Efficient calculation of formation energies of kink-pairs in BCC crystals

En materiales con estructura cristalina BCC el movimiento de dislocaciones de tipo tornillo a baja temperatura está asociado con la formación y el crecimiento de escalones en la línea de la dislocación. Para entender la movilidad de dislocaciones de tipo tornillo en estos materiales es muy importante la correcta predicción de las energías de nucleación de estos escalones. El cálculo a nivel atomístico de la mecánica de dislocaciones constituye un problema complicado desde el punto de vista tanto numérico como computacional. Este trabajo se centra en el cálculo de las energías de formación de distintas configuraciones de escalones dobles en cristales BCC y en ausencia de cargas exteriores. En nuestro modelo, basado en la teoría discreta de dislocaciones desarrollada por Ariza y Ortiz, la energía almacenada se calcula de forma eficiente mediante un algoritmo de programación basado en NVIDIA Compute Unified Device Architecture (CUDA). Los resultados obtenidos presentan un buen acuerdo con los calculados utilizando primeros principios y potenciales atomísticos, y los correspondientes a la teoría elástica de dislocaciones.Motion of screw dislocations in BCC materials at low temperature is believed to be related to the formation of mobile kinks on the dislocation line. Therefore, the accurate prediction of kink nucleation energies is required to fully describe mobility of screw dislocations in these materials. Studies of fundamental dislocation processes at atomic length scale are numerically and computationally intensive problems. This work studies the calculation of zero-stress formation energies of kink-pair configurations for BCC crystals. Our model for stored energy associated to a dislocation line configuration is based on the theory of discrete dislocations of Ariza and Ortiz. Its value is computed efficiently using an algorithm developed on the NVIDIA Compute Unified Device Architecture (CUDA). Results confirm those obtained using atomistic potentials and first principles calculations, and those based on the continuum theory of dislocations.Peer Reviewe

Finite-temperature nanovoid deformation in copper under tension

Tensile failure of metals often occurs through void nucleation, growth and coalescence. In high-purity metals, void nucleation often operates at the nanoscale and is followed by plastic cavitation when the void attains the critical size for dislocation emission. This work is concerned with the study of plastic nanovoid cavitation in facecentered cubic (fcc) crystals at finite temperature. In particular, the Quasicontinuum (QC) method, suitably extended to finite temperatures (HotQC), is taken as the basis for the analysis. The Quasicontinuum method is a multiscale modeling scheme that seamlessly links continuum and atomistic descriptions. HotQC is a method for systematically coarse-graining atomistic models at finite temperature. We specifically focus on nanovoids in copper single crystals deforming in uniaxial and triaxial tension. The results of the calculations provide a detailed characterization of the cavitation mechanism, including the geometry of the emitted dislocations, the dislocation reaction paths and attendant macroscopic quantities of interest such as the cavitation pressure as a function of triaxiality

Experimental and computational analysis of microbial inactivation in a solid by ohmic heating using pulsed electric fields

Pulsed electric field technology (PEF) has traditionally been used as a technique to inactivate microorganisms in liquid foods at temperatures below those used in heat treatments; however, application of high-intensity PEF (E>1 kV/cm) at high frequencies (>10 Hz) can allow rapid and volumetric solid food electrical heating in order to replace traditional convection/conduction heating that progresses from the heating medium to the inside of the product. This investigation is the first one to evaluate the inactivation of Salmonella Typhimurium 878 in a solid product (cylinder of technical agar used as reference solid) by applying PEF treatments (2.5 and 3.75 kV/cm, and up to 9000 microseconds) at 50 Hz. The evolution of temperature in different locations of the agar cylinder was measured by observing the variability of heating rates depending on location and PEF intensity. Microbial inactivation was determined and compared with isothermal heat treatments that predicted similar inactivation values, but did not detect additional inactivation. Computational analysis enabled us to predict temperature and microbial inactivation for any spatial and temporal distribution of the cylinder agar by detecting the coldest point in the transition zone between the high-voltage electrode, the agar, and the plastic container of the treatment chamber. In order to evaluate the variability of the temperature, computational predictions were done each 0.5-mm. The difference between the coldest and the hottest point (e.g. at the center of the cylinder) resulted in around 10 °C and 10 second variation in temperature and processing time, respectively. In any case, it was possible to obtain 5-log10-reductions after 60 s of PEF treatments when using 2.5 kV/cm and 50% reduction for 3.75 kV/cm. These results suggested the potential of PEF technology as a rapid heating system based on ohmic heating for microbial inactivation in solid food products

Atomistic modeling and simulation of long-term transport phenomena in nanomaterials

In the past two decades, extensive research has been conducted towards developing nanomaterials with superior transport properties, such as heat conductivity and mass diffusivity, for applications in various industries including, but not limited to,energy storage and microelectronics. In terms of modeling and simulation, along-standing difficulty lies in the separation of temporal and spatial scales. Indeed, many transport phenomena in nanomaterials are characterized by slow kinetic processes with time scale of the order of seconds, hours, or even years, far beyond the time windows of existing simulation technologies such as molecular dynamics (MD)and Monte Carlo (MC) methods. We have developed a novel deformation-diffusion coupled computational framework that allows long-term simulation of such slow processes, while at the same time maintains a strictly atomistic description of the material. Ournon-equilibrium statistical thermo-dynamics model includes discrete kinetic laws, which govern mass diffusion and head conductionion at atomic scale. In this work, we explore the capabilities and performance of this computational framework through its application to heat conduction problems

Characteristics and outcomes in patients with a prior myocardial infarction treated with extended dual antiplatelet therapy with ticagrelor 60 mg: findings from ALETHEIA, a multi-country observational study

Background Guidelines recommend extended dual antiplatelet therapy, including ticagrelor 60 mg twice daily, in high-risk post-myocardial infarction (MI) patients who have tolerated 12 months and are not at high bleeding risk. The real-world utilization and bleeding and ischaemic outcomes associated with long-term ticagrelor 60 mg in routine clinical practice have not been well described. Methods Register and claims data from the USA (Optum Clinformatics, IBM MarketScan, and Medicare) and Europe (Sweden, Italy, UK, and Germany) were extracted. Patients initiating ticagrelor 60 mg ≥12 months after MI, meeting eligibility criteria for the PEGASUS-TIMI (Prevention of Cardiovascular Events in Patients with Prior Heart Attack Using Ticagrelor Compared to Placebo on a Background of Aspirin – Thrombolysis in Myocardial Infarction 45) 54 trial, were included. The cumulative incidence of the composite of MI, stroke, or all-cause mortality and that of bleeding requiring hospitalization were calculated. Meta-analyses were performed to combine estimates from each source. Results A total of 7035 patients treated with ticagrelor 60 mg met eligibility criteria. Median age was 67 years and 29% were females; 12% had a history of multiple MIs. The majority (95%) had been treated with ticagrelor 90 mg prior to initiating ticagrelor 60 mg. At 12 months from initiation of ticagrelor 60 mg, the cumulative incidence [95% confidence interval (CI)] of MI, stroke, or mortality was 3.33% (2.73–4.04) and was approximately three-fold the risk of bleeding (0.96%; 0.69–1.33). Conclusions This study provides insights into the use of ticagrelor 60 mg in patients with prior MI in clinical practice. Observed event rates for ischaemic events and bleeding generally align with those in the pivotal trials, support the established safety profile of ticagrelor, and highlight the significant residual ischaemic risk in this population

A progressive damage based lattice model for dynamic fracture of composite materials

In this paper we present an extension of the linear elastic lattice model for anisotropic materials previously developed by the authors. This approach takes into consideration damage evolution in composite materials by effectively integrating a softening constitutive law into our earlier triangular lattice model. In this framework, the material constitutive law accounts for the fracture energy of the matrix in the fiber direction in a simple and direct way. To validate the proposed methodology, we conducted a dynamic fracture analysis of a unidirectional carbon fiber composite material. In particular, we studied rectangular notched beam specimens under impact loading conditions. Results are presented in terms of crack pattern, crack speed, and crack length evolution. Predictions obtained were in reasonable agreement with previous numerical and experimental observations.Fil: Braun, Matias Nicolas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina. Universidad Nacional de La Plata. Facultad de Ingeniería; ArgentinaFil: Ariza, M.P.. Universidad de Sevilla; Españ

Atomistic modeling and simulation of long-term transport phenomena in nanomaterials

In the past two decades, extensive research has been conducted towards developing nanomaterials with superior transport properties, such as heat conductivity and mass diffusivity, for applications in various industries including, but not limited to,energy storage and microelectronics. In terms of modeling and simulation, along-standing difficulty lies in the separation of temporal and spatial scales. Indeed, many transport phenomena in nanomaterials are characterized by slow kinetic processes with time scale of the order of seconds, hours, or even years, far beyond the time windows of existing simulation technologies such as molecular dynamics (MD)and Monte Carlo (MC) methods. We have developed a novel deformation-diffusion coupled computational framework that allows long-term simulation of such slow processes, while at the same time maintains a strictly atomistic description of the material. Ournon-equilibrium statistical thermo-dynamics model includes discrete kinetic laws, which govern mass diffusion and head conductionion at atomic scale. In this work, we explore the capabilities and performance of this computational framework through its application to heat conduction problems

Efficient calculation of formation energies of kink-pairs in BCC crystals

Motion of screw dislocations in BCC materials at low temperature is believed to be related to the formation of mobile kinks on the dislocation line. Therefore, the accurate prediction of kink nucleation energies is required to fully describe mobility of screw dislocations in these materials. Studies of fundamental dislocation processes at atomic length scale are numerically and computationally intensive problems. This work studies the calculation of zero-stress formation energies of kink-pair configurations for BCC crystals. Our model for stored energy associated to a dislocation line configuration is based on the theory of discrete dislocations of Ariza and Ortiz. Its value is computed efficiently using an algorithm developed on the NVIDIA Compute Unified Device Architecture (CUDA). Results confirm those obtained using atomistic potentials and first principles calculations, and those based on the continuum theory of dislocations

Finite-temperature nanovoid deformation in copper under tension

Tensile failure of metals often occurs through void nucleation, growth and coalescence. In high-purity metals, void nucleation often operates at the nanoscale and is followed by plastic cavitation when the void attains the critical size for dislocation emission. This work is concerned with the study of plastic nanovoid cavitation in facecentered cubic (fcc) crystals at finite temperature. In particular, the Quasicontinuum (QC) method, suitably extended to finite temperatures (HotQC), is taken as the basis for the analysis. The Quasicontinuum method is a multiscale modeling scheme that seamlessly links continuum and atomistic descriptions. HotQC is a method for systematically coarse-graining atomistic models at finite temperature. We specifically focus on nanovoids in copper single crystals deforming in uniaxial and triaxial tension. The results of the calculations provide a detailed characterization of the cavitation mechanism, including the geometry of the emitted dislocations, the dislocation reaction paths and attendant macroscopic quantities of interest such as the cavitation pressure as a function of triaxiality