Rare earth elements modelling

The problem is no longer the validity of Mendeleev s system, but the best way to represent it. Should it be the original short-form table with 8 columns, the familiar medium-long form with 18 columns, or perhaps even a long-form table with 32 columns, which more naturally accommodates the rare earth elements Into the main body of the table Altanahvely, some favor pyramidal tables, while others advocate the left-step form proposed by diaries Janet in the 1920s. Theodor Benfey and rhilip Stewart have proposed continuous spiral models. Hundreds, possibly even thousands, of periodic systems have been proposed, and each has its ardent supporters. 

RBa2Cu307 (R = rare earth element or Y), La2 (5r,.Cu04 (0 < X < 0.3) Eu-155(Gd-155) emission Mossbauer spectroscopy, EFG tensor at R sites, in good agreement with point charge model when holes are supposed to be mainly in sublattices of the chain and at oxygen in Cu-O plane... 

Van Orman JA, Grove TL, Shimizu N (2001) Rare earth element diffusion in diopside influence of temperature, pressure and ionic radius, and an elastic model for diffusion in silicates. Contrib Mineral Petrol 141 687-703... 

Hsi C, Langmuir D (1985) Adsorphon of uranyl onto ferric oxyhydroxides applications of the surface complexation site-binding model. Geochim Cosmochim Acta 49 1931-1941 Ingri J, Widerlund A, Land M, Gustafsson O, Anderson P, Ohlander B (2000) Temporal variation in the fractionation of the rare earth elements in a boreal river the role of colloidal particles. Chem Geol 166 23-45... 

Rare earth element data will also serve as the basis for a forward modeling study to better constrain melting systematics in the Galapagos. The melting model will invoke clinopyroxene-rare earth element partition coefficients, which vary with composition (Gallahan and Nielsen, 1992), and a polybaric or column melting process. 

Salah, S. 2000. Weathering Processes at the Natural Nuclear Reactor of Bangombe Gabon). Identification and Geochemical Modeling of the Retention and Migration Mechanisms of Uranium and Rare Earth Elements. PhD thesis, Universite Louis Pasteur, Strasbourg, France. 

The recoveries of several rare earth elements in leachates obtained from apatite concentrates were determined by Jorjani et al. [68] for ICP-AES and ICP-MS. A neural network model was used to predict the effects of operational variables on the La, Ce, Y and Nd recoveries in the leaching process. The neural network employed was a feed-forward one. 

Elements with ionic species commonly associated with quartz and mica minerals such as Na, Zr, and Hf are more likely to co-vary with those minerals rather than hematite. The ratio of these latter elements to Fe-substituting elements would be dependent on the relative amounts of hematite and other minerals in the sample rather than just die rock-forming processes. For this reason, elements that commonly substitute into quartz and other abundant minerals in the samples were excluded from the discriminant analysis. Some rare earth elements may also play a role in fingeiprinting the sources, and their importance was tested by comparing discriminant analysis models with and without La, Sm, and Th. 

The position of yttrium in rare earth chemistry has always been interesting and this is also the case with respect to complex formation. The electrostatic model suggests placement of yttrium between holmium and thulium. It has been shown that it is not the case [14]. When one considers the stability constant data of group 1 ligands, yttrium is similar to the heavy rare earths. When the second group of ligands is considered, yttrium exhibits a behaviour similar to the lighter rare earth elements. 

Spitz A. H. and Goodrich C. A. (1987) Rare earth element tests of ureifite petrogenesis models. Meteoritics 21, 515-516. 

Wood B. J. and Blundy J. D. (1997) A predictive model for rare earth element partitioning between clinopyroxene and anhydrous silicate melt. Contrib. Mineral. Petrol. 129, 166-181. 

Erel Y. and Stolper E. M. (1992) Modelling of rare-earth element partitioning between particles and solution in aquatic environments. Geochim. Cosmochim. Acta 57, 513-518. 

In summary, this work shows for the first time a marked influence of cerium species on the vanadium reducibility. Since rare earth elements in FCC catalysts depend on different preparation morphologies, it is necessary to develop a model to quantify the oxidation state of vanadium. 

Converting the absorption lines into abundances requires knowledge of line positions of neutral and ionized atoms, as well as their transition probabilities and lifetimes of the excited atomic states. In addition, a model of the solar atmosphere is needed. In the past years, atomic properties have seen many experimental updates, especially for the rare earth elements (see below). Older solar atmospheric models used local thermodynamic equilibrium (LTE) to describe the population of the quantum states of neutral and ionized atoms and molecules according to the Boltzmann and Saha equations. However, the ionization and excitation temperatures describing the state of the gas in a photospheric layer may not be identical as required for LTE. Models that include the deviations from LTE (=non-LTE) are used more frequently, and deviations from LTE are modeled by including treatments for radiative and collision processes (see, e.g., [27,28]). 

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