Conjugated effects of the compatibilization and the dynamic vulcanization on the phase inversion behavior in poly(butylene terephthalate)/epoxide-containing rubber reactive polymer blends

The conjugated effects of both reactive compatibilization and dynamic vulcanization on the phase inversion behavior of poly(butylene terephthalate) (PBT)/epoxide-containing rubber blends have been studied in detail. Pure ethylene-methyl acrylate random copolymer (E-MA) and ethylene-methyl acrylate-glycidyl methacrylate random terpolymer (E-MA-GMA) were used as non reactive or reactive rubber phase, respectively. Location of the phase inversion region was studied using several techniques, including transmission electron microscopy (TEM) and dynamical mechanical thermal analysis (DMTA). To evaluate the relative influence of the blend compatibilization and the dynamic vulcanization on the phase inversion behavior, the relative kinetics of the two reactions were modified using different PBT and E-MA-GMA grades. The obtained results show unambiguously that the position and the width of the phase inversion region is essentially governed by the kinetic of the dynamic vulcanization process. The effect of the blend compatibilization remains quite limited even in the case of fast interfacial reaction. The crosslinking of the rubber phase induces an important shift of the phase inversion composition to higher rubber content. For blends containing low molecular weight PBT, up to 60 wt% of rubber can be homogeneously dispersed in the PBT matrix at long mixing time. In this case, development of high performance PBT based thermoplastic vulcanisates can be envisioned.     

Mechanical characterization and modeling of the deformation and failure of the highly crosslinked RTM6 epoxy resin

The nonlinear deformation and fracture of RTM6 epoxy resin is characterized as a function of strain rate and temperature under various loading conditions involving uniaxial tension, notched tension, uniaxial compression, torsion, and shear. The parameters of the hardening law depend on the strain-rate and temperature. The pressure-dependency and hardening law, as well as four different phenomenological failure criteria, are identified using a subset of the experimental results. Detailed fractography analysis provides insight into the competition between shear yielding and maximum principal stress driven brittle failure. The constitutive model and a stress-triaxiality dependent effective plastic strain based failure criterion are readily introduced in the standard version of Abaqus, without the need for coding user subroutines, and can thus be directly used as an input in multi-scale modeling of fibre-reinforced composite material. The model is successfully validated against data not used for the identification and through the full simulation of the crack propagation process in the V-notched beam shear test.     

Close Shadowing Natural Versus Synthetic Speech

Close shadowing experiments involving natural and synthetic stimuli are described. Preliminary results show that speakers are able to follow natural stimuli with an average delay of 70 ms whereas this delay typically exceeds 100 ms for stimuli produced by text-to-speech systems. A complementary experiment shows that this contrast is mainly due to the inappropriate or impoverished prosody generated by actual text-to-speech systems.     

Dynamic behavior of an aggregate material at simultaneous high pressure and strain rate: SHPB triaxial tests

Low velocity impacts on energetic materials induce plastic deformations and sliding friction which can lead to ignition. If some ignition criteria have been proposed, the remaining difficulty is to characterize the mechanical behavior of the material when submitted to the corresponding solicitations (high pressure and high strain rate). Thus, a technique based on the Split Hopkinson Pressure Bars system is proposed to carry out a triaxial compression test. A cylindrical specimen is placed into a confining ring and is compressed by the system of bars. The ring prevents the radial extension of the specimen and creates a lateral confining pressure. The material and dimensions chosen for the ring maintain a constant radial pressure during the test. Some tests were carried out on an inert aggregate material and proved the validity of this experimental device. The experimental data processing shows the influence of both the pressure and the strain rate. The shear stresses, which contribute to thermal dissipation and then to the ignition threshold, increase according to the pressure.     

Tight binding of the antitumor drug ditercalinium to quadruplex DNA

The structural selectivity of the DNA-binding antitumor drug ditercalinium was investigated by competition dialysis with a series of nineteen different DNA substrates. The 7H-pyridocarbazole dimer was found to bind to double-stranded DNA with a preference for GC-rich species but can in addition form stable complexes with triplex and quadruplex structures. The preferential interaction of the drug with four-stranded DNA structures was independently confirmed by electrospray mass spectrometry and a detailed analysis of the binding reaction was performed by surface plasmon resonance (SPR) spectroscopy. The BIAcore SPR study showed that the kinetic parameters for the interaction of ditercalinium with the human telomeric quadruplex sequence are comparable to those measured with a duplex sequence. Slow association and dissociation were observed with both the quadruplex and duplex structures. The newly discovered preferential binding of ditercalinium to the antiparallel quadruplex sequence d(AG(3)[T(2)AG(3)](3)) provides new perspectives for the design of drugs that can bind to human telomeres.     

Low-dissipation and low-dispersion fourth-order Runge–Kutta algorithm

An optimized explicit low-storage fourth-order Runge–Kutta algorithm is proposed in the present work for time integration. Dispersion and dissipation of the scheme are minimized in the Fourier space over a large range of frequencies for linear operators while enforcing a wide stability range. The scheme remains of order four with nonlinear operators thanks to the low-storage algorithm. Linear and nonlinear propagation problems are finally solved to illustrate the accuracy of the present Runge–Kutta scheme.     

Component composition preserving behavioral contracts based on communication traces

This paper investigates the compositional properties of reusable software components defined with explicit dependencies and behavioural contracts expressing rely-guarantee specifications in the form of communication traces. In this setting, connection of components through their matching ports is indeed compositional and yields a new component or composite that respects its constituents’ contracts. Thus the behaviour of the composite is computed from the behaviours of its constituents and is known to conform to the contracts without any new proof.     

High Molecular Weights,Polydispersities, and Annealing Temperatures in the Optimization of Bulk‐Heterojunction Photovoltaic Cells Based on Poly(3‐hexylthiophene) or Poly(3‐butylthiophene)

A series of poly(3‐hexylthiophene)s (P3HTs) and poly(3‐butylthiophene)s (P3BTs) with predetermined molecular weights and varying polydispersities are prepared using a simplified Grignard metathesis chain‐growth polymerization. Techniques were elaborated to prepare extremely high molecular weight P3HT (number‐average molecular weight of around 280 000 g mol^–1) with a low polydispersity (< 1.1) without resorting to fractionation. Optimization of the annealing of a series of solar cells based on blends of poly(3‐alkylthiophene)s (P3ATs) and [6,6]‐phenyl C₆₁ butyric acid methyl ester indicates that the polydispersities, molecular weights, and degrees of conjugation of the P3ATs all have an important impact not only on cell characteristics but also on the most effective annealing temperature required. The results indicate that each cell requires annealing treatments specific to the type of polymer and its molecular weight distribution.     

Thermally induced redistribution and degradation of bisphenol-A polycarbonate fractions in open and closed systems

Thermally induced chain-scission and redistribution reactions in as-polymerized and fractionated bisphenol-A polycarbonate (PC) materials made by melt-transesterification and interfacial polymerization were studied at temperatures between 200 and 300 °C in open systems, where volatile reaction products are continuously removed, and in closed systems, where these products are retained. Under the applied conditions, PC made via interfacial polymerization shows no measurable susceptibility towards redistribution. This is the result of an extremely low concentration of hydroxyl end-groups. Upon similar thermal treatment, PC made by melt-transesterification undergoes fast redistribution which leads to post-condensation in open systems and strong changes of molecular weight distributions (MWDs) for fractions in all cases. Redistribution effects were visualized through changes in the MWD of mixed fractions. The initial stages of redistribution were simulated using a Monte Carlo method based on a random sampling technique. From comparison between experimental and simulation results, it can be concluded that approximately half a percent of all carbonate linkages is involved in a redistribution reaction per minute at 250 °C for the studied samples.