Molecular simulation of shale gas adsorption and diffusion in inorganic nanopores

We studied the structural and dynamical properties of methane and ethane in montmorillonite (MMT) slit pore of sizes 10, 20 and 30 Å using grand canonical Monte Carlo and classical molecular dynamics (MD) simulations. The isotherm, at 298.15 K, is generated for pressures up to 60 bar. The molecules preferentially adsorb at the surface as indicated by the density profile. In case of methane, we observe only a single layer, at the pore wall, whose density increases with increasing pressure. However, ethane also displays a second layer, though of low density in case of pore widths 20 and 30 Å. In-plane self-diffusion coefficient, D_‖, of methane and ethane is of the order of 10^? 6 m²/s. At low pressure, D_‖ increases significantly with the pore size. However, D_‖ decreases rapidly with increasing pressure. Furthermore, the effect of pore size on D_‖ diminishes at high pressure. Ideal adsorbed solution theory is used to understand the adsorption behaviour of the binary mixture of methane (80%) and ethane (20%) at 298.15 K. Furthermore, we calculate the selectivity of the gases at various pressures of the mixture, and found high selectivity for ethane in MMT pores. However, selectivity of ethane decreases with increase in pressure or pore size.     

The evolution of the prebiotic atmosphere

One-dimensional radiative convective and photochemical models are used to estimate the vertical temperature structure and composition of the earth's prebiotic atmosphere. Greatly enhanced CO2 levels (100-1000 times present) are required to keep the mean surface temperature above freezing in the face of decreased solar luminosity during the earth's early history. Such high CO2 partial pressures would have affected the atmospheric oxidation state by facilitating the photochemical production of soluble species including H2O2 and H2CO. Oxidation of ferrous iron in the oceans by H2O2 dissolved in rainwater should have kept the atmospheric H2 mixing ratio above 2x10(-4) and the ground-level O2 mixing ratio below 10(-11), regardless of the magnitude of the rate of volcanic release of reduced gases.     

First ecosystems on Earth

Theories attempting to explain the origin of life on Earth should be based on the assumption that habitability precedes habitation. The hypotheses of the first organism should be based on the evaluation of its possible life-supporting ecosystem. The ecosystem should necessarily include primary autotrophic producers, and hydrogenotrophy appears to be an adequate physiological type for primitive ecosystems. Consideration of life on Earth should differentiate between the origin of organisms in situ and the transportation of organisms from outside with cosmic bodies in the framework of life as a widespread phenomenon of the Universe. In the case of transport of life with cosmic bodies, there are no limitations on the transfer of a community rather than an individual cell. In the case of the transport of the community with a large piece of “dirty ice,” the problem lies in the correspondence between the community and its ecosystem on the parent body and the conditions on the primeval Earth rather than functional divergence from a primary ancestor. Subsequent events are within the framework of paleontologically observed evolution and can be described as biogeochemical succession without any additional speculations.     

Cometary origin of carbon,nitrogen and water on the Earth

Two independent assumptions are substantiated; firstly, that the Earth accreted from dust particles that were hot enough not to contain any volatiles; secondly, that after the accretion was finished, all the volatiles of the biosphere, including the atmosphere and the oceans, were brought by a cometary bombardment.The first assumption is based on the empirical evidence that the planets originated from minor bodies. These minor bodies were generated by accumulation of fine dust particles, which sedimented from the gas of the solar nebula. We will demonstrate that, when the particles from the Earth's zone were separated from the nebular gas, they were close to 1000 K and at a thermochemical equilibrium with this gas. This implies that almost all carbon, nitrogen and water remained in the gas phase, respectively as CO, N₂ and steam. Since there was no volatile left in the minor bodies, they could produce neither atmosphere nor oceans.The second assumption is based on the existence of the giant planets in the outer reaches of the solar system. Over there the solar nebula was very cold; the minor bodies were generated by accumulation of frosty particles and became cometary nuclei containing a large amount of ice and volatile stuff. When the giant planets' embryos reached a mass of 10 to 20 terrestrial masses, the orbits of billions of minor icy bodies were perturbed enough to send some of them to the inner solar system. A model shows that the icy bodies which hit the Earth are more than enough to explain the whole biosphere, including the atmosphere and the oceans.     

Evidence for Mass Flow in Flowering Individuals of the Submersed Vascular Plant Myriophyllum heterophyllum

Myriophyllum heterophyllum Michx. is a rhizomatous submersed aquatic plant that produces a short, emergent floral spike. We hypothesized that lacunar pressures in emergent spikes should be at or near atmospheric pressure and that a mass flow of gases from submersed stems through the rhizome to emergent stems may occur as lacunar O2 concentrations and pressures in submersed stems increase during photosynthesis. We examined the potential for a pressure gradient ([delta]P) to develop along this pathway by measuring diurnal changes in lacunar gas composition and pressure in submersed stems of nonflowering plants and emergent stems of flowering individuals. Methane release from emergent spikes was also monitored during three diurnal cycles to evaluate the hypothesis that the [delta]P is maintained by the release of lacunar gases to the atmosphere. Lacunar O2 concentrations and pressures in submersed stems increased at sunrise and reached maximum levels by midday. Although O2 fluctuated similarly in emergent stems, lacunar pressures remained at or near atmospheric pressure, indicating that a [delta]P is generated between submersed and emergent stems during photosynthesis. Methane release from emergent spikes increased as lacunar pressures increased, indicating that rhizome gases are transported through emergent stems by mass flow and the [delta]P is maintained by venting lacunar gases from emergent spikes. The potential for mass flow in both flowering and nonflowering individuals is discussed.     

Synthesis of purine and pyrimidine nucleosides under the action of high temperature and UV-radiation]

By means of UV-spectroscopy, gel filtration, thin layer and paper chromatography, it has been shown that the action of UV irradiation and heat on a dry mixture of nitrogenous bases and deoxyribose results in the formation of nucleoside pool, particulary deoxyadenosine. These energy sources were chosen in order to imitate at least approximately the conditions assumed to exist on the primitive Earth. Similar synthesis takes place in the atmosphere of the three gases studied, being more intensive in CO2 than in N2 or O2.     

Physical conditions on the early Earth

The formation of the Earth as a planet was a large stochastic process in which the rapid assembly of asteroidal-to-Mars-sized bodies was followed by a more extended period of growth through collisions of these objects, facilitated by the gravitational perturbations associated with Jupiter. The Earth's inventory of water and organic molecules may have come from diverse sources, not more than 10% roughly from comets, the rest from asteroidal precursors to chondritic bodies and possibly objects near Earth's orbit for which no representative class of meteorites exists today in laboratory collections. The final assembly of the Earth included a catastrophic impact with a Mars-sized body, ejecting mantle and crustal material to form the Moon, and also devolatilizing part of the Earth. A magma ocean and steam atmosphere (possibly with silica vapour) existed briefly in this period, but terrestrial surface waters were below the critical point within 100 million years after Earth's formation, and liquid water existed continuously on the surface within a few hundred million years. Organic material delivered by comets and asteroids would have survived, in part, this violent early period, but frequent impacts of remaining debris probably prevented the continuous habitability of the Earth for one to several hundred million years. Planetary analogues to or records of this early time when life began include Io (heat flow), Titan (organic chemistry) and Venus (remnant early granites).     

Field measurements of internal pressurization in Phragmites australis (Poaceae) and implications for regulation of methane emissions in a midlatitude prairie wetland

Emergent aquatic macrophytes in vegetated wetlands provide routes for methane (CH(4)) transport from sites of production in oxygen-poor sediments, where CH(4) concentrations are relatively high, to the atmosphere, which typically has much lower CH(4) concentrations. Transport can occur through aerenchymatous tissue via simple diffusion. Recently, the importance of convective throughflow (i.e., mass transport of gases through plants driven by pressure gradients) in enhancing gas transport has been demonstrated in several genera (e.g., Nuphar, Nymphaea, Nelumbo, Typha, and Phragmites). This study was conducted to elucidate the governing plant-mediated gas transport mechanisms in a midlatitude prairie wetland and to determine both their diel and seasonal variations and the importance of environmental controlling factors. Pressures inside culms of the two dominant emergent aquatic macrophytes (Scirpus acutus and Phragmites australis) were measured directly throughout the growing season and on selected days in midseason. Supporting measurements included solar radiation, air temperature, relative humidity, and windspeed. Results indicated pressures inside green healthy culms of Phragmites were above atmospheric pressure by up to 1650 Pa during the day. At night culm pressures were at or slightly above atmospheric. No pressurization was detected in Scirpus. Highest pressures in Phragmites occurred during midseason when biomass and foliage area index were at their maxima (920 g/m(2) and 2.8, respectively). High internal pressures also coincided with periods of high solar radiation (>500 W/m(2)), high temperature (>20°C), and low relative humidity (<60%). Periods of high internal pressures also coincided with periods of high CH(4) efflux from the wetland as measured in concomitant studies. Convective throughflow driven by internal pressure gradients in Phragmites thus explains much of the diel variation in methane efflux previously reported from this wetland.     

New concepts of microbial treatment processes for the nitrogen removal in wastewater

Many countries strive to reduce the emissions of nitrogen compounds (ammonia, nitrate, NOx) to the surface waters and the atmosphere. Since mainstream domestic wastewater treatment systems are usually already overloaded with ammonia, a dedicated nitrogen removal from concentrated secondary or industrial wastewaters is often more cost-effective than the disposal of such wastes to domestic wastewater treatment. The cost-effectiveness of separate treatment has increased dramatically in the past few years, since several processes for the biological removal of ammonia from concentrated waste streams have become available. Here, we review those processes that make use of new concepts in microbiology: partial nitrification, nitrifier denitrification and anaerobic ammonia oxidation (the anammox process). These processes target the removal of ammonia from gases, and ammonium-bicarbonate from concentrated wastewaters (i.e. sludge liquor and landfill leachate). The review addresses the microbiology, its consequences for their application, the current status regarding application, and the future developments.     

The Metabolism of Low Molecular Weight Hydrocarbon Gases in Man

The metabolism of ethane and pentane in man is demonstrated to occur from the uptake of an enriched atmosphere of these gases in a rebreathe spirometer circuit. Dithiocarb, an inhibitor of alkane metabolism, reduced uptake and increased the respiratory excretion of these gases. This effect was least marked for the slowly metabolised ethane. Therefore the endogenous production of ethane as measured by respiratory excretion is less affected. However pentane is rapidly metabolised and this limits the use of simple respiratory excretion of pentane as a measure of in vivo lipid peroxidation.     

Sources and Sinks for Ammonia and Nitrite on the Early Earth and the Reaction of Nitrite with Ammonia

An analysis of sources and sinks for ammonia and nitrite on the early Earth was conducted. Rates of formation and destruction, and steady state concentrations of both species were determined by steady state kinetics. The importance of the reaction of nitrite with ammonia on the feasibility of ammonia formation from nitrite was evaluated. The analysis considered conditions such as temperature, ferrous iron concentration, and pH. For sinks we considered the reduction of nitrite to ammonia, reaction between nitrite and ammonia, photochemical destruction of both species, and destruction at hydrothermal vents. Under most environmental conditions, the primary sink for nitrite is reduction to ammonia. The reaction between ammonia and nitrite is not an important sink for either nitrite or ammonia. Destruction at hydrothermal vents is important at acidic pH's and at low ferrous iron concentrations. Photochemical destruction, even in a worst case scenario, is unimportant under many conditions except possibly under acidic, low iron concentration, or low temperature conditions. The primary sink for ammonia is photochemical destruction in the atmosphere. Under acidic conditions, more of the ammonia is tied up as ammonium (reducing its vapor pressure and keeping it in solution) and hydrothermal destruction becomes more important.     

Diffusion from a Circular Stoma through a Boundary Layer: A FIELD-THEORETICAL ANALYSIS

The case of diffusion of a gas from a single circular stoma through an unstirred boundary layer of finite thickness into a perfectly stirred atmosphere free of convective effects is examined theoretically, with the gas assumed to be at constant concentration across the stoma. The analysis employs a mathematical solution to an analogous problem in electrostatic physics previously obtained by Kuz'min (1972 Sov Phys Tech Phys 17: 473-476). The diffusion flux is shown to be no more than 1% greater than that into a perfectly unstirred atmosphere if the boundary layer is thicker than 40 times the stomatal radius. Under the conditions assumed, for realistic boundary-layer and stomatal dimensions, taking the diffusion flux through the boundary layer to be linear with the stomatal radius would usually involve no significant error. This result may indicate that the principal effect of wind velocity on mass exchange between leaf and atmosphere may be exerted through influencing convection outside the boundary layer rather than through determining the thickness of that layer.     

Ecosystem feedbacks on climate at the landscape scale

Vegetation controls aspects of climate at all scales. These controls operate through fluxes of mass (water vapour, particulates, trace gases, condensation nuclei, and ice nuclei) and energy (latent and sensible heat, radiative exchanges, and momentum dissipation) between the biosphere and the atmosphere. The role these fluxes play in controlling minimum and maximum temperature, temperature range, rainfall, and precipitation processes are detailed. On the hemispheric scale, the importance of evapotranspiration, vegetation surface roughness, and vegetation albedo in the current generation of atmospheric general circulation models is reviewed. Finally, I assess at the planetary scale the global climate effects of biogenic emissions that are well mixed throughout the troposphere. I show that daily maximum and minimum temperatures are, in part, controlled by the emission of non-methane hydrocarbons and transpired water vapour. In many regions, a substantial fraction of the rainfall arises from upstream evapotranspiration rather than from oceanic evaporation. Biosphere evapotranspiration, surface roughness, and albedo are key controls in the general circulation of the atmosphere: climate models that lack adequate specifications for these biosphere attributes fail. The biosphere modulates climate at all scales.     

Modelling of pyrolysis of large wood particles

A fully transient mathematical model has been developed to describe the pyrolysis of large biomass particles. The kinetic model consists of both primary and secondary reactions. The heat transfer model includes conductive and internal convection within the particle and convective and radiative heat transfer between the external surface and the bulk. An implicit Finite Volume Method (FVM) with Tridiagonal Matrix Algorithm (TDMA) is employed to solve the energy conservation equation. Experimental investigations are carried out for wood fines and large wood cylinder and sphere in an electrically heated furnace under inert atmosphere. The model predictions for temperature and mass loss histories are in excellent agreement with experimental results. The effect of internal convection and particle shrinkage on pyrolysis behaviour is investigated and found to be significant. Finally, simulation studies are carried out to analyze the effect of bulk temperature and particle size on total pyrolysis time and the final yield of char.     

THE INFLUENCE OF THE CALIFORNIA MARINE LAYER ON BILL SIZE IN A GENERALIST SONGBIRD

The hypothesis is tested that birds in hotter and drier environments may have larger bills to increase the surface area for heat dissipation. California provides a climatic gradient to test the influence of climate on bill size. Much of California experiences dry warm/hot summers and coastal areas experience cooler summers than interior localities. Based on measurements from 1488 museum skins, song sparrows showed increasing body‐size‐corrected bill surface area from the coast to the interior and declining in the far eastern desert. As predicted by Newton's convective heat transfer equation, relative bill size increased monotonically with temperature, and then decreased where average high temperatures exceed body temperature. Of the variables considered, distance from coast, average high summer temperature, and potential evapotranspiration showed a strong quadratic association with bill size and rainfall had a weaker negative relationship. Song sparrows on larger, warmer islands also had larger bills. A subsample of radiographed specimens showed that skeletal bill size is also correlated with temperature, demonstrating that bill size differences are not a result of variation in growth and wear of keratin. Combined with recent thermographic studies of heat loss in song sparrow bills, these results support the hypothesis that bill size in California song sparrows is selected for heat dissipation.     

A model of evaporative cooling of wet skin surface and fur layer

(1) A theoretical model that simultaneously solves heat and mass transfer in a wet skin surface and fur layer that occurs when an animal is cooled by blowing air over its wetted skin surface and hair coat is presented. (2) The model predicts evaporative and convective heat losses for different levels of wetness, air velocity, ambient temperature, relative humidity and fur properties. (3) Model predictions provide insight about evaporative and convective cooling processes of cows in stressful hot environments.     

Abiotic Formation of Valine Peptides Under Conditions of High Temperature and High Pressure

We investigated the oligomerization of solid valine and the stabilities of valine and valine peptides under conditions of high temperature (150–200 °C) and high pressure (50–150 MPa). Experiments were performed under non-aqueous condition in order to promote dehydration reaction. After prolonged exposure of monomeric valine to elevated temperatures and pressures, the products were analyzed by liquid chromatography mass spectrometry comparing their retention times and masses. We identified linear peptides that ranged in size from dimer to hexamer, as well as a cyclic dimer. Previous studies that attempted abiotic oligomerization of valine in the absence of a catalyst have never reported valine peptides larger than a dimer. Increased reaction temperature increased the dissociative decomposition of valine and valine peptides to products such as glycine, β-alanine, ammonia, and amines by processes such as deamination, decarboxylation, and cracking. The amount of residual valine and peptide yields was greater at higher pressures at a given temperature, pressure, and reaction time. This suggests that dissociative decomposition of valine and valine peptides is reduced by pressure. Our findings are relevant to the investigation of diagenetic processes in prebiotic marine sediments where similar pressures occur under water-poor conditions. These findings also suggest that amino acids, such as valine, could have been polymerized to peptides in deep prebiotic marine sediments within a few hundred million years.     

Collisions with ice/volatile objects: geological implications--a qualitative treatment

An aperiodic collision of the Earth with extra-terrestria] ice/volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record. Due to the volatile nature of these bodies, evidence for their impacts, particularly in the ocean might be subtle and best seen as 'spikes' in the geochemical or fossil record against normal background. Differing effects would result depending on the site of the major break-up of the object: in the atmosphere, on land, or in the ocean. This paper focuses on the effects of adding material to the seas, oceans, and atmosphere. The treatment is largely qualitative, however mass balance calculations were used to estimate the relative mass needed to affect changes in a variety of reservoirs. Although actual impactors probably have a variable composition, the effects of water-, C-, N-, and S-containing objects are discussed. In the atmosphere, effects could include increased rain acidity, increased levels of nutrients, and enhanced greenhouse warming/cooling. Oceanic effects might include increased oceanic productivity (nitrogen-containing objects). As a result of increased chemical weathering and/or greenhouse effects, increased temperatures coupled with enhanced productivity could result in wider-spread oceanic anoxia or altered calcite/aragonite stability. Possible examples of such impacts from the geologic record and potential biotic effects are given.     

Insights into interstitial flow,shear stress,and mass transport effects on ECM heterogeneity in bioreactor-cultivated engineered cartilage hydrogels

Interstitial flow in articular cartilage is secondary to compressive and shear deformations during joint motion and has been linked with the well-characterized heterogeneity in structure and composition of its extracellular matrix. In this study, we investigated the effects of introducing gradients of interstitial flow on the evolution of compositional heterogeneity in engineered cartilage. Using a parallel-plate bioreactor, we observed that Poiseuille flow stimulation of chondrocyte-seeded agarose hydrogels led to an increase in glycosaminoglycan and type II collagen deposition in the surface region of the hydrogel exposed to flow. Experimental measurements of the interstitial flow fields based on the fluorescence recovery after photobleaching technique suggested that the observed heterogeneity in composition is associated with gradients in interstitial flow in a boundary layer at the hydrogel surface. Interestingly, the interstitial flow velocity profiles were nonlinearly influenced by flow rate, which upon closer examination led us to the original observation that the apparent hydrogel permeability decreased exponentially with increased interfacial shear stress. We also observed that interstitial flow enhances convective mass transport irrespective of molecular size within the boundary layer near the hydrogel surface and that the convective contribution to transport diminishes with depth in association with interstitial flow gradients. The implications of the nonlinearly inverse relationship between the interfacial shear stress and the interstitial flux and permeability and its consequences for convective transport are important for tissue engineering, since porous scaffolds comprise networks of Poiseuille channels (pores) through which interstitial flow must navigate under mechanical stimulation or direct perfusion.     

Life conditions on the early Earth after 4.0 Ga

The organization level of Precambrian fossils is the most reliable indicator of the state and parameters of the biosphere, such as the atmosphere composition, average temperature of the earth’s surface, and others. At present, cyanobacteria, unicellular and multicellular eukaryotes, and coelomates are considered to appear in the geological history of the Earth much earlier than it was supposed previously. Our knowledge and ideas of the early Earth are very important for considering the problems of the origin of life. A key boundary of the earliest period was probably about 4 Ga. This boundary is between the periods documented and undocumented by the geological record. The Earth history and probable surface conditions before 4 Ga are considered by L.M. Mukhina, A.V. Vityazeva, G.V. Pechernikova, and L.V. Ksanfomaliti in this volume.