Viscoelastic

The physical-chemical, thermal and rheological properties of starches isolated from four commercial potato cultivars (Colparina, Huayro, Canchan and Yungay) were evaluated and characterized. The starches presented ovoid and spherical shapes, with average size from 20.08 ± 2.48 to 25.33 ± 6.54 μm and B-type granules, with amylose content from 15.49 ± 2.02 to 32.10 ± 0.14% and relative crystallinity, between 34.6 and 37.3%. The rheological properties measured using a dynamic rheometer, showed predominance storage module (G') on the loss module (G'') during the frequency range (0.01-3.20 Hz) studied, which would classify them as weak gels. The starches presented low syneresis, high clarity, pasting temperature from 65.70 ± 0.31 °C to 67.70 ± 0.23 °C, gelatinization start temperature (To); peak temperature (Tp); gelatinization final temperature (Tf) and gelatinization enthalpy (ΔH) values between 57.90 ± 0.24 and 62.23 ± 0.17 °C; 61.18 ± 0.01 and 64.85 ± 0.01 °C; 65.5 ± 0.31 and 68.34 ± 0.29 °C; 11.49 ± 0.8 and 15.43 ± 0.51 J/g, respectively. The starches evaluated had suitable properties to be used as ingredients in specific foods to improve their textural characteristics.

Resume Ce travail porte sur l'etude des effets d'une modulation en phase des conditions aux limites relatives a la temperature sur le seuil convectif d'une couche liquide viscoelastique horizontale et d'extension infinie. Dans ce cadre, nous supposons que le comportement du liquide est regi par une loi de type Maxwell lineaire et que la temperature imposee resulte de la superposition d'une composante stationnaire et d'une composante variable au cours du temps. La theorie de Floquet combinee avec une methode numerique transformant le probleme aux valeurs propres obtenu en un probleme aux conditions initiales, nous permettent de mettre en evidence, les effets dus a cette modulation et a la nature viscoelastique du fluide sur le seuil critique de convection. Pour citer cet article : B. Oukada et al., C. R. Mecanique 334 (2006).

The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue because the muscle is an anisotropic, viscoelastic and dynamic medium. In this article, these mechanical properties are characterized for the brachialis muscle in vivo using a noninvasive ultrasound-based technique. This supersonic shear imaging technique combines an ultra-fast ultrasonic system and the remote generation of transient mechanical forces into tissue via the radiation force of focused ultrasonic beams. Such an ultrasonic radiation force is induced deep within the muscle by a conventional ultrasonic probe and the resulting shear waves are then imaged with the same probe (5 MHz) at an ultra-fast framerate (up to 5000 frames/s). Local tissue velocity maps are obtained with a conventional speckle tracking technique and provide a full movie of the shear wave propagation through the entire muscle. Shear wave group velocities are then estimated using a time of flight algorithm. Thi...

A series viscous-elastic-plastic (VEP) indentation model was expanded to include analysis of the common trapezoidal testing condition, consisting of constant loading---and unloading---rates with an intervening creep hold period. This full VEP model was applied to analyze nanoindentation test of three polymers and five different types of bone. The full VEP solution allows for direct determination of the viscous term as calculated from the creep hold, while the elastic and plastic material parameters were determined from a non-linear curve-fit of the unloading displacement-time data. Additionally, the use of the trapezoidal loading procedure permitted analysis of the unloading load-displacement data with traditional Oliver-Pharr analysis; the material properties from this analysis compared well with those obtained with VEP analysis. Using the full VEP solution and fitted material constants the loading and creep hold displacement-time curves were simulated and matched well to both polymer and bone experimental data. The full VEP solution shows great promise in for obtaining material parameters for many viscoelastic materials such as hydrated bone, polymers, and other biological tissues.

The impact dynamics of water drops on thin films of viscoelastic wormlike micelle solutions is experimentally studied using a high-speed digital video camera at frame rates up to 4000frame/s. The composition and thickness of the thin film is modified to investigate the effect of fluid rheology on the evolution of crown growth, the formation of satellite droplets and the formation