Plasma synthetic jet actuators are investigated experimentally, in which the geometrical design of single dielectric barrier discharge (SDBD) plasma actuators is modified to produce zero-mass flux jets similar to those created by mechanical devices. The SDBD plasma actuator consists of two rectangular electrodes oriented asymmetrically and separated by a layer of dielectric material. Under an input of high voltage, high frequency AC or pulsed DC, a region of plasma is created in the interfacial air gap on account of electrical breakdown of the ambient air. A coupling between the electric field in the plasma and the neutral air near the actuator is introduced, such that the latter experiences a net force which results in a horizontal wall jet. This effect of the actuator has been demonstrated to be useful in mitigating boundary layer separation in aerodynamic flows. To increase the impact that a plasma actuator may have on the flow field, this research investigates the development and characterization of a novel flow control device, the plasma synthetic jet actuator, which tailors the residual air in the form of a vertical jet resembling conventional continuous and synthetic jets. This jet can be either three dimensional using annular electrode arrays, or nearly two dimensional using two rectangular strip exposed electrodes and one embedded electrode. Detailed measurements on the isolated plasma synthetic jet reveal that pulsed operation of the actuator results in the formation of multiple counterrotating vortical structures in the flow field. The output jet velocity and momentum are found to be higher for unsteady pulsing as compared to steady operation. In the case of flow over a flat plate, the actuator is observed to create a localized interaction region within which the baseline flow direction and boundary layer characteristics are modified. The efficiency of the actuator in coupling momentum to the neutral air is found to be related to the plasma morphology, pulsing frequency, actuator dimension, and input power. An analytical scaling model is proposed to describe the effects of varying the above variables on the output jet characteristics and actuator efficiency, and the experimental data is used for model validation.

A new approach to large-eddy simulation (LES) based on the use of explicit spatial filtering combined with backscatter forcing is presented. The forcing uses a discrete dynamical system (DDS) called the compressible ``poor man's'' Navier--Stokes (CPMNS) equations. This DDS is derived from the governing equations and is shown to exhibit good spectral and dynamical properties for use in a turbulence model. An overview and critique of existing turbulence theory and turbulence models is given. A comprehensive theoretical case is presented arguing that traditional LES equations contain unresolved scales in terms generally thought to be resolved, and that this can only be solved with explicit filtering. The CPMNS equations are then incorporated into a simple forcing in the OVERFLOW compressible flow code, and tests are done on homogeneous, isotropic, decaying turbulence, a Mach 3 compression ramp, and a Mach 0.8 open cavity. The numerical results validate the general filter-forcing approach, although they also reveal inadequacies in OVERFLOW and that the current approach is likely too simple to be universally applicable. Two new proposals for constructing better forcing models are presented at the end of the work.

This manuscript demonstrates the regularity and uniqueness of some geometric heat flows with critical nonlinearity. First, under the assumption of smallness of renormalized energy, several issues of the regularity and uniqueness of heat flow of harmonic maps into a unit sphere or a compact Riemannian homogeneous manifold without boundary are established. For a class of heat flow of harmonic maps to any compact Riemannian manifold without boundary, satisfying the Serrin's condition, the regularity and uniqueness is also established. As an application, the hydrodynamic flow of nematic liquid crystals in Serrin's class is proved to be regular and unique. The natural extension of all the results to the heat flow of biharmonic maps is also presented in this manuscript.

I studied how geology, land use and rainfall, correlated with peak flow responses in 110 headwater stream sites during a drought year. Highest discharges were observed in the most developed catchments and in the most poorly drained soils, but specific responses were variable depending on both geology and land disturbance. Redundancy analysis indicated that both surficial geology and land disturbance were important predictors of discharge and that rainfall was in general a poor predictor of discharge. I conclude that responses of headwater streams to individual storms are unpredictable from data generated using GIS, but increased peak flows occur associated with human development, mitigated by surficial geology. The headwater streams that are most vulnerable to flow alterations occur on poorly drained soils, and where urbanization tends to concentrate. Much greater attention to managing water is required if further degradation of stream ecosystems is to be prevented from our future land use.

River environments are complex and dynamic ecosystems, and provide valuable ecosystem services such as clean water. The species rich riparian vegetation performs many important ecosystem functions such as reducing erosion and filter inputs from upland areas. Regulated flow regimes have decreased riparian plant species richness, cover and plant performance. To restore the integrity of riparian ecosystems, mitigation measures such as re-regulation of water-level regimes toward more natural seasonal fluctuations may be needed. The aim of this study was to assess potential responses of riparian plants to changes in water-level regulation in run-of-river impoundments to better match natural flow regimes. The elevational extent of plant species on riverbanks of two run-of-river impoundments in the Ume River were surveyed and their probability of occurrence along the gradient of inundation duration was modelled and compared to their distribution in the free-flowing Vindel River. Most species showed similar tolerance to flooding in the Ume and Vindel Rivers. Changes in elevational extent in response to three simulated environmental flow regimes were predicted by using the relationship between plant occurrence and inundation duration. A simulated spring flood and low water levels during the latter part of the growing season is predicted to result in the largest increase in elevational extent, with increases of 70-80% for several riparian species. However, only 47% of the riverbanks along run-of-river impoundments in the Ume River is deemed to be suitable for plant establishment, since many riverbanks are steep and devoid of fine-grained substrate as a result of erosion. / Älvmiljöer utgör komplexa och dynamiska ekosystem som tillhandahåller värdefulla ekosystemtjänster så som rent vatten. Den artrika strandvegetation bidrar till många viktiga ekosystemsfunktioner som närings- och giftupptag och till minskad erosion. Vattenregleringen med förändrade flödesregimer har minskat artrikedom, täckningsgrad och tillväxt av strandväxter. För restaurering av strandekosystemen kan omreglering till mer naturliga säsongsvariationer i vattenståndet vara nödvändigt. Den här studien syftade till att förutsäga hur utbredningen av strandväxter längs stränder i vattenkraftsmagasin potentiellt skulle förändras vid användande av miljöanpassade flöden för att mer likna naturliga flödesregimer i outbyggda älvar. Jag undersökte växternas utbredning i höjdled på stranden längs två magasin i Umeälven och beräknade sannolikheten för varje arts förekomst längs strandens översvämningsgradient. Av de arter som förekom i både Umeälven och den närliggande, outbyggda Vindelälven jämfördes växternas utbredningsgränser i respektive älv. De flesta arterna uppvisade liknande översvämningstolerans i Umeälven och Vindelälven. För att förutsäga förändringar i utbredning som respons på tre olika simulerade miljöanpassade vattenståndsregimer, jämfördes arternas översvämningstolerans vid nuvarade vattenstånd med simulerade vattenståndsregimer. En simulerad vårflod och lågt vattenstånd under sensommaren förväntas ge de största responserna i artutbredning med ökningar på 70-80% för ett flertal strandväxter. Endast 47% av älvstränderna i magasinen i Umeälven bedöms vara lämpliga för växtetablering eftersom stora delar av strandsträckorna är branta och saknar finkornigt substrat till följd av erosion.

The focus of this thesis is the study of turbulent solid-liquid stirred suspensions, which are involved in many common unit operations in the chemical, pharmaceutical and food industries. The studies of two-phase flows present a big challenge to researchers due to the complexity of experiments; hence there is a lack of quantitative solid and liquid hydrodynamic measurements. Therefore, an investigation of turbulence modulation by dispersed particles on the surrounding fluid in stirred vessels has been carried out, via two-phase fluorescent Particle Image Velocimetry (FPIV) and micromixing experiments. The main property of interest has been the local dissipation rate, as well as root-mean-square (rms) velocities and turbulent kinetic energy (TKE) of the fluid. Initially a single-phase PIV study was conducted to investigate the flow field generated by a sawtooth (EkatoMizer) impeller. The purpose of this study was to gain insight into various PIV techniques before moving on to more complex two-phase flows. Subsequently stereo-, highspeed and angle-resolved measurements were obtained. The EkatoMizer formed a good case study as information regarding its hydrodynamics is not readily available in literature, hence knowledge has been extended in this area. An analysis of the mean flow field elucidated the general structure of fluid drawn into the impeller region axially and discharged radially; the latter characterised the impeller stream. The radial rms velocity was considered to represent best the system turbulence, even though the tangential rms velocity was greater close to the blade; however the radial component was more prevalent in the discharge stream. Due to differences in rms velocities, TKE estimates obtained from two and three velocity components deviated, being greater in the latter case. Integral (1-D and 2-D) length scales were overestimated by the quantity W / 2 in the impeller region. Ratios of longitudinal-to-lateral length scales also indicated flow anisotropy (as they deviated from 2:1). The anisotropy tensor showed that the flow was anisotropic close to the blade, and returned to isotropy further away from the impeller. Instantaneous vector plots revealed vortices in the discharge stream, but these were not associated with flow periodicity. Alternatively, the vortex structures were interpreted as low frequency phenomena between 0-200 Hz; macro-instabilities were found to have a high probability of occurrence in the discharge stream. Dissipation is the turbulent property of most interest as it directly influences micromixing processes, and its calculation is also the most difficult to achieve. Its direct determination from definition requires highly resolved data. Alternative methods have been proposed in the literature, namely dimensional analysis, large eddy simulation (LES) analogy and deduction from the TKE balance. All methods were employed using 2-D and 3-D approximations from stereo-PIV data. The LES analogy was deemed to provide the best estimate, since it accounts for three-dimensionality of the flow and models turbulence at the smallest scales using a subgrid scale model. (Continues...).

Tensions exist in the way that the European Union is conceptualised. How do we reconcile the persistence of a Europe of fragmented nation-states and the European integration project based on the principle of free movement? This duality is indicative of different geographical visions: between space defined as places and space defined as unifying flows. While places tend to be associated with fixed territories and borders, it is argued that complex global flows and connections may disrupt such notions. Addressing these theoretical tensions, this thesis examines transnational frameworks for discussing the reconfiguration of borders and spaces within the European Union. The aim of this research is to explore the extent to which European Union citizens, with freedom of movement, experience mobility between member states in a frictionless manner. The thesis adopts a “bottom-up” approach of migrants’ experiences and perceptions of internal borders, as barriers or opportunities to their movement and settlement. This is illustrated through the case of Britons resident in France. The thesis draws on data generated through qualitative methods, including fifty-three in-depth interviews undertaken in an ethnographic setting. The case study demonstrates how a frictionless European space does not exist for ordinary European Union citizens, for a variety of political, legal, economic and socio-cultural reasons. The analysis reveals how Britons recreate (national) state borders, by adapting to French politico-legal structures, and identifying boundaries between “us” and “them”. The thesis also identifies how transnational spaces are created through immigrants’ social networks. By exploring the everyday lives of intra-EU migrants, the thesis contributes to literature on British migrants in France, and provides an original contribution to studies of EU integration, focused on ordinary citizens on the move.

On considère un écoulement compressible bidimensionnel, autour d'une cavité ouverte. Des d'instabilité, auto-entretenues par l'effet de rétroaction de l'écrasement de la couche de cisaillement sur le bord aval de la cavité, génèrent des émissions acoustiques qu'il faut réduire. Des simulations numériques directes (DNS) permettent d'obtenir, avec ou sans actionnement, un modèle précis de l'écoulement. A partir des champs issus de la simulation, des décompositions orthogonales de modes propres (POD) sont proposées pour bâtir, par projection de Galerkin sur les équations isentropiques, des modèles d'ordre réduit non linéaires en prenant en compte l'actionnement (le contrôle). Pour éviter la divergence temporelle, les coefficients du système dynamique non forcé sont calibrés par diverses approches originales dont une basée sur la sensiblité modale. A partir du système dynamique forcé par un actionnement multifréquentiel (présent aussi dans les DNS), un contrôle en boucle fermée linéaire quadratique gaussien est proposé sur un système linéarisé. La reconstruction de l'état est basée sur une estimation stochastique linéaire sur 6 points de pression. Le contrôle optimal obtenu s'avère être périodique à la fréquence du second mode de Rossiter, qui est exactement celles des instabilits auto-entretenues dans la cavité. Par introduction de ce contrôle dans les simulations numériques directes, nous avons obtenu une réduction du bruit (faible) sur la fréquence du contrôle. / We consider a two dimensional compressible flow around an open cavity. The Flow around a cavity is characterised by a self-sustained mechanism in which the shear layer impinges on the downstream edge of the cavity resulting in an acoustic feedback mechanism which must be reduced. Direct Numerical Simulations (DNS) of the flow at a representative Reynolds number has been carried to obtain pressure and velocity fields, both for the case of unactuated and multi frequency actuation. These fields are then used to extract energy ranked coherent structures also called as the Proper Orthogonal Decomposition (POD) modes. A Reduced Order Model is constructed by a Galerkin projections of the isentropic compressible equations. The model is then extended to include the effect of control. To avoid the divergence of the model while integrating in time various calibration techniques has been utillized. A new method of calibration which minimizes a linear functional of error, based on modal sensitivity is proposed. The calibrated low order model is used to design a feedback control of the Linear Quadratic Gaussian (LQG) type, coupled with an observer. For the experimental implementation of the controller, a state estimate based on the observed pressure measurements at 6 different locations, is obtained through a Linear Stochastic Estimation (LSE). The optimal control obtained is periodic with a frequency corresponding to the second Rossiter mode of the cavity. Finally the control obtained is introduced into the DNS to obtain a decrease in spectra of the cavity acoustic mode.

The West Elk Breccia has been studied since the late 1800’s with many interpretations regarding its origin. One unrecognized possibility is that parts of it are debris-avalanche deposits. This study has recognized evidence for this interpretation at three scales: volcano scale, outcrop scale, and intra-outcrop scale. At the volcano scale, a scarp in the old volcano reveals underlying Mesozoic bedrock, suggesting sector collapse. At the outcrop scale, megablocks of the original edifice, up to hundreds of meters in length, have atypical orientations and are surrounded by a gravel matrix. At the intra-outcrop scale, jigsaw-fit fracturing and rip-up clasts are common in distal deposits, which are documented in analogous debris-avalanche deposits. Similar to the debris-avalanche deposit at Mt. Shasta, medial-to-distal-matrix volcaniclast content decreases by 23%; Paleozoic and Mesozoic clasts increase by 5%; and the size of megablocks decreases. The geochemical and petrographic signatures reveal breccia blocks composed of pyroxene-andesite, a more silicic matrix facies, and the andesitic-to-dacitic East Elk Creek Tuff, all compositions that corroborate previous work on this northern extension of the San Juan volcanic field. Measured sections in the 100-km² study area allow for an estimation of total formation volume of approximately 8.5 km3.

The goal of this study is to quantify the transient performance of microfabricated superhydrophobic surfaces when used in underwater applications. A mathematical framework is developed and used to predict the stability, longevity, and drag reduction benefits of submerged superhydrophobic surfaces with two- or three-dimensional micro-textures. In addition, a novel design is proposed to improve the drag-reduction benefits of lubricant-infused surfaces, by placing a layer of trapped air underneath the lubricant layer. The new design is referred to as lubricant–infused surfaces with trapped air, and it is designed to eliminate the long-lasting longevity problem of submerged superhydrophobic surfaces. The effectiveness of liquid-infused surface with trapped air design was examined via numerical simulation, and it was found to outperform its liquid-infused surface counterpart by about 37%.