Igpet software for modeling igneous processes: examples of application using the open educational version

NASA Astrophysics Data System (ADS)

Carr, Michael J.; Gazel, Esteban

2017-04-01

We provide here an open version of Igpet software, called t-Igpet to emphasize its application for teaching and research in forward modeling of igneous geochemistry. There are three programs, a norm utility, a petrologic mixing program using least squares and Igpet, a graphics program that includes many forms of numerical modeling. Igpet is a multifaceted tool that provides the following basic capabilities: igneous rock identification using the IUGS (International Union of Geological Sciences) classification and several supplementary diagrams; tectonic discrimination diagrams; pseudo-quaternary projections; least squares fitting of lines, polynomials and hyperbolae; magma mixing using two endmembers, histograms, x-y plots, ternary plots and spider-diagrams. The advanced capabilities of Igpet are multi-element mixing and magma evolution modeling. Mixing models are particularly useful for understanding the isotopic variations in rock suites that evolved by mixing different sources. The important melting models include, batch melting, fractional melting and aggregated fractional melting. Crystallization models include equilibrium and fractional crystallization and AFC (assimilation and fractional crystallization). Theses, reports and proposals concerning igneous petrology are improved by numerical modeling. For reviewed publications some elements of modeling are practically a requirement. Our intention in providing this software is to facilitate improved communication and lower entry barriers to research, especially for students.

Crustal contamination and crystal entrapment during polybaric magma evolution at Mt. Somma-Vesuvius volcano, Italy: Geochemical and Sr isotope evidence

USGS Publications Warehouse

Piochi, M.; Ayuso, R.A.; de Vivo, B.; Somma, R.

2006-01-01

New major and trace element analyses and Sr-isotope determinations of rocks from Mt. Somma-Vesuvius volcano produced from 25 ky BP to 1944 AD are part of an extensive database documenting the geochemical evolution of this classic region. Volcanic rocks include silica undersaturated, potassic and ultrapotassic lavas and tephras characterized by variable mineralogy and different crystal abundance, as well as by wide ranges of trace element contents and a wide span of initial Sr-isotopic compositions. Both the degree of undersaturation in silica and the crystal content increase through time, being higher in rocks produced after the eruption at 472 AD (Pollena eruption). Compositional variations have been generally thought to reflect contributions from diverse types of mantle and crust. Magma mixing is commonly invoked as a fundamental process affecting the magmas, in addition to crystal fractionation. Our assessment of geochemical and Sr-isotopic data indicates that compositional variability also reflects the influence of crustal contamination during magma evolution during upward migration to shallow crustal levels and/or by entrapment of crystal mush generated during previous magma storage in the crust. Using a variant of the assimilation fractional crystallization model (Energy Conservation-Assimilation Fractional Crystallization; [Spera and Bohrson, 2001. Energy-constrained open-system magmatic processes I: General model and energy-constrained assimilation and fractional crystallization (EC-AFC) formulation. J. Petrol. 999-1018]; [Bohrson, W.A. and Spera, F.J., 2001. Energy-constrained open-system magmatic process II: application of energy-constrained assimilation-fractional crystallization (EC-AFC) model to magmatic systems. J. Petrol. 1019-1041]) we estimated the contributions from the crust and suggest that contamination by carbonate rocks that underlie the volcano (2 km down to 9-10 km) is a fundamental process controlling magma compositions at Mt. Somma-Vesuvius in the last 8 ky BP. Contamination in the mid- to upper crust occurred repeatedly, after the magma chamber waxed with influx of new mantle- and crustal-derived magmas and fluids, and waned as a result of magma withdrawal and production of large and energetic plinian and subplinian eruptions. ?? 2005 Elsevier B.V. All rights reserved.

Self-Consistency of the Lauritzen-Hoffman and Strobl Models of Polymer Crystallization Evaluated for Poly(epsilon-caprolactone) Fractions and Effect of Composition on the Phenomenon of Concurrent Crystallization in Polyethylene Blends

NASA Astrophysics Data System (ADS)

Sheth, Swapnil Suhas

Narrow molecular weight fractions of poly(epsilon-caprolactone) were successfully obtained using the successive precipitation fractionation technique with toluene/n-heptane as a solvent/nonsolvent pair. Calorimetric studies of the melting behavior of fractions that were crystallized either isothermally or under constant cooling rate conditions suggested that the isothermal crystallization of the samples should be used for a proper evaluation of the molecular weight dependence of the observed melting temperature and degree of crystallinity in PCL. The molecular weight and temperature dependence of the spherulitic growth rate of fractions was studied in the context of the Lauritzen-Hoffman two-phase model and the Strobl three-phase model of polymer crystallization. The zero-growth rate temperatures, determined from spherulitic growth rates using four different methods, are consistent with each other and increase with chain length. The concomitant increase in the apparent secondary nucleation constant was attributed to two factors. First, for longer chains there is an increase in the probability that crystalline stems belong to loose chain-folds, hence, an increase in fold surface free energy. It is speculated that the increase in loose folding and resulting decrease in crystallinity with increasing chain length are associated with the ester group registration requirement in PCL crystals. The second contribution to the apparent nucleation constant arises from chain friction associated with segmental transport across the melt/crystal interface. These factors were responsible for the much stronger chain length dependence of spherulitic growth rates at fixed undercooling observed here with PCL than previously reported for PE and PEO. In the case of PCL, the scaling exponent associated with the chain length dependence of spherulitic growth rates exceeds the upper theoretical bound of 2 predicted from the Brochard- DeGennes chain pullout model. Observation that zero-growth and equilibrium melting temperature values are identical with each other within the uncertainty of their determinations casts serious doubt on the validity of Strobl three-phase model. A novel method is proposed to determine the Porod constant necessary to extrapolate the small angle X-ray scattering intensity data to large scattering vectors. The one-dimensional correlation function determined using this Porod constant yielded the values of lamellar crystal thickness, which were similar to these estimated using the Hosemann-Bagchi Paracrystalline Lattice model. The temperature dependence of the lamellar crystal thickness was consistent with both LH and the Strobl model of polymer crystallization. However, in contrast to the predictions of Strobl's model, the value of the mesomorph-to-crystal equilibrium transition temperature was very close to the zero-growth temperature. Moreover, the lateral block sizes (obtained using wide angle X-ray diffraction) and the lamellar thicknesses were not found to be controlled by the mesomorph-to-crystal equilibrium transition temperature. Hence, we concluded that the crystallization of PCL is not mediated by a mesophase. Metallocene-catalyzed linear low-density (m-LLDPE with 3.4 mol% 1-octene) and conventional low-density (LDPE) polyethylene blends of different compositions were investigated for their melt-state miscibility and concurrent crystallization tendency. Differential scanning calorimetric studies and morphological studies using atomic force microscopy confirm that these blends are miscible in the melt-state for all compositions. LDPE chains are found to crystallize concurrently with m-LLDPE chains during cooling in the m-LLDPE crystallization temperature range. While the extent of concurrent crystallization was found to be optimal in .. .. iv blends with highest m-LLDPE content studied, strong evidence was uncovered for the existence of a saturation effect in the concurrent crystallization behavior. This observation leads us to suggest that co-crystallization, rather than mere concurrent crystallization, of LDPE with m- LLDPE can indeed take place. Matching of the respective sequence length distributions in LDPE and m-LLDPE is suggested to control the extent of co-crystallization.

Numerical simulation of crystal fractionation in shergottite meteorites

NASA Astrophysics Data System (ADS)

Grimm, R. E.; McSween, H. Y., Jr.

Cumulus clinopyroxenes in the Shergotty and Zagami meteorites suggest crystal fractionation occurred, possibly by gravitative settling. Numerical models of this process in a nonconvecting environment argue that the small phenocrysts can segregate only under extreme conditions of cooling time or gravitational field strength. Since textures indicate that cooling time was not excessive, a large (planetary) g is required by these models, in agreement with other suggestions that the shergottite parent body may be Mars. Other calculations indicate that it is extremely difficult to produce the observed textures in a convecting environment, unless crystal setting occurred in a quiescent zone at the bottom of the magma chamber.

Numerical simulation of crystal fractionation in shergottite meteorites

NASA Technical Reports Server (NTRS)

Grimm, R. E.; Mcsween, H. Y., Jr.

1982-01-01

Cumulus clinopyroxenes in the Shergotty and Zagami meteorites suggest crystal fractionation occurred, possibly by gravitative settling. Numerical models of this process in a nonconvecting environment argue that the small phenocrysts can segregate only under extreme conditions of cooling time or gravitational field strength. Since textures indicate that cooling time was not excessive, a large (planetary) g is required by these models, in agreement with other suggestions that the shergottite parent body may be Mars. Other calculations indicate that it is extremely difficult to produce the observed textures in a convecting environment, unless crystal setting occurred in a quiescent zone at the bottom of the magma chamber.

Analyses of Cometary Silicate Crystals: DDA Spectral Modeling of Forsterite

NASA Technical Reports Server (NTRS)

Wooden, Diane

2012-01-01

Comets are the Solar System's deep freezers of gases, ices, and particulates that were present in the outer protoplanetary disk. Where comet nuclei accreted was so cold that CO ice (approximately 50K) and other supervolatile ices like ethane (C2H2) were preserved. However, comets also accreted high temperature minerals: silicate crystals that either condensed (greater than or equal to 1400 K) or that were annealed from amorphous (glassy) silicates (greater than 850-1000 K). By their rarity in the interstellar medium, cometary crystalline silicates are thought to be grains that formed in the inner disk and were then radially transported out to the cold and ice-rich regimes near Neptune. The questions that comets can potentially address are: How fast, how far, and over what duration were crystals that formed in the inner disk transported out to the comet-forming region(s)? In comets, the mass fractions of silicates that are crystalline, f_cryst, translate to benchmarks for protoplanetary disk radial transport models. The infamous comet Hale-Bopp has crystalline fractions of over 55%. The values for cometary crystalline mass fractions, however, are derived assuming that the mineralogy assessed for the submicron to micron-sized portion of the size distribution represents the compositional makeup of all larger grains in the coma. Models for fitting cometary SEDs make this assumption because models can only fit the observed features with submicron to micron-sized discrete crystals. On the other hand, larger (0.1-100 micrometer radii) porous grains composed of amorphous silicates and amorphous carbon can be easily computed with mixed medium theory wherein vacuum mixed into a spherical particle mimics a porous aggregate. If crystalline silicates are mixed in, the models completely fail to match the observations. Moreover, models for a size distribution of discrete crystalline forsterite grains commonly employs the CDE computational method for ellipsoidal platelets (c:a:b=8.14x8.14xl in shape with geometrical factors of x:y:z=1:1:10, Fabian et al. 2001; Harker et al. 2007). Alternatively, models for forsterite employ statistical methods like the Distribution of Hollow Spheres (Min et al. 2008; Oliveira et al. 2011) or Gaussian Random Spheres (GRS) or RGF (Gielen et al. 200S). Pancakes, hollow spheres, or GRS shapes similar to wheat sheaf crystal habit (e.g., Volten et al. 2001; Veihelmann et al. 2006), however, do not have the sharp edges, flat faces, and vertices seen in images of cometary crystals in interplanetary dust particles (IDPs) or in Stardust samples. Cometary forsterite crystals often have equant or tabular crystal habit (J. Bradley). To simulate cometary crystals, we have computed absorption efficiencies of forsterite using the Discrete Dipole Approximation (DDA) DDSCAT code on NAS supercomputers. We compute thermal models that employ a size distribution of discrete irregularly shaped forsterite crystals (nonspherical shapes with faces and vertices) to explore how crystal shape affects the shape and wavelength positions of the forsterite spectral features and to explore whether cometary crystal shapes support either condensation or annealing scenarios (Lindsay et al. 2012a, b). We find forsterite crystal shapes that best-fit comet Hale-Bopp are tetrahedron, bricks or brick platelets, essentially equant or tabular (Lindsay et al. 2012a,b), commensurate with high temperature condensation experiments (Kobatake et al. 2008). We also have computed porous aggregates with crystal monomers and find that the crystal resonances are amplified. i.e., the crystalline fraction is lower in the aggregate than is derived by fitting a linear mix of spectral features from discrete subcomponents, and the crystal resonances 'appear' to be from larger crystals (Wooden et al. 2012). These results may indicate that the crystalline mass fraction in comets with comae dominated by aggregates may be lower than deduced by popular methods that only emoy ensembles of discrete crystals.

The temperature of the Icelandic mantle from olivine-spinel aluminum exchange thermometry

NASA Astrophysics Data System (ADS)

Matthews, S.; Shorttle, O.; Maclennan, J.

2016-11-01

New crystallization temperatures for four eruptions from the Northern Volcanic Zone of Iceland are determined using olivine-spinel aluminum exchange thermometry. Differences in the olivine crystallization temperatures between these eruptions are consistent with variable extents of cooling during fractional crystallization. However, the crystallization temperatures for Iceland are systematically offset to higher temperatures than equivalent olivine-spinel aluminum exchange crystallization temperatures published for MORB, an effect that cannot be explained by fractional crystallization. The highest observed crystallization temperature in Iceland is 1399 ± 20°C. In order to convert crystallization temperatures to mantle potential temperature, we developed a model of multilithology mantle melting that tracks the thermal evolution of the mantle during isentropic decompression melting. With this model, we explore the controls on the temperature at which primary melts begin to crystallize, as a function of source composition and the depth from which the magmas are derived. Large differences (200°C) in crystallization temperature can be generated by variations in mantle lithology, a magma's inferred depth of origin, and its thermal history. Combining this model with independent constraints on the magma volume flux and the effect of lithological heterogeneity on melt production, restricted regions of potential temperature-lithology space can be identified as consistent with the observed crystallization temperatures. Mantle potential temperature is constrained to be 1480-30+37 °C for Iceland and 1318-32+44 °C for MORB.

Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust

NASA Astrophysics Data System (ADS)

Sarkar, Saheli; Saha, Lopamudra; Satyanarayan, Manavalan; Pati, Jayanta

2015-04-01

Fractional Crystallisation of Archaean Trondhjemite Magma at 12-7 Kbar: Constraints on Rheology of Archaean Continental Crust Sarkar, S.1, Saha, L.1, Satyanarayan, M2. and Pati, J.K.3 1. Department of Earth Sciences, Indian Institute of Technology Roorkee, Roorkee-247667, Haridwar, India, 2. HR-ICPMS Lab, Geochemistry Group, CSIR-National Geophysical Research Institute, Hyderabad-50007, India. 3. Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad-211002, India. Tonalite-Trondhjemite-Granodiorite (TTGs) group of rocks, that mostly constitute the Archaean continental crusts, evolved through a time period of ~3.8 Ga-2.7 Ga with major episodes of juvenile magma generations at ~3.6 Ga and ~2.7 Ga. Geochemical signatures, especially HREE depletions of most TTGs conform to formation of this type of magma by partial melting of amphibolites or eclogites at 15-20 kbar pressure. While TTGs (mostly sodic in compositions) dominates the Eoarchaean (~3.8-3.6 Ga) to Mesoarchaean (~3.2-3.0 Ga) domains, granitic rocks (with significantly high potassium contents) became more dominant in the Neoarchaean period. The most commonly accepted model proposed for the formation of the potassic granite in the Neoarchaean time is by partial melting of TTGs along subduction zones. However Archaean granite intrusive into the gabbro-ultramafic complex from Scourie, NW Scotland has been interpreted to have formed by fractional crystallization of hornblende and plagioclase from co-existing trondhjemitic gneiss. In this study we have studied fractional crystallization paths from a Mesoarchaean trondhjemite from the central Bundelkhand craton, India using MELTS algorithm. Fractional crystallization modeling has been performed at pressure ranges of 20 kbar to 7 kbar. Calculations have shown crystallization of garnet-clinopyroxene bearing assemblages with progressive cooling of the magma at 20 kbar. At pressure ranges 19-16 kbar, solid phases fractionating from the magma are mostly clinopyroxene with minor orthopyroxene. Plagioclase crystals appear at pressures ≤ 15 kbar. Plagioclase crystals are mostly albitic in composition (XAb ~0.70-0.75). At each pressure, with progressive cooling and fractionation of solid phases, crystal-melt ratio becomes significantly higher, magma becomes more depleted in Al2O3, MgO, with significant increase in K2O/Na2O ratio and water content. With progressive cooling and fractionation, overall composition of the magma changes from trondhjemitic to granitic, with increase in viscosity from 4.5 poise to 5.5 poise. The study thus reveals that fractional crystallization of trondhemitic magmas at different depths can form more potassic granitic magma with higher viscosity. As Hf isotope signatures from most Archaean TTGs reveal longer crustal residence, it is likely that granitic magmas that became more common in the Neoarchaean period, could also possibly been derived by fractional crystallization from trondhjemitic magmas in Mesoarchaean time. Granitic magmas hence generated have much higher viscosity compared to the parent trondhjemitic magma. Low viscosity of trondhjemitic magmas and low crystal-melt ratios in the initial stages of crystallization (as derived in this study), may be the cause of formation of large bodies of TTGs in Early Archaean period. Close to Neoarchaean period more granitic magmas are observed. In this study it has been observed that crystallization of these magmas lead to high crystal-melt ratios and the magmas have higher viscosity. Such change in composition from Early to Neoarchaean time must have made Archaean crusts stronger and hence more prone to deformation. This observation hence support occurrence of Phanerozoic style signatures from poly-deformed terrains of Neoarchaean time.

Investigations on solid-solid phase transformation of 5-methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile.

PubMed

Li, Hui; Stowell, Joseph G; He, Xiaorong; Morris, Kenneth R; Byrn, Stephen R

2007-05-01

Solid-solid transformation of 5-methyl-2-[(4-methyl-2-nitrophenyl)amino]-3-thiophenecarbonitrile from the dark-red to the red form was investigated. By controlled crystallization, the dark-red form was prepared and the crystals were sieved into fractions: coarse (>250 microm), medium (125-177 microm), and fine (<88 microm). The transformation rate order (fastest to slowest) of the different fractions is coarse > medium > fine. However, milling accelerates the transformation, that is, smaller particles generated by milling transforms faster. Furthermore, ethanol vapor annealing slows both the transformation of the coarse and medium fractions, especially the latter. Therefore, the mechanism of transformation is not directly related to the crystal-size and most likely related to the amount and activity of the defects in the crystals. The three-dimensional (3-D) Avrami-Erofe'ev model, know as "random nucleation and growth" model, fits the kinetics of coarse fraction best. Higher relative humidity accelerates the transformation dramatically even though the compound is highly-hydrophobic. With minimal hydrogen bonding interaction involved, it appears even small amounts of water can serve as a nucleation catalyst by binding to the crystal surface, especially at defect sites, thus increasing the molecular mobility of these sites, promoting the transformation to the second phase and thereby increasing the transformation rate. (c) 2007 Wiley-Liss, Inc. and the American Pharmacists Association.

Hydrogen isotopic fractionation during crystallization of the terrestrial magma ocean

NASA Astrophysics Data System (ADS)

Pahlevan, K.; Karato, S. I.

2016-12-01

Models of the Moon-forming giant impact extensively melt and partially vaporize the silicate Earth and deliver a substantial mass of metal to the Earth's core. The subsequent evolution of the terrestrial magma ocean and overlying vapor atmosphere over the ensuing 105-6 years has been largely constrained by theoretical models with remnant signatures from this epoch proving somewhat elusive. We have calculated equilibrium hydrogen isotopic fractionation between the magma ocean and overlying steam atmosphere to determine the extent to which H isotopes trace the evolution during this epoch. By analogy with the modern silicate Earth, the magma ocean-steam atmosphere system is often assumed to be chemically oxidized (log fO2 QFM) with the dominant atmospheric vapor species taken to be water vapor. However, the terrestrial magma ocean - having held metallic droplets in suspension - may also exhibit a much more reducing character (log fO2 IW) such that equilibration with the overlying atmosphere renders molecular hydrogen the dominant H-bearing vapor species. This variable - the redox state of the magma ocean - has not been explicitly included in prior models of the coupled evolution of the magma ocean-steam atmosphere system. We find that the redox state of the magma ocean influences not only the vapor speciation and liquid-vapor partitioning of hydrogen but also the equilibrium isotopic fractionation during the crystallization epoch. The liquid-vapor isotopic fractionation of H is substantial under reducing conditions and can generate measurable D/H signatures in the crystallization products but is largely muted in an oxidizing magma ocean and steam atmosphere. We couple equilibrium isotopic fractionation with magma ocean crystallization calculations to forward model the behavior of hydrogen isotopes during this epoch and find that the distribution of H isotopes in the silicate Earth immediately following crystallization represents an oxybarometer for the terrestrial magma ocean. Whether such endogenous isotopic heterogeneity would survive as an observable signature in the modern silicate Earth is an open question.

Crystallization kinetics of orthorhombic paracetamol from supercooled melts studied by non-isothermal DSC.

PubMed

Nikolakakis, Ioannis; Kachrimanis, Kyriakos

2017-02-01

A simple and highly reproducible procedure was established for the study of orthorhombic paracetamol crystallization kinetics, comprising melting, quench-cooling of the melt and scanning the formed glass by DSC at different heating rates. Results were analyzed on the basis of the mean as well as local values of the Avrami exponent, n, the energy of activation, as well as the Šesták-Berggren two-parameter autocatalytic kinetic model. The mean value of the Avrami kinetic exponent, n, ranged between 3 and 5, indicating deviation from the nucleation and growth mechanism underlying the Johnson-Mehl, Avrami-Kolmogorov (JMAK) model. To verify the extent of the deviation, local values of the Avrami exponent as a function of the volume fraction transformed were calculated. Inspection of the local exponent values indicates that the crystallization mechanism changes over time, possibly reflecting the uncertainty of crystallization onset, instability of nucleation due to an autocatalytic effect of the crystalline phase, and growth anisotropy due to impingement of spherulites in the last stages of crystallization. The apparent energy of activation, E a , has a rather low mean value, close to 81 kJ/mol, which is in agreement with the observed instability of glassy-state paracetamol. Isoconversional methods revealed that E a tends to decrease with the volume fraction transformed, possibly because of the different energy demands of nucleation and growth. The exponents of the Šesták-Berggren two-parameter model showed that the crystallized fraction influences the process, confirming the complexity of the crystallization mechanism.

Bingham fluid behavior of plagioclase-bearing basaltic magma: Approach from laboratory viscosity measurements

NASA Astrophysics Data System (ADS)

Ishibashi, H.; Sato, H.

2010-12-01

Datasets of one atmosphere high temperature rotational viscometry of the Fuji 1707 basalt (Ishibashi, 2009) were analyzed based on the Bingham fluid model, and both yield stress and Bingham viscosity were determined. Reproducibility of the dataset by the Bingham fluid model was slightly better than that by the power law fluid modes adopted in our previous study although both the fluid models well represent the dataset in practical perspective. The relation between Bingham viscosity and crystallinity was compared with the Krieger-Dougherty equation, and both the maximum packing fraction of crystals and intrinsic viscosity for Bingham viscosity were determined ca. 0.45 and ca. 5.25, respectively, revealing that the maximum packing fraction decreased and intrinsic viscosity increased concomitantly with the increase in shape-anisotropy of crystals. However, the obtained value of the product of the maximum packing fraction and intrinsic viscosity (= ca. 2.36) was similar to that of uniform, isotropic-shaped particles (= 2.5), indicating that the effect of crystal shape-anisotropy on Bingham viscosity might be predicted only by change of the maximum packing fraction. Finite yield stress was detected for crystallinity larger than 0.133; it increased with crystallinity which suggests that critical crystallinity for onset of yield stress is at least lower than 0.133. The upper limit value of the critical crystallinity resembles the value calculated numerically for randomly oriented uniform particles by Saar et al. (2001) (0.10-0.15 for width/length ratio of 0.1-0.2, which is similar to the ratios in the basalt) whereas crystals in the basalt were moderately parallel arranged and their sizes vary significantly. That fact might be explained as follows; effects of parallel arrangement and size variation of crystals on the critical crystallinity are offset by the effect of variation in crystal shape-anisotropy, which suggests that shape-anisotropy distribution of crystals must be a critical factor for the onset of yield stress. Keywords: magma, viscosity, Bingham fluid, yield stress, plagioclase

Chain confinement, phase transitions, and lamellar structure in semicrystalline polymers, polymer blends and polymer nanocomposites

NASA Astrophysics Data System (ADS)

Chen, Huipeng

Recent studies suggest that there are three phase fractions in semicrystalline polymers, the crystalline, the mobile amorphous and the rigid amorphous phases. Due to the distinct properties of the rigid amorphous fraction, RAF, it has been investigated for more than twenty years. In this thesis, a general method using quasi-isothermal temperature-modulated differential scaning calorimetry, DSC, is provided for the first time to obtain the temperature dependent RAF and the other two fractions, crystalline fraction and mobile amorphous fraction, MAF. For poly(ethylene terephthalate), PET, our results show RAF was vitrified during quasi-isothermal cooling after crystallization had been completed and became totally devitrified during quasi-isothermal heating before the start of melting. Several years after people initially discovered the existence of RAF, another issue arose relating to the physical location of RAF and mobile amorphous fraction, MAF, within a lamellar stack model. Two very different models to describe the location of RAF were proposed. In the Heterogeneous Stack Model, HET, RAF is located outside the lamellar stacks. In the Homogeneous Stack Model, HSM, RAF was located inside the lamellar stacks. To determine the lamellar structure of semicrystalline polymers comprising three phase, a general method is given in this thesis by using a combination of the DSC and small angle X-ray scattering, SAXS techniques. It has been applied to Nylon 6, isotactic polystyrene, iPS, and PET. It was found for all of these materials, the HSM model is correct to describe the lamellar structure. In addition to the determination of lamellar structures, this method can also provide the exact fraction of MAF inside and outside lamellar stacks for binary polymer blends. For binary polymer blends, MAF, normally is located partially inside and partially outside the lamellar stacks. However, the quantification of the MAF inside and outside the lamellar stacks has now been provided and is applied to the iPS/atactic polystyrene, aPS, blends. The fractions of MAF inside and outside the lamellar stacks were quantified for the first time. For A/B binary polymer blends, it has been reported that if B is already crystalline, the crystalline fraction would serve as a restriction on the subsequent growth of the crystallizable partner A, while amorphous fraction could be diffused from the crystalline growth front of the crystallizing A component. Considering the effect of RAF on binary blends, a new concept is provided: like the crystals, the RAF of one polymer component may inhibit the growth of crystals of the other blend partner. The non-isothermal crystallization of PET/poly(lactic acid), PLA, blends were investigated and the results confirmed the new concept is correct: PET forms a large amount of RAF and inhibits crystal formation in PLA. Then, we broadened the concept of RAF and investigated the RAF in recent 'hot' materials, polymer nanocomposites. It was found the fraction of RAF greatly increased with a small amount of multi-wall carbon nanotubes, MWCNT, loading in PET electrospun, ES, fibers. A general model is given for polymer ES fibers with MWCNTs: the addition of MWCNTs causes polymer chains in the ES fibers to become more extended, (ie, more stretched), resulting in more confinement of PET chains and an increase in the RAF.

The Role of Body Crystallization in Asteroidal Cores

NASA Astrophysics Data System (ADS)

Wasson, J. T.

1993-07-01

Large fractionations (factors of 2000-6000) in Ir/Ni and other ratios demonstrate that the magmatic groups of iron meteorites formed by fractional crystallization, and thus that the residual liquid remained well stirred during core crystallization. Past models have relied on solidification at the base or the top of the core, but body crystallization offers an attractive alternative. The simplest of the earlier models involved convective maxing induced by the liberation of heat and light elements (especially S) during upward crystallization from the center of the core. Other models involving downward crystallization from the core-mantle interface are based on the fact that temperatures at this location are slightly lower than those at the center; no whole-core stirring mechanism is provided by these models. Haack and Scott recently published a variant of the downward crystallization model involving the growth of giant (kilometer-scale) dendrites. Because crystallization creates a boundary layer enriched in S that does not participate in the convection, these models require several K of supercooling to induce crystallization (this undercooling is much greater than the temperature difference between the center of the core and the core-mantle interface). Buoyant forces will occasionally remove droplets of the basal boundary fluid; thus it was thinner and its degree of undercooling less than in that at the ceiling of the magma chamber. Homogeneous nucleation of metals is difficult to achieve; generally 200-300 K of undercooling is required, much more than could possibly occur in an asteroidal core. Crystals could, however, nucleate in the magma body on chromite, probably the first liquidus phase (A. Kracher, personal communication, notes that this is required to explain why Cr behaved like a compatible element despite having a solid/liquid D < 1). In addition, some tiny, submillimeter dendrites that formed at the top of the core must have pinched off and fallen into the magma. Such seeds settle as a result of buoyant forces (thus stirring the magma) and, as a result, achieve very thin boundary layers and require low degrees of undercooling in order to crystallize. The rate of core crystallization is limited by the rate of heat transport across the core-mantle interface. If sufficient nuclei are available at different sites, the bulk of the crystallization occurs where undercooling is least. It is possible that a larger fraction of the total crystallization occurred in the body of the magma than at its base or ceiling.

Reduced-temperature crystallization of thin amorphous Fe80B20 films studied via empirical modeling of extended x-ray absorption fine structure

NASA Astrophysics Data System (ADS)

Harris, V. G.; Oliver, S. A.; Ayers, J. D.; Das, B. N.; Koon, N. C.

1996-04-01

The evolution of the local atomic environment around Fe atoms in very thin (15 nm), amorphous, partially crystallized and fully crystallized films of Fe80B20 was studied using extended x-ray absorption fine structure (EXAFS) measurements. The relative atomic fraction of each crystalline phase present in the annealed samples was extracted from the Fe EXAFS data by a least-squares fitting procedure, using data collected from t-Fe3B, t-Fe2B, and α-Fe standards. The type and relative fraction of the crystallization products follows the trends previously measured in Fe80B20 melt-spun ribbons, except for the fact that crystallization temperatures are ≊200 K lower than those measured in bulk equivalents. This greatly reduced crystallization temperature may arise from the dominant role of surface nucleation sites in the crystallization of very thin amorphous films.

Numerical simulation of flow and melting characteristics of seawater-ice crystals two-phase flow in inlet straight pipe of shell and tube heat exchanger of polar ship

NASA Astrophysics Data System (ADS)

Xu, Li; Huang, Chang-Xu; Huang, Zhen-Fei; Sun, Qiang; Li, Jie

2018-05-01

The ice crystal particles are easy to enter into the seawater cooling system of polar ship together with seawater when it sails in the Arctic. They are easy to accumulate in the pipeline, causing serious blockage of the cooling pipe. In this study, the flow and melting characteristics of ice particles-seawater two-phase flow in inlet straight pipe of shell-and-tube heat exchanger were numerically simulated by using Eulerian-Eulerian two-fluid model coupled with the interphase heat and mass transfer model. The influences of inlet ice packing factor, ice crystal particle diameter, and inlet velocity on the distribution and melting characteristics of ice crystals were investigated. The degree of asymmetry of the distribution of ice crystals in the cross section decreases gradually when the IPF changes from 5 to 15%. The volume fractions of ice crystals near the top of the outlet cross section are 19.59, 19.51, and 22.24% respectively for ice packing factor of 5, 10 and 15%. When the particle diameter is 0.5 mm, the ice crystals are gradually stratified during the flow process. With particle diameters of 1.0 and 2.0 mm, the region with the highest volume fraction of ice crystals is a small circle and the contours in the cloud map are compact. The greater the inlet flow velocity, the less stratified the ice crystals and the more obvious the turbulence on the outlet cross section. The average volume fraction of ice crystals along the flow direction is firstly rapidly reduced and then stabilized after 300 mm.

Structure of the mixed-metal carbonate KAgCO₃ revisited: order-disorder (OD) polytypism and allotwinning.

PubMed

Hans, Philipp; Stöger, Berthold; Weil, Matthias; Zobetz, Erich

2015-04-01

Crystals of KAgCO3 belong to an order-disorder (OD) family of structures composed of layers of two kinds. There are two polytypes with a maximum degree of order [MDO1: Pccb; MDO2: Ibca, doubled a-axis compared with MDO1], which are both realised to a different extent in two crystals under investigation [volume fraction MDO1:MDO2 in crystal (I): 0.0216:0.9784 (3) and in crystal (II): 0.9657:0.0343 (3)]. Sharp diffraction spots and the absence of diffuse scattering indicate highly ordered macroscopic domains. The structure of KAgCO3 was refined concurrently against all reflections using an allotwin model (addition of the intensities of both domains). It is shown that a disorder model refined against reflections of only one domain can lead to a significant overestimation of the volume fraction of this domain.

Magma differentiation rates from ( 226Ra / 230Th) and the size and power output of magma chambers

NASA Astrophysics Data System (ADS)

Blake, Stephen; Rogers, Nick

2005-08-01

We present a mathematical model for the evolution of the ( 226Ra / 230Th) activity ratio during simultaneous fractional crystallization and ageing of magma. The model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization. These are tholeiitic basalt from Ardoukoba, Djibouti, MORB from the East Pacific Rise, alkali basalt to mugearite from Vestmannaeyjar, Iceland, and basaltic andesites from Miyakejima, Izu-Bonin arc. In all cases ( 226Ra / 230Th) correlates with indices of fractional crystallization, such as Th, and the data fall close to model curves of constant fractional crystallization rate. The best fit rates vary from 2 to 6 × 10 - 4 yr - 1 . Consequently, the time required to generate moderately evolved magmas ( F ≤ 0.7) is of the order of 500 to 1500 yrs and closed magma chambers will have lifetimes of 1700 to 5000 yrs. These rates and timescales are argued to depend principally on the specific power output (i.e., power output per unit volume) of the magma chambers that are the sites of fractional crystallization. Equating the heat flux at the EPR to the heat flux from the sub-axial magma chamber that evolves at a rate of ca. 3 × 10 - 4 yr - 1 implies that the magma body is a sill of ca. 100 m thickness, a value which coincides with independent estimates from seismology. The similarity of the four inferred differentiation rates suggests that the specific power output of shallow magma chambers in a range of tectonic settings covers a similarly narrow range of ca. 10 to 50 MW km - 3 . Their differentiation rates are some two orders of magnitude slower than that of the basaltic Makaopuhi lava lake, Hawaii, that cooled to the atmosphere. This is consistent with the two orders of magnitude difference in heat flux between Makaopuhi and the East Pacific Rise. ( 226Ra / 230Th) data for magma suites related by fractional crystallization allow the magma differentiation rate to be estimated and, from this, the thermal budget of the magma chamber addressed, and where an independent measurement of heat flux exists, to place constraints on the size of the magma chamber. Such results have the potential to constrain the likely timescale and size of future eruptions of evolved magmas.

Premature melt solidification during mold filling and its influence on the as-cast structure

NASA Astrophysics Data System (ADS)

Wu, M.; Ahmadein, M.; Ludwig, A.

2018-03-01

Premature melt solidification is the solidification of a melt during mold filling. In this study, a numerical model is used to analyze the influence of the pouring process on the premature solidification. The numerical model considers three phases, namely, air, melt, and equiaxed crystals. The crystals are assumed to have originated from the heterogeneous nucleation in the undercooled melt resulting from the first contact of the melt with the cold mold during pouring. The transport of the crystals by the melt flow, in accordance with the socalled "big bang" theory, is considered. The crystals are assumed globular in morphology and capable of growing according to the local constitutional undercooling. These crystals can also be remelted by mixing with the superheated melt. As the modeling results, the evolutionary trends of the number density of the crystals and the volume fraction of the solid crystals in the melt during pouring are presented. The calculated number density of the crystals and the volume fraction of the solid crystals in the melt at the end of pouring are used as the initial conditions for the subsequent solidification simulation of the evolution of the as-cast structure. A five-phase volume-average model for mixed columnar-equiaxed solidification is used for the solidification simulation. An improved agreement between the simulation and experimental results is achieved by considering the effect of premature melt solidification during mold filling. Finally, the influences of pouring parameters, namely, pouring temperature, initial mold temperature, and pouring rate, on the premature melt solidification are discussed.

Petrogenesis of Western Cascades Silicic Volcanics Near Sweet Home, Oregon

NASA Astrophysics Data System (ADS)

Cook, G. W.; White, C. M.

2002-12-01

Silicic lavas in the Menagerie Wilderness east of Sweet Home, Oregon are Oligocene to Miocene in age and range in composition from dacite (low K) to trachydacite (high K) and rhyolite (medium K). Three distinct silicic centers have been distinguished through a combination of field observation, chemistry and petrography. Phenocryst assemblages in rocks of the centers are plagioclase-hornblende-magnetite (Rooster Rock rhyolite), plagioclase-quartz-magnetite (Soda Fork rhyolite) and quartz-plagioclase-biotite-hornblende-magnetite (Moose Mt. rhyolite). The silicic volcanics in the study area are similar in terms of mineral content and overall chemical composition. Despite this, chemical evidence suggests that the three centers are petrologically unrelated. REE variations and least squares modeling of major element compositions are consistent with fractionation of plagioclase and hornblende. The rhyolites have moderate Eu anomalies and have flat MREE and HREE signatures. Least squares models and bivariate plots of major and trace elements also suggest fractionation of the aforementioned phases for both the andesite to dacite, and dacite to rhyolite steps. Comparisons with similar silicic centers show the Menagerie rocks share affinities with High Cascades rocks thought to have been derived through fractional crystallization (Crater Lake and South Sister). Plots of ratios of incompatible trace elements were utilized to determine if assimilation played some role alongside fractional crystallization in differentiation. Plots of Ba/La vs. Ba, Rb/Zr vs. Rb and Rb/Th vs. Rb show systematic positive increases in the ratios between a plausible parent magma (icelandite) and the rhyolites. These increases are not easily explained by fractional crystallization but can be modeled by assimilation of silicic crust. Overall, it seems likely that the three centers evolved independently through similar petrogenetic processes from an andesitic parent. The most plausible petrogenetic scenario involves some combination of fractional crystallization and assimilation of partial melts of silicic crust.

The evolution of the magmatic arc of Southern Peru (200-60 Ma), Arequipa area: insight from geochemical modeling

NASA Astrophysics Data System (ADS)

Demouy, S.; Benoit, M.; De Saint Blanquat, M.; Brunet, P.

2012-12-01

Cordilleran-type batholiths are built by prolonged arc activity along continental margins and may provide detailed magmatic records of the subduction system evolution. The magmas produced in subduction context involve both mantellic and crustal end members and are subject to various petrological processes. The MASH zones (Hildreth and Moorbath, 1988), at the basis of the continental crust, are the best places for the genesis of such hybrid magmas. The various geochemical signatures observed in the plutonic rocks, may also be attributed to source heterogeneities or generated by subsequent petrological processes. This study has focused in the Arequipa section of the Coastal Batholith of Southern Peru (200-60 Ma), in an area extending over 80x40 km. Major and trace elements as well as Sr and Nd isotopic analyses were performed in a set of 100 samples ranging from gabbro to granite. The obtained data highlight the wide heterogeneity of the geochemical signatures that is not related to the classification of the rocks. In first step, Rb/Sr systematic was used to isolate a set of samples plotting along a Paleocene isochron and defining a cogenetic suite. This suite appears to have evolved by simple fractional crystallization. By using reverse modeling, the parameters controlling the fractional crystallization process were defined, as partition coefficients, initial concentrations and amount of fractional crystallization. The other magmatic suites display a wide range of isotopic and geochemical signatures. To explain this heterogeneity, a model involving competition between fractional crystallization and magma mixing into MASH zones was proposed. A large range of hybrid magma types is potentially generated during the maturation of the system, but this range tends to disappear as fractionation and mixing occurs. Finally the model predicts the genesis of a homogeneous reservoir created at depth, from which magmas may evolve only by fractional crystallization. Therefore stabilization of this reservoir is directly related to the thermal conditions present at the basis of the continental crust, and allows the production of large volumes at the batholiths level, known as flare-up events. These results are critical in order to estimate the amount of crustal growth and thickening in the Arequipa area, as they provide the basis for the estimation of the mantle versus crustal contribution during the magma genesis.

Evolution of the Craters of the Moon Lavas from primitive Snake River Plain basalts: inferences from plagioclase-melt thermobarometers and whole rock compositions

NASA Astrophysics Data System (ADS)

Vaid, N.; Putirka, K.; Kuntz, M.

2005-12-01

The volcanic rocks of the Craters of the Mon Lava field provide an ideal laboratory for testing models of magma transport and evolution. Their compositions, relative ages and volumes are well known, as are the fractionation processes leading to their evolution (Leeman, 1976). The COM is somewhat distinctive in the Snake River Plain (SRP) region, due to its evolved character, and an apparent compositional segregation from associated SRP basalts. Some have suggested that the high Fe liquids of the COM demand an origin separate from that of SRP basalts, possibly involving an Fe-enriched mantle, while others have suggested that the COM lavas may be derived by fractionation at moderate depths (30 km). In either case, there are important implications in regard to mantle composition and the nature and distribution of thermal energy. We use plagioclase-melt pairs and an analysis of whole rock compositions in attempt to test models of COM magmatic evolution. Plagioclase-melt thermobarometers provide rough estimates of crystallization depths, and show that COM and SRP lavas partially crystallized at similar depths of 14 +/- 6 km. However, plagioclase crystallization temperatures for SRP basalts (1400 +/- 25 K; Kings Bowl, Cerro Grande, North and South Robbers) exceed temperatures for COM lavas (1358 +/- 45 K) by 40 K. Our data also show that fractional crystallization (ol + plag) can explain the evolution of surrounding SRP basalt flows, and that the most evolved SRP basalts approach primitive COM lava compositions. The most primitive of COM magmas appear to be characterized by the appearance of apatite + magnetite as fractionating phases. Our results thus confirm the geochemical model of Leeman (1976) and the physical model of Kuntz (1992), with the added insight that SRP basalts are parental to the more evolved COM lavas, through low-pressure fractional crystallization in the upper crust. The principal differences between SRP and COM magmas appear to relate more to the presence or absence of density contrasts in the crust than differences in composition or temperature of mantle source materials. SRP basalts lie near the axis of the SRP where the granitic upper crust may have been obliterated by earlier volcanic episodes. In contrast, COM lavas, whose vents lie off axis, appear to have been trapped within the upper crust for longer periods, sufficient for further differentiation. Finally, SRP rhyolite compositions lie on the same fractionation trend as COM and SRP lavas, at very low values of MgO. We propose that highly evolved lavas throughout the SRP may form by fractional crystallization mechanisms alone, rather than through the partial melting and remobilization of preexisting felsic crustal materials.

The rheology of crystal-rich magmas (Kuno Award Lecture)

NASA Astrophysics Data System (ADS)

Huber, Christian; Aldin Faroughi, Salah; Degruyter, Wim

2016-04-01

The rheology of magmas controls not only eruption dynamics but also the rate of transport of magmas through the crust and to a large extent the rate of magma differentiation and degassing. Magma bodies stalled in the upper crust are known to spend most of their lifespan above the solidus at a high crystal content (Cooper and Kent, 2014; Huber et al., 2009), where the probability of melt extraction (crystal fractionation) is the greatest (Dufek and Bachmann, 2010). In this study, we explore a new theoretical framework to study the viscosity of crystal bearing magmas. Since the seminal work of A. Einstein and W. Sutherland in the early 20th century, it has been shown theoretically and tested experimentally that a simple self-similar behavior exist between the relative viscosity of dilute (low crystal content) suspensions and the particle volume fraction. The self-similar nature of that relationship is quickly lost as we consider crystal fractions beyond a few volume percent. We propose that the relative viscosity of crystal-bearing magmas can be fully described by two state variables, the intrinsic viscosity and the crowding factor (a measure of the packing threshold in the suspension). These two state variables can be measured experimentally under different conditions, which allows us to develop closure relationships in terms of the applied shear stress and the crystal shape and size distributions. We build these closure equations from the extensive literature on the rheology of synthetic suspensions, where the nature of the particle shape and size distributions is better constrained and apply the newly developed model to published experiments on crystal-bearing magmas. We find that we recover a self-similar behavior (unique rheology curve) up to the packing threshold and show that the commonly reported break in slope between the relative viscosity and crystal volume fraction around the expected packing threshold is most likely caused by a sudden change in the state of dispersion of the magma (change in the state variables caused by either shear localization or crystal breakage). We argue that the model we propose is a first step to go beyond fitting experimental data and towards building a predictive rheology model for crystal-bearing magmas. Cooper, K.M., and Kent, A.J.R. (2014) Rapid remobilization of magmatic crystals kept in cold storage. Nature, 506(7489), 480-483. Dufek, J., and Bachmann, O. (2010) Quantum magmatism: Magmatic compositional gaps generated by melt-crystal dynamics. Geology, 38(8), 687-690. Huber, C., Bachmann, O., and Manga, M. (2009) Homogenization processes in silicic magma chambers by stirring and mushification (latent heat buffering). Earth and Planetary Science Letters, 283(1-4), 38-47.

Damage, Self-Healing, and Hysteresis in Spider Silks

PubMed Central

De Tommasi, D.; Puglisi, G.; Saccomandi, G.

2010-01-01

Abstract In this article, we propose a microstructure-based continuum model to describe the material behavior of spider silks. We suppose that the material is composed of a soft fraction with entropic elasticity and a hard, damageable fraction. The hard fraction models the presence of stiffer, crystal-rich, oriented regions and accounts for the effect of softening induced by the breaking of hydrogen bonds. To describe the observed presence of crystals with different size, composition, and orientation, this hard fraction is modeled as a distribution of materials with variable properties. The soft fraction describes the remaining regions of amorphous material and is here modeled as a wormlike chain. During stretching, we consider the effect of bond-breaking as a transition from the hard- to the soft-material phase. As we demonstrate, a crucial effect of bond-breaking that accompanies the softening of the material is an increase in contour length associated with chains unraveling. The model describes also the self-healing properties of the material by assuming partial bond reconnection upon unloading. Despite its simplicity, the proposed mechanical system reproduces the main experimental effects observed in cyclic loading of spider silks. Moreover, our approach is amenable to two- or three-dimensional extensions and may prove to be a useful tool in the field of microstructure optimization for bioinspired materials. PMID:20441758

Thorium and uranium variations in Apollo 17 basalts, and K-U systematics

NASA Technical Reports Server (NTRS)

Laul, J. C.; Fruchter, J. S.

1976-01-01

It is found that Apollo 11 low-K and in particular Apollo 17 mare basalts show a wide range of Th/U ratios unlike other rocks; such variations cannot be explained by near surface crystal fractionation. A two-stage fractional crystallization-partial melting model involving a clinopyroxene cumulate as the major phase can explain the variations in Th/U ratios. Due to the Sm-Nd systematics constraint, several source cumulates are invoked to explain the observed Th/U continuum.

LOR-interleaving image reconstruction for PET imaging with fractional-crystal collimation

NASA Astrophysics Data System (ADS)

Li, Yusheng; Matej, Samuel; Karp, Joel S.; Metzler, Scott D.

2015-01-01

Positron emission tomography (PET) has become an important modality in medical and molecular imaging. However, in most PET applications, the resolution is still mainly limited by the physical crystal sizes or the detector’s intrinsic spatial resolution. To achieve images with better spatial resolution in a central region of interest (ROI), we have previously proposed using collimation in PET scanners. The collimator is designed to partially mask detector crystals to detect lines of response (LORs) within fractional crystals. A sequence of collimator-encoded LORs is measured with different collimation configurations. This novel collimated scanner geometry makes the reconstruction problem challenging, as both detector and collimator effects need to be modeled to reconstruct high-resolution images from collimated LORs. In this paper, we present a LOR-interleaving (LORI) algorithm, which incorporates these effects and has the advantage of reusing existing reconstruction software, to reconstruct high-resolution images for PET with fractional-crystal collimation. We also develop a 3D ray-tracing model incorporating both the collimator and crystal penetration for simulations and reconstructions of the collimated PET. By registering the collimator-encoded LORs with the collimator configurations, high-resolution LORs are restored based on the modeled transfer matrices using the non-negative least-squares method and EM algorithm. The resolution-enhanced images are then reconstructed from the high-resolution LORs using the MLEM or OSEM algorithm. For validation, we applied the LORI method to a small-animal PET scanner, A-PET, with a specially designed collimator. We demonstrate through simulated reconstructions with a hot-rod phantom and MOBY phantom that the LORI reconstructions can substantially improve spatial resolution and quantification compared to the uncollimated reconstructions. The LORI algorithm is crucial to improve overall image quality of collimated PET, which can have significant implications in preclinical and clinical ROI imaging applications.

HANFORD MEDIUM-LOW CURIE WASTE PRETREATMENT ALTERNATIVES PROJECT FRACTIONAL CRYSTALLIZATION PILOT SCALE TESTING FINAL REPORT

DOE Office of Scientific and Technical Information (OSTI.GOV)

HERTING DL

2008-09-16

The Fractional Crystallization Pilot Plant was designed and constructed to demonstrate that fractional crystallization is a viable way to separate the high-level and low-activity radioactive waste streams from retrieved Hanford single-shell tank saltcake. The focus of this report is to review the design, construction, and testing details of the fractional crystallization pilot plant not previously disseminated.

Interpretation of open system petrogenetic processes: Phase equilibria constraints on magma evolution

NASA Astrophysics Data System (ADS)

Defant, Marc J.; Nielsen, Roger L.

1990-01-01

We have used a computer model (TRACES) to simulate low pressure differentiation of natural basaltic magmas in an attempt to investigate the chemical dynamics of open system magmatic processes. Our results, in the form of simulated liquid lines of descent and the calculated equilibrium mineralogy, were determined for perfect fractional crystallization; fractionation paired with recharge and eruption (PRF); fractionation paired with assimilation (AFC); and fractionation paired with recharge, eruption, and assimilation (FEAR). These simulations were calculated in an attempt to assess the effects of combinations of petrogenetic processes on major and trace element evolution of natural systems and to test techniques that have been used to decipher the relative roles of these processes. If the results of PRF calculations are interpreted in terms of a mass balance based fractionation model (e.g., Bryan et al., 1969), it is possible to generate low residuals even if one assumes that fractional crystallization was the only active process. In effect, the chemical consequences of recharge are invisible to mass balance models. Pearce element ratio analyses, however, can effectively discern the effects of PRF versus simple fractionation. The fractionating mineral proportions, and therefore, bulk distribution coefficients ( D¯) of a differentiating system are dependent on the recharge or assimilation rate. Comparison of the results of simulations assuming constant D¯ with the results calculated by TRACES show that the steady state liquid concentrations of some elements can differ by a factor of 2 to 5. If the PRF simulation is periodic, with episodes of mixing separated by intervals of fractionation, parallel liquidus mineral control lines are produced. Most of these control lines do not project back to the parental composition. This must be an important consideration when attempting to calculate a potential parental magma for any natural suite where magma chamber recharge has occurred. Most basaltic magmas cannot evolve to high silica compositions without magnetite fractionation. Small amounts of rhyolite assimilation (assimilation/fractionation < 0.1), however, can drive evolving basalts to more silica rich compositions. If mass balance models are used to interpret these synthetic AFC data, low residuals are obtained if magnetite is added to the crystallizing assemblage. This approach works even for cases where magnetite was not a fractionating phase. Thus, the mass balance results are mathematically correct, but are geologically irrelevant.

Electronegativity, charge transfer, crystal field strength, and the point charge model revisited.

PubMed

Tanner, Peter A; Ning, Lixin

2013-02-21

Although the optical spectra of LnCl(6)(3-) systems are complex, only two crystal field parameters, B(40) and B(60), are required to model the J-multiplet crystal field splittings in octahedral symmetry. It is found that these parameters exhibit R(-5) and R(-7) dependence, respectively, upon the ionic radius Ln(3+)(VI), but not upon the Ln-Cl distance. More generally, the crystal field strengths of LnX(6) systems (X = Br, Cl, F, O) exhibit linear relationships with ligand electronegativity, charge transfer energy, and fractional ionic character of the Ln-X bond.

Crystallization of the Pulsating White Dwarf Star, BPM 37093

NASA Astrophysics Data System (ADS)

Salois, Amee; Winget, D.

2010-01-01

BPM 37093 is unique among pulsating white dwarf stars because it is expected to have a highly crystallized interior. By understanding how this star is crystallizing, we gain a better understanding of extreme physics. Theoretical models of the evolution of white dwarf stars suggest that they crystallize from the inside out. The pulsations of the star, which we see as intensity variations, cannot penetrate this crystallized interior. Therefore, as the star crystallizes there is a smaller volume for the propagation of the pulsations and the pulsation periods are changed accordingly. We studied these changes in the periods of the pulsations of the star over ten weeks during the McDonald Observatory Research Experience for Undergraduates Program. By studying the changes in the pulsations periods of the star we can determine the mass fraction of the star that is crystallized. Comparing Fourier transforms of our observed light curves taken in 2004 and 2005 at CTIO with data taken in 1998 and 1999 by Kanaan et al. we hope to see the changes that have occurred in the star as well as determining a better approximation of the star's crystallized mass fraction.

Trapped Melt in IIIAB Irons: Solid/Liquid Elemental Partitioning During the Fractionation of the IIIAB Magma

NASA Technical Reports Server (NTRS)

Wasson, John T.

1999-01-01

Group IIIAB, the largest iron-meteorite group, shows compositional trends (including a three-order-of-magnitude It concentration range) indicating that it formed by fractional crystallization of a metallic magma. Because about 200 irons are available, and all degrees of crystallization are well represented, IIIAB offers an excellent set of samples for the study of crystallization at all depths of the asteroidal core. On log-log Ir-Au, and Ir-As diagrams IIIAB forms a broad band; the breadth represents real meteorite-to-meteorite variations, far outside experimental or sampling uncertainties. A successful model must explain the width of this band; I suggest that it mainly resulted from the trapping of parental magma within the crystallizing solid. Because S is essentially insoluble in metal, the abundance of FeS is a measure of the fraction of trapped liquid. The trapped-melt model is supported by the observation that irons having higher S contents plot closer to the inferred composition of the magmatic parental liquid. The lowest S values are found in the irons occupying the left envelope of the IIIAB Ir-Au or Ir-As compositional fields, thus it is this set of irons that should be interpreted as the solid products of a fractionating magma. This simplifies the modeling of the crystallization process and allows inferences regarding the distribution ratios for other elements in the evolved IIIAB system. The large (multiton) Cape York irons show wide variations in their trapped-melt fractions; their compositions seem best understood in terms of a low initial S content of the IIIAB magma, about 20 mg/g. The inferred initial IIIAB distribution coefficient for Ir, 4.6, is much higher than published values based on laboratory studies of low-S systems; I suggest that low-S (and low-P) partition-ratio measurements tend to err in the direction of unity. In IIIAB distribution coefficients for Au, As, and Ni were still < 1 when the most evolved IIIAB irons formed, another indication of a low initial S content.

Inhibition of ice crystal growth in ice cream mix by gelatin hydrolysate.

PubMed

Damodaran, Srinivasan

2007-12-26

The inhibition of ice crystal growth in ice cream mix by gelatin hydrolysate produced by papain action was studied. The ice crystal growth was monitored by thermal cycling between -14 and -12 degrees C at a rate of one cycle per 3 min. It is shown that the hydrolysate fraction containing peptides in the molecular weight range of about 2000-5000 Da exhibited the highest inhibitory activity on ice crystal growth in ice cream mix, whereas fractions containing peptides greater than 7000 Da did not inhibit ice crystal growth. The size distribution of gelatin peptides formed in the hydrolysate was influenced by the pH of hydrolysis. The optimum hydrolysis conditions for producing peptides with maximum ice crystal growth inhibitory activity was pH 7 at 37 degrees C for 10 min at a papain to gelatin ratio of 1:100. However, this may depend on the type and source of gelatin. The possible mechanism of ice crystal growth inhibition by peptides from gelatin is discussed. Molecular modeling of model gelatin peptides revealed that they form an oxygen triad plane at the C-terminus with oxygen-oxygen distances similar to those found in ice nuclei. Binding of this oxygen triad plane to the prism face of ice nuclei via hydrogen bonding appears to be the mechanism by which gelatin hydrolysate might be inhibiting ice crystal growth in ice cream mix.

Phenomenological model of spin crossover in molecular crystals as derived from atom-atom potentials.

PubMed

Sinitskiy, Anton V; Tchougréeff, Andrei L; Dronskowski, Richard

2011-08-07

The method of atom-atom potentials, previously applied to the analysis of pure molecular crystals formed by either low-spin (LS) or high-spin (HS) forms (spin isomers) of Fe(II) coordination compounds (Sinitskiy et al., Phys. Chem. Chem. Phys., 2009, 11, 10983), is used to estimate the lattice enthalpies of mixed crystals containing different fractions of the spin isomers. The crystals under study were formed by LS and HS isomers of Fe(phen)(2)(NCS)(2) (phen = 1,10-phenanthroline), Fe(btz)(2)(NCS)(2) (btz = 5,5',6,6'-tetrahydro-4H,4'H-2,2'-bi-1,3-thiazine), and Fe(bpz)(2)(bipy) (bpz = dihydrobis(1-pyrazolil)borate, and bipy = 2,2'-bipyridine). For the first time the phenomenological parameters Γ pertinent to the Slichter-Drickamer model (SDM) of several materials were independently derived from the microscopic model of the crystals with use of atom-atom potentials of intermolecular interaction. The accuracy of the SDM was checked against the numerical data on the enthalpies of mixed crystals. Fair semiquantitative agreement with the experimental dependence of the HS fraction on temperature was achieved with use of these values. Prediction of trends in Γ values as a function of chemical composition and geometry of the crystals is possible with the proposed approach, which opens a way to rational design of spin crossover materials with desired properties. This journal is © the Owner Societies 2011

Lunar Magma Ocean Crystallization: Constraints from Fractional Crystallization Experiments

NASA Technical Reports Server (NTRS)

Rapp, J. F.; Draper, D. S.

2015-01-01

The currently accepted paradigm of lunar formation is that of accretion from the ejecta of a giant impact, followed by crystallization of a global scale magma ocean. This model accounts for the formation of the anorthosite highlands crust, which is globally distributed and old, and the formation of the younger mare basalts which are derived from a source region that has experienced plagioclase extraction. Several attempts at modelling the crystallization of such a lunar magma ocean (LMO) have been made, but our ever-increasing knowledge of the lunar samples and surface have raised as many questions as these models have answered. Geodynamic models of lunar accretion suggest that shortly following accretion the bulk of the lunar mass was hot, likely at least above the solidus]. Models of LMO crystallization that assume a deep magma ocean are therefore geodynamically favorable, but they have been difficult to reconcile with a thick plagioclase-rich crust. A refractory element enriched bulk composition, a shallow magma ocean, or a combination of the two have been suggested as a way to produce enough plagioclase to account for the assumed thickness of the crust. Recently however, geophysical data from the GRAIL mission have indicated that the lunar anorthositic crust is not as thick as was initially estimated, which allows for both a deeper magma ocean and a bulk composition more similar to the terrestrial upper mantle. We report on experimental simulations of the fractional crystallization of a deep (approximately 100km) LMO with a terrestrial upper mantle-like (LPUM) bulk composition. Our experimental results will help to define the composition of the lunar crust and mantle cumulates, and allow us to consider important questions such as source regions of the mare basalts and Mg-suite, the role of mantle overturn after magma ocean crystallization and the nature of KREEP

Iron Isotope Systematics of the Bushveld Complex, South Africa: Initial Results

NASA Astrophysics Data System (ADS)

Stausberg, N.; Lesher, C. E.; Hoffmann-Barfod, G.; Glessner, J. J.; Tegner, C.

2014-12-01

Iron isotopes show systematic changes in igneous rocks that have been ascribed to fractional crystallization, partial melting, as well as, diffusion effects. Layered mafic intrusions, such as the Paleoproterozoic Bushveld Igneous Complex, are ideally suited to investigate stable isotope fractionation arising principally by fractional crystallization. The upper 2.1km of the Bushveld Complex (Upper and Upper Main Zone, UUMZ) crystallized from a basaltic magma produced by a major recharge event, building up a sequence of tholeiitic, Fe-rich, gabbroic cumulate rocks that display systematic variations in mineralogy and mineral compositions consistent with fractional crystallization. Within this sequence, magnetite joins the liquidus assemblage at ˜260m, followed by olivine at 460m and apatite at 1000m. Here, we present iron isotope measurements of bulk cumulate rocks from the Bierkraal drill core of UUMZ of the western limb. Iron was chemically separated from its matrix and analyzed for δ56Fe (relative to IRMM- 014) with a Nu plasma MC-ICPMS at the University of California, Davis, using (pseudo-) high resolution and sample-standard bracketing. The δ56Fe values for Bushveld cumulates span a range from 0.04‰ to 0.36‰, and systematically correlate with the relative abundance of pyroxene + olivine, magnetite and plagioclase. Notably, the highest δ56Fe values are found in plagioclase-rich cumulates that formed prior to magnetite crystallization. δ56Fe is also high in magnetite-rich cumulates at the onset of magnetite crystallization, while subsequent cumulates exhibit lower and variable δ56Fe principally reflecting fractionation of and modal variations in magnetite, pyroxene and fayalitic olivine. The overall relationships for δ56Fe are consistent with positive mineral - liquid Fe isotope fractionation factors for magnetite and plagioclase, and negative to near zero values for pyroxene and olivine. These initial results are being integrated into a forward model of the Bushveld liquid line of descent and will be compared to complementary work on the Skaergaard intrusion.

Possible Mechanisms for Turbofan Engine Ice Crystal Icing at High Altitude

NASA Technical Reports Server (NTRS)

Tsao, Jen-Ching; Struk, Peter M.; Oliver, Michael

2014-01-01

A thermodynamic model is presented to describe possible mechanisms of ice formation on unheated surfaces inside a turbofan engine compression system from fully glaciated ice crystal clouds often formed at high altitude near deep convective weather systems. It is shown from the analysis that generally there could be two distinct types of ice formation: (1) when the "surface freezing fraction" is in the range of 0 to 1, dominated by the freezing of water melt from fully or partially melted ice crystals, the ice structure is formed from accretion with strong adhesion to the surface, and (2) when the "surface melting fraction" is the range of 0 to 1, dominated by the further melting of ice crystals, the ice structure is formed from accumulation of un-melted ice crystals with relatively weak bonding to the surface. The model captures important qualitative trends of the fundamental ice-crystal icing phenomenon reported earlier1,2 from the research collaboration work by NASA and the National Research Council (NRC) of Canada. Further, preliminary analysis of test data from the 2013 full scale turbofan engine ice crystal icing test3 conducted in the NASA Glenn Propulsion Systems Laboratory (PSL) has also suggested that (1) both types of ice formation occurred during the test, and (2) the model has captured some important qualitative trend of turning on (or off) the ice crystal ice formation process in the tested engine low pressure compressor (LPC) targeted area under different icing conditions that ultimately would lead to (or suppress) an engine core roll back (RB) event.

Possible Mechanisms for Turbofan Engine Ice Crystal Icing at High Altitude

NASA Technical Reports Server (NTRS)

Tsao, Jen-Ching; Struk, Peter M.; Oliver, Michael J.

2016-01-01

A thermodynamic model is presented to describe possible mechanisms of ice formation on unheated surfaces inside a turbofan engine compression system from fully glaciated ice crystal clouds often formed at high altitude near deep convective weather systems. It is shown from the analysis that generally there could be two distinct types of ice formation: (1) when the "surface freezing fraction" is in the range of 0 to 1, dominated by the freezing of water melt from fully or partially melted ice crystals, the ice structure is formed from accretion with strong adhesion to the surface, and (2) when the "surface melting fraction" is the range of 0 to 1, dominated by the further melting of ice crystals, the ice structure is formed from accumulation of un-melted ice crystals with relatively weak bonding to the surface. The model captures important qualitative trends of the fundamental ice-crystal icing phenomenon reported earlier (Refs. 1 and 2) from the research collaboration work by NASA and the National Research Council (NRC) of Canada. Further, preliminary analysis of test data from the 2013 full scale turbofan engine ice crystal icing test (Ref. 3) conducted in the NASA Glenn Propulsion Systems Laboratory (PSL) has also suggested that (1) both types of ice formation occurred during the test, and (2) the model has captured some important qualitative trend of turning on (or off) the ice crystal ice formation process in the tested engine low pressure compressor (LPC) targeted area under different icing conditions that ultimately would lead to (or suppress) an engine core roll back (RB) event.

Diffusion-driven magnesium and iron isotope fractionation in Hawaiian olivine

USGS Publications Warehouse

Teng, F.-Z.; Dauphas, N.; Helz, R.T.; Gao, S.; Huang, S.

2011-01-01

Diffusion plays an important role in Earth sciences to estimate the timescales of geological processes such as erosion, sediment burial, and magma cooling. In igneous systems, these diffusive processes are recorded in the form of crystal zoning. However, meaningful interpretation of these signatures is often hampered by the fact that they cannot be unambiguously ascribed to a single process (e.g., magmatic fractionation, diffusion limited transport in the crystal or in the liquid). Here we show that Mg and Fe isotope fractionations in olivine crystals can be used to trace diffusive processes in magmatic systems. Over sixty olivine fragments from Hawaiian basalts show isotopically fractionated Mg and Fe relative to basalts worldwide, with up to 0.4??? variation in 26Mg/24Mg ratios and 1.6??? variation in 56Fe/54Fe ratios. The linearly and negatively correlated Mg and Fe isotopic compositions [i.e., ??56Fe=(??3.3??0.3)????26Mg], co-variations of Mg and Fe isotopic compositions with Fe/Mg ratios of olivine fragments, and modeling results based on Mg and Fe elemental profiles demonstrate the coupled Mg and Fe isotope fractionation to be a manifestation of Mg-Fe inter-diffusion in zoned olivines during magmatic differentiation. This characteristic can be used to constrain the nature of mineral zoning in igneous and metamorphic rocks, and hence determine the residence times of crystals in magmas, the composition of primary melts, and the duration of metamorphic events. With improvements in methodology, in situ isotope mapping will become an essential tool of petrology to identify diffusion in crystals. ?? 2011 Elsevier B.V.

SilMush: A procedure for modeling of the geochemical evolution of silicic magmas and granitic rocks

NASA Astrophysics Data System (ADS)

Hertogen, Jan; Mareels, Joyce

2016-07-01

A boundary layer crystallization modeling program is presented that specifically addresses the chemical fractionation in silicic magma systems and the solidification of plutonic bodies. The model is a Langmuir (1989) type approach and does not invoke crystal settling in high-viscosity silicic melts. The primary aim is to model a granitic rock as a congealed crystal-liquid mush, and to integrate major element and trace element modeling. The procedure allows for some exploratory investigation of the exsolution of H2O-fluids and of the fluid/melt partitioning of trace elements. The procedure is implemented as a collection of subroutines for the MS Excel spreadsheet environment and is coded in the Visual Basic for Applications (VBA) language. To increase the flexibility of the modeling, the procedure is based on discrete numeric process simulation rather than on solution of continuous differential equations. The program is applied to a study of the geochemical variation within and among three granitic units (Senones, Natzwiller, Kagenfels) from the Variscan Northern Vosges Massif, France. The three units cover the compositional range from monzogranite, over syenogranite to alkali-feldspar granite. An extensive set of new major element and trace element data is presented. Special attention is paid to the essential role of accessory minerals in the fractionation of the Rare Earth Elements. The crystallization model is able to reproduce the essential major and trace element variation trends in the data sets of the three separate granitic plutons. The Kagenfels alkali-feldspar leucogranite couples very limited variation in major element composition to a considerable and complex variation of trace elements. The modeling results can serve as a guide for the reconstruction of the emplacement sequence of petrographically distinct units. Although the modeling procedure essentially deals with geochemical fractionation within a single pluton, the modeling results bring up a number of questions about the petrogenetic relationships among parental magmas of nearly coeval granitic units emplaced in close proximity.

Fractional crystallization-induced variations in sulfides from the Noril’sk-Talnakh mining district (polar Siberia, Russia)

USGS Publications Warehouse

Duran, C.J.; Barnes, S-J.; Pleše, P.; Prašek, M. Kudrna; Zientek, Michael L.; Pagé, P.

2017-01-01

The distribution of platinum-group elements (PGE) within zoned magmatic ore bodies has been extensively studied and appears to be controlled by the partitioning behavior of the PGE during fractional crystallization of magmatic sulfide liquids. However, other chalcophile elements, especially TABS (Te, As, Bi, Sb, and Sn) have been neglected despite their critical role in forming platinum-group minerals (PGM). TABS are volatile trace elements that are considered to be mobile so investigating their primary distribution may be challenging in magmatic ore bodies that have been somewhat altered. Magmatic sulfide ore bodies from the Noril’sk-Talnakh mining district (polar Siberia, Russia) offer an exceptional opportunity to investigate the behavior of TABS during fractional crystallization of sulfide liquids and PGM formation as the primary features of the ore bodies have been relatively well preserved. In this study, new petrographic (2D and 3D) and whole-rock geochemical data from Cu-poor to Cu-rich sulfide ores of the Noril’sk-Talnakh mining district are integrated with published data to consider the role of fractional crystallization in generating mineralogical and geochemical variations across the different ore types (disseminated to massive). Despite textural variations in Cu-rich massive sulfides (lenses, veins, and breccias), these sulfides have similar chemical compositions, which suggests that Cu-rich veins and breccias formed from fractionated sulfide liquids that were injected into the surrounding rocks. Numerical modeling using the median disseminated sulfide composition as the initial sulfide liquid composition and recent DMSS/liq and DISS/liq predicts the compositional variations observed in the massive sulfides, especially in terms of Pt, Pd, and TABS. Therefore, distribution of these elements in the massive sulfides was likely controlled by their partitioning behavior during sulfide liquid fractional crystallization, prior to PGM formation. Our observations indicate that in the Cu-poor massive sulfides the PGM formed as the result of exsolution from sulfide minerals whereas in the Cu-rich massive sulfides the PGM formed by crystallization from late-stage fractionated sulfide liquids. We suggest that the significant amount of Sn-bearing PGM may be related to crustal contamination from granodiorite, whereas As, Bi, Te, and Sb were likely added to the magma along with S from sedimentary rocks. Large PGM that are scarce and randomly distributed may account for most of the whole-rock Pt budget. Based on our results, we propose a holistic genetic model for the formation of the magmatic sulfide ore bodies of the Noril’sk-Talnakh mining district.

Phase equilibria constraints on the chemical and physical evolution of the campanian ignimbrite

USGS Publications Warehouse

Fowler, S.J.; Spera, F.J.; Bohrson, W.A.; Belkin, H.E.; de Vivo, B.

2007-01-01

The Campanian Ignimbrite is a > 200 km3 trachyte-phonolite pyroclastic deposit that erupted at 39.3 ?? 0.1 ka within the Campi Flegrei west of Naples, Italy. Here we test the hypothesis that Campanian Ignimbrite magma was derived by isobaric crystal fractionation of a parental basaltic trachyandesitic melt that reacted and came into local equilibrium with small amounts (5-10 wt%) of crustal rock (skarns and foid-syenites) during crystallization. Comparison of observed crystal and magma compositions with results of phase equilibria assimilation-fractionation simulations (MELTS) is generally very good. Oxygen fugacity was approximately buffered along QFM+1 (where QFM is the quartz-fayalite-magnetite buffer) during isobaric fractionation at 0.15 GPa (???6 km depth). The parental melt, reconstructed from melt inclusion and host clinopyroxene compositions, is found to be basaltic trachyandesite liquid (51.1 wt% SiO2, 9.3 wt% MgO, 3 wt% H2O). A significant feature of phase equilibria simulations is the existence of a pseudo-invariant temperature, ???883??C, at which the fraction of melt remaining in the system decreases abruptly from ???0.5 to < 0.1. Crystallization at the pseudo-invariant point leads to abrupt changes in the composition, properties (density, dissolved water content), and physical state (viscosity, volume fraction fluid) of melt and magma. A dramatic decrease in melt viscosity (from 1700 Pa s to ???200 Pa s), coupled with a change in the volume fraction of water in magma (from ??? 0.1 to 0.8) and a dramatic decrease in melt and magma density acted as a destabilizing eruption trigger. Thermal models suggest a timescale of ??? 200 kyr from the beginning of fractionation until eruption, leading to an apparent rate of evolved magma generation of about 10-3 km3/year. In situ crystallization and crystal settling in density-stratified regions, as well as in convectively mixed, less evolved subjacent magma, operate rapidly enough to match this apparent volumetric rate of evolved magma production. ?? Copyright 2007 Oxford University Press.

Raman tensor elements for tetragonal BaTiO3 and their use for in-plane domain texture assessments

NASA Astrophysics Data System (ADS)

Deluca, Marco; Higashino, Masayuki; Pezzotti, Giuseppe

2007-08-01

A quantitative assessment of c-axis oriented domains in a textured BaTiO3 (BT) single crystal has been carried out by polarized Raman microprobe spectroscopy. The relative intensity modulation of the Raman phonon modes has been theoretically modeled as a function of crystal rotation and linked to the volume fraction of c-axis oriented domains. Raman tensor elements have also been experimentally determined for the Ag and B1 vibrational modes. As an application, the internal in-plane texture and the volume fraction of c-oriented domains in the BT single crystal have been nondestructively visualized by monitoring the relative intensity of Ag and B1 Raman modes.

Characterization of Coconut Oil Fractions Obtained from Solvent Fractionation Using Acetone.

PubMed

Sonwai, Sopark; Rungprasertphol, Poonyawee; Nantipipat, Nantinee; Tungvongcharoan, Satinee; Laiyangkoon, Nantikan

2017-09-01

This work was aimed to study the solvent fraction of coconut oil (CNO). The fatty acid and triacylglycerol compositions, solid fat content (SFC) and the crystallization properties of CNO and its solid and liquid fractions obtained from fractionation at different conditions were investigated using various techniques. CNO was dissolved in acetone (1:1 w/v) and left to crystallize isothermally at 10°C for 0.5, 1 and 2 h and at 12°C for 2, 3 and 6 h. The solid fractions contained significantly lower contents of saturated fatty acids of ≤ 10 carbon atoms but considerably higher contents of saturated fatty acids with > 12 carbon atoms with respect to those of CNO and the liquid fractions. They also contained higher contents of high-melting triacylglycerol species with carbon number ≥ 38. Because of this, the DSC crystallization onset temperatures and the crystallization peak temperatures of the solid fractions were higher than CNO and the liquid fractions. The SFC values of the solid fractions were significantly higher than CNO at all measuring temperatures before reaching 0% just below the body temperature with the fraction obtained at 12°C for 2 h exhibiting the highest SFC. On the contrary, the SFC values of the liquid fractions were lower than CNO. The crystallization duration exhibited strong influence on the solid fractions. There was no effect on the crystal polymorphic structure possibly because CNO has β'-2 as a stable polymorph. The enhanced SFC of the solid fractions would allow them to find use in food applications where a specific melting temperature is desired such as sophisticated confectionery fats, and the decreased SFC of the liquid fractions would provide them with a higher cold stability which would be useful during extended storage time.

Planetoid core crystallisation and fractionation - Evidence from the Agpalilik mass of the Cape York iron meteorite shower

NASA Astrophysics Data System (ADS)

Esbensen, K. H.; Buchwald, V. F.

1982-09-01

Metallographic and chemical study of the Agpalik mass of the Cape York iron meteorite shower reveals evidence of the mode of crystallization and fractionation of key elements consistent with a dendritic solidification of at least part of the once fully molten parent body's metallic core. Chemical gradients of Ir and Au are assessed across an 85 cm section that is inferred to be perpendicular to the parent body's gravitational field, and are interpreted as representing a dendritic growth mode. The characteristic elongated and orientated sulfide nodules found in Agpalik signify trapped liquid of the latest stages of crystallization. Detailed mineralogical and chemical characterization of the Agpalik liquid-solid transformation products allow modelling of the entire crystallization history commencing with dendritic metal precipitation through an ultimate troilite-taenite-Cu eutectic, representing a crystallization range spanning approximately 1350-700 C.

Liquid fractionation. Part I: Basic principles and experimental simulations

NASA Astrophysics Data System (ADS)

McBirney, Alexander R.; Baker, Brian H.; Nilson, Robert H.

1985-03-01

A possible explanation for the closely associated magmas of contrasting compositions erupted from many mature volcanic centers can be found in the large differences of density produced by relatively small compositional variations in liquids that evolve by crystallization or melting at the walls of shallow magma chambers. A mechanism of liquid fractionation in which differentiated liquids segragate gravitationally to form compositionally graded columns of magma may surmount the long-standing problem of explaining large volumes of highly evolved liquids that reach advanced degrees of differentiation in times that are too short to be consistent with conventional models of crystal fractionation based on crystal settling. In those types of magmas that decrease in density as they differentiate, a fractionated liquid next to a wall may form a buoyant compositional boundary layer that flows up the wall and accumulates as a separate zone in the upper levels of the reservoir. Magmas that increase in density as they differentiate will have the opposite behavior; they descend along the wall and pond on the floor. Both types of systems can be modeled using simple aqueous solutions and techniques similar to those developed by Chen and Turner (1980). The insights gained through experiments of this kind suggest a number of processes that may be responsible for common types of volcanic behavior and patterns of differentiation in shallow plutons.

Trace element evaluation of a suite of rocks from Reunion Island, Indian Ocean

USGS Publications Warehouse

Zielinski, R.A.

1975-01-01

Reunion Island consists of an olivine-basalt shield capped by a series of flows and intrusives ranging from hawaiite through trachyte. Eleven rocks representing the total compositional sequence have been analyzed for U, Th and REE. Eight of the rocks (group 1) have positive-slope, parallel, chondrite-normalized REE fractionation patterns. Using a computer model, the major element compositions of group 1 whole rocks and observed phenocrysts were used to predict the crystallization histories of increasingly residual liquids, and allowed semi-quantitative verification of origin by fractional crystallization of the olivine-basalt parent magma. Results were combined with mineral-liquid distribution coefficient data to predict trace element abundances, and existing data on Cr, Ni, Sr and Ba were also successfully incorporated in the model. The remaining three rocks (group 2) have nonuniform positive-slope REE fractionation patterns not parallel to group 1 patterns. Rare earth fractionation in a syenite is explained by partial melting of a source rich in clinopyroxene and/or hornblende. The other two rocks of group 2 are explained as hybrids resulting from mixing of syenite and magmas of group 1. ?? 1975.

Equilibrium carbon and hydrogen isotope fractionation in iron

NASA Astrophysics Data System (ADS)

Schauble, E. A.

2009-12-01

Recent theoretical and experimental studies (e.g., [1-3]) have suggested that Si- and Fe-isotopic signatures can be used to characterize the compositions and conditions of segregation of metallic cores in planetary interiors. This study expands the theoretical framework to include carbon and hydrogen, which may also be alloying elements. Hydrogen (D/H) and carbon (13C/12C) fractionations in iron-rich metallic melts are estimated by modeling analogous iron-rich crystals, i.e., dhcp-FeH and η-Fe2C. C- and H-atoms in these crystals are completely coordinated by iron. The driving energy for equilibrium fractionation is assumed to come from the reduction of vibrational frequencies when heavy isotopes are substituted for light ones; vibrations are assumed to be harmonic. This treatment is crude at high temperature, and for the relatively anharmonic vibrations typical of hydrogen-bearing substances, but may provide a reasonably accurate, semi-quantitative approximation of real fractionation behavior. Vibrational frequencies of all crystals are modeled with density functional theory, using gradient-corrected functionals and ultrasoft pseudopotentials. For both carbon and hydrogen, the models suggest that the metal phase will be strongly depleted in heavy isotopes. At 2000 K, 1 atm, η-Fe2C will have 3‰ lower 13C/12C than coexisting diamond. Combining this result with previous high-temperature theoretical and experimental studies (e.g., [4]), metal-graphite fractionation is expected to be very similar, while metal-CO2 fractionation will be almost twice as large, ca. -5‰. Deuterium/hydrogen fractionations are expected to be an order of magnitude larger, with 50-70‰ lower D/H in dhcp-FeH than in coexisting H2 gas at 2000 K, and approximately 100‰ lower D/H than water vapor. These fractionations are much larger than those inferred for silicon and iron, as expected given the differences in atomic mass. References: 1. Georg et al. (2007) Nature 447:1102; 2. Rustad & Yin (2009) Nature Geoscience doi:10.1038/ngeo546; 3. Polyakov (2009) Science 323:912; 4. Polyakov & Kharlashina (1995) GCA 59:2561.

Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: role of crystal fractionation and mantle heterogeneity.

USGS Publications Warehouse

Clague, D.A.; Frey, F.A.; Thompson, G.; Rindge, S.

1981-01-01

A wide range of rock types (abyssal tholeiite, Fe-Ti-rich basalt, andesite, and rhyodacite) were dredged from near 95oW and 85oW on the Galapagos spreading center. Computer modeling of major element compositions has shown that these rocks could be derived from common parental magmas by successive degrees of fractional crystallization. However, the P2O5/K2O ratio implies distinct mantle source compositions for the two areas. These source regions also have different rare earth element (REE) abundance patterns. The sequence of fractionated lavas differs for the two areas and indicates earlier fractionation of apatite and titanomagnetite in the lavas from 95oW. The mantle source regions for these two areas are interpreted to be depleted in incompatible (and volatile?) elements, although the source region beneath 95oW is less severely depleted in La and K. -Authors

The Effects of Impurities on Protein Crystal Growth and Nucleation: A Preliminary Study

NASA Technical Reports Server (NTRS)

Schall, Constance A.

1998-01-01

Kubota and Mullin (1995) devised a simple model to account for the effects of impurities on crystal growth of small inorganic and organic molecules in aqueous solutions. Experimentally, the relative step velocity and crystal growth of these molecules asymptotically approach zero or non-zero values with increasing concentrations of impurities. Alternatively, the step velocity and crystal growth can linearly approach zero as the impurity concentration increases. The Kubota-Mullin model assumes that the impurity exhibits Langmuirian adsorption onto the crystal surface. Decreases in step velocities and subsequent growth rates are related to the fractional coverage (theta) of the crystal surface by adsorbed impurities; theta = Kx / (I +Kx), x = mole fraction of impurity in solution. In the presence of impurities, the relative step velocity, V/Vo, and the relative growth rate of a crystal face, G/Go, are proposed to conform to the following equations: V/Vo approx. = G/Go = 1 - (alpha)(theta). The adsorption of impurity is assumed to be rapid and in quasi-equilibrium with the crystal surface sites available. When the value of alpha, an effectiveness factor, is one the growth will asymptotically approach zero with increasing concentrations of impurity. At values less than one, growth approaches a non-zero value asymptotically. When alpha is much greater than one, there will be a linear relationship between impurity concentration and growth rates. Kubota and Mullin expect alpha to decrease with increasing supersaturation and shrinking size of a two dimensional nucleus. It is expected that impurity effects on protein crystal growth will exhibit behavior similar to that of impurities in small molecule growth. A number of proteins were added to purified chicken egg white lysozyme, the effect on crystal nucleation and growth assessed.

Nature of the magma storage system beneath the Damavand volcano (N. Iran): An integrated study

NASA Astrophysics Data System (ADS)

Eskandari, Amir; Amini, Sadraddin; De Rosa, Rosanna; Donato, Paola

2018-02-01

Damavand intraplate stratovolcano constructed upon a moderately thick crust (58-67 km) over the last 2 Ma. The erupted products are dominantly trachyandesite-trachyte (TT) lavas and pyroclasts, with minor mafic magmas including tephrite-basanite-trachybasalt and alkali olivine basalts emplaced as cinder cones at the base of the stratovolcano. The TT products are characterized by a mineral assemblage of clinopyroxene (diopside-augite), orthopyroxene (clinoenstatite), feldspar (An2-58, Ab6-69, Or2-56), high Ti phlogopite, F-apatite, Fesbnd Ti oxides, and minor amounts of olivine (Fo73-80), amphibole and zircon, whereas olivine (Fo78-88), high Mg# (80-89) diopside, feldspar, apatite and Fesbnd Ti oxide occur in the mafic magmas. The presence of hydrous and anhydrous minerals, normal zonings, mafic cumulates, and the composition of magmatic inclusions in the TT products suggest evolutionary processes in polybaric conditions. In the same way, disequilibrium textures - including orthopyroxene mantled with clinopyroxene, reaction rim of phlogopite and amphibole, the coexistence of olivine and orthopyroxene, reverse, oscillatory and complex zonings of pyroxene and feldspar crystals - suggest magmatic evolutions in open systems with a varying temperature, oxygen fugacity, water as well as pressure and, to a lesser extent, melt chemistry. Mineral assemblages are used to model the physicochemical conditions and assess default parameters for the thermodynamic simulation of crystallization using MELTS software to track the P-T-H2O-ƒO2 evolution of the magma plumbing system. Thermobarometry and MELTS models estimated the initial nucleation depth at 16-17 kb (56-60 km) for olivine (Fo89) and high Al diopside crystals occurring in the mafic primary magma; it then stopped and underwent fractionation between 8 and 10 kb (28-35 km), corresponding with Moho depth, and continued to differentiate in the lower crust, in agreement with the geophysical models. The mafic rocks were formed by crystal fractionation from the reconstructed primary magma (13 wt% MgO) with the minor role of recharge and crustal assimilation. Phenocrysts in TT lavas recorded a wide range of temperature and pressure of crystallization; at least three main levels of magma storage can be recognized according to the statistical analysis of the models, at 6-8 kb (22-28 km), 4-6 kb (15-22 km), and 0.6-3 kb (2-11 km), respectively. The temperature of crystallization ranged from 1430 to 1180 °C for primary mafic magma to alkali olivine basalts and 1180-800 °C for TT suite. According to the current geophysical models, the present structure of the magma storage system in the crust beneath the Damavand volcano consists of three major accumulation zones located at 20 km, 6-8 km and 3-4.5 km depth. Our data enlarge this scenario, suggesting a more complex magma storage system strongly controlled by the transpressional tectonic regime. Multi-depth magma reservoirs may account for the local thickening of crust below the volcano. The polybaric fractionation model, using the MELTS algorithm, reproduces mineralogy and chemical variations of minerals and whole rock of the Damavand TT lavas. However, some discrepancies between major elements of models and trends of data can be ascribed to the recharge of more mafic magma, minor crustal assimilation, disaggregation of crystal-rich mushes and uptake of magmatic inclusions, as well as crystals from different crustal levels. The polybaric differentiation as the fractionation and/or accumulation of crystals was the probable mechanism for explaining the scarcity of mafic volcanic rocks at the Damavand volcano.

An unmetasomatized source for the Malaitan alnoeite (Solomon Islands): Petrogenesis involving zone refining, megacryst fractionation, and assimilation of oceanic lithosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neal, C.R.; Davidson, J.P.

The Malaitan alnoite contains a rich and varied megacryst suite of unprecedented compositional range. The authors have undertaken trace element and isotope modeling in order to formulate a petrogenetic scheme which links the host alnoeite to its entrained megacrysts. This requires that a proto-alnoeite magma is the product of zone refining initiated by diapiric upwelling (where the initial melt passes through 200 times its volume of mantle). Isotopic evidence indicates the source of the proto-alnoeite contains a time-integrated LREE-depleted signature. Impingement upon the rigid lithosphere halts or dramatically slows the upward progress of the mantle diapir. At this point, themore » magma cools and megacryst fractionation begins with augites crystallizing first, followed by subcalcic diopsides and finally phlogopites. Garnet probably crystallizes over the entire range of clinopyroxene fractionation. Estimated proportions of fractionating phases are 30% augite, 24.5% subcalcic diopside, 27% garnet, 12.9% phlogopite, 5% bronzite, 0.5% ilmenite, and 0.1% zircon. As this proto-alnoeite magma crystallizes, it assimilates a subducted component of seawater-altered basalt which underplates the Ontong Java Plateau. This is witnessed in the isotopic composition of the megacrysts and alnoeite.« less

The assessment of pore connectivity in hierarchical zeolites using positron annihilation lifetime spectroscopy: instrumental and morphological aspects.

PubMed

Zubiaga, Asier; Warringham, Robbie; Boltz, Marilyne; Cooke, David; Crivelli, Paolo; Gidley, David; Pérez-Ramírez, Javier; Mitchell, Sharon

2016-04-07

Recent studies demonstrated the power of positron annihilation lifetime spectroscopy (PALS) to characterise the connectivity and corresponding effectiveness of hierarchical pore networks in zeolites. This was based on the fractional escape of ortho-positronium (Ps), formed within the micropore framework, to vacuum. To further develop this technique, here we assess the impact of the positron implantation energy and of the zeolite crystal size and the particle morphology. Conventional measurements using fast positrons and beam measurements applying moderated positrons both readily distinguish purely microporous ZSM-5 zeolites comprised of single crystals or crystal aggregates. Unlike beam measurements, however, conventional measurements fail to discriminate model hierarchical zeolites with open or constricted mesopore architectures. Several steps are taken to rationalise these observations. The dominant contribution of Ps diffusion to the PALS response is confirmed by capping the external surface of the zeolite crystals with tetraethylorthosilicate, which greatly enhances the sensitivity to the micropore network. A one-dimensional model is constructed to predict the out-diffusion of Ps from a zeolite crystal, which is validated experimentally by comparing coffin-shaped single crystals of varying size. Calculation of the trends expected on the application of fast or moderated positrons indicates that the distinctions in the initial distribution of Ps at the crystal level cannot explain the limited sensitivity of the former to the mesopore architecture. Instead, we propose that the greater penetration of fast positrons within the sample increases the probability of Ps re-entry from intercrystalline voids into mesopores connected with the external surface of zeolite crystals, thereby reducing their fractional escape.

Effects of Microstructural Parameters on Creep of Nickel-Base Superalloy Single Crystals

NASA Technical Reports Server (NTRS)

MacKay, Rebecca A.; Gabb, Timothy P.; Nathal, Michael V.

2013-01-01

Microstructure-sensitive creep models have been developed for Ni-base superalloy single crystals. Creep rupture testing was conducted on fourteen single crystal alloys at two applied stress levels at each of two temperatures, 982 and 1093 C. The variation in creep lives among the different alloys could be explained with regression models containing relatively few microstructural parameters. At 982 C, gamma-gamma prime lattice mismatch, gamma prime volume fraction, and initial gamma prime size were statistically significant in explaining the creep rupture lives. At 1093 C, only lattice mismatch and gamma prime volume fraction were significant. These models could explain from 84 to 94 percent of the variation in creep lives, depending on test condition. Longer creep lives were associated with alloys having more negative lattice mismatch, lower gamma prime volume fractions, and finer gamma prime sizes. The gamma-gamma prime lattice mismatch exhibited the strongest influence of all the microstructural parameters at both temperatures. Although a majority of the alloys in this study were stable with respect to topologically close packed (TCP) phases, it appeared that up to approximately 2 vol% TCP phase did not affect the 1093 C creep lives under applied stresses that produced lives of approximately 200 to 300 h. In contrast, TCP phase contents of approximately 2 vol% were detrimental at lower applied stresses where creep lives were longer. A regression model was also developed for the as-heat treated initial gamma prime size; this model showed that gamma prime solvus temperature, gamma-gamma prime lattice mismatch, and bulk Re content were all statistically significant.

Gravity driven and in situ fractional crystallization processes in the Centre Hill complex, Abitibi Subprovince, Canada: Evidence from bilaterally-paired cyclic units

NASA Astrophysics Data System (ADS)

Thériault, R. D.; Fowler, A. D.

1996-12-01

The formation of layers in mafic intrusions has been explained by various processes, making it the subject of much controversy. The concept that layering originates from gravitational settling of crystals has been superseded in recent years by models involving in situ fractional crystallization. Here we present evidence from the Centre Hill complex that both processes may be operative simultaneously within the same intrusion. The Centre Hill complex is part of the Munro Lake sill, an Archean layered mafic intrusion emplaced in volcanic rocks of the Abitibi Subprovince. The Centre Hill complex comprises the following lithostratigraphic units: six lower cyclic units of peridotite and clinopyroxenite; a middle unit of leucogabbro; six upper cyclic units of branching-textured gabbro (BTG) and clotted-textured gabbro (CTG), the uppermost of these units being overlain by a marginal zone of fine-grained gabbro. The cyclic units of peridotite/clinopyroxenite and BTG/CTG are interpreted to have formed concurrently through fractional crystallization, associated with periodic replenishment of magma to the chamber. The units of peridotite and clinopyroxenite formed by gravitational accumulation of crystals that grew under the roof. The cyclic units of BTG and CTG formed along the upper margin of the sill by two different mechanisms: (1) layers of BTG crystallized in situ along an inward-growing roof and (2) layers of CTG formed by accumulation of buoyant plagioclase crystals. The layers of BTG are characterized by branching pseudomorphs after fayalite up to 50 cm in length that extend away from the upper margin. The original branching crystals are interpreted to have grown from stagnant intercumulus melt in a high thermal gradient resulting from the injection of new magma to the chamber.

Determining Kinetic Parameters for Isothermal Crystallization of Glasses

NASA Technical Reports Server (NTRS)

Ray, C. S.; Zhang, T.; Reis, S. T.; Brow, R. K.

2006-01-01

Non-isothermal crystallization techniques are frequently used to determine the kinetic parameters for crystallization in glasses. These techniques are experimentally simple and quick compared to the isothermal techniques. However, the analytical models used for non-isothermal data analysis, originally developed for describing isothermal transformation kinetics, are fundamentally flawed. The present paper describes a technique for determining the kinetic parameters for isothermal crystallization in glasses, which eliminates most of the common problems that generally make the studies of isothermal crystallization laborious and time consuming. In this technique, the volume fraction of glass that is crystallized as a function of time during an isothermal hold was determined using differential thermal analysis (DTA). The crystallization parameters for the lithium-disilicate (Li2O.2SiO2) model glass were first determined and compared to the same parameters determined by other techniques to establish the accuracy and usefulness of the present technique. This technique was then used to describe the crystallization kinetics of a complex Ca-Sr-Zn-silicate glass developed for sealing solid oxide fuel cells.

The effect of crystal shape, size and bimodality on the maximum packing and the rheology of crystal bearing magma

NASA Astrophysics Data System (ADS)

Moitra, Pranabendu; Gonnermann, Helge

2014-05-01

Magma often contains crystals of various shapes and sizes. We present experimental results on the effect of the shape- and size-distribution of solid particles on the rheological properties of solid-liquid suspensions, which are hydrodynamically analogous to crystal-bearing magmas. The suspensions were comprised of either a single particle shape and size (unimodal) or a mixture of two different particle shapes and sizes (bimodal). For each type of suspension we characterized the dry maximum packing fraction of the particle mixture using the tap density method. We then systematically varied the total volume fraction of particles in the suspension, as well as the relative proportion of the two different particle types in the bimodal suspensions. For each of the resultant mixtures (suspensions) we performed controlled shear stress experiments using a rotational rheometer in parallel-plate geometry spanning 4 orders of magnitude in shear stress. The resultant data curves of shear stress as a function of shear rate were fitted using a Herschel-Bulkley rheological model. We find that the dry maximum packing decreases with increasing particle aspect ratio (ar) and decreasing particle size ratio (Λ). The highest dry maximum packing was obtained at 60-75% volume of larger particles for bimodal spherical particle mixture. Normalized consistency, Kr, defined as the ratio of the consistency of the suspension and the viscosity of the suspending liquid, was fitted using a Krieger-Dougherty model as a function of the total solid volume fraction (φ). The maximum packing fractions (φm) obtained from the shear experimental data fitting of the unimodal suspensions were similar in magnitude with the dry maximum packing fractions of the unimodal particles. Subsequently, we used the dry maximum packing fractions of the bimodal particle mixtures to fit Kr as a function of φ for the bimodal suspensions. We find that Kr increases rapidly for suspensions with larger ar and smaller Λ. We also find that both the apparent yield stress and the shear thinning behavior of the suspensions increase with increasing ar and become significant at φ/φm ≥ 0.4.

An expanded model and application of the combined effect of crystal-size distribution and crystal shape on the relative viscosity of magmas

NASA Astrophysics Data System (ADS)

Klein, Johannes; Mueller, Sebastian P.; Helo, Christoph; Schweitzer, Silja; Gurioli, Lucia; Castro, Jonathan M.

2018-05-01

This study examines the combined effect of crystal-size distributions (CSD) and crystal shape on the rheology of vesicle free magmatic suspensions and provides the first practical application of an empirical model to estimate the relative effect of crystal content and CSD's on the viscosity of magma directly from textural image analysis of natural rock samples in the form of a user-friendly texture-rheology spreadsheet calculator. We extend and apply established relationships between the maximum packing fraction ϕm of a crystal bearing suspension and both its rheological properties and the polydispersity γ of a CSD. By using analogue rotational rheometric experiments with glass fibres and glass flakes in silicone oil acting as magma equivalent, this study also provides new insights in the relationship between ϕm and the aspect ratio rp of suspended particles.

Effects of polymer type and storage relative humidity on the kinetics of felodipine crystallization from amorphous solid dispersions.

PubMed

Rumondor, Alfred C F; Stanford, Lindsay A; Taylor, Lynne S

2009-12-01

The objective of this study was to investigate the effects of polymer type and storage relative humidity (RH) on the crystallization kinetics of felodipine from amorphous solid dispersions. Crystallization of the model drug felodipine from amorphous solid dispersion samples containing poly(vinyl pyrrolidone) (PVP) and hypromellose acetate succinate (HPMCAS) were evaluated. Samples at three different drug-polymer weight ratios (10, 25, and 50 wt. % polymer) were prepared and stored at six different RHs (0%, 32%, 52% or 66%, 75%, 86%, and 93%). Periodically, the fraction of the drug that had crystallized from the samples was quantified using powder X-ray diffractometry (PXRD). Felodipine crystallization rates from PVP-containing dispersions were found to be very sensitive to changes in storage RH, while crystallization rates from HPMCAS-containing dispersions were not. PVP and HPMCAS were similar in terms of their ability to inhibit crystallization at low RH, but when the storage RH was increased to 75% or above, felodipine crystallization from PVP-containing solid dispersions proceeded much faster. It is hypothesized that this trend was caused by moisture-induced drug-polymer immiscibility in PVP-felodipine system. For PVP-containing solid dispersion samples stored at 75% RH and above, crystallization of the model drug felodipine seemed to approach a kinetic plateau, whereby a fraction of the drug still remained amorphous even after storage for 500 days or more. The physical stability of solid dispersions as a function of RH is highly dependent on the polymer used to form the solid dispersion, with PVP-containing dispersions being much less physically stable at high RH than HPMCAS-containing dispersions.

Differentiation of magma oceans and the thickness of the depleted layer on Venus

NASA Technical Reports Server (NTRS)

Solomatov, V. S.; Stevenson, D. J.

1993-01-01

Various arguments suggest that Venus probably has no asthenosphere, and it is likely that beneath the crust there is a highly depleted and highly viscous mantle layer which was probably formed in the early history of the planet when it was partially or completely molten. Models of crystallization of magma oceans suggest that just after crystallization of a hypothetical magma ocean, the internal structure of Venus consists of a crust up to about 70 km thickness, a depleted layer up to about 500 km, and an enriched lower layer which probably consists of an undepleted 'lower mantle' and heavy enriched accumulates near the core-mantle boundary. Partial or even complete melting of Venus due to large impacts during the formation period eventually results in differentiation. However, the final result of such a differentiation can vary from a completely differentiated mantle to an almost completely preserved homogeneous mantle depending on competition between convection and differentiation: between low viscosity ('liquid') convection and crystal settling at small crystal fractions, or between high viscosity ('solid') convection and percolation at large crystal fractions.

Investigation of crystalline morphology in poly (ether ether ketone) using dielectric relaxation spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalika, D.S.; Krishnaswamy, R.K.

1993-12-31

The relaxation behavior of poly (ether ether ketone) [PEEK] has been investigated using dielectric relaxation spectroscopy; the glass-rubber ({alpha}) relaxation and a sub-glass ({beta}) relaxation were examined for the amorphous material and both cold-crystallized and melt-crystallized specimens. Analysis of the data using the Cole-Cole modification of the Debye equation allowed determination of the dielectric relaxation strength and relaxation broadening parameter for both transitions as a function of material crystallization history. The crystallized specimens displayed a positive offset in isochronal loss temperature for both the {alpha} and {beta} relaxations, with the {alpha} relaxation broadened significantly. The measured dipolar response was interpretedmore » using a three-phase morphological model encompassing a crystalline phase, a mobile amorphous phase, and a rigid amorphous phase. Determination of phase fractions based on dipolar mobilization across the glass-rubber relaxation revealed a finite rigid amorphous phase fraction for both the cold-crystallized specimens which was relatively insensitive to thermal history and degree of crystallinity (W{sub RAP}40.20).« less

Control of crystal growth in water purification by directional freeze crystallization

NASA Technical Reports Server (NTRS)

Conlon, William M. (Inventor)

1996-01-01

A Directional Freeze Crystallization system employs an indirect contact heat exchanger to freeze a fraction of liquid to be purified. The unfrozen fraction is drained away and the purified frozen fraction is melted. The heat exchanger must be designed in accordance with a Growth Habit Index to achieve efficient separation of contaminants. If gases are dissolved in the liquid, the system must be pressurized.

Crystallization of Deformable Spherical Colloids

NASA Astrophysics Data System (ADS)

Batista, Vera M. O.; Miller, Mark A.

2010-08-01

We introduce and characterize a first-order model for a generic class of colloidal particles that have a preferred spherical shape but can undergo deformations while always maintaining hard-body interactions. The model consists of hard spheres that can continuously change shape at fixed volume into prolate or oblate ellipsoids of revolution, subject to an energetic penalty. The severity of this penalty is specified by a single parameter that determines the flexibility of the particles. The deformable hard spheres crystallize at higher packing fractions than rigid hard spheres, have a narrower solid-fluid coexistence region and can reach high densities by a second transition to an orientationally ordered crystal.

CrystalMoM: a tool for modeling the evolution of Crystals Size Distributions in magmas with the Method of Moments

NASA Astrophysics Data System (ADS)

Colucci, Simone; de'Michieli Vitturi, Mattia; Landi, Patrizia

2016-04-01

It is well known that nucleation and growth of crystals play a fundamental role in controlling magma ascent dynamics and eruptive behavior. Size- and shape-distribution of crystal populations can affect mixture viscosity, causing, potentially, transitions between effusive and explosive eruptions. Furthermore, volcanic samples are usually characterized in terms of Crystal Size Distribution (CSD), which provide a valuable insight into the physical processes that led to the observed distributions. For example, a large average size can be representative of a slow magma ascent, and a bimodal CSD may indicate two events of nucleation, determined by two degassing events within the conduit. The Method of Moments (MoM), well established in the field of chemical engineering, represents a mesoscopic modeling approach that rigorously tracks the polydispersity by considering the evolution in time and space of integral parameters characterizing the distribution, the moments, by solving their transport differential-integral equations. One important advantage of this approach is that the moments of the distribution correspond to quantities that have meaningful physical interpretations and are directly measurable in natural eruptive products, as well as in experimental samples. For example, when the CSD is defined by the number of particles of size D per unit volume of the magmatic mixture, the zeroth moment gives the total number of crystals, the third moment gives the crystal volume fraction in the magmatic mixture and ratios between successive moments provide different ways to evaluate average crystal length. Tracking these quantities, instead of volume fraction only, will allow using, for example, more accurate viscosity models in numerical code for magma ascent. Here we adopted, for the first time, a quadrature based method of moments to track the temporal evolution of CSD in a magmatic mixture and we verified and calibrated the model again experimental data. We also show how the equations and the tool developed can be integrated in a magma ascent numerical model, with application to eruptive events occurred at Stromboli volcano (Italy).

Diffusion-controlled magnesium isotopic fractionation of a single crystal forsterite evaporated from the solid state

NASA Technical Reports Server (NTRS)

Wang, Jianhua; Davis, Andrew M.; Hashimoto, Akihiko; Clayton, Robert N.

1993-01-01

Though the origin of calcium- and aluminum-rich inclusions (CAI's) in carbonaceous chondrites is till a disputed issue, evaporation is no doubt one of the most important processes for the formation of CAI's in the early solar nebula. The mechanism for production of large isotopic mass fractionation effects in magnesium, silicon, oxygen, and chromium in CAI's can be better understood by examining isotopic fractionation during the evaporation of minerals. New evaporation experiments were performed on single-crystal forsterite. The magnesium isotopic distribution near the evaporating surfaces of the residues using a modified AEI IM-20 ion microprobe to obtain rastered beam depth profiles was measured. A theoretical model was used to explain the profiles and allowed determination of the diffusion coefficient of Mg(++) in forsterite at higher temperatures than previous measurements. The gas/solid isotopic fractionation factor for magnesium for evaporation from solid forsterite was also determined and found to be nearly the same as that for evaporation of liquid Mg2SiO4.

NMR signal analysis to attribute the components to the solid/liquid phases present in mixes and ice creams.

PubMed

Mariette, François; Lucas, Tiphaine

2005-03-09

The NMR relaxation signals from complex products such as ice cream are hard to interpret because of the multiexponential behavior of the relaxation signal and the difficulty of attributing the NMR relaxation components to specific molecule fractions. An attribution of the NMR relaxation parameters is proposed, however, based on an approach that combines quantitative analysis of the spin-spin and spin-lattice relaxation times and the signal intensities with characterization of the ice cream components. We have been able to show that NMR can be used to describe the crystallized and liquid phases separately. The first component of the spin-spin and spin-lattice relaxation describes the behavior of the protons of the crystallized fat in the mix. The amount of fat crystals can then be estimated. In the case of ice cream, only the spin-lattice relaxation signal from the crystallized fraction is relevant. However, it enables the ice protons and the protons of the crystallized fat to be distinguished. The spin-lattice relaxation time can be used to describe the mobility of the protons in the different crystallized phases and also to quantify the amount of ice crystals and fat crystals in the ice cream. The NMR relaxation of the liquid phase of the mix has a biexponential behavior. A first component is attributable to the liquid fraction of the fat and to the sugars, while a second component is attributable to the aqueous phase. Overall, the study shows that despite the complexity of the NMR signal from ice cream, a number of relevant parameters can be extracted to study the influence of the formulation and of the process stages on the ice fraction, the crystallized fat fraction, and the liquid aqueous fraction.

Fourier transform imaging of impurities in the unit cells of crystals: Mn in GaAs

NASA Astrophysics Data System (ADS)

Lee, T.-L.; Bihler, C.; Schoch, W.; Limmer, W.; Daeubler, J.; Thieß, S.; Brandt, M. S.; Zegenhagen, J.

2010-06-01

The lattice sites of Mn in ferromagnetic (Ga,Mn)As thin films were imaged using the x-ray standing wave technique. The model-free images, obtained straightforwardly by Fourier inversion, disclose immediately that the Mn mostly substitutes the Ga with a small fraction residing on minority sites. The images further reveal variations in the Mn concentrations of the different sites upon post-growth treatments. Subsequent model refinement based on the directly reconstructed images resolves with high precision the complete Mn site distributions. It is found that post-growth annealing increases the fraction of substitutional Mn at the expense of interstitial Mn whereas hydrogenation has little influence on the Mn site distribution. Our study offers an element-specific high-resolution imaging approach for accurately determining the detailed site distributions of dilute concentrations of atoms in crystals.

Propagation of optical vortices with fractional topological charge in free space

NASA Astrophysics Data System (ADS)

Ali, Tamelia; Kreminska, Liubov; Golovin, Andrii B.; Crouse, David T.

2014-10-01

The behavior of the optical vortices with fractional topological charges in the far-field is assessed through numerical modeling and confirmed by experimental results. The generation of fractional topological charge variations of the phase within a Gaussian beam was achieved by using a liquid crystal spatial light modulator (LCoS SLM). It is shown that a laser beam carrying an optical vortex with a fractional topological charge evolves into a beam with a topological charge of integer value, specifically an integer value closer to the fractional number in the far field. A potential application of this work is for data transmission within optical telecommunication systems.

Oxygen isotopes reveal crustal contamination and a large, still partially molten magma chamber in Chaîne des Puys (French Massif Central)

NASA Astrophysics Data System (ADS)

France, Lydéric; Demacon, Mickael; Gurenko, Andrey A.; Briot, Danielle

2016-09-01

The two main magmatic properties associated with explosive eruptions are high viscosity of silica-rich magmas and/or high volatile contents. Magmatic processes responsible for the genesis of such magmas are differentiation through crystallization, and crustal contamination (or assimilation) as this process has the potential to enhance crystallization and add volatiles to the initial budget. In the Chaîne des Puy series (French Massif Central), silica- and H2O-rich magmas were only emitted during the most recent eruptions (ca. 6-15 ka). Here, we use in situ measurements of oxygen isotopes in zircons from two of the main trachytic eruptions from the Chaîne des Puys to track the crustal contamination component in a sequence that was previously presented as an archetypal fractional crystallization series. Zircons from Sarcoui volcano and Puy de Dôme display homogeneous oxygen isotope compositions with δ18O = 5.6 ± 0.25‰ and 5.6 ± 0.3‰, respectively, and have therefore crystallized from homogeneous melts with δ18Omelt = 7.1 ± 0.3‰. Compared to mantle derived melts resulting from pure fractional crystallization (δ18Odif.mant. = 6.4 ± 0.4‰), those δ18Omelt values are enriched in 18O and support a significant role of crustal contamination in the genesis of silica-rich melts in the Chaîne des Puys. Assimilation-fractional-crystallization models highlight that the degree of contamination was probably restricted to 5.5-9.5% with Rcrystallization/Rassimilation varying between 8 and 14. The very strong intra-site homogeneity of the isotopic data highlights that magmas were well homogenized before eruption, and consequently that crustal contamination was not the trigger of silica-rich eruptions in the Chaîne des Puys. The exceptionally strong inter-site homogeneity of the isotopic data brings to light that Sarcoui volcano and Puy de Dôme were fed by a single large magma chamber. Our results, together with recent thermo-kinetic models and an experimental simulation (Martel et al., 2013), support the existence of a large ( 6-15 km3), still partially molten mid-crustal reservoir (10-12 km deep) that is filled with silica-rich magma. Calculated oxygen isotope compositions of the trachytic melts that crystallized the analyzed zircons for Puy de Dôme, Sarcoui dome, and Sarcoui phreatomagmatic deposits, and the range of values for each analyzed zircon grain. The range for trachytes obtained by pure fractional crystallization of mantle melts is given for comparison. See text for details on calculations. Chemical differentiation trend of Chaîne des Puys magmas (data from Boivin et al., 2009), and results of the fractional crystallization models presented herein and in Table 3. L1 is obtained after the first step of differentiation, and L2 after the second. The composition of Sarcoui trachytes is identified by an X. S3.1. Core-rim variations for oxygen isotope compositions of the studied zircons. S3.2. Oxygen isotope compositions of the various zircon domains observed with cathodoluminescence imaging (dark versus bright), and for zircons with different types of zoning (oscillatory versus sector). No systematic variation is observed.

Influence of Al content on non-equilibrium solidification behavior of Ni-Al-Ta model single crystal alloys

NASA Astrophysics Data System (ADS)

Ai, Cheng; Zhou, Jian; Zhang, Heng; Zhao, Xinbao; Pei, Yanling; Li, Shusuo; Gong, Shengkai

2016-01-01

The non-equilibrium solidification behaviors of five Ni-Al-Ta ternary model single crystal alloys with different Al contents were investigated by experimental analysis and theoretical calculation (by JMatPro) in this study. These model alloys respectively represented the γ' phase with various volume fractions (100%, 75%, 50%, 25% and 0%) at 900 °C. It was found that with decreasing Al content, liquidus temperature of experimental alloys first decreased and then increased. Meanwhile, the solidification range showed a continued downward trend. In addition, with decreasing Al content, the primary phases of non-equilibrium solidified model alloys gradually transformed from γ' phase to γ phase, and the area fraction of which first decreased and then increased. Moreover, the interdendritic/intercellular precipitation of model alloys changed from β phase (for 100% γ') to (γ+γ')Eutectic (for 75% γ'), (γ+γ')Eutectic+γ' (for 50% γ' and 25% γ') and none interdendritic precipitation (for 0% γ'), and the last stage non-equilibrium solidification sequence of model alloys was determined by the nominal Al content and different microsegregation behaviors of Al element.

Platinum-group element, Gold, Silver and Base Metal distribution in compositionally zoned sulfide droplets from the Medvezky Creek Mine, Noril'sk, Russia

USGS Publications Warehouse

Barnes, S.-J.; Cox, R.A.; Zientek, M.L.

2006-01-01

Concentrations of Ag, Au, Cd, Co, Re, Zn and Platinum-group elements (PGE) have been determined in sulfide minerals from zoned sulfide droplets of the Noril'sk 1 Medvezky Creek Mine. The aims of the study were; to establish whether these elements are located in the major sulfide minerals (pentlandite, pyrrhotite, chalcopyrite and cubanite), to establish whether the elements show a preference for a particular sulfide mineral and to investigate the model, which suggests that the zonation in the droplets is caused by the crystal fractionation of monosulfide solid solution (mss). Nickel, Cu, Ag, Re, Os, Ir, Ru, Rh and Pd, were found to be largely located in the major sulfide minerals. In contrast, less than 25% of the Au, Cd, Pt and Zn in the rock was found to be present in these sulfides. Osmium, Ir, Ru, Rh and Re were found to be concentrated in pyrrhotite and pentlandite. Palladium and Co was found to be concentrated in pentlandite. Silver, Cd and Zn concentrations are highest in chalcopyrite and cubanite. Gold and platinum showed no preference for any of the major sulfide minerals. The enrichment of Os, Ir, Ru, Rh and Re in pyrrhotite and pentlandite (exsolution products of mss) and the low levels of these elements in the cubanite and chalcopyrite (exsolution products of intermediate solid solution, iss) support the mss crystal fractionation model, because Os, Ir, Ru, Rh and Re are compatible with mss. The enrichment of Ag, Cd and Zn in chalcopyrite and cubanite also supports the mss fractionation model these minerals are derived from the fractionated liquid and these elements are incompatible with mss and thus should be enriched in the fractionated liquid. Gold and Pt do not partition into either iss or mss and become sufficiently enriched in the final fractionated liquid to crystallize among the iss and mss grains as tellurides, bismithides and alloys. During pentlandite exsolution Pd appears to have diffused from the Cu-rich portion of the droplet into pentlandite. ?? Springer-Verlag 2006.

Evidence for hydrous high-MgO melts in the Precambrian

NASA Astrophysics Data System (ADS)

Stone, William E.; Deloule, Etienne; Larson, Michelle S.; Lesher, C. Michael

1997-02-01

Prevailing petrogenetic models for Precambrian high-MgO melts such as komatiites invoke crystallization from nearly anhydrous melts (≪0.5% H2O) generated by partial melting of mantle peridotite at temperatures of (≤ 1900 °C and pressures of (18 GPa. However, ultramafic cumulate and gabbro zones of komatiitic and other high-MgO units in Precambrian greenstone belts contain vesicles and minor to major amounts (≤ 25%) of igneous amphibole. The textures (oikocrysts, rims on intercumulate pyroxene, and mineral inclusions within orthocumulate olivine) and the water-rich compositions (1.00% 2.50% H2O) of igneous amphiboles from the Archean Abitibi belt indicate crystallization in situ from significantly hydrous melts while the melt fraction was still as high as 40% 50%. Comparisons to experimental phase equilibria suggest that the residual melts from which the amphiboles crystallized contained 3% 4% H2O, and adjustments for fractional crystallization suggest that the initial melts may have contained as much as 2% H2O. H2O contents of this magnitude would require substantial revision of the nearly anhydrous models for Precambrian high-MgO melts, possibly permitting generation at lower temperatures and pressures, lowering their densities and viscosities, increasing their eruptibility, and enhancing the formation of spinifex textures.

Non-Newtonian behavior of plagioclase-bearing basaltic magma: Subliquidus viscosity measurement of the 1707 basalt of Fuji volcano, Japan

NASA Astrophysics Data System (ADS)

Ishibashi, Hidemi

2009-03-01

Laboratory measurements of viscosity were done for basalt erupted in 1707 AD from Fuji volcano, Japan, using a concentric cylinder rotational viscometer at temperatures of 1297-1157 °C, 1 atm pressure, and fO 2 near the Ni-NiO buffer. On cooling, elongated plagioclase crystals with a mean length/width ratio of ca. 8.5 appeared at 1237 °C, followed by olivine at 1157 °C. At progressively lower temperatures, the total crystal volume fraction increased monotonously to ca. 0.25; viscosity increased from 38.9 to 765 Pa s at a shear strain rate of 1 s - 1 . This basalt magma behaves as a Newtonian fluid at temperatures greater than 1217 °C, but shear-thinning behavior occurs at temperatures less than 1197 °C because of the suspended plagioclase crystals. This behavior is well approximated as a power law fluid. At the onset of shear thinning, the crystal volume fraction was between 0.06 and 0.13, which is attributed to the pronounced lath-shape of plagioclase crystals. The relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate, and with decrease of shear strain rate at a constant crystal volume fraction. A modified form of the Krieger-Dougherty equation is introduced herein. It enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate, and consequently the onset of shear-thinning behavior.

Micromechanical models for the stiffness and strength of UHMWPE macrofibrils

NASA Astrophysics Data System (ADS)

Dong, Hai; Wang, Zheliang; O'Connor, Thomas C.; Azoug, Aurelie; Robbins, Mark O.; Nguyen, Thao D.

2018-07-01

Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a complex hierarchical structure that at the micron-scale is composed of oriented chain crystals, lamellar crystals, and amorphous domains organized into macrofibrils. We developed a computational micromechanical modeling study of the effects of the morphological structure and constituent material properties on the deformation mechanisms, stiffness and strength of the UHMWPE macrofibrils. Specifically, we developed four representative volume elements, which differed in the arrangement and orientation of the lamellar crystals, to describe the various macrofibrillar microstructures observed in recent experiments. The stiffness and strength of the crystals were determined from molecular dynamic simulations of a pure PE crystal. A finite deformation crystal plasticity model was used to describe the crystals and an isotropic viscoplastic model was used for the amorphous phase. The results show that yielding in UHMWPE macrofibrils under axial tension is dominated by the slip in the oriented crystals, while yielding under transverse compression and shear is dominated by slips in both the oriented and lamellar crystals. The results also show that the axial modulus and strength are mainly determined by the volume fraction of the oriented crystals and are insensitive to the arrangements of the lamellar crystals when the modulus of the amorphous phase is significantly smaller than that of the crystals. In contrast, the arrangement and size of the lamellar crystals have a significant effect on the stiffness and strength under transverse compression and shear. These findings can provide a guide for new materials and processing design to improve the properties of UHMWPE fibers by controlling the macrofibrillar morphologies.

Production, crystallization and X-ray characterization of chemically glycosylated hen egg-white lysozyme

DOE Office of Scientific and Technical Information (OSTI.GOV)

López-Jaramillo, F. J., E-mail: javier@lec.ugr.es; Instituto de Biotecnología, Facultad de Ciencias, Universidad de Granada, E-18071; Pérez-Banderas, F.

The feasibility of glycosylation post-purification has been demonstrated by introducing glucose into the model protein lysozyme via a novel reaction that is compatible with biological samples. The crystallization of glycoproteins is one of the challenges to be confronted by the crystallographic community in the frame of what is known as glycobiology. The state of the art for the crystallization of glycoproteins is not promising and removal of the carbohydrate chains is generally suggested since they are flexible and a source of heterogeneity. In this paper, the feasibility of introducing glucose into the model protein hen egg-white lysozyme via a post-purificationmore » glycosylation reaction that may turn any protein into a model glycoprotein whose carbohydrate fraction can be manipulated is demonstrated.« less

Mesozoic high-Mg andesites from the Daohugou area, Inner Mongolia: Upper-crustal fractional crystallization of parental melt derived from metasomatized lithospheric mantle wedge

NASA Astrophysics Data System (ADS)

Meng, Fanxue; Gao, Shan; Song, Zhaojun; Niu, Yaoling; Li, Xuping

2018-03-01

Mineral chemistry, major- and trace-element data, zircon U-Pb ages, and Sr-Nd isotopic data are presented for a suite of volcanic rocks from the Daohugou area, Ningcheng City, Inner Mongolia, on the northern margin of the North China Craton. Samples from the suite are of basaltic andesite to rhyolite in composition, with the rocks containing <60 wt% SiO2 have high MgO, Cr, and Ni contents, and classify as high-Mg andesites (HMAs). Zircons from a rhyolite yielded weighted mean 206Pb/238U age of 164 ± 1 Ma, indicating that the Daohugou volcanic suite is coeval with the Tiaojishan Formation of northern Hebei and western Liaoning Province. The HMAs have similar enriched-mantle I (EMI)-type isotopic compositions to each other, with low εNd (t) values, moderate (87Sr/86Sr) i ratios, enrichment in LREEs relative to LILEs, and depletion in HFSEs (e.g., Nb, Ta, Ti), indicating formation through protracted fractional crystallization of a common parental magma. The unusually low CaO contents and CaO/FeO ratios of olivine phenocrysts in the HMAs suggest that the parental melt was subduction-related. The results of Rhyolite-MELTS modelling indicates that HMAs may form through upper-crustal fractional crystallization from arc basalts. Therefore, the Daohugou HMAs were most likely formed through fractional crystallization of a parental melt derived from metasomatized lithospheric mantle at crustal depths. The addition of "water" to the cratonic keel may have played a key role in the destruction of the North China Craton.

High alumina (HA) and very high potassium (VHK) basalt clasts from Apollo 14 breccias. II - Whole rock geochemistry - Further evidence for combined assimilation and fractional crystallization within the lunar crust

NASA Technical Reports Server (NTRS)

Neal, C. R.; Taylor, L. A.; Schmitt, R. A.; Hughes, S. S.; Lindstrom, M. M.

1989-01-01

The understanding of basalt petrogenesis at the Apollo 14 site has increased markedly due to the study of 'new' samples from breccia 'pull-apart' efforts. Whole-rock compositions of 26 new high alumina (HA) and 7 very high potassium (VHK) basalts emphasize the importance of combined assimilation and fractional crystallization in a lunar regime. Previously formulated models for HA and VHK basalt petrogenesis are modified in order to accomodate these new data, although modeling parameters are essentially the same. The required range in HA basalt compositions is generated by the assimilation of KREEP by a 'primitive' parental magma. The VHK basalts can be generated by three parental HA basalts assimilating granite. Results indicate that VHK basalt compositions are dominated by the parental magma, and only up to 8 percent granite assimilation is required. This modeling indicates that at least three VHK basalt flows must be present at the Apollo 14 site.

Particles at fluid-fluid interfaces: A new Navier-Stokes-Cahn-Hilliard surface- phase-field-crystal model.

PubMed

Aland, Sebastian; Lowengrub, John; Voigt, Axel

2012-10-01

Colloid particles that are partially wetted by two immiscible fluids can become confined to fluid-fluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids form an emulsion with interesting material properties and offer an important route to new soft materials. A promising approach to simulate these emulsions was presented in Aland et al. [Phys. Fluids 23, 062103 (2011)], where a Navier-Stokes-Cahn-Hilliard model for the macroscopic two-phase fluid system was combined with a surface phase-field-crystal model for the microscopic colloidal particles along the interface. Unfortunately this model leads to spurious velocities which require very fine spatial and temporal resolutions to accurately and stably simulate. In this paper we develop an improved Navier-Stokes-Cahn-Hilliard-surface phase-field-crystal model based on the principles of mass conservation and thermodynamic consistency. To validate our approach, we derive a sharp interface model and show agreement with the improved diffuse interface model. Using simple flow configurations, we show that the new model has much better properties and does not lead to spurious velocities. Finally, we demonstrate the solid-like behavior of the crystallized interface by simulating the fall of a solid ball through a colloid-laden multiphase fluid.

Geochemical and Nd-Sr-Pb isotope characteristics of synorogenic lower crust-derived granodiorites (Central Damara orogen, Namibia)

NASA Astrophysics Data System (ADS)

Simon, I.; Jung, S.; Romer, R. L.; Garbe-Schönberg, D.; Berndt, J.

2017-03-01

The 547 ± 7 Ma old Achas intrusion (Damara orogen, Namibia) includes magnesian, metaluminous to slightly peraluminous, calcic to calc-alkalic granodiorites and ferroan, metaluminous to slightly peraluminous, calc-alkalic to alkali-calcic leucogranites. For the granodiorites, major and trace element variations show weak if any evidence for fractional crystallization whereas some leucogranites are highly fractionated. Both, granodiorites and leucogranites are isotopically evolved (granodiorites: εNdinit: - 12.4 to - 20.5; TDM: 2.4-1.9; leucogranites: εNdinit: - 12.1 to - 20.6, TDM: 2.5-2.0), show similar Pb isotopic compositions, and may be derived from late Archean to Paleoproterozoic crustal source rocks. Comparison with melting experiments and simple partial melting modeling indicate that the granodiorites may be derived by extensive melting (> 40%) at 900-950 °C under water-undersaturated conditions (< 5 wt.% H2O) of felsic gneisses. Al-Ti and zircon saturation thermometry of the most primitive granodiorite sample yielded temperatures of ca. 930 °C and ca. 800 °C. In contrast to other lower crust-derived granodiorites and granites of the Central Damara orogen, the composition of the magma source is considered the first-order cause of the compositional diversity of the Achas granite. Second-order processes such as fractional crystallization at least for the granodiorites were minor and evidence for coupled assimilation-fractional crystallization processes is lacking. The most likely petrogenetic model involves high temperature partial melting of a Paleoproterozoic felsic source in the lower crust ca. 10-20 Ma before the first peak of regional high-temperature metamorphism. Underplating of the lower crust by magmas derived from the lithospheric mantle may have provided the heat for melting of the basement to produce anhydrous granodioritic melts.

A detailed investigation of the strain hardening response of aluminum alloyed Hadfield steel

NASA Astrophysics Data System (ADS)

Canadinc, Demircan

The unusual strain hardening response exhibited by Hadfield steel single and polycrystals under tensile loading was investigated. Hadfield steel, which deforms plastically through the competing mechanisms slip and twinning, was alloyed with aluminum in order to suppress twinning and study the role of slip only. To avoid complications due to a grained structure, only single crystals of the aluminum alloyed Hadfield steel were considered at the initial stage of the current study. As a result of alloying with aluminum, twinning was suppressed; however a significant increase in the strain hardening response was also present. A detailed microstructural analysis showed the presence of high-density dislocation walls that evolve in volume fraction due to plastic deformation and interaction with slip systems. The very high strain hardening rates exhibited by the aluminum alloyed Hadfield steel single crystals was attributed to the blockage of glide dislocations by the high-density dislocation walls. A crystal plasticity model was proposed, that accounts for the volume fraction evolution and rotation of the dense dislocation walls, as well as their interaction with the active slip systems. The novelty of the model lies in the simplicity of the constitutive equations that define the strain hardening, and the fact that it is based on experimental data regarding the microstructure. The success of the model was tested by its application to different crystallographic orientations, and finally the polycrystals of the aluminum alloyed Hadfield steel. Meanwhile, the capability of the model to predict texture was also observed through the rotation of the loading axis in single crystals. The ability of the model to capture the polycrystalline deformation response provides a venue for its utilization in other alloys that exhibit dislocation sheet structures.

Cobalt and scandium partitioning versus iron content for crystalline phases in ultramafic nodules

USGS Publications Warehouse

Glassley, W.E.; Piper, D.Z.

1978-01-01

Fractionation of Co and Sc between garnets, olivines, and clino- and orthopyroxenes, separated from a suite of Salt Lake Crater ultramafic nodules that equilibrated at the same T and P, is strongly dependent on Fe contents. This observation suggests that petrogenetic equilibrium models of partial melting and crystal fractionation must take into account effects of magma composition, if they are to describe quantitatively geochemical evolutionary trends. ?? 1978.

Magmatic processes that generated the rhyolite of Glass Mountain, Medicine Lake volcano, N. California

USGS Publications Warehouse

Grove, T.L.; Donnelly-Nolan, J. M.; Housh, T.

1997-01-01

Glass Mountain consists of a 1 km3, compositionally zoned rhyolite to dacite glass flow containing magmatic inclusions and xenoliths of underlying shallow crust. Mixing of magmas produced by fractional crystallization of andesite and crustal melting generated the rhyolite of Glass Mountain. Melting experiments were carried out on basaltic andesite and andesite magmatic inclusions at 100, 150 and 200 MPa, H2O-saturated with oxygen fugacity controlled at the nickel-nickel oxide buffer to provide evidence of the role of fractional crystallization in the origin of the rhyolite of Glass Mountain. Isotopic evidence indicates that the crustal component assimilated at Glass Mountain constitutes at least 55 to 60% of the mass of erupted rhyolite. A large volume of mafic andesite (2 to 2.5 km3) periodically replenished the magma reservoir(s) beneath Glass Mountain, underwent extensive fractional crystallization and provided the heat necessary to melt the crust. The crystalline residues of fractionation as well as residual liquids expelled from the cumulate residues are preserved as magmatic inclusions and indicate that this fractionation process occurred at two distinct depths. The presence and composition of amphibole in magmatic inclusions preserve evidence for crystallization of the andesite at pressures of at least 200 MPa (6 km depth) under near H2O-saturated conditions. Mineralogical evidence preserved in olivine-plagioclase and olivine-plagioclase-high-Ca clinopyroxene-bearing magmatic inclusions indicates that crystallization under near H2O-saturated conditions also occurred at pressures of 100 MPa (3 km depth) or less. Petrologic, isotopic and geochemical evidence indicate that the andesite underwent fractional crystallization to form the differentiated melts but had no chemical interaction with the melted crustal component. Heat released by the fractionation process was responsible for heating and melting the crust.

Thermal crystallization mechanism of silk fibroin protein

NASA Astrophysics Data System (ADS)

Hu, Xiao

In this thesis, the thermal crystallization mechanism of silk fibroin protein from Bombyx mori silkworm, was treated as a model for the general study of protein based materials, combining theories from both biophysics and polymer physics fields. A systematic and scientific path way to model the dynamic beta-sheet crystallization process of silk fibroin protein was presented in the following sequence: (1) The crystallinity, fractions of secondary structures, and phase compositions in silk fibroin proteins at any transition stage were determined. Two experimental methods, Fourier transform infrared spectroscopy (FTIR) with Fourier self-deconvolution, and specific reversing heat capacity, were used together for the first time for modeling the static structures and phases in the silk fibroin proteins. The protein secondary structure fractions during the crystallization were quantitatively determined. The possibility of existence of a "rigid amorphous phase" in silk protein was also discussed. (2) The function of bound water during the crystallization process of silk fibroin was studied using heat capacity, and used to build a silk-water dynamic crystallization model. The fundamental concepts and thermal properties of silk fibroin with/without bound water were discussed. Results show that intermolecular bound water molecules, acting as a plasticizer, will cause silk to display a water-induced glass transition around 80°C. During heating, water is lost, and the change of the microenvironment in the silk fibroin chains induces a mesophase prior to thermal crystallization. Real time FTIR during heating and isothermal holding above Tg show the tyrosine side chain changes only during the former process, while beta sheet crystallization occurs only during the latter process. Analogy is made between the crystallization of synthetic polymers according to the four-state scheme of Strobl, and the crystallization process of silk fibroin, which includes an intermediate precursor stage before crystallization. (3) The beta-sheet crystallization kinetics in silk fibroin protein were measured using X-ray, FTIR and heat flow, and the structure reveals the formation mechanism of the silk crystal network. Avrami kinetics theories, which were established for studies of synthetic polymer crystal growth, were for the first time extended to investigate protein self-assembly in multiblock silk fibroin samples. The Avrami exponent, n, was close to two for all methods, indicating formation of beta sheet crystals in silk proteins is different from the 3-D spherulitic crystal growth found in most synthetic homopolymers. A microphase separation pattern after chymotrypsin enzyme biodegradation was shown in the protein structures using scanning electron microscopy. A model was then used to explain the crystallization of silk fibroin protein by analogy to block copolymers. (4) The effects of metal ions during the crystallization of silk fibroin was investigated using thermal analysis. Advanced thermal analysis methods were used to analyze the thermal protein-metallic ion interactions in silk fibroin proteins. Results show that K+ and Ca2+ metallic salts play different roles in silk fibroin proteins, which either reduce (K+) or increase (Ca2+ ) the glass transition (Tg) of pure silk protein and affect the thermal stability of this structure.

Competition between crystallization and vitrification of the rigid amorphous fraction in poly(3-hydroxybutyrate)

NASA Astrophysics Data System (ADS)

Di Lorenzo, Maria Laura; Righetti, Maria Cristina; Gazzano, Massimo

2012-07-01

Semicrystalline polymers have a metastable nanophase structure, where the various nanophases can be crystal, liquid, glass, or mesophase. This multi-level structure is determined by a competition among self-organization, crystallization, and vitrification of the amorphous segments and is established during material processing. The kinetics of such competition is here determined for poly(3-hydroxybutyrate) (PHB), as vitrification/devitrification of the rigid amorphous fraction strongly affects crystallization kinetics of PHB.

Fractional Wigner Crystal in the Helical Luttinger Liquid.

PubMed

Traverso Ziani, N; Crépin, F; Trauzettel, B

2015-11-13

The properties of the strongly interacting edge states of two dimensional topological insulators in the presence of two-particle backscattering are investigated. We find an anomalous behavior of the density-density correlation functions, which show oscillations that are neither of Friedel nor of Wigner type: they, instead, represent a Wigner crystal of fermions of fractional charge e/2, with e the electron charge. By studying the Fermi operator, we demonstrate that the state characterized by such fractional oscillations still bears the signatures of spin-momentum locking. Finally, we compare the spin-spin correlation functions and the density-density correlation functions to argue that the fractional Wigner crystal is characterized by a nontrivial spin texture.

Early differentiation of the Moon: Experimental and modeling studies

NASA Technical Reports Server (NTRS)

Longhi, J.

1986-01-01

Major accomplishments include the mapping out of liquidus boundaries of lunar and meteoritic basalts at low pressure; the refinement of computer models that simulate low pressure fractional crystallization; the development of a computer model to calculate high pressure partial melting of the lunar and Martian interiors; and the proposal of a hypothesis of early lunar differentiation based upon terrestrial analogs.

Crystallization processes in Ge{sub 2}Sb{sub 2}Se{sub 4}Te glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Svoboda, Roman, E-mail: roman.svoboda@upce.cz; Bezdička, Petr; Gutwirth, Jan

2015-01-15

Highlights: • Crystallization kinetics of Ge{sub 2}Sb{sub 2}Se{sub 4}Te glass was studied in dependence on particle size by DSC. • All studied fractions were described in terms of the SB autocatalytic model. • Relatively high amount of Te enhances manifestation of bulk crystallization mechanisms. • XRD analysis of samples crystallized under different conditions showed correlation with DSC data. • XRD analysis revealed a new crystallization mechanism indistinguishable by DSC. - Abstract: Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis were used to study crystallization in Ge{sub 2}Sb{sub 2}Se{sub 4}Te glass under non-isothermal conditions as a function of the particlemore » size. The crystallization kinetics was described in terms of the autocatalytic Šesták–Berggren model. An extensive discussion of all aspects of a full-scale kinetic study of a crystallization process was undertaken. Dominance of the crystallization process originating from mechanically induced strains and heterogeneities was confirmed. Substitution of Se by Te was found to enhance the manifestation of the bulk crystallization mechanisms (at the expense of surface crystallization). The XRD analysis showed significant dependence of the crystalline structural parameters on the crystallization conditions (initial particle size of the glassy grains and applied heating rate). Based on this information, a new microstructural crystallization mechanism, indistinguishable by DSC, was proposed.« less

Polymorphic Transformation in Mixtures of High- and Low-Melting Fractions of Milk Fat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cisneros,A.; Mazzanti, G.; Campos, R.

2006-01-01

The kinetics of crystallization of high-melting fraction (HMF) and a mixture of 40% HMF and 60% low-melting fraction (LMF) of milk fat were studied at 5 C by time-resolved in-situ synchrotron X-ray diffraction. HMF crystallized in the {alpha} polymorph, had a longer lifetime than the ones previously reported in pure milk fat, and was almost completely solid. The HMF/LMF mixture crystallized initially in the {alpha} form and transformed into the {beta}' polymorph, with a solid fat content much lower than that of HMF. The polymorphic change was therefore attributed to a delayed sudden formation of {beta}' mixed crystals from themore » uncrystallized melt. These findings are important for the food industry and as fundamental knowledge to improve our understanding of the origin of the macroscopic physical properties of solid milk fat fractions used in many manufacturing processes.« less

Increasing low frequency sound attenuation using compounded single layer of sonic crystal

NASA Astrophysics Data System (ADS)

Gulia, Preeti; Gupta, Arpan

2018-05-01

Sonic crystals (SC) are man-made periodic structures where sound hard scatterers are arranged in a crystalline manner. SC reduces noise in a particular range of frequencies called as band gap. Sonic crystals have a promising application in noise shielding; however, the application is limited due to the size of structure. Particularly for low frequencies, the structure becomes quite bulky, restricting its practical application. This paper presents a compounded model of SC, which has the same overall area and filling fraction but with increased low frequency sound attenuation. Two cases have been considered, a three layer SC and a compounded single layer SC. Both models have been analyzed using finite element simulation and plane wave expansion method. Band gaps for periodic structures have been obtained using both methods which are in good agreement. Further, sound transmission loss has been evaluated using finite element method. The results demonstrate the use of compounded model of Sonic Crystal for low frequency sound attenuation.

New optical solitons of space-time conformable fractional perturbed Gerdjikov-Ivanov equation by sine-Gordon equation method

NASA Astrophysics Data System (ADS)

Yaşar, Elif; Yıldırım, Yakup; Yaşar, Emrullah

2018-06-01

This paper devotes to conformable fractional space-time perturbed Gerdjikov-Ivanov (GI) equation which appears in nonlinear fiber optics and photonic crystal fibers (PCF). We consider the model with full nonlinearity in order to give a generalized flavor. The sine-Gordon equation approach is carried out to model equation for retrieving the dark, bright, dark-bright, singular and combined singular optical solitons. The constraint conditions are also reported for guaranteeing the existence of these solitons. We also present some graphical simulations of the solutions for better understanding the physical phenomena of the behind the considered model.

Competition of the connectivity with the local and the global order in polymer melts and crystals

NASA Astrophysics Data System (ADS)

Bernini, S.; Puosi, F.; Barucco, M.; Leporini, D.

2013-11-01

The competition between the connectivity and the local or global order in model fully flexible chain molecules is investigated by molecular-dynamics simulations. States with both missing (melts) and high (crystal) global order are considered. Local order is characterized within the first coordination shell (FCS) of a tagged monomer and found to be lower than in atomic systems in both melt and crystal. The role played by the bonds linking the tagged monomer to FCS monomers (radial bonds), and the bonds linking two FCS monomers (shell bonds) is investigated. The detailed analysis in terms of Steinhardt's orientation order parameters Ql (l = 2 - 10) reveals that increasing the number of shell bonds decreases the FCS order in both melt and crystal. Differently, the FCS arrangements organize the radial bonds. Even if the molecular chains are fully flexible, the distribution of the angle formed by adjacent radial bonds exhibits sharp contributions at the characteristic angles θ ≈ 70°, 122°, 180°. The fractions of adjacent radial bonds with θ ≈ 122°, 180° are enhanced by the global order of the crystal, whereas the fraction with 70° ≲ θ ≲ 110° is nearly unaffected by the crystallization. Kink defects, i.e., large lateral displacements of the chains, are evidenced in the crystalline state.

The origin and evolution of silicic magmas during continental rifting: new constraints from trace elements and oxygen isotopes from Ethiopian volcanoes

NASA Astrophysics Data System (ADS)

Hutchison, W.; Boyce, A.; Mather, T. A.; Pyle, D. M.; Yirgu, G.; Gleeson, M. L.

2017-12-01

The petrologic diversity of rift magmas is generated by two key processes: interaction with the crust via partial melting or assimilation; and closed-system fractional crystallization of the parental magma. It is not yet known whether these two petrogenetic processes vary spatially between different rift settings, and whether there are any significant secular variations during rift evolution. The Ethiopian Rift is the ideal setting to test these hypotheses because it captures the transition from continental rifting to sea-floor spreading and has witnessed the eruption of large volumes of mafic and silicic volcanic rocks since 30 Ma. We use new oxygen isotope (δ18O) and trace element data to fingerprint fractional crystallisation and partial crustal melting processes in Ethiopia and evaluate spatial variations between three active rift segments. δ18O measurements are used to examine partial crustal melting processes. We find that most δ18O data from basalts to rhyolites fall within the bounds of modelled fractional crystallization trajectories (i.e., 5.5-6.5 ‰). Few samples deviate from this trend, emphasising that fractional crystallization is the dominant petrogenetic processes and that little fusible Precambrian crustal material (δ18O of 7-18 ‰) remain to be assimilated beneath the magmatic segments. Trace element systematics (e.g., Ba, Sr, Rb, Th and Zr) further underscore the dominant role of fractional crystallization but also reveal important variations in the degree of melt evolution between the volcanic systems. We find that the most evolved silicic magmas, i.e., those with greatest peralkalinity (molar Na2O+K2O>Al2O3), are promoted in regions of lowest magma flux off-axis and along rift. Our findings provide new information on the nature of the crust beneath Ethiopia's active magmatic segments and also have relevance for understanding ancient rift zones and the geotectonic settings that promote genesis of economically-valuable mineral deposits.

Basalt generation at the Apollo 12 site. Part 2: Source heterogeneity, multiple melts, and crustal contamination

NASA Technical Reports Server (NTRS)

Neal, Clive R.; Hacker, Matthew D.; Snyder, Gregory A.; Taylor, Lawrence A.; Liu, Yun-Gang; Schmitt, Roman A.

1994-01-01

The petrogenesis of Apollo 12 mare basalts has been examined with emphasis on trace-element ratios and abundances. Vitrophyric basalts were used as parental compositions for the modeling, and proportions of fractionating phases were determined using the MAGFOX prograqm of Longhi (1991). Crystal fractionation processes within crustal and sub-crustal magma chambers are evaluated as a function of pressure. Knowledge of the fractionating phases allows trace-element variations to be considered as either source related or as a product of post-magma-generation processes. For the ilmenite and olivine basalts, trace-element variations are inherited from the source, but the pigeonite basalt data have been interpreted with open-system evolution processes through crustal assimilation. Three groups of basalts have been examined: (1) Pigeonite basalts-produced by the assimilation of lunar crustal material by a parental melt (up to 3% assimilation and 10% crystal fractionation, with an 'r' value of 0.3). (2) Ilmenite basalts-produced by variable degrees of partial melting (4-8%) of a source of olivine, pigeonite, augite, and plagioclase, brought together by overturn of the Lunar Magma Ocean (LMO) cumulate pile. After generation, which did not exhaust any of the minerals in the source, these melts experienced closed-system crystal fractionation/accumulation. (3) Olivine basalts-produced by variable degrees of partial melting (5-10%) of a source of olivine, pigeonite, and augite. After generation, again without exhausting any of the minerals in the source, these melts evolved through crystal accumulation. The evolved liquid counterparts of these cumulates have not been sampled. The source compositions for the ilmenite and olivine basalts were calculated by assuming that the vitrophyric compositions were primary and the magmas were produced by non-modal batch melting. Although the magnitude is unclear, evaluation of these source regions indicates that both be composed of early- and late-stage Lunar Magma Ocean (LMO) cumulates, requiring an overturn of the cumulate pile.

Experimental Constraints on a Vesta Magma Ocean

NASA Technical Reports Server (NTRS)

Hoff, C.; Jones, J. H.; Le, L.

2014-01-01

A magma ocean model was devised to relate eucrites (basalts) and diogenites (orthopyroxenites), which are found mixed together as clasts in a suite of polymict breccias known as howardites. The intimate association of eucritic and diogenitic clasts in howardites argues strongly that these three classes of achondritic meteorites all originated from the same planetoid. Reflectance spectral evidence (including that from the DAWN mission) has long suggested that Vesta is indeed the Eucrite Parent Body. Specifically, the magma ocean model was generated as follows: (i) the bulk Vesta composition was taken to be 0.3 CV chondrite + 0.7 L chondrite but using only 10% of the Na2O from this mixture; (ii) this composition is allowed to crystallize at 500 bar until approx. 80% of the system is solid olivine + low-Ca pyroxene; (iii) the remaining 20% liquid crystallizes at one bar from 1250C to 1110C, a temperature slightly above the eucrite solidus. All crystallization calculations were performed using MELTS. In this model, diogenites are produced by cocrystallization of olivine and pyroxene in the >1250C temperature regime, with Main Group eucrite liquids being generated in the 1300-1250C temperature interval. Low-Ca pyroxene reappears at 1210C in the one-bar calculations and fractionates the residual liquid to produce evolved eucrite compositions (Stannern Trend). We have attempted to experimentally reproduce the <1250C portion of the MELTS Vesta magma ocean. In the MELTS calculation, the change from 500 bar to one bar results in a shift of the olivine:low-Ca pyroxene boundary so that the 1250C liquid is now in the olivine field and, consequently, olivine should be the first-crystallizing phase, followed by low-Ca pyroxene at 1210C, and plagioclase at 1170C. Because at one bar the olivine:low-Ca pyroxene boundary is a peritectic, fractional crystallization of the 1210C liquid proceeds with only pyroxene crystallization until plagioclase appears. Thus, the predictions of the MELTS calculation are clear and straightforward.

Pretreatment of Hanford medium-curie wastes by fractional crystallization.

PubMed

Nassif, Laurent; Dumont, George; Alysouri, Hatem; Rousseau, Ronald W

2008-07-01

Acceleration of the schedule for decontamination of the Hanford site using bulk vitrification requires implementation of a pretreatment operation. Medium-curie waste must be separated into two fractions: one is to go to a waste treatment and immobilization plant and a second, which is low-activity waste, is to be processed by bulk vitrification. The work described here reports research on using fractional crystallization for that pretreatment. Sodium salts are crystallized by evaporation of water from solutions simulating those removed from single-shell tanks, while leaving cesium in solution. The crystalline products are then recovered and qualified as low-activity waste, which is suitable upon redissolution for processing by bulk vitrification. The experimental program used semibatch operation in which a feed solution was continuously added to maintain a constant level in the crystallizer while evaporating water. The slurry recovered at the end of a run was filtered to recover product crystals, which were then analyzed to determine their composition. The results demonstrated that targets on cesium separation from the solids, fractional recovery of sodium salts, and sulfate content of the recovered salts can be achieved by the process tested.

Particles at fluid-fluid interfaces: A new Navier-Stokes-Cahn-Hilliard surface-phase-field-crystal model

PubMed Central

Aland, Sebastian; Lowengrub, John; Voigt, Axel

2013-01-01

Colloid particles that are partially wetted by two immiscible fluids can become confined to fluid-fluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids form an emulsion with interesting material properties and offer an important route to new soft materials. A promising approach to simulate these emulsions was presented in Aland et al. [Phys. Fluids 23, 062103 (2011)], where a Navier-Stokes-Cahn-Hilliard model for the macroscopic two-phase fluid system was combined with a surface phase-field-crystal model for the microscopic colloidal particles along the interface. Unfortunately this model leads to spurious velocities which require very fine spatial and temporal resolutions to accurately and stably simulate. In this paper we develop an improved Navier-Stokes-Cahn-Hilliard-surface phase-field-crystal model based on the principles of mass conservation and thermodynamic consistency. To validate our approach, we derive a sharp interface model and show agreement with the improved diffuse interface model. Using simple flow configurations, we show that the new model has much better properties and does not lead to spurious velocities. Finally, we demonstrate the solid-like behavior of the crystallized interface by simulating the fall of a solid ball through a colloid-laden multiphase fluid. PMID:23214691

Random close packing in protein cores

NASA Astrophysics Data System (ADS)

Gaines, Jennifer C.; Smith, W. Wendell; Regan, Lynne; O'Hern, Corey S.

2016-03-01

Shortly after the determination of the first protein x-ray crystal structures, researchers analyzed their cores and reported packing fractions ϕ ≈0.75 , a value that is similar to close packing of equal-sized spheres. A limitation of these analyses was the use of extended atom models, rather than the more physically accurate explicit hydrogen model. The validity of the explicit hydrogen model was proved in our previous studies by its ability to predict the side chain dihedral angle distributions observed in proteins. In contrast, the extended atom model is not able to recapitulate the side chain dihedral angle distributions, and gives rise to large atomic clashes at side chain dihedral angle combinations that are highly probable in protein crystal structures. Here, we employ the explicit hydrogen model to calculate the packing fraction of the cores of over 200 high-resolution protein structures. We find that these protein cores have ϕ ≈0.56 , which is similar to results obtained from simulations of random packings of individual amino acids. This result provides a deeper understanding of the physical basis of protein structure that will enable predictions of the effects of amino acid mutations to protein cores and interfaces of known structure.

Random close packing in protein cores.

PubMed

Gaines, Jennifer C; Smith, W Wendell; Regan, Lynne; O'Hern, Corey S

2016-03-01

Shortly after the determination of the first protein x-ray crystal structures, researchers analyzed their cores and reported packing fractions ϕ ≈ 0.75, a value that is similar to close packing of equal-sized spheres. A limitation of these analyses was the use of extended atom models, rather than the more physically accurate explicit hydrogen model. The validity of the explicit hydrogen model was proved in our previous studies by its ability to predict the side chain dihedral angle distributions observed in proteins. In contrast, the extended atom model is not able to recapitulate the side chain dihedral angle distributions, and gives rise to large atomic clashes at side chain dihedral angle combinations that are highly probable in protein crystal structures. Here, we employ the explicit hydrogen model to calculate the packing fraction of the cores of over 200 high-resolution protein structures. We find that these protein cores have ϕ ≈ 0.56, which is similar to results obtained from simulations of random packings of individual amino acids. This result provides a deeper understanding of the physical basis of protein structure that will enable predictions of the effects of amino acid mutations to protein cores and interfaces of known structure.

Enriched continental flood basalts from depleted mantle melts: modeling the lithospheric contamination of Karoo lavas from Antarctica

NASA Astrophysics Data System (ADS)

Heinonen, Jussi S.; Luttinen, Arto V.; Bohrson, Wendy A.

2016-01-01

Continental flood basalts (CFBs) represent large-scale melting events in the Earth's upper mantle and show considerable geochemical heterogeneity that is typically linked to substantial contribution from underlying continental lithosphere. Large-scale partial melting of the cold subcontinental lithospheric mantle and the large amounts of crustal contamination suggested by traditional binary mixing or assimilation-fractional crystallization models are difficult to reconcile with the thermal and compositional characteristics of continental lithosphere, however. The well-exposed CFBs of Vestfjella, western Dronning Maud Land, Antarctica, belong to the Jurassic Karoo large igneous province and provide a prime locality to quantify mass contributions of lithospheric and sublithospheric sources for two reasons: (1) recently discovered CFB dikes show isotopic characteristics akin to mid-ocean ridge basalts, and thus help to constrain asthenospheric parental melt compositions and (2) the well-exposed basaltic lavas have been divided into four different geochemical magma types that exhibit considerable trace element and radiogenic isotope heterogeneity (e.g., initial ɛ Nd from -16 to +2 at 180 Ma). We simulate the geochemical evolution of Vestfjella CFBs using (1) energy-constrained assimilation-fractional crystallization equations that account for heating and partial melting of crustal wall rock and (2) assimilation-fractional crystallization equations for lithospheric mantle contamination by using highly alkaline continental volcanic rocks (i.e., partial melts of mantle lithosphere) as contaminants. Calculations indicate that the different magma types can be produced by just minor (1-15 wt%) contamination of asthenospheric parental magmas by melts from variable lithospheric reservoirs. Our models imply that the role of continental lithosphere as a CFB source component or contaminant may have been overestimated in many cases. Thus, CFBs may represent major juvenile crustal growth events rather than just recycling of old lithospheric materials.

Sulfur-in-apatite: An indicator of the volatile evolution during lunar magmatism

NASA Astrophysics Data System (ADS)

Konecke, B.; Fiege, A.; Simon, A. C.; Holtz, F.

2017-12-01

The volatile content of lunar magmas remains controversial despite nearly five decades of interrogating samples from the NASA Apollo missions. Recently, the mineral apatite in lunar mare basalts has been investigated owing to its potential to constrain the volatile (F, Cl, H, S) budget of magmas [1-3]. The F-Cl-H signatures of lunar apatite were interpreted to record fractional crystallization, with nucleation and growth of apatite from a late-stage, interstitial, nearly anhydrous (<10 μg/g H2O), rhyolitic melt that evolved from a sulfide-undersaturated mare basalt [1]. The enigmatic S signature reported for those apatite grains was not interpreted due to the absence of published thermodynamic (partitioning) data for S. Here, we report new experimentally determined apatite/melt partition coefficients for S (DSap/m) at conditions applicable to lunar systems. The DSap/m values and thermodynamically modeled S content (XS) of lunar residual melt were used to constrain plausible S contents of lunar apatite produced by crystal fractionation (Sap = XS * DSap/m). Our results demonstrate that apatite crystallizing under lunar-like conditions from rhyolitic melt cannot obtain the reported 430 μg/g of S [2] by fractional crystallization. The results indicate that 5-35x higher S contents than feasible in sulfide-undersaturated, hydrous and dry rhyolitic melt, respectively, would be required to support crystal fractionation models [1]. Even elevated water concentrations in a sulfide-saturated rhyolitic melt cannot explain the S contents of lunar apatite rims. We propose two plausible scenarios: (A) The necessary concentration of S in rhyolitic melts may be achieved at >5 orders of magnitude higher fO2 (>ΔFMQ+1.2) than reported for lunar magmas, where S6+ is the prevalent oxidation state of S in rhyolitic melt, related to the significant degassing and preferential loss of H2 that drives oxidation of the residual melt [4]. (B) The volatile (F-Cl-H-S) signatures of lunar apatites may reflect cryptic metasomatic reactions between apatite and a S-Cl-rich, F-poor volatile phase released by underlying magma reservoirs. [1] Boyce et at., 2014, Science 344:400-402. [2] Greenwood et al., 2011, Nat. Geosci 4:79-82. [3] Webster et al., 2009, Geochim. Cosmochim. Acta 73, 559-581. [4] McCanta et al., 2017, Icarus 285, 95-102.

Nepheline structural and chemical dependence on melt composition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marcial, José; Crum, Jarrod; Neill, Owen

Nepheline crystallizes upon slow-cooling in some melts concentrated in Na2O and Al2O3, which can result in a residual glass phase of low chemical durability. Nepheline can incorporate many components often found in high-level waste radioactive borosilicate glass, including glass network ions (e.g., Si, Al, Fe), alkali metals (e.g., Cs, K, Na, and possibly Li), alkaline-earth metals (e.g., Ba, Sr, Ca, Mg), and transition metals (e.g., Mn, and possibly Cr, Zn, Ni). When crystallized from melts of different compositions, nepheline chemistry varies as a function of starting glass composition. Five simulated high level nuclear waste borosilicate glasses shown to crystallize largemore » fractions of nepheline on slow cooling, were selected for study. These melts constituted a range of Al2O3, B2O3, CaO, Na2O, K2O, Fe2O3, and SiO2 compositions. Compositional analyses of nepheline crystals in glass by electron probe micro-analysis (EPMA) indicate that boron is unlikely to be present in any significant concentration, if at all, in nepheline. Also, several models are presented for calculating the fraction of vacancies in the nepheline structure.« less

Crystallization of aqueous inorganic-malonic acid particles: nucleation rates, dependence on size, and dependence on the ammonium-to-sulfate ratio.

PubMed

Parsons, Matthew T; Riffell, Jenna L; Bertram, Allan K

2006-07-06

Using an electrodynamic balance, we determined the relative humidity (RH) at which aqueous inorganic-malonic acid particles crystallized, with ammonium sulfate ((NH(4))(2)SO(4)), letovicite ((NH(4))(3)H(SO(4))(2)), or ammonium bisulfate (NH(4)HSO(4)) as the inorganic component. The results for (NH(4))(2)SO(4)-malonic acid particles and (NH(4))(3)H(SO(4))(2)-malonic acid particles show that malonic acid decreases the crystallization RH of the inorganic particles by less than 7% RH when the dry malonic acid mole fraction is less than 0.25. At a dry malonic acid mole fraction of about 0.5, the presence of malonic acid can decrease the crystallization RH of the inorganic particles by up to 35% RH. For the NH(4)HSO(4)-malonic acid particles, the presence of malonic acid does not significantly modify the crystallization RH of the inorganic particles for the entire range of dry malonic acid mole fractions studied; in all cases, either the particles did not crystallize or the crystallization RH was close to 0% RH. Size dependent measurements show that the crystallization RH of aqueous (NH(4))(2)SO(4) particles is not a strong function of particle volume. However, for aqueous (NH(4))(2)SO(4)-malonic acid particles (with dry malonic acid mole fraction = 0.36), the crystallization RH is a stronger function of particle volume, with the crystallization RH decreasing by 6 +/- 3% RH when the particle volume decreases by an order of magnitude. To our knowledge, these are the first size dependent measurements of the crystallization RH of atmospherically relevant inorganic-organic particles. These results suggest that for certain organic mole fractions the particle size and observation time need to be considered when extrapolating laboratory crystallization results to atmospheric scenarios. For aqueous (NH(4))(2)SO(4) particles, the homogeneous nucleation rate data are a strong function of RH, but for aqueous (NH(4))(2)SO(4)-malonic acid particles (with dry organic mole fraction = 0.36), the rates are not as dependent on RH. The homogeneous nucleation rates for aqueous (NH(4))(2)SO(4) particles were parametrized using classical nucleation theory, and from this analysis we determined that the interfacial surface tension between the crystalline ammonium sulfate critical nucleus and an aqueous ammonium sulfate solution is between 0.053 and 0.070 J m(-2).

Modelling Equilibrium and Fractional Crystallization in the System MgO-FeO-CaO-Al2O3-SiO2

NASA Technical Reports Server (NTRS)

Herbert, F.

1985-01-01

A mathematical modelling technique for use in petrogenesis calculations in the system MgO-FeO-CaO-Al2O3-SiO2 is reported. Semiempirical phase boundary and elemental distribution information was combined with mass balance to compute approximate equilibrium crystallization paths for arbitrary system compositions. The calculation is applicable to a range of system compositions and fractionation calculations are possible. The goal of the calculation is the computation of the composition and quantity of each phase present as a function of the degree of solidification. The degree of solidification is parameterized by the heat released by the solidifying phases. The mathematical requirement for the solution of this problem is: (1) An equation constraining the composition of the magma for each solid phase in equilibrium with the liquidus phase, and (2) an equation for each solid phase and each component giving the distribution of that element between that phase and the magma.

Effect of microstructure on the coupled electromagnetic-thermo-mechanical response of cyclotrimethylenetrinitramine-estane energetic aggregates to infrared laser radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Judith A.; Zikry, M. A., E-mail: zikry@ncsu.edu

2015-09-28

The coupled electromagnetic (EM)-thermo-mechanical response of cyclotrimethylenetrinitramine-estane energetic aggregates under laser irradiation and high strain rate loads has been investigated for various aggregate sizes and binder volume fractions. The cyclotrimethylenetrinitramine (RDX) crystals are modeled with a dislocation density-based crystalline plasticity formulation and the estane binder is modeled with finite viscoelasticity through a nonlinear finite element approach that couples EM wave propagation with laser heat absorption, thermal conduction, and inelastic deformation. Material property and local behavior mismatch at the crystal-binder interfaces resulted in geometric scattering of the EM wave, electric field and laser heating localization, high stress gradients, dislocation density, andmore » crystalline shear slip accumulation. Viscous sliding in the binder was another energy dissipation mechanism that reduced stresses in aggregates with thicker binder ligaments and larger binder volume fractions. This investigation indicates the complex interactions between EM waves and mechanical behavior, for accurate predictions of laser irradiation of heterogeneous materials.« less

Phase equilibria constraints on models of subduction zone magmatism

NASA Astrophysics Data System (ADS)

Myers, James D.; Johnston, Dana A.

Petrologic models of subduction zone magmatism can be grouped into three broad classes: (1) predominantly slab-derived, (2) mainly mantle-derived, and (3) multi-source. Slab-derived models assume high-alumina basalt (HAB) approximates primary magma and is derived by partial fusion of the subducting slab. Such melts must, therefore, be saturated with some combination of eclogite phases, e.g. cpx, garnet, qtz, at the pressures, temperatures and water contents of magma generation. In contrast, mantle-dominated models suggest partial melting of the mantle wedge produces primary high-magnesia basalts (HMB) which fractionate to yield derivative HAB magmas. In this context, HMB melts should be saturated with a combination of peridotite phases, i.e. ol, cpx and opx, and have liquid-lines-of-descent that produce high-alumina basalts. HAB generated in this manner must be saturated with a mafic phase assemblage at the intensive conditions of fractionation. Multi-source models combine slab and mantle components in varying proportions to generate the four main lava types (HMB, HAB, high-magnesia andesites (HMA) and evolved lavas) characteristic of subduction zones. The mechanism of mass transfer from slab to wedge as well as the nature and fate of primary magmas vary considerably among these models. Because of their complexity, these models imply a wide range of phase equilibria. Although the experiments conducted on calc-alkaline lavas are limited, they place the following limitations on arc petrologic models: (1) HAB cannot be derived from HMB by crystal fractionation at the intensive conditions thus far investigated, (2) HAB could be produced by anhydrous partial fusion of eclogite at high pressure, (3) HMB liquids can be produced by peridotite partial fusion 50-60 km above the slab-mantle interface, (4) HMA cannot be primary magmas derived by partial melting of the subducted slab, but could have formed by slab melt-peridotite interaction, and (5) many evolved calc-alkaline lavas could have been formed by crystal fractionation at a range of crustal pressures.

Petrogenesis of calcic plagioclase megacrysts in Archean rocks

NASA Technical Reports Server (NTRS)

Phinney, W. C.; Morrison, D. A.

1986-01-01

Anorthositic complexes with large equidimensional plagioclase grains of highly calcic composition occur in nearly all Archean cratons. Similar plagioclase occur as megacrysts in many Archean sills, dikes, and volcanic flows. In the Canadian Shield these units occur throughout the Archean portions of the entire shield and are particularly common as dikes over an area of a few 100,000 sq km in Ontario and Manitoba during a period of at least 100 m.y. in many different rock types and metamorphic grades. The plagioclase generally occurs in three modes: as inclusions in mafic intrusions at various stages of fractionation, as crystal segregations in anorthosite complexes, or as megacrysts in fractionated sills, dikes, and flows. Most occurrences suggest that the plagioclase was formed elsewhere before being transported to its present location. The evidence seems to be quite clear that occurrences of these types of calcic plagioclase require: (1) ponding of a relatively undifferentiated Archean tholeiitic melt at some depth; (2) isothermal crystallization of large, equidimensional homogeneous plagioclase crystals; (3) separation of the plagioclase crystals from any other crystalline phases; (4) further fractionation of melt; (5)transport of various combinations of individual plagioclase crystals and clusters of crystals by variously fractionated melts; and (6) emplacement as various types of igneous intrusions or flows.

Characterization of calcium isotopes in natural and synthetic barite

USGS Publications Warehouse

Griffith, E.M.; Schauble, E.A.; Bullen, T.D.; Paytan, A.

2008-01-01

The mineral barite (BaSO4) accommodates calcium in its crystal lattice, providing an archive of Ca-isotopes in the highly stable sulfate mineral. Holocene marine (pelagic) barite samples from the major ocean basins are isotopically indistinguishable from each other (??44/40Ca = -2.01 ?? 0.15???) but are different from hydrothermal and cold seep barite samples (??44/40Ca = -4.13 to -2.72???). Laboratory precipitated (synthetic) barite samples are more depleted in the heavy Ca-isotopes than pelagic marine barite and span a range of Ca-isotope compositions, ??44/40Ca = -3.42 to -2.40???. Temperature, saturation state, a Ba2 + / a SO42 -, and aCa2+/aBa2+ each influence the fractionation of Ca-isotopes in synthetic barite; however, the fractionation in marine barite samples is not strongly related to any measured environmental parameter. First-principles lattice dynamical modeling predicts that at equilibrium Ca-substituted barite will have much lower 44Ca/40Ca than calcite, by -9??? at 0 ??C and -8??? at 25 ??C. Based on this model, none of the measured barite samples appear to be in isotopic equilibrium with their parent solutions, although as predicted they do record lower ??44/40Ca values than seawater and calcite. Kinetic fractionation processes therefore most likely control the extent of isotopic fractionation exhibited in barite. Potential fractionation mechanisms include factors influencing Ca2+ substitution for Ba2+ in barite (e.g. ionic strength and trace element concentration of the solution, competing complexation reactions, precipitation or growth rate, temperature, pressure, and saturation state) as well as nucleation and crystal growth rates. These factors should be considered when investigating controls on isotopic fractionation of Ca2+ and other elements in inorganic and biogenic minerals. ?? 2008 Elsevier Ltd.

Radical chiral Floquet phases in a periodically driven Kitaev model and beyond

NASA Astrophysics Data System (ADS)

Po, Hoi Chun; Fidkowski, Lukasz; Vishwanath, Ashvin; Potter, Andrew C.

2017-12-01

We theoretically discover a family of nonequilibrium fractional topological phases in which time-periodic driving of a 2D system produces excitations with fractional statistics, and produces chiral quantum channels that propagate a quantized fractional number of qubits along the sample edge during each driving period. These phases share some common features with fractional quantum Hall states, but are sharply distinct dynamical phenomena. Unlike the integer-valued invariant characterizing the equilibrium quantum Hall conductance, these phases are characterized by a dynamical topological invariant that is a square root of a rational number, inspiring the label: radical chiral Floquet phases. We construct solvable models of driven and interacting spin systems with these properties, and identify an unusual bulk-boundary correspondence between the chiral edge dynamics and bulk "anyon time-crystal" order characterized by dynamical transmutation of electric-charge into magnetic-flux excitations in the bulk.

Pore and grain boundary migration under a temperature gradient: A phase-field model study

DOE PAGES

Biner, S. B.

2016-03-16

In this study, the collective migration behavior of pores and grain boundaries under a temperature gradient is studied for simple single crystal, bi-crystal and polycrystal configurations with a phase-field model formulism. For simulation of the microstructure of solids, composed of pores and grain boundaries, the results indicate that not only the volume fraction of pores, but also its spatial partitioning between the grain boundary junctions and the grain boundary segments appears to be important. In addition to various physical properties, the evolution kinetics, under given temperature gradients, will be strongly influenced with the initial morphology of a poly-crystalline microstructure.

The ferroan-anorthositic suite and the extent of primordial lunar melting

NASA Technical Reports Server (NTRS)

Warren, Paul H.; Kallemeyn, Gregory W.

1992-01-01

The Apollo highlands rock collection includes more than 100 'pristine' fragments that survived the intense meteoritic bombardment of the ancient lunar crust with unmixed, endogenously igneous compositions. The geochemical anomaly manifested by the 'ferroan-anorthositic suite' (FAS) appears to reflect a geochemical, and probably also a genetic, bimodality among the ancient lunar cumulates. Early models that purported to account for this bimodality as a product of a single magma have been discredited. The model of the present paper implies that the Mg-suite rocks formed by a comparatively normal variety of basaltic fractional crystallization (FC) shortly after the era of magma ocean (MO) crystallization and FAS genesis.

Experimental Fractional Crystallization of the Lunar Magma Ocean

NASA Technical Reports Server (NTRS)

Rapp, J. F.; Draper, D. S.

2012-01-01

The current paradigm for lunar evolution is of crystallization of a global scale magma ocean, giving rise to the anorthositic crust and mafic cumulate interior. It is thought that all other lunar rocks have arisen from this differentiated interior. However, until recently this paradigm has remained untested experimentally. Presented here are the first experimental results of fractional crystallization of a Lunar Magma Ocean (LMO) using the Taylor Whole Moon (TWM) bulk lunar composition [1].

Fractional Brownian motion run with a multi-scaling clock mimics diffusion of spherical colloids in microstructural fluids.

PubMed

Park, Moongyu; Cushman, John Howard; O'Malley, Dan

2014-09-30

The collective molecular reorientations within a nematic liquid crystal fluid bathing a spherical colloid cause the colloid to diffuse anomalously on a short time scale (i.e., as a non-Brownian particle). The deformations and fluctuations of long-range orientational order in the liquid crystal profoundly influence the transient diffusive regimes. Here we show that an anisotropic fractional Brownian process run with a nonlinear multiscaling clock effectively mimics this collective and transient phenomenon. This novel process has memory, Gaussian increments, and a multiscale mean square displacement that can be chosen independently from the fractal dimension of a particle trajectory. The process is capable of modeling multiscale sub-, super-, or classical diffusion. The finite-size Lyapunov exponents for this multiscaling process are defined for future analysis of related mixing processes.

Strengthening and Improving Yield Asymmetry of Magnesium Alloys by Second Phase Particle Refinement Under the Guidance of Integrated Computational Materials Engineering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Dongsheng; Lavender, Curt

2015-05-08

Improving yield strength and asymmetry is critical to expand applications of magnesium alloys in industry for higher fuel efficiency and lower CO 2 production. Grain refinement is an efficient method for strengthening low symmetry magnesium alloys, achievable by precipitate refinement. This study provides guidance on how precipitate engineering will improve mechanical properties through grain refinement. Precipitate refinement for improving yield strengths and asymmetry is simulated quantitatively by coupling a stochastic second phase grain refinement model and a modified polycrystalline crystal viscoplasticity φ-model. Using the stochastic second phase grain refinement model, grain size is quantitatively determined from the precipitate size andmore » volume fraction. Yield strengths, yield asymmetry, and deformation behavior are calculated from the modified φ-model. If the precipitate shape and size remain constant, grain size decreases with increasing precipitate volume fraction. If the precipitate volume fraction is kept constant, grain size decreases with decreasing precipitate size during precipitate refinement. Yield strengths increase and asymmetry approves to one with decreasing grain size, contributed by increasing precipitate volume fraction or decreasing precipitate size.« less

Calculation of spontaneous emission from a V-type three-level atom in photonic crystals using fractional calculus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Chih-Hsien; Hsieh, Wen-Feng; Institute of Electro-Optical Science and Engineering, National Cheng Kung University, 1 Dahsueh Rd., Tainan 701, Taiwan

2011-07-15

Fractional time derivative, an abstract mathematical operator of fractional calculus, is used to describe the real optical system of a V-type three-level atom embedded in a photonic crystal. A fractional kinetic equation governing the dynamics of the spontaneous emission from this optical system is obtained as a fractional Langevin equation. Solving this fractional kinetic equation by fractional calculus leads to the analytical solutions expressed in terms of fractional exponential functions. The accuracy of the obtained solutions is verified through reducing the system into the special cases whose results are consistent with the experimental observation. With accurate physical results and avoidingmore » the complex integration for solving this optical system, we propose fractional calculus with fractional time derivative as a better mathematical method to study spontaneous emission dynamics from the optical system with non-Markovian dynamics.« less

Crystallization and dynamical arrest of attractive hard spheres.

PubMed

Babu, Sujin; Gimel, Jean-Christophe; Nicolai, Taco

2009-02-14

Crystallization of hard spheres interacting with a square well potential was investigated by numerical simulations using so-called Brownian cluster dynamics. The phase diagram was determined over a broad range of volume fractions. The crystallization rate was studied as a function of the interaction strength expressed in terms of the second virial coefficient. For volume fractions below about 0.3 the rate was found to increase abruptly with increasing attraction at the binodal of the metastable liquid-liquid phase separation. The rate increased until a maximum was reached after which it decreased with a power law dependence on the second virial coefficient. Above a critical percolation concentration, a transient system spanning network of connected particles was formed. Crystals were formed initially as part of the network, but eventually crystallization led to the breakup of the network. The lifetime of the transient gels increased very rapidly over a small range of interaction energies. Weak attraction destabilized the so-called repulsive crystals formed in pure hard sphere systems and shifted the coexistence line to higher volume fractions. Stronger attraction led to the formation of a denser, so-called attractive, crystalline phase. Nucleation of attractive crystals in the repulsive crystalline phase was observed close to the transition.

From Modeling of Plasticity in Single-Crystal Superalloys to High-Resolution X-rays Three-Crystal Diffractometer Peaks Simulation

NASA Astrophysics Data System (ADS)

Jacques, Alain

2016-12-01

The dislocation-based modeling of the high-temperature creep of two-phased single-crystal superalloys requires input data beyond strain vs time curves. This may be obtained by use of in situ experiments combining high-temperature creep tests with high-resolution synchrotron three-crystal diffractometry. Such tests give access to changes in phase volume fractions and to the average components of the stress tensor in each phase as well as the plastic strain of each phase. Further progress may be obtained by a new method making intensive use of the Fast Fourier Transform, and first modeling the behavior of a representative volume of material (stress fields, plastic strain, dislocation densities…), then simulating directly the corresponding diffraction peaks, taking into account the displacement field within the material, chemical variations, and beam coherence. Initial tests indicate that the simulated peak shapes are close to the experimental ones and are quite sensitive to the details of the microstructure and to dislocation densities at interfaces and within the soft γ phase.

A fundamental dispute: A discussion of "On some fundamentals of igneous petrology" by Bruce D. Marsh, Contributions to Mineralogy and Petrology (2013) 166: 665-690

NASA Astrophysics Data System (ADS)

Latypov, Rais; Morse, Tony; Robins, Brian; Wilson, Richard; Cawthorn, Grant; Tegner, Christian; Holness, Marian; Lesher, Charles; Barnes, Steve; O'Driscoll, Brian; Veksler, Ilya; Higgins, Michael; Wilson, Allan; Namur, Olivier; Chistyakova, Sofya; Naslund, Richard; Thy, Peter

2015-02-01

Marsh (Contrib Miner Petrol 166:665-690, 2013) again claims that crystal-free basalt magmas are unable to differentiate in crustal magma chambers and regards layered intrusions as primarily due to the repeated emplacement of crystal suspensions. He ignores an earlier critique of his unconventional inferences (Latypov, J Petrol 50:1047-1069, 2009) as well as a wealth of petrographic, geochemical and experimental evidence supporting the dominant role of fractional crystallization in the solidification of layered intrusions. Most tellingly, the cryptic variations preserved in the Skaergaard and many other basaltic layered intrusions would require an exceedingly implausible sequence of phenocrystic magmas but are wholly consistent with in situ fractional crystallization. A major flaw in Marsh's hypothesis is that it dismisses progressive fractional crystallization within any magma chamber and hence prohibits the formation of crystal slurries with phenocrysts and melts that change systematically in composition in any feeder system. This inherent attribute of the hypothesis excludes the formation of layered intrusions anywhere.

Sb2Te3 and Its Superlattices: Optimization by Statistical Design.

PubMed

Behera, Jitendra K; Zhou, Xilin; Ranjan, Alok; Simpson, Robert E

2018-05-02

The objective of this work is to demonstrate the usefulness of fractional factorial design for optimizing the crystal quality of chalcogenide van der Waals (vdW) crystals. We statistically analyze the growth parameters of highly c axis oriented Sb 2 Te 3 crystals and Sb 2 Te 3 -GeTe phase change vdW heterostructured superlattices. The statistical significance of the growth parameters of temperature, pressure, power, buffer materials, and buffer layer thickness was found by fractional factorial design and response surface analysis. Temperature, pressure, power, and their second-order interactions are the major factors that significantly influence the quality of the crystals. Additionally, using tungsten rather than molybdenum as a buffer layer significantly enhances the crystal quality. Fractional factorial design minimizes the number of experiments that are necessary to find the optimal growth conditions, resulting in an order of magnitude improvement in the crystal quality. We highlight that statistical design of experiment methods, which is more commonly used in product design, should be considered more broadly by those designing and optimizing materials.

Nucleation and Growth of Crystalline Grains in RF-Sputtered TiO 2 Films

DOE PAGES

Johnson, J. C.; Ahrenkiel, S. P.; Dutta, P.; ...

2009-01-01

Amore » morphous TiO 2 thin films were radio frequency sputtered onto siliconmonoxide and carbon support films on molybdenum transmission electron microscope (TEM) grids and observed during in situ annealing in a TEM heating stage at 250 ∘ C. The evolution of crystallization is consistent with a classical model of homogeneous nucleation and isotropic grain growth. The two-dimensional grain morphology of the TEM foil allowed straightforward recognition of amorphous and crystallized regions of the films, for measurement of crystalline volume fraction and grain number density. By assuming that the kinetic parameters remain constant beyond the onset of crystallization, the final average grain size was computed, using an analytical extrapolation to the fully crystallized state. Electron diffraction reveals a predominance of the anatase crystallographic phase.« less

Formation of Intermediate Plutonic Rocks by Magma Mixing: the Shoshonite Suite of Timna, Southern Israel.

NASA Astrophysics Data System (ADS)

Fox, S.; Katzir, Y.

2017-12-01

In magmatic series considered to form by crystal fractionation intermediate rocks are usually much less abundant than expected. Yet, intermediate plutonic rocks, predominantly monzodiorites, are very abundant in the Neoproterozoic Timna igneous complex, S. Israel. A previously unnoticed plutonic shoshonitic suite was recently defined and mapped in Timna (Litvinovsky et al., 2015). It mostly comprises intermediate rocks in a seemingly 'continuous' trend from monzodiorite through monzonite to quartz syenite. Macroscale textures including gradational boundaries of mafic and felsic rocks and MME suggest that magma mixing is central in forming intermediate rocks in Timna. Our petrographic, microtextural and mineral chemistry study delineates the mode of incipient mixing, ultimate mingling and crystal equilibration in hybrid melts. An EMP study of plagioclase from rocks across the suite provides a quantitative evaluation of textures indicative of magma mixing/mingling, including recurrent/patchy zoning, Ca spike, boxy/sponge cellular texture and anti-Rapakivi texture. Each texture has an affinity to a particular mixing region. A modal count of these textures leads to a kinetic mixing model involving multi temporal and spatial scales necessary to form the hybrid intermediate rocks. A `shell'-like model for varying degrees of mixing is developed with the more intensive mixing at the core and more abundant felsic and mafic end-members towards the outer layer. REE patterns in zircon shows that it originated from both mafic and felsic parent melts. Whole rock Fe vs Sr plot suggests a two-stage mixing between the monzogabbro and quartz-syenite producing first mesocratic syenite, and subsequent mixing with a fractionating monzogabbro resulting in monzonitic compositions. A fractionating monzogabbro intruded into a syenitic melt sequentially. While slowly cooling, the monzogabbro heated the immediate syenitic melt, lowering the viscosity and rheological obstruction to overturn the boundary, and thus facilitated mixing. Increasing melt hybridization, tandem with crystallization, produced mixing textures in the turbulent crystal mush zone, synchronously with `pure end-member' crystallization. As a result, a large volume of intermediate rock was created through a hybridization process.

Controlled crystallization of the lipophilic drug fenofibrate during freeze-drying: elucidation of the mechanism by in-line Raman spectroscopy.

PubMed

de Waard, Hans; De Beer, Thomas; Hinrichs, Wouter L J; Vervaet, Chris; Remon, Jean-Paul; Frijlink, Henderik W

2010-12-01

We developed a novel process, "controlled crystallization during freeze-drying" to produce drug nanocrystals of poorly water-soluble drugs. This process involves freeze-drying at a relatively high temperature of a drug and a matrix material from a mixture of tertiary butyl alcohol and water, resulting in drug nanocrystals incorporated in a matrix. The aim of this study was to elucidate the mechanisms that determine the size of the drug crystals. Fenofibrate was used as a model lipophilic drug. To monitor the crystallization during freeze-drying, a Raman probe was placed just above the sample in the freeze-dryer. These in-line Raman spectroscopy measurements clearly revealed when the different components crystallized during freeze-drying. The solvents crystallized only during the freezing step, while the solutes only crystallized after the temperature was increased, but before drying started. Although the solutes crystallized only after the freezing step, both the freezing rate and the shelf temperature were critical parameters that determined the final crystal size. At a higher freezing rate, smaller interstitial spaces containing the freeze-concentrated fraction were formed, resulting in smaller drug crystals (based on dissolution data). On the other hand, when the solutes crystallized at a lower shelf temperature, the degree of supersaturation is higher, resulting in a higher nucleation rate and consequently more and therefore smaller crystals. In conclusion, for the model drug fenofibrate, a high freezing rate and a relatively low crystallization temperature resulted in the smallest crystals and therefore the highest dissolution rate.

Effects of heavy-ion irradiation on the microwave surface impedance of (Ba1-x K x )Fe2As2 single crystals

NASA Astrophysics Data System (ADS)

Ghigo, G.; Torsello, D.; Gerbaldo, R.; Gozzelino, L.; Laviano, F.; Tamegai, T.

2018-07-01

The electrodynamic response of Ba1-x K x Fe2As2 single crystals at the microwave frequencies has been investigated by means of a coplanar resonator technique, at different values of non-magnetic disorder introduced into the samples by heavy-ion irradiation. The surface impedance Z s = R s + iX s conforms to the classical skin effect above the critical temperature. Below T c, R s monotonically decreases while X s shows a peak, which evolves as a function of the irradiation fluence. The disorder-dependent Z s (T) curves are analyzed within a two-fluid model, suitably modified to account for a finite quasiparticle fraction at T = 0. The analysis gives, for the unirradiated crystal, quasiparticle relaxation times τ that are in good agreement with previous literature. Smaller τ values are deduced for the disordered crystals, both in the normal and in the superconducting states. The limits of application of the model are discussed.

Ore-forming adakitic porphyry produced by fractional crystallization of oxidized basaltic magmas in a subcrustal chamber (Jiamate, East Junggar, NW China)

NASA Astrophysics Data System (ADS)

Hong, Tao; Xu, Xing-Wang; Gao, Jun; Peters, Stephen G.; Zhang, Di; Jielili, Reyaniguli; Xiang, Peng; Li, Hao; Wu, Chu; You, Jun; Liu, Jie; Ke, Qiang

2018-01-01

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages. The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA). The ore-bearing adakitic intrusions in the KPCB and the adakitic Jiamate Complex intrusions were both probably generated from the same basaltic parental magmas through fractional crystallization. In addition, characteristics of the layered, magnetite-bearing, oxidized, basaltic Jiamate Complex intrusive rocks indicate that they are likely to be the parental arc magmas for the nearby porphyry Cu deposits. This conclusion is based on new interpretations of the regional and local geology, on interpretation of new geochemical analysis, new stable isotope analysis, new geothermobarometry, and new zircon age dating as well as other techniques and interpretations.

Ore-forming adakitic porphyry produced by fractional crystallization of oxidized basaltic magmas in a subcrustal chamber (Jiamate, East Junggar, NW China)

USGS Publications Warehouse

Hong, Tao; Xu, Xing-Wang; Gao, Jun; Peters, Stephen; Zhang, Di; Jielili, Reyaniguli; Xiang, Peng; Li, Hao; Wu, Chu; You, Jun; Liu, Jie; Ke, Qiang

2018-01-01

Adakitic intrusions are supposed to have a close genetic and spatial relationship to porphyry Cu deposits. However, the genesis of adakitic intrusions is still under dispute. Here, we describe newly discovered intrusive complex rocks, which are composed of ore-bearing, layered magnetite-bearing gabbroic and adakitic rocks in Jiamate, East Junggar, NW China. These Jiamate Complex intrusions have diagnostic petrologic, geochronologic and geochemical signatures that indicate they were all generated from the same oxidized precursor magma source. Additionally, these layered rocks underwent the same fractional crystallization process as the ore-bearing adakitic rocks in the adjacent Kalaxiangar Porphyry Cu Belt (KPCB) in an oceanic island arc (OIA) setting. The rocks studied for this paper include layered magnetite-bearing gabbroic intrusive rocks that contain: (1) gradual contact changes between lithological units of mafic and intermediate rocks, (2) geochemical signatures that are the same as those found in oceanic island arc (OIA) rocks, (3) typical adakitic geochemistry, and (4) similar characteristics and apparent fractional crystallization relationships of ultra-basic to basic rocks to those in the nearby Beitashan Formation and to ore-bearing adakitic rocks in the KPCB. They also display similar zircon U-Pb and zircon Hf model ages.The Jiamate Complex intrusions contain intergrowths of magnetite and layered gabbro, and the intermediate-acidic intrusions of the Complex display typical adakitic affinities. Moreover, in conjunction with previously published geochronological and geochemistry data of the mafic rocks in the Beitashan Formation and in the KPCB area, additional data generated for the Jiamate Complex intrusions rocks indicate that they were formed from fractional crystallization processes. The Jiamate Complex intrusions most likely were derived from a metasomatized mantle wedge that was underplated at the root of the Saur oceanic island arc (Saur OIA). The ore-bearing adakitic intrusions in the KPCB and the adakitic Jiamate Complex intrusions were both probably generated from the same basaltic parental magmas through fractional crystallization. In addition, characteristics of the layered, magnetite-bearing, oxidized, basaltic Jiamate Complex intrusive rocks indicate that they are likely to be the parental arc magmas for the nearby porphyry Cu deposits. This conclusion is based on new interpretations of the regional and local geology, on interpretation of new geochemical analysis, new stable isotope analysis, new geothermobarometry, and new zircon age dating as well as other techniques and interpretations.

Origins of cryptic variation in the Ediacaran-Fortunian rhyolitic ignimbrites of the Saldanha Bay Volcanic Complex, Western Cape, South Africa

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Stevens, G.; Frei, D.; Joseph, C. S. A.

2017-12-01

The Saldanha eruption centre, on the West Coast of South Africa, consists of 542 Ma, intracaldera, S-type, rhyolite ignimbrites divided into the basal Saldanha Ignimbrite and the partly overlying Jacob's Bay Ignimbrite. Depleted-mantle Nd model ages suggest magma sources younger than the Early Mesoproterozoic, and located within the Neoproterozoic Malmesbury Group and Swartland complex metasedimentary and metavolcanic rocks that form the regional basement. The Sr isotope systematics suggest that the dominant source rocks were metavolcaniclastic rocks and metagreywackes, and that the magmas formed from separate batches extracted from the same heterogeneous source. No apparent magma mixing trends relate the Saldanha to the Jacob's Bay Ignimbrites, or either of these to the magmas that formed the Plankiesbaai or Tsaarsbank Ignimbrites in the neighbouring Postberg eruption centre. The magmas were extracted from their source rocks carrying small but significant proportions of peritectic and restitic accessory minerals. Variations in the content of this entrained crystal cargo were responsible for most of the chemical variations in the magmas. Although we cannot construct a cogent crystal fractionation model to relate these groups of magmas, at least some crystal fractionation occurred, as an overlay on the primary signal due to peritectic assemblage entrainment (PAE). Thus, the causes of the cryptic chemical variation among the ignimbrite magmas of the Saldanha centre are variable, but dominated by the compositions of the parent melts and PAE. The preservation of clear, source-inherited chemical signatures, in individual samples, calls into question the common interpretation of silicic calderas as having been formed in large magma reservoirs, with magma compositions shaped by magma mingling, mixing, and fractional crystallization. The Saldanha rocks suggest a more intimate connection between source and erupted magma, and perhaps indicate that silicic magmas are too viscous to be significantly modified by magma-chamber processes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Yoreo, J; Orme, C; Dove, P

Since the dawn of life on earth, organisms have directed the crystallization of inorganic ions from solution to form minerals that meet specific biological needs. The resulting materials often exhibit remarkable properties, making the processes involved in biomineralization of interest to a wide array of scientific disciplines. From a geochemical standpoint, perhaps the most important consequence is that CaCO{sub 3} biomineral formation occurs in the Oceans on such a large scale that it influences many aspects of seawater chemistry and results in sequestration of carbon in the form of carbonate sediments. In this manner, the products of biomineralization are preservedmore » in the rock record and serve as an extensive chronicle of the interplay between biota and the earth system environment. From the point of view of materials synthesis, biological control over epitaxy is an elegant example of self-organization in complex molecular systems. Through selective introduction of peptides and proteins, living organisms deterministically modify nucleation, step kinetics, surface morphologies, and facet stabilities to produce nanophase materials, topologically complex single-crystals, and multi-layer composite. The resulting materials have biological functions as diverse as structural supports, porous filtration media, grinding and cutting tools, lenses, gravity sensors and magnetic guidance systems. As Table I shows, calcium carbonate minerals are ubiquitous amongst these biomineral structures. In addition , calcium carbonate is a well studied material that is easily crystallized and has known solution chemistry. Consequently, the calcium carbonate system provides an excellent model for investigating biomineralization processes. Surprisingly, in spite of the identification of carbonate biogenesis as a critical contributor to the carbon reservoir mediating climate change, and the enormous potential of biomimetic synthesis for production of tailored, crystalline nano- and micro-structured materials, the fundamental physical controls on carbonate biomineral formation remain poorly understood. Carbonates are formed in diverse environments almost exclusively by living organisms. These naturally occurring marine and fresh water minerals most commonly occur as the polymorphs of calcite, aragonite and vaterite which are nucleated and grown in the exoskeletons and tissues of marine and freshwater organisms ranging from simple bacteria and algae to crustaceans, molluscs, or sponges. It is known that the soluble fraction associated with mineralizing parts of organisms plays a primary role in crystal formation. In the formation of molluscan shells, this fraction is distinguished by the common presence of aspartic acid rich amino acid mixtures. It is also known that carbonates exposed to different polyamino acids exhibit different crystal habits. Belcher et al. showed that exposing growing CaCO{sub 3} crystals alternately to solutions containing polyanionic proteins associated with the aragonitic and calcitic layers of mollusc shells led to sequential switching of the crystal structure of the newly grown material between that of aragonite and calcite. Further work has demonstrated that these protein mixtures alter the morphology of the calcite growth surface and that they contain two fractions effecting growth: a step-binding fraction that inhibits step advancement on calcite surfaces, and a surface binding fraction that appears to lead to the subsequent nucleation of aragonite. Wierzbicki et al. found that polyaspartate molecules (ASP{sub 20}) bind to calcite surfaces. Finally, modeling of ASP{sub 15} binding to calcite planes predicts large binding energies for well defined orientations. This and related evidence shows that systematic relationships between crystal morphology and surface interactions with the reactive groups of the organic molecules must exist. However, the interplay between surface chemistry and the physical processes of nucleation and crystal growth are poorly understood because, until recently only ex situ biochemical studies focusing on the effect of changes in solution chemistry and/or surface stereo-chemistry on macroscopic crystal morphology had been performed.« less

Nature of the anomalies in the supercooled liquid state of the mW model of water.

PubMed

Holten, Vincent; Limmer, David T; Molinero, Valeria; Anisimov, Mikhail A

2013-05-07

The thermodynamic properties of the supercooled liquid state of the mW model of water show anomalous behavior. Like in real water, the heat capacity and compressibility sharply increase upon supercooling. One of the possible explanations of these anomalies, the existence of a second (liquid-liquid) critical point, is not supported by simulations for this model. In this work, we reproduce the anomalies of the mW model with two thermodynamic scenarios: one based on a non-ideal "mixture" with two different types of local order of the water molecules, and one based on weak crystallization theory. We show that both descriptions accurately reproduce the model's basic thermodynamic properties. However, the coupling constant required for the power laws implied by weak crystallization theory is too large relative to the regular backgrounds, contradicting assumptions of weak crystallization theory. Fluctuation corrections outside the scope of this work would be necessary to fit the forms predicted by weak crystallization theory. For the two-state approach, the direct computation of the low-density fraction of molecules in the mW model is in agreement with the prediction of the phenomenological equation of state. The non-ideality of the "mixture" of the two states never becomes strong enough to cause liquid-liquid phase separation, also in agreement with simulation results.

Nature of the anomalies in the supercooled liquid state of the mW model of water

NASA Astrophysics Data System (ADS)

Holten, Vincent; Limmer, David T.; Molinero, Valeria; Anisimov, Mikhail A.

2013-05-01

The thermodynamic properties of the supercooled liquid state of the mW model of water show anomalous behavior. Like in real water, the heat capacity and compressibility sharply increase upon supercooling. One of the possible explanations of these anomalies, the existence of a second (liquid-liquid) critical point, is not supported by simulations for this model. In this work, we reproduce the anomalies of the mW model with two thermodynamic scenarios: one based on a non-ideal "mixture" with two different types of local order of the water molecules, and one based on weak crystallization theory. We show that both descriptions accurately reproduce the model's basic thermodynamic properties. However, the coupling constant required for the power laws implied by weak crystallization theory is too large relative to the regular backgrounds, contradicting assumptions of weak crystallization theory. Fluctuation corrections outside the scope of this work would be necessary to fit the forms predicted by weak crystallization theory. For the two-state approach, the direct computation of the low-density fraction of molecules in the mW model is in agreement with the prediction of the phenomenological equation of state. The non-ideality of the "mixture" of the two states never becomes strong enough to cause liquid-liquid phase separation, also in agreement with simulation results.

On the Role of Mantle Overturn during Magma Ocean Solidification

NASA Astrophysics Data System (ADS)

Boukaré, C. E.; Parmentier, E.; Parman, S. W.

2017-12-01

Solidification of potential global magma ocean(s) (MO) early in the history of terrestrial planets may play a key role in the evolution of planetary interiors by setting initial conditions for their long-term evolution. Constraining this initial structure of solid mantles is thus crucial but remains poorly understood. MO fractional crystallization has been proposed to generate gravitationally unstable Fe-Mg chemical stratification capable of driving solid-state mantle overturn. Fractional solidification and overturn hypothesis, while only an ideal limiting case, can explain important geochemical features of both the Moon and Mars. Current overturn models consider generally post-MO overturn where the cumulate pile remains immobile until the end of MO solidification. However, if the cumulate pile overturns during MO solidification, the general picture of early planet evolution might differ significantly from the static crystallization models. We show that the timing of mantle overturn can be characterized with a dimensionless number measuring the ratio of the MO solidification time and the purely compositional overturn timescale. Syn-solidification overturn occurs if this dimensionless parameter, Rc, exceeds a critical value. Rc is mostly affected by the competition between the MO solidification time and mantle viscosity. Overturn that occurs during solidification can result in smaller scales of mantle chemical heterogeneity that could persist for long times thus influencing the whole evolution of a planetary body. We will discuss the effects of compaction/percolation on mantle viscosity. If partially molten cumulate do not have time to compact during MO solidification, viscosity of cumulates would be significantly lower as the interstitcial melt fraction would be large. Both solid mantle remelting during syn-solidification overturn and porous convection of melt retained with the cumulates are expected to reduce the degree of fractional crystallization. Syn-solidification overturn of a sluggish mantle can thus be an alternative to solid-state post-MO solidification overturn.

Space-Time Crystals of Trapped Ions

DTIC Science & Technology

2012-10-15

Spontaneous symmetry breaking can lead to the formation of time crystals, as well as spatial crystals. Here we propose a space- time crystal of...fields with fractional fluxes. The persistent rotation of trapped ions produces the temporal order, leading to the formation of a space- time crystal . We

Variation in trace element content of magnetite crystallized from a fractionating sulfide liquid, Sudbury, Canada: Implications for provenance discrimination

NASA Astrophysics Data System (ADS)

Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges

2012-07-01

Laser ablation ICP-MS analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination. We have determined trace element concentrations of Fe-oxides in massive sulfides that form Ni-Cu-PGE deposits at the base of the Sudbury Igneous Complex in Canada. The samples represent the crystallization products of fractionating sulfide liquids and consist of early-forming Fe-rich monosulfide solution (MSS) cumulates and residual Cu-rich intermediate solid solution (ISS). This study shows that Fe-oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and Fe-oxide phases. In addition, it is useful in determining the provenance of detrital Fe-oxide. In a sulfide melt, all lithophile elements (Cr, Ti, V, Al, Mn, Sc, Nb, Ga, Ge, Ta, Hf, W and Zr) are compatible into Fe-oxide. The concentrations of these elements are highest in the early-forming Fe-oxide (titanomagnetite) which crystallized with Fe-rich MSS. Upon the continual crystallization of Fe-oxide from the sulfide liquid, the lithophile elements gradually decrease so that late-forming Fe-oxide (magnetite), which crystallized from the residual Cu-rich liquid, is depleted in these elements. This behavior is in contrast with Fe-oxides that crystallized from a fractionating silicate melt, whereby the concentration of incompatible elements, such as Ti, increases rather than decreases. The behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only Ni, Co, Zn, Mo, Sn and Pb present above detection limit in magnetite. Nickel, Mo and Co are compatible in Fe-rich MSS and thus the co-crystallizing Fe-oxide is depleted in these elements. In contrast, magnetite that crystallized later from the fractionated liquid with Cu-rich ISS is enriched in Ni, Mo and Co because Fe-rich MSS is absent. The concentrations of Sn and Pb, which are incompatible with Fe-rich MSS, are highest in magnetite that formed from the fractionated Cu-rich liquid. At subsolidus temperatures, ilmenite exsolved from titanomagnetite whereas Al-spinel exsolved from the cores of some magnetite, locally redistributing the trace elements. However, during laser ablation ICP-MS analysis of these Fe-oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the Fe-oxide that crystallized from the sulfide melt.

Plagioclase zonation styles in hornblende gabbro inclusions from Little Glass Mountain, Medicine Lake volcano, California: Implications for fractionation mechanisms and the formation of composition gaps

USGS Publications Warehouse

Brophy, J.G.; Dorais, M.J.; Donnelly-Nolan, J.; Singer, B.S.

1997-01-01

The rhyolite of Little Glass Mountain (73-74% SiO2) is a single eruptive unit that contains inclusions of quenched andesite liquid (54-61% SiO2) and partially crystalline cumulate hornblende gabbro (53-55% SiO2). Based on previous studies, the quenched andesite inclusions and host rhyolite lava are related to one another through fractional crystallization and represent an example of a fractionation-generated composition gap. The hornblende gabbros represent the cumulate residue associated with the rhyolite-producing and composition gap-forming fractionation event. This study combines textural (Nomarski Differential Interference Contrast, NDIC, imaging), major element (An content) and trace element (Mg, Fe, Sr, K, Ti, Ba) data on the style of zonation of plagioclase crystals from representative andesite and gabbro inclusions, to assess the physical environment in which the fractionation event and composition gap formation took place. The andesite inclusions (54-61% SiO2) are sparsely phyric with phenocrysts of plagioclase, augite and Fe-oxide??olivine, +/-orthopyroxene, +/-hornblende set within a glassy to crystalline matrix. The gabbro cumulates (53-55% SiO2) consist of an interconnected framework of plagioclase, augite, olivine, orthopyroxene, hornblende and Fe-oxide along with highly vesicular interstitial glass (70-74% SiO2). The gabbros record a two-stage crystallization history of plagioclase + olivine + augite (Stage I) followed by plagioclase+orthopyroxene + hornblende + Fe-oxide (Stage II). Texturally, the plagioclase crystals in the andesite inclusions are characterized by complex, fine-scale oscillatory zonation and abundant dissolution surfaces. Compositionally (An content) the crystals are essentially unzoned from core-to-rim. These features indicate growth within a dynamic (convecting?), reservoir of andesite magma. In contrast, the plagioclase crystals in the gabbros are texturally smooth and featureless with strong normal zonation from An74 at the core to around An30, K, and Ba abundances increase and Mg abundances decrease steadily towards the rim. Ti, Fe, and Sr abundances increase and then decrease towards the rim. The trace element variations are fully consistent with the two-stage crystallization sequence inferred from the gabbro mineralogy. These results indicate progressive closed-system in situ crystallization in a quiescent magmatic boundary layer environment located along the margins of the andesite magma body. The fractional crystallization that generated the host rhyolite lava is one of inward solidification of a crystallizing boundary layer followed by melt extraction and accumulation of highly evolved interstitial liquid. This mechanism explains the formation of the composition gap between parental andesite and rhyolite magma compositions.

Compositional and microstructural design of highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics.

PubMed

Peitl, Oscar; Zanotto, Edgar D; Serbena, Francisco C; Hench, Larry L

2012-01-01

Bioactive glasses having chemical compositions between 1Na(2)O-2CaO-3SiO(2) (1N2C3S) and 1.5Na(2)O-1.5CaO-3SiO(2) (1N1C2S) containing 0, 4 and 6 wt.% P(2)O(5) were crystallized through two stage thermal treatments. By carefully controlling these treatments we separately studied the effects on the mechanical properties of two important microstructural features not studied before, crystallized volume fraction and crystal size. Fracture strength, elastic modulus and indentation fracture toughness were measured as a function of crystallized volume fraction for a constant crystal size. Glass-ceramics with a crystalline volume fraction between 34% and 60% exhibited a three-fold improvement in fracture strength and an increase of 40% in indentation fracture toughness compared with the parent glass. For the optimal crystalline concentration (34% and 60%) these mechanical properties were then measured for different grain sizes, from 5 to 21 μm. The glass-ceramic with the highest fracture strength and indentation fracture toughness was that with 34% crystallized volume fracture and 13 μm crystals. Compared with the parent glass, the average fracture strength of this glass-ceramic was increased from 80 to 210 MPa, and the fracture toughness from 0.60 to 0.95 MPa.m(1/2). The increase in indentation fracture toughness was analyzed using different theoretical models, which demonstrated that it is due to crack deflection. Fortunately, the elastic modulus E increased only slightly; from 60 to 70 GPa (the elastic modulus of biomaterials should be as close as possible to that of cortical bone). In summary, the flexural strength of our best material (215 MPa) is significantly greater than that of cortical bone and comparable with that of apatite-wollastonite (A/W) bioglass ceramics, with the advantage that it shows a much lower elastic modulus. These results thus provide a relevant guide for the design of bioactive glass-ceramics with improved microstructure. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Polycrystalline magma behaviour in dykes: Insights from high-resolution numerical models

NASA Astrophysics Data System (ADS)

Yamato, Philippe; Duretz, Thibault; Tartèse, Romain; May, Dave

2013-04-01

The presence of a crystalline load in magmas modifies their effective rheology and thus their flow behaviour. In dykes, for instance, the presence of crystals denser than the melt reduces the ascent velocity and modifies the shape of the velocity profile from a Newtonian Poiseuille flow to a Bingham type flow. Nevertheless, several unresolved issues still remain poorly understood and need to be quantified: (1) What are the mechanisms controlling crystals segregation during magma ascent in dykes? (2) How does crystals transportation within a melt depend on their concentration, geometry, size and density? (3) Do crystals evolve in isolation to each other or as a cluster? (4) What is the influence of considering inertia of the melt within the system? In this study, we present numerical models following the setup previously used in Yamato et al. (2012). Our model setup simulates an effective pressure gradient between the base and the top of a channel (representing a dyke), by pushing a rigid piston into a magmatic mush that comprised crystals and melt and perforated by a hole. The initial resolution of the models (401x1551 nodes) has been doubled in order to ensure that the smallest crystalline fractions are sufficiently well resolved. Results show that the melt phase can be squeezed out from a crystal-rich magma when subjected to a given pressure gradient range and that clustering of crystals might be an important parameter controlling their behaviour. This demonstrates that crystal-melt segregation in dykes during magma ascent constitutes a viable mechanism for magmatic differentiation of residual melts. These results also explain how isolated crystal clusters and melt pockets, with different chemistry, can be formed. In addition, we discuss the impact of taking into account inertia in our models. Reference: Yamato, P., Tartèse, R., Duretz, T., May, D.A., 2012. Numerical modelling of magma transport in dykes. Tectonophysics 526-529, 97-109.

An inverse modeling strategy and a computer program to model garnet growth and resorption

NASA Astrophysics Data System (ADS)

Lanari, Pierre; Giuntoli, Francesco

2017-04-01

GrtMod is a computer program that allows numerical simulation of the pressure-temperature (P-T) evolution of garnet porphyroblasts based on the composition of successive growth zones preserved in natural samples. For each garnet growth stage, a new reactive bulk composition is optimized, allowing for resorption and/or fractionation of the previously crystalized garnet. The successive minimizations are performed using a heuristic search method and an objective function that quantify the amount by which the predicted garnet composition deviates from the measured values. The automated strategy of GrtMod includes a two stages optimization and one refinement stage. In this contribution, we will present several application examples. The new strategy provides quantitative estimates of the optimal P-T conditions whereas it was generally derived in a qualitatively way by using garnet isopleth intersections in equilibrium phase diagrams. GrtMod can also be used to model the evolution of the reactive bulk composition along any P-T trajectories. The results for typical MORB and metapelite compositions demonstrate that fractional crystallization models are required to derive accurate P-T information from garnet compositional zoning. GrtMod can also be used to retrieve complex garnet histories involving several stages of resorption. For instance, it has been used to model the P-T condition of garnet growth in grains from the Sesia Zone (Western Alps). The compositional variability of successive growth zones is characterized using standardized X-ray maps and the program XMapTools. Permian garnet cores crystalized under granulite facies conditions (T > 800°C and P = 6 kbar), whereas Alpine garnet rims grew at eclogite facies conditions (650°C and 16 kbar) involving several successive episodes of resorption. The model predicts that up to 50 vol% of garnet was dissolved before a new episode of garnet growth.

LABORATORY AND FIELD EVALUATION OF CRYSTALLIZED DOW 704 OIL ON THE PERFORMANCE OF THE PM2.5 WINS FRACTIONATOR

EPA Science Inventory

Subsequent to the PM2.5 FRM's 1997 promulgation, technicians at the CT Dept. of Env. Protection observed that the DOW 704 diffusion oil used in the method's WINS fractionator would occasionally crystallize during field use - particularly under wintertime conditions. While the f...

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Moore, John A.; Barton, Nathan R.; Florando, Jeff; Mulay, Rupalee; Kumar, Mukul

2017-10-01

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material’s structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V’s mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments or lower fidelity models. The results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.

Magma oceanography. I - Thermal evolution. [of lunar surface

NASA Technical Reports Server (NTRS)

Solomon, S. C.; Longhi, J.

1977-01-01

Fractional crystallization and flotation of cumulate plagioclase in a cooling 'magma ocean' provides the simplest explanation for early emplacement of a thick feldspar-rich lunar crust. The complementary mafic cumulates resulting from the differentiation of such a magma ocean have been identified as the ultimate source of mare basalt liquids on the basis or rare-earth abundance patterns and experimental petrology studies. A study is conducted concerning the thermal evolution of the early differentiation processes. A range of models of increasing sophistication are considered. The models developed contain the essence of the energetics and the time scale for magma ocean differentiation. Attention is given to constraints on a magma ocean, modeling procedures, single-component magma oceans, fractionating magma oceans, and evolving magma oceans.

Energy-Constrained Recharge, Assimilation, and Fractional Crystallization (EC-RAχFC): A Visual Basic computer code for calculating trace element and isotope variations of open-system magmatic systems

NASA Astrophysics Data System (ADS)

Bohrson, Wendy A.; Spera, Frank J.

2007-11-01

Volcanic and plutonic rocks provide abundant evidence for complex processes that occur in magma storage and transport systems. The fingerprint of these processes, which include fractional crystallization, assimilation, and magma recharge, is captured in petrologic and geochemical characteristics of suites of cogenetic rocks. Quantitatively evaluating the relative contributions of each process requires integration of mass, species, and energy constraints, applied in a self-consistent way. The energy-constrained model Energy-Constrained Recharge, Assimilation, and Fractional Crystallization (EC-RaχFC) tracks the trace element and isotopic evolution of a magmatic system (melt + solids) undergoing simultaneous fractional crystallization, recharge, and assimilation. Mass, thermal, and compositional (trace element and isotope) output is provided for melt in the magma body, cumulates, enclaves, and anatectic (i.e., country rock) melt. Theory of the EC computational method has been presented by Spera and Bohrson (2001, 2002, 2004), and applications to natural systems have been elucidated by Bohrson and Spera (2001, 2003) and Fowler et al. (2004). The purpose of this contribution is to make the final version of the EC-RAχFC computer code available and to provide instructions for code implementation, description of input and output parameters, and estimates of typical values for some input parameters. A brief discussion highlights measures by which the user may evaluate the quality of the output and also provides some guidelines for implementing nonlinear productivity functions. The EC-RAχFC computer code is written in Visual Basic, the programming language of Excel. The code therefore launches in Excel and is compatible with both PC and MAC platforms. The code is available on the authors' Web sites http://magma.geol.ucsb.edu/and http://www.geology.cwu.edu/ecrafc) as well as in the auxiliary material.

Concanavalin A-binding cholesterol crystallization inhibiting and promoting activity in bile from patients with Crohn's disease compared to patients with ulcerative colitis.

PubMed

Keulemans, Y C; Mok, K S; Slors, J F; Brink, M A; Gouma, D J; Tytgat, G N; Groen, A K

1999-10-01

Crohn's disease is a risk factor for gallstone formation. In contrast, patients with ulcerative colitis have an incidence of gallstone formation comparable to the general population. The reason for this difference is not known. The aim of this study was to elucidate the factors controlling cholesterol crystallization in gallbladder bile of Crohn's disease and ulcerative colitis patients. Gallbladder bile was obtained by aspiration during bowel resections (26 Crohn's disease patients, 20 ulcerative colitis patients). Biliary lipid composition, crystal detection time and the effect of extraction of the concanavalin A-binding fraction on crystal formation were determined. Cholesterol crystals were present in seven of the 26 bile samples of Crohn's disease-patients and one of the 20 ulcerative colitis patients. Four of the bile samples of Crohn's disease patients were fast nucleating. None of the 20 ulcerative colitis patients had fast nucleating bile. Lipid composition, total lipid concentration and CSI were not significantly different between the two groups. In Crohn's disease patients extraction of concanavalin A-binding fraction decreased crystallization in 10 bile samples but accelerated crystallization in one bile sample. In eight bile samples from ulcerative colitis patients crystallization increased after concanavalin A-binding fraction extraction. Compared to ulcerative colitis patients, gallbladder bile of Crohn's disease patients showed increased cholesterol crystallization despite comparable lipid composition and cholesterol saturation index. This difference is caused by increased cholesterol crystallization-promoting activity. Bile from ulcerative colitis patients contains a Con A-binding factor which inhibits cholesterol crystallization.

Fractional conductivity in 2D and 3D crystals

NASA Astrophysics Data System (ADS)

Sidharth, B. G.; Das, Abhishek; Valluri, S. R.

2018-04-01

In this work, we show that the phenomenon of fractional quantum Hall effect can be obtained for 2D and 3D crystal structures, using the noncommutative nature of spacetime and the Lambert W function. This fractional conductivity has been shown to be a consequence of the noncommutative geometry underlying the structure of graphene. Also, it has been shown, for graphene, that in the 3D case the conductivity is extremely small and depends on the self-energy that arises due to random fluctuations or zitterbewegung.

Monitoring of Batch Industrial Crystallization with Growth, Nucleation, and Agglomeration. Part 2: Structure Design for State Estimation with Secondary Measurements

PubMed Central

2017-01-01

This work investigates the design of alternative monitoring tools based on state estimators for industrial crystallization systems with nucleation, growth, and agglomeration kinetics. The estimation problem is regarded as a structure design problem where the estimation model and the set of innovated states have to be chosen; the estimator is driven by the available measurements of secondary variables. On the basis of Robust Exponential estimability arguments, it is found that the concentration is distinguishable with temperature and solid fraction measurements while the crystal size distribution (CSD) is not. Accordingly, a state estimator structure is selected such that (i) the concentration (and other distinguishable states) are innovated by means of the secondary measurements processed with the geometric estimator (GE), and (ii) the CSD is estimated by means of a rigorous model in open loop mode. The proposed estimator has been tested through simulations showing good performance in the case of mismatch in the initial conditions, parametric plant-model mismatch, and noisy measurements. PMID:28890604

Monitoring of Batch Industrial Crystallization with Growth, Nucleation, and Agglomeration. Part 2: Structure Design for State Estimation with Secondary Measurements.

PubMed

Porru, Marcella; Özkan, Leyla

2017-08-30

This work investigates the design of alternative monitoring tools based on state estimators for industrial crystallization systems with nucleation, growth, and agglomeration kinetics. The estimation problem is regarded as a structure design problem where the estimation model and the set of innovated states have to be chosen; the estimator is driven by the available measurements of secondary variables. On the basis of Robust Exponential estimability arguments, it is found that the concentration is distinguishable with temperature and solid fraction measurements while the crystal size distribution (CSD) is not. Accordingly, a state estimator structure is selected such that (i) the concentration (and other distinguishable states) are innovated by means of the secondary measurements processed with the geometric estimator (GE), and (ii) the CSD is estimated by means of a rigorous model in open loop mode. The proposed estimator has been tested through simulations showing good performance in the case of mismatch in the initial conditions, parametric plant-model mismatch, and noisy measurements.

A Study of the Optical Properties of Ice Crystals with Black Carbon Inclusions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arienti, Marco; Yang, Xiaoyuan; Kopacz, Adrian M

2015-09-01

The report focu ses on the modification of the optical properties of ice crystals due to atmospheric black car bon (BC) contamination : the objective is to advance the predictive capabilities of climate models through an improved understanding of the radiative properties of compound particles . The shape of the ice crystal (as commonly found in cirrus clouds and cont rails) , the volume fraction of the BC inclusion , and its location inside the crystal are the three factors examined in this study. In the multiscale description of this problem, where a small absorbing inclusion modifies the optical propertiesmore » of a much la rger non - absorbing particle, state - of - the - art discretization techniques are combined to provide the best compromise of flexibility and accuracy over a broad range of sizes .« less

Evidence for Cyclical Fractional Crystallization, Recharge, and Assimilation in Basalts of the Kimama Core, Central Snake River Plain, Idaho: A 5.5-million-year Highlight Reel of Petrogenetic processes in a Mid-Crustal Sill Complex

NASA Astrophysics Data System (ADS)

Potter, Katherine E.; Shervais, John W.; Christiansen, Eric H.; Vetter, Scott K.

2018-02-01

Basalts erupted in the Snake River Plain of central Idaho and sampled in the Kimama drill core link eruptive processes to the construction of mafic intrusions over 5.5 Ma. Cyclic variations in basalt composition reveal temporal chemical heterogeneity related to fractional crystallization and the assimilation of previously-intruded mafic sills. A range of compositional types are identified within 1912 m of continuous drill core: Snake River olivine tholeiite (SROT), low K SROT, high Fe-Ti, and evolved and high K-Fe lavas similar to those erupted at Craters of the Moon National Monument. Detailed lithologic and geophysical logs document 432 flow units comprising 183 distinct lava flows and 78 flow groups. Each lava flow represents a single eruptive episode, while flow groups document chemically and temporally related flows that formed over extended periods of time. Temporal chemical variation demonstrates the importance of source heterogeneity and magma processing in basalt petrogenesis. Low-K SROT and high Fe-Ti basalts are genetically related to SROT as, respectively, hydrothermally-altered and fractionated daughters. Cyclic variations in the chemical composition of Kimama flow groups are apparent as 21 upward fractionation cycles, six recharge cycles, eight recharge-fractionation cycles, and five fractionation-recharge cycles. We propose that most Kimama basalt flows represent typical fractionation and recharge patterns, consistent with the repeated influx of primitive SROT parental magmas and extensive fractional crystallization coupled with varying degrees of assimilation of gabbroic to ferrodioritic sills at shallow to intermediate depths over short durations. Trace element models show that parental SROT basalts were generated by 5-10% partial melting of enriched mantle at shallow depths above the garnet-spinel lherzolite transition. The distinctive evolved and high K-Fe lavas are rare. Found at four depths, 319 m, 1045 m, 1078 m, and 1189 m, evolved and high K-Fe flows are compositionally unrelated to SROT magmas and represent highly fractionated basalt, probably accompanied by crustal assimilation. These evolved lavas may be sourced from the Craters of the Moon/Great Rift system to the northeast. The Kimama drill core is the longest record of geochemical variation in the central Snake River Plain and reinforces the concept of magma processing in a layered complex.

Crystal fractionation in the SNC meteorites: Implications for sample selection

NASA Technical Reports Server (NTRS)

Treiman, Allan H.

1988-01-01

Almost all rock types in the SNC meteorites are cumulates, products of magma differentiation by crystal fractionation (addition or removal of crystals). If the SNC meteorites are from the surface of Mars or near subsurface, then most of the igneous units on Mars are differentiated. Basaltic units probably experienced minor to moderate differientation, but ultrabasic units probably experienced extreme differentiation. Products of this differentiation may include Fe-rich gabbro, pyroxenite, periodotite (and thus serpentine), and possibly massive sulfides. The SNC meteorites include ten lithologies (three in EETA79001), eight of which are crystal cumulates. The other lithologies, EETA79001 A and B are subophitic basalts.

Rheological flow laws for multiphase magmas: An empirical approach

NASA Astrophysics Data System (ADS)

Pistone, Mattia; Cordonnier, Benoît; Ulmer, Peter; Caricchi, Luca

2016-07-01

The physical properties of magmas play a fundamental role in controlling the eruptive dynamics of volcanoes. Magmas are multiphase mixtures of crystals and gas bubbles suspended in a silicate melt and, to date, no flow laws describe their rheological behaviour. In this study we present a set of equations quantifying the flow of high-viscosity (> 105 Pa·s) silica-rich multiphase magmas, containing both crystals (24-65 vol.%) and gas bubbles (9-12 vol.%). Flow laws were obtained using deformation experiments performed at high temperature (673-1023 K) and pressure (200-250 MPa) over a range of strain-rates (5 · 10- 6 s- 1 to 4 · 10- 3 s- 1), conditions that are relevant for volcanic conduit processes of silica-rich systems ranging from crystal-rich lava domes to crystal-poor obsidian flows. We propose flow laws in which stress exponent, activation energy, and pre-exponential factor depend on a parameter that includes the volume fraction of weak phases (i.e. melt and gas bubbles) present in the magma. The bubble volume fraction has opposing effects depending on the relative crystal volume fraction: at low crystallinity bubble deformation generates gas connectivity and permeability pathways, whereas at high crystallinity bubbles do not connect and act as ;lubricant; objects during strain localisation within shear bands. We show that such difference in the evolution of texture is mainly controlled by the strain-rate (i.e. the local stress within shear bands) at which the experiments are performed, and affect the empirical parameters used for the flow laws. At low crystallinity (< 44 vol.%) we observe an increase of viscosity with increasing strain-rate, while at high crystallinity (> 44 vol.%) the viscosity decreases with increasing strain-rate. Because these behaviours are also associated with modifications of sample textures during the experiment and, thus, are not purely the result of different deformation rates, we refer to ;apparent shear-thickening; and ;apparent shear-thinning; for the behaviours observed at low and high crystallinity, respectively. At low crystallinity, increasing deformation rate favours the transfer of gas bubbles in regions of high strain localisation, which, in turn, leads to outgassing and the observed increase of viscosity with increasing strain-rate. At high crystallinity gas bubbles remain trapped within crystals and no outgassing occurs, leading to strain localisation in melt-rich shear bands and to a decrease of viscosity with increasing strain-rate, behaviour observed also in crystal-bearing suspensions. Increasing the volume fraction of weak phases induces limited variation of the stress exponent and pre-exponential factor in both apparent shear-thickening and apparent shear-thinning regimes; conversely, the activation energy is strongly dependent on gas bubble and melt volume fractions. A transient rheology from apparent shear-thickening to apparent shear-thinning behaviour is observed for a crystallinity of 44 vol.%. The proposed equations can be implemented in numerical models dealing with the flow of crystal- and bubble-bearing magmas. We present results of analytical simulations showing the effect of the rheology of three-phase magmas on conduit flow dynamics, and show that limited bubble volumes (< 10 vol.%) lead to strain localisation at the conduit margins during the ascent of crystal-rich lava domes and crystal-poor obsidian flows.

Aerosol processing in mixed-phase clouds in ECHAM5-HAM: Model description and comparison to observations

NASA Astrophysics Data System (ADS)

Hoose, C.; Lohmann, U.; Stier, P.; Verheggen, B.; Weingartner, E.

2008-04-01

The global aerosol-climate model ECHAM5-HAM has been extended by an explicit treatment of cloud-borne particles. Two additional modes for in-droplet and in-crystal particles are introduced, which are coupled to the number of cloud droplet and ice crystal concentrations simulated by the ECHAM5 double-moment cloud microphysics scheme. Transfer, production, and removal of cloud-borne aerosol number and mass by cloud droplet activation, collision scavenging, aqueous-phase sulfate production, freezing, melting, evaporation, sublimation, and precipitation formation are taken into account. The model performance is demonstrated and validated with observations of the evolution of total and interstitial aerosol concentrations and size distributions during three different mixed-phase cloud events at the alpine high-altitude research station Jungfraujoch (Switzerland). Although the single-column simulations cannot be compared one-to-one with the observations, the governing processes in the evolution of the cloud and aerosol parameters are captured qualitatively well. High scavenged fractions are found during the presence of liquid water, while the release of particles during the Bergeron-Findeisen process results in low scavenged fractions after cloud glaciation. The observed coexistence of liquid and ice, which might be related to cloud heterogeneity at subgrid scales, can only be simulated in the model when assuming nonequilibrium conditions.

Slow positrons in the study of surface and near-surface defects

NASA Astrophysics Data System (ADS)

Lynn, K. G.

A general theoretical model is presented which includes the probability of a positron diffusing back to the surface after implantation, and thermalization in samples containing various defects. This model incorporates surface state and thermal desorption from this state, as well as reflection back into the bulk. With this model vacancy formation enthalpies, activation energies of positrons from surface states, and specific trapping rates are deduced from the positronium fraction data. An amorphous Al/sub x/O/sub y/ overlayer on Al is discussed as an example of trapping in overlayers. In well-annealed single crystal samples, the positron is shown to be freely diffusing at low temperatures, whereas in a neutron-irradiatied Al single crystal sample the positron is localized at low positron binding energy defects presumably created during irradiation.

Scales of magmatic replenishment and differentiation on an intermediate spreading mid-ocean ridge segment: Endeavour, Juan de Fuca Ridge

NASA Astrophysics Data System (ADS)

Dreyer, B. M.; Gill, J.; Clague, D. A.

2016-12-01

The aggregate chemistry of mid-ocean ridge (MOR) basalts cannot be produced by fractional crystallization alone. Recent modeling suggests that repeated magmatic replenishment is required (O'Neill and Jenner, 2012; Coogan and O'Hara, 2015; Shorttle, 2015). Does this inference hold when considering recent advancements in characterizing geological/volcanological context, geochemical variability, and temporal parameters on the scale of individual lava units (Rubin et al., 2009)? We evaluate the scales of magmatic replenishment through examination of compositionally diverse lavas from the Endeavour segment of the Juan de Fuca (JdF) MOR interpreted as comagmatic or coeruptive based on robust geological (Clague et al., 2014), geochemical (Gill et al., 2016), and geochronological (Jamieson et al., 2013; Clague et al., 2014) evidence. This approach is similar to that used for historical MOR eruptions (Rubin et al., 2001). We identified 15 "chemomagmatic" units that are spatially proximate and chemically relatable and separable that collectively represent eruptions since 11ka. Some units may be single lava flows. Other units appear to have erupted batches intermittently over hundreds to thousands of years during which chemically dissimilar lava also erupted. Melt evolution was modeled using MELTS for units with reasonably broad major element variations. Fractional crystallization models can adequately reproduce most of the major and incompatible trace element behavior observed within each unit. Consistent differences in trace element ratios between units argue against intermixing. Thus, magmatic batches typically lie within analytical resolution of fractional crystallizing systems, notwithstanding growing evidence that magmatic systems are repeatedly replenished at the segment scale. Melting and mixing of heterogeneous mantle sources are responsible for the overall compositional diversity at Endeavour. Chemomagmatic units, in contrast, reflect smaller scale processing of magma after exiting the melt column during ascent through the crust. Age and spatial relationships among the chemomagmatic units reflect fluctuations in productivity and composition during assembly of primitive mantle melts and the geometry of networked magma-hosting reservoirs.

SU-C-201-01: Investigation of the Effects of Scintillator Surface Treatment On Light Output Measurements with SiPM Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valenciaga, Y; Prout, D; Chatziioannou, A

2015-06-15

Purpose: To examine the effect of different scintillator surface treatments (BGO crystals) on the fraction of scintillation photons that exit the crystal and reach the photodetector (SiPM). Methods: Positron Emission Tomography is based on the detection of light that exits scintillator crystals, after annihilation photons deposit energy inside these crystals. A considerable fraction of the scintillation light gets trapped or absorbed after going through multiple internal reflections on the interfaces surrounding the crystals. BGO scintillator crystals generate considerably less scintillation light than crystals made of LSO and its variants. Therefore, it is crucial that the small amount of light producedmore » by BGO exits towards the light detector. The surface treatment of scintillator crystals is among the factors affecting the ability of scintillation light to reach the detectors. In this study, we analyze the effect of different crystal surface treatments on the fraction of scintillation light that is detected by the solid state photodetector (SiPM), once energy is deposited inside a BGO crystal. Simulations were performed by a Monte Carlo based software named GATE, and validated by measurements from individual BGO crystals coupled to Philips digital-SiPM sensor (DPC-3200). Results: The results showed an increment in light collection of about 4 percent when only the exit face of the BGO crystal, is unpolished; compared to when all the faces are polished. However, leaving several faces unpolished caused a reduction of at least 10 percent of light output when the interaction occurs as far from the exit face of the crystal as possible compared to when it occurs very close to the exit face. Conclusion: This work demonstrates the advantages on light collection from leaving unpolished the exit face of BGO crystals. The configuration with best light output will be used to obtain flood images from BGO crystal arrays coupled to SiPM sensors.« less

Red Sea rift-related Quseir basalts, central Eastern Desert, Egypt: Petrogenesis and tectonic processes

NASA Astrophysics Data System (ADS)

Farahat, Esam S.; Ali, Shehata; Hauzenberger, Christoph

2017-01-01

Mineral and whole-rock chemistry of Red Sea rift-related Tertiary basalts from south Quseir city, central Eastern Desert of Egypt is presented to investigate their petrogenesis and relationship to tectonic processes. The south Quseir basalts (SQB) are classified as high-Ti (TiO2 >2 wt.%) subalkaline transitional lava emplaced in an anorogenic tectonic setting. Their Mg# varies from 48 to 53 indicating the evolved nature of the SQB. Pearce element ratios suggest that the SQB magmas evolved via fractional crystallization of olivine + clinopyroxene ± plagioclase, but the absence of Eu anomalies argues against significant plagioclase fractionation. Clinopyroxene compositions provide evidence for polybaric fractionation of the parental mafic magmas. Estimated temperatures of crystallization are 1015 to 1207 °C for clinopyroxene and 1076 to 1155 °C for plagioclase. These values are interpreted to result from early stage crystallization of clinopyroxene followed by concurrent crystallization of clinopyroxene and plagioclase. The incompatible trace element signatures of the SQB (La/Ba = 0.08-0.10 and La/Nb = 0.89-1.04) are comparable to those of ocean island basalts (OIB) generated from an asthenospheric mantle source unaffected by subduction components. Modeling calculations indicate that the SQB primary magmas were derived from 4-5% partial melting of a garnet-bearing lherzolite mantle source. The NE Egyptian basaltic volcanism is spatially and temporally related to Red Sea rifting and to the local E-W striking faults, confirming a relationship to tectonic activity. Our results suggest that the extensional regime associated with Red Sea rifting controlled the generation of the Egyptian basalts, likely as a result of passive upwelling of asthenospheric mantle.

Substructure based modeling of nickel single crystals cycled at low plastic strain amplitudes

NASA Astrophysics Data System (ADS)

Zhou, Dong

In this dissertation a meso-scale, substructure-based, composite single crystal model is fully developed from the simple uniaxial model to the 3-D finite element method (FEM) model with explicit substructures and further with substructure evolution parameters, to simulate the completely reversed, strain controlled, low plastic strain amplitude cyclic deformation of nickel single crystals. Rate-dependent viscoplasticity and Armstrong-Frederick type kinematic hardening rules are applied to substructures on slip systems in the model to describe the kinematic hardening behavior of crystals. Three explicit substructure components are assumed in the composite single crystal model, namely "loop patches" and "channels" which are aligned in parallel in a "vein matrix," and persistent slip bands (PSBs) connected in series with the vein matrix. A magnetic domain rotation model is presented to describe the reverse magnetostriction of single crystal nickel. Kinematic hardening parameters are obtained by fitting responses to experimental data in the uniaxial model, and the validity of uniaxial assumption is verified in the 3-D FEM model with explicit substructures. With information gathered from experiments, all control parameters in the model including hardening parameters, volume fraction of loop patches and PSBs, and variation of Young's modulus etc. are correlated to cumulative plastic strain and/or plastic strain amplitude; and the whole cyclic deformation history of single crystal nickel at low plastic strain amplitudes is simulated in the uniaxial model. Then these parameters are implanted in the 3-D FEM model to simulate the formation of PSB bands. A resolved shear stress criterion is set to trigger the formation of PSBs, and stress perturbation in the specimen is obtained by several elements assigned with PSB material properties a priori. Displacement increment, plastic strain amplitude control and overall stress-strain monitor and output are carried out in the user subroutine DISP and URDFIL of ABAQUS, respectively, while constitutive formulations of the FEM model are coded and implemented in UMAT. The results of the simulations are compared to experiments. This model verified the validity of Winter's two-phase model and Taylor's uniform stress assumption, explored substructure evolution and "intrinsic" behavior in substructures and successfully simulated the process of PSB band formation and propagation.

Uncertainty associated with convective wet removal of entrained aerosols in a global climate model

NASA Astrophysics Data System (ADS)

Croft, B.; Pierce, J. R.; Martin, R. V.; Hoose, C.; Lohmann, U.

2012-11-01

The uncertainties associated with the wet removal of aerosols entrained above convective cloud bases are investigated in a global aerosol-climate model (ECHAM5-HAM) under a set of limiting assumptions for the wet removal of the entrained aerosols. The limiting assumptions for the wet removal of entrained aerosols are negligible scavenging and vigorous scavenging (either through activation, with size-dependent impaction scavenging, or with the prescribed fractions of the standard model). To facilitate this process-based study, an explicit representation of cloud-droplet-borne and ice-crystal-borne aerosol mass and number, for the purpose of wet removal, is introduced into the ECHAM5-HAM model. This replaces and is compared with the prescribed cloud-droplet-borne and ice-crystal-borne aerosol fraction scavenging scheme of the standard model. A 20% to 35% uncertainty in simulated global, annual mean aerosol mass burdens and optical depth (AOD) is attributed to different assumptions for the wet removal of aerosols entrained above convective cloud bases. Assumptions about the removal of aerosols entrained above convective cloud bases control modeled upper tropospheric aerosol concentrations by as much as one order of magnitude. Simulated aerosols entrained above convective cloud bases contribute 20% to 50% of modeled global, annual mean aerosol mass convective wet deposition (about 5% to 10% of the total dry and wet deposition), depending on the aerosol species, when including wet scavenging of those entrained aerosols (either by activation, size-dependent impaction, or with the prescribed fraction scheme). Among the simulations, the prescribed fraction and size-dependent impaction schemes yield the largest global, annual mean aerosol mass convective wet deposition (by about two-fold). However, the prescribed fraction scheme has more vigorous convective mixed-phase wet removal (by two to five-fold relative to the size-dependent impaction scheme) since nearly all entrained accumulation and coarse mode aerosols are assumed to be cloud-droplet borne or ice-crystal borne, and evaporation due to the Bergeron-Findeisen process is neglected. The simulated convective wet scavenging of entrained accumulation and coarse mode aerosols has feedbacks on new particle formation and the number of Aitken mode aerosols, which control stratiform and convective cloud droplet number concentrations and yield precipitation changes in the ECHAM5-HAM model. However, the geographic distribution of aerosol annual mean convective wet deposition change in the model is driven by changes to the assumptions regarding the scavenging of aerosols entrained above cloud bases rather than by precipitation changes, except for sea salt deposition in the tropics. Uncertainty in the seasonal, regional cycles of AOD due to assumptions about entrained aerosol wet scavenging is similar in magnitude to the estimated error in the AOD retrievals. The uncertainty in aerosol concentrations, burdens, and AOD attributed to different assumptions for the wet scavenging of aerosols entrained above convective cloud bases in a global model motivates the ongoing need to better understand and model the activation and impaction processes that aerosols undergo after entrainment into convective updrafts.

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, John A.; Barton, Nathan R.; Florando, Jeff

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE PAGES

Moore, John A.; Barton, Nathan R.; Florando, Jeff; ...

2017-08-24

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Geochemical studies of abyssal lavas recovered by DSRV Alvin from Eastern Galapagos Rift, Inca Transform, and Ecuador Rift: 2. Phase chemistry and crystallization history

NASA Astrophysics Data System (ADS)

Perfit, Michael R.; Fornari, Daniel J.

1983-12-01

A diverse suite of lavas recovered by DSRV Alvin from the eastern Galapagos rift and Inca transform includes mid-ocean ridge tholeiitic basalts (MORB), iron- and titanium-enriched basalts (FeTi basalts), and abyssal andesites. Rock types transitional in character (ferrobasalts and basaltic andesites) were also recovered. The most mafic glassy basalts contain plagioclase, augite, and olivine as near-liquidus phases, whereas in more fractionated basalts, pigeonite replaces olivine and iron-titanium oxides crystallize. Plagioclase crystallizes after pyroxenes and iron-titanium oxides in andesites, possibly due to increased water contents or cooling rates. Apatite phenocrysts are present in some andesitic glasses. Ovoid sulfide globules are also common in many lavas. Compositional variations of phenocrysts in glassy lavas reflect changes in magma chemistry, temperature of crystallization, and cooling rate. The overall chemical variations parallel the chemical evolution of the lava suite and are similar to those in other fractionated tholeiitic complexes. Elemental partitioning between plagioclase-, pyroxene-, and olivine-glass pairs suggests that equilibration occurred at low pressure in a rather restricted temperature range. Various geothermometers indicate that the most primitive MORB began to crystallize between 1150° and 1200°C with fo2 < 10-7 atm. Coexisting iron-titanium oxides in more evolved lavas yield temperatures ˜1025°C to as low as 910°C withfo2 from 10-8 to 10-12 atm. PH 2 o could have been as high as 1 kbar during andesite crystallization. Compositions of the lavas from the Galapagos rift follow the experimentally determined (1 atm-QFM) liquid line of descent. Least squares calculations for the major elements indicate that the entire suite of lavas can be produced by fractional crystallization of successive residual liquids from a MORB parent magma. FeTi basalts represent 30-65 cumulative weight percent crystallization of plagioclase, augite, and olivine. An additional 30-50% fractionation of pyroxenes, plagioclase, titanomagnetite, and possible apatite is required to generate andesite from FeTi basalt liquids. The presence of partially resorbed mafic xenocrysts in some andesites, FeTi basalt inclusions in these xenocrysts, high-silica glass inclusions in basaltic andesites, and the transitional chemistry of basaltic andesites are evidence that some magma mixing occurred during crystal fractionation. The diversity of lava types recovered at single dive sites suggests that low-pressure fractional crystallization is a very efficient process beneath the eastern Galapagos rift and that isolated magma bodies must be present at shallow levels beneath the accretionary locus. Voluminous FeTi basalts erupted at the rift-transform intersection are genetically related to the rift lavas, but their restricted chemistry reflects different thermal and tectonic controls on their petrogenesis.

Internal protein motions in molecular-dynamics simulations of Bragg and diffuse X-ray scattering.

PubMed

Wall, Michael E

2018-03-01

Molecular-dynamics (MD) simulations of Bragg and diffuse X-ray scattering provide a means of obtaining experimentally validated models of protein conformational ensembles. This paper shows that compared with a single periodic unit-cell model, the accuracy of simulating diffuse scattering is increased when the crystal is modeled as a periodic supercell consisting of a 2 × 2 × 2 layout of eight unit cells. The MD simulations capture the general dependence of correlations on the separation of atoms. There is substantial agreement between the simulated Bragg reflections and the crystal structure; there are local deviations, however, indicating both the limitation of using a single structure to model disordered regions of the protein and local deviations of the average structure away from the crystal structure. Although it was anticipated that a simulation of longer duration might be required to achieve maximal agreement of the diffuse scattering calculation with the data using the supercell model, only a microsecond is required, the same as for the unit cell. Rigid protein motions only account for a minority fraction of the variation in atom positions from the simulation. The results indicate that protein crystal dynamics may be dominated by internal motions rather than packing interactions, and that MD simulations can be combined with Bragg and diffuse X-ray scattering to model the protein conformational ensemble.

Internal protein motions in molecular-dynamics simulations of Bragg and diffuse X-ray scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wall, Michael E.

Molecular-dynamics (MD) simulations of Bragg and diffuse X-ray scattering provide a means of obtaining experimentally validated models of protein conformational ensembles. This paper shows that compared with a single periodic unit-cell model, the accuracy of simulating diffuse scattering is increased when the crystal is modeled as a periodic supercell consisting of a 2 × 2 × 2 layout of eight unit cells. The MD simulations capture the general dependence of correlations on the separation of atoms. There is substantial agreement between the simulated Bragg reflections and the crystal structure; there are local deviations, however, indicating both the limitation of using a single structuremore » to model disordered regions of the protein and local deviations of the average structure away from the crystal structure. Although it was anticipated that a simulation of longer duration might be required to achieve maximal agreement of the diffuse scattering calculation with the data using the supercell model, only a microsecond is required, the same as for the unit cell. Rigid protein motions only account for a minority fraction of the variation in atom positions from the simulation. The results indicate that protein crystal dynamics may be dominated by internal motions rather than packing interactions, and that MD simulations can be combined with Bragg and diffuse X-ray scattering to model the protein conformational ensemble.« less

Internal protein motions in molecular-dynamics simulations of Bragg and diffuse X-ray scattering

DOE PAGES

Wall, Michael E.

2018-01-25

Molecular-dynamics (MD) simulations of Bragg and diffuse X-ray scattering provide a means of obtaining experimentally validated models of protein conformational ensembles. This paper shows that compared with a single periodic unit-cell model, the accuracy of simulating diffuse scattering is increased when the crystal is modeled as a periodic supercell consisting of a 2 × 2 × 2 layout of eight unit cells. The MD simulations capture the general dependence of correlations on the separation of atoms. There is substantial agreement between the simulated Bragg reflections and the crystal structure; there are local deviations, however, indicating both the limitation of using a single structuremore » to model disordered regions of the protein and local deviations of the average structure away from the crystal structure. Although it was anticipated that a simulation of longer duration might be required to achieve maximal agreement of the diffuse scattering calculation with the data using the supercell model, only a microsecond is required, the same as for the unit cell. Rigid protein motions only account for a minority fraction of the variation in atom positions from the simulation. The results indicate that protein crystal dynamics may be dominated by internal motions rather than packing interactions, and that MD simulations can be combined with Bragg and diffuse X-ray scattering to model the protein conformational ensemble.« less

Determination of Ice Cloud Models Using MODIS and MISR Data

NASA Technical Reports Server (NTRS)

Xie, Yu; Yang, Ping; Kattawar, George W.; Minnis, Patrick; Hu, Yongxiang; Wu, Dong L.

2012-01-01

Representation of ice clouds in radiative transfer simulations is subject to uncertainties associated with the shapes and sizes of ice crystals within cirrus clouds. In this study, we examined several ice cloud models consisting of smooth, roughened, homogeneous and inhomogeneous hexagonal ice crystals with various aspect ratios. The sensitivity of the bulk scattering properties and solar reflectances of cirrus clouds to specific ice cloud models is investigated using the improved geometric optics method (IGOM) and the discrete ordinates radiative transfer (DISORT) model. The ice crystal habit fractions in the ice cloud model may significantly affect the simulations of cloud reflectances. A new algorithm was developed to help determine an appropriate ice cloud model for application to the satellite-based retrieval of ice cloud properties. The ice cloud particle size retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS) data, collocated with Multi-angle Imaging Spectroradiometer (MISR) observations, is used to infer the optical thicknesses of ice clouds for nine MISR viewing angles. The relative differences between view-dependent cloud optical thickness and the averaged value over the nine MISR viewing angles can vary from -0.5 to 0.5 and are used to evaluate the ice cloud models. In the case for 2 July 2009, the ice cloud model with mixed ice crystal habits is the best fit to the observations (the root mean square (RMS) error of cloud optical thickness reaches 0.365). This ice cloud model also produces consistent cloud property retrievals for the nine MISR viewing configurations within the measurement uncertainties.

Early differentiation of the Moon: Experimental and modeling studies and experimental and modeling studies of massif anorthosites

NASA Technical Reports Server (NTRS)

Longhi, John

1994-01-01

NASA grant NAG9-329 was in effect from 3/1/89 to 8/31/94, the last 18 months being a no-cost extension. While the grant was in effect, the P.I., coworkers, and students gave 22 talks and poster sessions at professional meetings, published 12 articles in referred journals (one more is in press, and another is in review), and edited 2 workshop reports relevant to this project. Copies of all the publications are appended to this report. The major accomplishments during the grant period have derived from three quarters: 1) the application of quantitative models of fractional crystallization and partial melting to various problems in planetary science, such as the petrogenesis of picritic glasses and mare basalts and the implications of the SNC meteorites for martian evolution; 2) an experimental study of silicate liquid immiscibility relevant to early lunar differentiation and the petrogenesis of evolved highlands rocks; and 3) experimental studies of massif anorthosites and related rocks that provide terrestrial analogs for the proposed origin of lunar anorthosites by multistage processes. The low-pressure aspects of the quantitative models were developed by the P.I. in the 1980s with NASA support and culminated with a paper comparing the crystallization of terrestrial and lunar lavas. The basis for the high-pressure modifications to the quantitative models is a data set gleaned from high pressure melting experiments done at Lamont and is supplemented by published data from other labs that constrain the baric and compositional dependences of various liquidus phase boundaries such as olivine/orthopyroxene, relevant to the melting of the mantles of the terrestrial planets. With these models it is possible to predict not only the thermal and compositional evolution of magmatic liquids ranging in composition from lumar mare basalt to terrestrial calc-alkaline basalts, but also the small increments of fractional melting that are produced when mantle rises adiabatically. Copies of the crystallization/melting programs have been given to several colleagues in planetary science. Additionally, a series of computer graphics programs, based on the algorithms in the crystallization programs have been developed that display liquidus diagrams appropriate to input compositions.

Predicting equilibrium uranium isotope fractionation in crystals and solution

NASA Astrophysics Data System (ADS)

Schauble, E. A.

2015-12-01

Despite the rapidly growing interest in using 238U/235U measurements as a proxy for changes in oxygen abundance in surface and near-surface environments, the present theoretical understanding of uranium isotope fractionation is limited to a few simple gas-phase molecules and analogues of dissolved species (e.g., 1,2,3). Understanding uranium isotope fractionation behavior in more complicated species, such as crystals and adsorption complexes, will help in the design and interpretation of experiments and field studies, and may suggest other uses for 38U/235U measurements. In this study, a recently developed first-principles method for estimating the nuclear volume component of field shift fractionation in crystals and complex molecular species (4) is combined with mass-dependent fractionation theory to predict equilibrium 38U/235U fractionations in aqueous and crystalline uranium compounds, including uraninite (UO2). The nuclear field shift effect, caused by the interaction of electrons with the finite volume of the positive charge distribution in uranium nuclei, is estimated using Density Functional Theory and the Projector Augmented Wave method (DFT-PAW). Tests against relativistic electronic structure calculations and Mössbauer isomer shift data indicate that the DFT-PAW method is reasonably accurate, while being much better suited to models of complex and crystalline species. Initial results confirm previous predictions that the nuclear volume effect overwhelms mass depdendent fractionation in U(VI)-U(IV) exchange reactions, leading to higher 238U/235U in U(IV) species (i.e., for UO2 xtal vs. UO22+aq, ln αNV ≈ +1.8‰ , ln αMD ≈ -0.8‰, ln αTotal ≈ +1.0‰ at 25ºC). UO2 and U(H2O)94+, are within ~0.4‰ of each other, while U(VI) species appear to be more variable. This suggests that speciation is likely to significantly affect natural uranium isotope fractionations, in addition to oxidation state. Tentatively, it appears that uranyl-type (UO22+-bearing) structures will tend to have higher 238U/235U than uranate-type structures that lack strong U=O bonds. References: 1. Bigeleisen (1996) JACS 118:3676; 2. Schauble (2006) Eos 87:V21B-0570; 3. Abe et al. (2008) J Chem Phys 128:144309, 129:164309, & Abe et al. (2010) J Chem Phys 133:044309; 4. Schauble (2013) PNAS 110:17714.

Rocks of the early lunar crust

NASA Technical Reports Server (NTRS)

James, O. B.

1980-01-01

Data are summarized which suggest a model for the early evolution of the lunar crust. According to the model, during the final stages of accretion, the outer part of the moon melted to form a magma ocean approximately 300 km deep. This ocean fractionated to form mafic and ultramafic cumulates at depth and an overlying anorthositic crust made up of ferroan anorthosites. Subsequent partial melting in the primitive mantle underlying the crystallized magma ocean produced melts which segregated, moved upward, intruded the primordial crust, and crystallized to form layered plutons consisting of Mg-rich plutonic rocks. Intense impact bombardment at the lunar surface mixed and melted the rocks of the two suites to form a thick layer of granulated debris, granulitic breccias, and impact-melt rocks.

Thermochronological evolution of an intra-plate magmatic event inferred from an integrated modeling approach: A case study in the Westerwald, Germany

NASA Astrophysics Data System (ADS)

Tirone, M.; Rokitta, K.; Schreiber, U.

2016-09-01

A lava sample from the Tertiary Westerwald volcanic field was selected for a detailed study using various analytical techniques in combination with petrological, thermodynamic and diffusion modeling to extract information related to the thermochronological evolution of a magmatic event before eruption. The lava sample contains large olivine phenocrysts which are compositionally zoned and two coexisting but chemically distinct melts, a host melt with basaltic composition and small spherical pockets of a less abundant trachytic melt (globules). The sample was analyzed by electron microprobe, x-ray fluorescence (XRF) X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). The primary melt of the host lava was determined using the program PRIMELT2.XLS. Partial fractional crystallization of olivine was modeled using the program alphaMELTS. Timescale and cooling rate were retrieved by fitting the measured Fe-Mg zoning along two directions in four olivine grains from the host lava using a 3-D numerical diffusion model. The measured variation of Ca is also consistent with a chemical diffusion process, while a numerical growth model applied to the same olivines does not appear to explain the Fe-Mg zoning. Chemical zoning of major elements in the melt globules were reproduced with a multicomponent diffusion model. The results of this study show that the host magma fractionated about 9% of olivine in a first stage, then the crystallization proceeded without further separation of mineral phases. Modeling of diffusion in the olivine crystals suggests that this second stage lasted at least 5 yrs and the temperature of the melt decreased from 1120-1150 °C to 1090 °C during this time. According to the results of the multicomponent diffusion model applied to the melt globules, the coexistence of the two melts was extremely short (less than few hours), possibly recording the assimilation of the globules during eruption or cooling of the whole system on the surface.

Reflectance properties of one-dimensional metal-dielectric ternary photonic crystal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pandey, G. N., E-mail: gnpandey2009@gmail.com; Kumar, Narendra; Thapa, Khem B.

2016-05-06

Metallic photonic crystal has a very important application in absorption enhancement in solar cells. It has been found that an ultra-thin metallic layer becomes transparent due to internal scattering of light through the each interface of the dielectric and metal surfaces. The metal has absorption due to their surface plasmon and the plasmon has important parameters for changing optical properties of the metal. We consider ternary metallic-dielectric photonic crystal (MDPC) for having large probabilities to change the optical properties of the MDPC and the photonic crystals may be changed by changing dimensionality, symmetry, lattice parameters, Filling fraction and effective refractivemore » index refractive index contrast. In this present communication, we try to show that the photonic band gap in ternary metal-dielectric photonic crystal can be significantly enlarged when air dielectric constant is considered. All the theoretical analyses are made based on the transfer matrix method together with the Drude model of metal.« less

Origin of howardites, diogenites and eucrites - A mass balance constraint

NASA Technical Reports Server (NTRS)

Warren, P. H.

1985-01-01

Two petrogenetic models for the noncumulate-basaltic parts of howardite meteorites are discussed. A mass balance constraint is developed which indicates that more than half of the basaltic components in howardites formed as residual liquids from fractional crystallization of melts that had earlier produced diogentelike pyroxene cumulate components. Other model constriants involving scandium trends, clustering near olivine-pyroxene-plagioclase peritectic, and MgO/(MgO + FeO) ratios are discussed.

Trondhjemitic melts produced by in-situ differentiation of a tholeiitic lava flow, Reykjanes Peninsula, Iceland.

NASA Astrophysics Data System (ADS)

Martin, E.; Sigmarsson, O.

2006-12-01

How the continental crust began to form early in Earth's history is unconstrained. However, it is reasonable to presume that higher heat flow in the past, resulted in more frequent interaction of mantle plumes and mid- oceanic ridges. If true, then Iceland could be a good analogue for processes occurring on Earth at its youth stage. This is supported by the relatively high abundance of silicic rocks in Iceland but their rarity on other oceanic hot spots. The origin of Icelandic silicic rocks has been a subject of a lively debate but has been shown to be principally formed by partial melting of hydrothermally altered basaltic crust. However, in rare cases, their origin by fractional crystallization from mantle derived basalts is suggested. Segregation veins in lava flows frequently contain interstitial glasses of silicic compositions. Moreover, they allow an exceptional overview of the fractional crystallization mechanism. These veins form by gas filter pressing during cooling and degassing of solidifying lava flows, after approximately 50% fractional crystallization of anhydrous minerals. Pairs of samples, host lava and associated segregation veins, from Reykjanes Peninsula (Iceland), Lanzarote (Canary Island) and Masaya's volcano (Nicaragua), allow the assessment of a near-complete fractional crystallization of olivine tholeiitic basalt at pressure close to one atmosphere. Interstitial glass patches in segregation veins represent the final product of this process (80 97 % of fractional crystallization). These ultimate liquids are of granitic composition in the case of Lanzarote and Masaya but overwhelmingly trondhjemitic at Reykjanes. It appears that the initial K2O/Na2O of the basaltic liquid controls the evolution path of the residual liquid composition produced at pressure close to 0.1 MPa (1 bar). Granitic liquids are generated from basalts of high initial K2O/Na2O whereas low initial K2O/Na2O leads to trondhjemitic compositions. The trondhjemitic composition of glass patches from the segregation vein at Reykjanes Peninsula differs from Icelandic silicic magmas but is close to those of the Archaean TTG (trondhjemite-tonalite-granodiorite) suite. Taken at face value, this may imply that fractional crystallisation of olivine tholeiites (low K2O/Na2O) could have played a significant role during the formation of the early continental crust. At higher pressure, where garnet is on liquidus, fractional crystallisation can generate the observed trace element patterns observed in TTG. The progressive cooling, crystallization and degassing of basaltic magma ocean, thought to have been prevailing during the Hadean, could have led to high degree of fractional crystallization producing significant volume of trondhjemitic melts that because of its buoyancy contributed to the formation of the earliest continental crust.

Optical properties of anisotropic 3D nanoparticles arrays

NASA Astrophysics Data System (ADS)

Santiago, E. Y.; Esquivel-Sirvent, R.

2017-07-01

The optical properties of 3D periodic arrays of spheroidal Au nanoparticles are calculated using a Bruggeman effective medium approximation. The optical response of the supra-crystal depends on the volume fraction of the nanoparticles and their aspect or size ratio (major/minor axis). All the nanoparticles have the same orientation, and this defines an anisotropic dielectric function of the crystal. As a function of the filling fraction, while keeping the size ratio fixed, the maximum in the extinction spectra along the major and minor axes does not show a significant change. However, for a fixed filling fraction, varying the aspect ratio of the particles induces a shift of several hundred of nanometers in the maximum of the extinction spectra along the major axis and almost no changes along the minor axis. Depending on the aspect ratio and the filling fraction, we show that the supra-crystal has three regimes with different values of an effective plasma frequency. Contribution to the Focus Issue Self-assemblies of Inorganic and Organic Nanomaterials edited by Marie-Paule Pileni.

Magma Chamber of the 26.5 ka Oruanui Eruption, Taupo Volcano, New Zealand

NASA Astrophysics Data System (ADS)

Liu, Y.; Anderson, A. T.; Wilson, C. J.; Davis, A. M.

2004-12-01

We have investigated melt inclusions and their host quartz crystals from the Bishop-Tuff-sized 26.5 ka Oruanui eruption at Taupo volcano, New Zealand. Compositions (major and trace elements, H2O and CO2) of melt inclusions and cathodoluminescence (CL) images of quartz were obtained for eight individual pumices from early, middle and late depositional units. All melt inclusions are high-silica weakly peraluminous rhyolites. Melt inclusions for different eruptive phases have similar ranges of H2O contents (3.8-5.2 wt %), but late-erupted samples have higher CO2 contents (mostly > 140 ppm). A positive correlation between CO2 and compatible trace elements such as Sr suggests that crystallization and melt entrapment occurred under gas-saturated conditions. Trace elements variations in melt inclusions are consistent with fractionation of 30-40 wt % crystals (plagioclase+quartz+pyroxene+amphibole). Crystal contents in pumices, trace-element contents in melt inclusions, and CL zoning patterns of quartz show no correlation with eruptive phases, suggesting that the Oruanui magma was well mixed before eruption. Some Oruanui quartz crystals contain distinctive CL zonings with a jagged ('restitic') core mantled by a black CL zone. Trace element variations in melt inclusions in the 'restitic' cores are consistent with fractionation of Ba-bearing minerals such as sanidine and/or biotite, both of which are rare or absent in rocks erupted from Taupo volcanic center. The above evidence suggests that Oruanui rhyolite is generated by assimilation of previous intruded rocks or country rocks, differentiated by crystal fractionation, and then mixed prior to eruption. Despite the differences in trace element and volatile contents, and crystal assemblages, both Bishop Tuff and Oruanui magmas involve crystal fractionation as one of the main differentiation mechanisms during their evolution. However, there are pronounced differences in the pre-eruptive stratification of the two chambers, which may reflect the tectonic settings, eruption rates, and ages of the systems.

Calcite growth-rate inhibition by fulvic acids isolated from Big Soda Lake, Nevada, USA, The Suwannee River, Georgia, USA and by polycarboxylic acids

USGS Publications Warehouse

Reddy, Michael M.; Leenheer, Jerry

2011-01-01

Calcite crystallization rates are characterized using a constant solution composition at 25°C, pH=8.5, and calcite supersaturation (Ω) of 4.5 in the absence and presence of fulvic acids isolated from Big Soda Lake, Nevada (BSLFA), and a fulvic acid from the Suwannee River, Georgia (SRFA). Rates are also measured in the presence and absence of low-molar mass, aliphatic-alicyclic polycarboxylic acids (PCA). BSLFA inhibits calcite crystal-growth rates with increasing BSLFA concentration, suggesting that BSLFA adsorbs at growth sites on the calcite crystal surface. Calcite growth morphology in the presence of BSLFA differed from growth in its absence, supporting an adsorption mechanism of calcite-growth inhibition by BSLFA. Calcite growth-rate inhibition by BSLFA is consistent with a model indicating that polycarboxylic acid molecules present in BSLFA adsorb at growth sites on the calcite crystal surface. In contrast to published results for an unfractionated SRFA, there is dramatic calcite growth inhibition (at a concentration of 1 mg/L) by a SRFA fraction eluted by pH 5 solution from XAD-8 resin, indicating that calcite growth-rate inhibition is related to specific SRFA component fractions. A cyclic PCA, 1, 2, 3, 4, 5, 6-cyclohexane hexacarboxylic acid (CHXHCA) is a strong calcite growth-rate inhibitor at concentrations less than 0.1 mg/L. Two other cyclic PCAs, 1, 1 cyclopentanedicarboxylic acid (CPDCA) and 1, 1 cyclobutanedicarboxylic acid (CBDCA) with the carboxylic acid groups attached to the same ring carbon atom, have no effect on calcite growth rates up to concentrations of 10 mg/L. Organic matter ad-sorbed from the air onto the seed crystals has no effect on the measured calcite crystal-growth rates.

Orientation Dependence of Functional Properties in Heterophase Single Crystals of the Ti36.5Ni51.0Hf12.5 and Ti48.5Ni51.5 Alloys

NASA Astrophysics Data System (ADS)

Panchenko, E. Yu.; Chumlyakov, Yu. I.; Surikov, N. Yu.; Tagiltsev, A. I.; Vetoshkina, N. G.; Osipovich, K. S.; Maier, H.; Sehitoglu, H.

2016-03-01

The features of orientation dependence of stress-induced thermoelastic B2-( R)- B19'-martensitic transformations in single crystals of the Ti48.5Ni51.5 and Ni51.0Ti36.5Hf12.5 (at.%) alloys, which contain disperse particles of the Ti3Ni4 and H-phase, respectively, are revealed along with those of their shape-memory effects (SME) and superelasticity (SE). It is experimentally demonstrated that irrespective of the crystal structure of disperse particles measuring more than 100 nm, for their volume fraction f > 16% there is a weaker orientation dependence of the reversible strain in the cases of manifestation of SME and SE. In the orientations of Class I, wherein martensitic detwinning introduces a considerable contribution into transformation strain, the values of SME |ɛ SME | and SE |ɛ SE | decrease by over a factor of two compared to the theoretical lattice strain value |ɛ tr0 | for a B2- B19'-transformation and the experimental values of reversible strain for quenched TiNi crystals. In the orientations of Class 2, wherein detwinning of the martensite is suppressed as is the case in quenched single-phase single crystals, the reversible strain is maintained close to its theoretical value |ɛ tr0 |. Micromechanical models of interaction between the martensite and the disperse particles are proposed, which account for the weaker orientation dependence of |ɛ SME | and |ɛ SE | due to suppression of detwinning of the B19'-martensite crystals by the particles and a transition from a single-variant evolution of the stress-induced martensitic transformations to a multiple-variant evolution of transformations in the cases of increased size of the particles and their larger volume fractions.

Structure of a mushy layer under hypergravity with implications for Earth's inner core

NASA Astrophysics Data System (ADS)

Huguet, Ludovic; Alboussière, Thierry; Bergman, Michael I.; Deguen, Renaud; Labrosse, Stéphane; Lesœur, Germain

2016-03-01

Crystallization experiments in the dendritic regime have been carried out in hypergravity conditions (from 1 to 1300 g) from an ammonium chloride solution (NH4Cl and H2O). A commercial centrifuge was equipped with a slip ring so that electric power (needed for a Peltier device and a heating element), temperature and ultrasonic signals could be transmitted between the experimental setup and the laboratory. Ultrasound measurements (2-6 MHz) were used to detect the position of the front of the mushy zone and to determine attenuation in the mush. Temperature measurements were used to control a Peltier element extracting heat from the bottom of the setup and to monitor the evolution of crystallization in the mush and in the liquid. A significant increase of solid fraction and attenuation in the mush is observed as gravity is increased. Kinetic undercooling is significant in our experiments and has been included in a macroscopic mush model. The other ingredients of the model are conservation of energy and chemical species, along with heat/species transfer between the mush and the liquid phase: boundary-layer exchanges at the top of the mush and bulk convection within the mush (formation of chimneys). The outputs of the model compare well with our experiments. We have then run the model in a range of parameters suitable for the Earth's inner core. This has shown the role of bulk mush convection for the inner core and the reason why a solid fraction very close to unity should be expected. We have also run melting experiments: after crystallization of a mush, the liquid has been heated from above until the mush started to melt, while the bottom cold temperature was maintained. These melting experiments were motivated by the possible local melting at the inner core boundary that has been invoked to explain the formation of the anomalously slow F-layer at the bottom of the outer core or inner core hemispherical asymmetry. Oddly, the consequences of melting are an increase in solid fraction and a decrease in attenuation. It is hence possible that surface seismic velocity and attenuation of the inner core are strongly affected by melting.

The Component Slope Linear Model for Calculating Intensive Partial Molar Properties: Application to Waste Glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, Jacob G.

2013-01-11

Partial molar properties are the changes occurring when the fraction of one component is varied while the fractions of all other component mole fractions change proportionally. They have many practical and theoretical applications in chemical thermodynamics. Partial molar properties of chemical mixtures are difficult to measure because the component mole fractions must sum to one, so a change in fraction of one component must be offset with a change in one or more other components. Given that more than one component fraction is changing at a time, it is difficult to assign a change in measured response to a changemore » in a single component. In this study, the Component Slope Linear Model (CSLM), a model previously published in the statistics literature, is shown to have coefficients that correspond to the intensive partial molar properties. If a measured property is plotted against the mole fraction of a component while keeping the proportions of all other components constant, the slope at any given point on a graph of this curve is the partial molar property for that constituent. Actually plotting this graph has been used to determine partial molar properties for many years. The CSLM directly includes this slope in a model that predicts properties as a function of the component mole fractions. This model is demonstrated by applying it to the constant pressure heat capacity data from the NaOH-NaAl(OH{sub 4}H{sub 2}O system, a system that simplifies Hanford nuclear waste. The partial molar properties of H{sub 2}O, NaOH, and NaAl(OH){sub 4} are determined. The equivalence of the CSLM and the graphical method is verified by comparing results detennined by the two methods. The CSLM model has been previously used to predict the liquidus temperature of spinel crystals precipitated from Hanford waste glass. Those model coefficients are re-interpreted here as the partial molar spinel liquidus temperature of the glass components.« less

Phase behavior of binary and polydisperse suspensions of compressible microgels controlled by selective particle deswelling

NASA Astrophysics Data System (ADS)

Scotti, A.; Gasser, U.; Herman, E. S.; Han, Jun; Menzel, A.; Lyon, L. A.; Fernandez-Nieves, A.

2017-09-01

We investigate the phase behavior of suspensions of poly(N -isopropylacrylamide) (pNIPAM) microgels with either bimodal or polydisperse size distribution. We observe a shift of the fluid-crystal transition to higher concentrations depending on the polydispersity or the fraction of large particles in suspension. Crystallization is observed up to polydispersities as high as 18.5%, and up to a number fraction of large particles of 29% in bidisperse suspensions. The crystal structure is random hexagonal close-packed as in monodisperse pNIPAM microgel suspensions. We explain our experimental results by considering the effect of bound counterions. Above a critical particle concentration, these cause deswelling of the largest microgels, which are the softest, changing the size distribution of the suspension and enabling crystal formation in conditions where incompressible particles would not crystallize.

Crystal morphology optimization of thiamine hydrochloride in solvent system: Experimental and molecular dynamics simulation studies

NASA Astrophysics Data System (ADS)

Yang, Yang; Han, Dandan; Du, Shichao; Wu, Songgu; Gong, Junbo

2018-01-01

Thiamine hydrochloride (THCL) was produced in methanol accompanied with agglomeration in industry, the plate like morphology of THCL in methanol was not deserve to have a good quality. Selecting a suitable solvent should be considered because solvent could be one of the essential factors to impact morphology. Methanol and methanol/ethyl acetate solvent (0.2 vol fraction of methanol) was selected as the solvent system in reactive crystallization of THCL. The experiment results show the THCL crystal morphology in methanol/ethyl acetate solvent system was granular and more regular than that in methanol. In order to explicate the different crystal morphology in different solvents, molecular dynamics (MD) simulation was introduced to simulate crystal morphology in different solvents. The attachment energy (AE) model was employed to investigate the morphology of THCL under vacuum conditions, methanol and methanol/ethyl acetate solvent conditions, respectively. The simulation crystal morphology was in a good agreement with that of experimented. The particle of THCL in methanol/ethyl acetate solvent has less tendency to agglomeration, and then it is favorable to the downstream process, such as filtration, storage and transportation.

Zinc and volatile element loss during planetary magma ocean phases

NASA Astrophysics Data System (ADS)

Dhaliwal, Jasmeet K.; Day, James M. D.; Moynier, Frédéric

2016-10-01

Zinc is a moderately volatile element and a key tracer of volatile depletion on planetary bodies due to lack of significant isotopic fractionation under high-temperature processes. Terrestrial basalts have δ66Zn values similar to some chondrites (+ 0.15 to 0.3‰ where [{66Zn/64Znsample/66Zn/64ZnJMC-Lyon-1} × 1000]) and elevated Zn concentrations (100 ppm). Lunar mare basalts yield a mean δ66Zn value of +1.4 ± 0.5‰ and have low Zn concentrations (~2 ppm). Late-stage lunar magmatic products, such as ferroan anorthosite, Mg-suite and Alkali suite rocks exhibit heavier δ66Zn values (+3 to +6‰). The heavy δ66Zn lunar signature is thought to reflect evaporative loss and fractionation of zinc, either during a giant impact or in a magma ocean phase.We explore conditions of volatile element loss within a lunar magma ocean (LMO) using models of Zn isotopic fractionation that are widely applicable to planetary magma oceans. For the Moon, our objective was to identify conditions that would yield a δ66Zn signature of ~ +1.4‰ within the mantle, assuming a terrestrial mantle zinc starting composition.We examine two cases of zinc evaporative fractionation: (1) lunar surface zinc fractionation that was completed prior to LMO crystallization and (2) lunar surface zinc fractionation that was concurrent with LMO crystallization. The first case resulted in a homogeneous lunar mantle and the second case yielded a stratified lunar mantle, with the greatest zinc isotopic enrichment in late-stage crystallization products. This latter case reproduces the distribution of zinc isotope compositions in lunar materials quite well.We find that hydrodynamic escape was not a dominant process in losing Zn, but that erosion of a nascent lunar atmosphere, or separation of condensates into a proto-lunar crust are possible. While lunar volatile depletion is still possible as a consequence of the giant impact, this process cannot reproduce the variable δ66Zn found in the Moon. Outgassing during magma ocean phases would have led to volatile-depleted planetesimal feed-stocks that would have profoundly affected the ultimate volatile inventories of larger planetary bodies.

Experimentally determined isotope effect during Mg-Fe interdiffusion in olivine

NASA Astrophysics Data System (ADS)

Sio, C. K. I.; Roskosz, M.; Dauphas, N.; Bennett, N.; Mock, T. D.; Shahar, A.

2017-12-01

Isotopic fractionation provides the most direct means to investigate the nature of chemical zoning in minerals, which can be produced by either diffusive transport or crystal growth. Misinterpreting the nature of chemical zoning can result in erroneous conclusions regarding magmatic cooling rates and diffusion timescales. Isotopes are useful in this regard because the light isotopes diffuse faster than their heavier counterparts. As a result, isotopic fractionations should be associated with chemical zoning profiles if they are diffusion-driven. In contrast, little isotopic fractionation is associated with crystal growth during slow cooling at magmatic temperatures. The isotope effect for diffusion is described by β and is related to the mass (m) and diffusivity (D) of isotopes i and j of an element via: Di/Dj = (mj/mi)β. To model isotopic profiles, knowledge of β is required. Several estimates of β for Mg and Fe diffusion in olivine have been reported using natural samples but these estimates are uncertain because they depend on the choice of modeling parameters (Sio et al., 2013; Oeser et al., 2015; Collinet et al., 2017). We have experimentally determined β for Fe (βFe) in olivine as a function of crystallographic orientation, composition, and temperature. Thirty experiments have been conducted by juxtaposing crystallographically oriented olivine crystals to make Fo83.4-Fo88.8 and Fo88.8-Fo100 diffusion couples. These diffusion couples were annealed in a 1 atm gas mixing furnace at 1200 °C, 1300 °C or 1400 °C at QFM - 1.5 for up to 15 days. Chemical profiles were characterized using an electron microprobe and isotopic analyses were done using laser ablation MC-ICPMS. We found a crystallographic dependence of βFe for the Fo88.8-Fo100 couple where βFe [100] ≈ βFe [010] > βFe [001]. For the Fo83.4-Fo88.8 couple, βFe is 0.16 ± 0.09 (2σ) for all 3 major crystallographic axes. A temperature dependence of βFe could not be resolved. These experimentally determined β-values can be used in conjunction with the Mg-Fe diffusivities given in Dohmen and Chakraborty (2007) to simultaneously model the chemical-isotopic profiles of olivine to retrieve cooling and crystallization histories of magmatic rocks.

Geochronology, geochemical and Sr-Nd-Hf-Pb isotopic compositions of the granitoids in the Yemaquan orefield, East Kunlun orogenic belt, northern Qinghai-Tibet Plateau: Implications for magmatic fractional crystallization and sub-solidus hydrothermal alteration

NASA Astrophysics Data System (ADS)

Yin, Shuo; Ma, Changqian; Xu, Jiannan

2017-12-01

A general consensus has emerged that high field strength elements (HFSE) can mobile to some extent in a hydrothermal fluid. However, there are hot debates on whether sub-solidus hydrothermal alteration can lower the Nb/Ta ratio in evolved melts. In this study, we present petrography, geochronology and geochemistry of the barren and mineralized rocks in the Yemaquan skarn iron deposit, northern Qinghai-Tibet Plateau, to probe magmatic-hydrothermal transition. The barren rocks consist of diorites, granodiorites, granites and syenogranites, whereas the porphyritic granodiorites are associated with mineralization for an excellent consistency between the magmatic zircon U-Pb age (225 ± 2 Ma) and the hydrothermal phlogopite 40Ar-39Ar age (225 ± 1.5 Ma). The Sr-Nd-Hf-Pb isotopic data demonstrate that the Yemaquan granitoids are originated from a relatively homogenous enriched mantle with different degrees of crust contamination (assimilation fractional crystallization, AFC). Trace elements signatures indicate that the porphyritic granodiorites related to mineralization display amphibole crystallization for high water contents, whereas the barren granites have gone through biotite crystallization due to potassium enrichment by continuous upper crust contamination, both of which are responsible for their Nb/Ta ratios, respectively. Modeling results suggest that a basaltic melt with Nb/Ta ratio of 15.3 can reach a minimum Nb/Ta ratio of 12 in the producing granodioritic melt by amphibole fractional crystallization based on partition coefficients of Nb and Ta between amphibole and melts from previous experiments. This may explain the average Nb/Ta ratio (13.7) of the barren granodiorites, while it cannot account for the average Nb/Ta ratio (8.4) of the mineralized porphyritic granodiorites, and it is even lower than that of the granites (10.3) with biotite fractional crystallization. Exsolution of a magmatic-hydrothermal fluid is inevitable when a water saturated magma emplaced in shallow crust, leading to a transportation of certain chemical components from the magmatic melts to exsolved fluids. Because Nb seems more mobile than Ta in fluorine-bearing fluids, we contend that a preferentially transport Nb over Ta by sub-solidus hydrothermal alteration can further lower the Nb/Ta ratios of the mineralized porphyritic granodiorites, which may also result in a broad range of HFSE contents and their ratios in the altered porphyritic granodiorites formed in a post-magmatic process.

Effect of crystal length on the thermal characteristic in Nd: YLF laser with 20W diode pumped

NASA Astrophysics Data System (ADS)

Yahya, K. A.; Hussein, O. A.; Mustafa, O. H.

2016-03-01

Theoretical results are reported on thermal effects along the π- 1047nm and σ- 1053nm polarizations in a cut Nd: YLF rod crystal by using 20W Diode -End-pumped. The crystal length effects on the fraction of absorbed pump radiation converted into heat, radial temperature distribution, and the change in a radial refractive index. The result from this study has shown that a maximum fraction converted into heat is calculated to be around 24% and thermal effects of π-polarized 1047 nm stronger than σ-polarized 1053 nm.

The microphysical and radiative properties of tropical cirrus from the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE)

NASA Astrophysics Data System (ADS)

Um, Jun Shik

During the 2006 Tropical Warm Pool International Cloud Experiment conducted in the region near Darwin, Australia, the Scaled Composites Proteus aircraft executed spiral profiles and flew horizontal legs through aging cirrus, fresh anvils, and cirrus of unknown origin. Data from 27 Jan., 29 Jan., and 2 Feb., when all the microphysical probes a Cloud and Aerosol Spectrometer (CAS), a Cloud Droplet Probe (CDP), a Cloud Imaging Probe (CIP), and a Cloud Particle Imager (CPI) were working, are used to investigate whether a single parameterization can be used to characterize tropical cirrus in terms of prognostic variables used in large-scale models, to calculate the single-scattering properties (scattering phase function P11 and asymmetry parameter g) of aggregates and small ice crystals that more closely match observed ice crystals, and to quantify the influences of small ice crystals on the bulk scattering properties of tropical cirrus. A combination of CDP (D < 50 mum), fits (50 < D < 125 microm), and CIP (D > 125 mum) distributions is used to represent ice crystal size distributions. The CDP measurements are used for small ice crystals because comparison between the CAS and CDP suggested the CAS was artificially amplifying small ice crystal concentrations by detecting remnants of shattered large ice crystals. Artifacts in CIP images are removed or corrected and then CIP measurements are used to represent large ice crystals. Because of the uncertainties in both the CPI and CIP for 50 < D < 125 mum, the incomplete gamma fitting method with the CDP (D < 50 mum) and CIP (D > 125 mum) measurements as input is used to characterize these distributions. A new quasi-automatic habit classification scheme is developed. For all days, small quasi-spheres dominated the contributions from all ice crystal sizes (D > 0 mum, by number) for all 3 days. The areal fraction (D > 200 mum) from bullet rosettes and their aggregates was 48% and 60% for 27 and 29 Jan., respectively, but only 7% for 2 Feb, whereas the fraction of aggregates of plates was 46.2% for 2 Feb. and only 7.2% and 1% for 27 and 29 Jan., respectively. The difference in ice crystal habits sampled on the different days is likely associated with the difference between fresh anvil cirrus on 2 Feb. and aged cirrus bands on the 27 and 29 of Jan. Because of variations in microphysical properties (i.e., number concentration, median mass dimension, and fit variables of gamma distributions) it is also shown that variables in addition to ice water content and temperature are required to represent the characteristics of cirrus with different origins in large-scale models. Aggregates of bullet rosettes and aggregates of plates are shown to scatter more light in the lateral and backward scattering region and less light in the forward scattering region compared to their component crystals, leading to a decrease in g for aggregates. To represent the three-dimensional shape of aggregates of plates, three parameters, the aggregation index ( AI), the area ratio (AR), and the normalized projected area (An), are introduced and the single-scattering properties of aggregates of plates are shown to depend heavily on AI. A new model (budding Bucky ball, 3B) for the shape of small ice crystals is developed based on the shapes of ice analogues grown in laboratory experiments. The 3B scatters more light in the lateral, and backward direction and less in the forward direction compared with other existing models currently used to describe small crystal shape (i.e., Gaussian random sphere and droxtal). The combination of the reduction in the forward scattering and enhancement in the lateral and backward scattering causes 11.13% and 8.74% decreases in g for the 3B compared with that for Gaussian random sphere and droxtal, respectively. The impacts of variations in small ice crystal shapes and concentrations on bulk scattering properties of tropical cirrus are quantified. The calculated mean asymmetry parameter ḡ for the fresh anvil (i.e., 2 Feb) is larger than that for cirrus bands of varying ages (i.e., 27 and 29 Jan.) for -60 < T < -45°C and -45 < T < -30°C where the fractional contributions of small ice crystals to total cross sectional area are small. The impact using different models for small ice crystals on ḡ is largest at lower temperatures (T < -60°C). The impact of enhanced number concentrations of small ice crystals on the bulk scattering properties depends on the assumed shapes of small ice crystals, which is largest (smallest) in the temperature ranges of -45 < T < -30 T (T < -60°C) where the CAS/CDP ratio of N of small ice crystals is maximum (minimum).

Real-time observation of the isothermal crystallization kinetics in a deeply supercooled liquid

NASA Astrophysics Data System (ADS)

Zanatta, M.; Cormier, L.; Hennet, L.; Petrillo, C.; Sacchetti, F.

2017-03-01

Below the melting temperature Tm, crystals are the stable phase of typical elemental or molecular systems. However, cooling down a liquid below Tm, crystallization is anything but inevitable. The liquid can be supercooled, eventually forming a glass below the glass transition temperature Tg. Despite their long lifetimes and the presence of strong barriers that produces an apparent stability, supercooled liquids and glasses remain intrinsically a metastable state and thermodynamically unstable towards the crystal. Here we investigated the isothermal crystallization kinetics of the prototypical strong glassformer GeO2 in the deep supercooled liquid at 1100 K, about half-way between Tm and Tg. The crystallization process has been observed through time-resolved neutron diffraction for about three days. Data show a continuous reorganization of the amorphous structure towards the alpha-quartz phase with the final material composed by crystalline domains plunged into a low-density, residual amorphous matrix. A quantitative analysis of the diffraction patterns allows determining the time evolution of the relative fractions of crystal and amorphous, that was interpreted through an empirical model for the crystallization kinetics. This approach provides a very good description of the experimental data and identifies a predator-prey-like mechanism between crystal and amorphous, where the density variation acts as a blocking barrier.

Mesoscale modeling of strain induced solid state amorphization in crystalline materials

NASA Astrophysics Data System (ADS)

Lei, Lei

Solid state amorphization, and in particular crystalline to amorphous transformation, can be observed in metallic alloys, semiconductors, intermetallics, minerals, and also molecular crystals when they undergo irradiation, hydrogen gas dissolution, thermal interdiffusion, mechanical alloying, or mechanical milling. Although the amorphization mechanisms may be different, the transformation occurs due to the high level of disorder introduced into the material. Milling induced solid state amorphization is proposed to be the result of accumulation of crystal defects, specifically dislocations, as the material is subjected to large deformations during the high energy process. Thus, understanding the deformation mechanisms of crystalline materials will be the first step in studying solid state amorphization in crystalline materials, which not only has scientific contributions, but also technical consequences. A phase field dislocation dynamics (PFDD) approach is employed in this work to simulate plastic deformation of molecular crystals. This PFDD model has the advantage of tracking all of the dislocations in a material simultaneously. The model takes into account the elastic interaction between dislocations, the lattice resistance to dislocation motion, and the elastic interaction of dislocations with an external stress field. The PFDD model is employed to describe the deformation of molecular crystals with pharmaceutical applications, namely, single crystal sucrose, acetaminophen, gamma-indomethacin, and aspirin. Stress-strain curves are produced that result in expected anisotropic material response due to the activation of different slip systems and yield stresses that agree well with those from experiments. The PFDD model is coupled to a phase transformation model to study the relation between plastic deformation and the solid state amorphization of crystals that undergo milling. This model predicts the amorphous volume fraction in excellent agreement with experimental observation. Finally, we incorporate the effect of stress free surfaces to model the behavior of dislocations close to these surfaces and in the presence of voids.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szcześ, Aleksandra, E-mail: aszczes@poczta.umcs.lublin.pl; Czemierska, Magdalena; Jarosz-Wilkołazka, Anna

Extracellular polymeric substance (EPS) extracted from Rhodococcus opacus bacterial strain was used as a matrix for calcium carbonate precipitation using the vapour diffusion method. The total exopolymer and water-soluble exopolymer fraction of different concentrations were spread on the mica surface by the spin-coating method. The obtained layers were characterized using the atomic force microscopy measurement and XPS analysis. The effects of polymer concentration, initial pH of calcium chloride solution and precipitation time on the obtained crystals properties were investigated. Raman spectroscopy and scanning electron microscopy were used to characterize the precipitated minerals. It was found that the type of precipitatedmore » CaCO{sub 3} polymorph and the crystal size depend on the kind of EPS fraction. The obtained results indicates that the water soluble fraction favours vaterite dissolution and calcite growth, whereas the total EPS stabilizes vaterite and this effect is stronger at basic pH. It seems to be due to different contents of the functional group of EPS fractions. - Highlights: • CaCO{sub 3} crystal size and polymorph can be controlled by EPS substance obtained from R. opacus. • The water soluble fraction favours vaterite dissolution and calcite growth. • The total EPS stabilizes vaterite. • This effect is stronger at basic pH.« less

Mineralogy and petrology of cretaceous subsurface lamproite sills, southeastern Kansas, USA

USGS Publications Warehouse

Cullers, R.L.; Dorais, M.J.; Berendsen, P.; Chaudhuri, Sambhudas

1996-01-01

Cores and cuttings of lamproite sills and host sedimentary country rocks in southeastern Kansas from up to 312 m depth were analyzed for major elements in whole rocks and minerals, certain trace elements in whole rocks (including the REE) and Sr isotopic composition of the whole rocks. The lamproites are ultrapotassic (K2O/Na2O = 2.0-19.9), alkalic [molecular (K2O/Na2O)/Al2O3 = 1.3-2.8], enriched in mantle-incompatible elements (light REE, Ba, Rb, Sr, Th, Hf, Ta) and have nearly homogeneous initial Sr isotopic compositions (0.707764-0.708114). These lamproites could have formed by variable degrees of partial melting of harzburgite country rock and cross-cutting veins composed of phlogopite, K-Ti richterite, titanite, diopside, K-Ti silicates, or K-Ba-phosphate under high H2O/CO2 ratios and reducing conditions. Variability in melting of veins and wall rock and variable composition of the metasomatized veins could explain the significantly different composition of the Kansas lamproites. Least squares fractionation models preclude the derivation of the Kansas lamproites by fractional crystallization from magmas similar in composition to higher silica phlogopite-sanidine lamproites some believe to be primary lamproite melts found elsewhere. In all but one case, least squares fractionation models also preclude the derivation of magmas similar in composition to any of the Kansas lamproites from one another. A magma similar in composition to the average composition of the higher SiO2 Ecco Ranch lamproite (237.5-247.5 m depth) could, however, have marginally crystallized about 12% richterite, 12% sanidine, 7% diopside and 6% phlogopite to produce the average composition of the Guess lamproite (305-312 m depth). Lamproite from the Ecco Ranch core is internally fractionated in K2O, Al2O3, Ba, MgO, Fe2O3, Co and Cr most likely by crystal accumulation-removal of ferromagnesian minerals and sanidine. In contrast, the Guess core (305-312 m depth) has little fractionation throughout most of the sill except in several narrow zones. Lamproite in the Guess core has large enrichments in TiO2, Ba, REE, Th, Ta and Sc and depletions in MgO, Cr, Co and Rb possibly concentrated in these narrow zones during the last dregs of crystallization of this magma. The Ecco Ranch sill did not show any evidence of loss of volatiles or soluble elements into the country rock. This contrasts to the previously studied, shallow Silver City lamproite which did apparently lose H2O-rich fluid to the country rock. Perhaps a greater confining pressure and lesser amount of H2O-rich fluid prevented it from escaping.

Descartesites - Missing(?) pristine rocks

NASA Astrophysics Data System (ADS)

Longhi, J.

1997-03-01

A thermal divide that is stable to comparatively low temperatures in lunar compositions because of their low alkalies is presently invoked in order to explain the absence of granitoids called 'descartesites' which are residual to the formation of lunar ferroan anorthosites (FANs). Attention is given to the composition paths generated by fractional crystallization of a model FAN parent liquid at pressures of 0 and 3 kb.

The Atlantis Bank gabbro-suite was not a "normal" magma-chamber that produced basalts

NASA Astrophysics Data System (ADS)

Kvassnes, A. J.; Dick, H. J. B.; Grove, T. L.

2003-04-01

The differentiation of the basalts sampled at Atlantis II Fracture Zone, South-West Indian Ridge, is not the result of simple fractionation of gabbroic mineral-assemblages like those recovered from the adjacent Atlantis Bank and ODP Hole 735B. Large mineral data sets for the gabbros (Dick, et al 2002) are now available for analysis and comparison to spatially associated basalts. We have used Melts and pMelts (Ghiorso and Sack, 1995) to estimate the fractional crystallization trend gabbros from a primitive mantle melt or of the AII F.Z. MORB. Thermodynamic models (Grove et al (1992), Putirka (1999)) were also used to model the glasses hypothetical mafic and felsic mineral equilibrium-compositions. Our results show that while the basalts suggest 30-50% crystallization, the gabbros indicate 35-90% crystallization of a primary melt. It is therefore unlikely that the gabbros sampled from Atlantis Bank are the fossil magma-chambers that expelled melts that formed the spatially associated basalts. The models also show that the most primitive gabbros have elevated clinopyroxene Mg#s (Mg/(Mg+Fe)) relative to the coexisting plagioclase An%. This was unexpected, as the clinopyroxene frequently occurs as oikocrysts surrounding the plagioclase and encloses rounded olivine chadacrysts, indicating that the clinopyroxene precipitated late. Elthon (1992) noted the same problem for Cayman Trough gabbros; suggesting that this was the result of intermediate pressure fractionation. In our models, pressure does have some effect up to 5kbar, but is not enough to explain the discrepancy. We propose a model where melts are modified in a porous network or mush. Plagioclase-olivine networks form by accumulation of buoyant glomerocrysts and then work as filters as new melts pass through. Dissolution of the minerals would make the new melt appear to be more primitive with regards to increased Mg#s, as the dissolution happens fast without complete internal re-equilibration with the gabbro matrix. When clinopyroxene precipitates onto the plagioclase network, the oikocrysts appear more primitive than the original melt that produced the chadacrysts. The oikocryst also become reversely zoned, nucleating on the plagioclase network and growing inward. The resulting melt affected this way will have crystallized Mg-rich clinopyroxene. It is possible that this effect commonly occurs during melt transport in the lower crust and solve the well-known pyroxene paradox previously explained by high-pressure crystallization. If a melt containing dissolved minerals pools, it may be erupted and would result in basalts that appear more primitive than they otherwise would be. The gabbro-suite at Atlantis Bank is not, then, a result of simple fractional crystallization or magma mixing but rather represent part of a complex system of repeated intrusions a mush. Furthermore, if the melts that produced the crust were mantle derived, they fractionated 30-40% elsewhere before they reached the crustal levels sampled in this study and 600+ meters of gabbro exist either below the Hole or in the mantle, though the latter is apparently not required. References: Dick, H. J. B., Ozawa, K., Meyer, P. S., Niu, Y., Robinson, P.T., Constantin, M., Hebert, R., Natland, J. H., Hirth, J. G., Mackie, S. M., 2002. Primary Silicate Mineral Chemistry of a 1.5-km Section of Very Slow Spreading Lower Ocean Crust: ODP Hole 735B, South West Indian Ridge. In: Proceeding of the Ocean Drilling Program, Vol. 176, Scientific Results, Return to Hole 735B, pp 1-60. Elthon, D., Stewart, M., Ross, D. K., 1992. Compositional Trends of Minerals in Oceanic Cumulates. Journal of Geophysical Research, Vol 97, B11, p15,189-15,199. Ghiorso M. S., Sack, R. O., 1995. Chemical Mass Transfer in magmatic Processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures. Cont. Min. Petr., 119, p. 197-212. Grove, T. L., Kinzler, R. J., Bryan, W., 1992. Fractionation of Mid-Ocean Ridge Basalt (MORB). In: Mantle Flow and Melt Generation at Mid-Ocean ridges. Geophysical Monograph 71. 281pp. Muller, J. H., Robinson, C. J., Minshall, T.A., White, R. S., Bickle, M. J., 1997. Thin crust beneath ocean drilling program borehole 735B at the South West Indian Ridge? Earth Planet. Sci. Lett., v. 148, p. 93-107 Putirka, K., 1999. Clinopyroxene + liquid equilibria to 100kbar and 2450K. Cont. Min. Petr. 135: 151-163

Derivation of intermediate to silicic magma from the basalt analyzed at the Vega 2 landing site, Venus.

PubMed

Shellnutt, J Gregory

2018-01-01

Geochemical modeling using the basalt composition analyzed at the Vega 2 landing site indicates that intermediate to silicic liquids can be generated by fractional crystallization and equilibrium partial melting. Fractional crystallization modeling using variable pressures (0.01 GPa to 0.5 GPa) and relative oxidation states (FMQ 0 and FMQ -1) of either a wet (H2O = 0.5 wt%) or dry (H2O = 0 wt%) parental magma can yield silicic (SiO2 > 60 wt%) compositions that are similar to terrestrial ferroan rhyolite. Hydrous (H2O = 0.5 wt%) partial melting can yield intermediate (trachyandesite to andesite) to silicic (trachydacite) compositions at all pressures but requires relatively high temperatures (≥ 950°C) to generate the initial melt at intermediate to low pressure whereas at high pressure (0.5 GPa) the first melts will be generated at much lower temperatures (< 800°C). Anhydrous partial melt modeling yielded mafic (basaltic andesite) and alkaline compositions (trachybasalt) but the temperature required to produce the first liquid is very high (≥ 1130°C). Consequently, anhydrous partial melting is an unlikely process to generate derivative liquids. The modeling results indicate that, under certain conditions, the Vega 2 composition can generate silicic liquids that produce granitic and rhyolitic rocks. The implication is that silicic igneous rocks may form a small but important component of the northeast Aphrodite Terra.

Derivation of intermediate to silicic magma from the basalt analyzed at the Vega 2 landing site, Venus

PubMed Central

2018-01-01

Geochemical modeling using the basalt composition analyzed at the Vega 2 landing site indicates that intermediate to silicic liquids can be generated by fractional crystallization and equilibrium partial melting. Fractional crystallization modeling using variable pressures (0.01 GPa to 0.5 GPa) and relative oxidation states (FMQ 0 and FMQ -1) of either a wet (H2O = 0.5 wt%) or dry (H2O = 0 wt%) parental magma can yield silicic (SiO2 > 60 wt%) compositions that are similar to terrestrial ferroan rhyolite. Hydrous (H2O = 0.5 wt%) partial melting can yield intermediate (trachyandesite to andesite) to silicic (trachydacite) compositions at all pressures but requires relatively high temperatures (≥ 950°C) to generate the initial melt at intermediate to low pressure whereas at high pressure (0.5 GPa) the first melts will be generated at much lower temperatures (< 800°C). Anhydrous partial melt modeling yielded mafic (basaltic andesite) and alkaline compositions (trachybasalt) but the temperature required to produce the first liquid is very high (≥ 1130°C). Consequently, anhydrous partial melting is an unlikely process to generate derivative liquids. The modeling results indicate that, under certain conditions, the Vega 2 composition can generate silicic liquids that produce granitic and rhyolitic rocks. The implication is that silicic igneous rocks may form a small but important component of the northeast Aphrodite Terra. PMID:29584745

Les premières phases d'édification du stratovolcan du Cantal (Massif central, France) entre 9,5 et 8,0Ma : géologie et géochimie du secteur de l'ÉlancèzeFirst stage of the Cantal stratovolcano (Massif Central, France) construction between 9.5 and 8.0Ma: geology and geochemistry of the Élancèze area

NASA Astrophysics Data System (ADS)

Legendre, Christelle; Caroff, Martial; Leyrit, Hervé; Nehlig, Pierre; Thièblemont, Denis

2001-05-01

Recent cartography of the Élancèze area resulted in the identification of a residual ancient topographic relief comprised of basaltic and intermediate silica-saturated lavas partly covered by brecciated formations, emplaced during the first stage of edification of the Cantal stratovolcano (9.5-8.0 Ma). The ancient relief has been the subject of a specified petrological study. Although the corresponding mineralogical and geochemical data are rather consistent with the assumption of a differentiation mainly governed by fractional crystallization, the study of some incompatible trace element diagrams suggests that this process cannot have occurred in closed-system. A model of crustal assimilation coupled with fractional crystallization involving an amphibole-bearing cumulate is proposed.

Constitutive modeling of intrinsic and oxygen-contaminated silicon monocrystals in easy glide

NASA Astrophysics Data System (ADS)

Cochard, J.; Yonenaga, I.; Gouttebroze, S.; M'Hamdi, M.; Zhang, Z. L.

2010-11-01

We generalize in this work the constitutive model for silicon crystals of Alexander and Haasen. Strain-rate and temperature dependency of the mechanical behavior of intrinsic crystals are correctly accounted for into stage I of hardening. We show that the steady-state of deformation in stage I is very well reproduced in a wide range of temperature and strain rate. The case of extrinsic crystals containing high levels of dissolved oxygen is examined. The introduction of an effective density of mobile dislocations dependent on the unlocking stress created by oxygen atoms gathered at the dislocation cores is combined to an alteration of the dislocation multiplication rate, due to pinning of the dislocation line by oxygen atoms. This increases the upper yield stress with the bulk oxygen concentration in agreement with experimental observations. The fraction of effectively mobile dislocations is found to decay exponentially with the unlocking stress. Finally, the influence of oxygen migration back onto the dislocations from the bulk on the stress distribution in silicon bars is investigated.

Site-specific equilibrium isotopic fractionation of oxygen, carbon and calcium in apatite

NASA Astrophysics Data System (ADS)

Aufort, Julie; Ségalen, Loïc; Gervais, Christel; Paulatto, Lorenzo; Blanchard, Marc; Balan, Etienne

2017-12-01

The stable isotope composition of biogenic apatite is an important geochemical marker that can record environmental parameters and is widely used to infer past climates, biomineralization processes, dietary preferences and habitat of vertebrates. In this study, theoretical equilibrium isotopic fractionation of oxygen, carbon and calcium in hydroxyapatite and carbonate-bearing hydroxyapatite is investigated using first-principles methods based on density-functional theory and compared to the theoretical isotopic fractionation properties of calcite, CO2 and H2O. Considering the variability of apatite crystal-chemistry, special attention is given to specific contributions of crystal sites to isotopic fractionation. Significant internal fractionation is calculated for oxygen and carbon isotopes in CO3 between the different structural sites occupied by carbonate groups in apatite (typically 7‰ for both 18O/16O and 13C/12C fractionation at 37 °C). Compared with calcite-water oxygen isotope fractionation, occurrence of A-type substitution in apatite structure, in addition to the main B-type substitution, could explain the larger temperature dependence of oxygen isotope fractionation measured at low temperature between carbonate in apatite and water. Theoretical internal fractionation of oxygen isotopes between carbonate and phosphate in B-type carbonated apatite (∼8‰ at 37 °C) is consistent with experimental values obtained from modern and well-preserved fossil bio-apatites. Concerning calcium, theoretical results suggest a small fractionation between apatite and calcite (-0.17‰ at 37 °C). Internal fractionation reaching 0.8‰ at 37 °C occurs between the two Ca sites in hydroxyapatite. Furthermore, the Ca isotopic fractionation properties of apatite are affected by the occurrence of carbonate groups, which could contribute to the variability observed on natural samples. Owing to the complexity of apatite crystal-chemistry and in light of the theoretical results, measurements of site-specific isotopic fractionation properties could improve our understanding and the interpretation of isotopic records in apatites.

Modeling nuclear field shift isotope fractionation in crystals

NASA Astrophysics Data System (ADS)

Schauble, E. A.

2013-12-01

In this study nuclear field shift fractionations in solids (and chemically similar liquids) are estimated using calibrated density functional theory calculations. The nuclear field shift effect is a potential driver of mass independent isotope fractionation(1,2), especially for elements with high atomic number such as Hg, Tl and U. This effect is caused by the different shapes and volumes of isotopic nuclei, and their interactions with electronic structures and energies. Nuclear field shift isotope fractionations can be estimated with first principles methods, but the calculations are computationally difficult, limiting most theoretical studies so far to small gas-phase molecules and molecular clusters. Many natural materials of interest are more complex, and it is important to develop ways to estimate field shift effects that can be applied to minerals, solutions, in biomolecules, and at mineral-solution interfaces. Plane-wave density functional theory, in combination with the projector augmented wave method (DFT-PAW), is much more readily adapted to complex materials than the relativistic all-electron calculations that have been the focus of most previous studies. DFT-PAW is a particularly effective tool for studying crystals with periodic boundary conditions, and may also be incorporated into molecular dynamics simulations of solutions and other disordered phases. Initial calibrations of DFT-PAW calculations against high-level all-electron models of field shift fractionation suggest that there may be broad applicability of this method to a variety of elements and types of materials. In addition, the close relationship between the isomer shift of Mössbauer spectroscopy and the nuclear field shift isotope effect makes it possible, at least in principle, to estimate the volume component of field shift fractionations in some species that are too complex even for DFT-PAW models, so long as there is a Mössbauer isotope for the element of interest. Initial results will be presented for calculations of liquid-vapor fractionation of cadmium and mercury, which indicate an affinity for heavy isotopes in the liquid phase. In the case of mercury the results match well with recent experiments. Mössbauer-calibrated fractionation factors will also be presented for tin and platinum species. Platinum isotope behaviour in metals appears to particularly interesting, with very distinct isotope partitioning behaviour for iron-rich alloys, relative to pure platinum metal. References: 1) Bigeleisen, J. (1996) J. Am. Chem. Soc. 118, 3676-3680. 2) Nomura, M., Higuchi, N., Fujii, Y. (1996) J. Am. Chem. Soc. 118, 9127-9130.

Evolution of rhyolitic magmas in the crustal magmatic system beneath the Taupo Volcanic Zone, New Zealand

NASA Astrophysics Data System (ADS)

Johnson, E. R.; Kamenetsky, V.; McPhie, J.; Wallace, P. J.

2009-12-01

The Taupo Volcanic Zone (TVZ) produces the most frequent rhyolitic eruptions on Earth. This volcanic arc is also characterized by bimodal volcanism, with eruptions of andesite (primarily in the NE and SW of the zone) and minor basalt. Here we use melt inclusions (MI) to investigate the magmatic evolution of rhyolites in the TVZ and their link to TVZ basalts. Our study focuses on recent (<50 ka) explosive rhyolitic eruptions, as well as several small-volume explosive basaltic eruptions, from the Okataina Volcanic Centre in the northern part of the TVZ. The rhyolitic melts of the TVZ are thought to be formed via fractionation of a basaltic parent plus assimilation of metasedimentary crust. Trace element data from our TVZ melt inclusions lend support to this idea, with constant ratios of incompatible trace elements (e.g., U/Th) in the TVZ basalts and rhyolites. Assuming that these elements are completely incompatible, we have calculated that the TVZ rhyolites can be produced by ~80% fractional crystallization of a basaltic parent. We have also used MI volatile contents to assess the pressures (and thus depths) in the crust of magma emplacement and differentiation. Both the TVZ rhyolites and basalts are volatile-rich. Quartz-hosted MI in the rhyolites typically contain 5.5- 7.6 wt% H2O and up to 2500 ppm Cl, and olivine-hosted MI in the basalts contain up to 4.5 wt% H2O and 1250 ppm Cl. The H2O concentrations imply crystallization pressures of at least 200-440 MPa for the rhyolites, which correspond to depths of ~8-16 km. However, the presence of rhyolitic MI with lower H2O (3.5-5 wt%) suggests that crystallization may have occurred over a wide range of pressures. Additionally, the basalts erupted in the TVZ likely crystallized at minimum pressures of 100-200 MPa. Together, this suggests that basaltic and rhyolitic melt zones occur over a wide range of depths (~4-16 km). Furthermore, the emplacement of the basaltic parent and the AFC process to create the rhyolites had to occur at depths >8-16 km. Our findings are consistent with geophysical models which suggest partial melts are present at depths of 6-16 km beneath portions of the TVZ (Bannister et al., 2004). We have also used MI analyses and cathodoluminescence (CL) images of quartz to assess degassing, mixing and fractionation in these magma systems. Our MI data indicate that the rhyolites underwent vapour-saturated crystallization. Concentrations of both H2O and Cl increase slightly during crystallization, suggesting that these volatiles behaved as moderately incompatible elements during fractionation. The extents of such fractionation are variable, and in some cases mixing of several rhyolitic magmas occurred, but in general we find that the range in U and Th in MI indicates ~7-20% crystallization from the least to most evolved rhyolitic melt. The results of this study provide important insights into the origin and evolution of rhyolitic magmas in an arc environment.

Isolation of isoelectrically pure cholera toxin for crystallization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spangler, B.D.; Westbrook, E.M.

1989-01-01

We have determined that the failure of cholera toxin to crystallize well results from its isoelectric heterogeneity, which is probably due to a post-translational process such as deamidation of its B subunit. Every sample of cholera toxin we have examined from commercial or academic suppliers has been heterogeneous; heterogeneous cholera toxin does not crystallize satisfactorily. We have overcome this problem by using ion-exchange fast protein liquid chromatography (FPLC) to obtain an isoelectrically homogeneous species of cholera toxin. Homogeneous cholera toxin crystallizes readily, forming single, nonmosaic crystals suitable for x-ray diffraction studies. For this process, protein was applied to a MonoQmore » ion-exchange column, then eluted with an isocratic low salt buffer followed by a linear salt gradient (0-100 mM NaCl). Column fractions were analyzed on isoelectric focusing gels, and those fractions containing the desired homogeneous species were pooled and concentrated. Crystals formed within 24 to 48 hours in a MOPS/PEG buffer, which made use of slow isoelectric precipitation to induce crystallization. 23 refs., 6 figs.« less

Resonant coherent excitation of 390 MeV/u Ar ions planar channeled in Si crystals

NASA Astrophysics Data System (ADS)

Komaki, K.; Azuma, T.; Ito, T.; Takabayashi, Y.; Yamazaki, Y.; Sano, M.; Torikoshi, M.; Kitagawa, A.; Takada, E.; Murakami, T.

1998-12-01

Resonant coherent excitation of the 1s electron to n=2 states in a hydrogen-like ion was studied through measurements of the survived fraction of 390 MeV/u Ar17+ planar channeled in a Si crystal. Adopting a totally depleted Si surface barrier detector as a target crystal, the charge state of the individual emerged ion was measured in coincidence with the energy deposition in the target. By changing the incident direction along the (2 overline2 0), (0 0 4), and (1 overline1 1) planes, a series of clear resonances were observed as the decrease in the survived charge fraction due to higher electron loss probability for the excited state. Each resonance profile reflects energy splitting of the n=2 manifold originated from l-s interaction and Stark effect due to the crystal field. From the correlation between the energy loss and survived charge fraction, transition energy as a function of the ion trajectory amplitude is deduced which is in good agreement with calculated results.

Chemical consequences of compaction within the freezing front of a crystallizing magma ocean

NASA Astrophysics Data System (ADS)

Hier-Majumder, S.; Hirschmann, M. M.

2013-12-01

The thermal and compositional evolution of planetary magma oceans have profound influences on the early development and differentiation of terrestrial planets. During crystallization, rejection of elements incompatible in precipitating solids leads to petrologic and geochemical planetary differentiation, including potentially development of a compositionally stratified early mantle and evolution of thick overlying atmospheres. In cases of extremely efficient segregation of melt and crystals, solidified early mantles can be nearly devoid of key incompatible species including heat-producing (U, Th, K) and volatile (H,C,N,& noble gas) elements. A key structural component of a crystallizing magma ocean is the partially molten freezing front. The dynamics of this region influences the distribution of incompatible elements between the earliest mantle and the initial surficial reservoirs. It also can be the locus of heating owing to the dissipation of large amounts of tidal energy potentially available from the early Moon. The dynamics are influenced by the solidification rate, which is coupled to the liberation of volatiles owing to the modulating greenhouse effects in the overlying thick atmosphere. Compaction and melt retention in the freezing front of a magma ocean has received little previous attention. While the front advances during the course of crystallization, coupled conservation of mass, momentum, and energy within the front controls distribution and retention of melt within this layer. Due to compaction within this layer, melt distribution is far from uniform, and the fraction of melt trapped within this front depends on the rate of freezing of the magma ocean. During phases of rapid freezing, high amount of trapped melt within the freezing front retains a larger quantity of dissolved volatiles and the reverse is true during slow periods of crystallization. Similar effects are known from inferred trapped liquid fractions in layered mafic intrusions. Here we develop a simple 1-D model of melt retention in the freezing front of a crystallizing magma ocean, and apply it to the thermal and chemical evolution of the early Earth.

Diffusive Fractionation of Lithium Isotopes in Olivine Grain Boundaries

NASA Astrophysics Data System (ADS)

Homolova, V.; Watson, E. B.

2012-12-01

Diffusive fractionation of isotopes has been documented in silicate melts, aqueous fluids, and single crystals. In polycrystalline rocks, the meeting place of two grains, or grain boundaries, may also be a site of diffusive fractionation of isotopes. We have undertaken an experimental and modeling approach to investigate diffusive fractionation of lithium (Li) isotopes by grain boundary diffusion. The experimental procedure consists of packing a Ni metal capsule with predominantly ground San Carlos olivine and subjecting the capsule to 1100C and 1GPa for two days in a piston cylinder apparatus to create a nominally dry, 'dunite rock'. After this synthesis step, the capsule is sectioned and polished. One of the polished faces of the 'dunite rock' is then juxtaposed to a source material of spodumene and this diffusion couple is subject to the same experimental conditions as the synthesis step. Li abundances and isotopic profiles (ratios of count rates) were analyzed using LA-ICP-MS. Li concentrations linearly decrease away from the source from 550ppm to the average concentration of the starting olivine (2.5ppm). As a function of distance from the source, the 7Li/6Li ratio decreases to a minimum before increasing to the background ratio of the 'dunite rock'. The 7Li/6Li ratio minimum coincides with the lowest Li concentrations above average 'dunite rock' abundances. The initial decrease in the 7Li/6Li ratio is similar to that seen in other studies of diffusive fractionation of isotopes and is thought to be caused by the higher diffusivity (D) of the lighter isotope relative to the heavier isotope. The relationship between D and mass (m) is given by (D1/D2) =(m2/m1)^β, where β is an empirical fractionation factor; 1 and 2 denote the lighter and heavier isotope, respectively. A fit to the Li isotopic data reveals an effective DLi of ~1.2x10^-12 m/s^2 and a β of 0.1. Numerical modelling was utilized to elucidate the relationship between diffusive fractionation produced in the grain boundaries versus the lattices of the individual grains of the 'dunite rock'. The model assumes a linear grain boundary juxtaposed to the long side of a rectangular crystal lattice. During a simulation, the diffusant may directly enter the lattice or the grain boundary. Once in the grain boundary, the diffusant may then continue to diffuse away from the source until the end of the simulation or, alternatively, it may be incorporated into the lattice at some point during its travels down the grain boundary. The model system is similar to that considered by Whipple-LeClaire (1963) and our model results agree well with their analytical solution. Preliminary modeling results show that the distinctive minimum in the isotopic ratio is only produced when diffusive fractionation occurs in the grain boundary and not when the fractionation occurs only in the lattice. This suggests that the isotopic profile observed in the experiments may be a product of diffusive fractionation in grain boundaries. Implications of these results extend to the longevity of Li isotopic heterogeneities in the mantle, and suggest that the isotopes of other elements, which have a large relative mass difference, may also be diffusively fractionated by grain boundary diffusion.

The "New Polyethylene Glycol Dilemma": Polyethylene Glycol Impurities and Their Paradox Role in mAb Crystallization.

PubMed

Hildebrandt, Christian; Joos, Lea; Saedler, Rainer; Winter, Gerhard

2015-06-01

Polyethylene glycols (PEG) represent the most successful and frequently applied class of excipients used for protein crystallization. PEG auto-oxidation and formation of impurities such as peroxides and formaldehydes that foster protein drug degradation is known. However, their effect on mAb crystallization has not been studied in detail before. During the present study, a model IgG1 antibody (mAb1) was crystallized in PEG solutions. Aggregate formation was observed during crystallization and storage that was ascribed to PEG degradation products. Reduction of peroxide and formaldehyde levels prior to crystallization by vacuum and freeze-drying was investigated for its effect on protein degradation. Vacuum drying was superior in removal of peroxides but inferior in reducing formaldehyde residues. Consequently, double purification allowed extensive removal of both impurities. Applying of purified PEG led to 50% lower aggregate fractions. Surprisingly, PEG double purification or addition of methionine prior to crystallization prevented crystal formation. With increased PEG concentration or spiking with peroxides and formaldehydes, crystal formation could be recovered again. With these results, we demonstrate that minimum amounts of oxidizing impurities and thus in consequence chemically altered proteins are vital to initiate mAb1 crystallization. The present study calls PEG as good precipitant for therapeutic biopharmaceuticals into question. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Self-organized chiral colloidal crystals of Brownian square crosses.

PubMed

Zhao, Kun; Mason, Thomas G

2014-04-16

We study aqueous Brownian dispersions of microscale, hard, monodisperse platelets, shaped as achiral square crosses, in two dimensions (2D). When slowly concentrated while experiencing thermal excitations, the crosses self-organize into fluctuating 2D colloidal crystals. As the particle area fraction φA is raised, an achiral rhombic crystal phase forms at φA ≈ 0.52. Above φA ≈ 0.56, the rhombic crystal gives way to a square crystal phase that exhibits long-range chiral symmetry breaking (CSB) via a crystal-crystal phase transition; the observed chirality in a particular square crystallite has either a positive or a negative enantiomeric sense. By contrast to triangles and rhombs, which exhibit weak CSB as a result of total entropy maximization, square crosses display robust long-range CSB that is primarily dictated by how they tile space at high densities. We measure the thermal distribution of orientation angles γ of the crosses' arms relative to the diagonal bisector of the local square crystal lattice as a function of φA, and the average measured γ (φA) agrees with a re-scaled model involving efficient packing of rotated cross shapes. Our findings imply that a variety of hard achiral shapes can be designed to form equilibrium chiral phases by considering their tiling at high densities.

Fractionation products of basaltic komatiite magmas at lower crustal pressures: implications for genesis of silicic magmas in the Archean

NASA Astrophysics Data System (ADS)

Mandler, B. E.; Grove, T. L.

2015-12-01

Hypotheses for the origin of crustal silicic magmas include both partial melting of basalts and fractional crystallization of mantle-derived melts[1]. Both are recognized as important processes in modern environments. When it comes to Archean rocks, however, partial melting hypotheses dominate the literature. Tonalite-trondhjemite-granodiorite (TTG)-type silicic magmas, ubiquitous in the Archean, are widely thought to be produced by partial melting of subducted, delaminated or otherwise deeply buried hydrated basalts[2]. The potential for a fractional crystallization origin for TTG-type magmas remains largely unexplored. To rectify this asymmetry in approaches to modern vs. ancient rocks, we have performed experiments at high pressures and temperatures to closely simulate fractional crystallization of a basaltic komatiite magma in the lowermost crust. These represent the first experimental determinations of the fractionation products of komatiite-type magmas at elevated pressures. The aim is to test the possibility of a genetic link between basaltic komatiites and TTGs, which are both magmas found predominantly in Archean terranes and less so in modern environments. We will present the 12-kbar fractionation paths of both Al-depleted and Al-undepleted basaltic komatiite magmas, and discuss their implications for the relative importance of magmatic fractionation vs. partial melting in producing more evolved, silicic magmas in the Archean. [1] Annen et al., J. Petrol., 47, 505-539, 2006. [2] Moyen J-F. & Martin H., Lithos, 148, 312-336, 2012.

Tracking the evolution of a giant magmatic system from assembly to supereruption

NASA Astrophysics Data System (ADS)

Wotzlaw, J. F.; Schaltegger, U.; Frick, D. A.; Dungan, M. A.; Gerdes, A.; Günther, D.

2012-12-01

The chemical and physical characteristics of large magma bodies prior to eruption are closely related consequences of the balance between the rate of magma influx and the rate of cooling. The products of caldera-related silicic supereruptions, and less voluminous associated precursor and post-caldera activity preserve information about the thermal and chemical states of the system at the moment of evacuation of the magma chamber. Numerous studies of the Oligocene Fish Canyon Tuff (5000 km3; Colorado, USA) and related eruptive products of the La Garita caldera have addressed the origin and evolution of large-volume crystal-rich magmas. We use the presence of zircon in all eruptive products of the Fish Canyon magmatic system to gain a high-resolution geochronologic control on the thermal evolution of the magmatic system by using the trace element composition of U-Pb dated zircons as a proxy for magma crystallinity. New analytical protocols permit to obtain age, chemical and isotopic information from the exact same volume of single zircons (Schoene et al., 2010, GCA) allowing us to trace magma crystallinity as a function of time. Zircon U-Pb dates record ~400,000 years of crystallization. Variations in trace element composition in U-Pb dated zircons can be attributed to trace element fractionation imposed by co-crystallization of titanite. Due to the relatively high modal abundance of titanite in Fish Canyon magma and the extreme compatibility of the rare earth elements (REE) in this phase, titanite is the major control on many trace element concentrations and ratios (e.g. Yb/Dy) in coexisting zircons via varying degrees of depletion of these elements in the host melt. Modeling of compositional variations as a result of fractional crystallization suggests that the range of zircon compositions can be explained by 50-70% crystallization of a fractionating assemblage containing 0.4-0.8 vol.% titanite. The period of cooling centered around 28.4 Ma and is marked by an apparent crystallinity that is ~30% higher than at the time of eruption, implying that the Fish Canyon magma was perilously close to complete solidification, hence 'plutonic death', prior to late reheating. We estimate the duration of the reheating event from the age difference of the chemically most evolved (highest Yb/Dy) and the youngest dated zircon to be ~170 ka. This duration for reactivation of the near solidus crystal mush is in excellent agreement with estimates derived from numerical modeling of remelting by upward percolation of a hot gas-phase derived from underplated mafic magma ('gas sparging'; Bachmann and Bergantz, 2003, Geology). This investigation, which is the first in which high resolution U-Pb zircon geochronology has been coupled with geochemical modeling of systematic compositional variations in an accessory mineral, ties together many of the threads which have been developed independently during previous studies of the Fish Canyon magmatic system and places related petrogenetic processes into an absolute time frame.

Moonage Daydream: Reassessing the Simple Model for Lunar Magma Ocean Crystallization

NASA Technical Reports Server (NTRS)

Rapp, J. F.; Draper, D. S.

2016-01-01

Details of the differentiation of a global-scale lunar magma ocean (LMO) remain enigmatic, as the Moon is not simply composed of highlands anorthosite and a suite of mare basalts as inferred from early studies. Results from recent orbital missions, and the increasingly detailed study of lunar samples, have revealed a much larger range of lithologies, from relatively MgO-rich and "purest anorthosite" discovered on the lunar far side by the M3 instrument on Chandraayan-1 to more exotic lithologies such as Si-rich domes and spinel-rich clasts distributed globally. To understand this increasingly complex geology, we must understand the initial formation and evolution of the LMO, and the composition of the cumulates this differentiation could have produced. Several attempts at modelling such a crystallization sequence have been made, and have raised as many questions as they have answered. We present results from our ongoing experimental simulations of magma ocean crystallization, investigating two end-member bulk compositions (TWM and LPUM) under fully fractional crystallization conditions. These simulations represent melting of the entire silicate portion of the Moon, as an end-member starting point from which to begin assessing the evolution of the lunar interior and formation of the lunar crust.

Zircon trace element and isotopic (Sr, Nd, Hf, Pb) effects of assimilation-fractional crystallization of pegmatite magma: A case study of the Guangshigou biotite pegmatites from the North Qinling Orogen, central China

NASA Astrophysics Data System (ADS)

Yuan, Feng; Liu, Jia-Jun; Carranza, Emmanuel John M.; Zhang, Shuai; Zhai, De-Gao; Liu, Gang; Wang, Gong-Wen; Zhang, Hong-Yuan; Sha, Ya-Zhou; Yang, Shang-Song

2018-03-01

Evidence for open-system magmatic processes related to wallrock assimilation accompanied by fractional crystallization (AFC) is present in the Guangshigou biotite pegmatites, North Qinling Orogen. The biotite pegmatite-gneiss contacts generally coincide with the greatest enrichment of U and Th. Zircon Usbnd Pb dating constrains the crystallization ages of the biotite pegmatite (rim zone-415 ± 2.6 Ma; internal zone-413.5 ± 2.5 Ma), in line with a pyrite Pbsbnd Pb isochron age (413 ± 22 Ma). Metamict areas in zircon show generally elevated concentrations of trace elements and expulsion of radioactive Pb. Internal zone samples, representing uncontaminated magma, have negative to positive zircon ( 413 Ma) εHf(t) (- 1.53 - + 3.24), low εNd(t) values (- 2.4), and old Hf and Nd model ages (tDM2 = 1.5-1.19 Ga, T2DM = 1.35 Ga, respectively), indicating a dominantly recycled Mesoproterozoic lower crustal material with involvement of some juvenile materials in the source region. The magmatic oxygen fugacity (fO2) and crystallization temperatures ranges from - 24.81 to - 13.34 of log fO2 and 570 °C to 793 °C, respectively. Compared to the internal zone, pegmatite rim samples display a variable and lower εNd(t) values (- 3.9 to - 2.8) and T2DM (1.47-1.37 Ga), but similar Hf isotopic compositions, favouring a three-component isotopic mixing model (recycled Mesoproterozoic lower crust materials, juvenile materials, and host gneiss). Pronounced variations of Ti, Y, U, Th, Hf, and REE concentrations in zircon from grain to grain in individual samples and from area to area within individual grains suggest a fluctuating crystallization environment in hybridized magma from which the rim-hosted zircons crystallized. Variable and high radiogenic Pb ratios of pyrites forming in the hybridized magma were inherited from the matrix. Zircons from both zones exhibit similar Hf isotope patterns, indicating the rim-hosted zircons crystallized during the early stage of hybridization of magma. However, the heterogeneous Nd isotopic composition in individual pegmatites imply an incorporation of wallrock-derived melt with less radiogenic Nd.

Closed system oxygen isotope redistribution in igneous CAIs upon spinel dissolution

NASA Astrophysics Data System (ADS)

Aléon, Jérôme

2018-01-01

In several Calcium-Aluminum-rich Inclusions (CAIs) from the CV3 chondrites Allende and Efremovka, representative of the most common igneous CAI types (type A, type B and Fractionated with Unknown Nuclear isotopic anomalies, FUN), the relationship between 16O-excesses and TiO2 content in pyroxene indicates that the latter commonly begins to crystallize with a near-terrestrial 16O-poor composition and becomes 16O-enriched during crystallization, reaching a near-solar composition. Mass balance calculations were performed to investigate the contribution of spinel to this 16O-enrichment. It is found that a back-reaction of early-crystallized 16O-rich spinel with a silicate partial melt having undergone a 16O-depletion is consistent with the O isotopic evolution of CAI minerals during magmatic crystallization. Dissolution of spinel explains the O isotopic composition (16O-excess and extent of mass fractionation) of pyroxene as well as that of primary anorthite/dmisteinbergite and possibly that of the last melilite crystallizing immediately before pyroxene. It requires that igneous CAIs behaved as closed-systems relative to oxygen from nebular gas during a significant fraction of their cooling history, contrary to the common assumption that CAI partial melts constantly equilibrated with gas. The mineralogical control on O isotopes in igneous CAIs is thus simply explained by a single 16O-depletion during magmatic crystallization. This 16O-depletion occurred in an early stage of the thermal history, after the crystallization of spinel, i.e. in the temperature range for melilite crystallization/partial melting and did not require multiple, complex or late isotope exchange. More experimental work is however required to deduce the protoplanetary disk conditions associated with this 16O-depletion.

Role of crystallizational differention in the origin of island-arc andesitic melts: evidence from data on melt inclusions and oxygen isotopes

NASA Astrophysics Data System (ADS)

Krasheninnikov, S. P.; Portnyagin, M.; Bindeman, I. N.; Bazanova, L. I.

2012-12-01

Several recent studies of melt inclusions in island-arc rocks revealed a strong bimodality of the melt compositions at the predominance of basic and silicic melts and the scarcity of intermediate melts with SiO2=59-66 wt% (e.g. [1]). These observations were used to interpret the origin of island-arc andesites by magma mingling, crustal assimilation and crystal accumulation rather than by fractional crystallization of basaltic magmas. In this work we addressed the question about the scarcity of andesitic melts in island-arc setting by systematic study of bulk compositions, melt inclusions and oxygen isotopes in minerals from Avachinskiy volcano in Kamchatka. We studied ~500 melt inclusions in 6 different mineral phases (Ol, Cpx, Opx, Pl, Amph, Mt), and concentrated on rapidly-quenched tephra samples from 40 Holocene eruptions of andesites and basaltic andesites. The melt inclusions span a large range of compositions from basalts to rhyolites. In comparison with host bulk tephra samples, melt inclusions tend to have more silicic compositions (up to 10 wt% of SiO2), and this disparity tend to increase with increasing SiO2 content in the host rocks. Both melt inclusion and host rock compositions form trends along the line dividing low- and middle-K island-arc series, and variations of major elements are continuous, without apparent bimodality, which is observed in data set from [1]. The MI statistical distribution is rather three-modal with maxima at ~56-58, ~66 and 74 wt% of SiO2. Much of the major element variability in MI can be explained by fractional crystallization from parental basaltic melts using numerical modeling of crystallization path. Magnetite crystallization starts at ~58 wt% of SiO2 and affects significantly on the evolutional path of melts. Abundant crystallization of magnetite lead to formation of more silica rich coexistent melts and change of crystallizing assemblage occurred at ~60 wt% of SiO2, when Opx replaced Ol, and Amph and Ap become stable. Paragenesis of OPx, CPx, Amph, Pl, Mt, Ilm and Ap dominated the following evolution of melts toward strongly acid compositions with 78-80 wt% SiO2. Individual Pl and Amph crystals are in magmatic isotopic equilibrium, have heavy δ18O values increasing from 6.3 ‰ in basaltic andesites to 7.1 ‰ in andesites, suggesting that magmatic evolution started from primary high-d18O basalt likely related to the abundant high-d18O sources described for Kamchatkan primitive magmas. The oxygen isotopic data support the conclusion that island-arc andesitic melts of Avachinsky Volcano generate predominantly due to the processes of fractional crystallization of high-d18O. The new data on composition of melt inclusions allowed us to reconstruct the entire spectrum of parental melts for Avacha volcano. Melt inclusions in different minerals form coherent trends of major elements, which can be well explained by fractional crystallization. Unlike some other island-arc volcanoes, Avachinskiy melts do not display clear bimodality of SiO2 content. Melts of intermediate compositions are relatively abundant and found in minerals from basaltic andesites. [1] Reuby & Blundy (2009) Nature, 461(7268), 1269-1273.

KREEP basalt petrogenesis: Insights from 15434,181

NASA Astrophysics Data System (ADS)

Cronberger, Karl; Neal, Clive R.

2017-05-01

Returned lunar KREEP basalts originated through impact processes or endogenous melting of the lunar interior. Various methods have been used to distinguish between these two origins, with varying degrees of success. Apollo 15 KREEP basalts are generally considered to be endogenous melts of the lunar interior. For example, sample 15434,181 is reported to have formed by a two-stage cooling process, with large orthopyroxene (Opx) phenocrysts forming first and eventually cocrystalizing with smaller plagioclase crystals. However, major and trace element analyses of Opx and plagioclase coupled with calculated equilibrium liquids are inconsistent with the large orthopyroxenes being a phenocryst phase. Equilibrium liquid rare earth element (REE) profiles are enriched relative to the whole rock (WR) composition, inconsistent with Opx being an early crystallizing phase, and these are distinct from the plagioclase REE equilibrium liquids. Fractional crystallization modeling using the Opx equilibrium liquids as a parental composition cannot reproduce the WR values even with crystallization of late-stage phosphates and zircon. This work concludes that instead of being a phenocryst phase, the large Opx crystals are actually xenocrysts that were subsequently affected by pyroxene overgrowths that formed intergrowths with cocrystallizing plagioclase.

Controlling Crystal Microstructure to Minimize Loss in Polymer Dielectrics

NASA Astrophysics Data System (ADS)

Miranda, Daniel; Iacob, Ciprian; Zhang, Shihai; Runt, James

Polymer dielectric films are of great importance for high performance capacitors. For these films it is critical to reduce dielectric loss, as it diminishes efficiency and contributes to waste heat generation during device operation. Here, a model semi-crystalline polymer, poly(ethylene naphthalate) (PEN), was used to examine how morphological factors inhibit chain relaxations responsible for loss. This was achieved by manipulating the extent of crystallization and the crystalline microstructure through a combination of annealing and uniaxial drawing, and investigating their effects on dielectric performance. Varying crystallization conditions influenced the dynamic Tg and extent of rigid amorphous fraction formation, but had a limited effect on loss magnitude. Film orientation however greatly reduced loss, through strain-induced crystallization and development of oriented amorphous mesophasic regions. Post-drawing annealing conditions were capable of further refining the crystal microstructure and, in turn, the dielectric properties. These findings demonstrate that semi-crystalline polymer morphology has a very strong influence on amorphous chain relaxations, and understanding how processing conditions affect morphology is critical to the rational design of polymer dielectrics. Office of Naval Research.

Thermal control of low-pressure fractionation processes. [in basaltic magma solidification

NASA Technical Reports Server (NTRS)

Usselman, T. M.; Hodge, D. S.

1978-01-01

Thermal models detailing the solidification paths for shallow basaltic magma chambers (both open and closed systems) were calculated using finite-difference techniques. The total solidification time for closed chambers are comparable to previously published calculations; however, the temperature-time paths are not. These paths are dependent on the phase relations and the crystallinity of the system, because both affect the manner in which the latent heat of crystallization is distributed. In open systems, where a chamber would be periodically replenished with additional parental liquid, calculations indicate that the possibility is strong that a steady-state temperature interval is achieved near a major phase boundary. In these cases it is straightforward to analyze fractionation models of the basaltic liquid evolution and their corresponding cumulate sequences. This steady thermal fractionating state can be invoked to explain large amounts of erupted basalts of similar composition over long time periods from the same volcanic center and some rhythmically layered basic cumulate sequences.

Studies of quaternary saline lakes-I. Hydrogen isotope fractionation in saline minerals

USGS Publications Warehouse

Matsuo, S.; Friedman, I.; Smith, G.I.

1972-01-01

Borax, gaylussite, nahcolite and trona were synthesized in aqueous solution at temperatures ranging from 8?? to 35??C. Except for borax, deuterium was always depleted in these hydrated minerals relative to the solutions from which they were crystallized. In borax, no significant fractionation was found. The fractionation factor of D H for the trona-water system exhibited a marked temperature dependence. By combining the deuterium contents of trona and the solution from which trona was crystallized, the following thermometer scale was obtained: In ( D H) trona ( D H)water = 1.420 ?? 104 T2 + 23.56 T (1). An attempt to establish a geothermometer based on C13 C12 fractionation between carbonate minerals and carbonate ions in aqueous solution was not successful. ?? 1972.

Equilibrium fractionation of H and O isotopes in water from path integral molecular dynamics

NASA Astrophysics Data System (ADS)

Pinilla, Carlos; Blanchard, Marc; Balan, Etienne; Ferlat, Guillaume; Vuilleumier, Rodolphe; Mauri, Francesco

2014-06-01

The equilibrium fractionation factor between two phases is of importance for the understanding of many planetary and environmental processes. Although thermodynamic equilibrium can be achieved between minerals at high temperature, many natural processes involve reactions between liquids or aqueous solutions and solids. For crystals, the fractionation factor α can be theoretically determined using a statistical thermodynamic approach based on the vibrational properties of the phases. These calculations are mostly performed in the harmonic approximation, using empirical or ab-initio force fields. In the case of aperiodic and dynamic systems such as liquids or solutions, similar calculations can be done using finite-size molecular clusters or snapshots obtained from molecular dynamics (MD) runs. It is however difficult to assess the effect of these approximate models on the isotopic fractionation properties. In this work we present a systematic study of the calculation of the D/H and 18O/16O equilibrium fractionation factors in water for the liquid/vapour and ice/vapour phases using several levels of theory within the simulations. Namely, we use a thermodynamic integration approach based on Path Integral MD calculations (PIMD) and an empirical potential model of water. Compared with standard MD, PIMD takes into account quantum effects in the thermodynamic modeling of systems and the exact fractionation factor for a given potential can be obtained. We compare these exact results with those of modeling strategies usually used, which involve the mapping of the quantum system on its harmonic counterpart. The results show the importance of including configurational disorder for the estimation of isotope fractionation in liquid phases. In addition, the convergence of the fractionation factor as a function of parameters such as the size of the simulated system and multiple isotope substitution is analyzed, showing that isotope fractionation is essentially a local effect in the investigated system.

Dynamic Properties of DNA-Programmable Nanoparticle Crystallization.

PubMed

Yu, Qiuyan; Zhang, Xuena; Hu, Yi; Zhang, Zhihao; Wang, Rong

2016-08-23

The dynamics of DNA hybridization is very important in DNA-programmable nanoparticle crystallization. Here, coarse-grained molecular dynamics is utilized to explore the structural and dynamic properties of DNA hybridizations for a self-complementary DNA-directed nanoparticle self-assembly system. The hexagonal close-packed (HCP) and close-packed face-centered cubic (FCC) ordered structures are identified for the systems of different grafted DNA chains per nanoparticle, which are in good agreement with the experimental results. Most importantly, the dynamic crystallization processes of DNA hybridizations are elucidated by virtue of the mean square displacement, the percentage of hybridizations, and the lifetime of DNA bonds. The lifetime can be modeled by the DNA dehybridization, which has an exponential form. The lifetime of DNA bonds closely depends on the temperature. A suitable temperature for the DNA-nanoparticle crystallization is obtained in the work. Moreover, a too large volume fraction hinders the self-assembly process due to steric effects. This work provides some essential information for future design of nanomaterials.

Crystallization kinetics from mixture Na2SO4/glycerol droplets of Na2SO4 by FTIR-ATR

NASA Astrophysics Data System (ADS)

Tan, Dan-Ting; Cai, Chen; Zhang, Yun; Wang, Na; Pang, Shu-Feng; Zhang, Yun-Hong

2016-08-01

The efflorescence of mixed Na2SO4/glycerol aerosols on the ZnSe substrate with various mole ratios (Na2SO4/glycerol = 1:1, 1:2, 1:4) has been studied in the relative humidity (RH) linearly decline process, using a situ Fourier transform infrared attenuated total reflection (FTIR-ATR) technique. The crystal ratio at a given RH can be gained by the absorbance of the band at 1132 cm-1, which shows the incomplete nucleation for mixed Na2SO4/glycerol aerosols and the decreased amount of the droplets crystallized at the lowest RH with the glycerol increase. Using the volume fraction of droplets that have yet to crystallize, the heterogeneous nucleation kinetics has been gained. By the Extended Aerosol Inorganics Model (E-AIM), the nucleation rate as the function of solute saturation degree has been gained for various mixed Na2SO4/glycerol aerosols.

Compositional Effects on Nickel-Base Superalloy Single Crystal Microstructures

NASA Technical Reports Server (NTRS)

MacKay, Rebecca A.; Gabb, Timothy P.; Garg,Anita; Rogers, Richard B.; Nathal, Michael V.

2012-01-01

Fourteen nickel-base superalloy single crystals containing 0 to 5 wt% chromium (Cr), 0 to 11 wt% cobalt (Co), 6 to 12 wt% molybdenum (Mo), 0 to 4 wt% rhenium (Re), and fixed amounts of aluminum (Al) and tantalum (Ta) were examined to determine the effect of bulk composition on basic microstructural parameters, including gamma' solvus, gamma' volume fraction, volume fraction of topologically close-packed (TCP) phases, phase chemistries, and gamma - gamma'. lattice mismatch. Regression models were developed to describe the influence of bulk alloy composition on the microstructural parameters and were compared to predictions by a commercially available software tool that used computational thermodynamics. Co produced the largest change in gamma' solvus over the wide compositional range used in this study, and Mo produced the largest effect on the gamma lattice parameter and the gamma - gamma' lattice mismatch over its compositional range, although Re had a very potent influence on all microstructural parameters investigated. Changing the Cr, Co, Mo, and Re contents in the bulk alloy had a significant impact on their concentrations in the gamma matrix and, to a smaller extent, in the gamma' phase. The gamma phase chemistries exhibited strong temperature dependencies that were influenced by the gamma and gamma' volume fractions. A computational thermodynamic modeling tool significantly underpredicted gamma' solvus temperatures and grossly overpredicted the amount of TCP phase at 982 C. Furthermore, the predictions by the software tool for the gamma - gamma' lattice mismatch were typically of the wrong sign and magnitude, but predictions could be improved if TCP formation was suspended within the software program. However, the statistical regression models provided excellent estimations of the microstructural parameters based on bulk alloy composition, thereby demonstrating their usefulness.

Partially deuterated potassium dihydrogen phosphate optimized for ultra-broadband optical parametric amplification

NASA Astrophysics Data System (ADS)

Fujioka, K.; Fujimoto, Y.; Tsubakimoto, K.; Kawanaka, J.; Shoji, I.; Miyanaga, N.

2015-03-01

The refractive index of a potassium dihydrogen phosphate (KDP) crystal strongly depends on the deuteration fraction of the crystal. The wavelength dependence of the phase-matching angle in the near-infrared optical parametric process shows convex and concave characteristics for pure KDP and pure deuterated KDP (DKDP), respectively, when pumped by the second harmonic of Nd- or Yb-doped solid state lasers. Using these characteristics, ultra-broadband phase matching can be realized by optimization of the deuteration fraction. The refractive index of DKDP that was grown with a different deuteration fraction (known as partially deuterated KDP or pDKDP) was measured over a wide wavelength range of 0.4-1.5 μm by the minimum deviation method. The wavelength dispersions of the measured refractive indices were fitted using a modified Sellmeier equation, and the deuteration fraction dependence was analyzed using the Lorentz-Lorenz equation. The wavelength-dependent phase-matching angle for an arbitrary deuteration fraction was then calculated for optical parametric amplification with pumping at a wavelength of 526.5 nm. The results revealed that a refractive index database with precision of more than 2 × 10-5 was necessary for exact evaluation of the phase-matching condition. An ultra-broad gain bandwidth of up to 490 nm will be feasible when using the 68% pDKDP crystal.

Quantification of the intrusion process at Kīlauea volcano, Hawai'i

NASA Astrophysics Data System (ADS)

Wright, Thomas L.; Marsh, Bruce

2016-12-01

The characteristic size of two types of intrusions identified beneath Kīlauea's East Rift zone are uniquely estimated by combining time constraints from fractional crystallization and the rates of magma solidification during cooling. Some intrusions were rapidly emplaced as dikes, but stalled before reaching the surface, and cooled and crystallized to feed later fractionated eruptions. More specifically, using the observed time interval between initial emplacement and eruption of fractionated lava, whose degree of fractionation is estimated from petrologic mixing calculations, the extent of solidification or cooling needed to produce this amount of fractionation can be directly inferred. And from the known erupted volumes the spatial extent or size of this fractionated volume can be analytically related to the full size of the source body itself. Two examples yield dike widths of 82 and 68 m. Other intrusions remain close to the east rift magma transport path and are observed to last for decades or longer as viable magma bodies that may participate in feeding later eruptions. The thickness of semi-permanent reservoirs near the East Rift Zone magma transport path can be estimated by assuming a resupply rate that is sufficiently frequent to restrict cooling to < 10 °C. It is inferred that both types of intrusions likely began as dike offshoots from the East Rift Zone magma transport path, but the frequently resupplied bodies may have later been converted to sills or laccoliths of heights estimated at 43-62 m. Our modeled intrusions contrast with models of rapidly emplaced thinner dikes feeding shallow intrusions, which are accompanied by intense rift earthquake swarms and are often associated with eruptions. These calculations show that long-term heating of the wallrock of the magma transport paths serves to slow conduit cooling, which may be partly responsible for sustaining long East Rift Zone eruptions. Adjacent to the vertical transport path beneath Kīlauea's summit, the combined effects of heating and ever-increasing magma supply rate may have forced a commensurate enlarging of the conduit, perhaps explaining the occurrence of a temporary burst of deep (5-15 km) long-period earthquake swarms between 1987 and 1992.

Petrological constraints on the high-Mg basalts from Capo Marargiu (Sardinia, Italy): Evidence of cryptic amphibole fractionation in polybaric environments

NASA Astrophysics Data System (ADS)

Tecchiato, Vanni; Gaeta, Mario; Mollo, Silvio; Scarlato, Piergiorgio; Bachmann, Olivier; Perinelli, Cristina

2018-01-01

This study deals with the textural and compositional characteristics of the calc-alkaline stratigraphic sequence from Capo Marargiu Volcanic District (CMVD; Sardinia island, Italy). The area is dominated by basaltic to intermediate hypabyssal (dikes and sills) and volcanic rocks (lava flows and pyroclastic deposits) emplaced during the Oligo-Miocene orogenic magmatism of Sardinia. Interestingly, a basaltic andesitic dome hosts dark-grey, crystal-rich enclaves containing up 50% of millimetre- to centimetre-sized clinopyroxene and amphibole crystals. This mineral assemblage is in equilibrium with a high-Mg basalt recognised as the parental magma of the entire stratigraphic succession at CMVD. Analogously, centimetre-sized clots of medium- and coarse-grained amphibole + plagioclase crystals are entrapped in andesitic dikes that ultimately intrude the stratigraphic sequence. Amphibole-plagioclase cosaturation occurs at equilibrium with a differentiated basaltic andesite. Major and trace element modelling indicates that the evolutionary path of magma is controlled by a two-step process driven by early olivine + clinopyroxene and late amphibole + plagioclase fractionation. In this context, enclaves represent parts of a cumulate horizon segregated at the early stage of differentiation of the precursory high-Mg basalt. This is denoted by i) resorption effects and sharp transitions between Mg-rich and Mg-poor clinopyroxenes, indicative of pervasive dissolution phenomena followed by crystal re-equilibration and overgrowth, and ii) reaction minerals found in amphibole coronas formed at the interface with more differentiated melts infiltrating within the cumulate horizon, and carrying the crystal-rich material with them upon eruption. Coherently, the mineral chemistry and phase relations of enclaves indicate crystallisation in a high-temperature, high-pressure environment under water-rich conditions. On the other hand, the upward migration and subsequent fractionation of the residual basaltic andesite in a shallower, colder, and hydrous region of the CMVD plumbing system lead to the formation of the amphibole-plagioclase crystal clots finally entrained by the andesitic dikes. Indeed, phenocrysts from these more evolved products record the final crystallisation path of magma during ascent towards the surface. Magma decompression and volatile loss cause the formation of amphibole reaction coronas and the crystallisation of a more sodic plagioclase in equilibrium with basaltic andesitic to andesitic melts. The bulk-rock geochemical signature of these products testifies to open-system, polybaric magma dynamics, accounting for variable degrees of crustal assimilation of the Hercynian basement of Sardinia.

In situ major and trace element analysis of amphiboles in quartz monzodiorite porphyry from the Tonglvshan Cu-Fe (Au) deposit, Hubei Province, China: insights into magma evolution and related mineralization

NASA Astrophysics Data System (ADS)

Duan, Deng-Fei; Jiang, Shao-Yong

2017-05-01

The Tonglvshan deposit is the largest Cu-Fe (Au) skarn deposit in the Edong district, which is located in the westernmost part of the Middle and Lower Yangtze River metallogenic belt, China. In this study, we performed a detailed in situ analysis of major and trace elements in amphiboles from the ore-related Tonglvshan quartz monzodiorite porphyry using electron microprobe (EMPA) analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two distinct populations of amphiboles, which can be distinguished by their aluminum content, are found in the quartz monzodiorite porphyry. The low-aluminum (Low-Al) amphiboles are subhedral or anhedral and formed at 46.3-73.5 MPa and 713-763 °C. In contrast, the high-aluminum (High-Al) amphiboles are euhedral and formed at 88-165 MPa and 778-854 °C. Some euhedral amphiboles are partially or completely replaced by Low-Al amphibole. The compositions of parental melts in equilibrium with the High-Al amphibole ( Melt 1) and Low-Al amphibole ( Melt 2) were computed by applying solid/liquid partition coefficients. This modeling shows that magma in equilibrium with High-Al amphibole ( Melt 1) underwent 40% fractional crystallization of amphibole, plagioclase and apatite at a depth of 5 km to evolve to magma in equilibrium with Low-Al amphibole ( Melt 2). Copper enrichment occurred in the magma after undergoing fractional crystallization. The magma had a high oxygen fugacity, increasing from NNO + 1 ( Melt 1) through NNO + 2 to HM ( Melt 2), which could have prevented the loss of Cu (and possibly Au) to sulfide minerals during crystallization. Finally, the evolved magma intruded to shallower depths, where it presumably exsolved aqueous ore-forming fluids. Therefore, the large Cu-Fe-Au reserves of the Tonglvshan deposit can likely be attributed to a combination of controlling factors, including high oxygen fugacity, fractional crystallization, fluid exsolution, and a shallow emplacement depth.

Group IVA irons: New constraints on the crystallization and cooling history of an asteroidal core with a complex history

NASA Astrophysics Data System (ADS)

McCoy, T. J.; Walker, R. J.; Goldstein, J. I.; Yang, J.; McDonough, W. F.; Rumble, D.; Chabot, N. L.; Ash, R. D.; Corrigan, C. M.; Michael, J. R.; Kotula, P. G.

2011-11-01

We report analyses of 14 group IVA iron meteorites, and the ungrouped but possibly related, Elephant Moraine (EET) 83230, for siderophile elements by laser ablation ICP-MS and isotope dilution. EET was also analyzed for oxygen isotopic composition and metallographic structure, and Fuzzy Creek, currently the IVA with the highest Ni concentration, was analyzed for metallographic structure. Highly siderophile elements (HSE) Re, Os and Ir concentrations vary by nearly three orders of magnitude over the entire range of IVA irons, while Ru, Pt and Pd vary by less than factors of five. Chondrite normalized abundances of HSE form nested patterns consistent with progressive crystal-liquid fractionation. Attempts to collectively model the HSE abundances resulting from fractional crystallization achieved best results for 3 wt.% S, compared to 0.5 or 9 wt.% S. Consistent with prior studies, concentrations of HSE and other refractory siderophile elements estimated for the bulk IVA core and its parent body are in generally chondritic proportions. Projected abundances of Pd and Au, relative to more refractory HSE, are slightly elevated and modestly differ from L/LL chondrites, which some have linked with group IVA, based on oxygen isotope similarities. Abundance trends for the moderately volatile and siderophile element Ga cannot be adequately modeled for any S concentration, the cause of which remains enigmatic. Further, concentrations of some moderately volatile and siderophile elements indicate marked, progressive depletions in the IVA system. However, if the IVA core began crystallization with ˜3 wt.% S, depletions of more volatile elements cannot be explained as a result of prior volatilization/condensation processes. The initial IVA core had an approximately chondritic Ni/Co ratio, but a fractionated Fe/Ni ratio of ˜10, indicates an Fe-depleted core. This composition is most easily accounted for by assuming that the surrounding silicate shell was enriched in iron, consistent with an oxidized parent body. The depletions in Ga may reflect decreased siderophilic behavior in a relatively oxidized body, and more favorable partitioning into the silicate portion of the parent body. Phosphate inclusions in EET show Δ 17O values within the range measured for silicates in IVA iron meteorites. EET has a typical ataxitic microstructure with precipitates of kamacite within a matrix of plessite. Chemical and isotopic evidence for a genetic relation between EET and group IVA is strong, but the high Ni content and the newly determined, rapid cooling rate of this meteorite show that it should continue to be classified as ungrouped. Previously reported metallographic cooling rates for IVA iron meteorites have been interpreted to indicate an inwardly crystallizing, ˜150 km radius metallic body with little or no silicate mantle. Hence, the IVA group was likely formed as a mass of molten metal separated from a much larger parent body that was broken apart by a large impact. Given the apparent genetic relation with IVA, EET was most likely generated via crystal-liquid fractionation in another, smaller body spawned from the same initial liquid during the impact event that generated the IVA body.

Disequilibrium dihedral angles in layered intrusions: the microstructural record of fractionation

NASA Astrophysics Data System (ADS)

Holness, Marian; Namur, Olivier; Cawthorn, Grant

2013-04-01

The dihedral angle formed at junctions between two plagioclase grains and a grain of augite is only rarely in textural equilibrium in gabbros from km-scale crustal layered intrusions. The median of a population of these disequilibrium angles, Θcpp, varies systematically within individual layered intrusions, remaining constant over large stretches of stratigraphy with significant increases or decreases associated with the addition or reduction respectively of the number of phases on the liquidus of the bulk magma. The step-wise changes in Θcpp are present in Upper Zone of the Bushveld Complex, the Megacyclic Unit I of the Sept Iles Intrusion, and the Layered Series of the Skaergaard Intrusion. The plagioclase-bearing cumulates of Rum have a bimodal distribution of Θcpp, dependent on whether the cumulus assemblage includes clinopyroxene. The presence of the step-wise changes is independent of the order of arrival of cumulus phases and of the composition of either the cumulus phases or the interstitial liquid inferred to be present in the crystal mush. Step-wise changes in the rate of change in enthalpy with temperature (ΔH) of the cooling and crystallizing magma correspond to the observed variation of Θcpp, with increases of both ΔH and Θcpp associated with the addition of another liquidus phase, and decreases of both associated with the removal of a liquidus phase. The replacement of one phase by another (e.g. olivine ⇔ orthpyroxene) has little effect on ΔH and no discernible effect on Θcpp. An increase of ΔH is manifest by an increase in the fraction of the total enthalpy budget that is the latent heat of crystallization (the fractional latent heat). It also results in an increase in the amount crystallized in each incremental temperature drop (the crystal productivity). An increased fractional latent heat and crystal productivity result in an increased rate of plagioclase growth compared to that of augite during the final stages of solidification, causing a step-wise increase in Θcpp. Step-wise changes in the geometry of three-grain junctions in fully solidified gabbros thus provide a clear microstructural marker for the progress of fractionation.

Reinvestigation of growth of 'L-valine zinc sulphate' crystal.

PubMed

Srinivasan, Bikshandarkoil R; Jyai, Rita N

2014-01-01

A reinvestigation of the growth of l-valine zinc sulphate crystal is reported. The slow evaporation of an aqueous solution containing l-valine and zinc sulphate heptahydrate results in the fractional crystallization of l-valine and not the organic inorganic hybrid nonlinear optical l-valine zinc sulphate crystal, as reported by Puhal Raj and Ramachandra Raja (2012). Copyright © 2013 Elsevier B.V. All rights reserved.

An Interactive Computer Program for Simulating the Effects of Olivine Fractionation from Basaltic and Ultrabasic Liquids.

ERIC Educational Resources Information Center

Pearce, Thomas H.

1983-01-01

Describes interactive computer program (listing available from author) which simulates olivine fractionation from basaltic/ultrabasic liquid. The menu-driven nature of the program (for Apple II microcomputer) allows students to select ideal Rayleigh fractionation or equilibrium crystallization. (JN)

The component slope linear model for calculating intensive partial molar properties /application to waste glasses and aluminate solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, Jacob G.

2013-01-11

Partial molar properties are the changes occurring when the fraction of one component is varied while the fractions of all other component mole fractions change proportionally. They have many practical and theoretical applications in chemical thermodynamics. Partial molar properties of chemical mixtures are difficult to measure because the component mole fractions must sum to one, so a change in fraction of one component must be offset with a change in one or more other components. Given that more than one component fraction is changing at a time, it is difficult to assign a change in measured response to a changemore » in a single component. In this study, the Component Slope Linear Model (CSLM), a model previously published in the statistics literature, is shown to have coefficients that correspond to the intensive partial molar properties. If a measured property is plotted against the mole fraction of a component while keeping the proportions of all other components constant, the slope at any given point on a graph of this curve is the partial molar property for that constituent. Actually plotting this graph has been used to determine partial molar properties for many years. The CSLM directly includes this slope in a model that predicts properties as a function of the component mole fractions. This model is demonstrated by applying it to the constant pressure heat capacity data from the NaOH-NaAl(OH){sub 4}-H{sub 2}O system, a system that simplifies Hanford nuclear waste. The partial molar properties of H{sub 2}O, NaOH, and NaAl(OH){sub 4} are determined. The equivalence of the CSLM and the graphical method is verified by comparing results determined by the two methods. The CSLM model has been previously used to predict the liquidus temperature of spinel crystals precipitated from Hanford waste glass. Those model coefficients are re-interpreted here as the partial molar spinel liquidus temperature of the glass components.« less

The Component Slope Linear Model for Calculating Intensive Partial Molar Properties: Application to Waste Glasses and Aluminate Solutions - 13099

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, Jacob G.

2013-07-01

Partial molar properties are the changes occurring when the fraction of one component is varied while the fractions of all other component mole fractions change proportionally. They have many practical and theoretical applications in chemical thermodynamics. Partial molar properties of chemical mixtures are difficult to measure because the component mole fractions must sum to one, so a change in fraction of one component must be offset with a change in one or more other components. Given that more than one component fraction is changing at a time, it is difficult to assign a change in measured response to a changemore » in a single component. In this study, the Component Slope Linear Model (CSLM), a model previously published in the statistics literature, is shown to have coefficients that correspond to the intensive partial molar properties. If a measured property is plotted against the mole fraction of a component while keeping the proportions of all other components constant, the slope at any given point on a graph of this curve is the partial molar property for that constituent. Actually plotting this graph has been used to determine partial molar properties for many years. The CSLM directly includes this slope in a model that predicts properties as a function of the component mole fractions. This model is demonstrated by applying it to the constant pressure heat capacity data from the NaOHNaAl(OH){sub 4}-H{sub 2}O system, a system that simplifies Hanford nuclear waste. The partial molar properties of H{sub 2}O, NaOH, and NaAl(OH){sub 4} are determined. The equivalence of the CSLM and the graphical method is verified by comparing results determined by the two methods. The CSLM model has been previously used to predict the liquidus temperature of spinel crystals precipitated from Hanford waste glass. Those model coefficients are re-interpreted here as the partial molar spinel liquidus temperature of the glass components. (authors)« less

Folding of Polymer Chains in Early Stage of Crystallization

NASA Astrophysics Data System (ADS)

Yuan, Shichen; Miyoshi, Toshikazu

Understanding the structural formation of long polymer chains in the early stage of crystallization is one of the long-standing problems in polymer science. Using solid state NMR, we investigated chain trajectory of isotactic polypropylene in the mesomorphic nano-domains formed via rapid and deep quenching. Comparison of experimental and simulated 13C-13C Double Quantum (DQ) buildup curves demonstrated that instead of random re-entry models and solidification models, individual chains in the mesomorphic form iPP adopt adjacent reentry sequences with an average folding number of = 3-4 (assuming an adjacent re-entry fraction of of 100%) during mesomorphic formation process via nucleation and growth in the early stage. This work was financially supported by the National Science Foundation (Grant DMR-1105829 and 1408855) and startup funds from the UA.

Chronology and petrogenesis of a 1.8 g lunar granitic clast:14321,1062

NASA Technical Reports Server (NTRS)

Shih, C.-Y.; Bansal, B. M.; Wiesmann, H.; Nyquist, L. E.; Bogard, D. D.; Wooden, J. L.

1985-01-01

Geochronological, isotopic, and trace element data for a pristine granite clast from Apollo 14 breccia 14321 obtained using Rb-Sr, Sm-Nd, and (Ar-39)-(Ar-40) methods are presented. Trace element data for a possibly related evolved rock, the quartz-monodiorite clast from breccia 15404 are also presented, and the relationship between these two rock types is discussed. The concordancy of the Rb-Sr and Sm-Nd internal isochron ages and especially the Rb-Sr model age strongly suggest that the granite clast formed 4.1 AE ago. It probably crystallized slowly in the crust and was later excavated and brecciated about 3.88 AE ago, as indicated by the Ar-Ar age. A two-stage model involving crystal fractionation followed by silicate liquid immiscibility is proposed for the lunar granite genesis.

Petrology and geochemistry of the orbicular granitoid of Caldera, northern Chile. Models and hypotheses on the formation of radial orbicular textures

NASA Astrophysics Data System (ADS)

Díaz-Alvarado, Juan; Rodríguez, Natalia; Rodríguez, Carmen; Fernández, Carlos; Constanzo, Ítalo

2017-07-01

The orbicular granitoid of Caldera, located at the northern part of the Chilean Coastal Range, is a spectacular example of radial textures in orbicular structures. The orbicular body crops out as a 375 m2 tabular to lensoidal intrusive sheet emplaced in the Lower Jurassic Relincho pluton. The orbicular structures are 3-7 cm in diameter ellipsoids hosted in a porphyritic matrix. The orbicules are comprised by a Qtz-dioritic core (3-5 cm in diameter) composed by Pl + Hbl + Qtz + Bt ± Kfs with equiaxial textures and a gabbroic shell (2-3 cm in diameter) characterized by feathery and radiate textures with a plagioclase + hornblende paragenesis. The radial shell crystals are rooted and orthogonally disposed in the irregular contact with the core. The radial shell, called here inner shell, is in contact with the granodioritic equiaxial interorbicular matrix through a 2-3 mm wide poikilitic band around the orbicule (outer shell). The outer shell and the matrix surrounding the orbicules are characterized by the presence of large hornblende and biotite oikocrystals that include fine-grained rounded plagioclase and magnetite. The oikocrystals of both the outer shell and the matrix have a circumferential arrangement around the orbicule, i.e. orthogonal to the radial inner shell. The coarse-grained granodioritic interorbicular matrix present pegmatitic domains with large acicular hornblende and K-feldspar megacrysts. This work presents a review of the textural characteristics of the orbicules and a complete new mineral and whole-rock geochemical study of the different parts of the orbicular granitoid, together with thermobarometric and crystallographic data, and theoretical modeling of the crystallization and element partitioning processes. We propose a model for the formation of the orbicular radial textures consisting of several processes that are suggested to occur fast and consecutively: superheating, volatile exsolution, undercooling, geochemical fractionation and columnar and equiaxial crystallization. According to the obtained results, the formation of the orbicular granitoid of Caldera may have initiated 1) during the generation of a magmatic fracture in the crystallization front of the Relincho pluton, where the water released by the host crystal mush was dissolved in the new batch of dioritic magma. 2) The high influx of water-rich liquids induced superheating conditions in the newly intruding magma that became a depolymerized liquid, where the only solid particules were the small irregular fragments of the host mush dragged from the fracture walls. 3) Volatile exsolution promoted crystallization under undercooling conditions. 4) Undercooling and nucleation around the core (cold germs) involved the physical and geochemical fractionation between two sub-systems: a gabbroic sub-system that comprises the solid paragénesis with a residual water-rich liquid and a granodioritic sub-system. 5) The orbicules, including core and inner shell, behaved as viscous bodies (crystals + residual liquid) floating in the granodioritic magma. 6) Higher undercooling rates occurred at the starting stage, close to the liquidus, promoting columnar crystallization around the cores and formation of the shells. Conversely, in the granodioritic matrix sub-system, equiaxial crystallization was promoted by low relative crystallization rates. 7) The rest of the crystallization process evolved later in the outer shell and the matrix, as suggested by the poikilitic textures observed in both sides of the orbicule contact, and under conditions close to the solidus of both sub-systems (shell and matrix). The water-rich residual liquid expelled during the orbicular shell crystallization was mingled with the partially crystallized matrix magma, generating the pegmatitic domains with large Kfs megacrysts.

Ab initio solution of macromolecular crystal structures without direct methods.

PubMed

McCoy, Airlie J; Oeffner, Robert D; Wrobel, Antoni G; Ojala, Juha R M; Tryggvason, Karl; Lohkamp, Bernhard; Read, Randy J

2017-04-04

The majority of macromolecular crystal structures are determined using the method of molecular replacement, in which known related structures are rotated and translated to provide an initial atomic model for the new structure. A theoretical understanding of the signal-to-noise ratio in likelihood-based molecular replacement searches has been developed to account for the influence of model quality and completeness, as well as the resolution of the diffraction data. Here we show that, contrary to current belief, molecular replacement need not be restricted to the use of models comprising a substantial fraction of the unknown structure. Instead, likelihood-based methods allow a continuum of applications depending predictably on the quality of the model and the resolution of the data. Unexpectedly, our understanding of the signal-to-noise ratio in molecular replacement leads to the finding that, with data to sufficiently high resolution, fragments as small as single atoms of elements usually found in proteins can yield ab initio solutions of macromolecular structures, including some that elude traditional direct methods.

Production of extreme-purity aluminum and silicon by fractional crystallization processing

NASA Astrophysics Data System (ADS)

Dawless, R. K.; Troup, R. L.; Meier, D. L.; Rohatgi, A.

1988-06-01

Large scale fractional crystallization is used commercially at Alcoa to produce extreme purity aluminum (99.999+% Al). The primary market is sputtering targets used to make interconnects for integrated circuits. For some applications the impurities uranium and thorium are reduced to less than 1 ppbw to avoid "soft errors" associated with α particle emission. The crystallization process achieves segregation coefficients which are close to theoretical at normal yields, and this, coupled with the scale of the units, allows practical production of this material. The silicon purification process involves crystallization of Si from molten aluminum alloys containing about 30% silicon. The crystallites from this process are further treated to remove residual Al and an extreme purity ingot is obtained. This material is considered suitable for single crystal or ribbon type photovoltaic cells and for certain IC applications, including highly doped substrates used for epitaxial growth. In production of both extreme purity Al and Si, impurities are rejected to the remaining melt as the crystals form and some separation is achieved by draining this downgraded melt from the unit. Purification of this downgrade by crystallization has also been demonstrated for both systems and is important for achieving high recoveries.

Multi-Scale Computational Modeling of Two-Phased Metal Using GMC Method

NASA Technical Reports Server (NTRS)

Moghaddam, Masoud Ghorbani; Achuthan, A.; Bednacyk, B. A.; Arnold, S. M.; Pineda, E. J.

2014-01-01

A multi-scale computational model for determining plastic behavior in two-phased CMSX-4 Ni-based superalloys is developed on a finite element analysis (FEA) framework employing crystal plasticity constitutive model that can capture the microstructural scale stress field. The generalized method of cells (GMC) micromechanics model is used for homogenizing the local field quantities. At first, GMC as stand-alone is validated by analyzing a repeating unit cell (RUC) as a two-phased sample with 72.9% volume fraction of gamma'-precipitate in the gamma-matrix phase and comparing the results with those predicted by finite element analysis (FEA) models incorporating the same crystal plasticity constitutive model. The global stress-strain behavior and the local field quantity distributions predicted by GMC demonstrated good agreement with FEA. High computational saving, at the expense of some accuracy in the components of local tensor field quantities, was obtained with GMC. Finally, the capability of the developed multi-scale model linking FEA and GMC to solve real life sized structures is demonstrated by analyzing an engine disc component and determining the microstructural scale details of the field quantities.

Evaluating crustal contributions to enriched shergottites from the petrology, trace elements, and Rb-Sr and Sm-Nd isotope systematics of Northwest Africa 856

NASA Astrophysics Data System (ADS)

Ferdous, J.; Brandon, A. D.; Peslier, A. H.; Pirotte, Z.

2017-08-01

The origin of the incompatible trace element (ITE) characteristics of enriched shergottites has been critical for examining two contradicting scenarios to explain how these Martian meteorites form. The first scenario is that it reflects ITE enrichment in an early-formed mantle reservoir whereas the second scenario attributes it to assimilation of ancient Martian crust (∼4-4.5 Ga) by ITE-depleted magmas. Strongly differentiated shergottite magmas may yield added constraints for determining which scenario can best explain this signature in enriched shergottites. The meteorite Northwest Africa (NWA) 856 is a basaltic shergottite that, unlike many enriched shergottites, lacks olivine and has undergone extensive differentiation from more primitive parent magma. In similarity to other basaltic shergottites, NWA 856 is comprised primarily of compositionally zoned clinopyroxenes (45% pigeonite and 23% augite), maskelynite (23%) and accessory minerals such as ulvöspinel, merrillite, Cl-apatite, ilmenite, pyrrhotite, baddeleyite and silica polymorph. The CI-chondrite normalized rare earth element (REE) abundance patterns for its maskelynite, phosphates, and its whole rock are flat with corresponding light-REE depletions in clinopyroxenes. The 87Rb-87Sr and 147Sm-143Nd internal isochron ages are 162 ± 14 (all errors are ±2σ) Ma and 162.7 ± 5.5 Ma, respectively, with an initial εNdI = -6.6 ± 0.2. The Rb-Sr isotope systematics are affected by terrestrial alteration resulting in larger scatter and a less precise internal isochron age. The whole rock composition is used in MELTS simulations to model equilibrium and fractional crystallization sequences to compare with the crystallization sequence from textural observations and to the mineral compositions. These models constrain the depth of initial crystallization to a pressure range of 0.4-0.5 GPa (equivalent to 34-42 km) in anhydrous conditions at the Fayalite-Magnetite-Quartz buffer, and consistently reproduce the observed mineralogy throughout the sequence with progressive crystallization. The Ti/Al ratios in the clinopyroxenes are consistent with initial crystallization occurring at these depths followed by polybaric crystallization as the parent magma ascended to the surface. The REE abundances in the clinopyroxenes and maskelynite are consistent with progressive crystallization in a closed system. The new results for NWA 856 are combined with other shergottite data and are compared to mixing and assimilation and fractional crystallization (AFC) models using depleted shergottite magmas and ancient Martian crust as end-members. The models indicate that the range of REE abundances and ratios, when taken in isolation, can be successfully explained for all shergottites by crustal contamination. However, no successful crustal contamination model can explain the restricted εNdI of -6.8 ± 0.2 over the wide range of Mg# (0.65-0.25), and corresponding trace element variations from enriched shergottites to depleted shergottites. The findings indicate that the origin of the long-term ITE-enriched signature in enriched shergottites and the geochemical variability seen in shergottites is not a result of crustal contamination but instead reflects ancient mantle heterogeneity.

The study of the thermal behavior of a new semicrystalline polyimide

NASA Technical Reports Server (NTRS)

Cheng, Stephen Z. D.; Chalmers, Tammy M.

1992-01-01

Thermal properties of a new semicrystalline polyimide synthesized from 3,3',4,4' benzophenone tetracarboxylic dianhydride (BTDA) and 2,2 dimethyl 1,2-(4 aminophenoxy) propane (DMDA) were studied. Heat capacities in the solid and liquid states of BTDA-DMDA were measured. The heat capacity increase at the glass transition temperature (T sub g = 230 C) is 145 J/(C mol) for amorphous BTDA-DMDA. The equilibrium heat of fusion of the BTDA-DMDA crystals was obtained using wide angle X ray diffraction and differential scanning calorimetry measurements, and it is 75.8 kJ/mol. Based on the information of crystallinity and the heat capacity increase at T sub g, a rigid amorphous fraction is identified in semicrystalline BTDA-DMDA samples. The rigid amorphous fraction represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample which should be associated with crystal sizes, and therefore, with crystal morphology. It was also found that this polymer has a high temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies are determined to be 154 and 150 kJ/mol in nitrogen and air, respectively.

The origin of volatiles in the Earth's mantle

NASA Astrophysics Data System (ADS)

Hier-Majumder, Saswata; Hirschmann, Marc M.

2017-08-01

The Earth's deep interior contains significant reservoirs of volatiles such as H, C, and N. Due to the incompatible nature of these volatile species, it has been difficult to reconcile their storage in the residual mantle immediately following crystallization of the terrestrial magma ocean (MO). As the magma ocean freezes, it is commonly assumed that very small amounts of melt are retained in the residual mantle, limiting the trapped volatile concentration in the primordial mantle. In this article, we show that inefficient melt drainage out of the freezing front can retain large amounts of volatiles hosted in the trapped melt in the residual mantle while creating a thick early atmosphere. Using a two-phase flow model, we demonstrate that compaction within the moving freezing front is inefficient over time scales characteristic of magma ocean solidification. We employ a scaling relation between the trapped melt fraction, the rate of compaction, and the rate of freezing in our magma ocean evolution model. For cosmochemically plausible fractions of volatiles delivered during the later stages of accretion, our calculations suggest that up to 77% of total H2O and 12% of CO2 could have been trapped in the mantle during magma ocean crystallization. The assumption of a constant trapped melt fraction underestimates the mass of volatiles in the residual mantle by more than an order of magnitude.