Nas últimas décadas o uso de equipamentos para posicionamento, principalmente os receptores de navegação pessoal, ganhou relativa importância, e a aquisição desses receptores aumentou consideravelmente. Estes receptores, entretanto, não foram desenvolvidos para trabalhos que exijam acurácia, pois estimam e armazenam as posições com precisão e acurácia da ordem de 03-15 m, com 95% de probabilidade, não armazenam os dados de código e fase e não possuem antenas com centro de fase determinado. Com a disponibilização do protocolo de transmissão dos dados destes receptores, foram desenvolvidos alguns programas para, estando conectados ao receptor por meio de hardware e software, extrair e registrar as observações de navegação (código CA e fase da portadora). Desta forma, o uso de receptores de navegação pessoal para medições de coordenadas com boa acurácia, em linhas base curtas, pode tornar-se uma grande alternativa para área de mensuração com aplicações na Engenharia de Transportes. O alto custo de outras técnicas frente à proposta deste trabalho à uma das grandes dificuldades encontradas para uma maior acurácia nos trabalhos geodésicos aplicados aos transportes. Neste trabalho procurou-se analisar o processamento de dados da fase portadora L1 e código CA, coletados com receptores de navegação pessoal,obtidos por meio de softwares auxiliares, levando-se em consideração a algumas variáveis como a distância entre as estações, o tempo de rastreio, softwares de processamento e diferentes equipamentos. Os resultados obtidos promissores confirmando as vantagens de armazenamento das observáveis dos receptores de navegação pessoal para o seu posterior pré-processamento para a obtenção de coordenadas acuradas em linhas bases curtas. / In recent decades the use of equipment for positioning, particularly the personal navigation receivers gained relative importance, and the acquisition of these receivers has increased considerably. These eceivers, however, were not developed for task that requiring accuracy, because it estimate and store positions with precision and accuracy of the order of 03 to 15 meters, with 95% probability, do not store the code and carrier phase data and have no determined Xntennae center stage. With the provision of the protocol for data transmission of these receivers have been developed some programs and is connected to the receiver by way of hardware and software, extract and record the navigation observable (CA code and carrier phase). Thus, the use of the navigation eceivers staff to measurements of coordinates with good accuracy, based on short baselines, can become a great alternative to main measurement in Transport Engineering applications. The high cost of other technologies front to the proposal in this work is one of the difficulties found for a greater accuracy in the applied transports geodesic works. In this research it is looked to analyze the data processing of the L1 carrying phase and CA code collected with the aid of specific software, taking itself consideration changeable as in the baseline between the stations, the observation time, software and different equipments. The results was promising, confirming the benefits of storage observable from the personal navigation receivers for further post-processing to obtain accurate coordinates in short baselines.

The use of e-mail communication between consumers has been growing and companies are seeking to increase their understanding of this type of private communication medium between consumers. The privacy and cost-effectiveness characteristics of e-mail make it an important communication medium for consumers. Consumers use e-mail to exchange a variety of information including electronic word of mouth (eWOM) about products, services and organisations. The travel industry, the context of this study, is increasingly being delivered online. Understanding what influences consumers and how consumers evaluate eWOM will increase the travel industry’s knowledge about its consumer base. This study aims to contribute to existing knowledge on the impact of eWOM on consumer purchase intention. Its focus is on an interpersonal context where eWOM is sent from the source to the receiver in an e-mail about holiday destination. The study, which was undertaken from a positivist perspective, used qualitative and quantitative research techniques to better understand the influence of eWOM on purchase intention. The literature on word of mouth (WOM) and eWOM was initially examined to identify the major factors that have an influence on the receiver of eWOM. Consistent with previous studies, both perceived expertise and similarity were identified as source characteristics that have an influence on the receiver’s purchase intention. The literature also indicated that trustworthiness belief would have a key effect on the influence of eWOM on the attitude of the receiver. Consequently, this study examined each trustworthiness dimension – ability, benevolence, and integrity – with respect to its role in the influence of eWOM on purchase intention. The literature review also revealed that certain receiver characteristics were important in the process of influence, especially consumer susceptibility to interpersonal influence. The relationships between the variables identified were further developed into the research model, which has its roots in the theory of reasoned-action (Fishbein and Ajzen, 1975) and the dual process theory of influence (Deutsch and Gerard, 1955). Methodologically, a scenario-building approach to developing authentic e-mail was used. The qualitative data gathered from eight focus group discussions were analysed using “framework analysis” (Ritchie and Spencer, 1994) to develop eight scenarios. This was then used to manipulate the moderating variables in the scenario. Three manipulations, each with two levels, were included: eWOM direction “positive and negative”; source characteristic of “expert/non-expert”; and source characteristic of “similar/non-similar”. These scenarios formed part of a questionnaire. The questionnaire was used to collect data from a sample of University of Bradford students. The final number of usable questionnaires was 477. Structural equation modelling was used to determine the validity of the conceptual model and test the hypotheses. In particular, multiple group analysis was used to assess both the measurement and structural models, and to identify the impact of the eWOM direction. The theoretical model that describes the relationships between the exogenous variables (source’s and receiver’s characteristics) and the endogenous variables (trustworthiness dimensions, interpersonal influence and purchase intention) was accepted. The research findings provided empirical evidence on the difference in the impact of positive and negative eWOM on purchase intention. The source’s and receiver’s characteristics and related trustworthiness beliefs, (i.e. ability, benevolence, and integrity) are influenced by the direction of eWOM. The findings show that positive and negative eWOM differ with respect to how they impact on consumers’ attitudes and intentions. For instance, consumers have more belief in the credibility of a source who provides negative eWOM. However, the overall influence of the source’s characteristics tends to be stronger with positive than with negative eWOM. The findings of this study provide insights for both academics and practitioners to understand the potential of eWOM. This might be tailored to help develop more private relationships with customers through e-mail marketing strategies that incorporate eWOM. Negative eWOM is more credible but less directly useful to marketers. Nevertheless, it is important for marketers to realise the significance of managing dissatisfaction and to harness the power of negative eWOM. Similarly, positive eWOM is effective especially when the source is both expert and similar. This might be translated into online marketing campaigns that use consumer-to-consumer discussions in addition to viral marketing. Future research might test the model in different contexts, (e.g. financial services), to provide a more comprehensive picture of the influence of eWOM on purchase intention.

Les observations astronomiques nous permettent d’étudier l’univers et de comprendre les phénomènes qui le gouvernent. La matière visible dans l’univers émet des ondes à des fréquences très diverses, réparties sur tout le spectre électromagnétique (domaines radio, submillimétrique, infrarouge, visible, ultraviolet, X et gamma). Ces ondes nous renseignent sur certaines caractéristiques physico-chimiques des éléments observés (nature, température, mouvement, etc.). Des télescopes couvrant différentes plages de fréquences sont nécessaires pour observer l’ensemble du spectre électromagnétique. Les radio-télescopes, sensibles aux ondes (sub)millimétriques, sont principalement dédiés à l’observation de la matière froide présente dans le milieu interstellaire. Le milieu interstellaire est le berceau des étoiles et son étude est essentielle pour comprendre les différentes étapes de la vie des étoiles. La fréquence maximale d’observation des radio-télescopes est en augmentation depuis la fabrication des premiers radio-télescopes dans les années 1930. Récemment, des radio-télescopes capables de détecter des signaux dans l’infrarouge lointain, au delà de 1 THz, ont été développés. Ces avancées technologiques ont été motivées, entre autres, par la présence, dans le milieu interstellaire, de molécules et d’ions uniquement observables à des fréquences supérieures à 1 THz. Pour observer des raies avec une haute résolution spectrale, les radio-télescopes sont équipés de récepteurs hétérodynes. Ce type de récepteur permet d’abaisser la fréquence de la raie spectrale observée tout en conservant ses caractéristiques (une raie observée à 1 THz peut, par exemple, être décalée à une fréquence de 1 GHz). Cette technique permet d’observer des raies avec une très haute résolution spectrale et c’est pourquoi les récepteurs hétérodynes sont largement utilisés pour les observations de raies spectrales aux fréquences GHz et THz. Dans les récepteurs hétérodynes, un oscillateur local (OL) émet un signal monochromatique à une fréquence très proche de celle du signal observé. Les deux signaux sont superposés à l’aide d’un diplexeur et transmis à un mélangeur. Ce dernier réalise le battement des deux signaux et génère un signal identique au signal observé mais à une fréquence plus faible. Durant ma thèse, j’ai travaillé sur la construction, la caractérisation et l’amélioration d’un récepteur hétérodyne à 2.6 THz. Cette fréquence d’observation (2.6 THz) est l’une des plus hautes atteintes par les récepteurs hétérodynes THz existant actuellement, ce qui constitue un défi technologique très important. Dans le but de caractériser et d’améliorer ce récepteur, je me suis concentré sur trois aspects essentiels ..... / (Sub)Millimeter-telescopes are often used to observe the interstellar medium in the universe and they enable us to study the stellar life cycle. To detect and study some important molecules and ions, we need receivers able to observe at frequencies above 1 THz. Receivers working at such high frequencies are quite new and the 2.6 THz heterodyne receiver I built and characterized during my PhD represents the state-of-the-art of THz heterodyne receivers. I especially focused on three important aspects of this receiver: its stability, the superimposition of the local oscillator signal (LO) and the observed signal by a diplexer, and the splitting of the LO signal by a phase grating. The stability was calculated with the Allan variance and I found that the two elements limiting the stability of our receiver were the 1.4 THz local oscillator and the mixer bias supply. The Martin-Puplett interferometer (MPI) diplexer I designed, built and tested is able to transmit 76 % of the LO power at 2.6 THz and we estimate a transmittance around 79 % for the observed signal. This MPI is operational and ready for the next generation of heterodyne receivers. Splitting the LO signal is essential to build heterodyne receivers with several pixels, which allows us to get spectra of the universe at many positions in the sky simultaneously. I have developed a new kind of grating, called Global gratings, and I made two prototypes of these Global phase gratings able to split the LO beam into four beams. These two phase grating prototypes, a transmissive and a reflective one, were optimized for 610 GHz and showed, respectively, an efficiency of 62 ± 2 % and 76 ± 2 %. These excellent results validate the design and fabrication processes of this new kind of grating. In conclusion, the work accomplished during this PhD constitutes an important step toward the realization of a very stable and highly sensitive 2.6 THz multi-pixel heterodyne receiver using a MPI diplexer.

Abstract The aim of this thesis was to develop time-to-digital converters (TDC) for the integrated receiver of a pulsed time-of-flight (TOF) laser rangefinder aiming at cm-level accuracy over an input range of 10 m – 15 m. A simple structure, a high integration level and low power consumption are the desired features for such a TDC. From the pulsed TOF laser rangefinder point of view an integrated receiver consisting of both the TDC and the receiver channel on the same die offers the possibility of manufacturing these laser rangefinders with a high integration level and at a low price to fulfil the needs of mass industrial markets. The heart of the TDC is a CMOS ring oscillator, the clock frequency of which is used to calculate the full clock cycles between timing signals, the positions of the timing signals inside the clock period being determined by storing the state of the phase of the ring oscillator for each timing signal. This will improve the resolution of the TDC. Also, additional delay lines are used to generate multiple timing signals, each having a time difference of a fraction of that of the ring oscillator. This will further improve the resolution of the whole TDC. To achieve stable results regardless of temperature and supply voltage variations, the TDC is locked to an on-chip reference voltage, or the resolution of the TDC is calibrated before the actual time interval measurement. The systematic walk error in the receiver channel caused by amplitude variation in the received pulse is compensated for by the TDC measuring the slew rate of the received pulse. This time domain compensation method is not affected by the low supply voltage range of modern CMOS technologies. Three TDC prototypes were tested. A single-shot precision standard deviation of 16 ps (2.4 mm) and a power consumption of 5.3 mW/channel were achieved at best over an input range of 100 ns (15 m). The temperature drifts of an on-chip voltage reference-locked TDC and a TDC based on the calibration method were 90 ppm/°C and 0.27 ps/°C, respectively. The results also showed that a pulsed TOF laser rangefinder with cm-level accuracy over a 0 – 15 m input range can be realized using the integrated receiver with the time domain walk error compensation described here. / Tiivistelmä Väitöskirjatyön tavoitteena oli kehittää aika-digitaalimuunninrakenteita valopulssin kulkuajan mittaukseen perustuvan lasertutkan integroituun vastaanottimeen. Tavoitteena oli saavuttaa senttimetriluokan tarkkuus 10 m – 15 m mittausalueella koko lasertutkan osalta. Aika-digitaalimuuntimelta vaaditaan yksinkertaista rakennetta, korkeaa integroimisastetta ja matalaa tehonkulutusta. Integroitu vastaanotin sisältää sekä aika-digitaalimuuntimen että vastaanotinkanavan ja tarjoaa mahdollisuuden korkeasti integroidun lasertutkan valmistukseen halvalla teollisuuden massamarkkinoiden tarpeisiin. Aika-digitaalimuuntimen ytimenä toimii monivaiheinen CMOS-rengasoskillaattori. Aika-digitaalimuunnos perustuu rengasoskillaattorin täysien kellojaksojen laskentaan laskurilla ajoitussignaalien välillä. Lisäksi rengasoskillaatorin jokaisesta vaiheesta otetaan näyte ajoitussignaaleilla niiden paikkojen määrittämiseksi kellojakson sisällä, jolloin aika-digitaalimuuntimen erottelutarkkuutta saadaan parannettua. Erottelutarkkuutta parannetaan lisää viivästämällä ajoitussignaaleja viive-elementeillä ja muodostamalla näin useita erillisiä ajoitussignaaleja, joiden väliset viive-erot ovat murto-osa rengasoskillaattorin viive-elementin viiveestä. Aika-digitaalimuunnin stabiloidaan käyttöjännite- ja lämpötilavaihteluja vastaan lukitsemalla se integroidun piirin sisäiseen jännitereferenssiin, tai sen erottelutarkkuus määritetään ennen varsinaista aikavälinmittausta erillisellä kalibrointimittauksella. Vastaanotetun valopulssin amplitudivaihtelun aiheuttama systemaattinen ajoitusvirhe integroidussa vastaanotinkanavassa kompensoidaan mittaamalla vastaanotetun valopulssin nousunopeus aika-digitaalimuuntimella. Tällainen aikatasoon perustuva kompensointimetodi on myös suorituskykyinen nykyisissä matalakäyttöjännitteisissä CMOS-teknologioissa. Työssä valmistettiin ja testattiin kolme aika-digitaalimuunninprototyyppiä. Muuntimien kertamittaustarkkuuden keskihajonta oli parhaimmillaan 16 ps (2,4 mm) ja tehonkulutus alle 5,3 mW/kanava mittausetäisyyden olessa alle 100 ns (15 m). Sisäiseen jännitereferenssiin lukitun aika-digitaalimuuntimen lämpötilariippuvuudeksi mitattiin 90 ppm/°C ja kalibrointimenetelmällä saavutettiin 0,27 ps/°C lämpötilariipuvuus. Työssä saavutetut tulokset osoittavat lisäksi, että valopulssin kulkuajan mittaukseen perustuvalla lasertutkalla on saavutettavissa senttimetriluokan tarkkuus 0 – 15 m mittausalueella käyttämällä tässä työssä esitettyä integroitua vastaanotinta ja aikatason ajoitusvirhekompensointia.

L'inversion conjointe géophysique est la méthode la plus efficace pour imager l'intérieur de la Terre. En intégrant plusieurs techniques géophysiques elle permet de réduire les incertitudes inhérentes à chacune et ainsi améliorer la compréhension de la Terre. Dans cette étude, nous utilisons les techniques des fonctions récepteur (RF) en sismologie, de la magnétotellurique (MT) et de la gravimétrie qui permettent de caractériser respectivement la vitesse des ondes S, la résistivité électrique et la densité du sous-sol.Le but de ce travail de recherche se divise en deux parties: une première, méthodologique, sur le développement d'une nouvelle approche d'inversion conjointe en 3D et une deuxième avec l'application de ces techniques (en approche jointe ou séparée) sur la Divergence Nord Tanzanienne pour mieux comprendre le phénomène de rupture continentale. Pour la partie méthodologie deux approches ont été développées : une entre les données de MT et de gravimétrie avec un calcul original de l'effet gravimétrique de la topographie qui permet de réduire le nombre de mailles tout en gardant une résolution satisfaisante ; et une deuxième méthode entre les données de MT et de RF par une nouvelle approche d'extrapolation des modèles 1D de vitesse en pseudo modèle 3D de vitesse. L'application de ces techniques sur la Tanzanie a permis de mettre en évidence un certain nombre de structures lithosphériques dont deux zones majeures à faible vitesse dans la croûte inférieure et dans le manteau supérieur. Cette dernière semble refléter des interactions entre des structures héritées d'âge protérozoïque et le panache mantellique Africain. / Geophysical joint inversion attempts to reproduce as best as possible the interior of the Earth. By integrating several geophysical techniques the joint inversion reduces the uncertainties of each methods and improves our understanding of the Earth structure. In this study we use the receiver functions (RF), the magnetotelluric (MT) and the gravity methods which enable to charaterize the Swave velocity, the electrical resistivity and the density, respectively. The objective of this research work is divided in two parts; first with the development of a new 3D joint inversion approach and then with the application of these methods (on a joint or separate approach) on the North Tanzanian Divergence to better understand the continental breakup.For the methodologic part two approaches have been developed; one between the MT and gravity data with an original computation of the topographic effect which decreases the number of cells while keeping a satisfaying resolution. And a second method between the MT and RF data where pseudo 3D velocity model are created and combined with the MT models to better takes into account the physical properties of the receiver function. The application of these methods on the Tanzania highlighted several lithospheric structures and particularly two low-velocity areas in the lower crust and the upper mantle. This latter suggests interactions with Proterozoic inherited structures and the African plume material.

Abstract The crustal and upper mantle structures of the Shield on the regional scale were investigated using the data of the POLENET/LAPNET passive seismic array and the previously published models of active and passive seismic experiments in the study area. This area is centred in northern Finland and it extends to surrounding areas in Sweden, Norway and northwestern Russia. The bedrock there is mostly of the Archaean origin and the lithosphere of the region was reworked by two orogenies during Palaeoproterozoic. One of the results of the thesis was a new map of the Moho depth of the study area, for which new estimates of the crustal thickness were obtained using receiver function method and complemented by published results of receiver function studies and controlled source seismic profiles. The map differs from the previously published maps in two locations, where we found significant deepening of the Moho. The 3D structure of the upper mantle was studied using teleseismic traveltime tomography method. The resulting model shows high seismic velocities below three cratonic units of the study area, which may correspond to non-reworked fragments of cratonic lithosphere and a low velocity anomaly separating these cratonic units from each other. The regional scale studies were complemented by two smaller scale studies in upper crust level using combined interpretation of seismic profiling and gravity data. These studies were centred on Archaean Kuhmo Greenstone Belt in eastern Finland and central Lapland in northern Finland located in the crust reworked during Palaeoproterozoic. Both areas are considered as prospective ones for mineral exploration. Both studies demonstrate the advantage of gravity data inversion in studying 3D density structure of geologically interesting formations, when the Bouguer anomaly data is combined with a priori information from petrophysical and seismic datasets.

The main objective of our research was to develop a new bankruptcy prediction model for the Czech economy. For that purpose we used the logistic regression and 150,000 financial statements collected for the 2002-2016 period. We defined 41 explanatory variables (25 financial ratios and 16 dummy variables) and used Bayesian model averaging to select the best set of explanatory variables. The resulting model has been estimated for three prediction horizons: one, two, and three years before bankruptcy, so that we could assess the changes in the importance of explanatory variables and models' prediction accuracy. To deal with high skew in our dataset due to small number of bankrupt firms, we applied over- and under- sampling methods on the train sample (80% of data). These methods proved to enhance our classifier's accuracy for all specifications and periods. The accuracy of our models has been evaluated by Receiver operating characteristics curves, Sensitivity-Specificity curves, and Precision-Recall curves. In comparison with models examined on similar data, our model performed very well. In addition, we have selected the most powerful predictors for short- and long-term horizons, which is potentially of high relevance for practice. JEL Classification C11, C51, C53, G33, M21 Keywords Bankruptcy...

La filière solaire thermodynamique, et plus précisément la technologie des centrales à tour, est l'une des ressources d'énergies renouvelables les plus prometteuses. Le travail de thèse s’inscrit dans le cadre général de l’augmentation des rendements de centrales solaires à tour où l’augmentation de l'efficacité et de la température du récepteur joue un rôle clé. L’originalité de la thèse réside dans l’étude du rôle des sélectivités spectrale et directionnelle sur le rendement de récepteurs surfaciques à haute température. L’objectif poursuivit a été d’améliorer simultanément la géométrie, le matériau, la rugosité et la microstructuration des récepteurs surfaciques pour créer une sélectivité permettant l’augmentation des rendements. La première étape a consisté à l’élaboration d’un modèle approché d’une centrale solaire pour quantifier l’influence du rendement du récepteur sur le rendement de la centrale. Dans un second temps, un modèle de récepteur détaillé incluant la résolution précise des transferts radiatifs (grâce à la méthode Monte Carlo) a été développé pour déterminer le gain en rendement que l’on peut obtenir grâce à la sélectivité spectrale et directionnelle. Ensuite, la modification des propriétés radiatives des surfaces par des microstructures unipériodiques et bipériodiques a été étudiée dans l'objectif d'augmenter la sélectivité spectrale du récepteur. Cette étape a nécessité la résolution des équations de Maxwell par la méthode RCWA. La microstructure retenue et qui offre le meilleur potentiel possède un relief pyramidal bipériodique. L’optimisation de la période et de la hauteur de ce relief permet d’obtenir une absorptivité solaire maximale égale à 0,98. / Concentrated solar power (CSP) technology is an alternative for renewable thermal energy generation and a promising source of energy. Managing the optical properties of a cavity solar receiver to create spectral and directional selectivities is a solution to improve receiver and solar power plant efficiencies in order to reduce cost. The two main steps of the development are to quantify the potential gain that may result from theoretical selectivities and then the optimization of microstructuration to increase as possible the spectral selectivity. At first, a calculation code was built in order to quantify the influence of receiver on the global solar power plant efficiency. Then a parametric study which takes into account thegeometry, the material, the roughness and the microstructure of the receiver was conducted. At last, an optimization of microstructuration with uniperiodic and biperiodic structures was studied. As a conclusion the best structure is a biperiodic pyramidal relief which offers a huge gain of absorptivity.

Traditional implementations of optical receivers are designed to operate with external photodetectors or require integration in a hybrid technology. By integrating a CMOS photodetector monolithically with an optical receiver, it can lead to the advantage of speed performance and cost. This dissertation describes the implementation of a photodetector in CMOS technology and the design of an optical receiver front-end and a clock and data recovery system. The CMOS detector converts the light input into an electrical signal, which is then amplified by the receiver front-end. The recovery system subsequently processes the amplified signal to extract the clock signal and retime the data. An inductive peaking methodology has been used extensively in the front-end. It allows the accomplishment of a necessary gain to compensate for an underperformed responsivity from the photodetector. The recovery circuits based on a nonlinear circuit technique were designed to detect the timing information contained in the data input. The clock and data recovery system consists of two units viz. a frequency-locked loop and a phase-locked loop. The frequency-locked loop adjusts the oscillator’s frequency to the vicinity of data rate before phase locking takes place. The phase-locked loop detects the relative locations between the data transition and the clock edge. It then synchronises the input data to the clock signal generated by the oscillator. A system level simulation was performed and it was found to function correctly and to comply with the gigabit fibre channel specification. / Dissertation (MEng (Micro-Electronics))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / unrestricted

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