Pressure and temperature dependence of the viscosity of a NaAlSi<Subscript>2</Subscript>O<Subscript>6</Subscript> melt

The viscosity of a silicate melt of composition NaAlSi₂O₆ was measured at pressures from 1.6 to 5.5 GPa and at temperatures from 1,350 to 1,880°C. We employed in situ falling sphere viscometry using X-ray radiography. We found that the viscosity of the NaAlSi₂O₆ melt decreased with increasing pressure up to 2 GPa. The pressure dependence of viscosity is diminished above 2 GPa. By using the relationship between the logarithm of viscosity and the reciprocal temperature, the activation energies for viscous flow were calculated to be 3.7 ± 0.4 × 10² and 3.7 ± 0.5 × 10² kJ/mol at 2.2 and 2.9 GPa, respectively.     

Sorption of selenite in a multi-component system using the “dialysis membrane” method

⁷⁹Se is a potentially mobile long-lived fission product, which may make a dominant contribution to the long-term radiation exposure resulting from deep geological disposal of radioactive waste. Its mobility is affected by sorption on minerals. Selenium sorption processes have been studied mainly by considering interaction with a single mineral surface. In the case of multi-component systems (e.g. soils), it is difficult to predict the radioelement behaviour only from the mineral constituents. This study contributes to the understanding of multi-component controls of Se concentrations towards predicting Se behaviour in soils after migration from a disposal site. This goal was approached by measuring selenite sorption on mono and multi-phase systems physically separated by dialysis membranes. To the best of the authors’ knowledge, very few studies have used dialysis membranes to study the sorption competition of selenite between several mineral phases. Other workers have used this method to study the sorption of pesticides on montmorillonite in the presence of dissolved organic matter. Indeed, this method allows measurement of individual K_d in a system composed of several mineral phases. Dialysis membranes allowed (i) determination of the competition of two mineral phases for selenite sorption (ii) and determination of the role of humic acids (HAs) on selenite sorption in oxidising conditions. Experimental results at pH 7.0 show an average Se(IV) sorption distribution coefficient (K_d) of approximately 125 and 9410 L kg⁻¹ for bentonite and goethite, respectively. The average K_d for goethite decreases to 613 L kg⁻¹ or 3215 L kg⁻¹ in the presence of bentonite or HA, respectively. For bentonite, the average K_d decreases slightly in the presence of goethite (60 L kg⁻¹) and remains unchanged in the presence of HA. The experimental data were successfully modelled with a surface complexation model using the PHREEQC geochemical code. The drastic decrease in Se(IV) sorption on goethite in a multi-phase system is attributed to competition with dissolved silica released by bentonite. As with Si the HA compete with Se for sorption sites on goethite.     

Assessing the potential for a ‘railway renaissance’ in Great Britain

British Rail was privatised by the Conservative government of 1992-1997. This privatisation was driven primarily by political ideology and there is little to suggest the policy was implemented as part of an integrated transport strategy designed to encourage modal shift from road to rail. Since privatisation, however, passenger numbers and freight shipments have risen in absolute and relative terms and the current Labour administration has stated that its transport strategy offers the potential for a ‘railway renaissance’. In this paper, we question whether, four years on from the publication of the new strategy, such a renaissance--that is, a 50% increase in passenger kilometres and an 80% increase in freight kilometres by 2010, along with a degree of modal shift to rail from car and lorry--can be achieved given recent developments both within the rail industry and in government transport policy.     

Contribution of a Dense Population of the Brittle Star <Emphasis Type="Italic">Acrocnida brachiata</Emphasis> (Montagu) to the Biogeochemical Fluxes of CO<Subscript>2</Subscript> in a Temperate Coastal Ecosystem

The production of organic matter and calcium carbonate by a dense population of the brittle star Acrocnida brachiata (Echinodermata) was calculated using demographic structure, population density, and relations between the size (disk diameter) and the ash-free dry weight (AFDW) or the calcimass. During a 2-year survey in the Bay of Seine (Eastern English Channel, France), organic production varied from 29 to 50 g_AFDW m⁻² year⁻¹ and CaCO₃ production from 69 to 104 g_CaCO3 m⁻² year⁻¹. Respiration was estimated between 1.7 and 2.0 mol_CO2 m⁻² year⁻¹. Using the molar ratio (ψ) of CO₂ released: CaCO₃ precipitated, this biogenic precipitation of calcium carbonate would result in an additional release between 0.5 and 0.7 mol_CO2 m⁻² year⁻¹ that represented 23% and 26% of total CO₂ fluxes (sum of calcification and respiration). The results of the present study suggest that calcification in temperate shallow environments should be considered as a significant source of CO₂ to seawater and thus a potential source of CO₂ to the atmosphere, emphasizing the important role of the biomineralization (estimated here) and dissolution (endoskeletons of dead individuals) in the carbon budget of temperate coastal ecosystems.     

Determination of the <Emphasis Type="Italic">PT</Emphasis> Conditions that Accompanied a Seismogenic Slip along a Deep Segment of the Marginal Suture of the Siberian Craton

This paper reports data on the structure of the central zone of the seismogenic fault in the originally deep segments of the fault zone. The isotopic analyses have made it possible to estimate the absolute age of the ancient coseismic faults at 673 ± 5 Ma, which is indicative of seismic activation of deep faults in the studied segment of the marginal suture of the Siberian Craton in the Neoproterozoic.     

Variability of the gas transfer velocity of CO<Subscript>2</Subscript> in a macrotidal estuary (the Scheldt)

We report a large set of 295 interfacial carbon dioxide (CO₂) flux measurements obtained in the Scheldt estuary in November 2002 and April 2003, using the floating chamber method. From concomitant measurements of the air-water CO₂ gradient, we computed the gas transfer velocity of CO₂. The gas transfer velocity is well correlated to wind speed and a simple linear regression function gives the most consistent fit to the data. Based on water current measurements, we estimated the contribution of water current induced turbulence to the gas transfer velocity, using the conceptual relationship of O'Connor and Dobbins (1958). This allowed us to construct an empirical relationship to compute the gas transfer velocity of CO₂ that accounts for the contribution of wind and water current. Based on this relationship, the spatial and temporal variability of the gas transfer velocity in the Scheldt estuary was investigated. Water currents contribute significantly to the gas transfer velocity, but the spatial and temporal variability (from daily to seasonal scales) is mainly related to wind speed variability.     

Stratigraphy and volcanology of the Türkbükü volcanics: products of a stratovolcano in the Bodrum Peninsula,SW Anatolia

The Middle‐Upper Miocene Bodrum magmatic complex of the Aegean region, southwestern Turkey, is mainly represented by intermediate stocks, lavas, pyroclastic and volcaniclastic deposits. Monzonitic stocks and connected porphyry intrusions and extrusions are the first products of the magmatism. These are followed by a volcanic succession consisting of andesitic‐latitic lavas, autobrecciated lavas, pyroclastic and volcaniclastic deposits. The final stage is represented by basaltic and basaltic andesitic flows and dykes intruded into previous units. The volcanic succession crops out in the northern part of the Bodrum peninsula. In the lower part of this succession are widespread pyroclastic deposits, composed of pyroclastic fall and flow units, alternating with epiclastic deposits. Grain size, volume and thickness of the pyroclastic deposits were mainly controlled by the type, magnitude and intensity of the eruption. Further up the section, there are two horizons of debris avalanche deposits forming the coarsest and thickest deposits of the volcaniclastic succession. The debris avalanche deposits indicate at least two different flank collapses coeval with the volcanism. The stratigraphy and map pattern of these volcanic units imply that the northern part of the Bodrum peninsula was the north‐facing flank of a stratovolcano during the mid‐Late Miocene. Copyright © 2006 John Wiley & Sons, Ltd.     

Modeling of the three‐dimensional subsidence diffusion–convection problem above a trapdoor

In a series of previous works, the plane strain and the axisymmetric cases of the so‐called active trapdoor problem have been modeled by virtue of Litwiniszyn's theory of deep subsidence. However, in reality, there exist trapdoor base geometries—in plan view—which can be very well approximated by an elliptical boundary. Following the elliptical shape of the trapdoor, the contour lines of subsidence also appear to be similar ellipses. In this work, an elliptic model of deep subsidence is presented, the mentioned hypothesis of the self‐similar subsidence contour lines is validated, and finally a simplified model is presented. For completeness of the present three‐dimensional model analysis, a rectangular model is also considered. Results are finally presented and compared with those of plane strain and axisymmetric problems. Some suggestions that have been proposed in previous similar works are also evaluated and compared with the results of the present study. Finally, some estimates are proposed for different trapdoor base geometries. Copyright © 2011 John Wiley & Sons, Ltd.     

Observation of line emission of the isotope <Superscript>22</Superscript>Na from a classical nova

Data on detections of gamma-ray line emission with COMPTEL experiment on board the Compton Gamma-Ray Observatory in 1991–2000 are discussed and used to analyze the properties of classical novae. This emission is radiated during the decay of the radioactive isotope ²²Na, which should be synthesized in thermonuclear explosions occurring on these novae.     

Benchmarking the thermomechanical behaviour of clays — a progress report — the CEC interclay project

In 1989 a small-scale exercise conducted by the CEC as part of its research programme into the underground storage of radioactive waste highlighted the difficulty of making accurate predictions a priori, of the geomechanical behaviour of clay. Given source data about the Boom clay from the underground research facility at Mol, three organisations independently performed f.e. analyses of two somewhat hypothetical problems. While the results were very broadly in agreement, they were shown to be sensitive to both the type of constitutive model used and the way data was fitted to the model.

Subsequently, the CEC sponsored a more comprehensive benchmark exercise called INTERCLAY II. This involves eleven organisations from various member states of the EC in a project encompassing the three aspects of software development for predictive modelling: verification, validation on the laboratory scale and the treatment of in-situ tests. The paper briefly describes the exercise currently in progress and presents the main results achieved to date concentrating on validation aspects.     

Pan-glacial—a third state in the climate system

Radiative energy-balance models reveal that Earth could exist in any one of three discrete climate states—'non-glacial' (no continental ice-sheets), 'glacial-interglacial' (high-latitude ice-sheets) or 'pan-glacial' (ice-sheets at all latitudes)—yet only the first two were represented in Phanerozoic time. There is mounting evidence that pan-glacial states existed at least twice in the Cryogenian (roughly 750–635 Ma), the penultimate period of the Neoproterozoic. Consensus is lacking on whether the world ocean was fully glaciated ('snowball' model) or largely unglaciated ('slushball' model). The first appearances of multicellular animal fossils (diapause eggs and embryos in China, and sponge-specific biomarkers in Oman), being closely associated with the last pan-glacial state, revive speculation that environmental forces had a hand in the origin of metazoa.     

The Lassee segment of the Vienna Basin fault system as a potential source of the earthquake of <Emphasis Type="Italic">Carnuntum</Emphasis> in the fourth century <Emphasis Type="SmallCaps">a.d.</Emphasis>

The Vienna Basin fault system is a slow moving (1–2 mm/y) active sinistral fault extending from the Alps through the Vienna Basin into the Carpathians. It comprises an array of NE-striking sinistral strike-slip segments, which differ both by their kinematic and seismologic properties. Among these, the Lassee segment 30 km east of Vienna is of particular interest for seismic hazard assessment as it shows a significant seismic slip deficit. The segment is located about 8 km from the Roman city of Carnuntum, for which archaeological data indicate a destructive earthquake in the fourth century a.d. (local intensity about 9 EMS-98). Mapping of the Lassee segment using 2D seismic, GPR, tectonic geomorphology and Pleistocene basin analysis shows a negative flower structure at a releasing bend of the Vienna Basin fault. The hanging wall of the flower structure includes a Quaternary basin filled with up to 100-m thick Pleistocene growth strata. Faults root in the basal detachment of the Alpine-Carpathian floor thrust at about 8 km depth. The active faults east of the flower structure offset a Middle Pleistocene terrace of the Danube River forming an up to 20-m high composite fault scarp. High-resolution GPR (40, 500 MHz) mapped at least four distinct surface-breaking faults along this scarp including three faults, which are covered by about 2 m of post-tectonic strata. The youngest fault offsets these strata and coincides with a 0.5-m high scarp. This scarp may be interpreted as the product of a single surface-breaking earthquake, provided that the mapped fault offset formed during coseismic surface rupture. Data indicate that the Lassee segment may well be regarded the source of the fourth century earthquake. The interpretation is in line with local attenuation relations indicating a source close to the damaged site, observed fault dimensions and the fault offsets recorded by GPR and morphology.     

Interaction of the stream from <Emphasis Type="Italic">L</Emphasis><Subscript>1</Subscript> with the outer edge of the accretion disk in a cataclysmic variable

Vertical oscillations of the gas at the outer edge of the accretion disk in a semi-detached binary due to interaction with the stream of matter from the inner Lagrangian point L ₁ are considered. Mixing of the matter from the stream from L ₁ with matter of the disk halo results in the formation of a system of two diverging shocks and a contact discontinuity, or so-called “hot line”. The passage of matter through the region of the hot line leads to an increase in its vertical velocity and a thickening of the disk at phases 0.7?0.8. Subsequently, the matter moving along the outer edge of the disk also experiences vertical oscillations, forming secondary maxima at phases 0.2?0.4. It is shown that, for systems with component mass ratios of 0.6, these oscillations will be amplified with each passage of the matter through the hotline zone, while the observations will be quenched in systems with component mass ratios ~0.07 and ~7. The most favorable conditions for the flow of matter from the stream through the edge of the disk arise for component mass ratios ~0.62. A theoretical relation between the phases of disk thickenings and the component mass ratio of the system is derived.     

On the determination of a set of material constants for a high‐cycle accumulation model for non‐cohesive soils

The paper discusses the determination of a set of constants for the high‐cycle accumulation model (HCA) proposed by the authors. The HCA model predicts permanent strains or excess pore water pressures in non‐cohesive soils due to a cyclic loading with a large number of cycles and with small to intermediate strain amplitudes. The laboratory tests necessary for the determination of the material constants and their analysis are explained in detail in this paper. Copyright © 2009 John Wiley & Sons, Ltd.     

Self‐similar solution of a plane‐strain fracture driven by a power‐law fluid

This paper analyses the problem of a hydraulically driven fracture, propagating in an impermeable, linear elastic medium. The fracture is driven by injection of an incompressible, viscous fluid with power‐law rheology and behaviour index n?0. The opening of the fracture and the internal fluid pressure are related through the elastic singular integral equation, and the flow of fluid inside the crack is modelled using the lubrication theory. Under the additional assumptions of negligible toughness and no lag between the fluid front and the crack tip, the problem is reduced to self‐similar form. A solution that describes the crack length evolution, the fracture opening, the net fluid pressure and the fluid flow rate inside the crack is presented. This self‐similar solution is obtained by expanding the fracture opening in a series of Gegenbauer polynomials, with the series coefficients calculated using a numerical minimization procedure. The influence of the fluid index n in the crack propagation is also analysed. Copyright © 2002 John Wiley & Sons, Ltd.     

Vibration of a rigid footing—a finite model for the elastic half space

A problem common to most numerical methods of analysing the vibration of a rigid body on an elastic half space is indentified especially as regards the arbitrary truncation of the semi-infinite half space or the numerically expensive computations involved in some of the methods. This paper presents a boundary integral equation (BIE) method of defining a finite domain to replace the half space and consists of evaluating the BIE over the domain. A mathematical justification is provided for defining the domain, and the error involved in such truncation of the half space in shown to be small. Yet the computations are very cheap owing to the simple trigonometric/algebraic functions involved in the BIE. The accuracy of the method is quite commendable especially as seen from the results presented for the circular foundation for which analytical and experimental solutions are available for comparison.