2,346 research outputs found
The effect of fluid loading on the generation of extraterrestrial sound
No full textIn recent years increased attention has been paid to the potential uses of acoustics for extraterrestrial exploration. Acoustical instrumentation can be deployed in gas, liquid, or solid media for measurement. This report deals specifically with acoustic sensors in gaseous media. Given the variety of atmospheric conditions that could be encountered in other worlds, and the cost and effort associated with sending sensors to them, it is vital that predictive modelling be done to inform the design of the instrumentation and associated acquisition systems, and for mission planning. To this end, it is important to revisit assumptions which have become embedded in our predictions for acoustics in Earth’s atmosphere. This report deals specifically with the issue of fluid loading, and assesses the extent to which the radiation mass associated with immersion of an acoustic source in a gas (an effect which is usually negligible on Earth) affects its resonance frequency
The use of acoustics in space exploration
No full textIn recent years increased attention has been paid to the potential uses of acoustics forextraterrestrial exploration. The extent to which acoustics per se is used in these studiesvaries greatly. First, there are the cases in which acoustics is simply the medium throughwhich some other time-varying non-acoustic signal (such as the output of a cosmic raydetector) is communicated to humans. Second, perturbations in a non-acoustic signal (e.g.EM) are interpreted through mechanisms relating to acoustic perturbations in the sourcematerial itself. Third, some probes have made direct measurements of acoustic signalswhich have been generated by the probe itself, as is done for example to infer the localatmospheric sound speed from the time-of-flight of an acoustic pulses over a shortdistance (O(10 cm)). Fourth, some studies have discussed ways of interpreting thenatural acoustic signals generated by the extraterrestrial environment itself. The reportdiscusses these cases and the limitations, implications and opportunities forextraterrestrial exploration using acoustics
Dolphin-inspired target detection for sonar and radar
No full textGas bubbles in the ocean are produced by breaking waves, rainfall, methane seeps, exsolution, and a range of biological processes including decomposition, photosynthesis, respiration and digestion. However one biological process that produces particularly dense clouds of large bubbles, is bubble netting. This is practiced by several species of cetacean. Given their propensity to use acoustics, and the powerful acoustical attenuation and scattering that bubbles can cause, the relationship between sound and bubble nets is intriguing. It has been postulated that humpback whales produce ‘walls of sound’ at audio frequencies in their bubble nets, trapping prey. Dolphins, on the other hand, use high frequency acoustics for echolocation. This begs the question of whether, in producing bubble nets, they are generating echolocation clutter that potentially helps prey avoid detection (as their bubble nets would do with man-made sonar), or whether they have developed sonar techniques to detect prey within such bubble nets and distinguish it from clutter. Possible sonar schemes that could detect targets in bubble clouds are proposed, and shown to work both in the laboratory and at sea. Following this, similar radar schemes are proposed for the detection of buried explosives and catastrophe victims, and successful laboratory tests are undertaken
Effect of moisture on tuffstone weathering
No full textTuffstone elements with a large length/width ratio, as e.g. mullions, often suffer damage in the form of cracks parallel to the surface and spalling of the outer layer. The response of tuff to moisture might be a reason for this behaviour. This research aimed at verifying if a differential dilation between parts with different moisture content (as outer and inner part of partially encased mullion) can lead to damage. The effect of moisture on the degradation of Ettringen and Weibern tuff has been investigated. A purpose-made weathering test was carried out to simulate the wetting-drying process. Despite no cracks developed during the test, existing cracks widened up and the flexural tensile strength of both materials decreased. The moisture transport properties of the stones were determined as well as their porosity and pore size. Ettringen tuff has a considerable amount of very fine porosity, resulting in slow moisture transport and significant hygroscopic adsorption. Both tuffstones have an extreme hydric dilation. Environmental X-ray diffraction analyses showed that Ettringen tuff undergoes (reversible) mineralogical changes when subjected to RH cycles, whereas this does not occur for Weibern. All results support the hypothesis that moisture gradients in tuff elements may enhance decay in this stone
Een plaag van alle tijden: zout: Over oude en toekomstige schade, oud en toekomstig onderzoek
No full textIn deze bijdrage wordt nader ingegaan op de achtergronden van zoutschade, de vraag of we er in de toekomst meer last van zullen krijgen, en op oud, nieuw en gewenst onderzoek.Heritage & Technolog
Charity and integrity of life the pure essentials of Christian religion: or meditations on James I. 27. By T.G. M.A [electronic resource]
No full textT.G. = Thomas Gregory.Reproduction of the original in the Lambeth Palace Library.Wing (2nd ed.)Electronic reproduction
T.G. Jones / Thos G Jones
No full texthttps://scholarship.law.wm.edu/scinscriptions/2039/thumbnail.jp
T.G. Jones / Thos G Jones
No full texthttps://scholarship.law.wm.edu/scinscriptions/2039/thumbnail.jp
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