The total amount of frequency deviations have during the last decade increased exponentially in the Nordic synchronous power system. The transmission system operators have therefore decided to implement load frequency control as a new automatic control system to stem these frequency deviations. The aim of this feasibility study is to analyse the effects of an LFC implementation in Swedish hydropower stations by using a more dynamic river governing. The method chosen to analyse the effects of LFC-governing was to create a Matlab Simulink hydropower station library including dynamic modules for rivers and turbine governors. The library is then used to create a river reach that is implemented in an ENTSO-E model for the Nordic frequency reserves. The governing of the river uses economical dispatch theory to optimally distribute a LFC setpoint signal from the ENTSO-E model to the different hydropower stations. Results show that the developed method has a future potential to create more frequency controlled reserves. By creating a central governing unit it was possible to govern frequency controlled reserves over an entire river reach under certain scenarios, but there are still many obstacles to overcome before an actual implementation. The method does however show both the possibilities and drawback of frequency controlled reserves in cascade coupled hydropower systems.

The Deep Brain Stimulation (DBS) is an invasive therapy that alleviates the symptoms of several neurological disorders by electrically stimulating specific regions of the brain, generally within the basal ganglia. Until now Medtronic DBS system is the only approved by the Food and Drug Administration, nevertheless European and Australian countries  have recently approved St. Jude DBS systems to treat Parkinson’s disease and related movement disorders.      Traditionally, voltage-controlled stimulation (the type of systems provided by Medtronic) has been used and clinicians are familiar with its settings; however the knowledge about systems based in current-controlled stimulation (St. Jude systems) is rather scarce. One of the key factors for a successful therapy is the optimal selection of the electrical parameters for stimulation. Due to the critical zone where the surgery is performed, modeling and simulations of DBS systems have been extensively used to observe how the electric field is distributed in the brain tissue and ultimately to help the clinicians to select the best parameters.      In this thesis two finite element models of the DBS systems mentioned above have been developed; five examinations were designed, based on the physical and electrical differences between the systems, to observe and quantitatively compare the electric field distribution.     The aim of this thesis was to investigate the differences between two representative models of each company but moreover to contribute with information regarding current-controlled stimulation. The results obtained are expected to be useful for further investigations where the magnitude and distribution of the electric field generated by this type of electrodes are needed.

The biomaterial component of a tissue engineered device has been shown to enhance the immune response to a co-delivered model shed antigen. The purpose of this research was to investigate in vivo the differential level of the immune response toward different forms of the biomaterial. A model shed antigen, ovalbumin (OVA), was incorporated into polymeric biomaterial carriers made of 50:50 poly(lactic-co-glycolic acid) (PLGA) in the form of microparticles (MP) or scaffolds (SC). These MP and SC biomaterial carrier vehicles with incorporated antigen were then injected or implanted, respectively, into C57BL6 mice to investigate the differential level of the immune response towards OVA controlled release from PLGA MP and PLGA SC. For each polymeric carrier, the resulting time-dependent systemic humoral immune response towards the incorporated OVA, the OVA-specific IgG concentration and isotypes (IgG2a or IgG1, indicating a predominant Th1 or Th2 response, respectively) were determined using ELISA. To assess the differential level of the immune response depending on the form of PLGA, the total amounts of polymer and OVA delivered were kept constant as well as the release rate of OVA. The in vitro protein release kinetics were studied for both PLGA MPs and PLGA scaffolds to examine the release rate of OVA from the polymeric carriers. The level of the humoral immune response was higher and sustained for OVA released from PLGA SC which were implanted with associated tissue damage, and lower and transient when the same amount of polymer and OVA were delivered from PLGA MP, which were minimally invasively delivered by injection. This immune response was primarily Th2 helper T cell-dependent as exemplified by the predominance of IgG1 isotype, although for the strong adjuvant, Complete Freunds adjuvant (CFA), and PLGA SC carriers the anti-OVA IgG2a isotype levels were also significant, potentially indicating both a Th2 and Th1 response. The PLGA SC and PLGA MP exhibited similar protein release kinetics, releasing similar amounts of OVA at each time point. Each carrier incubated contained the same ratio of OVA to polymer. In vitro protein release kinetics experiments suggest that the rate of release of OVA from PLGA SC and PLGA MP was similar, and therefore the enhanced immune response induced by PLGA SC is most likely due to danger signals from implantation which primed the system for an enhanced immune response and not from a difference in concentration of OVA released from the carriers.

The goal of this work is to increase the current understanding of Controlled Radical Polymerizations (CRPs) in two areas. Progressing closer towards employing an aqueous system, specifically miniemulsion, to produce poly(vinyl acetate) via reversible addition fragmentation chain transfer (RAFT) chemistry constitutes the first part of this goal. Presented are the results of miniemulsion polymerizations using both water and oil-soluble initiators. Limiting conversions in both are examined and explained in terms of radical loss. The second part of the goal is to further the understanding of the nature of the RAFT/miniemulsion system when employed in continuous tubular reactors. The development of the recipe using mixed surfactants, the results of styrene homopolymerizations in batch and tube, and the results of a chain extension experiment demonstrating the living nature of the chains formed in the tubular reactor are presented. Kinetic anomalies are addressed, as well as polydispersity (PDI) differences between batch and tube. Flow phenomenon and their influence on residence time distribution and by implication the polydispersity of the polymer formed are offered as explanations for the variance in PDI and are subsequently quantified. A model of RAFT in laminar flow is presented and the results and implications are discussed in general terms. The flow profile of the reactor is examined using a tracer technique developed specifically for this system. Experiments are presented directly relating the residence time distribution to the polydispersity of the polymer. Transient behavior of the reactor in isolated plug flow is explained in terms of initiator loss. Both experimental data and a model are used to support this hypothesis. Finally, conclusions and implications are presented and unanswered questions and the ideas for future work that they generated are addressed.

Thin-film niobium mechanically controlled break junctions and resistively shunted niobium mechanically-controlled break junctions were developed and successfully microfabricated. Using these devices, high-stability atomic size contacts were routinely produced and investigated both in the normal and superconducting states. Investigations of the two-level conductance fluctuations in the smallest contacts allowed the calculation of their specific atomic structure. Embedding resistive shunts close to the superconducting atomic-sized junctions affected the coherence of the electronic transport. Finally, point contact spectroscopy measurements provide evidence of the interaction of conduction electrons with the mechanical degrees of freedom of the atomic-size niobium contacts.

The grid voltage is normally required to avoid transient current of the inverter due to asynchronously grid-paralleling connection. This paper presents a seamless transition method to allow the inverter to connect to the grid at any time with no requirement of the grid voltage. The control of the inverter consists of the droop control and the riding-through control. In the droop-controlled mode, the inverter can connect to the utility and supply power according to its rated capacity. On the other hand, the riding-through mode is proposed to suppress the transient current due to asynchronous paralleling. In this mode, the zero-current control is realized to reduce transient current and a phase-locked loop is designed to correct the angle of the inverter output voltage. In addition, the virtual inductance is implemented to improve transient current resulting from the mode transition back to the droop control mode. Design considerations of the seamless transition method are provided and test results are conducted to verify its effectiveness.

A high efficiency driver is designed for light emitting diode (LED) street lamps in the thesis. The main power conversion circuit employs a phase-controlled rectifier to convert the power from the ac mains of 110/220 V, 60 Hz directly into a dc source, providing the required output current for the street lamps formed by arrayed high brightness white LEDs. The phase-controlled rectifier of the LED driver circuit can be a conventional semi-converter or a rectifier with symmetrical phase control, which makes use of thyristors and power transistors, respectively, to regulate the LED current by means of adjusting the conduction angles in a cycle of the ac line. The phase-controlled rectifiers may exclude the use the bulky electrolyte capacitor with acceptable variation in the chromaticity and the color temperature. Operating at the low frequency, the phase-controlled rectifiers can avoid the problems of electromagnetic interference caused by high-frequency switching and adopt low cost power switches. Furthermore, a relatively high power factor can be achieved when the line source voltage varies within a small allowable range. The research is targeted to a design of a 200 W LED street lamp. To facilitate the changes of the control functions and circuit parameters, the control circuit is realized with a microcontroller. In addition, over-voltage/current protections can be included easily. Experimental results demonstrate that the phase-controlled rectifiers with appropriately designated circuit parameters can approach a power factor of 0.92 and a circuit efficiency of 93% at the rated output.

Presence of cultural refuse has long posed a serious challenge to meaningful geological interpretation of near surface controlled–source electromagnetic data (CSEM). Cultural refuse, such as buried pipes, underground storage tanks, unexploded ordnance, is often highly conductive and magnetically permeable. Interpretation of the CSEM response in the presence of cultural noise requires an understanding of electromagnetic field diffusion and the effects of anomalous highly conductive and permeable structures embedded in geologic media. While many numerical techniques have been used to evaluate the response of three dimensional subsurface conductivity distributions, there is a lack of approaches for modeling the EM response incorporating variations in both subsurface conductivity σ and relative permeability μr. In this dissertation, I present a new three dimensional edge–based finite element (FE) algorithm capable of modeling the CSEM response of buried conductive and permeable targets. A coupled potential formulation for variable μ using the vector magnetic potential A and scalar electric potential V gives rise to an ungauged curl–curl equation. Using reluctivity (v=1/mu ), a new term in geophysical applications instead of traditional magnetic susceptibility, facilitates a separation of primary and secondary potentials. The resulting differential equation is solved using the finite element method (FEM) on a tetrahedral mesh with local refinement capabilities. The secondary A and V potentials are expressed in terms of the vector edge basis vectors and the scalar nodal basis functions respectively. The finite element matrix is solved using a Jacobi preconditioned QMR solver. Post processing steps to interpolate the vector potentials on the nodes of the mesh are described. The algorithm is validated against a number of analytic and multi dimensional numeric solutions. The code has been deployed to estimate the influence of magnetic permeability on the mutual coupling between multiple geological and cultural targets. Some limitations of the code with regards to speed and performance at high frequency, conductivity and permeability values have been noted. Directions for further improvement and expanding the range of applicability have been proposed.

Nanoporous materials have attracted tremendous interest, investment and effort in research and development due to their potential applications in various areas such as membranes, catalysis, sensors, delivery, and micro devices. Controlling a nanoporous material’s microstructure is of great interest due to the strong influence on efficiency and performance. For particles, microstructure refers to particle size, shape, surface morphology, and composition. When discussing thin films, microstructure includes film thickness, crystal orientation and grain boundaries. In this respect, we focus to develop novel methods for the synthesis and characterization of nanoporous materials and their films, which are capable of controlling the microstructure of material. This dissertation is composed of two main sections and each explores the fabrication of a different nanoporous material: 1) A simple fabrication method for producing oriented MFI zeolite membranes with controlled thickness, orientation, and grain boundary; 2) A microfluidic synthesis of ordered mesoporous silica particles with controllable size, shape, surface morphology, and composition. The first section of this dissertation demonstrates a simple and commercially viable method termed the micro-tiles-and-mortar method to make continuous b-oriented MFI membranes with controlled membrane microstructure. This simple method allows for control of the thickness of the membrane by using plate-like seed crystals with different thicknesses along the b-axis (0.5 μm to 2.0 μm), as well as to manipulate the density and structure of grain boundaries. Microstructural effects of silicalite-1 membranes on the gas separation are investigated by measuring the permeation and separation for xylene isomers. In the second section of this dissertation, a new synthesis method for the ordered mesoporous silica particles with controllable microstructure is demonstrated. This novel method combines a microfluidic emulsification technique and nonaqueous inorganic synthesis with a diffusion-induced self-assembly (DISA). The systematic control of the particle microstructure such as size, shape, and surface morphology is shown by adjusting microfluidic conditions.

Because of IC technology evolution and the increase of market demand, the communication industry grows vigorously in recent years. The voltage-controlled oscillator plays a key role in the RF transceiver and provides oscillation signals needed for upconversin and downconvertion. Usually, we separate the signals into I/Q channels for modulation and demodulation in upconversin and downconvertion. Because the quality of the local oscillator influences the performance of communication system, designing a voltage-controlled oscillator that can provide two identical signals in accurate quadrature is necessary. In this thesis, a new quadrature voltage-controlled oscillator is presented. We use two identical relaxation oscillators with adjustable Schmitt triggers to construct the cross-coupled architecture. This oscillator has accurate ( <1¢X) and stable quadrature outputs which are independent of operating frequency and process variations. This oscillator circuit is fabricated in TSMC 0.35£gm CMOS Mixed-Signal process provided by National Chip Implementation Center (CIC). Our design is verified by simulation and measurement results.