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

Corneal epithelial wavefront error as a novel diagnostic marker for epithelial basement membrane dystrophy

Synopsis: Corneal epithelial wavefront error and epithelial thickness variance qualify as highly sensitive and specific biomarkers for epithelial basement membrane dystrophy (EBMD). The biomarkers show a normalization after treatment of EBMD with phototherapeutic keratectomy. Purpose: To gauge the diagnostic value of epithelial basement membrane dystrophy (EBMD), a novel spectral-domain optical coherence tomography (SD-OCT)-based imaging modality for simultaneous morphological (thickness profile) and refractive (optical wavefront) assessment of the corneal epithelial layer in one of the most common but often underdiagnosed corneal dystrophies. Methods: In this prospective observational study, a total of 32 eyes of 32 patients diagnosed with EBMD and 32 eyes of 32 healthy control subjects were examined with high-resolution anterior segment SD-OCT (MS-39; CSO, Florence, Italy). Various epithelial thickness and epithelial wavefront-derived terms were compared between groups and receiver operating characteristic (ROC) curves were computed to analyze the diagnostic capacity of the respective parameters. A total of 17 of 32 EBMD patients underwent treatment with phototherapeutic keratectomy (PTK) and were followed up for 3 months. Results: Epithelial thickness variance (60.4 ± 56.7 µm versus 7.6 ± 6.1 µm) and interquartile range (11.0 ± 6.9 versus 3.3 ± 1.9 µm) were markedly elevated in EBMD patients as compared with healthy controls (both with p < 0.001). Epithelial wavefront analysis showed a highly statistically significant excess in all examined aberration terms in EBMD patients (all with p < 0.001). Significantly greater areas under the curve (AUCs) were yielded by the epithelial wavefront-derived parameters (e.g., total epithelial wavefront error: AUC = 0.966; 95% confidence interval (CI) 0.932–1) than by the epithelial thickness-derived parameters (e.g., variance: AUC = 0.919; 95% CI 0.848–0.990). Conclusions: Corneal epithelial wavefront aberrometry proved valuable as an objective biomarker for EBMD, with high sensitivity and specificity. PTK resulted in a reduction of morphological and refractive epithelial irregularities in EBMD

Entwicklung einer Ammoniak-betriebenen Cracker- Motor-Einheit als Antriebssystem für Binnenschiffe

Schiffe sind ein wesentlicher Bestandteil der globalen Transportsysteme für Waren und Menschen. Sie stellen die effizienteste und klimafreundlichste Transportmethode dar. Dennoch ist eine weitere Reduzierung der Emissionen, insbesondere von CO2, notwendig. Da eine reine Elektrifizierung durch den Einsatz von Batterien als Energiespeicher aufgrund der erforderlichen Reichweite in den meisten Fällen nicht in Frage kommt, ist der Einsatz von alternativen Kraftstoffen auf Basis erneuerbarer Energien sinnvoll. Die CAMPFIREPartnerallianz arbeitet daher intensiv an der Nutzung von regenerativ erzeugtem Ammoniak als maritimen Treibstoff und Energiespeicher von regenerativ erzeugtem Wasserstoff. Wegen der zukünftig größeren Nachfragen an Wasserstoff wird dieser importiert werden müssen und für den Transport in Ammoniak gespeichert werden. Damit wird u. a. auch die benötigte Transportkapazität in der Binnenschifffahrt steigen, um die Energie von den Seehäfen ins Landesinnere zu verteilen. Vor diesem Hintergrund entwickelt und erprobt ein Projektkonsortium ein Antriebssystem für Binnenschiffe, das ausschließlich mit Ammoniak betrieben wird. Das Herzstück dieses Projekts ist eine Cracker-Motor-Einheit. Im Rahmen der Arbeiten wird der Ammoniak-Cracker entwickelt und gebaut, die Eigenschaften und Herausforderungen der Ammoniakverbrennung im Motor systematisch untersucht, das Gesamtsystem ausgelegt, die komplette Motoreinheit mit Generator containerisiert und schließlich ganzheitlich getestet. Darüber hinaus werden die besonderen Sicherheitsaspekte beim Einsatz von Ammoniak in der maritimen Umgebung analysiert. Die Kombination der eingesetzten Technologien soll einen vollständig klimaneutralen Schiffsbetrieb ermöglichen. Das Manuskript gibt einen Überblick über die laufenden Arbeiten. Dazu gehören Beispiele aus den Ergebnissen systematischer Verbrennungsstudien zum Einzylindermotor und der erforderlichen Injektortechnologie. Die verschiedenen Konfigurationen werden hinsichtlich Leistung und Emissionen für eine maritime Anwendung bewertet und dann als Grundlage für die vollständige Motorkonfiguration verwendet. Außerdem werden die Entwicklungsarbeiten am Cracker vorgestellt, der einen Teilstrom von Ammoniak in Wasserstoff und Stickstoff aufspaltet und damit den Zündbrennstoff für den Motor liefert

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

Aspects of Ammonia as Green Fuel for Propulsion Systems of Inland Water Vessels

Ships are a crucial backbone of the transport system for goods and people. However, the currently utilized fossil fuels require a green replacement. Ammonia produced from green hydrogen is an interesting, carbon-free green fuel, which has been demonstrated to be promising for maritime applications. Its application under the specific boundary conditions of river ships and other inland water vessels still deserves a closer evaluation. In this work, ammonia as a green fuel for propulsion systems of inland water vessels is evaluated regarding several technological aspects. These include onboard decomposition for hydrogen release, combustion of ammonia–hydrogen mixtures in internal combustion engines and the thermal integration of the different components. To achieve favorable combustion properties of the fuel, a certain share of the ammonia has to be decomposed in an ammonia cracker to produce a mixture of hydrogen and ammonia. First single-cylinder engine tests show that the combined combustion of ammonia and hydrogen allow an efficient and reliable process for the investigated high-speed engine concept. Efficiency values of nearly 40% at part load already are achieved. With proper system integration, it is possible to reasonably operate small- and medium-sized ships with ammonia as a green fuel