Physics Today Daily Edition
Nature: Online preprint servers, such as arXiv, allow researchers to publicly share their papers prior to peer review. The sites are growing in popularity because they provide free access to cutting-edge research, albeit in draft form. Journal publisher Elsevier, which has tried unsuccessfully to establish its own preprint server, has now purchased the Social Science Research Network, one of the most popular preprint servers for economics, law, and the social sciences. The move appears to be part of the publisher's larger effort to broaden its services in order to increase web traffic and protect its subscription-based journals.
Gizmodo: Aside from their wavelength, photons also have a measurable angular momentum that characterizes their rotation along their axis of travel. That value has always been observed to be some integer multiple of Planck's constant. Now Paul Eastham of Trinity College Dublin and his colleagues have manipulated photons so they have half-integer angular momentum. To do that, the researchers made use of a phenomenon first discovered in the 1830s: When light is passed through certain crystals, it creates a cylinder-like structure. Theoretical analysis of the system suggested that the resulting photons had half-integer angular momentum, and measurements proved the predictions correct. The team thinks that such photons could be used for encrypted light-based communications.
Science: The carbon dioxide monitoring station at Cape Grim, on the northwestern tip of Tasmania, recorded readings above 400 ppm for four consecutive days last week, according to Paul Krummel of Australia's Commonwealth Scientific and Industrial Research Organisation. That level stands in stark contrast to the baseline of 280 ppm for atmospheric CO2, the level at the beginning of the industrial age 200 years ago. Scientists estimate that a level of 450 ppm would correspond to a global temperature increase of 2 °C, the maximum increase allowable to avoid the most devastating consequences of global warming. Cape Grim isn't the first monitoring station to pass 400 ppm; an outpost on Mauna Loa in Hawaii reached that mark in 2013 and has occasionally done so ever since. Unlike the Mauna Loa station, the Cape Grim station is not as significantly affected by seasonal changes that cause regular rises and falls in CO2 levels. Cape Grim is also located at a latitude where strong winds perpetually blow, which prevents localized buildups of pollution. As such, measurements taken at the station are used as a proxy for global CO2 levels.
Space.com: A magnetic reconnection is an explosive release of protons and electrons that occurs when plasma from the Sun collides with a region of Earth's magnetosphere that has an oppositely directed magnetic field. The radiation released poses a threat to astronauts and satellites in orbit and to electrical systems and nuclear fusion experiments on the ground. But until recently, magnetic reconnection was studied only via theory and in laboratories. NASA's Magnetospheric Multiscale (MMS) mission—a set of four satellites in orbit around Earth—has now provided the first direct observations of those events. The satellites, which are each equipped with 25 of the fastest sensors NASA has put into orbit, take readings every 30 ms to track the motion of electrons. On 16 October 2015 MMS passed directly through a magnetic reconnection region, where the local magnetic field dropped to nearly zero, ions traveled in opposite directions, and electrons got accelerated by a strong electric field. The satellites detected a spike in the electric power generated by the electrons, a predicted behavior that had not been seen before. The mission research team next plans to move the satellites closer together so they can all enter a magnetic reconnection region simultaneously.