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Sample records for 2d hubbard model

  1. Bond Order Correlations in the 2D Hubbard Model

    NASA Astrophysics Data System (ADS)

    Moore, Conrad; Abu Asal, Sameer; Yang, Shuxiang; Moreno, Juana; Jarrell, Mark

    We use the dynamical cluster approximation to study the bond correlations in the Hubbard model with next nearest neighbor (nnn) hopping to explore the region of the phase diagram where the Fermi liquid phase is separated from the pseudogap phase by the Lifshitz line at zero temperature. We implement the Hirsch-Fye cluster solver that has the advantage of providing direct access to the computation of the bond operators via the decoupling field. In the pseudogap phase, the parallel bond order susceptibility is shown to persist at zero temperature while it vanishes for the Fermi liquid phase which allows the shape of the Lifshitz line to be mapped as a function of filling and nnn hopping. Our cluster solver implements NVIDIA's CUDA language to accelerate the linear algebra of the Quantum Monte Carlo to help alleviate the sign problem by allowing for more Monte Carlo updates to be performed in a reasonable amount of computation time. Work supported by the NSF EPSCoR Cooperative Agreement No. EPS-1003897 with additional support from the Louisiana Board of Regents.

  2. Knight shift and spin relaxation in the single band 2D Hubbard model

    NASA Astrophysics Data System (ADS)

    Leblanc, James; Chen, Xi; Gull, Emanuel

    We study in detail the roles of spin and charge fluctuations in the single band 2D Hubbard model. Using dynamical mean field theory and cluster extensions such as the dynamical cluster approximation (DCA), we compute the full two particle susceptibilities in the spin and charge representations. By performing analytic continuations we obtain the temperature and doping dependence of the spin-lattice relaxation (T1- 1) and knight shift in the 2D Hubbard model relevant to NMR results on doped cuprates and connect these to RPA results in weak coupling limits.

  3. Mott Quantum Criticality in the Anisotropic 2D Hubbard Model

    NASA Astrophysics Data System (ADS)

    Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin

    2016-02-01

    We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t⊥ acts as a control parameter driving the second-order critical end point Tc of the metal-insulator transition down to zero at t⊥c/t ≃0.2 . Below t⊥c, the volume of the hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t⊥c, the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors, whose location remains elusive so far.

  4. Mott Quantum Criticality in the Anisotropic 2D Hubbard Model.

    PubMed

    Lenz, Benjamin; Manmana, Salvatore R; Pruschke, Thomas; Assaad, Fakher F; Raczkowski, Marcin

    2016-02-26

    We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t_{⊥} acts as a control parameter driving the second-order critical end point T_{c} of the metal-insulator transition down to zero at t_{⊥}^{c}/t≃0.2. Below t_{⊥}^{c}, the volume of the hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t_{⊥}^{c}, the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors, whose location remains elusive so far. PMID:26967431

  5. Mott Quantum Criticality in the Anisotropic 2D Hubbard Model

    NASA Astrophysics Data System (ADS)

    Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin

    We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t⊥ acts as control parameter driving the second-order critical endpoint Tc of the metal-insulator transition down to zero at t⊥c / t ~= 0 . 2 . Below t⊥c the volume of hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t⊥c the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors whose location remains elusive so far. We acknowledge support by DFG research units FOR1807 and FOR1346, ERC Starting Grant No. 306897 and NSF Grant No. PHY11-25915, and computer support by the GWDG and Jülich Supercomputing Centre.

  6. Spectral functions in the 1D and 2D Bose Hubbard model

    NASA Astrophysics Data System (ADS)

    Ivancic, Robert; Duchon, Eric; Trivedi, Nandini

    2014-03-01

    We use state of the art numerical techniques including quantum Monte Carlo and maximum entropy methods to obtain the low energy excitation spectra in the superfluid and Mott-insulator phases of the Bose Hubbard model. These results are checked in 1D against Bethe Ansatz and tDMRG results and extended to 2D where such approaches are impossible. In the superfluid, we find linearly dispersing Bogoliubov sound modes as well as additional gapped modes broadened by interaction effects. In the Mott insulator, we find evidence for a finite gap and well defined quasiparticle excitations. We examine properties such as the excitation lifetime, density of states, and speed of sound as the system is tuned across the quantum phase transition that separates the superfluid and Mott states. These results provide an important theoretical framework for upcoming ultracold atom experiments in one and two dimensions. We acknowledge support from the NSF DMR-0907275 (R.I., E.D. and N.T.).

  7. Constrained Path Monte Carlo and Its Application to the 2-D Hubbard Model

    NASA Astrophysics Data System (ADS)

    Zhang, Shiwei

    1996-03-01

    A recently proposed^1 quantum Monte Carlo (MC) simulation algorithm will be described for studying the ground-state (T=0K) properties of many-fermion systems. The method relies on the usual Hubbard-Stratonovich transformation. It consists of branching random walks in an over-complete basis space of Slater determinants. Asymptotically, the random walks produce determinants |φ_i> non-orthogonal to each other that collectively represent the ground-state wave function in an MC sense: |Ψ_0>=sumi |φ_i>. This reformulation combines important advantages of existing ground-state MC methods and provides an algorithm closely linked to traditional quantum chemistry approaches. In cases free of the fermion MC ``sign'' problem (e.g., half-filled or negative U Hubbard model), the formulation is exact, as is the standard projector MC^2. In cases with the sign problem, we constrain^3 each |φ_i> in the random walk to maintain a positive overlap with a trial wave function |ψ_T>. This constraint eliminates the exponential scaling of CPU time with system size. The computed ground-state energy is an upper bound. The method becomes exact if |ψ_T> is exact. Test results on the two-dimensional Hubbard model show that, even with a simple |ψ_T> such as a free-electron or an unrestricted Hartree-Fock wave function, the method yields very accurate energy and correlation function values when compared with available data from exact diagonalization and quantum MC. Results will be presented on correlation functions (e.g., pair-field) for up to 16× 16 lattices, at various electron fillings and interaction strengths. Work supported in part by the Department of Energy's High Performance Computing and Communication Program at Los Alamos National Laboratory, and at OSU by DOE-Basic Energy Sciences, Division of Materials Sciences. ^1 Shiwei Zhang, J. Carlson, and J. E. Gubernatis, Phys. Rev. Lett. 74, 3652 (1995). ^2 R. Blankenbecler, D. J. Scalapino, and R. L. Sugar, Phys. Rev. D 24, 2278 (1981

  8. Hubbard Model study of Off Diagonally Confined fermions in a 2D Optical Lattice

    NASA Astrophysics Data System (ADS)

    Cone, Dave; Chiesa, Simone; Scalettar, Richard; Batrouni, George

    2010-03-01

    We report Quantum Monte Carlo simulations of a Hubbard Hamiltonian which incorporates a proposed new method for confining atoms in an optical lattice employing an inhomogeneous array of hopping matrix elements which trap atoms by going to zero at the lattice edges. This has been termed ``Off Diagonal Confinement (ODC)'' [1] to distinguish it from the more conventional use of a parabolic trap coupling to (diagonal) density operators. It has the advantage of producing systems which, while still being inhomogeneous, are entirely in the Mott phase, and allow simulations which are free of the sign problem at low temperatures. We analyze the effects of using ODC traps on the local density, density fluctuation, spin, and pairing correlation functions. Finally, we will discuss the advantages and importance of this new confinement technique for modeling correlated systems. Research supported by the Department of Energy, Office of Science SCIDAC program, DOE-DE-FC0206ER25793. [1] V.G. Rousseau et al., arXiv:0909.3543

  9. Numerical simulations - Some results for the 2- and 3-D Hubbard models and a 2-D electron phonon model

    NASA Technical Reports Server (NTRS)

    Scalapino, D. J.; Sugar, R. L.; White, S. R.; Bickers, N. E.; Scalettar, R. T.

    1989-01-01

    Numerical simulations on the half-filled three-dimensional Hubbard model clearly show the onset of Neel order. Simulations of the two-dimensional electron-phonon Holstein model show the competition between the formation of a Peierls-CDW state and a superconducting state. However, the behavior of the partly filled two-dimensional Hubbard model is more difficult to determine. At half-filling, the antiferromagnetic correlations grow as T is reduced. Doping away from half-filling suppresses these correlations, and it is found that there is a weak attractive pairing interaction in the d-wave channel. However, the strength of the pair field susceptibility is weak at the temperatures and lattice sizes that have been simulated, and the nature of the low-temperature state of the nearly half-filled Hubbard model remains open.

  10. Computational Studies of Condensed Matter Systems: Manganese Vanadium Oxide and 2D attractive Hubbard model with spin-dependent disorder

    NASA Astrophysics Data System (ADS)

    Nanguneri, Ravindra

    -dependent disorder. Further, the finite temperature phase diagram for the 2D attractive fermion Hubbard model with spin-dependent disorder is also considered within BdG mean field theory. Three types of disorder are studied. In the first, only one species is coupled to a random site energy; in the second, the two species both move in random site energy landscapes which are of the same amplitude, but different realizations; and finally, in the third, the disorder is in the hopping rather than the site energy. For all three cases we find that, unlike the case of spin-symmetric randomness, where the energy gap and average order parameter do not vanish as the disorder strength increases, a critical disorder strength exists separating distinct phases. In fact, the energy gap and the average order parameter vanish at distinct transitions, Vcgap and Vc op, allowing for a gapless superconducting (gSC) phase. The gSC phase becomes smaller with increasing temperature, until it vanishes at a temperature T*.

  11. Fermionization and Hubbard models

    NASA Astrophysics Data System (ADS)

    Dargis, P.; Maassarani, Z.

    1998-12-01

    We introduce a transformation which allows the fermionization of operators of any one-dimensional spin-chain. This fermionization procedure is independent of any eventual integrable structure and is compatible with it. We illustrate this method on various integrable and non-integrable chains, and deduce some general results. In particular, we fermionize XXC spin-chains and study their symmetries. Fermionic realizations of certain Lie algebras and superalgebras appear naturally as symmetries of some models. We also fermionize recently obtained Hubbard models, and obtain for the first time multispecies analogues of the Hubbard model, in their fermionic form. We comment on the conflict between symmetry enhancement and integrability of these models. Finally, the fermionic versions of the non-integrable spin-1 and spin- {3}/{2} Heisenberg chains are obtained.

  12. Bosonic Kondo-Hubbard model

    NASA Astrophysics Data System (ADS)

    Flottat, T.; Hébert, F.; Rousseau, V. G.; Scalettar, R. T.; Batrouni, G. G.

    2015-07-01

    We study, using quantum Monte Carlo simulations, the bosonic Kondo-Hubbard model in a two-dimensional square lattice. We explore the phase diagram and analyze the mobility of particles and magnetic properties. At unit filling, the transition from a paramagnetic Mott insulator to a ferromagnetic superfluid appears continuous, contrary to what was predicted with mean field. For double occupation per site, both the Mott insulating and superfluid phases are ferromagnetic and the transition is still continuous. Multiband tight-binding Hamiltonians can be realized in optical lattice experiments, which offer not only the possibility of tuning the different energy scales over wide ranges, but also the option of loading the system with either fermionic or bosonic atoms.

  13. An algebraic approach to the Hubbard model

    NASA Astrophysics Data System (ADS)

    de Leeuw, Marius; Regelskis, Vidas

    2016-02-01

    We study the algebraic structure of an integrable Hubbard-Shastry type lattice model associated with the centrally extended su (2 | 2) superalgebra. This superalgebra underlies Beisert's AdS/CFT worldsheet R-matrix and Shastry's R-matrix. The considered model specializes to the one-dimensional Hubbard model in a certain limit. We demonstrate that Yangian symmetries of the R-matrix specialize to the Yangian symmetry of the Hubbard model found by Korepin and Uglov. Moreover, we show that the Hubbard model Hamiltonian has an algebraic interpretation as the so-called secret symmetry. We also discuss Yangian symmetries of the A and B models introduced by Frolov and Quinn.

  14. Fermionic Symmetry-Protected Topological Phase in a Two-Dimensional Hubbard Model.

    PubMed

    Chen, Cheng-Chien; Muechler, Lukas; Car, Roberto; Neupert, Titus; Maciejko, Joseph

    2016-08-26

    We study the two-dimensional (2D) Hubbard model using exact diagonalization for spin-1/2 fermions on the triangular and honeycomb lattices decorated with a single hexagon per site. In certain parameter ranges, the Hubbard model maps to a quantum compass model on those lattices. On the triangular lattice, the compass model exhibits collinear stripe antiferromagnetism, implying d-density wave charge order in the original Hubbard model. On the honeycomb lattice, the compass model has a unique, quantum disordered ground state that transforms nontrivially under lattice reflection. The ground state of the Hubbard model on the decorated honeycomb lattice is thus a 2D fermionic symmetry-protected topological phase. This state-protected by time-reversal and reflection symmetries-cannot be connected adiabatically to a free-fermion topological phase. PMID:27610869

  15. Thermalization of Bipartite Bose-Hubbard Models.

    PubMed

    Khripkov, Christine; Cohen, Doron; Vardi, Amichay

    2016-05-19

    We study the time evolution of a bipartite Bose-Hubbard model prepared far from equilibrium. When the classical dynamics is chaotic, we observe ergodization of the number distribution and a constant increase of the entanglement entropy between the constituent subsystems until it saturates to thermal equilibrium values. No thermalization is obtained when the system is launched in quasi-integrable phase space regions. PMID:26701599

  16. Spectral properties near the Mott transition in the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Kohno, Masanori

    2013-03-01

    Single-particle excitations near the Mott transition in the two-dimensional (2D) Hubbard model are investigated by using cluster perturbation theory. The Mott transition is characterized by the loss of the spectral weight from the dispersing mode that leads continuously to the spin-wave excitation of the Mott insulator. The origins of the dominant modes of the 2D Hubbard model near the Mott transition can be traced back to those of the one-dimensional Hubbard model. Various anomalous spectral features observed in cuprate high-temperature superconductors, such as the pseudogap, Fermi arc, flat band, doping-induced states, hole pockets, and spinon-like and holon-like branches, as well as giant kink and waterfall in the dispersion relation, are explained in a unified manner as properties near the Mott transition in a 2D system.

  17. Disordered spinor Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Łącki, Mateusz; Paganelli, Simone; Ahufinger, Veronica; Sanpera, Anna; Zakrzewski, Jakub

    2011-01-01

    We study the zero-temperature phase diagram of the disordered spin-1 Bose-Hubbard model in a two-dimensional square lattice. To this aim, we use a mean-field Gutzwiller ansatz and a probabilistic mean-field perturbation theory. The spin interaction induces two different regimes, corresponding to a ferromagnetic and antiferromagnetic order. In the ferromagnetic case, the introduction of disorder reproduces analogous features of the disordered scalar Bose-Hubbard model, consisting in the formation of a Bose glass phase between Mott insulator lobes. In the antiferromagnetic regime, the phase diagram differs more from the scalar case. Disorder in the chemical potential can lead to the disappearance of Mott insulator lobes with an odd-integer filling factor and, for sufficiently strong spin coupling, to Bose glass of singlets between even-filling Mott insulator lobes. Disorder in the spinor coupling parameter results in the appearance of a Bose glass phase only between the n and the n+1 lobes for n odd. Disorder in the scalar Hubbard interaction inhibits Mott insulator regions for occupation larger than a critical value.

  18. Nonequilibrium dynamics in the antiferromagnetic Hubbard model

    NASA Astrophysics Data System (ADS)

    Sandri, Matteo; Fabrizio, Michele

    2013-10-01

    We investigate by means of the time-dependent Gutzwiller variational approach the out-of-equilibrium dynamics of an antiferromagnetic state evolved with the Hubbard model Hamiltonian after a sudden change of the repulsion strength U. We find that magnetic order survives more than what is expected on the basis of thermalization arguments, in agreement with recent dynamical mean field theory calculations. In addition, we find evidence of a dynamical transition for quenches to large values of U between a coherent antiferromagnet characterized by a finite quasiparticle residue to an incoherent one with vanishing residue, which finally turns into a paramagnet for even larger U.

  19. Dynamical Vertex Approximation for the Hubbard Model

    NASA Astrophysics Data System (ADS)

    Toschi, Alessandro

    A full understanding of correlated electron systems in the physically relevant situations of three and two dimensions represents a challenge for the contemporary condensed matter theory. However, in the last years considerable progress has been achieved by means of increasingly more powerful quantum many-body algorithms, applied to the basic model for correlated electrons, the Hubbard Hamiltonian. Here, I will review the physics emerging from studies performed with the dynamical vertex approximation, which includes diagrammatic corrections to the local description of the dynamical mean field theory (DMFT). In particular, I will first discuss the phase diagram in three dimensions with a special focus on the commensurate and incommensurate magnetic phases, their (quantum) critical properties, and the impact of fluctuations on electronic lifetimes and spectral functions. In two dimensions, the effects of non-local fluctuations beyond DMFT grow enormously, determining the appearance of a low-temperature insulating behavior for all values of the interaction in the unfrustrated model: Here the prototypical features of the Mott-Hubbard metal-insulator transition, as well as the existence of magnetically ordered phases, are completely overwhelmed by antiferromagnetic fluctuations of exponentially large extension, in accordance with the Mermin-Wagner theorem. Eventually, by a fluctuation diagnostics analysis of cluster DMFT self-energies, the same magnetic fluctuations are identified as responsible for the pseudogap regime in the holed-doped frustrated case, with important implications for the theoretical modeling of the cuprate physics.

  20. Nonperturbative approach to the attractive Hubbard model

    SciTech Connect

    Allen, S.; Tremblay, A.-M. S.

    2001-08-15

    A nonperturbative approach to the single-band attractive Hubbard model is presented in the general context of functional-derivative approaches to many-body theories. As in previous work on the repulsive model, the first step is based on a local-field-type ansatz, on enforcement of the Pauli principle and a number of crucial sumrules. The Mermin-Wagner theorem in two dimensions is automatically satisfied. At this level, two-particle self-consistency has been achieved. In the second step of the approximation, an improved expression for the self-energy is obtained by using the results of the first step in an exact expression for the self-energy, where the high- and low-frequency behaviors appear separately. The result is a cooperon-like formula. The required vertex corrections are included in this self-energy expression, as required by the absence of a Migdal theorem for this problem. Other approaches to the attractive Hubbard model are critically compared. Physical consequences of the present approach and agreement with Monte Carlo simulations are demonstrated in the accompanying paper (following this one).

  1. Thermodynamics of the planar Hubbard model

    NASA Astrophysics Data System (ADS)

    Bonča, J.; Prelovšek, P.

    2003-02-01

    The thermodynamic properties of specific heat, entropy, chemical potential, spin susceptibility χs, and charge susceptibility χc are studied as functions of temperature and doping within the two-dimensional Hubbard model with various U/t=4 12. Quantities are calculated using the finite-temperature Lanczos method with additional phase averaging for a system of 4×4 sites. Results show that the entropy at low T reaches a maximum near half-filling at the electron density n˜1±0.15 in the whole regime of studied U/t. The pseudogap in χs(T) becomes clearly pronounced for U/t⩾8 while χc shows a maximum close to half-filling. The relation of results to those within the t-J model and to experiments is discussed.

  2. Phases of the infinite U Hubbard model on square lattices.

    PubMed

    Liu, Li; Yao, Hong; Berg, Erez; White, Steven R; Kivelson, Steven A

    2012-03-23

    We apply the density matrix renormalization group to study the phase diagram of the infinite U Hubbard model on 2- to 6-leg ladders. Where the results are largely insensitive to the ladder width, we consider the results representative of the 2D square lattice. We find a fully polarized ferromagnetic Fermi liquid phase when n, the density of electrons per site, is in the range 1>n≳0.800. For n=3/4 we find an unexpected insulating checkerboard phase with coexisting bond-density order with 4 sites per unit cell and block-spin antiferromagnetic order with 8 sites per unit cell. For 3/4>n, all ladders with width >2 have unpolarized ground states. PMID:22540606

  3. Effect of Quantum Correction in the Bose-Hubbard Model

    SciTech Connect

    Matsumoto, Hideki; Takahashi, Kiyoshi; Ohashi, Yoji

    2006-09-07

    Effects of quantum correction in the Bose-Hubbard model at finite temperature are investigated for a homogeneous atomic Bose gas in an optical lattice near its superfluid-insulator transition. Starting from a strong coupling limit, higher order quantum corrections due to the hopping interaction is included in a local approximation (a dynamical mean field approximation) of the non-crossing approximation. When the upper or lower Hubbard band approaches zero energy, there appears a shallow band in the middle of the Hubbard gap due to a strong correlation in the system.

  4. Reexamination of the variational Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Major, Jan; Łącki, Mateusz; Zakrzewski, Jakub

    2014-04-01

    For strongly interacting bosons in optical lattices, the standard description using the Bose-Hubbard model becomes questionable. The role of excited bands becomes important. In such a situation, we compare results of simulations using the multiband Bose-Hubbard model with a recent proposition based on a time-dependent variational approach. It is shown that the latter, in its original formulation, uses a too small variational space, often leading to spurious effects. Possible expansion of the variational approach is discussed.

  5. Quasiparticel Spectra of the Hubbard Model

    NASA Astrophysics Data System (ADS)

    Annett, James F.; Beere, William H.

    1998-03-01

    We examine the quasiparticle lifetime and spectral weight near the Fermi surface in the two-dimensional Hubbard model using the FLEX approximation. Examining the spectral functions over a wide range temperature, doping, and at different values of t' and U, we can separate the effects of nesting, the van Hove singularity and short-ranged antiferromagnetic correlations. Near half-filling the quasiparticle scarreting rate, Γ, shows `hot spots' on the Fermi surface assosciated with the proximity to the antiferromagnetic phase transition.( J. Altmann, W. Brenig and A.P. Kampf, cond-mat/9707267) Further away from half filling there is a wide range of doing and temperature where Marginal Fermi Liquid (MFL) behaviour is seen: Γ ~ T. The MFL behavior occurs even when U is reduced below the threshold for antiferromagnetism to occur (for t'neq 0). The MFL region is clearly centered on dopings around to the Van Hove singularity. We conclude that the low temperature upturn in Γ(T) observed in underdoped cuprates is due to antiferromagnetic fluctuations, while the MFL behavior at optimal doping is due to the Van Hove singularity. (P.C. Pattnaik, C.L. Kane, D.M. Newns, and C.C. Tsuei, Phys. Rev. B 45) 5714 (1992).

  6. Flow equations for the ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Hafez, Mohsen; Jafari, S. A.; Abolhassani, M. R.

    2009-12-01

    Taking the site-diagonal terms of the ionic Hubbard model (IHM) in one and two spatial dimensions, as H, we employ Continuous Unitary Transformations (CUT) to obtain a “classical” effective Hamiltonian in which hopping term has been renormalized to zero. For this Hamiltonian spin gap and charge gap are calculated at half-filling and subject to periodic boundary conditions. Our calculations indicate two transition points. In fixed Δ, as U increases from zero, there is a region in which both spin gap and charge gap are positive and identical; characteristic of band insulators. Upon further increasing U, first transition occurs at U=Uc_1, where spin and charge gaps both vanish and remain zero up to U=Uc_2. A gap-less state in charge and spin sectors characterizes a metal. For U>Uc_2 spin gap remains zero and charge gap becomes positive. This third region corresponds to a Mott insulator in which charge excitations are gaped, while spin excitations remain gap-less.

  7. Non-standard Hubbard models in optical lattices: a review

    NASA Astrophysics Data System (ADS)

    Dutta, Omjyoti; Gajda, Mariusz; Hauke, Philipp; Lewenstein, Maciej; Lühmann, Dirk-Sören; Malomed, Boris A.; Sowiński, Tomasz; Zakrzewski, Jakub

    2015-06-01

    Originally, the Hubbard model was derived for describing the behavior of strongly correlated electrons in solids. However, for over a decade now, variations of it have also routinely been implemented with ultracold atoms in optical lattices, allowing their study in a clean, essentially defect-free environment. Here, we review some of the vast literature on this subject, with a focus on more recent non-standard forms of the Hubbard model. After giving an introduction to standard (fermionic and bosonic) Hubbard models, we discuss briefly common models for mixtures, as well as the so-called extended Bose-Hubbard models, that include interactions between neighboring sites, next-neighbor sites, and so on. The main part of the review discusses the importance of additional terms appearing when refining the tight-binding approximation for the original physical Hamiltonian. Even when restricting the models to the lowest Bloch band is justified, the standard approach neglects the density-induced tunneling (which has the same origin as the usual on-site interaction). The importance of these contributions is discussed for both contact and dipolar interactions. For sufficiently strong interactions, the effects related to higher Bloch bands also become important even for deep optical lattices. Different approaches that aim at incorporating these effects, mainly via dressing the basis, Wannier functions with interactions, leading to effective, density-dependent Hubbard-type models, are reviewed. We discuss also examples of Hubbard-like models that explicitly involve higher p orbitals, as well as models that dynamically couple spin and orbital degrees of freedom. Finally, we review mean-field nonlinear Schrödinger models of the Salerno type that share with the non-standard Hubbard models nonlinear coupling between the adjacent sites. In that part, discrete solitons are the main subject of consideration. We conclude by listing some open problems, to be addressed in the future.

  8. Non-standard Hubbard models in optical lattices: a review.

    PubMed

    Dutta, Omjyoti; Gajda, Mariusz; Hauke, Philipp; Lewenstein, Maciej; Lühmann, Dirk-Sören; Malomed, Boris A; Sowiński, Tomasz; Zakrzewski, Jakub

    2015-06-01

    Originally, the Hubbard model was derived for describing the behavior of strongly correlated electrons in solids. However, for over a decade now, variations of it have also routinely been implemented with ultracold atoms in optical lattices, allowing their study in a clean, essentially defect-free environment. Here, we review some of the vast literature on this subject, with a focus on more recent non-standard forms of the Hubbard model. After giving an introduction to standard (fermionic and bosonic) Hubbard models, we discuss briefly common models for mixtures, as well as the so-called extended Bose-Hubbard models, that include interactions between neighboring sites, next-neighbor sites, and so on. The main part of the review discusses the importance of additional terms appearing when refining the tight-binding approximation for the original physical Hamiltonian. Even when restricting the models to the lowest Bloch band is justified, the standard approach neglects the density-induced tunneling (which has the same origin as the usual on-site interaction). The importance of these contributions is discussed for both contact and dipolar interactions. For sufficiently strong interactions, the effects related to higher Bloch bands also become important even for deep optical lattices. Different approaches that aim at incorporating these effects, mainly via dressing the basis, Wannier functions with interactions, leading to effective, density-dependent Hubbard-type models, are reviewed. We discuss also examples of Hubbard-like models that explicitly involve higher p orbitals, as well as models that dynamically couple spin and orbital degrees of freedom. Finally, we review mean-field nonlinear Schrödinger models of the Salerno type that share with the non-standard Hubbard models nonlinear coupling between the adjacent sites. In that part, discrete solitons are the main subject of consideration. We conclude by listing some open problems, to be addressed in the future

  9. Exploring unconventional Hubbard models with doubly modulated lattice gases.

    PubMed

    Greschner, Sebastian; Santos, Luis; Poletti, Dario

    2014-10-31

    Recent experiments show that periodic modulations of cold atoms in optical lattices may be used to engineer and explore interesting models. We show that double modulation combining lattice shaking and modulated interactions allows for the engineering of a much broader class of lattice with correlated hopping, which we study for the particular case of one-dimensional systems. We show, in particular, that by using this double modulation it is possible to study Hubbard models with asymmetric hopping, which, contrary to the standard Hubbard model, present insulating phases with both parity and string order. Moreover, double modulation allows for the simulation of lattice models in unconventional parameter regimes, as we illustrate for the case of the spin-1/2 Fermi-Hubbard model with correlated hopping, a relevant model for cuprate superconductors. PMID:25396367

  10. Quantum phase transitions in the Fermi-Bose Hubbard model

    SciTech Connect

    Carr, L.D.; Holland, M.J.

    2005-09-15

    We propose a multiband Fermi-Bose Hubbard model with on-site fermion-boson conversion and general filling factor in three dimensions. Such a Hamiltonian models an atomic Fermi gas trapped in a lattice potential and subject to a Feshbach resonance. We solve this model in the two-state approximation for paired fermions at zero temperature. The problem then maps onto a coupled Heisenberg spin model. In the limit of large positive and negative detuning, the quantum phase transitions in the Bose Hubbard and paired-Fermi Hubbard models are correctly reproduced. Near resonance, the Mott states are given by a superposition of the paired-fermion and boson fields and the Mott-superfluid borders go through an avoided crossing in the phase diagram.

  11. Hubbard operator density functional theory for Fermionic lattice models

    NASA Astrophysics Data System (ADS)

    Cheng, Zhengqian; Marianetti, Chris

    We formulate an effective action as a functional of Hubbard operator densities whose stationary point delivers all local static information of the interacting lattice model. Using the variational principle, we get a self-consistent equation for Hubbard operator densities. The computational cost of our approach is set by diagonalizing the local Fock space. We apply our method to the one and two band Hubbard model (including crystal field and on-site exchange) in infinite dimensions where the exact solution is known. Excellent agreement is obtained for the one-band model. In the two-band model, good agreement is obtained in the metallic region of the phase diagram in addition to the metal-insulator transition. While our approach does not address frequency dependent observables, it has a negligible computational cost as compared to dynamical mean field theory and could be highly applicable in the context total energies of strongly correlated materials and molecules.

  12. Quantum Paramagnet in a π Flux Triangular Lattice Hubbard Model.

    PubMed

    Rachel, Stephan; Laubach, Manuel; Reuther, Johannes; Thomale, Ronny

    2015-04-24

    We propose the π flux triangular lattice Hubbard model (π THM) as a prototypical setup to stabilize magnetically disordered quantum states of matter in the presence of charge fluctuations. The quantum paramagnetic domain of the π THM that we identify for intermediate Hubbard U is framed by a Dirac semimetal for weak coupling and by 120° Néel order for strong coupling. Generalizing the Klein duality from spin Hamiltonians to tight-binding models, the π THM maps to a Hubbard model which corresponds to the (J_{H},J_{K})=(-1,2) Heisenberg-Kitaev model in its strong coupling limit. The π THM provides a promising microscopic testing ground for exotic finite-U spin liquid ground states amenable to numerical investigation. PMID:25955072

  13. Quantum Monte Carlo study of bilayer ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Jiang, M.; Schulthess, T. C.

    2016-04-01

    The interaction-driven insulator-to-metal transition has been reported in the ionic Hubbard model (IHM) for moderate interaction U , while its metallic phase only occupies a narrow region in the phase diagram. To explore the enlargement of the metallic regime, we extend the ionic Hubbard model to two coupled layers and study the interplay of interlayer hybridization V and two types of intralayer staggered potentials Δ : one with the same (in-phase) and the other with a π -phase shift (antiphase) potential between layers. Our determinant quantum Monte Carlo (DQMC) simulations at lowest accessible temperatures demonstrate that the interaction-driven metallic phase between Mott and band insulators expands in the Δ -V phase diagram of bilayer IHM only for in-phase ionic potentials; while antiphase potential always induces an insulator with charge density order. This implies possible further extension of the ionic Hubbard model from the bilayer case here to a realistic three-dimensional model.

  14. Pseudogaps in the three-band Hubbard model

    NASA Astrophysics Data System (ADS)

    Sherman, Alexei

    2016-04-01

    Using the strong coupling diagram technique, the energy spectrum of the three-band Hubbard model is investigated. In these calculations, the series in powers of the copper-oxygen hybridization for the irreducible part is approximated by two lowest-order terms. For parameters of hole-doped cuprates the calculated energy spectrum consists of lower and upper Hubbard subbands of predominantly copper nature, oxygen bands with some admixture of copper states and the Zhang-Rice states of mixed nature. The spectrum contains two pseudogaps, the lower of which separates the Hubbard subband from Zhang-Rice and oxygen bands. The pseudogaps arise due to multiple reabsorption of carriers in states with double occupancy of sites by holes or electrons.

  15. A bespoke single-band Hubbard model material

    NASA Astrophysics Data System (ADS)

    Griffin, S. M.; Staar, P.; Schulthess, T. C.; Troyer, M.; Spaldin, N. A.

    2016-02-01

    The Hubbard model, which augments independent-electron band theory with a single parameter to describe electron-electron correlations, is widely regarded to be the "standard model" of condensed-matter physics. The model has been remarkably successful at addressing a range of correlation phenomena in solids, but it neglects many behaviors that occur in real materials, such as phonons, long-range interactions, and, in its simplest form, multiorbital effects. Here, we use ab initio electronic structure methods to design a material whose Hamiltonian matches as closely as possible that of the single-band Hubbard model. Our motivation is to compare the measured properties of our new material to those predicted by reliable theoretical solutions of the Hubbard model to determine the relevance of the model in the description of real materials. After identifying an appropriate crystal class and several appropriate chemistries, we use density-functional theory and dynamical mean-field theory to screen for the desired electronic band structure and metal-insulator transition. We then explore the most promising candidates for structural stability and suitability for doping, and we propose specific materials for subsequent synthesis. Finally, we identify a regime—that should manifest in our bespoke material—in which the single-band Hubbard model on a triangular lattice exhibits exotic d -wave superconductivity.

  16. Critical points of the anyon-Hubbard model

    NASA Astrophysics Data System (ADS)

    Arcila-Forero, J.; Franco, R.; Silva-Valencia, J.

    2016-07-01

    Anyons are particles with fractional statistics that exhibit a nontrivial change in the wave function under an exchange of particles. Anyons can be considered to be a general category of particles that interpolate between fermions and bosons. We determined the position of the critical points of the one-dimensional anyon-Hubbard model, which was mapped to a modified Bose-Hubbard model where the tunneling depends on the local density and the interchange angle. We studied the latter model by using the density-matrix renormalization-group method and observed that gapped (Mott insulator) and gapless (superfluid) phases characterized the phase diagram, regardless of the value of the statistical angle. The phase diagram for higher densities was calculated and showed that the Mott lobes increase (decrease) as a function of the statistical angle (global density). The position of the critical point separating the gapped and gapless phases was found using quantum information tools, namely the block von Neumann entropy. We also studied the evolution of the critical point with the global density and the statistical angle and showed that the anyon-Hubbard model with a statistical angle θ =π /4 is in the same universality class as the Bose-Hubbard model with two-body interactions.

  17. Correlation driven dimensional reduction in a two orbital Hubbard model

    NASA Astrophysics Data System (ADS)

    Mukherjee, Anamitra; Patel, Niravkumar D.; Moreo, Adrianna; Dagotto, Elbio

    We apply a recently developed many-body technique that allows for the incorporation of thermal effects, to a two orbital Hubbard model of relevance for the pnictides. In this `Mean Field-Monte Carlo' (MF-MC) approach, we first perform a mean field (MF) decomposition of the Hubbard model and then treat the mean field parameters via the standard finite-temperature classical Monte Carlo (MC). We have earlier established that for the one orbital Hubbard model, this MF-MC approach provides remarkable improvement over simple finite-temperature mean field methods and is in good agreement with Determinantal Quantum Monte Carlo results. In this talk we will discuss our MC-MF results applied to the two orbital Hubbard model with degenerate dxz and dyz orbitals for the undoped pnictides. The onsite repulsion strength U vs. temperature phase diagram is rich and has a narrow window of nematicity above the N'eel temperature. Our main result is the discovery of a novel intermediate coupling regime characterized by an unexpected spontaneous dimensional reduction that renders one direction insulating and the other metallic.

  18. Quantum cluster approach to the spinful Haldane-Hubbard model

    NASA Astrophysics Data System (ADS)

    Wu, Jingxiang; Faye, Jean Paul Latyr; Sénéchal, David; Maciejko, Joseph

    2016-02-01

    We study the spinful fermionic Haldane-Hubbard model at half-filling using a combination of quantum cluster methods: cluster perturbation theory, the variational cluster approximation, and cluster dynamical mean-field theory. We explore possible zero-temperature phases of the model as a function of onsite repulsive interaction strength and next-nearest-neighbor hopping amplitude and phase. Our approach allows us to access the regime of intermediate interaction strength, where charge fluctuations are significant and effective spin model descriptions may not be justified. Our approach also improves upon mean-field solutions of the Haldane-Hubbard model by retaining local quantum fluctuations and treating them nonperturbatively. We find a correlated topological Chern insulator for weak interactions and a topologically trivial Néel antiferromagnetic insulator for strong interactions. For intermediate interactions, we find that topologically nontrivial Néel antiferromagnetic insulating phases and/or a topologically nontrivial nonmagnetic insulating phase may be stabilized.

  19. The 2-site Hubbard and {t}-{J} models

    NASA Astrophysics Data System (ADS)

    Avella, A.; Mancini, F.; Saikawa, T.

    2003-12-01

    The fermionic and bosonic sectors of the 2-site Hubbard model have been exactly solved by means of the equation of motion and Green’s function formalism. The exact solution of the t- J model has been also reported to investigate the low-energy dynamics. We have successfully searched for the exact eigenoperators, and the corresponding eigenenergies, having in mind the possibility to use them as an operatorial basis on the lattice. Many local, single-particle, thermodynamical and response properties have been studied as functions of the external parameters and compared between the two models and with some numerical and exact results. It has been shown that the 2-site Hubbard model already contains the most relevant energy scales of the Hubbard model: the local Coulomb interaction U and the spin-exchange one J = frac{4t^2}U. As a consequence of this, for some relevant properties (kinetic energy, double occupancy, energy, specific heat and entropy) and as regards the metal-insulator transition issue, it has resulted possible to almost exactly mime the behavior of larger systems, sometimes using a higher temperature to get a comparable level spacing. The 2-site models have been also used as toy models to test the efficiency of the Green’s function formalism for composite operators. The capability to reproduce the exact solutions, obtained by the exact diagonalization technique, gives a firm ground to the approximate treatments based on this formalism.

  20. Equation of State of the Two-Dimensional Hubbard Model.

    PubMed

    Cocchi, Eugenio; Miller, Luke A; Drewes, Jan H; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-04-29

    The subtle interplay between kinetic energy, interactions, and dimensionality challenges our comprehension of strongly correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions 0≲U/t≲20 and temperatures, down to k_{B}T/t=0.63(2) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities, and double occupancies over the whole doping range, and, hence, our results constitute benchmarks for state-of-the-art theoretical approaches. PMID:27176527

  1. Equation of State of the Two-Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Cocchi, Eugenio; Miller, Luke A.; Drewes, Jan H.; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-04-01

    The subtle interplay between kinetic energy, interactions, and dimensionality challenges our comprehension of strongly correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions 0 ≲U /t ≲20 and temperatures, down to kBT /t =0.63 (2 ) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities, and double occupancies over the whole doping range, and, hence, our results constitute benchmarks for state-of-the-art theoretical approaches.

  2. Magnon edge states in the hardcore- Bose-Hubbard model.

    PubMed

    Owerre, S A

    2016-11-01

    Quantum Monte Carlo (QMC) simulation has uncovered nonzero Berry curvature and bosonic edge states in the hardcore-Bose-Hubbard model on the gapped honeycomb lattice. The competition between the chemical potential and staggered onsite potential leads to an interesting quantum phase diagram comprising the superfluid phase, Mott insulator, and charge density wave insulator. In this paper, we present a semiclassical perspective of this system by mapping to a spin-1/2 quantum XY model. We give an explicit analytical origin of the quantum phase diagram, the Berry curvatures, and the edge states using semiclassical approximations. We find very good agreement between the semiclassical analyses and the QMC results. Our results show that the topological properties of the hardcore-Bose-Hubbard model are the same as those of magnon in the corresponding quantum spin system. Our results are applicable to systems of ultracold bosonic atoms trapped in honeycomb optical lattices. PMID:27603092

  3. U(1) slave-particle study of the finite-temperature doped Hubbard model in one and two dimensions

    SciTech Connect

    Ribeiro, P.; Sacramento, P.D.; Araujo, M.A.N.

    2011-05-15

    Research Highlights: > Mean-field U(1) slave-particle description of Hubbard model. > Fractionalized phases at finite-temperature in Hubbard model. > Spectral function of 1d and 2d Hubbard model. - Abstract: One-dimensional systems have unusual properties such as fractionalization of degrees of freedom. The occurrence of similar phenomena in higher dimensional systems has been considered in the literature for the description of quantum spin liquids and some non-fermi liquid phases. In this work we construct a mean field (MF) theory of the Hubbard model which is based on a representation of the electronic fields that explicitly introduces a separation of the charge and spin degrees of freedom (the so-called Zou-Anderson transformation) and study the finite-temperature phase diagram for the Hubbard chain and square lattice. The mean field variables are defined along the links of the underlying lattice. We obtain the spectral function and identify the regions of higher spectral weight with the fractionalized fermionic (spin) and bosonic (charge) excitations.

  4. Local properties of the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Drewes, Jan; Miller, Luke; Cocchi, Eugenio; Chan, Chun Fai; Pertot, Daniel; Brennecke, Ferdinand; Köhl, Michael

    2016-05-01

    Quantum gases of interacting fermionic atoms in optical lattices promise to shed new light on the low-temperature phases of the Hubbard model such as spin-ordered phases, or in particular, on possible d-wave superconductivity. In this context it remains challenging to further reduce the temperature of the trapped gas. We experimentally realize the two-dimensional Hubbard model by loading a quantum degenerate Fermi gas of 40K atoms into a three-dimensional optical lattice geometry. By tuning the interaction between the two lowest hyperfine states to strong repulsion the two-dimensional Mott-insulator is created. High resolution absorption imaging in combination with radio-frequency spectroscopy is applied to spatially resolve the atomic distribution in a single layer in the vertical direction. This measurement scheme gives direct access to the local properties of the trapped gas and we present most recent data on the distribution of entropy and density-density fluctuations.

  5. Extended Bose-Hubbard models with ultracold magnetic atoms

    NASA Astrophysics Data System (ADS)

    Baier, S.; Mark, M. J.; Petter, D.; Aikawa, K.; Chomaz, L.; Cai, Z.; Baranov, M.; Zoller, P.; Ferlaino, F.

    2016-04-01

    The Hubbard model underlies our understanding of strongly correlated materials. Whereas its standard form only comprises interactions between particles at the same lattice site, extending it to encompass long-range interactions is predicted to profoundly alter the quantum behavior of the system. We realize the extended Bose-Hubbard model for an ultracold gas of strongly magnetic erbium atoms in a three-dimensional optical lattice. Controlling the orientation of the atomic dipoles, we reveal the anisotropic character of the onsite interaction and hopping dynamics and their influence on the superfluid-to-Mott insulator quantum phase transition. Moreover, we observe nearest-neighbor interactions, a genuine consequence of the long-range nature of dipolar interactions. Our results lay the groundwork for future studies of exotic many-body quantum phases.

  6. Quantum Monte Carlo study of bilayer ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Jiang, Mi

    The interaction-driven insulator-to-metal transition has been reported in the ionic Hubbard model (IHM) for intermediate interaction U, which poses fundamental interest in the correlated electronic systems. Here we use determinant quantum Monte Carlo to study the interplay of interlayer hybridization V and two types of intralayer staggered potentials: one with the same (in-phase) and the other with a π-phase shift (anti-phase) potential in two layers termed as ``bilayer ionic Hubbard model''. We demonstrate that the interaction-driven Insulator-Metal transition extends to bilayer IHM with finite V for both types of staggered potentials. Besides, the system with in-phase potential is prone to metallic phase with turning on interlayer hybridization while that with anti-phase potential tends to insulators with stronger charge density order. The author thanks CSCS, Lugano, Switzerland for computing facilities.

  7. Extended Bose-Hubbard models with ultracold magnetic atoms.

    PubMed

    Baier, S; Mark, M J; Petter, D; Aikawa, K; Chomaz, L; Cai, Z; Baranov, M; Zoller, P; Ferlaino, F

    2016-04-01

    The Hubbard model underlies our understanding of strongly correlated materials. Whereas its standard form only comprises interactions between particles at the same lattice site, extending it to encompass long-range interactions is predicted to profoundly alter the quantum behavior of the system. We realize the extended Bose-Hubbard model for an ultracold gas of strongly magnetic erbium atoms in a three-dimensional optical lattice. Controlling the orientation of the atomic dipoles, we reveal the anisotropic character of the onsite interaction and hopping dynamics and their influence on the superfluid-to-Mott insulator quantum phase transition. Moreover, we observe nearest-neighbor interactions, a genuine consequence of the long-range nature of dipolar interactions. Our results lay the groundwork for future studies of exotic many-body quantum phases. PMID:27124454

  8. Bose-Hubbard model on a checkerboard superlattice

    NASA Astrophysics Data System (ADS)

    Iskin, Menderes

    2011-05-01

    We study the ground-state phases of the Bose-Hubbard model on a checkerboard superlattice in two dimensions, including the superfluid phase and the Mott and charge-density-wave insulators. First, we discuss the single-particle Hofstadter problem, and show that the presence of a checkerboard superlattice gives rise to a magnetic flux-independent energy gap in the excitation spectrum. Then, we consider the many-particle problem, and derive an analytical mean-field expression for the superfluid-Mott and superfluid-charge-density-wave insulator phase transition boundaries. Finally, since the phase diagram of the Bose-Hubbard model on a checkerboard superlattice is in many ways similar to that of the extended Bose-Hubbard model, we comment on the effects of magnetic field on the latter model, and derive an analytical mean-field expression for the superfluid-insulator phase transition boundaries as well. This work is supported by Marie Curie International Reintegration Grant (FP7-PEOPLE-IRG-2010-268239).

  9. Entanglement entropies of the quarter filled Hubbard model

    NASA Astrophysics Data System (ADS)

    Calabrese, Pasquale; Essler, Fabian H. L.; Läuchli, Andreas M.

    2014-09-01

    We study Rényi and von Neumann entanglement entropies in the ground state of the one dimensional quarter-filled Hubbard model with periodic boundary conditions. We show that they exhibit an unexpected dependence on system size: for L = 4mod 8 the results are in agreement with expectations based on conformal field theory, while for L = 0mod 8 additional contributions arise. We show that these can be understood in terms of a ‘shell-filling’ effect and we develop a conformal field theory approach to calculate the additional contributions to the entropies. These analytic results are found to be in excellent agreement with density matrix renormalization group computations for weak Hubbard interactions. We argue that for larger interactions the presence of a marginal irrelevant operator in the spin sector strongly affects the entropies at the finite sizes accessible numerically and we present an effective way to take them into account.

  10. Brittle damage models in DYNA2D

    SciTech Connect

    Faux, D.R.

    1997-09-01

    DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.

  11. Route to supersolidity for the extended Bose-Hubbard model

    SciTech Connect

    Iskin, M.

    2011-05-15

    We use the Gutzwiller ansatz and analyze the phase diagram of the extended Bose-Hubbard Hamiltonian with on-site (U) and nearest-neighbor (V) repulsions. For d-dimensional hypercubic lattices, when 2dV2dV>U, in this Rapid Communication, we show that the ground state has only CDW insulators, and more importantly, the SS phase occupies a much larger region in the phase diagram, existing up to very large hopping values which could be orders of magnitude higher than that of the well-known case. In particular, the SS-superfluid phase boundary increases linearly as a function of hopping when 2dV > or approx. 1.5U, for which the prospects of observing the SS phase with dipolar Bose gases loaded into optical lattices is much higher.

  12. Universal quantum criticality in Hubbard models with massless Dirac dispersion

    NASA Astrophysics Data System (ADS)

    Otsuka, Yuichi; Yunoki, Seiji; Sorella, Sandro

    We investigate the metal-insulator transition of two-dimensional interacting electrons with massless Dirac-like dispersion, describe by the Hubbard models on two geometrically different lattices: honeycomb and π-flux square lattices. By performing large-scale quantum Monte Carlo simulations followed by careful finite-size scaling analyses, we find that the transition from semi-metallic to antiferromagnetic insulating phases is continuous and evaluate the critical exponents with a high degree of accuracy for the corresponding universality class, which is described in the continuous limit by the Gross-Neveu model. We furthermore discuss the fate of the quasiparticle weight and the Fermi velocity across this transition.

  13. Spectral analysis of two-dimensional Bose-Hubbard models

    NASA Astrophysics Data System (ADS)

    Fischer, David; Hoffmann, Darius; Wimberger, Sandro

    2016-04-01

    One-dimensional Bose-Hubbard models are well known to obey a transition from regular to quantum-chaotic spectral statistics. We are extending this concept to relatively simple two-dimensional many-body models. Also in two dimensions a transition from regular to chaotic spectral statistics is found and discussed. In particular, we analyze the dependence of the spectral properties on the bond number of the two-dimensional lattices and the applied boundary conditions. For maximal connectivity, the systems behave most regularly in agreement with the applicability of mean-field approaches in the limit of many nearest-neighbor couplings at each site.

  14. Matrix models of 2d gravity

    SciTech Connect

    Ginsparg, P.

    1991-01-01

    These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.

  15. Matrix models of 2d gravity

    SciTech Connect

    Ginsparg, P.

    1991-12-31

    These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.

  16. The Bosonic Kane-Mele Hubbard model

    NASA Astrophysics Data System (ADS)

    Nirwan, Rajbir; Vasic, Ivana; Petrescu, Alexandru; Le Hur, Karyn; Hofstetter, Walter

    We investigate the bosonic equivalent of the Kane-Mele model on the honeycomb lattice including spin-orbit and interaction effects. This model is a generalization of the interacting bosonic Haldane model introduced in Ref.. We also allow for an on-site conversion (coherent) term between the two species. We analyze the phase diagram using bosonic dynamical mean-field theory and analytical methods. In the Mott phase, a strong-coupling expansion is performed to investigate the magnetism and frustration effects. A connection is drawn with the quantum theory of an antiferromagnet on a triangular lattice in a magnetic field. This model can be realized in ultra-cold atom systems with current technology Replace MAR16-2015-003145.

  17. Superconductivity in the two-dimensional generalized Hubbard model

    NASA Astrophysics Data System (ADS)

    Lima, L. S.

    2016-08-01

    We have used the Green's functions method at finite temperature and the Kubo's formalism, to calculate the electron conductivity σ(ω) in the generalized two-dimensional Hubbard model. We have obtained a behavior superconductor for the system to T > T0. The AC conductivity falls to zero in ω =ω0 , where ω0 depends on Δ, which is the gap of the system. The behavior gotten is according of with the behavior of the superconductors of high Tc where there is a changes abruptly from a Mott's insulator state to superconductor.

  18. Theory of spin and charge fluctuations in the Hubbard model

    SciTech Connect

    Vilk, Y.M.; Chen, L.; Tremblay, A.S. )

    1994-05-01

    A self-consistent theory of both spin and charge fluctuations in the Hubbard model is presented. It is in quantitative agreement with Monte Carlo data at least up to intermediate coupling ([ital U][similar to]8[ital t]). It includes both short-wavelength quantum renormalization effects, and long-wavelength thermal fluctuations, which can destroy long-range order in two dimensions. The last effect leads to a small energy scale, as often observed in high-temperature superconductors. The theory is conserving, satisfies the Pauli principle, and includes three-particle correlations necessary to account for the incipient Mott transition.

  19. Analysis of the dynamical cluster approximation for the Hubbard model

    NASA Astrophysics Data System (ADS)

    Aryanpour, K.; Hettler, M. H.; Jarrell, M.

    2002-04-01

    We examine a central approximation of the recently introduced dynamical cluster approximation (DCA) by example of the Hubbard model. By both analytical and numerical means we study noncompact and compact contributions to the thermodynamic potential. We show that approximating noncompact diagrams by their cluster analogs results in a larger systematic error as compared to the compact diagrams. Consequently, only the compact contributions should be taken from the cluster, whereas noncompact graphs should be inferred from the appropriate Dyson equation. The distinction between noncompact and compact diagrams persists even in the limit of infinite dimensions. Nonlocal corrections beyond the DCA exist for the noncompact diagrams, whereas they vanish for compact diagrams.

  20. Anomalous properties of the Hubbard model in infinite dimensions

    NASA Astrophysics Data System (ADS)

    Jarrell, M.; Pruschke, Th.

    1994-01-01

    Anomalies are found in the resistivity ρ and NMR rate 1/T1 of the infinite-dimensional Hubbard model using quantum Monte Carlo calculations and the noncrossing approximation. For temperatures greater than the ``Kondo scale'' T0, we obtain 1/T1~a+bT and ρ~c+dT (a, b, c, d constants). For temperatures T<

  1. Hubbard Model Approach to X-ray Spectroscopy

    NASA Astrophysics Data System (ADS)

    Ahmed, Towfiq

    We have implemented a Hubbard model based first-principles approach for real-space calculations of x-ray spectroscopy, which allows one to study excited state electronic structure of correlated systems. Theoretical understanding of many electronic features in d and f electron systems remains beyond the scope of conventional density functional theory (DFT). In this work our main effort is to go beyond the local density approximation (LDA) by incorporating the Hubbard model within the real-space multiple-scattering Green's function (RSGF) formalism. Historically, the first theoretical description of correlated systems was published by Sir Neville Mott and others in 1937. They realized that the insulating gap and antiferromagnetism in the transition metal oxides are mainly caused by the strong on-site Coulomb interaction of the localized unfilled 3d orbitals. Even with the recent progress of first principles methods (e.g. DFT) and model Hamiltonian approaches (e.g., Hubbard-Anderson model), the electronic description of many of these systems remains a non-trivial combination of both. X-ray absorption near edge spectra (XANES) and x-ray emission spectra (XES) are very powerful spectroscopic probes for many electronic features near Fermi energy (EF), which are caused by the on-site Coulomb interaction of localized electrons. In this work we focus on three different cases of many-body effects due to the interaction of localized d electrons. Here, for the first time, we have applied the Hubbard model in the real-space multiple scattering (RSGF) formalism for the calculation of x-ray spectra of Mott insulators (e.g., NiO and MnO). Secondly, we have implemented in our RSGF approach a doping dependent self-energy that was constructed from a single-band Hubbard model for the over doped high-T c cuprate La2-xSrxCuO4. Finally our RSGF calculation of XANES is calculated with the spectral function from Lee and Hedin's charge transfer satellite model. For all these cases our

  2. Phase diagrams of the Bose-Hubbard model and the Haldane-Bose-Hubbard model with complex hopping amplitudes

    NASA Astrophysics Data System (ADS)

    Kuno, Yoshihito; Nakafuji, Takashi; Ichinose, Ikuo

    2015-12-01

    In this paper, we study Bose-Hubbard models on square and honeycomb lattices with complex hopping amplitudes, which are feasible by recent experiments of cold atomic gases in optical lattices. To clarify phase diagrams, we use extended quantum Monte Carlo simulations (eQMC). For the system on the square lattice, the complex hopping is realized by an artificial magnetic field. We found that vortex-solid states form for certain set of magnetic field, i.e., the magnetic field with the flux quanta per plaquette f =p /q , where p and q are co-prime natural numbers. For the system on the honeycomb lattice, we add the next-nearest-neighbor complex hopping. The model is a bosonic analog of the Haldane-Hubbard model. By means of eQMC, we study the model with both weak and strong onsite repulsions. Numerical study shows that the model has a rich phase diagram. We also found that in the system defined on the honeycomb lattice of the cylinder geometry, an interesting edge state appears.

  3. Dynamics of holes in the extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Sherman, A. V.

    1992-09-01

    The strong-correlation limit of the extended Hubbard model of plane cuprate perovskites is considered for two ratios of material parameters allowed by the uncertainty of their known values: the Cu-O electron promotion energy is of the order of the Cu-O hybridization at a negligibly small Hubbard repulsion on oxygen sites and the hybridization is much smaller than other energy parameters. By taking into account the antiferromagnetic ordering of lightly doped samples and using the spin-wave approximation, for these two cases effective Hamiltonians are obtained, in which charge and spin degrees of freedom are described by practically independent operators. On the basis of these Hamiltonians it is shown that the low-energy hole dynamics is essentially different in the two cases. In the latter case it can approximately be mapped on the one-band t-J model describing the movement of the Zhang-Rice singlet. However, essential deviations might arise if the oxygen and copper on-site repulsions were comparable. The Hamiltonian in the former case is intrinsically a two-band one which differs from the one-band Hamiltonian in shapes and widths of energy bands and in conditions of the formation of a ferromagnetically ordered region around a hole in the limit of large repulsions.

  4. Generalized slave-particle method for extended Hubbard models

    NASA Astrophysics Data System (ADS)

    Georgescu, Alexandru B.; Ismail-Beigi, Sohrab

    2015-12-01

    We introduce a set of generalized slave-particle models for extended Hubbard models that treat localized electronic correlations using slave-boson decompositions. Our models automatically include two slave-particle methods of recent interest, the slave-rotor and slave-spin methods, as well as a ladder of new intermediate models where one can choose which of the electronic degrees of freedom (e.g., spin or orbital labels) are treated as correlated degrees of freedom by the slave bosons. In addition, our method removes the aberrant behavior of the slave-rotor model, where it systematically overestimates the importance of electronic correlation effects for weak interaction strength, by removing the contribution of unphysical states from the bosonic Hilbert space. The flexibility of our formalism permits one to separate and isolate the effect of correlations on the key degrees of freedom.

  5. Extended hubbard model with ring exchange: a route to a non-Abelian topological phase.

    PubMed

    Freedman, Michael; Nayak, Chetan; Shtengel, Kirill

    2005-02-18

    We propose an extended Hubbard model on a 2D kagome lattice with an additional ring exchange term. The particles can be either bosons or spinless fermions. We analyze the model at the special filling fraction 1/6, where it is closely related to the quantum dimer model. We show how to arrive at an exactly soluble point whose ground state is the "d-isotopy" transition point into a stable phase with a certain type of non-Abelian topological order. Near the "special" values, d=2cos(pi/(k+2), this topological phase has anyonic excitations closely related to SU(2) Chern-Simons theory at level k. PMID:15783757

  6. Equation of state of the fermionic two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    LeBlanc, J. P. F.; Gull, Emanuel

    2013-10-01

    We present results for the equation of state of the two-dimensional Hubbard model on an isotropic square lattice as obtained from a controlled and numerically exact large-cluster dynamical mean field simulation. Our results are obtained for large but finite systems and are extrapolated to infinite system size using a known finite-size scaling relation, and are supplemented by reliable error bars accounting for all sources of errors. We establish the importance of examining the decay of spatial spin correlations to determine whether a sufficiently large cluster has been used and with this in mind we present the energy, entropy, double occupancy, and nearest-neighbor spin correlations extrapolated to the thermodynamic limit. We discuss the implications of these calculations on pseudogap physics of the 2D Hubbard model away from half filling, where we find a strong behavioral shift in energy below a temperature T* which becomes more pronounced for larger clusters. Finally, we provide reference calculations and tables for the equation of state for values of doping away from half filling which are of interest to cold-atom experiments.

  7. Dynamical instability in the S =1 Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Asaoka, Rui; Tsuchiura, Hiroki; Yamashita, Makoto; Toga, Yuta

    2016-01-01

    We study the dynamical instabilities of superfluid flows in the S =1 Bose-Hubbard model. The time evolution of each spin component in a condensate is calculated based on the dynamical Gutzwiller approximation for a wide range of interactions, from a weakly correlated regime to a strongly correlated regime near the Mott-insulator transition. Owing to the spin-dependent interactions, the superfluid flow of the spin-1 condensate decays at a different critical momentum from a spinless case when the interaction strength is the same. We furthermore calculate the dynamical phase diagram of this model and clarify that the obtained phase boundary has very different features depending on whether the average number of particles per site is even or odd. Finally, we analyze the density and spin modulations that appear in association with the dynamical instability. We find that spin modulations are highly sensitive to the presence of a uniform magnetic field.

  8. Gutzwiller study of extended Hubbard models with fixed boson densities

    SciTech Connect

    Kimura, Takashi

    2011-12-15

    We studied all possible ground states, including supersolid (SS) phases and phase separations of hard-core- and soft-core-extended Bose-Hubbard models with fixed boson densities by using the Gutzwiller variational wave function and the linear programming method. We found that the phase diagram of the soft-core model depends strongly on its transfer integral. Furthermore, for a large transfer integral, we showed that an SS phase can be the ground state even below or at half filling against the phase separation. We also found that the density difference between nearest-neighbor sites, which indicates the density order of the SS phase, depends strongly on the boson density and transfer integral.

  9. Phase Diagram of the Bose Hubbard Model with Weak Links

    NASA Astrophysics Data System (ADS)

    Hettiarachchilage, Kalani; Rousseau, Valy; Tam, Ka-Ming; Moreno, Juana; Jarrell, Mark; Sheehy, Daniel

    2012-02-01

    We study the ground state phase diagram of strongly interacting ultracold Bose gas in a one-dimensional optical lattice with a tunable weak link, by means of Quantum Monte Carlo simulation. This model contains an on-site repulsive interaction (U) and two different near-neighbor hopping terms, J and t, for the weak link and the remainder of the chain, respectively. We show that by reducing the strength of J, a novel intermediate phase develops which is compressible and non-superfluid. This novel phase is identified as a Normal Bose Liquid (NBL) which does not appear in the phase diagram of the homogeneous bosonic Hubbard model. Further, we find a linear variation of the phase boundary of Normal Bose Liquid (NBL) to SuperFluid (SF) as a function of the strength of the weak link. These results may provide a new path to design advanced atomtronic devices in the future.

  10. Bose-Hubbard model with occupation-parity couplings

    NASA Astrophysics Data System (ADS)

    Sun, Kuei; Bolech, C. J.

    2014-02-01

    We study a Bose-Hubbard model having on-site repulsion, nearest-neighbor tunneling, and ferromagneticlike coupling between occupation parities of nearest-neighbor sites. For a uniform system in any dimension at zero tunneling, we obtain an exact phase diagram characterized by Mott-insulator (MI) and pair liquid phases and regions of phase separation of two MIs. For a general trapped system in one and two dimensions with finite tunneling, we perform quantum Monte Carlo and Gutzwiller mean-field calculations, both of which show the evolution of the system, as the parity coupling increases, from a superfluid to wedding-cake-structure MIs with their occupations jumping by 2. We also identify an exotic pair superfluid at relatively large tunneling strength. Our model ought to effectively describe recent findings in imbalanced Fermi gases in two-dimensional optical lattices and also potentially apply to an anisotropic version of bilinear-biquadratic spin systems.

  11. Detection of Antiferromagnetic Correlations in the Fermi-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Hulet, Randall

    2014-05-01

    The Hubbard model, consisting of a cubic lattice with on-site interactions and kinetic energy arising from tunneling to nearest neighbors is a ``standard model'' of strongly correlated many-body physics, and it may also contain the essential ingredients of high-temperature superconductivity. While the Hamiltonian has only two terms it cannot be numerically solved for arbitrary density of spin-1/2 fermions due to exponential growth in the basis size. At a density of one spin-1/2 particle per site, however, the Hubbard model is known to exhibit antiferromagnetism at temperatures below the Néel temperature TN, a property shared by most of the undoped parent compounds of high-Tc superconductors. The realization of antiferromagnetism in a 3D optical lattice with atomic fermions has been impeded by the inability to attain sufficiently low temperatures. We have developed a method to perform evaporative cooling in a 3D cubic lattice by compensating the confinement envelope of the infrared optical lattice beams with blue-detuned laser beams. Evaporation can be controlled by the intensity of these non-retroreflected compensating beams. We observe significantly lower temperatures of a two-spin component gas of 6Li atoms in the lattice using this method. The cooling enables us to detect the development of short-range antiferromagnetic correlations using spin-sensitive Bragg scattering of light. Comparison with quantum Monte Carlo constrains the temperature in the lattice to 2-3 TN. We will discuss the prospects of attaining even lower temperatures with this method. Supported by DARPA/ARO, ONR, and NSF.

  12. EPR pairing dynamics in Hubbard model with resonant U

    PubMed Central

    Zhang, X. Z.; Song, Z.

    2016-01-01

    We study the dynamics of the collision between two fermions in Hubbard model with on-site interaction strength U. The exact solution shows that the scattering matrix for two-wavepacket collision is separable into two independent parts, operating on spatial and spin degrees of freedom, respectively. The S-matrix for spin configuration is equivalent to that of Heisenberg-type pulsed interaction with the strength depending on U and relative group velocity vr. This can be applied to create distant EPR pair, through a collision process for two fermions with opposite spins in the case of |vr/U| = 1, without the need for temporal control and measurement process. Multiple collision process for many particles is also discussed. PMID:26728282

  13. Phase diagram of the two-dimensional extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Onari, Seiichiro; Arita, Ryotaro; Aoki, Hideo; Kuroki, Kazuhiko

    2004-03-01

    In order to explore how superconductivity arises when charge fluctuations and spin fluctuations coexist, we have obtained a phase diagram against the off-site repulsion V and charge density n for the extended, repulsive Hubbard model on the square lattice with the fluctuation exchange approximation. We have found the existence of (i) a quantum phase transition between d_xy and d_x^2-y^2 pairing symmetries, (ii) f-pairing phase in between the d_x^2-y^2 and CDW phases for intermediate 0.5

  14. Anyon Hubbard Model in One-Dimensional Optical Lattices.

    PubMed

    Greschner, Sebastian; Santos, Luis

    2015-07-31

    Raman-assisted hopping may be used to realize the anyon Hubbard model in one-dimensional optical lattices. We propose a feasible scenario that significantly improves the proposal of T. Keilmann et al. [Nat. Commun. 2, 361 (2011)], allowing as well for an exact realization of the two-body hard-core constraint, and for controllable effective interactions without the need of Feshbach resonances. We show that the combination of anyonic statistics and two-body hard-core constraint leads to a rich ground-state physics, including Mott insulators with attractive interactions, pair superfluids, dimer phases, and multicritical points. Moreover, the anyonic statistics results in a novel two-component superfluid of holon and doublon dimers, characterized by a large but finite compressibility and a multipeaked momentum distribution, which may be easily revealed experimentally. PMID:26274417

  15. Phase transitions in the Hubbard model for the bismuth nickelate

    NASA Astrophysics Data System (ADS)

    Kojima, Shoya; Nasu, Joji; Koga, Akihisa

    2016-07-01

    We study low temperature properties of the Hubbard model for the bismuth nickelate, where degenerate orbitals in the nickel ions and a single orbital in the bismuth ions are taken into account, combining dynamical mean-field theory with the continuous-time quantum Monte Carlo method. We discuss the effect of the attractive interactions to mimic the valence skipping phenomenon in the bismuth ions. We demonstrate how the charge and magnetically ordered states are stable against thermal fluctuations. It is furthermore clarified that the ferromagnetically ordered and orbital ordered states are stabilized due to the presence of the orbital degeneracy at low temperatures. The crossover between metallic and insulating states is also discussed.

  16. Charge dynamics and spin order in doped Hubbard models

    SciTech Connect

    Kampf, A.P.; Brenig, W.

    1994-04-01

    Hole motion in an antiferromagnetic (AF) environment is accompanied by the emission of spin wave excitations. Spin-wave shakeoffs are responsible for incoherent contributions to the dynamics of propagating holes. Using a spin-density-wave polaron scheme the authors calculate the optical conductivity {sigma}({omega}) and show that the incoherent part of the hole spectrum contributes to the low-frequency part of {sigma}({omega}). Separately, the authors discuss the possible formation of spiral spin patterns upon doping of the half-filled one-band Hubbard model. In particular, the authors consider the influence of band structure effects arising from nearest- and next-nearest-neighbor hopping processes on a square lattice. Differences in the ground state spin patterns for hole and electron doping are obtained offering a possible explanation for the persistence of AF order in low electron-doped cuprate superconductors.

  17. One-dimensional Hubbard-Luttinger model for carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Ishkhanyan, H. A.; Krainov, V. P.

    2015-06-01

    A Hubbard-Luttinger model is developed for qualitative description of one-dimensional motion of interacting Pi-conductivity-electrons in carbon single-wall nanotubes at low temperatures. The low-lying excitations in one-dimensional electron gas are described in terms of interacting bosons. The Bogolyubov transformation allows one to describe the system as an ensemble of non-interacting quasi-bosons. Operators of Fermi excitations and Green functions of fermions are introduced. The electric current is derived as a function of potential difference on the contact between a nanotube and a normal metal. Deviations from Ohm law produced by electron-electron short-range repulsion as well as by the transverse quantization in single-wall nanotubes are discussed. The results are compared with experimental data.

  18. Exploring the Hubbard model: the interplay of geometry and interactions

    NASA Astrophysics Data System (ADS)

    Desbuquois, Rémi; Messer, Michael; Uehlinger, Thomas; Jotzu, Gregor; Görg, Frederik; Greif, Daniel; Huber, Sebastian; Esslinger, Tilman

    2016-05-01

    The nature of the ground state of many-body systems not only depends on the relative strength of kinetic and interaction energies, but also on the geometry imposed by the Hamiltonian. We show here two different experiments performed with ultracold fermions, where the geometry of the optical lattice strongly influences the many-body state. In the Ionic Hubbard model, a new energy scale associated with the breaking of the inversion symmetry of the lattice can be tuned to shift from a Mott insulating to a band insulating state. In the spin sector as well, the geometry of the lattice also plays an important role. Even above the transition temperature, the influence of the lattice geometry is revealed by nearest-neighbour (NN) magnetic correlations, and provides key insights on their formation.

  19. Three-band Hubbard model: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Dopf, G.; Muramatsu, A.; Hanke, W.

    1990-05-01

    We have studied a two-dimensional multiband Hubbard model describing CuO2 sheets in the high-Tc oxides. The simulations were performed for a grand-canonical ensemble on lattice sizes up to 16 unit cells of three atoms each and temperatures down to kBT~t/30, where t is the Cu-O hybridization. For generally accepted values of the Hubbard coupling on the Cu sites Ud>~6t, two different regimes can be distinguished in the magnetic properties of the model. In the half-filled band case we see for Δ>Ud/2 (Δ=ɛp-ɛd being the charge-transfer energy) the formation of a correlation gap, as expected for a charge-transfer insulator. For Δ~4/t, although no phase transition to a superconducting state could be seen.

  20. Conductivite dans le modele de Hubbard bi-dimensionnel a faible couplage

    NASA Astrophysics Data System (ADS)

    Bergeron, Dominic

    Le modele de Hubbard bi-dimensionnel (2D) est souvent considere comme le modele minimal pour les supraconducteurs a haute temperature critique a base d'oxyde de cuivre (SCHT). Sur un reseau carre, ce modele possede les phases qui sont communes a tous les SCHT, la phase antiferromagnetique, la phase supraconductrice et la phase dite du pseudogap. Il n'a pas de solution exacte, toutefois, plusieurs methodes approximatives permettent d'etudier ses proprietes de facon numerique. Les proprietes optiques et de transport sont bien connues dans les SCHT et sont donc de bonne candidates pour valider un modele theorique et aider a comprendre mieux la physique de ces materiaux. La presente these porte sur le calcul de ces proprietes pour le modele de Hubbard 2D a couplage faible ou intermediaire. La methode de calcul utilisee est l'approche auto-coherente a deux particules (ACDP), qui est non-perturbative et inclue l'effet des fluctuations de spin et de charge a toutes les longueurs d'onde. La derivation complete de l'expression de la conductivite dans l'approche ACDP est presentee. Cette expression contient ce qu'on appelle les corrections de vertex, qui tiennent compte des correlations entre quasi-particules. Pour rendre possible le calcul numerique de ces corrections, des algorithmes utilisant, entre autres, des transformees de Fourier rapides et des splines cubiques sont developpes. Les calculs sont faits pour le reseau carre avec sauts aux plus proches voisins autour du point critique antiferromagnetique. Aux dopages plus faibles que le point critique, la conductivite optique presente une bosse dans l'infrarouge moyen a basse temperature, tel qu'observe dans plusieurs SCHT. Dans la resistivite en fonction de la temperature, on trouve un comportement isolant dans le pseudogap lorsque les corrections de vertex sont negligees et metallique lorsqu'elles sont prises en compte. Pres du point critique, la resistivite est lineaire en T a basse temperature et devient

  1. Ising tricriticality in the extended Hubbard model with bond dimerization

    NASA Astrophysics Data System (ADS)

    Ejima, Satoshi; Essler, Fabian H. L.; Lange, Florian; Fehske, Holger

    2016-06-01

    We explore the quantum phase transition between Peierls and charge-density-wave insulating states in the one-dimensional, half-filled, extended Hubbard model with explicit bond dimerization. We show that the critical line of the continuous Ising transition terminates at a tricritical point, belonging to the universality class of the tricritical Ising model with central charge c =7 /10 . Above this point, the quantum phase transition becomes first order. Employing a numerical matrix-product-state based (infinite) density-matrix renormalization group method we determine the ground-state phase diagram, the spin and two-particle charge excitations gaps, and the entanglement properties of the model with high precision. Performing a bosonization analysis we can derive a field description of the transition region in terms of a triple sine-Gordon model. This allows us to derive field theory predictions for the power-law (exponential) decay of the density-density (spin-spin) and bond-order-wave correlation functions, which are found to be in excellent agreement with our numerical results.

  2. Electronic orders in multiorbital Hubbard models with lifted orbital degeneracy

    NASA Astrophysics Data System (ADS)

    Hoshino, Shintaro; Werner, Philipp

    2016-04-01

    We study the symmetry-broken phases in two- and three-orbital Hubbard models with lifted orbital degeneracy using dynamical mean-field theory. On the technical level, we explain how symmetry relations can be exploited to measure the four-point correlation functions needed for the calculation of the lattice susceptibilities. In the half-filled two-orbital model with crystal-field splitting, we find an instability of the metallic phase to spin-orbital order with neither spin nor orbital moment. This ordered phase is shown to be related to the recently discovered fluctuating-moment induced spin-triplet superconducting state in the orbitally degenerate model with shifted chemical potential. In the three-orbital case, we consider the effect of a crystal-field splitting on the spin-triplet superconducting state in the model with positive Hund coupling, and the spin-singlet superconducting state in the case of negative Hund coupling. It is demonstrated that for certain crystal-field splittings the higher energy orbitals instead of the lower ones are relevant for superconductivity, and that Tc can be slightly enhanced by the crystal-field effect. We comment on the implications of our results for the superconductivity in strontium ruthenates, and for the recently reported light-enhanced superconducting state in alkali-metal-doped fullerides.

  3. Phase diagram of the half-filled ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Bag, Soumen; Garg, Arti; Krishnamurthy, H. R.

    2015-06-01

    We study the phase diagram of the ionic Hubbard model (IHM) at half filling on a Bethe lattice of infinite connectivity using dynamical mean-field theory (DMFT), with two impurity solvers, namely, iterated perturbation theory (IPT) and continuous time quantum Monte Carlo (CTQMC). The physics of the IHM is governed by the competition between the staggered ionic potential Δ and the on-site Hubbard U . We find that for a finite Δ and at zero temperature, long-range antiferromagnetic (AFM) order sets in beyond a threshold U =UA F via a first-order phase transition. For U smaller than UA F the system is a correlated band insulator. Both methods show a clear evidence for a quantum transition to a half-metal (HM) phase just after the AFM order is turned on, followed by the formation of an AFM insulator on further increasing U . We show that the results obtained within both methods have good qualitative and quantitative consistency in the intermediate-to-strong-coupling regime at zero temperature as well as at finite temperature. On increasing the temperature, the AFM order is lost via a first-order phase transition at a transition temperature TA F(U ,Δ ) [or, equivalently, on decreasing U below UA F(T ,Δ ) ], within both methods, for weak to intermediate values of U /t . In the strongly correlated regime, where the effective low-energy Hamiltonian is the Heisenberg model, IPT is unable to capture the thermal (Neel) transition from the AFM phase to the paramagnetic phase, but the CTQMC does. At a finite temperature T , DMFT +CTQMC shows a second phase transition (not seen within DMFT +IPT ) on increasing U beyond UA F. At UN>UA F , when the Neel temperature TN for the effective Heisenberg model becomes lower than T , the AFM order is lost via a second-order transition. For U ≫Δ , TN˜t2/U (1 -x2) , where x =2 Δ /U and thus TN increases with increase in Δ /U . In the three-dimensional parameter space of (U /t ,T /t ,andΔ /t ) , as T increases, the surface of first

  4. Ground-State of the Bose-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Mancini, J. D.; Fessatidis, V.; Bowen, S. P.; Murawski, R. K.; Maly, J.

    The Bose-Hubbard Model represents a s simple theoretical model to describe the physics of interacting Boson systems. In particular it has proved to be an effective description of a number of physical systems such as arrays of Josephson arrays as well as dilute alkali gases in optical lattices. Here we wish to study the ground-state of this system using two disparate but related moments calculational schemes: the Lanczos (tridiagonal) method as well as a Generalized moments approach. The Hamiltonian to be studied is given by (in second-quantized notation): H = - t ∑ < i , j > bi†bj +U/2 ∑ inini - 1 - μ ∑ ini . Here i is summed over all lattice sites, and < i , j > denotes summation over all neighbhoring sites i and j, while bi† and bi are bosonic creation and annihilation operators. ni = bi†bi gives the number of particles on site i. Parameter t is the hopping amplitude, describing mobility of bosons in the lattice. Parameter U describes the on-site interaction, repulsive, if U > 0 , and attractive for U < 0 . μ is the chemical potential. Both the ground-state energy and energy gap are evaluated as a function of t, U and μ.

  5. Phase diagram of the disordered Bose-Hubbard model

    SciTech Connect

    Gurarie, V.; Pollet, L.; Prokof'ev, N. V.; Svistunov, B. V.; Troyer, M.

    2009-12-01

    We establish the phase diagram of the disordered three-dimensional Bose-Hubbard model at unity filling which has been controversial for many years. The theorem of inclusions, proven by Pollet et al. [Phys. Rev. Lett. 103, 140402 (2009)] states that the Bose-glass phase always intervenes between the Mott insulating and superfluid phases. Here, we note that assumptions on which the theorem is based exclude phase transitions between gapped (Mott insulator) and gapless phases (Bose glass). The apparent paradox is resolved through a unique mechanism: such transitions have to be of the Griffiths type when the vanishing of the gap at the critical point is due to a zero concentration of rare regions where extreme fluctuations of disorder mimic a regular gapless system. An exactly solvable random transverse field Ising model in one dimension is used to illustrate the point. A highly nontrivial overall shape of the phase diagram is revealed with the worm algorithm. The phase diagram features a long superfluid finger at strong disorder and on-site interaction. Moreover, bosonic superfluidity is extremely robust against disorder in a broad range of interaction parameters; it persists in random potentials nearly 50 ({exclamation_point}) times larger than the particle half-bandwidth. Finally, we comment on the feasibility of obtaining this phase diagram in cold-atom experiments, which work with trapped systems at finite temperature.

  6. One-dimensional extended Hubbard model in the atomic limit

    NASA Astrophysics Data System (ADS)

    Mancini, F.; Mancini, F. P.

    2008-06-01

    We present the exact solution of the one-dimensional extended Hubbard model in the atomic limit within the Green’s function and equations of motion formalism. We provide a comprehensive and systematic analysis of the model by considering all the relevant response and correlation functions as well as thermodynamic quantities in the whole parameters space. At zero temperature we identify four phases in the plane (U,n) ( U is the on-site potential and n is the filling) and relative phase transitions as well as different types of charge ordering. These features are endorsed by investigating at T=0 the chemical potential and pertinent local correlators, the particle and double occupancy correlation functions, the entropy, and by studying the behavior in the limit T→0 of the charge and spin susceptibilities. A detailed study of the thermodynamic quantities is also presented at finite temperature. This study evidences that a finite-range order persists for a wide range of the temperature, as shown by the behavior of the correlation functions and by the two-peak structure exhibited by the charge susceptibility and by the entropy. Moreover, the equations of motion formalism, together with the use of composite operators, allows us to exactly determine the set of elementary excitations. As a result, the density of states can be determined and a detailed analysis of the specific heat allows for identifying the excitations and for ascribing its two-peak structure to a redistribution of the charge density.

  7. From the Jaynes-Cummings-Hubbard to the Dicke model

    NASA Astrophysics Data System (ADS)

    Schmidt, S.; Blatter, G.; Keeling, J.

    2013-11-01

    We discuss the Jaynes-Cummings-Hubbard model describing the superfluid-Mott insulator transition of polaritons (i.e., dressed photon-qubit states) in coupled qubit-cavity arrays in the crossover from strong to weak correlations. In the strongly correlated regime the phase diagram and the elementary excitations of lattice polaritons near the Mott lobes are calculated analytically using a slave-boson theory (SBT). The opposite regime of weakly interacting polariton superfluids is described by a weak-coupling mean-field theory for a generalized multi-mode Dicke model. We show that a remarkable relation between the two theories exists in the limit of large photon bandwidth and large negative detuning, i.e., when the nature of polariton quasiparticles becomes qubit-like. In this regime, the weak-coupling theory predicts the existence of a single Mott lobe with a change of the universality class of the phase transition at the tip of the lobe, in perfect agreement with the SBT. Moreover, the spectra of low energy excitations, i.e., the sound velocity of the Goldstone mode and the gap of the amplitude mode match exactly as calculated from both theories.

  8. Diffusion dynamics in the disordered Bose Hubbard model

    NASA Astrophysics Data System (ADS)

    Wadleigh, Laura; Russ, Philip; Demarco, Brian

    2016-05-01

    We explore the dynamics of diffusion for out-of-equilibrium superfluid, Mott insulator, and Bose glass states using an atomic realization of the disordered Bose Hubbard (DBH) model. Dynamics in strongly correlated systems, especially far from equilibrium, are not well understood. The introduction of disorder further complicates these systems. We realize the DBH model--which has been central to our understanding of quantum phase transitions in disordered systems--using ultracold Rubidium-87 atoms trapped in a cubic disordered optical lattice. By tightly focusing a beam into the center of the gas, we create a hole in the atomic density profile. We achieve Mott insulator, superfluid, or Bose glass states by varying the interaction and disorder strength, and measure the time evolution of the density profile after removing the central barrier. This allows us to infer diffusion rates from the velocities at the edge of the hole and to look for signatures of superfluid puddles in the Bose glass state. We acknowledge funding from NSF Grant PHY 15-05468, NSF Grant DGE-1144245, and ARO Grant W911NF-12-1-0462.

  9. Attractive Hubbard model: Homogeneous Ginzburg-Landau expansion and disorder

    NASA Astrophysics Data System (ADS)

    Kuchinskii, E. Z.; Kuleeva, N. A.; Sadovskii, M. V.

    2016-02-01

    We derive a Ginzburg-Landau (GL) expansion in the disordered attractive Hubbard model within the combined Nozieres-Schmitt-Rink and DMFT+Σ approximation. Restricting ourselves to the homogeneous expansion, we analyze the disorder dependence of GL expansion coefficients for a wide range of attractive potentials U, from the weak BCS coupling region to the strong-coupling limit, where superconductivity is described by Bose-Einstein condensation (BEC) of preformed Cooper pairs. We show that for the a semielliptic "bare" density of states of the conduction band, the disorder influence on the GL coefficients A and B before quadratic and quartic terms of the order parameter, as well as on the specific heat discontinuity at the superconducting transition, is of a universal nature at any strength of the attractive interaction and is related only to the general widening of the conduction band by disorder. In general, disorder growth increases the values of the coefficients A and B, leading either to a suppression of the specific heat discontinuity (in the weak-coupling limit), or to its significant growth (in the strong-coupling region). However, this behavior actually confirms the validity of the generalized Anderson theorem, because the disorder dependence of the superconducting transition temperature T c, is also controlled only by disorder widening of the conduction band (density of states).

  10. Ground state of the three-band Hubbard model

    NASA Astrophysics Data System (ADS)

    Yanagisawa, Takashi; Koike, Soh; Yamaji, Kunihiko

    2001-11-01

    The ground state of the two-dimensional three-band Hubbard model in oxide superconductors is investigated by using the variational Monte Carlo method. The Gutzwiller-projected BCS and spin density wave (SDW) functions are employed in the search for a possible ground state with respect to dependences on electron density. Antiferromagnetic correlations are considerably strong near half-filling. It is shown that the d-wave state may exist away from half-filling for both the hole and electron doping cases. The overall structure of the phase diagram obtained by our calculations qualitatively agrees with experimental indications. The superconducting condensation energy is in reasonable agreement with the experimental value obtained from specific heat and critical magnetic field measurements for optimally doped samples. The inhomogeneous SDW state is also examined near 1/8 doping. Incommensurate magnetic structures become stable due to hole doping in the underdoped region, where the transfer tpp between oxygen orbitals plays an important role in determining a stable stripe structure.

  11. Pairing fluctuations and pseudogaps in the attractive Hubbard model

    SciTech Connect

    Kyung, B.; Allen, S.; Tremblay, A.-M. S.

    2001-08-15

    The two-dimensional attractive Hubbard model is studied in the weak-to-intermediate-coupling regime by employing a nonperturbative approach. It is shown that this approach is in quantitative agreement with Monte Carlo calculations for both single-particle and two-particle quantities. Both the density of states and the single-particle spectral weight show a pseudogap at the Fermi energy below some characteristic temperature T{sup *}, also in good agreement with quantum Monte Carlo calculations. The pseudogap is caused by critical pairing fluctuations in the low-temperature renormalized classical regime ({Dirac_h}{omega}

  12. Doping induced Mott transition in the two dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Sordi, Giovanni; Tremblay, A.-M. S.

    2010-03-01

    The description of the Mott transition by single-site dynamical mean-field theory is exact in infinite dimensions but, in two dimensions, substantial deviations from those results have been found for the interaction driven transition [1]. In addition, the experimentally relevant transition for layered systems such as the high-Tc cuprates is doping driven. We thus study this transition in the two dimensional Hubbard model on the square lattice using cluster dynamical mean-field theory with continuous-time quantum Monte Carlo in the hybridization expansion [2]. We find that the Mott transition is strongly influenced by the inclusion of short-range antiferromagnetic correlations. Doping of the Mott insulating state occurs gradually in the different momentum sectors, as found in previous studies [3], but in addition we find a first order transition between an incoherent metal and an insulator or between two incoherent metals, depending on interaction strength. Short range spin correlations create a pseudogap in a doping range that increases with interaction. [1] H. Park et al., PRL 101, 186403 (2008) [2] K. Haule, PRB 75, 155113 (2007) [3] E. Gull et al., arXiv:0909.1795 (2009)

  13. High-temperature transport in the Hubbard Model

    NASA Astrophysics Data System (ADS)

    Shastry, B. Sriram; Perepelitsky, Edward; Galatas, Andrew; Khatami, Ehsan; Mravlje, Jernej; Georges, Antoine

    We examine the general behavior of the frequency and momentum dependent single-particle scattering rate and the transport coefficients, of many-body systems in the high-temperature limit. We find that the single-particle scattering rate always saturates in temperature, while the transport coefficients always decay like 1/T, where T is the temperature. A consequence of this is a resistivity which is ubiquitously linear in T at high temperatures. For the Hubbard model, by using the high-temperature series, we are able to calculate the first few moments of the single particle scattering rate Σ (k --> , ω) and the conductivity σ (k --> , ω) in the high-temperature regime in d spatial dimensions. Further in the case of d --> ∞ , we are able to calculate a large number of moments using symbolic computation. We make a direct comparison between these moments and those obtained through Dynamical Mean Field Theory (DMFT). Finally, we use the moments to reconstruct the ω-dependent optical conductivity σ (ω) =limk-->0 σ (k --> , ω) in the high-temperature regime. The work at UCSC was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award # FG02-06ER46319.

  14. Strong coupling diagram technique for the three-band Hubbard model

    NASA Astrophysics Data System (ADS)

    Sherman, A.

    2016-03-01

    Strong coupling diagram technique equations are derived for hole Green’s functions of the three-band Hubbard model, which describes Cu-O planes of high-Tc cuprates. The equations are self-consistently solved in the approximation, in which the series for the irreducible part in powers of the oxygen-copper hopping constant is truncated to two lowest-order terms. For parameters used for hole-doped cuprates, the calculated energy spectrum consists of lower and upper Hubbard subbands of predominantly copper nature, oxygen bands with a small admixture of copper states and the Zhang-Rice states of mixed nature, which are located between the lower Hubbard subband and oxygen bands. The spectrum contains also pseudogaps near transition frequencies of Hubbard atoms on copper sites.

  15. Attractive Hubbard model with disorder and the generalized Anderson theorem

    SciTech Connect

    Kuchinskii, E. Z. Kuleeva, N. A. Sadovskii, M. V.

    2015-06-15

    Using the generalized DMFT+Σ approach, we study the influence of disorder on single-particle properties of the normal phase and the superconducting transition temperature in the attractive Hubbard model. A wide range of attractive potentials U is studied, from the weak coupling region, where both the instability of the normal phase and superconductivity are well described by the BCS model, to the strong-coupling region, where the superconducting transition is due to Bose-Einstein condensation (BEC) of compact Cooper pairs, formed at temperatures much higher than the superconducting transition temperature. We study two typical models of the conduction band with semi-elliptic and flat densities of states, respectively appropriate for three-dimensional and two-dimensional systems. For the semi-elliptic density of states, the disorder influence on all single-particle properties (e.g., density of states) is universal for an arbitrary strength of electronic correlations and disorder and is due to only the general disorder widening of the conduction band. In the case of a flat density of states, universality is absent in the general case, but still the disorder influence is mainly due to band widening, and the universal behavior is restored for large enough disorder. Using the combination of DMFT+Σ and Nozieres-Schmitt-Rink approximations, we study the disorder influence on the superconducting transition temperature T{sub c} for a range of characteristic values of U and disorder, including the BCS-BEC crossover region and the limit of strong-coupling. Disorder can either suppress T{sub c} (in the weak-coupling region) or significantly increase T{sub c} (in the strong-coupling region). However, in all cases, the generalized Anderson theorem is valid and all changes of the superconducting critical temperature are essentially due to only the general disorder widening of the conduction band.

  16. Quantum simulation of the Hubbard model with dopant atoms in silicon

    PubMed Central

    Salfi, J.; Mol, J. A.; Rahman, R.; Klimeck, G.; Simmons, M. Y.; Hollenberg, L. C. L.; Rogge, S.

    2016-01-01

    In quantum simulation, many-body phenomena are probed in controllable quantum systems. Recently, simulation of Bose–Hubbard Hamiltonians using cold atoms revealed previously hidden local correlations. However, fermionic many-body Hubbard phenomena such as unconventional superconductivity and spin liquids are more difficult to simulate using cold atoms. To date the required single-site measurements and cooling remain problematic, while only ensemble measurements have been achieved. Here we simulate a two-site Hubbard Hamiltonian at low effective temperatures with single-site resolution using subsurface dopants in silicon. We measure quasi-particle tunnelling maps of spin-resolved states with atomic resolution, finding interference processes from which the entanglement entropy and Hubbard interactions are quantified. Entanglement, determined by spin and orbital degrees of freedom, increases with increasing valence bond length. We find separation-tunable Hubbard interaction strengths that are suitable for simulating strongly correlated phenomena in larger arrays of dopants, establishing dopants as a platform for quantum simulation of the Hubbard model. PMID:27094205

  17. Quantum simulation of the Hubbard model with dopant atoms in silicon

    NASA Astrophysics Data System (ADS)

    Salfi, J.; Mol, J. A.; Rahman, R.; Klimeck, G.; Simmons, M. Y.; Hollenberg, L. C. L.; Rogge, S.

    2016-04-01

    In quantum simulation, many-body phenomena are probed in controllable quantum systems. Recently, simulation of Bose-Hubbard Hamiltonians using cold atoms revealed previously hidden local correlations. However, fermionic many-body Hubbard phenomena such as unconventional superconductivity and spin liquids are more difficult to simulate using cold atoms. To date the required single-site measurements and cooling remain problematic, while only ensemble measurements have been achieved. Here we simulate a two-site Hubbard Hamiltonian at low effective temperatures with single-site resolution using subsurface dopants in silicon. We measure quasi-particle tunnelling maps of spin-resolved states with atomic resolution, finding interference processes from which the entanglement entropy and Hubbard interactions are quantified. Entanglement, determined by spin and orbital degrees of freedom, increases with increasing valence bond length. We find separation-tunable Hubbard interaction strengths that are suitable for simulating strongly correlated phenomena in larger arrays of dopants, establishing dopants as a platform for quantum simulation of the Hubbard model.

  18. Quantum simulation of the Hubbard model with dopant atoms in silicon.

    PubMed

    Salfi, J; Mol, J A; Rahman, R; Klimeck, G; Simmons, M Y; Hollenberg, L C L; Rogge, S

    2016-01-01

    In quantum simulation, many-body phenomena are probed in controllable quantum systems. Recently, simulation of Bose-Hubbard Hamiltonians using cold atoms revealed previously hidden local correlations. However, fermionic many-body Hubbard phenomena such as unconventional superconductivity and spin liquids are more difficult to simulate using cold atoms. To date the required single-site measurements and cooling remain problematic, while only ensemble measurements have been achieved. Here we simulate a two-site Hubbard Hamiltonian at low effective temperatures with single-site resolution using subsurface dopants in silicon. We measure quasi-particle tunnelling maps of spin-resolved states with atomic resolution, finding interference processes from which the entanglement entropy and Hubbard interactions are quantified. Entanglement, determined by spin and orbital degrees of freedom, increases with increasing valence bond length. We find separation-tunable Hubbard interaction strengths that are suitable for simulating strongly correlated phenomena in larger arrays of dopants, establishing dopants as a platform for quantum simulation of the Hubbard model. PMID:27094205

  19. Modelling one-dimensional insulating materials with the ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Refolio, M. C.; Lòpez Sancho, J. M.; Rubio, J.

    2005-10-01

    The single-particle spectral-weight function of the ionic Hubbard model (IHM) at half-filling shows an abrupt change of regime at a critical value of the coupling constant (Hubbard U). Specifically, this function jumps at the Fermi points kF = ± π/2 from a two-peak to a four-peak structure accompanied by a (non-vanishing) minimum of the single-particle charge gap. This jump separates a weak-coupling regime, the band insulating phase, from a strong-coupling regime which evolves gradually into the Mott Hubbard phase. We take advantage of this critical behaviour to model several quasi-one-dimensional materials in terms of the IHM instead of the simpler one-band Hubbard model. For instance, the two regimes are physically realized in the angle-resolved photoelectron spectra of (TaSe4)2I, and the blue-bronze K0.3MoO3, respectively.

  20. Functional renormalization group study of charge and spin orders of the extended Hubbard model in frustrated lattices

    NASA Astrophysics Data System (ADS)

    Takashima, Hirokazu; Ishihara, Sumio

    2010-03-01

    In order to study for novel spin and charge orders in strongly correlated electron systems in frustrated lattices,we investigated extended Hubbard model in 2 dimensional (2D) checkerboard and triangular lattices using the functional renormalization group method(fRG) with an improved algorithm [1]. In this method, both the quantum effect and the geometrical frustration effect at finite temperature are taken into account properly. Non-monotonic temperature dependence of the spin susceptibility was observed both in the models . In a 2D isotropic triangular lattice at half-filling, divergence of the particle-particle channel vertex functions was observed in a region of the intermediate value of the on-site Coulomb interaction. We have also investigated the extended Hubbard model with long-range Coulomb interactions. A possibility of the ferromagnetic order and calculations with including the self-energy correction will be introduced .[1] H. Takashima, R. Arita, K. Kuroki, and H. Aoki, J. Phys.: Conf. Ser, 150, 052261 (2009)

  1. Pseudofermion dynamical theory for the spin dynamical correlation functions of the half-filled 1D Hubbard model

    NASA Astrophysics Data System (ADS)

    Carmelo, J. M. P.; Čadež, T.

    2016-03-01

    A modified version of the metallic-phase pseudofermion dynamical theory (PDT) of the 1D Hubbard model is introduced for the spin dynamical correlation functions of the half-filled 1D Hubbard model Mott-Hubbard phase. The Mott-Hubbard insulator phase PDT is applied to the study of the model longitudinal and transverse spin dynamical structure factors at finite magnetic field h, focusing in particular on the singularities at excitation energies in the vicinity of the lower thresholds. The relation of our theoretical results to both condensed-matter and ultra-cold atom systems is discussed.

  2. Electron-phonon driven spin frustration in multi-band Hubbard models: MX chains and oxide superconductors

    SciTech Connect

    Gammel, J.T.; Yonemitsu, K.; Saxena, A.; Bishop, A.R.; Roeder, H.

    1992-12-01

    We discuss the consequences of both electron-phonon and electron-electron couplings in 1D and 2D multi-band (Peierls-Hubbard) models are discussed. After a brief discussion of various analytic limits, we focused on (Hartree-Fock and exact) numerical studies in the intermediate regime for both couplings, where unusual spin-Peierls as well as long-period, frustrated ground states are found. Doping into such phases or near the phase boundaries can lead to further interesting phenomena such as separation of spin and charge, a dopant-induced phase transition of the global (parent) phase, or real-space (``bipolaronic``) pairing. Possible experimentally observable consequences of this rich phase diagram for halogen-bridged, transition metal, linear chain complexes (MX chains) in 1D and the oxide superconductors in 2D are discussed.

  3. Mechanism of hole attraction in the extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Sherman, A. V.

    1993-05-01

    The expansion in the Cu-O hybridization energy, t, usually used for the simplification of the extended Hubbard Hamiltonian, is shown to meet with difficulties for the known parameters of CuO2 planes of cuprate perovskites. An expansion in a power series in λt, λ~=0.1, is suggested, which is applicable for these values of parameters and in which the Hubbard repulsion and the Cu-O hybridization are considered on an equal footing. A Hamiltonian obtained with the help of the expansion for the lower part of the energy spectrum, is equivalent to the t-J Hamiltonian and the corresponding states are some generalizations of the Zhang-Rice singlets. The Hamiltonian contains terms describing a static attraction between holes and for reasonable sets of parameters the attraction is approximately equal to a half of the superexchange constant.

  4. Observation of a Superradiant Mott Insulator in the Dicke-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Klinder, J.; Keßler, H.; Bakhtiari, M. Reza; Thorwart, M.; Hemmerich, A.

    2015-12-01

    It is well known that the bosonic Hubbard model possesses a Mott insulator phase. Likewise, it is known that the Dicke model exhibits a self-organized superradiant phase. By implementing an optical lattice inside of a high-finesse optical cavity, both models are merged such that an extended Hubbard model with cavity-mediated infinite range interactions arises. In addition to a normal superfluid phase, two superradiant phases are found, one of them coherent and hence superfluid and one incoherent Mott insulating.

  5. Interaction effect in the Kondo energy of the periodic Anderson-Hubbard model

    NASA Astrophysics Data System (ADS)

    Itai, K.; Fazekas, P.

    1996-07-01

    We extend the periodic Anderson model by switching on a Hubbard U for the conduction band. The nearly integral valent limit of the Anderson-Hubbard model is studied with the Gutzwiller variational method. The lattice Kondo energy shows U dependence both in the prefactor and the exponent. Switching on U reduces the Kondo scale, which can be understood to result from the blocking of hybridization. At half filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator. Our findings should be relevant for a number of correlated two-band models of recent interest.

  6. Density-dependent tunneling in the extended Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Maik, Michał; Hauke, Philipp; Dutta, Omjyoti; Lewenstein, Maciej; Zakrzewski, Jakub

    2013-11-01

    Recently, it has become apparent that when the interactions between polar molecules in optical lattices become strong, the conventional description using the extended Hubbard model has to be modified by additional terms, in particular a density-dependent tunneling term. We investigate here the influence of this term on the ground-state phase diagrams of the two-dimensional extended Bose-Hubbard model. Using quantum Monte Carlo simulations, we investigate the changes of the superfluid, supersolid and phase-separated parameter regions in the phase diagram of the system. By studying the interplay of the density-dependent hopping with the usual on-site interaction U and nearest-neighbor repulsion V , we show that the ground-state phase diagrams differ significantly from those expected from the standard extended Bose-Hubbard model.

  7. Neutron and ARPES constraints on the couplings of the multiorbital Hubbard model for the iron pnictides

    SciTech Connect

    Luo, Qinlong; Martins, G. B.; Daghofer, M.; Yu, Rong; Yildirim, Yucel; Moreo, Adriana; Dagotto, Elbio R

    2010-01-01

    The results of neutron-scattering and angle-resolved photoemission experiments for the Fe-pnictide parent compounds, and their metallic nature, are shown to impose severe constraints on the range of values that can be considered realistic for the intraorbital Hubbard repulsion U and Hund coupling J in multiorbital Hubbard models treated in the mean-field approximation. Phase diagrams for three- and five-orbital models are here provided, and the physically realistic regime of couplings is highlighted, to guide future theoretical work into the proper region of parameters of Hubbard models. In addition, using the random phase approximation, the pairing tendencies in these realistic coupling regions are investigated. It is shown that the dominant spin-singlet pairing channels in these coupling regimes correspond to nodal superconductivity, with strong competition between several states that belong to different irreducible representations. This is compatible with experimental bulk measurements that have reported the existence of nodes in several Fe-pnictide compounds.

  8. Metallic Ferromagnetism Supported by a Single Band in a Multi-band Hubbard Model

    NASA Astrophysics Data System (ADS)

    Tanaka, Akinori; Tasaki, Hal

    2016-06-01

    We construct a multi-band Hubbard model on the lattice obtained by "decorating" a closely packed d-dimensional lattice {M} (such as the triangular lattice) where d≥ 2. We take the limits in which the Coulomb interaction and the band gap become infinitely large. Then there remains only a single band with finite energy, on which electrons are supported. Let the electron number be N_{e}=|{M}|-N_{h}, where |{M}| corresponds to the electron number which makes the lowest (finite energy) band half-filled, and N_{h} is the number of "holes". It is expected that the model exhibits metallic ferromagnetism if N_{h}/|{M}| is nonvanishing but sufficiently small. We prove that the ground states exhibit saturated ferromagnetism if N_{h}≤ ( {const.})|{M}|^{2/(d+2)}, and exhibit (not necessarily saturated) ferromagnetism if N_{h}≤ ( {const.})|{M}|^{(d+1)/(d+2)}. This may be regarded as a rigorous example of metallic ferromagnetism provided that the system size |{M}| is not too large.

  9. Communication: Generalization of Koopmans’ theorem to optical transitions in the Hubbard model of graphene nanodots

    SciTech Connect

    Sheng, Weidong; Luo, Kaikai; Zhou, Aiping

    2015-01-14

    Koopmans’ theorem implies that the Hartree-Fock quasiparticle gap in a closed-shell system is equal to its single-particle energy gap. In this work, the theorem is generalized to optical transitions in the Hubbard model of graphene nanodots. Based on systematic configuration interaction calculations, it is proposed that the optical gap of a closed-shell graphene system within the Hubbard model is equal to its tight-binding single-particle energy gap in the absence of electron correlation. In these systems, the quasiparticle energy gap and exciton binding energy are found to be dominated by the long-range Coulomb interaction, and thus, both become small when only on-site Hubbard interactions are present. Moreover, the contributions of the quasiparticle and excitonic effects to the optical gap are revealed to nearly cancel each other, which results in an unexpected overlap of the optical and single-particle gaps of the graphene systems.

  10. Superconductivity and Gutzwiller correlations in a two band Hubbard-Fröhlich model

    NASA Astrophysics Data System (ADS)

    Qin, Tao; Fabrizio, Michele; Naghavi, S. Shahab; Tosatti, Erio; Condensed Matter Physics Team

    2014-03-01

    We studied the two-band Hubbard-Fröhlich model with the hopping parameters from the first-principle calculation for La-Phenanthrene. The mean-field approximation shows that two-band superconductivity with opposite signs is possible even with the presence of a large Hubbard U. Using Gutzwiller approximation, we show that the Hubbard U can help the superconductivity in this system. When U is too large, it will go into the insulator state. Roughly, we determined the critical U for this superconductor-insulator (SI) transition. We further shows that before the SI transition, the antiferromagnetic order will come into being. However, there is still a large range of U for the superconductivity to win. We also discussed the possibility to apply our model to other polycyclic aromatic hydrocarbons. Sponsored by EU LEMSUPER Grant 283214.

  11. Quench Dynamics and Nonequilibrium Phase Diagram of the Bose-Hubbard Model

    SciTech Connect

    Kollath, Corinna; Laeuchli, Andreas M.; Altman, Ehud

    2007-05-04

    We investigate the time evolution of correlations in the Bose-Hubbard model following a quench from the superfluid to the Mott insulator. For large values of the final interaction strength the system approaches a distinctly nonequilibrium steady state that bears strong memory of the initial conditions. In contrast, when the final interaction strength is comparable to the hopping, the correlations are rather well approximated by those at thermal equilibrium. The existence of two distinct nonequilibrium regimes is surprising given the nonintegrability of the Bose-Hubbard model. We relate this phenomenon to the role of quasiparticle interactions in the Mott insulator.

  12. WFR-2D: an analytical model for PWAS-generated 2D ultrasonic guided wave propagation

    NASA Astrophysics Data System (ADS)

    Shen, Yanfeng; Giurgiutiu, Victor

    2014-03-01

    This paper presents WaveFormRevealer 2-D (WFR-2D), an analytical predictive tool for the simulation of 2-D ultrasonic guided wave propagation and interaction with damage. The design of structural health monitoring (SHM) systems and self-aware smart structures requires the exploration of a wide range of parameters to achieve best detection and quantification of certain types of damage. Such need for parameter exploration on sensor dimension, location, guided wave characteristics (mode type, frequency, wavelength, etc.) can be best satisfied with analytical models which are fast and efficient. The analytical model was constructed based on the exact 2-D Lamb wave solution using Bessel and Hankel functions. Damage effects were inserted in the model by considering the damage as a secondary wave source with complex-valued directivity scattering coefficients containing both amplitude and phase information from wave-damage interaction. The analytical procedure was coded with MATLAB, and a predictive simulation tool called WaveFormRevealer 2-D was developed. The wave-damage interaction coefficients (WDICs) were extracted from harmonic analysis of local finite element model (FEM) with artificial non-reflective boundaries (NRB). The WFR-2D analytical simulation results were compared and verified with full scale multiphysics finite element models and experiments with scanning laser vibrometer. First, Lamb wave propagation in a pristine aluminum plate was simulated with WFR-2D, compared with finite element results, and verified by experiments. Then, an inhomogeneity was machined into the plate to represent damage. Analytical modeling was carried out, and verified by finite element simulation and experiments. This paper finishes with conclusions and suggestions for future work.

  13. Superconductor-insulator phase transition in the boson Hubbard model

    SciTech Connect

    Kampf, A.P. ); Zimanyi, G.T. Department of Physics, University of California, Davis, California 95616 )

    1993-01-01

    We investigate the superconductor-insulator phase transition in the two-dimensional boson Hubbard system with short-range interactions. Fluctuations of [ital both] the phase and the amplitude of the superfluid order parameter are included in the determination of the phase diagram at zero and finite temperatures. The mean-field phase boundary is compared to quantum Monte Carlo results. We also calculate the frequency-dependent conductivity in the vicinity of the phase transition and find it universal at the multicritical point.

  14. Coherent quench dynamics in the one-dimensional Fermi-Hubbard model

    NASA Astrophysics Data System (ADS)

    Iyer, Deepak; Mondaini, Rubem; Will, Sebastian; Rigol, Marcos

    2014-09-01

    Recently, it has been shown that the momentum distribution of a metallic state of fermionic atoms in a lattice Fermi-Bose mixture exhibits coherent oscillations after a global quench that suppresses tunneling. The oscillation period is determined by the Fermi-Bose interaction strength. Here we show that similar coherent dynamics, but with a different functional form, occurs in the fermionic Hubbard model when we quench a noninteracting metallic state by introducing a Hubbard interaction and suppressing tunneling. The period is determined primarily by the interaction strength. Conversely, we show that one can accurately determine the Hubbard interaction strength from the oscillation period, taking into account corrections from any small residual tunneling present in the final Hamiltonian. Such residual tunneling shortens the period and damps the oscillations, the latter being visible in the Fermi-Bose experiment.

  15. Numerical studies of ground-state fidelity of the Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    ŁÄ cki, Mateusz; Damski, Bogdan; Zakrzewski, Jakub

    2014-03-01

    We compute ground-state fidelity of the one-dimensional Bose-Hubbard model at unit filling factor. To this aim, we apply the density matrix renormalization group algorithm to systems with open and periodic boundary conditions. We find that fidelity differs significantly in the two cases and study its scaling properties in the quantum critical regime.

  16. Lifetime of double occupancies in the Fermi-Hubbard model

    SciTech Connect

    Sensarma, Rajdeep; Pekker, David; Demler, Eugene; Altman, Ehud; Strohmaier, Niels; Moritz, Henning; Greif, Daniel; Joerdens, Robert; Tarruell, Leticia; Esslinger, Tilman

    2010-12-01

    We investigate the decay of artificially created double occupancies in a repulsive Fermi-Hubbard system in the strongly interacting limit using diagrammatic many-body theory and experiments with ultracold fermions in optical lattices. The lifetime of the doublons is found to scale exponentially with the ratio of the on-site repulsion to the bandwidth. We show that the dominant decay process in presence of background holes is the excitation of a large number of particle-hole pairs to absorb the energy of the doublon. We also show that the strongly interacting nature of the background state is crucial in obtaining the correct estimate of the doublon lifetime in these systems. The theoretical estimates and the experimental data are in agreement.

  17. Universal quantum computation by scattering in the Fermi-Hubbard model

    NASA Astrophysics Data System (ADS)

    Bao, Ning; Hayden, Patrick; Salton, Grant; Thomas, Nathaniel

    2015-09-01

    The Hubbard model may be the simplest model of particles interacting on a lattice, but simulation of its dynamics remains beyond the reach of current numerical methods. In this article, we show that general quantum computations can be encoded into the physics of wave packets propagating through a planar graph, with scattering interactions governed by the fermionic Hubbard model. Therefore, simulating the model on planar graphs is as hard as simulating quantum computation. We give two different arguments, demonstrating that the simulation is difficult both for wave packets prepared as excitations of the fermionic vacuum, and for hole wave packets at filling fraction one-half in the limit of strong coupling. In the latter case, which is described by the t-J model, there is only reflection and no transmission in the scattering events, as would be the case for classical hard spheres. In that sense, the construction provides a quantum mechanical analog of the Fredkin-Toffoli billiard ball computer.

  18. Ground state and excitations of the supersymmetric extended Hubbard model with long-range interaction

    SciTech Connect

    Wang, D.F.; Liu, J.T.

    1996-07-01

    We examine the ground state and excitations of the one-dimensional supersymmetric extended Hubbard model with long-range interaction. The ground state wave-function and low lying excitations are given explicitly in the form of a Jastrow product of two-body terms. This result motivates an asymptotic Bethe ansatz solution for the model. We present evidence that this solution is in fact exact and spans the complete spectrum of states. {copyright} {ital 1996 The American Physical Society.}

  19. Emulating the 1-Dimensional Fermi-Hubbard Model with Superconducting Qubits

    NASA Astrophysics Data System (ADS)

    Reiner, Jan-Michael; Marthaler, Michael; Schön, Gerd

    A chain of qubits with both ZZ and XX couplings is described by a Hamiltonian which coincides with the Fermi-Hubbard model in one dimension. The qubit system can thus be used to study the quantum properties of this model. We investigate the specific implementation of such an analog quantum simulator by a chain of tunable Transmon qubits, where the ZZ interaction arises due to an inductive coupling and the XX interaction due to a capacitive coupling.

  20. Measurement of the Equation of State of the Two-Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Miller, Luke; Cocchi, Eugenio; Drewes, Jan; Koschorreck, Marco; Pertot, Daniel; Brennecke, Ferdinand; Koehl, Michael

    2016-05-01

    The subtle interplay between kinetic energy, interactions and dimensionality challenges our comprehension of strongly-correlated physics observed, for example, in the solid state. In this quest, the Hubbard model has emerged as a conceptually simple, yet rich model describing such physics. Here we present an experimental determination of the equation of state of the repulsive two-dimensional Hubbard model over a broad range of interactions, 0 <= U / t <= 20 , and temperatures, down to kB T / t = 0 . 63(2) using high-resolution imaging of ultracold fermionic atoms in optical lattices. We show density profiles, compressibilities and double occupancies over the whole doping range, and hence our results constitute benchmarks for state-of-the-art theoretical approaches.

  1. Exact Solution of Two-Site Bose-Hubbard Model with Generic Open Boundaries

    NASA Astrophysics Data System (ADS)

    Xin, Zhi-Rong; Yang, Tao; Hao, Kun; Yang, Wen-Li

    2015-12-01

    The Bose-Hubbard model is a paradigm for the study of strongly correlated bosonic systems. We study the two-site Bose-Hubbard model with generic integrable open boundaries specified by the most general non-diagonal reflecting matrices. Besides the inhomogeneous parameters, the model itself has three free boundary parameters, which break the U(1)-symmetry, in other words, break the particle number conservation. The Hamiltonian H under these circumstances is constructed. With the help of the off-diagonal Bethe Ansatz method, we successfully obtain the corresponding Bethe Ansatz equations as well as the eigenvalues. Supported by the National Natural Science Foundation of China under Grant Nos. 11375141, 11425522, 11434013, 11347025, 11447239, and Beijing Center for Mathematics and Information Interdisciplinary Sciences are gratefully acknowledged.

  2. Homogenization models for 2-D grid structures

    NASA Technical Reports Server (NTRS)

    Banks, H. T.; Cioranescu, D.; Rebnord, D. A.

    1992-01-01

    In the past several years, we have pursued efforts related to the development of accurate models for the dynamics of flexible structures made of composite materials. Rather than viewing periodicity and sparseness as obstacles to be overcome, we exploit them to our advantage. We consider a variational problem on a domain that has large, periodically distributed holes. Using homogenization techniques we show that the solution to this problem is in some topology 'close' to the solution of a similar problem that holds on a much simpler domain. We study the behavior of the solution of the variational problem as the holes increase in number, but decrease in size in such a way that the total amount of material remains constant. The result is an equation that is in general more complex, but with a domain that is simply connected rather than perforated. We study the limit of the solution as the amount of material goes to zero. This second limit will, in most cases, retrieve much of the simplicity that was lost in the first limit without sacrificing the simplicity of the domain. Finally, we show that these results can be applied to the case of a vibrating Love-Kirchhoff plate with Kelvin-Voigt damping. We rely heavily on earlier results of (Du), (CS) for the static, undamped Love-Kirchhoff equation. Our efforts here result in a modification of those results to include both time dependence and Kelvin-Voigt damping.

  3. 2D model of the Nucleus

    NASA Astrophysics Data System (ADS)

    Lach, Theodore M.

    2003-10-01

    The CBM (model) of the nucleus has resulted in the prediction of two new quarks, an "up" quark of mass 237.31 MeV/c2 and a "dn" quark of mass 42.392 MeV/c2. These two new predicted quarks helped to determine that the masses of the quarks and leptons are all related by a geometric progression relationship. The mass of each quark or lepton is just the "geometric mean" of two related elementary particles, either in the same generation or in the same family. This numerology predicts the following masses for the electron family: 0.511000 (electron), 7.74 (predicted), 117.3, 1778.4 (tau), 26950.1 MeV. The geometric ratio of this progression is 15.154 (e to the power e). The mass of the tau in this theory agrees very well with accepted values. This theory suggests that all the "dn like" quarks have a mass of just 10X multiples of 4.24 MeV (the mass of the "d" quark). The first 3 "up like" quark masses are 38, 237.31 and 1500 MeV. This theory also predicts a new heavy generation with a lepton mass of 27 GeV, a "dn like" quark of 42.4 GeV, and an "up like" quark of 65 GeV. Significant evidence already exists for the existence of these new quarks, and lepton. Ref. Masses of the Sub-Nuclear Particles, nucl-th/ 0008026, @ http://xxx.lanl.gov. Infinite Energy, Vol 5, issue 30.

  4. Competition between disorder and Coulomb interaction in a two-dimensional plaquette Hubbard model

    NASA Astrophysics Data System (ADS)

    Lee, Hunpyo; Jeschke, Harald O.; Valentí, Roser

    2016-06-01

    We have studied a disordered Nc×Nc plaquette Hubbard model on a two-dimensional square lattice at half-filling using a coherent potential approximation (CPA) in combination with a single-site dynamical mean field theory (DMFT) approach with a paramagnetic bath. Such a model conveniently interpolates between the ionic Hubbard model at Nc=√{2 } and the Anderson model at Nc=∞ and enables the analysis of the various limiting properties. We confirmed that within the CPA approach a band insulator behavior appears for noninteracting strongly disordered systems with a small plaquette size Nc=4 , while the paramagnetic Anderson insulator with nearly gapless density of states is present for large plaquette sizes Nc=48 . When the interaction U is turned on in the strongly fluctuating random potential regions, the electrons on the low energy states push each other into high energy states in DMFT in a paramagnetic bath and correlated metallic states with a quasiparticle peak and Hubbard bands emerge, though a larger critical interaction U is needed to obtain this state from the paramagnetic Anderson insulator (Nc=48 ) than from the band insulator (Nc=4 ). Finally, we observe a Mott insulator behavior in the strong interaction U regions for both Nc=4 and Nc=48 independent of the disorder strength. We discuss the application of this model to real materials.

  5. The energy spectrum and the optical absorption spectrum of C{sub 60} fullerene within the Hubbard model

    SciTech Connect

    Silant’ev, A. V.

    2015-10-15

    Anticommutator Green’s functions and the energy spectrum of C{sub 60} fullerene are calculated in the approximation of static fluctuations within the Hubbard model. On the basis of this spectrum, an interpretation is proposed for the experimentally observed optical absorption bands of C{sub 60} fullerene. The parameters of C{sub 60} fullerene that characterize it within the Hubbard model are calculated by the optical absorption spectrum.

  6. Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model

    SciTech Connect

    Carmelo, J.M.P.; Gu, Shi-Jian; Sacramento, P.D.

    2013-12-15

    Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to Mott–Hubbard-insulator transition.) The interplay of the η-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: •The charge stiffness of the half-filled 1D Hubbard model is evaluated. •Its value is controlled by the model symmetry operator algebras. •We find that there is no charge ballistic transport at finite temperatures T>0. •The hidden U(1) symmetry controls the U=0 phase transition for T>0.

  7. Observation of antiferromagnetic correlations in the Hubbard model with ultracold atoms.

    PubMed

    Hart, Russell A; Duarte, Pedro M; Yang, Tsung-Lin; Liu, Xinxing; Paiva, Thereza; Khatami, Ehsan; Scalettar, Richard T; Trivedi, Nandini; Huse, David A; Hulet, Randall G

    2015-03-12

    Ultracold atoms in optical lattices have great potential to contribute to a better understanding of some of the most important issues in many-body physics, such as high-temperature superconductivity. The Hubbard model--a simplified representation of fermions moving on a periodic lattice--is thought to describe the essential details of copper oxide superconductivity. This model describes many of the features shared by the copper oxides, including an interaction-driven Mott insulating state and an antiferromagnetic (AFM) state. Optical lattices filled with a two-spin-component Fermi gas of ultracold atoms can faithfully realize the Hubbard model with readily tunable parameters, and thus provide a platform for the systematic exploration of its phase diagram. Realization of strongly correlated phases, however, has been hindered by the need to cool the atoms to temperatures as low as the magnetic exchange energy, and also by the lack of reliable thermometry. Here we demonstrate spin-sensitive Bragg scattering of light to measure AFM spin correlations in a realization of the three-dimensional Hubbard model at temperatures down to 1.4 times that of the AFM phase transition. This temperature regime is beyond the range of validity of a simple high-temperature series expansion, which brings our experiment close to the limit of the capabilities of current numerical techniques, particularly at metallic densities. We reach these low temperatures using a compensated optical lattice technique, in which the confinement of each lattice beam is compensated by a blue-detuned laser beam. The temperature of the atoms in the lattice is deduced by comparing the light scattering to determinant quantum Monte Carlo simulations and numerical linked-cluster expansion calculations. Further refinement of the compensated lattice may produce even lower temperatures which, along with light scattering thermometry, would open avenues for producing and characterizing other novel quantum states of

  8. Density matrix renormalization group study of the Anyon-Hubbard model

    NASA Astrophysics Data System (ADS)

    Arcila-Forero, J.; Franco, R.; Silva-Valencia, J.

    2016-02-01

    Recently optical lattices allow us to observe phase transition without the uncertainty posed by complex materials, and the simulations of these systems are an excellent bridge between materials-based condensed matter physics and cold atoms. In this way, the computational physics related to many-body problems have increased in importance. Using the density matrix renormalization group method, we studied a Hubbard model for anyons, which is an equivalent to a variant of the Bose-Hubbard model in which the bosonic hopping depends on the local density. This is an exact mapping between anyons and bosons in one dimension. The anyons interlope between bosons and fermions. For two anyons under particle exchange, the wave function acquires a fractional phase eiθ . We conclude that this system exhibits two phases: Mott-insulator and superfluid. We present the phase diagram for some angles. The Mott lobe increases with an increase of the statistical. We observed a reentrance phase transition for all lobes. We showed that the model studied is in the same universality class as the Bose-Hubbard model with two-body interactions.

  9. Two-polariton bound states in the Jaynes-Cummings-Hubbard model

    SciTech Connect

    Wong, Max T. C.; Law, C. K.

    2011-05-15

    We examine the eigenstates of the one-dimensional Jaynes-Cummings-Hubbard model in the two-excitation subspace. We discover that two-excitation bound states emerge when the ratio of vacuum Rabi frequency to the tunneling rate between cavities exceeds a critical value. We determine the critical value as a function of the quasimomentum quantum number, and indicate that the bound states carry a strong correlation in which the two polaritons appear to be spatially confined together.

  10. Exact solution of the one-dimensional Hubbard model with arbitrary boundary magnetic fields

    NASA Astrophysics Data System (ADS)

    Li, Yuan-Yuan; Cao, Junpeng; Yang, Wen-Li; Shi, Kangjie; Wang, Yupeng

    2014-02-01

    The one-dimensional Hubbard model with arbitrary boundary magnetic fields is solved exactly via the Bethe ansatz methods. With the coordinate Bethe ansatz in the charge sector, the second eigenvalue problem associated with the spin sector is constructed. It is shown that the second eigenvalue problem can be transformed into that of the inhomogeneous XXX spin chain with arbitrary boundary fields which can be solved via the off-diagonal Bethe ansatz method.

  11. Coexistence of Incommensurate Magnetism and Superconductivity in the Two-Dimensional Hubbard Model.

    PubMed

    Yamase, Hiroyuki; Eberlein, Andreas; Metzner, Walter

    2016-03-01

    We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Néel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order. PMID:26991188

  12. Density matrix embedding theory studies of the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Zheng, Bo-Xiao

    Density matrix embedding theory (DMET) provides a quantum embedding framework to compute the electronic structure in strongly correlated lattice systems. It has been applied to various model Hamiltonians and ab initio systems. In this talk, I will review the results obtained in the two-dimensional one-band Hubbard model using DMET. Over the last years, we mapped a calibrated ground-state phase diagram of the two-dimensional Hubbard model, concerning magnetic, superconducting and various inhomogeneous phases. Based on the results from this work, as well as the consistent data from other numerical methods, we are able to conclude that many parts of the Hubbard phase diagram is already settled up to an accurate energy scale of 0.001t. Recently, by using large-scale auxiliary-field quantum Monte Carlo (AFQMC) in the impurity problem, we are able to treat much larger embedded clusters at half-filling (and with the constrained path approximation at non-half-filling), which provides a deeper understanding on the finite-size effects of energy and observables in both quantum embedding and finite cluster numerical methods. Finally, we systematically investigated the putative inhomogeneous phases in the underdoped, strong coupling Hubbard model, proposing new inhomogeneous patterns as strong candidates for the ground state. Reference: [1] Bo-Xiao Zheng, Garnet K.-L. Chan, arXiv:1504.01784 [2] J.P.F. Leblanc, Andrey E. Antipov, et al., arXiv:1505.02290 We acknowledge funding from the US Department of Energy, Office of Science, through DE-SC0008624 and DE-SC0010530. This work was also performed as part of the Simons Collaboration on the Many Electron Problem, sponsored by the Simons Foundation.

  13. Monte Carlo calculation of dynamical properties of the two-dimensional Hubbard model

    NASA Technical Reports Server (NTRS)

    White, S. R.; Scalapino, D. J.; Sugar, R. L.; Bickers, N. E.

    1989-01-01

    A new method is introduced for analytically continuing imaginary-time data from quantum Monte Carlo calculations to the real-frequency axis. The method is based on a least-squares-fitting procedure with constraints of positivity and smoothness on the real-frequency quantities. Results are shown for the single-particle spectral-weight function and density of states for the half-filled, two-dimensional Hubbard model.

  14. Critical behavior near the Mott transition in the half-filled asymmetric Hubbard model

    NASA Astrophysics Data System (ADS)

    Hoang, Anh-Tuan; Le, Duc-Anh

    2016-03-01

    We study the half-filled asymmetric Hubbard model within the two-site dynamical mean field theory. At zero temperature, explicit expressions of the critical interaction Uc for the Mott transition and the local self-energy are analytically derived. Critical behavior of the quasiparticle weights and the double occupancy are obtained analytically as functions of the on-site interaction U and the hopping asymmetry r. Our results are in good agreement with the ones obtained by much more sophisticated theory.

  15. Experimental realization of the ionic Hubbard model on a honeycomb lattice with ultracold fermions

    NASA Astrophysics Data System (ADS)

    Desbuquois, Rémi; Messer, Michael; Uehlinger, Thomas; Jotzu, Gregor; Görg, Frederik; Greif, Daniel; Huber, Sebastian; Esslinger, Tilman

    2016-05-01

    Ultracold atoms in optical lattices constitute a tool of choice to realize the Fermi-Hubbard model. There, the on-site interaction energy opens a gap in the charge excitation spectrum, leading to a Mott insulating ground state. However, in the ionic Hubbard model, the addition of a staggered energy offset on each lattice site also leads to an insulating ground state with charge-density-wave ordering, even in the absence of inter-particle interactions. In our experiment we realize the Ionic Hubbard model on a honeycomb lattice by loading a two-component interacting Fermi gas into an optical lattice with a staggered energy offset on alternating sites. The underlying density order of the ground state is revealed through the correlations in the noise of the measured momentum distribution. For a large energy offset, we observe a charge density-wave ordering, which is suppressed as the on-site interactions are increased. To further elucidate the nature of the ground state, we measure the double occupancy of lattice sites and the charge excitation spectrum for a wide range of parameters.

  16. Mean field study of the topological Haldane-Hubbard model of spin-1/2 fermions

    NASA Astrophysics Data System (ADS)

    Arun, V. S.; Sohal, R.; Hickey, C.; Paramekanti, A.

    2016-03-01

    Motivated by exploring the effect of interactions on Chern insulators, and by recent experiments realizing topological bands for ultracold atoms in synthetic gauge fields, we study the honeycomb lattice Haldane-Hubbard model of spin-1/2 fermions. Using an unrestricted mean field approach, we map out the instability of the topological band insulator towards magnetically ordered insulators which emerge with increasing Hubbard repulsion. In addition to the topological Néel phase, we recover various chiral noncoplanar magnetic orders previously identified within a strong-coupling approach. We compute the band structure of these ordered phases, showing that the triple-Q tetrahedral phase harbors topological Chern bands with large Chern numbers.

  17. Compressibility of the Two-Dimensional Infinite-U Hubbard Model

    SciTech Connect

    Tandon, A.; Wang, Z.; Tandon, A.; Kotliar, G.

    1999-09-01

    We study the interactions between the coherent quasiparticles and the incoherent Mott-Hubbard excitations and their effects on the low-energy properties in the U={infinity} Hubbard model. Within the framework of a systematic large-N expansion, these effects first occur in the next-to-leading order in 1/N . We calculate the scattering phase shift and the free energy, and determine the quasiparticle weight Z , mass renormalization, and the compressibility. It is found that the compressibility is strongly renormalized and diverges at a critical doping {delta}{sub c}=0.07{plus_minus}0.01 . We discuss the nature of this zero-temperature phase transition and its connection to phase separation and superconductivity. {copyright} {ital 1999} {ital The American Physical Society}

  18. Pseudospin S = 1 formalism and skyrmion-like excitations in the three-body constrained extended Bose–Hubbard model

    SciTech Connect

    Moskvin, A. S.

    2015-09-15

    We discuss the most prominent and intensively studied S = 1 pseudospin formalism for the extended bosonic Hubbard model (EBHM) with the on-site Hilbert space truncated to the three lowest occupation states n = 0, 1, 2. The EBHM Hamiltonian is a paradigmatic model for the highly topical field of ultracold gases in optical lattices. The generalized non-Heisenberg effective pseudospin Hamiltonian does provide a deep link with a boson system and a physically clear description of “the myriad of phases,” from uniform Mott insulating phases and density waves to two types of superfluids and supersolids. We argue that the 2D pseudospin system is prone to a topological phase separation and focus on several types of unconventional skyrmion-like topological structures in 2D boson systems, which have not been analyzed until now. The structures are characterized by a complicated interplay of insulating and two superfluid phases with a single- boson and two-boson condensation, respectively.

  19. Technical Review of the UNET2D Hydraulic Model

    SciTech Connect

    Perkins, William A.; Richmond, Marshall C.

    2009-05-18

    The Kansas City District of the US Army Corps of Engineers is engaged in a broad range of river management projects that require knowledge of spatially-varied hydraulic conditions such as velocities and water surface elevations. This information is needed to design new structures, improve existing operations, and assess aquatic habitat. Two-dimensional (2D) depth-averaged numerical hydraulic models are a common tool that can be used to provide velocity and depth information. Kansas City District is currently using a specific 2D model, UNET2D, that has been developed to meet the needs of their river engineering applications. This report documents a tech- nical review of UNET2D.

  20. Local moment approach as a quantum impurity solver for the Hubbard model

    NASA Astrophysics Data System (ADS)

    Barman, Himadri

    2016-07-01

    The local moment approach (LMA) has presented itself as a powerful semianalytical quantum impurity solver (QIS) in the context of the dynamical mean-field theory (DMFT) for the periodic Anderson model and it correctly captures the low-energy Kondo scale for the single impurity model, having excellent agreement with the Bethe ansatz and numerical renormalization group (NRG) results. However, the most common correlated lattice model, the Hubbard model, has not been explored well within the LMA+DMFT framework beyond the insulating phase. Here in our work, within the framework we complete the filling-interaction phase diagram of the single band Hubbard model at zero temperature. Our formalism is generic to any particle filling and can be extended to finite temperature. We contrast our results with another QIS, namely the iterated perturbation theory (IPT) and show that the second spectral moment sum rule improves better as the Hubbard interaction strength grows stronger in LMA, whereas it severely breaks down after the Mott transition in IPT. For the metallic case, the Fermi liquid (FL) scaling agreement with the NRG spectral density supports the fact that the FL scale emerges from the inherent Kondo physics of the impurity model. We also show that, in the metallic phase, the FL scaling of the spectral density leads to universality which extends to infinite frequency range at infinite correlation strength (strong coupling). At large interaction strength, the off half-filling spectral density forms a pseudogap near the Fermi level and filling-controlled Mott transition occurs as one approaches the half-filling. As a response property, we finally study the zero temperature optical conductivity and find universal features such as absorption peak position governed by the FL scale and a doping independent crossing point, often dubbed the isosbestic point in experiments.

  1. An Intercomparison of 2-D Models Within a Common Framework

    NASA Technical Reports Server (NTRS)

    Weisenstein, Debra K.; Ko, Malcolm K. W.; Scott, Courtney J.; Jackman, Charles H.; Fleming, Eric L.; Considine, David B.; Kinnison, Douglas E.; Connell, Peter S.; Rotman, Douglas A.; Bhartia, P. K. (Technical Monitor)

    2002-01-01

    A model intercomparison among the Atmospheric and Environmental Research (AER) 2-D model, the Goddard Space Flight Center (GSFC) 2-D model, and the Lawrence Livermore National Laboratory 2-D model allows us to separate differences due to model transport from those due to the model's chemical formulation. This is accomplished by constructing two hybrid models incorporating the transport parameters of the GSFC and LLNL models within the AER model framework. By comparing the results from the native models (AER and e.g. GSFC) with those from the hybrid model (e.g. AER chemistry with GSFC transport), differences due to chemistry and transport can be identified. For the analysis, we examined an inert tracer whose emission pattern is based on emission from a High Speed Civil Transport (HSCT) fleet; distributions of trace species in the 2015 atmosphere; and the response of stratospheric ozone to an HSCT fleet. Differences in NO(y) in the upper stratosphere are found between models with identical transport, implying different model representations of atmospheric chemical processes. The response of O3 concentration to HSCT aircraft emissions differs in the models from both transport-dominated differences in the HSCT-induced perturbations of H2O and NO(y) as well as from differences in the model represent at ions of O3 chemical processes. The model formulations of cold polar processes are found to be the most significant factor in creating large differences in the calculated ozone perturbations

  2. Topological Phase Transitions in the Repulsively Interacting Haldane-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Vanhala, Tuomas I.; Siro, Topi; Liang, Long; Troyer, Matthias; Harju, Ari; Törmä, Päivi

    2016-06-01

    Using dynamical mean-field theory and exact diagonalization we study the phase diagram of the repulsive Haldane-Hubbard model, varying the interaction strength and the sublattice potential difference. In addition to the quantum Hall phase with Chern number C =2 and the band insulator with C =0 present already in the noninteracting model, the system also exhibits a C =0 Mott insulating phase, and a C =1 quantum Hall phase. We explain the latter phase by a spontaneous symmetry breaking where one of the spin components is in the Hall state and the other in the band insulating state.

  3. Observation of Antiferromagnetic Correlations in the Hubbard Model with Ultracold Atoms

    NASA Astrophysics Data System (ADS)

    Hulet, Randall

    2015-03-01

    Ultracold atoms on optical lattices form a versatile platform for studying many-body physics, with the potential of addressing some of the most important issues in strongly correlated matter. Progress, however, has been stymied by an inability to create sufficiently low temperatures in an optical lattice. In this talk, I will present our experimental results on the characterization of the three-dimensional Hubbard model near half-filling, realized using two spin-states of fermionic atomic lithium (6Li). We have developed a compensated optical lattice that has enabled, for the first time, the achievement of temperatures that are below the tunneling energy, t. We use in-situ imaging to extract the central density of the gas, and to determine its local compressibility. For intermediate to strong interactions, we observe the emergence of a density plateau and a reduction of the compressibility, indicative of the formation of a Mott insulator. Comparisons to state-of-the-art numerical simulations of the Hubbard model over a wide range of interactions set an upper limit for the temperature T < t. The Hubbard model is known to exhibit antiferromagnetism at temperatures below the Néel temperature TN. We have detected antiferromagnetic correlations in this system by spin-sensitive Bragg scattering of light. We deduce the temperature of the atoms in the lattice by comparing the light scattering to determinantal quantum Monte Carlo and numerical linked-cluster expansion calculations to find that T / t = 0 . 51 +/- 0 . 06 , corresponding to 1 . 4TN. Further refinement of the compensated lattice may produce even lower temperatures which, along with light scattering thermometry, have important implications for achieving other novel quantum states of matter. Supported by DARPA/ARO, ONR, NSF.

  4. Bosonization study of quantum phase transitions in the one-dimensional asymmetric Hubbard model

    SciTech Connect

    Wang, Z. G.; Chen, Y. G.; Gu, S. J.

    2007-04-15

    The quantum phase transitions in the one-dimensional asymmetric Hubbard model are investigated with the bosonization approach. The conditions for the phase transition from density wave to phase separation, the correlation functions, and their exponents are obtained analytically. Our results show that the difference between the hopping integrals for up- and down-spin electrons is crucial for the occurrence of the phase separation. When the difference is large enough, the phase separation will appear even if the on-site interaction is small.

  5. Response to dynamical modulation of the optical lattice for fermions in the Hubbard model

    SciTech Connect

    Xu Zhaoxin; Yang Shuxiang; Sheehy, Daniel E.; Moreno, Juana; Jarrell, Mark; Chiesa, Simone; Su Shiquan; Scalettar, Richard T.

    2011-08-15

    Fermionic atoms in a periodic optical lattice provide a realization of the single-band Hubbard model. Using quantum Monte Carlo simulations along with the maximum-entropy method, we evaluate the effect of a time-dependent perturbative modulation of the optical lattice amplitude on atomic correlations, revealed in the fraction of doubly occupied sites. We find that the effect of modulation depends strongly on the filling--the response of the double occupation is significantly different in the half-filled Mott insulator from that in the doped Fermi liquid region.

  6. Generic incommensurate transition in the two-dimensional boson Hubbard model

    NASA Astrophysics Data System (ADS)

    Alet, Fabien; Sørensen, Erik S.

    2004-07-01

    The generic transition in the boson Hubbard model, occurring at an incommensurate chemical potential, is studied in the link-current representation using the recently developed directed geometrical worm algorithm. We find clear evidence for a multipeak structure in the energy distribution for finite lattices, usually indicative of a first-order phase transition. However, this multipeak structure is shown to disappear in the thermodynamic limit, revealing that the true phase transition is second order. These findings cast doubts over the conclusion drawn in a number of previous works considering the relevance of disorder at this transition.

  7. Orbital selective directional conductor in the two-orbital Hubbard model

    SciTech Connect

    Mukherjee, Anamitra; Patel, Niravkumar D.; Moreo, Adriana; Dagotto, Elbio R

    2016-01-01

    Employing a recently developed many-body technique that allows for the incorporation of thermal effects, the rich phase diagram of a two-dimensional two-orbital (degenerate dxz and dyz) Hubbard model is presented varying temperature and the repulsion U. Our main result is the finding at intermediate U of an antiferromagnetic orbital selective state where an effective dimensional reduction renders one direction insulating and the other metallic. Possible realizations of this state are discussed. In addition, we also study nematicity above the N eel temperature. After a careful finite-size scaling analysis, the nematicity temperature window appears to survive in the bulk limit, although it is very narrow.

  8. Quench field sensitivity of two-particle correlation in a Hubbard model

    NASA Astrophysics Data System (ADS)

    Zhang, X. Z.; Lin, S.; Song, Z.

    2016-06-01

    Short-range interaction can give rise to particle pairing with a short-range correlation, which may be destroyed in the presence of an external field. We study the transition between correlated and uncorrelated particle states in the framework of one- dimensional Hubbard model driven by a field. We show that the long time-scale transfer rate from an initial correlated state to final uncorrelated particle states is sensitive to the quench field strength and exhibits a periodic behavior. This process involves an irreversible energy transfer from the field to particles, leading to a quantum electrothermal effect.

  9. Dimerized ground state in the one-dimensional spin-1 boson Hubbard model

    SciTech Connect

    Apaja, Vesa; Syljuaasen, Olav F.

    2006-09-15

    We have investigated the one-dimensional spin-1 boson Hubbard model with antiferromagnetic interactions using quantum Monte Carlo methods. We obtain the shapes of the two lowest Mott lobes and show that the ground state within the lowest Mott lobe is dimerized. The results presented here are relevant for optically trapped antiferromagnetic spin-1 bosons. An experimental signature of the dimerized ground state is modulated Bragg peaks in the noise distribution of the atomic cloud obtained after switching off the trap. These Bragg peaks are located at wave vectors corresponding to half-integer multiples of the reciprocal wave vector of the optical lattice.

  10. Spectral Function of the One-Dimensional Hubbard Model away from Half Filling

    NASA Astrophysics Data System (ADS)

    Benthien, H.; Gebhard, F.; Jeckelmann, E.

    2004-06-01

    We calculate the photoemission spectral function of the one-dimensional Hubbard model away from half filling using the dynamical density-matrix renormalization group method. An approach for calculating momentum-dependent quantities in finite open chains is presented. Comparison with exact Bethe ansatz results demonstrates the unprecedented accuracy of our method. Our results show that the photoemission spectrum of the quasi-one-dimensional conductor TTF-TCNQ provides evidence for spin-charge separation on the scale of the conduction bandwidth.

  11. Spectral function of the one-dimensional Hubbard model away from half filling.

    PubMed

    Benthien, H; Gebhard, F; Jeckelmann, E

    2004-06-25

    We calculate the photoemission spectral function of the one-dimensional Hubbard model away from half filling using the dynamical density-matrix renormalization group method. An approach for calculating momentum-dependent quantities in finite open chains is presented. Comparison with exact Bethe ansatz results demonstrates the unprecedented accuracy of our method. Our results show that the photoemission spectrum of the quasi-one-dimensional conductor TTF-TCNQ provides evidence for spin-charge separation on the scale of the conduction bandwidth. PMID:15245039

  12. Metal-Insulator Transition in the Hubbard Model: Correlations and Spiral Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Timirgazin, Marat A.; Igoshev, Petr A.; Arzhnikov, Anatoly K.; Irkhin, Valentin Yu.

    2016-03-01

    The metal-insulator transition (MIT) for the square, simple cubic, and body-centered cubic lattices is investigated within the t-t^' Hubbard model at half-filling by using both the generalized for the case of spiral order Hartree-Fock approximation (HFA) and Kotliar-Ruckenstein slave-boson approach. It turns out that the magnetic scenario of MIT becomes superior over the non-magnetic one. The electron correlations lead to some suppression of the spiral phases in comparison with HFA. We found the presence of a metallic antiferromagnetic (spiral) phase in the case of three-dimensional lattices.

  13. Quench field sensitivity of two-particle correlation in a Hubbard model

    PubMed Central

    Zhang, X. Z.; Lin, S.; Song, Z.

    2016-01-01

    Short-range interaction can give rise to particle pairing with a short-range correlation, which may be destroyed in the presence of an external field. We study the transition between correlated and uncorrelated particle states in the framework of one- dimensional Hubbard model driven by a field. We show that the long time-scale transfer rate from an initial correlated state to final uncorrelated particle states is sensitive to the quench field strength and exhibits a periodic behavior. This process involves an irreversible energy transfer from the field to particles, leading to a quantum electrothermal effect. PMID:27250080

  14. The thermoelectric power and the Lorenz number for the infinite U Hubbard model using orthofermion approach

    NASA Astrophysics Data System (ADS)

    Mishra, A. K.; Kishore, R.

    2016-08-01

    We have obtained the exact expressions for the thermoelectric power and the Lorenz number for the infinite U Hubbard model using orthofermion approach. It is found that in one dimension, our results coincide with that of known exact results. In limiting cases, our exact expressions reduce to the known exact results at low and high temperature limits. We present our calculations for one and two dimensions for square as well as triangular lattices. A comparison between the thermoelectric power and Lorenz number for a free Fermi gas and noninteracting orthofermions has also been provided.

  15. Spin-dependent Hubbard model and a quantum phase transition in cold atoms

    SciTech Connect

    Liu, W. Vincent; Wilczek, Frank; Zoller, Peter

    2004-09-01

    We describe an experimental protocol for introducing spin-dependent lattice structure in a cold atomic Fermi gas using lasers. It can be used to realize Hubbard models whose hopping parameters depend on spin and whose interaction strength can be controlled with an external magnetic field. We suggest that exotic superfluidities will arise in this framework. An especially interesting possibility is a class of states that support coexisting superfluid and normal components, even at zero temperature. The quantity of normal component varies with external parameters. We discuss some aspects of the quantum phase transition that arises at the point where it vanishes.

  16. Mechanisms of finite-temperature magnetism in the three-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Hirschmeier, Daniel; Hafermann, Hartmut; Gull, Emanuel; Lichtenstein, Alexander I.; Antipov, Andrey E.

    We examine the nature of the transition to the antiferromagnetically ordered state in the half-filled three-dimensional Hubbard model using the dual-fermion multiscale approach. Consistent with analytics, in the weak-coupling regime we find that spin-flip excitations across the Fermi surface are important, and that the strong coupling regime is described by Heisenberg physics. In the intermediate interaction, strong correlation regime we find aspects of both local and non-local correlations. We analyze the critical exponents of the transition in the strong coupling regime and find them to be consistent with Heisenberg physics down to an interaction of U/t=10.

  17. A discrete ``three-particle'' Schrödinger operator in the Hubbard model

    NASA Astrophysics Data System (ADS)

    Eshkabilov, Yu. Kh.

    2006-11-01

    In the space L 2(T ν ×T ν ), where T ν is a ν-dimensional torus, we study the spectral properties of the “three-particle” discrete Schrödinger operator Ĥ = H0 + H1 + H2, where H0 is the operator of multiplication by a function and H1 and H2 are partial integral operators. We prove several theorems concerning the essential spectrum of Ĥ. We study the discrete and essential spectra of the Hamiltonians Ht and h arising in the Hubbard model on the three-dimensional lattice.

  18. Population imbalance in the extended Fermi-Hubbard model

    NASA Astrophysics Data System (ADS)

    Dhar, A.; Kinnunen, J. J.; Törmä, P.

    2016-08-01

    We study the interplay between population imbalance in a two-component fermionic system and nearest-neighbor interaction using the matrix product states method. Our analysis reveals a parameter regime for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov phase. Furthermore, we find distinct evidence for the presence of hidden order in the system. We present an effective model to understand the emergent oscillations in the string correlations due to the imbalance and show how they can become an efficient tool to investigate systems with imbalance.

  19. Extended Bose Hubbard model of interacting bosonic atoms in optical lattices: From superfluidity to density waves

    SciTech Connect

    Mazzarella, G.; Giampaolo, S. M.; Illuminati, F.

    2006-01-15

    For systems of interacting, ultracold spin-zero neutral bosonic atoms, harmonically trapped and subject to an optical lattice potential, we derive an Extended Bose Hubbard (EBH) model by developing a systematic expansion for the Hamiltonian of the system in powers of the lattice parameters and of a scale parameter, the lattice attenuation factor. We identify the dominant terms that need to be retained in realistic experimental conditions, up to nearest-neighbor interactions and nearest-neighbor hoppings conditioned by the on-site occupation numbers. In the mean field approximation, we determine the free energy of the system and study the phase diagram both at zero and at finite temperature. At variance with the standard on site Bose Hubbard model, the zero-temperature phase diagram of the EBH model possesses a dual structure in the Mott insulating regime. Namely, for specific ranges of the lattice parameters, a density wave phase characterizes the system at integer fillings, with domains of alternating mean occupation numbers that are the atomic counterparts of the domains of staggered magnetizations in an antiferromagnetic phase. We show as well that in the EBH model, a zero-temperature quantum phase transition to pair superfluidity is, in principle, possible, but completely suppressed at the lowest order in the lattice attenuation factor. Finally, we determine the possible occurrence of the different phases as a function of the experimentally controllable lattice parameters.

  20. Finite-temperature charge transport in the one-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Jin, F.; Steinigeweg, R.; Heidrich-Meisner, F.; Michielsen, K.; De Raedt, H.

    2015-11-01

    We study the charge conductivity of the one-dimensional repulsive Hubbard model at finite temperature using the method of dynamical quantum typicality, focusing at half filling. This numerical approach allows us to obtain current autocorrelation functions from systems with as many as 18 sites, way beyond the range of standard exact diagonalization. Our data clearly suggest that the charge Drude weight vanishes with a power law as a function of system size. The low-frequency dependence of the conductivity is consistent with a finite dc value and thus with diffusion, despite large finite-size effects. Furthermore, we consider the mass-imbalanced Hubbard model for which the charge Drude weight decays exponentially with system size, as expected for a nonintegrable model. We analyze the conductivity and diffusion constant as a function of the mass imbalance and we observe that the conductivity of the lighter component decreases exponentially fast with the mass-imbalance ratio. While in the extreme limit of immobile heavy particles, the Falicov-Kimball model, there is an effective Anderson-localization mechanism leading to a vanishing conductivity of the lighter species, we resolve finite conductivities for an inverse mass ratio of η ≳0.25 .

  1. Spectral function of the ionic Hubbard model (IHM)

    NASA Astrophysics Data System (ADS)

    Bulut, Sinan; Atkinson, Bill

    2010-03-01

    Using two-pole approximations, which are based on the equation of motion method, we calculate the excitation spectrum of the one dimensional IHM. To be specific, we use the composite operator method and the Roth-approximation. Though very simple in nature, these approximations capture the physics of the IHM qualitatively at least. As is predicted by several other numerical and/or theoretical studies, a bond-order (BO) phase is given by these approximate methods. In the BO phase, atoms in the system are dimerized leading to a gap in the excitation spectrum. We find that the BO phase flattens both low and high-energy bands. When the BO phase is suppressed, however, the system can be driven from the band-insulating phase to the metal one by electron-electron repulsions, which is somewhat counter-intuitive. Additionally, two-pole approximations generate a reasonably good DOS spectrum of this model when compared with exact numerical results for small systems.

  2. 2-D Magnetohydrodynamic Modeling of A Pulsed Plasma Thruster

    NASA Technical Reports Server (NTRS)

    Thio, Y. C. Francis; Cassibry, J. T.; Wu, S. T.; Rodgers, Stephen L. (Technical Monitor)

    2002-01-01

    Experiments are being performed on the NASA Marshall Space Flight Center (MSFC) MK-1 pulsed plasma thruster. Data produced from the experiments provide an opportunity to further understand the plasma dynamics in these thrusters via detailed computational modeling. The detailed and accurate understanding of the plasma dynamics in these devices holds the key towards extending their capabilities in a number of applications, including their applications as high power (greater than 1 MW) thrusters, and their use for producing high-velocity, uniform plasma jets for experimental purposes. For this study, the 2-D MHD modeling code, MACH2, is used to provide detailed interpretation of the experimental data. At the same time, a 0-D physics model of the plasma initial phase is developed to guide our 2-D modeling studies.

  3. 2 1/2 -D compressible reconnection model

    NASA Astrophysics Data System (ADS)

    Skender, M.; Vršnak, B.

    The exact solution of the jump conditions on the RD/SMS discontinuity system in a two-and-half-dimensional (2 1/2 -D) symmetrical reconnection model enables one to analyse the outflowing jet characteristics in dependence on the inflow velocity, and to follow changes in transition to the two-dimensional model. Implications arising from the exact solution and its relevance for solar flares are discussed.

  4. Interaction-energy functional of the Hubbard model: Local formulation and application to low-dimensional lattices

    NASA Astrophysics Data System (ADS)

    Saubanère, Matthieu; Lepetit, Marie Bernadette; Pastor, G. M.

    2016-07-01

    The interaction energy W [γ ] of the Hubbard model is regarded as a functional of the single-particle density matrix γ in the framework of lattice density-functional theory. The local character of the Hubbard interaction is exploited to express W as a sum of local contributions ωi[γ ] , for which a simple semilocal scaling approximation is proposed. The method is applied to the ionic Hubbard model on one- and two-dimensional lattices with homogeneous and inhomogeneous Coulomb repulsions. Results are given for the kinetic and Coulomb energies, interatomic charge transfers, local magnetic moments, and charge gaps. Goals and limitations of the functional are discussed by comparison with exact results.

  5. Hubbard Model for Atomic Impurities Bound by the Vortex Lattice of a Rotating Bose-Einstein Condensate.

    PubMed

    Johnson, T H; Yuan, Y; Bao, W; Clark, S R; Foot, C; Jaksch, D

    2016-06-17

    We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes. PMID:27367366

  6. Interplay Between Condensation Energy, Pseudogap, and the Specific Heat of a Hubbard Model in a $n$ n -Pole Approximation

    NASA Astrophysics Data System (ADS)

    Lausmann, A. C.; Calegari, E. J.; Magalhaes, S. G.; Chaves, C. M.; Troper, A.

    2015-04-01

    The condensation energy and the specific heat jump of a two-dimensional Hubbard model, suitable to discuss high- superconductors, are studied. In this work, the Hubbard model is investigated by the Green's function method within a -pole approximation, which allows to consider superconductivity with -wave pairing. In the present scenario, the pseudogap regime emerges when the antiferromagnetic correlations become sufficiently strong to move to lower energies the region around of the nodal point on the renormalized bands. It is observed that above a given total occupation , the specific heat jump and also the condensation energy decrease signaling the presence of the pseudogap.

  7. Hubbard Model for Atomic Impurities Bound by the Vortex Lattice of a Rotating Bose-Einstein Condensate

    NASA Astrophysics Data System (ADS)

    Johnson, T. H.; Yuan, Y.; Bao, W.; Clark, S. R.; Foot, C.; Jaksch, D.

    2016-06-01

    We investigate cold bosonic impurity atoms trapped in a vortex lattice formed by condensed bosons of another species. We describe the dynamics of the impurities by a bosonic Hubbard model containing occupation-dependent parameters to capture the effects of strong impurity-impurity interactions. These include both a repulsive direct interaction and an attractive effective interaction mediated by the Bose-Einstein condensate. The occupation dependence of these two competing interactions drastically affects the Hubbard model phase diagram, including causing the disappearance of some Mott lobes.

  8. Benchmarking the variational cluster approach by means of the one-dimensional Bose-Hubbard model

    SciTech Connect

    Knap, Michael; Arrigoni, Enrico; Linden, Wolfgang von der

    2010-06-15

    Convergence properties of the variational cluster approach with respect to the variational parameter space, cluster size, and boundary conditions of the reference system are investigated and discussed for bosonic many-body systems. Specifically, the variational cluster approach is applied to the one-dimensional Bose-Hubbard model, which exhibits a quantum phase transition from Mott to superfluid phase. In order to benchmark the variational cluster approach, results for the phase boundary delimiting the first Mott lobe are compared with essentially exact density matrix renormalization group data. Furthermore, static quantities, such as the ground state energy and the one-particle density matrix are compared with high-order strong coupling perturbation theory results. For reference systems with open boundary conditions the variational parameter space is extended by an additional variational parameter which allows for a more uniform particle density on the reference system and thus drastically improves the results. It turns out that the variational cluster approach yields accurate results with relatively low-computational effort for both the phase boundary as well as the static properties of the one-dimensional Bose-Hubbard model, even at the tip of the first Mott lobe where correlation effects are most pronounced.

  9. Madelung and Hubbard interactions in polaron band model of doped organic semiconductors.

    PubMed

    Png, Rui-Qi; Ang, Mervin C Y; Teo, Meng-How; Choo, Kim-Kian; Tang, Cindy Guanyu; Belaineh, Dagmawi; Chua, Lay-Lay; Ho, Peter K H

    2016-01-01

    The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π-π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine-fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime. PMID:27582355

  10. Hubbard models with nearly flat bands: Ground-state ferromagnetism driven by kinetic energy

    NASA Astrophysics Data System (ADS)

    Müller, Patrick; Richter, Johannes; Derzhko, Oleg

    2016-04-01

    We consider the standard repulsive Hubbard model with a flat lowest-energy band for two one-dimensional lattices (diamond chain and ladder) as well as for a two-dimensional lattice (bilayer) at half filling of the flat band. The considered models do not fall in the class of Mielke-Tasaki flat-band ferromagnets, since they do not obey the connectivity conditions. However, the ground-state ferromagnetism can emerge, if the flat band becomes dispersive. To study this kinetic-energy-driven ferromagnetism we use perturbation theory and exact diagonalization of finite lattices. We find as a typical scenario that small and moderate dispersion may lead to a ferromagnetic ground state for sufficiently large on-site Hubbard repulsion U >Uc , where Uc increases monotonically with the acquired bandwidth. However, we also observe for some specific parameter cases, that (i) ferromagnetism appears at already very small Uc, (ii) ferromagnetism does not show up at all, (iii) the critical on-site repulsion Uc is a nonmonotonic function of the bandwidth, or that (iv) a critical bandwidth is needed to open the window for ground-state ferromagnetism.

  11. 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.

  12. Hidden fermionic excitation in the superconductivity of the strongly attractive Hubbard model

    NASA Astrophysics Data System (ADS)

    Sakai, Shiro; Civelli, Marcello; Nomura, Yusuke; Imada, Masatoshi

    2015-11-01

    We study the attractive Hubbard model within the dynamical mean-field theory, to elucidate how the pseudogap and superconductivity at strong attractive interaction are related to those found in the repulsive Hubbard model, and thereby to bridge cold fermions and cuprate high-temperature superconductors from a microscopic point of view. We propose that a unified understanding is obtained by investigating single-particle excitation dynamics, in which emergent and hidden fermions coupled to quasiparticles consistently account for the numerical results in both attractive and repulsive cases. In the attractive case, the quasiparticle dynamics is observable by virtually breaking a tightly bound pair, where we find two qualitatively different regions crossing over each other within the strong-coupling superconductivity phase. Among them, the region close to the critical temperature shares characteristic dynamics with the repulsive interaction case, where the normal and anomalous parts of the self-energy show strong low-energy peaks while they are hidden in the quasiparticle spectral weight. These prominent self-energy peaks are understood by the coupling of the quasiparticle to the hidden fermionic excitation, emergent from a strong-coupling effect. The pseudogap above the critical temperature is also accounted for by the same hidden fermion.

  13. Correlation effects and non-collinear magnetism in the doped Hubbard model

    NASA Astrophysics Data System (ADS)

    Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu.

    2015-06-01

    The ground-state magnetic phase diagram is investigated for the two- and three-dimensional t- t ‧ Hubbard model. We take into account commensurate ferro-, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often missed in previous investigations. We trace the influence of correlation effects on the stability of both spiral and collinear magnetic order by comparing the results of employing both the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave boson approach by Kotliar and Ruckenstein with correlation effects included. We found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistic large Hubbard U, if the correlation effects are taken into account. The electronic phase separation plays an important role in the formation of magnetic states and corresponding regions are wide, especially in the vicinity of half-filling. The details of magnetic ordering for different cubic lattices are discussed.

  14. Long-range orders and spin/orbital freezing in the two-band Hubbard model

    NASA Astrophysics Data System (ADS)

    Steiner, Karim; Hoshino, Shintaro; Nomura, Yusuke; Werner, Philipp

    2016-08-01

    We solve the orbitally degenerate two-band Hubbard model within dynamical mean field theory and map out the instabilities to various symmetry-broken phases based on an analysis of the corresponding lattice susceptibilities. Phase diagrams as a function of the Hund coupling parameter J are obtained both for the model with rotationally invariant interaction and for the model with Ising-type anisotropy. For negative J , an intraorbital spin-singlet superconducting phase appears at low temperatures, while the normal state properties are characterized by an orbital-freezing phenomenon. This is the negative-J analog of the recently discovered fluctuating-moment induced s -wave spin-triplet superconductivity in the spin-freezing regime of multiorbital models with J >0 .

  15. Emery vs. Hubbard model for cuprate superconductors: a composite operator method study

    NASA Astrophysics Data System (ADS)

    Avella, Adolfo; Mancini, Ferdinando; Mancini, Francesco Paolo; Plekhanov, Evgeny

    2013-06-01

    Within the composite operator method (COM), we report the solution of the Emery model (also known as p- d or three band model), which is relevant for the cuprate high- T c superconductors. We also discuss the relevance of the often-neglected direct oxygen-oxygen hopping for a more accurate, sometimes unique, description of this class of materials. The benchmark of the solution is performed by comparing our results with the available quantum Monte Carlo ones. Both single-particle and thermodynamic properties of the model are studied in detail. Our solution features a metal-insulator transition at half filling. The resulting metal-insulator phase diagram agrees qualitatively very well with the one obtained within dynamical mean-field theory. We discuss the type of transition (Mott-Hubbard (MH) or charge-transfer (CT)) for the microscopic (ab initio) parameter range relevant for cuprates getting, as expected a CT type. The emerging single-particle scenario clearly suggests a very close relation between the relevant sub-bands of the three- (Emery) and the single-band (Hubbard) models, thus providing an independent and non-perturbative proof of the validity of the mapping between the two models for the model parameters optimal to describe cuprates. Such a result confirms the emergence of the Zhang-Rice scenario, which has been recently questioned. We also report the behavior of the specific heat and of the entropy as functions of the temperature on varying the model parameters as these quantities, more than any other, depend on and, consequently, reveal the most relevant energy scales of the system.

  16. Configuration Interaction as an Impurity Solver: Benchmark Dynamical Mean-Field Theory for the Hubbard Model

    NASA Astrophysics Data System (ADS)

    Go, Ara; Millis, Andrew J.

    2013-03-01

    The configuration interaction technique has been widely used in quantum chemistry to solve quantum many body systems with lower computational costs than exact diagonalization and was introduced by Dominika Zgid, Emanuel Gull, and Garnet Kin-Lic Chan [Phys. Rev. B 86, 165128 (2012)] as a solver for the impurity models of dynamical mean field theory. We extend their work, demonstrating for the one and two dimensional Hubbard model how the method reproduces the known results and allows convergence with bath size to be studied in cluster dynamical mean field theory. As an example of the power of the method, cluster dynamical mean field studies of the three band copper-oxygen model are presented. This work was supported by the CMCSN program of the US Department of Energy.

  17. From Nagaoka's Ferromagnetism to Flat-Band Ferromagnetism and Beyond --- An Introduction to Ferromagnetism in the Hubbard Model ---

    NASA Astrophysics Data System (ADS)

    Tasaki, H.

    1998-04-01

    It is believed that strong ferromagnetic interactions in some solids are generated by subtle interplay between quantum many-body effects and spin-independent Coulomb interactions between electrons. It is a challenging problem to verify this scenario in the Hubbard model, which is an idealized model for strongly interacting electrons in a solid. Nagaoka's ferromagnetism is a well-known rigorous example of ferromagnetism in the Hubbard model. It deals with the limiting situation in which there is one fewer electron than in the half-filling and the on-site Coulomb interaction is infinitely large. There are relatively new rigorous examples of ferromagnetism in Hubbard models called flat-band ferromagnetism. Flat-band ferromagnetism takes place in carefully prepared models in which the lowest bands (in the single-electron spectra) are ``flat.'' Usually, these two approaches are regarded as two complimentary routes to ferromagnetism in the Hubbard model. In the present paper we describe Nagaoka's ferromagnetism and flat-band ferromagnetism in detail, giving all the necessary background as well as complete (but elementary) mathematical proofs. By studying an intermediate model called the long-range hopping model, we also demonstrate that there is indeed a deep relation between these two seemingly different approaches to ferromagnetism. We further discuss some attempts to go beyond these approaches. We briefly discuss recent rigorous example of ferromagnetism in the Hubbard model which has neither infinitely large parameters nor completely flat bands. We give preliminary discussion regarding possible experimental realizations of the (nearly-)flat-band ferromagnetism. Finally, we focus on some theoretical attempts to understand metallic ferromagnetism. We discuss three artificial one-dimensional models in which the existence of metallic ferromagnetism can be easily proved. We have tried to make the present paper as self-contained as possible, keeping in mind readers who are

  18. Magnetic transitions and quantum criticality in the three-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Schäfer, Thomas; Katanin, Andrey; Held, Karsten; Toschi, Alessandro

    We analyze the (quantum) critical properties of the simplest model for electronic correlations, the Hubbard model, in three spatial dimensions by means of the dynamical mean field theory (DMFT, including all local correlations) and the dynamical vertex approximation (D ΓA, including non-local correlations on all length scales). Both in the half-filled/unfrustrated and in the hole-doped system the transition temperature is significantly lowered by including non-local fluctuations.In the latter case, however, the magnetic order becomes incommensurate, eventually leading to a complete suppression of the order and giving rise to a magnetic quantum critical point (QCP) at zero temperature. We analyze the (quantum) critical properties of this QCP (e.g. critical exponents) and relate our findings to the standard theory of quantum criticality in metals, the Hertz-Millis-Moriya theory. Solids4Fun, Austrian Science Fund (FWF, Project ID 1243).

  19. Out of equilibrium spatio-temporal correlations in the Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Kennett, Malcolm; Fitzpatrick, Matthew

    2016-05-01

    The Bose-Hubbard model (BHM) provides a model system to study quench dynamics across a quantum phase transition. Theoretically, it has proven challenging to study spatio-temporal correlations in the BHM in dimensions higher than one. We use the Schwinger-Keldysh technique and a strong-coupling expansion to develop a two-particle irreducible formalism to allow us to study spatio-temporal correlations in both the superfluid (SF) and Mott-insulating (MI) regimes during a quantum quench for dimensions higher than one. We obtain equations of motion for both the superfluid order parameter and two-point correlation functions and present numerical results for the evolution of two-time correlation functions. We relate our results to experiments on cold atoms in optical lattices. Supported by NSERC.

  20. Orientational bond and Néel order in the two-dimensional ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Hafez-Torbati, Mohsen; Uhrig, Götz S.

    2016-05-01

    Unconventional phases often occur where two competing mechanisms compensate. An excellent example is the ionic Hubbard model where the alternating local potential δ , favoring a band insulator (BI), competes with the local repulsion U , favoring a Mott insulator (MI). By continuous unitary transformations we derive effective models in which we study the softening of various excitons. The softening signals the instability towards new phases that we describe on the mean-field level. On increasing U from the BI in two dimensions, we find a bond-ordered phase breaking orientational symmetry due to a d -wave component. Then, antiferromagnetic order appears coexisting with the d -wave bond order. Finally, the d -wave order vanishes and a Néel-type MI persists.

  1. Exploring Competing Density Order in the Ionic Hubbard Model with Ultracold Fermions

    NASA Astrophysics Data System (ADS)

    Messer, Michael; Desbuquois, Rémi; Uehlinger, Thomas; Jotzu, Gregor; Huber, Sebastian; Greif, Daniel; Esslinger, Tilman

    2015-09-01

    We realize and study the ionic Hubbard model using an interacting two-component gas of fermionic atoms loaded into an optical lattice. The bipartite lattice has a honeycomb geometry with a staggered energy offset that explicitly breaks the inversion symmetry. Distinct density-ordered phases are identified using noise correlation measurements of the atomic momentum distribution. For weak interactions the geometry induces a charge density wave. For strong repulsive interactions we detect a strong suppression of doubly occupied sites, as expected for a Mott insulating state, and the externally broken inversion symmetry is not visible anymore in the density distribution. The local density distributions in different configurations are characterized by measuring the number of doubly occupied lattice sites as a function of interaction and energy offset. We further probe the excitations of the system using direction dependent modulation spectroscopy and discover a complex spectrum, which we compare with a theoretical model.

  2. Effective doublon and hole temperatures in the photo-doped dynamic Hubbard model.

    PubMed

    Werner, Philipp; Eckstein, Martin

    2016-03-01

    Hirsch's dynamic Hubbard model describes the effect of orbital expansion with occupancy by coupling the doublon operator to an auxiliary boson. In the Mott insulating phase, empty sites (holes) and doubly occupied orbitals (doublons) become charge carriers on top of the half-filled background. We use the nonequilibrium dynamical mean field method to study the properties of photo-doped doublons and holes in this model in the strongly correlated regime. In particular, we discuss how photodoping leads to doublon and hole populations with different effective temperatures, and we analyze the relaxation behavior as a function of the boson coupling and boson energy. In the polaronic regime, the nontrivial energy exchange between doublons, holes, and bosons can result in a negative temperature distribution for the holes. PMID:26798834

  3. Extended dynamic Mott transition in the two-band Hubbard model out of equilibrium

    NASA Astrophysics Data System (ADS)

    Behrmann, Malte; Fabrizio, Michele; Lechermann, Frank

    2013-07-01

    We reformulate the time-dependent Gutzwiller approximation by M. Schiró and M. Fabrizio, [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.076401 105, 076401 (2010)] in the framework of slave-boson mean-field theory, which is used to investigate the dynamical Mott transition of the generic two-band Hubbard model at half filling upon an interaction quench. Interorbital fluctuations lead to notable changes with respect to the single-band case. The singular dynamical transition is replaced by a broad regime of long-lived fluctuations between metallic and insulating states, accompanied by intriguing precursor behavior. A mapping to a spin model proves helpful to analyze the different regions in terms of the evolution of an Ising-like order parameter. Contrary to the static case, singlet occupations remain vital in the Mott-insulating regime with finite Hund's exchange.

  4. Phase Diagram of the Frustrated Square-Lattice Hubbard Model: Variational Cluster Approach

    NASA Astrophysics Data System (ADS)

    Misumi, Kazuma; Kaneko, Tatsuya; Ohta, Yukinori

    2016-06-01

    The variational cluster approximation is used to study the frustrated Hubbard model at half filling defined on the two-dimensional square lattice with anisotropic next-nearest-neighbor hopping parameters. We calculate the ground-state phase diagrams of the model in a wide parameter space for a variety of lattice geometries, including square, crossed-square, and triangular lattices. We examine the Mott metal-insulator transition and show that, in the Mott insulating phase, magnetic phases with Néel, collinear, and spiral orders appear in relevant parameter regions, and in an intermediate region between these phases, a nonmagnetic insulating phase caused by the quantum fluctuations in the geometrically frustrated spin degrees of freedom emerges.

  5. Exploring competing density order in the ionic Hubbard model with ultracold fermions.

    PubMed

    Messer, Michael; Desbuquois, Rémi; Uehlinger, Thomas; Jotzu, Gregor; Huber, Sebastian; Greif, Daniel; Esslinger, Tilman

    2015-09-11

    We realize and study the ionic Hubbard model using an interacting two-component gas of fermionic atoms loaded into an optical lattice. The bipartite lattice has a honeycomb geometry with a staggered energy offset that explicitly breaks the inversion symmetry. Distinct density-ordered phases are identified using noise correlation measurements of the atomic momentum distribution. For weak interactions the geometry induces a charge density wave. For strong repulsive interactions we detect a strong suppression of doubly occupied sites, as expected for a Mott insulating state, and the externally broken inversion symmetry is not visible anymore in the density distribution. The local density distributions in different configurations are characterized by measuring the number of doubly occupied lattice sites as a function of interaction and energy offset. We further probe the excitations of the system using direction dependent modulation spectroscopy and discover a complex spectrum, which we compare with a theoretical model. PMID:26406839

  6. Magnetic correlations and pairing in the 1/5-depleted square lattice Hubbard model.

    PubMed

    Khatami, Ehsan; Singh, Rajiv R P; Pickett, Warren E; Scalettar, Richard T

    2014-09-01

    We study the single-orbital Hubbard model on the 1/5-depleted square-lattice geometry, which arises in such diverse systems as the spin-gap magnetic insulator CaV4O9 and ordered-vacancy iron selenides, presenting new issues regarding the origin of both magnetic ordering and superconductivity in these materials. We find a rich phase diagram that includes a plaquette singlet phase, a dimer singlet phase, a Néel and a block-spin antiferromagnetic phase, and stripe phases. Quantum Monte Carlo simulations show that the dominant pairing correlations at half filling change character from d wave in the plaquette phase to extended s wave upon transition to the Néel phase. These findings have intriguing connections to iron-based superconductors, and suggest that some physics of multiorbital systems can be captured by a single-orbital model at different dopings. PMID:25238374

  7. Thermodynamics of the Hubbard model on stacked honeycomb and square lattices

    NASA Astrophysics Data System (ADS)

    Imriška, Jakub; Gull, Emanuel; Troyer, Matthias

    2016-07-01

    We present a numerical study of the Hubbard model on simply stacked honeycomb and square lattices, motivated by a recent experimental realization of such models with ultracold atoms in optical lattices. We perform simulations with different interlayer coupling and interaction strengths and obtain Néel transition temperatures and entropies. We provide data for the equation of state to enable comparisons of experiments and theory. We find an enhancement of the short-range correlations in the anisotropic lattices compared to the isotropic cubic lattice, in parameter regimes suitable for the interaction driven adiabatic cooling. Supplementary material in the form of one zip file available from the Jounal web page at http://dx.doi.org/10.1140/epjb/e2016-70146-y

  8. First-order topological phase transition of the Haldane-Hubbard model

    NASA Astrophysics Data System (ADS)

    Imriška, Jakub; Wang, Lei; Troyer, Matthias

    2016-07-01

    We study the interplay of topological band structure and conventional magnetic long-range order in spinful Haldane model with on-site repulsive interaction. Using the dynamical cluster approximation with clusters of up to 24 sites we find evidence of a first-order phase transition from a Chern insulator at weak coupling to a topologically trivial antiferromagnetic insulator at strong coupling. These results call into question a previously found intermediate state with coexisting topological character and antiferromagnetic long-range order. Experimentally measurable signatures of the first-order transition include hysteretic behavior of the double occupancy, single-particle excitation gap, and nearest neighbor spin-spin correlations. This first-order transition is contrasted with a continuous phase transition from the conventional band insulator to the antiferromagnetic insulator in the ionic Hubbard model on the honeycomb lattice.

  9. Absence of a Spin Liquid Phase in the Hubbard Model on the Honeycomb Lattice

    PubMed Central

    Sorella, Sandro; Yunoki, Seiji

    2012-01-01

    A spin liquid is a novel quantum state of matter with no conventional order parameter where a finite charge gap exists even though the band theory would predict metallic behavior. Finding a stable spin liquid in two or higher spatial dimensions is one of the most challenging and debated issues in condensed matter physics. Very recently, it has been reported that a model of graphene, i.e., the Hubbard model on the honeycomb lattice, can show a spin liquid ground state in a wide region of the phase diagram, between a semi-metal (SM) and an antiferromagnetic insulator (AFMI). Here, by performing numerically exact quantum Monte Carlo simulations, we extend the previous study to much larger clusters (containing up to 2592 sites), and find, if any, a very weak evidence of this spin liquid region. Instead, our calculations strongly indicate a direct and continuous quantum phase transition between SM and AFMI. PMID:23251778

  10. Variational identification of a fractional Chern insulator in an extended Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Shapourian, Hassan; Clark, Bryan K.

    2016-01-01

    We study the extended Bose-Hubbard model on the square lattice at half-filling as a function of next-nearest neighbor hopping amplitude and interaction strength. To variationally map out the phase diagram of this model, we develop a two-parameter family of wave functions based on the parton construction which can describe both topological and broken symmetry phases on equal footing. In addition, our wave functions resolve long standing issues with more conventional short-range Jastrow wave functions. Using this variational ansatz, we show that a spontaneous time-reversal symmetry-breaking fractional Chern insulator is energetically favored over a critical region between two superfluid phases. In verifying the properties of these parton wave functions we exemplify a more robust way to identify topology through the Hall conductance.

  11. Inclusion of intersite spatial correlations in the alloy analogy approach to the half-filled ionic Hubbard model.

    PubMed

    Rowlands, D A; Zhang, Yu-Zhong

    2014-07-01

    Using the nonlocal coherent-potential approximation we study the effect of intersite spatial correlations on the transition from band insulator to metal as well as from metal to Mott insulator in the 'alloy analogy' approach to the paramagnetic solution of the half-filled ionic Hubbard model. We find that intersite spatial correlations enhance the metallic phase. PMID:24935407

  12. Quantum critical behavior in three-dimensional one-band Hubbard model at half-filling

    SciTech Connect

    Karchev, Naoum

    2013-06-15

    A one-band Hubbard model with hopping parameter t and Coulomb repulsion U is considered at half-filling. By means of the Schwinger bosons and slave fermions representation of the electron operators and integrating out the spin–singlet Fermi fields an effective Heisenberg model with antiferromagnetic exchange constant is obtained for vectors which identifies the local orientation of the spin of the itinerant electrons. The amplitude of the spin vectors is an effective spin of the itinerant electrons accounting for the fact that some sites, in the ground state, are doubly occupied or empty. Accounting adequately for the magnon–magnon interaction the Néel temperature is calculated. When the ratio t/U is small enough (t/U ≤0.09) the effective model describes a system of localized electrons. Increasing the ratio increases the density of doubly occupied states which in turn decreases the effective spin and Néel temperature. The phase diagram in the plane of temperature (T{sub N})/U and parameter t/U is presented. The quantum critical point (T{sub N}=0) is reached at t/U =0.9. The magnons in the paramagnetic phase are studied and the contribution of the magnons’ fluctuations to the heat capacity is calculated. At the Néel temperature the heat capacity has a peak which is suppressed when the system approaches a quantum critical point. It is important to stress that, at half-filling, the ground state, determined by fermions, is antiferromagnetic. The magnon fluctuations drive the system to quantum criticality and when the effective spin is critically small these fluctuations suppress the magnetic order. -- Highlights: •Technique of calculation is introduced which permits us to study the magnons’ fluctuations. •Quantum critical point is obtained in the one-band 3D Hubbard model at half-filling. •The present analytical results supplement the numerical ones (see Fig. 7)

  13. Modelling RF sources using 2-D PIC codes

    SciTech Connect

    Eppley, K.R.

    1993-03-01

    In recent years, many types of RF sources have been successfully modelled using 2-D PIC codes. Both cross field devices (magnetrons, cross field amplifiers, etc.) and pencil beam devices (klystrons, gyrotrons, TWT`S, lasertrons, etc.) have been simulated. All these devices involve the interaction of an electron beam with an RF circuit. For many applications, the RF structure may be approximated by an equivalent circuit, which appears in the simulation as a boundary condition on the electric field (``port approximation``). The drive term for the circuit is calculated from the energy transfer between beam and field in the drift space. For some applications it may be necessary to model the actual geometry of the structure, although this is more expensive. One problem not entirely solved is how to accurately model in 2-D the coupling to an external waveguide. Frequently this is approximated by a radial transmission line, but this sometimes yields incorrect results. We also discuss issues in modelling the cathode and injecting the beam into the PIC simulation.

  14. Modelling RF sources using 2-D PIC codes

    SciTech Connect

    Eppley, K.R.

    1993-03-01

    In recent years, many types of RF sources have been successfully modelled using 2-D PIC codes. Both cross field devices (magnetrons, cross field amplifiers, etc.) and pencil beam devices (klystrons, gyrotrons, TWT'S, lasertrons, etc.) have been simulated. All these devices involve the interaction of an electron beam with an RF circuit. For many applications, the RF structure may be approximated by an equivalent circuit, which appears in the simulation as a boundary condition on the electric field ( port approximation''). The drive term for the circuit is calculated from the energy transfer between beam and field in the drift space. For some applications it may be necessary to model the actual geometry of the structure, although this is more expensive. One problem not entirely solved is how to accurately model in 2-D the coupling to an external waveguide. Frequently this is approximated by a radial transmission line, but this sometimes yields incorrect results. We also discuss issues in modelling the cathode and injecting the beam into the PIC simulation.

  15. Phase Separation of Superconducting Phases in the Penson-Kolb-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Jerzy Kapcia, Konrad; Czart, Wojciech Robert; Ptok, Andrzej

    2016-04-01

    In this paper, we determine the phase diagrams (for T = 0 as well as T > 0) of the Penson-Kolb-Hubbard model for two dimensional square lattice within Hartree-Fock mean-field theory focusing on an investigation of superconducting phases and on a possibility of the occurrence of the phase separation. We obtain that the phase separation, which is a state of coexistence of two different superconducting phases (with s- and η-wave symmetries), occurs in definite ranges of the electron concentration. In addition, increasing temperature can change the symmetry of the superconducting order parameter (from η-wave into s-wave). The system considered exhibits also an interesting multicritical behaviour including bicritical points. The relevance of the results to experiments for real materials is also discussed.

  16. Gutzwiller wave function for finite systems: superconductivity in the Hubbard model

    NASA Astrophysics Data System (ADS)

    Tomski, Andrzej; Kaczmarczyk, Jan

    2016-05-01

    We study the superconducting phase of the Hubbard model using the Gutzwiller variational wave function (GWF) and the recently proposed diagrammatic expansion technique (DE-GWF). The DE-GWF method works on the level of the full GWF and in the thermodynamic limit. Here, we consider a finite-size system to study the accuracy of the results as a function of the system size (which is practically unrestricted). We show that the finite-size scaling used, e.g. in the variational Monte Carlo method can lead to significant, uncontrolled errors. The presented research is the first step towards applying the DE-GWF method in studies of inhomogeneous situations, including systems with impurities, defects, inhomogeneous phases, or disorder.

  17. Temperature effects on superfluid phase transition in Bose-Hubbard model with three-body interaction

    NASA Astrophysics Data System (ADS)

    Kopeć, T. K.; Szymański, M. W.

    2014-10-01

    We theoretically investigate the effect of the three-body on-site interactions on the Mott-insulator-superfluid transition for ultracold bosonic atoms in the framework of the Bose-Hubbard model. In particular, we explore the combined effects of three-body interaction and finite temperature on the phase diagram in detail. In order to handle system with strong local interactions a resolvent expansion technique based on the contour integral representation of the partition function has been devised. Subsequently, we derive the Landau-type expansion for the free energy in terms of the superfluid order parameter and find the phase diagrams depicting the relationships between various physical quantities of interest.

  18. Retarded VS instantaneous: not so conflicting views on the pairing dynamics of the extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Reymbaut, A.; Fellous Asiani, M.; Fratino, L.; Charlebois, M.; Verret, S.; Sordi, G.; Sénéchal, D..; Tremblay, A.-M. S.

    While most experimental and theoretical clues lean towards a magnetic origin for the pairing mechanism of high temperature superconductors, the question of its degree of retardation in the strong correlation regime remains highly controversial [1-5]. Part of the answer to this question lies in the frequency dependence of the anomalous spectral function of doped Mott insulators. That spectral function is associated with the Gorkov function and can be extracted at finite temperature using the MaxEntAux method for analytic continuation. Using Cellular Dynamical Mean-Field Theory for the Hubbard model with nearest-neighbor repulsion, we show that the retarded contribution coming from the anomalous spectral function is accompanied by a contribution to the real part of the anomalous self-energy at infinite frequency. This contribution suggests the emergence of a ''mixed'' pairing mechanism, mostly retarded, slightly instantaneous. Supported by NSERC, CIFAR, and the Tier I Canada Research Chair.

  19. Nearest-Neighbor Repulsion and Competing Charge and Spin Order in the Extended Hubbard Model.

    NASA Astrophysics Data System (ADS)

    Bahman, Davoudi; Tremblay, A.-M. S.

    2006-03-01

    We generalize the Two-Particle Self-Consistent (TPSC) approach to study the extended Hubbard model where the nearest-neighbor interaction V is present in addition to the local interaction U. Our results are in good agreement with available Quantum Monte-Carlo results over the whole range of density n up to intermediate coupling. As a function of U, V and n we observe different kinds of charge and spin orders, like commensurate/incommensurate charge and spin density wave, phase separation, and ferromagnetic order. For attractive V superconductivity could exist in the regions where the other types of charge and spin orders do not dominate. Ref.: B. Davoudi and A.-M.S. Tremblay, cond-mat/0509707

  20. Orbital selective directional conductor in the two-orbital Hubbard model

    DOE PAGESBeta

    Mukherjee, Anamitra; Patel, Niravkumar D.; Moreo, Adriana; Dagotto, Elbio

    2016-02-29

    Recently, we employed a developed many-body technique that allows for the incorporation of thermal effects, the rich phase diagram of a two-dimensional two-orbital (degenerate dxz and dyz) Hubbard model is presented varying temperature and the repulsion U. The main result is the finding at intermediate U of an antiferromagnetic orbital selective state where an effective dimensional reduction renders one direction insulating and the other metallic. Possible realizations of this state are discussed. Additionally, we also study nematicity above the N eel temperature. After a careful finite-size scaling analysis, the nematicity temperature window appears to survive in the bulk limit, althoughmore » it is very narrow.« less

  1. Finite-temperature phase transitions in the SU (N ) Hubbard model

    NASA Astrophysics Data System (ADS)

    Yanatori, Hiromasa; Koga, Akihisa

    2016-07-01

    We investigate the SU (N ) Hubbard model for the multicomponent fermionic optical lattice system, combining dynamical mean-field theory with the continuous-time quantum Monte Carlo method. We obtain the finite-temperature phase diagrams with N ≤6 and find that low-temperature properties depend on the parity of the components. The magnetically ordered state competes with the correlated metallic state in the system with an even number of components (N ≥4 ) , yielding the first-order phase transition. It is also clarified that in the odd-component system, the ordered state is realized at relatively lower temperatures and the critical temperature is constant in the strong coupling limit.

  2. Existence of a metallic phase in a 1D Holstein Hubbard model at half filling

    NASA Astrophysics Data System (ADS)

    Krishna, Phani Murali; Chatterjee, Ashok

    2007-06-01

    The one-dimensional half-filled Holstein-Hubbard model is studied using a series of canonical transformations including phonon coherence effect that partly depends on the electron density and is partly independent and also incorporating the on-site and the nearest-neighbour phonon correlations and the exact Bethe-ansatz solution of Lieb and Wu. It is shown that choosing a better variational phonon state makes the polarons more mobile and widens the intermediate metallic region at the charge-density-wave-spin-density-wave crossover recently predicted by Takada and Chatterjee. The presence of this metallic phase is indeed a favourable situation from the point of view of high temperature superconductivity.

  3. Optical properties of MX chain materials: An extended Peierls-Hubbard model

    SciTech Connect

    Bishop, A.R.; Batistic, I.; Gammel, J.T.; Saxena, A.

    1991-01-01

    We describe theoretical modeling of both pure (MX) and mixed-halide (MX{sub x}X{prime}{sub 1-x}) halogen (X)-bridged transition metal (M) linear chain complexes in terms of an extended Peierls-Hubbard, tight-binding Hamiltonian with 3/4-filling of two-bands. Both inter- and intra-site electron-phonon coupling are included. Electronic (optical absorption), lattice dynamic (IR, Raman) and spin (ESR) signatures are obtained for the ground states, localized excited states produced by impurities, doping or photo-excitation -- excitons, polarons, bipolarons, solitons; and the edge states (which occur in mixed-halide crystals, e.g. PtCl{sub x}Br{sub 1-x}). Adiabatic molecular dynamics is used to explore photodecay channels in pure and impure systems for ground states as well as in the presence of pre-existing polaronic states. 12 refs., 3 figs., 1 tab.

  4. Sodium doped TiOCl as a realization of a multiband ionic Hubbard model

    NASA Astrophysics Data System (ADS)

    Jeschke, Harald O.; Zhang, Yu-Zhong; Foyevtsova, Kateryna; Schmidt, Martin U.; Valenti, Roser

    2010-03-01

    Using first principles molecular dynamics simulations, we investigate the effect of Na intercalation in the layered Mott insulator TiOCl. In agreement with recent photoemission experiments, we find that the system remains insulating for all studied Na concentrations. Our calculations also explain the evolution of the spectral weight upon Na doping. This is possible due to a prediction of the Na-doped superlattice structures. In the search for alternatives to metallize TiOCl, we also carried out simulations of substitutions of O by F, Cl by S, or Ti by V (or Sc), respectively, but all resulting structures turn out to be insulating. We propose a description in terms of a multiorbital ionic Hubbard model in a quasi-two-dimensional lattice and discuss the nature of the insulating state under doping. Finally, a different route for metallizing TiOCl by doping is proposed.

  5. Charged Stripes in the Two-Orbital Hubbard Model for Pnictides

    NASA Astrophysics Data System (ADS)

    Yao, Dao-Xin; Luo, Qinlong; Prestel, Thomas; Daghofer, Maria; Moreo, Adriana; Dagotto, Elbio

    2011-03-01

    The two-orbital Hubbard model for the pnictides is studied numerically in the real-space Hartree-Fock approximation. Upon electron doping, states with a nonuniform ditribution of charge are stabilized. The patterns observed correspond to charge stripes that run perpendicular to the direction of the spin stripes of the undoped magnetic ground state. These striped states are robust when the undoped state has a gap, although with a decreasing amplitude as the gap decreases. Results for hole doping and implications for recent experiments that reported electronic nematic states and spin incommensurability in the pnictides are also discussed. This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (Q.L., A.M., E.D.), the SYSU and NSFC-11074310 (D.X.Y.), the DFG under the Emmy-Noether program (T.P., M.D.).

  6. Origami rules for the construction of localized eigenstates of the Hubbard model in decorated lattices

    PubMed Central

    Dias, R. G.; Gouveia, J. D.

    2015-01-01

    We present a method of construction of exact localized many-body eigenstates of the Hubbard model in decorated lattices, both for U = 0 and U → ∞. These states are localized in what concerns both hole and particle movement. The starting point of the method is the construction of a plaquette or a set of plaquettes with a higher symmetry than that of the whole lattice. Using a simple set of rules, the tight-binding localized state in such a plaquette can be divided, folded and unfolded to new plaquette geometries. This set of rules is also valid for the construction of a localized state for one hole in the U → ∞ limit of the same plaquette, assuming a spin configuration which is a uniform linear combination of all possible permutations of the set of spins in the plaquette. PMID:26581296

  7. Gutzwiller wave function for finite systems: superconductivity in the Hubbard model.

    PubMed

    Tomski, Andrzej; Kaczmarczyk, Jan

    2016-05-01

    We study the superconducting phase of the Hubbard model using the Gutzwiller variational wave function (GWF) and the recently proposed diagrammatic expansion technique (DE-GWF). The DE-GWF method works on the level of the full GWF and in the thermodynamic limit. Here, we consider a finite-size system to study the accuracy of the results as a function of the system size (which is practically unrestricted). We show that the finite-size scaling used, e.g. in the variational Monte Carlo method can lead to significant, uncontrolled errors. The presented research is the first step towards applying the DE-GWF method in studies of inhomogeneous situations, including systems with impurities, defects, inhomogeneous phases, or disorder. PMID:27023047

  8. Algebraic geometry methods associated to the one-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Martins, M. J.

    2016-06-01

    In this paper we study the covering vertex model of the one-dimensional Hubbard Hamiltonian constructed by Shastry in the realm of algebraic geometry. We show that the Lax operator sits in a genus one curve which is not isomorphic but only isogenous to the curve suitable for the AdS/CFT context. We provide an uniformization of the Lax operator in terms of ratios of theta functions allowing us to establish relativistic like properties such as crossing and unitarity. We show that the respective R-matrix weights lie on an Abelian surface being birational to the product of two elliptic curves with distinct J-invariants. One of the curves is isomorphic to that of the Lax operator but the other is solely fourfold isogenous. These results clarify the reason the R-matrix can not be written using only difference of spectral parameters of the Lax operator.

  9. Hybrid-Space Density Matrix Renormalization Group Study of the Two-Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Ehlers, Georg; Noack, Reinhard M.

    We investigate the ground state of the two-dimensional Hubbard model on a cylinder geometry at intermediate coupling and weak doping. We study properties such as the behavior of the ground-state energy, pair-field correlations, and the appearance of stripes. We find striped ground states generically, with the width of the stripes depending on the filling, the boundary conditions, and the circumference of the cylinder. Furthermore, we analyse the interplay between the different stripe configurations and the decay of the pairing correlations. Our analysis is based on a hybrid-space density matrix renormalization group (DMRG) approach, which uses a momentum-space representation in the transverse and a real-space representation in the longitudinal direction. Exploiting the transverse momentum quantum number makes significant speedup and memory savings compared to the real-space DMRG possible. In particular, we obtain computational costs that are independent of the cylinder width for fixed size of the truncated Hilbert space.

  10. Long-lived nonequilibrium states in the Hubbard model with an electric field

    NASA Astrophysics Data System (ADS)

    Joura, Alexander V.; Freericks, J. K.; Lichtenstein, Alexander I.

    2015-06-01

    We study the single-band Hubbard model in the presence of a large spatially uniform electric field out of equilibrium. Using the Keldysh nonequilibrium formalism, we solve the problem using perturbation theory in the Coulomb interaction U . We present numerical results for the charge current, the total energy of the system, and the double occupancy on an infinite-dimensional hypercubic lattice with nearest-neighbor hopping. The system is isolated from an external bath and is in the paramagnetic state. We show that an electric field pulse can drive the system to a steady nonequilibrium state, which does not evolve into a thermal state. We compare results obtained within second-order perturbation theory (SOPT), self-consistent SOPT, and iterated perturbation theory (IPT). We also discuss the importance of initial conditions for a system which is not coupled to an external bath.

  11. Equivalent spin-orbit interaction in the two-polariton Jaynes-Cummings-Hubbard model.

    PubMed

    Li, C; Zhang, X Z; Song, Z

    2015-01-01

    A cavity quantum electrodynamics (cavity-QED) system combines two or more distinct quantum components, exhibiting features not seen in the individual systems. In this work, we study the one-dimensional Jaynes-Cummings-Hubbard model in the two-excitation (two-polariton) subspace. We find that the centre momentum of two-excitation induces a magnetic flux piercing the equivalent Hamiltonian Hk in the invariant subspace with momentum k, which can be described as a 4-leg ladder in the auxiliary space. Furthermore, it is shown that the system in π-centre-momentum subspace is equivalent to a lattice system for spin-1 particle with spin-orbit coupling. On the basis of this concise description, a series of bound-pair eigenstates which display long-range polaritonic entanglement is presented as a simple application. PMID:26159665

  12. Unitary matrix models and 2D quantum gravity

    SciTech Connect

    Dalley, S. . Joseph Henry Labs.); Johnson, C.V.; Morris, T.R. . Dept. of Physics); Watterstam, A. )

    1992-09-21

    In this paper the KdV and modified KdV integrable hierarchies are shown to be different descriptions of the same 2D gravitational system - open-closed string theory. Non-perturbative solutions of the multicritical unitary matrix models map to non-singular solutions of the renormalization group equation for the string susceptibility, [P, Q] = Q. The authors also demonstrate that the large-N solutions of unitary matrix integrals in external fields, studied by Gross and Newman, equal the non-singular pure closed-string solutions of [[bar P], Q] = Q.

  13. 2D numerical modelling of meandering channel formation

    NASA Astrophysics Data System (ADS)

    XIAO, Y.; ZHOU, G.; YANG, F. S.

    2016-03-01

    A 2D depth-averaged model for hydrodynamic sediment transport and river morphological adjustment was established. The sediment transport submodel takes into account the influence of non-uniform sediment with bed surface armoring and considers the impact of secondary flow in the direction of bed-load transport and transverse slope of the river bed. The bank erosion submodel incorporates a simple simulation method for updating bank geometry during either degradational or aggradational bed evolution. Comparison of the results obtained by the extended model with experimental and field data, and numerical predictions validate that the proposed model can simulate grain sorting in river bends and duplicate the characteristics of meandering river and its development. The results illustrate that by using its control factors, the improved numerical model can be applied to simulate channel evolution under different scenarios and improve understanding of patterning processes.

  14. Brane brick models and 2 d (0 , 2) triality

    NASA Astrophysics Data System (ADS)

    Franco, Sebastián; Lee, Sangmin; Seong, Rak-Kyeong

    2016-05-01

    We provide a brane realization of 2 d (0 , 2) Gadde-Gukov-Putrov triality in terms of brane brick models. These are Type IIA brane configurations that are T-dual to D1-branes over singular toric Calabi-Yau 4-folds. Triality translates into a local transformation of brane brick models, whose simplest representative is a cube move. We present explicit examples and construct their triality networks. We also argue that the classical mesonic moduli space of brane brick model theories, which corresponds to the probed Calabi-Yau 4-fold, is invariant under triality. Finally, we discuss triality in terms of phase boundaries, which play a central role in connecting Calabi-Yau 4-folds to brane brick models.

  15. Approximation auto-coherente a deux particules, pseudogap et supraconductivite dans le modele de Hubbard attractif

    NASA Astrophysics Data System (ADS)

    Allen, Steve

    2000-10-01

    Dans cette these nous presentons une nouvelle methode non perturbative pour le calcul des proprietes d'un systeme de fermions. Notre methode generalise l'approximation auto-coherente a deux particules proposee par Vilk et Tremblay pour le modele de Hubbard repulsif. Notre methode peut s'appliquer a l'etude du comportement pre-critique lorsque la symetrie du parametre d'ordre est suffisamment elevee. Nous appliquons la methode au probleme du pseudogap dans le modele de Hubbard attractif. Nos resultats montrent un excellent accord avec les donnees Monte Carlo pour de petits systemes. Nous observons que le regime ou apparait le pseudogap dans le poids spectral a une particule est un regime classique renormalise caracterise par une frequence caracteristique des fluctuations supraconductrices inferieure a la temperature. Une autre caracteristique est la faible densite de superfluide de cette phase demontrant que nous ne sommes pas en presence de paires preformees. Les resultats obtenus semblent montrer que la haute symetrie du parametre d'ordre et la bidimensionalite du systeme etudie elargissent le domaine de temperature pour lequel le regime pseudogap est observe. Nous argumentons que ce resultat est transposable aux supraconducteurs a haute temperature critique ou le pseudogap apparait a des' temperatures beaucoup plus grandes que la temperature critique. La forte symetrie dans ces systemes pourraient etre reliee a la theorie SO(5) de Zhang. En annexe, nous demontrons un resultat tout recent qui permettrait d'assurer l'auto-coherence entre les proprietes a une et a deux particules par l'ajout d'une dynamique au vertex irreductible. Cet ajout laisse entrevoir la possibilite d'etendre la methode au cas d'une forte interaction.

  16. Experimental validation of 2D profile photoresist shrinkage model

    NASA Astrophysics Data System (ADS)

    Bunday, Benjamin; Cordes, Aaron; Self, Andy; Ferry, Lorena; Danilevsky, Alex

    2011-03-01

    For many years, lithographic resolution has been the main obstacle in allowing the pace of transistor densification to meet Moore's Law. For the 32 nm node and beyond, new lithography techniques will be used, including immersion ArF (iArF) lithography and extreme ultraviolet lithography (EUVL). As in the past, these techniques will use new types of photoresists with the capability to print smaller feature widths and pitches. These smaller feature sizes will also require the use of thinner layers of photoresists, such as under 100 nm. In previous papers, we focused on ArF and iArF photoresist shrinkage. We evaluated the magnitude of shrinkage for both R&D and mature resists as a function of chemical formulation, lithographic sensitivity, scanning electron microscope (SEM) beam condition, and feature size. Shrinkage results were determined by the well accepted methodology described in SEMATECH's CD-SEM Unified Specification. In other associated works, we first developed a 1-D model for resist shrinkage for the bottom linewidth and then a 2-D profile model that accounted for shrinkage of all aspects of a trapezoidal profile along a given linescan. A fundamental understanding of the phenomenology of the shrinkage trends was achieved, including how the shrinkage behaves differently for different sized and shaped features. In the 1-D case, calibration of the parameters to describe the photoresist material and the electron beam was all that was required to fit the models to real shrinkage data, as long as the photoresist was thick enough that the beam could not penetrate the entire layer of resist. The later 2-D model included improvements for solving the CD shrinkage in thin photoresists, which is now of great interest for upcoming realistic lithographic processing to explore the change in resist profile with electron dose and to predict the influence of initial resist profile on shrinkage characteristics. The 2-D model also included shrinkage due to both the primary

  17. Predicting acidification recovery at the Hubbard Brook Experimental Forest, New Hampshire: evaluation of four models.

    PubMed

    Tominaga, Koji; Aherne, Julian; Watmough, Shaun A; Alveteg, Mattias; Cosby, Bernard J; Driscoll, Charles T; Posch, Maximilian; Pourmokhtarian, Afshin

    2010-12-01

    The performance and prediction uncertainty (owing to parameter and structural uncertainties) of four dynamic watershed acidification models (MAGIC, PnET-BGC, SAFE, and VSD) were assessed by systematically applying them to data from the Hubbard Brook Experimental Forest (HBEF), New Hampshire, where long-term records of precipitation and stream chemistry were available. In order to facilitate systematic evaluation, Monte Carlo simulation was used to randomly generate common model input data sets (n = 10,000) from parameter distributions; input data were subsequently translated among models to retain consistency. The model simulations were objectively calibrated against observed data (streamwater: 1963-2004, soil: 1983). The ensemble of calibrated models was used to assess future response of soil and stream chemistry to reduced sulfur deposition at the HBEF. Although both hindcast (1850-1962) and forecast (2005-2100) predictions were qualitatively similar across the four models, the temporal pattern of key indicators of acidification recovery (stream acid neutralizing capacity and soil base saturation) differed substantially. The range in predictions resulted from differences in model structure and their associated posterior parameter distributions. These differences can be accommodated by employing multiple models (ensemble analysis) but have implications for individual model applications. PMID:21028800

  18. A 2D channel-clogging biofilm model.

    PubMed

    Winstanley, H F; Chapwanya, M; Fowler, A C; O'Brien, S B G

    2015-09-01

    We present a model of biofilm growth in a long channel where the biomass is assumed to have the rheology of a viscous polymer solution. We examine the competition between growth and erosion-like surface detachment due to the flow. A particular focus of our investigation is the effect of the biofilm growth on the fluid flow in the pores, and the issue of whether biomass can grow sufficiently to shut off fluid flow through the pores, thus clogging the pore space. Net biofilm growth is coupled along the pore length via flow rate and nutrient transport in the pore flow. Our 2D model extends existing results on stability of 1D steady state biofilm thicknesses to show that, in the case of flows driven by a fixed pressure drop, full clogging of the pore can indeed happen in certain cases dependent on the functional form of the detachment term. PMID:25240390

  19. Mass loss in 2D rotating stellar models

    SciTech Connect

    Lovekin, Caterine; Deupree, Bob

    2010-10-05

    Radiatively driven mass loss is an important factor in the evolution of massive stars . The mass loss rates depend on a number of stellar parameters, including the effective temperature and luminosity. Massive stars are also often rapidly rotating, which affects their structure and evolution. In sufficiently rapidly rotating stars, both the effective temperature and radius vary significantly as a function of latitude, and hence mass loss rates can vary appreciably between the poles and the equator. In this work, we discuss the addition of mass loss to a 2D stellar evolution code (ROTORC) and compare evolution sequences with and without mass loss. Preliminary results indicate that a full 2D calculation of mass loss using the local effective temperature and luminosity can significantly affect the distribution of mass loss in rotating main sequence stars. More mass is lost from the pole than predicted by 1D models, while less mass is lost at the equator. This change in the distribution of mass loss will affect the angular momentum loss, the surface temperature and luminosity, and even the interior structure of the star. After a single mass loss event, these effects are small, but can be expected to accumulate over the course of the main sequence evolution.

  20. 2D Quantum Transport Modeling in Nanoscale MOSFETs

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, Bryan

    2001-01-01

    With the onset of quantum confinement in the inversion layer in nanoscale MOSFETs, behavior of the resonant level inevitably determines all device characteristics. While most classical device simulators take quantization into account in some simplified manner, the important details of electrostatics are missing. Our work addresses this shortcoming and provides: (a) a framework to quantitatively explore device physics issues such as the source-drain and gate leakage currents, DIBL, and threshold voltage shift due to quantization, and b) a means of benchmarking quantum corrections to semiclassical models (such as density- gradient and quantum-corrected MEDICI). We have developed physical approximations and computer code capable of realistically simulating 2-D nanoscale transistors, using the non-equilibrium Green's function (NEGF) method. This is the most accurate full quantum model yet applied to 2-D device simulation. Open boundary conditions, oxide tunneling and phase-breaking scattering are treated on equal footing. Electrons in the ellipsoids of the conduction band are treated within the anisotropic effective mass approximation. Quantum simulations are focused on MIT 25, 50 and 90 nm "well- tempered" MOSFETs and compared to classical and quantum corrected models. The important feature of quantum model is smaller slope of Id-Vg curve and consequently higher threshold voltage. These results are quantitatively consistent with I D Schroedinger-Poisson calculations. The effect of gate length on gate-oxide leakage and sub-threshold current has been studied. The shorter gate length device has an order of magnitude smaller current at zero gate bias than the longer gate length device without a significant trade-off in on-current. This should be a device design consideration.

  1. Cascading rainfall uncertainties into 2D inundation impact models

    NASA Astrophysics Data System (ADS)

    Souvignet, Maxime; de Almeida, Gustavo; Champion, Adrian; Garcia Pintado, Javier; Neal, Jeff; Freer, Jim; Cloke, Hannah; Odoni, Nick; Coxon, Gemma; Bates, Paul; Mason, David

    2013-04-01

    Existing precipitation products show differences in their spatial and temporal distribution and several studies have presented how these differences influence the ability to predict hydrological responses. However, an atmospheric-hydrologic-hydraulic uncertainty cascade is seldom explored and how, importantly, input uncertainties propagate through this cascade is still poorly understood. Such a project requires a combination of modelling capabilities, runoff generation predictions based on those rainfall forecasts, and hydraulic flood wave propagation based on the runoff predictions. Accounting for uncertainty in each component is important in decision making for issuing flood warnings, monitoring or planning. We suggest a better understanding of uncertainties in inundation impact modelling must consider these differences in rainfall products. This will improve our understanding of the input uncertainties on our predictive capability. In this paper, we propose to address this issue by i) exploring the effects of errors in rainfall on inundation predictive capacity within an uncertainty framework, i.e. testing inundation uncertainty against different comparable meteorological conditions (i.e. using different rainfall products). Our method cascades rainfall uncertainties into a lumped hydrologic model (FUSE) within the GLUE uncertainty framework. The resultant prediction uncertainties in discharge provide uncertain boundary conditions, which are cascaded into a simplified shallow water 2D hydraulic model (LISFLOOD-FP). Rainfall data captured by three different measurement techniques - rain gauges, gridded data and numerical weather predictions (NWP) models are used to assess the combined input data and model parameter uncertainty. The study is performed in the Severn catchment over the period between June and July 2007, where a series of rainfall events causing record floods in the study area). Changes in flood area extent are compared and the uncertainty envelope is

  2. Multiplons in the two-hole excitation spectra of the one-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Rausch, Roman; Potthoff, Michael

    2016-02-01

    Using the density-matrix renormalization group in combination with the Chebyshev polynomial expansion technique, we study the two-hole excitation spectrum of the one-dimensional Hubbard model in the entire filling range from the completely occupied band (n = 2) down to half-filling (n = 1). For strong interactions, the spectra reveal multiplon physics, i.e., relevant final states are characterized by two (doublon), three (triplon), four (quadruplon) and more holes, potentially forming stable compound objects or resonances with finite lifetime. These give rise to several satellites in the spectra with largely different spectral weights as well as to different two-hole, doublon-hole, two-doublon etc continua. The complex multiplon phenomenology is analyzed by interpreting not only local and k-resolved two-hole spectra but also three- and four-hole spectra for the Hubbard model and by referring to effective low-energy models. In addition, a filter-operator technique is presented and applied which allows to extract specific information on the final states at a given excitation energy. While multiplons composed of an odd number of holes do neither form stable compounds nor well-defined resonances unless a nearest-neighbor density interaction V is added to the Hamiltonian, the doublon and the quadruplon are well-defined resonances. The k-resolved four-hole spectrum at n = 2 represents an interesting special case where a completely stable quadruplon turns into a resonance by merging with the doublon-doublon continuum at a critical wave vector. For all fillings with n\\gt 1, the doublon lifetime is strongly k-dependent and is even infinite at the Brillouin zone edges as demonstrated by k-resolved two-hole spectra. This can be traced back to the ‘hidden’ charge-SU(2) symmetry of the model which is explicitly broken off half-filling and gives rise to a massive collective excitation, even for arbitrary higher-dimensional but bipartite lattices.

  3. Duality Between Spin Networks and the 2D Ising Model

    NASA Astrophysics Data System (ADS)

    Bonzom, Valentin; Costantino, Francesco; Livine, Etera R.

    2016-06-01

    The goal of this paper is to exhibit a deep relation between the partition function of the Ising model on a planar trivalent graph and the generating series of the spin network evaluations on the same graph. We provide respectively a fermionic and a bosonic Gaussian integral formulation for each of these functions and we show that they are the inverse of each other (up to some explicit constants) by exhibiting a supersymmetry relating the two formulations. We investigate three aspects and applications of this duality. First, we propose higher order supersymmetric theories that couple the geometry of the spin networks to the Ising model and for which supersymmetric localization still holds. Secondly, after interpreting the generating function of spin network evaluations as the projection of a coherent state of loop quantum gravity onto the flat connection state, we find the probability distribution induced by that coherent state on the edge spins and study its stationary phase approximation. It is found that the stationary points correspond to the critical values of the couplings of the 2D Ising model, at least for isoradial graphs. Third, we analyze the mapping of the correlations of the Ising model to spin network observables, and describe the phase transition on those observables on the hexagonal lattice. This opens the door to many new possibilities, especially for the study of the coarse-graining and continuum limit of spin networks in the context of quantum gravity.

  4. Des proprietes de l'etat normal du modele de Hubbard bidimensionnel

    NASA Astrophysics Data System (ADS)

    Lemay, Francois

    Depuis leur decouverte, les etudes experimentales ont demontre que les supra-conducteurs a haute temperature ont une phase normale tres etrange. Les proprietes de ces materiaux ne sont pas bien decrites par la theorie du liquide de Fermi. Le modele de Hubbard bidimensionnel, bien qu'il ne soit pas encore resolu, est toujours considere comme un candidat pour expliquer la physique de ces composes. Dans cet ouvrage, nous mettons en evidence plusieurs proprietes electroniques du modele qui sont incompatibles avec l'existence de quasi-particules. Nous montrons notamment que la susceptibilite des electrons libres sur reseau contient des singularites logarithmiques qui influencent de facon determinante les proprietes de la self-energie a basse frequence. Ces singularites sont responsables de la destruction des quasi-particules. En l'absence de fluctuations antiferromagnetiques, elles sont aussi responsables de l'existence d'un petit pseudogap dans le poids spectral au niveau de Fermi. Les proprietes du modele sont egalement etudiees pour une surface de Fermi similaire a celle des supraconducteurs a haute temperature. Un parallele est etabli entre certaines caracteristiques du modele et celles de ces materiaux.

  5. Bose-Hubbard models in confining potentials: Inhomogeneous mean-field theory

    NASA Astrophysics Data System (ADS)

    Pai, Ramesh V.; Kurdestany, Jamshid Moradi; Sheshadri, K.; Pandit, Rahul

    2012-06-01

    We present an extensive study of Mott insulator (MI) and superfluid (SF) shells in Bose-Hubbard (BH) models for bosons in optical lattices with harmonic traps. For this we apply the inhomogeneous mean-field theory developed by Sheshadri [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.75.4075 75, 4075 (1995)]. Our results for the BH model with one type of spinless bosons agree quantitatively with quantum Monte Carlo simulations. Our approach is numerically less intensive than such simulations, so we are able to perform calculations on experimentally realistic, large three-dimensional systems, explore a wide range of parameter values, and make direct contact with a variety of experimental measurements. We also extend our inhomogeneous mean-field theory to study BH models with harmonic traps and (a) two species of bosons or (b) spin-1 bosons. With two species of bosons, we obtain rich phase diagrams with a variety of SF and MI phases and associated shells when we include a quadratic confining potential. For the spin-1 BH model, we show, in a representative case, that the system can display alternating shells of polar SF and MI phases, and we make interesting predictions for experiments in such systems.

  6. Hole-hole correlations in the [ital U]=[infinity] limit of the Hubbard model and the stability of the Nagaoka state

    SciTech Connect

    Long, M.W. ); Zotos, X. , PHB-Ecublens, CH-1015 Lausanne )

    1993-07-01

    We use exact diagonalization in order to study the infinite-[ital U] limit of the two-dimensional Hubbard model. As well as looking at single-particle correlations, such as [ital n][sub [ital k][sigma

  7. Effects of Agent's Repulsion in 2d Flocking Models

    NASA Astrophysics Data System (ADS)

    Moussa, Najem; Tarras, Iliass; Mazroui, M'hammed; Boughaleb, Yahya

    In nature many animal groups, such as fish schools or bird flocks, clearly display structural order and appear to move as a single coherent entity. In order to understand the complex behavior of these systems, many models have been proposed and tested so far. This paper deals with an extension of the Vicsek model, by including a second zone of repulsion, where each agent attempts to maintain a minimum distance from the others. The consideration of this zone in our study seems to play an important role during the travel of agents in the two-dimensional (2D) flocking models. Our numerical investigations show that depending on the basic ingredients such as repulsion radius (R1), effect of density of agents (ρ) and noise (η), our nonequilibrium system can undergo a kinetic phase transition from no transport to finite net transport. For different values of ρ, kinetic phase diagrams in the plane (η ,R1) are found. Implications of these findings are discussed.

  8. 2-D Model for Normal and Sickle Cell Blood Microcirculation

    NASA Astrophysics Data System (ADS)

    Tekleab, Yonatan; Harris, Wesley

    2011-11-01

    Sickle cell disease (SCD) is a genetic disorder that alters the red blood cell (RBC) structure and function such that hemoglobin (Hb) cannot effectively bind and release oxygen. Previous computational models have been designed to study the microcirculation for insight into blood disorders such as SCD. Our novel 2-D computational model represents a fast, time efficient method developed to analyze flow dynamics, O2 diffusion, and cell deformation in the microcirculation. The model uses a finite difference, Crank-Nicholson scheme to compute the flow and O2 concentration, and the level set computational method to advect the RBC membrane on a staggered grid. Several sets of initial and boundary conditions were tested. Simulation data indicate a few parameters to be significant in the perturbation of the blood flow and O2 concentration profiles. Specifically, the Hill coefficient, arterial O2 partial pressure, O2 partial pressure at 50% Hb saturation, and cell membrane stiffness are significant factors. Results were found to be consistent with those of Le Floch [2010] and Secomb [2006].

  9. Phase diagram of the strongly correlated Kane-Mele-Hubbard model

    NASA Astrophysics Data System (ADS)

    Vaezi, Abolhassan; Mashkoori, Mahdi; Hosseini, Mehdi

    2012-05-01

    The phase diagram of the strongly correlated Hubbard model with intrinsic spin-orbit coupling on the honeycomb lattice is explored here. We obtain the low-energy effective model describing the spin degree of freedom. The resulting model is then studied by the Schwinger boson and Schwinger fermion approaches. The Schwinger boson method elucidates the boundary between the spin liquid phase and the magnetically ordered phases, Neel order, and incommensurate Neel order. Increasing the strength of the spin-orbit coupling is shown to narrow the width of the spin liquid region. The Schwinger fermion approach sheds further light on the nature of the spin liquid phase. We obtained three different candidates for the spin liquid phase within the mean-field approximation, namely, the gapless spin liquid, topological Mott insulator (fractionalized topological insulator), and chiral spin liquid phases. However, we argue that the gauge fluctuations and the instanton effect may suppress the first two spin liquids, while the chiral spin liquid is stable against gauge fluctuations due to its nontrivial topology.

  10. Ab initio derivation of multi-orbital extended Hubbard model for molecular crystals

    NASA Astrophysics Data System (ADS)

    Tsuchiizu, Masahisa; Omori, Yukiko; Suzumura, Yoshikazu; Bonnet, Marie-Laure; Robert, Vincent

    2012-01-01

    From configuration interaction (CI) ab initio calculations, we derive an effective two-orbital extended Hubbard model based on the gerade (g) and ungerade (u) molecular orbitals (MOs) of the charge-transfer molecular conductor (TTM-TTP)I3 and the single-component molecular conductor [Au(tmdt)2]. First, by focusing on the isolated molecule, we determine the parameters for the model Hamiltonian so as to reproduce the CI Hamiltonian matrix. Next, we extend the analysis to two neighboring molecule pairs in the crystal and we perform similar calculations to evaluate the inter-molecular interactions. From the resulting tight-binding parameters, we analyze the band structure to confirm that two bands overlap and mix in together, supporting the multi-band feature. Furthermore, using a fragment decomposition, we derive the effective model based on the fragment MOs and show that the staking TTM-TTP molecules can be described by the zig-zag two-leg ladder with the inter-molecular transfer integral being larger than the intra-fragment transfer integral within the molecule. The inter-site interactions between the fragments follow a Coulomb law, supporting the fragment decomposition strategy.

  11. Direct Probing of the Mott Crossover in the SU (N ) Fermi-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Hofrichter, Christian; Riegger, Luis; Scazza, Francesco; Höfer, Moritz; Fernandes, Diogo Rio; Bloch, Immanuel; Fölling, Simon

    2016-04-01

    We report on a detailed experimental investigation of the equation of state (EoS) of the three-dimensional Fermi-Hubbard model (FHM) in its generalized SU (N ) -symmetric form, using a degenerate ytterbium gas in an optical lattice. In its more common spin-1 /2 form, the FHM is a central model of condensed-matter physics. The generalization to N >2 was first used to describe multi-orbital materials and is expected to exhibit novel many-body phases in a complex phase diagram. By realizing and locally probing the SU (N ) FHM with ultracold atoms, we obtain model-free access to thermodynamic quantities. The measurement of the EoS and the local compressibility allows us to characterize the crossover from a compressible metal to an incompressible Mott insulator. We reach specific entropies above Néel order but below that of uncorrelated spins. Having access to the EoS of such a system represents an important step towards probing predicted novel SU (N ) phases.

  12. Doping Dependence of Superconducting Properties in the Hubbard-Holstein Model.

    NASA Astrophysics Data System (ADS)

    Hotta, T.; Takada, Y.

    1997-03-01

    The Hubbard-Holstein (HH) model describes the competition between the electron-electron short-range repulsion U_ee and the phonon-mediated attractive interaction -U_ph. The numerical result for the superconducting susceptibility \\chis in 2-site half-filled HH model reveals that superconductivity appears only in the competing region (U_ee ≈ 2U_ph).(Y. Takada, J. Phys. Soc. Jpn. 65), 1544 (1996). In this talk, further developments are reported on this superconductivity, especially the dependence on the electron density n, based on the expansion in terms of the transfer integral in the strong-coupling region. This expansion transforms the HH model into an effective Hamiltonian, H_eff, consisting of polaron hopping term, Heisenberg-like spin exchange interaction, and repulsive interaction between charges in nearest-neighbor sites. The numerical evaluation of \\chis in H_eff with larger sites shows that \\chis takes a maximum at half filling as a function of n. This distinctive feature agrees qualitatively well with the experimental results on n-dependence of the transition temperature in fullerides.(T. Yildirim et al)., Phys. Rev. Lett. 77, 167 (1996).

  13. Magnetic and pair correlations of the Hubbard model with next-nearest-neighbor hopping

    SciTech Connect

    Veilleux, A.F.; Dare, A.; Chen, L.; Vilk, Y.M.; Tremblay, A.S.

    1995-12-01

    A combination of analytical approaches and quantum Monte Carlo simulations is used to study both magnetic and pairing correlations for a version of the Hubbard model that includes second-neighbor hopping {ital t}{sup {prime}}={minus}0.35{ital t} as a model for high-temperature superconductors. Magnetic properties are analyzed using the two-particle self-consistent approach. The maximum in magnetic susceptibility as a function of doping appears both at finite {ital t}{sup {prime}} and at {ital t}{sup {prime}}=0 but for two totally different physical reasons. When {ital t}{sup {prime}}=0, it is induced by antiferromagnetic correlations while at {ital t}{sup {prime}}={minus}0.35{ital t} it is a band structure effect amplified by interactions. Finally, pairing fluctuations are compared with {ital T}-matrix results to disentangle the effects of van Hove singularity and of nesting on superconducting correlations. The addition of antiferromagnetic fluctuations increases slightly the {ital d}-wave superconducting correlations despite the presence of a van Hove singularity which tends to decrease them in the repulsive model. Some aspects of the phase diagram and some subtleties of finite-size scaling in Monte Carlo simulations, such as inverted finite-size dependence, are also discussed.

  14. Mott-insulator phase of the one-dimensional Bose-Hubbard model: A high-order perturbative study

    NASA Astrophysics Data System (ADS)

    Damski, Bogdan; Zakrzewski, Jakub

    2006-10-01

    The one-dimensional Bose-Hubbard model at a unit filling factor is studied by means of a very high-order symbolic perturbative expansion. Analytical expressions are derived for the ground-state quantities such as energy per site, variance of on-site occupation, and correlation functions: ⟨âj†âj+r⟩ and ⟨n̂jn̂j+r⟩ . These findings are compared to numerics and good agreement is found in the Mott insulator phase. Our results provide analytical approximations to important observables in the Mott phase, and are also of direct relevance to future experiments with ultracold atomic gases placed in optical lattices. We also discuss the symmetry of the Bose-Hubbard model associated with the sign change of the tunneling coupling.

  15. Non-Perturbative Many-Body Approach to the Hubbard Model and Single-Particle Pseudogap

    NASA Astrophysics Data System (ADS)

    Vilk, Y. M.; Tremblay, A.-M. S.

    1997-11-01

    A new approach to the single-band Hubbard model is described in the general context of many-body theories. It is based on enforcing conservation laws, the Pauli principle and a number of crucial sum-rules. More specifically, spin and charge susceptibilities are expressed, in a conserving approximation, as a function of two irreducible vertices whose values are found by imposing the local Pauli principle <~ngle n^2_\\uparrowrangle = <~ngle n_\\uparrowrangle as well as the local-moment sum-rule and consistency with the equations of motion in a local-field approximation. The Mermin-Wagner theorem in two dimensions is automatically satisfied. The effect of collective modes on single-particle properties is then obtained by a paramagnon-like formula that is consistent with the two-particle properties in the sense that the potential energy obtained from Tr Σ G is identical to that obtained using the fluctuation-dissipation theorem for susceptibilities. Since there is no Migdal theorem controlling the effect of spin and charge fluctuations on the self-energy, the required vertex corrections are included. It is shown that the theory is in quantitative agreement with Monte Carlo simulations for both single-particle and two-particle properties. The theory predicts a magnetic phase diagram where magnetic order persists away from half-filling but where ferromagnetism is completely suppressed. Both quantum-critical and renormalized-classical behavior can occur in certain parameter ranges. It is shown that in the renormalized classical regime, spin fluctuations lead to precursors of antiferromagnetic bands (shadow bands) and to the destruction of the Fermi-liquid quasiparticles in a wide temperature range above the zero-temperature phase transition. The upper critical dimension for this phenomenon is three. The analogous phenomenon of pairing pseudogap can occur in the attractive model in two dimensions when the pairing fluctuations become critical. Simple analytical expressions

  16. Superconductivity in the single-band Hubbard model: Mean-field treatment of slave-boson pairing

    SciTech Connect

    Kopp, T.; Seco, F.J.; Schiller, S.; Woelfle, P.

    1988-12-01

    We investigate the possibility of superconductivity in the large-U limit of the Hubbard model near half filling, using a slave-boson representation. The local constraint is treated in a novel way, incorporating short-range fluctuations in addition to the global constraint. We find slave-boson pairing and a superconducting extended s-wave phase at hole concentrations delta above 4% and below 32%.

  17. Accurate determination of the superfluid-insulator transition in the one-dimensional Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Zakrzewski, Jakub; Delande, Dominique

    2008-11-01

    The quantum phase transition point between the insulator and the superfluid phase at unit filling factor of the infinite one-dimensional Bose-Hubbard model is numerically computed with a high accuracy. The method uses the infinite system version of the time evolving block decimation algorithm, here tested in a challenging case. We provide also the accurate estimate of the phase transition point at double occupancy.

  18. Antiferromagnetic order driven chiral topological spin density waves on the repulsive Haldane-Hubbard model on square lattices

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Jie; Li, Ning; He, Jing; Kou, Su-Peng

    2016-03-01

    In this paper, based on mean-field approach and random-phase-approximation, we study the magnetic properties of the repulsive Haldane-Hubbard model on a square lattice. We find antiferromagnetic order driven topological spin density waves beyond Landau’s symmetry-breaking paradigm, for which the effective low energy physics is determined by Chern-Simons-Hopf gauge field theories with different K matrices.

  19. Ab initio modeling of 2D layered organohalide lead perovskites.

    PubMed

    Fraccarollo, Alberto; Cantatore, Valentina; Boschetto, Gabriele; Marchese, Leonardo; Cossi, Maurizio

    2016-04-28

    A number of 2D layered perovskites A2PbI4 and BPbI4, with A and B mono- and divalent ammonium and imidazolium cations, have been modeled with different theoretical methods. The periodic structures have been optimized (both in monoclinic and in triclinic systems, corresponding to eclipsed and staggered arrangements of the inorganic layers) at the DFT level, with hybrid functionals, Gaussian-type orbitals and dispersion energy corrections. With the same methods, the various contributions to the solid stabilization energy have been discussed, separating electrostatic and dispersion energies, organic-organic intralayer interactions and H-bonding effects, when applicable. Then the electronic band gaps have been computed with plane waves, at the DFT level with scalar and full relativistic potentials, and including the correlation energy through the GW approximation. Spin orbit coupling and GW effects have been combined in an additive scheme, validated by comparing the computed gap with well known experimental and theoretical results for a model system. Finally, various contributions to the computed band gaps have been discussed on some of the studied systems, by varying some geometrical parameters and by substituting one cation in another's place. PMID:27131557

  20. 2-D Inhomogeneous Modeling of the Solar CO Bands

    NASA Astrophysics Data System (ADS)

    Ayres, T. R.

    1996-05-01

    The recent discovery of off-limb emissions in the mid-IR ( ~ 5 mu m) vibration-rotation bands of solar carbon monoxide (CO) has sparked new interest in the formation of the molecular lines, and their ability to diagnose thermal conditions at high altitudes. The off-limb extensions of the strong CO lines indicate the penetration of cool material (T ~ 3500 K) several hundred kilometers into the otherwise hot (T ~ 6000 K) chromosphere. The origin of the cool gas, and its role in the thermal energy balance, remain controversial. The interpretation of the CO observations must rely heavily upon numerical modeling, in particular highly-inhomogeneous thermal structures arrayed in a 2-D scheme that can properly treat the geometry of the grazing rays at the solar limb. The radiation transport, itself, is especially simple for the CO off-limb emissions, because the fundamental bands form quite close to LTE (high collision rates; low spontaneous decay rates) and the background continuum is purely thermal as well (f--f transitions in H(-) and H). Thus, the geometrical aspects of the problem can be treated in considerably more detail than would be practical for typical NLTE scattering lines. I describe the recent modeling efforts, and the diagnostic potential of the CO bands for future observational studies of inhomogeneous surface structure on the Sun, and on other stars of late spectral type. This work was supported by NSF grant AST-9218063 to the University of Colorado.

  1. Ab initio modeling of 2D layered organohalide lead perovskites

    NASA Astrophysics Data System (ADS)

    Fraccarollo, Alberto; Cantatore, Valentina; Boschetto, Gabriele; Marchese, Leonardo; Cossi, Maurizio

    2016-04-01

    A number of 2D layered perovskites A2PbI4 and BPbI4, with A and B mono- and divalent ammonium and imidazolium cations, have been modeled with different theoretical methods. The periodic structures have been optimized (both in monoclinic and in triclinic systems, corresponding to eclipsed and staggered arrangements of the inorganic layers) at the DFT level, with hybrid functionals, Gaussian-type orbitals and dispersion energy corrections. With the same methods, the various contributions to the solid stabilization energy have been discussed, separating electrostatic and dispersion energies, organic-organic intralayer interactions and H-bonding effects, when applicable. Then the electronic band gaps have been computed with plane waves, at the DFT level with scalar and full relativistic potentials, and including the correlation energy through the GW approximation. Spin orbit coupling and GW effects have been combined in an additive scheme, validated by comparing the computed gap with well known experimental and theoretical results for a model system. Finally, various contributions to the computed band gaps have been discussed on some of the studied systems, by varying some geometrical parameters and by substituting one cation in another's place.

  2. Slow dynamics in a two-dimensional Anderson-Hubbard model

    NASA Astrophysics Data System (ADS)

    Bar Lev, Yevgeny; Reichman, David R.

    2016-02-01

    We study the real-time dynamics of a two-dimensional Anderson-Hubbard model using nonequilibrium self-consistent perturbation theory within the second-Born approximation. When compared with exact diagonalization performed on small clusters, we demonstrate that for strong disorder this technique approaches the exact result on all available timescales, while for intermediate disorder, in the vicinity of the many-body localization transition, it produces quantitatively accurate results up to nontrivial times. Our method allows for the treatment of system sizes inaccessible by any numerically exact method and for the complete elimination of finite-size effects for the times considered. We show that for a sufficiently strong disorder the system becomes nonergodic, while for intermediate disorder strengths and for all accessible timescales transport in the system is strictly subdiffusive. We argue that these results are incompatible with a simple percolation picture, but are consistent with the heuristic random resistor network model where subdiffusion may be observed for long times until a crossover to diffusion occurs. The prediction of slow finite-time dynamics in a two-dimensional interacting and disordered system can be directly verified in future cold-atoms experiments.

  3. Charge instabilities of the two-dimensional Hubbard model with attractive nearest neighbour interaction

    NASA Astrophysics Data System (ADS)

    Frésard, Raymond; Steffen, Kevin; Kopp, Thilo

    2016-03-01

    Attractive non-local interactions jointly with repulsive local interaction in a microscopic modelling of electronic Fermi liquids generate a competition between an enhancement of the static charge susceptibility–ultimately signalling charge instability and phase separation–and its correlation induced suppression. We analyse this scenario through the investigation of the extended Hubbard model on a two-dimensional square lattice, using the spin rotation invariant slave-boson representation of Kotliar and Ruckenstein. The quasiparticle density of states, the renormalised effective mass and the Landau parameter F s 0 are presented, whereby the positivity of F s 0 – 1 constitutes a criterion for stability. Van Hove singularities in the density of states support possible charge instabilities. A (negative) next-nearest neighbour hopping parameter t' shifts their positions and produces a tendency towards charge instability even for low filling whereas the t'-controlled particle-hole asymmetry of the correlation driven effective mass is small. A region of instability on account of the attractive interaction V is identified, either at half filling in the absence of strong electronic correlations or, in the case of large on-site interaction U, at densities far from half filling.

  4. Superconducting properties of the attractive Hubbard model: A slave-boson study

    SciTech Connect

    Bul Robaszkiewicz, S.

    1996-11-01

    The superfluid characteristics of the attractive Hubbard model are analyzed for any coupling {vert_bar}{ital U}{vert_bar} and arbitrary electron concentration (0{lt}{ital n}{lt}2) by means of the slave-boson mean-field method and also by the perturbative treatment of the strong-coupling limit. The slave boson method takes into account correlations of electrons and yields a reliable description of the crossover from BCS-type superconductivity to local pair (composite bosons) superconductivity with increasing {vert_bar}{ital U}{vert_bar}. The results for the ground state (the free energy, the gap in the excitation spectrum) and the electromagnetic characteristics (the critical magnetic field, the London penetration depth, the coherence length) are compared with those obtained by the Hartree-Fock approximation and by the self-consistent second-order perturbation theory in the weak-coupling limit as well as with those obtained using perturbational approaches in the strong-coupling limit. We show that the slave-boson method, in contrast to the Hartree-Fock approximation, gives credible results for all investigated quantities in the whole interaction range, interpolating smoothly between the BCS and local pair regimes. A comparison of theoretical predictions for our simple model with experimental data for various families of short-coherence-length superconductors suggests that the best agreement can be obtained for intermediate values of the local attraction. {copyright} {ital 1996 The American Physical Society.}

  5. Topological pumping in the one-dimensional Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Rossini, Davide; Gibertini, Marco; Giovannetti, Vittorio; Fazio, Rosario

    2013-02-01

    By means of time-dependent density-matrix renormalization-group calculations, we study topological quantum pumping in a strongly interacting system. The system under consideration is described by the Hamiltonian of a one-dimensional extended Bose-Hubbard model in the presence of a correlated hopping which breaks lattice inversion symmetry. This model has been predicted to support topological pumping [E. Berg, M. Levin, and E. Altman, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.110405 106, 110405 (2011)]. The pumped charge is quantized and of a topological nature. We provide a detailed analysis of the finite-size scaling behavior of the pumped charge and its deviations from the quantized value. Furthermore, we also analyze the nonadiabatic corrections due to the finite frequency of the modulation. We consider two configurations: a closed ring where the time dependence of the parameter induces a circulating current and a finite open-ended chain where particles are dragged from one edge to the opposite edge, due to the pumping mechanism induced by the bulk.

  6. Ground state of the one-dimensional half-filled Hubbard model

    NASA Astrophysics Data System (ADS)

    Chashchin, N. I.

    2016-07-01

    We investigate the ground state ( T = 0 K) of the one-dimensional symmetrical ( n = 1) Hubbard model formalized in terms of the system of integral equations, which we previously obtained using the method of the generating functional of Green's functions with the subsequent Legendre transformation. In a wide range of variations in the parameter of Coulomb interaction U, the following characteristics of the system have been calculated: the electron density of states, the electron band spectrum, the number of doubly occupied lattice sites, the localized magnetic moment, the correlator of the square of the longitudinal component of spin at a site,< S Z 2>, and the internal energy of the system. It has been shown that, for all U > 0, the model yields two solutions, i.e., an antiferromagnetic insulator and a paramagnetic insulator, in which there are no single-electron quasi-particles at the Fermi level. The energy of the paramagnetic solution in the region of U < 1.1 is considerably less than that of the antiferromagnetic solution for the case of U > 1.1, we have the opposite situation.

  7. Characterizing the three-orbital Hubbard model with determinant quantum Monte Carlo

    DOE PAGESBeta

    Kung, Y. F.; Chen, C. -C.; Wang, Yao; Huang, E. W.; Nowadnick, E. A.; Moritz, B.; Scalettar, R. T.; Johnston, S.; Devereaux, T. P.

    2016-04-29

    Here, we characterize the three-orbital Hubbard model using state-of-the-art determinant quantum Monte Carlo (DQMC) simulations with parameters relevant to the cuprate high-temperature superconductors. The simulations find that doped holes preferentially reside on oxygen orbitals and that the (π,π) antiferromagnetic ordering vector dominates in the vicinity of the undoped system, as known from experiments. The orbitally-resolved spectral functions agree well with photoemission spectroscopy studies and enable identification of orbital content in the bands. A comparison of DQMC results with exact diagonalization and cluster perturbation theory studies elucidates how these different numerical techniques complement one another to produce a more complete understandingmore » of the model and the cuprates. Interestingly, our DQMC simulations predict a charge-transfer gap that is significantly smaller than the direct (optical) gap measured in experiment. Most likely, it corresponds to the indirect gap that has recently been suggested to be on the order of 0.8 eV, and demonstrates the subtlety in identifying charge gaps.« less

  8. Topological order in 1D super-lattice Bose-Hubbard models

    NASA Astrophysics Data System (ADS)

    Fleischhauer, Michael; Grusdt, Fabian; Hoening, Michael

    2013-05-01

    After the discovery of topological insulators as a new state of matter and their consequent classification for free fermions, the question arises what kind of topological order can be supported by incompressible systems of interacting bosons. We consider a 1D super-lattice Hamiltonian with a non-trivial band structure (the Su-Schrieffer-Heeger model) and show that its Mott-insulating (MI) states can be classified by a quantized many-body winding number. This quantization is protected by sub-lattice and time-reversal symmetries, and it allows the implementation of a quantized cyclic pumping process (Thouless pump) in a simple super-lattice Bose-Hubbard model (BHM). For extended BHMs we discuss a connection of such a pump with the fractional quantum Hall effect. Furthermore we show that the quantization of the winding number leads to localized, protected edge states at sharp interfaces between topologically distinct MI phases which can be experimentally realized using Bose-Fermi mixtures in optical superlattices. DMRG simulations show that these edge states manifest themself either in localized density maxima or localized density minima, which can easily be detected. Supported by research center OPTIMAS and graduate school MAINZ.

  9. Study of the multi-orbital Hubbard model at finite temperature

    NASA Astrophysics Data System (ADS)

    Mukherjee, Anamitra; Dong, Shuai; Alvarez, Gonzalo; Dagotto, Elbio

    2014-03-01

    Research in pnictide superconductors have clearly established the need for the study of multi-orbital Hubbard models. With this motivation, here we apply a combination of the real-space Exact Diagonalization and Classical Monte Carlo (ED+MC) method, widely used in manganites, with the standard Hartree-Fock mean field (MF) theory to investigate the properties of multiorbital models as a function of temperature. In this approach the MF parameters are treated via a classical MC and the fermions moving in the MF background are solved by exact diagonalization. The temperature dependence of the dynamical spin susceptibility S(q --> , ω) , orbital resolved single particle spectral function A(k --> , ω) , optical conductivity, and real space charge/spin/orbital density maps are calculated at different dopings. These results are relevant in understanding the role of the multiple degrees of freedom in governing the magnetic and transport properties of the Fe based superconductor materials. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.

  10. Characterizing the three-orbital Hubbard model with determinant quantum Monte Carlo

    NASA Astrophysics Data System (ADS)

    Kung, Y. F.; Chen, C.-C.; Wang, Yao; Huang, E. W.; Nowadnick, E. A.; Moritz, B.; Scalettar, R. T.; Johnston, S.; Devereaux, T. P.

    2016-04-01

    We characterize the three-orbital Hubbard model using state-of-the-art determinant quantum Monte Carlo (DQMC) simulations with parameters relevant to the cuprate high-temperature superconductors. The simulations find that doped holes preferentially reside on oxygen orbitals and that the (π ,π ) antiferromagnetic ordering vector dominates in the vicinity of the undoped system, as known from experiments. The orbitally-resolved spectral functions agree well with photoemission spectroscopy studies and enable identification of orbital content in the bands. A comparison of DQMC results with exact diagonalization and cluster perturbation theory studies elucidates how these different numerical techniques complement one another to produce a more complete understanding of the model and the cuprates. Interestingly, our DQMC simulations predict a charge-transfer gap that is significantly smaller than the direct (optical) gap measured in experiment. Most likely, it corresponds to the indirect gap that has recently been suggested to be on the order of 0.8 eV, and demonstrates the subtlety in identifying charge gaps.

  11. Robust Supersolidity in the V1- V2 Extended Bose-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Greene, Nicole; Pixley, Jedediah

    2016-05-01

    Motivated by ultra-cold atomic gases with long-range interactions in an optical lattice we study the effects of the next-nearest neighbor interaction on the extended Bose-Hubbard model on a square lattice. Using the variational Gutzwiller approach with a four-site unit cell we determine the ground state phase diagrams as a function of the model parameters. We focus on the interplay of each interaction between the nearest neighbor (V1) , the next-nearest neighbor (V2) , and the onsite repulsion (U). We find various super-solid phases that can be described by one of the ordering wave-vectors (π, 0), (0, π) , and (π, π) . In the limits V1, V2 U we find phases reminiscent of the limit V2 = 0 but with a richer super solid structure. For V1

  12. Magnetic properties of the two-dimensional Hubbard model and normal-state T1 of high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Jackson, Francis; Vilk, Y. M.; Tremblay, A.-M. S.

    1997-03-01

    The spin-lattice relaxation time T1 and the uniform magnetic susceptibility of the two-dimensional Hubbard model is calculated in the paramagnetic state using the Two-Particle Self-Consistent approach. This approach (Y.M. Vilk, Liang Chen and A.-M.S. Tremblay, Phys. Rev. B Rapid Comm. 49), 13 267-13 270 (1994) has no adjustable parameter, satisfies the Mermin-Wagner theorem and is in agreement with Monte Carlo simulations. The best overall agreement with measurements in La_2-xSr_xCuO4 is obtained for the Hubbard model with repulsion U>6.5t and second-neighbor hopping t'=-0.28t. However, the agreement with experiment at low temperature is spoiled by the fact that the renormalized classical regime occurs over too wide a region of band fillings. The growth of fluctuations can be stopped by including phenomenologically the effect of disorder. Orthorhombicity is insufficient to appreciably decrease the size of the renormalized classical regime. It is argued that the simple one-band Hubbard model will give a better description of Cu T1 and susceptibility measurements in Nd_2-xCe_xCuO4 than in La_2-xSr_xCuO_4. (Two-Particle Self-Consistent approach) including single-particle properties

  13. Non-adiabatic exchange-correlation kernel for the non-equilibrium response of three-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Acharya, Shree Ram; Baral, Nisha; Turkowski, Volodymyr; Rahman, Talat S.

    2015-03-01

    We apply Dynamical Mean-Field Theory (DMFT) to calculate the non-adiabatic (frequency-dependent) exchange-correlation kernel for the three-dimensional Hubbard model. We analyze the dependence of the kernel on the electron doping, local Coulomb repulsion and frequency by using three different impurity solvers: Hubbard-I, Iterative Perturbation Theory (IPT) and Continuous-Time Quantum Monte Carlo (CT-QMC). From the calculated data, we obtain approximate analytical expressions for the kernel. We apply the exact numerical and analytical kernels to study the non-equilibrium response of the system for applied ultrafast laser pulse. We demonstrate that the non-adiabaticity of the kernel plays an important role in the system response; in particular, leading to new excited-states involved in the system dynamics. Work supported in part by DOE Grant No. DOE-DE-FG02-07ER46354.

  14. A 2D electrohydrodynamic model for electrorotation of fluid drops.

    PubMed

    Feng, James Q

    2002-02-01

    A theoretical analysis of spontaneous electrorotation of deformable fluid drops in a DC electric field is presented with a 2D electrohydrodynamic model. The fluids in the system are assumed to be leaky dielectric and Newtonian. If the rotating flow is dominant over the cellular convection type of electrohydrodynamic flow, closed-form solutions for drops of small deformations can be obtained. Because the governing equations are in general nonlinear even when drop deformations are ignored, the general solution for even undeformed drop takes a form of infinite series and can only be evaluated by numerical means. Both closed-form solutions for special cases and numerical solutions for more general cases are obtained here to describe steady-state field variables and first-order drop deformations. In a DC electric field of strength beyond the threshold value, spontaneous electrorotation of a drop is shown to occur when charge relaxation in the surrounding fluid is faster than the fluid inside the drop. With increasing the strength of the applied electric field from the threshold for onset of electrorotation, the axis of drop contraction deviates from from that of the applied electric field in the direction of the rotating flow with an angle increasing with the field strength. PMID:16290391

  15. 2D modeling of electromagnetic waves in cold plasmas

    SciTech Connect

    Crombé, K.; Van Eester, D.; Koch, R.; Kyrytsya, V.

    2014-02-12

    The consequences of sheath (rectified) electric fields, resulting from the different mobility of electrons and ions as a response to radio frequency (RF) fields, are a concern for RF antenna design as it can cause damage to antenna parts, limiters and other in-vessel components. As a first step to a more complete description, the usual cold plasma dielectric description has been adopted, and the density profile was assumed to be known as input. Ultimately, the relevant equations describing the wave-particle interaction both on the fast and slow timescale will need to be tackled but prior to doing so was felt as a necessity to get a feeling of the wave dynamics involved. Maxwell's equations are solved for a cold plasma in a 2D antenna box with strongly varying density profiles crossing also lower hybrid and ion-ion hybrid resonance layers. Numerical modelling quickly becomes demanding on computer power, since a fine grid spacing is required to capture the small wavelengths effects of strongly evanescent modes.

  16. Numerical modeling of seismogram envelopes in 2-D random media

    NASA Astrophysics Data System (ADS)

    Fehler, Michael

    2002-11-01

    Several portions of seismograms recorded from regional earthquakes cannot be easily explained as resulting from waves propagating along deterministic paths within the Earth. For example, seismic coda, which is the tail portion of the seismogram of an earthquake recorded at distances of less than 100 km, is considered as resulting from waves that are multiply scattered from random heterogeneities in the Earth's lithosphere. At greater distances, observations that the duration of the initial arriving wave packet is much longer than the source-time duration is explained as being due to multiple forward scattering along the path between the source and the receiver. To investigate these phenomena, we use a finite difference method to numerically simulate 2-D scalar-waves that propagate through random media characterized by a von Karman autocorrelation function. Such media are considered to be appropriate models for the random component of the structure of the Earth's lithosphere. We investigate the characteristics of the resulting wavefields and compare them with those of observed seismograms.

  17. VAM2D: Variably saturated analysis model in two dimensions

    SciTech Connect

    Huyakorn, P.S.; Kool, J.B.; Wu, Y.S. )

    1991-10-01

    This report documents a two-dimensional finite element model, VAM2D, developed to simulate water flow and solute transport in variably saturated porous media. Both flow and transport simulation can be handled concurrently or sequentially. The formulation of the governing equations and the numerical procedures used in the code are presented. The flow equation is approximated using the Galerkin finite element method. Nonlinear soil moisture characteristics and atmospheric boundary conditions (e.g., infiltration, evaporation and seepage face), are treated using Picard and Newton-Raphson iterations. Hysteresis effects and anisotropy in the unsaturated hydraulic conductivity can be taken into account if needed. The contaminant transport simulation can account for advection, hydrodynamic dispersion, linear equilibrium sorption, and first-order degradation. Transport of a single component or a multi-component decay chain can be handled. The transport equation is approximated using an upstream weighted residual method. Several test problems are presented to verify the code and demonstrate its utility. These problems range from simple one-dimensional to complex two-dimensional and axisymmetric problems. This document has been produced as a user's manual. It contains detailed information on the code structure along with instructions for input data preparation and sample input and printed output for selected test problems. Also included are instructions for job set up and restarting procedures. 44 refs., 54 figs., 24 tabs.

  18. Doping evolution of spin and charge excitations in the Hubbard model

    SciTech Connect

    Kung, Y. F.; Nowadnick, E. A.; Jia, C. J.; Johnston, S.; Moritz, B.; Scalettar, R. T.; Devereaux, T. P.

    2015-11-05

    We shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, examining the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achieved in the cuprates). Ultimately, these fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.

  19. Ab Initio Dynamical Correlations from Auxiliary-field quantum Monte Carlo: applications in the Hubbard model

    NASA Astrophysics Data System (ADS)

    Vitali, Ettore; Shi, Hao; Qin, Mingpu; Zhang, Shiwei

    The possibility of calculating dynamical correlation functions from first principles provides a unique opportunity to explore the manifold of the excited states of a quantum many-body system. Such calculations allow us to predict interesting physical properties like spectral functions, excitation spectra and charge and spin gaps, which are more difficult to access from usual equilibrium calculations. We address the ab-initio calculation of dynamical Green functions and two-body correlation functions in the Auxiliary-field Quantum Monte Carlo method, using the two-dimensional Hubbard model as an example. When the sign problem is not present, an unbiased estimation of imaginary time correlation functions is obtained. We discuss in detail the complexity and the stability of the calculations. Moreover, we propose a new approach which is expected to be very useful when dealing with dilute systems, e.g. for cold gases, allowing calculations with a very favorable complexity in the system size. Supported by NSF, DOE SciDAC, and Simons Foundation.

  20. Superconducting fluctuations in the normal state of the two-dimensional Hubbard model.

    PubMed

    Chen, Xi; LeBlanc, J P F; Gull, Emanuel

    2015-09-11

    We compute the two-particle quantities relevant for superconducting correlations in the two-dimensional Hubbard model within the dynamical cluster approximation. In the normal state we identify the parameter regime in density, interaction, and second-nearest-neighbor hopping strength that maximizes the d_{x^{2}-y^{2}} superconducting transition temperature. We find in all cases that the optimal transition temperature occurs at intermediate coupling strength, and is suppressed at strong and weak interaction strengths. Similarly, superconducting fluctuations are strongest at intermediate doping and suppressed towards large doping and half filling. We find a change in sign of the vertex contributions to d_{xy} superconductivity from repulsive near half filling to attractive at large doping. p-wave superconductivity is not found at the parameters we study, and s-wave contributions are always repulsive. For negative second-nearest-neighbor hopping the optimal transition temperature shifts towards the electron-doped side in opposition to the van Hove singularity, which moves towards hole doping. We surmise that an increase of the local interaction of the electron-doped compounds would increase T_{c}. PMID:26406843

  1. Doping evolution of spin and charge excitations in the Hubbard model

    DOE PAGESBeta

    Kung, Y. F.; Nowadnick, E. A.; Jia, C. J.; Johnston, S.; Moritz, B.; Scalettar, R. T.; Devereaux, T. P.

    2015-11-05

    We shed light on how electronic correlations vary across the phase diagram of the cuprate superconductors, examining the doping evolution of spin and charge excitations in the single-band Hubbard model using determinant quantum Monte Carlo (DQMC). In the single-particle response, we observe that the effects of correlations weaken rapidly with doping, such that one may expect the random phase approximation (RPA) to provide an adequate description of the two-particle response. In contrast, when compared to RPA, we find that significant residual correlations in the two-particle excitations persist up to 40% hole and 15% electron doping (the range of dopings achievedmore » in the cuprates). Ultimately, these fundamental differences between the doping evolution of single- and multi-particle renormalizations show that conclusions drawn from single-particle processes cannot necessarily be applied to multi-particle excitations. Eventually, the system smoothly transitions via a momentum-dependent crossover into a weakly correlated metallic state where the spin and charge excitation spectra exhibit similar behavior and where RPA provides an adequate description.« less

  2. Occupation number and fluctuations in the finite-temperature Bose-Hubbard model

    SciTech Connect

    Plimak, L.I.; Fleischhauer, M.; Olsen, M.K.

    2004-07-01

    We study the occupation numbers and number fluctuations of ultracold atoms in deep optical lattices for finite-temperatures within the Bose-Hubbard model. Simple analytical expressions for the mean occupation number and number fluctuations are obtained in the weak-hopping regime using an interpolation between results from different perturbation approaches in the Mott-insulator and superfluid phases. With this approach the magnitude of number fluctuations under a wide range of experimental conditions can be estimated and the properties of the finite-temperature phase diagram can be studied. These analytical results are compared to exact one-dimensional numerical calculations using a finite temperature variant of the density-matrix renormalization group (DMRG) method and found to have a high degree of accuracy. We find very good agreement, also in the crossover 'thermal' region. We also analyze the influence of finite temperature on the behavior of the system in the vicinity of the zero-temperature phase transition, in one, two, and three dimensions.

  3. Monte Carlo simulations of two-dimensional Hubbard models with string bond tensor-network states

    NASA Astrophysics Data System (ADS)

    Song, Jeong-Pil; Wee, Daehyun; Clay, R. T.

    2015-03-01

    We study charge- and spin-ordered states in the two-dimensional extended Hubbard model on a triangular lattice at 1/3 filling. While the nearest-neighbor Coulomb repulsion V induces charge-ordered states, the competition between on-site U and nearest-neighbor V interactions lead to quantum phase transitions to an antiferromagnetic spin-ordered phase with honeycomb charge order. In order to avoid the fermion sign problem and handle frustrations here we use quantum Monte Carlo methods with the string-bond tensor network ansatz for fermionic systems in two dimensions. We determine the phase boundaries of the several spin- and charge-ordered states and show a phase diagram in the on-site U and the nearest-neighbor V plane. The numerical accuracy of the method is compared with exact diagonalization results in terms of the size of matrices D. We also test the use of lattice symmetries to improve the string-bond ansatz. Work at Mississippi State University was supported by the US Department of Energy grant DE-FG02-06ER46315.

  4. Specific heat of the two-dimensional Hubbard model at weak to intermediate coupling.

    NASA Astrophysics Data System (ADS)

    Roy, S.; Tremblay, A.-M. S.

    2004-03-01

    We show how, in the weak to intermediate coupling regime, the thermodynamics of the two-dimensional t-t'-U Hubbard model can be obtained from the Two-Particle Self-Consistent approach.[1] The results agree with Quantum Monte Carlo simulations. We then compute the specific heat and the double occupancy. Close to half-filling, the rapid decrease of double occupancy with decreasing temperature signals a growing antiferromagnetic correlation length and a concomitant pseudogap. The decrease in double occupancy corresponds to an increase in the local magnetic moment and to a decrease in potential energy. These phenomena manifest themselves as a low temperature peak in the specific heat. The high-temperature peak in the specific heat arises from the kinetic energy and is much less sensitive to antiferromagnetic correlations. We obtain the domain, in the temperature-doping plane, where a pseudogap appears and we study the evolution of this domain with U and t'. With a large enough frustration t', there is a complete suppression of the pseudogap. [1] Y.M. Vilk and A.-M.S. Tremblay, J. Phys. I France 7, 1309 (1997).

  5. The Hubbard model description of the TCNQ related singular features in photoemission of TTF-TCNQ

    NASA Astrophysics Data System (ADS)

    Carmelo, J. M. P.; Penc, K.; Sacramento, P. D.; Sing, M.; Claessen, R.

    2006-06-01

    In this paper we use the pseudofermion dynamical theory (PDT) to study the singular spectral features due to one-electron removal within the one-dimensional Hubbard model. The PDT reveals that in the whole (k, ω)-plane such features are of the power-law type and correspond to well defined lines of three types: charge singular branch lines, spin singular branch lines and border lines. One of our goals is the study of the momentum and energy dependence of the distribution of the spectral weight in the vicinity of such lines. We find that the charge and spin branch lines correspond to the main tetracyanoquinodimethane (TCNQ) peak dispersions observed with angle-resolved photoelectron spectroscopy in the quasi-1D organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). Our expressions refer to all values of the electronic density and on-site repulsion U. The weight distribution in the vicinity of the singular spectral lines is fully controlled by the overall pseudofermion phase shifts. Moreover, the shape of these lines is determined by the bare-momentum dependence of the pseudofermion energy dispersions.

  6. Phase transitions of the ionic Hubbard model on the honeycomb lattice.

    PubMed

    Lin, Heng-Fu; Liu, Hai-Di; Tao, Hong-Shuai; Liu, Wu-Ming

    2015-01-01

    Many-body problem on the honeycomb lattice systems have been the subject of considerable experimental and theoretical interest. Here we investigate the phase transitions of the ionic Hubbard model on the honeycomb lattice with an alternate ionic potential for the half filling and hole doping cases by means of cellular dynamical mean field theory combining with continue time quantum Monte Carlo as an impurity solver. At half filling, as the increase of the interaction at a fixed ionic potential, we find the single particle gap decreases firstly, reaches a minimum at a critical interaction Uc, then increases upturn. At Uc, there is a band insulator to Mott insulator transition accompanying with the presence of the antiferromagnetic order. Away from half filing, the system shows three phases for the different values of hole density and interaction, paramagnetic metal, antiferromagnetic metal and ferromagnetic metal. Further, we present the staggered particle number, the double occupancy, the staggered magnetization, the uniform magnetization and the single particle spectral properties, which exhibit characteristic features for those phases. PMID:25961417

  7. Orbital nematic order and interplay with magnetism in the two-orbital Hubbard model.

    PubMed

    Wang, Zhentao; Nevidomskyy, Andriy H

    2015-06-10

    Motivated by the recent angle-resolved photoemission spectroscopy (ARPES) on FeSe and iron pnictide families of iron-based superconductors, we have studied the orbital nematic order and its interplay with antiferromagnetism within the two-orbital Hubbard model. We used random phase approximation (RPA) to calculate the dependence of the orbital and magnetic susceptibilities on the strength of interactions and electron density (doping). To account for strong electron correlations not captured by RPA, we further employed non-perturbative variational cluster approximation (VCA) capable of capturing symmetry broken magnetic and orbitally ordered phases. Both approaches show that the electron and hole doping affect the two orders differently. While hole doping tends to suppress both magnetism and orbital ordering, the electron doping suppresses magnetism faster. Crucially, we find a realistic parameter regime for moderate electron doping that stabilizes orbital nematicity in the absence of long-range antiferromagnetic order. This is reminiscent of the non-magnetic orbital nematic phase observed recently in FeSe and a number of iron pnictide materials and raises the possibility that at least in some cases, the observed electronic nematicity may be primarily due to orbital rather than magnetic fluctuations. PMID:25988222

  8. Correlated properties of the doped Hubbard model on a honeycomb lattice

    NASA Astrophysics Data System (ADS)

    Ma, Tianxing; Zhang, Lufeng; Lin, Hai-Qing

    Low doped graphene has a finite density of state, while heavily doped graphene have a Van Hove sigularity in the density of states, in combination with pronounced antiferromagnetic spin fluctuations close to half filling, and strong ferromagnetic correlation as doping is bellow the location of Van Hove singularity, which may lead to different unconventional superconductivity. We performed a systematic quantum Monte Carlo study of the pairing correlation in the Hubbard model on a honeycomb lattice. Close to half filling, we find that pairing with d +id symmetry dominates over pairing with extended-s symmetry. When the next-nearest-neighbor t' is larger than t/6, the single-particle spectrum is featured by the continuously distributed Van Hove saddle points at the band bottom, where the density of states diverges in a power law. We investigate possible unconventional superconductivity in such systems with the Fermi level close to the band bottom by employing both random-phase-approximation and determinant quantum Monte Carlo approaches. Our study reveals a possible triplet p +ip superconductivity with appropriate interactions in low-filled graphene. We also explore the effect of the disorder and spin-orbit coupling on the magnetic correlation in doped graphene.

  9. Quantum bright solitons in the Bose-Hubbard model with site-dependent repulsive interactions

    NASA Astrophysics Data System (ADS)

    Barbiero, L.; Malomed, B. A.; Salasnich, L.

    2014-12-01

    We introduce a one-dimensional spatially inhomogeneous Bose-Hubbard model (BHM) with the strength of the onsite repulsive interactions growing, with the discrete coordinate zj, as | zj|α with α >0 . Recently, the analysis of the mean-field (MF) counterpart of this system has demonstrated self-trapping of robust unstaggered discrete solitons, under the condition α >1 . By using the numerically implemented method of the density matrix renormalization group, we demonstrate that, in a certain range of the interaction, the BHM also features self-trapping of the ground state into a soliton-like configuration, at α >1 , and remains weakly localized at α <1 . An essential quantum feature found in the BHM is a residual quasi-constant density of the background surrounding the soliton-like peak in the ground state, while in the MF limit the finite-density background is absent. Very strong onsite repulsion eventually destroys soliton-like states, driving the system, at integer densities, into the Mott phase with a spatially uniform density.

  10. Coexistence of Pairing Tendencies and Ferromagnetism in a Doped Two-Orbital Hubbard Model on Two-Leg Ladders

    SciTech Connect

    Xavier, J. C.; Alvarez, Gonzalo; Moreo, Adriana; Dagotto, Elbio R

    2010-01-01

    Using the Density Matrix Renormalization Group and two-leg ladders, we investigate an electronic two-orbital Hubbard model including plaquette-diagonal hopping amplitudes. Our goal is to search for regimes where charges added to the undoped state form pairs, presumably a precursor of a superconducting state. For the electronic density {rho}=2, i.e., the undoped limit, our investigations show a robust ({pi},0) antiferromagnetic ground state, as in previous investigations. Doping away from {rho}=2 and for large values of the Hund coupling J, a ferromagnetic region is found to be stable. Moreover, when the interorbital on-site Hubbard repulsion is smaller than the Hund coupling, i.e., for U' < J in the standard notation of multiorbital Hubbard models, our results indicate the coexistence of pairing tendencies and ferromagnetism close to {rho}=2. These results are compatible with previous investigations using one-dimensional systems. Although further research is needed to clarify if the range of couplings used here is of relevance for real materials, such as superconducting heavy fermions or pnictides, our theoretical results address a possible mechanism for pairing that may be active in the presence of short-range ferromagnetic fluctuations.

  11. Hückel-Hubbard-Ohno modeling of π-bonds in ethene and ethyne with application to trans-polyacetylene.

    PubMed

    Timár, Máté; Barcza, Gergely; Gebhard, Florian; Veis, Libor; Legeza, Örs

    2016-07-28

    Quantum chemistry calculations provide the potential energy between two carbon atoms in ethane (H3C-CH3), ethene (H2C[double bond, length as m-dash]CH2), and ethyne (HC[triple bond, length as m-dash]CH) as a function of the atomic distance. Based on the energy function for the σ-bond in ethane, Vσ(r), we use the Hückel model with Hubbard-Ohno interaction for the π electrons to describe the energies Vσπ(r) and Vσππ(r) for the σπ double bond in ethene and the σππ triple bond in ethyne, respectively. The fit of the force functions shows that the electron transfer matrix element and the Peierls coupling can be estimated with some precision whereas the Hubbard-Ohno parameters are insignificant at the distances under consideration. We apply the Hückel-Hubbard-Ohno model to describe the bond lengths and the energies of elementary electronic excitations of trans-polyacetylene, (CH)n, whereby we adjust the σ-bond potential for conjugated polymers. PMID:27348188

  12. Predicting Fracture Using 2D Finite Element Modeling

    PubMed Central

    MacNeil, J.A.M.; Adachi, J.D; Goltzman, D; Josse, R.G; Kovacs, C.S; Prior, J.C; Olszynski, W; Davison, K.S.; Kaiser, S.M

    2013-01-01

    A decrease in bone density at the hip or spine has been shown to increase the risk of fracture. A limitation of the bone mineral density (BMD) measurement is that it provides only a measure of a bone samples average density when projected onto a 2D surface. Effectively, what determines bone fracture is whether an applied load exceeds ultimate strength, with both bone tissue material properties (can be approximated through bone density), and geometry playing a role. The goal of this project was to use bone geometry and BMD obtained from radiographs and DXA measurements respectively to estimate fracture risk, using a two-dimensional finite element model (FEM) of the sagittal plane of lumbar vertebrae. The Canadian Multicenter Osteoporosis Study (CaMos) data was used for this study. There were 4194 men and women over the age of 50 years, with 786 having fractures. Each subject had BMD testing and radiographs of their lumbar vertebrae. A single two dimensional FEM of the first to fourth lumbar vertebra was automatically generated for each subject. Bone tissue stiffness was assigned based on the BMD of the individual vertebrae, and adjusted for patient age. Axial compression boundary conditions were applied with a force proportional to body mass. The resulting overall strain from the applied force was found. Men and women were analyzed separately. At baseline, the sensitivity of BMD to predict fragility fractures in women and men was 3.77 % and 0.86 %, while the sensitivity of FEM to predict fragility fractures for women and men was 10.8 % and 11.3 %. The FEM ROC curve demonstrated better performance compared to BMD. The relative risk of being considered at high fracture risk using FEM at baseline, was a better predictor of 5 year incident fragility fracture risk compared to BMD. PMID:21959170

  13. A 2-D modeling contribution to river training design

    NASA Astrophysics Data System (ADS)

    Anselmo, V.; Coccato, M.; Frank, E.; Guiot, E.

    2003-04-01

    In the last ten years, two major floods (1994 and 2000) occurred in North-western Italy and a few questions arose about the hydraulic behavior of the streams as well about the choice and design of protection works. The River Po Authority is oriented to assign "design flows" in selected cross sections of the main rivers, as a design constraint to land management and river training in the upstream areas. Since the region has been fully developed in the last century and somewhere it is overcrowded, space for spreading flood flows is strongly reduced, while large partially developed areas are prone to flooding and residents ask for being protected. A first question regards the contribution to flood peak reduction of the still existing flood prone undeveloped areas beside the main channels, and a second question is about the best way to improve such a behavior. A 2-D unsteady model (Sobek, originated by Delft Hydraulics) was applied to a 25 km reach of the upper River Po. The effects of major floods was investigated, proving that the reduction of the peak flow is minor mainly because of the rather high slope (0.0015) and of the flood volume (500·106 m3). Aiming to enhance the role of the flooded areas, a few types of river training schemes were checked, with particular attention to the so called "Po system". Depth and extension of compartments are the main variables. Results are interesting, but must be evaluated in front of the cost-benefit analysis. The investigation is being extended to more steep stream reaches (up to 0.01), which are representative of the main upper Po tributaries.

  14. A 2D simulation model for urban flood management

    NASA Astrophysics Data System (ADS)

    Price, Roland; van der Wielen, Jonathan; Velickov, Slavco; Galvao, Diogo

    2014-05-01

    The European Floods Directive, which came into force on 26 November 2007, requires member states to assess all their water courses and coast lines for risk of flooding, to map flood extents and assets and humans at risk, and to take adequate and coordinated measures to reduce the flood risk in consultation with the public. Flood Risk Management Plans are to be in place by 2015. There are a number of reasons for the promotion of this Directive, not least because there has been much urban and other infrastructural development in flood plains, which puts many at risk of flooding along with vital societal assets. In addition there is growing awareness that the changing climate appears to be inducing more frequent extremes of rainfall with a consequent increases in the frequency of flooding. Thirdly, the growing urban populations in Europe, and especially in the developing countries, means that more people are being put at risk from a greater frequency of urban flooding in particular. There are urgent needs therefore to assess flood risk accurately and consistently, to reduce this risk where it is important to do so or where the benefit is greater than the damage cost, to improve flood forecasting and warning, to provide where necessary (and possible) flood insurance cover, and to involve all stakeholders in decision making affecting flood protection and flood risk management plans. Key data for assessing risk are water levels achieved or forecasted during a flood. Such levels should of course be monitored, but they also need to be predicted, whether for design or simulation. A 2D simulation model (PriceXD) solving the shallow water wave equations is presented specifically for determining flood risk, assessing flood defense schemes and generating flood forecasts and warnings. The simulation model is required to have a number of important properties: -Solve the full shallow water wave equations using a range of possible solutions; -Automatically adjust the time step and

  15. Phase diagram of the Bose-Hubbard model with T{sub 3} symmetry

    SciTech Connect

    Rizzi, Matteo; Fazio, Rosario; Cataudella, Vittorio

    2006-04-01

    We study the quantum phase transition between the insulating and the globally coherent superfluid phases in the Bose-Hubbard model with T{sub 3} structure, the 'dice lattice'. Even in the absence of any frustration the superfluid phase is characterized by modulation of the order parameter on the different sublattices of the T{sub 3} structure. The zero-temperature critical point as a function of magnetic field shows the characteristic 'butterfly' form. At full frustration the superfluid region is strongly suppressed. In addition, due to the existence of the Aharonov-Bohm cages at f=1/2, we find some evidence for the existence of an intermediate insulating phase characterized by a zero superfluid stiffness but finite compressibility. In this intermediate phase bosons are localized due to the external frustration and the topology of the T{sub 3} lattice. We name this new phase the Aharonov-Bohm insulator. In the presence of charge frustration the phase diagram acquires the typical lobe structure. The form and hierarchy of the Mott insulating states with fractional fillings are dictated by the particular topology of the T{sub 3} lattice. The results presented were obtained by a variety of analytical methods: mean-field and variational techniques to approach the phase boundary from the superconducting side and a strongly coupled expansion appropriate for the Mott insulating region. In addition we performed quantum Monte Carlo simulations of the corresponding (2+1)-dimensional XY model to corroborate the analytical calculations with a more accurate quantitative analysis. We finally discuss experimental realization of the T{sub 3} lattice both with optical lattices and with Josephson junction arrays.

  16. Modeling ecohydrologic processes at Hubbard Brook: Initial results for Watershed 6 stream discharge and chemistry

    EPA Science Inventory

    The Hubbard Brook Long Term Ecological Research site has produced some of the most extensive and long-running databases on the hydrology, biology and chemistry of forest ecosystem responses to climate and forest harvest. We used these long-term databases to calibrate and apply G...

  17. Band-Renormalization Effects and Predominant Antiferromagnetic Order in Two-Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Sato, Ryo; Yokoyama, Hisatoshi

    2016-07-01

    Band renormalization effects (BRE) are comprehensively studied for a mixed state of dx2 - y2-wave superconducting (d-SC) and antiferromagnetic (AF) orders, in addition to simple d-SC, AF, and normal (paramagnetic) states, by applying a variational Monte Carlo method to a two-dimensional Hubbard (t-t'-U) model. In a weakly correlated regime (U/t ≲ 6), BRE are negligible on all the states studied. As previously shown, the effective band of d-SC is greatly renormalized but the modifications of physical quantities, including energy improvement, are negligible. In contrast, BRE on the AF state considerably affects various features of the system. Because the energy is markedly improved for t'/t < 0, the AF state occupies almost the whole underdoped regime in phase diagrams. A doped metallic AF state undergoes a kind of Lifshitz transition at t' = t'{L} ˜ - 0.05t as t'/t varies, irrespective of the values of U/t and δ (doping rate). Pocket Fermi surfaces arise around (π ,0) [(π /2,π /2)] for t' > t'{L} [t' < t'{L}], which corresponds to the electron-hole asymmetry observed in angle-resolved photoemission spectroscopy (ARPES) spectra. The coexistent state of the two orders is possible basically for t' > t'{L}, because the existence of Fermi surfaces near (π ,0) is a requisite for the electron scattering of {q} = (π ,π ). Actually, the coexistent state appears mainly for t'{L}/t < t'/t ≲ 0.2 in the mixed state. Nevertheless, the AF and coexisting states become unstable toward phase separation for - 0.05 ≲ t'/t ≲ 0.2 but become stable at other values of t'/t owing to the energy reduction by the diagonal hopping of doped holes. We show that this instability does not directly correlate with the strength of d-SC.

  18. A 2D simulation model for urban flood management

    NASA Astrophysics Data System (ADS)

    Price, Roland; van der Wielen, Jonathan; Velickov, Slavco; Galvao, Diogo

    2014-05-01

    The European Floods Directive, which came into force on 26 November 2007, requires member states to assess all their water courses and coast lines for risk of flooding, to map flood extents and assets and humans at risk, and to take adequate and coordinated measures to reduce the flood risk in consultation with the public. Flood Risk Management Plans are to be in place by 2015. There are a number of reasons for the promotion of this Directive, not least because there has been much urban and other infrastructural development in flood plains, which puts many at risk of flooding along with vital societal assets. In addition there is growing awareness that the changing climate appears to be inducing more frequent extremes of rainfall with a consequent increases in the frequency of flooding. Thirdly, the growing urban populations in Europe, and especially in the developing countries, means that more people are being put at risk from a greater frequency of urban flooding in particular. There are urgent needs therefore to assess flood risk accurately and consistently, to reduce this risk where it is important to do so or where the benefit is greater than the damage cost, to improve flood forecasting and warning, to provide where necessary (and possible) flood insurance cover, and to involve all stakeholders in decision making affecting flood protection and flood risk management plans. Key data for assessing risk are water levels achieved or forecasted during a flood. Such levels should of course be monitored, but they also need to be predicted, whether for design or simulation. A 2D simulation model (PriceXD) solving the shallow water wave equations is presented specifically for determining flood risk, assessing flood defense schemes and generating flood forecasts and warnings. The simulation model is required to have a number of important properties: -Solve the full shallow water wave equations using a range of possible solutions; -Automatically adjust the time step and

  19. A distance-dependent parameterization of the extended Hubbard model for conjugated and aromatic hydrocarbons derived from stretched ethene

    NASA Astrophysics Data System (ADS)

    Schmalz, Thomas G.; Serrano-Andrés, Luis; Sauri, Vicenta; Merchán, Manuela; Oliva, Josep M.

    2011-11-01

    The Hubbard model, which is widely used in physics but is mostly unfamiliar to chemists, provides an attractive yet simple model for chemistry beyond the self consistent field molecular orbital approximation. The Hubbard model adds an effective electron-electron repulsion when two electrons occupy the same atomic orbital to the familiar Hückel Hamiltonian. Thus it breaks the degeneracy between excited singlet and triplet states and allows an explicit treatment of electron correlation. We show how to evaluate the parameters of the model from high-level ab initio calculations on two-atom fragments and then to transfer the parameters to large molecules and polymers where accurate ab initio calculations are difficult or impossible. The recently developed MS-RASPT2 method is used to generate accurate potential energy curves for ethene as a function of carbon-carbon bond length, which are used to parameterize the model for conjugated hydrocarbons. Test applications to several conjugated/aromatic molecules show that even though the model is very simple, it is capable of reasonably accurate predictions for bond lengths, and predicts molecular excitation energies in reasonable agreement with those from the MS-RASPT2 method.

  20. Properties of the one-dimensional Bose-Hubbard model from a high-order perturbative expansion

    NASA Astrophysics Data System (ADS)

    Damski, Bogdan; Zakrzewski, Jakub

    2015-12-01

    We employ a high-order perturbative expansion to characterize the ground state of the Mott phase of the one-dimensional Bose-Hubbard model. We compute for different integer filling factors the energy per lattice site, the two-point and density-density correlations, and expectation values of powers of the on-site number operator determining the local atom number fluctuations (variance, skewness, kurtosis). We compare these expansions to numerical simulations of the infinite-size system to determine their range of applicability. We also discuss a new sum rule for the density-density correlations that can be used in both equilibrium and non-equilibrium systems.

  1. Spectral function of the two-dimensional Hubbard model: A density matrix renormalization group plus cluster perturbation theory study

    NASA Astrophysics Data System (ADS)

    Yang, Chun; Feiguin, Adrian E.

    2016-02-01

    We study the spectral function of the two-dimensional Hubbard model using cluster perturbation theory, and a density matrix renormalization group as a cluster solver. We reconstruct the two-dimensional dispersion at and away from half-filling using 2 ×L ladders, with L up to 80 sites, yielding results with unprecedented resolution in excellent agreement with quantum Monte Carlo. The main features of the spectrum can be described with a mean-field dispersion, with kinks and pseudogap traced back to scattering between spin and charge degrees of freedom.

  2. Screening and nonlocal correlations in the extended Hubbard model from self-consistent combined GW and dynamical mean field theory

    NASA Astrophysics Data System (ADS)

    Ayral, Thomas; Biermann, Silke; Werner, Philipp

    2013-03-01

    We describe a recent implementation of the combined GW and dynamical mean field method (GW+DMFT) for the two-dimensional Hubbard model with onsite and nearest-neighbor repulsion. We clarify the relation of the GW+DMFT scheme to alternative approaches in the literature, and discuss the corresponding approximations to the free-energy functional of the model. Furthermore, we describe a numerically exact technique for the solution of the GW+DMFT equations, namely, the hybridization expansion continuous-time algorithm for impurity models with retarded interactions. We compute the low-temperature phase diagram of the half-filled extended Hubbard model, addressing the metal-insulator transition at small intersite interactions and the transition to a charge-ordered state for stronger intersite repulsions. GW+DMFT introduces a nontrivial momentum dependence into the many-body self-energy and polarization. We find that the charge fluctuations included in the present approach have a larger impact on the latter than on the former. Finally, within the GW+DMFT framework, as in extended DMFT, the intersite repulsion translates into a frequency dependence of the local effective interaction. We analyze this dependence and show how it affects the local spectral function.

  3. The Implementation of C-ID, R2D2 Model on Learning Reading Comprehension

    ERIC Educational Resources Information Center

    Rayanto, Yudi Hari; Rusmawan, Putu Ngurah

    2016-01-01

    The purposes of this research are to find out, (1) whether C-ID, R2D2 model is effective to be implemented on learning Reading comprehension, (2) college students' activity during the implementation of C-ID, R2D2 model on learning Reading comprehension, and 3) college students' learning achievement during the implementation of C-ID, R2D2 model on…

  4. Interplay between electron-phonon interaction and Hubbard repulsion: Bipolaron formation

    SciTech Connect

    Nath, S.; Mondal, N. S.; Ghosh, N. K.

    2015-06-24

    In the weak coupling limit, the 2D Hubbard model extended by on-site (local) and inter-site (long range) electron-phonon (EP) interaction has been investigated within Lanczos method of exact diagonalization (ED). On-site (S0) bipolaron formation has been favored by on-site EP interaction induced effective attraction between electrons. But, inter-site phonon mediated interaction between electrons helps to form both S0 and neighboring site (S1) bipolaron. It is further observed that both types of bipolaron formation are suppressed by on-site Hubbard repulsion.

  5. Le modele de Hubbard bidimensionnel a faible couplage: Thermodynamique et phenomenes critiques

    NASA Astrophysics Data System (ADS)

    Roy, Sebastien

    Une etude systematique du modele de Hubbard en deux dimensions a faible couplage a l'aide de la theorie Auto-Coherente a Deux Particules (ACDP) dans le diagramme temperature-dopage-interaction-sauts permet de mettre en evidence l'influence des fluctuations magnetiques sur les proprietes thermodynamiques du systeme electronique sur reseau. Le regime classique renormalise a temperature finie pres du dopage nul est marque par la grandeur de la longueur de correlation de spin comparee a la longueur thermique de de Broglie et est caracterisee par un accroissement drastique de la longueur de correlation de spin. Cette croissance exponentielle a dopage nul marque la presence d'un pic de chaleur specifique en fonction de la temperature a basse temperature. Une temperature de crossover est alors associee a la temperature a laquelle la longueur de correlation de spin est egale a la longueur thermique de de Broglie. C'est a cette temperature caracteristique, ou est observee l'ouverture du pseudogap dans le poids spectral, que se situe le maximum du pic de chaleur specifique. La presence de ce pic a des consequences sur l'evolution du potentiel chimique avec le dopage lorsque l'uniformite thermodynamique est respectee. Les contraintes imposees par les lois de la thermodynamique font en sorte que l'evolution du potentiel chimique avec le dopage est non triviale. On demontre entre autres que le potentiel chimique est proportionnel a la double occupation qui est reliee au moment local. Par ailleurs, une derivation de la fonction de mise a l'echelle de la susceptibilite de spin a frequence nulle au voisinage d'un point critique marque sans equivoque la presence d'un point critique quantique en dopage pour une valeur donnee de l'interaction. Ce point critique, associe a une transition de phase magnetique en fonction du dopage a temperature nulle, induit un comportement non trivial sur les proprietes physiques du systeme a temperature finie. L'approche quantitative ACDP permet de

  6. An Incompressible 2D Didactic Model with Singularity and Explicit Solutions of the 2D Boussinesq Equations

    NASA Astrophysics Data System (ADS)

    Chae, Dongho; Constantin, Peter; Wu, Jiahong

    2014-09-01

    We give an example of a well posed, finite energy, 2D incompressible active scalar equation with the same scaling as the surface quasi-geostrophic equation and prove that it can produce finite time singularities. In spite of its simplicity, this seems to be the first such example. Further, we construct explicit solutions of the 2D Boussinesq equations whose gradients grow exponentially in time for all time. In addition, we introduce a variant of the 2D Boussinesq equations which is perhaps a more faithful companion of the 3D axisymmetric Euler equations than the usual 2D Boussinesq equations.

  7. Bose-Hubbard model with ferromagnetic-like occupation-parity couplings and its realization in imbalanced fermionic superfluids in tubular optical lattices

    NASA Astrophysics Data System (ADS)

    Sun, Kuei; Bolech, Carlos J.

    2014-03-01

    We study a Bose-Hubbard model with a nearest-neighbor occupation-parity coupling that can be considered as energy cost for a domain-wall link between two adjacent sites if their occupation parity is different (one even and the other odd). Our analysis shows that the parity coupling has non-trivial interplay with the tunneling and onsite repulsion, resulting in several exotic quantum phases. For example, a uniform system with zero tunneling can exhibit a pair-liquid phase or phase separation of two Mott insulators, while a trapped system with finite tunneling shows a wedding-cake structure of only even-filling Mott insulators or a structure of central regular superfluid and outer pair superfluid. In addition, we find similar physics in a recent experimental system of imbalanced Fermi gases in optical lattices producing a 2D array of 1D tubes, with the presence of an oscillatory superfluid order parameter (the Fulde-Ferrell-Larkin-Ovchinnikov or FFLO state). We show that the unpaired majority fermions on each tube have a bosonic behavior with cross-tube tunneling, on-tube repulsion, and interplay with the spatial parity of the FFLO order that contributes to the occupation-parity coupling. Therefore, such system provides a realization of our model in two dimensions. Supported by the DARPA-ARO Award No. W911NF-07-1-0464 and by the University of Cincinnati.

  8. Ordered phases in the Holstein-Hubbard model: Interplay of strong Coulomb interaction and electron-phonon coupling

    NASA Astrophysics Data System (ADS)

    Murakami, Yuta; Werner, Philipp; Tsuji, Naoto; Aoki, Hideo

    2013-09-01

    We study the Holstein-Hubbard model at half filling to explore ordered phases including superconductivity (SC), antiferromagnetism (AF), and charge order (CO) in situations where the electron-electron and electron-phonon interactions are strong (comparable to the electronic bandwidth). The model is solved in the dynamical mean-field approximation with a continuous-time quantum Monte Carlo impurity solver. We determine the superconducting transition temperature Tc and the SC order parameter and show that the phonon-induced retardation or the strong Coulomb interaction leads to a significant reduction and shift of the Tc dome against the effective electron-electron interaction Ueff given by the Hubbard U reduced by the phonon-mediated attraction in the static limit. This behavior is analyzed by comparison to an effective static model in the polaron representation with a renormalized bandwidth. In addition, we discuss the superconducting gap Δ and 2Δ/Tc to reveal the effect of the retardation and the Coulomb interaction. We also determine the finite-temperature phase diagram including AF and CO. In the moderate-coupling regime, there is a hysteretic region of AF and CO around Ueff=0, while the two phases are separated by a paramagnetic metal in the weak-coupling regime and a paramagnetic insulator in the strong-coupling regime.

  9. A method to efficiently simulate the thermodynamic properties of the Fermi-Hubbard model on a quantum computer

    NASA Astrophysics Data System (ADS)

    Dallaire-Demers, Pierre-Luc; Wilhelm-Mauch, Frank

    Many phenomena of strongly correlated materials are encapsulated in the Fermi-Hubbard model whose thermodynamic properties can be computed from its grand canonical potential. In general, there is no closed form expression of the grand canonical potential for lattices of more than one spatial dimension, but solutions can be approximated with cluster perturbation theory. To model long-range effects such as order parameters, a powerful method to compute the cluster's Green's function consists in finding its self-energy through a variational principle. This opens the possibility of studying various phase transitions at finite temperature in the Fermi-Hubbard model. However, a classical cluster solver quickly hits an exponential wall in the memory (or computation time) required to store the computation variables. Here it is shown theoretically that that the cluster solver can be mapped to a subroutine on a quantum computer whose quantum memory scales as the number of orbitals in the simulated cluster. A quantum computer with a few tens of qubits could therefore simulate the thermodynamic properties of complex fermionic lattices inaccessible to classical supercomputers.

  10. Method to efficiently simulate the thermodynamic properties of the Fermi-Hubbard model on a quantum computer

    NASA Astrophysics Data System (ADS)

    Dallaire-Demers, Pierre-Luc; Wilhelm, Frank K.

    2016-03-01

    Many phenomena of strongly correlated materials are encapsulated in the Fermi-Hubbard model whose thermodynamic properties can be computed from its grand-canonical potential. In general, there is no closed-form expression of the grand-canonical potential for lattices of more than one spatial dimension, but solutions can be numerically approximated using cluster methods. To model long-range effects such as order parameters, a powerful method to compute the cluster's Green's function consists of finding its self-energy through a variational principle. This allows the possibility of studying various phase transitions at finite temperature in the Fermi-Hubbard model. However, a classical cluster solver quickly hits an exponential wall in the memory (or computation time) required to store the computation variables. Here it is shown theoretically that the cluster solver can be mapped to a subroutine on a quantum computer whose quantum memory usage scales linearly with the number of orbitals in the simulated cluster and the number of measurements scales quadratically. A quantum computer with a few tens of qubits could therefore simulate the thermodynamic properties of complex fermionic lattices inaccessible to classical supercomputers.

  11. Density Matrix Renormalization Group Study of a One Dimensional Three-Orbital Hubbard Model: The role of pair hopping and spin-flip interactions

    NASA Astrophysics Data System (ADS)

    Kaushal, Nitin; Liu, Guangkun; Bishop, Chris; Liang, Shuhua; Li, Shaozhi; Johnston, Steve; Dagotto, Elbio

    Using the Density Matrix Renormalization Group technique, we extensively study a three-orbital Hubbard model in one dimension without pair hopping and spin-flip Hund interactions. The phase diagram varying the electronic density n and Hubbard U is constructed and compared against previous results obtained using the full interaction Hamiltonian. Our results suggest that spin-flip and pair hopping terms are not crucially important to address the orbital-selective Mott phase. This analysis paves the way to study multiorbital Hubbard models using techniques such as the Constrained-Path Quantum Monte Carlo (CPQMC) and Determinant Quantum Monte Carlo (DQMC) methods since they perform better, reducing for instance the severity of the ``sign problem'', in the absence of pair hopping and spin flip terms in the interaction.

  12. 2-D model of the streamer zone of a leader

    NASA Astrophysics Data System (ADS)

    Milikh, G. M.; Likhanskii, A. V.; Shneider, M. N.; Raina, A.; George, A.

    2016-02-01

    Formation of the streamer zone of a leader is an outstanding problem in the physics of electric discharges which is relevant to laboratory leaders, as well as to the leaders formed by lightning. Despite substantial progress in the theoretical understanding of this complicated phenomenon, significant puzzles, such as the low propagation velocity of a leader compared to the fast streamers, remain. The objective of this paper is to present 2-D plasma simulations of the formation and propagation of the streamer zone of a leader. In these simulations we will generate a group of streamers that propagate in a discharge gap while interacting with each other. It is shown that interaction between the streamers significantly reduces their propagation velocity. This explains why the leader, which consists of many streamers, is much slower than a single streamer formed in the same discharge gap. It is shown that the mean velocity suppression of the group of streamers is determined by the inter-streamer distance. The critical value of the packing factor of the streamers at which the interactions between them can be neglected, and thus the discussed process can be treated as caused by a single streamer, is obtained.

  13. Ground-state phase diagram of the repulsive fermionic t -t' Hubbard model on the square lattice from weak coupling

    NASA Astrophysics Data System (ADS)

    Šimkovic, Fedor; Liu, Xuan-Wen; Deng, Youjin; Kozik, Evgeny

    2016-08-01

    We obtain a complete and numerically exact in the weak-coupling limit (U →0 ) ground-state phase diagram of the repulsive fermionic Hubbard model on the square lattice for filling factors 0 Hubbard model.

  14. Fermi-liquid Landau parameters for a nondegenerate band: Spin and charge instabilities in the extended Hubbard model

    NASA Astrophysics Data System (ADS)

    Lhoutellier, Grégoire; Frésard, Raymond; Oleś, Andrzej M.

    2015-06-01

    We investigate the Landau parameters for the instabilities in spin and charge channels in the nondegenerate extended Hubbard model with intersite Coulomb and exchange interactions. To this aim we use the spin rotationally invariant slave boson approach and we determine the necessary inverse propagator matrix. The analytically derived spin Landau parameter F0a for the half filled band uncovers the intrinsic instability of the nondegenerate Hubbard model towards ferromagnetism—negative intersite exchange interaction triggers a ferromagnetic instability at half filling before the metal-insulator transition, indicated by the divergence of the magnetic susceptibility at F0a=-1 . This result is general and the instability occurs in the strongly correlated metallic regime for any lattice, in three or two dimensions. Next as an illustrative example we present numerical results obtained for the cubic lattice with nearest neighbor exchange J and Coulomb V elements and arbitrary electron density. One finds that the range of small doping near half filling is the most unstable one towards spin polarization, but only in the case of ferromagnetic intersite exchange J <0 . Charge Landau parameter F0s is lowered near half filling by increasing U when the intersite Coulomb interaction V is attractive, but in contrast to F0a at J <0 it requires an attraction beyond a critical value Vc to generate the divergence of the charge susceptibility at F0s=-1 in the metallic phase. This instability was found for a broad range of electronic filling away from half filling for moderate attraction.

  15. Two-component Bose-Hubbard model with higher-angular-momentum states

    NASA Astrophysics Data System (ADS)

    Pietraszewicz, Joanna; Sowiński, Tomasz; Brewczyk, Mirosław; Zakrzewski, Jakub; Lewenstein, Maciej; Gajda, Mariusz

    2012-05-01

    Bose-Hubbard Hamiltonian of cold two-component Bose gas of spinor chromium atoms is studied. Dipolar interactions of magnetic moments while tuned resonantly by an ultralow magnetic field can lead to a transfer of atoms from the ground to excited Wannier states with a nonvanishing angular orbital momentum. Hence we propose the way of creating Px+iPy orbital superfluid. The spin introduces an additional degree of control and leads to a variety of different stable phases of the system. The Mott insulator of atoms in a superposition of the ground and vortex Wannier states as well as a superposition of the Mott insulator with orbital superfluid are predicted.

  16. Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches

    NASA Astrophysics Data System (ADS)

    Igoshev, P. A.; Timirgazin, M. A.; Gilmutdinov, V. F.; Arzhnikov, A. K.; Irkhin, V. Yu

    2015-11-01

    The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed.

  17. Benchmark study of the two-dimensional Hubbard model with auxiliary-field quantum Monte Carlo method

    NASA Astrophysics Data System (ADS)

    Qin, Mingpu; Shi, Hao; Zhang, Shiwei

    2016-08-01

    Ground-state properties of the Hubbard model on a two-dimensional square lattice are studied by the auxiliary-field quantum Monte Carlo method. Accurate results for energy, double occupancy, effective hopping, magnetization, and momentum distribution are calculated for interaction strengths of U /t from 2 to 8, for a range of densities including half-filling and n =0.3 ,0.5 ,0.6 ,0.75 , and 0.875 . At half-filling, the results are numerically exact. Away from half-filling, the constrained path Monte Carlo method is employed to control the sign problem. Our results are obtained with several advances in the computational algorithm, which are described in detail. We discuss the advantages of generalized Hartree-Fock trial wave functions and its connection to pairing wave functions, as well as the interplay with different forms of Hubbard-Stratonovich decompositions. We study the use of different twist angle sets when applying the twist averaged boundary conditions. We propose the use of quasirandom sequences, which improves the convergence to the thermodynamic limit over pseudorandom and other sequences. With it and a careful finite size scaling analysis, we are able to obtain accurate values of ground-state properties in the thermodynamic limit. Detailed results for finite-sized systems up to 16 ×16 are also provided for benchmark purposes.

  18. Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches.

    PubMed

    Igoshev, P A; Timirgazin, M A; Gilmutdinov, V F; Arzhnikov, A K; Irkhin, V Yu

    2015-11-11

    The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed. PMID:26465091

  19. FLEX+DMFT approach to the d -wave superconducting phase diagram of the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Kitatani, Motoharu; Tsuji, Naoto; Aoki, Hideo

    2015-08-01

    The dynamical mean-field theory (DMFT) combined with the fluctuation exchange (FLEX) method, namely, FLEX+DMFT, is an approach for correlated electron systems to incorporate both local and nonlocal long-range correlations in a self-consistent manner. We formulate FLEX+DMFT in a systematic way starting from a Luttinger-Ward functional, and apply it to study the d -wave superconductivity in the two-dimensional repulsive Hubbard model. The critical temperature (Tc) curve obtained in the FLEX+DMFT exhibits a dome structure as a function of the filling, which has not been clearly observed in the FLEX approach alone. We trace back the origin of the dome to the local vertex correction from DMFT that renders a filling dependence in the FLEX self-energy. We compare the results with those of GW+DMFT, where the Tc-dome structure is qualitatively reproduced due to the same vertex correction effect, but a crucial difference from FLEX+DMFT is that Tc is always estimated below the Néel temperature in GW+DMFT. The single-particle spectral function obtained with FLEX+DMFT exhibits a double-peak structure as a precursor of the Hubbard bands at temperatures above Tc.

  20. 2D quantum double models from a 3D perspective

    NASA Astrophysics Data System (ADS)

    Bernabé Ferreira, Miguel Jorge; Padmanabhan, Pramod; Teotonio-Sobrinho, Paulo

    2014-09-01

    In this paper we look at three dimensional (3D) lattice models that are generalizations of the state sum model used to define the Kuperberg invariant of 3-manifolds. The partition function is a scalar constructed as a tensor network where the building blocks are tensors given by the structure constants of an involutory Hopf algebra A. These models are very general and are hard to solve in its entire parameter space. One can obtain familiar models, such as ordinary gauge theories, by letting A be the group algebra {C}(G) of a discrete group G and staying on a certain region of the parameter space. We consider the transfer matrix of the model and show that quantum double Hamiltonians are derived from a particular choice of the parameters. Such a construction naturally leads to the star and plaquette operators of the quantum double Hamiltonians, of which the toric code is a special case when A={C}({{{Z}}_{2}}). This formulation is convenient to study ground states of these generalized quantum double models where they can naturally be interpreted as tensor network states. For a surface Σ, the ground state degeneracy is determined by the Kuperberg 3-manifold invariant of \\Sigma \\times {{S}^{1}}. It is also possible to obtain extra models by simply enlarging the allowed parameter space but keeping the solubility of the model. While some of these extra models have appeared before in the literature, our 3D perspective allows for an uniform description of them.

  1. Global SO(3) x SO(3) x U(1) symmetry of the Hubbard model on bipartite lattices

    SciTech Connect

    Carmelo, J.M.P.; Ostlund, Stellan; Sampaio, M.J.

    2010-08-15

    In this paper the global symmetry of the Hubbard model on a bipartite lattice is found to be larger than SO(4). The model is one of the most studied many-particle quantum problems, yet except in one dimension it has no exact solution, so that there remain many open questions about its properties. Symmetry plays an important role in physics and often can be used to extract useful information on unsolved non-perturbative quantum problems. Specifically, here it is found that for on-site interaction U {ne} 0 the local SU(2) x SU(2) x U(1) gauge symmetry of the Hubbard model on a bipartite lattice with N{sub a}{sup D} sites and vanishing transfer integral t = 0 can be lifted to a global [SU(2) x SU(2) x U(1)]/Z{sub 2}{sup 2} = SO(3) x SO(3) x U(1) symmetry in the presence of the kinetic-energy hopping term of the Hamiltonian with t > 0. (Examples of a bipartite lattice are the D-dimensional cubic lattices of lattice constant a and edge length L = N{sub a}a for which D = 1, 2, 3,... in the number N{sub a}{sup D} of sites.) The generator of the new found hidden independent charge global U(1) symmetry, which is not related to the ordinary U(1) gauge subgroup of electromagnetism, is one half the rotated-electron number of singly occupied sites operator. Although addition of chemical-potential and magnetic-field operator terms to the model Hamiltonian lowers its symmetry, such terms commute with it. Therefore, its 4{sup N}{sub a}{sup D} energy eigenstates refer to representations of the new found global [SU(2) x SU(2) x U(1)]/Z{sub 2}{sup 2} = SO(3) x SO(3) x U(1) symmetry. Consistently, we find that for the Hubbard model on a bipartite lattice the number of independent representations of the group SO(3) x SO(3) x U(1) equals the Hilbert-space dimension 4{sup N}{sub a}{sup D}. It is confirmed elsewhere that the new found symmetry has important physical consequences.

  2. A fully coupled 2D model of equiaxed eutectic solidification

    SciTech Connect

    Charbon, Ch.; LeSar, R.

    1995-12-31

    We propose a model of equiaxed eutectic solidification that couples the macroscopic level of heat diffusion with the microscopic level of nucleation and growth of the eutectic grains. The heat equation with the source term corresponding to the latent heat release due to solidification is calculated numerically by means of an implicit finite difference method. In the time stepping scheme, the evolution of solid fraction is deduced from a stochastic model of nucleation and growth which uses the local temperature (interpolated from the FDM mesh) to determine the local grain density and the local growth rate. The solid-liquid interface of each grain is tracked by using a subdivision of each grain perimeter in a large number of sectors. The state of each sector (i.e. whether it is still in contact with the liquid or already captured by an other grain) and the increase of radius of each grain during one time step allows one to compute the increase of solid fraction. As for deterministic models, the results of the model are the evolution of temperature and of solid fraction at any point of the sample. Moreover the model provides a complete picture of the microstructure, thus not limiting the microstructural information to the average grain density but allowing one to compute any stereological value of interest. We apply the model to the solidification of gray cast iron.

  3. Improvement of a 2D numerical model of lava flows

    NASA Astrophysics Data System (ADS)

    Ishimine, Y.

    2013-12-01

    I propose an improved procedure that reduces an improper dependence of lava flow directions on the orientation of Digital Elevation Model (DEM) in two-dimensional simulations based on Ishihara et al. (in Lava Flows and Domes, Fink, JH eds., 1990). The numerical model for lava flow simulations proposed by Ishihara et al. (1990) is based on two-dimensional shallow water model combined with a constitutive equation for a Bingham fluid. It is simple but useful because it properly reproduces distributions of actual lava flows. Thus, it has been regarded as one of pioneer work of numerical simulations of lava flows and it is still now widely used in practical hazard prediction map for civil defense officials in Japan. However, the model include an improper dependence of lava flow directions on the orientation of DEM because the model separately assigns the condition for the lava flow to stop due to yield stress for each of two orthogonal axes of rectangular calculating grid based on DEM. This procedure brings a diamond-shaped distribution as shown in Fig. 1 when calculating a lava flow supplied from a point source on a virtual flat plane although the distribution should be circle-shaped. To improve the drawback, I proposed a modified procedure that uses the absolute value of yield stress derived from both components of two orthogonal directions of the slope steepness to assign the condition for lava flows to stop. This brings a better result as shown in Fig. 2. Fig. 1. (a) Contour plots calculated with the original model of Ishihara et al. (1990). (b) Contour plots calculated with a proposed model.

  4. Stratosphere chemistry in a 2-D model with residual circulation

    NASA Technical Reports Server (NTRS)

    Guthrie, Paul D.; Jackman, Charles H.

    1990-01-01

    The objective of this research was to examine the effects of chemical perturbations on the stratosphere using models which can incorporate fully interactive radiative, chemical, and dynamical responses, in the context of a zonally averaged model. Model runs for the unperturbed, chlorine-perturbed and simultaneously chlorine-and CO2-perturbed cases were completed using the JPL-87 chemical kinetics data. The base case was analyzed and submitted for publication. The perturbed cases show substantial sensitivity of the predicted column ozone depletion to the perturbations affecting lower stratosphere temperature, but less to far dynamical perturbations. The column ozone distribution changed substantially when the kinetics data was changed. This implies a greater-than-expected uncertainty in predicted latitude distributions of ozone depletion, due to uncertainty about the accuracy and completeness of the chemical kinetics data set.

  5. Development of CCHE2D embankment break model

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Earthen embankment breach often results in detrimental impact on downstream residents and infrastructure, especially those located in the flooding zone. Embankment failures are most commonly caused by overtopping or internal erosion. This study is to develop a practical numerical model for simulat...

  6. Phase Structure of the Random Zq Models in 2D

    NASA Astrophysics Data System (ADS)

    Sasamoto, T.; Nishimori, H.

    We discuss the phase diagram of the random Zq models in two dimensions. It is argued that, when q is large enough, there exist three phases in the phase diagram with two axes being the temperature and the strength of randomness. Our conlusions are derived based on the application of the duality arguments for random systems, which have been formulated recently by Maillard et al.

  7. First- and Second-Order Phase Transitions between the Uniform and FFLO Excitonic States in the Three-Chain Hubbard Model for Ta2NiSe5

    NASA Astrophysics Data System (ADS)

    Domon, Kaoru; Yamada, Takemi; Ōno, Yoshiaki

    2016-06-01

    We examine the free energy and the thermodynamic properties in the three-chain Hubbard model for Ta2NiSe5 to clarify the phase transitions between the uniform and the FFLO excitonic states which are expected to be observed in Ta2NiSe5 under high pressure.

  8. Simulation of subgrid orographic precipitation with an embedded 2-D cloud-resolving model

    NASA Astrophysics Data System (ADS)

    Jung, Joon-Hee; Arakawa, Akio

    2016-03-01

    By explicitly resolving cloud-scale processes with embedded two-dimensional (2-D) cloud-resolving models (CRMs), superparameterized global atmospheric models have successfully simulated various atmospheric events over a wide range of time scales. Up to now, however, such models have not included the effects of topography on the CRM grid scale. We have used both 3-D and 2-D CRMs to simulate the effects of topography with prescribed "large-scale" winds. The 3-D CRM is used as a benchmark. The results show that the mean precipitation can be simulated reasonably well by using a 2-D representation of topography as long as the statistics of the topography such as the mean and standard deviation are closely represented. It is also shown that the use of a set of two perpendicular 2-D grids can significantly reduce the error due to a 2-D representation of topography.

  9. Analytic Differentiation of Barlat's 2D Criteria for Inverse Modeling

    SciTech Connect

    Endelt, Benny; Nielsen, Karl Brian; Danckert, Joachim

    2005-08-05

    The demand for alternative identification schemes for identification of constitutive parameters is getting more pronounced as the complexity of the constitutive equations increases, i.e. the number of parameters subject to identification. A general framework for inverse identification of constitutive parameters associated with sheet metal forming is proposed in the article. The inverse problem is solved, through minimization of the least square error between an experimental punch force sampled from a deep drawing and a predicted punch force produced from a coherent finite element model.

  10. Google Earth as a tool in 2-D hydrodynamic modeling

    NASA Astrophysics Data System (ADS)

    Chien, Nguyen Quang; Keat Tan, Soon

    2011-01-01

    A method for coupling virtual globes with geophysical hydrodynamic models is presented. Virtual globes such as Google TM Earth can be used as a visualization tool to help users create and enter input data. The authors discuss techniques for representing linear and areal geographical objects with KML (Keyhole Markup Language) files generated using computer codes (scripts). Although virtual globes offer very limited tools for data input, some data of categorical or vector type can be entered by users, and then transformed into inputs for the hydrodynamic program by using appropriate scripts. An application with the AnuGA hydrodynamic model was used as an illustration of the method. Firstly, users draw polygons on the Google Earth screen. These features are then saved in a KML file which is read using a script file written in the Lua programming language. After the hydrodynamic simulation has been performed, another script file is used to convert the resulting output text file to a KML file for visualization, where the depths of inundation are represented by the color of discrete point icons. The visualization of a wind speed vector field was also included as a supplementary example.

  11. Conservation laws and LETKF with 2D Shallow Water Model

    NASA Astrophysics Data System (ADS)

    Zeng, Yuefei; Janjic, Tijana

    2016-04-01

    Numerous approaches have been proposed to maintain physical conservation laws in the numerical weather prediction models. However, to achieve a reliable prediction, adequate initial conditions are also necessary, which are produced by a data assimilation algorithm. If an ensemble Kalman filters (EnKF) is used for this purpose, it has been shown that it could yield unphysical analysis ensemble that for example violates principles of mass conservation and positivity preservation (e.g. Janjic et al 2014) . In this presentation, we discuss the selection of conservation criteria for the analysis step, and start with testing the conservation of mass, energy and enstrophy. The simple experiments deal with nonlinear shallow water equations and simulated observations that are assimilated with LETKF (Localized Ensemble Transform Kalman Filter, Hunt et al. 2007). The model is discretized in a specific way to conserve mass, angular momentum, energy and enstrophy. The effects of the data assimilation on the conserved quantities (of mass, energy and enstrophy) depend on observation covarage, localization radius, observed variable and observation operator. Having in mind that Arakawa (1966) and Arakawa and Lamb (1977) showed that the conservation of both kinetic energy and enstrophy by momentum advection schemes in the case of nondivergent flow prevents systematic and unrealistic energy cascade towards high wave numbers, a cause of excessive numerical noise and possible eventual nonlinear instability, we test the effects on prediction depending on the type of errors in the initial condition. The performance with respect to nonlinear energy cascade is assessed as well.

  12. Floquet Engineering of Correlated Tunneling in the Bose-Hubbard Model with Ultracold Atoms

    NASA Astrophysics Data System (ADS)

    Meinert, F.; Mark, M. J.; Lauber, K.; Daley, A. J.; Nägerl, H.-C.

    2016-05-01

    We report on the experimental implementation of tunable occupation-dependent tunneling in a Bose-Hubbard system of ultracold atoms via time-periodic modulation of the on-site interaction energy. The tunneling rate is inferred from a time-resolved measurement of the lattice site occupation after a quantum quench. We demonstrate coherent control of the tunneling dynamics in the correlated many-body system, including full suppression of tunneling as predicted within the framework of Floquet theory. We find that the tunneling rate explicitly depends on the atom number difference in neighboring lattice sites. Our results may open up ways to realize artificial gauge fields that feature density dependence with ultracold atoms.

  13. Incremental expansions for the ground-state energy of the two-dimensional Hubbard model

    SciTech Connect

    Malek, J.; Flach, S.; Kladko, K.

    1999-02-01

    A generalization of Faddeev{close_quote}s approach of the three-body problem to the many-body problem leads to the method of increments. This method was recently applied to account for the ground-state properties of Hubbard-Peierls chains [J. Malek, K. Kladko, and S. Flach, JETP Lett. {bold 67}, 1052 (1998)]. Here we generalize this approach to two-dimensional square lattices and explicitly treat the incremental expansion up to third order. Comparing our numerical results with various other approaches (Monte Carlo, cumulant approaches) we show that incremental expansions are very efficient because good accuracy with these approaches is achieved treating lattice segments composed of eight sites only. {copyright} {ital 1999} {ital The American Physical Society}

  14. A 2D model to design MHD induction pumps

    NASA Astrophysics Data System (ADS)

    Stieglitz, R.; Zeininger, J.

    2006-09-01

    Technical liquid metal systems accompanied by a thermal transfer of energy such as reactor systems, metallurgical processes, metal refinement, casting, etc., require a forced convection of the fluid. The increased temperatures and more often the environmental conditions as, e.g., in a nuclear environment, pumping principles are required, in which rotating parts are absent. Additionally, in many applications a controlled atmosphere is indispensable, in order to ensure the structural integrity of the duct walls. An interesting option to overcome the sealing problem of a mechanical pump towards the surrounding is offered by induction systems. Although their efficiency compared to that of turbo machines is quite low, they have several advantages, which are attractive to the specific requirements in liquid metal applications such as: - low maintenance costs due to the absence of sealings, bearings and moving parts; - low degradation rate of the structural material; - simple replacement of the inductor without cut of the piping system; - fine regulation of flow rate by different inductor connections; - change of pump characteristics without change of the mechanical set-up. Within the article, general design requirements of electromagnetic pumps (EMP) are elaborated. The design of two annular linear induction pumps operating with sodium and lead-bismuth are presented and the calculated pump characteristics and experimentally obtained data are compared. In this context, physical effects leading to deviations between the model and the real data are addressed. Finally, the main results are summarized. Tables 4, Figs 4, Refs 12.

  15. Momentum structure of the self-energy and its parametrization for the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Pudleiner, P.; Schäfer, T.; Rost, D.; Li, G.; Held, K.; Blümer, N.

    2016-05-01

    We compute the self-energy for the half-filled Hubbard model on a square lattice using lattice quantum Monte Carlo simulations and the dynamical vertex approximation. The self-energy is strongly momentum-dependent, but it can be parametrized via the noninteracting energy-momentum dispersion ɛk, except for pseudogap features right at the Fermi edge. That is, it can be written as Σ (ɛk,ω ) , with two energylike parameters (ɛ , ω ) instead of three (kx, ky, and ω ). The self-energy has two rather broad and weakly dispersing high-energy features and a sharp ω =ɛk feature at high temperatures, which turns to ω =-ɛk at low temperatures. Altogether this yields a Z - and reversed-Z -like structure, respectively, for the imaginary part of Σ (ɛk,ω ) . We attribute the change of the low-energy structure to antiferromagnetic spin fluctuations.

  16. Solutions of the Two-Dimensional Hubbard Model: Benchmarks and Results from a Wide Range of Numerical Algorithms

    NASA Astrophysics Data System (ADS)

    LeBlanc, J. P. F.; Antipov, Andrey E.; Becca, Federico; Bulik, Ireneusz W.; Chan, Garnet Kin-Lic; Chung, Chia-Min; Deng, Youjin; Ferrero, Michel; Henderson, Thomas M.; Jiménez-Hoyos, Carlos A.; Kozik, E.; Liu, Xuan-Wen; Millis, Andrew J.; Prokof'ev, N. V.; Qin, Mingpu; Scuseria, Gustavo E.; Shi, Hao; Svistunov, B. V.; Tocchio, Luca F.; Tupitsyn, I. S.; White, Steven R.; Zhang, Shiwei; Zheng, Bo-Xiao; Zhu, Zhenyue; Gull, Emanuel; Simons Collaboration on the Many-Electron Problem

    2015-10-01

    Numerical results for ground-state and excited-state properties (energies, double occupancies, and Matsubara-axis self-energies) of the single-orbital Hubbard model on a two-dimensional square lattice are presented, in order to provide an assessment of our ability to compute accurate results in the thermodynamic limit. Many methods are employed, including auxiliary-field quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of dual fermions, density matrix embedding theory, density matrix renormalization group, dynamical cluster approximation, diffusion Monte Carlo within a fixed-node approximation, unrestricted coupled cluster theory, and multireference projected Hartree-Fock methods. Comparison of results obtained by different methods allows for the identification of uncertainties and systematic errors. The importance of extrapolation to converged thermodynamic-limit values is emphasized. Cases where agreement between different methods is obtained establish benchmark results that may be useful in the validation of new approaches and the improvement of existing methods.

  17. Conserving approximations for strongly correlated electron systems - Bethe-Salpeter equation and dynamics for the two-dimensional Hubbard model

    NASA Technical Reports Server (NTRS)

    Bickers, N. E.; Scalapino, D. J.; White, S. R.

    1989-01-01

    A semianalytical approach is described for strongly correlated electronic systems which satisfies microscopic conservation laws, treats strong frequency and momentum dependences, and provides information on both static and dynamic properties. This approach may be used to treat large systems and temperatures lower than those currently accessible to finite-temperature quantum Monte Carlo techniques. Examples of such systems include heavy-electron compounds, organic Bechegaard salts, bis-(ethylenedithiolo)-TTF superconductors, and the oxide superconductors. The technique is based on the derivation and self-consistent solution of infinite-order conserving approximations. The technique is used to derive a low-temperature phase diagram and dynamic correlation functions for the two-dimensional Hubbard lattice model.

  18. GEO2D - Two-Dimensional Computer Model of a Ground Source Heat Pump System

    DOE Data Explorer

    James Menart

    2013-06-07

    This file contains a zipped file that contains many files required to run GEO2D. GEO2D is a computer code for simulating ground source heat pump (GSHP) systems in two-dimensions. GEO2D performs a detailed finite difference simulation of the heat transfer occurring within the working fluid, the tube wall, the grout, and the ground. Both horizontal and vertical wells can be simulated with this program, but it should be noted that the vertical wall is modeled as a single tube. This program also models the heat pump in conjunction with the heat transfer occurring. GEO2D simulates the heat pump and ground loop as a system. Many results are produced by GEO2D as a function of time and position, such as heat transfer rates, temperatures and heat pump performance. On top of this information from an economic comparison between the geothermal system simulated and a comparable air heat pump systems or a comparable gas, oil or propane heating systems with a vapor compression air conditioner. The version of GEO2D in the attached file has been coupled to the DOE heating and cooling load software called ENERGYPLUS. This is a great convenience for the user because heating and cooling loads are an input to GEO2D. GEO2D is a user friendly program that uses a graphical user interface for inputs and outputs. These make entering data simple and they produce many plotted results that are easy to understand. In order to run GEO2D access to MATLAB is required. If this program is not available on your computer you can download the program MCRInstaller.exe, the 64 bit version, from the MATLAB website or from this geothermal depository. This is a free download which will enable you to run GEO2D..

  19. Comparison of 1D and 2D modelling with soil erosion model SMODERP

    NASA Astrophysics Data System (ADS)

    Kavka, Petr; Weyskrabova, Lenka; Zajicek, Jan

    2013-04-01

    The contribution presents a comparison of a runoff simulated by profile method (1D) and spatially distributed method (2D). Simulation model SMODERP is used for calculation and prediction of soil erosion and surface runoff from agricultural land. SMODERP is physically based model that includes the processes of infiltration (Phillips equation), surface runoff (kinematic wave based equation), surface retention, surface roughness and vegetation impact on runoff. 1D model was developed in past, new 2D model was developed in last two years. The model is being developed at the Department of Irrigation, Drainage and Landscape Engineering, Civil Engineering Faculty, CTU in Prague. 2D model was developed as a tool for widespread GIS software ArcGIS. The physical relations were implemented through Python script. This script uses ArcGIS system tools for raster and vectors treatment of the inputs. Flow direction is calculated by Steepest Descent algorithm in the preliminary version of 2D model. More advanced multiple flow algorithm is planned in the next version. Spatially distributed models enable to estimate not only surface runoff but also flow in the rills. Surface runoff is described in the model by kinematic wave equation. Equation uses Manning roughness coefficient for surface runoff. Parameters for five different soil textures were calibrated on the set of forty measurements performed on the laboratory rainfall simulator. For modelling of the rills a specific sub model was created. This sub model uses Manning formula for flow estimation. Numerical stability of the model is solved by Courant criterion. Spatial scale is fixed. Time step is dynamically changed depending on how flow is generated and developed. SMODERP is meant to be used not only for the research purposes, but mainly for the engineering practice. We also present how the input data can be obtained based on available resources (soil maps and data, land use, terrain models, field research, etc.) and how can

  20. Orbital-selective Mott phases of a one-dimensional three-orbital Hubbard model studied using computational techniques

    NASA Astrophysics Data System (ADS)

    Liu, Guangkun; Kaushal, Nitin; Li, Shaozhi; Bishop, Christopher B.; Wang, Yan; Johnston, Steve; Alvarez, Gonzalo; Moreo, Adriana; Dagotto, Elbio

    2016-06-01

    A recently introduced one-dimensional three-orbital Hubbard model displays orbital-selective Mott phases with exotic spin arrangements such as spin block states [J. Rincón et al., Phys. Rev. Lett. 112, 106405 (2014), 10.1103/PhysRevLett.112.106405]. In this publication we show that the constrained-path quantum Monte Carlo (CPQMC) technique can accurately reproduce the phase diagram of this multiorbital one-dimensional model, paving the way to future CPQMC studies in systems with more challenging geometries, such as ladders and planes. The success of this approach relies on using the Hartree-Fock technique to prepare the trial states needed in CPQMC. We also study a simplified version of the model where the pair-hopping term is neglected and the Hund coupling is restricted to its Ising component. The corresponding phase diagrams are shown to be only mildly affected by the absence of these technically difficult-to-implement terms. This is confirmed by additional density matrix renormalization group and determinant quantum Monte Carlo calculations carried out for the same simplified model, with the latter displaying only mild fermion sign problems. We conclude that these methods are able to capture quantitatively the rich physics of the several orbital-selective Mott phases (OSMP) displayed by this model, thus enabling computational studies of the OSMP regime in higher dimensions, beyond static or dynamic mean-field approximations.

  1. Orbital-selective Mott phases of a one-dimensional three-orbital Hubbard model studied using computational techniques.

    PubMed

    Liu, Guangkun; Kaushal, Nitin; Li, Shaozhi; Bishop, Christopher B; Wang, Yan; Johnston, Steve; Alvarez, Gonzalo; Moreo, Adriana; Dagotto, Elbio

    2016-06-01

    A recently introduced one-dimensional three-orbital Hubbard model displays orbital-selective Mott phases with exotic spin arrangements such as spin block states [J. Rincón et al., Phys. Rev. Lett. 112, 106405 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.106405]. In this publication we show that the constrained-path quantum Monte Carlo (CPQMC) technique can accurately reproduce the phase diagram of this multiorbital one-dimensional model, paving the way to future CPQMC studies in systems with more challenging geometries, such as ladders and planes. The success of this approach relies on using the Hartree-Fock technique to prepare the trial states needed in CPQMC. We also study a simplified version of the model where the pair-hopping term is neglected and the Hund coupling is restricted to its Ising component. The corresponding phase diagrams are shown to be only mildly affected by the absence of these technically difficult-to-implement terms. This is confirmed by additional density matrix renormalization group and determinant quantum Monte Carlo calculations carried out for the same simplified model, with the latter displaying only mild fermion sign problems. We conclude that these methods are able to capture quantitatively the rich physics of the several orbital-selective Mott phases (OSMP) displayed by this model, thus enabling computational studies of the OSMP regime in higher dimensions, beyond static or dynamic mean-field approximations. PMID:27415393

  2. Orbital-selective Mott phases of a one-dimensional three-orbital Hubbard model studied using computational techniques

    DOE PAGESBeta

    Liu, Guangkun; Kaushal, Nitin; Liu, Shaozhi; Bishop, Christopher B.; Wang, Yan; Johnston, Steve; Alvarez, Gonzalo; Moreo, Adriana; Dagotto, Elbio R.

    2016-06-24

    A recently introduced one-dimensional three-orbital Hubbard model displays orbital-selective Mott phases with exotic spin arrangements such as spin block states [J. Rincón et al., Phys. Rev. Lett. 112, 106405 (2014)]. In this paper we show that the constrained-path quantum Monte Carlo (CPQMC) technique can accurately reproduce the phase diagram of this multiorbital one-dimensional model, paving the way to future CPQMC studies in systems with more challenging geometries, such as ladders and planes. The success of this approach relies on using the Hartree-Fock technique to prepare the trial states needed in CPQMC. In addition, we study a simplified version of themore » model where the pair-hopping term is neglected and the Hund coupling is restricted to its Ising component. The corresponding phase diagrams are shown to be only mildly affected by the absence of these technically difficult-to-implement terms. This is confirmed by additional density matrix renormalization group and determinant quantum Monte Carlo calculations carried out for the same simplified model, with the latter displaying only mild fermion sign problems. Lastly, we conclude that these methods are able to capture quantitatively the rich physics of the several orbital-selective Mott phases (OSMP) displayed by this model, thus enabling computational studies of the OSMP regime in higher dimensions, beyond static or dynamic mean-field approximations.« less

  3. Magnetic state of K0.8Fe1.6Se2 from a five-orbital Hubbard model in the Hartree-Fock approximation

    NASA Astrophysics Data System (ADS)

    Luo, Qinlong; Nicholson, Andrew; Riera, José; Yao, Dao-Xin; Moreo, Adriana; Dagotto, Elbio

    2011-10-01

    Motivated by the recent discovery of Fe-based superconductors close to an antiferromagnetic insulator in the experimental phase diagram, here the five-orbital Hubbard model (without lattice distortions) is studied using the real-space Hartree-Fock approximation, employing a 10×10 Fe cluster with Fe vacancies in a 5×5 pattern. Varying the Hubbard and Hund couplings, and at electronic density n=6.0, the phase diagram contains an insulating state with the same spin pattern as observed experimentally, involving 2×2 ferromagnetic plaquettes coupled with one another antiferromagnetically. The presence of local ferromagnetic tendencies is in qualitative agreement with Lanczos results for the three-orbital model also reported here. The magnetic moment ˜3μB/Fe is in good agreement with experiments. Several other phases are also stabilized in the phase diagram, in agreement with recent calculations using phenomenological models.

  4. Magnetic state of K0.8Fe1.6Se2 from a five-orbital Hubbard model in the Hartree-Fock approximation

    SciTech Connect

    Luo, Qinlong; Nicholson, Andrew D; Riera, J. A.; Yao, Dao-Xin; Moreo, Adriana; Dagotto, Elbio R

    2011-01-01

    Motivated by the recent discovery of Fe-based superconductors close to an antiferromagnetic insulator in the experimental phase diagram, here the five-orbital Hubbard model (without lattice distortions) is studied using the real-space Hartree-Fock approximation, employing a 10 10 Fe cluster with Fe vacancies in a5 5 pattern. Varying the Hubbard and Hund couplings, and at electronic density n = 6.0, the phase diagram contains an insulating state with the same spin pattern as observed experimentally, involving 2 2 ferromagnetic plaquettes coupled with one another antiferromagnetically. The presence of local ferromagnetic tendencies is in qualitative agreement with Lanczos results for the three-orbital model also reported here. The magnetic moment 3 B /Fe is in good agreement with experiments. Several other phases are also stabilized in the phase diagram, in agreement with recent calculations using phenomenological models.

  5. Analysis of vegetation effect on waves using a vertical 2-D RANS model

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A vertical two-dimensional (2-D) model has been applied in the simulation of wave propagation through vegetated water bodies. The model is based on an existing model SOLA-VOF which solves the Reynolds-Averaged Navier-Stokes (RANS) equations with the finite difference method on a staggered rectangula...

  6. Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model

    PubMed Central

    Balakrishnan, Minimol; Chakravarthy, V. Srinivasa; Guhathakurta, Soma

    2015-01-01

    Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias. PMID:26733873

  7. Fast 2D flood modelling using GPU technology - recent applications and new developments

    NASA Astrophysics Data System (ADS)

    Crossley, Amanda; Lamb, Rob; Waller, Simon; Dunning, Paul

    2010-05-01

    In recent years there has been considerable interest amongst scientists and engineers in exploiting the potential of commodity graphics hardware for desktop parallel computing. The Graphics Processing Units (GPUs) that are used in PC graphics cards have now evolved into powerful parallel co-processors that can be used to accelerate the numerical codes used for floodplain inundation modelling. We report in this paper on experience over the past two years in developing and applying two dimensional (2D) flood inundation models using GPUs to achieve significant practical performance benefits. Starting with a solution scheme for the 2D diffusion wave approximation to the 2D Shallow Water Equations (SWEs), we have demonstrated the capability to reduce model run times in ‘real-world' applications using GPU hardware and programming techniques. We then present results from a GPU-based 2D finite volume SWE solver. A series of numerical test cases demonstrate that the model produces outputs that are accurate and consistent with reference results published elsewhere. In comparisons conducted for a real world test case, the GPU-based SWE model was over 100 times faster than the CPU version. We conclude with some discussion of practical experience in using the GPU technology for flood mapping applications, and for research projects investigating use of Monte Carlo simulation methods for the analysis of uncertainty in 2D flood modelling.

  8. Simulation of Cardiac Arrhythmias Using a 2D Heterogeneous Whole Heart Model.

    PubMed

    Balakrishnan, Minimol; Chakravarthy, V Srinivasa; Guhathakurta, Soma

    2015-01-01

    Simulation studies of cardiac arrhythmias at the whole heart level with electrocardiogram (ECG) gives an understanding of how the underlying cell and tissue level changes manifest as rhythm disturbances in the ECG. We present a 2D whole heart model (WHM2D) which can accommodate variations at the cellular level and can generate the ECG waveform. It is shown that, by varying cellular-level parameters like the gap junction conductance (GJC), excitability, action potential duration (APD) and frequency of oscillations of the auto-rhythmic cell in WHM2D a large variety of cardiac arrhythmias can be generated including sinus tachycardia, sinus bradycardia, sinus arrhythmia, sinus pause, junctional rhythm, Wolf Parkinson White syndrome and all types of AV conduction blocks. WHM2D includes key components of the electrical conduction system of the heart like the SA (Sino atrial) node cells, fast conducting intranodal pathways, slow conducting atriovenctricular (AV) node, bundle of His cells, Purkinje network, atrial, and ventricular myocardial cells. SA nodal cells, AV nodal cells, bundle of His cells, and Purkinje cells are represented by the Fitzhugh-Nagumo (FN) model which is a reduced model of the Hodgkin-Huxley neuron model. The atrial and ventricular myocardial cells are modeled by the Aliev-Panfilov (AP) two-variable model proposed for cardiac excitation. WHM2D can prove to be a valuable clinical tool for understanding cardiac arrhythmias. PMID:26733873

  9. 2D face database diversification based on 3D face modeling

    NASA Astrophysics Data System (ADS)

    Wang, Qun; Li, Jiang; Asari, Vijayan K.; Karim, Mohammad A.

    2011-05-01

    Pose and illumination are identified as major problems in 2D face recognition (FR). It has been theoretically proven that the more diversified instances in the training phase, the more accurate and adaptable the FR system appears to be. Based on this common awareness, researchers have developed a large number of photographic face databases to meet the demand for data training purposes. In this paper, we propose a novel scheme for 2D face database diversification based on 3D face modeling and computer graphics techniques, which supplies augmented variances of pose and illumination. Based on the existing samples from identical individuals of the database, a synthesized 3D face model is employed to create composited 2D scenarios with extra light and pose variations. The new model is based on a 3D Morphable Model (3DMM) and genetic type of optimization algorithm. The experimental results show that the complemented instances obviously increase diversification of the existing database.

  10. Pair correlations in doped Hubbard ladders

    NASA Astrophysics Data System (ADS)

    Dolfi, Michele; Bauer, Bela; Keller, Sebastian; Troyer, Matthias

    2015-11-01

    Hubbard ladders are an important stepping stone to the physics of the two-dimensional Hubbard model. While many of their properties are accessible to numerical and analytical techniques, the question of whether weakly hole-doped Hubbard ladders are dominated by superconducting or charge-density-wave correlations has so far eluded a definitive answer. In particular, previous numerical simulations of Hubbard ladders have seen a much faster decay of superconducting correlations than expected based on analytical arguments. We revisit this question using a state-of-the-art implementation of the density matrix renormalization group algorithm that allows us to simulate larger system sizes with higher accuracy than before. Performing careful extrapolations of the results, we obtain improved estimates for the Luttinger liquid parameter and the correlation functions at long distances. Our results confirm that, as suggested by analytical considerations, superconducting correlations become dominant in the limit of very small doping.

  11. A multispeed Discrete Boltzmann Model for transcritical 2D shallow water flows

    NASA Astrophysics Data System (ADS)

    La Rocca, Michele; Montessori, Andrea; Prestininzi, Pietro; Succi, Sauro

    2015-03-01

    In this work a Discrete Boltzmann Model for the solution of transcritical 2D shallow water flows is presented and validated. In order to provide the model with transcritical capabilities, a particular multispeed velocity set has been employed for the discretization of the Boltzmann equation. It is shown that this particular set naturally yields a simple and closed procedure to determine higher order equilibrium distribution functions needed to simulate transcritical flow. The model is validated through several classical benchmarks and is proven to correctly and accurately simulate both 1D and 2D transitions between the two flow regimes.

  12. A 2-D dynamical model of mesospheric temperature inversions in winter

    SciTech Connect

    Hauchecorne, A.; Maillard, A. )

    1990-11-01

    A 2-D stratospheric and mesospheric dynamical model including drag and diffusion due to gravity wave breaking is used to simulate winter mesospheric temperature inversions similar to those observed by Rayleigh lidar. It is shown that adiabatic heating associated to descending velocities in the mesosphere is the main mechanism involved in the formation of such inversions. Sensitivity tests are performed with the model and confirm this assumption. It is also explained why other previous similar studies with 2-D models did not show mesospheric inversion layers.

  13. Temperature dependence of the zero-bias anomaly in the Anderson-Hubbard model: insights from an ensemble of two-site systems

    NASA Astrophysics Data System (ADS)

    Wortis, R.; Atkinson, W. A.

    2011-03-01

    Motivated by experiments on doped transition metal oxides, this paper considers the interplay of interactions, disorder, kinetic energy and temperature in a simple system. An ensemble of two-site Anderson-Hubbard model systems has already been shown to display a zero-bias anomaly (Wortis and Atkinson 2010 Phys. Rev. B 82 073107) which shares features with that found in the two-dimensional Anderson-Hubbard model (Chiesa et al 2008 Phys. Rev. Lett. 101 086401). Here the temperature dependence of the density of states of this ensemble is examined. In the atomic limit, there is no zero-bias anomaly at zero temperature, but one develops at small nonzero temperatures. With hopping, small temperatures augment the zero-temperature kinetic-energy-driven zero-bias anomaly, while at larger temperatures the anomaly is filled in.

  14. Influence of the Kerr effect in a Mott insulator on the superfluid transition from the point of view of the Jaynes-Cummings-Hubbard model

    NASA Astrophysics Data System (ADS)

    Gomes, Clélio B. C.; Almeida, Francisco A. G.; Souza, Andre M. C.

    2016-04-01

    We have studied analytically the Jaynes-Cummings-Hubbard model for a one-dimensional optical lattice with the account of the Kerr-type nonlinearity under the fermionic approximation. We have found that an increase in the number of photons or in the detuning parameter favors the superfluid phase. We have also found that the nonlinear Kerr effect favors the Mott insulator phase, which is in agreement with experimental observations.

  15. Merging of RVR meander with CONCEPTS: Simplified 2D model for long-term meander evolution

    Technology Transfer Automated Retrieval System (TEKTRAN)

    RVR Meander is a simplified two-dimensional (2D) hydrodynamic and migration model (Abad and Garcia, 2006) while CONCEPTS (CONservational Channel Evolution and Pollutant Transport System) is a one-dimensional (1D) hydrodynamic and morphodynamic model (Langendoen and Alonso, 2008; Langendoen and Simon...

  16. Introducing the R2D2 Model: Online Learning for the Diverse Learners of This World

    ERIC Educational Resources Information Center

    Bonk, Curtis J.; Zhang, Ke

    2006-01-01

    The R2D2 method--read, reflect, display, and do--is a new model for designing and delivering distance education, and in particular, online learning. Such a model is especially important to address the diverse preferences of online learners of varied generations and varied Internet familiarity. Four quadrants can be utilized separately or as part…

  17. Evaluation of 2D shallow-water model for spillway flow with a complex geometry

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Although the two-dimensional (2D) shallow water model is formulated based on several assumptions such as hydrostatic pressure distribution and vertical velocity is negligible, as a simple alternative to the complex 3D model, it has been used to compute water flows in which these assumptions may be ...

  18. Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model

    NASA Astrophysics Data System (ADS)

    Higa, Ryota; Asano, Kenichi

    2016-06-01

    We study the metal-insulator transition in the half-filled Hubbard model on a Kagome lattice using the variational cluster approximation. The strong coupling limit of the model corresponds to the S =1 /2 Kagome Heisenberg antiferromagnet, which is known to have a singlet ground state, although its detail is still debated. As the results of the cluster methods generally depend much on the choice of the unit cluster, we have chosen the clusters that are compatible with these singlet ground states in the strong coupling case found so far, which basically consist of even number of sites. It is found that the correlated electrons on the Kagome lattice have a strong tendency to form valence-bond structures, which are the resonation of electrons on a single bond or several bonds forming loops. The zero-temperature metal-insulator transition at some interaction strength is possibly driven by the formation of such short range valence bonds and shows a second order character, which is distinctive from the Brinkman-Rice scenario. The electrons on these valence bonds further localizes onto each site as the interaction increases, and the valence bonds of electrons finally turn into magnetic singlet bonds between localized S =1 /2 spins, which are consistent with the ground states of the Kagome antiferromagnet.

  19. Doping-driven orbital-selective Mott transition in multi-band Hubbard models with crystal field splitting

    NASA Astrophysics Data System (ADS)

    Yilin, Wang; Li, Huang; Liang, Du; Xi, Dai

    2016-03-01

    We have studied the doping-driven orbital-selective Mott transition in multi-band Hubbard models with equal band width in the presence of crystal field splitting. Crystal field splitting lifts one of the bands while leaving the others degenerate. We use single-site dynamical mean-field theory combined with continuous time quantum Monte Carlo impurity solver to calculate a phase diagram as a function of total electron filling N and crystal field splitting Δ. We find a large region of orbital-selective Mott phase in the phase diagram when the doping is large enough. Further analysis indicates that the large region of orbital-selective Mott phase is driven and stabilized by doping. Such models may account for the orbital-selective Mott transition in some doped realistic strongly correlated materials. Project supported by the National Natural Science Foundation of China (Grant No. 2011CBA00108) and the National Basic Research Program of China (Grant No. 2013CB921700).

  20. Ground-state properties of the one-dimensional attractive Hubbard model with confinement: A comparative study

    SciTech Connect

    Hu Jihong; Wang Jingjing; Gao Xianlong; Okumura, Masahiko; Igarashi, Ryo; Yamada, Susumu; Machida, Masahiko

    2010-07-01

    We revisit the one-dimensional attractive Hubbard model by using the Bethe-ansatz-based density-functional theory and density-matrix renormalization method. The ground-state properties of this model are discussed in details for different fillings and different confining conditions in weak-to-intermediate coupling regime. We investigate the ground-state energy, energy gap, and pair-binding energy and compare them with those calculated from the canonical Bardeen-Cooper-Schrieffer approximation. We find that the Bethe-ansatz-based density-functional theory is computationally easy and yields an accurate description of the ground-state properties for weak-to-intermediate interaction strength, different fillings, and confinements. In order to characterize the quantum phase transition in the presence of a harmonic confinement, we calculate the thermodynamic stiffness, the density-functional fidelity, and fidelity susceptibility, respectively. It is shown that with the increase in the number of particles or attractive interaction strength, the system can be driven from the Luther-Emery-type phase to the composite phase of Luther-Emery-type in the wings and insulatinglike in the center.

  1. Exact solution of the 1D Hubbard model with NN and NNN interactions in the narrow-band limit

    NASA Astrophysics Data System (ADS)

    Mancini, Ferdinando; Plekhanov, Evgeny; Sica, Gerardo

    2013-10-01

    We present the exact solution, obtained by means of the Transfer Matrix (TM) method, of the 1D Hubbard model with nearest-neighbor (NN) and next-nearest-neighbor (NNN) Coulomb interactions in the atomic limit ( t = 0). The competition among the interactions ( U, V 1, and V 2) generates a plethora of T = 0 phases in the whole range of fillings. U, V 1, and V 2 are the intensities of the local, NN and NNN interactions, respectively. We report the T = 0 phase diagram, in which the phases are classified according to the behavior of the principal correlation functions, and reconstruct a representative electronic configuration for each phase. In order to do that, we make an analytic limit T → 0 in the transfer matrix, which allows us to obtain analytic expressions for the ground state energies even for extended transfer matrices. Such an extension of the standard TM technique can be easily applied to a wide class of 1D models with the interaction range beyond NN distance, allowing for a complete determination of the T = 0 phase diagrams.

  2. Minimally self-consistent T-matrix approximation to describe the low-temperature properties of the Hubbard model in the atomic limit

    NASA Astrophysics Data System (ADS)

    Verga, S.; Gooding, R. J.; Marsiglio, F.

    2005-04-01

    The atomic limit of the Hubbard model is a simple single-site problem which can be solved exactly, and all one- and two-particle Green’s functions can be obtained analytically. These solutions can thus serve as a means of critiquing the success of various approximate theories which might be applied to the full Hubbard model. In particular, we have examined the T -matrix approximation for the attractive Hubbard model in the atomic limit, which should give reasonable results at low electronic densities, if one can avoid the spurious phase transition that results when a fully non-self-consistent T -matrix approximation is employed—previously we have shown that any level of self-consistency guarantees that this phase transition is correctly suppressed to zero temperature in two dimensions or less. Here, a minimally self-consistent T -matrix approximation is shown to be successful in reproducing the exact results for the atomic limit, while fully self-consistent T -matrix results do not agree with the known solutions. Of particular note is that the minimally self-consistent T -matrix approximation reproduces not only one- and two-particle (static) thermodynamic quantities, but it also exactly reproduces the one-particle spectral function at low but nonzero temperatures. We also make a comparison to the two-particle self-consistent approach of Vilk and Tremblay, and find that the minimally self-consistent T -matrix theory can give better results over a broader temperature range.

  3. Error propagation for velocity and shear stress prediction using 2D models for environmental management

    NASA Astrophysics Data System (ADS)

    Pasternack, Gregory B.; Gilbert, Andrew T.; Wheaton, Joseph M.; Buckland, Evan M.

    2006-08-01

    SummaryResource managers, scientists, government regulators, and stakeholders are considering sophisticated numerical models for managing complex environmental problems. In this study, observations from a river-rehabilitation experiment involving gravel augmentation and spawning habitat enhancement were used to assess sources and magnitudes of error in depth, velocity, and shear velocity predictions made at the 1-m scale with a commercial two-dimensional (depth-averaged) model. Error in 2D model depth prediction averaged 21%. This error was attributable to topographic survey resolution, which at 1 pt per 1.14 m 2, was inadequate to resolve small humps and depressions influencing point measurements. Error in 2D model velocity prediction averaged 29%. More than half of this error was attributable to depth prediction error. Despite depth and velocity error, 56% of tested 2D model predictions of shear velocity were within the 95% confidence limit of the best field-based estimation method. Ninety percent of the error in shear velocity prediction was explained by velocity prediction error. Multiple field-based estimates of shear velocity differed by up to 160%, so the lower error for the 2D model's predictions suggests such models are at least as accurate as field measurement. 2D models enable detailed, spatially distributed estimates compared to the small number measurable in a field campaign of comparable cost. They also can be used for design evaluation. Although such numerical models are limited to channel types adhering to model assumptions and yield predictions only accurate to ˜20-30%, they can provide a useful tool for river-rehabilitation design and assessment, including spatially diverse habitat heterogeneity as well as for pre- and post-project appraisal.

  4. Validation of DYSTOOL for unsteady aerodynamic modeling of 2D airfoils

    NASA Astrophysics Data System (ADS)

    González, A.; Gomez-Iradi, S.; Munduate, X.

    2014-06-01

    From the point of view of wind turbine modeling, an important group of tools is based on blade element momentum (BEM) theory using 2D aerodynamic calculations on the blade elements. Due to the importance of this sectional computation of the blades, the National Renewable Wind Energy Center of Spain (CENER) developed DYSTOOL, an aerodynamic code for 2D airfoil modeling based on the Beddoes-Leishman model. The main focus here is related to the model parameters, whose values depend on the airfoil or the operating conditions. In this work, the values of the parameters are adjusted using available experimental or CFD data. The present document is mainly related to the validation of the results of DYSTOOL for 2D airfoils. The results of the computations have been compared with unsteady experimental data of the S809 and NACA0015 profiles. Some of the cases have also been modeled using the CFD code WMB (Wind Multi Block), within the framework of a collaboration with ACCIONA Windpower. The validation has been performed using pitch oscillations with different reduced frequencies, Reynolds numbers, amplitudes and mean angles of attack. The results have shown a good agreement using the methodology of adjustment for the value of the parameters. DYSTOOL have demonstrated to be a promising tool for 2D airfoil unsteady aerodynamic modeling.

  5. 2D-photochemical model for forbidden oxygen line emission for comet 1P/Halley

    NASA Astrophysics Data System (ADS)

    Cessateur, G.; De Keyser, J.; Maggiolo, R.; Rubin, M.; Gronoff, G.; Gibbons, A.; Jehin, E.; Dhooghe, F.; Gunell, H.; Vaeck, N.; Loreau, J.

    2016-08-01

    We present here a 2D-model of photochemistry for computing the production and loss mechanisms of the O(1S) and O(1D) states, which are responsible for the emission lines at 577.7 nm, 630 nm, and 636.4 nm, in case of the comet 1P/Halley. The presence of O2 within cometary atmospheres, measured by the in-situ ROSETTA and GIOTTO missions, necessitates a revision of the usual photochemical models. Indeed, the photodissociation of molecular oxygen also leads to a significant production of oxygen in excited electronic states. In order to correctly model the solar UV flux absorption, we consider here a 2D configuration. While the green to red-doublet ratio is not affected by the solar UV flux absorption, estimates of the red-doublet and green lines emissions are, however, overestimated by a factor of two in the 1D model compared to the 2D model. Considering a spherical symmetry, emission maps can be deduced from the 2D model in order to be directly compared to ground and/or in-situ observations.

  6. Oriented Gaussian mixture models for nonrigid 2D/3D coronary artery registration.

    PubMed

    Baka, N; Metz, C T; Schultz, C J; van Geuns, R-J; Niessen, W J; van Walsum, T

    2014-05-01

    2D/3D registration of patient vasculature from preinterventional computed tomography angiography (CTA) to interventional X-ray angiography is of interest to improve guidance in percutaneous coronary interventions. In this paper we present a novel feature based 2D/3D registration framework, that is based on probabilistic point correspondences, and show its usefulness on aligning 3D coronary artery centerlines derived from CTA images with their 2D projection derived from interventional X-ray angiography. The registration framework is an extension of the Gaussian mixture model (GMM) based point-set registration to the 2D/3D setting, with a modified distance metric. We also propose a way to incorporate orientation in the registration, and show its added value for artery registration on patient datasets as well as in simulation experiments. The oriented GMM registration achieved a median accuracy of 1.06 mm, with a convergence rate of 81% for nonrigid vessel centerline registration on 12 patient datasets, using a statistical shape model. The method thereby outperformed the iterative closest point algorithm, the GMM registration without orientation, and two recently published methods on 2D/3D coronary artery registration. PMID:24770908

  7. Suppression of s-wave superconductivity by kinetic disorder in a two-dimensional attractive Hubbard model

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjeev; Chakraborty, Prabuddha B.

    2015-03-01

    We investigate the influence of diagonal and off-diagonal disorder potentials on superconductivity in an attractive Hubbard model. The study is motivated by recent experimental and theoretical interest in understanding the microscopic mechanism by which impurities destroy superconductivity. In order to capture the spatial correlations accurately, we make use of the real-space Bogoliubov-de Gennes mean field method. We find that the response of a superconductor to disorder crucially depends, even qualitatively, on the type of disorder considered. Superconductivity is suppressed spatially homogeneously by off-diagonal (kinetic) disorder in comparison to the suppression by diagonal (potential) disorder which proceeds via the formation of strongly superconducting islands. Moreover, the non-superconducting phase is gapless in the case of kinetic disorder, suggesting a fermionic superconductor-insulator transition (SIT). This is in sharp contrast to the SIT tuned by diagonal disorder, which is understood to be bosonic in nature. A qualitatively distinct mechanism that allows for a BCS-like suppression of superconductivity with increasing disorder is, in fact, consistent with recent experiments on amorphous Bi films.

  8. Full self-consistency versus quasiparticle self-consistency in diagrammatic approaches: Exactly solvable two-site Hubbard model

    SciTech Connect

    Kutepov, A. L.

    2015-07-22

    Self-consistent solutions of Hedin's equations (HE) for the two-site Hubbard model (HM) have been studied. They have been found for three-point vertices of increasing complexity (Γ = 1 (GW approximation), Γ₁ from the first-order perturbation theory, and the exact vertex ΓE). Comparison is made between the cases when an additional quasiparticle (QP) approximation for Green's functions is applied during the self-consistent iterative solving of HE and when QP approximation is not applied. Results obtained with the exact vertex are directly related to the present open question—which approximation is more advantageous for future implementations, GW + DMFT or QPGW + DMFT. It is shown that in a regime of strong correlations only the originally proposed GW + DMFT scheme is able to provide reliable results. Vertex corrections based on Perturbation Theory systematically improve the GW results when full self-consistency is applied. The application of QP self-consistency combined with PT vertex corrections shows similar problems to the case when the exact vertex is applied combined with QP sc. An analysis of Ward Identity violation is performed for all studied in this work's approximations and its relation to the general accuracy of the schemes used is provided.

  9. Fractional Mott insulator-to-superfluid transition of Bose–Hubbard model in a trimerized Kagomé optical lattice

    NASA Astrophysics Data System (ADS)

    Chen, Qi-Hui; Li, Peng; Su, Haibin

    2016-06-01

    By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose–Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.

  10. FFLO Excitonic State in the Three-Chain Hubbard Model for Ta2NiSe5

    NASA Astrophysics Data System (ADS)

    Yamada, Takemi; Domon, Kaoru; Ōno, Yoshiaki

    2016-05-01

    The three-chain Hubbard model for Ta2NiSe5, known as a candidate material for an excitonic insulator, is investigated over the wide range of the energy gap D between the twofold degenerate conduction bands and the nondegenerate valence band including both semiconducting (D > 0) and semimetallic (D < 0) cases. In the semimetallic case, the difference in the band degeneracy inevitably causes the imbalance of each Fermi wavenumber, resulting in a remarkable excitonic state characterized by the condensation of excitons with finite center-of-mass momentum q, the so-called Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) excitonic state. With decreasing D corresponding to increasing pressure, the obtained excitonic phase diagram shows a crossover from BEC (D ≳ 0) to BCS (D ≲ 0) regime, and then shows a distinct phase transition at a certain critical value Dc (< 0) from the uniform (q = 0) to the FFLO (q ≠ 0) excitonic state, as expected to be observed in Ta2NiSe5 under high pressure.

  11. Hubbard model for ultracold bosonic atoms interacting via zero-point-energy-induced three-body interactions

    NASA Astrophysics Data System (ADS)

    Paul, Saurabh; Johnson, P. R.; Tiesinga, Eite

    2016-04-01

    We show that, for ultracold neutral bosonic atoms held in a three-dimensional periodic potential or optical lattice, a Hubbard model with dominant, attractive three-body interactions can be generated. In fact, we derive that the effect of pairwise interactions can be made small or zero starting from the realization that collisions occur at the zero-point energy of an optical lattice site and the strength of the interactions is energy dependent from effective-range contributions. We determine the strength of the two- and three-body interactions for scattering from van der Waals potentials and near Fano-Feshbach resonances. For van der Waals potentials, which for example describe scattering of alkaline-earth atoms, we find that the pairwise interaction can only be turned off for species with a small negative scattering length, leaving the 88Sr isotope a possible candidate. Interestingly, for collisional magnetic Feshbach resonances this restriction does not apply and there often exist magnetic fields where the two-body interaction is small. We illustrate this result for several known narrow resonances between alkali-metal atoms as well as chromium atoms. Finally, we compare the size of the three-body interaction with hopping rates and describe limits due to three-body recombination.

  12. Chiral spin density wave order on the frustrated honeycomb and bilayer triangle lattice hubbard model at half-filling.

    PubMed

    Jiang, Kun; Zhang, Yi; Zhou, Sen; Wang, Ziqiang

    2015-05-29

    We study the Hubbard model on the frustrated honeycomb lattice with nearest-neighbor hopping t_{1} and second nearest-neighbor hopping t_{2}, which is isomorphic to the bilayer triangle lattice, using the SU(2)-invariant slave boson theory. We show that the Coulomb interaction U induces antiferromagnetic (AF) chiral spin density wave (χSDW) order in a wide range of κ=t_{2}/t_{1} where both the two-sublattice AF order at small κ and the decoupled three-sublattice 120° order at large κ are strongly frustrated, leading to three distinct phases with different anomalous Hall responses. We find a continuous transition from a χSDW semimetal with the anomalous Hall effect to a topological chiral Chern insulator exhibiting the quantum anomalous Hall effect, followed by a discontinuous transition to a χSDW insulator with a zero total Chern number but an anomalous ac Hall effect. The χSDW is likely a generic phase of strongly correlated and highly frustrated hexagonal lattice electrons. PMID:26066448

  13. Solutions of the two-dimensional Hubbard model: Benchmarks and results from a wide range of numerical algorithms

    DOE PAGESBeta

    LeBlanc, J. P. F.; Antipov, Andrey E.; Becca, Federico; Bulik, Ireneusz W.; Chan, Garnet Kin-Lic; Chung, Chia -Min; Deng, Youjin; Ferrero, Michel; Henderson, Thomas M.; Jiménez-Hoyos, Carlos A.; et al

    2015-12-14

    Numerical results for ground-state and excited-state properties (energies, double occupancies, and Matsubara-axis self-energies) of the single-orbital Hubbard model on a two-dimensional square lattice are presented, in order to provide an assessment of our ability to compute accurate results in the thermodynamic limit. Many methods are employed, including auxiliary-field quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of dual fermions, density matrix embedding theory, density matrix renormalization group, dynamical cluster approximation, diffusion Monte Carlo within a fixed-node approximation, unrestricted coupled cluster theory, and multireference projected Hartree-Fock methods. Comparison of results obtained by different methods allows for the identification ofmore » uncertainties and systematic errors. The importance of extrapolation to converged thermodynamic-limit values is emphasized. Furthermore, cases where agreement between different methods is obtained establish benchmark results that may be useful in the validation of new approaches and the improvement of existing methods.« less

  14. Fractional Mott insulator-to-superfluid transition of Bose-Hubbard model in a trimerized Kagomé optical lattice.

    PubMed

    Chen, Qi-Hui; Li, Peng; Su, Haibin

    2016-06-29

    By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose-Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy. PMID:27165440

  15. Spin-orbit-induced exotic insulators in a three-orbital Hubbard model with (t2g) 5 electrons

    NASA Astrophysics Data System (ADS)

    Sato, Toshihiro; Shirakawa, Tomonori; Yunoki, Seiji

    2015-03-01

    On the basis of the multiorbital dynamical mean-field theory, a three-orbital Hubbard model with relativistic spin-orbit coupling (SOC) is studied at five electrons per site. The numerical calculations are performed by employing the continuous-time quantum Monte Carlo (CTQMC) method based on the strong-coupling expansion. We find that appropriately choosing bases, i.e., the maximally spin-orbit-entangled bases, drastically improves the sign problem in the CTQMC calculations, which enables us to treat exactly the full Hund's coupling and pair-hopping terms. This improvement is also essential to reach at low temperatures for a large SOC region where the SOC most significantly affects the electronic structure. We show that a metal-insulator transition is induced by the SOC for fixed Coulomb interactions. The insulating state for smaller Coulomb interactions is antiferromagnetically ordered with the local effective total angular momentum j =1 /2 , in which the (j =1 /2 )-based band is essentially half filled, while the (j =3 /2 )-based bands are completely occupied. More interestingly, for larger Coulomb interactions, we find that an excitonic insulating state emerges, where the condensation of an electron-hole pair in the (j =1 /2 )- and (j =3 /2 )-based bands occurs. The origin of the excitonic insulator as well as the experimental implication is discussed.

  16. Orbital Optimization in the Resonating Hartree-Fock Approximation and Its Application to the One Dimensional Hubbard Model

    NASA Astrophysics Data System (ADS)

    Ikawa, Atsushi; Yamamoto, Shoji; Fukutome, Hideo

    1993-05-01

    A tractable direct optimization algorithm is developed to optimize orbitals in the Slater determinants (S-dets) in a resonating Hartree-Fock (Res HF) wave function. We reduce the variation space using the orbitals to put the first order energy variation in the steepest descent direction. The orbitals in the next iteration are determined so as to minimize the energy functional including up to the second order variation. This algorithm is applied to the one dimensional Hubbard model of half-filling. The optimized S-dets much deviate from the trial S-dets prepared from the HF calculations. The Res HF ground state generated with a few S-dets explains from 99.9 to 95.0% of the ground state correlation energy in all the correlation regimes. We have spin correlation functions with the correct short and long range behaviors and the lowest triplet and singlet spin excitations with correct dispersions, suggesting that the optimization of orbitals incorporates long range spin fluctuations and their mode-mode couplings.

  17. Chiral Spin Density Wave Order on the Frustrated Honeycomb and Bilayer Triangle Lattice Hubbard Model at Half-Filling

    NASA Astrophysics Data System (ADS)

    Jiang, Kun; Zhang, Yi; Zhou, Sen; Wang, Ziqiang

    2015-05-01

    We study the Hubbard model on the frustrated honeycomb lattice with nearest-neighbor hopping t1 and second nearest-neighbor hopping t2, which is isomorphic to the bilayer triangle lattice, using the SU(2)-invariant slave boson theory. We show that the Coulomb interaction U induces antiferromagnetic (AF) chiral spin density wave (χ SDW ) order in a wide range of κ =t2/t1 where both the two-sublattice AF order at small κ and the decoupled three-sublattice 120° order at large κ are strongly frustrated, leading to three distinct phases with different anomalous Hall responses. We find a continuous transition from a χ SDW semimetal with the anomalous Hall effect to a topological chiral Chern insulator exhibiting the quantum anomalous Hall effect, followed by a discontinuous transition to a χ SDW insulator with a zero total Chern number but an anomalous ac Hall effect. The χ SDW is likely a generic phase of strongly correlated and highly frustrated hexagonal lattice electrons.

  18. The influence of lattice geometry on anti-ferromagnetic correlations and their dynamics in the Fermi-Hubbard model

    NASA Astrophysics Data System (ADS)

    Jotzu, Gregor; Greif, Daniel; Messer, Michael; Desbuqois, Rémi; Görg, Frederik; Esslinger, Tilman

    2016-05-01

    It is well known that in the thermodynamic limit, quantum effects hinder the formation of true long-range order in lower dimensions. However, on shorter length-scales correlations can actually be enhanced by reducing the connectivity of a lattice. Here we report on the observation of anti-ferromagnetic correlations of ultracold fermions in a variety of optical lattice geometries that are well described by the Hubbard model, including dimers, 1D chains, ladders, isolated and coupled honeycomb planes, as well as square and cubic lattices. The dependence of total correlations and their distribution on the specific geometry is experimentally probed by measuring the spin correlator along different lattice tunnelling bonds. We study distinct geometries as well as continuous crossovers between them, and find a strong dependence on the specific configuration. By dynamically changing the lattice geometry and studying the time-evolution of the system, we determine the time required for the formation and redistribution of spin correlations. Timescales ranging from a sudden quench of the lattice geometry to an adiabatic evolution are probed.

  19. Solutions of the two-dimensional Hubbard model: Benchmarks and results from a wide range of numerical algorithms

    SciTech Connect

    LeBlanc, J. P. F.; Antipov, Andrey E.; Becca, Federico; Bulik, Ireneusz W.; Chan, Garnet Kin-Lic; Chung, Chia -Min; Deng, Youjin; Ferrero, Michel; Henderson, Thomas M.; Jiménez-Hoyos, Carlos A.; Kozik, E.; Liu, Xuan -Wen; Millis, Andrew J.; Prokof’ev, N. V.; Qin, Mingpu; Scuseria, Gustavo E.; Shi, Hao; Svistunov, B. V.; Tocchio, Luca F.; Tupitsyn, I. S.; White, Steven R.; Zhang, Shiwei; Zheng, Bo -Xiao; Zhu, Zhenyue; Gull, Emanuel

    2015-12-14

    Numerical results for ground-state and excited-state properties (energies, double occupancies, and Matsubara-axis self-energies) of the single-orbital Hubbard model on a two-dimensional square lattice are presented, in order to provide an assessment of our ability to compute accurate results in the thermodynamic limit. Many methods are employed, including auxiliary-field quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of dual fermions, density matrix embedding theory, density matrix renormalization group, dynamical cluster approximation, diffusion Monte Carlo within a fixed-node approximation, unrestricted coupled cluster theory, and multireference projected Hartree-Fock methods. Comparison of results obtained by different methods allows for the identification of uncertainties and systematic errors. The importance of extrapolation to converged thermodynamic-limit values is emphasized. Furthermore, cases where agreement between different methods is obtained establish benchmark results that may be useful in the validation of new approaches and the improvement of existing methods.

  20. Full self-consistency versus quasiparticle self-consistency in diagrammatic approaches: Exactly solvable two-site Hubbard model

    DOE PAGESBeta

    Kutepov, A. L.

    2015-07-22

    Self-consistent solutions of Hedin's equations (HE) for the two-site Hubbard model (HM) have been studied. They have been found for three-point vertices of increasing complexity (Γ = 1 (GW approximation), Γ₁ from the first-order perturbation theory, and the exact vertex ΓE). Comparison is made between the cases when an additional quasiparticle (QP) approximation for Green's functions is applied during the self-consistent iterative solving of HE and when QP approximation is not applied. Results obtained with the exact vertex are directly related to the present open question—which approximation is more advantageous for future implementations, GW + DMFT or QPGW + DMFT.more » It is shown that in a regime of strong correlations only the originally proposed GW + DMFT scheme is able to provide reliable results. Vertex corrections based on Perturbation Theory systematically improve the GW results when full self-consistency is applied. The application of QP self-consistency combined with PT vertex corrections shows similar problems to the case when the exact vertex is applied combined with QP sc. An analysis of Ward Identity violation is performed for all studied in this work's approximations and its relation to the general accuracy of the schemes used is provided.« less

  1. The simulation of 3D mass models in 2D digital mammography and breast tomosynthesis

    SciTech Connect

    Shaheen, Eman De Keyzer, Frederik; Bosmans, Hilde; Ongeval, Chantal Van; Dance, David R.; Young, Kenneth C.

    2014-08-15

    Purpose: This work proposes a new method of building 3D breast mass models with different morphological shapes and describes the validation of the realism of their appearance after simulation into 2D digital mammograms and breast tomosynthesis images. Methods: Twenty-five contrast enhanced MRI breast lesions were collected and each mass was manually segmented in the three orthogonal views: sagittal, coronal, and transversal. The segmented models were combined, resampled to have isotropic voxel sizes, triangularly meshed, and scaled to different sizes. These masses were referred to as nonspiculated masses and were then used as nuclei onto which spicules were grown with an iterative branching algorithm forming a total of 30 spiculated masses. These 55 mass models were projected into 2D projection images to obtain mammograms after image processing and into tomographic sequences of projection images, which were then reconstructed to form 3D tomosynthesis datasets. The realism of the appearance of these mass models was assessed by five radiologists via receiver operating characteristic (ROC) analysis when compared to 54 real masses. All lesions were also given a breast imaging reporting and data system (BIRADS) score. The data sets of 2D mammography and tomosynthesis were read separately. The Kendall's coefficient of concordance was used for the interrater observer agreement assessment for the BIRADS scores per modality. Further paired analysis, using the Wilcoxon signed rank test, of the BIRADS assessment between 2D and tomosynthesis was separately performed for the real masses and for the simulated masses. Results: The area under the ROC curves, averaged over all observers, was 0.54 (95% confidence interval [0.50, 0.66]) for the 2D study, and 0.67 (95% confidence interval [0.55, 0.79]) for the tomosynthesis study. According to the BIRADS scores, the nonspiculated and the spiculated masses varied in their degrees of malignancy from normal (BIRADS 1) to highly

  2. Impact of high speed civil transports on stratospheric ozone: A 2-D model investigation

    SciTech Connect

    Kinnison, D.E.; Connell, P.S.

    1996-12-01

    This study investigates the effect on stratospheric ozone from a fleet of proposed High Speed Civil Transports (HSCTs). The new LLNL 2-D operator-split chemical-radiative-transport model of the troposphere and stratosphere is used for this HSCT investigation. This model is integrated in a diurnal manner, using an implicit numerical solver. Therefore, rate coefficients are not modified by any sort of diurnal average factor. This model also does not make any assumptions on lumping of chemical species into families. Comparisons to previous model-derived HSCT assessment of ozone change are made, both to the previous LLNL 2-D model and to other models from the international assessment modeling community. The sensitivity to the NO{sub x} emission index and sulfate surface area density is also explored.

  3. Extension and application of the Preissmann slot model to 2D transient mixed flows

    NASA Astrophysics Data System (ADS)

    Maranzoni, Andrea; Dazzi, Susanna; Aureli, Francesca; Mignosa, Paolo

    2015-08-01

    This paper presents an extension of the Preissmann slot concept for the modeling of highly transient two-dimensional (2D) mixed flows. The classic conservative formulation of the 2D shallow water equations for free surface flows is adapted by assuming that two fictitious vertical slots, aligned along the two Cartesian plane directions and normally intersecting, are added on the ceiling of each integration element. Accordingly, transitions between free surface and pressurized flow can be handled in a natural and straightforward way by using the same set of governing equations. The opportunity of coupling free surface and pressurized flows is actually useful not only in one-dimensional (1D) problems concerning sewer systems but also for modeling 2D flooding phenomena in which the pressurization of bridges, culverts, or other crossing hydraulic structures can be expected. Numerical simulations are performed by using a shock-capturing MUSCL-Hancock finite volume scheme combined with the FORCE (First-Order Centred) solver for the evaluation of the numerical fluxes. The validation of the mathematical model is accomplished on the basis of both exact solutions of 1D discontinuous initial value problems and reference radial solutions of idealized test cases with cylindrical symmetry. Furthermore, the capability of the model to deal with practical field-scale applications is assessed by simulating the transit of a bore under an arch bridge. Numerical results show that the proposed model is suitable for the prediction of highly transient 2D mixed flows.

  4. Comparison of 3-D finite element model of ashlar masonry with 2-D numerical models of ashlar masonry

    NASA Astrophysics Data System (ADS)

    Beran, Pavel

    2016-06-01

    3-D state of stress in heterogeneous ashlar masonry can be also computed by several suitable chosen 2-D numerical models of ashlar masonry. The results obtained from 2-D numerical models well correspond to the results obtained from 3-D numerical model. The character of thermal stress is the same. While using 2-D models the computational time is reduced more than hundredfold and therefore this method could be used for computation of thermal stresses during long time periods with 10 000 of steps.

  5. 2D-Raman-THz spectroscopy: A sensitive test of polarizable water models

    NASA Astrophysics Data System (ADS)

    Hamm, Peter

    2014-11-01

    In a recent paper, the experimental 2D-Raman-THz response of liquid water at ambient conditions has been presented [J. Savolainen, S. Ahmed, and P. Hamm, Proc. Natl. Acad. Sci. U. S. A. 110, 20402 (2013)]. Here, all-atom molecular dynamics simulations are performed with the goal to reproduce the experimental results. To that end, the molecular response functions are calculated in a first step, and are then convoluted with the laser pulses in order to enable a direct comparison with the experimental results. The molecular dynamics simulation are performed with several different water models: TIP4P/2005, SWM4-NDP, and TL4P. As polarizability is essential to describe the 2D-Raman-THz response, the TIP4P/2005 water molecules are amended with either an isotropic or a anisotropic polarizability a posteriori after the molecular dynamics simulation. In contrast, SWM4-NDP and TL4P are intrinsically polarizable, and hence the 2D-Raman-THz response can be calculated in a self-consistent way, using the same force field as during the molecular dynamics simulation. It is found that the 2D-Raman-THz response depends extremely sensitively on details of the water model, and in particular on details of the description of polarizability. Despite the limited time resolution of the experiment, it could easily distinguish between various water models. Albeit not perfect, the overall best agreement with the experimental data is obtained for the TL4P water model.

  6. Parallelized CCHE2D flow model with CUDA Fortran on Graphics Process Units

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This paper presents the CCHE2D implicit flow model parallelized using CUDA Fortran programming technique on Graphics Processing Units (GPUs). A parallelized implicit Alternating Direction Implicit (ADI) solver using Parallel Cyclic Reduction (PCR) algorithm on GPU is developed and tested. This solve...

  7. Analysis of Korean Students' International Mobility by 2-D Model: Driving Force Factor and Directional Factor

    ERIC Educational Resources Information Center

    Park, Elisa L.

    2009-01-01

    The purpose of this study is to understand the dynamics of Korean students' international mobility to study abroad by using the 2-D Model. The first D, "the driving force factor," explains how and what components of the dissatisfaction with domestic higher education perceived by Korean students drives students' outward mobility to seek foreign…

  8. 2D-Raman-THz spectroscopy: A sensitive test of polarizable water models

    SciTech Connect

    Hamm, Peter

    2014-11-14

    In a recent paper, the experimental 2D-Raman-THz response of liquid water at ambient conditions has been presented [J. Savolainen, S. Ahmed, and P. Hamm, Proc. Natl. Acad. Sci. U. S. A. 110, 20402 (2013)]. Here, all-atom molecular dynamics simulations are performed with the goal to reproduce the experimental results. To that end, the molecular response functions are calculated in a first step, and are then convoluted with the laser pulses in order to enable a direct comparison with the experimental results. The molecular dynamics simulation are performed with several different water models: TIP4P/2005, SWM4-NDP, and TL4P. As polarizability is essential to describe the 2D-Raman-THz response, the TIP4P/2005 water molecules are amended with either an isotropic or a anisotropic polarizability a posteriori after the molecular dynamics simulation. In contrast, SWM4-NDP and TL4P are intrinsically polarizable, and hence the 2D-Raman-THz response can be calculated in a self-consistent way, using the same force field as during the molecular dynamics simulation. It is found that the 2D-Raman-THz response depends extremely sensitively on details of the water model, and in particular on details of the description of polarizability. Despite the limited time resolution of the experiment, it could easily distinguish between various water models. Albeit not perfect, the overall best agreement with the experimental data is obtained for the TL4P water model.

  9. Justification for a 2D versus 3D fingertip finite element model during static contact simulations.

    PubMed

    Harih, Gregor; Tada, Mitsunori; Dolšak, Bojan

    2016-10-01

    The biomechanical response of a human hand during contact with various products has not been investigated in details yet. It has been shown that excessive contact pressure on the soft tissue can result in discomfort, pain and also cumulative traumatic disorders. This manuscript explores the benefits and limitations of a simplified two-dimensional vs. an anatomically correct three-dimensional finite element model of a human fingertip. Most authors still use 2D FE fingertip models due to their simplicity and reduced computational costs. However we show that an anatomically correct 3D FE fingertip model can provide additional insight into the biomechanical behaviour. The use of 2D fingertip FE models is justified when observing peak contact pressure values as well as displacement during the contact for the given studied cross-section. On the other hand, an anatomically correct 3D FE fingertip model provides a contact pressure distribution, which reflects the fingertip's anatomy. PMID:26856769

  10. Molecular Dynamics implementation of BN2D or 'Mercedes Benz' water model

    NASA Astrophysics Data System (ADS)

    Scukins, Arturs; Bardik, Vitaliy; Pavlov, Evgen; Nerukh, Dmitry

    2015-05-01

    Two-dimensional 'Mercedes Benz' (MB) or BN2D water model (Naim, 1971) is implemented in Molecular Dynamics. It is known that the MB model can capture abnormal properties of real water (high heat capacity, minima of pressure and isothermal compressibility, negative thermal expansion coefficient) (Silverstein et al., 1998). In this work formulas for calculating the thermodynamic, structural and dynamic properties in microcanonical (NVE) and isothermal-isobaric (NPT) ensembles for the model from Molecular Dynamics simulation are derived and verified against known Monte Carlo results. The convergence of the thermodynamic properties and the system's numerical stability are investigated. The results qualitatively reproduce the peculiarities of real water making the model a visually convenient tool that also requires less computational resources, thus allowing simulations of large (hydrodynamic scale) molecular systems. We provide the open source code written in C/C++ for the BN2D water model implementation using Molecular Dynamics.

  11. MODELING THE TRANSVERSE THERMAL CONDUCTIVITY OF 2-D SICF/SIC COMPOSITES MADE WITH WOVEN FABRIC

    SciTech Connect

    Youngblood, Gerald E; Senor, David J; Jones, Russell H

    2004-06-01

    The hierarchical two-layer (H2L) model describes the effective transverse thermal conductivity (Keff) of a 2D-SiCf/SiC composite plate made from stacked and infiltrated woven fabric layers in terms of constituent properties and microstructural and architectural variables. The H2L model includes the effects of fiber-matrix interfacial conductance, high fiber packing fractions within individual tows and the non-uniform nature of 2D fabric/matrix layers that usually include a significant amount of interlayer porosity. Previously, H2L model Keff-predictions were compared to measured values for two versions of 2D Hi-Nicalon/PyC/ICVI-SiC composite, one with a “thin” (0.11m) and the other with a “thick” (1.04m) pyrocarbon (PyC) fiber coating, and for a 2D Tyranno SA/”thin” PyC/FCVI-SIC composite. In this study, H2L model Keff-predictions were compared to measured values for a 2D-SiCf/SiC composite made using the ICVI-process with Hi-Nicalon type S fabric and a “thin” PyC fiber coating. The values of Keff determined for the latter composite were significantly greater than the Keff-values determined for the composites made with either the Hi-Nicalon or the Tyranno SA fabrics. Differences in Keff-values were expected for the different fiber types, but major differences also were due to observed microstructural and architectural variations between the composite systems, and as predicted by the H2L model.

  12. The 2dF Galaxy Redshift Survey: voids and hierarchical scaling models

    NASA Astrophysics Data System (ADS)

    Croton, Darren J.; Colless, Matthew; Gaztañaga, Enrique; Baugh, Carlton M.; Norberg, Peder; Baldry, I. K.; Bland-Hawthorn, J.; Bridges, T.; Cannon, R.; Cole, S.; Collins, C.; Couch, W.; Dalton, G.; de Propris, R.; Driver, S. P.; Efstathiou, G.; Ellis, R. S.; Frenk, C. S.; Glazebrook, K.; Jackson, C.; Lahav, O.; Lewis, I.; Lumsden, S.; Maddox, S.; Madgwick, D.; Peacock, J. A.; Peterson, B. A.; Sutherland, W.; Taylor, K.

    2004-08-01

    We measure the redshift-space reduced void probability function (VPF) for 2dFGRS volume-limited galaxy samples covering the absolute magnitude range MbJ-5log10h=-18 to -22. Theoretically, the VPF connects the distribution of voids to the moments of galaxy clustering of all orders, and can be used to discriminate clustering models in the weakly non-linear regime. The reduced VPF measured from the 2dFGRS is in excellent agreement with the paradigm of hierarchical scaling of the galaxy clustering moments. The accuracy of our measurement is such that we can rule out, at a very high significance, popular models for galaxy clustering, including the lognormal distribution. We demonstrate that the negative binomial model gives a very good approximation to the 2dFGRS data over a wide range of scales, out to at least 20 h-1 Mpc. Conversely, the reduced VPF for dark matter in a Λ cold dark matter (ΛCDM) universe does appear to be lognormal on small scales but deviates significantly beyond ~4 h-1 Mpc. We find little dependence of the 2dFGRS reduced VPF on galaxy luminosity. Our results hold independently in both the North and South Galactic Pole survey regions.

  13. Simplified 2D Bidomain Model of Whole Heart Electrical Activity and ECG Generation

    NASA Astrophysics Data System (ADS)

    Sovilj, Siniša; Magjarević, Ratko; Abed, Amr Al; Lovell, Nigel H.; Dokos, Socrates

    2014-06-01

    The aim of this study was the development of a geometrically simple and highly computationally-efficient two dimensional (2D) biophysical model of whole heart electrical activity, incorporating spontaneous activation of the sinoatrial node (SAN), the specialized conduction system, and realistic surface ECG morphology computed on the torso. The FitzHugh-Nagumo (FHN) equations were incorporated into a bidomain finite element model of cardiac electrical activity, which was comprised of a simplified geometry of the whole heart with the blood cavities, the lungs and the torso as an extracellular volume conductor. To model the ECG, we placed four electrodes on the surface of the torso to simulate three Einthoven leads VI, VII and VIII from the standard 12-lead system. The 2D model was able to reconstruct ECG morphology on the torso from action potentials generated at various regions of the heart, including the sinoatrial node, atria, atrioventricular node, His bundle, bundle branches, Purkinje fibers, and ventricles. Our 2D cardiac model offers a good compromise between computational load and model complexity, and can be used as a first step towards three dimensional (3D) ECG models with more complex, precise and accurate geometry of anatomical structures, to investigate the effect of various cardiac electrophysiological parameters on ECG morphology.

  14. Approximate analytic solutions to 3D unconfined groundwater flow within regional 2D models

    NASA Astrophysics Data System (ADS)

    Luther, K.; Haitjema, H. M.

    2000-04-01

    We present methods for finding approximate analytic solutions to three-dimensional (3D) unconfined steady state groundwater flow near partially penetrating and horizontal wells, and for combining those solutions with regional two-dimensional (2D) models. The 3D solutions use distributed singularities (analytic elements) to enforce boundary conditions on the phreatic surface and seepage faces at vertical wells, and to maintain fixed-head boundary conditions, obtained from the 2D model, at the perimeter of the 3D model. The approximate 3D solutions are analytic (continuous and differentiable) everywhere, including on the phreatic surface itself. While continuity of flow is satisfied exactly in the infinite 3D flow domain, water balance errors can occur across the phreatic surface.

  15. 2D and 3D numerical models on compositionally buoyant diapirs in the mantle wedge

    NASA Astrophysics Data System (ADS)

    Hasenclever, Jörg; Morgan, Jason Phipps; Hort, Matthias; Rüpke, Lars H.

    2011-11-01

    We present 2D and 3D numerical model calculations that focus on the physics of compositionally buoyant diapirs rising within a mantle wedge corner flow. Compositional buoyancy is assumed to arise from slab dehydration during which water-rich volatiles enter the mantle wedge and form a wet, less dense boundary layer on top of the slab. Slab dehydration is prescribed to occur in the 80-180 km deep slab interval, and the water transport is treated as a diffusion-like process. In this study, the mantle's rheology is modeled as being isoviscous for the benefit of easier-to-interpret feedbacks between water migration and buoyant viscous flow of the mantle. We use a simple subduction geometry that does not change during the numerical calculation. In a large set of 2D calculations we have identified that five different flow regimes can form, in which the position, number, and formation time of the diapirs vary as a function of four parameters: subduction angle, subduction rate, water diffusivity (mobility), and mantle viscosity. Using the same numerical method and numerical resolution we also conducted a suite of 3D calculations for 16 selected parameter combinations. Comparing the 2D and 3D results for the same model parameters reveals that the 2D models can only give limited insights into the inherently 3D problem of mantle wedge diapirism. While often correctly predicting the position and onset time of the first diapir(s), the 2D models fail to capture the dynamics of diapir ascent as well as the formation of secondary diapirs that result from boundary layer perturbations caused by previous diapirs. Of greatest importance for physically correct results is the numerical resolution in the region where diapirs nucleate, which must be high enough to accurately capture the growth of the thin wet boundary layer on top of the slab and, subsequently, the formation, morphology, and ascent of diapirs. Here 2D models can be very useful to quantify the required resolution, which we

  16. TRENT2D WG: a smart web infrastructure for debris-flow modelling and hazard assessment

    NASA Astrophysics Data System (ADS)

    Zorzi, Nadia; Rosatti, Giorgio; Zugliani, Daniel; Rizzi, Alessandro; Piffer, Stefano

    2016-04-01

    Mountain regions are naturally exposed to geomorphic flows, which involve large amounts of sediments and induce significant morphological modifications. The physical complexity of this class of phenomena represents a challenging issue for modelling, leading to elaborate theoretical frameworks and sophisticated numerical techniques. In general, geomorphic-flows models proved to be valid tools in hazard assessment and management. However, model complexity seems to represent one of the main obstacles to the diffusion of advanced modelling tools between practitioners and stakeholders, although the UE Flood Directive (2007/60/EC) requires risk management and assessment to be based on "best practices and best available technologies". Furthermore, several cutting-edge models are not particularly user-friendly and multiple stand-alone software are needed to pre- and post-process modelling data. For all these reasons, users often resort to quicker and rougher approaches, leading possibly to unreliable results. Therefore, some effort seems to be necessary to overcome these drawbacks, with the purpose of supporting and encouraging a widespread diffusion of the most reliable, although sophisticated, modelling tools. With this aim, this work presents TRENT2D WG, a new smart modelling solution for the state-of-the-art model TRENT2D (Armanini et al., 2009, Rosatti and Begnudelli, 2013), which simulates debris flows and hyperconcentrated flows adopting a two-phase description over a mobile bed. TRENT2D WG is a web infrastructure joining advantages offered by the software-delivering model SaaS (Software as a Service) and by WebGIS technology and hosting a complete and user-friendly working environment for modelling. In order to develop TRENT2D WG, the model TRENT2D was converted into a service and exposed on a cloud server, transferring computational burdens from the user hardware to a high-performing server and reducing computational time. Then, the system was equipped with an

  17. A Convective Vorticity Vector Associated With Tropical Convection: A 2D Cloud-Resolving Modeling Study

    NASA Technical Reports Server (NTRS)

    Gao, Shou-Ting; Ping, Fan; Li, Xiao-Fan; Tao, Wei-Kuo

    2004-01-01

    Although dry/moist potential vorticity is a useful physical quantity for meteorological analysis, it cannot be applied to the analysis of 2D simulations. A convective vorticity vector (CVV) is introduced in this study to analyze 2D cloud-resolving simulation data associated with 2D tropical convection. The cloud model is forced by the vertical velocity, zonal wind, horizontal advection, and sea surface temperature obtained from the TOGA COARE, and is integrated for a selected 10-day period. The CVV has zonal and vertical components in the 2D x-z frame. Analysis of zonally-averaged and mass-integrated quantities shows that the correlation coefficient between the vertical component of the CVV and the sum of the cloud hydrometeor mixing ratios is 0.81, whereas the correlation coefficient between the zonal component and the sum of the mixing ratios is only 0.18. This indicates that the vertical component of the CVV is closely associated with tropical convection. The tendency equation for the vertical component of the CVV is derived and the zonally-averaged and mass-integrated tendency budgets are analyzed. The tendency of the vertical component of the CVV is determined by the interaction between the vorticity and the zonal gradient of cloud heating. The results demonstrate that the vertical component of the CVV is a cloud-linked parameter and can be used to study tropical convection.

  18. Variational description of the ground state of the repulsive two-dimensional Hubbard model in terms of nonorthogonal symmetry-projected Slater determinants

    NASA Astrophysics Data System (ADS)

    Rodríguez-Guzmán, R.; Jiménez-Hoyos, Carlos A.; Scuseria, Gustavo E.

    2014-11-01

    The few-determinant (FED) methodology, introduced in our previous works [R. Rodríguez-Guzmán et al., Phys. Rev. B 87, 235129 (2013);, 10.1103/PhysRevB.87.235129 Phys. Rev. B 89, 195109 (2014), 10.1103/PhysRevB.89.195109] for one-dimensional (1D) lattices, is here adapted for the repulsive two-dimensional Hubbard model at half filling and with finite doping fractions. Within this configuration mixing scheme, a given ground state with well-defined spin and space group quantum numbers is expanded in terms of a nonorthogonal symmetry-projected basis determined through chains of variation-after-projection calculations. The results obtained for the ground-state and correlation energies of half-filled and doped 4 ×4 ,6 ×6 ,8 ×8 , and 10 ×10 lattices, as well as momentum distributions and spin-spin correlation functions in small lattices, compare well with those obtained using other state-of-the-art approximations. The structure of the intrinsic determinants resulting from the variational strategy is interpreted in terms of defects that encode information on the basic units of quantum fluctuations in the considered 2D systems. The varying nature of the underlying quantum fluctuations, reflected in a transition to a stripe regime for increasing on-site repulsions, is discussed using the intrinsic determinants belonging to a 16 ×4 lattice with 56 electrons. Such a transition is further illustrated by computing spin-spin and charge-charge correlation functions with the corresponding multireference FED wave functions. In good agreement with previous studies, the analysis of the pairing correlation functions reveals a weak enhancement of the extended s -wave and dx2-y2 pairing modes. Given the quality of results here reported together with those previously obtained for 1D lattices and the parallelization properties of the FED scheme, we believe that symmetry projection techniques are very well suited for building ground-state wave functions of correlated electronic

  19. Parameterising root system growth models using 2D neutron radiography images

    NASA Astrophysics Data System (ADS)

    Schnepf, Andrea; Felderer, Bernd; Vontobel, Peter; Leitner, Daniel

    2013-04-01

    Root architecture is a key factor for plant acquisition of water and nutrients from soil. In particular in view of a second green revolution where the below ground parts of agricultural crops are important, it is essential to characterise and quantify root architecture and its effect on plant resource acquisition. Mathematical models can help to understand the processes occurring in the soil-plant system, they can be used to quantify the effect of root and rhizosphere traits on resource acquisition and the response to environmental conditions. In order to do so, root architectural models are coupled with a model of water and solute transport in soil. However, dynamic root architectural models are difficult to parameterise. Novel imaging techniques such as x-ray computed tomography, neutron radiography and magnetic resonance imaging enable the in situ visualisation of plant root systems. Therefore, these images facilitate the parameterisation of dynamic root architecture models. These imaging techniques are capable of producing 3D or 2D images. Moreover, 2D images are also available in the form of hand drawings or from images of standard cameras. While full 3D imaging tools are still limited in resolutions, 2D techniques are a more accurate and less expensive option for observing roots in their environment. However, analysis of 2D images has additional difficulties compared to the 3D case, because of overlapping roots. We present a novel algorithm for the parameterisation of root system growth models based on 2D images of root system. The algorithm analyses dynamic image data. These are a series of 2D images of the root system at different points in time. Image data has already been adjusted for missing links and artefacts and segmentation was performed by applying a matched filter response. From this time series of binary 2D images, we parameterise the dynamic root architecture model in the following way: First, a morphological skeleton is derived from the binary

  20. Validation of a 2-D semi-coupled numerical model for fluid-structure-seabed interaction

    NASA Astrophysics Data System (ADS)

    Ye, Jianhong; Jeng, Dongsheng; Wang, Ren; Zhu, Changqi

    2013-10-01

    A 2-D semi-coupled model PORO-WSSI 2D (also be referred as FSSI-CAS 2D) for the Fluid-Structure-Seabed Interaction (FSSI) has been developed by employing RANS equations for wave motion in fluid domain, VARANS equations for porous flow in porous structures; and taking the dynamic Biot's equations (known as "u - p" approximation) for soil as the governing equations. The finite difference two-step projection method and the forward time difference method are adopted to solve the RANS, VARANS equations; and the finite element method is adopted to solve the "u - p" approximation. A data exchange port is developed to couple the RANS, VARANS equations and the dynamic Biot's equations together. The analytical solution proposed by Hsu and Jeng (1994) and some experiments conducted in wave flume or geotechnical centrifuge in which various waves involved are used to validate the developed semi-coupled numerical model. The sandy bed involved in these experiments is poro-elastic or poro-elastoplastic. The inclusion of the interaction between fluid, marine structures and poro-elastoplastic seabed foundation is a special point and highlight in this paper, which is essentially different with other previous coupled models The excellent agreement between the numerical results and the experiment data indicates that the developed coupled model is highly reliablefor the FSSI problem.

  1. 2D density model of the Chinese continental lithosphere along a NW-SE transect

    NASA Astrophysics Data System (ADS)

    Šimonová, Barbora; Bielik, Miroslav; Dérerová, Jana

    2015-06-01

    This paper presents a 2D density model along a transect from NW to SE China. The model was first constructed by the transformation of seismic velocity to density, revealed by previous deep seismic soundings (DSS) investigations in China. Then, the 2D density model was updated using the GM-SYS software by fitting the computed to the observed gravity data. Based on the density distribution of anomalous layers we divided the Chinese continental crust along the transect into three regions: north-western, central and south-eastern. The first one includes the Junggar Basin, Tianshan and Tarim Basin. The second part consists of the Qilian Orogen, the Qaidam Basin and the Songpan Ganzi Basin. The third region is represented by the Yangtze and the Cathaysia blocks. The low velocity body (vp =5.2 - 6.2 km/s) at the junction of the North-western and Central parts at a depth between 21 - 31 km, which was discovered out by DSS, was also confirmed by our 2D density modelling.

  2. A Neural-FEM tool for the 2-D magnetic hysteresis modeling

    NASA Astrophysics Data System (ADS)

    Cardelli, E.; Faba, A.; Laudani, A.; Lozito, G. M.; Riganti Fulginei, F.; Salvini, A.

    2016-04-01

    The aim of this work is to present a new tool for the analysis of magnetic field problems considering 2-D magnetic hysteresis. In particular, this tool makes use of the Finite Element Method to solve the magnetic field problem in real device, and fruitfully exploits a neural network (NN) for the modeling of 2-D magnetic hysteresis of materials. The NS has as input the magnetic inductions components B at the k-th simulation step and returns as output the corresponding values of the magnetic field H corresponding to the input pattern. It is trained by vector measurements performed on the magnetic material to be modeled. This input/output scheme is directly implemented in a FEM code employing the magnetic potential vector A formulation. Validations through measurements on a real device have been performed.

  3. TMRPres2D: high quality visual representation of transmembrane protein models.

    PubMed

    Spyropoulos, Ioannis C; Liakopoulos, Theodore D; Bagos, Pantelis G; Hamodrakas, Stavros J

    2004-11-22

    The 'TransMembrane protein Re-Presentation in 2-Dimensions' (TMRPres2D) tool, automates the creation of uniform, two-dimensional, high analysis graphical images/models of alpha-helical or beta-barrel transmembrane proteins. Protein sequence data and structural information may be acquired from public protein knowledge bases, emanate from prediction algorithms, or even be defined by the user. Several important biological and physical sequence attributes can be embedded in the graphical representation. PMID:15201184

  4. Bose-Hubbard model with random impurities: Multiband and nonlinear hopping effects

    NASA Astrophysics Data System (ADS)

    Stasińska, Julia; Łacki, Mateusz; Dutta, Omjyoti; Zakrzewski, Jakub; Lewenstein, Maciej

    2014-12-01

    We investigate the phase diagrams of theoretical models describing bosonic atoms in a lattice in the presence of randomly localized impurities. By including multiband and nonlinear hopping effects we enrich the standard model containing only the chemical-potential disorder with the site-dependent hopping term. We compare the extension of the MI and the BG phase in both models using a combination of the local mean-field method and a Hartree-Fock-like procedure, as well as the Gutzwiller-ansatz approach. We show analytical argument for the presence of triple points in the phase diagram of the model with chemical-potential disorder. These triple points, however, cease to exist after the addition of the hopping disorder.

  5. Effective single-band Hubbard model for the cuprates: Coulomb interactions and apical oxygen

    NASA Astrophysics Data System (ADS)

    Feiner, L. F.; Jefferson, J. H.; Raimondi, R.

    1995-02-01

    Starting with the three-band d-p model representing the high- Tc cuprates, we make a systematic reduction to an effective single-band model using a previously developed cell-perturbation method. In particular, we consider the effect of Coulomb repulsions on oxygen ( Up) and between copper and oxygen ( Vpd), and show that the resulting net Coloumb interaction between doped holes on neighbouring cells can be attractive due to locally enhanced pd hybridization, while this cannot occur for electrons. Extending to a five-band model, by including d 3 z2- r2 and apex p z orbitals, we show that there is, in addition to the usual Zhang-Rice singlet, a two-hole cell state which can be low in energy (depending on the proximity of the apicals), and may lead to a breakdown of the effective single-band model.

  6. A simple 2-D inundation model for incorporating flood damage in urban drainage planning

    NASA Astrophysics Data System (ADS)

    Pathirana, A.; Tsegaye, S.; Gersonius, B.; Vairavamoorthy, K.

    2008-11-01

    In this paper a new inundation model code is developed and coupled with Storm Water Management Model, SWMM, to relate spatial information associated with urban drainage systems as criteria for planning of storm water drainage networks. The prime objective is to achive a model code that is simple and fast enough to be consistently be used in planning stages of urban drainage projects. The formulation for the two-dimensional (2-D) surface flow model algorithms is based on the Navier Stokes equation in two dimensions. An Alternating Direction Implicit (ADI) finite difference numerical scheme is applied to solve the governing equations. This numerical scheme is used to express the partial differential equations with time steps split into two halves. The model algorithm is written using C++ computer programming language. This 2-D surface flow model is then coupled with SWMM for simulation of both pipe flow component and surcharge induced inundation in urban areas. In addition, a damage calculation block is integrated within the inundation model code. The coupled model is shown to be capable of dealing with various flow conditions, as well as being able to simulate wetting and drying processes that will occur as the flood flows over an urban area. It has been applied under idealized and semi-hypothetical cases to determine detailed inundation zones, depths and velocities due to surcharged water on overland surface.

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

    SciTech Connect

    Carvalho, Vanuildo S de; Freire, Hermann

    2014-09-15

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

  8. Comparison between 2D and 3D Numerical Modelling of a hot forging simulative test

    SciTech Connect

    Croin, M.; Ghiotti, A.; Bruschi, S.

    2007-04-07

    The paper presents the comparative analysis between 2D and 3D modelling of a simulative experiment, performed in laboratory environment, in which operating conditions approximate hot forging of a turbine aerofoil section. The plane strain deformation was chosen as an ideal case to analyze the process because of the thickness variations in the final section and the consequent distributions of contact pressure and sliding velocity at the interface that are closed to the conditions of the real industrial process. In order to compare the performances of 2D and 3D approaches, two different analyses were performed and compared with the experiments in terms of loads and temperatures peaks at the interface between the dies and the workpiece.

  9. Dynamic Cluster Quantum Monte Carlo Simulations of a Two-Dimensional Hubbard Model with Stripelike Charge-Density-Wave Modulations: Interplay between Inhomogeneities and the Superconducting State

    SciTech Connect

    Maier, Thomas A; Alvarez, Gonzalo; Summers, Michael Stuart; Schulthess, Thomas C

    2010-01-01

    Using dynamic cluster quantum Monte Carlo simulations, we study the superconducting behavior of a 1=8 doped two-dimensional Hubbard model with imposed unidirectional stripelike charge-density-wave modulation. We find a significant increase of the pairing correlations and critical temperature relative to the homogeneous system when the modulation length scale is sufficiently large. With a separable form of the irreducible particle-particle vertex, we show that optimized superconductivity is obtained for a moderate modulation strength due to a delicate balance between the modulation enhanced pairing interaction, and a concomitant suppression of the bare particle-particle excitations by a modulation reduction of the quasiparticle weight.

  10. Quantum phase transition in a one-dimensional Holstein-Hubbard model at half-filling in the thermodynamic limit: A quantum entanglement approach

    NASA Astrophysics Data System (ADS)

    Sankar, I. V.; Chatterjee, Ashok

    2016-05-01

    The quantum phase transition from a spin-density wave phase to a charge-density wave phase is studied within the framework of the one-dimensional Holstein-Hubbard model. The phonons are first eliminated by using a variational phonon state and the effective electronic Hamiltonian is then exactly solved using the Bethe ansatz technique to get the ground state energy. The entanglement entropy is finally calculated to show the possibility of existence of an intervening metallic phase at the cross-over region of the spin-density and charge-density wave phases in the thermodynamic limit at half-filling.

  11. Nested 1D-2D approach for urban surface flood modeling

    NASA Astrophysics Data System (ADS)

    Murla, Damian; Willems, Patrick

    2015-04-01

    Floods in urban areas as a consequence of sewer capacity exceedance receive increased attention because of trends in urbanization (increased population density and impermeability of the surface) and climate change. Despite the strong recent developments in numerical modeling of water systems, urban surface flood modeling is still a major challenge. Whereas very advanced and accurate flood modeling systems are in place and operation by many river authorities in support of flood management along rivers, this is not yet the case in urban water management. Reasons include the small scale of the urban inundation processes, the need to have very high resolution topographical information available, and the huge computational demands. Urban drainage related inundation modeling requires a 1D full hydrodynamic model of the sewer network to be coupled with a 2D surface flood model. To reduce the computational times, 0D (flood cones), 1D/quasi-2D surface flood modeling approaches have been developed and applied in some case studies. In this research, a nested 1D/2D hydraulic model has been developed for an urban catchment at the city of Gent (Belgium), linking the underground sewer (minor system) with the overland surface (major system). For the overland surface flood modelling, comparison was made of 0D, 1D/quasi-2D and full 2D approaches. The approaches are advanced by considering nested 1D-2D approaches, including infiltration in the green city areas, and allowing the effects of surface storm water storage to be simulated. An optimal nested combination of three different mesh resolutions was identified; based on a compromise between precision and simulation time for further real-time flood forecasting, warning and control applications. Main streets as mesh zones together with buildings as void regions constitute one of these mesh resolution (3.75m2 - 15m2); they have been included since they channel most of the flood water from the manholes and they improve the accuracy of

  12. Magnetic states of the five-orbital Hubbard model for one-dimensional iron-based superconductors

    SciTech Connect

    Luo, Qinlong; Foyevtsova, Kateryna; Samolyuk, German D; Reboredo, Fernando A; Dagotto, G

    2014-01-01

    Themagneticphasediagramsofmodelsforquasi-one-dimensionalcompoundsbelongingtotheiron-based-superconductorfamilyarepresented.The ve-orbitalHubbardmodelandthereal-spaceHartree Fockapproximationareemployed,supplementedbydensityfunctionaltheorytoobtainthehoppingamplitudes.PhasediagramsareconstructedbyvaryingtheHubbardUandHundJcouplingsatzerotemperature.Thestudyiscarriedoutatelectronicdensity(electronsperiron)n=5.0,whichisofrelevanceforthealready-knownmaterialTlFeSe2,andalsoatn=6.0,whererepresentativecompoundsstillneedtobesynthesized.Atn=5.0thereisacleardominanceofstaggeredspinorderalongthechaindirection.Atn=6.0andwiththerealisticHundcouplingJ/U=0.25,thephasediagramisfarricher,includingavarietyof block statesinvolvingferromagneticclustersthatareantiferromagneticallycoupled,inqualitativeagreementwithrecentdensitymatrixrenormalizationgroupcalculationsforthethree-orbitalHubbardmodelinadifferentcontext.Theseblockstatesarisefromthecompetitionbetweenferromagneticorder(inducedbydoubleexchangeandprevailingatlargeJ/U)andantiferromagneticorder(dominatingatsmallJ/U).Thedensityofstatesandorbitalcompositionsofthemanyphasesarealsoprovided.

  13. Mechanical Modelling of Pultrusion Process: 2D and 3D Numerical Approaches

    NASA Astrophysics Data System (ADS)

    Baran, Ismet; Hattel, Jesper H.; Akkerman, Remko; Tutum, Cem C.

    2015-02-01

    The process induced variations such as residual stresses and distortions are a critical issue in pultrusion, since they affect the structural behavior as well as the mechanical properties and geometrical precision of the final product. In order to capture and investigate these variations, a mechanical analysis should be performed. In the present work, the two dimensional (2D) quasi-static plane strain mechanical model for the pultrusion of a thick square profile developed by the authors is further improved using generalized plane strain elements. In addition to that, a more advanced 3D thermo-chemical-mechanical analysis is carried out using 3D quadratic elements which is a novel application for the numerical modelling of the pultrusion process. It is found that the 2D mechanical models give relatively reasonable and accurate stress and displacement evolutions in the transverse direction as compared to the 3D model. Moreover, the generalized plane strain model predicts the longitudinal process induced stresses more similar to the ones calculated in the 3D model as compared with the plane strain model.

  14. Canonical vs. micro-canonical sampling methods in a 2D Ising model

    SciTech Connect

    Kepner, J.

    1990-12-01

    Canonical and micro-canonical Monte Carlo algorithms were implemented on a 2D Ising model. Expressions for the internal energy, U, inverse temperature, Z, and specific heat, C, are given. These quantities were calculated over a range of temperature, lattice sizes, and time steps. Both algorithms accurately simulate the Ising model. To obtain greater than three decimal accuracy from the micro-canonical method requires that the more complicated expression for Z be used. The overall difference between the algorithms is small. The physics of the problem under study should be the deciding factor in determining which algorithm to use. 13 refs., 6 figs., 2 tabs.

  15. Complex zeros of the 2 d Ising model on dynamical random lattices

    NASA Astrophysics Data System (ADS)

    Ambjørn, J.; Anagnostopoulos, K. N.; Magnea, U.

    1998-04-01

    We study the zeros in the complex plane of the partition function for the Ising model coupled to 2 d quantum gravity for complex magnetic field and for complex temperature. We compute the zeros by using the exact solution coming from a two matrix model and by Monte Carlo simulations of Ising spins on dynamical triangulations. We present evidence that the zeros form simple one-dimensional patterns in the complex plane, and that the critical behaviour of the system is governed by the scaling of the distribution of singularities near the critical point.

  16. Brane brick models, toric Calabi-Yau 4-folds and 2d (0,2) quivers

    NASA Astrophysics Data System (ADS)

    Franco, Sebastián; Lee, Sangmin; Seong, Rak-Kyeong

    2016-02-01

    We introduce brane brick models, a novel type of Type IIA brane configurations consisting of D4-branes ending on an NS5-brane. Brane brick models are T-dual to D1-branes over singular toric Calabi-Yau 4-folds. They fully encode the infinite class of 2 d (generically) {N}=(0,2) gauge theories on the worldvolume of the D1-branes and streamline their connection to the probed geometries. For this purpose, we also introduce new combinatorial procedures for deriving the Calabi-Yau associated to a given gauge theory and vice versa.

  17. Topological Edge States in the One-Dimensional Superlattice Bose-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Grusdt, Fabian; Höning, Michael; Fleischhauer, Michael

    2013-06-01

    We analyze interacting ultracold bosonic atoms in a one-dimensional superlattice potential with alternating tunneling rates t1 and t2 and inversion symmetry, which is the bosonic analogue of the Su-Schrieffer-Heeger model. A Z2 topological order parameter is introduced which is quantized for the Mott insulating (MI) phases. Depending on the ratio t1/t2 the n=1/2 MI phase is topologically nontrivial, which results in many-body edge states at open boundaries. In contrast to the Su-Schrieffer-Heeger model the bosonic counterpart lacks chiral symmetry and the edge states are no longer midgap. This leads to a generalization of the bulk-edge correspondence, which we discuss in detail. The edge states can be observed in cold atom experiments by creating a step in the effective confining potential, e.g., by a second heavy atom species, which leads to an interface between two MI regions with filling n=1 and n=1/2. The shape and energy of the edge states as well as the conditions for their occupation are determined analytically in the strong coupling limit and in general by density-matrix renormalization group simulations.

  18. Topological edge States in the one-dimensional superlattice Bose-Hubbard model.

    PubMed

    Grusdt, Fabian; Höning, Michael; Fleischhauer, Michael

    2013-06-28

    We analyze interacting ultracold bosonic atoms in a one-dimensional superlattice potential with alternating tunneling rates t1 and t2 and inversion symmetry, which is the bosonic analogue of the Su-Schrieffer-Heeger model. A Z2 topological order parameter is introduced which is quantized for the Mott insulating (MI) phases. Depending on the ratio t1/t2 the n=1/2 MI phase is topologically nontrivial, which results in many-body edge states at open boundaries. In contrast to the Su-Schrieffer-Heeger model the bosonic counterpart lacks chiral symmetry and the edge states are no longer midgap. This leads to a generalization of the bulk-edge correspondence, which we discuss in detail. The edge states can be observed in cold atom experiments by creating a step in the effective confining potential, e.g., by a second heavy atom species, which leads to an interface between two MI regions with filling n=1 and n=1/2. The shape and energy of the edge states as well as the conditions for their occupation are determined analytically in the strong coupling limit and in general by density-matrix renormalization group simulations. PMID:23848851

  19. 2D-3D Registration of CT Vertebra Volume to Fluoroscopy Projection: A Calibration Model Assessment

    NASA Astrophysics Data System (ADS)

    Bifulco, P.; Cesarelli, M.; Allen, R.; Romano, M.; Fratini, A.; Pasquariello, G.

    2009-12-01

    This study extends a previous research concerning intervertebral motion registration by means of 2D dynamic fluoroscopy to obtain a more comprehensive 3D description of vertebral kinematics. The problem of estimating the 3D rigid pose of a CT volume of a vertebra from its 2D X-ray fluoroscopy projection is addressed. 2D-3D registration is obtained maximising a measure of similarity between Digitally Reconstructed Radiographs (obtained from the CT volume) and real fluoroscopic projection. X-ray energy correction was performed. To assess the method a calibration model was realised a sheep dry vertebra was rigidly fixed to a frame of reference including metallic markers. Accurate measurement of 3D orientation was obtained via single-camera calibration of the markers and held as true 3D vertebra position; then, vertebra 3D pose was estimated and results compared. Error analysis revealed accuracy of the order of 0.1 degree for the rotation angles of about 1 mm for displacements parallel to the fluoroscopic plane, and of order of 10 mm for the orthogonal displacement.

  20. Robust s± superconductivity in a two-band Hubbard-Fröhlich model of alkali-doped organics

    NASA Astrophysics Data System (ADS)

    Qin, Tao; Fabrizio, Michele; Naghavi, S. Shahab; Tosatti, Erio

    2014-08-01

    The damaging effect of strong electron-electron repulsion on regular, electron-phonon superconductivity is a standard tenet. In spite of that, an increasing number of compounds such as fullerides and more recently alkali-doped aromatics exhibit superconductivity despite very narrow bands and very strong electron repulsion. Here, we explore superconducting solutions of a model Hamiltonian inspired by the electronic structure of alkali-doped aromatics. The model is a two-site, two-narrow-band metal with a single intersite phonon, leading to attraction-mediated, two-order parameter superconductivity. On top of that, the model includes a repulsive onsite Hubbard U, whose effect on the superconductivity we study. Starting within mean field, we find that s± superconductivity is the best solution surviving the presence of U, whose effect is canceled out by the opposite signs of the two order parameters. The correlated Gutzwiller study that follows is necessary because without electron correlations, the superconducting state would in this model be superseded by an antiferromagnetic insulating state with lower energy. The Gutzwiller correlations lower the energy of the metallic state, with the consequence that the s± superconducting state is stabilized and even strengthened for small Hubbard U.

  1. Three-site Bose-Hubbard model subject to atom losses: Boson-pair dissipation channel and failure of the mean-field approach

    SciTech Connect

    Shchesnovich, V. S.; Mogilevtsev, D. S.

    2010-10-15

    We employ the perturbation series expansion for derivation of the reduced master equations for the three-site Bose-Hubbard model subject to strong atom losses from the central site. The model describes a condensate trapped in a triple-well potential subject to externally controlled removal of atoms. We find that the {pi}-phase state of the coherent superposition between the side wells decays via two dissipation channels, the single-boson channel (similar to the externally applied dissipation) and the boson-pair channel. The quantum derivation is compared to the classical adiabatic elimination within the mean-field approximation. We find that the boson-pair dissipation channel is not captured by the mean-field model, whereas the single-boson channel is described by it. Moreover, there is a matching condition between the zero-point energy bias of the side wells and the nonlinear interaction parameter which separates the regions where either the single-boson or the boson-pair dissipation channel dominate. Our results indicate that the M-site Bose-Hubbard models, for M>2, subject to atom losses may require an analysis which goes beyond the usual mean-field approximation for correct description of their dissipative features. This is an important result in view of the recent experimental works on the single-site addressability of condensates trapped in optical lattices.

  2. A 2-D semi-analytical model of double-gate tunnel field-effect transistor

    NASA Astrophysics Data System (ADS)

    Huifang, Xu; Yuehua, Dai; Ning, Li; Jianbin, Xu

    2015-05-01

    A 2-D semi-analytical model of double gate (DG) tunneling field-effect transistor (TFET) is proposed. By aid of introducing two rectangular sources located in the gate dielectric layer and the channel, the 2-D Poisson equation is solved by using a semi-analytical method combined with an eigenfunction expansion method. The expression of the surface potential is obtained, which is a special function for the infinite series expressions. The influence of the mobile charges on the potential profile is taken into account in the proposed model. On the basis of the potential profile, the shortest tunneling length and the average electrical field can be derived, and the drain current is then constructed by using Kane's model. In particular, the changes of the tunneling parameters Ak and Bk influenced by the drain—source voltage are also incorporated in the predicted model. The proposed model shows a good agreement with TCAD simulation results under different drain—source voltages, silicon film thicknesses, gate dielectric layer thicknesses, and gate dielectric layer constants. Therefore, it is useful to optimize the DG TFET and this provides a physical insight for circuit level design. Project supported by the National Natural Science Foundation of China (No. 61376106) and the Graduate Innovation Fund of Anhui University.

  3. Gender and ethnicity specific generic elastic models from a single 2D image for novel 2D pose face synthesis and recognition.

    PubMed

    Heo, Jingu; Savvides, Marios

    2012-12-01

    In this paper, we propose a novel method for generating a realistic 3D human face from a single 2D face image for the purpose of synthesizing new 2D face images at arbitrary poses using gender and ethnicity specific models. We employ the Generic Elastic Model (GEM) approach, which elastically deforms a generic 3D depth-map based on the sparse observations of an input face image in order to estimate the depth of the face image. Particularly, we show that Gender and Ethnicity specific GEMs (GE-GEMs) can approximate the 3D shape of the input face image more accurately, achieving a better generalization of 3D face modeling and reconstruction compared to the original GEM approach. We qualitatively validate our method using publicly available databases by showing each reconstructed 3D shape generated from a single image and new synthesized poses of the same person at arbitrary angles. For quantitative comparisons, we compare our synthesized results against 3D scanned data and also perform face recognition using synthesized images generated from a single enrollment frontal image. We obtain promising results for handling pose and expression changes based on the proposed method. PMID:22201062

  4. Modeling the Elastic Modulus of 2D Woven CVI SiC Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.

    2006-01-01

    The use of fiber, interphase, CVI SiC minicomposites as structural elements for 2D-woven SiC fiber reinforced chemically vapor infiltrated (CVI) SiC matrix composites is demonstrated to be a viable approach to model the elastic modulus of these composite systems when tensile loaded in an orthogonal direction. The 0deg (loading direction) and 90deg (perpendicular to loading direction) oriented minicomposites as well as the open porosity and excess SiC associated with CVI SiC composites were all modeled as parallel elements using simple Rule of Mixtures techniques. Excellent agreement for a variety of 2D woven Hi-Nicalon(TradeMark) fiber-reinforced and Sylramic-iBN reinforced CVI SiC matrix composites that differed in numbers of plies, constituent content, thickness, density, and number of woven tows in either direction (i.e, balanced weaves versus unbalanced weaves) was achieved. It was found that elastic modulus was not only dependent on constituent content, but also the degree to which 90deg minicomposites carried load. This depended on the degree of interaction between 90deg and 0deg minicomposites which was quantified to some extent by composite density. The relationships developed here for elastic modulus only necessitated the knowledge of the fractional contents of fiber, interphase and CVI SiC as well as the tow size and shape. It was concluded that such relationships are fairly robust for orthogonally loaded 2D woven CVI SiC composite system and can be implemented by ceramic matrix composite component modelers and designers for modeling the local stiffness in simple or complex parts fabricated with variable constituent contents.

  5. A solidification constitutive model for NIKE2D and NIKE3D

    SciTech Connect

    Raboin, P.J.

    1994-03-17

    This memo updates the current status of a solidification material model development which has been underway for more than a year. Significant modeling goals such as predicting cut-off stresses, thermo-elasto-plasticity, strain rate dependent plasticity and dynamic recovery have been completed. The model is called SOLMAT for solidification material model, and while developed for NIKE2D, it has already been implemented in NIKE3D and NIT03D by B. Maker. This memo details the future development strategy of SOLMAT including liquid and solid constitutive improvements, coupling of deviatoric and dilatational deformation and a plan to switch between constitutive theories. It explains some of the difficulties associated solidification modeling and proposes two experiments to measure properties for using SOLMAT. Due to the sensitive nature of these plans in relation to programmatic and CRADA concerns, this memo should be treated as confidential document.

  6. An Integrative Model of Excitation Driven Fluid Flow in a 2D Uterine Channel

    NASA Astrophysics Data System (ADS)

    Maggio, Charles; Fauci, Lisa; Chrispell, John

    2009-11-01

    We present a model of intra-uterine fluid flow in a sagittal cross-section of the uterus by inducing peristalsis in a 2D channel. This is an integrative multiscale computational model that takes as input fluid viscosity, passive tissue properties of the uterine channel and a prescribed wave of membrane depolarization. This voltage pulse is coupled to a model of calcium dynamics inside a uterine smooth muscle cell, which in turn drives a kinetic model of myosin phosphorylation governing contractile muscle forces. Using the immersed boundary method, these muscle forces are communicated to a fluid domain to simulate the contractions which occur in a human uterus. An analysis of the effects of model parameters on the flow properties and emergent geometry of the peristaltic channel will be presented.

  7. Global regularity for the 2D Oldroyd-B model in the corotational case

    NASA Astrophysics Data System (ADS)

    Ye, Zhuan; Xu, Xiaojing

    2016-09-01

    This paper is dedicated to the Oldroyd-B model with fractional dissipation $(-\\Delta)^{\\alpha}\\tau$ for any $\\alpha>0$. We establish the global smooth solutions to the Oldroyd-B model in the corotational case with arbitrarily small fractional powers of the Laplacian in two spatial dimensions. The methods described here are quite different from the tedious iterative approach used in recent paper \\cite{XY}. Moreover, in the Appendix we provide some a priori estimates to the Oldroyd-B model in the critical case which may be useful and of interest for future improvement. Finally, the global regularity to to the Oldroyd-B model in the corotational case with $-\\Delta u$ replaced by $(-\\Delta)^{\\gamma}u$ for $\\gamma>1$ are also collected in the Appendix. Therefore our result is more closer to the resolution of the well-known global regularity issue on the critical 2D Oldroyd-B model.

  8. A velocity-dependent anomalous radial transport model for (2-D, 2-V) kinetic transport codes

    NASA Astrophysics Data System (ADS)

    Bodi, Kowsik; Krasheninnikov, Sergei; Cohen, Ron; Rognlien, Tom

    2008-11-01

    Plasma turbulence constitutes a significant part of radial plasma transport in magnetically confined plasmas. This turbulent transport is modeled in the form of anomalous convection and diffusion coefficients in fluid transport codes. There is a need to model the same in continuum kinetic edge codes [such as the (2-D, 2-V) transport version of TEMPEST, NEO, and the code being developed by the Edge Simulation Laboratory] with non-Maxwellian distributions. We present an anomalous transport model with velocity-dependent convection and diffusion coefficients leading to a diagonal transport matrix similar to that used in contemporary fluid transport models (e.g., UEDGE). Also presented are results of simulations corresponding to radial transport due to long-wavelength ExB turbulence using a velocity-independent diffusion coefficient. A BGK collision model is used to enable comparison with fluid transport codes.

  9. Dynamical DMRG study of non-linear optical response in one-dimensional dimerized Hubbard model with nearest neighbor Coulomb interaction and alternating on-site potential

    NASA Astrophysics Data System (ADS)

    Sota, Shigetoshi; Tohyama, Takami; Brazovskii, Serguei

    2012-02-01

    The optical response of organic compounds has been attracting much attention. The one of the reasons is the huge non-linear and ultrafast optical response [K. Yamamoto et. al., J. Phys. Soc. Jpn. 77, 074709(2008)]. In order to investigate such optical properties, we carry out dynamical DMRG calculations to obtain optical responses in the 1/4-filled one-dimensional Hubbard model including the nearest neighbor Coulomb interaction and the alternating electron hopping. The charge gap [S. Nishimoto, M. Takahashi, and Y. Ohta, J. Phys. Soc. Jpn. 69, 1594(2000)] and the bound state [H. Benthien and E. Jeckelmann, Eur. Phys. J. B 44, 287(2005)] in this model have been discussed based on DMRG calculations. In the present study, we introduce an alternating on-site potential giving the polarization in the system into the dimerized Hubbard model, which breaks the reflection symmetry of the system. In this talk, we discuss the obtained linear and the 2nd order non-linear optical susceptibility in order to make a prediction for non-linear optical experiments in the future.

  10. Evaluation of Hydrus-2D model for solute distribution in subsurface drip

    NASA Astrophysics Data System (ADS)

    Souza, Claudinei; Bizari, Douglas; Grecco, Katarina

    2015-04-01

    The competition for water use between agriculture, industry and population has become intense over the years, requiring a rational use of this resource for food production. The subsurface drip irrigation can help producers with the optimization of operating parameters such as frequency and duration of irrigation, flow, spacing and depth of the dripper installation. This information can be obtained by numerical simulations using mathematical models, thus the aim of this study was to evaluate the HYDRUS-2D model from experimental data to predict the size of the wet bulbs generated by emitters of different application rates (1.0 and 1.6 L h-1). The results showed that horizontal displacement (bulb diameter) remained the largest in all the bulbs, observed both in experimental trials and estimated by the model and the correlation between them was high, above 0.90 to below 16% error. We conclude that the HYDRUS-2D model can be used to estimate the dimensions of the wet bulb getting new information on the sizing of the irrigation system.

  11. Exact solution of an anisotropic 2D random walk model with strong memory correlations

    NASA Astrophysics Data System (ADS)

    Cressoni, J. C.; Viswanathan, G. M.; da Silva, M. A. A.

    2013-12-01

    Over the last decade, there has been progress in understanding one-dimensional non-Markovian processes via analytic, sometimes exact, solutions. The extension of these ideas and methods to two and higher dimensions is challenging. We report the first exactly solvable two-dimensional (2D) non-Markovian random walk model belonging to the family of the elephant random walk model. In contrast to Lévy walks or fractional Brownian motion, such models incorporate memory effects by keeping an explicit history of the random walk trajectory. We study a memory driven 2D random walk with correlated memory and stops, i.e. pauses in motion. The model has an inherent anisotropy with consequences for its diffusive properties, thereby mixing the dominant regime along one dimension with a subdiffusive walk along a perpendicular dimension. The anomalous diffusion regimes are fully characterized by an exact determination of the Hurst exponent. We discuss the remarkably rich phase diagram, as well as several possible combinations of the independent walks in both directions. The relationship between the exponents of the first and second moments is also unveiled.

  12. Molecular-dynamics of a 2D Model of the Shape Memory Effect

    NASA Astrophysics Data System (ADS)

    Kastner, Oliver

    2006-08-01

    This work investigates the thermodynamic properties of a qualitative atomistic model for austenite martensite transitions. The model, still in 2D, employs Lennard-Jones potentials for the determination of the atomic interactions. By use of two atom species it is possible to identify three stable lattice structures in 2D, interpreted as austenite and two variants of martensite. The model is described in the first part of the work [6] in detail. The present work studies the thermodynamic properties of the model concerning a small, 2-dimensional test assembly consisting of 41 atoms. The phase stability is investigated by exploitation of the condition of minimal free energy. The free energy is calculated from the thermal equation of state, which is measured in numerical tensile tests. In the second part of this work a chain of eleven 41-atom assemblies is investigated. The chain is interpreted as an idealized larger body, where the individual crystallites represent crystallographic layers allowing for the creation of micro structure. By use of tensile tests at various temperature conditions we sketch how such chain may exhibit quasi-plasticity, pseudo-elasticity and the shape memory effect.

  13. Momentum Transport: 2D and 3D Cloud Resolving Model Simulations

    NASA Technical Reports Server (NTRS)

    Tao, Wei-Kuo

    2001-01-01

    The major objective of this study is to investigate the momentum budgets associated with several convective systems that developed during the TOGA COARE IOP (west Pacific warm pool region) and GATE (east Atlantic region). The tool for this study is the improved Goddard Cumulas Ensemble (GCE) model which includes a 3-class ice-phase microphysical scheme, explicit cloud radiative interactive processes and air-sea interactive surface processes. The model domain contains 256 x 256 grid points (with 2 km resolution) in the horizontal and 38 grid points (to a depth of 22 km) in the vertical. The 2D domain has 1024 grid points. The simulations were performed over a 7-day time period (December 19-26, 1992, for TOGA COARE and September 1-7, 1994 for GATE). Cyclic literal boundary conditions are required for this type of long-term integration. Two well organized squall systems (TOGA, COARE February 22, 1993, and GATE September 12, 1994) were also simulated using the 3D GCE model. Only 9 h simulations were required to cover the life time of the squall systems. the lateral boundary conditions were open for these two squall systems simulations. the following will be examined: (1) the momentum budgets in the convective and stratiform regions, (2) the relationship between momentum transport and cloud organization (i.e., well organized squall lines versus less organized convective), (3) the differences and similarities in momentum transport between 2D and 3D simulated convective systems, and (4) the differences and similarities in momentum budgets between cloud systems simulated with open and cyclic lateral boundary conditions. Preliminary results indicate that there are only small differences between 2D and 3D simulated momentum budgets. Major differences occur, however, between momentum budgets associated with squall systems simulated using different lateral boundary conditions.

  14. A quasi 2D semianalytical model for the potential profile in hetero and homojunction tunnel FETs

    NASA Astrophysics Data System (ADS)

    Villani, F.; Gnani, E.; Gnudi, A.; Reggiani, S.; Baccarani, G.

    2015-11-01

    A quasi 2D semianalytical model for the potential profile in hetero and homojunction tunnel FETs is developed and compared with full-quantum simulation results. It will be shown that the pure analytical solution perfectly matches results at high VDS. However, a coupling with the numerical solution of the 1D Poisson equation in the radial direction is necessary at low VDS, in order to properly account for the charge density in equilibrium with the drain contact. With such an approach we are able to correctly predict the potential profile for both the linear and saturation regimes.

  15. Vector chiral phases in the frustrated 2D XY model and quantum spin chains.

    PubMed

    Schenck, H; Pokrovsky, V L; Nattermann, T

    2014-04-18

    The phase diagram of the frustrated 2D classical and 1D quantum XY models is calculated analytically. Four transitions are found: the vortex unbinding transitions triggered by strong fluctuations occur above and below the chiral transition temperature. Vortex interaction is short range on small and logarithmic on large scales. The chiral transition, though belonging to the Ising universality class by symmetry, has different critical exponents due to nonlocal interaction. In a narrow region close to the Lifshitz point a reentrant phase transition between paramagnetic and quasiferromagnetic phase appears. Applications to antiferromagnetic quantum spin chains and multiferroics are discussed. PMID:24785067

  16. Effect of River Training Project on Hydrodynamics Flow Circumstances by 2D Finite Element Numerical Model

    NASA Astrophysics Data System (ADS)

    Zou, B.; Li, D. F.; Hu, H. J.; Zhang, H. W.; Lou, L. H.; Chen, M.; Lv, Z. Y.

    Based on the verified two dimensional(2D) finite element model for river flow simulation, the effect of estuary training levees on the water flow and sediment movement in the Yellow River estuary is analyzed. For disclosing the effect of setting the two training levees on the flow and sediment motion, the calculation and analysis for the two projects, (one is no levees, the other is setting up two no levees) are given. The results show that when setting up two training levees, water flow is bound by levees and the water flows become more concentrated. As a result, velocity increases in the main channel, sediment carrying capacity of water flow increases correspondingly.

  17. Image restoration using 2D autoregressive texture model and structure curve construction

    NASA Astrophysics Data System (ADS)

    Voronin, V. V.; Marchuk, V. I.; Petrosov, S. P.; Svirin, I.; Agaian, S.; Egiazarian, K.

    2015-05-01

    In this paper an image inpainting approach based on the construction of a composite curve for the restoration of the edges of objects in an image using the concepts of parametric and geometric continuity is presented. It is shown that this approach allows to restore the curved edges and provide more flexibility for curve design in damaged image by interpolating the boundaries of objects by cubic splines. After edge restoration stage, a texture restoration using 2D autoregressive texture model is carried out. The image intensity is locally modeled by a first spatial autoregressive model with support in a strongly causal prediction region on the plane. Model parameters are estimated by Yule-Walker method. Several examples considered in this paper show the effectiveness of the proposed approach for large objects removal as well as recovery of small regions on several test images.

  18. Kosaki-Longo index and classification of charges in 2D quantum spin models

    NASA Astrophysics Data System (ADS)

    Naaijkens, Pieter

    2013-08-01

    We consider charge superselection sectors of two-dimensional quantum spin models corresponding to cone localisable charges, and prove that the number of equivalence classes of such charges is bounded by the Kosaki-Longo index of an inclusion of certain observable algebras. To demonstrate the power of this result we apply the theory to the toric code on a 2D infinite lattice. For this model we can compute the index of this inclusion, and conclude that there are four distinct irreducible charges in this model, in accordance with the analysis of the toric code model on compact surfaces. We also give a sufficient criterion for the non-degeneracy of the charge sectors, in the sense that Verlinde's matrix S is invertible.

  19. Accelerating numerical modeling of wave propagation through 2-D anisotropic materials using OpenCL.

    PubMed

    Molero, Miguel; Iturrarán-Viveros, Ursula

    2013-03-01

    We present an implementation of the numerical modeling of elastic waves propagation, in 2D anisotropic materials, using the new parallel computing devices (PCDs). Our study is aimed both to model laboratory experiments and explore the capabilities of the emerging PCDs by discussing performance issues. In the experiments a sample plate of an anisotropic material placed inside a water tank is rotated and, for every angle of rotation it is subjected to an ultrasonic wave (produced by a large source transducer) that propagates in the water and through the material producing some reflection and transmission signals that are recording by a "point-like" receiver. This experiment is numerically modeled by running a finite difference code covering a set of angles θ∈[-50°, 50°], and recorded the signals for the transmission and reflection results. Transversely anisotropic and weakly orthorhombic materials are considered. We accelerated the computation using an open-source toolkit called PyOpenCL, which lets one to easily access the OpenCL parallel computation API's from the high-level programming environment of Python. A speedup factor over 19 using the GPU is obtained when compared with the execution of the same program in parallel using a CPU multi-core (in this case we use the 4-cores that has the CPU). The performance for different graphic cards and operating systems is included together with the full 2-D finite difference code with PyOpenCL. PMID:23290584

  20. Self-Organization in 2D Traffic Flow Model with Jam-Avoiding Drive

    NASA Astrophysics Data System (ADS)

    Nagatani, Takashi

    1995-04-01

    A stochastic cellular automaton (CA) model is presented to investigate the traffic jam by self-organization in the two-dimensional (2D) traffic flow. The CA model is the extended version of the 2D asymmetric exclusion model to take into account jam-avoiding drive. Each site contains either a car moving to the up, a car moving to the right, or is empty. A up car can shift right with probability p ja if it is blocked ahead by other cars. It is shown that the three phases (the low-density phase, the intermediate-density phase and the high-density phase) appear in the traffic flow. The intermediate-density phase is characterized by the right moving of up cars. The jamming transition to the high-density jamming phase occurs with higher density of cars than that without jam-avoiding drive. The jamming transition point p 2c increases with the shifting probability p ja. In the deterministic limit of p ja=1, it is found that a new jamming transition occurs from the low-density synchronized-shifting phase to the high-density moving phase with increasing density of cars. In the synchronized-shifting phase, all up cars do not move to the up but shift to the right by synchronizing with the move of right cars. We show that the jam-avoiding drive has an important effect on the dynamical jamming transition.

  1. Stochastic dynamics of phase singularities under ventricular fibrillation in 2D Beeler-Reuter model

    NASA Astrophysics Data System (ADS)

    Suzuki, Akio; Konno, Hidetoshi

    2011-09-01

    The dynamics of ventricular fibrillation (VF) has been studied extensively, and the initiation mechanism of VF has been elucidated to some extent. However, the stochastic dynamical nature of sustained VF remains unclear so far due to the complexity of high dimensional chaos in a heterogeneous system. In this paper, various statistical mechanical properties of sustained VF are studied numerically in 2D Beeler-Reuter-Drouhard-Roberge (BRDR) model with normal and modified ionic current conductance. The nature of sustained VF is analyzed by measuring various fluctuations of spatial phase singularity (PS) such as velocity, lifetime, the rates of birth and death. It is found that the probability density function (pdf) for lifetime of PSs is independent of system size. It is also found that the hyper-Gamma distribution serves as a universal pdf for the counting number of PSs for various system sizes and various parameters of our model tissue under VF. Further, it is demonstrated that the nonlinear Langevin equation associated with a hyper-Gamma process can mimic the pdf and temporal variation of the number of PSs in the 2D BRDR model.

  2. Adaptive finite element modeling of direct current resistivity in 2-D generally anisotropic structures

    NASA Astrophysics Data System (ADS)

    Yan, Bo; Li, Yuguo; Liu, Ying

    2016-07-01

    In this paper, we present an adaptive finite element (FE) algorithm for direct current (DC) resistivity modeling in 2-D generally anisotropic conductivity structures. Our algorithm is implemented on an unstructured triangular mesh that readily accommodates complex structures such as topography and dipping layers and so on. We implement a self-adaptive, goal-oriented grid refinement algorithm in which the finite element analysis is performed on a sequence of refined grids. The grid refinement process is guided by an a posteriori error estimator. The problem is formulated in terms of total potentials where mixed boundary conditions are incorporated. This type of boundary condition is superior to the Dirichlet type of conditions and improves numerical accuracy considerably according to model calculations. We have verified the adaptive finite element algorithm using a two-layered earth with azimuthal anisotropy. The FE algorithm with incorporation of mixed boundary conditions achieves high accuracy. The relative error between the numerical and analytical solutions is less than 1% except in the vicinity of the current source location, where the relative error is up to 2.4%. A 2-D anisotropic model is used to demonstrate the effects of anisotropy upon the apparent resistivity in DC soundings.

  3. Inhibitory effects of phytochemicals on metabolic capabilities of CYP2D6*1 and CYP2D6*10 using cell-based models in vitro

    PubMed Central

    Qu, Qiang; Qu, Jian; Han, Lu; Zhan, Min; Wu, Lan-xiang; Zhang, Yi-wen; Zhang, Wei; Zhou, Hong-hao

    2014-01-01

    Aim: Herbal products have been widely used, and the safety of herb-drug interactions has aroused intensive concerns. This study aimed to investigate the effects of phytochemicals on the catalytic activities of human CYP2D6*1 and CYP2D6*10 in vitro. Methods: HepG2 cells were stably transfected with CYP2D6*1 and CYP2D6*10 expression vectors. The metabolic kinetics of the enzymes was studied using HPLC and fluorimetry. Results: HepG2-CYP2D6*1 and HepG2-CYP2D6*10 cell lines were successfully constructed. Among the 63 phytochemicals screened, 6 compounds, including coptisine sulfate, bilobalide, schizandrin B, luteolin, schizandrin A and puerarin, at 100 μmol/L inhibited CYP2D6*1- and CYP2D6*10-mediated O-demethylation of a coumarin compound AMMC by more than 50%. Furthermore, the inhibition by these compounds was dose-dependent. Eadie-Hofstee plots demonstrated that these compounds competitively inhibited CYP2D6*1 and CYP2D6*10. However, their Ki values for CYP2D6*1 and CYP2D6*10 were very close, suggesting that genotype-dependent herb-drug inhibition was similar between the two variants. Conclusion: Six phytochemicals inhibit CYP2D6*1 and CYP2D6*10-mediated catalytic activities in a dose-dependent manner in vitro. Thus herbal products containing these phytochemicals may inhibit the in vivo metabolism of co-administered drugs whose primary route of elimination is CYP2D6. PMID:24786236

  4. Modeling and Control of 2-D Grasping of an Object with Arbitrary Shape under Rolling Contact

    NASA Astrophysics Data System (ADS)

    Arimoto, Suguru; Yoshida, Morio; Sekimoto, Masahiro; Tahara, Kenji

    Modeling, control, and stabilization of dynamics of two-dimensional object grasping by using a pair of multi-joint robot fingers are investigated under rolling contact constraints and an arbitrary geometry of the object and fingertips. First, a fundamental testbed problem of modeling and control of rolling motion between 2-D rigid bodies with an arbitrary shape is treated under the assumption that the two contour curves coincide at the contact point and share the same tangent. The rolling constraint induces the Euler equation of motion that is parameterized by a common arclength parameter and constrained onto the kernel space orthogonally complemented to the image space spanned from the constraint gradient. By extending the analysis to the problem of stable grasp of a 2-D object with an arbitrary shape by a pair of robot fingers, the Euler-Lagrange equation of motion of the overall fingers/object system parametrized by arclength parameters is derived, together with a couple of first-order differential equations that express evolutions of contact points in terms of the second fundamental form. It is shown that 2-D rolling constraints are integrable in the sense of Frobonius even if their Pfaffian forms are characterized by arclength parameters. A control signal called “blind grasping” is introduced and shown to be effective in stabilization of grasping without using the details of the object shape and parameters or external sensing. An extension of the Dirichlet-Lagrange stability theorem to a class of systems with DOF-redundancy under constraints is suggested by using a Morse-Bott-Lyapunov function.

  5. Uncertainties in modelling Mt. Pinatubo eruption with 2-D AER model and CCM SOCOL

    NASA Astrophysics Data System (ADS)

    Kenzelmann, P.; Weisenstein, D.; Peter, T.; Luo, B. P.; Rozanov, E.; Fueglistaler, S.; Thomason, L. W.

    2009-04-01

    Large volcanic eruptions may introduce a strong forcing on climate. They challenge the skills of climate models. In addition to the short time attenuation of solar light by ashes the formation of stratospheric sulphate aerosols, due to volcanic sulphur dioxide injection into the lower stratosphere, may lead to a significant enhancement of the global albedo. The sulphate aerosols have a residence time of about 2 years. As a consequence of the enhanced sulphate aerosol concentration both the stratospheric chemistry and dynamics are strongly affected. Due to absorption of longwave and near infrared radiation the temperature in the lower stratosphere increases. So far chemistry climate models overestimate this warming [Eyring et al. 2006]. We present an extensive validation of extinction measurements and model runs of the eruption of Mt. Pinatubo in 1991. Even if Mt. Pinatubo eruption has been the best quantified volcanic eruption of this magnitude, the measurements show considerable uncertainties. For instance the total amount of sulphur emitted to the stratosphere ranges from 5-12 Mt sulphur [e.g. Guo et al. 2004, McCormick, 1992]. The largest uncertainties are in the specification of the main aerosol cloud. SAGE II, for instance, could not measure the peak of the aerosol extinction for about 1.5 years, because optical termination was reached. The gap-filling of the SAGE II [Thomason and Peter, 2006] using lidar measurements underestimates the total extinctions in the tropics for the first half year after the eruption by 30% compared to AVHRR [Rusell et. al 1992]. The same applies to the optical dataset described by Stenchikov et al. [1998]. We compare these extinction data derived from measurements with extinctions derived from AER 2D aerosol model calculations [Weisenstein et al., 2007]. Full microphysical calculations with injections of 14, 17, 20 and 26 Mt SO2 in the lower stratosphere were performed. The optical aerosol properties derived from SAGE II

  6. Longtime Well-posedness for the 2D Groma-Balogh Model

    NASA Astrophysics Data System (ADS)

    Wan, Renhui; Chen, Jiecheng

    2016-07-01

    In this paper, we consider the cauchy problem for the 2D Groma-Balogh model (Acta Mater 47:3647-3654, 1999). From the works Cannone et al. (Arch Ration Mech Anal 196:71-96, 2010) and El Hajj (Ann Inst Henri Poincaré Anal Nonlinéaire 27:21-35, 2010), one can see global well-posedness for this model is an open question. However, we can prove longtime well-posedness. In particular, we show that this model admits a unique solution with the lifespan T^star satisfying T^star log ^2(1+T^star )≳ ɛ ^{-2} if the initial data is of size ɛ . To achieve this, we first establish some new decay estimates concerning the operator e^{-{R}_{12}^2t} . Then, we prove the longtime well-posedness by utilizing the weak dissipation to deal with the nonlinear terms.

  7. Well-posedness and generalized plane waves simulations of a 2D mode conversion model

    NASA Astrophysics Data System (ADS)

    Imbert-Gérard, Lise-Marie

    2015-12-01

    Certain types of electro-magnetic waves propagating in a plasma can undergo a mode conversion process. In magnetic confinement fusion, this phenomenon is very useful to heat the plasma, since it permits to transfer the heat at or near the plasma center. This work focuses on a mathematical model of wave propagation around the mode conversion region, from both theoretical and numerical points of view. It aims at developing, for a well-posed equation, specific basis functions to study a wave mode conversion process. These basis functions, called generalized plane waves, are intrinsically based on variable coefficients. As such, they are particularly adapted to the mode conversion problem. The design of generalized plane waves for the proposed model is described in detail. Their implementation within a discontinuous Galerkin method then provides numerical simulations of the process. These first 2D simulations for this model agree with qualitative aspects studied in previous works.

  8. The concept models and implementations of multiport neural net associative memory for 2D patterns

    NASA Astrophysics Data System (ADS)

    Krasilenko, Vladimir G.; Nikolskyy, Aleksandr I.; Yatskovskaya, Rimma A.; Yatskovsky, Victor I.

    2011-04-01

    The paper considers neural net models and training and recognizing algorithms with base neurobiologic operations: p-step autoequivalence and non-equivalenc The Modified equivalently models (MEMs) of multiport neural net associative memory (MNNAM) are offered with double adaptive - equivalently weighing (DAEW) for recognition of 2D-patterns (images). It is shown, the computing process in MNNAM under using the proposed MEMs, is reduced to two-step and multi-step algorithms and step-by-step matrix-matrix (tensor-tensor) procedures. The given results of computer simulations confirmed the perspective of such models. Besides the result was received when MNNAM capacity on base of MEMs exceeded the amount of neurons.

  9. Persistence of energy-dependent localization in the Anderson-Hubbard model with increasing system size and doping

    NASA Astrophysics Data System (ADS)

    Daley, P.; Wortis, R.

    2016-05-01

    Non-interacting systems with bounded disorder have been shown to exhibit sharp density of state peaks at the band edge which coincide with an energy range of abruptly suppressed localization. Recent work has shown that these features also occur in the presence of on-site interactions in ensembles of two-site Anderson-Hubbard systems at half filling. Here we demonstrate that this effect in interacting systems persists away from half filling, and moreover that energy regions with suppressed localization continue to appear in ensembles of larger systems despite a loss of sharp features in the density of states.

  10. Modeling floods in a dense urban area using 2D shallow water equations

    NASA Astrophysics Data System (ADS)

    Mignot, E.; Paquier, A.; Haider, S.

    2006-07-01

    SummaryA code solving the 2D shallow water equations by an explicit second-order scheme is used to simulate the severe October 1988 flood in the Richelieu urban locality of the French city of Nîmes. A reference calculation using a detailed description of the street network and of the cross-sections of the streets, considering impervious residence blocks and neglecting the flow interaction with the sewer network provides a mean peak water elevation 0.13 m lower than the measured flood marks with a standard deviation between the measured and computed water depths of 0.53 m. Sensitivity analysis of various topographical and numerical parameters shows that globally, the results keep the same level of accuracy, which reflects both the stability of the calculation method and the smoothening of results. However, the local flow modifications due to change of parameter values can drastically modify the local water depths, especially when the local flow regime is modified. Furthermore, the flow distribution to the downstream parts of the city can be altered depending on the set of parameters used. Finally, a second event, the 2002 flood, was simulated with the calibrated model providing results similar to 1988 flood calculation. Thus, the article shows that, after calibration, a 2D model can be used to help planning mitigation measures in a dense urban area.

  11. Modeling and 2-D discrete simulation of dislocation dynamics for plastic deformation of metal

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Cui, Zhenshan; Ou, Hengan; Ruan, Liqun

    2013-05-01

    Two methods are employed in this paper to investigate the dislocation evolution during plastic deformation of metal. One method is dislocation dynamic simulation of two-dimensional discrete dislocation dynamics (2D-DDD), and the other is dislocation dynamics modeling by means of nonlinear analysis. As screw dislocation is prone to disappear by cross-slip, only edge dislocation is taken into account in simulation. First, an approach of 2D-DDD is used to graphically simulate and exhibit the collective motion of a large number of discrete dislocations. In the beginning, initial grains are generated in the simulation cells according to the mechanism of grain growth and the initial dislocation is randomly distributed in grains and relaxed under the internal stress. During the simulation process, the externally imposed stress, the long range stress contribution of all dislocations and the short range stress caused by the grain boundaries are calculated. Under the action of these forces, dislocations begin to glide, climb, multiply, annihilate and react with each other. Besides, thermal activation process is included. Through the simulation, the distribution of dislocation and the stress-strain curves can be obtained. On the other hand, based on the classic dislocation theory, the variation of the dislocation density with time is described by nonlinear differential equations. Finite difference method (FDM) is used to solve the built differential equations. The dislocation evolution at a constant strain rate is taken as an example to verify the rationality of the model.

  12. 2D and 3D shape based segmentation using deformable models.

    PubMed

    El-Baz, Ayman; Yuksel, Seniha E; Shi, Hongjian; Farag, Aly A; El-Ghar, Mohamed A; Eldiasty, Tarek; Ghoneim, Mohamed A

    2005-01-01

    A novel shape based segmentation approach is proposed by modifying the external energy component of a deformable model. The proposed external energy component depends not only on the gray level of the images but also on the shape information which is obtained from the signed distance maps of objects in a given data set. The gray level distribution and the signed distance map of the points inside and outside the object of interest are accurately estimated by modelling the empirical density function with a linear combination of discrete Gaussians (LCDG) with positive and negative components. Experimental results on the segmentation of the kidneys from low-contrast DCE-MRI and on the segmentation of the ventricles from brain MRI's show how the approach is accurate in segmenting 2-D and 3-D data sets. The 2D results for the kidney segmentation have been validated by a radiologist and the 3D results of the ventricle segmentation have been validated with a geometrical phantom. PMID:16686036

  13. Interpretation of gravity data using 2-D continuous wavelet transformation and 3-D inverse modeling

    NASA Astrophysics Data System (ADS)

    Roshandel Kahoo, Amin; Nejati Kalateh, Ali; Salajegheh, Farshad

    2015-10-01

    Recently the continuous wavelet transform has been proposed for interpretation of potential field anomalies. In this paper, we introduced a 2D wavelet based method that uses a new mother wavelet for determination of the location and the depth to the top and base of gravity anomaly. The new wavelet is the first horizontal derivatives of gravity anomaly of a buried cube with unit dimensions. The effectiveness of the proposed method is compared with Li and Oldenburg inversion algorithm and is demonstrated with synthetics and real gravity data. The real gravity data is taken over the Mobrun massive sulfide ore body in Noranda, Quebec, Canada. The obtained results of the 2D wavelet based algorithm and Li and Oldenburg inversion on the Mobrun ore body had desired similarities to the drill-hole depth information. In all of the inversion algorithms the model non-uniqueness is the challenging problem. Proposed method is based on a simple theory and there is no model non-uniqueness on it.

  14. A 2D Electromechanical Model of Human Atrial Tissue Using the Discrete Element Method

    PubMed Central

    Brocklehurst, Paul; Adeniran, Ismail; Yang, Dongmin; Sheng, Yong; Zhang, Henggui; Ye, Jianqiao

    2015-01-01

    Cardiac tissue is a syncytium of coupled cells with pronounced intrinsic discrete nature. Previous models of cardiac electromechanics often ignore such discrete properties and treat cardiac tissue as a continuous medium, which has fundamental limitations. In the present study, we introduce a 2D electromechanical model for human atrial tissue based on the discrete element method (DEM). In the model, single-cell dynamics are governed by strongly coupling the electrophysiological model of Courtemanche et al. to the myofilament model of Rice et al. with two-way feedbacks. Each cell is treated as a viscoelastic body, which is physically represented by a clump of nine particles. Cell aggregations are arranged so that the anisotropic nature of cardiac tissue due to fibre orientations can be modelled. Each cell is electrically coupled to neighbouring cells, allowing excitation waves to propagate through the tissue. Cell-to-cell mechanical interactions are modelled using a linear contact bond model in DEM. By coupling cardiac electrophysiology with mechanics via the intracellular Ca2+ concentration, the DEM model successfully simulates the conduction of cardiac electrical waves and the tissue's corresponding mechanical contractions. The developed DEM model is numerically stable and provides a powerful method for studying the electromechanical coupling problem in the heart. PMID:26583141

  15. Locally adaptive 2D-3D registration using vascular structure model for liver catheterization.

    PubMed

    Kim, Jihye; Lee, Jeongjin; Chung, Jin Wook; Shin, Yeong-Gil

    2016-03-01

    Two-dimensional-three-dimensional (2D-3D) registration between intra-operative 2D digital subtraction angiography (DSA) and pre-operative 3D computed tomography angiography (CTA) can be used for roadmapping purposes. However, through the projection of 3D vessels, incorrect intersections and overlaps between vessels are produced because of the complex vascular structure, which makes it difficult to obtain the correct solution of 2D-3D registration. To overcome these problems, we propose a registration method that selects a suitable part of a 3D vascular structure for a given DSA image and finds the optimized solution to the partial 3D structure. The proposed algorithm can reduce the registration errors because it restricts the range of the 3D vascular structure for the registration by using only the relevant 3D vessels with the given DSA. To search for the appropriate 3D partial structure, we first construct a tree model of the 3D vascular structure and divide it into several subtrees in accordance with the connectivity. Then, the best matched subtree with the given DSA image is selected using the results from the coarse registration between each subtree and the vessels in the DSA image. Finally, a fine registration is conducted to minimize the difference between the selected subtree and the vessels of the DSA image. In experimental results obtained using 10 clinical datasets, the average distance errors in the case of the proposed method were 2.34±1.94mm. The proposed algorithm converges faster and produces more correct results than the conventional method in evaluations on patient datasets. PMID:26824922

  16. 2-D Modeling of Nanoscale MOSFETs: Non-Equilibrium Green's Function Approach

    NASA Technical Reports Server (NTRS)

    Svizhenko, Alexei; Anantram, M. P.; Govindan, T. R.; Biegel, Bryan

    2001-01-01

    We have developed physical approximations and computer code capable of realistically simulating 2-D nanoscale transistors, using the non-equilibrium Green's function (NEGF) method. This is the most accurate full quantum model yet applied to 2-D device simulation. Open boundary conditions and oxide tunneling are treated on an equal footing. Electrons in the ellipsoids of the conduction band are treated within the anisotropic effective mass approximation. Electron-electron interaction is treated within Hartree approximation by solving NEGF and Poisson equations self-consistently. For the calculations presented here, parallelization is performed by distributing the solution of NEGF equations to various processors, energy wise. We present simulation of the "benchmark" MIT 25nm and 90nm MOSFETs and compare our results to those from the drift-diffusion simulator and the quantum-corrected results available. In the 25nm MOSFET, the channel length is less than ten times the electron wavelength, and the electron scattering time is comparable to its transit time. Our main results are: (1) Simulated drain subthreshold current characteristics are shown, where the potential profiles are calculated self-consistently by the corresponding simulation methods. The current predicted by our quantum simulation has smaller subthreshold slope of the Vg dependence which results in higher threshold voltage. (2) When gate oxide thickness is less than 2 nm, gate oxide leakage is a primary factor which determines off-current of a MOSFET (3) Using our 2-D NEGF simulator, we found several ways to drastically decrease oxide leakage current without compromising drive current. (4) Quantum mechanically calculated electron density is much smaller than the background doping density in the poly silicon gate region near oxide interface. This creates an additional effective gate voltage. Different ways to. include this effect approximately will be discussed.

  17. Be2D: A model to understand the distribution of meteoric 10Be in soilscapes

    NASA Astrophysics Data System (ADS)

    Campforts, Benjamin; Vanacker, Veerle; Vanderborght, Jan; Govers, Gerard

    2016-04-01

    Cosmogenic nuclides have revolutionised our understanding of earth surface process rates. They have become one of the standard tools to quantify soil production by weathering, soil redistribution and erosion. Especially Beryllium-10 has gained much attention due to its long half-live and propensity to be relatively conservative in the landscape. The latter makes 10Be an excellent tool to assess denudation rates over the last 1000 to 100 × 103 years, bridging the anthropogenic and geological time scale. Nevertheless, the mobility of meteoric 10Be in soil systems makes translation of meteoric 10Be inventories into erosion and deposition rates difficult. Here we present a coupled soil hillslope model, Be2D, that is applied to synthetic and real topography to address the following three research questions. (i) What is the influence of vertical meteoric Be10 mobility, caused by chemical mobility, clay translocation and bioturbation, on its lateral redistribution over the soilscape, (ii) How does vertical mobility influence erosion rates and soil residence times inferred from meteoric 10Be inventories and (iii) To what extent can a tracer with a half-life of 1.36 Myr be used to distinguish between natural and human-disturbed soil redistribution rates? The model architecture of Be2D is designed to answer these research questions. Be2D is a dynamic model including physical processes such as soil formation, physical weathering, clay migration, bioturbation, creep, overland flow and tillage erosion. Pathways of meteoric 10Be mobility are simulated using a two step approach which is updated each timestep. First, advective and diffusive mobility of meteoric 10Be is simulated within the soil profile and second, lateral redistribution because of lateral soil fluxes is calculated. The performance and functionality of the model is demonstrated through a number of synthetic and real model runs using existing datasets of meteoric 10Be from case-studies in southeastern US. Brute

  18. Estimating nitrogen losses in furrow irrigated soil amended by compost using HYDRUS-2D model

    NASA Astrophysics Data System (ADS)

    Iqbal, Shahid; Guber, Andrey; Zaman Khan, Haroon; ullah, Ehsan

    2014-05-01

    Furrow irrigation commonly results in high nitrogen (N) losses from soil profile via deep infiltration. Estimation of such losses and their reduction is not a trivial task because furrow irrigation creates highly nonuniform distribution of soil water that leads to preferential water and N fluxes in soil profile. Direct measurements of such fluxes are impractical. The objective of this study was to assess applicability of HYDRUS-2D model for estimating nitrogen balance in manure amended soil under furrow irrigation. Field experiments were conducted in a sandy loam soil amended by poultry manure compost (PMC) and pressmud compost (PrMC) fertilizers. The PMC and PrMC contained 2.5% and 0.9% N and were applied at 5 rates: 2, 4, 6, 8 and 10 ton/ha. Plots were irrigated starting from 26th day from planting using furrows with 1x1 ridge to furrow aspect ratio. Irrigation depths were 7.5 cm and time interval between irrigations varied from 8 to 15 days. Results of the field experiments showed that approximately the same corn yield was obtained with considerably higher N application rates using PMC than using PrMC as a fertilizer. HYDRUS-2D model was implemented to evaluate N fluxes in soil amended by PMC and PrMC fertilizers. Nitrogen exchange between two pools of organic N (compost and soil) and two pools of mineral N (soil NH4-N and soil NO3-N) was modeled using mineralization and nitrification reactions. Sources of mineral N losses from soil profile included denitrification, root N uptake and leaching with deep infiltration of water. HYDRUS-2D simulations showed that the observed increases in N root water uptake and corn yields associated with compost application could not be explained by the amount of N added to soil profile with the compost. Predicted N uptake by roots significantly underestimated the field data. Good agreement between simulated and field-estimated values of N root uptake was achieved when the rate of organic N mineralization was increased

  19. Comparative modeling of vertical and planar organic phototransistors with 2D drift-diffusion simulations

    NASA Astrophysics Data System (ADS)

    Bezzeccheri, E.; Colasanti, S.; Falco, A.; Liguori, R.; Rubino, A.; Lugli, P.

    2016-05-01

    Vertical Organic Transistors and Phototransistors have been proven to be promising technologies due to the advantages of reduced channel length and larger sensitive area with respect to planar devices. Nevertheless, a real improvement of their performance is subordinate to the quantitative description of their operation mechanisms. In this work, we present a comparative study on the modeling of vertical and planar Organic Phototransistor (OPT) structures. Computer-based simulations of the devices have been carried out with Synopsys Sentaurus TCAD in a 2D Drift-Diffusion framework. The photoactive semiconductor material has been modeled using the virtual semiconductor approach as the archetypal P3HT:PC61BM bulk heterojunction. It has been found that both simulated devices have comparable electrical and optical characteristics, accordingly to recent experimental reports on the subject.

  20. An investigation of DTNS2D for use as an incompressible turbulence modelling test-bed

    NASA Technical Reports Server (NTRS)

    Steffen, Christopher J., Jr.

    1992-01-01

    This paper documents an investigation of a two dimensional, incompressible Navier-Stokes solver for use as a test-bed for turbulence modelling. DTNS2D is the code under consideration for use at the Center for Modelling of Turbulence and Transition (CMOTT). This code was created by Gorski at the David Taylor Research Center and incorporates the pseudo compressibility method. Two laminar benchmark flows are used to measure the performance and implementation of the method. The classical solution of the Blasius boundary layer is used for validating the flat plate flow, while experimental data is incorporated in the validation of backward facing step flow. Velocity profiles, convergence histories, and reattachment lengths are used to quantify these calculations. The organization and adaptability of the code are also examined in light of the role as a numerical test-bed.

  1. Singularities of the Partition Function for the Ising Model Coupled to 2D Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Ambjørn, J.; Anagnostopoulos, K. N.; Magnea, U.

    We study the zeros in the complex plane of the partition function for the Ising model coupled to 2D quantum gravity for complex magnetic field and real temperature, and for complex temperature and real magnetic field, respectively. We compute the zeros by using the exact solution coming from a two-matrix model and by Monte-Carlo simulations of Ising spins on dynamical triangulations. We present evidence that the zeros form simple one-dimensional curves in the complex plane, and that the critical behaviour of the system is governed by the scaling of the distribution of the singularities near the critical point. Despite the small size of the systems studied, we can obtain a reasonable estimate of the (known) critical exponents.

  2. A guide to using material model No. 11 in NIKE2D: An internal variable, viscoplasticity model

    SciTech Connect

    Flower, E.C.; Nikkel, D.J. Jr.

    1990-10-30

    The need to accurately model the superplastic forming process which is highly rate and temperature dependent motivated the evaluation of Bammann's internal variable, viscoplasticity material model. The model is based upon the concepts of unified creep plasticity, but employs a yield surface for efficient implementation into large-scale numerical computer codes. It has proven elsewhere to be quite successful in describing large strain, thermal-mechanical behavior of crystalline materials. Features of the model enable it to simulate the apparent strain-rate behavior exhibited by many metals above one half the melt temperature. It is the efficient incorporation of features that make the model attractive for use in finite element modeling of metal deformation processes. Although this model was implemented into the Lawrence Livermore National Laboratory's NIKE2D finite element program in 1986, there have been no known reports of successful use by NIKE2D users. The purpose of this report is to provide the user the proper format to input model parameters, a procedure for determining appropriate values for material constants from experimental data, and supplemental information on the model relevant to the implementation in the NIKE2D finite element program. Detailed accounts of the theoretical aspects of the model can be found in the cited references. 4 refs., 8 figs.

  3. Neutrino-electron Scattering in 2-D Models of Supernova Convection

    NASA Astrophysics Data System (ADS)

    DeNisco, K. R.; Swesty, F. D.; Myra, E. S.

    2005-12-01

    We present results from 2-D supernova simulations which include the effects of neutrino-electron scattering. The importance of neutrino-electron scattering in stellar collapse has been known for two decades. Yet it has often been neglected in multidimensional simulations due to the difficulty of implementing it consistently. The inclusion of this process is numerically challenging because of the extremely short scattering timescales involved. The stiffness resulting from this short timescale precludes an explicit numerical treatment of this phenomenon, such as those that have recently been utilized in some 2-D models. We describe our fully-implicit treatment of this process and present our initial results. This work was performed at the State University of New York at Stony Brook as part of the TeraScale Supernova Initiative, and is funded by SciDAC grant DE-FC02-01ER41185 from the U.S. Department of Energy, Office of Science High-Energy, Nuclear, and Advanced Scientific Computing Research Programs. We gratefully acknowledge support of the National Energy Research Scientific Computing Center (NERSC) for computational and consulting support.

  4. Implications of lack-of-ergodicity in 2D Potts model

    NASA Astrophysics Data System (ADS)

    Ota, Smita

    2015-03-01

    Microcanonical Monte Carlo simulation is used to study two dimensional (2D) q state Potts model. We consider a 2D square lattice having NxN spins with periodic boundary condition and simulated the system with N =15 and q =10. The demon energy distribution is found to be exponential for high system energy and large system size. For smaller system size and above the first order transition the demon energy distribution is found to deviate from exp(- βED) and has the form exp(- βED + γ ED2). Here β = 1/kBT and kB is the Boltzmann constant. It is found that γ is finite at higher temperatures. As the system energy is reduced γ becomes zero near the first order transition. It is found that during cooling γ changes sign from negative to positive and then to negative again near the 1st order transition. Therefore the demon energy distribution becomes exp(- βED) (or ergodic) at two values of system energy near the 1st order transition. Further cooling or at still lower temperatures the system shows lack of ergodicity. However, difference in heating cooling curves are apparent in E vs γ. The system energies for which γ is zero during cooling can represent the 'ergodic' states. This can be related to the two-level systems observed in glasses at low temperatures.

  5. GRAV2D: an interactive 2-1/2 dimensional gravity modeling program (user's guide and documentation for Rev. 1)

    SciTech Connect

    Nutter, C.

    1980-11-01

    GRAV2D is an interactive computer program used for modeling 2-1/2 dimensional gravity data. A forward algorithm is used to give the theoretical attraction of gravity intensity at a station due to a perturbing body given by the initial model. The resultant model can then be adjusted for a better fit by a combination of manual adjustment, one-dimensional automatic search, and Marquardt inversion. GRAV2D has an interactive data management system for data manipulation and display built around subroutines to do a forward problem, a one-dimensional direct search and an inversion. This is a user's guide and documentation for GRAV2D.

  6. 2D time-domain finite-difference modeling for viscoelastic seismic wave propagation

    NASA Astrophysics Data System (ADS)

    Fan, Na; Zhao, Lian-Feng; Xie, Xiao-Bi; Ge, Zengxi; Yao, Zhen-Xing

    2016-07-01

    Real Earth media are not perfectly elastic. Instead, they attenuate propagating mechanical waves. This anelastic phenomenon in wave propagation can be modeled by a viscoelastic mechanical model consisting of several standard linear solids. Using this viscoelastic model, we approximate a constant Q over a frequency band of interest. We use a four-element viscoelastic model with a tradeoff between accuracy and computational costs to incorporate Q into 2D time-domain first-order velocity-stress wave equations. To improve the computational efficiency, we limit the Q in the model to a list of discrete values between 2 and 1000. The related stress and strain relaxation times that characterize the viscoelastic model are pre-calculated and stored in a database for use by the finite-difference calculation. A viscoelastic finite-difference scheme that is second-order in time and fourth-order in space is developed based on the MacCormack algorithm. The new method is validated by comparing the numerical result with analytical solutions that are calculated using the generalized reflection/transmission coefficient method. The synthetic seismograms exhibit greater than 95 per cent consistency in a two-layer viscoelastic model. The dispersion generated from the simulation is consistent with the Kolsky-Futterman dispersion relationship.

  7. Transforming 2d Cadastral Data Into a Dynamic Smart 3d Model

    NASA Astrophysics Data System (ADS)

    Tsiliakou, E.; Labropoulos, T.; Dimopoulou, E.

    2013-08-01

    3D property registration has become an imperative need in order to optimally reflect all complex cases of the multilayer reality of property rights and restrictions, revealing their vertical component. This paper refers to the potentials and multiple applications of 3D cadastral systems and explores the current state-of-the art, especially the available software with which 3D visualization can be achieved. Within this context, the Hellenic Cadastre's current state is investigated, in particular its data modeling frame. Presenting the methodologies and specifications addressing the registration of 3D properties, the operating cadastral system's shortcomings and merits are pointed out. Nonetheless, current technological advances as well as the availability of sophisticated software packages (proprietary or open source) call for 3D modeling. In order to register and visualize the complex reality in 3D, Esri's CityEngine modeling software has been used, which is specialized in the generation of 3D urban environments, transforming 2D GIS Data into Smart 3D City Models. The application of the 3D model concerns the Campus of the National Technical University of Athens, in which a complex ownership status is established along with approved special zoning regulations. The 3D model was built using different parameters based on input data, derived from cadastral and urban planning datasets, as well as legal documents and architectural plans. The process resulted in a final 3D model, optimally describing the cadastral situation and built environment and proved to be a good practice example of 3D visualization.

  8. The development and testing of a 2D laboratory seismic modelling system for heterogeneous structure investigations

    NASA Astrophysics Data System (ADS)

    Mo, Yike; Greenhalgh, Stewart A.; Robertsson, Johan O. A.; Karaman, Hakki

    2015-05-01

    Lateral velocity variations and low velocity near-surface layers can produce strong scattered and guided waves which interfere with reflections and lead to severe imaging problems in seismic exploration. In order to investigate these specific problems by laboratory seismic modelling, a simple 2D ultrasonic model facility has been recently assembled within the Wave Propagation Lab at ETH Zurich. The simulated geological structures are constructed from 2 mm thick metal and plastic sheets, cut and bonded together. The experiments entail the use of a piezoelectric source driven by a pulse amplifier at ultrasonic frequencies to generate Lamb waves in the plate, which are detected by piezoelectric receivers and recorded digitally on a National Instruments recording system, under LabVIEW software control. The 2D models employed were constructed in-house in full recognition of the similitude relations. The first heterogeneous model features a flat uniform low velocity near-surface layer and deeper dipping and flat interfaces separating different materials. The second model is comparable but also incorporates two rectangular shaped inserts, one of low velocity, the other of high velocity. The third model is identical to the second other than it has an irregular low velocity surface layer of variable thickness. Reflection as well as transmission experiments (crosshole & vertical seismic profiling) were performed on each model. The two dominant Lamb waves recorded are the fundamental symmetric mode (non-dispersive) and the fundamental antisymmetric (flexural) dispersive mode, the latter normally being absent when the source transducer is located on a model edge but dominant when it is on the flat planar surface of the plate. Experimental group and phase velocity dispersion curves were determined and plotted for both modes in a uniform aluminium plate. For the reflection seismic data, various processing techniques were applied, as far as pre-stack Kirchhoff migration. The

  9. Turbulence modeling for subsonic separated flows over 2-D airfoils and 3-D wings

    NASA Astrophysics Data System (ADS)

    Rosen, Aaron M.

    Accurate predictions of turbulent boundary layers and flow separation through computational fluid dynamics (CFD) are becoming more and more essential for the prediction of loads in the design of aerodynamic flight components. Standard eddy viscosity models used in many commercial codes today do not capture the nonequilibrium effects seen in a separated flow and thus do not generally make accurate separation predictions. Part of the reason for this is that under nonequilibrium conditions such as a strong adverse pressure gradient, the history effects of the flow play an important role in the growth and decay of turbulence. More recent turbulence models such as Olsen and Coakley's Lag model and Lillard's lagRST model seek to simulate these effects by lagging the turbulent variables when nonequilibrium effects become important. The purpose of the current research is to assess how these nonequilibrium turbulence models capture the separated regions on various 2-D airfoils and 3-D wings. Nonequilibrium models including the Lag model and the lagRST model are evaluated in comparison with three baseline models (Spalart-Allmaras, Wilcox's k-omega, and Menter's SST) using a modified version of the OVERFLOW code. Tuning the model coefficients of the Lag and lagRST models is also explored. Results show that the various lagRST formulations display an improvement in velocity profile predictions over the standard RANS models, but have trouble capturing the edge of the boundary layer. Experimental separation location measurements were not available, but several trends are noted which may be useful to tuning the model coefficients in the future.

  10. 2D-photochemical modeling of Saturn’s stratosphere: hydrocarbon and water distributions

    NASA Astrophysics Data System (ADS)

    Hue, Vincent; Cavalié, Thibault; Hersant, Franck; Dobrijevic, Michel; Greathouse, Thomas; Lellouch, Emmanuel; Hartogh, Paul; Cassidy, Timothy; Spiga, Aymeric; Guerlet, Sandrine; Sylvestre, Melody

    2014-11-01

    Saturn’s axial tilt of 27° produces seasons in a similar way as on Earth. The seasonal forcing over Saturn’s 30 years period influences the production/loss of the major atmospheric absorbers and coolants through photochemistry, and influences therefore Saturn’s stratospheric temperatures. We have developed a 2D time-dependent photochemical model of Saturn’s atmosphere [Hue et al., in prep.], coupled to a radiative-climate model [Greathouse et al., 2008] to study seasonal effects on its atmospheric composition. Cassini spacecraft has revealed that the distribution of hydrocarbons in Saturn’s stratosphere [Guerlet et al., 2009] differs from pure photochemical predictions, i.e. without meridional transport [Moses et al., 2005]. Differences between the observed distribution of hydrocarbons and 2D-photochemical predictions are likely to be an indicator of dynamical forcing.Disentangling the origin of water in the stratosphere of this planet has been a long-term issue. Due to Saturn’s cold tropopause trap, which acts as a transport barrier, the water vapor observed by the Infrared Space Observatory (ISO) [Feuchtgruber et al., 1997] has an external origin. Three external sources have been identified: (i) permanent flux from interplanetary dust particles, (ii) local sources form planetary environments (rings, satellites), (iii) large cometary impacts, similar to Shoemaker-Levy 9 on Jupiter. Previous observations of Saturn with Herschel’s Hsso program [Hartogh et al., 2009] led to the detection of a water torus around Saturn [Hartogh et al., 2011], fed by Enceladus’ geysers. A substantial fraction of this torus is predicted to be a local source of water for Saturn’s and its satellites, as it will spread in this system [Cassidy et al., 2010]. Using the new 2D-photochemical model, we test here the validity of Enceladus’ torus as the source of Saturn’s stratospheric water.References : Hue et al., in prep. Greathouse et al., 2008. AGU Fall Meeting

  11. On the assimilation of flood extension images into 2D shallow-water models

    NASA Astrophysics Data System (ADS)

    Monnier, J.; Couderc, F.; Dartus, D.; Madec, R.; Vila, J.

    2012-12-01

    In river hydraulics, assimilation of water level measurements at gauging stations is well controlled, while assimilation of images (e.g. from satellite) is still delicate. In the present talk, we address the richness of satellite information to constraint a 2D shallow-water model, and present also related difficulties. A preliminary study done on Mosel river is presented in [LaMo] [HoLaMoPu]. On selected parts of the image, an 0th order model flow allows to obtain some reliable water levels with quantified uncertainties (C. Puech et al.). Next, variationnal sensitivities (based on a gradient computation and adjoint equations) reveal some difficulties that a model designer have to tackle (e.g. roughness parameters at open boundaries), and allow to better understand both the model and the flow. Next, a variational data assimilation algorithm (4D-var) shows that such data lead to a better calibration of the model (e.g. roughness coefficients) and potentially allows to identify the incoming and/or outgoing flow at open boundaries, [LaMo] [HoLaMoPu]. On the other side, the flood dynamic extension is difficult to represent accurately using a 2D SW model since the wet-dry front dynamics is difficult to compute. We compare some 2nd order finite volume solvers and obtain an accurate and stable scheme at wet-dry front. Then, we present some basic rules of compatibility between data and mesh resolution in order to be reliable enough to constraint the model with flood extension data, [CoMaMoViDa]. All the algorithms are implemented into DassFlow software (Fortran, MPI, adjoint) [Da]. [CoMaMoViDa] F. Couderc, R. Madec, J. Monnier, J.-P. Vila, D. Dartus. "Sensitivity analysis and variational data assimilation for geophysical shallow water flows". Submitted. [Da] DassFlow - Data Assimilation for Free Surface Flows. Open-source computational software http://www-gmm.insa-toulouse.fr/~monnier/DassFlow/ [HoLaMoPu] R. Hostache, X. Lai, J. Monnier, C. Puech. "Assimilation of spatial

  12. The combined effect of attraction and orientation zones in 2D flocking models

    NASA Astrophysics Data System (ADS)

    Iliass, Tarras; Cambui, Dorilson

    2016-01-01

    In nature, many animal groups, such as fish schools or bird flocks, clearly display structural order and appear to move as a single coherent entity. In order to understand the complex motion of these systems, we study the Vicsek model of self-propelled particles (SPP) which is an important tool to investigate the behavior of collective motion of live organisms. This model reproduces the biological behavior patterns in the two-dimensional (2D) space. Within the framework of this model, the particles move with the same absolute velocity and interact locally in the zone of orientation by trying to align their direction with that of the neighbors. In this paper, we model the collective movement of SPP using an agent-based model which follows biologically motivated behavioral rules, by adding a second region called the attraction zone, where each particles move towards each other avoiding being isolated. Our main goal is to present a detailed numerical study on the effect of the zone of attraction on the kinetic phase transition of our system. In our study, the consideration of this zone seems to play an important role in the cohesion. Consequently, in the directional orientation, the zone that we added forms the compact particle group. In our simulation, we show clearly that the model proposed here can produce two collective behavior patterns: torus and dynamic parallel group. Implications of these findings are discussed.

  13. Coronary arteries motion modeling on 2D x-ray images

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Sundar, Hari

    2012-02-01

    During interventional procedures, 3D imaging modalities like CT and MRI are not commonly used due to interference with the surgery and radiation exposure concerns. Therefore, real-time information is usually limited and building models of cardiac motion are difficult. In such case, vessel motion modeling based on 2-D angiography images become indispensable. Due to issues with existing vessel segmentation algorithms and the lack of contrast in occluded vessels, manual segmentation of certain branches is usually necessary. In addition, such occluded branches are the most important vessels during coronary interventions and obtaining motion models for these can greatly help in reducing the procedure time and radiation exposure. Segmenting different cardiac phases independently does not guarantee temporal consistency and is not efficient for occluded branches required manual segmentation. In this paper, we propose a coronary motion modeling system which extracts the coronary tree for every cardiac phase, maintaining the segmentation by tracking the coronary tree during the cardiac cycle. It is able to map every frame to the specific cardiac phase, thereby inferring the shape information of the coronary arteries using the model corresponding to its phase. Our experiments show that our motion modeling system can achieve promising results with real-time performance.

  14. 2-D modeling of laterally acoustically coupled thin film bulk acoustic wave resonator filters.

    PubMed

    Pensala, Tuomas; Meltaus, Johanna; Kokkonen, Kimmo; Ylilammi, Markku

    2010-11-01

    A 2-D model is developed for calculating lateral acoustical coupling between adjacent thin film BAW resonators forming an electrical N-port. The model is based on solution and superposition of lateral eigenmodes and eigenfrequencies in a structure consisting of adjacent regions with known plate wave dispersion properties. Mechanical and electrical response of the device are calculated as a superposition of eigenmodes according to voltage drive at one electrical port at a time while extracting current induced in the other ports, leading to a full Y-parameter description of the device. Exemplary cases are simulated to show the usefulness of the model in the study of the basic design rules of laterally coupled thin film BAW resonator filters. Model predictions are compared to an experimental 1.9-GHz band-pass filter based on aluminum nitride thin film technology and lateral acoustical coupling. Good agreement is obtained in prediction of passband behavior. The eigenmode-based model forms a useful tool for fast simulation of laterally coupled acoustic devices. It allows one to gain insight into basic device physics in a very intuitive fashion compared with more detailed but heavier finite element method. Shortcomings of this model and possible improvements are discussed. PMID:21041141

  15. Models Ion Trajectories in 2D and 3D Electrostatic and Magnetic Fields

    Energy Science and Technology Software Center (ESTSC)

    2000-02-21

    SIMION3D7.0REV is a C based ion optics simulation program that can model complex problems using Laplace equation solutions for potential fields. The program uses an ion optics workbench that can hold up to 200 2D and/or 3D electrostatic/magnetic potential arrays. Arrays can have up to 50,000,000 points. SIMION3D7.0''s 32 bit virtual Graphics User Interface provides a highly interactive advanced user environment. All potential arrays are visualized as 3D objects that the user can cut awaymore » to inspect ion trajectories and potential energy surfaces. User programs allow the user to customize the program for specific simulations. A geometry file option supports the definition of highly complex array geometry. Algorithm modifications have improved this version''s computational speed and accuracy.« less

  16. Surface delta interaction in the g7/2 - d5/2 model space

    NASA Astrophysics Data System (ADS)

    Yu, Xiaofei; Zamick, Larry

    2016-05-01

    Using an attractive surface delta interaction we obtain wave functions for 2 neutrons (or neutron holes) in the g7/2 -d5/2 model space. If we take the single particle energies to be degenerate we find that the g factors for I = 2 , 4 and 6 are all the same G (J) =gl, the orbital g factor of the nucleon. For a free neutron gl = 0, so in this case all 2 particles or 2 holes' g factors are equal to zero. Only the orbital part of the g-factors contributes - the spin part cancels out. We then consider the effects of introducing a single energy splitting between the 2 orbits. We make a linear approximation for all other n values.

  17. 3D prostate boundary segmentation from ultrasound images using 2D active shape models.

    PubMed

    Hodge, Adam C; Ladak, Hanif M

    2006-01-01

    Boundary outlining, or segmentation, of the prostate is an important task in diagnosis and treatment planning for prostate cancer. This paper describes an algorithm for semi-automatic, three-dimensional (3D) segmentation of the prostate boundary from ultrasound images based on two-dimensional (2D) active shape models (ASM) and rotation-based slicing. Evaluation of the algorithm used distance- and volume-based error metrics to compare algorithm generated boundary outlines to gold standard (manually generated) boundary outlines. The mean absolute distance between the algorithm and gold standard boundaries was 1.09+/-0.49 mm, the average percent absolute volume difference was 3.28+/-3.16%, and a 5x speed increase as compared manual planimetry was achieved. PMID:17946106

  18. Optical fiber poling by induction: analysis by 2D numerical modeling.

    PubMed

    De Lucia, F; Huang, D; Corbari, C; Healy, N; Sazio, P J A

    2016-04-15

    Since their first demonstration some 25 years ago, thermally poled silica fibers have been used to realize device functions such as electro-optic modulation, switching, polarization-entangled photons, and optical frequency conversion with a number of advantages over bulk free-space components. We have recently developed an innovative induction poling technique that could allow for the development of complex microstructured fiber geometries for highly efficient χ(2)-based device applications. To systematically implement these more advanced poled fiber designs, we report here the development of comprehensive numerical models of the induction poling mechanism itself via two-dimensional (2D) simulations of ion migration and space-charge region formation using finite element analysis. PMID:27082323

  19. Models Ion Trajectories in 2D and 3D Electrostatic and Magnetic Fields

    SciTech Connect

    Dahl, David

    2000-02-21

    SIMION3D7.0REV is a C based ion optics simulation program that can model complex problems using Laplace equation solutions for potential fields. The program uses an ion optics workbench that can hold up to 200 2D and/or 3D electrostatic/magnetic potential arrays. Arrays can have up to 50,000,000 points. SIMION3D7.0''s 32 bit virtual Graphics User Interface provides a highly interactive advanced user environment. All potential arrays are visualized as 3D objects that the user can cut away to inspect ion trajectories and potential energy surfaces. User programs allow the user to customize the program for specific simulations. A geometry file option supports the definition of highly complex array geometry. Algorithm modifications have improved this version''s computational speed and accuracy.

  20. Robust autonomous model learning from 2D and 3D data sets.

    PubMed

    Langs, Georg; Donner, René; Peloschek, Philipp; Bischof, Horst

    2007-01-01

    In this paper we propose a weakly supervised learning algorithm for appearance models based on the minimum description length (MDL) principle. From a set of training images or volumes depicting examples of an anatomical structure, correspondences for a set of landmarks are established by group-wise registration. The approach does not require any annotation. In contrast to existing methods no assumptions about the topology of the data are made, and the topology can change throughout the data set. Instead of a continuous representation of the volumes or images, only sparse finite sets of interest points are used to represent the examples during optimization. This enables the algorithm to efficiently use distinctive points, and to handle texture variations robustly. In contrast to standard elasticity based deformation constraints the MDL criterion accounts for systematic deformations typical for training sets stemming from medical image data. Experimental results are reported for five different 2D and 3D data sets. PMID:18051152

  1. Calibration Of 2D Hydraulic Inundation Models In The Floodplain Region Of The Lower Tagus River

    NASA Astrophysics Data System (ADS)

    Pestanana, R.; Matias, M.; Canelas, R.; Araujo, A.; Roque, D.; Van Zeller, E.; Trigo-Teixeira, A.; Ferreira, R.; Oliveira, R.; Heleno, S.

    2013-12-01

    In terms of inundated area, the largest floods in Portugal occur in the Lower Tagus River. On average, the river overflows every 2.5 years, at times blocking roads and causing important agricultural damages. This paper focus on the calibration of 2D-horizontal flood simulation models for the floods of 2001 and 2006 on a 70-km stretch of the Lower Tagus River. Flood extent maps, derived from ERS SAR and ENVISAT ASAR imagery were compared with the flood extent maps obtained for each simulation, to calibrate roughness coefficients. The combination of the calibration results from the 2001 and 2006 floods provided a preliminary Manning coefficient map of the study area.

  2. Universality Class of the Nishimori Point in the 2D +/-J Random-Bond Ising Model

    NASA Astrophysics Data System (ADS)

    Honecker, A.; Picco, M.; Pujol, P.

    2001-07-01

    We study the universality class of the Nishimori point in the 2D +/-J random-bond Ising model by means of the numerical transfer-matrix method. Using the domain-wall free energy, we locate the position of the fixed point along the Nishimori line at the critical concentration value pc = 0.1094+/-0.0002 and estimate ν = 1.33+/-0.03. Then, we obtain the exponents for the moments of the spin-spin correlation functions as well as the value for the central charge c = 0.464+/-0.004. The main qualitative result is the fact that percolation is now excluded as a candidate for describing the universality class of this fixed point.

  3. Universality class of the Nishimori point in the 2D +/- J random-bond Ising model.

    PubMed

    Honecker, A; Picco, M; Pujol, P

    2001-07-23

    We study the universality class of the Nishimori point in the 2D +/- J random-bond Ising model by means of the numerical transfer-matrix method. Using the domain-wall free energy, we locate the position of the fixed point along the Nishimori line at the critical concentration value p(c) = 0.1094 +/- 0.0002 and estimate nu = 1.33 +/- 0.03. Then, we obtain the exponents for the moments of the spin-spin correlation functions as well as the value for the central charge c = 0.464 +/- 0.004. The main qualitative result is the fact that percolation is now excluded as a candidate for describing the universality class of this fixed point. PMID:11461639

  4. Structure-approximating inverse protein folding problem in the 2D HP model.

    PubMed

    Gupta, Arvind; Manuch, Ján; Stacho, Ladislav

    2005-12-01

    The inverse protein folding problem is that of designing an amino acid sequence which has a particular native protein fold. This problem arises in drug design where a particular structure is necessary to ensure proper protein-protein interactions. In this paper, we show that in the 2D HP model of Dill it is possible to solve this problem for a broad class of structures. These structures can be used to closely approximate any given structure. One of the most important properties of a good protein (in drug design) is its stability--the aptitude not to fold simultaneously into other structures. We show that for a number of basic structures, our sequences have a unique fold. PMID:16379538

  5. FAST TRACK COMMUNICATION: Spin waves in the (0, π) and (0, π, π) ordered SDW states of the t-t' Hubbard model: application to doped iron pnictides

    NASA Astrophysics Data System (ADS)

    Raghuvanshi, Nimisha; Singh, Avinash

    2010-10-01

    Spin waves in the (0, π) and (0, π, π) ordered spin-density-wave (SDW) states of the t-t' Hubbard model are investigated at finite doping. In the presence of small t', these composite ferro-antiferromagnetic (F-AF) states are found to be strongly stabilized at finite hole doping due to enhanced carrier-induced ferromagnetic spin couplings as in metallic ferromagnets. Anisotropic spin-wave velocities, a spin-wave energy scale of around 200 meV, reduced magnetic moment and rapid suppression of magnetic order with electron doping x (corresponding to F substitution of O atoms in LaO1 - xFxFeAs or Ni substitution of Fe atoms in BaFe2 - xNixAs2) obtained in this model are in agreement with observed magnetic properties of doped iron pnictides.

  6. An application of the distributed hydrologic model CASC2D to a tropical montane watershed

    NASA Astrophysics Data System (ADS)

    Marsik, Matt; Waylen, Peter

    2006-11-01

    SummaryIncreased stormflow in the Quebrada Estero watershed (2.5 km 2), in the northwestern Central Valley tectonic depression of Costa Rica, reportedly has caused flooding of the city of San Ramón in recent decades. Although scientifically untested, urban expansion was deemed the cause and remedial measures were recommended by the Programa de Investigación en Desarrollo Humano Sostenible (ProDUS). CASC2D, a physically-based, spatially explicit hydrologic model, was constructed and calibrated to a June 10th 2002 storm that delivered 110.5 mm of precipitation in 4.5 h visibly exceeded the bankfull stage (0.9 m) of the Quebrada flooding portions of San Ramón. The calibrated hydrograph showed a peak discharge 16.68% (2.5 m 3 s -1) higher, an above flood stage duration 20% shorter, and time to peak discharge 11 min later than the same observed discharge hydrograph characteristics. Simulations of changing land cover conditions from 1979 to 1999 showed an increase also in the peak discharge, above flood stage duration, and time to peak discharge. Analysis using a modified location quotient identified increased urbanization in lower portions of the watershed over the time period studied. These results suggest that increased urbanization in the Quebrada Estero watershed have increased flooding peaks, and durations above threshold, confirming the ProDUS report. These results and the CASC2D model offer an easy-to-use, pragmatic planning tool for policymakers in San Ramón to assess future development scenarios and their potential flooding impacts to San Ramón.

  7. 2D Distinct Element Method (DEM) models of the initiation, propagation and saturation of rock joints

    NASA Astrophysics Data System (ADS)

    Arslan, A.; Schöpfer, M. P.; Walsh, J. J.; Childs, C.

    2009-12-01

    In layered sequences, rock joints usually best develop within the more brittle layers and commonly display a regular spacing that scales with layer thickness. A variety of conceptual and mechanical models have been developed for these observations. A limitation of previous approaches, however, is that fracture initiation and associated interface slip are not explicitly simulated; instead, fractures were predefined and interfaces were welded. To surmount this problem, we have modelled the formation and growth of joints in layered sequences by using the two-dimensional Distinct Element Method (DEM) as implemented in the Particle Flow Code (PFC-2D). In PFC-2D, rock is represented by an assemblage of circular particles that are bonded at particle-particle contacts. Failure occurs if either the tensile or shear strength of a bond is exceeded. The models comprise a central brittle layer with high Young’s modulus, which is embedded in a low Young’s modulus matrix. The interfaces between the layers are defined by ‘smooth joint’ contacts, a modelling feature that eliminates interparticle bumpiness and associated interlocking friction. Consequently, this feature allows the user to assign macroscopic properties such as friction and cohesion along layer interfaces in a controlled manner. Layer parallel extension is applied by assigning a velocity to particles at the lateral boundaries of the model while maintaining a constant vertical confining pressure. Models were extended until joint saturation in the central layer was reached. We thereby explored the impact of confining pressure and interface properties (friction, cohesion) on joint spacing. A number of important conclusions can be drawn from our models: (i) The distributions of average horizontal normal stress within the layer and of shear stress at the interface are consistent with analytical solutions (stress-transfer theory). (ii) At low interfacial shear strength, new joints form preferentially midway between

  8. Assessment of the Impacts of Compensation Flow Changes Upon Instream Habitat Using 2D Modelling

    NASA Astrophysics Data System (ADS)

    Mould, D. C.; Lane, S. N.; Christmas, M.

    2004-05-01

    Many millstone-grit rivers in northern England are impounded. In such cases the water company in the area has to release compensation flows from the reservoirs, traditionally to meet industrial needs: these flows are rarely set with ecology in mind; and have commonly involved constant flow. Dam overtopping may create spates, but spawning in many fish species is prompted by a spate flow in the early autumn when dams are rarely full enough to overtop. Such flows are important for fine sediment flushing and controlling the wetted useable area for spawning. Classical physical habitat modelling for instream habitat has been largely reliant upon 1D approaches, such as the Instream Flow Incremental Methodology (IFIM). Here we use a 2D finite element model (FESWMS), to simulate changes in instream habitat with variations in the compensation flow regimes. The spatial resolution of 2D models can be adapted to the scale of fish habitats so providing better representation of the reach-scale flow processes (such as slack water in the margins, wetting and drying) than the 1D case. The model is applied to the Rivers Rivelin and Loxley in Sheffield, Northern England. At the confluence of the two rivers, the compensation flow level is set at 30.6 Thousand Cubic Metres per Day (TCMD). Due to historical reasons, the compensation is not divided equally, as the Loxley receives 28 TCMD whilst the Rivelin receives only 2.6 TCMD. The model is used to simulate a transfer of 6 TCMD from the Loxley to the Rivelin. After validation, model predictions are combined with available habitat requirement data (e.g. velocity and depth needs) to develop an index of change in habitat suitability in terms of first order variables (e.g. velocity, depth and wetted useable area). This suggests that the change in compensation may significantly improve instream ecology in relation to macroinvertebrates, brown trout (Salmo trutta) and bullhead (Cottus gobio) in the Rivelin without causing detrimental impacts

  9. Spin Circuit Model for Spin Orbit Torques in 2D Channels

    NASA Astrophysics Data System (ADS)

    Hong, Seokmin

    2015-03-01

    Recently, the unique coupling between charge and spin in topological insulators has been explored through various types of electrical measurements, which could have interesting applications. In this talk, we present a spin circuit model for spin orbit torques in topological insulator surface states and other 2D channels. We show with a simple example that results from the circuit model agree well with those obtained from nonequilibrium Green's function (NEGF) based quantum transport simulation. Some predictions of our model have already received experimental support and we hope this model can provide a unifying framework that can be used to critically evaluate experimental results, to explore new types of devices as well as to answer fundamental questions regarding these materials. The model for spin-orbit torques described here can be incorporated into a broader spin-circuit approach which, we believe, provides a natural platform for multi-physics, multi-component spintronic devices. This work was supported by FAME, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.

  10. Spin Circuit Model for 2D Channels with Spin-Orbit Coupling

    PubMed Central

    Hong, Seokmin; Sayed, Shehrin; Datta, Supriyo

    2016-01-01

    In this paper we present a general theory for an arbitrary 2D channel with “spin momentum locking” due to spin-orbit coupling. It is based on a semiclassical model that classifies all the channel electronic states into four groups based on the sign of the z-component of the spin (up (U), down (D)) and the sign of the x-component of the velocity (+, −). This could be viewed as an extension of the standard spin diffusion model which uses two separate electrochemical potentials for U and D states. Our model uses four: U+, D+, U−, and D−. We use this formulation to develop an equivalent spin circuit that is also benchmarked against a full non-equilibrium Green’s function (NEGF) model. The circuit representation can be used to interpret experiments and estimate important quantities of interest like the charge to spin conversion ratio or the maximum spin current that can be extracted. The model should be applicable to topological insulator surface states with parallel channels as well as to other layered structures with interfacial spin-orbit coupling. PMID:26932563

  11. Thermochemical Nonequilibrium 2D Modeling of Nitrogen Inductively Coupled Plasma Flow

    NASA Astrophysics Data System (ADS)

    Yu, Minghao; Yusuke, Takahashi; Hisashi, Kihara; Ken-ichi, Abe; Kazuhiko, Yamada; Takashi, Abe; Satoshi, Miyatani

    2015-09-01

    Two-dimensional (2D) numerical simulations of thermochemical nonequilibrium inductively coupled plasma (ICP) flows inside a 10-kW inductively coupled plasma wind tunnel (ICPWT) were carried out with nitrogen as the working gas. Compressible axisymmetric Navier-Stokes (N-S) equations coupled with magnetic vector potential equations were solved. A four-temperature model including an improved electron-vibration relaxation time was used to model the internal energy exchange between electron and heavy particles. The third-order accuracy electron transport properties (3rd AETP) were applied to the simulations. A hybrid chemical kinetic model was adopted to model the chemical nonequilibrium process. The flow characteristics such as thermal nonequilibrium, inductive discharge, effects of Lorentz force were made clear through the present study. It was clarified that the thermal nonequilibrium model played an important role in properly predicting the temperature field. The prediction accuracy can be improved by applying the 3rd AETP to the simulation for this ICPWT. supported by Grant-in-Aid for Scientific Research (No. 23560954), sponsored by the Japan Society for the Promotion of Science

  12. Incorporating a Turbulence Transport Model into 2-D Hybrid Hall Thruster Simulations

    NASA Astrophysics Data System (ADS)

    Cha, Eunsun; Cappelli, Mark A.; Fernandez, Eduardo

    2014-10-01

    2-D hybrid simulations of Hall plasma thrusters that do not resolve cross-field transport-generating fluctuations require a model to capture how electrons migrate across the magnetic field. We describe the results of integrating a turbulent electron transport model into simulations of plasma behavior in a plane spanned by the E and B field vectors. The simulations treat the electrons as a fluid and the heavy species (ions/neutrals) as discrete particles. The transport model assumes that the turbulent eddy cascade in the electron fluid to smaller scales is the primary means of electron energy dissipation. Using this model, we compare simulations to experimental measurements made on a laboratory Hall discharge over a range of discharge voltage. Both the current-voltage trends as well as the plasma properties such as plasma temperature, electron density, and ion velocities seem agree favorably with experiments, where a simple Bohm transport model tends to perform poorly in capturing much of the discharge behavior.

  13. Spin Circuit Model for 2D Channels with Spin-Orbit Coupling.

    PubMed

    Hong, Seokmin; Sayed, Shehrin; Datta, Supriyo

    2016-01-01

    In this paper we present a general theory for an arbitrary 2D channel with "spin momentum locking" due to spin-orbit coupling. It is based on a semiclassical model that classifies all the channel electronic states into four groups based on the sign of the z-component of the spin (up (U), down (D)) and the sign of the x-component of the velocity (+, -). This could be viewed as an extension of the standard spin diffusion model which uses two separate electrochemical potentials for U and D states. Our model uses four: U+, D+, U-, and D-. We use this formulation to develop an equivalent spin circuit that is also benchmarked against a full non-equilibrium Green's function (NEGF) model. The circuit representation can be used to interpret experiments and estimate important quantities of interest like the charge to spin conversion ratio or the maximum spin current that can be extracted. The model should be applicable to topological insulator surface states with parallel channels as well as to other layered structures with interfacial spin-orbit coupling. PMID:26932563

  14. Spin Circuit Model for 2D Channels with Spin-Orbit Coupling

    NASA Astrophysics Data System (ADS)

    Hong, Seokmin; Sayed, Shehrin; Datta, Supriyo

    2016-03-01

    In this paper we present a general theory for an arbitrary 2D channel with “spin momentum locking” due to spin-orbit coupling. It is based on a semiclassical model that classifies all the channel electronic states into four groups based on the sign of the z-component of the spin (up (U), down (D)) and the sign of the x-component of the velocity (+, -). This could be viewed as an extension of the standard spin diffusion model which uses two separate electrochemical potentials for U and D states. Our model uses four: U+, D+, U-, and D-. We use this formulation to develop an equivalent spin circuit that is also benchmarked against a full non-equilibrium Green’s function (NEGF) model. The circuit representation can be used to interpret experiments and estimate important quantities of interest like the charge to spin conversion ratio or the maximum spin current that can be extracted. The model should be applicable to topological insulator surface states with parallel channels as well as to other layered structures with interfacial spin-orbit coupling.

  15. Field Evaluation of a Novel 2D Preferential Flow Snowpack Hydrology Model

    NASA Astrophysics Data System (ADS)

    Leroux, N.; Pomeroy, J. W.; Kinar, N. J.

    2015-12-01

    Accurate estimation of snowmelt flux is of primary importance for runoff hydrograph prediction, which is used for water management and flood forecasting. Lateral flows and preferential flow pathways in porous media flow have proven critical for improving soil and groundwater flow models, but though many physically-based layered snowmelt models have been developed, only 1D matrix flow is accounted for in these models. Therefore, there is a need for snowmelt models that include these processes so as to examine the potential to improve snowmelt hydrological modelling. A 2D model is proposed that enables an improved understanding of energy and water flows within deep heterogeneous snowpacks, including those on slopes. A dual pathway theory is presented that simulates the formation of preferential flow paths, vertical and lateral water flows through the snow matrix and flow fingers, internal energy fluxes, melt, wet snow metamorphism, and internal refreezing. The dual pathway model utilizes an explicit finite volume method to solve for the energy and water flux equations over a non-orthogonal grid. It was run and evaluated using in-situ data collected from snowpit - accessed gravimetric, thermometric, photographic, and dielectric observations and novel non-invasive acoustic observations of layering, temperature, flowpath geometry, density and wetness at the Fortress Mountain Snow Laboratory, Alberta, Canada. The melt of a natural snowpack was artificially generated after detailed observation of snowpack initial conditions such as snow layer properties, temperature, and liquid water content. Snowpack ablation and liquid water content distribution over time were then measured and used for model parameterization and validation. Energy available at the snow surface and soil slope angle were set as mondel inputs. Model verification was based on snowpack property evolution. The heterogeneous flow model can be an important tool to help understand snowmelt flow processes, how

  16. Integration of 2-D hydraulic model and high-resolution LiDAR-derived DEM for floodplain flow modeling

    NASA Astrophysics Data System (ADS)

    Shen, D.; Wang, J.; Cheng, X.; Rui, Y.; Ye, S.

    2015-02-01

    The rapid progress of Light Detection And Ranging (LiDAR) technology has made acquirement and application of high-resolution digital elevation model (DEM) data increasingly popular, especially with regards to the study of floodplain flow modeling. High-resolution DEM data include many redundant interpolation points, needs a high amount of calculation, and does not match the size of computational mesh. These disadvantages are a common problem for floodplain flow modeling studies. Two-dimensional (2-D) hydraulic modeling, a popular method of analyzing floodplain flow, offers high precision of elevation parameterization for computational mesh while ignoring much micro-topographic information of the DEM data itself. We offer a flood simulation method that integrates 2-D hydraulic model results and high-resolution DEM data, enabling the calculation of flood water levels in DEM grid cells through local inverse distance weighted interpolation. To get rid of the false inundation areas during interpolation, it employs the run-length encoding method to mark the inundated DEM grid cells and determine the real inundation areas through the run-length boundary tracing technique, which solves the complicated problem of the connectivity between DEM grid cells. We constructed a 2-D hydraulic model for the Gongshuangcha polder, a flood storage area of Dongting Lake, using our integrated method to simulate the floodplain flow. The results demonstrate that this method can solve DEM associated problems efficiently and simulate flooding processes with greater accuracy than DEM only simulations.

  17. A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds

    SciTech Connect

    Li, Tingwen; Zhang, Yongmin

    2013-10-11

    Pseudo-two dimensional (pseudo-2D) fluidized beds, for which the thickness of the system is much smaller than the other two dimensions, is widely used to perform fundamental studies on bubble behavior, solids mixing, or clustering phenomenon in different gas-solids fluidization systems. The abundant data from such experimental systems are very useful for numerical model development and validation. However, it has been reported that two-dimensional (2D) computational fluid dynamic (CFD) simulations of pseudo-2D gas-solids fluidized beds usually predict poor quantitative agreement with the experimental data, especially for the solids velocity field. In this paper, a new model is proposed to improve the 2D numerical simulations of pseudo-2D gas-solids fluidized beds by properly accounting for the frictional effect of the front and back walls. Two previously reported pseudo-2D experimental systems were simulated with this model. Compared to the traditional 2D simulations, significant improvements in the numerical predictions have been observed and the predicted results are in better agreement with the available experimental data.

  18. A case study of fluid flow in fractured rock mass based on 2-D DFN modeling

    NASA Astrophysics Data System (ADS)

    Han, Jisu; Noh, Young-Hwan; Um, Jeong-Gi; Choi, Yosoon

    2014-05-01

    A two dimensional steady-state fluid flow through fractured rock mass of an abandoned copper mine in Korea is addressed based on discrete fracture network modeling. An injection well and three observation wells were installed at the field site to monitor the variations of total heads induced by injection of fresh water. A series of packer tests were performed to estimate the rock mass permeability. First, the two dimensional stochastic fracture network model was built and validated for a granitic rock mass using the geometrical and statistical data obtained from surface exposures and borehole logs. This validated fracture network model was combined with the fracture data observed on boreholes to generate a stochastic-deterministic fracture network system. Estimated apertures for each of the fracture sets using permeability data obtained from borehole packer tests were discussed next. Finally, a systematic procedure for fluid flow modeling in fractured rock mass in two dimensional domain was presented to estimate the conductance, flow quantity and nodal head in 2-D conceptual linear pipe channel network. The results obtained in this study clearly show that fracture geometry parameters (orientation, density and size) play an important role in the hydraulic behavior of fractured rock masses.

  19. Distributed and coupled 2D electro-thermal model of power semiconductor devices

    NASA Astrophysics Data System (ADS)

    Belkacem, Ghania; Lefebvre, Stéphane; Joubert, Pierre-Yves; Bouarroudj-Berkani, Mounira; Labrousse, Denis; Rostaing, Gilles

    2014-05-01

    The development of power electronics in the field of transportations (automotive, aeronautics) requires the use of power semiconductor devices providing protection and diagnostic functions. In the case of series protections power semiconductor devices which provide protection may operate in shortcircuit and act as a current limiting device. This mode of operations is very constraining due to the large dissipation of power. In these particular conditions of operation, electro-thermal models of power semiconductor devices are of key importance in order to optimize their thermal design and increase their reliability. The development of such an electro-thermal model for power MOSFET transistors based on the coupling between two computation softwares (Matlab and Cast3M) is described in this paper. The 2D electro-thermal model is able to predict (i) the temperature distribution on chip surface well as in the volume under short-circuit operations, (ii) the effect of the temperature on the distribution of the current flowing within the die and (iii) the effects of the ageing of the metallization layer on the current density and the temperature. In this paper, the electrical and thermal models are described as well as the implemented coupling scheme.

  20. Studies of Arctic stratospheric ozone in a 2-D model including some effects of zonal asymmetries

    SciTech Connect

    Isaksen, I.S.A.; Rognerud, B.; Stordal, F. ); Coffey, M.T.; Mankin, W.G. )

    1990-03-01

    A two-dimensional (2-D) zonally averaged chemistry-transport model of the stratosphere has been extended to include some zonally asymmetric effects to study the chemically disturbed conditions in the Arctic winter during the occurrence of polar stratospheric clouds (PSCs). The model allows air parcels that have been in PSCs in the polar night to be exposed to sunlight during the passage south through a wave trough. Large enhancements of ClO are estimated as well as significant ozone reductions, most pronounced around the 20 km height level. The ozone depletions maximize in late March, about one month after the cease in PSC activity in the model, and amount to 5-8% in column ozone at 70{degree}N. In agreement with column measurements made from the DC-8, the model estimates an increase in the columns of HNO{sub 3} and ClONO{sub 2}, and a decrease in the HCl column within the polar vortex.

  1. LBQ2D, Extending the Line Broadened Quasilinear Model to TAE-EP Interaction

    NASA Astrophysics Data System (ADS)

    Ghantous, Katy; Gorelenkov, Nikolai; Berk, Herbert

    2012-10-01

    The line broadened quasilinear model was proposed and tested on the one dimensional electrostatic case of the bump on tailfootnotetextH.L Berk, B. Breizman and J. Fitzpatrick, Nucl. Fusion, 35:1661, 1995 to study the wave particle interaction. In conventional quasilinear theory, the sea of overlapping modes evolve with time as the particle distribution function self consistently undergo diffusion in phase space. The line broadened quasilinear model is an extension to the conventional theory in a way that allows treatment of isolated modes as well as overlapping modes by broadening the resonant line in phase space. This makes it possible to treat the evolution of modes self consistently from onset to saturation in either case. We describe here the model denoted by LBQ2D which is an extension of the proposed one dimensional line broadened quasilinear model to the case of TAEs interacting with energetic particles in two dimensional phase space, energy as well as canonical angular momentum. We study the saturation of isolated modes in various regimes and present the analytical derivation and numerical results. Finally, we present, using ITER parameters, the case where multiple modes overlap and describe the techniques used for the numerical treatment.

  2. Slave-boson study in the SU(2)-invariant representation: Coupled layers in the one-band Hubbard model

    SciTech Connect

    Ziegler, W.; Dieterich, P.; Muramatsu, A.; Hanke, W.

    1996-01-01

    Using the spin-rotation-invariant form of the slave-boson formalism we emphasize formal aspects of this method concerning the SU(2) transformation properties and the physical content of the constraints which are necessary to project onto the physical subspace. As a result, a consistent scheme of coherent states within the functional integral of the SU(2)-invariant slave-boson theory is provided. As an application, a system of two Hubbard layers coupled by an interlayer hopping {ital t}{sub {perpendicular}} is investigated. Numerical results from a saddle-point approximation of the partition function are used to consider the magnetic order in and between the layers as a fact of {ital t}{sub {perpendicular}}. {copyright} {ital 1996 The American Physical Society.}

  3. Obtaining instantaneous water levels relative to a geoid with a 2D storm surge model

    NASA Astrophysics Data System (ADS)

    Slobbe, D. C.; Verlaan, M.; Klees, R.; Gerritsen, H.

    2013-01-01

    Current and new applications of 2D storm surge models such as the Dutch Continental Shelf Model (DCSM) require that the models provide proper estimates of the instantaneous water levels expressed relative to a particular geoid, rather than only the tide and surge components expressed relative to the ill-defined model's zero height surface. For DCSM, this is realized by adding the depth-averaged horizontal baroclinic pressure gradients to the model equations, which are derived from 4D salinity and temperature fields provided by the Proudman Oceanographic Laboratory hydrodynamic model (POL's hindcast). The vertical datum of the extended model is fixed to that of the European Gravimetric Geoid model 2008 (EGG08). This is done by an adjustment of the model parameters that depend on the choice of the reference surface (e.g., bathymetry) and by referring the water levels along the open boundaries to this reference surface. Using different numerical experiments we investigate the effects on the water levels of several approximations we have made during the implementation. The ability of the model to reproduce both the mean sea level (MSL) and instantaneous water levels is assessed by a comparison with the MSL derived from POL's hindcast as well as with instantaneous water levels acquired by various radar altimeter satellites. From this comparison we conclude that our modeled MSL is in good agreement with the MSL derived from POL's hindcast; the standard deviation of the differences is below 2 cm. However, larger differences in MSL are observed when comparing the model output with the MSL derived from radar altimeter data. They are attributed to either geoid errors or errors in the used salinity and temperature fields. The root mean squared (rms) differences between observed and modeled instantaneous water levels over the entire model domain varies from 9 cm for data acquired by the TOPEX satellite to 11 cm for data acquired by the GFO-1 satellite. These numbers improve to

  4. Dynamics of two-site Fermi-Hubbard and Bose-Hubbard systems

    SciTech Connect

    Ziegler, K.

    2010-03-15

    This paper analyzes dynamical properties of small Fermi-Hubbard and Bose-Hubbard systems, focusing on the structure of the underlying Hilbert space. We evaluate time-dependent quantities such as the return probability to the initial state and the spin imbalance of spin-1/2 fermions. For the symmetric two-site Fermi-Hubbard model we find that the spin imbalance and the return probability are controlled by two and three frequencies, respectively. The spin imbalance and the return probability are identical for the asymmetric Falicov-Kimball limit and controlled by only one frequency. In general, the transition probabilities between the initial state and the energy eigenstates depend strongly on the particle-particle interaction. This is discussed for 'self-trapping' of spinless bosons in a double-well potential. We observe that the available Hilbert space is reduced significantly by strong interaction.

  5. A New 2D-Advection-Diffusion Model Simulating Trace Gas Distributions in the Lowermost Stratosphere

    NASA Astrophysics Data System (ADS)

    Hegglin, M. I.; Brunner, D.; Peter, T.; Wirth, V.; Fischer, H.; Hoor, P.

    2004-12-01

    Tracer distributions in the lowermost stratosphere are affected by both, transport (advective and non-advective) and in situ sources and sinks. They influence ozone photochemistry, radiative forcing, and heating budgets. In-situ measurements of long-lived species during eight measurement campaigns revealed relatively simple behavior of the tracers in the lowermost stratosphere when represented in an equivalent-latitude versus potential temperature framework. We here present a new 2D-advection-diffusion model that simulates the main transport pathways influencing the tracer distributions in the lowermost stratosphere. The model includes slow diabatic descent of aged stratospheric air and vertical and/or horizontal diffusion across the tropopause and within the lowermost stratosphere. The diffusion coefficients used in the model represent the combined effects of different processes with the potential of mixing tropospheric air into the lowermost stratosphere such as breaking Rossby and gravity waves, deep convection penetrating the tropopause, turbulent diffusion, radiatively driven upwelling etc. They were specified by matching model simulations to observed distributions of long-lived trace gases such as CO and N2O obtained during the project SPURT. The seasonally conducted campaigns allow us to study the seasonal dependency of the diffusion coefficients. Despite its simplicity the model yields a surprisingly good description of the small scale features of the measurements and in particular of the observed tracer gradients at the tropopause. The correlation coefficients between modeled and measured trace gas distributions were up to 0.95. Moreover, mixing across isentropes appears to be more important than mixing across surfaces of constant equivalent latitude (or PV). With the aid of the model, the distribution of the fraction of tropospheric air in the lowermost stratosphere can be determined.

  6. Transectional heat transfer in thermoregulating bigeye tuna (Thunnus obesus) - a 2D heat flux model.

    PubMed

    Boye, Jess; Musyl, Michael; Brill, Richard; Malte, Hans

    2009-11-01

    We developed a 2D heat flux model to elucidate routes and rates of heat transfer within bigeye tuna Thunnus obesus Lowe 1839 in both steady-state and time-dependent settings. In modeling the former situation, we adjusted the efficiencies of heat conservation in the red and the white muscle so as to make the output of the model agree as closely as possible with observed cross-sectional isotherms. In modeling the latter situation, we applied the heat exchanger efficiencies from the steady-state model to predict the distribution of temperature and heat fluxes in bigeye tuna during their extensive daily vertical excursions. The simulations yielded a close match to the data recorded in free-swimming fish and strongly point to the importance of the heat-producing and heat-conserving properties of the white muscle. The best correspondence between model output and observed data was obtained when the countercurrent heat exchangers in the blood flow pathways to the red and white muscle retained 99% and 96% (respectively) of the heat produced in these tissues. Our model confirms that the ability of bigeye tuna to maintain elevated muscle temperatures during their extensive daily vertical movements depends on their ability to rapidly modulate heating and cooling rates. This study shows that the differential cooling and heating rates could be fully accounted for by a mechanism where blood flow to the swimming muscles is either exclusively through the heat exchangers or completely shunted around them, depending on the ambient temperature relative to the body temperature. Our results therefore strongly suggest that such a mechanism is involved in the extensive physiological thermoregulatory abilities of endothermic bigeye tuna. PMID:19880733

  7. Scaling of the gap, fidelity susceptibility, and Bloch oscillations across the superfluid-to-Mott-insulator transition in the one-dimensional Bose-Hubbard model

    NASA Astrophysics Data System (ADS)

    Carrasquilla, Juan; Manmana, Salvatore R.; Rigol, Marcos

    2013-04-01

    We investigate the interaction-induced superfluid-to-Mott-insulator transition in the one-dimensional Bose-Hubbard model (BHM) for fillings n=1, n=2, and n=3 by studying the single-particle gap, the fidelity susceptibility, and the amplitude of Bloch oscillations via density-matrix renormalization-group methods. We apply a generic scaling procedure for the gap, which allows us to determine the critical points with very high accuracy. We also study how the fidelity susceptibility behaves across the phase transition. Furthermore, we show that in the BHM, and in a system of spinless fermions, the amplitude of Bloch oscillations after a tilt of the lattice vanishes at the critical points. This indicates that Bloch oscillations can serve as a tool to detect the transition point in ongoing experiments with ultracold gases.

  8. Effect of dominant three-body interaction to the hard-core boson Hubbard model on a two-dimensional square lattice

    NASA Astrophysics Data System (ADS)

    Liang, Ying; Guo, Huaiming

    2012-09-01

    The effect of dominant three-body interaction to the hard-core boson Hubbard model is studied on a two-dimensional square lattice. In terms of the quantum Monte Carlo method, a ρ = 2/3 solid phase is shown explicitly with the coexistence of a charge-density wave and a bond-order wave appearing due to the presence of the dominant three-body interaction. For the strong three-body interaction, the ρ = 2/3 solid phase appears between superfluid phases and shrinks as the strength of the three-body interaction decreases, forming a lobe structure in the phase diagram. For weak three-body interactions, the superfluid phase exists for the whole range of hard-core densities except the full filled case, where the system is a Mott insulator. Our results may be realized in cold-atom experiments.

  9. Self-energy effects in functional renormalization group flows of the two-dimensional t -t' Hubbard model away from van Hove filling

    NASA Astrophysics Data System (ADS)

    Eberlein, Andreas

    2015-12-01

    We study the impact of the fermionic self-energy on one-loop functional renormalization group flows of the two-dimensional t -t' Hubbard model, with emphasis on electronic densities away from van Hove filling. In the presence of antiferromagnetic hot spots, antiferromagnetic fluctuations lead to a flattening of the Fermi surface, shift magnetic phase boundaries, and significantly enhance critical scales. We trace back this effect to the presence of a magnetic first-order transition. For some parameters, the first-order character of the latter is reduced by self-energy effects. For reliably determining phase diagrams, the fermionic self-energy should be taken into account in functional renormalization group studies if scattering between hot spots is important.

  10. Comparing a 2D fluid model of the DC planar magnetron cathode to experiments

    SciTech Connect

    Garcia, M.

    1996-05-01

    Planar magnetron cathodes have arching magnetic field lines which concentrate plasma density near the electrode surface. This enhances the ion bombardment of the surface and the yield of sputtered atoms. Magnetron cathodes are used in the Plasma Electrode Pockels Cell (PEPC) devices of the Laser Program because they provide for significantly higher conduction than do glow discharges. An essential feature of magnetron cathodes is that the vector product of the perpendicular electric field, E[sub y], with the parallel component of the magnetic field, B[sub x], forms a closed track with a circulating current along the cathode surface. An analytical, 2D, two component, quasi-neutral, continuum model yields formulas for the plasma density, the total and component current densities, the electric field, and the positive electrical potential, between the cathode surface and a distant, uniform plasma. For a specific gas, the free parameters are electron temperature, gas number density, and total current. The model is applied to the interpretation of experimental data from the PEPC device, as well as a small vacuum facility for testing magnetron cathodes. Finally, the model has been applied to generate cross sectional views of a PEPC magnetron cathode track.

  11. Doubled CO2 Effects on NO(y) in a Coupled 2D Model

    NASA Technical Reports Server (NTRS)

    Rosenfield, J. E.; Douglass, A. R.

    1998-01-01

    Changes in temperature and ozone have been the main focus of studies of the stratospheric impact of doubled CO2. Increased CO2 is expected to cool the stratosphere, which will result in increases in stratospheric ozone through temperature dependent loss rates. Less attention has been paid to changes in minor constituents which affect the O3 balance and which may provide additional feedbacks. Stratospheric NO(y) fields calculated using the GSFC 2D interactive chemistry-radiation-dynamics model show significant sensitivity to the model CO2. Modeled upper stratospheric NO(y) decreases by about 15% in response to CO2 doubling, mainly due to the temperature decrease calculated to result from increased cooling. The abundance of atomic nitrogen, N, increases because the rate of the strongly temperature dependent reaction N + O2 yields NO + O decreases at lower temperatures. Increased N leads to an increase in the loss of NO(y) which is controlled by the reaction N + NO yields N2 + O. The NO(y) reduction is shown to be sensitive to the NO photolysis rate. The decrease in the O3 loss rate due to the NO(y) changes is significant when compared to the decrease in the O3 loss rate due to the temperature changes.

  12. Simulation of abrasive flow machining process for 2D and 3D mixture models

    NASA Astrophysics Data System (ADS)

    Dash, Rupalika; Maity, Kalipada

    2015-12-01

    Improvement of surface finish and material removal has been quite a challenge in a finishing operation such as abrasive flow machining (AFM). Factors that affect the surface finish and material removal are media viscosity, extrusion pressure, piston velocity, and particle size in abrasive flow machining process. Performing experiments for all the parameters and accurately obtaining an optimized parameter in a short time are difficult to accomplish because the operation requires a precise finish. Computational fluid dynamics (CFD) simulation was employed to accurately determine optimum parameters. In the current work, a 2D model was designed, and the flow analysis, force calculation, and material removal prediction were performed and compared with the available experimental data. Another 3D model for a swaging die finishing using AFM was simulated at different viscosities of the media to study the effects on the controlling parameters. A CFD simulation was performed by using commercially available ANSYS FLUENT. Two phases were considered for the flow analysis, and multiphase mixture model was taken into account. The fluid was considered to be a

  13. Complex 2D matrix model and geometrical map on the complex-Nc plane

    NASA Astrophysics Data System (ADS)

    Nawa, Kanabu; Ozaki, Sho; Nagahiro, Hideko; Jido, Daisuke; Hosaka, Atsushi

    2013-08-01

    We study the parameter dependence of the internal structure of resonance states by formulating a complex two-dimensional (2D) matrix model, where the two dimensions represent two levels of resonances. We calculate a critical value of the parameter at which a "nature transition" with character exchange occurs between two resonance states, from the viewpoint of geometry on complex-parameter space. Such a critical value is useful for identifying the internal structure of resonance states with variation of the parameter in the system. We apply the model to analyze the internal structure of hadrons with variation of the color number N_c from infty to a realistic value 3. By regarding 1/N_c as the variable parameter in our model, we calculate a critical color number of the nature transition between hadronic states in terms of a quark-antiquark pair and a mesonic molecule as exotics from the geometry on the complex-N_c plane. For large-N_c effective theory, we employ the chiral Lagrangian induced by holographic QCD with a D4/D8/overline {D8} multi-D brane system in type IIA superstring theory.

  14. Field-induced magnetization jumps and quantum criticality in the 2D J-Q model

    NASA Astrophysics Data System (ADS)

    Iaizzi, Adam; Sandvik, Anders

    The J-Q model is a `designer hamiltonian' formed by adding a four spin `Q' term to the standard antiferromagnetic S = 1 / 2 Heisenberg model. The Q term drives a quantum phase transition to a valence-bond solid (VBS) state: a non-magnetic state with a pattern of local singlets which breaks lattice symmetries. The elementary excitations of the VBS are triplons, i.e. gapped S=1 quasiparticles. There is considerable interest in the quantum phase transition between the Néel and VBS states as an example of deconfined quantum criticality. Near the phase boundary, triplons deconfine into pairs of bosonic spin-1/2 excitations known as spinons. Using exact diagonalization and the stochastic series expansion quantum monte carlo method, we study the 2D J-Q model in the presence of an external magnetic field. We use the field to force a nonzero density of magnetic excitations at T=0 and look for signatures of Bose-Einstein condensation of spinons. At higher magnetic fields, there is a jump in the induced magnetization caused by the onset of an effective attractive interaction between magnons on a ferromagnetic background. We characterize the first order quantum phase transition and determine the minimum value of the coupling ratio q ≡ Q / J required to produce this jump. Funded by NSF DMR-1410126.

  15. 2d Affine XY-Spin Model/4d Gauge Theory Duality and Deconfinement

    SciTech Connect

    Anber, Mohamed M.; Poppitz, Erich; Unsal, Mithat; /SLAC /Stanford U., Phys. Dept. /San Francisco State U.

    2012-08-16

    We introduce a duality between two-dimensional XY-spin models with symmetry-breaking perturbations and certain four-dimensional SU(2) and SU(2) = Z{sub 2} gauge theories, compactified on a small spatial circle R{sup 1,2} x S{sup 1}, and considered at temperatures near the deconfinement transition. In a Euclidean set up, the theory is defined on R{sup 2} x T{sup 2}. Similarly, thermal gauge theories of higher rank are dual to new families of 'affine' XY-spin models with perturbations. For rank two, these are related to models used to describe the melting of a 2d crystal with a triangular lattice. The connection is made through a multi-component electric-magnetic Coulomb gas representation for both systems. Perturbations in the spin system map to topological defects in the gauge theory, such as monopole-instantons or magnetic bions, and the vortices in the spin system map to the electrically charged W-bosons in field theory (or vice versa, depending on the duality frame). The duality permits one to use the two-dimensional technology of spin systems to study the thermal deconfinement and discrete chiral transitions in four-dimensional SU(N{sub c}) gauge theories with n{sub f} {ge} 1 adjoint Weyl fermions.

  16. Prominence fine-structure dynamics as inferred from 2D non-LTE models

    NASA Astrophysics Data System (ADS)

    Gunar, Stanislav; Schmieder, Brigitte; Mein, Pierre; Heinzel, Petr

    2012-07-01

    2D multi-thread prominence fine structure models are able to produce synthetic Lyman spectra in very good agreement with spectral observations by SOHO/SUMER including the spectral line asymmetries. The synthetic differential emission measure curves derived from these models are also in a good agreement with observations. Now we show that these models are also able to produce synthetic H-alpha line profiles in very good agreement with observations which allows us to analyze not only the physical parameters of the prominence fine-structure plasma but also some aspects of its dynamical behaviour. We compare the synthetic H-alpha spectra with the observed spectra of the April 26, 2007 prominence using three statistical parameters: the line integrated intensity, the line full-width at the half-maximum (FWHM), and the Doppler velocity derived from shifts of the line profiles. This statistical analysis allows us to conclude that the overall statistical distribution of the LOS velocities in the April 26, 2007 prominence at the time of the observations was below +/-15 km/s and in the prominence core was close to +/-10 km/s. In combination with the analysis of the Lyman spectra we determine several physical parameters of the observed prominence fine structures which show that the April 26, 2007 prominence was relatively less massive. We are also able to put some constrains on the prominence core temperature that might be relatively low, reaching values below 6000 K.

  17. Automatic 3D high-fidelity traffic interchange modeling using 2D road GIS data

    NASA Astrophysics Data System (ADS)

    Wang, Jie; Shen, Yuzhong

    2011-03-01

    3D road models are widely used in many computer applications such as racing games and driving simulations. However, almost all high-fidelity 3D road models were generated manually by professional artists at the expense of intensive labor. There are very few existing methods for automatically generating 3D high-fidelity road networks, especially for those existing in the real world. Real road network contains various elements such as road segments, road intersections and traffic interchanges. Among them, traffic interchanges present the most challenges to model due to their complexity and the lack of height information (vertical position) of traffic interchanges in existing road GIS data. This paper proposes a novel approach that can automatically produce 3D high-fidelity road network models, including traffic interchange models, from real 2D road GIS data that mainly contain road centerline information. The proposed method consists of several steps. The raw road GIS data are first preprocessed to extract road network topology, merge redundant links, and classify road types. Then overlapped points in the interchanges are detected and their elevations are determined based on a set of level estimation rules. Parametric representations of the road centerlines are then generated through link segmentation and fitting, and they have the advantages of arbitrary levels of detail with reduced memory usage. Finally a set of civil engineering rules for road design (e.g., cross slope, superelevation) are selected and used to generate realistic road surfaces. In addition to traffic interchange modeling, the proposed method also applies to other more general road elements. Preliminary results show that the proposed method is highly effective and useful in many applications.

  18. Generalized Mechanistic Model for the Chemical Vapor Deposition of 2D Transition Metal Dichalcogenide Monolayers.

    PubMed

    Govind Rajan, Ananth; Warner, Jamie H; Blankschtein, Daniel; Strano, Michael S

    2016-04-26

    Transition metal dichalcogenides (TMDs) like molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are layered materials capable of growth to one monolayer thickness via chemical vapor deposition (CVD). Such CVD methods, while powerful, are notoriously difficult to extend across different reactor types and conditions, with subtle variations often confounding reproducibility, particularly for 2D TMD growth. In this work, we formulate the first generalized TMD synthetic theory by constructing a thermodynamic and kinetic growth mechanism linked to CVD reactor parameters that is predictive of specific geometric shape, size, and aspect ratio from triangular to hexagonal growth, depending on specific CVD reactor conditions. We validate our model using experimental data from Wang et al. (Chem. Mater. 2014, 26, 6371-6379) that demonstrate the systemic evolution of MoS2 morphology down the length of a flow CVD reactor where variations in gas phase concentrations can be accurately estimated using a transport model (CSulfur = 9-965 μmol/m(3); CMoO3 = 15-16 mmol/m(3)) under otherwise isothermal conditions (700 °C). A stochastic model which utilizes a site-dependent activation energy barrier based on the intrinsic TMD bond energies and a series of Evans-Polanyi relations leads to remarkable, quantitative agreement with both shape and size evolution along the reactor. The model is shown to extend to the growth of WS2 at 800 °C and MoS2 under varied process conditions. Finally, a simplified theory is developed to translate the model into a "kinetic phase diagram" of the growth process. The predictive capability of this model and its extension to other TMD systems promise to significantly increase the controlled synthesis of such materials. PMID:26937889

  19. 2D dynamical magma propagation modeling: application to the 2001 Mount Etna eruption

    NASA Astrophysics Data System (ADS)

    Pinel, Virginie; Carrara, Alexandre; Maccaferri, Francesco; Rivalta, Eleonora; Corbi, Fabio

    2016-04-01

    Numerical and analog studies of dike propagation in a stress field induced by volcanic edifice construction have shown that surface loading tends both to attract the magma and to reduce its velocity. Available numerical models can either calculate the trajectory or the velocity of the ascending dikes, but not both of them simultaneously. We developed a hybrid model of dyke propagation in two dimensions solving both for the magma trajectory and velocity as a function of the source overpressure, the magma physical properties (density and viscosity) as well as the crustal density and stress field. We first calculate a dyke trajectory in 2D and secondly run a 1D dynamical model of dyke propagation along this trajectory taken into account the influence of the stress field seen by the magma along this path. This model is used to characterize the influence of surface load on magma migration towards the surface and compared to previous results obtained by analog modeling.We find that the amplitude of dyke deflection and magma velocity variation depend on the ratio between the dyke driving pressure (source overpressure as well buoyancy) and the stress field perturbation. Our model is then applied to the July 2001 eruption of Etna, where the final dyke deflection had been previously interpreted as due to the topographic load by Bonaccorso et al. [2010]. We show that the velocity decrease observed during the last stage of the propagation can also be attributed to the local stress field. We use the dyke propagation duration to estimate the magma overpressure at the dyke bottom to be less than 4 MPa.

  20. Effects of CYP2D6 Status on Harmaline Metabolism, Pharmacokinetics and Pharmacodynamics, and a Pharmacogenetics-Based Pharmacokinetic Model

    PubMed Central

    Wu, Chao; Jiang, Xi-Ling; Shen, Hong-Wu; Yu, Ai-Ming

    2009-01-01

    Harmaline is a β-carboline alkaloid showing neuroprotective and neurotoxic properties. Our recent studies have revealed an important role for cytochrome P450 2D6 (CYP2D6) in harmaline O-demethylation. This study, therefore, aimed to delineate the effects of CYP2D6 phenotype/genotype on harmaline metabolism, pharmacokinetics (PK) and pharmacodynamics (PD), and to develop a pharmacogenetics mechanism-based compartmental PK model. In vitro kinetic studies on metabolite formation in human CYP2D6 extensive metabolizer (EM) and poor metabolizer (PM) hepatocytes indicated that harmaline O-demethylase activity (Vmax/Km) was about 9-fold higher in EM hepatocytes. Substrate depletion showed mono-exponential decay trait, and estimated in vitro harmaline clearance (CLint, μL/min/106 cells) was significantly lower in PM hepatocytes (28.5) than EM hepatocytes (71.1). In vivo studies in CYP2D6-humanized and wild-type mouse models showed that wild-type mice were subjected to higher and longer exposure to harmaline (5 and 15 mg/kg; i.v. and i.p.), and more severe hypothermic responses. The PK/PD data were nicely described by our pharmacogenetics-based PK model involving the clearance of drug by CYP2D6 (CLCYP2D6) and other mechanisms (CLother), and an indirect response PD model, respectively. Wild-type mice were also more sensitive to harmaline in marble-burying tests, as manifested by significantly lower ED50 and steeper Hill slope. These findings suggest that distinct CYP2D6 status may cause considerable variations in harmaline metabolism, PK and PD. In addition, the pharmacogenetics-based PK model may be extended to define PK difference caused by other polymorphic drug-metabolizing enzyme in different populations. PMID:19445902