Building initial models of rotating white dwarfs with SPH

A general procedure to build self-gravitational, rotating equilibrium structures with the Smoothed Particle Hydrodynamics (SPH) technique does not exist. In particular, obtaining stable rotating configurations for white dwarf (WD) stars is currently a major drawback of many astrophysical simulations. Rotating WDs with low internal temperatures are connected with both, explosive and implosive scenarios such as type Ia supernova explosions or neutron stars formation. Simulations of these events with SPH codes demand stable enough particle configurations as initial models. In this work we have developed and tested a relaxation method to obtain equilibrium configurations of rotating WDs. This method is straightforward and takes advantage of the excellent mass and angular momentum conservation properties of the SPH technique. Although we focus on rigid rotation and its potential applications to several Type Ia supernova scenarios, we also show that our proposal is also able to provide good initial models in differential rotation, which has the potential to benefit many other types of simulations where rotation plays a capital role, like disk evolution and stellar formation.Peer ReviewedPostprint (published version

Cambios morfológicos y funcionales en los espermatozoides de ganado vacuno después de ser sometidos a diferentes tratamientos

En el presente trabajo, elaborado y presentado para optar al grado de doctor por la Universidad de Santiago de Compostela, se ha realizado un estudio sobre los efectos del colesterol en la criopreservación del semen del ganado vacuno. A tal efecto se han utilizado doce sementales previamente probados y estabulados en las instalaciones de la empresa Xenética Fontao S.A., ubicada en la provincia de Lugo. Cuatro de esos sementales eran de raza frisona, cuatro de raza limusina y los otros cuatro de la raza rubia gallega. Siguiendo el procediento habitual que incluye las fases de recogida de material, preparación de las ciclodextrinas, procesado y dilución del semen, y posterior envasado y congelación, que se describen con detalle en el correspondiente capítulo, las dosis seminales se analizaron mediante citometría de flujo. Se programaron tres experimentos distintos para evaluar las variables de viabilidad, resistencia térmica, reacción acrosómica y fragmentación de la cromatina. Por otro lado, siguiendo una sistemática convencional y rutinaria en este caso, se recogieron datos sobre los defectos morfológicos más habituales que presentan los espermatozoides. Los resultados obtenidos, presentados en esta memoria en tres apartados diferentes, ponen de manifiesto el efecto beneficioso del colesterol durante el proceso de la criopreservación cuando se añade al semen asociado a las ciclodextrinas. Ese efecto, que es manifiesto en cuanto a la viabilidad, fragmentación de la cromatina y reacción acrosómica, es corroborado porcentualmente por medio del pertinente análisis estadístic

Integral SPH: Connecting the partition of unit to accurate gradient estimation

AYA2017-86274-P Del enfriamiento a las explosiones: la física de los objetos compactosPostprint (published version

An upper bound for the magnetic force gradient in graphite

Cervenka et al. have recently reported ferromagnetism along graphite steps. We present Magnetic Force microscopy (MFM) data showing that the signal along the steps is independent of an external magnetic field. Moreover, by combining Kelvin Probe Force Microscopy (KPFM) and MFM, we are able to separate the electrostatic and magnetic interactions along the steps obtaining an upper bound for the magnetic force gradient of about16 microN/m, a figure six times lower than the lowest theoretical bound reported by Cervenka et al. Our experiments suggest absence of MFM signal in graphite at room temperature.Comment: 14 pages, including supplemetary informatio

Exostosis versus osteocondroma: importance of the differential diagnosis

The appearance, more and more common in the daily office of injuries similar to dematological pathologies as bony, are easily confusing with subungueal exostosis, provides to the podiatrist the necessity to remain alert with any bone anormality. Nevertheless the difficulty is at the time of making a differential diagnosis and the impossibility to treat this pathology with other methods differents from the surgery, makes very important the criterion of any specialized professionals which are involved as part of the multidiscipline team, with the podiatrist, to treat this pathology.The appearance, more and more common in the daily office of injuries similar to dematological pathologies as bony, are easily confusing with subungueal exostosis, provides to the podiatrist the necessity to remain alert with any bone anormality. Nevertheless the difficulty is at the time of making a differential diagnosis and the impossibility to treat this pathology with other methods differents from the surgery, makes very important the criterion of any specialized professionals which are involved as part of the multidiscipline team, with the podiatrist, to treat this pathology

Surface and core detonations in rotating white dwarfs

The feasibility of the double detonation mechanism—surface helium detonation followed by complete carbon detonation of the core—in a rotating white dwarf with mass ;1Me is studied using three-dimensional hydrodynamic simulations. A rapid rigid rotation of the white dwarf was assumed, so that its initial spherical geometry is considerably distorted. Unlike spherically symmetric models, we found that when helium ignition is located far from the spinning axis, the detonation fronts converge asynchronically at the antipodes of the ignition point. Nevertheless, the detonation of the carbon core still remains as the most probable outcome. The detonation of the core gives rise to a strong explosion, matching many of the basic observational constraints of Type Ia supernovae (SNe Ia). We conclude that the double detonation mechanism also works when the white dwarf is rapidly rotating. These results provide further evidence for the viability of sub-Chandrasekhar-mass models as well as some double degenerate models (those having some helium fuel at the merging moment), making them appealing channels for the production of SN Ia events.Peer ReviewedPostprint (published version

A moderately-sized nuclear network to assist multi-D hydrodynamic simulations of supernova explosions

A key ingredient in any numerical study of supernova explosions is the nuclear network routine that is coupled with the hydrodynamic simulation code. When these studies are performed in more than one dimension, the size of the network is severely limited by computational issues. In this work, we propose a nuclear network (net87) which is close to one hundred nuclei and could be appropriate to simulate supernova explosions in multidimensional studies. One relevant feature is that electron and positron captures on free protons and neutrons have been incorporated to the network. Such addition allows for a better track of both, the neutronized species and the gas pressure. A second important feature is that the reactions are implicitly coupled with the temperature, which enhances the stability in the nuclear statistical equilibrium (NSE) regime. Here we analyze the performance of net87 in light of both: the computational overhead of the algorithm and the outcome in terms of the released nuclear energy and produced yields in typical Type Ia Supernova conditions.Postprint (published version

Conformational Flexibility as a Tool for Enabling Site-Selective Functionalization of Unactivated sp(3) C-O Bonds in Cyclic Acetals

A dual catalytic manifold that enables site-selective functionalization of unactivated sp(3) C-O bonds in cyclic acetals with aryl and alkyl halides is reported. The reaction is triggered by an appropriate sigma*-p orbital overlap prior to sp(3) C-O cleavage, thus highlighting the importance of conformational flexibility in both reactivity and site selectivity. The protocol is characterized by its excellent chemoselectivity profile, thus offering new vistas for activating strong sigma sp(3) C-O linkages.We thank ICIQ, FEDER/MCI-AEI/PGC2018-096839-B-I00, MCIN-PID2019-110008GB-I00, European Research Council (ERC) under European Union's Horizon 2020 research and innovation program (Grant Agreement No. 883756) for financial support. E.G.-B. thanks SGIker (UPV/EHU) for providing human and computational resources. C.R. thanks the European Union's Horizon 2020 and innovation program under the Marie Sklodowska-Curie grant agreement (839980)