Injection-moulded α- and β-polypropylenes: II. Tensile properties vs. processing parameters

Resuming our comprehensive study, present Part II directs attention towards the effects of mould temperature and holding pressure on the tensile properties of neat and β-nucleated isotactic polypropylenes. A commercial-grade of isotactic polypropylene was modified with a β-specific nucleator. From both the original material (α-iPP) and the β-nucleated material (β-iPP), tensile test specimens were injection-moulded. Stress-strain measurements performed at room temperature revealed a positive influence of higher mould temperatures but negligible effect of holding pressure on the elastic modulus of injection-moulded specimens. It was suggested that at optimum processing conditions the elastic modulus of both α- and β-iPP may be comparable. The softening effect of β-form manifested itself in systematically lower yield stress values of β-iPP as compared to α-iPP. The yield strain of both α- and β-iPP decreased with the increase of mould temperature and the decrease of holding pressure. Prolonged solidification times at higher mould temperatures negatively influenced the strain at break of the specimens; the values of β-iPP exceeded by several folds those of α-iPP. The stress at break of β-iPP decreased correspondingly to strain at break. On the contrary, the increase of strain at break in α-iPP was followed by a decrease of stress at break.     

Two-level Preconditioner with Small Coarse Grid Appropriate for Unstructured Meshes

The presented paper contains a suggestion and an analysis of a two-level preconditioner appropriate for unstructured meshes. The convergence analysis is done for H¹-equivalent forms in the two-dimensional case; ways for generalization are discussed, too. The efficiency is demonstrated by numerical experiments.     

Portfolio optimization via stochastic programming: Methods of output analysis

Solutions of portfolio optimization problems are often influenced by errors or misspecifications due to approximation, estimation and incomplete information. Selected methods for analysis of results obtained by solving stochastic programs are presented and their scope illustrated on generic examples – the Markowitz model, a multiperiod bond portfolio management problem and a general strategic investment problem. The approaches are based on asymptotic and robust statistics, on the moment problem and on results of parametric optimization.     

A solvent recirculation trapping device for supercritical fluid extraction of polyaromatic hydrocarbons

A new device has been developed for the trapping of volatile pollutants in trapping solvents. The device allows solvent recirculation and cryogenic trapping of evaporated volatiles to minimize the stripping effect and any losses of volatile analytes. Due to solvent recirculation, the trapping solvent column height remains constant during the extraction without any need for replenishment. Also mass transfer conditions are favorable due to the flattened shape of bubbles of CO2 and the longer extraction time. The bubbles have higher interfacial area and they have to pass a three times longer distance in the solvent column. The device produces more concentrated extracts, reduces solvent consumption, and reduces or eliminates its evaporation to the environment. The cryotrapping part reduces losses of volatile analytes and the stripping effect. It also enables single-phase extraction into much smaller solvent volumes. Due to constant and favorable extraction conditions, the precision of the method was also greatly improved (RSDs decreased from 2.2 to 0.8%). As proved by a set of rapid spiked-sample extractions of highly volatile compounds at very high flow rates, the relative standard deviation of the experiments performed in the new device is 3.5 times lower.     

Scenarios for Multistage Stochastic Programs

A major issue in any application of multistage stochastic programming is the representation of the underlying random data process. We discuss the case when enough data paths can be generated according to an accepted parametric or nonparametric stochastic model. No assumptions on convexity with respect to the random parameters are required. We emphasize the notion of representative scenarios (or a representative scenario tree) relative to the problem being modeled.     

Effect of oxidant on electronic transport in polypyrrole nanotubes synthesized in the presence of methyl orange

Polypyrrole nanotubes with diameter 60–400 nm are synthesized with methyl orange as template and various oxidants, iron(III) chloride hexahydrate, iron(III) sulfate hydrate, and ammonium peroxydisulfate. The highest electrical conductivity of compressed pellets, 66 S cm^?1, is found for iron(III) chloride. Regions with 3D variable range hopping in series with ordered regions near metal–insulator transition govern the charge transport. Other oxidants and globular morphology provide less conducting samples, <10 S cm^?1. The transport mechanism is identified with the heterogeneous model of tunneling between (bi)polaronic clusters with parallel contribution of Arrhenius‐like activated conductivity. The results of conductivity are correlated with the protonation level reflected in the infrared spectra and with the ratio of bipolaron/polaron bands revealed by Raman spectroscopy. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1147–1159     

The fluorescence properties and NMR analysis of protopine and allocryptopine

The fluorescence properties of protopine and allocryptopine in aqueous and organic environments are described for the first time. The fluorescence of alkaloids and their pH-dependent interconversion to cationic forms (transannular interaction) were studied using steady-state and time-resolved fluorescence techniques. For the analysis of tricyclic base and cis/trans tetracyclic cations of the alkaloids, NMR and X-ray crystallography were used.     

Robustness of optimal portfolios under risk and stochastic dominance constraints

Solutions of portfolio optimization problems are often influenced by a model misspecification or by errors due to approximation, estimation and incomplete information. The obtained results, recommendations for the risk and portfolio manager, should be then carefully analyzed. We shall deal with output analysis and stress testing with respect to uncertainty or perturbations of input data for static risk constrained portfolio optimization problems by means of the contamination technique. Dependence of the set of feasible solutions on the probability distribution rules out the straightforward construction of convexity-based global contamination bounds. Results obtained in our paper [Dupa?ová, J., & Kopa, M. (2012). Robustness in stochastic programs with risk constraints. Annals of Operations Research, 200, 55–74.] were derived for the risk and second order stochastic dominance constraints under suitable smoothness and/or convexity assumptions that are fulfilled, e.g. for the Markowitz mean–variance model. In this paper we relax these assumptions having in mind the first order stochastic dominance and probabilistic risk constraints. Local bounds for problems of a special structure are obtained. Under suitable conditions on the structure of the problem and for discrete distributions we shall exploit the contamination technique to derive a new robust first order stochastic dominance portfolio efficiency test.     

Determination of genetic transferrin variants in human serum by high‐resolution capillary zone electrophoresis†

High‐resolution capillary zone electrophoresis in the routine arena with stringent quality assurance is employed for the determination of carbohydrate‐deficient transferrin in human serum. The assay comprises mixing of human serum with a Fe^III‐containing solution prior to analysis of the iron‐saturated mixture in a dynamically double‐coated capillary using a commercial buffer at alkaline pH. In contrast to other assays, it provides sufficient resolution for proper recognition of genetic transferrin variants. Analysis of 7290 patient sera revealed 166 isoform patterns that could be assigned to genetic variants, namely, 109 BC, 53 CD, one BD and three CC variants. Several subtypes of transferrin D can be distinguished as they have large enough differences in pI values. Subtypes of transferrin C and B cannot be resolved. However, analysis of the detection time ratios of tetrasialo isoforms of transferrin BC and transferrin CD variants revealed multimodal frequency histograms, indicating the presence of subtypes of transferrin C, B and D. The data gathered over 11 years demonstrate the robustness of the high‐resolution capillary zone electrophoresis assay. This is the first account of a capillary zone electrophoresis based carbohydrate‐deficient transferrin assay with a broad overview on transferrin isoform patterns associated with genetic transferrin variants.     

Mechanism of the antioxidant action of silybin and 2,3-dehydrosilybin flavonolignans: a joint experimental and theoretical study

Flavonolignans from silymarin, the standardized plant extract obtained from thistle, exhibit various antioxidant activities, which correlate with the other biological and therapeutic properties of that extract. To highlight the mode of action of flavonolignans as free radical scavengers and antioxidants, 10 flavonolignans, selectively methylated at different positions, were tested in vitro for their capacity to scavenge radicals (DPPH and superoxide) and to inhibit the lipid peroxidation induced on microsome membranes. The results are rationalized on the basis of (i) the oxidation potentials experimentally obtained by cyclic voltammetry and (ii) the theoretical redox properties obtained by quantum-chemical calculations (using a polarizable continuum model (PCM)-density functional theory (DFT) approach) of the ionization potentials and the O-H bond dissociation enthalpies (BDEs) of each OH group of the 10 compounds. We clearly establish the importance of the 3-OH and 20-OH groups as H donors, in the presence of the 2,3 double bond and the catechol moiety in the E-ring, respectively. For silybin derivatives (i.e., in the absence of the 2,3 double bond), secondary mechanisms (i.e., electron transfer (ET) mechanism and adduct formation with radicals) could become more important (or predominant) as the active sites for H atom transfer (HAT) mechanism are much less effective (high BDEs).