Search results for "function"
showing 10 items of 14432 documents
Bowl-shape electron donors with absorptions in the visible range of the solar spectrum and their supramolecular assemblies with C 60
2012
We describe the synthesis, electronic, optical and photophysical properties of a family of three electron-donor bowl-shaped organic molecules that absorb light in the whole range of the visible spectrum (up to 800 nm in one case), and associate C60 in solution with binding constants in the range of 104–102 M−1 as measured from both UV-vis and fluorescence titrations in several solvents. These molecules are π-extended derivatives of tetrathiafulvalene, based on a truxene core to which two or three units of dithiole are covalently attached. The inclusion of the bulky dithiole groups is responsible for their bowl-shape geometry, which allows them to associate with C60, and their electron-donor…
DFT Study on the Interaction of Tris(benzene-1,2-dithiolato)molybdenum Complex with Water. A Hydrolysis Mechanism Involving a Feasible Seven-Coordina…
2016
In the present work, the reactivity of the tris(benzene-1,2-dithiolato)molybdenum complex ([Mo(bdt)3]) toward water is studied by means of the density functional theory (DFT). DFT calculations were performed using the M06, B3P86, and B3PW91 hybrid functionals for comparison purposes. The M06 method was employed to elucidate the reaction pathway, relative stability of the intermediate products, nature of the Mo–S bond cleavage, and electronic structure of the involved molybdenum species. This functional was also used to study the transference of electrons from the molybdenum center toward the ligands. The reaction pathway confirms that [Mo(bdt)3] undergoes hydrolysis, yielding dihydroxo-bis(…
Theoretical study on the decomposition mechanism of bisphenol A polycarbonate induced by the combined effect of humidity and UV irradiation.
2020
Polycarbonate (PC) is a good material for covering and protecting cultural heritage sites because of its durability, mechanical properties, and transparency. When bisphenol A polycarbonate is subjected to weathering conditions this polymer shows several degradation processes depending on the irradiation wavelength, humidity and temperature. In particular, the combined effects of humidity and UV irradiation speed up the PC molecular weight reduction. In this work, the decomposition mechanisms associated to the hydrolysis process are scrutinized and the effects of UV irradiation on the hydrolysis process are evaluated throughout the Density Functional Theory (DFT) approach. It was found that …
An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape
2016
Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrubâgrassland site in central Oregon (USA) using a modified version of Cellular Automata TreeâGrassâShrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics represented by the model were first evaluated using satellite-derived leaf area index and measured evapotranspiration data. Reconstruc…
Global trends in NDVI-derived parameters obtained from GIMMS data
2011
The Normalized Difference Vegetation Index (NDVI) has been proven to be useful to assess vegetation changes around the world, in spite of limitations such as sensitivity to cloud or snow contamination. In order to map vegetation changes at global scale, this study uses NDVI time series provided by the GIMMS (Global Inventory Modeling and Mapping Studies) group, which were fitted annually to a double logistic function. This fitting procedure allowed for retrieval of NDVI-derived parameters which were tested for trends using Mann-Kendall statistics. These trends were validated by comparison at 73 ground control points documented as change hotspots. The obtained trends for NDVI-derived paramet…
Analysis of directional effects on atmospheric correction
2013
Abstract Atmospheric correction in the Visible and Near Infrared (VNIR) spectral range of remotely sensed data is significantly simplified if we assume a Lambertian target. However, natural surfaces are anisotropic. Therefore, this assumption will introduce an error in surface directional reflectance estimates and consequently in the estimation of vegetation indexes such as the Normalized Difference Vegetation Index (NDVI) and the surface albedo retrieval. In this paper we evaluate the influence of directional effects on the atmospheric correction and its impact in the NDVI and albedo estimation. First, we derived the NDVI and surface albedo from data corrected assuming a Lambertian surface…
Quantifying and easing conflicting goals between interest groups in natural resource planning
2019
Management of natural resources at the regional level is a compromise between a variety of objectives and interests. At the local level, management of the forests depends upon the ownership structure, with forest owners using their forests as they see fit. A potential conflict occurs if the forest owners’ management decisions are counter to the interests of society in general or the industry that relies on the forest resource as their raw material. We explore the intensity of this conflict at the regional level in several large boreal forest production landscapes. To explore the conflict, we investigate three main interest groups: (i) economically oriented forest owners; (ii) industry grou…
Automatic emulator and optimized look-up table generation for radiative transfer models
2017
This paper introduces an automatic methodology to construct emulators for costly radiative transfer models (RTMs). The proposed method is sequential and adaptive, and it is based on the notion of the acquisition function by which instead of optimizing the unknown RTM underlying function we propose to achieve accurate approximations. The Automatic Gaussian Process Emulator (AGAPE) methodology combines the interpolation capabilities of Gaussian processes (GPs) with the accurate design of an acquisition function that favors sampling in low density regions and flatness of the interpolation function. We illustrate the good capabilities of the method in toy examples and for the construction of an…
Multioutput Automatic Emulator for Radiative Transfer Models
2018
This paper introduces a methodology to construct emulators of costly radiative transfer models (RTMs). The proposed methodology is sequential and adaptive, and it is based on the notion of acquisition functions in Bayesian optimization. Here, instead of optimizing the unknown underlying RTM function, one aims to achieve accurate approximations. The Automatic Multi-Output Gaussian Process Emulator (AMO-GAPE) methodology combines the interpolation capabilities of Gaussian processes (GPs) with the accurate design of an acquisition function that favors sampling in low density regions and flatness of the interpolation function. We illustrate the promising capabilities of the method for the const…
Optimal modalities for radiative transfer-neural network estimation of canopy biophysical characteristics: Evaluation over an agricultural area with …
2011
International audience; Neural networks trained over radiative transfer simulations constitute the basis of several operational algorithms to estimate canopy biophysical variables from satellite reflectance measurements. However, only little attention was paid to the training process which has a major impact on retrieval performances. This study focused on the several modalities of the training process within neural network estimation of LAI, FCOVER and FAPAR biophysical variables. Performances were evaluated over both actual experimental observations and model simulations. The SAIL and PROSPECT radiative transfer models were used here to simulate the training and the synthetic test dataset…