Optimizing Melt‐Processing Conditions for the Preparation of iPP/Fumed Silica Nanocomposites: Morphology,Mechanical and Gas Permeability Properties

A series of iPP/SiO₂ nanocomposites, containing 1, 2.5, 5, 7.5, and 10 wt.‐% fumed silica nanoparticles, were prepared by melt mixing in a twin screw co‐rotating extruder. The effect of different extrusion parameters was evaluated. The size of aggregates increased with increase in SiO₂ content and repetition of the mixing process improved the filler's dispersion. A similar effect was also exhibited by either increasing the rotor speed or the mixing temperature, with the latter being more pronounced at the ranges studied. The mechanical properties of the prepared nanocomposites were evaluated and various models used to explain the observed enhancements. However, only the three‐phase model could provide some correlation with the experimental results. All nanocomposites displayed lower permeability to gases.

     

Complexity issues on bounded restrictive H-coloring

We consider a bounded version of the restrictive and the restrictive list H-coloring problem in which the number of pre-images of certain vertices of H is taken as parameter. We consider the decision and the counting versions, as well as, further variations of those problems. We provide complexity results identifying the cases when the problems are NP-complete or #P-complete or polynomial time solvable. We conclude stating some open problems.     

Evidence for a SN2-type pathway for phosphine exchange in phosphine-phosphenium cations, [R2P--PR'3]+

Abstraction of a Cl(-) ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the P--P bonded cations [R4C4P--P(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl(2)) of [Et4C4P-(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P-(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with DeltaS( not equal)=(-106.3+/-6.7) J mol(-1) K(-1), DeltaH( not equal)=(14.9+/-1.6) kJ mol(-1) and DeltaG( not equal) (298.15 K)=(46.6+/-2.6) kJ mol(-1), values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (S(N)1-type) pathway reported for the analogous exchange reactions of the [ArNCH2CH2N(Ar)P(PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [ArNCH2CH2N(Ar)P(PMe3)](+) is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong pi-pi interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective pi-donation from the amide groups reduces the intrinsic electrophilicity of [ArNCH2CH2N(Ar)P]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway.     

Graphs with Branchwidth at Most Three

In this paper we investigate both the structure of graphs with branchwidth at most three, as well as algorithms to recognise such graphs. We show that a graph has branchwidth at most three if and only if it has treewidth at most three and does not contain the three-dimensional binary cube graph as a minor. A set of four graphs is shown to be the obstruction set for the class of graphs with branchwidth at most three. Moreover, we give a safe and complete set of reduction rules for the graphs with branchwidth at most three. Using this set, a linear time algorithm is given that verifies if a given graph has branchwidth at most three, and, if so, outputs a minimum width branch decomposition.     

Network formation as a cluster-cluster diffusion-limited aggregation process, 2. Modelling the polyethylene crosslinking process using Monte Carlo and graph techniques

A Monte Carlo simulation of the network formation of polyethylene radicals has been carried out using the reaction modelling scheme and a graph exploration algorithm based on the breadth-first search technique. The results are obtained in a three dimensional cubic continuum space simulation with periodic boundary conditions. Results for three different polyethylene concentrations are reported. The structural evolution of the studied system was followed in terms of: number of reactions, molecular mass, aggregate dimension and fractal dimension analysis.     

Solitary wave solutions and their interactions for fully nonlinear water waves with surface tension in the generalized Serre equations

Some effects of surface tension on fully nonlinear, long, surface water waves are studied by numerical means. The differences between various solitary waves and their interactions in subcritical and supercritical surface tension regimes are presented. Analytical expressions for new peaked traveling wave solutions are presented in the dispersionless case of critical surface tension. Numerical experiments are performed using a high-accurate finite element method based on smooth cubic splines and the four-stage, classical, explicit Runge–Kutta method of order 4.     

Raman Spectroscopy for Intracellular Monitoring of Carotenoid in <Emphasis Type="Italic">Blakeslea trispora</Emphasis>

In the present study, we explore the feasibility of Raman spectroscopy for intracellular monitoring of carotenoid in filamentous fungi Blakeslea trispora. Although carotenoid production from this fungus has been extensively studied through various chromatographic methods and ultraviolet-visible spectroscopy, no intracellular monitoring has been demonstrated until now. The intensity of the Raman spectrum, and more conveniently that of the strongest ν ₁ carotenoid band at ∼1,519 cm⁻¹, exhibits a good linear correlation with the carotenoid content of the sample as determined by high-performance liquid chromatography (HPLC) and ultraviolet-visible (UV-Vis) spectroscopy. Our results suggest that Raman spectroscopy can serve as an alternative method for the study and quantification of carotenoid in batch-mated submerged cultivations of B. trispora and similar organisms. Although not as accurate as HPLC, it allows a rapid sampling and analysis, avoiding the prolonged and tedious classical isolation procedures required for carotenoid determination by HPLC and UV-Vis spectroscopy.     

Dendritic effects of crown ether-functionalized dendrimers on the solvent extraction of metal ions

The ability of a series of crown ether-functionalized dendrimers to function as alkali metal picrate extraction agents is assessed by liquid-liquid extraction and ¹H NMR titration experiments. Crown ether-functionalized dendrimers that contain Fréchet-type poly(benzyl ether) dendrons of different generation as building blocks display different extraction characteristics toward alkali metal cations. Positive and negative dendritic effects depending on the generation of the dendrimer are assigned in the complexation behaviour of the dendritic host compounds.