Ferromagnetism and d-wave superconductivity in the 2D Hubbard model
International Nuclear Information System (INIS)
By using the functional renormalization group we compute detailed momentum dependencies of the scale-dependent interaction vertex of the 2D (t,t')-Hubbard model. Compared to previous studies we improve accuracy by separating dominant parts from a remainder term. The former explicitly describe, for example, the interaction of Cooper pairs or spin operators. Applying the method to the repulsive Hubbard model we find d-wave superconductivity or ferromagnetism for larger next-to-nearest neighbor hopping amplitude t' at Van Hove Filling. Both ordering tendencies strongly compete with each other.
System-parameter dependence of the metallic phase of the non-doped 2D Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Yamaji, K., E-mail: yamaji-kuni@aist.go.j [Nanoelectronics Research Institute, AIST Central 2, 1-1-1 Umezono, Tsukuba 305-8568 (Japan); Yanagisawa, T. [Nanoelectronics Research Institute, AIST Central 2, 1-1-1 Umezono, Tsukuba 305-8568 (Japan); Miyazaki, M. [Hakodate National College of Technology, 14-1 Tokura-cho, Hakodate 042-8501 (Japan); Kadono, R. [Institute of Materials Structure Science, KEK, 1-1 Oho, Tsukuba 305-0801 (Japan)
2009-10-15
Naito et al. reported that some non-doped T'-214-type compounds drive high-T{sub c} superconductivity. The compounds are considered to be metallic since on-site Coulomb energy U is moderate and the Fermi surface is much deformed in these compounds. In order to confirm this picture and extract electronic structure information, we have examined the phase diagram of the metallic state of the 2D Hubbard model as a function of U and t' (with t'' we fixed at -t'/2 here; t' and t'' are the second- and third-neighbor transfer energies, respectively) by means of the variational Monte-Carlo method. We employed a Jastrow-type Gutzwiller trial wave function. In the studied range of U 2-12, the boundary value for |t'| at which SDW disappears increases almost linearly with U. Jump-wise transition to the Mott insulator state was not observed. Using the boundary curve and experimental band parameter values, we estimate U approx 5 for T'-214 compounds. Preceding works are discussed in the last part.
Hubbard model with geometrical frustration
Energy Technology Data Exchange (ETDEWEB)
Lee, Hunpyo
2009-10-15
At first we present the details of the dual fermion (DF), the cluster extension of dynamical mean field theory (CDMFT) and continuous-time quantum Monte Carlo (CT QMC) methods. Using a panoply of these methods we explore the Hubbard model on the triangular and hyperkagome lattice. We find a first-order transition and continuous transition on the triangular and hyper-kagome lattice, respectively. Moreover, we find the reentrant behavior due to competition between the magnetic correlation and itinerancy of electrons by source of geometrical frustration on both lattices. (orig.)
Fermionic Symmetry-Protected Topological Phase in a Two-Dimensional Hubbard Model.
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
Phase separation in the Hubbard model
Macridin, A.; Jarrell, M.; Maier, Th.
2005-01-01
Phase separation in the Hubbard model is investigated with the dynamical cluster approximation. We find that it is present in the paramagnetic solution for values of filling smaller than one and at finite temperature when a positive next-nearest neighbor hopping is considered. The phase separated region is characterized by a mixture of a strongly correlated metallic and Mott insulating phases. Our results indicate that phase separation is driven by the formation of doped regions with strong a...
Activated sludge model No. 2d, ASM2d
DEFF Research Database (Denmark)
Henze, M.
1999-01-01
The Activated Sludge Model No. 2d (ASM2d) presents a model for biological phosphorus removal with simultaneous nitrification-denitrification in activated sludge systems. ASM2d is based on ASM2 and is expanded to include the denitrifying activity of the phosphorus accumulating organisms (PAOs...
Dynamical Vertex Approximation for the Hubbard Model
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.
Yanagisawa, Takashi
2016-11-01
The ground state of the two-dimensional (2D) Hubbard model is investigated by adopting improved wave functions that take into account intersite electron correlation beyond the Gutzwiller ansatz. The ground-state energy is lowered considerably, giving the best estimate of the ground-state energy for the 2D Hubbard model. There is a crossover from weakly to strongly correlated regions as the on-site Coulomb interaction U increases. The antiferromagnetic correlation induced by U is reduced for hole doping when U is large, being greater than the bandwidth, thus increasing the kinetic energy gain. The spin and charge fluctuations are induced in the strongly correlated region. These antiferromagnetic and kinetic charge fluctuations induce electron pairings, which results in high-temperature superconductivity.
Electron-phonon interaction in the Hubbard model
International Nuclear Information System (INIS)
Superconductivity existence in the Hubbard model is studied, taking into account both electron-phonon and electron-electron interactions. Using Sarker's functional integral formalism a system of equations for the dynamical order parameters is derived. (author). 7 refs
Reexamination of the variational Bose-Hubbard model
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.
Flow equations for the ionic Hubbard model
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.
Quantum Monte Carlo study of bilayer ionic Hubbard model
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.
Variation tests of current order parameters in Hubbard model
Ovchinnikov, A A
2001-01-01
Variation tests of current order parameters as assumed sources of pseudogap normal state of cuprates were conducted. The calculations were made on the basis of the state with valency bond type correlations, their formation being able to induce both superconducting order of d-symmetry, and current phases. For the Hubbard t-t'-U-models with great U(approx 8t) and Hubbard's splitting of the area it is shown that phases of alternating charge and longitudinal spin currents can not be realized; transverse spin currents are incompatible with superconducting order, which could exist in a very narrow doping range near the optimal one. The range does not correspond the pseudogap existence range in cuprates, which is at variance with the mentioned hypothesis about the pseudogap origin. Existence of current phases in the Hubbard t-t'-U-V-models with great interaction (V > 0.25 t) of the adjacent node particles with utterly suppressed d-superconductivity is presented
Time-dependent Gutzwiller theory for multiband Hubbard models.
Oelsen, E v; Seibold, G; Bünemann, J
2011-08-12
Based on the variational Gutzwiller theory, we present a method for the computation of response functions for multiband Hubbard models with general local Coulomb interactions. The improvement over the conventional random-phase approximation is exemplified for an infinite-dimensional two-band Hubbard model where the incorporation of the local multiplet structure leads to a much larger sensitivity of ferromagnetism on the Hund coupling. Our method can be implemented into local-density approximation and Gutzwiller schemes and will therefore be an important tool for the computation of response functions for strongly correlated materials.
Block Entanglement in the Single-Hole Hubbard Model
Institute of Scientific and Technical Information of China (English)
YAO Kai-Lun; SUN Xiao-Zhong; LIU Zu-Li; LI Yan-Chao; YU Li; GAO Guo-Ying
2006-01-01
@@ We investigate the distribution of the entanglement of the one-dimensional single-hole Hubbard model (HM)and study the relationship between the entanglement and quantum phase transition in the model. The von Neumann entropy of a block with neighbouring spins L for a single-hole HM is calculated using the densitymatrix renormalization group.
A bespoke single-band Hubbard model material
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.
Critical points of the anyon-Hubbard model
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.
Ground state phase diagram of extended attractive Hubbard model
International Nuclear Information System (INIS)
The ground state phase diagram of the extended Hubbard model with intraatomic attraction has been derived in the Hartree-Fock approximation formulated in terms of the Bogoliubov variational approach. For a given value of electron density, the nature of the ordered ground state depends essentially on the sign and the strength of the nearest neighbor coupling. (author)
The Quantum Inverse Scattering Method for Hubbard-like Models
Martins, M J
1997-01-01
This work is concerned with various aspects of the formulation of the quantum inverse scattering method for the one-dimensional Hubbard model. We first establish the essential tools to solve the eigenvalue problem for the transfer matrix of the classical ``covering'' Hubbard model within the algebraic Bethe Ansatz framework. The fundamental commutation rules exhibit a hidden 6-vertex symmetry which plays a crucial role in the whole algebraic construction. Next we apply this formalism to study the SU(2) highest weights properties of the eigenvectors and the solution of a related coupled spin model with twisted boundary conditions. The machinery developed in this paper is applicable to many other models, and as an example we present the algebraic solution of the Bariev XY coupled model.
The 2-site Hubbard and t-J models
Avella, Adolfo; Mancini, Ferdinando; Saikawa, Taiichiro
2001-01-01
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 proper...
The 2-site Hubbard and {t}-{J} models
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.
Bose-Hubbard model on a checkerboard superlattice
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).
Negativity in the Extended Hubbard Model under External Magnetic Field
Institute of Scientific and Technical Information of China (English)
YANG Zhen; NING Wen-Qiang
2008-01-01
We exactly calculate the negativity,a measurement of entanglement,in the two-site extended Hubbard model with external magnetic field.Its behaviour at different temperatures is presented.The negativity reduces with the increasing temperature or with the increasing uniform external magnetic field.It is also found that a non-uniform external magnetic field can be used to modulate or to increase the negativity.
Local origin of the pseudogap in the attractive Hubbard model
PETERS, Robert; Bauer, Johannes
2015-01-01
We provide a new perspective on the pseudogap physics for attractive fermions as described by the three-dimensional Hubbard model. The pseudogap in the single-particle spectral function, which occurs for temperatures above the critical temperature $T_c$ of the superfluid transition, is often interpreted in terms of preformed, uncondensed pairs. Here we show that the occurrence of pseudogap physics can be consistently understood in terms of local excitations which lead to a splitting of the qu...
Damping of Bloch oscillations in the Hubbard model.
Eckstein, Martin; Werner, Philipp
2011-10-28
Using nonequilibrium dynamical mean-field theory, we study the isolated Hubbard model in a static electric field in the limit of weak interactions. Linear response behavior is established at long times, but only if the interaction exceeds a critical value, below which the system exhibits an ac-type response with Bloch oscillations. The transition from ac to dc response is defined in terms of the universal long-time behavior of the system, which does not depend on the initial condition.
Iterated perturbation theory for the attractive Holstein and Hubbard models
Freericks, J. K.; Jarrell, Mark (Eds. )
1994-01-01
A strictly truncated (weak-coupling) perturbation theory is applied to the attractive Holstein and Hubbard models in infinite dimensions. These results are qualified by comparison with essentially exact Monte Carlo results. The second order iterated perturbation theory is shown to be quite accurate in calculating transition temperatures for retarded interactions, but is not as accurate for the self energy or the irreducible vertex functions themselves. Iterated perturbation theory is carried ...
Gutzwiller variational theory for the Hubbard model with attractive interaction.
Bünemann, Jörg; Gebhard, Florian; Radnóczi, Katalin; Fazekas, Patrik
2005-06-29
We investigate the electronic and superconducting properties of a negative-U Hubbard model. For this purpose we evaluate a recently introduced variational theory based on Gutzwiller-correlated BCS wavefunctions. We find significant differences between our approach and standard BCS theory, especially for the superconducting gap. For small values of |U|, we derive analytical expressions for the order parameter and the superconducting gap which we compare to exact results from perturbation theory.
The one-dimensional extended Bose-Hubbard model
Indian Academy of Sciences (India)
Ramesh V Pai; Rahul Pandit
2003-10-01
We use the finite-size, density-matrix-renormalization-group (DMRG) method to obtain the zero-temperature phase diagram of the one-dimensional, extended Bose-Hubbard model, for mean boson density ρ = 1, in the - plane ( and are respectively, onsite and nearest-neighbour repulsive interactions between bosons). The phase diagram includes superfluid (SF), bosonic-Mott-insulator (MI), and mass-density-wave (MDW) phases. We determine the natures of the quantum phase transitions between these phases.
DEFF Research Database (Denmark)
Burcharth, Hans F.; Andersen, Thomas Lykke; Jensen, Palle Meinert
This report present the results of 2D physical model tests (length scale 1:50) carried out in a waveflume at Dept. of Civil Engineering, Aalborg University (AAU).......This report present the results of 2D physical model tests (length scale 1:50) carried out in a waveflume at Dept. of Civil Engineering, Aalborg University (AAU)....
Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model
International Nuclear Information System (INIS)
Despite its apparent simplicity, the two-dimensional Hubbard model for locally interacting fermions on a square lattice is widely considered as a promising approach for the understanding of Cooper pair formation in the quasi two-dimensional high-Tc cuprate materials. In the present work this model is investigated by means of the functional renormalization group, based on an exact flow equation for the effective average action. In addition to the fermionic degrees of freedom of the Hubbard Hamiltonian, bosonic fields are introduced which correspond to the different possible collective orders of the system, for example magnetism and superconductivity. The interactions between bosons and fermions are determined by means of the method of ''rebosonization'' (or ''flowing bosonization''), which can be described as a continuous, scale-dependent Hubbard-Stratonovich transformation. This method allows an efficient parameterization of the momentum-dependent effective two-particle interaction between fermions (four-point vertex), and it makes it possible to follow the flow of the running couplings into the regimes exhibiting spontaneous symmetry breaking, where bosonic fluctuations determine the types of order which are present on large length scales. Numerical results for the phase diagram are presented, which include the mutual influence of different, competing types of order. (orig.)
Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Friederich, Simon
2010-12-08
Despite its apparent simplicity, the two-dimensional Hubbard model for locally interacting fermions on a square lattice is widely considered as a promising approach for the understanding of Cooper pair formation in the quasi two-dimensional high-T{sub c} cuprate materials. In the present work this model is investigated by means of the functional renormalization group, based on an exact flow equation for the effective average action. In addition to the fermionic degrees of freedom of the Hubbard Hamiltonian, bosonic fields are introduced which correspond to the different possible collective orders of the system, for example magnetism and superconductivity. The interactions between bosons and fermions are determined by means of the method of ''rebosonization'' (or ''flowing bosonization''), which can be described as a continuous, scale-dependent Hubbard-Stratonovich transformation. This method allows an efficient parameterization of the momentum-dependent effective two-particle interaction between fermions (four-point vertex), and it makes it possible to follow the flow of the running couplings into the regimes exhibiting spontaneous symmetry breaking, where bosonic fluctuations determine the types of order which are present on large length scales. Numerical results for the phase diagram are presented, which include the mutual influence of different, competing types of order. (orig.)
Spectral analysis of two-dimensional Bose-Hubbard models
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.
Pseudospin symmetry and new collective modes of the Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Zhang, S. (IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120 (USA))
1990-07-02
The Hubbard model possesses a SU(2) pseudospin symmetry, which contains the U(1) phase symmetry as a subgroup. The existence of such symmetry leads to interesting experimental consequences if the U(1) phase symmetry is spontaneously broken, i.e., if the ground state is superconducting. In this case, there must exist a pair of {ital massive} collective modes which together with the usual Goldstone mode form a triplet representation of the psuedospin group. These collective modes are collisionless and couple directly to external charge disturbances with wave number {pi} and can therefore be detected experimentally as sharp resonances.
Exact diagonalization: the Bose-Hubbard model as an example
Zhang, J. M.; Dong, R. X.
2010-05-01
We take the Bose-Hubbard model to illustrate exact diagonalization techniques in a pedagogical way. We follow the route of first generating all the basis vectors, then setting up the Hamiltonian matrix with respect to this basis and finally using the Lanczos algorithm to solve low lying eigenstates and eigenvalues. Emphasis is placed on how to enumerate all the basis vectors and how to use the hashing trick to set up the Hamiltonian matrix or matrices corresponding to other quantities. Although our route is not necessarily the most efficient one in practice, the techniques and ideas introduced are quite general and may find use in many other problems.
Quantum spin structures and phase separation in the Hubbard model
Asghar, Z B
2001-01-01
In this thesis we focus on a systematic study of the ground state of the one-dimensional one-band Hubbard model in the Hartree-Fock approximation. Phases with non-uniform charge density and states with coexisting phases separated by a domain wall are included in the study. We calculate the full Hartree-Fock phase diagram for uniform and non-uniform phases, and we show that at particular electron densities the uniform phase is unstable to phase separation. Supercell calculations are carried out, and we use the computational minimisation procedure to calculate the Hartree-Fock energies for the self-consistent spin configurations.
Superconductivity in the two-dimensional generalized Hubbard model
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.
Possible phase separation in square and honeycomb Hubbard model: A variational cluster study
International Nuclear Information System (INIS)
The VCA ground state of the 2D Hubbard model is examined for possible phase separation under hole doping manifested by spatial inhomogeneities of coexisting different electron densities at equilibrium. Phase separation is accompanied by spectral weight loss and first Brillouin zone boundary deformation. Such an instability is observed in square structures and it is absent in honeycomb lattices. To our knowledge, no previous publications have revealed relationship between a Fermi surface instability and phase separation. Our VCA calculations provide strong support for this spontaneous instability, driven by electron correlations in specific lattice geometries, proposed in our earlier publications using exact quantum cluster calculations. - Highlights: • VCA study of possible spontaneous phase separation in 2D square and honeycomb Hubbard lattices. • Phase separation instabilities and density inhomogeneities driven by proximity to level crossing. • Contrasting differences in behaviors of spectral functions in square and honeycomb near first Brillouin zone. • VCA strongly confirms spontaneous phase separation obtained at level crossings in cluster calculations
Possible phase separation in square and honeycomb Hubbard model: A variational cluster study
Energy Technology Data Exchange (ETDEWEB)
Fang, Kun; Fernando, G.W. [Department of Physics, University of Connecticut, Storrs, CT 06269 (United States); Balatsky, A.V. [Institute for Materials Science, Los Alamos, NM 87545 (United States); NORDITA, Roslagstullsbacken 23, SE-106 91 Stockholm (Sweden); Kocharian, A.N., E-mail: armen.kocharian@calstatela.edu [Department of Physics, California State University, Los Angeles, CA 90032 (United States)
2015-10-02
The VCA ground state of the 2D Hubbard model is examined for possible phase separation under hole doping manifested by spatial inhomogeneities of coexisting different electron densities at equilibrium. Phase separation is accompanied by spectral weight loss and first Brillouin zone boundary deformation. Such an instability is observed in square structures and it is absent in honeycomb lattices. To our knowledge, no previous publications have revealed relationship between a Fermi surface instability and phase separation. Our VCA calculations provide strong support for this spontaneous instability, driven by electron correlations in specific lattice geometries, proposed in our earlier publications using exact quantum cluster calculations. - Highlights: • VCA study of possible spontaneous phase separation in 2D square and honeycomb Hubbard lattices. • Phase separation instabilities and density inhomogeneities driven by proximity to level crossing. • Contrasting differences in behaviors of spectral functions in square and honeycomb near first Brillouin zone. • VCA strongly confirms spontaneous phase separation obtained at level crossings in cluster calculations.
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.
Fermion Coherent State Studies of One-Dimensional Hubbard Model
Institute of Scientific and Technical Information of China (English)
LIN Ji; GAO Xian-Long; WANG Ke-Lin
2007-01-01
We present a comparative study of the ground state of the one-dimensional Hubbard model. We first use a new fermion coherent state method in the framework of Fermi liquid theory by introducing a hole operator and considering the interactions of two pairs electrons and holes. We construct the ground state of the Hubbard model as ｜〉 = [f + ∑′ψc+k1σ1 h+k2σ2 c+k3σ3 h+k4σ4 ∏exp(ρc+k1σ1 h+k2σ2)] [〉0, where ψ and ρ are the coupling constants. Our results are then compared to those of variational methods, density functional theory based on the exact solvable Bethe ansatz solutions, variational Monto-Carlo method (VMC) as well as to the exact result of the infinite system. We find satisfactory agreement between the fermion coherent state scheme and the VMC data, and provide a new picture to deal with the strongly correlated system.
Equation of state of the fermionic two-dimensional Hubbard model
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.
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Frigaard, Peter
This report present the results of 2D physical model tests carried out in the shallow wave flume at Dept. of Civil Engineering, Aalborg University (AAU), on behalf of Energy E2 A/S part of DONG Energy A/S, Denmark. The objective of the tests was: to investigate the combined influence of the pile...
Gutzwiller study of extended Hubbard models with fixed boson densities
Energy Technology Data Exchange (ETDEWEB)
Kimura, Takashi [Department of Information Sciences, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa 259-1293 (Japan)
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.
Dynamical instability in the S =1 Bose-Hubbard model
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.
The Bose-Hubbard model with squeezed dissipation
Quijandría, Fernando; Naether, Uta; Porras, Diego; José García-Ripoll, Juan; Zueco, David
2015-03-01
The stationary properties of the Bose-Hubbard model under squeezed dissipation are investigated. The dissipative model does not possess a U(1) symmetry but conserves parity. We find that =0 always holds, so no symmetry breaking occurs. Without the onsite repulsion, the linear case is known to be critical. At the critical point the system freezes to an EPR state with infinite two mode entanglement. We show here that the correlations are rapidly destroyed whenever the repulsion is switched on. As we increase the latter, the system approaches a thermal state with an effective temperature defined in terms of the squeezing parameter in the dissipators. We characterize this transition by means of a Gutzwiller ansatz and the Gaussian Hartree-Fock-Bogoliubov approximation.
Phase transitions in the Hubbard model for the bismuth nickelate
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.
Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model
International Nuclear Information System (INIS)
Results of a renormalization group study for the 2-dimensional Hubbard model close to half-filling at finite temperature are presented. Bosonic degrees of freedom corresponding to antiferromagnetic and d-wave superconducting order are introduced, and flow equations for the corresponding coupling constants are deduced from an exact flow equation for the effective average action. The influence of bosonic fluctuations on the onset of local antiferromagnetic order is discussed. At low enough temperatures and close to half-filling the discrete symmetry of the lattice is broken and incommensurate antiferromagnetic fluctuations dominate. The phase diagram is shown for the parameter regime close to half-filling in the presence of vanishing as well as non-vanishing next-to-nearest-neighbor hopping t'. Finally, the potential emergence of d-wave superconducting order at larger distances from half-filling is discussed.
One-dimensional Hubbard-Luttinger model for carbon nanotubes
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.
BCS-Hubbard model applied to anisotropic superconductors
Energy Technology Data Exchange (ETDEWEB)
Millan, J.S., E-mail: smillan@pampano.unacar.mx [Facultad de Ingenieria, Universidad Autonoma del Carmen, Cd. del Carmen, 24180 Campeche (Mexico); Perez, L.A. [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, A.P. 20-364, 01000, Mexico D.F. (Mexico); Wang, C. [Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, A.P. 70-360, 04510, Mexico D.F. (Mexico)
2011-11-15
The BCS formalism applied to a Hubbard model, including correlated hoppings, is used to study d-wave superconductors. The theoretical T{sub c} vs. n relationship is compared with experimental data from BiSr{sub 2-x}La{sub x}CuO{sub 6+{delta}} and La{sub 2-x}Sr{sub x}CuO{sub 4}. The results suggest a nontrivial correlation between the hole and the doping concentrations. Based on the BCS formalism, we study the critical temperature (T{sub c}) as a function of electron density (n) in a square lattice by means of a generalized Hubbard model, in which first ({Delta}t) and second neighbors ({Delta}t{sub 3}) correlated-hopping interactions are included in addition to the repulsive Coulomb ones. We compare the theoretical T{sub c} vs. n relationship with experimental data of cuprate superconductors BiSr{sub 2-x}La{sub x}CuO{sub 6+{delta}} (BSCO) and La{sub 2-x}Sr{sub x}CuO{sub 4}, (LSCO). The theory agrees very well with BSCO data even though the complicated association between Sr concentration (x) and hole doping (p). For the LSCO system, it is observed that in the underdoped regime, the T{sub c} vs. n behavior can be associated to different systems with small variations of t'. For the overdoped regime, a more complicated dependence n = 1 - p/2 fits better than n = 1 - p. On the other hand, it is proposed that the second neighbor hopping ratio (t'/t) should be replaced by the effective mean field hopping ratio t{sub MF}{sup '}/t{sub MF}, which can be very sensitive to small changes of t' due to the doping.
Conductivite dans le modele de Hubbard bi-dimensionnel a faible couplage
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
Energy Technology Data Exchange (ETDEWEB)
Bracken, Anthony J.; Ge Xiangyu; Gould, Mark D.; Links, Jon; Zhou Huanqiang [Centre for Mathematical Physics, University of Queensland, Brisbane, QLD (Australia)
2001-06-01
Integrable extended Hubbard models arising from symmetric group solutions are examined in the framework of the graded quantum inverse scattering method. The Bethe ansatz equations for all these models are derived by using the algebraic Bethe ansatz method. (author)
Dynamical Model and Path Integral Formalism for Hubbard Operators
Foussats, A.; Greco, A. (Anna); Zandron, O. S.
1998-01-01
In this paper, the possibility to construct a path integral formalism by using the Hubbard operators as field dynamical variables is investigated. By means of arguments coming from the Faddeev-Jackiw symplectic Lagrangian formalism as well as from the Hamiltonian Dirac method, it can be shown that it is not possible to define a classical dynamics consistent with the full algebra of the Hubbard $X$-operators. Moreover, from the Faddeev-Jackiw symplectic algorithm, and in order to satisfy the H...
Ising tricriticality in the extended Hubbard model with bond dimerization
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.
Phase diagram of the half-filled ionic Hubbard model
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
Time-of-flight images of Mott insulators in the Hofstadter- Bose-Hubbard model
Işkın, Menderes
2015-01-01
PHYSICAL REVIEW A 92, 023636 (2015) Time-of-flight images of Mott insulators in the Hofstadter-Bose-Hubbard model M. Iskin Department of Physics, Koc¸ University, Rumelifeneri Yolu, 34450 Sarıyer, Istanbul, Turkey (Received 10 April 2015; published 26 August 2015) We analyze the momentum distribution function and its artificial-gauge-field dependence for theMott insulator phases of the Hofstadter-Bose-Hubbard model. By benchmarking the results of the random-phase approximati...
Hubbard model versus t-J model : The one-particle spectrum
Eskes, H; Eder, R
1996-01-01
The origin of the apparent discrepancies between the one-particle spectra of the Hubbard and t-J models is revealed: Wave-function corrections, in addition to the three-site terms, should supplement the bare t-J model. In this way a quantitative agreement between the two models is obtained, even for
Diffusion dynamics in the disordered Bose Hubbard model
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.
Exact solutions of the high dimensional hard-core Fermi-Hubbard model
Institute of Scientific and Technical Information of China (English)
PAN; Feng
2001-01-01
［1］Hubbard, J., Electron correlations in narrow energy bands, Proc. R. Soc. London, A, 963, 276: 238.［2］Hubbard, J., Electron correlations in narrow energy bands II. The degenerate band case, Proc. R. Soc. London A, 963, A277: 237.［3］Anderson, P. W., The resonating valence bond state in La2CuOand superconductivity, Science, 987, 235: 96.［4］Lieb, E. H, Wu, F. Y., Absence of Mott transition in an exact solution of the short-range one-band model in one dimension, Phys. Rev. Lett., 968, 20: 445.［5］Ogata, M., Shiba, H., Bethe-ansatz wave function, momentum distribution, and spin correlation in the one-dimensional strongly correlated Hubbard model, Phys. Rev., 990, B4: 326.［6］Ogata, M., Sugiyama, T., Shiba, H., Magnetic-field effects on the correlation functions in the one-dimensional strongly correlated Hubbard model, Phys. Rev., 990, B43: 840.［7］Mei, C., Chen, L., Study of the interaction between two electrons in the single band Hubbard model, Z. Phys., 988, B72: 429.［8］Caspers, W. J., Iske, P. L., Exact spectrum for n electrons in the single band Hubbard model, Physica, 989, A, 57: 033.［9］Kirson, M. W., A dynamical supersymmetry in the Hubbard model, Phys. Rev. Lett., 997, 78: 24.［10］Woynarovich, F., Excitations with complex wavefunctions in a Hubbard chain: II. States with several pairs of complex wavenumbers, J. Phys., 982, C5: 97.
Attractive Hubbard model: Homogeneous Ginzburg-Landau expansion and disorder
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).
Ground state of the three-band Hubbard model
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.
Attractive Hubbard model with disorder and the generalized Anderson theorem
International Nuclear Information System (INIS)
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 Tc 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 Tc (in the weak-coupling region) or significantly increase Tc (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
Surface modelling for 2D imagery
Lieng, Henrik
2014-01-01
Vector graphics provides powerful tools for drawing scalable 2D imagery. With the rise of mobile computers, of different types of displays and image resolutions, vector graphics is receiving an increasing amount of attention. However, vector graphics is not the leading framework for creating and manipulating 2D imagery. The reason for this reluctance of employing vector graphical frameworks is that it is difficult to handle complex behaviour of colour across the 2D domain. ...
Quantum simulation of the Hubbard model with dopant atoms in silicon
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.
Modelling one-dimensional insulating materials with the ionic Hubbard model
International Nuclear Information System (INIS)
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
Density-dependent tunneling in the extended Bose–Hubbard model
International Nuclear Information System (INIS)
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. (paper)
Density-dependent tunneling in the extended Bose-Hubbard model
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.
Energy Technology Data Exchange (ETDEWEB)
Afchain, St
2005-02-15
The Hubbard model is the simplest model to describe the behaviour of fermions on a network, it takes into account only fermion scattering and only interactions with other fermions located on the same site. Half-filling means that the total number of fermions is equal to half the number of sites. In the first chapter we show how we can pass trough successive approximations from a very general Hamiltonian to the Hubbard Hamiltonian. The second chapter is dedicated to the passage from the Hamiltonian formalism to the Grassmanian functional formalism. The main idea is to show that the correlation functions of the Hamiltonian approach can be described through fermionic functional integrals which implies the possibility of speaking of the model in terms of field theory. The chapter 3 deals with the main constructive techniques that allow the strict and consistent construction of models inside the frame of field theory. We show by proving the violation of a condition concerning self-energy, that the two-dimensional Hubbard model at half-filling has not the behaviour of a Fermi liquid in the Landau's interpretation. (A.C.)
WFR-2D: an analytical model for PWAS-generated 2D ultrasonic guided wave propagation
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.
Classical mapping for Hubbard operators: application to the double-Anderson model.
Li, Bin; Miller, William H; Levy, Tal J; Rabani, Eran
2014-05-28
A classical Cartesian mapping for Hubbard operators is developed to describe the nonequilibrium transport of an open quantum system with many electrons. The mapping of the Hubbard operators representing the many-body Hamiltonian is derived by using analogies from classical mappings of boson creation and annihilation operators vis-à-vis a coherent state representation. The approach provides qualitative results for a double quantum dot array (double Anderson impurity model) coupled to fermionic leads for a range of bias voltages, Coulomb couplings, and hopping terms. While the width and height of the conduction peaks show deviations from the master equation approach considered to be accurate in the limit of weak system-leads couplings and high temperatures, the Hubbard mapping captures all transport channels involving transition between many electron states, some of which are not captured by approximate nonequilibrium Green function closures.
Similarities between the t-J and Hubbard models in weakly correlated regimes
Lepetit, M.-B.; Doublet, M.-L.; Maurel, Ph.
2002-07-01
We present a comparative study of the Hubbard and t - J models far away from half-filling. We show that, at such fillings the t - J Hamiltonian can be seen as an effective model of the repulsive Hubbard Hamiltonian over the whole range of correlation strength. Indeed, the | t/U| ∈ 0, + ∞ range of the Hubbard model can be mapped onto the finite range | J/t| ∈ 2, 0 of the t - J model, provided that the effective exchange parameter J is defined variationally as the local singlet-triplet excitation energy. In this picture the uncorrelated limit U = 0 is associated with the super-symmetric point J = - 2| t| and the infinitely correlated U = + ∞ limit with the usual J = 0 limit. A numerical comparison between the two models is presented using different macroscopic and microscopic properties such as energies, charge gaps and bond orders on a quarter-filled infinite chain. The usage of the t - J Hamiltonian in low-filled systems can therefore be a good alternative to the Hubbard model in large time-consuming calculations.
Relative and center-of-mass motion in the attractive Bose-Hubbard model
DEFF Research Database (Denmark)
Sørensen, Ole Søe; Gammelmark, Søren; Mølmer, Klaus
2012-01-01
We present first-principles numerical calculations for few-particle solutions of the attractive Bose-Hubbard model with periodic boundary conditions. We show that the low-energy many-body states found by numerical diagonalization can be written as translational superposition states of compact...
NEW PHASES IN AN EXTENDED HUBBARD-MODEL EXPLICITLY INCLUDING ATOMIC POLARIZABILITIES
van den Brink, J.; Meinders, M.B J; Lorenzana, J.; Eder, R; Sawatzky, G.A
1995-01-01
We consider the influence of a nearest-neighbor Coulomb interaction in an extended Hubbard model and introduce a new interaction term which simulates atomic polarizabilities. This has the effect of screening the on-site Coulomb interaction for charged excitations, unlike a neighbor Coulomb interacti
Gutzwiller variational wave function for multiorbital Hubbard models in finite dimensions
Münster, Kevin zu; Bünemann, Jörg
2016-07-01
We develop a diagrammatic method for the evaluation of general multiband Gutzwiller wave functions in finite dimensions. Our approach provides a systematic improvement of the widely used Gutzwiller approximation. As a first application, we investigate itinerant ferromagnetism and correlation-induced deformations of the Fermi surface for a two-band Hubbard model on a square lattice.
Numerical studies of ground-state fidelity of the Bose-Hubbard model
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.
Fermion spectrum of Bose-Fermi-Hubbard model in the phase with Bose-Einstein condensate
International Nuclear Information System (INIS)
We investigate the fermion spectrum within the Bose- Fermi-Hubbard model used for the description of boson-fermion mixtures of ultra-cold atoms in optical lattices. We used the method based on the Hubbard operator approach for an on-site basis. The equation for fermion Green's function in the Bose-Fermi-Hubbard model is built; Green's functions of higher orders are decoupled in the Hubbard-I approximation (the case of the strong on-site interaction). The corresponding spectral densities are calculated. In the case of hard-core bosons, the condition of appearance of additional bands in the fermion spectrum is investigated. It is shown that these bands exist only in the state with a Bose- Einstein condensate and appear because of the mixing of states with different numbers of bosons. These additional bands can be interpreted as a manifestation of composite excitations (when the appearance of a fermion on the site is accompanied by the simultaneous creation (or annihilation) of a boson)
Symmetries and solvable models for evaporating 2D black holes
Cruz Muñoz, José Luis; Navarro-Salas, José; Navarro Navarro, Miguel; Talavera, C. F.
1997-01-01
We study the evaporation process of a 2D black hole in thermal equilibrium when the ingoing radiation is suddenly switched off. We also introduce global symmetries of generic 2D dilaton gravity models which generalize the extra symmetry of the CGHS model. © Elsevier Science B.V
Maximizing entropy of image models for 2-D constrained coding
Forchhammer, Søren; Danieli, Matteo; Burini, Nino; Zamarin, Marco; Ukhanova, Ann
2010-01-01
This paper considers estimating and maximizing the entropy of two-dimensional (2-D) fields with application to 2-D constrained coding. We consider Markov random fields (MRF), which have a non-causal description, and the special case of Pickard random fields (PRF). The PRF are 2-D causal finite context models, which define stationary probability distributions on finite rectangles and thus allow for calculation of the entropy. We consider two binary constraints and revisit the hard square const...
Competing interactions and symmetry breaking in the Hubbard-Holstein model
Bauer, Johannes
2009-01-01
Competing interactions are often responsible for intriguing phase diagrams in correlated electron systems. Here we analyze the competition of instantaneous short range Coulomb interaction $U$ with the retarded electron-electron interaction induced by an electron-phonon coupling $g$ as described by the Hubbard-Holstein model. The ground state phase diagram of this model in the limit of large dimensions at half filling is established. The study is based on dynamical mean field theory combined w...
Effective electron-electron and electron-phonon interactions in the Hubbard-Holstein model
Aprea, G; Di Castro, C.; Grilli, M.; Lorenzana, J.
2006-01-01
We investigate the interplay between the electron-electron and the electron-phonon interaction in the Hubbard-Holstein model. We implement the flow-equation method to investigate within this model the effect of correlation on the electron-phonon effective coupling and, conversely, the effect of phonons in the effective electron-electron interaction. Using this technique we obtain analytical momentum-dependent expressions for the effective couplings and we study their behavior for different ph...
DEFF Research Database (Denmark)
Burcharth, Hans F.; Meinert, Palle; Andersen, Thomas Lykke
and the crown have been recorded. The maximum of horizontal wave force and the related tilting moment together with the pressure distribution are documented for waves in the range of design conditions. The parameters and results in the report are given in full-scale values, if nothing else is stated....... the crown wall have been measured. The model has been subjected to irregular waves corresponding to typical conditions offshore from the intended prototype location. Characteristic situations have been video recorded. The stability of the toe has been investigated. The wave-generated forces on the caisson...
Energy Technology Data Exchange (ETDEWEB)
Silant’ev, A. V., E-mail: kvvant@rambler.ru [Mari State University (Russian Federation)
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.
Kalman Filter for Generalized 2-D Roesser Models
Institute of Scientific and Technical Information of China (English)
SHENG Mei; ZOU Yun
2007-01-01
The design problem of the state filter for the generalized stochastic 2-D Roesser models, which appears when both the state and measurement are simultaneously subjected to the interference from white noise, is discussed. The wellknown Kalman filter design is extended to the generalized 2-D Roesser models. Based on the method of "scanning line by line", the filtering problem of generalized 2-D Roesser models with mode-energy reconstruction is solved. The formula of the optimal filtering, which minimizes the variance of the estimation error of the state vectors, is derived. The validity of the designed filter is verified by the calculation steps and the examples are introduced.
Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Carmelo, J.M.P., E-mail: carmelo@fisica.uminho.pt [Center and Department of Physics, University of Minho, Campus Gualtar, P-4710-057 Braga (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China); Institut für Theoretische Physik III, Universität Stuttgart, D-70550 Stuttgart (Germany); Gu, Shi-Jian [Beijing Computational Science Research Center, Beijing 100084 (China); Department of Physics and ITP, Chinese University of Hong Kong, Hong Kong (China); Sacramento, P.D. [CFIF, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Beijing Computational Science Research Center, Beijing 100084 (China)
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.
Detecting phase transitions and crossovers in Hubbard models using the fidelity susceptibility
Huang, Li; Wang, Lei; Werner, Philipp
2016-01-01
A generalized version of the fidelity susceptibility of single-band and multi-orbital Hubbard models is systematically studied using single-site dynamical mean-field theory in combination with a hybridization expansion continuous-time quantum Monte Carlo impurity solver. We find that the fidelity susceptibility is extremely sensitive to changes in the state of the system. It can be used as a numerically inexpensive tool to detect and characterize a broad range of phase transitions and crossovers in Hubbard models, including (orbital-selective) Mott metal-insulator transitions, high-spin to low-spin transitions, Fermi-liquid to non-Fermi-liquid crossovers, and spin-freezing crossovers.
Emergent phases in the spin orbit coupled spin-1 Bose Hubbard model
Natu, Stefan; Pixley, Jedediah
2015-05-01
Motivated by recent experiments on spin orbit coupled, ultra-cold Bose gases, we theoretically study the spin-1 Bose Hubbard model in the presence and absence of spin orbit coupling (SOC). In the absence of SOC, using a spatially homogenous Gutzwiller mean field theory, we determine the phase diagram and excitation spectrum of the spin-1 Bose Hubbard model on a hyper-cubic lattice in both the polar and ferromagnetic phases. We focus on the evolution of various density, spin, and nematic order parameters across the phase diagram as a function of chemical potential and nearest neighbor hopping. We then generalize the Gutzwiller mean-field theory to incorporate spin-orbit coupling by allowing the mean-fields to be spatially inhomogeneous, which enable us to study spontaneous translational symmetry broken phases. To connect with ongoing experiments, we focus on the lattice generalization of the experimentally realized 1D spin-orbit coupling.
Quantum phase diagram of the half filled Hubbard model with bond-charge interaction
Energy Technology Data Exchange (ETDEWEB)
Dobry, A.O., E-mail: dobry@ifir-conicet.gov.a [Facultad de Ciencias Exactas Ingenieria y Agrimensura, Universidad Nacional de Rosario and Instituto de Fisica Rosario, Bv. 27 de Febrero 210 bis, 2000 Rosario (Argentina); Aligia, A.A. [Centro Atomico Bariloche and Instituto Balseiro, Comision Nacional de Energia Atomica, 8400 Bariloche (Argentina)
2011-02-21
Using quantum field theory and bosonization, we determine the quantum phase diagram of the one-dimensional Hubbard model with bond-charge interaction X in addition to the usual Coulomb repulsion U at half-filling, for small values of the interactions. We show that it is essential to take into account formally irrelevant terms of order X. They generate relevant terms proportional to X{sup 2} in the flow of the renormalization group (RG). These terms are calculated using operator product expansions. The model shows three phases separated by a charge transition at U=U{sub c} and a spin transition at U=U{sub s}>U{sub c}. For UU{sub s}, the system is in the spin-density wave phase as in the usual Hubbard model. For intermediate values U{sub c}Hubbard model with X=0. We obtain that the charge transition remains at U{sub c}=0 for X{ne}0. Solving the RG equations for the spin sector, we provide an analytical expression for U{sub s}(X). The results, with only one adjustable parameter, are in excellent agreement with numerical ones for X
Exact solution of a generalized two-sites Bose-Hubbard model
Filho, Gilberto N Santos
2016-01-01
I introduce a new parametrization of a bosonic Lax operator for the algebraic Bethe ansatz method with the $gl(2)$-invariant $R$-matrix and use it to present the exact solution of a generalized two-sites Bose-Hubbard model with asymmetric tunnelling. In the no interaction limit I show that the Bethe ansatz equations can be written as a $S^{N-1}$ sphere, where $N$ is the total number of atoms in the condensate.
Four-point vertex in the Hubbard model and partial bosonization
Friederich, S.; Krahl, H. C.; Wetterich, C.
2010-01-01
Magnetic and superconducting instabilities in the two-dimensional t-t'-Hubbard model are discussed within a functional renormalization group approach. The fermionic four-point vertex is efficiently parametrized by means of partial bosonization. The exchange of composite bosons in the magnetic, charge density and superconducting channels accounts for the increase of the effective couplings with increasing length scale. We compute the pseudocritical temperature for the onset of local order in v...
Spin-state transition and phase separation in multi-orbital Hubbard model
Suzuki, Ryo; Watanabe, Tsutomu; Ishihara, Sumio
2009-01-01
We study spin-state transition and phase separation involving this transition based on the milti-orbital Hubbard model. Multiple spin states are realized by changing the energy separation between the two orbitals and the on-site Hund coupling. By utilizing the variational Monte-Carlo simulation, we analyze the electronic and magnetic structures in hole doped and undoped states. Electronic phase separation occurs between the low-spin band insulating state and the high-spin ferromagnetic metall...
Bosonization study of quantum phase transitions in the one-dimensional asymmetric Hubbard model
Wang, Z. G.; Chen, Y G; Gu, S. J.
2007-01-01
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 happening of the phase separation. When the difference is large enough, the phase separation will ap...
Supersolid Phase in One-Dimensional Hard-Core Boson Hubbard Model with a Superlattice Potential
Institute of Scientific and Technical Information of China (English)
GUO Huai-Ming; LIANG Ying
2008-01-01
The ground state of the one-dimensional hard-core boson Hubbard model with a superlattice potential is studied by quantum Monte Carlo methods. We demonstrate that besides the CDW phase and the Mort insulator phase, the supersolid phase emerges due to the presence of the superlattice potential, which reflects the competition with the hopping term. We also study the densities of sublattices and have a clear idea about the distribution of the bosons on the lattice.
Bethe states for the two-site Bose-Hubbard model: a binomial approach
Santos, Gilberto; Foerster, Angela; Roditi, Itzhak
2015-01-01
We calculate explicitly the Bethe vectors states by the algebraic Bethe ansatz method with the $gl(2)$-invariant $R$-matrix for the two-site Bose-Hubbard model. Using a binomial expansion of the n-th power of a sum of two operators we get and solve a recursion equation. We calculate the scalar product and the norm of the Bethe vectors states. The form factors of the imbalance current operator are also computed.
On spectral properties of three-electron systems in the Hubbard model
International Nuclear Information System (INIS)
We investigate spectral properties of a three-electron system in the framework of the Hubbard model. We prove that the essential spectrum of the system in a quartet state consists of a single segment and the three-electron bound state is absent. We show that the essential spectrum of the system in doublet states consists of unification of no more then three segments. We also prove that three-electron bound states exist in doublet states. (authors)
The pairing correlations in the phased t-U Hubbard model
Institute of Scientific and Technical Information of China (English)
Liu Zi-Xin; Liu Ping; Liu Ya; Wen Sheng-Hui
2004-01-01
In this paper we have studied the phased t U Hubbard model. Using the constrained path Monte Carlo method,we investigated the effects of phase factor on pairing correlation functions in the ground state, and we found that the long-range correlations are dependent on the choice of phase factor, and for some special values of phase factor there exist long-range pairing correlations only in the strong coupling region.
Exact solution of the one-dimensional Hubbard model with arbitrary boundary magnetic fields
Energy Technology Data Exchange (ETDEWEB)
Li, Yuan-Yuan; Cao, Junpeng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Yang, Wen-Li [Institute of Modern Physics, Northwest University, Xian 710069 (China); Beijing Center for Mathematics and Information Interdisciplinary Sciences, Beijing, 100048 (China); Shi, Kangjie [Institute of Modern Physics, Northwest University, Xian 710069 (China); Wang, Yupeng, E-mail: yupeng@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)
2014-02-15
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.
Anisotropic Hubbard model on a triangular lattice - spin dynamics in HoMnO3
Indian Academy of Sciences (India)
Saptarshi Ghosh; Avinash Singh
2008-01-01
The recent neutron scattering data for spin-wave dispersion in HoMnO3 are well-described by an anisotropic Hubbard model on a triangular lattice with a planar (XY) spin anisotropy. Best fit indicates that magnetic excitations in HoMnO3 correspond to the strong-coupling limit / > ∼ 15, with planar exchange energy = 42/ ≃ 2.5 meV and planar anisotropy ≃ 0.35 meV.
Lacki, M.; Delande, D; Zakrzewski, J.
2011-01-01
Using Fourier transform on a time series generated by unitary evolution, we extract many-body eigenstates of the Bose-Hubbard model corresponding to low energy excitations, which are generated when the insulator-superfluid phase transition is realized in a typical experiment. The analysis is conducted in a symmetric external potential both without and with and disorder. A simple classification of excitations in the absence disorder is provided. The evolution is performed assuming the presence...
Quantum Bose-Hubbard model with an evolving graph as a toy model for emergent spacetime
International Nuclear Information System (INIS)
We present a toy model for interacting matter and geometry that explores quantum dynamics in a spin system as a precursor to a quantum theory of gravity. The model has no a priori geometric properties; instead, locality is inferred from the more fundamental notion of interaction between the matter degrees of freedom. The interaction terms are themselves quantum degrees of freedom so that the structure of interactions and hence the resulting local and causal structures are dynamical. The system is a Hubbard model where the graph of the interactions is a set of quantum evolving variables. We show entanglement between spatial and matter degrees of freedom. We study numerically the quantum system and analyze its entanglement dynamics. We analyze the asymptotic behavior of the classical model. Finally, we discuss analogues of trapped surfaces and gravitational attraction in this simple model.
SU(2) symmetry in a Hubbard model with spin-orbit coupling
Institute of Scientific and Technical Information of China (English)
ZHANG XiZheng; JIN Liang; SONG Zhi
2014-01-01
We study the underlying symmetry in a spin-orbit coupled tight-binding model with Hubbard interaction.It is shown that,in the absence of the on-site interaction,the system possesses the SU(2) symmetry arising from the time reversal symmetry.The influence of the on-site interaction on the symmetry depends on the topology of the networks:The SU(2) symmetry is shown to be the spin rotation symmetry of a simply-connected lattice even in the presence of the Hubbard interaction.On the contrary,the on-site interaction breaks the SU(2) symmetry of a multi-connected lattice.This fact indicates that a discrete spin-orbit coupled system has exclusive features from its counterpart in a continuous system.The obtained rigorous result is illustrated by a simple ring system.
Energy Technology Data Exchange (ETDEWEB)
Mishra, A.K., E-mail: mishra@imsc.res.i [Insitituto Nacional de Pesquidas Espaciais - INPE, P.O. Box 103, CP 515, S. J. Campos, SP 12245-970 (Brazil); Kishore, R., E-mail: kishore@las.inpe.b [Insitituto Nacional de Pesquidas Espaciais - INPE, P.O. Box 103, CP 515, S. J. Campos, SP 12245-970 (Brazil)
2009-10-15
The exact nested Bethe ansatz solution for the one dimensional (1-D) U infinity Hubbard model show that the state vectors are a product of spin-less fermion and spin wavefunctions, or an appropriate superposition of such factorized wavefunctions. The spin-less fermion component of the wavefunctions ensures no double occupancy at any site. It had been demonstrated that the nested Bethe ansatz wavefunctions in the U infinity limit obey orthofermi statistics. Gutzwiller projection operator formalism is the another well known technique employed to handle U infinity Hubbard model. In general, this approach does not lead to spin-less fermion wavefunctions. Therefore, the nested Bethe ansatz and Gutzwiller projection operator approach give rise to different kinds of the wavefunctions for the U infinity limit of 1-D Hubbard Hamiltonian. To compare the consequences of this dissimilarity in the wavefunctions, we have obtained the ground state energy of a finite system consisting of three particles on a four site closed chain. It is shown that in the nested Bethe ansatz implemented through orthofermion algebra, all the permissible 2{sup 3} spin configurations are degenerate in the ground state. This eight fold degeneracy of the ground state is absent in the Gutzwiller projection operator approach. This finding becomes relevant in the context of known exact U infinity results, which require that all the energy levels are 2{sup N}-fold degenerate for an N particle system.
Energy Technology Data Exchange (ETDEWEB)
Moskvin, A. S., E-mail: alexander.moskvin@urfu.ru [Ural Federal University (Russian Federation)
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.
Technical Review of the UNET2D Hydraulic Model
Energy Technology Data Exchange (ETDEWEB)
Perkins, William A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Richmond, Marshall C. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
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.
Collins Model and Phase Diagram of 2D Ternary System
Institute of Scientific and Technical Information of China (English)
XIE Chuan-Mei; CHEN Li-Rong
2004-01-01
The Collins model is introduced into the two-dimensional (2D) alternative ternary system having the Lennard-Jones (L-J) potential. The Gibbs free energy of this ternary system is calculated, and according to thermodynamic theory, a group of equations that determine the solid-liquid diagram of ternary system are derived, some isothermal sectional diagrams of the 2D ternary system are obtained. The results are quite similar to the behavior of three-dimensional substances.
Local moment approach as a quantum impurity solver for the Hubbard model
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.
UPLAND EROSION MODELING WITH CASC2D-SED
Institute of Scientific and Technical Information of China (English)
Pierre JULIEN; Rosalía ROJAS
2002-01-01
Developed at Colorado State University, CASC2D-SED is a physically-based model simulating the hydrologic response of a watershed to a distributed rainfall field. The time-dependent processes include:precipitation, interception, infiltration, surface runoff and channel routing, upland erosion, transport and sedimentation. CASC2D-SED is applied to Goodwin Creek, Mississippi. The watershed covers 21 km2and has been extensively monitored both at the outlet and at several internal locations by the ARS-NSL at Oxford, MS. The model has been calibrated and validated using rainfall data from 16 meteorological stations, 6 stream gauging stations and 6 sediment gauging stations. Sediment erosion/deposition rates by size fraction are predicted both in space and time. Geovisualization, a powerful data exploration technique based on GIS technology, is used to analyze and display the dynamic output time series generated by the CASC2D-SED model.
A VARIATIONAL MODEL FOR 2-D MICROPOLAR BLOOD FLOW
Institute of Scientific and Technical Information of China (English)
He Ji-huan
2003-01-01
The micropolar fluid model is an essential generalization of the well-established Navier-Stokes model in the sense that it takes into account the microstructure of the fluid.This paper is devolted to establishing a variational principle for 2-D incompressible micropolar blood flow.
The Mott metal-insulator transition in half-filled two-dimensional Hubbard models
Directory of Open Access Journals (Sweden)
Peyman Sahebsara
2008-06-01
Full Text Available We study the Mott transition in the two dimensional Hubbard model by using the variational cluster approximation. The transition potential obtained is roughly Uc ≈ 2 and 6 for square and triangular lattices, respectively. A comparison between results of this approximation and other quantum cluster methods is presented. Our zero-temperature calculation at strong coupling show that the transition on the triangular and square lattices occur at lower values of compared with other numerical techniques such as DMFT, CDMFT, and DCA. We also study the thermodynamic limit by an extrapolation to infinite size.
Superfluid-Mott-insulator transition in the spin-orbit-coupled Bose-Hubbard model
Işkın, Menderes; Bölükbaşı, Ahmet Tuna
2014-01-01
PHYSICAL REVIEW A 89, 043603 (2014) Superfluid–Mott-insulator transition in the spin-orbit-coupled Bose-Hubbard model A. T. Bolukbasi and M. Iskin Department of Physics, Koc¸ University, Rumelifeneri Yolu, 34450 Sariyer, Istanbul, Turkey (Received 3 January 2014; published 4 April 2014) We consider a square optical lattice in two dimensions and study the effects of both the strength and symmetry of spin-orbit coupling and Zeeman field on the ground-state, i.e.,Mott-insulator...
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.
Fractional charge separation in the hard-core Bose Hubbard Model on the Kagome Lattice
Zhang, Xue Feng; Eggert, Sebastian
2013-03-01
We consider the hard core Bose Hubbard Model on a Kagome lattice with fixed (open) boundary conditions on two edges. We find that the fixed boundary conditions lift the degeneracy and freeze the system at 1/3 and 2/3 filling at small hopping. At larger hopping strengths, fractional charges spontaneously separate and are free to move to the edges of the system, which leads to a novel compressible phase with solid order. The compressibility is due to excitations on the edge which display a chrial symmetry breaking that is reminiscent of the quantum Hall effect. Large scale Monte Carlo simulations confirm the analytical calculations.
Many-site coherence revivals in the extended Bose-Hubbard model and the Gutzwiller approximation
Energy Technology Data Exchange (ETDEWEB)
Fischer, Uwe R.; Xiong Bo [Seoul National University, Department of Physics and Astronomy, Center for Theoretical Physics, 151-747 Seoul (Korea, Republic of)
2011-12-15
We investigate the collapse and revival of first-order coherence in deep optical lattices when long-range interactions are turned on and find that the first few revival peaks are strongly attenuated already for moderate values of the nearest-neighbor interaction coupling. It is shown that the conventionally employed Gutzwiller wave function, with only on-site number dependence of the variational amplitudes, leads to incorrect predictions for the collapse and revival oscillations within the extended Bose-Hubbard model. We provide a modified variant of the Gutzwiller ansatz, reproducing the analytically calculated time dependence of first-order coherence in the limit of zero tunneling.
QSAR Models for P-450 (2D6) Substrate Activity
DEFF Research Database (Denmark)
Ringsted, Tine; Nikolov, Nikolai Georgiev; Jensen, Gunde Egeskov;
2009-01-01
drugs and other chemicals. A training set of 747 chemicals primarily based on in vivo human data for the CYP isoenzyme 2D6 was collected from the literature. QSAR models focusing on substrate/non substrate activity were constructed by the use of MultiCASE, Leadscope and MDL quantitative structure......Human Cytochrome P450 (CYP) is a large group of enzymes that possess an essential function in metabolising different exogenous and endogenous compounds. Humans have more than 50 different genes encoding CYP enzymes, among these a gene encoding for the CYP isoenzyme 2D6, a CYP able to metabolise...
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Brorsen, Michael
This report is an extension of the study presented in Lykke Andersen and Brorsen, 2006 and includes results from the irregular wave tests, where Lykke Andersen & Brorsen, 2006 focused on regular waves. The 2D physical model tests were carried out in the shallow wave flume at Dept. of Civil...
Phase diagram of the bosonic Kondo-Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Foss-Feig, Michael; Rey, Ana Maria [JILA, National Institute of Standards and Technology, and University of Colorado, Boulder, Colorado 80309 (United States)
2011-11-15
We study a bosonic version of the Kondo lattice model with an onsite repulsion in the conduction band, implemented with alkali-metal atoms in two bands of an optical lattice. Using both weak- and strong-coupling perturbation theory, we find that at unit filling of the conduction bosons the superfluid-to-Mott-insulator transition should be accompanied by a magnetic transition from a ferromagnet (in the superfluid) to a paramagnet (in the Mott insulator). Furthermore, an analytic treatment of Gutzwiller mean-field theory reveals that quantum spin fluctuations induced by the Kondo exchange cause the otherwise continuous superfluid-to-Mott-insulator phase transition to be first order. We show that lattice separability imposes a serious constraint on proposals to exploit excited bands for quantum simulations, and discuss a way to overcome this constraint in the context of our model by using an experimentally realized nonseparable lattice. A method to probe the first-order nature of the transition based on collapses and revivals of the matter-wave field is also discussed.
International Nuclear Information System (INIS)
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
Spectral function of the ionic Hubbard model (IHM)
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.
2D Models for Dust-driven AGB Star Winds
Woitke, P
2006-01-01
New axisymmetric (2D) models for dust-driven winds of C-stars are presented which include hydrodynamics with radiation pressure on dust, equilibrium chemistry and time-dependent dust formation with coupled grey Monte Carlo radiative transfer. Considering the most simple case without stellar pulsation (hydrostatic inner boundary condition) these models reveal a more complex picture of the dust formation and wind acceleration as compared to earlier published spherically symmetric (1D) models. The so-called exterior $\\kappa$-mechanism causes radial oscillations with short phases of active dust formation between longer phases without appreciable dust formation, just like in the 1D models. However, in 2D geometry, the oscillations can be out-of-phase at different places above the stellar atmosphere which result in the formation of dust arcs or smaller caps that only occupy a certain fraction of the total solid angle. These dust structures are accelerated outward by radiation pressure, expanding radially and tangen...
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.
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.
Interplay between electron correlations and quantum orders in the Hubbard model
Witczak-Kremp, William
We discuss the appearance of quantum orders in the Hubbard model for interacting electrons, at half-filling. Such phases do not have local order parameters and need to be characterized by the quantum mechanical properties of their ground state. On one hand, we study the Mott transition from a metal to a spin liquid insulator in two dimensions, of potential relevance to some layered organic compounds. The correlation-driven transition occurs at fixed filling and involves fractionalization of the electron: upon entering the insulator, a Fermi surface of neutral spinons coupled to an internal gauge field emerges. We focus on the transport properties near the quantum critical point and find that the emergent gauge uctuations play a key role in determining the universal scaling. Second, motivated by a class of three-dimensional transition metal oxides, the pyrochlore iridates, we study the interplay of non-trivial band topology and correlations. Building on the strong spin orbit coupling in these compounds, we construct a general microscopic Hubbard model and determine its mean-field phase diagram, which contains topological insulators, Weyl semimetals, axion insulators and various antiferromagnets. We also discuss the effects many-body correlations on theses phases. We close by examining a fractionalized topological insulator that combines the two main themes of the thesis: fractionalization and non-trivial band topology. Specifically, we study how the twodimensional protected surface states of a topological Mott insulator interact with a threedimensional emergent gauge field. Various correlation effects on observables are identified.
Can the Hubbard model explain the steps observed in the magnetization curve of {Ni4Mo12}?
International Nuclear Information System (INIS)
The low-temperature magnetization curve of the magnetic molecule {Ni4Mo12} features four nonequidistant steps which cannot be explained using a Heisenberg model. In his article, V. Kostyuchenko presents a spin-1 model with biquadratic and three-spin interactions and claims that it is the strong coupling limit of a certain Hubbard model. This spin-1 model correctly predicts the position of the steps in the magnetization curve. We investigate whether the Hubbard model proposed in is really capable of describing {Ni4Mo12}. To this end, we calculate its eigenvalues using numerical exact diagonalization and try to fit its parameters to the experimental magnetization data. We are unable to find suitable fit parameters although the parameter space of the model is only two-dimensional. Therefore, we analyze the strong coupling limit of the Hubbard model and rederive its effective spin model up to order O(U-3). The spin Hamiltonian which we obtain differs from the one presented by Kostyuchenko. We arrive at the final conclusion that the Hubbard model as proposed in is not suited to describe the molecule {Ni4Mo12}.
Long-range orders and spin/orbital freezing in the two-band Hubbard model
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 .
A Quantum Mermin-Wagner Theorem for a Generalized Hubbard Model
Directory of Open Access Journals (Sweden)
Mark Kelbert
2013-01-01
Full Text Available This paper is the second in a series of papers considering symmetry properties of bosonic quantum systems over 2D graphs, with continuous spins, in the spirit of the Mermin-Wagner theorem. In the model considered here the phase space of a single spin is ℋ1=L2(M, where M is a d-dimensional unit torus M=ℝd/ℤd with a flat metric. The phase space of k spins is ℋk=L2sym(Mk, the subspace of L2(Mk formed by functions symmetric under the permutations of the arguments. The Fock space H=⊕k=0,1,…ℋk yields the phase space of a system of a varying (but finite number of particles. We associate a space H≃H(i with each vertex i∈Γ of a graph (Γ,ℰ satisfying a special bidimensionality property. (Physically, vertex i represents a heavy “atom” or “ion” that does not move but attracts a number of “light” particles. The kinetic energy part of the Hamiltonian includes (i -Δ/2, the minus a half of the Laplace operator on M, responsible for the motion of a particle while “trapped” by a given atom, and (ii an integral term describing possible “jumps” where a particle may join another atom. The potential part is an operator of multiplication by a function (the potential energy of a classical configuration which is a sum of (a one-body potentials U(1(x, x∈M, describing a field generated by a heavy atom, (b two-body potentials U(2(x,y, x,y∈M, showing the interaction between pairs of particles belonging to the same atom, and (c two-body potentials V(x,y, x,y∈M, scaled along the graph distance d(i,j between vertices i,j∈Γ, which gives the interaction between particles belonging to different atoms. The system under consideration can be considered as a generalized (bosonic Hubbard model. We assume that a connected Lie group G acts on M, represented by a Euclidean space or torus of dimension d'≤d, preserving the metric and the volume in M. Furthermore, we suppose that the potentials U(1, U(2, and V are G-invariant. The result
Influence of Elevation Data Source on 2D Hydraulic Modelling
Bakuła, Krzysztof; Stępnik, Mateusz; Kurczyński, Zdzisław
2016-08-01
The aim of this paper is to analyse the influence of the source of various elevation data on hydraulic modelling in open channels. In the research, digital terrain models from different datasets were evaluated and used in two-dimensional hydraulic models. The following aerial and satellite elevation data were used to create the representation of terrain - digital terrain model: airborne laser scanning, image matching, elevation data collected in the LPIS, EuroDEM, and ASTER GDEM. From the results of five 2D hydrodynamic models with different input elevation data, the maximum depth and flow velocity of water were derived and compared with the results of the most accurate ALS data. For such an analysis a statistical evaluation and differences between hydraulic modelling results were prepared. The presented research proved the importance of the quality of elevation data in hydraulic modelling and showed that only ALS and photogrammetric data can be the most reliable elevation data source in accurate 2D hydraulic modelling.
Magnetic properties of Hubbard-sigma model with three-dimensionality
International Nuclear Information System (INIS)
It has been broadly accepted that the magnetism may play an important role in the high-Tc superconductivity in the lamellar CuO2 materials. In this paper, based on a Hubbard-inspired CP1 or S2 nonlinear σ model, we give a quantitative study of some magnetic properties in and around the Neel ordered state of three-dimensional quantum antiferromagnets such as La2CuO4 with and without small hole doping. Our model is a (3+1) dimensional effective field theory describing the low energy spin dynamics of a three-dimensional Hubbard model with a very weak interlayer coupling. The effect of hole dynamics is taken into account in the leading approximation by substituting the CP1 coupling and the spin-wave velocity with 'effective' ones determined by the concentration and the one-loop correction of hole fermions. Stationary-phase equations for the one-loop effective potential of S2 model are analyzed. Based on them, various magnetic properties of the system, such as the behavior of Neel temperature, spin correlation length, staggered magnetization, specific heat and susceptibility as functions of anisotropic parameter, temperature, etc. are investigated in detail. The results show that our anisotropic field theory model with certain values of parameters gives a good description of the magnetic properties in both the ordered and the disordered phases indicated by experiments on La2CuO4. The part of the above results is supported by the renormalization-group analysis. In the doped case it is observed that the existence of holes destroys the long-range order and their hopping effect is large. (author)
A Simple Hubbard Model for the Excited States of $\\pi$ Conjugated -acene Molecules
Sadeq, Z S
2015-01-01
In this paper we present a model that elucidates in a simple way the electronic excited states of $\\pi$ conjugated -acene molecules such as tetracene, pentacene, and hexacene. We use a tight-binding and truncated Hubbard model written in the electron-hole basis to describe the low lying excitations with reasonable quantitative accuracy. We are able to produce semi-analytic wavefunctions for the electronic states of the system, which allows us to compute the density correlation functions for various states such as the ground state, the first two singly excited states, and the lowest lying doubly excited state. We show that in this lowest lying doubly excited state, a state which has been speculated as to being involved in the singlet fission process, the electrons and holes behave in a triplet like manner.
Spectral properties of the one-dimensional Hubbard model: cluster dynamical mean-field approaches
Go, Ara; Jeon, Gun Sang
2011-03-01
We investigate static and dynamic properties of the one-dimensional Hubbard model using cluster extensions of the dynamical mean-field theory. It is shown that the two different extensions, the cellular dynamical mean-field theory and the dynamic cluster approximation, yield the ground-state properties which are qualitatively in good agreement with each other. We compare the results with the Bethe ansatz results to check the accuracy of the calculation with finite sizes of clusters. We also analyze the spectral properties of the model with the focus on the spin-charge separation and discuss the dependency on the cluster size in the two approaches. This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology(2010-0010937).
Thermodynamics of the Hubbard model on stacked honeycomb and square lattices
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
Bilayer Hubbard model for 3He: a cluster dynamical mean-field calculation
International Nuclear Information System (INIS)
Inspired by recent experiments on bilayer 3He, we consider a bilayer Hubbard model on a triangular lattice. For appropriate model parameters, we observe a band-selective Mott transition at a critical chemical potential, μc, corresponding to the solidification of the fermions in the first layer. The growth of the effective mass on the metallic side (μ c) is cut off by a first order transition in which the first layer fermions drop out of the Luttinger volume and their spin degrees of freedom become locked in a spin singlet state. These results are obtained from a cluster dynamical mean-field calculation on an eight-site cluster with a quantum Monte Carlo cluster solver.
Exact diagonalization of the one-dimensional Bose-Hubbard model with local three-body interactions
Sowiński, Tomasz
2012-06-01
In this Brief Report the extended Bose-Hubbard model with local two- and three-body interactions is studied by the exact diagonalization approach. The shapes of the first two insulating lobes are discussed and the values of the critical tunneling for which the insulating phase loses stability for repulsive and attractive three-body interactions are predicted.
Zakrzewski, Jakub; Delande, Dominique
2007-01-01
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, better than current state of the art calculations. The method uses the infinite system version of the time evolving block decimation algorithm, here tested in a challenging case.
Quantum Monte Carlo simulations of the one-dimensional extended Hubbard model
International Nuclear Information System (INIS)
We report preliminary results of an investigation of the thermodynamic properties of the extended Hubbard model in one- dimension, calculated with the world-line Monte Carlo method described by Hirsch et al. With strictly continuous world-lines, we are able to measure the expectation of operators that conserve fermion number locally, such as the energy and (spatial) occupation number. By permitting the world-lines to be ''broken'' stochastically, we may also measure the expectation of operators that conserve fermion number only globally, such as the single-particle Green's function. For a 32 site lattice we present preliminary calculations of the average electron occupancy as a function of wavenumber when U = 4, V = 0 and β = 16. For a half-filled band we find no indications of a Fermi surface. Slightly away from half-filling, we find Fermi-surface-like behavior similar to that found in other numerical investigations. 8 refs., 3 figs
Algebraic geometry methods associated to the one-dimensional Hubbard model
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.
Hybrid-Space Density Matrix Renormalization Group Study of the Two-Dimensional Hubbard Model
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.
Effect of interactions, disorder and magnetic field in the Hubbard model in two dimensions
Indian Academy of Sciences (India)
N Trivedi; P J H Denteneer; D Heidarian; R T Scaletar
2005-06-01
The effects of both interactions and Zeeman magnetic field in disordered electronic systems are explored in the Hubbard model on a square lattice. We investigate the thermodynamic (density, magnetization, density of states) and transport (conductivity) properties using determinantal quantum Monte Carlo and inhomogeneous Hartree Fock techniques. We find that at half filling there is a novel metallic phase at intermediate disorder that is sandwiched between a Mott insulator and an Anderson insulator. The metallic phase is highly inhomogeneous and coexists with antiferromagnetic long-range order. At quarter filling also the combined effects of disorder and interactions produce a conducting state which can be destroyed by applying a Zeeman field, resulting in a magnetic field-driven transition. We discuss the implication of our results for experiments.
Moradi Kurdestany, Jamshid; Satpathy, Sashi
Motivated by the recent progress in understanding of Mott insulators away from half filling, observed in many perovskite oxides, we study the metal-insulator transition in the Hubbard-Holstein model, which contains both the Coulomb and the electron-lattice (Jahn Teller) interactions by using the Gutzwiller variational method. We find that strong electron-lattice Interaction leads to phase separation, which however can be frustrated due to the long-range Coulomb interaction, resulting in a mixed phase consisting of puddles of metallic phases embedded in an insulating matrix. When the dopant concentration exceeds a threshold value xc , the metallic part forms a percolating network leading to metallic conduction. Depending on the strength of the electron-lattice interaction, xc can be of the order of 0.05 - 0.20 or so, which is the typical value observed in the perovskites.
Phase coexistence and Mott metal-insulator transition in the doped Hubbard-Holstein model
Moradi Kurdestany, Jamshid; Satpathy, Sashi
2015-03-01
Motivated by recent progress in the understanding of the Mott insulators away from half filling [?], often observed in the oxide materials, we study the role of the electron-lattice interaction vis-à-vis the electron correlations by studying the one-band Hubbard-Holstein model using the Gutzwiller variational method. Our theory predicts phase separation for sufficiently strong electron-lattice interaction, which however is frustrated in the solid due to the long-range Coulomb interaction of the dopant atoms, resulting in puddles of metallic phases embedded in the insulating matrix. Metallic state occurs when the volume fraction of the metallic phase exceeds the percolation threshold, as the dopant concentration is increased. Connection is made with the experimentally observed metal-insulator transition in the complex oxides.
Gutzwiller wave function for finite systems: superconductivity in the Hubbard model
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.
Phase transitions in a Bose-Hubbard model with cavity-mediated global-range interactions
Dogra, N.; Brennecke, F.; Huber, S. D.; Donner, T.
2016-08-01
We study a system with competing short- and global-range interactions in the framework of the Bose-Hubbard model. Using a mean-field approximation we obtain the phase diagram of the system and observe four different phases: a superfluid, a supersolid, a Mott insulator, and a charge-density wave, where the transitions between the various phases can be either of first or second order. We qualitatively support these results using Monte Carlo simulations. An analysis of the low-energy excitations shows that the second-order phase transition from the charge-density wave to the supersolid is associated with the softening of particle- and holelike excitations which give rise to a gapless mode and an amplitude Higgs mode in the supersolid phase. This amplitude Higgs mode is further transformed into a roton mode which softens at the supersolid to superfluid phase transition.
2D numerical modelling of meandering channel formation
Indian Academy of Sciences (India)
Y Xiao; G Zhou; F S Yang
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-loadtransport 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 numericalpredictions 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 differentscenarios and improve understanding of patterning processes.
Statistical mechanics of shell models for 2D-Turbulence
Aurell, E; Crisanti, A; Frick, P; Paladin, G; Vulpiani, A
1994-01-01
We study shell models that conserve the analogues of energy and enstrophy, hence designed to mimic fluid turbulence in 2D. The main result is that the observed state is well described as a formal statistical equilibrium, closely analogous to the approach to two-dimensional ideal hydrodynamics of Onsager, Hopf and Lee. In the presence of forcing and dissipation we observe a forward flux of enstrophy and a backward flux of energy. These fluxes can be understood as mean diffusive drifts from a source to two sinks in a system which is close to local equilibrium with Lagrange multipliers (``shell temperatures'') changing slowly with scale. The dimensional predictions on the power spectra from a supposed forward cascade of enstrophy, and from one branch of the formal statistical equilibrium, coincide in these shell models at difference to the corresponding predictions for the Navier-Stokes and Euler equations in 2D. This coincidence have previously led to the mistaken conclusion that shell models exhibit a forward ...
2-D Composite Model for Numerical Simulations of Nonlinear Waves
Institute of Scientific and Technical Information of China (English)
2000-01-01
－ A composite model, which is the combination of Boussinesq equations and Volume of Fluid (VOF) method, has been developed for 2-D time-domain computations of nonlinear waves in a large region. The whole computational region Ω is divided into two subregions. In the near-field around a structure, Ω2, the flow is governed by 2-D Reynolds Averaged Navier-Stokes equations with a turbulence closure model of k-ε equations and numerically solved by the improved VOF method; whereas in the subregion Ω1 (Ω1 = Ω - Ω2) the flow is governed by one-D Boussinesq equations and numerically solved with the predictor-corrector algorithm. The velocity and the wave surface elevation are matched on the common boundary of the two subregions. Numerical tests have been conducted for the case of wave propagation and interaction with a wave barrier. It is shown that the composite model can help perform efficient computation of nonlinear waves in a large region with the complicated flow fields near structures taken into account.
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Frigaard, Peter
This report present the results of 2D physical model tests carried out in the shallow wave flume at Dept. of Civil Engineering, Aalborg University (AAU). The objective of the tests was: To investigate the combined influence of the pile diameter to water depth ratio and the wave height to water...... depth ratio on wave run-up of piles. The measurements should be used to design access platforms on piles. The Model tests include: Calibration of regular and irregular sea states at the location of the pile (without structure in place). Measurement of wave run-up for the calibrated sea states...... on the front side of the pile (0 to 90 degrees). These tests have been conducted at Aalborg University from 9. October, 2006 to 8. November, 2006. Unless otherwise mentioned, all values given in this report are in model scale....
Bayesian 2D Deconvolution: A Model for Diffuse Ultrasound Scattering
Directory of Open Access Journals (Sweden)
Oddvar Husby
2001-10-01
Full Text Available Observed medical ultrasound images are degraded representations of the true acoustic tissue reflectance. The degradation is due to blur and speckle, and significantly reduces the diagnostic value of the images. In order to remove both blur and speckle we have developed a new statistical model for diffuse scattering in 2D ultrasound radio-frequency images, incorporating both spatial smoothness constraints and a physical model for diffuse scattering. The modeling approach is Bayesian in nature, and we use Markov chain Monte Carlo methods to obtain the restorations. The results from restorations of some real and simulated radio-frequency ultrasound images are presented and compared with results produced by Wiener filtering.
Finite state models of constrained 2d data
DEFF Research Database (Denmark)
Justesen, Jørn
2004-01-01
This paper considers a class of discrete finite alphabet 2D fields that can be characterized using tools front finite state machines and Markov chains. These fields have several properties that greatly simplify the analysis of 2D coding methods.......This paper considers a class of discrete finite alphabet 2D fields that can be characterized using tools front finite state machines and Markov chains. These fields have several properties that greatly simplify the analysis of 2D coding methods....
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Brorsen, Michael
. The objective of the tests was to investigate the impact pressures generated on a horizontal platform and a cone platform for selected sea states calibrated by Lykke Andersen & Frigaard, 2006. The measurements should be used for assessment of slamming coefficients for the design of horizontal and cone......This report present the results of 2D physical model tests carried out in the shallow wave flume at Dept. of Civil Engineering, Aalborg University (AAU), Denmark. The starting point for the present report is the previously carried out run-up tests described in Lykke Andersen & Frigaard, 2006......-shaped access platforms on piles. The Model tests include mainly regular waves and a few irregular wave tests. These tests have been conducted at Aalborg University from 9. November, 2006 to 17. November, 2006....
On the particle-hole symmetry of the fermionic spinless Hubbard model in D=1
Directory of Open Access Journals (Sweden)
M.T. Thomaz
2014-06-01
Full Text Available We revisit the particle-hole symmetry of the one-dimensional (D=1 fermionic spinless Hubbard model, associating that symmetry to the invariance of the Helmholtz free energy of the one-dimensional spin-1/2 XXZ Heisenberg model, under reversal of the longitudinal magnetic field and at any finite temperature. Upon comparing two regimes of that chain model so that the number of particles in one regime equals the number of holes in the other, one finds that, in general, their thermodynamics is similar, but not identical: both models share the specific heat and entropy functions, but not the internal energy per site, the first-neighbor correlation functions, and the number of particles per site. Due to that symmetry, the difference between the first-neighbor correlation functions is proportional to the z-component of magnetization of the XXZ Heisenberg model. The results presented in this paper are valid for any value of the interaction strength parameter V, which describes the attractive/null/repulsive interaction of neighboring fermions.
2D scaled model of the TURBOPROP wing
Directory of Open Access Journals (Sweden)
Adrian DOBRE
2011-12-01
Full Text Available The 2D Turbo Prop wing is part of the European Clean Sky JTI GRA Low Noise programme. For this, the model is equipped with interchangeable T.E. noise reducing systems.The scope of the tests in the INCAS Subsonic wind tunnel is to investigate and compare the aerodynamic and aero acoustic performances of a series of different T.E. High Lift Devices noise reducing systems of the “Turbo Prop wing configuration”. For this, the distribution of the pressure at the surface of the model should be determined. The measurement of the pressure is classically made through orifices of small size connected to a common transducer via a tubing system and a scanning device. The aerodynamic forces and moments are obtained by integration of the pressure and shear stress distributions. The wing span of the model is equal to the width of the test section.Due to the large wing span B = 2500 mm and the testing speed V = 90 m/s, the aerodynamic forces and moments occurring on the model exceed more than two times the measuring capacity of the TEM external balance of the INCAS Subsonic wind tunnel. This imposes attaching the model to supports situated outside the wind tunnel.
2-D Chemical-Dynamical Modeling of Venus's Sulfur Variability
Bierson, Carver J.; Zhang, Xi
2016-10-01
Over the last decade a combination of ground based and Venus Express observations have been made of the concentration of sulfur species in Venus's atmosphere, both above [1, 2] and below the clouds [3, 4]. These observations put constraints on both the vertical and meridional variations of the major sulfur species in Venus's atmosphere.. It has also been observed that SO2 concentrations varies on both timescales of hours and years [1,4]. The spatial and temporal distribution of tracer species is owing to two possibilities: mutual chemical interaction and dynamical tracer transport.Previous Chemical modeling of Venus's middle atmosphere has only been explored in 1-D. We will present the first 2-D (altitude and latitude) chemical-dynamical model for Venus's middle atmosphere. The sulfur chemistry is based on of the 1D model of Zhang et al. 2012 [5]. We do model runs over multiple Venus decades testing two scenarios: first one with varying sulfur fluxes from below, and second with secular dynamical perturbations in the atmosphere [6]. By comparing to Venus Express and ground based observations, we put constraints on the dynamics of Venus's middle atmosphere.References: [1] Belyaev et al. Icarus 2012 [2] Marcq et al. Nature geoscience, 2013 [3] Marcq et al. JGR:Planets, 2008 [4] Arney et al. JGR:Planets, 2014 [5] Zhang et al. Icarus 2012 [6] Parish et al. Icarus 2012
Duality Between Spin Networks and the 2D Ising Model
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.
Mott-insulator phase of the one-dimensional Bose-Hubbard model: A high-order perturbative study
International Nuclear Information System (INIS)
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: j†aj+r> and jnj+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
Effects of Agent's Repulsion in 2d Flocking Models
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.
Shastry, Sriram
2009-03-01
An exactly solvable model of spin half particles on a certain 2-dimensional frustrated lattice has been recently realized in the compound SrCu2(BO3)2, and other similar systems have been found more recently. These systems appear to be ideal testing grounds for contemporary theoretical ideas on the role of correlations and frustration in Mott Hubbard systems. In this talk I will summarize the work on these systems emphasizing their role in testing key concepts.
Kumar, Manoranjan; Soos, Zolt'an G.
2011-01-01
The bond order wave (BOW) phase of the extended Hubbard model (EHM) in one dimension (1D) is characterized at intermediate correlation $U = 4t$ by exact treatment of $N$-site systems. Linear coupling to lattice (Peierls) phonons and molecular (Holstein) vibrations are treated in the adiabatic approximation. The molar magnetic susceptibility $\\chi_M(T)$ is obtained directly up to $N = 10$. The goal is to find the consequences of a doubly degenerate ground state (gs) and finite magnetic gap $E_...
Properties of the one-dimensional Bose-Hubbard model from a high-order perturbative expansion
Damski, Bogdan; Zakrzewski, Jakub
2015-01-01
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 dete...
The Mott insulator phase of the one dimensional Bose-Hubbard model: a high order perturbative study
Damski, Bogdan; Zakrzewski, Jakub
2006-01-01
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 different correlation functions. 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 als...
Study of the multi-orbital Hubbard model at finite temperature
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.
Phonon-like excitations in the two-state Bose-Hubbard model
Directory of Open Access Journals (Sweden)
I.V. Stasyuk
2015-12-01
Full Text Available The spectrum of phonon-like collective excitations in the system of Bose-atoms in optical lattice (more generally, in the system of quantum particles described by the Bose-Hubbard model is investigated. Such excitations appear due to displacements of particles with respect to their local equilibrium positions. The two-level model taking into account the transitions of bosons between the ground state and the first excited state in potential wells, as well as interaction between them, is used. Calculations are performed within the random phase approximation in the hard-core boson limit. It is shown that excitation spectrum in normal phase consists of the one exciton-like band, while in the phase with BE condensate an additional band appears. The positions, spectral weights and widths of bands strongly depend on chemical potential of bosons and temperature. The conditions of stability of a system with respect to the lowering of symmetry and displacement modulation are discussed.
Slow dynamics in a two-dimensional Anderson-Hubbard model
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.
Robust Supersolidity in the V1- V2 Extended Bose-Hubbard Model
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
Ab initio modeling of 2D layered organohalide lead perovskites
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.
Maximizing entropy of image models for 2-D constrained coding
DEFF Research Database (Denmark)
Forchhammer, Søren; Danieli, Matteo; Burini, Nino;
2010-01-01
This paper considers estimating and maximizing the entropy of two-dimensional (2-D) fields with application to 2-D constrained coding. We consider Markov random fields (MRF), which have a non-causal description, and the special case of Pickard random fields (PRF). The PRF are 2-D causal finite...... £ 2 squares contains all 0s or all 1s. The maximum values of the entropy for the constraints are estimated and binary PRF satisfying the constraint are characterized and optimized w.r.t. the entropy. The maximum binary PRF entropy is 0.839 bits/symbol for the no uniform squares constraint. The entropy...
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 t'{L} [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.
Competing order in the fermionic Hubbard model on the hexagonal graphene lattice
Buividovich, Pavel; Ulybyshev, Maksim; von Smekal, Lorenz
2016-01-01
We study the phase diagram of the fermionic Hubbard model on the hexagonal lattice in the space of on-site and nearest neighbor couplings with Hybrid-Monte-Carlo simulations. With pure on-site repulsion this allows to determine the critical coupling strength for spin-density wave formation with the standard approach of introducing a small mass term, explicitly breaking the sublattice symmetry. The analogous mass term for charge-density wave formation above a critical nearest-neighbor repulsion, on the other hand, would introduce a fermion sign problem. The competition between the two and the phase diagram in the space of the two coouplings can however be studied in simulations without explicit sublattice symmetry breaking. Our results compare qualitatively well with the Hartree-Fock phase diagram. We furthermore demonstrate how spin-symmetry breaking by the Euclidean time discretization can be avoided also, when using an improved fermion action based on an exponetial transfer matrix with exact sublattice symm...
Monte Carlo simulations of two-dimensional Hubbard models with string bond tensor-network states
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.
Orbital nematic order and interplay with magnetism in the two-orbital Hubbard model
International Nuclear Information System (INIS)
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. (paper)
Interaction-induced topological and magnetic phases in the Hofstadter-Hubbard model
Kumar, Pramod; Mertz, Thomas; Hofstetter, Walter
2016-09-01
Interaction effects have been a subject of contemporary interest in topological phases of matter. But in the presence of interactions, the accurate determination of topological invariants in their general form is difficult due to their dependence on multiple integrals containing Green's functions and their derivatives. Here we employ the recently proposed "effective topological Hamiltonian" approach to explore interaction-induced topological phases in the time-reversal-invariant Hofstadter-Hubbard model. Within this approach, the zero-frequency part of the self-energy is sufficient to determine the correct topological invariant. We combine the topological Hamiltonian approach with the local self-energy approximation, both for the static and the full dynamical self-energy evaluated using dynamical mean field theory (DMFT), and present the resulting phase diagram in the presence of many-body interactions. We investigate the emergence of quantum spin Hall (QSH) states for different interaction strengths by calculating the Z2 invariant. The interplay of strong correlations and a staggered potential also induces magnetic long-range order with an associated first order transition. We present results for the staggered magnetization (ms), staggered occupancy (ns), and double occupancy across the transition.
Two-state Bose-Hubbard model in the hard-core boson limit
Directory of Open Access Journals (Sweden)
O.V. Velychk
2011-03-01
Full Text Available Phase transition into the phase with Bose-Einstein (BE condensate in the two-band Bose-Hubbard model with the particle hopping in the excited band only is investigated. Instability connected with such a transition (which appears at excitation energies δ0|, where |t'0| is the particle hopping parameter is considered. The re-entrant behaviour of spinodales is revealed in the hard-core boson limit in the region of positive values of chemical potential. It is found that the order of the phase transition undergoes a change in this case and becomes the first one; the re-entrant transition into the normal phase does not take place in reality. First order phase transitions also exist at negative values of δ (under the condition δ>δcrit≈ − 0.12|t'0|. At μ0|, μ phase diagrams are built and localizations of tricritical points are established. The conditions are found at which the separation on the normal phase and the phase with the BE condensate takes place.
Correlations in the ground state of the one-dimensional Hubbard model
Energy Technology Data Exchange (ETDEWEB)
Wang Qingwei, E-mail: wqw03@mails.thu.edu.c [Institute for Advanced Study, Tsinghua University, Beijing 100084 (China); Liu Yuliang, E-mail: ylliu@ruc.edu.c [Department of Physics, Renmin University of China, Beijing 100872 (China)
2009-12-14
With eigenfunctional theory and a rigorous expression of exchange-correlation energy of a general interacting electron system, we study the ground state properties of the one-dimensional Hubbard model, and calculate the ground-state energy as well as the charge gap at half-filling for arbitrary coupling strength u=U/(4t) and electron density n{sub c}. We find that the simple linear approximation of the phase field works well in weak coupling case, but it becomes inappropriate as the on-site Coulomb interaction becomes strong where the fluctuations of the bosonic auxiliary field are strong. Then we propose a new scheme by adding Gutzwiller projection which suppresses the density fluctuations and the new results are quite close to the exact ones up to considerably strong coupling strength u=3.0 and for arbitrary electron density n{sub c}. Our calculation scheme is proved to be effective for strongly correlated electron systems in one dimension, and its extension to higher dimensions is straightforward.
VAM2D: Variably saturated analysis model in two dimensions
International Nuclear Information System (INIS)
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
2D modeling of electromagnetic waves in cold plasmas
Energy Technology Data Exchange (ETDEWEB)
Crombé, K. [Laboratory for Plasma Physics, Association EURATOM - Belgian State Trilateral Euregio Cluster, Renaissancelaan 30 Avenue de la Renaissance, B-1000 Brussels, Belgium and Department of Applied Physics, Ghent University, Sint-Pietersnieuwstraat 41 B4, B (Belgium); Van Eester, D.; Koch, R.; Kyrytsya, V. [Laboratory for Plasma Physics, Association EURATOM - Belgian State Trilateral Euregio Cluster, Renaissancelaan 30 Avenue de la Renaissance, B-1000 Brussels (Belgium)
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.
Dynamics of fermionic Hubbard models after interaction quenches in one and two dimensions
Energy Technology Data Exchange (ETDEWEB)
Hamerla, Simone Anke
2013-10-15
In the last years the impressive progress on the experimental side led to a variety of new experiments allowing to address systems out of equilibrium. In this way the behavior of such systems far from equilibrium is no longer a purely theoretical issue but indeed observable. New experimental techniques, like particles trapped in optical lattices, render a realization of quantum systems with nearly arbitrary system parameters possible and provide a possibility to study their time evolution. Systems out of equilibrium are characterized by the fact, that these systems are in highly excited states giving rise to totally new fascinating properties. In the present thesis one- and two-dimensional fermionic Hubbard models out of equilibrium are discussed. The system is taken out of equilibrium by a so-called interaction quench. At the beginning the system is prepared in the groundstate of the non-interacting Hamiltonian. At a time t the interaction between the fermions is suddenly turned on so that the time evolution is governed by the whole, interacting Hamiltonian. Hence the system is prepared in the groundstate of one Hamiltonian but evolves according to a different Hamiltonian. Consequently the system ends up in a highly excited state. To describe such a system a method based on an expansion of the Heisenberg equations of motion to highest order possible is developed in this thesis. This method provides an exact description of the time evolution on short and intermediate time scales after the quench. As the method reveal exact results and does not rely on any perturbative assumption, a study of arbitrarily large interaction strengths is possible. Besides, the method is one of the few methods capable of two-dimensional systems. In the following the method used in this thesis is explained and advantages and disadvantages of the approach are thematized. For this purpose the results of the developed iterated equation of motion approach are compared to results obtained in
Janani, C.; Merino, J.; McCulloch, I. P.; Powell, B. J.
2014-01-01
Motivated by Mo$_3$S$_7$(dmit)$_3$, we investigate the Hubbard model on the triangular necklace lattice at two-thirds filling. We show, using second order perturbation theory, that in the molecular limit, the ground state and the low energy excitations of this model are identical to those of the spin-one Heisenberg chain. The latter model is known to be in the symmetry protected topological Haldane phase. Away from this limit we show, on the basis of symmetry arguments and density matrix reno...
Phase transitions in Bose-Fermi-Hubbard model in the heavy fermion limit: Hard-core boson approach
Directory of Open Access Journals (Sweden)
I.V. Stasyuk
2015-12-01
Full Text Available Phase transitions are investigated in the Bose-Fermi-Hubbard model in the mean field and hard-core boson approximations for the case of infinitely small fermion transfer and repulsive on-site boson-fermion interaction. The behavior of the Bose-Einstein condensate order parameter and grand canonical potential is analyzed as functions of the chemical potential of bosons at zero temperature. The possibility of change of order of the phase transition to the superfluid phase in the regime of fixed values of the chemical potentials of Bose- and Fermi-particles is established. The relevant phase diagrams are built.
Institute of Scientific and Technical Information of China (English)
王为忠; 姚凯伦
2002-01-01
Using an exact diagonalization method, we study an extended Hubbard model with an electron-lattice interaction for an organic ferromagnetic chain with radical coupling. The result shows that the ferromagnetic ground state originates from the antiferromagnetic correlation between adjoining sites, which is enhanced by the on-site e-e repulsion. The intersite e-e repulsion induces the inhomogeneous distribution of the charge density. The dimerization is decreased by the e-e interaction and the radical coupling. The electron--lattice interaction and the radical coupling can transfer the spin density and charge density between the main chain and the radicals.
Properties of the one-dimensional Bose-Hubbard model from a high-order perturbative expansion
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.
Real-space renormalization group study of the Hubbard model on a non-bipartite lattice
Directory of Open Access Journals (Sweden)
R. D. Levine
2002-01-01
Full Text Available Abstract: We present the real-space block renormalization group equations for fermion systems described by a Hubbard Hamiltonian on a triangular lattice with hexagonal blocks. The conditions that keep the equations from proliferation of the couplings are derived. Computational results are presented including the occurrence of a first-order metal-insulator transition at the critical value of U/t Ã¢Â‰Âˆ 12.5.
How to control pairing fluctuations: SU(2) slave-rotor gauge theory of the Hubbard model
Kim, Ki-Seok
2006-01-01
We study how to incorporate Mott physics in the BCS-type superconductor, motivated from the fact that high $T_c$ superconductivity results from a Mott insulator via hole doping. The U(1) slave-rotor representation was proposed to take local density fluctuations into account non-perturbatively, describing the Mott-Hubbard transition at half filling. Since this decomposition cannot control local pairing fluctuations, the U(1) slave-rotor representation does not give a satisfactory treatment for...
Standard model of the rare earths analyzed from the Hubbard I approximation
Locht, I. L. M.; Kvashnin, Y. O.; Rodrigues, D. C. M.; Pereiro, M.; Bergman, A.; Bergqvist, L.; Lichtenstein, A. I.; Katsnelson, M. I.; Delin, A.; Klautau, A. B.; Johansson, B.; Di Marco, I.; Eriksson, O.
2016-08-01
In this work we examine critically the electronic structure of the rare-earth elements by use of the so-called Hubbard I approximation. From the theoretical side all measured features of both occupied and unoccupied states are reproduced, without significant deviations between observations and theory. We also examine cohesive properties like the equilibrium volume and bulk modulus, where we find, in general, a good agreement between theory and measurements. In addition, we have reproduced the spin and orbital moments of these elements as they are reflected from measurements of the saturation moment. We have also employed the Hubbard I approximation to extract the interatomic exchange parameters of an effective spin Hamiltonian for the heavy rare earths. We show that the Hubbard I approximation gives results which are consistent with calculations where 4 f electrons are treated as core states for Gd. The latter approach was also used to address the series of the heavy/late rare earths. Via Monte Carlo simulations we obtained ordering temperatures which reproduce measurements within about 20 % . We have further illustrated the accuracy of these exchange parameters by comparing measured and calculated magnetic configurations for the heavy rare earths and the magnon dispersion for Gd. The Hubbard I approximation is compared to other theories of the electronic structure, and we argue that it is superior. We discuss the relevance of our results in general and how this makes it possible to treat the electronic structure of materials containing rare-earth elements, such as permanent magnets, magnetostrictive compounds, photovoltaics, optical fibers, topological insulators, and molecular magnets.
Phase separation instabilities and magnetism in two dimensional square and honeycomb Hubbard model
International Nuclear Information System (INIS)
The variational cluster approximation is applied to rigorously calculate intrinsic local electron correlations in bipartite square and honeycomb Hubbard lattices. The Mott–Hubbard gap at half filling is manifested by a smooth metal–insulator transition in both lattices in agreement with the generic two-dimensional phase diagram. However, a density variation with the chemical potential shows the distinct structural differences away from half filling. The square lattice exhibits electron density discontinuity accompanied with spontaneous transition from antiferromagnetic Mott–Hubbard insulator into nonmagnetic metal. The spectral density anomaly and spin susceptibility peaks also are signaling on coexistence of hole rich metallic and hole poor insulating regions. In contrast, honeycomb lattice does not show density anomaly but displays a smooth transition with continuous evolution of a homogenous metallic state. These calculations provide strong evidence for spontaneous phase separation instability found in our quantum cluster calculations at moderate U - Highlights: • Variational cluster approximation (VCA) captures phase separation in various lattices under doping. • The conditions are formulated for continuous and discontinuous transitions. • Discontinuous phase separation is found in square lattices under doping and pressure. • Honeycomb lattice displays continuous evolution of a homogenous metallic state. • Spectral function anomaly in square geometry displays the folding of the first Brillouin zone
The Implementation of C-ID, R2D2 Model on Learning Reading Comprehension
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…
Le modele de Hubbard bidimensionnel a faible couplage: Thermodynamique et phenomenes critiques
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
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.
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.
Chung, Chung-Hou; Lee, Der-Hau; Chao, Sung-Po
2014-07-01
We study the quantum phases and phase transitions of the Kane-Mele Hubbard (KMH) model on a zigzag ribbon of honeycomb lattice at a finite size via the weak-coupling renormalization group (RG) approach. In the noninteracting limit, the Kane-Mele (KM) model is known to support topological edge states where electrons show helical property with orientations of the spin and momentum being locked. The effective interedge hopping terms are generated due to finite-size effect. In the presence of an on-site Coulomb (Hubbard) interaction and the interedge hoppings, special focus is put on the stability of the topological edge states (TI phase) in the KMH model against (i) the charge and spin gaped (II) phase, (ii) the charge gaped but spin gapless (IC) phase, and (iii) the spin gaped but charge gapless (CI) phase depending on the number (even/odd) of the zigzag ribbons, doping level (electron filling factor) and the ratio of the Coulomb interaction to the interedge tunneling. We discuss different phase diagrams for even and odd numbers of zigzag ribbons. We find the TI-CI, II-IC, and II-CI quantum phase transitions are of the Kosterlitz-Thouless (KT) type. By computing various correlation functions, we further analyze the nature and leading instabilities of these phases. The relevance of our results for graphene is discussed.
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.
Two-component Bose-Hubbard model with higher-angular-momentum states
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.
Spiral magnetism in the single-band Hubbard model: the Hartree–Fock and slave-boson approaches
International Nuclear Information System (INIS)
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. (paper)
Qin, Mingpu; Zhang, Shiwei
2016-01-01
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 quasi-random sequences, whi...
The selection of soil models parameters in Plaxis 2D
Directory of Open Access Journals (Sweden)
O.V. Sokolova
2014-06-01
Full Text Available Finite element method is often used to solve complex geotechnical problems. The application of FEM-based programs demands special attention to setting models parameters and simulating soil behavior. The paper considers the problem of the model selection to describe the behavior of soils when calculating soil settlement in the check task, referring to complicated geotechnical conditions of Saint Petersburg. The obtained settlement values in Linear Elastic model, Mohr – Coulomb model, Hardening Soil model and Hardening Soil Small model were compared. The paper presents results of calibrating parameters for a geotechnical model obtained on the data of compression testing. The necessity of prior calculations to evaluate the accuracy of a soil model is confirmed.
Kuno, Yoshihito; Sakane, Shinya; Kasamatsu, Kenichi; Ichinose, Ikuo; Matsui, Tetsuo
2016-01-01
In this paper, we study atomic quantum simulations of $(1+1)$-dimensional($(1+1)$D) U(1) gauge-Higgs models (GHMs) defined on a lattice. We explain how U(1) lattice GHMs appear from an extended Bose-Hubbard model (EBHM) describing ultra-cold atoms with a nearest neighbor repulsion in a 1D optical lattice. We first study a phase diagram of the 1D EBHM at low fillings by means of a quantum Monte-Carlo(MC) simulation. Next, we study the EBHM at large fillings and also GHMs by the MC simulations in the path-integral formalism and show that there are four phases, i.e., the Higgs phase(superfluid), the confinement phase (Mott insulator), and phases corresponding to the density wave and the supersolid. With the obtained phase diagrams, we investigate the relationship between the two models. Finally, we study real-time dynamic of an electric flux in the GHMs by the Gross-Pitaevskii equations and the truncated Wigner approximation.
Modeling Overlapping Laminations in Magnetic Core Materials Using 2-D Finite-Element Analysis
DEFF Research Database (Denmark)
Jensen, Bogi Bech; Guest, Emerson David; Mecrow, Barrie C.
2015-01-01
This paper describes a technique for modeling overlapping laminations in magnetic core materials using two-dimensional finite-element (2-D FE) analysis. The magnetizing characteristic of the overlapping region is captured using a simple 2-D FE model of the periodic overlapping geometry and a comp...
2D semiclassical model for high harmonic generation from gas
Institute of Scientific and Technical Information of China (English)
陈黎明; 余玮; 张杰; 陈朝阳; 江文勉
2000-01-01
The electron behavior in laser field is described in detail. Based on the 1D semiclassical model, a 20 semiclassical model is proposed analytically using 3D DC-tunneling ionization theory. Lots of harmonic features are explained by this model, including the analytical demonstration of the maximum electron energy 3.17 Up. Finally, some experimental phenomena such as the increase of the cutoff harmonic energy with the decrease of pulse duration and the "anomalous" fluctuations in the cutoff region are explained by this model.
2-D Model Test Study of the Suape Breakwater, Brazil
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Burcharth, Hans F.; Sopavicius, A.;
This report deals with a two-dimensional model test study of the extension of the breakwater in Suape, Brazil. One cross-section was tested for stability and overtopping in various sea conditions. The length scale used for the model tests was 1:35. Unless otherwise specified all values given...
2D - Finite element model of a CIGS module
Energy Technology Data Exchange (ETDEWEB)
Janssen, G.J.M.; Slooff, L.H.; Bende, E.E. [ECN Solar Energy, Petten (Netherlands)
2012-09-15
The performance of thin-film CIGS modules is often limited due to inhomogeneities in CIGS layers. A 2-dimensional Finite Element Model for CIGS modules is demonstrated that predicts the impact of such inhomogeneities on the module performance. Results are presented of a module with a region of poor diode characteristics. It is concluded that according to this model the effects of poor diodes depend strongly on their location in the module and on their dispersion over the module surface. Due to its generic character the model can also be applied to other series connections of photovoltaic cells.
Practical aspects of a 2-D edge-plasma model
International Nuclear Information System (INIS)
The poloidal divertor configuration is considered the most promising solution to the particle and energy exhaust problem for a tokamak reactor. The scrape-off layer plasma surrounding the core and the high-recycling plasma near the divertor plates can be modelled by fluid equations for particle, momentum and energy transport. A numerical code (B2) based on a two-dimensional multi-fluid model has been developed for the study of edge plasmas in tokamaks. In this report we identify some key features of this model as applied to the DIII-D tokamak. 2 refs., 1 fig
Vibration induced flow in hoppers: DEM 2D polygon model
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
A two-dimensional discrete element model (DEM) simulation of cohesive polygonal particles has been developed to assess the benefit of point source vibration to induce flow in wedge-shaped hoppers. The particle-particle interaction model used is based on a multi-contact principle.The first part of the study investigated particle discharge under gravity without vibration to determine the critical orifice size (Be) to just sustain flow as a function of particle shape. It is shown that polygonal-shaped particles need a larger orifice than circular particles. It is also shown that Be decreases as the number of particle vertices increases. Addition of circular particles promotes flow of polygons in a linear manner.The second part of the study showed that vibration could enhance flow, effectively reducing Be. The model demonstrated the importance of vibrator location (height), consistent with previous continuum model results, and vibration amplitude in enhancing flow.
Analytical Crack Model for 2-D Reinforced Concrete Structures
Institute of Scientific and Technical Information of China (English)
车铁; 宋玉普
2002-01-01
A two-dimensional smeared crack model for reinforced concrete members is presented. Special emphasis is placedon the bond between concrete and reinforcement as the main factor influencing tension stiffening in cracked reinforcedconcrete. With the derived tangential stress-strain equations for concrete in the direction perpendicular to the cracks, theconstitutive relationship for cracked reinforced concrete is established. Experimental specimens have been analyzed withthe analytical model, and the analytical and experimental results are found to be in good agreement.
Percolation properties of the 2D Heisenberg model
Allès, B; Criado, C; Pepé, M
1999-01-01
We analyze the percolation properties of certain clusters defined on configurations of the 2--dimensional Heisenberg model thermalized at a temperature T=0.5. We find that, given any direction in O(3) space, \\vec{n}, the spins almost perpendicular to \\vec{n} form a percolating cluster. Given a fixed configuration, this is true for any \\vec{n}. We briefly comment on the critical properties of the model.
Simulations of Quantum Spin Models on 2D Frustrated Lattices
Melko, Roger
2006-03-01
Algorithmic advances in quantum Monte Carlo techniques have opened up the possibility of studying models in the general class of the S=1/2 XXZ model (equivalent to hard-core bosons) on frustrated lattices. With an antiferromagnetic diagonal interaction (Jz), these models can be solved exactly with QMC, albeit with some effort required to retain ergodicity in the near-degenerate manifold of states that exists for large Jz. The application of the quantum (ferromagnetic off-diagonal) interaction to this classically degenerate manifold produces a variety of intriguing physics, including an order-by-disorder supersolid phase, novel insulating states, and possible exotic quantum critical phenomena. We discuss numerical results for the triangular and kagome lattices with nearest and next-nearest neighbor exchange interactions, and focus on the relevance of the simulations to related areas of physics, such as experiments of cold trapped atomic gasses and the recent theory of deconfined quantum criticality.
A Full Hydrodynamic Modelling of 2D Breaker Bar Development
DEFF Research Database (Denmark)
Jacobsen, Niels Gjøl; Fredsøe, Jørgen
2011-01-01
The free surface simulation of breaking waves is studied using a combination of VOF and RANS closures. Further, a numerical model for the detailed study of sediment transport and morphological development is presented. In the present study it is applied to the case of sediment transport in the surf...
Hewson, Alex C; Bauer, Johannes
2010-03-24
We show that information on the probability density of local fluctuations can be obtained from a numerical renormalization group calculation of a reduced density matrix. We apply this approach to the Anderson-Holstein impurity model to calculate the ground state probability density ρ(x) for the displacement x of the local oscillator. From this density we can deduce an effective local potential for the oscillator and compare its form with that obtained from a semiclassical approximation as a function of the coupling strength. The method is extended to the infinite dimensional Holstein-Hubbard model using dynamical mean field theory. We use this approach to compare the probability densities for the displacement of the local oscillator in the normal, antiferromagnetic and charge ordered phases.
Simulation of subgrid orographic precipitation with an embedded 2-D cloud-resolving model
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.
Conservation laws and LETKF with 2D Shallow Water Model
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.
Point Contacts in Modeling Conducting 2D Planar Structures
Thiel, David V; Hettenhausen, Jan; Lewis, Andrew
2015-01-01
Use of an optimization algorithm to improve performance of antennas and electromagnetic structures usually ends up in planar unusual shapes. Using rectangular conducting elements the proposed structures sometimes have connections with only one single point in common between two neighboring areas. The single point connections (point crossing) can affect the electromagnetic performance of the structure. In this letter, we illustrate the influence of point crossing on dipole and loop antennas using MoM, FDTD, and FEM solvers. Current distribution, radiation pattern, and impedance properties for different junctions are different. These solvers do not agree in the modeling of the point crossing junctions which is a warning about uncertainty in using such junctions. However, solvers agree that a negligible change in the junction would significantly change the antenna performance. We propose that one should consider both bridging and chamfering of the conflicting cells to find optimized structures. This reduces the ...
A HORIZONTAL 2-D HYDRAULIC NUMERICAL MODEL AND IT'S APPLICATIONS TO FLOOD FORECAST
Institute of Scientific and Technical Information of China (English)
Minghui YU; Guolu YANG; Jinjun XU
2002-01-01
In this paper,a horizontal 2-D numerical model has been developed to simulate flow processes in dike burst. The finite difference method is used in computation. The model employs 2-D flow equations and can simulate complex flows when supercritical flow and sub-critical flow exist simultaneously such as hydraulic jumps. Several simulated results are worked out to demonstrate the applicability of the numerical model,such as flood propagation on a dry bed of a complex terrain.
An effective depression filling algorithm for DEM-based 2-D surface flow modelling
Zhu, D.; Ren, Q.; Xuan, Y.; Y. Chen; I. D. Cluckie
2013-01-01
The surface runoff process in fluvial/pluvial flood modelling is often simulated employing a two-dimensional (2-D) diffusive wave approximation described by grid based digital elevation models (DEMs). However, this approach may cause potential problems when using the 2-D surface flow model which exchanges flows through adjacent cells, with conventional sink removal algorithms which also allow for flow exchange along diagonal directions, due to the existence of artificial dep...
Ghostine, Rabih
2014-12-01
In open channel networks, flow is usually approximated by the one-dimensional (1D) Saint-Venant equations coupled with an empirical junction model. In this work, a comparison in terms of accuracy and computational cost between a coupled 1D-2D shallow water model and a fully two-dimensional (2D) model is presented. The paper explores the ability of a coupled model to simulate the flow processes during supercritical flows in crossroads. This combination leads to a significant reduction in the computational time, as a 1D approach is used in branches and a 2D approach is employed in selected areas only where detailed flow information is essential. Overall, the numerical results suggest that the coupled model is able to accurately simulate the main flow processes. In particular, hydraulic jumps, recirculation zones, and discharge distribution are reasonably well reproduced and clearly identified. Overall, the proposed model leads to a 30% reduction in run times. © 2014 International Association for Hydro-Environment Engineering and Research.
Comparison of 1D and 2D modelling with soil erosion model SMODERP
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
Activated sludge models ASM1, ASM2, ASM2d and ASM3
DEFF Research Database (Denmark)
Henze, Mogens; Gujer, W.; Mino, T.;
: Introduction, ASM 2, Typical Wastewater Characteristics and Kinetic and Stoichiometric Constants, Wastewater Characterization for Activated Sludge Processes, Calibration of the ASM 2, Model Limitations, Conclusion, Bibliography ASM 1: Introduction, Method of Model Presentation, Model Incorporating Carbon......This book has been produced to give a total overview of the Activated Sludge Model (ASM) family at the start of 2000 and to give the reader easy access to the different models in their original versions. It thus presents ASM1, ASM2, ASM2d and ASM3 together for the first time.Modelling of activated...... in the Model, ASM3: Stoichiometry, ASM3: Kinetics, Limitations of ASM3, Aspects of application of ASM3, ASM3C: A Carbon based model, Conclusion ASM 2d: Introduction, Conceptual Approach, ASM 2d, Typical Wastewater Characteristics and Kinetic and Stoichiometric Constants, Limitations, Conclusion ASM 2...
DEVELOPMENT OF COUPLED 1D-2D MATHEMATICAL MODELS FOR TIDAL RIVERS
Institute of Scientific and Technical Information of China (English)
XU Zu-xin; YIN Hai-long
2004-01-01
Some coupled 1D-2D hydrodynamic and water quality models depicting tidal water bodies with complex topography were presented. For the coupled models, finite element method was used to solve the governing equations so as to study tidal rivers with complex topography. Since the 1D and 2D models were coupled, the principle of model coupling was proposed to account appropriately for the factors of water level, flow and pollutant flux and the related dynamical behavior was simulated. Specifically the models were used to probe quantitative pollution contribution of receiving water from neighboring Jiangsu and Zhejiang Provinces to the pollution in the Huangpu River passing through Shanghai City. Numerical examples indicated that the developed coupled 1D-2D models are applicable in tidal river network region of Shanghai.
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.
Fast 2D flood modelling using GPU technology - recent applications and new developments
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.
Tidal regime in Gulf of Kutch, west coast of India, by 2D model
Digital Repository Service at National Institute of Oceanography (India)
Unnikrishnan, A; Gouveia, A; Vethamony, P.
A 2D barotropic numerical model is developed for the Gulf of Kutch with a view to synthesize available information on tides and currents in the Gulf. A comparison of model results with moored current meter observations shows that the model...
Analysis of vegetation effect on waves using a vertical 2-D RANS model
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...
Energy Technology Data Exchange (ETDEWEB)
Brehm, Sascha
2009-02-26
Two-particle excitations, such as spin and charge excitations, play a key role in high-T{sub c} cuprate superconductors (HTSC). Due to the antiferromagnetism of the parent compound the magnetic excitations are supposed to be directly related to the mechanism of superconductivity. In particular, the so-called resonance mode is a promising candidate for the pairing glue, a bosonic excitation mediating the electronic pairing. In addition, its interactions with itinerant electrons may be responsible for some of the observed properties of HTSC. Hence, getting to the bottom of the resonance mode is crucial for a deeper understanding of the cuprate materials. To analyze the corresponding two-particle correlation functions we develop in the present thesis a new, non-perturbative and parameter-free technique for T=0 which is based on the Variational Cluster Approach (VCA, an embedded cluster method for one-particle Green's functions). Guided by the spirit of the VCA we extract an effective electron-hole vertex from an isolated cluster and use a fully renormalized bubble susceptibility {chi}{sub 0} including the VCA one-particle propagators. Within our new approach, the magnetic excitations of HTSC are shown to be reproduced for the Hubbard model within the relevant strong-coupling regime. Exceptionally, the famous resonance mode occurring in the underdoped regime within the superconductivity-induced gap of spin-flip electron-hole excitations is obtained. Its intensity and hourglass dispersion are in good overall agreement with experiments. Furthermore, characteristic features such as the position in energy of the resonance mode and the difference of the imaginary part of the susceptibility in the superconducting and the normal states are in accord with Inelastic Neutron Scattering (INS) experiments. For the first time, a strongly-correlated parameter-free calculation revealed these salient magnetic properties supporting the S=1 magnetic exciton scenario for the
International Nuclear Information System (INIS)
Two-particle excitations, such as spin and charge excitations, play a key role in high-Tc cuprate superconductors (HTSC). Due to the antiferromagnetism of the parent compound the magnetic excitations are supposed to be directly related to the mechanism of superconductivity. In particular, the so-called resonance mode is a promising candidate for the pairing glue, a bosonic excitation mediating the electronic pairing. In addition, its interactions with itinerant electrons may be responsible for some of the observed properties of HTSC. Hence, getting to the bottom of the resonance mode is crucial for a deeper understanding of the cuprate materials. To analyze the corresponding two-particle correlation functions we develop in the present thesis a new, non-perturbative and parameter-free technique for T=0 which is based on the Variational Cluster Approach (VCA, an embedded cluster method for one-particle Green's functions). Guided by the spirit of the VCA we extract an effective electron-hole vertex from an isolated cluster and use a fully renormalized bubble susceptibility χ0 including the VCA one-particle propagators. Within our new approach, the magnetic excitations of HTSC are shown to be reproduced for the Hubbard model within the relevant strong-coupling regime. Exceptionally, the famous resonance mode occurring in the underdoped regime within the superconductivity-induced gap of spin-flip electron-hole excitations is obtained. Its intensity and hourglass dispersion are in good overall agreement with experiments. Furthermore, characteristic features such as the position in energy of the resonance mode and the difference of the imaginary part of the susceptibility in the superconducting and the normal states are in accord with Inelastic Neutron Scattering (INS) experiments. For the first time, a strongly-correlated parameter-free calculation revealed these salient magnetic properties supporting the S=1 magnetic exciton scenario for the resonance mode. Besides the
Pair correlations in doped Hubbard ladders
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.
2D and 3D modelling of magnetic and resistivity data from Aespoe
Energy Technology Data Exchange (ETDEWEB)
Mattsson, Haakan (GeoVista AB, Luleaa (Sweden))
2011-05-15
This report presents results from modelling of geophysical data. Ground magnetic and geo electric data were collected in 1988 as part of the pre-investigations carried out before the construction of the Aespoe Hard Rock Laboratory (HRL). The work presented in this report is an evaluation of the magnetic and geo electric data with the focus on estimating variations in geometry and dip of some of the possible deformation zones indicated in lineament interpretations presented earlier. This was done by 2D forward magnetic modelling, 2D forward resistivity modelling and 3D inversion of the magnetic data. The specific aims of this work are: 1. Produce magnetic 2D forward models across 12 selected linked lineaments. 2. Produce a 3D susceptibility model of the entire data set of Aespoe. 3. Use 2D forward resistivity modelling to produce electric anomaly response diagrams for a dipole-dipole survey across low resistivity zones with various dips. The results of the modelling work will mainly be used as supportive information for deterministic geological modelling of deformation zones and rock units in the vicinity of the Aespoe HRL. The results of the 2D forward modelling of magnetic data show geologically reasonable solutions, and in most cases it is possible to make reliable estimates of the width and orientation of the cause of the targeted lineament. The possible deformation zones generally dip steeply (80 deg-90 deg) and have a width of c. 30-50 m. In some cases the modelled lineament has a diffuse character with low amplitude, which makes the model solution uncertain. Two 3D susceptibility models were created by use of inversion of the ground magnetic data; one coarse model of the entire Island of Aespoe and one more detailed model of the south-eastern peninsula of the Island, covering the volume of the Aespoe HRL. The two models fit nicely to the measured data and they are geologically realistic. It is possible to identify well-defined bodies (rock volumes) of
Exact solution of the 1D Hubbard model with NN and NNN interactions in the narrow-band limit
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.
Bond formation effects on the metal-insulator transition in the half-filled kagome Hubbard model
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.
Comparison between 2D turbulence model ESEL and experimental data from AUG and COMPASS tokamaks
DEFF Research Database (Denmark)
Ondac, Peter; Horacek, Jan; Seidl, Jakub;
2015-01-01
In this article we have used the 2D fluid turbulence numerical model, ESEL, to simulate turbulent transport in edge tokamak plasma. Basic plasma parameters from the ASDEX Upgrade and COMPASS tokamaks are used as input for the model, and the output is compared with experimental observations obtained...
Universality and Non-Perturbative Definitions of 2D Quantum Gravity from Matrix Models
Miramontes, J. Luis; Guillen, Joaquin Sanchez
1991-01-01
The universality of the non-perturbative definition of Hermitian one-matrix models following the quantum, stochastic, or $d=1$-like stabilization is discussed in comparison with other procedures. We also present another alternative definition, which illustrates the need of new physical input for $d=0$ matrix models to make contact with 2D quantum gravity at the non-perturbative level.
Universality and nonperturbative definitions of 2D quantum gravity from matrix models
International Nuclear Information System (INIS)
The universality of the nonperturbative definition of Hermitian one-matrix models following the quantum stochastic, or d = 1-like stabilization is discussed in comparison with other procedures. The authors also present another alternative definition, which illustrates the need of new physical input for d = 0 matrix models to make contact with 2D quantum gravity at the nonperturbative level
2D cyclic pure shear of granular materials, simulations and model
Krijgsman, D.; Luding, S.; Luding, S.; Yu, A.; Dong, K.; Yang, R.
2013-01-01
Discrete particle simulations of granular materials under 2D, isochoric, cyclic pure shear have been performed and are compared to a recently developed constitutive model involving a deviatoric yield stress, dilatant stresses and structural anisotropy. The original model shows the cyclic response qu
Evaluation of 2D shallow-water model for spillway flow with a complex geometry
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 ...
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.
Logan, David E.; Galpin, Martin R.
2016-01-01
The paramagnetic phase of the one-band Hubbard model is studied at zero-temperature, within the framework of dynamical mean-field theory, and for general particle-hole asymmetry where a doping-induced Mott transition occurs. Our primary focus is the Mott insulator (MI) phase, and our main aim to establish what can be shown exactly about it. To handle the locally doubly-degenerate MI requires two distinct self-energies, which reflect the broken symmetry nature of the phase and together determine the standard single self-energy. Exact results are obtained for the local charge, local magnetic moment and associated spin susceptibilities, the interaction-renormalised levels, and the low-energy behaviour of the self-energy in the MI phase. The metallic phase is also considered briefly, and shown to acquire an emergent particle-hole symmetry as the Mott transition is approached. Throughout the metal, Luttinger’s theorem is reflected in the vanishing of the Luttinger integral; for the generic MI by contrast this is shown to be non-vanishing, but again to have a universal magnitude. Numerical results are also obtained using NRG, for the metal/MI phase boundary, the scaling behaviour of the charge as the Mott transition is aproached from the metal, and associated universal scaling of single-particle dynamics as the low-energy Kondo scale vanishes.
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.
Validation of DYSTOOL for unsteady aerodynamic modeling of 2D airfoils
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.
Validation of DYSTOOL for unsteady aerodynamic modeling of 2D airfoils
International Nuclear Information System (INIS)
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
2D-photochemical model for forbidden oxygen line emission for comet 1P/Halley
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.
The FLO Diffusive 1D-2D Model for Simulation of River Flooding
Directory of Open Access Journals (Sweden)
Costanza Aricò
2016-05-01
Full Text Available An integrated 1D-2D model for the solution of the diffusive approximation of the shallow water equations, named FLO, is proposed in the present paper. Governing equations are solved using the MArching in Space and Time (MAST approach. The 2D floodplain domain is discretized using a triangular mesh, and standard river sections are used for modeling 1D flow inside the section width occurring with low or standard discharges. 1D elements, inside the 1D domain, are quadrilaterals bounded by the trace of two consecutive sections and by the sides connecting their extreme points. The water level is assumed to vary linearly inside each quadrilateral along the flow direction, but to remain constant along the direction normal to the flow. The computational cell can share zero, one or two nodes with triangles of the 2D domain when lateral coupling occurs and more than two nodes in the case of frontal coupling, if the corresponding section is at one end of the 1D channel. No boundary condition at the transition between the 1D-2D domain has to be solved, and no additional variable has to be introduced. Discontinuities arising between 1D and 2D domains at 1D sections with a top width smaller than the trace of the section are properly solved without any special restriction on the time step.
The simulation of 3D mass models in 2D digital mammography and breast tomosynthesis
Energy Technology Data Exchange (ETDEWEB)
Shaheen, Eman, E-mail: eman.shaheen@uzleuven.be; De Keyzer, Frederik; Bosmans, Hilde; Ongeval, Chantal Van [Department of Radiology, University Hospitals Leuven, Herestraat 49, 3000 Leuven (Belgium); Dance, David R.; Young, Kenneth C. [National Coordinating Centre for the Physics of Mammography, Royal Surrey County Hospital, Guildford GU2 7XX, United Kingdom and Department of Physics, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford GU2 7XH (United Kingdom)
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
The simulation of 3D mass models in 2D digital mammography and breast tomosynthesis
International Nuclear Information System (INIS)
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
Impact of high speed civil transports on stratospheric ozone. A 2-D model investigation
Energy Technology Data Exchange (ETDEWEB)
Kinnison, D.E.; Connell, P.S. [Lawrence Livermore National Lab., CA (United States)
1997-12-31
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. (author) 7 refs.
KPLS-RWBFNN model for MFL 2D defect profile reconstruction
Xu, Chao; Wang, Changlong; Ji, Fengzhu
2013-03-01
Kernel partial least squares (KPLS) is normally very efficient for tackling nonlinear systems by mapping an original input space into a high-dimensional feature space and creating a linear PLS model in the feature space. Unlike other nonlinear PLS techniques, KPLS does not entail any nonlinear optimisation procedures. However, due to the linear inner model of PLS, KPLS is still inappropriate for describing the significant nonlinear characteristic data structure while dealing with complex physical systems in practical situations. Under this circumstance, radial wavelet basic function neural network (RWBFNN) can replace the linear inner model of PLS in the nonlinear kernel-based algorithm. Thus, KPLS-RWBFNN model is proposed in this paper and applied to multi-resolution approximation reconstruction of 2D defect profiles in magnetic flux leakage testing. The reconstructions of 2D defect profiles by this method are implemented, and the comparisons among reconstructions by KPLS, RWBFNN and the proposed approach are also undertaken. Meanwhile, the reconstructions of 2D defects by RWBFNN and the proposed approach at different SNR are also executed. The results indicate that KPLS-RWBFNN model could simplify the structure of the network while holding well-behaved generalisation and multi-resolution approximation and predict the 2D defect profiles accurately and rapidly with good robustness.
Global 6DOF Pose Estimation from Untextured 2D City Models
Arth, Clemens; Pirchheim, Christian; Ventura, Jonathan; Lepetit, Vincent
2015-01-01
We propose a method for estimating the 3D pose for the camera of a mobile device in outdoor conditions, using only an untextured 2D model. Previous methods compute only a relative pose using a SLAM algorithm, or require many registered images, which are cumbersome to acquire. By contrast, our method returns an accurate, absolute camera pose in an absolute referential using simple 2D+height maps, which are broadly available, to refine a first estimate of the pose provided by the device's senso...
2D modelling of clad geometry and resulting thermal cycles during laser cladding
Ya, Wei; Pathiraj, B.; Liu, Shaojie
2016-01-01
A 2D thermal model of laser cladding process based on mass and energy balance is built incorporating the powder efficiency and solved with the finite element software COMSOL MULTIPHYSICS® v4.4. Powder efficiency was used as one of the input parameters. Powder efficiency was determined with weight me
New technologies of 2-D and 3-D modeling for analysis and management of natural resources
Cheremisina, E. N.; Lyubimova, A. V.; Kirpicheva, E. Yu.
2016-09-01
For ensuring technological support of research and administrative activity in the sphere of environmental management a specialized modular program complex was developed. The special attention in developing a program complex is focused to creation of convenient and effective tools for creation and visualization 2d and 3D models providing the solution of tasks of the analysis and management of natural resources.
Strict System Equivalence of 2D Linear Discrete State Space Models
Directory of Open Access Journals (Sweden)
Mohamed S. Boudellioua
2012-01-01
Full Text Available The connection between the polynomial matrix descriptions (PMDs of the well-known regular and singular 2D linear discrete state space models is considered. It is shown that the transformation of strict system equivalence in the sense of Fuhrmann provides the basis for this connection. The exact form of the transformation is established for both the regular and singular cases.
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…
2D-Raman-THz spectroscopy: A sensitive test of polarizable water models
Energy Technology Data Exchange (ETDEWEB)
Hamm, Peter, E-mail: peter.hamm@chem.uzh.ch [Department of Chemistry, University of Zurich, Winterthurerstr. 190, CH-8057 Zürich (Switzerland)
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.
A simple model for 2D image upconversion of incoherent light
DEFF Research Database (Denmark)
Dam, Jeppe Seidelin; Pedersen, Christian; Tidemand-Lichtenberg, Peter
2011-01-01
We present a simple theoretical model for 2 dimensional (2-D) image up-conversion of incoherent light. While image upconversion has been known for more than 40 years, the technology has been hindered by very low conversion quantum efficiency (~10-7). We show that our implementation compared to pr...
N=2, D=4 supersymmetric σ-models and Hamiltonian mechanics
International Nuclear Information System (INIS)
A deep similarity is established between the Hamiltonian mechanics of point particle and supersymmetric N=2, D=4 σ-models formulated within harmonic superspace. An essential part of the latter, the sphere S2, comes out as a counterpart of the time variable. (author). 7 refs
Parallelized CCHE2D flow model with CUDA Fortran on Graphics Process Units
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...
Structure of a model salt bridge in solution investigated with 2D-IR spectroscopy
Huerta-Viga, Adriana; Amirjalayer, Saeed; Woutersen, Sander
2013-01-01
Salt bridges are known to be important for the stability of protein conformation, but up to now it has been difficult to study their geometry in solution. Here we characterize the spatial structure of a model salt bridge between guanidinium (Gdm+) and acetate (Ac-) using two-dimensional vibrational (2D-IR) spectroscopy. We find that as a result of salt bridging the infrared response of Gdm+ and Ac- change significantly, and in the 2D-IR spectrum, salt bridging of the molecules appears as cross peaks. From the 2D-IR spectrum we determine the relative orientation of the transition-dipole moments of the vibrational modes involved in the salt bridge, as well as the coupling between them. In this manner we reconstruct the geometry of the solvated salt bridge.
Justification for a 2D versus 3D fingertip finite element model during static contact simulations.
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
Molecular Dynamics implementation of BN2D or 'Mercedes Benz' water model
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.
The 2dF Galaxy Redshift Survey: Voids and hierarchical scaling models
Croton, D J; Gaztañaga, E; Baugh, C M; Norberg, P; Baldry, I K; Bland-Hawthorn, J; Bridges, T J; Cannon, R; Cole, S; Collins, C; Couch, W; Dalton, G B; De Propris, R; Driver, S P; Efstathiou, G P; Ellis, Richard 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
2004-01-01
We study the void distribution in the completed 2dFGRS using counts-in-cells to measure the reduced void probability function (VPF). Theoretically, the VPF connects the distribution of voids to the moments of galaxy clustering of all orders. The reduced VPF measured from the 2dFGRS is in excellent agreement with the paradigm of hierarchical scaling of the galaxy clustering moments. This scaling results in a universal form for the VPF when plotted as a function of $\\Nbar\\xibar_2$, where $\\Nbar$ is the expected mean number of galaxies and $\\bar{\\xi_2}$ is the volume-averaged 2-point correlation function. Models of galaxy clustering which display hierarchical scaling yield different predictions for the reduced VPF. The accuracy of our measurement of the VPF from the 2dFGRS is such that we can rule out, at a very high significance, popular models for clustering, such as the lognormal distribution. We demonstrate that the negative binomial model gives a very good approximation to the 2dFGRS data over a wide range ...
The 2dF Galaxy Redshift Survey: voids and hierarchical scaling models
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.
Reliability of a Novel Model for Drug Release from 2D HPMC-Matrices
Directory of Open Access Journals (Sweden)
Rumiana Blagoeva
2010-04-01
Full Text Available A novel model of drug release from 2D-HPMC matrices is considered. Detailed mathematical description of matrix swelling and the effect of the initial drug loading are introduced. A numerical approach to solution of the posed nonlinear 2D problem is used on the basis of finite element domain approximation and time difference method. The reliability of the model is investigated in two steps: numerical evaluation of the water uptake parameters; evaluation of drug release parameters under available experimental data. The proposed numerical procedure for fitting the model is validated performing different numerical examples of drug release in two cases (with and without taking into account initial drug loading. The goodness of fit evaluated by the coefficient of determination is presented to be very good with few exceptions. The obtained results show better model fitting when accounting the effect of initial drug loading (especially for larger values.
Reliability analysis of diesel engine crankshaft based on 2D stress strength interference model
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
A 2D stress strength interference model (2D-SSIM) considering that the fatigue reliability of engineering structural components has close relationship to load asymmetric ratio and its variability to some extent is put forward. The principle, geometric schematic and limit state equation of this model are presented. Reliability evaluation for a kind of diesel engine crankshaft was made based on this theory, in which multi-axial loading fatigue criteria was employed. Because more important factors, i.e.stress asymmetric ratio and its variability, are considered, it theoretically can make more accurate evaluation for structural component reliability than the traditional interference model. Correspondingly, a Monte-Carlo Method simulation solution is also given. The computation suggests that this model can yield satisfactory reliability evaluation.
Simplified 2D Bidomain Model of Whole Heart Electrical Activity and ECG Generation
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.
A U(1) Current Algebra Model Coupled to 2D-Gravity
Stoilov, M.; Zaikov, R.
1993-01-01
We consider a simple model of a scalar field with $U(1)$ current algebra gauge symmetry coupled to $2D$-gravity in order to clarify the origin of Stuckelberg symmetry in the $w_{\\infty}$-gravity theory. An analogous symmetry takes place in our model too. The possible central extension of the complete symmetry algebra and the corresponding critical dimension have been found. The analysis of the Hamiltonian and the constraints shows that the generators of the current algebra, the reparametrizat...
Stochastic 2-D Models of Galaxy Disk Evolution. The Galaxy M33
Mineikis, Tadas; Vansevičius, Vladas
2015-01-01
We have developed a fast numerical 2-D model of galaxy disk evolution (resolved along the galaxy radius and azimuth) by adopting a scheme of parameterized stochastic self-propagating star formation. We explore the parameter space of the model and demonstrate its capability to reproduce 1-D radial profiles of the galaxy M33: gas surface density, surface brightness in the i and GALEX FUV passbands, and metallicity.
Directory of Open Access Journals (Sweden)
Wu Steven H
2012-06-01
Full Text Available Abstract Background Two-dimensional polyacrylamide gel electrophoresis (2D PAGE is commonly used to identify differentially expressed proteins under two or more experimental or observational conditions. Wu et al (2009 developed a univariate probabilistic model which was used to identify differential expression between Case and Control groups, by applying a Likelihood Ratio Test (LRT to each protein on a 2D PAGE. In contrast to commonly used statistical approaches, this model takes into account the two possible causes of missing values in 2D PAGE: either (1 the non-expression of a protein; or (2 a level of expression that falls below the limit of detection. Results We develop a global Bayesian model which extends the previously described model. Unlike the univariate approach, the model reported here is able treat all differentially expressed proteins simultaneously. Whereas each protein is modelled by the univariate likelihood function previously described, several global distributions are used to model the underlying relationship between the parameters associated with individual proteins. These global distributions are able to combine information from each protein to give more accurate estimates of the true parameters. In our implementation of the procedure, all parameters are recovered by Markov chain Monte Carlo (MCMC integration. The 95% highest posterior density (HPD intervals for the marginal posterior distributions are used to determine whether differences in protein expression are due to differences in mean expression intensities, and/or differences in the probabilities of expression. Conclusions Simulation analyses showed that the global model is able to accurately recover the underlying global distributions, and identify more differentially expressed proteins than the simple application of a LRT. Additionally, simulations also indicate that the probability of incorrectly identifying a protein as differentially expressed (i.e., the False
Numerical Methods and Comparisons for 1D and Quasi 2D Streamer Propagation Models
Huang, Mengmin; Guan, Huizhe; Zeng, Rong
2016-01-01
In this work, we propose four different strategies to simulate the one-dimensional (1D) and quasi two-dimensional (2D) model for streamer propagation. Each strategy involves of one numerical method for solving Poisson's equation and another method for solving continuity equations in the models, and a total variation diminishing three-stage Runge-Kutta method in temporal discretization. The numerical methods for Poisson's equation include finite volume method, discontinuous Galerkin methods, mixed finite element method and least-squared finite element method. The numerical method for continuity equations is chosen from the family of discontinuous Galerkin methods. The accuracy tests and comparisons show that all of these four strategies are suitable and competitive in streamer simulations from the aspects of accuracy and efficiency. By applying any strategy in real simulations, we can study the dynamics of streamer propagations and influences due to the change of parameters in both of 1D and quasi 2D models. T...
Mechanical Modelling of Pultrusion Process: 2D and 3D Numerical Approaches
DEFF Research Database (Denmark)
Baran, Ismet; Hattel, Jesper Henri; Akkerman, Remko;
2015-01-01
, 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......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...... 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...
An effective depression filling algorithm for DEM-based 2-D surface flow modelling
Directory of Open Access Journals (Sweden)
D. Zhu
2013-02-01
Full Text Available The surface runoff process in fluvial/pluvial flood modelling is often simulated employing a two-dimensional (2-D diffusive wave approximation described by grid based digital elevation models (DEMs. However, this approach may cause potential problems when using the 2-D surface flow model which exchanges flows through adjacent cells, with conventional sink removal algorithms which also allow for flow exchange along diagonal directions, due to the existence of artificial depression in DEMs. In this paper, we propose an effective method for filling artificial depressions in DEM so that the problem can be addressed. We firstly analyse two types of depressions in DEMs and demonstrate the issues caused by the current depression filling algorithms using the surface flow simulations from the MIKE SHE model built for a medium-sized basin in Southeast England. The proposed depression-filling algorithm for 2-D overland flow modelling is applied and evaluated by comparing the simulated flows at the outlet of the catchment represented by DEMs at various resolutions (50 m, 100 m and 200 m. The results suggest that the existence of depressions in DEMs can substantially influence the overland flow estimation and the new depression filling algorithm is shown to be effective in tackling this issue based upon the comparison of simulations for sink-dominated and sink-free DEMs, especially in the areas with relatively flat topography.
TRENT2D WG: a smart web infrastructure for debris-flow modelling and hazard assessment
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
Parameterising root system growth models using 2D neutron radiography images
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
Characteristic polynomial assignment in F-M model Ⅱ of 2-D systems
Institute of Scientific and Technical Information of China (English)
唐万生; 亢京力
2004-01-01
The problems of characteristic polynomial assignment in Fornasini-Marchesini (F-M) model Ⅱ of 2-D systems are investigated. The corresponding closed-loop systems described by F-M model Ⅱ are obtained via the state feedback.Using the algebraic geometry method, the characteristic polynomial assignment in the closed-loop systems is discussed. In terms of the theory of algebraic geometry, the problem of characteristic polynomial assignment is transferred to the one whether a rational mapping is onto. Sufficient conditions for almost arbitrary assignment coefficients of characteristic polynomial in F-M model Ⅱ of 2-D systems via state feedback are derived, and they are available for multi-input cases. It also has been shown that this method can be applied to assign the characteristic polynomial with output feedback. The sufficient conditions for almost arbitrary assignment coefficients of characteristic polynomial of multi-input 2-D systems described by F-M model Ⅱ with output feedback are established.
Dotsenko, V S; Pujol, P; Dotsenko, Vladimir; Picco, Marco; Pujol, Pierre
1995-01-01
We find the cross-over behavior for the spin-spin correlation function for the 2D Ising and 3-states Potts model with random bonds at the critical point. The procedure employed is the renormalisation approach of the perturbation series around the conformal field theories representing the pure models. We obtain a crossover in the amplitude for the correlation function for the Ising model which doesn't change the critical exponent, and a shift in the critical exponent produced by randomness in the case of the Potts model. A comparison with numerical data is discussed briefly.
2D edge plasma modeling extended up to the main chamber
Energy Technology Data Exchange (ETDEWEB)
Dekeyser, W., E-mail: wouter.dekeyser@mech.kuleuven.be [Department of Mechanical Engineering, Katholieke Universiteit Leuven, Celestijnenlaan 300A, 3001 Leuven (Belgium); Baelmans, M. [Department of Mechanical Engineering, Katholieke Universiteit Leuven, Celestijnenlaan 300A, 3001 Leuven (Belgium); Reiter, D.; Boerner, P.; Kotov, V. [Institut fuer Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM-Association, Trilateral Euregio Cluster, D-52425 Juelich (Germany)
2011-08-01
Far SOL plasma flow, and hence main chamber recycling and plasma surface interaction, are today still only very poorly described by current 2D fluid edge codes, such as B2, UEDGE or EDGE2D, due to a common technical limitation. We have extended the B2 plasma fluid solver in the current ITER version of B2-EIRENE (SOLPS4.3) to allow plasma solutions to be obtained up to the 'real vessel wall', at least on the basis of ad hoc far SOL transport models. We apply here the kinetic Monte Carlo Code EIRENE on such plasma solutions to study effects of this model refinement on main chamber fluxes and sputtering, for an ITER configuration. We show that main chamber sputtering may be significantly modified both due to thermalization of CX neutrals in the far SOL and poloidally highly asymmetric plasma wall contact, as compared to hitherto applied teleportation of particle fluxes across this domain.
A Neural-FEM tool for the 2-D magnetic hysteresis modeling
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.
Hybrid 2D-3D modelling of GTA welding with filler wire addition
Traidia, Abderrazak
2012-07-01
A hybrid 2D-3D model for the numerical simulation of Gas Tungsten Arc welding is proposed in this paper. It offers the possibility to predict the temperature field as well as the shape of the solidified weld joint for different operating parameters, with relatively good accuracy and reasonable computational cost. Also, an original approach to simulate the effect of immersing a cold filler wire in the weld pool is presented. The simulation results reveal two important observations. First, the weld pool depth is locally decreased in the presence of filler metal, which is due to the energy absorption by the cold feeding wire from the hot molten pool. In addition, the weld shape, maximum temperature and thermal cycles in the workpiece are relatively well predicted even when a 2D model for the arc plasma region is used. © 2012 Elsevier Ltd. All rights reserved.
Exotic magnetisation plateaus in a quasi-2D Shastry-Sutherland model
Foltin, G. R.; Manmana, S. R.; Schmidt, K. P.
2014-01-01
We find unconventional Mott insulators in a quasi-2D version of the Shastry-Sutherland model in a magnetic field. In our realization on a 4-leg tube geometry, these are stabilized by correlated hopping of localized magnetic excitations. Using perturbative continuous unitary transformations (pCUTs, plus classical approximation or exact diagonalization) and the density matrix renormalisation group method (DMRG), we identify prominent magnetization plateaus at magnetizations M=1/8, M=3/16, M=1/4...
Anisotropy effects and friction maps in the framework of the 2d PT model
International Nuclear Information System (INIS)
We present a series of numerical simulations on the friction–anisotropy behavior and stick–slip dynamics of a point mass in the framework of a 2d Prandtl–Tomlinson model. Results for three representative surface lattice are shown: square, hexagonal and honeycomb. Curves for scan angle dependence of static friction force, and kinetic one at T=0 K and T=300 K are shown. Friction force maps are computed at different directions
Anisotropy effects and friction maps in the framework of the 2d PT model
Energy Technology Data Exchange (ETDEWEB)
Fajardo, O.Y. [Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, E-50009 Zaragoza (Spain); Gnecco, E. [Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, 28049 Madrid (Spain); Mazo, J.J., E-mail: juanjo@unizar.es [Instituto de Ciencia de Materiales de Aragón and Departamento de Física de la Materia Condensada, CSIC-Universidad de Zaragoza, E-50009 Zaragoza (Spain)
2014-12-15
We present a series of numerical simulations on the friction–anisotropy behavior and stick–slip dynamics of a point mass in the framework of a 2d Prandtl–Tomlinson model. Results for three representative surface lattice are shown: square, hexagonal and honeycomb. Curves for scan angle dependence of static friction force, and kinetic one at T=0 K and T=300 K are shown. Friction force maps are computed at different directions.
TMRPres2D: high quality visual representation of transmembrane protein models.
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
Effects of vegetation on high waters in 2D hydraulic modeling
Müller, Matej
2009-01-01
Due to increasing impervious surfaces and climate change, the frequency of high water is increasing in recent decades. In parallel, the damage produced by them also increases. The need for preparedness for such events and for constructing flood measures grows. Hydraulic analysis are necessary for the assessment of the flood hazard and for flood extension forecasting. In recent years the development of advanced computers increased the use of complex 2D hydraulic models. The accuracy of such...
A 2D wavenumber domain phase model for ground moving vehicles in synthetic aperture radar imagery
International Nuclear Information System (INIS)
In this paper, fundamental phase characteristics of moving vehicles in synthetic aperture radar (SAR) data are reviewed. A 2D phase model for a moving point scatterer is expressed in terms of range and azimuth wavenumbers. The moving point scatterer impulse response is then the 2D Fourier transform of the associated complex sinusoid. Numerical computation of the 2D phase for arbitrary relative radar-point scatter motion is organized as a composition of functions expressing time, frequency and angle in terms of wavenumber vectors. An analytic model for the phase is subsequently derived in the special case that the Doppler cone angle is 90°. With that model it is observed that the map from velocity and acceleration to quadratic phase is not one-to-one and therefore the associated inverse problem is ill-posed. An example of moving vehicle Doppler energy dispersion and corresponding phase measured in clutter suppressed SAR image data is provided. Clutter suppression is achieved by application of spacetime adaptive processing. (paper)
Bose-Hubbard model with random impurities: Multiband and nonlinear hopping effects
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.
Optimizing the transverse thermal conductivity of 2D-SiCf/SiC composites, I. Modeling
Energy Technology Data Exchange (ETDEWEB)
Youngblood, Gerald E.; Senor, David J.; Jones, Russell H.
2002-12-31
For potential fusion applications, considerable fabrication efforts have been directed to obtaining transverse thermal conductivity (Keff) values in excess of 30 W/mK (unirradiated) in the 800-1000°C temperature range for 2D-SiCf/SiC composites. To gain insight into the factors affecting Keff, at PNNL we have tested three different analytic models for predicting Keff in terms of constituent (fiber, matrix and interphase) properties. The tested models were: the Hasselman-Johnson (H-J) “2-Cylinder” model, which examines the effects of fiber-matrix (f/m) thermal barriers; the Markworth “3-Cylinder” model, which specifically examines the effects of interphase thickness and thermal conductivity; and a newly-developed Anisotropic “3-Square” model, which examines the potential effect of introducing a fiber coating with anisotropic properties to enhance (or diminish) f/m thermal coupling. The first two models are effective medium models, while the third model is a simple combination of parallel and series conductances. Model predictions suggest specific designs and/or development efforts directed to optimize the overall thermal transport performance of 2D-SiCf/SiC.
APPLICATION OF MULTIGRID METHOD IN 2-D MATHEMATICAL MODEL IN OPEN CHANNELS
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
In 2-D mathematical model, one of the important problems is to improve computational speed. The multigrid method is a new rapid iteration method developed in the resent 20 years, and it has been widely used in many fields, but in sediment mathematical model it has been rarely used, especially in plane mathematical model with large scale computational scope. In this paper, the multigrid method is introduced and expected to be used widely in this field. And it is verified that the more layers are adopted, the higher convergent speed will be reached in computation.
Energy Technology Data Exchange (ETDEWEB)
Carvalho, Vanuildo S de [Instituto de Física, Universidade Federal de Goiás, 74.001-970, Goiânia-GO (Brazil); Freire, Hermann, E-mail: hfreire@mit.edu [Instituto de Física, Universidade Federal de Goiás, 74.001-970, Goiânia-GO (Brazil); Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 2139 (United States)
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.
A simple 2-D inundation model for incorporating flood damage in urban drainage planning
Directory of Open Access Journals (Sweden)
A. Pathirana
2008-11-01
Full Text Available 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.
International Nuclear Information System (INIS)
It has been shown that the spin-density wave instability does not coexist with s-like anisotropic superconductivity in the molecular field approach to the nearly half-filled two-dimensional Hubbard model. The phase diagram of the interplay of normal state, spin density wave, d-wave and extended s-wave superconducting orderings has been constructed. The possibility of the first order transition from the normal state and the superconducting state to the SDW-phase has been discussed. (author). 14 refs, 2 figs
Nested 1D-2D approach for urban surface flood modeling
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
Bose-Hubbard model on a kagome lattice with sextic ring-exchange terms
Rousseau, Valéry G.; Tam, Ka-Ming; Jarrell, Mark; Moreno, Juana
2013-02-01
High-order ring-exchange interactions are crucial for the study of quantum fluctuations on many highly frustrated systems. A versatile and efficient quantum Monte Carlo method, which can handle finite and essentially zero temperature and canonical and grand-canonical ensembles, has long been sought. In this paper, we present an exact quantum Monte Carlo study of a model of hard-core bosons with sixth-order ring-exchange interactions on a two-dimensional kagome lattice. By using the stochastic Green function algorithm with global space-time update, we show that the system becomes unstable in the limit of large ring-exchange interactions. It undergoes a phase separation at all fillings, except at (1)/(3) and (2)/(3) fillings for which the superfluid density vanishes and an unusual mixed valence bond and charge density ordered solid is formed. This explains the universal features seen in previous studies on various different models, such as the transverse-field Ising models, on a kagome lattice near the classical limit.
Optimal implicit 2-D finite differences to model wave propagation in poroelastic media
Itzá, Reymundo; Iturrarán-Viveros, Ursula; Parra, Jorge O.
2016-08-01
Numerical modeling of seismic waves in heterogeneous porous reservoir rocks is an important tool for the interpretation of seismic surveys in reservoir engineering. We apply globally optimal implicit staggered-grid finite differences (FD) to model 2-D wave propagation in heterogeneous poroelastic media at a low-frequency range (computational cost will not be as expensive while maintaining the accuracy. Here, we compute weights for the optimal implicit FD scheme to attain an accuracy of γ = 10-8. The implicit spatial differentiation involves solving tridiagonal linear systems of equations through Thomas' algorithm.
On Spectral Laws of 2D--Turbulence in Shell Models
Frick, Peter; Aurell, Erik
1993-01-01
We consider a class of shell models of 2D-turbulence. They conserve inertially the analogues of energy and enstrophy, two quadratic forms in the shell amplitudes. Inertially conserving two quadratic integrals leads to two spectral ranges. We study in detail the one characterized by a forward cascade of enstrophy and spectrum close to Kraichnan's $k^{-3}$--law. In an inertial range over more than 15 octaves, the spectrum falls off as $k^{-3.05\\pm 0.01}$, with the same slope in all models. We i...
2D-3D Registration of CT Vertebra Volume to Fluoroscopy Projection: A Calibration Model Assessment
Directory of Open Access Journals (Sweden)
P. Bifulco
2010-01-01
Full Text Available 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.
2D-3D Registration of CT Vertebra Volume to Fluoroscopy Projection: A Calibration Model Assessment
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.
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
Comparison of 1D and 2D CSR Models with Application to the FERMI(at)ELETTRA Bunch Compressors
International Nuclear Information System (INIS)
We compare our 2D mean field (Vlasov-Maxwell) treatment of coherent synchrotron radiation (CSR) effects with 1D approximations of the CSR force which are commonly implemented in CSR codes. In our model we track particles in 4D phase space and calculate 2D forces (1). The major cost in our calculation is the computation of the 2D force. To speed up the computation and improve 1D models we also investigate approximations to our exact 2D force. As an application, we present numerical results for the Fermi(at)Elettra first bunch compressor with the configuration described in (1).
Comparison of 1D and 2D CSR Models with Application to the FERMI@ELETTRA Bunch Compressors
Energy Technology Data Exchange (ETDEWEB)
Bassi, G.; Ellison, J.A.; Heinemann, K.
2011-03-28
We compare our 2D mean field (Vlasov-Maxwell) treatment of coherent synchrotron radiation (CSR) effects with 1D approximations of the CSR force which are commonly implemented in CSR codes. In our model we track particles in 4D phase space and calculate 2D forces [1]. The major cost in our calculation is the computation of the 2D force. To speed up the computation and improve 1D models we also investigate approximations to our exact 2D force. As an application, we present numerical results for the Fermi{at}Elettra first bunch compressor with the configuration described in [1].
Methodology for Modeling 2-D Groundwater Motion in a Geographic Information System (GIS)
International Nuclear Information System (INIS)
From the mid-1950's through the 1980's, the U.S. Department of Energy's Savannah River Site (SRS) produced nuclear materials for the weapons stockpile, for medical and industrial applications, and for space exploration. A legacy of this production is groundwater contamination located near previous production sites. This contamination is comprised mainly of heavy metals, organic degreasers, and radionuclides such as tritium. To monitor this contamination, a network of more than 1000 groundwater wells has been established across SRS. As a result of this contamination, extensive remediation activities are ongoing at SRS. Modeling the 3-D flow and transport of groundwater to support these efforts is a time consuming and arduous task involving discretizing a model domain representing geological and hydrogeological surfaces, specifying appropriate boundary conditions, and calibrating the model to measured piezometric and potentiometric data. For SRS areas where the groundwater motion is essentially 2-D with negligible vertical gradients, a simplified modeling capability was developed in a GIS software framework providing the capability to simulate 2-D groundwater motion with results that could be obtained in hours, versus weeks or months often required for a full 3-D model
A solidification constitutive model for NIKE2D and NIKE3D
Energy Technology Data Exchange (ETDEWEB)
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.
Global regularity for the 2D Oldroyd-B model in the corotational case
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.
2D cellular automaton model for the evolution of active region coronal plasmas
Fuentes, Marcelo López
2016-01-01
We study a 2D cellular automaton (CA) model for the evolution of coronal loop plasmas. The model is based on the idea that coronal loops are made of elementary magnetic strands that are tangled and stressed by the displacement of their footpoints by photospheric motions. The magnetic stress accumulated between neighbor strands is released in sudden reconnection events or nanoflares that heat the plasma. We combine the CA model with the Enthalpy Based Thermal Evolution of Loops (EBTEL) model to compute the response of the plasma to the heating events. Using the known response of the XRT telescope on board Hinode we also obtain synthetic data. The model obeys easy to understand scaling laws relating the output (nanoflare energy, temperature, density, intensity) to the input parameters (field strength, strand length, critical misalignment angle). The nanoflares have a power-law distribution with a universal slope of -2.5, independent of the input parameters. The repetition frequency of nanoflares, expressed in t...
Evaluation of Hydrus-2D model for solute distribution in subsurface drip
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.
Momentum Transport: 2D and 3D Cloud Resolving Model Simulations
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.
Entanglement entropy through conformal interfaces in the 2D Ising model
Brehm, Enrico M
2015-01-01
We consider the entanglement entropy for the 2D Ising model at the conformal fixed point in the presence of interfaces. More precisely, we investigate the situation where the two subsystems are separated by a defect line that preserves conformal invariance. Using the replica trick, we compute the entanglement entropy between the two subsystems. We observe that the entropy, just like in the case without defects, shows a logarithmic scaling behavior with respect to the size of the system. Here, the prefactor of the logarithm depends on the strength of the defect encoded in the transmission coefficient. We also commend on the supersymmetric case.
A quasi 2D semianalytical model for the potential profile in hetero and homojunction tunnel FETs
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.
Verification of Numerical Modeling in 2-D Wave Propagation in Rock
Institute of Scientific and Technical Information of China (English)
LEI Wei-dong; HEFNY Ashraf; TENG Jun; ZHAO Jian; SONG Hong-wei
2005-01-01
Compressional harmonic wave propagation from a cylindrical tunnel or borehole in an intact rock is the basis for investigation of the practical explosion waves in a fractured rock mass. The amplitudes of the radial stress wave obtained from the universal distinct element code (UDEC) were compared with the analytical solutions for two cases with different conditions. Good agreements between the UDEC results and the analytical solutions have been achieved. It indicates that UDEC can model 2-D dynamic problems at a high degree of accuracy.
Fusion of Critical Defect Lines in the 2D Ising Model
Bachas, Costas; Brunner, Ilka; Roggenkamp, Daniel
2013-01-01
Two defect lines separated by a distance delta look from much larger distances like a single defect. In the critical theory, when all scales are large compared to the cutoff scale, this fusion of defect lines is universal. We calculate the universal fusion rule in the critical 2D Ising model and show that it is given by the Verlinde algebra of primary fields, combined with group multiplication in O(1,1)/Z_2. Fusion is in general singular and requires the subtraction of a divergent Casimir ene...
Image restoration using 2D autoregressive texture model and structure curve construction
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.
Directory of Open Access Journals (Sweden)
Debora Finocchio
2014-02-01
Full Text Available The Altotiberina low-angle normal fault in central Italy has been a focus of many recent studies. Although the existence of this fault has long been known, its seismicity and relationship to other faults are still debated. We present a 2D elastoplastic finite-element model that reproduces the interseismic deformation of the Altotiberina Fault. The model predictions are compared to observed geodetic velocities, stress orientations and geological data. The influence of the Altotiberina Fault on interseismic evolution is tested by building several models with different boundary conditions. The best model is 180 km long, 40 km deep and contains two layers with different rheological parameters, two ramps, two faults and four freely slipping segments. The main factors contributing to the large-scale interseismic deformation include basal traction, rheology and the Altotiberina Fault itself, whereas the local, small-scale variations are due to two secondary high-angle faults.
Improving object detection in 2D images using a 3D world model
Viggh, Herbert E. M.; Cho, Peter L.; Armstrong-Crews, Nicholas; Nam, Myra; Shah, Danelle C.; Brown, Geoffrey E.
2014-05-01
A mobile robot operating in a netcentric environment can utilize offboard resources on the network to improve its local perception. One such offboard resource is a world model built and maintained by other sensor systems. In this paper we present results from research into improving the performance of Deformable Parts Model object detection algorithms by using an offboard 3D world model. Experiments were run for detecting both people and cars in 2D photographs taken in an urban environment. After generating candidate object detections, a 3D world model built from airborne Light Detection and Ranging (LIDAR) and aerial photographs was used to filter out false alarm using several types of geometric reasoning. Comparison of the baseline detection performance to the performance after false alarm filtering showed a significant decrease in false alarms for a given probability of detection.
Quasi 2D hydrodynamic modelling of the flooded hinterland due to dyke breaching on the Elbe River
Directory of Open Access Journals (Sweden)
S. Huang
2007-01-01
Full Text Available In flood modeling, many 1D and 2D combination and 2D models are used to simulate diversion of water from rivers through dyke breaches into the hinterland for extreme flood events. However, these models are too demanding in data requirements and computational resources which is an important consideration when uncertainty analysis using Monte Carlo techniques is used to complement the modeling exercise. The goal of this paper is to show the development of a quasi-2D modeling approach, which still calculates the dynamic wave in 1D but the discretisation of the computational units are in 2D, allowing a better spatial representation of the flow in the hinterland due to dyke breaching without a large additional expenditure on data pre-processing and computational time. A 2D representation of the flow and velocity fields is required to model sediment and micro-pollutant transport. The model DYNHYD (1D hydrodynamics from the WASP5 modeling package was used as a basis for the simulations. The model was extended to incorporate the quasi-2D approach and a Monte-Carlo Analysis was used to conduct a flood sensitivity analysis to determine the sensitivity of parameters and boundary conditions to the resulting water flow. An extreme flood event on the Elbe River, Germany, with a possible dyke breach area was used as a test case. The results show a good similarity with those obtained from another 1D/2D modeling study.
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.
Stochastic dynamics of phase singularities under ventricular fibrillation in 2D Beeler-Reuter model
Directory of Open Access Journals (Sweden)
Akio Suzuki
2011-09-01
Full Text Available 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.
Self-Organization in 2D Traffic Flow Model with Jam-Avoiding Drive
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.
EDGE2D modelling of edge profiles obtained in JET diagnostic optimized configuration
Energy Technology Data Exchange (ETDEWEB)
Kallenbach, A [MPI fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany); Andrew, Y [EURATOM/UKAEA Fusion Association, Culham (United Kingdom); Beurskens, M [FOM-Rijnhuizen, Ass. Euratom-FOM, TEC (Netherlands); Corrigan, G [EURATOM/UKAEA Fusion Association, Culham (United Kingdom); Eich, T [MPI fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany); Jachmich, S [ERM, Brussels (Belgium); Kempenaars, M [FOM-Rijnhuizen, Ass. Euratom-FOM, TEC (Netherlands); Korotkov, A [EURATOM/UKAEA Fusion Association, Culham (United Kingdom); Loarte, A [EFDA Close Support Unit, Garching (Germany); Matthews, G [EURATOM/UKAEA Fusion Association, Culham (United Kingdom); Monier-Garbet, P [CEA Cadarache (France); Saibene, G [EFDA Close Support Unit, Garching (Germany); Spence, J [EURATOM/UKAEA Fusion Association, Culham (United Kingdom); Suttrop, W [MPI fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany)
2004-03-01
Nine type-I ELMy H-mode discharges in diagnostic optimized configuration in JET are analysed with the EDGE2D/NIMBUS package. EDGE2D solves the fluid equations for the conservation of particles, momentum and energy for hydrogenic and impurity ions, while neutrals are followed with the two-dimensional Monte Carlo module NIMBUS. Using external boundary conditions from the experiment, the perpendicular heat conductivities {chi}{sub i,e} and the particle transport coefficients D, v are varied until good agreement between code result and measured data is obtained. A step-like ansatz is used for the edge transport parameters for the outer core region, the edge transport barrier and the outer scrape-off layer. The time-dependent effect of edge localized modes on the edge profiles is simulated with an ad hoc ELM model based on the repetitive increase of the transport coefficients {chi}{sub i,e} and D. The values of the transport coefficients are matched to experimental data mapped to the outer midplane, in the course of which radial shifts of experimental profiles of the order of 1 cm caused by the accuracy limit of the equilibrium reconstruction are taken into account. Simulated divertor profiles obtained from the upstream transport ansatz and the experimental boundary conditions agree with measurements, except a small region localized at the separatrix strike points which is supposed to be affected by direct ion losses. The integrated analysis using EDGE2D modelling, although still limited by the marginal spatial resolution of individual diagnostics, allows the characterization of profiles in the edge/pedestal region and supplies additional information on the separatrix position. The steep density gradient zone inside the separatrix shrinks compared to the electron temperature with increasing density, indicating the effect of the neutral penetration depth becoming shorter than the region of reduced transport.
International Nuclear Information System (INIS)
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. (paper)
Assessing soil fluxes using meteoric 10Be: development and application of the Be2D model
Campforts, Benjamin; Govers, Gerard; Vanacker, Veerle; Baken, Stijn; Smolders, Erik; Vanderborght, Jan
2015-04-01
Meteoric 10Be is a promising and increasingly popular tool to better understand soil fluxes at different timescales. Unlike other, more classical, methods such as the study of sedimentary archives it enables a direct coupling between eroding and deposition sites. However, meteoric 10Be can be mobilized within the soil. Therefore, spatial variations in meteoric 10Be inventories cannot directly be translated into spatial variations in erosion and sedimentation rates: a correct interpretation of measured 10Be inventories requires that both lateral and vertical movement of meteoric 10Be are accounted for. Here, we present a spatially explicit 2D model that allows to simulate the behaviour of meteoric 10Be in the soil system over timescales of up to 1 million year and use the model to investigate the impact of accelerated erosion on meteoric 10Be inventories. The model consists of two parts. A first component deals with advective and diffusive mobility within the soil profile, whereas a second component describes lateral soil (and meteoric 10Be) fluxes over the hillslope. Soil depth is calculated dynamically, accounting for soil production through weathering and lateral soil fluxes. Different types of erosion such as creep, water and tillage erosion are supported. Model runs show that natural soil fluxes can be well reconstructed based on meteoric 10Be inventories, and this for a wide range of geomorphological and pedological conditions. However, extracting signals of human impact and distinguishing them from natural soil fluxes is only feasible when the soil has a rather high retention capacity so that meteoric 10Be is retained in the top soil layer. Application of the Be2D model to an existing data set in the Appalachian Mountains [West et al.,2013] using realistic parameter values for the soil retention capacity as well as for vertical advection resulted in a good agreement between simulated and observed 10Be inventories. This confirms the robustness of the model. We
Boontian, Nittaya
2012-01-01
Carbon sources are considered as one of the most important factors in the performance of enhanced biological phosphorus removal (EBPR). Disintegrated sludge (DS) can act as carbon source to increase the efficiency of EBPR. This research explores the influence of DS upon phosphorus removal efficiency using mathematical simulation modeling. Activated Sludge Model No. 2d (ASM2d) is one of the most useful of activated sludge (AS) models. This is because ASM2d can express the integrated mechanisms...
A coupled $2\\times2$D Babcock-Leighton solar dynamo model. II. Reference dynamo solutions
Lemerle, Alexandre
2016-01-01
In this paper we complete the presentation of a new hybrid $2\\times2$D flux transport dynamo (FTD) model of the solar cycle based on the Babcock-Leighton mechanism of poloidal magnetic field regeneration via the surface decay of bipolar magnetic regions (BMRs). This hybrid model is constructed by allowing the surface flux transport (SFT) simulation described in Lemerle et al. 2015 to provide the poloidal source term to an axisymmetric FTD simulation defined in a meridional plane, which in turn generates the BMRs required by the SFT. A key aspect of this coupling is the definition of an emergence function describing the probability of BMR emergence as a function of the spatial distribution of the internal axisymmetric magnetic field. We use a genetic algorithm to calibrate this function, together with other model parameters, against observed cycle 21 emergence data. We present a reference dynamo solution reproducing many solar cycle characteristics, including good hemispheric coupling, phase relationship betwe...
Numerical Modelling of Drug Release from 2D HPMC-Matrices
Directory of Open Access Journals (Sweden)
Rumiana Blagoeva
2009-08-01
Full Text Available The article considers numerical modelling of drug release from HPMC-matrices assuming the main controlling processes are diffusion of water and drug and swelling of the matrix. A detailed mathematical description of matrix swelling, connected with the free boundary conditions of the arisen model problem, is introduced. A numerical approach to solution of the posed nonlinear 2D problem is developed on the basis of finite element domain approximation and time difference method. It is implemented in noncommercial software which is used for numerical simulation of fractional drug release under various shapes and sizes of the tablets. This investigation of the effect of aspect ratio (radius/height and sizes of HPMC tablets on drug release is an inexpensive and effective tool to modify the release kinetics. The proposed numerical approach enables further generalization of the model and performing more profound investigations of the effect of the initial drug loading, matrix erosion and type of release medium.
Well-posedness and generalized plane waves simulations of a 2D mode conversion model
Imbert-Gérard, Lise-Marie
2015-01-01
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.
2-D IMAGE-BASED VOLUMETRIC MODELING FOR PARTICLE OF RANDOM SHAPE
Institute of Scientific and Technical Information of China (English)
Chen Ken; Larry E. Banta; Jiang Gangyi
2006-01-01
In this paper, an approach to predicting randomly-shaped particle volume based on its twoDimensional (2-D) digital image is explored. Conversion of gray-scale image of the particles to its binary counterpart is first performed using backlighting technique. The silhouette of particle is thus obtained, and consequently, informative features such as particle area, centroid and shape-related descriptors are collected. Several dimensionless parameters are defined, and used as regressor variables in a multiple linear regression model to predict particle volume. Regressor coefficients are found by fitting to a randomly selected sample of 501 particles ranging in size from 4.75mm to 25mm. The model testing experiment is conducted against a different aggregate sample of the similar statistical properties, the errors of the model-predicted volume of the batch is within ±2%.
Uncertainties in modelling Mt. Pinatubo eruption with 2-D AER model and CCM SOCOL
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
Modeling floods in a dense urban area using 2D shallow water equations
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.
Interpretation of gravity data using 2-D continuous wavelet transformation and 3-D inverse modeling
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.
Locally adaptive 2D-3D registration using vascular structure model for liver catheterization.
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
A Bayesian approach to modeling 2D gravity data using polygon states
Titus, W. J.; Titus, S.; Davis, J. R.
2015-12-01
We present a Bayesian Markov chain Monte Carlo (MCMC) method for the 2D gravity inversion of a localized subsurface object with constant density contrast. Our models have four parameters: the density contrast, the number of vertices in a polygonal approximation of the object, an upper bound on the ratio of the perimeter squared to the area, and the vertices of a polygon container that bounds the object. Reasonable parameter values can be estimated prior to inversion using a forward model and geologic information. In addition, we assume that the field data have a common random uncertainty that lies between two bounds but that it has no systematic uncertainty. Finally, we assume that there is no uncertainty in the spatial locations of the measurement stations. For any set of model parameters, we use MCMC methods to generate an approximate probability distribution of polygons for the object. We then compute various probability distributions for the object, including the variance between the observed and predicted fields (an important quantity in the MCMC method), the area, the center of area, and the occupancy probability (the probability that a spatial point lies within the object). In addition, we compare probabilities of different models using parallel tempering, a technique which also mitigates trapping in local optima that can occur in certain model geometries. We apply our method to several synthetic data sets generated from objects of varying shape and location. We also analyze a natural data set collected across the Rio Grande Gorge Bridge in New Mexico, where the object (i.e. the air below the bridge) is known and the canyon is approximately 2D. Although there are many ways to view results, the occupancy probability proves quite powerful. We also find that the choice of the container is important. In particular, large containers should be avoided, because the more closely a container confines the object, the better the predictions match properties of object.
Be2D: A model to understand the distribution of meteoric 10Be in soilscapes
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
Estimating nitrogen losses in furrow irrigated soil amended by compost using HYDRUS-2D model
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
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.
On Spectral Laws of 2D-Turbulence in Shell Models
Frick, P; Frick, Peter; Aurell, Erik
1993-01-01
We consider a class of shell models of 2D-turbulence. They conserve inertially the analogues of energy and enstrophy, two quadratic forms in the shell amplitudes. Inertially conserving two quadratic integrals leads to two spectral ranges. We study in detail the one characterized by a forward cascade of enstrophy and spectrum close to Kraichnan's $k^{-3}$--law. In an inertial range over more than 15 octaves, the spectrum falls off as $k^{-3.05\\pm 0.01}$, with the same slope in all models. We identify a ``spurious'' intermittency effect, in that the energy spectrum over a rather wide interval adjoing the viscous cut-off, is well approximated by a power-law with fall-off significantly steeper than $k^{-3}$.
2D and 3D numerical modeling of seismic waves from explosion sources
International Nuclear Information System (INIS)
Over the last decade, nonlinear and linear 2D axisymmetric finite difference codes have been used in conjunction with far-field seismic Green's functions to simulate seismic waves from a variety of sources. In this paper we briefly review some of the results and conclusions that have resulted from numerical simulations and explosion modeling in support of treaty verification research at S-CUBED in the last decade. We then describe in more detail the results from two recent projects. Our goal is to provide a flavor for the kinds of problems that can be examined with numerical methods for modeling excitation of seismic waves from explosions. Two classes of problems have been addressed; nonlinear and linear near-source interactions. In both classes of problems displacements and tractions are saved on a closed surface in the linear region and the representation theorem is used to propagate the seismic waves to the far-field
A VERTICAL 2D MATHEMATICAL MODEL FOR HYDRODYNAMIC FLOWS WITH FREE SURFACE IN σ COORDINATE
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
Numerical models with hydrostatic pressure have been widely utilized in studying flows in rivers, estuaries and coastal areas. The hydrostatic assumption is valid for the large-scale surface flows where the vertical acceleration can be ignored, but for some particular cases the hydrodynamic pressure is important. In this paper, a vertical 2D mathematical model with non-hydrostatic pressure was implemented in the σ coordinate. A fractional step method was used to enable the pressure to be decomposed into hydrostatic and hydrodynamic components and the predictor-corrector approach was applied to integration in time domain. Finally, several computational cases were studied to validate the importance of contributions of the hydrodynamic pressure.
Complex-temperature properties of the Ising model on 2D heteropolygonal lattices
Matveev, V; Matveev, Victor; Shrock, Robert
1995-01-01
Using exact results, we determine the complex-temperature phase diagrams of the 2D Ising model on three regular heteropolygonal lattices, (3 \\cdot 6 \\cdot 3 \\cdot 6) (kagom\\'{e}), (3 \\cdot 12^2), and (4 \\cdot 8^2) (bathroom tile), where the notation denotes the regular n-sided polygons adjacent to each vertex. We also work out the exact complex-temperature singularities of the spontaneous magnetisation. A comparison with the properties on the square, triangular, and hexagonal lattices is given. In particular, we find the first case where, even for isotropic spin-spin exchange couplings, the nontrivial non-analyticities of the free energy of the Ising model lie in a two-dimensional, rather than one-dimensional, algebraic variety in the z=e^{-2K} plane.
A New Material Model for 2D FE Analysis of Adhesively Bonded Composite Joints
Directory of Open Access Journals (Sweden)
Libin ZHAO
2014-12-01
Full Text Available Effective and convenient stress analysis techniques play important roles in the analysis and design of adhesively bonded composite joints. A new material model is presented at the level of composite ply according to the orthotropic elastic mechanics theory and plane strain assumption. The model proposed has the potential to reserve nature properties of laminates with ply-to-ply modeling. The equivalent engineering constants in the model are obtained only by the material properties of unidirectional composites. Based on commercial FE software ABAQUS, a 2D FE model of a single-lap adhesively bonded joint was established conveniently by using the new model without complex modeling process and much professional knowledge. Stress distributions in adhesive were compared with the numerical results by Tsai and Morton and interlaminar stresses between adhesive and adherents were compared with the results from a detailed 3D FE analysis. Good agreements in both cases verify the validity of the proposed model. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.5960
2D time-domain finite-difference modeling for viscoelastic seismic wave propagation
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.
Transforming 2d Cadastral Data Into a Dynamic Smart 3d Model
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.
The combined effect of attraction and orientation zones in 2D flocking models
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.
Time domain numerical modeling of wave propagation in 2D acoustic / porous media
Chiavassa, Guillaume
2011-01-01
Numerical methods are developed to simulate the wave propagation in 2D heterogeneous fluid / poroelastic media. Wave propagation is described by the usual acoustics equations (in the fluid medium) and by the low-frequency Biot's equations (in the porous medium). Interface conditions are introduced to model various hydraulic contacts between the two media: open pores, sealed pores, and imperfect pores. Well-possedness of the initial-boundary value problem is proven. Cartesian grid numerical methods previously developed in porous heterogeneous media are adapted to the present context: a fourth-order ADER scheme with Strang splitting for time-marching; a space-time mesh-refinement to capture the slow compressional wave predicted by Biot's theory; and an immersed interface method to discretize the interface conditions and to introduce a subcell resolution. Numerical experiments and comparisons with exact solutions are proposed for the three types of interface conditions, demonstrating the accuracy of the approach...
Transition from static to kinetic friction: Insights from a 2D model
Trømborg, Jørgen; Amundsen, David Skålid; Thøgersen, Kjetil; Malthe-Sørenssen, Anders
2013-01-01
We describe a 2D spring-block model for the transition from static to kinetic friction at an elastic slider/rigid substrate interface obeying a minimalistic friction law (Amontons-Coulomb). By using realistic boundary conditions, a number of previously unexplained experimental results on precursory micro-slip fronts are successfully reproduced. From the analysis of the interfacial stresses, we derive a prediction for the evolution of the precursor length as a function of the applied loads, as well as an approximate relationship between microscopic and macroscopic friction coefficients. We show that the stress build-up due to both elastic loading and micro-slip-related relaxations depend only weakly on the underlying shear crack propagation dynamics. Conversely, crack speed depends strongly on both the instantaneous stresses and the friction coefficients, through a non-trivial scaling parameter.
Surface delta interaction in the g7/2 - d5/2 model space
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.
Entire solutions for a mono-stable delay population model in a 2D lattice strip
Directory of Open Access Journals (Sweden)
Hai-Qin Zhao
2014-11-01
Full Text Available This article concerns the entire solutions of a mono-stable age-structured population model in a 2D lattice strip. In a previous publication, we established the existence of entire solutions related to traveling wave solutions with speeds larger than the minimal wave speed $c_{\\rm min}$. However, the existence of entire solutions related to the minimal wave fronts remains open open question. In this article, we first establish a new comparison theorem. Then, applying the theorem we obtain the existence of entire solutions by mixing any finite number of traveling wave fronts with speeds $c\\geq c_{\\rm min}$, and a solution without the $j$ variable. In particular, we show the relationship between the entire solution and the traveling wave fronts that they originate.
The strong-weak coupling symmetry in 2D Φ4 field models
Directory of Open Access Journals (Sweden)
B.N.Shalaev
2005-01-01
Full Text Available It is found that the exact beta-function β(g of the continuous 2D gΦ4 model possesses two types of dual symmetries, these being the Kramers-Wannier (KW duality symmetry and the strong-weak (SW coupling symmetry f(g, or S-duality. All these transformations are explicitly constructed. The S-duality transformation f(g is shown to connect domains of weak and strong couplings, i.e. above and below g*. Basically it means that there is a tempting possibility to compute multiloop Feynman diagrams for the β-function using high-temperature lattice expansions. The regular scheme developed is found to be strongly unstable. Approximate values of the renormalized coupling constant g* found from duality symmetry equations are in an agreement with available numerical results.
An application of the distributed hydrologic model CASC2D to a tropical montane watershed
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.
Thermochemical Nonequilibrium 2D Modeling of Nitrogen Inductively Coupled Plasma Flow
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
Field Evaluation of a Novel 2D Preferential Flow Snowpack Hydrology Model
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
A new model for two-dimensional numerical simulation of pseudo-2D gas-solids fluidized beds
Energy Technology Data Exchange (ETDEWEB)
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.
2-D Finite Difference Modeling of the D'' Structure Beneath the Eastern Cocos Plate: Part I
Helmberger, D. V.; Song, T. A.; Sun, D.
2005-12-01
The discovery of phase transition from Perovskite (Pv) to Post-Perovskite (PPv) at depth nears the lowermost mantle has revealed a new view of the earth's D'' layer (Oganov et al. 2004; Murakami et al. 2004). Hernlund et al. (2004) recently pusposed that, depending on the geotherm at the core-mantle boundary (CMB), a double-crossing of the phase boundary by the geotherm at two different depths may also occur. To explore these new findings, we adopt 2-D finite difference scheme (Helmberger and Vidale, 1988) to model wave propagation in rapidly varying structure. We collect broadband waveform data recorded by several Passcal experiments, such as La Ristra transect and CDROM transect in the southwest US to constrain the lateral variations in D'' structure. These data provide fairly dense sampling (~ 20 km) in the lowermost mantle beneath the eastern Cocos plate. Since the source-receiver paths are mostly in the same azimuth, we make 2-D cross-sections from global tomography model (Grand, 2002) and compute finite difference synthetics. We modify the lowermost mantle below 2500 km with constraints from transverse-component waveform data at epicentral distances of 70-82 degrees in the time window between S and ScS, essentially foward modeling waveforms. Assuming a velocity jump of 3 % at D'', our preferred model shows that the D'' topography deepens from the north to the south by about 120 km over a lateral distance of 300 km. Such large topography jumps have been proposed by Thomas et al. (2004) using data recorded by TriNet. In addition, there is a negative velocity jump (-3 %) 100 km above the CMB in the south. This simple model compare favorably with results from a study by Sun, Song and Helmberger (2005), who follow Sidorin et al. (1999) approach and produce a thermodynamically consistent velocity model with Pv-PPv phase boundary. It appears that much of this complexity exists in Grand's tomographic maps with rapid variation in velocities just above the D''. We also
Distributed and coupled 2D electro-thermal model of power semiconductor devices
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.
LBQ2D, Extending the Line Broadened Quasilinear Model to TAE-EP Interaction
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.
Aespoe Pillar Stability Experiment. Final 2D coupled thermo-mechanical modelling
International Nuclear Information System (INIS)
A site scale Pillar Stability Experiment is planned in the Aespoe Hard Rock Laboratory. One of the experiment's aims is to demonstrate the possibilities of predicting spalling in the fractured rock mass. In order to investigate the probability and conditions for spalling in the pillar 'prior to experiment' numerical simulations have been undertaken. This report presents the results obtained from 2D coupled thermo-mechanical numerical simulations that have been done with the Finite Element based programme JobFem. The 2D numerical simulations were conducted at two different depth levels, 0.5 and 1.5 m below tunnel floor. The in situ stresses have been confirmed with convergence measurements during the excavation of the tunnel. After updating the mechanical and thermal properties of the rock mass the final simulations have been undertaken. According to the modelling results the temperature in the pillar will increase from the initial 15.2 deg up to 58 deg after 120 days of heating. Based on these numerical simulations and on the thermal induced stresses the total stresses are expected to exceed 210 MPa at the border of the pillar for the level at 0.5 m below tunnel floor and might reach 180-182 MPa for the level at 1.5 m below tunnel floor. The stresses are slightly higher at the border of the confined hole. Upon these results and according to the rock mechanical properties the Crack Initiation Stress is exceeded at the border of the pillar already after the excavation phase. These results also illustrate that the Crack Damage Stress is exceeded only for the level at 0.5 m below tunnel floor and after at least 80 days of heating. The interpretation of the results shows that the required level of stress for spalling can be reached in the pillar
Zegrodnik, Michał
2015-02-01
Universal aspects of the Hund's rule induced spin-triplet pairing are analysed within the two-band Hubbard model on a square lattice. According to our calculations, this pairing mechanism in conjunction with the correlation effect can result in stability of the paired phase in the so-called purely repulsive interactions regime, in which there is no effectively attractive interaction. Furthermore, even though all of the interaction terms are of intrasite character, the pairing contains both intra- and inter-site components. In effect, the gap parameter has a mixture of s-wave and extended s-wave symmetries. The calculations have been carried out with the use of the Statistically Consistent Gutzwiller Approximation developed by us in recent years.
2d Affine XY-Spin Model/4d Gauge Theory Duality and Deconfinement
Energy Technology Data Exchange (ETDEWEB)
Anber, Mohamed M.; Poppitz, Erich; /Toronto U.; 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.
Field-induced magnetization jumps and quantum criticality in the 2D J-Q model
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.
On the assimilation of SWOT type data into 2D shallow-water models
Frédéric, Couderc; Denis, Dartus; Pierre-André, Garambois; Ronan, Madec; Jérôme, Monnier; Jean-Paul, Villa
2013-04-01
In river hydraulics, assimilation of water level measurements at gauging stations is well controlled, while assimilation of images is still delicate. In the present talk, we address the richness of satellite mapped information to constrain a 2D shallow-water model, but also related difficulties. 2D shallow models may be necessary for small scale modelling in particular for low-water and flood plain flows. Since in both cases, the dynamics of the wet-dry front is essential, one has to elaborate robust and accurate solvers. In this contribution we introduce robust second order, stable finite volume scheme [CoMaMoViDaLa]. Comparisons of real like tests cases with more classical solvers highlight the importance of an accurate flood plain modelling. A preliminary inverse study is presented in a flood plain flow case, [LaMo] [HoLaMoPu]. As a first step, a 0th order data processing model improves observation operator and produces more reliable water level derived from rough measurements [PuRa]. Then, both model and flow behaviours can be better understood thanks to variational sensitivities based on a gradient computation and adjoint equations. It can reveal several difficulties that a model designer has to tackle. Next, a 4D-Var data assimilation algorithm used with spatialized data leads to improved model calibration and potentially leads to identify river discharges. All the algorithms are implemented into DassFlow software (Fortran, MPI, adjoint) [Da]. All these results and experiments (accurate wet-dry front dynamics, sensitivities analysis, identification of discharges and calibration of model) are currently performed in view to use data from the future SWOT mission. [CoMaMoViDaLa] F. Couderc, R. Madec, J. Monnier, J.-P. Vila, D. Dartus, K. Larnier. "Sensitivity analysis and variational data assimilation for geophysical shallow water flows". Submitted. [Da] DassFlow - Data Assimilation for Free Surface Flows. Computational software http
2D spectral element modeling of GPR wave propagation in inhomogeneous media
Zarei, Sajad; Oskooi, Behrooz; Amini, Navid; Dalkhani, Amin Rahimi
2016-10-01
We present a spectral element method, for simulation of ground-penetrating radar (GPR) in two dimensions. The technique is based upon a weak formulation of the equations of Maxwell and combines the flexibility of the elemental-based methods with the accuracy of the spectral based methods. The wave field on the elements is discretized using high-degree Lagrange interpolation and integration over an element is accomplished based upon the Gauss-Lobatto-Legendre integration rule. As a result, the mass matrix and the damping matrix are always diagonal, which drastically reduces the computational cost. We first develop the formulation of 2D spectral element method (SEM) in the time-domain based on Maxwell's equations. The presented formulation is with matrix notation that simplifies the implementation of the relations in computer programs, especially in MATLAB application. We discuss the differences between spectral element method and finite-element method in the time-domain. Also, we show that the SEM numerical dispersion is much lower than FEM. To absorb waves at the edges of the modeling domain, we implement first order Clayton and Engquist absorbing boundary conditions (CE-ABC) introduced in numerical finite-difference modeling of seismic wave propagation. We used the SEM to simulate a complex model to show its abilities and limitations. As well as, one distinct advantage of SEM is that we can easily define our model features in nodal points, because the integration points and the interpolation points are similar that makes it very flexible in simulation of complex models.
BEYOND FLOOD HAZARD MAPS: DETAILED FLOOD CHARACTERIZATION WITH REMOTE SENSING, GIS AND 2D MODELLING
Directory of Open Access Journals (Sweden)
J. R. Santillan
2016-09-01
Full Text Available Flooding is considered to be one of the most destructive among many natural disasters such that understanding floods and assessing the risks associated to it are becoming more important nowadays. In the Philippines, Remote Sensing (RS and Geographic Information System (GIS are two main technologies used in the nationwide modelling and mapping of flood hazards. Although the currently available high resolution flood hazard maps have become very valuable, their use for flood preparedness and mitigation can be maximized by enhancing the layers of information these maps portrays. In this paper, we present an approach based on RS, GIS and two-dimensional (2D flood modelling to generate new flood layers (in addition to the usual flood depths and hazard layers that are also very useful in flood disaster management such as flood arrival times, flood velocities, flood duration, flood recession times, and the percentage within a given flood event period a particular location is inundated. The availability of these new layers of flood information are crucial for better decision making before, during, and after occurrence of a flood disaster. The generation of these new flood characteristic layers is illustrated using the Cabadbaran River Basin in Mindanao, Philippines as case study area. It is envisioned that these detailed maps can be considered as additional inputs in flood disaster risk reduction and management in the Philippines.
A 2D Mathematical Model for Sediment Transport by Waves and Tidal Currents
Institute of Scientific and Technical Information of China (English)
LU Yong-jun; ZUO Li-qin; SHAO Xue-jun; WANG Hong-chuan; LI Hao-lin
2005-01-01
In this study, the combined actions of waves and tidal currents in estuarine and coastal areas are considered and a 2D mathematical model for sediment transport by waves and tidal currents has been established in orthogonal curvilinear coordinates. Non-equilibrium transport equations of suspended load and bed load are used in the model. The concept of background concentration is introduced, and the formula of sediment transport capacity of tidal currents for the Oujiang River estuary is obtained. The Dou Guoren formula is employed for the sediment transport capacity of waves. Sediment transport capacity in the form of mud and the intensity of back silting are calculated by use of Luo Zaosen's formula. The calculated tidal stages are in good agreement with the field data, and the calculated velocities and flow directions of 46 vertical lines for 8 cross sections are also in good agreement with the measured data. On such a basis, simulations of back silting after excavation of the waterway with a sand bar under complicated boundary conditions in the navigation channel induced by suspended load, bed load and mud by waves and tidal currents are discussed.
Basic Brackets of a 2D Model for the Hodge Theory Without its Canonical Conjugate Momenta
Kumar, R.; Gupta, S.; Malik, R. P.
2016-06-01
We deduce the canonical brackets for a two (1+1)-dimensional (2D) free Abelian 1-form gauge theory by exploiting the beauty and strength of the continuous symmetries of a Becchi-Rouet-Stora-Tyutin (BRST) invariant Lagrangian density that respects, in totality, six continuous symmetries. These symmetries entail upon this model to become a field theoretic example of Hodge theory. Taken together, these symmetries enforce the existence of exactly the same canonical brackets amongst the creation and annihilation operators that are found to exist within the standard canonical quantization scheme. These creation and annihilation operators appear in the normal mode expansion of the basic fields of this theory. In other words, we provide an alternative to the canonical method of quantization for our present model of Hodge theory where the continuous internal symmetries play a decisive role. We conjecture that our method of quantization is valid for a class of field theories that are tractable physical examples for the Hodge theory. This statement is true in any arbitrary dimension of spacetime.
Numerical analysis using 2D modeling of optical fiber poled by induction
Huang, D.; De Lucia, F.; Corbari, C.; Healy, N.; Sazio, P. J. A.
2016-03-01
Thermal poling, a technique to introduce effective second-order nonlinearities in silica optical fibers, has found widespread applications in frequency conversion, electro-optic modulation, switching and polarization-entangled photon pair generation. Since its first demonstration around 25 years ago, studies into thermal poling were primarily based on anode-cathode electrode configurations. However, more recently, superior electrode configurations have been investigated that allow for robust and reliable thermally poled fibers with excellent second order nonlinear properties [1, 2]. Very recently, we experimentally demonstrated an electrostatic induction poling technique that creates a stable second-order nonlinearity in a twin-hole fiber without any direct physical contact to internal fiber electrodes whatsoever [3]. This innovative technique lifts a number of restrictions on the use of complex microstructured optical fibers (MOF) for poling, as it is no longer necessary to individually contact internal electrodes and presents a general methodology for selective liquid electrode filling of complex MOF geometries. In order to systematically implement these more advanced device embodiments, it is first necessary to develop comprehensive numerical models of the induction poling mechanism itself. To this end, we have developed two-dimensional (2D) simulations of space-charge region formation using COMSOL finite element analysis, by building on current numerical models [4].
Risk zone of wrack hitting marine structure simulated by 2D hydraulic model
Institute of Scientific and Technical Information of China (English)
MA Jin-rong; GUO Ya-qiong; NAN Wei
2010-01-01
The wrack or the ship out of control will drift with flow.One of the most important factors that drive the ship is flow current which moves circularly in tidal area.The wrack from same place always drifts in different ways if the start time is different.So,during the ship drifting period,the drift trace is also determined by both wave and wind forces.The drift direction is limited by water depth which must be deeper than ship draft.These marine structures that can not afford the hit of wrack or will destroy the wrack must be well considered when they are placed near harbor and waterway or other water area with ship running.The risk zone should be consulted according to tide and weather conditions to protect structures and ships in necessary.A method is presented here to simulate the risk zone by 2D numerical hydraulic model with tidal current,wave,wind and water depth considered.This model can be used to built early-warning and protect system for special maline structure.
Multi-GPU Accelerated Multi-Spin Monte Carlo Simulations of the 2D Ising Model
Block, Benjamin; Preis, Tobias; 10.1016/j.cpc.2010.05.005
2010-01-01
A modern graphics processing unit (GPU) is able to perform massively parallel scientific computations at low cost. We extend our implementation of the checkerboard algorithm for the two dimensional Ising model [T. Preis et al., J. Comp. Phys. 228, 4468 (2009)] in order to overcome the memory limitations of a single GPU which enables us to simulate significantly larger systems. Using multi-spin coding techniques, we are able to accelerate simulations on a single GPU by factors up to 35 compared to an optimized single Central Processor Unit (CPU) core implementation which employs multi-spin coding. By combining the Compute Unified Device Architecture (CUDA) with the Message Parsing Interface (MPI) on the CPU level, a single Ising lattice can be updated by a cluster of GPUs in parallel. For large systems, the computation time scales nearly linearly with the number of GPUs used. As proof of concept we reproduce the critical temperature of the 2D Ising model using finite size scaling techniques.
Beyond Flood Hazard Maps: Detailed Flood Characterization with Remote Sensing, GIS and 2d Modelling
Santillan, J. R.; Marqueso, J. T.; Makinano-Santillan, M.; Serviano, J. L.
2016-09-01
Flooding is considered to be one of the most destructive among many natural disasters such that understanding floods and assessing the risks associated to it are becoming more important nowadays. In the Philippines, Remote Sensing (RS) and Geographic Information System (GIS) are two main technologies used in the nationwide modelling and mapping of flood hazards. Although the currently available high resolution flood hazard maps have become very valuable, their use for flood preparedness and mitigation can be maximized by enhancing the layers of information these maps portrays. In this paper, we present an approach based on RS, GIS and two-dimensional (2D) flood modelling to generate new flood layers (in addition to the usual flood depths and hazard layers) that are also very useful in flood disaster management such as flood arrival times, flood velocities, flood duration, flood recession times, and the percentage within a given flood event period a particular location is inundated. The availability of these new layers of flood information are crucial for better decision making before, during, and after occurrence of a flood disaster. The generation of these new flood characteristic layers is illustrated using the Cabadbaran River Basin in Mindanao, Philippines as case study area. It is envisioned that these detailed maps can be considered as additional inputs in flood disaster risk reduction and management in the Philippines.
DEFF Research Database (Denmark)
Antonsson, Arni Valur; Nguyen, Frederic; Engesgaard, Peter Knudegaard;
to calibrate a 2D synthetic seawater intrusion model. A vertical 2D density-dependent flow and transport model was established for a synthetic coastal aquifer in order to simulate saltwater intrusion. All the relevant hydraulic parameters applied in the model were given realistic values. The result...... of the synthetic model, basically a salinity distribution in the coastal aquifer, was converted to resistivity distribution by assuming a certain petrophysical relation between water salinity and electrical conductivity. The obtained resistivity distribution was then used when electrical data acquisition...
Hammer, Manfred; Honsa, R.; Richter, L.
2003-01-01
Superpositions of two perpendicularly oriented bidirectional eigenmode propagation (BEP) fields, composed of basis modes that satisfy Dirichlet boundary conditions, can establish rigorous semianalytical solutions for problems of 2-D fixed-frequency wave propagation on unbounded, cross-shaped domains
Two-dimensional (2-D) pellet-cladding modelling using fem at NRI rex PLC
International Nuclear Information System (INIS)
The method and calculation results of 2-D (r-z) and 2-D (r-φ) contact elasto-thermal solutions of pellet-cladding configuration are presented. Calculations were performed with coupled thermal and mechanical methods with inner sources and appropriate material properties dependent on temperature. Preliminary results of those simulations will be appropriate for advanced Russian TVEL fuel geometry recently delivered to the Dukovany NPP. Validation on experiment will be the subject of further work. (authors)
Modeling of two-storey precast school building using Ruaumoko 2D program
Energy Technology Data Exchange (ETDEWEB)
Hamid, N. H.; Tarmizi, L. H.; Ghani, K. D. [Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor (Malaysia)
2015-05-15
The long-distant earthquake loading from Sumatra and Java Island had caused some slight damages to precast and reinforced concrete buildings in West Malaysia such as cracks on wall panels, columns and beams. Subsequently, the safety of existing precast concrete building is needed to be analyzed because these buildings were designed using BS 8110 which did not include the seismic loading in the design. Thus, this paper emphasizes on the seismic performance and dynamic behavior of precast school building constructed in Malaysia under three selected past earthquakes excitations ; El Centro 1940 North-South, El Centro East-West components and San Fernando 1971 using RUAUMOKO 2D program. This program is fully utilized by using prototype precast school model and dynamic non-linear time history analysis. From the results, it can be concluded that two-storey precast school building has experienced severe damage and partial collapse especially at beam-column joint under San Fernando and El Centro North-South Earthquake as its exceeds the allowable inter-storey drift and displacement as specified in Eurocode 8. The San Fernando earthquake has produced a massive destruction to the precast building under viscous damping, ξ = 5% and this building has generated maximum building displacement of 435mm, maximum building drift of 0.68% and maximum bending moment at 8458kNm.
2D BEM modeling of a singular thermal diffusion free boundary problem with phase change
Nikolayev, Vadim
2016-01-01
We report a 2D Boundary Element Method (BEM) modeling of the thermal diffusion-controlled growth of a vapor bubble attached to a heating surface during saturated pool boiling. The transient heat conduction problem is solved in a liquid that surrounds a bubble with a free boundary and in a semi-infinite solid heater. The heat generated homogeneously in the heater causes evaporation, i. e. the bubble growth. A singularity exists at the point of the triple (liquid-vapor-solid) contact. At high system pressure the bubble is assumed to grow slowly, its shape being defined by the surface tension and the vapor recoil force, a force coming from the liquid evaporating into the bubble. It is shown that at some typical time the dry spot under the bubble begins to grow rapidly under the action of the vapor recoil. Such a bubble can eventually spread into a vapor film that can separate the liquid from the heater, thus triggering the boiling crisis (Critical Heat Flux phenomenon).
GPU computing with OpenCL to model 2D elastic wave propagation: exploring memory usage
Iturrarán-Viveros, Ursula; Molero-Armenta, Miguel
2015-01-01
Graphics processing units (GPUs) have become increasingly powerful in recent years. Programs exploring the advantages of this architecture could achieve large performance gains and this is the aim of new initiatives in high performance computing. The objective of this work is to develop an efficient tool to model 2D elastic wave propagation on parallel computing devices. To this end, we implement the elastodynamic finite integration technique, using the industry open standard open computing language (OpenCL) for cross-platform, parallel programming of modern processors, and an open-source toolkit called [Py]OpenCL. The code written with [Py]OpenCL can run on a wide variety of platforms; it can be used on AMD or NVIDIA GPUs as well as classical multicore CPUs, adapting to the underlying architecture. Our main contribution is its implementation with local and global memory and the performance analysis using five different computing devices (including Kepler, one of the fastest and most efficient high performance computing technologies) with various operating systems.
A 2D MODELLING OF THERMAL HEAT SINK FOR IMPATT AT HIGH POWER MMW FREQUENCY
Directory of Open Access Journals (Sweden)
Sohom Kumar Mitra
2013-02-01
Full Text Available A very useful method of formulating the Total Thermal Resistance of ordinary mesa structure of DDR IMPATT diode oscillators are presented in this paper. The main aim of this paper is to provide a 2D model for Si and SiC based IMPATT having different heat sinks (Type IIA diamond and copper at high power MMW frequency and study the characteristics of Total thermal resistance versus diode diameter for both the devices. Calculations of Total thermal resistances associated with different DDR IMPATT diodes with different base materials operating at 94 GHz (W-Band are included in this paper using the author’s developed formulation for both type-IIA diamond and copper semi-infinite heat sinks separately. Heat Sinks are designed using both type-IIA diamond and copper for all those diodes to operate near 500 K (which is well below the burn-out temperatures of all those base materials for CW steady state operation. Results are provided in the form of necessary graphs and tables.
Modeling of two-storey precast school building using Ruaumoko 2D program
International Nuclear Information System (INIS)
The long-distant earthquake loading from Sumatra and Java Island had caused some slight damages to precast and reinforced concrete buildings in West Malaysia such as cracks on wall panels, columns and beams. Subsequently, the safety of existing precast concrete building is needed to be analyzed because these buildings were designed using BS 8110 which did not include the seismic loading in the design. Thus, this paper emphasizes on the seismic performance and dynamic behavior of precast school building constructed in Malaysia under three selected past earthquakes excitations ; El Centro 1940 North-South, El Centro East-West components and San Fernando 1971 using RUAUMOKO 2D program. This program is fully utilized by using prototype precast school model and dynamic non-linear time history analysis. From the results, it can be concluded that two-storey precast school building has experienced severe damage and partial collapse especially at beam-column joint under San Fernando and El Centro North-South Earthquake as its exceeds the allowable inter-storey drift and displacement as specified in Eurocode 8. The San Fernando earthquake has produced a massive destruction to the precast building under viscous damping, ξ = 5% and this building has generated maximum building displacement of 435mm, maximum building drift of 0.68% and maximum bending moment at 8458kNm
2D and 3D multipactor modeling in dielectric-loaded accelerator structures
Sinitsyn, Oleksandr; Nusinovich, Gregory; Antonsen, Thomas
2010-11-01
Multipactor (MP) is known as the avalanche growth of the number of secondary electrons emitted from a solid surface exposed to an RF electric field under vacuum conditions. MP is a severe problem in modern rf systems and, therefore, theoretical and experimental studies of MP are of great interest to the researchers working in various areas of physics and engineering. In this work we present results of MP studies in dielectric-loaded accelerator (DLA) structures. First, we show simulation results obtained with the use of the 2D self-consistent MP model (O. V. Sinitsyn, et. al., Phys. Plasmas, vol. 16, 073102 (2009)) and compare those to experimental ones obtained during recent extensive studies of DLA structures performed by Argonne National Laboratory, Naval Research Laboratory, SLAC National Accelerator Laboratory and Euclid TechLabs (C. Jing, et al., IEEE Trans. Plasma Sci., vol. 38, pp. 1354-1360 (2010)). Then we present some new results of 3D analysis of MP which include studies of particle trajectories and studies of MP development at the early stage.
Real-time thermal field theory analyses of 2D Gross-Neveu model
Bang-Rong, Z
2000-01-01
Discrete symmetry breaking and possible restoration at finite temperature $T$ are analysed in 2D Gross-Neveu model by the real-time thermal field theory in the fermion bubble approximation. The dynamical fermion mass $m$ is proven to be scale-independent and this fact indicates the equivalence between the fermion bubble diagram approximation and the mean field approximation used in the auxialiary scalar field approach. Reproducing of the non-zero critical temperature $T_c=0.567 m(0)$, ($m(0)$ is the dynamical fermion mass at T=0), shows the equivalence between the real-time and the imaginary-time thermal field theory in this problem. However, in the real-time formalism, more results including absence of scalar bound state, the equation of criticality curve of chemical potential-temperature and the $\\ln(T_c/T)$ behavior of $m^2$ at $T\\stackrel{<}{\\sim} T_c$ can be easily obtained. The last one indicates the second-order phase transition feature of the symmetry restoration.
Straatsma, Menno; Huthoff, Fredrik
2011-01-01
In The Netherlands, 2D-hydrodynamic simulations are used to evaluate the effect of potential safety measures against river floods. In the investigated scenarios, the floodplains are completely inundated, thus requiring realistic representations of hydraulic roughness of floodplain vegetation. The current study aims at providing better insight into the uncertainty of flood water levels due to uncertain floodplain roughness parameterization. The study focuses on three key elements in the uncertainty of floodplain roughness: (1) classification error of the landcover map, (2), within class variation of vegetation structural characteristics, and (3) mapping scale. To assess the effect of the first error source, new realizations of ecotope maps were made based on the current floodplain ecotope map and an error matrix of the classification. For the second error source, field measurements of vegetation structure were used to obtain uncertainty ranges for each vegetation structural type. The scale error was investigated by reassigning roughness codes on a smaller spatial scale. It is shown that classification accuracy of 69% leads to an uncertainty range of predicted water levels in the order of decimeters. The other error sources are less relevant. The quantification of the uncertainty in water levels can help to make better decisions on suitable flood protection measures. Moreover, the relation between uncertain floodplain roughness and the error bands in water levels may serve as a guideline for the desired accuracy of floodplain characteristics in hydrodynamic models.
D Recording for 2d Delivering - the Employment of 3d Models for Studies and Analyses -
Rizzi, A.; Baratti, G.; Jiménez, B.; Girardi, S.; Remondino, F.
2011-09-01
In the last years, thanks to the advances of surveying sensors and techniques, many heritage sites could be accurately replicated in digital form with very detailed and impressive results. The actual limits are mainly related to hardware capabilities, computation time and low performance of personal computer. Often, the produced models are not visible on a normal computer and the only solution to easily visualized them is offline using rendered videos. This kind of 3D representations is useful for digital conservation, divulgation purposes or virtual tourism where people can visit places otherwise closed for preservation or security reasons. But many more potentialities and possible applications are available using a 3D model. The problem is the ability to handle 3D data as without adequate knowledge this information is reduced to standard 2D data. This article presents some surveying and 3D modeling experiences within the APSAT project ("Ambiente e Paesaggi dei Siti d'Altura Trentini", i.e. Environment and Landscapes of Upland Sites in Trentino). APSAT is a multidisciplinary project funded by the Autonomous Province of Trento (Italy) with the aim documenting, surveying, studying, analysing and preserving mountainous and hill-top heritage sites located in the region. The project focuses on theoretical, methodological and technological aspects of the archaeological investigation of mountain landscape, considered as the product of sequences of settlements, parcelling-outs, communication networks, resources, and symbolic places. The mountain environment preserves better than others the traces of hunting and gathering, breeding, agricultural, metallurgical, symbolic activities characterised by different lengths and environmental impacts, from Prehistory to the Modern Period. Therefore the correct surveying and documentation of this heritage sites and material is very important. Within the project, the 3DOM unit of FBK is delivering all the surveying and 3D material to
1D and 2D urban dam-break flood modelling in Istanbul, Turkey
Ozdemir, Hasan; Neal, Jeffrey; Bates, Paul; Döker, Fatih
2014-05-01
Urban flood events are increasing in frequency and severity as a consequence of several factors such as reduced infiltration capacities due to continued watershed development, increased construction in flood prone areas due to population growth, the possible amplification of rainfall intensity due to climate change, sea level rise which threatens coastal development, and poorly engineered flood control infrastructure (Gallegos et al., 2009). These factors will contribute to increased urban flood risk in the future, and as a result improved modelling of urban flooding according to different causative factor has been identified as a research priority (Gallegos et al., 2009; Ozdemir et al. 2013). The flooding disaster caused by dam failures is always a threat against lives and properties especially in urban environments. Therefore, the prediction of dynamics of dam-break flows plays a vital role in the forecast and evaluation of flooding disasters, and is of long-standing interest for researchers. Flooding occurred on the Ayamama River (Istanbul-Turkey) due to high intensity rainfall and dam-breaching of Ata Pond in 9th September 2009. The settlements, industrial areas and transportation system on the floodplain of the Ayamama River were inundated. Therefore, 32 people were dead and millions of Euros economic loses were occurred. The aim of this study is 1 and 2-Dimensional flood modelling of the Ata Pond breaching using HEC-RAS and LISFLOOD-Roe models and comparison of the model results using the real flood extent. The HEC-RAS model solves the full 1-D Saint Venant equations for unsteady open channel flow whereas LISFLOOD-Roe is the 2-D shallow water model which calculates the flow according to the complete Saint Venant formulation (Villanueva and Wright, 2006; Neal et al., 2011). The model consists a shock capturing Godunov-type scheme based on the Roe Riemann solver (Roe, 1981). 3 m high resolution Digital Surface Model (DSM), natural characteristics of the pond
Facial Sketch Synthesis Using 2D Direct Combined Model-Based Face-Specific Markov Network.
Tu, Ching-Ting; Chan, Yu-Hsien; Chen, Yi-Chung
2016-08-01
A facial sketch synthesis system is proposed, featuring a 2D direct combined model (2DDCM)-based face-specific Markov network. In contrast to the existing facial sketch synthesis systems, the proposed scheme aims to synthesize sketches, which reproduce the unique drawing style of a particular artist, where this drawing style is learned from a data set consisting of a large number of image/sketch pairwise training samples. The synthesis system comprises three modules, namely, a global module, a local module, and an enhancement module. The global module applies a 2DDCM approach to synthesize the global facial geometry and texture of the input image. The detailed texture is then added to the synthesized sketch in a local patch-based manner using a parametric 2DDCM model and a non-parametric Markov random field (MRF) network. Notably, the MRF approach gives the synthesized results an appearance more consistent with the drawing style of the training samples, while the 2DDCM approach enables the synthesis of outcomes with a more derivative style. As a result, the similarity between the synthesized sketches and the input images is greatly improved. Finally, a post-processing operation is performed to enhance the shadowed regions of the synthesized image by adding strong lines or curves to emphasize the lighting conditions. The experimental results confirm that the synthesized facial images are in good qualitative and quantitative agreement with the input images as well as the ground-truth sketches provided by the same artist. The representing power of the proposed framework is demonstrated by synthesizing facial sketches from input images with a wide variety of facial poses, lighting conditions, and races even when such images are not included in the training data set. Moreover, the practical applicability of the proposed framework is demonstrated by means of automatic facial recognition tests. PMID:27244737
Modelling thermal stratification in the North Sea: Application of a 2-D potential energy model
DEFF Research Database (Denmark)
Nielsen, Morten Holtegaard; St. John, Michael
2001-01-01
in these years available from the ICES hydrographic database. We find that the model is able to simulate variations in thermal stratification including the seasonal onset and breakdown of stratification, the thermocline depth, and the effects of discrete wind and cooling events. For the years 1988–1990 we find...... an R2=0·97 between observed and predicted upper layer temperatures. However, the model is less successful in the prediction of temperatures of the intermediate and deep layers (R2=0·46 and 0·14) due to small deviations in thermocline depth and variations in tidal amplitude. The model was then applied...
Building a 2.5D Digital Elevation Model from 2D Imagery
Padgett, Curtis W.; Ansar, Adnan I.; Brennan, Shane; Cheng, Yang; Clouse, Daniel S.; Almeida, Eduardo
2013-01-01
When projecting imagery into a georeferenced coordinate frame, one needs to have some model of the geographical region that is being projected to. This model can sometimes be a simple geometrical curve, such as an ellipse or even a plane. However, to obtain accurate projections, one needs to have a more sophisticated model that encodes the undulations in the terrain including things like mountains, valleys, and even manmade structures. The product that is often used for this purpose is a Digital Elevation Model (DEM). The technology presented here generates a high-quality DEM from a collection of 2D images taken from multiple viewpoints, plus pose data for each of the images and a camera model for the sensor. The technology assumes that the images are all of the same region of the environment. The pose data for each image is used as an initial estimate of the geometric relationship between the images, but the pose data is often noisy and not of sufficient quality to build a high-quality DEM. Therefore, the source imagery is passed through a feature-tracking algorithm and multi-plane-homography algorithm, which refine the geometric transforms between images. The images and their refined poses are then passed to a stereo algorithm, which generates dense 3D data for each image in the sequence. The 3D data from each image is then placed into a consistent coordinate frame and passed to a routine that divides the coordinate frame into a number of cells. The 3D points that fall into each cell are collected, and basic statistics are applied to determine the elevation of that cell. The result of this step is a DEM that is in an arbitrary coordinate frame. This DEM is then filtered and smoothed in order to remove small artifacts. The final step in the algorithm is to take the initial DEM and rotate and translate it to be in the world coordinate frame [such as UTM (Universal Transverse Mercator), MGRS (Military Grid Reference System), or geodetic] such that it can be saved in
Croissant, Thomas; Lague, Dimitri; Davy, Philippe; Steer, Philippe
2016-04-01
In active mountain ranges, large earthquakes (Mw > 5-6) trigger numerous landslides that impact river dynamics. These landslides bring local and sudden sediment piles that will be eroded and transported along the river network causing downstream changes in river geometry, transport capacity and erosion efficiency. The progressive removal of landslide materials has implications for downstream hazards management and also for understanding landscape dynamics at the timescale of the seismic cycle. The export time of landslide-derived sediments after large-magnitude earthquakes has been studied from suspended load measurements but a full understanding of the total process, including the coupling between sediment transfer and channel geometry change, still remains an issue. Note that the transport of small sediment pulses has been studied in the context of river restoration, but the magnitude of sediment pulses generated by landslides may make the problem different. Here, we study the export of large volumes (>106 m3) of sediments with the 2D hydro-morphodynamic model, Eros. This model uses a new hydrodynamic module that resolves a reduced form of the Saint-Venant equations with a particle method. It is coupled with a sediment transport and lateral and vertical erosion model. Eros accounts for the complex retroactions between sediment transport and fluvial geometry, with a stochastic description of the floods experienced by the river. Moreover, it is able to reproduce several features deemed necessary to study the evacuation of large sediment pulses, such as river regime modification (single-thread to multi-thread), river avulsion and aggradation, floods and bank erosion. Using a synthetic and simple topography we first present how granulometry, landslide volume and geometry, channel slope and flood frequency influence 1) the dominance of pulse advection vs. diffusion during its evacuation, 2) the pulse export time and 3) the remaining volume of sediment in the catchment
2D condensation model for the inner Solar Nebula: an enstatite-rich environment
Pignatale, F. C.; Liffman, Kurt; Maddison, Sarah T.; Brooks, Geoffrey
2016-04-01
Infrared observations provide the dust composition in the protoplanetary discs surface layers, but cannot probe the dust chemistry in the mid-plane, where planet formation occurs. Meteorites show that dynamics was important in determining the dust distribution in the Solar Nebula and needs to be considered if we are to understand the global chemistry in discs. 1D radial condensation sequences can only simulate one disc layer at a time and cannot describe the global chemistry or the complexity of meteorites. To address these limitations, we compute for the first time the 2D distribution of condensates in the inner Solar Nebula using a thermodynamic equilibrium model, and derive time-scales for vertical settling and radial migration of dust. We find two enstatite-rich zones within 1 AU from the young Sun: a band ˜0.1 AU thick in the upper optically-thin layer of the disc interior to 0.8 AU, and in the optically-thick disc mid-plane out to ˜0.4 AU. The two enstatite-rich zones support recent evidence that Mercury and enstatite chondrites (ECs) shared a bulk material with similar composition. Our results are also consistent with infrared observation of protoplanetary disc which show emission of enstatite-rich dust in the inner surface of discs. The resulting chemistry and dynamics suggests that the formation of the bulk material of ECs occurred in the inner surface layer of the disc, within 0.4 AU. We also propose a simple alternative scenario in which gas fractionation and vertical settling of the condensates lead to an enstatite-chondritic bulk material.
The space-scale cube: An integrated model for 2D polygonal areas and scale
Meijers, B.M.; Van Oosterom, P.J.M.
2011-01-01
This paper introduces the concept of a space-scale partition, which we term the space-scale cube – analogous with the space-time cube (first introduced by Hägerstrand, 1970). We take the view of ‘map generalization is extrusion of 2D data into the third dimension’ (as introduced by Vermeij et al., 2
Modeling of Nitrate Leaching from a Potato Field using HYDRUS-2D
DEFF Research Database (Denmark)
Shekofteh, Hosein; Afyuni, Majid; Hajabbasi, Mohammad Ali;
2013-01-01
Excessive use of nitrogen (N) fertilizers is likely to be responsible for the increasing nitrate in groundwater. Thus, appropriate water and nutrient management is required to minimize groundwater pollution and to maximize the nutrient-use efficiency. In this study HYDRUS-2D software package...
Comparison of the 1D flux theory with a 2D hydrodynamic secondary settling tank model.
Ekama, G A; Marais, P
2004-01-01
The applicability of the 1D idealized flux theory (1DFT) for design of secondary settling tanks (SSTs) is evaluated by comparing its predicted maximum surface overflow (SOR) and solids loading (SLR) rates with that calculated from the 2D hydrodynamic model SettlerCAD using as a basis 35 full scale SST stress tests conducted on different SSTs with diameters from 30 to 45m and 2.25 to 4.1 m side water depth, with and without Stamford baffles. From the simulations, a relatively consistent pattern appeared, i.e. that the 1DFT can be used for design but its predicted maximum SLR needs to be reduced by an appropriate flux rating, the magnitude of which depends mainly on SST depth and hydraulic loading rate (HLR). Simulations of the sloping bottom shallow (1.5-2.5 m SWD) Dutch SSTs tested by STOWa and the Watts et al. SST, all with doubled SWDs, and the Darvill new (4.1 m) and old (2.5 m) SSTs with interchanged depths, were run to confirm the sensitivity of the flux rating to depth and HLR. Simulations with and without a Stamford baffle were also done. While the design of the internal features of the SST, such as baffling, have a marked influence on the effluent SS concentration for underloaded SSTs, these features appeared to have only a small influence on the flux rating, i.e. capacity, of the SST, In the meantime until more information is obtained, it would appear that from the simulations so far that the flux rating of 0.80 of the 1DFT maximum SLR recommended by Ekama and Marais remains a reasonable value to apply in the design of full scale SSTs--for deep SSTs (4 m SWD) the flux rating could be increased to 0.85 and for shallow SSTs (2.5 m SWD) decreased to 0.75. It is recommended that (i) while the apparent interrelationship between SST flux rating and depth suggests some optimization of the volume of the SST, that this be avoided and that (ii) the depth of the SST be designed independently of the surface area as is usually the practice and once selected, the
Bandrowski, D.; Lai, Y.; Bradley, N.; Gaeuman, D. A.; Murauskas, J.; Som, N. A.; Martin, A.; Goodman, D.; Alvarez, J.
2014-12-01
In the field of river restoration sciences there is a growing need for analytical modeling tools and quantitative processes to help identify and prioritize project sites. 2D hydraulic models have become more common in recent years and with the availability of robust data sets and computing technology, it is now possible to evaluate large river systems at the reach scale. The Trinity River Restoration Program is now analyzing a 40 mile segment of the Trinity River to determine priority and implementation sequencing for its Phase II rehabilitation projects. A comprehensive approach and quantitative tool has recently been developed to analyze this complex river system referred to as: 2D-Hydrodynamic Based Logic Modeling (2D-HBLM). This tool utilizes various hydraulic output parameters combined with biological, ecological, and physical metrics at user-defined spatial scales. These metrics and their associated algorithms are the underpinnings of the 2D-HBLM habitat module used to evaluate geomorphic characteristics, riverine processes, and habitat complexity. The habitat metrics are further integrated into a comprehensive Logic Model framework to perform statistical analyses to assess project prioritization. The Logic Model will analyze various potential project sites by evaluating connectivity using principal component methods. The 2D-HBLM tool will help inform management and decision makers by using a quantitative process to optimize desired response variables with balancing important limiting factors in determining the highest priority locations within the river corridor to implement restoration projects. Effective river restoration prioritization starts with well-crafted goals that identify the biological objectives, address underlying causes of habitat change, and recognizes that social, economic, and land use limiting factors may constrain restoration options (Bechie et. al. 2008). Applying natural resources management actions, like restoration prioritization, is
Novel Method Fusing (2D) 2 LDA with Multichannel Model for Face Recognition
Institute of Scientific and Technical Information of China (English)
Xia Liu∗; Yang Cao; Yu Cao; Bo Wang
2015-01-01
A fusion method of Gabor features and (2D)2LDA for face feature extraction is proposed in this paper. Gabor filters are utilized to extract multi⁃direction and multi⁃scale features from facial image to employ its robust performance for illumination, expressional variability and other factors. The extracted features have the defect of high dimension and redundancy data. (2D)2LDA is implemented to reduce the dimension of Gabor features and select effective feature data. Finally, the nearest neighbor classifier is used to classify characteristics and complete face recognition. The experiments are implemented by using ORL database and Yale database respectively. The experimental results show that the proposed method significantly reduces the dimension of Gabor features and decrease the influence of other factors. The proposed method acquires excellent recognition accuracy and has light architectures as well.
Fire Analysis of Reinforced Concrete Beams with 2-D Plane Stress Concrete Model
Yousef Zandi; Oğuz Burnaz; Ahmet Durmuş
2013-01-01
The main purpose of this study is to investigate the nonlinear response of reinforced concrete beams under standard fire conditions. With this purpose, the 2-D nonlinear structural analysis of a chosen reinforced concrete simple beam is carried out. This beam is exposed to fire form three sides and fixed distributed loads on top of it. In these structural analyses the changes of material properties of concrete and reinforcements according to increasing temperatures are taken into account. Res...
Driven microswimmers on a 2D substrate: A stochastic towed sled model
Marchegiani, Giampiero; Marchesoni, Fabio
2015-11-01
We investigate, both numerically and analytically, the diffusion properties of a stochastic sled sliding on a substrate, subject to a constant towing force. The problem is motivated by the growing interest in controlling transport of artificial microswimmers in 2D geometries at low Reynolds numbers. We simulated both symmetric and asymmetric towed sleds. Remarkable properties of their mobilities and diffusion constants include sidewise drifts and excess diffusion peaks. We interpret our numerical findings by making use of stochastic approximation techniques.
Driven microswimmers on a 2D substrate: A stochastic towed sled model
International Nuclear Information System (INIS)
We investigate, both numerically and analytically, the diffusion properties of a stochastic sled sliding on a substrate, subject to a constant towing force. The problem is motivated by the growing interest in controlling transport of artificial microswimmers in 2D geometries at low Reynolds numbers. We simulated both symmetric and asymmetric towed sleds. Remarkable properties of their mobilities and diffusion constants include sidewise drifts and excess diffusion peaks. We interpret our numerical findings by making use of stochastic approximation techniques
Numerical Simulations of High-Frequency Respiratory Flows in 2D and 3D Lung Bifurcation Models
Chen, Zixi; Parameswaran, Shamini; Hu, Yingying; He, Zhaoming; Raj, Rishi; Parameswaran, Siva
2014-07-01
To better understand the human pulmonary system and optimize the high-frequency oscillatory ventilation (HFOV) design, numerical simulations were conducted under normal breathing frequency and HFOV condition using a CFD code Ansys Fluent and its user-defined C programs. 2D and 3D double bifurcating lung models were created, and the geometry corresponds to fifth to seventh generations of airways with the dimensions based on the Weibel's pulmonary model. Computations were carried out for different Reynolds numbers (Re = 400 and 1000) and Womersley numbers (α = 4 and 16) to study the air flow fields, gas transportation, and wall shear stresses in the lung airways. Flow structure was compared with experimental results. Both 2D and 3D numerical models successfully reproduced many results observed in the experiment. The oxygen concentration distribution in the lung model was investigated to analyze the influence of flow oscillation on gas transport inside the lung model.
2D MHD AND 1D HD MODELS OF A SOLAR FLARE—A COMPREHENSIVE COMPARISON OF THE RESULTS
Energy Technology Data Exchange (ETDEWEB)
Falewicz, R.; Rudawy, P. [Astronomical Institute, University of Wrocław, 51-622 Wrocław, ul. Kopernika 11 (Poland); Murawski, K. [Group of Astrophysics, UMCS, ul. Radziszewskiego 10, 20-031 Lublin (Poland); Srivastava, A. K., E-mail: falewicz@astro.uni.wroc.pl, E-mail: rudawy@astro.uni.wroc.pl, E-mail: kmur@kft.umcs.lublin.pl, E-mail: asrivastava.app@iitbhu.ac.in [Department of Physics, Indian Institute of Technology (Banaras Hindu University), Varanasi-221005 (India)
2015-11-01
Without any doubt, solar flaring loops possess a multithread internal structure that is poorly resolved, and there are no means to observe heating episodes and thermodynamic evolution of the individual threads. These limitations cause fundamental problems in numerical modeling of flaring loops, such as selection of a structure and a number of threads, and an implementation of a proper model of the energy deposition process. A set of one-dimensional (1D) hydrodynamic and two-dimensional (2D) magnetohydrodynamic models of a flaring loop are developed to compare energy redistribution and plasma dynamics in the course of a prototypical solar flare. Basic parameters of the modeled loop are set according to the progenitor M1.8 flare recorded in AR 10126 on 2002 September 20 between 09:21 UT and 09:50 UT. The nonideal 1D models include thermal conduction and radiative losses of the optically thin plasma as energy-loss mechanisms, while the nonideal 2D models take into account viscosity and thermal conduction as energy-loss mechanisms only. The 2D models have a continuous distribution of the parameters of the plasma across the loop and are powered by varying in time and space along and across the loop heating flux. We show that such 2D models are an extreme borderline case of a multithread internal structure of the flaring loop, with a filling factor equal to 1. Nevertheless, these simple models ensure the general correctness of the obtained results and can be adopted as a correct approximation of the real flaring structures.
Sato, Toshihiro; Tsunetsugu, Hirokazu
2016-08-01
We numerically study optical conductivity σ (ω ) near the "antiferromagnetic" phase transition in the square-lattice Hubbard model at half filling. We use a cluster dynamical mean field theory and calculate conductivity including vertex corrections and, to this end, we have reformulated the vertex corrections in the antiferromagnetic phase. We find that the vertex corrections change various important details in temperature and ω dependencies of conductivity in the square lattice, and this contrasts sharply the case of the Mott transition in the frustrated triangular lattice. Generally, the vertex corrections enhance variations in the ω dependence, and sharpen the Drude peak and a high-ω incoherent peak in the paramagnetic phase. They also enhance the dip in σ (ω ) at ω =0 in the antiferromagnetic phase. Therefore, the dc conductivity is enhanced in the paramagnetic phase and suppressed in the antiferromagnetic phase, but this change occurs slightly below the transition temperature. We also find a temperature region above the transition temperature in which the dc conductivity shows an insulating behavior but σ (ω ) retains the Drude peak, and this region is stabilized by the vertex corrections. We also investigate which fluctuations are important in the vertex corrections and analyze momentum dependence of the vertex function in detail.
Nocera, A.; Soltanieh-ha, M.; Perroni, C. A.; Cataudella, V.; Feiguin, A. E.
2014-11-01
We calculate the spectral function of the one-dimensional Hubbard-Holstein model using the time-dependent density matrix renormalization group, focusing on the regime of large local Coulomb repulsion, and away from electronic half-filling. We argue that, from weak to intermediate electron-phonon coupling, phonons interact only with the electronic charge, and not with the spin degrees of freedom. For strong electron-phonon interaction, spinon and holon bands are not discernible anymore and the system is well described by a spinless polaronic liquid. In this regime, we observe multiple peaks in the spectrum with an energy separation corresponding to the energy of the lattice vibrations (i.e., phonons). We support the numerical results by introducing a well controlled analytical approach based on Ogata-Shiba's factorized wave function, showing that the spectrum can be understood as a convolution of three contributions, originating from charge, spin, and lattice sectors. We recognize and interpret these signatures in the spectral properties and discuss the experimental implications.
International Nuclear Information System (INIS)
Finite-temperature T > 0 transport properties of integrable and nonintegrable one-dimensional (1D) many-particle quantum systems are rather different, showing ballistic and diffusive behavior, respectively. The repulsive 1D Hubbard model is a prominent example of an integrable correlated system. For electronic densities n ≠ 1 (and spin densities m ≠ 0) it is an ideal charge (and spin) conductor, with ballistic charge (and spin) transport for T ⩾ 0. In spite of the fact that it is solvable by the Bethe ansatz, at n = 1 (and m = 0) its T > 0 charge (and spin) transport properties are an issue that remains poorly understood. Here we combine this solution with symmetry and the explicit calculation of current-operator matrix elements between energy eigenstates to show that for on-site repulsion U > 0 and at n = 1 the charge stiffness Dη(T) vanishes for T > 0 in the thermodynamic limit. A similar behavior is found by such methods for the spin stiffness Ds(T) for U > 0 and T > 0, which vanishes at m = 0. This absence of finite temperature n = 1 ballistic charge transport and m = 0 ballistic spin transport are exact results that clarify long-standing open problems. (paper)
Bose-Hubbard Hamiltonian: Quantum chaos approach
Kolovsky, Andrey R.
2016-03-01
We discuss applications of the theory of quantum chaos to one of the paradigm models of many-body quantum physics — the Bose-Hubbard (BH) model, which describes, in particular, interacting ultracold Bose atoms in an optical lattice. After preliminary, pure quantum analysis of the system we introduce the classical counterpart of the BH model and the governing semiclassical equations of motion. We analyze these equations for the problem of Bloch oscillations (BOs) of cold atoms where a number of experimental results are available. The paper is written for nonexperts and can be viewed as an introduction to the field.
Rigorous 2D Model for Study of Pulsed and Monochromatic Waves Propagation Near the Earth’s Surface
Sautbekov, Seil S.; Yuriy K. Sirenko; Nataliya P. Yashina; Aleksey A. Vertiy
2014-01-01
A model problem considered in the paper allows solving rather complex 2D problems of the electromagnetic wave propagation with a required accuracy using conventional personal computers. The problems are of great importance for the theory and practical applications. The association of FDTD schemes with exact absorbing conditions makes up the basis for constructing models of the kind. This approach reduces the original open initial boundary value problems to the equivalent closed problems which...
Comparison between a 1D and a 2D numerical model of an active magnetic regenerative refrigerator
DEFF Research Database (Denmark)
Petersen, Thomas Frank; Engelbrecht, Kurt; Bahl, Christian Robert Haffenden;
2008-01-01
a reciprocating AMR and can determine the cyclical steady-state temperature profile of the system as well as performance parameters such as the refrigeration capacity, the work input and the coefficient of performance (COP). The models are used to analyse an AMR with a regenerator made of flat parallel plates...... results of overall results such as the refrigeration capacity but that a 2D model is required for a detailed analysis of the phenomena occurring inside the AMR....
Simulating floods : On the application of a 2D-hydraulic model for flood hazard and risk assessment
Alkema, D.
2007-01-01
Over the last decades, river floods in Europe seem to occur more frequently and are causing more and more economic and emotional damage. Understanding the processes causing flooding and the development of simulation models to evaluate countermeasures to control that damage are important issues. This study deals with the application of a 2D hydraulic flood propagation model for flood hazard and risk assessment. It focuses on two components: 1) how well does it predict the spatial-dynamic chara...
A. Caserta; L. Malagnini; A. Rovelli; Marra, F
1995-01-01
The geological information collected in the last years by the Istituto Nazionale di Geofisica for the city of Rome is used to construct 1- and 2-D models of the nearsurface structure. These models are the basis for the numerical generation of synthetic accelerograms which can simulate the horizontal ground motion (SH waves) produced in the different areas of the city by a large (M ? 7) potential earthquake 100 km away in Central Apennines. The proposed methodology yields earthquake engineerin...
Harman Ajiwibowo
2011-01-01
The effectiveness of a breakwater can be measured by quantifying the transmission coefficient (KT). The smaller the coefficient, the better the performance of the breakwater. A physical modeling on the proposed breakwater was conducted to identify the coefficient of Perforated Skirt Breakwater (PSB). The PSB model was tested in 2-D wave flume at Ocean Wave Research Laboratory FTSL ITB, to obtain the effectiveness of PSB for short-period waves (prototype periods, Tp= 4 second and smaller). The...
Fire Analysis of Reinforced Concrete Beams with 2-D Plane Stress Concrete Model
Directory of Open Access Journals (Sweden)
Yousef Zandi
2013-01-01
Full Text Available The main purpose of this study is to investigate the nonlinear response of reinforced concrete beams under standard fire conditions. With this purpose, the 2-D nonlinear structural analysis of a chosen reinforced concrete simple beam is carried out. This beam is exposed to fire form three sides and fixed distributed loads on top of it. In these structural analyses the changes of material properties of concrete and reinforcements according to increasing temperatures are taken into account. Results drawn from these analyses are compared with the results from some simplified methods and put forward some conclusions and recommendations concerning the fire design of reinforced concrete beams.
Diego A. Garzón-Alvarado; CARLOS GALEANO; JUAN MANTILLA
2012-01-01
Este articulo presenta distintas pruebas numéricas en dominios que presenta variación de parámetros, de forma espacial, de la ecuación de reacción- difusión en el espacio de Turing. Las pruebas son desarrolladas en cuadrados de lado unitario 2D en el cual se realizan subdivisiones (subdominios). En cada subdomminio se ingresan parámetros que corresponden a los diferentes números de onda, por lo tanto presentan un medio heterogéneo. Cada número de onda fue predicho mediante la teoría lineal de...
Directory of Open Access Journals (Sweden)
Sri Atmaja P. Rosidi
2007-01-01
Full Text Available The Spectral Analysis of Surface Wave (SASW method is a non-destructive in situ seismic technique used to assess and evaluate the material stiffness (dynamic elastic modulus and thickness of pavement layers at low strains. These values can be used analytically to calculate load capacities in order to predict the performance of pavement system. The SASW method is based on the dispersion phenomena of Rayleigh waves in layered media. In order to get the actual shear wave velocities, 2-D and 3-D models are used in the simulation of the inversion process for best fitting between theoretical and empirical dispersion curves. The objective of this study is to simulate and compare the 2-D and 3-D model of SASW analysis in the construction of the theoretical dispersion curve for pavement structure evaluation. The result showed that the dispersion curve from the 3-D model was similar with the dispersion curve of the actual pavement profile compared to the 2-D model. The wave velocity profiles also showed that the 3-D model used in the SASW analysis is able to detect all the distinct layers of flexible pavement units.
Institute of Scientific and Technical Information of China (English)
LI Haifeng; HU Zunhe; LIU Jingtai
2016-01-01
To facilitate scene understanding and robot navigation in large scale urban environment, a two-layer enhanced geometric map (EGMap) is designed using videos from a monocular onboard camera. The 2D layer of EGMap consists of a 2D building boundary map from top-down view and a 2D road map, which can support localization and advanced map-matching when compared with standard polyline-based maps. The 3D layer includes features such as 3D road model, and building facades with coplanar 3D vertical and horizontal line segments, which can provide the 3D metric features to localize the vehicles and flying-robots in 3D space. Starting from the 2D building boundary and road map, EGMap is initially constructed using feature fusion with geometric constraints under a line feature-based simultaneous localization and mapping (SLAM) framework iteratively and progressively. Then, a local bundle adjustment algorithm is proposed to jointly refine the camera localizations and EGMap features. Furthermore, the issues of uncertainty, memory use, time efficiency and obstacle effect in EGMap construction are discussed and analyzed. Physical experiments show that EGMap can be successfully constructed in large scale urban environment and the construction method is demonstrated to be very accurate and robust.
Spin-spin critical point correlation functions for the 2D random bond Ising and Potts models
Dotsenko, V S; Pujol, P; Vladimir Dotsenko; Marco Picco; Pierre Pujol
1994-01-01
We compute the combined two and three loop order correction to the spin-spin correlation functions for the 2D Ising and q-states Potts model with random bonds at the critical point. The procedure employed is the renormalisation group approach for the perturbation series around the conformal field theories representing the pure models. We obtain corrections for the correlations functions which produce crossover in the amplitude but don't change the critical exponent in the case of the Ising model and which produce a shift in the critical exponent, due to randomness, in the case of the Potts model. Comparison with numerical data is discussed briefly.
Small-amplitude 2D patterns with nontrivial symmetry in a simple nonlinear field model
International Nuclear Information System (INIS)
Quasiperiodic (QP) small-amplitude patterns are studied in a scalar field theory with quadratic nonlinearity. QP solutions of the class in interest are found as a projection of strictly periodic solutions of an associated 4D problem onto an 'irrationally oriented' 2D subspace. The periodic solutions of the 4D problem are constructed using a version of the method of asymptotic expansions. The analysis reveals complex patterns. In particular, there exists a one-parametric QP pattern with strict 12-fold symmetry, which contains infinitely many local patches with approximate 5-fold symmetry. In limit cases, the complex patterns transform into a simple pattern: a close pack of hexagonal cells. In certain resonance cases there exist patterns consisting of alternating pieces of close cell packs with either hexagonal or quadrangular symmetry. The relation between the 12-fold and 5-fold approximate symmetries is discussed. (author)
MATHEMATICAL MODEL FOR 2-D TIDAL FLOW AND WATER QUALITY WITH ORTHOGONAL CURVILINEAR COORDINATES
Institute of Scientific and Technical Information of China (English)
Liu Yu-ling; Wei Wen-li; Shen Yong-ming
2003-01-01
This paper presents a numerical method forsimulating the 2-D tidal flow and water quality with the or-thogonal curvilinear coordinates. In order to overcome thecomputational difficulties in natural rivers, such as the com-plicated boundary figures, the great disparity between lengthand width of computational domain, etc. , orthogonal bounda-ry-fitted grid was used. The irregular domain in physical planewas transformed into a rectangular domain in a transformedplane, and the depth-averaged momentum equations and massequation were given and discretized based on the alternatingdirection implicit finite difference scheme in curvilinear coordi-nates. The application of the presented method was illustratedby an example of analyzing the Yangtze River in the vicinity ofNanjing city. A fair agreement between the measured data andcomputed results demonstrates the validity of the developedmethod.
Ute Weckmann; A. Jung; T. Branch; Oliver Ritter
2007-01-01
Two of the Earth´s largest geophysical anomalies, the Beattie Magnetic Anomaly (BMA) and the Southern Cape Conductive Belt (SCCB) extend across the southern African continent for more than 1000 km in an east-west direction. Based on previous electrical and magnetometer array measurements it is believed that both anomalies have a common crustal source with a width of 50 km represented by serpentinized palaeo-oceanic srust. New two-dimensional (2D) electrical conductivity models along a profile...
I. Kalisperakis; Stentoumis, Ch.; L. Grammatikopoulos; K. Karantzalos
2015-01-01
The indirect estimation of leaf area index (LAI) in large spatial scales is crucial for several environmental and agricultural applications. To this end, in this paper, we compare and evaluate LAI estimation in vineyards from different UAV imaging datasets. In particular, canopy levels were estimated from i.e., (i) hyperspectral data, (ii) 2D RGB orthophotomosaics and (iii) 3D crop surface models. The computed canopy levels have been used to establish relationships with the measured ...
Energy Technology Data Exchange (ETDEWEB)
Ramazani, A., E-mail: ali.ramazani@iehk.rwth-aachen.de [Department of Ferrous Metallurgy, RWTH Aachen University, Intzestr.1, D-52072 Aachen (Germany); Mukherjee, K.; Quade, H.; Prahl, U.; Bleck, W. [Department of Ferrous Metallurgy, RWTH Aachen University, Intzestr.1, D-52072 Aachen (Germany)
2013-01-10
A microstructure-based approach by means of representative volume elements (RVEs) is employed to evaluate the flow curve of DP steels using virtual tensile tests. Microstructures with different martensite fractions and morphologies are studied in two- and three-dimensional approaches. Micro sections of DP microstructures with various amounts of martensite have been converted to 2D RVEs, while 3D RVEs were constructed statistically with randomly distributed phases. A dislocation-based model is used to describe the flow curve of each ferrite and martensite phase separately as a function of carbon partitioning and microstructural features. Numerical tensile tests of RVE were carried out using the ABAQUS/Standard code to predict the flow behaviour of DP steels. It is observed that 2D plane strain modelling gives an underpredicted flow curve for DP steels, while the 3D modelling gives a quantitatively reasonable description of flow curve in comparison to the experimental data. In this work, a von Mises stress correlation factor {sigma}{sub 3D}/{sigma}{sub 2D} has been identified to compare the predicted flow curves of these two dimensionalities showing a third order polynomial relation with respect to martensite fraction and a second order polynomial relation with respect to equivalent plastic strain, respectively. The quantification of this polynomial correlation factor is performed based on laboratory-annealed DP600 chemistry with varying martensite content and it is validated for industrially produced DP qualities with various chemistry, strength level and martensite fraction.
Stability Analysis of State Saturation 2D Discrete Time-Delay Systems Based on F-M Model
Directory of Open Access Journals (Sweden)
Dongyan Chen
2013-01-01
Full Text Available The problem of stability analysis is investigated for a class of state saturation two-dimensional (2D discrete time-delay systems described by the Fornasini-Marchesini (F-M model. The delay is allowed to be a bounded time-varying function. By constructing the delay-dependent 2D discrete Lyapunov functional and introducing a nonnegative scalar β, a sufficient condition is proposed to guarantee the global asymptotic stability of the addressed systems. Subsequently, the criterion is converted into the linear matrix inequalities (LMIs which can be easily tested by using the standard numerical software. Finally, two numerical examples are given to show the effectiveness of the proposed stability criterion.
A new approach for assimilation of 2D radar precipitation in a high-resolution NWP model
DEFF Research Database (Denmark)
Korsholm, Ulrik Smith; Petersen, Claus; Sass, Bent Hansen;
2015-01-01
. The method was implemented in the Danish Meteorological Institute numerical weather prediction (DMI NWP) nowcasting system, running with hourly cycles, performing a surface analysis and 3D variational analysis for upper air assimilation at each cycle restart, followed by nudging assimilation of precipitation......A new approach for assimilation of 2D precipitation in numerical weather prediction models is presented and tested in a case with convective, heavy precipitation. In the scheme a nudging term is added to the horizontal velocity divergence tendency equation. In case of underproduction...... and then a free forecast. The precipitation fields are based on a 2D composite CAPPI (constant altitude plan position indicator) field made from observations with the DMI weather radars, and have a 10 min time resolution. The results obtained in this study indicate that the new method implies fast adjustment...
International Nuclear Information System (INIS)
Purpose: [123I]Epidepride is a radio-tracer with very high affinity for dopamine D2/D3 receptors in brain. The importance of alteration in dopamine D2/D3 receptor binding condition has been wildly verified in schizophrenia. In the present study we set up a rat schizophrenia model by chronic injection of a non-competitive NMDA receptor antagonist, MK-801, to examine if [123I]epidepride could be used to evaluate the alterations of dopamine D2/D3 receptor binding condition in specific brain regions. Method: Rats were given repeated injection of MK-801 (dissolved in saline, 0.3 mg/kg) or saline for 1 month. Afterwards, total distance traveled (cm) and social interaction changes were recorded. Radiochemical purity of [123I]epidepride was analyzed by Radio-Thin-Layer Chromatography (chloroform: methanol, 9:1, v/v) and [123I]epidepride neuroimages were obtained by ex vivo autoradiography and small animal SPECT/CT. Data obtained were then analyzed to determine the changes of specific binding ratio. Result: Chronic MK-801 treatment for a month caused significantly increased local motor activity and induced an inhibition of social interaction. As shown in [123I]epidepride ex vivo autoradiographs, MK-801 induced a decrease of specific binding ratio in the striatum (24.01%), hypothalamus (35.43%), midbrain (41.73%) and substantia nigra (37.93%). In addition, [123I]epidepride small animal SPECT/CT neuroimaging was performed in the striatum and midbrain. There were statistically significant decreases in specific binding ratio in both the striatum (P 123I]epidepride is a useful radio-tracer to reveal the alterations of dopamine D2/D3 receptor binding in a rat schizophrenia model and is also helpful to evaluate therapeutic effects of schizophrenia in the future.
A review on 2D models for the description of pantographic fabrics
Placidi, Luca; Barchiesi, Emilio; Turco, Emilio; Rizzi, Nicola Luigi
2016-10-01
A review on models for pantographic fabrics, a new promising kind of metamaterials, is presented. We treat those models that are able to capture the peculiar effects conferred by their specific microstructure and that can be generalized for the description of more complex metamaterials. For each approach, model formulation and modeling assumptions are discussed along with the presentation of numerical solutions in exemplary cases and no attempt is made to model damage and failure phenomena.
Directory of Open Access Journals (Sweden)
H. H. Gerke
2011-06-01
Full Text Available Subsurface drained experimental fields are frequently used for studying preferential flow (PF in structured soils. Considering two-dimensional (2-D transport towards the drain, however, the relevance of mass transfer coefficients, apparently reflecting small-scale soil structural properties, for the water and solute balances of the entire drained field is largely unknown. This paper reviews and analyzes effects of mass transfer reductions on Br^{−} leaching for a subsurface drained experimental field using a numerical 2-D dual-permeability model (2D-DPERM. The sensitivity of the "diffusive" mass transfer component on bromide (Br^{−} leaching patterns is discussed. Flow and transport is simulated in a 2-D vertical cross-section using parameters, boundary conditions (BC, and data of a Br^{−} tracer irrigation experiment on a subsurface drained field (5000 m^{2} area at Bokhorst (Germany, where soils have developed from glacial till sediments. The 2D-DPERM simulation scenarios assume realistic irrigation and rainfall rates, and Br-application in the soil matrix (SM domain. The mass transfer reduction controls preferential tracer movement and can be related to physical and chemical properties at the interface between flow path and soil matrix in structured soil. A reduced solute mass transfer rate coefficient allows a better match of the Br^{−} mass flow observed in the tile drain discharge. The results suggest that coefficients of water and solute transfer between PF and SM domains have a clear impact on Br^{−} effluent from the drain. Amount and composition of the drain effluent is analyzed as a highly complex interrelation between temporally and spatially variable mass transfer in the 2-D vertical flow domain that depends on varying "advective" and "diffusive" transfer components, the spatial distribution of residual tracer concentrations, and the lateral flow fields in both domains from
Local Mass Transfer Coefficient for Idealized 2D Urban Street Canyon Models
Leung, Ka Kit; Liu, Chun-Ho
2011-09-01
Human activities in urban areas is one of the major sources of anthropogenic releases in the atmospheric boundary layer (ABL). The mechanism of urban morphology for the heat and mass transfer in built environment is thus an attractive topic in the research community. In this paper, a series of laboratory measurements is conducted to elucidate the mass transfer from hypothetical urban roughness constructed by idealized 2D street canyons. The experiments are carried out in the wind tunnel in the University of Hong Kong. The urban ABL structure inside the wind tunnel is controlled by placing small cubic Styrofoam blocks upstream of the test section. The street canyons are fabricated by movable rectangular acrylic blocks so that different building height to street width (aspect) ratios are examined. The height of building blocks is kept minimum to make sure that the urban ABL over the street canyons is high enough for fully developed turbulent flows. The prevailing wind is normal to the street axis, demonstrating the scenario of least pollutant removal from the street canyons to the urban ABL. The sample street canyon is covered by soaked filter papers to represent uniform mass concentrations on the building facades and ground surface. The wet bulb temperature of the filter papers is continuously monitored to ensure saturated conditions. Their weight before and after an experiment is used to measure the amount of water evaporated. Preliminary results illustrate the local mass transfer coefficient distribution for aspect ratios 1/4, 1/2, 1, and 2, which are comparable with those available in literuatre.
Rigorous 2D Model for Study of Pulsed and Monochromatic Waves Propagation Near the Earth’s Surface
Directory of Open Access Journals (Sweden)
Seil S. Sautbekov
2014-01-01
Full Text Available A model problem considered in the paper allows solving rather complex 2D problems of the electromagnetic wave propagation with a required accuracy using conventional personal computers. The problems are of great importance for the theory and practical applications. The association of FDTD schemes with exact absorbing conditions makes up the basis for constructing models of the kind. This approach reduces the original open initial boundary value problems to the equivalent closed problems which can be solved numerically using the standard grid methods.
Autovino, Dario; Negm, Amro; Rallo, Giovanni; Provenzano, Giuseppe
2016-04-01
In Mediterranean countries characterized by limited water resources for agricultural and societal sectors, irrigation management plays a major role to improve water use efficiency at farm scale, mainly where irrigation systems are correctly designed to guarantee a suitable application efficiency and the uniform water distribution throughout the field. In the last two decades, physically-based agro-hydrological models have been developed to simulate mass and energy exchange processes in the soil-plant-atmosphere (SPA) system. Mechanistic models like HYDRUS 2D/3D (Šimunek et al., 2011) have been proposed to simulate all the components of water balance, including actual crop transpiration fluxes estimated according to a soil potential-dependent sink term. Even though the suitability of these models to simulate the temporal dynamics of soil and crop water status has been reported in the literature for different horticultural crops, a few researches have been considering arboreal crops where the higher gradients of root water uptake are the combination between the localized irrigation supply and the three dimensional root system distribution. The main objective of the paper was to assess the performance of HYDRUS-2D model to evaluate soil water contents and transpiration fluxes of an olive orchard irrigated with two different water distribution systems. Experiments were carried out in Castelvetrano (Sicily) during irrigation seasons 2011 and 2012, in a commercial farm specialized in the production of table olives (Olea europaea L., var. Nocellara del Belice), representing the typical variety of the surrounding area. During the first season, irrigation water was provided by a single lateral placed along the plant row with four emitters per plant (ordinary irrigation), whereas during the second season a grid of emitters laid on the soil was installed in order to irrigate the whole soil surface around the selected trees. The model performance was assessed based on the
2D MHD and 1D HD models of a solar flare -- a comprehensive comparison of the results
Falewicz, R; Murawski, K; Srivastava, A K
2015-01-01
Without any doubt solar flaring loops possess a multi-thread internal structure that is poorly resolved and there are no means to observe heating episodes and thermodynamic evolution of the individual threads. These limitations cause fundamental problems in numerical modelling of flaring loops, such as selection of a structure and a number of threads, and an implementation of a proper model of the energy deposition process. A set of 1D hydrodynamic and 2D magnetohydrodynamic models of a flaring loop are developed to compare energy redistribution and plasma dynamics in the course of a prototypical solar flare. Basic parameters of the modeled loop are set according to the progenitor M1.8 flare recorded in the AR10126 on September 20, 2002 between 09:21 UT and 09:50 UT. The non-ideal 1D models include thermal conduction and radiative losses of the optically thin plasma as energy loss mechanisms, while the non-ideal 2D models take into account viscosity and thermal conduction as energy loss mechanisms only. The 2...
International Nuclear Information System (INIS)
In order to design and define appropriate dimensions for a supercritical oxidation reactor, a comparative 2D and 3D simulation of the fluid dynamics and heat transfer during an oxidation process has been performed. The solver used is a commercial code, Fluent 6.2 (R). The turbulent flow field in the reactor, created by the stirrer, is taken into account with a k-omega model and a swirl imposed to the fluid. In the 3D case the rotation of the stirrer can be modelled using the sliding mesh model and the moving reference frame model. This work allows comparing 2D and 3D velocity and heat transfer calculations. The predicted values (mainly species concentrations and temperature profiles) are of the same order in both cases. The reactivity of the system is taken into account with a classical Eddy Dissipation Concept combustion model. Comparisons with experimental temperature measurements validate the ability of the CFD modelling to simulate the supercritical water oxidation reactive medium. Results indicate that the flow can be considered as plug flow-like and that heat transfer is strongly enhanced by the stirring. (authors)
Development of 2D dynamic model for hydrogen-fed and methane-fed solid oxide fuel cells
Luo, X. J.; Fong, K. F.
2016-10-01
A new two-dimensional (2D) dynamic model is developed in Fortran to study the mass and energy transport, the velocity field and the electrochemical phenomena of high-temperature solid oxide fuel cell (SOFC). The key feature of this model is that gas properties, reaction heat, open circuit voltage, ohmic voltage and exchange current density are temperature-dependent. Based on this, the change of gas temperature and related characteristics can be evaluated in this study. The transient performances of SOFC, like heat-up and start-up processes, are therefore assessed accordingly. In this 2D dynamic SOFC model, chemical and electrochemical reaction, flow field, mass and energy transfer models are coupled in order to determine the current density, the mass fraction and the temperature of gas species. Mass, momentum and energy balance equations are discretized by finite difference method. Performance evaluation in current density, electrical efficiency and overall efficiency is conducted for the effects of different operating parameters in SOFC. The present model can serve as a valuable tool for in-depth performance evaluation of other design and operating parameters of SOFC unit, as well as further dynamic simulation and optimization of SOFC as a prime mover in cogeneration or trigeneration system.
Directory of Open Access Journals (Sweden)
Kowit Boonrawd
2015-04-01
Full Text Available A coupling of a 1-D flood routing model and quasi 2-D floodplain inundation model is applied for mapping spacetime flood extent. The routing model is formulated based on a non-linear storage-discharge relationship which is converted from an observed and synthetic rating curve. To draw the rating curve, required parameters for each reaches are estimated from hydraulic properties, floodplain geometry and vegetation and building cover of compound channels. The shape of the floodplain is defined by using fitting exercise based on the reverse approach between past and simulated inundation flood extent, to solve the current problem of inadequate topographic input data for floodplain. Mapping of daily flood can be generated relying on flat water levels. The quasi 2-D raster model is tested and applied to generate more realistic water surface and is used to estimate flood extent. The model is applied to the floodplains of Chiang Mai, north of Thailand and used to estimate a time series of hourly flood maps. Extending from daily to hourly flood extent, mapping development provides more details of flood inundation extent and depth.
A microscopic nuclear collective rotation-vibration model: 2D submodel
Gulshani, Parviz
2016-01-01
The previous microscopic collective rotation-vibration model is improved to include interaction between collective oscillations in a pair of spatial directions, and to remove many of the previous-model approximations. As in the previous model, the nuclear Schrodinger equation (instead of the Hamiltonian) is canonically transformed to obtain a Schrodinger equation for collective rotation and vibration of a nucleus coupled to an intrinsic motion, with the related constraints imposed on the wave...
New urban area flood model: a comparison with MIKE11-quasi2d
Sole, A.; Zuccaro, G.
2005-01-01
Recent hydrogeological events have increased both public interest and that of the Scientific Community in a more accurate study of flooding in urban areas. The present project proposes a new model which offers an optimal integration of two models, one for flood wave propagation in riverbeds and the other for flooding in urban areas. We consider it necessary to not only treat the modelling of the outflow in riverbeds and outside riverbeds.together but to integrate them thoroughly. We simulate...
Institute of Scientific and Technical Information of China (English)
吴修广; 沈永明; 郑永红
2004-01-01
A numerical model for shallow water flow has been developed based on the unsteady Reynolds-averaged NavierStokes equations with the hydrodynamic pressure instead of hydrostatic pressure assumption. The equations are transformed into the σ-coordinate system and the eddy viscosity is calculated with the standard k - e turbulence model. The control volume method is used to discrete the equations, and the boundary conditions at the bed for shallow water models only include vertical diffusion terms expressed with wall functions. And the semi-implicit method for pressure linked equation arithmetic is adopted to solve the equations. The model is applied to the 2D vertical plane flow of a curent over two steep-sided trenches for which experiment data are available for comparison and good agreement is obtained. And the model is used to predicting the flow in a channel with a steep-sided submerged breakwater at the bottom, and the streamline is drawn.
Filipović, Vilim; Romić, Davor; Romić, Marija; Matijević, Lana; Mallmann, Fábio J. K.; Robinson, David A.
2016-04-01
Growing vegetables commercially requires intensive management and involves high irrigation demands and input of agrochemicals. Plastic mulch application in combination with drip irrigation is a common agricultural management technique practiced due to variety of benefits to the crop, mostly vegetable biomass production. However, the use of these techniques can result in various impacts on water and nutrient distribution in underlying soil and consequently affect nutrient leaching towards groundwater resources. The aim of this work is to estimate the effect of plastic mulch cover in combination with drip irrigation on water and nitrate dynamics in soil using HYDRUS-2D model. The field site was located in Croatian costal karst area on a Gleysol (WRB). The experiment was designed according to the split-plot design in three repetitions and was divided into plots with plastic mulch cover (MULCH) and control plots with bare soil (CONT). Each of these plots received applications of three levels of nitrogen fertilizer: 70, 140, and 210 kg per ha. All plots were equipped with drip irrigation and cropped with bell pepper (Capsicum annuum L. cv. Bianca F1). Lysimeters were installed at 90 cm depth in all plots and were used for monitoring the water and nitrate outflow. HYDRUS-2D was used for modeling the water and nitrogen outflow in the MULCH and CONT plots, implementing the proper boundary conditions. HYDRUS-2D simulated results showed good fitting to the field site observed data in both cumulative water and nitrate outflow, with high level of agreement. Water flow simulations produced model efficiency of 0.84 for CONT and 0.56 for MULCH plots, while nitrate simulations showed model efficiency ranging from 0.67 to 0.83 and from 0.70 to 0.93, respectively. Additional simulations were performed with the absence of the lysimeter, revealing faster transport of nitrates below drip line in the CONT plots, mostly because of the increased surface area subjected to precipitation
Numerical study of the classical 2D discrete frustrated phi(4) model
Savkin, V.; Rubtsov, A.N.; Janssen, T.
2004-01-01
The two-dimensional discrete frustrated phi(4) model is studied by Monte Carlo simulations for two sets of the parameters of the model. Two phase transitions and a floating-incommensurate phase are observed for the case of stronger frustration. The phase transition from the floating-fluid phase to t
Hemodynamic simulation of the heart using a 2D model and MR data
DEFF Research Database (Denmark)
Adeler, Pernille Thorup
2002-01-01
Computational models of the blood flow in the heart are a useful tool for studying the functioning of the heart. The purpose of this thesis is to achieve a better understanding of hemodynamics of the normal and diseased hearts through the use of a computational model and magnetic resonance (MR) d...
The critical points of the multimatrix model as the theories of 2-d W-gravity
International Nuclear Information System (INIS)
We further explore the connections between the generalized KdV hierarchy, the multimatrix model and Wn-gravity. We show that the Lax-pair formulation of the generalized KdV hierarchy is nothing but the Hamiltonian equations of W-gravity. Thus we demonstrate that the multicritical points of the multimatrix model are W-gravity theories. 16 refs
2-D Model Test Study of the Breakwater at Porto de Dande , Angola
DEFF Research Database (Denmark)
Andersen, Thomas Lykke; Ramirez, Jorge Robert Rodriguez; Burcharth, Hans F.
This report deals with a two-dimensional model test study of the new breakwater at Porto de Dande, Angola. One cross-section was tested for stability and overtopping in various sea conditions. The length scale used for the model tests was 1:32. Unless otherwise specified all values given in this ...
Li, Yunfeng; Pizlo, Zygmunt; Steinman, Robert M
2009-05-01
Human beings perceive 3D shapes veridically, but the underlying mechanisms remain unknown. The problem of producing veridical shape percepts is computationally difficult because the 3D shapes have to be recovered from 2D retinal images. This paper describes a new model, based on a regularization approach, that does this very well. It uses a new simplicity principle composed of four shape constraints: viz., symmetry, planarity, maximum compactness and minimum surface. Maximum compactness and minimum surface have never been used before. The model was tested with random symmetrical polyhedra. It recovered their 3D shapes from a single randomly-chosen 2D image. Neither learning, nor depth perception, was required. The effectiveness of the maximum compactness and the minimum surface constraints were measured by how well the aspect ratio of the 3D shapes was recovered. These constraints were effective; they recovered the aspect ratio of the 3D shapes very well. Aspect ratios recovered by the model were compared to aspect ratios adjusted by four human observers. They also adjusted aspect ratios very well. In those rare cases, in which the human observers showed large errors in adjusted aspect ratios, their errors were very similar to the errors made by the model. PMID:18621410
Simulation of Ultra-Small MOSFETs Using a 2-D Quantum-Corrected Drift-Diffusion Model
Biegal, Bryan A.; Rafferty, Connor S.; Yu, Zhiping; Ancona, Mario G.; Dutton, Robert W.; Saini, Subhash (Technical Monitor)
1998-01-01
The continued down-scaling of electronic devices, in particular the commercially dominant MOSFET, will force a fundamental change in the process of new electronics technology development in the next five to ten years. The cost of developing new technology generations is soaring along with the price of new fabrication facilities, even as competitive pressure intensifies to bring this new technology to market faster than ever before. To reduce cost and time to market, device simulation must become a more fundamental, indeed dominant, part of the technology development cycle. In order to produce these benefits, simulation accuracy must improve markedly. At the same time, device physics will become more complex, with the rapid increase in various small-geometry and quantum effects. This work describes both an approach to device simulator development and a physical model which advance the effort to meet the tremendous electronic device simulation challenge described above. The device simulation approach is to specify the physical model at a high level to a general-purpose (but highly efficient) partial differential equation solver (in this case PROPHET, developed by Lucent Technologies), which then simulates the model in 1-D, 2-D, or 3-D for a specified device and test regime. This approach allows for the rapid investigation of a wide range of device models and effects, which is certainly essential for device simulation to catch up with, and then stay ahead of, electronic device technology of the present and future. The physical device model used in this work is the density-gradient (DG) quantum correction to the drift-diffusion model [Ancona, Phys. Rev. B 35(5), 7959 (1987)]. This model adds tunneling and quantum smoothing of carrier density profiles to the drift-diffusion model. We used the DG model in 1-D and 2-D (for the first time) to simulate both bipolar and unipolar devices. Simulations of heavily-doped, short-base diodes indicated that the DG quantum
Application of 2-D sediment model to fluctuating backwater area of Yangtze River
Directory of Open Access Journals (Sweden)
Yong FAN
2009-09-01
Full Text Available Based on the characteristics of backflow, a two-dimensional mathematical model of sediment movement was established. The complexity of the watercourse boundary at the confluence of the main stream and the tributary was dealt with using a boundary-fitting orthogonal coordinate system. The basic equation of the two-dimensional total sediment load model, the numerical calculation format, and key problems associated with using the orthogonal curvilinear coordinate system were discussed. Water and sediment flow in the Chongqing reach of the Yangtze River were simulated. The calculated water level, flow velocity distribution, amount of silting and scouring, and alluvial distribution are found to be in agreement with the measured data, which indicates that the numerical model and calculation method are reasonable. The model can be used for calculation of flow in a relatively complicated river network.
Baryon Acoustic Oscillations in 2D: Modeling Redshift-space Power Spectrum from Perturbation Theory
Taruya, Atsushi; Saito, Shun
2010-01-01
We present an improved prescription for matter power spectrum in redshift space taking a proper account of both the non-linear gravitational clustering and redshift distortion, which are of particular importance for accurately modeling baryon acoustic oscillations (BAOs). Contrary to the models of redshift distortion phenomenologically introduced but frequently used in the literature, the new model includes the corrections arising from the non-linear coupling between the density and velocity fields associated with two competitive effects of redshift distortion, i.e., Kaiser and Finger-of-God effects. Based on the improved treatment of perturbation theory for gravitational clustering, we compare our model predictions with monopole and quadrupole power spectra of N-body simulations, and an excellent agreement is achieved over the scales of BAOs. Potential impacts on constraining dark energy and modified gravity from the redshift-space power spectrum are also investigated based on the Fisher-matrix formalism. We...
Application of 2-D sediment model to fluctuating backwater area of Yangtze River
Institute of Scientific and Technical Information of China (English)
Yong FAN
2009-01-01
Based on the characteristics of backflow,a two-dimensional mathematical model of sediment movement was established.The complexity of the watercourse boundary at the confluence of the main stream and the tributary was dealt with using a boundary-fitting orthogonal coordinate system.The basic equation of the two-dimensional total sediment load model,the numerical calculation format,and key problems associated with using the orthogonal curvilinear coordinate system were discussed.Water and sediment flow in the Chongqing reach of the Yangtze River were simulated.The calculated water level,flow velocity distribution,amount of silting and scouring,and alluvial distribution are found to be in agreement with the measured data,which indicates that the numerical model and calculation method are reasonable.The model can be used for calculation of flow in a relatively complicated river network.
A microscopic nuclear collective rotation-vibration model: 2D submodel
Gulshani, Parviz
2016-01-01
The previous microscopic collective rotation-vibration model is improved to include interaction between collective oscillations in a pair of spatial directions, and to remove many of the previous-model approximations. As in the previous model, the nuclear Schrodinger equation (instead of the Hamiltonian) is canonically transformed to obtain a Schrodinger equation for collective rotation and vibration of a nucleus coupled to an intrinsic motion, with the related constraints imposed on the wavefunction (rather than on the particle co-ordinates). The resulting equation is then effectively linearized into three self-consistent, time-reversal invariant, cranking-type equations using a variational method. The relation of the equations to the phenomenological hydrodynamic collective Bohr-Davydov-Faessler-Greiner model is discussed. To facilitate the solution of the equations and enhance physical insight, we consider in this article the collective oscillations in only two space directions. For harmonic oscillator mea...
A 2D analytical cylindrical gate tunnel FET (CG-TFET) model: impact of shortest tunneling distance
Dash, S.; Mishra, G. P.
2015-09-01
A 2D analytical tunnel field-effect transistor (FET) potential model with cylindrical gate (CG-TFET) based on the solution of Laplace’s equation is proposed. The band-to-band tunneling (BTBT) current is derived by the help of lateral electric field and the shortest tunneling distance. However, the analysis is extended to obtain the subthreshold swing (SS) and transfer characteristics of the device. The dependency of drain current, SS and transconductance on gate voltage and shortest tunneling distance is discussed. Also, the effect of scaling the gate oxide thickness and the cylindrical body diameter on the electrical parameters of the device is analyzed.
Large-N limit of the gradient flow in the 2D O(N) nonlinear sigma model
International Nuclear Information System (INIS)
The gradient flow equation in the 2D O(N) nonlinear sigma model with lattice regularization is solved in the leading order of the 1/N expansion. By using this solution, we analytically compute the thermal expectation value of a lattice energy–momentum tensor defined through the gradient flow. The expectation value reproduces thermodynamic quantities obtained by the standard large-N method. This analysis confirms that the above lattice energy–momentum tensor restores the correct normalization automatically in the continuum limit, in a system with a non-perturbative mass gap
Development of a 1D-2D coupled hydrodynamic model for the Øyeren Delta in southern Norway
2011-01-01
In this study a coupled 1D-2D hydrodynamic model, MIKE FLOOD was used to simulate flood inundation extent, water levels and water velocities in the delta region of Lake Øyeren in southern Norway. The objective was to evaluate the improvement gained using a more complex framework. In addition, the credibility of existing flood zone maps made for Lillestrøm by Norges Vassdrag- og Energidirektorat (NVE) in 2005 was assessed. They were based on the assumption that the water levels predicted for F...
Estimating 3D movements from 2D observations using a continuous model of helical swimming.
Gurarie, Eliezer; Grünbaum, Daniel; Nishizaki, Michael T
2011-06-01
Helical swimming is among the most common movement behaviors in a wide range of microorganisms, and these movements have direct impacts on distributions, aggregations, encounter rates with prey, and many other fundamental ecological processes. Microscopy and video technology enable the automated acquisition of large amounts of tracking data; however, these data are typically two-dimensional. The difficulty of quantifying the third movement component complicates understanding of the biomechanical causes and ecological consequences of helical swimming. We present a versatile continuous stochastic model-the correlated velocity helical movement (CVHM) model-that characterizes helical swimming with intrinsic randomness and autocorrelation. The model separates an organism's instantaneous velocity into a slowly varying advective component and a perpendicularly oriented rotation, with velocities, magnitude of stochasticity, and autocorrelation scales defined for both components. All but one of the parameters of the 3D model can be estimated directly from a two-dimensional projection of helical movement with no numerical fitting, making it computationally very efficient. As a case study, we estimate swimming parameters from videotaped trajectories of a toxic unicellular alga, Heterosigma akashiwo (Raphidophyceae). The algae were reared from five strains originally collected from locations in the Atlantic and Pacific Oceans, where they have caused Harmful Algal Blooms (HABs). We use the CVHM model to quantify cell-level and strain-level differences in all movement parameters, demonstrating the utility of the model for identifying strains that are difficult to distinguish by other means. PMID:20725795
From 2D to 3D: Using Illumination Cones to Build 3d Face Model
Energy Technology Data Exchange (ETDEWEB)
Xiao, S S; Jin, M [TianJin University, Collage of Precision Instrument and Opto-Ectronics Engineering (China)
2006-10-15
To solve the problem derivate by lighting condition and position of the camera, a new method using illumination cones to build 3d face model has been proposed. Due to illumination variability, the same object can show dramatic difference even as being viewed in fixed pose. To handle this variability, an object recognition system must employ a representation that is either invariant to, or can model this variability. The proposed technique presents an appearance-based method for modeling the variability due to illumination in the images of objects. The method differs from past appearance-based methods. Evenmore, a small set of training images is used to generate a representation that the illumination cone models the complete set of images of an object with Lambertian reflectance surface under a combination of arbitrary point light sources at infinity. After building up the illumination cones, researches focus on how to present the 3d model of the face. Combining illumination and texture feature to build up 3d model of the face make it easy solving the problem in recognition of face under different pose.
From 2D to 3D: Using Illumination Cones to Build 3d Face Model
International Nuclear Information System (INIS)
To solve the problem derivate by lighting condition and position of the camera, a new method using illumination cones to build 3d face model has been proposed. Due to illumination variability, the same object can show dramatic difference even as being viewed in fixed pose. To handle this variability, an object recognition system must employ a representation that is either invariant to, or can model this variability. The proposed technique presents an appearance-based method for modeling the variability due to illumination in the images of objects. The method differs from past appearance-based methods. Evenmore, a small set of training images is used to generate a representation that the illumination cone models the complete set of images of an object with Lambertian reflectance surface under a combination of arbitrary point light sources at infinity. After building up the illumination cones, researches focus on how to present the 3d model of the face. Combining illumination and texture feature to build up 3d model of the face make it easy solving the problem in recognition of face under different pose
Enhanced Kalman Filtering for a 2D CFD NS Wind Farm Flow Model
Doekemeijer, B. M.; van Wingerden, J. W.; Boersma, S.; Pao, L. Y.
2016-09-01
Wind turbines are often grouped together for financial reasons, but due to wake development this usually results in decreased turbine lifetimes and power capture, and thereby an increased levelized cost of energy (LCOE). Wind farm control aims to minimize this cost by operating turbines at their optimal control settings. Most state-of-the-art control algorithms are open-loop and rely on low fidelity, static flow models. Closed-loop control relying on a dynamic model and state observer has real potential to further decrease wind's LCOE, but is often too computationally expensive for practical use. In this paper two time-efficient Kalman filter (KF) variants are outlined incorporating the medium fidelity, dynamic flow model “WindFarmSimulator” (WFSim). This model relies on a discretized set of Navier-Stokes equations in two dimensions to predict the flow in wind farms at low computational cost. The filters implemented are an Ensemble KF and an Approximate KF. Simulations in which a high fidelity simulation model represents the true wind farm show that these filters are 101 —102 times faster than a regular KF with comparable or better performance, correcting for wake dynamics that are not modeled in WFSim (noticeably, wake meandering and turbine hub effects). This is a first big step towards real-time closed-loop control for wind farms.
Directory of Open Access Journals (Sweden)
Peter Flaschel
2014-01-01
Full Text Available The paper argues that applicable macro is high frequency macro and the data generating process is therefore to be modeled in continuous time. It exemplifies this with a misuse of a 2D period model of monetarist type which becomes extremely overshooting, allowing for routes to “chaos,” when iterated at low frequencies. Instead of such low frequency procedures, we augment the model by a Keynesian feedback chain (the real rate of interest channel to introduce local instability into the model. We also introduce heterogeneous opinion dynamics into it. The implied 4D dynamics are made bounded thereby, but seem to allow only complex limit cycles, with no transition towards strange attractors anymore.
New urban area flood model: a comparison with MIKE11-quasi2d
Directory of Open Access Journals (Sweden)
A. Sole
2005-01-01
Full Text Available Recent hydrogeological events have increased both public interest and that of the Scientific Community in a more accurate study of flooding in urban areas. The present project proposes a new model which offers an optimal integration of two models, one for flood wave propagation in riverbeds and the other for flooding in urban areas. We consider it necessary to not only treat the modelling of the outflow in riverbeds and outside riverbeds.together but to integrate them thoroughly. We simulate the propagation in riverbed of the flood event with a model solving the equations of De Saint Venant with the explicit scheme at the finite differences by McCormack. The propagation outside the riverbed is simulated using an algorithm proposed by Braschi et al. (1990. This algorithm is based on a local discretization of the urban territory, divided in a series of "tanks" and "channels". Each tank is associated with an area of an extension related to the position of the other tanks and the quantity of buildings, modelled as insurmountable obstacles. The model facilitates the simultaneous performance of the two simulations: at each instant, the quantitiy of water overflow, depending on the piezometric level in every section, is calculated as a function of the dimensions of the weirs (the banks, assuming it passes through the critical state. Then, it is transferred to the tanks placed in the surroundings of the overflow points. Those points are the starting nodes for the propagation of the flood because they are connected to the network of tanks in which the surrounding land has been schematised. In this paper, we present a comparison of one of the most powerful models of inundation simulation in urban and no-urban areas. The field area is the city of Albenga (SV, Italy and the simulated event is the inundation of the 1994 (return period of about 25 years.
Tian, Junfang; Li, Geng; Treiber, Martin; Zhu, Chenqiang; Jia, Bin
2016-01-01
This paper firstly show that 2 Dimensional Intelligent Driver Model (Jiang et al., PloS one, 9(4), e94351, 2014) is not able to replicate the synchronized traffic flow. Then we propose an improved model by considering the difference between the driving behaviors at high speeds and that at low speeds. Simulations show that the improved model can reproduce the phase transition from synchronized flow to wide moving jams, the spatiotemporal patterns of traffic flow induced by traffic bottleneck, and the evolution concavity of traffic oscillations (i.e. the standard deviation of the velocities of vehicles increases in a concave/linear way along the platoon). Validating results show that the empirical time series of traffic speed obtained from Floating Car Data can be well simulated as well.
2D fuzzy anti-de Sitter space from matrix models
Energy Technology Data Exchange (ETDEWEB)
Jurman, Danijel [Theoretical Physics Division, Rudjer Boskovic InstituteP.O. Box 180, 10002 Zagreb (Croatia); Steinacker, Harold [Faculty of Physics, University of ViennaBoltzmanngasse 5, A-1090 Vienna (Austria)
2014-01-20
We study the fuzzy hyperboloids AdS{sup 2} and dS{sup 2} as brane solutions in matrix models. The unitary representations of SO(2,1) required for quantum field theory are identified, and explicit formulae for their realization in terms of fuzzy wavefunctions are given. In a second part, we study the (A)dS{sup 2} brane geometry and its dynamics, as governed by a suitable matrix model. In particular, we show that trace of the energy-momentum tensor of matter induces transversal perturbations of the brane and of the Ricci scalar. This leads to a linearized form of Henneaux-Teitelboim-type gravity, illustrating the mechanism of emergent gravity in matrix models.
Time domain numerical modeling of wave propagation in 2D heterogeneous porous media
Chiavassa, Guillaume
2010-01-01
This paper deals with the numerical modeling of wave propagation in porous media described by Biot's theory. The viscous efforts between the fluid and the elastic skeleton are assumed to be a linear function of the relative velocity, which is valid in the low-frequency range. The coexistence of propagating fast compressional wave and shear wave, and of a diffusive slow compressional wave, makes numerical modeling tricky. To avoid restrictions on the time step, the Biot's system is splitted into two parts: the propagative part is discretized by a fourth-order ADER scheme, while the diffusive part is solved analytically. Near the material interfaces, a space-time mesh refinement is implemented to capture the small spatial scales related to the slow compressional wave. The jump conditions along the interfaces are discretized by an immersed interface method. Numerical experiments and comparisons with exact solutions confirm the accuracy of the numerical modeling. The efficiency of the approach is illustrated by s...
A new model of quantum chaotic billiards Spectral Statistics and Wavefunctions in 2D
Cuevas, E; Vergés, J A
1996-01-01
Quantum chaotic dynamics is obtained for a tight-binding model in which the energies of the atomic levels at the boundary sites are chosen at random. Results for the square lattice indicate that the energy spectrum shows a complex behavior with regions that obey the Wigner-Dyson statistics and localized and quasi-ideal states distributed according to Poisson statistics. Although the averaged spatial extension of the eigenstates in the present model scales with the size of the system as in the Gaussian Orthogonal Ensemble, the fluctuations are much larger.
Two-loop effective potentials in general N=2, d=3 chiral superfield model
International Nuclear Information System (INIS)
We study local superspace contributions to the low-energy effective action in general chiral three-dimensional superfield model. The effective Kähler and chiral potentials are computed in an explicit form up to the two-loop order. In accordance with the non-renormalization theorem, the ultraviolet divergences appear only in the full superspace while the effective chiral potential receives only finite quantum contributions in the massless case. As an application, the two-loop effective scalar potential is found for the three-dimensional N=2 supersymmetric Wess-Zumino model.
Hewson, Alex C.; Bauer, Johannes
2010-01-01
We show that information on the probability density of local fluctuations can be obtained from a numerical renormalisation group calculation of a reduced density matrix. We apply this approach to the Anderson-Holstein impurity model to calculate the ground state probability density $\\rho(x)$ for the displacement $x$ of the local oscillator. From this density we can deduce an effective local potential for the oscillator and compare its form with that obtained from a semiclassical approximation...
2-D model for pollutant dispersion at the coastal outfall off Paradip
Digital Repository Service at National Institute of Oceanography (India)
Suryanarayana, A.; Babu, M.T.; Vethamony, P.; Gouveia, A.D.
was performed for low wind speed conditions when mixing is expected to be minimum in the region. Based on the model results the pollutant patch moved and diffused parallel to the coastline in the direction of the along-shore current...
Edge gradients evaluation for 2D hybrid finite volume method model
In this study, a two-dimensional depth-integrated hydrodynamic model was developed using FVM on a hybrid unstructured collocated mesh system. To alleviate the negative effects of mesh irregularity and non-uniformity, a conservative evaluation method for edge gradients based on the second-order Tayl...
Exact solution of the 2d dimer model: Corner free energy, correlation functions and combinatorics
Energy Technology Data Exchange (ETDEWEB)
Allegra, Nicolas, E-mail: nicolas.allegra@univ-lorraine.fr
2015-05-15
In this work, some classical results of the pfaffian theory of the dimer model based on the work of Kasteleyn, Fisher and Temperley are introduced in a fermionic framework. Then we shall detail the bosonic formulation of the model via the so-called height mapping and the nature of boundary conditions is unravelled. The complete and detailed fermionic solution of the dimer model on the square lattice with an arbitrary number of monomers is presented, and finite size effect analysis is performed to study surface and corner effects, leading to the extrapolation of the central charge of the model. The solution allows for exact calculations of monomer and dimer correlation functions in the discrete level and the scaling behavior can be inferred in order to find the set of scaling dimensions and compare to the bosonic theory which predicts particular features concerning corner behaviors. Finally, some combinatorial and numerical properties of partition functions with boundary monomers are discussed, proved and checked with enumeration algorithms.
Large N transition in the 2D SU(N)xSU(N) nonlinear sigma model
Narayanan, Rajamani; Neuberger, Herbert; Vicari, Ettore
2008-01-01
We consider the characteristic polynomial associated with the smoothed two point function in two dimensional large N principal chiral model. We numerically show that it undergoes a transition at a critical distance of the order of the correlation length. The transition is in the same universality class as two dimensional large N QCD.
Hard Copy to Digital Transfer: 3D Models that Match 2D Maps
Kellie, Andrew C.
2011-01-01
This research describes technical drawing techniques applied in a project involving digitizing of existing hard copy subsurface mapping for the preparation of three dimensional graphic and mathematical models. The intent of this research was to identify work flows that would support the project, ensure the accuracy of the digital data obtained,…
Zero-temperature renormalization of the 2D transverse Ising model
International Nuclear Information System (INIS)
A zero-temperature real-space renormalization-group method is applied to the transverse Ising model on planar hexagonal, triangular and quadratic lattices. The critical fields and the critical exponents describing low-field large-field transition are calculated. (author)
Azcoiti, V; Follana, E; Giordano, M
2012-01-01
We study the two-dimensional Antiferromagnetic Ising Model with an imaginary magnetic field i\\theta at \\theta=\\pi. We use a new geometric algorithm which does not present a sign problem. This allows us to perform efficient numerical simulations of this system.
Computational modeling of hypersingular integral equations for 2D pre-cantor scattering structure
Directory of Open Access Journals (Sweden)
Kateryna Nesvit
2015-11-01
Full Text Available This paper presents the investigative study to derive a computational model based on hypersingular integral equations for the pre-Cantor plane-parallel diffraction structure. Such structure consists of finite numbers of the thin impedance strips located in the XY plane. A plane transverse magnetic wave is incident from infinity on considered diffraction structure at an angle and need to find the total field resulting from the scattering. The model which is considered in this work is an approximation of real fractal antennas in two-dimensional case. Pre-fractal properties of grating allow producing the newest antennas for modern mobile devices due to their compact size and broadband properties. The purpose of this work is to develop computer model their structure using parametric representation of hypersingular integral operator, Nystrom method with specific quadrature formulas. The numerical results have been obtained and investigated for pre-Cantor structures for calculating physics characteristics. These results have been compared and analyzed in different mathematical models and softwares.
Adaptive Fault-Tolerant Routing in 2D Mesh with Cracky Rectangular Model
Directory of Open Access Journals (Sweden)
Yi Yang
2014-01-01
Full Text Available This paper mainly focuses on routing in two-dimensional mesh networks. We propose a novel faulty block model, which is cracky rectangular block, for fault-tolerant adaptive routing. All the faulty nodes and faulty links are surrounded in this type of block, which is a convex structure, in order to avoid routing livelock. Additionally, the model constructs the interior spanning forest for each block in order to keep in touch with the nodes inside of each block. The procedure for block construction is dynamically and totally distributed. The construction algorithm is simple and ease of implementation. And this is a fully adaptive block which will dynamically adjust its scale in accordance with the situation of networks, either the fault emergence or the fault recovery, without shutdown of the system. Based on this model, we also develop a distributed fault-tolerant routing algorithm. Then we give the formal proof for this algorithm to guarantee that messages will always reach their destinations if and only if the destination nodes keep connecting with these mesh networks. So the new model and routing algorithm maximize the availability of the nodes in networks. This is a noticeable overall improvement of fault tolerability of the system.
Structure of a model salt bridge in solution investigated with 2D-IR spectroscopy
A. Huerta-Viga; S.R. Domingos; S. Amirjalayer; S. Woutersen
2013-01-01
Salt bridges are known to be important for the stability of protein conformation, but up to now it has been difficult to study their geometry in soln. Here we characterize the spatial structure of a model salt bridge between guanidinium (Gdm+) and acetate (Ac-) using two-dimensional vibrational (2
2D transport modeling of tritium-helium in an aquifer with Alliances
Energy Technology Data Exchange (ETDEWEB)
Dimier, A.; Appelo, C.A.J. [Andra, France, Hydrochemical Consultant (Netherlands)
2005-07-01
Full text of publication follows: ANDRA is the French organization in charge of the safety assessment of nuclear waste disposals. In a joint cooperation with other French organizations (CEA), tools are developed for predicting the migration of radionuclides and chemical species through geological media, all combined in the 'Alliances' platform. For the coupling of geochemistry and transport different codes have now been implemented: PHREEQC or CHESS for the chemical part, CASTEM, MT3D or TRACES for 3D transport and diffusion. Validation of the coupled codes was done on various hypothetical problems with complicated chemistry involving speciation, dissolution-precipitation, sorption and surface complexation. At present, the tool has matured sufficiently to simulate 'real world' configurations, and we present the modeling of tritium/helium profiles in an aquifer near Bocholt, Germany. A major challenge of reactive transport modeling in aquifers is the delineation of the flow field. Many profiles with environmental tracers such as tritium, tritium/helium and CFC's or SF6 have been reported and were compared with flow model results, but it appears difficult to generate a satisfactory model from many possible alternatives. Schlosser et al. (1988, 1989) analyzed {sup 3}H/{sup 3}He profiles in an aquifer using multilevel sampling wells. The profiles show a relatively low concentration of total {sup 3}H+{sup 3}He which led Schlosser to assume a small effective infiltration rate of 0.1 m/yr. However, the precipitation surplus in the area is at least 0.3 m/yr. Alternatively, total {sup 3}H+{sup 3}He decreases if 3He escapes into soil air by large dispersion in the aquifer, as shown by Schlosser et al. in 1D profiles. However, the large dispersion originates from heterogeneities in the flow field and is, in principle, connected with aquifer properties, thus presenting an ideal test case for Alliances. For initiating the hydraulic model, the {sup 3}H
van den Berg, J. H.; Schuurman, F.; Kleinhans, M. G.; Lentink, H.
2010-12-01
Our objective is to understand general causes of different river channel patterns in unconfined alluvial plains. We discuss the principles and compare the performance of an empirical stream power-based classification and a physics-based bar pattern predictor. We present a careful selection of data from literature that contains rivers with discharge and median bed particle size ranging several orders of magnitude with various channel patterns and bar types, but no obvious eroding or aggrading tendency. Empirically a continuum of patterns is found for increasing specific stream power from single-thread, laterally immobile channels, meandering styles with scroll bars and with chute bars and moderately and highly braided channel patterns. Stream power is calculated with pattern-independent variables: mean annual flood, valley gradient and channel width predicted with a hydraulic geometry relation. `Thresholds', above which these patterns emerge, increase with bed sediment size. Linear bar theory predicts nature and presence of bars and bar mode, here converted to active braiding index. The most important variables are actual width-to-depth ratio and nonlinearity of bed sediment transport. Numerical modelling with the same equations as underlying the bar theory allow for nonlinear effects. We modelled hypothetical rivers over a large range of stream power and particle sizes with various choices for hydraulic roughness, sediment transport and transverse slope relations. Results agree well with the empirical diagram as well as empirical relations for bar and channel dimensions. Increasing potential specific stream power implies more energy to erode banks and indeed correlates to channels with high width-to-depth ratio. Bar theory and numerical modelling predict that such rivers develop more bars across the width (higher braiding index). At the transition from meandering to braiding weakly braided rivers and meandering rivers with chutes are found in nature and in the
Hubbard physics in the PAW GW approximation.
Booth, J M; Drumm, D W; Casey, P S; Smith, J S; Russo, S P
2016-06-28
It is demonstrated that the signatures of the Hubbard Model in the strongly interacting regime can be simulated by modifying the screening in the limit of zero wavevector in Projector-Augmented Wave GW calculations for systems without significant nesting. This modification, when applied to the Mott insulator CuO, results in the opening of the Mott gap by the splitting of states at the Fermi level into upper and lower Hubbard bands, and exhibits a giant transfer of spectral weight upon electron doping. The method is also employed to clearly illustrate that the M1 and M2 forms of vanadium dioxide are fundamentally different types of insulator. Standard GW calculations are sufficient to open a gap in M1 VO2, which arise from the Peierls pairing filling the valence band, creating homopolar bonds. The valence band wavefunctions are stabilized with respect to the conduction band, reducing polarizability and pushing the conduction band eigenvalues to higher energy. The M2 structure, however, opens a gap from strong on-site interactions; it is a Mott insulator.
A 2D Time Domain DRBEM Computer Model for MagnetoThermoelastic Coupled Wave Propagation Problems
Directory of Open Access Journals (Sweden)
Mohamed Abdelsabour Fahmy
2014-07-01
Full Text Available A numerical computer model based on the dual reciprocity boundary element method (DRBEM is extended to study magneto-thermoelastic coupled wave propagation problems with relaxation times involving anisotropic functionally graded solids. The model formulation is tested through its application to the problem of a solid placed in a constant primary magnetic field acting in the direction of the z-axis and rotating about this axis with a constant angular velocity. In the case of two-dimensional deformation, an implicit-explicit time domain DRBEM was presented and implemented to obtain the solution for the displacement and temperature fields. A comparison of the results is presented graphically in the context of Lord and Shulman (LS and Green and Lindsay (GL theories. Numerical results that demonstrate the validity of the proposed method are also presented graphically.
Applying Contact Angle to a 2D Multiphase Smoothed Particle Hydrodynamics Model
Farrokhpanah, Amirsaman; Mostaghimi, Javad
2016-01-01
Equilibrium contact angle of liquid drops over horizontal surfaces has been modeled using Smoothed Particle Hydrodynamics (SPH). The model is capable of accurate implementation of contact angles to stationary and moving contact lines. In this scheme, the desired value for stationary or dynamic contact angle is used to correct the profile near the triple point. This is achieved by correcting the surface normals near the contact line and also interpolating the drop profile into the boundaries. Simulations show that a close match to the chosen contact angle values can be achieved for both stationary and moving contact lines. This technique has proven to reduce the amount of nonphysical shear stresses near the triple point and to enhance the convergence characteristics of the solver.
Hue, V; Cavalié, T; Dobrijevic, M; Hersant, F
2015-01-01
Saturn's axial tilt produces seasons in a similar way as on Earth. Both the stratospheric temperature and composition are affected by this latitudinally varying insolation along the seasons. The thermal structure is controlled and regulated by the amount of hydrocarbons in the stratosphere, which act as absorbers and coolants from the UV to the far-IR spectral range, and this structure influences the amount of hydrocarbons. We study here the feedback between the chemical composition and the thermal structure by coupling a latitudinal and seasonal photochemical model with a radiative seasonal model. Our results show that the seasonal temperature peak in the higher stratosphere, associated with the seasonal increase of insolation, is shifted earlier than the maximum insolation peak. This shift is increased with increasing latitudes and is caused by the low amount of stratospheric coolants in the spring season. At 80$^{\\circ}$ in both hemispheres, the temperature peak at 1d-2mbar is seen to occur half a season e...
Numerical Modeling of 2-D and 3-D Flows using Artificial Compressibility Method and Collocated Mesh
Directory of Open Access Journals (Sweden)
Yasin Aghaee-Shalmani
2016-01-01
Full Text Available In this paper, applications of a numerical model on simulation of two and three-dimensional ﬂows are presented. This model solves Navier-Stokes equations using ﬁnite volume method and large eddy simulation (LES in a collocated mesh. Artiﬁcial compressibility method with dual t ime stepping is used to solve the time dependent equations. Also a modiﬁed m omentum i nterpolation method (MIM based on the unsteady ﬂows i s deployed t o overcome t he non-physical pressure oscillation. Capability of the presented numerical code for ﬂow s imulation, i s a ssessed by a pplication f or twodimensional square and three-dimensional lid-driven cavity ﬂows. Numerical r esults of cavity ﬂow presents very good agreement with the numerical and experimental data of other existent researches.
New 2D Thermal Model Applied to an LHC Inner Triplet Quadrupole Magnet
Bielert, ER; Ten Kate, HHJ; Verweij, AP
2011-01-01
A newly developed numerical model is presented that enables to compute two-dimensional heat transfer and temperature distributions over the cross-section of superconducting accelerator magnets. The entire thermal path from strand-in-cable to heat sink, including helium channels is considered. Superfluid helium properties are combined with temperature- and field-dependent non-linear solid material properties. Interfacial interactions are also taken into account. The model is applied to the cross-section of an inner triplet quadrupole magnet featuring a new concept for the ground insulation. Beam loss profiles are implemented as main heat source. It is concluded that operational margins can be considerably increased by opening additional thermal paths, improving the cooling conditions.
Hassan, Ehab; Morrison, P J; Horton, W
2016-01-01
Progress in understanding the coupling between plasma instabilities in the equatorial electrojet based on a unified fluid model is reported. A deeper understanding of the linear and nonlinear evolution and the coupling of the gradient-drift and Farley-Buneman instabilities is achieved by studying the e?ect of di?erent combinations of the density-gradient scale-lengths (Ln) and cross-?eld (E?B) drifts on the plasma turbulence. Mechanisms and channels of energy transfer are illucidated for these multiscale instabilities. Energy for the uni?ed model is examined, including the injected, conservative redistribution (between ?elds and scales), and ultimate dissipation. Various physical mechanisms involved in the energetics are categorized as sources, sinks, nonlinear transfer, and coupling to show that the system satisfies the fundamental law of energy Oonservation. The physics of the nonlinear transfer terms is studied to identify their roles in producing energy cascades { the transference of energy from the domin...
Cooperative Research on 2-D Soil-Structure Interaction Model with P-SV Plane Wave
Gicev, Vlado
2008-01-01
The main goal of the proposed research was to study the phenomena accompanying the soil-foundation-structure interaction and based on this study to propose improvements of the existing codes for blasting and building structures resistant to strong ground motion (earthquakes, underground explosions, and blasting). We proposed the research conducted with computer simulations on numerical models of wave propagation in three media (soil, foundation, and structure). We also proposed that at the en...
The 2d Gross-Neveu Model for Pseudovector Fermions and Tachyonic Mass Generation
Oikonomou, V K
2011-01-01
Recent observations in the OPERA experiment suggest that the neutrino could propagate with speed that is superluminal. Based on early theoretical work on tachyonic fermions we shall study a modification of the Gross-Neveu model in two dimensions. We shall see that the theory results to the dynamical generation of real and imaginary masses. These imaginary masses indicate the possibility that tachyonic solutions (or instabilities) could exist in the theory.
A Finite-Volume Version of Aizenman-Higuchi Theorem for the 2d Ising Model
Coquille, Loren; Velenik, Yvan Alain
2010-01-01
In the late 1970s, in two celebrated papers, Aizenman and Higuchi independently established that all infinite-volume Gibbs measures of the two-dimensional ferromagnetic nearest-neighbor Ising model are convex combinations of the two pure phases. We present here a new approach to this result, with a number of advantages: (i) We obtain an optimal finite-volume, quantitative analogue (implying the classical claim); (ii) the scheme of our proof seems more natural and provides a better picture of ...
Dynamic Linkages Between the Transition Zone & Surface Plate Motion in 2D Models of Subduction
Arredondo, K.; Billen, M. I.
2014-12-01
Subduction zones exhibit a wide range of behavior, from slab stagnation at 660 km to direct penetration into the lower mantle. Due to uncertainties in the tectonic history of individual subduction zones, such as trench velocities, potential mechanisms for controlling slab behavior in the transition zone are explored using numerical models. Numerical simulations have utilized a range of assumptions to improve computational efficiency, such as ignoring latent heat, ignoring compositional effects or fixing the trench location: the net effect of these assumptions resulting modeled dynamics remains unclear. Additionally the eight major, composition-dependent, phase transitions for pyrolite, harzburgite and eclogite may be an important influence on subducting slab dynamics due to the additional forces that are dependent on depth and compositional layering within the slab (e.g., Ricard et al., 2005). With the goal of developing more complete, self-consistent, and less idealized simulations, we test the importance of various factors on slab behavior: the presence of shear, adiabatic and latent heating, compositional layering, composition-dependent phase transitions and explicit plate speeds versus dynamically evolving plate and trench velocities. Preliminary results indicate that individual components have a relatively minor effect, but produce large changes when combined together. The extent of slab folding and stagnation is overestimated by only modeling the 410 and 660 km phase transitions. Dynamic models with all seven composition-dependent phase transitions are very sensitive to the plate strength and weak zone viscosity, causing large changes in plate speed and slab detachment. Changes to the overriding plate buoyance and strength investigate the origin and influence of trench movement on slab deformation. These feedbacks and parameter-sensitive behavior indicate that the wide range of observed slab behavior may result from subtle differences in plate and plate
Impact of a hydrogen economy on the stratosphere and troposphere studied in a 2-D model
Warwick, N. J.; Bekki, S.; Nisbet, Euan; Pyle, J.A.
2004-01-01
A switch from a fossil fuel to a hydrogen-based energy system could cause significant changes in the magnitude and composition of anthropogenic emissions. Model simulations suggest the most significant impact of these emission changes would occur in the troposphere, affecting OH. This impact is dependent upon the magnitude and nature of trade-offs in changing fossil fuel use. In the stratosphere, changes in water vapour resulting from expected increases in surface molecular hydrogen emissio...
A hierarchical lattice spring model to simulate the mechanics of 2-D materials-based composites
Directory of Open Access Journals (Sweden)
Lucas eBrely
2015-07-01
Full Text Available In the field of engineering materials, strength and toughness are typically two mutually exclusive properties. Structural biological materials such as bone, tendon or dentin have resolved this conflict and show unprecedented damage tolerance, toughness and strength levels. The common feature of these materials is their hierarchical heterogeneous structure, which contributes to increased energy dissipation before failure occurring at different scale levels. These structural properties are the key to exceptional bioinspired material mechanical properties, in particular for nanocomposites. Here, we develop a numerical model in order to simulate the mechanisms involved in damage progression and energy dissipation at different size scales in nano- and macro-composites, which depend both on the heterogeneity of the material and on the type of hierarchical structure. Both these aspects have been incorporated into a 2-dimensional model based on a Lattice Spring Model, accounting for geometrical nonlinearities and including statistically-based fracture phenomena. The model has been validated by comparing numerical results to continuum and fracture mechanics results as well as finite elements simulations, and then employed to study how structural aspects impact on hierarchical composite material properties. Results obtained with the numerical code highlight the dependence of stress distributions on matrix properties and reinforcement dispersion, geometry and properties, and how failure of sacrificial elements is directly involved in the damage tolerance of the material. Thanks to the rapidly developing field of nanocomposite manufacture, it is already possible to artificially create materials with multi-scale hierarchical reinforcements. The developed code could be a valuable support in the design and optimization of these advanced materials, drawing inspiration and going beyond biological materials with exceptional mechanical properties.
A STUDY FOR THE MATHEMATIC MODELING OF 2D IRREGULAR SHAPES FOR FOOTWEAR CAD SYSTEM
Directory of Open Access Journals (Sweden)
DRIŞCU Mariana
2015-05-01
Full Text Available For using a specialized footwear CAD system it's imperative to know the analytical expression of the outlines of the footwear patterns. This brings us to the field of mathematical modeling. Mathematic modeling is based on the equation of the function defining the outline of the model contour. Shapes, contours cannot be identified, in designing, by simple function of the form y=f(x, because most of them have irregular forms, with many concavities and convexities, which explains why their form is intrinsically dependent on the coordinates system. For example, if we want to plot a curve, it is absolutely necessary that we choose the right set of contour points in a system of coordinates, but the important factor in determining the form of the object is the relation between these points, not that between the points and the randomly chosen coordinates system. Further more, the contour forms may have vertical tangents. If the shape were represented by a function y=f(x, the vertical tangents would be an inconvenient in designing, which might be avoided by an approximation of analytic function (e.g. of polynomials For all these reasons, the dominant representation of shapes in CAD is not possible a function y=f(x but a set of function which can be obtained on various portions. This paper presents a study regarding the interpolation of the footwear components and outlines contours and the graphic visualization, using the following methods: Lagrange, B-Spline, Bezier.
Unsteady 2D PEM fuel cell modeling for a stack emphasizing thermal effects
Energy Technology Data Exchange (ETDEWEB)
Shan, Yuyao; Choe, Song-Yul [Department of Mechanical Engineering, Auburn University, Auburn (United States); Choi, Seo-Ho [Fuel Cell Vehicle Team, Hyundai Motor Company and Kia Motors Corporation (United States)
2007-02-25
Models currently used for analyses of thermal and water behavior of a PEM fuel cell are based 3D computational fluid dynamics (CFD). However, the analyses are limited to a single cell with static behavior. Thus, these models cannot be used for analyses of dynamic behavior of a stack that continuously varies according to operating conditions. The model proposed describes dynamic behavior of a stack with two adjoining cells and endplate assembly, and work as a current controlled voltage source that can be used for optimization of BOPs and the associated controls. Simulations have been conducted to analyze start-up behaviors and the performance of the stack. Our analyses deliver following results: (1) dynamic temperature distribution in both the through-plane direction and the along channel direction of the fuel cell stack, (2) effects influencing the source terms of current density, and (3) dynamic oxygen concentration distribution. The temperature profile and its variation propensity are comparable to the previous results [Y. Shan, S.Y. Choe, J. Power Sources, 145 (1) (2005) 30-39; Y. Shan, S.Y. Choe, J. Power Sources, in press]. (author)
Finite-Element 2D and 3D PIC Modeling of RF Devices with Applications to Multipacting
De Ford, John F; Petillo, John
2005-01-01
Multipacting currently limits the performance of many high power radio-frequency (RF) devices, particularly couplers and windows. Models have helped researchers understand and mitigate this problem in 2D structures, but useful multipacting models for complicated 3D structures are still a challenge. A combination of three recent technologies that have been developed in the Analyst and MICHELLE codes begin to address this challenge: high-order adaptive finite-element RF field calculations, advanced particle tracking on unstructured grids, and comprehensive secondary emission models. Analyst employs high-order adaptive finite-element methods to accurately compute driven RF fields and eigenmodes in complex geometries, particularly near edges, corners, and curved surfaces. To perform a multipacting analysis, we use the mesh and fields from Analyst in a modified version of the self-consistent, finite-element gun code MICHELLE. MICHELLE has both a fast, accurate, and reliable particle tracker for unstructured grids ...
Quark-Antiquark and Diquark Condensates in Vacuum in a 2D Two-Flavor Gross-Neveu Model
Institute of Scientific and Technical Information of China (English)
ZHOU Bang-Rong
2007-01-01
The analysis based on the renormalized effective potential indicates that, similar to in the 4D two-flavor Nambu-Jona-Lasinio (NJL) model, in a 2D two-flavor Gross-Neveu model, the interplay between the quark-antiquark and the diquark condensates in vacuum also depends on Gs/Hs, the ratio of the coupling constants in scalar quark antiquark and scalar diquark channel. Only the pure quark-antiquark condensates exist if Gs/Hs ＞ 2/3, which is just the ratio of the color numbers of the quarks participating in the diquark and quark-antiquark condensates. The two condensates will coexist if 0 ＜ Gs/Hs ＜ 2/3. However, different from the 4D NJL model, the pure diquark condensates arise only at Gs/Hs = 0 and are not in a possibly finite region of Gs/Hs below 2/3.
1D and 2D Numerical Modeling for Solving Dam-Break Flow Problems Using Finite Volume Method
Directory of Open Access Journals (Sweden)
Szu-Hsien Peng
2012-01-01
Full Text Available The purpose of this study is to model the flow movement in an idealized dam-break configuration. One-dimensional and two-dimensional motion of a shallow flow over a rigid inclined bed is considered. The resulting shallow water equations are solved by finite volumes using the Roe and HLL schemes. At first, the one-dimensional model is considered in the development process. With conservative finite volume method, splitting is applied to manage the combination of hyperbolic term and source term of the shallow water equation and then to promote 1D to 2D. The simulations are validated by the comparison with flume experiments. Unsteady dam-break flow movement is found to be reasonably well captured by the model. The proposed concept could be further developed to the numerical calculation of non-Newtonian fluid or multilayers fluid flow.
Pseudo-2D model of a cross-flow membrane humidifier for a PEM fuel cell under multiphase conditions
Energy Technology Data Exchange (ETDEWEB)
Dalet, C.; Diny, M. [Peugeot Citroen Automobile, Carrieres sous Poissy (France). Fuel Cell Program; Maranzana, G.; Lottin, O.; Dillet, J. [Nancy Univ., Vanoeuvre les Nancy (France). Centre national de la recherche scientifique
2009-07-01
Membrane dehydration can reduce the performance of proton exchange membrane fuel cells (PEMFCs). However, excessive water at the inlet of the fuel cells can flood cathodes. An understanding of the coupled mass and heat transfer processes involved in membrane humidifiers is needed in order to successfully manage water in PEMFCs. This paper discussed a pseudo-2D model of a cross-flow membrane humidifier for PEMFCs. The model was used to test correlations of the water transport coefficient through a Nafion 115 membrane. The study showed that results obtained using the model differed from experimental results. The effects of inlet operating conditions, flow rates, and temperature on the performance of a planar membrane humidifier under both single- and multi-phase conditions were also investigated.
Directory of Open Access Journals (Sweden)
Somboon PORNPINATEPONG
2006-01-01
Full Text Available A 2-D vertically averaged boundary-fitted coordinate hydrodynamic model was employed to simulate circulation in Thale Sap Songkhla due to tides in the Gulf of Thailand. The model was calibrated against a set of current velocity data collected between June and July 1997. The best fit for observations at Ko Yo and Pak Ro was achieved. To comprehend the hydrodynamic in the lake, the current vectors were illustrated for both the flood and ebb stages. Detailed analysis indicated that there existed a turning current at the northern tip of Ko Yo Island, which induced a significant current along its northern shoreline. The calculations show the current was stronger in the deep channel north of Ko Yo than in the southern circuit. The model also predicted a gyre near the deep channel of the lake entrance, which persisted for some time during the changing direction of the flood and ebb currents.
Lectures on 2D gravity and 2D string theory
International Nuclear Information System (INIS)
This report the following topics: loops and states in conformal field theory; brief review of the Liouville theory; 2D Euclidean quantum gravity I: path integral approach; 2D Euclidean quantum gravity II: canonical approach; states in 2D string theory; matrix model technology I: method of orthogonal polynomials; matrix model technology II: loops on the lattice; matrix model technology III: free fermions from the lattice; loops and states in matrix model quantum gravity; loops and states in the C=1 matrix model; 6V model fermi sea dynamics and collective field theory; and string scattering in two spacetime dimensions
International Nuclear Information System (INIS)
Planar 2D x-ray mammography is generally accepted as the preferred screening technique used for breast cancer detection. Recently, digital breast tomosynthesis (DBT) has been introduced to overcome some of the inherent limitations of conventional planar imaging, and future technological enhancements are expected to result in the introduction of further innovative modalities. However, it is crucial to understand the impact of any new imaging technology or methodology on cancer detection rates and patient recall. Any such assessment conventionally requires large scale clinical trials demanding significant investment in time and resources. The concept of virtual clinical trials and virtual performance assessment may offer a viable alternative to this approach. However, virtual approaches require a collection of specialized modelling tools which can be used to emulate the image acquisition process and simulate images of a quality indistinguishable from their real clinical counterparts. In this paper, we present two image simulation chains constructed using modelling tools that can be used for the evaluation of 2D-mammography and DBT systems. We validate both approaches by comparing simulated images with real images acquired using the system being simulated. A comparison of the contrast-to-noise ratios and image blurring for real and simulated images of test objects shows good agreement ( < 9% error). This suggests that our simulation approach is a promising alternative to conventional physical performance assessment followed by large scale clinical trials. (paper)
Hassan, Ehab; Hatch, D. R.; Morrison, P. J.; Horton, W.
2016-01-01
Progress in understanding the coupling between plasma instabilities in the equatorial electrojet based on a unified fluid model is reported. A deeper understanding of the linear and nonlinear evolution and the coupling of the gradient-drift and Farley-Buneman instabilities is achieved by studying the e?ect of di?erent combinations of the density-gradient scale-lengths (Ln) and cross-?eld (E?B) drifts on the plasma turbulence. Mechanisms and channels of energy transfer are illucidated for thes...
An Asymptotic Analysis of a 2-D Model of Dynamically Active Compartments Coupled by Bulk Diffusion
Gou, J.; Ward, M. J.
2016-08-01
A class of coupled cell-bulk ODE-PDE models is formulated and analyzed in a two-dimensional domain, which is relevant to studying quorum-sensing behavior on thin substrates. In this model, spatially segregated dynamically active signaling cells of a common small radius ɛ ≪ 1 are coupled through a passive bulk diffusion field. For this coupled system, the method of matched asymptotic expansions is used to construct steady-state solutions and to formulate a spectral problem that characterizes the linear stability properties of the steady-state solutions, with the aim of predicting whether temporal oscillations can be triggered by the cell-bulk coupling. Phase diagrams in parameter space where such collective oscillations can occur, as obtained from our linear stability analysis, are illustrated for two specific choices of the intracellular kinetics. In the limit of very large bulk diffusion, it is shown that solutions to the ODE-PDE cell-bulk system can be approximated by a finite-dimensional dynamical system. This limiting system is studied both analytically, using a linear stability analysis and, globally, using numerical bifurcation software. For one illustrative example of the theory, it is shown that when the number of cells exceeds some critical number, i.e., when a quorum is attained, the passive bulk diffusion field can trigger oscillations through a Hopf bifurcation that would otherwise not occur without the coupling. Moreover, for two specific models for the intracellular dynamics, we show that there are rather wide regions in parameter space where these triggered oscillations are synchronous in nature. Unless the bulk diffusivity is asymptotically large, it is shown that a diffusion-sensing behavior is possible whereby more clustered spatial configurations of cells inside the domain lead to larger regions in parameter space where synchronous collective oscillations between the small cells can occur. Finally, the linear stability analysis for these cell
A comprehensive parameter study of an active magnetic regenerator using a 2D numerical model
DEFF Research Database (Denmark)
Nielsen, Kaspar Kirstein; Bahl, Christian Robert Haffenden; Smith, Anders;
2010-01-01
, cycle frequency and fluid movement. These are cast into the non-dimensional units utilization, porosity and number of transfer units (NTU). The cooling capacity vs. temperature span is mapped as a function of these parameters and each configuration is evaluated through the maximum temperature span......A two-dimensional numerical heat transfer model is used to investigate an active magnetic regenerator (AMR) based on parallel plates of magnetocaloric material. A large range of parameter variations are performed to study the optimal AMR. The parameters varied are the plate and channel thicknesses...
Acid/base front propagation in saturated porous media: 2D laboratory experiments and modeling
Loyaux-Lawniczak, Stéphanie; Lehmann, François; Ackerer, Philippe
2012-09-01
We perform laboratory scale reactive transport experiments involving acid-basic reactions between nitric acid and sodium hydroxide. A two-dimensional experimental setup is designed to provide continuous on-line measurements of physico-chemical parameters such as pH, redox potential (Eh) and electrical conductivity (EC) inside the system under saturated flow through conditions. The electrodes provide reliable values of pH and EC, while sharp fronts associated with redox potential dynamics could not be captured. Care should be taken to properly incorporate within a numerical model the mixing processes occurring inside the electrodes. The available observations are modeled through a numerical code based on the advection-dispersion equation. In this framework, EC is considered as a variable behaving as a conservative tracer and pH and Eh require solving the advection dispersion equation only once. The agreement between the computed and measured pH and EC is good even without recurring to parameters calibration on the basis of the experiments. Our findings suggest that the classical advection-dispersion equation can be used to interpret these kinds of experiments if mixing inside the electrodes is adequately considered.
Competition among reputations in the 2D Sznajd model: Spontaneous emergence of democratic states
Crokidakis, Nuno
2011-01-01
We propose a modification in the Sznajd sociophysics model defined on the square lattice. For this purpose, we consider reputation-a mechanism limiting the agents' persuasive power. The reputation is introduced as a time-dependent score, which can be positive or negative. This mechanism avoids dictatorship (full consensus, all spins parallel) for a wide range of model parameters. We consider two different situations: case 1, in which the agents' reputation increases for each persuaded neighbor, and case 2, in which the agents' reputation increases for each persuasion and decreases when a neighbor keeps his opinion. Our results show that the introduction of reputation avoids full consensus even for initial densities of up spins greater than 1/2. The relaxation times follow a log-normal-like distribution in both cases, but they are larger in case 2 due to the competition among reputations. In addition, we show that the usual phase transition occurs and depends on the initial concentration $d$ of individuals wit...
Comparative 2D BRT and seismic modeling of CO2 plumes in deep saline reservoirs
Hagrey, Said Attia Al; Strahser, Matthias; Rabbel, Wolfgang
2010-05-01
The multi-disciplinary research project 'CO2 MoPa' (modeling and parameterization of CO2 storage in deep saline formations for dimensions and risk analysis) deals, among others, with the parameterization of virtual subsurface storage sites to characterize rock properties with modeling of processes related to CCS in deep saline reservoirs. The geophysical task is to estimate the sensitivity and the resolution of reflection seismic and geoelectrical time-lapses in order to determine the propagation of CO2 within the sediments and the development of the CO2 reservoir. Compared with seismic, borehole electric resistivity tomography (BRT) has lower resolution, but its permanent installation and continuous monitoring can make it an economical alternative or complement. Seismic and geoelectric applications to quantify changes of intrinsic aquifer properties with time are justified by the lower density and velocity and the higher electric resistivity of CO2 in comparison to pore brine. We present here modeling results on scenarios with realistic parameters of deep saline formations of the German Basin (candidate for CCS). The study focuses on effects of parameters related to depth (temperature, pressure), petrophysics (salinity, porosity), plume dimensions/saturations and data acquisition, processing and inversions. Both methods show stronger effects with increasing brine salinity, CO2 reservoir thickness, porosity and CO2 saturation in the pores. Both methods have a pronounced depth dependence due to the pressure and temperature dependence of the velocities, densities and resistivities of the host rock, brine and CO2. Increasing depth means also decreasing frequencies of the seismic signal and hence weaker resolution. Because of the expected limited thickness of the CO2 reservoir, the reflections from its top and bottom will most likely interfere with each other, making it difficult to determine the exact dimensions of the reservoir. In BRT, the resulting resistivity
A new algorithm for bank-failure mechanisms in 2D morphodynamic models with unstructured grids
Institute of Scientific and Technical Information of China (English)
Stefania Evangelista; Massimo Greco; Michele Iervolino; Angelo Leopardi; Andrea Vacca
2015-01-01
Bank failure is an important phenomenon in geomorphic processes. In the presence of river banks or steep bedforms, collapse mechanisms induced by the water-level rise deeply affect the bed evolution along with the sediment-transport processes. In this paper an algorithm capable of simulating such mechanisms in a two-dimensional two-phase morphodynamic model is presented. A mixed Cell-Centered and Node-Centered Finite-Volume discretization, which makes use of an unstructured trian-gular mesh and allows the slope in each cell to be univocally defined, is proposed. The geo-failure operator guarantees that when in the cell the bed slope exceeds a critical angle, the corresponding bed material and pore water will become part of the bed transport and will then follow the dynamic equations of the two-phase flow. The algorithm effectiveness is shown by the numerical reproduction of some experimental tests from the literature.
Palma, G
2009-01-01
The probability density function (PDF) of some global average quantity plays a fundamental role in critical and highly correlated systems. We explicitly compute this quantity as a function of the magnetization for the two dimensional XY model in its harmonic approximation. Numerical simulations and perturbative results have shown a Gumbel-like shape of the PDF, in spite of the fact that the average magnetization is not an extreme variable. Our analytical result allows to test both perturbative analytical expansions and also numerical computations performed previously. Perfect agreement is found for the first moments of the PDF. Also for large volume and in the high temperature limit the distribution becomes Gaussian, as it should be. In the low temperature regime its numerical evaluation is compatible with a Gumbel distribution.
A mathematical model for a didactic device able to simulate a 2D Newtonian gravitational field
De Marchi, Fabrizio
2015-01-01
In this paper we propose a mathematical model to describe a theoretical device able to simulate an inverse-square force on a test mass moving on a horizontal plane. We use two pulleys, a counterweight, a wire and a smooth rail, in addition to the test mass. The tension of the wire (i.e. the attractive force on the test mass) is determined by the position of a counterweight free to move on a rail placed under the plane. The profile of the rail is calculated in order to obtain the required Newtonian force. Details of this calculation are reported in the paper, and numerical simulations are provided in order to investigate the stability of the orbits under the effect of the main friction forces and other perturbative effects. This work points out that there are some criticalities intrinsic to the apparatus and gives some suggestions about how to minimize their impact.
Improving 2D and 3D Skin In Vitro Models Using Macromolecular Crowding.
Benny, Paula; Badowski, Cedric; Lane, E Birgitte; Raghunath, Michael
2016-01-01
The glycoprotein family of collagens represents the main structural proteins in the human body, and are key components of biomaterials used in modern tissue engineering. A technical bottleneck is the deposition of collagen in vitro, as it is notoriously slow, resulting in sub-optimal formation of connective tissue and subsequent tissue cohesion, particularly in skin models. Here, we describe a method which involves the addition of differentially-sized sucrose co-polymers to skin cultures to generate macromolecular crowding (MMC), which results in a dramatic enhancement of collagen deposition. Particularly, dermal fibroblasts deposited a significant amount of collagen I/IV/VII and fibronectin under MMC in comparison to controls. The protocol also describes a method to decellularize crowded cell layers, exposing significant amounts of extracellular matrix (ECM) which were retained on the culture surface as evidenced by immunocytochemistry. Total matrix mass and distribution pattern was studied using interference reflection microscopy. Interestingly, fibroblasts, keratinocytes and co-cultures produced cell-derived matrices (CDM) of varying composition and morphology. CDM could be used as "bio-scaffolds" for secondary cell seeding, where the current use of coatings or scaffolds, typically from xenogenic animal sources, can be avoided, thus moving towards more clinically relevant applications. In addition, this protocol describes the application of MMC during the submerged phase of a 3D-organotypic skin co-culture model which was sufficient to enhance ECM deposition in the dermo-epidermal junction (DEJ), in particular, collagen VII, the major component of anchoring fibrils. Electron microscopy confirmed the presence of anchoring fibrils in cultures developed with MMC, as compared to controls. This is significant as anchoring fibrils tether the dermis to the epidermis, hence, having a pre-formed mature DEJ may benefit skin graft recipients in terms of graft stability and
Pestana, Rita; Matias, Magda; Canelas, Ricardo; Roque, Dora; Araujo, Amelia; Van Zeller, Emilia; Trigo-Teixeira, Antonio; Ferreira, Rui; Oliveira, Rodrigo; Heleno, Sandra; Falcão, Ana Paula; Gonçalves, Alexandre B.
2014-05-01
Floods account for 40% of all natural hazards worldwide and were responsible for the loss of about 100 thousand human lives and affected more than 1,4 million people in the last decade of the 20th century alone. Floods have been the deadliest natural hazard in Portugal in the last 100 years. In terms of inundated area, the largest floods in Portugal occur in the Lower Tagus (LT) River. On average, the river overflows every 2.5 years, at times blocking roads and causing important agricultural damages. The economical relevance of the area and the high frequency of the relevant flood events make the LT floodplain a good pilot region to conduct a data-driven, systematic calibration work of flood hydraulic models. This paper focus on the calibration of 2D-horizontal flood simulation models for the floods of 1997, 2001 and 2006 on a 70-km stretch of the LT River, between Tramagal and Omnias, using the software Tuflow. This computational engine provides 2D solutions based on the Stelling finite-difference, alternating direction implicit (ADI) scheme that solves the full 2D free surface shallow-water flow equations and allowed the introduction of structures that constrain water flow. The models were based on a digital terrain model (DTM) acquired in 2008 by radar techniques (5m of spatial resolution) and on in situ measurements of water elevation in Omnias (downstream boundary condition) and discharge in Tramagal and Zezere (upstream boundary conditions). Due to the relevancy of several dykes on this stretch of the LT River, non-existent on the available DTM, five of them were introduced in the models. All models have the same boundaries and were simulated using steady-state flow initial conditions. The resolution of the 2D grid mesh was 30m. Land cover data for the study area was retrieved from Corine Land Cover 2006 (CO-ordination of INformation on the Environment) with spatial resolution of 100m, and combined with estimated manning coefficients obtained in literature
2D condensation model for the inner Solar Nebula: an enstatite-rich environment
Pignatale, Francesco C; Maddison, Sarah T; Brooks, Geoffrey
2016-01-01
Infrared observations provide the dust composition in the protoplanetary discs surface layers, but can not probe the dust chemistry in the midplane, where planet formation occurs. Meteorites show that dynamics was important in determining the dust distribution in the Solar Nebula and needs to be considered if we are to understand the global chemistry in discs. 1D radial condensation sequences can only simulate one disc layer at a time and cannot describe the global chemistry or the complexity of meteorites. To address these limitations, we compute for the first time the two dimensional distribution of condensates in the inner Solar Nebula using a thermodynamic equilibrium model, and derive timescales for vertical settling and radial migration of dust. We find two enstatite-rich zones within 1 AU from the young Sun: a band ~0.1 AU thick in the upper optically-thin layer of the disc interior to 0.8 AU, and in the optically-thick disc midplane out to ~0.4 AU. The two enstatite-rich zones support recent evidence ...
Generalized 2d-dilaton models, the true black hole and quantum integrability
Katanaev, M O; Liebl, H; Vasilevich, D V
1997-01-01
All 1+1 dimensional dipheomorphism-invariant models can be viewed in a unified manner. This includes also general dilaton theories and especially spherically symmetric gravity (SSG) and Witten's dilatonic black hole (DBH). A common feature --- also in the presence of matter fields of any type --- is the appearance of an absolutely conserved quantity C which is determined by the influx of matter. Only for a subclass of generalized dilaton theories the singularity structure vanishes together with C. Such `physical' theories include, of course, SSG and DBH. It seems to have been overlooked until recently that the (classical) 'black hole' singularity of the DBH deviates from SSG in a physically nontrivial manner. At the quantum level for all generalized dilaton theories --- in the absence of matter --- the local quantum effects are shown to disappear. This enables us to compute e.g. the second loop order correction to the Polyakov term. For non-minimal scalar coupling we also believe to have settled the controver...
Time-Dependent 2D Modeling of Magnetron Plasma Torch in Turbulent Flow
Institute of Scientific and Technical Information of China (English)
LI Lincun; XIA Weidong
2008-01-01
A theoretical model is presented to describe the electromagnetic, heat transfer and fluid flow phenomena within a magnetron plasma torch and in the resultant plume, by using a commercial computational fluid dynamics (CFD) code FLUENT. Specific calculations are pre-sented for a pure argon system (i.e., an argon plasma discharging into an argon environment), operated in a turbulent mode. An important finding of this work is that the external axial mag-netic field (AMF) may have a significant effect on the behavior of arc plasma and thus affects the resulting plume. The AMF impels the plasma to retract axially and expand radially. As a result, the plasma intensity distribution on the cross section of torch seems to be more uniform. Numerical results also show that with AMF, the highest plasma temperature decreases and the anode arc root moves upstream significantly, while the current density distribution at the anode is more concentrated with a higher peak value. In addition, the use of AMF then induces a strong backflow at the torch spout and its magnitude increases with the AMF strength but decreases with the inlet gas velocity.
Directory of Open Access Journals (Sweden)
Luc R. Dupré
1997-01-01
Full Text Available The main purpose of this paper is to incorporate a refined hysteresis model, viz. a vector Preisach model, in 2D magnetic field computations. To this end the governing Maxwell equations are rewritten in a suitable way, which allows to take into account the proper magnetic material parameters and, moreover, to pass to a variational formulation. The variational problem is solved numerically by a FE approximation, using a quadratic mesh, followed by the time discretisation based upon a modified Cranck Nicholson algorithm. The latter includes a suitable iteration procedure to deal with the nonlinear hysteresis behaviour. Finally, the effectiveness of the presented mathematical tool has been confirmed by several numerical experiments.
Guzik, Joyce A; Nelson, N J; Lovekin, C; Kosak, K; Kitiashvili, I N; Mansour, N N; Kosovichev, A
2016-01-01
We present multidimensional modeling of convection and oscillations in main-sequence stars somewhat more massive than the Sun, using three separate approaches: 1) Using the 3-D planar StellarBox radiation hydrodynamics code to model the envelope convection zone and part of the radiative zone. Our goals are to examine the interaction of stellar pulsations with turbulent convection in the envelope, excitation of acoustic modes, and the role of convective overshooting; 2) Applying the spherical 3-D MHD ASH (Anelastic Spherical Harmonics) code to simulate the core convection and radiative zone. Our goal is to determine whether core convection can excite low-frequency gravity modes, and thereby explain the presence of low frequencies for some hybrid gamma Doradus/delta Scuti variables for which the envelope convection zone is too shallow for the convective blocking mechanism to drive gravity modes; 3) Applying the ROTORC 2-D stellar evolution and dynamics code to calculate evolution with a variety of initial rotat...
Institute of Scientific and Technical Information of China (English)
V.MEDINA; A.BATEMAN; M.H(U)RLIMANN
2008-01-01
FLATModel is a 2D finite volume code that contains several original approaches to improve debris-flow simulation.Firstly,FLATModel incorporates a "stop-and-go" technique in each cell to allow continuous collapses and remobilizations of the debris-flow mass.Secondly,flow velocity and consequently yield stress is directly associated with the type of rheology to improve boundary accuracy.Thirdly,a simple approach for entrainment is also included in the model to analyse the effect of basal erosion of debris flows.FLATMODEL was tested at several events that occurred in the Eastern Pyrenees and simulation results indicated that the model can represent rather well the different characteristics observed in the field.
Directory of Open Access Journals (Sweden)
A. Caserta
1995-06-01
Full Text Available The geological information collected in the last years by the Istituto Nazionale di Geofisica for the city of Rome is used to construct 1- and 2-D models of the nearsurface structure. These models are the basis for the numerical generation of synthetic accelerograms which can simulate the horizontal ground motion (SH waves produced in the different areas of the city by a large (M ? 7 potential earthquake 100 km away in Central Apennines. The proposed methodology yields earthquake engineering parameters (peak ground acceleration and velocity, Arias intensity, energy flux, response spectra whose spatial variations are consistent with the damage distribution caused by the strongest earthquakes felt in Rome during its long history. Based on the macroseismic inforination and the results of the numerical simulations, general criteria for seismic zonation of the city of Rome are proposed.
Liu, L.; Liu, Y.; Wang, X.; Yu, D.; Liu, K.; Huang, H.; Hu, G.
2015-03-01
Flash floods have occurred frequently in the urban areas of southern China. An effective process-oriented urban flood inundation model is urgently needed for urban storm-water and emergency management. This study develops an efficient and flexible cellular automaton (CA) model to simulate storm-water runoff and the flood inundation process during extreme storm events. The process of infiltration, inlets discharge and flow dynamics can be simulated with little preprocessing on commonly available basic urban geographic data. In this model, a set of gravitational diverging rules are implemented to govern the water flow in a rectangular template of three cells by three cells of a raster layer. The model is calibrated by one storm event and validated by another in a small urban catchment in Guangzhou of southern China. The depth of accumulated water at the catchment outlet is interpreted from street-monitoring closed-circuit television (CCTV) videos and verified by on-site survey. A good level of agreement between the simulated process and the reality is reached for both storm events. The model reproduces the changing extent and depth of flooded areas at the catchment outlet with an accuracy of 4 cm in water depth. Comparisons with a physically based 2-D model (FloodMap) show that the model is capable of effectively simulating flow dynamics. The high computational efficiency of the CA model can meet the needs of city emergency management.
Zhao, Dongmiao; Tang, Jun; Wu, Xiuguang; Lin, Changning; Liu, Lijun; Chen, Jian
2016-05-01
A 2D vertical (2DV) numerical model, without σ-coordinate transformation in the vertical direction, is developed for the simulation of fl ow and sediment transport in open channels. In the model, time-averaged Reynolds equations are closed by the k-ɛ nonlinear turbulence model. The modifi ed Youngs-VOF method is introduced to capture free surface dynamics, and the free surface slope is simulated using the ELVIRA method. Based on the power-law scheme, the k-ɛ model and the suspended-load transport model are solved numerically with an implicit scheme applied in the vertical plane and an explicit scheme applied in the horizontal plane. Bedload transport is modeled using the Euler-WENO scheme, and the grid-closing skill is adopted to deal with the moving channel bed boundary. Verifi cation of the model using laboratory data shows that the model is able to adequately simulate fl ow and sediment transport in open channels, and is a good starting point for the study of sediment transport dynamics in strong nonlinear fl ow scenarios.
International Nuclear Information System (INIS)
The study addresses the issues of groundwater flow and particle transport in a 2-D heterogenous porous medium. We follow here the line of G. Dagan and Y. Rubin. In a series of articles these authors propose and represent the variables involves ((transmissivity, head, Darcy velocity, particle position and travel time) by means of stochastic processes. The (unconditional) moments are first derived by solving the partial differential equations corresponding to a 2-D flow in a saturated medium, with no recharge. In a second step, the variances of the processes are reduced bu taking local data into account within the conditional probabilities framework. In this document we present a complete theoretical study of the method and apply it on synthetical test cases. We deal with the following matters: study the impact of different data type and configurations on the conditional estimation of the flow and transport variables; study the robustness of the model for increasing levels of heterogeneity by means of comparison with the moments obtained by Monte-Carlo simulations. The method is enlarged to weakly un-stationary flow cases (non constant transmissivity and head gradient means) and applied on synthetical test cases. (author)
Institute of Scientific and Technical Information of China (English)
LI WeiFeng; CHEN QiuWen; MAO JingQiao
2009-01-01
Urban inundation due to anomalous storms is a serious problem for many cities worldwide. Therefore, it is important to accurately simulate urban hydrological processes and efficiently predict the potential risks of urban floods for the improvement of drainage designs and implementation of emergency ac-tions. However, the complexity of urban landforma and the diversity of hydraulic infrastructure pose particular challenges for the simulation and risk assessment of urban drainage processes. This study developed a methodology to comprehensively simulate inundation processes by dynamically coupling 1D and 2D hydrodynamic models. By allowing the simultaneous solution of the processes of rainfall and runoff, urban drainage, and flooding, this method can be used to estimate the potential inundation risks of any designed drainage system. Furthermore, a Geographical Information System (GIS) based platform was fully integrated with the model engine to effectively illustrate the context of the problem. The developed model was then demonstrated on the Beijing 2008 Olympic Village under the conditions of the 5-year and 50-year design storms. The sewer discharge, channel discharge, and flood propaga-tion (inundation initiation, extent, depths, and duration) were numerically validated and analyzed. The results identified the potential inundation risks. From the study, it is found that the coupled GIS and 1D and 2D hydrodynamic models have the potential to simulate urban inundation processes, and hence efficiently predict flood risks and support cost-effective drainage design and management. It also im-plies promising prospects about the wide availability of high quality digital data, GIS techniques, and well-developed monitoring infrastructure to develop online urban inundation forecasts.
Campforts, Benjamin; Vanacker, Veerle; Vanderborght, Jan; Baken, Stijn; Smolders, Erik; Govers, Gerard
2016-04-01
Meteoric 10Be allows for the quantification of vertical and lateral soil fluxes over long time scales (103-105 yr). However, the mobility of meteoric 10Be in the soil system makes a translation of meteoric 10Be inventories into erosion and deposition rates complex. Here, we present a spatially explicit 2D model simulating the behaviour of meteoric 10Be on a hillslope. The model consists of two parts. The first component deals with advective and diffusive mobility of meteoric 10Be within the soil profile, and the second component describes lateral soil and meteoric 10Be fluxes over the hillslope. Soil depth is calculated dynamically, accounting for soil production through weathering as well as downslope fluxes of soil due to creep, water and tillage erosion. Synthetic model simulations show that meteoric 10Be inventories can be related to erosion and deposition across a wide range of geomorphological and pedological settings. Our results also show that meteoric 10Be can be used as a tracer to detect human impact on soil fluxes for soils with a high affinity for meteoric 10Be. However, the quantification of vertical mobility is essential for a correct interpretation of the observed variations in meteoric 10Be profiles and inventories. Application of the Be2D model to natural conditions using data sets from the Southern Piedmont (Bacon et al., 2012) and Appalachian Mountains (Jungers et al., 2009; West et al., 2013) allows to reliably constrain parameter values. Good agreement between simulated and observed meteoric 10Be concentrations and inventories is obtained with realistic parameter values. Furthermore, our results provide detailed insights into the processes redistributing meteoric 10Be at the soil-hillslope scale.
QSAR modeling of toxicity of diverse organic chemicals to Daphnia magna using 2D and 3D descriptors
Energy Technology Data Exchange (ETDEWEB)
Kar, Supratik [Drug Theoretics and Cheminformatics Laboratory, Department of Pharmaceutical Technology, Jadavpur University, Raja S C Mullick Road, Kolkata 700032 (India); Roy, Kunal, E-mail: kunalroy_in@yahoo.com [Drug Theoretics and Cheminformatics Laboratory, Department of Pharmaceutical Technology, Jadavpur University, Raja S C Mullick Road, Kolkata 700032 (India)
2010-05-15
One of the major economic alternatives to experimental toxicity testing is the use of quantitative structure-activity relationships (QSARs) which are used in formulating regulatory decisions of environmental protection agencies. In this background, we have modeled a large diverse group of 297 chemicals for their toxicity to Daphnia magna using mechanistically interpretable descriptors. Three-dimensional (3D) (electronic and spatial) and two-dimensional (2D) (topological and information content indices) descriptors along with physicochemical parameter log K{sub o/w} (n-octanol/water partition coefficient) and structural descriptors were used as predictor variables. The QSAR models were developed by stepwise multiple linear regression (MLR), partial least squares (PLS), genetic function approximation (GFA), and genetic PLS (G/PLS). All the models were validated internally and externally. Among several models developed using different chemometric tools, the best model based on both internal and external validation characteristics was a PLS equation with 7 descriptors and three latent variables explaining 67.8% leave-one-out predicted variance and 74.1% external predicted variance. The PLS model suggests that higher lipophilicity and electrophilicity, less negative charge surface area and presence of ether linkage, hydrogen bond donor groups and acetylenic carbons are responsible for greater toxicity of chemicals. The developed model may be used for prediction of toxicity, safety and risk assessment of chemicals to achieve better ecotoxicological management and prevent adverse health consequences.