Elastic wave scattering from a strained region

This dissertation considers elastic wave scattering from a micro-sphere embedded in a rubber substrate which has been initially strained. Its aim is to ascertain the extent to which the strained region affects the scattering process. It is proposed that under hydrostatic loading a micro-sphere will compress nonlinearly. This is justified by calculating the compressed radius of a micro-sphere for different forms of the stored energy function corresponding to linear and nonlinear elasticity. It is shown that linear elasticity, as used in current TMSL models, predicts that the micro-sphere compresses to a smaller radius than that predicted by standard nonlinear elastic models of rubber-like materials. The initial strain modifies the Lame moduli and therefore further experimental work is necessary in order to calculate the full equations of motion for small displacements superposed on top of the initial finite strain. Without this further experimental knowledge the equations are correct only to leading order. The low frequency scattering problem is solved at leading order so that we can ascertain how monopole scattering is affected by the strained region. It is shown that the monopole scattering cross section for scattering from a spherical cavity in a strained region is three orders of magnitude smaller than that for an isotropic region. Hence, the scattering process is significantly affected by the strained region. Two modifications to the current TMSL model are proposed. Firstly, the prediction of the compressed radius should be made according to nonlinear elasticity. Secondly, scattering effects due to the strained region should be included in the model since they contribute significantly to the scattering process

Some notes on worms in sheep in southern Western Australia

DURING the last fifty or more years several surveys have been made of the worm parasites which occur in southern Western Australia. In the \u27fifties, thanks to the stimulus of Mr. H. McL. Gordon, supported by Dr. H. W. Bennetts, observations were made on the sequence of the infestations in autumn-born weaners in the country stretching from Moora to Cranbrook and Bridgetown, and later near Geraldton and Esperance

Cadmium sulfide in a Mesoproterozoic terrestrial environment

Peer reviewedPostprin

The combustion characteristics and stable carbon isotopic compositions of irradiated organic matter: implications for terrestrial and extraterrestrial sample analysis

Exposure to ionizing radiation causes the mean combustion temperature of naturally occurring, solid, terrestrial organic matter, derived from the radiation-induced polymerization of methane, to increase

Compression properties of polymeric syntactic foam composites under cyclic loading

Syntactic foams are composite materials frequently used in applications requiring the properties of low density and high damage tolerance. In the present work, polymer-based syntactic foams were studied under cyclic compression in order to investigate their compressibility, recoverability, energy dissipation and damage tolerance. These syntactic foams were manufactured by adding hollow polymer microspheres of various sizes and wall thicknesses into a polyurethane matrix. The associated loading and unloading curves during cyclic testing were recorded, revealing the viscoelastic nature of the materials. SEM images of the samples were obtained in order to study potential damage mechanisms during compression. It was observed that these syntactic foams exhibit high elastic recovery and energy dissipation over a wide range of compressional strains and the addition of polymer microspheres mitigate the damage under compressional loading.Comment: 25 pages, 13 figure

Employing pre-stress to generate finite cloaks for antiplane elastic waves

It is shown that nonlinear elastic pre-stress of neo-Hookean hyperelastic materials can be used as a mechanism to generate finite cloaks and thus render objects near-invisible to incoming antiplane elastic waves. This approach appears to negate the requirement for special cloaking metamaterials with inhomogeneous and anisotropic material properties in this case. These properties are induced naturally by virtue of the pre-stress. This appears to provide a mechanism for broadband cloaking since dispersive effects due to metamaterial microstructure will not arise.Comment: 4 pages, 2 figure

Hopane biomarkers traced from bedrock to recent sediments and ice at the Haughton Impact Structure, Devon Island: Implications for the search for biomarkers on Mars

Hopanoid biomarkers have been traced from bedrock to ice in the Haughton Impact Structure, suggesting that they represent a promising strategy in the search for life in ice deposits on Mars and other icy bodies

A measurement of the cosmic ray elements C to Fe in the two energy intervals 0.5-2.0 GeV/n and 20-60 GeV/n

The study of the cosmic ray abundances beyond 20 GeV/n provides additional information on the propagation and containment of the cosmic rays in the galaxy. Since the average amount of interstellar material traversed by cosmic rays decreases as its energy increases, the source composition undergoes less distortion in this higher energy region. However, data over a wide energy range is necessary to study propagation parameters. Some measurements of some of the primary cosmic ray abundance ratios at both low (near 2 GeV/n) and high (above 20 GeV/n) energy are given and compared to the predictions of the leaky box mode. In particular, the integrated values (above 23.7 GeV/n) for the more abundant cosmic ray elements in the interval C through Fe and the differential flux for carbon, oxygen, and the Ne, Mg, Si group are presented. Limited statistics prevented the inclusion of the odd Z elements

Prediction of LDEF ionizing radiation environment

The Long Duration Exposure Facility (LDEF) spacecraft flew in a 28.5 deg inclination circular orbit with an altitude in the range from 172 to 258.5 nautical miles. For this orbital altitude and inclination two components contribute most of the penetrating charge particle radiation encountered - the galactic cosmic rays and the geomagnetically trapped Van Allen protons. Where shielding is less than 1.0 g/sq cm geomagnetically trapped electrons make a significant contribution. The 'Vette' models together with the associated magnetic filed models were used to obtain the trapped electron and proton fluences. The mission proton doses were obtained from the fluence using the Burrell proton dose program. For the electron and bremsstrahlung dose we used the Marshall Space Flight Center (MSFC) electron dose program. The predicted doses were in general agreement with those measured with on-board thermoluminescent detector (TLD) dosimeters. The NRL package of programs, Cosmic Ray Effects on MicroElectronics (CREME), was used to calculate the linear energy transfer (LET) spectrum due to galactic cosmic rays (GCR) and trapped protons for comparison with LDEF measurements