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The Global ETD Search service is a free service for researchers
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Showing 21 to 28 of 28 (0.014 seconds)| 21 |
Optical And Physical Properties Of Ceramic Crystal Laser MaterialsSimmons, Jed 01 January 2007 (has links)
Historically ceramic crystal laser material has had disadvantages compared to single crystal laser material. However, progress has been made in the last decade and a half to overcome the disadvantages associated with ceramic crystal. Today, because of the promise of ceramic crystal as a high power laser material, investigation into its properties, both physical and optical, is warranted and important. Thermal expansion was measured in this thesis for Nd:YAG (yttrium aluminum garnet) ceramic crystal using an interferometric method. The interferometer employed a spatially filtered HeNe at 633 nm wavelength. Thermal expansion coefficients measured for the ceramic crystal samples were near the reported values for single crystal Nd:YAG. With a similar experimental setup as that for the thermal expansion measurements, dn/dT for ceramic crystal Nd:YAG was measured and found to be slightly higher than the reported value for single crystal. Depolarization loss due to thermal gradient induced stresses can limit laser performance. As a result this phenomenon was modeled for ceramic crystal materials and compared to single crystals for slab and rod shaped gain media. This was accomplished using COMSOL Multiphysics, and MATLAB. Results indicate a dependence of the depolarization loss on the grain size where the loss decreases with decreased grain size even to the point where lower loss may be expected in ceramic crystals than in single crystal samples when the grain sizes in the ceramic crystal are sufficiently small. Deformation-induced thermal lensing was modeled for a single crystal slab and its relevance to ceramic crystal is discussed. Data indicates the most notable cause of deformation-induced thermal lensing is a consequence of the deformation of the top and bottom surfaces. Also, the strength of the lensing along the thickness is greater than the width and greater than that due to other causes of lensing along the thickness of the slab. Emission spectra, absorption spectra, and fluorescence lifetime were measured for Nd:YAG ceramic crystal and Yb:Lu2O3 ceramic crystal. No apparent inhomogeneous broadening appears to exist in the Nd:YAG ceramic at low concentrations. Concentration and temperature dependence effects on emission spectra were measured and are presented. Laser action in a thin disk of Yb:Y2O3 ceramic crystal was achieved. Pumping was accomplished with a fiber coupled diode laser stack at 938 nm. A slope efficiency of 34% was achieved with maximum output energy of 28.8 mJ/pulse.
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Investigacao dos processos de excitacao multifotonica da configuracao 4fsup(2)5d nos cristais de LiYFsub(4), LuLiFsub(4) e BaYsub(2)Fsub(8) dopados com neodimio trivalenteLIBRANTZ, ANDRE F.H. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:49:27Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:34Z (GMT). No. of bitstreams: 1
09988.pdf: 6876378 bytes, checksum: 2340a8ae19e74e0088633e68ecefaec3 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Investigacao dos processos de excitacao multifotonica da configuracao 4fsup(2)5d nos cristais de LiYFsub(4), LuLiFsub(4) e BaYsub(2)Fsub(8) dopados com neodimio trivalenteLIBRANTZ, ANDRE F.H. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:49:27Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:34Z (GMT). No. of bitstreams: 1
09988.pdf: 6876378 bytes, checksum: 2340a8ae19e74e0088633e68ecefaec3 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Presença de elementos metálicos em cosméticos labiais: investigação dos impactos na saúde e o descarte no meio ambiente / Metallic elements presence in lip cosmetics: investigation of health impacts and their disposal in the environmentMAEHATA, PATRICIA 22 December 2016 (has links)
Submitted by Marco Antonio Oliveira da Silva (maosilva@ipen.br) on 2016-12-22T12:01:06Z
No. of bitstreams: 0 / Made available in DSpace on 2016-12-22T12:01:06Z (GMT). No. of bitstreams: 0 / Os cosméticos labiais estão envolvidos em duas importantes discussões: os problemas de saúde pública e os problemas ambientais. A partir dessas informações, pretende-se analisar qual o impacto na saúde humana, verificar se há relação entre preço, duração e cor e investigar quais os prováveis impactos para o meio ambiente, supondo algumas vias de descarte. Os cosméticos analisados foram batons, divididos por marca, preço e cor. A primeira análise foi por fluorescência de raios-x (FRX). Em seguida, as matérias primas passaram por digestão com ácido nítrico e clorídrico sob aquecimento e foram diluídas com água destilada e filtradas. A seguir, foram realizadas leituras por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP-OES). A partir dos resultados da análise por FRX (foram encontrados 18 elementos metálicos) e a matriz para análise por ICP-OES foi composta por: alumínio, cálcio, cádmio, cobalto, cromo, cobre, ferro, potássio, manganês, níquel, chumbo, silício e titânio. Apesar de terem sido identificados metais tóxicos (Ni, Mn, Cd e Cr) nas amostras, os batons analisados cumprem com o requerido pela legislação nacional em relação aos limites impostos para metais pesados (Pb, Cd, Ni, Cr e Mn) em cosméticos e alimentos. Entretanto, é importante destacar que as legislações cosmética e alimentícia possuem grandes diferenças quanto aos limites impostos para metais pesados. O estudo do descarte dos batons mostrou que mesmo os batons que são mais utilizados, há um desperdício de quase 1/3 do produto por conta da embalagem interna. Essa informação pode auxiliar em um consumo consciente dos batons, tanto para a quantidade desperdiçada, quanto ao risco associado à utilização de um conjunto de maquiagens (bases, sombras, rímel, blush e batom) com outros cosméticos (cremes, perfumes, esmaltes, tintas para cabelo). Risco esse, associado a possíveis problemas à saúde. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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An x-ray spectroscopic study of novel materials for electronic applicationsRaekers, Michael 08 June 2009 (has links)
The electronic and magnetic structure of the colossal magneto resistance material La1-xSrxMnO3, the high-k and strain tailoring compounds REScO3 (Sm, Gd, Dy) and the multiferroic LuFe2O4 was investigated by means of x-ray spectroscopic techniques. SQUID measurements of La1-xSrxMnO3 (x = 0.125, 0.17, 0.36) were compared with XMCD results. The very good agreement between these two experiments proofs the applicability of the correction factor for the spin magnetic moment and the importance of charge transfer. The magnetic moment measured by SQUID and that determined from XMCD proofs that the magnetic moment is completely localized at the Mn ions for different temperatures and magnetic fields. For x = 0.125 the orbital magnetic moment determined from XMCD corresponds to the structural changes in the phase diagram. Additionally the measured orbital moments correspond to anomalies in magnetization versus temperature curves. The magnetic and electronic structure of the rare earth scandates (SmScO3, GdScO3 and DyScO3) were investigated by means of XPS, XES, XAS, SQUID and neutron powder diffraction. The magnetic measurements reveal antiferromagnetic coupling at low temperatures in agreement with neutron diffraction data. With XAS and XES at the O K-edge in comparison with band structure calculations of the unoccupied oxygen states, the band gaps of REScO3 were determined and it was found that these values are corresponding to the Sc-O mean distances. The electronic and magnetic structure of LuFe2O4 was presented. The valence state of Fe ions was determined to 50% divalent and 50% trivalent by XPS of Fe 2p and 3s levels. The big orbital magnetic moment found by XMCD could explain a discrepancy between the magnetic measurements and the spin configuration, which was confirmed by XMCD.
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Ultrafast Structural and Electron Dynamics in Soft Matter Exposed to Intense X-ray PulsesJönsson, Olof January 2017 (has links)
Investigations of soft matter using ultrashort high intensity pulses have been made possible through the advent of X-ray free-electrons lasers. The last decade has seen the development of a new type of protein crystallography where femtosecond dynamics can be studied, and single particle imaging with atomic resolution is on the horizon. The pulses are so intense that any sample quickly turns into a plasma. This thesis studies the ultrafast transition from soft matter to warm dense matter, and the implications for structural determination of proteins. We use non-thermal plasma simulations to predict ultrafast structural and electron dynamics. Changes in atomic form factors due to the electronic state, and displacement as a function of temperature, are used to predict Bragg signal intensity in protein nanocrystals. The damage processes started by the pulse will gate the diffracted signal within the pulse duration, suggesting that long pulses are useful to study protein structure. This illustrates diffraction-before-destruction in crystallography. The effect from a varying temporal photon distribution within a pulse is also investigated. A well-defined initial front determines the quality of the diffracted signal. At lower intensities, the temporal shape of the X-ray pulse will affect the overall signal strength; at high intensities the signal level will be strongly dependent on the resolution. Water is routinely used to deliver biological samples into the X-ray beam. Structural dynamics in water exposed to intense X-rays were investigated with simulations and experiments. Using pulses of different duration, we found that non-thermal heating will affect the water structure on a time scale longer than 25 fs but shorter than 75 fs. Modeling suggests that a loss of long-range coordination of the solvation shells accounts for the observed decrease in scattering signal. The feasibility of using X-ray emission from plasma as an indicator for hits in serial diffraction experiments is studied. Specific line emission from sulfur at high X-ray energies is suitable for distinguishing spectral features from proteins, compared to emission from delivery liquids. We find that plasma emission continues long after the femtosecond pulse has ended, suggesting that spectrum-during-destruction could reveal information complementary to diffraction.
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Untersuchungen zur elektronischen und geometrischen Struktur ausgewählter oxidischer und sulfidischer Materialien mittels Photoelektronen- und RöntgenspektroskopieSchneider, Bernd 08 January 2002 (has links)
Oxidische Materialien bieten ein weites Spektrum an möglichen Anwendungen. Vor allem Isolatoren mit Perowskitstruktur eignen sich hervorragend für die optische Datenverarbeitung und -speicherung. Andere, leitende, Oxide können für die magnetische Datenspeicherung eingesetzt werden. Vorraussetzung für den praktischen Einsatz der Werkstoffe sind jedoch grundlegende Kenntnisse über deren mikroskopischen Eigenschaften und ablaufende Prozesse. Mittels Photoelektronen- und Röntgenspektroskopie können Aussagen über die elektronische Struktur getroffen werden. Die noch junge Methode der Fluoreszenz weicher Röntgenstrahlung (SXF) wurde zur Charakterisierung der elektronischen Struktur hinzugezogen. SXF-Messungen wurden an der Beamline 8.0.1 am ALS in Berkeley, Kalifornien, durchgeführt.
An der Modellsubstanz MgO wurden Röntgenabsorptions- und Röntgenemissionsspektren an der Sauerstoffkante erstellt. Es zeigt sich eine hervorragende Übereinstimmung mit Modellrechnungen. Ein Bandmapping unter Ausnutzung von Resonanzphänomenen, ähnlich wie in Graphit, scheint jedoch nicht möglich zu sein.
In TiO2 wurde das Ti 3d Niveau untersucht. Die Emissionsspetkren zeigen Verluststrukturen, deren Feinstruktur mit der berechneten rJDOS nachvollzogen werden konnte.
In KNbO3 wurde der Beitrag der Nb 5p und O 2p-Zustandsdichte zum Valenzband untersucht. Es wurde versucht, die Anregungsenergieabhängigkeit der O 2p-Emissionsspektren mit der Bandstruktur in Verbindung zu bringen.
In KTaO3 wurde erstmals der Ta 5d-pDOS-Anteil am Valenzband direkt nachgewiesen. Zudem weisen die anregungsenergieabhängigen Emissionsspektren Verluststrukturen auf, die auf eine O 2p-Ta 5d Interbandanregung schließen lassen.
An Sr2FeMoO6 wurden erstmals XES-Messungen zur Bestimmung der elektronischen Struktur durchgeführt. Es zeigen sich hybridisierte O 2p-Mo 4d Zustände, die Leitungselektronen haben einen leichten Fe-Charakter. Eine gute Übereinstimmung mit Bandstrukturrechnungen wird beobachtet.
Für photorefraktive Material Sn2P2S6 wurde die elektronische Struktur mittels XPS, XES und FP-LAW-Rechnungen detailliert bestimmt.
An Fe-dotiertem Ba0.77Ca0.23TiO3 wurde mittels XPD unter erstmaliger Erstellung von Azimuthalspektren der Einbauplatz von Ca verifiziert und der Einbauplatz von Eisen bestimmt. Für beide Elemente ergibt sich ein vollständiger bzw. überwiegender Einbau auf dem Ba-Platz.
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Synthesis of Thiophene-Vinyl-Benzothiazole Based Ligand Analogues for Detection of Aβ and Tau Pathology in Alzheimer's DiseaseJohansson, Joel January 2024 (has links)
As of today, Alzheimer’s disease is the leading cause of dementia among neurodegenerative disorders, affecting many millions of people worldwide. As the average life span of populations increase, more and more people succumb to the illness each year. Like other neurodegenerative disorders, Alzheimer’s disease can be attributed to the accumulation of protein aggregates in the brain. These amyloid-β peptides and tau proteins can presumably be detected in the brain many years before the onset of clinical symptoms. Development of fluorescent ligands, capable of binding to these neuropathological hallmarks and highlighting them, could serve as molecular diagnostic tools and facilitate an early diagnosis of the disease. The method could also be useful in studying disease progression and evaluating the effects of novel treatments. One such ligand is HS-259. The aim of this project was to synthetize different analogues of HS-259, and test their selectivity towards the aforementioned aggregates in brain tissue from an individual with Alzheimer’s disease. Staining of tissue samples with analogue solution enables visualization of aggregate sites through fluorescence imaging. In the end, five analogues were synthetized, albeit in relatively low overall yields. Synthetic methods included Suzuki-Miyara cross-couplings, Ullmann-type arylations and condensations. Liquid Chromatography-Mass Spectrometry (LC-MS) and Nuclear Magnetic Resonance (NMR) were used for analysis of the compounds. Two of the five analogues could be tested for staining of aggregates and assessed for photophysical characteristics, i.e. absorption- and emission spectra. One analogue stained both amyloid-β aggregates and some tau aggregates, whereas the other stained neither. Since only two analogues were tested and rendered inconsistent results, further studies are needed to assess the binding properties of HS-259 analogues in general.
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