Archive for the ‘waves’ Category

Hearing the Japanese Earthquake

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Le séisme au Japon retranscrit en ondes sonores

Le sismographe du séisme au Japon enregistré depuis Strasbourg en France. Crédits photo : FREDERICK FLORIN/AFP

AUDIO – Des chercheurs de l’université de Georgia Tech ont converti sous forme audio les ondes sismiques enregistrées au large de Fukushima.

Écouter le terrible bruit du séisme de Fukushima tel qu’il a été au plus près de la côte japonaise et ses répercussions ailleurs dans le monde, c’est ce que propose Zhigang Peng, professeur associé à l’université Georgia Tech qui a converti les ondes sismiques en ondes sonores. Ce travail vient d’être publié dans la dernière revue Seismological Research Letters (mars-avril).

«Les gens peuvent entendre le début du séisme et les changements d’amplitudes tout en regardant sur des graphiques les changements des fréquences sismiques», explique le scientifique qui ajoute: «On peut rapprocher les signaux du tremblement de terre à des sons plus familiers tel que le tonnerre, la fabrication de pop-corn et des feux d’artifice».

Certaines mesures ont été prises le long de la côte japonaise entre Fukushima (près du site nucléaire) et Tokyo. Les plaques terrestres ont glissé sur des douzaines de mètres, des ajustements qui continueront durant des années.

Ce tremblement de terre a eu des répercussions à des milliers de kilomètres. Des répercussions ont ainsi été perçues dans la faille San Andreas au large de la Californie. Ces bruits ont été accélérés d’un facteur 100. Cela permet notamment d’entendre en quelques secondes des bruits qui ont eu lieu sur plusieurs minutes, voire heures.

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Written by physicsgg

March 8, 2012 at 1:20 pm

Posted in waves

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Proposed Cloaking Device for Water Waves Could Protect Ships at Sea

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Underpass. Appropriately sculpted ripples on the ocean floor could convert surface waves into internal interfacial waves, allowing them to pass under a floating object and protecting the thing from jostling. Credit: M.-R. Alam, PhysRevLett, 108 (24 February, 2012)

The weird science of invisibility has entered uncharted waters. By altering the sea floor in just the right way, it should be possible to hide an object floating on the sea from passing waves, a fluid mechanician predicts. The technique might help to protect ships and floating structures from rough seas. And because the scheme works entirely differently from the “cloaks” developed to hide objects from light and other electromagnetic waves, it breaks new ground for research….

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Written by physicsgg

March 3, 2012 at 7:39 am

Posted in waves

Teaching Waves with Google Earth

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a) Diffraction produced by a boat: Cyprus, 7/7/2007, coordinates: 34 0 56 ′ 27.21”N, 33 0 39 ′ 17.36”E. b) Diffraction of waves against the end of a protection barrier: La Grande-Motte, France, 8/21/2006, coordinates: 43 0 33 ′ 18.71”N, 4 0 05 ′ 20.01”E.

Examples of diffraction and reflection of circular waves: a) Port Elizabeth, South Africa 11/8/2006, coordinates: 33 0 57 ′ 19.98” S, 25 0 38 ′ 33.05” E. Reflections of a boat wake by an obstacle: b) River Thames, London, England, 11/06/2006, coordinates: 51 0 29 ′ 42.06” N, 0 0 03 ′ 37.86” E. c) River Thames, London, England, 11/06/2006, coordinates: 51 0 28 ′ 05.40” N, 0 0 15 ′ 18.12” E

Interference between wave fronts producted by the wakes of two boats: a) River Thames, London, England, 11/06/2006, coordinates: 51 0 27 ′ 40.79” N, 0 0 16 ′ 05.69” E. Interference between circular waves coming from two openings: b) Rimini, Italy, 5/28/2002, coordinates: 44 0 05 ′ 15.02” N, 12 0 32 ′ 26.07” E. Interference from secondary sources: c) Chao Phraya River, Bangkok, Thailand, 8/20/2010, coordinates: 13 0 36 ′ 40.11” N, 100 0 34 ′ 46.60”W.

Wave diffraction through an opening: a) Alexandria of Egypt, 12/14/2010, coordinates: 31 0 12 ′ 28.56” N, 29 0 53 ′ 34.66” E; b) Th´eoule-sur-Mer,France,10/26/2006, coordinates: 43 0 31 ′ 54.86” N, 6 0 56 ′ 59.41” E. c) Wave diffraction causes circular erosion of the beach: Campo di Mare, Italy, 4/18/2010, coordinates: 40 0 32 ′ 27.33” N, 18 0 04 ′ 09.17” E

Fabrizio Logiurato
Google Earth is a huge source of interesting illustrations of various natural phenomena. It can represent a valuable tool for science education, not only for teaching geography and geology, but also physics. Here we suggest that Google Earth can be used for introducing in an attractive way the physics of waves…
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Written by physicsgg

January 4, 2012 at 6:41 pm

Posted in EDUCATION, waves

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Amazing visualization of a solar magnetic storm

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20 Hz: A Semiconductor work by Ruth Jarman and Joe Gerhardt.

Audio Data courtesy of CARISMA, operated by the University of Alberta, funded by the Canadian Space Agency. Special Thanks to Andy Kale.
Made for the exhibition Invisible Fields at Arts Santa Monica in Barcelona Spain.
20 Hz observes a geo-magnetic storm occurring in the Earth’s upper atmosphere. Working with data collected from the CARISMA radio array and interpreted as audio, we hear tweeting and rumbles caused by incoming solar wind, captured at the frequency of 20 Hertz. Generated directly by the sound, tangible and sculptural forms emerge suggestive of scientific visualisations. As different frequencies interact both visually and aurally, complex patterns emerge to create interference phenomena that probe the limits of our perception.
05.00 minutes. / HD / 2011
HD single channel and HD 3D single channel.
20Hz is co-commissioned by Arts Santa Monica + Lighthouse . Supported by the British Council.

Written by physicsgg

December 1, 2011 at 4:35 pm

Posted in TECHNOLOGY, waves

Cloak could hide ships from flowing water

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A motorboat cuts a wake. Could vessels of the future evade detection using metamaterials?

Ships of the future may be able to move through the water without a creating a wake. That is according to a pair of physicists in the US, who have proposed a new type of material that lets water flow around an object as if it were not there at all. The design, which has yet to be built, could boost the energy efficiency of ships and submarines – and even prevent them from being detected. “The main function of [our] structure is to prevent fluid flowing around an object from ‘feeling’ that object,” says Yaroslav Urzhumov of Duke University.

The past five years have seen a flurry of research into invisibility cloaks. The first functioning cloak, which operated for electromagnetic waves in the microwave range, was demonstrated by a team led by David Smith at Duke University in 2006, and since then researchers have proposed and demonstrated cloaks that work for visible light, sound and even events in time….. Read the rest of this entry »

Written by physicsgg

July 21, 2011 at 2:20 pm

Posted in Fluid Dynamics, waves

Soft-drink cans beat the diffraction limit

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To focus sound to a point, all you need is a thirst for fizzy drinks.
Jon Cartwright

An acoustic lens made of soda cans can focus sound waves to a spot as small as 1/25th of a wavelength.

Sound, like light, can be tricky to manipulate on small scales. Try to focus it to a point much smaller than one wavelength and the waves bend uncontrollably — a phenomenon known as the diffraction limit. But now, a group of physicists in France has shown how to beat the acoustic diffraction limit — and all it needs is a bunch of soft-drink cans.

Scientists have attempted to overcome the acoustic diffraction limit before, but not using such everyday apparatus. The key to controlling and focusing sound is to look beyond normal waves to ‘evanescent’ waves, which exist very close to an object’s surface. Evanescent waves can reveal details smaller than a wavelength, but they are hard to capture because they peter out so quickly. To amplify them so that they become detectable, scientists have resorted to using advanced man-made ‘metamaterials’ that bend sound and light in exotic ways….. Read the rest of this entry »

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July 11, 2011 at 7:44 am

Posted in waves

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