare earths shows that the Mn and R contributions to the anisotropic component of the transferred hyperfine fields are similar in magnitude.

  4. Bosons with Artificial Gauge Fields and Mott Physics on the Honeycomb Lattice

    NASA Astrophysics Data System (ADS)

    Vidanovic, Ivana; Petrescu, Alexandru; Le Hur, Karyn; Hofstetter, Walter

    2014-03-01

    We study bosons in the tight-binding model on the honeycomb lattice introduced by Haldane. We analyze the ground state topology and quasiparticle properties in the Mott phase by applying bosonic dynamical mean field theory, strong-coupling perturbation theory, exact diagonalization and numerical evaluations of sample Hall conductivity. The phase diagram also contains two different superfluid phases. The quasiparticle dynamics, number fluctuations, and local currents are measurable in cold atom experiments.

  5. Dust Lattice Waves in Two-Dimensional Hexagonal Dust Crystals with an External Magnetic Field

    SciTech Connect

    Farokhi, B.; Shahmansouri, M.

    2008-09-07

    The influence of a constant magnetic field on the propagation of dust-lattice (DL) modes in a two-dimensional hexagonal strongly coupled plasma crystal formed by paramagnetic particles is considered. The expression for the wave dispersion relation clearly shows that high-frequency and low-frequency branches exist as a result of the coupling of longitudinal and transverse modes due to the Lorentz force acting on the dust particles.

  6. Evidence for lattice-polarization-enhanced field effects at the SrTiO3-based heterointerface

    PubMed Central

    Li, Y.; Zhang, H. R.; Lei, Y.; Chen, Y. Z.; Pryds, N.; Shen, Baogen; Sun, Jirong

    2016-01-01

    Electrostatic gating provides a powerful approach to tune the conductivity of the two-dimensional electron liquid between two insulating oxides. For the LaAlO3/SrTiO3 (LAO/STO) interface, such gating effect could be further enhanced by a strong lattice polarization of STO caused by simultaneous application of gate field and illumination light. Herein, by monitoring the discharging process upon removing the gate field, we give firm evidence for the occurrence of this lattice polarization at the amorphous-LaAlO3/SrTiO3 interface. Moreover, we find that the lattice polarization is accompanied with a large expansion of the out-of-plane lattice of STO. Photo excitation affects the polarization process by accelerating the field-induced lattice expansion. The present work demonstrates the great potential of combined stimuli in exploring emergent phenomenon at complex oxide interfaces. PMID:26926433

  7. Bloch oscillations and mean-field effects of Bose-Einstein condensates in 1D optical lattices.

    PubMed

    Morsch, O; Müller, J H; Cristiani, M; Ciampini, D; Arimondo, E

    2001-10-01

    We have loaded Bose-Einstein condensates into one-dimensional, off-resonant optical lattices and accelerated them by chirping the frequency difference between the two lattice beams. For small values of the lattice well depth, Bloch oscillations were observed. Reducing the potential depth further, Landau-Zener tunneling out of the lowest lattice band, leading to a breakdown of the oscillations, was also studied and used as a probe for the effective potential resulting from mean-field interactions as predicted by Choi and Niu [Phys. Rev. Lett. 82, 2022 (1999)]. The effective potential was measured for various condensate densities and trap geometries, yielding good qualitative agreement with theoretical calculations.

  8. Spin-nematic and spin-density-wave orders in spatially anisotropic frustrated magnets in a magnetic field.

    PubMed

    Sato, Masahiro; Hikihara, Toshiya; Momoi, Tsutomu

    2013-02-15

    We develop a microscopic theory of finite-temperature spin-nematic orderings in three-dimensional spatially anisotropic magnets consisting of weakly coupled frustrated spin-1/2 chains with nearest-neighbor and next-nearest-neighbor couplings in a magnetic field. Combining a field theoretical technique with density-matrix renormalization group results, we complete finite-temperature phase diagrams in a wide magnetic-field range that possess spin-bond-nematic and incommensurate spin-density-wave ordered phases. The effects of a four-spin interaction are also studied. The relevance of our results to quasi-one-dimensional edge-shared cuprate magnets such as LiCuVO(4) is discussed.

  9. Displacement Fields and Self-Energies of Circular and Polygonal Dislocation Loops in Homogeneous and Layered Anisotropic Solids

    SciTech Connect

    Gao, Yanfei; Larson, Ben C.

    2015-06-19

    There are large classes of materials problems that involve the solutions of stress, displacement, and strain energy of dislocation loops in elastically anisotropic solids, including increasingly detailed investigations of the generation and evolution of irradiation induced defect clusters ranging in sizes from the micro- to meso-scopic length scales. Based on a two-dimensional Fourier transform and Stroh formalism that are ideal for homogeneous and layered anisotropic solids, we have developed robust and computationally efficient methods to calculate the displacement fields for circular and polygonal dislocation loops. Using the homogeneous nature of the Green tensor of order -1, we have shown that the displacement and stress fields of dislocation loops can be obtained by numerical quadrature of a line integral. In addition, it is shown that the sextuple integrals associated with the strain energy of loops can be represented by the product of a pre-factor containing elastic anisotropy effects and a universal term that is singular and equal to that for elastic isotropic case. Furthermore, we have found that the self-energy pre-factor of prismatic loops is identical to the effective modulus of normal contact, and the pre-factor of shear loops differs from the effective indentation modulus in shear by only a few percent. These results provide a convenient method for examining dislocation reaction energetic and efficient procedures for numerical computation of local displacements and stresses of dislocation loops, both of which play integral roles in quantitative defect analyses within combined experimental–theoretical investigations.

  10. The Transport Properties of the Cell Membrane Ion Channels in Electric Fields: Bethe Lattice Treatment

    NASA Astrophysics Data System (ADS)

    Erdem, Rıza; Ekiz, Cesur

    2007-11-01

    The interactive two-state model of cell membrane ion channels in an electric field is formulated on the Bethe lattice by means of the exact recursion relations. The probability of channel opening or maximum fractions of open potassium and sodium channels are obtained by solving a non-linear algebraic equation. Using known parameters for the conventional mean-field theory the model gives a good agreement with the experiment both at low and high trans-membrane potential values. For intermediate voltages, the numerical results imply that collective effects are introduced by trans-membrane voltage.

  11. Hysteresis in random-field Ising model on a Bethe lattice with a mixed coordination number

    NASA Astrophysics Data System (ADS)

    Shukla, Prabodh; Thongjaomayum, Diana

    2016-06-01

    We study zero-temperature hysteresis in the random-field Ising model on a Bethe lattice where a fraction c of the sites have coordination number z = 4 while the remaining fraction 1-c have z = 3. Numerical simulations as well as probabilistic methods are used to show the existence of critical hysteresis for all values of c\\gt 0. This extends earlier results for c = 0 and c = 1 to the entire range 0≤slant c≤slant 1, and provides new insight in non-equilibrium critical phenomena. Our analysis shows that a spanning avalanche can occur on a lattice even in the absence of a spanning cluster of z = 4 sites.

  12. Relevance of Cooperative Lattice Effects and Stress Fields in Phase-Separation Theories for CMR Manganites

    NASA Astrophysics Data System (ADS)

    Burgy, Jan; Moreo, Adriana; Dagotto, Elbio

    2004-03-01

    Previous theoretical investigations of colossal magnetoresistance (CMR) materials explain this effect using a “clustered” state with preformed ferromagnetic islands that rapidly align their moments with increasing external magnetic fields. While qualitatively successful, explicit calculations indicate drastically different typical resistivity values in two- and three-dimensional lattices, contrary to experimental observations. This conceptual bottleneck in the phase-separated CMR scenario is resolved here considering the cooperative nature of the Mn-oxide lattice distortions. This effectively induces power-law correlations in the quenched disorder used in toy models with phase competition. When these effects are incorporated, resistor-network calculations reveal very similar results in two and three dimensions, qualitatively modifying previous scenarios and solving the puzzle.

  13. Instability of field-aligned electron-cyclotron waves in a magnetic mirror plasma with anisotropic temperature

    NASA Astrophysics Data System (ADS)

    Grishanov, N. I.; Azarenkov, N. A.

    2016-08-01

    > Dispersion characteristics have been analysed for field-aligned electron-cyclotron waves (also known as right-hand polarized waves, extraordinary waves or whistlers) in a cylindrical magnetic mirror plasma including electrons with anisotropic temperature. It is shown that the instability of these waves is possible only in the range below the minimal electron-cyclotron frequency, which is much lower than the gyrotron frequency used for electron-cyclotron resonance power input into the plasma, under the condition where the perpendicular temperature of the resonant electrons is larger than their parallel temperature. The growth rates of whistler instability in the two magnetized plasma models, where the stationary magnetic field is either uniform or has a non-uniform magnetic mirror configuration, are compared.

  14. Plane wave propagation in a rotating anisotropic medium with voids under the action of a uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Maity, Narottam; Barik, S. P.; Chaudhuri, P. K.

    2016-09-01

    In this paper, plane wave propagation in a rotating anisotropic material of general nature under the action of a magnetic field of constant magnitude has been investigated. The material is supposed to be porous in nature and contains voids. Following the concept of [Cowin S. C. and Nunziato, J. W. [1983] “Linear elastic materials with voids,” J. Elasticity 13, 125-147.] the governing equations of motion have been written in tensor notation taking account of rotation, magnetic field effect and presence of voids in the medium and the possibility of plane wave propagation has been examined. A number of particular cases have been derived from our general results to match with previously obtained results in this area. Effects of various parameters on the velocity of wave propagation have been presented graphically.

  15. Spark-plasma-sintering magnetic field assisted compaction of Co80Ni20 nanowires for anisotropic ferromagnetic bulk materials

    NASA Astrophysics Data System (ADS)

    Ouar, Nassima; Schoenstein, Frédéric; Mercone, Silvana; Farhat, Samir; Villeroy, Benjamin; Leridon, Brigitte; Jouini, Noureddine

    2013-10-01

    We developed a two-step process showing the way for sintering anisotropic nanostructured bulk ferromagnetic materials. A new reactor has been optimized allowing the synthesis of several grams per batch of nanopowders via a polyol soft chemistry route. The feasibility of the scale-up has been successfully demonstrated for Co80Ni20 nanowires and a massic yield of ˜97% was obtained. The thus obtained nanowires show an average diameter of ˜6 nm and a length of ˜270 nm. A new bottom-up strategy allowed us to compact the powder into a bulk nanostructured system. We used a spark-plasma-sintering technique under uniaxial compression and low temperature assisted by a permanent magnetic field of 1 T. A macroscopic pellet of partially aligned nanowire arrays has been easily obtained. This showed optimized coercive properties along the direction of the magnetic field applied during compaction (i.e., the nanowires' direction).

  16. Field-induced dynamical properties of the XXZ model on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Maksimov, P. A.; Chernyshev, A. L.

    2016-01-01

    We present a comprehensive 1 /S study of the field-induced dynamical properties of the nearest-neighbor XXZ antiferromagnet on a honeycomb lattice using the formalism of nonlinear spin-wave theory developed for this model. The external magnetic field controls spin frustration in the system and induces noncollinearity of the spin structure, which is essential for the two-magnon decay processes. Our results include an intriguing field-evolution of the regions of the Brillouin zone wherein decays of spin excitations are prominent, a detailed classification of the decay channels involving magnons from both excitation branches, and a thorough analysis of the singularities in the magnon spectra due to coupling to the two-magnon continuum, all of which are illustrated for several field and anisotropy values. We highlight a number of features related to either the non-Bravais nature of the lattice or the existence of the Dirac-like points in the spectrum. In addition, the asymptotic behavior of the decay rates near high-symmetry points is analyzed in detail. The inelastic neutron-scattering spin-spin structure factor is obtained in the leading 1 /S order and is shown to exhibit qualitatively distinct fingerprints of the decay-induced magnon dynamics such as quasiparticle peaks broadened by decays and strong spectral weight redistribution.

  17. Phase-field-based lattice Boltzmann finite-difference model for simulating thermocapillary flows

    NASA Astrophysics Data System (ADS)

    Liu, Haihu; Valocchi, Albert J.; Zhang, Yonghao; Kang, Qinjun

    2013-01-01

    A phase-field-based hybrid model that combines the lattice Boltzmann method with the finite difference method is proposed for simulating immiscible thermocapillary flows with variable fluid-property ratios. Using a phase field methodology, an interfacial force formula is analytically derived to model the interfacial tension force and the Marangoni stress. We present an improved lattice Boltzmann equation (LBE) method to capture the interface between different phases and solve the pressure and velocity fields, which can recover the correct Cahn-Hilliard equation (CHE) and Navier-Stokes equations. The LBE method allows not only use of variable mobility in the CHE, but also simulation of multiphase flows with high density ratio because a stable discretization scheme is used for calculating the derivative terms in forcing terms. An additional convection-diffusion equation is solved by the finite difference method for spatial discretization and the Runge-Kutta method for time marching to obtain the temperature field, which is coupled to the interfacial tension through an equation of state. The model is first validated against analytical solutions for the thermocapillary driven convection in two superimposed fluids at negligibly small Reynolds and Marangoni numbers. It is then used to simulate thermocapillary migration of a three-dimensional deformable droplet and bubble at various Marangoni numbers and density ratios, and satisfactory agreement is obtained between numerical results and theoretical predictions.

  18. Phase-field-based lattice Boltzmann finite-difference model for simulating thermocapillary flows.

    PubMed

    Liu, Haihu; Valocchi, Albert J; Zhang, Yonghao; Kang, Qinjun

    2013-01-01

    A phase-field-based hybrid model that combines the lattice Boltzmann method with the finite difference method is proposed for simulating immiscible thermocapillary flows with variable fluid-property ratios. Using a phase field methodology, an interfacial force formula is analytically derived to model the interfacial tension force and the Marangoni stress. We present an improved lattice Boltzmann equation (LBE) method to capture the interface between different phases and solve the pressure and velocity fields, which can recover the correct Cahn-Hilliard equation (CHE) and Navier-Stokes equations. The LBE method allows not only use of variable mobility in the CHE, but also simulation of multiphase flows with high density ratio because a stable discretization scheme is used for calculating the derivative terms in forcing terms. An additional convection-diffusion equation is solved by the finite difference method for spatial discretization and the Runge-Kutta method for time marching to obtain the temperature field, which is coupled to the interfacial tension through an equation of state. The model is first validated against analytical solutions for the thermocapillary driven convection in two superimposed fluids at negligibly small Reynolds and Marangoni numbers. It is then used to simulate thermocapillary migration of a three-dimensional deformable droplet and bubble at various Marangoni numbers and density ratios, and satisfactory agreement is obtained between numerical results and theoretical predictions. PMID:23410429

  19. Intentional anisotropic strain relaxation in (112{sup ¯}2) oriented Al{sub 1−x}In{sub x}N one-dimensionally lattice matched to GaN

    SciTech Connect

    Buß, E. R. Rossow, U.; Bremers, H.; Hangleiter, A.; Meisch, T.; Caliebe, M.; Scholz, F.

    2014-09-22

    We report on (112{sup ¯}2) oriented Al{sub 1−x}In{sub x}N grown by low pressure metal organic vapor phase epitaxy on (112{sup ¯}2) GaN templates on patterned r-plane sapphire. The indium incorporation efficiency as well as the growth rate of (112{sup ¯}2) oriented layers are similar to c-plane oriented Al{sub 1−x}In{sub x}N layers. Deposition of thick Al{sub 1−x}In{sub x}N layers does not lead to additional roughening like in case of c-plane oriented Al{sub 1−x}In{sub x}N. Independent of the thickness, the degree of relaxation of layers lattice matched in m-direction is in the range of 33%–45% in [112{sup ¯}3{sup ¯}]-direction. Associated with the relaxation in [112{sup ¯}3{sup ¯}]-direction, there is a tilt of the Al{sub 1−x}In{sub x}N layers around the [11{sup ¯}00] axis due to slip of threading dislocations on the basal (0001)-plane. Relaxation in m-direction is not observable for layers lattice matched in [112{sup ¯}3{sup ¯}] direction. The possibility to adjust the lattice parameter of AlInN in [112{sup ¯}3{sup ¯}] direction without changing the lattice parameter in m-direction by anisotropic strain relaxation opens up opportunities for subsequent growth of optically active structures. One possibility is to form relaxed buffer layers for GaInN quantum well structures.

  20. Anisotropic propagator for the Goldstone modes in color-flavor locked phase in the presence of a magnetic field

    NASA Astrophysics Data System (ADS)

    Sen, Srimoyee

    2015-07-01

    We consider the phase diagram of QCD at very high baryon density and at zero temperature in the presence of a strong magnetic field. The state of matter at such high densities and low temperatures is believed to be a phase known as the color-flavor locked phase which breaks color and electromagnetic gauge invariance, leaving a linear combination of them, denoted as U (1 )e m ˜ , unbroken. Of the nine quarks (three flavors and three colors), five are neutral under this unbroken generator and four are oppositely charged (two with a charge of +1 and two with -1 ). In the presence of a magnetic field corresponding to U (1 )em ˜, however, the properties of the condensate change and a new phase known as the magnetic color-flavor locked (MCFL) phase is realized. This phase breaks an approximate S U (3 )C×S U (2 )L×S U (2 )R×U (1 )B×U (1 )A- symmetry of the Lagrangian to S U (2 )C+L +R×U (1 )em ˜ giving rise to six Goldstone modes, five of which are pseudo Goldstone modes. These Goldstone modes are composed of excitations that correspond to both neutral quarks and charged quarks. Hence it is natural to expect that the propagators of these Goldstone modes are affected in the presence of a magnetic field, and their speed becomes considerably anisotropic. Although this anisotropy is self-evident from symmetry arguments, it has not been quantified yet. We calculate this anisotropy in the speed of the Goldstone modes using a Nambu-Jona-Lasinio model type of interaction between the quarks and comment on the impact of such anisotropic modes on transport properties of the MCFL phase.

  1. Critical-field theory of the Kondo lattice model in two dimensions

    SciTech Connect

    Kim, Ki-Seok

    2005-05-15

    In the context of the U(1) slave-boson theory we derive a critical-field theory near the quantum-critical point of the Kondo lattice model in two spatial dimensions. First, we argue that strong gauge fluctuations in the U(1) slave-boson theory give rise to confinement between spinons and holons, thus causing 'neutralized' spinons in association with the slave-boson U(1) gauge field. Second, we show that critical fluctuations of Kondo singlets near the quantum-critical point result in a new U(1) gauge field. This emergent gauge field has nothing to do with the slave-boson U(1) gauge field. Third, we find that the slave-boson U(1) gauge field can be exactly integrated out in the low-energy limit. As a result we find a critical-field theory in terms of renormalized conduction electrons and neutralized spinons interacting via the new emergent U(1) gauge field. Based on this critical-field theory we obtain the temperature dependence of the specific heat and the imaginary part of the self-energy of the renormalized electrons. These quantities display non-Fermi-liquid behavior near the quantum-critical point.

  2. GPU phase-field lattice Boltzmann simulations of growth and motion of a binary alloy dendrite

    NASA Astrophysics Data System (ADS)

    Takaki, T.; Rojas, R.; Ohno, M.; Shimokawabe, T.; Aoki, T.

    2015-06-01

    A GPU code has been developed for a phase-field lattice Boltzmann (PFLB) method, which can simulate the dendritic growth with motion of solids in a dilute binary alloy melt. The GPU accelerated PFLB method has been implemented using CUDA C. The equiaxed dendritic growth in a shear flow and settling condition have been simulated by the developed GPU code. It has been confirmed that the PFLB simulations were efficiently accelerated by introducing the GPU computation. The characteristic dendrite morphologies which depend on the melt flow and the motion of the dendrite could also be confirmed by the simulations.

  3. Dynamics of an Electron in a Magnetic Field and in a Periodic Lattice

    NASA Astrophysics Data System (ADS)

    Adorjan, A. J.; Kaufman, M.

    1996-11-01

    We study the trajectory and the time dependence of the velocity of an electron moving in a 2d crystal in the presence of a magnetic field. This model is relevant to artificial 2d lattices(T.Geisel, J.Wagenhuber, P.Niebauer, G.Obermair, Phys.Rev.Lett.64,1581(1990)). The model is analyzed numerically by approximating the differential equations of motion with difference equations. To perform the calculations we use the mathematical package MathCad. We plan to use this study in undergraduate classes as an as an example of a research topic of current interest.

  4. Creation of Scalar and Dirac Particles in the Presence of a Time Varying Electric Field in an Anisotropic Universe

    NASA Astrophysics Data System (ADS)

    Villalba, Víctor M.

    We compute the density of scalar and Dirac particles created by a cosmological anisotropic universe1,2 in the presence of a time dependent homogeneous electric field. In order to compute the rate of particles created we apply a quasiclassical approach that has been used successfully in different scenarios3,4. The idea behind the method is the following: First, we solve the relativistic Hamilton-Jacobi equation and, looking at its solutions, we identify positive and negative frequency modes. Second, after separating variables5,6, we solve the Klein-Gordon and Dirac equations and, after comparing with the results obtained for the quasiclassical limit, we identify the positive and negative frequency states. We show that the particle distribution becomes thermal when one neglects the electric interaction.

  5. Field-induced dynamical properties of the XXZ model on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Maksimov, Pavel; Chernyshev, Alexander

    We present a comprehensive 1 / S study of the field-induced dynamical properties of the nearest-neighbor XXZ antiferromagnet on a honeycomb lattice using the formalism of the nonlinear spin-wave theory developed for this model. External magnetic field controls spin frustration in the system and induces non-collinearity of the spin structure, which is essential for the two-magnon decay processes. Our results include an intriguing field-evolution of the regions of the Brillouin zone where decays of spin excitations are prominent, a thorough analysis of the singularities in the magnon spectra due to coupling to the two-magnon continuum, the asymptotic behavior of the decay rates near high-symmetry points, and inelastic neutron-scattering spin-spin structure factor obtained in the leading 1 / S order. Supported by DOE.

  6. Analysis of two-dimensional photonic crystal with anisotropic gain.

    PubMed

    Takigawa, Shinichi; Noda, Susumu

    2011-05-01

    Photonic modes in a two-dimensional square-lattice photonic crystal (PC) with anisotropic gain are analyzed for the first time. A plane-wave expansion method is improved to include the gain, which depends on not only the position but also the propagation direction of each plane wave. The anisotropic gain varies the photonic band structure, the near-field distributions, and the gain dispersion curves through variation in PC symmetry. Low-threshold operation of a PC laser with anisotropic-gain material such as nonpolar InGaN requires that the direction of higher gain in the material aligns along the ΓX direction of the PC. PMID:21643205

  7. Displacement Fields and Self-Energies of Circular and Polygonal Dislocation Loops in Homogeneous and Layered Anisotropic Solids

    DOE PAGESBeta

    Gao, Yanfei; Larson, Ben C.

    2015-06-19

    There are large classes of materials problems that involve the solutions of stress, displacement, and strain energy of dislocation loops in elastically anisotropic solids, including increasingly detailed investigations of the generation and evolution of irradiation induced defect clusters ranging in sizes from the micro- to meso-scopic length scales. Based on a two-dimensional Fourier transform and Stroh formalism that are ideal for homogeneous and layered anisotropic solids, we have developed robust and computationally efficient methods to calculate the displacement fields for circular and polygonal dislocation loops. Using the homogeneous nature of the Green tensor of order -1, we have shown thatmore » the displacement and stress fields of dislocation loops can be obtained by numerical quadrature of a line integral. In addition, it is shown that the sextuple integrals associated with the strain energy of loops can be represented by the product of a pre-factor containing elastic anisotropy effects and a universal term that is singular and equal to that for elastic isotropic case. Furthermore, we have found that the self-energy pre-factor of prismatic loops is identical to the effective modulus of normal contact, and the pre-factor of shear loops differs from the effective indentation modulus in shear by only a few percent. These results provide a convenient method for examining dislocation reaction energetic and efficient procedures for numerical computation of local displacements and stresses of dislocation loops, both of which play integral roles in quantitative defect analyses within combined experimental–theoretical investigations.« less

  8. Microscopic 57 Fe electric-field-gradient and anisotropic mean-squared-displacement tensors: ferrous chloride tetrahydrate

    NASA Astrophysics Data System (ADS)

    Bull, James N.; Fitchett, Christopher M.; Tennant, W. Craighead

    2010-06-01

    This paper reports the determination of the electric-field-gradient and mean-squared-displacement tensors in 57Fe symmetry-related sites of bar {1} Laue class in monoclinic FeCl2.4H2O at room temperature by single-crystal Mössbauer spectroscopy. Contrary to all previous work, the mean-squared-displacement matrix (tensor), , is not constrained to be isotropic resulting in the determination of physically meaningful estimates of microscopic (local) electric-field gradient (efg) and tensors. As a consequence of anisotropy in the tensor the absorber recoilless fractions are also anisotropic. As expected of a low-symmetry site, Laue class bar{1} in this case, no two principal axes of the efg and tensors are coaxial, within the combined errors in the two. Further, no principal direction of the efg tensor seems related to bond directions in the unit cell. Within error, and in agreement with an earlier study of sodium nitroprusside, it appears that the tensor principal directions lie close to the crystallographic axes suggesting that they are determined by long wavelength (phonon) vibrations in the crystal rather than by approximate local symmetry about the 57Fe nucleus. Concurrent with the Mössbauer measurements, we determined as part of a new X-ray structural determination, precise atomic displacement parameters (ADPs) leading to an alternative determination of the matrix (tensor). The average of the eigenvalues of the Mössbauer-determined exceeds that of the average of the X-ray-determined eigenvalues by a factor of around 2.2. Assuming isotropic absorber recoilless fractions leads to substantially the same (macroscopic) efg tensor as had been determined in earlier work. Taking 1/3× the trace of the anisotropic absorber recoilless fractions leads to an isotropic value of 0.304 in good agreement with earlier single crystal studies where isotropy was assumed.

  9. Spin-lattice relaxation within a dimerized Ising chain in a magnetic field

    SciTech Connect

    Erdem, Rıza E-mail: rerdem29@hotmail.com; Gülpınar, Gül; Yalçın, Orhan; Pawlak, Andrzej

    2014-07-21

    A qualitative study of the spin-lattice relaxation within a dimerized Ising chain in a magnetic field is presented. We have first determined the time dependence of the deviation of the lattice distortion parameter δΔ from the equilibrium state within framework of a technique combining the statistical equilibrium theory based on the transfer matrix method and the linear theory of irreversible thermodynamics. We have shown that the time dependence of the lattice distortion parameter is characterized by a single time constant (τ) which diverges around the critical point in both dimerized (Δ≠0) and uniform (Δ=0) phase regions. When the temperature and magnetic field are fixed to certain values, the time τ depends only on exchange coupling between the spins. It is a characteristic time associated with the long wavelength fluctuations of distortion. We have also taken into account the effects of spatial fluctuations on the relaxation time using the full Landau-Ginzburg free energy functional. We have found an explicit expression for the relaxation time as a function of temperature, coupling constant and wave vector (q) and shown that the critical mode corresponds to the case q=0. Finally, our results are found to be in good qualitative agreement with the results obtained in recent experimental study on synchrotron x-ray scattering and muon spin relaxation in diluted material Cu{sub 1−y}Mg{sub y}GeO{sub 3} where the composition y is very close to 0.0209. These results can be considered as natural extensions of some previous works on static aspects of the problem.

  10. Extracting Electric Polarizabilities from Lattice QCD

    SciTech Connect

    Will Detmold, William Detmold, Brian Tiburzi, Andre Walker-Loud

    2009-05-01

    Charged and neutral, pion and kaon electric polarizabilities are extracted from lattice QCD using an ensemble of anisotropic gauge configurations with dynamical clover fermions. We utilize classical background fields to access the polarizabilities from two-point correlation functions. Uniform background fields are achieved by quantizing the electric field strength with the proper treatment of boundary flux. These external fields, however, are implemented only in the valence quark sector. A novel method to extract charge particle polarizabilities is successfully demonstrated for the first time.

  11. Angular spectrum method and ray algorithm for the acoustic field of a focusing transducer in an anisotropic solid.

    PubMed

    Every, Arthur G; Amulele, George M

    2002-03-01

    The angular spectrum method is applied to calculating the acoustic field of a liquid-coupled focusing transducer in an anisotropic slab-shaped solid with surfaces normal to the axis of the transducer. The stationary phase approximation (SPA) is used to determine the dominant contributions to this field and calculate the echo signals produced by waves that have been reflected off the rear surface of the solid. The dominant features of this field and of the echoes are reproduced well by a hybrid ray method devised to simulate the finite point-spread function of the lens. Both approaches in the paraxial approximation yield a split focus for each wave polarization branch for a general direction of the surface normal. Echo arrival times and amplitudes calculated by the two methods are in good agreement. The hybrid ray method is shown to be particularly suited to handling multiple stationary phase points within the angular spectrum of the incident field and stationary phase points not associated with the normally incident ray, and should be useful for dealing with scattering from cracks and other defects. Pulse echo calculations for different crystallographic directions in a nickel-based superalloy are shown to be in good agreement with measurements carried out on single crystal specimens of the alloy. PMID:12322879

  12. Angular spectrum method and ray algorithm for the acoustic field of a focusing transducer in an anisotropic solid.

    PubMed

    Every, Arthur G; Amulele, George M

    2002-03-01

    The angular spectrum method is applied to calculating the acoustic field of a liquid-coupled focusing transducer in an anisotropic slab-shaped solid with surfaces normal to the axis of the transducer. The stationary phase approximation (SPA) is used to determine the dominant contributions to this field and calculate the echo signals produced by waves that have been reflected off the rear surface of the solid. The dominant features of this field and of the echoes are reproduced well by a hybrid ray method devised to simulate the finite point-spread function of the lens. Both approaches in the paraxial approximation yield a split focus for each wave polarization branch for a general direction of the surface normal. Echo arrival times and amplitudes calculated by the two methods are in good agreement. The hybrid ray method is shown to be particularly suited to handling multiple stationary phase points within the angular spectrum of the incident field and stationary phase points not associated with the normally incident ray, and should be useful for dealing with scattering from cracks and other defects. Pulse echo calculations for different crystallographic directions in a nickel-based superalloy are shown to be in good agreement with measurements carried out on single crystal specimens of the alloy.

  13. Regional electric field induced by electroconvulsive therapy in a realistic finite element head model: influence of white matter anisotropic conductivity.

    PubMed

    Lee, Won Hee; Deng, Zhi-De; Kim, Tae-Seong; Laine, Andrew F; Lisanby, Sarah H; Peterchev, Angel V

    2012-02-01

    We present the first computational study investigating the electric field (E-field) strength generated by various electroconvulsive therapy (ECT) electrode configurations in specific brain regions of interest (ROIs) that have putative roles in the therapeutic action and/or adverse side effects of ECT. This study also characterizes the impact of the white matter (WM) conductivity anisotropy on the E-field distribution. A finite element head model incorporating tissue heterogeneity and WM anisotropic conductivity was constructed based on structural magnetic resonance imaging (MRI) and diffusion tensor MRI data. We computed the spatial E-field distributions generated by three standard ECT electrode placements including bilateral (BL), bifrontal (BF), and right unilateral (RUL) and an investigational electrode configuration for focal electrically administered seizure therapy (FEAST). The key results are that (1) the median E-field strength over the whole brain is 3.9, 1.5, 2.3, and 2.6 V/cm for the BL, BF, RUL, and FEAST electrode configurations, respectively, which coupled with the broad spread of the BL E-field suggests a biophysical basis for observations of superior efficacy of BL ECT compared to BF and RUL ECT; (2) in the hippocampi, BL ECT produces a median E-field of 4.8 V/cm that is 1.5-2.8 times stronger than that for the other electrode configurations, consistent with the more pronounced amnestic effects of BL ECT; and (3) neglecting the WM conductivity anisotropy results in E-field strength error up to 18% overall and up to 39% in specific ROIs, motivating the inclusion of the WM conductivity anisotropy in accurate head models. This computational study demonstrates how the realistic finite element head model incorporating tissue conductivity anisotropy provides quantitative insight into the biophysics of ECT, which may shed light on the differential clinical outcomes seen with various forms of ECT, and may guide the development of novel stimulation paradigms

  14. Cluster dynamic mean-field study on the superconductivity in doped honeycomb lattice Hubbard model

    NASA Astrophysics Data System (ADS)

    Xu, Xiao Yan; Dang, Hung T.; Wessel, Stefen; Meng, Zi Yang

    The issue of superconductivities emerging from doped honeycomb lattice Mott insulator remains inconclusive. Existing proposals, such as p+ip triplet pairing driven by ferromagnetic fluctuations, d+id singlet pairing driven by antiferromagnetic fluctuations or van Hove singularities in the band structure, are not compatible. This is mainly due to the limitation of various approximated techniques employed in addressing such question with inherent strongly correlated nature. Trying to clarify the situation, we perform large-scale cluster dynamic mean-field simulations to explore the superconductivity instabilities in the doped honeycomb lattice Hubbard model, from medium to strong coupling. To benchmark, we make use of both interaction- and hybridization-expansion continuous time quantum Monte Carlo methods to exactly solve the quantum cluster embedded in self-consistently determined mean-field bath. Temperature dependence of various superconducting susceptibilities are calculated, hence, we provide the least biased results of the competition of the superconductivity in different channels in the phase diagram spanned by doping and electronic interaction.

  15. Bogoliubov theory of interacting bosons on a lattice in a synthetic magnetic field

    SciTech Connect

    Powell, Stephen; Barnett, Ryan; Sensarma, Rajdeep; Das Sarma, Sankar

    2011-01-15

    We consider theoretically the problem of an artificial gauge potential applied to a cold atomic system of interacting neutral bosons in a tight-binding optical lattice. Using the Bose-Hubbard model, we show that an effective magnetic field leads to superfluid phases with simultaneous spatial order, which we analyze using Bogliubov theory. This gives a consistent expansion in terms of quantum and thermal fluctuations, in which the lowest order gives a Gross-Pitaevskii equation determining the condensate configuration. We apply an analysis based on the magnetic symmetry group to show how the spatial structure of this configuration depends on commensuration between the magnetic field and the lattice. Higher orders describe the quasiparticle excitations, whose spectrum combines the intricacy of the Hofstadter butterfly with the characteristic features of the superfluid phase. We use the depletion of the condensate to determine the range of validity of our approximations and also to find an estimate for the onset of the Mott insulator phase. Our theory provides concrete experimental predictions for both time-of-flight imagery and Bragg spectroscopy.

  16. Hydraulic-fracture growth in dipping anisotropic strata as viewed through the surface deformation field

    SciTech Connect

    Holzhausen, G.R.; Haase, C.S.; Stow, S.H.; Gazonas, G.

    1985-01-01

    In 1983 and 1984 Oak Rdige National Laboratory conducted a series of precision ground deformation measurements before, during, and after the generation of several large hydraulic fractures in a dipping member of the Cambrian Conasauga Shale. Each fracture was produced by the injection of approximately 500,000 L of slurry on a single day. Injection depth was 300 m. Leveling surveys were run several days before and several days after the injections. An array of eight high-precision borehole tiltmeters monitored ground deformations continuously for a period of several weeks. Analysis of the leveling and the tilt measurements revealed surface uplifts as great as 25 mm and tilts of tens of microradians during each injection. Furthermore, partial recovery (subsidence) of the ground took place during the days following an injection, accompanied by shifts in the position of maximum resultant uplift. Interpretation of the tilt measurements is consistent with stable widening and extension of hydraulic fractures with subhorizontal orientations. Comparison of the measured tilt patterns with fracture orientations established from logging of observation wells suggests that shearing parallel to the fracture planes accompanied fracture dilation. This interpretation is supported by measured tilts and ground uplifts that were as much as 100 percent greater than those expected from fracture dilation alone. Models of elastically anisotropic overburden rock do not explain the measured tilt patterns in the absence of shear stresses in the fracture planes. This work represents the first large-scale hydraulic-fracturing experiment in which the possible effects of material anisotropy and fracture-parallel shears have been measured and interpreted.

  17. Thermodynamic properties of anisotropic spin ladder in a longitudinal magnetic field

    NASA Astrophysics Data System (ADS)

    Rezania, H.

    2015-08-01

    We address thermodynamic properties of quasi-one dimensional two leg antiferromagnetic ladder in the presence of magnetic field. A generalized bond operator formalism is used to transform the spin model to a hard core bosonic gas. We have implemented Green's function approach to obtain the temperature dependence of spin excitation spectrum in field induced spin polarized phase. The results show energy gap that vanishes at critical magnetic field for fixed values of temperatures. We have also found the temperature dependence of the specific heat and magnetization component in the magnetic field direction for various magnetic field strengths and anisotropies in the Heisenberg interactions on both leg and rung couplings. At low temperatures, the specific heat is found to be monotonically increasing with temperature for magnetic fields in the spin polarized phase region. Furthermore we studied the temperature dependence of the longitudinal magnetization for different magnetic field and anisotropy parameters.

  18. Mean-field dynamics of two-mode Bose-Einstein condensates in highly anisotropic potentials: interference, dimensionality and entanglement

    NASA Astrophysics Data System (ADS)

    Tacla, Alexandre B.; Caves, Carlton M.

    2013-02-01

    We study the mean-field dynamics and the reduced-dimension character of two-mode Bose-Einstein condensates (BECs) in highly anisotropic traps. By means of perturbative techniques, we show that the tightly confined (transverse) degrees of freedom can be decoupled from the dynamical equations at the expense of introducing additional effective three-body, attractive, intra- and inter-mode interactions into the dynamics of the loosely confined (longitudinal) degrees of freedom. These effective interactions are mediated by changes in the transverse wave function. The perturbation theory is valid as long as the nonlinear scattering energy is small compared to the transverse energy scales. This approach leads to reduced-dimension mean-field equations that optimally describe the evolution of a two-mode condensate in general quasi-one-dimensional (1D) and quasi-two-dimensional geometries. We use this model to investigate the relative phase and density dynamics of a two-mode, cigar-shaped 87Rb BEC. We study the relative-phase dynamics in the context of a nonlinear Ramsey interferometry scheme, which has recently been proposed as a novel platform for high-precision interferometry. Numerical integration of the coupled, time-dependent, three-dimensional, two-mode Gross-Pitaevskii equations for various atom numbers shows that this model gives a considerably more refined analytical account of the mean-field evolution than an idealized quasi-1D description.

  19. Determination of dimensional flow fields in hydrogeological settings via the MRT lattice-Boltzmann method

    NASA Astrophysics Data System (ADS)

    Hilpert, Markus

    2011-09-01

    In this paper we demonstrate how the single and multiple-relaxation-time (MRT) lattice-Boltzmann (LB) method can be used to simulate hydrogeological flows under standard conditions. We explain in detail how real-world hydrogeological flow problems, which are formulated in terms of dimensional boundary and initial conditions, can be related to the nondimensional LB world, in which both the lattice spacing and the time step are nondimensional and typically set to unity. We first demonstrate the method in two examples where analytical solutions are known: steady state and transient flow of water in a square duct where fluid inertia is either negligible or not, respectively. Finally we simulate the flow of water in a sand where inertial forces are not negligible. For steady state flow we also present equations for calculating the permeability. Moreover, we demonstrate and advocate the usage of Richardson's extrapolation, which allows one to estimate LB modeling results for an infinite numerical resolution that include uncertainty intervals. For pressure-driven simulations of steady state creeping flow, we show how one can improve the numerical convergence behavior by performing "light-water" simulations at a lower Reynolds number while still predicting the correct velocity field.

  20. ERL with non-scaling fixed field alternating gradient lattice for eRHIC

    SciTech Connect

    Trbojevic, D.; Berg, J. S.; Brooks, S.; Hao, Y.; Litvinenko, V. N.; Liu, C.; Meot, F.; Minty, M.; Ptitsyn, V.; Roser, T.; Thieberger, P.; Tsoupas, N.

    2015-05-03

    The proposed eRHIC electron-hadron collider uses a "non-scaling FFAG" (NS-FFAG) lattice to recirculate 16 turns of different energy through just two beam lines located in the RHIC tunnel. This paper presents lattices for these two FFAGs that are optimized for low magnet field and to minimize total synchrotron radiation across the energy range. The higher number of recirculations in the FFAG allows a shorter linac (1.322GeV) to be used, drastically reducing cost, while still achieving a 21.2 GeV maximum energy to collide with one of the existing RHIC hadron rings at up to 250GeV. eRHIC uses many cost-saving measures in addition to the FFAG: the linac operates in energy recovery mode, so the beams also decelerate via the same FFAG loops and energy is recovered from the interacted beam. All magnets will be constructed from NdFeB permanent magnet material, meaning chillers and large magnet power supplies are not needed. This paper also describes a small prototype ERL-FFAG accelerator that will test all of these technologies in combination to reduce technical risk for eRHIC.

  1. ANALYTIC SOLUTIONS FOR CURRENT SHEET STRUCTURE DETERMINED BY SELF-CONSISTENT, ANISOTROPIC TRANSPORT PROCESSES IN A GRAVITATIONAL FIELD

    SciTech Connect

    Goodman, Michael L.

    2011-04-10

    A Harris sheet magnetic field with maximum magnitude B{sub 0} and length scale L is combined with the anisotropic electrical conductivity, viscosity, and thermoelectric tensors for an electron-proton plasma to define a magnetohydrodynamic model that determines the steady state of the plasma. The transport tensors are functions of temperature, density, and magnetic field strength, and are computed self-consistently as functions of position x normal to the current sheet. The flow velocity, magnetic field, and gravitational force lie along the z-axis. The plasma is supported against gravity by the viscous force. Analytic solutions are obtained for temperature, density, and velocity. They are valid over a broad range of temperature, density, and magnetic field strength, and so may be generally useful in astrophysical applications. Numerical examples of solutions in the parameter range of the solar atmosphere are presented. The objective is to compare Joule and viscous heating rates, determine the velocity shear that generates viscous forces that support the plasma and are self-consistent with a mean outward mass flux comparable to the solar wind mass flux, and compare the thermoelectric and conduction current contributions to the Joule heating rate. The ratio of the viscous to Joule heating rates per unit mass can exceed unity by orders of magnitude, and increases rapidly with L. The viscous heating rate can be concentrated outside the region where the current density is localized, corresponding to a resistively heated layer of plasma bounded by viscously heated plasma. The temperature gradient drives a thermoelectric current density that can have a magnitude greater than that of the electric-field-driven conduction current density, so thermoelectric effects are important in determining the Joule heating rate.

  2. Highly anisotropic exchange interactions of jeff=1/2 iridium moments on the fcc lattice in La2B IrO6 (B =Mg ,Zn )

    NASA Astrophysics Data System (ADS)

    Aczel, A. A.; Cook, A. M.; Williams, T. J.; Calder, S.; Christianson, A. D.; Cao, G.-X.; Mandrus, D.; Kim, Yong-Baek; Paramekanti, A.

    2016-06-01

    We have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites La2ZnIrO6 and La2MgIrO6 , which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated jeff=1/2 Mott insulators provide clear evidence for gapped spin-wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in jeff=1/2 Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly directional Kitaev interaction is a type of exchange anisotropy which is symmetry allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order by disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry lowering due to lattice distortions can pin the order and enhance the magnon gap. Our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly directional exchange interactions rooted in strong spin-orbit coupling.

  3. Highly anisotropic exchange interactions of jeff=12 iridium moments on the fcc lattice in La2BIrO6 (B=Mg,Zn)

    DOE PAGESBeta

    Aczel, A. A.; Cook, A. M.; Williams, T. J.; Calder, S.; Christianson, A. D.; Cao, G. -X.; Mandrus, D.; Kim, Yong-Baek; Paramekanti, A.

    2016-06-20

    Here we have performed inelastic neutron scattering (INS) experiments to investigate the magnetic excitations in the weakly distorted face-centered-cubic (fcc) iridate double perovskites Lamore » $_2$ZnIrO$_6$ and La$_2$MgIrO$_6$, which are characterized by A-type antiferromagnetic ground states. The powder inelastic neutron scattering data on these geometrically frustrated $$j_{\\rm eff}=1/2$$ Mott insulators provide clear evidence for gapped spin wave excitations with very weak dispersion. The INS results and thermodynamic data on these materials can be reproduced by conventional Heisenberg-Ising models with significant uniaxial Ising anisotropy and sizeable second-neighbor ferromagnetic interactions. Such a uniaxial Ising exchange interaction is symmetry-forbidden on the ideal fcc lattice, so that it can only arise from the weak crystal distortions away from the ideal fcc limit. This may suggest that even weak distortions in $$j_{\\rm eff}=1/2$$ Mott insulators might lead to strong exchange anisotropies. More tantalizingly, however, we find an alternative viable explanation of the INS results in terms of spin models with a dominant Kitaev interaction. In contrast to the uniaxial Ising exchange, the highly-directional Kitaev interaction is a type of exchange anisotropy which is symmetry-allowed even on the ideal fcc lattice. The Kitaev model has a magnon gap induced by quantum order-by-disorder, while weak anisotropies of the Kitaev couplings generated by the symmetry-lowering due to lattice distortions can pin the order and enhance the magnon gap. In conclusion, our findings highlight how even conventional magnetic orders in heavy transition metal oxides may be driven by highly-directional exchange interactions rooted in strong spin-orbit coupling.« less

  4. Spin structure of the anisotropic helimagnet Cr{sub 1∕3}NbS{sub 2} in a magnetic field

    SciTech Connect

    Chapman, Benjamin J.; Bornstein, Alexander C.; Lee, Minhyea; Ghimire, Nirmal J.; Mandrus, David

    2014-08-18

    In this letter, we describe the ground-state magnetic structure of the highly anisotropic helimagnet Cr{sub 1∕3}NbS{sub 2} in a magnetic field. A Heisenberg spin model with Dyzaloshinkii-Moriya interactions and magnetocrystalline anisotropy allows the ground state spin structure to be calculated for magnetic fields of arbitrary strength and direction. Comparison with magnetization measurements shows excellent agreement with the predicted spin structure.

  5. The polarization electric field and its effects in an anisotropic rotating magnetospheric plasma

    NASA Technical Reports Server (NTRS)

    Huang, T. S.; Birmingham, T. J.

    1992-01-01

    Spatial variations of density and temperature along a magnetic field line are evaluated for a plasma undergoing adiabatic motion in a rotating magnetosphere. The effects of centrifugal and gravitational forces are accounted for, as is anisotropy in the pitch angle distribution functions of individual species. A polarization electric field is invoked to eliminate the net electric charge density resulting from the aforementioned mass dependent forces and different anisotropies. The position of maximum density in a two-component, electron-ion plasma is determined both in the absence and in the presence of the polarization effect and compared. A scale height, generalized to include anisotropies, is derived for the density fall-off. The polarization electric field is also included in the parallel guiding center equation; equilibrium points are determined and compared in both individual and average senses with the position of density maximum. Finally a transverse (to magnetic field lines) electric component is deduced as a consequence of dissimilar charge neutralization on adjacent field lines. The E x B velocity resultant from such a 'fringing' electric field is calculated and compared with the magnitude of other drifts.

  6. Consistent simulation of droplet evaporation based on the phase-field multiphase lattice Boltzmann method.

    PubMed

    Safari, Hesameddin; Rahimian, Mohammad Hassan; Krafczyk, Manfred

    2014-09-01

    In the present article, we extend and generalize our previous article [H. Safari, M. H. Rahimian, and M. Krafczyk, Phys. Rev. E 88, 013304 (2013)] to include the gradient of the vapor concentration at the liquid-vapor interface as the driving force for vaporization allowing the evaporation from the phase interface to work for arbitrary temperatures. The lattice Boltzmann phase-field multiphase modeling approach with a suitable source term, accounting for the effect of the phase change on the velocity field, is used to solve the two-phase flow field. The modified convective Cahn-Hilliard equation is employed to reconstruct the dynamics of the interface topology. The coupling between the vapor concentration and temperature field at the interface is modeled by the well-known Clausius-Clapeyron correlation. Numerous validation tests including one-dimensional and two-dimensional cases are carried out to demonstrate the consistency of the presented model. Results show that the model is able to predict the flow features around and inside an evaporating droplet quantitatively in quiescent as well as convective environments. PMID:25314562

  7. Anisotropic magnetostriction in a <110> oriented crystal Tb0.36Dy0.64(Fe0.85Co0.15)2 after coaxial field annealing

    NASA Astrophysics Data System (ADS)

    Zhang, Changsheng; Ma, Tianyu; Qi, Ruilei; Yan, Mi

    2010-08-01

    Axial magnetostriction of Terfenol-D oriented crystals is highly anisotropic when changing the magnetization direction. Magnetostrictions of a ⟨110⟩ oriented crystal Tb0.36Dy0.64(Fe0.85Co0.15)2 were investigated under magnetic fields with a series of angles θ to its axis. Totally different anisotropic magnetostrictive behaviors are observed after annealing under a coaxial field of 240 kA/m. The magnetostriction for the field annealed specimen seems unsaturated even under 640 kA/m for angles θ in the range from 0° to 55°. At these angles, magnetostriction "ascending" is observed during the final magnetization process, while magnetostriction "dropping" occurs at angles above 35° for the untreated crystal. With the increase in angle θ, the corresponding field where magnetostriction starts dropping decreases for the untreated crystal, while the field at which magnetostriction starts ascending increases for the field annealed one. A simplified model based on moment "jump" and "rotation" is proposed to explain such anisotropic behaviors.

  8. LDN 1780: A Translucent High-Galactic Latitude Interstellar Cloud in a UV-rich, Anisotropic Radiation Field

    NASA Astrophysics Data System (ADS)

    DeRoo, Casey T.; Witt, A. N.; Barnes, F. S., III; Vijh, U. P.; Gordon, K. D.

    2010-01-01

    We combined high-resolution optical imaging observations in 12 intermediate-band (BATC) filter and deep mid- and far-IR Spitzer maps of LDN 1780 to characterize the external radiation field illuminating this high-latitude (l = 359 deg; b = 36.5 deg; distance 100 pc) translucent cloud and the infrared emission of dust within LDN 1780 in response to this external illumination. The overall energy density of the incident radiation field is approximately equal to that of the ISRF near the Sun, resulting in a large dust grain equilibrium temperature ranging from 14.5 K -16.8 K. However, the incident radiation field is highly anisotropic, with the southern portions of LDN 1780 being most strongly illuminated, especially at shorter wavelengths. This anisotropy is a result of the cloud's proximity to the Sco OB2 association (est. center: l = 322 deg; b = 10 deg). The southwestern portion and the optically-thin eastern tail of LDN 1780 exhibit strong intensity excesses at 24 micron (Spitzer MIPS) and at 8 micron (Spitzer IRAC Ch. #4) compared to dust in the diffuse ISM of the Milky Way Galaxy. We interpret these excesses as enhanced emission from stochastically-heated very small grains (VSG) and from PAH ions, respectively. These excesses, however, are not necessarily the result a greater relative abundance of these two small-particle components but rather reflect the increased frequency of photon-grain interactions (e.g. heating, excitation, or ionization) within a UV-rich radiation field. This research has been supported by grants from NASA and the NSF to the University of Toledo as well as by contributions from corporate sponsors AstroDon, RC Optical Systems, Santa Barbara Instrument Group, Software Bisque, and New Mexico Skies, for which we are grateful. We especially acknowledge the NSF-REU program at the University of Toledo, which supported the analysis of these data.

  9. Observation of the vortex lattice melting by NMR spin-lattice relaxation in the mixed state

    SciTech Connect

    Bulaevskii, L.N.; Hammel, P.C.; Vinokur, V.M.

    1994-01-01

    For anisotropic layered superconductors the effect of moving vortices on the nuclear spin magnetization is calculated. Current is supposed to flow along layers, and applied magnetic field is tilted with respect to c-axis. In the solid phase the motion of the vortex lattice produces an alternating magnetic field perpendicular to the applied field which causes the decay of the spin-echo amplitude. This decay rate will display an array of peaks as a function of frequency. In the liquid phase this alternating field contribute to the longitudinal relaxation rate W{sub 1} which has a single peak.

  10. Characterization of a random anisotropic conductivity field with Karhunen-Loeve methods

    SciTech Connect

    Cherry, Matthew R.; Sabbagh, Harold S.; Pilchak, Adam L.; Knopp, Jeremy S.

    2014-02-18

    While parametric uncertainty quantification for NDE models has been addressed in recent years, the problem of stochastic field parameters such as spatially distributed electrical conductivity has only been investigated minimally in the last year. In that work, the authors treated the field as a one-dimensional random process and Karhunen-Loeve methods were used to discretize this process to make it amenable to UQ methods such as ANOVA expansions. In the present work, we will treat the field as a two dimensional random process, and the eigenvalues and eigenfunctions of the integral operator will be determined via Galerkin methods. The Karhunen-Loeve methods is extended to two dimensions and implemented to represent this process. Several different choices for basis functions will be discussed, as well as convergence criteria for each. The methods are applied to correlation functions collected over electron backscatter data from highly micro textured Ti-7Al.

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

    SciTech Connect

    Du, Yingzhou; Lograsso, Thomas A.; McQueeney, Robert J.

    2012-06-28

    The rapid growth of the magnetostriction coefficient of ferromagnetic Fe1−xGax alloys that occurs at a composition range from 0anisotropic 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.

  12. Regional electric field induced by electroconvulsive therapy in a realistic finite element head model: Influence of white matter anisotropic conductivity

    PubMed Central

    Lee, Won Hee; Deng, Zhi-De; Kim, Tae-Seong; Laine, Andrew F.; Lisanby, Sarah H.; Peterchev, Angel V.

    2012-01-01

    We present the first computational study investigating the electric field (E-field) strength generated by various electroconvulsive therapy (ECT) electrode configurations in specific brain regions of interest (ROIs) that have putative roles in the therapeutic action and/or adverse side effects of ECT. This study also characterizes the impact of the white matter (WM) conductivity anisotropy on the E-field distribution. A finite element head model incorporating tissue heterogeneity and WM anisotropic conductivity was constructed based on structural magnetic resonance imaging (MRI) and diffusion tensor MRI data. We computed the spatial E-field distributions generated by three standard ECT electrode placements including bilateral (BL), bifrontal (BF), and right unilateral (RUL) and an investigational electrode configuration for focal electrically administered seizure therapy (FEAST). The key results are that (1) the median E-field strength over the whole brain is 3.9, 1.5, 2.3, and 2.6 V/cm for the BL, BF, RUL, and FEAST electrode configurations, respectively, which coupled with the broad spread of the BL E-field suggests a biophysical basis for observations of superior efficacy of BL ECT compared to BF and RUL ECT; (2) in the hippocampi, BL ECT produces a median E-field of 4.8 V/cm that is 1.5–2.8 times stronger than that for the other electrode configurations, consistent with the more pronounced amnestic effects of BL ECT; and (3) neglecting the WM conductivity anisotropy results in E-field strength error up to 18% overall and up to 39% in specific ROIs, motivating the inclusion of the WM conductivity anisotropy in accurate head models. This computational study demonstrates how the realistic finite element head model incorporating tissue conductivity anisotropy provides quantitative insight into the biophysics of ECT, which may shed light on the differential clinical outcomes seen with various forms of ECT, and may guide the development of novel stimulation

  13. Superradiance Lattice

    NASA Astrophysics Data System (ADS)

    Wang, Da-Wei; Liu, Ren-Bao; Zhu, Shi-Yao; Scully, Marlan O.

    2015-01-01

    We show that the timed Dicke states of a collection of three-level atoms can form a tight-binding lattice in momentum space. This lattice, coined the superradiance lattice (SL), can be constructed based on electromagnetically induced transparency (EIT). For a one-dimensional SL, we need the coupling field of the EIT system to be a standing wave. The detuning between the two components of the standing wave introduces an effective uniform force in momentum space. The quantum lattice dynamics, such as Bloch oscillations, Wannier-Stark ladders, Bloch band collapsing, and dynamic localization can be observed in the SL. The two-dimensional SL provides a flexible platform for Dirac physics in graphene. The SL can be extended to three and higher dimensions where no analogous real space lattices exist with new physics waiting to be explored.

  14. A phase-field model coupled with lattice kinetics solver for modeling crystal growth in furnaces

    SciTech Connect

    Lin, Guang; Bao, Jie; Xu, Zhijie; Tartakovsky, Alexandre M.; Henager, Charles H.

    2014-02-02

    In this study, we present a new numerical model for crystal growth in a vertical solidification system. This model takes into account the buoyancy induced convective flow and its effect on the crystal growth process. The evolution of the crystal growth interface is simulated using the phase-field method. Two novel phase-field models are developed to model the crystal growth interface in vertical gradient furnaces with two temperature profile setups: 1) fixed wall temperature profile setup and 2) time-dependent temperature profile setup. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. This model is used to investigate the effect of furnace operational conditions on crystal growth interface profiles and growth velocities. For a simple case of macroscopic radial growth, the phase-field model is validated against an analytical solution. Crystal growth in vertical gradient furnaces with two temperature profile setups have been also investigated using the developed model. The numerical simulations reveal that for a certain set of temperature boundary conditions, the heat transport in the melt near the phase interface is diffusion dominant and advection is suppressed.

  15. Lattice models for granular-like velocity fields: finite-size effects

    NASA Astrophysics Data System (ADS)

    Plata, C. A.; Manacorda, A.; Lasanta, A.; Puglisi, A.; Prados, A.

    2016-09-01

    Long-range spatial correlations in the velocity and energy fields of a granular fluid are discussed in the framework of a 1d lattice model. The dynamics of the velocity field occurs through nearest-neighbour inelastic collisions that conserve momentum but dissipate energy. A set of equations for the fluctuating hydrodynamics of the velocity and energy mesoscopic fields give a first approximation for (i) the velocity structure factor and (ii) the finite-size correction to the Haff law, both in the homogeneous cooling regime. At a more refined level, we have derived the equations for the two-site velocity correlations and the total energy fluctuations. First, we seek a perturbative solution thereof, in powers of the inverse of system size. On the one hand, when scaled with the granular temperature, the velocity correlations tend to a stationary value in the long time limit. On the other hand, the scaled standard deviation of the total energy diverges, that is, the system shows multiscaling. Second, we find an exact solution for the velocity correlations in terms of the spectrum of eigenvalues of a certain matrix. The results of numerical simulations of the microscopic model confirm our theoretical results, including the above described multiscaling phenomenon.

  16. Field Tolerances for the Triplet Quadrupoles of the LHC High Luminosity Lattice

    SciTech Connect

    Nosochkov, Yuri; Cai, Y.; Jiao, Y.; Wang, M-H.; Fartoukh, S.; Giovannozzi, M.; Maria, R.de; McIntosh, E.

    2012-06-25

    It has been proposed to implement the so-called Achromatic Telescopic Squeezing (ATS) scheme in the LHC high luminosity (HL) lattice to reduce beta functions at the Interaction Points (IP) up to a factor of 8. As a result, the nominal 4.5 km peak beta functions reached in the Inner Triplets (IT) at collision will be increased by the same factor. This, therefore, justifies the installation of new, larger aperture, superconducting IT quadrupoles. The higher beta functions will enhance the effects of the triplet quadrupole field errors leading to smaller beam dynamic aperture (DA). To maintain the acceptable DA, the effects of the triplet field errors must be re-evaluated, thus specifying new tolerances. Such a study has been performed for the so-called '4444' collision option of the HL-LHC layout version SLHCV3.01, where the IP beta functions are reduced by a factor of 4 in both planes with respect to a pre-squeezed value of 60 cm at two collision points. The dynamic aperture calculations were performed using SixTrack. The impact on the triplet field quality is presented.

  17. The thermal instability in a sheared magnetic field - Filament condensation with anisotropic heat conduction. [solar physics

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.; Mok, Y.

    1984-01-01

    The condensation-mode growth rate of the thermal instability in an empirically motivated sheared field is shown to depend upon the existence of perpendicular thermal conduction. This typically very small effect (perpendicular conductivity/parallel conductivity less than about 10 to the -10th for the solar corona) increases the spatial-derivative order of the compressible temperature-perturbation equation, and thereby eliminates the singularities which appear when perpendicular conductivity = 0. The resulting growth rate is less than 1.5 times the controlling constant-density radiation rate, and has a clear maximum at a cross-field length of order 100 times and a width of about 0.1 the magnetic shear scale for solar conditions. The profiles of the observable temperature and density perturbations are independent of the thermal conductivity, and thus agree with those found previously. An analytic solution to the short-wavelength incompressible case is also given.

  18. Tensor of the nonlinear polarizability of anisotropic medium and ``local'' field method

    NASA Astrophysics Data System (ADS)

    Lavric, V. V.; Ovander, L. N.; Shunyakov, V. T.

    1983-08-01

    The nonlinear polarizability tensor (NPT) for a molecular crystal of arbitrary symmetry has been obtained within the framework of polariton theory. Use of the Göppert-Mayer unitary transformation for the Hamiltonian of the crystal plus quantized electromagnetic field system made it possible to represent finally the result for the NPT in a compact form and to compare with results of semiphenomenological calculation of the NPT and to go out of the framework of the Gaitler-London approximation.

  19. Controlling the plasmon resonance of single metal nanoparticles by near-field anisotropic nanoscale photopolymerization.

    PubMed

    Ibn-El-Ahrach, H; Bachelot, R; Lérondel, G; Vial, A; Grimault, A-S; Plain, J; Royer, P; Soppera, O

    2008-03-01

    We propose a new approach for tuning the Surface Plasmon (SP) resonance wavelength using hybrid nanoparticles. Our approach is based on nanoscale photopolymerization around metal nanoparticles. The enhanced optical near-field of silver nanoparticles triggers local photopolymerization. As a result, atomic force microscopy reveals two nanoscale polymerized lobes around nanoparticles, with a controlled effective index distribution. A spectral breaking degeneracy of surface plasmon resonance of the nanoparticles has been demonstrated by polarized extinction spectroscopy.

  20. Comment on ``Spin-glass attractor on tridimensional hierarchical lattices in the presence of an external magnetic field''

    NASA Astrophysics Data System (ADS)

    Berker, A. Nihat

    2010-04-01

    The effect of random or uniform magnetic fields on spin glasses on some d=3 hierarchical lattices has been studied, using renormalization-group theory, by Salmon and Nobre. In this work, the recursion relation for the local magnetic field is incorrect. It erroneously weakens the amplitude of the renormalization contribution to the magnetic field by a factor of 1/qμ , where qμ is the site coordination number.

  1. Multimodal brain-tumor segmentation based on Dirichlet process mixture model with anisotropic diffusion and Markov random field prior.

    PubMed

    Lu, Yisu; Jiang, Jun; Yang, Wei; Feng, Qianjin; Chen, Wufan

    2014-01-01

    Brain-tumor segmentation is an important clinical requirement for brain-tumor diagnosis and radiotherapy planning. It is well-known that the number of clusters is one of the most important parameters for automatic segmentation. However, it is difficult to define owing to the high diversity in appearance of tumor tissue among different patients and the ambiguous boundaries of lesions. In this study, a nonparametric mixture of Dirichlet process (MDP) model is applied to segment the tumor images, and the MDP segmentation can be performed without the initialization of the number of clusters. Because the classical MDP segmentation cannot be applied for real-time diagnosis, a new nonparametric segmentation algorithm combined with anisotropic diffusion and a Markov random field (MRF) smooth constraint is proposed in this study. Besides the segmentation of single modal brain-tumor images, we developed the algorithm to segment multimodal brain-tumor images by the magnetic resonance (MR) multimodal features and obtain the active tumor and edema in the same time. The proposed algorithm is evaluated using 32 multimodal MR glioma image sequences, and the segmentation results are compared with other approaches. The accuracy and computation time of our algorithm demonstrates very impressive performance and has a great potential for practical real-time clinical use.

  2. Multimodal brain-tumor segmentation based on Dirichlet process mixture model with anisotropic diffusion and Markov random field prior.

    PubMed

    Lu, Yisu; Jiang, Jun; Yang, Wei; Feng, Qianjin; Chen, Wufan

    2014-01-01

    Brain-tumor segmentation is an important clinical requirement for brain-tumor diagnosis and radiotherapy planning. It is well-known that the number of clusters is one of the most important parameters for automatic segmentation. However, it is difficult to define owing to the high diversity in appearance of tumor tissue among different patients and the ambiguous boundaries of lesions. In this study, a nonparametric mixture of Dirichlet process (MDP) model is applied to segment the tumor images, and the MDP segmentation can be performed without the initialization of the number of clusters. Because the classical MDP segmentation cannot be applied for real-time diagnosis, a new nonparametric segmentation algorithm combined with anisotropic diffusion and a Markov random field (MRF) smooth constraint is proposed in this study. Besides the segmentation of single modal brain-tumor images, we developed the algorithm to segment multimodal brain-tumor images by the magnetic resonance (MR) multimodal features and obtain the active tumor and edema in the same time. The proposed algorithm is evaluated using 32 multimodal MR glioma image sequences, and the segmentation results are compared with other approaches. The accuracy and computation time of our algorithm demonstrates very impressive performance and has a great potential for practical real-time clinical use. PMID:25254064

  3. Multimodal Brain-Tumor Segmentation Based on Dirichlet Process Mixture Model with Anisotropic Diffusion and Markov Random Field Prior

    PubMed Central

    Lu, Yisu; Jiang, Jun; Chen, Wufan

    2014-01-01

    Brain-tumor segmentation is an important clinical requirement for brain-tumor diagnosis and radiotherapy planning. It is well-known that the number of clusters is one of the most important parameters for automatic segmentation. However, it is difficult to define owing to the high diversity in appearance of tumor tissue among different patients and the ambiguous boundaries of lesions. In this study, a nonparametric mixture of Dirichlet process (MDP) model is applied to segment the tumor images, and the MDP segmentation can be performed without the initialization of the number of clusters. Because the classical MDP segmentation cannot be applied for real-time diagnosis, a new nonparametric segmentation algorithm combined with anisotropic diffusion and a Markov random field (MRF) smooth constraint is proposed in this study. Besides the segmentation of single modal brain-tumor images, we developed the algorithm to segment multimodal brain-tumor images by the magnetic resonance (MR) multimodal features and obtain the active tumor and edema in the same time. The proposed algorithm is evaluated using 32 multimodal MR glioma image sequences, and the segmentation results are compared with other approaches. The accuracy and computation time of our algorithm demonstrates very impressive performance and has a great potential for practical real-time clinical use. PMID:25254064

  4. Mode I crack analysis in single crystals with anisotropic discrete dislocation plasticity: II. Stationary crack-tip fields

    NASA Astrophysics Data System (ADS)

    Soleymani Shishvan, Siamak; Van der Giessen, Erik

    2013-09-01

    Small-scale yielding around a stationary mode I crack in a cubic single crystal is analyzed in terms of plane-strain elastically anisotropic discrete dislocation plasticity (DDP). Two symmetric crack orientations are considered with two objectives in mind. First, we study the sensitivity to materials aspects such as dislocation source density and elastic anisotropy as well as orientation dependence. Plastic deformation around the crack tip in a single crystal is a patchy field due to the discreteness of the slip systems, as demonstrated in analytical solutions and experimental observations. While these solutions/observations have in common that the plastic zone is composed of sectors with specific slip system(s) active inside each sector, detailed comparisons—recapitulated in this paper—reveal a few, yet significant, discrepancies. In an attempt to resolve these issues, the second objective of this paper is to construct sector arrangements of active slip system(s) from the present DDP simulations and compare those with the analytical solutions. We find that the estimated sector arrangements are in best agreement with the hardening analytical solutions of Saeedvafa and Rice (1989 J. Mech. Phys. Solids 37 673-91) indeed, angular variations of stresses around the crack tip confirm this observation.

  5. Kubo number and magnetic field line diffusion coefficient for anisotropic magnetic turbulence.

    PubMed

    Pommois, P; Veltri, P; Zimbardo, G

    2001-06-01

    The magnetic field line diffusion coefficients Dx and D(y) are obtained by numerical simulations in the case that all the magnetic turbulence correlation lengths l(x), l(y), and l(z) are different. We find that the variety of numerical results can be organized in terms of the Kubo number, the definition of which is extended from R=(deltaB/B(0))(l(parallel)/l(perpendicular)) to R=(deltaB/B(0))(l(z)/l(x)), for l(x) > or = l(y). Here, l(parallel) (l(perpendicular)) is the correlation length along (perpendicular to) the average field B(0)=B(0)ê(z). We have anomalous, non-Gaussian transport for R less, similar 0.1, in which case the mean square deviation scales nonlinearly with time. For R greater, similar 1 we have several Gaussian regimes: an almost quasilinear regime for 0.1 less, similar R less, similar 1, an intermediate, transition regime for 1 less, similar R less, similar 10, and a percolative regime for R greater, similar 10. An analytical form of the diffusion coefficient is proposed, D(i)=D(deltaBl(z)/B(0)l(x))(mu)(l(i)/l(x))(nu)l(2)(x)/l(z), which well describes the numerical simulation results in the quasilinear, intermediate, and percolative regimes.

  6. Anisotropic mechanical behaviour of sedimentary basins inferred by advanced radar interferometry above gas storage fields

    NASA Astrophysics Data System (ADS)

    Teatini, P.; Gambolati, G.; Ferretti, A.

    2010-12-01

    Natural gas is commonly stored underground in depleted oil and gas fields to provide safe storage capacity and deliverability to market areas where production is limited, or to take advantage of seasonal price swings. In response to summer gas injection and winter gas withdrawal the reservoir expands and contracts with the overlying land that moves accordingly. Depending on the field burial depth, a few kilometres of the upper lithosphere are subject to local three-dimensional deformations with the related cyclic motion of the ground surface being both vertical and horizontal. Advanced Persistent Scatterer Interferometry (PSI) data, obtained by combining ascending and descending RADARSAT-1 images acquired from 2003 to 2008 above gas storage fields located in the sedimentary basin of the Po river plain, Italy, provide reliable measurement of these seasonal vertical ups and downs as well as horizontal displacements to and from the injection/withdrawal wells. Combination of the land surface movements together with an accurate reconstruction of the subsurface geology made available by three-dimensional seismic surveys and long-time records of fluid pore pressure within the 1000-1500 m deep reservoirs has allowed for the development of an accurate 3D poro-mechanical finite-element model of the gas injection/removal occurrence. Model calibration based on the observed cyclic motions, which are on the range of 10-15 mm and 5-10 mm in the vertical and horizontal west-east directions, respectively, helps characterize the nonlinear hysteretic geomechanical properties of the basin. First, using a basin-scale relationship between the oedometric rock compressibility cM in virgin loading conditions versus the effective intergranular stress derived from previous experimental studies, the modeling results show that the ratio s between loading and unloading-reloading cM is about 4, consistent with in-situ expansions measured by the radioactive marker technique in similar reservoirs

  7. Molecular determinants for drug-receptor interactions. 8. Anisotropic and internal motions in morphine, nalorphine, oxymorphone, naloxone and naltrexone in aqueous solution by carbon-13 NMR spin-lattice relaxation times

    NASA Astrophysics Data System (ADS)

    Grassi, Antonio; Perly, Bruno; Pappalardo, Giuseppe C.

    1989-02-01

    Carbon-13 NMR spin-lattice relaxation times ( T1) were measured for morphine, oxymorphone, nalorphine, naloxone and naltrexone as hydrochloride salts in 2H 2O solution. The data refer to the molecules in the N-equatorial configuration. The experimental T1 values were interpreted using a model of anisotropic reorientation of a rigid body with superimposed internal motions of the flexible N-methyl, N-methyl-allyl and N-methyl-cyclopropyl fragments. The calculated internal motional rates were found to markedly decrease on passing from agonists to mixed (nalorphine) and pure (naloxone, naltrexone) antagonists. For these latter the observed trend of the internal flexibility about NC and CC bonds of the N-substituents is discussed in terms of a correlation with their relative antagonistic potencies. In fact, such an evidence of decreasing internal conformational dynamics in the order nalorphine, naloxone, naltrexone, appeared interestingly in line with the "two-state" model of opiate receptor operation mode proposed by Snyder.

  8. Plasma β scaling of anisotropic magnetic field fluctuations in the solar wind flux tube

    SciTech Connect

    Sarkar, Aveek; Bhattacharjee, Amitava; Ebrahimi, Fatima E-mail: amitava@princeton.edu

    2014-03-10

    Based on various observations, it has been suggested that at 1 AU, solar wind consists of 'spaghetti'-like magnetic field structures that have the magnetic topology of flux tubes. It is also observed that the plasma fluctuation spectra at 1 AU show a plasma β dependence. Reconciling these two sets of observations and using the Invariance Principle, Bhattacharjee et al. suggested that the plasma inside every flux tube may become unstable with respect to pressure-driven instabilities and gives rise to fluctuation spectra that depend on the local plasma β. The present work is the first direct numerical simulation of such a flux tube. We solve the full magnetohydrodynamic equations using the DEBS code and show that if the plasma inside the flux tube is driven unstable by spatial inhomogeneities in the background plasma pressure, the observed nature of the fluctuating power spectra agrees reasonably well with observations, as well as the analytical prediction of Bhattacharjee et al.

  9. Tunable Lattice Coupling of Multipole Plasmon Modes and Near-Field Enhancement in Closely Spaced Gold Nanorod Arrays

    PubMed Central

    Huang, Yu; Zhang, Xian; Ringe, Emilie; Hou, Mengjing; Ma, Lingwei; Zhang, Zhengjun

    2016-01-01

    Considering the nanogap and lattice effects, there is an attractive structure in plasmonics: closely spaced metallic nanoarrays. In this work, we demonstrate experimentally and theoretically the lattice coupling of multipole plasmon modes for closely spaced gold nanorod arrays, offering a new insight into the higher order cavity modes coupled with each other in the lattice. The resonances can be greatly tuned by changes in inter-rod gaps and nanorod heights while the influence of the nanorod diameter is relatively insignificant. Experimentally, pronounced suppressions of the reflectance are observed. Meanwhile, the near-field enhancement can be further enhanced, as demonstrated through surface enhanced Raman scattering (SERS). We then confirm the correlation between the near-field and far-field plasmonic responses, which is significantly important for maximizing the near-field enhancement at a specific excitation wavelength. This lattice coupling of multipole plasmon modes is of broad interest not only for SERS but also for other plasmonic applications, such as subwavelength imaging or metamaterials. PMID:26983501

  10. Anisotropic Nanoantenna-Based Magnetoplasmonic Crystals for Highly Enhanced and Tunable Magneto-Optical Activity.

    PubMed

    Maccaferri, Nicolò; Bergamini, Luca; Pancaldi, Matteo; Schmidt, Mikolaj K; Kataja, Mikko; Dijken, Sebastiaan van; Zabala, Nerea; Aizpurua, Javier; Vavassori, Paolo

    2016-04-13

    We present a novel concept of a magnetically tunable plasmonic crystal based on the excitation of Fano lattice surface modes in periodic arrays of magnetic and optically anisotropic nanoantennas. We show how coherent diffractive far-field coupling between elliptical nickel nanoantennas is governed by the two in-plane, orthogonal and spectrally detuned plasmonic responses of the individual building block, one directly induced by the incident radiation and the other induced by the application of an external magnetic field. The consequent excitation of magnetic field-induced Fano lattice surface modes leads to highly tunable and amplified magneto-optical effects as compared to a continuous film or metasurfaces made of disordered noninteracting magnetoplasmonic anisotropic nanoantennas. The concepts presented here can be exploited to design novel magnetoplasmonic sensors based on coupled localized plasmonic resonances, and nanoscale metamaterials for precise control and magnetically driven tunability of light polarization states.

  11. Anisotropic Nanoantenna-Based Magnetoplasmonic Crystals for Highly Enhanced and Tunable Magneto-Optical Activity.

    PubMed

    Maccaferri, Nicolò; Bergamini, Luca; Pancaldi, Matteo; Schmidt, Mikolaj K; Kataja, Mikko; Dijken, Sebastiaan van; Zabala, Nerea; Aizpurua, Javier; Vavassori, Paolo

    2016-04-13

    We present a novel concept of a magnetically tunable plasmonic crystal based on the excitation of Fano lattice surface modes in periodic arrays of magnetic and optically anisotropic nanoantennas. We show how coherent diffractive far-field coupling between elliptical nickel nanoantennas is governed by the two in-plane, orthogonal and spectrally detuned plasmonic responses of the individual building block, one directly induced by the incident radiation and the other induced by the application of an external magnetic field. The consequent excitation of magnetic field-induced Fano lattice surface modes leads to highly tunable and amplified magneto-optical effects as compared to a continuous film or metasurfaces made of disordered noninteracting magnetoplasmonic anisotropic nanoantennas. The concepts presented here can be exploited to design novel magnetoplasmonic sensors based on coupled localized plasmonic resonances, and nanoscale metamaterials for precise control and magnetically driven tunability of light polarization states. PMID:26967047

  12. Anisotropic ray trace

    NASA Astrophysics Data System (ADS)

    Lam, Wai Sze Tiffany

    anisotropic ray tracing. x. Chapter 4 presents the data reduction of the P matrix of a crystal waveplate. The diattenuation is embedded in the singular values of P. The retardance is divided into two parts: (A) The physical retardance induced by OPLs and surface interactions, and (B) the geometrical transformation induced by geometry of a ray path, which is calculated by the geometrical transform Q matrix. The Q matrix of an anisotropic intercept is derived from the generalization of s- and p-bases at the anisotropic intercept; the p basis is not confined to the plane of incidence due to the anisotropic refraction or reflection. Chapter 5 shows how the multiple P matrices associated with the eigenmodes resulting from propagation through multiple anisotropic surfaces can be combined into one P matrix when the multiple modes interfere in their overlapping regions. The resultant P matrix contains diattenuation induced at each surface interaction as well as the retardance due to ray propagation and total internal reflections. The polarization aberrations of crystal waveplates and crystal polarizers are studied in Chapter 6 and Chapter 7. A wavefront simulated by a grid of rays is traced through the anisotropic system and the resultant grid of rays is analyzed. The analysis is complicated by the ray doubling effects and the partially overlapping eigen-wavefronts propagating in various directions. The wavefront and polarization aberrations of each eigenmode can be evaluated from the electric field distributions. The overall polarization at the plane of interest or the image quality at the image plane are affected by each of these eigen-wavefronts. Isotropic materials become anisotropic due to stress, strain, or applied electric or magnetic fields. In Chapter 8, the P matrix for anisotropic materials is extended to ray tracing in stress birefringent materials which are treated as spatially varying anisotropic materials. Such simulations can predict the spatial retardance variation

  13. Solutions of the Einstein's field equations with anisotropic pressure compatible with cold star model

    NASA Astrophysics Data System (ADS)

    Singh, Ksh. Newton; Bhar, Piyali; Pant, Neeraj

    2016-10-01

    In this paper we obtain a new static and spherically symmetric model of compact star whose spacetime satisfies Karmarkar's condition (1948). The Einstein's field equations are solved by employing a physically reasonable choice of the metric coefficient g_{rr} so that the obtained solution is free from central singularities. Our model satisfies all the energy conditions as well as the causality condition. By assigning some particular values mass and radius of the compact stars PSR J0347+0432, Cen X-3 and Vela X-1 have been obtained which are very close to the observational data proposed by Antoniadis et al. (Science 340:1233232, 2013), Abubekerov et al. (Astron. Rep. 48:89, 2004) and Ash et al. (Mon. Not. R. Astron. Soc. 307:357, 1999). For the neutron star candidate PSR J0348+0432, we expect a very stiff equation of state to support its massive mass which corresponds to a large value of the adiabatic index of 6.66 at the center.

  14. Field-dependent anisotropic microrheological and microstructural properties of dilute ferrofluids.

    PubMed

    Yendeti, Balaji; Thirupathi, G; Vudaygiri, Ashok; Singh, R

    2014-08-01

    We have measured microrheological and microstructural properties of a superparamagnetic ferrofluid made of Mn0.75Zn0.25Fe2O4 (MZF) nanoparticles, using passive microrheology in a home-built inverted microscope. Thermal motion of a probe microsphere was measured for different values of an applied external magnetic field and analysed. The analysis shows anisotropy in magneto-viscous effect. Additional microrheological properties, such as storage modulus and loss modulus and their transition are also seen. We have also obtained microstructural properties such as elongational flow coefficient [Formula: see text] , relaxation time constant [Formula: see text] , coefficient of dissipative magnetization [Formula: see text] , etc., using the analysis given in Oliver Muller et al., J. Phys.: Condens. Matter 18, S2623, (2006) and Stefan Mahle et al., Phys. Rev. E 77, 016305 (2008) over our measured viscosity data. Our values for the above parameters are in agreement with earlier theoretical calculations and macro-rheological experimental measurements. These theoretical calculations consider an ideal situation of zero-shear limit, which is best approximated only in the passive microrheology technique described here and a first time measurement of all these parameters with passive microrheology. PMID:25117500

  15. Anisotropic lattice thermal expansion of PbFeBO4: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

    SciTech Connect

    Murshed, M. Mangir; Mendive, Cecilia B.; Curti, Mariano; Nénert, Gwilherm; Kalita, Patricia E.; Lipinska, Kris; Cornelius, Andrew L.; Huq, Ashfia; Gesing, Thorsten M.

    2014-11-01

    We present the lattice thermal expansion of mullite-type PbFeBO4 in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. Moreover, the unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO4, FeO6 and BO3 polyhedra as a function of temperature.

  16. Anisotropic lattice thermal expansion of PbFeBO4: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

    DOE PAGESBeta

    Murshed, M. Mangir; Mendive, Cecilia B.; Curti, Mariano; Nénert, Gwilherm; Kalita, Patricia E.; Lipinska, Kris; Cornelius, Andrew L.; Huq, Ashfia; Gesing, Thorsten M.

    2014-11-01

    We present the lattice thermal expansion of mullite-type PbFeBO4 in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. Moreover, the unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies ofmore » the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO4, FeO6 and BO3 polyhedra as a function of temperature.« less

  17. Strong Local-Field Effect on the Dynamics of a Dilute Atomic Gas Irradiated by Two Counterpropagating Optical Fields: Beyond Standard Optical Lattices

    SciTech Connect

    Zhu Jiang; Dong Guangjiong; Zhang Weiping; Shneider, Mikhail N.

    2011-05-27

    We study a recent experiment [K. Li et al., Phys. Rev. Lett. 101, 250401 (2008)] on diffracting a Bose-Einstein condensate by two counterpropagating optical fields. Including the local-field effect, we explain the asymmetric momentum distribution and self-imaging of the Bose-Einstein condensate self-consistently. Moreover, we find that the two counterpropagating optical fields could not produce a perfect optical lattice, which is actually deformed by the local-field effect. Our work implies that the local-field effect could be essential for getting a better quantitative analysis of other optical lattice experiments. In particular, the intensity imbalance of the two optical fields could act as a new means to tailor both cold atom dynamics and light propagation.

  18. Vortex Lattice Formation in High Magnetic Fields in an Underdoped Single Crystal of Hg1201 from 17O NMR

    NASA Astrophysics Data System (ADS)

    Lee, Jeongseop; Xin, Yizhou; Halperin, W. P.; Reyes, A. P.; Kuhns, P. L.

    The vortex lattice in HgBa2CuO4+δ forms at a vortex melting temperature, Tv, typically ~40K for underdoped crystals with a hole doping ~ 0.11. We present our results from 17O NMR for investigation of the vortex lattice as a function of external magnetic field up to 30 T and temperature as low as 5 K. The vortex contribution to the NMR linewidth can be separated from inhomogeneous broadening by deconvolution of the normal state spectra which was measured separately above, Tv. The vortex melting temperature was measured for two underdoped samples marked by the onset of extra linewidth broadening due to the inhomogeneous magnetic field distribution from the solid vortex lattice consistent with transverse relaxation measurements. We have found evidence for a change in the vortex lattice symmetry as a function of external fields. This work was supported by the DOE BES under Grant No. DE-FG02-05ER46248 and the NHMFL through the NSF and State of Florida.

  19. Highly excited and exotic meson spectrum from dynamical lattice QCD

    SciTech Connect

    Jozef Dudek, Robert Edwards, David Richards, Christopher Thomas

    2009-12-01

    Using a new quark-field construction algorithm and a large variational basis of operators, we extract a highly excited isovector meson spectrum on dynamical anisotropic lattices. We show how carefully constructed operators can be used to identify the continuum spin of extracted states. This method allows us to extract, with confidence, excited states, states of high spin and states with exotic quantum numbers, including, for the first time, spin-four states.

  20. Lattice model for amyloid peptides: OPEP force field parametrization and applications to the nucleus size of Alzheimer's peptides.

    PubMed

    Tran, Thanh Thuy; Nguyen, Phuong H; Derreumaux, Philippe

    2016-05-28

    Coarse-grained protein lattice models approximate atomistic details and keep the essential interactions. They are, therefore, suitable for capturing generic features of protein folding and amyloid formation at low computational cost. As our aim is to study the critical nucleus sizes of two experimentally well-characterized peptide fragments Aβ16-22 and Aβ37-42 of the full length Aβ1-42 Alzheimer's peptide, it is important that simulations with the lattice model reproduce all-atom simulations. In this study, we present a comprehensive force field parameterization based on the OPEP (Optimized Potential for Efficient protein structure Prediction) force field for an on-lattice protein model, which incorporates explicitly the formation of hydrogen bonds and directions of side-chains. Our bottom-up approach starts with the determination of the best lattice force parameters for the Aβ16-22 dimer by fitting its equilibrium parallel and anti-parallel β-sheet populations to all-atom simulation results. Surprisingly, the calibrated force field is transferable to the trimer of Aβ16-22 and the dimer and trimer of Aβ37-42. Encouraged by this finding, we characterized the free energy landscapes of the two decamers. The dominant structure of the Aβ16-22 decamer matches the microcrystal structure. Pushing the simulations for aggregates between 4-mer and 12-mer suggests a nucleus size for fibril formation of 10 chains. In contrast, the Aβ37-42 decamer is largely disordered with mixed by parallel and antiparallel chains, suggesting that the nucleus size is >10 peptides. Our refined force field coupled to this on-lattice model should provide useful insights into the critical nucleation number associated with neurodegenerative diseases. PMID:27250331

  1. Lattice model for amyloid peptides: OPEP force field parametrization and applications to the nucleus size of Alzheimer's peptides

    NASA Astrophysics Data System (ADS)

    Tran, Thanh Thuy; Nguyen, Phuong H.; Derreumaux, Philippe

    2016-05-01

    Coarse-grained protein lattice models approximate atomistic details and keep the essential interactions. They are, therefore, suitable for capturing generic features of protein folding and amyloid formation at low computational cost. As our aim is to study the critical nucleus sizes of two experimentally well-characterized peptide fragments Aβ16-22 and Aβ37-42 of the full length Aβ1-42 Alzheimer's peptide, it is important that simulations with the lattice model reproduce all-atom simulations. In this study, we present a comprehensive force field parameterization based on the OPEP (Optimized Potential for Efficient protein structure Prediction) force field for an on-lattice protein model, which incorporates explicitly the formation of hydrogen bonds and directions of side-chains. Our bottom-up approach starts with the determination of the best lattice force parameters for the Aβ16-22 dimer by fitting its equilibrium parallel and anti-parallel β-sheet populations to all-atom simulation results. Surprisingly, the calibrated force field is transferable to the trimer of Aβ16-22 and the dimer and trimer of Aβ37-42. Encouraged by this finding, we characterized the free energy landscapes of the two decamers. The dominant structure of the Aβ16-22 decamer matches the microcrystal structure. Pushing the simulations for aggregates between 4-mer and 12-mer suggests a nucleus size for fibril formation of 10 chains. In contrast, the Aβ37-42 decamer is largely disordered with mixed by parallel and antiparallel chains, suggesting that the nucleus size is >10 peptides. Our refined force field coupled to this on-lattice model should provide useful insights into the critical nucleation number associated with neurodegenerative diseases.

  2. Pair correlations as a signature of entanglement: A bosonic mixture in gauge field ring lattices

    NASA Astrophysics Data System (ADS)

    Morales-Molina, L.; Reyes, S. A.; Arévalo, E.

    2016-08-01

    We study the pair-superfluid phase and entanglement of a Bose-Bose mixture of ultracold atoms in a ring lattice in the presence of a synthetic gauge field. Special attention is given to a quantum phase transition region of the phase diagram observed in the parameter space that characterizes the intra- and inter- species interactions of the system. In the scenario of large interaction, it is shown that the ground and excited states of the lowest-energy band exhibit features of a pair-superfluid phase. We demonstrate that in the subspace associated with the lowest-energy band there is a maximally entangled eigenstate that is a perfect pair-superfluid. We suggest to use this connection between the bipartite entanglement and the pair-superfluidity as a signature of the presence of entanglement in the eigenstates associated with the lowest-energy band. Moreover, we find strong indications that the interference pattern of the pair-superfluid phase in momentum space can be used as a tool for the characterization of the entanglement in the ground state.

  3. CP(N - 1) quantum field theories with alkaline-earth atoms in optical lattices

    NASA Astrophysics Data System (ADS)

    Laflamme, C.; Evans, W.; Dalmonte, M.; Gerber, U.; Mejía-Díaz, H.; Bietenholz, W.; Wiese, U.-J.; Zoller, P.

    2016-07-01

    We propose a cold atom implementation to attain the continuum limit of (1 + 1) -d CP(N - 1) quantum field theories. These theories share important features with (3 + 1) -d QCD, such as asymptotic freedom and θ-vacua. Moreover, their continuum limit can be accessed via the mechanism of dimensional reduction. In our scheme, the CP(N - 1) degrees of freedom emerge at low energies from a ladder system of SU(N) quantum spins, where the N spin states are embodied by the nuclear Zeeman states of alkaline-earth atoms, trapped in an optical lattice. Based on Monte Carlo results, we establish that the continuum limit can be demonstrated by an atomic quantum simulation by employing the feature of asymptotic freedom. We discuss a protocol for the adiabatic preparation of the ground state of the system, the real-time evolution of a false θ-vacuum state after a quench, and we propose experiments to unravel the phase diagram at non-zero density.

  4. Spectra and scattering of light lattice nuclei from effective field theory

    NASA Astrophysics Data System (ADS)

    Kirscher, J.; Barnea, N.; Gazit, D.; Pederiva, F.; van Kolck, U.

    2015-11-01

    An effective field theory is used to describe light nuclei, calculated from quantum chromodynamics on a lattice at unphysically large pion masses. The theory is calibrated at leading order to two available data sets on two- and three-body nuclei for two pion masses. At those pion masses we predict the quartet and doublet neutron-deuteron scattering lengths, and the α -particle binding energy. For mπ=510 MeV we obtain, respectively, 4anD=2.3 ±1.3 fm, 2anD=2.2 ±2.1 fm, and Bα=35 ±22 MeV, while for mπ=805 MeV 4anD=1.6 ±1.3 fm, 2anD=0.62 ±1.0 fm, and Bα=94 ±45 MeV are found. Phillips- and Tjon-like correlations to the triton binding energy are established. We find the theoretical uncertainty in the respective correlation bands to be independent of the pion mass. As a benchmark, we present results for the physical pion mass, using experimental two-body scattering lengths and the triton binding energy as input. Hints of subtle changes in the structure of the triton and α particle are discussed.

  5. Far-field Fano resonance in nanoring lattices modeled from extracted, point dipole polarizability

    NASA Astrophysics Data System (ADS)

    DeJarnette, Drew; Blake, Phillip; Forcherio, Gregory T.; Keith Roper, D.

    2014-01-01

    Coupling and extinction of light among particles representable as point dipoles can be characterized using the coupled dipole approximation (CDA). The analytic form for dipole polarizability of spheroidal particles supports rapid electrodynamic analysis of nanoparticle lattices using CDA. However, computational expense increases for complex shapes with non-analytical polarizabilities which require discrete dipole (DDA) or higher order approximations. This work shows fast CDA analysis of assembled nanorings is possible using a single dipole nanoring polarizability extrapolated from a DDA calculation by summing contributions from individual polarizable volume elements. Plasmon resonance wavelengths of nanorings obtained using extracted polarizabilities blueshift as wall dimensions-to-inner radius aspect ratio increases, consistent with published theory and experiment. Calculated far-field Fano resonance energy maximum and minimum wavelengths were within 1% of full volume element results. Considering polarizability allows a more complete physical picture of predicting plasmon resonance location than metal dielectric alone. This method reduces time required for calculation of diffractive coupling more than 40 000-fold in ordered nanoring systems for 400-1400 nm incident wavelengths. Extension of this technique beyond nanorings is possible for more complex shapes that exhibit dipolar or quadrupole radiation patterns.

  6. Field determination of the three-dimensional hydraulic conductivity tensor of anisotropic media 2. Methodology and application to fractured rocks.

    USGS Publications Warehouse

    Hsieh, P.A.; Neuman, S.P.; Stiles, G.K.; Simpson, E.S.

    1985-01-01

    The analytical solutions developed in the first paper can be used to interpret the results of cross-hole tests conducted in anisotropic porous or fractured media. Test results from a granitic rock near Oracle in southern Arizona are presented to illustrate how the method works for fractured rocks. At the site, the Oracle granite is shown to respond as a near-uniform, anisotropic medium, the hydraulic conductivity of which is strongly controlled by the orientations of major fracture sets. The cross-hole test results are shown to be consistent with the results of more than 100 single- hole packer tests conducted at the site. -from Authors

  7. Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks.

    PubMed

    Taichenachev, A V; Yudin, V I; Oates, C W; Hoyt, C W; Barber, Z W; Hollberg, L

    2006-03-01

    We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

  8. Phase Diagram of Spin-1/2 Triangular-Lattice Antiferromagnets with Exchange Anisotropy and a Magnetic Field

    NASA Astrophysics Data System (ADS)

    Yamamoto, Daisuke; Marmorini, Giacomo; Danshita, Ippei

    2014-03-01

    A triangular-lattice spin system is a fundamental model of geometric frustration. Recent experimental developments in magnetic materials synthesis and in frustrated optical lattices of ultracold atoms have renewed interest in studying magnetic properties of ideal two-dimensional frustrated systems over wide range of external field and anisotropy. We study the spin structures of S = 1/2 antiferromagnets on a triangular lattice using a large-size cluster mean-field method combined with a scaling scheme. We determine the ground-state phase diagram of the spin model in the plane of magnetic field and XXZ anisotropy, and compare it with the classical counterpart in order to discuss the quantum effects. We find that a nontrivial continuous degeneracy existing in the classical model is broken up into two first-order phase transitions between which a non-classical phase emerges as a result of the selection by quantum fluctuations. We also use the dilute Bose gas expansion in the vicinity of the saturation field and interpret one of the first-order transitions as the 0- π transition of the relative phase between two magnon Bose-Einstein condensates. We suggest that the quantum phase transitions can be observed in current or near-future experiments. G.M. is supported by a RIKEN FPR fellowship. I.D. is supported by KAKENHI from JSPS Grants No. 25800228 and No. 25220711.

  9. Coherence of interacting bosons in optical lattices in synthetic magnetic fields with a large number of subbands

    NASA Astrophysics Data System (ADS)

    Grygiel, B.; Patucha, K.; Zaleski, T. A.

    2016-05-01

    We study the behavior of interacting ultracold bosons in optical lattices in synthetic magnetic fields with wide range of in-cell fluxes α =p /q . The problem is similar to the one of an electron moving in a tight-binding scheme in the magnetic field and becomes difficult to tackle for a growing number of magnetic subbands, q . To overcome this, we focus on the interplay of the width, shape, and number of the subbands on the formation of the coherent state of cold bosons. Using the quantum rotor approach, which goes beyond the mean-field approximation, we are able to pinpoint the elements of the band structure, which are the most significant in a proper theoretical description of the synthetic magnetic field in a bosonic lattice system. As a result, we propose a method of reconstruction of the Hofstadter butterfly spectrum by replacing the magnetic subbands with renormalized bands of a square lattice. This allows us to effectively investigate the properties of the studied system for a wide range of magnetic fluxes and their impact on the Mott-insulator-superfluid transition.

  10. Field dependence of the magnon dispersion in the Kondo lattice CeCu2 up to 12 T

    NASA Astrophysics Data System (ADS)

    Schedler, R.; Witte, U.; Rotter, M.; Loewenhaupt, M.; Schmidt, W.

    2005-05-01

    CeCu2 can be classified as a Kondo lattice which shows antiferromagnetic (AF) order below TN=3.5K [R. Trump et al., J. Appl. Phys. 69, 4699 (1991)]. The orthorhombic crystal and the simple AF magnetic structure with two magnetic moments in the primitive unit cell requires two magnon modes which are observed in zero and low magnetic fields and well described by spin wave theory. However, at higher fields, at and above 3T, an unexpected, additional magnetic excitation is observed. In contrast to the two low-energy magnon modes, it exhibits a steeper (factor 2) field dependence and a flat dispersion. Its origin is unclear.

  11. In-plane gradient-magnetic-field-induced vortex lattices in spin-orbit-coupled Bose-Einstein condensations

    NASA Astrophysics Data System (ADS)

    Zhou, Xiang-Fa; Zhou, Zheng-Wei; Wu, Congjun; Guo, Guang-Can

    2015-03-01

    We consider the ground-state properties of the two-component spin-orbit-coupled ultracold bosons subject to a rotationally symmetric in-plane gradient magnetic field. In the noninteracting case, the ground state supports giant vortices carrying large angular momenta without rotating the trap. The vorticity is highly tunable by varying the amplitudes and orientations of the magnetic field. Interactions drive the system from a giant-vortex state to various configurations of vortex lattice states along a ring. Vortices exhibit ellipse-shaped envelopes with the major and minor axes determined by the spin-orbit coupling and healing lengths, respectively. Phase diagrams of vortex lattice configurations are constructed and their stabilities are analyzed.

  12. Artificial Gauge Field and Topological Phase in a Conventional Two-dimensional Electron Gas with Antidot Lattices

    PubMed Central

    Shi, Likun; Lou, Wenkai; Cheng, F.; Zou, Y. L.; Yang, Wen; Chang, Kai

    2015-01-01

    Based on the Born-Oppemheimer approximation, we divide the total electron Hamiltonian in a spin-orbit coupled system into the slow orbital motion and the fast interband transition processes. We find that the fast motion induces a gauge field on the slow orbital motion, perpendicular to the electron momentum, inducing a topological phase. From this general designing principle, we present a theory for generating artificial gauge field and topological phase in a conventional two-dimensional electron gas embedded in parabolically graded GaAs/InxGa1−xAs/GaAs quantum wells with antidot lattices. By tuning the etching depth and period of the antidot lattices, the band folding caused by the antidot potential leads to the formation of minibands and band inversions between neighboring subbands. The intersubband spin-orbit interaction opens considerably large nontrivial minigaps and leads to many pairs of helical edge states in these gaps. PMID:26471126

  13. Quantum Monte Carlo study of long-range transverse-field Ising models on the triangular lattice

    NASA Astrophysics Data System (ADS)

    Humeniuk, Stephan

    2016-03-01

    Motivated by recent experiments with a Penning ion trap quantum simulator, we perform numerically exact Stochastic Series Expansion quantum Monte Carlo simulations of long-range transverse-field Ising models on a triangular lattice for different decay powers α of the interactions. The phase boundary for the ferromagnet is obtained as a function of α . For antiferromagnetic interactions, there is strong indication that the transverse field stabilizes a clock ordered phase with sublattice magnetization (M ,-M/2 ,-M/2 ) with unsaturated M <1 in a process known as "order by disorder" similar to the nearest-neighbor antiferromagnet on the triangular lattice. Connecting the known limiting cases of nearest-neighbor and infinite-range interactions, a semiquantitative phase diagram is obtained. Magnetization curves for the ferromagnet for experimentally relevant system sizes and with open boundary conditions are presented.

  14. Anisotropic domain structure of KTiOPO4 crystals

    NASA Astrophysics Data System (ADS)

    Urenski, P.; Lesnykh, M.; Rosenwaks, Y.; Rosenman, G.; Molotskii, M.

    2001-08-01

    Highly anisotropic ferroelectric domain structure is observed in KTiOPO4 (KTP) crystals reversed by low electric field. The applied Miller-Weinreich model for sidewise motion of domain walls indicates that this anisotropy results from the peculiarities of KTP crystal lattice. The domain nuclei of dozen nanometer size, imaged by atomic force microscopy method, demonstrate regular hexagonal forms. The orientation of domain walls of the elementary nuclei coincides with the orientation of the facets of macroscopic KTP crystals. The observed strong domain elongation along one principal crystal axis allows us to improve tailoring of ferroelectric domain engineered structures for nonlinear optical converters.

  15. Simulating the hydraulic stimulation of multiple fractures in an anisotropic stress field applying the discrete element method

    NASA Astrophysics Data System (ADS)

    Zeeb, Conny; Frühwirt, Thomas; Konietzky, Heinz

    2015-04-01

    Key to a successful exploitation of deep geothermal reservoirs in a petrothermal environment is the hydraulic stimulation of the host rock to increase permeability. The presented research investigates the fracture propagation and interaction during hydraulic stimulation of multiple fractures in a highly anisotropic stress field. The presented work was conducted within the framework of the OPTIRISS project, which is a cooperation of industry partners and universities in Thuringia and Saxony (Federal States of Germany) and was funded by the European Fond for Regional Development. One objective was the design optimization of the subsurface geothermal heat exchanger (SGHE) by means of numerical simulations. The presented simulations were conducted applying 3DEC (Itasca™), a software tool based on the discrete element method. The simulation results indicate that the main direction of fracture propagation is towards lower stresses and thus towards the biosphere. Therefore, barriers might be necessary to limit fracture propagation to the designated geological formation. Moreover, the hydraulic stimulation significantly alters the stresses in the vicinity of newly created fractures. Especially the change of the minimum stress component affects the hydraulic stimulation of subsequent fractures, which are deflected away from the previously stimulated fractures. This fracture deflection can render it impossible to connect all fractures with a second borehole for the later production. The results of continuative simulations indicate that a fracture deflection cannot be avoided completely. Therefore, the stage alignment was modified to minimize fracture deflection by varying (1) the pauses between stages, (2) the spacing's between adjacent stages, and (3) the angle between stimulation borehole and minimum stress component. An optimum SGHE design, which implies that all stimulated fractures are connected to the production borehole, can be achieved by aligning the stimulation

  16. Lattice Boltzmann phase-field modeling of thermocapillary flows in a confined microchannel

    NASA Astrophysics Data System (ADS)

    Liu, Haihu; Valocchi, Albert J.; Zhang, Yonghao; Kang, Qinjun

    2014-01-01

    To understand how thermocapillary forces manipulate the droplet motion in a confined microchannel, a lattice Boltzmann phase-field model is developed to simulate immiscible thermocapillary flows with consideration of fluid-surface interactions. Based on our recent work of Liu et al., 2013 [54], an interfacial force of potential form is proposed to model the interfacial tension force and the Marangoni stress. As only the first-order derivatives are involved, the proposed interfacial force is easily combined with the wetting boundary condition to account for fluid-surface interactions. The hydrodynamic equations are solved using a multiple-relaxation-time algorithm with the interfacial force treated as a forcing term, while an additional convection-diffusion equation is solved by a passive-scalar approach to obtain the temperature field, which is coupled to the interfacial tension by an equation of state. The model is first validated against analytical solutions for the thermocapillary-driven convection in two superimposed fluids at negligibly small Reynolds and Marangoni numbers. It is then demonstrated to produce the correct equilibrium contact angle for a binary fluid with different viscosities when a constant interfacial tension is taken into account. Finally, we numerically simulate the thermocapillary flows for a microfluidic droplet adhering on a solid wall and subject to a simple shear flow when a laser is applied to locally heat the fluids, and investigate the influence of contact angle and fluid viscosity ratio on the droplet dynamical behavior. The droplet motion can be completely blocked provided that the contact angle exceeds a threshold value, below which the droplet motion successively undergoes four stages: constant velocity, deceleration, acceleration, and approximately constant velocity. When the droplet motion is completely blocked, three steady vortices are clearly visible, and the droplet is fully filled by two counter-rotating vortices with the

  17. Optical trapping of anisotropic nanocylinder

    NASA Astrophysics Data System (ADS)

    Bareil, Paul B.; Sheng, Yunlong

    2013-09-01

    The T-matrix method with the Vector Spherical Wave Function (VSWF) expansions represents some difficulties for computing optical scattering of anisotropic particles. As the divergence of the electric field is nonzero in the anisotropic medium and the VSWFs do not satisfy the anisotropic wave equations one questioned whether the VSWFs are still a suitable basis in the anisotropic medium. We made a systematic and careful review on the vector basis functions and the VSWFs. We found that a field vector in Euclidean space can be decomposed to triplet vectors {L, M, N}, which as non-coplanar. Especially, the vector L is designed to represent non-zero divergence component of the vector solution, so that the VSWF basis is sufficiently general to represent the solutions of the anisotropic wave equation. The mathematical proof can be that when the anisotropic wave equations is solved in the Fourier space, the solution is expanded in the basis of the plan waves with angular spectrum amplitude distributions. The plane waves constitute an orthogonal and complete set for the anisotropic solutions. Furthermore, the plane waves are expanded into the VSWF basis. These two-step expansions are equivalent to the one-step direct expansion of the anisotropic solution to the VSWF basis. We used direct VSWF expansion, along with the point-matching method in the T-matrix, and applied the boundary condition to the normal components displacement field in order to compute the stress and the related forces and torques and to show the mechanism of the optical trap of the anisotropic nano-cylinders.

  18. Anisotropic inflation with general potentials

    NASA Astrophysics Data System (ADS)

    Shi, JiaMing; Huang, XiaoTian; Qiu, TaoTao

    2016-04-01

    Anomalies in recent observational data indicate that there might be some "anisotropic hair" generated in an inflation period. To obtain general information about the effects of this anisotropic hair to inflation models, we studied anisotropic inflation models that involve one vector and one scalar using several types of potentials. We determined the general relationship between the degree of anisotropy and the fraction of the vector and scalar fields, and concluded that the anisotropies behave independently of the potentials. We also generalized our study to the case of multi-directional anisotropies.

  19. Anisotropic universe with anisotropic sources

    SciTech Connect

    Aluri, Pavan K.; Panda, Sukanta; Sharma, Manabendra; Thakur, Snigdha E-mail: sukanta@iiserb.ac.in E-mail: snigdha@iiserb.ac.in

    2013-12-01

    We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union 2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found.

  20. Anisotropy-induced wave steering in periodic linear and nonlinear lattices

    NASA Astrophysics Data System (ADS)

    Casadei, Filippo; Rimoli, Julian; Ruzzene, Massimo

    2012-02-01

    Structural lattice configurations can be designed with tailored topologies which provide them with unusual behaviors, such as negative bulk modulus, negative Poisson's ratios, or extreme anisotropyootnotetextM. Ruzzene et al. Phisica Status Solidi B, 242, 665 (2005). The latter is of particular relevance to explore the inherent anisotropic behavior of periodic lattices as a design paradigm for wave guiding and steering applications. The equivalent material anisotropy of square and skew periodic lattices is investigated through the application of Bloch's theoremootnotetextBloch F., Z. Physik 52, 555 (1928) to the finite element discretization of the representative unit cell. The in-plane directions of wave propagation are determined through detailed analysis of the longitudinal and shear wave velocities, and verified through full-field wave propagation simulations. Similar wave behaviors are investigated analytically and experimentally for multilayer composite panels with anisotropic lay-ups in order to demonstrate the feasibility of micro structural design as an effective approach for wave management.

  1. The right circular polarized waves in the three-dimensional anisotropic dispersive photonic crystals consisting of the magnetized plasma and uniaxial material as the Faraday effects considered

    SciTech Connect

    Zhang, Hai-Feng E-mail: lsb@nuaa.edu.cn; Liu, Shao-Bin E-mail: lsb@nuaa.edu.cn; Tang, Yi-Jun; Zhen, Jian-Ping

    2014-03-15

    In this paper, the properties of the right circular polarized (RCP) waves in the three-dimensional (3D) dispersive photonic crystals (PCs) consisting of the magnetized plasma and uniaxial material with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, which the homogeneous anisotropic dielectric spheres (the uniaxial material) immersed in the magnetized plasma background, as the Faraday effects of magnetized plasma are considered (the incidence electromagnetic wave vector is parallel to the external magnetic field at any time). The equations for calculating the anisotropic photonic band gaps (PBGs) for the RCP waves in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, anisotropic dielectric filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the properties of first two anisotropic PBGs for the RCP waves are investigated in detail, respectively. The numerical results show that the anisotropy can open partial band gaps in fcc lattices at U and W points, and the complete PBGs for the RCP waves can be achieved compared to the conventional 3D dispersive PCs composed of the magnetized plasma and isotropic material. It is also shown that the first two anisotropic PBGs can be tuned by those parameters as mentioned above. Those PBGs can be enlarged by introducing the uniaxial material into such 3D PCs as the Faraday effects are considered.

  2. The right circular polarized waves in the three-dimensional anisotropic dispersive photonic crystals consisting of the magnetized plasma and uniaxial material as the Faraday effects considered

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Zhen, Jian-Ping; Tang, Yi-Jun

    2014-03-01

    In this paper, the properties of the right circular polarized (RCP) waves in the three-dimensional (3D) dispersive photonic crystals (PCs) consisting of the magnetized plasma and uniaxial material with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, which the homogeneous anisotropic dielectric spheres (the uniaxial material) immersed in the magnetized plasma background, as the Faraday effects of magnetized plasma are considered (the incidence electromagnetic wave vector is parallel to the external magnetic field at any time). The equations for calculating the anisotropic photonic band gaps (PBGs) for the RCP waves in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, anisotropic dielectric filling factor, plasma frequency, and plasma cyclotron frequency (the external magnetic field) on the properties of first two anisotropic PBGs for the RCP waves are investigated in detail, respectively. The numerical results show that the anisotropy can open partial band gaps in fcc lattices at U and W points, and the complete PBGs for the RCP waves can be achieved compared to the conventional 3D dispersive PCs composed of the magnetized plasma and isotropic material. It is also shown that the first two anisotropic PBGs can be tuned by those parameters as mentioned above. Those PBGs can be enlarged by introducing the uniaxial material into such 3D PCs as the Faraday effects are considered.

  3. Modulation of periodic field on the atomic current in optical lattices with Landau-Zener tunneling considered

    NASA Astrophysics Data System (ADS)

    Yan, Jie-Yun; Wang, Lan-Yu

    2016-09-01

    We investigate the atomic current in optical lattices under the presence of both constant and periodic external field with Landau-Zener tunneling considered. By simplifying the system to a two-band model, the atomic current is obtained based on the Boltzmann equations. We focus on three situations to discuss the influence of the Landau-Zener tunneling and periodic field on the atomic current. Numerical calculations show the atomic transient current would finally become the stable oscillation, whose amplitude and average value can be further adjusted by the periodic external field. It is concluded that the periodic external field could provide an effective modulation on the atomic current even when the Landau-Zener tunneling probability has almostly become a constant.

  4. Commensurate states on incommensurate lattices. [for superconducting arrays in magnetic fields

    NASA Technical Reports Server (NTRS)

    Grest, Gary S.; Chaikin, Paul M.; Levine, Dov

    1988-01-01

    A simple one-dimensional model related to flux quantization on superconducting networks or charged particles on a substrate is proposed to investigate whether commensurate states can exist on incommensurate lattices. For both periodic and quasi-crystalline patterns, a set of low-energy states is found which is related to decimation symmetry and periodicity. It is suggested that the present quasi-periodic arrays which possess a decimation operation can be generalized to more-dimensional quasi-crystalline systems.

  5. OH MASER SOURCES IN W49N: PROBING MAGNETIC FIELD AND DIFFERENTIAL ANISOTROPIC SCATTERING WITH ZEEMAN PAIRS USING THE VERY LONG BASELINE ARRAY

    SciTech Connect

    Deshpande, Avinash A.; Goss, W. M.; Mendoza-Torres, J. E. E-mail: mgoss@aoc.nrao.edu

    2013-09-20

    Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ∼20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ∼10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6σ) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s{sup –1}. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region.

  6. Anisotropic resistivity tomography

    NASA Astrophysics Data System (ADS)

    Herwanger, J. V.; Pain, C. C.; Binley, A.; de Oliveira, C. R. E.; Worthington, M. H.

    2004-08-01

    Geophysical tomographic techniques have the potential to remotely detect and characterize geological features, such as fractures and spatially varying lithologies, by their response to signals passed through these features. Anisotropic behaviour in many geological materials necessitates the generalization of tomographic methods to include anisotropic material properties in order to attain high-quality images of the subsurface. In this paper, we present a finite element (FE) based direct-current electrical inversion method to reconstruct the conductivity tensor at each node point of a FE mesh from electrical resistance measurements. The inverse problem is formulated as a functional optimization and the non-uniqueness of the electrical inverse problem is overcome by adding penalty terms for structure and anisotropy. We use a modified Levenberg-Marquardt method for the functional optimization and the resulting set of linear equation is solved using pre-conditioned conjugate gradients. The method is tested using both synthetic and field experiments in cross-well geometry. The acquisition geometry for both experiments uses a cross-well experiment at a hard-rock test site in Cornwall, southwest England. Two wells, spaced at 25.7 m, were equipped with electrodes at a 1 m spacing at depths from 21-108 m and data were gathered in pole-pole geometry. The test synthetic model consists of a strongly anisotropic and conductive body underlain by an isotropic resistive formation. Beneath the resistive formation, the model comprises a moderately anisotropic and moderately conductive half-space, intersected by an isotropic conductive layer. This model geometry was derived from the interpretation of a seismic tomogram and available geological logs and the conductivity values are based on observed conductivities. We use the test model to confirm the ability of the inversion scheme to recover the (known) true model. We find that all key features of the model are recovered. However

  7. Raman study of the temperature and magnetic-field dependence of the electronic and lattice properties of MnSi

    NASA Astrophysics Data System (ADS)

    Eiter, H.-M.; Jaschke, P.; Hackl, R.; Bauer, A.; Gangl, M.; Pfleiderer, C.

    2014-07-01

    The temperature and magnetic-field dependence of lattice and carrier excitations in MnSi is studied in detail using inelastic light scattering. The pure symmetry components of the electronic response are derived from the polarization-dependent spectra. The E and T2 responses agree by and large with longitudinal and optical transport data. However, an anomaly is observed right above the magnetic ordering temperature TC=29 K that is associated with the fluctuations that drive the transition into the helimagnetic phase first order. The T1 spectra, reflecting mostly chiral spin excitations, have a temperature dependence similar to that of the E and T2 symmetries. The response in the fully symmetric A1 representation has a considerably weaker temperature dependence than that in the other symmetries. All nine Raman active phonon lines can be resolved at low temperature. The positions and linewidths of the strongest four lines in E and T2 symmetry are analyzed in the temperature range 4lattice expansion. Distinct anomalies are observed in the range of the helimagnetic transition and in the ordered phase. Applying a magnetic field of 4 T, well above the critical field, removes all anomalies and restores a conventional behavior highlighting the relationship between the anomalies and magnetism. The anomaly directly above TC in the fluctuation range goes along with an anomaly in the thermal expansion. While the lattice constant changes continuously and has only a kink at TC, all optical phonons soften abruptly, suggesting a direct microscopic coupling between spin order and optical phonons rather than a reaction to magnetostriction effects.

  8. Magnetoresistivity in a tilted magnetic field in p-Si/SiGe/Si heterostructures with an anisotropic g-factor. Part II

    SciTech Connect

    Drichko, I. L.; Smirnov, I. Yu.; Suslov, A. V.; Mironov, O. A.; Leadley, D. R.

    2012-09-15

    The magnetoresistance components {rho}xx and {rho}xy are measured in two p-Si/SiGe/Si quantum wells that have an anisotropic g-factor in a tilted magnetic field as a function of the temperature, field, and tilt angle. Activation energy measurements demonstrate the existence of a ferromagnetic-paramagnetic (F-P) transition for the sample with the hole density p = 2 Multiplication-Sign 10{sup 11} cm{sup -2}. This transition is due to the crossing of the 0{up_arrow} and 1{down_arrow} Landau levels. However, in another sample with p = 7.2 Multiplication-Sign 10{sup 10} cm{sup -2}, the 0{up_arrow} and 1{down_arrow} Landau levels coincide for angles {theta} = 0-70 Degree-Sign . Only for {theta} > 70 Degree-Sign do the levels start to diverge which, in turn, results in the energy gap opening.

  9. Specific heat of the Skyrmion lattice phase and field-induced tricritical point in MnSi.

    PubMed

    Bauer, A; Garst, M; Pfleiderer, C

    2013-04-26

    We report high-precision measurements of the temperature and magnetic field dependence of the specific heat, C(T,H), across the magnetic phase diagram of MnSi. Clear anomalies establish the Skyrmion lattice unambiguously as a thermodynamic phase. The evolution of the specific heat anomalies, the field dependence of the entropy released at the phase transitions, and the temperature versus field dependence of crossover lines provide striking evidence of a tricritical point at μ0H(TCP)(int) = 340  mT and T(TCP) = 28.5  K. The existence of this tricritical point represents strong support of a helimagnetic Brazovskii transition, i.e., a fluctuation-induced first-order transition at H = 0. PMID:23679769

  10. The influence of time-dependent electric and magnetic fields on the dynamic localization of lattice electrons

    NASA Astrophysics Data System (ADS)

    Papp, E.; Micu, C.; Aur, L.

    2008-12-01

    In this paper we deal with the derivation of dynamic localization conditions for electrons on the one-dimensional (1D) lattice under the influence of ac electric and magnetic fields of the same frequency. We resort, for convenience, to a tight-binding single-band Hamiltonian. Our emphasis is on a more fundamental theoretical understanding by investigating interplays between such fields and the nearest-neighbor hopping interactions characterizing the Hamiltonian. In general, such conditions get expressed in terms of infinite sums of binary products of Bessel functions of the first kind. These sums are hardly tractable, but we found that selecting in a suitable manner the phases of time-dependent modulations leads to controllable frequency-mixing effects providing appreciable simplifications. Such mixings concern competitions between the number of flux quanta and the quotients of field amplitudes and field frequencies. More exactly, tuning one of the mixed frequencies to zero opens the way to establishing the simplified dynamic localization conditions. By resorting again to the zeros of the Bessel function of zeroth order. This results in quickly tractable relationships between the amplitudes of electric and magnetic fields, the field frequency, and the zeros referred to just above. Pure field limits and superpositions between uniform electric and time-dependent magnetic fields are also discussed. Comments concerning the role of disorder and of the Coulomb interaction are also made.

  11. Field-wide flow simulation in fractured porous media within lattice Boltzmann framework

    NASA Astrophysics Data System (ADS)

    Benamram, Z.; Tarakanov, A.; Nasrabadi, H.; Gildin, E.

    2016-10-01

    In this paper, a generalized lattice Boltzmann model for simulating fluid flow in porous media at the representative volume element scale is extended towards applications of hydraulically and naturally fractured reservoirs. The key element within the model is the development of boundary conditions for a vertical well and horizontal fracture with minimal node usage. In addition, the governing non-dimensional equations are derived and a new set of dimensionless numbers are presented for the simulation of a fractured reservoir system. Homogenous and heterogeneous vertical well and fracture systems are simulated and verified against commercial reservoir simulation suites. Results are in excellent agreement to analytical and finite difference solutions.

  12. Superalloy Lattice Block Structures

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Nathal, M. V.; Hebsur, M. G.; Kraus, D. L.

    2003-01-01

    In their simplest form, lattice block panels are produced by direct casting and result in lightweight, fully triangulated truss-like configurations which provide strength and stiffness [2]. The earliest realizations of lattice block were made from A1 and steels, primarily under funding from the US Navy [3]. This work also showed that the mechanical efficiency (eg., specific stiffness) of lattice block structures approached that of honeycomb structures [2]. The lattice architectures are also less anisotropic, and the investment casting route should provide a large advantage in cost and temperature capability over honeycombs which are limited to alloys that can be processed into foils. Based on this early work, a program was initiated to determine the feasibility of extending the high temperature superalloy lattice block [3]. The objective of this effort was to provide an alternative to intermetallics and composites in achieving a lightweight high temperature structure without sacrificing the damage tolerance and moderate cost inherent in superalloys. To establish the feasibility of the superalloy lattice block concept, work was performed in conjunction with JAMCORP, Inc. Billerica, MA, to produce a number of lattice block panels from both IN71 8 and Mar-M247.

  13. Anisotropic relaxation of a CuO/TiO2 surface under an electric field and its impact on visible light absorption: ab initio calculations.

    PubMed

    Li, Lei; Li, Wenshi; Ji, Aimin; Wang, Ziou; Zhu, Canyan; Zhang, Lijun; Yang, Jianfeng; Mao, Ling-Feng

    2015-07-21

    Ab initio calculations on the anisotropic relaxation of a CuO/TiO2 surface under electric fields and the visible light absorption of these relaxed surfaces are reported. We compare the relaxation of the CuO/TiO2 surface under the electric fields in the direction of [001] or [010]. Fewer Cu-O bonds with highly coordinated Cu-ions are found in the CuO/TiO2 relaxed surface under the electric field in the [010] direction. The Cu-O bonds in the interface of the CuO/TiO2 surface led to an improved visible light absorption in the polarization direction of [001]. The CuO/TiO2 relaxed surface under the electric field in the [010] direction exhibits a more effective absorption of visible light. However, the electric field in the [001] direction induces more relaxation on the CuO/TiO2 surface, breaking the Cu-O bonds. This leads to the partial reduction of CuO to Cu2O on the CuO/TiO2 relaxed surface under the electric field in the [001] direction and inefficient absorption of visible light is observed for this surface.

  14. Numerical evidence for a chiral spin liquid in the XXZ model on the kagome lattice in a magnetic field

    NASA Astrophysics Data System (ADS)

    Changlani, Hitesh; Kumar, Krishna; Clark, Bryan; Fradkin, Eduardo

    Frustrated spin systems in two dimensions provide a fertile ground for discovering exotic states of matter, often with topologically non-trivial properties. In this work, we investigate the possible existence of a chiral spin liquid state in the spin 1/2 XXZ model on the frustrated kagome lattice in the presence of a magnetic field. This model is equivalent to a hard-core bosonic one with density-density interactions at finite filling fraction. Motivated by previous field theoretic predictions utilizing a Chern-Simons theory adapted for this lattice, we focus our attention to understanding the XY limit for the 2/3 magnetization plateau (equivalent to a system of hard-core bosons at 1/6 filling with weak nearest-neighbor repulsive interactions). Performing exact or accurate numerical computations, and based on energetics and construction of minimally entangled states and associated modular matrices, we provide evidence for such a spin liquid. We study the nature of this phase and examine its stability to additional interactions. We acknowledge support from the SciDAC program under Award Number DE-FG02-12ER46875.

  15. Beyond mean-field bistability in driven-dissipative lattices: Bunching-antibunching transition and quantum simulation

    NASA Astrophysics Data System (ADS)

    Mendoza-Arenas, J. J.; Clark, S. R.; Felicetti, S.; Romero, G.; Solano, E.; Angelakis, D. G.; Jaksch, D.

    2016-02-01

    In the present work we investigate the existence of multiple nonequilibrium steady states in a coherently driven X Y lattice of dissipative two-level systems. A commonly used mean-field ansatz, in which spatial correlations are neglected, predicts a bistable behavior with a sharp shift between low- and high-density states. In contrast one-dimensional matrix product methods reveal these effects to be artifacts of the mean-field approach, with both disappearing once correlations are taken fully into account. Instead, a bunching-antibunching transition emerges. This indicates that alternative approaches should be considered for higher spatial dimensions, where classical simulations are currently infeasible. Thus we propose a circuit QED quantum simulator implementable with current technology to enable an experimental investigation of the model considered.

  16. Transferable Anisotropic United-Atom Force Field Based on the Mie Potential for Phase Equilibrium Calculations: n-Alkanes and n-Olefins.

    PubMed

    Hemmen, Andrea; Gross, Joachim

    2015-09-01

    A new transferable force field parametrization for n-alkanes and n-olefins is proposed in this work. A united-atom approach is taken, where hydrogen atoms are lumped with neighboring atoms to single interaction sites. A comprehensive study is conducted for alkanes, optimizing van der Waals force field parameters in 6 dimensions. A Mie n-6 potential is considered for the van der Waals interaction, where for n-alkanes we simultaneously optimize the energy parameters ϵCH3 and ϵCH2 as well as the size parameters σCH3 and σCH2 of the CH3(sp(3)) and CH2(sp(3)) groups. Further, the repulsive exponent n of the Mie n-6 potential is varied. Moreover, we investigate the bond length toward the terminal CH3 group as a degree of freedom. According to the AUA (anisotropic united-atom) force field, the bond length between the terminal CH3 group and the neighboring interaction site should be increased by Δl compared with the carbon-carbon distance in order to better account for the hydrogen atoms. The parameter Δl is considered as a degree of freedom. The intramolecular force field parametrization is taken from existing force fields. A single objective function for the optimization is defined as squared relative deviations in vapor pressure and in liquid density of propane, n-butane, n-hexane, and n-octane. A similar study is also done for olefins, where the objective function includes 1-butene, 1-hexene, 1-octene, cis-2-pentene, and trans-2-pentene. Molecular simulations are performed in the grand canonical ensemble with transition-matrix sampling where the phase equilibrium properties are obtained with the histogram reweighting technique. The 6-dimensional optimization of strongly correlated parameters is possible, because the analytic PC-SAFT equation of state is used to locally correlate simulation results. The procedure is iterative but leads to very efficient convergence. An implementation is proposed, where the converged result is not affected (disturbed) by the

  17. Prestack inversion based on anisotropic Markov random field-maximum posterior probability inversion and its application to identify shale gas sweet spots

    NASA Astrophysics Data System (ADS)

    Wang, Kang-Ning; Sun, Zan-Dong; Dong, Ning

    2015-12-01

    Economic shale gas production requires hydraulic fracture stimulation to increase the formation permeability. Hydraulic fracturing strongly depends on geomechanical parameters such as Young's modulus and Poisson's ratio. Fracture-prone sweet spots can be predicted by prestack inversion, which is an ill-posed problem; thus, regularization is needed to obtain unique and stable solutions. To characterize gas-bearing shale sedimentary bodies, elastic parameter variations are regarded as an anisotropic Markov random field. Bayesian statistics are adopted for transforming prestack inversion to the maximum posterior probability. Two energy functions for the lateral and vertical directions are used to describe the distribution, and the expectation-maximization algorithm is used to estimate the hyperparameters of the prior probability of elastic parameters. Finally, the inversion yields clear geological boundaries, high vertical resolution, and reasonable lateral continuity using the conjugate gradient method to minimize the objective function. Antinoise and imaging ability of the method were tested using synthetic and real data.

  18. Anisotropic local modification of crystal field levels in Pr-based pyrochlores: a muon-induced effect modeled using density functional theory.

    PubMed

    Foronda, F R; Lang, F; Möller, J S; Lancaster, T; Boothroyd, A T; Pratt, F L; Giblin, S R; Prabhakaran, D; Blundell, S J

    2015-01-01

    Although muon spin relaxation is commonly used to probe local magnetic order, spin freezing, and spin dynamics, we identify an experimental situation in which the measured response is dominated by an effect resulting from the muon-induced local distortion rather than the intrinsic behavior of the host compound. We demonstrate this effect in some quantum spin ice candidate materials Pr(2)B(2)O(7) (B=Sn, Zr, Hf), where we detect a static distribution of magnetic moments that appears to grow on cooling. Using density functional theory we show how this effect can be explained via a hyperfine enhancement arising from a splitting of the non-Kramers doublet ground states on Pr ions close to the muon, which itself causes a highly anisotropic distortion field. We provide a quantitative relationship between this effect and the measured temperature dependence of the muon relaxation and discuss the relevance of these observations to muon experiments in other magnetic materials.

  19. Dynamical analysis of anisotropic inflation

    NASA Astrophysics Data System (ADS)

    Karčiauskas, Mindaugas

    2016-06-01

    The inflaton coupling to a vector field via the f(φ)2F μνFμν term is used in several contexts in the literature, such as to generate primordial magnetic fields, to produce statistically anisotropic curvature perturbation, to support anisotropic inflation, and to circumvent the η-problem. In this work, I perform dynamical analysis of this system allowing for the most general Bianchi I initial conditions. I also confirm the stability of attractor fixed points along phase-space directions that had not been investigated before.

  20. Fractures in anisotropic media

    NASA Astrophysics Data System (ADS)

    Shao, Siyi

    theory and experimental results in this report demonstrate that the presence of fractures in anisotropic material can be unambiguously interpreted if experimental measurements are made as a function of stress, which eliminates many fracture-generated discrete modes (e.g., interface waves, and leaky guided-modes). Orthogonal fracture networks that are often encountered in field exploration bring in additional challenges for seismic/acoustic data interpretation. An innovative wavefront imaging system with a bi-axial load frame was designed and implemented on orthogonally-fractured samples to determine the effect of fracture networks on elastic wave propagation. The effects of central wave guiding and extra time delays along a fracture intersection were observed in experiments and was analyzed. Interpreting data from media with intersecting fracture sets must account for fracture intersections and the non-uniformity of fracture properties caused by local tectonic conditions or other physical process such as non-uniform fluid distributions within a network and/or chemical alterations.

  1. Fluctuating pancake vortices revealed by dissipation of Josephson vortex lattice.

    SciTech Connect

    Koshelev, A. E.; Buzdin, A. I.; Kakeya, I.; Yamamoto, T.; Kadowaki, K.

    2011-06-01

    In strongly anisotropic layered superconductors in tilted magnetic fields, the Josephson vortex lattice coexists with the lattice of pancake vortices. Due to the interaction between them, the dissipation of the Josephson vortex lattice is very sensitive to the presence of the pancake vortices. If the c-axis magnetic field is smaller than the corresponding lower critical field, the pancake stacks are not formed but the individual pancakes may exist in the fluctuational regime either near the surface in large-size samples or in the central region for small-size mesas. We calculate the contribution of such fluctuating pancake vortices to the c-axis conductivity of the Josephson vortex lattice and compare the theoretical results with measurements on small mesas fabricated out of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} crystals. A fingerprint of fluctuating pancakes is a characteristic exponential dependence of the c-axis conductivity observed experimentally. Our results provide strong evidence of the existence of the fluctuating pancakes and their influence on the Josephson vortex lattice dissipation.

  2. Electron drift velocity in lattice-matched AlInN/AlN/GaN channel at high electric fields

    NASA Astrophysics Data System (ADS)

    Ardaravičius, L.; Ramonas, M.; Liberis, J.; Kiprijanovič, O.; Matulionis, A.; Xie, J.; Wu, M.; Leach, J. H.; Morkoç, H.

    2009-10-01

    Hot-electron transport was probed by nanosecond-pulsed measurements for a nominally undoped two-dimensional channel confined in a nearly lattice-matched Al0.82In0.18N/AlN/GaN structure at room temperature. The electric field was applied parallel to the interface, the pulsed technique enabled minimization of Joule heating. No current saturation was reached at fields up to 180 kV/cm. The effect of the channel length on the current is considered. The electron drift velocity is deduced under the assumption of uniform electric field and field-independent electron density. The highest estimated drift velocity reaches ˜3.2×107 cm/s when the AlN spacer thickness is 1 nm. At high fields, a weak (if any) dependence of the drift velocity on the spacer thickness is found in the range from 1 to 2 nm. The measured drift velocity is low for heterostructures with thinner spacers (0.3 nm).

  3. Anisotropically structured magnetic aerogel monoliths

    NASA Astrophysics Data System (ADS)

    Heiligtag, Florian J.; Airaghi Leccardi, Marta J. I.; Erdem, Derya; Süess, Martin J.; Niederberger, Markus

    2014-10-01

    Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture.Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture. Electronic supplementary information (ESI) available: Digital photographs of dispersions and gels with different water-to-ethanol ratios; magnetic measurements of an anatase aerogel containing 0.25 mol% Fe3O4 nanoparticles; XRD patterns of the iron oxide and

  4. Logic gates realized by nonvolatile GeTe/Sb2Te3 super lattice phase-change memory with a magnetic field input

    NASA Astrophysics Data System (ADS)

    Lu, Bin; Cheng, Xiaomin; Feng, Jinlong; Guan, Xiawei; Miao, Xiangshui

    2016-07-01

    Nonvolatile memory devices or circuits that can implement both storage and calculation are a crucial requirement for the efficiency improvement of modern computer. In this work, we realize logic functions by using [GeTe/Sb2Te3]n super lattice phase change memory (PCM) cell in which higher threshold voltage is needed for phase change with a magnetic field applied. First, the [GeTe/Sb2Te3]n super lattice cells were fabricated and the R-V curve was measured. Then we designed the logic circuits with the super lattice PCM cell verified by HSPICE simulation and experiments. Seven basic logic functions are first demonstrated in this letter; then several multi-input logic gates are presented. The proposed logic devices offer the advantages of simple structures and low power consumption, indicating that the super lattice PCM has the potential in the future nonvolatile central processing unit design, facilitating the development of massive parallel computing architecture.

  5. Engineering novel optical lattices.

    PubMed

    Windpassinger, Patrick; Sengstock, Klaus

    2013-08-01

    Optical lattices have developed into a widely used and highly recognized tool to study many-body quantum physics with special relevance for solid state type systems. One of the most prominent reasons for this success is the high degree of tunability in the experimental setups. While at the beginning quasi-static, cubic geometries were mainly explored, the focus of the field has now shifted toward new lattice topologies and the dynamical control of lattice structures. In this review we intend to give an overview of the progress recently achieved in this field on the experimental side. In addition, we discuss theoretical proposals exploiting specifically these novel lattice geometries. PMID:23828639

  6. Nuclear spin-lattice relaxation at field-induced level crossings in a Cr8F8 pivalate single crystal

    NASA Astrophysics Data System (ADS)

    Yamamoto, Shoji

    2016-01-01

    We construct a microscopic theory for the proton spin-lattice relaxation-rate 1 / T1 measurements around field-induced level crossings in a single crystal of the trivalent chromium ion wheel complex [Cr8F8(OOCtBu)16] at sufficiently low temperatures [E. Micotti et al., Phys. Rev. B 72 (2005) 020405(R)]. Exactly diagonalizing a well-equipped spin Hamiltonian for the individual clusters and giving further consideration to their possible interactions, we reveal the mechanism of 1 / T1 being single-peaked normally at the first level crossing but double-peaked intriguingly around the second level crossing. We wipe out the doubt about poor crystallization and find out a solution-intramolecular alternating Dzyaloshinsky-Moriya interaction combined with intermolecular coupling of antiferromagnetic character, each of which is so weak as several tens of mK in magnitude.

  7. Simulated flux-lattice melting and magnetic-field distributions in high-{ital T}{sub {ital c}} superconductors

    SciTech Connect

    Schneider, J.W.; Schafroth, S.; Meier, P.F.

    1995-08-01

    Numerical calculations of the magnetic-field distribution {ital p}({ital B}) in high-{ital T}{sub {ital c}} superconductors have been performed for different regimes of the {ital B}-{ital T} phase diagram to provide a basis for the interpretation of results from muon spin rotation experiments, which measure {ital p}({ital B}) directly. Using a Monte Carlo approach, flux-lattice melting was simulated and the corresponding {ital p}({ital B}) was obtained. Both above and below the melting transition, we find excellent agreement with the line shapes measured in a recent experiment in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} if in addition the shape of the sample is taken into account.

  8. Field-Induced Quantum Phase Transitions in S = 1/2 J1-J2 Heisenberg Model on Square Lattice

    NASA Astrophysics Data System (ADS)

    Morita, Katsuhiro; Shibata, Naokazu

    2016-09-01

    We study the magnetic field dependence of the ground state of the S = 1/2 J1-J2 Heisenberg model on the square lattice by the density matrix renormalization group (DMRG) method. With the use of the sine-square deformation, we obtain eight different ground states including plaquette valence-bond crystal with a finite spin gap, transverse Néel, transverse stripe, 1/2 magnetization plateau with up-up-up-down (uuud), and three new states we named the Y-like, V-like, and Ψ states around J2/J1 = 0.55-0.6. The phase transitions from the transverse Néel (at J2/J1 = 0.55) and stripe (at J2/J1 = 0.6) states to the uuud and Y-like states, respectively, are discontinuous, as in the case of a spin flop.

  9. Study of the phase structure of Abelian field theories through non-lattice, non-perturbative calculations

    SciTech Connect

    Karanikas, A.I.; Ktorides, C.N.; Mavromatos, N.E.

    1986-12-01

    A recently proposed approach to gauge field theories, by which one formulates them non-locally and subsequently approaches locality arbitrarily close, is applied to U(1) gauge theories. We test the possibility that the aformentioned methodology might introduce a measure in the functional integral which supports non-perturbative calculations in the continuum. In particular, we are able to carry relevant calculations pertaining to the expectation value of the Wilson's loop operator in 3+1, 2+1 and 1+1 dimensions. The results are similar to ones obtained through the lattice regularization of R(1) gauge theory, with the important difference that in our case they refer to continuum U(1) gauge theory, as a function of the bare coupling constant. We further solidify the validity of our approach by conducting a calculation referring to the 2-dimensional scalar Heisenberg model, remaining always in the continuum. copyright 1986 Academic Press, Inc.

  10. Multiple lattice instabilities resolved by magnetic-field and disorder sensitivities in MgV2O4

    NASA Astrophysics Data System (ADS)

    Watanabe, Tadataka; Ishikawa, Takashi; Hara, Shigeo; Islam, A. T. M. Nazmul; Wheeler, Elisa M.; Lake, Bella

    2014-09-01

    Ultrasound velocity measurements of the orbitally degenerate frustrated spinel MgV2O4 are performed in a high-purity single crystal which exhibits successive structural and antiferromagnetic phase transitions, and in the disorder-introduced single crystal which exhibits spin-glass-like behavior. The measurements reveal that two types of unusual temperature dependence of the elastic moduli coexist in the cubic paramagnetic phase, which are resolved by magnetic-field and disorder sensitivities: huge Curie-type softening with decreasing temperature (convex temperature dependence), and concave temperature dependence with a characteristic minimum. These elastic anomalies suggest the coupling of the lattice to coexisting orbital fluctuations and spin-cluster excitations.

  11. Spectral-domain-based scattering analysis of fields radiated by distributed sources in planar-stratified environments with arbitrarily anisotropic layers

    NASA Astrophysics Data System (ADS)

    Sainath, Kamalesh; Teixeira, Fernando L.

    2014-12-01

    We discuss the numerically stable, spectral-domain computation and extraction of the scattered electromagnetic field excited by distributed sources embedded in planar-layered environments, where each layer may exhibit arbitrary and independent electrical and magnetic anisotropic response and loss profiles. This stands in contrast to many standard spectral-domain algorithms that are restricted to computing the fields radiated by Hertzian dipole sources in planar-layered environments where the media possess azimuthal-symmetric material tensors (i.e., isotropic, and certain classes of uniaxial, media). Although computing the scattered field, particularly when due to distributed sources, appears (from the analytical perspective, at least) relatively straightforward, different procedures within the computation chain, if not treated carefully, are inherently susceptible to numerical instabilities and (or) accuracy limitations due to the potential manifestation of numerically overflown and (or) numerically unbalanced terms entering the chain. Therefore, primary emphasis herein is given to effecting these tasks in a numerically stable and robust manner for all ranges of physical parameters. After discussing the causes behind, and means to mitigate, these sources of numerical instability, we validate the algorithm's performance against closed-form solutions. Finally, we validate and illustrate the applicability of the proposed algorithm in case studies concerning active remote sensing of marine hydrocarbon reserves embedded deep within lossy, planar-layered media.

  12. A three-dimensional phase field model coupled with lattice kinetics solver for modeling crystal growth in furnaces with accelerated crucible rotation and traveling magnetic field

    SciTech Connect

    Lin, Guang; Bao, Jie; Xu, Zhijie

    2014-11-01

    In this study, which builds on other related work, we present a new three-dimensional numerical model for crystal growth in a vertical solidification system. This model accounts for buoyancy, accelerated crucible rotation technique (ACRT), and traveling magnetic field (TMF) induced convective flow and their effect on crystal growth and the chemical component's transport process. The evolution of the crystal growth interface is simulated using the phase field method. A semi-implicit lattice kinetics solver based on the Boltzmann equation is employed to model the unsteady incompressible flow. A one-way coupled concentration transport model is used to simulate the component fraction variation in both the liquid and solid phases, which can be used to check the quality of the crystal growth.

  13. Effects of the quark field on the ghost propagator of lattice Landau gauge QCD

    SciTech Connect

    Furui, Sadataka; Nakajima, Hideo

    2006-05-01

    Infrared features of the ghost propagator of color-diagonal and color antisymmetric ghost propagator of quenched SU(2) and quenched SU(3) are compared with those of unquenched Kogut-Susskind fermion SU(3) lattice Landau gauge. We compare (i) the fluctuation of the ghost propagator (ii) the ghost condensate parameter v of the local composite operator (LCO) approach, and (iii) the Binder cumulant of color antisymmetric ghost propagator between quenched and unquenched configurations. The color-diagonal SU(3) ghost dressing function of unquenched configurations has weaker singularity than the quenched configurations. In both cases fluctuations become large in q<0.5 GeV. The ghost condensate parameter v in the ghost propagator of the unquenched MILC{sub c} configuration samples is {approx}0.002-0.04 GeV{sup 2} while that of the SU(2) parallel tempering samples is consistent with 0. The Binder cumulant defined as U(q)=1-(1/3)(<{phi}-vector{sup 4}>/(<{phi}-vector{sup 2}>){sup 2}), where {phi}-vector(q) is the color antisymmetric ghost propagator measured by the sample average of gauge fixed configurations via parallel tempering method, becomes {approx}4/9 in all the momentum region. The Binder cumulant of the color antisymmetric ghost propagator of quenched SU(2) can be explained by the 3D Gaussian distribution, but that of the unquenched MILC{sub c} deviates slightly from that of the eight-dimensional Gaussian distribution. The stronger singularity and large fluctuation in the quenched configuration could be the cause of the deviation of the Kugo-Ojima confinement parameter c from 1, and the presence of ordering in the ghost propagator of unquenched configurations makes it closer to 1.

  14. Effect of anisotropy in the S=1 underscreened Kondo lattice

    NASA Astrophysics Data System (ADS)

    Thomas, Christopher; da Rosa Simões, Acirete S.; Lacroix, Claudine; Iglesias, José Roberto; Coqblin, Bernard

    2014-12-01

    We study the effect of crystal field anisotropy in the underscreened S=1 Kondo lattice model. Starting from the two orbital Anderson lattice model and including a local anisotropy term, we show, through Schrieffer-Wolff transformation, that local anisotropy is equivalent to an anisotropic Kondo interaction (J∥≠J⊥). The competition and coexistence between ferromagnetism and Kondo effect in this effective model is studied within a generalized mean-field approximation. Several regimes are obtained, depending on the parameters, exhibiting or not coexistence of magnetic order and Kondo effect. Particularly, we show that a re-entrant Kondo phase at low temperature can be obtained. We are also able to describe phases where the Kondo temperature is smaller than the Curie temperature (TK

  15. Canonical quantization of lattice Higgs-Yang-Mills fields: Krein essential selfadjointness of the Hamiltonian

    NASA Astrophysics Data System (ADS)

    Challifour, John L.; Timko, Edward J.

    2016-06-01

    Using a Krein indefinite metric in Fock space, the Hamiltonian for cut-off models of canonically quantized Higgs-Yang-Mills fields interpolating between the Gupta-Bleuler-Feynman and Landau gauges is shown to be essentially maximal accretive and essentially Krein selfadjoint.

  16. Chiral Spin Liquids in Triangular-Lattice SU (N ) Fermionic Mott Insulators with Artificial Gauge Fields

    NASA Astrophysics Data System (ADS)

    Nataf, Pierre; Lajkó, Miklós; Wietek, Alexander; Penc, Karlo; Mila, Frédéric; Läuchli, Andreas M.

    2016-10-01

    We show that, in the presence of a π /2 artificial gauge field per plaquette, Mott insulating phases of ultracold fermions with SU (N ) symmetry and one particle per site generically possess an extended chiral phase with intrinsic topological order characterized by an approximate ground space of N low-lying singlets for periodic boundary conditions, and by chiral edge states described by the SU(N ) 1 Wess-Zumino-Novikov-Witten conformal field theory for open boundary conditions. This has been achieved by extensive exact diagonalizations for N between 3 and 9, and by a parton construction based on a set of N Gutzwiller projected fermionic wave functions with flux π /N per triangular plaquette. Experimental implications are briefly discussed.

  17. Lattice-induced double-valley degeneracy lifting in graphene by a magnetic field.

    PubMed

    Luk'yanchuk, Igor A; Bratkovsky, Alexander M

    2008-05-01

    We show that the recently discovered double-valley splitting of the Landau levels in the quantum Hall effect in graphene can be explained as the perturbative orbital interaction of intravalley and intervalley microscopic orbital currents with a magnetic field. This effect is facilitated by the translationally noninvariant terms that correspond to graphene's crystallographic honeycomb symmetry but do not exist in the relativistic theory of massless Dirac fermions in quantum electrodynamics. We discuss recent data in view of these findings.

  18. Optical lattice quantum simulator for quantum electrodynamics in strong external fields: spontaneous pair creation and the Sauter-Schwinger effect

    NASA Astrophysics Data System (ADS)

    Szpak, N.; Schützhold, R.

    2012-03-01

    The spontaneous creation of electron-positron pairs out of the vacuum due to a strong electric field is a spectacular manifestation of the relativistic energy-momentum relation for the Dirac fermions. This fundamental prediction of quantum electrodynamics has not yet been confirmed experimentally, as the generation of a sufficiently strong electric field extending over a large enough space-time volume still presents a challenge. Surprisingly, distant areas of physics may help us to circumvent this difficulty. In condensed matter and solid state physics (areas commonly considered as low-energy physics), one usually deals with quasi-particles instead of real electrons and positrons. Since their mass gap can often be freely tuned, it is much easier to create these light quasi-particles by an analogue of the Sauter-Schwinger effect. This motivates our proposal for a quantum simulator in which excitations of ultra-cold atoms moving in a bichromatic optical lattice represent particles and antiparticles (holes) satisfying a discretized version of the Dirac equation together with fermionic anti-commutation relations. Using the language of second quantization, we are able to construct an analogue of the spontaneous pair creation which can be realized in an (almost) table-top experiment.

  19. Terminal shape and velocity of a rising bubble by phase-field-based incompressible Lattice Boltzmann model

    NASA Astrophysics Data System (ADS)

    Ren, Feng; Song, Baowei; Sukop, Michael C.

    2016-11-01

    This article describes the simulation of three-dimensional buoyancy-driven bubble rise using a phase-field-based incompressible Lattice Boltzmann model. The effect of the Cahn-Hilliard mobility parameter, which is the rate of diffusion relaxation from non-equilibrium toward equilibrium state of chemical potential, is evaluated in detail. In contrast with previous work that pursues a high density ratio of binary fluids in the hydrodynamic equation, we apply a large dynamic viscosity ratio, together with a matched density pair and a separate compensating gas phase buoyant force, and the numerical results fit previous experimental results well. Through analysis, it is noted that for cases with moderate Reynolds number, a large value of mobility keeps a relatively sharp interface, while smaller values of mobility would result in diffusive interfacial regions. Moreover, for cases with large Reynolds number, small bubbles at the tail tend to separate more easily when the value of mobility is larger. This article offers some potentially useful details for performing phase-field-based simulations.

  20. Lattice Boltzmann method for binary fluids based on mass-conserving quasi-incompressible phase-field theory

    NASA Astrophysics Data System (ADS)

    Yang, Kang; Guo, Zhaoli

    2016-04-01

    In this paper, a lattice Boltzmann equation (LBE) model is proposed for binary fluids based on a quasi-incompressible phase-field model [J. Shen et al., Commun. Comput. Phys. 13, 1045 (2013), 10.4208/cicp.300711.160212a]. Compared with the other incompressible LBE models based on the incompressible phase-field theory, the quasi-incompressible model conserves mass locally. A series of numerical simulations are performed to validate the proposed model, and comparisons with an incompressible LBE model [H. Liang et al., Phys. Rev. E 89, 053320 (2014), 10.1103/PhysRevE.89.053320] are also carried out. It is shown that the proposed model can track the interface accurately. As the stationary droplet and rising bubble problems, the quasi-incompressible LBE gives nearly the same predictions as the incompressible model, but the compressible effect in the present model plays a significant role in the phase separation problem. Therefore, in general cases the present mass-conserving model should be adopted.

  1. Quantum field theory for the three-body constrained lattice Bose gas. II. Application to the many-body problem

    NASA Astrophysics Data System (ADS)

    Diehl, S.; Baranov, M.; Daley, A. J.; Zoller, P.

    2010-08-01

    We analyze the ground-state phase diagram of attractive lattice bosons, which are stabilized by a three-body onsite hardcore constraint. A salient feature of this model is an Ising-type transition from a conventional atomic superfluid to a dimer superfluid with vanishing atomic condensate. The study builds on an exact mapping of the constrained model to a theory of coupled bosons with polynomial interactions, proposed in a related paper [S. Diehl, M. Baranov, A. Daley, and P. Zoller, Phys. Rev. B 82, 064509 (2010).10.1103/PhysRevB.82.064509]. In this framework, we focus by analytical means on aspects of the phase diagram which are intimately connected to interactions, and are thus not accessible in a mean-field plus spin-wave approach. First, we determine shifts in the mean-field phase border, which are most pronounced in the low-density regime. Second, the investigation of the strong coupling limit reveals the existence of a “continuous supersolid,” which emerges as a consequence of enhanced symmetries in this regime. We discuss its experimental signatures. Third, we show that the Ising-type phase transition, driven first order via the competition of long-wavelength modes at generic fillings, terminates into a true Ising quantum critical point in the vicinity of half filling.

  2. Anisotropic Thermal Diffusion

    NASA Astrophysics Data System (ADS)

    Gardiner, Thomas

    2013-10-01

    Anisotropic thermal diffusion in magnetized plasmas is an important physical phenomena for a diverse set of physical conditions ranging from astrophysical plasmas to MFE and ICF. Yet numerically simulating this phenomenon accurately poses significant challenges when the computational mesh is misaligned with respect to the magnetic field. Particularly when the temperature gradients are unresolved, one frequently finds entropy violating solutions with heat flowing from cold to hot zones for χ∥ /χ⊥ >=102 which is substantially smaller than the range of interest which can reach 1010 or higher. In this talk we present a new implicit algorithm for solving the anisotropic thermal diffusion equations and demonstrate its characteristics on what has become a fairly standard set of test problems in the literature. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2013-5687A.

  3. Constraining anisotropic baryon oscillations

    NASA Astrophysics Data System (ADS)

    Padmanabhan, Nikhil; White, Martin

    2008-06-01

    We present an analysis of anisotropic baryon acoustic oscillations and elucidate how a mis-estimation of the cosmology, which leads to incorrect values of the angular diameter distance, dA, and Hubble parameter, H, manifest themselves in changes to the monopole and quadrupole power spectrum of biased tracers of the density field. Previous work has focused on the monopole power spectrum, and shown that the isotropic dilation combination dA2H-1 is robustly constrained by an overall shift in the scale of the baryon feature. We extend this by demonstrating that the quadrupole power spectrum is sensitive to an anisotropic warping mode dAH, allowing one to break the degeneracy between dA and H. We describe a method for measuring this warping, explicitly marginalizing over the form of redshift-space distortions. We verify this method on N-body simulations and estimate that dAH can be measured with a fractional accuracy of ˜(3/V)% where the survey volume is estimated in h-3Gpc3.

  4. Coarsening dynamics in elastically anisotropic alloys

    SciTech Connect

    Pfau, B.; Stadler, L.-M.; Sepiol, B.; Vogl, G.; Weinkamer, R.; Kantelhardt, J. W.; Zontone, F.

    2006-05-01

    We study in situ the coarsening dynamics in elastically anisotropic phase-separating alloys, taking advantage of coherent x rays. Temporally fluctuating speckle intensities are analyzed for two different Ni-Al-Mo samples with different lattice misfits between precipitates and matrix. The detected long-term correlations depend not only on the norm but strongly on the direction of the scattering vector--an unambiguous proof of direction-dependent coarsening dynamics. For strong lattice misfits, our results indicate coalescence of precipitates in the {l_brace}100{r_brace} planes.

  5. Elucidation of Ground-State Spin Configurations of Ising Models in a Magnetic Field with Frustration on a Diamond Hierarchical Lattice

    NASA Astrophysics Data System (ADS)

    Hirose, Yuhei; Oguchi, Akihide; Fukumoto, Yoshiyuki

    2015-10-01

    To study the ground-state spin configuration as a function of magnetic field, the spin configurations at each stage lattice are determined by analyzing recursion equations. The exact calculation of the magnetization curve by Hirose et al. [J. Phys. Soc. Jpn. 83, 074716 (2014)] shows that an infinitely small applied magnetic field on the zero-field classical spin-liquid phase can induce an infinitely small magnetization, which is as if this Ising system has a gapless spectrum. In this study, we reveal that an infinitely small applied field makes a large number of spins flip upwards with the exchange-energy loss remaining finite. This exotic behavior originates from the frustration effect of diamond structures and an inherent long-range nature of hierarchical lattices.

  6. Modeling of anisotropic two-dimensional materials monolayer HfS{sub 2} and phosphorene metal-oxide semiconductor field effect transistors

    SciTech Connect

    Chang, Jiwon

    2015-06-07

    Ballistic transport characteristics of metal-oxide semiconductor field effect transistors (MOSFETs) based on anisotropic two-dimensional materials monolayer HfS{sub 2} and phosphorene are explored through quantum transport simulations. We focus on the effects of the channel crystal orientation and the channel length scaling on device performances. Especially, the role of degenerate conduction band (CB) valleys in monolayer HfS{sub 2} is comprehensively analyzed. Benchmarking monolayer HfS{sub 2} with phosphorene MOSFETs, we predict that the effect of channel orientation on device performances is much weaker in monolayer HfS{sub 2} than in phosphorene due to the degenerate CB valleys of monolayer HfS{sub 2}. Our simulations also reveal that at 10 nm channel length scale, phosphorene MOSFETs outperform monolayer HfS{sub 2} MOSFETs in terms of the on-state current. However, it is observed that monolayer HfS{sub 2} MOSFETs may offer comparable, but a little bit degraded, device performances as compared with phosphorene MOSFETs at 5 nm channel length.

  7. Does the temperature dependence at constant volume of the hyperfine field of heavy impurities in ferromagnetic metals depend explicitly upon the amplitude of lattice vibrations?

    NASA Astrophysics Data System (ADS)

    Riedi, P. C.; Webber, G. D.

    1983-12-01

    Lattice dynamics seem to have little effect on the temperature dependence of the hyperfine field of pure iron and nickel and of most impurities in these metals but it is shown that Au in iron may be an exception to this rule. The hyperfine fields of other heavy impurities ( FeRu, FeIr, NiPt) were found to have a normal temperature dependence.

  8. Dynamic mean field theory for lattice gas models of fluid mixtures confined in mesoporous materials.

    PubMed

    Edison, J R; Monson, P A

    2013-11-12

    We present the extension of dynamic mean field theory (DMFT) for fluids in porous materials (Monson, P. A. J. Chem. Phys. 2008, 128, 084701) to the case of mixtures. The theory can be used to describe the relaxation processes in the approach to equilibrium or metastable equilibrium states for fluids in pores after a change in the bulk pressure or composition. It is especially useful for studying systems where there are capillary condensation or evaporation transitions. Nucleation processes associated with these transitions are emergent features of the theory and can be visualized via the time dependence of the density distribution and composition distribution in the system. For mixtures an important component of the dynamics is relaxation of the composition distribution in the system, especially in the neighborhood of vapor-liquid interfaces. We consider two different types of mixtures, modeling hydrocarbon adsorption in carbon-like slit pores. We first present results on bulk phase equilibria of the mixtures and then the equilibrium (stable/metastable) behavior of these mixtures in a finite slit pore and an inkbottle pore. We then use DMFT to describe the evolution of the density and composition in the pore in the approach to equilibrium after changing the state of the bulk fluid via composition or pressure changes. PMID:24102541

  9. Bulk viscosity of anisotropically expanding hot QCD plasma

    SciTech Connect

    Chandra, Vinod

    2011-11-01

    The bulk viscosity, {zeta} and its ratio with the shear viscosity, {zeta}/{eta} have been studied in an anisotropically expanding pure glue plasma in the presence of turbulent color fields. It has been shown that the anisotropy in the momentum distribution function of gluons, which has been determined from a linearized transport equation eventually leads to the bulk viscosity. For the isotropic (equilibrium) state, a recently proposed quasiparticle model of pure SU(3) lattice QCD equation of state has been employed where the interactions are encoded in the effective fugacity. It has been argued that the interactions present in the equation of state, significantly contribute to the bulk viscosity. Its ratio with the shear viscosity is significant even at 1.5T{sub c}. Thus, one needs to take in account the effects of the bulk viscosity while studying the hydrodynamic expansion of quark-gluon plasma in the Relativistic Heavy Ion Collider and the Large Hadron Collider.

  10. Direct observation of an anisotropic in-plane residual stress induced by B addition as an origin of high magnetic anisotropy field of Ru/FeCoB film

    SciTech Connect

    Hirata, Ken-ichiro; Gomi, Shunsuke; Mashiko, Yasuhiro; Nakagawa, Shigeki

    2010-05-15

    Although boron-free FeCo films prepared on a Ru underlayer exhibits isotropic in-plane magnetic property, boron added FeCoB films prepared on Ru underlayer revealed large in-plane magnetic anisotropy with a high anisotropy field of 500 Oe. The effect of boron addition on the in-plane anisotropic residual stress in FeCoB film was investigated using sin{sup 2} {psi} method of x-ray diffraction analysis. Large isotropic compressive stress was observed in Ru/FeCo film. In contrast, anisotropic in-plane residual stress was observed in Ru/FeCoB film. The compressive stress along the easy axis of Ru/FeCoB film is released more than that along the hard axis. Such anisotropic residual stress is regarded as an origin of the in-plane magnetic anisotropy through inverse magnetostriction effect. Owing to the configuration of the facing targets sputtering system, boron atoms are sputtered and deposited anisotropically, and so they penetrate FeCo crystals and release the compressive stress along the incidence direction.

  11. Josephson Coupling along the c-Axis in Highly Anisotropic High Temperature Superconductors at High-Magnetic-Fields

    NASA Astrophysics Data System (ADS)

    Gray, K. E.; Hettinger+, J. D.; Washburn, B.; Veal, B. W.; Paulikas, A. P.; Kostic, P.

    1996-03-01

    We have extended previous measurements of oxygen deficient YBa_2Cu_3O_y^1 to magnetic fields as high as 27T and temperatures down to 4K. Measurements were made on three samples with different oxygen contents with critical temperatures ranging from 25K to 70K. The results are consistent with those previously reported and extend those measurements over a broader range in parameter space. These measurements demonstrate an unusual temperature dependent electron transmission suggesting increased c-axis coherency below T_c. The temperature dependence of the electron transmission extends to the lowest temperatures measured. ^+Present address: Rowan College of New Jersey. High-magnetic field measurements performed with the assistance of S. T. Hannahs at the NHMFL funded by the NSF. We acknowledge the support of the D.O.E., Divisions of Basic Energy Sciences-Materials Sciences under contract W-31-109-ENG-38, and the NSF-Office of Science and Technology Centers under contract DMR 91-20000. ^1J. D. Hettinger, K. E. Gray, B.W. Veal, A. P. Paulikas, P. Kostic, B. R. Washburn, W. C. Tonjes, and A. C. Flewelling, Phys. Rev. Lett. 74, 4726 (1995).

  12. Cascade Baryon Spectrum from Lattice QCD

    SciTech Connect

    Mathur, Nilmani; Bulava, John; Edwards, Robert; Engelson, Eric; Joo, Balint; Lichtl, Adam; Lin, Huey-Wen; Morningstar, Colin; Richards, David; Wallace, Stephen

    2008-12-01

    A comprehensive study of the cascade baryon spectrum using lattice QCD affords the prospect of predicting the masses of states not yet discovered experimentally, and determining the spin and parity of those states for which the quantum numbers are not yet known. The study of the cascades, containing two strange quarks, is particularly attractive for lattice QCD in that the chiral effects are reduced compared to states composed only of u/d quarks, and the states are typically narrow. We report preliminary results for the cascade spectrum obtained by using anisotropic Nf = 2 Wilson lattices with temporal lattice spacing 5.56 GeV?1.

  13. Lattice QCD determination of states with spin 5/2 or higher in the spectrum of nucleons

    SciTech Connect

    Stephen Wallace; S. Basak; R. Edwards; George Fleming; J. Juge; A. Lichtl; C. Morningstar; D. Richards; I. Sato

    2006-09-28

    Energies for excited isospin 1/2 states that include the nucleon are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G{sub 2} irreducible representations of the octahedral group. States with spin 5/2 or higher are identified as degenerate energies that occur in irreducible representations of the octahedral group corresponding to the subduction of the continuum spin.

  14. Lattice QCD determination of patterns of excited baryon states

    SciTech Connect

    Basak, Subhasish; Edwards, R. G.; Richards, D. G.; Fleming, G. T.; Juge, K. J.; Lichtl, A.; Morningstar, C.; Sato, I.; Wallace, S. J.

    2007-10-01

    Energies for excited isospin I=(1/2) and I=(3/2) states that include the nucleon and {delta} families of baryons are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G{sub 2} irreducible representations of the octahedral group. The decomposition of spin (5/2) or higher spin states is realized for the first time in a lattice QCD calculation. We observe patterns of degenerate energies in the irreducible representations of the octahedral group that correspond to the subduction of the continuum spin (5/2) or higher. The overall pattern of low-lying excited states corresponds well to the pattern of physical states subduced to the irreducible representations of the octahedral group.

  15. Lattice QCD determination of patterns of excited baryon states

    SciTech Connect

    Subhasish Basak; Robert Edwards; George Fleming; Keisuke Juge; Adam Lichtl; Colin Morningstar; David Richards; Ikuro Sato; Stephen Wallace

    2007-10-01

    Energies for excited isospin I = 1/2 and I = 3/2 states that include the nucleon and Delta families of baryons are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G2 irreducible representations of the octahedral group. The decomposition of spin 5/2 or higher spin states is realized for the first time in a lattice QCD calculation. We observe patterns of degenerate energies in the irreducible representations of the octahedral group that correspond to the subduction of the continuum spin 5/2 or higher. The overall pattern of low-lying excited states corresponds well to the pattern of physical states subduced to the irreducible representations of the octahedral group.

  16. Evidence for a Bound H Dibaryon from Lattice QCD

    SciTech Connect

    Beane, S. R.; Chang, E.; Parreno, A.; Detmold, W.; Orginos, K.; Joo, B.; Lin, H. W.; Savage, M. J.; Luu, T. C.; Torok, A.; Walker-Loud, A.

    2011-04-22

    We present evidence for the existence of a bound H dibaryon, an I=0, J=0, s=-2 state with valence quark structure uuddss, at a pion mass of m{sub {pi}{approx}3}89 MeV. Using the results of lattice QCD calculations performed on four ensembles of anisotropic clover gauge-field configurations, with spatial extents of L{approx}2.0, 2.5, 3.0, and 3.9 fm at a spatial lattice spacing of b{sub s{approx}}0.123 fm, we find an H dibaryon bound by B{sub {infinity}}{sup H}=16.6{+-}2.1{+-}4.6 MeV at a pion mass of m{sub {pi}{approx}3}89 MeV.

  17. Evidence for a bound H-dibaryon from lattice QCD

    SciTech Connect

    Beane, S R; Detmold, W; Lin, H W; Luu, T C; Orginos, K; Parreno, A; Savage, M J; Torok, A; Walker-Loud, A

    2011-04-01

    We present evidence for the existence of a bound H-dibaryon, an I = 0, J = 0, s = -2 state with valence quark structure uuddss, at a pion mass of m_\\pi < 389 MeV. Extrapolating the results of lattice QCD calculations performed on four ensembles of anisotropic clover gauge-field configurations, with spatial extents of L < 2.0, 2.5, 3.0 and 3.9 fm at a spatial lattice spacing of b_s < 0.123 fm, we find an H-dibaryon bound by B_ ^H = 16.6±2.1±4.6 MeV at a pion mass of m_\\pi < 389 MeV.

  18. Effects of anisotropy in simple lattice geometries on many-body properties of ultracold fermions in optical lattices

    NASA Astrophysics Data System (ADS)

    Golubeva, Anna; Sotnikov, Andrii; Hofstetter, Walter

    2015-10-01

    We study the effects of anisotropic hopping amplitudes on quantum phases of ultracold fermions in optical lattices described by the repulsive Fermi-Hubbard model. In particular, using dynamical mean-field theory (DMFT) we investigate the dimensional crossover between the isotropic square and the isotropic cubic lattice. We analyze the phase transition from the antiferromagnetic to the paramagnetic state and observe a significant change in the critical temperature: depending on the interaction strength, the anisotropy can lead to both a suppression or increase. We also investigate the localization properties of the system, such as the compressibility and double occupancy. Using the local-density approximation in combination with DMFT we conclude that density profiles can be used to detect the mentioned anisotropy-driven transitions.

  19. Tight-binding electrons on triangular and kagomé lattices under staggered modulated magnetic fields: quantum Hall effects and Hofstadter butterflies.

    PubMed

    Li, Juan; Wang, Yi-Fei; Gong, Chang-De

    2011-04-20

    We consider the tight-binding models of electrons on a two-dimensional triangular lattice and kagomé lattice under staggered modulated magnetic fields. Such fields have two components: a uniform-flux part with strength φ, and a staggered-flux part with strength Δφ. Various properties of the Hall conductances and Hofstadter butterflies are studied. When φ is fixed, variation of Δφ leads to the quantum Hall transitions and Chern numbers of Landau subbands being redistributed between neighboring pairs. The energy spectra with nonzero Δφs have similar fractal structures but quite different energy gaps compared with the original Hofstadter butterflies of Δφ = 0. Moreover, the fan-like structure of Landau levels in the low magnetic field region is also modified appreciably by Δφ.

  20. Crystal-field states of Kondo lattice heavy fermions CeRuSn3 and CeRhSn3

    NASA Astrophysics Data System (ADS)

    Anand, V. K.; Adroja, D. T.; Britz, D.; Strydom, A. M.; Taylor, J. W.; Kockelmann, W.

    2016-07-01

    Inelastic neutron scattering experiments have been carried out to determine the crystal-field states of the Kondo lattice heavy fermions CeRuSn3 and CeRhSn3. Both the compounds crystallize in LaRuSn3-type cubic structure (space group P m 3 ¯n ) in which the Ce atoms occupy two distinct crystallographic sites with cubic (m 3 ¯ ) and tetragonal (4 ¯m .2 ) point symmetries. The INS data of CeRuSn3 reveal the presence of a broad excitation centered around 6-8 meV, which is accounted by a model based on crystal electric field (CEF) excitations. On the other hand, the INS data of isostructural CeRhSn3 reveal three CEF excitations around 7.0, 12.2, and 37.2 meV. The neutron intensity sum rule indicates that the Ce ions at both cubic and tetragonal Ce sites are in Ce3 + state in both CeRuSn3 and CeRhSn3. The CEF level schemes for both the compounds are deduced. We estimate the Kondo temperature TK=3.1 (2 ) K for CeRuSn3 from neutron quasielastic linewidth in excellent agreement with that determined from the scaling of magnetoresistance which gives TK=3.2 (1 ) K. For CeRhSn3, the neutron quasielastic linewidth gives TK≈4.6 K. For both CeRuSn3 and CeRhSn3, the ground state of Ce3 + turns out to be a quartet for the cubic site and a doublet for the tetragonal site.

  1. Modeling a tracer test at the Grimsel Test Site (GTS) using a lattice Boltzmann method and transmissivity field

    NASA Astrophysics Data System (ADS)

    Kim, J. W.; Lanyon, G. W.; Baik, M. H.; Blechschmidt, I.

    2015-12-01

    A series of tracer tests have been conducted in the Migration (MI) Shear Zone at the Grimsel Test Site (GTS) for the Colloid Formation and Migration Project (CFM). As a part of the series, a dipole test (Tracer Test Run 13-05) using radionuclides, colloids and conservative tracers was performed to determine the breakthrough between CRR99.002-i2 and BOMI87.010-i2. To date, the breakthrough data of only the conservative dye tracer (Amino-G acid) are available. In the preceding project, the Colloid and Radionuclide Retardation Project (CRR), a transmissivity field for the MI shear zone was obtained by the geostatistical inverse modeling approach. In this study, the breakthrough of the tracer was computed by a gray lattice Boltzmann method (LBM). The transmissivity field with finite elements grid was transformed to the effective fracture aperture or flow porosity according to the cubic law, and the grid was uniformalized by the interpolation. The uniform mesh of the effective aperture was utilized as the model domain of the gray LBM. In the gray LBM, the heterogeneity of the aperture was dealt with a partial-bounceback scheme. The profiles of hydraulic heads monitored at the boreholes nearby were used as the reference values in the calculation of the pressure distribution in the model domain. The modeling results could reveal a dominant pathway of tracers in the dipole test. The developed model can be utilized in the calculation of the reactive transports of radionuclides and colloids by coupling with a geochemical model, such as Phreeqc, the Geochemist's Workbench, etc.

  2. Anisotropic inflation in Gauss-Bonnet gravity

    NASA Astrophysics Data System (ADS)

    Lahiri, Sayantani

    2016-09-01

    We study anisotropic inflation with Gauss-Bonnet correction in presence of a massless vector field. In this scenario, exact anisotropic power-law inflation is realized when the inflaton potential, gauge coupling function and the Gauss-Bonnet coupling are exponential functions. We show that anisotropy becomes proportional to two slow-roll parameters of the theory and hence gets enhanced in presence of quadratic curvature corrections. The stability analysis reveals that anisotropic power-law solutions remain stable over a substantially large parameter region.

  3. Optical trapping of the anisotropic crystal nanorod.

    PubMed

    Bareil, Paul B; Sheng, Yunlong

    2015-05-18

    We observed in the optical tweezers experiment that some anisotropic nanorod was stably trapped in an orientation tiled to the beam axis. We explain this trapping with the T-matrix calculation. As the vector spherical wave functions do not individually satisfy the anisotropic vector wave equation, we expand the incident and scattered fields in the isotropic buffer in terms of E→, and the internal field in the anisotropic nanoparticle in terms of D→, and use the boundary condition for the normal components of D→ to compute the T-matrix. We found that when the optical axes of an anisotropic nanorod are not aligned to the nanorod axis, the nanorod may be trapped stably at a tilted angle, under which the lateral torque equals to zero and the derivative of the torque is negative. PMID:26074566

  4. Scanning phononic lattices with ultrasound

    SciTech Connect

    Vines, R.E.; Wolfe, J.P.; Every, A.V.

    1999-11-01

    A method for probing the elastic properties of newly developed periodic structures using acoustic waves is introduced. Highly anisotropic transmission of surface acoustic waves is observed by continuously scanning the wave vector angle. Preliminary models of wave propagation through multilayers and two-dimensional lattices explain some of the experimental features, while other features can be attributed to the resonant excitation of interface waves. {copyright} {ital 1999} {ital The American Physical Society}

  5. THE EMMA LATTICE DESIGN

    SciTech Connect

    BERG,J.S.; RUGGIERO, A.; MACHIDA, S.; KOSCIELNIAK, S.

    2007-06-25

    EMMA is a 10 to 20 MeV electron ring designed to test our understanding of beam dynamics in a relativistic linear non-scaling fixed field alternating gradient accelerator (FFAG). This paper describes the design of the EMMA lattice. We begin with a summary of the experimental goals that impact the lattice design, and then outline what motivated the choice for the basic lattice parameters, such as the type of cells, the number of cells, and the RF frequency. We next list the different configurations that we wish to operate the machine in so as to accomplish our experimental goals. Finally, we enumerate the detailed lattice parameters, showing how these parameters result from the various lattice configurations.

  6. Inflation in anisotropic scalar-tensor theories

    NASA Technical Reports Server (NTRS)

    Pimentel, Luis O.; Stein-Schabes, Jaime

    1988-01-01

    The existence of an inflationary phase in anisotropic Scalar-Tensor Theories is investigated by means of a conformal transformation that allows us to rewrite these theories as gravity minimally coupled to a scalar field with a nontrivial potential. The explicit form of the potential is then used and the No Hair Theorem concludes that there is an inflationary phase in all open or flat anisotropic spacetimes in these theories. Several examples are constructed where the effect becomes manifest.

  7. Competing orders in a dipolar Bose-Fermi mixture on a square optical lattice: mean-field perspective

    NASA Astrophysics Data System (ADS)

    Scaramazza, Jasen A.; Kain, Ben; Ling, Hong Y.

    2016-07-01

    We consider a mixture of a two-component Fermi gas and a single-component dipolar Bose gas in a square optical lattice and reduce it into an effective Fermi system where the Fermi-Fermi interaction includes the attractive interaction induced by the phonons of a uniform dipolar Bose-Einstein condensate. Focusing on this effective Fermi system in the parameter regime that preserves the symmetry of D4, the point group of a square, we explore, within the Hartree-Fock-Bogoliubov mean-field theory, the phase competition among density wave orderings and superfluid pairings. We construct the matrix representation of the linearized gap equation in the irreducible representations of D4. We show that in the weak coupling regime, each matrix element, which is a four-dimensional (4D) integral in momentum space, can be put in a separable form involving a 1D integral, which is only a function of temperature and the chemical potential, and a pairing-specific "effective" interaction, which is an analytical function of the parameters that characterize the Fermi-Fermi interactions in our system. We analyze the critical temperatures of various competing orders as functions of different system parameters in both the absence and presence of the dipolar interaction. We find that close to half filling, the dx2 - y2-wave pairing with a critical temperature in the order of a fraction of Fermi energy (at half filling) may dominate all other phases, and at a higher filling factor, the p-wave pairing with a critical temperature in the order of a hundredth of Fermi energy may emerge as a winner. We find that tuning a dipolar interaction can dramatically enhance the pairings with dxy- and g-wave symmetries but not enough for them to dominate other competing phases.

  8. New charged anisotropic compact models

    NASA Astrophysics Data System (ADS)

    Kileba Matondo, D.; Maharaj, S. D.

    2016-07-01

    We find new exact solutions to the Einstein-Maxwell field equations which are relevant in the description of highly compact stellar objects. The relativistic star is charged and anisotropic with a quark equation of state. Exact solutions of the field equations are found in terms of elementary functions. It is interesting to note that we regain earlier quark models with uncharged and charged matter distributions. A physical analysis indicates that the matter distributions are well behaved and regular throughout the stellar structure. A range of stellar masses are generated for particular parameter values in the electric field. In particular the observed mass for a binary pulsar is regained.

  9. Mean field phase diagram of an SU(2){sub {ital L}}{times}SU(2){sub {ital R}} lattice Higgs-Yukawa model at finite {lambda}

    SciTech Connect

    Pryor, C.

    1996-02-01

    The phase diagram of an SU(2){sub {ital L}}{times}SU(2){sub {ital R}} lattice Higgs-Yukawa model with finite {lambda} is constructed using mean field theory. The phase diagram bears a superficial resemblance to that for {lambda}={infinity}; however, as {lambda} is decreased the paramagnetic region shrinks in size. For small {lambda} the phase transitions remain second order, and no new first order transitions are seen. {copyright} {ital 1996 The American Physical Society.}

  10. Anisotropic Peridotite Rheology and Regional Upper Mantle Flow Patterns

    NASA Astrophysics Data System (ADS)

    Blackman, D. K.; Boyce, D.; Dawson, P.; Castelnau, O.

    2014-12-01

    We investigate the rheologic impact of strong lattice preferred orientation (LPO), such as develops due to plate-driven shear, on the pattern of upper mantle flow near plate boundaries. We use finite element models to simulate a regional system of mantle flow, that includes LPO evolution in olivine polycrystal aggregates tracked along flow paths and anisotropic viscosity tensors based on the LPO. Our first, loosely coupled approach begins with a flow field based on a scalar viscosity. The results are postprocessed to compute LPO by integration along streamlines, and an anisotropic viscosity tensor field is derived from LPO. A new flow field is then computed based on the viscosity tensor field. For this case, the predicted flow field differed in a modest but geologically relevant way from the isotropic case. In preparation for incorporating the LPO and effective viscosity calculation directly into the flow code, we have been testing this step separately to assess the sensitivity of the computed tensor to specified deformation parameters. New work explores a power law stress:strain rate relation for the LPO development, upon which the aggregate's effective viscosity tensor depends. The pattern and amplitude of predicted deviation from isotropic viscosity are stronger than for the previously assumed linear stress:strain rate case, as expected. Initial runs that employ the power law viscosity tensor in updated flow calculations are underway at the time of this writing. In addition to the stress exponent for LPO and the resulting viscosity tensor, flow model parameters that notably impact the predictions include the specified stiffening as asthenosphere cools to lithospheric temperatures and mesh resolution within the axial and the base of lithosphere regions. We will present results for subaxial oceanic spreading center flow and report the outcomes of model parameter testing.

  11. Anisotropic Model Colloids

    NASA Astrophysics Data System (ADS)

    van Kats, C. M.

    2008-10-01

    The driving forces for fundamental research in colloid science are the ability to manage the material properties of colloids and to unravel the forces that play a role between colloids to be able to control and understand the processes where colloids play an important role. Therefore we are searching for colloidal materials with specific physical properties to better understand our surrounding world.Until recently research in colloid science was mainly focused on spherical (isotropic) particles. Monodisperse spherical colloids serve as a model system as they exhibit similar phase behaviour as molecular and atomic systems. Nevertheless, in many cases the spherical shape is not sufficient to reach the desired research goals. Recently the more complex synthesis methods of anisotropic model colloids has strongly developed. This thesis should be regarded as a contribution to this research area. Anisotropic colloids can be used as a building block for complex structures and are expected not only to lead to the construction of full photonic band gap materials. They will also serve as new, more realistic, models systems for their molecular analogues. Therefore the term ‘molecular colloids” is sometimes used to qualify these anisotropic colloidal particles. In the introduction of this thesis, we give an overview of the main synthesis techniques for anisotropic colloids. Chapter 2 describes the method of etching silicon wafers to construct monodisperse silicon rods. They subsequently were oxidized and labeled (coated) with a fluorescent silica layer. The first explorative phase behaviour of these silica rods was studied. The particles showed a nematic ordering in charge stabilized suspensions. Chapter 3 describes the synthesis of colloidal gold rods and the (mesoporous) silica coating of gold rods. Chapter 4 describes the physical and optical properties of these particles when thermal energy is added. This is compared to the case where the particles are irradiated with

  12. Mie scattering by a uniaxial anisotropic sphere

    SciTech Connect

    Geng Youlin; Wu Xinbao; Li Lewei; Guan Boran

    2004-11-01

    The field solution to the electromagnetic scattering of a plane wave by a uniaxial anisotropic sphere is obtained in terms of a spherical vector wave function expansion form. Using the source-free Maxwell's equations for uniaxial anisotropic media and making the Fourier transform of the field quantities, the electromagnetic fields in the spectral domain in uniaxial anisotropic media are assumed to have a form similar to the plane wave expanded also in terms of the spherical vector wave functions. Applying the continuous boundary conditions of electromagnetic fields on the surface between the air region and uniaxial anisotropic sphere, the coefficients of transmitted fields and the scattered fields in uniaxial anisotropic media can be obtained analytically in the expansion form of vector wave eigenfunctions. Numerical results for some special cases are obtained and compared with those of the classical Lorenz-Mie theory and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach. We also present some new numerical results for the more general uniaxial dielectric material media.

  13. Mie scattering by a uniaxial anisotropic sphere.

    PubMed

    Geng, You-Lin; Wu, Xin-Bao; Li, Le-Wei; Guan, Bo-Ran

    2004-11-01

    The field solution to the electromagnetic scattering of a plane wave by a uniaxial anisotropic sphere is obtained in terms of a spherical vector wave function expansion form. Using the source-free Maxwell's equations for uniaxial anisotropic media and making the Fourier transform of the field quantities, the electromagnetic fields in the spectral domain in uniaxial anisotropic media are assumed to have a form similar to the plane wave expanded also in terms of the spherical vector wave functions. Applying the continuous boundary conditions of electromagnetic fields on the surface between the air region and uniaxial anisotropic sphere, the coefficients of transmitted fields and the scattered fields in uniaxial anisotropic media can be obtained analytically in the expansion form of vector wave eigenfunctions. Numerical results for some special cases are obtained and compared with those of the classical Lorenz-Mie theory and the method of moments accelerated with the conjugate-gradient fast-Fourier-transform approach. We also present some new numerical results for the more general uniaxial dielectric material media.

  14. Lennard-Jones and lattice models of driven fluids.

    PubMed

    Díez-Minguito, M; Garrido, P L; Marro, J

    2005-08-01

    We introduce a nonequilibrium off-lattice model for anisotropic phenomena in fluids. This is a Lennard-Jones generalization of the driven lattice-gas model in which the particles' spatial coordinates vary continuously. A comparison between the two models allows us to discuss some exceptional, hardly realistic features of the original discrete system--which has been considered a prototype for nonequilibrium anisotropic phase transitions. We thus help to clarify open issues, and discuss on the implications of our observations for future investigation of anisotropic phase transitions.

  15. Magnetic properties of an Ising ferromagnetic model on a square lattice with next-nearest-neighbor and crystal field interactions

    NASA Astrophysics Data System (ADS)

    De La Espriella, N.; Arenas, Abraham J.; Páez Meza, M. S.

    2016-11-01

    We studied an Ising ferromagnet on a bipartite square lattice with nearest-neighbor ferromagnetic exchange couplings between spin values SiA = 2 and σjB = 5 / 2, next-nearest-neighbor exchange couplings between spins, SiA = 2 and an average term of single-ion anisotropy for each lattice site. We carried out Monte Carlo simulations on the planes (D‧ ,kB T‧) and (J2‧ ,kB T‧) to investigate the influence of exchange parameters J2‧ and anisotropy of D‧ lattice on the critical temperature of the system. The thermal behaviors of the sublattice magnetizations, total magnetization and specific heat were investigated. We found that the critical behavior system depends linearly on the next-nearest-neighbor interaction J2‧ and for antiferromagnetic exchange interactions the system undergoes reentrant phenomena.

  16. Spectroscopy of doubly charmed baryons from lattice QCD

    SciTech Connect

    Padmanath, M.; Edwards, Robert G.; Mathur, Nilmani; Peardon, Michael

    2015-05-06

    This study presents the ground and excited state spectra of doubly charmed baryons from lattice QCD with dynamical quark fields. Calculations are performed on anisotropic lattices of size 16³ × 128, with inverse spacing in temporal direction at⁻¹=5.67(4) GeV and with a pion mass of about 390 MeV. A large set of baryonic operators that respect the symmetries of the lattice yet which retain a memory of their continuum analogues are used. These operators transform as irreducible representations of SU(3)F symmetry for flavor, SU(4) symmetry for Dirac spins of quarks and O(3) for spatial symmetry. The distillation method is utilized to generate baryon correlation functions which are analyzed using the variational fitting method to extract excited states. The lattice spectra obtained have baryonic states with well-defined total spins up to 7/2 and the pattern of low-lying states does not support the diquark picture for doubly charmed baryons. On the contrary the calculated spectra are remarkably similar to the expectations from models with an SU(6)×O(3) symmetry. Various spin-dependent energy splittings between the extracted states are also evaluated.

  17. Polarisation of Thermal Emission under an Anisotropic Radiation

    NASA Astrophysics Data System (ADS)

    Onaka, T.

    1999-12-01

    Aspherical dust grains in an anisotropic radiation field have different temperatures depending on the cross-sections projected to the radiation. The temperature difference produces polarized thermal emission even without alignment, if the observer looks at the grains from a direction different from the anisotropic radiation. When the dust grains are aligned, the anisotropic radiation makes various affects on the polarization of the thermal emission, depending on the relative angle between the anisotropy and alignment directions. This paper presents examples of the effects and demonstrates the importance of anisotropic radiation field on the polarized thermal emission.

  18. Investigation of anisotropic photonic band gaps in three-dimensional magnetized plasma photonic crystals containing the uniaxial material

    SciTech Connect

    Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun

    2013-09-15

    In this paper, the dispersive properties of three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic photonic band gaps (PBGs) in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatbands regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field on the dispersive properties of the 3D MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D MPPCs with fcc lattices and the complete PBGs can be found compared to the conventional 3D MPPCs doped by the isotropic material. The bandwidths of PBGs can be tuned by introducing the magnetized plasma into 3D PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field, respectively. The locations of flatbands regions cannot be manipulated by any parameters except for the plasma frequency and external magnetic field. Introducing the uniaxial material can obtain the complete PBGs as the 3D MPPCs with high symmetry and also provides a way to design the tunable devices.

  19. Investigation of anisotropic photonic band gaps in three-dimensional magnetized plasma photonic crystals containing the uniaxial material

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Feng; Liu, Shao-Bin; Kong, Xiang-Kun

    2013-09-01

    In this paper, the dispersive properties of three-dimensional (3D) magnetized plasma photonic crystals (MPPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in homogeneous magnetized plasma background with face-centered-cubic (fcc) lattices are theoretically investigated by the plane wave expansion method, as the Voigt effects of magnetized plasma are considered. The equations for calculating the anisotropic photonic band gaps (PBGs) in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and two flatbands regions can be obtained. The effects of the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field on the dispersive properties of the 3D MPPCs are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D MPPCs with fcc lattices and the complete PBGs can be found compared to the conventional 3D MPPCs doped by the isotropic material. The bandwidths of PBGs can be tuned by introducing the magnetized plasma into 3D PCs containing the uniaxial material. It is also shown that the anisotropic PBGs can be manipulated by the ordinary-refractive index, extraordinary-refractive index, filling factor, plasma frequency, and external magnetic field, respectively. The locations of flatbands regions cannot be manipulated by any parameters except for the plasma frequency and external magnetic field. Introducing the uniaxial material can obtain the complete PBGs as the 3D MPPCs with high symmetry and also provides a way to design the tunable devices.

  20. Analysis of electromagnetic scattering by uniaxial anisotropic bispheres.

    PubMed

    Li, Zheng-Jun; Wu, Zhen-Sen; Li, Hai-Ying

    2011-02-01

    Based on the generalized multiparticle Mie theory and the Fourier transformation approach, electromagnetic (EM) scattering of two interacting homogeneous uniaxial anisotropic spheres with parallel primary optical axes is investigated. By introducing the Fourier transformation, the EM fields in the uniaxial anisotropic spheres are expanded in terms of the spherical vector wave functions. The interactive scattering coefficients and the expansion coefficients of the internal fields are derived through the continuous boundary conditions on which the interaction of the bispheres is considered. Some selected calculations on the effects of the size parameter, the uniaxial anisotropic absorbing dielectric, and the sphere separation distance are described. The backward radar cross section of two uniaxial anisotropic spheres with a complex permittivity tensor changing with the sphere separation distance is numerically studied. The authors are hopeful that the work in this paper will help provide an effective calibration for further research on the scattering characteristic of an aggregate of anisotropic spheres or other shaped anisotropic particles.

  1. Magnetic vortex lattice in HgBa2CuO4+δ observed by small-angle neutron scattering

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Egetenmeyer, N.; Gavilano, J. L.; Barišić, N.; Greven, M.

    2011-02-01

    We report the direct observation of the magnetic vortex lattice in the model high-temperature superconductor HgBa2CuO4+δ. Using small-angle neutron scattering on high-quality crystals, we observe two equal domains of undistorted triangular vortex lattices well aligned with the tetragonal crystallographic axes. The signal decreases rapidly with increasing magnetic field and vanishes above 0.4 T, which we attribute to a crossover from a three-dimensional to a two-dimensional vortex system, similar to previous results for the more anisotropic compound Bi2.15Sr1.95CaCu2O8+δ. Our result indicates that a triangular vortex lattice (with or without distortion) at low magnetic fields is a generic property of cuprates with critical temperatures above 80 K.

  2. Lattice QCD

    SciTech Connect

    Bornyakov, V.G.

    2005-06-01

    Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.

  3. Spin-lattice coupling in uranium dioxide probed by magnetostriction measurements at high magnetic fields (P08358-E001-PF)

    SciTech Connect

    Gofryk, K.; Jaime, M.

    2014-12-01

    Our preliminary magnetostriction measurements have already shown a strong interplay of lattice dynamic and magnetism in both antiferromagnetic and paramagnetic states, and give unambiguous evidence of strong spin- phonon coupling in uranium dioxide. Further studies are planned to address the puzzling behavior of UO2 in magnetic and paramagnetic states and details of the spin-phonon coupling.

  4. Optimal lattice-structured materials

    DOE PAGESBeta

    Messner, Mark C.

    2016-07-09

    This paper describes a method for optimizing the mesostructure of lattice-structured materials. These materials are periodic arrays of slender members resembling efficient, lightweight macroscale structures like bridges and frame buildings. Current additive manufacturing technologies can assemble lattice structures with length scales ranging from nanometers to millimeters. Previous work demonstrates that lattice materials have excellent stiffness- and strength-to-weight scaling, outperforming natural materials. However, there are currently no methods for producing optimal mesostructures that consider the full space of possible 3D lattice topologies. The inverse homogenization approach for optimizing the periodic structure of lattice materials requires a parameterized, homogenized material model describingmore » the response of an arbitrary structure. This work develops such a model, starting with a method for describing the long-wavelength, macroscale deformation of an arbitrary lattice. The work combines the homogenized model with a parameterized description of the total design space to generate a parameterized model. Finally, the work describes an optimization method capable of producing optimal mesostructures. Several examples demonstrate the optimization method. One of these examples produces an elastically isotropic, maximally stiff structure, here called the isotruss, that arguably outperforms the anisotropic octet truss topology.« less

  5. δN formalism in anisotropic inflation and large anisotropic bispectrum and trispectrum

    SciTech Connect

    Abolhasani, Ali Akbar; Emami, Razieh; Firouzjaee, Javad T.; Firouzjahi, Hassan E-mail: emami@ipm.ir E-mail: firouz@mail.ipm.ir

    2013-08-01

    We present the consistent δN formalism for curvature perturbations in anisotropic cosmological backgrounds. We employ our δN formalism to calculate the power spectrum, the bispectrum and the trispectrum in models of anisotropic inflation with the background gauge fields in Bianchi I universe. Our results coincide exactly with the recent results obtained from in-in formalism. To satisfy the observational constraints the anisotropies generated on power spectrum are kept small but large orientation-dependent non-Gaussianities can be generated. We study the Suyama-Yamaguchi inequality for the amplitudes of the bispectrum and the trispectrum in the presence of anisotropic shapes.

  6. Anisotropic microturbulence near the Sun

    NASA Technical Reports Server (NTRS)

    Coles, William A.; Grall, R. R.; Spangler, S. R.; Sakurai, T.; Harmon, J. K.

    1995-01-01

    Interplanetary scintillation observations which sample the spatial spectrum of electron density at scales between 10 and 100 km show power-law spectra which are flatter than the Kolmogorov spectra observed at larger scales by spacecraft and also, indirectly, by phase scintillation of coherent radio signals. Furthermore, angular broadening observations of compact radio sources have shown that the microscale density fluctuations are field-aligned and become more anisotropic as R decreases inside 10 solar radius. We present angular broadening observations taken in October of 1992 which were recorded nearly simultaneously on the VLA and VLBA arrays. The VLA samples structure at scales between 3 and 30 km, whereas the VLBA samples scales between 200 and 4000 km. The small scale VLA measurements of the south polar source 1246-075 showed lower turbulence than those of the equatorial source 1256-057, consistent with previous work showing that the density delta N(exp 2)(sub e) is a factor of 10-15 lower in coronal holes. The VLA observations inside of 10 solar radius were anisotropic, as expected. We were not able to measure the equatorial source with the VLBA inside of 10 solar radius because the scattering was too strong, however we did observe the polar source just inside this distance with both the VLA and the VLBA. Significant anisotropy was seen on the smaller scales, but the larger scales were essentially isotropic. This suggests that the process responsible for the anisotropic microturbulence is distinct from the larger scale isotropic turbulence.

  7. Finite-volume energy spectrum, fractionalized strings, and low-energy effective field theory for the quantum dimer model on the square lattice

    NASA Astrophysics Data System (ADS)

    Banerjee, D.; Bögli, M.; Hofmann, C. P.; Jiang, F.-J.; Widmer, P.; Wiese, U.-J.

    2016-09-01

    We present detailed analytic calculations of finite-volume energy spectra, mean-field theory, as well as a systematic low-energy effective field theory for the square lattice quantum dimer model. An emergent approximate spontaneously broken SO(2 ) symmetry gives rise to a pseudo-Goldstone boson. Remarkably, this soft phononlike excitation, which is massless at the Rokhsar-Kivelson (RK) point, exists far beyond this point. The Goldstone physics is captured by a systematic low-energy effective field theory. We determine its low-energy parameters by matching the analytic effective field theory with exact diagonalization results. This confirms that the model exists in the columnar (and not in a plaquette or mixed) phase all the way to the RK point.

  8. Magnetic field effects on ultrafast lattice compression dynamics of Si(111) crystal when excited by linearly-polarized femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Hatanaka, Koji; Odaka, Hideho; Ono, Kimitoshi; Fukumura, Hiroshi

    2007-03-01

    Time-resolved X-ray diffraction measurements of Si (111) single crystal are performed when excited by linearly-polarized femtosecond laser pulses (780 nm, 260 fs, negatively-chirped, 1 kHz) under a magnetic field (0.47 T). Laser fluence on the sample surface is 40 mJ/cm^2, which is enough lower than the ablation threshold at 200 mJ/cm^2. Probing X-ray pulses of iron characteristic X-ray lines at 0.193604 and 0.193998 nm are generated by focusing femtosecond laser pulses onto audio-cassette tapes in air. Linearly-polarized femtosecond laser pulse irradiation onto Si(111) crystal surface induces transient lattice compression in the picosecond time range, which is confirmed by transient angle shift of X-ray diffraction to higher angles. Little difference of compression dynamics is observed when the laser polarization is changed from p to s-pol. without a magnetic field. On the other hand, under a magnetic field, the lattice compression dynamics changes when the laser is p-polarized which is vertical to the magnetic field vector. These results may be assigned to photo-carrier formation and energy-band distortion.

  9. Cluster dynamical mean field theory study of antiferromagnetic transition in the square-lattice Hubbard model: Optical conductivity and electronic structure

    NASA Astrophysics Data System (ADS)

    Sato, Toshihiro; Tsunetsugu, Hirokazu

    2016-08-01

    We numerically study optical conductivity σ (ω ) near the "antiferromagnetic" phase transition in the square-lattice Hubbard model at half filling. We use a cluster dynamical mean field theory and calculate conductivity including vertex corrections and, to this end, we have reformulated the vertex corrections in the antiferromagnetic phase. We find that the vertex corrections change various important details in temperature and ω dependencies of conductivity in the square lattice, and this contrasts sharply the case of the Mott transition in the frustrated triangular lattice. Generally, the vertex corrections enhance variations in the ω dependence, and sharpen the Drude peak and a high-ω incoherent peak in the paramagnetic phase. They also enhance the dip in σ (ω ) at ω =0 in the antiferromagnetic phase. Therefore, the dc conductivity is enhanced in the paramagnetic phase and suppressed in the antiferromagnetic phase, but this change occurs slightly below the transition temperature. We also find a temperature region above the transition temperature in which the dc conductivity shows an insulating behavior but σ (ω ) retains the Drude peak, and this region is stabilized by the vertex corrections. We also investigate which fluctuations are important in the vertex corrections and analyze momentum dependence of the vertex function in detail.

  10. Field induced domain switching as the origin of anomalous lattice strain along non-polar direction in rhombohedral BiScO{sub 3}-PbTiO{sub 3} close to the morphotropic phase boundary

    SciTech Connect

    Lalitha, K. V.; Ranjan, Rajeev; Fancher, Chris M.; Jones, Jacob L.

    2015-08-03

    The lattice strain and domain switching behavior of xBiScO{sub 3}–(1-x)PbTiO{sub 3} (x = 0.40) was investigated as a function of cyclic field and grain orientation by in situ X-ray diffraction during application of electric fields. The electric field induced 200 lattice strain was measured to be five times larger than the 111 lattice strain in pseudorhombohedral xBiScO{sub 3}–(1-x)PbTiO{sub 3} (x = 0.40). It is shown that the anomalous 200 lattice strain is not an intrinsic phenomenon, but arises primarily due to stress associated with the reorientation of the 111 domains in dense polycrystalline ceramic.

  11. Quantum states of p-band bosons in optical lattices

    SciTech Connect

    Collin, A.; Larson, J.; Martikainen, J.-P.

    2010-02-15

    We study a gas of repulsively interacting bosons in the first excited band of an optical lattice. We explore this p-band physics both within the framework of a standard mean-field theory as well as with the more accurate generalized Gutzwiller ansatz. We find the phase diagrams for two- and three-dimensional systems and characterize the first Mott-states which typically possess an integer or half-integer vortex structure. Furthermore, we find that even though the p-band model has strongly anisotropic kinetic energies and interflavor interaction terms are missing in the lowest band theory, the mean-field theory becomes useful quite rapidly once the transition from the Mott insulator to the superfluid is crossed.

  12. Anisotropic scaling of magnetohydrodynamic turbulence.

    PubMed

    Horbury, Timothy S; Forman, Miriam; Oughton, Sean

    2008-10-24

    We present a quantitative estimate of the anisotropic power and scaling of magnetic field fluctuations in inertial range magnetohydrodynamic turbulence, using a novel wavelet technique applied to spacecraft measurements in the solar wind. We show for the first time that, when the local magnetic field direction is parallel to the flow, the spacecraft-frame spectrum has a spectral index near 2. This can be interpreted as the signature of a population of fluctuations in field-parallel wave numbers with a k(-2)_(||) spectrum but is also consistent with the presence of a "critical balance" style turbulent cascade. We also find, in common with previous studies, that most of the power is contained in wave vectors at large angles to the local magnetic field and that this component of the turbulence has a spectral index of 5/3.

  13. Magnetization of anisotropic Type II superconductors

    SciTech Connect

    Mints, R.G.

    1989-04-10

    Peculiarities of magnetization of anisotropic type II superconductors are of considerable interest in view of the discovery of high-T/sub c/ superconductors characterized by strongly asymmetric layered structure. Specifics of the penetration of magnetic flux into an anisotropic type II superconductor were discussed in the literature. This analysis gave the distribution of induction in an isolated vortex, its energy, and critical magnetic field H/sub c1/. However, the magnetization curve of anisotropic superconductors was not considered. This paper deals with the magnetic moment of uniaxial London superconductor in the interval H/sub c1/ /le/ H/sub 0/ << H/sub c2/, where H/sub 0/ is the external magnetic field strength.

  14. Gravitational stresses in anisotropic rock masses

    USGS Publications Warehouse

    Amadei, B.; Savage, W.Z.; Swolfs, H.S.

    1987-01-01

    This paper presents closed-form solutions for the stress field induced by gravity in anisotropic rock masses. These rocks are assumed to be laterally restrained and are modelled as a homogeneous, orthotropic or transversely isotropic, linearly elastic material. The analysis, constrained by the thermodynamic requirement that strain energy be positive definite, gives the following important result: inclusion of anisotropy broadens the range of permissible values of gravity-induced horizontal stresses. In fact, for some ranges of anisotropic rock properties, it is thermodynamically admissible for gravity-induced horizontal stresses to exceed the vertical stress component; this is not possible for the classical isotropic solution. Specific examples are presented to explore the nature of the gravity-induced stress field in anisotropic rocks and its dependence on the type, degree and orientation of anisotropy with respect to the horizontal ground surface. ?? 1987.

  15. A simulation study of microwave field effects on a 3D orthorhombic lattice of rotating dipoles: short-range potential energy variation

    NASA Astrophysics Data System (ADS)

    Kapranov, Sergey V.; Kouzaev, Guennadi A.

    2016-05-01

    Variation of the short-range potential energy of interaction of nearest dipoles in a three-dimensional (3D) orthorhombic lattice exposed to microwave electric fields is studied by means of the Langevin dynamics simulations. The global increase of the mean potential energy is typical for all the frequencies and intensities at lower temperatures, whereas separate potential energy peaks or peak chains are observed at intermediate temperatures. A simple statistical model proposed to account for the temperature dependence of the field intensity for potential energy peaks suggests the concerted collective rotation of the dipoles. The temperature dependence of the peak frequency is explained using a combination of the one-dimensional Kramers and the resonant activation theories applied to the field-driven collective rotation, with the nearly degenerate angular coordinates of the dipoles being used as a single effective coordinate.

  16. An investigation of meson spectroscopy on isotropic clover lattices at the SU(3) flavor-symmetric point

    SciTech Connect

    Richards, David G.; Orginos, Konstantinos

    2014-06-23

    We present an investigation of the excited meson spectrum at the N_f= 3 point obtained on isotropic clover lattices with a plaquette Wilson gauge action, and a NP-improved clover fermion action, at a lattice spacing of a \\simeq 0.08 fm, and compare with corresponding calculations on an anisotropic lattice at fine temporal lattice spacing but a spatial lattice spacing of a_s \\simeq 0.125 fm. The methodology adopted follows that employed in the calculation of the spectrum on anisotropic lattices, and we test the efficacy of that approach for isotropic lattices. In particular, we explore the extent to which rotational symmetry for predominantly single-hadron states is realized. By comparison of the energy levels with that obtained using the anisotropic lattice, we obtain an indication of discretization uncertainties in the single-hadron spectrum.

  17. Cryogenic microwave anisotropic artificial materials

    NASA Astrophysics Data System (ADS)

    Trang, Frank

    This thesis addresses analysis and design of a cryogenic microwave anisotropic wave guiding structure that isolates an antenna from external incident fields from specific directions. The focus of this research is to design and optimize the radome's constituent material parameters for maximizing the isolation between an interior receiver antenna and an exterior transmitter without significantly disturbing the transmitter antenna far field characteristics. The design, characterization, and optimization of high-temperature superconducting metamaterials constitutive parameters are developed in this work at X-band frequencies. A calibrated characterization method for testing arrays of split-ring resonators at cryogenic temperature inside a TE10 waveguide was developed and used to back-out anisotropic equivalent material parameters. The artificial material elements (YBCO split-ring resonators on MgO substrate) are optimized to improve the narrowband performance of the metamaterial radome with respect to maximizing isolation and minimizing shadowing, defined as a reduction of the transmitted power external to the radome. The optimized radome is fabricated and characterized in a parallel plate waveguide in a cryogenic environment to demonstrate the degree of isolation and shadowing resulting from its presence. At 11.12 GHz, measurements show that the HTS metamaterial radome achieved an isolation of 10.5 dB and the external power at 100 mm behind the radome is reduced by 1.9 dB. This work demonstrates the feasibility of fabricating a structure that provides good isolation between two antennas and low disturbance of the transmitter's fields.

  18. Speckle reducing anisotropic diffusion.

    PubMed

    Yu, Yongjian; Acton, Scott T

    2002-01-01

    This paper provides the derivation of speckle reducing anisotropic diffusion (SRAD), a diffusion method tailored to ultrasonic and radar imaging applications. SRAD is the edge-sensitive diffusion for speckled images, in the same way that conventional anisotropic diffusion is the edge-sensitive diffusion for images corrupted with additive noise. We first show that the Lee and Frost filters can be cast as partial differential equations, and then we derive SRAD by allowing edge-sensitive anisotropic diffusion within this context. Just as the Lee and Frost filters utilize the coefficient of variation in adaptive filtering, SRAD exploits the instantaneous coefficient of variation, which is shown to be a function of the local gradient magnitude and Laplacian operators. We validate the new algorithm using both synthetic and real linear scan ultrasonic imagery of the carotid artery. We also demonstrate the algorithm performance with real SAR data. The performance measures obtained by means of computer simulation of carotid artery images are compared with three existing speckle reduction schemes. In the presence of speckle noise, speckle reducing anisotropic diffusion excels over the traditional speckle removal filters and over the conventional anisotropic diffusion method in terms of mean preservation, variance reduction, and edge localization.

  19. Electric field induced lattice strain in pseudocubic Bi(Mg1/2Ti1/2)O3-modified BaTiO3-BiFeO3 piezoelectric ceramics

    NASA Astrophysics Data System (ADS)

    Fujii, Ichiro; Iizuka, Ryo; Nakahira, Yuki; Sunada, Yuya; Ueno, Shintaro; Nakashima, Kouichi; Magome, Eisuke; Moriyoshi, Chikako; Kuroiwa, Yoshihiro; Wada, Satoshi

    2016-04-01

    Contributions to the piezoelectric response in pseudocubic 0.3BaTiO3-0.1Bi(Mg1/2Ti1/2)O3-0.6BiFeO3 ceramics were investigated by synchrotron X-ray diffraction under electric fields. All of the lattice strain determined from the 110, 111, and 200 pseudocubic diffraction peaks showed similar lattice strain hysteresis that was comparable to the bulk butterfly-like strain curve. It was suggested that the hysteresis of the lattice strain and the lack of anisotropy were related to the complex domain structure and the phase boundary composition.

  20. Periodic ordering of clusters and stripes in a two-dimensional lattice model. I. Ground state, mean-field phase diagram and structure of the disordered phases

    SciTech Connect

    Pekalski, J.; Ciach, A.; Almarza, N. G.

    2014-03-21

    The short-range attraction and long-range repulsion between nanoparticles or macromolecules can lead to spontaneous pattern formation on solid surfaces, fluid interfaces, or membranes. In order to study the self-assembly in such systems we consider a triangular lattice model with nearest-neighbor attraction and third-neighbor repulsion. At the ground state of the model (T = 0) the lattice is empty for small values of the chemical potential μ, and fully occupied for large μ. For intermediate values of μ periodically distributed clusters, bubbles, or stripes appear if the repulsion is sufficiently strong. At the phase coexistences between the vacuum and the ordered cluster phases and between the cluster and the lamellar (stripe) phases the entropy per site does not vanish. As a consequence of this ground state degeneracy, disordered fluid phases consisting of clusters or stripes are stable, and the surface tension vanishes. For T > 0 we construct the phase diagram in the mean-field approximation and calculate the correlation function in the self-consistent Brazovskii-type field theory.

  1. Quantum magnetic phase transition in square-octagon lattice

    NASA Astrophysics Data System (ADS)

    Bao, An; Tao, Hong-Shuai; Liu, Hai-Di; Zhang, Xiaozhong; Liu, Wu-Ming

    2014-11-01

    Quantum magnetic phase transition in square-octagon lattice was investigated by cellular dynamical mean field theory combining with continuous time quantum Monte Carlo algorithm. Based on the systematic calculation on the density of states, the double occupancy and the Fermi surface evolution of square-octagon lattice, we presented the phase diagrams of this splendid many particle system. The competition between the temperature and the on-site repulsive interaction in the isotropic square-octagon lattice has shown that both antiferromagnetic and paramagnetic order can be found not only in the metal phase, but also in the insulating phase. Antiferromagnetic metal phase disappeared in the phase diagram that consists of the anisotropic parameter λ and the on-site repulsive interaction U while the other phases still can be detected at T = 0.17. The results found in this work may contribute to understand well the properties of some consuming systems that have square-octagon structure, quasi square-octagon structure, such as ZnO.

  2. Development of an immersed boundary-phase field-lattice Boltzmann method for Neumann boundary condition to study contact line dynamics

    NASA Astrophysics Data System (ADS)

    Shao, J. Y.; Shu, C.; Chew, Y. T.

    2013-02-01

    The implementation of Neumann boundary condition in the framework of immersed boundary method (IBM) is presented in this paper to simulate contact line dynamics using a phase field-lattice Boltzmann method. Immersed boundary method [10] is known as an efficient algorithm for modelling fluid-solid interaction. Abundance of prominent works have been devoted to refine IBM [1,11,12]. However, they are mainly restricted to problems with Dirichlet boundary condition. Research that implements the Neumann boundary condition in IBM is very limited to the best of our knowledge. This deficiency significantly limits the application of IBM in computational fluid dynamics (CFD) since physical phenomena associated with Neumann boundary conditions are extremely diverse. The difficulty is attributed to the fact that implementation of Neumann boundary condition is much more complex than that of Dirichlet boundary condition. In the present work, we initiate the first endeavour to implement Neumann boundary condition in IBM with assistance of its physical interpretation rather than simple mathematical manipulation. Concretely speaking, rooted from physical conservation law, the Neumann boundary condition is considered as contribution of flux from the boundary to its relevant physical parameter in a control volume. Moreover, the link between the flux and its corresponding flow field variable is directly manipulated through the immersed boundary concept. In this way, the Neumann boundary conditions can be implemented in IBM. The developed method is applied together with phase field-lattice Boltzmann method to study contact line dynamics. The phase field method [27,39], which becomes increasingly popular in multiphase flow simulation, can efficiently capture complex interface topology and naturally resolve the contact line singularity. Meanwhile, the lattice Boltzmann method is known as an alternative to model fluid dynamics and holds good prospect to simulate multiphase flows with

  3. Mixture of Anisotropic Fluids

    NASA Astrophysics Data System (ADS)

    Florkowski, W.; Maj, R.

    The recently introduced approach describing coupled quark and gluon anisotropic fluids is generalized to include explicitly the transitions between quarks and gluons. We study the effects of such processes on the thermalization rate of anisotropic systems. We find that the quark-gluon transitions may enhance the overall thermalization rate in the cases where the initial momentum anisotropies correspond to mixed oblate-prolate or prolate configurations. On the other hand, no effect on the thermalization rate is found in the case of oblate configurations. The observed regularities are connected with the late-time behavior of the analyzed systems which is described either by the exponential decay or the power law.

  4. Molecular anisotropic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy

    2015-12-01

    Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3 d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.

  5. Charge-regulation phase transition on surface lattices of titratable sites adjacent to electrolyte solutions: An analog of the Ising antiferromagnet in a magnetic field

    NASA Astrophysics Data System (ADS)

    Shore, Joel D.; Thurston, George M.

    2015-12-01

    We report a charge-patterning phase transition on two-dimensional square lattices of titratable sites, here regarded as protonation sites, placed in a low-dielectric medium just below the planar interface between this medium and a salt solution. We calculate the work-of-charging matrix of the lattice with use of a linear Debye-Hückel model, as input to a grand-canonical partition function for the distribution of occupancy patterns. For a large range of parameter values, this model exhibits an approximate inverse cubic power-law decrease of the voltage produced by an individual charge, as a function of its in-lattice separation from neighboring titratable sites. Thus, the charge coupling voltage biases the local probabilities of proton binding as a function of the occupancy of sites for many neighbors beyond the nearest ones. We find that even in the presence of these longer-range interactions, the site couplings give rise to a phase transition in which the site occupancies exhibit an alternating, checkerboard pattern that is an analog of antiferromagnetic ordering. The overall strength W of this canonical charge coupling voltage, per unit charge, is a function of the Debye length, the charge depth, the Bjerrum length, and the dielectric coefficients of the medium and the solvent. The alternating occupancy transition occurs above a curve of thermodynamic critical points in the (p H-p K ,W ) plane, the curve representing a charge-regulation analog of variation of the Néel temperature of an Ising antiferromagnet as a function of an applied, uniform magnetic field. The analog of a uniform magnetic field in the antiferromagnet problem is a combination of p H-p K and W , and 1 /W is the analog of the temperature in the antiferromagnet problem. We use Monte Carlo simulations to study the occupancy patterns of the titratable sites, including interactions out to the 37th nearest-neighbor category (a distance of √{74 } lattice constants), first validating simulations

  6. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4

    DOE PAGESBeta

    S. -H. Baek; Gu, G. D.; Utz, Y.; Hucker, M.; Buchner, B.; Grafe, H. -J.

    2015-10-26

    We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T–11 sharply upturns at the charge-ordering temperature TCO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T–11 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for largemore » fields along the CuO2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less

  7. Anisotropic magnetoresistance in an antiferromagnetic semiconductor.

    PubMed

    Fina, I; Marti, X; Yi, D; Liu, J; Chu, J H; Rayan-Serrao, C; Suresha, S; Shick, A B; Zelezný, J; Jungwirth, T; Fontcuberta, J; Ramesh, R

    2014-01-01

    Recent studies in devices comprising metal antiferromagnets have demonstrated the feasibility of a novel spintronic concept in which spin-dependent phenomena are governed by an antiferromagnet instead of a ferromagnet. Here we report experimental observation of the anisotropic magnetoresistance in an antiferromagnetic semiconductor Sr2IrO4. Based on ab initio calculations, we associate the origin of the phenomenon with large anisotropies in the relativistic electronic structure. The antiferromagnet film is exchange coupled to a ferromagnet, which allows us to reorient the antiferromagnet spin-axis in applied magnetic fields via the exchange spring effect. We demonstrate that the semiconducting nature of our AFM electrode allows us to perform anisotropic magnetoresistance measurements in the current-perpendicular-to-plane geometry without introducing a tunnel barrier into the stack. Temperature-dependent measurements of the resistance and anisotropic magnetoresistance highlight the large, entangled tunabilities of the ordinary charge and spin-dependent transport in a spintronic device utilizing the antiferromagnet semiconductor.

  8. Elastic properties of spherically anisotropic piezoelectric composites

    NASA Astrophysics Data System (ADS)

    Wei, En-Bo; Gu, Guo-Qing; Poon, Ying-Ming

    2010-09-01

    Effective elastic properties of spherically anisotropic piezoelectric composites, whose spherically anisotropic piezoelectric inclusions are embedded in an infinite non-piezoelectric matrix, are theoretically investigated. Analytical solutions for the elastic displacements and the electric potentials under a uniform external strain are derived exactly. Taking into account of the coupling effects of elasticity, permittivity and piezoelectricity, the formula is derived for estimating the effective elastic properties based on the average field theory in the dilute limit. An elastic response mechanism is revealed, in which the effective elastic properties increase as inclusion piezoelectric properties increase and inclusion dielectric properties decrease. Moreover, a piezoelectric response mechanism, of which the effective piezoelectric response vanishes due to the symmetry of spherically anisotropic composite, is also disclosed.

  9. Anisotropic eddy viscosity models

    NASA Technical Reports Server (NTRS)

    Carati, D.; Cabot, W.

    1996-01-01

    A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.

  10. Dynamics of Anisotropic Universes

    NASA Astrophysics Data System (ADS)

    Perez, Jérôme

    2006-11-01

    We present a general study of the dynamical properties of Anisotropic Bianchi Universes in the context of Einstein General Relativity. Integrability results using Kovalevskaya exponents are reported and connected to general knowledge about Bianchi dynamics. Finally, dynamics toward singularity in Bianchi type VIII and IX universes are showed to be equivalent in some precise sence.

  11. Supersymmetry on the Lattice

    NASA Astrophysics Data System (ADS)

    Schaich, David

    2016-03-01

    Lattice field theory provides a non-perturbative regularization of strongly interacting systems, which has proven crucial to the study of quantum chromodynamics among many other theories. Supersymmetry plays prominent roles in the study of physics beyond the standard model, both as an ingredient in model building and as a tool to improve our understanding of quantum field theory. Attempts to apply lattice techniques to supersymmetric field theories have a long history, but until recently these efforts have generally encountered insurmountable difficulties related to the interplay of supersymmetry with the lattice discretization of spacetime. In recent years these difficulties have been overcome for a class of theories that includes the particularly interesting case of maximally supersymmetric Yang-Mills (N = 4 SYM) in four dimensions, which is a cornerstone of AdS/CFT duality. In combination with computational advances this progress enables practical numerical investigations of N = 4 SYM on the lattice, which can address questions that are difficult or impossible to handle through perturbation theory, AdS/CFT duality, or the conformal bootstrap program. I will briefly review some of the new ideas underlying this recent progress, and present some results from ongoing large-scale numerical calculations, including comparisons with analytic predictions.

  12. Anisotropic charged core envelope star

    NASA Astrophysics Data System (ADS)

    Mafa Takisa, P.; Maharaj, S. D.

    2016-08-01

    We study a charged compact object with anisotropic pressures in a core envelope setting. The equation of state is quadratic in the core and linear in the envelope. There is smooth matching between the three regions: the core, envelope and the Reissner-Nordström exterior. We show that the presence of the electric field affects the masses, radii and compactification factors of stellar objects with values which are in agreement with previous studies. We investigate in particular the effect of electric field on the physical features of the pulsar PSR J1614-2230 in the core envelope model. The gravitational potentials and the matter variables are well behaved within the stellar object. We demonstrate that the radius of the core and the envelope can vary by changing the parameters in the speed of sound.

  13. Dynamic mean field theory for lattice gas models of fluids confined in porous materials: Higher order theory based on the Bethe-Peierls and path probability method approximations

    SciTech Connect

    Edison, John R.; Monson, Peter A.

    2014-07-14

    Recently we have developed a dynamic mean field theory (DMFT) for lattice gas models of fluids in porous materials [P. A. Monson, J. Chem. Phys. 128(8), 084701 (2008)]. The theory can be used to describe the relaxation processes in the approach to equilibrium or metastable states for fluids in pores and is especially useful for studying system exhibiting adsorption/desorption hysteresis. In this paper we discuss the extension of the theory to higher order by means of the path probability method (PPM) of Kikuchi and co-workers. We show that this leads to a treatment of the dynamics that is consistent with thermodynamics coming from the Bethe-Peierls or Quasi-Chemical approximation for the equilibrium or metastable equilibrium states of the lattice model. We compare the results from the PPM with those from DMFT and from dynamic Monte Carlo simulations. We find that the predictions from PPM are qualitatively similar to those from DMFT but give somewhat improved quantitative accuracy, in part due to the superior treatment of the underlying thermodynamics. This comes at the cost of greater computational expense associated with the larger number of equations that must be solved.

  14. Competing Orders in a Dipolar Bose - Fermi Mixture on a Square Optical Lattice: Mean-Field Perspective

    NASA Astrophysics Data System (ADS)

    Ling, Hong; Scaramaazza, Jasen; Kain, Ben

    2015-05-01

    We study superfluid pairings of two-component fermions interacting by exchanging virtual phonons of a dipolar condensate in an optical lattice that preserves the symmetry of D4. We construct, within the Hartree-Fock-Bogoliubov theory, the matrix representation of the linearized gap equation in the irreducible representations of D4. We find that each matrix element, which is a four-dimensional (4D) integral in momentum space, can be put in a separable form involving a 1D integral, which is only a function of temperature and the chemical potential, and a pairing-specific ``effective'' interaction, which is an analytical function of the parameters that characterize Fermi-Fermi interactions. We analyze the critical temperatures of various competing orders (superfluids with s-, dx2-y2-, dxy-, and g-wave symmetries and density waves) as functions of different system parameters in both the absence and presence of the dipolar interaction. We find that tuning a dipolar interaction can dramatically enhance various unconventional pairings. KITP, University of Santa Barbara; ITAMP, Harvard-Smithsonian Center for Astrophysics.

  15. Hemispherical anisotropic patterns of the Earth's inner core.

    PubMed

    Mattesini, Maurizio; Belonoshko, Anatoly B; Buforn, Elisa; Ramírez, María; Simak, Sergei I; Udías, Agustín; Mao, Ho-Kwang; Ahuja, Rajeev

    2010-05-25

    It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves traveling approximately 3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth's inner core. PMID:20457937

  16. Hemispherical Anisotropic Patterns of the Earth's Inner Core

    NASA Astrophysics Data System (ADS)

    Mattesini, M.; Belonoshko, A. B.; Buforn, E.; Ramirez, M.; Simak, S. I.; Udias, A.; Mao, H.; Ahuja, R.

    2010-12-01

    It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves travelling ˜3% faster along polar paths than along equatorial directions. However, hemispherical anisotropic patterns of solid Earth's core are rather complex, and the commonly used hexagonal-close-packed (hcp) iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice preferred orientation of a body-centered-cubic iron aggregate (bcc), having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is a compelling evidence for the presence of a body-centered-cubic Fe phase at the top 100 km of the Earth's inner core.

  17. Stripe glass and stripe supersolid of two-dimensional dipolar bosons in an optical lattice

    NASA Astrophysics Data System (ADS)

    Roscilde, Tommaso; Boninsegni, Massimo

    2010-03-01

    Making use of mean-field theory and quantum Monte Carlo simulations, we investigate the zero-temperature phase diagram of dipolar bosons (with hardcore on-site interactions) on a square and triangular lattice. We consider dipoles forming an angle of 45 degrees with respect to the lattice plane, so that the dipolar interaction takes a spatially anisotropic nature, and it is attractive along the dipole direction and repulsive perpendicular to it. In the case of the square lattice, the attractive part of the interaction leads to the collapse of the dipolar gas and phase separation. On the contrary, in the case of the triangular lattice a stripe crystal is stabilized at most commensurate fillings of the form n/L, where 1 < n < L and L is the linear size. Yet, dislocations in the stripe crystal give rise to highly metastable states, which can be systematically studied at the mean-field level. Metastability is most pronounced close to half filling, and it leads to a strong tendency towards the formation of a ``stripe glass,'' which exhibits a characteristic signature in the structure factor. For higher fillings crystal phase exhibits strong quantum fluctuations, and it hosts a superfluid fraction for sufficiently low strength of the dipolar potential, resulting in a stripe supersolid phase.

  18. Anisotropic Packing of DNA-Mediated Colloidal Self-Assembly

    NASA Astrophysics Data System (ADS)

    Vo, Thi; Lu, Fang; Zhang, Yugang; Gang, Oleg; Kumar, Sanat

    The self-assembly of DNA-grafted nanoparticles has garnered considerable interest in recent years. However, many efforts focused on the usage of spherical nanoparticles, which limits us to the formation of only a handful of crystal lattices. Recent advances in the synthesis of non-spherical particles have directed attention towards the usage of these anisotropic particles for self-assembly. Here we combine experiments and theory on a series of DNA-grafted nanocubes. Our studies indicate that anisotropy not only directs where DNA linkers graft onto the particle but also affects how they pack and orient within a lattice, giving rise to both a preferential attachment effect and orientation-directed self-assembly. These results emphasize anisotropic self-assembly as a powerful new tool that allows for precise and directed control of nanoparticle self-assembly.

  19. Tunable anisotropic superfluidity in an optical kagome superlattice

    NASA Astrophysics Data System (ADS)

    Zhang, Xue-Feng; Wang, Tao; Eggert, Sebastian; Pelster, Axel

    2015-07-01

    We study the phase diagram of the Bose-Hubbard model on the kagome lattice with a broken sublattice symmetry. Such a superlattice structure can naturally be created and tuned by changing the potential offset of one sublattice in the optical generation of the frustrated lattice. The superstructure gives rise to a rich quantum phase diagram, which is analyzed by combining quantum Monte Carlo simulations with the generalized effective potential Landau theory. Mott phases with noninteger filling and a characteristic order along stripes are found, which show a transition to a superfluid phase with an anisotropic superfluid density. Surprisingly, the direction of the superfluid anisotropy can be tuned by changing the particle number, the hopping strength, or the interaction. Finally, we discuss characteristic signatures of anisotropic phases in time-of-flight absorption measurements.

  20. Bottomonium above Deconfinement in Lattice Nonrelativistic QCD

    SciTech Connect

    Aarts, G.; Kim, S.; Lombardo, M. P.; Oktay, M. B.; Ryan, S. M.; Sinclair, D. K.; Skullerud, J.-I.

    2011-02-11

    We study the temperature dependence of bottomonium for temperatures in the range 0.4T{sub c}lattice QCD simulations for N{sub f}=2 light flavors on a highly anisotropic lattice. We find that the {Upsilon} is insensitive to the temperature in this range, while the {chi}{sub b} propagators show a crossover from the exponential decay characterizing the hadronic phase to a power-law behavior consistent with nearly free dynamics at T{approx_equal}2T{sub c}.

  1. Magnetic field orientation dependence of flux pinning in (Gd,Y)Ba2Cu3O7-x coated conductor with tilted lattice and nanostructures

    SciTech Connect

    Zhang, Yifei; Specht, Eliot D; Cantoni, Claudia; Christen, David K; Zuev, Yuri L; Goyal, Amit; Sinclair, J.; Thompson, James R; Aytug, Tolga; Paranthaman, Mariappan Parans; Chen, Y; Selvamanickam, V.

    2009-01-01

    The dependence of the critical current density (J{sub c}) on the orientation of an applied magnetic field was studied for a prototype (Gd,Y)Ba{sub 2}Cu{sub 3}O{sub 7?x} (GdYBCO) coated conductor fabricated by MOCVD on an IBAD-MgO template. Additional rare-earth cations (Y and Gd) and Zr were incorporated into the superconducting film to form (Y,Gd){sub 2}O{sub 3} and BaZrO{sub 3} nanoparticles extended nearly parallel to the a-b planes and to the c-axis, respectively, to enhance the flux pinning. In-field measurement of J{sub c} was carried out with electrical current flowing either along or perpendicular to the longitudinal axis of the tape, while a maximum Lorentz force configuration was always maintained. Details in the angular dependence of J{sub c} were related to the unique structure of the film, specifically the tilt in the GdYBCO lattice and the tilts in the extended (Y,Gd){sub 2}O{sub 3} and BaZrO{sub 3} nanoparticles. XRD and TEM were used to study the structure of the coated conductor. The effect of the misalignment between the external field H and the internal field B on the angular dependence of J{sub c} is discussed.

  2. Theory of lattice response to external magnetic field in SrCu2(BO3)2: magnetostriction driven by panthograph effect

    NASA Astrophysics Data System (ADS)

    Saul, Andres; Radtke, Guillaume; Jaime, Marcelo; Salamon, Myron; Dabkowska, Hanna

    2015-03-01

    Recent magnetostriction experiments have shown that the macroscopic physical dimensions of the Shastry-Sutherland compound SrCu2(BO3)2 change with the applied magnetic field mimicking the same complex behavior observed in the magnetization. Using Density Functional based methods we find that the driving force behind the magnetoelastic coupling is the Cu-O-Cu superexchange angle which, thanks to the orthogonal Cu2+ dimers acting as pantographs, can shrink significantly (0.44%) with minute (0.01%) variations in the lattice parameters. The consequence is a reduction of the order of ~10% in the antiferromagnetic intra-dimer exchange integral J, sufficient to compensate the elastic energy loss in the deformation.

  3. Meson and baryon spectroscopy on the lattice

    SciTech Connect

    David Richards

    2010-12-01

    Recent progress at understanding the excited state spectrum of mesons and baryons is described. I begin by outlining the application of the variational method to compute the spectrum, and the program of anisotropic clover lattice generation designed for hadron spectroscopy. I present results for the excited meson spectrum, with continuum quantum numbers of the states clearly delineated. I conclude with recent results for the low lying baryon spectrum, and the prospects for future calculations.

  4. Parallel Anisotropic Tetrahedral Adaptation

    NASA Technical Reports Server (NTRS)

    Park, Michael A.; Darmofal, David L.

    2008-01-01

    An adaptive method that robustly produces high aspect ratio tetrahedra to a general 3D metric specification without introducing hybrid semi-structured regions is presented. The elemental operators and higher-level logic is described with their respective domain-decomposed parallelizations. An anisotropic tetrahedral grid adaptation scheme is demonstrated for 1000-1 stretching for a simple cube geometry. This form of adaptation is applicable to more complex domain boundaries via a cut-cell approach as demonstrated by a parallel 3D supersonic simulation of a complex fighter aircraft. To avoid the assumptions and approximations required to form a metric to specify adaptation, an approach is introduced that directly evaluates interpolation error. The grid is adapted to reduce and equidistribute this interpolation error calculation without the use of an intervening anisotropic metric. Direct interpolation error adaptation is illustrated for 1D and 3D domains.

  5. Probes for investigating the effect of magnetic field, field orientation, temperature and strain on the critical current density of anisotropic high-temperature superconducting tapes in a split-pair 15 T horizontal magnet

    SciTech Connect

    Sunwong, P.; Higgins, J. S.; Hampshire, D. P.

    2014-06-15

    We present the designs of probes for making critical current density (J{sub c}) measurements on anisotropic high-temperature superconducting tapes as a function of field, field orientation, temperature and strain in our 40 mm bore, split-pair 15 T horizontal magnet. Emphasis is placed on the design of three components: the vapour-cooled current leads, the variable temperature enclosure, and the springboard-shaped bending beam sample holder. The vapour-cooled brass critical-current leads used superconducting tapes and in operation ran hot with a duty cycle (D) of ∼0.2. This work provides formulae for optimising cryogenic consumption and calculating cryogenic boil-off, associated with current leads used to make J{sub c} measurements, made by uniformly ramping the current up to a maximum current (I{sub max}) and then reducing the current very quickly to zero. They include consideration of the effects of duty cycle, static helium boil-off from the magnet and Dewar (b{sup ′}), and the maximum safe temperature for the critical-current leads (T{sub max}). Our optimized critical-current leads have a boil-off that is about 30% less than leads optimized for magnet operation at the same maximum current. Numerical calculations show that the optimum cross-sectional area (A) for each current lead can be parameterized by LI{sub max}/A=[1.46D{sup −0.18}L{sup 0.4}(T{sub max}−300){sup 0.25D{sup −{sup 0{sup .{sup 0{sup 9}}}}}}+750(b{sup ′}/I{sub max})D{sup 10{sup −{sup 3I{sub m}{sub a}{sub x}−2.87b{sup ′}}}}]× 10{sup 6}A m{sup −1} where L is the current lead's length and the current lead is operated in liquid helium. An optimum A of 132 mm{sup 2} is obtained when I{sub max} = 1000 A, T{sub max} = 400 K, D = 0.2, b{sup ′} = 0.3 l h{sup −1} and L = 1.0 m. The optimized helium consumption was found to be 0.7 l h{sup −1}. When the static boil-off is small, optimized leads have a boil-off that can be roughly parameterized by: b/I{sub max } ≈ (1.35 × 10

  6. A high-resolution field-emission-gun, scanning electron microscope investigation of anisotropic hydrogen decrepitation in Nd-Fe-B-based sintered magnets

    SciTech Connect

    Soderznik, Marko; McGuiness, Paul; Zuzek-Rozman, Kristina; Kobe, Spomenka; Skulj, Irena; Yan Gaolin

    2010-05-15

    In this investigation commercial magnets based on (Nd,Dy){sub 14}(Fe,Co){sub 79}B{sub 7} were prepared by a conventional powder-metallurgy route with a degree of alignment equal to {approx}90% and then exposed to hydrogen at a pressure of 1 bar. The magnets, in the form of cylinders, were observed to decrepitate exclusively from the ends. High-resolution electron microscopy was able to identify the presence of crack formation within the Nd{sub 2}Fe{sub 14}B grains, with the cracks running parallel to the c axis of these grains. Based on the concentration profile for hydrogen in a rare-earth transition-metal material, it is clear that the presence of hydrogen-induced cracks running perpendicular to the ends of the magnet provides for a much more rapidly progressing hydrogen front in this direction than from the sides of the magnet. This results in the magnet exhibiting a macroscopic tendency to decrepitate from the poles of the magnet toward the center. This combination of microstructural modification via particle alignment as part of the sintering process and direct observation via high-resolution electron microscopy has led to a satisfying explanation for the anisotropic hydrogen-decrepitation effect.

  7. Elimination of spurious lattice fermion solutions and noncompact lattice QCD

    SciTech Connect

    Lee, T.D.

    1997-09-22

    It is well known that the Dirac equation on a discrete hyper-cubic lattice in D dimension has 2{sup D} degenerate solutions. The usual method of removing these spurious solutions encounters difficulties with chiral symmetry when the lattice spacing l {ne} 0, as exemplified by the persistent problem of the pion mass. On the other hand, we recall that in any crystal in nature, all the electrons do move in a lattice and satisfy the Dirac equation; yet there is not a single physical result that has ever been entangled with a spurious fermion solution. Therefore it should not be difficult to eliminate these unphysical elements. On a discrete lattice, particle hop from point to point, whereas in a real crystal the lattice structure in embedded in a continuum and electrons move continuously from lattice cell to lattice cell. In a discrete system, the lattice functions are defined only on individual points (or links as in the case of gauge fields). However, in a crystal the electron state vector is represented by the Bloch wave functions which are continuous functions in {rvec {gamma}}, and herein lies one of the essential differences.

  8. Observation of an Anisotropic Wigner Crystal

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Hasdemir, S.; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.

    2016-09-01

    We report a new correlated phase of two-dimensional charged carriers in high magnetic fields, manifested by an anisotropic insulating behavior at low temperatures. It appears in a large range of low Landau level fillings 1 /3 ≲ν ≲2 /3 in hole systems confined to wide GaAs quantum wells when the sample is tilted in magnetic field to an intermediate angle. The parallel field component (B∥) leads to a crossing of the lowest two Landau levels, and an elongated hole wave function in the direction of B∥. Under these conditions, the in-plane resistance exhibits an insulating behavior, with the resistance along B∥ about 10 times smaller than the resistance perpendicular to B∥. We interpret this anisotropic insulating phase as a two-component, striped Wigner crystal.

  9. Observation of an Anisotropic Wigner Crystal.

    PubMed

    Liu, Yang; Hasdemir, S; Pfeiffer, L N; West, K W; Baldwin, K W; Shayegan, M

    2016-09-01

    We report a new correlated phase of two-dimensional charged carriers in high magnetic fields, manifested by an anisotropic insulating behavior at low temperatures. It appears in a large range of low Landau level fillings 1/3≲ν≲2/3 in hole systems confined to wide GaAs quantum wells when the sample is tilted in magnetic field to an intermediate angle. The parallel field component (B_{∥}) leads to a crossing of the lowest two Landau levels, and an elongated hole wave function in the direction of B_{∥}. Under these conditions, the in-plane resistance exhibits an insulating behavior, with the resistance along B_{∥} about 10 times smaller than the resistance perpendicular to B_{∥}. We interpret this anisotropic insulating phase as a two-component, striped Wigner crystal. PMID:27636486

  10. Differential dynamic microscopy for anisotropic colloidal dynamics.

    PubMed

    Reufer, Mathias; Martinez, Vincent A; Schurtenberger, Peter; Poon, Wilson C K

    2012-03-13

    Differential dynamic microscopy (DDM) is a low-cost, high-throughput technique recently developed for characterizing the isotropic diffusion of spherical colloids using white-light optical microscopy. (1) We develop the theory for applying DDM to probe the dynamics of anisotropic colloidal samples such as various ordered phases, or particles interacting with an external field. The q-dependent dynamics can be measured in any direction in the image plane. We demonstrate the method on a dilute aqueous dispersion of anisotropic magnetic particles (hematite) aligned in a magnetic field. The measured diffusion coefficients parallel and perpendicular to the field direction are in good agreement with theoretical values. We show how these measurements allow us to extract the orientational order parameter S(2) of the system.

  11. Anisotropic Total Variation Filtering

    SciTech Connect

    Grasmair, Markus; Lenzen, Frank

    2010-12-15

    Total variation regularization and anisotropic filtering have been established as standard methods for image denoising because of their ability to detect and keep prominent edges in the data. Both methods, however, introduce artifacts: In the case of anisotropic filtering, the preservation of edges comes at the cost of the creation of additional structures out of noise; total variation regularization, on the other hand, suffers from the stair-casing effect, which leads to gradual contrast changes in homogeneous objects, especially near curved edges and corners. In order to circumvent these drawbacks, we propose to combine the two regularization techniques. To that end we replace the isotropic TV semi-norm by an anisotropic term that mirrors the directional structure of either the noisy original data or the smoothed image. We provide a detailed existence theory for our regularization method by using the concept of relaxation. The numerical examples concluding the paper show that the proposed introduction of an anisotropy to TV regularization indeed leads to improved denoising: the stair-casing effect is reduced while at the same time the creation of artifacts is suppressed.

  12. Oxygen-driven anisotropic transport in ultra-thin manganite films.

    PubMed

    Wang, Baomin; You, Lu; Ren, Peng; Yin, Xinmao; Peng, Yuan; Xia, Bin; Wang, Lan; Yu, Xiaojiang; Poh, Sock Mui; Yang, Ping; Yuan, Guoliang; Chen, Lang; Rusydi, Andrivo; Wang, Junling

    2013-01-01

    Transition metal oxides have a range of unique properties due to coupling of charge, spin, orbital and lattice degrees of freedom and nearly degenerate multiple ground states. These properties make them interesting for applications and for fundamental investigations. Here we report a new phase with abnormal transport anisotropy in La(0.7)Sr(0.3)MnO3 ultra-thin films under large tensile strain. This anisotropy is absent in films under smaller tensile strain or compressive strain. Furthermore, thickness and magnetic-field-dependent experiments suggest that the tensile-strain-induced two-dimensional character is crucial for the observed phenomena. X-ray absorption spectroscopy results indicate that this anisotropy is likely driven by O 2p orbital, which hybridizes with Mn 3d. Ab initio calculations confirm this result. Our results may help to understand the anisotropic transport behaviour observed in other systems.

  13. DNA-nanoparticle superlattices formed from anisotropic building blocks

    SciTech Connect

    Jones, Matthew R.; Macfarlane, Robert John; Lee, Byeongdu; Zhang, Jian; Young, Kaylie L.; Senesi, Andrew J.; Mirkin, Chad A.

    2010-10-03

    Directional bonding interactions in solid-state atomic lattices dictate the unique symmetries of atomic crystals, resulting in a diverse and complex assortment of three-dimensional structures that exhibit a wide variety of material properties. Methods to create analogous nanoparticle superlattices are beginning to be realized, but the concept of anisotropy is still largely underdeveloped in most particle assembly schemes. Some examples provide interesting methods to take advantage of anisotropic effects, but most are able to make only small clusters or lattices that are limited in crystallinity and especially in lattice parameter programmability. Anisotropic nanoparticles can be used to impart directional bonding interactions on the nanoscale, both through face-selective functionalization of the particle with recognition elements to introduce the concept of valency, and through anisotropic interactions resulting from particle shape. In this work, we examine the concept of inherent shape-directed crystallization in the context of DNA-mediated nanoparticle assembly. Importantly, we show how the anisotropy of these particles can be used to synthesize one-, two- and three-dimensional structures that cannot be made through the assembly of spherical particles.

  14. Design of a Kagome lattice from soft anisotropic particles.

    PubMed

    Fejer, Szilard N; Wales, David J

    2015-09-01

    We present a simple model of triblock Janus particles based on discoidal building blocks, which can form energetically stabilized Kagome structures. We find 'magic number' global minima in small clusters whenever particle numbers are compatible with a perfect Kagome structure, without constraining the accessible three-dimensional configuration space. The preference for planar structures with two bonds per patch among all other possible minima on the landscape is enhanced when sedimentation forces are included. For the building blocks in question, structures containing three bonds per patch become progressively higher in energy compared to Kagome structures as sedimentation forces increase. Rearrangements between competing structures, as well as ring formation mechanisms are characterised and found to be highly cooperative.

  15. Spin-1 J1 -J2 -J3 ferromagnetic Heisenberg model with an easy-plane crystal field on the cubic lattice: A bosonic approach

    NASA Astrophysics Data System (ADS)

    Carvalho, D. C.; Pires, A. S. T.; Mól, L. A. S.

    2016-06-01

    We examine the phase diagram of the spin-1 J1 -J2 -J3 ferromagnetic Heisenberg model with an easy-plane crystal field on the cubic lattice, in which J1 is the ferromagnetic exchange interaction between nearest neighbors, J2 is the antiferromagnetic exchange interaction between next-nearest neighbors and J3 is the antiferromagnetic exchange interaction between next-next-nearest neighbors. Using the bond-operator formalism, we investigate the phase transitions between the disordered paramagnetic phase and the ordered ones. We show that the nature of the quantum phase transitions changes as the frustration parameters (J2/J1, J3/J1) are varied. The zero-temperature phase diagram exhibits second- and first-order transitions, depending on the energy gap behavior. Remarkably, we find a disordered nonmagnetic phase, even in the absence of a crystal field, which is suggested to be a quantum spin liquid candidate. We also depict the phase diagram at finite temperature for some values of crystal field and frustration parameters.

  16. Assessing the influence of van der Waals corrected exchange-correlation functionals on the anisotropic mechanical properties of coinage metals

    NASA Astrophysics Data System (ADS)

    Lee, Ji-Hwan; Park, Jong-Hun; Soon, Aloysius

    2016-07-01

    Current materials-related calculations employ density-functional theory (DFT), commonly using the (semi-)local-density approximations for the exchange-correlation (xc) functional. The difficulties in arriving at a reasonable description of van der Waals (vdW) interactions by DFT-based models is to date a big challenge. In this work, we use various flavors of vdW-corrected DFT xc functionals—ranging from the quasiempirical force-field add-on vdW corrections to self-consistent nonlocal correlation functionals—to study the bulk lattice and mechanical properties (including the elastic constants and anisotropic indices) of the coinage metals (copper, silver, and gold). We critically assess the reliability of the different vdW-corrected DFT methods in describing their anisotropic mechanical properties which have been less reported in the literature. In the context of this work, we regard that our results reiterate the fact that advocating a so-called perfect vdW-inclusive xc functional for describing the general physics and chemistry of these coinage metals could be a little premature. These challenges to modern-day functionals for anisotropically strained coinage metals (e.g., at the faceted surfaces of nanostructures) may well be relevant to other strained material systems.

  17. Monte Carlo simulation with aspect-ratio optimization: Anomalous anisotropic scaling in dimerized antiferromagnets

    NASA Astrophysics Data System (ADS)

    Yasuda, Shinya; Todo, Synge

    2013-12-01

    We present a method that optimizes the aspect ratio of a spatially anisotropic quantum lattice model during the quantum Monte Carlo simulation, and realizes the virtually isotropic lattice automatically. The anisotropy is removed by using the Robbins-Monro algorithm based on the correlation length in each direction. The method allows for comparing directly the value of the critical amplitude among different anisotropic models, and identifying the universality more precisely. We apply our method to the staggered dimer antiferromagnetic Heisenberg model and demonstrate that the apparent nonuniversal behavior is attributed mainly to the strong size correction of the effective aspect ratio due to the existence of the cubic interaction.

  18. Conductivity of SU(2) gluodynamics vacuum induced by magnetic field

    SciTech Connect

    Polikarpov, M. I.; Larina, O. V.; Buividovich, P. V.; Chernodub, M. N.; Kalaydzhyan, T. K.; Kharzeev, D. E.; Luschevskaya, E. V.

    2011-05-23

    We study the electric conductivity of the vacuum of quenched SU(2) lattice gauge theory in the magnetic field, B, both in the confinement and in the deconfinement phases. In the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field. We also find that the conductivity grows as the quark mass decreases, the behavior has a form B/{radical}(m).

  19. Magnetospheric equilibrium with anisotropic pressure

    SciTech Connect

    Cheng, C.Z.

    1991-07-01

    Self-consistent magnetospheric equilibrium with anisotropic pressure is obtained by employing an iterative metric method for solving the inverse equilibrium equation in an optimal flux coordinate system. A method of determining plasma parallel and perpendicular pressures from either analytic particle distribution or particle distribution measured along the satellite's path is presented. The numerical results of axisymmetric magnetospheric equilibrium including the effects of finite beta, pressure anisotropy, and boundary conditions are presented for a bi-Maxwellian particle distribution. For the isotropic pressure cases, the finite beta effect produces an outward expansion of the constant magnetic flux surfaces in relation to the dipole field lines, and along the magnetic field the toroidal ring current is maximum at the magnetic equator. The effect of pressure anisotropy is found to further expand the flux surfaces outward. Along the magnetic field lines the westward ring current can be peak away from the equator due to an eastward current contribution resulting from pressure anisotropy. As pressure anisotropy increases, the peak westward current can become more singular. The outer boundary flux surface has significant effect on the magnetospheric equilibrium. For the outer flux boundary resembling dayside compressed flux surface due to solar wind pressure, the deformation of the magnetic field can be quite different from that for the outer flux boundary resembling the tail-like surface. 23 refs., 17 figs.

  20. The spin glass-antiferromagnetism competition in Kondo-lattice systems in the presence of a transverse applied magnetic field

    NASA Astrophysics Data System (ADS)

    Magalhaes, S. G.; Zimmer, F. M.; Coqblin, B.

    2006-05-01

    A theory is proposed to describe the competition among antiferromagnetism (AF), spin glass (SG) and Kondo effect. The model describes two Kondo sublattices with an intrasite Kondo interaction strength JK and a random Gaussian interlattice interaction in the presence of a transverse field Γ. The Γ field is introduced as a quantum mechanism to produce spin flipping and the random coupling has average -2J0/N and variance 32J2/N. The path integral formalism with Grassmann fields is used to study this fermionic problem, in which the disorder is treated within the framework of the replica trick. The free energy and the order parameters are obtained using the static ansatz. In this many parameters problem, we choose J0/J≈(JK/J)2 and Γ/J≈(JK/J)2 to allow a better comparison with the experimental findings. The obtained phase diagram has not only the same sequence as the experimental one for Ce2Au1-xCoxSi3, but mainly, it also shows a qualitative agreement concerning the behavior of the freezing temperature and the Neel temperature which decreases until a quantum critical point (QCP).

  1. Impurity-induced magnetic moments on the graphene-lattice Hubbard model: An inhomogeneous cluster dynamical mean-field theory study

    NASA Astrophysics Data System (ADS)

    Charlebois, M.; Sénéchal, D.; Gagnon, A.-M.; Tremblay, A.-M. S.

    2015-01-01

    Defect-induced magnetic moments are at the center of the research effort on spintronic applications of graphene. Here, we study the problem of a nonmagnetic impurity in graphene with a new theoretical method, inhomogeneous cluster dynamical mean-field theory (I-CDMFT), which takes into account interaction-induced short-range correlations while allowing long-range inhomogeneities. The system is described by a Hubbard model on the honeycomb lattice. The impurity is modeled by a local potential. For a large enough potential, interactions induce local antiferromagnetic correlations around the impurity and a net total spin 1/2 appears, in agreement with Lieb's theorem. Bound states caused by the impurity are visible in the local density of states (LDOS) and have their energies shifted by interactions in a spin-dependent way, leading to the antiferromagnetic correlations. Our results take into account dynamical correlations; nevertheless they qualitatively agree with previous mean-field and density functional theory (DFT) studies. Moreover, they provide a relation between impurity potential and on-site repulsion U that could in principle be used to determine experimentally the value of U .

  2. Magnetic Field Induced Phase Transitions in Gd5(Si1.95Ge2.05)Single Crystal and the Anisotropic Magnetocaloric Effect

    SciTech Connect

    H. Tang; V.K. Pecharsky; A.O. Pecharsky; D.L. Schlagel; T.A. Lograsso; K.A. Gschneidner,jr.

    2004-09-30

    The magnetization measurements using a Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}) single crystal with the magnetic field applied along three crystallographic directions, [001], [010] and [100], were carried out as function of applied field (0-56 kOe) at various temperatures ({approx}5-320 K). The magnetic-field induced phase transformations at temperature above the zero-field critical temperature, i.e. the paramagnetic (PM) {leftrightarrow} ferromagnetic (FM) transitions with application or removal of magnetic field, are found to be temperature dependent and hysteretic. The corresponding critical fields increase with increasing temperature. The magnetic field (H)-temperature (T) phase diagrams have been constructed for the Gd{sub 5}(Si{sub 1.95}Ge{sub 2.05}) single crystal with field along the three directions. A small anisotropy has been observed. The magnetocaloric effect (MCE) has been calculated from the isothermal magnetization data, and the observed anisotropy correlates with H-T phase diagrams. The results are discussed in connection with the magnetic-field induced martensitic-like structural transition observed in the Gd{sub 5}(Si{sub 2}Ge{sub 2})-type compounds.

  3. Anisotropic spinfoam cosmology

    NASA Astrophysics Data System (ADS)

    Rennert, Julian; Sloan, David

    2014-01-01

    The dynamics of a homogeneous, anisotropic universe are investigated within the context of spinfoam cosmology. Transition amplitudes are calculated for a graph consisting of a single node and three links—the ‘Daisy graph’—probing the behaviour a classical Bianchi I spacetime. It is shown further how the use of such single node graphs gives rise to a simplification of states such that all orders in the spin expansion can be calculated, indicating that it is the vertex expansion that contains information about quantum dynamics.

  4. Anisotropic magnetocapacitance in ferromagnetic-plate capacitors

    NASA Astrophysics Data System (ADS)

    Haigh, J. A.; Ciccarelli, C.; Betz, A. C.; Irvine, A.; Novák, V.; Jungwirth, T.; Wunderlich, J.

    2015-04-01

    The capacitance of a parallel-plate capacitor can depend on the applied magnetic field. Previous studies have identified capacitance changes induced via classical Lorentz force or spin-dependent Zeeman effects. Here we measure a magnetization direction-dependent capacitance in parallel-plate capacitors where one plate is a ferromagnetic semiconductor, gallium manganese arsenide. This anisotropic magnetocapacitance is due to the anisotropy in the density of states dependent on the magnetization through the strong spin-orbit interaction.

  5. Anisotropic conducting films for electromagnetic radiation applications

    DOEpatents

    Cavallo, Francesca; Lagally, Max G.; Rojas-Delgado, Richard

    2015-06-16

    Electronic devices for the generation of electromagnetic radiation are provided. Also provided are methods for using the devices to generate electromagnetic radiation. The radiation sources include an anisotropic electrically conducting thin film that is characterized by a periodically varying charge carrier mobility in the plane of the film. The periodic variation in carrier mobility gives rise to a spatially varying electric field, which produces electromagnetic radiation as charged particles pass through the film.

  6. Multidimensional Contact Moduli of Elastically Anisotropic Solids

    SciTech Connect

    Gao, Yanfei; Pharr, George Mathews

    2007-01-01

    Effective moduli of elastically anisotropic solids under normal and tangential contacts are derived using the Stroh formalism and the two dimensional Fourier transform. Each Fourier component corresponds to a plane field in the plane spanned by the surface normal and a wavevector, the solution of which only involves an algebraic eigenvalue problem. Exact solutions are obtained for indenters described by parabolae of revolution, which are found to be a good approximation for arbitrary axisymmetric indenters.

  7. On anisotropy function in crystal growth simulations using Lattice Boltzmann equation

    NASA Astrophysics Data System (ADS)

    Younsi, Amina; Cartalade, Alain

    2016-11-01

    In this paper, we present the ability of the Lattice Boltzmann (LB) equation, usually applied to simulate fluid flows, to simulate various shapes of crystals. Crystal growth is modeled with a phase-field model for a pure substance, numerically solved with a LB method in 2D and 3D. This study focuses on the anisotropy function that is responsible for the anisotropic surface tension between the solid phase and the liquid phase. The anisotropy function involves the unit normal vectors of the interface, defined by gradients of phase-field. Those gradients have to be consistent with the underlying lattice of the LB method in order to avoid unwanted effects of numerical anisotropy. Isotropy of the solution is obtained when the directional derivatives method, specific for each lattice, is applied for computing the gradient terms. With the central finite differences method, the phase-field does not match with its rotation and the solution is not any more isotropic. Next, the method is applied to simulate simultaneous growth of several crystals, each of them being defined by its own anisotropy function. Finally, various shapes of 3D crystals are simulated with standard and nonstandard anisotropy functions which favor growth in <100>-, <110>- and <111>-directions.

  8. Anisotropic Bianchi types VIII and IX locally rotationally symmetric cosmologies

    SciTech Connect

    Assad, M.J.D.; Soares, I.D.

    1983-10-15

    We present a class of exact cosmological solutions of Einstein-Maxwell equations, which are anisotropic and spatially homogeneous of Bianchi types VIII and IX, and class IIIb in the Stewart-Ellis classification of locally rotationally symmetric models. If we take the electromagnetic field equal to zero, a class of Bianchi types VIII/IX spatially homogeneous anisotropic cosmological solutions with perfect fluid is obtained.

  9. On the electrodynamics of Josephson effect in anisotropic superconductors

    SciTech Connect

    Mints, R.G.

    1989-01-01

    Specificities of Josephson effect electrodynamics in anisotropic superconductors are of considerable interest for the study of high temperature superconductors with strongly anisotropic layered structure. In this paper the authors give the calculation for the tunnel Josephson contact of an isolated vortex, the law of dispersion of its low-amplitude oscillations, the critical field H/sub cl/ for the penetration of magnetic flux, and the maximum current across a rectangular contact.

  10. Anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets

    NASA Astrophysics Data System (ADS)

    Li, Yao-Dong; Wang, Xiaoqun; Chen, Gang

    2016-07-01

    Motivated by the recent experimental progress on the strong spin-orbit-coupled rare-earth triangular antiferromagnet, we analyze the highly anisotropic spin model that describes the interaction between the spin-orbit-entangled Kramers' doublet local moments on the triangular lattice. We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and the self-consistent spin wave theory to analyze the anisotropic spin Hamiltonian. The classical phase diagram includes the 120∘ state and two distinct stripe-ordered phases. The frustration is very strong and significantly suppresses the ordering temperature in the regimes close to the phase boundary between two ordered phases. Going beyond the semiclassical analysis, we include the quantum fluctuations of the spin moments within a self-consistent Dyson-Maleev spin-wave treatment. We find that the strong quantum fluctuations melt the magnetic order in the frustrated regions. We explore the magnetic excitations in the three different ordered phases as well as in strong magnetic fields. Our results provide a guidance for the future theoretical study of the generic model and are broadly relevant for strong spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3 , RZn3P3 , RCd3As3 , RZn3As3 , and R2O2CO3 .

  11. Dynamic optical lattices: two-dimensional rotating and accordion lattices for ultracold atoms.

    PubMed

    Williams, R A; Pillet, J D; Al-Assam, S; Fletcher, B; Shotter, M; Foot, C J

    2008-10-13

    We demonstrate a novel experimental arrangement which can rotate a 2D optical lattice at frequencies up to several kilohertz. Ultracold atoms in such a rotating lattice can be used for the direct quantum simulation of strongly correlated systems under large effective magnetic fields, allowing investigation of phenomena such as the fractional quantum Hall effect. Our arrangement also allows the periodicity of a 2D optical lattice to be varied dynamically, producing a 2D accordion lattice.

  12. Inhomogeneous anisotropic cosmology

    NASA Astrophysics Data System (ADS)

    Kleban, Matthew; Senatore, Leonardo

    2016-10-01

    In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with ``flat'' (including toroidal) and ``open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are ``flat'' or ``open''. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with ``flat'' or ``open'' topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.

  13. Anisotropic diffusion limited aggregation in three dimensions: universality and nonuniversality.

    PubMed

    Goold, Nicholas R; Somfai, Ellák; Ball, Robin C

    2005-09-01

    We explore the macroscopic consequences of lattice anisotropy for diffusion limited aggregation (DLA) in three dimensions. Simple cubic and bcc lattice growths are shown to approach universal asymptotic states in a coherent fashion, and the approach is accelerated by the use of noise reduction. These states are strikingly anisotropic dendrites with a rich hierarchy of structure. For growth on an fcc lattice, our data suggest at least two stable fixed points of anisotropy, one matching the bcc case. Hexagonal growths, favoring six planar and two polar directions, appear to approach a line of asymptotic states with continuously tunable polar anisotropy. The more planar of these growths visually resembles real snowflake morphologies. Our simulations use a new and dimension-independent implementation of the DLA model. The algorithm maintains a hierarchy of sphere coverings of the growth, supporting efficient random walks onto the growth by spherical moves. Anisotropy was introduced by restricting growth to certain preferred directions. PMID:16241431

  14. Anisotropic diffusion limited aggregation in three dimensions: Universality and nonuniversality

    NASA Astrophysics Data System (ADS)

    Goold, Nicholas R.; Somfai, Ellák; Ball, Robin C.

    2005-09-01

    We explore the macroscopic consequences of lattice anisotropy for diffusion limited aggregation (DLA) in three dimensions. Simple cubic and bcc lattice growths are shown to approach universal asymptotic states in a coherent fashion, and the approach is accelerated by the use of noise reduction. These states are strikingly anisotropic dendrites with a rich hierarchy of structure. For growth on an fcc lattice, our data suggest at least two stable fixed points of anisotropy, one matching the bcc case. Hexagonal growths, favoring six planar and two polar directions, appear to approach a line of asymptotic states with continuously tunable polar anisotropy. The more planar of these growths visually resembles real snowflake morphologies. Our simulations use a new and dimension-independent implementation of the DLA model. The algorithm maintains a hierarchy of sphere coverings of the growth, supporting efficient random walks onto the growth by spherical moves. Anisotropy was introduced by restricting growth to certain preferred directions.

  15. Excited state baryon spectroscopy from lattice QCD

    DOE PAGESBeta

    Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.

    2011-10-31

    Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting ofmore » levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.« less

  16. Excited state baryon spectroscopy from lattice QCD

    SciTech Connect

    Edwards, Robert G.; Richards, David G.; Dudek, Jozef J.; Wallace, Stephen J.

    2011-10-01

    We present a calculation of the Nucleon and Delta excited state spectra on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including J=(7/2), of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of SU(6) x O(3) representations and a counting of levels that is consistent with the nonrelativistic qqq constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the 'missing resonance problem' and shows no signs of parity doubling of states.

  17. Excited state baryon spectroscopy from lattice QCD

    SciTech Connect

    Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.

    2011-10-31

    Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting of levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.

  18. CHARMONIUM EXCITED STATES FROM LATTICE QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards

    2007-11-20

    We apply the variational method with a large basis of interpolating operators to demonstrate the feasibility of extracting multiple excited states in charmonium from lattice QCD. The calculation is performed in the quenched approximation to QCD, using the clover fermion action on an anisotropic lattice. A crucial element of our approach is a knowledge of the continuum limit of the interpolating operators, providing important additional information on the spin assignment of the states, even at a single value of the lattice spacing. Though we find excited-state masses that are systematically high with respect to the quark potential model, and the experimental masses where known, we attribute this as most likely an artifact of the quenched approximation.

  19. Lattice Strain Defects in a Ceria Nanolayer

    PubMed Central

    2016-01-01

    An ultrathin two-dimensional CeO2 (ceria) phase on a Cu(110) surface has been fabricated and fully characterized by high-resolution scanning tunneling microscopy, photoelectron spectroscopy, and density functional theory. The atomic lattice structure of the ceria/Cu(110) system is revealed as a hexagonal CeO2(111)-type monolayer separated from the Cu(110) surface by a partly disordered Cu–O intercalated buffer layer. The epitaxial coupling of the two-dimensional ceria overlayer to the Cu(110)-O surface leads to a nanoscopic stripe pattern, which creates defect regions of quasi-periodic lattice distortions. The symmetry and lattice mismatch at the interface is clarified to be responsible for the topographic stripe geometry and the related anisotropic strain defect regions at the ceria surface. This ceria monolayer is in a fully oxidized and thermodynamically stable state. PMID:26988695

  20. Wave propagation on a random lattice

    SciTech Connect

    Sahlmann, Hanno

    2010-09-15

    Motivated by phenomenological questions in quantum gravity, we consider the propagation of a scalar field on a random lattice. We describe a procedure to calculate the dispersion relation for the field by taking a limit of a periodic lattice. We use this to calculate the lowest order coefficients of the dispersion relation for a specific one-dimensional model.

  1. Anisotropic power-law inflation

    SciTech Connect

    Kanno, Sugumi; Soda, Jiro; Watanabe, Masa-aki E-mail: jiro@tap.scphys.kyoto-u.ac.jp

    2010-12-01

    We study an inflationary scenario in supergravity model with a gauge kinetic function. We find exact anisotropic power-law inflationary solutions when both the potential function for an inflaton and the gauge kinetic function are exponential type. The dynamical system analysis tells us that the anisotropic power-law inflation is an attractor for a large parameter region.

  2. High electron mobility in nearly lattice-matched AlInN /AlN/GaN heterostructure field effect transistors

    NASA Astrophysics Data System (ADS)

    Xie, Jinqiao; Ni, Xianfeng; Wu, Mo; Leach, Jacob H.; Özgür, Ümit; Morkoç, Hadis

    2007-09-01

    High electron mobility was achieved in Al1-xInxN/AlN/GaN (x=0.20-0.12) heterostructure field effect transistors (HFETs) grown by metal-organic chemical vapor deposition. Reduction of In composition from 20% to 12% increased the room temperature equivalent two-dimensional-electron-gas density from 0.90×1013to1.64×1013cm-2 with corresponding electron mobilities of 1600 and 1410cm2/Vs, respectively. The 10K mobility reached 17600cm2/Vs for the nearly lattice-matched Al0.82In0.18N/AlN/GaN heterostructure with a sheet carrier density of 9.6×1012cm-2. For comparison, the AlInN /GaN heterostructure without the AlN spacer exhibited a high sheet carrier density (2.42×1013cm-2) with low mobility (120cm2/Vs) at room temperature. The high mobility in our samples is in part attributed to ˜1nm AlN spacer which significantly reduces the alloy scattering as well as provides a smooth interface. The HFETs having gate dimensions of 1.5×40μm2 and a 5μm source-drain separation exhibited a maximum transconductance of ˜200mS/mm with good pinch-off characteristics and over 10GHz current gain cutoff frequency.

  3. A phase-field-lattice Boltzmann method for modeling motion and growth of a dendrite for binary alloy solidification in the presence of melt convection

    NASA Astrophysics Data System (ADS)

    Rojas, Roberto; Takaki, Tomohiro; Ohno, Munekazu

    2015-10-01

    In this study, a combination of the lattice Boltzmann method (LBM) and the phase-field method (PFM) is used for modeling simultaneous growth and motion of a dendrite during solidification. PFM is used as a numerical tool to simulate the morphological changes of the solid phase, and the fluid flow of the liquid phase is described by using LBM. The no-slip boundary condition at the liquid-solid interface is satisfied by adding a diffusive-forcing term in the LBM formulation. The equations of motion are solved for tracking the translational and rotational motion of the solid phase. The proposed method is easily implemented on a single Cartesian grid and is suitable for parallel computation. Two-dimensional benchmark computations show that the no-slip boundary condition and the shape preservation condition are satisfied in this method. Then, the present method is applied to the calculation of dendritic growth of a binary alloy under melt convection. Initially, the solid is stationary, and then, the solid moves freely due to the influence of fluid flow. Simultaneous growth and motion are effectively simulated. As a result, it is found that motion and melt convection enhance dendritic growth along the flow direction.

  4. Cross-Permeability of the Semisolid Region in Directional Solidification: A Combined Phase-Field and Lattice-Boltzmann Simulation Approach

    NASA Astrophysics Data System (ADS)

    Böttger, B.; Haberstroh, C.; Giesselmann, N.

    2016-01-01

    Based on the results of microstructure simulations, fluid flow through the semisolid region during directional solidification of the technical Ni-base alloy 718 has been studied. Three-dimensional microstructures at different positions in the semisolid region were obtained by using a multicomponent multiphase-field model that was online coupled to a commercial thermodynamic database. For the range of five different primary dendrite distances λ 1 between 50 µm and 250 µm, the flow velocity and the permeability perpendicular to the dendrite growth direction was evaluated by using a proprietary Lattice-Boltzmann model. The commercial CFD software ANSYS FLUENT was alternatively applied for reference. Consistent values of the average flow velocity along the dendrites were obtained for both methods. From the results of the fluid flow simulations, the cross-permeability was evaluated as a function of temperature and fraction liquid for each of the five different primary dendrite distances λ 1. The obtained permeability values can be approximated by a single analytical function of the fraction liquid and λ 1 and are discussed and compared with known relations from the literature.

  5. Magnetoresistivity and acoustoelectronic effects in a tilted magnetic field in p-Si/SiGe/Si structures with an anisotropic g factor

    SciTech Connect

    Drichko, I. L. Smirnov, I. Yu.; Suslov, A. V.; Mironov, O. A.; Leadley, D. R.

    2010-09-15

    Magnetoresistivity {rho}{sub xx} and {rho}{sub xy} and the acoustoelectronic effects are measured in p-Si/SiGe/Si with an impurity concentration p = 1.99 x 10{sup 11} cm{sup -2} in the temperature range 0.3-2.0 K and an tilted magnetic field up to 18 T. The dependence of the effective g factor on the angle of magnetic field tilt {theta} to the normal to the plane of a two-dimensional p-Si/SiGe/Si channel is determined. A first-order ferromagnet-paramagnet phase transition is observed in the magnetic fields corresponding to a filling factor {nu} = 2 at {theta} {approx} 59{sup o}-60{sup o}.

  6. Oligonucleotide-Functionalized Anisotropic Gold Nanoparticles

    NASA Astrophysics Data System (ADS)

    Jones, Matthew Robert

    In this thesis, we describe the properties of oligonucleotide-functionalized gold colloids under the unique set of conditions where the particles are geometrically anisotropic and have nanometer-scale dimensions. While nearly two decades of previous work elucidated numerous unexpected and emergent phenomena arising from the combination of inorganic nanoparticles with surface-bound DNA strands, virtually nothing was known about how these properties are altered when the shape of the nanoparticle core is chosen to be non-spherical. In particular, we are interested in understanding, and ultimately controlling, the ways in which these DNA-conjugated anisotropic nanostructures interact when their attraction is governed by programmable DNA hybridization events. Chapter 1 introduces the field of DNA-based materials assembly by discussing how nanoscale building blocks which present rigid, directional interactions can be thought of as possessing artificial versions of the familiar chemical principles of "bonds" and "valency". In chapter 2 we explore the fundamental interparticle binding thermodynamics of DNA-functionalized spherical and anisotropic nanoparticles, which reveals enormous preferences for collective ligand interactions occurring between flat surfaces over those that occur between curved surfaces. Using these insights, chapter 3 demonstrates that when syntheses produce mixtures of different nanoparticle shapes, the tailorable nature of DNA-mediated interparticle association can be used to selectively crystallize and purify the desired anisotropic nanostructure products, leaving spherical impurity particles behind. Chapter 4 leverages the principle that the flat facets of anisotropic particles generate directional DNA-based hybridization interactions to assemble a variety of tailorable nanoparticle superlattices whose symmetry and dimensionality are a direct consequence of the shape of the nanoparticle building block used in their construction. Chapter 5 explores

  7. Introduction to lattice gauge theory

    SciTech Connect

    Gupta, R.

    1987-01-01

    The lattice formulation of Quantum Field Theory (QFT) can be exploited in many ways. We can derive the lattice Feynman rules and carry out weak coupling perturbation expansions. The lattice then serves as a manifestly gauge invariant regularization scheme, albeit one that is more complicated than standard continuum schemes. Strong coupling expansions: these give us useful qualitative information, but unfortunately no hard numbers. The lattice theory is amenable to numerical simulations by which one calculates the long distance properties of a strongly interacting theory from first principles. The observables are measured as a function of the bare coupling g and a gauge invariant cut-off approx. = 1/..cap alpha.., where ..cap alpha.. is the lattice spacing. The continuum (physical) behavior is recovered in the limit ..cap alpha.. ..-->.. 0, at which point the lattice artifacts go to zero. This is the more powerful use of lattice formulation, so in these lectures the author focuses on setting up the theory for the purpose of numerical simulations to get hard numbers. The numerical techniques used in Lattice Gauge Theories have their roots in statistical mechanics, so it is important to develop an intuition for the interconnection between quantum mechanics and statistical mechanics. This will be the emphasis of the first lecture. In the second lecture, the author reviews the essential ingredients of formulating QCD on the lattice and discusses scaling and the continuum limit. In the last lecture the author summarizes the status of some of the main results. He also mentions the bottlenecks and possible directions for research. 88 refs.

  8. Soft particles with anisotropic interactions

    NASA Astrophysics Data System (ADS)

    Schurtenberger, Peter

    Responsive colloids such as thermo- or pH-sensitive microgels are ideal model systems to investigate the relationship between the nature of interparticle interactions and the plethora of self-assembled structures that can form in colloidal suspensions. They allow for a variation of the form, strength and range of the interaction potential almost at will. While microgels have extensively been used as model systems to investigate various condensed matter problems such as glass formation, jamming or crystallization, they can also be used to study systems with anisotropic interactions. Here we show results from a systematic investigation of the influence of softness and anisotropy on the structural and dynamic properties of strongly interacting suspensions. We focus first on ionic microgels. Due to their large number of internal counterions they possess very large polarisabilities, and we can thus use external electrical ac fields to generate large dipolar contributions to the interparticle interaction potential. This leads to a number of new crystal phases, and we can trigger crystal-crystal phase transitions through the appropriate choice of the field strength. We then show that this approach can be extended to more complex particle shapes in an attempt to copy nature's well documented success in fabricating complex nanostructures such as virus shells via self assembly. European Research Council (ERC-339678-COMPASS).

  9. Weibel Instability Driven by Spatially Anisotropic Density Structures

    NASA Astrophysics Data System (ADS)

    Tomita, Sara; Ohira, Yutaka

    2016-07-01

    Observations of afterglows of gamma-ray bursts (GRBs) suggest that post-shock magnetic fields are strongly amplified to about 100 times the shock-compressed value. The Weibel instability appears to play an important role in generating the magnetic field. However, recent simulations of collisionless shocks in homogeneous plasmas show that the magnetic field generated by the Weibel instability rapidly decays. There must be some density fluctuations in interstellar and circumstellar media. The density fluctuations are anisotropically compressed in the downstream region of relativistic shocks. In this paper, we study the Weibel instability in electron-positron plasmas with spatially anisotropic density distributions by means of two-dimensional particle-in-cell simulations. We find that large magnetic fields are maintained for a longer time by the Weibel instability driven by spatially anisotropic density structure. Particles anisotropically escape from the high density region, so that a temperature anisotropy is generated and the Weibel instability becomes unstable. Our simulation results suggest that the Weibel instability driven by an anisotropic density structure can generate sufficiently large magnetic fields and they can cover sufficiently large regions to explain the afterglow emission of GRBs.

  10. Scattering of electromagnetic light waves from a deterministic anisotropic medium

    NASA Astrophysics Data System (ADS)

    Li, Jia; Chang, Liping; Wu, Pinghui

    2015-11-01

    Based on the weak scattering theory of electromagnetic waves, analytical expressions are derived for the spectral densities and degrees of polarization of an electromagnetic plane wave scattered from a deterministic anisotropic medium. It is shown that the normalized spectral densities of scattered field is highly dependent of changes of the scattering angle and degrees of polarization of incident plane waves. The degrees of polarization of scattered field are also subjective to variations of these parameters. In addition, the anisotropic effective radii of the dielectric susceptibility can lead essential influences on both spectral densities and degrees of polarization of scattered field. They are highly dependent of the effective radii of the medium. The obtained results may be applicable to determine anisotropic parameters of medium by quantitatively measuring statistics of a far-zone scattered field.

  11. Anisotropic Kepler and anisotropic two fixed centres problems

    NASA Astrophysics Data System (ADS)

    Maciejewski, Andrzej J.; Przybylska, Maria; Szumiński, Wojciech

    2016-09-01

    In this paper we show that the anisotropic Kepler problem is dynamically equivalent to a system of two point masses which move in perpendicular lines (or planes) and interact according to Newton's law of universal gravitation. Moreover, we prove that generalised version of anisotropic Kepler problem as well as anisotropic two centres problem are non-integrable. This was achieved thanks to investigation of differential Galois groups of variational equations along certain particular solutions. Properties of these groups yield very strong necessary integrability conditions.

  12. A lattice approach to spinorial quantum gravity

    NASA Technical Reports Server (NTRS)

    Renteln, Paul; Smolin, Lee

    1989-01-01

    A new lattice regularization of quantum general relativity based on Ashtekar's reformulation of Hamiltonian general relativity is presented. In this form, quantum states of the gravitational field are represented within the physical Hilbert space of a Kogut-Susskind lattice gauge theory. The gauge field of the theory is a complexified SU(2) connection which is the gravitational connection for left-handed spinor fields. The physical states of the gravitational field are those which are annihilated by additional constraints which correspond to the four constraints of general relativity. Lattice versions of these constraints are constructed. Those corresponding to the three-dimensional diffeomorphism generators move states associated with Wilson loops around on the lattice. The lattice Hamiltonian constraint has a simple form, and a correspondingly simple interpretation: it is an operator which cuts and joins Wilson loops at points of intersection.

  13. Transverse anisotropic magnetoresistance effects in pseudo-single-crystal γ'-Fe4N thin films

    NASA Astrophysics Data System (ADS)

    Kabara, Kazuki; Tsunoda, Masakiyo; Kokado, Satoshi

    2016-05-01

    Transverse anisotropic magnetoresistance (AMR) effects, for which magnetization is rotated in an orthogonal plane to the current direction, were investigated at various temperatures, in order to clarify the structural transformation from a cubic to a tetragonal symmetry in a pseudo-single-crystal Fe4N film, which is predicted from the usual in-plane AMR measurements by the theory taking into account the spin-orbit interaction and crystal field splitting of 3d bands. According to a phenomenological theory of AMR, which derives only from the crystal symmetry, a cos 2θ component ( C2 tr ) exists in transverse AMR curves for a tetragonal system but does not for a cubic system. In the Fe4N film, the C2 tr shows a positive small value (0.12%) from 300 K to 50 K. However, the C2 t r increases to negative value below 50 K and reaches to -2% at 5 K. The drastic increasing of the C2 tr demonstrates the structural transformation from a cubic to a tetragonal symmetry below 50 K in the Fe4N film. In addition, the out-of-plane and in-plane lattice constants (c and a) were precisely determined with X-ray diffraction at room temperature using the Nelson-Riely function. As a result, the positive small C2 t r above 50 K is attributed to a slightly distorted Fe4N lattice (c/a = 1.002).

  14. Analysis of quantum spin models on hyperbolic lattices and Bethe lattice

    NASA Astrophysics Data System (ADS)

    Daniška, Michal; Gendiar, Andrej

    2016-04-01

    The quantum XY, Heisenberg, and transverse field Ising models on hyperbolic lattices are studied by means of the tensor product variational formulation algorithm. The lattices are constructed by tessellation of congruent polygons with coordination number equal to four. The calculated ground-state energies of the XY and Heisenberg models and the phase transition magnetic field of the Ising model on the series of lattices are used to estimate the corresponding quantities of the respective models on the Bethe lattice. The hyperbolic lattice geometry induces mean-field-like behavior of the models. The ambition to obtain results on the non-Euclidean lattice geometries has been motivated by theoretical studies of the anti-de Sitter/conformal field theory correspondence.

  15. Leading-order anisotropic hydrodynamics for central collisions

    NASA Astrophysics Data System (ADS)

    Nopoush, Mohammad; Strickland, Michael; Ryblewski, Radoslaw; Bazow, Dennis; Heinz, Ulrich; Martinez, Mauricio

    2015-10-01

    We use leading-order anisotropic hydrodynamics to study an azimuthally symmetric boost-invariant quark-gluon plasma. We impose a realistic lattice-based equation of state and perform self-consistent anisotropic freeze-out to hadronic degrees of freedom. We then compare our results for the full spatiotemporal evolution of the quark-gluon plasma and its subsequent freeze-out to results obtained using 1+1D Israel-Stewart second-order viscous hydrodynamics. We find that for small shear viscosities, 4 π η /s ˜1 , the two methods agree well for nucleus-nucleus collisions; however, for large-shear-viscosity-to-entropy-density ratios or proton-nucleus collisions we find important corrections to the Israel-Stewart results for the final particle spectra and the total number of charged particles. Finally, we demonstrate that the total number of charged particles produced is a monotonically increasing function of 4 π η /s in Israel-Stewart viscous hydrodynamics, whereas in anisotropic hydrodynamics it has a maximum at 4 π η /s ˜10 . For all 4 π η /s >0 , we find that for Pb-Pb collisions Israel-Stewart viscous hydrodynamics predicts more dissipative particle production than anisotropic hydrodynamics.

  16. Finite-difference schemes for anisotropic diffusion

    SciTech Connect

    Es, Bram van; Koren, Barry; Blank, Hugo J. de

    2014-09-01

    In fusion plasmas diffusion tensors are extremely anisotropic due to the high temperature and large magnetic field strength. This causes diffusion, heat conduction, and viscous momentum loss, to effectively be aligned with the magnetic field lines. This alignment leads to different values for the respective diffusive coefficients in the magnetic field direction and in the perpendicular direction, to the extent that heat diffusion coefficients can be up to 10{sup 12} times larger in the parallel direction than in the perpendicular direction. This anisotropy puts stringent requirements on the numerical methods used to approximate the MHD-equations since any misalignment of the grid may cause the perpendicular diffusion to be polluted by the numerical error in approximating the parallel diffusion. Currently the common approach is to apply magnetic field-aligned coordinates, an approach that automatically takes care of the directionality of the diffusive coefficients. This approach runs into problems at x-points and at points where there is magnetic re-connection, since this causes local non-alignment. It is therefore useful to consider numerical schemes that are tolerant to the misalignment of the grid with the magnetic field lines, both to improve existing methods and to help open the possibility of applying regular non-aligned grids. To investigate this, in this paper several discretization schemes are developed and applied to the anisotropic heat diffusion equation on a non-aligned grid.

  17. Active Damping Using Distributed Anisotropic Actuators

    NASA Technical Reports Server (NTRS)

    Schiller, Noah H.; Cabell, Randolph H.; Quinones, Juan D.; Wier, Nathan C.

    2010-01-01

    A helicopter structure experiences substantial high-frequency mechanical excitation from powertrain components such as gearboxes and drive shafts. The resulting structure-borne vibration excites the windows which then radiate sound into the passenger cabin. In many cases the radiated sound power can be reduced by adding damping. This can be accomplished using passive or active approaches. Passive treatments such as constrained layer damping tend to reduce window transparency. Therefore this paper focuses on an active approach utilizing compact decentralized control units distributed around the perimeter of the window. Each control unit consists of a triangularly shaped piezoelectric actuator, a miniature accelerometer, and analog electronics. Earlier work has shown that this type of system can increase damping up to approximately 1 kHz. However at higher frequencies the mismatch between the distributed actuator and the point sensor caused control spillover. This paper describes new anisotropic actuators that can be used to improve the bandwidth of the control system. The anisotropic actuators are composed of piezoelectric material sandwiched between interdigitated electrodes, which enables the application of the electric field in a preferred in-plane direction. When shaped correctly the anisotropic actuators outperform traditional isotropic actuators by reducing the mismatch between the distributed actuator and point sensor at high frequencies. Testing performed on a Plexiglas panel, representative of a helicopter window, shows that the control units can increase damping at low frequencies. However high frequency performance was still limited due to the flexible boundary conditions present on the test structure.

  18. Production and characterization of anisotropic particles from biodegradable materials.

    PubMed

    Romanski, Francis S; Winkler, Jennifer S; Riccobene, Ryan C; Tomassone, M Silvina

    2012-02-28

    In recent years, production and characterization of anisotropic particles has become of interest in a wide range of scientific fields including polymer chemistry, drug delivery, electronics, energy, and nanotechnology. In this work, we demonstrate a novel formulation for production of anisotropic particles via an internal phase separation of biodegradable components. Specifically, binary mixtures of biodegradable polymers poly(lactic-co-glycolic acid), polycaprolactone, and biodegradable lipid Precirol (glyceryl palmitostearate) were dissolved in dichloromethane, emulsified, and prepared into anisotropic particles using a modified solvent evaporation technique. During the slow evaporation process the components self-assembled into anisotropic particles with distinct morphologies. Polymer/polymer formulations resulted in compartmentalized anisotropic heterodimer particles, while polymer/lipid combinations yielded "ice cream cone" shaped particles. It was found that addition of certain active pharmaceuticals resulted in an altered, pox-like segregation at the particle surface of polymer/polymer formulations. The anisotropic nature of the particles was subsequently characterized using optical microscopy, scanning electron microscopy, zeta potential, electrophoresis, and X-ray diffraction. Successful formulations presented here may potentially be employed as multicompartmental drug carriers with staggered drug release rates or alternatively as a colloidal excipient for an arsenal of pharmaceutical applications.

  19. Observational signatures of anisotropic inflationary models

    SciTech Connect

    Ohashi, Junko; Tsujikawa, Shinji; Soda, Jiro E-mail: jiro@phys.sci.kobe-u.ac.jp

    2013-12-01

    We study observational signatures of two classes of anisotropic inflationary models in which an inflaton field couples to (i) a vector kinetic term F{sub μν}F{sup μν} and (ii) a two-form kinetic term H{sub μνλ}H{sup μνλ}. We compute the corrections from the anisotropic sources to the power spectrum of gravitational waves as well as the two-point cross correlation between scalar and tensor perturbations. The signs of the anisotropic parameter g{sub *} are different depending on the vector and the two-form models, but the statistical anisotropies generally lead to a suppressed tensor-to-scalar ratio r and a smaller scalar spectral index n{sub s} in both models. In the light of the recent Planck bounds of n{sub s} and r, we place observational constraints on several different inflaton potentials such as those in chaotic and natural inflation in the presence of anisotropic interactions. In the two-form model we also find that there is no cross correlation between scalar and tensor perturbations, while in the vector model the cross correlation does not vanish. The non-linear estimator f{sub NL} of scalar non-Gaussianities in the two-form model is generally smaller than that in the vector model for the same orders of |g{sub *}|, so that the former is easier to be compatible with observational bounds of non-Gaussianities than the latter.

  20. Nuclear quadrupole spin-lattice relaxation in Bi{sub 4}Ge{sub 3}O{sub 12} single crystals doped with atoms of d or f elements. Crystal field effects in compounds exhibiting anomalous magnetic properties

    SciTech Connect

    Orlov, V. G. Sergeev, G. S.; Asaji, Tetsuo; Kravchenko, E. A.; Kargin, Yu. F.

    2010-02-15

    The nuclear quadrupole spin-lattice relaxation was studied in the range 4.2-300 K for single crystals of Bi{sub 4}Ge{sub 3}O{sub 12} doped with minor amounts (the tenth fractions of mol%) of paramagnetic atoms of Cr, Nd, and Gd. Unusual spin dynamic features were recently found for these crystals at room temperature: a dramatic (up to 8-fold) increase in the effective nuclear quadrupole spin-spin relaxation time T{sub 2}* occurred upon doping the pure Bi{sub 4}Ge{sub 3}O{sub 12} sample. Unlike T{sub 2}*, the effective spin-lattice relaxation time T{sub 1}* at room temperature differs insignificantly for both doped and pure samples. But at lower temperatures, the samples exhibit considerably different behavior of the spin-lattice relaxation with temperature, which is caused by different contributions to the relaxation process of the dopant paramagnetic atoms. The distinctive maximum in the temperature dependence of the spin-lattice relaxation time for the Nd-doped crystal is shown to result from the crystal electric field effects.