The Earth's gravity is generally perceived as a constant, with one "g" indicating an acceleration of 9.8 meters per second per second. However, small variations in the gravitational field are discernable at different locations, typically with magnitudes of one-ten thousandth of the average gravitational attraction, implying a "mass deficit" in such places. These undulations, known as gravity anomalies, are spread throughout the Earth, but one of the largest is centered over Hudson Bay, Canada. Using a new approach to analyzing planetary gravity fields, two geophysicists, Mark Simons at the California Institute of Technology and Bradford Hager at M.I.T., have shown that incomplete glacial rebound can account for a substantial portion of the Hudson Bay gravity anomaly. About 18,000 years ago, Hudson Bay was at the center of a continental-sized glacier with a thickness of several kilometers. The weight of the ice bowed the surface of the Earth down and after it receded, it left depression in its wake. Having an estimate of incomplete post-glacial rebound allowed Simons and Hager to derive a model of how the viscosity of the mantle changes with depth. Their favored model suggests that underneath the oldest parts of continents the viscosity of the outer 400 kilometers of Earth is much stiffer than under the oceans. Therefore, these continental keels can resist the erosion by the convective flow that drives plate tectonics. For more information, Robert Tindol, "Caltech", at (626) 395-3631.
If you see a hitchhiker along the road in Canada this summer, it may not be human. That’s because a robot is thumbing its way across our neighbor to the north as part of a collaborative research project by several Canadian universities.
Stanford University researchers have found a way to realize what’s been called the “Holy Grail” of battery-design research -- designing a pure lithium anode for lithium-based batteries. The design has great potential to provide unprecedented efficiency and performance in lithium-based batteries that could substantially drive down the cost of electric vehicles and solve the charging problems associated with smartphones.
Robots in films during the 2000s hit the big time; no longer are they the sidekicks of nerdy character actors. Robots we see on the big screen in recent years include Nicole Kidman, Arnold Schwarzenegger, and Eddie Murphy. Top star of the era, Will Smith, takes a spin as a robot investigator in I, Robot. Robots (or androids or cyborgs) are fully mainstream in the 2000s.
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