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Publications

Publications by Nuno Azevedo Silva

2019

Simulating N-body systems for alternative theories of gravity using solvers from nonlocal optics

Authors
Ferreira, TD; Silva, NA; Bertolami, O; Gomes, C; Guerreiro, A;

Publication
FOURTH INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
This paper reports the development of a numerical module for the HiLight simulation platform dedicated to the propagation of light in nonlocal nonlinear optical media and the adaptions implemented for it to be used as a numerical test-bed to evaluate the impact of new extensions of the Theory of General Relativity in the dynamics of a N-body system. The phenomenology of light in nonlocal and nonlinear media is very rich and can be described by a multitude of effective models, with different levels of detail and approximations, which coincide with few or no differences with those found in many other fields of physics. In particular, nonlocal extensions of the Generalized Nonlinear Schrodinger equation (also known as the generalized Schrodinger-Newton system) constitute a wide class of physical models that can be found in both optics and in the studies of alternative theories for gravity. Therefore, numerical solvers developed for the former can be adapted to address the later. Indeed, this paper discusses the adaptation of a numerical solver of the generalized Schrodinger-Newton system based on GPGPU supercomputing, initially developed to investigate the properties of light in exotic nonlocal media, to tackle the dynamics of large distributions of matter whose interaction is governed by extensions of the Theory of General Relativity, namely those based on non-minimal coupling between curvature and matter. This paper analysis the structure of the resulting simulation module, its performance and validation tests.

2019

Developing tunable optical analogues using nematic liquid crystals

Authors
Ferreira, TD; Silva, NA; Guerreiro, A;

Publication
FOURTH INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
This paper proposes the use of nematic liquid crystals as tunable setups to implement optical analogues of physical systems and phenomena that are hard or even impossible to study experimentally under controlled conditions. Optical analogues share the same physical model with the systems that they emulate and can be understood as a form of physical simulations or optical computation. However, their success relies not only on the existence of media with optical properties capable of emulating the models associated with the original system as they interact with light, but also on the possibility of being able to tune those properties in order to cover the multitude of conditions or range of parameters. In particular, the Schrodinger-Newton model is a good target for this kind of studies as it can describe a plethora of different phenomena in physics and can be implemented in the laboratory using optical analogues, usually using thermo-optical materials. However, such materials have limitations, and in this work we propose nematic liquid crystals as a more advantageous alternative. We discuss how nematic liquid crystals can be used as a tunable support medium for optical analogues of superfluids by analyzing the dispersion relation of light under specific conditions and using numerical simulations based on GPGPU supercomputing to verify our findings. Extending on this, we explore more direct manifestations of superfluid effects in nematic liquid crystals, such as drag-force cancellation in the superfluid regime and the possibility of creating a roton-minimum in the dispersion relation.

2019

FUNCTIONAL METAMATERIALS FOR OPTICAL SENSING OF HYDROGEN

Authors
Guerreiro, A; Apolinario, A; Lopes, A; Hierro Rodriguez, A; Aguilar, G; Baptista, JM; Silva, NA; Frazao, O; Quiterio, P; Jorge, P; Rodrigues, P; Moraes, SS; Silva, S; Ferreira, TD; Santos, JL; Araujo, JP;

Publication
FOURTH INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
We present the design, fabrication and optical characterization of functional metamaterials for optical sensing of Hydrogen based on inexpensive self-assembly processes of metallic nanowires integrated in nanoporous alumina templates([37-42]). The optical properties of these materials strongly depend on the environmental concentration or partial pressure of hydrogen and can be used to develop fully optical sensors that reduce the danger of explosion. Optical metamaterials are artificial media, usually combining metallic and dielectric sub-wavelength structures, that exhibit optical properties that cannot be found in naturally occurring materials. Among these, functional metamaterials offer the added possibility of altering or controlling these properties externally after fabrication, in our case by contact with a hydrogen rich atmosphere. This dependency can be used to design([43-45]) and develop optical sensors that respond to this gas or to chemical compounds that contain or release hydrogen. In this paper we present some designs for hydrogen functional metamaterials and discuss the main parameters relevant in the optimization of their response.

2019

High performance solver of the multidimensional generalized nonlinear Schrodinger equation with coupled fields

Authors
Ferreira, TD; Silva, NA; Guerreiro, A;

Publication
FOURTH INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
We report on the development of numerical module for the HiLight simulation platform based on GPGPU supercomputing to solve a system of coupled fields governed by the Generalized Nonlinear Schrodinger Equation with local and/or nonlocal nonlinearities. This models plays an important role in describing a plethora of different phenomena in various areas of physics. In optics, this model was initially used to describe the propagation of light through local and/or nonlocal systems under the paraxial approximation, but more recently it has been extensively used as a support model to develop optical analogues. However, establishing the relation between the original system and the analogue, as well as, between their model and the actual experimental setup is not an easy task. First and foremost because in most cases the governing equations are nonintegrable, preventing from obtaining analytical solutions and hindering the optimization of the experiments. Alternatively, despite numerical methods not providing exact solutions, they allow to test different experimental scenarios and provide a better insight to what to expect in an actual experiment, while giving access to all the variables of the optical system being simulated. However, the numerical solution of a system of N-coupled Schrodinger fields in systems with two or three spatial dimensions requires massive computation resources, and must employ advanced supercomputing and parallelization techniques, such as GPGPU. This paper focuses on the numerical aspects behind this challenge, describing the structure of our simulation module, its performance and the tests performed.

2019

HILIGHT: A NEW SIMULATION PLATFORM FOR ADVANCED PHOTONICS

Authors
Guerreiro, A; Silva, NA; Costa, J; Gomes, M; Alves, R; Ferreira, TD; Madureira, IS; Pereira, AAM; Almeida, AL;

Publication
FOURTH INTERNATIONAL CONFERENCE ON APPLICATIONS OF OPTICS AND PHOTONICS

Abstract
We report on the development of HiLight, a new multiphysics simulation platform for advanced photonics with interactive modules dedicated to the study of the propagation of light in multitude of spatially structured optical media, including nonlocal and nonlinear media, optical lattices with atomic gases and plasmas, among others.

2020

Using numerical methods from nonlocal optics to simulate the dynamics of N-body systems in alternative theories of gravity

Authors
Ferreira, TD; Silva, NA; Bertolami, O; Gomes, C; Guerreiro, A;

Publication
PHYSICAL REVIEW E

Abstract
The generalized Schrodinger-Newton system of equations with both local and nonlocal nonlinearities is widely used to describe light propagating in nonlinear media under the paraxial approximation. However, its use is not limited to optical systems and can be found to describe a plethora of different physical phenomena, for example, dark matter or alternative theories for gravity. Thus, the numerical solvers developed for studying light propagating under this model can be adapted to address these other phenomena. Indeed, in this work we report the development of a solver for the HiLight simulations platform based on GPGPU supercomputing and the required adaptations for this solver to be used to test the impact of new extensions of the Theory of General Relativity in the dynamics of the systems. In this work we shall analyze theories with nonminimal coupling between curvature and matter. This approach in the study of these new models offers a quick way to validate them since their analytical analysis is difficult. The simulation module, its performance, and some preliminary tests are presented in this paper.

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