Métodos de reducción de escala : aplicaciones al tiempo, clima, variabilidad climática y cambio climático

Los Modelos de Circulación General Atmosféricos-Oceánicos Acoplados muestran buena habilidad para simular la evolución de las circulaciones de escala global. Sin embargo, esta bondad no es muy útil para el estudio de impactos locales debido a que la resolución espacial de esos modelos está por encima de la escala de los impactos locales que se desean analizar. Es importante tomar esto en cuenta al estudiar impactos del clima en las actividades del hombre, en la biodiversidad, en ambientes marino-costeros y en arrecifes en las regiones tropicales, por ejemplo. Existen dos aproximaciones para lidiar con esta diferencia de escala e información: los métodos de reducción de escala dinámica y estadística. En este trabajo, se discuten los elementos básicos del sistema climático y las posibles causas de los cambios atmosféricos observados en este sistema. Se discuten brevemente los principales conceptos físicos del sistema climático, el clima de una región, la variabilidad climática y las generalidades del problema del cambio climático global con énfasis en el aspecto regional del mismo. Se describen también los esquemas metodológicos del proceso de reducción de escala y se presenta una discusión sobre sus ventajas y limitaciones, así como algunas aplicaciones al tiempo atmosférico y clima regional.Coupled Atmosphere-Ocean General Circulation Models demonstrate good skill in simulating large scale circulations. However this output is not very useful to study local impacts, as its spatial resolution is courser than the scale of local impacts. It is very important to consider this issue when studying, for instance, climate impacts on human activities, coastal-marine biodiversity and tropical coral reefs. In general terms, there have been two different approaches to deal with this scale and information difference: the dynamic and the statistic downscaling methods. In this work, the basic climate elements are presented and the possible physical causes of atmospheric changes are discussed. Also, a summary of the main physical concepts that define the climate system as well as the climate and climate variability of a region with respect to the mean atmospheric state and the general aspects of the problem of climate change with emphasis on regional scales, is presented. In addition, this study describes the methodological schemes of the downscaling process and presents a discussion of downscaling advantages and disadvantages, while providing applications for regional weather and climate as well as for socio-economic benefits in coastal, agricultural and tourism activities, among others

Response of Nitrous Oxide Flux to Addition of Anecic Earthworms to an Agricultural Field

The burrowing and feeding activities of earthworms may have a strong effect on the flux of N2O from agricultural soils. As such, shifts to agricultural management practices that increase the number of earthworms require an understanding of the role of earthworms in N2O dynamics. We conducted a field experiment to examine the effects of addition of anecic earthworms (Lumbricus terrestris) on N2O flux in a field previously planted with corn (Zea mays) in southern Rhode Island, USA. Plots were amended with (15NH4)2SO4 and either 0 (CTL) or 48 L. terrestris m-2 (EW). The flux of N2O, 15N2O and 15N2 was measured over 28 days between October and November 2008. The EW treatment had a significantly higher flux of N2O and 15N2O 1 - 3 days after 15NH4 addition. No treatment effects were observed on 15N2 flux. The addition of earthworms significantly increased (Day 1) and decreased (Day 12) the mole fraction of N2O relative to the CTL. Our results suggest that anecic earthworm additions can increase N2O flux from inorganic fertilizer N amendments, but the effects appear to short-lived

Métodos de reducción de escala: aplicaciones al tiempo, clima, variabilidad climática y cambio climático

Los Modelos de Circulación General Atmosféricos-Oceánicos Acoplados muestran buena habilidad para simular la evolución de las circulaciones de escala global. Sin embargo, esta bondad no es muy útil para el estudio de impactos locales debido a que la resolución espacial de esos modelos está por encima de la escala de los impactos locales que se desean analizar. Es importante tomar esto en cuenta al estudiar impactos del clima en las actividades del hombre, en la biodiversidad, en ambientes marino-costeros y en arrecifes en las regiones tropicales, por ejemplo. Existen dos aproximaciones para lidiar con esta diferencia de escala e información: los métodos de reducción de escala dinámica y estadística. En este trabajo, se discuten los elementos básicos del sistema climático y las posibles causas de los cambios atmosféricos observados en este sistema. Se discuten brevemente los principales conceptos físicos del sistema climático, el clima de una región, la variabilidad climática y las generalidades del problema del cambio climático global con énfasis en el aspecto regional del mismo. Se describen también los esquemas metodológicos del proceso de reducción de escala y se presenta una discusión sobre sus ventajas y limitaciones, así como algunas aplicaciones al tiempo atmosférico y clima regional.Reducción dinámica de escala, reducción estadística de escala, clima, variabilidad climática, cambio climático

Spin-dependent electronic conduction along zigzag graphene nanoribbons bearing adsorbed Ni and Fe nanostructures

Using SMEAGOL, an ab initio computational method that combines the non-equilibrium Green's function formalism with density-functional theory, we calculated spin-specific electronic conduction in systems consisting of single Fen and Nin nanostructures (n = 1−4) adsorbed on a hydrogen-passivated zigzag graphene nanoribbon. For each cluster we considered both ferromagnetically and antiferromagnetically coupled ribbon edges (Ferro-F and Ferro-A systems, respectively). Adstructures located laterally on Ferro-A ribbons caused significant transmittance loss at energies 0.6–0.25 eV below the Fermi level for one spin and 0.2–0.4 eV above the Fermi level for the other, allowing the potential use of these systems in transistors to create a moderately spin-polarized current of one or the other sign depending on the gate voltage. Ni₃ and Ni₄ clusters located at the centre of Ferro-F ribbons exhibited a strong spin-filtering effect in a narrow energy window around the Fermi level

Spin currents and filtering behavior in zigzag graphene nanoribbons with adsorbed molybdenum chains

By means of density-functional-theoretic calculations, we investigated the structural, electronic and transport properties of hydrogen-passivated zigzag graphene nanoribbons (ZGNRs) on which a one-atom-thick Mo chain was adsorbed (with or without one or two missing atoms), or in which the passivating hydrogen atoms were replaced by Mo atoms. Mo-passivated ZGNRs proved to be nonmagnetic. ZGNRs with an adsorbed defect-free Mo chain were most stable with the Mo atoms forming dimers above edge bay sites, which suppressed the magnetic moments of the C atoms in that half of the ribbon; around the Fermi level of these systems, each spin component had a transmission channel via the Mo spz band and one had an additional channel created by polarization of the ZGNR π* band, leading to a net spin current. The absence of an Mo dimer from an Mo chain adsorbed at the ZGNR edge made the system a perfect spin filter at low voltage bias by suppressing the Mo spz band channels. Thus this last kind of hybrid system is a potential spin valve

Congenital anomalies of the optic nerve

AbstractCongenital optic nerve head anomalies are a group of structural malformations of the optic nerve head and surrounding tissues, which may cause congenital visual impairment and blindness. Each entity in this group of optic nerve anomalies has individually become more prevalent as our ability to differentiate between them has improved due to better characterization of cases. Access to better medical technology (e.g., neuroimaging and genetic analysis advances in recent years) has helped to expand our knowledge of these abnormalities. However, visual impairment may not be the only problem in these patients, some of these entities will be related to ophthalmologic, neurologic and systemic features that will help the physician to identify and predict possible outcomes in these patients, which sometimes may be life-threatening. Herein we present helpful hints, associations and management (when plausible) for them

Primary cilia regulate proliferation of amplifying progenitors in adult hippocampus: implications for learning and memory

Integration of new neurons into the adult hippocampus has been linked to specific types of learning. Primary cilia were found to be required for the formation of adult neural stem cells (NSCs) in the hippocampal dentate gyrus during development. However, the requirement of cilia in maintenance of adult NSCs is unknown. We developed a genetic mouse model in which fetal/perinatal brain development is unaffected, but adult hippocampal neurogenesis is constantly reduced by conditional ablation of primary cilia in adult GFAP(+) neural stem/progenitor cells. We found that this approach specifically reduces the number of hippocampal amplifying progenitors (also called type 2a cells) without affecting the number of radial NSCs (or type 1 cells). Constant reduction of adult hippocampal neurogenesis produced a delay rather than a permanent deficiency in spatial learning without affecting the retention of long-term memories. Decreased neurogenesis also altered spatial novelty recognition and hippocampus-independent cue conditioning. Here, we propose that adult hippocampal newborn neurons increase the efficiency of generating the new representations of spatial memories and that reduction of adult hippocampal neurogenesis may be biased toward cue-based strategies. This novel mouse model provides evidences that cognitive deficits associated with ciliary defects (ciliopathies) might be, in part, mediated by the deficiency of primary cilia in adult hippocampal stem/progenitor cells

CCD Photometry of Trapezia Stars I

We present photometric CCD observations of stars in four stellar trapezia ADS 15184, ADS 4728, ADS 2843, and ADS 16795. This study is performed on images obtained at the Observatorio Astron\'omico Nacional at San Pedro M\'artir (OAN), Baja California, M\'exico. In this work we utilise aperture photometry to measure the $U$, $B$, $V$, $R$ and $I$ magnitudes of some of the stars in these dynamically unstable stellar clusters (trapezia). Using the $Q=(U-B)-0.72(B-V)$ parameter we obtained the spectral type of the studied stars as well as their distance to the Sun and their reddening. Slight differences between the $Q$-derived Spectral types and those listed in SIMBAD might be due to a different value, from $0.72$, for the slope of the reddening line on the two-colour diagram.Comment: 34 pages, 12 figures, 31 tables, accepted for publication in RevMexAA, vol. 60, num. 1, April 2

Métodos de reducción de escala : aplicaciones al tiempo, clima, variabilidad climática y cambio climático

Los Modelos de Circulación General Atmosféricos-Oceánicos Acoplados muestran buena habilidad para simular la evolución de las circulaciones de escala global. Sin embargo, esta bondad no es muy útil para el estudio de impactos locales debido a que la resolución espacial de esos modelos está por encima de la escala de los impactos locales que se desean analizar. Es importante tomar esto en cuenta al estudiar impactos del clima en las actividades del hombre, en la biodiversidad, en ambientes marino-costeros y en arrecifes en las regiones tropicales, por ejemplo. Existen dos aproximaciones para lidiar con esta diferencia de escala e información: los métodos de reducción de escala dinámica y estadística. En este trabajo, se discuten los elementos básicos del sistema climático y las posibles causas de los cambios atmosféricos observados en este sistema. Se discuten brevemente los principales conceptos físicos del sistema climático, el clima de una región, la variabilidad climática y las generalidades del problema del cambio climático global con énfasis en el aspecto regional del mismo. Se describen también los esquemas metodológicos del proceso de reducción de escala y se presenta una discusión sobre sus ventajas y limitaciones, así como algunas aplicaciones al tiempo atmosférico y clima regional.Coupled Atmosphere-Ocean General Circulation Models demonstrate good skill in simulating large scale circulations. However this output is not very useful to study local impacts, as its spatial resolution is courser than the scale of local impacts. It is very important to consider this issue when studying, for instance, climate impacts on human activities, coastal-marine biodiversity and tropical coral reefs. In general terms, there have been two different approaches to deal with this scale and information difference: the dynamic and the statistic downscaling methods. In this work, the basic climate elements are presented and the possible physical causes of atmospheric changes are discussed. Also, a summary of the main physical concepts that define the climate system as well as the climate and climate variability of a region with respect to the mean atmospheric state and the general aspects of the problem of climate change with emphasis on regional scales, is presented. In addition, this study describes the methodological schemes of the downscaling process and presents a discussion of downscaling advantages and disadvantages, while providing applications for regional weather and climate as well as for socio-economic benefits in coastal, agricultural and tourism activities, among others