Recent technological advances have allowed silicon (Si) semiconductor technology to approach the theoretical limits of the Si material; however, power device requirements for many applications are at a stage that the present Si-based power devices cannot handle. The requirements include higher blocking voltages, switching frequencies, efficiency, and reliability. Material technologies superior to Si are needed for future power device developments. Silicon Carbide (SiC) based semiconductor devices offer one such alternative. SiC based power devices exhibit superior properties such as very low switching losses, fast switching behavior, improved reliability and high temperature operation capabilities. Power factor correction stage of power supplies is identified as an area where application of these devices would prove advantageous. In this thesis a high performance, high efficiency, SiC based power factor correction stage is discussed. The proposed topology takes advantage of the superior properties of SiC semiconductor based devices and the reduced number of devices that the dual boost power factor correction topology requires to achieve high efficiency, small size and better performance at high temperature. In addition to this analysis of SiC based power devices is carried out to study their characteristics and performance.

Artifacts caused by head motion are a substantial source of error in fMRI that limits its use in neuroscience research and clinical settings. Real-time scan-plane correction by optical tracking has been shown to correct slice misalignment and non-linear spin-history artifacts, however residual artifacts due to dynamic magnetic field non-uniformity may remain in the data. A recently developed correction technique, PLACE, can correct for absolute geometric distortion using the complex image data from two EPI images, with slightly shifted k-space trajectories. We present a correction approach that integrates PLACE into a real-time scan-plane update system by optical tracking, applied to a tissue-equivalent phantom undergoing complex motion and an fMRI finger tapping experiment with overt head motion to induce dynamic field non-uniformity. Experiments suggest that including volume by volume geometric distortion correction by PLACE can suppress dynamic geometric distortion artifacts in a phantom and in vivo and provide more robust activation maps.

Artifacts caused by head motion are a substantial source of error in fMRI that limits its use in neuroscience research and clinical settings. Real-time scan-plane correction by optical tracking has been shown to correct slice misalignment and non-linear spin-history artifacts, however residual artifacts due to dynamic magnetic field non-uniformity may remain in the data. A recently developed correction technique, PLACE, can correct for absolute geometric distortion using the complex image data from two EPI images, with slightly shifted k-space trajectories. We present a correction approach that integrates PLACE into a real-time scan-plane update system by optical tracking, applied to a tissue-equivalent phantom undergoing complex motion and an fMRI finger tapping experiment with overt head motion to induce dynamic field non-uniformity. Experiments suggest that including volume by volume geometric distortion correction by PLACE can suppress dynamic geometric distortion artifacts in a phantom and in vivo and provide more robust activation maps.

Two-photon calcium imaging (TPCI) is a functional neuroimaging technique that simultaneously reveals the function of small populations of cells as well as the structure of surrounding brain tissue. These unique properties cause TPCI to be increasingly popular for experimental basic neuroscience. Unfortunately, methodological development for data processing has not kept pace with experimental needs. I address this lack by developing and testing new methodology for several key tasks. Specifically, I address two primary analysis steps which are nearly universally required in early data processing: region of interest segmentation and motion correction. For each task I organize the sparse existing literature, clearly define the requirements of the problem, propose a solution, and evaluate it on experimental data. I develop MaSCS, an automated adaptable multi-class segmentation system that improves with use. I carefully define and describe the impact of motion artifacts on imaging data, and quantify the effects of standard and innovative motion correction approaches. Finally, I apply my work on segmentation and motion correction to explore one scientific target, namely discovering correlation-based cell clustering. I show that estimating such correlation-based clustering remains an open question, as it is highly sensitive to motion artifacts, even after motion correction techniques are applied. The contributions of this work include the organization of existing resources, methodological advances in segmentation, motion correction and clustering, and the development of prototype analysis software.

Quantum computing offers the potential for efficiently solving otherwise classically difficult problems, with applications in material and drug design, cryptography, theoretical physics, number theory and more. However, quantum systems are notoriously fragile; interaction with the surrounding environment and lack of precise control constitute noise, which makes construction of a reliable quantum computer extremely challenging. Threshold theorems show that by adding enough redundancy, reliable and arbitrarily long quantum computation is possible so long as the amount of noise is relatively low---below a ``threshold'' value. The amount of redundancy required is reasonable in the asymptotic sense, but in absolute terms the resource overhead of existing protocols is enormous when compared to current experimental capabilities. In this thesis we examine a variety of techniques for reducing the resources required for fault-tolerant quantum computation. First, we show how to simplify universal encoded computation by using only transversal gates and standard error correction procedures, circumventing existing no-go theorems. The cost of certain error correction procedures is dominated by preparation of special ancillary states. We show how to simplify ancilla preparation, reducing the cost of error correction by more than a factor of four. Using this optimized ancilla preparation, we then develop improved techniques for proving rigorous lower bounds on the noise threshold. The techniques are specifically intended for analysis of relatively large codes such as the 23-qubit Golay code, for which we compute a lower bound on the threshold error rate of 0.132 percent per gate for depolarizing noise. This bound is the best known for any scheme. Additional overhead can be incurred because quantum algorithms must be translated into sequences of gates that are actually available in the quantum computer. In particular, arbitrary single-qubit rotations must be decomposed into a discrete set of fault-tolerant gates. We find that by using a special class of non-deterministic circuits, the cost of decomposition can be reduced by as much as a factor of four over state-of-the-art techniques, which typically use deterministic circuits. Finally, we examine global optimization of fault-tolerant quantum circuits. Physical connectivity constraints require that qubits are moved close together before they can interact, but such movement can cause data to lay idle, wasting time and space. We adapt techniques from VLSI in order to minimize time and space usage for computations in the surface code, and we develop a software prototype to demonstrate the potential savings.

In young healthy adults, characteristic obstacle avoidance reflexes (stumble corrective) were elicited with electrical stimulation during walking that were dependent on the anatomical location of cutaneous afferents stimulated (sole versus dorsum of the foot). We previously demonstrated an age-related erosion of these stumble corrective responses when the perturbation was applied to the dorsum of the foot. However, it is unknown whether similar age-related reflex erosion is present with stimulation to the sole of the foot. The purpose of this study was to identify age-dependent differences in stumbling reactions to electrically evoked stimulation of the tibial nerve at the ankle during walking in healthy young (19-39) and older adult (70 years and older) groups. Electromyograms (EMG) of the tibialis anterior (TA), soleus (SOL), medial gastrocnemius (MG), biceps femoris (BF) and vastus lateralis (VL) were recorded along with gait kinematics including angular displacement and velocity at the ankle and knee joint as well as toe clearance relative to the walking surface. The main finding of this study was the significant erosion of the kinematic and EMG stumbling reactions seen in the older adults compared to the young. Specifically, during mid-swing phase, there was reduced peak toe clearance and significantly smaller amplitudes in ankle dorsiflexion and knee flexion angular displacement as well as absent responses in TA and MG in older adults compared to the young. Further, these degraded responses were superimposed on altered mid-swing phase kinematics during unstimulated walking in the older adults showing reduced toe clearance, knee flexion and increased ankle dorsiflexion compared to the young. This combination of degraded reflexes and altered unstimulated kinematics resulted in significantly reduced toe clearance in the older adults and could suggest that these adults are in the prodromal stage of fall risk. / Graduate / 0566

No description available.

This thesis work focuses on the study and improvement of single-stage power factor correction techniques. The generalized structures of the present pulse-width-modulation (PWM) integrated single-stage power factor correction (PFC) converters are presented. The typical PFC cells in the single-stage PFC converter are identified. After that, the necessary PFC condition is derived and verified to understand the principle of the single-stage PFC converters. As an example, the continuous current mode (CCM) current source single-stage PFC converter is studied. The circuit intuitions and design consideration of this converter are presented. Also, an improved current source single-stage PFC converter with a low-frequency auxiliary switch is proposed to overcome the problem of the previous converter. Experimental verification shows the improvement is effective. To evaluate single-stage PFC technique, a comparison study between the current source single-stage and the boost two-stage PFC converters is done in this thesis. It shows that for universal line application, due to the wide bus-capacitor voltage range, single-stage PFC converters have higher component ratings than two-stage PFC converters. This limits the application of single-stage PFC converter. Therefore, an interesting future work will be how to reduce the bus voltage range of single-stage PFC converters. / Master of Science

This dissertation presents the in-depth study and innovative solutions of the advanced integrated single-stage power-factor-correction (S2PFC) techniques, which target at the low- to medium-level power supplies, for wide range of applications, from power adapters and computers to various communication equipment. To limit the undesirable power converter input-current-harmonic's impact on the power line and other electronics equipment, stringent current harmonic regulations such as IEC 61000-3-2 have already been enforced. The S2PFC techniques have been proposed and intensively studied, in order to comply these regulations with minimal additional component count and cost. This dissertation provides a systematic study of the S2PFC input-current-shaping (ICS) mechanism, circuit topology generalization and variation, bulk capacitor voltage stress and switch current stress, converter design and optimization, and evaluation of the state-of-the-art S2PFC techniques with universal-line input. Besides, this presentation also presents the development of novel S2PFC techniques with a voltage-doubler-rectifier front end to both improve the performance and reduce the cost of S2PFC converters for (international voltage range) universal-line applications. The calculation and experimental results show that the proposed techniques offer a more cost-effective and efficient solution than industries' current practice, with universal-line input and converter power level up to 600 W. Finally, further improved technique is also presented with reduced filter inductor size and increased power density. / Ph. D.

Norintis savo kalba patraukti dėmesį, sukelti teigiamas ar neigiamas emocijas, pabrėžti sakomą dalyką žmogus gali pasirinkti ir vartoti tam skirtas kalbos figūras. Vienas iš pastaruoju metu populiarėjančių ir kalbiniuose aktuose vis dažniau aptinkamų būdų yra korekcija. Toks kalbėjimas atkreipia adresato dėmesį, korekcijos figūros atliekama tikslinimo funkcija aktuali tiek kalbėtojui ar rašančiajam, tiek klausytojui ar skaitytojui. Esama atvejų, kai kalbėtojas savo kalbinę raišką tikslina dalykiniais sumetimais – taip kuriama dalykinė korekcija. Jeigu adresantas siekia ekspresyviai, vaizdžiai pakoreguoti jau pasakytą ar ketinamą pasakyti mintį, pasitelkiama figūrinė korekcija. Bakalauro darbo tikslas – išnagrinėti metakalbinių komentarų su prieveiksmiais tiksliau, teisingiau, tikriau, geriau vartojimą kalbiniuose aktuose kaip savos kalbos korekcijos priemonę. Nagrinėjami 281 dalykinės ir figūrinės korekcijos atvejai – jų vartosenos polinkiai, taip pat metakalbinių komentarų su tam tikrais prieveiksmiais dažnumas. Medžiaga tyrimui rinkta iš Dabartinės lietuvių kalbos tekstyno, o tyrimas atliktas aprašomuoju analitiniu ir skaičiavimo metodais. Išanalizavus pavyzdžius nustatyta, kad turinčios tiesioginę reikšmę frazės su prieveiksmiais tiksliau, teisingiau, tikriau, geriau vartojamos patikslinti pasakymą, t. y. sukuriama dalykinė korekcija. Toks tikslinimas skamba paprastai, nereikalauja iš adresanto rimtesnių pastangų ir nepatraukia adresato dėmesio. Figūrinė korekcija... [toliau žr. visą tekstą] / When trying to catch reader’s attention, evoke positive or negative emotions, emphasize a certain thing, a person may choose some special language forms. Nowadays, correction is one of the most popular and quite often used language forms in the linguistic acts. This kind of speaking catches receiver’s attention, correction forms perform the function of specification which is relevant to the speaker, writer, listener or reader. There are cases, when the speaker specifies his/her linguistic expression due to the constructive considerations and in this way a constructive correction is created. If the addressee seeks expressively, visually correct his/her already said idea or the idea he/she is going to say, he/she invokes form correction. The objective of the bachelor’s work is to investigate the usage of metalanguage comments along with adverbs accurately, fairer, rather, better in the linguistic acts as language correction mean. There are 281 constructive and form correction cases being analyzed i.e. their usage tendency, also, the frequency of metalanguage comments along with certain adverbs. The material for the survey was collected from the Corpus of the Current Lithuanian Language and the survey itself was carried out using descriptive analytical and computation methods. After analyzing the examples there was defined that phrases which are literal and are used along with adverbs accurately, fairer, rather, better are practiced in order to specify the expression i.e. in... [to full text]