<p>The superior high-temperature elastic-plastic properties coupled with greater damage tolerance when compared with monolithic ceramics make ceramic matrix composites, CMCs, promising candidates for challenging applications such as engine components, rocket nozzles, cutting tools and nuclear energy reactor core components. Anelastic recovery is the time-dependent back strain observed upon the load removal following creep. In whisker-reinforced CMCs this can be a factor limiting operating conditions. Plastic strain misfit between two phases is thought to be the main driver in terms of the interactions within a percolating network. However, the network deformation mechanisms are still unclear and a previous neutron diffraction study showed an unexpected decrease of peak width after creep contradicting the theoretical predictions.</p> <p>In this contribution, the finite element method (FEM) is applied to a representative volume element (RVE) with proper boundary conditions in order to simulate the creep deformation and hot pressing processes. Three geometries have been generated and studied: a 3D randomly-oriented short-fiber unit cell without fiber to fiber contact, generated by a random sequential adsorption algorithm; 3D regularly aligned single fiber unit cells; and 2D regularly aligned percolating unit cells. Deformation mechanism has been studied from an energy point of view and compared with a modified analytical model. Then a virtual diffraction model has been developed providing a framework to transfer information between the FEM simulations (strain fields) and the diffraction pattern in terms of the peak width (full width at half maximum: <strong><em>FWHM</em></strong>) and peak position as a measure of stress distribution and mean stress state respectively. Furthermore, the coupling effects of external stress, deformation mode, and thermal stress on the diffraction patterns have been studied.</p> <p>The critical importance of a percolating whisker network for the anelastic recovery is demonstrated based on the 3D multi-whisker random unit cell. Whisker bending is shown to be the dominant mechanism over contact effects during the creep deformation of a composite containing a well aligned percolating whisker network based on the 2D unit cell model. Good qualitative agreement was found between our FEM simulations and the analytical model of Wilkinson and Pompe with regards to the maximum recoverable strain and the characteristic relaxation time. The analytical model captures all the critical factors characterizing the strain recovery, e.g., the effect of creep pre-exponent constant, whisker Young’s modulus and aspect ratio. Furthermore, it is found that the deformation from an initial stress-free state inevitably introduces peak broadening of whiskers inside the matrix. Several factors determine the peak-width and -shift, i.e., creep strain, applied stress, aspect ratio and geometry. However, thermal stress from the cooling stages following creep and hot pressing processes shelters this broadening effect and complicates the trends. Wide-ranging peak-width changes from narrowing to broadening are predicted depending on the geometry and applied stress. The peak position is shifted to a lower angle due to this thermal effect. This clearly explains the contradicting phenomena motivating this work and leads to that recommendation that a diffraction source with high angular resolution is needed to detect the subtle change of peak profile during creep.</p> / Doctor of Philosophy (PhD)

Essa dissertação de mestrado descreve o desenvolvimento de hardwares de colunas para cromatografia líquida capilar. O processo de desenvolvimentos desses dispositivos é descrito gradativamente e os pontos fortes e as limitações de cada modelo de hardware são discutidos. O melhor modelo de hardware desenvolvido apresentou produção simples, fácil conexão ao sistema cromatográfico e resistência a pressões superiores a 900 bar. Sucessivamente ao estabelecimento de um modelo de hardware apropriado, os efeitos dos materiais do hardware na eficiência das colunas foram avaliados. Poucos estudos relatam a influência do hardware nas separações em escala capilar, de forma que essa dissertação contribui para o preenchimento dessa lacuna. Capilares de aço inoxidável e sílica fundida e frits de aço inoxidável e fibra de vidro foram avaliados. Colunas com eficiências superiores a 100.000 pratos por metro foram produzidas. / This master\'s dissertation describes the development of hardware for capillary liquid chromatography columns. The development process of the devices is described gradually and the strengths and limitations of each model of hardware are discussed. The best-developed hardware model presented easy production, practice connection to the chromatographic system and resistance to pressures greater than 900 bar. After the establishment of an appropriate hardware model, the effects of hardware materials on the efficiency of the columns were evaluated. Few studies report the influence of the hardware on capillary scale separations; therefore, this dissertation contributes to fill this gap. Capillaries of stainless steel and fused silica and frits of stainless steel and glass fiber were evaluated. Columns with efficiencies greater than 100,000 plates per meter were produced.

Essa dissertação de mestrado descreve o desenvolvimento de hardwares de colunas para cromatografia líquida capilar. O processo de desenvolvimentos desses dispositivos é descrito gradativamente e os pontos fortes e as limitações de cada modelo de hardware são discutidos. O melhor modelo de hardware desenvolvido apresentou produção simples, fácil conexão ao sistema cromatográfico e resistência a pressões superiores a 900 bar. Sucessivamente ao estabelecimento de um modelo de hardware apropriado, os efeitos dos materiais do hardware na eficiência das colunas foram avaliados. Poucos estudos relatam a influência do hardware nas separações em escala capilar, de forma que essa dissertação contribui para o preenchimento dessa lacuna. Capilares de aço inoxidável e sílica fundida e frits de aço inoxidável e fibra de vidro foram avaliados. Colunas com eficiências superiores a 100.000 pratos por metro foram produzidas. / This master\'s dissertation describes the development of hardware for capillary liquid chromatography columns. The development process of the devices is described gradually and the strengths and limitations of each model of hardware are discussed. The best-developed hardware model presented easy production, practice connection to the chromatographic system and resistance to pressures greater than 900 bar. After the establishment of an appropriate hardware model, the effects of hardware materials on the efficiency of the columns were evaluated. Few studies report the influence of the hardware on capillary scale separations; therefore, this dissertation contributes to fill this gap. Capillaries of stainless steel and fused silica and frits of stainless steel and glass fiber were evaluated. Columns with efficiencies greater than 100,000 plates per meter were produced.

<p>Theoretical investigations of spectroscopic and magnetic properties of metallic systems in the bulk, as well as in nanostructured materials, have been performed within the density functional theory. The major part of the present work studies the differences between binding energies of electrons tightly bound to the atoms, the so-called core electrons (in contrast with the valence electrons), that is, core-level binding energy shift (CLS). </p><p>By comparison between corresponding elemental core-levels for atoms situated in different chemical environments we obtain fundamental understanding of bonding properties of materials. The method of choice was the complete screening picture, which includes initial and final state effects on the same footing. The usefulness of CLS stems from that it is sensitive to differences in the chemical environment of an atom, which can be affected on one hand by the global composition of e.g. disordered materials, surfaces and interfaces, and on the other hand by the very local environment around an atom. Here CLSs have been obtained for both components in the fcc random alloys AgPd, CuPd, CuNi, CuPt, CuAu, PdAu, NiPd and NiPt. Moreover the model was extended to the Auger kinetic energy shift for the LMM Auger transition in AgPd alloys. Studies were also applied to the near surface and interface regions of PdMn nano structures on Pd(100), thin CuPd and AgPd films on inert Ru(0001), and at interfaces. The disorder broadening on CLS due to local environment effects was calculated in selected alloys.</p><p>A part of the thesis concern investigations related to the magnetic ordering in Invar alloys, including the influence of local environment effects. A study was made for the dependence of effective exchange parameter on the electron concentration, volume and local chemical composition.</p>

Theoretical investigations of spectroscopic and magnetic properties of metallic systems in the bulk, as well as in nanostructured materials, have been performed within the density functional theory. The major part of the present work studies the differences between binding energies of electrons tightly bound to the atoms, the so-called core electrons (in contrast with the valence electrons), that is, core-level binding energy shift (CLS). By comparison between corresponding elemental core-levels for atoms situated in different chemical environments we obtain fundamental understanding of bonding properties of materials. The method of choice was the complete screening picture, which includes initial and final state effects on the same footing. The usefulness of CLS stems from that it is sensitive to differences in the chemical environment of an atom, which can be affected on one hand by the global composition of e.g. disordered materials, surfaces and interfaces, and on the other hand by the very local environment around an atom. Here CLSs have been obtained for both components in the fcc random alloys AgPd, CuPd, CuNi, CuPt, CuAu, PdAu, NiPd and NiPt. Moreover the model was extended to the Auger kinetic energy shift for the LMM Auger transition in AgPd alloys. Studies were also applied to the near surface and interface regions of PdMn nano structures on Pd(100), thin CuPd and AgPd films on inert Ru(0001), and at interfaces. The disorder broadening on CLS due to local environment effects was calculated in selected alloys. A part of the thesis concern investigations related to the magnetic ordering in Invar alloys, including the influence of local environment effects. A study was made for the dependence of effective exchange parameter on the electron concentration, volume and local chemical composition.

No description available.

Le présent travail de thèse a porté sur l’étude expérimentale et théorique de signatures spectroscopiques de molécules atmosphériques clés: CO2 et CH3D. 11 a été divise en partie expérimentale, consacrée aux mesures a haute pression des spectres IR CO2, et a la partie théorique, a. savoir le calcul des largeurs de ligne de collision pour CH3D perturbé par divers gaz. Dans la première partie, j'ai présenté des mesures &absorption de CO2 a haute pression a température ambiance dans l'intervalle spectral 600-9650 cm (sondes dans des études d’atmosphère planétaire) pour deux raisons principales: fournit des données exactes et étendues et suivre l’évolution de effets de "line-mixing" avec des variations graduelles de pression. Dans la deuxième partie, j'ai présenté des calculs semi-classiques des coefficients d'élargissement de CH3D -N2 (-H2) en utilisant le modèle de trajectoire exacte dans les bandes v3 parallèles et perpendiculaires vs, v6 de CH3D ---N2 ainsi que dans la bande v3 parallèle de CH3D -142 pour de grands intervalles les de nombres quantiques de rotation requis pour les bases de données spectroscopiques. / Present Ph.D work has focused on experimental and theoretical studying of spectroscopic signatures of key atmospheric molecules: CO2 and CH3D. It was divided into experimental part, devoted to high-pressure measurements of IR CO2 spectra, and theoretical part, namely calculation of collisional line-widths for CH3D perturbed by various gases. In the first part, I reported room-temperature high-pressure CO2 absorption measurements in the spectral interval 600-9650 cm-1 (probed in planetary atmosphere studies) with the double goals: to provide accurate and extensive data and to trace evolution of the line-mixing effects with gradual pressure variations. In the second part, I presented semi-classical calculations of CH3D-N2 and -142 line-broadening coefficients using exact trajectory model in the parallel v3 and perpendicular vs, v6 bands of CH3D-N2 as well as in the parallel v3 band of CH3D-112 for large intervals of rotational quantum numbers required for spectroscopic databases.

Spatially-resolved measurements of flame temperature have been demonstrated with diode lasers for the first time. The technique is based on the use of blue diode lasers to perform laser-induced fluorescence on indium atoms seeded to the flame. Temperature measurements have been carried out in laminar flames both by the two-line atomic fluorescence technique, and also by a novel line-shape thermometry method that requires the use of only a single diode laser. The first part of this work involved the development of blue extended cavity diode lasers with favourable tuning properties. Two custom-designed extended cavity diode lasers (ECDL) have been built, emitting at wavelengths of around 410 nm and 451 nm respectively. These devices are capable of mode-hop free tuning over ranges greater than 90 GHz. The performance of these devices exceeds that of commercially available systems and a patent application has been filed. High resolution fluorescence spectroscopy has been performed on both the 52P1/2→62S1/2 and 52P3/2→62S1/2 transitions of indium atoms seeded at trace quantities into atmospheric pressure flames. In both cases, the spectra obtained show excellent agreement with a theoretical fit based on the individual hyperfine components of the transition. The two ECDLs have been used to build a sensor for the measurement of temperature in combustion systems. It is much simpler, more compact, less expensive, and more versatile than any previously existing device. The two lasers were used sequentially to probe indium atoms seeded to the flame. The ratio of the resulting fluorescence signals is related to the relative populations in the two sub-levels of the spin-orbit split ground state of indium, and thus to the temperature. Temperature measurements have been successfully performed in a laminar flame and the data thus obtained do not need to be corrected by any ‘calibration constant’. This novel thermometry technique offers a robust alternative to traditional methods involving bulky high power lasers. A further development has been made by demonstrating a fluorescence line-shape thermometry technique requiring only a single diode laser excitation source. Progress has been made towards the goal of rapid temperature measurements appropriate to the study of turbulent flames. This involved the development of a simple technique for actively locking the wavelength of the blue diode laser to a resonance line of the tellurium molecule. A high-speed thermometry system would work by rapidly switching between the two locked laser beams using an optical modulator.

Abstract This thesis makes a novel and original contribution to the discourse surrounding engineering education, and how it can be made more accessible to underrepresented groups. The study includes two contexts representing two different perspectives. Two studies are conducted, one examines upper secondary school pupils’ views of engineering students and the other the societal and cultural production of the engineering student in a recruitment campaign for KTH Royal Institute of Technology. Few earlier studies have examined the messages communicated in initiatives aiming to increase and broaden the recruitment of underrepresented groups to technical universities. Still, many initiatives sharing this goal are initialised in Sweden. The theoretical framework applied by discourse analysis and governmentality analysis enables a critical examination of the discursive framework surrounding the engineering student. The thesis concludes that there is a power struggle between a discourse of a contemporary technologist and a traditional technologist and that this position is exclusively but only for the most advanced engineering students, excluding BSc students as communicated by a KTH recruitment campaign. / Moderna samhällen förutsätter att människor är ansvariga för att göra val av olika slag, till exempel av utbildning och yrke. Dessutom förväntas yrkesvalet överensstämma med individens självuppfattning. Det finns ett stort engagemang i Sverige och globalt för att öka och bredda rekryteringen till tekniska utbildningar som leder till yrken inom teknik och naturvetenskap. Detta är synligt i den stora mängd av initiativ som görs med syfte att öka ungas intresse för utbildningar av detta slag. Ungas intresse för teknikintensiva utbildningar är ett väl utforskat område. Detta är däremot inte budskap som kommuniceras med syfte att öka och bredda rekryteringen till teknisk intensiva utbildningar.  Denna uppsats syftar till att undersöka det diskursiva ramverket som definierar subjektet ingenjörsstudenten i en rekryteringskontext i Sverige. Det teoretiska och metodmässiga tillvägagångsättet är inspirerat av diskursanalys och governmentalitetsstudier. Detta perspektiv förser analysen med en kritisk blick vilket resulterat i ett intressant bidrag till forskningen om diskursen som omger ingenjörsutbildningens tillgängliggörande för underrepresenterade studentgrupper. Uppsatsen består av en sammanhållande kappa och två artiklar som beskriver två olika studier och perspektiv. Den första studien undersöker gymnasieungdomars uppfattningar om ingenjörsutbildningar och ingenjörsstudien. Det metodmässiga tillvägagångsättet kombinerar klassrumsstudier gjorda med hjälp av mindmapping-tekniker och diskursanalys på ett unikt sätt. I den andra studien analyseras de budskap som kommuniceras i en rekryteringskampanj för KTH. I den sammanhållande kappan analyseras det samlade resultatet av studierna. Denna analys visar att det pågår en diskursiv kamp mellan en diskurs av traditionell karaktär och en av nutida karaktär. Den traditionella som lyfts fram av gymnasieeleverna bygger på ett reduktionistiskt förhållningsätt och traditionella värden som personlig framgång (ekonomisk framgång och social status). Den nutida som lyfts fram i kampanjen i bygger på ett holistiskt förhållningsätt och vikten av att bidra till en gynnsam samhällsutvecklingen för alla. I teorin bjuder den nutida in nya studentgrupper i högre grad än den traditionella. Intressant nog sker inte detta i kampanjen, vilket beror på att endast de mest avancerade grundstudenterna, civilingenjörsstudenter som studerar på det äldsta av KTH:s campus, representeras i kampanjen. Detta får till följd att den breddning som sker endast är gällande för en liten skara individer  Uppsatsens viktigaste bidrag är insikter om diskursen som omger ingenjörsutbildningen, som trots försök till breddning verkar exkluderande för många presumtiva studenter. Vidare är det teoretiska och metodmässiga tillvägagångsättet ett intressant bidrag till forskning och en breddad rekrytering till tekniska lärosäten.

We study the expansion velocity and ion temperature evolution of ultracold neutral plasmas (UNPs) of calcium atoms under the influence of a uniform magnetic field that ranges up to 200 G. In the experiments, we use a magneto-optical trap (MOT) to capture the neutral atoms and laser-induced fluorescence (LIF) to take images of the plasma. We vary the magnetic field strengths and the initial electron temperatures and observe the plasma evolution in time. We compare the ion temperature evolution to the theory introduced in the paper by Pohl et. al. [Phys. Rev. A 70, 033416 (2004)]. The evolution of the gradient of expansion velocity suggests the presence of ion acoustic waves (IAWs). We speculate that our measurements showing that the ion temperature remains relatively high throughout the evolution is a biproduct of the IAW.