This thesis gives an overview over mathematical modeling of complex fluids with the discussion of underlying mechanical principles, the introduction of the energetic variational framework, and examples and applications. The purpose is to present a formal energetic variational treatment of energies corresponding to the models of physical phenomena and to derive PDEs for the complex fluid systems. The advantages of this approach over force-based modeling are, e.g., that for complex systems energy terms can be established in a relatively easy way, that force components within a system are not counted twice, and that this approach can naturally combine effects on different scales. We follow a lecture of Professor Dr. Chun Liu from Penn State University, USA, on complex fluids which he gave at the University of Wuerzburg during his Giovanni Prodi professorship in summer 2012. We elaborate on this lecture and consider also parts of his work and publications, and substantially extend the lecture by own calculations and arguments (for papers including an overview over the energetic variational treatment see [HKL10], [Liu11] and references therein).
Baumgraphen
(2013)
Die meisten Ansätze zur Analyse von Sätzen eröffnen die Möglichkeit einer graphischen Darstellung. Eine solche graphische Darstellung wird oft als „Baumgraph“ oder „Baumdiagramm“ bezeichnet. Um solche Baumgraphen verschiedener Analysemodelle geht es in der vorliegenden Arbeit. Einleitend wird kurz ihre Geschichte behandelt. Im ersten Teil der Arbeit wird dann auf eine Variante des Konstituentenmodells des französischen Linguisten Monneret eingegangen, im zweiten Teil wird das Dependenzmodell nach Tesnière betrachtet und im dritten Teil wird schließlich das Analysemodell der Germanistik Würzburg, welches Elemente der beiden zuvor gesehenen Ansätze vereint, vorgestellt und der französischen Sprache angepasst. Zuerst wird jeweils ein Blick auf die Modelle selbst geworfen, dann jedoch steht vor allem die Anwendung – und somit die graphische Darstellung von Satzanalysen in Baumgraphen – im Vordergrund: Es werden nach den drei vorgestellten Modellen stets sowohl die Fabel „La Cigale et la Fourmi“ von Jean de La Fontaine als auch ein Satz aus Bossuets „Panégyrique de saint Paul“ analysiert und abgebildet. Über die wiederholte Analyse derselben Sätze soll ein besserer Vergleich der Baumgraphen ermöglicht werden. Im letzten Teil werden die Baumgraphen der drei Modelle kritisch betrachtet. Es versteht sich von selbst, dass eine solche kritische Betrachtung nicht allumfassend sein kann. Die Aufmerksamkeit soll darum gezielt auf einige bedeutende Vor- und Nachteile der Baumgraphen gerichtet werden.
In this thesis it is shown how the spread of infectious diseases can be described via mathematical models that show the dynamic behavior of epidemics. Ordinary differential equations are used for the modeling process. SIR and SIRS models are distinguished, depending on whether a disease confers immunity to individuals after recovery or not. There are characteristic parameters for each disease like the infection rate or the recovery rate. These parameters indicate how aggressive a disease acts and how long it takes for an individual to recover, respectively. In general the parameters are time-varying and depend on population groups. For this reason, models with multiple subgroups are introduced, and switched systems are used to carry out time-variant parameters.
When investigating such models, the so called disease-free equilibrium is of interest, where no infectives appear within the population. The question is whether there are conditions, under which this equilibrium is stable. Necessary mathematical tools for the stability analysis are presented. The theory of ordinary differential equations, including Lyapunov stability theory, is fundamental. Moreover, convex and nonsmooth analysis, positive systems and differential inclusions are introduced. With these tools, sufficient conditions are given for the disease-free equilibrium of SIS, SIR and SIRS systems to be asymptotically stable.
Interkomprehension im gegenwärtigen Westeuropa : Internationalismen im romanischen Grundwortschatz
(2013)
Die Arbeit untersucht 2500 Wörter des italienischen Grundwortschatzes in einem fünfsprachigen Vergleich. Sie ergänzt damit die an gleicher Stelle erschienene Magisterarbeit „Internationalismen im Grundwortschatz: Untersuchungen zur romanistischen Mehrsprachigkeitsdidaktik” von Anja Büttner (2012). Hier werden nun die Ergebnisse beider Untersuchungen zusammengefasst. Dabei werden erstmalig konkrete Zahlen zur Beantwortung der Frage vorgestellt, wie viele Wörter z.B. ein deutscher Muttersprachler, der Französisch gelernt hat und nun italienische Texte lesen will, tatsächlich lernen muss, um die 5000 häufigsten Wörter erkennen und damit durchschnittliche Texte nahezu vollständig verstehen zu können.
Streaming of videos has become the major traffic generator in today's Internet and the video traffic share is still increasing. According to Cisco's annual Visual Networking Index report, in 2012, 60% of the global Internet IP traffic was generated by video streaming services. Furthermore, the study predicts further increase to 73% by 2017. At the same time, advances in the fields of mobile communications and embedded devices lead to a widespread adoption of Internet video enabled mobile and wireless devices (e.g. Smartphones). The report predicts that by 2017, the traffic originating from mobile and wireless devices will exceed the traffic from wired devices and states that mobile video traffic was the source of roughly half of the mobile IP traffic at the end of 2012.
With the increasing importance of Internet video streaming in today's world, video content provider find themselves in a highly competitive market where user expectations are high and customer loyalty depends strongly on the user's satisfaction with the provided service. In particular paying customers expect their viewing experience to be the same across all their viewing devices and independently of their currently utilized Internet access technology. However, providing video streaming services is costly in terms of storage space, required bandwidth and generated traffic. Therefore, content providers face a trade-off between the user perceived Quality of Experience (QoE) and the costs for providing the service.
Today, a variety of transport and application protocols exist for providing video streaming services, but the one utilized depends on the scenario in mind. Video streaming services can be divided up in three categories: Video conferencing, IPTV and Video-on-Demand services. IPTV and video-conferencing have severe real-time constraints and thus utilize mostly datagram-based protocols like the RTP/UDP protocol for the video transmission. Video-on-Demand services in contrast can profit from pre-encoded content, buffers at the end user's device, and mostly utilize TCP-based protocols in combination with progressive streaming for the media delivery.
In recent years, the HTTP protocol on top of the TCP protocol gained widespread popularity as a cost-efficient way to distribute pre-encoded video content to customers via progressive streaming. This is due to the fact that HTTP-based video streaming profits from a well-established infrastructure which was originally implemented to efficiently satisfy the increasing demand for web browsing and file downloads. Large Content Delivery Networks (CDN) are the key components of that distribution infrastructure. CDNs prevent expensive long-haul data traffic and delays by distributing HTTP content to world-wide locations close to the customers. As of 2012, already 53% of the global video traffic in the Internet originates from Content Delivery Networks and that percentage is expected to increase to 65% by the year 2017. Furthermore, HTTP media streaming profits from existing HTTP caching infrastructure, ease of NAT and proxy traversal and firewall friendliness.
Video delivery through heterogeneous wired and wireless communications networks is prone to distortions due to insufficient network resources. This is especially true in wireless scenarios, where user mobility and insufficient signal strength can result in a very poor transport service performance (e.g. high packet loss, delays and low and varying bandwidth). A poor performance of the transport in turn may degrade the Quality of Experience as perceived by the user, either due to buffer underruns (i.e. playback interruptions) for TCP-based delivery or image distortions for datagram-based real-time video delivery.
In order to overcome QoE degradations due to insufficient network resources, content provider have to consider adaptive video streaming. One possibility to implement this for HTTP/TCP streaming is by partitioning the content into small segments, encode the segments into different quality levels and provide access to the segments and the quality level details (e.g. resolution, average bitrate). During the streaming session, a client-centric adaptation algorithm can use the supplied details to adapt the playback to the current environment. However, a lack of a common HTTP adaptive streaming standard led to multiple proprietary solutions developed by major Internet companies like Microsoft (Smooth Streaming), Apple (HTTP Live Streaming) and Adobe (HTTP Dynamic Streaming) loosely based on the aforementioned principle. In 2012, the ISO/IEC published the Dynamic Adaptive Streaming over HTTP (MPEG-DASH) standard. As of today, DASH is becoming widely accepted with major companies announcing their support or having already implemented the standard into their products. MPEG-DASH is typically used with single layer codecs like H.264/AVC, but recent publications show that scalable video coding can use the existing HTTP infrastructure more efficiently. Furthermore, the layered approach of scalable video coding extends the adaptation options for the client, since already downloaded segments can be enhanced at a later time.
The influence of distortions on the perceived QoE for non-adaptive video streaming are well reviewed and published. For HTTP streaming, the QoE of the user is influenced by the initial delay (i.e. the time the client pre-buffers video data) and the length and frequency of playback interruptions due to a depleted video playback buffer. Studies highlight that even low stalling times and frequencies have a negative impact on the QoE of the user and should therefore be avoided. The first contribution of this thesis is the identification of QoE influence factors of adaptive video streaming by the means of crowd-sourcing and a laboratory study.
MPEG-DASH does not specify how to adapt the playback to the available bandwidth and therefore the design of a download/adaptation algorithm is left to the developer of the client logic. The second contribution of this thesis is the design of a novel user-centric adaption logic for DASH with SVC. Other download algorithms for segmented HTTP streaming with single layer and scalable video coding have been published lately. However, there is little information about the behavior of these algorithms regarding the identified QoE-influence factors. The third contribution is a user-centric performance evaluation of three existing adaptation algorithms and a comparison to the proposed algorithm. In the performance evaluation we also evaluate the fairness of the algorithms. In one fairness scenario, two clients deploy the same adaptation algorithm and share one Internet connection. For a fair adaptation algorithm, we expect the behavior of the two clients to be identical. In a second fairness scenario, one client shares the Internet connection with a large HTTP file download and we expect an even bandwidth distribution between the video streaming and the file download. The forth contribution of this thesis is an evaluation of the behavior of the algorithms in a two-client and HTTP cross traffic scenario.
The remainder of this thesis is structured as follows. Chapter II gives a brief introduction to video coding with H.264, the HTTP adaptive streaming standard MPEG-DASH, the investigated adaptation algorithms and metrics of Quality of Experience (QoE) for video streaming. Chapter III presents the methodology and results of the subjective studies conducted in the course of this thesis to identify the QoE influence factors of adaptive video streaming. In Chapter IV, we introduce the proposed adaptation algorithm and the methodology of the performance evaluation. Chapter V highlights the results of the performance evaluation and compares the investigated adaptation algorithms. Section VI summarizes the main findings and gives an outlook towards QoE-centric management of DASH with SVC.
Klimawandelbedingte bzw. potenziell klimawandelbedingte Umweltmigration ist ein sehr komplexes und breites Feld. Es existiert eine Fülle von Studien, die sich in ihrer Herangehensweise unterscheiden, weshalb hier ein Systematisierungsvorschlag aufgezeigt wird. Mittels einer an den Richtlinien der Grounded Theory orientierten Analyse wurden Studien auf zentrale gemeinsame Kategorien hin untersucht und als Modell präsentiert. Dieses stellt jedoch kein abgeschlossenes System dar, sondern dient durch seine Offenheit als Gerüst, das mit Ergebnissen aus weiteren Fallstudien gefestigt werden kann.
Die Untersuchung beschäftigt sich mit der Entwicklung der Berichterstattung über das Judentum in Seesen. Das Hauptaugenmerk liegt auf auf Israel Jacobson, der einst Begründer des Reformjudentums in Seesen war, in Vergessenheit geriet und seit einigen Jahren wieder von einigen engagierten Seesenern mit Ausstellungen, Büchern und Vorträgen geehrt wird. Zudem stellt sich der Arbeit die Frage, wie es zu dem "Vergessen" dieser berühmten Seesener Persönlichkeit kam und was zu einem Umdenken geführt haben könnte.