Jožef Stefan Institute

About: Jožef Stefan Institute is a facility organization based out in Ljubljana, Slovenia. It is known for research contribution in the topics: Liquid crystal & Dielectric. The organization has 3828 authors who have published 12614 publications receiving 291025 citations.

Topological Function Optimization for Continuous Shape Matching

Abstract: We present a novel approach for optimizing real-valued functions based on a wide range of topological criteria. In particular, we show how to modify a given function in order to remove topological noise and to exhibit prescribed topological features. Our method is based on using the previously-proposed persistence diagrams associated with real-valued functions, and on the analysis of the derivatives of these diagrams with respect to changes in the function values. This analysis allows us to use continuous optimization techniques to modify a given function, while optimizing an energy based purely on the values in the persistence diagrams. We also present a procedure for aligning persistence diagrams of functions on different domains, without requiring a mapping between them. Finally, we demonstrate the utility of these constructions in the context of the functional map framework, by first giving a characterization of functional maps that are associated with continuous point-to-point correspondences, directly in the functional domain, and then by presenting an optimization scheme that helps to promote the continuity of functional maps, when expressed in the reduced basis, without imposing any restrictions on metric distortion. We demonstrate that our approach is efficient and can lead to improvement in the accuracy of maps computed in practice.

Monitoring Network Evolution using MDL

Abstract: Given publication titles and authors, what can we say about the evolution of scientific topics and communities over time? Which communities shrunk, which emerged, and which split, over time? And, when in time were the turning points? We propose TimeFall, which can automatically answer these questions given a social network/graph that evolves over time. The main novelty of the proposed approach is that it needs no user-defined parameters, relying instead on the principle of minimum description length (MDL), to extract the communities, and to find good cut-points in time when communities change abruptly: a cut-point is good, if it leads to shorter data description. We illustrate our algorithm on synthetic and large real datasets, and we show that the results of the TimeFall agree with human intuition.

Characterization of low temperature CrN and TiN (PVD) hard coatings

Abstract: The plasma beam sputtering process was used to prepare CrN and TiN hard coatings on steel, sapphire and alumina Superstrate substrates at a temperature of 200 °C. The microstructural characteristics, coating morphology, interfacial properties, microhardness and internal stresses were studied for coatings 3 μm thick. Their oxidation behaviour in an oxygen flow in a tube furnace was studied at temperatures up to 600 °C for TiN and up to 800 °C for CrN coatings. The initial stage of oxidation of TiN and CrN coatings 350 nm thick was also studied by continuous in-situ electrical resistivity measurements. This measurement technique offers high reproducibility and accuracy, so can be used to study oxidation for all types of hard coating, and especially for new multilayer and duplex coatings. Weight gain measurements and Auger electron spectroscopy depth profile analyses of oxidized stoichiometric CrN coatings showed that oxidation in an oxygen flow at 800 °C for 4 h induced the growth of a stable Cr2O3 film. The thickness of this oxide film was only 15% of the total (3 μm) coating thickness. The surface morphology and small roughness changes — as also observed after a long-term test at 800 °C for 200 h in oxygen — indicated that a stoichiometric CrN coating with the measured properties can be successfully used as a hard and oxidation-resistant coating in industrial practice, even if the working temperatures are higher than 750 °C.