Search results for " Spectra"
showing 10 items of 709 documents
Direct determination of polymerised triacylglycerides in deep-frying vegetable oil by near infrared spectroscopy using Partial Least Squares regressi…
2012
Abstract A green method for the determination of polymerised triacylglyceride (PTG) in deep-frying vegetable oils of different botanic origin has been developed employing near infrared (NIR) spectroscopy and Partial Least Squares (PLS) regression. Four different types of oil were heated during several hours, with and without the addition of foodstuff. NIR transmission spectra were obtained directly from sample aliquots stored in glass vials, thus avoiding the consumption of solvents and minimising waste generation. Variables employed for building the PLS models were selected applying interval PLS (iPLS) as well as Uninformative Variable Elimination-PLS (UVE-PLS). A global PLS model using sp…
Radiation hardening of Rare-Earth doped fiber amplifiers
2012
We investigated the radiation hardening of optical fiber amplifiers operating in space environments. Through a real-time analysis in active configuration, we evaluated the role of Ce in the improvement of the amplifier performance against ionizing radiations. Ce-codoping is an efficient hardening solution, acting both in the limitation of defects in the host glass matrix of RE-doped optical fibers and in the stabilization of lasing properties of the Er3+-ions. On the one hand, in the nearinfrared region, radiation induced attenuation measurements show the absence of radiation induced P-related defect species in host glass matrix of the Ce-codoped active fibers; on the other hand, in the Ce-…
Linear and nonlinear fiber propagation of partially coherent fields exhibiting temporal correlations
2019
International audience; Using ultrafast photonic first-order differentiator applied on a partially coherent field, we report the generation of two correlated temporal waveforms and study their correlation properties upon linear and nonlinear propagation along the two orthogonal polarization axis of a dispersive optical fiber. Temporal correlations are maintained in linear propagation whereas Kerr nonlinearity generates anti-correlated temporal intensity patterns for both partially and uncorrelated fields. Experiments are in close agreement with the theoretical analysis.
Tunable microwave photonic filter based on chirped fiber gratings working with a single optical carrier at constant wavelength
2007
This paper presents a tunable transversal filter working with a single optical carrier at constant wavelength. The filter consists of a set of chirped gratings whose time delay is tuned with respect to the emission wavelength of a fiber laser by a piezoelectric actuator; extra lengths of fiber are inserted in the filter arms in order to avoid interferences between signals reflected in different gratings. Two and three taps filters are experimentally demonstrated, the filters transfer function is electronically tuned within the free spectral range.
Plasmonics co-integrated with silicon nitride photonics for high-sensitivity interferometric biosensing
2019
We demonstrate a photonic integrated Mach-Zehnder interferometric sensor, utilizing a plasmonic stripe waveguide in the sensing branch and a photonic variable optical attenuator and a phase shifter in the reference arm to optimize the interferometer operation. The plasmonic sensor is used to detect changes in the refractive index of the surrounding medium exploiting the accumulated phase change of the propagating Surface-Plasmon-Polariton (SPP) mode that is fully exposed in an aqueous buffer solution. The variable optical attenuation stage is incorporated in the reference Si3N4 branch, as the means to counter-balance the optical losses introduced by the plasmonic branch and optimize interfe…
Scene-based spectral calibration assessment of high spectral resolution imaging spectrometers
2009
An accurate knowledge of the spectral calibration of imaging spectrometers is required for optimum data processing and interpretation. The scene-based spectral characterization of imaging spectrometers is frequently necessary to update or replace the pre-flight laboratory-based spectral characterization supplied by the data provider. An automatic method for the estimation of spectral calibration parameters (channel position and bandwidth) at atmospheric absorption regions from high spectral resolution imaging spectrometers (spectral sampling interval below 5 nm) is presented in this contribution. The method has been tested on two commercial instruments with spectral sampling intervals below…
Spectral properties of random non-self-adjoint operators
2015
In this thesis we are interested in the spectral properties of random non-self-adjoint operators. Weare going to consider primarily the case of small random perturbations of the following two types of operators: 1. a class of non-self-adjoint h-differential operators Ph, introduced by M. Hager [32], in the semiclassical limit (h→0); 2. large Jordan block matrices as the dimension of the matrix gets large (N→∞). In case 1 we are going to consider the operator Ph subject to small Gaussian random perturbations. We let the perturbation coupling constant δ be e (-1/Ch) ≤ δ ⩽ h(k), for constants C, k > 0 suitably large. Let ∑ be the closure of the range of the principal symbol. Previous results o…
High-pressure NMR spectroscopy: An in situ tool to study tin-catalyzed synthesis of organic carbonates from carbon dioxide and alcohols. Part 2 [1]
2015
Dialkoxide diorganotin(IV) complexes are known to readily react with carbon dioxide under pressure and they are considered as suitable catalyst precursor models for the direct synthesis of organic carbonates. To gain a better understanding of CO2 insertion processes with Sn-OR bonds, the reactivity of n-Bu2Sn(OCH(CH3)(2))(2) (2) was investigated using high-pressure NMR (HP-NMR) spectroscopy. In deuterated solvents (isopropanol-d(8) and toluene-d(8)) under 50 bar of CO2 pressure at 80 degrees C, Sn-119{H-1} NMR experiments revealed the exclusive formation of an unprecedented tetraorganodistannoxane species, characterized as the bis[diisopropycarbonatotetrabutyldistannoxane] complex, {[n-Bu2S…
Substituted methyl 5β-cholan-24-oates. I—17O NMR spectral characterization
1994
Methyl esters of four common bile acids, 3α-hydroxy-5-β-cholan-24-oic (lithocholic) acid, 3α, 7α-dihydroxy-5β-cholan-24-oic (chenodeoxycholic) acid, 3α,12α-dihydroxy-5β-cholan-24-oic (deoxycholic) acid and 3α,7α,12α-trihydroxy-5β-cholan-24-oic (cholic) acid, and 14 acetylated, trifluoroacetylated, mesylated and oxo derivatives of methyl 5β-cholan-24-oates were prepared and their 17O NMR spectra recorded. In spite of their relatively high molecular masses and the rigid molecular structure of the steroid skeleton, most of the oxygens included in these structures gave well resolved 17O NMR resonance lines at natural abundance in 0.25–0.5 M acetonitrile solutions at 75°C. In agreement with the …
High-Resolution Fluorescence Spectra of Airborne Biogenic Secondary Organic Aerosols: Comparisons to Primary Biological Aerosol Particles and Implica…
2021
Aqueous extracts of biogenic secondary organic aerosols (BSOAs) have been found to exhibit fluorescence that may interfere with the laser/light-induced fluorescence (LIF) detection of primary biological aerosol particles (PBAPs). In this study, we quantified the interference of BSOAs to PBAPs by directly measuring airborne BSOA particles, rather than aqueous extracts. BSOAs were generated by the reaction of d-limonene (LIM) or α-pinene (PIN) and ozone (O3) with or without ammonia in a chamber under controlled conditions. With an excitation wavelength of 355 nm, BSOAs exhibited peak emissions at 464–475 nm, while fungal spores exhibited peak emissions at 460–483 nm; the fluorescence intensit…