Trace element partitioning Research Papers (original) (raw)

Steels containing reverted nanoscale austenite (cRN) islands or films dispersed in a martensitic matrix show excellent strength, ductility
and toughness. The underlying microstructural mechanisms responsible for these improvements are not yet understood, but are observed to be strongly connected to the cRN island or film size. Two main micromechanical effects are conceivable in this context, namely: (i) interaction of cRN with microcracks from the matrix (crack blunting or arresting); and (ii) deformation-induced phase transformation of cRN to martensite (TRIP effect). The focus here is on the latter phenomenon. To investigate size effects on cRN transformation independent of other factors that can influence austenite stability (composition, crystallographic orientation, defect density, surrounding phase, etc.), a model (TRIP-maraging steel) microstructure is designed with support from diffusion simulations (using DICTRA software) to have the same, homogeneous chemical composition in all cRN grains. Characterization is conducted by in-situ tension and bending experiments in conjunction with high-resolution electron backscatter diffraction mapping and scanning electron microscopy imaging, as well as post-mortem transmission electron microscopy and synchrotron X-ray diffraction analysis. Results reveal an unexpected “smaller is less stable” effect due to the size-dependent competition between mechanical twinning and deformation-induced phase transformation.

The partitioning of P, Sc, Ti, Sr, Y, Nb, the rare earth elements (REE), Hf, Ta, Th and U between zircon and a synthetic andesitic melt was determined as a function of oxygen fugacity (fO 2) over a range of fourteen log units, from QFMÀ8 to QFM+6 (where QFM is the quartz-fayalite-magnetite oxygen buffer) at $1300 °C and 1 atm, using SIMS and LA–ICP– MS. The partition coefficients of Ce and Eu were found to vary systematically with fO 2 , relative to those of the other REE, producing Ce and Eu anomalies similar to those that are characteristic of natural igneous zircon. These anomalies coex-ist at terrestrial fO 2 s and were used to quantify Eu 3+ /(Eu 2+ + Eu 3+) and Ce 4+ /(Ce 3+ + Ce 4+) in the melt. The partition coefficients of the redox invariant trivalent cations are in excellent agreement with lattice strain theory. The values of D REE are related to those determined for natural samples by the expected dependence on temperature. The incorporation of REE 3+ in zircon was independent of the presence of P. D U /D Th was found to vary systematically with fO 2 indicating the presence of U 4+ , U 5+ and U 6+ in the melt at terrestrial conditions. D Ti was independent of fO 2 despite an expectation of significant Ti 3+ in the most reduced experiments.

""ERDOĞU, B. , I. T. UYSAL, O. ÖZBEK, Ü. ULUSOY, 2013, Speleothems of Çatalhöyük, Turkey, Mediterranean Archaeology & Archaeometry: An International Journal, Volume 13, No.1 1Trakya University, Department of Archaeology, EDIRNE,... more

""ERDOĞU, B. , I. T. UYSAL, O. ÖZBEK, Ü. ULUSOY, 2013, Speleothems of Çatalhöyük, Turkey, Mediterranean Archaeology & Archaeometry: An International Journal, Volume 13, No.1

1Trakya University, Department of Archaeology, EDIRNE, TURKEY
2 The Queensland Geothermal Energy Centre of Excellence,
The University of Queensland, AUSTRALIA
3 Çanakkale (18th March) University, Department of Archaeology, TURKEY
4 Hacettepe University, Department of Physics Engineering, ANKARA, TURKEY

ABSTRACT
Speleothem samples such as flowstone, stalagmite and stalactites are one of the important finds at Çatalhöyük, which they have been carried hundreds of kilometers from its source. The “Çatalhöyük Speleothem Project” have been initiated with the aim of investigating Çatalhöyük’s speleothems and identifying their provenance. In order to achieve this, speleothem samples at Çatalhöyük have been recognized and documented, and caves around Çatalhöyük have been investigated. Later, both selected Çatalhöyük speleothem and cave samples of flowstone, stalagmite and stalactites have been analysed by ICP-MS to recognize similar trace elements. In addition, the ages of samples have been obtained by U-Th method to find similarities between the Çatalhöyük samples and speleothem deposits from surrounding caves. The comparative results have been used to identify the sources of Çatalhöyük’s speleothems.""

Mantle-derived peridotites sampled at three dredge sites between the Discovery and Indomed fracture zones on the Southwest Indian Ridge axis are analyzed for petrography and major and trace element mineral compositions. While textures and microstructures are those typical of normal residual peridotites these rocks display a large compositional variation encompassing the whole spectrum of abyssal peridotites even at the scale of a single dredge site (≤ 1 km). Particularly, clinopyroxenes in peridotites dredged at 44.03°E show a huge variation in sodium contents positively correlated with chromium concentrations. Observed Na\ \Cr enrich-ments exceed the commonly reported contents of the spinel abyssal peridotites. Similar values are also found in very few peridotite samples collected at ultra-slow spreading ridges. Major substitutions governing the compositions of these clinopyroxenes suggest that Na\ \Cr covariation is caused by a more rapid decrease in Al-Tschermak's molecule with respect to the sodic components jadeite ± kosmochlor, as Cr/Al increases and modal clinopyroxene decreases. We conclude that sodium and chromium enrichments must have occurred contemporaneously with aluminum depletion, i.e., during partial melting. Our modelling suggests that partial, non-modal, melting of a depleted peridotite in association with addition of sodium, by percolation of a Na-rich melt in the upwelling mantle, or Na diffusion from a nearby alkaline melt, may explain this enigmatic and counterintuitive trend.

High resolution in situ trace element μXRF maps and profiles were measured on the enamel exposed in cross sections through archaeological human permanent molars from seven Late Neolithic/Early Chalcolithic funerary caves and megalithic graves of north-central Iberia. Changes in concentrations of Fe, Zn and Sr in inward direction into the enamel shed light on diagenetic and endogenous trace element concentrations in archaeological tooth enamel. Most of these profiles resemble sigmoid-shaped leaching profiles, suggesting that a combination of diffusion and advection processes govern the uptake of trace elements into the enamel from pore fluids on the outside of the tooth and in the more porous dentine. The present study shows how diffusion-advection (DA) models can be fitted to these trace element profiles to explain changes in trace element concentrations that happen during diagenesis. DA models explain a major part of the variation observed in leaching profiles into the enamel and can be used to reconstruct endogenous trace element concentrations, leaching times and leaching depth as well as trace element concentrations in ambient pore water during diagenesis. Models of trace element leaching together with trace element mapping reveal that Fe, Zn and Sr concentrations consistently increase during diagenesis, regardless of the type of burial site (i.e. funerary caves vs. megalithic graves). Profiles of Pb concentrations show much smaller concentration gradients, causing DA model fitting to be less accurate. Modelled leaching depths of 300-400 μm warrant a careful approach when sampling for endogenous archaeological tooth enamel for trace element and stable isotope analysis. Results also show that it is possible to reconstruct endogenous trace element concentrations from these samples, even without applying pretreatment procedures, because leaching of trace elements into the enamel often remains limited to the outer 300-400 μm of the enamel on archaeological timescales. Modelled leaching times are about ten times lower than the age of the samples, suggesting that the rate of trace element leaching into tooth enamel slows down or even halts during the burial period.

- by Niels de Winter and +1
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- Archaeology, Trace element partitioning, X-Ray Fluorescence (XRF) Spectroscopy, Neolithic Europe
- by James Rae
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- Earth Sciences, Climate Change, Paleoclimatology, Paleoceanography
- by Jonathan Erez
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- Earth Sciences, Climate Change, Paleoclimatology, Paleoceanography
- by Kennedy, Allen K.
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- Earth Sciences, Geology, Geochemistry, High Pressure

This paper presents a genetic based approach to the partitioning and mapping of multicore SoC cores over a NoC system that uses mesh topology. The proposed algorithm performs the partitioning and mapping by reducing communication cost and minimizing power consumption by placing those intercommunicated cores as close as possible together. A program developed in C++ in which the provided specification of the multicore MPSoC system captures all data dependencies before any start of the design process. Experimental results of several multimedia benchmarks demonstrates that the genetic-based approach able to find different satisfied implementations to the problem of partitioning and mapping of MPSoC cores over mesh-based NoC system that satisfies design goals.

- by Kennedy, Allen K.
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- Earth Sciences, Geology, Geochemistry, High Pressure
- by Kennedy, Allen K.
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- Earth Sciences, Geology, Geochemistry, High Pressure

Coupled equations describing diffusion and cross-diffusion of tracer particles in hard-sphere suspen-sions are derived and solved numerically. In concentrated systems with strong excluded volume and viscous interactions the tracer motion is subdiffusive. Cross diffusion generates transient perturbations to the host-particle matrix, which affect the motion of the tracer particles leading to nonlinear mean squared displacements. Above a critical host-matrix concentration the tracers experience clustering and uphill diffusion, moving in opposition to their own concentration gradient. A linear stability analysis indicates that cross diffusion can lead to unstable concentration fluctuations in the suspension. The instability is a potential mechanism for the appearance of dynamic and structural heterogeneity in suspensions near the glass transition.

Inclusions of calcite within large euhedral apatite crystals from the pyroxenite-carbonatite-syenite complex of Sevattur, Tamil Nadu, south India, were identified to represent inclusions of a primary carbonatitic melt (calcite I) from which the apatites have crystallized. The apatites themselves are embedded into a younger batch of calcite-carbonatitic melt (calcite II). Using the synchrotron XRF microprobe at beamline L at HASYLAB/DESY (Hamburg), the concentrations of the trace elements Ba, Sr, Y, Zr, Th, La, Ce, Nd, Sm, Gd, Dy, and Er were determined both in melt inclusions as well as in host apatites and younger carbonatite matrix. Unexpected high REE concentrations were found not only in apatite but also in calcite, especially of the younger matrix phase, in agreement with the whole rock geochemistry. The data reveal an equilibrium distribution between melt inclusions and host apatite that allows the calculation of partition coefficients D = C i Ap / C i Cc=melt for elements of interest. Assuming 9% crystallization of the melt, which can be calculated from the whole rock analyses, the composition of the primary carbonatite melt prior to apatite crystallization can be determined. This composition is, with the exception of only few elements, nearly equal to that of the younger matrix carbonatite melt (calcite II), and thus gives evidence for the existence of different pulses of carbonatite melt during crystallization and consolidation of the carbonatite body. The results allow new insights into the processes of trace element and REE distribution between the two major igneous components of carbonatites and thus into the question of carbonatitic fractionation processes. The data reveal that mere apatite crystallization and fractionation does not lead to enriched REE compositions during carbonatite evolution but lowers their concentrations in the residual melts. But alternatively, if segregated apatite is collected and incorporated by a new melt batch, the overall REE of this melt will be increased.

- by Helmut Schleicher
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- Trace element partitioning, Carbonatites, Melt Inclusions, Apatite

The divalent cation Be 2+ is considerably smaller than other divalent cations (Mg 2+ , Fe 2+ , Ca 2+ , et cetera), leading to a strong preference for tetrahedral coordination in minerals. Its thermodynamic properties in silicate melts may accordingly differ from these other divalent cations, potentially distinguishing its mineral/melt partition coefficients. In order to investigate this possibility, the partitioning of Be between silicate melt and forsterite was examined for 16 melt compositions in the systems CaO–MgO–Al 2 O 3 –SiO 2 at 1400 °C with additional experiments to investigate the effect of added Na 2 O and TiO 2 , and temperature at 1300 °C. The relative activity coefficient of BeO in the melts decreases with increasing CaO and NaO 1.5. The results are compared to Mg and Ca partitioning in the same experiments, and to the partitioning of other divalent cations (Ni, Co, Mn) from the literature. While the partition coefficient of the latter correlate positively with the Mg partition coefficient, Be shows only a weak negative correlation. Compared to Ca, Be partitions less strongly into forsterite when the melt has high Na and/or Ca. Partition coefficients for Na, Al and Ti are also reported.

- by Jonathan Erez
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- Earth Sciences, Climate Change, Paleoclimatology, Paleoceanography
- by Horst R Marschall
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- Geology, Geochemistry, Cosmochemistry, Trace element Geochemistry

The processes that controlled accretion of water and volatiles to the inner solar system remain enigmatic, because it is difficult to determine the absolute concentrations of volatile elements in planetary bodies. In this contribution we study rare unequilibrated eucrites derived from the asteroid 4 Vesta, to determine the water and fluorine content of this asteroid by measuring the volatile content of pyroxene. Common thermal metamorphism in most equilibrated eucrites would have diffusively reset magmatic volatile contents. The unequilibrated eucrites are, therefore, the most suitable samples to determine primary magmatic volatile contents of 4 Vesta. We find H 2 O and F contents in pyroxenes of 4-11 mg/g and 0.12-0.23 mg/g. We also determine a H 2 O partition coefficient for clinopyroxene and melt equilibrated at 0.1 MPa of D H2O = 0.1, which is higher than values previously reported for higher pressures. The higher compatibility of H 2 O in this experiment could partially be due to high OH/H 2 O ratio at the low total water contents in this experimental charge, but only further more detailed experiments will fully delineate the reasons for the more compatible behavior for water at lower pressures. However, given the lack of H 2 O partitioning data at low pressures we conclude that our 0.1 MPa experiment is the most appropriate to calculate magmatic water contents for melt in equilibrium with eucrite pyroxene. After using appropriate partition coefficients we calculate melt concentrations of 50-70 mg/g H 2 O and 1.5-2.4 mg/g F. In turn, these are converted into bulk 4 Vesta water and F contents of 10-70 mg/g H 2 O and 0.3-2 mg/g F by assuming eucrite formation via either mantle partial melting or extraction from a magma ocean. We also measure the D/H of the clinopyroxenes and show that these are identical to the results of previous studies that reported D/H in eucrite apatite. These values match those found in carbonaceous chondrites suggesting that water in 4 Vesta accreted from carbonaceous chondrites and not from cometary material.

Support Vector Machines (SVM) is a state-of-the-art, powerful algorithm in machine learning which has strong regularization attributes. Regularization points to the model generalization to the new data. Therefore, SVM can be very efficient for spam detection. Although the experimental results represent that the performance of SVM is usually more than other algorithms, but its efficiency is decreased when the number of feature of spam is increased. In this paper, a scalable SVM is proposed by using J48 tree for spam detection. In the proposed method, dataset is firstly partitioned by using J48 tree, then, features selection are applied in each partition in parallel. Consistently, selected features are used in the training phase of SVM. The propose method is evaluated conducted some benchmark datasets and the results are compared with other algorithms such as SVM and GA-SVM. The experimental results show that the proposed method is scalable when the number of features are increased and has higher accuracy compared to SVM and GA-SVM.