Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / The main objective of this research was to compare evaporation measured in two Class A evaporation pans. The first one installed 15 cm over the surface and the second one installed at surface level in a small reservoir. The experiment was carried out at the Fisheries Station of the Federal University of CearÃ, in Fortaleza. An automated weather station was installed at the same site. During February to November of 2008, evaporation data were measured in a daily basis. The weather data were collected in a weekly basis using a radio frequency system. The evaporation measured at a soil surface was 5.3% higher than the evaporation measured at a water surface level of the reservoir. The different installation conditions were influenced differently by the weather parameters. The evaporation estimation methods of Penman, Linsley and Linacre underestimated the evaporation measured in the reservoir, and the Penman method presented the smaller error. / As condiÃÃes climÃticas das regiÃes semi-Ãridas favorecem a evaporaÃÃo que representa a maior perda do volume lÃquido dos aÃudes, portanto, um parÃmetro importante para o gerenciamento dos recursos hÃdricos. Um dos instrumentos mais difundidos e utilizados para estimar a evaporaÃÃo em reservatÃrios à o Tanque Classe A. Assim, este trabalho teve como objetivo principal comparar a evaporaÃÃo medida em dois tanques Classe A, sendo um instalado em ambiente aquÃtico e outro em ambiente terrestre, e como objetivo secundÃrio avaliar estimativas da evaporaÃÃo obtidas pelos mÃtodos propostos por Penman (1948), Linsley (1982) e Linacre (1993) em relaÃÃo Ãs medidas de evaporaÃÃo obtidas nos referidos tanques evaporimÃtricos. O experimento foi conduzido na EstaÃÃo de Piscicultura do Centro de CiÃncias AgrÃrias da Universidade Federal do CearÃ, em Fortaleza, CE. Neste local, alÃm dos tanques Classe A, foi instalada uma estaÃÃo meteorolÃgica automÃtica. No perÃodo de fevereiro a novembro de 2008 foram realizadas medidas diÃrias de evaporaÃÃo e coletados, semanalmente, os dados meteorolÃgicos armazenados no sistema de aquisiÃÃo da estaÃÃo, utilizando rÃdio freqÃÃncia. O total evaporado no tanque Classe A instalado em ambiente terrestre foi 5,3% superior ao total evaporado no tanque Classe A em ambiente aquÃtico. A instalaÃÃo do tanque Classe A em ambiente aquÃtico reduziu os efeitos diretos da radiaÃÃo solar incidente, umidade relativa, temperatura do ar e velocidade do vento sobre a evaporaÃÃo assim com a amplitude tÃrmica da Ãgua no seu interior. O mÃtodo proposto por Penman (1948) apresentou os melhores desempenhos, com erros relativos de -3,0% em relaÃÃo ao tanque Classe A no ambiente aquÃtico e -7,9% em relaÃÃo ao tanque Classe A no ambiente terrestre.

Orientador: Nelson Luis Saldanha da Fonseca / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação / Made available in DSpace on 2018-08-19T00:15:10Z (GMT). No. of bitstreams: 1 Silva_PedroHenriqueGomesda_M.pdf: 2438089 bytes, checksum: 1531b4c3213529b3d7064cb49b95e0c8 (MD5) Previous issue date: 2011 / Resumo: A tecnologia de Rádio sobre Fibra (Radio over Fiber - RoF) possibilita o barateamento da instalação e manutenção de redes de acesso sem fio, dado que a distribuição da utilização dos sinais de radiofrequência (RF) pode ser otimizada, bem como emprega-se, nessas redes, antenas mais simples e baratas. Dentre as tecnologias de redes sem fio de acesso banda larga (Broadband Wireless Access - BWA), o padrão IEEE 802.16, conhecido como WiMAX, vem sendo apresentado como uma solução de baixo custo para o acesso última milha à Internet ou como meio de distribuição backhaul. Suas características, muito semelhantes às das redes celulares, tornam interessante o emprego da tecnologia de RoF para a instalação e expansão das redes WiMAX a um baixo custo. Nesta dissertação, apresenta-se um estudo sobre o dimensionamento da tecnologia RoF para redes WiMAX. Apresentam-se medidas de desempenho que levam em consideração os ajustes dos parâmetros de sincronização das camadas física e de controle de acesso ao meio. O objetivo desse estudo é servir de base para o planejamento e instalação dessas redes, levando em consideração restrições devido à degradação de desempenho que a introdução da fibra óptica impõe. Esta dissertação estuda, adicionalmente, o problema de otimização do uso dos recursos de rádio da rede, mais especificamente do posicionamento e alocação das estações base. A proposta considera uma arquitetura de rede sem fio com diversas camadas de antenas, cada camada com células de diferentes raios de cobertura. As células são implantadas através de associações entre as antenas e as estações base disponíveis. Para a otimização da rede, propõe-se um modelo baseado em programação linear inteira que distribui, de maneira ótima, os recursos e encontra a melhor configuração de células para minimizar o número de BSs usadas na rede, para maximizar a receita, ou para obter esses dois critérios simultaneamente. O custo computacional do problema de otimização proposto é bastante alto, o que inviabiliza o seu emprego em redes móveis. Para contornar esse problema, são apresentados também algoritmos rápidos baseados em relaxação linear da programação linear inteira que possibilitam a obtenção de soluções de boa qualidade em tempo reduzido / Abstract: The Radio over Fiber technology allows the reduction of the cost of installation and maintenance of wireless access networks, since it can allow an optimized use of radio frequency (RF). Moreover, it employs simplified and inexpensive antennas. The IEEE 802.16 wireless networks, known as WiMAX, are low cost solutions for the last mile access to the Internet. Its characteristics are very similar to those of cellular networks, which makes attractive the use of RoF technology for the installation and expansion of WiMAX networks at low cost. This dissertation studies the use of RoF technology for WiMAX networks, which considers the parameters of physical layer and medium access synchronization. Results can be used as guideline for planning of these networks. This dissertation also studies the optimization of the use of radio resources of the network, specifically the problem of positioning base stations. The proposed architecture considers a wireless network with several layers of antennas, each layer with cells of different radii of coverage. The cells are deployed dynamically by the association between antennas and the available base stations. It is proposed a network optimization model based on integer linear programming that optimally distributes the radio resources and finds the best configuration to either minimize the number of Base Stations used in the network, or to maximize the operator revenue, as well as ato try to achieve both criteria simultaneously. The computational cost of the proposed optimization problem is quite high, which prevents its use in mobile networks. To circumvent this problem, it is also presented fast algorithms based on linear relaxation of the integer linear programming model, which enable the obtainment of good solutions in short time frames / Mestrado / Ciência da Computação / Mestre em Ciência da Computação

dreimal im Jahr erscheinende Zeitschrift über aktuelle Themen der TU Chemnitz

dreimal im Jahr erscheinende Zeitschrift über aktuelle Themen der TU Chemnitz

Dans cette thèse, j’étudie la compressibilité électronique de deux isolants topologiques tridimensionnels : Le tellurure de mercure (HgTe) sous contrainte et le séléniure de bismuth (Bi2Se3).Je présente des mesures d’admittance électronique à basse température résolues en phase sur une large gamme de fréquence. Cela permet d’extraire la capacité quantique associé à la densité d’états et la résistivité des matériaux étudiés.Nous montrons qu’un isolant topologique intrinsèque présente une réponse dominée par les états de surface topologiques sur une large gamme d’énergie qui s’étend au-delà du gap de transport du matériau massif. Ce régime, appelé « écrantage de Dirac », est caractérisé par une compressibilité électronique proportionnelle à l’énergie de surface et une haute mobilité.Dans la suite, nous nous intéressons à la limite de ce régime. Nous observons qu’à haute énergie et sous l’influence de forts champs électriques perpendiculaires, des états excités massifs de surface sont peuplés ce qui se manifeste expérimentalement de différentes façons : Une chute dans la constante de diffusion électronique, un pic de conductivité ainsi que l’apparition d’un deuxième type de porteurs en magnéto-transport et de métastabilité dans la relation charge-tension.Un modèle théorique basé sur un traitement quasi-relativiste du Hamiltonien de surface est présenté. Il permet d’identifier la dépendance en énergie et champ électrique des états massifs de surface.Cette thèse est complémenté par des résultats expérimentaux sur Bi2Se3 obtenu par croissance sur nitrure de bore mettent en évidence l’importance de la pureté des interfaces d’isolants topologiques. / This thesis discusses the electronic compressibility of two representative three dimensional topological insulators: Strained mercury telluride (HgTe) and bismuth selenide (Bi2Se3).I present low temperature phase-sensitive electron admittance data over a broad frequency range. This allows to extract the quantum capacitance related to the density of states and the resistivity of the investigated materials.We show that the response of an intrinsic topological insulator is dominated by topological surface states over a large energy range exceeding the bulk material’s transport gap. This regime, named “Dirac screening” is characterized by an electron compressibility proportional to the surface Fermi level and a high mobility.Subsequently, we investigate the limits of this regime. At high energy and large perpendicular electric fields we observe the population of excited massive surface states. Experimentally, these manifest themselves in multiple signatures: A drop in the electronic diffusion constant, a peak in the conductivity, appearance of a second carrier type in magneto-transport and meta-stability in the charge-voltage relation.A theoretical model based on a quasi-relativistic treatment of the surface Hamiltonian is presented. It allows to identify the electric field and energy dependence of the massive surface states.This thesis is complemented by experimental results on Bi2Se3 grown on boron nitride, where we demonstrate the importance of clean surfaces for the study of electronic properties in topological insulators.

Abstract This thesis studies the design methods and properties of supply-modulated switch-mode radio frequency power amplifiers. Besides simulation based studies and theory review, two amplifiers were designed: a discrete MESFET class E amplifier (0.5 W at 1 GHz), and an integrated pHEMT class E-1 amplifier (2.0 W at 1.6 GHz) with an on-chip resonator. The existing design methods of the resonant output network of switching amplifiers were reviewed and some extensions on the handling of nonlinear capacitances were proposed. The effects of varying supply voltage were studied and suggestions were given to minimize Vdd / AM and Vdd / PM distortion in supply modulated amplifiers. The implementation of the bias feed was also discussed resulting in proposing a combination of a short transmission line and a small inductor, which provides both fast supply modulation and little effect on harmonic impedances. The main contributions are related to the study of the input impedance of a class E power amplifier, where the effects of supply dependent input impedance and timing skew generated by injected harmonic distortion were analyzed. The stabilization of the amplifier was also discussed. Based on the findings, a push-pull class E amplifier with extra cross-coupled feedback capacitors and second harmonic traps at the gates appears to be a very good starting point for a further study. / Tiivistelmä Tämä väitöstyö käsittelee radiotaajuuksilla toimivien käyttöjännitemoduloitujen kytkintehovahvistimien ominaisuuksia ja suunnittelumenetelmiä. Suunnittelumenetelmiin liittyvän katsauksen ja simulaatioihin perustuvan tutkimusten lisäksi kaksi vahvistinta toteutettiin väitöstutkimuksen aikana: diskreettikomponentein toteutettu E-luokan vahvistin (MESFET, 0.5 W ja 1 GHz) ja integroituna piirinä toteutettu käänteinen E-luokan vahvistin (pHEMT, 2.0 W ja 1.6 GHz), jonka lähdön resonaattoripiiri sisällytettiin integroituun piiriin. Kytkinvahvistimien suunnittelumenetelmiä verrattiin ja kehitettiin edelleen siten, että suunnitteluvaiheessa voidaan ottaa huomioon esim. transistoripiirin takaisinkytkennässä olevan kapasitanssin epälineaarisuus. Työssä tutkittiin myös käyttöjännitemodulaation vaikutusta kytkinvahvistimien toimintaan, ja tutkimuksen tuloksena annettiin muutamia ehdotuksia käyttöjänniteriippuvan amplitudi- (Vdd / AM) ja vaihemodulaation (Vdd / PM) vähentämiseksi. Lähdön biasointipiirin toteutukseen suositeltiin pienen kelan ja siirtolinjan yhdistelmää. Yhdistelmän avulla pyritään maksimoimaan modulaationopeus ja minimoimaan vaikutukset harmonisiin impedansseihin. Pääkohtina väitöksessä ovat E-luokan kytkinvahvistimesta saadut tutkimus- ja mittaushavainnot käyttöjännitteen funktiona muuttuvasta transistorin tuloimpedanssista sekä suurikokoisen transistorin tuloissa tapahtuvan, säröytymisen aiheuttaman tulosignaalien ajoitusvirheen analyysi. Näiden lisäksi vahvistimen stabiilisuuteen kiinnitettiin huomiota. Saatujen havaintojen perusteella voimme todeta, että push-pull -tyyppinen E-luokan vahvistin olisi mielenkiintoinen valinta jatkotutkimuksille.

La technologie RFID (Radio Frequency Identification) prend une place de plus en plus importante dans la société d'aujourd'hui notamment dans des domaines aussi variés que la santé, la sécurité, la logistique... Le développement de cette technologie met en évidence de nouvelles contraintes comme la réduction des zones de lecture et la géo-localisation pour le stockage et le suivi de marchandises. Dans ce contexte, la thèse s'est focalisée sur le développement d'antennes pour lecteur RFID dans le cadre du projet SPINNAKER piloté par TAGSYS RFID et soutenu par OSEO. L'objectif de cette étude est de concevoir des antennes compactes et directives à polarisation circulaire en bande UHF et SHF. L'antenne hélice présente toutes ces caractéristiques à l'exception de la hauteur, très importante dès que l'on souhaite obtenir des performances élevées surtout en gain. Dans ce manuscrit, trois solutions sont proposées pour réduire la hauteur de l'antenne hélice tout en répondant aux cahiers des charges. La première solution consiste à utiliser un réflecteur de forme cylindrique ou conique qui permet de réduire la hauteur d'une antenne hélice classique d'un facteur quatre pour atteindre 0,9λ. La réduction de la hauteur se traduit par une augmentation de la surface autour de l'antenne avec une dimension latérale de 2,3λ. La seconde solution consiste à utiliser l'antenne hélice avec une cavité Fabry-pérot. La hauteur du système antennaire obtenue est de 0,5λ avec un diamètre de 2λ. La dernière solution développée dans la thèse introduit une surface CMA à la solution précédente qui permet de réduire la hauteur à 0,25λ. Toutes les solutions proposées ont été validées expérimentalement. / Over the past 20 years, the RFID (Radio Frequency Identification) technology is having a huge expansion. Nowadays, it is frequently used in different areas as the health, the security and the logistic. A lot of researches are ongoing on this topic, especially in order to reduce the reading zone of the readers and to locate the tags. This thesis focuses on the development of new antennas for Readers RFID devices and is part of the SPINNAKER project supported by OSEO. The antennas requirements are circular polarization, high directivity and gain with low profile. The helix antennas meet all these requirements except the axial length. In this manuscript, we propose three solutions to reduce the helix antenna axial length. The first one uses a cylindrical or conical optimal reflector to reduce the length by four. This reduction affects directly the surface witch increases up to 2.3λ. The second solution uses the helix antenna as a circular polarization feed for a Fabry-Perot (FP) cavity. The final antenna presents a cavity height of 0.5λ and a 2λ diameter. The last solution conserves the FP cavity in which we include an Artificial Magnetic Conductor (AMC) to reduce the cavity height to 0.25λ. All these solutions are validated by measurements.

Radio Frequency Identification (RFID) technology is a ethod of identifying unique items using radio waves that communicate between RFID tags and readers without line-of-sight readability. RFID technology provides great potential in many industries and a wide spectrum of possible uses. Areas of application include person identification, logistics, pharmaceutical, access control, security guard monitoring and asset management. One of the areas where RFID is being used and where it promises excellent results is the retail industry. While RFID systems have the potential to revolutionise the way products and goods are tracked and traced in the retail supply chain, barriers to its widespread adoption exist: for example; technical constraints, return on investment constraints, a lack of awareness and education and as well as privacy and security issues. The research aims to identify the barriers to the adoption of RFID and to investigate the perceptions of RFID held by members of the retail sector in South Africa (SA). Current research and available literature are used to identify RFID adoption barriers and a conceptual framework on this subject is proposed, which is then verified by SA retailers’ perceptions, established by means of a survey. Initial barriers to widespread adoption include a shortage in skills, a lack of standards, high costs associated with RFID devices, the difficulty of integrating with current legacy systems, and a lack of familiarity with the system. Finally, an enhanced framework is proposed, describing RFID adoption barriers within the South African retail sector. In summary, the framework is an outline of the barriers impacting RFID adoption in the SA retail sector that need to be considered and addressed. The framework identifies six categories of RFID adoption barriers, with each category containing two or more barriers relating to that particular category. These categories are Technological, Cost and return on investment, Privacy and security, Implementation, Organisational factors and People.

Le présent travail est réalisé dans le cadre de l’étude d’un procédé industriel de densification de matériaux composites carbone/carbone (C/C) destinés aux freins d’avion. Une préforme poreuse de fibres de carbone baigne dans un précurseur liquide et elle est chauffée par induction électromagnétique radio-fréquence. Le précurseur porté à ébullition dans l’espace poral crée un dépôt de carbone dans les zones les plus chaudes ; ce dépôt constitue la matrice du composite. On propose une modélisation physico-chimique de ce procédé afin d’en assurer le contrôle et l’optimisation. Le travail a consisté à développer un solveur couplant l’induction électromagnétique avec les transferts de masse, de chaleur, de mouvement et d’espèces chimiques, en incluant l’ébullition et le dépôt chimique. Le modèle inclut le circuit électrique complet permettant d’effectuer le chauffage : il permet donc de suivre en temps réel et de façon non destructive l’avancement de la densification par l’évolution des grandeurs électriques. Une formulation originale adaptée à la représentation simultanée du liquide, du gaz et de la zone en ébullition a été développée et implémentée avec succès dans un logiciel commercial d’éléments finis. Les résultats de la simulation sont comparés avec les données obtenues sur le moyen expérimental, avec un bon accord. Enfin, la simulation est utilisée pour proposer des pistes d’amélioration du procédé, en altérant la géométrie du dispositif de chauffage par induction et en modifiant la stratégie de pilotage en puissance. / This work has been carried out in the frame of the study of an industrial process for the manufacturing of carbon/carbon (C/C) composite aircraft brake discs. A porous preform made of carbon fibres is immersed in a liquid precursor and is heated by Radio-Frequency electromagnetic induction. The boiling precursor enters the porous preform and yields a carbon deposit in the hottest zones; this deposit will be the carbon matrix of the composite. A physico-chemical process model is proposed in the aim of ensuring its control and optimisation. The work consisted in developing a numerical solver coupling electromagnetic induction heating with heat, mass and species balances accounting for boiling, diffusion and chemical deposition reactions. The model includes the complete electrical circuit of the heating device: it therefore allows real-time, non-destructive monitoring of the infiltration progress through the evolution of the electrical properties. An original formulation has been designed to simultaneously describe the liquid, the gas and the boiling zone; it has been implemented in a commercial Finite Element software package and validated physically with respect to experimental data, with a good agreement. Finally, the simulation software has been used to propose directions for process improvements, through alterations of the inductive heating device geometry or of the heating power supply program.

The diploma thesis deals with the rationalization of the flow of transport units among the company Continental Teves CZ, s.r.o. and suppliers. The objective of the thesis is to map the flow of transport units, to suggest possible solutions and to pass judgment on a possible implementation of automatic identification that can facilitate monitoring of such marked transport units. The theoretical part of the thesis describes specifics of automotive industry and of supply chains that operate there.