Modelling users in networks with path choice: four studies in telecommunications and transit

Networks of interacting users arise in many important modelling applications. Commuters interact with each other and form traffic jams during peak-time. Network protocols are users in a communication network that control sending rate and server choice. When protocols send with too high rates, network links get overloaded resulting in lost data and high delays. Although these two example users seem very different, they are similar on a conceptual modelling level. Accurate user models are essential to study complex interactions in networks. The behaviour of a user with access to different paths in a network can be modelled as an optimisation problem. Users who choose paths with the highest utility are common in many different application areas, for example road traffic, Internet protocol modelling, and general societal networks, i.e. networks of humans in everyday life. Optimisation-based user models are also attractive from the perspective of a modeller since they often allow the derivation of insights about the behaviour of the entire system by only describing a user model. The aim of this thesis is to show, in four practical studies from telecommunications and transit networks, where optimisation-based models have limitations when modelling users with path choice. We study users who have access to a limited number of paths in large scale data centers and investigate how many paths per user are realistically needed in order to get high throughput in the network. In multimedia streaming, we study a protocol that streams data on multiple paths and path properties matter. We also investigate complex energy models for data interfaces on mobile phones and evaluate how to switch interfaces to save energy. Finally, we analyse a long-term data set from 20,000 transit commuters and give insights on how they change their travel behaviour in response to incentives and targeted offers. We use tools from optimisation, simulation, and statistics to evaluate the four studies and point out problems we faced when modelling and implementing the system. The findings of this thesis indicate where user models need to be extended in order to be of practical use. The results can serve as a guide towards better user models for future modelling applications

Niederschlags- und Temperaturextreme: Wie gut werden sie vom statistischen Klimamodell WEREX V wiedergegeben?

KlimawandelKlimatische Extreme sind meist von besonderem Interesse, wenn mögliche Folgen eines sich ändernden Klimas auf verschiedene sozio-ökonomische Bereiche der Gesellschaft betrachtet werden. Derzeit weisen Globale und Regionale Klimamodelle (GCM/ RCM) jedoch meist noch große Unzulänglichkeiten bei der Abbildung von Extremen auf. Statistische Regionalisierungsmethoden stimmen methodenbedingt meist besser mit klimatischen Beobachtungen überein als RCMs, zumindest bei klimatischen Mittelwerten. Die Güte der Abbildung von Klimaextremen des Modells WERX V soll Inhalt dieses Beitrages sein. WEREX V ist der aktuellste regionale Klimaprojektionsdatensatz für den Freistaat Sachsen. Ein Ensemble (12 Mitglieder) aus drei GCM (ECHAM 5/MPI-OM, HadCM3C, HadGEM2), genesteten RCM (CLM, REMO, RACMO) und Szenarien (A1B, E1) wurden als Antrieb für die statistische Regionalisierungsmethode WEREX V verwendet, die eine auf Sachsen fokussierte Instanz der WETTREG-Methode darstellt. Die insgesamt 120 Klimaprojektionen werden hauptsächlich mittels ihrer Perzentile für die Periode 1961-2000 analysiert. Für die Temperatur sind dies das 10. und 90. und für den Niederschlag das 80., 90., 95. und 99. Perzentil. Mit Beobachtungsdaten verglichen wird zum einen die Höhe der Perzentile. Für Sachsen wurde eine zeitlich variable Auftretenshäufigkeit von Extremniederschlägen in den letzten 40 Jahren festgestellt. Deshalb wird zum anderen überprüft, ob WEREX V diese Variabilität abbildet. Des Weiteren werden Extremperioden wie Hitzewellen und Dürreperioden untersucht. Für letztere wird der Standardisierte Niederschlags-Evaporations-Index SPEI verwendet, der somit auch Aussagen zur elementübergreifenden Konsistenz der simulierten Datensätze ermöglicht. Ziel ist es, Stärken und Schwächen der Projektionsdatensätze zu identifizieren, um gezielte Anwendungen für die Impaktmodellierung zu ermöglichen. Perspektivisch sollen Lösungsmöglichkeiten aufgezeigt werden, die Güte der Modelle für die Abbildung von Klimaextremen zu verbessern

Use of past precipitation data for regionalisation of hourly rainfall in the low mountain ranges of saxony, germany

Within the context of flood forecasting we deal with the improvement of regionalisation methods for the generation of highly resolved (1 h, 1x1km(2)) precipitation fields, which can be used as input for rainfall-runoff models or for verification of weather forecasts. Although radar observations of precipitation are available in many regions, it might be necessary to apply regionalisation methods near real-time for the cases that radar is not available or observations are of low quality. The aim of this paper is to investigate whether past precipitation information can be used to improve regionalisation of rainfall. Within a case study we determined typical precipitation Background-Fields (BGF) for the mountainous and hilly regions of Saxony using hourly and daily rain gauge data. Additionally, calibrated radar data served as past information for the BGF generation. For regionalisation of precipitation we used de-trended kriging and compared the results with another kriging based regionalisation method and with Inverse Distance Weighting (IDW). The performance of the methods was assessed by applying cross-validation, by inspection and by evaluation with rainfall-runoff simulations. The regionalisation of rainfall yielded better results in case of advective events than in case of convective events. The performance of the applied regionalisation methods showed no significant disagreement for different precipitation types. Cross-validation results were rather similar in most cases. Subjectively judged, the BGF-method reproduced best the structures of rain cells. Precipitation input derived from radar or kriging resulted in a better matching between observed and simulated flood hydrographs. Simple techniques like IDW also deliver satisfying results in some occasions. Implementation of past radar data into the BGF-method rendered no improvement, because of data shortages. Thus, no method proved to outperform the others generally. The decision, which method is appropriate for an event, should be made objectively using cross-validation, but also subjectively, using the expert knowledge of the forecaster.BMBF/0330700

A modeling framework to assess water and nitrate balances in the Western Bug river basin, Ukraine

The objective of this study was to assess the utility of the eco-hydrological SWAT model (Soil and Water Assessment Tool, Arnold et al., 1998) for representing water balance and nitrate fluxes given limited input and calibration data. The investigated catchment is located in Western Ukraine with an area of approximately 2616 km². Land use is currently dominated by agriculture with significant areas of pasture, and has undergone a high degree of changes in land-use and agricultural practice since the end of the Soviet Union. Model application produced a fitted water balance (calibration: <i>R</i>² = 0.52, NS = 0.46; validation: <i>R</i>² = 0.47, NS = 0.51) and plausible ranges and dynamics of nitrate in stream loadings. Groundwater parameters were found to be highly sensitive. The results indicate that SWAT is an appropriate tool for water resource investigations in the Western Bug catchment, and can provide a useful tool for further eco-hydrologic research in the region (i.e. diffuse pollution impacts)

Starkregenereignisse von 1961 bis 2015: Analyse von Starkregenereignissen von 1961 bis 2015 für den Freistaat Sachsen

Die Starkregenanalyse Sachsen 1961-2015 wurde auf der Grundlage von 1-km-Rasterdaten für tägliche Niederschlagssummen durchgeführt. Die Definition für Starkregenereignisse erfolgte hier mittels der lokalen 90- und 95-Perzentile im Referenzzeitraum. Demnach wurden Ereignisse einbezogen, deren Regenmenge im Zeitraum 1961-1990 zu den größten 10 bzw. 5 % der lokal aufgetretenen Regenmengen gehörte. Mit Bezug zum Jahr haben Auftretenshäufigkeit und mittlere Intensität von Starkregenereignissen im Zeitraum 1991-2015 gegenüber 1961-1990 zugenommen. Dabei besitzt die Auftretenshäufigkeit gegenüber der Intensität das stärkere Signal. Diese Zunahmen sind entscheidend durch die starken Zunahmen in den Sommermonaten begründet. Die Analyse lieferte deutliche Hinweise auf eine Intensivierung des konvektiven Starkregengeschehens. Die Veröffentlichung richtet sich an regionale Akteure sowie Planungsbüros, Bildungseinrichtungen und Unternehmen

Witterungsextreme im WEREX-V-Ensemble: Analyse und Bewertung des WEREX-V-Ensembles hinsichtlich der Abbildung von Extremen in Sachsen

Die aktuelle Klimaprojektion für den Freistaat Sachsen, das »WEREX-V-Ensemble« (2011), wurde hinsichtlich einer plausiblen Abbildung witterungsbedingter Extreme bewertet. Die Bewertung in den Kategorien Starkniederschlag, Temperaturextreme und Trockenheit erfolgte anhand von Kernaussagen aus der aktuellen Klimadiagnose »Analyse der Klimaentwicklung in Sachsen« (Schriftenreihe, Heft 3/2015) und der »Charakterisierung von meteorologischer Trockenheit« (Schriftenreihe, Heft 7/2015). Hierbei stand auch die Nutzung des Projektionsdatensatzes als Input in der Klimafolgenforschung im Fokus. Neben der Bewertung erfolgte auch die selektive Abschätzung einer Entwicklung bis zum Ende des 21. Jahrhunderts. Die Veröffentlichung richtet sich an regionale Akteure, Planungsbüros, Bildungseinrichtungen und Unternehmen

Saving mobile device energy with multipath TCP

Multipath TCP is a backwards-compatible TCP extension that en-ables using multiple network paths between two end systems for a single TCP connection, increasing performance and reliability. It can also be used to “shift ” active connections from one network path to another without breakage. This feature is especially attrac-tive on mobile devices with multiple radio interfaces, because it can be used to continuously shift active connections to the most energy-efficient network path. This paper describes a novel method for deriving such a multipath scheduler using MPTCP that maximises energy savings. Based on energy models for the different radio in-terfaces as well as a continuously accumulated communication his-tory of the device user, we compute schedulers for different appli-cations by solving a Markov decision process offline. We evaluate these schedulers for a large number of random application mod-els and selected realistic applications derived from measurements. Evaluations based on energy models for a mobile device with Wifi and 3G radio interfaces show that it performs comparably in terms of energy efficiency to a theoretically optimal omniscient oracle scheduler

Calcium carbonate crystal growth beneath Langmuir monolayers of acidic beta-hairpin peptides

Gong H, Yang Y, Pluntke M, et al. Calcium carbonate crystal growth beneath Langmuir monolayers of acidic beta-hairpin peptides. Dalton Transactions. 2014;43(44):16857-16871.Four amphiphilic peptides with designed hairpin structure were synthesized and their monolayers were employed as model systems to study biologically inspired calcium carbonate crystallization. Langmuir monolayers of hairpin peptides were investigated by surface pressure area isotherms, surface potential isotherms, Brewster angle microscopy (BAM), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy. A beta-hairpin conformation was found for all peptides at the air-water interface although their packing arrangements seem to be different. Crystallization of calcium carbonate under these peptide monolayers was investigated at different surface pressures and growth times both by in situ optical microscopy, BAM and ex situ investigations such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An amorphous calcium carbonate precursor was found at the initial crystallization stage. The crystallization process occurred in three stages. It starts from the nucleation of amorphous particles being a kinetically controlled process. Crystal nuclei subsequently aggregate to large particles and vaterite crystals start to form inside the amorphous layer, with the monolayer fluidity exerting an important role. The third process includes the re-crystallization of vaterite to calcite, which is thermodynamically controlled by monolayer structural factors including the monolayer flexibility and packing arrangement of the polar headgroups. Thus, the kinetic factors, monolayer fluidity and flexibility as well as structure factors govern the crystal morphology and polymorph distribution simultaneously and synergistically