2,019 research outputs found
Las nuevas formas de colonización de la arquitectura de postguerra en la obra de Fernando de Urrutia Usaola: arquitectura para regiones devastadas, los poblados hidroeléctricos y ciudades-jardín en la periferia
Chemical composition of phytoplankton and Particulate Organic Matter in the Ría de Vigo (NW Spain)
15 pages, 2 figures, 7 tables.Elemental (C, H, O, N, Si, P) and biochemical composition (proteins, carbohydrates, lipids, phosphorus compounds,
chlorophyll and opal) in particulate organic matter, diatoms, other autotrophs, heterotrophs and detritus from natural
plankton were established simultaneously by measuring relatively few components. Using standard techniques in
marine chemistry on board ship, it is possible to infer a great deal about the composition and condition of the plankton. In
addition, the organic matter content in terms of cell volume was determined for each group of plankton. Variation of chemical
composition with depth was also considered. The ratio carbohydrates/lipids (Cbh/Lip) was used as an indicator of the
chemical quality of the plankton.This paper was supported by the Consellería
de Educación of the Xunta de Galicia and Comisión
Interministerial de Ciencia y Tecnología (CICYT)
Grant No. MAR88-245.Peer reviewe
Diseño, fundamentación y validación de un programa virtual colaborativo en educación ambiental
Los programas colaborativos constituyen una adecuada herramienta para hacer Educación Ambiental. A lo largo del texto fundamentamos el modelo didáctico MACELEA que ha servido para la creación y puesta en marcha del programa colaborativo virtual de innovación curricular Ecourban. Describimos los aspectos más relevantes para su diseño e implementación, y damos cuenta de los criterios de validez y componentes de innovación virtual que lo sustentan: contextual, pedagógico-didáctica, epistemológica, multimedia, cognitiva y comunicacional.Collaborative programmes are an appropriate tool for Environmental Education. In this work we show the foundations of the didactic model, that we have named MACELEA and which has served for the implementation of a virtual collaborative program to promote the curricular innovation: Ecourban. Here we describe the most relevant dimensions of its design and development, so as the validity criteria and components of virtual innovation: contextual, pedagogical-didactic, epistemological, multimedia, cognitive and communicative
Caracterización química y cuantificación del rendimiento de extracción de pigmento en siete accesiones mexicanas de Bixa orellana
Achiote (Bixa orellana) is a plant used for obtaining a natural dye rich on carotenoids (mainly bixin and norbixin); it is also the plant species with the highest content of tocotrienols in nature. In the present work, the pigment extraction yield of seven Mexican accessions of Bixa orellana was quantified. Also color parameters and content of tocotrienols, tocopherols, norbixin, bixin, total phenolic compounds and antioxidant capacity were evaluated in the corresponding annatto extracts. The highest percentage of pigment extraction yield was obtained with KOH (4.84%). Accessions 43 (L*= 4.01 ± 0.79, C*= 7.33 ± 1.07, h= 25.76 ± 6.35) and 50 (L*= 3.17 ± 0.64, C*= 6.81 ± 0.53, h= 26.41 ± 4.41) had the lowest color values, meaning these accessions had a darker and redder color. Four accessions showed the highest content of bixin: accession 48 (3.1%), 45 (2.6%) 43 (2.4%) and 47 (2.2%). Accession 50 had showed the highest content of total phenolic compounds and of tocotrienols (T3), mainly the isoform δ-T3 (5.03 ± 0.64 mg g−1 Seed Dry Weight), as well as the highest antioxidant capacity.El achiote (Bixa orellana) es una planta utilizada para obtener un colorante natural rico en carotenoides (principalmente bixina y norbixina); además, es la especie vegetal con el mayor contenido de tocotrienoles. En este trabajo, se determinó el rendimiento de extracción de pigmento de siete accesiones mexicanas de Bixa orellana. También se evaluaron los parámetros de color y el contenido de tocotrienoles, tocoferoles, norbixina, bixina, compuestos fenólicos totales y la capacidad antioxidante en extractos de annato. El mayor porcentaje de rendimiento de extracción de pigmento fue obtenido con KOH (4.847905%). Las accesiones 43 (L*= 4.01 ± 0.79, C*= 7.33 ± 1.07, h= 25.76 ± 6.35) y 50 (L*= 3.17 ± 0.64, C*= 6.81 ± 0.53, h= 26.41 ± 4.41) presentaron los valores más bajos de los párametros de color, lo que significa que estas accesiones tuvieron un color más oscuro y más rojo. Cuatro accesiones mostraron el mayor contenido de bixina: accesión 48 (3.1%), 45 (2.6%) 43 (2.4%) and 47 (2.2%). La accession 50 mostró el mayor contenido de compuestos fenólicos totales y de tocotrienoles (T3), principalmente la isoforma δ-T3 (5.03 ± 0.64 mg g-1 Peso Seco), así como también la mayor capacidad antioxidante.Fil: Raddatz Mota, D.. Universidad Autónoma Metropolitana; MéxicoFil: Pérez Flores, L. J.. Universidad Autónoma Metropolitana; MéxicoFil: Carrari, Fernando Oscar. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Biotecnología; ArgentinaFil: Insani, Ester Marina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Biotecnología; ArgentinaFil: Asis, Ramón. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Córdoba. Centro de Investigaciones en Bioquímica Clínica e Inmunología; ArgentinaFil: Mendoza Espinoza, J. A.. Universidad Nacional Autónoma de México; MéxicoFil: Díaz de León Sánchez, F.. Universidad Autónoma Metropolitana; MéxicoFil: Rivera Cabrera, F.. Universidad Autónoma Metropolitana; Méxic
Recycled hybrid material for use as shielding in operations with ionizing radiation
One of the most efficient measures to prevent gamma radiation is shielding, which can take the form of protection barriers, storage containers, wall coating, bunkers, or many others aimed at minimizing the exposure of people to radiation. The materials used to this end have not changed much since the invention of X-rays, when materials with high attenuation capacity were employed, such as lead, tungsten, or concrete. These are all high-density materials and, therefore, also very heavy, and some of them are expensive and not environmentally friendly, as they do not have many possibilities with regards to their recycling. Circular economy provides an opportunity to reintroduce subproducts and waste in the same production processes that generated them or as raw matters in others. The use of sustainable materials is one of these options; however, there is little research in the field of radiation protection about the use of recycled material to this end, and there are few alternative sustainable options different from conventional materials that show similar behaviour. In our study, we have designed and built shielded panels called Mixlead® for gammagraphy, made of 100 % recyclable materials with sandwich structures combining polymeric fractions of electric cables and lead-alloy protection sheets used in the packaging of radiographic plates. With a methodology combining shielding calculations and a series of thermomechanical-radiological tests, it was possible to accurately determine the thickness of Mixlead® necessary to perform the tests with security guarantees and meeting sustainability requirements for radioactive sources of Iridium (192Ir) and Selenium (75Se), the use of the former being predominant, with an average activity of 1 GBq. In order to reduce this activity 2 and 10 times, the necessary thickness would be 24 and 79 mm respectively, which represents 3 or 4 layers of Mixlead® material.15 página
Arrested dynamics of the dipolar hard-sphere model
We report the combined results of molecular dynamics simulations and
theoretical calculations concerning various dynamical arrest transitions in a
model system representing a dipolar fluid, namely, N (softcore) rigid spheres
interacting through a truncated dipole-dipole potential. By exploring different
regimes of concentration and temperature, we find three distinct scenarios for
the slowing down of the dynamics of the translational and orientational degrees
of freedom: At low ({} = 0.2) and intermediate ( = 0.4) volume
fractions, both dynamics are strongly coupled and become simultaneously
arrested upon cooling. At high concentrations ({} 0.6), the
translational dynamics shows the features of an ordinary glass transition,
either by compressing or cooling down the system, but with the orientations
remaining ergodic, thus indicating the existence of partially arrested states.
In this density regime, but at lower temperatures, the relaxation of the
orientational dynamics also freezes. The physical scenario provided by the
simulations is discussed and compared against results obtained with the
self-consistent generalized Langevin equation theory, and both provide a
consistent description of the dynamical arrest transitions in the system. Our
results are summarized in an arrested states diagram which qualitatively
organizes the simulation data and provides a generic picture of the glass
transitions of a dipolar fluid
Banks’ Net Interest Margin in the 2000s: A Macro-Accounting International Perspective
This paper re-examines the determinants of Net Interest Margin (NIM) in the banking industries
of 15 developed and emerging economies. It presents three main contributions
with respect to previous studies: first, we analyze the determinants of NIM in the years
leading to the 2008 financial crisis; second, we account for the role of different accounting
standards across countries; third, we use multi-way cluster estimation methodologies
which control for cross-sectional and time-series dependence in macroeconomic and
banking variables. We find that the introduction of International Financial Reporting
Standards (IFRSs) contributed to lower NIM variations unexplained by standard accounting
variables. Interest rate volatility is found to be positively and strongly related to
NIM dynamics, whereas inflation risk is often found to be a relevant driver of NIM crosscountry
differences
Selección de variables en la predicción de llamadas en un centro de atención telefónica
En este artículo se ilustra la importancia de la selección de variables independientes para modelos neuronales destinados a la predicción de la demanda en un centro de atención telefónica. Los modelos tienen como objetivo ayudar en la planificación semanal del personal del centro, tarea que se realiza con 14 días de antelación.
Los modelos requeridos pueden hacer uso de gran cantidad de variables independientes. Sin embargo, el número de casos que pueden ser usados para obtener los parámetros del modelo es escaso debido a los cambios socio-económicos. Esto plantea la necesidad de seleccionar cuidadosamente las variables independientes y utilizar el menor número posible de ellas, de otro modo la generalización del modelo se degradaría.
Para resolver el problema se utiliza un método mixto que permite trabajar con un alto número de variables candidatas, en una primera fase, y seleccionar más cuidadosamente un número menor de variables en una segunda fase. Los resultados obtenidos por los modelos resultantes de aplicar el método propuesto y sus variantes son analizados utilizando datos reales de un centro de atención telefónica. Los resultados de la comparación muestran que la correcta selección de variables independientes es vital para este tipo de aplicación.Unión Europea HYCON FP6-511368
Wannier-Bloch approach to localization in high harmonics generation in solids
Emission of high-order harmonics from solids provides a new avenue in
attosecond science. On one hand, it allows to investigate fundamental processes
of the non-linear response of electrons driven by a strong laser pulse in a
periodic crystal lattice. On the other hand, it opens new paths toward
efficient attosecond pulse generation, novel imaging of electronic wave
functions, and enhancement of high-order harmonic generation (HHG) intensity. A
key feature of HHG in a solid (as compared to the well-understood phenomena of
HHG in an atomic gas) is the delocalization of the process, whereby an electron
ionized from one site in the periodic lattice may recombine with any other.
Here, we develop an analytic model, based on the localized Wannier wave
functions in the valence band and delocalized Bloch functions in the conduction
band. This Wannier-Bloch approach assesses the contributions of individual
lattice sites to the HHG process, and hence addresses precisely the question of
localization of harmonic emission in solids. We apply this model to investigate
HHG in a ZnO crystal for two different orientations, corresponding to wider and
narrower valence and conduction bands, respectively. Interestingly, for
narrower bands, the HHG process shows significant localization, similar to
harmonic generation in atoms. For all cases, the delocalized contributions to
HHG emission are highest near the band-gap energy. Our results pave the way to
controlling localized contributions to HHG in a solid crystal, with hard to
overestimate implications for the emerging area of atto-nanoscience
Time Series
This paper first shows that survey-based expectations (SBE) outperform standard time
series models in U.S. quarterly inflation out-of-sample prediction and that the term structure
of survey-based inflation forecasts has predictive power over the path of future inflation
changes. It then proposes some empirical explanations for the forecasting success
of survey-based inflation expectations. We show that SBE pool a large amount of heterogeneous
information on inflation expectations and react more flexibly and accurately
to macro conditions both contemporaneously and dynamically. We illustrate the flexibility
of SBE forecasts in the context of the recent financial crisis
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