Gauge transformations to combine multi-component many-boby interatomic potentials

Many-body interatomic potentials play an important role in atomistic modelling of materials. For pure elements it is known that there exist gauge transformations that can change the form of the potential functions without modifying its properties. These same transformations, however, fail when applied to alloys. Even though different research groups may use the same potentials to describe pure elements, the gauges employed for fitting alloys will generally be different. In this scenario, it is a priori impossible to merge them into one potential describing the combined system, and thus no advantage is taken from state-of-the-art developments in the literature. Here, we generalise the gauge transformations applied to pure species in order to leave the properties of alloys invariant. Based on these transformations, a strategy to merge potentials developed within different gauges is presented, aiming at the description of the combined system. Advantage of existing state-of-the-art potentials is so taken, thus focusing the efforts on fitting only the missing interactions. Such a procedure constitutes a helpful tool for the development of potentials targeted to alloys of increased complexity, while maintaining the description quality of their constituents.Fil: Bonny, G.. Nuclear Materials Science Institute; BélgicaFil: Pasianot, Roberto Cesar. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes. Departamento de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentin

Solute effects on edge dislocation pinning in complex alpha-Fe alloys

Reactor pressure vessel steels are well-known to harden and embrittle under neutron irradiation, mainly because of the formation of obstacles to the motion of dislocations, in particular, precipitates and clusters composed of Cu, Ni, Mn, Si and P. In this paper, we employ two complementary atomistic modelling techniques to study the heterogeneous precipitation and segregation of these elements and their effects on the edge dislocations in BCC iron. We use a special and highly computationally efficient Monte Carlo algorithm in a constrained semi-grand canonical ensemble to compute the equilibrium configurations for solute clusters around the dislocation core. Next, we use standard molecular dynamics to predict and analyze the effect of this segregation on the dislocation mobility. Consistently with expectations our results confirm that the required stress for dislocation unpinning from the precipitates formed on top of it is quite large. The identification of the precipitate resistance allows a quantitative treatment of atomistic results, enabling scale transition towards larger scale simulations, such as dislocation dynamics or phase field.Fil: Pascuet, Maria Ines Magdalena. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comision Nacional de Energia Atomica. Centro Atomico Constituyentes. Departamento de Materiales; ArgentinaFil: Martínez, E.. Los Alamos National High Magnetic Field Laboratory; Estados UnidosFil: Monnet, G.. EDF–R&D; FranciaFil: Malerba, L.. SCK•CEN. Structural Materials Expert Group. Nuclear Materials Institute; Bélgic

Practice patterns of kidney stone management across European and non-European centers: an in-depth investigation from the European Renal Stone Network (ERSN).

Kidney stones are a common condition in the general population, however, high-quality evidence for its management is scarce. We propose the creation of an international network with the aim of sharing practice patterns and patient data towards an improvement of our knowledge of the disease. Cross-sectional survey. An online survey was circulated through several scientific societies. Items were grouped into six domains. Each center's overall score (OS) was also calculated. Chi square and Mann-Whitney tests were performed for differences across centers. The countries that contributed most were Italy (8.6%), Turkey (6.6%), France and Spain (6.1%). Some type of nutritional work-up was implemented in 62% of centers. A DEXA scan was performed by 46% of centers, whereas some kind of acidification test was performed by 25% of centers. Most centers (80%) implemented blood investigations at least at baseline. With regard to 24-h urine exams, 7 out of 16 were performed by at least 50% of centers. Information on stone composition was collected by 58% of centers. The OS was significantly higher among higher-volume centers compared with lower-volume centers (p = 0.002). Significant differences between EU and non-EU centers were found. Cross-sectional design; no validation on information. Our survey highlights the potential for the creation of a network of centers that could share information in a common database for observational research and for enrollment of patients in interventional trials

Iron chromium potential to model high-chromium ferritic alloys

We present an Fe­Cr interatomic potential to model high-Cr ferritic alloys.The potential is fitted to thermodynamic and point-defect propertiesobtained from density functional theory (DFT) calculations and experi-ments. The developed potential is also benchmarked against otherpotentials available in literature. It shows particularly good agreementwith the DFT obtained mixing enthalpy of the random alloy, the formationenergy of intermetallics and experimental excess vibrational entropy andphase diagram. In addition, DFT calculated point-defect properties,both interstitial and substitutional, are well reproduced, as is the screwdislocation core structure. As a first validation of the potential, we studythe precipitation hardening of Fe­Cr alloys via static simulations of theinteraction between Cr precipitates and screw dislocations. It is concludedthat the description of the dislocation core modification near a precipitatemight have a significant influence on the interaction mechanisms observedin dynamic simulations.Fil: Bonny, G.. No especifíca;Fil: Pasianot, Roberto Cesar. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Terentyev, D.. No especifíca;Fil: Malerba, L.. No especifíca

Many-body interatomic U and Al-U potentials

In the present work, an interatomic potential in the framework of the embedded atom method (EAM) is developed for the Al–U binary system. A methodology is detailed to fit the U potential that reproduces the stability of the a phase at low temperatures and the g phase at high ones. The thermal stability of both phases, thermal expansion and vacancy driven self diffusion are studied. The Al–U potential is fit to first principles calculated formation energies of the experimentally observed intermetallic phases, Al2U (cubic C15), Al3U (cubic L12) and Al4U (orthorhombic D1b). As a first validation the potentials are tested against available experimental measurements.Fil: Pascuet, Maria Ines Magdalena. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bonny, G.. No especifíca;Fil: Fernandez, Julian Roberto. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Exact mean field concept to compute defect energetics in random alloys on rigid lattices

In modern materials science modeling, the evolution of the energetics of random alloys with composition are desirable input parameters for several meso-scale and continuum scale models. When using atomistic methods to parameterize the above mentioned concentration dependent function, a mean field theory can significantly reduce the computational burden associated to obtaining the desired statistics in a random alloy. In this work, a mean field concept is developed to obtain the energetics of point-defect clusters in perfect random alloys. It is demonstrated that for a rigid lattice the concept is mathematically exact. In addition to the accuracy of the presented method, it is also computationally efficient as a small box can be used and perfect statistics are obtained in a single run. The method is illustrated by computing the formation and binding energy of solute and vacancy pairs in FeCr and FeW binaries. Also, the dissociation energy of small vacancy clusters was computed in FeCr and FeCr-2%W alloys, which are considered model alloys for Eurofer steels. As a result, it was concluded that the dissociation energy is not expected to vary by more than 0.1 eV in the 0?10% Cr and 0?2% W composition range. The present mean field concept can be directly applied to parameterize meso-scale models, such as cluster dynamics and object kinetic Monte Carlo models.Fil: Bonny, G.. Sck-Cen Centre Detude de Lénergie Nucléaire; FranciaFil: Castin, N.. Sck-Cen Centre Detude de Lénergie Nucléaire; FranciaFil: Pascuet, Maria Ines Magdalena. Comision Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Çelik, Y.. Sck-Cen Centre Detude de Lénergie Nucléaire; Franci

Effects of cascade-induced dislocation structures on the long-term microstructural evolution in tungsten

In recent years, a number of systematic investigations of high-energy collision cascades in tungsten employing advanced defect analysis tools have shown that interstitial clusters can form complex non-planar dislocation structures. These structures are sessile in nature and may potentially have a strong impact on the long-term evolution of the radiation microstructure. To clarify this aspect, we selected several representative primary damage states of cascades debris and performed annealing simulations using molecular dynamics (MD). We found that immobile complexes of non-planar dislocation structures (CDS) evolve into glissile and planar shaped 1/2 loops with an activation energy of similar to 1.5 eV. The CDS objects were implemented in an object kinetic Monte Carlo (OKMC) model accounting for the event of transformation into 1-D migrating loops, following the MD data. OKMC was then used to investigate the impact of the transformation event (and the associated activation energy) on the evolution of the microstructure.Peer reviewe

PTH and 1.25 vitamin D response to a low-calcium diet is associated with bone mineral density in renal stone formers

Background. Renal calcium stones and hypercalciuria are associated with a reduced bone mineral density (BMD). Therefore, the effect of changes in calcium homeostasis is of interest for both stones and bones. We hypothesized that the response of calciuria, parathyroid hormone (PTH) and 1.25 vitamin D to changes in dietary calcium might be related to BMD. Methods. A single-centre prospective interventional study of 94 hyper- and non-hypercalciuric calcium stone formers consecutively retrieved from our stone clinic. The patients were investigated on a free-choice diet, a low-calcium diet, while fasting and after an oral calcium load. Patient groups were defined according to lumbar BMD (z-score) obtained by dual X-ray absorptiometry (group 1: z-score 0.5, n = 28). The effect of the dietary interventions on calciuria, 1.25 vitamin D and PTH in relation to BMD was measured. Results. An inverse relationship between BMD and calciuria was observed on all four calcium intakes (P = 0.009). On a free-choice diet, 1.25 vitamin D and PTH levels were identical in the three patient groups. However, the relative responses of 1.25 vitamin D and PTH to the low-calcium diet were opposite in the three groups with the highest increase of 1.25 vitamin D in group 1 and the lowest in group 3, whereas PTH increase was most pronounced in group 3 and least in group 1. Conclusion. Calcium stone formers with a low lumbar BMD exhibit a blunted response of PTH release and an apparently overshooting production of 1.25 vitamin D following a low-calcium die

Manajemen Risiko Kesehatan Dan Keselamatan Kerja (K3) (Study Kasus Pada Pembangunan Gedung SMA Eben Haezar)

Keselamatan dan Kesehatan Kerja merupakan suatu permasalahan yang banyak menyita perhatian berbagai organisasi saat ini karena mencakup permasalahan segi perikemanusiaan, biaya dan manfaat ekonomi, aspek hukum, pertanggungjawaban serta citra organisasi itu sendiri. Pada penelitian ini akan diteliti mengenai identifikasi risiko K3 , penilaian risiko K3 serta bagaimana tindakan pengendalian terhadap risiko K3 pada kegiatan proyek pembangunan infrastruktur gedung. Metode penilaian menggunakan matriks penilaian risiko yang bersumber dari AS/NZS 4360 : 2004. Sesuai dengan pengolahan data diperoleh nilai risiko yang tinggi, yaitu material terjatuh dari ketinggian dan menimpa pekerja dengan indeks risiko sebesar 20 dan penggolongan risiko pada Very High Risk. Untuk penggolongan risiko pada level High Risk sebanyak 21 variabel yang dapat membahayakan pekerja dan pekerjaan, sedangkan untuk penggolongan pada level Medium Risk didapatkan sebanyak 18 variabel