A simulated study of implicit feedback models

In this paper we report on a study of implicit feedback models for unobtrusively tracking the information needs of searchers. Such models use relevance information gathered from searcher interaction and can be a potential substitute for explicit relevance feedback. We introduce a variety of implicit feedback models designed to enhance an Information Retrieval (IR) system's representation of searchers' information needs. To benchmark their performance we use a simulation-centric evaluation methodology that measures how well each model learns relevance and improves search effectiveness. The results show that a heuristic-based binary voting model and one based on Jeffrey's rule of conditioning [5] outperform the other models under investigation

The effect of grain size on magnetic properties in Sm\u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e17\u3c/sub\u3eN\u3csub\u3ex\u3c/sub\u3e

The microstructures of melt spun Sm11Fe89 and (Sm11Fe89)94Ti3C3 have been investigated under different solidification conditions. The magnetic properties of the nitrided materials have been related to the observed microstructures. Melt spinning of the Sm11Fe89 alloys resulted in grain sizes at or above the single domain limit. The addition of Ti and C resulted in an order of magnitude refinement in the microstructural scale. The magnetic properties of the samples with grain sizes below the single domain limit decreased with decreasing grain size due to increased intergranular exchange coupling

Defect configurations and dynamical behavior in a Gay-Berne nematic emulsion

To model a nematic emulsion consisting of a surfactant-coated water droplet dispersed in a nematic host, we performed a molecular dynamics simulation of a droplet immersed in a system of 2048 Gay-Berne ellipsoids in a nematic phase. Strong radial anchoring at the surface of the droplet induced a Saturn ring defect configuration, consistent with theoretical predictions for very small droplets. A surface ring configuration was observed for lower radial anchoring strengths, and a pair of point defects was found near the poles of the droplet for tangential anchoring. We also simulated the falling ball experiment and measured the drag force anisotropy, in the presence of strong radial anchoring as well as zero anchoring strength.Comment: 17 pages, 15 figure

Gain reversal studies in photorefractive waveguides

We report on low-loss photorefractive BaTiO3 H+ implanted waveguides exhibiting reversal of two-beam-coupling gain direction, caused by induced colour centres. The anomalous two-beam-coupling gain has been investigated as a function of the input beam ratio

BaTiO₃ waveguide self-pumped phase conjugator

For the first time to our knowledge, self-pumped phase conjugation is reported in a planar waveguide structure in a BaTiO3 single crystal. The waveguide was fabricated by the technique of ion implantation, with 1.5-MeV H+ ions at a dose of 1016 ions/cm2. Phase-conjugate reflectivities >20% have been measured for waveguide self-pumped phase conjugation, and, for a given input power, an order-of-magnitude reduction in the response time is observed in the waveguide compared with the bulk. The fidelity of phase conjugation in the guide is also discussed

Accountability educacional : posibilidades y desafíos para América Latina a partir de la experiencia internacional

Recoge algunos trabajos seleccionados de entre las varias ponencias presentadas en el “Seminario Accountability educacional: posibilidades y desafíos para América Latina a partir de la experiencia internacional”, una iniciativa conjunta del Preal y el CIDE desarrollada en Santiago de Chile bajo los auspicios de la USAID y la Fundación Tinker. El concepto, de aplicación reciente en América Latina, remite a la necesidad de asignar responsabilidades por las acciones propias y los resultados de las mismas. Se lo usa en el mundo financiero para aludir a los resultados de quienes resultan responsables por el manejo de dineros encomendados por terceros. Ellos están obligados a informar a sus clientes sobre los movimientos de recursos y a rendir cuentas sobre cómo se han utilizado y qué se ha logrado con ellos. Esto no sucede en el mundo de las políticas públicas y, menos aún, en aquel de la educación y la enseñanza. De hecho, los conceptos de transparencia, rendición de cuentas y responsabilidad por los resultados son relativamente novedosos cuando se refieren al quehacer de personeros que administran o manejan recursos públicos y que deben responder por el desempeño de personas y organizaciones bajo su control. En el campo educativo el concepto remite a los resultados del aprendizaje escolar y a la responsabilidad que le cabe a las escuelas –y dentro de ellas a la comunidad escolar– por los resultados que obtienen sus alumnos. Entre las acciones orientadas a lograr estos propósitos resulta prioritario evaluar periódicamente los resultados del aprendizaje y el cumplimiento de metas curriculares; alinear estas evaluaciones con estándares de contenido, desempeño y oportunidades de aprendizaje, dentro y fuera del aparato escolar; premiar o castigar el buen desempeño de los actores del sistema y, tan importante como esto, cuidar que estos ejercicios de medición y regulación no acaben distorsionando el contenido y orientación de la práctica educativa y permitan –paralelamente– fortalecer las capacidades de gestión en los establecimientos rezagados y prestar, a los maestros, el respaldo técnico necesario para realizar sus proyectos educativos con resultados de excelencia

An unexpected nitrate distribution in the tropical North Atlantic at 18°N, 30°W—implications for new production

During a R.V. Meteor JGOFS-NABE cruise to a tropical site in the northeast Atlantic in spring 1989, three different vertical regimes with respect to nitrate distribution and availability within the euphotic zone were observed. Besides dramatic variations in the depth of the nitracline, a previously undescribed nose-like nitrate maximum within the euphotic zone was the most prominent feature during this study. Both the vertical structure of phytoplankton biomass and the degree of absolute and relative new production were related to the depth of the nitracline, which in turn was dependent on the occurrence/non-occurrence of the subsurface subtropical salinity maximum (S(max)). The mesoscale variability of the nitracline depth, as indicated from a pre-survey grid, and published data on the frequent occurrence of the S(max) in tropical waters suggest higher variability of new production and F-ratio than usually expected for oligotrophic oceans. The importance of salt fingering and double diffusion for nitrate transport into the euphotic zone is discussed

Synthetic prions with novel strain-specified properties

Prions are infectious proteins that possess multiple self-propagating structures. The information for strains and structural specific barriers appears to be contained exclusively in the folding of the pathological isoform, PrP(Sc). Many recent studies determined that de novo prion strains could be generated in vitro from the structural conversion of recombinant (rec) prion protein (PrP) into amyloidal structures. Our aim was to elucidate the conformational diversity of pathological recPrP amyloids and their biological activities, as well as to gain novel insights in characterizing molecular events involved in mammalian prion conversion and propagation. To this end we generated infectious materials that possess different conformational structures. Our methodology for the prion conversion of recPrP required only purified rec full-length mouse (Mo) PrP and common chemicals. Neither infected brain extracts nor amplified PrP(Sc) were used. Following two different in vitro protocols recMoPrP converted to amyloid fibrils without any seeding factor. Mouse hypothalamic GT1 and neuroblastoma N2a cell lines were infected with these amyloid preparations as fast screening methodology to characterize the infectious materials. Remarkably, a large number of amyloid preparations were able to induce the conformational change of endogenous PrPC to harbor several distinctive proteinase-resistant PrP forms. One such preparation was characterized in vivo habouring a synthetic prion with novel strain specified neuropathological and biochemical properties