Handling Concept Drifts in Regression Problems -- the Error Intersection Approach

Machine learning models are omnipresent for predictions on big data. One challenge of deployed models is the change of the data over time, a phenomenon called concept drift. If not handled correctly, a concept drift can lead to significant mispredictions. We explore a novel approach for concept drift handling, which depicts a strategy to switch between the application of simple and complex machine learning models for regression tasks. We assume that the approach plays out the individual strengths of each model, switching to the simpler model if a drift occurs and switching back to the complex model for typical situations. We instantiate the approach on a real-world data set of taxi demand in New York City, which is prone to multiple drifts, e.g. the weather phenomena of blizzards, resulting in a sudden decrease of taxi demand. We are able to show that our suggested approach outperforms all regarded baselines significantly

OCT angiography in optic disc drusen: comparison with structural and functional parameters

Background: Optic disc drusen (ODD) can cause retinal nerve fibre layer (RNFL) defects with progressive visual field (VF) loss. Microvascular changes are discussed as a cause. We measured the vessel density (VD) of the optic disc in ODD using optical coherence tomography angiography and compared it with a normal population. Another intent was to determine the sensitivity and correlations in comparison with functional (VF) and structural parameters (RNFL, minimum rim width (MRW), ganglion cell complex (GCC)). Methods: We analysed the VD of 25 patients with ODD and an age-matched control population including 25 healthy participants using AngioVue (Optovue, Fremont, CA, USA). We obtained data about RNFL, GCC, Bruch's membrane opening MRW (Spectralis HRA & OCT;Heidelberg Engineering, Germany) and VF (standard automated perimetry;SITA 24-2). Low image quality and pathologies interfering with the diagnostics were excluded. Parametric data were analysed using the t-test and non-parametric values using the Mann-Whitney U test. Linear regression analysis was used to determine correlations using the Bravais-Pearson test. Results: The VD was significantly reduced in the ODD group especially the peripapillary capillary VD (n=45 vs 50 eyes;mean 43.15% vs 51.70%). Peripapillary RNFL thickness correlated with the VD significantly (r=0.902 (n=44), 0.901 (n=44), 0.866 (n=45)). The RNFL analysis showed a reduction in ODD, especially the superior hemisphere (mean 107 mu m, 129 mu m;49 vs 50 eyes). The GCC was significantly lower in the ODD group (n=38 vs 40;mean 87 mu m vs 98 mu m). Positive correlation between the VD and the GCC was significant (n=37, r=0.532). There is a significant negative correlation (n=19;r=-0.726) between the VD and the pattern standard deviation (PSD). Conclusion This study reveals significant peripapillary microvascular changes in patients with ODD correlating with the RNFL and GCC reduction. There is a negative correlation between the PSD and the VD

The Shapley super-cluster. New X-ray detections and mass distribution

The largest and the deepest super-structure known today is the Shapley super-cluster. This is the sky area with the highest over-density of galaxy clusters and therefore also an ideal region to test the effects of a high density environment on galaxies and on clusters. We performed an X-ray survey of a wide region surrounding the Shapley super-structure. Additionally to previously known super-cluster X-ray members, we identified diffuse X-ray emission from 35 cluster candidates without previous X-ray detection. 21 of them were previously known, optically selected super-cluster members, while the other candidates had not been previously detected in any wavelength range. Optical follow-up observations revealed that at least four of these new candidates also have optical cluster counterparts. The super-cluster shows a slightly flattened and elongated morphology. Clusters outside the central dense core are preferentially located in four perpendicular filaments in a similar way to what is seen in simulations of Large Scale Structure. We measure the cluster number density in the region to be more than one order of magnitude higher than the mean density of rich Abell clusters previously observed at similar Galactic latitudes; this over-density, in the super-cluster outskirts, is mainly due to an excess of low X-ray luminous clusters (with respect to an average population), which leads us to think that the whole region is still accreting low luminosity, small objects from the outskirts. Pushing our total X-ray mass estimate to fainter clusters would drastically increase the total super-cluster mass measure, because of the presence of the rich X-ray low luminosity population.Comment: 27 pages; accepted for publication in A&A. A version of the paper with higher resolution images can be downloaded at: http://people.na.infn.it/~betty/publications_files/Shapley.ps.g

Compound events in Germany in 2018: drivers and case studies

The European continent is regularly affected by a wide range of extreme events and natural hazards including heatwaves, extreme precipitation, droughts, cold spells, windstorms, and storm surges. Many of these events do not occur as single extreme events, but rather show a multivariate character, the so-called compound events. Within the scope of the interdisciplinary project climXtreme (https://climxtreme.net/), we investigate the interplay of extreme weather events, their characteristics and changes, intensity, frequency and uncertainties in the past, present and future and associated impacts on various socio-economic sectors in Germany and Central Europe. This contribution presents several case studies with special emphasis on the calendar year of 2018, which is of particular interest given the exceptional sequence of different compound events across large parts of Europe, with devastating impacts on human lives, ecosystems and infrastructure. We provide new evidence on drivers of spatially and temporally compound events (heat and drought; heavy precipitation in combination with extreme winds) with adverse impacts on ecosystems and society using large-scale atmospheric patterns. We shed light on the interannual influence of droughts on surface water and the impact of water scarcity and heatwaves on agriculture and forests. We assessed projected changes in compound events at different current and future global surface temperature levels, demonstrating the importance of better quantifying the likelihood of future extreme events for adaptation planning. Finally, we addressed research needs and future pathways, emphasising the need to define composite events primarily in terms of their impacts prior to their statistical characterisation

Examining the generalizability of research findings from archival data

This initiative examined systematically the extent to which a large set of archival research findings generalizes across contexts. We repeated the key analyses for 29 original strategic management effects in the same context (direct reproduction) as well as in 52 novel time periods and geographies; 45% of the reproductions returned results matching the original reports together with 55% of tests in different spans of years and 40% of tests in novel geographies. Some original findings were associated with multiple new tests. Reproducibility was the best predictor of generalizability—for the findings that proved directly reproducible, 84% emerged in other available time periods and 57% emerged in other geographies. Overall, only limited empirical evidence emerged for context sensitivity. In a forecasting survey, independent scientists were able to anticipate which effects would find support in tests in new samples