BIRD, BCAM's Institutional Repository DataThe BIRD digital repository system captures, stores, indexes, preserves, and distributes digital research material.http://bird.bcamath.org:802018-04-19T14:12:42Z2018-04-19T14:12:42ZRevealing the Mechanism of Sodium Diffusion in NaxFePO4 Using an Improved Force FieldBonilla M.R.Lozano A.Escribano B.Carrasco J.Akhmatskaya E.http://hdl.handle.net/20.500.11824/7792018-04-18T01:00:10Z2018-04-02T00:00:00ZRevealing the Mechanism of Sodium Diffusion in NaxFePO4 Using an Improved Force Field
Bonilla M.R.; Lozano A.; Escribano B.; Carrasco J.; Akhmatskaya E.
Olivine NaFePO4 is a promising cathode material for Na-ion batteries. Intermediate
phases such as Na0.66FePO4 govern phase stability during intercalation-deintercalation
processes, yet little is known about Na+ diffusion in NaxFePO4 (0 < x < 1). Here
we use an advanced simulation technique, Randomized Shell Mass Generalized Shadow
Hybrid Monte Carlo Method (RSM-GSHMC) in combination with a specifically developed
force field for describing NaxFePO4 over the whole range of sodium compositions,
to thoroughly examine Na+ diffusion in this material. We reveal a novel mechanism
through which Na+/Fe2+ antisite defect formation halts transport of Na+ in the main
diffusion direction [010], while simultaneously activating diffusion in the [001] channels.
A similar mechanism was reported for Li+ in LiFePO4, suggesting that a transition from
one- to two-dimensional diffusion prompted by antisite defect formation is common to
olivine structures, in general.
2018-04-02T00:00:00ZSuggestion of reduced cancer risks following cardiac x-ray exposures is unconvincingHarbron R.W.Chapple C.-L.O'Sullivan J.J.Lee C.McHugh K.Higueras M.Pearce MSHhttp://hdl.handle.net/20.500.11824/7782018-04-04T01:00:09Z2018-03-31T00:00:00ZSuggestion of reduced cancer risks following cardiac x-ray exposures is unconvincing
Harbron R.W.; Chapple C.-L.; O'Sullivan J.J.; Lee C.; McHugh K.; Higueras M.; Pearce MS; H
2018-03-31T00:00:00ZOn Adomian Based Numerical Schemes for Euler and Navier-Stokes Equations, and Application to Aeroacoustic PropagationGarcia I.http://hdl.handle.net/20.500.11824/7772018-03-17T02:00:10Z2018-03-12T00:00:00ZOn Adomian Based Numerical Schemes for Euler and Navier-Stokes Equations, and Application to Aeroacoustic Propagation
Garcia I.
In this thesis, an Adomian Based Scheme (ABS) for the compressible
Navier-Stokes equations is constructed, resulting in a new multiderivative type
scheme not found in the context of fluid dynamics. Moreover, this scheme is
developed as a means to reduce the computational cost associated with
aeroacoustic simulations, which are unsteady in nature with high-order
requirements for the acoustic wave propagation. We start by constructing a set
of governing equations for the hybrid computational aeroacoustics method,
splitting the problem into two steps: acoustic source computation and
wave propagation.
The first step solves the incompressible Navier-Stokes equation using Chorin's
projection method, which can be understood as a prediction-correction method.
First, the velocity prediction is obtained solving the viscous Burgers'
equation. Then, its divergence-free correction is performed using a pressure
Poisson type projection. In the velocity prediction substep, Burgers' equation
is solved using two ABS variants: a MAC type implementation, and a ``modern''
ADER method. The second step in the hybrid method, related to wave propagation,
is solved combining ABS with the discontinuous Galerkin high-order approach.
Described solvers are validated against several test cases: vortex shedding
and Taylor-Green vortex problems for the first step, and a Gaussian wave
propagation in the second case.
Although ABS is a multiderivative type scheme, it is easily programmed with an
elegant recursive formulation, even for the general Navier-Stokes equations.
Results show that its simplicity combined with excellent adaptivity
capabilities allows for a successful extension to very high-order accuracy
at relatively low cost, obtaining considerable time savings in all test cases
considered.
2018-03-12T00:00:00ZQuantitative weighted estimates for singular integrals and commutatorsRivera-Ríos I.P.http://hdl.handle.net/20.500.11824/7762018-03-08T02:00:13Z2018-02-27T00:00:00ZQuantitative weighted estimates for singular integrals and commutators
Rivera-Ríos I.P.
In this dissertation several quantitative weighted estimates for singular integral op- erators, commutators and some vector valued extensions are obtained. In particular strong and weak type $(p, p)$ estimates, Coifman-Fe erman estimates, Fe erman-Stein estimates, Bloom type estimates and endpoint estimates are provided. Most of the proofs of those results rely upon suitable sparse domination results that are provided as well in this dissertation. Also, as an application of the sparse estimates, local ex- ponential decay estimates are revisited, providing new proofs and results for vector valued extensions.
2018-02-27T00:00:00Z