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Flash Physics: Ocean tides are magnetic, speedy electrons, new millimetre-wavelength telescope camera

20 Oct 2016 Hamish Johnston

Flash Physics is our daily pick of the latest need-to-know developments from the global physics community selected by Physics World‘s team of editors and reporters

Component of the Earth's magnetic field that is caused by ocean tides
Electric oceans: effect of tides on the Earth's magnetic field. (Courtesy: DTU/NASA/ETH Zurich)

Magnetic tides shed light on plate tectonics

Electrical currents in the oceans have a small but measureable effect on the Earth’s magnetic field and can be used to peer deep below the lithosphere. That’s the conclusion of geophysicists who have used three Swarm satellites operated by the European Space Agency (ESA) to make an extremely detailed map of the Earth’s magnetic field. Writing in Science Advances, the team explains that small electrical currents are generated when salty seawater is pushed by tidal forces. This induces a weak current in the Earth’s crust, which contributes to the overall magnetic field of the Earth. The team used measurements of the tidal magnetic fields to generate images of the electrical structure of the lithosphere and upper mantle down to a depth of about 250 km below the oceans. The study reveals a sharp increase in electrical conductivity at about 72 km depth, which could signify a boundary between the colder lithosphere on top and the hotter asthenosphere beneath. “These new results are important for understanding plate tectonics, the theory which argues that Earth’s lithosphere consists of rigid plates that glide on the hotter and less rigid asthenosphere that serves as a lubricant, enabling plate motion,” explains team-member Alexander Grayver from the Swiss Federal Institute of Technology in Zurich.

Laser-driven electrons break speed record

Illustration of how an intense laser pulse causes electrons to oscillate

Electrons have been set oscillating at 8 PHz by Eleftherios Goulielmakis and colleagues at the Max Planck Institute of Quantum Optics in Garching, Germany. This smashes the previous speed record for the fastest human control of electrons by a factor of 100. Writing in Nature, the team describes how it created the oscillations by firing intense laser pulses at a piece of silicon dioxide. This material is normally an insulator, but when exposed to the pulses its electrical conductivity is boosted by a factor of about 10 billion billion. The rapid oscillation of the electrons caused the material to emit very short bursts of extreme-ultraviolet light, which were detected by the researchers. The research could someday lead to the development of computers that can run much faster than conventional electronic devices used today. “The idea of using lasers for guiding the motion of electrons inside solids such as to create high-frequency electronic currents is rapidly gaining momentum,” Goulielmakis explains.

New millimetre-wavelength eye on the sky

Photograph of the Large Millimeter Telescope on the summit of Sierra Negra

Astronomers have unveiled a next-generation millimetre-wavelength polarimetric camera that will become part of the Large Millimeter Telescope (LMT) in Sierra Negra, Mexico. The device has been built by a team of astronomers led by Grant Wilson at the University of Massachusetts Amherst. It is the most sensitive polarimetric camera to date and will be used to conduct a series of surveys in star formation and galaxy evolution. Dubbed TolTEC, the camera will be operational by late 2018 and will offer a mapping speed that’s 100 times faster than LMT’s current capability. Observations that today take five years to complete will be done by TolTEC in a little more than one week, say the researchers. Another benefit of the camera is that it is capable of surveying the sky simultaneously in three frequency bands, compared with the current instrument’s single band. It is also sensitive to polarization as well as intensity. The researchers say that their camera will improve our understanding of star formation and galaxy-cluster physics. It will also carry out ultra-deep galactic exploration and magnetic-field surveys of the universe.

 

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