Atomic-scale representation and statistical learning of tensorial properties

This chapter discusses the importance of incorporating three-dimensional symmetries in the context of statistical learning models geared towards the interpolation of the tensorial properties of atomic-scale structures. We focus on Gaussian process regression, and in particular on the construction of structural representations, and the associated kernel functions, that are endowed with the geometric covariance properties compatible with those of the learning targets. We summarize the general formulation of such a symmetry-adapted Gaussian process regression model, and how it can be implemented based on a scheme that generalizes the popular smooth overlap of atomic positions representation. We give examples of the performance of this framework when learning the polarizability and the ground-state electron density of a molecule

Solitary magnetic perturbations at the ELM onset

Edge localised modes (ELMs) allow maintaining sufficient purity of tokamak H-mode plasmas and thus enable stationary H-mode. On the other hand in a future device ELMs may cause divertor power flux densities far in excess of tolerable material limits. The size of the energy loss per ELM is determined by saturation effects in the non-linear phase of the ELM, which at present is hardly understood. Solitary magnetic perturbations (SMPs) are identified as dominant features in the radial magnetic fluctuations below 100kHz. They are typically observed close (+-0.1ms) to the onset of pedestal erosion. SMPs are field aligned structures rotating in the electron diamagnetic drift direction with perpendicular velocities of about 10km/s. A comparison of perpendicular velocities suggests that the perturbation evoking SMPs is located at or inside the separatrix. Analysis of very pronounced examples showed that the number of peaks per toroidal turn is 1 or 2, which is clearly lower than corresponding numbers in linear stability calculations. In combination with strong peaking of the magnetic signals this results in a solitary appearance resembling modes like palm tree modes, edge snakes or outer modes. This behavior has been quantified as solitariness and correlated to main plasma parameters. SMPs may be considered as a signature of the non-linear ELM-phase originating at the separatrix or further inside. Thus they provide a handle to investigate the transition from linear to non-linear ELM phase. By comparison with data from gas puff imaging processes in the non-linear phase at or inside the separatrix and in the scrape-off-layer (SOL) can be correlated. A connection between the passing of an SMP and the onset of radial filament propagation has been found. Eventually the findings related to SMPs may contribute to a future quantitative understanding of the non-linear ELM evolution.Comment: submitted to Nuclear Fusio

Confidential enquiry into maternal deaths in the Netherlands, 2006-2018

Introduction To calculate the maternal mortality ratio (MMR) for 2006-2018 in the Netherlands and compare this with 1993-2005, and to describe women's characteristics, causes of death and improvable factors. Material and Methods We performed a nationwide, cohort study of all maternal deaths between January 1, 2006 and December 31, 2018 reported to the Audit Committee Maternal Mortality and Morbidity. Main outcome measures were the national MMR and causes of death. Results Overall MMR was 6.2 per 100 000 live births, a decrease from 12.1 in 1993-2005 (risk ratio [RR] 0.5). Women with a non-western ethnic background had an increased MMR compared with Dutch women (MMR 6.5 vs. 5.0, RR 1.3). The MMR was increased among women with a background from Surinam/Dutch Antilles (MMR 14.7, RR 2.9). Half of all women had an uncomplicated medical history (79/161, 49.1%). Of 171 pregnancy-related deaths within 1 year postpartum, 102 (60%) had a direct and 69 (40%) an indirect cause of death. Leading causes within 42 days postpartum were cardiac disease (n = 21, 14.9%), hypertensive disorders (n = 20, 14.2%) and thrombosis (n = 19, 13.5%). Up to 1 year postpartum, the most common cause of death was cardiac disease (n = 32, 18.7%). Improvable care factors were identified in 76 (47.5%) of all deaths. Conclusions Maternal mortality halved in 2006-2018 compared with 1993-2005. Cardiac disease became the main cause. In almost half of all deaths, improvable factors were identified and women with a background from Surinam/Dutch Antilles had a threefold increased risk of death compared with Dutch women without a background of migration

Nationwide confidential enquiries into maternal deaths because of obstetric hemorrhage in the Netherlands between 2006 and 2019

Introduction: Obstetric hemorrhage-related deaths are rare in high income countries. Yet, with increasing incidences of obstetric hemorrhage in these countries, it is of utmost importance to learn lessons from each obstetric hemorrhage-related death to improve maternity care. Our objective was to calculate the obstetric hemorrhage-related maternal mortality ratio (MMR), assess causes of obstetric hemorrhage-related deaths, and identify lessons learned. Material and methods: Nationwide mixed-methods prospective case-series with confidential enquiries into maternal deaths due to obstetric hemorrhage in the Netherlands from January 1, 2006 to December 31, 2019. Results: The obstetric hemorrhage-related MMR in the Netherlands in 2006–2019 was 0.7 per 100 000 livebirths and was not statistically significantly different compared with the previous MMR of 1.0 per 100 000 livebirths in 1993–2005 (odds ratio 0.70, 95% confidence interval 0.38–1.30). Leading underlying cause of hemorrhage was retained placenta. Early recognition of persistent bleeding, prompt involvement of a senior clinician and timely management tailored to the cause of hemorrhage with attention to coagulopathy were prominent lessons learned. Also, timely recourse to surgical interventions, including hysterectomy, in case other management options fail to stop bleeding came up as an important lesson in several obstetric hemorrhage-related deaths. Conclusions: The obstetric hemorrhage-related MMR in the Netherlands in 2006–2019 has not substantially changed compared to the MMR of the previous enquiry in 1993–2005. Although obstetric hemorrhage is commonly encountered by maternity care professionals, it is important to remain vigilant for possible adverse maternal outcomes and act upon an ongoing bleeding following birth in a more timely and adequate manner. Our confidential enquiries still led to important lessons learned with clinical advice to professionals as how to improve maternity care and avoid maternal deaths. Drawing lessons from maternal deaths should remain a qualitative and moral imperative

Machine-learning of atomic-scale properties based on physical principles

We briefly summarize the kernel regression approach, as used recently in materials modelling, to fitting functions, particularly potential energy surfaces, and highlight how the linear algebra framework can be used to both predict and train from linear functionals of the potential energy, such as the total energy and atomic forces. We then give a detailed account of the Smooth Overlap of Atomic Positions (SOAP) representation and kernel, showing how it arises from an abstract representation of smooth atomic densities, and how it is related to several popular density-based representations of atomic structure. We also discuss recent generalisations that allow fine control of correlations between different atomic species, prediction and fitting of tensorial properties, and also how to construct structural kernels---applicable to comparing entire molecules or periodic systems---that go beyond an additive combination of local environments

Dutch home-based pre-reading intervention with children at familial risk of dyslexia

Children (5 and 6 years old, n = 30) at familial risk of dyslexia received a home-based intervention that focused on phoneme awareness and letter knowledge in the year prior to formal reading instruction. The children were compared to a no-training at-risk control group (n = 27), which was selected a year earlier. After training, we found a small effect on a composite score of phoneme awareness (d = 0.29) and a large effect on receptive letter knowledge (d = 0.88). In first grade, however, this did not result in beneficial effects for the experimental group in word reading and spelling. Results are compared to three former intervention studies in The Netherlands and comparable studies from Denmark and Australia

EUROfusion-theory and advanced simulation coordination (E-TASC): programme and the role of high performance computing

The paper is a written summary of an overview oral presentation given at the 1st Spanish Fusion HPC Workshop that took place on the 27th November 2020 as an online event. Given that over the next few years ITER will move to its operation phase and the European-DEMO design will be significantly advanced, the EUROfusion consortium has initiated a coordination effort in theory and advanced simulation to address some of the challenges of the fusion research in Horizon EUROPE (2021-2027), i.e. the next EU Framework Programme for Research and Technological Development. This initiative has been called E-TASC that stands for EUROfusion-Theory and Advanced Simulation Coordination. The general and guiding principles of E-TASC are summarized in the paper. In addition, an overview of the scientific results obtained in a pilot phase (2019-2020) of E-TASC are provided while highlighting the importance of the required progress in computational methods and HPC techniques. In the initial phase, five pilot theory and simulation tasks were initiated: 1. Towards a validated predictive capability of the L-H transition and pedestal physics; 2. Electron runaway in tokamak disruptions in the presence of massive material injection; 3. Fast code for the calculation of neoclassical toroidal viscosity in stellarators and tokamaks; 4. Development of a neutral gas kinetics modular code; 5. European edge and boundary code for reactor-relevant devices. In this paper we report on recent progress made by each of these projects.</p

EUROfusion-theory and advanced simulation coordination (E-TASC) : programme and the role of high performance computing

This paper is a written summary of an overview oral presentation given at the 1st Spanish Fusion High Performance Computer (HPC) Workshop that took place on the 27 November 2020 as an online event. Given that over the next few years ITER24 will move to its operation phase and the European-DEMO design will be significantly advanced, the EUROfusion consortium has initiated a coordination effort in theory and advanced simulation to address some of the challenges of the fusion research in Horizon EUROPE (2021-2027), i.e. the next EU Framework Programme for Research and Technological Development. This initiative has been called E-TASC, which stands for EUROfusion-Theory and Advanced Simulation Coordination. The general and guiding principles of E-TASC are summarized in this paper. In addition, an overview of the scientific results obtained in the pilot phase (2019-2020) of E-TASC are provided while highlighting the importance of the required progress in computational methods and HPC techniques. In the initial phase, five pilot theory and simulation tasks were initiated: towards a validated predictive capability of the low to high transition and pedestal physics; runaway electrons in tokamak disruptions in the presence of massive material injection; fast code for the calculation of neoclassical toroidal viscosity in stellarators and tokamaks; development of a neutral gas kinetics modular code; European edge and boundary code for reactor-relevant devices. In this paper, we report on recent progress made by each of these projects.Peer reviewe

Development and Validation of a Tokamak Skin Effect Transformer model

A control oriented, lumped parameter model for the tokamak transformer including the slow flux penetration in the plasma (skin effect transformer model) is presented. The model does not require detailed or explicit information about plasma profiles or geometry. Instead, this information is lumped in system variables, parameters and inputs. The model has an exact mathematical structure built from energy and flux conservation theorems, predicting the evolution and non linear interaction of the plasma current and internal inductance as functions of the primary coil currents, plasma resistance, non-inductive current drive and the loop voltage at a specific location inside the plasma (equilibrium loop voltage). Loop voltage profile in the plasma is substituted by a three-point discretization, and ordinary differential equations are used to predict the equilibrium loop voltage as function of the boundary and resistive loop voltages. This provides a model for equilibrium loop voltage evolution, which is reminiscent of the skin effect. The order and parameters of this differential equation are determined empirically using system identification techniques. Fast plasma current modulation experiments with Random Binary Signals (RBS) have been conducted in the TCV tokamak to generate the required data for the analysis. Plasma current was modulated in Ohmic conditions between 200kA and 300kA with 30ms rise time, several times faster than its time constant L/R\approx200ms. The model explains the most salient features of the plasma current transients without requiring detailed or explicit information about resistivity profiles. This proves that lumped parameter modeling approach can be used to predict the time evolution of bulk plasma properties such as plasma inductance or current with reasonable accuracy; at least in Ohmic conditions without external heating and current drive sources

Risk-taking, delay discounting, and time perspective in adolescent gamblers: an experimental study

Previous research has demonstrated that adult pathological gamblers (compared to controls) show risk-proneness, foreshortened time horizon, and preference for immediate rewards. No study has ever examined the interplay of these factors in adolescent gambling. A total of 104 adolescents took part in the research. Two equal-number groups of adolescent non-problem and problem gamblers, defined using the South Oaks Gambling Screen-Revised for Adolescents (SOGS-RA), were administered the Balloon Analogue Risk Task (BART), the Consideration of Future Consequences (CFC-14) Scale, and the Monetary Choice Questionnaire (MCQ). Adolescent problem gamblers were found to be more risk-prone, more oriented to the present, and to discount delay rewards more steeply than adolescent non-problem gamblers. Results of logistic regression analysis revealed that BART, MCQ, and CFC scores predicted gambling severity. These novel finding provides the first evidence of an association among problematic gambling, high risk-taking proneness, steep delay discounting, and foreshortened time horizon among adolescents. It may be that excessive gambling induces shortsighted behaviors that, in turn, facilitate gambling involvement