February 23, 2014

Science Briefs

Fertilizer could be too much of a good thing for the world’s grasslands, according to a study published online by the journal Nature.

Go easy on fertilizing grasslands

Fertilizer could be too much of a good thing for the world’s grasslands, according to a study published online by the journal Nature.

The worldwide study shows that, on average, additional nitrogen increases the amount of grass that can be grown. But a smaller number of species thrive, crowding out others that are better adapted to survive in harsher times. That results in wilder swings in the amount of available forage.

“More nitrogen means more production, but it’s less stable,” said paper co-author Johannes Knops, a University of Nebraska-Lincoln biologist. “There are more good years and more bad years. Not all years are going to be good, and the bad years are going to be worse.”

The three-year study monitored grasslands at 41 locations on five continents. Two sites in Nebraska were part of the study.

Knops said fertilizer overuse could intensify the detrimental effects of drought on grasslands, such as the drought that devastated cattle herds in the southern Plains from 2011 to 2013, when Texas lost about 15 percent of its cattle herd. Drought also could have ripple effects during bad years by reducing plant cover, which increases erosion, and decreases water filtration and carbon sequestration benefits provided by grasslands.

Busy brain aids dream recall

Some people recall a dream every morning; others rarely recall one. A team at France’s Lyon Neuroscience Research Center studied the brain activity of these two types of dreamers to understand the differences between them. In a study published in the journal Neuropsychopharmacology, the researchers show that the temporoparietal junction – an information-processing hub in the brain – is more active in people who recalled dreams 5.2 mornings per week on average. In 2013, in the journal Cerebral Cortex, the team observed that “high dream recallers” have twice as many times of wakefulness during sleep as “low dream recallers” – who reported 2 dreams per month on average – and their brains are more reactive to auditory stimuli during sleep and wakefulness. This increased brain reactivity may promote awakenings during the night, and that may promote recall of dreams during brief periods of wakefulness.

In this new study, the scientists sought to identify which areas of the brain differentiate the two types of dream recallers by using positron emission tomography to measure spontaneous brain activity. “High dream recallers,” while awake and while asleep, showed stronger spontaneous brain activity in the medial prefrontal cortex and in the temporoparietal junction, an area of the brain involved in attention orienting toward external stimuli.

Fruit design for lithium-ion battery?

An electrode designed like a pomegranate – with silicon nanoparticles clustered like seeds in a tough carbon rind – overcomes several remaining obstacles to using silicon for a new generation of lithium-ion batteries, say its inventors at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

“While a couple of challenges remain, this design brings us closer to using silicon anodes in smaller, lighter and more powerful batteries for products like cellphones, tablets and electric cars,” said research leader Yi Cui in Nature Nanotechnology. “Experiments showed our pomegranate-inspired anode operates at 97 percent capacity even after 1,000 cycles of charging and discharging, which puts it well within the desired range for commercial operation.”

The anode (negative electrode) is where energy is stored when a battery charges. Silicon anodes could store 10 times more charge than the graphite anodes in today’s rechargeable lithium-ion batteries, but they also have major drawbacks: The brittle silicon swells and falls apart during battery charging, and it reacts with the battery’s electrolyte to form gunk that coats the anode and degrades its performance.

Researchers used a micro-emulsion technique common in the oil, paint and cosmetic industries to gather silicon yolk shells into clusters, and coated each cluster with a second, thicker layer of carbon. These carbon rinds hold the pomegranate clusters together and provide a sturdy highway for electrical currents. Since each pomegranate cluster has just one-tenth the surface area of the individual particles inside it, a much smaller area is exposed to the electrolyte, thereby reducing the amount of gunk that forms to a manageable level.

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