Transient and steady-state shear banding in a lamellar phase as studied by Rheo-NMR

Flow fields and shear-induced structures in the lamellar (L-alpha) phase of the system triethylene glycol mono n-decyl ether (C10E3)/water were investigated by NMR velocimetry, diffusometry, and H-2 NMR spectroscopy. The transformation from multilamellar vesicles (MLVs) to aligned planar lamellae is accompanied by a transient gradient shear banding. A high-shear-rate band of aligned lamellae forms next to the moving inner wall of the cylindrical Couette shear cell while a low-shear-rate band of the initial MLV structure remains close to the outer stationary wall. The band of layers grows at the expense of the band of MLVs until the transformation is completed. This process scales with the applied strain. Wall slip is a characteristic of the MLV state, while aligned layers show no deviation from Newtonian flow. The homogeneous nature of the opposite transformation from well aligned layers to MLVs via an intermediate structure resembling undulated multilamellar cylinders is confirmed. The strain dependence of this transformation appears to be independent of temperature. The shear diagram, which represents the shear-induced structures as a function of temperature and shear rate, contains a transition region between stable layers and stable MLVs. The steady-state structures in the transition region show a continuous change from layer-like at high temperature to MLV-like at lower temperature. These structures are homogeneous on a length scale above a few micrometers

Diffusion Correlation NMR Spectroscopic Study of Anisotropic Diffusion of Water in Plant Tissues

AbstractThe anisotropic diffusion of water in chive (Allium schoenoprasum) tissues has been investigated using two-dimensional nuclear magnetic resonance methods: diffusion-diffusion correlation spectroscopy and diffusion-relaxation correlation spectroscopy. Corresponding one-dimensional T2 and diffusion measurements confirm independently the results of the two-dimensional investigations. In particular the diffusion-diffusion correlation spectroscopy method proves to be very powerful in resolving the different components of the diffusion tensor at different sites in the sample

Robust spatially resolved pressure measurements using MRI with novel buoyant advection-free preparations of stable microbubbles in polysaccharide gels

MRI of fluids containing lipid coated microbubbles has been shown to be an effective tool for measuring the local fluid pressure. However, the intrinsically buoyant nature of these microbubbles precludes lengthy measurements due to their vertical migration under gravity and pressure-induced coalescence. A novel preparation is presented which is shown to minimize both these effects for at least 25 min. By using a 2% polysaccharide gel base with a small concentration of glycerol and 1,2-distearoyl-sn-glycero-3-phosphocholine coated gas microbubbles, MR measurements are made for pressures between 0.95 and 1.44 bar. The signal drifts due to migration and amalgamation are shown to be minimized for such an experiment whilst yielding very high NMR sensitivities up to 38% signal change per bar

New applications of low field NMR in soil science.

Despite the wide application of low field NMR in different fields, from petrophysics to food science and industry, its use in Soil Science is still inconspicuous. To demonstrate opportunities for low field NMR in this area we will present a few examples of so far unpublished new applications of this powerful and more affordable technique in Soil Sciencebitstream/item/218344/1/New-applications-of-low-field-NMR-in-soil-science-2020.pd

Measurements of the velocity distribution for granular flow in a Couette cell

© 2018 American Physical Society. In this paper, magnetic resonance velocimetry is used to measure the spatially resolved velocity and velocity fluctuations for granular flow in a Couette cell for four different particle sizes. The largest particles studied (dp=1.7mm) showed significant slip at the inner wall. The remaining particles showed no slip and all exhibit the same behavior in the profiles of the mean velocity and variance of velocity. The measurements demonstrate that the velocity and variance in velocity scale with the inner wall velocity U; the variance does not scale with U2. The experimental data were compared with a kinetic theory based model of granular flow and a hydrodynamic model. It was found that the shear rate scales with an exponent of 1.5-2.0 with respect to the velocity fluctuations (uy2), compared with the value of 1.0 expected from kinetic theory. The difference in the exponent is consistent with the effect of collective dynamics as described by the hydrodynamic model

Quantitative permeability imaging of plant tissues

A method for mapping tissue permeability based on time-dependent diffusion measurements is presented. A pulsed field gradient sequence to measure the diffusion encoding time dependence of the diffusion coefficients based on the detection of stimulated spin echoes to enable long diffusion times is combined with a turbo spin echo sequence for fast NMR imaging (MRI). A fitting function is suggested to describe the time dependence of the apparent diffusion constant in porous (bio-)materials, even if the time range of the apparent diffusion coefficient is limited due to relaxation of the magnetization. The method is demonstrated by characterizing anisotropic cell dimensions and permeability on a subpixel level of different tissues of a carrot (Daucus carota) taproot in the radial and axial directions

Special Issue \u201cMagnetic Resonance in Porous Media\u201d

Editorial del Volume contenente una selezione di contributi presentati al "10th International Bologna Conference Magnetic Resonance in Porous Media" (MRPM 10) September 2010, Leipzig, Germany, www.diffusion-fundamentals.or