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Query: UMLS:C0851184 (thinning)
 11,252 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The electromagnet provides a favorable environment for certain applications of NMR microscopy. These include plant imaging experiments and measurements of slow molecular diffusion, where high magnetic field gradients for the pulsed gradient spin echo (PGSE) technique are required. In this paper, two probes designed specifically for these two applications are described. In the first case, the open space within the probe has been maximized in order to incorporate environmental support systems for the plant, while in the second the smallest possible PGSE gradient coil former has been used to maximize the gradient strength. Examples are given of Dynamic NMR Microscopy experiments on a castor bean stem and on poly(ethylene oxide)/water solutions under shear thinning conditions.
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PMID:Purpose-designed probes and their applications for dynamic NMR microscopy in an electromagnet. 140 91

Evolutionary processes have adapted nektonic animals to interact efficiently with the water that surrounds them. Not all these adaptations serve the same purpose. This paper concentrates on reduction of drag due to friction in the boundary layer close to the body surface. Mucus, compliant skins, scales, riblets and roughness may influence the flow velocity gradient, the type of flow and the thickness of the boundary layer around animals, and may seriously affect their drag in a positive or negative way. The long-chain polymers found in mucus decrease the pressure gradient and considerably reduced drag due to friction. The effect is probably due to channelling of the flow particles in the direction of the main flow, resulting in a reduction of turbulence. Compliant surfaces could probably reduce drag by equalising and distributing pressure pulses. However, the existing evidence that drag reduction actually occurs is not convincing. There is no indication that instantaneous heating, reducing the viscosity in the boundary layer, is used by animals as a drag-reducing technique. Small longitudinal ridges on rows of scales on fish can reduce shear stress in the boundary by a maximum of 10% compared with the shear stress of a smooth surface. The mechanism is based on the impedance of cross flow under well-defined conditions. The effect has been visualized with the use of particle image velocimetry techniques. The function of the swords and spears of several fast, pelagic, predatory fish species is still enigmatic. The surface structure of the sword of a swordfish is shown to be both rough and porous. The height of the roughness elements on the tip of the sword is close to the critical value for the induction of a laminar-to-turbulent flow transition at moderate cruising speeds. A flow tank is described that is designed to visualize the effects of surface imperfections on flow in the boundary layer in direct comparison with a smooth flat wall. The flow in a 1 m long, 10 cm high and 1 cm wide channel is visualized by illuminating the particles in a thin laser light sheet. The first results show that a rough surface increases the shear stress in the boundary layer and makes it thinner. The function of the roughness on the sword of a swordfish is probably to reduce the total drag by generating premature turbulence and by boundary layer thinning, despite an increased friction over the surface of the sword. The function of the porous surface structures on the sword, and of the porous skins of sharks and of the castor oil fish, will probably be discovered soon using new particle image velocimetry techniques applied under strong magnification to visualize the local behaviour of the flow.
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PMID:Body surface adaptations to boundary-layer dynamics. 857 Dec 18

Several di- or tri-functional epoxides were used to chemically modify an industrial grade cellulose pulp from Eucalyptus globulus in order to thicken castor oil by dispersing epoxidized cellulose pulp fibers, resulting gel-like formulations with potential applications as biolubricants. Rheological properties of these colloidal suspensions were evaluated by analysing the effects of epoxidation degree and the epoxide chemical structure. With this aim, epoxidized cellulose pulp samples were characterized by means of epoxy index determination, thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. It was found that linear viscoelastic functions, determined in small-amplitude oscillatory shear (SAOS), and viscosity values of epoxidized cellulose pulp gel-like dispersions decreased by increasing the epoxy index, whereas the shear-thinning character was dampened with the extension of epoxidation. Aromatic di-functional epoxides provide higher values of these rheological functions than aliphatic ones.
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PMID:Rheology of epoxidized cellulose pulp gel-like dispersions in castor oil: Influence of epoxidation degree and the epoxide chemical structure. 3014 63