A review of wildland fire spread modelling, 1990-present 3: Mathematical analogues and simulation models

In recent years, advances in computational power and spatial data analysis (GIS, remote sensing, etc) have led to an increase in attempts to model the spread and behvaiour of wildland fires across the landscape. This series of review papers endeavours to critically and comprehensively review all types of surface fire spread models developed since 1990. This paper reviews models of a simulation or mathematical analogue nature. Most simulation models are implementations of existing empirical or quasi-empirical models and their primary function is to convert these generally one dimensional models to two dimensions and then propagate a fire perimeter across a modelled landscape. Mathematical analogue models are those that are based on some mathematical conceit (rather than a physical representation of fire spread) that coincidentally simulates the spread of fire. Other papers in the series review models of an physical or quasi-physical nature and empirical or quasi-empirical nature. Many models are extensions or refinements of models developed before 1990. Where this is the case, these models are also discussed but much less comprehensively.Comment: 20 pages + 9 pages references + 1 page figures. Submitted to the International Journal of Wildland Fir

Glucose-6-phosphate dehydrogenase in cold hardy insects: Kinetic properties, freezing stabilization, and control of hexose monophosphate shunt activity

Properties of glucose-6-phosphate dehydrogenase were assessed from the larvae of three insect species, the freeze tolerant Eurosta solidaginis, the freeze avoiding Epiblema scudderiana, and warm-acclimated Tenebrio molitor. Maximal enzyme activities were 16-17 fold higher in the cold hardy larvae than in T. molitor in line with the key role of G6PDH in providing NADPH for the synthesis of cryoprotectant polyols in these species. Km values for glucose-6-P and NADP were determined at both high (24°C) and low (4°C) temperatures for all three enzymes. Temperature decrease had the greatest effect on T. molitor G6PDH increasing Km glucose-6-P by 3-fold and Km NADP by 2-fold; Km values for G6PDH from the cold hardy species were less temperature-sensitive. The addition of polyols (glycerol, sorbitol) or KCl caused selected changes in the Km values for both substrates in all species. Cryoprotectant action in the freezing protection of G6PDH was also examined, comparing G6PDH from E. solidaginis, E. scudderiana and yeast. A range of polyols (glycerol, sorbitol), other carbohydrates (trehalose, glucose, lactate) and amino acids (alanine, glutamate, proline) were effective in protecting activity during freezing. Without cryoprotectant, enzyme activity after 1 h freezing at -77°C was <10% compared to controls. Low concentrations of protectants (typically <50 mM) gave

Characterization of three areas of interactions stabilizing complexes between SecA and SecB, two proteins involved in protein export

The general secretory, Sec, system translocates precursor polypeptides from the cytosol across the cytoplasmic membrane in Escherichia coli. SecB, a small cytosolic chaperone, captures the precursor polypeptides before they fold and delivers them to the membrane translocon through interactions with SecA. Both SecB and SecA display twofold symmetry and yet the complex between the two is stabilized by contacts that are distributed asymmetrically. Two distinct regions of interaction have been defined previously and here we identify a third. Calorimetric studies of complexes stabilized by different subsets of these interactions were carried out to determine the binding affinities and the thermodynamic parameters that underlie them. We show here that there is no change in affinity when either one of two contact areas out of the three is lacking. This fact and the asymmetry of the binding contacts may be important to the function of the complex in protein export