Thermomechanical analysis of a toughened thermosetting system

The experimental results of viscoelastic mechanical tests, at five different levels of conversion, are reported for a thermoset composite matrix system toughened with an appropriate percentage of a thermoplastic polymer. The results from static tests are used to construct the master curves at a specific degree of cure, while the shift factors are compared with the corresponding values from dynamic experiments in order to assess the validity of the time-temperature superposition for each conversion. Neat resin plates were cured accurately, according to the full kinetics model for a dynamic and isothermal temperature regime; the conversion gradient in the plane and across the thickness of the plates was assessed by a thermal analysis of samples taken from different locations before extracting the samples from them. The viscoelastic behaviour of the resin matrix showed a sensible difference in the relaxation time spectrum upon conversion according to the provisional trend of mobility theory; a higher conversion induced a horizontal shift of the principal relaxation time for each level of conversion, which could be related very well to the glass transition at the same conversion. Good results were also obtained for the ultimate modulus of the resin at a temperature just before the onset of the co-curing phase for partially cured samples. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 2, pp. 265–278, March–April, 2008.     

Bond exciton model of alkenes and diene polymers

The bond exciton model, developed originally for alkane molecules, is applied here to a range of alkene molecules and diene polymers. The necessary empirical parameters are derived by comparison of the theory with the vacuum-ultraviolet absorption spectra of ethylene and a number of alkyl-substituted ethylenes, and these values are used to predict the energies, intensities and polarizations of the lower energy allowed valence transitions of fine diene polymers. Despite its simplicity the bond exciton model is found to give results in quite reasonable agreement with the available experimental data, and suggests that considerable excitation energy transfer may occur along the main chains of certain diene polymers.     

Finite element simulation of water circulation in the North Sea

The modelling of tidal effects, storm surges and currents in large bodies of water is considered. The solution is attempted using the evolutionary shallow water equations with velocities and wave heights as unknowns. Two finite element simulation models are described based on six noded triangular elements. Special consideration has been given to the adequacy of the models which were applied to the North Sea only after extensive tests in channels. Results for velocities and wave heights are compared and discussed. A set of conclusions on the applicability and scope of the models is presented.     

Deformation of a trapped Fermi gas with unequal spin populations

The real-space densities of a polarized strongly interacting two-component Fermi gas of 6Li atoms reveal two low-temperature regimes, both with a fully paired core. At the lowest temperatures, the unpolarized core deforms with increasing polarization. Sharp boundaries between the core and the excess unpaired atoms are consistent with a phase separation driven by a first-order phase transition. In contrast, at higher temperatures the core does not deform but remains unpolarized up to a critical polarization. The boundaries are not sharp in this case, indicating a partially polarized shell between the core and the unpaired atoms. The temperature dependence is consistent with a tricritical point in the phase diagram.     

Diffusion tensor magnetic resonance imaging of the normal breast

Purpose

The objective of this study was to evaluate diffusion anisotropy of the breast parenchyma and assess the range and repeatability of diffusion tensor imaging (DTI) parameters in normal breast tissue.

Materials and Methods

The study was approved by our institutional review board and included 12 healthy females (median age, 36 years). Diffusion tensor imaging was performed at 1.5 T using a diffusion-weighted echo planar imaging sequence. Diffusion tensor imaging parameters including tensor eigenvalues (λ₁, λ₂, λ₃), fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured for anterior, central and posterior breast regions.

Results

Mean normal breast DTI measures were λ₁=2.51×10⁻³ mm²/s, λ₂=1.89×10⁻³ mm²/s, λ₃=1.39×10⁻³ mm²/s, ADC=1.95±0.24×10⁻³ mm²/s and FA=0.29±0.05 for b=600 s/mm². Significant regional differences were observed for both FA and ADC (P<.05), with higher ADC in the central breast and higher FA in the posterior breast. Comparison of DTI values calculated using b=0, 600 s/mm² vs. b=0, 1000 s/mm², showed significant differences in ADC (P<.001), but not FA. Repeatability assessment produced within-subject coefficient of variations of 4.5% for ADC and 11.4% for FA measures.

Conclusion

This study demonstrates anisotropy of water diffusion in normal breast tissue and establishes a normative range of breast FA values. Attention to the influence of breast region and b value on breast DTI measurements may be important for clinical interpretation and standardization of techniques.     

HPLC–MS Profiling and Structural Identification of [14C]-Diclofenac Metabolites in Mouse Bile

Biliary metabolites present at 6 h post-dose following a single oral dose of [¹⁴C]-diclofenac (10 mg kg^?1) to male bile duct-cannulated C57BL/6 J mice were profiled and identified. Over the 6 h duration of the study ~19.5 % of the administered radioactivity was excreted into the bile as either [¹⁴C]-diclofenac or metabolites. When profiled using HPLC with online radiodetection, the presence of at least 13 radiolabelled components was indicated. These compounds were shown, by consecutive reaction mass spectrometry, to comprise a range of hydroxylated metabolites conjugated to either taurine, glucose and/or glucuronic acid. Both phenolic and acylglucuronide-containing metabolites were observed. The confirmation of the presence of these glucuronide conjugates in mouse bile may have important consequences in the light of emerging theories concerning the role of bacterial glucuronidases for the GI-tract toxicity of NSAIDs such as diclofenac.     

Mechanism of copper underpotential deposition at Pt(<Emphasis Type="Italic">hkl</Emphasis>)-electrodes: Quantum-chemical modelling

Mechanism of copper underpotential deposition at stepped faces of platinum single crystals Pt(hkl) is studied using cyclic voltammetry, scanning probe microscopy, and quantum-chemical modelling. It is shown that the first stage of UPD is one-dimensional decoration of the (100)- or (110)-orientated steps, then copper monolayer forms at (111)-terraces. The final stage is the secondary step decoration. Quantum-chemical modelling, with the using of long-distance potentials of the Cu-Pt and Cu-Cu pair interactions, allows estimating the energy of copper adsorption at different structure elements of the substrate (steps, kinks, terraces) and revealing the succession of the adatom monolayer formation; it also provides additional information for the identifying of the nature of voltametric peaks for different stages of the copper adsorption-desorption.     

Plasma Copolymerization of Pyrrole with Si-Compounds

The plasma copolymerization of pyrrole with hexamethyldisiloxane, hexamethyldisilane and hexamethyldisilazane was investigated with regard to the polymer deposition characteristics and the properties of the product films. Deposition rates were evaluated by monitoring the weight increase of the deposits over time, and the effect of varying the experimental set up parameters was determined. The results of deposition rates and quantitative IR analysis suggested that the increasing amounts of Si-components were incorporated into the polymer matrix as the supply ratio of the Si-monomer was increased. The Si-component in the copolymer brought some dramatic effects on the physical properties of the films and changed the hydrophobicity of the surfaces, as reflected in the advancing and receding contact angle measurements. The experimental results obtained are discussed in terms of the contribution of the polar and dispersion components of surface energy.