Numerical simulation aided relative optical density analysis of TEM images for soot morphology determination

The relative optical density (ROD) method provides a means to measure three-dimensional information about soot aggregates from two-dimensional transmission electron microscopy (TEM) micrographs of soot. The method is dependent on accurate calibration of the relationship between the measured soot ROD in TEM images and the actual soot thickness perpendicular to the imaging plane. A novel calibration method based on the comparison between probability distributions of measured soot ROD in TEM images and that of virtual soot thickness of numerically simulated soot is introduced. Soot aggregates of various prescribed fractal structure parameters were numerically generated using a tunable cluster-cluster aggregation model. The probability histograms of the local soot thickness for the simulated soot aggregates and ROD of the TEM images of flame generated soot aggregates were found to be quite similar and were used as a basis to establish a quantitative relationship between ROD and the local soot thickness. The calibration constant obtained from the analysis of the simulated soot was found to be insensitive to the fractal structure parameters over a wide range. The calibrated ROD method is successfully applied to the morphology analysis of soot aggregates generated in an atmospheric laminar co-flow ethylene-air diffusion flame based on thermophoretic sampling (TS) and TEM analysis techniques. With the ROD method, an overlap coefficient is introduced to identify and eliminate non-soot-aggregate structures and the selection of a cut-off overlap coefficient was found to have little influence on the final results over a relatively wide range. ROD is independent of empirical constants and human judgments and has been found to be an accurate and reliable TEM image analysis method for studying the morphology of soot aggregates.     

Fluorocarbon derivatives of nitrogen. Part 11. Synthesis of some 2-(trifluoromethyl)imidazo[1,2-a]pyridines from trifluoroacetonitrile

3-(t-Butoxycarbonyl)-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine, prepared from trifluoroacetonitrile and pyridinium t-butoxycarbonylmethylide, reacts smoothly with trifluoroacetic acid to provide 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine-3-carboxylic acid, which gives 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine when heated. 3-Cyano-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine can be obtained $\text{via}$ treatment of trifluoroacetonitrile with pyridinium cyanomethylide, which is sufficiently reactive to effect nucleophilic displacement of fluorine from pentafluoropyridine under mild conditions [→pyridinium cyano(tetrafluoro-4-pyridyl)methylide].     

Nickel-Catalyzed α-Allylation of Aldehydes and Tandem Aldol Condensation/Allylation Reaction with Allylic Alcohols

An additive-free nickel-catalyzed α-allylation of aldehydes with allyl alcohol is reported. The reaction is promoted by 1 mol % of in situ formed nickel complex in methanol, and water is the sole by-product of the reaction. The experimental conditions allow the conversion of various α-branched aldehydes and α,β-unsaturated aldehydes as nucleophiles. The same catalyst and reaction conditions enabled a tandem aldol condensation of aldehyde/α-allylation reaction.     

Cellular-indecomposable subnormal operators II

This work continues that begun in [9]. Our investigation has led us to the following conjecture: a cyclic subnormal operator is cellular-indecomposable if and only if it is quasi-similar to an analytic Toeplitz operator whose symbol is a weak-star generator of H. In this paper some particular cases of the conjecture are verified.This work was supported in part by a grant from the National Science Foundation.     

The low temperature specific heat of a single crystal of La<Subscript>2</Subscript>CuO<Subscript>4+δ</Subscript> in magetic fields of 0, 2 and 4 Tesla

A single crystal of La₂CuO₄ was made superconducting after treatment in a high pressure oxygen furnace. Measurements are presented of the low temperature heat capacity of the insulating crystal in zero field between 1K and 3K, and of the superconducting crystal in fields of 0, 2 and 4 Tesla applied parallel to the ab plane between 0.2K and 3K. A linear heat capacity contribution is observed for the crystal in both the insulating and superconducting states. This linear heat capacity contribution is larger in the superconducting state and is insensitive to the applied magnetic field.     

Quantum chemical investigations of charge transfer interactions in relation to the electronic theory of cancer. II

The results of ab initio “supermolecule” calculations of the charge transfer between formamide and methylglyoxal, ethylglyoxal, and dimethylglyoxal are compared for several different relative conformations of the constituent molecules. The charge transfer properties of ethylglyoxal were found to be quite different to those of the other two glyoxals.