Research problem

This section appears from time to time. Contributions are invited, and should be submitted to R C. Thompson, Mathematics Department. University of California, Santa Barbara, CA93106-3080, USA.     

Stability and electronic properties of carbon in α-Al2O3

The stability and electronic properties of carbon in α-Al₂O₃ are investigated using density functional theory. In the host lattice, the substitutional C prefers the Al site under the O-rich conditions, whereas the O site is preferred by carbon under the Al-rich conditions. The calculated results predict a direct relationship between the thermodynamic and optical transition levels with the degree of the local distortion induced by C in the alumina lattice. We also find C at the O site acts as a charge compensator to stabilize the F⁺ center, thereby enhancing the TL signal at 465 K. Also, C at Al site can serve as electron traps for TL emission process in α-Al₂O₃.     

A method for predicting the anharmonicity constants ωeχe of halides of sodium

A method is proposed for estimation of the vibrational anharmonicity constants ω_eχ_e of diatomic molecules. The procedure involves fitting of the potential energy curve obtained by the RKRV method with that obtained by using the 5-parameter Hulburt-Hirschfelder potential function. We have predicted values of ω_eχ_e for alkali halides for which accurate data are not available.     

Response of duffing-type harvesters to band-limited noise

This paper aims to experimentally investigate the influence of stiffness-type nonlinearities on the transduction of vibratory energy harvesters (VEHs) under band-limited noise. For the purpose of the study, an energy harvester consisting of a clamped–clamped piezoelectric beam bi-morph is considered. The shape of the harvester's potential function is altered by applying a static compressive axial load at one end of the beam. The axial load permits the harvester to operate with different potential energy characteristics, namely, the mono-stable (pre-buckling) and bi-stable (post-buckling) configurations. The performance of the harvester in both the configurations is investigated and compared by tuning the harvester's oscillation frequencies around the static equilibria such that they have equal values in both scenarios. The harvester is then subjected to random base excitations of different levels, bandwidths, and center frequencies. The variance of the output voltage is measured across an arbitrary, purely resistive load and used for the purpose of performance comparison. Critical conclusions pertinent to the influence of the nonlinearity and relative performance in both configurations are presented and discussed.     

Arylbenzo[<Emphasis Type="Italic">h</Emphasis>][1, 6]naphthyridine Derivatives: Synthesis and Photophysical Properties

Suzuki-Miyaura cross coupling was successfully used for C5-arylation in 4-amino-2-chloroquinoline-3-carbaldehyde using arylbornic acid and tetrakistriphenylphosphine palladium catalyst in water. Friedländer condensation reaction on 4-amino-2-chloro/2-arylquinoline-3-carbaldehyde and aromatic ketones gave novel aryl and diarylbenzo[h] [1, 6]naphthyridines in good yields. Fluorescence quantum yields were increased by introducing C2 and C5 π donor aryl benzo[h][1, 6]naphthyridines derivatives.

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Figure Synthesis of Fluorescent Arylbenzo[h][1, 6]naphthyridine

     

Application of the two stage ascorbic acid-iodate titration to the determination of iodine and iodide

Summary An extension of the two stage titration of ascorbic acid against iodate to the determination of iodine and iodide in a solution is described. A known excess of ascorbic acid, standardized against iodate, is added to a mixed iodine and iodide solution and the excess ascorbic acid together with the total iodide is titrated against the same iodate to the two end points under controlled conditions of acidity. The differential method of calculation gives the amount of iodine and iodide with a blank and a direct titration. The accuracy of the results provides a useful evidence for the mechanism suggested for the two stage titration of ascorbic acid against iodate.Our sincere thanks are due to Professor S. S. Joshi for kind interest in the work.     

Response Factor Correction for Estimation of Ester Content in Biodiesel

EN 14103 is generally used for quantification of ester content in biodiesel free of heptadecanoate ester (C17:0) or methyl nonadecanoate (C19:0), which are employed as internal standards. It was observed that ester content obtained by EN 14103 method did not match with theoretical value of biodiesel, as the method did not take care of response factors of each component to compensate for changes in detector sensitivities. In this study, the whole range of fatty acid (C₆–C_24:1) methyl esters have been taken into consideration for the calculation of the ester content. Methyl nonadecanoate (C19:0) was used as an internal standard. The response factors of both the saturated and unsaturated methyl esters in the range C₆–C_24:1 were estimated and found in the range 0.97–1.16. The ester content was calculated after applying the response factors of each methyl ester. The results obtained by this method agreed well with the theoretical value as compared to estimated value using EN14103 method. The results obtained from this method also show good correlation (R ² = 0.98) with ¹H-NMR method. Further, this method does not depend on nature of biodiesel feed stock and is applicable to all methyl biodiesel samples obtained from different raw materials.