Elusive particles found

IN THE PAST YEAR, PRINCETON PHYSICISTS have detected two particles that were predicted decades ago to exist but had not been found until now. Both particles were detected using a scanning-tunneling microscope to image the particles inside a crystal. The particles may someday enable powerful computers based on quantum mechanics.

A team led by Ali Yazdani, the Class of 1909 Professor of Physics, detected the “Majorana fermion,” which behaves simultaneously like matter and antimatter and was first proposed in 1937 by Italian physicist Ettore Majorana. The team, which received funding from the National Science Foundation and the Office of Naval Research, included B. Andrei Bernevig, an associate professor of physics, and other colleagues at Princeton and at the University of Texas-Austin. They published their results in the Oct. 2, 2014, issue of the journal Science.

A few months later, an international team led by M. Zahid Hasan, professor of physics, detected another elusive particle, the “Weyl fermion,” first theorized by the mathematician and physicist Hermann Weyl in 1929. The particle is massless and can also behave like matter and antimatter. The research team, which received support from the Gordon and Betty Moore Foundation and the U.S. Department of Energy, published their work in Science on July 16, 2015.

–By Steven Schultz and Morgan Kelly

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COMPUTER SCIENCE: Internet traffic moves smoothly with Pyretic

60_Hudson_StreetAT 60 HUDSON ST. IN LOWER MANHATTAN, a fortress-like building houses one of the Internet’s busiest exchange points. Packets of data zip into the building, are routed to their next destination, and zip out again, all in milliseconds. Until recently, however, the software for managing these networks required a great deal of specialized knowledge, even for network experts.

Now, computer scientists at Princeton have developed a programming language called Pyretic that makes controlling the flow of data packets easy and intuitive — and more reliable. The new language is part of a trend known as Software-Defined Networking, which gives a network operator direct control over the underlying switches that regulate network traffic.

“In order to make these networks work, we have to be able to program them effectively, to route traffic to the right places, and to balance the traffic load effectively across the network instead of creating traffic jams,” said David Walker, professor of computer science, who leads the project with Jennifer Rexford, the Gordon Y.S. Wu Professor of Engineering and professor of computer science. “Pyretic allows us to make sure packets of information get to where they are going as quickly, reliably and securely as possible.”

Pyretic is open-source software that uses the Python programming language and lowers the barrier to managing network switches, routers, firewalls and other components of a network. Since its initial release in April 2013, the community of developers who are using the language to govern networks has grown quickly.

Additional contributors include Associate Research Scholar Joshua Reich and graduate student Christopher Monsanto of Princeton’s Department of Computer Science as well as Nate Foster, an assistant professor of computer science at Cornell University. The project received support from the U.S. Office of Naval Research, the National Science Foundation and Google.

-By Catherine Zandonella

Computer visions: A selection of research projects in Computer Science

Princeton’s Department of Computer Science has strong groups in theory, networks/systems, graphics/vision, programming languages, security/policy, machine learning, and computational biology. Find out what the researchers have been up to lately in these stories:

Computer VisionsArmchair victory: Computers that recognize everyday objects

JIANXIONG XIAO TYPES “CHAIR” INTO GOOGLE’S search engine and watches as hundreds of images populate his screen. He isn’t shopping — he is using the images to…

 

 

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FROM TRANSLATING FOREIGN LANGUAGES to finding information in minutes, computers have extended our productivity and capability. But can they make us better artists?

 

 

ArtFierce, fiercer, fiercest: Software enables rapid creations

A NEW SOFTWARE PROGRAM MAKES IT EASY for novices to create computer-based 3-D models using simple instructions such as “make it look scarier.” The software could be useful for…

 

 

60_Hudson_StreetInternet traffic moves smoothly with Pyretic

AT 60 HUDSON ST. IN LOWER MANHATTAN, a fortress-like building houses one of the Internet’s busiest exchange points. Packets of data zip…

 

 

Heartbleed bugSecurity check: A strategy for verifying software that could prevent bugs

IN APRIL 2014, INTERNET USERS WERE SHOCKED to learn of the Heartbleed bug, a vulnerability in the open-source software used to encrypt Internet content and passwords…

Collective behavior could help animals survive a changing environment

Princeton researchers found that collective intelligence is vital to certain animals’ ability to evaluate and respond to their environment. Conducted on golden shiners, the research demonstrated that social animals such as schooling fish rely heavily on grouping to effectively navigate their environment. (Image by Sean Fogarty)

Princeton researchers found that collective intelligence is vital to certain animals’ ability to evaluate and respond to their environment. Conducted on golden shiners, the research demonstrated that social animals such as schooling fish rely heavily on grouping to effectively navigate their environment. (Image by Sean Fogarty)

For social animals such as schooling fish, the loss of their numbers to human activity could eventually threaten entire populations, according to a finding that such animals rely heavily on grouping to effectively navigate their environment.

Princeton researchers have found that collective intelligence is vital to certain animals’ ability to evaluate and respond to their environment. Conducted on fish, the research demonstrated that small groups and individuals become disoriented in complex, changing environments. However, as group size is increased, the fish suddenly became highly responsive to their surroundings.

These results should prompt a close examination of how endangered group or herd animals are preserved and managed, said Iain Couzin, a professor of ecology and evolutionary biology. If wild animals depend on collective intelligence for migration, breeding and locating essential resources, they could be imperiled by any activity that diminishes or divides the group, such as overhunting and habitat loss, he explained.

“Processes that increase group fragmentation or reduce population density may initially appear to have little influence, yet a further reduction in group size may suddenly and dramatically impact the capacity of a species to respond effectively to their environment,” Couzin said. “If the mechanism we observed is found to be widespread, then we need to be aware of tipping points that could result in the sudden collapse of migratory species.”

The work is among the first to experimentally explain the extent to which collective intelligence improves awareness of complex environments, the researchers write. As it’s understood, a group of individuals gain an advantage by pooling imperfect estimates with those around them, which more or less “averages” single experiences into surprisingly accurate common knowledge.

With their work, Couzin and his co-authors uncovered an additional layer to understanding collective intelligence. The conventional view assumes that individual group members have some level of knowledge albeit incomplete. Yet the Princeton researchers found that in some cases individuals have no ability to estimate how a problem needs to be solved, while the group as a whole can find a solution through their social interactions. Moreover, they found that the more numerous the neighbors, the richer the individual — and thus group — knowledge is.

These findings correlate with recent research showing that collective intelligence — even in humans — can rely less on the intelligence of each group member than on the effectiveness of their communal interaction, Couzin said. In humans, research suggests that such cooperation would take the form of open and equal communication among individuals regardless of their respective smarts, he said.

The researchers placed fish known as golden shiners in experimental tanks in groups as low as one and as high as 256. The tanks featured a moving light field that was bright on the outer edges and tapered into a dark center. To reflect the changing nature of natural environments, they also incorporated small patches of darkness that moved around randomly. Prolific schoolers and enthusiasts of darkness, the golden shiners would pursue the shaded areas as the researchers recorded their movement using computer vision software. Although the fish sought the shade regardless of group size, their capability to do so increased dramatically once groups spanned a large enough area.

The researchers then tracked the motion of individual fish to gauge the role of social influence on their movement. They found that individuals adjusted their speed according to local light level by moving faster in more brightly lit areas, but without social influence the fish did not necessarily turn toward the darker regions. Groups, however, readily swam to dark areas and were able to track those preferred regions as they moved.

This collective sensing emerged due to the coherent nature of social interactions, the authors report. As one side of the group slowed and turned toward the shaded area, the other members did as well. Also, slowing down increased density and resulted in darker regions becoming more attractive to these social animals.

Couzin worked with lead authors Andrew Berdahl, a Princeton graduate student, and postdoctoral fellow Colin Torney, both in Couzin’s lab, as well as with former lab members Christos Ioannou and Jolyon Faria, who are now at the University of Bristol and the University of Oxford, respectively. The work was published in the Jan. 31, 2013, issue of Science, and was supported in part by grants from the National Science Foundation, the U.S. Office of Naval Research, the U.S. Army Research Office and the Natural Sciences and Engineering Research Council of Canada.

–By Morgan Kelly