Dynamics of domain walls in pattern formation under traveling-wave forcing

We study dynamics of domain walls in pattern forming systems that are externally forced by a moving space-periodic modulation close to 2:1 spatial resonance. The motion of the forcing induces nongradient dynamics, while the wave number mismatch breaks explicitly the chiral symmetry of the domain walls. The combination of both effects yields an imperfect nonequilibrium Ising-Bloch bifurcation, where all kinks (including the Ising-like one) drift. Kink velocities and interactions are studied within the generic amplitude equation. For nonzero mismatch, a transition to traveling bound kink-antikink pairs and chaotic wave trains occurs.

Quantum tunneling of domain walls in ferromagnets

We present a theoretical study of the quantum depinning of domain walls. Our approach extends earlier work by Stamp and confirms his suggestion that quantum tunneling of domain walls in ferromagnets may reveal itself at a macroscopic level in a manner similar to the Josephson effect in superconductors. The rate of tunneling of a domain wall through a barrier formed by a planar defect is calculated in terms of macroscopic parameters of the ferromagnet. A universal behavior of the WKB exponent in the limit of small barriers is demonstrated. The effect of dissipation on the tunneling rate is studied. It is argued that quantum diffusion of domain walls apparently explains a nonthermal magnetic relaxation observed in some materials at low temperatures.

Dynamics of transient domain structures in nematic liquid crystals: The splay Fréedericksz transition

We discuss the dynamics of the transient pattern formation process corresponding to the splay Fréedericksz transition. The emergence and subsequent evolution of the spatial periodicity is here described in terms of the temporal dependence of the wave numbers corresponding to the maxima of the structure factor. Situations of perpendicular as well as oblique field-induced stripes relative to the initial orientation of the director are both examined with explicit indications of the time scales needed for their appearance and posterior development.

Vacancy-assisted domain-growth in asymmetric binary alloys: A Monte Carlo Study

A Monte Carlo simulation study of the vacancy-assisted domain growth in asymmetric binary alloys is presented. The system is modeled using a three-state ABV Hamiltonian which includes an asymmetry term. Our simulated system is a stoichiometric two-dimensional binary alloy with a single vacancy which evolves according to the vacancy-atom exchange mechanism. We obtain that, compared to the symmetric case, the ordering process slows down dramatically. Concerning the asymptotic behavior it is algebraic and characterized by the Allen-Cahn growth exponent x51/2. The late stages of the evolution are preceded by a transient regime strongly affected by both the temperature and the degree of asymmetry of the alloy. The results are discussed and compared to those obtained for the symmetric case.

Utilization of a Time Domain Simulator in the Technical and Economic Analysis of a Wind Turbine Electric Drive Train

The amount of installed wind power has been growing exponentially during the past ten years. As wind turbines have become a significant source of electrical energy, the interactions between the turbines and the electric power network need to be studied more thoroughly than before. Especially, the behavior of the turbines in fault situations is of prime importance; simply disconnecting all wind turbines from the network during a voltage drop is no longer acceptable, since this would contribute to a total network collapse. These requirements have been a contributor to the increased role of simulations in the study and design of the electric drive train of a wind turbine. When planning a wind power investment, the selection of the site and the turbine are crucial for the economic feasibility of the installation. Economic feasibility, on the other hand, is the factor that determines whether or not investment in wind power will continue, contributing to green electricity production and reduction of emissions. In the selection of the installation site and the turbine (siting and site matching), the properties of the electric drive train of the planned turbine have so far been generally not been taken into account. Additionally, although the loss minimization of some of the individual components of the drive train has been studied, the drive train as a whole has received less attention. Furthermore, as a wind turbine will typically operate at a power level lower than the nominal most of the time, efficiency analysis in the nominal operating point is not sufficient. This doctoral dissertation attempts to combine the two aforementioned areas of interest by studying the applicability of time domain simulations in the analysis of the economicfeasibility of a wind turbine. The utilization of a general-purpose time domain simulator, otherwise applied to the study of network interactions and control systems, in the economic analysis of the wind energy conversion system is studied. The main benefits of the simulation-based method over traditional methods based on analytic calculation of losses include the ability to reuse and recombine existing models, the ability to analyze interactions between the components and subsystems in the electric drive train (something which is impossible when considering different subsystems as independent blocks, as is commonly done in theanalytical calculation of efficiencies), the ability to analyze in a rather straightforward manner the effect of selections other than physical components, for example control algorithms, and the ability to verify assumptions of the effects of a particular design change on the efficiency of the whole system. Based on the work, it can be concluded that differences between two configurations can be seen in the economic performance with only minor modifications to the simulation models used in the network interaction and control method study. This eliminates the need ofdeveloping analytic expressions for losses and enables the study of the system as a whole instead of modeling it as series connection of independent blocks with no lossinterdependencies. Three example cases (site matching, component selection, control principle selection) are provided to illustrate the usage of the approach and analyze its performance.

From women to gender: a diachronic exploration of participant representation in texts from the United Nations

De förändrade ansatserna inom feministisk utvecklingsekonomi för med sig nya sätt att tala om kvinnor, män och utveckling. Genom att analysera texter skrivna inom området feministisk ekonomi från 1960-talet fram till början av 2000-talet dokumenterar den föreliggande studien på vilket sätt språket hos textproducenter inom utvecklingsekonomi konstituerar och är beroende av dessa skribenters inställning till utvecklingsfrågor och till kvinnor och män. Analysen fokuserar på hur aktiverings- och passiveringsprocesser används i representationen av de två huvuddeltagarna, kvinnor och män, hur begreppet genus introduceras och hur utvecklingsfrågor förändras genom ansatser, över tid och mellan genrer. Den teoretiska ramen sträcker sig över olika discipliner: systemisk funktionell grammatik och kritisk diskursanalys, men även organisatorisk diskursanalys och utvecklingsstudier. Texterna som valts för analysen härstammar från tre olika källor: planer från världskvinnokonferenserna organiserade av Förenta Nationerna, resolutioner om kvinnor och utveckling antagna av Förenta Nationernas generalförsamling samt handlingsplaner för kvinnor och utveckling författade av Förenta Nationernas livsmedels- och jordbruksorganisation FAO. Den lingvistiska analysmetoden bygger på det system av roller och sätt att representera deltagare som utvecklats av Halliday och Van Leeuwen. För varje årtionde och varje genre granskar studien förändringarna i processtyper och deltagarroller, samt förändringen av fokus på kvinnorelaterade frågor och konceptualiseringen av genus. Den kvantitativa analysen kompletteras och förstärks av en detaljerad analys av textfragment från olika tidpunkter och ansatser. Studiens resultat är av grammatisk och lexikal natur och de är relaterade till genus, genre och tid. Studien visar att aktiveringsprocesserna är betydligt talrikare än passiveringsprocesserna i representationen av kvinnor. En bättre förståelse av deltagarrepresentation uppnås dock via en omgruppering av de grammatiska processerna i identifierande, aktiverande och riktade processer. Skiftet från fokus på kvinnor till fokus på genus är inte så mycket en förändring av processerna som representerar deltagarna, utan mer en förändring av retoriken i ansatserna och deras fokus: från integration av kvinnor till kvinnors empowerment, från kvinnors situation till genusrelationer, från brådskande tillägg till social konflikt och samarbete.

A Foucauldian Analysis of Power and Representation in an Attempt to Run a Photovoice Project with Youth

This project evolved out of a search for ways to conduct research on “others” in a way that does not exploit, stigmatize or misrepresent their experience. This thesis is an ethnographic study in leisure research and youth work and an experiment in running a photovoice project. Photovoice is a participatory visual method that embodies the emancipatory ideal of empowering others through self-representation. The literature on photovoice lacks a comprehensive discussion on the complexity of power and representation. Postmodern theorists have proposed that participatory methods are not benign and that initiatives are acts of power in themselves that produce effects (Cook & Kothari, 2001). A Foucauldian analysis of power is used to deconstruct the researcher’s practice and reflect on why and how youth are “engaged”. This project seeks to embrace the principle of working “with” others, but also work from a postmodern perspective that acknowledges power and representation as ongoing problems.