Surface properties, solubility and dissolution kinetics of bamboo phytoliths

Although phytoliths, constituted mainly by micrometric opal, exhibit an important control on silicon cycle in superficial continental environments, their thermodynamic properties and reactivity in aqueous solution are still poorly known. In this work, we determined the solubility and dissolution rates of bamboo phytoliths collected in the Réunion Island and characterized their surface properties via electrophoretic measurements and potentiometric titrations in a wide range of pH. The solubility product of “soil” phytoliths ( at 25 °C) is equal to that of vitreous silica and is 17 times higher than that of quartz. Similarly, the enthalpy of phytoliths dissolution reaction is close to that of amorphous silica but is significantly lower than the enthalpy of quartz dissolution. Electrophoretic measurements yield isoelectric point pH_IEP = 1.2 ± 0.1 and 2.5 ± 0.2 for “soil” (native) and “heated” (450 °C heating to remove organic matter) phytoliths, respectively. Surface acid-base titrations allowed generation of a 2-pK surface complexation model. Phytoliths dissolution rates, measured in mixed-flow reactors at far from equilibrium conditions at 2 ? pH ? 12, were found to be intermediate between those of quartz and vitreous silica. The dissolution rate dependence on pH was modeled within the concept of surface coordination theory using the equation:

     

Seasonal and interannual variability of vertical turbulent exchange coefficient in the Black Sea pycnocline in 2013–2016 and its relation to variability of mean kinetic energy of surface currents

Ocean Dynamics - In this paper, we analyze seasonal and interannual variability of vertical turbulent diffusion coefficient (Kt). Our calculations are based on the time series from 2013 to 2016,...     

A new regional tectonic map of the consolidated crystalline basement of sedimentary basins and near-surface fold structures of the Ural region

A new approach to the tectonic zoning of the consolidated crystalline basement and near-surface fold structures, taking into account the specific features of the structure of the Earth’s crust is suggested. As a result, a new regional tectonic map of these complexes of the Ural region was created.     

Effects of Dispersion of Wave Packets in the Determination of Lifetimes of High-Degree Solar <Emphasis Type="Italic">p</Emphasis> Modes from Time – Distance Analysis: MDI Data

The cross-correlation function of solar p modes in a time – distance analysis changes with travel distance (or travel time). The exponential decrease in the amplitude of the cross-correlation function with travel distance has been interpreted as the dissipation of solar p-mode power and used to determine the lifetimes of high-degree p modes. It is found that the width of the cross-correlation function increases with travel distance. We interpret the increase in width as the dispersion of the wave packet in a time – distance analysis. The dispersion would also cause a decrease in amplitude and affect the determination of lifetimes. We include the dispersion effect in the determination of lifetimes of high-degree p modes in a time – distance analysis and find that the derived lifetime increases significantly compared with the previous study for degree less than 400.     

Stratigraphic and structural control on the distribution of gas hydrates and active gas seeps on the Posolsky Bank, Lake Baikal

The distribution and origin of shallow gas seeps in the vicinity of the Posolsky Bank in Lake Baikal were studied based on the integration of detailed seismic, multibeam, and hydro-acoustic water-column investigations. In all, 65 acoustic flares have been detected on the Posolsky Fault scarp near the crest of the bank and in a similar, nearby setting at water depths of ?43 to ?332?m. The seismic data reveal BSRs (bottom-simulating reflectors) occurring up to water depths of ?300?m. Calculations involving hydrate stability, heat flow, and topographic modulation based on BSR occurrence and multibeam bathymetry enabled prediction of a methane–ethane gas mixture and heat-flow values that would account for gas hydrate stability in the lake sediments under prevailing ambient conditions. These predictions are supported by ground truth data. The findings suggest that seeps concentrated along the crest of the Posolsky Bank are fed mainly by gas coming from below the base of the gas hydrate stability zone, which would migrate updip via permeable stratigraphic pathways beneath the bank. Gas would ultimately be released into the water column where these pathways are cut off by faults.

Finite element modeling of net panels using a consistent net element

A consistent finite element is proposed to model the hydrodynamic response of net panels to environmental loading. This equivalent net element is constructed to reproduce the drag, buoyancy, inertial and elastic forces exerted on the netting by current and waves. To evaluate the accuracy of the proposed finite element modeling, numerical predictions have been compared with the experimental observations and (simplified) analytical results of other authors. This new modeling technique has been applied to evaluate the performance of a tension leg fish cage in the open ocean environment.     

A piecewise curve-fitting technique for vertical oceanographic profiles and its application to density distribution

A unified method of approximation, extrapolation, and objective layering is offered for processing vertical oceanographic profiles. The method is demonstrated using seawater density and consists of adjustable splitting of each individual profile into N vertical layers based on tentative, piecewise linear homogeneous approximation with specified accuracy and a final fitting of an N-layered analytical model to data. A set of 3N coefficients of the model includes one density value at the sea surface; N−1 depths of layer interfaces; and N pairs of coefficients that describe a profile shape within the n-th layer—an asymptotic density value (a key parameter for extrapolation) and a vertical scale of maximum density variability (related to vertical gradient). Several distinctive characteristics of the technique are: (1) It can be used for the analysis of the vertical structure of individual profiles when N is an unknown parameter, and spatial interpolation when N should be equal for all profiles. (2) A justified downward extrapolation of incomplete data is possible with the model, especially if historical deepwater profiles are available. (3) Layer interfaces, as well as other coefficients, are derived with only one fitting to the entire profile. (4) The technique, using its general formulation, can serve as a parent for developing various types of models. The simpler step-like (with hyperbolic or exponential approximation) and more complicated smooth (continuous in gradient space) models were designed and tested against a large number of density profiles from the Sea of Okhotsk and the Gulf of California. Comparison of parametric, z-levels and isopycnal averaging was done for the region off the northeastern coast of Sakhalin.     

Oblique Wave-Induced Responses of A VLFS Edged with A Pair of Inclined Perforated Plates

This paper is concerned with the hydroelastic responses of a mat-like, rectangular very large floating structure (VLFS) edged with a pair of horizontal/inclined perforated anti-motion plates in the context of the direct coupling method. The updated Lagrangian formulae are applied to establish the equilibrium equations of the VLFS and the total potential formula is employed for fluids in the numerical model including the viscous effect of the perforated plates through the Darcy''s law. The hybrid finite element-boundary element (FE-BE) method is implemented to determine the response reduction of VLFS with attached perforated plates under various oblique incident waves. Also, the numerical solutions are validated against a series of experimental tests. The effectiveness of the attached perforated plates in reducing the deflections of the VLFS can be significantly improved by selecting the proper design parameters such as the porous parameter, submergence depth, plate width and inclination angle for the given sea conditions.     

Distribution of radioactive isotopes in rock and ore of Arkhangelskaya pipe from the Arkhangelsk diamond province

The contents of radioactive elements and the uranium isotopic composition of kimberlite in the Arkhangelskaya pipe at the M.V. Lomonosov deposit and of nearby country rocks have been studied. A surplus of ²³⁴U isotope has been established in rocks from the near-pipe space. The high γ = ²³⁴U/²³⁸U ratio is controlled by the geological structure of the near-pipe space. A nonequilibrium uranium halo reaches two pipe diameters in size and can be regarded as a local ore guide for kimberlite discovery. The rocks in the nearpipe space are also characterized by elevated or anomalous U, Th, and K contents with respect to the background.