TY - JOUR A1 - Dineva, Ekaterina A1 - Pearson, Jeniveve A1 - Ilyin, Ilya A1 - Verma, Meetu A1 - Diercke, Andrea A1 - Strassmeier, Klaus A1 - Denker, Carsten T1 - Characterization of chromospheric activity based on Sun-as-a-star spectral and disk-resolved activity indices JF - Astronomische Nachrichten = Astronomical notes N2 - The strong chromospheric absorption lines Ca ii H & K are tightly connected to stellar surface magnetic fields. Only for the Sun, spectral activity indices can be related to evolving magnetic features on the solar disk. The Solar Disk-Integrated (SDI) telescope feeds the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) of the Large Binocular Telescope (LBT) at Mt. Graham International Observatory, Arizona, U.S.A. We present high-resolution, high-fidelity spectra that were recorded on 184 & 82 days in 2018 & 2019 and derive the Ca ii H & K emission ratio, that is, the S-index. In addition, we compile excess brightness and area indices based on full-disk Ca ii K-line-core filtergrams of the Chromospheric Telescope (ChroTel) at Observatorio del Teide, Tenerife, Spain and full-disk ultraviolet (UV) 1600 angstrom images of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). Thus, Sun-as-a-star spectral indices are related to their counterparts derived from resolved images of the solar chromosphere. All indices display signatures of rotational modulation, even during the very low magnetic activity in the minimum of Solar Cycle 24. Bringing together different types of activity indices has the potential to join disparate chromospheric datasets yielding a comprehensive description of chromospheric activity across many solar cycles. KW - astronomical databases KW - miscellaneous KW - methods KW - data analysis KW - activity KW - Sun KW - atmosphere KW - chromosphere KW - techniques KW - spectroscopic Y1 - 2022 U6 - https://doi.org/10.1002/asna.20223996 SN - 0004-6337 SN - 1521-3994 VL - 343 IS - 5 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Adnan, Hassan Sami A1 - Srsic, Amanda A1 - Venticich, Pete Milos A1 - Townend, David M.R. T1 - Using AI for mental health analysis and prediction in school surveys JF - European journal of public health N2 - Background: Childhood and adolescence are critical stages of life for mental health and well-being. Schools are a key setting for mental health promotion and illness prevention. One in five children and adolescents have a mental disorder, about half of mental disorders beginning before the age of 14. Beneficial and explainable artificial intelligence can replace current paper- based and online approaches to school mental health surveys. This can enhance data acquisition, interoperability, data driven analysis, trust and compliance. This paper presents a model for using chatbots for non-obtrusive data collection and supervised machine learning models for data analysis; and discusses ethical considerations pertaining to the use of these models. Methods: For data acquisition, the proposed model uses chatbots which interact with students. The conversation log acts as the source of raw data for the machine learning. Pre-processing of the data is automated by filtering for keywords and phrases. Existing survey results, obtained through current paper-based data collection methods, are evaluated by domain experts (health professionals). These can be used to create a test dataset to validate the machine learning models. Supervised learning can then be deployed to classify specific behaviour and mental health patterns. Results: We present a model that can be used to improve upon current paper-based data collection and manual data analysis methods. An open-source GitHub repository contains necessary tools and components of this model. Privacy is respected through rigorous observance of confidentiality and data protection requirements. Critical reflection on these ethics and law aspects is included in the project. Conclusions: This model strengthens mental health surveillance in schools. The same tools and components could be applied to other public health data. Future extensions of this model could also incorporate unsupervised learning to find clusters and patterns of unknown effects. KW - ethics KW - artificial intelligence KW - adolescent KW - child KW - confidentiality KW - health personnel KW - mental disorders KW - mental health KW - personal satisfaction KW - privacy KW - school (environment) KW - statutes and laws KW - public health medicine KW - surveillance KW - medical KW - prevention KW - datasets KW - machine learning KW - supervised machine learning KW - data analysis Y1 - 2020 U6 - https://doi.org/10.1093/eurpub/ckaa165.336 SN - 1101-1262 SN - 1464-360X VL - 30 SP - V125 EP - V125 PB - Oxford Univ. Press CY - Oxford [u.a.] ER - TY - THES A1 - Duy, Nguyen Le T1 - Hydrological processes in the Vietnamese Mekong Delta BT - Insights from stable water isotopes and monitoring data analysis BT - Erkenntnisse aus stabilen Wasserisotopen und Überwachungsdatenanalyse N2 - Understanding hydrological processes is of fundamental importance for the Vietnamese national food security and the livelihood of the population in the Vietnamese Mekong Delta (VMD). As a consequence of sparse data in this region, however, hydrologic processes, such as the controlling processes of precipitation, the interaction between surface and groundwater, and groundwater dynamics, have not been thoroughly studied. The lack of this knowledge may negatively impact the long-term strategic planning for sustainable groundwater resources management and may result in insufficient groundwater recharge and freshwater scarcity. It is essential to develop useful methods for a better understanding of hydrological processes in such data-sparse regions. The goal of this dissertation is to advance methodologies that can improve the understanding of fundamental hydrological processes in the VMD, based on the analyses of stable water isotopes and monitoring data. The thesis mainly focuses on the controlling processes of precipitation, the mechanism of surface–groundwater interaction, and the groundwater dynamics. These processes have not been fully addressed in the VMD so far. The thesis is based on statistical analyses of the isotopic data of Global Network of Isotopes in Precipitation (GNIP), of meteorological and hydrological data from Vietnamese agencies, and of the stable water isotopes and monitoring data collected as part of this work. First, the controlling processes of precipitation were quantified by the combination of trajectory analysis, multi-factor linear regression, and relative importance analysis (hereafter, a model‐based statistical approach). The validity of this approach is confirmed by similar, but mainly qualitative results obtained in other studies. The total variation in precipitation isotopes (δ18O and δ2H) can be better explained by multiple linear regression (up to 80%) than single-factor linear regression (30%). The relative importance analysis indicates that atmospheric moisture regimes control precipitation isotopes rather than local climatic conditions. The most crucial factor is the upstream rainfall along the trajectories of air mass movement. However, the influences of regional and local climatic factors vary in importance over the seasons. The developed model‐based statistical approach is a robust tool for the interpretation of precipitation isotopes and could also be applied to understand the controlling processes of precipitation in other regions. Second, the concept of the two-component lumped-parameter model (LPM) in conjunction with stable water isotopes was applied to examine the surface–groundwater interaction in the VMD. A calibration framework was also set up to evaluate the behaviour, parameter identifiability, and uncertainties of two-component LPMs. The modelling results provided insights on the subsurface flow conditions, the recharge contributions, and the spatial variation of groundwater transit time. The subsurface flow conditions at the study site can be best represented by the linear-piston flow distribution. The contributions of the recharge sources change with distance to the river. The mean transit time (mTT) of riverbank infiltration increases with the length of the horizontal flow path and the decreasing gradient between river and groundwater. River water infiltrates horizontally mainly via the highly permeable aquifer, resulting in short mTTs (<40 weeks) for locations close to the river (<200 m). The vertical infiltration from precipitation takes place primarily via a low‐permeable overlying aquitard, resulting in considerably longer mTTs (>80 weeks). Notably, the transit time of precipitation infiltration is independent of the distance to the river. All these results are hydrologically plausible and could be quantified by the presented method for the first time. This study indicates that the highly complex mechanism of surface–groundwater interaction at riverbank infiltration systems can be conceptualized by exploiting two‐component LPMs. It is illustrated that the model concept can be used as a tool to investigate the hydrological functioning of mixing processes and the flow path of multiple water components in riverbank infiltration systems. Lastly, a suite of time series analysis approaches was applied to examine the groundwater dynamics in the VMD. The assessment was focused on the time-variant trends of groundwater levels (GWLs), the groundwater memory effect (representing the time that an aquifer holds water), and the hydraulic response between surface water and multi-layer alluvial aquifers. The analysis indicates that the aquifers act as low-pass filters to reduce the high‐frequency signals in the GWL variations, and limit the recharge to the deep groundwater. The groundwater abstraction has exceeded groundwater recharge between 1997 and 2017, leading to the decline of groundwater levels (0.01-0.55 m/year) in all considered aquifers in the VMD. The memory effect varies according to the geographical location, being shorter in shallow aquifers and flood-prone areas and longer in deep aquifers and coastal regions. Groundwater depth, season, and location primarily control the variation of the response time between the river and alluvial aquifers. These findings are important contributions to the hydrogeological literature of a little-known groundwater system in an alluvial setting. It is suggested that time series analysis can be used as an efficient tool to understand groundwater systems where resources are insufficient to develop a physical-based groundwater model. This doctoral thesis demonstrates that important aspects of hydrological processes can be understood by statistical analysis of stable water isotope and monitoring data. The approaches developed in this thesis can be easily transferred to regions in similar tropical environments, particularly those in alluvial settings. The results of the thesis can be used as a baseline for future isotope-based studies and contribute to the hydrogeological literature of little-known groundwater systems in the VMD. N2 - Ein fundiertes Verständnis der hydrologischen Prozesse im vietnamesischen Mekong Delta (VMD) ist von grundlegender Bedeutung für den Lebensunterhalt der Bevölkerung im Mekong Delta, und darüber hinaus auch für die nationale Ernährungssicherheit. Aufgrund des Fehlens einer belastbaren Datenbasis konnten bislang eine Reihe von wichtigen hydrologischen Prozessen nur unzureichend untersucht und quantifiziert werden. Dazu zählen unter anderem die Analyse des Ursprungs des Niederschlages im Delta, die Interaktion zwischen Oberflächen- und Grundwasser, sowie die Grundwasserdynamik. Diese Lücken im Wissensstand verhindern eine solide datenbasierte Wasserwirtschaftsplanung, was unter Berücksichtigung der derzeitigen Trends mittelfristig zu weiter fallenden Grundwasserständen und Wasserknappheit führen wird. Daher ist es von großer Bedeutung, Methoden und Werkzeuge zu entwickeln, die auch unter der bestehenden Datenknappheit belastbare quantitative Ergebnisse für eine nachhaltige Wasserbewirtschaftung liefern können. Das Ziel dieser Dissertation ist es, solche Methoden zu entwickeln und zu testen, um grundlegende hydrologische Prozesse im VMD besser verstehen und quantifizieren zu können. Hierzu werden die existierenden Messdaten sowie im Rahmen dieser Arbeit gesammelte Daten zum Gehalt an stabilen Wasserisotopen verwendet. Mit Hilfe dieser Daten wurden folgende Prozesse untersucht: 1. Der Ursprung und die Fraktionierung des Niederschlages im VMD. 2. Die Interaktion zwischen Oberflächen- und Grundwasser mit einem besonderen Fokus auf die ufernahen Gebiete. 3. Die großflächige Dynamik in den verschiedenen Grundwasserleitern der letzten Jahrzehnte. Die Prozesse, die den Ursprung und die Verteilung des Niederschlagsbestimmen, wurden mittels einer Kombination aus Isotopendaten, Trajektorienanalyse, multifaktorieller Regression, und relativer Wichtigkeitsanalyse untersucht. Diese Kombination ist nachfolgend „modelbasierter statistischer Ansatz“ betitelt. Hierbei wurde festgestellt, dass die Varianz im Isotopengehalt des Niederschlags (δ18O and δ2H) mit der multifaktoriellen Regression zu 80% erklärt werden konnte, was im Vergleich zu einer einfachen Regression mit 30% erklärter Varianz eine deutliche Verbesserung darstellt. Die Wichtigkeitsanalyse ergab zudem, dass großskalige atmosphärische Feuchtigkeitsverteilungen einen weitaus größeren Einfluss auf die Isotopenverteilung im Niederschlag haben, als lokale klimatische Bedingungen im VMD. Der hierbei wichtigste Faktor ist die Regenmenge entlang der Trajektorien der Luftmassenbewegungen. Die Wichtigkeit der Faktoren variiert jedoch saisonal zwischen Regen- und Trockenzeit. Der in dieser Dissertation entwickelte modelbasierte statistische Ansatz ist ein robustes Werkzeug zur Analyse und Interpretation der Isotopenverteilung im Niederschlag, der auch auf ähnliche Fragestellungen in andere Regionen übertragbar ist. Im zweiten Teil der Dissertation wurden Zweikomponentenmodelle (LPM) in Verbindung mit Isotopenmessungen im Niederschlag, Oberflächen- und Grundwasser verwendet, um die Interaktion zwischen Oberflächen- und Grundwasser qualitativ und quantitativ zu beschreiben. Verschiedene Modellansätze wurden hierbei in einem automatischen Kalibrieransatz getestet, und deren Unsicherheit bestimmt. Hierbei hat sich das lineare Kolbenfließmodell (linear piston flow model) als das am besten geeignetste herausgestellt. Die Modellierungsergebnisse ermöglichten daraufhin eine modellbasierte Abschätzung der Grundwasserschwankungen und -flüsse, der Grundwasserneubildung und der räumlichen Variabilität der Grundwasserlaufzeiten. Hierbei zeigte sich, dass Grundwasserneubildung und deren Quellen räumlich variabel ist, und sich mit zunehmender Entfernung vom Fluss die Neubildung von primär Uferinfiltration hin zu Neubildung durch Niederschläge ändert. Analog dazu erhöhen sich die Grundwasserlaufzeiten mit der Länge der horizontalen Fließwege (= Entfernung vom Vorfluter) und mit sinkendem Gradienten zwischen Grundwasserstand und Wasserstand im Fluss. Flusswasser infiltriert über das Flussufer in den wasserleitenden Aquifer, mit mittleren Transferzeiten (mTT) von < 40 Wochen für Bereiche mit weniger als 200 m Entfernung zum Fluss. In größeren Entfernungen findet die Neubildung im Wesentlichen durch Versickerung von Regenwaser statt. Da der betrachtete holozäne Grundwasserleiter mit einer schwerdurchlässigen Deckschicht überlagert ist, liegen die mTT in diesen Bereichen mit > 80 Wochen wesentlich höher. Es konnte mit dieser Studie gezeigt werden, dass die komplexe Interaktion zwischen Grund- und Oberflächenwasser mittels eines konzeptionellen Modells in Verbindung mit aus Wasserproben bestimmten Isotopendaten konzeptionalisiert und quantifiziert werden kann. Der Ansatz empfiehlt sich daher als Werkzeug für die Untersuchung der Mischungsprozesse der Ufer- und Regenwasserinfiltration, sowie der Fließwege des Grundwassers in ähnlichen Gebieten. Im letzten Teil der Dissertation wurden Trends in den Grundwasserständen im gesamtem VMD untersucht. Hierzu wurde eine Reihe von Methoden zur Zeitreihenanalyse angewandt. Der Fokus der Untersuchungen lag auf zeitvariablen Trends in den Grundwasserständen, der Wasserspeicherdauer (memory effect), und der hydraulischen Reaktionszeit zwischen dem Oberflächenwasser und den verschiedenen Aquiferen im VMD. Die Analyse ergab, dass die verschiedenen Schichten von Aquiferen und Aquitarden wie ein Tiefpassfilter auf die hydraulischen Signale des Oberflächenwassers wirken, was wiederum die Grundwasserneubildung in den tieferen Aquiferen stark reduziert. Die Zeitreihenanalyse ergab, dass die Entnahmemengen an Grundwasser insbesondere in den tieferen, stark genutzten Aquiferen die Neubildung im gesamten Analysezeitraum 1997 – 2017 überschritten hat. Dies führte zu Absenkung des Grundwasserspiegels von 0.01 – 0.55 m pro Jahr in den verschiedenen Aquiferen des VMD. Die Speicherdauer variiert zwischen den verschiedenen Regionen und Aquiferen des VMD. In den flacheren Aquiferen und in der Region mit tiefen Überflutungen während der Hochwassersaison sind die Speicherdauern kürzer, während sie in den tieferen Aquiferen und in den küstennahen Regionen wesentlich länger sind. Die Reaktionszeit variiert ebenfalls im Raum, wobei die wichtigsten Einflussfaktoren der Abstand des Grundwasserspiegels zur Oberfläche, die Saison und die Lage, hier besonders die Entfernung zum Fluss oder der Küste, sind. Diese qualitativen wie quantitativen Ergebnisse fügen wichtige und wesentlich Erkenntnisse zum Wissensstand über das Grundwasser im VMD hinzu. Die verwendeten Methoden empfehlen sich darüber hinaus für die Analyse von Grundwasserdynamiken in alluvialen Aquifersystemen im Generellen, wenn Daten und Ressourcen für ein physisches numerisches Grundwassermodell fehlen. Die vorliegende Dissertation zeigt, dass wichtige hydrologische Prozesse auch über statistische Analysen von Mess- und Isotopendaten quantitativ analysiert werden können. Die Ergebnisse stellen eine Basisanalyse der Grundwasserdynamik und der sie beeinflussenden Prozesse im VMD dar, und sollten in weiteren Studien ausgebaut werden. Die Analyse der Isotopendaten liefert darüber hinaus die Basislinie für hydrologische Analysen mit stabilen Isotopen im VMD und aufgrund der ähnlichen klimatischen und geografischen Lage auch für weite Teile Südostasiens. Die entwickelten Methodenkombinationen können aufgrund ihrer generellen Natur auch problemlos auf andere tropische Regionen, insbesondere solche mit alluvialen Aquiferen, übertragen werden. T2 - Hydrologische Prozesse im Mekong Delta KW - Vietnamese Mekong Delta KW - stable isotopes KW - data analysis KW - hydrological processes KW - Mekong Delta KW - Datenanalyse KW - hydrologische Prozesse KW - stabile Isotope Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-602607 ER - TY - THES A1 - Antonelli, Andrea T1 - Accurate waveform models for gravitational-wave astrophysics: synergetic approaches from analytical relativity N2 - Gravitational-wave (GW) astrophysics is a field in full blossom. Since the landmark detection of GWs from a binary black hole on September 14th 2015, fifty-two compact-object binaries have been reported by the LIGO-Virgo collaboration. Such events carry astrophysical and cosmological information ranging from an understanding of how black holes and neutron stars are formed, what neutron stars are composed of, how the Universe expands, and allow testing general relativity in the highly-dynamical strong-field regime. It is the goal of GW astrophysics to extract such information as accurately as possible. Yet, this is only possible if the tools and technology used to detect and analyze GWs are advanced enough. A key aspect of GW searches are waveform models, which encapsulate our best predictions for the gravitational radiation under a certain set of parameters, and that need to be cross-correlated with data to extract GW signals. Waveforms must be very accurate to avoid missing important physics in the data, which might be the key to answer the fundamental questions of GW astrophysics. The continuous improvements of the current LIGO-Virgo detectors, the development of next-generation ground-based detectors such as the Einstein Telescope or the Cosmic Explorer, as well as the development of the Laser Interferometer Space Antenna (LISA), demand accurate waveform models. While available models are enough to capture the low spins, comparable-mass binaries routinely detected in LIGO-Virgo searches, those for sources from both current and next-generation ground-based and spaceborne detectors must be accurate enough to detect binaries with large spins and asymmetry in the masses. Moreover, the thousands of sources that we expect to detect with future detectors demand accurate waveforms to mitigate biases in the estimation of signals’ parameters due to the presence of a foreground of many sources that overlap in the frequency band. This is recognized as one of the biggest challenges for the analysis of future-detectors’ data, since biases might hinder the extraction of important astrophysical and cosmological information from future detectors’ data. In the first part of this thesis, we discuss how to improve waveform models for binaries with high spins and asymmetry in the masses. In the second, we present the first generic metrics that have been proposed to predict biases in the presence of a foreground of many overlapping signals in GW data. For the first task, we will focus on several classes of analytical techniques. Current models for LIGO and Virgo studies are based on the post-Newtonian (PN, weak-field, small velocities) approximation that is most natural for the bound orbits that are routinely detected in GW searches. However, two other approximations have risen in prominence, the post-Minkowskian (PM, weak- field only) approximation natural for unbound (scattering) orbits and the small-mass-ratio (SMR) approximation typical of binaries in which the mass of one body is much bigger than the other. These are most appropriate to binaries with high asymmetry in the masses that challenge current waveform models. Moreover, they allow one to “cover” regions of the parameter space of coalescing binaries, thereby improving the interpolation (and faithfulness) of waveform models. The analytical approximations to the relativistic two-body problem can synergically be included within the effective-one-body (EOB) formalism, in which the two-body information from each approximation can be recast into an effective problem of a mass orbiting a deformed Schwarzschild (or Kerr) black hole. The hope is that the resultant models can cover both the low-spin comparable-mass binaries that are routinely detected, and the ones that challenge current models. The first part of this thesis is dedicated to a study about how to best incorporate information from the PN, PM, SMR and EOB approaches in a synergistic way. We also discuss how accurate the resulting waveforms are, as compared against numerical-relativity (NR) simulations. We begin by comparing PM models, whether alone or recast in the EOB framework, against PN models and NR simulations. We will show that PM information has the potential to improve currently-employed models for LIGO and Virgo, especially if recast within the EOB formalism. This is very important, as the PM approximation comes with a host of new computational techniques from particle physics to exploit. Then, we show how a combination of PM and SMR approximations can be employed to access previously-unknown PN orders, deriving the third subleading PN dynamics for spin-orbit and (aligned) spin1-spin2 couplings. Such new results can then be included in the EOB models currently used in GW searches and parameter estimation studies, thereby improving them when the binaries have high spins. Finally, we build an EOB model for quasi-circular nonspinning binaries based on the SMR approximation (rather than the PN one as usually done). We show how this is done in detail without incurring in the divergences that had affected previous attempts, and compare the resultant model against NR simulations. We find that the SMR approximation is an excellent approximation for all (quasi-circular nonspinning) binaries, including both the equal-mass binaries that are routinely detected in GW searches and the ones with highly asymmetric masses. In particular, the SMR-based models compare much better than the PN models, suggesting that SMR-informed EOB models might be the key to model binaries in the future. In the second task of this thesis, we work within the linear-signal ap- proximation and describe generic metrics to predict inference biases on the parameters of a GW source of interest in the presence of confusion noise from unfitted foregrounds and from residuals of other signals that have been incorrectly fitted out. We illustrate the formalism with simple (yet realistic) LISA sources, and demonstrate its validity against Monte-Carlo simulations. The metrics we describe pave the way for more realistic studies to quantify the biases with future ground-based and spaceborne detectors. N2 - Wenn zwei kompakte Objekte wie Schwarze Löcher oder Neutronensterne kollidieren, wird der Raum und die Zeit um sie herum stark gekrümmt. Der effekt sind Störungen der Raumzeit, sogenannte Gravitationswellen, die sich im gesamten Universum ausbreiten. Mit den leistungsstarken und präzisen Netzwerken von Detektoren und der Arbeit vieler Wissenschaftler rund um den Globus kann man Gravitationswellen auf der Erde messen. Gravitationswellen tragen Informationen über das System, das sie erzeugt hat. Insbesondere kann man erfahren, wie sich die kompakten Objekte gebildet haben und woraus sie bestehen. Daraus lässt sich ableiten, wie sich das Universum ausdehnt, und man kann die Allgemeine Relativitätstheorie in Regionen mit starker Gravitation testen. Um diese Informationen zu extrahieren, werden genaue Modelle benötigt. Modelle können entweder numerisch durch Lösen der berühmten Einstein-Gleichungen oder analytisch durch Annäherung an deren Lösungen gewonnen werden. In meiner Arbeit haben wir den zweiten Ansatz verfolgt, um sehr genaue Vorhersagen für die Signale zu erhalten, die bei kommenden Beobachtungen durch Gravitationswellendetektoren verwendet werden können. KW - gravitational waves KW - Gravitationswellen KW - general relativity KW - allgemeine Relativitätstheorie KW - data analysis KW - Datenanalyse Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-576671 ER - TY - THES A1 - Giuri, Chiara T1 - VERITAS Dark Matter search in dwarf spheroidal galaxies: an extended analysis T1 - VERITAS-Suche nach dunkler Materie in sphäroidischen Zwerggalaxien: eine erweiterte Analyse” N2 - In the last century, several astronomical measurements have supported that a significant percentage (about 22%) of the total mass of the Universe, on galactic and extragalactic scales, is composed of a mysterious ”dark” matter (DM). DM does not interact with the electromagnetic force; in other words it does not reflect, absorb or emit light. It is possible that DM particles are weakly interacting massive particles (WIMPs) that can annihilate (or decay) into Standard Model (SM) particles, and modern very- high-energy (VHE; > 100 GeV) instruments such as imaging atmospheric Cherenkov telescopes (IACTs) can play an important role in constraining the main properties of such DM particles, by detecting these products. One of the most privileged targets where to look for DM signal are dwarf spheroidal galaxies (dSphs), as they are expected to be high DM-dominated objects with a clean, gas-free environment. Some dSphs could be considered as extended sources, considering the angular resolution of IACTs; their angu- lar resolution is adequate to detect extended emission from dSphs. For this reason, we performed an extended-source analysis, by taking into account in the unbinned maximum likelihood estimation both the energy and the angular extension dependency of observed events. The goal was to set more constrained upper limits on the velocity-averaged cross-section annihilation of WIMPs with VERITAS data. VERITAS is an array of four IACTs, able to detect γ-ray photons ranging between 100 GeV and 30 TeV. The results of this extended analysis were compared against the traditional spectral analysis. We found that a 2D analysis may lead to more constrained results, depending on the DM mass, channel, and source. Moreover, in this thesis, the results of a multi-instrument project are presented too. Its goal was to combine already published 20 dSphs data from five different experiments, such as Fermi-LAT, MAGIC, H.E.S.S., VERITAS and HAWC, in order to set upper limits on the WIMP annihilation cross-section in the widest mass range ever reported. N2 - Im letzten Jahrhundert haben verschiedene mehrere astronomische Messungen gezeigt, dass ein erheblicher Prozentsatz (etwa 22 %) der Gesamtmasse des Universums auf galaktischer und extragalaktischer Ebene aus einer geheimnisvollen ”dunklen” Materie (DM) besteht. DM interagiert nicht mit der elektromagnetischen Kraft und reflektiert, absorbiert oder emittiert daher kein Licht. Es ist möglich, dass es sich bei DM-Teilchen um schwach wechselwirkende massive Teilchen (engl. weakly interacting massive particles, WIMPs) handelt, die in Teilchen des Standardmodells (SM) annihilieren (oder zerfallen) können. Indem sie diese Produkte nachweisen, können moderne Detektoren für sehr hoch energetische (engl. very-high-energy, VHE; 100 GeV) Gammastrahlung, wie zum Beispiel bildgebende atmosphärische Cherenkov-Teleskope (engl. imaging atmospheric Cherenkov telescopes, IACTs), eine wichtige Rolle bei der Bestimmung der Haupteigenschaften solcher DM-Teilchen spielen. Eines der am besten geeignetsten Ziele für die Suche nach DM-Signalen sind sphäroidische Zwerggalaxien (engl. dwarf spheroidal galaxies, dSphs), da diese stark DM-dominierte Objekte mit einer gasfreien Umgebung sind. Die Winkelauflösung von IACTs ist ausreichend, um ausgedehnte Emission von dSphs zu entdecken. Aus diesem Grund haben wir eine Analyse dieser Quellen durchgeführt, indem wir in der unbinned Maximum-Likelihood-Schätzung sowohl die Energie als auch die Abhängigkeit der Winkelausdehnung der beobachteten Gammastrahlung berücksichtigt haben. Das Ziel war es, mit Hilfe der VERITAS-Daten genauere Obergrenzen für den geschwindigkeitsgemittelten Annihilationsquerschnitt von WIMPs zu bestimmen. VERITAS ist eine Anordnung von vier IACTs, die Gammastrahlen im Bereich von 100 GeV bis 30 TeV detektieren können. Die Ergebnisse dieser erweiterten Analyse wurden mit der traditionellen Spektralanalyse verglichen. Es zeigte sich, dass je nach DM-Masse, Kanal und Quelle eine 2D-Analyse zu aussagekräftigeren Ergebnissen führen kann. Darüber hinaus werden in dieser Arbeit auch die Ergebnisse eines Multi-Instrumenten-Projekts vorgestellt. Das Ziel war es, die bereits veröffentlichte 20 dSphs-Datensätze von Fermi-LAT, MAGIC, H.E.S.S., VERITAS und HAWC zu kombinieren, um obere Grenzwerte für den WIMP-Annihilationsquerschnitt im breitesten jemals veröffentlichten Massenbereich zu bestimmen. KW - Dark Matter KW - data analysis KW - Cherenkov telescopes KW - dwarf spheroidal galaxies KW - Dunkle Materie KW - Datenanalyse KW - Cherenkov-Teleskope KW - sphäroidische Zwerggalaxien Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-575869 ER - TY - JOUR A1 - Topçu, Çağdaş A1 - Frühwirth, Matthias A1 - Moser, Maximilian A1 - Rosenblum, Michael A1 - Pikovskij, Arkadij T1 - Disentangling respiratory sinus arrhythmia in heart rate variability records JF - Physiological Measurement N2 - Objective: Several different measures of heart rate variability, and particularly of respiratory sinus arrhythmia, are widely used in research and clinical applications. For many purposes it is important to know which features of heart rate variability are directly related to respiration and which are caused by other aspects of cardiac dynamics. Approach: Inspired by ideas from the theory of coupled oscillators, we use simultaneous measurements of respiratory and cardiac activity to perform a nonlinear disentanglement of the heart rate variability into the respiratory-related component and the rest. Main results: The theoretical consideration is illustrated by the analysis of 25 data sets from healthy subjects. In all cases we show how the disentanglement is manifested in the different measures of heart rate variability. Significance: The suggested technique can be exploited as a universal preprocessing tool, both for the analysis of respiratory influence on the heart rate and in cases when effects of other factors on the heart rate variability are in focus. KW - respiratory sinus arrhythmia KW - heart rate variability KW - coupled oscillators model KW - phase dynamics KW - data analysis Y1 - 2018 U6 - https://doi.org/10.1088/1361-6579/aabea4 SN - 0967-3334 SN - 1361-6579 VL - 39 IS - 5 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Verma, Meetu A1 - Kummerow, P. A1 - Denker, Carsten T1 - On the extent of the moat flow in axisymmetric sunspots JF - Astronomische Nachrichten = Astronomical notes N2 - Unipolar, axisymmetric sunspots are figuratively called “theoretician's sunspots” because their simplicity supposedly makes them more suitable for theoretical descriptions or numerical models. On November 18, 2013, a very large specimen (active region NOAA 11899) crossed the central meridian of the sun. The moat flow associated with this very large spot is quantitatively compared to that of a medium and a small sunspot to determine the extent of the moat flow in different environments. We employ continuum images and magnetograms of the Helioseismic and Magnetic Imager (HMI) as well as extreme ultraviolet (EUV) images at λ160 nm of the Atmospheric Imaging Assembly (AIA), both on board the Solar Dynamics Observatory (SDO), to measure horizontal proper motions with Local Correlation Tracking (LCT) and flux transport velocities with the Differential Affine Velocity Estimator (DAVE). We compute time-averaged flow maps (±6 hr around meridian passage) and radial averages of photometric, magnetic, and flow properties. Flow fields of a small- and a medium-sized axisymmetric sunspot provide the context for interpreting the results. All sunspots show outward moat flow and the advection of moving magnetic features (MMFs). However, the extent of the moat flow varies from spot to spot, and a correlation of flow properties with size is tenuous, if at all present. The moat flow is asymmetric and predominantly in the east–west direction, whereby deviations are related to the tilt angle of the sunspot group as well as to the topology and activity level of the trailing plage. KW - activity KW - data analysis KW - image processing KW - photosphere KW - sunspots Y1 - 2018 U6 - https://doi.org/10.1002/asna.201813482 SN - 0004-6337 SN - 1521-3994 VL - 339 IS - 4 SP - 268 EP - 276 PB - Wiley-VCH CY - Weinheim ER - TY - GEN A1 - Topçu, Çağdaş A1 - Frühwirth, Matthias A1 - Moser, Maximilian A1 - Rosenblum, Michael A1 - Pikovskij, Arkadij T1 - Disentangling respiratory sinus arrhythmia in heart rate variability records T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Objective: Several different measures of heart rate variability, and particularly of respiratory sinus arrhythmia, are widely used in research and clinical applications. For many purposes it is important to know which features of heart rate variability are directly related to respiration and which are caused by other aspects of cardiac dynamics. Approach: Inspired by ideas from the theory of coupled oscillators, we use simultaneous measurements of respiratory and cardiac activity to perform a nonlinear disentanglement of the heart rate variability into the respiratory-related component and the rest. Main results: The theoretical consideration is illustrated by the analysis of 25 data sets from healthy subjects. In all cases we show how the disentanglement is manifested in the different measures of heart rate variability. Significance: The suggested technique can be exploited as a universal preprocessing tool, both for the analysis of respiratory influence on the heart rate and in cases when effects of other factors on the heart rate variability are in focus. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 913 KW - respiratory sinus arrhythmia KW - heart rate variability KW - coupled oscillators model KW - phase dynamics KW - data analysis Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436315 SN - 1866-8372 IS - 913 ER - TY - GEN A1 - Driel-Gesztelyi, L. van A1 - Baker, Daniel N. A1 - Török, Tibor A1 - Pariat, Etienne A1 - Green, L. M. A1 - Williams, D. R. A1 - Carlyle, J. A1 - Valori, G. A1 - Démoulin, Pascal A1 - Matthews, S. A. A1 - Kliem, Bernhard A1 - Malherbe, J.-M. T1 - Magnetic reconnection driven by filament eruption in the 7 June 2011 event T2 - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe N2 - During an unusually massive filament eruption on 7 June 2011, SDO/AIA imaged for the first time significant EUV emission around a magnetic reconnection region in the solar corona. The reconnection occurred between magnetic fields of the laterally expanding CME and a neighbouring active region. A pre-existing quasi-separatrix layer was activated in the process. This scenario is supported by data-constrained numerical simulations of the eruption. Observations show that dense cool filament plasma was re-directed and heated in situ, producing coronal-temperature emission around the reconnection region. These results provide the first direct observational evidence, supported by MHD simulations and magnetic modelling, that a large-scale re-configuration of the coronal magnetic field takes place during solar eruptions via the process of magnetic reconnection. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 608 KW - MHD KW - instabilities KW - Sun: activity KW - magnetic fields KW - coronal mass ejections (CMEs) KW - filaments KW - methods: numerical KW - data analysis Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-415671 IS - 608 SP - 502 EP - 503 ER - TY - JOUR A1 - Kralemann, Bjoern A1 - Pikovskij, Arkadij A1 - Rosenblum, Michael T1 - Reconstructing effective phase connectivity of oscillator networks from observations JF - New journal of physics : the open-access journal for physics N2 - We present a novel approach for recovery of the directional connectivity of a small oscillator network by means of the phase dynamics reconstruction from multivariate time series data. The main idea is to use a triplet analysis instead of the traditional pairwise one. Our technique reveals an effective phase connectivity which is generally not equivalent to a structural one. We demonstrate that by comparing the coupling functions from all possible triplets of oscillators, we are able to achieve in the reconstruction a good separation between existing and non-existing connections, and thus reliably reproduce the network structure. KW - network reconstruction KW - coupled oscillators KW - connectivity KW - data analysis Y1 - 2014 U6 - https://doi.org/10.1088/1367-2630/16/8/085013 SN - 1367-2630 VL - 16 PB - IOP Publ. Ltd. CY - Bristol ER -