Global ETD Search

1	Effective Properties of Li-ion Batteries Using a Homogenization Method With Focus on Electrical Conductivity Dhakal, Subash January 2018 (has links) Additives used in the cathode of a Lithium-ion (Li-ion) battery to improve electrical conductivity can negatively impact the ionic conductivity and specific capacity. Therefore, recent focus on the design of Li-ion battery is on the additive-free cathodes. This research work aims to provide a simple rule for the design of cathode microstructure using extensive study of the effect of particle size and volume fraction on effective electrical conductivity. Most design methods used to model the effective transport properties of lithium ion battery electrodes utilize the approximations based on Bruggeman’s formula. However, this formula does not consider the microstructure geometry and hence cannot accurately predict the effective transport properties of complicated microstructure like those of Li-ion battery electrodes. In this thesis, based on the principles of mathematical homogenization, an extensive analysis of randomly generated two-phase microstructures idealized for li-ion battery cells is carried out to obtain more accurate estimates of the effective electrical conductivity. To this end, a wide range of values of particle size, volume fraction and conductivity ratios are considered to evaluate the effective conductivity values. From these results, an explicit formulation based on these three parameters to predict the effective conductivity is provided to establish a framework for a simple design rule for additive-free cathode microstructures. Finally, the significance of the microstructural information is highlighted by studying the discharge characteristics of a battery for a theoretical battery model using the Brugemman’s formulation as well as the proposed formulation based on the mathematical homogenization technique. / Thesis / Master of Applied Science (MASc) Lithium ion Additive-free cathodes Bruggeman Homogenization
2	Characterization of gold black and its application in un-cooled infrared detectors Panjwani, Deep 01 January 2015 (has links) Gold black porous coatings were thermally evaporated in the chamber backfilled with inert gas pressure and their optical properties were studied in near-far-IR wavelengths. The porosities of coatings were found to be extremely high around ~ 99%. Different approaches of effective medium theories such as Maxwell-Garnett, Bruggeman, Landau-Lifshitz-Looyenga and Bergman Formalism were utilized to calculate refractive index (n) and extinction coefficient (k). The aging induced changes on electrical and optical properties were studied in regular laboratory conditions using transmission electron microscopy, Fourier transform infrared spectroscopy, and fore-probe electrical measurements. A significant decrease in electrical resistance in as deposited coating was found to be consistent with changes in the granular structure with aging at room temperature. Electrical relaxation model was applied to calculate structural relaxation time in the coatings prepared with different porosities. Interestingly, with aging, absorptance of the coatings improved, which is explained using conductivity form of Bergman Formulism. Underlying aim of this work was to utilize gold blacks to improve sensitivity in un-cooled IR sensors consist of pixel arrays. To achieve this, fragile gold blacks were patterned on sub-mm length scale areas using both stenciling and conventional photolithography. Infrared spectral imaging with sub-micron spatial resolution revealed the spatial distribution of absorption across the gold black patterns produced with both the methods. Initial experiments on VOx-Au bolometers showed that, gold black improved the responsivity by 42%. This work successfully establishes promising role of gold black coatings in commercial un-cooled infrared detectors. Gold black porous gold infrared detector infrared sensing effective medium theory bruggeman bergman theroy looyenga resistive bolometer vanadium oxide metal blacks aging in metal blacks Physics
3	Etude par spectroscopie infrarouge de l'électrodynamique du supraconducteur Pr2-xCexCuO4 et de la manganite La2/3 Ca1/3 Mn03 ZIMMERS, Alexandre 17 September 2004 (has links) (PDF) Nous présentons la dépendance en température de la réponse infrarouge-visible des plans ab de Pr2-xCexCuO4. Dans l'état normal, en variant le dopage de couches minces de x=0.11 (non-supraconductrice) à x=0.17 (supraconductrice surdopée), on observe l'ouverture d'un gap partiel jusqu'au dopage optimal x=0.15. Un modèle d'onde de densité de spin reproduit qualitativement des données. En extrapolant l'amplitude de ce gap, celui-ci s'annule pour x=0.17 indiquant la présence d'un point critique quantique ainsi que la coexistence de magnétisme et de supraconductivité. En dessous de Tc, pour x=0.15 et x=0.17, la modification des spectres optiques à des énergies inférieures à 2Delta=4.7kBTc est interprétée comme la signature de l'ouverture du gap supraconducteur. La réponse optique de La2/3Ca1/3MnO3 mesurée est analysée par un modèle de milieu effectif. L'absorption supplémentaire proche de la transition isolant/métal est interprétée comme la signature d'une percolation dans le système. infrarouge supraconducteur supraconducteur dopé aux électrons Pr2-xCexCuO4 PCCO manganite La2/3Ca1/3MnO3 La0.66Ca0.33MnO3 LCMO conductivité optique onde de densité de spin milieu effectif EMA Bruggeman inhomogénéité couche mince
4	Macroscopic and Microscopic surface features of Hydrogenated silicon thin films Pepenene, Refuoe Donald January 2018 (has links) Magister Scientiae - MSc (Physics) / An increasing energy demand and growing environmental concerns regarding the use of fossil fuels in South Africa has led to the challenge to explore cheap, alternative sources of energy. The generation of electricity from Photovoltaic (PV) devices such as solar cells is currently seen as a viable alternative source of clean energy. As such, crystalline, amorphous and nanocrystalline silicon thin films are expected to play increasingly important roles as economically viable materials for PV development. Despite the growing interest shown in these materials, challenges such as the partial understanding of standardized measurement protocols, and the relationship between the structure and optoelectronic properties still need to be overcome.
5	Surface Plasmons Polaritons and Single Dust Particles Cilwa, Katherine E. 20 July 2011 (has links) No description available. Atmospheric Chemistry Atmospheric Sciences Chemistry Condensed Matter Physics Environmental Education Environmental Geology Environmental Health Environmental Management Environmental Science Environmental Studies Geochemistry Mineralogy Molecular Physics surface plasmon surface plasmon polariton dispersion Mie scattering Lorentz Bruggeman micron particles particulate PM10 dust single particle interaction IR infrared mesh hole arrays extraordinary transmission hexagonal absorption

1

Page generated in 0.0263 seconds