Reproducibility, accuracy and performance of the Feltor code and library on parallel computer architectures

Feltor is a modular and free scientific software package. It allows developing platform independent code that runs on a variety of parallel computer architectures ranging from laptop CPUs to multi-GPU distributed memory systems. Feltor consists of both a numerical library and a collection of application codes built on top of the library. Its main target are two- and three-dimensional drift- and gyro-fluid simulations with discontinuous Galerkin methods as the main numerical discretization technique. We observe that numerical simulations of a recently developed gyro-fluid model produce non-deterministic results in parallel computations. First, we show how we restore accuracy and bitwise reproducibility algorithmically and programmatically. In particular, we adopt an implementation of the exactly rounded dot product based on long accumulators, which avoids accuracy losses especially in parallel applications. However, reproducibility and accuracy alone fail to indicate correct simulation behaviour. In fact, in the physical model slightly different initial conditions lead to vastly different end states. This behaviour translates to its numerical representation. Pointwise convergence, even in principle, becomes impossible for long simulation times. In a second part, we explore important performance tuning considerations. We identify latency and memory bandwidth as the main performance indicators of our routines. Based on these, we propose a parallel performance model that predicts the execution time of algorithms implemented in Feltor and test our model on a selection of parallel hardware architectures. We are able to predict the execution time with a relative error of less than 25% for problem sizes between 0.1 and 1000 MB. Finally, we find that the product of latency and bandwidth gives a minimum array size per compute node to achieve a scaling efficiency above 50% (both strong and weak)

Catalytic Low-Temperature Dehydration of Fructose to 5-Hydroxymethylfurfural Using Acidic Deep Eutectic Solvents and Polyoxometalate Catalysts

HMF synthesis typically requires high temperature and is carried out in aqueous solutions. In this work, the low-temperature dehydration of fructose to HMF in different deep eutectic solvents (DES) was investigated. We found a very active and selective reaction system consisting of the DES tetraethyl ammonium chloride as hydrogen bond acceptor (HBA) and levulinic acid as hydrogen bond donor (HBD) in a molar ratio of 1:2 leading to a maximum HMF yield of 68% after 120 h at 323 K. The DES still contained a low amount of water at the initial reaction, and water was also produced during the reaction. Considering the DES properties, neither the molar ratio in the DES nor the reaction temperature had a significant influence on the overall performance of the reaction system. However, the nature of the HBA as well as the acidity of the HBD play an important role for the maximum achievable HMF yield. This was validated by measured yields in a DES with different combinations of HBD (levulinic acid and lactic acid) and HBA (choline chloride and tetra-n-alkyl ammonium chlorides). Moreover, addition of vanadium containing catalysts, especially the polyoxometalate HPA-5 (H8PV5Mo7O40) leads to drastically increased reaction kinetics. Using HPA-5 and the DES tetraethyl ammonium chloride—levulinic acid we could reach a maximum HMF yield of 57% after only 5 h reaction time without decreasing the very high product selectivity

Clustered multidimensional scaling with Rulkov neurons

Copyright ©2016 IEICEWhen dealing with high-dimensional measurements that often show non-linear characteristics at multiple scales, a need for unbiased and robust classification and interpretation techniques has emerged. Here, we present a method for mapping high-dimensional data onto low-dimensional spaces, allowing for a fast visual interpretation of the data. Classical approaches of dimensionality reduction attempt to preserve the geometry of the data. They often fail to correctly grasp cluster structures, for instance in high-dimensional situations, where distances between data points tend to become more similar. In order to cope with this clustering problem, we propose to combine classical multi-dimensional scaling with data clustering based on self-organization processes in neural networks, where the goal is to amplify rather than preserve local cluster structures. We find that applying dimensionality reduction techniques to the output of neural network based clustering not only allows for a convenient visual inspection, but also leads to further insights into the intraand inter-cluster connectivity. We report on an implementation of the method with Rulkov-Hebbian-learning clustering and illustrate its suitability in comparison to traditional methods by means of an artificial dataset and a real world example

Certification of the Mass Concentrations of Ammonium, Chloride, Fluoride, Magnesium, Nitrate, Ortho-Phosphate, Sulfate and of pH and Conductivity in Simulated Rainwater - Certified Reference Material ERM®-CA408

This report presents the preparation and certification of the simulated rainwater certified reference material ERM-CA408. All the steps required for the production of this water-matrix certified reference material are described in detail, from the preparation of the simulated rainwater until the characterization exercise that lead to the final assignment of the certified values, following ISO Guide 34:2009 [1] and ISO Guide 35:2006 [2]. Homogeneity and stability of the water material were investigated with dedicated studies and the certification campaign for the material characterisation was based on an inter-comparison among several experienced laboratories. IRMM organised and coordinated all the phases of this project including evaluation of data. The certified values were calculated as the unweighted mean of the laboratory means of the accepted sets of results for each parameter, see below. Uncertainties were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM, ISO/IEC Guide 98-3:2008) [3]. The stated expanded uncertainties include contributions from characterisation, homogeneity and stability.JRC.DG.D.2-Reference material

Dynamic Bradley–Terry modelling of sports tournaments

Summary.  In the course of national sports tournaments, usually lasting several months, it is expected that the abilities of teams taking part in the tournament will change over time. A dynamic extension of the Bradley–Terry model for paired comparison data is introduced to model the outcomes of sporting contests, allowing for time varying abilities. It is assumed that teams’ home and away abilities depend on past results through exponentially weighted moving average processes. The model proposed is applied to sports data with and without tied contests, namely the 2009–2010 regular season of the National Basketball Association tournament and the 2008–2009 Italian Serie A football season

Modeling relaxation and jamming in granular media

We introduce a stochastic microscopic model to investigate the jamming and reorganization of grains induced by an object moving through a granular medium. The model reproduces the experimentally observed periodic sawtooth fluctuations in the jamming force and predicts the period and the power spectrum in terms of the controllable physical parameters. It also predicts that the avalanche sizes, defined as the number of displaced grains during a single advance of the object, follow a power-law, $P(s)\sim s^{-\tau}$, where the exponent is independent of the physical parameters

Certification of the mass concentration of arsenic, cadmium, chromium, copper, iron, manganese, mercury, lead, nickel and selenium in wastewater: ERM®-CA713

The report describes the production and certification of the certified reference material ERM-CA713 Wastewater. The material was produced to replace the existing materials BCR-713, BCR-714 and BCR-715 because of changes in the legislation, in particular the requirement for the monitoring of Hg as a priority substance. The material is certified for As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Se. and will serve as a quality control tool for the laboratories involved in the mandatory monitoring of the Priority Substances prescribed under the Water Framework Directive (WFD, 2000/60/EC).JRC.D.2-Standards for Innovation and sustainable Developmen

CERTIFICATION REPORT The certification of the mass fraction and mass concentration of total Hg in seawater: ERM®-CA400

This report describes the production of ERM-CA400, a seawater material certified for the mass concentration and mass fraction (calculated from the (certified) density) of total Hg. The material was produced following ISO Guide 34:2009 [[i]]. Approximately 500 litres of surface seawater were collected from The Netherlands and transferred into a pre-cleaned polyester tank. Upon arrival at the JRC Geel, the water was acidified and passed first through a 0.8 µm , then through a 0.45 µm filter into another pre-cleaned tank. After filtration, the water was spiked with mercury to achieve a final concentration of total Hg of approximately 20 ng/L. Aliquots of 100 mL were dispensed into borosilicate glass ampoules which were flame sealed and sterilised by gamma ray irradiation. Between ampoule-homogeneity was quantified and stability during dispatch and storage were assessed following ISO Guide 35:2006 [[ii]]. The material was characterised by means of an inter-comparison among laboratories of demonstrated competence and adhering to ISO/IEC 17025 for Hg and by a primary method of measurement, confirmed by independent results for density. Technically invalid results were removed, but no outlier was eliminated on statistical grounds only. Uncertainties of the certified values were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM) [[iii]] and include uncertainties related to possible inhomogeneity, instability and characterisation. The material is intended for the quality control and assessment of method performance. As any reference material, it can also be used for control charts or validation studies. The CRM is available as a set of three borosilicate glass ampoules each containing 100 mL of acidified seawater. The minimum amount of sample to be used is 10 g. The CRM was accepted as European Reference Material (ERM®) after peer evaluation by the partners of the European Reference Materials consortium.JRC.F.6-Reference Material