Thèses sur le sujet « Chemical ABsorbent »
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1
Ellison, S. L. « The chemical evolution of QSO absorbers ». Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598835.
Texte intégralRésumé :
Using quasar absorption lines as a probe of the high redshift universe is a powerful tool in the field of chemical evolution. In this thesis, I consider the elemental abundances in absorbers that correspond to a variety of environments, ranging from high redshift galaxies to the low density intergalactic medium. I firstly address the question of abundances in intermediate redshift (zabs < 1.5) damped Lyα systems (DLAs), objects believed to correspond to the progenitors of present day massive galaxies. I present Hubble Space Telescope (HST) spectra of six intermediate redshift DLAs which have been supplemented with high resolution spectroscopy obtained with the high resolution echelle spectrograph (HIRES) on the Keck telescope. The chemical abundances of a range of elements are investigated and compared with local Galactic values in order to gain an insight into the metallicities, dust-to-gas ratios and star formation histories of these systems. The results from this work have inspired a new survey for DLAs based on a radio-selected sample of QSOs. The motivation for this endeavour has been to determine the extent to which our current view of distant galaxies is obscured by dust. I present intermediate resolution spectra obtained at the Anglo-Australian Telescope (AAT) from which DLAs may be identified. The number statistics of the newly discovered DLAs are analysed in order to determine whether obscuration by dust of background QSOs causes a significant observational bias. Finally, I consider the metallicity of the IGM by studying C IV systems associated with the Lyα forest at z ~ 3. The extent to which the IGM has been polluted with metals will provide important clues to the enrichment mechanism. I firstly investigate the column density distribution function of strong C IV absorbers associated with high column density Lyα clouds. This work is then extended to consider the C IV/H 1 ratio in low column density absorbers which are associated with physically less dense material. The spectra of two high redshift QSOs are analysed using two different techniques, both of which are critically assessed using synthetic spectra.
2
Grubbs, Laura Michelle Sprunger. « Characterization of Novel Solvents and Absorbents for Chemical Separations ». Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc67989/.
Texte intégralRésumé :
Predictive methods have been employed to characterize chemical separation mediums including solvents and absorbents. These studies included creating Abraham solvation parameter models for room-temperature ionic liquids (RTILs) utilizing novel ion-specific and group contribution methodologies, polydimethyl siloxane (PDMS) utilizing standard methodology, and the micelles cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS) utilizing a combined experimental setup methodology with indicator variables. These predictive models allows for the characterization of both standard and new chemicals for use in chemical separations including gas chromatography (GC), solid phase microextraction (SPME), and micellar electrokinetic chromatography (MEKC). Gas-to-RTIL and water-to-RTIL predictive models were created with a standard deviation of 0.112 and 0.139 log units, respectively, for the ion-specific model and with a standard deviation of 0.155 and 0.177 log units, respectively, for the group contribution fragment method. Enthalpy of solvation for solutes dissolved into ionic liquids predictive models were created with ion-specific coefficients to within standard deviations of 1.7 kJ/mol. These models allow for the characterization of studied ionic liquids as well as prediction of solute-solvent properties of previously unstudied ionic liquids. Predictive models were created for the logarithm of solute's gas-to-fiber sorption and water-to-fiber sorption coefficient for polydimethyl siloxane for wet and dry conditions. These models were created to standard deviations of 0.198 and 0.122 logunits for gas-to-PDMS wet and dry, respectively, as well as 0.164 and 0.134 log units for water-to-PDMS wet and dry, respectively. These models are particularly useful in solid phase microextraction separations. Micelles were studied to create predictive models of the measured micelle-water partition coefficient as well as models of measured MEKC chromatographic retention factors for CTAB and SDS. The resultant predictive models were created with standard deviations of 0.190 log units for the logarithm of the mole fraction concentration of water-to-CTAB, 0.171 log units for the combined logarithms of both the mole fraction concentration of water-to-CTAB and measured MEKC chromatographic retention factors for CTAB, and 0.153 log units for the combined logarithms of both the mole fraction concentration of water-to-SDS and measured MEKC chromatographic retention factors for SDS.
3
Tontiwachwuthikul, Paitoon. « New pilot plant technique for designing gas absorbers with chemical reactions ». Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/32182.
Texte intégralRésumé :
Gas absorption with chemical reaction is an important unit operation in the chemical and petroleum industries for the selective removal of components from industrial gas streams. Apart from choosing absorption media, the most difficult problems facing the design engineer are the sizing and performance prediction of the absorption tower due to the scarcity of fundamental design data, especially when novel absorption media and/or packings are used.
The solubility of carbon dioxide in 2 and 3 M solutions of 2-amino-2-methyl-1-propanol (AMP), which is a newly introduced absorbent, was determined at 20, 40, 60 and 80 °C and for CO₂ partial pressures ranging from approximately 1 to 100 kPa. The results were interpreted with a modified Kent-Eisenberg model which predicted the present and previous experimental results well. The absorption capacities of AMP and monoethanolamine (MEA) solutions were also compared.
Detailed concentration and temperature measurements were reported for the absorption of carbon dioxide from air into NaOH, MEA and AMP solutions. A full-length absorber (0.1 m ID, packed with 12.7 mm Berl Saddles up to heights of 6.55 m) was used. It was operated in countercurrent mode and at 30 to 75 % flooding velocities which are typical for gas
absorber operations. The following ranges of operating conditions were employed: superficial gas flow rate 11.1 to 14.8 mol/m² s; superficial liquid flow rate 9.5 to 13.5 m³/m² h; feed CO₂ concentration 11.5 to 19.8 %; total absorbent concentration 1.2 to 3.8 kmol/m³; liquid feed temperature 14 to 20 °C; total pressure 103 kPa. The measurements for the CO₂-NaOH and CO₂-MEA systems were compared with predictions from a previously developed mathematical model. Generally good agreement was obtained except at high CO₂ loadings of MEA solutions. Compared with MEA, AMP was found to have superior CO₂ absorption capacities and inferior mass transfer rates.
A new procedure, called the Pilot Plant Technique (PPT), for designing gas absorbers with chemical reactions has been developed. The PPT is primarily intended for designing absorbers for which fundamental design information is lacking. It is based on the premise that full-length absorption columns can be sized by making a minimum number of tests using a small-scale pilot plant. Two special features of the PPT are (i) the details of hydrodynamic parameters (i.e. mass transfer coefficients, effective interfacial area and liquid hold-up) and the physico-chemical information of the system (e.g. reaction mechanism, reaction rate constants) need not be known and (ii) complex calculations are avoided.
Using the PPT to size the height or to predict the performance of a given full-length absorber, the specific absorption rate, which is the essential information, can be measured directly using the pilot plant model (PPM) column if both columns have the same hydrodynamic conditions. This can be achieved by using the same type and size of packing in the PPM and the full-length columns and ensuring that the end and wall effects are negligible. The PPM column must also be operated at the same superficial fluid velocities as those of the full-length column. The specific absorption rate was then obtained from the gradient of the fluid composition profile along the PPM column. The validity of the PPT was demonstrated by determining the height and predicting the performance of the full-length column in which carbon dioxide was absorbed from air by aqueous solutions of NaOH and AMP at various operating conditions; good agreement was obtained.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
4
Trease, Claire Heather. « Design and development of novel absorber coating for solar collector applications ». Thesis, Kingston University, 2017. http://eprints.kingston.ac.uk/41036/.
Texte intégralRésumé :
Global average power consumption is 17 terawatts (10[to the power of]12W) and the rate of solar energy received at the Earth's surface is more than 120 petawatts (10[to the power of]15W). Therefore, the earth receives as much solar energy in one day as is used by the entire world in 20 years. Solar thermal collectors use absorber coatings and layers to convert incident radiation, via photothermal conversion, into useful energy i.e. heat. Re-radiation of this heat is minimised using a solar selective surface. Patterning non-thermal curing epoxy resins, in the micron scale, using electrohydrodynamic instability (EHD) patterning, could mitigate some of the challenges presented by other materials and methods used to produce these surfaces such as cost. Therefore, this was the objective of this study. As a contribution to the field of electrohydrodynamic instability patterning, the method of using this process to shape a thin, non-thermal curing epoxy resin film, was developed and the materials and equipment used are presented. Epoxy pillared surfaces, with pillar spcings from 3-200 [micrometres], were manufactured on silicon substrates using 30, 61 or 162 V and electrode gaps ranging from 3- 40 [micrometres]. A way of replicating the fabricated surfaces using moulding was also developed and is also described here. The patterned surfaces were replicated onto various substrates and were tested for their interaction with infrared (IR) radiation. In order to explore the range of versatility of theis technique for fabricating functional surfaces the structures surfaces were also tested as sustrates for tissue culture. To gain a better understanding and hence control over the use of electrohydrodynamic instability patterning with an epoxy resin, theories and numerical models of the process of electrohydrodynamic instability patterning were examined. Comparisons between predictions of results given by theory and our practical results are discussed since it was found that there was more disagreement between our results and theory when lower electric fields were being used. The studies of the interaction of the surfaces with IR radiation, and for use as tissue culture substrates, is also assessed and commented on. Lastly improvements that could be made and future work that could be undertaken is suggested.
5
Youh, Meng-Jey. « Development of microwave absorbing diamond coated fibres ». Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326038.
Texte intégral
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Hales, Joel McCajah. « CHEMICAL STRUCTURE - NONLINEAR OPTICAL PROPERTY RELATIONSHIPS FOR A SERIES OF TWO-PHOTON ABSORBING FLUORENE MOLECULES ». Doctoral diss., University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4403.
Texte intégralRésumé :
This dissertation reports on the investigation of two-photon absorption (2PA) in a series of fluorenyl molecules. Several current and emerging technologies exploit this optical nonlinearity including two-photon fluorescence imaging, three-dimensional microfabrication, site-specific photodynamic cancer therapy and biological caging studies. The two key features of this nonlinearity which make it an ideal candidate for the above applications are its quadratic dependence on the incident irradiance and the improved penetration into absorbing media that it affords. As a consequence of the burgeoning field which exploits 2PA, it is a goal to find materials that exhibit strong two-photon absorbing capabilities. Organic materials are promising candidates for 2PA applications because their material properties can be tailored through molecular engineering thereby facilitating optimization of their nonlinear optical properties. Fluorene derivatives are particularly interesting since they possess high photochemical stability for organic molecules and are generally strongly fluorescent. By systematically altering the structural properties in a series of fluorenyl molecules, we have determined how these changes affect their two-photon absorbing capabilities. This was accomplished through characterization of both the strength and location of their 2PA spectra. In order to ensure the validity of these results, three separate nonlinear characterization techniques were employed: two-photon fluorescence spectroscopy, white-light continuum pump-probe spectroscopy, and the Z-scan technique. In addition, full linear spectroscopic characterization was performed on these molecules along with supplementary quantum chemical calculations to obtain certain molecular properties that might impact the nonlinearity. Different designs in chemical architecture allowed investigation of the effects of symmetry, solvism, donor-acceptor strengths, conjugation length, and multi-branched geometries on the two-photon absorbing properties of these molecules. In addition, the means to enhance 2PA via intermediate state resonances was investigated. To provide plausible explanations for the experimentally observed trends, a conceptually simple three level model was employed. The subsequent correlations found between chemical structure and the linear and nonlinear optical properties of these molecules provided definitive conclusions on how to properly optimize their two-photon absorbing capabilities. The resulting large nonlinearities found in these molecules have already shown promise in a variety of the aforementioned applications.Ph.D.
Optics and Photonics
Optics and Photonics;
Optics
7
Gulston, Melanie Katharine. « The effects of the sunscreen chemicals Padimate-O and 2-ethylhexyl-P-methoxycinnamate on DNA ». Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301520.
Texte intégral
8
Boström, Tobias. « Solution-Chemically Derived Spectrally Selective Solar Absorbers : With System Perspectives on Solar Heating ». Doctoral thesis, Uppsala University, Department of Engineering Sciences, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7160.
Texte intégralRésumé :
This thesis consists of two parts, one dominating part concerning spectrally selective solar absorbers and one dealing with thermal solar systems. The appended papers I to VIII concern the solar absorber part, papers dealing with the systems part have not been included in the thesis.
A new spectrally selective absorber derived from a novel solution-chemistry method has been developed and optimized. The main objective was to investigate the potential of the spectrally selective surface. Some of the questions at issue were; would it be possible to create a suitable absorber composite using this method, how high selectivity could be obtained, could the performance be enhanced by using anti-reflection coatings, which was the optimal layer composition, would the thin films be durable and what was the structure and morphology like on a nano scale? The absorber consists of absorbing thin films of nickel nano-particles embedded in a dielectric matrix of alumina and an overlying anti-reflection film consisting of one of the following materials silica, hybrid-silica, alumina or silica-titania. Solution and sol-gel chemistry were used in the process. The thin films were spin-coated onto an aluminum substrate followed by a heat-treatment that generated the multi layer selective solar absorber.
The optical constants for the thin film materials in question were determined. An optimal three layer structure was modeled using the experimentally determined optical constants. The theoretical three layer stack was experimentally confirmed and achieved a solar absorptance of 0.97 and a thermal emittance of 0.05 which definitely are commercially competitive values. The configuration of the three layer stack is: an 80%nickel-20%alumina film at the base, a 40%nickel-60%alumina film in the middle and a silica or hybrid-silica film at the top. The three layer absorber was subjected to high temperature and condensation accelerated ageing tests designed by IEA Task 27. The condensation test did not degrade the absorber whatsoever but the high temperature test did reveal some oxidation of the nickel particles. The oxidation occurs initially and then stops. A formed nickel-oxide layer hinders further oxidation. The level of oxidation is small and the absorber is qualified according to the IEA Task 27 test procedure.
9
Schmidt, David Daniel. « Simulating aerosol formation and effects in NOx absorption in oxy-fired boiler gas processing units using Aspen Plus ». Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/15304.
Texte intégralRésumé :
Master of ScienceDepartment of Chemical Engineering
Larry Erickson
Oxy-fired boilers are receiving increasing focus as a potential response to reduced boiler emissions limits and greenhouse gas legislation. Among the challenges in cleaning boiler gas for sequestration is attaining the necessary purity of the CO[subscript]2. A key component in the oxy-fired cleaning path is high purity SO[subscript]x and NO[subscript]x removal, often through absorption using the lead-chamber or similar process. Aerosol formation has been found to be a source of product contamination in many flue gas absorption processes. A number of authors presented simulation methods to determine the formation of aerosols in gas absorption. But these methods are numerically challenging and not suitable for day-to-day analysis of live processes in the field. The goal of this study is to devise a simple and practical method to predict the potential for and effect of aerosol formation in gas absorption using information from Aspen Plus, a commonly used process simulation tool. The NO[subscript]x absorber in an oxy-fired boiler CO[subscript]2 purification system is used as a basis for this investigation. A comprehensive review of available data suitable for simulating NO[subscript]x absorption in an oxy-fired boiler slipstream is presented. Reaction rates for eight reactions in both liquid and vapor phases are covered. These are entered into an Aspen Plus simulation using a RadFrac block for both rate-based and equilibrium reactions. A detailed description of the simulation format is given. The resulting simulation was compared to a previously published simulation and process data with good agreement. An overall description of the aerosol formation mechanism is presented, along with an estimate of expected aerosol nuclei reaching the NO[subscript]x absorption process. A method to estimate aerosol quantities produced based on inlet gas nuclei concentration and available condensable water vapor is presented. To estimate aerosol composition and emissions, an exit gas slipstream is used to equilibrate with a pure water aerosol using an Aspen Plus Equilibrium Reactor block. Changing the composition of the initial aerosol feed liquid suggests that the location of aerosol formation may influence the final composition and emissions.
10
Unsworth, Christopher Adam. « The use of visible light absorbing bismuth-containing semiconductors as heterogeneous photocatalysts for selective chemical transformations ». Thesis, University of York, 2017. http://etheses.whiterose.ac.uk/19361/.
Texte intégralRésumé :
Bismuth-containing semiconducting materials were used as visible light absorbing heterogeneous photocatalysts for selective chemical transformations. The work demonstrates the importance of kinetic control in achieving selectivity; either through photocatalyst inhibition or through the presence of reagents capable of fast reactions with known intermediates. Bismuth oxide (β-Bi2O3), bismuth ferrite (BiFeO3), bismuth tungstate microflowers (Bi2WO6) and bismuth vanadate nanoparticles (nan-BiVO4) were synthesised and characterised by PXRD, SEM, DRUVS and BET. The bismuth-containing oxides were compared as photocatalysts for the aerobic oxidation of benzyl alcohol. The highest benzyl alcohol conversion (88%) and benzaldehyde selectivity (95%) was achieved with the use of nan-BiVO4. Further modifications to nan-BiVO4 resulted in materials that were less active for selective benzyl alcohol oxidation than unmodified nan-BiVO4. Further study of nan-BiVO4 as a heterogeneous photocatalysts for the selective oxidation of para-substituted benzyl alcohols was carried out. It was found that alcohol conversions and aldehyde selectivities were affected by by-product inhibition. The addition of 1 mol% 4-methoxybenzoic acid significantly reduced 4-methoxybenzyl alcohol conversion (to 49%). Isotopically labelled benzyl alcohols were used to show that α C-H bond cleavage was not rate limiting. However, changes in charge carrier lifetimes observed using TRPLS suggested that the charge carriers associated to the lifetimes observed were relevant to benzyl alcohol oxidation. Bismuth-containing semiconductors were also investigated as trifluoromethylation heterogeneous photocatalysts. Nan-BiVO4 was capable of oxytrifluoromethylation of styrene via the reduction of Umemoto’s reagents. The highly selective reaction produced the corresponding trifluoromethylated ketone in an 88% yield. Platinised bismuth tungstate (0.15-Pt-Bi2WO6) was found to give high conversions and product selectivities for the formation of Photo-Giese products (phenylacetic acid conversion = 99%, Photo-Giese product selectivity = 94%). Several coupling products were synthesised from different carboxylic acids and electron deficient alkenes. Competitive adsorption from by-products inhibition had an impact on acid conversions and Photo-Giese product selectivities.
11
Gu, Zipeng. « Emulsion Templated Polyimide Aerogel Foam and Hybrid Aerogel Foam as Absorbents for Oil Cleanup ». University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525711842824095.
Texte intégral
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Boström, Tobias. « Solution-chemically derived spectrally selective solar absorbers : with system perspectives on solar heating / ». Uppsala : Acta Universitatis Upsaliensis, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7160.
Texte intégral
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Böhm, Walter, et Kurt Hornik. « On Two-Periodic Random Walks with Boundaries ». Department of Statistics and Mathematics, WU Vienna University of Economics and Business, 2008. http://epub.wu.ac.at/936/1/document.pdf.
Texte intégralRésumé :
Two-periodic random walks are models for the one-dimensional motion of particles in which the jump probabilities depend on the parity of the currently occupied state. Such processes have interesting applications, for instance in chemical physics where they arise as embedded random walk of a special queueing problem. In this paper we discuss in some detail first passage time problems of two-periodic walks, the distribution of their maximum and the transition functions when the motion of the particle is restricted by one or two absorbing boundaries. As particular applications we show how our results can be used to derive the distribution of the busy period of a chemical queue and give an analysis of a somewhat weird coin tossing game.Series: Research Report Series / Department of Statistics and Mathematics
14
CAPELETI, FELIPE F. « Dosimetria em tomografia computadorizada e avaliação do perfil de dose empregando dosímetro fricke gel e a técnica de imageamento por ressonância magnética ». reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11789.
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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2014-11-10T10:43:39Z
No. of bitstreams: 0Made available in DSpace on 2014-11-10T10:43:39Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
15
Bullock, Elizabeth Raub. « Synthesis and Electrochemical Properties of {[(bpy)₂Ru(dpp)]₂RhCl₂}(PF₆)₅ : A Light Absorber - Electron Collector - Light Absorber Triad AND Development and Evaluation of Integrated Molecular Modeling, Synthesis, and Characterization Laboratory Experiments for the Undergraduate Chemistry Curriculum ». Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/28043.
Texte intégralRésumé :
The research detailed herein has been conducted in two different areas. The first research goal was to develop and study a supramolecular system coupling two light absorber units to a central metal site capable of collecting two electrons; this has been accomplished.
The complex {[(bpy)2Ru(dpp)]2RhCl2}(PF6)5 was synthesized and characterized using electrochemistry and electronic absorption spectroscopy. The electrochemical properties of {[(bpy)2Ru(dpp)]2RhCl₂}(PF6)5 were probed with cyclic voltammetry and bulk electrolysis studies to investigate the behavior of the system upon two-electron reduction of the rhodium metal center. Bulk electrolysis showed that the rhodium center underwent two-electron reduction. A water modulation of product distribution for the bulk electrolysis studies was found, and the nature of this process was studied. In the presence of water, two-electron reduction of the rhodium metal center afforded a RhI complex that had lost two chloride ligands: {[(bpy)2Ru(dpp)]2RhI}+5. In the absence of sufficient water, two-electron reduction yields a breakdown of the trimetallic resulting in [(bpy)2Ru(dpp)]+2 and {[(bpy)2Ru(dpp)]RhICl₂}+.
The second research goal was to develop integrated molecular modeling, synthesis, and characterization laboratory experiments, to incorporate into the undergraduate inorganic laboratory curriculum, and to evaluate and modify this curricular approach. This was accomplished with organometallic [Mo(CO)4(N-N)] complexes, where N-N is a bidentate nitrogen donor ligand. [Mo(CO)4(N-N)] complexes were selected because they were amendable to molecular modeling and could be synthesized via two synthetic routes with reasonable yields, low reaction times, and were air stable.
Many of these complexes are new, so a series of [Mo(CO)4(N-N)] complexes were synthesized by either thermal or photochemical substitution reactions. The systems were characterized using cyclic voltammetry, electronic absorption spectroscopy, and ¹H NMR spectroscopy.
Molecular modeling was performed on the series of [Mo(CO)4(N-N)] complexes using the CAChe software from Oxford Molecular, Ltd. These calculations typically provided reasonable structures, orbital locations, and relative orbital energies for the [Mo(CO)4(N-N)] systems.
Correlations between the computational and experimental data were established. The electronic absorption spectral MLCT frequency versus calculated HOMO-LUMO energy gap, Epa versus calculated HOMO energy, E1/2red versus calculated LUMO energy, and 1H NMR chemical shift for [Mo(CO)4(1,10-phen)] and the substituted [Mo(CO)4(1,10-phen)] complexes versus ZINDO calculated partial charge were compared, where 1,10-phen = 1,10-phenanthroline. From the analyses of physical versus computational data, it was concluded that molecular modeling results are useful in predicting physical data for these complexes.
The integrated molecular modeling, synthesis, and characterization experiment was developed and incorporated into the undergraduate inorganic chemistry laboratory. In both 1998 and 1999, a qualitative evaluation of student response was completed. This was done using a recorded interview technique; interviews were subsequently transcribed and rendered to extract themes. This interview style was an effective evaluation technique for this project, providing the detailed comments and student feedback that were desired. These interviews showed that the majority of the students both enjoyed this experiment and felt that the exposure to molecular modeling was worthwhile within this type of integrated lab forum. The students felt this experiment aided in their understanding of the orbital properties of inorganic systems. Student comments and suggestions facilitated modifications for future offerings in 1999 and 2000. Continued evaluation and expansion of this curricular approach are in progress.Ph. D.
16
Largeteau, Alain. « Elaboration, caractérisation et modélisation de céramiques magnetodiélectriques à couches d'arrêt ». Phd thesis, Université Sciences et Technologies - Bordeaux I, 1990. http://tel.archives-ouvertes.fr/tel-00173432.
Texte intégralRésumé :
Des céramiques ferrites à couches d'ârret de type spinelle et hautement densifiées ont été élaborées. Si les propriétés diélectriques varient fortement selon les conditions d' élaboration, les propriétés magnétiques sont au contraire peu altérées. Des relaxations diélectrique et d'impedance ont été mises en évidence, elles ont été modélisées; leurs caractéristiques ont été déterminées en fonction de la composition des grains et des paramètres de préparation des échantillons.
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Shah, Ali, Petri Stenberg, Lasse Karvonen, Rizwan Ali, Seppo Honkanen, Harri Lipsanen, N. Peyghambarian, Markku Kuittinen, Yuri Svirko et Tommi Kaplas. « Pyrolytic carbon coated black silicon ». NATURE PUBLISHING GROUP, 2016. http://hdl.handle.net/10150/614762.
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Carbon is the most well-known black material in the history of man. Throughout the centuries, carbon has been used as a black material for paintings, camouflage, and optics. Although, the techniques to make other black surfaces have evolved and become more sophisticated with time, carbon still remains one of the best black materials. Another well-known black surface is black silicon, reflecting less than 0.5% of incident light in visible spectral range but becomes a highly reflecting surface in wavelengths above 1000 nm. On the other hand, carbon absorbs at those and longer wavelengths. Thus, it is possible to combine black silicon with carbon to create an artificial material with very low reflectivity over a wide spectral range. Here we report our results on coating conformally black silicon substrate with amorphous pyrolytic carbon. We present a superior black surface with reflectance of light less than 0.5% in the spectral range of 350 nm to 2000 nm.
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Hettiarachchi, Chaminda Lakmal. « Organometal Halide Perovskite Solar Absorbers and Ferroelectric Nanocomposites for Harvesting Solar Energy ». Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/7034.
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Organometal halide perovskite absorbers such as methylammonium lead iodide chloride (CH3NH3PbI3-xClx), have emerged as an exciting new material family for photovoltaics due to its appealing features that include suitable direct bandgap with intense light absorbance, band gap tunability, ultra-fast charge carrier generation, slow electron-hole recombination rates, long electron and hole diffusion lengths, microsecond-long balanced carrier mobilities, and ambipolarity. The standard method of preparing CH3NH3PbI3-xClx perovskite precursors is a tedious process involving multiple synthesis steps and, the chemicals being used (hydroiodic acid and methylamine) are quite expensive. This work describes a novel, single-step, simple, and cost-effective solution approach to prepare CH3NH3PbI3-xClx thin films by the direct reaction of the commercially available CH3NH3Cl (or MACl) and PbI2. A detailed analysis of the structural and optical properties of CH3NH3PbI3-xClx thin films deposited by aerosol assisted chemical vapor deposition is presented. Optimum growth conditions have been identified. It is shown that the deposited thin films are highly crystalline with intense optical absorbance.
Charge carrier separation of these thin films can be enhanced by establishing a local internal electric field that can reduce electron-hole recombination resulting in increased photo current. The intrinsic ferroelectricity in nanoparticles of Barium Titanate (BaTiO3 -BTO) embedded in the solar absorber can generate such an internal field. A hybrid structure of CH3NH3PbI3-xClx perovskite and ferroelectric BTO nanocomposite FTO/TiO2/CH3NH3PbI3-xClx: BTO/P3HT/Cu as a new type of photovoltaic device is investigated. Aerosol assisted chemical vapor deposition process that is scalable to large-scale manufacturing was used for the growth of the multilayer structure. TiO2 and P3HT with additives were used as ETL and HTL respectively. The growth process of the solar absorber layer includes the nebulization of a mixture of PbI2 and CH3NH3Cl perovskite precursors and BTO nanoparticles dissolved in DMF, and injection of the aerosol into the growth chamber and subsequent deposition on TiO2. While high percentage of BTO in the film increases the carrier separation, it also leads to reduced carrier generation. A model was developed to guide the optimum BTO nanoparticle concentration in the nanocomposite films. Characterization of perovskite solar cells indicated that ferroelectric polarization of BTO nanoparticles leads to the increase of the width of depletion regions in the perovskite layer hence the photo current was increased by one order of magnitude after poling the devices. The ferroelectric polarization of BTO nanoparticles within the perovskite solar absorber provides a new perspective for tailoring the working mechanism and photovoltaic performance of perovskite solar cells.
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Čajágiová, Martina. « Odolnosť ľudského pachu voči chemickým detergentom ». Master's thesis, Česká zemědělská univerzita v Praze, 2016. http://www.nusl.cz/ntk/nusl-260847.
Texte intégralRésumé :
In the recherche part of our thesis we familiarize ourselves with the human odor, theories of its origin, definition, anatomy of human skin and odors, composition of individual human odors and with odor secretion. We also look closer on the topics of odor absorbent and its use in the world, the transmission of odors to odor sensors and securing of scents. This section of our thesis discusses the resistance and survival abilities of odor, scent identification method and its history, organic acids, and defines the application of laundry detergents and ultrasonic washers. Aim of our thesis was to verify the relevance of the use of chemical detergents in the purification process when working with scents. We tried to verify the ability of detergents to degrade the human scent on odor absorbents to such an extent, that specially trained dogs would not be able to identify it. Our experiment was following a precise determination methodology. In the first phase samples were collected from the hands of targeted persons to a scent carrier - a metal cylinder (extirpate odour), by one researcher. In the second phase samples were collected from the body to a textile carrier, by another researcher. The metal scent carriers were processed. Some of them were left as they were (control sample) and some were exposed to chemical detergents with and without usage of an ultrasonic washer.
In the experiment where we tried to identify the odour samples, six bitches of German shepherd were used. They were specially trained for odour identification. Each dog was let three times to identify the target scent exposed to a detergent and three times to identify the target scent not exposed to a detergent. Target smell was randomly deposited between other samples and its position was changed, so that the handler did not know its position and thus was unable to affect the work of his dog. The indicator of positive identification was a sign the dogs were taught - to sit or lay in front of a sample.
Any dog was unable to identify the scent which was exposed to chemical detergent and all dogs identify the scent unexposed to a chemical detergent. Our experiment has shown that the use of chemical detergents in the purification process when working with scents is relevant to the degradation of individual human scent.
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Dai, Letian. « Silicon nanowire solar cells with μc-Si˸H absorbers for tandem radial junction devices ». Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS303.
Texte intégralRésumé :
Dans cette thèse, nous avons fabriqué des cellules solaires à jonction radiale en nanofils de silicium avec du silicium microcristallin hydrogéné (µc-Si:H) comme absorbeur, par dépôt chimique en phase vapeur assisté par plasma à basse température (PECVD). Pour contrôler la densité de nanofils sur les substrats, nous avons utilisé des nanoparticules (NP) de dioxyde d'étain (SnO₂) d'un diamètre moyen de 55 nm, disponibles dans le commerce, comme précurseur du catalyseur Sn pour la croissance des nanofils de silicium. La distribution des nanoparticules de SnO₂ sur le substrat a été contrôlée par centrifugation et dilution du colloïde de SnO₂, en combinaison avec la fonctionnalisation du substrat. Par la suite, le SnO₂ est réduit en Sn métallique après le traitement par plasma de H₂, suivi de la croissance, par la technique vapeur-liquide-solide (VLS) assistée par plasma, de nanofils de Si sur lesquels sont déposées les couches P, I et N constituant les cellules solaires à jonction radiale. Nous avons atteint un taux de croissance élevé des nanofils de Si, jusqu'à 70%, avec une très large gamme de densité, de 10⁶ à 10⁹ /cm². Comme approche supplémentaire de contrôle de la densité des nanofils, nous avons utilisé du Sn évaporé comme précurseur du catalyseur Sn. Nous avons étudié l'effet de l'épaisseur de Sn évaporé, l'effet de la durée du traitement au plasma de H₂ et l'effet du débit de gaz H₂ dans le dans le mélange de précurseurs, sur la densité des nanofils. L'ellipsométrie spectroscopique in-situ (SE) a été utilisée pour contrôler la croissance des nanofils et le dépôt des couches de µc-Si:H sur les SiNWs. En combinant les résultats de in-situ SE et de microscopie électronique à balayage, une relation entre l'intensité du signal de SE pendant la croissance et la longueur et la densité des nanofils a été démontrée, ce qui permet d'estimer ces paramètres en cours de croissance. Nous avons réalisé une étude systématique des matériaux (couches intrinsèques et dopées de type n ou p de µc-Si:H, couches dopées d'oxyde de silicium microcristallin hydrogéné, µcSiOx:H) et des cellules solaires obtenues dans deux réacteurs à plasma appelés "PLASFIL" et "ARCAM". Les épaisseurs de revêtement sur substrat lisse et sur les nanofils ont été déterminées et nous avons obtenu une relation linéaire entre les deux, ce qui permet de concevoir un revêtement conforme sur les nanofils pour chaque couche avec une épaisseur optimale. Les paramètres des nanofils et des matériaux, affectant la performance des cellules solaires à jonction radiale, ont été systématiquement étudiés, les principaux étant la longueur et la densité des nanofils, l'épaisseur de la couche intrinsèque de µc-Si:H, l'utilisation de µc-SiOx:H et le réflecteur arrière en Ag. Enfin, avec les cellules solaires à jonction radiale en nanofils de silicium optimisées utilisant le µc-Si:H comme absorbeur, nous avons atteint un rendement de conversion de l'énergie de 4,13 % avec Voc = 0,41 V, Jsc = 14,4 mA/cm² et FF = 69,7%. Cette performance est supérieure de plus de 40 % à l'efficacité record de 2,9 % publiée précédemmentIn this thesis, we have fabricated silicon nanowire (SiNW) radial junction solar cells with hydrogenated microcrystalline silicon (μc-Si:H) as the absorber via low-temperature plasma-enhanced chemical vapor deposition (PECVD). To control the density of NW on the substrates, we have used commercially available tin dioxide (SnO₂) nanoparticles (NPs) with an average diameter of 55 nm as the precursor of Sn catalyst for the growth of SiNWs. The distribution of SnO₂ NPs on the substrate has been controlled by centrifugation and the dilution of the SnO₂ colloid, combined with the functionalization of the substrate. Subsequently, SnO₂ is reduced to metallic Sn after the H₂ plasma treatment, followed by the plasma-assisted vapor-liquid-solid (VLS) growth of SiNWs upon which the P, I and N layers constituting the radial junction solar cells are deposited. We have achieved a high yield growth of SiNWs up to 70% with a very wide range of NW density, from 10⁶ to 10⁹ /cm². As an additional approach of controlling the density of SiNWs we have used evaporated Sn as the precursor of Sn catalyst. We have studied the effect of the thickness of evaporated Sn, the effect of duration of H₂ plasma treatment and the effect of H₂ gas flow rate in the plasma, on the density of SiNWs.In-situ spectroscopic ellipsometry (SE) was used for monitoring the growth of SiNWs and the deposition of the layers of μc-Si:H on SiNWs. Combining in-situ SE and SEM results, a relationship between the intensity of SE signal and the length and the density of SiNWs during the growth was demonstrated, which allows to estimate the density and the length of SiNWs during the growth. We have carried out a systematic study of materials (intrinsic, p-type,n-type µc-Si:H and µcSiOx:H doped layers) and solar cells obtained in two plasma reactors named “PLASFIL” and “ARCAM”. The thicknesses of coating on the flat substrate and on the SiNWs have been determined with a linear relation which helps to design a conformal coating on SiNWs for each layer with an optimal thickness. The parameters of the SiNWs and the materials, affecting the performance of radial junction solar cells, have been systematically studied, the main ones being the length and the density of SiNWs, the thickness of intrinsic layer of μc-Si:H on SiNWs, the use of the hydrogenated microcrystalline silicon oxide (μc-SiOx:H) and the back reflector Ag. Finally, with the optimized silicon nanowire radial junction solar cells using the μc-Si:H as the absorber we have achieved an energy conversion efficiency of 4.13 % with Voc = 0.41 V, Jsc = 14.4 mA/cm² and FF = 69.7%. This performance is more than 40 % better than the previous published record efficiency of 2.9 %
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Buffet, Noémie. « ROPYRENEQUINONES vers des cristaux liquides colonnaires fortement absorbants, de type accepteur pour cellules photovoltaïques ». Phd thesis, Université Sciences et Technologies - Bordeaux I, 2008. http://tel.archives-ouvertes.fr/tel-00585321.
Texte intégralRésumé :
Au cours de cette thèse, j'ai mis au point et validé une voie de synthèse inédite donnant accès à une nouvelle famille de chromophores oligo-péri-naphtyléniques. Notre approche repose sur le couplage de deux briques facilement synthétisables (l'une centrale, l'autre terminale), puis sur une réaction de cyclodéshydrogénation multiple en milieu fortement basique. Aisément fonctionnalisés ensuite par estérification à leurs extrémités, ces colorants présentent un comportement cristallin liquide. Nous avons ainsi réussi à élaborer des cristaux liquides colonnaires absorbant fortement les grandes longueurs d'onde de la lumière visible tout en présentant leur mésophase à température ambiante.
22
Lundstedt, Evert. « Adsorption av Sb på zeolit ». Thesis, Växjö University, School of Technology and Design, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-1591.
Texte intégralRésumé :
Detta examensarbete är en förundersökning till Glafos undersökning angående rening av glasbrukens processvatten från antimon med zeolit.
Förundersökningen gick ut på att via experiment ta reda på hur mycket antimon som adsorberas av behandlad (för optimering: dels med NaNO3 och dels med NaCl) och obehandlad zeolit (porstorlek 0.4 nm). pH mättes och ställdes eftersom det har betydelse för adsorptionen, åtminstone vid väldigt lågt pH. När lösningarna hade filtrerats mättes den kvarvarande antimonhalten med atomabsorptionsspektrofotometri. Mätningarna visade att i genomsnitt 53 % av Sb-halten i lösningarna hade adsorberats av zeoliten. Förundersökningen visade att det inte blir någon adsorption då pH är väldigt lågt (under 1). Den visade också att när pH är över 4 verkar det inte ha någon betydelse om zeoliten är behandlad eller inte.
Zeoliten bör behandlas med NaCl först i en tank med omrörning, sedan blandas i processvattnet (vars pH justerats till pH 4) i en tank eller bassäng och därefter filtreras.
Tidsfaktorn för hur lång tid det tar för zeoliten att nå jämvikt och temperaturens inverkan bör även undersökas.
The aim of this diploma work is to study the removal of antimony from glassworks process water using zeolites.
The experimental part of the studies were carried out to find the quantity of antimony adsorbed by the zeolite. The studies included treated (for optimization: partly with NaNO3 and partly with NaCl) and untreated zeolite. The pore size is 0.4 nm. pH was measured and adjusted because it is important for the antimony adsorption. When the solutions were filtrated the content of antimony left was measured with atomic absorption spectrophotometry. The measurements showed an average uptake of antimony by the zeolite of 53 %.The preinvestigation indicates that with a very low pH (below 1) there is no antimony adsorption. It also indicates that with pH above 4 it does not matter if the zeolite are treated or not.
In further investigations the zeolite should be treated with NaCl in a stirred tank, then be mixed in the process water (pH is set to 4) in a tank or basin and then be filtrated.
The time to reach equilibrium and the influence of temperature should also be investigated.
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Lindström, Frida. « Chemical and physical changes in PET fibres due to exhaust dyeing : Issues in thermo-mechanical recycling of dyed PET textiles ». Thesis, Högskolan i Borås, Akademin för textil, teknik och ekonomi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-14772.
Texte intégralRésumé :
Polyethylene terephthalate (PET) is the most used fibre in the textile industry. PET is also used in other products, e.g. soft-drink bottles and food packaging. Approximately 60% of the globally produced PET is intended for production of textile fibres and the demand for polyester fibres have steadily increased over the last decade. Yet, most of the recycled PET fibres are produced from discarded bottles and not discarded textiles even though the generation of textile waste is increasing year by year. The importance of finding efficient recycling routes for discarded PET textiles is obvious. In thermo-mechanical recycling the thermoplastic characteristic of PET is utilized to re-melt and re-form PET waste into new valuable products. Today, this is used for bottle-to-fibre recycling but not for fibre-to-fibre recycling. The main research question asked in this Master thesis is if the process of exhaust dyeing compromise the possibility to recycle PET textiles through remelt spinning. It is believed that PET degradation through hydrolysis may occur during dyeing. The degradation behaviour of PET has been widely studied. However, degradation during exhaust dyeing has not been investigated. The process parameters temperature, time and number of dyeing cycles have been investigated. Also, possible effects of different auxiliary chemicals have been studied. Dyeing and characterisation of two PET fabrics with filaments of different titer was performed in order to investigate if the filament titer is also a parameter to consider. Tensile testing and surface characterisation through demand absorbency test showed that the filament titer seems to affect how the tensile and moisture related properties change due to dyeing. Differential scanning calorimetry showed that the crystallisation rate is affected by the dyeing process. This can be an effect of formation of shorter PET chains during dyeing. The auxiliary chemicals have been shown to be the most critical factor in changes of the crystallisation behaviour. Fourier-Transform infrared spectroscopy indicated that chain scission has occurred during dyeing. The results have shown that the exhaust dyeing process causes changes in tensile properties, moisture related properties, degree of crystallinity as well as crystallisation behaviour. DSC and FTIR results indicate chain scission. Based on the results it cannot be concluded if the changes are large enough to compromise the possibility to recycle PET textiles thermo-mechanically. Further research is required in order to correlate the observed changes with possible problems in thermomechanical recycling of dyed PET textiles.
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Sobhani, Negin. « Applications, performance analysis, and optimization of weather and air quality models ». Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5996.
Texte intégralRésumé :
Atmospheric particulate matter (PM) is linked to various adverse environmental and health impacts. PM in the atmosphere reduces visibility, alters precipitation patterns by acting as cloud condensation nuclei (CCN), and changes the Earth’s radiative balance by absorbing or scattering solar radiation in the atmosphere. The long-range transport of pollutants leads to increase in PM concentrations even in remote locations such as polar regions and mountain ranges. One significant effect of PM on the earth’s climate occurs while light absorbing PM, such as Black Carbon (BC), deposits over snow. In the Arctic, BC deposition on highly reflective surfaces (e.g. glaciers and sea ices) has very intense effects, causing snow to melt more quickly. Thus, characterizing PM sources, identifying long-range transport pathways, and quantifying the climate impacts of PM are crucial in order to inform emission abatement policies for reducing both health and environmental impacts of PM.
Chemical transport models provide mathematical tools for better understanding atmospheric system including chemical and particle transport, pollution diffusion, and deposition. The technological and computational advances in the past decades allow higher resolution air quality and weather forecast simulations with more accurate representations of physical and chemical mechanisms of the atmosphere.
Due to the significant role of air pollutants on public health and environment, several countries and cities perform air quality forecasts for warning the population about the future air pollution events and taking local preventive measures such as traffic regulations to minimize the impacts of the forecasted episode. However, the costs associated with the complex air quality forecast models especially for simulations with higher resolution simulations make “forecasting” a challenge. This dissertation also focuses on applications, performance analysis, and optimization of meteorology and air quality modeling forecasting models.
This dissertation presents several modeling studies with various scales to better understand transport of aerosols from different geographical sources and economic sectors (i.e. transportation, residential, industry, biomass burning, and power) and quantify their climate impacts. The simulations are evaluated using various observations including ground site measurements, field campaigns, and satellite data.
The sector-based modeling studies elucidated the importance of various economical sector and geographical regions on global air quality and the climatic impacts associated with BC. This dissertation provides the policy makers with some implications to inform emission mitigation policies in order to target source sectors and regions with highest impacts. Furthermore, advances were made to better understand the impacts of light absorbing particles on climate and surface albedo.
Finally, for improving the modeling speed, the performances of the models are analyzed, and optimizations were proposed for improving the computational efficiencies of the models. Theses optimizations show a significant improvement in the performance of Weather Research and Forecasting (WRF) and WRF-Chem models. The modified codes were validated and incorporated back into the WRF source code to benefit all WRF users. Although weather and air quality models are shown to be an excellent means for forecasting applications both for local and hemispheric scale, further studies are needed to optimize the models and improve the performance of the simulations.
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Goubin, Fabrice. « RELATION ENTRE FONCTION DIÉLECTRIQUE ET PROPRIÉTÉS OPTIQUES : APPLICATION À LA RECHERCHE D'ABSORBEURS UV INORGANIQUES DE DEUXIÈME GÉNÉRATION ». Phd thesis, Université de Nantes, 2003. http://tel.archives-ouvertes.fr/tel-00003749.
Texte intégralRésumé :
La thèse traite de la synthèse et de la caractérisation d'absorbeurs UV inorganiques de deuxième génération. L'analyse de leurs propriétés optiques est effectuée au moyen de la spectroscopie de pertes d'énergie (EELS) et de calculs de la fonction diélectrique par DFT. Cette démarche est appliquée à l'étude de borates de cérium III, d'oxydes de cérium IV, d'oxiphosphates, silicates et oxisilicates de titane et des solutions solides A3PMo(12-x)WxO40 (A = Na, K, Rb). L'étude des borates montre que l'intensité de la transition Ce4f-5d est d'un ordre de grandeur inférieure à celle d'un transfert de charge anion-cation, la rendant inefficace pour l'application absorbeur UV. Pour les autres composés, l'étude qualitative et quantitative du transfert de charge oxygène-métal (ou lanthanide) permet de mettre en exergue le rôle primordial de la coordinence des éléments impliqués dans le processus d'absorption, et de la covalence de la liaison oxygène-métal (ou lanthanide), sur la position du seuil d'absorption, l'intensité de la transition et, par conséquent, l'indice de réfraction. Par ailleurs, K3PMo12O40, matériau contenant des entités discrètes de type ion de Keggin, présente des propriétés optiques (coefficients Lab) tout à fait comparable à celles des pigments jaunes commerciaux. L'utilisation des solutions solides molybdène-tungstène, permet de faire varier le seuil d'absorption entre 2,5 et 3,2 eV, et de réduire la réductibilité du composé.
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Elias, Jamil. « Réseaux de nanofils et de nanotubes d'oxyde de zinc de dimensions contrôlées obtenus par voie électrochimique : application aux cellules solaires nanostructurées ». Phd thesis, Université Paris-Est, 2008. http://tel.archives-ouvertes.fr/tel-00461690.
Texte intégralRésumé :
Le but de cette thèse a été de fabriquer des réseaux de nanofils et de nanotubes de l'oxyde de zinc (ZnO) de dimensions contrôlées en utilisant la méthode de réduction électrochimique de l'oxygène moléculaire. Plusieurs approches concernant le contrôle des dimensions de ces nanofils ont été investiguées. Des réseaux formés de nanofils de ZnO ont été obtenus dans une large gamme de diamètre (25-500 nm), de longueur (0,25-10 µm) et de densité (1x108-8x109 nanofils/cm2). Après l'étude du mécanisme de formation des nanofils, nous avons proposé une nouvelle méthode pour obtenir des réseaux de nanotubes de ZnO par dissolution des coeurs des nanofils. Les dimensions des réseaux de nanotubes ont été contrôlées en contrôlant celles des nanofils lors de la première étape d'électrodépôt. Nous avons aussi montré que les épaisseurs des parois de ces nanotubes peuvent aisément être contrôlées par l'ajout d'une troisième étape d'électrodépôt. Les propriétés optiques, électriques et structurales des nanofils et des nanotubes de différentes dimensions, obtenus avec différents conditions de dépôt ont été étudiées dans cette thèse. Finalement, des cellules ETA, constituées de ZnO/CdSe/CuSCN, ont été étudiées en utilisant les réseaux obtenus. Les effets de la morphologie et des dimensions des nanofils et nanotubes sur la diffusion de la lumière et la performance électronique des dispositifs ont été étudiés. Cela nous a permis de mieux comprendre les mécanismes optiques et électroniques impliqués dans ce type de cellule solaire ouvrant de nombreuses possibilités pour améliorer leur performance
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Wünsche, Dominik. « Diagnostika a hodnocení mostní konstrukce ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2021. http://www.nusl.cz/ntk/nusl-433535.
Texte intégralRésumé :
The diploma thesis deals with the issue of bridge strustures, especially their diagnostics and evaluation. The work consists of two parts, theoretical and practical. The theoretical part deals with the basic description and division of bridge structures, brigde inspections and test methods, especially those that were used in the thesis during bridge inspections. The practical part includes a visual inspection of two bridges, their description, detection of faults and defects and their documentation. In the practical part, the basic maretial characteristics of concrete bridges were determined, the condition of structures was assessed and a proposal for the elimination of failures and defects was developed. In the end, the work deals with the evaluation of both bridges.
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STRUBE, ROBERT. « Solutions for CO2 capturefrom coal-fired power plants - Influence on plant performanceand environmental impact ». Doctoral thesis, 2009. http://hdl.handle.net/2158/599203.
Texte intégral
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Lyambila, Waudo. « A study of photoinduced transformations of sunscreen chemical absorbers ». Thesis, 2009. http://hdl.handle.net/10413/8306.
Texte intégralRésumé :
Solar ultraviolet radiation is known to have deleterious effects on human skin and is a
major cause of skin cancer. Therefore, the topical application of sunscreen preparations
has gained wide usage for skin protection. These preparations typically contain a
variety of chemical absorbers that absorb ultraviolet (UV) radiation and physical
blockers that scatter, absorb and reflect UV light. The efficacy of sunscreens can be
estimated by the Sun Protection Factor (SPF) which depends on the UV filters present
in the formulations. However, although some of these commercial sunscreens have
beneficial effects, they can also have undesirable results. It is known that the sunscreens
undergo electronic excitation when exposed to UV light which may make them
susceptible to photochemical modification. The production of reactive intermediates
(e.g. free radicals) and stable photoproducts, either due to photoisomerisation or
photofragmentation is a major concern because these species may be toxic and may lead
to a reduction in efficacy. Hence a study of the photochemistry of these chemical
absorbers found in commercial sunscreens is of great importance.
Photostability and broad-spectrum studies of some Australian commercial sunscreen
products were undertaken by means of spectrophotometric and chromatographic
methods. The sunscreen products dissolved in methanol solutions were irradiated using
simulated solar radiation. High performance liquid chromatography (HPLC) was used
to identify and quantify the active chemical ingredients. UV spectrophotometry was
used to monitor the spectral absorbance before and after UV exposure of the
formulations. Our results show that some of the evaluated photoactive chemical
absorbers currently used in sunscreens are unstable upon UV radiation. This was mainly
due to either photoisomerisation and/or photofragmentation of some active chemical
ingredients.
An examination of the photochemistry of 2-ethylhexyl-p-methoxycinnamate (2-
EHMC), an ultraviolet B absorber that was found in all the suncare products
investigated in this study was undertaken. Irradiation of dilute (~ 10-6 M) solutions of
EHMC with wavelengths of light greater than 300 nm results in trans - cis
photoisomerisation leading to a photostationary equilibrium mixture. However, pure or
concentrated solutions of 2-EHMC upon prolonged irradiation showed additional
photoproducts. These were isolated by preparative high performance liquid
chromatography (HPLC) and characterised by nuclear magnetic resonance (1H NMR)
spectroscopy, which was used to identify them as [2 +2] cycloadducts of 2-EHMC.
There are 13 possible dimers formed via a [2+2] cycloaddition reaction mechanism
across the ethylenic double bond, however only the stable and energetically favoured
isomers were isolated.
In addition, ab initio molecular orbital calculations have been used to investigate the
structures and the transition states of the various dimers resulting from the cycloaddition
reactions. Geometry optimizations and energy calculations were performed with the
Gaussian 98 program, using the B3LYP density functional and 6-31+G (d) basis set.
GaussView was used to visualize the transition state structures. The theoretical
calculations predicted the most stable dimer forms. The trans-trans configuration at the
cyclobutane ring of the 2-EHMC adduct gave relatively more stable photoproducts. The
theoretical results have been confirmed by HPLC isolation experiments, which together
with the UV spectra of the different products; verify the presence of the different
conformers of 2-EHMC.Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2009.
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Prithipal, Rasmika. « Selective production of difluorodimethyl ether from chlorodifluoromethane - a kinetic study using a well-mixed batch absorber ». Thesis, 2013. http://hdl.handle.net/10413/8868.
Texte intégralRésumé :
The gas-liquid reaction between chlorodifluoromethane (R-22) and methanol, in the presence of
sodium hydroxide, was investigated in an isothermal, stirred, semi-batch reactor. The objective of
the study was to develop a model for the reaction and to identify the kinetic parameters. Reactor
temperature was varied from 283 to 303 K, with inlet R-22 partial pressures between 40.5 and 60.8
kPa (absolute). Solutions containing sodium hydroxide concentrations of between 1.5 and 2.5
mol·dm-3 were charged into the reactor prior to each experiment. Preliminary investigations using
the R-22-methanol system revealed that stainless steel was an inappropriate choice of material for
the reactor as it displayed catalytic tendencies toward trimethyl orthoformate formation.
Consequently, the reactor was constructed from glass and was equipped with an internal cooling
coil, a single heating jacket and a temperature control unit. Liquid samples that were withdrawn
from the reactor were degassed under vacuum to remove residual chlorodifluoromethane, and
thereby inhibit further reaction. Spectrophotometry was used to analyze the liquid samples to
determine the concentration of chloride ions in solution. The products obtained were
difluorodimethyl ether (major product) and trimethyl orthoformate (by-product) as well as sodium
chloride and sodium fluoride salts. Difluorodimethyl ether is a potential replacement for ozone
depleting CFC refrigerants. A Box-Behnken experimental design was used to investigate the effect
of reaction conditions on the product distribution. Variations in the reaction temperature, initial
concentration of sodium hydroxide and inlet partial pressure of R-22 were considered.
The modeling of the gas-liquid reactions was based on the -dehydrohalogenation mechanism.
Since gas solubility in a liquid decreases in the presence of dissolved salts, the "salting-out" effect
on mass transfer was included in the reactor model. Sechenov coefficients for sodium chloride and
sodium fluoride were combined to give a salt Sechenov coefficient Ksalt . It was known from the
literature that the presence of precipitated salts causes inefficient mixing and inhibits mass transfer,
particularly in this system due to the relatively low salt solubilities in methanol. This mixing effect
was also included in the appropriate mass transfer terms of the reactor model. The experimental
data was fitted to a proposed kinetic scheme. Kinetic parameters for each of the proposed reactions,
the Sechenov ‘salting out’ coefficients and the mixing parameter were obtained through the use of a
non-linear, least-squares optimization algorithm. For the kinetic study, activation energies of 89.12
and 45.83 kJ·mol-1 were obtained for the difluorodimethyl ether and trimethyl orthoformate
formation reactions, respectively, with a Sechenov salt coefficient of 0.712 and a mixing parameter
of 22.43.Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.
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Salazar, Raul. « Cellules solaires avec un absorbeur ll-Vl nanostructuré Matériaux et Propriétés ». Phd thesis, 2012. http://tel.archives-ouvertes.fr/tel-00815056.
Texte intégralRésumé :
L'objectif de ce travail est d'élaborer des méthodes peu chères pour produire des matériaux semi-conducteurs pouvant entrer dans la fabrication de cellules solaires de type "eta" (extremely thin absorber). Ces cellules sont constituées d'une couche extrêmement fine d'un absorbeur inorganique dont la bande interdite est situé entre 1.1 et 1.8 eV placée entre deux nanostructures transparentes l'une de type n et l'autre de type p et dont les bandes interdites doivent être supérieurs à 3.3 eV. Une couche compacte et des nanofils de ZnO ont été préparés en mode galvanostatique. Les dimensions des nanofils ont été contrôles à l'aide de la couche compacte et de la densité du courant appliqué. La photosensibilisation des nanofils par des couches uniformes de CdS, CdSe et CdTe prÈparÈe par la méthode SILAR (Successive Ionic Layer Adsorption and Reaction) a été étudiée. Les propriétés de ces couches ont été améliorées par recuit et traitement chimique. En ce qui concerne les fines coquilles de CdTe deux autres méthodes de sensibilisation ont été également étudiées : la CSS (Close Space Sublimation) et les QDs (Quantum Dots). La première méthode conduit à un faible recouvrement alors que la seconde produit un matériau mal défini optiquement. Les hétérostructures formées sur les nanofils ont été complétées par une couche de CuSCN, un semi-conducteur de type p, préparée par trois méthodes différentes. L'influence de la morphologie de ces couches sur les propriétés des cellules eta a été étudiée. Les films préparés par électrodéposition et SILAR sont plus rugueux que ceux obtenus par imprégnation et leur conductivité est moins bonne. Les hétérostructures (avec CdS et CdSe comme absorbeurs) ont été testées dans une cellule photoélectrochimique et les rendements obtenus (jusque 2%) montrent une amélioration certaine des propriétés de ces matériaux préparée par SILAR-modifiée ainsi que des interfaces ZnO/absorbeur. La qualité des matériaux obtenus par SILAR montre qu'aujourd'hui on peut s'attendre à une Renaissance de cette technique.
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Ullberg, Nathan. « Characterizing optical and electrical properties of monolayer MoS2 by backside absorbing layer microscopy ». Thesis, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-419630.
Texte intégralRésumé :
Nanomaterials are playing an increasing role in novel technologies, and it is important to develop optical methods to characterize them in situ. To that end, backside absorbing layer microscopy (BALM) has emerged as a powerful tool, being capable to resolve sub-nanometer height profiles, with video-rate acquisition speeds and a suitable geometry to couple live experiments. In the internship, several techniques involving BALM were developed, and applied to study optical and electrical properties of the transition metal dichalcogenide (TMD) monolayer MoS2, a type of 2-dimensional (2D) crystalline semiconductor. A simulations toolkit was created in MATLAB to model BALM, a workflow to reliably extract linear intensities from the CMOS detector was realized, and 2D MoS2 was synthesized by chemical vapor deposition followed by transfer to appropriate substrates. BALM data of the 2D MoS2 was acquired and combined with simulations, giving a preliminary result for its complex refractive index at 5 optical wavelengths. In addition, the first steps towards coupling BALM with a gate biased 2D MoS2 field-effect transistor were explored. To complement BALM measurements, the grown samples were also characterized by conventional optical microscopy, scanning electron microscopy, atomic force microscopy, photoluminescence spectroscopy, and Raman spectroscopy. This work provides new additions to an existing platform of BALM techniques, enabling novel BALM experiments with nanomaterial systems. In particular, it introduces a new alternative for local extraction of optical parameters and for probing of electrical charging effects, both of which are vital in the research and development of nano-optoelectronics.
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Syu, Yu-Fan, et 徐郁帆. « Direct growth of Mg-Al-Cl LDH film on Mg alloy die casting flash scrap by chemical conversion treatment and the application of the material on absorbing fluoride ions in aqueous solution ». Thesis, 2012. http://ndltd.ncl.edu.tw/handle/8yk8u2.
Texte intégralRésumé :
碩士國立中興大學
材料科學與工程學系所
100
This work presents a novel method to develop Mg-Al-Cl layered double hydroxide (Mg-Al-Cl LDH) on Mg alloy die casting flash scrap by simply dipping the sample in chemical conversion solution (an aqueous HCl of initial pH 1.5 with 3.5 wt.% NaCl solution) for 30 min at room temperature. The Mg-Al-Cl LDH has anion-exchangeability and can be used to absorb fluoride ions in aqueous solution. By this method, we can directly produce the Cl-intercalated LDH on Mg alloy die casting flash and do not need deintercalation of carbonate ions from CO3-intercalated LDH. Experimentally, the chemical reaction should be sufficiently strong to raise the pH value of the system to ~9 as soon as possible for favoring the LDH formation. The chemical conversion treatment time usually is 30 min. Because of the Al concentration difference between AM60 and AZ91, we try to add different amount of AlCl3 in chemical conversion solution. However, adding 0.22 g AlCl3 in chemical conversion solution cause the pH value to rise slowly. Thus, increasing treatment time to 120 min is necessary as treating AM60 flash scrap in chemical conversion solution containing AlCl3. Using post-treatment samples to absorb fluoride ions for 60 min, the concentration of fluoride ions from 100 ppm fluoride ions aqueous solution (pH 6.0 ± 0.5) is decreased significantly. According to the experimental results, the different effect of absorbing fluoride ions caused by different alloys’ composition (AM60 and AZ91) can improve by adding aluminum ions in the chemical conversion solution. Moreover, increasing treatment time can make good growth of LDH and can also improve the effect of absorbing fluoride ions. The Mg alloy die casting flash scrap after chemical conversion treatment can be used to absorb fluoride ions in aqueous solution such as high concentration of fluoride wastewater generated by the semiconductor manufacturing process, making Mg alloy die casting flash scrap develop a new usage.
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Banavoth, Murali. « Earth Abundant Alternate Energy Materials for Thin Film Photovoltaics ». Thesis, 2013. http://etd.iisc.ernet.in/2005/3353.
Texte intégralRésumé :
Inexhaustible solar energy, which provides a clean, economic and green energy, seems to be an alternative solution, for current and future energy demands. Harvesting solar energy presents a challenge in using eco-friendly, earth abundant and inexpensive materials. Although present CdTe and Cu (In, Ga)Se2 (CIGS) technologies, provide light-to-electricity comparable to silicon technology, toxicity of Cd and scarcity of In limits the widespread utilization. Future tera-watt level module capacity would then be feasible by the low-cost technologies. The chalcogenide thin film technology would therefore provide the exceptional utilization in the large-area module monolithic integrations benefitting from the low material consumption owing to the direct band gap. The current thesis presents the results obtained from the quest of other thin film materials and their utilization to an unconventional Cd-free buffer layer. The films suitability for the future applications was assessed through photovoltaics device studies in a comparative manner.
Chapter-1 deals with the motivation for the solar energy and the importance of thin film photovoltaics. Alternative materials which are abundantly available would help to reach the future tera watt level production, where the conventional silicon technology alone cannot satisfy the global energy demand. The utilization of non-conventional thin film based solar cells and their working principles were elucidated. The histories of the copper based alternative materials were introduced.
Chapter-2 deals with the versatile thin film growth technique that has been designed fabricated and installed further which can handle the growth of the absorber and the top TCO layers with insitu sulphurisation. The methodology of the absorber deposition was discussed in detail. The experimental details for the co-sputtering of CuInAl alloy were presented. A novel selenization method, assisted by the combination of inert gases was developed for the annealing of CuInAl alloyed precursor films.
Chapter-3 deals with the presentation of the results obtained on buffer and window layers. Chemical Bath deposition technique was employed for the growth and optimization of the conventional CdS and non-toxic buffer ZnS buffer layers. A) Cadmium sulphide thin films suitable for the utilization of high efficiency solar cells were optimized. Optimization of the buffer involved the effects of cadmium precursors, ammonia concentration and buffer capsule effect. A green route was presented so as to consume the precursors to the maximum extent possible. B) The alternative non-toxic buffer Zinc Sulphide (ZnS) thin films were successfully grown using the above optimized conditions.
Moreover the window layer was also optimized for better device partner. Zinc Oxide was used as a n-type partner for the p-type CIS films. The ZnO films were grown by the RF-sputtering from the single cathode exhibited good crystallinity with Zincite structure (hexagonal ZnS, a= 3.249A0 and c= 5.205A0). All the grown films showed high resistivity. Al: ZnO thin films were optimized in two methods 1) by dc co-sputtering from the elemental cathodes, Zinc and Aluminum, 2) dc-sputtering from the single 2% Al-doped ZnO cathode. Low resistivity Al:ZnO thin films were deposited in both the cases. Effect of Aluminum doping into ZnO crystal lattice upon the optical and electrical properties were discussed.
Chapter-4 deals with the synthesis of various absorber materials, characterizations and some properties. Briefly the A) Optimization of the CuIn1-xAlxSe2 phase with better adhesion and better crystallinity. Aluminum doping into the crystal lattice of CuInSe2 aided the wide band gap tuning of CIAS thin films. Morphological investigations were carried out for the different set of thin films before and after selenization. Effects of copper and Aluminum concentrations on the lattice parameter of the selenized thin films were addressed. The present chapter deals with the A) electrical properties of CIAS films and its heterojunction partners. Resistivity measurements and effects of Cu/In ratio and the effect of Al doping were described in detail. The CIAS/ZnO heterostructure, CIAS/Al:ZnO heterostructure junction properties as a function of different sun illuminations were discussed.
B) The alternative earth abundant, eco-friendly, non-toxic elements Cu2ZnSnS4, absorber thin films synthesis and characterizations. Photo conductive photo measurements showed CZTS a potential candidate for near infra-red photodectection. C) Cu2CoSnS4 (CCTS) nanostructures and quantum dots were synthesized via simple chemical routes. CCTS quantum dots were tuned to exhibit the red edge effect and cold white phosphors. D) Cu3BiS3 nano rods were synthesized and characterized structurally and optically. The transport properties of Cu3BiS3 nanorods were tailored for showing the metallic to semiconducting transitions.
Chapter-5 Discusses the A) Efforts made in understanding the CIAS based solar cells through interfaces such as CIAS/ZnO, Mo/CIAS, CIAS/CdS/i-ZnO/Al:ZnO and improving the open circuit voltage VOC upon a rotating substrate, involving the inline and in situ processes, for fabricating the cell/ module were discussed. The device statistics for various set of cells were analyzed. B) Solar cells of CTS absorber with the non-toxic buffer ZnS were fabricated and device properties were analyzed. C) CCTS quantum dots embedded in the polymer matrix were utilized for making the inverted hybrid solar devices in combination of ITO/AZnO bilayered contact replacing the acidic PEDOT: PSS. D) The solar cells made of CCTS hollow spheres by spin coating the absorber in the configuration SLG/Mo/CCTS/CdS/ iZno-AZnO/Ni-Al-Al showed a lower efficiency of 0.02%.
Chapter-6 concludes with the summary of present investigations and the scope for future work.