Kinetics of simultaneous decrystallization and crystallization induced in high-modulus rayon by bromine water

Studies of the effect of aqueous Br₂ solution on the fine structure of cellulose have shown that the accessibility of the cellulose is a complex function of the duration of treatment. Following immersion of rayon-cellulose in the Br₂ solution, its accessibility is observed to increase until a peak is reached, after which the accessibility decreases with time. For higher temperatures and greater concentrations of Br₂, a sharper peak and faster rates of increase and decrease of accessibility are obtained. In order to explain this behavior, a mathematical model of the kinetics is postulated involving two opposing first-order processes occurring simultaneously. One process describes the decrystallization of crystalline regions within the cellulose by opening intermediate linkages due to Van-der-Waals forces involved. The second process relates to the crystallization of the less-ordered regions. The rate constants for these processes are determined by fitting experimental curves to the postulated analytical expression with the aid of a digital computer program. Experiments carried out on high-modulus rayon showed that for this type of cellulose, the effect described above was very pronounced. From the calculated rate constants, the activation energies of the crystallization and decrystallization reactions were determined. The plots of the rate constants versus 1/T showed that a break occurs at 25°C, corresponding to a second-order transition point of cellulose. The energies of activation of the crystallization process are in the range of 7–9 and 10–13 kcal/mol in the temperature ranges 10–25 and 25–40°C, respectively. The activation energies of the decrystallization process are 13 and 18–24 kcal/mol in these temperature ranges.     

A proof of Shelah's partition theorem

A self contained proof of Shelah's theorem is presented: If is a strong limit singular cardinal of uncountable cofinality and 2 > ⁺ then .     

Universal abelian groups

We examine the existence of universal elements in classes of infinite abelian groups. The main method is using group invariants which are defined relative to club guessing sequences. We prove, for example:Theorem:For n≧2, there is a purely universal separable p-group in ℵ _n if, and only if, . Partially supported by the United States-Israel Binational Science Foundation. Publication number 455.     

Role of surface proteins in the deposition kinetics of Cryptosporidium parvum oocysts

A radial stagnation point flow system was used to investigate the influence of Cryptosporidium parvum surface properties on oocyst deposition kinetics onto solid surfaces. To determine the role of oocyst surface proteins in adhesion, the deposition kinetics of viable oocysts were compared with the deposition kinetics of oocysts treated (inactivated) with either heat or formalin. Results showed a significantly higher deposition rate with formalin and heat-treated oocysts compared to viable oocysts under identical solution ionic strengths. Low deposition rates and corresponding attachment efficiencies were observed with viable oocysts over the entire range of solution conditions investigated, even at high ionic strengths where DLVO theory predicts the absence of an electrostatic energy barrier. An "electrosteric" repulsion between the viable Cryptosporidium oocyst and the quartz substrate, attributed to proteins on the oocyst surface, is surmised to cause this low deposition rate. Inactivation of the oocysts with either formalin or heat resulted in increased attachment efficiencies over the entire range of ionic strengths examined. It is hypothesized that formalin and heat treatments alter the structure of surface proteins and thus reduce steric repulsion. Formalin treatment was also found to impart an increased hydrophobicity to the oocyst surface and thus greater enhancement in oocyst deposition kinetics compared to heat treatment.     

Effect of depletion interactions on transport of colloidal particles in porous media

The influence of depletion interactions on the transport of micrometer-sized, negatively charged polystyrene latex particles through porous media was studied by analysis of particle breakthrough curves as a response to short-pulse particle injections to the inlet of a packed column of glass beads. The column outlet latex particle concentration profiles and the total amount of particles exiting the column were determined as a function of the concentration of small, silica nanoparticles in the solution and the bulk flow rate. Because of similar charges, the silica particles do not adsorb to either the latex particles or glass beads and thus induce an attractive depletion force between the latex particles and glass bead collectors. The total column outlet latex particle amount was calculated by integrating the measured breakthrough concentration curve and compared to the known amount of injected particles at the column inlet. It was found that the particle recovery was a decreasing function of the silica nanoparticle concentration and the carrier fluid residence time, and an increasing function of the velocity in the bed. In addition, removing the silica nanoparticles from the flowing solution caused a second outlet peak to appear, suggesting that some of the polystyrene particles were captured in secondary energy wells. The experimental data were interpreted using the predicted potential energy profile between a single particle and a glass bead, which was assumed to consist of electrostatic, van der Waals, and depletion components. The results indicate that secondary energy wells significantly affect particle transport behavior through porous media.     

Precipitous ideals and Σ 1 4 setssets

We prove under the assumption of the existence of a measurable, cardinal and precipitous ideal onw ¹ that every Σ ₁ ³ set is Lebesgue measurable, has the Baire property and is either countable or contians a perfect subset. We get similar results for Σ ₁ ⁴ sets, if we add the additional assumptions of C. H. and that carries a normal precipitous ideal.     

Flame retarding polyamide 6 with melamine cyanurate and layered silicates

The flammability behavior of the system polyamide 6 (PA 6) + melamine cyanurate (MC) with or without organically modified layered montmorillonite (OMMT) or sodium montmorillonite (Na⁺MMT) was studied. The high degree of flame retardancy (FR) obtained with 13 wt% MC is maintained upon adding up to 0.2 wt% OMMT or Na⁺MMT. Increase mass % of OMMT is antagonistic to the MC effect. The rate of dripping decreases while the size and mass of drops in the UL‐94 tests increases with increasing wt% OMMT indicating increase in viscosity of the melt and decrease in the rate of sublimation of melamine. Addition of poly vinyl pyrrolidone (PVP) decreases the viscosity and partially restores the FR rating. Na⁺MMT does not increase the viscosity and the FR ratings are partially preserved. The peak of heat release rate (PHRR) in the cone calorimeter decreases with increased loading of OMMT. Addition of Na⁺MMT or PVP has little influence on the PHRR. The time of ignition decreases with increase in OMMT, but is not affected when Na⁺MMT is used. This is explained by the low thermal conductivity of the clay containing surface layer of samples during pyrolysis and combustion. Mechanistic considerations are presented. Copyright © 2008 John Wiley & Sons, Ltd.     

A ZFC Dowker space in : An application of pcf theory to topology

The existence of a Dowker space of cardinality and weight is proved in ZFC using pcf theory.

     

Polyamide 6 treated with pentabromobenzyl acrylate and layered silicates

A study of the simultaneous application of a brominated flame retardant and an organically layered silicate (OLS) for the flame retarding of polyamide 6 (PA6) is presented. Upon treating PA6 with at least 7 wt% monomeric pentabromobenzyl acrylate (PMA), a UL‐94 V‐0 rating and an oxygen index (OI) value of 29.7 were obtained. By adding 1 wt% organically layered montorillonite (OMMT) and 10 wt% PMA, the V‐0 rating remained, indicating cooperation between PMA and OMMT. Higher concentrations of OMMT result in a decreased UL‐94 rating showing an antagonism. The size and mass of drops formed in the UL‐94 test increased with increasing OMMT, suggesting an increase in the viscosity and density of the pyrolyzing matrix. The effect of the Br additive on the peak heat release rate (PHRR) measured in the cone calorimeter is similar, but smaller, than that of clay. A calculation of the synergistic effectivity related to PHRR enabling a numerical estimate of the extent of synergism or antagonism is presented. When the ill‐dispersed pristine clay (Na⁺MMT) is used, the viscosity does not increase, the PHRR decreases slightly, but the mass loss rate (MLR) is close to that of the matrix. The time of ignition (TOI) decreases upon the addition of PMA, similarly to the addition of OMMT. This is explained by migration of the Br additive to the surface barrier similar to that of clay so that the low thermal conductivity (TC) barrier is formed before the ignition. Accumulation of heat in the barrier decreases the TOI. Copyright © 2010 John Wiley & Sons, Ltd.     

Proton antenna effect of the gamma-cyclodextrin outer surface, measured by excited state proton transfer

The reversible proton dissociation and geminate recombination of the common photoacid, 8-hydroxypyrene-1,3,6-trisulfonate (pyranine), either in dilute aqueous solution or when forming a complex with gamma-cyclodextrin (gamma-CD), has been studied by time-resolved fluorescence spectroscopy and supplemented by molecular modeling and dynamics simulations. We find that the dissociation rate of the proton from the excited molecule was decreased to about approximately 50% of its value in water, while the rate of recombination was doubled. These observations were evaluated by molecular modeling of the reactants at atomic resolution. The combination of the two methodologies indicates that the pyranine in the complex can assume more than one level of interaction with the solvent. The polysugar torus surrounding the pyranine perturbs the hydrogen bond in the dye's immediate vicinity and deforms the electrostatic potential inside the Coulomb cage, causing major deviations from a simple spheric symmetry. These observations can account for the special kinetic features measured for the complex. We suggest that this system can be used as a basic model for evaluating the mechanism of proton transfer in non-homogeneous systems, such as the surface of proteins or biomembranes.