Physics Today Daily Edition

Subscribe to Physics Today Daily Edition feed
Please follow the links to view the content.
Updated: 47 min 30 sec ago

Questions and answers with Adrienne Kolb

18 March 2016
The recently retired Fermilab archivist and historian discusses her role in piecing together the puzzle that was the ill-fated Superconducting Super Collider project.

Supercomputer simulates blood flow in circulatory system

18 March 2016

BBC: A supercomputer simulation presented at the American Physical Society meeting in Baltimore, Maryland, this week, models the human circulatory system in three dimensions. The simulated network, which tracks blood flow through all arteries larger than 1 mm across, is based on images captured by full-body CT and MRI scans of the circulatory system of a single person. Flow measurements in the simulation closely matched those of a 3D printed version of the circulatory system, both when the blood was free-flowing and when it was pulsed in a way that mimicked a heartbeat. Amanda Randles of Duke University and her team attempted the project primarily as a proof-of-concept because most previous simulations have focused on smaller sections of the circulatory system. The goal is to model how medical interventions, such as stents or other surgical modifications, might affect the system as a whole.

Hints of new particle in LHC data grow somewhat stronger

18 March 2016
Nature: Last December, the ATLAS and CMS detector teams at CERN's Large Hadron Collider (LHC) announced that they had seen a bump in the data that indicated the possibility of a new particle with a mass around 750 GeV. Both teams found the signal in the production of pairs of gamma-ray photons, but neither detector approached the 5 σ confidence level necessary to confirm a discovery. A secondary analysis of the data presented on 17 March at a conference in La Thuile, Italy, has somewhat increased the confidence level. The CMS reanalysis included 23% more data and a recalibration to account for radiation affecting the measurements. The resulting signal increased from a 1.2 σ to a 1.6 σ confidence level. A reanalysis of the ATLAS data saw a drop in confidence, though not enough of one to outweigh the increase in the CMS data. A new particle at 750 GeV is not predicted by any widely accepted theories, which makes the potential discovery so exciting. LHC researchers believe they will have enough data by midsummer to declare whether the signal is a new particle or just a statistical fluctuation.

A biologically inspired artificial eye

17 March 2016
An array of tiny, laser-cut light concentrators helps the eye achieve high sensitivity.

Stroke patients may benefit from transcranial electrical stimulation

17 March 2016
IEEE Spectrum: Transcranial direct current stimulation (tDCS) is a touchy subject for neuroscientists. Claims that the technique, in which current flows through electrodes connected to the head, can improve memory and cognition have been met with considerable skepticism. Rather than employing tDCS for cognitive enhancement, scientists from the University of Oxford used it on stroke victims during rounds of physical therapy. The team reports in Science Translational Medicine that over the long term, patients receiving tDCS treatment had a better ability to move their arms than those who received a sham treatment. Compared with the control group, the tDCS patients scored better on two of three measures of recovery three months after treatment and had more activity in the brain regions responsible for motor skills. Future research will be needed to replicate the finding, since the study had only 24 participants.

High-energy cosmic rays traced to Milky Way's central black hole

17 March 2016
Science: Earth's atmosphere is constantly pelted by charged subatomic particles from space called cosmic rays. Scientists have traced the particles' origins to several sources inside and outside the galaxy, though such detective work is difficult because the particles don't travel on straight-line trajectories. Now a team of researchers has identified a new culprit in the production of high-energy cosmic rays: Sagittarius A*, the supermassive black hole at the center of the Milky Way. Scientists with the High Energy Stereoscopic System (HESS), a five-telescope array in Namibia, based their conclusion on an abundance of gamma rays emanating from the central region of the galaxy. Although Sagittarius A* seems relatively inactive, the researchers propose that strong electric and magnetic fields near the black hole fling protons at enormous speeds. Those protons then crash into gas molecules and produce gamma rays, which HESS can detect. The study concludes that while supernova explosions are thought to produce many of the speediest cosmic rays within the galaxy, Sagittarius A* may be responsible for particles with especially high PeV energies.

Reexamining the hydrodynamics of sharkskin

17 March 2016
Los Angeles Times: Covering surfaces with a sharkskin-like material called riblets has long been thought to reduce drag through a surrounding fluid. Until recently, however, it's been hard to evaluate the actual benefits of such a structured material. Now researchers have used data on shortfin mako shark denticles to develop a computer model that compares the fluid flow over those natural structures with the flow over the manmade riblets. Whereas the riblets were found to reduce drag by 5.2%, the denticles actually increased drag. Moreover, when rows of denticles were aligned, they increased drag by 44%; when staggered, they increased drag by 50%. The researchers attribute the difference to the fact that riblets are two-dimensional structures, while denticles are three dimensional. The denticles’ thickness causes the flows to become more turbulent and complicated. The researchers conclude that further study will be needed to determine whether denticles can indeed reduce drag or whether they work better on the body of a living, moving creature than attached to an inanimate object.

Trees' respiration may adapt to climate change

17 March 2016
New York Times: Plants take in carbon dioxide and then release it through a metabolic process known as respiration. Terrestrial plant life can release six times as much carbon dioxide as that found in the emissions from fossil fuel burning. Because studies had shown that warming temperatures can cause plants to increase their CO2 output, scientists have been concerned over what effect that could have on climate change. To find out, a team of researchers monitored the respiration rates of 10 different North American tree species from boreal and temperate forests grown in two different conditions: ambient temperatures and 3.4 °C warmer than ambient temperature. The researchers also looked at how the trees responded by exposing some to short bursts of warmth, lasting minutes or hours, and allowing others to acclimate over time. They found that the trees allowed to acclimate were able to adjust their CO2 output so that it increased by just 5%. The CO2 output of trees exposed to rapid warming increased by 23%. Because the earlier studies had been conducted over shorter time scales, the researchers say that climate change may not cause plants to raise atmospheric CO2 concentrations as much as previously thought.

Patent concerns arise at UK National Graphene Institute

16 March 2016
The Sunday Times: Researchers working on graphene at Manchester University in the UK are refusing to work at the new £61 million National Graphene Institute. They are concerned that the center, set up last year to find commercial ways to exploit the material, does not have adequate security to protect their research from exploitation by some of NGI's outside partners, such as the Taiwanese company BGT Materials. The university denies the claims. Since graphene was discovered at the university in 2004, the UK has filed 1% of the patents related to the material, compared with 50% by China.

Metamaterials based on Islamic art

16 March 2016
BBC: Metamaterials have specific unusual properties that don't occur in nature, such as changing to predetermined shapes when heat is applied to them. At the American Physical Society's March meeting in Baltimore, Maryland Ahmad Rafsanjani from McGill University in Montreal talked about some new metamaterials based on Islamic art. Many aspects of Islamic art contain geometric patterns, and Rafsanjani and his colleagues discovered that two of them allow laser-perforated rubber sheets to become wider when stretched instead of narrower. Applications could include developing new foldable solar panels for satellites or medical applications for keyhole surgery.

Horst Afheldt

16 March 2016

How to use Twitter to enhance your conference experience

16 March 2016
Effective use of the popular social media service can help you network and advance your career.

Bright spots on Ceres remain a mystery

16 March 2016
Guardian: Last year when NASA’s Dawn spacecraft arrived at Ceres—a dwarf planet located in the asteroid belt between Mars and Jupiter—it observed some 130 bright spots dotting the otherwise dark surface. Because the spots appeared to brighten during the day and grow dimmer at night, it had been proposed that they were caused by the presence of water vapor that emanated from a layer of ice trapped beneath the surface and warmed by the Sun’s rays. New data from the European Southern Observatory in Chile, however, show that whereas the spots brightened and dimmed in July, there was little change in August. According to Paolo Molaro of the Trieste Astronomical Observatory and colleagues, it is possible that “the cycle of evaporation and freezing could last more than one rotational period,” and so the system may be more complex than previously thought.

Centralized routing scheme could relieve traffic congestion

16 March 2016
IEEE Spectrum: Sometimes the road less traveled is the best way to go—even if it takes a little longer. That is the finding of a recent study that analyzed rush-hour traffic in five major cities: Boston, San Francisco, Rio de Janeiro, and the Portuguese cities of Lisbon and Porto. Major traffic jams, the researchers found, occur because most people, and most GPS units, generally choose the shortest, fastest route to a given destination. That congestion can be relieved, they say, by drivers choosing alternate routes, which may add a few minutes to their own travel times but reduce collective travel times overall. Because such an optimized routing system would require a great deal of coordination and willingness on the part of some drivers to slightly inconvenience themselves for the benefit of others, it is unlikely to be implemented any time soon. However, it could work well for a fleet of autonomous cars connected to a central routing network.

Europe could lose significant neutron beam resources over next decade

15 March 2016

Science: The Neutron Landscape Group (NLG) was commissioned to determine the effect of the upcoming closures of a variety of neutron beam sources in Europe. According to the NLG, two-thirds of Europe's current neutron sources were built in the 1960s and 1970s and are scheduled to be shut down. The group's report, released last week, says that if all the aging facilities that are scheduled to close over the next 15 years do so, then the supply of neutrons for research will be reduced by 40–50%. That reduction accounts for the addition of the European Spallation Source (ESS) in Lund, Sweden, which will be the world's largest neutron source when it begins operating around 2019. However, due to limited funding, the ESS will have only 16 instruments running in the first 10 years of operation. That would not be close to offsetting the 40 instruments present at the Institut Laue–Langevin (ILL) in Grenoble, France, which is expected to close in 2023. The NLG suggests that maintaining the ILL, which would cost around €200 million ($222 million), would help reduce the loss of neutron production to just 20%.

Nanoscale magnet tests the Landauer limit

15 March 2016

IEEE Spectrum: In 1961 Rolf Landauer of IBM theorized that there is a minimum amount of energy required by computational systems to reset or erase a bit of information. His calculations showed that at room temperature, that limit is 3 × 10−21 J (3 zJ). In 2012 a team of researchers demonstrated that the limit could be reached in a nonmagnetic physical system. Now Jeffrey Bokor of the University of California, Berkeley, and his colleagues have shown that Landauer's principle does apply to a magnetic system more representative of actual computer storage. Bokor's team created an array of nano-sized magnetic dots that were magnetically aligned. Using an external magnetic field, the scientists could flip the dots between binary states and effectively erase the data that the dots stored. The team found that the dots consumed around 6 zJ of energy at room temperature—twice the Landauer limit but within the level of uncertainty of the experiment. The researchers suggest that slight variations in the orientations of the magnets were enough to account for the higher value.

Rising sea levels could affect millions more people than previously thought

15 March 2016
New York Times: Sea-level rise due to climate change could affect three times as many people in the US as previously estimated, according to a new study. The reason, the researchers say, is that most climate change projections have not included ongoing population growth, which has been especially rapid in coastal areas. By combining future population estimates based on census data with predictions of sea-level rise from the National Oceanic and Atmospheric Administration, Mathew Hauer of the University of Georgia and colleagues found that a rise in sea levels of 0.9 meters could displace as many as 4.2 million people. A rise of 1.8 meters could displace 13.1 million. Alarmingly, some 70% of the people expected to be displaced will be in the southeastern US. Other areas, such as coastal Louisiana and the Chesapeake Bay region, are already sinking and so will experience even faster rates of change. The estimated cost of relocating all the displaced people could reach $14 trillion, the researchers say.

Mysterious “fairy circles” may arise from plants competing for water

15 March 2016
Atlantic: Circular areas of bare soil freckling low-lying patches of vegetation in Australia and Namibia, known as fairy circles, have perplexed scientists for almost a century. Proposed causes have included sand termites, grazing ants, poisonous plants, and even radioactive gas leaks. Because of the circles’ regular, hexagonal spacing, Stephan Getzin of the University of Goettingen in Germany ruled out insect activity. While in Australia, Getzin and colleagues found that lack of rain probably drives the fairy circles’ formation. Bigger plants have deeper roots and draw more water than their smaller neighbors. The smaller plants die, leaving empty circles of soil that act as rain collectors and nourish the remaining plants. That proposal has been backed up by computer simulations. To add support to their theory, Getzin and colleagues are searching for more examples of fairy circles through the use of satellite imaging.

Dissipation in breaking waves

15 March 2016
Bubbles not only give breaking waves their white caps, they also control how the waves' energy is transferred.

<em>New York Times</em> commentary argues that all research papers should be free

14 March 2016
A home page blurb cites “one woman’s guerrilla campaign” against paywalls.