791 research outputs found
Measurement of streaming potential coupling coefficient in sandstones saturated with natural and artificial brines at high selenity
We report experimental measurements of the streaming potential coupling coefficient in sandstones saturated with NaCl-dominated artificial and natural brines up to 5.5 M (321.4 g L−1 of NaCl; electrical conductivity of 23 S m−1). We find that the magnitude of the coupling coefficient decreases with increasing brine salinity, as observed in previous experimental studies and predicted by models of the electrical double layer. However, the magnitude of the coupling coefficient remains greater than zero up to the saturated brine salinity. The magnitude of the zeta potential we interpret from our measurements also decreases with increasing brine salinity in the low-salinity domain (0.4 M). We hypothesize that the constant value of zeta potential observed at high salinity reflects the maximum packing of counterions in the diffuse part of the electrical double layer. Our hypothesis predicts that the zeta potential becomes independent of brine salinity when the diffuse layer thickness is similar to the diameter of the hydrated counterion. This prediction is confirmed by our experimental data and also by published measurements on alumina in KCl brine. At high salinity (>0.4 M), values of the streaming potential coupling coefficient and the corresponding zeta potential are the same within experimental error regardless of sample mineralogy and texture and the composition of the brine
Single magnetic molecule between conducting leads: Effect of mechanical rotations
We study spin-rotation effects in a magnetic molecule bridged between two
conducting leads. Dynamics of the total angular momentum couples spin tunneling
to the mechanical rotations. Landau-Zener spin transition produced by the
time-dependent magnetic field generates a unique pattern of mechanical
oscillations that can be detected by measuring the electronic tunneling current
through the molecule.Comment: 5 pages, 2 figure
Dynamics of Einstein - de Haas Effect: Application to Magnetic Cantilever
Local time-dependent theory of Einstein - de Haas effect is developed. We
begin with microscopicinteractions and derive dynamical equations that couple
elastic deformations with internal twists due to spins. The theory is applied
to the description of the motion of a magnetic cantilever caused by the
oscillation of the domain wall. Theoretical results are compared with a recent
experiment on Einstein - de Haas effect in a microcantilever.Comment: 7 PR pages, 5 figures, submitted to PR
Influence of torsion on the inelastic response of three-dimensional r.c. frames
A three-dimensional reinforced concrete framed building was modelled using finite element method. Two types of elements, the beam-column element and flat shell element were used for modelling the frame and floor slabs, respectively. A computer program has been developed for the analysis of 3D framed building by integrating the finite element and stiffness method. The lumped inelasticity model with three-dimensional point hinges at the ends of the beam-column element was implemented. A yield surface for a reinforced section of the member subjected to simultaneous actions of biaxial bending, torsion and axial forces was evolved. The developed yield surface integrated with the theory of plasticity was used to develop a suitable procedure for inelastic analysis of three-dimensional problems with the floor slab assumed to remain elastic throughout the analysis. The inelastic procedure is able to predict the sequential formation of plastic hinges in the frame members and the continuous deterioration of the stiffness of the frame. A single storey one bay reinforced concrete space frame was analysed for twist loading to study the inelastic response of the reinforced concrete frame. The results indicate that, the consideration of torsion in defining the yielding surface plays a significant role in the inelastic behaviour and estimation of failure load for reinforced concrete frames under torsional loading
Grande tache pigmentée pileuse révélant une forme familiale de la maladie de Von Recklinghausen
La neurofibromatose de type 1 (NF1) ou maladie de Von Recklinghausen appartient au groupe de maladies appelées phacomatoses. C'est une affection autosomique dominante relativement rare. La NF1 est caractérisée par une extrême variabilité clinique que l'on retrouve également au sein d'une même famille. Le tableau clinique de la NF1 associe, le plus souvent, de multiples taches café au lait, des lentigines axillaires ou inguinales, des neurofibromes cutanés et des nodules de Lisch. Les difficultés d'apprentissage sont fréquentes et peuvent être graves dans certaines formes cliniques. Il est important de détecter précocement les neurofibromes plexiformes, les gliomes intracérébraux, les tumeurs des gaines nerveuses, les anomalies vasculaires et les dysplasies osseuses. L'évolution est imprévisible ce qui rend le pronostic incertain par une éventuelle survenue dedégénérescence malignes. Nous rapportons ici l'observation d'une grande tache cutanée pigmentée pilleuse de découverte fortuite qui nous a révélé deux cas familiaux de neurofibromatose 1 d'expression différente
Tailoring the magnetic properties of Fe asymmetric nanodots
Asymmetric dots as a function of their geometry have been investigated using
three-dimensional (3D) object oriented micromagnetic framework (OOMMF) code.
The effect of shape asymmetry of the disk on coercivity and remanence is
studied. Angular dependence of the remanence and coercivity is also addressed.
Asymmetric dots are found to reverse their magnetization by nucleation and
propagation of a vortex, when the field is applied parallel to the direction of
asymmetry. However, complex reversal modes appear when the angle at which the
external field is applied is varied, leading to a non monotonic behavior of the
coercivity and remanence.Comment: 5 pages, 7 figure
Strength Estimation of Concrete in Different Environments Using UPV
Deterioration of concrete in a structure is a result of several internal and external degradation mechanisms which decrease the strength or the integrity of the structure. This paper presents results of use of non-destructive ultrasonic pulse velocity tests (UPV) to determine the strength of concrete in three different environments, namely oven-dry, air-dry and saturated conditions, as
the full potential of UPV in different environments is still not fully explored. Moisture is known to have a significant effect on ultrasonic pulse velocity. In
order to improve the efficiency of UPV in estimating the concrete strength, the
degree of moisture present in the concrete i.e. the physical condition of the
concrete is to be considered. Pulse velocity path in the different physical conditions of concrete also has to be examined. In the present investigations, four different grades of concrete in three different environments were
considered. Extensive series of tests were carried out in the laboratory to obtain
a correlation of the UPV test results with the actual compressive strength of
concrete. A total of 108 cubes were cast. The cement used was the ordinary Portland cement and the coarse aggregate consisted of granite with the
maximum aggregate size of 19mm as is generally used in conventional RC
structures. The DOE-method of mix-design was used to design four different
grades of concrete in order to simulate concrete strengths found in practice.
Test results indicated that the presence of moisture in concrete changes the
UPV values significantly. The UPV tests through the direct transmission
measurements display better estimates compared to the indirect measurements.
Exponential expressions have been proposed for the strength estimation of
concrete under oven dry and air dry conditions
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