Accuracy and transferability of Gaussian approximation potential models for tungsten

We introduce interatomic potentials for tungsten in the bcc crystal phase and its defects within the Gaussian approximation potential framework, fitted to a database of first-principles density functional theory calculations. We investigate the performance of a sequence of models based on databases of increasing coverage in configuration space and showcase our strategy of choosing representative small unit cells to train models that predict properties observable only using thousands of atoms. The most comprehensive model is then used to calculate properties of the screw dislocation, including its structure, the Peierls barrier and the energetics of the vacancy-dislocation interaction. All software and raw data are available at www.libatoms.org

Influence of Differential Thermochemical Treatment of Bolts on Tightening Parameters in a Bolted Joint

This article presents the results of the research into the influence of heat treatment, with application of differential parameters and gas atmosphere, on the friction coefficient during the tightening of a bolted joint. The study consisted of several stages – it included metallographic examinations, hardness evaluation and joint tightening tests. This paper presents the research process, the obtained results and the analysis of the impact of thermochemical treatment on functional parameters, such as friction coefficient and torque, during the tightening of a bolted joint

Building nonparametric nn-body force fields using Gaussian process regression

Constructing a classical potential suited to simulate a given atomic system is a remarkably difficult task. This chapter presents a framework under which this problem can be tackled, based on the Bayesian construction of nonparametric force fields of a given order using Gaussian process (GP) priors. The formalism of GP regression is first reviewed, particularly in relation to its application in learning local atomic energies and forces. For accurate regression it is fundamental to incorporate prior knowledge into the GP kernel function. To this end, this chapter details how properties of smoothness, invariance and interaction order of a force field can be encoded into corresponding kernel properties. A range of kernels is then proposed, possessing all the required properties and an adjustable parameter $n$ governing the interaction order modelled. The order $n$ best suited to describe a given system can be found automatically within the Bayesian framework by maximisation of the marginal likelihood. The procedure is first tested on a toy model of known interaction and later applied to two real materials described at the DFT level of accuracy. The models automatically selected for the two materials were found to be in agreement with physical intuition. More in general, it was found that lower order (simpler) models should be chosen when the data are not sufficient to resolve more complex interactions. Low $n$ GPs can be further sped up by orders of magnitude by constructing the corresponding tabulated force field, here named "MFF".Comment: 31 pages, 11 figures, book chapte

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

Reducing the development gaps between regions in Poland with the use of European Union funds

The paper evaluates the processes of regional income convergence in Poland. This new research approach involves an attempt to assess the process of convergence from the point of view of development gaps. Six key development gaps were considered in the region of Eastern Poland, which is a singular case, significantly different from other regions. A dynamic panel data model was applied to investigate the impact of EU funds on the progress made towards closing these development gaps. Among the analysed development gaps, only the structural gap was not reduced in the period 2004–2015. Studies have also revealed the different impact of structural funds on each category of development gaps (a positive impact on reducing the regional transport accessibility gap and the investment gap, but negative – on reducing the innovation gap). Research has suggested the need for a change in the structure of using EU funds in the period 2014–2020 to favour stronger support for entrepreneurship and the creation of new jobs. Greater stimulation of the economic structure of peripheral regions has been proposed as the prerequisite for the future reduction in the discrepancies between regions and for the intensification of convergence. First published online 2 April 201

Państwo, gospodarka, społeczeństwo w integrującej się Europie TOM 1

Ze wstępu: "III Międzynarodowa Konferencja Naukowa, jaką w pierwszych dniach czerwca 2003 roku zorganizowała Krakowska Szkoła Wyższa, poświęcona była uczczeniu wyjątkowego jubileuszu 500-lecia urodzin jej patrona - Andrzeja Frycza Modrzewskiego. Jednak to nie myśl polityczna tego wielkiego Polaka i reformatora stała się wiodącym tematem konferencji. W centrum zainteresowań znalazły się zagadnienia 0 wiele bardziej aktualne, dotyczące bowiem integracji europejskiej. Problematyka tym bardziej żywotna, gdyż dotykająca bieżącego życia politycznego - zwłaszcza w kontekście referendum akcesyjnego, które odbyło się w równy tydzień po konferencji. Tak więc jej uczestnicy mieli doskonałą okazję do podjęcia interesujących rozważań związanych z perspektywą rozwoju państwa, gospodarki i społeczeństwa w warunkach integracji europejskiej."(...