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Examining Perspectives On China's Near-Monopoly Of Rare EarthsBryant, Gregory J 24 March 2015 (has links)
China’s behavior as a near-monopolist of rare earths has come under increasing scrutiny in recent years. This thesis first examines the underlying causes behind China’s rise to the status of rare-earths near-monopolist, including government support; lax environmental controls; unregulated production; and relatively low costs compared to the rest of the world. Second, the thesis also examines the preeminent international and domestic factors influencing China’s behavior as a near-monopolist of rare earths. International factors include international demand; international trade pressure; international price-setting authority issues; and geopolitical factors. I next identify domestic factors that exert influence over China’s rare earths-related behavior: environmental protection; rare earth resource protection; rare earths industry regulation; and protecting and aiding China’s domestic rare earths industry. The study concludes with a synthesis of the factors influencing China’s rare-earths-related behavior in the overall context of support and direction by China’s Central Government.
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Evolução das propriedades magnéticas ao longo da série de compostos intermetálicos RTBi2 (R = Ce, Pr, Nd, Sm, Gd; T = Cu, Au) / Evolution of the magnetic properties along the RTBi2 (R = Ce, Pr, Nd, Sm, Gd; T = Cu, Au) series of intermetallic compoundsJesus, Camilo Bruno Ramos de, 1987- 31 August 2018 (has links)
Orientador: Pascoal José Giglio Pagliuso / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-31T09:11:43Z (GMT). No. of bitstreams: 1
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Previous issue date: 2016 / Resumo: Neste trabalho investigamos as propriedades estruturais e magnéticas da família de compostos intermetálicos RTBi2 (R = Ce, Pr, Nd, Sm, Gd; T = Cu, Au) além do composto CeCd0,7Sb2. As amostras foram crescidas pelo método de fluxo metálico, a maioria delas de forma inédita. Medidas macroscópicas de resistividade elétrica, susceptibilidade magnética e calor específico foram realizadas, além de medidas de espectroscopia de raios X de energia dispersiva ¿ EDS e difração de raios X. Medidas microscópicas de difração magnética de raios X e ressonância magnética nuclear (RMN) foram realizadas, com ajuda de colaboradores, no composto CeCuBi2. Um modelo de campo médio que inclui uma interação de troca isotrópica entre primeiros vizinhos e efeitos de campo cristalino tetragonal foi utilizado para ajustar as medidas de magnetização e calor específico. Esses ajustes forneceram os parâmetros e esquemas de campo cristalino e os valores das constantes da interação de troca. A partir dessas análises encontramos como que efeitos de campo cristalino e a competição entre interações magnéticas, ferromagnética e antiferromagnética, governam as propriedades magnéticas desses compostos / Abstract: In this work we have investigated the structural and magnetic properties of the family of intermetallic compounds RTBi2 (R = Ce, Pr, Nd, Sm, Gd, T = Cu, Au) and, additionally, the CeCd0.7Sb2 compound. The samples were grown by Bi metallic flux method, most of them for the first time. Macroscopic measurements of electrical resistivity, magnetic susceptibility, specific heat were carried out with supplementary measurements of Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction. Microscopic measurements of magnetic X-ray diffraction and nuclear magnetic resonance (NMR) were carried out with the help of collaborators in the CeCuBi2 compound. A mean-field model that includes an anisotropic exchange interaction between nearest neighbors and tetragonal crystal field effects was used to fit the magnetization and specific heat data. The best fits yield the crystal field parameters and schemes of level and the values of the constants of exchange interaction for each compound in the RTBi2 series. From these analyzes, we have described how the crystal field effects and the competition between magnetic interactions, ferromagnetic and antiferromagnetic, govern the magnetic properties of these compounds / Doutorado / Física / Doutor em Ciências / 1141235/2012 / CAPES
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High pressure, high temperature synthesis of selected rare earth polysulfides and polyselenidesWebb, Alan Wendell 01 May 1969 (has links)
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.
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Photon avalanching in Tm³⁺:NaYF₄ nanocrystals and its applicationsLee, Changhwan January 2022 (has links)
Photon avalanching (PA), one of the more unique nonlinear optical processes due to its combination of efficiency and extreme response, first attracted attention from the optics community more than four decades ago. But interest waned as researchers found that it did not provide immediately useful features observed in other nonlinear optical systems, such as amplified coherent light generation from lasing or optoelectronic amplification and transduction afforded by light-stimulated electron avalanching. The material systems supporting PA were also found to be rather limited, with reports concentrating on fragile, bulk lanthanide-doped crystals. However, the inter-ionic energy transfer mechanisms responsible for PA and its extreme nonlinearity are, in principle, realizable in objects with dimensions at the nanoscale. Further, new applications for PA in nanomaterials including simple super-resolution microscopy have recently been proposed. These factors motivated my research on the development of the first-ever lanthanide-doped nanoparticles capable of supporting PA behavior.
In this thesis, the optical properties of Tm³⁺-doped NaYF₄ nanocrystals are investigated with photoluminescence microscopy, spectroscopy and differential rate equation model simulations. First, the photon avalanching behavior of Tm³⁺-doped NaYF₄ nanocrystals is studied. Specifically, the excitation-power-dependent luminescence of 1%, 4%, 8%, 20%, and 100% Tm³⁺-doped NaYF₄ is measured. The slopes of log-log excitation intensity versus emission intensity plots show that photon avalanche is realized in the nanocrystals when Tm³⁺ content is 8% and above. Time-resolved luminescence and rate equation model fitting to the experimental data validate the existence of photon avalanche, showing luminescence rise times > 600 ms, and the ratio of the ³F₄-to-³F₃ excited state absorption to the ³H₆-to-³F₄ ground state absorption is > 10⁴, which are signatures of photon avalanche. The design-dependent shift of the photon avalanching threshold also shows that photon avalanche is the main excitation scheme for the nanocrystals and implies potential applications for ultra-sensitive nano-sensing with the help of extreme nonlinearity. Additionally, the steep nonlinearity leads to super-resolution microscopy of single 8% Tm³⁺-doped nanocrystals with resolution down to <70 nm using conventional confocal microscopy without sophisticated techniques.
In the second part of the thesis, the photodarkening effect of Tm³⁺-doped NaYF₄ nanocrystals is studied. We have found that photodarkening behavior is observed in Tm³⁺-doped nanocrystals that exhibit the photon avalanche effect. Power-dependent luminescence of a single 8% Tm3+-doped nanocrystal reveals that photodarkened nanocrystals still support photon avalanche behavior, but the avalanching threshold is shifted to a higher value. A photodarkening mechanism is proposed based on the concentration-dependent and power-dependent luminescence properties, and optical spectroscopic data. Notably, photodarkened nanocrystals are found to recover their original brightness and behavior under Vis-NIR optical illumination. This so-called “photobrightening” allows novel photoswitching of the inorganic nanocrystals, which has never before been achieved. We observe robust single nanocrystal photoswitching over 1000 cycles without permanent photodegradation. In addition, rewritable photolithography of multiple patterns using NIR lasers at 700 nm and 1064 nm is demonstrated.
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Rare-earth distributions in the marine environment.Spirn, Regina Volfovsky January 1966 (has links)
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Geology and Geophysics, 1966. / Vita. / Bibliography: leaves 137-143. / Ph.D.
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Perturbed Angular Correlation Studies in the Ferromagnetic Rare EarthsMcMath, Thompson Andrew 10 1900 (has links)
<p> A low temperature apparatus has been constructed for the purpose of studying perturbed angular correlations in the ferromagnetic rare earth elements. The rotation of the 966.4 keV gamma vibrational state in 160Dy was measured to be (1.61 ± 0.33) milliradians.</p> / Thesis / Master of Science (MSc)
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Linking Super Earth Composition to Planet Formation HistoryAlessi, Matthew January 2016 (has links)
Super Earths are a class of exoplanets with masses between 1-10 M⊕. Comprising nearly 70 % of the discovered planet population, they are largest class of exoplanets known. Super Earths exhibit an interesting variety of compositions, as their densities imply that they range from dense, rocky planets to those with substantial amounts of water. This thesis aims to understand why super Earths form so frequently, and to connect the final compositions of super Earths to the regions where they form in protoplanetary disks. To do this, we combine a model that calculates the physical and chemical conditions within a protoplanetary disk with a core accretion model of planet formation. A key feature of our planet formation model is planet traps that act as barriers to rapid type-I migration. The traps we include in our model are the dead zone, which can be caused by cosmic ray or X-ray ionization, the ice line, and the heat transition. In disks with lifetimes > 4 Myr we find that planet formation in all traps results in Jovian planets. Typically, the X-ray dead zone and heat transition traps produce hot Jupiters orbiting near 0.05 AU while the cosmic ray dead zone and ice line traps produce Jupiters near 1 AU. Super Earths are found to form in disks with short lifetimes < 2 Myr that photoevaporate prior to planets undergoing runaway gas accretion. Additionally, we find that super Earth formation takes place in low-mass disks (< 0.05 M⊙), where planet formation timescales exceed disk lifetimes inferred through observations. The location of various traps throughout the disk play a key role in allowing super Earths to achieve a range of compositions. Super Earths forming in the ice line or heat transition accrete solids from cold regions of the disk, resulting in planets with large ice contents (up to 50 % by mass). Conversely, super Earths formed in the dead zone trap accrete solids from warm regions of the disk and are therefore composed of mostly rocky materials (less than 5 % ice by mass). / Thesis / Master of Science (MSc)
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Photonic Applications of Rare Earth Doped TEOS Based Silica Thin Films and WaveguidesHudgins, Robert Anthony 30 June 2003 (has links)
No description available.
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Evaluation of partial melting models of the origin of some Australian basalts : trace element evidence.Roy, Stephen Donald January 1975 (has links)
Thesis. 1975. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Bibliography : leaves 137-144. / M.S.
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I Am Because We Are: Africana Womanism as a Vehicle of Empowerment and InfluenceBlackmon, Janiece L. 04 February 2009 (has links)
The purpose of this research project has been to shed light on the experiences of Black women in Afrocentric groups' Nation of Gods and Earths, the Black Panther Party, and Rastafarians' that operated on the fringes of society during the 1960s through the early 2000s. This work articulates the gender dynamics between the men and women of the groups. In it, I trace the history of Black nationalism and identity in the United States in the late 19th century to the 20th century which set the framework for the formation of the Nation of Gods and Earths (NGE), the Black Panther Party(BPP), and Rastafarianism and its members to see themselves as a part of the Black nation or community and the women of these groups to see their identity tied in with the goals and desires of the group not as one set on individualistic ambitions.
The Africana womanist did not see herself as an individual but rather a vital part of the entire Black community. From a feminist perspective, it would appear as though the women of these Afrocentric fringe groups were marginalized and oppressed by the men but this perspective fails to give credence to the fact that Rasta women, Earths—the female members of the NGE—and women Panthers saw race and racism as a more pressing issue than that of sexism. That is not to say that women in these groups did not question or challenge some of the sexist actions of their male counterparts. When there was a challenge it was done so in a way that reminded the men of the tenets of their respective group and their responsibility to uphold those principles; principles that required the men to consider the women as equally valuable in the cause of the group and deserving of just treatment.
While adhering to a gender order that afforded the male members a more visible position, the women of this study did not view their positions as mothers, wives, and sister members as a hindrance to their own personal joy or freedom. In fact, using an Africana womanist point of view, they would argue that it was in the best interest of the entire Rasta, NGE, or BPP and by extension, the Black community for them to own their statuses as a form of empowerment. For it was through their wombs and nurturing that the next generation would be born, through their providing a stable home that would allow their husbands to focus their attentions on the issues concerning their communities outward and through their role as supportive "sisters" encouraging the men that the community could advance socially. / Master of Arts
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