Curvature stabilized skyrmions with angular momentum

We examine skyrmionic field configurations on a spherical ferromagnet with large normal anisotropy. Exploiting variational concepts of angular momentum we find a new family of localized solutions to the Landau-Lifshitz equation that are topologically distinct from the ground state and not equivariant. Significantly, we observe an emergent spin-orbit coupling on the level of magnetization dynamics in a simple system without individual rotational invariance in spin and coordinate space

Inverse scattering on the line for a generalized nonlinear Schroedinger equation

A one-dimensional generalized nonlinear Schroedinger equation is considered, and the corresponding inverse scattering problem is analyzed when the potential is compactly supported and depends on the wave function. The unique recovery of the potential is established from an appropriate set of scattering data.Comment: 20 page

Bridging democratic gaps or building political brands? : perceptions of representation from the participation of MEPs in social media

This thesis provides a study of the Members of the European Parliament (MEPs) from Ireland, Greece and Cyprus and their use of Social Media Platforms (SMPs). Specifically, the thesis explores MEPs’ motivations for online engagement and the strategies they apply through their social media accounts. The MEPs face a growing demand for approachability and responsiveness within an expanding framework of disconnection and Euroscepticism. The objective is to determine whether they engage online to embrace citizens’ inclusion and the bridging of the democratic gaps which have been exacerbated by the recent crises or whether they focus more on exploiting the promotional advantages of SMPs to enhance their political brand.Central to the thesis purpose is to collect and interpret the perceptions of the MEPs about the functions of accountability, policy discussion and branding. The collection and analysis of data from semi-structured interviews with the MEPs and the qualitative analysis of content from their social media accounts revealed a series of accountability, policy discussion and branding motivations and strategies. These in combination with the post-crisis social media landscape, determine the types, volume and quality of the interactions that MEPs from crisis-inflicted states pursue online during routine (non- campaigning) timeframes.The contribution of the thesis is that it approaches a contemporary phenomenon from an overlooked angle, i.e. how European representatives perceive and prioritise the parameters of online interaction and how this affects the engagement with constituents. Approaching the online activities of the MEPs from a non-traditional theory of representation becomes the key to accommodate their branding incentives and understand and acknowledge their particularities as supranational representatives. This also contributes to outlining an area of theoretical interest where the profiling of representational brands and the use of descriptive features find their place within a participatory framework which surpasses the sanction/reward scheme of the electoral mandate

Biobanking with Big Data: A Need for Developing “Big Data Metrics”

The term “big data” has often been used as an all-encompassing phrase for research that involves the use of large-scale data sets. However, the use of the term does little to signify the underlying complexity of definitions, of data sets, and of the requirements that need to be taken into consideration for sustainable research and the estimation of downstream impact. In particular, “big data” is frequently connected with biobanks and biobank networks as the institutions involved in tissue preservation are increasingly and perhaps unavoidably linked to the de facto preservation of information. “Big data” is commonly defined as collections of data sets so large and complex that its manipulation and management present significant logistical challenges (Oxford English Dictionary, 2013). Within the sphere of clinically oriented research, the term is often synonymous to electronic patient records from large hospitals, clinical trials, and/or -omics-based consortia and their associated banked samples. These data can be structured or unstructured, generated from diverse sources (sometimes in real time), and in very large volumes

Application of advanced surface patterning techniques to study cellular behavior

Surface manipulation for the fabrication of chemical or topographic micro- and nanopatterns, has been central to the evolution of in vitro biology research. A high variety of surface patterning methods have been implemented in a wide spectrum of applications, including fundamental cell biology studies, development of diagnostic tools, biosensors and drug delivery systems, as well as implant design. Surface engineering has increased our understanding of cell functions such as cell adhesion and cell-cell interaction mechanics, cell proliferation, cell spreading and migration. From a plethora of existing surface engineering techniques, we use standard microcontact printing methods followed by click chemistry to study the role of intercellular contacts in collective cancer cell migration. Cell dispersion from a confined area is fundamental in a number of biological processes, including cancer metastasis. To date, a quantitative understanding of the interplay of single cell motility, cell proliferation, and intercellular contacts remains elusive. In particular, the role of E- and N-Cadherin junctions, central components of intercellular contacts, is still controversial. Combining theoretical modeling with in vitro observations, we investigate the collective spreading behavior of colonies of human cancer cells (T24). The spreading of these colonies is driven by stochastic single-cell migration with frequent transient cell-cell contacts. We find that inhibition of E- and N-Cadherin junctions decreases colony spreading and average spreading velocities, without affecting the strength of correlations in spreading velocities of neighboring cells. Based on a biophysical simulation model for cell migration, we show that the behavioral changes upon disruption of these junctions can be explained by reduced repulsive excluded volume interactions between cells. This suggests that in cancer cell migration, cadherin-based intercellular contacts sharpen cell boundaries leading to repulsive rather than cohesive interactions between cells, thereby promoting efficient cell spreading during collective migration. Despite the remarkable progress in surface engineering technology and its applications, a combination of pattern properties such as stability, precision, specificity, high-throughput outcome and spatiotemporal control is highly desirable but challenging to achieve. Here, we introduce a versatile and high-throughput covalent photo-immobilization technique, comprising a light-dose dependent patterning step and a subsequent functionalization of the pattern via click chemistry. This two-step process is feasible on arbitrary surfaces and allows for generation of sustainable patterns and gradients. The method is validated in different biological systems by patterning adhesive ligands on cell repellent surfaces, thereby constraining the growth and migration of cells to the designated areas. We then implement a sequential photopatterning approach by adding a second switchable pattering step, allowing for spatiotemporal control over two distinct surface patterns. As a proof of concept, we reconstruct the dynamics of the tip/stalk cell switch during angiogenesis. Our results show that the spatiotemporal control provided by our “sequential photopatterning” system is essential for mimicking dynamic biological processes, and that our innovative approach has a great potential for further applications in cell science. In summary, this work introduces two novel and versatile paradigms of surface patterning for studying different aspects of cell behaviour in different cell types. The reliability of both setups is experimentally confirmed, providing new insight into the role of cell-cell contacts during collective cancer cell migration as well as the tip/stalk switch behaviour during angiogenesis

Εφαρμογή της μεθόδου Melnikov σε μη γραμμικά δυναμικά συστήματα με διχρωματική διέγερση

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Μαθηματική Προτυποποίηση σε Σύγχρονες Τεχνολογίες στην Οικονομία