Thermal decomposition process in algaenan of Botryococcus braunii race L. Part 2: Molecular dynamics simulations using the ReaxFF reactive force field

This paper reports ReaxFF MD simulation results on pyrolysis of a molecular model of the algaenan Botryococcus braunii race L biopolymer, specifically, ReaxFF predictions on the pyrolysis of prototypical chemical structures involving aliphatic chain esters and aldehydes. These preliminary computational experiments are then used to analyze the thermal cracking process within algaenan race L biopolymers. The simulations indicate that the thermal decomposition of the algaenan biopolymer is initiated by the cleavage of a C–O bond in the ester group, followed by the release of carbon dioxide. We also observe a significant, strongly temperature dependent, release of ethylene. This degradation mechanism leads to products similar to those observed in pyrolysis experiments, validating this computational approach.     

Early maturation processes in coal. Part 1: Pyrolysis mass balance and structural evolution of coalified wood from the Morwell Brown Coal seam

We have developed a theoretical approach for evaluating the maturation of kerogen-like material, involving molecular dynamic reactive modelling with a reactive force field to simulate thermal stress. Morwell Brown Coal was selected to study the thermal evolution of terrestrial organic matter (OM). To achieve this, a structural model is first constructed on the basis of literature models and analytical characterization of our samples using modern 1and 2D nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and elemental analysis. Then, artificial maturation of the coal is performed at low conversion in order to obtain quantitative and qualitative detailed evidence for the structural evolution of the kerogen upon maturation. The chemical changes include defunctionalization of carboxyl, carbonyl and methoxy functional groups, coupled with an increase in cross linking in the residual matured kerogen. Gaseous and liquid hydrocarbons, essentially CH₄, C₄H₈ and C₁₄₊ hydrocarbons, are generated in low amount, merely via cleavage of the lignin side chain.     

Avalanche and landslide simulation using the material point method: flow dynamics and force interaction with structures

In this paper, the material point method (MPM) is presented as a tool for simulating large deformation, gravity-driven landslides. The primary goal is to assess the interaction of these flow-like events with the built environment. This includes an evaluation of earthen mounds when energy dissipating devices are placed in the path of a snow avalanche. The effectiveness of the embankments is characterized using displacement, velocity, mass, and energy measures. A second example quantifies the force interaction between a landslide and a square rigid column. Multiple slide approach angles are considered, and various aspects of the impact force are discussed.     

Aerosol particles in the Mexican East Pacific. Part II: Numerical simulations of the impact of enhanced CCN on precipitation development

A number of studies have explored the effect of anthropogenic emissions on the development and evolution of precipitation in different types of clouds; however, the magnitude of the effect is still not clear, particularly for the case of deep, mixed-phase clouds. In this study, changes in the parameterization of the autoconversión process were introduced in the Advanced Regional Prediction System (ARPS) model to further evaluate this question. The simulations were initialized with cloud droplet distributions measured from an instrumented C-130 aircraft flying 600-800 km offshore in the intertropical convergence zone during the East Pacific Investigations of Climate (EPIC) project. Two contrasting cases were selected, one with and the other without the influence of anthropogenic aerosols. The simulations indicate that the increased cloud condensation nuclei (CCN) concentrations lead to a delay in the formation of rain and to a decrease in precipitation that reaches the surface as a result of the inhibition of the autoconversion of cloud water to rain water and the subsequent delay in the formation of hail. In addition, hail forms at higher levels in the cloud for the case of anthropogenic CCN. The most important process in the production of rain water in both cases is the melting of hail. A decrease in the mass of hail that falls below the freezing level in the polluted case, leads to a decrease in the resulting precipitation at the surface. Changes in the initial concentration of CCN do not appear to influence the storm strength in terms of updrafts and cloud top height, suggesting little sensitivity of the cloud dynamics. A control case simulation using the old microphysics scheme produces much more precipitation than either of the clean and polluted cases. In addition, the clean case with the modified parameterization shows a better agreement to observations than the control case. It is suggested to use the new scheme to simulate deep convective development over tropical maritime regions.     

Studies in the selective flocculation of hematite from gangue using high molecular weight polymers. Part 2: Physical factors

Having previously established a system of hematite and silica which can be separated effectively using long-chain polyacrylamide flocculants (Part 1) a stirred tank system was chosen to enable physical variables of flocculant concentration, impeller speed, time of flocculation, slurry concentration, ratio of hematite to quartz in the feed and particle size distribution to be studied.It was concluded that the time of flocculation allowed should be kept short and that there is an optimum of impeller speed though not a sharp one. Slurry concentration must be kept to 1% w/w to prevent serious performance deterioration. A clear optimum flocculant concentration was not found under present circumstances though very low concentrations (< 1 ppm) gave poor results while high concentrations gave no improvement on the results at about 2 ppm.Comparison between an impeller and a propeller of the same diameter and location in the tank pointed to the possibility of critical agitation configurations and the need for caution in scaling up results.The grade of material settling from a selective aggregation process is heavily dependent on the particle size distributions of the mineral species. Larger flocculated minerals produce richer flocs.     

Trace element cycling in a subterranean estuary: Part 2. Geochemistry of the pore water

Submarine groundwater discharge (SGD) is an important source of dissolved elements to the ocean, yet little is known regarding the chemical reactions that control their flux from sandy coastal aquifers. The net flux of elements from SGD to the coastal ocean is dependent on biogeochemical reactions in the groundwater-seawater mixing zone, recently termed the “subterranean estuary.” This paper is the second in a two part series on the biogeochemistry of the Waquoit Bay coastal aquifer/subterranean estuary. The first paper addressed the biogeochemistry of Fe, Mn, P, Ba, U, and Th from the perspective of the sediment composition of cores Charette et al. [Charette, M.A., Sholkovitz, E.R., Hansell, C.M., 2005. Trace element cycling in a subterranean estuary: Part 1. Geochemistry of the permeable sediments. Geochim. Cosmochim. Acta, 69, 2095-2109]. This paper uses pore water data from the subterranean estuary, along with Bay surface water data, to establish a more detailed view into the estuarine chemistry and the chemical diagenesis of Fe, Mn, U, Ba and Sr in coastal aquifers. Nine high-resolution pore water (groundwater) profiles were collected from the head of the Bay during July 2002. There were non-conservative additions of both Ba and Sr in the salinity transition zone of the subterranean estuary. However, the extent of Sr release was significantly less than that of its alkaline earth neighbor Ba. Pore water Ba concentrations approached 3000 nM compared with 25-50 nM in the surface waters of the Bay; the pore water Sr-salinity distribution suggests a 26% elevation in the amount of Sr added to the subterranean estuary. The release of dissolved Ba to the mixing zone of surface estuaries is frequently attributed to an ion-exchange process whereby seawater cations react with Ba from river suspended clay mineral particles at low to intermediate salinity. Results presented here suggest that reductive dissolution of Mn oxides, in conjunction with changes in salinity, may also be an important process in maintaining high concentrations of Ba in the pore water of subterranean estuaries. In contrast, pore water U was significantly depleted in the subterranean estuary, a result of SGD-driven circulation of seawater through reducing permeable sediments. This finding is supported by surface water concentrations of U in the Bay, which were significantly depleted in U compared with adjacent coastal waters. Using a global estimate of SGD, we calculate U removal in subterranean estuaries at 20 × 10⁶ mol U y⁻¹, which is the same order of magnitude as the other major U sinks for the ocean. Our results suggest a need to revisit and reevaluate the oceanic budgets for elements that are likely influenced by SGD-associated processes.     

Magnetite scavenging and the buoyancy of bubbles in magmas. Part 2: Energetics of crystal-bubble attachment in magmas

The fate of pre-eruptive bubbles depends largely on their buoyancy, which can be strongly modified by the presence of crystals attached to the bubble–melt interface. We define the attachment energy and attachment force as those resulting from the attachment of a crystal to a bubble. The attachment energy is such that (1) attachment of crystals to bubbles is always favored energetically, and (2) oxide minerals attach to bubbles much more strongly than silicates, because the attachment energy is a strong function of the wetting angle. Attaching crystals to bubbles can cause bubble–crystal pairs to become neutrally buoyant. There is a critical bubble radius below which the attachment force will be strong enough to keep the pair together; we show that crystals as large as 1 mm in diameter can form neutrally buoyant pairs. For early erupted Bishop magma, if all magnetite forms neutrally buoyant pairs with gas bubbles, ca. 0.1–0.2 vol% gas can be stored in the magma; 2–3 vol% of gas can be accounted for if all minerals form neutrally buoyant aggregates. These values are an order of magnitude lower than what is inferred from melt inclusions. Hence, both magnetite-free and magnetite-rich bubbles might have existed, but only a very small fraction of them could have been neutrally buoyant. Importantly, an intrinsic association between magnetite crystals and bubbles is expected. However, most magnetite crystals in the early erupted Bishop are free of bubbles; the puzzling conclusion is that nucleation away from crystals is favored over heterogeneous nucleation on crystal substrates. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Studies in the selective flocculation of hematite from gangue using high molecular weight polymers. Part 1: Chemical factors

The selective flocculation of hematite from silica has been studied from a chemical standpoint. Flocculation was induced in a stirred vessel under various reagent dosages, flocculant, dispersant and electrolyte, various pHs and slurry densities. The effectiveness of a given treatment was examined by the resulting grade of material reaching the outlet of a setting tube compared with the quantity.It was confirmed that selective flocculation is more favourable with more highly charged anionic polyacrylamide flocculants and with higher molecular weight. The process appears insensitive to dosage of flocculant in the range 1.5 to 10 ppm, but slurry densities must be kept low.Under such conditions the use of redispersion produced little gain in grade of hematite fraction but considerable loss in recovery.     

Flooding of the Saguenay region in 1996. Part 2: Aux Sables River flood mitigation and environmental impact assessment

Natural Hazards - In 2008, Wenchuan earthquake shook Sichuan Province in China. The questions of how to value the economic loss that would result if a catastrophe were to occur in Capital Beijing...     

Coprecipitation in the barite isostructural family: 2. Numerical simulations of reactions and mass transport

Coprecipitation of barite with trace constituents was simulated with consideration of aqueous speciation and complexation, mixing properties for the binary solid solutions (Zhu, this issue), precipitation and dissolution kinetics, and advective-dispersive transport. Speciation-solubility modeling was used to reproduce BaSO₄-RaSO₄ coprecipitation experimental results, and to calculate CrO₄²⁻ aqueous concentrations in equilibrium with a Ba(SO₄,CrO₄) solid solution. Kinetic reaction path modeling was used to simulate the coprecipitation of barite with RaSO₄ to form an onion-like chemically zoned solid upon the cooling of oil field brine.A one-dimensional coupled reactive mass transport model shows a strikingly different transport pattern for the tracer Ra²⁺, when the dominant attenuation reaction is with solid solution (Ba, Ra) SO₄ as compared to the case when it is controlled by pure RaSO₄ and barite solids under local equilibrium conditions. A self-enrichment of Ra²⁺ in the groundwater and aquifer solid matrix—higher concentrations of Ra²⁺ downstream from the reaction front—results from the coprecipitation reaction and advective-dispersive transport. This self-enrichment process generates a secondary tracer source, which has tracer concentrations higher than that of the original source. On the other hand, coprecipitation reactions can reduce Ra²⁺ concentrations in groundwater to a much lower level (below ppb) than that of pure RaSO₄(c) solubility (near ppm), which has been used to establish the Ra²⁺ concentration limits in groundwater, soil, and nuclear waste repositories.     

Anomalous Concentrations of Trace Elements in the Spetsugli Germanium Deposit (Pavlovka Brown Coal Deposit,Southern Primorye): Communication 2. Rubidium and Cesium

Data on Rb and Cs concentrations in typical (in terms of Ge content) and Ge-bearing coals, as well as host sedimentary rocks and underlying granites, are reported. It is shown that all Miocene deposits within ore zone are strongly enriched in these elements relative to Ge-barren areas of the deposit. The relative Cs accumulation is several times higher relative to Rb, because Ge-bearing sediments are characterized by anomalously low Rb/Cs ratio (up to 0.9). The average Cs concentration in coals (30.3 ppm) is more than one order of magnitude higher than the typical content in such rocks, while the maximal contents (57.2 ppm) exceed all known highest Cs contents found in solid fuel. Differences in Rb and Cs accumulation were found in the following sequence: coals (A^d < 50%)–coaly siltsones (50% < A^d < 75%)–coal-free and low-coaly silty sandstones and mudstones (A^d > 75%). The Rb content in this sequence increases, while the Cs content reaches maximum (up to 118.1 ppm) in the coaly siltstones. The anomalous Rb and Cs accumulation in Ge-bearing sediments is related to the circulation of volcanogenic thermal solutions, which are enriched in Ge, Rb, and Cs. It is suggested that Rb is mainly sorbed by clayey particles, whereas Cs is concentrated in the organic matter as well. This work presents the first data on high contents and distribution of Rb and Cs in Ge-bearing coals of the Pavlovka deposit. The data obtained make its possible to consider Rb and Cs as new associated elements of Ge mineralization, although their occurrence mode differs from that of Ge.     

Hydrothermal alteration of organic matter in sediments of the Northeastern Pacific Ocean: Part 2. Escanaba Trough,Gorda Ridge

Samples from the Ocean Drilling Program Leg 169 in Escanaba Trough, Gorda Ridge, NE Pacific Ocean, were analyzed to study maturation by accelerated diagenesis and/or by catagenesis of the sedimentary organic matter to hydrothermal petroleum. At Site 1038 the hydrothermal petroleums have migrated after generation to shallower horizons. The n-alkane maturation was indicated by the strong even C number preference (i.e., CPI <1.0) as in the case of Middle Valley. All samples contained admixed organic matter of terrigenous and marine components as indicated by the distributions of the biomarkers. The biological precursors were catagenetically altered to their equivalent mature compounds. The presence of high molecular weight PAHs in some sediment sections at Site 1038 reflected the high temperature alteration and reworking of organic matter into mature hydrothermal petroleum. At Site 1037, the reference hole in the Escanaba Trough, the n-alkanes with a strong predominance of odd C number homologs reflected immature non-marine lipid components essentially throughout the hole. Maturation of organic matter was only observed below 450 mbsf with n-alkanes showing a CPI <1.0. The strong even C number predominance in those intervals was attributed to initial maturation by high heat flow during the early rifting process.     

Infrazonal biostratigraphy of the Upper Cretaceous in the East European province based on benthic foraminifers,Part 2: Santonian-Maastrichtian

A chart of infrazonal biostratigraphic subdivisions in the Cenomanian-Coniacian succession of the East European paleobiogeographic province is substantiated based on distribution of benthic foraminifers. The suggested chart characterizes successive trend of changes in ecologic assemblages of benthic foraminifers and morphologic evolution of certain agglutinated (Gaudryina, Ataxophragmium, Ataxoorbignyina, Arenobulimina, Novatrix, Voloshinovella, Orbignyina, Bolivinopsis) and secretory (Neoflabellina, Globorotalites, Stensioeina, Osangularia, Eponides, Gavelinella, Pseudovalvulineria, Pseudogavelinella, Brotzenella, Cibicides, Cibicidoides, Angulogavelinella, Falsoplanulina, Anomalinoides, Coryphostoma, Bolivinoides, Praebulimina) foraminiferal genera. The chart includes 23 biostratigraphic units (zones and subzones), most of which are recognizable over the vast territory from the Mangyshlak to southern Baltic areas. It is correlated with the acknowledged belemnite, inoceramid, ammonoid and echinoid zonations. Eight stadia of taxonomic changes in foraminiferal assemblages, which are distinguished in this work, show that principal biotic events took place across the middle-late Santonian and Santonian-Campanian boundaries, in the earliest Campanian, at the early-late Campanian boundary time, during the late and terminal Campanian, and in the mid-early Maastrichtian.     

Petrology and Geochemistry of Early Cretaceous Bimodal Continental Flood Volcanism of the NW Etendeka, Namibia. Part 2: Characteristics and Petrogenesis of the High-Ti Latite and High-Ti and Low-Ti Voluminous Quartz Latite Eruptives

As a result of their relative concentration towards the respectiveAtlantic margins, the silicic eruptives of the Paraná(Brazil)–Etendeka large igneous province are disproportionatelyabundant in the Etendeka of Namibia. The NW Etendeka silicicunits, dated at     

Elision systems of the dnieper-donets aulacogen: Communication 2. Catagenetic processes in the donets and Pripyat depressions and some metallogenic features of the aulacogen

Elision processes associated with the formation and migration of brines and development of salt diapirs in the stratisphere in the Pripyat and Dnieper-Donets depressions are discussed. It is shown that salt stocks and mud volcanoes are characterized by the morphological similarity. Metallogeny of the Dnieper-Donets and Pripyat depressions is analyzed and problems of its further investigation are formulated.     

The effect of air flow rate on the kinetics of flotation. Part 2: The transfer of material from the froth over the cell lip

The flotation rate of galena was investigated as a function of air flow rate (AFR) and froth thickness (from 0 to 6 cm) in a batch flotation cell designed to produce a quiescent froth-liquid interface. This cell design limits mechanical breakage of the froth and prevents the hydraulic entrainment of fine particles into the froth phase. The overall transfer rate was characterized by a first-order rate constant, the overall rate constant (ORC). The ORC was found to increase with increasing AFR and with decreasing froth thickness. The transfer rate of material from the slurry to the froth was also determined as a function of AFR, and characterizes by its first-order rate constant, the flotation rate constant (FRC).The froth transport constant (FTC), the first-order constant which characterizes the transport of galena from the froth over the cell lip, was then determined from the ORC and the FRC. The FTC was found to increase with increasing AFR and decreasing froth thickness. For a froth thickness of 5 cm and low-to-intermediate AFR, the FTC was found to be significantly lower than the FRC.The FTC of galena particles of 0–12, 12–32 and 22–40 μm was also determined. At a froth thickness of 5 cm, the FTC decreased with increasing particle size over the full experimental range of AFRs.     

Geochronology of Pliocene volcanism in the Dzhavakheti Highland (the Lesser Caucasus). Part 2: Eastern part of the Dzhavakheti Highland. Regional geological correlation

The results of isotopic-geochronological study of the Pliocene volcanic rocks in reference sections and volcanic edifices of eastern part of the Dzhavakheti Highland (the northwestern Lesser Caucasus) are considered. The isotopic-geochronological data obtained here are correlated with data on western part of the Dzhavakheti Highland, which have been considered in previous part of this work. Based on correlation, time spans of principal volcanic events of the Pliocene in the study region as a whole are determined, and general trends of the young magmatism evolution within the region are established. In sum, the isotopic-geochronological dates evidence that the Pliocene magmatism of the Dzhavakheti Highland developed practically without essential breaks during the period of about 2 Ma long, from 3.75 to 1.75–1.55 Ma ago. The areal basic volcanism that was most widespread at that time is divisible into five discrete phases according to the isotopic dates obtained. Comparatively short pauses, which separated these phases of magmatic activity, were a few hundreds thousand years long, not more. Chemical composition of moderately acidic to silicic volcanics, which are of a limited distribution in the Dzhavakheti Highland, and their age relations with basic lavas of the region suggest that they are most likely the differentiation products of parental basic mantle-derived magmas. The analyzed distribution of volcanic centers, which erupted basic lavas of the Dzhavakheti Highland, evidence that first two phases of basic magmatism were connected here with volcanic activity in southwestern part of the region (northern termination of the Egnakhag Ridge), whereas activity of volcanoes situated on the east, predominantly in water-shed part and on slopes of the submeridional Dzhavakheti Ridge, controlled development of the third and fourth phases. Consequently, magmatic activity of the Pliocene stage in history of the Neogene-Quaternary magmatism of the Dzhavakheti Highland laterally migrated from the west to the east, being controlled by development of regional submeridional extension zones. Volcanic ridges marking the latter are formed by volcanic edifices, which are amalgamated at their bases and have erupted lavas of close age and composition. The migration of volcanic activity can be described in terms of the “domino effect,” when cessation of volcanism in one zone led to formation of the other submeridional zone of extension and magmatic activity displaced from the west eastward in sublatitudinal direction. In general, evolution of the Pliocene magmatism of the Dzhavakheti Highland, was similar, despite the essential regional peculiarities, to the generalized trend of magmatism evolution in the continental rifts and intraplate zones of the “hot-spot” type.