Astronomy
Get Ready: Mars Reverses Its Course In The Sky Saturday
Look up this weekend to catch bright Mars as it begins a zigzag detour across the spring sky.
In just six weeks, the planet Mars will make its closest approach to Earth since November 2005. These days, the Red Planet appears in the southeast skies just before midnight, glowing brightly like a yellowish-orange ember, and it is brightening noticeably with each passing week.
If you have been following Mars since New Year's Day, you may recall that back on the first day of the New Year, it was shining in the zodiacal constellation of Virgo. It was then 156 million miles (252 million kilometers) from Earth. In contrast, by the end of next week, Mars' distance from Earth will have diminished to less than 59 million miles (95 million km); it now shines about 10 times more brightly than it did at the start of this year.
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Actually, for the past few weeks, Mars has appeared to slow in its eastward trajectory; almost seeming to waver, as if it had become uncertain. Finally, on April 16, it will pause entirely. Then, for almost 11 weeks, it will reverse its course in the heavens and move backward against the star background — toward the west. On June 30, it will pause again, before resuming its normal eastward trek.
The Greeks were stumped
All the planets exhibit this "retrograde motion" at one time or another, but for the longest time, ancient astronomers were unable to come up with a satisfactory explanation for it. For one thing, while behaving in this strange manner, Mars will also appear to deviate somewhat from its normal course; the retrograde motion will appear to bring it to a place that's noticeably below its regular orbital track. In other words, for those people watching from Earth, Mars will appear to travel along a zigzag path. Yet, the Greeks staunchly believed that the sun, moon and planets all moved around the earth in perfect circles. They had great difficulty explaining and calculating why Mars mysteriously seemed to "zig" on a westerly course for more than two months, then abruptly "zag" back on its "normal," eastward course. For a long time they had no adequate explanation for it.
The Greeks finally explained away this anomaly by asserting that the planets moved around Earth in smaller "epicycles" — that is, a small circle whose center moves along its main orbital path around Earth, resulting in complex, almost coil-like curves. Unfortunately, the actual observations of the planets never seemed to fit this strange orbital mechanism, ultimately making the Greeks' explanation quite useless.
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Moons of Saturn May Be Younger Than The Dinosaurs
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“Moons are always changing their orbits. That’s inevitable,” says Matija Cuk, principal investigator at the SETI Institute. “But that fact allows us to use computer simulations to tease out the history of Saturn’s inner moons. Doing so, we find that they were most likely born during the most recent two percent of the planet’s history.”
While Saturn’s rings have been known since the 1600s, there’s still debate about their age. The straightforward assumption is that they are primordial – as old as the planet itself, which is more than four billion years. However, in 2012, French astronomers found that tidal effects – the gravitational interaction of the inner moons with fluids deep in Saturn’s interior – are causing them to spiral to larger orbital radii comparatively quickly. The implication, given their present positions, is that these moons, and presumably the rings, are recent phenomena.
Cuk, together with Luke Dones and David Nesvorny of the Southwest Research Institute, used computer modeling to infer the past dynamic behavior of Saturn’s icy inner moons. While our own moon has its orbit around Earth to itself, Saturn’s many satellites have to share space with each other. All of their orbits slowly grow due to tidal effects, but at different rates. This results in pairs of moons occasionally entering so-called orbital resonances. These occur when one moon’s orbital period is a simple fraction (for example, one-half or two-thirds) of another moon’s period. In these special configurations, even small moons with weak gravity can strongly affect each other’s orbits, making them more elongated and tilting them out of their original orbital plane.
By comparing present orbital tilts and those predicted by computer simulations, the researchers could learn how much the orbits of Saturn’s moons grew. It turns out that for some of the most important satellites – Tethys, Dione and Rhea – the orbits are less dramatically altered than previously thought. The relatively small orbital tilts indicate that they haven’t crossed many orbital resonances, meaning that they must have formed not far from where they are now.
But how long ago was their birth? Cuk and his team used results from NASA’s Cassini mission to help answer this question. The Cassini spacecraft has observed ice geysers on Saturn’s moon Enceladus. Assuming that the energy powering these geysers comes directly from tidal interactions, and that Enceladus’ level of geothermal activity is more or less constant, then the tides within Saturn are quite strong. According to the team’s analysis, these would move the satellite by the small amount indicated by the simulations in only about 100 million years. This would date the formation of the major moons of Saturn, with the exception of more distant Titan and Iapetus, to the relatively recent Cretaceous Period, the era of the dinosaurs.
“So the question arises, what caused the recent birth of the inner moons?” asks Cuk. “Our best guess is that Saturn had a similar collection of moons before, but their orbits were disturbed by a special kind of orbital resonance involving Saturn’s motion around the Sun. Eventually, the orbits of neighboring moons crossed, and these objects collided. From this rubble, the present set of moons and rings formed.”
Biology
How The Brain Produces Consciousness In 'Time Slices'
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Continuous or discrete?
Consciousness seems to work as continuous stream: one image or sound or smell or touch smoothly follows the other, providing us with a continuous image of the world around us. As far as we are concerned, it seems that sensory information is continuously translated into conscious perception: we see objects move smoothly, we hear sounds continuously, and we smell and feel without interruption. However, another school of thought argues that our brain collects sensory information only at discrete time-points, like a camera taking snapshots. Even though there is a growing body of evidence against "continuous" consciousness, it also looks like that the "discrete" theory of snapshots is too simple to be true.
A two-stage model
Michael Herzog at EPFL, working with Frank Scharnowski at the University of Zurich, have now developed a new paradigm, or "conceptual framework", of how consciousness might actually work. They did this by reviewing data from previously published psychological and behavioral experiments that aim to determine if consciousness is continuous or discrete. Such experiments can involve showing a person two images in rapid succession and asking them to distinguish between them while monitoring their brain activity.
The new model proposes a two-stage processing of information. First comes the unconscious stage: The brain processes specific features of objects, e.g. color or shape, and analyzes them quasi-continuously and unconsciously with a very high time-resolution. However, the model suggests that there is no perception of time during this unconscious processing. Even time features, such as duration or color change, are not perceived during this period. Instead, the brain represents its duration as a kind of "number", just as it does for color and shape.
Then comes the conscious stage: Unconscious processing is completed, and the brain simultaneously renders all the features conscious. This produces the final "picture", which the brain finally presents to our consciousness, making us aware of the stimulus.
The whole process, from stimulus to conscious perception, can last up to 400 milliseconds, which is a considerable delay from a physiological point of view. "The reason is that the brain wants to give you the best, clearest information it can, and this demands a substantial amount of time," explains Michael Herzog. "There is no advantage in making you aware of its unconscious processing, because that would be immensely confusing." This model focuses on visual perception, but the time delay might be different for other sensory information, e.g. auditory or olfactory.
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Lip-Readers ‘Hear’ Silent Words
Lip-readers’ minds seem to “hear” the words their eyes see being formed. And the better a person is at lipreading, the more neural activity there is in the brain’s auditory cortex, scientists reported April 4 at the annual meeting of the Cognitive Neuroscience Society. Earlier studies have found that auditory brain areas are active during lipreading. But most of those studies focused on small bits of language — simple sentences or even single words, said study coauthor Satu Saalasti of Aalto University in Finland. In contrast, Saalasti and colleagues studied lipreading in more natural situations. Twenty-nine people read the silent lips of a person who spoke Finnish for eight minutes in a video. “We can all lip-read to some extent,” Saalasti said, and the participants, who had no lipreading experience, varied widely in their comprehension of the eight-minute story.
In the best lip-readers, activity in the auditory cortex was quite similar to that evoked when the story was read aloud, brain scans revealed. The results suggest that lipreading success depends on a person’s ability to “hear” the words formed by moving lips, Saalasti said.
Chemistry
New Technique Reclaims Mercury From Spent Compact Fluorescent Light Bulbs
Fluorescent lightbulbs use less energy than traditional incandescent bulbs, but many contain mercury, a neurotoxin that can accumulate in food sources and ultimately in our own tissues. Removing and reusing mercury from bulbs helps keep the toxic element out of landfills, where it can enter the environment. Now, researchers have developed a technique for recycling mercury from spent compact fluorescent light bulbs that’s more energy efficient than current methods.
Existing recovery methods often require high temperatures to evaporate the mercury, separating it from the other material inside the bulbs. Parisa A. Ariya of McGill University and her colleagues wanted to devise a technique that used natural, nontoxic compounds and minimal energy. Instead of heat, they used nanoparticles to trap the mercury.
Ariya’s group looked at two kinds of nanoparticles made of different forms of iron oxide, magnetite and maghemite, which they had found to be efficient at capturing various gases, including mercury. The particles’ magnetism makes them easy to transfer, and they exist in vast quantities in the environment as components of atmospheric dust particles. An initial test showed that in a flask, magnetite particles captured mercury vapor much more efficiently than maghemite, so the team focused further work on magnetite nanoparticles.
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The team’s prototype required only 20 W of power, little enough that a small solar panel could power the setup. The power requirements for a real-world system to remove mercury quickly and completely might be higher, since the study focuses more on the capture of mercury vapor released when the bulb breaks, says Robert H. Hurt of Brown University, whose group has also investigated using nanoparticles to remove mercury. But mercury can remain in trapped in the white powder coating in the bulb’s glass tubing, which would require additional heat to extract.
Although few products use mercury anymore, mercury recovery is still crucial, Hurt notes. The World Health Organization counts mercury among the top 10 chemicals of major public health concern. Hurt cites the “easy separation” of mercury from the magnetite nanoparticles without heating as a major strength of the technique. Ariya’s team is currently talking to environmental and governmental agencies about launching pilot studies of the technique at places like light bulb factories and local waste disposal sites.
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Caging Chemical Weapons
Organophosphorous chemical weapons, such as sarin and soman, interfere with signals between nerve cells, and have recently been used to deadly effect in places such as Syria. Researchers are therefore trying to develop techniques that detect these chemical weapons in the environment, and destroy them.
Mike Ward and his group at the University of Sheffield in the UK may have found a way, using self-assembled supramolecular cages – large, hollow molecular structures that can act as a host to smaller molecules. Such structures have been around for a while, but the ones made by Ward are exciting because they can bind alkyl phosphonates within them. Alkyl phosphonates have the same basic size and shape as the chemical weapons in question, but lack the reactive leaving group that makes them so dangerous so researchers often use them as chemical weapon simulants in the lab.
The host cages have a cobalt or cadmium dication at each vertex and a bis(pyrazolyl-pyridine) ligand along each edge. In water, the hydrophobic effect drives interactions between the cage and alkyl phosphonates. ‘The interior surface is lined with CH groups from the ligands, which is an archetypal hydrophobic surface – oil and water don’t mix for the same reason,’ explains Ward. ‘It thus acts as a haven for molecules that are not happy in water. For the guests, their alkyl chains provide the hydrophobic contribution to binding. We can see this because, as the size of the alkyl groups increases, binding gets stronger – even though the phosphonate bit stays the same in every case.’ It is energetically favourable for this hydrophobic guest to enter the hydrophobic cavity because each guest displaces two bound water molecules, allowing them to form hydrogen bonds with each other, and increasing the total entropy by being free to move around.
The cage is also luminescent, but dims when an alkyl phosphonate enters. ‘This approach is very elegant as it combines sequestration with a fluorescent response – locking up the chemical warfare agent simulant within a coordination cage and signalling its presence,’ comments supramolecular chemist Philip Gale, from the University of Southampton, UK. ‘Chemical weapons can be destroyed by chemicals such as powerful oxidants in bulk situations but highly selective analysis and detection systems are very much needed, particularly security-sensitive locations,’ adds inorganic chemist Jonathan Steed from Durham University, UK.
Ecology
Clear Cutting And Its Influence On Carbon Storage
Clear-cutting loosens up carbon stored in forest soils, increasing the chances it will return to the atmosphere as carbon dioxide and contribute to climate change, a Dartmouth College study shows.
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Soil is the world's largest terrestrial carbon pool. In northern hardwood forests in the United States, mineral soil pools store up to 50 percent of total ecosystem carbon. Logging and other land-use changes are a major cause of soil carbon release, but there has been recent interest to further understand soil carbon dynamics in forested ecosystems after logging. This is of particular importance in the northeastern U.S. because of the great potential for the use of biomass as part of a diversified renewable energy portfolio.
The Dartmouth researchers explored whether clear-cutting changes the strength of the chemical bonds of carbon stored in mineral soils in hardwood forests in the northeastern United States. Clear-cutting involves harvesting all timber from a site at once rather than selectively culling mature trees. Carbon is stored in soil by binding only to certain soil structures.
The researchers collected soils from recently clear-cut forests and from older forests, and pulled carbon from the soil in a sequence of gentle to stronger extractions. The results showed that mature forest stands stored significantly more soil organic carbon in strongly mineral-bound and stable carbon pools than did soils from cut stands.
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Fast Food May Expose Consumers To Harmful Chemicals Called Phthalates
People who reported consuming more fast food in a national survey were exposed to higher levels of potentially harmful chemicals known as phthalates, according to a study published today by researchers at Milken Institute School of Public Health (Milken Institute SPH) at the George Washington University. [...]
"People who ate the most fast food had phthalate levels that were as much as 40 percent higher," says lead author Ami Zota, ScD, MS, an assistant professor of environmental and occupational health at Milken Institute SPH. "Our findings raise concerns because phthalates have been linked to a number of serious health problems in children and adults."
Phthalates belong to a class of industrial chemicals used to make food packaging materials, tubing for dairy products, and other items used in the production of fast food. Other research suggests these chemicals can leach out of plastic food packaging and can contaminate highly processed food.
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The researchers also discovered that grain and meat items were the most significant contributors to phthalate exposure. Zota says the grain category contained a wide variety of items including bread, cake, pizza, burritos, rice dishes and noodles. She also notes that other studies have also identified grains as an important source of exposure to these potentially harmful chemicals.
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This study fits into a bigger field of ongoing research showing that phthalates are in a wide variety of personal products, toys, perfume and even food. In 2008 Congress banned the use of phthalates in the production of children's toys because of concerns about the health impact of these chemicals.
Physics
'Weirdest Martensite': Century-Old Smectic Riddle Finally Solved
Using the latest computer game technology, a Cornell-led team of physicists has come up with a "suitably beautiful" explanation to a puzzle that has baffled researchers in the materials and theoretical physics communities for a century.
Physics professor James Sethna has co-authored a paper on the unusual microstructure of smectics - liquid crystals whose molecules are arranged in layers and form ellipses and hyperbolas - and their similarity to martensites, a crystalline structure of steel.
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If you fill a glass with a smectic liquid, due to its layering pattern the liquid forms beautiful ellipses and hyperbolas. The ellipses are defects - places where the desired ordering breaks down.
In martensite steel, named for German metallurgist Adolf Martens in 1898, its different low-energy crystal orientations mesh together in microscopic layers to give it a hardness factor far superior to pearlitic and other forms of steel.
In 1910, French physicist Georges Friedel studied a fluid that formed ellipses and hyperbolas, and realized that they must be formed by equally spaced layers of molecules.
Sethna suggests that a possible reason Friedel knew enough to be able to identify these ellipses and hyperbolas is that "he was French.
And in France, they used to study much more sophisticated math in high school, and everybody in high school learned about the cyclides of Dupin."
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Fish-Eyed Lens Cuts Through The Dark
Combining the best features of a lobster and an African fish, University of Wisconsin-Madison engineers have created an artificial eye that can see in the dark. And their fishy false eyes could help search-and-rescue robots or surgical scopes make dim surroundings seem bright as day.
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Most attempts to improve night vision tweak the "retinas" of artificial eyes—such as changing the materials or electronics of a digital camera's sensor—so they respond more strongly to incoming packets of light.
However, rather than interfering with efforts to boost sensitivity at the back end, Jiang's group set out to increase intensity of incoming light through the front end, the optics that focus the light on the sensor. They found inspiration for the strategy from two aquatic animals that evolved different strategies to survive and see in murky waters.
Elephantnosed fishes resemble river-dwelling Cyrano de Bergerac impersonators. Looking between their prominent proboscises reveals two strikingly unusual eyes, with retinas composed of thousands of tiny crystal cups instead of the smooth surfaces common to most animals. These miniature vessels collect and intensify red light, which helps the fish discern its predators.
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The group emulated the fish's crystal cups by engineering thousands of miniscule parabolic mirrors, each as tall as a grain of pollen. Jiang's team then shaped arrays of the light-collecting structures across the surface of a uniform hemispherical dome. The arrangement, inspired by the superposition compound eyes of lobsters, concentrates incoming light to individual spots, further increasing intensity.