Chemico-diffusion kinetics and TTT cure diagrams of DGEBA-DGEBF/amine resins cured with phenol catalysts

Curing of epoxy-amine resins with bisphenol A (BPA) as an external catalyst was studied from differential scanning calorimetry analyses in isothermal and dynamic modes. Both phenomenological and mechanistic models have been tested. The mechanistic model where epoxy cure is postulated to only occur through hydroxyl-catalyzed reactions, and assuming a different reactivity of both types of hydroxyl groups (from BPA and epoxy chains) provided a reasonable fitting of the whole set of experimental data. In particular, the latter model provides good predictive behavior for changes in the mixture composition (BPA content varying in the range from 3 to 10 wt.%, relative to the weight of hardener), contrary to the model based on the same reactivity of both types of hydroxyl groups.The isothermal time-temperature-transformation (TTT) diagram including the time to vitrification and iso-T_g curves of the complex epoxy system was also established.     

Single-cell gel/comet assay applied to the analysis of UV radiation-induced DNA damage in Rhodomonas sp. (Cryptophyta).

The single-cell gel/comet assay is an electrophoretic technique used to detect single-strand breaks in DNA. Damage is assessed examining individual cells under an epifluorescent microscope. UV-induced DNA damage consists mostly of the formation of pyrimidine dimers; therefore, most of the damage cannot be detected using a standard comet assay. The enzyme T4 endonuclease V breaks DNA strands at sites of pyrimidine dimers. The main objective of this work is to evaluate the comet assay to detect UV-induced damage in DNA after an initial treatment of cells with T4 endonuclease V. This work was conducted on Rhodomonas sp. (Cryptophyta), a marine unicellular flagellate. Cells of Rhodomonas sp. were exposed to 12 h visible + ultraviolet-A + ultraviolet-B (VIS + UVA + UVB) and VIS (control), with and without T4 endonuclease V. Cells exposed to VIS + UVA + UVB showed approximately 200% more damage than control if these were treated with T4 endonuclease V. Rhodomonas sp. were exposed to 3, 6, 9 and 12 h of VIS, VIS + UVA and VIS + UVA + UVB. Damage induced by VIS + UVA + UVB as detected by the comet assay increased along with exposure time. However, damage caused by VIS and VIS + UVA remained relatively constant at all times. Results of this study indicate that the comet assay is more sensitive to UV radiation damage when used in conjunction with T4 endonuclease V. This modification of the comet assay can be used as an alternative technique to detect DNA damage in single cells caused by UV radiation.     

Dynamic behavior of ultrahigh molecular weight poly(methyl methacrylate) in semidilute solutions

The paper presents some rheological investigations on ultrahigh molecular weight (u.h.m.w.) (M_w > 10⁷) poly(methyl methacrylate) in semidilute solutions. The main interest was to study the viscoelastic behavior of the semidilute solutions at different concentrations and temperatures. In the 60‐600 rad/s frequency range, the experimental data show a predominantly elastic response (G′ > G″) for the long poly(methyl methacrylate) chains in toluene.     

Water transport in epoxy-aliphatic amine networks - Influence of curing cycles

In this work, polyepoxide network based on an aliphatic amine hardener were cured under different curing temperatures and their water sorption characteristics was systematically investigated as function of cure conditions. Attention was focused on the analysis of equilibrium properties, swelling behaviour and thermomechanical properties.For the undercured systems (epoxide conversion around 0.90), additional crosslinking reactions take part during water immersion, even at 20 °C. This effect was found to be mainly related to plasticizing of the network by water molecules.Local dynamics and plasticization effects were also monitored by dynamic mechanical analysis (DMA). The changes in the glass transition for the two well-crosslinked epoxies were greater than those predicted by considering the free volume changes only. The β process was significantly affected by the absorbed water. A decrease of the average relaxation time with moisture uptake was observed. The disruptions of the α and β relaxations were found to be reversible after re-drying of the wet material for the nearly fully cured epoxies.The fully crosslinked network was found to absorb slightly more water and at a greater rate than a slightly less crosslinked network (conversion around 0.98). This anomalous behaviour was analysed and a tentative explanation was presented in this paper.     

Comparison between train noise and road noise annoyance during sleep

Sleep disturbance by train and road noises was studied through in situ physiological recordings on two groups of people submitted to both types of exposure. At different sites acoustical parameters do not influence sleep in the same way. In a quiet place, emergence is an important factor of disturbance, but in a noisy place, noise duration and peak level are acting with interaction to disturb sleep.     

A Parallel Block-Structured Finite Volume Method for Flows in Complex Geometry with Sliding Interfaces

An implementation of the finite volume method is presented for the simulation of three dimensional flows in complex geometries, using block structured body fitted grids and an improved linear interpolation scheme. The interfaces between blocks are treated in a fully implicit manner, through modified linear solvers. The cells across block interfaces can be matching one-to-one or many-to-one. In addition, the use of sliding block interfaces allows the incorporation of moving rigid bodies inside the flow domain. An algebraic multigrid solver has been developed that works with this block structured approach, speeding up the iterations for the pressure. The flow solver is parallelized by domain decomposition using OpenMP, based on the same grid block structure. Application examples are presented that demonstrate these capabilities. This numerical model has been made freely available by the authors. G. Usera was supported by FPI/DPI2003-06725-C02-01 from DGI, Ministerio de Educación y Cultura y Fondos FEDER, Spain, grants 33/07 PDT, I+D CSIC, Uruguay.     

MAD: practical implementation of MCAO concepts

The European Southern Observatory (ESO) together with external research institutes have built a Multi-Conjugate Adaptive Optics (MCAO) Demonstrator (MAD) to perform wide field-of-view adaptive optics correction (2′ in K band). The aim of MAD is to demonstrate the on-sky feasibility of the MCAO technique and to evaluate its critical aspects in the framework of both the 2nd generation instrumentation for the Very Large Telescope (VLT) and the Overwhelmingly Large Telescope (OWL). The MAD module will be installed on the VLT to perform on-sky observations. MAD comprises two deformable mirrors and two different multi-reference wavefront sensors with natural guide stars. In this article we present the MAD design, some aspects of the MAD calibration and the first closed-loop results in the laboratory in Single Conjugated Adaptive Optics (SCAO) and Ground Layer Adaptive Optics (GLAO) configurations. To cite this article: E. Marchetti et al., C. R. Physique 6 (2005).     

Reactivite comparee en catalyse redox de plusieurs telogenes halogenes vis-a-vis du butadiene

Using copper chloride as catalyst, we have achieved telomerization of butadiene with several different halogenated compounds as telogens. These telogens must have a CCl₃ group to be active as transfer agents. There is a linear relationship between log (telogen reactivity) and the σ¹ Taft constant of the R group. Using this relation, we have determined the values of the σ¹ constants for some halogenated substances. The reactivities of the telogens can be measured by this means. The results confirm those obtained earlier with styrene.     

Slope effects on the fluid dynamics of a fire spreading across a fuel bed: PIV measurements and OH* chemiluminescence imaging

Slope is among the most influencing factor affecting the spread of wildfires. A contribution to the understanding of the fluid dynamics of a fire spreading in these terrain conditions is provided in the present paper. Coupled optical diagnostics are used to study the slope effects on the flow induced by a fire at laboratory scale. Optical diagnostics consist of particle image velocimetry, for investigating the 2D (vertical) velocity field of the reacting flow and chemiluminescence imaging, for visualizing the region of spontaneous emission of OH radical occurring during gaseous combustion processes. The coupling of these two techniques allows locating accurately the contour of the reaction zone within the computed velocity field. The series of experiments are performed across a bed of vegetative fuel, under both no-slope and 30° upslope conditions. The increase in the rate of fire spread with increasing slope is attributed to a significant change in fluid dynamics surrounding the flame. For horizontal fire spread, flame fronts exhibit quasi-vertical plume resulting in the buoyancy forces generated by the fire. These buoyancy effects induce an influx of ambient fresh air which is entrained laterally into the fire, equitably from both sides. For upward flame spread, the induced flow is strongly influenced by air entrainment on the burnt side of the fire and fire plume is tilted toward unburned vegetation. A particular attention is paid to the induced air flow ahead of the spreading flame. With increasing the slope angle beyond a threshold, highly dangerous conditions arise because this configuration induces wind blows away from the fire rather than toward it, suggesting the presence of convective heat transfers ahead of the fire front.     

Plasma Streamwise Vortex Generators for Flow Separation Control on Trucks

An experimental study of the effect of Dielectric Barrier Discharge plasma actuators on the flow separation on the A-pillar of a modern truck under cross-wind conditions has been carried out. The experiments were done in a wind tunnel with a 1:6 scale model of a tractor-trailer combination. The actuators were used as vortex generators positioned on the A-pillar on the leeward side of the tractor and the drag force was measured with a wind-tunnel balance. The results show that the effect at the largest yaw angle (9 degrees) can give a drag reduction of about 20% and that it results in a net power reduction. At lower yaw angles the reduction was smaller. The present results were obtained at a lower Reynolds number and a lower speed than for real driving conditions so it is still not yet confirmed if a similar positive result can be obtained in full scale.