Search results for "electromagnetic [current]"
showing 10 items of 1008 documents
Remote Estimation of Canopy Water Content in Different Crop Types with New Hyperspectral Indices
2018
A diverse range of vegetation indices have earlier been developed for the remote estimation of canopy water content (CWC), but most of them are not universally applicable. The aim of this study is to define new indices valid for a wide variety of crop types, that allow to obtain CWC maps at a large spatial scale. These indices were developed based on PROSAIL simulations and then optimized with an experimental dataset (SPARC03; Barrax, Spain), which consists of field data including water content and other biophysical parameters collected for 6 different crops (lucerne, corn, potato, sugar beet, garlic and onion) and associated TOC reflectance spectra acquired by the HyMap airborne sensor. Sp…
Estimating chlorophyll content of crops from hyperspectral data using a normalized area over reflectance curve (NAOC)
2010
Abstract The Normalized Area Over reflectance Curve (NAOC) is proposed as a new index for remote sensing estimation of the leaf chlorophyll content of heterogeneous areas with different crops, different canopies and different types of bare soil. This index is based on the calculation of the area over the reflectance curve obtained by high spectral resolution reflectance measurements, determined, from the integral of the red–near-infrared interval, divided by the maximum reflectance in that spectral region. For this, use has been made of the experimental data of the SPARC campaigns, where in situ measurements were made of leaf chlorophyll content, LAI and fCOVER of 9 different crops – thus, …
Synthesis and Characterization of Carbazole-Linked Porphyrin Tweezers
2015
Herein the synthesis, spectroscopic characterization, two-photon absorption and electrochemical properties of 3,6-disubstituted carbazole tweezers is reported. A dimer resulting from a Glaser homocoupling was isolated during a Sonogashira coupling reaction between a diethynyl-carbazole spacer and a 5-bromo-triarylporphyrin and the properties of this original compound were compared with the 3,6-disubstituted carbazole bisporphyrin tweezers. The dyads reported herein present a two-photon absorption maximum at 920 nm with two-photon absorption cross-section in the 1200 GM range. Despite a strong linear absorption in the Soret region and moderate fluorescence quantum yield, they both lead to a …
Experimental evidence of E’_gamma centers generation from oxygen vacancies in a-SiO2
2007
Abstract We report on the thermal treatment effects in a γ-ray irradiated oxygen deficient amorphous silicon dioxide (a-SiO2) containing Al impurities. We observed that by thermal treatments the intensity of the 7.6 eV optical absorption band, associated to an oxygen deficient center, and the EPR signal amplitude of irradiation induced [AlO4]0 centers gradually decrease. During these thermal treatments, the E γ ′ centers concentration is found to increase in a correlated way to the decrease of the 7.6 eV absorption amplitude. These results are interpreted assuming an hole-transfer process from the [AlO4]0 centers to the diamagnetic oxygen vacancies, resulting in the generation of E γ ′ cent…
Resonance ionization spectroscopy of fermium (Z=100)
2003
Laser spectroscopy has been applied for the first time to measure resonant transition frequencies of fermium (Zs 100). A number of 2.7=10 atoms was electrodeposited on a Ta filament and covered with a 1 mm Ti layer. Fm 10
Three-dimensional orientational colocalization of individual donor--acceptor pairs.
2004
We report on the determination of the three-dimensional orientation of the donor and acceptor transition dipoles in individual fluorescence resonance energy transfer (FRET) pairs by means of scanning optical microscopy with annular illumination. Knowledge of the mutual orientation of the donor and acceptor dipole is mandatory for reliable distance determination based on FRET efficiency measurements. In our model system perylenediimide as the donor and terryelenediimide as the acceptor are coupled via a stiff p-terphenyl linker. The absorption dipoles of the donor and acceptor are selectively addressed by the 488 nm and 647 line of an Ar/Kr mixed gas laser, respectively. A clear deviation fr…
Enhanced nonlinear optical properties and thermal stability of donor-acceptor substituted oligothiophenes
1997
Abstract Linear and nonlinear optical properties of a series of novel donor-acceptor substituted α-oligothiophenes were investigated by means of electrooptical absorption measurements (EOAM) and electric field induced second harmonic generation (EFISH). The second-order polarizabilities β(−2ω; ω, ω) were related to dipole changes Δμ ag and transition dipoles μ ag associated with low-lying charge-transfer (CT) excitations by using the perturbational two-level approximation. Systematic variation of the donor and acceptor groups led to compounds with exceptional nonlinearity and thermal stability. Too strong donor/acceptor pairs, however, yielded structures in the charge-resonance (CR) limit w…
Nonlinear optical spectra of conjugated polymers: Effect of long-range coulomb interactions
1993
Abstract Nonlinear optical spectra of conjugated polymers are theoretically studied in the Su-Schrieffer-Heeger model supplemented by long-range Coulomb interactions. Excitonic correlation for electron-hole excitations in explicitly taken into account by a standard method. Nonlinear susceptibilities χ (3) are calculated numerically with a standard sum-over-states method for finite chains (up to 1000 sites). Using moderate interaction strength, our calculations can reproduce many distinct features observed in the linear and nonlinear spectra (two-photon absorption, third-harmonic generation, and electroabsorption) of polydiacetylenes and some other polymers. Especially, a hump in the spectru…
Impact of the synergistic collaboration of oligothiophene bridges and ruthenium complexes on the optical properties of dumbbell-shaped compounds.
2012
The linear and non-linear optical properties of a family of dumbbell-shaped dinuclear complexes, in which an oligothiophene chain with various numbers of rings (1, 3, and 6) acts as a bridge between two homoleptic tris(2,2'-bipyridine)ruthenium(II) complexes, have been fully investigated by using a range of spectroscopic techniques (absorption and luminescence, transient absorption, Raman, and non-linear absorption), together with density functional theory calculations. Our results shed light on the impact of the synergistic collaboration between the electronic structures of the two chemical moieties on the optical properties of these materials. Experiments on the linear optical properties …
Time-resolved luminescence and induced absorption in PbWO4
1997
Abstract Luminescence and short-lived induced absorption are studied for two undoped PbWO4 crystals. Luminescence decay at LNT is delayed relative to irradiation pulse. The delay observed is either due to reabsorption of luminescence or due to creation of luminescence center excited states via energy or/and charge transfer after irradiation pulse. Short-lived absorption is observed within 1.1–3.6 eV spectral region at LNT as well as at RT. It is proposed that the short-lived absorption band peaking at ~ 3.5 eV is intrinsic.