Monday, March 8, 2010

TIDES, EARTH'S ROTATION AMONG SOURCES OF GIANT UNDERWATER WAVES

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Scientists at the University of Rhode Island are gaining new insight into the mechanisms that generate huge, steep underwater waves that occur between layers of warm and cold water in coastal regions of the world's oceans.

David Farmer, a physical oceanographer and dean of the URI Graduate School of Oceanography, together with student Qiang Li, said that large amplitude, nonlinear internal waves can reach heights of 150 meters or more in the South China Sea, and the effects they have on surface wave fields ensure that they are readily observable from space.

"The large waves in the South China Sea have attracted a fair bit of attention in recent years," Farmer said, "but much of this has been directed at the interaction of the waves with the sloping continental shelf of mainland China where they break, overturn and produce intense mixing. Our focus is on the way in which they are generated in Luzon Strait, between Taiwan and the Philippines, and the way they evolve as they propagate westwards across the deep ocean basin of the South China Sea."

Farmer and Li studied the evolution of large internal waves occurring at tidal periods generated by currents traversing submarine ridges in Luzon Strait. As these waves travel west through the South China Sea, they steepen and evolve into packets of steep, energetic waves occurring at periods of 20-30 minutes. It is these energetic short period waves that modulate the ocean surface roughness, making their presence observable from satellites in space.

The URI scientists' observations showed that the Earth's rotation modifies internal waves as they travel cross the deep basin. This effect mainly influences the internal waves that form on the 24-hour period of diurnal tides, dispersing the energy and inhibiting the steepening process. Internal waves that form on the semi-diurnal tides are not affected in this way, are more readily steepened and then break into the energetic, short period waves.

Farmer and Li studied internal waves in the South China Sea using pressure equipped inverted echo-sounders, instruments developed by scientists at the University of Rhode Island. From the seafloor, the device transmits an acoustic pulse and then listens for the echo from the sea surface. Sound travels faster through warm water than it does through cold water, so changes in the echo delay allow measurement of the thickness of the warm surface layer, enabling the shape and size of passing internal waves to be recorded.

According to Farmer, nonlinear internal waves impact the ocean in many ways: stirring up sediment on the sea floor, creating hazards to offshore engineering structures, interfering with submarine navigation, and greatly affecting propagation of underwater sound. Internal waves also appear to have significant, if not fully understood, biological impacts, and in shallow water environments they can mix water masses and modify coastal circulation.

University of Rhode Island

TREE-DWELLING MAMMALS CLIMB TO THE HEIGHTS OF LONGEVITY

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The squirrels littering your lawn with acorns as they bound overhead will live to plague your yard longer than the ones that aerate it with their burrows, according to a University of Illinois study.

Scientists know from previous studies that flying birds and bats live longer than earthbound animals of the same size. Milena Shattuck and Scott Williams, doctoral candidates in anthropology, decided to take a closer look at the relationship between habitat and lifespan in mammals, comparing terrestrial and treetop life. They published their findings in the Proceedings of the National Academy of Sciences.

The two hypothesized that, like flight, treetop or arboreal dwelling reduces a species’ extrinsic mortality – death from predation, disease and environmental hazards; that is, causes other than age.

“One of the predictions of the evolutionary theory of aging is that if you can reduce sources of extrinsic mortality, you’ll end up exposing some of the late-acting mutations to natural selection, and therefore evolve longer lifespans,” Williams said.

Williams and Shattuck found that for arboreality, the theory holds. Mammals who spend the majority of their time up a tree enjoy longevity over those who scurry along the ground. The pattern holds consistent both on the large scale among all mammals, and also in specific classes the pair studied, such as tree squirrels versus ground squirrels.

However, the pair also uncovered two classes of mammals that buck the longevity trend – marsupials, such as kangaroos, and primates, including ground walkers such as gorillas and humans and their branch-swinging counterparts. Aloft or not, these groups show no significant difference, although primates in general tend to lead long lives.

“These are the exceptions that prove the rule,” Shattuck said. “The defining feature that seems to connect those two groups is a long history of arboreal ancestors. Other mammals started out terrestrially, and separate groups developed arboreality independently. Marsupials and primates seem to have started off in the trees, and then the terrestrial marsupials and primates have descended from arboreal ancestors.”

This arboreal ancestry may partially explain why humans have such a long lifespan relative to other mammals. As primates descended from the trees, they had to develop new strategies for survival on the ground. Terrestrial primates, including humans, tend to be larger and more social, providing some security from predators and environmental obstacles.

“It’s interesting to think that humans, at least in part, live so long and do well because we had this evolutionary history when we were in the trees,” said Shattuck. “And now, we have the intervention of culture and medicine to help extend that further.”

(Photo: L. Brian Stauffer)

University of Illinois

SCIENTISTS DETERMINE MASSIVE PLANET IS BEING TORN APART BY ITS OWN TIDES, PROVIDING OPPORTUNITY TO WATCH A PLANETARY DEATH MARCH

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An international group of astrophysicists has determined that a massive planet outside our Solar System is being distorted and destroyed by its host star – a finding that helps explain the unexpectedly large size of the planet, WASP-12b.

It’s a discovery that not only explains what’s happening to WASP-12b; it also means scientists have a one-of-a-kind opportunity to observe how a planet enters this final stage of its life. “This is the first time that astronomers are witnessing the ongoing disruption and death march of a planet,” says UC Santa Cruz professor Douglas N.C. Lin. Lin is a co-author of the new study and the founding director of the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University, which was deeply involved with the research.

The findings were published in the February 25 issue of Nature.

The research was led by Shu-lin Li of the National Astronomical Observatories of China. A graduate of KIAA, Li and a research team analyzed observational data on the planet to show how the gravity of its parent star is both inflating its size and spurring its rapid dissolution.

WASP 12-b, discovered in 2008, is one of the most enigmatic of 400-plus planets that have been found outside our Solar System over the past 15 years. It orbits a star, in the constellation Auriga, roughly similar in mass to our Sun. Like most known extra-solar planets, it is large and gaseous, resembling Jupiter and Saturn in this respect. But unlike Jupiter, Saturn or most other extra-solar planets, it orbits its parent star at extremely close range – 75 times closer than the Earth is to the Sun, or just over 1 million miles. It is also larger than astrophysical models would predict. Its mass is estimated to be almost 50% larger than Jupiter’s and its 80% larger, giving it six times Jupiter’s volume. It is also unusually hot, with a daytime temperature of more than 2500°C.

Some mechanism must be responsible for expanding this planet to such an unexpected size, say the researchers. They have focused their analysis on tidal forces, which they say are strong enough to produce the effects observed on WASP 12b.

On Earth, tidal forces between the Earth and the Moon cause local sea levels rise and fall modestly twice a day. WASP-12b, however, is so close to its host star that the gravitational forces are enormous. The tremendous tidal forces acting on the planet completely change the shape of the planet into something similar to that of a rugby or American football.

These tides not only distort the shape of WASP 12-b. By continuously deforming the planet, they also create friction in the its interior. The friction produces heat, which causes the planet to expand. “This is the first time that there is direct evidence that internal heating (or ‘tidal heating’) is responsible for puffing up the planet to its current size,” says Lin.

Huge as it is, WASP 12-b faces an early demise, say the researchers. In fact, its size is part of its problem. It has ballooned to such a point that it cannot retain its mass against the pull of its parent star’s gravity. As the study’s lead author Li explains, ““WASP-12b is losing its mass to the host star at a tremendous rate of six billion metric tons each second. At this rate, the planet will be completely destroyed by its host star in about ten million years. This may sound like a long time, but for astronomers it's nothing. This planet will live less than 500 times less than the current age of the Earth.”

The material that is stripped off WASP-12b does not directly fall onto the parent star. Instead, it forms a disk around the star and slowly spirals inwards. A careful analysis of the orbital motion of WASP-12b suggests circumstantial evidence of the gravitational force of a second, lower-mass planet in the disk. This planet is most likely a massive version of the Earth -- a so-called “super-Earth.”

The disk of planetary material and the embedded super-Earth are detectable with currently available telescope facilities. Their properties can be used to further constrain the history and fate of the mysterious planet WASP-12b.

(Photo: ESA/C Carreau)

Kavli Institute for Astronomy and Astrophysics (KIAA)

AN ELECTRIFYING DISCOVERY: NEW MATERIAL TO HARVEST ELECTRICITY FROM BODY MOVEMENTS

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Scientists are reporting an advance toward scavenging energy from walking, breathing, and other natural body movements to power electronic devices like cell phones and heart pacemakers. In a study in ACS' monthly journal, Nano Letters, they describe development of flexible, biocompatible rubber films for use in implantable or wearable energy harvesting systems. The material could be used, for instance, to harvest energy from the motion of the lungs during breathing and use it to run pacemakers without the need for batteries that must be surgically replaced every few years.

Michael McAlpine and colleagues point out that popular hand-held consumer electronic devices are using smaller and smaller amounts of electricity. That opens the possibility of supplementing battery power with electricity harvested from body movements. So-called "piezoelectric" materials are the obvious candidates, since they generate electricity when flexed or subjected to pressure. However, manufacturing piezoelectric materials requires temperatures of more than 1,000 degrees F., making it difficult to combine them with rubber.

The scientists describe a new manufacturing method that solves this problem. It enabled them to apply nano-sized ribbons of lead zirconate titanate (PZT) — each strand about 1/50,000th the width of a human hair — to ribbons of flexible silicone rubber. PZT is one of the most efficient piezoelectric materials developed to date and can convert 80 percent of mechanical energy into electricity. The combination resulted in a super-thin film they call 'piezo-rubber' that seems to be an excellent candidate for scavenging energy from body movements.

(Photo: Frank Wojciechowski)

ACS Publications

INTELLIGENT PEOPLE HAVE "UNNATURAL" PREFERENCES AND VALUES THAT ARE NOVEL IN HUMAN EVOLUTIONARY HISTORY

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More intelligent people are statistically significantly more likely to exhibit social values and religious and political preferences that are novel to the human species in evolutionary history. Specifically, liberalism and atheism, and for men (but not women), preference for sexual exclusivity correlate with higher intelligence, a new study finds.

The study, published in the March 2010 issue of the peer-reviewed scientific journal Social Psychology Quarterly, advances a new theory to explain why people form particular preferences and values. The theory suggests that more intelligent people are more likely than less intelligent people to adopt evolutionarily novel preferences and values, but intelligence does not correlate with preferences and values that are old enough to have been shaped by evolution over millions of years.

"Evolutionarily novel" preferences and values are those that humans are not biologically designed to have and our ancestors probably did not possess. In contrast, those that our ancestors had for millions of years are "evolutionarily familiar."

"General intelligence, the ability to think and reason, endowed our ancestors with advantages in solving evolutionarily novel problems for which they did not have innate solutions," says Satoshi Kanazawa, an evolutionary psychologist at the London School of Economics and Political Science. "As a result, more intelligent people are more likely to recognize and understand such novel entities and situations than less intelligent people, and some of these entities and situations are preferences, values, and lifestyles."

An earlier study by Kanazawa found that more intelligent individuals were more nocturnal, waking up and staying up later than less intelligent individuals. Because our ancestors lacked artificial light, they tended to wake up shortly before dawn and go to sleep shortly after dusk. Being nocturnal is evolutionarily novel.

In the current study, Kanazawa argues that humans are evolutionarily designed to be conservative, caring mostly about their family and friends, and being liberal, caring about an indefinite number of genetically unrelated strangers they never meet or interact with, is evolutionarily novel. So more intelligent children may be more likely to grow up to be liberals.

Data from the National Longitudinal Study of Adolescent Health (Add Health) support Kanazawa's hypothesis. Young adults who subjectively identify themselves as "very liberal" have an average IQ of 106 during adolescence while those who identify themselves as "very conservative" have an average IQ of 95 during adolescence.

Similarly, religion is a byproduct of humans' tendency to perceive agency and intention as causes of events, to see "the hands of God" at work behind otherwise natural phenomena. "Humans are evolutionarily designed to be paranoid, and they believe in God because they are paranoid," says Kanazawa. This innate bias toward paranoia served humans well when self-preservation and protection of their families and clans depended on extreme vigilance to all potential dangers. "So, more intelligent children are more likely to grow up to go against their natural evolutionary tendency to believe in God, and they become atheists."

Young adults who identify themselves as "not at all religious" have an average IQ of 103 during adolescence, while those who identify themselves as "very religious" have an average IQ of 97 during adolescence.

In addition, humans have always been mildly polygynous in evolutionary history. Men in polygynous marriages were not expected to be sexually exclusive to one mate, whereas men in monogamous marriages were. In sharp contrast, whether they are in a monogamous or polygynous marriage, women were always expected to be sexually exclusive to one mate. So being sexually exclusive is evolutionarily novel for men, but not for women. And the theory predicts that more intelligent men are more likely to value sexual exclusivity than less intelligent men, but general intelligence makes no difference for women's value on sexual exclusivity. Kanazawa's analysis of Add Health data supports these sex-specific predictions as well.

One intriguing but theoretically predicted finding of the study is that more intelligent people are no more or no less likely to value such evolutionarily familiar entities as marriage, family, children, and friends.

American Sociological Association

THE BIGGER THE ANIMAL, THE STIFFER THE 'SHOES'

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If a Tiger's feet were built the same way as a mongoose's feet, they'd have to be about the size of a hippo's feet to support the big cat's weight. But they're not.

For decades, researchers have been looking at how different-sized legs and feet are put together across the four-legged animal kingdom, but until now they overlooked the "shoes," those soft pads on the bottom of the foot that bear the brunt of the animal's walking and running.

New research from scientists in Taiwan and at Duke University has found that the mechanical properties of the pads vary in predictable fashion as animals get larger. In short, bigger critters need stiffer shoes.

Kai-Jung Chi, an assistant professor of physics at National Chung Hsing University in Taiwan ran a series of carefully calibrated "compressive tests" on the footpads of carnivores that have that extra toe halfway up the foreleg, including dogs, wolves, domestic cats, leopards and hyenas. She was measuring the relative stiffness of the pads across species – how much they deformed under a given amount of compression.

"People hadn't looked at pads," said co-author V. Louise Roth, an associate professor of biology and evolutionary anthropology who was Chi's thesis adviser at Duke. "They've been looking at the bones and muscles, but not that soft tissue."

Whether running, walking or standing still, the bulk of the animal's weight is borne on that pillowy clover-shaped pad behind the four toes, the metapodial-phalangeal pad, or m-p pad for short. It's made from pockets of fatty tissue hemmed in by baffles of collagen. Chi carefully dissected these pads whole from the feet of deceased animals (none of which were euthanized for this study), so that they could be put in the strain meter by themselves without any surrounding structures.

Laid out on a graph, Chi's analysis of 47 carnivore species shows that the area of their m-p pads doesn't increase at the same rate as the body sizes. But the stiffness of pads does increase with size, and that's what keeps the larger animal's feet from being unwieldy.

The mass of the animal increases cubically with its greater size, but the feet don't scale up the same way. "A mouse and an elephant are made with the same ingredients," Roth said. "So how do you do that?"

Earlier research had found that the stresses on the long bones of the limbs stay fairly consistent over the range of sizes, in part because of changes in posture that distribute the stresses of walking differently, Roth said. But that clearly wasn't enough by itself.

The researchers also found that larger animals have a pronounced difference in stiffness between the pads on the forelimbs and the pads on the hind limbs. Bigger animals have relatively softer pads on their rear feet, whereas in smaller animals the front and rear are about the same stiffness.

Chi thinks the softer pads on the rear of the bigger animals may help them recover some energy from each step, and provide a bit more boost to their propulsion. (Think of the way a large predator folds up its forelimbs and launches itself with its hind legs.)

"It is as if the foot pads' stiffness is tuned to enhance how the animal moves and how strength is maintained in its bones," Roth said.

The research appears today in the Journal of the Royal Society, Interface. It was supported by the National Science Foundation.

Chi has new work under way that looks at the construction of the human heel in the same ways.

(Photo: HTO, Wikimedia Commons)

Duke University

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