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Hopcroft, Matthew A. "Temperature-stabilized silicon resonators for frequency references /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Döringshoff, Klaus. "Optical frequency references based on hyperfine transitions in molecular iodine." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19156.
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Diese Arbeit beschäftigt sich mit der Entwicklung und Untersuchung von optischen Absolutfrequenzreferenzen basierend auf rovibronischen Übergängen in molekularen Jod. Dabei werden Methoden der Doppler-freien Sättigungsspektroskopie angewendet, um einzelne Übergänge der Hyperfeinstruktur mit Linienbreiten unterhalb von 1 MHz im B-X System von molekularem Iod bei 532 nm, der zweiten harmonischen des Nd:YAG-Laser, aufzulösen. Elektronische Regelungstechniken ermöglichen eine präzise Stabilisierung der optischen Frequenz auf die Linienmitte der Übergänge mit einer Auflösung von Teilen in 10^5.
Mit dem Ziel einer weltraumtauglichen Absolutfrequenzreferenz für zukünftige Weltraummissionen, wurden zwei Spektroskopiemodule konzipiert und in quasi-monolithischen Glaskeramik-Aufbauten, als sogenanntes elegant breadboard model und engineering model, realisiert. Diese Jodfrequenzreferenzen wurden im Detail in Bezug auf ihre Frequenzstabilität und Reproduzierbarkeit untersucht und Letzteres wurde für die angestrebte Weltraumqualifizierung ersten Umwelttests, sowohl vibrations- als auch thermischen Belastungstests, unterzogen.
Für die Untersuchung der Frequenzstabilität dieser Jodreferenzen wurde ein auf einen optischen Resonator hoher Güte stabilisiertes Lasersystem für direkte Frequenzvergleiche bei 1064 nm realisiert. Die Analyse der Frequenzstabilität der Jod Referenzen zeigt eine Frequenzstabilität von 6x10^−15 bei 1 s, und weniger als 2x10^−15 bei 100 s Integrationszeit, was der bis heute besten veröffentlichten Frequenzstabilität entspricht die mit Jod Referenzen erreicht wurde.
Mit der erreichten Frequenzstabilität ermöglichen diese Absolutfrequenzreferenzen präzise Lasersysteme für zukünftige Weltraummissionen wie z.B. zur Detektion von Gravitationswellen, zur Vermessung des Gravitationsfelds der Erde oder für Präzisionstest fundamentaler Theorien der Physik.This thesis deals with the development and investigation of optical absolute frequency references based on rovibronic transitions in molecular iodine. Doppler-free saturation spectroscopy methods are employed to resolve individual transitions of the hyperfine structure with linewidths below 1 MHz in the B-X system of molecular iodine at 532 nm with the second harmonic of Nd:YAG lasers. Electronic feedback control systems are employed for laser frequency stabilization to the line center of the optical transitions with a line splitting of 10^5. With the goal of a space qualified optical absolute frequency reference for future laser-interferometric space missions, two spectroscopy setups were designed and realized in quasi-monolithic, glass-ceramic setups as so called elegant bread board model and engineering model. These iodine references were characterized in detail with respect to their frequency stability and reproducibility and the engineering model was subject to environmental tests, including vibrations and thermal cycling to verify its applicability in future space missions. For the investigation of the frequency instability of these iodine references, a frequency stabilized laser system was realized based on a temperature controlled high Finesse ULE cavity for direct frequency comparisons at 1064 nm. Analysis of the frequency stability of the iodine references revealed exceptionally low fractional frequency instability of 6x10^−15 at 1 s, averaging down to less than 2×10^−15 at 100 s integration time, constituting the best reported stability achieved with iodine references to date. With the demonstrated performance, these absolute frequency references enable precision laser systems required for future space missions that are dedicated to, e.g., the detection of gravitational waves, mapping of the Earth’s gravitational field or precision test of fundamental physics.
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Thapa, Rajesh. "Cr:forsterite laser frequency comb stabil[a]zation and development of portable frequency references inside a hollow optical fiber." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/994.
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Sundaresan, Krishnakumar. "Temperature Compensated CMOS and MEMS-CMOS Oscillators for Clock Generators and Frequency References." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13977.
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Silicon alternatives to quartz crystal based oscillators to electronic system clocking are explored. A study of clocking requirements reveals widely different specifications for different applications. Traditional CMOS oscillator-based solutions are optimized for low-cost fully integrated micro-controller clock applications. The frequency variability of these clock generators is studied and techniques to compensate for this variability are proposed. The efficacy of these techniques in reducing variability is proven theoretically and experimentally. MEMS-resonator based oscillators, due to their exceptional quality factors, are identified as suitable integrated replacements to quartz based oscillators for higher accuracy applications such as data converter clocks. The frequency variation in these oscillators is identified and techniques to minimize the same are proposed and demonstrated. The sources of short-term variation (phase noise) in these oscillators are discussed and an inclusive theory of phase noise is developed. Techniques to improve phase noise are proposed. Findings from this research indicate that MEMS resonator based oscillators, may in future, outperform quartz based solutions in certain applications such as voltage controlled oscillators. The implications of these findings and potential directions for future research are identified.
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Maurice, Vincent. "Design, microfabrication and characterization of alkali vapor cells for miniature atomic frequency references." Thesis, Besançon, 2016. http://www.theses.fr/2016BESA2001.
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Les horloges atomiques miniatures présentent des stabilités de fréquence inégalées avec des volumes de quelquescentimètres cubes et des consommations inférieures à 100mW.Dans cette thèse, les paramètres optimaux concernant la conception et la fabrication des cellules à vapeur decésium, un des composant clés de ce type d’horloges, sont définis. Ainsi, les performances de plusieurs cellulesont été caractérisées en condition d’horloge à court et long terme. En parallèle, des solutions sont proposéespour pallier à certaines limitations telles que la plage de température opérationnelle, le coût de fabrication dudispositif et la facilité d’assemblage du module physique.Un nouveau mélange de gaz tampon composé de néon et d’hélium peut étendre la plage de fonctionnementau-dessus de 80 C, en adéquation avec les besoins industriels. A l’inverse des gaz tampon usuels, ce mélangeest compatible avec les dispensers de césium solides, dont la fiabilité est établie.Outre les gaz tampon, les revêtements permettent également de limiter la relaxation induite par les parois dela cellule. Ici, des revêtements d’octadécyltrichlorosilane sont étudiés. Un effet anti-relaxant a été observé dansdes cellules centimétriques et un procédé a été développé pour revêtir des cellules micro-fabriquées.D’autres sources de césium sont présentées pour s’affranchir des inconvénients propres aux dispensers solides.Un dispenser sous forme de pâte, qui peut être déposée collectivement, a été étudié et montre des densitésatomiques stables jusqu’à présent. Un concept de vannes hermétiques micro-fabriquées a été proposé poursceller hermétiquement et séparer des cellules d’un réservoir de césium commun.Les premières étapes vers un module physique micro-fabriqué sont ensuite présentées. En particulier, un designoriginal de cellule combinant des réseaux de diffraction à une cavité en silicium formée par gravure anisotropea été caractérisé et a montré des contrastes CPT remarquables malgré un volume de cavité réduit, ce qui permettraitde réaliser un module physique particulièrement compact. Enfin, des cellules intégrant des résistanceschauffantes et thermométriques ont été fabriquées et leur compatibilité vis-à-vis du champ magnétique généréa été caractérisée dans un prototype de module physique compactChip-scale atomic clocks (CSACs) provide unprecedented frequency stability within volumes down to a fewcubic centimeters and power consumptions as low as 100mW.In this work, we determine the optimal parameters regarding the design and the fabrication of cesium vaporcells, one of the key components of a CSAC. For this purpose, cells were characterized on both short and longtermperformances in clock setups. In addition, we propose solutions to overcome present limitations includingthe operating temperature range, the device microfabrication cost and the ease of integration of the physicspackage.A novel mixture of buffer-gas composed of neon and helium was found to potentially extend the operating rangeof the device above 80 C, meeting the industrial requirements. Unlike the well-known buffer gas compositions,this mixture is compatible with solid cesium dispensers whose reliability is established. As an alternativeto buffer gases, wall coatings are known to limit the relaxation induced by sidewalls. Here, we investigatedoctadecyltrichlorosilane (OTS) coatings. An anti-relaxation effect has been observed in centimeter-scale cellsand a process was developed to coat microfabricated cells.Other cesium sources have been investigated to overcome the drawbacks imposed by solid cesium dispensers. Apaste-like dispenser, which can be deposited collectively, was explored and has shown stable atomic densities sofar. Single-use zero-leak micro valves were also proposed to hermetically seal and detach cells from a commoncesium reservoir.Eventually, the first steps toward a microfabricated physics package were made. In particular, an originalcell design combining diffraction gratings with an anisotropically etched single-crystalline silicon sidewalls wascharacterized and exhibited remarkable CPT contrasts despite a reduced cavity volume, which could lead to amore compact physics package. Finally, cells with integrated heating and temperature sensing resistors werefabricated and their magnetic field compliance was characterized in a compact physics package prototype
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Wang, Chenchen. "Optical frequency references in acetylene-filled hollow-core optical fiber and photonic microcells." Diss., Kansas State University, 2015. http://hdl.handle.net/2097/18831.
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Doctor of PhilosophyDepartment of Physics
Kristan L. Corwin
Optical frequency references have been widely used in applications such as navigation, remote sensing, and telecommunication industry. For stable frequency references in the near-infrared (NIR), lasers can be locked to narrow absorption features in gases such as acetylene. Currently, most Near NIR references are realized in free space setups. In this thesis, a low-loss hollow-core optical fiber with a diameter of sub millimeters is integrated into the reference setup to provide long interaction lengths between the filling gas and the laser field, also facilitate the optical interaction with low power levels. To make portable NIR reference, gas can be sealed inside the hollow-core fiber, by creating a photonic microcell. This work has demonstrated all-fiber optical frequency references in the Near IR by fabricating and integrating gas sealed photonic microcells in the reference setup. Also, a thoughtful study regarding the lineshape of the fiber-based reference has been accomplished. According the proper modeling of a shift due to lineshape, a correction was applied to our previous absolute frequency measurement of an NIR optical frequency reference. Furthermore, effects of the hollow-core fibers, including mode-dependence frequency shift related to surface modes are explored. In addition, angle splicing techniques, which will improve the performance of the fiber-based frequency reference have been created. Low transmission and return loss angle splices of photonic bandgap fiber, single mode PCF, and large core kagome to SMF-28 are developed and those fibers are demonstrated to be promising for photonic microcell based optical frequency references. Finally, a potentially portable optical metrology system is demonstrated by stabilizing a fiber-laser based frequency comb to an acetylene-filled optical fiber frequency reference. Further work is necessary to fabricate an all-fiber portable optical metrology system with high optical transmission and low molecular contamination.
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Döringshoff, Klaus [Verfasser], Achim [Gutachter] Peters, Heinz-Wilhelm [Gutachter] Hübers, and Leo [Gutachter] Hollberg. "Optical frequency references based on hyperfine transitions in molecular iodine / Klaus Döringshoff ; Gutachter: Achim Peters, Heinz-Wilhelm Hübers, Leo Hollberg." Berlin : Humboldt-Universität zu Berlin, 2018. http://d-nb.info/1182541704/34.
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Holman, Kevin W. "Distribution of an ultrastable frequency reference using optical frequency combs." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/cr/colorado/fullcit?p3190346.
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Li, Peter C. "A distributed frequency reference system for optical fiber communications." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13278.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1991.Includes bibliographical references (leaves 89-92).
by Peter Cheng-Lung Li.
M.S.
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Shubo, Jin, and Zhao Yanshan. "A MICROWAVE DIGITAL FREQUENCY SYNTHESIZER USED FOR S-BAND TELEMETRY RECEIVER." International Foundation for Telemetering, 1997. http://hdl.handle.net/10150/609681.
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International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, NevadaThis paper describes a kind of Microwave Digital Frequency Synthesizer used for S-band telemetry receivers. As well known many modern electronic systems employ a Frequency Synthesizer whose spectral purity is critical. The characteristics of a PLL (Phase-Locked Loop) Frequency Synthesizer, such as frequency resolution, phase noise, spurious suppression and switch time, should be compromised in our design. A heterodyne Frequency Synthesis is often considered as a good approach to solve the problem. But it is complicated in structure and circuit. A variable-reference-driven PLL Frequency Synthesizer was introduced which can give an improved trade-off among frequency resolution, phase noise, spurious suppression. In this paper the phase noise and spurious suppression characteristic of variable-reference-driven PLL Frequency Synthesizer is analyzed theoretically and compared with that of the heterodyne Frequency Synthesizer. For engineering application, a practical Microwave Digital Frequency Synthesizer used for telemetry receiver has been designed, which is characterized by simply structure, low phase noise and low spurious output. The output spectrum of experimental measurements is given.
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Grishina, Vera. "Blue laser for precision spectroscopy : toward optical frequency standard referenced to laser cooled calcium atoms." University of Western Australia. School of Physics, 2008. http://theses.library.uwa.edu.au/adt-WU2009.0046.
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Optical frequency standards with the reference to a narrow electronic transition of a laser-cooled collection of neutral atomic particles are becoming essential tools of research in modern precision physics experiments. In the core of a building block of an optical frequency standard is the optical continuous wave laser that has a good spectral purity of the emitted light. Such a stable optical oscillator is highly desirable in high resolution spectroscopy, if it emits in a good quality beam at a short visible wavelength. This Master thesis explores efficient techniques for building such an optical frequency source intended for use in the cooling and trapping of Calcium atoms scheme. The strong dipole transition at the blue wavelength in the atomic Calcium is needed to reduce the kinetic energy of atoms by nearly six orders of magnitude. A further reduction in the thermal energy of the laser cooled atoms is required to locate with ultra-high precision the 400 Hz narrow clock transition of the stable 40Ca isotope. The experimental methods that achieve this and approach sub-microkelvin temperature of the laser cooled bosonic isotopes of alkaline earths are inspected. The blue laser with a uniform intensity distribution in the beam is useful to maintain the trapped number of cold atoms during these experiments. The spectroscopic properties of the relative transitions in Calcium atom are also reviewed following relevant publications in the area. The constructed blue laser can be used as a primary wavelength source in the lasers network for cooling and trapping of Calcium atoms. These experiments will constitute part of the project to build an optical atom clock referenced to 40Ca narrow linewidth transition. The blue laser is constructed by generating second harmonic in a Potassium Niobate crystal, which is temperature controlled to use a type-I noncritical phase-matching of the optical nonlinear process. The power of the intracavity-generated second harmonic depends on the resonance properties of the optical resonator where this nonlinear crystal is placed. The study is aimed at characterising the designed optical resonator and the experimental parameters that describe it. The formula is derived that relates the resonance power enhancement coefficient with finesse and the power coupling contrast of a passive optical cavity. The obtained relationship is verfied during the experiments. The produced efficiency of the intracavity second harmonic generation is approx. 0.0023 mWblue/(mWred)2. The research work also examines the noise characteristics of the infrared diode laser that is used as a pump source for the intracavity generated second harmonic and determines the spectroscopic precision of the produced blue light. The frequency locking experiment is analysed using the unbalanced scheme of the polarisation stabilisation technique. The designed optical buildup cavity became a part of the unbalanced frequency discriminator in such a scheme. The results demonstrate high gain of frequency noise suppression of the stabilised laser. The unbalanced arrangement of the H}ansch-Couillaud technique has been possible due to a very low amplitude noise of semiconductor lasers.
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Dawkins, Samuel T. "Sapphire room temperature optical frequency reference : design, construction and application." University of Western Australia. School of Physics, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0200.
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A pair of high-stability optical frequency references has been developed. The devices are based on room temperature Fabry-Perot cavities with mirrors spaced apart by a hollow single-crystal sapphire element. The sapphire element delivers mechanical sti ness that provides improved immunity to vibrational perturbations compared with the more common spacers made from ultra-low expansion glass. The system is housed in an vacuum chamber designed to provide isolation from environmental perturbations through the use of an active thermal control system, suspension legs and a unique beam alignment system. The dimensional stability of the Fabry-Perot was translated into a highly stable laser frequency by frequency locking a 1064nm Nd:YAG laser to the centre of a mode of the cavity. This frequency lock was implemented by the Pound-Drever-Hall scheme. By careful design, this control system was able to hold the frequency of the laser to within parts in 1016 of the frequency of the fundamental cavity mode. The minimum fractional frequency stability of the laser frequency was measured at 2.1x10[-]14 for integration times of 0.8 s, limited by the residual instability of the Fabry-Perot cavity. The experimental methods used to measure the performance of the system have also been considered in depth. For example, the most common way of characterizing the frequency stability of a frequency standard is the Allan variance. It is demonstrated that, without care, data taken with modern frequency counters can produce erroneous and distorted results when their output is supplied to this algorithm. The method to avoid or account for these errors is also presented. The Fabry-Perot cavity performance is limited on long timescales by residual temperature uctuations, which can be ameliorated in future by enhancing the design of the thermal control system. At short timescales, the system is limited by vibration-induced uctuations together with a white noise source, that is yet to be identi ed, but may relate to fundamental thermodynamic temperature uctuations of the sapphire spacer. This system was used to measure the stability of an optical signal synthesised from a cryogenic microwave sapphire oscillator using an wide-band optical frequency comb. This was the rst demonstration of a multiplication of an ultra-stable signal from the microwave frequency domain into the optical frequency domain, without loss of delity at the level of 2x10[-]14.
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Patel, Bhagirath. "Model reference adaptive control system using frequency domain performance specifications." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0023/MQ52071.pdf.
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Vaudrey, Michael A. "A novel approach to multiple reference frequency domain adaptive control." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-08292008-063731/.
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Kergus, Pauline. "Data-driven model reference control in the frequency-domain : From model reference selection to controller validation." Thesis, Toulouse, ISAE, 2019. http://www.theses.fr/2019ESAE0031.
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Dans de nombreuses applications, aucun modèle physique du système n'est disponible, il s'agit alors de contrôler le système à partir de mesures entrées-sorties. Deux types d'approches sont envisageables : identifier un modèle du système puis l'utiliser afin de synthétiser un contrôleur, ce sont les méthodes indirectes, ou identifier le contrôleur directement à partir des données du système, ce sont les méthodes directes. Cette thèse se concentre sur les méthodes directes : l'objectif du travail présenté est de mettre en place une nouvelle méthode directe basée sur des données fréquentielles du système à contrôler. Après un tour d’horizon des méthodes indirectes existantes la méthode proposée est introduite. Il s’agit de résoudre un problème de suivi de modèle de référence : le problème d’identification est déporté du système vers le contrôleur. Dans ce cadre, deux techniques d’identification sont considérées dans cette thèse : l’interpolation de Loewner et l’approche des sous-espaces. De plus, les instabilités du système sont estimées en projetant les données fréquentielles disponibles. Cela permet de connaître les limites en performances du système et, par conséquent, de choisir des spécifications atteignables. Enfin, une analyse de la stabilité en boucle fermée permet d’obtenir un contrôleur stabilisant d’ordre réduit. Tout au long de ce travail, les différentes étapes de la méthode sont appliquées progressivement sur des exemples numériques. Pour finir, la méthode proposée est appliquée sur deux systèmes irrationnels, décrits par des équations aux dérivées partielles: un cristalliseur continu et un canal de génération. Ces deux exemples sont représentatifs de la catégorie de systèmes pour lesquels utiliser une méthode de contrôle directe est plus pertinentIn many applications, no physical description of the plant is available and the control law has to be designed on the basis of input-output measurements only. Two control strategies can then be considered : one can either identify a model of the plant and then use any kind of model-based technique (indirect methods) to obtain a control law, or use a data-driven strategy that directly compute the controller from the experimental data (direct methods). This work focuses on data-driven techniques : the objective of this thesis is to propose a new data-driven control technique based on frequency-domain data collected from the system to be controlled. After recalling some basics in feedback control, an overview of data-driven control is given. Then, the proposed method is introduced. It is a model reference technique : the identification problem is moved from the plant to the controller. In this work, two identification techniques are used to that purpose: the Loewner framework and the subspace approach. In addition, a technique is proposed to estimate the system’s instabilities. It allows to determine the performance limitations and to select achievable specifications. Finally, a stability condition, already known in data-driven control, is used during the reduction of the controller to ensure closed-loop stability. Along this thesis, the different steps of the method are progressively applied on two numercial examples. In the end, the proposed technique is applied on two irrational systems described by partial differential equations : a continuous crystallizer and an open-channel for hydroelectricity generation. These two examples illustrate the type of applications for which using a data-driven control method is indicated
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Tibbo, Maria S. "Optimization of a RF Single Ion Paul Trap for a 88Sr+ Ion Optical Clock Comparison." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26254.
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As part of the ongoing world-wide effort in improving time and frequency references, a high accuracy optical frequency standard was developed using the electric quadrupole allowed clock transition at 445 THz (674 nm) in a trapped and laser cooled 88Sr+ion. An ion trap system of the endcap design has been recently evaluated with a fractional frequency uncertainty which surpasses the accuracy of the current realization of the SI second. This thesis seeks to further evaluate the limiting systematic shifts of the device by optimizing a second ion trap reference based on a rf Paul trap design, which was then compared with the endcap trap reference frequency. The comparison of the two ion traps' reference frequencies confirmed an overall offset of -0.36 pm 0.08 Hz at the 445 THz reference frequency corresponding to a fractional frequency offset of 8 x 10^-16.
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RAYMUNDO, ELIZABETH VILCANAUPA. "DEVELOPMENT OF A METROLOGICAL STANDARD LASER FREQUENCY REFERENCE AT 532 NM." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2009. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=15143@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
Este trabalho faz parte do projeto do desenvolvimento do primeiro padrão de referência metrológica de frequência em torno de 532 nm no Brasil, para a realização prática da definição do metro. A pesquisa foi desenvolvida no Laboratório de Interferometria (Laint) da Divisão de Metrologia Óptica do Inmetro, em convenio com o Programa de Pós-Graduação em Metrologia para Qualidade Industrial da PUC-Rio. No âmbito deste projeto, a realização de uma nova referência em comprimento/freqüência é feita mediante a estabilização de um laser comercial Nd:YAG emitindo uma radiação em torno de 532 nm. A estabilização é realizada numa componente hiperfina de uma transição do iodo molecular (127)I(2), segundo as recomendações do Comitê Internacional de Pesos e Medidas (CIPM- Comité International des Poids et Mesures). O vapor de iodo é contido numa célula externa de absorção resfriada à uma temperatura entre -10 °C e -15 °C. Neste trabalho são apresentadas as seguintes etapas do projeto: Montagem opto-mecânica do sistema e alinhamentos ópticos. Detecção e registro dos sinais de absorção com célula à temperatura ambiente correspondendo às transições do iodo em torno de 532 nm.Caracterização do laser Nd:YAG ou seja determinação da freqüência de emissão laser em função da temperatura TLC do cristal laser, utilizando para este fim um medidor de comprimento de onda (wavemeter). Medições preliminares do sistema de resfriamento e de regulação da temperatura da célula de iodo por meio de um dispositivo termoelétrico Peltier. O controle automático duma temperatura teste de -13°C é realizado via programação LabView.
This work is part of the project for development of the first metrology reference for frequency standard around 532 nm in Brazil for the practical realization of the definition of the meter. The study was conducted at the Laboratory Interferometry (Laint) Inmetro, through an agreement with the Posgraduation Program in Metrology for Quality Industrial, PUC-Rio. In the scope of this project, the realization of a new reference length/frequency is made by the stabilization of a commercial laser Nd:YAG emitting radiation around 532 nm. The stabilization is performed on a component of a hyperfine transition of molecular iodine (127)I(2), according to the recommendations of the International Committee of Weights and Measures (CIPM- Comité International des Poids et Mesures).The iodine vapor is contained in an external absorption cell cooled to a temperature between -10°C and -15°C. This work presents the following stages of the project: Opto-mechanical assembly of the system and optical alignments. Detection and recording of signals with absorption cell at room temperature corresponding to iodine transitions around 532 nm. Characterization of Nd: YAG laser that is determining the frequency of the laser emission as a function of laser crystal temperature TLC, using for this purpose a meter wavelength (wavemeter). Preliminary measurements of the cooling system and temperature regulation of the iodine cell by a Peltier thermoelectric device. The automatic control of a test temperature of -13°C is achieved via LabView programming.
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Chao, David Ph D. Massachusetts Institute of Technology. "Self-referenced 1.5 [mu]m fiber frequency combs at GHz repetition rates." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70788.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.In title on title-age, "[mu]" appears as the lower case Greek letter. Page 142 blank. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 133-141).
Tremendous advances in recent years to the optical frequency comb, particularly frequency combs deriving from solid-state and fiber architectures, have enabled a host of important new applications to emerge - applications which include optical arbitrary waveform generation (OAWG), high-speed photonic analog-to-digital conversion (EPIC), space exploration (Astro- Comb) as well as precision spectroscopy and optical clocks. Fiber-based frequency combs have increasingly become attractive alternatives to solid-state systems due to their compact size and robust operation and have recently demonstrated performance comparable to their more traditional counterparts. One area for improvement, however, is in the repetition rate of such systems, as fiber frequency combs based on Ytterbium (Yb) and Erbium (Er) technologies currently only operate with repetition rates =/< 1GHz and =/< 300MHz, respectively, while solid-state frequency combs have been demonstrated up to 10GHz. This thesis reports on the development of a 1 GHz repetition rate Erbium-doped fiber laser frequency comb and discusses its potential to be scaled to even higher repetition rates. Nanojoule femtosecond pulses are produced at a GHz repetition rate and used to generate over an octave of supercontinuum spanning 1 [mu]m -2.4 [mu]m. Carrier-envelope offset frequency (fceo) detection using f-2f self-referencing provides confirmation that the continuum's frequency comb structure remains intact after undergoing amplification, compression, and supercontinuum generation. The fceo beat, along with the laser repetition rate frep, are locked to stable microwave reference oscillators, yielding, to the best of our knowledge, the first octave-spanning self-referenced optical frequency comb centered at the 1.5 [mu]m telecom band generated at or above a GHz repetition rate.
by David Chao.
Ph.D.
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Kock, Bjorn Ole. "Magneto-optical trapping of strontium for use as a mobile frequency reference." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4635/.
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Atomic Caesium clocks have made an astonishing development in the past few decades, with them gaining an order of magnitude in precision every decade. A new generation of atomic optical clocks is now emerging, which is moving to the forefront of timekeeping. By going from microwave to optical frequencies these clocks are now reaching fractional uncertainty levels in the 10\(^-\)\(^1\)\(^8\), opening a whole new range of exciting applications. This thesis presents the design and implementation of an experiment for laser cooling of strontium atoms, focusing on the mobility of the setup, opening a range of new applications as a mobile clock. The experimental apparatus applies a range of new techniques for strontium, such as the use of a two dimensional magneto-optical trap for pre cooling atoms, allowing for a compact and transportable system. A mobile laser system for laser cooling strontium atoms was realized. This includes a frequency doubling system for the main cooling transition. The constructed monolithic frequency doubling cavity has generated 300 mW of blue light and proven to be a stable setup suitable for a mobile system. The 3D-MOT was able to capture 4 * 10\(^5\) atoms with a long lifetime of 5.5 s, with further improvements for a significant increase in atom number currently being implemented.
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Kersalé, Yann. "References micro-ondes a resonateur saphir. Applications a la metrologie temps-frequence." Besançon, 2000. http://www.theses.fr/2000BESA2010.
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Dans ce memoire nous presentons l'etude et la realisation de references de frequence micro-ondes. Les oscillateurs etudies dans cette these sont tous developpes autour de resonateurs saphir a mode de galerie. La forte dependance de la frequence des resonateurs saphir a la temperature nous a amenes a etudier une structure compensee en temperature. Le modele permettant de simuler le comportement des resonateurs saphir, base sur la methode de raccordement modal, a ete adapte au cas de la structure compensee. Les resultats theoriques obtenus sont tout a fait en accord avec les resultats experimentaux. Le controle des fluctuations de temperature autour de la temperature d'inversion de la structure compensee est realise par un pid numerique utilisant un oscillateur a resonateur a quartz de coupe lc comme capteur. Ce regulateur assure un controle des fluctuations de temperature a mieux que 10 k pres et ceci aussi bien a temperature ambiante qu'a temperature cryogenique. Les resultats obtenus sur l'oscillateur a resonateur compense sont y() = 9. 10 1 3 pour des temps d'integration inferieurs a 40 secondes. Cependant, un vieillissement de l'ordre de 2. 10 8/jour est observe. Le resultat obtenu a court terme est principalement limite par le bruit propre de l'amplificateur d'entretien. Pour diminuer son influence nous avons developpe un detecteur de phase interferometrique qui, associe a une boucle de contre reaction, permet de corriger les fluctuations de phase de l'amplificateur. Nous obtenons un gain de 40 db sur le bruit de l'amplificateur. L'association du resonateur saphir cryogenique compense en temperature et de l'amplificateur corrige permettrait d'atteindre une stabilite de 10 1 4.
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Moon, Sung Tae. "Design of high performance frequency synthesizers in communication systems." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2329.
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Frequency synthesizer is a key building block of fully-integrated wireless communication
systems. Design of a frequency synthesizer requires the understanding of
not only the circuit-level but also of the transceiver system-level considerations. This
dissertation presents a full cycle of the synthesizer design procedure starting from the
interpretation of standards to the testing and measurement results.
A new methodology of interpreting communication standards into low level circuit
specifications is developed to clarify how the requirements are calculated. A
detailed procedure to determine important design variables is presented incorporating
the fundamental theory and non-ideal effects such as phase noise and reference
spurs. The design procedure can be easily adopted for different applications.
A BiCMOS frequency synthesizer compliant for both wireless local area network
(WLAN) 802.11a and 802.11b standards is presented as a design example. The two
standards are carefully studied according to the proposed standard interpretation
method. In order to satisfy stringent requirements due to the multi-standard architecture,
an improved adaptive dual-loop phase-locked loop (PLL) architecture is
proposed. The proposed improvements include a new loop filter topology with an
active capacitance multiplier and a tunable dead zone circuit. These improvements
are crucial for monolithic integration of the synthesizer with no off-chip components.
The proposed architecture extends the operation limit of conventional integerN type synthesizers by providing better reference spur rejection and settling time
performance while making it more suitable for monolithic integration. It opens a
new possibility of using an integer-N architecture for various other communication
standards, while maintaining the benefit of the integer-N architecture; an optimal
performance in area and power consumption.
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Yen, Shih-Wei. "Two-Satellite Positioning with a Stable Frequency Reference, Altimeters, and Bistatic Satellite Altimetry." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1483462536143397.
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Burress, Thomas Weston. "Mitigation of random and deterministic noise in mixed signal systems with examples in frequency synthesizer systems." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/13537.
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Master of ScienceDepartment of Electrical and Computer Engineering
William B. Kuhn
RF frequency synthesizer systems are prevalent in today’s electronics. In a synthesizer there is a sensitive analog oscillator that may be affected by two different types of noise. The first is random noise injection from active devices. This results in phase noise in the synthesizer’s spectrum. The second noise source is deterministic. A digital frequency divider with high-amplitude switching is an example of such a deterministic source. This noise enters the system through various forms of electric or magnetic field coupling and manifests itself as spurs or pulling. Both forms of noise can adversely affect system performance. We will first summarize methods for reducing noise. These already known steps have to do with layout techniques, device geometry, and general synthesizer topologies. Then we will show ways to isolate noisy interfering circuits from the sensitive analog systems. Finally, we present some considerations for reducing the effects of random noise. A power supply filter can improve the effects of deterministic noise such as undesired signals on the supply line. We show several ways to improve the rejection of high frequency supply noise (characterized by the power supply rejection ratio or PSRR) through the design of a voltage regulator. The emphasis is on new techniques for obtaining good PSRR at S-band frequencies and above. To validate the techniques, we designed a regulator in Peregrine Semiconductor’s .25µm ULTRA CMOS Silicon on Sapphire process. It produces a 2.5V output with an input ranging from 2.6V to 5V and has a maximum current sourcing of 70mA. The regulator’s low drop out performance is 60mV with no load and it achieves a power supply ripple reduction of 29.8 dB at 500 MHz. To address random noise in synthesizers, the thesis provides preliminary investigation of an oscillator topology change that has been proposed in the literature. This proposed change reduces the phase noise of the oscillator within the overall system. A differential cross-coupled design is the usual topology of choice, but it is not optimal for noise performance. We investigate current noise injection in the traditional design and present an updated design that uses a differential Colpitts oscillator as an alternative to classic cross-coupled designs.
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Guillot, Pierre. "Contribution à l’étude des architectures de radiocommunications à références d’horloges hautes fréquences : application des résonateurs BAW à la génération de fréquence de référence dans les systèmes de communication mobile." Thesis, Paris Est, 2011. http://www.theses.fr/2011PEST1025/document.
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Ces travaux de thèse portent principalement sur la génération de signal d'horloge haute fréquence. Dans un premier temps, la faisabilité d'un oscillateur à base de BAW y est démontrée par la conception d'un circuit en technologie CMOS 65 nm. Les deux principales innovations sont les performances en terme de stabilité (bruit de phase de -128dBc/Hz à 100kHz de la porteuse) et en précision (implémentation d'une banque de capacités ayant un pas de 0.4ppm) de l'oscillateur. Sa consommation est optimisée (0.9mW). Il est suivi d'un diviseur faible bruit (-140dBc/Hz à 100kHz de la porteuse) délivrant un signal à 500MHz. Dans un second temps, les imperfections des résonateurs BAW sont analysées. Une procédure de calibration comprenant une calibration initiale et une calibration en boucle ouverte est alors proposée. Cette dernière repose sur l'identification et l'utilisation d'un modèle comportemental du dispositif, régulièrement mis à jour grâce à un filtre de Kalman. Une précision de 0.4 ppm est atteinteThis thesis deals with the gigahertz range reference frequency generation. In a first part, this document presents the design of a 500 MHz oscillator in a 65 nm CMOS process using a 2 GHz Bulk Acoustic Wave resonator. A digital frequency control is implemented using a switched capacitor bank in parallel to the resonator. The tuning range is up to 500 kHz with a minimum step of 200 Hz. The oscillator core uses a differential topology and is designed for low phase noise (-128 dBc/Hz at 100 kHz offset) at low power consumption (0.9 mW). It is followed by a low noise divider which provides a 500 MHz output with a phase noise of -139 dBc/Hz at 100 kHz offset from the carrier. In a second part, we consider a method for the calibration of a BAW based frequency reference. In fact, the frequency variations of a BAW oscillator against process, supply, temperature and aging effects make difficult its use as a frequency reference. We propose here a method based on Kalman filtering to identify with high precision a behavioral model of this BAW reference, thus enabling its use in an open loop frequency tuning. A precision of 0.4 ppm is achieved
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Miri, Lavasani Seyed Hossein. "Design and phase-noise modeling of temperature-compensated high frequency MEMS-CMOS reference oscillators." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41096.
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Frequency reference oscillator is a critical component of modern radio transceivers. Currently, most reference oscillators are based on low-frequency quartz crystals that are inherently bulky and incompatible with standard micro-fabrication processes. Moreover, their frequency limitation (<200MHz) requires large up-conversion ratio in multigigahertz frequency synthesizers, which in turn, degrades the phase-noise. Recent advances in MEMS technology have made realization of high-frequency on-chip low phase-noise MEMS oscillators possible.
Although significant research has been directed toward replacing quartz crystal oscillators with integrated micromechanical oscillators, their phase-noise performance is not well modeled. In addition, little attention has been paid to developing electronic frequency tuning techniques to compensate for temperature/process variation and improve the absolute frequency accuracy.
The objective of this dissertation was to realize high-frequency temperature-compensated high-frequency (>100MHz) micromechanical oscillators and study their phase-noise performance. To this end, low-power low-noise CMOS transimpedance amplifiers (TIA) that employ novel gain and bandwidth enhancement techniques are interfaced with high frequency (>100MHz) micromechanical resonators. The oscillation frequency is varied by a tuning network that uses frequency tuning enhancement techniques to increase the tuning range with minimal effect on the phase-noise performance. Taking advantage of extended frequency tuning range, and on-chip temperature-compensation circuitry is embedded with the sustaining circuitry to electronically temperature-compensate the oscillator. Finally, detailed study of the phase-noise in micromechanical oscillators is performed and analytical phase-noise models are derived.
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Trimble, William L. "High-resolution spectroscopy in ¹¹⁵In⁺ and prospects for an indium ion optical frequency reference /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9661.
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LEVRAY, FREDERIQUE MYRIAM. "Evaluation en laboratoire et sur le terrain de trois cardiofrequencemetres par reference au systeme holter." Clermont-Ferrand 1, 1988. http://www.theses.fr/1988CLF11004.
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Burrell, M. D. "Assessment of time frequency warping for use as a reference degradation for assessing synthetic speech." Thesis, Aston University, 1992. http://publications.aston.ac.uk/15289/.
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At present there is no standard assessment method for rating and comparing the quality of synthesized speech. This study assesses the suitability of Time Frequency Warping (TFW) modulation for use as a reference device for assessing synthesized speech. Time Frequency Warping modulation introduces timing errors into natural speech that produce perceptual errors similar to those found in synthetic speech. It is proposed that TFW modulation used in conjunction with a listening effort test would provide a standard assessment method for rating the quality of synthesized speech. This study identifies the most suitable TFW modulation variable parameter to be used for assessing synthetic speech and assess the results of several assessment tests that rate examples of synthesized speech in terms of the TFW variable parameter and listening effort. The study also attempts to identify the attributes of speech that differentiate synthetic, TFW modulated and natural speech.
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Jansson, J. P. (Jussi-Pekka). "A stabilized multi-channel CMOS time-to-digital converter based on a low frequency reference." Doctoral thesis, Oulun yliopisto, 2012. http://urn.fi/urn:isbn:9789514299322.
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Abstract The aim of this work was to improve the performance and usability of a digital time-to-digital converter (TDC) in CMOS technology. The characteristics of the TDC were improved especially for the needs of pulsed laser time-of-flight (TOF) distance measurement, where picosecond-level precision with a long µs-level measurement range is needed in order to approach mm-level measurement accuracy. Stability in the face of process, voltage and temperature variations, multiple measurement channels, alternative measurement modes, a high integration level, standard interfaces and simple usage were the main features for development. The measurement architecture is based on counter and timing signal interpolation on two levels. The counter counts the full reference clock cycles between the timing signals, while a new recycling delay line developed in this thesis interpolates within the reference clock cycle. This technique utilizes a short delay line several times per reference clock cycle, which minimizes the interpolation nonlinearity. The same structure also makes the use of a low, MHz-level reference frequency possible, and thus only a crystal is needed as an external oscillator component. The parallel load capacitor-scaled delay line structure acts as the second, sub-gate-delay interpolation level. The INL does not accumulate in elements connected in parallel, and the load capacitance differences enable high, ps-level resolution to be achieved. Four TDC circuits in 0.35 µm CMOS technology were designed and tested in the course of this work, of which the latest, a 7-channel TDC, is able to measure the time intervals between the start pulse and three separate stop pulses in one measurement and to resolve the pulse widths or rise times at the same time. In laser TOF distance measurement this functionality can be used when several echoes arrive at the receiver, and also to compensate for the detection threshold problem known as timing walk error. The TDC achieves 8.9 ps interpolation resolution within the cycle time of a 20 MHz reference clock using only 8 delay elements on the first interpolation level and 14 delay elements on the second. A measurement precision better than 9 ps was achieved without using result post-processing or look-up tables. This work shows that versatile, high performance TDCs can be created in standard CMOS technologyTiivistelmä Väitöskirjatyön tavoitteena oli parantaa CMOS-aika-digitaalimuuntimien suorituskykyä ja käytettävyyttä. Muuntimen ominaisuuksia kehitettiin erityisesti laseretäisyysmittauksen tarpeita ajatellen, missä millimetritason mittaustarkkuus laajalla mittausaluella edellyttää aika-digitaalimuuntimelta pikosekuntitason tarkkuutta mikrosekuntien mittausalueella. Stabiilius prosessiparametri-, jännite- ja lämpötilavaihteluita vastaan, useat mittauskanavat, useat mittausmoodit, korkea integraatioaste, standardoidut liitäntäväylät ja helppo käytettävyys olivat erityisesti kehityksen kohteina. Suunniteltu mittausarkkitehtuuri koostuu laskurista ja kaksitasoisesta ajoitussignaali-interpolaattorista. Laskuri laskee kokonaiset referenssikellojaksot ajoitussignaalien välillä ja työssä kehitetty referenssiä kierrättävä viivelinjarakenne rekistereineen interpoloi ajoitussignaalien paikat referenssikellojaksojen sisältä. Referenssinkierrätystekniikka hyödyntää lyhyttä viivelinjaa useampaan kertaan kellojakson aikana, mikä minimoi epälineaarisuuden interpoloinnissa. Sama rakenne mahdollistaa myös MHz-tason referenssitaajuuden, jolloin matalataajuista kidettä voidaan käyttää referenssilähteenä. Toinen interpolointitaso koostuu rinnakkaisista kapasitanssiskaalatuista viive-elementeistä, mitkä mahdollistavat alle porttiviiveen mittausresoluution. Rinnakkaisessa rakenteessa elementtien epälineaarisuudet eivät summaudu, mikä mahdollistaa pikosekuntitason mittaustarkkuuden. Väitöskirjatyössä suunniteltiin ja toteutettiin neljä aikavälinmittauspiiriä käyttäen 0,35 µm CMOS-teknologiaa, joista viimeisin, 7-kanavainen muunnin kykenee mittaamaan aikavälin useampaan pulssiin yhdellä kertaa sekä voi selvittää samalla pulssien leveydet tai nousuajat. Laseretäisyysmittauksessa monikanavaisuutta voidaan käyttää kun useita kaikuja lähetetystä pulssista saapuu vastaanottimeen sekä kompensoimaan mittauksessa esiintyviä muita virhelähteitä. Käytettäessä 20 MHz:n kidettä referenssilähteenä muunnin saavuttaa alle 9 ps:n interpolointiresoluution ja tarkkuuden ilman epälineaarisuudenkorjaustaulukoita. Työ osoittaa, että edullisella CMOS-teknologialla voidaan toteuttaa monipuolinen ja erittäin suorituskykyinen aika-digitaalimuunnin
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Jansson, Anna. "Sodium and potassium regulation : with special reference to the athletic horse /." Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1999. http://epsilon.slu.se/avh/1999/91-576-5718-1.pdf.
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Dikgola, Kobamelo. "Spatial and temporal variation of inundation in the Okavango Delta, Botswana; with special reference to areas used for flood recession cultivation." University of the Western Cape, 2015. http://hdl.handle.net/11394/4677.
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Philosophiae Doctor - PhDThe Okavango Delta is recognized as one of the famous inland wetlands and its sustainable use is important for socio-economic development of Botswana. The Okavango delta comprises permanent swamps, seasonal swamps, and drylands on islands within the delta and the surrounding areas, sustained by Okavango river inflows from upstream and local rainfall. TheOkavango River splits into several distributary channels within the delta. Areas which are flooded annually vary in response to varying inflows into the delta. Peak inflows into the delta occur during the February to May period. Due to the low gradient over the delta, these inflows move slowly resulting in peak outflows from the delta occurring during the June to August period. The inundated area over the entire delta increases from May until it reaches maximum inAugust and starts to decrease from September, reaching minimum inundated area in the months of December and January. The incoming flood wave into the delta and maximum inundation is out of phase with the local rainfall season.Communities living within and around the delta derive their livelihoods from tourism, hunting, fishing, livestock rearing, and crop production. Crop production is carried out on drylands and within floodplains. Some of the households take advantage of the increase in soil moisture arising from this inundation along floodplains to cultivate their crops as the floods recede. This practice is locally referred to as molapo farming which highly depends on inundation of floodplains. The availability of floodplain inundation highly depends on the magnitude of inflows into the delta and the local rainfall which are highly variable resulting in uncertainty regarding successful crop production, availability of livestock grazing areas, and uncertainty in reliance on the wetlands resources such as fishing. The uncertainty experienced in timing of extreme events which cause flooding of resulting in water reaching areas or floodplains where it is not wanted, and also uncertainity in timing of low flows, therefore water not reaching some parts of the delta.Several hydrological studies have been carried out with the aim of improving the understanding of the spatial and temporal dynamics of flows throughout the delta including predicting areas that are likely to be inundated each year. The significant gap addressed by this research is to improve the understanding of the spatial and temporal influence of magnitude and timing of flows on floodplain inundation. Local rainfall on the delta is highly variable over time and space due to its convective nature. This research also addresses the rainfall temporal and spatial variations and its implications on floodplain inundation. The knowledge about spatial extent and duration of floodplain inundation should assist in predicting each year the viability of molapo farming. Three research site, Shorobe, Tubu and Xobe are selected as case studies to understand the dynamics of floodplain inundation induced either by inflows or local rainfall. Local rainfall during the December to March period enables the crops to reach maturity. The onset of the rainy season is very important in supporting sowing of crop seeds. Local rainfall on the delta varies considerably. Aerial rainfall interpolation shows a change in rainfall magnitudes over space in different rainfall months, i.e different parts of the delta receive different rainfall magnitudes in different months of the rainy season. The spatial variation is mainly associated with the migration of the ITCZ southwards first through East Africa during October andNovember and down over Southern Africa in December to February. The movement of the ITCZ brings rainfall concentration on the northern and eastern parts of the Okavango Delta during December to January and bringing rainfall concentration to the northwestern part of the delta around February. However, rainfall spatial correlation between stations can be poor even within the first 150 km therefore implying neighboring places do not experience floodplain inundation by rainfall at the same time. The poor spatial correlation of rainfall between neighboring stations reflects the erratic nature of rainfall in the Okavango Delta characterised by localized thunderstorms. Change detection shows change points in rainfall which can be associated with ENSO episodes. A change point is identified in 1976 and 1977 which can be associated with the El Nino episodes during those years and two change points identified in 1999 and 2004 which can be associated with the La Nina episodes, therefore rainfall induced floodplain inundation can also be associated with wet and dry ENSO episodes. Rainfall does not show any significant trends except for an increasing trend on 10th percentile of Shakawe rainfall. Rainfall also does not show any cyclic behavior. Rainfall over the Okavango Delta can be divided into three unique homogenious sub-regions; sub-region 1: the northern part following the GEV probability distribution and being the region with highest rainfall amounts; sub-region 2: the lower northern and the outlet parts of the Okavango Delta following the GPA distribution with moderate rainfall; and sub-region 3: the middle part of the delta extending to the western and the eastern fringes of the delta, following the P3 distribution and having the lowest rainfall.The main characteristic that defines the Okavango Delta flows at Mohembo is its cyclic behavior. Three significant cycles are identified, close to 10, 20 and 40 years. No significant trends are identified, only a decreasing trend in minimum flows. Change points are identified in 1979 and 1988 and these can be explained by the existing cyclicity since no major land use changes have taken place in the Okavango River Basin upstream before 1989. The existence of cyclicity in Okavango River flows at Mohembo also explains the periodic wetting and drying of different floodplains in the delta. A long period of low flows was experienced from 1983 until 2003 and floodplain inundation extent was greatly reduced, more especially during the 1993-2003. During the 1993-2003 period, flows could no longer reach Maun Bridge along Thamalakne River, therefore leaving molapo floodplains around Boteti River, Gomoti River and Thaoge River to dry out. The 10 and 40 year return floods are important as they indicate the probability of a flood magnitude which has potential to result in major inundation in the Okavango Delta. Therefore, flood magnitudes with recurrence interval 10 and 40 years have high probability of occurring and can cause major floodplain inundation as they can be above the 2009 flood of 969 m3/s, which was the return of major inundation of Okavango Delta floodplains after a long period of dryness. The Ngoqa-Maunachira distributary channel of the Okavango River receives 32% of flow volumes entering the Okavango Delta at Mohembo. 12 % of the Mohembo flow volumes reach the Jao-Boro distributary whilst 1% is received by the Thaoge distributary. Therefore more inundation is experienced along the Ngoqa-Maunachira system compared to the other two. Only about 2% of the Mohembo flow volumes leave the Okavango Delta through Boteti River. Long term shifting of flow direction amongst reaches along the Okavango Delta distributaries is evident more especially along the Ngoqa-Maunachira River system. This results in shifting of inundation. Sub-surface water respond significantly to local rainfall and inflows with high soil moisture conditions retained at 60 cm and 100 cm below the ground.
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Penrod, Bruce M. "A NEW CLASS OF PRECISION UTC AND FREQUENCY REFERENCE USING IS-95 CDMA BASE STATION TRANSMISSIONS." International Foundation for Telemetering, 2004. http://hdl.handle.net/10150/605296.
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International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, CaliforniaA new class of precision timing and frequency reference is introduced that indirectly receives GPS timing and frequency information via TIA/EIA Standard IS-95 Code Division Multiple Access (CDMA) mobile telecommunications base station transmissions. Like cell phones, these products operate indoors without external antennas and provide accuracy, low cost and ease of installation. The technology fits particularly well in IP network synchronization and quality-of-service monitoring applications where rooftop antenna installation is often impossible. The salient characteristics of the IS-95 CDMA signals that make them suitable for this purpose and a general CDMA timing receiver architecture are described. Performance data versus similar references that use conventional GPS reception are also presented.
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Esseili, Fatima A. "Deictic Reference: Arabs vs. Arab Americans." University of Toledo / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1147284821.
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Hopper, David J. "Investigation of laser frequency stabilisation using modulation transfer spectroscopy." Queensland University of Technology, 2008. http://eprints.qut.edu.au/16667/.
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Optical frequency standards are necessary tools for accurate measurement of time and length. In practice these standards are stabilised laser systems locked to a known frequency reference. These references are typically the resonant frequencies of the atoms of an absorption medium that have been theoretically calculated to a high degree of accuracy. This thesis describes a combination of experimental and theoretical research performed on modulation transfer spectroscopy (MTS)--a technique used to frequency stabilise a laser in order to produce an accurate frequency reference--with emphasis placed on developing techniques and procedures to overcome the limitations found in existing MTS stabilised laser systems. The focus of the thesis is to generate a highly accurate frequency reference by researching the system parameters that will increase the signal to noise ratio and improve the accuracy of the reference through refinement of the signal structure. The early theoretical interpretation of MTS was effectively a low absorption approximation that occurs at low pressures. This approximation ignores the depletion of beam energy through absorption and is a distinct limitation of the theoretical model in its ability to accurately predict the influence of a range of system parameters on signal strength and structure. To overcome this limitation a 3-D (or volumetric) analysis was developed and is presented here for the first time. This volumetric model is a measure of two depleted beams interacting collinearly in an absorbing medium of iodine and is described to accurately predict the signal maximum as a function of pressure for all wavelengths. This model was found to be more accurate in predicting the influence of system parameters on the signal strength and structure, including that of pump beam intensity, pressure, saturation parameter, cell length and modulation parameters. The volumetric model is a novel approach to MTS theory but is more complex computationally than the traditional low pressure model and therefore more difficult to implement in many situations. To overcome this problem a hybrid model was developed as a combination of the low pressure and volumetric models. The comparison between the rigorous volume model and the hybrid model indicate that there is a deviation in the signal strength at high pressures. However, the agreement was very good in the pressure regimes that are commonly used to realise actual frequency references. Comparison of the hybrid model to experimental data was performed over a range of different wavelengths (532 nm, 543.5 nm, 612 nm and 633 nm) and found to be in close agreement. This gives confidence in the model to accurately predict signal strength and structure in any situation. Three mechanisms have been identified that limit the accuracy of frequency references due to the creation of residual amplitude modulation (RAM) where it shifts the frequency of the reference. The influence of RAM is included in the hybrid model as a ratio of the amplitude modulated and frequency modulated components of the saturating beam. These RAM production mechanisms result from the modulation of the saturating beam, the overlap of the beams in the medium, and the differential absorption of the sidebands in the medium. While the first mechanism has been previously reported the latter two are discussed here in detail for the first time. RAM generated by the modulators used (acousto-optic or electro-optic modulators) was typically of the order of 10% to 12%, depending on the excursion of the created sidebands. RAM generated by an asymmetric beam overlap with the modulators used was found to be as large as 30%. A combination of these two independent mechanisms can be used to provide a "RAM-free" state of the system by using one to cancel the effects of the other. The third RAM generation process--medium induced RAM--is difficult to remove but through a careful combination of absorption related parameters--namely, pump intensity, cell length, pressure and detector phase--the effects of RAM can be removed, leading to a distortion free MTS signal. Further investigation into the predictions provided by the hybrid model shows that there is a complex relationship between cell length and the optimum pressure required for maximum signal strength, such that longer cell lengths will not necessarily improve the signal strength. This is contrary to conventional thinking and is important in the MTS design process to reduce unnecessary costs and improve the signal to noise ratio and frequency accuracy. Optimisation of frequency stabilised laser systems using MTS are generally performed using trial and error. Comparison of these optimum parameter values to those predicted by the hybrid model show that for popular wavelengths such as 532 nm they are similar. In addition, the hybrid model is able to predict the frequency shifts that arise within the system parameters used and has shown that existing systems being used at 532 nm, 633 nm and 778 nm could improve their signal to noise ratio and accuracy through a variation in the parameters. A methodology based on the hybrid model is presented that can be used to calculate the optimum parameters for maximum signal strength and a "RAM-free" state for any wavelength. This systematic approach can therefore be used to guide the design of actual frequency stabilised laser systems prior to and during the design process.
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Knabe, Kevin. "Using saturated absorption spectroscopy on acetylene-filled hollow-core fibers for absolute frequency measurements." Diss., Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/4126.
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Lei, Feiran. "Injection Locked Synchronous Oscillators (SOs) and Reference Injected Phase-Locke Loops (PLL-RIs)." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492789278258943.
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Pourkamali, Siavash. "High frequency capacitive single crystal silicon resonators and coupled resonator systems." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/26563.
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Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2007.Committee Chair: Ayazi, Farrokh; Committee Member: Allen, Mark; Committee Member: Brand, Oliver; Committee Member: Degertekin, Levent; Committee Member: Papapolymerou, John. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Hsiao, Sen-Wen. "Built-in test for performance characterization and calibration of phase-locked loops." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51790.
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The objective of this dissertation is to propose circuit architectures and techniques for built-in test and calibration of phase-locked loops. The design of phase-locked loops is first investigated to achieve a robust performance over process, temperature, voltage corners with minimum overhead. Different design techniques including adding loop programmability, increasing area efficiency, reducing noise immunity, and increasing frequency coverage are discussed. Secondly, built-in testing of phase-lock loops using sensors are proposed for loop dynamic parameters and reference spur. An integrator is designed to extract the subtle response from the system so that target parameters can be predicted. Different testing methodologies are applied different specification testing as well. Finally, an on chip phase-locked loop design is implemented for reference spur calibration. The phase-locked loop is designed with a programmable reference spur range. A static phase offset detector is included to identify the optimal setting of reference spur in the feedback system. The integrated jitter performance is improved by the calibration mechanism. The results of this thesis serve as an on-chip built-in self-test and self-calibration solution for embedded phase-locked loops in a high integration system.
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Samur-San, Martin Juan Eduardo 1967. "Frequencia da obesidade e seus fatores determinantes em crianças e adolescentes com sindrome de down atendidas em um centro de referencia." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/309386.
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Orientador: Gabriel HesselDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas
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Resumo: A obesidade é definida como um excesso de gordura corporal em relação à massa magra, sendo uma doença com aumento da prevalência nos últimos anos. O Objetivo desse trabalho foi estudar a frequência da obesidade e os fatores determinantes em crianças e adolescentes com síndrome de Down. Casuística e Métodos: O estudo foi realizado em 47 crianças e adolescentes matriculados no Centro de Educação Especial Síndrome de Down, divididos em 3 sub-grupos, em faixas etárias, para a análise dos resultados: A) de 5 a 10 anos; B) de 11 a 15 anos e C) de 16 a 20 anos de idade. As variáveis estudadas foram: peso, estatura, índice de massa corporal (IMC), dobra cutânea triciptal (DCT), dobra cutânea subescapular (DCSE), circunferência da cintura (CC), bioimpedância (BIA) e prática de atividade física com a interpretação pelo IPAQ versão curta. Para comparação das proporções foi empregado o teste do Qui-quadrado ou teste exato de Fischer. Para correlação entre o IMC e a DCT, DCSE, CC e BIA foi utilizado o coeficiente de correlação de Pearson. O nível de significância adotado foi de 5%. Resultados: A idade das crianças e adolescentes com SD variou de 5 a 20 anos com média de 12,17 anos. Em relação à estatura, observou-se que empregando os valores de referência do Center for Disease Control and Prevention (CDC), 25/47 (51,19%) apresentaram baixa estatura. Contudo, empregando-se uma curva especifica para a síndrome de Down, curvas de Cronk et al., apenas 1/47 (2,12%) apresentou baixa estatura. A freqüência da obesidade por meio dos diferentes indicadores foi: IMC = 36,17%, DCT = 30%, DCSE = 62,50%, CC = 22,85% e BIA = 7,31%. A freqüência de obesidade por meio do IMC não apresentou diferença estatisticamente significativa nas seguintes faixas etárias: 5 a 10 anos, 11 a 15 anos e de 16 a 20 anos. O coeficiente de correlação entre o IMC e os outros métodos de avalição nutricional foi de: 0,67 com a DCT, 0,71 com a DCSE, 0,95 com a CC e 0,55 com o percentual de massa gorda da bioimpedância. Em relação à atividade física observou-se que 4/17 (23,52%) foram classificados como sedentários, 1/17 (5,88%) foram classificados como insuficiente ativo A, 5/17 (29,41%) foram classificados como insuficiente ativo B, 4/17 (23,52%) como ativo e 3/17 (17,64%) como muito ativo. Quando esses resultados foram comparados com o estado nutricional, não foi observada correlação significativa. Nas mães de crianças e adolescentes com síndrome de Down, observou-se sobrepeso em 4/10 e obesidade em 4/10. Conclusões: 1. Há baixa estatura na maioria das crianças e adolescentes se for adotada como referência a curva do CDC. 2. É alta a freqüência de obesidade nas crianças e adolescentes com SD na faixa etária de 5 a 20 anos, variando de 22,85% a 62,50%, de acordo com o método adotado (IMC, DCT, DCSE e CC). 3. Não há diferença da freqüência de obesidade em relação ao gênero nas diferentes faixas-etárias avaliadas. 4. Observou-se correlação entre IMC e os diferentes métodos aplicados para avaliação nutricional (DCT, DCSE, CC e BIA). 5. Não foi observada relação entre obesidade e nível de atividade física em 17 questionários analisados.
Abstract: Obesity is defined as an excess of body fat relative to lean body mass, is a disease with increasing prevalence in recent years. The objective of this work was to study the frequency of obesity and its determinants in children and adolescents with Down syndrome. Methods: The study was conducted in 47 children and adolescents enrolled at the Centro de Educa?o Especial S?drome de Down (Center for Special Education Down Syndrome) divided into 3 sub-groups by age, for the analysis of the results: A) from 5 to 10 years old, B) 11 to 15 years old and C) from 16 to 20 years old. The variables studied were: weight, height, body mass index (BMI), triceps skinfold, subscapular skinfold, waist circumference (WC), bioelectrical impedance analysis (BIA) and physical activity with the interpretation the IPAQ short version. To compare proportions, the chi-square or Fisher exact test were applied. For correlation between BMI and triceps skinfold, subscapular skinfold, WC and BIA used the correlation coefficient of Pearson. The level of significance was 5%. Results: The age of children and adolescents with Down syndrome ranged from 5 to 20 years old with an average of 12.17 years. About height, it was observed that using benchmarks from the Center for Disease Control and Prevention (CDC), 25/47 (51.19%) had short stature. However, using an specific curves for Down syndrome, curves Cronk et al., Only 1 / 47 (2.12%) had short stature. The frequency of obesity through the different indicators were: BMI = 36.17%, triceps skinfold = 30%, subscapular skinfold = 62.50%, WC = 22.85% and BIA = 7.31%. The prevalence of obesity by BMI did not show a statistically significant difference in the ages 5 to 10 years, 11 to 15 years and 16 to 20 years. The correlation coefficient between BMI and other methods of nutritional assessment was: 0.67 with the triceps skinfold, with subscapular skinfold 0.71, 0.95 to WC and 0.55 with percentage of fat mass in elderly women. In relation to physical activity showed that 4 / 17 (23.52%) were classified as sedentary, 1 / 17 (5.88%) were classified as insufficiently active A, 5 / 17 (29.41%) were classified as insufficient asset B, 4 / 17 (23.52%) as active and 3 / 17 (17.64%) as very active. When these results were compared with the nutritional status, there was no significant correlation. In mothers of children and adolescents with Down syndrome, overweight was observed in 4 / 10 and obesity in 4 / 10. Conclusions: 1. There's stature in most children and adolescents if adopted as a reference curve of the CDC. 2. The high frequency of obesity in children and adolescents with DS aged 5 to 20 years, ranging from 22.85% to 62.50%, according to the method adopted (BMI, skinfolds, and WC). 3. There is no difference in the frequency of obesity in relation to gender in different age-groups studied. 4. A correlation between BMI and the various methods used for nutritional assessment (triceps skinfold, subscapular skinfold, waist circumference and BIA). 5. There was no relationship between obesity and physical activity in 17 questionnaires analyzed.
Mestrado
Saude da Criança e do Adolescente
Mestre em Saude da Criança e do Adolescente
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Tabrizian, Roozbeh. "Temperature-compensated silicon-based bulk acoustic resonators." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52929.
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Microelectromechanical resonators have found widespread applications in timing, sensing and spectral processing. One of the important performance metrics of MEMS resonators is the temperature sensitivity of their frequency. The main objective of this dissertation is the compensation and control of the temperature sensitivity of silicon resonators through engineering of device geometry and structural composition. This has been accomplished through formation of composite platforms or novel geometries based on dispersion characteristics of guided acoustic waves in single crystalline silicon (SCS) microstructures. Furthermore, another objective of this dissertation is to develop efficient longitudinal piezoelectric transduction for in-plane resonance modes of SCS resonators that have lithographically-defined frequencies, to reduce their motional resistance (Rm).
A uniformly distributed matrix of silicon dioxide pillars is embedded inside the silicon substrate to form a homogenous composite silicon-oxide platform (SilOx) with nearly perfect temperature-compensated stiffness moduli. Temperature-stable micro-resonators implemented in SilOx platform operating in any desired in- and out-of-plane resonance modes show full compensation of linear temperature coefficient of frequency (TCF). Overall frequency drifts as small as 80 ppm has been achieved over the industrial temperature range (-40°C to 80°C) showing a 40x improvement compared to uncompensated native silicon resonators. A 27 MHz temperature-compensated MEMS oscillator implemented using SilOx resonator demonstrated sub-ppm instability over the industrial temperature range. Besides this, a new formulation of different resonance modes of SCS resonators based on their constituent acoustic waves is presented in this dissertation. This enables engineering of the acoustic resonator to provide several resonance modes with mechanical energy trapped in central part of the resonator, thus obviating narrow tethers traditionally used for anchoring the cavity to the substrate. This facilitates simultaneous piezoelectric-transduction of multiple modes with different TCFs through independent electrical ports, which can realize highly accurate self-temperature sensing of the device using a beat frequency (fb) generated from linear combination of different modes. Piezoelectrically-transduced multi-port silicon resonators implemented using this technique provide highly temperature-sensitive fb with a large TCF of ~8500 ppm/°C showing 100x improvement compared to other Quartz/MEMS counterparts, suggesting these devices as highly sensitive temperature sensors for environmental sensing and temperature-compensated/oven-controlled crystal oscillator (TCXO/OCXO) applications.
Another part of this dissertation introduces a novel longitudinal piezoelectric transduction technique developed for implementation of low Rm silicon resonators operating in lithographically defined in-plane modes. Aluminum nitride films deposited on the sidewalls of thick silicon microstructures provides efficient electromechanical transduction required to achieve low Rm. 100 MHz SCS bulk acoustic resonators implemented using this transduction technique demonstrates Rm of 33Ω showing a 100x improvement compared to electrostatically transduced counterparts. Low-loss narrow-band filters with tunable bandwidth and frequency have been implemented by electrical coupling of these devices, showing their potential for realization of truly reconfigurable and programmable filter arrays required for software-defined radios.
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Briggs, Kristen Phelps. "Establishing a high-frequency standard reference sequence stratigraphy, sea-level curve, and biostratigraphy for Morrowan strata of the Lower Absaroka I time slice based upon the Bird Spring Formation, Arrow Canyon, Nevada /." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd807.pdf.
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Briggs, Kristen Phelps. "Establising a high-frequency standard reference sequence stratigraphy, sea-level curve, and biostratigraphy for Morrowan strata of the Lower Absaroka I time slice based upon the Bird Spring Formation, Arrow Canyon, Nevada." BYU ScholarsArchive, 2005. https://scholarsarchive.byu.edu/etd/301.
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For the same reasons which prompted its ratification in 1990 as the Global Stratotype Section and Point for the Mid-Carboniferous boundary, namely, section completeness, abundant fossils, and excellent exposure, the Morrowan Arrow Canyon Bird Spring strata is recommended as a candidate standard sequence stratigraphic reference for the Morrowan portion of the Lower Absaroka I supersequence. The stratigraphic architecture of Morrowan strata in Arrow Canyon was largely controlled by high-amplitude (100-m), high-frequency sea-level changes. Outcrop data and facies stacking patterns define 59 fifth-order fundamental cycles. These fundamental cycles stack into ten third-order sequences with an average duration of 320 ka. Changes in both cycle thickness and fundamental cycle type indicate that the second-order sea-level curve of Golonka and Keissling for the Lower Absaroka Ia supersequence should be modified to reflect rising sea-level from the Mid-Carboniferous boundary with maximum flooding conditions ~120 to 135 meters above the Mid-Carboniferous boundary, followed by falling sea-level to ~6 meters below the Morrowan-Atokan boundary in Arrow Canyon. Additionally, cycle diagnostic conodonts and foraminifera permit correlation of selected third-order sequences to basins containing time-equivalent strata.
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Holmberg, Pär. "Modelling the transient response of windings, laminated steel coresand electromagnetic power devices by means of lumped circuits : With special reference to windings with a coaxial insulation system." Doctoral thesis, Uppsala University, Department of High Voltage Research, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-548.
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Electromagnetic transients impinging on electromagnetic power devices - such as electric machines, transformers and reactors - can stress the design severely. Thus the magnitudes of the transients are often decisive for the design of the devices. Further, the operation of a device can be transient in itself. This is the case for the explosive magnetic flux compression generator (EMG) and a ferromagnetic actuator.
Models are presented that are mainly intended for transients in the millisecond range and faster. Hence, eddy currents and the related skin and proximity effect become significant in windings, magnetic cores and in the armatures of the devices. These effects are important for, e.g., the damping of the transients. Further, the displacement current in the insulation of the winding is significant. It changes the response of the windings dramatically, as it manifests the finite velocity of propagation of the electromagnetic fields. Under such circumstances, reflections and excited resonances can make the transient voltage and current distribution highly irregular.
Induced voltages are modelled with self and mutual inductances or reluctances combined with winding templates. The displacement currents are modelled with capacitances or coefficients of potential. Cauer circuits and their dual form are used to model eddy currents in laminated cores and in conductors. The Cauer circuit enables one to consider hysteresis and the non-linear response of a magnetic core. It is also used to model the eddy currents in the moving armature of an EMG.
A set-up is presented that can be used to study the transient voltage and the current distribution along a coil.
The transient response of coaxially insulated windings is analysed and modelled in detail. A lumped circuit model is developed for a coil, DryformerTM - the new high-voltage transformer - and PowerformerTM, the new high-voltage generator. An alternative model, a combined lumped circuit and FEM model, is presented for a coaxially insulated winding in two slot cores.
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Barbosa, Danilo Hisano. "Desenvolvimento de um modelo de referência para a aplicação da tecnologia RFID na logística de ambulatórios de ensino." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/18/18156/tde-11072014-101719/.
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As aplicações da tecnologia de identificação por radiofrequência (RFID) em hospitais movimenta uma importante área de estudo no setor de saúde. Acompanhando o crescente número de trabalhos na área, encontra-se a necessidade de sistematização e categorização destas aplicações e de estudos que apresente soluções para o processo logístico hospitalar, particularmente, sob a perspectiva do fluxo de pacientes em ambulatórios de ensino. Diante deste cenário, a presente tese propõe um modelo de referência para a identificação e análise de aplicações RFID, considerando o objeto de estudo em questão. A revisão da literatura inicia-se abordando a Logística Hospitalar, apresentando os principais autores e correntes dessa área de pesquisa, apontando para a importância do fluxo de pacientes como elemento direcionador dos demais fluxos logísticos. Em seguida, é realizado um levantamento e categorização das aplicações da RFID em organizações hospitalares, permitindo a análise e o entendimento de suas principais características. Dessa forma, três bases apoiam o método de pesquisa. O primeiro é a revisão bibliográfica. O segundo é a metodologia para o desenvolvimento de modelos de referência na área de TI e por final, a avaliação do modelo por profissionais de saúde e TI, futuros usuários do modelo. Como contribuição da pesquisa, destaca-se o desenvolvimento e prescrição de um conjunto de atividades voltadas à identificação e análise de aplicações RFID dentro da visão de Logística Hospitalar, objetivando uma maior aproximação entre profissionais de saúde e TI na etapa de planejamento do processo de implantação da tecnologia em um ambiente ambulatorial de ensino.The applications of radio frequency identification technology (RFID) in hospitals move an important area of study in the healthcare. Accompanying the growing body of research on this topic, there is a need for systematization of such applications and proposals for solutions to the hospital logistics processes, particularly from the perspective of patient flow logistics in teaching ambulatory care setting. In this way, this thesis proposes a reference model for the identification and analysis of RFID applications, considering this object of research. The literature review begins by addressing the hospital logistics management, presenting the main authors of this emerging area of research, pointing to the importance of patient flow. Next, we conducted a review and categorization of RFID applications in hospital organizations, theme of this research, allowing the analysis and understanding of its main characteristics. Thus, three bases support the research method. The first is the literature review. The second is the methods for reference model development in IT field and the third, the evaluation by health and IT professionals, potential users of model. As a research contribution, a set of activities designed to identifying and analyzing RFID applications in hospital logistics was developed, aimed to approach health and IT professionals in the planning stage of RFID implementation process.
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Felicetti, Roberto. "Field Current Control for the Damping of Rotor Oscillations and for the Alternative Start of Synchronous Machines : Further Innovative Applications of Field Current Active Control besides UMP-Compensation." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353669.
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The possibility to save energy in synchronous machines operation by dismissing d-axis damping bars and surrogating them with active excitation current control in sectored field winding is proved. In particular a way to recover the energy of rotor oscillations during power regulation is shown by means of a studycase generator whereas a self-starting machine is analytically and numerically designed in view of its next construction and test. Principal design requirements and limits for both applications are presented and discussed.
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Bourgeois, Pierre-Yves. "Référence Secondaire de Fréquence à Résonateur Saphir Cryogénique." Phd thesis, Université de Franche-Comté, 2004. http://tel.archives-ouvertes.fr/tel-00008331.
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Ce mémoire présente l'élaboration et la caractérisation d'un étalon secondaire de fréquence à résonateur saphir cryogénique, dans la gamme des fréquences microondes.\\ Le monocristal de saphir ($Al_2O_3$), excité sur des modes électromagnétiques d'ordre élevé, les modes de galerie, et utilisé au voisinage de la température de l'hélium liquide, représente le meilleur candidat pour réaliser un oscillateur présentant une instabilité relative de fréquence de l'ordre de $1\cdot 10^(-14)$.\\ Une dégénérescence du mode généralement observée aux températures cryogéniques rend difficile l'ajustement des couplages. Nous présentons ici un modèle simple expliquant correctement la séparation du mode en fréquence et les formes d'onde observées expérimentalement.\\ D'autre part, le problème des modes parasites est résolu par la mise au point d'une structure résonante en cavité ouverte.\\ Tous les éléments nécessaires à la construction de cet oscillateur sont analysés en détails.\\ Les résultats obtenus sont tout à fait exceptionnels. Sur le court terme, l'instabilité relative de fréquence est inférieure à $7.5\cdot 10^(-15)$. Dans le domaine du long terme, aucune dérive n'est clairement identifiée. La stabilité sur 1 jour est $<2\cdot 10^(-14)$. Ce dernier résultat constitue l'état de l'art pour des références secondaires de fréquence sur le long terme. \\ Enfin, d'autres travaux concernant la mesure des propriétés diélectriques d'un cristal de langasite, la caractérisation d'oscillateurs ultrastables, la chaîne de synthèse, un oscillateur saphir-rutile compensé thermiquement, et l'observation d'un phénomène de bistabilité du résonateur saphir né de la coïncidence fortuite d'un mode de galerie du cristal avec celle de l'ion paramagnétique $Fe^(3+)$, sont également présentés.
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Schedin, Oscar. "Target Spectrums For Mastering : A comparison of spectral stylistic conventions between rock and vocal-based electronic music." Thesis, Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-84660.
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Through the analysis of the spectral characteristics of thousands of mastered (or remastered) commercial recordings from a variety of genres over the history of popular music, researchers have studied stylistic trends and spectral conventions. The aim of this study was to further explore, analyse and compare the spectral characteristics of two broad but distinct popular music genres: rock and vocal-based electronic music. The main reason for this choice of genres being that rock generally predominantly is based on (amplified) acoustical elements (e.g. acoustic drums and acoustic/electric bass/guitars) and that electronic music generally predominantly is based on electronic elements (e.g. beats and synthesizers). The stimuli for the study consisted of 24 top-five hit songs from the Billboard charts between 2016-2020, divided by genre. A fast fourier transform approach was used for the computation of target spectrums as well as low level descriptors for the two independent datasets of recordings. Spectral analysis followed with the goal of answering the following research questions: What do the spectral stylistic conventions appear to be in rock versus vocal-based electronic music and what spectral differences/similarities exists between these two distinct popular music genres? The results showed that there were some significant spectral differences between the two genres, especially noticeable in the low end of the frequency spectrum. Other genre-specific spectral trends and overall spectral conventions were found as well.
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Černoch, Adam. "Vyhodnocování dopravního hluku a jeho modelování." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226952.
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The task of the master's thesis is introduction with the problems of traffic noise, focusing on noise from road traffic. There is a description what is the noise, how it is formed, its resources and what are the methods of measuring. The following are the various noise reduction measures such as noise barriers and low noise pavements. The main attention is devoted to the noise generated at the tire / road that is reduced by these pavements. The practical part describes the implemented measurements on individual sections at various locations in our country. The measurement was carried by slightly modified method CPX with reference tire directly at the vehicle. The main aim was to evaluate the measurement data, make comparison of different low-noise surfaces with each other and with the commonly used surfaces. Then quantification of the rate reduction of the noise emission for a given section and verification of input data for noise modeling. In conclusion, the obtained results are summarized and based on them were confirmed very good acoustic properties with the recommendation to continue with measurements in the future.
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"Frequency stabilization using matched Fabry-Perots as references." Massachusetts Institute of Technology, Laboratory for Information and Decision Systems, 1991. http://hdl.handle.net/1721.1/1223.
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Corcovilos, Theodore Allen. "Fluid Phase Thermodynamics: I) Nucleate Pool Boiling of Oxygen under Magnetically Enhanced Gravity and II) Superconducting Cavity Resonators for High-Stability Frequency References and Precision Density Measurements of Helium-4 Gas." Thesis, 2008. https://thesis.library.caltech.edu/2914/2/thesis.pdf.
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Although fluids are typically the first systems studied in undergraduate thermodynamics classes, we still have only a rudimentary phenomenological understanding of these systems outside of the classical and equilibrium regimes. Two experiments will be presented. First, we present progress on precise measurements of helium-4 gas at low temperatures (1 K-5 K). We study helium because at low densities it is an approximately ideal gas but at high densities the thermodynamic properties can be predicted by numerical solutions of Schroedinger's equation. By utilizing the high resolution and stability in frequency of a superconducting microwave cavity resonator we can measure the dielectric constant of helium-4 to parts in 109, corresponding to an equivalent resolution in density. These data will be used to calculate the virial coefficients of the helium gas so that we may compare with numerical predictions from the literature. Additionally, our data may allow us to measure Boltzmann's constant to parts in 108, a factor of 100 improvement over previous measurements. This work contains a description of the nearly-completed apparatus and the methods of operation and data analysis for this experiment. Data will be taken by future researchers.
The second experiment discussed is a study of nucleate pool boiling. To date, no adequate quantitative model exists of this everyday phenomenon. In our experiment, we vary one parameter inaccessible to most researchers, gravity, by applying a magnetic force to our test fluid, oxygen. Using this technique, we may apply effective gravities of 0-80 times Earth's gravitational acceleration (g). In this work we present heat transfer data for the boiling of oxygen at one atmosphere ambient pressure for effective gravity values between 1g and 16g . Our data describe two relationships between applied heat flux and temperature differential: at low heat flux the system obeys a power law and at high heat flux the behavior is linear. We find that the transition heat flux between these two regimes scales as the 4th root of the gravitational acceleration, which may indicate a relationship to the critical heat flux. Additionally, we find that the low heat flux power law exponent is independent of gravity and the power law scale coefficient increases linearly with gravity.