Research Notes - Fall 2006

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

This issue features news on:

  • Light vibes: Physicists' techniques could improve medical imaging.
  • Breath of the forest: Tropical forests leak nitrogen back into atmosphere.
  • Glass matters: Chemists look through glass to find secrets that are less clear.
  • Teaching atoms: Carter shapes future breakthroughs one student at a time.
  • The shape of music: Composer reveals musical chords' hidden geometry.
  • Air and water: Global atmospheric carbon level may depend primarily on Southern Ocean.
  • Can't buy me happiness: The link between income and happiness is mainly an illusion.
  • Next frontier for stem cells: Princeton scientists explore the next frontier of stem cell research.
  • Computer chips: Scientists build 'magnetic semiconductors' one atom at a time.
  • Think fast: Snap judgments decide a face's character, study finds.
  • Say what?: Stock performance tied to ease of pronouncing a company's name.
  • The 'burbs: Suburbia a rich source of scholarship for Princeton historian.
  • Migration song: Tiny transmitters allow researchers to follow flies.
  • In the balance: Ward unravels bacteria's role in global nitrogen cycle.
  • Self-abuse: Students who have suffered abuse are prone to injure themselves.

Physicists' techniques could improve medical imaging

Shining laser light through a transparent substance could reveal new details about the orientation of atoms in the material, reports a Princeton research team. The finding could potentially improve the effectiveness of medical and scientific imaging technology such as magnetic resonance imagers (MRIs).

Physicist Michael Romalis and his research group have invented a new form of nuclear magnetic resonance (NMR) that involves shining a beam of laser light through a sample of liquid and measuring how much the sample rotates the polarization of the beam. The technique represents an improvement over standard NMR in that it could provide higher resolution images than can be obtained today.

Because atomic nuclei have magnetic properties, sufficiently strong magnetic fields can cause nuclei to align themselves parallel to the field. Perturbing this alignment with radio waves causes the nuclei to resonate in ways that can then provide scientists with information about the substance's physical, chemical and structural properties. Standard NMR takes advantage of these effects, and MRI machines use them to create images of living tissue without dangerous radiation or intrusive surgery. The technique provides good overall information about the material, but obtaining the details of regions within the sample is more difficult.

To overcome this limitation, the group has beamed laser light through the material, and then measured the rotation caused by the NMR's magnetic field on the polarized light beam. The new technique can return information about small volumes of fluid, limited only by the focal power of the laser.

The team observed the effect in water and liquid xenon, two transparent fluids that are commonly used in NMR. Romalis, an associate professor of physics, said that the technique was general enough to be used in any transparent liquid and some solids, and could therefore reveal new information about how well-aligned the nuclei in the illuminated area are with one another. 

"It is possible that this technique could enable us to explore turbulence and fluid flow in greater detail," Romalis said. "We also might use it to visualize the internal components of living cells, though we would need to improve the sensitivity of the equipment first."

The team published their findings in the Aug. 31 issue of Nature. Romalis can be reached at or (609) 258-5586.

Tropical forests leak nitrogen back into atmosphere

In findings that could influence our understanding of climate change, a Princeton University research team has learned that tropical forests return to the atmosphere up to half the nitrogen they receive each year, thanks to a particular type of bacteria that live in those forests.
The bacteria, referred to as "denitrifiers," exist in forest soil, where they live by converting the nitrates fed upon by tree roots back into nitrogen gas, which is lost to the atmosphere. The researchers recently discovered this behavior by examining nitrogen isotopes in the soil. Lars Hedin, a researcher on the team, said the findings are important for our understanding of how tropical forests fit into the Earth's climate system.
"Tropical forests play a major role in regulating the planet's climate, and these findings indicate that we are still working on our basic understanding of the nitrogen cycle," said Hedin, a professor of ecology and evolutionary biology at Princeton. "That a group of bacteria can have such a dramatic impact on forest nutrition debunks our previous theories about how nitrogen behaves in forests, and shows us that these microorganisms affect soil nutrients and forest growth."

Lead author Benjamin Houlton said that while the findings do not indicate any harmful or helpful effects on the planet, they will affect computer models of the Earth's climate.

"Previously, scientists thought these forests were essentially 'non-leaky,' and conserved nitrogen and other nutrients," said Houlton, a student from Hedin's lab now doing postdoctoral work at Stanford. "Tropical forest fluxes have been one of the most uncertain aspects of the global nitrogen cycle, and this discovery will affect how we factor them into our understanding of climate change."
The research team, which also includes Daniel Sigman, a Princeton professor of geosciences, published its findings on May 22 in the Web version of the journal Proceedings of the National Academy of Sciences. Hedin is available for comment at (609) 558-9096, and Houlton can be reached at or (650) 862-4144.

Chemists look through glass to find secrets that are less clear

A new understanding of how glass is formed may assist with our understanding of everything from the design of golf club heads to the structure of the early universe.

Princeton chemists have found that the formation of glass -- a familiar substance that nonetheless retains some elusive scientific mysteries -- always occurs differently depending on how quickly a liquid substance is cooled into its solid form. Though the findings will likely dash the hopes of condensed matter physicists who have long sought in vain for what is known as an "ideal" glass transition, they may also one day contribute to industrialists' efforts to create better plastics and other useful polymers.

"Glasses can be formed from any substance, and the way their molecules interact places them somewhere at the border between solids and liquids, giving them some properties that manufacturers can exploit," said Sal Torquato, a professor of chemistry who is also affiliated with the Princeton Center for Theoretical Physics. "Golf club heads made of metallic glasses, for example, can make golf balls fly farther. While our research could be utilized by industry, it can actually help us understand any 'glassy' multi-particle system, such as the early universe -- which cosmologists have described as a glass."

Torquato emphasized that it would probably be years before such practical applications become a reality, and that the findings were most significant for advancing our fundamental understanding of how the state of matter known as glasses behaves.

The research team, which also includes Princeton's Aleksandar Donev, a graduate student in computational and applied mathematics, and Frank Stillinger, a senior theoretical chemist, published its findings in the June 6 issue of the journal, Physical Review Letters. Torquato is available for comment at (609) 258-3341 or


Carter shapes future breakthroughs one student at a time

Emily Carter opens students' eyes to the microscopic world of nanotechnology, which could influence the future of engineering in a significant way. Full text.

Composer reveals musical chords' hidden geometry

Composers often speak of fitting chords and melodies together, as though sounds were physical objects with geometric shape -- and now a Princeton University musician has shown that advanced geometry actually does offer a tool for understanding musical structure. Full text.

Global atmospheric carbon level may depend primarily on Southern Ocean

Circulation in the waters near the Antarctic coast may be one of the planet's critical means of regulating levels of carbon dioxide, a greenhouse gas, in the Earth's atmosphere. Full text.

Link between income and happiness is mainly an illusion

While most people believe that having more income would make them happier, Princeton researchers have found that the link is greatly exaggerated and mostly an illusion. Full text.

Princeton scientists explore the next frontier of stem cell research

Several scientists across campus are making strides in the highly scrutinized field of stem cell research, and they examine the need to counter rampant public misconceptions on the subject. Full text.

Scientists build 'magnetic semiconductors' one atom at a time

In a move that could hasten the development of computer chips that both calculate and store data, a team of Princeton scientists has turned semiconductors into magnets by the precise placement of metal atoms within a material from which chips are made. Full text.

Snap judgments decide a face's character, psychologist finds

When we see a new face, our brains decide whether a person is attractive and trustworthy within a tenth of a second. Full text.

Stock performance tied to ease of pronouncing company's name

The ease of pronouncing the name of a company and its stock ticker symbol influences how well that stock performs in the days immediately after its initial public offering. Full text.

Suburbia is a rich source of scholarship for Princeton historian

Kevin Kruse argues that segregationists moved to the suburbs and adopted a new kind of separatist philosophy that led to the ascendancy of the Republican Party and a transformation of American politics. Full text.

Tiny transmitters allow researchers to follow flies

The latest in high technology and some old-fashioned improvisation have helped Martin Wikelski show that dragonflies -- some of the most ancient animal species on the planet -- may operate on the same travel instincts as birds do. Full text.

Ward unravels bacteria's role in global nitrogen cycle

Understanding bacteria's role in the nitrogen cycle is critical to unraveling the impact of human activity on the planet's delicate nitrogen balance, according to biogeochemist Bess Ward. Full text.

Students who have suffered abuse are prone to injure themselves

Daniel Silverman discusses his team's findings that self-abuse is prevalent among college students, particularly those who have been emotionally abused. Full text.