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  • 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.
311

Radial orbit error reduction and sea surface topography determination using satellite altimetry /

Engelis, Theodossios January 1987 (has links)
No description available.
312

Level of aspiration and social stress /

Cutsumbis, Michael N. January 1965 (has links)
No description available.
313

HIGH-RESOLUTION CHARACTERZATION OF LOW-DIMENSIONAL DEFECTS IN SrTiO3

Zhu, Guozhen 10 1900 (has links)
<p>I want delay publication of my dissertation until April 30 2013. Thanks.</p> / <p>Strontium titanate (SrTiO<sub>3</sub>) has a wide range of applications in the electronic industry and attracts growing world-widely interest recently because of novel discoveries at its surfaces, interfaces and with selected dopants. The understanding of some of the structural properties of SrTiO<sub>3</sub> and its optical properties have been lagging due to limited characterization techniques available to study single monolayers and dopants in this material.</p> <p>In the present thesis, pure SrTiO<sub>3</sub> single crystals with (2x1) and c(4x2) surface patterns were synthesized and samples (Pr, Al) doped SrTiO<sub>3</sub> were prepared through ion implantation. The atomic and electronic structures of these samples were investigated by various high-resolution imaging and spectroscopic techniques available in an aberration-corrected transmission electron microscope. Particularly, the direct imaging of individual light atoms and vacancies within a bulk material containing heavier elements was demonstrated for the first time via the STEM-annular dark-field (ADF)/annular bright-field (ABF) images. In addition, the first electron energy-loss spectroscopy (EELS) 2-dimensional maps of dopants located in a lattice were obtained. These results provided a solid foundation regarding the mechanism of red light emission in doped SrTiO<sub>3</sub>. More importantly, a new experimental approach allowing the effective extraction of weak EELS signals from low-dimensional defects was developed and successfully applied to understand the chemical state and coordination of Ti cations within a single monolayer on a reconstructured SrTiO<sub>3 </sub>surface and the local defect configurations of injected Pr<sup>+</sup> and Al<sup>+</sup> ions within SrTiO<sub>3</sub> single crystals.</p> / Doctor of Philosophy (PhD)
314

Online Teacher Candidates' Experiences in a Virtual World for the Preparation to Teach Middle School

Miller, Nicole C 15 December 2012 (has links)
Increasingly virtual worlds are being used to provide new and varied learning opportunities by various educational organizations such as universities, K-12 schools, and museums (Dembo, 2008; Ketelhut, Nelson, Clarke, & Dede, 2010; The Forbidden City: Beyond Space and Time, 2008). Simultaneously teacher preparation programs are increasingly being offered online (Minsun & Yoon-Joo, 2009; Saltmarsh & Sutherland-Smith, 2010; Sawchuk, 2009; Schrum, Burbank, & Capps, 2007). However, these more traditional online asynchronous learning experiences are often more challenging in several ways: (a) they require greater self-regulation (Artino & Stephens, 2009; Bol & Garner, 2011), (b) they have been reported as sometimes less effective than face-toace learning (Hudson, 2006; C. L. Peterson & Bond, 2004; Saltmarsh & Sutherland-Smith, 2010; Zirkle, 2002); and (c) they have sometimes been perceived as less effective (E. I. Allen & Seaman, 2011; Huss, 2007). Given the potential of virtual worlds for teaching and learning, it was believed that the use of a virtual world for middle level teacher preparation might provide a solution to some of these reported challenges of online learning. The purpose of this study was to describe and examine the experiences of online middle level teacher candidates using a multi-user virtual environment (MUVE) for teacher preparation. Case study methodology was employed, using multiple data sources including interviews, surveys, observations, snapshots, course artifacts, and the primary researcher’s journal. All data were coded and reviewed iteratively to inductively deduce the nature of the participants’ experiences. The data indicate middle level teacher preparation in the MUVE was more supportive and engaging than traditional online-learning experience, and was useful for learning about middle level education. Though the participants found the experiences to be positive, distractions including personal and technical issues played a role. This study offers insights on the use and implementation of MUVEs in online middle level teacher preparation.
315

Is Hypoxic (Altitude) Training More Effective than Sea Level Training for Competition at Sea Level?

Melissa, Lori 08 1900 (has links)
The purpose of the present study was to determine whether or not the combination of normobaric hypoxia and exercise training would enhance adaptations in skeletal muscle over and above that which occurs with the same amount of training under normoxic conditions. Also investigated was the effect of such training conditions on performance as assessed by V0_2max and maximal aerobic capacity (MAC). Ten males performed unilateral cycle ergometry training 3 times per week for 8 weeks so that one leg was trained under normoxic conditions and the other while breathing an hypoxic gas mixture (FI0_2= 13.5%; equivalent to an altitude of 3,292 meters). Absolute power output was kept constant for both conditions and subjects performed both continuous (75% pre-training maximal power output) and interval (100% pre-training maximal power output) training. Needle biopsies were taken from the vastus lateralis of both legs to assess pre- and post-training differences in morphometric and biochemical data. Performance measures included V0_2max and MAC (time to fatigue at 95% pre-training maximal power output) for each leg. Significant increases in V0_2max (p <0.05) occurred in both legs with higher peak ventilation and blood lactate concentrations (p <0.05) post-training. Marked improvements (p <0.05) in MAC were also seen with an increase of 402% in the normoxically-trained leg and 513% in the hypoxically-trained leg. Citrate synthase (CS), succinate dehydrogenase, and phosphofructokinase activity was significantly (p <0.05) higher in both legs following training with a significantly greater (p <0.05) increase in CS in the hypoxically-trained leg. There were no differences in capillary/fiber ratio, capillary density, fiber area, fiber type, and mitochondrial volume density for either condition, pre- or post-training. It is concluded that hypoxia enhanced the muscle oxidative capacity (as marked by cs activity) but was unable to improve performance over and above that which occurs with the same training at sea level. / Thesis / Master of Science (MS)
316

A Power Conditioning System for Superconductive Magnetic Energy Storage based on Multi-Level Voltage Source Converter

Lee, Dong-Ho 15 July 1999 (has links)
A new power conditioning system (PCS) for superconductive magnetic energy storage (SMES) is developed and its prototype test system is built and tested. The PCS uses IGBTs for high-speed PWM operation and has a multi-level chopper-VSC structure. The prototype test system has three-level that can handle up to 250-kVA with a 1800-V DC link, a 200-A maximum load current , and a switching frequency reaching 20-kHz with the help of zero-current-transition (ZCT) soft-switching. This PCS has a great number of advantages over conventional ones in terms of size, speed, and cost. Conventional PCSs use thyristors, due to the power capacity of the SMES system. The speed limit of the thyristor uses a six-pulse operation that generates a high harmonic. To reduce the harmonic, multiple PCSs are connected together with phase-matching transformers that need to be precise to be effective in reducing the harmonics. So, the system becomes large and expensive. In addition, the dynamic range of the PCSs are also limited by the six-pulse operation, because it limits the useful area of the PCS applications. By employing a high-speed PWM, the new PCS can reduce the harmonics without using the transformers reducing size and cost, and has wide dynamic range. However, the speed of a switching device is generally inversely proportional to its power handling capacity. Therefore, employing a multi-level structure is one method of extending the power-handling capability of the high-speed device. Switching loss is another factor that limits the speed of the switch, but it can be reduced by soft-switching techniques. The 20-kHz switching frequency can be obtained with the help of the ZCT soft-switching technique, which can reduce about 90% of switching losses from the IGBT during both turn-on and turn-off transients. There are two different topologies of the PCS; the current source converter (CSC) type and the chopper and voltage source converter (VSC) type. In terms of the SMES system efficiency, the chopper-VSC type shows a less volt-ampere requirement of the power device. Therefore, the new PCS system has a chopper-VSC structure. Since the chopper-VSC structure consists of multiple legs that can be modularized, a power electronics building block (PEBB) leg is a good choice; all of the system problems caused by the high frequency can be solved within the PEBB leg. The VSC is built with three of the PEBB legs. Three-phase AC is implemented with a three-level space vector modulation (SVM) that can reduce the number of switching and harmonic contents from the output current. A closed-loop control system is also implemented for the VSC, and shows 600-Hz control bandwidth. The multi-level structure used requires too many high-speed switches. However, not all of them are used at the same time during normal multi-level operation. A new multi-level topology is suggested that requires only two high-speed switches, regardless of the number of levels. Other switches can be replaced with slow-speed switches that can allow additional cost savings. / Ph. D.
317

Identifying the Defining Characteristics of College-level Course Work: Perceptions of Accounting and Business Management Faculty

McMillian, Norwood 16 July 1998 (has links)
Community college transfer students may have to repeat one or more courses at the four-year institution or may have to take more than the required number of courses to obtain a baccalaureate degree. This uncertainty about the transfer of credits and the extra cost in higher education that goes along with it, has come about mainly due to the lack of a working definition for college-level course work. Community colleges need to insure that every course designated as a transfer course will be transferable to a receiving institution. Four-year colleges and universities should expect the courses they accept in transfer to meet the same standards required within their own curricula. The defining characteristics of "college-level" should be identified to facilitate equitable transfer of course credit and insure that transfer students are prepared academically to continue their baccalaureate studies. This study explored the defining characteristics of lower-level college course work in two North Carolina community college and universities, specifically in the areas of study in accounting and business management. Simultaneously, the characteristics of community college-level course work were compared with those of the university. The data gathering methodology utilized the qualitative research method of semi-structured elite-interviewing which allowed for in-dept exploration of the opinions of the knowledgeable individuals involved in the issue being studied. A set of broad, open-ended interview questions were designed to gather information from community college and university professors of accounting and business management. A total of 16 professors were interviewed. The analysis of the interviews included organizing the data into domains; generating categories, themes, and patterns; and comparing and contrasting the two-year analysis with the four-year analysis and the areas of study against each other. There are more similarities than differences in the comments among and between the groups, and the analysis resulted in the identification of ten categories of characteristics defining college-level course work. They include (a) Problem solving using higher level thinking skills, (b) Mastery of the subject matter, (c) Connections within and across disciplines, (d) Student maturity, (e) Essential knowledge base from high school, (f) Course content/professor expectations, (g) Pedagogical issues which include writing, reading, mathematics, student evaluation and textbook, (h) Rigor, (i) Application of the subject matter, and (j) Interpersonal skills. / Ph. D.
318

Effects of Lumbar Extensor Fatigue on Ankle Joint Motion Sense and Prolonged Effect on Postural Sway

Pline, Kevin Michael 18 May 2005 (has links)
Falls from heights are a major concern in the occupational setting, and are often the result of a loss of balance. Lumbar extensor fatigue (LEF) increases postural sway which has been associated with degradations in balance. Study one focuses on the effects of fatiguing time and fatigue level on the duration of these increases in postural sway. Measures of postural sway were collected before fatigue and at 3 minute intervals for 30 minutes following fatigue. LEF had a significant effect on postural sway immediately following fatigue but this effect had only minor dependence on fatigue condition. During the 30 minutes following fatigue, the effects of fatiguing time and fatigue level became more apparent. Longer fatiguing time and higher fatigue levels resulted in significantly greater prolonged effects. While it is important to understand the immediate effect of LEF on sway, this study has demonstrated that the prolonged effect of such fatigue should be considered when addressing falls from heights. Study two attempts to explain the increases in postural sway associated with LEF. The ankle plays a major role in upright standing and degradations in proprioception could contribute to increases in sway, thus the effect of LEF on ankle proprioception was studied. Additionally, the effect of circumferential ankle pressure (CAP) on ankle proprioception was assessed to evaluate it as a potential intervention to improve proprioception. Results showed that both LEF and CAP impaired proprioception. These results may help to explain observed increases in postural sway subsequent to LEF. / Master of Science
319

FleXilicon: a New Coarse-grained Reconfigurable Architecture for Multimedia and Wireless Communications

Lee, Jong-Suk Mark 23 March 2010 (has links)
High computing power and flexibility are important design factors for multimedia and wireless communication applications due to the demand for high quality services and frequent evolution of standards. The ASIC (Application Specific Integrated Circuit) approach provides an area efficient, high performance solution, but is inflexible. In contrast, the general purpose processor approach is flexible, but often fails to provide sufficient computing power. Reconfigurable architectures, which have been introduced as a compromise between the two extreme solutions, have been applied successfully for multimedia and wireless communication applications. In this thesis, we investigated a new coarse-grained reconfigurable architecture called FleXilicon which is designed to execute critical loops efficiently, and is embedded in an SOC with a host processor. FleXilicon improves resource utilization and achieves a high degree of loop level parallelism (LLP). The proposed architecture aims to mitigate major shortcomings with existing architectures through adoption of three schemes, (i) wider memory bandwidth, (ii) adoption of a reconfigurable controller, and (iii) flexible wordlength support. Increased memory bandwidth satisfies memory access requirement in LLP execution. New design of reconfigurable controller minimizes overhead in reconfiguration and improves area efficiency and reconfiguration overhead. Flexible word-length support improves LLP by increasing the number of processing elements executable. The simulation results indicate that FleXilicon reduces the number of clock cycles and increases the speed for all five applications simulated. The speedup ratios compared with conventional architectures are as large as two orders of magnitude for some applications. VLSI implementation of FleXilicon in 65 nm CMOS process indicates that the proposed architecture can operate at a high frequency up to 1 GHz with moderate silicon area. / Ph. D.
320

Optimierung von Echtzeit‑Videoübertragung im Kontext von teleoperiertem Fahren: Fallstudie: Modell‑LKW bei unterschiedlichen Datenübertragungsraten

Ehlert, Patrick 10 May 2024 (has links)
In den letzten Jahren wurden zahlreiche Probleme im Zusammenhang mit autonomem Fahren gelöst. Es gibt jedoch noch immer Einschränkungen, die die Einführung von autonomen Fahrfunktionen über das SAE‑Level 3 hinaus verhindern. Ein Fernoperator kann eine vielversprechende Ausfalllösung sein. Es bietet eine Antwort auf die Herausforderung, dass bei autonomen Fahrten ein menschlicher Fahrer als Notlösung benötigt wird. Die vorhandene Infrastruktur, wie Mobilfunknetze, muss genutzt werden, um eine funktionierende Lösung bereitzustellen. Allerdings leiden Rechnernetzwerke unter variabler Bandbreite, variabler Verzögerung und Paketverlust. Daher werden verschiedene Übertragungsprofile auf Basis von Bebauungsdichte vorgeschlagen. Da sich Netzwerkparameter über die Zeit hinweg ändern, wird vorgeschlagen aktuelle Netzwerkbedingungen mit einzubeziehen, um dem Fernbediener zu ermöglichen, in jeder Situation schnell genug zu reagieren. Es wird gezeigt, dass der Ansatz unter Verwendung neuer Übertragungsmechanismen grundsätzlich funktionieren kann, aber weitere Langzeitmessungen erforderlich sind, um potenzielle Probleme zu identifizieren und zu beseitigen.:Abbildungsverzeichnis Tabellenverzeichnis Abkürzungsverzeichnis 1. Einleitung 1.1. Motivation 1.2. Zielsetzung der Arbeit 1.3. Vorgehensweise 2. Grundlagen 2.1. Definitionen 2.1.1. Realzeit 2.1.2. Echtzeit 2.1.3. Latenz 2.1.4. Wahrnehmung von Echtzeit 2.1.5. Bandbreite 2.1.6. SAE Level 2.1.7. Teleoperiertes Fahren 2.2. Videoparameter 2.2.1. Auflösung und Bildrate 2.2.2. Bitrate und Codec 2.3. Zusammenhang von Latenz, Qualität und Bandbreite 2.4. Übertragungsprotokolle 2.4.1. RTSP 2.4.2. RTMP 2.4.3. SRT 2.4.4. WebRTC 2.4.5. Media over QUIC 2.5. Mobilfunkgrößen 3. Methodik 3.1. Aufbau der Messungen 3.2. Bandbreite und Bitrate 3.3. Messkonzepte für Latenz‑erzeugende Komponenten 3.3.1. Aufnahme 3.3.2. Encoder 3.3.3. Gesamtsystem 3.4. Projektbeschreibung und Zieldefinition 4. Implementierung 5. Ergebnisse 5.1. Benötigte Bandbreite 5.2. Aufnahme 5.3. Encoder 5.3.1. Videos mit einem Frame 5.3.2. Ausgeschnittene Videoclips 5.3.3. Gesamte Videolänge 5.4. Gesamtsystem und Protokolle 6. Diskussion 7. Zusammenfassung und Ausblick Literaturverzeichnis A. Quellcode B. Tabellen

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