High Anisotropy Ratio Research Articles

Simulation of Pollutant Transport Using a Particle Method

A Lagrangian scheme is presented for the two-dimensional simulation of pollutant transport in a porous medium. The anisotropic extension of the particle strength exchange method is implemented to describe the diffusive–dispersive process. By applying the scheme to a benchmark problem with an analytical solution, the method is shown to be accurate and stable even in the limiting cases of vanishing diffusion–dispersion coefficients and high anisotropy ratios. The scheme is shown to perform well with spatially variable velocity fields also.

Numerical simulations of topography-induced saltwater upconing in the state of Brandenburg, Germany

Saltwater intrusion from saline formation waters in the shallow lowlands of the state of Brandenburg, Germany, is simulated using a 2D density-dependent (dd) flow and transport model. Based on the geological situation and the present-day chemical composition of the groundwaters in that region, migration scenarios with and without inclusion of density effects are modelled. We find that, due to the shallowness of the aquifer system, the surficial topography has a large effect on the flow and migration patterns and, especially, gives rises to upwelling flow underneath the discharge area of the Nuthe river. Comparing models, with and without density effects included, we then investigate possible saltwater upconing due this natural discharge flow pattern. A sensitivity study of the hydrodynamic dispersion and of the anisotropy of the aquifer is at the heart of the investigation. The results of the models show that density effects are diminishing for large values of the dispersivity and high anisotropy ratios. This means that for the management of saltwater intrusion, instead of using a complicated dd flow and transport model, it may be sufficient in most practical situation to use a passive transport model, which would have a much smaller computational time.

Properties of a large La 1.92Sr 0.08CuO 4+ δ single crystal grown by the travelling-solvent floating-zone method

A centimeter size single crystal of La 2− x Sr x CuO 4+ δ (volume=1.32 cm 3) with x Sr=0.08 has been grown by the travelling-solvent floating-zone (TSFZ) method using a double ellipsoidal-type optical furnace as the heat source. The crystallised phase was checked solvent free by X-ray powder diffraction experiments, the crystal dimensions and quality being investigated by X-ray and neutron Laüe techniques. Several rocking curves of the Bragg peaks were performed by neutron diffraction giving a full width at half maximum (FWHM) of 0.200° for (006) reflection and clearly showing the presence of twin domains as expected for such an orthorhombic structure. The superconducting critical temperature of the as-grown crystal under 2 oxygen bar was determined by SQUID measurements with T c=18–20 K. Thermal treatments at different oxygen pressures were carried out showing no significant improvement of the transition sharpness and the T c value. Normal state susceptibility was also measured from 6 to 800 K for two different field orientations and can be interpreted as an antiferromagnetic insulating state behaviour. The resistivity measurements display an insulating behaviour perpendicular to the CuO 2 planes and a metallic behaviour in the planes, with a high anisotropy ratio R c / R b ∼350 at room temperature and a zero resistivity achieved at 27 K in both directions. The specific heat measurements have revealed no anomalies in the temperature range 15–300 K.

Détermination des propriétés élastiques d'éléments individuels du plan ligneux du chêne par des essais de traction sur micro-éprouvettes

Determination of the elastic properties using tensile tests on micro-samples for different anatomical elements for oak. This work proposes elastic values measured in the cross section of wood for different anatomical elements of oak. The experi- mental device, conceived and developed in our laboratory, allows the Young's modulus and Poisson's ratio to be determined on very small samples. In this work, four components of the anatomical pattern have been differentiated. The corresponding micro samples have been prepared by careful polishing, which is difficult at best. Finally, we are able to propose values for ray cells, longitudinal parenchyma cells, initial ring porous zone and fibres. The ray cells depict the highest rigidity in the transverse plane. On the contrary, the ring porous zone is the weakest, with a value almost ten times less important. Fibres and longitudinal parenchyma cells exhibit average values. The later only seem to present a high anisotropy ratio (E a 2). (© Inra/Elsevier, Paris.)

Magnetoresistance effect of Ni-Co alloy films

Ni-Co alloy is worth notice as a material for fabricating a magnetoresistance element, because of the highest magnetoresistance anisotropy (Δρ/ρ0) in the ferromagnetic alloys. We studied the magnetoresistance anisotropy and the crystal structure on the films of the Ni-Co alloy system (40 Ni–60Co∼81Ni–19Co). In this study we found the following facts: (1) A new ordered phase exists in the films around at the composition 50Ni–50Co prepared at a substrate temperature above about 550 °K. (2) This ordered phase is accompanied with a newly proposed superstructure. (3) A close relation exists between the magnetoresistance anisotropy and the degree of order, and the films in the ordered state have a higher anisotropy ratio (Δρ/ρ0) than the bulk value. This fact is important in the practical application, such as a magnetic field sensor.