Search results for "surface energy"

Effects of Gamma Irradiation on the Kinetics of the Adsorption and Desorption of Hydrogen in Carbon Microfibres

2013

In this study, three types of carbon fibres were used, they were ex-polyacrylonitrile carbon fibres with high bulk modulus, ex-polyacrylonitrile fibres with high strength, and vapour grown carbon fibres. All the samples were subjected to a hydrogen adsorption process at room temperature in an over-pressured atmosphere of 25 bars. The adsorption process was monitored through electrical resistivity measurements. As conditioning of the fibres, a chemical activation by acid etching followed by ¿-ray irradiation with 60Co radioisotopes was performed. The surface energy was deter-mined by means of the sessile drop test. Both conditioning treatments are supplementary; the chemical activation works…

Assessing opportunities for water savings in large-scale pressurized irrigation systems using actual evapotranspiration retrieved by surface energy b…

Remote sensing allows the observation of large land stretches and the acquisition of worthwhile information that can be used efficaciously in agro-hydrologic systems. Satellite imagery associated to computational models provide a reliable resource in estimating evapotranspiration (ET) fluxes based on surface energy balance. On irrigated crops, quantifying the spatial distribution of actual ET enables a broad range of applications such as irrigation management, monitoring water distribution, assessing crop water status and irrigation system performance. The general objective of the research was to propose a methodology to estimate ET by using Landsat Thematic Mapper (TM) images and surface e…

Assessing the performance of a large-scale irrigation system by estimations of actual evapotranspiration obtained by Landsat satellite images resampl…

2019

Abstract Remote sensing techniques allow monitoring the Earth surface and acquiring worthwhile information that can be used efficiently in agro-hydrological systems. Satellite images associated to computational models represent reliable resources to estimate actual evapotranspiration fluxes, ETa, based on surface energy balance. The knowledge of ETa and its spatial distribution is crucial for a broad range of applications at different scales, from fields to large irrigation districts. In single plots and/or in irrigation districts, linking water volumes delivered to the plots with the estimations of remote sensed ETa can have a great potential to develop new cost-effective indicators of irr…

Comparison between energy balance and mass balance models for actual evapotranspiration assessment

2009

The assessment of the water needs for a specific crop has a fundamental importance in the management of water resources. The application of empirical models able to retrieve estimates of the actual evapotranspiration (ETa) to assess the need for water could give a valid tool for the planning of water supply, avoiding unnecessary water losses. In this context, two independent models for estimating actual evapotranspiration were compared. The first model is based on an energy balance and uses remotely sensed data and ancillary data from weather stations to assess the ETa. The second model also uses remotely sensed data and climatic data on a daily basis from a weather network. Field measureme…

Hydrogenation of acetylene-ethylene mixtures on Pd catalysts: study of the surface mechanism by computational approaches. Metal dispersion and cataly…

2000

The hydrogenation mechanism of acetylene–ethylene mixtures on Pd catalysts under different experimental conditions was studied by employing a time-dependent Monte Carlo approach set to use a fixed series of event probabilities. The dependence of the catalyst activity and selectivity on the sizes of the metal particles was simulated at microscopic level and the results, also refined by fitting procedures, suggested proper explanations for the apparent nonuniformity of the related experimental findings. The use of the steric hindrance parameter of the surface species and the available surface energy on the metallic catalyst sites was decisive for reproducing the experimental results.

The structure of reactive grain-boundaries under stress containing confined fluids

2006

We present numerical experiments on structure development in grain-boundaries during dissolution–precipitation creep. Two solids that are represented by an elastic spring configuration are pressed together with a compressible fluid in the grain-boundary. The solid can dissolve or precipitate depending on elastic and surface energy as well as fluid pressure and concentration of dissolved material in the fluid. We perform a number of numerical experiments with different starting configurations that represent a large-scale island-channel interface with solid–solid contacts across the islands, a rough grain-boundary interface with a fluid along the whole interface and a smooth thin-film interfa…

An empirical model for free surface energy of strained solids at different temperature regimes.

2006

Abstract We have developed an empirical formulation, based on the elastic theory, to calculate the variation of the surface free energy when a crystal is strained in the elastic regime. The model permits to obtain the variation of the surface energy at different strains and temperatures when are known the thermal dependence on the bulk and surface elastic constants. Molecular dynamics (MD) simulations were performed using the three low index surfaces of Al, to validate the accuracy of the model. The comparison between the empirical model and the MD simulations shows a good agreement for temperatures ranging between 0 and 900 K, and for deformation between −2% and 2%.

Atomistic Simulations of the LaMnO3 (110) Polar Surface.

2003

The results of atomic structure calculations, with a focus on the surface relaxation and polarization, are presented for the LaMnO3 (110) O-terminated polar surface. We compare results of the classical shell model calculations for four possible terminations, including (1 × 2) (110) surface reconstruction, and demonstrate that the latter has the lowest surface energy. The surface energy is saturated only when six to eight near-surface atomic planes are relaxed which is accompanied by the considerable dipole moments perpendicular to the surface. Results are compared with those for iso-structural BaTiO3 (110) surfaces.

Ab Initio Calculations of SrTiO3 (111) Surfaces

2012

The paper presents the results of calculations of SrTiO3 polar (111) surface relaxations and energetics using the ab initio code CRYSTAL and a hybrid description of exchange and correlation. Using a hybrid B3LYP approach, the surface relaxation has been calculated for the two possible Ti and SrO3 SrTiO3 (111) surface terminations. For both Ti and SrO3-terminated SrTiO3 (111) surfaces upper layer atoms, with the sole exception of SrO3-terminated surface Sr atom, relax inwards. The calculated surface relaxation energy for Ti-terminated SrTiO3 (111) surface is almost five times larger, than the surface relaxation energy for SrO3-terminated SrTiO3 (111) surface. The surface energy for Ti-termin…

Ab InitioCalculations of the Atomic and Electronic Structure of SrZrO3(111) Surfaces

2012

The paper presents and discusses the results of calculations of surface relaxations and energetics for the polar (111) surface of SrZrO3 using a hybrid B3LYP description of exchange and correlation. On the (111) surface, I consider both Zr- and SrO3-terminations. For both Zr and SrO3-terminated SrZrO3 (111) surfaces upper layer atoms relax inwards. The second layer atoms, with the sole exception of Zr-terminated SrZrO3 (111) surface Sr atom, relax outwards. The calculated surface relaxation energy for Zr-terminated SrZrO3 (111) surface is almost sixteen times larger, than the surface relaxation energy for SrO3-terminated SrZrO3 (111) surface. The surface energy for Zr-terminated SrZrO3 (111…