Search results for "Boundary value problem"
showing 10 items of 551 documents
Modeling electron dynamics coupled to continuum states in finite volumes with absorbing boundaries
2015
arXiv:1409.1689v1
Monte Carlo simulation of dimensional crossover in the XY model.
1993
We report Monte Carlo simulations of Villain's periodic Gaussian XY model on ${\mathit{L}}^{2}$\ifmmode\times\else\texttimes\fi{}N lattices of film geometry (L\ensuremath{\gg}N) with up to N=16 layers, employing the single-cluster update algorithm combined with improved estimators for measurements. The boundary conditions are periodic within each layer and free at the bottom and top layer. Based on data for the specific heat, the spin-spin correlation function, and the susceptibility in the high-temperature phase we study the crossover from three- to two-dimensional behavior as criticality is approached. For the transition temperatures, determined from Kosterlitz-Thouless fits to the correl…
Modification of the Bloch law in ferromagnetic nanostructures
2014
The temperature dependence of magnetization in ferromagnetic nanostructures (e.g., nanoparticles or nanoclusters) is usually analyzed by means of an empirical extension of the Bloch law sufficiently flexible for a good fitting to the observed data and indicates a strong softening of magnetic coupling compared to the bulk material. We analytically derive a microscopic generalization of the Bloch law for the Heisenberg spin model which takes into account the effects of size, shape and various surface boundary conditions. The result establishes explicit connection to the microscopic parameters and differs significantly from the existing description. In particular, we show with a specific examp…
Coupling of density wave oscillations in parallel channels with high order modal kinetics: application to BWR out of phase oscillations
2000
Abstract In this paper, we study the behavior of a system formed by two parallel channels coupled to a multimodal kinetics. The first problem that arises is the calculation of the reactivity coefficients for the higher modes. This problem is solved by means of the introduction of distribution factors for a given reactor region which depend on the involved modes. We have also performed a detailed analysis of the different instability types which can be obtained from the model changing the boundary conditions and the feedback gains of the fundamental and first harmonic modes.
Equivalence betweenXYand dimerized models
2010
The spin-$1/2$ chain with $\mathit{XY}$ anisotropic coupling in the plane and the $\mathit{XX}$ isotropic dimerized chain are shown to be equivalent in the bulk. For finite systems, we prove that the equivalence is exact in given parity sectors, after taking care of the precise boundary conditions. The proof is given constructively by finding unitary transformations that map the models onto each other. Moreover, we considerably generalized our mapping and showed that even in the case of fully site-dependent couplings the $\mathit{XY}$ chain can be mapped onto an $\mathit{XX}$ model. This result has potential application in the study of disordered systems.
Equivalent-Single-Layer discontinuous Galerkin methods for static analysis of multilayered shells
2021
Abstract An original formulation for the elastic analysis of multilayered shells is presented in this work. The key features of the formulation are: the representation of the shell mean surface via a generic system of curvilinear coordinates; the unified treatment of general shell theories via an Equivalent-Single-Layer approach based on the through-the-thickness expansion of the covariant components of the displacement field; and an Interior Penalty discontinuous Galerkin scheme for the solution of the set of governing equations. The combined use of these features enables a high-order solution of the multilayered shell problem. Several numerical tests are presented for isotropic, orthotrop…
Hole-doped Hubbard ladders
2005
The formation of stripes in six-leg Hubbard ladders with cylindrical boundary conditions is investigated for two different hole dopings, where the amplitude of the hole density modulation is determined in the limits of vanishing DMRG truncation errors and infinitely long ladders. The results give strong evidence that stripes exist in the ground state of these systems for strong but not for weak Hubbard couplings. The doping dependence of these findings is analysed.
Influence of rotational diffusion on the electric field induced effect on the fluorescence spectrum of diluted solutions I. Theory and numerical simu…
1997
Abstract The theory for the calculation of excited state dipole moments from electrooptical emission measurements, developed by Baumann and Deckers (Ber. Bunsenges. Phys. Chem. 81 (1977) 786) presupposes a Boltzmann distribution for the emitting molecules. Using the anisotropic rotational diffusion model and taking into account all important electric field induced effects, we derive equations that describe quantitatively the electric field effect on the fluorescence of an ensemble of solute rigid molecules which are not yet equilibrated with respect to their orientation when emitting. Numerical simulations are performed to compare the general case and the limiting case of a prevailing Boltz…
A new algorithm for simulating flows of conducting fluids in the presence of electric fields
2012
Abstract We propose an algorithm based on dissipative particle dynamics (DPD) for simulations of conducting fluids in the presence of an electric field. In this model, the electrostatic equations are solved in each DPD time step to determine the charge density at the fluid surfaces. These surface charges are distributed on a thin layer of fluid particles near the interface, and the corresponding interfacial electric forces are added to other DPD forces. The algorithm is applied to the electrospinning process at the Taylor cone formation stage. It is shown that, when the applied voltage is sufficiently high, the algorithm captures the formation of a Taylor cone with analytical apex angle 98.…
Existence and Uniqueness Results for Quasi-linear Elliptic and Parabolic Equations with Nonlinear Boundary Conditions
2006
We study the questions of existence and uniqueness of weak and entropy solutions for equations of type -div a(x, Du)+γ(u) ∋ φ, posed in an open bounded subset Ω of ℝN, with nonlinear boundary conditions of the form a(x, Du)·η+β(u) ∋ ψ. The nonlinear elliptic operator div a(x, Du) is modeled on the p-Laplacian operator Δp(u) = div (|Du|p−2Du), with p > 1, γ and β are maximal monotone graphs in ℝ2 such that 0 ∈ γ(0) and 0 ∈ β(0), and the data φ ∈ L1 (Ω) and ψ ∈ L1 (∂Ω). We also study existence and uniqueness of weak solutions for a general degenerate elliptic-parabolic problem with nonlinear dynamical boundary conditions. Particular instances of this problem appear in various phenomena with c…