Laser ablation-laser induced breakdown spectroscopy for the measurement of total elemental concentration in soils.

The performances of traditional laser-induced breakdown spectroscopy (LIBS) and laser ablation-LIBS (LA-LIBS) were compared by quantifying the total elemental concentration of potassium in highly heterogeneous solid samples, namely soils. Calibration curves for a set of fifteen samples with a wide range of potassium concentrations were generated. The LA-LIBS approach produced a superior linear response different than the traditional LIBS scheme. The analytical response of LA-LIBS was tested with a large set of different soil samples for the quantification of the total concentration of Fe, Mn, Mg, Ca, Na, and K. Results showed an acceptable linear response for Ca, Fe, Mg, and K while poor signal responses were found for Na and Mn. Signs of remaining matrix effects for the LA-LIBS approach in the case of soil analysis were found and discussed. Finally, some improvements and possibilities for future studies toward quantitative soil analysis with the LA-LIBS technique are suggested.

Nature of inclined growth in thin-layer electrodeposition under uniform magnetic fields.

Electrochemical deposition (ECD) in thin cells in a vertical position relative to gravity, subject to an external uniform magnetic field, yields a growth pattern formation with dense branched morphology with branches tilted in the direction of the magnetic force. We study the nature of the inclined growth through experiments and theory. Experiments in ECD, in the absence of magnetic forces, reveal that a branch grows by allowing fluid to penetrate its tip and to be ejected from the sides through a pair of symmetric vortices attached to the tip. The upper vortices zone defines an arch separating an inner zone ion depleted and an outer zone in a funnel-like form with a concentrated solution through which metal ions are carried into the tip. When a magnetic field is turned on, vortex symmetry is broken, one vortex becoming weaker than the other, inducing an inclination of the funnel. Consequently, particles entering the funnel give rise to branch growth tilted in the same direction. Theory predicts, in the absence of a magnetic force, funnel symmetry induced through symmetric vortices driven by electric and gravitational forces; when the magnetic force is on, it is composed with the pair of clockwise and counterclockwise vortices, reducing or amplifying one or the other. In turn, funnel tilting modifies particle trajectories, thus, growth orientation.

Comportamiento de los clips metálicos intracraneales en Resonancia Magnética (Estudio Experimental I) / Experimental study of the movement of metalic clips in magnetic fields

La Resonancia Magnética (RM) es actualmente una de las modalida, modalidades diagnósticas más importantes en la patología vascular cerebral. Existen ciertas contraindicaciones para su realización, tales como implantes metálicos cocleares, presencia de neuroestimuladores y clips metálicos intracraneales. En la actualidad, para evitar este inconveniente, los clips son elebados con material no ferromagnético y constan de diversas aleaciones. Se estudiaron 20 lips para aneurisma en un equipo de Resonancia Magnética de 1.5 Tesla, para valorar la presencia de movimiento y la fuerza de desplazamiento de los clips, observando que el 95 por ciento de los clips presentaron cierto grado de movimiento, por lo que sugerimos que ningún clip sea implantado antes de que se analicen sus propiedades, si el paciente no conoce el tipo de clip que le ha sido implantado no deberá ser sometido a estudios de Resonancia Magnética a menos de que el beneficio que se pueda obtener sea realmente mayor a las complicaciones que pudiesen surgir