Dissertations / Theses on the topic 'Propagation effects'
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Chandler-Wilde, S. N. "Ground effects in environmental sound propagation." Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384241.
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Shardlow, Peter John. "Propagation effects on precise GPS heighting." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239483.
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Davis, James Louis. "Atmospheric propagation effects on radio interferometry." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/27953.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN.
Bibliography: leaves 278-284.
by James Louis Davis.
Ph.D.
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Cramond, A. J. "Topographical and meteorological effects on impulse propagation." Thesis, University of Salford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381829.
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El-Aassar, Ahmed. "MODELING OF ATMOSPHERIC REFRACTION EFFECTS ON TRAFFIC NOISE PROPAGATION." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3804.
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Traffic noise has been shown to have negative effects on exposed persons in the communities along highways. Noise from transportation systems is considered a nuisance in the U.S. and the government agencies require a determination of noise impacts for federally funded projects. There are several models available for assessing noise levels impacts. These models vary from simple charts to computer design models. Some computer models, i.e. Standard Method In Noise Analysis (STAMINA), the Traffic Noise Model (TNM) and the UCF Community Noise Model (CNM), have been used to predict geometric spreading, atmospheric absorption, diffraction, and ground impedance. However, they have largely neglected the atmospheric effects on noise propagation in their algorithms. The purpose of this research was to better understand and predict the meteorological effects on traffic noise propagation though measurements and comparison to acoustic theory. It should be noted that this represents an approach to incorporate refraction algorithms affecting outdoor noise propagation that must also work with algorithms for geometric spreading, ground effects, diffraction, and turbulence. The new empirical model for predicting atmospheric refraction shows that wind direction is a significant parameter and should be included in future modeling for atmospheric refraction. To accomplish this, the model includes a "wind shear" and "lapse rate" terms instead of wind speed and temperature as previously needed for input of the most used models. The model is an attempt to explain atmospheric refraction by including the parameters of wind direction, wind shear, and lapse rate that directly affect atmospheric refraction.Ph.D.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engineering
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Otto, Tobias. "Propagation effects influencing polarimetric weather radar measurements." Doctoral thesis, Universitätsbibliothek Chemnitz, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-71125.
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Ground-based weather radars provide information on the temporal evolution and the spatial distribution of precipitation on a macroscopic scale over a large area. However, the echoes measured by weather radars are always a superposition of forward and backward scattering effects which complicates their interpretation. The use of polarisation diversity enhances the number of independent observables measured simultaneously. This allows an effective separation of forward and backward scattering effects. Furthermore, it extends the capability of weather radars to retrieve also microphysical information about the precipitation. The dissertation at hand introduces new aspects in the field of polarimetric, ground-based, monostatic weather radars at S-, C-, and X-band. Relations are provided to change the polarisation basis of reflectivities. A fully polarimetric weather radar measurement at circular polarisation basis is analysed. Methods to check operationally the polarimetric calibration of weather radars operating at circular polarisation basis are introduced. Moreover, attenuation correction methods for weather radar measurements at linear horizontal / vertical polarisation basis are compared to each other, and the robustly working methods are identifiedBodengebundene Wetterradare bieten Informationen über die zeitliche Entwicklung und die räumliche Verteilung von Niederschlag in einer makroskopischen Skala über eine große Fläche. Die Interpretation der Wetterradarechos wird erschwert, da sie sich aus einer Überlagerung von Vorwärts- und Rückwärtsstreueffekten ergeben. Die Anzahl der unabhängigen Wetterradarmessgrößen kann durch den Einsatz von Polarisationsdiversität erhöht werden. Dies ermöglicht eine effektive Trennung von Vorwärts- und Rückwärtsstreueffekten. Desweiteren erlaubt es die Bestimmung von mikrophysikalischen Niederschlagsparametern. Die vorliegende Dissertation betrachtet neue Aspekte für polarimetrische, bodengebundene, monostatische Wetterradare im S-, C- und X-Band. Gleichungen zur Polarisationsbasistransformation von Reflektivitätsmessungen werden eingeführt. Eine vollpolarimetrische Wetterradarmessung in zirkularer Polarisationsbasis wird analysiert. Neue Methoden, die eine Überprüfung der polarimetrischen Kalibrierung von Wetterradarmessungen in zirkularer Polarisationsbasis erlauben, werden betrachtet. Weiterhin werden Methoden zur Dämpfungskorrektur von Wetterradarmessungen in linearer horizontaler / vertikaler Polarisationsbasis miteinander verglichen und Empfehlungen von zuverlässigen Methoden gegeben
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Smith, Rasler W. "Low latitude ionospheric effects on radiowave propagation." Thesis, Monterey, California. Naval Postgraduate School, 1998. http://hdl.handle.net/10945/8638.
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This dissertation provides experimental observations and analyses that associate low-latitude transionospheric signal scintillation with transequatorial VHF radio propagation and errors in transionospheric geopositioning. The experiment observed equatorial-region ionospheric total electron content (TEC) derived from Global Positioning System (GPS) signals using receivers on Oahu, Hawaii, Christmas Island, and Rarotonga, Cook Islands. The experiment simultaneously measured VHF transequatorial propagation of VHF television signals from Hawaii to Rarotonga Analysis shows that a moving second moment of vertical-equivalent TEC strongly correlates to each VHF transequatorial radio propagation event From experimental observation analysis, the author develops models for prediction of TEP and nine-space distribution of low-latitude transionospheric scintillation. The author also develops equations that show the potential errors in nine, frequency, and angle used in geopositioning solutions. These three parameters are potentially correctable using these techniques
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Otto, Tobias. "Propagation effects influencing polarimetric weather radar measurements." Doctoral thesis, Universitätsverlag der Technischen Universität Chemnitz, 2010. https://monarch.qucosa.de/id/qucosa%3A19554.
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Ground-based weather radars provide information on the temporal evolution and the spatial distribution of precipitation on a macroscopic scale over a large area. However, the echoes measured by weather radars are always a superposition of forward and backward scattering effects which complicates their interpretation. The use of polarisation diversity enhances the number of independent observables measured simultaneously. This allows an effective separation of forward and backward scattering effects. Furthermore, it extends the capability of weather radars to retrieve also microphysical information about the precipitation. The dissertation at hand introduces new aspects in the field of polarimetric, ground-based, monostatic weather radars at S-, C-, and X-band. Relations are provided to change the polarisation basis of reflectivities. A fully polarimetric weather radar measurement at circular polarisation basis is analysed. Methods to check operationally the polarimetric calibration of weather radars operating at circular polarisation basis are introduced. Moreover, attenuation correction methods for weather radar measurements at linear horizontal / vertical polarisation basis are compared to each other, and the robustly working methods are identified.Bodengebundene Wetterradare bieten Informationen über die zeitliche Entwicklung und die räumliche Verteilung von Niederschlag in einer makroskopischen Skala über eine große Fläche. Die Interpretation der Wetterradarechos wird erschwert, da sie sich aus einer Überlagerung von Vorwärts- und Rückwärtsstreueffekten ergeben. Die Anzahl der unabhängigen Wetterradarmessgrößen kann durch den Einsatz von Polarisationsdiversität erhöht werden. Dies ermöglicht eine effektive Trennung von Vorwärts- und Rückwärtsstreueffekten. Desweiteren erlaubt es die Bestimmung von mikrophysikalischen Niederschlagsparametern. Die vorliegende Dissertation betrachtet neue Aspekte für polarimetrische, bodengebundene, monostatische Wetterradare im S-, C- und X-Band. Gleichungen zur Polarisationsbasistransformation von Reflektivitätsmessungen werden eingeführt. Eine vollpolarimetrische Wetterradarmessung in zirkularer Polarisationsbasis wird analysiert. Neue Methoden, die eine Überprüfung der polarimetrischen Kalibrierung von Wetterradarmessungen in zirkularer Polarisationsbasis erlauben, werden betrachtet. Weiterhin werden Methoden zur Dämpfungskorrektur von Wetterradarmessungen in linearer horizontaler / vertikaler Polarisationsbasis miteinander verglichen und Empfehlungen von zuverlässigen Methoden gegeben.
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Ozkok, Okan. "Investigation Of Fluid Rheology Effects On Ultrasound Propagation." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614621/index.pdf.
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In this study, a mathematical model is developed for investigating the discrete sound propagation in viscoelastic medium to identify its viscoelastic properties. The outcome of the model suggests that pulse repetition frequency is a very important parameter for the determination of relaxation time. Adjusting the order of magnitude of the pulse repetition frequency, the corresponding relaxation time which has similar magnitude with pulse repetition frequency is filtered while the others in the spectrum are discarded. Discrete relaxation spectrum can be obtained by changing the magnitude of the pulse repetition frequency. Therefore, the model enables to characterize the relaxation times by ultrasonic measurements.
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Tomljenovic-Hanic, Snjezana, and snjezana@physics usyd edu au. "Propagation effects in optical waveguides, fibres and devices." The Australian National University. Research School of Physical Sciences and Engineering, 2003. http://thesis.anu.edu.au./public/adt-ANU20040921.104741.
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This thesis consist of a theoretical study of propagation effects in optical waveguides, fibres and photonic crystals, with some comparison with experiment.¶
Chapter 1 gives a brief introduction with the current view of optical components in photonic integrated circuits and issues related to the loss mechanism.¶
In Chapter 2 the characteristics of single-mode propagation and transient effects in practical square- and rectangular-core buried channel planar waveguides are quantified, assuming a cladding which is unbounded in one transverse dimension and bounded in the other. The wavelength cut-off condition for the fundamental mode is determined when the cladding index is asymmetric and composed of step-wise, uniform index regions.¶
In Chapter 3, the application of segmented reflection gratings in planar devices that can function as either a single- or two-wavelength add/drop filter is investigated and a numerical technique developed in Chapter 2 is applied to the waveguides with high extinction ratio. The role of the segmented gratings is analogous to that of a blazed grating, but they can provide a higher reflectivity level at the Bragg wavelength, eliminate back reflection into the fundamental mode and provide arbitrarily small channel spacing in the two-wavelength case.¶
Chapters 4 address the problem of bend loss in a single-mode slab waveguide. A new theoretical strategy for reducing bend loss is presented and compared to existing designs. The results obtained in this chapter are the basis for the following two chapters.¶
Chapter 5 deals with bend loss in single-mode buried channel waveguides and demonstrates that the new strategy can lead to significant bend loss reduction when compared to other strategies, and, conversely, can be used to enhance bend loss for a fixed bend radius for application to devices such as optical attenuators.¶
In Chapter 6, a novel design of a variable optical attenuator based on a bent channel waveguide is proposed, realized by applying a new strategy for bend loss control in a polymer buried channel waveguide.¶
Chapter 7 investigates effects of the additional rings in a single mode step-index fibre on bend loss. It is supported with the experimental results of Ron Bailey from Optical the Fibre Technology Centre, University in Sydney.¶
In Chapter 8, bend loss of a one-dimensional photonic crystal is quantified and compared to bend loss of a standard single-mode slab waveguide and a bend-resistant waveguide.¶
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ALMEIDA, MARTA PUDWELL CHAVES DE. "PROPAGATION EFFECTS IN LOW EARTH ORBIT SATTELITE LINKS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2003. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=4245@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO efeito da atenuação por chuvas em enlaces satélites que operam em frequências acima de 10 GHz é decisivo no cálculo de desempenho do sistema. A evolução da tecnologia dos sistemas satélite e a necessidade de expansão dos serviços de comunicações móveis pessoais levaram ao uso de sistemas de comunicação com satélites de órbita baixa. Estes sistemas são particularmente interessantes para o oferecimento destes serviços por suas características de pequeno atraso de propagação e uso de potência de transmissão mais baixas que os sistemas geoestacionários. Satélites em órbita baixas (LEO) operam em altitudes de cerca de 1000km e possuem movimento em relação à estação terrena. Esta característica de mobilidade traz novas questões sobre o comportamento da atenuação por chuvas, em particular a necessidade de um modelo de previsão de atenuação para estes enlaces com ângulo de elevação variante no tempo. Neste trabalho um modelo para a previsão de atenuação em enlaces com ângulo de elevação fixo, mais preciso do que os existentes na literatura técnica, foi desenvolvido como primeiro passo para o tratamento do problema de enlaces com ângulo de elevação variável. A seguir foi feita uma simulação de medidas em enlaces LEO a partir do banco de dados de medidas de atenuação em enlaces fixos no Brasil, considerando um modelo de constelação de satélites. Foi implementado um método geral que utiliza o histograma dos ângulos de elevação do satélite como ponderação da distribuição cumulativa de atenuação em cada ângulo. O método foi testado contra os resultados obtidos com simulações para a constelação Globalstar sendo obtida muito boa concordância entre o modelo de predição desenvolvido e a simulação.
Rain attenuation is the most important propagation effect to be taken into account in the performance calculation for satellite systems operation at frequencies above 10 GHz. The technological evolution of such systems and the need for personal communication systems with global coverage lead to the use of low earth orbit communication systems, that not only have shorter propagation delays but also allow the use of lower transmission power than the traditional geostationary systems. Low earth orbit (LEO) satellites have altitudes around 1.000 Km and are in motion relatively to the earth stations. This mobility requires a new approach to the problem of rain attenuation prediction, particularly the need for a prediction model that takes into account the elevation angle variability. In this work, an improved rain attenuation prediction method for the geostationary case has been developed as a starting point for the analysis of the nongeostationary case. Then, the rain attenuation in the a LEO system has been simulated using measured data from fixed system systems and the satellite constellation model. A general method for slant path rain attenuation prediction considering variable elevation angles is proposed. The method uses the histogram of the elevation angles to weight the distributions obtained for fixed elevation. The method has been tested with simulations performed for the Globalstar LEO system and a very good agreement was obtained.
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Nuzzo, Nicholas C. (Nicholas Christopher) 1974. "Effects of propagation techniques on relative GPS navigation." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/8965.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999.Includes bibliographical references (p. 173-176).
Various service vehicles are being developed to resupply the International Space Station (ISS). These service vehicles and the ISS will perform automated space rendezvous. The performance of a relative GPS navigation filter for this application is presented. Specifically, the effects of four different techniques for propagating the filter state are demonstrated and evaluated. These techniques include, (1) integration of the equations of motion accounting for J2, J3, J4 and aerodynamic drag, (2) first-order equations of relative motion that account for the effects of J2 and include a second-order conic approximation, (3) the Universal Keplerian state transition matrix, and (4) the use of the Clohessy-Wiltshire equations of relative motion. GPS measurements were simulated and included errors due to Selective Availability, clock bias, clock drift, and receiver noise. The relative navigation filter used pseudorange and delta-range measurements to estimate the filter state which included the relative position and relative velocity between the vehicles conducting the space rendezvous. The results demonstrated that all four techniques surpassed the performance requirements on relative position and velocity errors. However, integrating the equations of motion, technique (1), resulted in the best performance. The filter state errors for this technique were the smallest and remained within the 3 [sigma] covariance bounds for all the cases studied. Effects due to eccentricity were observed in the remaining propagation techniques with the worst noted in technique (4). The most significant perturbation was shown to be J2, producing significant propagation and filter errors when the state was being propagated by methods (3) and (4), which did not account for it.
by Nicholas C. Nuzzo.
S.M.
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Tomljenovic-Hanic, Snjezana. "Propagation effects in optical waveguides, fibres and devices /." View thesis entry in Australian Digital Theses Program, 2003. http://thesis.anu.edu.au/public/adt-ANU20040921.104741/index.html.
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Ackerman, Rodney Rex. "The effects of complex additives and growth regulators on the growth and clonal propagation of Phalaenopsis orchids." Virtual Press, 1988. http://liblink.bsu.edu/uhtbin/catkey/546145.
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The goal of this study was two fold, the first was to determine the effect of different basal medium formulationsand medium supplements (complex additives and growth hormones) on the development and growth rate of Phalaenopsis orchids, while the second goal was to find or develop an efficent method for the clonal propagation of Phalaenopsis orchids.MethodsThe first part of this study was further subdivided in to several phases; the first of these involved a comparative study of the germination of Phalaenopsis ovules on six different basal medium formulations and seven different sets of medium supplements. The second phase involved a comparative study of the development of Phalaenopsis protocorms on six different basal medium formulations and ninteen different sets of medium supplements. The third phase involved a comparative study of the growth of Phalaenopsis seedlings on six different basal medium formulations and twelve sets of medium supplements. The forth and final phase involved a comparative study of the development and growth of Phalaenopsis protocorms and seedlings on media containing varing concentrations and combinations of auxins and cytokinins. The second part of this study involved a comparative study designed-to determine the suitability of several sizes of axillary buds and plantlets for the clonal propagation of Phalaenopsis orchids and the modification of several procedures in an attempt to determine suitable explant material and procedures for the commercial clonal propagation of Phalaenopsis orchids.Results and DiscussionResults of this study indicated that of the basal medium formulations and medium supplements tested Modified Heller's salt base medium and to a lesser extent Modified Vacin and Went salt base medium supplemented with vitamin formulation 1 and Bactopeptone yielded the highest percent germination and development up to the seedling stage. At the seedling stage the growth rate of seedlings grown on media supplemented with banana homogenate nearly doubled the growth rate of the seedlings grown on all of the other medium supplementstested.Results of the second part of this study indicated that by modifying the procedures of Bouriquet, Broly, and Legrand (1982) the proliferation rate (shoots per plantlet) could be increased by a factor of two to eight. This can be translated into an increase from two to five shoots per plantlet per six weeks to an increase of eight shoots per plantlet per six weeks with a minimal mortality rate. With further modification of the procedure of Bouriquet, Broly, and Legrand (1982), other results indicated that it may be possible to increase to forty the number of shoots per plantlet produced per six week period.Department of Biology
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Söderström, Emma. "Reducing Effects of Multipath Propagation With a Blind Equalizer." Thesis, Linköpings universitet, Kommunikationssystem, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-151598.
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When transmitting data from an aircraft being prepared at the apron (the area in front of the hangar) telemetry data is transmitted to ground personnel. The transmitted data is subject to severe distortion due to multipath propagation created by the surroundings, resulting in erroneous detection. By equalizing the signal using the Constant Modulus Algorithm a significant increase in detection performance has been observed, both in simulations and tests on collected data. The most sufficient parameters were chosen after testing a set of different parameter combinations on simulations with single delays. These parameters were then used to equalize simulated multipath as well as collected data. The results show that short delays with low power can be resolved without any equalizer. Longer delays with relatively low power can be resolved using the proposed equalizer but long delays with high power cannot be resolved by the equalizer at all. The thesis shows that it is worth investigating implementation of the equalizer.
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Sarwar, Muhammad. "Effects of terrain features on wave propagation: high-frequency techniques." Thesis, University of Kalmar, Department of Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hik:diva-2281.
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This Master thesis deals with wave propagation and starts with wave propagation basics. It briefly presents the theory for the diffraction over terrain obstacles and describes two different path loss models, the Hata model and a FFT-based model. The significance of this paper is that it gives the simulation results for the models mentioned above and presents a comparison between the results obtained from an empirical formula and the FFT-model. The comparison shows that the approach based on Fast Fourier Transform is good enough for prediction of the path loss and that it is a time efficient method.
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Kappel, Marcel. "Scattering effects in the sound wave propagation of instrument soundboards." Phd thesis, Universität Potsdam, 2012. http://opus.kobv.de/ubp/volltexte/2012/6267/.
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In the western hemisphere, the piano is one of the most important instruments. While its evolution lasted for more than three centuries, and the most important physical aspects have already been investigated, some parts in the characterization of the piano remain not well understood. Considering the pivotal piano soundboard, the effect of ribs mounted on the board exerted on the sound radiation and propagation in particular, is mostly neglected in the literature. The present investigation deals exactly with the sound wave propagation effects that emerge in the presence of an array of equally-distant mounted ribs at a soundboard. Solid-state theory proposes particular eigenmodes and -frequencies for such arrangements, which are comparable to single units in a crystal. Following this 'linear chain model' (LCM), differences in the frequency spectrum are observable as a distinct band structure. Also, the amplitudes of the modes are changed, due to differences of the damping factor.
These scattering effects were not only investigated for a well-understood conceptional rectangular soundboard (multichord), but also for a genuine piano resonance board manufactured by the piano maker company 'C. Bechstein Pianofortefabrik'. To obtain the possibility to distinguish between the characterizing spectra both with and without mounted ribs, the typical assembly plan for the Bechstein instrument was specially customized. Spectral similarities and differences between both boards are found in terms of damping and tone.
Furthermore, specially prepared minimal-invasive piezoelectric polymer sensors made from polyvinylidene fluoride (PVDF) were used to record solid-state vibrations of the investigated system. The essential calibration and characterization of these polymer sensors was performed by determining the electromechanical conversion, which is represented by the piezoelectric coefficient. Therefore, the robust 'sinusoidally varying external force' method was applied, where a dynamic force perpendicular to the sensor's surface, generates movable charge carriers. Crucial parameters were monitored, with the frequency response function as the most important one for acousticians.
Along with conventional condenser microphones, the sound was measured as solid-state vibration as well as airborne wave. On this basis, statements can be made about emergence, propagation, and also the overall radiation of the generated modes of the vibrating system. Ultimately, these results acoustically characterize the entire system.Betrachtet man den westlichen Kulturkreis, ist der Flügel bzw. das Klavier wohl eines der bedeutendsten Instrumente. Trotz einer stetigen, empirischen Weiterentwicklung dieses Instrumentes in den letzten drei Jahrhunderten und des Wissens um die wichtigsten physikalischen Effekte, sind viele Teile der Charakterisierung des Klaviers (sowohl akustisch als auch physikalisch) immer noch nicht vollständig verstanden. Nehmen wir nur den Resonanzboden - das entscheidende Bauteil für die Akustik eines Klaviers - und betrachten die Auswirkung, den die Berippung auf die Schallausbreitung des Instruments hat. Bis auf wenige Ausnahmen wird dieser Struktur-Aspekt in der Literatur weitestgehend übergangen. Die vorliegende Arbeit untersucht genau diese Ausbreitungscharakteristiken und Streueffekte, welche dadurch entstehen, dass Rippen, die denselben Abstand zueinander haben, auf dem Resonanzboden angebracht werden. Die Festkörperphysik stellt ein einfaches Modell über die Eigenfrequenzen für solche Anordnungen bereit. Dafür werden die Rippen und deren Abstände wie Einheitszellen eines Kristalls betrachtet. Ausgehend vom sogenannten 'Modell der linearen Ketten', werden gemessene Frequenzbänder im Spektrum erklärbar. Zusätzlich ändern sich auch die spektralen Amplituden des Resonanzbodens durch das Anbringen der Rippen. Diese Streueffekte wurden nicht nur an einem konzeptionellen rechteckigen Resonanzboden untersucht, sondern auch an einem originalen Klavier-Resonanzboden, welcher von dem Klavierbauer 'C. Bechstein Pianofortefabrik' hergestellt wurde und auch später in einem fertigen Klavier zum Einsatz kommen wird. Der traditionelle Zusammenbau des Klaviers wurde speziell für diese Untersuchung abgeändert, um die Möglichkeit zu haben, die Berippung des Resonanzbodens spektral zu charakterisieren. Alle gefundenen Eigenschaften des konzeptionellen und des originalen Bodens wurden verglichen. Für die Dämpfung und für die Brillianz des Tons wurden Übereinstimmungen, aber auch Unterschiede gefunden. Ein großer Teil dieser Untersuchung erforderte den Einsatz von speziell angefertigten piezoelektrischen Polymer-Beschleunigungsaufnehmern aus Polyvinylidenfluorid. Direkt fest eingeklebt im Instrument, wurden diese eingesetzt, um die Körperschwingungen des vibrierenden Systems aufzunehmen. Die essentielle Kalibrierung und Charakterisierung dieser Sensoren wurde durchgeführt, indem die elektromechanische Umwandlung bestimmt wurde, die durch den piezoelektrischen Koeffizienten gegeben ist. Durch eine sinusförmig variierende, externe Kraft und die dadurch entstehenden Ladungsträger an den Oberflächen des Sensormaterials kann dieser Koeffizient sehr genau bestimmt werden. In Abhängigkeit entscheidender physikalischer Größen, z.B. der Frequenz-Antwort-Funktion, wurde das Verhalten des piezoelektrischen Koeffizienten untersucht. Die erzeugten Vibrationen als Körperschall (aufgenommen durch die Piezopolymere) und als Luftschallwelle (aufgenommen durch konventionelle Kondensator-Mikrophone) wurden simultan gemessen und dann untersucht. Daraus kann man Aussagen über Entstehung, Ausbreitung und Abstrahlung der erzeugten Moden in das umgebende Medium ableiten. Letztlich charakterisieren diese Ergebnisse das gesamte vibrierende System akustisch.
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Aksen, Ernest, Jacek Cukrowski, and Manfred M. Fischer. "Propagation of Crises Across Countries: Trade Roots of Contagion Effects." WU Vienna University of Economics and Business, 2001. http://epub.wu.ac.at/4235/1/WGI_DP_7801.pdf.
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The paper provides an explanation of the mechanisms underlying trade roots of the contagion
effects emanating from the recent turmoils. It is argued that under demand uncertainty risk averse
behavior of firms provides a basis for international trade. The paper shows by means of a simple
two-country model that risk averse firms operating in perfectly competitive markets with
uncertainty of demand tend to diversify markets what gives a basis for international trade in
identical commodities even between identical countries. It is shown that such trade may be welfare
improving despite efficiency losses due to cross-hauling and transportation costs. The analysis
reveals that change of the expectations concerning market conditions caused by the turmoil in the
neighbor country (i.e., shift in the perception of market conditions) may lead to macroeconomic
destabilization (increase in price level and unemployment, worsening of terms of trade, and
deterioration of trade balance).Series: Discussion Papers of the Institute for Economic Geography and GIScience
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Groves, Keith Michael. "Nonlinear ionospheric propagation effects on UHF and VLF radio signals." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/52949.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991.Includes bibliographical references (p. 179-184).
by Keith Michael Groves.
Ph.D.
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Fecteau, Andre. "The Effects of Compressibility on the Propagation of Premixed Deflagration." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39402.
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The thesis addresses the influence of compressible effects on the stability of deflagration waves. Due to the quasi-isobaric nature of slow flames, compressible effects in laminar flames are usually neglected. Nevertheless, turbulent deflagrations may propagate at substantially higher speeds, suggesting that compressible effects may play a role in their dynamics. In the present thesis, the stability of diffusion-dominated high-speed deflagrations is addressed. The deflagration is studied in the thickened regime, hence addressing the long wavelength limit of these deflagrations. The deflagrations are modelled by the compressible reactive Navier-Stokes equations with a single-step Arrhenius reaction model. The 2D stability of the steady traveling-wave solution is studied by direct simulation. It is found that, as the flame compressibility becomes significant, not only does the growth rates of the cellular profile of the deflagration waves increase, but the traditional correlation of the burning velocity and the flame surface area become far less strong. Significant compression regions form in front of the nonlinear flames. These compression regions have been found to increase the growth rates by increasing the temperature of the unburned gas in front of the flames, as well as convecting the flame forward. The results show that the flame propagation velocity in references to the unburned gas was significantly faster than the burning velocity. The vorticity was given consideration, as the compressibility of flame increase one can expect the baroclinic source to be of greater significance. The vorticity was show to, in effect, increase as compressibility increases while unexpectedly having a stabilizing direction of rotation on the cellular structure of the flames.
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Öhlund, Olof. "Wind Turbine Sound Propagation in the Atmospheric Boundary Layer." Licentiate thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-224205.
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Wind turbines have grown both in size and number in the past decades. The taller turbines has made it possible to place them in forest areas which is fortunate for a country like Sweden with lots of forest. An issue with wind turbines is the sound they produce. The sound mainly comes from the rotor blades when they pass through the air. The sound heard some distance away from the turbine is sometimes masked by ambient background noise such as wind induced sound in the vegetation, but this is not always the case. Noise concerns among some people living in the vicinity of wind turbines are sometimes raised. Sound propagation models are used to predict the wind turbine sound level at certain distance. It is important that these models are accurate. Sound propagation is greatly influenced by the meteorological conditions. These conditions change over the day and year and vary a lot depending on the terrain conditions. In the past, large meteorological propagation effects have been found for sound sources close to the ground. Higher elevated sources like wind turbines have not been studied as much. One reason for this is that wind turbines are a relatively new sound source. In this thesis the meteorological influence on the wind turbine sound propagation is studied. Continuous simultaneous acoustic and meteorological measurements are performed at two different wind turbine sites during two years to capture all variations in the weather. The two sites are covered by forest, one is flat and the other has shifting terrain. The sites are representative for many locations in Sweden and around the world. The differences between the measured and expected wind turbine sound levels are established for different meteorological categories. The median of all deviations within each meteorological category is then compared. During no snow cover conditions the variation of the median under different meteorological conditions is 6 dBA and during snow cover the variation of the median is 14 dBA. The variations are due to the combined effect of refraction, ground conditions and terrain shape. The deviations from an expected value are seen for all octave bands from 63 Hz to 1000 Hz but are found to most distinct at low frequencies of around 125Hz. Meteorological effects starts to be important somewhere between 400 m and 1000 m from wind turbines.The characteristic "swish" sound from wind turbines are also studied in this thesis. The swish sound or as it is also called, the amplitude modulated sound, is found to be more common under some meteorological conditions such as temperature inversions and downwind conditions. A metric for detection of amplitude modulation duration and strength is proposed. Amplitude modulation, is according to some, the reason why wind turbine sound is perceived as more annoying than other typical environmental sounds at the same sound level. The swishes probably increase the probability to hear the wind turbine sound in presence of other background noise.
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Singh, Pooja. "Quantum Coherent Control and Propagation in Lambda System." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849750/.
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Strong coherence in quasi-resonant laser driven system interferes with effective relaxations, resulting in behaviors like, coherent population trapping and Electromagnetically induced transparency. The Raman system can optimize this utilizing excited coherence in the lambda system when exposed to counter- intuitive pump-stokes pulses. The phenomenon can result in complete population transfer between vibrational levels called Stimulated Raman adiabatic passage(STIRAP). STIRAP and CHIRAP have been studied with Gaussian and chirped pulses. The optical propagation effects in dense medium for these phenomenon is studied to calculate the limitations and induced coherences. Further, the effect of rotational levels has been investigated. The molecular vibrational coherence strongly depends on the effect of rotational levels. The change in coherence interaction for ro-vibrational levels are reported and explained. We have considered the effects on the phase of radiation related to rotational mechanical motion of quantum system by taking advantages in ultra strong dispersion medium provided by quantum coherence in lambda system. The enhanced Fizeau effect on a single atom is observed.
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Trenggono, Praditio Putra. "Statistical modelling of wind effects on signal propagation for wireless sensor networks." Thesis, Queensland University of Technology, 2011. https://eprints.qut.edu.au/49841/1/Praditio_Trenggono_Thesis.pdf.
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A wireless sensor network system must have the ability to tolerate harsh environmental conditions and reduce communication failures. In a typical outdoor situation, the presence of wind can introduce movement in the foliage. This motion of vegetation structures causes large and rapid signal fading in the communication link and must be accounted for when deploying a wireless sensor network system in such conditions.
This thesis examines the fading characteristics experienced by wireless sensor nodes due to the effect of varying wind speed in a foliage obstructed transmission path. It presents extensive measurement campaigns at two locations with the approach of a typical wireless sensor networks configuration. The significance of this research lies in the varied approaches of its different experiments, involving a variety of vegetation types, scenarios and the use of different polarisations (vertical and horizontal).
Non–line of sight (NLoS) scenario conditions investigate the wind effect based on different vegetation densities including that of the Acacia tree, Dogbane tree and tall grass. Whereas the line of sight (LoS) scenario investigates the effect of wind when the grass is swaying and affecting the ground-reflected component of the signal. Vegetation type and scenarios are envisaged to simulate real life working conditions of wireless sensor network systems in outdoor foliated environments.
The results from the measurements are presented in statistical models involving first and second order statistics. We found that in most of the cases, the fading amplitude could be approximated by both Lognormal and Nakagami distribution, whose m parameter was found to depend on received power fluctuations. Lognormal distribution is known as the result of slow fading characteristics due to shadowing.
This study concludes that fading caused by variations in received power due to wind in wireless sensor networks systems are found to be insignificant. There is no notable difference in Nakagami m values for low, calm, and windy wind speed categories. It is also shown in the second order analysis, the duration of the deep fades are very short, 0.1 second for 10 dB attenuation below RMS level for vertical polarization and 0.01 second for 10 dB attenuation below RMS level for horizontal polarization. Another key finding is that the received signal strength for horizontal polarisation demonstrates more than 3 dB better performances than the vertical polarisation for LoS and near LoS (thin vegetation) conditions and up to 10 dB better for denser vegetation conditions.
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Marshall, Andrew. "Turbulent flame propagation characteristics of high hydrogen content fuels." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53859.
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Increasingly stringent pollution and emission controls have caused a rise in the use of combustors operating under lean, premixed conditions. Operating lean (excess air) lowers the level of nitrous oxides (NOx) emitted to the environment. In addition, concerns over climate change due to increased carbon dioxide (CO2) emissions and the need for energy independence in the United States have spurred interest in developing combustors capable of operating with a wide range of fuel compositions. One method to decrease the carbon footprint of modern combustors is the use of high hydrogen content (HHC) fuels. The objective of this research is to develop tools to better understand the physics of turbulent flame propagation in highly stretch sensitive premixed flames in order to predict their behavior at conditions realistic to the environment of gas turbine combustors.
This thesis presents the results of an experimental study into the flame propagation characteristics of highly stretch-sensitive, turbulent premixed flames generated in a low swirl burner (LSB). This study uses a scaling law, developed in an earlier thesis from leading point concepts for turbulent premixed flames, to collapse turbulent flame speed data over a wide range of conditions. The flow and flame structure are characterized using high speed particle image velocimetry (PIV) over a wide range of fuel compositions, mean flow velocities, and turbulence levels. The first part of this study looks at turbulent flame speeds for these mixtures and applies the previously developed leading points scaling model in order to test its validity in an alternate geometry. The model was found to collapse the turbulent flame speed data over a wide range of fuel compositions and turbulence levels, giving merit to the leading points model as a method that can produce meaningful results with different geometries and turbulent flame speed definitions. The second part of this thesis examines flame front topologies and stretch statistics of these highly stretch sensitive, turbulent premixed flames. Instantaneous flame front locations and local flow velocities are used to calculate flame curvatures and tangential strain rates. Statistics of these two quantities are calculated both over the entire flame surface and also conditioned at the leading points of the flames. Results presented do not support the arguments made in the development of the leading points model. Only minor effects of fuel composition are noted on curvature statistics, which are mostly dominated by the turbulence. There is a stronger sensitivity for tangential strain rate statistics, however, time-averaged values are still well below the values hypothesized from the leading points model. The results of this study emphasize the importance of local flame topology measurements towards the development of predictive models of the turbulent flame speed.
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Ruan, Youyi. "Surface wave propagation in 3-D anelastic media." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/28945.
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Lateral perturbations in anelasticity (Q) and wave speed together provide important constraints
on thermal and chemical structures in the mantle. In present-day tomography studies of global wave
speed and anelasticity, the significance of 3-D wave speed and 3-D Q structures on surface wave
travel times and amplitudes has not been well understood. In this dissertation, the effects of lateral perturbations in anelasticity (Q) and wave speed on surface wave observables are quantified based upon wave propagation simulations in 3-D earth models using a Spectral Element Method.
Comparison between phase delays caused by 3-D wave speed structures and those caused by 3-D
Q variations show that anelastic dispersion due to lateral perturbation in Q is important in long-period surface wave and can account for 15-20% observed phase delays. For amplitude perturbations, elastic focusing/defocusing effects associated with 3-D wave speed structures are dominant while energy dissipation is important in short-period (â ¼ 50 s) surface waves but decreases quickly with increasing
wave period. Anelastic focusing/defocusing associated with 3-D anelastic dispersion becomes more important than wave attenuation in longer period surface waves.
In tomography studies, ray theory breaks down and finite frequency effects become important
when the length scale of heterogenities are smaller than seismic wavelength. Finite frequency effects in 3-D earth models are investigated by comparing theoretical predictions of travel times and amplitudes with â ground truthâ measurements made on synthetic seismograms generated in SEM
simulations. The comparisons show that finite frequency effects are stronger in amplitudes than in phases, especially at long periods.Ph. D.
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Wojcik, Stefanie E. "Effects of internal waves and turbulent fluctuations on underwater acoustic propagation." Link to electronic thesis, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-030906-152505/.
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Koyuncu, Hakan. "Transoceanic Propagation Of Sumatra Tsunamis And Their Effects On Maldives Islands." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612813/index.pdf.
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In recent years the negative effects of tsunamis in the Indian Ocean dramatically increased. Although, this subject became very popular lately, the far-field activities of tsunamis are needed to be evaluated in Indian Ocean. In this thesis, Maldives and Sumatra islands were emphasized to analyze the effects of the transoceanic propagation of tsunamis in Indian Ocean. At first, using GIS Based softwares, the geographical data of the region were extracted and organized for analyzing. Secondly, a worst earthquake scenario was initiated at Sumatra which is located at a long distance from Maldives Islands. Then, corresponding effects of transoceanic tsunami were analyzed and accordingly coastal amplifications near Maldivian Islands were computed by NAMI DANCE. As a final step, an evaluation study was carried out to understand the transoceanic propagation behavior of tsunamis in Indian Ocean and results were discussed.
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Lundström, Erik. "Overload effects on the fatigue crack propagation behaviour in Inconel 718." Thesis, Linköpings universitet, Hållfasthetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-77494.
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In this master thesis, work done in the TURBO POWER project High temperature fatigue crack propagation in nickel-based superalloys during spring 2012 will be presented. The overall objective of this project is to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the crack propagation in the nickel-based superalloy Inconel 718. Experiments have been performed to study the effect of initial overloads, and it has been shown that even for small initial overloads a significant reduction of the crack growth rate is received. Furthermore, FE simulations have been carried out in order to describe the local stress state in front of the crack tip since it is believed to control, at least partly the diffusion of oxygen into the crack tip and thus also the hold time crack growth behaviour of the material. Finally, an evaluation method for the stresses is presented, where the results are averaged over an identifiable process/damaged zone in front of the crack tip.
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Warrington, E. Michael. "Ionospheric radiowave propagation effects observed with a large aperture antenna array." Thesis, University of Leicester, 1986. http://hdl.handle.net/2381/35817.
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The wavefronts of high frequency (HF) radio waves received after reflection from the ionosphere exhibit both spatial non-linearities and temporal variations which limit the performance of large aperture receiving arrays. The first objective of this investigation was to measure the phase and amplitude of ionospherically propagated signals at several widely spaced antennas in order to relate these parameters to the reflection process. From the amplitudes and phases measured at pairs of spaced antennas, the direction of arrival (DOA) of the signal in both azimuth and elevation was determined. Furthermore. by combining the DOA and reflection height measurements the transmitter location can be estimated from a single receiving site. The second objective of this study was to investigate the ability of the system to determine DOA and transmitter locations correctly. Two seven element antenna arrays were employed with maximum apertures of 1526 m and 294 m respectively. The associated multi-channel receiving and data logging equipment is described together with a pulsed sounding system employed for mode identification. Signals received from several European transmitters exhibited widely differing behaviour and this was interpreted in terms of their modal content. For predominantly single moded signals the observations indicate that the diffracted components normally contribute less than 10% of the received power, moreover the DOA varies in both azimuth and elevation by approximately 1-2° over time periods of several minutes. The use of the smaller array for DF and SSL applications is discussed in detail. In particular, the performance of the system was severly affected by multi-moded propagation. Techniques were developed for recognising periods of single moded propagation, when accurate measurements are to be expected. Good position fixes were obtained when measurements were restricted to these periods provided accurate reflection height information was also available.
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Gu, Lian Sheng. "Effects of boundary conditions on the propagation of quasi-detonation waves." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63863.
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Poh, Soon Huat. "The effects of soil restraint on crack propagation in gas pipelines." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/12787.
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Nagaraj, Nagaraj. "Effects of Dissipation on Propagation of Surface Electromagnetic and Acoustic Waves." Thesis, University of North Texas, 2012. https://digital.library.unt.edu/ark:/67531/metadc115126/.
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With the recent emergence of the field of metamaterials, the study of subwavelength propagation of plane waves and the dissipation of their energy either in the form of Joule losses in the case of electomagnetic waves or in the form of viscous dissipation in the case of acoustic waves in different interfaced media assumes great importance. with this motivation, I have worked on problems in two different areas, viz., plasmonics and surface acoustics. the first part (chapters 2 & 3) of the dissertation deals with the emerging field of plasmonics. Researchers have come up with various designs in an efort to fabricate efficient plasmonic waveguides capable of guiding plasmonic signals. However, the inherent dissipation in the form of Joule losses limits efficient usage of surface plasmon signal. a dielectric-metal-¬dielectric planar structure is one of the most practical plasmonic structures that can serve as an efficient waveguide to guide electromagnetic waves along the metal-dielectric boundary. I present here a theoretical study of propagation of surface plasmons along a symmetric dielectric-metal-dielectric structure and show how proper orientation of the optical axis of the anisotropic substrate enhances the propagation length. an equation for propagation length is derived in a wide range of frequencies. I also show how the frequency of coupled surface plasmons can be modulated by changing the thickness of the metal film. I propose a Kronig-Penny model for the plasmonic crystal, which in the long wavelength limit, may serve as a homogeneous dielectric substrate with high anisotropy which do not exist for natural optical crystals. in the second part (chapters 4 & 5) of the dissertation, I discuss an interesting effect of extraordinary absorption of acoustic energy due to resonant excitation of Rayleigh waves in a narrow water channel clad between two metal plates. Starting from the elastic properties of the metal plates, I derive a dispersion equation that gives resonant frequencies, which coincide with those observed in the experiment that was performed by Wave Phenomena Group at Polytechnic University of Valencia, Spain. Two eigenmodes with different polarizations and phase velocities are obtained from the dispersion equation. at certain critical aperture of the channel, an interesting cutoff effect, which is unusual for an acoustic wave, is observed for one of the eigenmodes with symmetric distribution of the pressure field. the theoretical prediction of the coupling and synchronization of Rayleigh waves strongly supports the experimentally measured shift of the resonant frequencies in the transmission spectra with channel aperture. the observed high level of absorption may find applications in designing metamaterial acoustic absorbers.
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Cetnar, John S. "Atmospheric Effects on the Propagation of MMW and Sub-MMW Radiation." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1276703479.
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Bariar, Bhawana. "Effects of the components of the Get pathway on prion propagation." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/26659.
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Thesis (M. S.)--Biology, Georgia Institute of Technology, 2008.Committee Chair: Chernoff,Yury; Committee Member: Cairney,John; Committee Member: Choi,Jung; Committee Member: Doyle,Donald; Committee Member: Lobachev,Kirill. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Himel, Marc David. "Microstructure effects on light propagation in zinc-sulfide thin film waveguides." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184593.
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The optical propagation losses resulting from the internal microstructure of ZnS thin films were investigated using a wavelength technique. Waveguide losses were determined by measuring the scattered light as a function of propagation distance along the film. Accurate measurements were obtained by using a technique we developed that employees a coherent fiber bundle to transfer the scattered light streak to a remote image plane that was scanned with an apertured photomultiplier tube. Microstructure effects on losses were found to dominate effects caused by substrate surface finish. The magnitude of the loss was found to depend upon two independent parameters: the average grain size of the polycrystalline films and the refractive index difference between ZnS and the interstitial material. Increasing the H₂O partial pressure led to lower losses as a result of reduced crystallite size, and a change in preferential crystallite orientation. A similar change in orientation was observed for films deposited onto heated substrates. Increasing the O₂ partial pressure during deposition also resulted in slightly lower waveguide losses, possibly as a result of void filling with ZnO. The modal dependence of the losses for ZnS films deposited at ambient temperature suggests that volume losses dominate surface losses for the lowest order mode while the ratio of surface to volume losses increases for higher order modes. By depositing ZnS onto substrates cooled with liquid nitrogen, adatom surface mobility was reduced which resulted in amorphous films. Losses were minimized (≤0.5 dB/cm at λ = 633 nm) for a substrate temperature of -50°C. These losses are lower than any previously reported for ZnS. However, further reduction of the substrate temperature resulted in an increase in tensile stress which eventually led to higher waveguide losses and crazing. The films deposited onto cooled substrates exhibited a low refractive index which indicates a low packing density and increased porosity. Differential water desorption, which is further evidence of increased porosity, was most noticeable in films with lower refractive indices when nonlinear prism coupling was attempted.
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Dixon, Kristoffer Charles. "Analysis of Refractive Effects on Mid-Latitude SuperDARN Velocity Measurements." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/50615.
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First time ionospheric refractive index values have been determined at mid latitudes using frequency switched SuperDARN plasma convection velocity estimates. Previous works have found a disparity between high latitude SuperDARN plasma convection velocities and those made by other devices. It was noted that the scattering volume’s refractive index was being neglected when estimating plasma convection velocities, meaning a correction factor was needed in order to more accurately reflect other measurements. Later work proposed a solution which implemented frequency switching in SuperDARN radars and determined a single correction factor based off of many years of data. We present case study driven research which applies the principles of these previous works to mid latitudes in an attempt to determine the refractive effect in mid latitude SuperDARN plasma convection velocity data by examining frequency switched quiet time ionospheric scatter. It was found that the 1/2 hop ionospheric scatter exhibited little to no measurable refractive effect (n ∼ 1), while the 11/2 hop ionospheric scatter tended to exhibit measurable refractive effects (n ∼ 0.7). This is then expanded to a storm-time 1/2 hop ionospheric scatter case study. It was again found that the refractive effects were nearly negligible (n ∼ 1), indicating that the 1/2 hop plasma convection velocities reported by mid latitude SuperDARN radars only require a very small correction factor, if any at all.Master of Science
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Danklmayer, Andreas. "Propagation effects and polarimetric methods in synthetic aperture radar imaging : 15 Tabellen /." Köln : DLR, Bibliotheks- und Informationswesen, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016768338&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Podo, Smardie D. "Comparison of layering effects in the propagation of transient planar stress waves." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/18378.
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Cowan, Doris. "EFFECTS OF ATMOSPHERIC TURBULENCE ON THE PROPAGATION OF FLATTENED GAUSSIAN OPTICAL BEAMS." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2949.
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In an attempt to mitigate the effects of the atmosphere on the coherence of an optical (laser) beam, interest has recently been shown in changing the beam shape to determine if a different power distribution at the transmitter will reduce the effects of the random fluctuations in the refractive index. Here, a model is developed for the field of a flattened Gaussian beam as it propagates through atmospheric turbulence, and the resulting effects upon the scintillation of the beam and upon beam wander are determined. A comparison of these results is made with the like effects on a standard TEM00 Gaussian beam. The theoretical results are verified by comparison with a computer simulation model for the flattened Gaussian beam. Further, a determination of the probability of fade and of mean fade time under weak fluctuation conditions is determined using the widely accepted lognormal model. Although this model has been shown to be somewhat optimistic when compared to results obtained in field tests, it has value here in allowing us to compare the effects of atmospheric conditions on the fade statistics of the FGB with those of the lowest order Gaussian beam. The effective spot size of the beam, as it compares to the spot size of the lowest order Gaussian beam, is also analyzed using Carter's definition of spot size for higher order Gaussian beams.Ph.D.
Department of Mathematics
Sciences
Mathematics
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Busse, Christian. "Accounting for non-linear effects in fatigue crack propagation simulations using FRANC3D." Thesis, Linköpings universitet, Hållfasthetslära, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-110251.
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In this thesis methods to account for non-linear effects in fatigue crack propagation simulations using FRANC3D are evaluated. FRANC3D is a crack growth software that supports automated crack growth in the FE mesh using the power of an external FE code. Introductorily, a theoretical base in fracture mechanics, especially regarding crack propagation models is established. Furthermore, the functionality of FRANC3D is shown for several different applications. As a benchmark for the investigated methods the associated results are compared to data from laboratory tests. The conditions in the test are closely modeled, but with relevant simplifications. The cyclic life-times are calculated using Paris’ law incorporating the stress intensity factors computed by FRANC3D and with material parameters derived from a different set of experiments than those simulated. When comparing the calculated cyclic life-time with the test data it can be seen that the pure linear elastic simulation, for this particular test set-up, gives nearly as good results as the investigated approaches that account for non-linear effects.
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Coby, Weston R. T., and Jacob A. Fischer. "The effects of internal tides on acoustic propagation in the Philippine Sea." Thesis, Monterey, California: Naval Postgraduate School, 2013. http://hdl.handle.net/10945/37627.
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Approved for public release; distribution is unlimitedIn 2009, a monthlong study was conducted in the Western Philippine Sea. This experiment collected oceanographic and acoustic data from two moorings, the Distributed Vertical Line Array (DVLA) and T1 moorings. The T1 mooring used a 1,095m depth source to send broadband acoustic signals to DVLA receivers located between the depths of 800m and 1,385m. Jacob A. Fischer conducted the internal tide analysis presented in Chapter II. The oceanographic data were used to quantify the characteristics of internal tides in the sample area. Spectral analysis and mode fitting, shows that most of the energy within the internal tides is due to mode 1 of the tidal frequencies. Weston R.T. Coby conducted the acoustic analysis presented in Chapter III. The acoustic data were first used to identify acoustic timefronts across the observed depths, and track the timefronts arrivals. A ray prediction model was then used to match eigenray properties to the observed timefronts. Finally the Viterbi program was used to track timefront arrivals, and intensity for statistical analysis. Weston R.T. Coby and Jacob A. Fischer jointly compared the internal tide and acoustic variability presented in Chapter IV, proving internal tides significantly impact sound speed fluctuations in the Philippine Sea.
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O'Marr, Erin Elizabeth. "Atmospheric effects on signal propagation in adverse environmental conditions a validation of the advanced refractive effects prediction system." Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://edocs.nps.edu/npspubs/scholarly/theses/2008/Sept/08Sep%5FOMarr.pdf.
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Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, September 2008.Thesis Advisor(s): Davidson, Kenneth ; Pfeiffer, Karl. "September 2008." Description based on title screen as viewed on October 31, 2008. Includes bibliographical references (p. 73-74). Also available in print.
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Kitey, Rajesh Tippur Hareesh V. "Microstructural effects on fracture behavior of particulate composites investigation of toughening mechanisms using optical and boundary element methods /." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/doctoral/KITEY_RAJESH_50.pdf.
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Meehan, Eamonn James. "Sitka spruce (Picea sitchensis (Bong.) Carr.) propagation technologies : their effects on genetic diversity." Thesis, Queen's University Belfast, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.486558.
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The aim of this smdy v,'as to assess the genetic diversity of Sitka spruce seedling populations as produced by commercial growers and to detennine what effects the propagation technologies ofrooted cuttings and somatic embryogenesis had on genetic diversity. Seedling populations ,,,ere produced consisting of one hundred seedlings' from each of three families of Washington provenance material and from each of three families of Queen Charlotte Islands provenance. Rooted cutting populations were produced from twelve cuttings from each of fifty randomly selected plants [rom each of the six families. Somatic embryogenesis derived populations (emblings) were produced and fifty populations were provided by Coillte from the three Washington provenance families which represented the maximum number of cell lines produced by a successful commercial grower. Significant phenotypical differences betwe.en zygotic seedlings were found at both family and provenance level after 19 months of grov.1h. All 300 genotypes were able to produce rooted cuttings indicating that no significant loss of genetic diversity in cuttings from two-year-old trees. Seven pairs of microsatellite primers were multiplexed to amplify polymorphic microsatellite DNA loci from needle samples of seedlings and emblings. Capillary electrophoresis of the products yielded data which were analysed according to the Infinite Allele Model and Stepwise Mutation Model. No significant differences were found, using either mutation model, between the genetic diversity values (observed heterozygosity, gene diversity, allelic richness and inbreeding coefficient (Fis)) for the seedling populations and somatic embryogenesis derived populations. A low level of microsatellite variation was found to occur within mature individual trees and within somatic embryogenesis derived populations. The extent of microsatellite variation was found to be dependent on locus and genotype. The propagation technologies of somatic embryogenesis and rooted cuttings do not cause a loss of genetic diversity in the resulting populations.
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Hibbs, Kathryn Jane. "The Effects of Nonlinear Propagation and Dispersion on Quantitative Contrast-Enhanced Ultrasound Imaging." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525343.
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Kindervatter, Tim. "Survey of Ionospheric Propagation Effects and Modeling Techniques for Mitigation of GPS Error." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515106508878179.
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Mazzaro, Gregory. "Analysis and simulation of the effects of atmospheric turbulence on optical wave propagation." Diss., Online access via UMI:, 2006.
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Xiradakis, Pavlos. "The refractive effects of laser propagation through the ocean and within the ocean." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FXiradakis.pdf.
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Thesis (M.S. in Physics)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Walters, Donald. Second Reader: Borden, Brett. "December 2009." Description based on title screen as viewed on January 27, 2010. Author(s) subject terms: Ocean waves, Laser Scattering, Absorption, Refraction. Includes bibliographical references (p. 55). Also available in print.
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Backhaus, Thomas [Verfasser]. "Uncertainty Propagation of Real Geometry Effects on Jet Engine Compressor Blisks / Thomas Backhaus." Düren : Shaker, 2020. http://d-nb.info/1213472989/34.
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Reda, Hilal. "Modeling and computation of the effective static and dynamic properties of network materials accounting for microstructural effects and large deformations." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0007/document.
Full textAbstract:
Nous analysons les propriétés dynamiques de milieux architecturés périodiques et de réseaux fibreux aléatoires en petites et grandes déformations, à partie de méthodes d’homogénéisation afin de calculer leurs propriétés statiques et dynamiques. Des modèles effectifs de type micropolaire et du second gradient sont élaborés afin de prendre en compte l’impact de la microstructure sur le comportement effectif. L’influence des degrés de liberté en rotation additionnels et des gradients d’ordre supérieur du déplacement sur les relations de dispersion sont analysés pour des comportements élastique et viscoélastique du matériau constitutif. Les milieux continus généralisés ainsi construits conduisent à des effets dispersifs, en accord avec les observations. Dans la seconde partie du travail, nous analysons l’influence des grandes déformations sur la propagation des ondes élastiques dans des milieux architecturés périodiques. Des méthodes théoriques assortis de schémas numériques sont développés afin de prédire l’influence des déformations finies générées au sein des structures sur l’évolution de leur diagramme de bande. Un schéma incrémental d’évolution de la fréquence et de la vitesse de phase du milieu continu homogénéisé est établi, à partir d’une méthode de perturbation établie pour des structures 1D, 2D et 3D, en considérant plus particulièrement des structures auxétiques. Ce schéma montre un effet important de l’état de déformation appliquée et de la densité effective sur l’évolution de la fréquence et de la vitesse de phase des ondes. Une méthode de perturbation spécifique aux structures périodiques nonlinéaires est développée afin de généraliser le théorème de Bloch pour couvrir les non linéarités tant géométriques que matérielles. Des modèles hyperélastiques du premier et du second gradient de différentes structures sont identifiés par des tests virtuels reposant sur une méthode d’homogénéisation dédiée, qui permettent de formuler des équations d’onde spécifiques – équations de Burgers et de Boussinesq – dont les propriétés dispersives sont analyséesMicropolar and second gradient effective continua are constructed as two different strategies to account for microstructural effects. The influence of additional degrees of freedom or higher order displacement gradients on the dispersion relations is analyzed in both situations of elastic and viscoelastic behaviors of the material. Generalized effective continua lead to dispersive waves, as observed in experiments. In the second part of the thesis, we analyze the influence of large deformations on the propagation of acoustic waves in repetitive network materials. Both theoretical and numerical methods are developed in order to assess the influence of finite strains developing within the networks on the evolution of their band diagrams. An incremental scheme for the update of frequency and phase velocity of the computed homogenized medium is developed based on a perturbation method for 1D, 2D and 3D structures, considering with a special emphasis auxetic networks. This scheme shows an important effect of the applied finite deformation on the frequency and phase velocity of the propagating waves. A perturbation method for nonlinear periodic structures is developed to extend Bloch’s theorem to cover both geometrical and material nonlinearities. Hyperelastic first and second order gradient constitutive models of different network materials are identified based on dedicated homogenization methods, from which specific wave equations are formulated - Burgers and Boussinesq equations - the dispersion properties of which are analyzed