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Nach wie vor ist es der internationalen Gemeinschaft nicht gelungen, eine Lösung für die afghanische Krise zu präsentieren. Dabei macht die gegenwärtige Situation eine Beendigung des Kriegszustands sowie die Aufnahme von konstruktiven Verhandlungen unerlässlich. Die Genfer Verhandlungen der 1980er Jahre über den Abzug der Sowjetarmee aus Afghanistan könnten hierbei als Vorbild dienen.
In dieser Arbeit werden nichtlineare Kopplungsmechanismen von akustischen Oszillatoren untersucht, die zu Synchronisation führen können. Aufbauend auf die Fragestellungen vorangegangener Arbeiten werden mit Hilfe theoretischer und experimenteller Studien sowie mit Hilfe numerischer Simulationen die Elemente der Tonentstehung in der Orgelpfeife und die Mechanismen der gegenseitigen Wechselwirkung von Orgelpfeifen identifiziert. Daraus wird erstmalig ein vollständig auf den aeroakustischen und fluiddynamischen Grundprinzipien basierendes nichtlinear gekoppeltes Modell selbst-erregter Oszillatoren für die Beschreibung des Verhaltens zweier wechselwirkender Orgelpfeifen entwickelt. Die durchgeführten Modellrechnungen werden mit den experimentellen Befunden verglichen. Es zeigt sich, dass die Tonentstehung und die Kopplungsmechanismen von Orgelpfeifen durch das entwickelte Oszillatormodell in weiten Teilen richtig beschrieben werden. Insbesondere kann damit die Ursache für den nichtlinearen Zusammenhang von Kopplungsstärke und Synchronisation des gekoppelten Zwei-Pfeifen Systems, welcher sich in einem nichtlinearen Verlauf der Arnoldzunge darstellt, geklärt werden. Mit den gewonnenen Erkenntnissen wird der Einfluss des Raumes auf die Tonentstehung bei Orgelpfeifen betrachtet. Dafür werden numerische Simulationen der Wechselwirkung einer Orgelpfeife mit verschiedenen Raumgeometrien, wie z. B. ebene, konvexe, konkave, und gezahnte Geometrien, exemplarisch untersucht. Auch der Einfluss von Schwellkästen auf die Tonentstehung und die Klangbildung der Orgelpfeife wird studiert. In weiteren, neuartigen Synchronisationsexperimenten mit identisch gestimmten Orgelpfeifen, sowie mit Mixturen wird die Synchronisation für verschiedene, horizontale und vertikale Pfeifenabstände in der Ebene der Schallabstrahlung, untersucht. Die dabei erstmalig beobachteten räumlich isotropen Unstetigkeiten im Schwingungsverhalten der gekoppelten Pfeifensysteme, deuten auf abstandsabhängige Wechsel zwischen gegen- und gleichphasigen Sychronisationsregimen hin. Abschließend wird die Möglichkeit dokumentiert, das Phänomen der Synchronisation zweier Orgelpfeifen durch numerische Simulationen, also der Behandlung der kompressiblen Navier-Stokes Gleichungen mit entsprechenden Rand- und Anfangsbedingungen, realitätsnah abzubilden. Auch dies stellt ein Novum dar.
In dieser Arbeit werden die Effekte der Synchronisation nichtlinearer, akustischer Oszillatoren am Beispiel zweier Orgelpfeifen untersucht. Aus vorhandenen, experimentellen Messdaten werden die typischen Merkmale der Synchronisation extrahiert und dargestellt. Es folgt eine detaillierte Analyse der Übergangsbereiche in das Synchronisationsplateau, der Phänomene während der Synchronisation, als auch das Austreten aus der Synchronisationsregion beider Orgelpfeifen, bei verschiedenen Kopplungsstärken. Die experimentellen Befunde werfen Fragestellungen nach der Kopplungsfunktion auf. Dazu wird die Tonentstehung in einer Orgelpfeife untersucht. Mit Hilfe von numerischen Simulationen der Tonentstehung wird der Frage nachgegangen, welche fluiddynamischen und aero-akustischen Ursachen die Tonentstehung in der Orgelpfeife hat und inwiefern sich die Mechanismen auf das Modell eines selbsterregten akustischen Oszillators abbilden lässt. Mit der Methode des Coarse Graining wird ein Modellansatz formuliert.
The echo chamber model describes the development of groups in heterogeneous social networks. By heterogeneous social network we mean a set of individuals, each of whom represents exactly one opinion. The existing relationships between individuals can then be represented by a graph. The echo chamber model is a time-discrete model which, like a board game, is played in rounds. In each round, an existing relationship is randomly and uniformly selected from the network and the two connected individuals interact. If the opinions of the individuals involved are sufficiently similar, they continue to move closer together in their opinions, whereas in the case of opinions that are too far apart, they break off their relationship and one of the individuals seeks a new relationship. In this paper we examine the building blocks of this model. We start from the observation that changes in the structure of relationships in the network can be described by a system of interacting particles in a more abstract space.
These reflections lead to the definition of a new abstract graph that encompasses all possible relational configurations of the social network. This provides us with the geometric understanding necessary to analyse the dynamic components of the echo chamber model in Part III. As a first step, in Part 7, we leave aside the opinions of the inidividuals and assume that the position of the edges changes with each move as described above, in order to obtain a basic understanding of the underlying dynamics. Using Markov chain theory, we find upper bounds on the speed of convergence of an associated Markov chain to its unique stationary distribution and show that there are mutually identifiable networks that are not apparent in the dynamics under analysis, in the sense that the stationary distribution of the associated Markov chain gives equal weight to these networks.
In the reversible cases, we focus in particular on the explicit form of the stationary distribution as well as on the lower bounds of the Cheeger constant to describe the convergence speed.
The final result of Section 8, based on absorbing Markov chains, shows that in a reduced version of the echo chamber model, a hierarchical structure of the number of conflicting relations can be identified.
We can use this structure to determine an upper bound on the expected absorption time, using a quasi-stationary distribution. This hierarchy of structure also provides a bridge to classical theories of pure death processes. We conclude by showing how future research can exploit this link and by discussing the importance of the results as building blocks for a full theoretical understanding of the echo chamber model. Finally, Part IV presents a published paper on the birth-death process with partial catastrophe. The paper is based on the explicit calculation of the first moment of a catastrophe. This first part is entirely based on an analytical approach to second degree recurrences with linear coefficients. The convergence to 0 of the resulting sequence as well as the speed of convergence are proved. On the other hand, the determination of the upper bounds of the expected value of the population size as well as its variance and the difference between the determined upper bound and the actual value of the expected value. For these results we use almost exclusively the theory of ordinary nonlinear differential equations.
Das Zentrum für Lehrerbildung und Bildungsforschung (ZeLB) verantwortet im Projekt „PSI-Potsdam“ die Unterstützung der Qualifizierung in der Medienbildung/Digitalisierung der Lehrkräftebildung an der Universität Potsdam. Der Schwerpunkt der Tätigkeit lag zunächst auf der mediendidaktischen Qualifizierung und wurde ab der zweiten Förderphase des Programms 2018 mit Akzentuierung auf Herausforderungen und Chancen von Digitalisierung für das Lehren und Lernen in der Lehrkräftebildung fortgeführt. In diesem Beitrag werden die Entwicklungen und Beiträge in Bezug auf die digitale Medienbildung und Digitalisierung an der Universität Potsdam für die Lehrkräftebildung dargestellt. Weiterführend werden Perspektiven aufgezeigt, wie zukünftig digitale Medienbildung in der universitären Lehrkräftebildung verankert werden kann.
This paper deals with the teaching of grammar in the English as a foreign language (EFL) classroom. In this context, a course book (English G 21 A2) is examined in regard to whether it is compatible with current theories about second language acquisition (SLA).
At the beginning of this paper, views on grammar teaching from the past and the present are summarized and this is followed by an analysis of the current curriculum concerning its guidelines for grammar teaching in the foreign language classroom. This analysis concludes that the curriculum of Brandenburg hardly gives any recommendations regarding the question of which grammatical phenomena should to be taught. This explains, at least partly, the important position course books take in the foreign language classroom. Teachers use them as a source of material as well has a guideline for which topics can be taught and in which order.
The following part gives an overview of cognitive models of SLA and foreign language teaching, among others Krashen’s Monitor Hypothesis, R. Ellis’ Weak Interface Model and Pienemann’s Processability Theory. On the basis of these models criteria for the ideal design of a course book, which would support grammar teaching according to current findings, are developed. Among those criteria are the offering of a lot of input in the target language, provision of practice activities and consciousness-raising activities, taking into consideration the sequence of acquisition and the provision of a diagnostic tool which enables the students to find out in which areas of the target language they need to improve. Furthermore, the inclusion of opportunities for (individual) revision is regarded as essential. All of those criteria are of course given under the reservation that the influence of course books on the happenings in the classroom is restricted as the final decisions are made by the teacher in the teaching situation.
In the analysis, one communicative intention which is usually a topic in the English lessons between the third and sixth year of learning is focused on. This communicative intention is talking about the future. First, the possibilities to express futurity in the English language are analysed and reduced for the use in teaching. The chosen course book is then described and analysed and the way the book deals with the topic of talking about the future is compared to the criteria which where specified earlier in the paper. This comparison showed that the book is compatible with SLA theories in many ways (e.g. concerning the explanations of grammatical structures) but that there is still room for improvement (e.g. concerning the amount of input and the number of consciousness-raising activities).
Hardy inequalities on graphs
(2024)
The dissertation deals with a central inequality of non-linear potential theory, the Hardy inequality. It states that the non-linear energy functional can be estimated from below by a pth power of a weighted p-norm, p>1. The energy functional consists of a divergence part and an arbitrary potential part. Locally summable infinite graphs were chosen as the underlying space. Previous publications on Hardy inequalities on graphs have mainly considered the special case p=2, or locally finite graphs without a potential part.
Two fundamental questions now arise quite naturally: For which graphs is there a Hardy inequality at all? And, if it exists, is there a way to obtain an optimal weight? Answers to these questions are given in Theorem 10.1 and Theorem 12.1. Theorem 10.1 gives a number of characterizations; among others, there is a Hardy inequality on a graph if and only if there is a Green's function. Theorem 12.1 gives an explicit formula to compute optimal Hardy weights for locally finite graphs under some additional technical assumptions. Examples show that Green's functions are good candidates to be used in the formula.
Emphasis is also placed on illustrating the theory with examples. The focus is on natural numbers, Euclidean lattices, trees and star graphs. Finally, a non-linear version of the Heisenberg uncertainty principle and a Rellich inequality are derived from the Hardy inequality.
Molecules are often naturally embedded in a complex environment. As a consequence, characteristic properties of a molecular subsystem can be substantially altered or new properties emerge due to interactions between molecular and environmental degrees of freedom. The present thesis is concerned with the numerical study of quantum dynamical and stationary properties of molecular vibrational systems embedded in selected complex environments.
In the first part, we discuss "strong-coupling" model scenarios for molecular vibrations interacting with few quantized electromagnetic field modes of an optical Fabry-Pérot cavity. We thoroughly elaborate on properties of emerging "vibrational polariton" light-matter hybrid states and examine the relevance of the dipole self-energy. Further, we identify cavity-induced quantum effects and an emergent dynamical resonance in a cavity-altered thermal isomerization model, which lead to significant suppression of thermal reaction rates. Moreover, for a single rovibrating diatomic molecule in an optical cavity, we observe non-adiabatic signatures in dynamics due to "vibro-polaritonic conical intersections" and discuss spectroscopically accessible "rovibro-polaritonic" light-matter hybrid states.
In the second part, we study a weakly coupled but numerically challenging quantum mechanical adsorbate-surface model system comprising a few thousand surface modes. We introduce an efficient construction scheme for a "hierarchical effective mode" approach to reduce the number of surface modes in a controlled manner. In combination with the multilayer multiconfigurational time-dependent Hartree (ML-MCTDH) method, we examine the vibrational adsorbate relaxation dynamics from different excited adsorbate states by solving the full non-Markovian system-bath dynamics for the characteristic relaxation time scale. We examine half-lifetime scaling laws from vibrational populations and identify prominent non-Markovian signatures as deviations from Markovian reduced system density matrix theory in vibrational coherences, system-bath entanglement and energy transfer dynamics.
In the final part of this thesis, we approach the dynamics and spectroscopy of vibronic model systems at finite temperature by formulating the ML-MCTDH method in the non-stochastic framework of thermofield dynamics. We apply our method to thermally-altered ultrafast internal conversion in the well-known vibronic coupling model of pyrazine. Numerically beneficial representations of multilayer wave functions ("ML-trees") are identified for different temperature regimes, which allow us to access thermal effects on both electronic and vibrational dynamics as well as spectroscopic properties for several pyrazine models.
This article examines public service resilience during the COVID-19 pandemic and studies the switch to telework due to social distancing measures. We argue that the pandemic and related policies led to increasing demands on public organisations and their employees. Following the job demands-resources model, we argue that resilience only can arise in the presence of resources for buffering these demands. Survey data were collected from 1,189 German public employees, 380 participants were included for analysis. The results suggest that the public service was resilient against the crisis and that the shift to telework was not as demanding as expected.
Dieses Sonderheft der Schriftenreihe des Lehrstuhls für Public und Nonprofit Management präsentiert Ergebnisse eines studentischen Beratungsprojekts aus dem Wintersemester 2018/19. Dabei wurde eine Vision für eine digitalisierte öffentliche Verwaltung entworfen. Unter Anwendung von Szenariomethoden wurden Zukunftsszenarien entwickelt und getestet, die sich entweder mit Bürger*innen und Unternehmen als Kund*innen der Verwaltung, den öffentlich Beschäftigen oder der Aufbau- und Ablauforganisation in der Verwaltung beschäftigen.
Neue Talente braucht das Amt
(2018)
Stellenabbau und demografischer Wandel führen zu Rekrutierungsschwierigkeiten und einem Mangel an talentierten Nachwuchskräften in der öffentlichen Verwaltung. Gleichzeitig stellen sich neue Anforderungen an öffentliche Behörden, die eine andere Qualifikation der Beschäftigten nach sich ziehen. Gerade öffentliche Dienste mit geschlossenen Personalsystemen brauchen daher eine stärkere Flexibilität in der Nachwuchsrekrutierung und -ausbildung. Traineeprogramme können hier Abhilfe schaffen.
Traineeprogramme können im öffentlichen Dienst zur Rekrutierung und Ausbildung von Nachwuchskräften dienen. Solche Programme werden, im Gegensatz zur Privatwirtschaft, wo diese schon seit einigen Jahrzehnten Anwendung finden, im deutschen öffentlichen Dienst erst seit einigen Jahren durchgeführt. Eine erste empirische Erhebung zeigt nun, dass Traineeprogramme im öffentlichen Sektor gut geeignet sind, um Nachwuchskräfte auszubilden und in der Organisation zu sozialisieren. Als entscheidende Einflussfaktoren konnten eine klare Struktur des Programms, ein effektives off-the-job Training, bereichsübergreifende Projektarbeit, der Umfang der Betreuung der Trainees und der Einsatz der jeweiligen Behördenleitung für das Programm identifiziert werden. Deutlich wurde auch, dass während der Einführung eines Traineeprogramms die Trainee-Betreuer entsprechend vorbereitet werden müssen und in den Behörden Akzeptanz für diese neue Form der Nachwuchsgewinnung geschaffen werden muss (Change Management). Die Ergebnisse zeigen jedoch ebenso, dass sich solche Programme nicht zur Personalentwicklung bereits Beschäftigter eignen.
More than a century ago the phenomenon of non-Mendelian inheritance (NMI), defined as any type of inheritance pattern in which traits do not segregate in accordance with Mendel’s laws, was first reported. In the plant kingdom three genomic compartments, the nucleus, chloroplast, and mitochondrion, can participate in such a phenomenon. High-throughput sequencing (HTS) proved to be a key technology to investigate NMI phenomena by assembling and/or resequencing entire genomes. However, generation, analysis and interpretation of such datasets remain challenging by the multi-layered biological complexity. To advance our knowledge in the field of NMI, I conducted three studies involving different HTS technologies and implemented two new algorithms to analyze them.
In the first study I implemented a novel post-assembly pipeline, called Semi-Automated Graph-Based Assembly Curator (SAGBAC), which visualizes non-graph-based assemblies as graphs, identifies recombinogenic repeat pairs (RRPs), and reconstructs plant mitochondrial genomes (PMG) in a semiautomated workflow. We applied this pipeline to assemblies of three Oenothera species resulting in a spatially folded and circularized model. This model was confirmed by PCR and Southern blot analyses and was used to predict a defined set of 70 PMG isoforms. With Illumina Mate Pair and PacBio RSII data, the stoichiometry of the RRPs was determined quantitatively differing up to three-fold.
In the second study I developed a post-multiple sequence alignment algorithm, called correlation mapping (CM), which correlates segment-wise numbers of nucleotide changes to a numeric ascertainable phenotype. We applied this algorithm to 14 wild type and 18 mutagenized plastome assemblies within the Oenothera genus and identified two genes, accD and ycf2 that may cause the competitive behavior of plastid genotypes as plastids can be biparental inherited in Oenothera. Moreover, lipid composition of the plastid envelope membrane is affected by polymorphisms within these two genes.
For the third study, I programmed a pipeline to investigate a NMI phenomenon, known as paramutation, in tomato by analyzing DNA and bisulfite sequencing data as well as microarray data. We identified the responsible gene (Solyc02g0005200) and were able to fully repress its caused phenotype by heterologous complementation with a paramutation insensitive transgene of the Arabidopsis thaliana orthologue. Additionally, a suppressor mutant shows a globally altered DNA methylation pattern and carries a large deletion leading to a gene fusion involving a histone deacetylase.
In conclusion, my developed and implemented algorithms and data analysis pipelines are suitable to investigate NMI and led to novel insights about such phenomena by reconstructing PMGs (SAGBAC) as a requirement to study mitochondria-associated phenotypes, by identifying genes (CM) causing interplastidial competition as well by applying a DNA/Bisulfite-seq analysis pipeline to shed light in a transgenerational epigenetic inheritance phenomenon.
Horomedon und Laokoon
(2011)
Nanostructured inorganic materials are routinely synthesized by the use of templates. Depending on the synthesis conditions of the product material, either “soft” or “hard” templates can be applied. For sol-gel processes, usually “soft” templating techniques are employed, while “hard” templates are used for high temperature synthesis pathways. In classical templating approaches, the template has the unique role of structure directing agent, in the sense that it is not participating to the chemical formation of the resulting material. This work investigates a new templating pathway to nanostructured materials, where the template is also a reagent in the formation of the final material. This concept is described as “reactive templating” and opens a synthetic path toward materials which cannot be synthesised on a nanometre scale by classical templating approaches. Metal nitrides are such kind of materials. They are usually produced by the conversion of metals or metal oxides in ammonia flow at high temperature (T > 1000°C), which make the application of classical templating techniques difficult. Graphitic carbon nitride, g-C3N4, despite its fundamental and theoretical importance, is probably one of the most promising materials to complement carbon in material science and many efforts are put in the synthesis of this material. A simple polyaddition/elimination reaction path at high temperature (T = 550°C) allows the polymerisation of cyanamide toward graphitic carbon nitride solids. By hard templating, using nanostructured silica or aluminium oxide as nanotemplates, a variety of nanostructured graphitic carbon nitrides such as nanorods, nanotubes, meso- and macroporous powders could be obtained by nanocasting or nanocoating. Due to the special semi-conducting properties of the graphitic carbon nitride matrix, the nanostructured graphitic carbon nitrides show unexpected catalytic activity for the activation of benzene in Friedel-Crafts type reactions, making this material an interesting metal free catalyst. Furthermore, due to the chemical composition of g-C3N4 and the fact that it is totally decomposed at temperatures between 600°C and 800°C even under inert atmosphere, g-C3N4 was shown to be a good nitrogen donor for the synthesis of early transition metal nitrides at high temperatures. Thus using the nanostructured carbon nitrides as “reactive templates” or “nanoreactors”, various metal nitride nanostructures, such as nanoparticles and porous frameworks could be obtained at high temperature. In this approach the carbon nitride nanostructure played both the role of the nitrogen source and of the exotemplate, imprinting its size and shape to the resulting metal nitride nanostructure.