Physics Today’s online staff summarize the most important and interesting news about science from the world's top media outlets.
BBC: An international collaboration of marine scientists has published a paper in Science detailing the variety of threats the oceans face from rising carbon dioxide levels. The scientists say the combination of the effects is causing a change in ocean chemistry at a level unseen since the Permian–Triassic extinction event 250 million years ago. Since 1750, the oceans have absorbed 30% of the CO2 that humans have released into the atmosphere, and as a result, seawater is becoming more acidic. Since 1970, the oceans have also absorbed 90% of the additional heat generated by industrialization, which is making it harder for the oceans to store oxygen. That combination poses a threat to oceanic life that has not been addressed by climate change proposals.
Nature: Most electronic fingerprint scanners identify prints by generating a current where the fingers' ridges touch the scanner and mapping their pattern. The scanners are susceptible to failure, however, due to moisture and dirt, which can prevent them from detecting the ridges and the valleys in between. Now David Horsley of the University of California, Davis, and his colleagues have developed an alternative scanner that uses ultrasound. The scanner employs a chip covered in aluminum nitride, which can convert mechanical stress to electrical signals. When a finger is pressed against the device, an ultrasound pulse is generated that reflects back from the finger with a pattern dependent on its ridges and valleys. With a longer pulse, the scanner can even measure the depth of the valleys, which can help identify fake fingerprints. Horsley's team says that the use of aluminum nitride—already used in chip manufacturing—may overcome some of the difficulties of incorporating ultrasound devices into commercial electronics.
Ars Technica: The European Space Agency's Rosetta spacecraft, which is in orbit around comet 67P/Churyumov-Gerasimenko, has been supplying astronomers with highly detailed pictures of the comet's surface. Many of those pictures have revealed sinkholes as wide as 200 m and as deep as 180 m. At first it was thought that the sinkholes could be the result of outgassing—as the comet approaches the Sun, frozen gases warm and explode—but the amount of material in outgassing events didn't match the size of any of the sinkholes. Instead, Dennis Bodewits of the University of Maryland, College Park, and his colleagues say it appears to be the other way around—the outgassing results from the formation of the sinkholes. The holes themselves form as surface ice sublimates and dust fills the depression until it collapses, creating a deeper hole. Bodewits's team believes that the comet's nucleus is 75–80% empty space, which is what allows so many sinkholes to form.
Nature: A study of 300 000 nuclear-industry employees from France, the UK, and the US has provided the first clear look at the risks of low-dose ionizing radiation. The researchers obtained exposure records dating back 60 years for employees who worked in the industry for at least one year while wearing a dosimeter. The researchers then followed up to track mortality from leukemia, lymphoma, and multiple myeloma. The study revealed that on average the workers received 1.1 mSv per year above the average yearly background radiation, which is about 2–3 mSv. As the amount of radiation exposure increased, there was a linear increase in the rate of leukemia as well. Similar patterns for other cancers were not statistically significant. Instead of the 134 deaths expected from leukemia, the researchers found there were 531. And while none of those deaths occurred in any employee who received less than 50 mSv of radiation, the linear extrapolations suggest that every 10 mSv of radiation exposure increases the risk of leukemia by 0.002%.
Ars Technica: Quasi-stellar radio sources, or "quasars," are supermassive black holes, found at the center of galaxies, that produce extreme amounts of light as they pull material into themselves. The material swirling around the black holes is much brighter than the starlight of their host galaxies and can be up to 100 times brighter than all the stars in the Milky Way put together. That brightness disparity makes it hard to study quasars and to look past them to study their host galaxies. However, the difference in brightness is much less in certain areas of the spectrum. C. Megan Urry of Yale University and her colleagues used a near-IR camera on the Hubble Space Telescope to examine 11 quasars, all roughly 12 billion light-years away. They were selected because each is partially obscured by dust, which further reduces the brightness disparity. Urry's team found that all 11 of the host galaxies were undergoing collisions with other galaxies. That discovery supports the theory that galactic collisions drive the feeding of the black holes by disrupting the material surrounding them.