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Visser, Schalk W. J. (Schalk Willem Jacobus). "Data capturing system using cellular phone, verified against propagation models." Thesis, Stellenbosch : University of Stellenbosch, 2004. http://hdl.handle.net/10019.1/16462.
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Thesis (MScIng)--University of Stellenbosch, 2004.ENGLISH ABSTRACT: Data capturing equipment are an expensive part of testing the coverage of a deployed or planned wireless service. This thesis presents the development of such a data capturing system that make use of 1800MHz GSM base stations as transmitters and a mobile phone connected to a laptop as receiver. The measurements taken, are then verified against know propagation models. Datavaslegging toerusting wat gebruik word om die dekking van draadlose stelsels te toets is baie duur en moeilik bekombaar. Hierdie tesis beskryf die ontwikkeling van so ’n datavaslegger wat baie goedkoper is en maklik gebruik kan word. Dit maak gebruik van ’n sellulêr foon en GPS gekoppel aan ’n skootrekenaar, wat die ontvanger is. Cell C basis staties word gebruik as die senders. Die data wat gemeet is word dan geverifieer deur gebruik te maak van bestaande radio frekwensie voortplanting modelle.
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Coombs, Richard. "Models for information propagation in opportunistic networks." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/68235/.
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The topic of this thesis is Opportunistic Networks (OPNETS), a type of mobile ad hoc network in which data are propagated by the movement of the network devices and by short-range wireless transmissions. This allows data to spread to many devices across large distances without the use of any infrastructure or powerful hardware. OPNET technology is in its fairly early stages of development and has a lot of potential for research. There are many applications that could benefit from OPNETS, such as sensor networks or social networks. However, before the technology can be used with confidence, research must be undertaken to better understand its behaviour and how it can be improved. In this thesis, the way in which information propagates in an OPNET is studied. Methodical parameter studies are performed to measure the rate at which information reaches new recipients, the speed at which information travels across space, and the persistence of information in the network. The key parameters being studied are device density, device speed, wireless signal radius and message transmission time. Furthermore, device interaction schemes based on epidemiological models are studied to find how they affect network performance. Another contribution of this thesis is the development of theoretical models for message spread in regions of one-dimensional (1D) and two-dimensional (2D) space. These models are based on preliminary theoretical models of network device interaction; specifically, the rate at which devices move within range of each other and the length of time that they remain within range. A key contribution of this thesis is in acknowledging that data transmissions between devices do not occur instantaneously. Due to latency in wireless communications, the time taken to transmit data is proportional to the amount of data being transferred. Non-instantaneous transmissions may fail before completion. Investigation is made into the effect this has on the rate of information propagation in OPNETS.
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Mohamed, Ramizi. "Partial discharge signal propagation, modelling and estimation in high voltage transformer windings." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/165433/.
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The thesis concerns partial discharge (PD) propagation within a high voltage transformer winding. Location of PDs and magnitude estimation are important tools for both diagnosis and prognosis of the health of large transformers. In reality there is limited access and knowledge of a winding and consequently any practical method requires the use of estimation techniques. The approach taken in this thesis is by considering lumped circuit parameter models. Firstly, a lumped capacitive parameter model was considered and secondly a transmission line lumped parameter approach developed. A technique of split winding analysis is introduced for both types of model. The derivation of the capacitive network considers the source location of a PD by defining the PD signal propagation in two directions. At the source, the currents are equal in magnitude and are attenuated as they flow in each direction. This provides information for a fixed distribution model equation. Under transmission line lumped parameter models, split winding analysis explains the development of accumulated harmonic waveforms of the PD propagation signal towards the neutral and bushing tap-point. At the source, a D’Alembert solution is employed to estimate the oscillation level and found to be in very good agreement with measured data using rectangular wave signal injection. PD signal behaviour is then considered using a time varying boundary conditions model with a principle of superposition equation of source signal. Duhamel’s principle is employed to find a solution for any waveform applied to some point on the transformer winding. Under the influence of losses and distortion, an accumulated harmonic amplitude analysis from the Duhamel’s principle estimates the PD propagation level. For different injection points along the transformer winding, the measured PD level at the neutral and bushing tap point caused by the accumulated harmonic amplitude reveals different patterns. As the PD injection point is altered from the bushing tap point to the neutral, the measured signals significantly change. This in turn contains information of the level of discharge signal at the source. From this analysis a technique based on minimum mean error (MME) calculation using the measurements at the bushing tap and neutral points can be used to identify the source location of PDs based on the analysis of accumulated harmonic amplitudes. With a known location, the information can then be used to estimate PD levels. As the actual charge transferred at the location of a partial discharge cannot be measured directly, by using the D’Alembert solution, the PD source level is found to have approximately twice the apparent magnitude. By using the predominantly capacitive model derived based on split current propagation, PD estimation at higher frequencies is also possible. As a result, an estimation of PD level can be estimated for measurement signals having bandwidth of up to 150MHz.
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Sani, Andrea. "Modelling and characterisation of antennas and propagation for body-centric wireless communication." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/596.
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Body-Centric Wireless Communication (BCWC) is a central point in the development of fourth generation mobile communications. The continuous miniaturisation of sensors, in addition to the advancement in wearable electronics, embedded software, digital signal processing and biomedical technologies, have led to a new concept of usercentric networks, where devices can be carried in the user’s pockets, attached to the user’s body or even implanted. Body-centric wireless networks take their place within the personal area networks, body area networks and body sensor networks which are all emerging technologies that have a broad range of applications such as healthcare and personal entertainment. The major difference between BCWC and conventional wireless systems is the radio channel over which the communication takes place. The human body is a hostile environment from radio propagation perspective and it is therefore important to understand and characterise the effect of the human body on the antenna elements, the radio channel parameters and hence the system performance. This is presented and highlighted in the thesis through a combination of experimental and electromagnetic numerical investigations, with a particular emphasis to the numerical analysis based on the finite-difference time-domain technique. The presented research work encapsulates the characteristics of the narrowband (2.4 GHz) and ultra wide-band (3-10 GHz) on-body radio channels with respect to different digital phantoms, body postures, and antenna types hence highlighting the effect of subject-specific modelling, static and dynamic environments and antenna performance on the overall body-centric network. The investigations covered extend further to include in-body communications where the radio channel for telemetry with medical implants is also analysed by considering the effect of different digital phantoms on the radio channel characteristics. The study supports the significance of developing powerful and reliable numerical modelling to be used in conjunction with measurement campaigns for a comprehensive understanding of the radio channel in body-centric wireless communication. It also emphasises the importance of considering subject-specific electromagnetic modelling to provide a reliable prediction of the network performance.
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Opperman, B. D. L. "Precision propagation and orbit decay predication of low earth orbit satellites." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53555.
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Thesis (MScEng)--Stellenbosch University, 2003.ENGLISH ABSTRACT: This study investigates the theory of precision satellite orbit propagation and satellite lifetime prediction and lead to the development of two necessary software tools for analysis in these fields. Precision propagation was achieved through the implementation of Cowell's method of special perturbations, considering perturbations due to a 70x70 asymmetrical gravity field, atmospheric drag, Luni-Solar attraction and Solar radiation pressure. The satellite's perturbed equations of motion were integrated utilizing a seveneighth order Runge-Kutta-Fehlberg numerical integration procedure, limiting error propagation by employing adaptive step size control. The MSlS-90 atmospheric density model, providing for diurnal and semi-annual variations, was employed to determine atmospheric density. Care was taken in the precision modelling of the motion of the 12000 equator and equinox. Propagation results for this test case proved to be superior to the SGP4 propagator and a commercial package. The long-term effects of Earth oblateness and atmospheric drag on a satellite's orbital elements were investigated and applied to the orbit decay prediction problem. Orbit decay was predicted by integrating the rates of change of the orbital elements due to Earth oblateness and atmospheric drag. A semi-analytical technique involving Runge-Kutta and Gauss-Legendre quadrature was employed in the solution process. Relevant software was developed to implement the decay theory. Optimum drag coefficients, estimated from drag analysis using precision propagation, were used in decay prediction. Two test cases of observed decayed satellites were used to evaluate the theory. Results for both test cases indicated that the theory fitted observational data well within acceptable limits.
AFRIKAANSE OPSOMMING: 'n Ondersoek is gedoen oor die teorie van presiesie satelliet-wentelbaan vooruitskatting en satelliet-wentelbaanleeftyd afskatting en het gelei tot die ontwikkeling van twee analiseprogramme vir gebruik in hierdie vakgebiede. Presiesie vooruitskatting is bereik deur die gebruik van Cowell se metode van spesiale perturbasies, wat die invloed van 'n nie-simmetriese 70x070 gravitasieveld, atmosferiese sleur, Son-Maan aantrekkingskragte en druk van sonradiasie, in ag neem. Die satelliet se versteurde bewegingsvergelykings is numeries ge-ïntegreer deur gebruik te maak van die sewe-agste orde Runge-Kutta- Fehlberg metode wat fout-voortplanting inhibeer deur gebruik te maak van 'n aanpasbare integrasiestaplengte. Die MSIS-90 atmosferies model, wat voorsiening maak vir dag-nag en half-jaarlikse atmosferiese variasies, is gebruik vir die berekening van atmosferiese digtheid. Sorg is gedra by die presiesie modellering van die beweging van die J2000 ekwator en ekwinokse. Resultate vir hierdie toetsgeval toon meer voortreflik te wees as die SPG4 - en 'n kommersieël-beskikbare vooruitskatter. Die langtermyn effekte van aard-afplatting en atmosferiese sleur op wentelbaanleeftyd is ondersoek en toegepas op die wentelbaanverval-afskattingsprobleem. Wentelbaanverval is bereken deur die integrasie van die tydsafgeleides van die wentelbaanelement onder invloed van aard-afplatting en atmosferiese sleur. Vir die doel is 'n semi-analitiese tegniek, wat gebruik maak van Gauss-Legendre kwadratuur en Runge-Kutta numeriese integrasie, gebruik gemaak. Nodige rekenaar programmatuur is ontwi kkeI om die vervalteorie te implimenteer. Optimale sleur-koëffisiënte is afgeskat deur van presiesie wentelbaananalise gebruik te maak. Twee gevallestudies van bekende vervalde satelliete is gebruik om die vervalteorie te evalueer. Resultate vir beide gevallestudies toon aan dat eksperimentele resultate werklike vervaltye binne aanvaarbare limiete navolg.
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Stevens, Randel J. "Neural regulation of the origin and propagation of muscle excitability in the gastrointestinal tract /." abstract and full text PDF (UNR users only), 1998. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9916962.
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Smith, Michael John. "Sandstorm a dynamics multi-contextual GPU-based particle system using vector fields for particle propagation /." abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1453635.
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Buchanan, William J. "Analysis of electromagnetic wave propagation using 3D finite-difference time-domain methods with parallel processing." Thesis, Edinburgh Napier University, 1996. http://researchrepository.napier.ac.uk/Output/4022.
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The 3D Finite-Difference Time-Domain (FDTD) method simulates structures in the time-domain using a direct form of Maxwell's curl equations. This method has the advantage over other simulation methods in that it does not use empirical approximations. Unfortunately, it requires large amounts of memory and long simulation times. This thesis applies parallel processing to the method so that simulation times are greatly reduced. Parallel processing, though, has the disadvantage in that simulation programs require to be segmented so that each processor processes a separate part of the simulation. Another disadvantage of parallel processing is that each processor communicates with neighbouring processors to report their conditions. For large processor arrays this can result in a large overhead in simulation time. Two main methods of parallel processing discussed: Transputer arrays and clustered workstations over a local area network (LAN). These have been chosen because of their relatively cheapness to use, and their widespread availability. The results presented apply to the simulation of a microstrip antenna and to propagation of electrical signals in a printed circuit board (PCB). Microstrip antennas are relatively difficult to simulate in the time-domain because they have resonant pulses. Methods that reduce this problem are discussed in the thesis. The thesis contains a novel analysis of the parallel processing showing, using equations, tables and graphs, the optimum array size for a given inter-processor communication speed and for a given iteration time. This can be easily applied to any processing system. Background material on the 3D FDTD method and microstrip antennas is also provided. From the work on the parallel processing of the 3D FDTD a novel technique for the simulation of the Finite-element (FE) method is also discussed.
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Neumann, James 1958. "THE INITIATION AND PROPAGATION OF HERTZIAN AND RADIAL CRACKS IN NICKEL-ZINC FERRITE." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/276523.
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This investigation was initiated by IBM to determine the types of cracks formed in hot-isostatic-pressed (HIP) Ni-Zn ferrite under impact and static loading conditions. A 1/8-inch tungsten carbide (WC) ball was used to apply the load in both cases. The impact loading condition was accomplished by dropping the WC ball from various heights between 40 and 200 cm. The static loading condition was accomplished by applying loads of 10 kg, 15 kg, and 30 kg on a Rockwell Hardness Tester. The response of HIP Ni-Zn ferrite to impact and static loading was elastic/plastic yielding permanent indentations. "Dimple" impressions, Hertzian-ring cracks, and radial cracks were formed upon applying increasing loads to the HIP Ni-Zn ferrite. As the grain size of the material was increased, both the Hertzian-ring and radial cracks were formed at lower loads compared to the as-received samples. The "dimple" impressions were not observed to follow this trend.
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Gamble, Stephanie Nicole. "Conical Intersections and Avoided Crossings of Electronic Energy Levels." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/101899.
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We study the unique phenomena which occur in certain systems characterized by the crossing or avoided crossing of two electronic eigenvalues. First, an example problem will be investigated for a given Hamiltonian resulting in a codimension 1 crossing by implementing results by Hagedorn from 1994. Then we perturb the Hamiltonian to study the system for the corresponding avoided crossing by implementing results by Hagedorn and Joye from 1998. The results from these demonstrate the behavior which occurs at a codimension 1 crossing and avoided crossing and illustrates the differences. These solutions may also be used in further studies with Herman-Kluk propagation and more.
Secondly, we study codimension 2 crossings by considering a more general type of wave packet. We focus on the case of Schrödinger equation but our methods are general enough to be adapted to other systems with the geometric conditions therein. The motivation comes from the construction of surface hopping algorithms giving an approximation of the solution of a system of Schrödinger equations coupled by a potential admitting a conical intersection, in the spirit of Herman-Kluk approximation (in close relation with frozen/thawed approximations). Our main Theorem gives explicit transition formulas for the profiles when passing through a conical crossing point, including precise computation of the transformation of the phase and its proof is based on a normal form approach.Doctor of Philosophy
We study energies of molecular systems in which special circumstances occur. In particular, when these energies intersect, or come close to intersecting. These phenomena give rise to unique physics which allows special reactions to occur and are thus of interest to study. We study one example of a more specific type of energy level crossing and avoided crossing, and then consider another type of crossing in a more general setting. We find solutions for these systems to draw our results from.
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Villaume, Sébastien Daniel Chantal Strich Alain. "Electronic spectroscopy and photochemistry of small transition metal complexes studies via coupled cluster calculations and wavepacket propagation." Strasbourg : Université Louis Pasteur, 2006. http://eprints-scd-ulp.u-strasbg.fr:8080/527/01/VILLAUME2005.pdf.
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Villaume, Sébastien. "Electronic spectroscopy and photochemistry of small transition metal complexes studies via coupled cluster calculations and wavepacket propagation." Université Louis Pasteur (Strasbourg) (1971-2008), 2005. https://publication-theses.unistra.fr/public/theses_doctorat/2005/VILLAUME_Sebastien_2005.pdf.
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Cette thèse de chimie informatique et théorique porte sur la spectroscopie électronique et la photochimie de petits complexes de métaux de transition. Ces molécules sont caractérisées par une grande densité d’états électroniques excités de nature très diverse dans le domaine énergétique UV-Visible. La position relative de ces états est contrôlée par la nature du centre métallique et des ligands, ce qui influe sur la réactivité induite par la lumièere. L’étude théorique de la photochimie de ces systèmes nécessite l’emploi de méthodes de chimie quantique prenant en compte la corrélation électronique. La première partie de la thèse décrit les méthodes ab initio et de dynamique quantique que nous avons utilisées. Le second chapitre présente une étude des réarrangements intramoléculaires dans PH2F3. La troisième partie rapporte une étude détaillée de la spectroscopie électronique de Cr(CO)6 ainsi que la photodissociation conduisant au départ d’un ligand carbonyle. Le quatrième chapitre porte sur l’étude de la structure électronique de la famille des petits complexes MCH+2 (M=Fe, Co, Ni) par des calculs Coupled Cluster. L’avant-dernière partie concerne la spectroscopie d’absorption et plus particulièrement d’émission des états à transfert de charge métal vers ligands du complexe HRe(CO)3(H-DAB). Enfin le dernier chapitre propose une nouvelle étude de la photochimie des complexes RCo(CO)4 (R=H, CH3) par des calculs ab initio et TD-DFT ainsi qu’une simulation par dynamique quantique de la photodissociation compétitive des ligands axiaux CO et H dans le cas de HCo(CO)4Electronic spectroscopy and photochemistry of small transition metal complexes studied via Coupled Cluster calculations and wavepacket propagation. The scope of this thesis in computational and theoretical chemistry is the study of the electronic spectroscopy and the photochemistry of transition metal compounds. These molecules are characterized by a high density of electronic excited states of different nature in the UV-Visible energy window. The relative position and the character of these excited states are controlled by the nature of the metal center and surrounding ligands which influence light-induced reactivity. The theoretical study of the photochemistry of these systems requires approaches based on highly correlated methods of quantum chemistry. The first part of the thesis describes quantum chemical methods and quantum dynamical formalism used in this work. The second chapter presents the study of the intramolecular rearrangement in trifluorophosphorane PH2F3. The third part focuses on the electronic spectroscopy of Cr(CO)6 the photodissociation processes that lead to the departure of a carbonyl. The fourth chapter deals with the detailed study of the electronic structure of the MCH+2 (M=Fe, Co, Ni) series. The fifth part is dedicated to the absorption and emission spectroscopy of a metal to ligand charge transfer states of HRe(CO)3(H-DAB). The last part is devoted to the photochemistry of RCo(CO)4 (R=H, CH3) studied via ab initio and TD-DFT calculations and a quantum dynamical simulation of the competitive photodissociation of axial ligands CO and H in the case oh HCo(CO)4
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Urban, Brian L. "Propagation analysis of a 900 MHz spread spectrum centralized traffic signal control system." Thesis, University of North Texas, 2006. https://digital.library.unt.edu/ark:/67531/metadc5242/.
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The objective of this research is to investigate different propagation models to determine if specified models accurately predict received signal levels for short path 900 MHz spread spectrum radio systems. The City of Denton, Texas provided data and physical facilities used in the course of this study. The literature review indicates that propagation models have not been studied specifically for short path spread spectrum radio systems. This work should provide guidelines and be a useful example for planning and implementing such radio systems. The propagation model involves the following considerations: analysis of intervening terrain, path length, and fixed system gains and losses.
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Otterskog, Magnus. "Propagation Environment Modeling Using Scattered Field Chamber." Doctoral thesis, Örebro : Universitetsbiblioteket : Örebro University, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-731.
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Braly, S. Katharine. "Environmental variables influencing sexual reproduction of sea oats, Uniola paniculata (Poaceae) across a natural dune field on Bear Island, North Carolina." View electronic thesis (PDF), 2009. http://dl.uncw.edu/etd/2009-1/r1/bralys/sbraly.pdf.
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Nagaraj, Mahavir. "Short time scale thermal mechanical shock wave propagation in high performance microelectronic packaging configuration." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/1087.
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The generalized theory of thermoelasticity was employed to characterize the coupled thermal and mechanical wave propagation in high performance microelectronic packages. Application of a Gaussian heat source of spectral profile similar to high performance devices was shown to induce rapid thermal and mechanical transient phenomena. The stresses and temporal gradient of stresses (power density) induced by the thermal and mechanical disturbances were analyzed using the Gabor Wavelet Transform (GWT). The arrival time of frequency components and their magnitude was studied at various locations in the package. Comparison of the results from the classical thermoelasticity theory and generalized theory was also conducted. It was found that the two theories predict vastly different results in the vicinity of the heat source but that the differences diminish within a larger time window. Results from both theories indicate that the rapid thermal-mechanical waves cause high frequency, broadband stress waves to propagate through the package for a very short period of time. The power density associated with these stress waves was found to be of significant magnitude indicating that even though the effect, titled short time scale effect, is short lived, it could have significant impact on package reliability. The high frequency and high power density associated with the stress waves indicate that the probability of sub-micron cracking and/or delamination due to short time scale effect is high. The findings demonstrate that in processes involving rapid thermal transients, there is a non-negligible transient phenomenon worthy of further investigation.
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Ehn, Jonas. "Propagation of Radio Waves in a Realistic Environment using a Parabolic Equation Approach." Thesis, Linköpings universitet, Teoretisk Fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-157610.
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Radars are used for range estimation of distant objects. They operate on the principle of sending electromagnetic pulses that are reflected off a target. This leads to the propagation of electromagnetic waves over large distances. As the waves propagate, they are affected by several aspects that decrease the performance of the radar system. In this master thesis, we derive a mathematical model that describes electromagnetic propagation in the troposphere. The model developed is based on a parabolic equation and uses the split-step Fourier method for its numerical solution. Using the model, we estimate the influence of a varying, complex, refractive index of the atmosphere, different lossy materials in the ground, terrain, and oceans. The terrain is described using a piecewise linear shift map method. The modelling of the ocean is done using a novel model which is a combination of terrain for large swells and Miller surface roughness for smaller waves, both based on a Pierson-Moskowitz sea spectrum. The model is validated and found to agree very well, with results found in the literature.
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Abi, Akl Marie-José. "Propagation dans l'ionosphère en présence de turbulences : applications aux radars HF." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066374.
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Le radar haute fréquence (HF : 3 MHz à 30 MHz) à mode hybride est une solution prometteuse pour assurer la surveillance permanente, jusqu'à 2000 km, de zones maritimes et terrestres. Ce mode est une combinaison des modes de fonctionnement des radars à onde de ciel et à ondes de surface. Lorsque l'intégration du signal est effectuée sur une cible lente, les instabilités ionosphériques affectent les images Doppler-distance. Pour rendre compte de ce phénomène en simulation, un module logiciel basé sur des modèles probabilistes du fouillis ionosphérique a été développé dans le but de simuler le comportement spatial et temporel de l'ionosphère dans le traitement radar. La version finale de ce module est basée sur le profil de densité électronique de Booker, aléatoirement modifié en espace à partir de la fonction de densité spectrale de puissance de Shkarofsky. L'aspect temporel a été aussi pris en compte dans le traitement radar en appliquant aux chemins de phase aléatoires ainsi générés un filtrage passe-bas en prenant en considération les variations du TEC (Contenu Électronique Total). La sensibilité des étalements en décalage Doppler et en distance aux paramètres de la densité spectrale de puissance et à la valeur de la fréquence de coupure du filtre passe-bas, a également été étudiée. Enfin, les images synthétisées ont été comparées aux images réelles obtenues à partir d'un radar HF situé dans le Sud de la FranceHigh-frequency (HF: 3 MHz to 30 MHz) hybrid mode radar is a promising solution for continuous monitoring of sea and land areas up to 2000 km. This mode is a combination of the modes of operation of the sky wave and surface wave radars. When signal processing is performed on a slow target, the ionospheric irregularities degrade the Doppler-distance images. To take this phenomenon into account in simulation, a software module based on probabilistic models of the ionospheric clutter has been developed with the aim of simulating the spatial and temporal behavior of the ionosphere in radar processing.The final version of this module is based on Booker's electron density profile, randomly modified in space from the Shkarofsky power spectral density function. The temporal aspect has also been taken into account in the radar processing by applying to the random phase paths thus generated a low-pass filtering taking into consideration the TEC (Total Electron Content) variation. The sensitivity of the Doppler shift and distance spreading to the parameters of the power spectral density and the cut-off frequency of the low-pass filter has also been studied. Finally, the synthesized images have been compared with the actual images obtained from an HF radar located in the South of France
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Law, Yiu Kui. "Design and Testing of Off-The-Shelf Electronic Components for an Acoustic Emission Structural Health Monitoring System Using Piezoelectric Sensors." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/34477.
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The safety concern of aging aircraft is a rising issue in terms of both safety and cost. An aircraft structure failure during flight is unacceptable. A method needs to be developed and standardized to test the integrity of both commercial and military aircrafts. The current method to test the structure of an aircraft requires the aircraft to be taken out of service for inspection; this is costly due to the inspection required to be performed and the lost use from downtime.
A novice idea of an on-site structural health monitoring (SHM) system has been proposed to test the integrity of aircraft structure. An on-site system is a system that can be used to perform inspection on an aircraft simultaneously while the aircraft is in use. This SHM system uses the principles of active lamb wave and passive acoustic emission through the use of piezoelectric sensors as the sensing elements. Piezoelectric sensors can be used both as an input device and as a sensing element.
This research focuses on the development of the major data acquisition electronic components of the system. These components are charge amplifier, high pass filter, low pass filter and line driver. A charge amplifier converts a high impedance signal to a low impedance signal. A high pass filter attenuates the low frequency content of a signal, while a low pass filter attenuates the high frequency content of a signal. A line driver converts a low current signal to a high current signal. All of these components need to operate up to a frequency of 2 MHz. Off-the-shelf electronics will be used for prototyping as custom components will not be feasible at this point of the research.Master of Science
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Styliaras, Nikolaos. "INVESTIGATION OF THE EFFECT OF THE TRANSFORMER CONNECTION TYPE ON VOLTAGE UNBALANCE PROPAGATION: CASE STUDY AT NÄSUDDEN WIND FARM." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-318969.
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The objective of this Thesis is to investigate the phenomenon of voltage unbalance on electrical wind power systems. A large part of this work is the literature review of all relative work that has been done so far. This serves first as a guideline to define and measure voltage unbalance and second as a tool to spot open research questions that can inspire future work. A case study is then used to investigate the voltage unbalance at a wind farm in Näsudden, Gotland. Using real-time measurements and a simulation of the power system in MATLAB/Simulink, an evaluation of the propagation of the voltage unbalance from the distribution to the turbine level is carried out. The effect that different transformer connection types have on the propagation is studied through simulations. Many assumptions and simplifications had to be made due to several limiting factors during this work, mainly related to time and data restrictions. The main result shows that when Delta – Wye Grounded and Wye – Wye Grounded transformers are used, the unbalance is halved when it passes to the turbine side. On the other hand, when Wye Grounded – Wye Grounded configuration was used, the unbalance was unaffected. The results also include a comparison of the use of different indices to quantify a voltage unbalance.
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Midgley, Stuart. "Quantum waveguide theory." University of Western Australia. School of Physics, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0036.
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The study of nano-electronic devices is fundamental to the advancement of the semiconductor industry. As electronic devices become increasingly smaller, they will eventually move into a regime where the classical nature of the electrons no longer applies. As the quantum nature of the electrons becomes increasingly important, classical or semiclassical theories and methods will no longer serve their purpose. For example, the simplest non-classical effect that will occur is the tunnelling of electrons through the potential barriers that form wires and transistors. This results in an increase in noise and a reduction in the device?s ability to function correctly. Other quantum effects include coulomb blockade, resonant tunnelling, interference and diffraction, coulomb drag, resonant blockade and the list goes on. This thesis develops both a theoretical model and computational method to allow nanoelectronic devices to be studied in detail. Through the use of computer code and an appropriate model description, potential problems and new novel devices may be identified and studied. The model is as accurate to the physical realisation of the devices as possible to allow direct comparison with experimental outcomes. Using simple geometric shapes of varying potential heights, simple devices are readily accessible: quantum wires; quantum transistors; resonant cavities; and coupled quantum wires. Such devices will form the building blocks of future complex devices and thus need to be fully understood. Results obtained studying the connection of a quantum wire with its surroundings demonstrate non-intuitive behaviour and the importance of device geometry to electrical characteristics. The application of magnetic fields to various nano-devices produced a range of interesting phenomenon with promising novel applications. The magnetic field can be used to alter the phase of the electron, modifying the interaction between the electronic potential and the transport electrons. This thesis studies in detail the Aharonov-Bohm oscillation and impurity characterisation in quantum wires. By studying various devices considerable information can be added to the knowledge base of nano-electronic devices and provide a basis to further research. The computational algorithms developed in this thesis are highly accurate, numerically efficient and unconditionally stable, which can also be used to study many other physical phenomena in the quantum world. As an example, the computational algorithms were applied to positron-hydrogen scattering with the results indicating positronium formation.
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Lin, Yu Chu. "E-government website performance evaluation based on BP neural network." Thesis, University of Macau, 2017. http://umaclib3.umac.mo/record=b3691489.
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Du, Toit Daniel N. J. "Low Earth orbit satellite constellation control using atmospheric drag." Thesis, Link to the online version, 1997. http://hdl.handle.net/10019/2999.
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Hrnčíř, Petr. "Role marketingu v hudebním průmyslu se zaměřením na EDM a DJing." Master's thesis, Vysoká škola ekonomická v Praze, 2014. http://www.nusl.cz/ntk/nusl-193347.
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This thesis examines the influence of marketing communication on music industry with focus on electronic dance music. In theoretical part are processed basic terms defining marketing communication. Consequently is described development of electronic dance music from seventies. The main objective of this thesis is define important marketing tools in allotted age group and confirm knowledge of this area of music industry. The practical part is focused on the research of popularity, target group determination and also evaluates interview with specialists and artists. Base on the research results from questionnaires and interview the thesis also proposes own marketing campaign of unknown artist.
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Ferrari, Jair Feldens. "Refractive conditions of Amazon environment and its effects on ground and airborne radar and ESM systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03sep%5FFerrari.pdf.
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Thesis (M.S. in Systems Engineering)--Naval Postgraduate School, September 2003.Thesis advisor(s): Kenneth L. Davidson, David C. Jenn. Includes bibliographical references (p. 67-68). Also available online.
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Ayday, Erman. "Iterative algorithms for trust and reputation management and recommender systems." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45868.
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This thesis investigates both theoretical and practical aspects of the design and analysis of iterative algorithms for trust and reputation management and recommender systems. It also studies the application of iterative trust and reputation management mechanisms in ad-hoc networks and P2P systems.
First, an algebraic and iterative trust and reputation management scheme (ITRM) is proposed. The proposed ITRM can be applied to centralized schemes, in which a central authority collects the reports and forms the reputations of the service providers (sellers) as well as report/rating trustworthiness of the (service) consumers (buyers). It is shown that ITRM is robust in filtering out the peers who provide unreliable ratings. Next, the first application of Belief Propagation algorithm, a fully iterative probabilistic algorithm, on trust and reputation management (BP-ITRM) is proposed. In BP-ITRM, the reputation management problem is formulated as an inference problem, and it is described as computing marginal likelihood distributions from complicated global functions of many variables. However, it is observed that computing the marginal probability functions is computationally prohibitive for large scale reputation systems. Therefore, the belief propagation algorithm is utilized to efficiently (in linear complexity) compute these marginal probability distributions. In BP-ITRM, the reputation system is modeled by using a factor graph and reputation values of the service providers (sellers) are computed by iterative probabilistic message passing between the factor and variable nodes on the graph. It is shown that BP-ITRM is reliable in filtering out malicious/unreliable reports. It is proven that BP-ITRM iteratively reduces the error in the reputation values of service providers due to the malicious raters with a high probability. Further, comparison of BP-ITRM with some well-known and commonly used reputation management techniques (e.g., Averaging Scheme, Bayesian Approach and Cluster Filtering) indicates the superiority of the proposed scheme both in terms of robustness against attacks and efficiency.
The introduction of the belief propagation and iterative message passing methods onto trust and reputation management has opened up several research directions. Thus, next, the first application of the belief propagation algorithm in the design of recommender systems (BPRS) is proposed. In BPRS, recommendations (predicted ratings) for each active user are iteratively computed by probabilistic message passing between variable and factor nodes in a factor graph. It is shown that as opposed to the previous recommender algorithms, BPRS does not require solving the recommendation problem for all users if it wishes to update the recommendations for only a single active user using the most recent data (ratings). Further, BPRS computes the recommendations for each user with linear complexity, without requiring a training period while it remains comparable to the state of art methods such as Correlation-based neighborhood model (CorNgbr) and Singular Value Decomposition (SVD) in terms of rating and precision accuracy.
This work also explores fundamental research problems related to application of iterative and probabilistic reputation management systems in various fields (such as ad-hoc networks and P2P systems). A distributed malicious node detection mechanism is proposed for delay tolerant networks (DTNs) using ITRM which enables every node to evaluate other nodes based on their past behavior, without requiring a central authority. Further, for the first time. the belief propagation algorithm is utilized in the design and evaluation of distributed trust and reputation management systems for P2P networks. Several schemes are extensively simulated and are compared to demonstrate the effectiveness of the iterative algorithms and belief propagation on these applications.
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Karis, Klas, Deborah Merzan, and Jacob Wärnhjelm. "Electron Propagation in Periodic Potentials." Thesis, KTH, Teoretisk fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103467.
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In this bachelor thesis we study the propagation of electrons in crystals. The crystalline structure is modeled as a one dimensional periodic potential primarily composed of delta function potential barriers. We use two different models to describe how a particle behaves in such a periodic structure. The first model is the Kronig Penney model described by S. Gasiorowicz in [ 1]. The second model is described by Olsen and Vignale in the article "The Quantum mechanics of electric conduction in crystals" [ 3]. We show that there exists certain ranges of energy for which electron propagation can occur, namely the allowed energy bands separeted by regions of forbidden energies. In addition, we solve the Schrödinger equation numerically for some simple cases and reproduce some of the results seen from the two mentioned models.
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Bordet, Maxime. "Contribution du bruit aux phénomènes de résonance et à la propagation de l'information dans les réseaux électroniques non linéaires." Thesis, Dijon, 2015. http://www.theses.fr/2015DIJOS051/document.
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Les possibles effets bénéfiques de perturbations déterministes ou stochastiques sur la réponse de différents systèmes non linéaires sont étudiés. À cet effet, des études numériques et expérimentales sont conjointement proposées sur deux structures distinctes : un oscillateur électronique de type FitzHugh-Nagumo et une ligne électrique constituée de 45 de ces oscillateurs couplés résistivement. La caractérisation de l’oscillateur élémentaire est d’abord réalisée en régime déterministe. En présence d’une excitation bichromatique, il est notamment montré que lorsque la composante de fréquence la plus faible est subliminale, sa détection en sortie du système peut être maximisée pour une amplitude particulière de la seconde composante, qui agit alors comme une perturbation haute fréquence. Par la suite, il est établi que ce phénomène de résonance vibrationnelle peut être amélioré pour quelques fréquences spécifiques de cette perturbation déterministe. Par ailleurs, en introduisant une composante stochastique dans l’excitation, l’attention est ensuite portée sur le phénomène de résonance stochastique fantôme. Celui-ci se distingue par le fait que la fréquence d’intérêt en sortie du système ne fait désormais plus partie du signal excitateur. La dernière partie est consacrée à l’étude de la structure couplée. Il est montré que la propagation d’une information à travers les cellules de la ligne peut être améliorée via les phénomènes de propagation vibrationnelle et de propagation assistée par le bruit. Ceux-ci se produisent sous certaines conditions, lorsque le système est respectivement sous l’influence d’une perturbation déterministe haute fréquence ou d’une source de bruitThis manuscript presents research aiming to show possible positive effects of deterministic and stochastic perturbations on the responses of different nonlinear systems. To that end, both numerical and experimental studies were carried out on two kinds of structures : an elementary electronic FitzHugh-Nagumo oscillator and an electrical line developed by resistively coupling 45 elementary cells. In the first section, the elementary cell characterization was undertaken in a deterministic regime. In the presence of a bichromatic stimulus, it is shown that when the low frequency component is subthreshold, its detection can be maximized for an optimal magnitude of the second component thanks to vibrational resonance. Next, it is established that this resonance may be enhanced for specific frequencies of the second component ; this phenomenon is referred to as frequency resonance. Furthermore, white and colored noise sources effects on vibrational resonance are reported. Then, for any other bichromatic excitation configuration, attention was focused on ghost stochastic resonance. Contrary to the other phenomena introduced in this manuscript, this one differs in the fact that the frequency of interest in the system output is here not applied on the input. Finally, the last part of the manuscript is devoted to the study of the coupled structure. It is shown that information propagation through line cells can be enhanced by vibrational propagation and noise assisted propagation phenomena. These nonlinear effects respectively occur when the system is under a high frequency deterministic perturbation or a random noise source
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Krehl, Jonas. "Incorporating Fresnel-Propagation into Electron Holographic Tomography." Master's thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-217919.
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Tomographic electron holography combines tomography, the reconstruction of three-dimensionally resolved data from multiple measurements with different specimen orientations, with electron holography, an interferometrical method for measuring the complex wave function inside a transmission electron microscope (TEM). Due to multiple scattering and free wave propagation conventional, ray projection based, tomography does perform badly when approaching atomic resolution. This is remedied by incorporating propagation effects into the projection while maintaining linearity in the object potential. Using the Rytov approach an approximation is derived, where the logarithm of the complex wave is linear in the potential. The ray projection becomes a convolution with a Fresnel propagation kernel, which is considerably more computationally expensive. A framework for such calculations has been implemented in Python. So has a multislice electron scattering algorithm, optimised for large fields of view and high numbers of atoms for simulations of scattering at nanoparticles. The Rytov approximation gives a remarkable increase in resolution and signal quality over the conventional approach in the tested system of a tungsten disulfide nanotube. The response to noise seems to be similar as in conventional tomography, so rather benign. This comes at the downside of much longer calculation time per iterationTomographische Elektronenholographie kombiniert Tomographie, die Rekonstruktion dreidimensional aufgelößter Daten aus einem Satz von mehreren Messungen bei verschiedenen Objektorientierungen, mit Elektronenholographie, eine interferrometrische Messung der komplexen Elektronenwelle im Transmissionselektronenmikroskop (TEM). Wegen Mehrfachstreuung und Propagationseffekten erzeugt konventionelle, auf einer Strahlprojektion basierende, Tomography ernste Probleme bei Hochauflösung hin zu atomarer Auflösung. Diese sollen durch ein Modell, welches Fresnel-Propagation beinhaltet, aber weiterhin linear im Potential des Objektes ist, vermindert werden. Mit dem Rytov-Ansatz wird eine Näherung abgeleitet, wobei der Logarithmus der komplexen Welle linear im Potential ist. Die Strahlen-Projektion ist dann eine Faltung mit dem Fresnel-Propagations-Faltungskernel welche rechentechnisch wesentlich aufwendiger ist. Ein Programm-Paket für solche Rechnungen wurde in Python implementiert. Weiterhin wurde ein Multislice Algorithmus für große Gesichtsfelder und Objekte mit vielen Atomen wie Nanopartikel optimiert. Die Rytov-Näherung verbessert sowohl die Auflösung als auch die Signalqualität immens gegenüber konventioneller Tomographie, zumindest in dem getesteten System eines Wolframdisulfid-Nanoröhrchens. Das Rauschverhalten scheint ähnlich der konventionallen Tomographie zu sein, also eher gutmütig. Im Gegenzug braucht die Tomographie basierend auf der Rytov-Näherung wesentlich mehr Rechenzeit pro Iteration
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Kamanzi, Janvier. "Development of a low energy cooling technology for a mobile satellite ground station." Thesis, Cape Peninsula University of Technology, 2013. http://hdl.handle.net/20.500.11838/1072.
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Thesis submitted in fulfillment of the requirements for the degree
Master of Technology:Electrical Engineering
in the Faculty ofEngineering
at the Cape Peninsula University of Technology
Supervisor:Prof MTE KAHN
Bellville
December 2013The work presented in this thesis consists of the simulation of a cooling plant for a future mobile satellite ground station in order to minimize the effects of the thermal noise and to maintain comfort temperatures onboard the same station. Thermal problems encountered in mobile satellite ground stations are a source of poor quality signals and also of the premature destruction of the front end microwave amplifiers. In addition, they cause extreme discomfort to the mission operators aboard the mobile station especially in hot seasons. The main concerns of effective satellite system are the quality of the received signal and the lifespan of the front end low noise amplifier (LNA). Although the quality of the signal is affected by different sources of noise observed at various stages of a telecommunication system, thermal noise resulting from thermal agitation of electrons generated within the LNA is the predominant type. This thermal noise is the one that affects the sensitivity of the LNA and can lead to its destruction. Research indicated that this thermal noise can be minimized by using a suitable cooling system. A moveable truck was proposed as the equipment vehicle for a mobile ground station. In the process of the cooling system development, a detailed quantitative study on the effects of thermal noise on the LNA was conducted. To cool the LNA and the truck, a 2 kW solar electric vapor compression system was found the best for its compliance to the IEA standards: clean, human and environment friendly. The principal difficulty in the development of the cooling system was to design a photovoltaic topology that would ensure the solar panels were always exposed to the sun, regardless the situation of the truck. Simulation result suggested that a 3.3 kW three sided pyramid photovoltaic topology would be the most effective to supply the power to the cooling system. A battery system rated 48 V, 41.6 Ah was suggested to be charged by the PV system and then supply the power to the vapor compression system. The project was a success as the objective of this project has been met and the research questions were answered.
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Subramanian, Arunkumar. "Coding techniques for information-theoretic strong secrecy on wiretap channels." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42776.
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Traditional solutions to information security in communication systems act in the application layer and are oblivious to the effects in the physical layer. Physical-layer security methods, of which information-theoretic security is a special case, try to extract security from the random effects in the physical layer. In information-theoretic security, there are two asymptotic notions of secrecy---weak and strong secrecy
This dissertation investigates the problem of information-theoretic strong secrecy on the binary erasure wiretap channel (BEWC) with a specific focus on designing practical codes. The codes designed in this work are based on analysis and techniques from error-correcting codes. In particular, the dual codes of certain low-density parity-check (LDPC) codes are shown to achieve strong secrecy in a coset coding scheme.
First, we analyze the asymptotic block-error rate of short-cycle-free LDPC codes when they are transmitted over a binary erasure channel (BEC) and decoded using the belief propagation (BP) decoder. Under certain conditions, we show that the asymptotic block-error rate falls according to an inverse square law in block length, which is shown to be a sufficient condition for the dual codes to achieve strong secrecy.
Next, we construct large-girth LDPC codes using algorithms from graph theory and show that the asymptotic bit-error rate of these codes follow a sub-exponential decay as the block length increases, which is a sufficient condition for strong secrecy. The secrecy rates achieved by the duals of large-girth LDPC codes are shown to be an improvement over that of the duals of short-cycle-free LDPC codes.
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Bui, Man Duc. "Propagation of transients in dispersive dielectric media." Thesis, University of Ottawa (Canada), 1990. http://hdl.handle.net/10393/5733.
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Propagation of transient electromagnetic fields in dispersive dielectric media is studied. The dielectric medium is assumed to be linear, isotropic, and homogeneous and is described by the Debye model. Incident fields are assumed to be TEM plane wave pulses. The dielectric can assume the form of infinite half space or infinite circular cylinder; either of which may be homogeneous or stratified. The electric fields induced in the dielectric are calculated from Time Domain Maxwell's equations using Finite Difference Time Domain method. The results of this investigation can be used for geophysical probing, subsurface communication and for investigating possible biological effects of pulsed electromagnetic fields.
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Arkeholt, Simon. "Induction in Printed Circuit Boards using Magnetic Near-Field Transmissions." Thesis, Linköpings universitet, Teoretisk Fysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-148788.
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In 1865 Maxwell outlined the theoretical framework for electromagnetic field propagation. Since then many important developments have been made in the field, with an emphasis on systems using high frequencies for long-range interactions. It was not until recent years that applications based on short-range inductive coupling demonstrated the advantages of using low frequency transmissions with magnetic fields to transfer power and information. This thesis investigates magnetic transmissions in the near-field and the possibility of producing induced voltages in printed circuit boards. A near-field magnetic induction system is designed to generate a magnetic flux in the very low frequency region, and used experimentally to evaluate circuit board induction in several interesting environments. The resulting voltages are measured with digital signal processing techniques, using Welch’s method to estimate the spectrum of the received voltage signal. The results show that the amount of induced voltage is proportional to the inverse cube of the transmission distance, and that the system is able to achieve a maximum induced voltage of 65 \micro V at a distance of 2.5 m and under line-of-sight conditions. It is also concluded that conductive obstructions, electromagnetic shielding and background noise all have a large impact on the obtained voltage, either cancelling the signal or causing it to fluctuate.
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Dai, Ji-Dong. "Acoustic and optical wave propagation in anisotropic fiber waveguides." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39525.
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In this thesis analyses of the optical wave propagation characteristics in uniaxial and weakly biaxial fibers are presented. Analytical closed form solutions are obtained for optical wave propagation in uniaxial fibers with field and modal power distributions investigated in detail for the first time. Optical dispersion characteristics in weakly biaxial fibers are studied by a perturbation method with the exact solution for the uniaxial fibers as the perturbation base. The analysis of optical second harmonic generation in LiNbO$ sb3$ fibers of practical interest is also carried out by a scalar coupled mode theory where the quasi-phase match grating design for cladded fiber geometry is obtained.Pioneer work of fundamental value on the investigation of acoustic wave propagation properties in hexagonal, trigonal and cubic fibers has also been carried out. Exact analytical solutions are achieved for acoustic wave propagation in hexagonal fibers and simplified closed form formulas are deduced for the weakly guiding case. Acoustic wave propagation in a three-layer structure consisting of a hexagonal-core, a thin isotropic interface layer and an isotropic cladding is analyzed by a perturbation method based on the exact solutions for hexagonal and isotropic acoustic fibers. Based on the exact results for acoustic wave propagation in hexagonal and isotropic fibers respectively, coupled mode equations are applied to acoustic wave propagation analyses in trigonal and cubic fibers.
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Hosseini-Doust, Zahra. "Mapping Gaussian belief propagation on the graphics processing unit." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=121472.
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With the introduction of programmable graphical processing units (GPU) in the last decade, Heterogeneous computing systems have become more popular. It has been predicted that by leveraging the power of the GPU's many cores, many applications can experience improved performance in the near future. However porting applications to the GPU in most cases cannot be automated due to the GPU's unique architecture. Mapping problems on the GPU has been researched in many diverse fields. Many problems in science and engineering come down to solving sparse systems of linear equations. Nevertheless conventional iterative solvers are not feasible tools for large sparse systems. One of the novel iterative solvers proposed in recent literature is the Gaussian belief propagation (GaBP) method. This method uses recursive message updates on a graphical model. In this work a variant of GaBP algorithm was implemented on the GPU. The implementation was successfully tested with FEM (finite element method) data. The parallel implementations achieved up to 4× improvement in execution time, compared to the serial CPU implementation.Avec l'introduction d'unités de traitement graphiques programmables (GPU) durant la dernière décennie, les systèmes informatiques hétérogènes sont devenus plus populaires. On pense qu'en exploitant la puissance des nombreux cœurs du GPU, de nombreuses applications pourront bénéficier de meilleures performances dans un avenir rapproché. Cependant, dans la plupart des cas le fait de porter des applications vers le GPU ne peut pas être automatisé à cause de l'architecture unique du GPU. Les problèmes de mappage sur le GPU ont été l'objet de recherches dans de nombreux domaines. Beaucoup de problèmes en science et en ingénierie consistent simplement à résoudre systèmes d'équations linéaires creux. Étant donné que les systèmes creux qui croissent à l'aide de solveurs itératifs classiques ne seront pas réalisables, un des nouveaux solveurs itératifs proposés dans la littérature récente est la méthode de croyance des propagations gaussiennes (GABP). Cette méthode utilise des messages de mise à jour récursifs sur un modèle graphique. Dans ce travail, une variante de l'algorithme GABP fut mise en place sur le GPU. La mise en œuvre a été testée avec succès avec des données FEM (méthode des éléments finis). Les implémentations parallèles ont atteint une amélioration du temps d'exécution jusqu'à 4 × par rapport à l'implémentation de série du CPU.
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Spring, Christopher Todd 1965. "Acoustic wave propagation in a cylindrical borehole with fractures." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277313.
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We study the problem of acoustic wave propagation in a cylindrical borehole possessing a finite number of transverse discontinuities. We model the field behavior through Green's function techniques. We formulate an integral equation whose solution will enable us to solve for the acoustic field everywhere within our structure. We investigate asymptotic forms to speed the numerical convergence of our solution. To solve the integral equation we employ both the method of moments and the low frequency approximation. We study the reflection coefficient in the time and frequency domains. Finally after presenting solutions for the one and two fracture case, we generalize our analysis for many fractures.
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Pereira, da Cunha Maurício. "Saw propagation and device modelling on arbitrarily oriented substrates." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28511.
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A detailed theoretical analysis is presented for calculating the surface acoustic wave (SAW) reflection coefficient of thin metallic layers. Based on this analysis, directions of propagation are classified as symmetric or asymmetric. An augmented scalar transmission line circuit model which contains a new lumped network element that accounts for asymmetry is introduced to describe SAW reflection and transmission through a strip. The resulting network model is used to analyze grating and transducer structures. Computed results based on this new network model are in excellent agreement with measured data, not only on devices oriented along symmetric directions, but also on devices which exhibit directivity due to asymmetric orientations. A simple procedure, based on physical arguments, is outlined for the identification of high directivity orientations. An algebraic construction is given which demonstrates that the coupling-of-modes (COM) modelling of gratings and transducers is derivable from the new network model. Approximate explicit analytical expressions, in terms of the network model, are given for the COM model parameters. The properties of pseudo-surface-waves are re-examined and a new high-velocity pseudo-surface acoustic wave (HVPSAW) is described. It is shown that this mode, not referenced in the SAW device literature, has a low attenuation along certain directions, and is thus very attractive for high-frequency low-loss SAW devices.
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Grecco, Ryan Francis. "Microwave Bessel-Beam Propagation through Spatially Inhomogeneous Media." ScholarWorks @ UVM, 2017. http://scholarworks.uvm.edu/graddis/726.
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Long range wireless power transmission (WPT) is a critical technology for the development of remote power systems for air and space vehicles as well as for point-to-point transmission on Earth. This can be achieved using either a laser for transmission in the infrared to optical frequency domain or by using microwaves. The objective of this research is to study the application of microwave power transmission (MPT) through the use of a so-called Bessel-beam whose unique propagation properties include a self-healing ability as well as non-diffractive properties. These two unique properties lead to an increase in the efficiency of microwave power transmission. In this research the propagation of a microwave Bessel-beam through a spatially inhomogeneous medium will be simulated in MATLAB using a plane wave spectrum representation of the electromagnetic beam field. The spatially inhomogeneous medium of interest here is the Earth's atmosphere whose electromagnetic properties (dielectric permittivity and electric conductivity) vary with altitude up through the ionosphere. The purpose of this research is to determine how efficiently a microwave Bessel beam can propagate in point-to-point transmission through the Earth's atmosphere as well as between satellites in Earth orbit.
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Hsu, Yaw-Dong 1959. "Locating logic design errors via test generation and don't-care propagation." Thesis, The University of Arizona, 1991. http://hdl.handle.net/10150/277847.
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This thesis presents a new technique, the don't-care propagation method, for logic design verification and functional error location in which a gate-level implementation of a circuit is compared with a functional-level specification. In this method, test pattern set which is generated to detect single stuck-line faults in the gate-level implementation, are used to compare the gate-level implementation with the functional-level specification. In the presence of logic design errors, such a test set will produce responses in the implementation that disagree with the responses in the specification. In the verification phase of the design of logic circuits using the top-down approach, it is necessary not only to detect but also to locate the source of any inconsistency that may exit between the functional-level specification and the gate-level implementation. The proposed technique determines the region which contains the function error. This method has very high resolution that the region usually contains a single gate or a line and therefore, reduces the time required for debugging by the designers.
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Seabra, Gustavo De Miranda. "Electron propagator theory calculations of photoionization intensities /." Search for this dissertation online, 2005. http://wwwlib.umi.com/cr/ksu/main.
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Peacock, Anna Claire. "Applications of light propagation in novel photonic devices." Thesis, University of Southampton, 2004. https://eprints.soton.ac.uk/42429/.
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In this thesis, the propagation of light in novel photonic devices has been studied theoretically, numerically and experimentally. In particular, self-similar solutions to the nonlinear Schrödinger equation have been investigated as a means of avoiding distortions associated with high power pulse propagation in optical fibres. The results show that it is the interplay between the nonlinear and dispersive effects that leads to stable formation of the self-similar solutions. By considering generalised nonlinear Schrödinger equations we have extended the previous investigations of linearly chirped parabolic pulse solutions, which exist in the normal dispersion regime, and have found a new broader class of self-similar solutions, which exist when the fibre parameters are allowed to vary longitudinally. Numerical simulations of these systems confirm the analytic predictions. Experimental confirmation of parabolic pulse generation in high gain cascaded amplifier systems and in highly nonlinear microstructured fibres is also reported. In addition, the propagation of light in modulated crystal structures has been investigated. By modifying the linear and nonlinear properties of the crystals it has been shown that it is possible to manipulate the speed and the wavelength of the propagating light. In particular, negative refractive index materials have been shown to support fast and/or slow propagating light, whilst two dimensional nonlinear photonic crystals have been used to demonstrate multiple harmonic generation over a wide range of phase matching angles. The influence of waveguiding geometries has also been considered to determine the optimum design for the efficiency of the devices
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Manara, Luca. "Investigating Antenna Placement on Autonomous Mining Vehicle." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204908.
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Future mines will benefit from connected intelligent transport system technologies. Autonomous mining vehicles will improve safety and productivity while decreasing the fuel consumption. Hence, it is necessary for Scania to increase the know-how regarding the design of vehicular communication systems for the harsh mine environment. The scope of this work is to examine the requirements for the antenna placement of a future autonomous mining truck and propose suitable antenna types and positions. By using the electromagnetic simulator suite CST Microwave Studio, the research estimates the impact of a simplified autonomous mining vehicle geometry on basic antenna radiation patterns. Some simulated antenna configurations are assessed with radiation pattern measurements. In order to radiate enough power towards the area surrounding the vehicle and guarantee reliable communications, the truck requires omnidirectional antennas in centered locations, or alternatively one patch antenna for each side. The method used to solve the problem is also assessed: flexibility provided by the simulation method is emphasized, whereas some relevant limitations are discussed. Hardware requirements, availability of the models and limited results provided by the software can make the simulation phase not suitable to evaluate the antenna placement.Framtidens gruvor kommer att gynnas av sammankopplade, intelligenta transportsystem. Autonoma gruvfordon kommer att förbättra säkerhet och produktivitet, och samtidigt minska bränslekonsumtion. Därför är det nödvändigt för Scania att öka kunskapen om design av kommunikationssystem för fordon i hård gruvmiljö. Målet för detta projekt är att undersöka kraven för antennplacering hos ett framtida autonomt gruvfordon och att ge förslag på passande antenntyper och -positioner. Det elektromagnetiska simuleringsverktyget CST Microwave Studio används för att uppskatta påverkan från en förenklad fordonsgeometri på grundläggande antennstrålningsmönster. Utvalda antennkonfigurationer utvärderas genom undersökningar av dess strålningsmönster. För att kunna stråla ut tillräcklig effekt i området kring fordonet och garantera tillförlitlig kommunikation krävs centralt placerade runtstrålande antenner, eller alternativt en patchantenn till varje sida. Problemlösningsmetoden utvärderas också: Flexibiliteten simuleringsmetoden ger betonas, medan några relevanta begränsningar diskuteras. Hårdvarukrav, tillgängligheten av modeller och begränsade resultat från mjukvaran kan bidra till att göra simuleringen olämplig för att utvärdera antennplaceringen.
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Ramos, Luis. "Atmospheric propagation simulations and Boeing's high average power free electron laser." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305947.
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Pelgur, Ali. "Modelling Of X-band Electromagnetic Wave Propagation." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/12608830/index.pdf.
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Calculation of electromagnetic wave propagation over irregular terrain is an important problem in many applications such as coverage calculations for radars or communication links. Many different approaches to this problem may be found in the literature. One of the most commonly used methods to solve electromagnetic boundary value problems is the Method of Moments (MoM). However, especially at high frequencies, the very large number of unknows required in the MoM formulation, limits the applicability of this method, since the memory requirement and the operation count increases by O(N2) and O(N3), respectively, where N is the number of the unknowns.
Several approaches have been proposed in the literature to reduce the memory requirement and the operation count of the MoM. These approaches rely on the special structure of the impedance matrix generated by the MoM. The Conjugate Gradient (CG) method is a non stationary iterative technique that can be used to solve general asymmetric/non-Hermitian systems with an operational cost of O(N2) per iteration. Furthermore, the computational time can be improved by the Fast Fourier Transform (FFT) algorithm to perform the matrix vector multiplication that appear in any iterative technique. This approach has been successfully used in the literature to solve scattering from electrically large objects and it has been shown that the computational cost and memory requirement can be reduced to O(KNlogN) with K being the number of iterations.
In this thesis, CG method accelerated with Fast Fourier Transform (CG FFT) method is applied to the problem of electromagnetic propagation over irregular terrain. Applications for electrically large rough terrain profiles are presented. The accuracy of the method is compared to the direct solution of the MoM, CG method and Free Space model with recoveries by Hata model or multiple knife-edge diffraction and reflection. The solution works on quasi-planar surfaces and profiles with small deviation like little breezy sea surface properly.
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Lee, Chang-Hwa 1957. "Analysis of approaches to synchronous faults simulation by surrogate propagation." Thesis, The University of Arizona, 1988. http://hdl.handle.net/10150/276771.
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This thesis describes a new simulation technique, Synchronous Faults Simulation by Surrogate with Exception, first proposed by Dr. F. J. Hill and has been initiated under the direction of Xiolin Wang. This paper reports early results of that project. The Sequential Circuit Test Sequence System, SCIRTSS, is an automatic test generation system which is developed in University of Arizona which will be used as a target to compare against the results of the new simulator. The major objective of this research is to analyze the results obtained by using the new simulator SFSSE against the results obtained by using the parallel simulator SCIRTSS. The results are listed in this paper to verify superiority of the new simulation technique.
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Wu, Xianyue. "Antennas and propagation for body area networks at 60 GHZ." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/4786/.
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The advent of wireless body area networks (WBANs) and their use in a wide range of applications from consumer electronics to military purposes, dictates the need to investigate to the behaviour of antennas and wave propagation on the body in depth. Although this area has been extensively studied in the past decade, some issues are still not satisfactorily solved for communication systems for WBANs at ISM bands and UWB such as compact and high efficiency antenna design, privacy and security, interference mitigation and achieving high data rates. This thesis proposed an alternative wireless solution for body area networks by adopting 60 GHz radio. On-body channels at 60 GHz have been characterised using monopole and horn antennas. Horn antennas achieve significantly improved path gain in the stable channels but are susceptible to shadowing in the mobile channels due to body movements. However, interference mitigation and covertness for 60 GHz WBANs at the physical layer are improved due to high attenuation of 60 GHz signals. Significant increase of carrier-to-interference ratio is observed for 60 GHz WBANs compared to 2.45 GHz. A model of estimating the maximum detection distance at a threshold probability for detecting a WBAN wearing soldier in a battlefield is proposed. Fixed-beam directional antennas and reconfigurable antennas are designed for 60 GHz WBANs and channel measurements using these antennas are conducted. Results show beam-reconfigurability of the antenna improves the link performance compared to fixed-beam antennas at 60 GHz.
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Huynh, Kevin Nhut. "Performance evaluation of FASTRAC ABR control algorithm with VSVD under long propagation delay." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/9010.
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There have been many control algorithms proposed in the literature for handling the flow control of the Available Bit Rate (ABR) class of service on ATM. But few have demonstrated sound theoretical development, compliance to TM4.0, and a practical design. This thesis attempts to formalize and present ABR flow control from fundamentals to illustrate the requirements for designing a better algorithm. It explains TM4.0 ABR control rules and highlights subtleties in the standards that are commonly missed in the literature; these factors result in non-compliance and render the proposed algorithms impractical. This thesis also attempts to present various practical switch designs and their capabilities for ABR support. It applies traditional control theory to ABR flow control. It demonstrates that understanding the combination of all these three aspects is key to designing ABR control algorithms that are theoretically sound and practical. A rate thresholding explicit rate (ER) based control algorithm, FASTRAC (FAST RAte Computation), is the focus of the simulation analysis. (Abstract shortened by UMI.)
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Rawat, Vineet. "High-order solution of radio propagation problems using the multi-level fast multipole algorithm." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81562.
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Wireless network planning requires accurate, site-specific urban and indoor radio propagation models. Traditionally, such models have been developed using approximate asymptotic methods. This thesis examines rigorous solution methods for radio propagation in electrically large environments.The high-order locally corrected Nystrom (LCN) method is applied to the combined field integral equation (CFIE) for scattering from perfect electrical conductors (PEC) in two dimensions. The direct solution of the resulting linear system of equations requires O(N2) time per iteration of an iterative solver. Application of the multi-level fast multipole algorithm (MLFMA) reduces iteration time to O(Nlog N). The MLFMA employs an approximation however, and the error introduced must be controlled via the selection of appropriate parameters.
An implementation of the LCN method and MLFMA is tested using various electrically large scattering bodies. The solution of a simple urban radio propagation problem is then examined and the feasibility of its rigorous solution is demonstrated.
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Boisvert, Mario. "Minimizing state error propagation in low-bit rate speech codec for voice over IP." Thesis, University of Ottawa (Canada), 2003. http://hdl.handle.net/10393/26360.
Full textAbstract:
Today's Internet and intranets are packet-switched networks where the Internet Protocol (IP) is the most widespread of all network protocols in use. Such network protocol poses serious constraints on the real-time transmission of packets such as in the case of voice applications, namely Voice over IP (VoIP) applications. The "best effort" delivery mechanism and the lack of guarantee of Quality of Service (QoS) of packet networks are known to cause packet arrival problems that result in packet losses. Obviously, the loss of packets impairs the quality of the speech at the receiving end.
In this thesis, we focus on two main areas in the implementation of VoIP systems. Initially, we review speech compression techniques to better understand the operation and characteristics of speech codecs. This allows us to select a promising speech codec, namely, the ITU-T G.729A speech codec that will be used during our demonstrations and investigations. Secondly, we review the operation of packet-switched networks, more specifically IP networks, for the purpose of understanding the degradation effects they cause to VoIP systems. With this knowledge, we formalize a set of constraints and requirements that allows us to properly analyze the effect of packet losses over IP networks.
Finally, we propose a closed-loop over the network method to assist the codec in improving its speech quality performance in periods of packet losses. The method, named State Error Correction (SEC), is described in detail and its performance is assessed through simulations.
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Schulte, Joseph Thomas 1957. "A system to measure the phase shift and attenuation of underground HF electromagnetic propagation." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/277177.
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This thesis discusses the theory and limitations of a system that has been designed and constructed for the purpose of measuring the phase shift and attenuation of high-frequency (15 MHZ) electromagnetic waves propagating between two insulated antennas that have been lowered down air-filled boreholes (cased with PVC pipe) at San Xavier Mine, Pima County, Arizona. Both the transmitting and receiving antennas are center-fed, sleeve dipoles that have been tuned to approximately their resonant lengths. The insulated-sleeve dipole antenna is modelled as the inner conductor of a radiating, coaxial transmission-line, which allows simple transmission-line formulas to be used in approximating the antenna impedance and current distribution along the antenna. Experimental results at the San Xavier Mine indicate the analogy is valid. Consequently, the most easily interpreted and repeatable measurements have been made with the antennas centered in the borehole.