Influence of individual aggressiveness on the dynamics of competitive populations

Two populations are subdivided into two categories of individuals (hawks and lows). Individuals fight to have access to a resource which is necessary for their survival. Conflicts occur between individuals belonging to the same population and to different populations. We investigate the long term effects of the conflicts on the stability of the community. The model is a set of ODE's with four variables corresponding to hawk and dove individuals of the two populations. Two time scales are considered. A fast time scale is used to describe frequent encounters and fightings between individuals trying to monopolize the resource. A slow time scale is used for the demography and the long term effects of encounters. We use aggregation methods in order to reduce this model into a system of two ODE's only for the total densities of the two populations which is found to be a classical Lotka-Volterra competition model. We study different cases of proportions of hawks and doves in both populations on the global coexistence and the mutual exclusion of the two populations. Pure dove tactics in both populations are unstable. In cases of mixed hawk and dove in both populations, there is coexistence. Pure dove or mixed hawk-dove tactics in one population can coexist with pure hawks in the other one when the costs of fightings between hawks are large enough.     

Corrosion behavior of Fe‐Si metallic coatings added with NiCrAlY in an environment of fuel oil ashes at 700°C

Electrochemical potentiodynamic polarization curves and immersion tests for 300 h at 700°C in a furnace have been used to evaluate the corrosion resistance of Fe‐Si metallic coatings added with up to 50 wt.% of NiCrAIY. The corrosive environment was fuel oil ashes from a steam generator. The composition of fuel oil ashes includes high content of vanadium, sodium and sulfur. The results obtained show that only the addition of 20 wt.% NiCrAlY to the Fe‐Si coating improves its corrosion resistance. The behavior of all tested coatings is explained by the results obtained from the analysis of every coating using electron microscopy and energy dispersive X‐ray analysis.     

Kinetics of fructose-glucose isomerization with sweetzyme type A

A study has been made of the kinetics of fructose-glucose enzymatic isomerization with an immobilized glucose isomerase, Sweetzyme A, at 60°C and with initial fructose concentrations of between 0.1 and 2.0 M. In the kinetic study, the effects of internal and external transport were considered, and it was found that when the data were fitted to a kinetic of a pseudo-first-order type, the non-enzymatic reaction could not be disregarded at low enzyme and high substrate concentrations. When non-enzymatic isomerization is taken into account, the true enzymatic-reaction constant can be calculated, giving values for maximum rate of 1.39 · 10^?6 mol (kg·s)^?1 and for Michaelis-Menten constant of 1.24 M. Establishing the influence of the transport in the interior of the catalyzing particles has enabled the determination of a value for effective diffusivity of 0.59 · 10^?10 m²·s^?1.     

Incorporation of a tungsten Fischer-type metal carbene covalently bound to functionalized SBA-15

A metal Fischer carbene [(CO)₅WC(φ)OCH₂CH₃] was covalently linked for the first time to the silanol groups of the mesoporous channels of SBA15 by following two different synthetic anchoring routes. The first one goes through the reaction of the SBA15 mesoporous silica walls functionalized by aminopropyltriethoxysilane (APTES) with a tungsten carbene Wφ, while in the second approach a precursor synthesized by reacting APTES with the carbene Wφ is then anchored via a direct bond to the silanol groups in the interior pore channels of SBA-15.

This tethering is helpful to prevent the decomposition of the metallic complex. XRD, N₂ adsorption–desorption, and TEM analysis provide strong evidence that the mesoporous support structure retains its long-range ordering after the grafting process, despite a significant reduction of its specific surface area, pore-volume and pore-size. The chemical bonding of the tungsten carbene to the silanol groups of SBA-15 materials was studied with solid-state NMR spectroscopy. Both ¹³C MAS NMR and ²⁹Si CP MAS NMR spectra confirm the covalent linking of the carbene to the silica-pore system.     

Synthesis,characterization and application of poly[(1‐vinyl‐2‐pyrrolidone)‐co‐(2‐hydroxyethyl methacrylate)] as controlled‐release polymeric system for 2,4‐dichlorophenoxyacetic chloride using an ultrafiltration technique

BACKGROUND: Polymers supporting chemicals used in agriculture have recently been developed to overcome the serious environmental problems of conventional agrochemicals. The success of these formulations is based on a suitable choice of polymer support. Degradable polymeric hydrogels are of particular interest. The gradual release of the bioactive agent can be achieved by hydrolytic or enzymatic cleavage of the linking bond. RESULTS: In this context, poly[(1‐vinyl‐2‐pyrrolidone)‐co‐(2‐hydroxyethyl methacrylate)] [poly(NVP‐co‐HEMA)] has been used as a bioactive carrier reagent. Herein, we report a controlled‐release system with the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) using an ultrafiltration system. Hydrolysis was studied by testing the release at various pH values. A high release with poly(NVP‐co‐HEMA)–2,4‐D was observed at pH = 7 and 10 after two days (Z = 2). The release percentage of copolymer–herbicide increased at pH = 10. It showed release values between 79.0 and 94.5%. Poly(NVP‐co‐HEMA)–herbicide can release a bioactive compound in aqueous solution at pH = 3, 7 and 10. CONCLUSION: Based on the results of homogeneous hydrolysis, it is argued that the herbicide release rate depends on the pH of the reaction environment. This functional polymer could be employed as a biodegradable material for applications in agrichemical release. Copyright © 2008 Society of Chemical Industry     

Biogenic sulfuric acid attack on different types of commercially produced concrete sewer pipes

Laboratory experiments were conducted to compare the degradation of low and high quality concrete under conditions simulating sewer pipes with and without bacteria. Small concrete samples were exposed to hydrogen sulfide, multiple species of bacteria found in corroding sewer pipes and artificial wastewater. Experiments without bacteria were used as controls. The corrosion rates of the concrete samples exposed to bacteria over 227 days were 0.08 mm/yr (millimeters per year) for the concrete from a domestic manufacturer with moderate strength and a lower water-cement ratio (Low-w/c) versus 0.208 mm/yr for the concrete samples from a foreign country with low strength and a higher water-cement ratio (High-w/c). The (Low-w/c) concrete was more resistant to the biodegradation even though a lower pH was attained for its bioactive systems. Experiments showed the influence of biogenic sulfuric acid production on short term corrosion rates.     

Water Resources Assessment at Piracicaba,Capivari and Jundiaí River Basins: A Dynamic Systems Approach

The Piracicaba, Capivari, and Jundiaí River Basins (RB-PCJ) are mainly located in the State of São Paulo, Brazil. Using a dynamics systems simulation model (WRM-PCJ) to assess water resources sustainability, five 50-year simulations were run. WRM-PCJ was developed as a tool to aid decision and policy makers on the RB-PCJ Watershed Committee. The model has 254 variables. The model was calibrated and validated using available information from the 80s. Falkenmark Water Stress Index went from 1,403 m³ person^???1 year^???1 in 2004 to 734 m³ P^???1 year^???1 in 2054, and Xu Sustainability Index from 0.44 to 0.20. In 2004, the Keller River Basin Development Phase was Conservation, and by 2054 was Augmentation. The three criteria used to evaluate water resources showed that the watershed is at crucial water resources management turning point. The WRM-PCJ performed well, and it proved to be an excellent tool for decision and policy makers at RB-PCJ.     

Production of lactic acid from vine‐trimming wastes and viticulture lees using a simultaneous saccharification fermentation method

An effective process for the chemical–biotechnological utilization of trimming wastes of vineshoots, an agricultural waste with little use, is reported. Initial treatment with sulfuric acid (prehydrolysis) allowed the solubilization of hemicelluloses to give xylose and glucose‐containing liquors (suitable to make fermentation media for lactic acid production with Lactobacillus pentosus) and a solid phase containing cellulose and lignin. The solid residues from prehydrolysis were treated with NaOH in order to increase their cellulase digestibility. In the alkaline treatments, the effects of temperature (in the range, 50–130 °C), reaction time (30–120 min) and NaOH concentration (4–12 wt% of solution) on the composition and susceptibility to enzymatic hydrolysis of solid residues were assessed by means of an experimental plan with factorial structure. The lignin content decreased, whereas the susceptibility towards the enzymatic hydrolysis increased with temperature, reaction time and NaOH concentration within the tested range. Using the cellulosic residues achieved under the harsher conditions, favorable fermentation kinetics during simultaneous saccharification and fermentation carried out by L rhamnosus for lactic acid production were observed. The nutrients employed were the complete MRS broth and a cheaper medium developed using viticulture lees coming from the white wine making technology. In all cases the final lactic acid concentration achieved was similar, although the volumetric productivity was lower when using lees due to inhibitory effects over the enzymatic hydrolysis. Copyright © 2004 Society of Chemical Industry