Formation and preservation of pedogenic carbonates in South India, links with paleo-monsoon and pedological conditions: Clues from Sr isotopes, U-Th series and REEs

The influence of the pedogenic and climatic contexts on the formation and preservation of pedogenic carbonates in a climosequence in the Western Ghats (Karnataka Plateau, South West India) has been studied. Along the climosequence, the current mean annual rainfall (MAR) varies within a 80 km transect from 6000 mm at the edge of the Plateau to 500 mm inland. Pedogenic carbonates occur in the MAR range of 500-1200 mm. In the semi-arid zone (MAR: 500-900 mm), carbonates occur (i) as rhick hardpan calcretes on pediment slopes and (ii) as nodular horizons in polygenic black soils (i.e. vertisols). In the sub-humid zone (MAR: 900-1500 mm), pedogenic carbonates are disseminated in the black soil matrices either as loose, irregular and friable nodules of millimetric size or as indurated botryoidal nodules of centimetric to pluricentimetric size. They also occur at the top layers of the saprolite either as disseminated pluricentimetric indurated nodules or carbonate-cemented lumps of centimetric to decimetric size. Chemical and isotopic (Sr-87/Sr-86) compositions of the carbonate fraction were determined after leaching with 0.25 N HCl. The corresponding residual fractions containing both primary minerals and authigenic clays were digested separately and analyzed. The trend defined by the Sr-87/Sr-86 signatures of both labile carbonate fractions and corresponding residual fractions indicates that a part of the labile carbonate fraction is genetically linked to the local soil composition. Considering the residual fraction of each sample as the most likely lithogenic source of Ca in carbonates, it is estimated that from 24% to 82% (55% on average) of Ca is derived from local bedrock weathering, leading to a consumption of an equivalent proportion of atmospheric CO2. These values indicate that climatic conditions were humid enough to allow silicate weathering: MAR at the time of carbonate formation likely ranged from 400 to 700 mm, which is 2- to 3-fold less than the current MAR at these locations. The Sr, U and Mg contents and the (U-234/U-238) activity ratio in the labile carbonate fraction help to understand the conditions of carbonate formation. The relatively high concentrations of Sr, U and Mg in black soil carbonates may indicate fast growth and accumulation compared to carbonates in saprolite, possibly due to a better confinement of the pore waters which is supported by their high (U-234/U-238) signatures, and/or to higher content of dissolved carbonates in the pore waters. The occurrence of Ce, Mn and Fe oxides in the cracks of carbonate reflects the existence of relatively humid periods after carbonate formation. The carbonate ages determined by the U-Th method range from 1.33 +/- 0.84 kyr to 7.5 +/- 2.7 kyr and to a cluster of five ages around 20 kyr, i.e. the Last Glacial Maximum period. The young occurrences are only located in the black soils, which therefore constitute sensitive environments for trapping and retaining atmospheric CO2 even on short time scales. The maximum age of carbonates depends on their location in the climatic gradient: from about 20 kyr for centimetric nodules at Mule Hole (MAR = 1100 mm/yr) to 200 kyr for the calcrete at Gundlupet (MAR = 700 mm/yr, Durand et al., 2007). The intensity of rainfall during wet periods would indeed control the lifetime of pedogenic carbonates and thus the duration of inorganic carbon storage in soils. (C) 2010 Elsevier Ltd. All rights reserved.

Bubble formation at closely spaced orifices in aqueous solutions

A filter cloth with 182 holes per 10−4 m2 has been used to generate air bubbles both in pure water and in aqueous solutions of electrolytes and non-electrolytes at various air flow rates. Potassium bromide and ammonium perchlorate were the electrolytes used, while the non-electrolytes were isopropanol, urea and glycerol. Bubble diameters and their size distribution were measured from photographs. The role of solutes in affecting bubble sizes and their distribution compared to that of pure water is discussed in the light of a hypothesis. This hypothesis assumes that if the final bubble diameter is less than the inter-orifice distance, then bubbles do not coalesce; on the other hand, if it is greater, then coalescence occurs when tf greater-or-equal, slantedti+ts, but does not occur when t

Formation of Single-Phase Indium Selenide Thin Films by Elemental Evaporation

Formation of crystalline, monophasic indium selenide (InSe) thin solid films by elemental evaporation on hot glass substrates (400 to 530 K) is reported. The compound formation as well as the composition of the formed films are confirmed by X-ray photoelectron spectroscopy (XPS) analysis. The crystallinity of the rhombohedral InSe films can be improved by post-depositional annealing for t < 30 min at 533 K. The InSe thin films become Se-deficient at higher temperatures of deposition or longer duration of annealing. Optical studies reveal the bandgap to be around 1.29 eV. Under optimum conditions of preparations the lowest resistivity of ≈ 12.8 Ω cm is obtained. Durch Verdampfen aus den Elementen auf heiße Glassubstrate (400 bis 530 k) werden dünne, kristalline, einphasige Indiumselenid (InSe)-Festkörperschichten gebildet. Sowohl die Bildung der Verbindung als auch die Zusammensetzung der Schichten werden durch Röntgen-Photoelektronenspektroskopie (XPS) untersucht. Die Kristallinität der rhomboedrischen InSe-Schichten kann durch eine Temperung bei 533 K für t < 30 min nach der Abscheidung verbessert werden. Die dünnen InSe-Schichten zeigen nach Abscheidung bei höheren Temperaturen oder längerer Temperungsdauer einen Se-Unterschuß. Optische Untersuchungen ergeben, daß die Bandlücke bei etwa 1,29 eV liegt. Unter optimalen Präperationsbedingungen wird ein niedrigster Widerstand von ≈ 12.8 Ω cm erreicht.

Kinetics of ceric ion oxidation of naphthalene and its derivatives. Formation of the radical cation intermediate in the rate limiting step

Ceric ammonium sulfate, CAS, oxidizes naphthalene to 1,4-naphthoquinone in essentially quantitative yield in CH3CN-dil. H2SO4. Stoichiometric studies indicate that 6 mol of CAS are required for the oxidation of 1 mol of naphthalene to 1,4-naphthoquinone. Kinetic investigations reveal that the reaction takes place through initial formation of a 1:1 complex of naphthalene and cerium(IV) in an equilibrium step followed by slow decomposition of the complex to naphthalene radical cation. Kinetic results on the effects of acid strength, polarity of the medium, temperature and substituents are in accordance with this mechanism. Further conversion of the radical cation into 1,4-naphthoquinone takes place in fast steps involving a further 5 mol of cerium(IV) and 2 mol of H2O.

Influence of Inclination Angle and Machining Direction on Friction and Transfer Layer Formation

In the present investigation, unidirectional grinding marks were created on a set of steel plates. Sliding experiments were then conducted with the prepared steel plates using Al-Mg alloy pins and an inclined pin-on-plate sliding tester. The goals of the experiments were to ascertain the influence of inclination angle and grinding mark direction on friction and transfer layer formation during sliding contact. The inclination angle of the plate was held at 0.2 deg, 0.6 deg, 1 deg, 1.4 deg, 1.8 deg, 2.2 deg, and 2.6 deg in the tests. The pins were slid both perpendicular and parallel to the grinding marks direction. The experiments were conducted under both dry and lubricated conditions on each plate in an ambient environment. Results showed that the coefficient of friction and the formation of transfer layer depend on the grinding marks direction and inclination angle of the hard surfaces. For a given inclination angle, under both dry and lubricated conditions, the coefficient of friction and transfer layer formation were found to be greater when the pins slid perpendicular to the unidirectional grinding marks than when the pins slid parallel to the grinding marks. In addition, a stick-slip phenomenon was observed under lubricated conditions at the highest inclination angle for sliding perpendicular to the grinding marks direction. This phenomenon could be attributed to the extent of plane strain conditions taking place at the asperity level during sliding. DOI: 10.1115/1.4002604]

Phase Relations in the System Cu-Gd-O and Gibbs Energy of Formation of CuGd204

The phase relations in the system Cu-Gd-O have been determined at 1273 K by X-ray diffrac- tion, optical microscopy, and electron microprobe analysis of samples equilibrated in quartz ampules and in pure oxygen. Only one ternary compound, CuGd2O4, was found to be stable. The Gibbs free energy of formation of this compound has been measured using the solid-state cell Pt, Cu2O + CuGd2O4 + Gd2O3 // (Y2O3) ZrO2 // CuO + Cu2O, Pt in the temperature range of 900 to 1350 K. For the formation of CuGd2O4 from its binary component oxides, CuO (s) + Gd2O3 (s) → CuGd2O4 (s) ΔG° = 8230 - 11.2T (±50) J mol-1 Since the formation is endothermic, CuGd2O4 becomes thermodynamically unstable with respect to CuO and Gd2O3 below 735 K. When the oxygen partial pressure over CuGd2O4 is lowered, it decomposes according to the reaction 4CuGd2O4 (s) → 4Gd2O3 (s) + 2Cu2O (s) + O2 (g) for which the equilibrium oxygen potential is given by Δμo 2 = −227,970 + 143.2T (±500) J mol−1 An oxygen potential diagram for the system Cu-Gd-O at 1273 K is presented.

Phase relations in the systems Cu–O–R2O3(R = Tm, Lu) and Gibbs energies of formation of Cu2R2O5 compounds

The phase relations in the systems Cu–O–R2O3(R = Tm, Lu) have been determined at 1273 K by X-ray diffraction, optical microscopy and electron probe microanalysis of samples equilibrated in evacuated quartz ampules and in pure oxygen. Only ternary compounds of the type Cu2R2O5 were found to be stable. The standard Gibbs energies of formation of the compounds have been measured using solid-state galvanic cells of the type, Pt|Cu2O + Cu2R2O5+ R2O3‖(Y2O3)ZrO2‖CuO + Cu2O‖Pt in the temperature range 950–1325 K. The standard Gibbs energy changes associated with the formation of Cu2R2O5 compounds from their binary component oxides are: 2CuO(s)+ Tm2O3(s)→Cu2Tm2O5(s), ΔG°=(10400 – 14.0 T/K)± 100 J mol–1, 2CuO(s)+ Lu2O3(s)→Cu2Lu2O5(s), ΔG°=(10210 – 14.4 T/K)± 100 J mol–1 Since the formation is endothermic, the compounds become thermodynamically unstable with respect to component oxides at low temperatures, Cu2Tm2O5 below 743 K and Cu2Lu2O5 below 709 K. When the chemical potential of oxygen over the Cu2R2O5 compounds is lowered, they decompose according to the reaction, 2Cu2R2O5(s)→2R2O3(s)+ 2Cu2O(s)+ O2(g) The equilibrium oxygen potential corresponding to this reaction is obtained from the emf. Oxygen potential diagrams for the Cu–O–R2O3 systems at 1273 K are presented.

Reaction of spironaphthalenones with hydroxylamine: Part III. A novel mechanism for the formation of products and trapping of an intermediate.

A mechanism involving the intermediacy of nitrene 5, formed from the oxime of spironaphthalenone 1 by acid catalysed dehydration, has been proposed to explain the formation of pyrrolotropones/pyrrolo esters from spironaphthalenones. The initially formed nitrene rearranges to the isopyrrole 6, which either undergoes sigmatropic migration to the pyrrolotropone 2 or adds alcohol to form the pyrrolo ester depending on substitution at 1′ position. The isopyrrole intermediate 6 has been trapped as a Diels-Alder adduct 8.

Reduction behaviour of Fe3+/Al2O3 obtained from the mixed oxalate precursor and the formation of the Fe0-Al2O3 metal-ceramic composite

Reduction behaviour of Fe3+/Al2O3 obtained by the decomposition of the oxalate precursor has been investigated by employing X-ray diffraction (XRD), Mössbauer spectroscopy and electron paramagnetic resonance (EPR) spectroscopy. Calcination of Fe3+/Al2O3 at or below 1070 K yields mainly a poorly ordered, fine particulate form of ?-Al2�xFexO3. Calcination at or above 1220 K yields ?-Al2�xFexO3. Reduction of Fe3+/Al2O3 samples calcined at or below 1070 K gives the FeAl2O4 spinel on reduction at 870 K; samples calcined at or above 1220 K give Al2-xFexO3 with a very small proportion of metallic iron. Fe3+/Al2O3 samples calcined at 1220 K or above yield metallic iron and a very small proportion of the spinel on reduction below 1270 K. In the samples reduced at or above 1270 K, the main product is metallic iron in both ferromagnetic and superparamagnetic forms. The oxalate precursor route yields more metallic iron than the sol�gel route.

Formation of a single, rotated-Brass (1 1 0)< 5 5 6 > texture by hot cross-rolling of an Al-Zn-Mg-Cu-Zr alloy

The present work describes the evolution of a strong, single-component rotated-Brass ((1 1 0) < 5 5 6 >) texture in an Al-Zn-Mg-Cu-Zr alloy by an uneven hot cross-rolling with frequent interpass annealing. This texture development is unique because hot rolling of aluminum alloys results in orientation distribution along the ``beta-fibre''. It has been demonstrated that the deformation by cross-rolling of a partially recrystallized grain structure having rotated-Cube and Goss orientations, and the recrystallization resistance of near-Brass-oriented elongated grains play a critical role in development of this texture. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Formation of a G-quadruplex at the BCL2 major breakpoint region of the t(14;18) translocation in follicular lymphoma

The t(14;18) translocation in follicular lymphoma is one of the most common chromosomal translocations. Most breaks on chromosome 18 are located at the 3'-UTR of the BCL2 gene and are mainly clustered in the major breakpoint region (MBR). Recently, we found that the BCL2 MBR has a non-B DNA character in genomic DNA. Here, we show that single-stranded DNA modeled from the template strand of the BCL2 MBR, forms secondary structures that migrate faster on native PAGE in the presence of potassium, due to the formation of intramolecular G-quadruplexes. Circular dichroism shows evidence for a parallel orientation for G-quadruplex structures in the template strand of the BCL2 MBR. Mutagenesis and the DMS modification assay confirm the presence of three guanine tetrads in the structure. 1H nuclear magnetic resonance studies further confirm the formation of an intramolecular G-quadruplex and a representative model has been built based on all of the experimental evidence. We also provide data consistent with the possible formation of a G-quadruplex structure at the BCL2 MBR within mammalian cells. In summary, these important features could contribute to the single-stranded character at the BCL2 MBR, thereby contributing to chromosomal fragility.

Highly dispersed ultrafine Pt and PtRu nanoparticles on graphene: formation mechanism and electrocatalytic activity

We demonstrate a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene by exploiting the nucleation of a metal precursor phase on graphite oxide surfaces. Our method opens up new possibilities to engineer graphene-based hybrids for applications in multifunctional nanoscale devices.