Extensional shear

With the advent of stable isotope paleoaltimetry towards the turn of the millennium the stable isotope and tectonics communities have witnessed an increasing number of isotopic mineral proxies developed to address the long-term topographic histories of orogenic belts and continental plateaus. These proxies include calcite from paleosols (see for example Quade et al. 2007, this volume and references therein), fluvial and lacustrine rocks the phosphate and carbonate component of mammal teeth (Kohn and Dettman 2007, this volume and references therein), smectite and kaolinite from paleosols, weathered sediments and volcanic ashes (e.g., Chamberlain et al. 1999 Takeuchi and Larson 2005 Mulch et al. 2006a) as well as white mica from extensional shear zones and fluid inclusions in hydrothermal veins (e.g., Mulch et al. 

It has often been stated that DR of surfactant solutions is related to their rheological properties. A rise in shear viscosity at a critical shear rate, caused by a shear-induced structure (SIS), viscoelasticity (nonzero first normal stress difference, quick recoil, and stress overshoot), and high extensional viscosity/shear viscosity ratios ( 100) are rheological properties found in many DR surfactant solutions. After reviewing the rheological behavior of many DR surfactant solutions, Qi and Zakin concluded that SIS and viscoelasticity are not always observed in DR surfactant solutions while high extensional/shear viscosity ratios may be a requirement for surfactant solutions to be DR. ... 

Grace has also reported comparisons between simple shear (Couette flow) versus extensional irrotational shear (4 roll mill). These are shown in Figure 14.8 with the full line representing shear and dotted line extension. It can be seen that for equal shear rates extensional shear produces more effective break-up and dispersion than simple rotational shear, even at low viscosity ratios. 

The corresponding comparison for simple shear is given in Figure 14.10. The comparison of Figures 14.9 and 14.10 substantiate that extensional shear is more effective than simple shear in promoting drop break-up. 

Mesophase pitch fibers are produced through melt spinning that is essentially the same as that used to spin commercial polymers. Figure 13 shows this process in which an extruder melts pitch particles and pumps the molten pitch through a multiholed spinnerette. The high extensional shear orients the liquid crystalline mesophase molecules as it approaches and flows through the spinnerette. The flbers emerging from the spinnerette are drawn by a windup spool. 

Velocimetry. - An analytic model for the velocity field within a tubeless siphon (Fano flow) was presented. The model was based on a simple differential equation in which extensional, shear and gravitational pressure gradient forces are balanced. The role of surface tension in determining boundary conditions for the flow is considered. The analysis is applied to NMR velocimetry data (Xia and Callaghan, J. Magn. Reson., 2003, 16, 365) on a... 

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