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.

Synthetic and physicochemical studies of uranium complexes with semicarbazone and hydrazone

Uranyl complexes of two Schiff bases, semicarbazone and hydrazone containing OON donor atoms have been synthesized and characterized on the basis of NMR, IR and electronic spectral studies, conductance, magnetic susceptibility and thermogravimetric data. The 1H NMR spectrum of the semicarbazone complex shows low field signals due to OH, NH and ---CH=N groups at 10.23, 9.31 and 8.17 ppm, respectively. The aromatic protons appear in the range 7.74–7.40 ppm. On complexation with U(VI) the signals due to OH and NH disappear evidently due to their participation in coordination. The coordination number of the o-vanillin semicarbazone (oVSC) complex is 6 whereas, that of the o-vanillin isonicotinic acid hydrazone (oVINAH) complex is 8, in addition to the two oxygen atoms already bonded to U(VI) in each species. The thermograms show the presence of 3 and 2 water molecules in these complexes, respectively and the IR spectral data also support the above conclusion. Suitable structures have been assigned.

Turbulent flow computations on a hybrid cartesian point distribution using meshless solver LSFD-U

This paper may be considered as a sequel to one of our earlier works pertaining to the development of an upwind algorithm for meshless solvers. While the earlier work dealt with the development of an inviscid solution procedure, the present work focuses on its extension to viscous flows. A robust viscous discretization strategy is chosen based on positivity of a discrete Laplacian. This work projects meshless solver as a viable cartesian grid methodology. The point distribution required for the meshless solver is obtained from a hybrid cartesian gridding strategy. Particularly considering the importance of an hybrid cartesian mesh for RANS computations, the difficulties encountered in a conventional least squares based discretization strategy are highlighted. In this context, importance of discretization strategies which exploit the local structure in the grid is presented, along with a suitable point sorting strategy. Of particular interest is the proposed discretization strategies (both inviscid and viscous) within the structured grid block; a rotated update for the inviscid part and a Green-Gauss procedure based positive update for the viscous part. Both these procedures conveniently avoid the ill-conditioning associated with a conventional least squares procedure in the critical region of structured grid block. The robustness and accuracy of such a strategy is demonstrated on a number of standard test cases including a case of a multi-element airfoil. The computational efficiency of the proposed meshless solver is also demonstrated. (C) 2010 Elsevier Ltd. All rights reserved.

Differential scanning calorimetry cure studies on the effect of addition of epoxy diluents of tetrafunctional epoxy resins

The effect of the addition of p-aminophenol and aniline-based epoxy diluents on the curing behavior of highly viscous tetraglycidyl diamino diphenyl methane resin with diamino diphenyl sulfone hardener have been investigated kinetically by differential scanning calorimetry. Dynamic scans were carried out over a temperature range 30–300°C for different resin formulations. Isothermal scans at four differnt temperatures have also been carried out for the evaluation of kinetic parameters. Heat flow measurements at different heating rates have indicated the evidence of autocatalytic behavior of curing reaction following a simple nth-order kinetics.

Dexamethasone negatively regulates phenobarbitone-activated transcription but synergistically enhances cytoplasmic levels of cytochrome P-450b/e messenger RNA

Dexamethasone has a potentiating effect on phenobarbitone mediated induction of cytochrome P-450b + e mRNAs in adult rat liver. However, the glucocorticoid inhibits phenobarbitone-activated transcription of cytochrome P-450b + e mRNAs by 60-70%. This inhibitory effect is evident in run-off transcription of the endogenous genes as well as in the transcription of an added cloned gene fragment. Dexamethasone inhibits the phenobarbitone-mediated increase in the binding of a transcription factor(s) to the upstream region of the gene as evidenced by gel retardation and Southwestern blot analysis. The glucocorticoid does not stabilize the phenobarbitone-induced polyribosomal cytochrome P-450b + e mRNAs but appears to stabilize the nuclear transcripts. It is proposed that a negative element may mediate the action of dexamethasone at the level of nuclear transcription and stabilization of the nuclear transcript may account for the potentiating effect of the glucocorticoid on phenobarbitone-mediated increase in cytochrome P-450b + e mRNAs in the cytoplasm of the adult rat liver. However, the cytochrome P-450b protein levels are slightly lower in phenobarbitone + dexamethasone treatment than in phenobarbitone-treated liver microsomes.

Demonstration of IgE Antibodies to Nucleic Acid Antigens in Patients with Sle

Using a combination of avidin-biotin microELISA and solid phase radioimmunoassay, we examined sera from 23 patients with systemic lupus erythematosus (SLE), two patients with established sensitivity to ingested shrimp, and 15 healthy normal subjects. In addition to IgG antibodies, varying amounts of IgE antibodies specific for native DNA (nDNA), denatured or single-stranded DNA (dnDNA), RNA, and tRNA were demonstrable in the sera of SLE patients, but not in the sera of normal subjects. A comparison of the specificity of nucleic acid-specific IgE antibodies present in the sera of shrimp-sensitive patients with those present in the sera of seven SLE patients revealed that the IgE antibodies in the sera of shrimp-sensitive patients specifically recognized shrimp tRNA but not yeast tRNA, calf thymus RNA, or calf thymus DNA, while those present in the sera of patients with SLE recognized all these nucleic acid antigens. The IgE antibodies directed against nDNA, dnDNA, RNA, and tRNA may mediate mast cell and basophil degranulation and thus contribute both to immediate-type hypersensitivity phenomena including hives seen in patients with SLE and to the localization of IgE-nucleic acid complexes in target

Analysis of sequence dependent variations in secondary and tertiary structure of tRNA molecules

The double helical regions of the five tRNA(Phe) and two tRNA(Asp) crystal structures have been analyzed using the local basepair step parameters. The sequence dependent effects in the mini double helices of tRNA are very similar to those observed in the crystal structures of oligonucleotides in the A-form, the purine-pyrimidine and purine-purine steps have small roll angles when compared to the fiber models of A-DNA as well as A-RNA, while the pyrimidine-purine doublet steps have large roll angles. The orientation of the basepairs in the D-stem is unusual and invariant i.e. they are different from the other three stems but are very similar in all the five tRNA(Phe) crystal structures, presumably due to tertiary interaction of the Watson-Crick basepairs with other bases, with all bases being highly conserved. The origin of the differences between the tertiary structures of tRNA(Phe) and tRNA(Asp) from yeast has also been investigated. It is found that even though the angle between the acceptor arm and the D-stem is very similar in the two structures, the angle subtended by the acceptor arm and the anticodon arm is smaller in the tRNA(Phe) structure (by more than 10 degrees). This is due to differences in the orientation of the two mini helices constituting the anticodon arm, which are inclined to each other by approximately 25 degrees in tRNA(Phe) and 16 degrees in tRNA(Asp). In addition, the acceptor arm, the D-stem and the anticodon stem are nearly coplanar in tRNA(Phe), while in tRNA(Asp) the anticodon stem projects out of the plane defined by the acceptor arm and the anticodon stem. These two features together lead to a larger separation between the acceptor and anticodon ends in tRNA(Asp) and indicate that the junction between the D-stem and the anticodon stem is quite variable, with features characteristic of a ball-and-socket type joint and determined for each tRNA molecule by the base sequence at the junction.

Double helix conformation, groove dimensions and ligand binding potential of a G/C stretch in B-DNA

The self-complementary DNA fragment CCGGCGCCGG crystallizes in the rhombohedral space group R3 with unit cell parameters a = 54.07 angstrom and c = 44.59 angstrom. The structure has been determined by X-ray diffraction methods at 2.2 angstrom resolution and refined to an R value of 16.7%. In the crystal, the decamer forms B-DNA double helices with characteristic groove dimensions: compared with B-DNA of random sequence, the minor groove is wide and deep and the major groove is rather shallow. Local base pair geometries and stacking patterns are within the range commonly observed in B-DNA crystal structures. The duplex bears no resemblance to A-form DNA as might have been expected for a sequence with only GC base pairs. The shallow major groove permits an unusual crystal packing pattern with several direct intermolecular hydrogen bonds between phosphate oxygens and cytosine amino groups. In addition, decameric duplexes form quasi-infinite double helices in the crystal by end-to-end stacking. The groove geometries and accessibilities of this molecule as observed in the crystal may be important for the mode of binding of both proteins and drug molecules to G/C stretches in DNA.

Computer modeling studies on the binding of 2',5'-linked dinucleoside phosphates to ribonuclease T1-influence of subsite interactions on the substrate specificity

The modes of binding of Gp(2',5')A, Gp(2',5')C, Gp(2',5')G and Gp(2',5')U to RNase T1 have been determined by computer modelling studies. All these dinucleoside phosphates assume extended conformations in the active site leading to better interactions with the enzyme. The 5'-terminal guanine of all these ligands is placed in the primary base binding site of the enzyme in an orientation similar to that of 2'-GMP in the RNase T1-2'-GMP complex. The 2'-terminal purines are placed close to the hydrophobic pocket formed by the residues Gly71, Ser72, Pro73 and Gly74 which occur in a loop region. However, the orientation of the 2'-terminal pyrimidines is different from that of 2'-terminal purines. This perhaps explains the higher binding affinity of the 2',5'-linked guanine dinucleoside phosphates with 2'-terminal purines than those with 2'-terminal pyrimidines. A comparison of the binding of the guanine dinucleoside phosphates with 2',5'- and 3',5'-linkages suggests significant differences in the ribose pucker and hydrogen bonding interactions between the catalytic residues and the bound nucleoside phosphate implying that 2',5'-linked dinucleoside phosphates may not be the ideal ligands to probe the role of the catalytic amino acid residues. A change in the amino acid sequence in the surface loop region formed by the residues Gly71 to Gly74 drastically affects the conformation of the base binding subsite, and this may account for the inactivity of the enzyme with altered sequence i.e., with Pro, Gly and Ser at positions 71 to 73 respectively. These results thus suggest that in addition to recognition and catalytic sites, interactions at the loop regions which constitute the subsite for base binding are also crucial in determining the substrate specificity.

Exotic Physics in the Negative-U, Extended-Hubbard Model for Barium Bismuthates?

We point out possibilities for exotic physics in barium bismuthates, from a detailed study of the negative-U, extended-Hubbard model proposed for these systems. We emphasize the different consequences of electronic and phononic mechanisms for negative U. We show that, for an electronic mechanism, the semiconducting phases must be unique, with their transport properties dominated by charge ± 2e Cooperon bound states. This can explain the observed difference between the optical and transport gaps. We propose other experimental tests for this novel mechanism of charge transport.