Clusters en cultivos ilícitos: determinantes y dinámicas

Los datos recientes de areas de cultivos ilícitos indican que a pesar de las fumigaciones, la producción total se ha reducido levemente y los cultivos se han dispersado. Se plantea un modelo teórico que analiza las decisiones tomadas por los cultivadores sobre la localizaci´on de sus parcelas, basando esta escogencia en la dinamización local de los costos esperados. Se utiliza un modelo de agentes para la simulación de la naturaleza compleja de las dinámicas estudiadas. Se encuentra que el incentivo para agruparse aumenta con las economías a escala y se reduce con la expectativa del castigo, sobretodo en zonas con alta densidad de cultivadores.

Counterpoise-corrected geometries and harmonic frequencies of N-body clusters: application to (HF)n (n=3,4)

A study was conducted on the methods of basis set superposition error (BSSE)-free geometry optimization and frequency calculations in clusters larger than a dimer. In particular, three different counterpoise schemes were critically examined. It was shown that the counterpoise-corrected supermolecule energy can be easily obtained in all the cases by using the many-body partitioning of energy

Clusters como modelo para alcanzar la productividad y competitividad industrial en el Ecuador

El desarrollo de una industria no puede ser impulsado desde un sentido únicamente económico, debe contemplar el desarrollo social como un factor fundamental. Un clúster es una opción para involucrar a diferentes sectores de la población en procesos de crecimiento social y económico. El nivel de la calidad de vida de una nación está determinado por la productividad con la cual utiliza su talento humano, recursos naturales y capital, y esto implica planificar procesos institucionales, educacionales y tecnológicos de una manera seria y responsable, considerando el largo plazo y el bienestar de la población. La productividad depende del valor de los productos y servicios en términos de diferenciación, calidad, y de la eficiencia con la que se producen. Si es que todos estos elementos se manejan estratégicamente, lo más lógico es alcanzar la competitividad industrial. Un análisis previo a la propuesta de clusters en el Ecuador es necesario, para definir las mejores condiciones que permitan tener éxito el momento de implementar un proceso productivo como el que se pretende definir con el estudio de los clusters competitivos. Raúl Prebisch precisó tres conceptos para definir el subdesarrollo: la heterogeneidad estructural, la especialización productiva, y, el desarrollo desigual. Desde este punto de vista, la generación de clusters es una alternativa que debe buscar fortalecer un desarrollo más equitativo, involucrando a todos los actores económicos. Esta visión integral del desarrollo va más allá de la complementariedad de las políticas sociales, económicas y ambientales y el ordenamiento democrático, entre capital humano, bienestar social, desarrollo sostenible y ciudadanía: debe interpretarse como el sentido mismo del desarrollo (CEPAL, 2000).

Relationships between lightning and properties of convective cloud clusters

Satellite observations of convective system properties and lightning flash rate are used to investigate the ability of potential lightning parameterizations to capture both the dominant land-ocean contrast in lightning occurrence and regional differences between Africa, the Amazon and the islands of the maritime continent. As found in previous studies, the radar storm height is tightly correlated with the lightning flash rate. A roughly second order power-law fit to the mean radar echo top height above the 0C isotherm is shown to capture both regional and land-ocean contrasts in lightning occurrence and flash rate using a single set of parameters. Recent developments should soon make it possible to implement a parameterization of this kind in global models. Parameterizations based on cloud top height, convective rain rate and convective rain fraction all require the use of separate fits over land and ocean and fail to capture observed differences between continental regions.

New insights on growth mechanisms of protein clusters at surfaces: an AFM and simulation study

Despite its relevance to a wide range of technological and fundamental areas, a quantitative understanding of protein surface clustering dynamics is often lacking. In inorganic crystal growth, surface clustering of adatoms is well described by diffusion-aggregation models. In such models, the statistical properties of the aggregate arrays often reveal the molecular scale aggregation processes. We investigate the potential of these theories to reveal hitherto hidden facets of protein clustering by carrying out concomitant observations of lysozyme adsorption onto mica surfaces, using atomic force microscopy. and Monte Carlo simulations of cluster nucleation and growth. We find that lysozyme clusters diffuse across the substrate at a rate that varies inversely with size. This result suggests which molecular scale mechanisms are responsible for the mobility of the proteins on the substrate. In addition the surface diffusion coefficient of the monomer can also be extracted from the comparison between experiments and simulations. While concentrating on a model system of lysozyme-on-mica, this 'proof of concept' study successfully demonstrates the potential of our approach to understand and influence more biomedically applicable protein-substrate couples.

Strategy clusters and sources of knowledge in French L2 listening comprehension

This article reports on an exploratory investigation into the listening strategies of lower-intermediate learners of French as an L2, including the sources of knowledge they employed in order to comprehend spoken French. Data from 14 learners were analysed to investigate whether employment of strategies in general and sources of knowledge in particular varied according to the underlying linguistic knowledge of the student. While low linguistic knowledge learners were less likely to deploy effectively certain strategies or strategy clusters, high linguistic knowledge levels were not always associated with effective strategy use. Similarly, while there was an association between linguistic knowledge and learners’ ability to draw on more than one source of knowledge in a facilitative manner, there was also evidence that learners tended to over-rely on linguistic knowledge where other sources, such as world knowledge, would have proved facilitative. We conclude by arguing for a fresh approach to listening pedagogy and research, including strategy instruction, bottom-up skill development and a consideration of the role of linguistic knowledge in strategy use.

Theory of enhanced magnetic anisotropy induced by Pt adatoms on two-dimensional Co clusters supported on a Pt(111) substrate

Calculations are reported of the magnetic anisotropy energy of two-dimensional (2D) Co nanostructures on a Pt(111) substrate. The perpendicular magnetic anisotropy (PMA) of the 2D Co clusters strongly depends on their size and shape, and rapidly decreases with increasing cluster size. The PMA calculated is in reasonable agreement with experimental results. The sensitivity of the results to the Co-Pt spacing at the interface is also investigated and, in particular, for a complete Co monolayer we note that the value of the spacing at the interface determines whether PMA or in-plane anisotropy occurs. We find that the PMA can be greatly enhanced by the addition of Pt adatoms to the top surface of the 2D Co clusters. A single Pt atom can induce in excess of 5 meV to the anisotropy energy of a cluster. In the absence of the Pt adatoms the PMA of the Co clusters falls below 1 meV/Co atom for clusters of about 10 atoms whereas, with Pt atoms added to the surface of the clusters, a PMA of 1 meV/Co atom can be maintained for clusters as large as about 40 atoms. The effect of placing Os atoms on the top of the Co clusters is also considered. The addition of 5d atoms and clusters on the top of ferromagnetic nanoparticles may provide an approach to tune the magnetic anisotropy and moment separately.

Ab initio and tight-binding calculations of noncollinear magnetism in manganese clusters

Combining ab initio and tight-binding calculations, we have studied the noncollinear magnetism in manganese clusters. The oscillations in the per-atom moments observed experimentally are reproduced theoretically. The tendency of antiferromagnetic coupling between near neighbors leads to noncollinear coupling between atoms within the clusters. For clusters containing 12, 13, 15, 19, and 23 atoms, the geometrical structures were optimized from ab initio calculations with collinear coupled spin moments among different atomic sites. For larger clusters such as Mn-36 and Mn-55, the geometries are taken as portions of an fcc structure. Although the local atomic moments have high values close to 4 mu(B), the net moments lie in the range of 0.4-1.2 mu(B)/atom. Taking the noncollinear coupling into account brings the calculated magnetic moments much closer to the experimental results.