A unified electrostatic and cavitation model for first-principles molecular dynamics in solution

The electrostatic continuum solvent model developed by Fattebert and Gygi is combined with a first-principles formulation of the cavitation energy based on a natural quantum-mechanical definition for the surface of a solute. Despite its simplicity, the cavitation contribution calculated by this approach is found to be in remarkable agreement with that obtained by more complex algorithms relying on a large set of parameters. Our model allows for very efficient Car-Parrinello simulations of finite or extended systems in solution, and demonstrates a level of accuracy as good as that of established quantum-chemistry continuum solvent methods. We apply this approach to the study of tetracyanoethylene dimers in dichloromethane, providing valuable structural and dynamical insights on the dimerization phenomenon

Cambios en la heterogeneidad del paisaje y organización espacial de bosques nativos en Patagonia, Argentina

Native forests in Patagonia have been influenced by human activities since the beginning of the past century. Nevertheless, the availability of aerial photographs to conduct analysis of changes at a landscape level due to anthropic factors is generally restricted to the last decades. Therefore this study was aimed to detect changes of the forest landscape heterogeneity during the last thirty years in the northwest region of Chubut, the middle-located Patagonian province, and to study spatial patterning of forest landscapes. For the first goal, we focused on a 2,000 ha landscape unit with prevailing Austrocedrus chilensis forests. In 466 ha covered by these forests, 41% of this area was negatively affected by forest fires, timber logging followed by livestock grazing and substitution with pine plantations. In contrast, growth of young Austrocedrus forests was verified in 9% of the forest area. Spatial patterns were studied on an area of 10,000 ha showing a high heterogeneity of the distinctive landscape configurations.Los bosques nativos en Patagonia han estado influidos por la acción del hombre desde principios del siglo pasado. Sin embargo, la disponibilidad de fotografías aéreas para efectuar análisis de cambios debidos a factores antrópicos a escala de paisaje está generalmente restringida a las últimas décadas. En consecuencia, este estudio estuvo orientado a detectar y analizar los cambios de la heterogeneidad del paisaje forestal durante los últimos treinta años en la región noroeste de Chubut, la provincia central de Patagonia en Argentina, y a estudiar la organización espacial de paisajes forestales. Para el primer objetivo, nos concentramos en una unidad de paisaje de 2.000 ha con predominancia de bosques de Austrocedrus chilensis. En 466 ha cubiertas con estos bosques, 41% de esta área fue negativamente afectado por incendios forestales, extracciones forestales seguidas de pastoreo y reemplazo de bosques nativos por plantaciones de pinos. En contraste, el crecimiento de bosques jóvenes de Austrocedrus se verificó en el 9% del área forestal. Los patrones espaciales se estudiaron en un área de 10.000 ha y mostraron una alta heterogeneidad de las configuraciones distintivas del paisaje

A self-consistent perturbative evaluation of ground state energies: application to cohesive energies of spin lattices

The work presents a simple formalism which proposes an estimate of the ground state energy from a single reference function. It is based on a perturbative expansion but leads to non linear coupled equations. It can be viewed as well as a modified coupled cluster formulation. Applied to a series of spin lattices governed by model Hamiltonians the method leads to simple analytic solutions. The so-calculated cohesive energies are surprisingly accurate. Two examples illustrate its applicability to locate phase transition.Comment: Accepted by Phys. Rev.

Structural characterization of low‐temperature molecular beam epitaxial In0.52Al0.48As/InP heterolayers

A systematic study of the structural quality and arsenic content of as‐grown In0.52Al0.48As/InP layers deposited on InP by molecular beam epitaxy at temperatures between 150 and 450 °C was performed using transmission electron microscopy and particle‐induced x‐ray emission. We found that the amount of As incorporated in the layers generally increases with decreasing growth temperature, with the crystalline quality of the layers being good at growth temperatures higher than 200 °C. At 150 °C, a large density of pyramidal defects is formed, the defects are related to the very large amount of excess As incorporated into the layer. The mechanisms leading to the formation of these defects are discussed. At 200 °C, however, the amount of excess As is lower than expected, and wavy streaks of diffuse scattering are seen in electron diffraction. It is shown that small ordered domains of the CuPt type on the group III atoms are responsible for these features.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70657/2/APPLAB-60-8-989-1.pd

The Sentinel-2 MSI Can Increase the Temporal Resolution of 30m Satellite-Derived LAI Estimates

The successful launch of the European Space Agency (ESA) Sentinel-2A (S2-A) on 23 June 2015 with its MultiSpectral Instrument (MSI) provides an important means to augment Earth-observation capabilities following the legacy of Landsat. After the three-month satellite commissioning campaign, the MSI onboard S-2A is performing very well (ESA, 2015). By 3 December 2015, the sensor data records have achieved provisional maturity status and have been accessed in level-1C Top-Of-Atmosphere (TOA) reflectance by the remote sensing community worldwide. Near-nadir observations by the MSI onboard S-2A and the Operational Land Imager (OLI) onboard Landsat 8 were collected during Simultaneous Nadir Overpasses as well as nearly coincident overpasses. This paper presents a processing chain using harmonized S-2A MSI and Landsat 8 OLI sensors to obtain increased temporal resolution in Leaf Area Index (LAI) estimates using the red-edge band B8A of MSI to replace the NIR band B08. Results demonstrate that LAI estimates from the MSI and OLI are comparable, and, given sufficient preprocessing for atmospheric correction and geometric rectification, can be used interchangeably to improve the frequency with which low LAI canopies can be monitored

Contenidos hepáticos y renales de hierro y cobre en ratas tratadas con cadmio y zinc

The influence of the Cd intraperitoneal (ip), and Cd (ip) + Zn subcutaneous (sc) administration on the Cu and Fe concentrations in liver and kidneys was studied. After five weeks, both Cd and Cd+Zn groups showed an abnormally low liver mass with respect to total body mass. The groups of rats treated with Cd alone presented Fe levels in both liver and kidneys lower than those levels observed in the control group. The levels of Cu in liver maintain approximatelly constant during the time of treatment while the Cu content in kidneys significantly increased after five weeks of treatment. With respect to the animals treated with Cd and Zn, the hepatic content of Fe decreased in the first week but tend to be normal after five weeks which suggest the protector role of Zn against to the hepatic depletion of Fe induced by Cd. Renal Fe as well as renal and hepatic Cu presented a similar behaviour. Significant decreases and significant increases were observed after one and five weeks respectively, which could be related with a higher synthesis of metallothioneins and abnormal redistriibution of essential metals.Se realizó un estudio de la influencia de la administración de Cd vía intraperitoneal (ip), y de Cd (ip) y Zn vía subcutánea (sc) sobre los niveles de Fe y Cu en hígado y riñones. Después de cinco semanas ambos grupos de tratamiento (Cd y Cd+Zn) mostraron pesos de hígados anormalmente bajos con respecto al peso corporal total. Los grupos de ratas tratados sólo con Cd presentaron niveles de Fe en ambos órganos (hígados y riñones) menores que los observado en el grupo control. Los niveles de Cu en hígados permanecen practicamente constantes en función del tiempo de tratamiento mientras que el contenido renal de Cu se incrementó significativamente después de cinco semanas de tratamiento. Con respecto a los grupos de animales tratados con Cd+Zn, el contenido hepático de Fe disminuye durante la primera semana pero tiende a normalizarse después de cinco semanas, lo cual sugiere el papel protector del Zn frente a la depleción hepática de Fe inducida por Cd. El Fe renal así como el Cu renal y hepático presentaron un comportamiento similar. Se observan disminuciones e incrementos significativos después de una y cinco semanas respectivamente, lo cual se relaciona con una mayor síntesis de metalotioneínas y redistribución anómala de los metales esenciales