Search results for "Zed"
showing 10 items of 5581 documents
Synthesis, molecular structures and EPR spectra of the paramagnetic cuboidal clusters with Mo3S4Ga cores
2017
Electron precise [Mo3(l3-S)(l-S)3(diphos)3Br3]Br (diphos = dppe, dmpe) incomplete cuboidal clusters with six cluster skeletal electrons (CSE) were converted into paramagnetic cuboidal [Mo3(GaBr)(l3-S)4- (diphos)3Br3] clusters by treatment with elemental Ga. The new heterobimetallic complexes with nine CSE possess a doublet ground state with the unpaired electron density delocalized over the three molybdenum atoms.
Copper-Catalyzed Aerobic Oxidative Alkynylation of 3,4-Dihydroquinoxalin-2-ones
2019
Herein, we described a ligand-free copper-catalyzed aerobic oxidative functionalization of 3,4-dihydroquinoxalin-2(1H)-ones with terminal alkynes using visible-light and oxygen as terminal oxidant to give 3-ethynyl-3,4-dihydroquinoxalin-2(1H)-one, cyclic propargylic amines, in moderate to good yields. Moreover, we demonstrate the versatility of the 3-ethynyl-3,4-dihydroquinoxalin-2(1H)-ones obtained by preparing several 3,4-dihydroquinoxalin-2-one derivatives.
Measuring rill erosion using structure from motion: A plot experiment
2017
Abstract In this paper the results of a plot experiment on rill erosion are reported. The rill network, manually incised on the soil and further shaped by a clear inflow discharge, was surveyed using the three-dimensional photo-reconstruction (3D-PR) technique which allows to obtain a digital terrain model (DTM) by a large series of oblique images of the channel from consumer un-calibrated and non-metric cameras. The three-dimensional (3D) DTM and the quasi-tridimensional (2.5D) model were generated by Agisoft Photoscan software. For a single rill channel, the reliability of the 3D image-based ground measurements of morphological and hydraulic variables was positively tested by the correspo…
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…
Estimating Missing Information by Cluster Analysis and Normalized Convolution
2018
International audience; Smart city deals with the improvement of their citizens' quality of life. Numerous ad-hoc sensors need to be deployed to know humans' activities as well as the conditions in which these actions take place. Even if these sensors are cheaper and cheaper, their installation and maintenance cost increases rapidly with their number. We propose a methodology to limit the number of sensors to deploy by using a standard clustering technique and the normalized convolution to estimate environmental information whereas sensors are actually missing. In spite of its simplicity, our methodology lets us provide accurate assesses.
Comparison of gap-filling techniques applied to the CCI soil moisture database in Southern Europe
2021
Abstract Soil moisture (SM) is a key variable that plays an important role in land-atmosphere interactions. Monitoring SM is crucial for many applications and can help to determine the impact of climate change. Therefore, it is essential to have continuous and long-term databases for this variable. Satellite missions have contributed to this; however, the continuity of the series is compromised due to the data gaps derived by different factors, including revisit time, presence of seasonal ice or Radio Frequency Interference (RFI) contamination. In this work, the applicability of different gap-filling techniques is evaluated on the ESA Climate Change Initiative (CCI) SM combined product, whi…
Estudio de bofedales en los Andes ecuatorianos a través de la comparación de imágenes Landsat-8 y Sentinel-2
2019
[EN] The objective of the present study was to compare the Landsat-8 and Sentinel-2 images to calculate the wetland´s extension, distribution and degree of conservation, in Reserva de Producción de Fauna Chinborazo (RPFCH) protected area located in the Andean region of Ecuador. This process was developed with in situ work in 16 wetlands, distributed in different conservation levels. The Landsat-8 and Sentinel-2 images were processed through a radiometric calibration (restoration of lost lines or píxels and correction of the stripe of the image) and an atmospheric correction (conversion of the digital levels to radiance values), to later calculate the Vegetation spectral indexes: NDVI, SAVI …
Channel forms recovery in an ephemeral river after gravel mining (Palancia River, Eastern Spain)
2017
[EN] During the 1970s, the Palancia River was intensively affected by gravel mining instream. This activity completely destroyed the fluvial forms, devastating the original wandering pattern. At the end of the 1980s, gravel mining ceased and the river started a process of recovery, only altered by several clearing operations. The aim of this work is to describe these processes of change, analyzing the river's morphosedimentary conditions through a GIS analysis of aerial photographs previous to, simultaneous with, and subsequent to the intense gravel mining activity. Results explain the current difficulties of some ephemeral rivers to recover their original forms, because of the sediment and…
Mapping land surface emissivity from NDVI: Application to European, African, and South American areas
1996
Thermal infrared emissivity is an important parameter both for surface characterization and for atmospheric correction methods. Mapping the emissivity from satellite data is therefore a very important question to solve. The main problem is the coupling of the temperature and emissivity effects in the thermal radiances. Several methods have been developed to obtain surface emissivity from satellite data. In this way we propose a theoretical model that relates the emissivity to the NDVI (normalized difference vegetation index) of a given surface and explains the experimental behavior observed by van de Griend and Owe. We can use it to obtain the emissivity in any thermal channel, but in this …