Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 47 for “"high frequency (HF)"”.
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Excitation of Langmuir wave turbulence in high-frequency (HF) pump waves over Gakona, Alaska
… by the parametric decay instability (PDI) in high-frequency space plasma heating experiments conducted at the NSF/DoD High Frequency Active Auroral Research Program (HAARP) facility in Gakona, Alaska during the spring and summer of 2006. The PDI is the decay of an electromagnetic (EM) wave …
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Low-loss inductor design for high-frequency power applications
… centers, and aerospace systems. Operation in the high frequency (HF) regime (3{ 30 MHz) has potential for miniaturizing power electronics, but designing small, efficient inductors at HF can be challenging. At these frequencies, losses due to skin and proximity effects are difficult to reduce, and …
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Testing the Re-designed SuperDARN HF Radar and Modeling of a Twin Terminated Folded Dipole Array
… near-space plasma environment. This group uses high frequency (HF) radars and backscatter from magnetic field-aligned plasma irregularities to study space weather manifested in the Earth's magnetosphere and ionosphere. Space weather impacts many technological systems including Global Positioning …
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Network Reliability Analysis under the Multivariate Normal Model
High Frequency (HF) radios have been used since the early 20th century for long-distance communication. HF communication systems primarily utilize skywave propagation in which the ionosphere is used to reflect radiowaves back to Earth. The performance of HF communication links is directly tied to …
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Analysis of Heart Rate Variability in Female Patient with Overactive Bladder
… NN intervals)는 대조군과 비교하여 통계적인 차이가 없었다. 심박동수 변이의 frequency domain 지표 분석에서 환자군의 total power (TP), high frequency (HF)는 대조군과 비교하여 통계적으로 유의하게 감소하였고, 이외의 다른 지표인 very low frequency (VLF), low frequency (LF)와 LF/HF ratio에서는 통계학적으로 두 군간의 유의한 차이를 보이지 않았다 결론: 과민성 방광 환자에서 심박동수 변이 지표는 TP, HF에서 대조군에 비하여 통계적으로 …
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Investigations of the cascade of Langmuir wave turbulence over HAARP Observatory in Gakona, Alaska
… the ionosphere. This effect is studied using a high-frequency (HF) heater located at the NSF/DoD High Frequency Active Auroral Research Program (HAARP) Observatory in Gakona, Alaska. Measurements were taken remotely in February 2005 and March 2006 in order to focus study on the altitude …
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Relationship between the autonomic nervous system and the recovering heart post exercise using heart rate variability
… ANS was assessed during rest by obtaining the high frequency (HF) component of the heart rate variability (HRV) frequency spectrum. The recovery time was estimated by fitting an exponential curve to the heart rate post exercise where the exponent was used to calculate the time constant to …
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High-Performance High-Power Inductor Design for High-Frequency Applications
… Frequencies (RF) of many MHz and above. In the High Frequency (HF, 3-30 MHz) range, coreless (or "air-core") inductors with a typical quality factor (Q) of 200-300 are conventionally used and are often the major contributor to the overall system’s loss and size. Even when they can achieve high …
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Design of Software Defined Radio for SuperDARN Radar
… study investigated the benefits and design of a high frequency (HF) SDR receiver for the next generation of Super Dual Auroral Network (SuperDARN) radars. This work analyzed digital beamforming and waveform design approaches that would be enabled by the adoption of a SDR based radar design and …
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Analysis of the Effect of the August 2017 Eclipse on the Ionosphere Using a Ray-trace Algorithm
… during eclipses, including changes in radio frequency (RF) propagation at high frequency (HF). Such changes in RF propagation were observed by the Super Dual Auroral Radar Network (SuperDARN) radars in Christmas Valley, Oregon and in Fort Hays, Kansas during the 2017 eclipse. At each site, …
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The effects of magnesium treatment on short-term changes in heart rate variability, ventricular function and lipid profile in streptozotocin-induced diabetic rats
… reduced heart rate and increased the low-frequency (LF)/high-frequency (HF) power ratio. Mg²⁺ treatment prevented theses diabetes-induced changes in heart rate and in the low-frequency (LF)/high-frequency (HF) power ratio (p < 0.05, n = 9/group). In addition, Mg²⁺ restored orthostatic …
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Do gender, anxiety sensitivity level, and timing of anxiety sensitivity assessment predict heart rate variability?
… of HRV, such as the relationship between high-frequency (HF) and low-frequency (LF) HRV, the timing of administration of the Anxiety Sensitivity Index-3 (ASI-3), gender, and level of AS. HF- and LF-HRV were perfectly linearly related, providing support in reporting one index since it can …
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Realised volatility estimators
… three categories of estimators: historical, high-frequency (HF) and implied. The need to estimate RV is predominantly in the hedging of options and is not concerned with speculation or forecasting. The main research questions are; (1) what is the best RV estimator in a historical study of S&P …
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Ray Tracing Analysis for the mid-latitude SuperDARN HF radar at Blackstone incorporating the IRI-2007 model
… (SuperDARN) is an international network of high frequency (HF) coherent scatter radars, employed to detect backscatter from magnetic field aligned plasma irregularities in the ionosphere and to study the near- Earth space weather. Space weather impacts many technological systems including HF …
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Design of a 405/430 kHz, 100 kW Transformer with Medium Voltage Insulation Sheets
To achieve higher power density, converters and components must be able to handle higher voltage and current ratings at higher percentages of efficiency while also maintaining low cost and a compact footprint. To meet such demands, medium-voltage resonant converters have been favored by researchers …
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Transient electromagnetic scattering by a radially uniaxial dielectric sphere: Debye series, Mie series and ray tracing methods
… the generalized Mie series solution. Following high frequency scattering solution of a large uniaxial sphere, the Mie series summation is split into the high frequency (HF) and low frequency terms where the HF term is replaced by its asymptotic expression allowing a significant reduction in …
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Design of a low-voltage low-power dc-dc HF converter
… benefit from a power converter able to achieve high efficiency across wide input and output voltage ranges at a small size. However, it is difficult for many conventional power converter designs to provide wide operation range while maintaining high efficiency, especially if both up-and-down …
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New Techniques in the Design of Distributed Power Systems
… design that features reduced complexity and higher efficiency. In the dissertation's second half, the overall DC distributed power system design concept is simplified through the elimination of power processing conversion steps - the result being the creation of a high-frequency (HF) AC …
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Calibration of a SuperDARN Radar Antenna by means of a Satellite Beacon
… year that will facilitate the reception of the high frequency (HF) beacon signal from the 1 U CubeSat ZACUBE 1 by the SuperDARN HF radar in Antarctica, and by the HF direction-finding (DF) systems in both Pretoria and Hermanus. The primary objective of the HF beacon on ZACUBE 1 is to provide a …
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Minimum-delay HF communications
HF radio communications offer latency advantages over fiber-optics and are more economical than satellite links in long-distance communication applications. As a result, there is renewed interest in the field of HF from the high-frequency trading industry, as a means of transmitting financial data. …
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