"Asphalt pavements are made up of several layers of materials and different types of materials are being used as base courses in these pavements. The properties of these pavement layers are affected significantly by temperature, and all of the layers are made up of heterogeneous mixtures of a wide variety of materials whose thermal properties are not readily available. Therefore, laboratory experiments were carried out with samples of pavements with different base course materials to determine temperature profiles along the depth, and finite element analysis was used to backcalculate thermal properties of the materials in the different layers of the different samples. The concept of extracting heat energy from asphalt pavements was evaluated by finite element modelling and testing small and large scale asphalt pavement samples. Water flowing through copper tubes inserted within asphalt pavements samples were used as heat exchangers in the experiments. The rise in temperature of water as a result of flow through the asphalt pavement was used as the indicator of efficiency of heat capture. The results of small scale testing show that the use of aggregates with high conductivity can significantly enhance the efficiency of heat capture. The efficiency can also be improved by using a reflectivity reducing and absorptivity increasing top layer over the pavement. Tests carried out with large scale slabs show that a larger surface area results in a higher amount of heat capture, and that the depth of heat exchanger is critical Heat-Islands are formed as a result of construction that replaces vegetation with absorptive surfaces (asphalt pavement). One suggested method to reduce the emitted heat from asphalt pavement surfaces is to reduce the temperature of the surface by flowing a suitable fluid through the pavement. Laboratory experiments were carried out using hand-compacted hot mix asphalt samples with quartzite and metagranodiorite aggregates. Pipes with different surface area were used to flow water through the samples, and the processes were modeled using finite element method. The results clearly show the feasibility of the proposed method, and indicate the beneficial effects of higher thermal conductivity of aggregates and larger surface area of pipes. "

Proton-Exchange Membrane (PEM) fuel cells are extremely attractive for replacing internal combustion engines in the next generation of automobiles. However, two major technical challenges remain to be resolved before PEM fuel cells become commercially successful. The first issue is that CO, produced in trace amounts in fuel reformer, severely limits the performance of the conventional platinum-based PEM fuel cell. A possible solution to the CO poisoning is higher temperature operation, as the CO adsorption and oxidation overpotential decrease considerably with increasing temperature. However, the process temperature is limited in atmospheric fuel cells because water is critical for high conductivity in the standard PEM. An increase in operating pressure allows higher temperature operation, although at the expense of parasitic power for the compressor. Further the conventional PEM, Nafion? is limited to 120°C due to it's low glass transition temperature. Thus, the design of higher temperature PEMs with stable performance under low relative humidity (RH) conditions is considered based on a proton transport model for the PEM and a fuel cell model that have been developed. These predictive models capture the significant aspects of the experimental results with a minimum number of fitted parameters and provides insight into the design of higher temperature PEMs operating at low RH. The design of an efficacious high temperature, low RH, PEM was based on enhancing the acidity and water sorption properties of a conventional PEM by impregnating it with a solid superacid. A systematic investigation of the composite Nafion?inorganic PEMs comprising experiments involving water uptake, ion-exchange capacity (IEC), conductivity and fuel cell polarization is presented in the work. The most promising composite is the nano-structured ZrO2/Nafion?PEM which exhibits an increase in the IEC, a 40% increase in water sorbed and a resulting 24% conductivity enhancement vs. unmodified Nafion?112 at 120°C and at RH < 40%.

Made available in DSpace on 2017-07-21T20:43:51Z (GMT). No. of bitstreams: 1 Tufy Kabbas Junior.pdf: 2988725 bytes, checksum: bd676d57a21df0604e836ad177676653 (MD5) Previous issue date: 2017-01-27 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / Due to the need for clean energy, an alternative that has gained worldwide prominence are like fuel cells. As proton conductive ceramics have an operating temperature in the range of 600 to 800 ° C, making them especially interesting for a fuel cell manufacturing. In this way, the objective of this work was to study a peroxide production with mixed proton-electronic conductivity to update as cell cathodes a solid oxide fuel with proton conductivity. These composites are produced using the mechanical mixture from a quality database, which has electronic conductivity in the proportions 25/75, 50/50 and 75/25, sintered at 1400 ° C. The composite 25 / 75 and 75/25 showed to be only of an electronic and ionic conductor (oxygen ions), respectively, showing no mixed-protonic conductivity. The 50/50 composite, through the obtained results, leads to believe that the mixed proton-electronic conductivity occurred. / Devido à necessidade de se produzir energia limpa, uma alternativa que tem ganho destaque mundial são as células a combustível. As cerâmicas condutoras protônicas possuem uma temperatura de operação na faixa de 600 a 800ºC, tornando-as especialmente interessantes para a fabricação de células a combustível. Desta forma, este trabalho teve por objetivo estudar a obtenção de perovisquitas com condutividade mista protônica-eletrônica para atuar como cátodos de células a combustível de óxido sólido com condutividade protônica. Estes compósitos foram produzidos utilizando-se mistura mecânica, da perovisquita BaCe0,2Zr0,7Y0,1O3-d (BCZY), a qual possui condutividade protônica, com a perovisquita LaNi0,5Cr0,5O3 (LNC), que possui condutividade eletrônica, nas proporções 25/75, 50/50 e 75/25, sinterizadas à 1400°C. Os compósitos 25/75 e 75/25 demonstraram ser apenas de um condutor eletrônico e iônico (íons oxigênio) respectivamente, não mostrando condutividade mista eletrônica-protônica. Já o compósito 50/50, através dos resultados obtidos através de mapeamento químico e espectroscopia de impedância, demonstram um provável aparecimento de condutividade mista protônica-eletrônica.

Dans le domaine de la microélectronique de puissance, les progrès de miniaturisation ne cessent de s’accroître. En effet, le nombre de composants par unité de surface a suivie durant de nombreuses années la loi de Moore. Cette évolution implique une augmentation de la densité d’énergie à évacuer sous forme de chaleur, ce qui rend le contrôle de la température de fonctionnement difficile et a pour effet de diminuer la fiabilité des systèmes électroniques.C’est pourquoi, le management thermique des matériaux d’interface thermique est indispensable pour pérenniser le bon fonctionnement des dispositifs de puissance dans leur environnement. L’utilité de ces matériaux est d’améliorer l’évacuation de la chaleur des composants électroniques vers le milieu environnant via un dissipateur thermique (radiateur, fluide caloporteur). Pour tenter de répondre à ces besoins, ce sujet de thèse est basé sur l’utilisation de nanotubes de carbone verticalement alignés, associée à des polymères fonctionnels. Les études se sont portées sur l’ensembledes résistances de contact existantes au sein d’un matériau d’interface thermique, depuis les nanotubes decarbone / Polymère / jusqu’au substrat de cuivre.L’optimisation des interactions est portée sur l’étude de différents polymères ayant la capacité d’engendrer des liaisons covalentes avec les nanotubes de carbone et avec le substrat de cuivre. L’intérêt de ces liaisons covalentes est d’améliorer le transfert de la chaleur via les phonons. Enfin, l’augmentation de la conductivité thermique intrinsèque des polymères est envisagée.Concernant les résultats obtenus, il apparait une nette diminution de chacune des résistances de contact étudiées. Afin de mieux comprendre ces résultats, des études de ces interfaces in-situ ont été réalisées. / With progress in microelectronics, the miniaturization of devices is a current issue and the component density on a device follows Moore’s law. As a consequence the power density reaches levels that challenge device reliability. New heat dissipation strategies are needed to efficiently drain heat.Thermal interface materials (TIMs) are used to transfer heat across interfaces, for example between the device and its packaging. However, to meet microelectronics requirement, commercials TIMs still need to be highly thermally conductive.In order to achieve these requirements, this work is focused on the use of vertically aligned carbon nanotubes (VACNTs) and functional polymers. All thermal contact resistances existing in TIMs, from VACNTs / Polymer / to substrate are studied.Interaction optimizations are based on the study of different polymers which are specially designed to develop covalent bonding with the CNTs sidewalls and/or metallic surface. The interest of these covalent bondings is to improve the thermal transfer by phonons. Finally, the increase of the intrinsic thermal conductivity of the polymer is considered.Regarding the results, a decrease of all thermal contact resistances is shown. In order to have a better understanding of these results, the thermal interfaces obtained are analyzed in situ.

Dans le domaine de l’isolation thermique du bâtiment, les évolutions réglementaires (RT2012)et normatives (NF BPE : Béton à Propriétés Thermiques, septembre 2016) incitent à évoluer vers des bétons isolants et structurels (BIS). La maîtrise de leur conductivité thermique est primordiale. Il est possible, en plus de faire appel à un squelette granulaire léger, de jouer sur la nature de la pâte en utilisant des inclusions qui apporteraient un pouvoir isolant supplémentaire : les cénosphères. Dans un contexte de facilité de mise en oeuvre, à ces propriétés est rajouté le critère auto plaçant des bétons. On parle alors de Bétons Isolants Structurels Autoplaçants (BISAP). La maitrise et la validation de ces nouvelles formules dans le respect d’une approche prescriptive a nécessité la caractérisation des matériaux à différentes échelles (de l’inclusion à l’échelle de l’ouvrage) en développant des approches expérimentales et numériques. Leur comportement à l’état frais et à l’état durci a été analysé. Les conductivités thermiques mesurées placent ces nouveaux bétons dans la catégorie Bétons Isolants Structurels au sens du nouveau référentiel. Le modèle numérique développé permet d’approcher correctement les valeurs expérimentales. D’autre part, la sensibilité des BISAP incorporant des cénosphères à plusieurs indicateurs de durabilité (porosité accessible à l’eau, perméabilité,carbonatation et retrait) a également été étudiée. L’influence des microsphères est plus ou moins notable en fonction du mécanisme abordé. / In the field of building thermal insulation, regulatory (RT2012) and standards (NF BPE: Béton à Propriétés Thermiques, September 2016) evolutions are encouraging the use of insulating structural concrete (BIS). The control of their thermal conductivity is essential. It is possible, in addition to using lightweight aggregates, to modify the composition of the cement paste by using hollow inclusions (fly ash cenospheres) to bring an additional thermal insulating potential. In a context of improved workability, to these properties is added the criterion of self-compacting concrete. The validation of these new formulas required the characterization of materials at different scales (from inclusion scale to building scale) by implementing experimental and numerical approaches. Their properties at fresh and hardened state were analyzed. The measured thermal conductivities place these new concretes in the Category of Structural Insulating Concrete in the sense of the new standard. The developed numerical model allowed approaching the experimental measurements correctly. The effect of cenospheres’ incorporation into cement paste on several durability indicators was also characterized.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science. / Vita. / Includes bibliographical references. / Ph.D.

Nano-materials are interesting material category with a single unit size between 1 and 1000 nanometers and possess unique mechanical, electrical, optical, and other physical properties that make them stand out from ordinary materials. With increasing demand for reduced size of electronic devices and integrated micro/nano-electro-mechanical systems (MEMS / NEMS), there is a high driving force in scientific research and technological advancement in nanotechnology. My research is about two popular novel nanomaterials: carbon nanotubes (1-dimensional material) and thin-layer transition metal dichalcogenides (2-dimensional materials). My first research direction is about the characterization of electrical properties of carbon nanotubes and using them as bio-sensors. Carbon nanotubes (CNTs), in general, are a material of great interest for many applications since their first discovery in 1991 [1], due to their unique structure, extraordinary electrical and mechanical properties, and unusual chemical properties. High-throughput fabrication of carbon nanotube field effect transistors (CNTFETs) with uniform properties has been a challenge since they were first fabricated in 1998. We invent a novel fabrication method to produce a 1×1 cm2 chip with over 700 CNTFETs fabricated around one single carbon nanotube. This large number of devices allows us to study the stability and uniformity of CNTFET properties. We grow flow-aligned CNTs on a SiO2/Si substrate by chemical vapor deposition and locate a single long CNT (as long as 1 cm) by scanning electron microscopy. Two photolithography steps are then used, first to pattern contacts and bonding pads, and next to define a mask to ‘burn’ away additional nanotubes by oxygen plasma etch. A fabrication yield of ~72% is achieved. The authors present statistics of the transport properties of these devices, which indicates that all the CNTFETs share the same threshold voltage, and similar on-state conductance. These devices are then used to measure DNA conductance by connecting DNA molecule of varying lengths to lithographically cut CNTFETs. While one single carbon nanotube is considered 1-dimensional material because it only has one side with “non-nano” length, the thin-layer transition metal dichalcogenides (TMDCs) are called the 2-dimensional materials since they have two sides of normal lengths and the other side of atomic size. Atomically thin materials such as graphene and semiconducting transition metal dichalcogenides have attracted extensive interests in recent years, motivating investigation into multiple properties. We use a refined version of the optothermal Raman technique [2][3] to measure the thermal transport properties of two TMDC materials, MoS2 and MoSe2, in single-layer (1L) and bi-layer (2L) forms. This new version incorporates two crucial improvements over previous implementations. First, we utilize more direct measurements of the optical absorption of the suspended samples under study and find values ~40% lower than previously assumed. Second, by comparing the response of fully supported and suspended samples using different laser spot sizes, we are able to independently measure the interfacial thermal conductance to the substrate and the lateral thermal conductivity of the supported and suspended materials. The approach is validated by examining the response of a suspended film illuminated in different positions in radial direction. For 1L MoS2 and MoSe2, the room-temperature thermal conductivities are (80±17) W/mK and (55±18) W/mK, respectively. For 2L MoS2 and MoSe2, we obtain values of (73±25) W/mK and (39±13) W/mK. Crucially, the interfacial thermal conductance is found to be of order 0.1-1 MW/m2K, substantially smaller than previously assumed, a finding that has important implications for design and modeling of electronic devices.

A homogeneidade do solo em sistema de plantio direto, é um assunto questionável, pois alguns autores têm considerado que, com o passar do tempo, há aumento da homogeneidade do solo, outros têm verificado a redução. A hipótese deste trabalho é que em sistema de plantio direto consolidado existe correlação e dependência espacial dos atributos físicos-hídrico do solo e do desenvolvimento vegetativo da soja, sendo a cokrigagem colocalizada interpolador mais representativo destas correlações. O objetivo foi avaliar a variabilidade espacial de atributos físicos do solo e do desenvolvimento vegetativo da soja em sistema de plantio direto, adotado há mais de 19 anos. O trabalho foi desenvolvido na fazenda-escola da Universidade Estadual de Ponta Grossa - Paraná. A área de estudo tem como cultura a soja e está inserida em um relevo cuja declividade máxima, no sentido da pendente, é de aproximadamente 10 %. Nesta área, foram avaliados atributos físicos e hídrico do solo, como: densidade do solo (Ds), granulometria (areia e argila) e condutividade hidráulica saturada (Kfs). Avaliou-se, ainda, atributos de planta: altura da planta, estádio reprodutivo e stand. Para tais avaliações, foi demarcado um grid com espaçamento 10 x 10 metros, onde as avaliações foram realizadas em cada ponto. A análise dos dados foi efetuada por geoestatística, utilizando o pacote de programas GEOSTAT, para todas as variáveis que apresentaram dependência espacial. Foi obtido mapa de krigagem, e para todas as que apresentaram correlação, mapas de cokrigagem e cokrigagem colocalizada. A precisão de tais mapas foi obtida por meio dos menores valores de variância e a raiz quadrada do erro médio (RMSE). Verificou-se existência de dependência espacial na área em estudo, sendo a declividade um dos fatores responsáveis pela variação e o outro fator pode ser atribuído ao manejo uniforme adotado na área. Existiu correlação direta e positiva entre Kfs e areia e negativa com argila. Os atributos que influenciaram positivamente o desenvolvimento da planta foram a Kfs e, negativamente, a densidade do solo (Ds). Quanto aos métodos de estimação, o que obteve o mapa mais representativo da condição real, para a maioria das variáveis estudadas, foi a cokrigagem colocalizada. Apenas para a correlação argila x areia não houve ganho no uso da cokrigagem colocalizada, por isso, a cokrigagem ordinária foi a mais indicada. / The homogeneity of the soil in no-tilled system is being a highly controversial question, as some authors have claimed that there is an increasing in the soil homogeneity over time, while others have proven it to be reduced. The hypothesis is that in established no-tillage system is no correlation and spatial dependence of the physical-hydric soil properties and soybean vegetative development, cokriging-located interpolator being most representative of these correlations The objective was to evaluate the spatial variability of the soil physical attributes and soybean vegetative growth along 19-years of no-tillage system. The study was carried out at the farm-school from the Universidade Estadual de Ponta Grossa - Paraná. The area was cultivated with soybean in a topossequence with a maximum slope of10 %. In this area, were evaluated physical and hydrical soil properties, e.g. soil bulk density (Ds), soil texture (sand and clay) and saturated hydraulic conductivity (Kfs). It was also evaluated plant characteristics such as plant height, reproductive stage and standFor these assessments, it was delimited a 10 x 10 meters grid, where the assessments were carried out in each point. The data analysis was performed using a specific geostatistic software GEOSTAT, for all spatial-dependent variables. A kriging map was obtained from the results, and for all those correlated variables cokriging maps and cokriging-located have been also performed. The maps accuracy were achieved from the smallest values of variance and square root of the mean error (RMSE). The results indicated the existence of spatial dependence in the study area with the slope and soil management the mainly dependent factors, wherein in the latter the spatial variability is disregarded. Kfs was direct and positively correlated with sand, and a negatively with clay. The soil attribute that influenced positively the plant development was Kfs, whilst the bulk density (Ds) influenced negatively. With regard to the estimative methods, cokriging-located produced the most accurate and representative map of the real conditions for most of the variables. The low correlation between sandy and clay fractions makes the ordinary cokriging is being more appropiate than the cokriging-located.

Nous avons cherché à fournir une estimation précise de la conductivité électrique des tissus cérébraux humains en clinique, en utilisant une stimulation pulsée locale de faible intensité. Méthodes : À l'aide de l'approximation quasi-statique des équations de Maxwell, nous avons établi un modèle analytique du champ électrique généré par les électrodes intracérébrales stéréotaxiques-EEG (SEEG). Nous avons couplé ce modèle de champ électrique avec un modèle de l'interface électrode-électrolyte pour fournir une expression analytique explicite de la conductivité du tissu cérébral basée sur la réponse enregistrée du tissu cérébral à la stimulation. Résultats: Nous avons validé notre modèle biophysique en utilisant i) des solutions salines calibrées en conductivité électrique,ii) des tissus cérébraux de rat, et iii) des données électrophysiologiques enregistrées en clinique chez sept patients épileptiques au cours de la SEEG. Nous avons trouvé une possible corrélation entre la conductivité et le caractère épileptique du tissu. Conclusion: Cette nouvelle méthode basée sur un modèle offre une estimation rapide et fiable de la conductivité électrique des tissus cérébraux en tenant compte des contributions de l'interface électrode-électrolyte. Signification: Cette méthode surpasse les mesures standard de bioimpédance. L'application pour le diagnostic est envisagée puisque les valeurs de conductivité diffèrent fortement lorsqu'elles sont estimées dans le tissu cérébral sain versus hyperexcitable. / We aimed at providing an accurate estimation of human brain tissue electrical conductivity in clinico, using local, low-intensity pulsed stimulation. Methods: Using the quasi-static approximation of Maxwell equations, we derived an analytical model of the electric field generated by intracerebral stereotactic-EEG (SEEG) electrodes. We coupled this electric field model with a model of the electrode-electrolyte interface to provide an explicit, analytical expression of brain tissue conductivity based on the recorded brain tissue response to pulse stimulation. Results: We validated our biophysical model using: i) saline solutions calibrated in electrical conductivity, ii) rat brain tissue, and iii) electrophysiological data recorded in clinico from two epileptic patients during SEEG. Conclusion: This new model-based method offers a fast and reliable estimation of brain tissue electrical conductivity by accounting for contributions from the electrode-electrolyte interface. Significance: This method outperforms standard bioimpedance measurements since it provides absolute (as opposed to relative) changes in brain tissue conductivity. Application for diagnosis is envisioned since conductivity values strongly differ when estimated in the healthy vs. hyperexcitable brain tissue.

A pesquisa teve como objetivo estudar procedimentos para a condução dos testes de deterioração controlada, envelhecimento acelerado, condutividade elétrica e lixiviação de potássio, procurando-se verificar sua eficiência para identificação de diferentes níveis de vigor de lotes de sementes de melão (Cucumis melo L.). Para tanto, o estudo foi conduzido em duas etapas, utilizando-se cinco lotes de sementes dos híbridos AF-646 e AF-682. Na primeira foram realizados os testes de germinação, primeira contagem de germinação, Método Agroflora, emergência de plântulas em casa de vegetação e estudos específicos para os testes de deterioração controlada (graus de umidade de 18%, 21% e 24%, a 45ºC, durante 24 e 48 horas), de envelhecimento acelerado, com e sem solução salina (períodos 48, 72 e 96 horas, a 38ºC ou 41ºC), de condutividade elétrica (temperaturas de 20ºC, 25ºC e 30ºC, volumes de 50 e 75mL de água, 25 e 50 sementes e períodos de 1, 2, 4, 8, 12, 16, 20 e 24 horas) e de lixiviação de potássio (25 e 50 sementes, 50 e 75mL de água, a 25ºC e 30ºC, durante 30, 60, e 90 minutos, 2h, 2h e 30 minutos, 3, 4 e 5 horas). Os procedimentos considerados mais promissores para cada teste, nesta primeira fase, foram comparados na segunda etapa, que também incluiu os testes de germinação, primeira contagem de germinação, Método Agroflora e emergência de plântulas em casa de vegetação. Diante dos resultados obtidos, concluiu-se que os testes de deterioração controlada (24%/45ºC/24h) e de envelhecimento acelerado (procedimento tradicional e com solução salina), utilizando a combinação 41ºC/72h, apresentam sensibilidade suficiente para avaliação do potencial fisiológico de sementes de melão. O teste de condutividade elétrica não constitui em opção eficiente para avaliação do vigor das sementes, enquanto o teste de lixiviação de potássio necessita de estudos adicionais para adequar sua metodologia e viabilizar a sua utilização para sementes de melão, considerando-se, inclusive, os prováveis efeitos do genótipo. / This research was conducted to study and select procedures for the controlled deterioration, accelerate aging, electrical conductivity and potassium lixiviation tests, to verify their sensitivity to identify different vigor levels of melon (Cucumis melo L.) seed lots. Five seed lots each from the hybrids AF-646 and AF-682 were used. In the first experimental stage, the following tests were performed: germination, germination first count, Agroflora Method and seedling emergence. Specific studies were also conducted to the following tests: controlled deterioration (seed moisture content of 18%, 21% and 24%, at 45ºC, for 24 and 48 hours), traditional accelerated aging, saturated salt accelerated aging (for 48, 72 and 96 hours, at 38 o C or 41 o C), electrical conductivity (25 or 50 seeds imbibed in 50mL or 75mL water, 20 o C, 25 o C and 30 o C, for 1, 2, 4, 8, 12, 16 and 20 hours) and potassium leachate (25 or 50 seeds, imbibed in 50mL and 75mL, at 25 o C and 30 o C, for 30, 60, 90, 120, 150, 180, 240 and 300 minutes). The procedures considered the most promising for each test in the first stage were compared, in the second stage. The later stage also included germination, germination first count, Agroflora Method and seedling emergence tests. From the results, it was concluded that controlled deterioration (24%/45 o C/24h) and accelerate aging (traditional procedure and salt saturated) tests, using the 41 o C/72h combination, showed to be sufficiently sensitive for the evaluation of the physiological potential of melon seeds. The electrical conductivity test does not constitute an efficient option for the vigor evaluation, while the potassium lixiviation test needs further studies in order to adjust its methodology and enable its use for melon seeds, also considering the probable genotype effects.