In this thesis a FIR filter generator has been designed. The program generates FIR filters in the form of VHDL-files. Four different filter structures have been implemented in the generator, Direct Form (DF), Differential Coefficients Method (DCM), polyphase filters and (2-by-2) filters. The focus of the thesis was to implement filter structures that create FIR filters with as low power consumption and area as possible. The generaterator has been implemented i C++. The C++ program creates text-files with VHDL-code. The user must then compile and synthesize the VHDL-files. The program uses an text-file with the filter coefficients as input.

The non-overlapping clock signal generator circuits are key elements in switched capacitor circuits since non-overlapping clock signals are generally required. Non-overlapping clock signals means signals running at the same frequency and there is a time between the pulses that none of them is high. This time (when both pulses are logic 0) takes place when the pulses are switching from logic 1 to logic 0 or from logic 0 to logic 1. In this thesis this type of clock signal generators are analyzed and designed for different requirements on the switched capacitor (S/C) circuits. Different analytical models for the delay in CMOS inverters are studied. The clock generators for digital circuits based on phase-locked loop and delay-locked loop are also studied. An algorithm, which can automatically size the non-overlapping clock generator circuits, was implemented.

Generating a single order statistic without generating the full sample can be an important task for simulations. If the density and the CDF of the distribution are given it is no problem to compute the density of the order statistic. In the main theorem it is shown that the concavity properties of that density depend directly on the distribution itself. Especially for log-concave distributions all order statistics have log-concave distributions themselves. So recently suggested automatic transformed density rejection algorithms can be used to generate single order statistics. This idea leads to very fast generators. For example for the normal and gamma distribution the suggested new algorithms are between 10 and 60 times faster than the algorithms suggested in the literature. (author's abstract) / Series: Preprint Series / Department of Applied Statistics and Data Processing

When more induction generator based wind farms are integrated into the power system, the system voltage dips and stability problems may arise due to the draw of reactive power by induction generators. The power system short-circuit event induced wind turbine trips could result in power imbalance and lead to power system instability. This thesis studies the influence of two compensation techniques on the wind turbine low voltage ride-through (LVRT) capability. One of which is based on a parallel compensation by a static synchronous compensator (STATCOM), and the other one is a series compensation by a dynamic voltage restorer (DVR). In this study, Matlab tools and models are used to simulate an active-stall controlled fixed-speed induction generator connected to a power system. Two system configurations are used to simulate three phase faults and compare the improvement of wind turbine LVRT capability due to the two studied compensation techniques. Simulation results indicate that wind turbine compensated by DVR would have better LVRT performance than that by STATCOM in dealing with the low voltage situations due to system faults.

This thesis study presents the design, simulation, micro fabrication, and testing steps of microelectromechanical systems (MEMS) based electromagnetic micro power generators. These generators are capable of generating power using already available environmental vibrations, by implementing the electromagnetic induction technique. There are mainly two objectives of the study: (i) to increase the bandwidth of the traditional micro generators and (ii) to improve their efficiency at low frequency environmental vibrations of 1-100 Hz where most vibrations exist. Four main types of generators have been proposed within the scope of this thesis study. The first type of generator is mainly composed of 20 parylene cantilevers on which coils are fabricated, where the cantilevers are capable of resonating with external vibrations with respect to a stationary magnet. This generator has dimensions of 9.5&times / 8&times / 6 mm3, and it has been shown that 0.67 mV of voltage and 56 pW of power output can be obtained from a single cantilever of this design at a vibration frequency of 3.45 kHz. The second type generator aims to increase the bandwidth of the traditional designs by implementing cantilevers with varying length. This generator is sized 14&times / 12.5&times / 8 mm3, and the mechanical design and energy generation concept is similar to the first design. The test results show that by using 40 cantilevers with a length increment of 3 &amp / #956 / m, the overall bandwidth of the generator can be increased to 1000 Hz. It has also been shown that 9 mV of constant voltage and 1.7 nW of constant power output can be obtained from the overall device in a vibration frequency range of 3.5 to 4.5 kHz. The third type is a standard large mass coil type generator that has been widely used in the literature. In this case, the generator is composed of a stationary base with a coil and a magnet-diaphragm assembly capable of resonating with vibrations. The fabricated device has dimensions of 8.5&times / 7&times / 2.5 mm3, and it has been considered in this study for benchmarking purposes only. The test results show that 0.3 mV of voltage and 40 pW of power output can be obtained from the fabricated design at a vibration frequency of 113 Hz. The final design aims to mechanically up-convert low frequency environmental vibrations of 1-100 Hz to a much higher frequency range of 2-3 kHz. This type of generator has been implemented for the first time in the literature. The generator is composed of two parts / a diaphragm-magnet assembly on the top, and 20 cantilevers that have coils connected in series at the base. The diaphragm oscillates by low frequency environmental vibrations, and catches and releases the cantilevers from the tip points where magnetic nickel (Ni) areas are deposited. The released cantilevers then start decaying out oscillations that is at their damped natural frequency of 2-3 kHz. It has been shown with tests that frequency up-conversion is realized in micro scale. The fabricated device has dimensions of 8.5&times / 7&times / 2.5 mm3, and a maximum voltage and power output of 0.57 mV and 0.25 nW can be obtained, respectively, from a single cantilever of the fabricated prototype at a vibration frequency of 113 Hz.

This thesis study presents the design, simulation, and fabrication of a low frequency electromagnetic micro power generator. This power generator can effectively harvest energy from low frequency external vibrations (1-100 Hz). The main objective of the study is to increase the efficiency of the previously proposed structure in METU-MEMS Center, which uses the frequency up-conversion technique to harvest energy from low frequency vibration. The proposed structure has been demonstrated by constructing several macro scale prototypes. In one of the constucted prototypes, the diaphragms are connected to a fixed frame via metal springs. The upper diaphragm having lower resonance frequency carries a magnet, and the lower diaphragm carries a hand wound coil and a magnetic piece for converting 6 Hz external vibrations up to 85 Hz, resulting a maximum voltage and power levels of 11.1 mV and 5.1 &micro / W, respectively. In an improved prototype, the metal springs are replaced with rubber ones, providing higher energy conversion efficiency and flexibility to tune the resonance frequency of both diaphragms to desired values. This prototype provides 104 &micro / W maximum power and 37.7 mV maximum voltage in response to vibration levels of 30 Hz. The proposed structure is also suitable to be realized by using microfabrication techniques. Hence, the structure to be microfabricated is studied and optimized for this purpose. When scaled to microelectromechanical dimensions, the expected maximum power and voltage from the 10 x 8.5 x 2.5 mm3 generator is 119 nW and 15.2 mV, respectively. A microfabrication process has also been designed for the proposed generator structure. According to this process, the structure consists of a stack of two pieces, each carrying different diaphragms. The diaphragms are made of parylene, and the coil and the magnetic piece are electroplated copper and nickel, respectively. As a result of this study, a new topology is proposed for harvesting energy at low frequency vibrations by the frequency up-conversion technique, and an efficiency improvement is expected with more than three orders of magnitude (119 nanoWatts output for the same size) compared to the study realized in our laboratory in converting low frequency (70-150 Hz) environmental vibrations to electrical energy.

This thesis presents the results of an experimental study that investigates the effects of steady vortex generator jets (VGJs) integrated to a low pressure turbine blade to control the laminar separation bubble occurring on the suction surface of the blade at low Reynolds numbers. The injection technique involves jets issued from the holes located near the suction peak of the test blade which is in the middle of a five-blade low speed linear cascade facility. Three injection cases are tested with different blowing ratio values ranging from low to high. Surface pressure and particle image velocimetry (PIV) measurements are performed. The results show that steady VGJ is effective in eliminating the laminar separation bubble. Also it is observed that to have fully developed attached boundary layer, blowing ratio should be chosen accordingly since a very thin separation zone still exists at low blowing ratios.

The purpose of this dissertation was to gain insight into spinal sensory regulation during locomotion. To this end, I developed a novel in vitro spinal cord-hindlimb preparation (SCHP) composed of the isolated in vitro neonatal rat spinal cord oriented dorsal-up with intact hindlimbs locomoting on a custom-built treadmill or instrumented force platforms. The SCHP combines the neural and pharmacological accessibility of classic in vitro spinal cord preparations with intact sensory feedback from physiological hindlimb movements. thereby expanding our ability to study spinal sensory function. I then validated the efficacy of the SCHP for studying behaviorally-relevant, sensory-modulated locomotion by showing the impact of sensory feedback on in vitro locomotion. When locomotion was activated by serotonin and N-methyl D-aspartate, the SCHP produced kinematics and muscle activation patterns similar to the intact rat. The mechanosensory environment could significantly alter SCHP kinematics and muscle activitation patterns, showing that sensory feedback regulates in vitro spinal function. I further demonstrated that sensory feedback could reinforce or initiate SCHP locomotion. Using the SCHP custom-designed force platform system, I then investigated how presynaptic inhibition dynamically regulates sensory feedback during locomotion and how hindlimb mechanics influence this regulation. I hypothesized that contralateral limb mechanics would modulate presynaptic inhibition on the ipsilateral limb. My results indicate that contralateral limb stance-phase loading regulates ipsilateral swing-phase sensory inflow. As contralateral stance-phase force increases, contralateral afferents act via a GABAergic pathway to increase ipsilateral presynaptic inhibition, thereby inhibiting sensory feedback entering the spinal cord. Such force-sensitive contralateral presynaptic inhibition may help preserve swing, coordinate the limbs during locomotion, and adjust the sensorimotor strategy for task-specific demands. This work has important implications for sensorimotor rehabilitation. After spinal cord injury, sensory feedback is one of the few remaining inputs available for accessing spinal locomotor circuitry. Therefore, understanding how sensory feedback regulates and reinforces spinally-generated locomotion is vital for designing effective rehabilitation strategies. Further, sensory regulation is degraded by many neural insults, including spinal cord injury, Parkinson's disease, and stroke, resulting in spasticity and impaired locomotor function. This work suggests that contralateral limb loading may be an important variable for restoring appropriate sensory regulation during locomotion.

Spinal cord injuries (SCI) sever communication between supraspinal centers and the central pattern generator (CPG) responsible for locomotion. Because the CPG is intact and retains the ability to initiate locomotor activity, it can be accessed electrically and pharmacologically. The goal of this thesis was to identify and characterize a novel spinal cord surface site along the sacral dorsal column (sDC) for electrically evoking locomotor-like activity in the neonatal rat spinal cord. Stimulation of the sDC robustly activated rhythmic left-right alternation in flexor-related ventral roots that was dependent on the activation of high-threshold C fiber afferents. The C fibers synapsed onto spinal neurons, which project to the lumbar segments as part of a pathway dependent on purinergic, adrenergic, and cholinergic receptor activation. In ventral roots containing only somatic efferents, rhythmic activity was rarely recruited. However, in ventral roots containing both autonomic and somatic efferents, sacral dorsal column stimulation recruited autonomic efferent rhythms, which subsequently recruited somatic efferent motor rhythms. The efferent rhythms revealed a half-center organization with very low stimulation frequencies, and the evoked alternating bursts entrained to the stimuli. Similar entrainment was seen when sDC stimuli were applied during ongoing neurochemically-induced locomotor rhythms. The rhythmic patterns evoked by sDC stimulation operated over a limited frequency range, with a discrete burst structure of fast-onset, frequency-independent peaks. In comparison, neurochemically-induced locomotor bursts operated over a wide frequency range and had slower time to peaks that varied with burst frequency. The overall findings support the discovery of an autonomic efferent pattern generator that is recruited by sacral visceral C fiber afferents. It is hoped that this research will advance the understanding of afferent activation of the lumbar central pattern generator and potentially provide insight useful for future development and design of neuroprosthetic devices.

<p>Locomotion is one of the most important behaviours and requires interaction between sensors at various levels of the nervous system and the limb muscles of an animal. The basic neural rhythm for locomotion in mammals has been shown to arise from local neural networks residing in the spinal cord and these networks are known as central pattern generators (CPGs). However, during the locomotion, these centres are constantly interacting with the sensory feedback signals coming from muscles, joints and peripheral skin receptors in order to adapt the stepping to varying environmental conditions. Conceptual models of mammalian locomotion have been constructed using</p><p>mathematical models of locomotor subsystems based on the abundance of neurophysiological evidence obtained primarily in the cat. Several aspects of locomotor control using the cat as an animal model have been investigated employing computer simulations and here we use the same approach to address number of questions or/and hypotheses related to rhythmic locomotion in quadrupeds. Some of the involve questions are, role of mechanical linkage during deafferented walking, finding inherent stabilities/instabilities of muscle-joint interactions during normal walking, estimating phase dependent controlability of muscle action over joints.</p><p>This thesis presents the basics of a biologically realistic model of mammalian locomotion and summarises methodological approaches in modelling quadruped locomotor subsystems such as CPGs, limb muscles and sensory pathways. In the first appended article, we extensively discuss the construction details of the three-dimensional computer simulator for the study of the hind leg neuro-musculo-skeletal-control system and its interactions during normal walking of the cat. The simulator with the walking model is programmed in Python scripting language with other supported open source libraries such as Open Dynamics Engine (ODE) for simulating body dynamics and OpenGL for three dimensional graphical representation. We have examined the</p><p>functionality of the simulator and the walking model by simulating deafferented walking. It was possible to obtain a realistic stepping in the hind legs even without sensory feedback to the two controllers (CPGs) for each leg. We conclude that the mechanical linkages between the legs also play a major role in producing alternating gait.</p><p>The use of simulations of walking in the cat for gaining insights into more complex interactions between the environment and the neuro-muscular-skeletal system is important especially for questions where a direct neurophysiological experiment can not be performed on a real walking animal. For instance, it is experimentally hard to isolate individual mechanisms without disrupting the natural walking pattern. In the second article, we introduce a different approach where we use the walking model to identify what control is necessary to maintain stability in the musculo-skeletal system. We show that the actions of most of the hindlimb muscles over the joints have an inherent stability during stepping, even without the involvement of proprioceptive feedback mechanisms. In addition, we observe that muscles generating movements in the ankle joint of the hind leg must be controlled by neural mechanisms, which may involve supraspinal structures, over the whole step cycle.</p>