Elasto-plastic deformations within a material point framework on modern GPU architectures

Plastic strain localization is an important process on Earth. It strongly influ- ences the mechanical behaviour of natural processes, such as fault mechanics, earthquakes or orogeny. At a smaller scale, a landslide is a fantastic example of elasto-plastic deformations. Such behaviour spans from pre-failure mech- anisms to post-failure propagation of the unstable material. To fully resolve the landslide mechanics, the selected numerical methods should be able to efficiently address a wide range of deformation magnitudes. Accurate and performant numerical modelling requires important compu- tational resources. Mesh-free numerical methods such as the material point method (MPM) or the smoothed-particle hydrodynamics (SPH) are particu- larly computationally expensive, when compared with mesh-based methods, such as the finite element method (FEM) or the finite difference method (FDM). Still, mesh-free methods are particularly well-suited to numerical problems involving large elasto-plastic deformations. But, the computational efficiency of these methods should be first improved in order to tackle complex three-dimensional problems, i.e., landslides. As such, this research work attempts to alleviate the computational cost of the material point method by using the most recent graphics processing unit (GPU) architectures available. GPUs are many-core processors originally designed to refresh screen pixels (e.g., for computer games) independently. This allows GPUs to delivers a massive parallelism when compared to central processing units (CPUs). To do so, this research work first investigates code prototyping in a high- level language, e.g., MATLAB. This allows to implement vectorized algorithms and benchmark numerical results of two-dimensional analysis with analytical solutions and/or experimental results in an affordable amount of time. After- wards, low-level language such as CUDA C is used to efficiently implement a GPU-based solver, i.e., ep2-3De v1.0, can resolve three-dimensional prob- lems in a decent amount of time. This part takes advantages of the massive parallelism of modern GPU architectures. In addition, a first attempt of GPU parallel computing, i.e., multi-GPU codes, is performed to increase even more the performance and to address the on-chip memory limitation. Finally, this GPU-based solver is used to investigate three-dimensional granular collapses and is compared with experimental evidences obtained in the laboratory. This research work demonstrates that the material point method is well suited to resolve small to large elasto-plastic deformations. Moreover, the computational efficiency of the method can be dramatically increased using modern GPU architectures. These allow fast, performant and accurate three- dimensional modelling of landslides, provided that the on-chip memory limi- tation is alleviated with an appropriate parallel strategy

Progress in Stimuli-Responsive Biomaterials for Treating Cardiovascular and Cerebrovascular Diseases

Cardiovascular and cerebrovascular diseases (CCVDs) describe abnormal vascular system conditions affecting the brain and heart. Among these, ischemic heart disease and ischemic stroke are the leading causes of death worldwide, resulting in 16% and 11% of deaths globally. Although several therapeutic approaches are presented over the years, the continuously increasing mortality rates suggest the need for more advanced strategies for their treatment. One of these strategies lies in the use of stimuli-responsive biomaterials. These "smart" biomaterials can specifically target the diseased tissue, and after "reading" the altered environmental cues, they can respond by altering their physicochemical properties and/or their morphology. In this review, the progress in the field of stimuli-responsive biomaterials for CCVDs in the last five years, aiming at highlighting their potential as early-stage therapeutics in the preclinical scenery, is described.Peer reviewe

Testing the gravitational phenomenology of compact objects: superradiance, scalarization and screening mechanisms

In the last decades, an interesting variety of extended models of gravity has been proposed with the goal of capturing cosmological effects such as the accelerated phases of expansion and/or the so-called "dark sector" of our universe. In parallel, the quest for a full-fledged theory of quantum gravity proceeds by investigating the low-energy limit of candidate models. Many of these modified gravity models might leave imprints in the physics of compact objects and with gravitational-wave astronomy we have the unprecedented opportunity to test them against data with improving accuracy. A popular class of models (scalar-tensor theories) extends the field content of general relativity with an additional scalar field. These theories provide multiple examples where black hole and neutron star physics deviates from general relativity and can be constrained with observations. In this sense, superradiance and spontaneous growth of scalar fields around black holes and neutron stars are potentially detectable signatures of new physics. Screening mechanisms can in principle hide scalar effects, but their effectiveness in the strong-field regime is still largely unmodeled. In this thesis I briefly review the traditional tests of gravity, from the weak-field observations to gravitational-wave tests, before moving to discuss in details a collection of personal contributions in modeling the aforementioned scalar effects

Pressure-induced structural transformations in nanomaterials: towards high accuracy large length- and time-scale simulations

The study of pressure-induced structural transformations in nanomaterials is both of fundamental and technological importance. Accurate simulations of these transformations are challenging because large length- and time-scales have to be simulated to make contact with experiments whilst retaining the atomic detail for a faithful description. In this thesis, both classical and quantum mechanical techniques are used to model pressure-induced structural transformations in realistic Si, Ge and CdS nanocrystals and comparison made to experiment where possible. We implement an electronic enthalpy method within the linear-scaling density-functional theory ONETEP code and, after introducing an approach for calibrating the volume definition, investigate the size-dependent pressure-induced amorphisation and polyamorphic transformations in hydrogenated Si and Ge nanocrystals. For the latter, we elucidate the surface-induced amorphisation and the new high-density amorphous metallic Ge phase observed experimentally. We combine this method with the projector-augmented wave and time-dependent density-functional theory methods to study the size and ligand dependence of deformation and optoelectronic properties of CdS nanocrystals with pressure. We develop a novel classical parametrisation for the simulation of bare and ligated CdS nanocrystals immersed in a pressure-transmitting medium and investigate their transformation under pressure using classical molecular dynamics and the metadynamics method for accelerating rare events. The resulting polymorphic transformation and pressure-induced amorphisation are analysed in detail.Open Acces

Evolutionary Computation

This book presents several recent advances on Evolutionary Computation, specially evolution-based optimization methods and hybrid algorithms for several applications, from optimization and learning to pattern recognition and bioinformatics. This book also presents new algorithms based on several analogies and metafores, where one of them is based on philosophy, specifically on the philosophy of praxis and dialectics. In this book it is also presented interesting applications on bioinformatics, specially the use of particle swarms to discover gene expression patterns in DNA microarrays. Therefore, this book features representative work on the field of evolutionary computation and applied sciences. The intended audience is graduate, undergraduate, researchers, and anyone who wishes to become familiar with the latest research work on this field