Pendulums and floating film: Two seemingly unrelated phenomena share surprising link

ScienceDaily (Oct. 11, 2011) — A coupled line of swinging pendulums apparently has nothing in common with an elastic film that buckles and folds under compression while floating on a liquid, but scientists at the University of Chicago and Tel Aviv University have discovered a deep connection between the two phenomena.

Energy carried in ordinary waves, like those seen on the ocean near a beach, quickly disperses. But the energy in the coupled pendulums and in compressed elastic film concentrates into different kinds of waves, ones with discrete packets of energy called "solitons."

Solitons express themselves in other realms as well. In telecommunications, for example, pulsing light travels as solitons through optical fibers. "What is special about solitons, and this very special way of localizing energy, is that it does not disperse," said Haim Diamant, associate professor of chemistry at Tel Aviv University. "It remains a very well-defined, focused packet."

The connection, which Diamant and UChicago's Thomas Witten report Oct. 14 in the journal Physical Review Letters, is subtle and more easily appreciated in visual form (see graphic). Witten graphed the swing angle of the pendulums as time progresses. Then he made a curve whose angle with the horizontal varies to match the swing angles along the diagonal edge of the graph. The resulting curve takes the same shape as the profile of a folded elastic film floating on a liquid, like the film shown at the bottom of the picture.

Witten and Diamant began collaborating while the latter worked at UChicago's James Franck Institute as a postdoctoral scientist from 1999 to 2002. They have been working together on puzzles emerging from the laboratory of another collaborator, Ka Yee Lee, UChicago professor in chemistry, ever since. Lee's research group studies the complex mixture of lipids and proteins that lines the sacs of the lung. These molecular linings fold and unfold as we inhale and exhale; the folding appears important for normal breathing.

Slowly growing energy

The energy applied to the film's deformation starts out weak, then grows stronger. Once the wrinkling energy in the film grows stronger, it concentrates itself into a fold shaped like the folding curve in the image.

Though the fold appears in a specific place on the film, "the motion resulting from folding extends over a big region. Usually big things are slow," said Witten, the Homer J. Livingston Professor in Physics. "But this is a big thing that is not slow. It's a rapid jerk, and we want to see what enables such rapid, large-scale motion."

Lee and her associates aim to understand breathing mechanics using synthetic films only one layer of molecules thick to simulate the surfactant that lines the microscopic air sacs found in the lungs. Diamant and Witten sought to solve the equation that exactly describes the fold shape of such a film. They knew it would be a difficult task, given that it was a nonlinear equation, one in which simple changes produce complicated effects.

A typical nonlinear problem might absorb decades of work without yielding a solution; this one seemed different. "There were strange hints that told us this problem might be solved exactly," Diamant said. "It's very rare that a nonlinear problem can be solved exactly."

Miracle solution

These hints had appeared in numerical simulations of the folding process generated by Enrique Cerda, a collaborator at the University of Santiago in Chile. "It was a miracle that we found an exact solution, but we had a strong feeling that it existed," Diamant said.

Once Diamant and Witten solved the problem, they realized that the solution resembled the sine-Gordon equation, well-known among mathematicians and physicists, which describes how a coupled line of swinging pendulums concentrate their energy.

Their resulting paper lays out the first example the authors know of in which soliton motion of a dynamical system can help scientists understand material deformation. The materials in this instance involve a thin, rigid layer floating on a fluid surface, a structure commonly found in biological tissues and synthetic coatings.

The finding has still-undetermined technological or biomedical applications, but it offers a way to control the film's deformation, including making the fold stick down into or up out of the water, forming a groove.

"This groove is controllable," Witten said. "You can shape the groove; you can make it come; you can make it go away." One also could control the location of the groove on the film, making it possible to manipulate the film on the scale of a few microns -- a fraction the width of a human hair.

"If there was some other material in the water that was attracted to the surface, we could make it nestle into this shape and we could capture it," Witten explained. "We think that this shape could have some potential that people don't realize."

As a next step, Diamant and Witten wonder if the dynamics of swinging pendulums can tell them anything about the dynamics of a folding elastic film. "All we have described at the moment is this static shape of the fold, but folding too is a dynamic phenomenon," Witten said.

Squeeze the film, and it will begin to fold after a period of time. Witten and Diamant would like to further describe how that process works based on what the swinging pendulums do.

"It seems only natural, but things like that are dangerous and they don't necessarily work," Witten noted. "But we do know that there is a lot known about the solitons that we can potentially harness to understand the folds."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Chicago. The original article was written by Steve Koppes.

Journal Reference:

Haim Diamant, Thomas Witten. Compression Induced Folding of a Sheet: An Integrable System. Physical Review Letters, 2011; 107 (16) DOI: 10.1103/PhysRevLett.107.164302

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Pendulums and floating film: Two seemingly unrelated phenomena share surprising link

ScienceDaily (Oct. 11, 2011) — A coupled line of swinging pendulums apparently has nothing in common with an elastic film that buckles and folds under compression while floating on a liquid, but scientists at the University of Chicago and Tel Aviv University have discovered a deep connection between the two phenomena.

Energy carried in ordinary waves, like those seen on the ocean near a beach, quickly disperses. But the energy in the coupled pendulums and in compressed elastic film concentrates into different kinds of waves, ones with discrete packets of energy called "solitons."

Solitons express themselves in other realms as well. In telecommunications, for example, pulsing light travels as solitons through optical fibers. "What is special about solitons, and this very special way of localizing energy, is that it does not disperse," said Haim Diamant, associate professor of chemistry at Tel Aviv University. "It remains a very well-defined, focused packet."

The connection, which Diamant and UChicago's Thomas Witten report Oct. 14 in the journal Physical Review Letters, is subtle and more easily appreciated in visual form (see graphic). Witten graphed the swing angle of the pendulums as time progresses. Then he made a curve whose angle with the horizontal varies to match the swing angles along the diagonal edge of the graph. The resulting curve takes the same shape as the profile of a folded elastic film floating on a liquid, like the film shown at the bottom of the picture.

Witten and Diamant began collaborating while the latter worked at UChicago's James Franck Institute as a postdoctoral scientist from 1999 to 2002. They have been working together on puzzles emerging from the laboratory of another collaborator, Ka Yee Lee, UChicago professor in chemistry, ever since. Lee's research group studies the complex mixture of lipids and proteins that lines the sacs of the lung. These molecular linings fold and unfold as we inhale and exhale; the folding appears important for normal breathing.

Slowly growing energy

The energy applied to the film's deformation starts out weak, then grows stronger. Once the wrinkling energy in the film grows stronger, it concentrates itself into a fold shaped like the folding curve in the image.

Though the fold appears in a specific place on the film, "the motion resulting from folding extends over a big region. Usually big things are slow," said Witten, the Homer J. Livingston Professor in Physics. "But this is a big thing that is not slow. It's a rapid jerk, and we want to see what enables such rapid, large-scale motion."

Lee and her associates aim to understand breathing mechanics using synthetic films only one layer of molecules thick to simulate the surfactant that lines the microscopic air sacs found in the lungs. Diamant and Witten sought to solve the equation that exactly describes the fold shape of such a film. They knew it would be a difficult task, given that it was a nonlinear equation, one in which simple changes produce complicated effects.

A typical nonlinear problem might absorb decades of work without yielding a solution; this one seemed different. "There were strange hints that told us this problem might be solved exactly," Diamant said. "It's very rare that a nonlinear problem can be solved exactly."

Miracle solution

These hints had appeared in numerical simulations of the folding process generated by Enrique Cerda, a collaborator at the University of Santiago in Chile. "It was a miracle that we found an exact solution, but we had a strong feeling that it existed," Diamant said.

Once Diamant and Witten solved the problem, they realized that the solution resembled the sine-Gordon equation, well-known among mathematicians and physicists, which describes how a coupled line of swinging pendulums concentrate their energy.

Their resulting paper lays out the first example the authors know of in which soliton motion of a dynamical system can help scientists understand material deformation. The materials in this instance involve a thin, rigid layer floating on a fluid surface, a structure commonly found in biological tissues and synthetic coatings.

The finding has still-undetermined technological or biomedical applications, but it offers a way to control the film's deformation, including making the fold stick down into or up out of the water, forming a groove.

"This groove is controllable," Witten said. "You can shape the groove; you can make it come; you can make it go away." One also could control the location of the groove on the film, making it possible to manipulate the film on the scale of a few microns -- a fraction the width of a human hair.

"If there was some other material in the water that was attracted to the surface, we could make it nestle into this shape and we could capture it," Witten explained. "We think that this shape could have some potential that people don't realize."

As a next step, Diamant and Witten wonder if the dynamics of swinging pendulums can tell them anything about the dynamics of a folding elastic film. "All we have described at the moment is this static shape of the fold, but folding too is a dynamic phenomenon," Witten said.

Squeeze the film, and it will begin to fold after a period of time. Witten and Diamant would like to further describe how that process works based on what the swinging pendulums do.

"It seems only natural, but things like that are dangerous and they don't necessarily work," Witten noted. "But we do know that there is a lot known about the solitons that we can potentially harness to understand the folds."

Recommend this story on Facebook, Twitter,
and Google +1:

Other bookmarking and sharing tools:

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Chicago. The original article was written by Steve Koppes.

Journal Reference:

Haim Diamant, Thomas Witten. Compression Induced Folding of a Sheet: An Integrable System. Physical Review Letters, 2011; 107 (16) DOI: 10.1103/PhysRevLett.107.164302

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Pacific volcanoes share split personality

Dual chemistry of island chains reflects variations in their deep source Web edition : Monday, September 19th, 2011 Kilauea powFireworks can ensue when lava meets ocean, seen here at Hawaii's Kilauea Volcano. Geochemical studies suggest that the molten rock forming Hawaii and other Pacific island chains may pull from two distinct sources.Michael Poland/USGS

Hawaii’s scenic volcanoes come in two chemical flavors, and now scientists think the igneous peaks on several other Pacific island chains do, too.

Two parallel lines of volcanoes stretch from the Big Island of Hawaii in the southeast to Molokai in the northwest.  Volcanoes on the Samoan and Marquesas islands are similarly paired. A new study finds that, as in Hawaii, one row is richer than the other in versions of elements such as lead and neodymium.

“This might be a common feature for all the Pacific hotspots,” says Shichun Huang, a geochemist at Harvard University and lead author of a paper appearing online September 18 in Nature Geoscience.

If so, these island chains may tap the same source deep in Earth’s mantle. Molten rock rises toward the surface in two chemically distinct streams, one stream feeding each row of volcanoes.

Geologists think Hawaii, Samoa, and the Marquesas each formed as a plate of Earth’s crust moved across a “hotspot,” the top of a plume carrying molten material from the planet’s deep interior. Like a welding torch passing across a piece of metal, the hotspot punched out island after island as the plate moved over it.

Recent studies have shown that the hotspots are more complex than once thought, says isotope geochemist Dominique Weis of the University of British Columbia. The mantle plume rising below Hawaii, for instance, feeds individual streams of chemically distinct magmas into Mauna Loa and Mauna Kea, both on the Big Island. Mauna Loa has a higher ratio of the most abundant form of lead on Earth, lead-208, compared with lead-206, which has two fewer neutrons in its nucleus.

By analyzing published data on lava samples, Huang and his colleagues have now shown that this chemical difference also exists in Samoa and the Marquesas.

The plumes feeding these island chains (as well as Hawaii’s) apparently tap a single massive reservoir that underlies much of the central and southern Pacific. This reservoir contains chemical signatures of ancient surface rock that plowed into the interior eons ago through plate tectonics. As a plume rises, it carries part of this material with it.

The new work shows how surface volcanoes can be linked to deep sources of magma, says geochemist Albrecht Hofmann of the Max Planck Institute for Chemistry in Mainz, Germany. A few other scientists have questioned the existence of mantle plumes, but the new work “strongly suggests that at least these particular hotspots are actually mantle plumes that ascend from the lowermost mantle,” Hofmann says.

Huang’s group is now checking other Pacific island chains to see if they too show this same two-faced nature.

Found in: Earth and Earth Science

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Robots learn to share: Why we go out of our way to help one another

ScienceDaily (May 4, 2011) — Using simple robots to simulate genetic evolution over hundreds of generations, Swiss scientists provide quantitative proof of kin selection and shed light on one of the most enduring puzzles in biology: Why do most social animals, including humans, go out of their way to help each other? In the online, open access journal PLoS Biology, EPFL robotics professor Dario Floreano teams up with University of Lausanne biologist Laurent Keller to weigh in on the oft-debated question of the evolution of altruism genes.

Altruism, the sacrificing of individual gains for the greater good, appears at first glance to go against the notion of "survival of the fittest." But altruistic gene expression is found in nature and is passed on from one generation to the next. Worker ants, for example, are sterile and make the ultimate altruistic sacrifice by not transmitting their genes at all in order to insure the survival of the queen's genetic makeup. The sacrifice of the individual in order to insure the survival of a relative's genetic code is known as kin selection. In 1964, biologist W.D. Hamilton proposed a precise set of conditions under which altruistic behavior may evolve, now known as Hamilton's rule of kin selection. Here's the gist: If an individual family member shares food with the rest of the family, it reduces his or her personal likelihood of survival but increases the chances of family members passing on their genes, many of which are common to the entire family. Hamilton's rule simply states that whether or not an organism shares its food with another depends on its genetic closeness (how many genes it shares) with the other organism.

Testing the evolution of altruism using quantitative studies in live organisms has been largely impossible because experiments need to span hundreds of generations and there are too many variables. However, Floreano's robots evolve rapidly using simulated gene and genome functions and allow scientists to measure the costs and benefits associated with the trait. Additionally, Hamilton's rule has long been a subject of much debate be-cause its equation seems too simple to be true. "This study mirrors Hamilton's rule re-markably well to explain when an altruistic gene is passed on from one generation to the next, and when it is not," says Keller.

Previous experiments by Floreano and Keller showed that foraging robots doing simple tasks, such as pushing seed-like objects across the floor to a destination, evolve over multiple generations. Those robots not able to push the seeds to the correct location are selected out and cannot pass on their code, while robots that perform comparatively better see their code reproduced, mutated, and recombined with that of other robots into the next generation -- a minimal model of natural selection. The new study by EPFL and UNIL researchers adds a novel dimension: once a foraging robot pushes a seed to the proper destination, it can decide whether it wants to share it or not. Evolutionary experiments lasting 500 generations were repeated for several scenarios of altruistic interaction -- how much is shared and to what cost for the individual -- and of genetic relatedness in the population. The researchers created groups of relatedness that, in the robot world, would be the equivalent of complete clones, siblings, cousins and non-relatives. The groups that shared along the lines of Hamilton's rule foraged better and passed their code onto the next generation.

The quantitative results matched surprisingly well the predictions of Hamilton's rule even in the presence of multiple interactions. Hamilton's original theory takes a limited and isolated vision of gene interaction into account, whereas the genetic simulations run in the foraging robots integrate effects of one gene on multiple other genes with Hamilton's rule still holding true. The findings are already proving useful in swarm robotics. "We have been able to take this experiment and extract an algorithm that we can use to evolve cooperation in any type of robot," explains Floreano. "We are using this altruism algo-rithm to improve the control system of our flying robots and we see that it allows them to effectively collaborate and fly in swarm formation more successfully."

This research was funded by the Swiss National Science Foundation, the Euro-pean Commission ECAgents and Swarmanoids projects, and the European Research Council.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Public Library of Science, via EurekAlert!, a service of AAAS.

Journal Reference:

Markus Waibel, Dario Floreano, Laurent Keller. A Quantitative Test of Hamilton's Rule for the Evolution of Altruism. PLoS Biology, 2011; 9 (5): e1000615 DOI: 10.1371/journal.pbio.1000615

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Robots learn to share: Why we go out of our way to help one another

ScienceDaily (May 4, 2011) — Using simple robots to simulate genetic evolution over hundreds of generations, Swiss scientists provide quantitative proof of kin selection and shed light on one of the most enduring puzzles in biology: Why do most social animals, including humans, go out of their way to help each other? In the online, open access journal PLoS Biology, EPFL robotics professor Dario Floreano teams up with University of Lausanne biologist Laurent Keller to weigh in on the oft-debated question of the evolution of altruism genes.

Altruism, the sacrificing of individual gains for the greater good, appears at first glance to go against the notion of "survival of the fittest." But altruistic gene expression is found in nature and is passed on from one generation to the next. Worker ants, for example, are sterile and make the ultimate altruistic sacrifice by not transmitting their genes at all in order to insure the survival of the queen's genetic makeup. The sacrifice of the individual in order to insure the survival of a relative's genetic code is known as kin selection. In 1964, biologist W.D. Hamilton proposed a precise set of conditions under which altruistic behavior may evolve, now known as Hamilton's rule of kin selection. Here's the gist: If an individual family member shares food with the rest of the family, it reduces his or her personal likelihood of survival but increases the chances of family members passing on their genes, many of which are common to the entire family. Hamilton's rule simply states that whether or not an organism shares its food with another depends on its genetic closeness (how many genes it shares) with the other organism.

Testing the evolution of altruism using quantitative studies in live organisms has been largely impossible because experiments need to span hundreds of generations and there are too many variables. However, Floreano's robots evolve rapidly using simulated gene and genome functions and allow scientists to measure the costs and benefits associated with the trait. Additionally, Hamilton's rule has long been a subject of much debate be-cause its equation seems too simple to be true. "This study mirrors Hamilton's rule re-markably well to explain when an altruistic gene is passed on from one generation to the next, and when it is not," says Keller.

Previous experiments by Floreano and Keller showed that foraging robots doing simple tasks, such as pushing seed-like objects across the floor to a destination, evolve over multiple generations. Those robots not able to push the seeds to the correct location are selected out and cannot pass on their code, while robots that perform comparatively better see their code reproduced, mutated, and recombined with that of other robots into the next generation -- a minimal model of natural selection. The new study by EPFL and UNIL researchers adds a novel dimension: once a foraging robot pushes a seed to the proper destination, it can decide whether it wants to share it or not. Evolutionary experiments lasting 500 generations were repeated for several scenarios of altruistic interaction -- how much is shared and to what cost for the individual -- and of genetic relatedness in the population. The researchers created groups of relatedness that, in the robot world, would be the equivalent of complete clones, siblings, cousins and non-relatives. The groups that shared along the lines of Hamilton's rule foraged better and passed their code onto the next generation.

The quantitative results matched surprisingly well the predictions of Hamilton's rule even in the presence of multiple interactions. Hamilton's original theory takes a limited and isolated vision of gene interaction into account, whereas the genetic simulations run in the foraging robots integrate effects of one gene on multiple other genes with Hamilton's rule still holding true. The findings are already proving useful in swarm robotics. "We have been able to take this experiment and extract an algorithm that we can use to evolve cooperation in any type of robot," explains Floreano. "We are using this altruism algo-rithm to improve the control system of our flying robots and we see that it allows them to effectively collaborate and fly in swarm formation more successfully."

This research was funded by the Swiss National Science Foundation, the Euro-pean Commission ECAgents and Swarmanoids projects, and the European Research Council.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Public Library of Science, via EurekAlert!, a service of AAAS.

Journal Reference:

Markus Waibel, Dario Floreano, Laurent Keller. A Quantitative Test of Hamilton's Rule for the Evolution of Altruism. PLoS Biology, 2011; 9 (5): e1000615 DOI: 10.1371/journal.pbio.1000615

Note: If no author is given, the source is cited instead.

Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of ScienceDaily or its staff.

View the original article here