Xylyl radicals are intermediates in combustion processes since their parent molecules, xylenes, are present as fuel additives. In this study we report on the photoelectron spectra of the three isomeric xylyl radicals and the subsequent decomposition reactions of the o-xylyl radical, generated in a tubular reactor and probed by mass selected threshold photoelectron spectroscopy and VUV synchrotron radiation. Franck-Condon simulations are applied to augment the assignment of elusive species. Below 1000 K, o-xylyl radicals decompose by hydrogen atom loss to form closed-shell o-xylylene, which equilibrates with benzocyclobutene. At higher temperatures relevant to combustion engines, o-xylylene generates styrene in a multistep rearrangement, whereas the p-xylylene isomer is thermally stable, a key point of difference in the combustion of these two isomeric fuels. Another striking result is that all three xylyl isomers can generate p-xylylene upon decomposition. In addition to C8H8 isomers, phenylacetylene and traces of benzocyclobutadiene are observed and identified as further reaction products of o-xylylene, while there is also some preliminary evidence for benzene and benzyne formation. The experimental results reported here are complemented by a comprehensive theoretical C8H8 potential energy surface, which together with the spectroscopic assignments can explain the complex high-temperature chemistry of o-xylyl radicals.

The jaggedness of the stress-strain relationship of two kinds of puffed extrudates stored under different humidity conditions was assessed by the power spectrum of the Fast Fourier Transform and the Natural Fractal dimension of normalized compression curves. Both analyses, performed with a micro-computer, provided a consistent measure of jaggedness. The apparent Fractal dimension, obtained using the Blanket algorithm, was the most convenient measure of overall ruggedness since it was expressed by a single number. The power spectrum that resulted from the Fourier transform, however, could be used to identity the length scale of structural features where fracture takes place, and its shape could be more directly related to structural features and textural properties.

Xylyl (methylbenzyl) radicals are important combustion intermediates, formed in the pyrolysis and oxidation of xylenes and other substituted aromatic fuel additives. We have used VUV synchrotron radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy techniques to identify para-xylylene as the dominant stable C 8 H 8 product arising from thermal decomposition of the meta-xylyl radical. A complex rearrangement from a meta-to a para-substituted aromatic, supported by quantum chemical calculations, can rationalize the observed reaction products. This work provides the first experimental evidence for the pyrolysis products of the meta-xylyl radical and can explain why the decomposition of this radical is considerably slower than that of the ortho and para isomers. This study emphasizes the utility of VUV synchrotron radiation and iPEPICO spectroscopy to tackle the reaction mechanism of combustion-relevant processes.

Three experiments were conducted to evaluate the nutritional value of the blue-green algae, Spirulina platensis, grown on a synthetic media. In Experiment 1, day-old, White Leghorn cockerel chicks (120) were fed isonitrogenous diets containing 0, 5, 10, 15, and 20% of dried spirulina. At 3 wk of age, the growth of the chicks fed 10 and 20% of spirulina was depressed (P less than .05), although feed efficiency was not affected. In Experiment 2, 250 1-day-old, Hubbard by Hubbard, male broiler chicks were fed experimental diets containing 0, 1.5, 3.0, 6.0, or 12.0% of spirulina for 41 days. Although the growth of the chicks fed the spirulina diets was not different from that of the chicks receiving the control diet, the birds receiving the 12% spirulina diet grew slower (P less than .05) than the chicks fed all of the other spirulina diets. In Experiment 3, 600 1-wk-old, Japanese qual were used to study the effects of 0, 1.5, 3.0, 6.0, and 12.0% of spirulina on growth, egg production, egg quality, fertility, hatchability, and the growth of the F1 generation of dams fed Spirulina. There were no significant differences due to the spirulina content in any of the parameters studied-except for yolk color, which increased with each succeeding level of spirulina, and for fertility, which was higher for all spirulina treatments versus the control.

No abstract

The "quasi-chemical" kinetics model accounts for all 4 phases of the microbial lifecycle based on a proposed series of chemical rate equations. The model fits continuous growth-death kinetics for Staphylococcus aureus in intermediate moisture bread in various conditions of water activity, pH, and temperature. Growth rates evaluated using the quasi-chemical model are compared with values obtained with the Gompertz model. Kinetics data obtained with the quasi-chemical model are integrated with a probabilistic approach to estimate the boundary between growth and no-growth conditions. Continuous modeling of microbial growth/death kinetics in actual foods advances predictive modeling that conventionally separates growth and death models.

The distribution of fracture intensities occurring during compression of puffed corn meal extrudates was described using an exponential function, and parameters from that analysis were used as fracturability indices. Since "jagged" or oscillating stress-strain functions are typical for porous and brittle materials, fracture intensities were determined by measuring the abrupt, sequential reductions in stress produced during compression. Both distribution exponent and cumulative fracture stress correlated strongly with fracturability measured by other techniques, including fractal and Fourier analysis of stress-strain functions.Distribution parameters also indicated textural differences due to process parameters (structural modification through addition of different levels of sucrose) and storage conditions (equilibration at various relative humidities).

No abstract