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Saturday, Sept. 20, 2014

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Research Notes - Winter 2007

Welcome to Research Notes, an online publication highlighting recent Princeton University research in the physical and social sciences, engineering, and the humanities. Research summarized here for which full online articles are available is listed in the Web stories section, along with links to the full text.

News on research in the fields of engineering and applied science is also distributed through the University's engineering school Web site, and most research conducted by faculty in the Woodrow Wilson School of Public and International Affairs is highlighted on the Wilson School Web site. For more information about Research Notes, contact Chad Boutin at (609) 268-5729 or cboutin@princeton.edu.

This issue features:


Climate stability

A tight link between two naturally occurring processes in the ocean prevents them from influencing the planet’s climate as much as previously thought, according to Princeton geoscientists.

These two biochemical processes are nitrogen fixation and denitrification, which respectively increase and decrease the level of biologically available nitrogen in the ocean. In a healthy ocean, the two processes keep each other in balance, and this stability has significance as a regulator of the amount of carbon dioxide that is stored in the ocean, away from the atmosphere.

The conventional wisdom among scientists is that imbalances may occur between nitrogen fixation and denitrification because of the ocean's routinely fluctuating levels of oxygen and iron, which are used in the chemical processes that determine nitrogen levels. Because carbon dioxide is a greenhouse gas, a long-term nitrogen discrepancy in the oceans that would result from an imbalance between the two processes could have an impact on the world’s climate, contributing to an ice age at one extreme or global warming at the other. Recent studies by other scientists have suggested that nitrogen fixation is currently outpaced by denitrification, and that significant climate change could occur in the 1,000 years it would take for balance to be re-established.

However, using computer models, the Princeton team has obtained a better estimate than was previously available for nitrogen fixation. In addition, the team has found that fixation and denitrification are so closely associated that they may have the ability to rebound from a disturbance within 40 to 50 years, which would be fast enough to keep any noticeable climate changes from happening.

“In short, an imbalance would indeed cause a ‘bump in the road,’ but a bump too small to cause concern in and of itself,” said team member Jorge Sarmiento, a professor of geosciences and director of Princeton's Program in Atmospheric and Oceanic Sciences. "The findings turn the conventional wisdom about nitrogen fixation on its head."

Sarmiento cautioned that more tests will be necessary to confirm these initially encouraging results. He next plans to analyze the ocean’s denitrification rates.

The lead author of the study, published in the Jan. 11 issue of Nature, is Curtis Deutsch, a former graduate student in Sarmiento’s group currently conducting postdoctoral research at the University of Washington. Sarmiento is available for comment at jls@princeton.edu or (609) 258-6585.

-by Carmen Drahl


Bat bearings

Bats have another extraordinary way of navigating, in addition to their well-known (and misnamed) "radar." Princeton University researchers have found that the animals also navigate over longer distances using an internal compass that senses the Earth's magnetic field.

Both to locate prey and to avoid nearby obstacles in the dark, bats bounce sound waves from objects and perceive the echoes in a manner roughly comparable to sonar aboard a submarine. However, this form of navigation, called echolocation, is less helpful over long distances, and scientists have wondered how the animals keep their bearings so they can return to their homes after flying all night.

Bats have long been suspected of keeping their general bearings by sensing the planet's magnetic field, which has a general north-south orientation. However, testing this theory has presented a problem because of the difficulty of tracking the flying mammals during their nightly search for food.

To overcome this difficulty, the research team attached tiny lightweight radio transmitters to big brown bats and prepared to follow them with a small aircraft at nightfall. Before releasing them, the team disoriented the bats by exposing them to artificial magnetic fields that pointed away from the Earth's field for a 90-minute period at dusk, in order to determine whether bats were using the sunset or stars as additional cues to calibrate the magnetic compass. The team divided the bats into two groups, exposing one to a field whose "north pole" faced eastward, and the other westward.

The bats were transported 20 kilometers north of home and released. After following the bats individually for 5 kilometers, the team found that each group had flown substantially in the direction its respective magnetic field had pointed. According to lead author Richard Holland, the finding suggests that big brown bats navigate using a magnetic compass that is calibrated around sunset.

"Some of the bats were able to reorient themselves as the night went on, which shows that they eventually may recognize that their compass is faulty and switch to some other, as yet unknown mechanism," said Holland, a Marie Curie Research Fellow at Princeton, who is visiting Princeton's Department of Ecology and Evolutionary Biology from the University of Leeds in England. “This research demonstrates that it is possible to study the orientation behavior of small, wide ranging, wild animals in the field. Given that it is possible to receive the signals of the transmitters used in our experiments from a low-orbit satellite, it will hopefully soon be possible to track small animals such as bats, birds and insects globally with significant consequences for disease, agriculture and conservation."

The team reported its findings in the Dec. 7 issue of Nature. Holland is available for comment at rahollan@princeton.edu or (609) 258-9722.

-by Chad Boutin


Funhouse telescope?

In an effort to reveal distant Earth-like planets far more clearly, a Princeton University group is using deformable mirrors to eliminate the visual noise that often masks planets in telescope images of faraway star systems.

Through the most powerful of telescopes, any terrestrial planet located even a few dozen light-years away would look like no more than a tiny dot, just another flicker in the random speckles found in all telescope images. These extraneous spots of light, which are generated by minute imperfections in the mirrors that direct and focus light, are particularly troublesome to planet finders because they may hide the exceptionally faint light of Earth-like planets.

But the Princeton Terrestrial Planet Finder Group, which is part of NASA’s Terrestrial Planet Finder (TPF) mission to find habitable planets orbiting the 200 stars closest to the Earth, may have found a way to eliminate some of these visual distractions.

The University’s two new 11-mm-by-11-mm deformable mirrors each feature 1,024 actuators, or movable parts, that can reshape the surfaces of the mirrors with great precision. In the lab, the team is designing a computer interface that can detect speckle-generating errors in telescopes and adjust the deformable mirrors to compensate for them.

“Telescope optics aren’t perfect,” said Jeremy Kasdin, associate professor of mechanical and aerospace engineering and the director of the Princeton planet finding lab. “We are correcting for errors in the mirrors themselves.”

Though funding for NASA’s TPF mission is uncertain, the Princeton researchers hope their system will one day control deformable mirrors in a space-based telescope launched to search for other planets similar to Earth. Regardless, their work has applications in existing ground and space-based telescopes, and long-distance laser-based communications.

The researchers also are continuing to work on a telescope design that could block starlight while allowing light reflected off nearby planets to shine through. The design is based on an idea from team member David Spergel, chair of the astrophysical sciences department.

The Princeton TPF group also includes mechanical and aerospace engineering professor Michael Littman, operations research and financial engineering chair Robert Vanderbei, astrophysical sciences professor Ed Turner, scientific instrumentation engineer Michael Carr and postdoctoral research associate Ruslan Belikov. Kasdin is available for comment at jkasdin@princeton.edu or (609) 258-5673.

-by Hilary Parker



WEB STORIES

Beyond encryption, new stealth technique hides messages

Princeton engineers have invented a method of stealth communication that disguises not only the information contained in a message, but also the existence of the message itself. Full text.

Laser experiments reveal strange properties of superfluids

Princeton engineers are using lasers to shed light on the behavior of superfluids -- strange, frictionless liquids that are hard to create and study. Their technique allows them to simulate experiments that are otherwise difficult or impossible to conduct. Full text.

Life of Emma Lazarus provides inspiration for Princeton’s Schor

Well known as the author of the sonnet at the Statue of Liberty's base, Lazarus reveals in her writings a complex woman who defied the female roles of her time in her career as a poet, critic and public figure. Full text.

Living coral reefs provide better protection from tsunami waves

Healthy coral reefs provide their adjacent coasts with substantially more protection from destructive tsunami waves than do unhealthy or dead reefs, a Princeton study suggests. Full text.

McCarty explores economic roots of today’s political strife

Why America is so politically polarized lies in the widening gulf between its richest and poorest citizens, according to a book by a Princeton political expert that has been cited as a breakthrough in the study of the country's bitterly divided political environment. Full text.

Researchers reveal vulnerabilities in e-voting machines

A group of Princeton computer scientists says it has created demonstration vote-stealing software that can be installed within a minute on a common electronic voting machine. The software can fraudulently change vote counts without being detected. Full text.

Researchers seek to incorporate street psychology into economics

Some economic policies, argues a Princeton psychologist, fail to consider important psychological factors that come into play when people handle their finances. Full text.

Scientists find potential 'off-switch' for HIV

While there is no cure for lingering infections such as HIV and herpes, it may be possible to deactivate such viruses indefinitely with the flick of a genetic switch. Full text.

Sloan survey team on a quest for the universe’s ‘rare birds’

Expanding their original research goal, Sloan astrophysicists now have the freedom to explore the Milky Way’s newly discovered entourage of satellite galaxies, as well as search for two rare types of stars. Full text.

Stock options may cost shareholders much less than previously thought

A Princeton researcher has demonstrated that, in many scenarios, stock options are worth far less than they would be valued if their worth were calculated using conventional methods. Full text.

Tangled fibers prove inspiring for Princeton chemists

An apparent setback in the effort to custom design proteins could provide answers to larger questions regarding how proteins fold, and even begin to shed light on how to treat illnesses such as Alzheimer’s disease. Full text.

Two miles underground, strange bacteria are found thriving

A Princeton-led research group has discovered an isolated community of bacteria nearly two miles underground that derives all of its energy from the decay of radioactive rocks rather than from sunlight. Full text.

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