• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 55
  • 12
  • 9
  • 6
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 98
  • 98
  • 13
  • 12
  • 11
  • 10
  • 9
  • 9
  • 9
  • 8
  • 7
  • 6
  • 6
  • 6
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

Financial liberalization, financial development and economic growth: the case for South Africa

Savanhu, Tatenda January 2012 (has links)
Financial liberalization in South Africa was a process that took the form of various legal reforms very a long period of time. This study uses quarterly financial data from 1969 quarter one to 2009 quarter four to analyse this process. The data used was pertinent to the financial liberalization theorem by McKinnon (1973) and Shaw (1973). The examination of the relationships between the various macro economic variables has important implications for effective policy formulation. The empirical analysis is carried out in four phases: the preliminary analysis, the principal component analysis (PCA), the cointegration analysis and pair wise Granger causality tests. The preliminary analysis examines trends over the sample period and reports the on the correlation between the selected variables. The PCA analysis was used to create indexes for financial liberalization, taking into account the phase wise nature of legal reforms. The generated index was representative of the process of financial liberalization from 1969 to 2009. A financial development index was also created using the various traditional measures of financial development and through PCA which investigated interrelationships among the variables according to their common sources of movement. Cointegration analysis is carried out using the Johansen cointegration procedure which investigates whether there is long-run comovement between South African economic growth and the selected macroeconomic variables. Where cointegration is found, Vector Error-Correction Models (VECMs) are estimated in order to examine the short-run adjustments. For robustness, many control variables were added into the model. The results showed that there are positive long run relationships between economic growth and financial liberalization, financial development and a negative relationship with interest rates. The Granger results suggested that the MS hypothesis does not manifest accurately in the South African data. The implications of the results were that financial liberalization has had positive effects on economic growth and thus any impediments to full financial liberalization must be removed albeit with considerations towards employment and local productivity. Financial development also possessed positive long run relationships with economic growth, although results differed based on the financial development proxy used. Thus, financial development must be improved primarily through liberalizing the banking sector and spurring savings.
92

Hypercomplex Numbers and Early Vector Systems: A History

Bushman, Nathan 29 September 2020 (has links)
No description available.
93

Low Switching Frequency Pulse Width Modulation for Induction Motor Drives

Tripathi, Avanish January 2017 (has links) (PDF)
Induction motor (IM) drives are employed in a wide range of industries due to low maintenance, improved efficiency and low emissions. Industrial installations of high-power IM drives rated up to 30 MW have been reported. The IM drives are also employed in ultra high-speed applications with shaft speeds as high as 500; 000 rpm. Certain applications of IM drives such as gas compressors demand high power at high speeds (e.g. 10 MW at 20; 000 rpm). In high-power voltage source inverter (VSI) fed induction motor drives, the semiconductor devices experience high switching energy losses during switching transitions. Hence, the switching frequency is kept low in such high-power drives. In high-speed drives, the maximum modulation frequency is quite high. Hence, at high speeds and/or high power levels, the ratio of switching frequency to fundamental frequency (i.e. pulse number, P ) of the motor drive is quite low. Induction motor drives, operating at low-pulse numbers, have significant low-order volt-age harmonics in the output. These low-order voltage harmonics are not filtered adequately by the motor inductance, leading to high total harmonic distortion (THD) in the line current as well as low-order harmonic torques. The low-order harmonic torques may lead to severe torsional vibrations which may eventually damage the motor shaft. This thesis addresses numerous issues related to low-pulse-number operation of VSI fed IM drives. In particular, optimal pulse width modulation (PWM) schemes for minimization of line current distortion and those for minimization of a set of low-order harmonic torques are proposed for two-level and three-level inverter fed IM drives. Analytical evaluation of current ripple and torque ripple is well established for the induction motor drives operating at high pulse numbers. However, certain important assumptions made in this regard are not valid when the pulse number is low. An analytical method is proposed here for evaluation of current ripple and torque ripple in low-pulse-number induction motor drives. The current and torque harmonic spectra can also be predicted using the proposed method. The analytical predictions of the proposed method are validated through simulations and experimental results on a 3:7-kW induction motor drive, operated at low pulse numbers. The waveform symmetries, namely, half-wave symmetry (HWS), quarter-wave symmetry (QWS) and three-phase symmetry (TPS), are usually maintained in induction motor drives, operating at low switching frequencies. Lack of HWS is well known to introduce even harmonics in the line current. Impact of three-phase symmetry on line current and torque harmonic spectra is analyzed in this thesis. When the TPS is preserved, there are no triplen frequency components in the line current and also no harmonic torques other than those of order 6, 12, 18 etc. While TPS ensures that the triplen harmonics in the three-phase pole voltages are in phase, these triplen frequency harmonics form balanced sets of three-phase voltages when TPS is not preserved. Hence, triplen frequency currents flow through the stator windings. These result in torque harmonics of order 2, 4, 6, 8, 10 etc., and not just integral multiples of 6. These findings are well supported by simulation and experimental results. One can see that two types of pole voltage waveforms are possible, when all waveform symmetries (i.e. HWS, TPS and QWS) are preserved in a two-level inverter, These are termed as type-A and type-B waveforms here. Also, QWS could be relaxed, while maintain-ing HWS and TPS, leading to yet another type of pole voltage waveform. Optimal switching angles to minimize line current THD are reported for all three types of pole voltage wave-forms. Theoretical and experimental results on a 3:7-kW IM drive show that optimal type-A PWM and optimal type-B PWM are better than each other in different ranges of modulation at any given low pulse number. In terms of current THD, the optimal PWM without QWS is found to be close to the better one between optimal type-A and optimal type-B at any modulation index for a given P . A combined optimal PWM to minimize THD is proposed, which utilizes the superior one between optimal type-A and optimal type-B at any given modulation index and pulse number. The performance of combined optimal PWM is shown to be better than those of synchronous sine-triangle (ST) PWM and selective harmonic elimination (SHE) PWM through simulations and experiments over a wide range of speed. A frequency domain (FD) based and another synchronous reference frame (SRF) based optimal PWM techniques are proposed to minimize low-order harmonic torques. The objective here is to minimize the combined value of low-order harmonic torques of order 6, 12, 18, ..., 6(N 1), where N is the number of switching angles per quarter cycle. The FD based optimal PWM is independent of load and machine parameters while the SRF based method considers both load and machine parameters. The offline calculations are much simpler in case of FD based optimal PWM than in case of SRF based optimal PWM. The performance of the two schemes are comparable and are much superior to those of synchronous ST PWM and SHE PWM in terms of low-order harmonic torques as shown by the simulation and experimental results presented over a wide range of fundamental frequency, The proposed optimal PWM methods for two level-inverter fed motor drives to minimize the line current distortion and low-order torque harmonics, are extended to neutral point clamped (NPC) three-level inverter fed drive. The proposed optimal PWM methods for the NPC inverter are compared with ST PWM and SHE PWM, having the same number of switching angles per quarter. Simulation and experimental results on a 3:7-kW induction motor drive demonstrate the superior performance of proposed optimal PWM schemes over ST PWM and SHE PWM schemes. The di_erent optimal PWM schemes proposed for two-level and three-level inverter fed drives, having di_erent objective functions and constraints, are all analyzed from a space vector perspective. The three-phase PWM waveforms are seen as a sequence of voltage vector applied in each case. The space vector analysis leads to determination of optimal vector sequences, fast o_ine calculation of optimal switching angles and e_cient digital implementation of the proposed optimal PWM schemes. A hybrid PWM scheme is proposed for two-level inverter fed IM drive, having a maximum switching frequency of 250 Hz. The proposed hybrid PWM utilizes ST PWM at a _xed frequency of 250 Hz at low speeds. This method employs the optimal vector sequence to minimize the current THD at any speed in the medium and high speed ranges. The proposed method is shown to reduce both THD as well as machine losses signi_cantly, over a wide range of speed, compared to ST PWM Position sensorless vector control of IM drive also becomes challenging when the ratio of inverter switching frequency to maximum modulation frequency is low. An improved procedure to design current controllers, and a closed-loop ux estimator are reviewed. These are utilized to design and implement successfully a position sensorless vector controlled IM drive, modulated with asynchronous third harmonic injected (THI) PWM at a constant switching frequency of 500 Hz. Sensorless vector control is also implemented successfully, when the inverter is modulated with synchronized THI PWM and the maximum switching frequency is limited to 500 Hz.
94

Inserção de conceitos de dinâmica rotacional no ensino médio através do laboratório não estruturado mediado por videoanálise

Barbosa, Wilton Gimenes 03 August 2016 (has links)
Acompanha produto / Nessa dissertação investiga-se a viabilidade de transposição didática do conteúdo de dinâmica rotacional para o ensino médio, utilizando-se dos conceitos do laboratório não estruturado mediado por videoanálise. Dentre os conceitos da dinâmica rotacional, focou-se em de inércia, energia cinética rotacional e momento angular. Para a videoanálise, utilizou-se o software Tracker, por favorecer a interação entre os experimentos propostos, com os recursos de imagem e vídeo, além de ser familiar aos estudantes que participaram das atividades. Esta pesquisa fundamentou-se nos princípios da transposição didática de José de Pinho Alves Filho, que inicialmente foram trabalhadas por Chevallard, e nas competências e habilidades apontadas pelos Parâmetros Curriculares Nacionais, bem como nos seus apontamentos para uma reestruturação do ensino de Física. A metodologia de pesquisa foi proposta de modo a investigar a viabilidade do processo de transposição didática segundo as regras propostas pelo referencial teórico, através da utilização do Tracker, no contexto do laboratório não estruturado. Para isso, três atividades experimentais foram realizadas com alunos da segunda série do ensino médio de um colégio da rede particular de Curitiba. A partir da análise do material produzido pelos alunos e registros do professor, procurou-se indícios de aprendizagem do tema proposto, por ser inédito no ensino médio. Nessa pesquisa verificou-se a viabilidade da transposição didática do conteúdo de dinâmica rotacional para o ensino médio. / This dissertation investigates the feasibility of transposition didactics of the content of rotational dynamics for high school, using the concepts of the lab not structured mediated by videoanalysis. Among the concepts of dynamic rotational, focused on inertia, kinetic energy and rotational angular momentum. For videoanalysis, we used the software Tracker, to encourage the interaction between the experiments proposed, with the resources of image and video, as well as be familiar to students who participated in the activities. This research was based on the principles of the transposition didactics of José de Pinho Alves Filho, who initially were worked by Chevallard, and skills and abilities identified by the National Curriculum Parameters, as well as in his notes for a restructuring of the teaching of Physics. The research methodology was proposed in order to investigate the feasibility of the process of transposition didactics according the rules proposed by the theoretical framework, through the use of Tracker, in the context of the lab not structured. For this reason, three experimental activities were conducted with students of the second series of high school in a college of the private network of Curitiba. From the analysis of the material produced by students and records of the teacher, it was evidence of learning the theme proposed by being unheard of in high school. In this study, it was found that the viability of the transposition didactics of the content of rotational dynamics for middle school.
95

Inserção de conceitos de dinâmica rotacional no ensino médio através do laboratório não estruturado mediado por videoanálise

Barbosa, Wilton Gimenes 03 August 2016 (has links)
Acompanha produto / Nessa dissertação investiga-se a viabilidade de transposição didática do conteúdo de dinâmica rotacional para o ensino médio, utilizando-se dos conceitos do laboratório não estruturado mediado por videoanálise. Dentre os conceitos da dinâmica rotacional, focou-se em de inércia, energia cinética rotacional e momento angular. Para a videoanálise, utilizou-se o software Tracker, por favorecer a interação entre os experimentos propostos, com os recursos de imagem e vídeo, além de ser familiar aos estudantes que participaram das atividades. Esta pesquisa fundamentou-se nos princípios da transposição didática de José de Pinho Alves Filho, que inicialmente foram trabalhadas por Chevallard, e nas competências e habilidades apontadas pelos Parâmetros Curriculares Nacionais, bem como nos seus apontamentos para uma reestruturação do ensino de Física. A metodologia de pesquisa foi proposta de modo a investigar a viabilidade do processo de transposição didática segundo as regras propostas pelo referencial teórico, através da utilização do Tracker, no contexto do laboratório não estruturado. Para isso, três atividades experimentais foram realizadas com alunos da segunda série do ensino médio de um colégio da rede particular de Curitiba. A partir da análise do material produzido pelos alunos e registros do professor, procurou-se indícios de aprendizagem do tema proposto, por ser inédito no ensino médio. Nessa pesquisa verificou-se a viabilidade da transposição didática do conteúdo de dinâmica rotacional para o ensino médio. / This dissertation investigates the feasibility of transposition didactics of the content of rotational dynamics for high school, using the concepts of the lab not structured mediated by videoanalysis. Among the concepts of dynamic rotational, focused on inertia, kinetic energy and rotational angular momentum. For videoanalysis, we used the software Tracker, to encourage the interaction between the experiments proposed, with the resources of image and video, as well as be familiar to students who participated in the activities. This research was based on the principles of the transposition didactics of José de Pinho Alves Filho, who initially were worked by Chevallard, and skills and abilities identified by the National Curriculum Parameters, as well as in his notes for a restructuring of the teaching of Physics. The research methodology was proposed in order to investigate the feasibility of the process of transposition didactics according the rules proposed by the theoretical framework, through the use of Tracker, in the context of the lab not structured. For this reason, three experimental activities were conducted with students of the second series of high school in a college of the private network of Curitiba. From the analysis of the material produced by students and records of the teacher, it was evidence of learning the theme proposed by being unheard of in high school. In this study, it was found that the viability of the transposition didactics of the content of rotational dynamics for middle school.
96

Rate-Distortion Performance And Complexity Optimized Structured Vector Quantization

Chatterjee, Saikat 07 1900 (has links)
Although vector quantization (VQ) is an established topic in communication, its practical utility has been limited due to (i) prohibitive complexity for higher quality and bit-rate, (ii) structured VQ methods which are not analyzed for optimum performance, (iii) difficulty of mapping theoretical performance of mean square error (MSE) to perceptual measures. However, an ever increasing demand for various source signal compression, points to VQ as the inevitable choice for high efficiency. This thesis addresses all the three above issues, utilizing the power of parametric stochastic modeling of the signal source, viz., Gaussian mixture model (GMM) and proposes new solutions. Addressing some of the new requirements of source coding in network applications, the thesis also presents solutions for scalable bit-rate, rate-independent complexity and decoder scalability. While structured VQ is a necessity to reduce the complexity, we have developed, analyzed and compared three different schemes of compensation for the loss due to structured VQ. Focusing on the widely used methods of split VQ (SVQ) and KLT based transform domain scalar quantization (TrSQ), we develop expressions for their optimum performance using high rate quantization theory. We propose the use of conditional PDF based SVQ (CSVQ) to compensate for the split loss in SVQ and analytically show that it achieves coding gain over SVQ. Using the analytical expressions of complexity, an algorithm to choose the optimum splits is proposed. We analyze these techniques for their complexity as well as perceptual distortion measure, considering the specific case of quantizing the wide band speech line spectrum frequency (LSF) parameters. Using natural speech data, it is shown that the new conditional PDF based methods provide better perceptual distortion performance than the traditional methods. Exploring the use of GMMs for the source, we take the approach of separately estimating the GMM parameters and then use the high rate quantization theory in a simplified manner to derive closed form expressions for optimum MSE performance. This has led to the development of non-linear prediction for compensating the split loss (in contrast to the linear prediction using a Gaussian model). We show that the GMM approach can improve the recently proposed adaptive VQ scheme of switched SVQ (SSVQ). We derive the optimum performance expressions for SSVQ, in both variable bit rate and fixed bit rate formats, using the simplified approach of GMM in high rate theory. As a third scheme for recovering the split loss in SVQ and reduce the complexity, we propose a two stage SVQ (TsSVQ), which is analyzed for minimum complexity as well as perceptual distortion. Utilizing the low complexity of transform domain SVQ (TrSVQ) as well as the two stage approach in a universal coding framework, it is shown that we can achieve low complexity as well as better performance than SSVQ. Further, the combination of GMM and universal coding led to the development of a highly scalable coder which can provide both bit-rate scalability, decoder scalability and rate-independent low complexity. Also, the perceptual distortion performance is comparable to that of SSVQ. Since GMM is a generic source model, we develop a new method of predicting the performance bound for perceptual distortion using VQ. Applying this method to LSF quantization, the minimum bit rates for quantizing telephone band LSF (TB-LSF) and wideband LSF (WB-LSF) are derived.
97

Parallel acceleration of deadlock detection and avoidance algorithms on GPUs

Abell, Stephen W. 08 1900 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Current mainstream computing systems have become increasingly complex. Most of which have Central Processing Units (CPUs) that invoke multiple threads for their computing tasks. The growing issue with these systems is resource contention and with resource contention comes the risk of encountering a deadlock status in the system. Various software and hardware approaches exist that implement deadlock detection/avoidance techniques; however, they lack either the speed or problem size capability needed for real-time systems. The research conducted for this thesis aims to resolve issues present in past approaches by converging the two platforms (software and hardware) by means of the Graphics Processing Unit (GPU). Presented in this thesis are two GPU-based deadlock detection algorithms and one GPU-based deadlock avoidance algorithm. These GPU-based algorithms are: (i) GPU-OSDDA: A GPU-based Single Unit Resource Deadlock Detection Algorithm, (ii) GPU-LMDDA: A GPU-based Multi-Unit Resource Deadlock Detection Algorithm, and (iii) GPU-PBA: A GPU-based Deadlock Avoidance Algorithm. Both GPU-OSDDA and GPU-LMDDA utilize the Resource Allocation Graph (RAG) to represent resource allocation status in the system. However, the RAG is represented using integer-length bit-vectors. The advantages brought forth by this approach are plenty: (i) less memory required for algorithm matrices, (ii) 32 computations performed per instruction (in most cases), and (iii) allows our algorithms to handle large numbers of processes and resources. The deadlock detection algorithms also require minimal interaction with the CPU by implementing matrix storage and algorithm computations on the GPU, thus providing an interactive service type of behavior. As a result of this approach, both algorithms were able to achieve speedups over two orders of magnitude higher than their serial CPU implementations (3.17-317.42x for GPU-OSDDA and 37.17-812.50x for GPU-LMDDA). Lastly, GPU-PBA is the first parallel deadlock avoidance algorithm implemented on the GPU. While it does not achieve two orders of magnitude speedup over its CPU implementation, it does provide a platform for future deadlock avoidance research for the GPU.
98

Remote sensing & GIS applications for drainage detection and modeling in agricultural watersheds

Roy, Samapriya 12 March 2014 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / The primary objective of this research involves mapping out and validating the existence of sub surface drainage tiles in a given cropland using Remote Sensing and GIS methodologies. The process is dependent on soil edge differentiation found in lighter versus darker IR reflectance values from tiled vs. untiled soils patches. Data is collected from various sources and a primary classifier is created using secondary field variables such as soil type, topography and land Use and land cover (LULC). The classifier mask reduces computational time and allows application of various filtering algorithms for detection of edges. The filtered image allows an efficient feature recognition platform allowing the tile drains to be better identified. User defined methods and natural vision based methodologies are also developed or adopted as novel techniques for edge detection. The generated results are validated with field data sets which were established using Ground Penetration Radar (GPR) studies. Overlay efficiency is calculated for each methodology along with omission and commission errors. This comparison yields adaptable and efficient edge detection techniques which can be used for similar areas allowing further development of the tile detection process.

Page generated in 0.0652 seconds