Second-order estimates for the large-deformation response of particle-reinforced rubbersEstimations homogénéisées pour le comportement mécanique des caoutchoucs renforcés en grandes déformations

This paper presents the application of a recently proposed ‘second-order’ homogenization method (J. Mech. Phys. Solids 50 (2002) 737–757) to the estimation of the effective behavior of hyperelastic composites subjected to finite deformations. The main feature of the method is the use of ‘generalized’ secant moduli that depend not only on the phases averages of the fields, but also on the phase covariance tensors. The use of the method is illustrated in the context of particle-, or fiber-reinforced elastomers and estimates analogous to the well-known Hashin–Shtrikman estimates for linear-elastic composites are generated. The new estimates improve on earlier estimates (J. Mech. Phys. Solids 48 (2000) 1389–1411) neglecting the use of fluctuations. In particular, the new estimates, unlike the earlier ones, are capable of recovering the exact incompressibility constraint when the matrix is also taken to be incompressible. To cite this article: O. Lopez-Pamies, P. Ponte Castañeda, C. R. Mecanique 331 (2003).     

SET-VALUED EXTENSION OF OPERATORS VIA STEINER SELECTIONS (Ⅰ)-THEORETICAL RESULTS

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｍａｉｎｔｏｐｉｃｉｎｔｈｉｓｐａｐｅｒｉｓ:Ｈｏｗｃａｎｏｎｅｅｘｔｅｎｄａｎｏｐｅｒａｔｏｒｄｅｆｉｎｅｄｉｎａｓｐａｃｅｏｆｃｏｎｔｉｎｕｏｕｓｆｕｎｃｔｉｏｎｓｔｏａｎｏｐｅｒａｔｏｒｄｅｆｉｎｅｄｉｎａｓｐａｃｅｏｆｃｏｎｔｉｎｕｏｕｓｓｅｔ＿ｖａｌｕｅｄｆｕｎｃｔｉｏｎｓ,ｖｉａｓｅｌｅｃｔｉｏｎｓ?Ａｆｉｒｓｔ,ｎａｉｖｅｉｄｅａｃｏｕｌｄｂｅｔｈｅｆｏｌｌｏｗｉｎｇ :ＧｉｖｅｎａＰｏｌｉｓｈｓｐａｃｅＥ ,ｌｅｔＸｂｅａｃｏｎｔｉｎｕｏｕｓｆｕｎｃｔｉｏｎ…     

Effect of pH and added electrolyte on the thermal-induced transitions of egg yolk

Thermally-induced transitions of egg yolk were studied using Differential Scanning Calorimetry (DSC) and temperature-controlled Small Amplitude Oscillatory Shear (SAOS). The influence of composition (pH and electrolyte content and type) was analysed. The results obtained under DSC measurements suggest a continuous evolution in protein denaturation that depends on pH and salt content. Cure experiments performed using SAOS show dramatic increases in viscoelasticity functions. Protein gelation is affected by the pH, ionic strength and salt type. SAOS was also used to obtain the mechanical spectra of egg yolk dispersions and gels as a function of composition. The microstructures of gels were also evaluated by Scanning Electron Microscopy (SEM). SEM results reveal an increase in microstructure homogeneity and a decrease in the size of aggregates at lowered pH. The influence of pH and ionic strength on linear viscoelastic properties and microstructure may be explained in terms of the model for the formation of gel networks of globular proteins. However, the characteristic structure of native yolk must also be considered.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Protein-based bioplastics: effect of thermo-mechanical processing

Bioplastics based on glycerol and different proteins (wheat gluten, albumen, rice and albumen/gluten blends) have been manufactured to determine the effect that processing and further thermal treatments exert on different thermo-mechanical properties of the bioplastics obtained. Oscillatory shear, modulated differential scanning calorimetry, dynamic mechanical thermal analysis, thermo-gravimetric analysis and water absorption tests were carried out to study the effect of processing on the physical characteristics of the bioplastics. The protein-based bioplastics studied in this work present a high capacity for thermosetting modification because of protein denaturation that may favour the development of a wide variety of materials. The use of albumen or rice protein allows the reduction in both protein concentration and thermosetting temperature, leading to linear viscoelastic moduli values similar to those of synthetic polymers such as LDPE and HDPE. The hygroscopic characteristics of protein-glycerol bioplastics may lead to a decrease in the values of the linear viscoelasticity functions. However, hygroscopic properties depend on the protein nature and may be used for industrial applications where water absorption is required. This paper was presented at Annual European Rheology Conference (AERC) held in Hersonisos, Crete, Greece, April 27–29, 2006.     

Complementary use of X‐ray methods to study ancient production remains and metals from Northern Portugal

Archaeological artefacts recovered at Castanheiro do Vento (Northern Portugal) were characterised by integrating macro and micro‐energy dispersive X‐ray fluorescence spectrometry (EDXRF) and scanning electron microscopy with X‐ray microanalysis. The collection includes metallurgical remains (ceramic crucibles, a metallic nodule and a vitrified fragment) and metals (tools and ornaments) whose chronology spans from the Chalcolithic to the Roman Age. The study of production remains was able to identify distinct copper‐based metallurgical operations including the smelting of copper ores, the melting of copper and tin and/or the melting of bronze scrap. Micro‐EDXRF identified copper and arsenical copper tools as well as bronze and leaded bronze ornaments. The composition of tools (Cu with varying As contents: 0.46–3.6%) reveals an incipient technology, typical of the Chalcolithic till the Middle Bronze Age. On the contrary, ornaments are composed by different alloys – low tin bronze (4.8% Sn), high tin bronze (14.9% Sn) and high tin‐leaded bronze (16.5% Sn and 2.4% Pb) ? evidencing technological and economic choices that clearly indicate a late period such as the Roman Age. In conclusion, this multiproxy approach was able to study those ancient artefacts with a minimum impact on their archaeological and museological significance while providing important answers to the interpretation of the archaeological settlement and to better understand the metallurgical evolution in the Portuguese territory. Copyright © 2014 John Wiley & Sons, Ltd.     

Emergent nesting of the Fermi surface from local-moment description of iron-pnictide high-T<Subscript>c</Subscript> superconductors

We uncover the low-energy spectrum of a t-J model for electrons on a square lattice of spin-1 iron atoms with 3d _xz and 3d _yz orbital character by applying Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of one hole roaming over a 4 × 4 × 2 lattice. Hopping matrix elements are set to produce hole bands centered at zero two-dimensional (2D) momentum in the free-electron limit. Holes can propagate coherently in the t-J model below a threshold Hund coupling when long-range antiferromagnetic order across the d + = 3d _{(x + iy)z} and d ? = 3d _{(x ? iy)z} orbitals is established by magnetic frustration that is off-diagonal in the orbital indices. This leads to two hole-pocket Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate spin-density wave (cSDW) that exists above the threshold Hund coupling results in emergent Fermi surface pockets about cSDW momenta at a quantum critical point (QCP). This motivates the introduction of a new Gutzwiller wavefunction for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta indicates that the dispersion of the nested band of one-particle states that emerges is electron-type. Increasing Hund coupling past the QCP can push the hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy level, in agreement with recent determinations of the electronic structure of mono-layer iron-selenide superconductors.     

Turbulent Entrainment in the Atmospheric Boundary Layer

Turbulent entrainment – the process by which turbulence inside of the atmospheric boundary layer entrains air from the free troposphere above it – has been investigated using direct numerical simulations in two configurations, one without a cloud and one with a cloud. With the first configuration, we have learned that the entrainment zone in a convective boundary layer growing into a linearly stratified troposphere is better described in terms of a two-layer structure, with different characteristic scales associated with each of the two sub-layers. With the second configuration, we have explained how wind shear across the entrainment zone capping a stratocumulus cloud can render evaporative cooling as important as radiative cooling in driving convective motions. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Factorization of a class of symbols with outer functions

In this paper the Wiener–Hopf (or Riemann–Hilbert) factorization of a class of symbols important in applications is studied. The symbols in this class involve outer functions that appear in applications such as diffraction by strip gratings and infinite-dimensional integrable systems. The method proposed is based on the reduction of a vector Riemann–Hilbert to a scalar problem on an appropriate Riemann surface. Two examples are given leading to the Riemann sphere and to an elliptic curve.     

Inhibitory activities on mammalian central nervous system receptors and computational studies of three sesquiterpene lactones from Coriaria ruscifolia subsp. ruscifolia

The electrophysiological characterization of sesquiterpene lactones from Coriaria ruscifolia subsp. ruscifolia has been tested on hippocampal neurons. The results for glycinergic rat hippocampal transmission and native γ-aminobutyric acid (GABA)ergic transmission on neurons (13DIV) are remarkably different for tutin, coriamyrtin, and dihydrotutin, being tutin the most potent inhibitor and dihydrotutin the least potent one. To understand the applied mechanism of action, we discuss the structural and electronic requirements for inhibitory activity by these sesquiterpene lactones when modulating receptors of the central nervous system. The structural and electrostatic properties of these compounds were compared to those of more active metabolites like picrotoxins. The minimal energy level of these structures was calculated and then optimized at the ab initio B3LYP/DGDZVP level of theory using Gaussian 03W software. This allowed calculation of the corresponding vibrational circular dichroism spectrum of coriamyrtin which rendered the molecular absolute configuration after comparison with an experimental spectrum. These results are consistent with those from studies of other models that provide the basis for the activity on the presence of the lactone at carbons 3 and 5, the presence of the hydroxyl group at position 6, and the different electronic distributions observed in tutin and coriamyrtin. The latter has an isopropenyl moiety at carbon 4 in contrast to the dihydrotutin isopropyl group at the same position, which could explain the difference in activity between dihydrotutin and tutin or coriamyrtin. The presence of the hydroxyl group at carbon 2 is not decisive since this functionality is present in tutin, the most active compound, and in dihydrotutin, the less active one.     

Determination of Vecuronium Bromide in Pharmaceuticals: Development, Validation and Comparative Study of HPLC and CZE Analytical Methods

Vecuronium bromide is a neuromuscular blocking agent used for anesthesia to induce skeletal muscle relaxation. HPLC and CZE analytical methods were developed and validated for the quantitative determination of vecuronium bromide. The HPLC method was achieved on an amino column (Luna 150 × 4.6 mm, 5 μm) using UV detection at 205 nm. The mobile phase was composed of acetonitrile:water containing 25.0 mmol L^?1 of sodium phosphate monobasic (50:50 v/v), pH 4.6 and flow rate of 1.0 mL min^?1. The CZE method was achieved on an uncoated fused-silica capillary (40.0 cm total length, 31.5 cm effective length and 50 μm i.d.) using indirect UV detection at 230 nm. The electrolyte comprised 1.0 mmol L^?1 of quinine sulfate dihydrate at pH 3.3 and 8.0% of acetonitrile. The results were used to compare both techniques. No significant differences were observed (p > 0.05).