Wednesday, October 28, 2009

PHYSICISTS MEASURE ELUSIVE PERSISTENT CURRENT THAT FLOWS FOREVER

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Physicists at Yale University have made the first definitive measurements of “persistent current,” a small but perpetual electric current that flows naturally through tiny rings of metal wire even without an external power source.

The team used nanoscale cantilevers, an entirely novel approach, to indirectly measure the current through changes in the magnetic force it produces as it flows through the ring. “They’re essentially little floppy diving boards with the rings sitting on top,” said team leader Jack Harris, associate professor of physics and applied physics at Yale. The findings appear in the October 9 issue of Science.

The counterintuitive current is the result of a quantum mechanical effect that influences how electrons travel through metals, and arises from the same kind of motion that allows the electrons inside an atom to orbit the nucleus forever. “These are ordinary, non-superconducting metal rings, which we typically think of as resistors,” Harris said. “Yet these currents will flow forever, even in the absence of an applied voltage.”

Although persistent current was first theorized decades ago, it is so faint and sensitive to its environment that physicists were unable to accurately measure it until now. It is not possible to measure the current with a traditional ammeter because it only flows within the tiny metal rings, which are about the same size as the wires used on computer chips.

Past experiments tried to indirectly measure persistent current via the magnetic field it produces (any current passing through a metal wire produces a magnetic field). They used extremely sensitive magnetometers known as superconducting quantum interference devices, or SQUIDs, but the results were inconsistent and even contradictory.

“SQUIDs had long been established as the tool used to measure extremely weak magnetic fields. It was extremely optimistic for us to think that a mechanical device could be more sensitive than a SQUID,” Harris said.

The team used the cantilevers to detect changes in the magnetic field produced by the current as it changed direction in the aluminum rings. This new experimental setup allowed the team to make measurements a full order of magnitude more precise than any previous attempts. They also measured the persistent current over a wider range of temperature, ring size and magnetic field than ever before.

“These measurements could tell us something about how electrons behave in metals,” Harris said, adding that the findings could lead to a better understanding of how qubits, used in quantum computing, are affected by their environment, as well as which metals could potentially be used as superconductors.

(Photo: Jack Harris/Yale University)

Yale University

MOMENTUM INFLUENCES BABY NAME CHOICES, COGNITIVE SCIENTISTS FIND

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Like momentum traders in the stock market, parents today appear to favor names that recently have risen in popularity relative to names that are on the decline, say cognitive science researchers from Indiana University and New York University.

Researchers have long noted that the overall popularity of a baby name exerts a strong influence on parents' preferences -- more popular names, such as Robert or Susan, are more frequent, and by their sheer ubiquity, drive more parents to adopt a similar choice. However, a new study by Todd Gureckis, assistant professor of psychology at New York University, and Robert Goldstone, director of the Cognitive Science Program at IU, suggests that the change in popularity of a name over time increasingly influences naming decisions in the United States.

"Parents in the United States are increasingly sensitive to the change in frequency of a name in recent time, such that names that are gaining in popularity are seen as more desirable than those that have fallen in popularity in the recent past," the authors noted. "This bias then becomes a self-fulfilling prophecy: names that are falling continue to fall while names on the rise reach new heights of popularity, in turn influencing a new generation of parents."

The research, which was supported by the National Institute of Mental Health and the National Science Foundation, is relevant to understanding how people's everyday decisions are influenced by aggregate cultural processes.

"Our results give support to the idea that individual naming choices are in a large part determined by the social environment that expecting parents experience," the authors wrote in Topics of Cognitive Science. "Like the stock market, cycles of boom and bust appear to arise out of the interactions of a large set of agents who are continually influencing one another."

The researchers note this pattern is a relatively new phenomenon. In the late 19th and early 20th centuries, the popularity of a name from one year to the next was correlated with a decrease in future popularity. The changing pattern, the authors suggest, arises from biases in how people estimate the overall desirability of cultural tokens like names. That is, tokens that are recently outpacing their long-term popularity are seen as better choices than those that appear to be falling out of favor.

The findings were based on a historical record of the frequency that particular names were given to babies during the last 127 years in the United States provided by the U.S. Social Security Administration.

Existing accounts of cultural evolution suggest that it is primarily the frequency of the token (i.e., name) in a parent's social environment that should drive aggregate patterns of name choice. However, by sorting through names and watching the way they rise and fall in popularity over time, the authors noted that many names appear to take surprisingly smooth trajectories through time such that increasing popularity one year is often associated with increasing popularity the next. Moreover, this trend has become more pronounced over the years.

In order to better quantify this effect, the authors analyzed the probability that a name goes up or down from one year to the next, given that it went up or down in the time period before. They found that around the turn of the last century (1880 to 1905) names tended to fluctuate in overall frequency from one year to the next. A name that increased its relative frequency one year was more likely to decrease rather than increase in frequency the following year. Similarly, decreases in frequency were more likely to be followed by increases than further decreases.

More recently (1981 to 2006), names moved in consistent ways such that a change in popularity in one year was predictive of the same direction of change the following year. Thus, names appear to carry with them a "momentum" that tends to push changes in popularity in the same direction year after year.

In the paper, the authors develop and test a number of formal models of cultural evolution in order to quantify the sources of bias that influence people's naming decisions. In particular, the authors incorporated well-known aspects of cognitive processing, including the way that novelty and familiarity bias our preferences. The authors found that a model that assumes that names which are outpacing their long-term popularity are preferentially selected better explains the distribution of names over time than do models which leave out this assumption.

The researchers argue that baby names provide a unique opportunity for studying the intersection of individual and group decision making for the following reasons:

-It's an important decision upon which parents devote significant time and energy;
-there are extensive historical records, making possible the detailed measurement of these choices and the social context in which those decisions were made;
-certain names (e.g., "Joshua", a popular name in 2007) do not appear to carry more intrinsic economic value than other names (e.g., "Damarion," an uncommon boys name the same year); and
-baby names are not subject to the forces of marketing or advertising -- factors that may complicate the analysis of other type of culturally-relevant decisions such as fashion or music preferences.

(Photo: Chris Meyer)

Indiana University

SKILLS TESTS LIKE 'CONNECT THE DOTS' MAY BE EARLY ALZHEIMER'S INDICATOR

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A study of mental decline in the years prior to diagnosis of Alzheimer's disease suggests that changing the focus of testing may allow physicians to detect signs of the disease three years earlier.

Current cognitive testing typically focuses on episodic memory, or the ability to remember things like word lists or information from a reading. But scientists at Washington University School of Medicine in St. Louis found that another class of mental abilities known as visuospatial skills begins to deteriorate up to three years prior to diagnosis. These skills are tested with tasks such as connecting the dots or using a guide to build a structure with blocks.

"We may need to rethink what we look for as the earliest signs of mental change associated with Alzheimer's disease," says senior author James Galvin, M.D., a Washington University neurologist who is also on staff at Barnes-Jewish Hospital. "If we can better recognize the first signs of disease, we can start treating patients earlier and hopefully with new treatments we can slow or perhaps even stop their progress into dementia."

The results are published in the October issue of Archives of Neurology.

Galvin and his coauthors analyzed long-term data from volunteers at the Memory and Aging Project at Washington University's Alzheimer's Disease Research Center (ADRC). For three decades, researchers have been regularly conducting extensive testing of volunteers to uncover the factors associated with the normal, healthy retention of mental function in seniors. The new study analyzes data on 444 volunteers aged 60 to 101 that were gathered between 1979 and 2006.

Scientists categorized cognitive testing results into a global measure of cognitive abilities as well as three specific types of mental skills: episodic memory, visuospatial skills and working memory, which assesses the ability to manipulate facts from memory, such as repeating a list of numbers backwards.

Declines in episodic memory and working memory became discernible a year before volunteers were diagnosed with Alzheimer's disease. Losses in the composite assessment of cognitive abilities were detectable two years prior to diagnosis, and visuospatial skills began to decay three years earlier. According to Galvin, the losses in visuospatial skills were particularly noticeable if testing tasks were timed.

Researchers also analyzed the data using a new model that not only tracks the speed of decline in a mental ability but also the acceleration of the decline. Episodic memory's decline accelerated more slowly than that of both visuospatial skills and working memory, which declined fastest.

The new perspective may allow doctors to detect signs of Alzheimer's earlier, but more information will be needed to make a firm diagnosis. To make that possible, researchers at the ADRC are trying to take what they've learned in the new study and correlate it with biomarkers, which are physical changes associated with preclinical Alzheimer's disease. These include such tests as scanning the brain for amyloid plaques or analyzing the levels of proteins in the cerebrospinal fluid.

Amyloid brain plaques, a primary characteristic of Alzheimer's disease, can begin building in patients 10 years or more before clinical symptoms become apparent, Galvin notes.

"The new findings raise the question of what changes are occurring in the brain during the one- to three-year period prior to diagnosis," Galvin says. "Patients have had plaques in their brain for years, and suddenly their cognitive abilities begin to deteriorate. Is a threshold being crossed where brain cell death begins to occur or really starts to pick up speed?"

Galvin and his coauthors also plan to apply their new approach for assessing mental decline to other dementias including Lewy body dementia and the form of dementia associated with Parkinson's disease.

Washington University in St. Louis

RADIO WAVES 'SEE' THROUGH WALLS

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University of Utah engineers showed that a wireless network of radio transmitters can track people moving behind solid walls. The system could help police, firefighters and others nab intruders, and rescue hostages, fire victims and elderly people who fall in their homes. It also might help retail marketing and border control.

"By showing the locations of people within a building during hostage situations, fires or other emergencies, radio tomography can help law enforcement and emergency responders to know where they should focus their attention," Joey Wilson and Neal Patwari wrote in one of two new studies of the method.

Both researchers are in the university's Department of Electrical and Computer Engineering - Patwari as an assistant professor and Wilson as a doctoral student.

Their method uses radio tomographic imaging (RTI), which can "see," locate and track moving people or objects in an area surrounded by inexpensive radio transceivers that send and receive signals. People don't need to wear radio-transmitting ID tags.

One of the studies - which outlines the method and tests it in an indoor atrium and a grassy area with trees - is awaiting publication soon in IEEE Transactions on Mobile Computing, a journal of the Institute of Electrical and Electronics Engineers.

The study involved placing a wireless network of 28 inexpensive radio transceivers - called nodes - around a square-shaped portion of the atrium and a similar part of the lawn. In the atrium, each side of the square was almost 14 feet long and had eight nodes spaced 2 feet apart. On the lawn, the square was about 21 feet on each side and nodes were 3 feet apart. The transceivers were placed on 4-foot-tall stands made of plastic pipe so they would make measurements at human torso level.

Radio signal strengths between all nodes were measured as a person walked in each area. Processed radio signal strength data were displayed on a computer screen, producing a bird's-eye-view, blob-like image of the person.

A second study detailed a test of an improved method that allows "tracking through walls." That study has been placed on arXiv.org, an online archive for preprints of scientific papers. The study details how variations in radio signal strength within a wireless network of 34 nodes allowed tracking of moving people behind a brick wall.

The method was tested around an addition to Patwari's Salt Lake City home. Variations in radio waves were measured as Wilson walked around inside. The system successfully tracked Wilson's location to within 3 feet.

The wireless system used in the experiments was not a Wi-Fi network like those that link home computers, printers and other devices. Patwari says the system is known as a Zigbee network - the kind of network often used by wireless home thermostats and other home or factory automation.

Wilson demonstrated radio tomographic imaging during a mobile communication conference last year, and won the MobiCom 2008 Student Research Demo Competition. The researchers now have a patent pending on the method.

"I have aspirations to commercialize this," says Wilson, who has founded a spinoff company named Xandem Technology LLC in Salt Lake City.

Radio tomographic imaging (RTI) is different and much less expensive than radar, in which radar or radio signals are bounced off targets and the returning echoes or reflections provide the target's location and speed. RTI instead measures "shadows" in radio waves created when they pass through a moving person or object.

RTI measures radio signal strengths on numerous paths as the radio waves pass through a person or other target. In that sense, it is quite similar to medical CT (computerized tomographic) scanning, which uses X-rays to make pictures of the human body, and seismic imaging, in which waves from earthquakes or explosions are used to look for oil, minerals and rock structures underground. In each method, measurements of the radio waves, X-rays or seismic waves are made along many different paths through the target, and those measurements are used to construct a computer image.

In their indoor, outdoor and through-the-wall experiments, Wilson and Patwari obtained radio signal strength measurements from all the transceivers - first when the rectangle was empty and then when a person walked through it. They developed math formulas and used them in a computer program to convert weaker or "attenuated" signals - which occur when someone creates "shadows" by walking through the radio signals - into a blob-like, bird's-eye-view image of that person walking.

RTI has advantages. "RF [radio frequency] signals can travel through obstructions such as walls, trees and smoke, while optical and infrared imaging systems cannot," the engineers wrote. "RF imaging will also work in the dark, where video cameras will fail."

Even "where video cameras could work, privacy concerns may prevent their deployment," Wilson and Patwari wrote. "An RTI system provides current images of the location of people and their movements, but cannot be used to identify a person."

Would bombardment by radio waves pose a hazard? Wilson says the devices "transmit radio waves at powers 500 times less than a typical cell phone."

"And you don't hold it against your head," Patwari adds.

Patwari says the system still needs improvements, "but the plan is that when there is a hostage situation, for example, or some kind of event that makes it dangerous for police or firefighters to enter a building, then instead of entering the building first, they would throw dozens of these radios around the building and immediately they would be able to see a computer image showing where people are moving inside the building."

"They are reusable and you can pick them up afterwards," he says.

The technique cannot distinguish good guys from bad guys, but at least will tell emergency personnel where people are located, he adds.

Patwari says radio tomography probably can be improved to detect people in a burning building, but also would "see" moving flames. "You may be able to look at the image and say this is a spreading fire and these are people," says Patwari.

Wilson believes radio imaging also could be used in "a smarter alarm system. … What if you put radios in your home [built into walls or plugged into outlets] and used tomography to locate people in your home. Not only would your security system be triggered by an intrusion, but you could track the intruder online or over your phone."

Radio tomography even might be used to study where people spend time in stores.

"Does a certain marketing display get people to stop or does it not?" Wilson asks. "I'm thinking of retail stores or grocery stores. They spend a lot of money to determine, 'Where should we put the cereal, where should we put the milk, where should we put the bread?' If I can offer that information using radio tomographic imaging, it's a big deal."

Radio image tracking might help some elderly people live at home. "The elderly want to stay in their homes but don't want a camera in their face all day," Wilson says. "With radio tomographic imaging, you could track where they are in their home, did they get up at the right time, did they go to the medicine cabinet, have they not moved today?"

Wilson says a computer monitoring the radio images might detect an elderly person falling down the stairs based on the unusually fast movement.

He says radio tracking also might be a relatively inexpensive method of border security, and would work in dark and fog unlike cameras.

Another possible use: automatic control of lighting, heating and air conditioning in buildings, says Wilson. Radio tracking might even control sound systems so that the best sound is aimed where people are located, as well as noise cancellation systems which could be aimed automatically at noise sources, Patwari says.

(Photo: Sarang Joshi and Joey Wilson, University of Utah)

University of Utah

PLANT FOSSILS GIVE FIRST REAL PICTURE OF EARLIEST NEOTROPICAL RAINFORESTS

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A team of researchers including a University of Florida paleontologist has used a rich cache of plant fossils discovered in Colombia to provide the first reliable evidence of how Neotropical rainforests looked 58 million years ago.

Researchers from the Smithsonian Institution and UF, among others, found that many of the dominant plant families existing in today’s Neotropical rainforests — including legumes, palms, avocado and banana — have maintained their ecological dominance despite major changes in South America’s climate and geological structure.

The study, which appears in the online edition of the Proceedings of the National Academy of Sciences, examined more than 2,000 megafossil specimens, some nearly 10 feet long, from the Cerrejón Formation in northern Colombia. The fossils are from the Paleocene epoch, which occurred in the 5- to 7-million-year period following the massive extinction event responsible for the demise of the dinosaurs.

“Neotropical rainforests have an almost nonexistent fossil record,” said study co-author Fabiany Herrera, a graduate student at the Florida Museum of Natural History on the UF campus. “These specimens allow us to actually test hypotheses about their origins for the first time ever.”

Herrera said the new specimens, discovered in 2003, also provide information for future studies that promise to provide an even stronger understanding of the plants that formed the earliest Neotropical communities.

Many previous assumptions and hypotheses on the earliest rainforests are based on studies of pollen fossils, which did not provide information about climate, forest structure, leaf morphology or insect herbivory.

The new study provides evidence Neotropical rainforests were warmer and wetter in the late Paleocene than today but were composed of the same plant families that now thrive in rainforests. “We have the fossils to prove this,” Herrera said. “It is also intriguing that while the Cerrejón rainforest shows many of the characteristics of modern equivalents, plant diversity is lower.”

The site, one of the world’s largest open-pit coal mines, also yielded the fossil for the giant snake known as Titanoboa, described by UF scientists earlier this year.

“These new plant fossils show us that the forest during the time of Titanoboa, 58 million years ago, was similar in many ways to that of today,” said Florida Museum vertebrate paleontologist Jonathan Bloch, who described Titanoboa but was not part of the rainforest study. “Like Titanoboa, which is clearly related to living boas and anacondas, the ancient forest of northern Colombia had similar families of plants as we see today in that ecosystem. The foundations of the Neotropical rainforests were there 58 million years ago.”

Megafossils found at the Cerrejón site made it possible to use leaf structure to identify specimens down to the genus level. This resolution allowed the identification of plant genera that still exist in Neotropical rainforests. With pollen fossils, specimens can be categorized only to the family level.

Researchers were surprised by the relative lack of diversity found in the Paleocene rainforest, Herrera said. Statistical analyses showed that the plant communities found in the Cerrejón Formation were 60 percent to 80 percent less diverse than those of modern Neotropical rainforests. Evidence of herbivory also showed a low diversity level among insects.

The study’s authors say the relative lack of diversity indicates either the beginning of rainforest species diversification or the recovery of existing species from the Cretaceous extinction event.

The researchers estimate the Paleocene rainforest received about 126 inches of rainfall annually and had an average annual temperature greater than 86 degrees. The Titanoboa study, which used different methods, estimated an average temperature between 89 and 91 degrees. Today the region’s temperatures average about 81 degrees.

Herrera is now comparing fossils from the Cerrejón site to specimens from other Paleocene sites in Colombia to see how far the early rainforest extended geographically. He is also examining fossils from a Cretaceous site to determine differences in composition before and after the extinction event.

University of Florida

IBEX EXPLORES GALACTIC FRONTIER, RELEASES FIRST-EVER ALL-SKY MAP

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NASA's Interstellar Boundary Explorer, or IBEX, spacecraft has made it possible for scientists to construct the first comprehensive sky map of our solar system and its location in the Milky Way galaxy. The new view will change the way researchers view and study the interaction between our galaxy and sun.

The sky map was produced with data that two detectors on the spacecraft collected during six months of observations. The detectors measured and counted particles scientists refer to as energetic neutral atoms.

The energetic neutral atoms are created in an area of our solar system known as the interstellar boundary region. This region is where charged particles from the sun, called the solar wind, flow outward far beyond the orbits of the planets and collide with material between stars. The energetic neutral atoms travel inward toward the sun from interstellar space at velocities ranging from 100,000 mph to more than 2.4 million mph. This interstellar boundary emits no light that can be collected by conventional telescopes.

The new map reveals the region that separates the nearest reaches of our galaxy, called the local interstellar medium, from our heliosphere -- a protective bubble that shields and protects our solar system from most of the dangerous cosmic radiation traveling through space.

"For the first time, we're sticking our heads out of the sun's atmosphere and beginning to really understand our place in the galaxy," said David J. McComas, IBEX principal investigator and assistant vice president of the Space Science and Engineering Division at Southwest Research Institute in San Antonio. "The IBEX results are truly remarkable, with a narrow ribbon of bright details or emissions not resembling any of the current theoretical models of this region."

NASA released the sky map image Oct. 15 in conjunction with publication of the findings in the journal Science. The IBEX data were complemented and extended by information collected using an imaging instrument sensor on NASA's Cassini spacecraft. Cassini has been observing Saturn, its moons and rings since the spacecraft entered the planet's orbit in 2004.

The IBEX sky maps also put observations from NASA's Voyager spacecraft into context. The twin Voyager spacecraft, launched in 1977, traveled to the outer solar system to explore Jupiter, Saturn, Uranus and Neptune. In 2007, Voyager 2 followed Voyager 1 into the interstellar boundary. Both spacecraft are now in the midst of this region where the energetic neutral atoms originate. However, the IBEX results show a ribbon of bright emissions undetected by the two Voyagers.

"The Voyagers are providing ground truth, but they're missing the most exciting region," said Eric Christian, the IBEX deputy mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It's like having two weather stations that miss the big storm that runs between them."

(Photo: NASA/Goddard Space Flight Center)

NASA

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