Chelator-soluble pectin was isolated from carrot under mild conditions and used as a model compound for an investigation of the heat degradation mechanism of pectin in an aqueous environment. Methyl ester content was modified with minimal changes in the polymer size. At pH 6.1 the heated pectin preparation degraded primarily through p-eliminative cleavage of the chain. The higher the methyl ester content the greater the degradation. Evidences also indicated a.small amount of hydrolytic cleavage of glycosidic bonds which was not affected by the presence of the methyl ester content. De-esterification of methyl ester groups proceeded at a faster rate than the eliminative cleavage of the chain; however, under the test conditions, it did not terminate the p-elimination.

Long-term growth patterns of red spruce (Picea rubens Sarg.) were analyzed from increment cores collected from over 1000 trees at 48 sites in the eastern United States. Principal objectives were the evaluation of the distribution, timing, and uniqueness of observed patterns of decreasing radial growth during the past 25 years and the examination of stand competition and climate as factors contributing to observed changes.Our analyses focused on historical records of spruce mortality and approximately 200 years of radial growth data to search for historical precedents for current trends. In this work we have used time series analysis to detect the temporal frequency of significant negative or positive shifts in radial growth rates, an analysis of relationships between a stand competition index and observed changes in growth and mortality, and modeling of past growth-climate relationships to determine whether recent growth changes could be predicted based on climate.Collectively, these analyses indicate that the observed growth decreases of surviving red spruce trees at northeastern sites with high mortality have been anomalous during the past 20 to 25 years with respect to both historical annual growth patterns and past relationships to climate or stand development at these sites. In general, reductions in radial increment that have also been noted at southern high elevation sites but not at low elevations occurred 5 to 10 years later than at northern sites and represent less substantive departures from growth trends predicted by linear climate models.These results suggest that regional and not local stresses have triggered the observed decline in radial growth of red spruce at these sites. While climatic change may have contributed to observed changes, the degree of radial growth suppression observed is greater than would be expected based on past growth-climate relationships. This unique relationship of growth to climate suggests the influences of either recent, unique combinations of climatic stresses or the possibly interactive intervention of other regional-scale stresses, such as atmospheric pollution.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.Two techniques of uncertainty analysis were applied to a mathematical model that estimates the dose-equivalent to man from the concentration of radioactivity in air, water, and food. The response-surface method involved screening of the model to determine the important parameters, development of the response-surface equation, calculating the moments using the response-surface model, and fitting a Pearson or Johnson distribution using the calculated moments. The second method sampled model inputs by Latin hypercube methods and iteratively simulated the model to obtain an empirical estimation of the cdf. Comparison of the two methods indicates that it is often difficult to ascertain the adequacy or reliability of the response-surface method. The empirical method is simpler to implement and, because all model inputs are included in the analysis, it is also a more reliable estimator of the cumulative distribution function of the model output than the response-surface method. Table 1. Input Parameters for SR Dose Model Standard Variable Distribution Mean Deviation Mode Minimum Maximum Dose Conversion Factor (DFI, rem/,u Sr) lognormal 1.575 .289 Weathering Loss Leaf (TW leaf, days) lognormal 12.795 4.5291 Nonleaf (TW nonleaf, days) lognormal 21.926 9.5982 Pasture (TW pasture, days) lognormal 12.799 4.5291 Interception Fraction Normalized for Biomass Leaf (RY leaf, m 2/kg) lognormal .1201 .0790 Nonleaf (RY nonleaf, m2/kg) lognormal .0725 .0486 Pasture (RY pasture, m 2/kg) lognormal 1.9523 .6911 Soil Surface Density (P, kg/m 2) lognormal 214.0159 23.6135