Multiscale Information Decomposition: Exact Computation for Multivariate Gaussian Processes

Exploiting the theory of state space models, we derive the exact expressions of the information transfer, as well as redundant and synergistic transfer, for coupled Gaussian processes observed at multiple temporal scales. All of the terms, constituting the frameworks known as interaction information decomposition and partial information decomposition, can thus be analytically obtained for different time scales from the parameters of the VAR model that fits the processes. We report the application of the proposed methodology firstly to benchmark Gaussian systems, showing that this class of systems may generate patterns of information decomposition characterized by mainly redundant or synergistic information transfer persisting across multiple time scales or even by the alternating prevalence of redundant and synergistic source interaction depending on the time scale. Then, we apply our method to an important topic in neuroscience, i.e., the detection of causal interactions in human epilepsy networks, for which we show the relevance of partial information decomposition to the detection of multiscale information transfer spreading from the seizure onset zone

Making visible the invisible through the analysis of acknowledgements in the humanities

Purpose: Science is subject to a normative structure that includes how the contributions and interactions between scientists are rewarded. Authorship and citations have been the key elements within the reward system of science, whereas acknowledgements, despite being a well-established element in scholarly communication, have not received the same attention. This paper aims to put forward the bearing of acknowledgements in the humanities to bring to the foreground contributions and interactions that, otherwise, would remain invisible through traditional indicators of research performance. Design/methodology/approach: The study provides a comprehensive framework to understanding acknowledgements as part of the reward system with a special focus on its value in the humanities as a reflection of intellectual indebtedness. The distinctive features of research in the humanities are outlined and the role of acknowledgements as a source of contributorship information is reviewed to support these assumptions. Findings: Peer interactive communication is the prevailing support thanked in the acknowledgements of humanities, so the notion of acknowledgements as super-citations can make special sense in this area. Since single-authored papers still predominate as publishing pattern in this domain, the study of acknowledgements might help to understand social interactions and intellectual influences that lie behind a piece of research and are not visible through authorship. Originality/value: Previous works have proposed and explored the prevailing acknowledgement types by domain. This paper focuses on the humanities to show the role of acknowledgements within the reward system and highlight publication patterns and inherent research features which make acknowledgements particularly interesting in the area as reflection of the socio-cognitive structure of research.Comment: 14 page

On the interpretability and computational reliability of frequency-domain Granger causality

This is a comment to the paper 'A study of problems encountered in Granger causality analysis from a neuroscience perspective'. We agree that interpretation issues of Granger Causality in Neuroscience exist (partially due to the historical unfortunate use of the name 'causality', as nicely described in previous literature). On the other hand we think that the paper uses a formulation of Granger causality which is outdated (albeit still used), and in doing so it dismisses the measure based on a suboptimal use of it. Furthermore, since data from simulated systems are used, the pitfalls that are found with the used formulation are intended to be general, and not limited to neuroscience. It would be a pity if this paper, even written in good faith, became a wildcard against all possible applications of Granger Causality, regardless of the hard work of colleagues aiming to seriously address the methodological and interpretation pitfalls. In order to provide a balanced view, we replicated their simulations used the updated State Space implementation, proposed already some years ago, in which the pitfalls are mitigated or directly solved

Experimental investigation of the weldability of tubular dissimilar materials using the electromagnetic welding process

This paper describes the magnetic pulse welding process (MPW) for tubes. Material combinations of aluminium to steel and copper to aluminium were experimentally evaluated. The first major goal of this work is to experimentally obtain the optimal input parameters like the discharge energy, the stand-off distance and the tool overlap for MPW of the material combinations. Welding windows with all possible input parameters are created for both material combinations. Furthermore, a comparison is done between three coil systems; a single turn coil with field shaper, a single turn coil with a field shaper and transformer and a multi-turn coil and field shaper. Metallographic investigation of the samples, hardness tests and leak tests were executed to determine the most suitable machine set-up and the optimal input parameters for each set-up. A second major goal is to determine the influence of the target tube wall thickness on the deformation of tube-tube welds when no internal support is used

Feasibility study of the friction surfacing process

Friction surfacing is a solid state cladding process based on the plastic deformation of a translating and rotating metallic consumable rod pressed against a stationary substrate. It is mostly used on mild and stainless steel and on aluminium. Thanks to the solid state nature of the process, it allows to join dissimilar metal combinations, e.g. aluminium to steel or to ceramics or several combinations of non-ferrous metals. Moreover, a continuous and fine-grained deposition is formed. Most research has been focussed on the feasibility of certain material combinations and on correlating the deposited layer quality to input parameters. In this work, a methodical approach to evaluate clad layers and to assess their properties is discussed. This approach consists of a visual assessment, a macrographic examination and a performance analysis and has shown to be apt to compare the clad layer quality

Investigation of the weldability of copper to steel tubes using the electromagnetic welding process

Magnetic pulse welding is an innovative joining method which allows joining of dissimilar metal combinations. However, much remains unknown about the process and its parameters. In this paper, the weldability of copper tubes to steel rods and tubes is discussed, with the goal of examining the influence of the wall thickness of the supporting steel tube on the weld and the deformation of the components. Large deformations were observed, causing an undesirable decrease in diameter of the tubes. The quality of the obtained welds was shown to decrease with decreasing inner tube thickness as well, most likely due to the deformation of the workpieces in radial direction. Because of this, it is advisable to use an internal support to prevent deformation of the support tubes. To gain more insight in the precise mechanisms of weld formation and failure, numerical simulations are advised

Metallographic evaluation of the weldability of high strength aluminium alloys using friction spot welding

Friction spot welding is a recent solid-state welding technique well suited for spot-joining lightweight materials in overlap condition. Aerospace and transport industries show great interest in this technique to join high-strength aluminium alloys, but published research is still limited. In this project, the link between process parameters and weld quality is investigated for EN AW-7075-T6 material. Techniques used are metallographic qualification, measurement of hardness reduction and lap shear strength. This paper focusses on the metallographic investigation of the weld region and its imperfections. Increasing joining time and heat input creates an easier material flow resulting in fewer imperfections. Limited plunge depths lead to typical interface imperfections. Variation in the rotational speed shows distinctive stir zone shapes as a consequence of severe stirring and frictional heat