Palaeomagnetism, rock magnetism and AMS of the Cabo Magmatic Province, NE Brazil, and the opening of South Atlantic

P>Reconstruction of the South Atlantic opening has long been a matter of debate and several models have been proposed. One problem in tracing properly the Atlantic history arises from the existence of a long interval without geomagnetic reversals, the Cretaceous Normal Superchron, for which ages are difficult to assign. Palaeomagnetism may help in addressing this issue if high-quality palaeomagnetic poles are available for the two drifting continental blocks, and if precise absolute ages are available. In this work we have investigated the Cabo Magmatic Province, northeastern Brazil, recently dated at 102 +/- 1 Ma (zircon fission tracks, Ar39/Ar40). All volcanic and plutonic rocks showed stable thermal and AF demagnetization patterns, and exhibit primary magnetic signatures. AMS data also support a primary origin for the magnetic fabric and is interpreted to be contemporaneous of the rock formation. The obtained pole is located at 335.9 degrees E/87.9 degrees S (N = 24; A(95) = 2.5; K = 138) and satisfies modern quality criteria, resulting in a reference pole for South America at similar to 100 Ma. This new pole also gives an insight to test and discuss the kinematic models currently proposed for the South Atlantic opening during mid-Cretaceous.

VELOCITY FIELD OF COMPRESSIBLE MAGNETOHYDRODYNAMIC TURBULENCE: WAVELET DECOMPOSITION AND MODE SCALINGS

We study compressible magnetohydrodynamic turbulence, which holds the key to many astrophysical processes, including star formation and cosmic-ray propagation. To account for the variations of the magnetic field in the strongly turbulent fluid, we use wavelet decomposition of the turbulent velocity field into Alfven, slow, and fast modes, which presents an extension of the Cho & Lazarian decomposition approach based on Fourier transforms. The wavelets allow us to follow the variations of the local direction of the magnetic field and therefore improve the quality of the decomposition compared to the Fourier transforms, which are done in the mean field reference frame. For each resulting component, we calculate the spectra and two-point statistics such as longitudinal and transverse structure functions as well as higher order intermittency statistics. In addition, we perform a Helmholtz-Hodge decomposition of the velocity field into incompressible and compressible parts and analyze these components. We find that the turbulence intermittency is different for different components, and we show that the intermittency statistics depend on whether the phenomenon was studied in the global reference frame related to the mean magnetic field or in the frame defined by the local magnetic field. The dependencies of the measures we obtained are different for different components of the velocity; for instance, we show that while the Alfven mode intermittency changes marginally with the Mach number, the intermittency of the fast mode is substantially affected by the change.

Synthesis of biodegradable polyhydroxyalcanoate copolymer from a renewable source by alternate feeding

Polyhydroxyalcanoates copolymers with 3-hydroxybutirate (3HB) and 3-hydroxyvalerate (3HV) co-monomers, P3(HB-co-x%HV), were produced in fed-batch culture by Ralstonia eutropha DSM428 using fructose as a single carbon source in the first step and adding propionic acid in the second step by alternating feeding. Polymer yield was 0.18 g/L with a content of 24 mol% of the 3HV fraction determined by H-1 NMR. NMR measurements indicated that the polymer obtained is isotactic. The copolymer attained 35% of crystallinity according to X-ray diffraction measurements, and two (020) planes were observed. Thermal behavior presented melting temperature at 154 degrees C and the crystallization temperature was 65 degrees C. A glass transition temperature was observed at -10 degrees C. Average molecular weight measured by GPC was 4.9 x 10(5) Dalton. Isothermal radial growth rates of spherulites of P3(HB-co-24%HV) were studied. All experimental facts and the analysis of the sequence distribution of diads and triads of 3HB and 3HV units led to the conclusion that it is not a completely statistical random copolymer once it contains different types of segments. POLYM.

An unstructured CVFEM and moving interface algorithm for non-Newtonian Hele-Shaw flows in injection molding

Purpose - The purpose of this paper is to develop a novel unstructured simulation approach for injection molding processes described by the Hele-Shaw model. Design/methodology/approach - The scheme involves dual dynamic meshes with active and inactive cells determined from an initial background pointset. The quasi-static pressure solution in each timestep for this evolving unstructured mesh system is approximated using a control volume finite element method formulation coupled to a corresponding modified volume of fluid method. The flow is considered to be isothermal and non-Newtonian. Findings - Supporting numerical tests and performance studies for polystyrene described by Carreau, Cross, Ellis and Power-law fluid models are conducted. Results for the present method are shown to be comparable to those from other methods for both Newtonian fluid and polystyrene fluid injected in different mold geometries. Research limitations/implications - With respect to the methodology, the background pointset infers a mesh that is dynamically reconstructed here, and there are a number of efficiency issues and improvements that would be relevant to industrial applications. For instance, one can use the pointset to construct special bases and invoke a so-called ""meshless"" scheme using the basis. This would require some interesting strategies to deal with the dynamic point enrichment of the moving front that could benefit from the present front treatment strategy. There are also issues related to mass conservation and fill-time errors that might be addressed by introducing suitable projections. The general question of ""rate of convergence"" of these schemes requires analysis. Numerical results here suggest first-order accuracy and are consistent with the approximations made, but theoretical results are not available yet for these methods. Originality/value - This novel unstructured simulation approach involves dual meshes with active and inactive cells determined from an initial background pointset: local active dual patches are constructed ""on-the-fly"" for each ""active point"" to form a dynamic virtual mesh of active elements that evolves with the moving interface.

Observing the Solubilization of Lipid Bilayers by Detergents with Optical Microscopy of GUVs

The solubilization of lipid bilayers by detergents was studied with optical microscopy of giant unilamellar vesicles (GUVs) composed of palmitoyl oleoyl phoshatidylcholine (POPC). A solution of the detergents Triton X-100 (TX-100) and sodium dodecyl sulfate (SDS) was injected with a micropipette close to single GUVs. The solubilization process was observed with phase contrast and fluorescence microscopy and found to be dependent on the detergent nature. In the presence of TX-100, GUVs initially showed an increase in their surface area, due to insertion of TX-100 with rapid equilibration between the two leaflets of the bilayer. Then, above a solubility threshold, several holes opened, rendering the bilayer a lace fabric appearance, and the bilayer gradually vanished. On the other hand, injection of SDS caused initially an increase in the membrane spontaneous curvature, which is mainly associated with incorporation of SDS in the outer layer only. This created a stress in the membrane, which caused either opening of transient macropores with substantial decrease in vesicle size or complete vesicle bursting. In another experimental setup, the extent of solubilization/destruction of a collection of GUVs was measured as a function of either TX-100 or SDS concentration.

Structural characterization of supported nanocrystalline ZnO thin films prepared by dip-coating

Nanocrystalline ZnO thin films prepared by the sol-gel dip-coating technique were characterized by grazing incidence X-ray diffraction (GIXD), atomic force microscopy (AFM), X-ray reflectivity (XR) and grazing incidence small-angle X-ray scattering (GISAXS). The structures of several thin films subjected to (i) isochronous annealing at 350, 450 and 550 degrees C, and (ii) isothermal annealing at 450 degrees C during different time periods, were characterized. The studied thin films are composed of ZnO nanocrystals as revealed by analysing several GIXD patterns, from which their average sizes were determined. Thin film thickness and roughness were determined from quantitative analyses of AFM images and XR patterns. The analysis of XR patterns also yielded the average density of the studied films. Our GISAXS study indicates that the studied ZnO thin films contain nanopores with an ellipsoidal shape, and flattened along the direction normal to the substrate surface. The thin film annealed at the highest temperature, T = 550 degrees C, exhibits higher density and lower thickness and nanoporosity volume fraction, than those annealed at 350 and 450 degrees C. These results indicate that thermal annealing at the highest temperature (550 degrees C) induces a noticeable compaction effect on the structure of the studied thin films. (C) 2011 Elsevier B.V. All rights reserved.

Growth and Melting of Metallic Nanoclusters in Glass: A Review of Recent Investigations

The mechanisms of nucleation and growth and the solid-to-liquid transition of metallic nanoclusters embedded in sodium borate glass were recently studied in situ via small-angle X-ray scattering (SAXS) and wide-an-le X-ray scattering (WAXS). SAXS results indicate that, under isothermal annealing conditions, the formation and growth of Bi or Ag nanoclusters embedded in sodium borate glass occurs through two successive stages after a short incubation period. The first stage is characterized by the nucleation and growth of spherical metal clusters promoted by the diffusion of Bi or Ag atoms through the initially supersaturated glass phase. The second stage is named the coarsening stage and occurs when the (Bi- or Ag-) doping level of the vitreous matrix is close to the equilibrium value. The experimental results demonstrated that, at advanced stages of the growth process, the time dependence of the average radius and density number of the clusters is in agreement with the classical Lifshitz-Slyozov-Waoner (LSW) theory. However, the radius distribution function is better described by a lognormal function than by the function derived from the theoretical LSW model. From the results of SAXS measurements at different temperatures, the activation energies for the diffusion of Ag and Bi through sodium borate glass were determined. In addition, via combination of the results of simultaneous WAXS and SAXS measurements at different temperatures, the crystallographic structure and the dependence of melting temperature T(m) on crystal radius R of Bi nanocrystals were established. The experimental results indicate that T(m) is a linear and decreasing function of nanocrystal reciprocal radius 1/R, in agreement with the Couchman and Jesser theoretical model. Finally, a weak contraction in the lattice parameters of Bi nanocrystals with respect to bulk crystals was established.

Thermodynamic Stabillity of Hydrogen-Bonded Systems in Polar and Nonpolar Environments

The thermodynamic properties of a selected set of benchmark hydrogen-bonded systems (acetic acid dimer and the complexes of acetic acid with acetamide and methanol) was studied with the goal of obtaining detailed information on solvent effects on the hydrogen-bonded interactions using water, chloroform, and n-heptane as representatives for a wide range in the dielectric constant. Solvent effects were investigated using both explicit and implicit solvation models. For the explicit description of the solvent, molecular dynamics and Monte Carlo simulations in the isothermal isobaric (NpT) ensemble combined with the free energy perturbation technique were performed to determine solvation free energies. Within the implicit solvation approach, the polarizable continuum model and the conductor-like screening model were applied. Combination of gas phase results with the results obtained from the different solvation models through an appropriate thermodynamic cycle allows estimation of complexation free energies, enthalpies, and the respective entropic contributions in solution. Owing to the strong solvation effects of water the cyclic acetic acid dimer is not stable in aqueous solution. In less polar solvents the double hydrogen bond structure of the acetic acid dimer remains stable. This finding is in agreement with previous theoretical and experimental results. A similar trend as for the acetic acid dimer is also observed for the acetamide complex. The methanol complex was found to be thermodynamically unstable in gas phase as well as in any of the three solvents. (C) 2010 Wiley Periodicals, Inc. J Comput Chem 31: 2046-2055, 2010

A model for the stabilization of atomic hydrogen centers in borate glasses

A previously proposed model describing the trapping site of the interstitial atomic hydrogen in borate glasses is analyzed. In this model the atomic hydrogen is stabilized at the centers of oxygen polygons belonging to B-O ring structures in the glass network by van der Waals forces. The previously reported atomic hydrogen isothermal decay experimental data are discussed in the light of this microscopic model. A coupled differential equation system of the observed decay kinetics was solved numerically using the Runge Kutta method. The experimental untrapping activation energy of 0.7 x 10(-19) J is in good agreement with the calculated results of dispersion interaction between the stabilized atomic hydrogen and the neighboring oxygen atoms at the vertices of hexagonal ring structures. (C) 2009 Elsevier B.V. All rights reserved.

Magnetic structures of quaternary intermetallic borocarbides RCo(2)B(2)C (R = Dy, Ho, Er)

The magnetic structures of the title compounds have been studied by neutron diffraction. In contrast to the isomorphous RNi(2)B(2)C compounds, wherein a variety of exotic incommensurate modulated structures has been observed, the magnetic structure of ErCo(2)B(2)C is found to be a collinear antiferromagnet with k = (12, 0, 12) while those of HoCo(2)B(2)C and DyCo(2)B(2)C are observed to be simple ferromagnets. For all studied compounds, the moments are found to be confined within the basal plane and their magnitudes are comparable to the values obtained from the low-temperature isothermal magnetization measurements. The absence of modulated magnetic structures in the RCo(2)B(2)C series (for ErCo(2)B(2)C, verified down to 50 mK) is attributed to the quenching of the Fermi surface nesting features.

Ab initio calculation of the BCC Fe-Al-Mo (Iron-Aluminum-Molybdenum) phase diagram: Implications for the nature of the tau(2) phase

The metastable phase diagram of the BCC-based ordering equilibria in the Fe-Al-Mo system has been calculated via a truncated cluster expansion, through the combination of Full-Potential-Linear augmented Plane Wave (FP-LAPW) electronic structure calculations and of Cluster Variation Method (CVM) thermodynamic calculations in the irregular tetrahedron approximation. Four isothermal sections at 1750 K, 2000 K, 2250 K and 2500 K are calculated and correlated with recently published experimental data on the system. The results confirm that the critical temperature for the order-disorder equilibrium between Fe(3)Al-D0(3) and FeAl-B2 is increased by Mo additions, while the critical temperature for the FeAl-B2/A2 equilibrium is kept approximately invariant with increasing Mo contents. The stabilization of the Al-rich A2 phase in equilibrium with overstoichiometric B2-(Fe,Mo)Al is also consistent with the attribution of the A2 structure to the tau(2) phase, stable at high temperatures in overstoichiometric B2-FeAl. (C) 2009 Elsevier Ltd. All rights reserved.

Defect centre responsible for production of 110 degrees C TL peak in quartz

110 degrees C thermoluminescence (TL) peak in quartz is well known due to its pre-dose effect, which is used in dating technique. The generally accepted mechanism for the production of this peak is based on Ge impurity contained in quartz. Its role is to substitute for Si in SiO(4) tetrahedron and under irradiation gives rise to [GeO(4)/e(-)](-) electron centre. Heating for TL read out liberates electron that recombines with hole in [AlO(4)/h]degrees or [H(3)O(4)/h]degrees centres emitting photon. The investigation, carried out on blue quartz, green quartz, black quartz, pink quartz, red quartz, sulphurous quartz, milky quartz, alpha quartz and synthetic quartz, has shown that the 110 degrees C TL peak in all these varieties of quartz has no correlation with the respective Ge content. Electron paramagnetic resonance (EPR) measurements on any of these varieties of quartz revealed a signal with g(1) = 2.0004, g(2) = 1.9986 and g(3) = 1.974 and this signal does not appear to correspond to any known EPR signals in alpha quartz. Furthermore, isothermal decay measurements are carried out on the above mentioned EPR signal and 110 degrees C TL peak in alpha, blue and green quartz. A close correlation has been observed in the decay behavior. A new mechanism is proposed based on an interstitial O(-) centre. (C) 2009 Elsevier Ltd. All rights reserved.

Catecholase and DNase activities of copper(II) complexes containing phenolate-type ligands

Three new homodinuclear complexes containing substituted phenolate-type ligands based on the N(5)O(2) donor (2-(N,N-Bis(2-pyridylmethyl)aminomethyl)-6-(N`,N`-(2-hydroxybenzyl)(2-pyridylmethyl))aminomethyl)-4-methylphenol (H(2)L-H) were synthesized and characterized by X-ray crystallography. Potentiometric titration studies in 70% (v/v) aqueous ethanol show that all three complexes exhibit a common {Cu(II)(mu-phenoxo)(mu-OH)Cu(II)(OH)} core in solution. Kinetic studies on the oxidation reaction of 3,5-di-tert-butylcatechol revealed that the catalytic activity of the metal complexes increases toward the ligand containing an electron-donating group. In addition, these complexes also carried out DNA cleavage by hydrolytic and oxidative pathways. Copyright (C) 2010 John Wiley & Sons, Ltd.

Quartz recrystallization regimes, c-axis texture transitions and fluid inclusion reequilibration in a prograde greenschist to amphibolite facies mylonite zone (Ribeira Shear Zone, SE Brazil)

The crystal-plastic behavior of quartz mylonites from the Ribeira Shear Zone (SE Brazil), a major strike-slip structure that was active during a prograde metamorphic phase related to the Neoproterozoic Brasiliano-Pan African Orogeny, was investigated using a multi-method approach. Geothermobarometry results indicate deformational conditions ranging from similar to 300 to similar to 630 degrees C and 500-700 MPa. A strong correlation between mapped metamorphic zones and a dominance of different dynamic recrystallization mechanisms of quartz occurs within the mylonite zone. Bulging recrystallization (BLG) dominates within the chlorite zone between 300 and 410 degrees C, subgrain rotation recrystallization (SGR) operates within the biotite zone from 410 to 520 degrees C, and grain boundary migration recrystallization (GBM) dominates in the garnet zone above 520 degrees C. The development of quartz c-axis textures is mainly governed by temperature and dynamic recrystallization mechanisms. Textures from BLG zone mylonites are characterized by maxima around Z; SGR zone mylonites display single girdles or asymmetric type I crossed girdles; and GBM zone mylonites comprise maxima around Y and intermediate between X and Z. The scarcity or absence of water-bearing fluid inclusions in quartz mylonites from the SGR and GBM zones, which are dominated by carbonic inclusions, suggests water-deficient conditions, whereas BLG zone mylonites are dominated by water-bearing inclusions. This evidence indicates that water was available in the protoliths but has been eliminated with increasing deformation and deformation temperature. No effect of the water content variation on the quartz microstructural and recrystallized grain size evolution was detected, and little influence on c-axis texture development was observed. Most of the fluid inclusion densities were reequilibrated during the shear zone exhumation history, recording a decompression in the range of 300-500 MPa, while microstructural reequilibration effects related to the prograde metamorphism are largely preserved. Fluid inclusion microstructures and densities from two SGR zone samples preserved evidence for a near isothermal compression within the interior of the Ribeira Shear Zone during the prograde metamorphism. (C) 2009 Elsevier B.V. All rights reserved.

Timelike Christoffel pairs in the split-quaternions

We characterize the Christoffel pairs of timelike isothermic surfaces in the four-dimensional split-quaternions. When restricting the receiving space to the three-dimensional imaginary split-quaternions, we establish an equivalent condition for a timelike surface in R(2)(3) to be real or complex isothermic in terms of the existence of integrating factors.