E.s.r. and spin-trapping studies of dihydropyrimidines. gamma-Radiolysis in the polycrystalline state and U.V. photolysis in aqueous solution

gamma-Radiolysis in the polycrystalline state and U.V. photolysis in aqueous solution at 220 nm of several dihydropyrimidines and their derivatives have been investigated by spin-trapping and electron spin resonance. 2-Methyl-2-nitrosopropane was used as the spin-trap. The spin-adducts of the 6-yl radicals obtained fall into two categories. Those from dihydro-1-methyluracil, dihydro-6-methyluracil, dihydro-1-ethyluracil and dihydro-1-methylcytosine exhibit a beta-nitrogen hyperfine coupling constant (alpha beta N) equal to or less than 2.0 G while the ones fom dihydro-orotic acid, dihydrouracil and dihydrothymine showed much larger alpha beta N values (greater than 3.3 G). Dihydrouridine gives radicals characteristic of both the dihydropyrimidine ring and the sugar moiety. The same radicals were obtained by gamma-radiolysis or U.V. photolysis. For all the 5-yl radicals obtained by U.V. photolysis, a direct photoexcitation mechanism is proposed.     

Persistence of D.D.T. and Benzene Hexachloride in Soils

Acid and alkaline soils, both alone and mixed with 2 % of D.D.T. or 2 % of benzene hexa-chloride (mixed isomers, containing 10% of the γ-isomer) have been exposed outdoors or subjected to controlled leaching in the laboratory. Residual insecticide has been estimated at intervals by a method involving dehydrohalogenation, and determinations have also been made of chloride content of soil, chloride leached and pH.
Results showed that both D.D.T. and benzene hexachloride were very stable in the soils, about 95 % of the former and 80 % of the latter being recoverable after 18 months. Very little chloride was leached during this period. The residual insecticide exhibited marked toxicity towards woodlice.
Eighteen months after treatment the benzene hexachloride soils prevented root growth of germinating seeds, while germination and early growth were normal in the D.D.T. soils. This harmful effect of the residual benzene hexachloride was still apparent when 1 part of the treated soil was mixed with 99 parts of the control soil (representing a concentration of less than 0–002 % of the γ-isomer).     

Information, discrimination and divergence in cytology. VI. Biases and errors of measurement in small samples.

Total discrimination and total divergence have been shown to be useful measures of performance in diagnostic cytology. The sample size, Ns (observed number of cytology-histology pairs, essential components of a confusion matrix), may be small for the comparison of two or more laboratories or periodic quality control using observed values. From actual data from previous reports in this series, the best estimation of the confusion matrix of a population was obtained by fitting a Gaussian-type curve after pseudoscalar transform of ranks (row and column numbers). Small sample confusion matrices were generated by Monte Carlo simulation to 2.5 x 10(-7) resolution. To keep measurement biases within +/- 0.5 decits, we found that 100-200 samples of cytology-histology pairs were required in the best classifications of three, four and five category-states. At these sample sizes, measurement errors (standard errors) were also contained within +/- 0.5 decits. This study also confirmed that previously reported overestimated propagated errors in small samples were in fact overestimation and that their use for testing a null hypothesis was valid. The number of samples with indefinable statistics due to a zero denominator can be as high as 30% when the sample sizes are 500 for three, four and five category-state classifications. Biases due to small samples were positive for most category-states except for the optimum three category-states, in which bias changed to negative ("bias inversion"), and observed errors of discrimination and divergence paradoxically decreased as Ns decreased ("error-sample paradox") for a small sample size (Ns less than 700).(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in heated and autoclaved forest soils of S.E. Australia. I. Carbon and nitrogen

The effect of heating and autoclaving on extractable nitrogen, N mineralisation and C metabolism was studied by heating five forest soils in the laboratory, simulating the range of effects of heat due to bushfire. Top soil (0–5 cm) was heated to 60 °C, 120 °C and 250 °C for 30 minutes; unheated soil was taken as a control. Samples of the soil heated to 250 °C were also inoculated with fresh soil to accelerate the recovery of the microbial population. Soil autoclaving was carried out as another heat treatment (moist heat). Soils were analysed immediately after heating and 3 times during seven months of incubation to assess immediate and longer-term effects of heating.Extractable N (organic and mineral forms) increased after heating to 120 °C, but decreased with further heating to 250 °C suggesting the volatilisation of N. N associated with microbial biomass diminished with heating and was barely detectable after the 250 °C treatment. Microbial biomass was an important source of soluble N in heated soils, and only partly recovered during subsequent long incubation. The amount of N mineralised during incubation depended on both soil and temperature. Nitrification did not occur when soils were heated to 250 °C (with or without inoculum), or after autoclaving, demonstrating the high sensitivity of nitrifiers to heat. At the beginning of soil incubation, respiration was enhanced in heated soils (250 °C, 250 °C inoculated) and autoclaved soils, but after 30 days of incubation respiration decreased to values either similar to or lower than those in control. This respiration pattern indicated that a fraction of labile C was released by heating, which was quickly mineralised within 30 days of incubation. These results demonstrate some effects of soil heating on C and N dynamics in forest soils.