| THE UNIVERSITY OF SYDNEY |
 "Understanding how a star rotates deep inside helps us to understand how stars like our sun will grow old." Image: adventtr/iStockphoto Scientists have made a new discovery about how old stars called 'red giants' rotate, giving an insight into what our sun will look like in five billion years. The international team of scientists, including University of Sydney astronomers Professor Tim Bedding and Dr Dennis Stello, has discovered red giants have slowed down on the outside, while their cores spin at least 10 times faster than their outer layers. The finding, just published in the prestigious journal Nature, tells us what the sun will look like in five billion years when it develops into a red giant. "The heart of a star determines how it evolves, and understanding how a star rotates deep inside helps us to understand how stars like our sun will grow old," said Professor Tim Bedding from the University of Sydney's School of Physics. Using NASA's Kepler space telescope, the team observed deep inside ageing red giants to make their discovery of the difference in rotation rate between the core and outer layers of the stars. The team, led by Paul Beck from Leuven University in Belgium, analysed waves inside the stars, which appear as rhythmic variations in the surface brightness of the stars. The effect of rotation on the frequencies of the waves is so small it took the team nearly two years of almost continuous data gathering from the Kepler satellite to make their discovery. "Red giants were once stars like our sun, but as they age their outer layers expand to more than five times their original size and cool down significantly, so they look red," explained Dr Dennis Stello, from the University of Sydney's School of Physics. "The opposite actually happens to the cores of red giants, as the core contracts and becomes extremely hot and dense," said Dr Stello. "We've just discovered that the core spins much faster than the outer layers in these old stars, which makes sense when you consider what happens to other spinning things like, say, an ice skater performing pirouettes. "A spinning ice skater will slow down if their arms are stretched far out, like the expanded outer layers of the red giants. The ice skater will spin faster if their arms are pulled tightly to the body, like the fast spinning contracted core of red giants." The Kepler space telescope - one of NASA's most successful space missions - is searching in the constellation Cygnus for potentially habitable planets by focussing on those similar in size to Earth. "Kepler is able to detect variations in a star's brightness of only a few parts in a million, so its measurements are ideally suited to detect the tiny brightness fluctuations of stars," explained Dr Stello. "We study these variations in brightness to work out what's going on deep inside stars. It's called asteroseismology - just as geologists use earthquakes to explore Earth's interior, we use star quakes to explore the interiors of stars," said Dr Stello. Different waves probe different parts of the star, and by a detailed comparison of the depth to which these waves travel inside the star the team found the rotation rate dramatically increased towards the stellar core. In addition to helping us understand how stars age, asteroseismology will help Kepler's mission of discovering Earth-sized planets outside our solar system by characterising the host stars around which these planets orbit. Editor's Note: Original news release can be found here. |
Science Daily — Engineers at Brown University have developed a system that cleanly and efficiently removes trace heavy metals from water. In experiments, the researchers showed the system reduced cadmium, copper, and nickel concentrations, returning contaminated water to near or below federally acceptable standards. The technique is scalable and has viable commercial applications, especially in the environmental remediation and metal recovery fields.
An unfortunate consequence of many industrial and manufacturing practices, from textile factories to metalworking operations, is the release of heavy metals in waterways. Those metals can remain for decades, even centuries, in low but still dangerous concentrations.Results appear in the Chemical Engineering Journal.
Ridding water of trace metals "is really hard to do," said Joseph Calo, professor emeritus of engineering who maintains an active laboratory at Brown. He noted the cost, inefficiency, and time needed for such efforts. "It's like trying to put the genie back in the bottle."
That may be changing. Calo and other engineers at Brown describe a novel method that collates trace heavy metals in water by increasing their concentration so that a proven metal-removal technique can take over. In a series of experiments, the engineers report the method, called the cyclic electrowinning/precipitation (CEP) system, removes up to 99 percent of copper, cadmium, and nickel, returning the contaminated water to federally accepted standards of cleanliness. The automated CEP system is scalable as well, Calo said, so it has viable commercial potential, especially in the environmental remediation and metal recovery fields. The system's mechanics and results are described in a paper published in the Chemical Engineering Journal.
A proven technique for removing heavy metals from water is through the reduction of heavy metal ions from an electrolyte. While the technique has various names, such as electrowinning, electrolytic removal/recovery or electroextraction, it all works the same way, by using an electrical current to transform positively charged metal ions (cations) into a stable, solid state where they can be easily separated from the water and removed. The main drawback to this technique is that there must be a high-enough concentration of metal cations in the water for it to be effective; if the cation concentration is too low -- roughly less than 100 parts per million -- the current efficiency becomes too low and the current acts on more than the heavy metal ions.
Another way to remove metals is through simple chemistry. The technique involves using hydroxides and sulfides to precipitate the metal ions from the water, so they form solids. The solids, however, constitute a toxic sludge, and there is no good way to deal with it. Landfills generally won't take it, and letting it sit in settling ponds is toxic and environmentally unsound. "Nobody wants it, because it's a huge liability," Calo said.
The dilemma, then, is how to remove the metals efficiently without creating an unhealthy byproduct. Calo and his co-authors, postdoctoral researcher Pengpeng Grimshaw and George Hradil, who earned his doctorate at Brown and is now an adjunct professor, combined the two techniques to form a closed-loop system. "We said, 'Let's use the attractive features of both methods by combining them in a cyclic process,'" Calo said.
It took a few years to build and develop the system. In the paper, the authors describe how it works. The CEP system involves two main units, one to concentrate the cations and another to turn them into stable, solid-state metals and remove them. In the first stage, the metal-laden water is fed into a tank in which an acid (sulfuric acid) or base (sodium hydroxide) is added to change the water's pH, effectively separating the water molecules from the metal precipitate, which settles at the bottom. The "clear" water is siphoned off, and more contaminated water is brought in. The pH swing is applied again, first redissolving the precipitate and then reprecipitating all the metal, increasing the metal concentration each time. This process is repeated until the concentration of the metal cations in the solution has reached a point at which electrowinning can be efficiently employed.
When that point is reached, the solution is sent to a second device, called a spouted particulate electrode (SPE). This is where the electrowinning takes place, and the metal cations are chemically changed to stable metal solids so they can be easily removed. The engineers used an SPE developed by Hradil, a senior research engineer at Technic Inc., located in Cranston, R.I. The cleaner water is returned to the precipitation tank, where metal ions can be precipitated once again. Further cleaned, the supernatant water is sent to another reservoir, where additional processes may be employed to further lower the metal ion concentration levels. These processes can be repeated in an automated, cyclic fashion as many times as necessary to achieve the desired performance, such as to federal drinking water standards.
In experiments, the engineers tested the CEP system with cadmium, copper, and nickel, individually and with water containing all three metals. The results showed cadmium, copper, and nickel were lowered to 1.50, 0.23 and 0.37 parts per million (ppm), respectively -- near or below maximum contaminant levels established by the Environmental Protection Agency. The sludge is continuously formed and redissolved within the system so that none is left as an environmental contaminant.
"This approach produces very large volume reductions from the original contaminated water by electrochemical reduction of the ions to zero-valent metal on the surfaces of the cathodic particles," the authors write. "For an initial 10 ppm ion concentration of the metals considered, the volume reduction is on the order of 106."
Calo said the approach can be used for other heavy metals, such as lead, mercury, and tin. The researchers are currently testing the system with samples contaminated with heavy metals and other substances, such as sediment, to confirm its operation.
The research was funded by the National Institute of Environmental Health Sciences, a branch of the National Institutes of Health, through the Brown University Superfund Research Program.
Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.
