Orientadores: Narcizo Marques de Souza Neto, Flávio César Guimarães Gandra / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-26T19:21:43Z (GMT). No. of bitstreams: 1 Reis_RicardoDonizethdos_D.pdf: 10140891 bytes, checksum: 060b8807511ae67be03dba829dddacaf (MD5) Previous issue date: 2015 / Resumo: Os resultados apresentados nesta tese mostram a potencialidade do uso das técnicas de espectroscopia de absorção de raio X no estudo das hibridizações (4f,5f )/(5d,6d) em compostos intermetálicos ajudando no entendimento de diversos fenômenos físicos. Na primeira parte do trabalho utilizamos as técnicas de espectroscopia para estudar o comportamento da valência e do magnetismo no composto de EuPt2Si2 quando submetido à pressão. Ao contrário do previamente reportado na literatura nossos resultados mostram que o composto de EuPt2Si2, encontra-se nas vizinhanças de um ponto crítico quântico de flutuação de valência, e a valência do íon de Eu, que é de 2.2 ã pressão ambiente, aumenta com o incremento da pressão se tornando 3+ para pressões maiores do que 15 GPa. A mudança de valência diminuiu o número de íons magnéticos da amostra o que provoca um colapso do seu momento magnético. Nossos dados suportados por cálculos de densidade de estados eletrônicos mostram que o processo de transição de valência ocorre com uma transferência de carga entre os níveis 4f e 5d do Európio, acompanhado de uma maior localização dos orbitais 5d do Eu, fazendo com que as cargas inicialmente compartilhadas pelos íons de Eu/Pt/Si se localizem no orbital 5d do Eu. Na segunda parte desta tese nós mostramos, até nosso conhecimento, os primeiros resultados de dicroísmo circular magnético de raios X (XMCD) nas bordas L2,3 do Urânio. Foram estudados os compostos de UM2(M=Ga,Ge) e UX(X=Te,Se) para os quais foi observada uma gigante contribuição quadrupolar nos espectros de dicroísmo na borda L3. Descrevemos uma metodologia associando a técnica de dicroísmo circular magnético com simulações da estrutura eletrônica usando teoria do funcional densidade (DFT), para estudar o grau de hibridização entre os orbitais 5f-6d e obter informações a respeito do caráter itinerante/localizado do magnetismo de cada um dos compostos. Por fim, a seletividade ao elemento químico da técnica de XMCD foi aplicada no estudo do magnetismo dos compostos de UCu2Si2 e UMn2Si2. A partir dos espectros de XMCD nas bordas L3 do Urânio e K do Cu e do Mn, mostramos que ao contrário do previamente reportado na literatura, tanto o Urânio como os metais 3d nesses materiais apresentam um momento magnético não nulo e que as hibridizações entre os níveis 5f e 3d regulam as propriedades magnéticas nestes dois materiais. Além disso, mostramos que no composto UCu2Si2 o momento magnético oriundo dos níveis 5f (contribuição quadrupolar do XMCD) é antiparalelo ao momento dos níveis 6d (contribuição dipolar do XMCD) / Abstract: The results reported in this thesis show the potential for the use of X-ray Absorption Spectroscopy (XAS) technique on the study of (4f,5f )/(5d,6d) hybridization in intermetallic compounds aiding the understanding of many physical phenomena. On the first part of this thesis, in order to probe the changes in the valence state and magnetic properties of EuPt2Si2 compound under extreme pressure, x-ray absorption near-edge spectroscopy (XANES) and x-ray magnetic circular dichroism (XMCD) were carried out. The XANES spectrum exhibitx a strong dependence with temperature and pressure. Contrary to previous reports, Eu was found to change the valence with the increase of the pressure from divalent to the trivalent state. The change in valence reduced the number of magnetic ions of the sample which causes a collapse of its magnetic moment. Density functional theory has been applied to give insight into the pressure-induced changes in Eu valence and the magnetic ordering on this compound. In the second part of this thesis we show, to the best of our knowledge, the first results of magnetic circular dichroism in Uranium L2,3 edges. A giant quadrupolar contribution was observed in U-L2,3 edges x-ray magnetic circular dichroism of a few representative Uranium compounds (UGa2, UGe2, UTe and USe). We support the spectroscopic data with density functional theory to assess the degree of 5f -6d electronic hybridization and the degree of itineracy/localization of 5f electrons in each of the compounds. Finally, we use the element and orbital selectivity of XANES and XMCD measurements combined on U-L3 and Cu and Mn K absorption edges to probe the eletronic and magnetic properties of the UMn2Si2 and UCu2Si2 compounds. Our results show that both Uranium and 3d elements present magnetic moment and therefore the 5f /3d hybridization regulates the magnetic properties on these compounds. Furthermore, we show for UCu2Si2 compound the aligment of magnetic moments of U 5f and U 6d orbitals is antiparallel / Doutorado / Física / Doutor em Ciências

The rare earth polysulfides and polyselenides of Tm, Yb, and Lu are unknown. The ionic radius of the rare earth has become too small to allow the structure common to the known members of the series, and with the polysulfides the stable temperature zone is too low to give the high sulfur pressure necessary for synthesis of RS_2. It was felt that high pressure, high temperature techniques could be used to overcome both problems and to allow synthesis of compounds not possible by ordinary methods. Synthesis studies were carried out on mixtures of the rare earth element plus sulfur in the 1:2 mole ratio for Nd, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. The known polysulfide series was extended three members, TmS_2, YbS_2, and LuS_2. A high pressure pseudo-cubic polymorph was found for nine members, GdS_2, TbS_2, DyS_2, HoS_2, ErS_2, TmS_2, YbS_2, LuS_2, and YS_2. The minimum pressure of formation for the cubic polymorphs was found to be a smooth function of the ionic radius of the rare earth elements except for Y. YS_2 required a higher pressure to form the cubic polymorph than expected from the usual value of the ionic radius of Y, but the compressibility of Y is somewhat higher than Dy, which Y otherwise closely resembles. The reaction product diagrams of the rare earth polysulfides were all very similar. Regions were found where Ho_2S_3 and Yb_2S_3 were found on their respective diagrams. These compounds had the recently reported cubic Th_3P_4 type structure. Synthesis studies were carried out on 1:2 molar mixtures of rare earth element plus selenium for Er, Tm, Yb, and Lu. The known polyselenide series was extended three members to include TmSe_2, YbSe_2, and LuSe_2. Cubic Er_2Se_3 with the Th_3P_4 type structure was found at the highest pressure and temperature tried for the Er + 2 Se system. Prior to this work Er_2Se_3 was known only with the orthorhombic Sc_2S_3 type structure. The results of this investigation suggest that high pressure, high temperature techniques can be used to extend other series of rare earth compounds and several possibilities are suggested.

The isomer distribution in the sulfonation of iodobenzene at -12.5°C. with sulfur tr~oxide (S-35) in liquid sulfur dioxide was found to be 1.40 ± 0.11% ortho, 0.34 ± 0.11% meta, and 98.26 ± 0.11% para. Pure sodium salts of each of the isomers were made from the corresponding aminobenzenesulfonic acids. After dilution with an aliquot of the sulfonation mixture, the salts were purified by recrystallization and were counted by liquid scintillation counting. Attempts to determine the relative rate of sulfonation between toluene and iodobenzene failed. The radioactive sodium p-iodobenzene sulfonate could not be separated from sodium p-toluenesulfonate by recrystallization. The lithium amides of methylamine, ethylamine, isopropylamine, tert-butylamine and 2-aminopropane-2-d were prepared from phenyl lithium and the amines. Infrared spectra of the amides were scanned in the C-H region. Comparison of the spectra of the amides and the amines showed no shifts like those found for the corresponding alcohol-alkoxide spectra. It was therefore concluded that anionic hyperconjugation could not account for the shift in the spectra of the alcohol-alkoxide system. The behavior of cyclooctatetraene, the silver adduct of cyclooctatetraene, norbornadiene, diphenylacetylene, tetraphenylcyclobutadiene-palladium chloride and ferrocene was studied under high pressures ranging from 15 to 55 kats. and with temperatures from 25 to 850°C. This work was carried out with Hall's tetrahedral anvil apparatus. If the temperature was high enough each of these compounds was found to decompose. When the temperature was below the decomposition temperature, cyclooctatetraene, diphenylacetylene and norbornadiene polymerized. No evidence of a valence tautomerization was found. The silver adduct of cyclooctatetraene and tetraphenylcyclobutadiene-palladium chloride decomposed at high temperatures. No other results were noted with these two compounds. Ferrocene underwent decomposition by iron catalysis to a mixture of iron carbides at pressures from ambient to 55 kats. and temperatures above 500°C. The same products were observed if no iron was added and the temperature and pressure were 55 kats. and 800°C., respectively. A preliminary spectrophotometric study of benzonitrile in 25%-ethyl alcohol-75% water was carried out. Cupric bromide and hydrobromic acid or cupric chloride and hydrochloric acid were added to constant ionic-strength solutions of benzonitrile. No evidence was found in the ultraviolet region for any complex ion formation. The same results were found for p-fluorobenzonitrile.

Part I. The rearrangement of α-anilinoketones was studied in an effort to determine the mode of movement of the nitrogen moiety. A crossover experiment was carried out with an equimolar mixture of 2-(4- bromoanilino)-1-(4-bromophenyl)-2-(4-methoxyphenyl) ethanone and 2-(4-chloroanilino)-1-(4-chlorophenyl) -2-(4-methoxyphenyl)ethanone with γ- picoline hydrobromide as the catalyst. The reaction product was analysed by means of a mass spectrograph. The results of the analysis indicate a crossover of the nitrogen moiety during rearrangement. This indicates that the nitrogen moiety moves in an intermolecular manner during the rearrangement. Part II. The isomer distribution from the sulfonation of bromobenzene with sulfur trioxide was determined by the isotope dilution technique. Bromobenzene was sulfonated with labeled sulfur trioxide (S-35) in refluxing sulfur dioxide and aliquots of the reaction mixture were added to equimolar quantities of the pure isomeric bromobenzenesulfonic acids. Each isomer was then recrystallized until a constant count rate was obtained. The isomer distribution was then obtained by comparing the activity of the individual isomers to the sum of the activities of all three isomers. This gave the following results: Ortho, 0.6 ± 0.2; Meta, 3.6 ± 0.8; Para, 95.9 ± 0.6. A competitive sulfonation between bromobenzene and toluene was run using sulfur trioxide (S-35) in liquid sulfur dioxide as the sulfonation agent. An isotope dilution technique was used to obtain the relative amounts of sulfonated bromobenzene and toluene in the reaction mixture. The relative rate of sulfonation of toluene to bromobenzene is 9.4. Comparing this with the toluene-benzene rate ratio of 29.5 gives a bromobenzene-benzene rate ratio of 3.1. Part III. Cycloöctatetraene and ferrocene have been submitted to very high pressure (up to 92 kiloatmospheres) and in the case of ferrocene moderate temperatures have been simultaneously applied (up to 900° C.). Cycloöctatetraene when held at pressures in excess of 54 kiloatmospheres for longer than one hour breaks down into a transparent solid and low boiling liquid. The identities of the solid and liquid have not been determined. Ferrocene breaks down into a mixture of iron carbides as shown by the x-ray powder pattern. This breakdown occurs at 605°C. at a pressure of 24.3 kiloatmospheres and the temperature of decomposition is proportional to the pressure with a proportionality constant of 0.74 kiloatmosphere/°C.

Hydroclimate in the United States (US) is climatologically divided by the 100th meridian. The semi-arid western US has experienced high-amplitude multidecadal swings in drought and soil moisture variability over the last millennium, culminating in anthropogenic warming-driven drying into the early part of the 21st century. In sharp contrast, the climatologically humid eastern US has experienced century-long increases in precipitation and soil moisture, and generally less warming than in the west, creating a fascinating wetting east – drying west contrast over North America. In eastern North America, a large proportion of the annual precipitation trend was driven by fall-season increases in the southeastern US (SE-US). A rigorous examination of this region would lead to greater insight into the broader causes of hydroclimatic change across North America. The objectives of this dissertation are to (1) identify the large-scale drivers of increased fall precipitation in the SE-US and (2) contextualize and evaluate the causes of regional-to-continental scale changes in soil moisture availability across North America.The first three research chapters of my dissertation focus on my first objective to address the causes of the 20th-century fall precipitation trend. In my first research chapter, I identify and describe fall-season precipitation increases in the SE-US. I show that fall precipitation in the SE-US has increased by nearly 40% during 1895-2016 due to increased circulation-driven moisture transport from the Gulf of Mexico into the SE-US, likely associated with a strengthening or relocation of the North Atlantic Subtropical High (NASH). The NASH is a semipermanent high pressure system located over the North Atlantic that directs moisture transport into the SE-US. Using atmospheric general circulation models forced by sea-surface temperatures (SSTs) and anthropogenic emissions, I demonstrate that models have the capability to simulate a precipitation response to the NASH, but the observed precipitation trend was extremely unlikely in both forced and unforced scenarios. This indicates that the fall precipitation trend was likely caused by processes not well represented in these models, suggesting more work is needed to address why models are unable to simulate observed circulation and SE-US precipitation trends. SST-forced simulations do simulate an enhanced, although displaced to the northwest, NASH and greenhouse gases appear to weakly increase the likelihood of fall wetting. In the first research chapter, I evaluated the proximate drivers of the SE-US fall precipitation variability and trends, working towards the goal of identifying the ultimate driver of observed NASH intensification and SE-US wetting. As a next step, it is important to understand how the increases in precipitation have been delivered, particularly given that fall overlaps with the peak of Atlantic hurricane season. In the second research chapter, I complete a daily-scale decomposition of storm types and precipitation intensity in the SE-US to understand how different precipitation events influenced the fall precipitation increase. I show that increases in SE-US fall precipitation occurred largely as a result of highest-intensity non-tropical (mostly frontal) precipitation days (72% contribution to the fall precipitation trend). In contrast, precipitation from tropical cyclones, a major contributor to extreme fall precipitation, demonstrated a nominal but positive contribution to the trend (13%). Nearly all of the precipitation was delivered on the most extreme (top 5%) intensity precipitation days. These results suggest the observed increase in SE-US fall precipitation has critical implications for flash flood risk from high-intensity rainfall events should the trend continue through the 21st century. Once I identified the types and intensity of storms that influence the fall precipitation trend, I sought to diagnose the physical causes of increased circulation into the SE-US and resultant increases in fall precipitation in the third research chapter. I find that fall precipitation was facilitated by an increase in zonal sea-level pressure (SLP) gradient over the Gulf of Mexico, almost entirely driven by increased SLP along the western edge of the NASH. The zonal SLP gradient was linked to an upper-tropospheric wave train over the North Pacific and North America, leading to increased circulation into the SE-US from the Gulf of Mexico. SST-forced simulations are capable of simulating the spatial features of the NASH and wave train but lack the circulation trends that lead to increased zonal SLP gradient and fall precipitation. The models simulated an enhanced tropical-to-subtropical wave train which increased subsidence and SLP over the subtropical Atlantic Ocean and North America and led to a stronger, more expansive modeled NASH intensification relative to reanalyses, suggesting there exists a stronger atmospheric response to tropical SSTs in models. Due to these discrepancies between models and reanalyses, we can anticipate limitations when using atmospheric models forced by observed SSTs to assess regional climate change in the North Atlantic basin. More research will be needed to understand the physical processes that influence this divergence. The ultimate cause of increased fall moisture transports into the SE-US and resulting precipitation increases remains elusive, but this work improves our understanding of the succession of climatic events that contribute to increased fall precipitation and identify key areas of research needed to reduce uncertainty in SST-forced models. In the final research chapter, I address my second dissertation objective and broaden the focus to all of North America to investigate and contextualize the recent increase in the contrast between soil moisture anomalies in eastern and western North America, termed the east-west North American aridity gradient. Positive aridity gradient values refer to periods during which soil moisture anomalies are more positive in eastern relative to western North America. Using observed and tree-ring reconstructed summer soil moisture anomalies, I show that the 2001-2020 aridity gradient was more positive than any 20-year period since 1400 CE, which followed the most negative aridity gradient during 1976-1995. Using hydrologic models, I find the 2001-2020 aridity gradient anomaly was predominantly driven by century-long summer precipitation increases in the East and to a lesser degree by annual temperature and humidity trends and spring precipitation decreases in the West. Model-simulated anthropogenic trends have minimal effects on the aridity gradient trend due to high inter-model spread in modeled precipitation trends and larger warming effects in the East relative to the West. My findings reveal significant uncertainty in how human and natural systems will be impacted by changes in future water resource availability and provide a benchmark for evaluating North American hydroclimatic change in a warming world through the end of the 21st century.

Thesis (Ph. D.)--University of Washington, 1998. / Vita. Includes bibliographical references (leaves [117]-123).

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 124-132).

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes vita. Includes bibliographical references (p. 138-157).

A series of impedance-mismatch experiments with aluminum-gold targets has been performed. These experiments are used to probe the equation of state (EOS) of gold at high pressure. By measuring the shock breakout time from the target rear surface, the shock trajectory is determined and found to be in good agreement with equation of state predictions. In addition, temperatures derived from temporally resolved luminescence measurements of the shocked target rear surface are compared with two different equation of state theoretical models. Our results indicate that whereas the SESAME (from Los Alamos National Laboratory) EOS seems to overestimate the shock temperature, the equation of state of gold which incoporated both the solid and liquid phases gives much closer agreement with observations. The measurements of gold at a shock pressure of ~ 6 Mbar and temperature of ~ 17500 K also represent the first study of gold under shock melting. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Ultra-pure reagents, platinum resistance thermometry and modern inert atmosphere glove box facilities have made possible a detailed examination of the NaK system at atmospheric pressure. A thermoanalytical study of solid-liquid phase equilibria in the NaK alloy system was conducted in the tetrahedral press to 55 kbars to investigate possible intermediate compound formation and shifting of the invariant points at various pressures. An expected shift in the eutectic composition to lower potassium content with an increase in the halt temperature on increasing pressure was confirmed. A merging of the meritectic and eutectic points at 343 ±2°K and 37 ±3 kbars occurred at 0.40 mole fraction K. Above 35 kbars the original meritectic halt behaves much like elemental cesium, suggesting new structural modifications. The possibility of a eutectoid with increased solid solubility limits is suggested for the invariant point which decreases with increasing pressure. The formation of NaK2 under pressure is suggested but not confirmed.