SIVR epidemic model with stochastic perturbation

We propose a stochastic disease model where vaccination is included and such that the immunity is permanent. The existence, uniqueness, and positivity of the solution and the stability of the disease-free equilibrium are studied.     

The influence of the preparing conditions of SiO2 supported Cp2ZrCl2 catalyst on ethylene polymerization

In this work, ethylene was polymerized by using Cp₂ZrCl₂ supported on silica pretreated with methylaluminoxane (MAO) as the catalyst system. The influence of the conditions for the preparation of the heterogeneous catalyst, such as temperature, washing method of the catalytic solid, MAO and metallocene concentration in the support treatment, time of MAO, and metallocene immobilization on the support, type of alkylaluminum used in the support pretreatment, and calcination temperature of the support were investigated. Aluminum and zirconium content fixed on the silica surface were determined by inductively coupled plasma emission spectroscopy. Polymer characteristics were determined by gel permeation chromatography and differential scanning calorimetry. According to the results, the activity of some supported catalysts were far higher than with the homogeneous system. Moreover, polyethylene with very high molecular weights were also obtained and with molecular weight distribution larger than those produced with the homogeneous precursor. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2054–2061, 2002     

Effect of nonionic detergents on lipoxygenase catalysis

In many studies on lipoxygenase catalysis, nonionic detergents are used to obtain an optically transparent solution of the fatty acid substrate. In order to resolve some controversies that exist with regard to the interpretation of kinetic data obtained with solutions containing nonionic detergents, a systematic investigation was undertaken into the effects of Lubrol, Tween-20 and Triton X-100 (0–0.8 g/L) on the kinetics of linoleate (2.5–110 μM) dioxygenation, catalyzed by lipoxygenase-1 or lipoxygenase-2 from soybean, at pH 9 or 10, at 25°C. Under most conditions, it was found that the detergents slowed down the reaction. However, at high linoleate concentrations, where substrate inhibition of lipoxygenase is significant, small amounts of detergent increased the dioxygenation rate. In a quantitative analysis of the results, a kinetic model in which the incorporation of linoleate in the detergent micelles is formulated as a simple reversible equilibrium, and in which both lipoxygenase-1 and-2 interact with free linoleate, but not with linoleate incorporated in the micelles, appeared to be sufficient to predict experimental results over a wide range of experimental conditions. According to this model, the changes in the dioxygenation kinetics caused by the presence of nonionic detergents are similar (but not equal) to those caused by competitive inhibitors. The conclusions that monomeric, nonmicellar linoleate is the preferred substrate for lipoxygenase and that the observed inhibition and stimulation are solely due to changes in the effective linoleate concentration strongly corroborate the earlier observations by Galpin and Allen [Biochim. Biophys. Acta 488 (1977), 392–401].     

The effect of cooling rate on the impact performance and dynamic mechanical properties of rotationally molded metallocene catalyzed linear low density polyethylene

This article examines changes to the morphology of rotationally molded metallocene catalyzed linear low density polyethylene brought about by varying the cooling rate during processing. These changes in morphology lead to variations in the impact performance, which is reflected in the dynamic mechanical characteristics of the materials. Various analytical techniques are used in an attempt to explain the differences in impact behavior. Slow cooling is shown to result in high crystallinity, and in the formation of large spherulites, which in turn is detrimental to the impact performance of the material, particularly at low temperatures. The high crystallinity corresponds with a shift in the β transition of the material to a higher temperature, and is shown to result in a higher brittle–ductile transition. A case study was also carried out on samples from a finished part provided by an industrial molder, one section of which failed in a brittle manner when impact tested while the other failed in a ductile manner. Microscopy results showed that the brittle material had large spherulites at the inside surface, while the ductile material showed incipient degradation at this surface, which has previously been shown to be of benefit to impact strength in rotationally molded parts. Dynamic mechanical studies again showed a β transition at a higher temperature in the brittle samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1963–1971, 2006     

Characterization of poly(diethoxyphosphazene) by size exclusion chromatography and viscometry

Two samples of poly(diethoxyphosphazene) (PDEP) having very different molecular weights have been studied by viscometry and size exclusion chromatography in THF solution. The results obtained, together with light scattering data of these samples, allow the calculation of the Mark-Houwink constants a=0.65 and K=2.5 10^-4 in THF at 25°C. The method of calculation employed takes into account the great polydispersity of the samples. The characteristic ratio of the unperturbed dimensions was also calculated giving C_n = r²_o/n² 18, a value slightly higher than those previously reported for poly(dihexoxyphosphazene), C_n13 and poly (dichlorophosphazene), C_n13.5.     

The content and composition of sterols and sterol esters in low erucic acid rapeseed (Brassica napus)

The low temperature crystallization technique for the enrichment of “minor” components, such as sterols and sterol esters, from vegetable oils was applied to low erucic acid rapeseed oils. The recovery of free sterols and sterol esters was estimated by use of¹⁴C-cholesterol and¹⁴C-cholesterol oleate. 80% of the free sterols and 45% of the sterol esters were recovered in the liquid fraction, while in two studies total recoveries were 95% and 99%, respectively. This technique showed some selectivity toward the sterol bound fatty acids when compared to direct preparative thin layer chromatography (TLC) of the crude oil. Gas liquid chromatography (GLC) analysis of the free and esterified sterols as TMS-derivatives showed very little selectivity in the enrichment procedure. The fatty acid patterns of the sterol esters demonstrated, however, a preference in the liquid fraction for those sterol esters which have a high linoleic and linolenic acid content. The content of free sterols was 0.3–0.4% and that of sterol esters 0.7–1.2% of the rapeseed oils in both winter and summer types of low erucic acid rapeseed (Brassica napus) when the lipid classes were isolated by direct preparative TLC of the oils. The free sterols in the seven cultivars or breeding lines analyzed were composed of 44–55% sitosterol, 27–36% campesterol, 17–21% brassicasterol, and a trace of cholesterol. The esterified sterols were 47–57% sitosterol, 36–44% campesterol, 6–9% brassicasterol, and traces of cholesterol and Δ5-avenasterol. The fatty acid patterns of these esters were characterized by ca. 30% oleic acid and ca. 50% linoleic acid, whereas these acids constitute 60% and 20%, respectively, of the total fatty acids in the oil. Little or no variation in sterol and sterol ester patterns with locality within Sweden was observed for the one cultivar of summer rapeseed investigated by the low temperature crystallization technique.     

In Situ EXAFS Study on the Chemical State of Arsenic Deposited on a NiMoP/Al2O3 Hydrotreating Catalyst

The chemical state of arsenic deposited on a NiMoP/Al₂O₃ hydrotreating catalyst exposed to ppb levels of arsenic over several years in a refinery reactor has been studied by in situ EXAFS. In the as-received As-NiMoP catalyst, arsenic is exclusively coordinated to oxygen atoms. Upon sulfiding the sample in 2%H₂S/2%H₂/96%He, the As atoms become surrounded by approximately two sulfur atoms. No evidence was found for Ni–As bond formation. A possible model for the As local environment is suggested on the basis of combined EXAFS results, STM data and FEFF8.0 simulations (program for ab initio calculations on multiple scattering XAFS and XANES). The FEFF8.0 simulations of the proposed model are in accord with the experimental data measured at the As K edge. In this model, an As atom is located at the edge of a hexagonally truncated Ni-MoS₂ slab and is blocking the active NiMoS site.     

Composition and thermal properties of Rhea oil and its fractions

The rhea (Rhea americana) is a large running bird of the ratite family, native to South America. Oil extracted from rhea fat tissue is used in cosmetic manufacture. Here, the thermal behaviour and the fatty acid and triacylglycerol composition of Uruguayan rhea oil are studied. The results are compared with those obtained from two commercial samples of emu oil. The fatty acid profiles of emu and rhea oils are similar. Small variations are reflected in the non‐identical thermal behaviour of the oils. The solid content of both oils is fairly similar at room temperature. Thus, emu oil and rhea oil may replace one another in certain formulations, without resulting in important changes in physicochemical behaviour. The semisolid rhea oil was fractionated in two successive stages: an olein was obtained at 15 °C, which was refractionated at 10 °C. The thermogram of the olein obtained by cooling at 15 °C does not have the peak found at 34 °C in the thermogram of the original oil and is a softer product than the original oil. A further stage of fractionation of this olein produced a new liquid phase of slightly different thermal behaviour from that of the original olein. This product has a solid fat index around 7% at 15 °C and has melted completely at 20 °C. This second olein has more appropriate physical characteristics than those of the olein obtained from the first fractionation when used in liquid cosmetic formulations.     

Digestibility and nutritional value of crude oil from three amaranth species

Oils from a selection ofAmaranthus caudatus, A. hypochondriacus andA. cruentus were extracted with hexane. The crude oils were analyzed for acid value, saponification and iodine number, and were included in basal casein diets for rat studies at 5 and 10% levels to replace equal amounts of refined cottonseed oil. The oils fromA. cruentus andA. hypochondriacus were similar in the oil properties studied and different fromA. caudatus. At either 5 or 10% food intake levels, weight gain and PER were not statistically different from values reported for cottonseed oil. True digestibility of amaranth oil was lower than that of cottonseed oil.A. cruentus oil gave the lowest digestibility. Oil levels induced statistical differences in food intake and digestibility. Oils fromA. caudatus, A. hypochondriacus and cottonseed induced similar serum cholesterol levels, while oil fromA. cruentus gave statistically higher values. Hemoglobin, hematocrit and serum proteins were similar among all groups. Microscopic analysis of the organs of the rats revealed some changes that were also found in cottonseed oil-fed rats. It was concluded that crude amaranth oil has lower digestibility than cottonseed oil, but that it is not responsible for growth-depressing effects when the seed is fed raw as compared to processed materials.     

Effect of low‐temperature plasma and chitosan treatment on wool dyeing with Acid Red 27

This study examines in detail the influence of low‐temperature plasma and biopolymer chitosan treatments on wool dyeability. Wool knitted fabrics were treated and characterized by whiteness and shrink‐resistance measurements. Surface modification was assessed by contact‐angle measurements of human hair fibers, which were used as a model to study the wetting properties of the treated wool knitted fabrics. The dyeing behavior was assessed from the diffusion mechanism point of view. The dyeing kinetics were measured at two different pHs (4.2 and 6.5) and three different temperatures (60, 85, and 100°C) to gain information about the contribution of the surface modification treatment to the dyeing mechanism. The exhaustion and reflectance data were compared, and the apparent diffusion coefficients were calculated. On the basis of the obtained results, a model for the dyeing mechanism of the chitosan treated wool was proposed. When treated with chitosan, the polymer sheath spread on the surface of the fibers acted as a predominant dyeing site in very short dyeing times, thus interacting with the dye and in later stages imparting the dye to the wool fiber. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2204–2214, 2005