In situ TEM observation of the Boudouard reaction: multi-layered graphene formation from CO on cobalt nanoparticles at atmospheric pressure.

Using a MEMS nanoreactor in combination with a specially designed in situ Transmission Electron Microscope (TEM) holder and gas supply system, we imaged the formation of multiple layers of graphene encapsulating a cobalt nanoparticle, at 1 bar CO : N2 (1 : 1) and 500 °C. The cobalt nanoparticle was imaged live in a TEM during the Boudouard reaction. The in situ/operando TEM studies give insight into the behaviour of the catalyst at the nanometer-scale, under industrially relevant conditions. When switching from Fischer-Tropsch syngas conditions (CO : H2 : N2 1 : 2 : 3 at 1 bar) to CO-rich conditions (CO : N2 1 : 1 at 1 bar), we observed the formation of multi-layered graphene on Co nanoparticles at 500 °C. Due to the high temperature, the surface of the Co nanoparticles facilitated the Boudouard reaction, causing CO dissociation and the formation of layers of graphene. After the formation of the first patches of graphene at the surface of the nanoparticle, more and more layers grew over the course of about 40 minutes. In its final state, around 10 layers of carbon capped the nanoparticle. During this process, the carbon shell caused mechanical stress in the nanoparticle, inducing permanent deformation.

In situ observation of self-assembled hydrocarbon Fischer-Tropsch products on a cobalt catalyst.

Fischer-Tropsch synthesis is a heterogeneous catalytic reaction that creates approximately 2% of the world's fuel. It involves the synthesis of linear hydrocarbon molecules from a gaseous mixture of carbon monoxide and hydrogen at high pressures (from a few to tens of bars) and high temperatures (200-350 °C). To gain further insight into the fundamental mechanisms of this industrial process, we have used a purpose-built scanning tunnelling microscope to monitor a cobalt model catalyst under reaction conditions. We show that, after 30 minutes of reaction, the terraces of the cobalt catalyst are covered by parallel arrays of stripes. We propose that the stripes are formed by the self-assembly of linear hydrocarbon product molecules. Surprisingly, the width of the stripes corresponds to molecules that are 14 or 15 carbon atoms long. We introduce a simple model that explains the accumulation of such long molecules by describing their monomer-by-monomer synthesis and explicitly accounting for their thermal desorption.

Effect of silver on the phase transition and wettability of titanium oxide films.

The effect of silver on the phase transition and microstructure of titanium oxide films grown by pulsed cathodic arc had been investigated by XRD, SEM and Raman spectroscopy. Following successive thermal annealing up to 1000 °C, microstructural analysis of annealed Ag-TiO2 films reveals that the incorporation of Ag nanoparticles strongly affects the transition temperature from the initial metastable amorphous phase to anatase and stable rutile phase. An increase of silver content into TiO2 matrix inhibits the amorphous to anatase phase transition, raising its temperature boundary and, simultaneously reduces the transition temperature to promote rutile structure at lower value of 600 °C. The results are interpreted in terms of the steric effects produced by agglomeration of Ag atoms into larger clusters following annealing which hinders diffusion of Ti and O ions for anatase formation and constrains the volume available for the anatase lattice, thus disrupting its structure to form rutile phase. The effect of silver on the optical and wetting properties of TiO2 was evaluated to demonstrate its improved photocatalytic performance.

Shape and Size of Cobalt Nanoislands Formed Spontaneously on Cobalt Terraces during Fischer-Tropsch Synthesis.

Cobalt-based catalysts undergo a massive and spontaneous reconstruction to form uniform triangular nanoislands under Fischer-Tropsch (FT) conditions. This reconstruction is driven by the unusual and synergistic adsorption of square-planar carbon and CO at the 4-fold edge sites of the nanoislands, driving the formation of triangular islands. The size of the nanoislands is determined by the balance between energy gain from creating C/CO-covered edges and energy penalty to create C/CO-covered corners. For carbon chemical potentials corresponding to FT conditions, triangular Co islands with 45 Co atoms (about 2 nm) are the most stable surface structure. Decreasing the carbon chemical potential and hence the stability of square-planar carbon favors the formation of larger islands, until reconstruction becomes unfavorable and CO-covered terraces are thermodynamically the most stable. The predicted structure of the islands is consistent with in situ scanning tunneling microscopy images obtained for the first time under realistic FT reaction conditions on a Co(0001) surface.

Experiencia del examen estatal en la carrera de Estomatología / Experience goined with the application of the state exam in stomatology

Se exponen los resultados alcanzados en la primera experiencia realizada con la aplicación del examen en la carrera de Estomatología, en el curso académico 1995-1996, con el nuevo plan de estudios (plan C) para formar estomatológos generales básicos. En los objetivos, propósitos y directrices de la salud pública cubana, orientados a elevar los niveles de salud de la población, se exigen una serie de decisiones y medidas entre las que se destacan por su importancia, la formación de profesionales de perfil amplio, con una sólida base teórico-práctica, cuyos modos de actuación profesional le permitan resolver con éxito los problemas de salud fundamentales en la atención primaria. En cursos académicos anteriores (plan B) se realizaba un examen final de la asignatura Estomatología Integral que, conjuntamente con la evaluación de las rotaciones de investigación y las especialidades, conforman la nota final del estudiante; paralelo a la puesta en marcha del plan de estudio C surge la necesidad de buscar un nuevo enfoque de integralidad, y se pone en vigor el examen estatal como forma de culminación de los estudios en esta carrera, sobre la base de la evaluación de la competencia y desempeño profesional frente a un problema de salud bucal, que afecta la individuo y a la colectividad. Estos resultados de forma general fueron satisfactorios

La formación de personal de enfermería y técnicos de la salud / Training of nursing staff and health technicians

En el presente artículo se hace una breve reseña histórica sobre la formación de técnicos de la salud en Cuba y se analizan los profundos cambios producidos en la estructura socioeconómica del país a partir del triunfo de la revolución, junto con las transformaciones esenciales que estos han provocado en el campo de la salud. Se expone la constante atención que se ha prestado al perfeccionamiento de los planes y programas de estudio de enfermeros y técnicos de la salud- reflejada en modificaciones de contenidos y de tiempo de formación- y se describen los modelos educativos, seleccionándose la especialidad de enfermería como un ejemplo del total de carreras técnicas de la salud existentes en el país. También se describen brevemente la formación básica y universitaria del personal de emfermería y sus modelos educativos. Al final se hace una proyección y se trazan alternativas de acción para la formación y el perfeccionamiento de los recursos humanos en especialidades técnicas de la salud a partir de la nueva estrategia de educación permanente trazada para el país. Esta estrategia permite una perspectiva amplia de trabajo y contribuye a la acción transformadora en los servicios

Algunas reflexiones de la bioética en las ciencias médicas / Some reflections of the bioethics in the medical sciences

En este artículo se realiza una exposición acerca de los principios básicos de la Bioética, así como una breve reseña con relación a su origen. Se presentan las principales esferas que aborda y se analizan sus objetivos fundamentales con vistas a concientizar la necesidad de adoptar una conducta moral diferente respecto a la vida en todas sus manifestaciones en los profesionales de la salud.

An explanation about the basic principles of Bioethics, as well as a brief review on its origin are included in this paper. The main aspects approached are presented and its fundamental objectives are analyzed in order to make health professionals aware of the need of adopting a different moral behaviour in all the spheres of their lives.