Visible And Near-infrared Spectra Research Articles

A critical evaluation of oxidation versus reduction during metamorphism of L and LL group chondrites, and implications for asteroid spectroscopy

Abstract— Modal mineralogies of individual, equilibrated (petrologic type 4–6 L and LL chondrites have been measured using an electron microprobe mapping technique, and the chemical compositions of coexisting silicate minerals have been analyzed. Progressive changes in the relative abundances and in the molar Fe/Mn and Fe/Mg ratios of olivine, low‐Ca pyroxene, and diopside occur with increasing metamorphic grade. Variations in olivine/low‐Ca pyroxene ratios (Ol/Px) and in metal abundances and compositions with petrologic type support the hypothesis that oxidation of metallic iron accompanied thermal metamorphism in ordinary chondrites. Modal Ol/Px ratios are systematically lower than normative Ol/Px ratios for the same meteorites, suggesting that the commonly used C.I.P.W. norm calculation procedure may not adequately estimate silicate mineral abundances in reduced chondrites. Ol/Px ratios calculated from visible and near‐infrared (VISNIR) reflectance spectra of the same meteorites are not in agreement with other Ol/Px determinations, possibly because of spectral complexities arising from other minerals in chondrites. Characteristic features in VISNIR spectra are sensitive to the proportions and compositions of olivine and pyroxenes, the minerals most affected by oxidative metamorphism. This work may allow spectral calibration for the determination of mineralogy and petrologic type, and thus may be useful for spectroscopic studies of asteroids.

Visible and near-infrared spectral changes in plasma of psychiatric patients

In the present study, the possible difference in visible and near-infrared (Vis-NIR) spectra of plasma in psychiatric patients compared to healthy control subjects was investigated. Mean Vis-NIR spectra of 60 psychiatric patients showed several specific peaks in the 630- to 930-nm region. Principal component analysis (PCA) and soft independent modeling of class analogy (SIMCA) were applied to manifest the spectral characteristics of each group. The PCA and SIMCA models demonstrated successful discrimination of the two groups using a score plot of the third versus fourth principal component and a Coomans plot, respectively. The PCA loadings were generally consistent with the discriminating power of the SIMCA model, indicating a specific pattern of Vis-NIR spectra in the plasma of psychiatric patients. The specific pattern possibly indicates altered superoxide, amine, and primary and secondary amides in plasma and may provide a possible indicator for the diagnosis of heterogeneous psychiatric disorders. This is the first step toward a clinical tool which has the potential to be applied in the diagnosis of psychiatric disease. Yet, there remain obstacles to its practical usage.

The absorption spectra of the anions of quinones and other acceptors in solution and as solids

The visible and near-infrared spectra of the negative ion-radicals of electron acceptors were studied. A linear relationship was found between the longest-wave-length π*π* bands of the semi-p-benzoquinones and the electron affinities of these molecules. The effect of the addition of a single electron on the ππ* transitions of p-fluoranil, p-bromanil, and p-chloranil was also considered.