Diffusion mechanisms for spinel ferrite NiFe2O4 by using kinetic activation-relaxation technique.

Mass transport in bulk spinel ferrites NiFe2O4 is studied computationally using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo algorithm. Diffusion mechanisms-difficult to observe with molecular dynamics-are described by k-ART. Point defects are assumed to be responsible for ionic diffusion; thus, both cation and anion defects are investigated. This work focuses on vacancies and interstitials by comparing their properties with two Buckingham potential parameterizations: one with nominal charges and the other with partial charges. Both potentials are corrected at short distances, thus allowing interstitial diffusion and avoiding the catastrophic infinite energies appearing with Buckingham at short distances. The energy landscape along different pathways is described in detail. Both potentials predict the same mechanisms but different migration energies. Mechanisms by which a normal spinel is transformed to an inverse spinel via cation diffusion are unveiled, and diffusion coefficients are predicted. We find that interstitial Ni diffusion involves the movement of two Ni ions and that O interstitials trigger a collective diffusion of O ions, while an O vacancy diffuses by an O ion moving to the center of a cuboctahedron.

Computer simulations of cluster impacts: effects of the atomic masses of the projectile and target.

Cluster secondary ion mass spectrometry is now widely used for the characterization of nanostructures. In order to gain a better understanding of the physics of keV cluster bombardment of surfaces and nanoparticles (NPs), the effects of the atomic masses of the projectile and of the target on the energy deposition and induced sputtering have been studied by means of molecular dynamics simulations. 10 keV C60 was used as a model projectile and impacts on both a flat polymer surface and a metal NP were analyzed. In the first case, the mass of the impinging carbon atoms was artificially varied and, in the second case, the mass of the NP atoms was varied. The results can be rationalized on the basis of the different atomic mass ratios of the projectile and target. In general, the emission is at its maximum, when the projectile and target have the same atomic masses. In the case of the supported NP, the emission of the underlying organic material increases as the atomic mass of the NP decreases. However, it is always less than that calculated for the bare organic surface, irrespective of the mass ratio. The results obtained with C60 impacts on the flat polymer are also compared to simulations of C60 and monoatomic Ga impacts on the NP.

[Neuropsychological study in patients with Parkinson's disease: the effects of deep brain stimulation]. / Estudio neuropsicológico en pacientes parkinsonianos: efectos de la estimulación cerebral profunda.

INTRODUCTION: Parkinson's disease (PD) is a disorder whose clinical manifestations are observed in the motor and neuropsychological domain and have an impact on the patient's quality of life. Several scientific studies evidence the effectiveness of deep brain stimulation as treatment for the motor symptoms, but further research is required on the neuropsychological symptoms. AIM: To analyse the existence of significant differences in neuropsychological processes, such as attention, memory, language, visuoperception and the executive functions in patients with PD prior to and following deep brain stimulation. PATIENTS AND METHODS: Our sample consisted of 20 patients of both sexes, aged 50-70 years, with PD, who were treated by healthcare service providers in Medellin. These subjects were administered the Continuous Performance Test and the Trail Making Test in order to assess attention, the Rey Complex Figure and Ardila memory tests to evaluate memory, the Boston and verbal fluency tests to assess language, the Rey Complex Figure Copy test for visuoperception, and the Wisconsin Card Sorting Test to appraise the executive functions. RESULTS: There are significant differences between the scores before and after deep brain stimulation in patients with PD on attention and memory. CONCLUSIONS: Knowledge of these findings is relevant for the neuropsychological therapy of patients with PD.

TITLE: Estudio neuropsicologico en pacientes parkinsonianos: efectos de la estimulacion cerebral profunda.Introduccion. La enfermedad de Parkinson (EP) es un trastorno cuyas manifestaciones clinicas se observan en el ambito motor y neuropsicologico e influyen en la calidad de vida del paciente. Diversos estudios cientificos muestran la eficacia de la estimulacion cerebral profunda como tratamiento sobre los sintomas motores, pero faltan estudios sobre los sintomas neuropsicologicos. Objetivo. Analizar la existencia de diferencias significativas en procesos neuropsicologicos, como la atencion, la memoria, el lenguaje, la visuopercepcion y la funcion ejecutiva en los pacientes con EP antes y despues de la estimulacion cerebral profunda. Pacientes y metodos. La muestra estuvo formada por 20 pacientes parkinsonianos de 50-70 años de ambos sexos, pertenecientes a entidades prestadoras de servicios de salud de Medellin, a los que se les administraron el Continuous Performance Test y el Trail Making Test para valorar la atencion, la figura compleja de Rey y la prueba de memoria de Ardila para evaluar la memoria, el test de Boston y fluidez verbal para valorar el lenguaje, la figura compleja de Rey copia para la visuopercepcion, y el test de clasificacion de cartas de Wisconsin para valorar la funcion ejecutiva. Resultados. Existen diferencias significativas entre las puntuaciones antes y despues de la estimulacion cerebral profunda en los pacientes con EP en la atencion y la memoria. Conclusiones. El conocimiento de estos hallazgos es relevante para la terapia neuropsicologica de los pacientes con EP.