On the validity of thermogravimetric determination of carbon gasification kinetics

Thermogravimetric analysis has been widely applied in kinetic studies of carbon gasification, with the associated temporal weight change profiles being used to extract kinetic information and to validate gasification models. However the weight change profiles are not always governed by the intrinsic gasification activity because of the effect of chemisorption and its dynamics. In the present work we theoretically determine the criteria under which weight change profiles can be used to determine intrinsic kinetics for CO2 and O2 gasification by examining the region in which the chemisorption dynamics can be assumed pseudo-steady. It is found that the validity of the pseudo-steady assumption depends on the experimental conditions as well as on the initial surface area of carbon. Based on known mechanisms and rate constants an active surface area region is identified within which the steady state assumption is valid and the effect of chemisorption dynamics is negligible. The size of the permissible region is sensitive to the reaction temperature and gas pressure. The results indicate that in some cases the thermogravimetric data should be used with caution in kinetic studies. A large amount of literature on thermogravimetric analyzer determined char gasification kinetics is examined and the importance of chemisorption dynamics for the data assessed.

In vivo and in vitro toxicities of pithraj and neem against rice green leafhopper (Nephotettix cincticeps Uhler)

Seed extracts of Aphanamixis polystachya Wall et Parker (pithraj) and Azadirachta indica A. Juss (neem) were evaluated for their in vivo and in vitro toxicity to Nephotettix cincticeps Uhler (rice green leafhopper). Crude extracts from both plants showed toxicity to leafhopper. Among them, the methanol extract of pithraj (MCX) was most toxic and showed 95% mortality effects at 72 h after treatment (HAT), followed by neem (74%). When LD50's were compared, it was found that the neem extract possessed the highest toxicity (LD50 16.59 μg/insect) at 72 HAT. Both the pithraj (MCX) and neem extracts showed their enzyme inhibition effectiveness against rice green leafhopper. The highest inhibition rate (IR) was caused by neem (60%) at the concentration of 2.0 mg/ml, followed by MCX (47%). The lowest IR50 value (0.97 mg/ml) was observed in neem at 30 min.

Bracken (Pteridium aquilinum)-induced DNA adducts in mouse tissues are different from the adduct induced by the activated form of the bracken carcinogen ptaquiloside

Following treatment with bracken fern (Pteridium aquilinum) extract and bracken spores a number of DNA adducts were detected by P-32-postlabeling. Three of these adducts have been described previously (Povey et al., Br. J. Cancer (1996) 74, 1342-1348) and in this study, using a slightly different protocol, four new adducts, with higher chromatographic mobility, were detected at levels ranging from 50 to 230% of those previously described, When DNA was treated in vitro with activated ptaquiloside (APT) and analysed by butanol extraction or nuclease P1 treatment, only one adduct was detected by P-32-postlabeling, This adduct was not present in the DNA from mice treated with bracken fern or spores, suggesting either that bracken contains genotoxins other than ptaquiloside or that the metabolism of ptaquiloside produces genotoxins not reflected by activated ptaquiloside. However, as the ATP-derived adduct has been detected previously in ileal DNA of bracken-fed calves, species-specific differences in the metabolism of bracken genotoxins may exist, thereby leading to differences in their biological outcomes. (C) 2001 Academic Press.

Leaf water relations of Eucalyptus cloeziana and Eucalyptus argophloia in response to water deficit

Leaf water relations responses to limited water supply were determined in 7-month-old plants of a dry inland provenance of Eucalyptus argophloia Blakely and in a humid coastal provenance (Gympie) and a dry inland provenance (Hungry Hills) of Eucalyptus cloeziana F. Muell. Each provenance of E. cloeziana exhibited a lower relative water content at the turgor loss point, a lower apoplastic water content, a smaller ratio of dry mass to turgid mass and a lower bulk modulus of elasticity than the single provenance of E. argophloia. Osmotic potential at full turgor and water potential at the turgor loss point were significantly lower in E. argophloia and the inland provenance of E. cloeziana than in the coastal provenance of E. cloeziana. There was limited osmotic adjustment in response to soil drying in E. cloeziana, but not in E. argophloia. Between-species differences in water relations parameters were larger than those between the E. cloeziana provenances. Both E. cloeziana provenances maintained turgor under moderate water stress through a combination of osmotic and elastic adjustments. Eucalyptus argophloia had more rigid cell walls and reached lower water potentials with less reduction in relative water content than either of the E. cloeziana provenances, thereby enabling it to extract water from dryer soils.