Search results for "Simulation."
showing 10 items of 4779 documents
Proposal of a Computational Approach for Simulating Thermal Bosonic Fields in Phase Space
2019
When a quantum field is in contact with a thermal bath, the vacuum state of the field may be generalized to a thermal vacuum state, which takes into account the thermal noise. In thermo field dynamics, this is realized by doubling the dimensionality of the Fock space of the system. Interestingly, the representation of thermal noise by means of an augmented space is also found in a distinctly different approach based on the Wigner transform of both the field operators and density matrix, which we pursue here. Specifically, the thermal noise is introduced by augmenting the classical-like Wigner phase space by means of Nosé
Watch-hand-like optical rogue waves in three-wave interactions
2015
11 págs.; 6 figs.; OCIS codes: (190.3100) Instabilities and chaos; (190.5530) Pulse propagation and temporal solitons; (190.4410) Nonlinear optics, parametric processes.
Cantor Dust Zone Plates
2013
In this paper we use the Cantor Dust to design zone plates based on a two-dimensional fractal for the first time. The pupil function that defines the coined Cantor Dust Zone Plates (CDZPs) can be written as a combination of rectangle functions. Thus CDZPs can be considered as photon sieves with rectangular holes. The axial irradiances produced by CDZPs of different fractal orders are obtained analitically and experimentally, analyzing the influence of the fractality. The transverse irradiance patterns generated by this kind of zone plates has been also investigated.
Testing the outflow theory of Malcherek by slit weir data
2018
Abstract In this paper the flow-process of a slit weir is analyzed by the outflow theory of Malcherek. Average flow velocity over the slit weir is expressed in terms of head over weir and the momentum correction coefficient. The theoretically deduced stage-discharge formula was then calibrated using experimental data obtained for a ratio between the weir and the channel width ranging from 0.05 to 0.25. The deduced stage–discharge relationship allows to measure discharge values characterized by errors which are, for 91% of the measured values, less than or equal to ± 5%.
Multipole solitary wave solutions of the higher-order nonlinear Schrödinger equation with quintic non-Kerr terms
2013
We consider a high-order nonlinear Schrodinger (HNLS) equation with third- and fourth-order dispersions, quintic non-Kerr terms, self steepening, and self-frequency-shift effects. The model applies to the description of ultrashort optical pulse propagation in highly nonlinear media. We propose a complex envelope function ansatz composed of single bright, single dark and the product of bright and dark solitary waves that allows us to obtain analytically different shapes of solitary wave solutions. Parametric conditions for the existence and uniqueness of such solitary waves are presented. The solutions comprise fundamental solitons, kink and anti-kink solitons, W-shaped, dipole, tripole, and…
Harmonic solution of semiconductor transport equations for microwave and millimetre-wave device modelling
2004
The transport equations for charges in a semiconductor have been solved for a periodic voltage excitation by means of a harmonic approach, for modelling of microwave and millimetre-wave active devices. The solution is based on the expansion of the unknown physical quantities in Fourier series in the time domain, and on the discretisation in the space domain. A Waveform-Balance technique in the time domain is used to solve the resulting non-linear equations system. In this way the time step is determined only by Nyquist's sampling requirements at the operating frequency, irrespective of the relaxation times of the semiconductor. This approach allows for a longer time step, and therefore a sh…
Step-Edge Induced Anisotropic Domain-Wall Propagation
1999
We report the observation of anisotropic domain-wall propagation in ultrathin magnetic films with perpendicular anisotropy. A controlled density of step edges was introduced which allowed us to quantify its influence on the domain-wall pinning. For a sawtooth arrangement of the step edges the corresponding wall movement resulted in triangular shaped domains. All aspects of this anisotropic domain-wall evolution could be reproduced by a simulation based on a modified Ginzburg-Landau-type soft-spin model.
Nonlinear nonviscous hydrodynamical models for charge transport in the framework of extended thermodynamic methods
2002
This paper develops a procedure, based on methods of extended thermodynamics, to design nonlinear hydrodynamical models for charge transport in metals or in semiconductors, neglecting viscous phenomena. Models obtained in this way allow the study of the motion of electric charges in the presence of arbitrary external electric fields and may be useful when one wishes to study phenomena in a neighborhood of a stationary nonequilibrium process: indeed, the drift velocity of the charge gas with respect to the crystal lattice is not regarded as a small parameter.
Simple Models for Wall Effect in Fiber Suspension Flows
2014
Jeffery's equation describes the dynamics of a non-inertial ellipsoidal particle immersed in a Stokes liquid and is used in various models of fiber suspension flow. However, it is not valid in close neighbourhood of a rigid wall. Geometrically impossible orientation states with the fiber penetrating the wall can result from this model. This paper proposes a modification of Jeffery's equation in close proximity to a wall so that the geometrical constraints are obeyed by the solution. A class of models differing in the distribution between the translational and rotational part of the response to the contact is derived. The model is upscaled to a Fokker–Planck equation. Another microscale mode…
Beyond the Vegard's law: solid mixing excess volume and thermodynamic potentials prediction, from end-members
2020
Abstract A method has been developed, herein presented, to model binary solid solutions' volume, enthalpy and Gibbs energy using the energy state functions, E ( V , S ) , of the end-members only. The E ( V , S ) s are expanded around an unknown mixing volume, V Mix , and the fundamental equilibrium equation − ( ∂ E / ∂ V ) S = P is used to determine V Mix . V Mix allows us to model enthalpy, straightforwardly. The same argument holds using Helmholtz energy, F ( V , T ) , in place of E ( V , S ) , and the equilibrium equation becomes − ( ∂ F / ∂ V ) T = P . One can readily determine the Gibbs free energy, too. The method presented remarkably simplifies computing of solid mixings' thermodynam…