Degradation of copolymers of acrylonitrile and styrene in alkaline dimethyl sulphoxide solution

Investigations on the alkaline degradation of copolymers of acrylonitrile and styrene dissolved in dimethyl sulphoxide were carried out by means of viscometry, titrimetry and GPC measurements. The degradation reaction takes place with alkali concentrations higher than 1·3–1·4 × 10^?4 moles of KOH per gram of copolymer. Four to five new macromolecules arise from each starting macromolecule. A consumption of 1·3–1·5 moles of KOH was calculated for each new macromolecule formed.     

Improvements in the gas chromatographic determination of trace amounts of aliphatic amines in aqueous solution

The analysis of aliphatic amines at the parts per million level in aqueous solution has been improved with respect to a previously reported chromatographic method which made use of Carbopack B modified with 0.8% potassium hydroxide and 4% PEG 20M by altering these concentrations to 0.3% and 4.8%, respectively, by using a modified coating procedure. By this means, difficulties in duplicating from batch to batch the chromatographic characteristics of the column packing have been eliminated, and the instability of the retention times of amines on prolonged use of the column, the intolerance of the packing to injections of water and overlapping of tailed peaks for alcohols with the amine peaks no longer affect the trace determination of amines.     

Differential scanning calorimetry study of thermal decomposition of benzoyl peroxide and 2,2′-azobisisobutyronitrile mixtures

The thermal decompositions of benzoyl peroxide (Bz₂O₂), 2,2′-azobisisobutyronitrile (AIBN) and their mixtures in the absence of a solvent have been studied with DSC alone. At 378 K (Bz₂O₂ m.p.=376.5 K, AIBN m.p.=374 K) mixtures of the two compounds show a higher decomposition ΔH than expected from ΔH isothermal measurements on the pure compounds; the same decomposition ΔH values can be calculated as the sum of values obtained from DSC dynamic experiments. At 353 K and 363 K, isothermally measured enthalpy variations show a possible induced decomposition effect in Bz₂O₂ caused by radicals generated by AIBN decomposition.     

Differential scanning calorimetry study of reactions of phenyl glycidyl ether with phosphoric acid

The reactions of phenyl glycidyl ether (PGE) with phosphoric acid in three molar ratios have been studied by means of DSC alone. The results obtained from isothermal measurements are as follows:H=–91.0 kJ/mole PGE(1:1 molar ratio);H=–100.5 kj/mole PGE (1:2/3 molar ratio).The DSC curves obtained from dynamic experiments are multipeaked and giveHvalues higher than those obtained from isothermal measurements. These results can be explained by taking into account the acid concentration, the different reactivities of the hydrogens of the phosphoric acid and the possibility that secondary reactions occur.

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Zusammenfassung Die Reaktion von Phenylglycidyläther (PGE) mit Phosphorsäure wurde bei drei verschiedenen molaren Verhältnissen allein mittels DSC untersucht. Isotherme Messungen ergaben folgende Werte:H=–91.0kJ/mol PGE (molares Verhältnis 1:1);H=–100.5 kJ/mol PGE (molares Verhältnis 3:2). Die bei dynamischen Experimenten erhaltenen DSC-Kurven weisen viele Peaks auf und ergebenH-Werte, die größer als die durch isotherme Messungen erhaltenen sind. Diese Ergebnisse können erklärt werden, wenn die Säurekonzentration, die unterschiedliche Reaktivität der Wasserstoffatome der Phosphorsäure und die Möglichkeit des Verlaufs sekundärer Reaktionen in Rechnung gestellt werden.

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() () . 11 12/3, H, –91.0 –100.5 ·^–1. , , H . , , .

     

Search for X(3872) in gammagamma fusion and radiative production at CLEO

We report on a search for the recently reported X(3872) state using 15.1 fb(-1) of e(+)e(-) data taken in the sqrt[s] = 9.46-11.30 GeV region. Separate searches for the production of the X(3872) in untagged gammagamma fusion and e(+)e(-) annihilation following initial state radiation are made by taking advantage of the unique angular correlation between the leptons from the decay J/psi --> l(+)l(-) in X(3872) decay to pi(+)pi(-)J/psi. No signals are observed in either case, and 90% confidence upper limits are established as (2J+1)Gamma(gammagamma)(X(3872))B(X --> pi(+)pi(-)J/psi) < 12.9 eV and Gamma(ee)(X(3872))B(X- -> pi(+)pi(-)J/psi) < 8.3 eV.     

Community structure in large-scale cortical networks during motor acts

The purpose of the present work is to evaluate the community structure of the cortical network subserving the neurophysiologic processes in simple motor acts.To this end, we studied the topological properties of the functional brain connectivity in the frequency domain. The functional networks were estimated by means of the imaginary coherence from a dataset of high-resolution EEG recordings (4094 cortical sources) in a group of healthy subjects (n = 10) during a finger extension task. The analysis of the community structure was addressed through a particular detection algorithm that optimizes the modularity, a function related to the level of internal clustering inside the communities in the network. The principal results indicate that the cortical network changes its structural organization during the motor execution with respect to a baseline condition. Notably in the Beta band (12.5–30 Hz), the level of intra-module connectivity decreases, while inter-module connectivity increases reflecting the need for a neural integration of distant regions. Notably, this distributed interaction involves anatomical regions belonging to both the hemispheres including pre-motor and primary motor areas in the frontal and central part of the cortex as well as parietal associative regions, which are related to the planning, selection and execution of actions.     

Environmental degradation of a novel ethylene-propylene copolymer in thick sheets

The outdoor ageing of a commercial ethylene-propylene copolymer (Adflex) is investigated. Different techniques (infrared spectroscopy, thermal analysis, scanning electron microscopy, mechanical tests and positron annihilation lifetime spectroscopy) are used in order to obtain a comprehensive view of the modifications occurring during the environmental ageing of thick sheets of this copolymer. The degradation of the material is ascribed to a morphology variation, arising from the separation of amorphous oxidised copolymers initially dispersed in the bulk of the material. Weathering process takes places with increase of the bulk density of the sample.     

A characterization of horizontal visibility graphs and combinatorics on words

A Horizontal Visibility Graph (HVG) is defined in association with an ordered set of non-negative reals. HVGs realize a methodology in the analysis of time series, their degree distribution being a good discriminator between randomness and chaos Luque et al. [B. Luque, L. Lacasa, F. Ballesteros, J. Luque, Horizontal visibility graphs: exact results for random time series, Phys. Rev. E 80 (2009), 046103]. We prove that a graph is an HVG if and only if it is outerplanar and has a Hamilton path. Therefore, an HVG is a noncrossing graph, as defined in algebraic combinatorics Flajolet and Noy [P. Flajolet, M. Noy, Analytic combinatorics of noncrossing configurations, Discrete Math., 204 (1999) 203-229]. Our characterization of HVGs implies a linear time recognition algorithm. Treating ordered sets as words, we characterize subfamilies of HVGs highlighting various connections with combinatorial statistics and introducing the notion of a visible pair. With this technique, we determine asymptotically the average number of edges of HVGs.