Person: Calvo Padilla, María Luisa
Universidad Complutense de Madrid
Faculty / Institute
Now showing 1 - 4 of 4
PublicationNeutron optics: new algorithm based on Green's functions for simulating waveguides with Dirichlet boundary conditions(Elsevier Science Inc, 2022-01) Molina de la Peña, Ignacio; Calvo Padilla, María Luisa; Álvarez Estrada, Ramón F.We present a new, efficient and robust method for computing scalar wave propagation for those cases in which Dirichlet boundary conditions play a key role. The algorithm is versatile and it allows to treat reflection, diffraction, waveguiding regime, scattering and free propagation. The analysis is based upon a representation for a slow neutron wavefunction in terms of the incoming wave and integrals, along the boundaries of an unbounded domain, involving a Green's function and certain auxiliary functions (warranting the Dirichlet boundary conditions). The analysis involves Fourier and Hilbert transforms defined only on the boundaries and enables to exploit the detailed advantages of Fast Fourier Transform (FFT) to perform simulations. Our algorithm proves to be highly effective both in terms in running time and memory load, compared to those based on Finite Differences Methods (FDM). Moreover, since the value of the field at each point may be calculated independently, this algorithm allows parallelization in a natural way. (c) 2021 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) PublicationThe International Day of Light in Spain: a three years perspective(SPIE, 2020) Moreno Soriano, Ignacio; Yzuel, María J.; Calvo Padilla, María LuisaIn this article we report on the activities in Spain related to the celebration of the International Day of Light (IDL). The Spanish Committee for the IDL was constituted in 2017, as a continuation of the previous Committee for the International Year of Light (2015). This Committee involves different academic, scientific and industrial partners in Spain related to light science and light technologies, and develops actions to promote and disseminate the IDL activities. After the success of the 2018 and 2019 editions, the 2020 IDL celebration has been totally affected by the Covid-19 pandemic, and most of the programmed events were cancelled. Nevertheless, some on-line activities were developed. The aim of this work is to review the IDL impact in Spain in these last three years. PublicationNeutron waveguides in neutron optics: Green's functions formalism with Dirichlet boundary conditions(Taylor and Francis Ltd., 2020-06-06) Molina de la Peña, Ignacio; Calvo Padilla, María Luisa; Álvarez Estrada, Ramón F.In neutron optics, we analyse the propagation of slow (thermal) neutrons along a semi-infinite waveguide limited by a large repulsive potential (reminding the propagation of light along an optical fibre). We set an ideal case of a straight empty two-dimensional semi-infinite waveguide limited by an infinitely repulsive potential (Dirichlet conditions on its boundaries). The neutron wave function is given through an integral representation involving the incoming wave with energyE, Green's function and certain functions defined on the boundaries. The latter functions follow from the Dirichlet conditions, thereby proposing a new formalism in neutron optics. We develop various approximations (through Fourier and Hilbert transforms) and numerical computations. We get: (a) the expected extinction of the incoming wave for very large penetration into the waveguide, (b) the generation of propagation modes and their number for suitably large penetration, asEincreases, (c) an estimate of the critical angle. PublicationNeutron waveguides with finite repulsive potential in clad(Springer, 2022-08-31) Molina de la Peña, Ignacio; Álvarez Estrada, Ramón F.; Calvo Padilla, María LuisaThe interaction of an incoming slow neutron with a straight semi-infinite material waveguide (physically, a very lengthy one) located in vacuum (clad) in the infinite three-dimensional (3D) space is studied. The waveguide creates an attractive potential on the neutron. The physical quantum-mechanical wave phenomena are: (i) reflection and scattering of the neutron by the waveguide and (ii) its confined propagation along the latter, in specific propagation modes. The direct application of standard scattering integral equations meets several difficulties, arising mainly from the infinite length of the waveguide and (ii). New and more convenient 3D scattering integral equations are proposed and discussed, using suitable Green functions, adequate for the semi-infinite waveguide and accounting for (i) and the above difficulties. Approximate formulae for the probability amplitudes and fluxes for (i) and (ii) are given: in particular, the formulas for slow neutron confined propagation extend the ones given previously for optical waveguides. Some detailed applications and numerical computations for two-dimensional media and waveguides are presented.