A form-factor method for determing the structure of distorted stars

The equilibrium equations of a uniformly rotating and tidally distorted star are reduced to the same form as for a spherical star except for the inclusion of two form factors. One factor, expressing the buoyancy effects of centrifugal force, is determined directly from the integrated structure variables. The other factor, expressing the deviation from spherical shape, is shown to be relatively insensitive to errors in the assumed shape, so that accurate solutions are obtained in spite of the use of ana priori shape. The method is employed by adding computations for the factors to an existing spherical model program. Upper Main Sequence models determined by this method compare closely with results from the double approximation method even for critical rotation and tidal distortion.     

Single-layer folding in marble and limestone: An experimental study

Folding experiments have been carried out on single-layers of Carrara marble and Solnhofen limestone at a confining pressure of 275 bars, temperature of 400°C, and strain rates of 5.5×10⁻⁷ to 8.2×10⁻⁷. The marble and limestone layers were embedded in a rock-salt matrix and in a matrix of a mixture of 60% fine-grained halite and 40% fine-grained calcite, respectively, and deformed to different percentages of bulk shortening. Aspect ratios of the layers varied between 11.25 and 15. The stress-strain relationship reveals that strain increased with a very small increment in compressive stresses, once folding was initiated.With progressive deformation the bulk strain is compensated by folding along one fold hinge. The resulting folds are concentric and a combination of class 1a, 1b and 3 type. The changes in the arc length, layer thickness, limb dip and wavelength with progressive folding in marble layers, are discussed.The microstructure and texture of the folded marble and limestone layers have been investigated optically and by means of an X-ray texture goniometer. The inner fold arc exhibits a strong preferred orientation, whereas in the outer fold are the preferred orientation is poorly developed. Differences in the fabric in medium-grained marble and fine-grained limestone layers have been attributed to the difference in mechanism of deformation.     

Plant growth and productivity along complex gradients in a Pacific northwest brackish intertidal marsh

Environmental characteristics were measured and recorded in the Skagit Marsh, a brackish intertidal marsh on Puget Sound, Washington. Four transects were placed perpendicular to a known gradient of increasing salinity which began with fresh water at the bank of one of the outlets of the Skagit River and reached a surface water salinity of 22‰ at a point alongshore 5 km north of the outlet. The environmental characteristics which were measured varied along gradients (soil texture, organic carbon in fines, soil column temperature, free soil water salinity) or had a patchy distribution (soil redox potential, soil macro-organic matter). Growth and production vary across the marsh. The maximum aboveground standing crop (1,742 g m^?2 dry weight) was measured at a site with 0–4‰ free soil water salinity, dominated by the sedgeCarex lyngbyei. In more saline areas (8–12‰), the bulrushScirpus americanus was dominant and standing crop values dropped to a third of the maximum. Species performance varied in a complex manner as did the environment.C. lyngbyei had diminished growth and decreased standing crop in areas where salinity was higher.S. americanus was equally productive in low elevation, high salinity sites and in high elevation, low salinity sites. An increase in shoot density for dominant species occurred in saline areas as individual shoot weights and leaf areas decreased. Because species responded differently, environmental variation was magnified in the population and community responses of the marsh vegetation.     

Deformation und Gefügeregelung von Steinsalz im Temperaturbereich 20–200° c

Cubic specimens of fine-grained artifical polycristalline rock salt were deformed at different principal stresses in the range of 20–200° C. The data from different types of tests are compared by plotting ₁–₃ against ₁, ₂, ₃. The deformation behavior is highly influenced by the intermediate principal stress ₂. An increase of the intermediate stress from compression (₁>₂=₃) to extension (₁=₂>₃) lowers the rate of deformation. An increase of temperature always gives rise to an increase of deformation rate.Translation gliding on (110) is assumed to be the dominant flow mechanism. Textural changes and development of preferred orientation were investigated by means of the X-ray diffractometer. Intensities were measured for (110), (111), and (100). Compression leads to girdle occupations about the unique principle compressive axis, extension to girdles about the unique principle axis of extension. When all principle stresses are different the polfigures tend to a position intermediate between the two occupations.     

Why a corrugated coast only influences a longshore current within a wave length of the coast

An inviscid zone of influence is postulated from a physical model to occur when a steady homogeneous fluid flows by a two-dimensional corrugated wall with small slopes. The thickness of the influence zone is calculated to be a constant times the wave length of the wall. The method used involves balancing pressure differences between extreme points along the wall and between the wall and the outer edge of the influence zone but does not involve the irrotational assumption. An influence zone forms because the curvature of the boundary induces cross-stream accelerations and pressure gradients in the fluid. The result for the thickness of the influence zone agrees qualitatively with the exponential decay scale of an available potential flow solution to a similar problem, which suggests that the influence zone may occur in some rotational (as well as irrotational) flows.     

Large-Scale Avalanche Braking Mound and Catching Dam Experiments with Snow: A Study of the Airborne Jet

We report a series of ongoing large-scale experiments to studythe interaction of a snow avalanche with a dam and a row of mounds which are of a comparable height to the flow depth.The experimental results indicate that the behaviour of thesupercritical flow around the obstacles is governed by the large-scale properties of the flowing avalanche rather than micro-scaleproperties of the granular current.The experiments show that, similarly to smaller-scale experimentswith glass particles, the avalanche detaches from the top of the dam or mound and forms a coherentairborne jet, which can be modelled as a two dimensional ballistic projectile with negligible air resistance.We study the two parameters that define the trajectory of thejet, namely the speed at which the jet is launched from the top of the obstacle and the deflection of the jet by the obstacle, and compare the resultswith a theory for the deflection of a jet of an ideal fluid.     

Effect of high-low quartz transition on compressional and shear wave velocities in rocks under high pressure

The compressional and shear wave velocities in quarzite, granite, and granulite are determined at a fixed confining pressure of 2 kb as a function of temperature up to 720° C. The high-low quartz transition of the constituent quartz minerals is associated with a pronounced decrease in velocity of the compressional waves when approaching the transition and with a significant velocity increase after the transition. In contrast, the effect of the α-β transition on shear wave velocities is small. The drop of V _P is explained by the elastic softening of structure of the constituent quartz minerals near the α-β transition and the opening of grain-boundary cracks, caused by the very high volumetric thermal expansion of the quartz relative to the other component minerals. The velocity increase in the β-field may be attributed to an elastic hardening of the quartz structure. Poisson ratios computed from the velocity data are anomalous for a solid: they become negative within the transition regime. The transition temperature, as indicated by the minimum velocities, is higher in the polycristalline rocks than is expected on grounds of single crystal behavior, and the discrepancy is more marked in granite than in quartzite. The shift of the transition temperature to higher values is explained by internal stresses that arise from the anisotropy of the thermal expansion and compressibility of individual grains and the differences in thermal expansion and compressibility between different component minerals. The role of the α-β quartz transition as a possible cause of low-velocity layers is discussed.     

The COUPLEX Test Cases: Nuclear Waste Disposal Simulation

The models appearing in the COUPLEX benchmark are a set of simplified albeit realistic test cases aimed at simulating the transport of radionuclides around a nuclear waste repository. Three different models were used. The first test case is related to simulations based on a simplified 2D far-field model close to those used for safety assessments in nuclear waste management. It leads to a classical convection diffusion type problem, but with highly variable parameters in space, highly concentrated sources in space and time, very different time scales and accurate results expected even after millions of years. The second test case is a simplification of a typical 3D near-field computation, taking into account the glass dissolution of vitrified waste, and the congruent release of several radionuclides (including daughter products), with their migration through the geological barrier. The aim of the third test case is to use the results of the near-field computation (COUPLEX 2) to drive the behavior of the nuclide source term in the far-field computation (COUPLEX 1). The modeling of this last case was purposely left rather open, unlike the previous two, leaving the choice to participants of the way the coupling should be made.