<p>The magnetospheric cusps are two funnel-like regions of Earth's magnetosphere where solar wind plasma can have direct access to the ionosphere. The cusps are very dynamic regions where wave-particle interactions continuously take place and redistribute energy among different particle populations. In this thesis, both low and high frequency plasma waves in the cusp have been studied in detail using data from the Cluster spacecraft mission. The waves were studied with respect to frequency, Poynting flux and polarization. Wavelengths have also been estimated using multi-spacecraft techniques. At low frequencies, kinetic Alfvén waves and nonpotential ion cyclotron waves are identified and at high frequencies, electron cyclotron waves, whistler waves, upper-hybrid and RX-waves are observed. A common generation mechanism called the shell-instability is proposed for several of the wave modes present in the cusp, both at low and high frequencies. </p><p>The plasma in the cusp is shown to be strongly inhomogeneous. In an inhomogeneous low-frequency magnetoplasma, kinetic Alfvén waves couple to drift-waves. Such drift-kinetic Alfvén waves have long been believed to nonlinearly self-interact and form coherent structures in the form of drift-kinetic Alfvén vortices. In this thesis the first unambiguous direct measurements confirming the existence of such vortices in a turbulent space plasma are presented. Some of the crucial parameters such as the vortex radius are determined. </p><p>Plasma theory is electrodynamics applied to a large collection of charged particles. In this thesis a new way of looking at the fundamental Maxwell tensor is presented. A covariant spectral density tensor containing information on electromagnetic waves is formed. This tensor is then decomposed into irreducible components by using the spinor formalism for an arbitrary metric. The obtained fundamental tensors are shown to correspond both to well known tensors in Maxwell's theory, as well as several physically interesting new tensors.</p>

A training method utilized in a few martial arts was found to agree strongly with current cognitive psychology theory. Further study extracted a procedural model for learning a complex set of whole-body, dyadic motor skills involving high-speed, interactive, continuous situation assessment and decision making. A broader literature survey found relevance in several fields of research, supporting the definition of four performance dimensions in the activity. Data collected from one experienced student partnering with each of ten students of various experience levels was analyzed on these four dimensions. These dimensions were found sufficient to show both individual differences and changes across an instructional intervention. Strong correlations found under linear regression were supportive of anecdotal evidence from the model??s long empirical history in training. Data provided evidence of a self-organizing dynamic emerging from the interaction of a dyad participating in this activity, and of individual differences in cognitive resource management dynamically setting allocation priorities among specific aspects of a complex motor/cognitive activity. Highly individual responses demonstrate a mechanism for insight into students that are difficult to read. Numerous comparisons and contrasts show interactivity of performance dimensions. Impact is foreseen for research, training and testing in motor learning fields, as well as situation awareness, decision making and military tactical training. Further research is recommended to replicate these findings, test hypotheses derived from them, and to extend testing of the drill-network model into other fields of learning.

The magnetospheric cusps are two funnel-like regions of Earth's magnetosphere where solar wind plasma can have direct access to the ionosphere. The cusps are very dynamic regions where wave-particle interactions continuously take place and redistribute energy among different particle populations. In this thesis, both low and high frequency plasma waves in the cusp have been studied in detail using data from the Cluster spacecraft mission. The waves were studied with respect to frequency, Poynting flux and polarization. Wavelengths have also been estimated using multi-spacecraft techniques. At low frequencies, kinetic Alfvén waves and nonpotential ion cyclotron waves are identified and at high frequencies, electron cyclotron waves, whistler waves, upper-hybrid and RX-waves are observed. A common generation mechanism called the shell-instability is proposed for several of the wave modes present in the cusp, both at low and high frequencies. The plasma in the cusp is shown to be strongly inhomogeneous. In an inhomogeneous low-frequency magnetoplasma, kinetic Alfvén waves couple to drift-waves. Such drift-kinetic Alfvén waves have long been believed to nonlinearly self-interact and form coherent structures in the form of drift-kinetic Alfvén vortices. In this thesis the first unambiguous direct measurements confirming the existence of such vortices in a turbulent space plasma are presented. Some of the crucial parameters such as the vortex radius are determined. Plasma theory is electrodynamics applied to a large collection of charged particles. In this thesis a new way of looking at the fundamental Maxwell tensor is presented. A covariant spectral density tensor containing information on electromagnetic waves is formed. This tensor is then decomposed into irreducible components by using the spinor formalism for an arbitrary metric. The obtained fundamental tensors are shown to correspond both to well known tensors in Maxwell's theory, as well as several physically interesting new tensors.

A method is described for preset-count irradiations between 1 and 100 ions singling-out individual ions from an ion beam with more than a billion ions arriving per second. The ion tracks are etched in a conductometric system with real-time evaluation of the acquired data. The etch process can be interrupted when reaching a preset channel diameter. Cylindrical channels are obtained by adding surfactants to the etch solution forming a self-assembled barrier between etching medium and polymer. Asymmetric etching of single ion tracks leads to pH sensitive conical pores with diode-like properties. Using etched channels as template, homogeneous and multilayer magnetic single-wires are electrodeposited. The magnetoresistivity of the wires is studied. Single-track applications comprise critical apertures (cylindric, conic, necked), asymmetric pores (pH sensitive, biospecific), Giant Magneto Resistance sensors, and spintronic devices. On the basis of studies with individual ion tracks we tackled tilted multiporous systems such as ion beam lithography with a masked ion beam leading to micro-structures with inclined walls and anisotropic superhydrophobic ion track textures, analogous to biological shingle structures on butterfly wings. We demonstrated qualitatively, that the asymmetry of the texture translates into motion under ultrasonic agitation. This could lead to the development of rotary drives.

Das stäbchenförmige Bakterium Escherichia coli teilt sich in zwei gleich große Tochterzellen. Dies ist nur möglich, wenn sich die Zelle in der Mitte teilt. Bei E. coli wird die Zellteilung durch den Zusammenschluss der FtsZ-Proteine an der Membran zum Z-Ring eingeleitet. Topologische Regulierung des Z-Ringes erfolgt durch räumlich-zeitliche Oszillationen von Min-Proteinen zwischen den beiden Zellpolen. MinC, MinD und MinE binden an und lösen sich von der Membran unter Hydrolyse von ATP und in antagonistischer Art und Weise, was zu einer alternierenden Ansammlung von MinC und MinD an den Zellpolen führt. Gemittelt über die Zeit ergibt sich somit ein MinD-Verteilungsprofil, das maximale Konzentration an den Zellpolen und ein Minimum in der Zellmitte aufweist. MinC bindet an MinD und folgt somit seiner Verteilung. Der Zusammenschluss von FtsZ-Proteinen wird durch MinC unterbunden, und somit kann sich der Z-ring nur an einer Position herausbilden, die ein Minimum an MinC aufweist - der Zellmitte. Das Min-system wurde in der Vergangenheit auch mit einem in-vitro-Ansatz untersucht, indem Min-Proteine in künstliche, aufliegende Lipiddoppelschichten (supported lipid bilayers, SLB) rekonstitutiert wurden. Dabei bildeten die Min-Proteine kein oszillierendes Muster aus, sondern organisierten sich vielmehr in parallelen und propagierenden Wellen (Loose, 2008, Science, 320). In diesen in-vitro-Experimenten war das Membransubstrat wesentlich größer als die Wellenlänge der Min-Proteinwellen. In vivo hingegen ist die Länge der Zelle in der gleichen Größenordnung wie die charakteristische Länge des Oszillationsmusters der Min-Proteine. Daher war es das Ziel dieser Arbeit, den Einfluß einer beschränkten Fläche und geometrischer Formgebung der künstlichen Lipiddoppelschichten auf die Wellenpropagation der Min-Protein zu untersuchen. Flächige Beschränkung künstlicher Membranen erfolgte durch Mikrostrukturtechnologie. Deckglässchen wurden mit einer Goldschicht und mikroskopischen Aussparungen unterschiedlicher geometrischer Formen strukturiert. Funktionale SLBs bildeten sich nur auf Glasflächen ohne Goldbeschichtung aus. Nach der Rekonstitution der Min-Proteine, organisierten sich diese auf den Membranstücken in parallele Wellen. Dabei bestimmte die flächige Beschränkung der künstlichen Membranen die Ausbreitungsrichtung der Min-Proteinwellen. Min-Proteinwellen konnten entlang gekrümmter Membranstreifen, in Ring- und sogar in Slalomstrukturen geleitet werden. In geraden, länglichen Strukturen richteten sich die Wellen entlang der längsten Achse aus. Kopplung von Proteinwellen auf räumlich getrennten Membranstücken in Abhängigkeit des Abstandes und des sogenannten Molecular Crowdings in der wässrigen Lösung konnte ebenfalls beobachtet werden. Diese Kopplung ist ein Indiz für inhomogene Proteinverteilungen in der Lösung oberhalb der Membran. Desweiteren konnten Min-Proteinwellen auch in diversen dreidimensionalen künstlichen Membranen rekonstitituiert werden. Im Wildtyp von E. coli ähneln die Min-Proteindynamiken der einer Oszillation mit einer charakteristischen Länge von 5 µm. Auf SLBs, bilden Min-Proteine Wellen mit einer Wellenlänge aus, die ca. zehnmal größer ist als in vivo. Dieser Unterschied zwischen der in-vivo- und der in-vitro-Welt wurde untersucht und diskutiert. In vitro konnte die Wellenlänge um 50 % durch Erhöhung des Molecular Crowding in der Lösung sowie um 33 % durch Temperaturerhöhung verkleinert werden. Das oszillierende Muster könnte dahingegen eine Folge der Kompartimentierung sein. Erste Versuche, das Min-System in geschlossene Membrankompartimente zu rekonstitutieren, wurden getestet. / Escherichia coli, a rod-like bacterium, divides by binary fission. Cell division into two daughter cells of equal size requires that fission takes place at a midcell position. In E. coli, cell division is initiated by assembly of the FtsZ-proteins at the inner membrane to the Z-ring. Topological regulation of the Z-ring is achieved by spatiotemporal pole-to-pole oscillations of Min-proteins. MinC, MinD and MinE bind to and detach from - under hydrolysis of ATP - the membrane in an antagonistic manner leading to an alternating accumulation of MinC and MinD at the cell poles. Averaged over time, the distribution profile of MinD exhibits maximal concentration at the cell poles and a minimum at the cell center. MinC binds to MinD and thus follows its distribution. FtsZ assembly is inhibited by MinC and therefore the Z-ring can only form at a cell position low in MinC - at the cell center. In the past, the Min-system was also investigated in an in vitro approach by reconstitution of Min-proteins into a supported lipid bilayer (SLB). Here, Min-proteins did not self-organize into an oscillatory pattern but into parallel and propagating waves (Loose, 2008, Science, 320). In this in vitro assay, the membrane substrate was infinitely large compared to the wavelength. However, in vivo, the cell length is on the same order of magnitude as the respective length scale of the oscillatory pattern of Min-proteins. Therefore, we wished to investigate the effect of lateral confinement and geometric structuring of artificial lipid bilayers on the Min-protein wave propagation. Lateral confinement of artificial membranes was achieved by microfabrication technology. Glass slides were patterned by a gold coating with microscopic windows of different geometries, and functional SLBs were only formed on uncoated areas. Upon reconstitution, Min-proteins organized into parallel waves on the geometric membrane patches. Confinement of the artificial membranes determined the direction of propagation of Min-protein waves. Min-protein waves could be guided along curved membrane stripes, in rings and even along slalom-geometries. In elongated membrane structures, the protein waves always propagate along the longest axis. Coupling of protein waves across spatially separated membrane patches was observed, dependent on gap size and level of molecular crowding of the aqueous media above the bilayer. This indicates the existence of an inhomogeneous and dynamic protein gradient in the solution above the membrane. Furthermore, reconstitution of Min-protein waves in various three-dimensional artificial membranes was achieved. In wild-type E. coli, Min-protein dynamics resemble that of an oscillation with a characteristic length scale of 5 µm. On supported lipid bilayers, Min-proteins self-organize into waves with a wavelength approximately 10-fold larger than in vivo. These discrepancies between the in vivo and in vitro world were investigated and discussed. In vitro, the wavelength could be decreased by a factor of 50 % by increase of the molecular crowding in solution and by 33 % through temperature increase. The oscillatory pattern is thought to be a consequence of compartmentalization and first attempts to encapsulate the Min-system in closed bilayer compartments are presented.

In this thesis, we study how and to what extent a self-organized mobile robot flock can be guided by informing some of the robots within the flock about a preferred direction of motion. Specifically, we extend a flocking behavior that was shown to maneuver a swarm of mobile robots as a cohesive group in free space, avoiding obstacles. In its original form, this behavior does not have a preferred direction and the flock would wander aimlessly. In this study, we incorporate a preference for a goal direction in some of the robots. These informed robots do not signal that they are informed (a.k.a. unacknowledged leadership) and instead guide the swarm by their tendency to move in the desired direction. Through experimental results with physical and simulated robots we show that the self-organized flocking of a robot swarm can be effectively guided by an informed minority of the flock. We evaluate the system using a number of quantitative metrics: First, we propose to use the mutual information metric from Information Theory as a dynamical measure of the information exchange. Then, we discuss the accuracy metric from directional statistics and size of the largest cluster as the measures of system performance. Using these metrics, we perform analyses from two points of views: In the transient analyses, we demonstrate the information exchange between the robots as the time advances, and the increase in the accuracy of the flock when the conditions are suitable for an adequate amount of information exchange. In the steady state analyses, we investigate the interdependent effects of the size of the flock in terms of the robots in it, the ratio of informed robots in the flock over the total flock size, the weight of the direction preference behavior, and the noise in the system.

A training method utilized in a few martial arts was found to agree strongly with current cognitive psychology theory. Further study extracted a procedural model for learning a complex set of whole-body, dyadic motor skills involving high-speed, interactive, continuous situation assessment and decision making. A broader literature survey found relevance in several fields of research, supporting the definition of four performance dimensions in the activity. Data collected from one experienced student partnering with each of ten students of various experience levels was analyzed on these four dimensions. These dimensions were found sufficient to show both individual differences and changes across an instructional intervention. Strong correlations found under linear regression were supportive of anecdotal evidence from the model??s long empirical history in training. Data provided evidence of a self-organizing dynamic emerging from the interaction of a dyad participating in this activity, and of individual differences in cognitive resource management dynamically setting allocation priorities among specific aspects of a complex motor/cognitive activity. Highly individual responses demonstrate a mechanism for insight into students that are difficult to read. Numerous comparisons and contrasts show interactivity of performance dimensions. Impact is foreseen for research, training and testing in motor learning fields, as well as situation awareness, decision making and military tactical training. Further research is recommended to replicate these findings, test hypotheses derived from them, and to extend testing of the drill-network model into other fields of learning.

Given the importance of entrepreneurship to individuals and to society, and given that the individual has come to be seen as not only an important function of social and economic processes but also as an important end of these processes, the link between entrepreneurship and well-being requires further investigation. To that end, this thesis provides a solid framework for understanding and measuring well-being in entrepreneurship, and a comprehensive theoretical and empirical examination of the intimate relationship between these two phenomena. Some new and very interesting results were produced: • Active engagement in the creation of new business activities leads to greater well-being by granting the freedom to self-organize work and working relationships, which satisfies individual’s needs for autonomy, competence, and relatedness. • Entrepreneurial engagement is detrimental to mental health during its early inception in planning and deliberation, which may explain why many fail to transition from thought to action in entrepreneurship. • The presence of a discrepancy between extrinsic life goals and motives is just as strong a predictor of well-being in entrepreneurship as the presence of strong intrinsic life goals and motives. • Entrepreneurial Well-Being, a context-specific state of mental wellness derived from engagement in entrepreneurship, uniquely contributes to entrepreneurs’ overall well-being and is associated with a range of cognitive and motivational processes crucial to entrepreneurship. The reasons for these findings, and the mechanisms involved, are explained at length. My hope is that this work will usher on the adoption of a more integrated approach to assessing and optimizing entrepreneurial performance in terms of both business outcomes and mental health outcomes, as well as offer insights relevant to well-being and its promotion on a more general level. / <p>Diss. Stockholm : Handelshögskolan i Stockholm, 2015</p>

Η παρούσα διατριβή αφορά την ανάπτυξη μαθηματικών μοντέλων και την εκτέλεση υπολογιστικών προσομοιώσεων Monte Carlo για την περιγραφή και μελέτη της θερμοδυναμικής συμπεριφοράς συστημάτων αποτελούμενων από πρότυπα σωματίδια πυρήνα–κελύφους σε επιφάνειες. Δύο κατηγορίες συστημάτων εξετάστηκαν, αμφίφιλων σωματιδίων μορφής ημιδίσκου καθώς και μορφής δίσκου με δύο διακριτές υποπεριοχές κελύφους. Ένα εύρος μοριακών δομών όπως μικύλια συμπολυμερών, σφαιρικά δενδριμερή, μεταλλικά ή κεραμικά νανοσωματίδια συνδεμένα με εύκαμπτες αλυσίδες μορίων, εμφανίζουν αρχιτεκτονική η οποία περιγράφεται από το προτεινόμενο μοριακό μοντέλο. Η κατάσταση πυκνής κατάληψης κάθε συστήματος ταυτίζεται ουσιαστικά με την υπερμοριακή αυτο-συναρμολόγηση δομών καθορισμένων μοτίβων σε υψηλές συγκεντρώσεις, συμπεριλαμβανομένων και επιφανειών με ανοιχτούς πόρους. Με την αυτο-οργάνωση και αυτο-συναρμολόγηση σαν από τις πιο αντιπροσωπευτικές των 'από κάτω προς τα πάνω' τεχνικών παρασκευής λειτουργικών νανοδομών και διατάξεων σήμερα, η μελέτη μας διαπραγματεύεται ταυτόχρονα ένα αυστηρά καθορισμένο πρόβλημα από φυσική άποψη αλλά και ένα ιδιαίτερο θέμα σύγχρονου τεχνολογικού ενδιαφέροντος. Η διατριβή χωρίζεται σε δύο μέρη. Στο πρώτο μέρος θα εισάγουμε το γενικότερο πλαίσιο κάτω από το οποίο θα γίνει η μελέτη των φυσικών συστημάτων σωματιδίων πυρήνα - κελύφους. Θα αναφερθούμε τόσο σε θεωρητικά θέμα όσο και τεχνολογικά. Στο δεύτερο, θα παρουσιαστούν και θα συζητηθούν εκτενώς τα αποτελέσματα προσομοιώσεων δισδιάστατων συστημάτων σωματιδίων πυρήνα-κελύφους. / In this thesis mathematical models are developed and Monte Carlo computer simulations are performed in order to describe and study the thermodynamic behavior of systems comprised of core – shell particles on surfaces. Two types of systems were studied, built on amphiphilic particles of either half-disc shape or disc shape with two distinct coronal regions. A range of molecular structures such as copolymer micelles, globular dendrimers, tethered metal and clay nanoparticles, bare an architecture well fitted to the proposed molecular model. The close packed structure of every system coincides with the supramolecular self-assembly at high concentrations of structures with well defined patterns, including surfaces with open pores. Given the fact that self-assembly and self-organization are among the most representative of the 'bottom-up' techniques for the fabrication of functional nanostructures and devices, our study deals with a strictly defined physical problem as well as with an issue of distinct technological interest. The thesis is made up of two parts. In the first part, we will introduce the general framework under which we will later investigate the physical systems of core-shell particles. Both theoretical and practical aspects will be mentioned. In the second part, the results of simulations of two dimensional systems of core-shell particles will be presented and discussed in detail.

Cette thèse est consacrée à la modélisation de la formation spontanée de chemins préférentiels par des marcheurs déposant des traces attractives sur leurs trajectoires. Plus précisément, par une démarche pluridisciplinaire couplant modélisation et expérimentation, elle vise à dégager un ensemble de règles minimales individuelles permettant l'apparition d'un tel phénomène. Dans ce but, nous avons étudié sous différents angles les modèles minimaux que sont les marches aléatoires renforcées (MAR).Ce travail comporte deux parties principales. La première démontre de nouveaux résultats dans le domaine des probabilités et statistiques. Nous avons généralisé le travail publié par M. Benaïm et O. Raimond en 2010 afin d'étudier l'asymptotique d'une classe de MAR auxquelles les demi-tours sont interdits. Nous avons également développé une procédure statistique permettant, sous certaines conditions adéquates de régularité, d'estimer les paramètres de MAR paramétrées et d'évaluer des marges d'erreur.Dans la seconde partie, sont décrits les résultats et analyses d'une étude comportementale et expérimentale de la fourmi Linepithema humile. Une partie de notre réflexion est centrée sur le rôle et la valeur des paramètres du modèle proposé par J.-L. Deneubourg et al. en 1990. Nous nous sommes aussi demandés dans quelle mesure une MAR peut reproduire les déplacements d'une fourmi dans un réseau. Dans ces objectifs, nous avons mené des expériences confrontant des fourmis à des réseaux à une ou plusieurs bifurcations. Nous avons appliqué aux données expérimentales les outils statistiques développés dans cette thèse. Nous avons aussi effectué une étude comparative entre les simulations de plusieurs modèles et les expériences. / This thesis is devoted to the modelisation of the spontaneous formation of preferential paths by walkers that deposit attractive trails on their trajectories. More precisely, through a multidisciplinary approach, which combines modelisation and experimentation, this thesis aims to bring out a set of minimal individual rules that allow the apparition of this phenomena. In this purpose, we study in several ways the minimal models, which are the Reinforced Random Walks (RRW).This work contains two main parts. The first one proves some new results in the field of probability and statistics. We have generalized the work published by M. Benaïm and O. Raimond in 2010 in order to study the asymptotics of a class of RRW, to which U-turns are forbidden. We developped also a statistical procedure that allows under some appropriate regularity hypotheses to estimate the parameters of parametized RRW and to evaluate margins of error.In the second part, we describe the results and the analyses of a experimental and behavioral study of the Linepithema humile ants. One part of our reflection is centered on the role and the value of the parameters of the model defined by J.-L. Deneubourg et al. in 1990. We investigated also the extent to which RRW could reproduce the moving of an ant in a network. To these purposes, we performed experiments that confront ants to a network of one or several forks. We applied to experimental data the statistical tools developed in this thesis and we performed a comparative study between experiments and simulations of several models.