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

A Statistical Perspective for Predicting the Strength of Metals: Revisiting the Hall-Petch Relationship using Machine Learning

The mechanical properties of a material are intimately related to its microstructure. This is particularly important for predicting mechanical behavior of polycrystalline metals, where microstructural variations dictate the expected material strength. Until now, the lack of microstructural variability in available datasets precluded the development of robust physics-based theoretical models that account for randomness of microstructures. To address this, we have developed a probabilistic machine learning framework to predict the flow stress as a function of variations in the microstructural features. In this framework, we first generated an extensive database of flow stress for a set of over a million randomly sampled microstructural features, and then applied a combination of mixture models and neural networks on the generated database to quantify the flow stress distribution and the relative importance of microstructural features. The results show excellent agreement with experiments and demonstrate that across a wide range of grain size, the conventional Hall-Petch relationship is statistically valid for correlating the strength to the average grain size and its comparative importance versus other microstructural features. This work demonstrates the power of the machine-learning based probabilistic approach for predicting polycrystalline strength, directly accounting for microstructural variations, resulting in a tool to guide the design of polycrystalline metallic materials with superior strength, and a method for overcoming sparse data limitations.Comment: The dataset generated and the demo codes used in this paper are available on Zenodo (https://doi.org/10.5281/zenodo.7762663

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