Physics Today Daily Edition
BBC: A cheaper, lower-temperature liquid-metal battery has been developed for use in the national electric grid. Such battery technology could improve the efficiency and reliability of intermittent renewable energy sources, such as wind turbines. The key component of the new battery design is lead, which is cheap and melts at low temperatures. The lead is mixed with antimony, and the combination makes up the bottom layer of the new three-layer battery. The top is composed of lithium, and a molten salt electrolyte is sandwiched in between. The lithium cycles between the top and bottom layers as the cell is charged and discharged. The lead allows the operating temperature to be about 450 °C, compared with the 700 °C required by an earlier design made of magnesium and antimony, but the lower-temperature mixture doesn't affect the battery’s efficiency, according to Donald Sadoway of MIT, the project's senior researcher. The group plans to test the design in Hawaii and at Cape Cod in Massachusetts, where both sunshine and wind are abundant.
Science: An excess of positrons has been detected by the Alpha Magnetic Spectrometer (AMS), which collects cosmic rays from its perch on the International Space Station. Although cosmic rays are composed of many different types of particles, including positrons, the increase noted by the AMS could be an indication of the presence of dark matter, according to Samuel Ting of MIT and colleagues, whose study appears in Physical Review Letters. They base their findings on the fact that the usual sources of positrons, such as supernova explosions, produce far more electrons than positrons. Dark-matter collisions would shift that balance. However, other astrophysicists disagree, saying there are many other potential sources, such as pulsars or the interactions of primary cosmic rays from supernova remnants with the interstellar medium. More data will be needed to narrow down the source.
Nature: The team operating the European Space Agency's Planck orbiter has released a preprint of the spacecraft's much-anticipated full-sky survey of interstellar dust. The new map shows that the polarization of dust in the section of sky observed by the BICEP2 experiment is much higher than was anticipated. In March 2014, the BICEP2 experiment detected in the cosmic microwave background radiation (CMB) what appeared to be signs of gravitational waves in the early universe. However, the results were questioned by many researchers who doubted that the signal from interstellar dust had been properly accounted for. The data from Planck confirm that the BICEP2 signal has a significant contribution from interstellar dust, but whether any of the signal arose from primordial gravitational waves remains unclear. Further analysis of the Planck data is under way.
Nature: For the first time, images of an ultracompact dwarf galaxy, M60-UCD1, have revealed what may be a supermassive black hole at its center. The discovery was made by Anil Seth of the University of Utah in Salt Lake City and his colleagues, whose findings were published this week in Nature. Based on data from the Hubble Space Telescope and the IR spectrometer on the Gemini North telescope on Hawaii’s Mauna Kea, the astronomers say that the black hole’s mass could be 18% of the mass of all the stars in its galaxy, compared with a typical supermassive black hole, which has only about 0.5% of the mass of its galaxy’s stars. Although no one knows how such supermassive black holes form, the researchers think that M60-UCD1 may have once been much bigger but that a collision with another galaxy resulted in the loss of much of its exterior. Because of the number of dwarf galaxies in the universe, there could be twice as many supermassive black holes as previously estimated.
MIT Technology Review: A device that looks like a climbing safety harness may one day help stroke victims to walk and soldiers to carry heavy loads over long distances. The harness, which is made of spandex and nylon, is connected to cables that run down the wearer’s legs. Small battery-powered motors pull the cables to help the heel come up or the leg go forward. To be as efficient as possible, the device has been designed to conform to the natural movements of a person’s muscles. And it is lightweight and flexible enough to be worn under one’s clothes. “Energy storage is still a challenge,” however, says Conor Walsh of Harvard University. He hopes that advances in battery technology will allow the device to become even lighter and more efficient.
New Scientist: Galaxies frequently collide and merge. Simulations of the collisions suggest that the outcome should be elliptical galaxies. However, most visible galaxies are disk shaped, either lenticular or spiral. Now, observations by Junko Ueda of the Japan Society for the Promotion of Science and her colleagues show that galaxy collisions may indeed produce disk-shaped galaxies. Using the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescope, they measured the movement of carbon monoxide gas in 37 merging galaxies. Of those, 30 showed signs of rotation around a central axis, which suggests they will eventually become disk shaped when the mergers are complete.
Nature: Based on geological evidence, the Sahara desert in northern Africa has been thought to be between 2 million and 3 million years old. However, studies of dune deposits in northern Chad and of dust and pollen in sediments from sea floors off northern Africa now indicate that the region may have experienced extended dry spells as long as 7 million to 8 million years ago. What could have caused that aridification is the subject of a recent study published in Nature. Zhongshi Zhang of the Bjerknes Centre for Climate Research in Norway and colleagues have ruled out major mountain-forming episodes, changes in Earth’s orbit, and excessive atmospheric carbon dioxide. Instead, climate simulations indicate that the African summer monsoon, which brought moisture from the tropical Atlantic to northern Africa, was weakened by the shrinking of the ancient Tethys Sea. Critics say the theory remains speculative because too little is known about the ancient geology of the region.
BBC: A chin strap made from a piezoelectric material generates electricity as wearers move their jaws. Designed by Aidin Delnavaz and Jeremie Voix of the École de Technologie Supérieure in Montreal, Canada, the proof-of-concept device can produce 18 µW of power after just 60 seconds of chewing. They say that to actually be useful, however, it will need to generate 20 times as much electricity, which could be achieved by simply increasing the amount of piezoelectric material in the strap. A 20-layer strap just 6 mm thick should be able to power an intelligent hearing protector, such as sound-canceling headphones that are used for communications in heavy industry or the military. It could also be used to power cochlear implants or other similar small electronics, but probably not anything as large as a smart phone.
Guardian: One of the goals Congress assigned NASA is to identify by 2020 at least 90% of the asteroids larger than 140 m in diameter that pass within 45 million km of Earth's orbit. A report by NASA's inspector general says that the agency will not meet that goal despite a 10-fold increase in funding over the last five years. So far, the report states, the agency has found just 10% of the asteroids believed to meet the given criteria. According to the report, the likely failure is due to understaffing and poor organization of detection efforts. The one major upside of the report is that 95% of the asteroids larger than 1 km have been found. Asteroids of that size could cause significant global destruction.
New Scientist: Although drinking-water wells near several hydraulic fracturing sites in Pennsylvania and Texas are increasingly becoming contaminated with hydrocarbons, the source is most likely leaky pipelines and boreholes, rather than the fracking process itself. Because fracking involves fracturing shale rock by pumping chemicals into the ground, it was feared that those chemicals, which can be toxic, or the natural gas that gets released might make its way into local water supplies. However, after studying the contaminants, Thomas Darrah of the Ohio State University and colleagues say they appear to be noble gases that have leaked as they were being piped to the surface. If so, improving the integrity of the equipment and better environmental monitoring could take care of the problem.