Effect of NBR partitioning agent on the mechanical properties of PVC/NBR blends and investigation of phase morphology by atomic force microscopy

Poly(vinyl chloride) (PVC)/acrylonitrile–butadiene rubber (NBR) blends with different types of partitioning agent were obtained through melt blending. The samples were characterized according to the viscosities properties, torque rheometry and mechanical resistance as tensile testing, tear strength, and hardness. The morphology and phase imaging were studied using an atomic force microscopy operating in tapping mode (TMAFM). It was observed that the PVC/NBR blends with PVC as partitioning agent showed an increase in the tensile stress and Young’s modulus compared to the PVC/NBR blends with calcium carbonate as partitioning agent. The morphology of the blends examined by TMAFM evidenced the effect of the partitioning agent as obtained with other techniques.     

A next-generation service overlay architecture

The rapid evolution of next-generation networks and, in particular, fixed mobile convergence infrastructures raises the issue of providing personalized services adapted to the user’s context such as its device, access network, preferences, or quality of service (QoS) requirements. To design such value-added services, one solution consists in composing dynamically distributed service entities. In this paper, we propose a service overlay architecture in which a service level path is dynamically established to fulfill the user’s requirements. In order to meet this goal, two main issues have to be considered: service components discovery and service path management (i.e., setup, reconfiguration, release). The former issue is addressed based on a peer-to-peer approach in which QoS features are integrated in service lookup. For the latter issue, we rely on the Session Initiation Protocol to automate the setup of the service composition as well as its adaptation in case of perturbations (e.g., user switching device or service component failure).     

Vibrational and thermal study on the in vitro and in vivo degradation of a poly(lactic acid)-based bioabsorbable periodontal membrane

Fourier transform Raman (FT-Raman), attenuated total reflection/Fourier transform infrared (ATR/FT-IR) spectra and differential scanning calorimetry (DSC) measurements were performed on a poly(lactic acid)-based biodegradable periodontal membrane in order to study its in vitro and in vivo degradation mechanism and kinetics. For this purpose, the hydrolitic in vitro degradation of the membrane was investigated in two aqueous media: saline phosphate buffer (SPB, pH=7.4) and 0.01 M NaOH solution. Moreover, a membrane implanted in vivo for four weeks for treatment of contiguous vertical bony defects, was examined. Vibrational and thermal measurements show that the membrane has a prevalently amorphous structure and is composed of low molecular weight polymeric chains. The degradation is faster in NaOH solution than in SPB and occurs heterogeneously without any significative increase in crystallinity. The DSC and spectroscopic measurements are discussed in comparison with the trend of % weight loss and show a progressive decrease in molecular weight. Regarding the Raman analysis, the I₈₇₅/I₁₄₅₂ intensity ratio was identified as a marker of the degree of degradation. Regarding the in vivo degradation, the presence, spectroscopically revealed, of a biological component entrapped in the membrane proves the good integration of the membrane with the surrounding tissues. The membrane seems to degrade faster in vivo than in vitro. A comparison with the degradation mechanism and kinetics of a periodontal membrane previously studied, Vicryl® periodontal mesh, is made.     

Determination of PAHs in various smoked meat products and different samples by enzyme immunoassay

An enzyme immunoassay was used to determine benzo[a ]pyrene (BaP) in smoked meat products and other samples of food and environmental origin. The method used has a detection limit (3 σ) of 0.1 μg kg⁻¹ and a coefficient of variation less than 10%. The main aim of the study was to compare the possible influence of different smoking processes and packaging material on the amount of BaP deposited on smoked meat product, mainly different sausages. The lowest amount of BaP was found when smoke produced by steam in the indirect method smoking‐chamber was used. A slightly protective effect of polyamide casing was noted. © 1999 Society of Chemical Industry     

Phase equilibrium and diffusivities of hydrofluorocarbons in a synthetic polyol ester lubricant

Detailed knowledge about the thermophysical properties of refrigerant/lubricant systems, such as solubility and diffusivity, are required for the design, operation, and long-term reliability of heating, ventilation, air-conditioning, and refrigeration equipment. Herein, vapor–liquid equilibrium of hydrofluorocarbons (HFCs) 1,1,1,2-tetrafluoroethane (R-134a), pentafluoroethane (R-125), and difluoromethane (R-32) in a polyol ester oil (ISO VG 32) were measured using a gravimetric microbalance at temperatures ranging from 248.15 to 348.15 K and up to 1.0 MPa of pressure. The experimental solubility data of each refrigerant/lubricant system were successfully modeled using the nonrandom two liquid activity coefficient model. A one-dimensional diffusion equation was applied on time-dependent absorption data to determine binary diffusion coefficients (D) for the refrigerants in the ISO VG 32 lubricant. Finally, Stokes–Einstein diffusing radius calculations support the hypothesis that HFCs dissolve into ISO VG 32 lubricant as individual molecules rather than associated complexes.     

Numerical difficulties and computational procedures for thermo-hydro-mechanical coupled problems of saturated porous media

This paper analyses the numerical difficulties commonly encountered in solving fully coupled numerical models and proposes a numerical strategy apt to overcome them. The proposed procedure is based on space refinement and time adaptivity. The latter, which in mainly studied here, is based on the use of a finite element approach in the space domain and a Discontinuous Galerkin approximation within each time span. Error measures are defined for the jump of the solution at each time station. These constitute the parameters allowing for the time adaptivity. Some care is however, needed for a useful definition of the jump measures. Numerical tests are presented firstly to demonstrate the advantages and shortcomings of the method over the more traditional use of finite differences in time, then to assess the efficiency of the proposed procedure for adapting the time step. The proposed method reveals its efficiency and simplicity to adapt the time step in the solution of coupled field problems.     

Solution and bulk rheological behavior of poly(ethylenes) based on VERSIPOL™ catalysts

Palladium catalysts [(ArNC(Me)-C(Me)NAr)Pd(CH₂)₃(COOMe)]⁺ (VERSIPOL™) or [(ArNC(Me)-C(Me)NAr)Pd(CH₂)₃(COOMe)]⁺ (Ar=2,6-i-Pr₂-C₆H₃, 2,6-Me₂-C₆H₃ or C₆H₅ and Ar′=3,5-(CF₃)₂-C₆H₃) were synthesized and tested, in dichloromethane, for the polymerization of ethylene. The influence of the substituent present on the diimine ligand on the molar mass of the resulting polymers was examined first. Poly(ethylene)s obtained in the presence of catalysts containing the bulky 2,6-i-Pr₂ group, prepared at different ethylene pressures, exhibited almost identical weight average molar mass values, but were characterized by great differences in hydrodynamic volume, radius of gyration and intrinsic viscosity values. These differences were attributed to the evolution of the topology going from hyperbranched to almost linear. Similar observations were made earlier. The major part of the work dealt with new results on the behavior of these PE samples examined in terms of particle scattering function q^5/3I(q) (Kratky-Porod) plot based on small angle neutron scattering experiments and on the semi-dilute solution behavior. Some results on the bulk rheological properties of these polymers were presented in the last section and corroborated the results obtained in dilute or semi-dilute solution. The data were compared also to PE obtained with other catalysts.     

Crystal chemistry of transuranium tungsten bronzes TuxWO3 (Tu = Np,Pu, Am)

Three transuranium tungsten bronzes have been synthetised for the first time in the systems TuO₂-WO₃-W systems (Tu=Np, Pu, Am). They were identified using X-ray powder diffraction; their structures are of perovskite type. Both plutonium and americium bronzes show a trivalent oxidation state, whereas Mőssbauer spectra reveal clearly a Np^IV ion in Np_xWO₃.