Physics Today Daily Edition
Nature: The Department of Energy's Fusion Energy Sciences Advisory Committee (FESAC) has released a report that recommends cutting two fusion projects in favor of increased focus on ITER. The report suggests that MIT's Alcator C-Mod reactor, which had been defunded in 2012 but restarted this year, be shut down in 2015. Depending on the budget outlook, it also recommends closing either General Atomics' DIII-D in San Diego, California, or the National Spherical Torus Experiment in Princeton, New Jersey, by 2020. The committee did recommend constructing some new facilities and upgrading current ones, but it was not allowed to reconsider the US contribution to ITER. ITER has already cost $50 billion, 10 times its projected cost, and is 11 years behind schedule.
Ars Technica: Quasars are black holes that pull in massive amounts of matter, shine brightly across the electromagnetic spectrum, and emit jets of extremely high-energy particles. They have been hard to categorize, however, because of their wide range of appearances and characteristics. Now, Yue Shen and Luis C. Ho of Peking University have compiled a database of more than 20 000 quasars found by the Sloan Digital Sky Survey. They recorded the quasars' spectra, the orientation of their accretion material, and a characteristic called the Eddington ratio, which compares a quasar's luminosity with its theoretical maximum and thus is a measure of the accretion efficiency. By comparing the disk orientation with accretion efficiency and spectral line strength, they created a graph that fits all of the quasars into a well-defined, orderly plot. Determining the cause of the distinctive pattern could provide significant insight into the properties of quasars. Separately, the study found that the highest-mass quasars (the ones with the lowest Eddington ratios) are clustered together, which hints at some connection between quasars and the large-scale structure of the universe.
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.