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Your search keyword '"R. L. Williams"' showing total 4 results
Start Over Author "R. L. Williams" Journal journal of physics d: applied physics
4 results on '"R. L. Williams"'

1. Cavitation of liquids under dynamic stressing by pulses of tension

Author

P R Williams and R L Williams

Subjects
Work (thermodynamics), Acoustics and Ultrasonics, business.industry, Tension (physics), Chemistry, Traction (engineering), Thermodynamics, Condensed Matter Physics, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Pulse (physics), Optics, Reflection (mathematics), Cavitation, Ultimate tensile strength, Newtonian fluid, business
Abstract

This paper addresses discrepancies between the results of different measurements of the effective tensile strength (Fc) of liquids, in experiments in which a pulse of tension (or `negative pressure') is created by the reflection of a pressure pulse at a suitable boundary. We show that a key feature of the pressure records previously reported in such experiments may have been misinterpreted. The first complete account of such pressure records reported here offers an explanation for the order-of-magnitude discrepancies in Fc which arise in work involving instruments such as the `Bullet-Piston' (B-P) pulse-reflection apparatus (Temperley H N V and Trevena D H 1987 J. Phys. D: Appl. Phys. 20 1080). We also report a new method of estimating Fc in a modified B-P apparatus and the results obtained indicate that samples of degassed, deionized water can sustain tensions which are an order-of-magnitude greater than previously reported in B-P work. Results are also reported for work involving samples of Newtonian silicone oils, for which the dependence of Fc on shear viscosity, µ, found in this work confirms that of an earlier study although the absolute values of Fc are found to be considerably greater than previously reported.

Published
2002
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2. Shear wave dispersion in mechanically self-similar gel networks

Author

P R Williams and R L Williams

Subjects
Length scale, Shear waves, Acoustics and Ultrasonics, business.industry, Chemistry, Mechanics, Condensed Matter Physics, Viscoelasticity, Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials, Quantitative Biology::Subcellular Processes, Condensed Matter::Soft Condensed Matter, Wavelength, Optics, S-wave, Cluster (physics), Dissipation factor, Dispersion (water waves), business
Abstract

A study of viscoelastic shear wave dispersion in a simulated gelation process involving mechanically self-similar nodal networks is reported. The network formed at the gel point (the infinite network cluster, or `critical gel') shares a common structural feature of smaller network clusters and the onset of a recognizably `gel-like' feature is shown to occur when the characteristic wavelength of the network cluster becomes twice that of an individual node. It is shown that, during gelation, the dispersion of shear waves can be exploited to assess the proximity of a system to an equivalent `critical gel' state at any single frequency, thereby identifying the smallest length scale at which gel-like characteristics are established prior to the gel point. In this way, and for the first time, a rheometrical basis is established for examining the gel-like, self-similar characteristics of pre-gel point viscoelastic liquid systems, in terms of the gel equation but in the absence of a frequency-independent loss tangent. Experiments are reported for a critical gel in which the high-frequency wave dispersion is in good agreement with theory.

Published
1998
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3. The use of reflection anisotropy spectroscopy to assess the alignment of collagen.

Author

A L Schofield, C I Smith, V R Kearns, D S Martin, T Farrell, P Weightman, and R L Williams

Subjects
OPTICAL reflection, ANISOTROPY, SPECTRUM analysis, COLLAGEN, TISSUE mechanics, LABORATORY mice, IMMUNOCHEMISTRY, ATOMIC force microscopy
Abstract

The alignment of collagen fibres in tissue has a major influence on their mechanical properties. This study investigated the ability of reflection anisotropy spectroscopy (RAS) to determine the degree of alignment of collagen fibres deposited onto surfaces and secreted by mouse fibroblast cells in vitro. Aligned nanofibres of polytetrafluoroethylene were deposited on glass coverslips using a simple friction transfer method. These linear parallel nanofibres were used as topographical cues to orientate and align L929 fibroblasts and their deposited collagen. The strength of the RAS signal was demonstrated to correlate with the degree of collagen alignment. Immunochemical staining and atomic force microscopy were used to visualize the topography of the fibres and confirm that the RAS signal was as a result of collagen fibres. Collagen deposited onto glass coverslips from a solution that had been subjected to dialysis that caused 'nanofibrillar' collagen to form also resulted in a strong RAS signal whereas collagen adsorbed from a simple solution of collagen in which collagen fibres are not formed resulted in no RAS signal. It was concluded that the RAS signal could be used to determine the degree of alignment of collagen and that this could have a potential application in the assessment of collagen orientation in tissue repair. [ABSTRACT FROM AUTHOR]

Published
2011
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4. Reflection anisotropy spectra of polydimethylsiloxane under a range of mechanically applied stress.

Author

T Farrell, C I Smith, A L Schofield, R L Williams, and P Weightman

Subjects
REFLECTANCE spectroscopy, ANISOTROPY, DIMETHYLPOLYSILOXANES, STRAINS & stresses (Mechanics), ELASTOMERS, MECHANICAL loads, SURFACES (Technology), DOUBLE refraction
Abstract

Reflection anisotropy spectra of transparent elastomeric polydimethylsiloxane (PDMS) have been determined over the spectral range 1.5 to 5.0 eV for a range of tensile loads. Using a slight wedge shaped sample the spectra from the incident air/PDMS surface are shown to be weak and largely featureless at all loads. By contrast the spectra from the light transmitted through the sample and reflected at the other interface are large in magnitude and exhibit features which arise from the small stress birefringence of PDMS.The birefringent dominated spectra can readily be simulated using expressions derived from a Stokes-Mueller treatment of the optical system and this enabled the stress-optical coefficient to be determined at any energy within the spectral range covered. It is shown that there is a small angle between the optical axes and the mechanical axes in the sample and that this is consistent with the model of an elastomer which comprises a network of soft linear chains cross linked with stiff bridges. [ABSTRACT FROM AUTHOR]

Published
2010
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