Molecular H2O in armenite, BaCa2Al6Si9O30·2H2O, and epididymite, Na2Be2Si6O15·H2O: Heat capacity, entropy and local-bonding behavior of confined H2O in microporous silicates

Armenite, ideal formula BaCa₂Al₆Si₉O₃₀·2H₂O, and its dehydrated analog BaCa₂Al₆Si₉O₃₀ and epididymite, ideal formula Na₂Be₂Si₆O₁₅·H₂O, and its dehydrated analog Na₂Be₂Si₆O₁₅ were studied by low-temperature relaxation calorimetry between 5 and 300 K to determine the heat capacity, C_p, behavior of their confined H₂O. Differential thermal analysis and thermogravimetry measurements, FTIR spectroscopy, electron microprobe analysis and powder Rietveld refinements were undertaken to characterize the phases and the local environment around the H₂O molecule.The determined structural formula for armenite is Ba_0.88(0.01)Ca_1.99(0.02)Na_0.04(0.01)Al_5.89(0.03)Si_9.12(0.02)O₃₀·2H₂O and for epididymite Na_1.88(0.03)K_0.05(0.004)Na_0.01(0.004)Be_2.02(0.008)Si_6.00(0.01)O₁₅·H₂O. The infrared (IR) spectra give information on the nature of the H₂O molecules in the natural phases via their H₂O stretching and bending vibrations, which in the case of epididymite only could be assigned. The powder X-ray diffraction data show that armenite and its dehydrated analog have similar structures, whereas in the case of epididymite there are structural differences between the natural and dehydrated phases. This is also reflected in the lattice IR mode behavior, as observed for the natural phases and the H₂O-free phases. The standard entropy at 298 K for armenite is S° = 795.7 ± 6.2 J/mol K and its dehydrated analog is S° = 737.0 ± 6.2 J/mol K. For epididymite S° = 425.7 ± 4.1 J/mol K was obtained and its dehydrated analog has S° = 372.5 ± 5.0 J/mol K. The heat capacity and entropy of dehydration at 298 K are Δ = 3.4 J/mol K and ΔS^rxn = 319.1 J/mol K and Δ = −14.3 J/mol K and ΔS^rxn = 135.7 J/mol K for armenite and epididymite, respectively. The H₂O molecules in both phases appear to be ordered. They are held in place via an ion-dipole interaction between the H₂O molecule and a Ca cation in the case of armenite and a Na cation in epididymite and through hydrogen-bonding between the H₂O molecule and oxygen atoms of the respective silicate frameworks. Of the three different H₂O phases ice, liquid water and steam, the C_p behavior of confined H₂O in both armenite and epididymite is most similar to that of ice, but there are differences between the two silicates and from the C_p behavior of ice. Hydrogen-bonding behavior and its relation to the entropy of confined H₂O at 298 K is analyzed for various microporous silicates.The entropy of confined H₂O at 298 K in various silicates increases approximately linearly with increasing average wavenumber of the OH-stretching vibrations. The interpretation is that decreased hydrogen-bonding strength between a H₂O molecule and the silicate framework, as well as weak ion-dipole interactions, results in increased entropy of H₂O. This results in increased amplitudes of external H₂O vibrations, especially translations of the molecule, and they contribute strongly to the entropy of confined H₂O at T < 298 K.     

Exponential time integrators for stochastic partial differential equations in 3D reservoir simulation

The transport of chemically reactive solutes (e.g. surfactants, CO₂ or dissolved minerals) is of fundamental importance to a wide range of applications in oil and gas reservoirs such as enhanced oil recovery and mineral scale formation. In this work, we investigate exponential time integrators, in conjunction with an upwind weighted finite volume discretisation in space, for the efficient and accurate simulation of advection–dispersion processes including non-linear chemical reactions in highly heterogeneous 3D oil reservoirs. We model sub-grid fluctuations in transport velocities and uncertainty in the reaction term by writing the advection–dispersion–reaction equation as a stochastic partial differential equation with multiplicative noise. The exponential integrators are based on the variation of constants solution and solve the linear system exactly. While this is at the expense of computing the exponential of the stiff matrix representing the finite volume discretisation, the use of real Léja point or the Krylov subspace technique to approximate the exponential makes these methods competitive compared to standard finite difference-based time integrators. For the deterministic system, we investigate two exponential time integrators, the second-order accurate exponential Euler midpoint (EEM) scheme and exponential time differencing of order one (ETD1). All our numerical examples demonstrate that our methods can compete in terms of efficiency and accuracy compared with standard first-order semi-implicit time integrators when solving (stochastic) partial differential equations that model mixing and chemical reactions in 3D heterogeneous porous media. Our results suggest that exponential time integrators such as the ETD1 and EEM schemes could be applied to typical 3D reservoir models comprising tens to hundreds of thousands unknowns.     

The stiff upper LIP: investigating the High Arctic Large Igneous Province

The Canadian Arctic Islands expose a complex network of dykes and sills that belong to the High Arctic Large Igneous Province (HALIP), which intruded volatile‐rich sedimentary rocks of the Sverdrup Basin (shale, limestone, sandstone and evaporite) some 130 to 120 million years ago. There is thus great potential in studying the HALIP to learn how volatile‐rich sedimentary rocks respond to magmatic heating events during LIP emplacement. The HALIP remains, however, one of the least well known LIPs on the planet due to its remote location, short field season, and harsh climate. A Canadian–Swedish team of geologists set out in summer 2015 to further explore HALIP sills and their sedimentary host rocks, including the sampling of igneous and meta‐sedimentary rocks for subsequent geochemical analysis, and high pressure‐temperature petrological experiments to help define the actual processes and time‐scales of magma–sediment interaction. The research results will advance our understanding of how climate‐active volatiles such as CO_2, SO₂ and CH₄ are mobilised during the magma–sediment interaction related to LIP events, a process which is hypothesised to have drastically affected Earth's carbon and sulphur cycles. In addition, assimilation of sulphate evaporites, for example, is anticipated to trigger sulphide immiscibility in the magma bodies and in so doing could promote the formation of Ni‐PGE ore bodies. Here we document the joys and challenges of ‘frontier arctic fieldwork’ and discuss some of our initial observations from the High Arctic Large Igneous Province.     

The orientation and vibrational states of H2O in synthetic alkali-free beryl

 The polarized single-crystal Raman spectra of synthetic H₂O-containing alkali-free beryl were recorded at room and low temperatures, and the polarized single-crystal IR spectra at room temperature. The H₂O molecule in the channel cavities is characterized by a Raman-active symmetric stretching vibration (ν₁) at 3607 cm⁻¹ and an IR-active asymmetric stretch (ν₃) at 3700 cm⁻¹ at room temperature. At low temperatures this ν₃ mode is observed in the Raman. Weak ν₁ and ν₃ modes of a second type of H₂O are also observed in the Raman spectra but only at 5 K. The H⋯&middot;H vector of the most abundant type of H₂O is parallel to the channel axis of beryl along [0 0 0 1]. The components of the polarizability tensor of the ν₁ mode of H₂O are similar to, but not exactly the same as, those of a free H₂O molecule. The Raman measurements indicate that the H₂O molecule is rotationally disordered around [0 0 0 1]. External translation and librational modes of H₂O could be observed as overtones with the internal H₂O-stretching modes. In the case of the librational motions, normal modes could also be observed directly in the Raman spectra at ∼200 cm⁻¹. The energies of the translational modes can be determined from an analysis of the overtones and are about 9 cm⁻¹ in energy (i.e., T_z). The energies of the librational modes are about 210 cm⁻¹ for R_x and 190 cm⁻¹ for R_y. Received: 8 April 1999 / Accepted: 5 April 2000     

Crustal motion and deformation in Greece from a decade of GPS measurements, 1993–2003

The Hellenic plate boundary region, located in the collision zone between the Nubian/Arabian and Eurasian lithospheric plates, is one of the seismo-tectonically most active areas of Europe. During the last 15 years, GPS measurements have been used to determine the crustal motion in the area of Greece with the aim to better understand the geodynamical processes of this region. An extended reoccupation network covering whole Greece has been measured periodically in numerous GPS campaigns since the late eighties, and a continuous GPS network has been operated in the region of the Ionian Sea since 1995. In this paper, we present a new detailed high-quality solution of continuous and campaign-type measurements acquired between 1993 and 2003. During the GPS processing, a special effort was made to obtain consistent results with highest possible accuracies and reliabilities. Data of 54 mainly European IGS and EUREF sites were included in the GPS processing in order to obtain results which are internally consistent with the European kinematic field and order to allow for a regional interpretation. After an overview of the results of the IGS/EUREF sites, the results from more than 80 stations in Greece are presented in terms of velocities, time series, trajectories and strain rates. Previous geodetic, geological and seismological findings are generally confirmed and substantially refined. New important results include the observation of deformation zones to the north and to the south of the North Aegean Trough and in the West Hellenic arc region, arc-parallel extension of about 19 mm/yr along the Hellenic arc, and compression between the Ionian islands and the Greek mainland. Due to continuous long-term observations of 4–8 years, it was possible to extract height changes from the GPS time series. In Greece, we observe a differential subsidence of the order of 2 mm/yr between the northern and central Ionian islands across the Kefalonia fault zone. The differential subsidence of the central Ionian islands with respect to the northwestern Greek mainland amounts to 4 mm/yr.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Finite prandtl number convection in spherical shells

Abstract

Finite amplitude convection in spherical shells with spherically symmetric gravity and heat source distribution is considered. The nonlinear problem of three-dimensional convection in shells with stress-free and isothermal boundaries is solved by expanding the dependent variables in terms of powers of the amplitude of convection. The preferred mode of convection is determined by a stability analysis in which arbitrary infinitesimal disturbances are superimposed on the steady solutions. The shell is assumed to be thick and only shells for which the ratio ζ of outer radius to inner radius is 2 or 3 are considered. Three cases, two of which lead to a self adjoint problem, are treated in this paper. The stable solutions are found to be l=2 modes for ζ=3 where l is the degree of the spherical harmonics and an l=3 non-axisymmetric mode which exhibits the symmetry of a tetrahedron for ζ=2. These stable solutions transport the maximum amount of heat. The Prandtl number dependence of the heat transport is computed for the various solutions analyzed in the paper.     

Survey on germination and species composition of dinoflagellates from ballast tanks and recent sediments in ports on the South Coast of Finland, North-Eastern Baltic Sea

Cyst beds in ships and ports in Finland have previously been unstudied. Therefore, sediments from ships' ballast water tanks and four Finnish ports were sampled for dinoflagellate cysts and other phytoplankton. Untreated sediments were incubated at 10 degrees C and 20 degrees C in the local 6 psu salinity for 1, 4 and 7 days, and vegetative cells were examined with light and scanning electron microscope. Sediments were inhabited by various dinoflagellates, diatoms, chlorophytes, cyanophytes and small flagellates. Germinated dinoflagellates were found in 90% of ballast tanks and in all ports. Gymnodiniales spp. and Heterocapsa rotundata formed a major proportion of the proliferating dinoflagellate cells. One species, Peridinium quinquecorne, not previously reported from the Baltic Sea, was identified with SEM. The study emphasises that ships are potential transport vehicles for dinoflagellate cysts even in the low salinity Finnish waters, and small-sized dinoflagellates should be focused upon in ballast water studies.     

Comparison of Different Strategies for Determining Raster‐Based Least‐Cost Paths with a Minimum Amount of Distortion

The conventional raster‐based least‐cost path technique, in which the connectivity graph is constructed by treating each raster cell as a node and linking each node to its adjacent neighbors, has been widely used to determine optimum paths in space. Unfortunately, paths calculated with this method are subject to distortions that stem from the imposed node‐link structure. Due to the distortions, the calculated paths may be longer than the true optimum paths in continuous space, and because of this, they may also look highly unrealistic when displayed on a map. This study examines how the quality of the raster‐based paths can be improved by using larger connectivity patterns on the one hand, and placing nodes on the sides of the cells of a raster instead of at their centers, on the other. In addition, the utility of the quadtree structure is examined. The different methods are evaluated against three different datasets using the cost distance of the calculated paths and processing times as evaluation criteria. The results indicate that raster‐based paths can be improved by using the evaluated techniques, although the degree of improvement is also dependent on the properties of the underlying cost raster.