Optical Spectral Data Research Articles

Linear spectral mixture modelling to estimate vegetation amount from optical spectral data

Abstract Spectral mixture modelling has developed in recent years as a suitable remote sensing tool for analysing the biophysical and compositional character of ground surfaces. In this paper the potentiality of the linear spectral mixture model to extract vegetation related parameters from 0·4-2·5 μm reflectance data has been tested. High spectral resolution reflectance measurements of soil-plant mixtures with different soil colour and plant densities were carried out in a laboratory experiment. The constrained least-squares and the factor analysis unmixing procedures were applied to generate endmember fractions of the components present in the mixtures and to test the validity of the model. It is concluded that the derived fraction of the vegetation endmember is less sensitive to soil background than the NDV[. The accuracy attainable by this modelling approach can be considered sufficient for many practical purposes, being operational in the monitoring of vegetation from satellite data.

Atrazine Complexation by Soil Humic Acids

Atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] complexation pathways with soil humic acid remain a controversial issue, in part because of the absence of direct spectroscopic information. Recent optical and magnetic resonance spectral data indicate that proton-transfer and, to a lesser extent, hydrogen bonding are as important as electron-transfer in the mechanisms of reaction between atrazine and humic acid, whereas other s-triazines appear to react more strongly by electron transfer mechanisms. Two representative temperate-zone humic acids were selected to probe the issue of complexation mechanisms more decisively. They were reacted at pH < 7 with 140 mmol m -3 atrazine solution under exdusion of light. Infrared and electron spin resonance spectra of the resulting products gave evidence for proton-transfer and, under certain conditions, electron-transfer reactions. The spectroscopic data, and those from other published studies, were analyzed in terms of the molecular properties of humic acids and s-triazines. The analysis suggested a general guiding principle to characterize the complexation mechanisms of s-triazines with soil humic acids. Proton-transfer is favored (and electron-transfer is disfavored) for humic acids of high acidic functional group content and for s-triazines of low basicity. Electron-transfer mechanisms are favored for humic acids of low acidic functional group content and for s-triazines of high basicity. This principle illustrates the importance of specific molecular structure, as opposed to class structure, to understanding reactivity between the s-triazines and humic acids.

Stability and Conformational Analysis of Tc-RC160 and Re-RC160: Experimental and Theoretical Analysis of the Influence of Metal Complexation on the Structural Requisites for Activity

The biological significance of somatostatin and related synthetic peptide analogs is well documented. These peptide analogs have demonstrated inhibitory effects on the growth of certain tumor lines including prostate, breast, and pancreas. Metal−peptide analogs have been developed for imaging small tumors overexpressing somatostatin receptors, i.e. receptor-based scintigraphy. Receptor-based scintigraphy requires that the binding constant of the metal−peptide analog be competitive with that of the native somatostatin analog. For these applications an isotope of technetium, 99mTc is a particularly useful label. To address the effect of added label on the native peptide conformation and predicted impact on its efficacy as a therapeutic imaging agent, a combination of experimental and computational techniques were used. In this work, a complete analysis of an active Tc- or Re-labeled somatostatin analog is provided through comparison of optical, MS, and NMR data. Computational modeling has assisted in providing a profile of energetic preferences for the various coordination isomers. Coupled with optical spectral data this modeling also provides a description of the electronic states giving the characteristic bands in the optical spectra and helps to describe the redox activity and stability of the complex. On the basis of this information the structure of a major isomer is proposed. The analysis suggests that only certain coordination isomers will be accommodated by peptide without significant distortion of the “active” conformation. Furthermore, this work provides useful information for the rational design of labeled peptides with increased stability.

Electron Paramagnetic Resonance (EPR) and optical absorption spectra of VO 2+ ions in K 2SO 4Na 2SO 4ZnSO 4 glasses

Electron Paramagnetic Resonance (EPR) spectra of K 2SO 4Na 2SO 4ZnSO 4 glasses containing 3 mol.% of vanadium sulphate have been studied. Spin-Hamiltonian parameters ( g ∥, g ⊥, A ∥, A ⊥), the dipolar hyperfine coupling parameter ( P), the Fermi contact interaction parameter ( K) and the tetragonality of the V 4+ site ( Δg ∥ Δg ⊥ ) have been calculated. The optical absorption spectra of VO 2+ ions doped these glasses show three bands. By correlating the EPR and optical spectral data, the molecular orbital parameters have been evaluated. Results agree with similar studies made earlier.

World Patent Information : HEКOTOPЫE BOзMOзHOCTИ БAзЫ ДAHHЫЧ “ПATEHTЫ” ПPИ OПPEДEЛEHИИ ПOЛИTИКИ ФИPMЫ Beнчиcлaв Cтeфaнoв Vol. 17(3), pp. 201–204

Na2O–PbO–Al2O3–B2O3 (NPAB) glasses mixed with different concentrations of WO3 (ranging from 0 to 2.5 mol%) are synthesized by conventional melt quenching method. The samples are characterized by X-ray diffraction (XRD), optical absorption, Electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) spectroscopic techniques. Glass formation is confirmed by X-ray diffraction spectra. The optical absorption spectra of these glasses exhibited a predominant broad band peak at about 850–870 nm is identified due to dxy–dx2−y2 transition of W5+ ions. From the optical absorption spectral data, optical band gap (Eopt) and Urbach energy (ΔE) are evaluated. From EPR spectra the strength of the signal is increased and hyperfine splitting is resolved with increasing concentration of WO3 in the glass matrix. The FT-IR spectral studies have pointed out the existence of conventional BO3, BO4, B–O–B, PbO4, WO4 and WO6 structural units of these glasses. Various physical properties and optical basicity are also evaluated with respect to the concentration of WO3 ions.

World Patent Information : КOMMEHTAPИЙ К ПATEHTHOMУ ДEКPETУ 1994 ГOДA (# 13 oт 1994 г.), ДOПOЛHЯЮЩEMУ ИHДИЙCКИЙ ПATEHTHЫЙ зAКOH 1970 г. qP.Гaнгyли Vol. 17(3), pp. 193–194

Na2O–PbO–Al2O3–B2O3 (NPAB) glasses mixed with different concentrations of WO3 (ranging from 0 to 2.5 mol%) are synthesized by conventional melt quenching method. The samples are characterized by X-ray diffraction (XRD), optical absorption, Electron paramagnetic resonance (EPR) and Fourier transform infrared (FT-IR) spectroscopic techniques. Glass formation is confirmed by X-ray diffraction spectra. The optical absorption spectra of these glasses exhibited a predominant broad band peak at about 850–870 nm is identified due to dxy–dx2−y2 transition of W5+ ions. From the optical absorption spectral data, optical band gap (Eopt) and Urbach energy (ΔE) are evaluated. From EPR spectra the strength of the signal is increased and hyperfine splitting is resolved with increasing concentration of WO3 in the glass matrix. The FT-IR spectral studies have pointed out the existence of conventional BO3, BO4, B–O–B, PbO4, WO4 and WO6 structural units of these glasses. Various physical properties and optical basicity are also evaluated with respect to the concentration of WO3 ions.

Spectra, energy levels and up-conversion effect of erbium ions in LiNbO 3 crystals

The Optical properties and spectral data of erbium-doped Lithium Niobate crystals, including absorption spectrum, emission spectrum, luminescence lifetime and up-conversion effects are reported in this paper. The energy level scheme, Stark splitting under crystal field and up-conversion mechanism are discussed in detail. The possible applications of this material in waveguide optics and opto-electronics are also prospected.

Investigation of True Ni2+–Halogen Distances in Alkali Halide Lattices

AbstractUsing the μkα model of Ni2+−6X− clusters the true distances between impurity Ni2+ cation and halogen anion in alkali halide lattices are estimated from the optical spectral data. The results suggest that the true impurity cation‐ligand anion distances are close to the sum of ionic radii of the impurity cation and anion but not the cation‐anion distance of the perfect lattices in the case that the ionic radius of host cation is larger than that of impurity cation.

Synthesis and spectroscopy of mono- and di-nuclear copper complexes of a pyrazolylcyclotriphosphazene. Crystal structure of an unusual cyclotriphosphazene-bridged dicopper complex

The mononuclear copper(II) complexes [CuL(ClO4)(H2O)2]ClO4 and [CuL(bipy)(ClO4)]ClO4[L = 2,2,4,4,6,6-hexakis(3,5-dimethylpyrazolyl)-2λ5,4λ5,6λ5-cyclotriphosphaza-1,3,5-triene] have been prepared and characterized by optical, EPR and IR spectral data. The crystal structure of an unusual cyclophosphazene-bridged dicopper complex [H2dmpz][(CuCl2)2{N3P3O(dmpz)5}](Hdmpz = 3,5-dimethylpyrazole) has been determined: space group P, a= 11.640(3), b= 14.497(14), c= 14.775(3), α= 77.62(6), β= 82.10(2), γ= 74.88(6)°, and Z= 2. The geometry around both copper atoms is a distorted trigonal bipyramidal with the axial positions occupied by pyrazolyl pyridinic nitrogens and the equatorial positions by one cyclophosphazene ring nitrogen and two chlorine atoms.

ESR and optical absorption spectra of VO 2+ ions in Na 2SO 4ZnSO 4 glasses

Electron spin resonance spectra of Na 2SO 4ZnSO 4 glasses doped with VO 2+ ions are reported at 300 K for different composition of the glasses. The spin-Hamiltonian parameters are determined from the ESR spectrum. The optical absorption spectra has also been studied. By correlating the ESR and optical spectral data, the molecular orbital coefficients have been evaluated. ESR and optical absorption studies reveal the VO 2+ ions go substitutionally to zinc ion sites.

Investigation and Modeling of Mixed Halogen Freon/Oxygen Plasma Chemistries for Tungsten Etching

Chlorofluorocarbon/oxygen reactive‐ion etch (RIE) chemistries for tungsten etching exhibit a thermal etch rate independence not associated with . Substitution of for in the system has led to the discovery that the role of the chlorofluorocarbon is essentially one of atomic Cl generation. Etch rate and optical emission spectral data obtained from plasma and RIE‐mode etching, from selective loading experiments, and from variation of the macroscopic process control parameters for the chlorofluorocarbon/oxygen systems, have led to the formulation of a hypothetical reaction pathway involving neutrals. By the proposed mechanism, atomic Cl is thought to be indirectly responsible for improving the contact efficiency between the plasma and metallic tungsten. Etch rate models based upon this hypothesis are shown to agree well with actual data.

EPR and optical studies of vanadyl ion in magnesium thallium sulphate hexahydrate

Results of EPR and optical studies of vanadyl ion (VO 2+ ) doped in magnesium thallium sulphate hexahydrate are reported. The spin-Hamiltonian parameters are determined from the powder EPR spectra at room temperature. The optical absorption spectra at room and liquid nitrogen temperatures have also been studied. By correlating the EPR and optical spectral data, the molecular orbital bonding parameters have been evaluated.

Evaporation and Energy Transfer for a Partially Molten, Laser‐Heated Sapphire Filament

Molten regions were formed on 0.025‐cm‐diameter sapphire filaments that were heated from one side with a continuouswave CO2 laser beam in a low‐pressure flow reactor. As the laser intensity was increased, the liquid/solid interface moved from the laser‐heated edge to the opposite edge of the filament, the apparent temperature measured in the molten region with an optical pyrometer increased from 1470 ± 25 to 2040 ± 30 K, and the filament evaporation rate increased by a factor of 1.6. This change in apparent temperature resulted from an increase in the spectral emittance with the liquid layer thickness. The change in evaporation rate resulted from a 1.09 times larger evaporating area, a 1.24 ± 0.09 times larger evaporation coefficient, and a 10 ± 5 K larger average temperature when the filament cross section was completely liquid than when liquid first formed on the solid filament. Optical and energy‐transfer properties of sapphire and liquid Al2O3 were calculated from optical pyrometry, energy‐balance measurements, and spectral absorption coefficient data for sapphire. At the melting temperature, the total emittance is approximately 0.051 and 0.31 ± 0.03 for the solid sapphire and liquid aluminum oxide filaments, respectively. The thermal accommodation coefficient for Ar atoms is 0.53 ± 0.07 on the solid and approximately unity on the liquid. The spectral absorption coefficient, kλ, at the optical pyrometer wavelength (0.665 μm) is 0.1 ± 0.04 cm−1 for the solid and 12 ± 12 cm−1 for the liquid. This value of kλ for solid sapphire at the melting point is 12 times that of pure, void‐free material and reflects the influence of impurities and small voids in the sapphire filaments that were used.

Mass loss in a B2 IIIe star - Omega Orionis 1978-1984

A combination of long-term optical polarimetric, photometric, spectrometric, and UV spectral data has confirmed that all the observed portions of Omega Ori's outer atmosphere are variable on a variety of time scales. The shortest confirmed variations are detectable over a few hours, and the longest changes are observed on time scales of years. A straightforward interpretation of the available data is that the continuum polarization, continuum-magnitude changes, and color changes produced are in a presumably equatorial disk close to the stellar photosphere.

Molecular hyperfine interactions in Ag(CO)3

Relativistic molecular orbital calculations in the multiple scattering approximation are reported for silver tricarbonyl, and comparisons are made to optical absorption and electron spin resonance spectra. Spin–orbit effects are modelled through the Dirac scattered-wave (DSW) formalism. Spin–polarization effects are estimated from quasirelativistic spin-unrestricted calculations. The influence of different local density potentials on the spin distributions and hyperfine tensors are examined. The calculations show good agreement with optical spectral data and with the observed 107Ag and 13C hyperfine tensors. The use of relativistic exchange–correlation potentials in calculating spin-dependent properties leads to a slightly better agreement with experiment. The calculations predict that the unpaired electron in Ag(CO)3 has about 40% silver 5pz character.

High-Resolution Optical and Ultraviolet Absorption-Line Studies of Interstellar Gas

Recent progress in the characterization of the interstellar medium (ISM) by means of optical and UV spectral data is summarized. The gas is studied by focusing on background stars whose spectra can be accurately modeled to provide the light source for the absorption-line scans. The capabilities of earth- and space-based instruments which have been and are used for the surveys are delineated. The distributions of diffuse gas densities and characteristics of the cold, warm and hot gas in the Galaxy are described in terms of the elemental abundances, kinetics and distributions of the gas. Particular note is taken of gas in the solar neighborhood and around SNR, and of absorption-line data of cosmological significance.

Comparison of the results of theoretical calculations with experimental measurements from the Los Alamos free electron laser oscillator experiment

A comparison between some of the measurements made with a uniform wiggler during the Los Alamos free electron laser oscillator experiment and the results of one-dimensional pulse propagation calculations using the mathematical model of Colson and Ride will be presented. Small-signal gain data will be discussed. Calculated output power vs optical resonator length will be compared with data. Time-integrated optical spectral data, which show clear evidence for Raman sidebands, will be compared with calculated spectra as a function of resonator length. The calculated electron energy distribution function, using the measured electron-beam micropulse shape, and the associated extraction efficiency will be compared with measurements.

Absorption spectrum of VO 2+ ion doped in caesium cadmium sulphate hexahydrate single crystal

Results of the optical absorption spectrum of VO 2+ ion doped in caesium cadmium sulphate hexahydrate studied at room (300 K) and liquid nitrogen (77 K) temperatures are reported. The site symmetry of the ion is found to be C 4ν. Correlating the optical and ESR spectral data, the molecular orbital coefficients are evaluated.

Preparation and m�ssbauer studies of tetraaquabis[maleato(1-)]-iron(II)

Tetraaquabis[maleato(1-)]iron(II), Fe(C4H3O4)2 · 4H2O has been synthesised. The compound is monomeric and is isomorphous with the manganese(II) analogue. The temperature dependence of quadrupole splitting and optical spectral data giveca. 10000 cm−1,ca. 650 cm−1,ca. 190 cm−1 andca. 1400 cm−1 for the 10 Dq, tetragonal field, rhombic field and the splitting of the Eg level, respectively. The quadrupole splitting data indicate that distortion from cubic symmetry increases in the order oxalate < malonate < maleate. DTA, TGA and Mossbauer studies indicate elimination of one molecule of maleic acid at 235 °C. The resulting product shows a less distorted structure and this is attributed to the formation of maleato(2-)iron(II).

The 〈110〉 oriented FCl− molecule–ion in KFa)

The heteronuclear diatomic molecule–ion FC1− with its molecular axis oriented along a crystal face diagonal, i.e., FC1− 〈110〉, has been produced by ionizing radiation in single crystal KF doped with PbCl2 and KC1. Evidence to support this species identification as well as its orientation relative to the lattice is obtained from anisotropic optical absorption spectral measurements as well as from electron spin resonance (ESR) absorption spectra. Optical absorption spectral data, estimates of the molecular reorientation temperature, as well as ESR absorption spectral parameters are given for the FCl− 〈110〉. A qualitative explanation of the differences of the optical and ESR parameters of FCl− 〈111〉 and FCl− 〈110〉 is discussed.